A light control film based on synergistic enhancement of contrast by photonic crystals and dynamic dye, and a preparation method and application thereof

Abstract

The application discloses a light-adjusting film based on synergistically enhanced contrast ratio of photonic crystals and dynamic dyes, and a preparation method and application thereof. The light-adjusting film comprises a first substrate layer, a first conductive layer, a polymer-dispersed dye liquid crystal layer, a second conductive layer, a photonic crystal layer and a second substrate layer which are sequentially stacked; the polymer-dispersed dye liquid crystal layer comprises a polymer matrix, liquid crystal droplets and a blackening agent, and the liquid crystal droplets disperse dichroic dyes; the photonic crystal layer is formed by high and low refractive index materials to form a non-strict periodic multilayer film structure. In an off state, the dye is randomly oriented to absorb, the blackening agent captures stray light, and the photonic crystal layer reflects residual light back to the liquid crystal layer to form a 'light trap', so that the off state is dark; in an on state, the electric field makes the dye orderly arranged to realize high light transmission. The application improves the contrast ratio without increasing the film thickness and dye concentration, and has low voltage driving and long-term reliability.

Description

Technical Field

[0001] This invention relates to the field of dimming films, and in particular to a dimming film based on the synergistic enhancement of contrast by photonic crystals and dynamic dyes, its preparation method, and its application. Background Technology

[0002] Intelligent dimming films, especially dye-doped polymer-dispersed liquid crystal (PDLC) films, have been widely used in automotive sunroofs, side windows, building curtain walls, and privacy partitions due to their ability to regulate light transmission and scattering states via electric fields. In practical applications, users have placed higher demands on dimming films: they need to present a deep black in the off-state (power-off state) to ensure privacy and sunshade effects, and maintain high light transmission in the on-state (power-on state) to provide a clear view. Simultaneously, they require low driving voltage, high reliability, and ease of large-area fabrication. However, existing dye-doped PDLC films generally exhibit a "gray film" rather than an ideal black film in the off-state, resulting in poor visual shading and a contrast ratio typically only 8-10 times. To address this issue, the industry mainly employs the following two solutions, but both have significant drawbacks.

[0003] The first approach involves significantly increasing the dye concentration to enhance the off-state light absorption by increasing the doping amount of the dichroic dye. However, this method leads to a significant increase in the intrinsic absorption of the dye in the on-state, resulting in a substantial decrease in transmittance. At the same time, the dye has limited solubility in liquid crystal and polymer matrix systems, and high concentrations can easily cause the dye to precipitate and aggregate later, forming irreversible "black spots" and "white spots" defects, which seriously affect product yield and service life.

[0004] The second option is to increase the thickness of the PDLC layer to enhance off-state scattering and absorption by extending the optical path. However, the increased film thickness leads to a linear increase in the saturation driving voltage, which places higher demands on the driving circuit and increases power consumption. In addition, the increased thickness will significantly worsen the haze when viewed from a large angle, affecting aesthetics and visual clarity.

[0005] Therefore, there is an urgent need for a new dimming film, its preparation method and application, which can achieve ultra-black in the off state, high transmittance in the on state, low voltage drive and long-term reliability without significantly increasing the dye concentration and film thickness. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a dimming film that enhances the contrast between powered and unpowered states through the synergistic effect of photonic crystals and dynamic dyes, while also enabling long-term reliable dimming.

[0007] To achieve the above objectives, the present invention employs the following technical solutions:

[0008] A contrast-enhancing dimming film based on the synergistic enhancement of contrast by photonic crystals and dynamic dyes includes a first substrate layer, a first conductive layer, a polymer dispersed dye liquid crystal layer, a second conductive layer, a photonic crystal layer, and a second substrate layer stacked sequentially. The polymer dispersed dye liquid crystal layer includes a polymer matrix, liquid crystal microdroplets dispersed in a matrix network, and a blackening agent. The liquid crystal microdroplets contain dihedral dyes. The photonic crystal layer is a multilayer structure formed by alternating layers of two transparent materials with high and low refractive indices. The thickness of each transparent material layer varies pseudo-randomly.

