Dual-band multilayer composite optical filter, preparation method thereof and transmittance regulation method

Abstract

The application belongs to the technical field of optical filters, and relates to a dual-band multilayer composite optical filter and a preparation method and a transmittance regulation method thereof. The optical filter comprises a bearing substrate, a filter function layer, an anti-reflection layer and a wear-resistant coating layer arranged on the surface of the bearing substrate in sequence. The wear-resistant coating layer is obtained after curing of wear-resistant coating material. The wear-resistant coating material comprises an acrylate emulsion, a reaction monomer, modified silicon dioxide, a photoinitiator, a defoaming agent, a dispersing agent, a leveling agent, a cosolvent and deionized water. The application has adjustable transmittance and wear resistance. The modified silicon dioxide can be uniformly dispersed in the coating system, thereby improving the structural strength of the wear-resistant coating layer. On the basis of the original multilayer composite protective coating structure, a double-layer coating film system is additionally arranged to avoid the defect that the transmittance of a traditional optical filter cannot be adjusted. The application overcomes the defect that the wear resistance of the surface protective layer of an existing optical filter is insufficient, and the optical filter is prone to wear and scratch, thereby affecting the filtering effect. The application is suitable for different infrared transmittance use scenarios in day and night.

Description

Technical Field

[0001] This invention belongs to the technical field of optical filters, and relates to a dual-band multilayer composite optical filter and its preparation method and transmittance control method. Background Technology

[0002] Optical filters are optical elements that can select specific wavelengths of light from polychromatic light. They are widely used in photographic optics, spectral detection, laser instruments, display lighting, and many other fields. In practical applications, optical filters either only adapt to a single wavelength band or have poor light transmission in both wavelength bands. Especially for filters used in the infrared band at night, if manufactured using ordinary fully transparent processes, their light transmission is often poor. Furthermore, filters are often directly exposed to the external environment and must withstand the effects of friction, moisture erosion, and external abrasion over a long period. The surface functional layer of ordinary filters has low hardness, making them prone to scratches and wear, which not only affects the filtering effect but also shortens the filter's lifespan.

[0003] In existing technologies, to improve the abrasion resistance of optical filters, an additional abrasion-resistant coating is typically applied to the filter surface. However, common abrasion-resistant coatings suffer from poor adhesion to the original functional layers of the filter, leading to issues such as coating peeling and cracking after prolonged use. Furthermore, some abrasion-resistant coatings can negatively impact the filter's light transmittance, making it difficult to simultaneously meet the requirements of high light transmittance and excellent abrasion resistance. In addition, existing modified abrasion-resistant fillers involve complex modification processes, exhibit poor compatibility with the coating matrix, and are difficult to disperse uniformly within the coating system, resulting in uneven coating performance and an inability to stably exert their abrasion-resistant and light-enhancing effects. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-band multilayer composite filter and its preparation method and transmittance control method. This invention has excellent transmittance and wear resistance. Modified silica can be uniformly dispersed in the coating system to improve the structural strength of the wear-resistant coating, while not negatively affecting the transmittance of the filter. It overcomes the defects of existing filter surface protective layers that are not wear-resistant enough and are prone to wear and scratches after long-term use, affecting the filtering effect. It is suitable for different infrared transmittance usage scenarios during the day and night.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] In a first aspect, this application provides a dual-band multilayer composite filter, comprising a carrier substrate and a filter functional layer and a wear-resistant coating sequentially disposed on the surface of the carrier substrate. The filter functional layer includes a first coating surface located on the upper surface of the carrier substrate and a second coating surface located on the lower surface of the carrier substrate. The first coating surface is deposited with a first multilayer film system, and the second coating surface is deposited with a second multilayer film system. The wear-resistant coating is obtained by curing a wear-resistant coating material. The wear-resistant coating material comprises the following components by weight: 60-72 parts of acrylate emulsion, 6-10 parts of reactive monomer, 2-4 parts of modified silica, 2.5-3.5 parts of photoinitiator, 0.2-0.3 parts of defoamer, 0.3-0.4 parts of dispersant, 1.2-1.8 parts of leveling agent, 2.5-4.0 parts of cosolvent, and 8-12 parts of deionized water.

[0007] The first multilayer film system is formed by alternating deposition of high / low refractive index materials, and the second multilayer film system is also formed by alternating deposition of high / low refractive index materials. The first multilayer film system is fully transparent in the visible light band and has high transmittance in the 900nm-950nm infrared band, while the second multilayer film system is fully transparent in the visible light band and curvilinearly reduces infrared transmittance. The first and second multilayer film systems work together to ensure that the filter is fully transparent in the visible light band and has a transmittance range of 50%-70% in the 900nm-950nm infrared band. The second coating surface includes a terminal control layer, which is used to terminate the coating using crystal-controlled deposition or photo-controlled deposition to control the film thickness error. Through the superposition and cooperation of the first and second coating surfaces, the infrared transmittance effect of the filter is differentiated during the day and at night.

