Filtering film based on PMMA (polymethyl methacrylate) substrate as well as preparation method and application of filtering film

Abstract

The invention discloses a PMMA (polymethyl methacrylate) substrate-based filter film and a preparation method thereof, and aims to solve the preparation problem caused by the fact that near-infrared broadband deep cut-off and visible light efficient transmission are both realized on the surface of an organic glass substrate and the complexity of a film layer is too high. According to the invention, a wide-band-gap high-transparency material system is optimized, a multi-layer film system structure is designed in combination with a combinatorial optimization algorithm, and technologies of composite buffer layer matching, light control / crystal control composite monitoring, stress release and the like are adopted; the preparation of the film with near-infrared broadband deep cut-off (the transmittance of 665-950nm is less than or equal to 1%) and visible light efficient transmission (the average transmittance of 410-640nm is more than or equal to 80%) on the PMMA substrate is realized. Through an optimized pretreatment process (including glue layer curing and vacuum constant-temperature aging treatment before film coating) and a post-treatment process (constant-temperature aging treatment after film coating), the film firmness and the spectral performance consistency are remarkably improved. The invention can be widely applied to optical imaging, display and sensing systems.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, specifically a polymethyl methacrylate (PMMA)-based filter film, its preparation method, and its application. By optimizing the material system, film structure, and preparation process, this filter film achieves the synergistic performance of high-efficiency transmission (average transmittance ≥80%) in the visible light band (410-640nm) and broadband, deep cutoff (transmittance ≤1%) in the near-infrared band (665-950nm). The invention is suitable for optical imaging, display, and sensing systems, and is particularly suitable for communication equipment and special protection applications requiring lightweight, cost-effective optical components. Background Art

[0002] PMMA substrates, with their excellent optical properties and ease of processing, play an important role in lightweight applications that replace traditional glass, but their limitations need to be weighed against specific needs. As the technology industry becomes more dependent on high-performance materials, optical systems are increasingly demanding on filter film optical components. Such filter films need to achieve efficient transmission in the visible light band to ensure image color reproduction; at the same time, they need to achieve broadband and deep cutoff in the near-infrared band to avoid the impact of interfering light on sensor imaging quality. However, traditional technical solutions face the following key challenges when applied to organic glass (PMMA) substrates:

[0003] First, in terms of materials and design, traditional infrared cutoff films often achieve deep cutoff by introducing absorptive materials such as silicon. However, such materials have intrinsic absorption in the visible light band, resulting in a significant decrease in visible light transmittance (usually <50%), which cannot meet the high transmittance requirements; although the regular film system based on the Fabry-Perot structure can achieve a certain cutoff effect, its bandwidth is narrow and the secondary peak suppression ability is poor, making it difficult to cover the near-infrared wide-band cutoff range.

[0004] Secondly, in terms of preparation technology, in order to achieve the coexistence of broadband deep cutoff and high visible light transmittance, the traditional design requires stacking more than 60 film layers, resulting in a total thickness that is too thick, and the thermal expansion coefficient of the PMMA substrate (~70×10 -6 The thermal stress accumulation between multilayer films can easily lead to cracking and delamination. Furthermore, the thickness errors of traditional coating processes (single crystal or optically controlled) can easily lead to cutoff wavelength shifts.

[0005] Currently, most existing patents are based on glass substrates, such as CN106324737B (sapphire-based bandpass filter) and CN217484961U (K9 glass-based filter). Given the significant differences in physical and chemical properties between PMMA and traditional glass, as well as the unique thermodynamic properties of PMMA substrates and the need for low-cost processing, there is an urgent need for innovative solutions for PMMA-based filter films that balance high spectral performance, film reliability, and process feasibility to meet the stringent requirements of optical systems for lightweight, cost-effective optical components. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a PMMA-based filter film and a preparation method thereof, so as to realize the preparation of a high-performance filter film through material optimization, film system optimization and process innovation.

[0007] The technical solution provided by the present invention is as follows:

[0008] The present invention optimizes a wide-bandgap, highly transparent material system, combines a combinatorial optimization algorithm to design a multilayer film structure, and employs composite buffer layer matching, stress release, and optical / crystal control composite monitoring technology to achieve the preparation of a thin film on a PMMA substrate that combines near-infrared broadband deep cutoff with high visible light transmission efficiency. Through optimized pre-treatment processes (including gluing, baking, and constant temperature aging treatment before coating) and post-treatment processes (constant temperature aging treatment after coating), the film layer firmness and spectral performance consistency are significantly improved. It is characterized by comprising the following steps:

[0009] (1) A wide bandgap, highly transparent material system (including high-refractive-index material H and low-refractive-index material L) was used to design a multilayer film system in combination with simulated annealing and needle-shape optimization algorithms. The initial structure of the film system was: Sub / MLM / a1(0.5LH0.5L)^n1 b1(HL)^n2 / Air, with a total number of layers ≤ 60, where H, M, and L were all λ / 4 optical thicknesses, a1 and a2 were structural coefficients, n1 and n2 were period numbers, and λ was the central wavelength.