[0009] As a preferred technical solution, the particle size range of the blackening agent is 1~100 nanometers, and the blackening agent is an insulating organic pigment dispersion or a core-shell inorganic blackening agent; 0.5%-2% wt of blackening agent is added to the polymer disperse dye liquid crystal layer.

[0010] As a preferred technical solution, the birefringence Δn of the liquid crystal microdroplets is greater than 0.2, and the dihedral ratio of the dihedral dye is greater than 10.

[0011] As a preferred technical solution, the polymer disperse dye liquid crystal layer comprises the following raw materials by mass fraction: liquid crystal 40%–60%; dihedral dye 2%–5%; UV-curable adhesive 40%–60%; blackening agent 0.5%–2%; photoinitiator 0.2%–2%; and spacers 0.5%–1%.

[0012] As a preferred technical solution, the polymer disperse dye liquid crystal layer coating thickness is 10–35 μm.

[0013] As a preferred technical solution, the high refractive index layer and the low refractive index layer are alternately arranged for 2-10 cycles, and the thickness of each low refractive index layer is greater than that of each high refractive index layer.

[0014] As a preferred technical solution, the low refractive index layer has a thickness of 10~80 nm, and the thickness difference between any low refractive index layer is 2~30 nm; the thickness of the high refractive index layer has a thickness of 5~50 nm, and the thickness difference between any high refractive index layer is 2~30 nm.

[0015] As a preferred technical solution, the high-refractive-index transparent material is titanium dioxide, and the low-refractive-index transparent material is silicon dioxide.

[0016] To address the shortcomings of existing technologies, a second objective of this invention is to provide a preparation method for preparing a dimming film based on the synergistic enhancement of pass-through contrast by photonic crystals and dynamic dyes.

[0017] A method for preparing a contrast-enhancing dimming film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye, characterized by comprising the following steps:

[0018] S1: A first conductive layer is formed on the first substrate layer by magnetron sputtering.

[0019] S2: Alternately deposit high-refractive-index and low-refractive-index materials on the second substrate layer to form a photonic crystal layer; then magnetron sputtering is used to form a second conductive layer on the surface of the photonic crystal layer.

[0020] S3: After mixing and stirring the UV-curable adhesive, photoinitiator, liquid crystal, dihedral dye, blackening agent, and spacer evenly and degassing, a dye PDLC material is obtained. Then, the dye PDLC material is coated between the first conductive layer and the second conductive layer, and then photocured to obtain the dimming film.

[0021] S4: Seal the edges of the prepared dimming film, bring out the electrodes, and test its electro-optical performance.

[0022] To address the shortcomings of existing technologies, the third objective of this invention is that the dimming film enhances the contrast between energized and de-energized states based on the synergistic effect of photonic crystals and dynamic dyes, while also providing long-term reliable dimming capabilities. This enables its application as a building material for automotive sunroofs, side windows, building curtain walls, and privacy space partitions.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention, by simultaneously adding appropriate amounts of a blackening agent and a dichroic dye to a polymer dispersed liquid crystal (PDLC) material, utilizes the synergistic effect of the blackening agent and dye to absorb visible light, avoiding the problems of dye precipitation, decreased on-state transmittance, and shortened dimming film lifespan caused by increasing the concentration of a single dye. Simultaneously, combined with the high reflectivity of the photonic crystal layer, residual light penetrating the liquid crystal layer is efficiently reflected back to the liquid crystal layer. The reflected light undergoes further absorption by the dye and trapping by the blackening agent, forming a "light trap" effect, causing the emitted light intensity to approach zero, thereby increasing the darkness of the dimming film in the off-state.

