High efficiency infrared reflector having reduced color

Abstract

To provide infrared reflectors with reduced off-axis color, which may be useful in laminated glass construction, particularly for applications where the glass may be exposed to water.SOLUTION: An infrared reflector 330 including a visible absorbing layer 370 is laminated between a first glass layer 310 and a second glass layer 312 via a first optically clear adhesive layer 320 and a second optically clear adhesive layer 322.SELECTED DRAWING: Figure 3

Description

[Background technology]

[0001] Infrared reflectors can be polymeric multilayer optical films formed by coextrusion of tens to hundreds of molten polymer layers followed by orienting or stretching the resulting film. These microlayers have different refractive index characteristics and are thin enough that light is reflected at the interfaces between adjacent microlayers. Infrared reflectors typically reflect a portion of the near infrared spectrum and can be useful in solar heat attenuation applications. Summary of the Invention

[0002] In one aspect, the present disclosure relates to an infrared reflective film. In particular, the infrared reflective film includes a multilayer optical core having a plurality of optical repeat units, the plurality of optical repeat units including a first birefringent polymer layer and a second polymer layer. The infrared reflective film also includes a visible light absorbing layer disposed adjacent to a major surface of the multilayer optical core, the visible light absorbing layer being an adhesive layer. Each of the plurality of optical repeat units has an optical thickness, the optical thickness of the plurality of optical repeat units being configured such that the plurality of optical repeat units exhibit a reflection band having a left band edge and a right band edge, each band edge of the reflection band being defined as the point closest to the center of the reflection band where the transmission crosses 45 percent. The reflection band shifts as a function of the angle of incidence and results in a maximum color shift at a L angle over a range of angles of incidence from 0 to 85 degrees measured in 5 degree increments. * a * b * The maximum distance in color space between two points of reflected color, ignoring lightness. At a 60 degree angle of incidence, the left band edge is below 750 nm, and the maximum color shift through the visible light absorbing layer with the visible light absorbing layer is reduced by at least 25% compared to the maximum color shift without the visible light absorbing layer.

[0003] In another aspect, the present disclosure relates to an infrared reflective film. The infrared reflective film includes a multilayer optical core having a plurality of optical repeat units, each optical repeat unit including a first birefringent polymer layer and a second polymer layer, and a visible light absorbing layer that is not an adhesive layer and is disposed adjacent to a major surface of the multilayer optical core. Each of the plurality of optical repeat units has an optical thickness, and the optical thicknesses of the plurality of optical repeat units are configured such that the plurality of optical repeat units exhibit a reflection band having a left band edge and a right band edge, the reflection band shifting with respect to the angle of incidence, and at an angle of incidence of 60 degrees, the left band edge is 750 nm or less. The reflection ratio of visible light from 400 nm to 700 nm at an angle of incidence of 50 degrees to an angle of incidence of 8 degrees is at least 150%. [Brief description of the drawings]

[0004] [Figure 1A] FIG. 2 is a schematic cross-sectional side view of an infrared reflector laminated to glass. [Figure 1B] FIG. 1 is a schematic cross-sectional side view of an infrared reflector laminated to glass having water droplets on one surface. [Diagram 2] 1 is a schematic cross-sectional side view of a conventional laminated stack including an infrared reflector. [Diagram 3] FIG. 2 is a schematic cross-sectional side view of a laminated stack including an infrared reflector having a visible light absorbing layer. [Figure 4] 1 is a schematic cross-sectional side view of an infrared reflector including a visible light absorbing skin layer. [Diagram 5] FIG. 2 is a schematic cross-sectional side view of an infrared reflector having a visible light absorbing layer. [Figure 6] 1 is a comparison of the reflected color of a modeled 700 nm left band edge infrared reflector with the reflected color of a measured 700 nm left band edge infrared reflector. [Figure 7] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments under standard reflection conditions for a modeled 850 nm left band edge infrared reflector without coating. [Figure 8]1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments for a modeled 800 nm left band edge infrared reflector without coating under standard reflection conditions. [Figure 9] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments for a modeled 700 nm left band edge infrared reflector without coating under standard reflection conditions. [Figure 10] 1 is a graph showing a*b* reflected color from 0 to 85 degrees in 5 degree increments at standard reflectance conditions for a modeled 850 nm left band edge infrared reflector with a 50% visible light transmission (VLT) absorbing layer. [Figure 11] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 850 nm left band edge infrared reflector with an absorbing layer of 20% VLT. [Figure 12] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 850 nm left band edge infrared reflector with an absorbing layer of 5% VLT. [Figure 13] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 800 nm left band edge infrared reflector with an absorbing layer of 50% VLT. [Figure 14] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 800 nm left band edge infrared reflector with an absorbing layer of 20% VLT. [Figure 15] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 800 nm left band edge infrared reflector with an absorbing layer of 5% VLT. [Figure 16] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 700 nm left band edge infrared reflector with an absorbing layer of 50% VLT. [Figure 17]1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 700 nm left band edge infrared reflector with an absorbing layer of 20% VLT. [Figure 18] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments at standard reflection conditions for a modeled 700 nm left band edge infrared reflector with an absorbing layer of 5% VLT. [Figure 19] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 850 nm left band edge infrared reflector without coating. [Figure 20] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 800 nm left band edge infrared reflector without coating. [Figure 21] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 700 nm left band edge infrared reflector without coating. [Figure 22] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 850 nm left band edge infrared reflector with an absorbing layer of 50% VLT. [Figure 23] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 850 nm left band edge infrared reflector with an absorbing layer of 20% VLT. [Figure 24] 1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 850 nm left band edge infrared reflector with an absorbing layer of 5% VLT. [Diagram 25] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 800 nm left band edge infrared reflector with an absorbing layer of 50% VLT. [Figure 26]1 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 800 nm left band edge infrared reflector with an absorbing layer of 20% VLT. [Figure 27] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 800 nm left band edge infrared reflector with an absorbing layer of 5% VLT. [Figure 28] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 700 nm left band edge infrared reflector with an absorbing layer of 50% VLT. [Figure 29] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 700 nm left band edge infrared reflector with an absorbing layer of 20% VLT. [Diagram 30] 13 is a graph showing a*b* reflection color from 0 to 85 degrees in 5 degree increments in raindrop reflection conditions for a modeled 700 nm left band edge infrared reflector with an absorbing layer of 5% VLT. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] Multilayer optical films, i.e. films that provide desired transmission and / or reflection properties at least in part through an arrangement of microlayers with different refractive indices, are known. It is known to fabricate such multilayer optical films by depositing a series of inorganic materials as optically thin layers ("microlayers") on a substrate in a vacuum chamber. Inorganic multilayer optical films are described, for example, in texts by HA Macleod, Thin-Film Optical Filters, 2nd Edition, Macmillan Publishing Co. (1986) and A. Thelan, Design of Optical Interference Filters, McGraw-Hill Inc. (1989).