[0008] As a preferred embodiment of the present invention, the carrier substrate is one or more of glass, PC and PET.

[0009] As a preferred embodiment of the present invention, the antireflective and anti-reflective coating is made of acrylic resin.

[0010] As a preferred embodiment of the present invention, the acrylic emulsion is of the Wanhua Chemical Archsol 8019 type.

[0011] As a preferred embodiment of the present invention, the reaction monomer is any one or a combination of two of trimethylolpropane triacrylate and tripropylene glycol diacrylate.

[0012] As a preferred embodiment of the present invention, the photoinitiator is photoinitiator 1173, the defoamer is BYK019, the dispersant is BYK-181, the leveling agent is BYK-3455, and the cosolvent is propylene glycol methyl ether acetate.

[0013] Secondly, this application provides a method for preparing a dual-band multilayer composite filter, comprising the following steps:

[0014] S1. Preparation of the support substrate: A first coating surface is formed on the upper surface of the support substrate, and a second coating surface is formed on the lower surface of the support substrate. The first coating surface is formed by alternating deposition of high / low refractive index materials to obtain a first multilayer film system, and the second coating surface is formed by alternating deposition of high / low refractive index materials to obtain a second multilayer film system.

[0015] S2. An anti-reflective layer is formed on the first coating surface;

[0016] S3. Add the acrylic emulsion, reactive monomer and photoinitiator to the reactor and stir at 600-800 r / min for 1-2 h. Then add the modified silica, cosolvent, dispersant, leveling agent, defoamer and deionized water and continue stirring at 600-800 r / min for 2-3 h to obtain the wear-resistant coating.

[0017] S4. After applying a wear-resistant coating to the antireflective and anti-reflective layer, UV curing is performed to complete the preparation.

[0018] As a preferred embodiment of the present invention, the modified silica is prepared by the following steps:

[0019] 1) Add anhydrous ethanol to the reaction vessel, add silica and mercaptobutyric acid, stir and mix, let stand, filter, take the filter cake and wash to obtain the complex;

[0020] 2) The complex was dispersed in anhydrous ethanol, a silane coupling agent was added, and the mixture was heated and stirred. The mixture was then filtered, and the filter cake was washed to obtain the intermediate product.

[0021] 3) Disperse the intermediate product in anhydrous ethanol, add fluorinated salicylaldehyde and stir at a constant temperature, filter, take the filter cake, wash and vacuum dry to complete the preparation.

[0022] As a preferred embodiment of the present invention, the stirring and mixing in step 1) is carried out at a speed of 300-400 rpm for 3-4 hours, and the mass ratio of anhydrous ethanol, silicon dioxide and mercaptobutyric acid is 60-70:10-12:1.5-2.0, wherein the mercaptobutyric acid is 4-mercaptobutyric acid.

[0023] As a preferred embodiment of the present invention, the heating and stirring in step 2) is carried out at 40-50°C for 3-4 hours, and the mass ratio of the complex, anhydrous ethanol and silane coupling agent is 12.0-13.5:60-70:0.7-1.0, wherein the silane coupling agent is diethylenetriaminepropylmethyldimethoxysilane.

[0024] As a preferred embodiment of the present invention, the constant temperature stirring in step 3) is stirring at 60-65℃ for 5-6 hours, the mass ratio of the intermediate product, anhydrous ethanol and fluorinated salicylaldehyde is 6.0-6.8:50-60:0.35-0.42, and the fluorinated salicylaldehyde is 3,5-difluorosalicylaldehyde.

[0025] Thirdly, this application provides a method for controlling the transmittance of a dual-band multilayer composite filter, wherein the dual-band multilayer composite filter performs the following steps during operation:

[0026] By utilizing a first multilayer film system deposited on the first coating surface of a substrate, the incident visible light band is transmitted through full transmission, while the first multilayer film system maintains high transmittance in the infrared band of 900nm-950nm.

[0027] By utilizing a second multilayer film system deposited on the second coating surface of the substrate, the visible light band passing through the first coating surface is fully transmitted, while the infrared band of 700nm-950nm passing through the first coating surface is linearly reduced to attenuate the transmittance of the infrared band.

[0028] Through the synergistic cooperation of the first and second multilayer film systems, the dual-band multilayer composite filter achieves full transmission in the visible light band and keeps the overall transmittance in the 900nm-950nm infrared band stably controlled between 50% and 70%.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention provides a wear-resistant coating containing modified silica on the outermost layer of the filter, thereby effectively improving the wear and scratch resistance of the filter surface while ensuring the overall light transmittance of the filter.

[0031] 2. The modified silica used in this invention undergoes a multi-step grafting modification process, which does not negatively affect the light transmittance of the filter. It can simultaneously meet the requirements of high light transmittance and high wear resistance of dual-band multilayer composite filters, extending the service life of the filter and making it suitable for various complex outdoor and high-frequency use scenarios.