[0025] 2. In this invention, the photonic crystal layer employs a multilayer structure formed by alternating high and low refractive index materials, with each layer exhibiting random or pseudo-random thickness variations. Compared to traditional strictly periodic photonic crystals, this non-periodic structure disrupts long-range periodicity, suppresses the blue shift of the reflection peak at large incident angles, and maintains stable and efficient reflection performance over a wide incident angle range of 0° to 70° by utilizing multiple scattering and localization effects. In the off-state of the dimming film, large-angle light scattered from the liquid crystal layer can be efficiently reflected back to the liquid crystal layer by this reflective layer, undergoing dye absorption and blackening agent trapping again, forming a stronger "light trapping" effect, thereby significantly reducing the off-state transmittance and improving the contrast between the off and on states.

[0026] 3. This invention achieves low visible light transmittance and high contrast in the off state with a conventional PDLC layer thickness, without the need to increase the thickness of the polymer disperse dye liquid crystal layer, thereby ensuring that the dimming film can be driven with a lower voltage and reducing energy consumption.

[0027] 4. The method for preparing the dimming film of this invention employs physical vapor deposition (PVD) to obtain a conductive layer and a photonic crystal layer, and then uses coating and UV curing to obtain a polymer-dispersed dye liquid crystal layer. This preparation method has good compatibility with existing dimming film production processes, which is beneficial for achieving stable mass production. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the dimming film of the present invention. Detailed Implementation

[0029] The following examples further illustrate the features and other related characteristics of the present invention in detail, to facilitate understanding by those skilled in the art:

[0030] The embodiments of the present invention provide a dimming film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye. The dimming film presents a deep black color in the off state (power off state) and the contrast ratio can reach more than 50:1. It is suitable for automotive sunroofs, side windows, building curtain walls and privacy partitions.

[0031] A contrast-enhancing dimming film based on the synergistic enhancement of contrast by photonic crystals and dynamic dyes comprises a first substrate layer (1), a first conductive layer (2), a polymer dispersed dye liquid crystal layer (3), a second conductive layer (4), a photonic crystal layer (5), and a second substrate layer (6) stacked sequentially. The polymer dispersed dye liquid crystal layer comprises a polymer matrix, liquid crystal microdroplets dispersed in a matrix network, and a blackening agent, wherein the liquid crystal microdroplets contain dihedral dyes; the photonic crystal layer is a multilayer structure formed by alternating high and low refractive indices, and the thickness of each transparent material layer has a pseudo-random variation.

[0032] In this embodiment, the dihedral dye within the liquid crystal microdroplets randomly oriented and absorbs visible light in the off state, while the blackening agent, uniformly dispersed in the polymer matrix, continuously absorbs stray light. The photonic crystal layer efficiently reflects residual light penetrating the liquid crystal layer back to it, creating a "light trap" effect that results in extremely low transmittance in the off state. In the on state, the electric field causes the liquid crystal and dye to align in an orderly manner, minimizing dye absorption and achieving high transmittance. Compared to existing technologies that improve contrast by increasing dye concentration or film thickness, this embodiment achieves a comprehensive performance of ultra-black in the off state, high transmittance in the on state, low-voltage drive, and long-term reliability through the synergistic effect of the blackening agent and the photonic crystal layer, without significantly increasing dye concentration or film thickness.

[0033] Specifically, the polymer disperse dye liquid crystal layer of the embodiment comprises the following raw materials by mass fraction: liquid crystal 40% to 60%; dihedral dye 2% to 5%; UV-curable adhesive 40% to 60%; blackening agent 0.5% to 2%; photoinitiator 0.2% to 1%; and spacer 0.5% to 1%.

[0034] In some examples, the liquid crystal is a nematic liquid crystal with a high birefringence value (Δn > 0.2). The mass fraction of the liquid crystal can be 40%, 45%, 50%, 55%, 60%, etc., used to induce orientation changes under the action of an electric field, driving the dichroic dyes to align synchronously, thereby controlling the light transmission and scattering states. If the liquid crystal content is less than 40%, it will result in excessive polymer matrix, insufficient liquid crystal droplet volume fraction, decreased off-state scattering ability, and reduced on-state transmittance due to poor liquid crystal continuity, leading to poor contrast. If the liquid crystal content is greater than 60%, it will result in increased driving voltage, and the relatively insufficient UV-curable adhesive will affect the structural strength of the polymer network.