[0006] Multilayer optical films have also been demonstrated by co-extrusion of alternating polymer layers. For example, see U.S. Pat. Nos. 3,610,729 (Rogers), 4,446,305 (Rogers et al.), 4,540,623 (Im et al.), 5,448,404 (Schrenk et al.), and 5,882,774 (Jonza et al.). In these polymeric multilayer optical films, the individual layers are made mostly or exclusively of polymeric materials. These are sometimes called thermoplastic multilayer optical films. Such films are compatible with mass production processes and can be made in large sheets and roll goods.

[0007] Multilayer optical films include individual microlayers with different refractive index characteristics, such that some light is reflected at the interfaces between adjacent microlayers. The microlayers are thin enough that the light reflected at the interfaces undergoes constructive or destructive interference to give the multilayer optical film the desired reflective or transmissive properties. In multilayer optical films designed to reflect ultraviolet, visible, or near infrared wavelengths of light, each microlayer typically has an optical thickness (physical thickness multiplied by refractive index) of less than about 1 μm. In general, the layers can be arranged from thinnest to thickest. In some embodiments, the alternating optical layers can vary substantially linearly with the number of layers. These layer profiles are sometimes referred to as linear layer profiles. Thicker layers can also be included, such as skin layers on the outer surfaces of the multilayer optical film, or protective boundary layers (PBLs) that separate groups of microlayers (referred to herein as "packets") arranged within the multilayer optical film. In some cases, the protective boundary layers can be the same material as at least one of the alternating layers of the multilayer optical film. In other cases, the protective boundary layers may be different materials selected for their physical or rheological properties. The protective boundary layers may be on one or both sides of the optical packet. In the case of a single packet of multilayer optical films, the protective boundary layers may be on one or both of the exterior surfaces of the multilayer optical film.

[0008] For purposes of this specification, a packet generally varies monotonically in the thickness of the optical repeat unit. For example, a packet may be monotonically increasing, monotonically decreasing, both increasing and unchanging, or both decreasing and unchanging, but not both increasing and decreasing. It should be understood that one or several layers that do not follow this pattern are not critical to the overall definition or identification of a particular group of optical repeat layers as a packet. In some embodiments, it may be useful to define a packet as the largest individual group of consecutive non-redundant layer pairs that collectively provide a reflectance over a particular subrange of the spectrum of interest (e.g., the visible spectrum or the near infrared spectrum).

[0009] In some cases, the microlayers are arranged as optical repeat units or unit cells each having two adjacent microlayers of equal optical thickness (f-ratio=50%) with thicknesses and refractive index values ​​resulting in a quarter wave stack, such that such optical repeat units are effective for reflection with constructively interfering light whose wavelength λ is about twice the total optical thickness of the optical repeat unit. Other layer arrangements are also known, such as multilayer optical films having optical repeat units of two microlayers with f-ratios different from 50%, or films in which the optical repeat unit includes more than two microlayers. The design of these optical repeat units can be configured to reduce or increase certain high order reflections. It is possible. See, for example, U.S. Patent No. 5,360,659 (Arends et al.) and U.S. Patent No. 5,103,337 (Schrenk et al.). A thickness gradient of the optical repeat unit along the thickness axis (e.g., z-axis) of the film can be used to provide an extended reflection band, such as a reflection band that spans the entire human visible range and the near infrared range, so that the microlayer stack continues to reflect across the entire visible spectrum even as the band shifts to shorter wavelengths at oblique incidence angles. A thickness gradient tailored to sharpen the band edges, i.e., the wavelength transition between high reflection and high transmission, is described in U.S. Patent No. 6,157,490 (Wheatley et al.).

[0010] Further details of multilayer optical films and related designs and constructions are described in U.S. Patent Nos. 5,882,774 (Jonza et al.) and 6,531,230 (Weber et al.), PCT Publication Nos. WO 95 / 17303 (Ouderkirk et al.) and WO 99 / 39224 (Ouderkirk et al.), and the publication entitled "Giant Birefringent Optics in Multilayer Polymer Mirrors", Science, Vol. 287, March 2000 (Weber et al.). Multilayer optical films and related articles can include additional layers and coatings selected for their optical, mechanical, and / or chemical properties. For example, a UV absorbing layer can be added to the incident side of the film to protect components from degradation caused by UV light. Multilayer optical films can be attached to a mechanical reinforcement layer using a UV-curable acrylate adhesive or other suitable material. Such reinforcing layers may include polymers such as PET or polycarbonate, and may include structured surfaces that provide optical functions such as light diffusion or collimation, for example, by using beads or prisms. Additional layers and coatings may also include scratch-resistant layers, tear-resistant layers, and hardeners. See, for example, U.S. Patent No. 6,368,699 (Gilbert et al.). Methods and apparatus for making multilayer optical films are described in U.S. Patent No. 6,783,349 (Neavin et al.).

