Optical system for side / rearview mirror of a vehicle

Abstract

A mirror system for a side or rearview mirror of a vehicle includes a light absorbing layer and an optical film having a plurality of layers disposed on the light absorbing layer. For substantially normally incident light and for at least one polarization state, the plurality of layers includes a reflection band having a substantially flat top region that is at least 100 nm wide. The reflection band includes left and right band edges on short and long wavelength sides, respectively. The plurality of layers has an average optical reflectance R1 in the substantially flat top region that is greater than about 70% and a standard deviation that is less than about 5%. In a blue wavelength range extending from about 420 nm to 485 nm, an average optical reflectance Rb is less than about 0.8 R1.

Description

Technical Field

[0001] This disclosure relates generally to optical systems, and more particularly to optical systems for side mirrors and / or rearview mirrors of vehicles. Background Technology

[0002] Interior and exterior mirrors in a vehicle help the driver observe other cars and / or objects behind the vehicle while driving. For example, during nighttime driving, the driver may experience glare from the mirrors due to strong reflections caused by factors such as the car's headlights or streetlights behind the vehicle, and may be unable to see ahead of the vehicle. Anti-glare mirror systems are used to prevent such reflections and associated glare. Summary of the Invention

[0003] Some aspects of this disclosure relate to a mirror system for a side or rearview mirror of a vehicle. The mirror system includes a substantially opaque light-absorbing layer and an optical film disposed on the light-absorbing layer. The optical film includes a plurality of layers totaling at least 10, each having an average thickness of less than about 300 nm. For substantially perpendicular incident light and for at least one polarization state, the plurality of layers include a reflective band. The reflective band includes a substantially flat top region at least 100 nm wide and including at least one green wavelength in the green wavelength range and at least one red wavelength in the red wavelength range. The reflective band also includes a left band edge on the shorter wavelength side of the reflective band, at which the reflectivity of the optical film generally increases with increasing wavelength. The reflection band also includes a right band edge on the long wavelength side of the reflection band, where the reflectivity of the optical film generally decreases with increasing wavelength. The multiple layers have an average optical reflectivity R1 greater than about 70% and a standard deviation less than about 5% in the substantially flat top region, and an average optical reflectivity Rb less than about 0.8R1 in the blue wavelength range.

[0004] Some other aspects of this disclosure relate to an optical stack comprising a light-absorbing layer and an optical film disposed on the light-absorbing layer. The optical film comprises a plurality of layers totaling at least 10, each having an average thickness of less than about 300 nm. For non-overlapping blue, green, and red wavelength ranges of substantially perpendicular incident light and visible light spectra, each wavelength range is at least 30 nm wide, and for at least one polarization state, the plurality of layers comprise a reflection spectrum. The reflection spectrum comprises a full width at half maximum (FWHM), wherein the FWHM comprises at least 80% of each of the green and red wavelength ranges and at most 20% of the blue wavelength range. For at least one wavelength in each of the green and red wavelength ranges, the reflection spectrum comprises at least 70% reflectance. For at least one wavelength in each of the blue, green, and red wavelength ranges, the light-absorbing layer absorbs at least 70% of the incident light.

[0005] Other aspects of this disclosure relate to mirror systems including optical stacking for side or rearview mirrors of vehicles. Attached Figure Description

[0006] Various aspects of this disclosure will be discussed in more detail with reference to the accompanying drawings, in which,

[0007] Figure 1 A vehicle with side mirrors and rearview mirrors according to some embodiments is schematically shown, the side mirrors and rearview mirrors having optical stacking;

[0008] Figure 2 A mirror system according to some embodiments is illustrated schematically;

[0009] Figure 3 The structure of an optical film according to some embodiments is schematically shown;

[0010] Figure 4 The reflectance spectra of the mirror system according to some implementation schemes are illustrated graphically; and

[0011] Figures 5 to 6 Other examples of the reflection spectra of mirror systems according to other embodiments are presented graphically.