[0035] In some examples, the dichroic dye is preferably anthraquinone dye with good weather resistance and a high dichroism ratio (>10), used to dissolve within the liquid crystal. The mass fraction of the dichroic dye can be 2%, 3%, 4%, 5%, etc. It strongly absorbs incident light in the off-state with random orientation and reduces absorption in the on-state with ordered alignment within the liquid crystal, thereby improving contrast. If the dye concentration is less than 2%, the off-state light absorption is insufficient, the off-state transmittance is too high, and the contrast improvement is limited. If the dye concentration is greater than 5%, it will not only exceed its solubility in the liquid crystal, leading to later precipitation and the formation of "black spot" defects, but will also produce significant residual absorption in the on-state, reducing the on-state transmittance.

[0036] In some examples, the UV-curable adhesive includes acrylate monomers, acrylate resins, and additives, such as leveling agents and defoamers. The acrylate monomers and acrylate resins can crosslink and cure under the action of a photoinitiator.

[0037] In some examples, the mass fraction of the UV-curable adhesive can be 40%, 45%, 50%, 55%, or 60%, used to undergo polymerization and cross-linking under UV irradiation to form a polymer matrix network, dispersing liquid crystal droplets within this network. If the amount of UV-curable adhesive is less than 40%, the resulting polymer matrix network is not dense enough, weakening its encapsulation and fixation of the liquid crystal droplets, leading to light leakage in the off-state and poor stability in the on-state. If the amount of UV-curable adhesive is greater than 60%, the relative liquid crystal content decreases, the on-state transmittance decreases, and the driving voltage increases.

[0038] In some examples, the blackening agent is an insulating organic pigment dispersion or a core-shell inorganic blackening agent. The blackening agent can be nano-aniline black, polymer core-shell iron oxide black, or polymer materials such as polystyrene or polymethyl methacrylate. The particle size of the blackening agent ranges from 10 to 100 nm, and it is uniformly dispersed in the polymer matrix, continuously absorbing leaked stray light and further reducing the off-state light transmittance. The resistivity is ≥10¹² Ω·cm, and the addition ratio is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. If the amount of blackening agent is less than 0.5%, the absorption of stray light is insufficient, making it difficult to further reduce the off-state transmittance and weakening the light trapping effect. If the amount of blackening agent is more than 2%, it will lead to an increase in on-state transmittance, a decrease in the contrast difference between the off and on states, and the blackening agent is prone to agglomeration to form black spots, affecting the quality of the dimming film.

[0039] In some examples, the mass fraction of the photoinitiator can be 0.2 parts, 0.5 parts, 0.8 parts, 1 part, etc. The photoinitiator is selected from benzyl ketone type, acylphosphine oxide type, oxime ester photoinitiators, such as 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) or 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), used to initiate the polymerization and curing of UV-curable adhesives under UV light irradiation.

[0040] In some examples, the spacer particle size is 10~30μm, and the spacer can be silica microspheres, PMMA microspheres, or styrene microspheres, to help maintain a fixed gap between the two substrate layers and avoid local thickness changes due to external forces or curing shrinkage.

[0041] In some examples, the photonic crystal layer is formed by alternating deposition of high-refractive-index materials (such as titanium dioxide) and low-refractive-index materials (such as silicon dioxide), with 2 to 10 periods. The thickness of each layer varies randomly, causing the photonic crystal multilayer film to lose its strict periodicity and no longer have a single Bragg reflection peak, but instead form a broad-spectrum reflection band. Because the liquid crystal in the off-state dimming film is randomly oriented, the residual light has a wide range of incident angles after reflection and refraction by the liquid crystal. When the incident angle increases from 0° to 70°, the traditional structure causes the reflection peak to deviate from the visible light range due to blue shift, while the random thickness structure, due to the existence of multiple local periods, can always maintain effective reflection in the visible light band, thereby achieving stable reflectivity over a wide angle range. This perfectly matches the angular distribution of scattered light in the off-state of the PDLC, significantly improving the blackness and contrast of the off-state. In the open state, the liquid crystal in the dimming film undergoes uniform orientation along the direction of the electric field under the action of the electric field. The residual light has a narrow incident angle range. The photonic crystal layer of the present invention has a low reflectivity and a high transmittance for light with a narrow incident angle range, ensuring that the dimming film maintains a transparent state with high light transmittance and low haze in the open state.