[0010] (2) Based on the near-infrared cutoff, visible light transmittance, bandwidth and other index requirements of the filter film, the film system is optimized using the film system design software. If the required index requirements are not met, the structural coefficients a1, a2 and the number of cycles n1, n2 are adjusted to further optimize until the requirements are met;

[0011] (3) PMMA substrate pretreatment: clean the substrate surface with alcohol and pure water in turn, evenly apply the adhesive layer, and bake the substrate in an oven at a constant temperature of 70-100°C for 2 hours. After the adhesive layer is cured, clamp the substrate in a coating machine and perform constant temperature aging treatment in a vacuum environment, baking at a constant temperature of 70-100°C for 1 hour;

[0012] (4) Buffer layer deposition: a certain thickness of TiO2 / SiO2 / TiO2 three dielectric layers and an adhesive layer are deposited on the surface of the PMMA substrate to form a composite buffer layer to match the physical properties of the PMMA substrate and the functional film layer;

[0013] (5) Coating process: Using ion-assisted deposition technology, combined with light control and crystal control composite monitoring, the film thickness error is controlled to ≤±1%;

[0014] (6) Post-treatment: After the coating is completed, it is subjected to constant temperature aging treatment again, baking at 70-100℃ for 24 hours to release the stress of the film layer.

[0015] The high refractive index material includes TiO2, Nb2O5, Ta2O5, HfO2 or ZrO2, and the low refractive index material includes SiO2 or Al2O3.

[0016] The structural coefficients a1 and a2 have a value range of 0.1-3, and the period numbers n1 and n2 have a value range of 5-15.

[0017] Achieve the following technical effects:

[0018] 1. Spectral performance: average transmittance ≥80% at 410-640nm, cutoff at 665-950nm (transmittance ≤1%);

[0019] 2. Film reliability: Through the buffer layer design and constant temperature aging treatment, the film firmness is improved, and there are no film cracks, peeling and other poor film quality problems;

[0020] 3. Process compatibility: Light control / crystal control composite monitoring controls the thickness error within ±1%.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (1) Provided is a filter film and preparation method based on a PMMA substrate surface that achieves both near-infrared broadband deep cutoff and high-efficiency visible light transmission.

[0023] (2) The present invention improves the film firmness through material system innovation, film structure optimization and process technology coordination, and solves the film quality problems such as film cracking and peeling on the PMMA substrate surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : Schematic diagram of the process flow of PMMA-based filter film.

[0025] Figure 2 : Schematic diagram of the PMMA-based filter film structure.

[0026] Figure 3: Spectral transmittance curve of Example 1 (high transmittance in visible light, deep cutoff in near infrared).

[0027] Figure 4 : Spectral transmittance curve of Example 2 (high transmittance in visible light, deep cutoff in near infrared).

[0028] Figure 5 : Quality comparison of PMMA substrate filter film with and without composite buffer layer. DETAILED DESCRIPTION

[0029] The specific examples of the present invention are described in detail below with reference to the accompanying drawings.

[0030] Example 1: PMMA substrate filter

[0031] Index requirements: average transmittance of visible light (410-640nm) ≥80%, cutoff of near-infrared band (665-950nm) (transmittance ≤1%), no film cracking, film peeling, etc.

[0032] The specific steps are as follows:

[0033] S1. Membrane system design:

[0034] A wide-bandgap, highly transparent material system, consisting of a high-refractive-index material H and a low-refractive-index material L, was used to design a multilayer film system using simulated annealing and a needle-shape optimization algorithm. The initial structure of the film system was: Sub / MLM / a1(0.5LH0.5L)^n1 b1(HL)^n2 / Air, with a total layer count of ≤60. H, M, and L were Ta2O5, TiO2, and SiO2, respectively. The structural coefficients a1 and a2 were 1 and 1.27, respectively. The period numbers n1 and n2 were 10 and 11, respectively. The central wavelength λ was 700 nm.

[0035] S2. Film system optimization:

[0036] Based on the near-infrared cutoff, visible light transmittance, bandwidth and other index requirements of the filter film, the film system is optimized using film system design software (TFCalc, Essential Macleod or Optilayer, etc.).