[0011] The reflective and transmissive properties of a multilayer optical film are a function of the refractive index of each microlayer and the thickness and thickness distribution of the microlayers. Each microlayer has an in-plane refractive index, n x , n y , and the refractive index associated with the thickness axis of the film, n zThese indices of refraction represent the refractive indices of the material of interest for light polarized along mutually orthogonal x-, y-, and z-axes, respectively. For ease of description in this patent application, unless otherwise specified, the x-, y-, and z-axes are assumed to be a local Cartesian coordinate system applicable to any point of interest on the multilayer optical film, with the microlayers extending parallel to the xy plane, and the x-axis being expressed as Δn x The film is oriented in the plane of the film to maximize the magnitude of Δn y The magnitude of is Δn x can be less than or equal to the magnitude of Δn x Furthermore, the difference Δn x , difference Δn y , and the difference Δn z The choice of which material layer to start with in the calculation of Δn x In other words, the refractive index difference between two layers forming an interface is Δn j =n 1j -n 2j where j=x, y, or z, and the layer designations 1, 2 are n 1x ≧n 2x , i.e., Δn x It is chosen to be ≧0.

[0012] In practice, the refractive index is controlled by appropriate material selection and processing conditions. Multilayer films are made by co-extruding many layers, for example tens or hundreds of layers, of two alternating polymers A, B, and optionally then passing the multilayer extrudate through one or more layer increment devices, followed by casting through a film die, and then stretching or otherwise orienting the extrudate to form the final film. The resulting film is typically composed of hundreds of individual microlayers whose thicknesses and refractive indices are tailored to provide one or more reflection bands in a desired region of the spectrum, such as the visible or near infrared. To achieve high reflectivity with a reasonable number of layers, adjacent microlayers typically have a refractive index difference (Δn x In some embodiments, the materials are selected so that the refractive index difference for light polarized along the x-axis is as high as possible after orientation. If high reflectivity for two orthogonal polarizations is desired, i.e., to act as a reflector, adjacent microlayers should exhibit a refractive index difference (Δn y ) can also be made to exhibit.

[0013] The above-referenced '774 (Jonza et al.) patent, among other things, focuses on the refractive index difference (Δn z ) to achieve the desired reflectance characteristics for the p-polarized component of obliquely incident light. To maintain high reflectance of p-polarized light at oblique incidence angles, the z-index mismatch Δn between the microlayers is z is the largest in-plane refractive index difference Δn x By controlling the Δn z ≦0.5×Δn x or Δn z ≦0.25×Δn x A z-index mismatch of zero or near-zero magnitude results in interfaces between microlayers whose reflectivity for p-polarized light is constant or nearly constant as a function of the angle of incidence. Furthermore, the z-index mismatch Δnz is the in-plane refractive index difference Δn x has the opposite polarity compared to, i.e., Δn z <0. This condition results in an interface whose reflectivity for p-polarized light increases with increasing angle of incidence, just as it does for s-polarized light.

[0014] Skin layers may be added. This is often done after the layers are formed and before the melt exits the film die. The multilayer melt is then cast onto a chill roll through a film die in the conventional manner for polyester films, where it is quenched. The cast web is then stretched in different ways to achieve birefringence in at least one of the optical layers, often producing either a reflective polarizer or a mirror film, as described, for example, in U.S. Patent Application Publication No. 2007 / 047080 (A1), U.S. Patent Application Publication No. 2011 / 0102891 (A1), and U.S. Patent No. 7,104,776 (Merrill et al.).

[0015] Infrared reflectors, sometimes called solar or solar control films or more commonly window films, selectively reflect the near infrared portion of the electromagnetic spectrum while transmitting the visible wavelength spectrum. This reduces the solar radiation passing through such reflectors while still appearing generally transparent or translucent. In closed or semi-closed environments such as buildings or vehicles, this can help reduce the temperature and cooling load required to maintain the environment at a desired temperature. In some cases, visible light absorbers may be provided to reduce visible light transmission, but such absorbers are typically selected to provide a neutral darkening.

[0016] It is known that the reflection band of a typical infrared reflector (or, in fact, any typical multilayer optical reflector that relies on interference between alternating microlayers) shifts to the left (to shorter wavelengths) with increasing incidence angle. For a detailed description of shifting band edges of multilayer optical films, see U.S. Pat. No. 6,531,230 (Weber et al.). To avoid observable off-axis reflection color, infrared reflectors are designed to have a left band edge that does not shift leftward into the visible range at the maximum light incidence angle, which corresponds to about 850 nm at normal incidence. At incidence angles less than the maximum incidence angle, this means that the infrared reflector transmits at least a portion of those wavelengths between the edge of the visible band and the normal incidence left band edge of the reflector, making the infrared reflector inefficient in attenuating solar radiation.

[0017] In real world conditions, the infrared reflector is laminated to or between glass. The refractive index of the glass creates an interface for Fresnel reflection from air above a certain angle of incidence, refracting the incident light into the infrared reflector. Therefore, the maximum propagation angle into the infrared reflector is only about 40 degrees, regardless of the external angle of incidence (on the glass).

[0018] However, in outdoor environments, water droplets may form on exterior glass due to rain, condensation, or washing. These hemispherical or semispherical droplets provide a geometric surface such that all incident light is essentially perpendicular to the surface and thus minimally refracted. Furthermore, the water droplets fill the gap between the refractive index of air and that of glass, helping to couple light into and out of the infrared reflector and glass. In such cases, the maximum propagation angle within the infrared reflector is larger, 55 degrees or more. Thus, even a carefully designed infrared reflector may appear highly colored in the presence of water droplets due to unusual propagation conditions.

[0019] Engineering the left band edge further to the right may help by reducing the reflected color, but may be undesirable in certain applications due to loss of efficiency for transmitting longer visible / near IR wavelengths.

