A p-polarization head-up display system, method and windshield based on an oriented nanosilver wire film

Abstract

This invention discloses a P-polarized head-up display system, method, and windshield based on an oriented silver nanowire thin film. The system includes an image generation unit emitting P-polarized light, an automotive windshield with an embedded oriented silver nanowire thin film, and a driver's eye box. The oriented silver nanowire thin film is prepared by a flow coating process. The silver nanowires are oriented using a Jeffery orbital mechanism, with a Herman orientation factor f ≥ 0.60 and a fill ratio controlled between 10% and 30%. According to the effective medium theory, the film has a P-polarized light reflectivity R_P ≥ 35% and a visible light transmittance T ≥ 70%, meeting the ECE R43 automotive glass standard. P-polarized light irradiates the inner film of the windshield at an incident angle of 40° to 65°, forming a virtual image through selective reflection. The driver observes the virtual image located 1 to 5 meters in front of the windshield at a downward viewing angle of 5° to 15°. This invention solves the problem of existing PHUD technology relying on high-cost reflective films from a single supplier, providing a novel P-polarized HUD light combining solution that is low-cost, high-transparency, and can be manufactured in large areas through flow coating.

Description

Technical Field

[0001] This invention relates to the field of automotive head-up display (HUD) technology, specifically to a P-polarized head-up display system based on flow-coated oriented silver nanowire thin film, its implementation method, and an automotive laminated windshield integrating the thin film. Background Technology

[0002] Head-up display (HUD) systems project vehicle speed, navigation, and driver assistance information onto a virtual image in front of the driver, allowing them to access driving information without looking down, effectively reducing the risk of traffic accidents. With the rapid increase in the penetration rate of intelligent driving, HUDs have become a standard feature in mid-to-high-end vehicles.

[0003] P-polarized HUD (PHUD) is the HUD technology with the highest imaging brightness and fewest ghosting. Its core principle is that the liquid crystal display (TFT LCD) naturally outputs P-polarized light. Near Brewster's angle, the reflectivity of P-polarized light at the glass interface is significantly higher than that of S-polarized light. By embedding a P-polarized selective reflective film inside the car windshield, the P-polarized light output by the PGU can be efficiently reflected to the driver's eye box to form a clear virtual image, while maintaining the high transmittance of the car windshield to natural light.

[0004] The existing PHUD system mainly has the following technical problems: (a) The existing P-polarization selective reflective film is mainly the broadband reflective film (WCF) of 3M Company. It is made by co-extrusion stretching of 200 to 500 layers of polymer optical films with alternating refractive indices. The manufacturing process is extremely complex, and the cost per vehicle is as high as RMB 200 to 500. Moreover, there is only one supplier in the world, 3M Company, which poses a very high risk to the supply chain security.

[0005] (ii) Holographic optical element (HOE) type beam combiners are limited by the wavelength selectivity of Bragg diffraction, resulting in limited color reproduction. They also have stringent requirements for the monochromaticity of the light source, making it difficult to achieve wide color gamut full-color display.

[0006] (III) In the field of polarization optics of silver nanowires (AgNW), the Industrial Technology Research Institute of Taiwan disclosed a preparation method in CN102565909A (application date 2010, rights expired in 2014) that guides the orientation and alignment of silver nanowires through substrate stretching or grooving, for use as a replacement for absorptive polarizers in LCD displays. This method is characterized by a high fill ratio of 85% to 95% and aims to maximize the polarization extinction ratio, resulting in a significant decrease in visible light transmittance, which fails to meet the transmittance requirements of the ECE R43 standard (T≥70%) for automotive windshields. More importantly, this method is positioned as a replacement for LCD components, and its substrate stretching or grooving process cannot be extended to the size of automotive windshields (typically wider than 1.2m), and this patent has never involved any HUD-related applications.

[0007] In summary, no existing PHUD solution can simultaneously meet the following conditions: low-cost manufacturing, high transmittance (T≥70%), large-area coating capability, and no dependence on a single supplier. This invention aims to fill this gap. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a low-cost, high-transparency, large-area flow-coating P-polarized HUD system and its implementation method, breaking through the dependence of existing technologies on high-cost reflective films from a single supplier.