[0032] 3. Based on the original multi-layer composite protective coating structure, the filter of this invention adopts a step-by-step transmittance design. In the first step, the first coating surface allows for the efficient transmission of visible light (400nm-600nm) and a specific band of infrared light (930nm-950nm). Then, the second coating surface enhances the transmittance of visible light (400nm-600nm) and linearly attenuates infrared light (700nm-950nm), thereby ensuring a high transmittance effect for visible light (400nm-600nm) in the final result. With a transmittance of 50%-70% in a specific band of infrared light (930nm-950nm), compared to existing double-layer coated filters, this filter is easier to produce, has a higher yield, and is more stable, maintaining a transmittance of over 80%. It is suitable for different infrared transmittance scenarios during day and night. The filter of this application can be used in optical systems such as cameras or sensors, allowing cameras or sensors to obtain clear and accurate images or signals under various lighting conditions. It is suitable for use in scenarios such as surveillance, vehicle-mounted 360-degree imaging equipment, etc. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the filter structure of a dual-band multilayer composite filter and its preparation method and transmittance control method according to this application;

[0034] Figure 2 This is a schematic diagram of the dual-band transmittance of the first coating surface of a dual-band multilayer composite filter and its preparation method and transmittance control method, as described in this application.

[0035] Figure 3 This is a schematic diagram of a dual-band multilayer composite filter and its preparation method, as well as a transmittance control method, of which the second coating surface of the filter has an infrared wavelength of 940nm and a transmittance of 55%-65%.

[0036] Figure 4 This is a schematic diagram of the combined transmittance of a dual-band multilayer composite filter and its preparation method, as well as a transmittance control method, according to the present application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Wear-resistant coating;

[0039] 2. Anti-reflective coating;

[0040] 31. First coated surface; 32. Second coated surface;

[0041] 4. Supporting substrate. Detailed Implementation

[0042] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific implementation methods, structure, features and effects of the present invention are described in detail below with reference to the embodiments.

[0043] See Figure 1 This application provides a dual-band multilayer composite filter, comprising a substrate 4 and a filtering functional layer, an anti-reflection layer 2, and a wear-resistant coating 1 sequentially disposed on the surface of the substrate 4. The filtering functional layer employs a double-layer coating process, including a first coating surface 31 and a second coating surface 32. The first coating surface 31 is deposited on the upper surface of the substrate 4, and the second coating surface 32 is deposited on the lower surface of the substrate 4, enabling the filter to function for both day and night use. Light sequentially passes through the wear-resistant coating 1, the anti-reflection layer 2, the first coating surface 31, the substrate 4, and the second coating surface 32 before being emitted.

[0044] The carrier substrate 4 is one or more of glass, PC (polycarbonate) and PET (polyethylene terephthalate).

[0045] The antireflective layer 2 can be made of acrylic resin, and its function is to reduce light reflection and increase light transmission, thereby improving the overall light transmittance of the filter. The antireflective layer 2 is disposed between the filter functional layer and the wear-resistant coating 1, and can serve as an intermediate transition layer. Through chemical compatibility and stress buffering, it can effectively promote the bonding between the wear-resistant coating 1 and the filter functional layer, thereby preventing the coating from peeling off, cracking, or other phenomena.

[0046] See Figure 1 and Figure 2 The first coating surface 31 is deposited with a first multilayer film system. The first coating surface 31 is a fully transparent film layer, which is used to enhance the visible light transmission in the main passband (400nm - 600nm) and form a first transmission peak and a second transmission peak with an interval cutoff region in the infrared narrow band (900nm-950nm), thus forming a dual passband transmission spectrum. This achieves the visible light transmission function of the main passband (visible light transmittance is greater than 90%), and provides a narrow band infrared window (900nm-950nm) outside the main passband, providing a channel for infrared supplementary lighting at night. Figure 2 , Figure 3 and Figure 4 The horizontal axis represents the wavelength of light (nm), and the vertical axis represents the transmittance (%).

[0047] See Figure 3 The second coating surface 32 has a second multilayer film system deposited thereon. The second multilayer film system is used to perform a curved reduction of transmittance for infrared light (700nm-950nm). While increasing transmittance in the visible light region, the second coating surface 32 also performs a curved reduction of transmittance in the 700nm-950nm infrared band, with the transmittance gradually decreasing from 100% to about 55%.

[0048] See Figure 4 With the first coating surface 31 and the second coating surface 32 superimposed and combined, the filter maintains full transmittance for visible light (400nm-600nm) and the transmittance for infrared light (930nm-950nm) changes gradually, approaching 55%. Therefore, the filter achieves the function of being used both day and night.

[0049] The wear-resistant coating 1 comprises: an acrylic emulsion, a reactive monomer, modified silica, a photoinitiator, a defoamer, a dispersant, a leveling agent, a cosolvent, and deionized water. The silica is silicon dioxide.