[0012] The figures are not necessarily drawn to scale. Similar numbers used in the figures refer to similar parts. However, it should be understood that using numbers to refer to parts in a given figure is not intended to restrict parts to be labeled with the same numbers in another figure. Detailed Implementation

[0013] Reference is made in the following description to the accompanying drawings, which form part of the invention and in which various embodiments are illustrated by way of example. It should be understood that other embodiments are conceivable and may be practiced without departing from the scope or spirit of this specification. Therefore, the following detailed description should not be considered limiting.

[0014] It is well known that vehicle headlights cause glare to other drivers when viewed through side or rearview mirrors. Attempts have been made to modify the spectral output of the headlights to reduce glare, but the problem persists. Specifically, the "blue" portion of the headlight spectrum causes more discomfort than other portions. Furthermore, high-intensity discharge (HID) headlights cause greater discomfort than halogen headlights when viewed while driving. The implementation scheme described herein addresses these and other challenges.

[0015] In some embodiments of this disclosure, the spectral reflectivity of the MOF incorporated in the side or rearview mirror has been modified, wherein the MOF may be substantially reflective for green and red spectral wavelengths, but substantially partially transmissive for lower wavelengths.

[0016] Figure 1 An example of a vehicle (10) is shown, which has a rearview mirror (12) and a side mirror (11) to help the driver of the vehicle to observe other vehicles and / or objects behind the vehicle while driving. The mirror system according to some aspects of this disclosure can be incorporated into the side mirrors and / or rearview mirrors (11, 12) of the vehicle (10).

[0017] Figure 2 A mirror system (200) according to several embodiments is shown. In some aspects, the mirror system may be an optical stack (200) and may include a light-absorbing layer (20). In some aspects, the light-absorbing layer may be opaque or substantially opaque. The light-absorbing layer (20) helps to control ambient light suppression of the mirror system. In some embodiments, the light-absorbing layer (20) may include one or more of carbon black, black dye, opaque particles, organic or inorganic pigments or particles, or nanoparticles, or a powder coating of such particles dispersed within a cured polymer binder material. The particles defining the light-absorbing layer (20) can have a wide variety of types and shapes. For example, the material may be dispersed in a liquid or solid binder system. In one embodiment, the light-absorbing layer (20) may include a transparent binder in which black particles are dispersed throughout. The binder may include, for example, acrylates or other UV-curable polymers. The light-absorbing layer (20) may be applied by conventional techniques, such as coating processes or powder coating. In some aspects, the light-absorbing layer (20) may include a linear absorption polarizer.

[0018] An optical film (30) may be disposed on a light-absorbing layer (20). In some aspects, a first adhesive layer (90) disposed between the substantially opaque light-absorbing layer (20) and the optical film (30) may be used to bond the substantially opaque light-absorbing layer (20) and the optical film (30) to each other.

[0019] The mirror system (200) may include a front protective layer (110) and a rear protective layer (130). In some embodiments, the front and rear protective layers (110, 130) may include glass. In some aspects, a second adhesive layer (100) disposed between the optical film (30) and the front protective layer (110) may be used to bond the optical film (30) and the front protective layer (110) together. In some aspects, a third adhesive layer (120) disposed between the light-absorbing layer (20) and the rear protective layer (130) may be used to bond the light-absorbing layer (20) and the rear protective layer (130) together.

[0020] In some implementation schemes, such as Figure 3 As shown, the optical film (30) disposed on the light-absorbing layer (20) may be a multilayer optical film (MOF) comprising multiple layers (31, 32), such that at least a portion of substantially perpendicularly incident light (40) may be transmitted, polarized, and / or reflected by the multiple optical layers (31, 32). In some cases, the total number of the multiple layers (31, 32) may be at least 10, at least 20, at least 50, or at least 100 layers, and each of these layers may have an average thickness (t) of less than about 300 nm, or less than about 270 nm, or less than about 250 nm. In some embodiments, the number of layers of the optical film (30) may be selected for reasons of film thickness, flexibility, and economy to achieve the desired optical properties using the minimum number of layers. In the case of reflective films, such as polarizers and mirrors, the number of layers may be less than about 2,000, or less than about 1,000, or less than about 750. In some embodiments, the number of layers may be at least 150 or 200. In other implementations, the number of layers can be at least 250.