[0020] The addition of a visible light absorbing material to an infrared reflector reduces the visible reflected color in water droplet conditions. Surprisingly, this visible light absorbing material allows the reflector design to be more efficient, i.e., the left band edge can be designed to be closer to (or even slightly inside) the edge of the visible wavelength band at normal and oblique angles of incidence. Color is often objectionable not because of its absolute value, but because of the magnitude of the color shift between two different observation angles. The maximum distance between two of these points may be considered the maximum color shift, and the most important amount to reduce. Measured in this way, the reduction in color in both normal reflected color conditions and water droplet color conditions can be 25% or even 50% when passing through a visible light absorbing layer, compared to the same infrared reflector without a visible light absorbing layer.

[0021] FIG. 1A is a schematic cross-sectional side view of an infrared reflector laminated to glass. The infrared reflector 30 is laminated between a first glass layer 10 and a second glass layer 12 via a first adhesive layer 20 and a second adhesive layer 22. FIG. 1A illustrates a general mechanism by which the propagation angle into the infrared reflector 30 is limited. Upon incidence on the first glass layer 10, an incident light ray 40 is refracted as a refracted light ray 42 (of course, due to the refractive index difference between the glass layer and the air, at least a portion of the light incident on the glass layer from the air is reflected by Fresnel reflection). The refracted light ray 42 passes through the first adhesive layer 20 with minimal refraction (refraction is not shown in FIG. 1A because the refractive indices are typically very close). At some point during its journey through the microlayer stack of the infrared reflector 30, the refracted light ray 42 is reflected as a reflected light ray 44. The reflected ray 44 travels through the same layers, the first adhesive layer, and the first glass layer 10, and refracts away from the normal as it travels back from the first glass layer 10 into the air as outgoing ray 46. Although the incident ray 40 is incident on the entire optical laminate at a relatively extreme angle, i.e., a glancing angle, the optics of the system limit the actual effective angle of incidence on the infrared reflector to more moderate angles. To an observer, the catadioptric ray 46 appears to have reflected from the optical stack of FIG. 1A at a large oblique angle, but due to refraction into the optical system, it does not exhibit the color artifacts otherwise associated with such angles.

[0022] FIG. 1B is a schematic cross-sectional side view of an infrared reflector laminated to glass having water droplets on one surface. The infrared reflector 30 is laminated between the first glass layer 10 and the second glass layer 12 via a first adhesive layer 20 and a second adhesive layer 22. A water droplet 60 is on the surface of the first glass layer 10. FIG. 1B illustrates how the presence of the water droplets can increase the maximum angle of incidence on the infrared reflector 30. As previously described, an incident light ray 50 (corresponding to the incident light ray 40 in FIG. 1A) is incident on the optical laminate. However, in FIG. 1B, the incident light ray 50 first passes through and is refracted by the hemispherical water droplet 60. Due to the shape and refractive index of water (which is between air and glass), the incident light ray 50 is refracted into a droplet ray 52, which is then further refracted after entering the first glass layer 10. The droplet shape and intermediate index of refraction may help couple more light into the infrared reflector (instead of being reflected at the air-glass interface). Refracted ray 54 travels through the first glass layer 10, the first adhesive layer 20, and is reflected somewhere within the multi-layer stack of the infrared reflector 30, as in FIG. 1A. (Similarly, the interfaces between the glass, adhesive layer, and infrared reflector provide relatively little refraction and are not shown here.) Reflected ray 56 travels back through the first adhesive layer 20 and the first glass layer 10, and refracts at the glass-water droplet interface. Reflected droplet ray 57 travels through the remainder of the water droplet 60, and is refracted again at the interface between the water droplet and the air as exit ray 58. Note that the vertical scale of FIG. 1B is greatly exaggerated, and that in reality the light would exit the same water droplet (or at most an adjacent droplet) that it entered. However, the water droplet mechanism results in a shallower angle of incidence on the infrared reflector and may therefore introduce color artifacts not seen under typical conditions (i.e., the configuration of FIG. 1A).

[0023] FIG. 2 is a schematic cross-sectional side view of a conventional laminated stack including an infrared reflector. The infrared reflector 230 is laminated between the first glass layer 210 and the second glass layer 212 via a first colored adhesive layer 220 and a second colored adhesive layer 222. The infrared reflector can be any suitable infrared reflector with a reflection band whose band edge shifts with the angle of incidence. In many embodiments, these are birefringent interference reflectors as described above. Here, the infrared reflector 230 can be considered a conventional multilayer optical film infrared reflector with a left band edge of 850 nm or greater. Conventionally, visible light absorption is controlled by the use of light absorbing dyes or pigments in the first colored adhesive layer 220, the second colored adhesive layer 222, or both, by extension for the control of high angle color artifacts. In the case of color artifacts, a visible light absorber (e.g., a colored adhesive layer) is typically placed between the viewer and the reflector.

[0024] Conventional approaches have several challenges. First, color and total visible light transmittance cannot be practically assessed until the laminate is fully laminated together. Also, because the visible light absorption of the colored layer depends on both the thickness of the layer and the density of the pigment / dye in the adhesive, applying the correct thickness of adhesive and subsequent handling of the colored adhesive layer can be difficult (and tedious). Furthermore, because the dye / pigment is present throughout the colored adhesive layer, UV absorbers present in the colored adhesive layer may not be effective in protecting the dye / pigment from UV exposure and degradation by the first glass layer.

[0025] 3 is a schematic cross-sectional side view of a laminated stack including an infrared reflector 330, including a visible light absorbing layer 370, laminated between a first glass layer 310 and a second glass layer 312 via an optically clear first adhesive layer 320 and an optically clear second adhesive layer 322.