[0050] A method for fabricating a dual-band multilayer composite filter includes the following steps:

[0051] S1. Preparation of the support substrate: A first coating surface 31 is formed on the upper surface of the support substrate, and a second coating surface 32 is formed on the lower surface of the support substrate. The first coating surface 31 is deposited with alternating high / low refractive index materials to obtain a first multilayer film system, and the second coating surface 32 is deposited with alternating high / low refractive index materials to obtain a second multilayer film system.

[0052] S2. An anti-reflection and anti-reflection layer 2 is provided on the first coating surface 31;

[0053] S3. Add the acrylic emulsion, reactive monomer and photoinitiator to the reactor and stir at 600-800 r / min for 1-2 h. Then add the modified silica, cosolvent, dispersant, leveling agent, defoamer and deionized water and continue stirring at 600-800 r / min for 2-3 h to obtain the wear-resistant coating.

[0054] S4. After applying a wear-resistant coating to the antireflective and anti-reflective layer 2, UV curing is performed to complete the preparation.

[0055] In some feasible solutions, the first coating surface 31 is deposited with alternating high refractive index materials (such as TiO2 or Ti3O5) and low refractive index materials (such as SiO2). The first multilayer film system of the first coating surface 31 can be optimized by optical thin film design software (such as TFCalc, Macleod) and the thickness of each layer and the total number of layers can be adjusted to balance visible light transmission enhancement and near-infrared narrowband transmission.

[0056] The second coating surface 32 also uses alternating deposition of high / low refractive index materials to form a second multilayer film system, but the number and thickness of the high refractive index material and the low refractive index material are different from those of the first multilayer film system. The second multilayer film system is used to attenuate the transmittance of infrared light.

[0057] In actual production, the second coating surface 32 may include a terminal control layer. The terminal control layer completes the coating termination using crystal-controlled deposition or photo-controlled deposition, which can precisely control the film thickness error. In this application, the terminal control layer refers to the last one or more film layers in the second coating surface 32 film system used to achieve the final infrared light transmittance cutoff point, and its thickness control accuracy directly affects the steepness of the cutoff edge.

[0058] Example 1

[0059] The wear-resistant coating comprises the following components by weight: 60 parts acrylic emulsion, 6 parts reactive monomer, 2 parts modified silica, 2.5 parts photoinitiator, 0.2 parts defoamer, 0.3 parts dispersant, 1.2 parts leveling agent, 2.5 parts cosolvent, and 8 parts deionized water;

[0060] The reaction monomer is trimethylolpropane triacrylate;

[0061] The photoinitiator is photoinitiator 1173 (i.e., 2-hydroxy-2-methyl-1-phenyl-1-propanone), the defoamer is an organosilicon defoamer, such as BYK019, the dispersant is a polymeric dispersant, such as BYK-181, the leveling agent is a polyether-modified siloxane leveling agent, such as BYK-3455, and the cosolvent is propylene glycol methyl ether acetate.

[0062] The method for preparing the modified silica includes the following steps:

[0063] 1) Add anhydrous ethanol to the reaction vessel, add silica and mercaptobutyric acid, stir at 300 rpm for 3 h, let stand, filter, take the filter cake and wash to obtain the complex; the mass ratio of anhydrous ethanol, silica and mercaptobutyric acid is 60:10:1.5, and the mercaptobutyric acid is 4-mercaptobutyric acid.

[0064] In thiolization, mercaptobutyric acid molecules form hydrogen bonds with silanol groups (-Si-OH) on the surface of silica (SiO2) through their terminal carboxyl groups (-COOH), thereby initially adsorbing or binding onto the silica surface to form a complex. The purpose of thiolization is to introduce two active functional groups, thiol (-SH) and carboxyl (-COOH), onto the silica surface, providing anchoring sites for the subsequent chemical grafting with a silane coupling agent in the second step.

[0065] 2) The complex was dispersed in anhydrous ethanol, a silane coupling agent was added and stirred at 40°C for 3 hours, filtered, and the filter cake was washed to obtain an intermediate product; the mass ratio of the complex, anhydrous ethanol and silane coupling agent was 12.0:60:0.7, and the silane coupling agent was diethylenetriaminepropylmethyldimethoxysilane.

[0066] In the silane coupling process, a silane coupling agent is grafted onto silicon dioxide to obtain an intermediate product.

[0067] 3) Disperse the intermediate product in anhydrous ethanol, add fluorinated salicylaldehyde and stir at 60°C for 5 hours, filter, take the filter cake, wash and vacuum dry to complete the preparation.

[0068] During the fluorination grafting process, the amino group at the other end of the silane coupling agent undergoes a Schiff base reaction with the aldehyde group of fluorinated salicylaldehyde to form a stable C=N double bond, thereby ultimately grafting the fluorinated group onto the silica, resulting in modified silica.