[0042] Existing optical devices, such as the Chinese patent with publication number CN201804887U, use photonic crystal selective reflective films. Traditional photonic crystals are periodic and can only reflect specific wavelengths and angles. Although the reflectivity of light at that incident angle and wavelength is extremely high, the reflectivity of other residual light is low, and most of the light cannot be reflected. The overall reflectivity of the photonic crystal is not high, making it difficult to reflect the remaining light back to the dye liquid crystal layer.

[0043] In some examples, the thickness of each low-refractive-index layer is greater than that of each high-refractive-index layer. The low-refractive-index layers are 10–80 nm thick, with a thickness difference of 2–30 nm between any two low-refractive-index layers. The high-refractive-index layers are 5–50 nm thick, with a thickness difference of 2–30 nm between any two high-refractive-index layers. This ensures significant and controllable differences in the thickness of each layer within the photonic crystal layer. This interlayer difference causes the multilayer film to lose its strict periodicity, no longer corresponding to a single Bragg reflection peak, but instead forming a broad-spectrum reflection band with multiple superimposed local reflection peaks.

[0044] In some examples, the first substrate layer and the second substrate layer are transparent plastic films selected from at least one of PET, PC, and PMMA, with PET substrate being preferred.

[0045] In some examples, the first conductive layer and the second conductive layer are transparent conductive films selected from indium tin oxide (ITO), silver nanowire films, graphene films or metal mesh films, with ITO films being preferred.

[0046] This embodiment also provides a method for preparing the above-mentioned dimming film, including the following steps:

[0047] S1: A first conductive layer is formed on the first substrate layer by magnetron sputtering to obtain a first conductive substrate.

[0048] S2: Optical thin film design software generates a non-strictly periodic layer thickness sequence of 2 to 10 periods, with one layer of high-refractive-index material and one layer of low-refractive-index material constituting one period. Software design method: Input a standard thickness d of titanium dioxide. 10 d 10 =7~48 nm, and set the thickness difference between titanium dioxide layers to Δx1=2~30 nm, the software randomly generates d1=d 10 ±Δx1, and the thickness of each titanium dioxide layer is different, but at the same time, d1 = 5~50 nm must be maintained. Input a standard thickness d for silicon dioxide. 20 d 20 =12~78 nm, and set the thickness difference between silicon dioxide layers to Δx2=2~30 nm, the software randomly generates d2=d 20 ±Δx2, and the thickness of each silicon dioxide layer is different, but at the same time, d2 = 10~80 nm must be ensured. On the second substrate layer, TiO2 and SiO2 are alternately deposited by magnetron sputtering to form a photonic crystal layer.

[0049] S3: A dye-based PDLC material is obtained by uniformly mixing and degassing a UV-curable adhesive, photoinitiator, liquid crystal, dihedral dye, blackening agent, and spacers. This dye-based PDLC material is then coated onto one surface of the first or second conductive layer, followed by a cover layer of the other conductive layer. Alternatively, the PDLC material can be directly coated between the first and second conductive layers using a two-roll coating method, with a coating thickness of 10–35 μm. Another conductive substrate is then used to cover the coating, ensuring the photonic crystal layer is on the outermost layer. The material is then cured by UV irradiation at an intensity of 4–100 mW / cm² for 120–300 s, initiating resin polymerization to form a polymer network. Simultaneously, the liquid crystal phase separates into microdroplets dispersed within the polymer network, resulting in a dimming film.

[0050] S4: Cut the dimming film and fabricate electrodes, then connect it to a power source to test its electro-optical performance.

[0051] The present invention will be further described in detail below through specific embodiments.