[0026] The first glass layer 310 may be or include any suitable type of glass formed by any suitable method. For example, the first glass layer 310 may include fused silica glass, borosilicate glass, soda-lime glass, or any other type of glass. The first glass layer 310 may be manufactured as flat glass, float glass, or even blown glass. The first glass layer 310 may be tempered or chemically strengthened glass. The first glass layer 310 may also have any suitable shape and thickness. In certain embodiments, the first glass layer 310 may be several millimeters thick, up to several centimeters thick. The first glass layer 310 may be substantially planar or flat, or may have a gentle curve or contour. Other three-dimensional shapes are possible, including curves with smaller radii of curvature or more complex curvatures. The first glass layer 310 may be textured or etched. The first glass layer 310 may be substantially clear or neutral in color, or the first glass layer 310 may be tinted glass. The second glass layer 312 may be the same as the first glass layer 310, or may be a different type, shape, color, or thickness.

[0027] The first optically clear adhesive layer 320 and the second optically clear adhesive layer 322 may be any suitable optically clear adhesive and may have any suitable thickness. In some embodiments, the first and second optically clear adhesive layers may have the same thickness or may have different thicknesses. In some embodiments, the optically clear adhesive layer may include polyvinyl butyral. In some embodiments, the optically clear adhesive layer may include an ultraviolet light absorber. In some embodiments, the optically clear adhesive layer may include a hindered amine light stabilizer. The optically clear adhesive may be applied and then cured by application of heat, light, or other radiation. In some embodiments, the glass may be laminated to an infrared reflector via the optically clear adhesive using an autoclave. The optically clear adhesive layer may have a high visible light transmittance, for example, the optically clear adhesive layers may each transmit greater than 80%, greater than 85%, greater than 90%, or even greater than 95% of light from 400 nm to 700 nm. The optically clear adhesive layer may also have low haze and high clarity, in some embodiments, the optically clear adhesive layer may have a haze of less than 20%, less than 15%, less than 10%, or less than 5%, and / or an optical clarity of greater than 80%, greater than 85%, greater than 90%, or greater than 95%.

[0028] The infrared reflector 330 has a reflection band having a left band edge and a right band edge. For purposes of this specification, each band edge of the reflection band is defined as the point closest to the center of the reflection band where the transmission crosses 45 percent. The left band edge is the band edge having the shorter (bluer) wavelengths and the right band edge is the band edge having the longer (redder) wavelengths. The infrared reflector 330 is substantially transparent to visible wavelengths at normal incidence angles, but at an incidence angle of 60 degrees, the infrared reflector has a left band edge of 750 nm or less. For a typical infrared reflector, this corresponds to a left band edge of 850 nm or less at a normal (0°) incidence angle. In some embodiments, the left band edge at normal incidence angles may be 800 nm or less. In some embodiments, the left band edge at normal incidence angles may be 750 nm or less. In some embodiments, the left band edge at normal incidence angles may be 700 nm or less.

[0029] The visible light absorbing layer 370 is adjacent to the infrared reflector 330, specifically adjacent to a major surface of the multilayer optical core of the infrared reflector 330. For purposes of FIG. 3, the attachment method or relationship between the visible light absorbing layer 370 and the infrared reflector 330 remains general, but these configurations (including lamination, coextrusion, and visible light absorbing skin layers) are discussed in more detail in FIGS. 4 and 5. The visible light absorbing layer 370 may include any suitable light absorbing material, including broadband light absorbing materials such as carbon black. In some embodiments, the visible light absorbing layer 370 may include wavelength-specific dyes or pigments. In some embodiments, these may include metal oxides such as iron manganese oxide or another transparent metal oxide. For maximum efficiency, the visible light absorbing material should only absorb wavelengths in the visible range, i.e., the infrared reflector should be relied upon to reflect incident infrared solar radiation without it being absorbed (and then converted to heat) by the visible light absorbing layer, although in practice broadband absorbing materials may be suitable for many applications. These pigments may be coextruded with a polymeric resin, including any suitable polymer, such as polycarbonate, polyester including polyethylene terephthalate, poly(methyl methacrylate), blends or copolymers thereof. In some embodiments, the visible light absorbing layer may be a dip-dyed polymeric resin. In some embodiments, the polymeric resin may be coextruded with a heat-resistant dye surrounded by at least two transparent encapsulating layers, such as by the process described in U.S. Pat. No. 9,630,384 (Haak et al.), which is incorporated herein by reference in its entirety.

[0030] Infrared reflectors are measured over the range 0 to 85 degrees in 5 degree increments because their reflection band shifts with the angle of incidence. * b * Space (L *The maximum color shift is the maximum distance between two color points at 100° C. (ignoring the light transmittance). Lightness is ignored because at high angles Fresnel reflections from the air-film interface dominate the reflected color and confuse the color measurements. For the purposes of this specification, the maximum color shift should be measured with and through a visible light absorbing layer and compared to the same construction without the visible light absorbing layer. In some embodiments, as further shown in the examples, a visible light absorbing layer with 50% visible light transmission (VLT) can reduce the maximum color shift by more than 25%, even more than 50% or even more than 60%. In some embodiments, a visible light absorbing layer with 20% VLT and 5% VLT can reduce the maximum color shift by more than 90% or even 99%.

[0031] The infrared reflector shown in FIG. 3 has an advantage over traditional pigmented adhesive layers because it can be more consistently manufactured and applied when combined with a visible light absorbing layer. In some cases, in-line testing can be done to ensure that the visible light transmittance and color shift are within proper specifications. In addition, optically clear adhesives (non-pigmented) can be used that provide a visible light transmittance that is relatively invariant with thickness. Also, ultraviolet light absorbers can be provided in the adhesive layer to protect all of the visible light absorbers in the visible light absorbing layer.

[0032] FIG. 4 is a schematic cross-sectional side view of an infrared reflector including a visible light absorbing skin layer. The infrared reflector 410 has a skin layer 412 including a visible light absorbing material. FIG. 4 illustrates a first method of incorporating a visible light absorbing layer into an infrared reflector. As mentioned above, the skin layers are often coextruded with the optically active core of the multilayer optical film, which in some embodiments helps to protect the optically active core from shear forces experienced during extrusion, orientation, and other manufacturing processes. Visible light absorbing dyes can be extruded into the skin layers. In some embodiments, these skin layers may be multi-layer skin layers, such as polyesters (see, for example, U.S. Pat. No. 9,630,384 (Haak et al.)) that include a heat stable dye surrounded by a transparent encapsulation layer. In some embodiments, only one side skin layer includes a visible light absorbing material. In some embodiments, both sides skin layers include a visible light absorbing material.