[0069] The mass ratio of the intermediate product, anhydrous ethanol, and fluorinated salicylaldehyde is 6.0:50:0.35, and the fluorinated salicylaldehyde is 3,5-difluorosalicylaldehyde.

[0070] A method for preparing a wear-resistant coating includes the following steps: adding acrylate emulsion, reactive monomer and photoinitiator into a reaction vessel, stirring at 600 r / min for 1 h, then adding modified silica, cosolvent, dispersant, leveling agent, defoamer and deionized water, and continuing to stir at 600 r / min for 2 h to obtain the coating.

[0071] Example 2

[0072] The wear-resistant coating comprises the following components by weight: 65 parts acrylic emulsion, 8 parts reactive monomer, 3 parts modified silica, 3 parts photoinitiator, 0.25 parts defoamer, 0.35 parts dispersant, 1.5 parts leveling agent, 3.0 parts cosolvent, and 10 parts deionized water.

[0073] The reaction monomer is trimethylolpropane triacrylate;

[0074] The photoinitiator is photoinitiator 1173, and the cosolvent is propylene glycol methyl ether acetate.

[0075] The method for preparing the modified silica includes the following steps:

[0076] 1) Add anhydrous ethanol to the reaction vessel, add silica and mercaptobutyric acid, stir at 350 rpm for 3.5 h, let stand, filter, take the filter cake and wash to obtain the complex; the mass ratio of anhydrous ethanol, silica and mercaptobutyric acid is 65:11:1.8, and the mercaptobutyric acid is 4-mercaptobutyric acid;

[0077] 2) The complex was dispersed in anhydrous ethanol, a silane coupling agent was added and stirred at 45°C for 3.5 h, filtered, and the filter cake was washed to obtain an intermediate product; the mass ratio of the complex, anhydrous ethanol and silane coupling agent was 12.5:65:0.8, and the silane coupling agent was diethylenetriaminepropylmethyldimethoxysilane;

[0078] 3) Disperse the intermediate product in anhydrous ethanol, add fluorinated salicylaldehyde and stir at 62°C for 5.5 h, filter, take the filter cake, wash and vacuum dry to complete the preparation;

[0079] The mass ratio of the intermediate product, anhydrous ethanol, and fluorinated salicylaldehyde is 6.4:55:0.38, and the fluorinated salicylaldehyde is 3,5-difluorosalicylaldehyde.

[0080] A method for preparing a wear-resistant coating includes the following steps: adding acrylate emulsion, reactive monomers and photoinitiator into a reaction vessel, stirring at 700 r / min for 1.5 h, then adding modified silica, cosolvent, dispersant, leveling agent, defoamer and deionized water, and continuing to stir at 700 r / min for 2.5 h to obtain the coating.

[0081] Example 3

[0082] The wear-resistant coating comprises the following components by weight: 72 parts acrylic emulsion, 10 parts reactive monomer, 4 parts modified silica, 3.5 parts photoinitiator, 0.3 parts defoamer, 0.4 parts dispersant, 1.8 parts leveling agent, 4.0 parts cosolvent, and 12 parts deionized water;

[0083] The reaction monomer is trimethylolpropane triacrylate;

[0084] The photoinitiator is photoinitiator 1173, and the cosolvent is propylene glycol methyl ether acetate.

[0085] The method for preparing the modified silica includes the following steps:

[0086] 1) Add anhydrous ethanol to the reaction vessel, add silica and mercaptobutyric acid, stir at 400 rpm for 4 h, let stand, filter, take the filter cake and wash to obtain the complex; the mass ratio of anhydrous ethanol, silica and mercaptobutyric acid is 70:12:2.0, and the mercaptobutyric acid is 4-mercaptobutyric acid;

[0087] 2) The complex was dispersed in anhydrous ethanol, a silane coupling agent was added and stirred at 50°C for 4 hours, filtered, and the filter cake was washed to obtain an intermediate product; the mass ratio of the complex, anhydrous ethanol and silane coupling agent was 13.5:70:1.0, and the silane coupling agent was diethylenetriaminepropylmethyldimethoxysilane;

[0088] 3) Disperse the intermediate product in anhydrous ethanol, add fluorinated salicylaldehyde and stir at 65°C for 6 hours, filter, take the filter cake, wash and vacuum dry to complete the preparation.

[0089] The mass ratio of the intermediate product, anhydrous ethanol, and fluorinated salicylaldehyde is 6.8:60:0.42, and the fluorinated salicylaldehyde is 3,5-difluorosalicylaldehyde.

[0090] A method for preparing a wear-resistant coating includes the following steps: adding acrylate emulsion, reactive monomer and photoinitiator into a reaction vessel, stirring at 800 r / min for 2 h, then adding modified silica, cosolvent, dispersant, leveling agent, defoamer and deionized water, and continuing to stir at 800 r / min for 3 h to obtain the coating.

[0091] Comparative Example 1

[0092] Compared with Example 2, Comparative Example 1 differs in that: step 1) does not use mercaptobutyric acid.