[0052] Example 1

[0053] The dimming film in this embodiment is manufactured using the following steps:

[0054] S1: A transparent PET base film with a thickness of 188μm is selected as the first substrate layer and the second substrate layer. The total light transmittance of the first substrate layer is 90%, and the haze is 0.5%. A first conductive film is formed by magnetron sputtering of an ITO target, with a sheet resistance of 120Ω.

[0055] S2: The second substrate layer is formed by sequentially depositing TiO2, SiO2, TiO2, and SiO2 films with thicknesses of 22 nm, 35 nm, 27 nm, and 55 nm using magnetron sputtering to form a photonic crystal layer. Then, ITO with a sheet resistance of 120 Ω is magnetron sputtered onto the surface of the photonic crystal layer to form the second conductive layer.

[0056] S3: Mix the following raw materials by mass fraction: 50 parts of nematic liquid crystal (Jiangsu Synthetic, Δn=0.21), 3.5 parts of dihedral black anthraquinone dye (Xingye self-mixed, dihedral ratio 12), 50 parts of UV-curable adhesive (Xingye, self-mixed adhesive based on polyurethane acrylic resin), 0.5 parts of blackening agent (commercially available nano-aniline black, average particle size 50nm), 1.5 parts of photoinitiator TPO-L (Bavs), and 0.6 parts of spacers with a particle size of 20μm (PMMA microspheres). Stir thoroughly and degas to obtain the dye PDLC material. Coat the above dye PDLC material with a double roller between the conductive surfaces of conductive film 1 and conductive film 2 to form a sandwich structure. Irradiate with 22mW / cm² UV light at 25℃ for 180s to initiate curing and obtain a dimming film.

[0057] S4: Cut the dimming film and fabricate the electrodes.

[0058] Example 2

[0059] Example 2, based on Example 1, adjusted the raw material amounts of the dye PDLC. The dye PDLC material included the following raw materials by mass fraction: 49.5 parts nematic liquid crystal, 3.5 parts dihedral black anthraquinone dye, 49.5 parts UV-curable adhesive, 1 part blackening agent, 1.6 parts photoinitiator TPO-L, and 0.6 parts spacers. It was irradiated with 25 mW / cm² UV light for 180 s at 25°C.

[0060] Example 3

[0061] Example 3, based on Example 1, adjusts the raw material amounts of the dye PDLC. The dye PDLC material includes the following raw materials by mass fraction: 49 parts nematic liquid crystal, 3.5 parts dihedral black anthraquinone dye, 49 parts UV-curable adhesive, 2 parts blackening agent, 1.8 parts photoinitiator TPO-L, and 0.6 parts spacers. The photonic crystal layer has four periods, namely four SiO2 films and four TiO2 films, with SiO2 and TiO2 overlapping. The thicknesses of each period are as follows: Period 1: SiO2 56.7 nm, TiO2 38.9 nm; Period 2: SiO2 50.3 nm, TiO2 30.9 nm; Period 3: SiO2 58.6 nm, TiO2 36.8 nm; Period 4: SiO2 43.3 nm, TiO2 40.2 nm.

[0062] Example 4

[0063] Example 4 is based on Example 1, but with adjustments made to the photonic crystal layer. The photonic crystal layer in Example 4 has 10 periods, with the following thicknesses for each period: Period 1: SiO2 45.2 nm, TiO2 28.5 nm; Period 2: SiO2 52.3 nm, TiO2 31.2 nm; Period 3: SiO2 38.7 nm, TiO2 22.1 nm; Period 4: SiO2 60.5 nm, TiO2 35.4 nm; Period 5: SiO2 42.8 nm, TiO2 25.6 nm; Period 6: SiO2 48.1 nm, TiO2 29.3 nm; Period 7: SiO2 55.6 nm, TiO2 33.8 nm; Period 8: SiO2 36.2 nm, TiO2 19.7 nm; Period 9: SiO2 58.9 nm, TiO2 37.2 nm; Period 10: SiO2 50.3 nm, TiO2 27.4 nm. nm.