[0037] If the required indicators are not met, further optimization can be performed by adjusting the structural coefficients a1, a2 and the number of cycles n1, n2 until the requirements are met. The final optimized membrane structure is: Sub / 0.15M0.20L1.57M / 1.32L0.10H0.23L1.17H0.04L0.40H0.17L1.77H1.52L1.33H1.41L1.34H1.40L1.34H1.44L1.03H0.19L0.32H0.78L1.53H1.34L1.40H1.38L1.35H1.43L1.42H1.55L1.71H1.89L1.66H1.53L1.49H1.53L1.65H1.86L1.73H1.63L1.45H1.57L1.41H0.78L / Air

[0038] S3.PMMA substrate pretreatment:

[0039] Clean the surface of the substrate with alcohol and pure water in turn, evenly apply the adhesive layer, and place the substrate in an oven and bake it at a constant temperature of 95℃ for 2 hours. After the adhesive layer is cured, clamp the substrate in a coating machine and perform constant temperature aging treatment in a vacuum environment, baking it at a constant temperature of 95℃ for 1 hour.

[0040] S4. Buffer layer deposition:

[0041] A composite buffer layer consisting of three dielectric layers of TiO2 / SiO2 / TiO2 and an adhesive layer is deposited on the surface of the PMMA substrate to match the physical properties of the PMMA substrate and the functional film layer.

[0042] S5. Coating process:

[0043] Using ion-assisted deposition technology, combined with light control and crystal control composite monitoring, the film thickness error is controlled to ≤±1%;

[0044] S6. Post-processing:

[0045] After coating, the film is subjected to constant temperature aging treatment again, baking at 95℃ for 24 hours to release the stress of the film.

[0046] S7. Spectral test results:

[0047] The PMMA substrate filter prepared by the above process has an average transmittance of 84.2% in the visible light band of 410-640nm and a maximum transmittance of 0.6% in the 665-950nm band, meeting the preset index requirements.

[0048] Refer to the GJB2485A-2019 adhesion test method. Within the effective light aperture, use a 2cm wide tape with a peel strength of not less than 2.74N / cm to fully adhere to the surface of the film layer. After pulling it up vertically and quickly, there should be no film peeling or cracking.

[0049] Comparative Example 1:

[0050] The main difference from Example 1 is that there is no composite buffer layer structure. The results show that the film layer without the buffer layer has film cracking.

[0051] Comparative Example 2:

[0052] The main difference from Example 1 is that the film was not subjected to constant temperature aging treatment before and after coating. The spectrum results show that the transmittance in the visible light band (410-640nm) is reduced by about 15%, which cannot meet the index requirements.

[0053] Example 2: PMMA substrate filter

[0054] Index requirements: average transmittance of visible light (410-640nm) ≥80%, cutoff of near-infrared band (665-950nm) (transmittance ≤1%), no film cracking, film peeling, etc.

[0055] The specific steps are as follows:

[0056] (1) A wide bandgap, highly transparent material system (including high-refractive-index material H and low-refractive-index material L) was used to design a multilayer film system in combination with simulated annealing and needle-shape optimization algorithm. The initial structure of the film system was: Sub / MLM / a1(0.5LH0.5L)^n1 b1(HL)^n2 / Air, with a total number of layers ≤ 60. H, M, and L were ZrO2, TiO2, and SiO2, respectively. The structural coefficients a1 and a2 were 0.95 and 1.20, respectively. The period numbers n1 and n2 were 10 and 10, respectively. The central wavelength λ was 680 nm.

[0057] (2) Combined with the near-infrared cutoff, visible light transmittance, bandwidth and other index requirements of the filter film, the film system is optimized using film system design software (TFCalc, Essential Macleod or Optilayer, etc.). If the required index requirements are not met, the structural coefficients a1, a2 and the number of cycles n1, n2 are adjusted to further optimize until the requirements are met. The final optimized film system structure is: Sub / 0.87M0.63L1.05M / 0.13L0.35H0.15L0.93H1.06L1.51H1.20L1.42H1.33L1 .33H1.37L1.28H1.37L1.25H1.34L1.33H1.34L1.40H1.39L1.58H1.76L1.81H1.61L1.46H1. 49L1.49H1.66L1.84H1.68L1.59H1.53L1.54H1.75L1.78H1.68L1.70H1.33L0.79H1.53L / Air

[0058] (3) PMMA substrate pretreatment: clean the substrate surface with alcohol and pure water in turn, evenly apply the adhesive layer, and bake the substrate in an oven at 90°C for 2 hours. After the adhesive layer is cured, clamp the substrate in a coating machine and perform constant temperature aging treatment in a vacuum environment, baking at 90°C for 1 hour.