[0009] The core technological insight of this invention is based on the Effective Medium Theory (EMT): when the diameter of the silver nanowires is much smaller than the wavelength of visible light (d < λ / 10, i.e., d < 38 nm), the subwavelength-scale oriented conductor array exhibits anisotropic equivalent refractive index for incident light. Specifically, when the electric field component of P-polarized light is parallel to the orientation direction of the silver nanowires, the equivalent refractive index is close to that of metallic silver, resulting in strong reflection (R_P ≥ 35%); when the electric field component of S-polarized light is perpendicular to the orientation direction, the equivalent refractive index is close to that of the substrate material, resulting in high transmittance through the thin film (T_S ≥ 80%). This anisotropy is entirely determined by the orientation direction of the silver nanowires and is independent of whether the silver nanowires are arranged periodically at equal intervals, thus eliminating the need for any complex patterning processes such as photolithography or nanoimprinting.

[0010] The key technological breakthrough lies in controlling the nano-silver wire filling ratio to a low range of 10% to 30% (far lower than the high filling ratio of 85% to 95% in CN102565909A), which simultaneously achieves R_P≥35% (meeting the brightness requirements of PHUD imaging) and T≥70% (meeting the ECE R43 standard). This breaks the inherent perception in existing technologies that "high polarization reflectivity inevitably comes at the cost of sacrificing transmittance," and achieves a fundamental breakthrough in the performance of PHUD beam combiners.

[0011] This invention provides the following technical solutions: Option 1 (System): A P-polarized head-up display system, comprising three parts: a P-polarized image generation unit (PGU), an automotive laminated windshield with an embedded oriented silver nanowire thin film, and a driver's eye box. The PGU is placed inside the dashboard, and its emitted P-polarized light illuminates the AgNW thin film on the inner surface of the automotive windshield at an oblique incidence, forming a virtual image through P-polarized selective reflection; the driver's eye box observes the virtual image located on the outer side of the automotive windshield from a downward viewing angle.

[0012] Option 2 (Method): An oriented AgNW thin film is prepared using a flow coating process. The shear flow field during the coating process is used to orient the silver nanowires along the coating direction, and the orientation is fixed after drying. The filling ratio of the silver nanowires is controlled so that the film has both P-polarization selective reflective properties and high transmittance that meets automotive regulations. The film is integrated into the automotive laminated windshield in the form of a thermoplastic film interlayer. A PGU optical path is configured to realize P-polarization selective reflective imaging.

[0013] Option 3 (Product): Automotive laminated windshield with an oriented AgNW film, the film covering a local area corresponding to the HUD virtual image area, while the remaining area is ordinary laminated glass.

[0014] The beneficial effects of this invention are: (1) Break the monopoly of a single supplier for existing P-polarization optical combiners, diversify the sources of raw materials for nano-silver wires, and significantly reduce supply chain risks and manufacturing costs.

[0015] (2) The transmittance meets the regulatory requirements for automotive windshields and can be directly used for front windshields without structural modifications to the existing vehicle body design.

[0016] (3) The flow coating process equipment is highly versatile and compatible with existing glass lamination production lines, making it suitable for mass production of large-size automotive windshields.

[0017] (4) Broadband optical characteristics, supporting full color gamut image sources, and the image color reproduction is better than that of wavelength selective combiners.

[0018] (5) The nano-silver wires have near-infrared blocking properties, which can improve the thermal comfort of the cabin while realizing the PHUD function. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of the oriented silver nanowire thin film of the present invention in the interlayer of an automobile windshield, showing the number of each functional layer, the P-polarized incident light path, and the reflected light path.

[0020] Figure 2 This is a top view of an oriented silver nanowire thin film, showing the first orientation direction of the silver nanowires, their non-equidistant arrangement characteristics, and the average spacing.