[0033] FIG. 5 is a schematic cross-sectional side view of an infrared reflector with a visible light absorbing layer. Visible light absorbing layer 520 is laminated to infrared reflector 510 via adhesive 530. FIG. 5 shows an alternative method for constructing an infrared reflector and a visible light absorbing layer. Visible light absorbing layer 520 may be separately manufactured via any suitable process, including any process described herein (e.g., dip-dyeing, extrusion with a heat stable dye, and transparent encapsulation layer, etc.), and then laminated to a major surface of the infrared reflector via an adhesive. Adhesive 530 may be any suitable adhesive, including an optically clear adhesive or even a pigmented adhesive. Adhesive 530 may be cured by the addition of radiation, heat, or any other mechanism. In some embodiments, visible light absorbing layer 520 may be laminated to infrared reflector 510 with heat and / or pressure or other suitable conditions, such that no adhesive is required. In some embodiments, the methods according to FIG. 4 and FIG. 5 may be combined such that there is a visible light absorbing skin layer and a separate visible light absorbing layer.

[0034] The constructions as described herein may be useful for automotive glass applications, such as sunroofs / moonroofs, windshields, and side windows. In some embodiments, the constructions as described herein may be useful for architectural windows (e.g., skylights) and exterior windows for commercial and residential buildings. The constructions as described herein may be useful for any application where solar heat attenuation and at least partial visible light transmission may be desirable.

[0035] Highly colored infrared reflective film In some embodiments, it may be desirable to provide an infrared reflective film that has an intentionally highly colorful appearance. As with other infrared reflective films described herein, the infrared reflective film includes a multilayer optical core having a plurality of optical repeat units, each optical repeat unit including a first birefringent polymer layer and a second polymer layer, and the infrared reflective film includes a visible light absorbing layer that is not an adhesive layer disposed adjacent to a major surface of the multilayer optical core. Each of the plurality of optical repeat units has an optical thickness, and the optical thicknesses of the plurality of optical repeat units are configured such that the plurality of optical repeat units exhibit a reflection band having a left band edge and a right band edge, the reflection band shifting as a function of the angle of incidence, and at an angle of incidence of 60 degrees, the left band edge is 750 nm or less.

[0036] In some embodiments, a large ratio between off-axis reflection and on-axis reflection may be desirable. In this way, such constructions may have an unobtrusive appearance when viewed on-axis, but a striking aesthetic when viewed at an angle. In some embodiments, the reflectance ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° is at least 100%. In some embodiments, the reflectance ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° is at least 150%. In some embodiments, the reflectance ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° is at least 200%. In some embodiments, the reflectance ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° is at least 300%. It should be noted that this reflectance ratio includes surface (Fresnel) reflection based on the refractive index difference between air and the outermost plastic layer of the multilayer film. By including surface reflections in the calculation, they are normalized to what an observer would see as on-axis reflection in a typical environment.

[0037] Such infrared reflective films may include a visible light absorbing layer on one side of the film. The visible light absorbing layer, which may include a pigment such as carbon black, may be configured such that in application, the visible light absorbing layer is on the side facing the interior of the window. For viewers within a vehicle or building, this may reduce or eliminate the magnitude of the color shift while still maintaining a striking aesthetic effect for an exterior viewer. In some embodiments, a protective hard coat is provided on the exterior or exposed surface of the infrared reflective film.

[0038] Descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. Because the above-described embodiments have been described in detail to facilitate explanation of various aspects of the invention, the present invention should not be considered limited to the specific examples and embodiments described above. Rather, the present invention should be understood to encompass all aspects of the invention, including various modifications, equivalent processes, and alternative devices, that fall within the scope of the invention as defined by the appended claims and their equivalents. EXAMPLES

[0039] An infrared reflector was made as described in Example 5 of U.S. Patent No. 6,797,396. The left reflection band edge of the film was adjusted to 850-700 nanometers, and the right reflection band edge was adjusted to approximately 1160 nanometers. The film was made, modeled, and / or tested. The test methods and modeling are described below. The targeted modeled color layer was based on a layer made with a commercial dispersion of manganese ferrite black spinel available as WRF-30X1 from Sumitomo Metal Mining Company, Tokyo, Japan. This dispersion was mixed into a solvent-based coating consisting of PVB resin (Mowitol B20H available from Kuraray Company, Tokyo, Japan). The coating solution consisted of 8-30% by weight WRF-30X1, 5-12% by weight Mowitol B20H, and the balance a solvent blend of methyl ethyl ketone, toluene, heptane, and methyl isobutyl ketone. The coating was dried to obtain the targeted dispersion in PVB resin coated on the infrared reflector referenced above. The percentage of WEF-30X1 in the coating solution was adjusted to obtain the visible light transmittance as described in the examples.

[0040] Test Method The reflectance spectra of the films were measured on a PerkinElmer LAMBDA 1050 spectrometer (Watham, Mass.) using a Total Absolute Measurement System (TAMS) accessory module (model #L6310240) that allows for automated rotation and measurement of samples to measure gonioreflectance. Color values ​​were then calculated for each gonioreflectance spectrum. The results are reported below. All color values ​​are measured using a D65 illuminant.