[0059] (4) Buffer layer deposition: a certain thickness of TiO2 / SiO2 / TiO2 three dielectric layers and an adhesive layer are deposited on the surface of the PMMA substrate to form a composite buffer layer to match the physical properties of the PMMA substrate and the functional film layer;

[0060] (5) Coating process: Using ion-assisted deposition technology, combined with light control and crystal control composite monitoring, the film thickness error is controlled to ≤±1%;

[0061] (6) Post-treatment: After the coating is completed, it is subjected to constant temperature aging treatment again, and baked at 90℃ for 24 hours to release the stress of the film layer.

[0062] (7) Spectral results: The average transmittance at 410-640nm is 84.4%, and the maximum transmittance at 665-950nm is 0.6%. Referring to the GJB2485A-2019 adhesion test method, within the effective aperture, a tape with a width of 2cm and a peel strength of not less than 2.74N / cm is fully adhered to the surface of the film layer. After being pulled up vertically and quickly, there is no film peeling or cracking.

[0063] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A PMMA-based filter film, characterized in that: include: PMMA substrate; A composite buffer layer, composed of three dielectric layers of TiO2 / SiO2 / TiO2 and an adhesive layer, is deposited on the surface of the PMMA substrate; A multilayer functional film layer is deposited on the composite buffer layer, and the film structure is Sub / MLM / a1(0.5LH0.5L)^n1 b1(HL)^n2 / Air, the total number of layers is ≤60 layers, the optical thicknesses of H, M and L are λ / 4, λ is the center wavelength, H is a high refractive index material selected from TiO2, Nb2O5, Ta2O5, HfO2 or ZrO2, M is an intermediate refractive index material selected from TiO2 or ZrO2, and L is a low refractive index material selected from SiO2 or Al2O3; a1 and a2 are structural coefficients, ranging from 0.1 to 3, and n1 and n2 are the number of periods, ranging from 5 to 15.

2. The PMMA-based filter film according to claim 1, characterized in that: The spectral performance of the filter film satisfies the following requirements: average transmittance in the wavelength range of 410-640nm is ≥80%, and any transmittance in the wavelength range of 665-950nm is ≤1%.

3. The PMMA-based filter film according to claim 1, wherein: The composite buffer layer is used to match the thermal expansion coefficients of the PMMA substrate and the functional film layer, thereby enhancing the adhesion of the film layer and preventing film cracking and delamination.

4. The PMMA-based filter film according to claim 3, characterized in that: The adhesive layer is an epoxy resin adhesive.

5. A method for preparing a filter film based on a PMMA substrate, characterized in that: The following steps are involved: S1. Membrane system design: Using a wide-bandgap, highly transparent material system, combined with simulated annealing and needle-shape optimization algorithms, the initial film structure is designed as: Sub / MLM / a1(0.5LH0.5L)^n1 b1(HL)^n2 / Air, with a total number of layers ≤ 60, where H, M, and L are all λ / 4 optical thicknesses, a1 and a2 are structural coefficients, n1 and n2 are period numbers, and λ is the central wavelength. Use film design software to adjust the structural coefficients a1, a2 and the number of periods n1, n2 until the spectral requirements of near-infrared cutoff and high visible light transmittance are met; S2.PMMA substrate pretreatment: Clean the substrate surface with alcohol and pure water in sequence; Apply the adhesive layer evenly and bake the substrate in an oven at 70-100°C for 2 hours to cure the adhesive layer. The substrate is clamped in the coating machine and subjected to constant temperature aging treatment in a vacuum environment, baking at a constant temperature of 70-100°C for 1 hour; S3. Buffer layer deposition: Depositing TiO2 / SiO2 / TiO2 three dielectric layers and an adhesive layer on the surface of the PMMA substrate to form a composite buffer layer that matches the physical properties of the PMMA substrate and the functional film layer; S4. Functional film coating: Based on the composite buffer layer structure, ion-assisted deposition technology is used, combined with light control and crystal control composite monitoring to control the film thickness error to ≤±1%; S.5 post-processing: After coating, the film is subjected to constant temperature aging treatment again, baking at 70-100℃ for 24 hours to release the stress of the film.

6. An optical imaging system, characterized in that: The optical filter film comprises the optical filter film according to any one of claims 1 to 4, wherein the optical filter film is arranged on the front surface of the CCD sensor to suppress near-infrared stray light.

7. A display device, characterized in that: The light filter film comprises the light filter film according to any one of claims 1 to 5, wherein the light filter film is integrated into the encapsulation layer of the OLED display panel to improve color purity.

8. The display device according to claim 7, wherein: The filter film, polarizer and phase difference film form a multi-layer optical film structure.

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