[0093] Comparative Example 2

[0094] Compared with Example 2, Comparative Example 2 differs in that the silane coupling agent in step 2) is KH550.

[0095] Comparative Example 3

[0096] Compared with Example 2, Comparative Example 3 differs in that: in step 3), salicylaldehyde is used instead of fluorinated salicylaldehyde.

[0097] The performance of the cured samples of Examples 1-3 and Comparative Examples 1-3 were tested respectively, and the test results are shown in Table 1.

[0098] Pencil hardness: GB / T6739-2022;

[0099] Visible light transmittance GB / T2410-2008;

[0100] Adhesion rating: GB / T9286-1998;

[0101] Water resistance: Performance of boiling water at 80℃ for 2 hours (GB / T1736-1979).

[0102] Table 1

[0103]

[0104] As shown in Table 1, compared with Comparative Examples 1-3, the multilayer composite filter prepared by the present invention has a higher pencil hardness and better adhesion in the wear-resistant coating 1, while maintaining excellent visible light transmittance and more stable water resistance. This indicates that the present invention effectively improves the dispersibility and compatibility of modified silica in the coating system by modifying silica stepwise with mercaptobutyric acid, silane coupling agent and fluorinated salicylaldehyde, and finally endows the composite filter with better comprehensive performance, meeting the filter's requirements for high light transmittance, high wear resistance and high weather resistance.

[0105] This invention introduces thiol and carboxyl active sites into silica through hydrogen bonding with mercaptobutyric acid, promoting the chemical grafting of silane coupling agent and fluorinated salicylaldehyde. The amino group of the silane coupling agent undergoes a Schiff base reaction with the aldehyde group of the fluorinated salicylaldehyde to achieve stable grafting, while the carbon-carbon double bond in the molecule participates in the UV curing crosslinking reaction of the acrylate. This allows the modified silica to be firmly bonded to the coating crosslinking system. Simultaneously, the introduction of fluorinated groups further reduces the surface energy of the coating, improving its water and weather resistance and preventing problems such as whitening, peeling, and yellowing during use, effectively ensuring the light transmittance of the filter.

[0106] A method for controlling the transmittance of a dual-band multilayer composite filter, wherein the dual-band multilayer composite filter performs the following steps during operation:

[0107] The first multilayer film system deposited on the first coating surface 31 of the substrate 4 enables full transmission of incident visible light, while maintaining high transmittance of the first multilayer film system for the infrared band of 900nm-950nm.

[0108] The second multilayer film system deposited on the second coating surface 32 of the substrate 4 is used to achieve full transmission of visible light passing through the first coating surface 31, while linear anti-reflection is performed on the 700nm-950nm infrared band passing through the first coating surface 31 to reduce the transmittance of the infrared band.

[0109] Through the synergistic cooperation of the first and second multilayer film systems, the dual-band multilayer composite filter achieves full transmission in the visible light band and keeps the overall transmittance in the 900nm-950nm infrared band stably controlled between 50% and 70%.

[0110] In some feasible schemes, the first multilayer film system has a 24-layer structure, with the first layer being SiO2 and the second layer being Ti3O5, deposited alternately. The second multilayer film system has a 14-layer structure, with the first layer being Ti3O5 and the second layer being SiO2, deposited alternately, and the thickness of each layer is set according to the actual light transmittance requirements.

[0111] like Figure 2As shown, in the 400nm-600nm (visible light) range, the first coated surface 31 exhibits extremely high transmittance (≥90%), forming the main passband and achieving high transmittance of visible light for daytime color imaging. In the 600nm-680nm range, transmittance drops sharply from nearly 100% to nearly 0%, forming a steep cutoff edge, which is the key boundary between visible and infrared light. In the 680nm-890nm range, transmittance is extremely low (≤3%), forming a strong cutoff region, achieving strong cutoff and effectively blocking ambient infrared light interference (such as 850nm), ensuring true color during the day and eliminating red glow. In the 900nm-950nm (narrow infrared band), a peak is formed centered at 940nm, with a transmittance of approximately 90%±5%, achieving high transmittance in the narrow infrared band, which can be used for the passage of 940nm infrared supplementary light at night. In the 950nm- At 1100nm, the transmittance drops sharply to extremely low levels (≤5%), forming a re-cutoff region to achieve long-wavelength cutoff, suppressing sensor thermal noise and dark current interference, and improving the signal-to-noise ratio at night. Therefore, during the day, the first coating surface 31 fully transmits visible light (400-600nm) while forcibly cutting off infrared light in the environment (especially in the 680-890nm band, such as 850nm), ensuring that the images captured during the day have true colors and no red overexposure. At night, the first coating surface 31 opens a narrow bandpass window near 940nm, allowing infrared light designed for the 940nm infrared supplement lamp to pass through efficiently (90%-95% transmittance), while stray light in other bands is strictly blocked, thus ensuring the clarity and signal-to-noise ratio of nighttime imaging. In other words, the first coating surface 31, as the main filter layer, is responsible for cutting off infrared light (680nm-890nm) during the day and transmitting specific infrared light (930nm-950nm) at night.