[0041] modeling The reflectance spectrum / color values ​​were obtained from an optical model of reflected color. The optical film stack was mathematically described and consisted of a polymer multilayer construction in which each 1-d layer of material A (PET) was interdigitated with alternating 1-d layers of material B (CoPMMA). The phase thickness of the first A / B layer pair was defined as 1 / 2λ0 (wavelength), where λ0 is typically around 850 nm. Adjacent A / B layer pairs were interdigitated with 1 / 2λ0 (wavelength). i and a physical thickness adjusted to have a phase thickness of λ i is incrementally larger than λ. Furthermore, adjacent A / B layer pairs are 1 / 2λ n 1 / 2λ through the entire optical film stack until the last A / B layer pair is reached, which has a phase thickness of i+1 and the phase thickness is adjusted to be equal to or less than λ. n is approximately 1160 nm. For all of the calculated examples, the film stack consisted of 112 A / B layer pairs in a monotonic, linear A / B layer pair thickness profile. In addition, within each A / B layer pair, both the A and B layers have a thickness of 1 / 4 λ i112 A / B layer pairs, creating a so-called quarter-wave configuration. Such a configuration of the interference structures described above creates resonant reflection bands at odd harmonics only. Suitable refractive index values ​​for biaxially oriented PET (A) and amorphous CoPMMA (B) are shown in Table 1 below. The refractive index values ​​used to mathematically create the optical film stack and its associated phase thickness are those in the 633 nm wavelength column of Table 1. Other embodiments may have a film stack configuration with λ0 approximately equal to 800 nm or approximately equal to 700 nm. An absorbing layer (that absorbs at visible wavelengths) can be mathematically placed on top of the optical film stack with 112 A / B layer pairs, facing the incident light. The real and imaginary parts of the refractive index of this absorbing layer are also shown in Table 1.

[0042] [Table 1]

[0043] A 4x4 transfer matrix solver for 1-d biaxial material film stacks was used to solve the reflection and transmission coefficients of the film stack structure with and without an absorbing layer facing the incident light. These reflection and transmission coefficients are determined for any set of light incidence angles θ and azimuthal angles φ over any range of wavelengths λ. The reflection and transmission coefficients can then be normalized to the intensity spectrum of the incident light. In these examples, the incident light intensity spectrum is considered to be the D65 intensity spectrum. The chromaticity coordinates of the reflected and transmitted colors can then be calculated to provide the perceived color for the reflected and transmitted light.

[0044] Reflection spectra / color values ​​were also obtained from an optical model of reflected color with hemispherical coupling (raindrop effect) at the surface of the film. Hemispherical coupling at the surface was modeled using the same model as for normal reflected color, except that in this case the incident light entered the surface through a liquid water droplet. The refractive index used for the liquid water droplet was 1.34. So the net difference between normal reflected color and the hemispherical coupling case is that in normal reflected color, the light entering the film or coated film comes from air with a refractive index of 1.0, rather than coming from water with a refractive index of 1.34. The higher the refractive index of water, the less the incident light refracts as it enters the film, and therefore the incident light can enter at a higher angle than without hemispherical coupling. See generally FIG. 1B and related discussion.

[0045] A film with a 700 nm left band edge was used to test the validity of the modeling because it provides the most deflection angle reflected color of any of the flat film examples that can be measured (as films with raindrops cannot be reliably measured due to instrument limitations). The measured and modeled reflected colors from the uncoated 700LBE film show both good qualitative and quantitative agreement in reflected color at points 10 degrees apart from 10 degrees to 60 degrees as shown in Figure 6. The offset in the data is easily explained by the fact that due to real world manufacturing errors, the properties of the real film did not perfectly match the assumed modeled film. However, both show similar slopes of color change with angle, as well as a good b at high angles. * The same increase in, and then a * Thus, the model can be trusted to be informative on both the magnitude and direction of color shift as a function of incidence angle, even if not the exact color values.

[0046] For the purposes of these examples, any two a on a color plot obtained from the reflected color of the model from 0 degrees up to 85 degrees * b* The maximum color shift was calculated as the maximum span or straight line distance between the points. * was ignored due to the amount of statistical noise in this data at high angles. This distance is a * The squared difference of and b * It is calculated as the square root of the sum of the squares of the differences between them.

number

[0047] The percent color reduction is calculated as the maximum color shift of the uncoated film minus the maximum color shift of the coated film divided by the maximum color shift of the uncoated film. In each case, the uncoated film has the same corresponding LBE as the coated film. These calculations were performed for both the reflection with hemispherical coupling (raindrops) and the reflection without hemispherical coupling (raindrops).

[0048] [Table 2]

[0049] Extremely colored infrared reflector A multi-layer film was made and a protective coating and adhesive were applied to both sides of the film. The resulting film was tested for on-axis and off-axis performance.

[0050] material

[0051] [Table 3]

[0052] Test Method On-axis and off-axis optical measurements Optical data was generated by applying the adhesive coated side of the samples to 3mm clear soda lime float glass. These laminates were then measured for transmission and reflectance spectra using a Perkin Elmer Lambda 950 UV / VIS Spectrometer. A Universal Reflectance Accessory (URA) module was installed to obtain reflectance spectra at various angles. The spectral data was then analyzed with the Optics 5 and Windows 5 software packages from Lawrence Berkeley National Labs.

[0053] Visible Light Transmittance (VLT) indicates the darkness of a film when viewed through the film. Visible Light Reflectance (VLR) indicates the percentage of incident light that an observer sees reflected back. All VLR measurements were taken with film samples mounted on 3mm thick soda-lime float glass. Measurements were taken with detectors at 8° and 50° from the angle of incident light to characterize how visual properties change with viewing angle.

[0054] [Table 4]

[0055] [Table 5]

[0056] A protective coating was applied to one side of the multilayer film. The coating was an acrylate monomer blended with a nanopigment and a photoinitiator sensitive to ultraviolet (UV) light. M2 was diluted to 40% solids in a 40:60 blend of MEK and 1-methoxy-2-propanol, and two photoinitiators, PH1 and PH2, were added at 1% of the monomer weight, respectively. The base formulation was blended with absorbing nanoparticles (nanopigment, P2) as shown in Table 1. Precision extrusion dies were used to apply the example coatings, and coating thicknesses were varied to obtain target transmittances (target on-axis VLTs in Table 3). The coatings were applied to a moving substrate by extrusion die coating, followed by convection drying to solidify the coating layer by driving off the carrier solvent. The coatings were then cured by exposure to UV radiation under a Fusion UV Systems Inc. Model I600M UV curing station with a 600W / inch H bulb operated with a nitrogen purge.