[0021] Figure 3 This is a schematic diagram of the overall optical path principle of the P-polarized head-up display system of the present invention, showing the geometric relationship of the image generation unit (71), the car windshield (73), the driver's eye box, the position of the virtual image and the viewing angle at 7°. The car windshield is at an angle of 45° to the horizontal plane. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0023] Example 1: BMW-style direct-view PHUD system This embodiment provides a P-polarized head-up display system suitable for passenger vehicles. See [link to documentation]. Figure 3 .

[0024] The image generation unit (PGU, number 71) uses a 5-inch TFT LCD screen and is equipped with a high extinction ratio P-polarizer (extinction ratio ≥500:1) on the output side, with an output P-polarized light brightness ≥3000 cd / m². The PGU is placed inside the dashboard, directly facing the inner surface of the car windshield (number 73), without a folding reflector. The angle between the P-polarized light emission direction and the normal to the inner surface of the car windshield (the angle of incidence) is 45°, matching the 45° tilt angle of the car windshield.

[0025] Automotive laminated windshields (73) are laminated structures (see...) Figure 1 The film is composed of an outer glass layer (5), a PVB film (4), a PET substrate (1), an oriented AgNW film (2), a protective layer (3), another PVB film (4), and an inner glass layer (6) laminated together sequentially. The AgNW film (2) has a silver nanowire filling ratio of 20%, a Herman orientation factor f = 0.72, and an average line spacing of 350 nm. At an incident angle of 45°, the P-polarized light reflectance R_P = 40%, and the total visible light transmittance T = 73%.

[0026] The driver's eye box is located inside the car's windshield, observing a virtual image 2.5m in front of the windshield from a 7° downward viewing angle. Based on the plane mirror imaging relationship of a 45° windshield, the virtual image of the horizontally placed PGU has a vertical image plane, located symmetrically on the outer side of the windshield, appearing 2 to 3m in front of the driver. Under daytime ambient light conditions of 10000 lux, the HUD image contrast ratio is ≥1.2:1, meeting the requirements for driver readability.

[0027] Example 2: Flow coating method for preparing oriented silver nanowire thin films This embodiment details the preparation process of the oriented AgNW thin film (2) in Embodiment 1, corresponding to the steps of claim 2.

[0028] Step 1, preparation of AgNW suspension: Take silver nanowires with an average diameter of 25 nm and an average length of 20 μm (aspect ratio of 800), add them to a mixed solvent of isopropanol / water (volume ratio 7:3) to prepare a suspension with a mass concentration of 0.5 mg / mL; add polyvinylpyrrolidone (PVP, K30) as a dispersant, with a mass fraction of 0.5%, ultrasonically disperse for 30 min, and let stand for 24 h to degas.

[0029] Step 2, Flow Coating Orientation: A slit coating head with a 100 μm coating gap and a coating speed of 15 mm / s is used for single-pass flow coating on a 125 μm thick PET film. The shear rate γ = coating speed / gap = 150 s⁻¹. In this shear flow field, the silver nanowires are subjected to fluid torque and undergo Jeffery orbital orientation along the coating direction (first direction), preferably with the orientation angle converging to within 0° ± 15°. The coating is dried within 3 seconds under 60°C hot air to fix the orientation state and prevent Brownian motion from re-randomizing. The resulting film has a Herman orientation factor f = 0.72 (determined by two-dimensional X-ray diffraction pole figures).

[0030] Step 3, parameter characterization: The P-polarized transmittance and reflectance of the thin film at an incident angle of 45° were measured using a spectrophotometer. The results showed R_P = 40%, T_S = 81%, and the total visible light transmittance T = 73% (calculated according to ISO 9050). Statistical analysis of the top-view image obtained by scanning electron microscopy (SEM) showed an area fill ratio of 19.8% and an average line spacing of 345 nm (< 700 nm), which meets the parameter range of the claims.

[0031] Example 3: Manufacturing method of automotive laminated windshield This embodiment details the manufacturing process of an automotive laminated windshield containing an oriented AgNW film (claim 3).