[0021] Various MOFs are well known. MOFs typically comprise alternating first polymer layers (31) and second polymer layers (32), which include at least one birefringent polymer (e.g., an oriented semi-crystalline polymer) and a second polymer. In some aspects, the optical film (30) may be a multilayer stack of alternating first and second optical layers (31, 32) having at least two materials. In one embodiment, the materials of the first layer (31) and the second layer (32) may be composed of polymers, such as polyesters. For example, an exemplary polymer used as the first birefringent layer (31) in the multilayer optical film (30) may be polyethylene naphthalate (PEN). Other semi-crystalline polyesters suitable as birefringent polymers as the first birefringent layer (31) in the multilayer optical film (30) may include, for example, polybutylene 2,6-naphthalene dicarboxylate (PBN), polyethylene terephthalate (PET), etc. The second layer (32) of the multilayer optical film (30) can be made of various polymers whose glass transition temperature is compatible with that of the first birefringent polymer layer (31) and whose refractive index is similar to that of the isotropic refractive index of the first birefringent polymer layer (31). Examples of other polymers suitable for optical films (particularly the second polymer layer (32)) may include olefin polymers and copolymers derived from monomers such as vinylnaphthalene, styrene, maleic anhydride, acrylates, and methacrylates. Examples of such polymers include polyacrylates, polymethacrylates (such as poly(methyl methacrylate) (PMMA)), and isotactic or syndiotactic polystyrene. Other polymers include condensation polymers such as polysulfones, polyamides, polyurethanes, polyamic acids, and polyimides. Alternatively, the second polymer layer (32) may be formed from homopolymers and copolymers of polyesters, polycarbonates, fluoropolymers, and polydimethylsiloxanes, and blends thereof. These layers are selected to achieve reflection of electromagnetic radiation with a specific bandwidth. In one embodiment, the materials of the plurality of layers (31, 32) have different refractive indices. In some embodiments, the optical film (30) may comprise a copolymer (coPMMA) of PET as the first optical layer (31) and PMMA as the second optical layer (32), or any other polymer (including copolyesters, fluorinated polymers) or combinations thereof with low refractive indices. The transmission and reflection properties of the optical film (30) are based on the coherent interference of light caused by the refractive index difference between the layers (31, 32) and the thickness of the layers (31, 32).

[0022] Figure 4 The reflection spectra of the mirror system according to some embodiments are presented graphically. In some respects, for substantially perpendicular incident light (40)( Figure 3For the blue wavelength range (50), green wavelength range (60), and red wavelength range (70) of the visible spectrum, the plurality of layers (31, 32) include a reflective band (80) having: a substantially flat top region (81); a left band edge (LBE) (82) on the short wavelength side (83) of the reflective band and a right band edge (RBE) (84) on the long wavelength side (85) of the reflective band, at which the reflectivity of the optical film (30) generally increases with increasing wavelength; and at which the reflectivity of the optical film (30) generally decreases with increasing wavelength.

[0023] In some embodiments, for a blue wavelength range (50) extending from about 420 nm to about 485 nm, a green wavelength range (60) extending from about 525 nm to about 575 nm, and a red wavelength range (70) extending from about 625 nm to about 740 nm, and for at least one polarization state, the reflection bands (80) of the plurality of layers (31, 32) may include a substantially flat top region (81) having a width of at least 100 nm. The substantially flat top region (81) may include at least one green wavelength (81g) in the green wavelength range (60) and at least one red wavelength (81r) in the red wavelength range (70). In some embodiments, the substantially flat top region may be at least 150 nm wide, or 200 nm wide, or 250 nm wide. In some aspects, the at least one polarization state may include a first polarization state along a first direction (x-axis) and a second polarization state along an orthogonal second direction (y-axis).