[0112] like Figure 3 As shown, in the range of 400nm to 700nm, the transmittance of the second coating surface 32 is close to 100%, achieving high transmittance of visible light (anti-reflection) and ensuring brightness for daytime imaging; in the range of 700nm to 950nm, the transmittance slowly decreases from about 100% to about 55%, achieving a smooth attenuation and avoiding steep interruptions or reflections in the spectrum; in the range of 950nm to 1100nm, the transmittance gradually recovers to about 70%.

[0113] It is important to note that excessively high infrared transmittance (e.g., 90%-100%) can lead to overly strong infrared light received by the sensor, causing overexposure, whitening, or red-blooming phenomena, resulting in loss of image detail and a decrease in signal-to-noise ratio. The second multilayer film system of this application maintains a transmittance of approximately 50%-70% in the 900nm-950nm infrared band, particularly the 930nm-950nm band, without exhibiting significant red-blooming (red light visible to the human eye). This makes it less likely to be detected by the monitored party at night, providing better concealment. It is suitable for surveillance and monitoring applications, and provides excellent imaging quality both day and night.

[0114] See Figure 4 Through the superposition and cooperation of the first coating surface 31 and the second coating surface 32, the filter maintains full transmittance for visible light (400nm-600nm) and exhibits a gradual change in transmittance for infrared light (930-950nm), approaching 55%. During the day, the filter allows high transmittance of visible light (400nm-600nm), enabling the camera to display color images. Simultaneously, it allows some near-infrared light (930nm-950nm) to pass through, ensuring that the sensor can collect infrared signals even during the day for auxiliary functions such as autofocus and white balance adjustment. At night, the filter allows high transmittance of both visible and near-infrared light (930nm-950nm). In this case, the camera primarily relies on infrared light emitted by the infrared supplementary light lamp to form black and white or monochrome images. The filter allows for differentiated settings for infrared transmittance during the day and night, catering to both daytime (primary visible light imaging) and nighttime (primary near-infrared imaging, covert imaging) needs. The filter can be used in scenarios such as the installation of surveillance cameras and 360° imaging devices in vehicles.

[0115] In addition, see Figure 4 The filter has a transmittance of ≤ 3% (strong cutoff) for the 680nm-890nm wavelength range and ≤ 5% (strong cutoff) for the 1000nm-1100nm wavelength range. This is because the commonly used wavelength range of traditional infrared LED supplementary lights (such as 850nm) is also a major radiation band of solar infrared light. Strong cutoff of the 680nm-890nm band prevents a large amount of infrared light in this range from entering the sensor, ensuring that the camera obtains true-to-color and clear images during the day and avoids red glow at night. Strong cutoff of the 1000nm-1100nm band is to prevent long-wave infrared light in this band from diffusing or leaking into the sensor and interfering with the target image formed by the 930nm-950nm supplementary light, thus ensuring the clarity and sharpness of nighttime imaging.

[0116] In summary, the filter of this application adopts a step-by-step transmittance control design. In the first step, the first coating surface 31 allows for the efficient transmission of visible light (400nm-600nm) and infrared light of a specific wavelength (930nm-950nm). Then, the second coating surface 32 enhances the transmittance of visible light (400nm-600nm) and linearly attenuates infrared light (700nm-950nm), thereby ensuring that the final result is a high transmittance of visible light (400nm-600nm) and a transmittance of 50%-70% of infrared light of a specific wavelength (930nm-950nm). Compared with existing double-layer coated filters, the production difficulty is lower, the yield rate is higher, and the transmittance is more stable, which can be maintained above 80%.

[0117] It should be specifically noted that, during the production process, when it is necessary to obtain filters with various infrared light transmittance, this is achieved by changing the number of layers and the thickness of each layer of the second multilayer film system on the second coating surface 32, without changing the first coating surface 31.