[0032] (1) Preparation of oriented AgNW film: An oriented AgNW film was prepared on a 125 μm PET film according to the method of Example 2. The coating was only applied to the HUD area (about 300 cm²) of the PET film, and the remaining areas were left blank.

[0033] (2) Protective coating: Spin-coat an acrylic protective layer with a thickness of 2μm onto the AgNW film (3), and UV cure to prevent AgNW from being damaged by temperature and pressure in subsequent sandwich processes.

[0034] (3) PVB sandwich assembly: 0.76mm PVB (4) film is laid on the inner glass (6, 2.1mm thick) in sequence, then AgNW / PET film (1+2+3) is laid, then 0.76mm PVB (4) is laid, and finally the outer glass (5, 2.1mm thick) is laid to form a sandwich structure.

[0035] (4) Autoclave pressing: Hold at 120°C and 10 bar for 40 minutes to allow PVB to flow and degas fully, forming a strong bond with the glass and PET film. After pressing, the visible light transmittance T=72% (measured according to ECE R43, ≥70% is acceptable).

[0036] Example 4: High reflectivity scheme (R_P≥50%) This embodiment provides a high reflectivity solution optimized for strong ambient light (direct sunlight during the day).

[0037] The AgNW filler ratio was increased to 28%, while the remaining preparation parameters remained the same as in Example 2. The resulting film had a Herman orientation factor f = 0.70 and an average line spacing of 260 nm. At a 45° incident angle, R_P = 52%, and the total visible light transmittance T = 71%, still meeting the ECE R43 requirements. This approach is suitable for scenarios with extremely high HUD brightness requirements (such as under direct sunlight), and the HUD image contrast remains ≥1.3:1 under 80,000 lux direct sunlight. The trade-off is slightly lower transmittance, but it still meets regulatory requirements.

[0038] Comparative Example: Performance Comparison with CN102565909A (ITRI) Solution To demonstrate the substantial progress of the technical solution of the present invention, the solution of Embodiment 2 of the present invention is compared with the typical parameters of CN102565909A (Industrial Technology Research Institute of Taiwan, 2010), and the results are shown in the table below.

[0039] Contrast index The invention (Example two) CN102565909A (ITRI) Fill ratio 20% (low) 85%~95% (high) Visible light transmittance T 73%（≥70%✓） About 30%~50% (unqualified ✗) P-polarized reflectance R_P 40% (PHUD applicable) ~0% (non-reflective, absorption type) Application target PHUD on-board light combiner LCD display polarizer Orientation process Flow coating (large area) Substrate stretching / slotting (size limited) ECE R43 compliance Compliant (T≥70%) Not compliant (T<70%)

[0040] As can be seen from the table above, this invention differs fundamentally from CN102565909A in terms of invention purpose, fill ratio design, optical characteristics, and application scenarios: CN102565909A's AgNW film is an absorptive polarizer that achieves a high extinction ratio with a high fill ratio, but its transmittance does not meet the requirements for automotive glass and has never been involved in HUD applications; this invention, through a low fill ratio design, enables the AgNW film to simultaneously possess the P-polarized reflectivity required for PHUD imaging and the high transmittance required by automotive regulations, representing a completely new technical path to solve the PHUD light combiner problem.

Claims

1. A P-polarized head-up display system, characterized in that, include: An image generation unit that outputs P-polarized light; An automotive windshield, wherein an oriented silver nanowire film is embedded in the windshield, wherein the silver nanowires in the oriented silver nanowire film are arranged along a first direction, and the average spacing between adjacent silver nanowires is less than the wavelength of visible light. The oriented silver nanowire film has selective reflection characteristics for P-polarized light, and its visible light transmittance meets the regulatory requirements for automotive windshields. The driver's eye box, located inside the car windshield, receives the P-polarized image reflected by the oriented silver nanowire film and observes the virtual image located outside the car windshield from a downward viewing angle.

2. The P-polarized head-up display system according to claim 1, characterized in that, The image generation unit includes a liquid crystal display screen and an emission-side P-polarizer. The liquid crystal display screen is placed inside the dashboard, and the emitted P-polarized light directly illuminates the inner surface of the car windshield without the need for a folding reflector.