[0064] Comparative Example 1

[0065] Comparative Example 1, based on Example 1, adjusted the raw material amounts of the dye PDLC. The dye PDLC material included the following raw materials by mass fraction: 50 parts nematic liquid crystal, 3.5 parts dihedral black anthraquinone dye, 50 parts UV-curable adhesive, 1.5 parts photoinitiator TPO-L, and 0.6 parts spacers. No photonic crystal layer was provided.

[0066] Comparative Example 2

[0067] Comparative Example 2, based on Example 1, adjusted the amount of raw materials used in the dye PDLC. The dye PDLC material included the following raw materials by mass fraction: 50 parts of nematic liquid crystal, 5.5 parts of dihedral black anthraquinone dye, 50 parts of UV-curable adhesive, 2 parts of photoinitiator TPO-L, and 0.6 parts of spacer.

[0068] Comparative Example 3

[0069] Comparative Example 3, based on Example 1, adjusted the amount of raw materials used in the dye PDLC. The dye PDLC material included the following raw materials by mass fraction: 50 parts of nematic liquid crystal, 3.5 parts of dihedral black anthraquinone dye, 50 parts of UV-curable adhesive, 1 part of blackening agent, 1.5 parts of photoinitiator TPO-L, and 0.6 parts of spacer, and no photonic crystal layer was provided.

[0070] Comparative Example 4

[0071] Comparative Example 4, based on Example 1, adjusted the coating thickness of the dye PDLC material and the amount of raw materials used in the dye PDLC. The thickness of the dye PDLC in Comparative Example 4 was 30 μm. The dye PDLC material included the following raw materials by mass fraction: 50 parts of nematic liquid crystal, 3.5 parts of dihedral black anthraquinone dye, 50 parts of UV-curable adhesive, 2 parts of photoinitiator TPO-L, and 0.6 parts of spacers.

[0072] Comparative Example 5

[0073] Comparative Example 5 adjusts the photonic crystal layer structure based on Example 1. The photonic crystal layer of Comparative Example 5 has two periods, each period consisting of a 22nm TiO2 layer and a 35nm SiO2 layer.

[0074] Performance testing

[0075] The dimming films obtained in Examples 1-4 and Comparative Examples 1-4 were subjected to the following tests.

[0076] (1) The average transmittance in the wavelength range of 380~780 nm was measured using a UV-Vis spectrophotometer in accordance with GB / T 2680-94 standard. The transmittance in the off state (T-off) and the haze (H-off) are the transmittance when no voltage is applied, and the transmittance in the on state (T-on) is the transmittance when a 48 V AC voltage (50 Hz) is applied.

[0077] (2) Contrast calculation: CR = T-on / T-off.

[0078] (3) Saturation voltage test: Gradually increase the applied voltage (AC 50 Hz), record the transmittance at 0 and 70V (the default is the maximum transmittance value), and then find the voltage value corresponding to 90% transmittance value of 70V by adjusting the voltage and record it as the saturation voltage (Vsat, unit V).

[0079] (4) Dye precipitation aging test: The dimming film sample was subjected to aging tests at 110℃ for 500h and PV3929 for 120h. After removal, the sample was observed with an optical microscope (×200x) to see if there were any "black spots" defects formed by dye precipitation inside the sample from 0 to 60V. Evaluation criteria: No black spots are "qualified", and visible black spots are "unqualified".

[0080] Table 1. Performance test results of the dimming films in the examples and comparative examples.

[0081]

[0082] This invention successfully breaks through the traditional technical dilemma that "increasing contrast requires either increasing dye concentration or increasing film thickness" by introducing a synergistic design of a blackening agent and a photonic crystal layer. As shown in Examples 1-3, under the same film thickness and moderate dye concentration, the contrast ratio of a traditional PDLC film without a blackening agent and photonic crystal layer is only 12, while the contrast ratio of Example 2 of this invention is increased to 41, and the contrast ratio of Example 3 is as high as 73, with a low off-state transmittance of 0.3%~0.6%, presenting a deep black. Although Comparative Example 2 increased the dye concentration to 5.5%, the contrast ratio only increased to 20, and severe dye precipitation occurred; Comparative Example 4 increased the film thickness to 30 μm, but the contrast ratio was only 18.5, while the saturation voltage increased to 45 V. The solution of this invention achieves the best balance between high-contrast "black film" and low-voltage drive and long-term reliability without introducing new risks such as dye precipitation and voltage increase, perfectly meeting the urgent needs of the current automotive and building dimming film industry upgrade.