[0024] In other embodiments, the substantially flat top region (81) may comprise at least 80%, or at least 90%, or in some cases greater than 95%, of each of the green and red wavelength ranges. In some other embodiments, the substantially flat top region (81) may exclude any wavelengths in the blue wavelength range (50), such as Figure 6 The best example shown is...

[0025] In some embodiments, for substantially perpendicularly incident light, the substantially opaque light-absorbing layer (20) may absorb at least 70% of the incident light for at least one wavelength in each of the blue, green, and red wavelength ranges of the visible spectrum. In other embodiments, the substantially opaque light-absorbing layer (20) may absorb at least 80%, at least 90%, or at least 95% of the incident light for at least one wavelength in each of the blue, green, and red wavelength ranges of the visible spectrum.

[0026] In some embodiments, the spectral reflectance of the multilayer optical films (30) of the optical stack (200) incorporated into the side or rearview mirror can be modified, wherein the MOF is substantially reflective for green and red spectral wavelengths and substantially partially transmissive for lower wavelengths. In some examples, the multiple layers may have an average optical reflectance R1 greater than about 70% and a standard deviation less than about 5% in a substantially flat top region. In other examples, R1 may be greater than about 80%, or 90%, or 95%. In some cases, the average optical reflectance Rb in the blue wavelength range may be less than about 0.8R1. In some other cases, Rb may be less than about 0.7R1, or 0.65R1, or 0.6R1, and in other cases, Rb may be less than about 0.5R1, or 0.4R1, or 0.3R1, or 0.2R1, or 0.1R1.

[0027] In other embodiments, the mirror system for a side mirror (11) or rearview mirror (12) of a vehicle (10) includes an optical stack (200) having a light-absorbing layer (20) and an optical film (30) having a plurality of layers (31, 32) disposed on the light-absorbing layer. For substantially perpendicular incident light (40) and non-overlapping blue wavelength ranges (50), green wavelength ranges (60), and red wavelength ranges (70) of the visible spectrum, and for at least one polarization state (x-axis), the plurality of layers (31, 32) may include a reflectance spectrum (86) having a full width at half maximum (FWHM) (87), such as... Figure 4 As shown. In some cases, the at least one polarization state may include a first polarization state along a first direction (x-axis) and a second polarization state along an orthogonal second direction (y-axis). In some aspects, each of the wavelength ranges (50, 60, 70) may be at least 30 nm wide or at least 50 nm wide. In some other aspects, the non-overlapping blue, green, and red wavelength ranges of the visible spectrum may be spaced apart by at least 10 nm, at least 20 nm, or at least 40 nm.

[0028] In some aspects, FWHM may include at least 80% of each of the green and red wavelength ranges. In some cases, FWHM may include at least 90%, or at least 95%, or greater than 99% of each of the green and red wavelength ranges. In other cases, FWHM may include up to 20% of the blue wavelength range, and in some other cases, FWHM may include up to 15% or up to 10% of the blue wavelength range.

[0029] In some embodiments, for at least one wavelength (81g, 81r) in each of the green and red wavelength ranges, the reflectance spectrum (86) may include at least 70%, at least 80%, or greater than 90% reflectance. In some other embodiments, for at least one wavelength (81b, 81g, 81r) in each of the blue, green, and red wavelength ranges, the light-absorbing layer (20) may absorb at least 70%, at least 80%, or greater than 90% of the incident light.

[0030] Figures 5 to 6 Different representative examples of the reflectance spectra of MOFs that can be used in side or rearview mirrors are shown. These figures illustrate reflectance bands at various locations for the left edge of the band, for example, these locations can be adjusted by appropriately selecting the thickness distribution of the multiple layers (31, 32), as generally described in the following patents: e.g., U.S. Patent Nos. 5,882,774 (Jonza et al.); 6,179,948 (Merrill et al.); 6,783,349 (Neavin et al.); 6,967,778 (Wheatley et al.); and 9,162,406 (Neavin et al.).