3. The P-polarized head-up display system according to claim 1, characterized in that, The virtual image observed by the driver's eye box is located outside the windshield of the car, and the distance between the virtual image and the driver's eye point is greater than 0.5m. The downward viewing angle is 2° to 20°.

4. A method for implementing a P-polarized head-up display system, characterized in that, Includes the following steps: Step 1: Configure the image generation unit to emit P-polarized light; Step 2, Preparation of oriented silver nanowire thin film: High aspect ratio silver nanowires are prepared into a suspension and coated on a transparent substrate using a flow coating process. The shear flow field during the coating process is used to orient the silver nanowires along the coating direction, and the orientation is fixed by drying. The filling ratio of silver nanowires is controlled so that the visible light transmittance of the resulting film meets the regulatory requirements for automotive windshields. Step 3: Integrate the oriented silver nanowire film into the interior of the car windshield in a sandwich manner; Step four: Configure the optical path of the image generation unit so that P-polarized light is obliquely incident on the oriented silver nanowire film inside the car windshield. Through the selective reflection of P-polarized light by the oriented silver nanowire film, the image information is transmitted to the driver's eye box.

5. The method according to claim 4, characterized in that, The flow coating process described in step two uses a slot coating head, doctor blade, or roller coating method, and the transparent substrate is polyethylene terephthalate (PET) film or other transparent flexible film.

6. The method according to claim 4, characterized in that, The interlayer integration in step three uses a thermoplastic interlayer film, which is either polyvinyl butyral (PVB) or ethylene-vinyl acetate copolymer (EVA).

7. A laminated windshield for an automotive system used in a P-polarized head-up display, characterized in that, It includes an outer glass layer, an inner glass layer, and an oriented silver nanowire film sandwiched therebetween; the silver nanowires in the oriented silver nanowire film are arranged along a first direction and the average spacing is less than the wavelength of visible light; The filling ratio of the oriented silver nanowire film enables the automotive laminated windshield to meet the regulatory requirements for light transmittance of automotive glass while exhibiting selective reflection characteristics for P-polarized light, which can reflect P-polarized images to the driver's eye box.

8. The automotive laminated windshield according to claim 7, characterized in that, The oriented silver nanowire film only covers a local area of ​​the head-up display virtual image area in the automotive laminated windshield, and the area outside this local area is ordinary laminated glass without the silver nanowire film.

9. The system or method according to claim 1 or 4, characterized in that, The P-polarized light emitted from the image generation unit irradiates the oriented silver nanowire thin film at an incident angle in the range of 25° to 75°.

10. The system or automotive laminated windshield according to claim 1 or 7, characterized in that, The area fill ratio of the oriented silver nanowire thin film is less than 50%, so that the film simultaneously possesses P-polarization selective reflectivity and high visible light transmittance.

11. The system or automotive laminated windshield according to claim 1 or 7, characterized in that, The Herman orientation factor f of the silver nanowires in the oriented silver nanowire film is not less than 0.

4.

12. The system or automotive laminated windshield according to claim 1 or 7, characterized in that, The oriented silver nanowire thin film has a reflectivity R_P of not less than 15% for P-polarized light and a visible light transmittance T of not less than 70%.

13. The system, method, or automotive laminated windshield according to claim 1, 4, or 7, characterized in that, The oriented silver nanowire thin film achieves polarization selectivity based on the Effective Medium Theory (EMT): P-polarized light, along the orientation direction of the silver nanowire, experiences the equivalent refractive index of the metal and produces strong reflection, while S-polarized light, perpendicular to the orientation direction, experiences the equivalent refractive index of the medium and has high transmission. The polarization selectivity is determined by the orientation direction of the silver nanowire and is independent of whether the silver nanowires are periodically arranged.

14. The system, method, or automotive laminated windshield according to claim 1, 4, or 7, characterized in that, The oriented silver nanowire film also has a blocking function for near-infrared solar radiation, and at the same time realizes the combined function of P-polarized head-up display light combining and vehicle heat insulation and cooling.

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