[0083] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A dimming film based on the synergistic enhancement of contrast using photonic crystals and dynamic dyes, characterized in that, It includes a first substrate layer, a first conductive layer, a polymer disperse dye liquid crystal layer, a second conductive layer, a photonic crystal layer, and a second substrate layer stacked sequentially. The polymer dispersed dye liquid crystal layer includes a polymer matrix, liquid crystal dispersed in a matrix network, and a blackening agent, wherein a dihedral dye is dispersed within the liquid crystal. The photonic crystal layer is a multilayer structure formed by alternating layers of two transparent materials with high and low refractive indices; the thickness of each transparent material layer varies pseudo-randomly.

2. The dimming film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye according to claim 1, characterized in that, The blackening agent has a particle size range of 1~100 nanometers, and the blackening agent is an insulating organic pigment dispersion or a core-shell inorganic blackening agent; 0.5%-2% wt of blackening agent is added to the polymer disperse dye liquid crystal layer.

3. The dimming film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye according to claim 1, characterized in that, The liquid crystal has a birefringence Δn > 0.2, and the dihedral ratio of the dihedral dye is > 10.

4. The dimming film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye according to claim 1, characterized in that, The polymer disperse dye liquid crystal layer comprises the following raw materials by mass fraction: liquid crystal 40%–60%; dihedral dye 2%–5%; UV-curable adhesive 40%–60%; blackening agent 0.5%–2%; photoinitiator 0.2%–1%; and spacer 0.5%–1%.

5. A dimming film for enhancing contrast based on the synergistic effect of photonic crystal and dynamic dye as described in claim 4, characterized in that, The polymer disperse dye liquid crystal layer has a coating thickness of 10–35 μm.

6. A dimming film for enhancing contrast based on the synergistic effect of photonic crystal and dynamic dye as described in claim 1, characterized in that, The high-refractive-index layer and the low-refractive-index layer are alternated for 2-10 cycles, and the thickness of each low-refractive-index layer is greater than that of each high-refractive-index layer.

7. A dimming film for enhancing contrast based on the synergistic effect of photonic crystal and dynamic dye according to claim 6, characterized in that, The low refractive index layer has a thickness of 10~80 nm, and the thickness difference between any low refractive index layer is 2~30 nm. The high refractive index layer has a thickness of 5~50 nm, and the thickness difference between any high refractive index layer is 2~30 nm.

8. A dimming film for enhancing contrast based on the synergistic effect of photonic crystal and dynamic dye according to claim 5, characterized in that, The high-refractive-index transparent material is titanium dioxide, and the low-refractive-index transparent material is silicon dioxide.

9. A method for preparing a contrast-enhancing film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1: A first conductive layer is formed on the first substrate layer by magnetron sputtering; S2: Alternately deposit high-refractive-index and low-refractive-index materials in the second substrate layer to form a photonic crystal layer; then, magnetron sputtering is used to form a second conductive layer on the surface of the photonic crystal layer. S3: After mixing and stirring the UV-curable adhesive, photoinitiator, liquid crystal, dihedral dye, blackening agent, and spacer evenly and degassing, a dye PDLC material is obtained. Then, the dye PDLC material is coated between the first conductive layer and the second conductive layer, and then photocured to obtain the dimming film. S4: Seal the edges of the prepared dimming film and bring out the electrodes.

10. The application of a dimming film based on the synergistic enhancement of contrast by photonic crystal and dynamic dye as described in any one of claims 1 to 8 as a building material for automotive sunroofs, side windows, building curtain walls, and privacy space partitions.

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