[0031] In some respects, other optical filters can also be used in combination with multilayer optical films (30), such as light-controlling films (e.g., 3M). TM ALCF), or other MOFs used as notch filters, broadband partial mirrors, or reflective polarizers, to further enhance the headlight spectrum or the generated reflective spectrum.

Claims

1. A mirror system for a side or rearview mirror of a vehicle, the mirror system comprising: A basically opaque light-absorbing layer; and An optical film disposed on the light-absorbing layer and comprising at least 10 layers, each of the plurality of layers having an average thickness of less than 300 nm, such that for substantially perpendicular incident light and for at least one polarization state of the substantially perpendicular incident light, the plurality of layers include a reflection band comprising: The substantially flat top region of the wavelength-reflectivity curve of the reflection band, the substantially flat top region being at least 100 nm wide and including at least one green wavelength in the green wavelength range and at least one red wavelength in the red wavelength range; At the left edge of the short-wavelength side of the reflection band and the right edge of the long-wavelength side of the reflection band, at the left edge, the reflectivity of the optical film generally increases with increasing wavelength; at the right edge, the reflectivity of the optical film generally decreases with increasing wavelength, wherein the plurality of layers have: The average optical reflectance R1 is greater than 70% and the standard deviation is less than 5% in the substantially flat top region; and The average optical reflectance Rb is less than 0.8R1 in the blue wavelength range.

2. The mirror system of claim 1, wherein the substantially flat top region is at least 150 nm wide.

3. The mirror system of claim 1, wherein for the substantially perpendicular incident light, for at least one wavelength of each of the blue wavelength range, the green wavelength range, and the red wavelength range, the substantially opaque light-absorbing layer absorbs at least 70% of the incident light.

4. The mirror system according to claim 1, wherein the at least one polarization state includes a first polarization state along a first direction and a second polarization state along an orthogonal second direction.

5. The mirror system of claim 1, wherein the substantially flat top region comprises at least 80% of each of the green wavelength range and the red wavelength range.

6. The mirror system of claim 1, wherein the substantially flat top region does not include any wavelengths in the blue wavelength range.

7. An optical stack, the optical stack comprising: Light absorption layer; and An optical film disposed on the light-absorbing layer and comprising a plurality of layers totaling at least 10, each of the plurality of layers having an average thickness of less than 300 nm, such that for substantially perpendicular incident light and for non-overlapping wavelengths in the blue, green, and red wavelength ranges of the visible spectrum, each of the wavelength ranges is at least 30 nm wide, and for at least one polarization state of the substantially perpendicular incident light, the plurality of layers comprises a reflection spectrum comprising a full width at half maximum (FWHM), wherein: The FWHM includes at least 80% of each of the green wavelength range and the red wavelength range; The FWHM includes up to 20% of the blue wavelength range; For at least one wavelength in each of the green wavelength range and the red wavelength range, the reflectance spectrum includes at least 70% reflectance; and For at least one wavelength in each of the blue wavelength range, the green wavelength range, and the red wavelength range, the light-absorbing layer absorbs at least 70% of the incident light.

8. The optical stack according to claim 7, wherein the non-overlapping blue wavelength range, green wavelength range and red wavelength range of the visible spectrum are spaced apart by at least 10 nm, wherein the at least one polarization state includes a first polarization state along a first direction and a second polarization state along an orthogonal second direction.

9. The optical stack of claim 7, wherein the blue wavelength range extends from 420 nm to 485 nm, the green wavelength range extends from 525 nm to 575 nm, and the red wavelength range extends from 625 nm to 740 nm, wherein the light-absorbing layer absorbs at least 70% of the incident light in each of the blue wavelength range, the green wavelength range, and the red wavelength range, and wherein the light-absorbing layer comprises a linear absorption polarizer.

10. A mirror system for a side or rearview mirror of a vehicle, the mirror system comprising the optical stack according to claim 7.

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