[0118] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A dual-band multilayer composite filter, characterized in that, It includes a carrier substrate and a light filtering functional layer and a wear-resistant coating (1) sequentially disposed on the surface of the carrier substrate (4). The light filtering functional layer includes a first coating surface (31) located on the upper surface of the carrier substrate (4) and a second coating surface (32) located on the lower surface of the carrier substrate (4). The first coating surface (31) is deposited with a first multilayer film system, and the second coating surface (32) is deposited with a second multilayer film system. The wear-resistant coating (1) is obtained by curing the wear-resistant coating. The wear-resistant coating comprises the following components by weight: 60-72 parts of acrylic emulsion, 6-10 parts of reactive monomer, 2-4 parts of modified silica, 2.5-3.5 parts of photoinitiator, 0.2-0.3 parts of defoamer, 0.3-0.4 parts of dispersant, 1.2-1.8 parts of leveling agent, 2.5-4.0 parts of cosolvent, and 8-12 parts of deionized water. The method for preparing the modified silica includes the following steps: 1) Add anhydrous ethanol to the reaction vessel, add silica and mercaptobutyric acid, stir and mix, let stand, filter, take the filter cake and wash to obtain the complex, wherein the mercaptobutyric acid is 4-mercaptobutyric acid; 2) The complex was dispersed in anhydrous ethanol, a silane coupling agent was added, and the mixture was heated and stirred. The mixture was then filtered, and the filter cake was washed to obtain an intermediate product. The silane coupling agent was diethylenetriaminepropylmethyldimethoxysilane. 3) Disperse the intermediate product in anhydrous ethanol, add fluorinated salicylaldehyde and stir at a constant temperature, filter, take the filter cake, wash and vacuum dry to complete the preparation. The fluorinated salicylaldehyde is 3,5-difluorosalicylaldehyde.

2. The dual-band multilayer composite filter according to claim 1, characterized in that: The carrier substrate (4) is one or more of glass, PC and PET; an anti-reflective layer (2) is also provided between the light filtering functional layer and the wear-resistant coating (1), and the material of the anti-reflective layer (2) includes acrylic resin.

3. The dual-band multilayer composite filter according to claim 1, characterized in that: The first multilayer film system is formed by alternating deposition of high / low refractive index materials, and the second multilayer film system is formed by alternating deposition of high / low refractive index materials. The first multilayer film system is fully transparent in the visible light band and has high transmittance in the 900nm-950nm infrared band. The second multilayer film system is fully transparent in the visible light band and has a curved reduction in transmittance in the infrared band. The first multilayer film system and the second multilayer film system work together to enable the filter to be fully transparent in the visible light band and have a transmittance in the 900nm-950nm infrared band between 50% and 70%.

4. The dual-band multilayer composite filter according to claim 1, characterized in that: The reaction monomer is any one or a combination of two of trimethylolpropane triacrylate and tripropylene glycol diacrylate. The photoinitiator is an α-hydroxyketone photoinitiator, and the cosolvent is propylene glycol methyl ether acetate.

5. A method for preparing a dual-band multilayer composite filter as described in any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: S1. A first coating surface (31) is formed on the upper surface of the substrate (4), and a second coating surface (32) is formed on the lower surface of the substrate (4). The first coating surface (31) is formed by alternating deposition of high / low refractive index materials to obtain a first multilayer film system, and the second coating surface (32) is formed by alternating deposition of high / low refractive index materials to obtain a second multilayer film system. S2. An anti-reflective layer (2) is provided on the first coating surface (31); S3. Add the acrylic emulsion, reactive monomer and photoinitiator to the reaction vessel and stir at 600-800 r / min for 1-2 h. Then add the modified silica, cosolvent, dispersant, leveling agent, defoamer and deionized water and continue stirring at 600-800 r / min for 2-3 h to obtain the wear-resistant coating. S4. After applying a wear-resistant coating to the antireflective and anti-reflective layer (2), UV curing is performed to complete the preparation.

6. The method for preparing a dual-band multilayer composite filter according to claim 5, characterized in that: The stirring and mixing described in step 1) is carried out at a speed of 300-400 rpm for 3-4 hours, and the mass ratio of anhydrous ethanol, silicon dioxide and mercaptobutyric acid is 60-70:10-12:1.5-2.

0.

7. The method for preparing a dual-band multilayer composite filter according to claim 6, characterized in that: The heating and stirring in step 2) is carried out at 40-50℃ for 3-4 hours, and the mass ratio of the complex, anhydrous ethanol and silane coupling agent is 12.0-13.5:60-70:0.7-1.

0.

8. The method for preparing a dual-band multilayer composite filter according to claim 7, characterized in that: The constant temperature stirring in step 3) is stirring at 60-65℃ for 5-6 hours, and the mass ratio of the intermediate product, anhydrous ethanol and fluorinated salicylaldehyde is 6.0-6.8:50-60:0.35-0.

42.

9. A method for controlling the transmittance of a dual-band multilayer composite filter as described in any one of claims 1-4, characterized in that, The dual-band multilayer composite filter performs the following steps during operation: The first multilayer film system deposited on the first coating surface (31) of the carrier substrate (4) enables full transmission of incident visible light, while maintaining high transmittance of the first multilayer film system for the infrared band of 900nm-950nm. The second multilayer film system deposited on the second coating surface (32) of the support substrate (4) is used to achieve full transmission of visible light passing through the first coating surface (31), while performing curved anti-reflection on the 700nm-950nm infrared band passing through the first coating surface (31) to reduce the transmittance of the infrared band. Through the synergistic cooperation of the first multilayer film system and the second multilayer film system, the dual-band multilayer composite filter achieves full transmission in the visible light band and keeps the overall transmittance in the 900nm-950nm infrared band stably controlled between 50% and 70%.

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