[0057] To allow the coated multilayer film to be applied to glass, an optically clear pressure sensitive adhesive (PSA) was applied to the coated multilayer film on the side opposite the protective coating. The PSA used was a blend of 25 parts of a soft acrylate polymer R1 and 75 parts of a hard acrylic resin R2. These resins were diluted to 24% total solids in a blend of solvents (8% isopropyl alcohol / 39% ethyl acetate / 40% toluene / 1% MEK / 8% heptane / 4% methyl hexane) designed to maintain the resins in a homogenous solution to a viscosity that would allow coatability. In addition, absorbers and stabilizers were added: 0.5% by weight A1, 0.2% by weight A2, and 1.8% by weight A3. The PSA was applied to the moving substrate by extrusion die coating, followed by convective drying to solidify the coating layer by driving off the carrier solvent. The PSA coating was applied at a dry thickness of 9-10 micrometers.

[0058] result

[0059]

Table 6

Claims

1. An infrared reflective film, a multilayer optical core having a plurality of optical repeat units, each optical repeat unit including a first birefringent polymer layer and a second polymer layer; a visible light absorbing layer, the visible light absorbing layer being not an adhesive layer, disposed adjacent a major surface of the multilayer optical core; each of the plurality of optical repeat units has an optical thickness; the optical thicknesses of the plurality of optical repeating units are configured such that the plurality of optical repeating units exhibit a reflective band having a left band edge and a right band edge; The reflection band shifts as a function of the angle of incidence, resulting in a maximum color shift, the maximum color shift being measured over a range of angles of incidence from 0 to 85 degrees in 5 degree increments. ＊ a ＊ b ＊ This is the maximum distance between two points of a specular color in color space, ignoring brightness. at an incidence angle of 60 degrees, the left band edge is less than or equal to 750 nm; An infrared reflective film, wherein the maximum color shift with and through the visible light absorbing layer is reduced by at least 25% compared to the maximum color shift without the visible light absorbing layer.

2. 10. The infrared reflective film of claim 1, wherein the maximum color shift with and through the visible light absorbing layer is reduced by at least 50%.

3. 10. The infrared reflective film of claim 1, wherein the left band edge at 0 degrees incidence is less than 850 nm.

4. 10. The infrared reflective film of claim 1, wherein the left band edge at 0 degrees incidence is less than 800 nm.

5. 10. The infrared reflective film of claim 1, wherein the left band edge at 0 degrees incidence is less than 750 nm.

6. 10. The infrared reflective film of claim 1, wherein the first birefringent polymer is polyethylene terephthalate or a copolymer thereof.

7. 10. The infrared reflective film of claim 1, wherein the second polymer is poly(methyl methacrylate) or a copolymer thereof.

8. A laminate comprising: The infrared reflective film according to claim 1 ; A glass layer; an optically clear adhesive layer; a laminate, wherein the infrared reflective film is attached to the glass layer by the optically clear adhesive layer.

9. 9. The laminate of claim 8, further comprising a second glass layer and a second optically clear adhesive layer, the infrared reflective film being attached to the second glass layer by the second optically clear adhesive layer.

10. 10. The laminate of claim 8 or 9, wherein the optically clear adhesive layer comprises polyvinyl butyral.

11. The infrared reflective film of claim 1 , wherein the absorbing layer comprises a visible light absorbing material.

12. 2. The infrared reflective film of claim 1, wherein the absorbing layer comprises a material that absorbs more light in the range of 400 to 800 nm than it absorbs light in the range of 800 to 1200 nm on average across those spectral ranges.

13. The infrared reflective film of claim 1 , wherein the absorbing layer comprises a transparent metal oxide.

14. The infrared reflective film of claim 1 , wherein the absorbing layer comprises carbon black.

15. The infrared reflective film of claim 1 , wherein the absorbing layer comprises at least two different absorbing materials.

16. 10. The infrared reflective film of claim 1, wherein the visible light absorbing layer is a polymeric film layer laminated to the multilayer optical core.

17. 10. The infrared reflective film of claim 1, wherein the visible light absorbing layer is a skin layer coextruded within the multilayer optical core.

18. The infrared reflective film of claim 1 further comprising a second absorbing layer adjacent a second major surface of the multilayer optical core.

19. 20. The infrared reflective film of claim 18, wherein the first absorbing layer and the second absorbing layer have different visible light transmittances.

20. 20. The infrared reflective film of claim 18, wherein the first absorbing layer and the second absorbing layer have the same visible light transmittance.

21. An infrared reflective film, a multilayer optical core having a plurality of optical repeat units, each optical repeat unit including a first birefringent polymer layer and a second polymer layer; a visible light absorbing layer, the visible light absorbing layer being not an adhesive layer, disposed adjacent a major surface of the multilayer optical core; each of the plurality of optical repeat units has an optical thickness; the optical thicknesses of the plurality of optical repeating units are configured such that the plurality of optical repeating units exhibit a reflective band having a left band edge and a right band edge; the reflection band shifts as a function of the angle of incidence; at an incidence angle of 60 degrees, the left band edge is less than or equal to 750 nm; An infrared reflective film having a reflectance ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° of at least 150%.

22. 22. The infrared reflective film of claim 21, wherein the reflection ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° is at least 200%.

23. 22. The infrared reflective film of claim 21, wherein the reflection ratio of visible light from 400 nm to 700 nm at an incidence angle of 50° to an incidence angle of 8° is at least 300%.

24. 22. The infrared reflective film of claim 21, wherein the visible light absorbing layer comprises carbon black.

25. 22. A window having an interior surface and an exterior surface, comprising the infrared reflective film of claim 21 , wherein the visible light absorbing layer of the infrared reflective film faces the interior surface.

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