Preparation method of anti-ultraviolet light absorption coating based on photoresist and nanocarbon

Abstract

The invention discloses a preparation method of an anti-ultraviolet light absorption coating based on photoresist and nanocarbon, which comprises the following steps: using a nanocarbon material and photoresist as raw materials; the light absorption coating with low fluorescent background, low reflectivity and deep ultraviolet light aging resistance under the deep ultraviolet condition is obtained through the steps of preparing mixed turbid liquid, coating, pre-baking, removing photoresist through optical etching, removing residual photoresist, post-baking to form more holes and the like. When the low-background light absorption coating is applied to a deep ultraviolet fluorescence detector, compared with a traditional coating material of an organic adhesive and nanocarbon, the low-background light absorption coating provided by the invention has the advantages that the baseline of the detector is reduced by 67%, the baseline drift is reduced by 75%, and the baseline change degree under deep ultraviolet long-term aging is lower than 0.5%; the material shows excellent deep ultraviolet light aging resistance and extremely low fluorescence background, and can be applied to space telescopes, night vision devices, microscopes and various fluorescence detectors / sensors based on the characteristic of low reflectivity so as to obtain lower background and noise.

Description

Technical Field

[0001] This invention patent relates to the technical field of light-absorbing materials. Specifically, it particularly relates to a preparation method of an anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon, which is mainly applied to an optical analysis system based on a deep ultraviolet light source. Background Art

[0002] A light-absorbing material is a material that can absorb the energy of electromagnetic waves and is commonly used in fields such as optics, aerospace, and military. Among them, in the field of optics, light-absorbing materials are commonly used as coatings on the inner walls of optical analysis instrument cavities to suppress the propagation of various stray lights in the absorption system. Currently, the processes for adding a light-absorbing coating to the surface of a substrate are mainly divided into three categories. One category is to improve the light-absorbing ability of the surface through certain chemical or physical reactions based on the nature of the substrate itself. For example, the copper blackening process and the alumina blackening process, etc. This type of coating technology is applicable to a small number of substrate types and is not applicable to the surfaces of any material. Another category is light-absorbing stickers. Most of these coatings deposit metal or organic light-absorbing materials on a sticky film on the other side. For example, the series of products produced by German company Ackter are this type of light-absorbing stickers. When using them, they need to be cut and then fixed to the surface of the substrate by pasting. Although this type of light-absorbing coating is applicable to substrates of any material, it is not applicable to cavities with complex inner surfaces. The last category is light-absorbing coatings, that is, a mixture mainly composed of a light-absorbing agent and an adhesive is applied to the surface of an object. Generally, the light-absorbing agent is a carbon material, and the adhesive is generally an organic resin. Although this type of coating is applicable to surfaces of any material and shape, due to the limited light-absorbing ability of the light-absorbing agent and the additional scattering effect of the adhesive-air interface on light, the reflectivity of this material is >1%. For example, patent CN113969068A uses carbon materials, adhesives, and various additives as raw materials to prepare a carbon super-black light-absorbing coating, and the reflectivity of this material is 1% - 2%. A lower reflectivity is the goal that light-absorbing materials constantly pursue, but light absorption only relying on the properties of the substance itself has a limit. Therefore, most of the existing technologies have adopted the method of manufacturing special surface structures on the material surface to further improve the light-absorbing ability of the material. For example, patent CN111393988 is made of graphene as the light-absorbing agent and silicone resin as the adhesive. Although micropores are formed between the carbon materials, the pores are still filled with the adhesive. On the other hand, there is an obvious relationship between the size of the pores on the material surface and the applicable wavelength range. From the surface pore size and applicable wavelength range of the series of light-absorbing materials produced by German company Ackter, for light-absorbing materials applicable to the deep ultraviolet band, the size of the pores on their surface is generally only 0.2 - 0.3 μm. How to form a light-absorbing coating in an optical analysis instrument with a complex inner surface by a simple and feasible method is also a difficult problem to be solved.

[0003] In addition, in a fluorescence analysis system, especially a fluorescence analysis system using a deep ultraviolet / ultraviolet light source, the light-absorbing material should also have the ability of low fluorescence background and resistance to deep ultraviolet light damage. However, most of the existing light-absorbing materials do not consider the low fluorescence background and the performance of resistance to deep ultraviolet light damage of the light-absorbing material under deep ultraviolet excitation conditions. The reason is that the light-absorbing material contains various organic substances introduced through adhesives or other auxiliary additives. Deep ultraviolet light has the characteristics of short wavelength and high energy. As shown in Table 1 and Table 2, it can easily break the common covalent bonds in organic substances. The chemical properties and optical properties of the damaged organic components change, not only losing their original performance but also affecting the stability of the light-absorbing coating, which will cause an unstable baseline and long-term drift in optical analysis instruments. The background fluorescence brought by the organic components remaining on the surface of the light-absorbing coating in the fluorescence analysis system will also additionally increase the background and noise.

[0004] Table 1. Energies of Lights with Different Wavelengths

[0005]

[0006] Table 2. Dissociation Energies of Common Chemical Bonds

[0007] Summary of the Invention

[0008] In view of the above technical problems, the present invention discloses a preparation method of an ultraviolet-resistant light-absorbing coating based on a mixture of photoresist and nano-carbon and removal of the surface layer of the photoresist. Only using photoresist and nano-carbon materials as raw materials, the prepared coating will form a porous surface with only a carbon particle skeleton after photolithography etching. As a light-absorbing coating in an optical analysis instrument (especially an instrument using a deep ultraviolet / ultraviolet light source), the combined light-absorbing method of the carbon material and the porous structure can effectively inhibit the propagation of stray light in the cavity. In addition, through the process of photoresist removal by etching, the organic component - the photoresist part located on the surface of the coating and that can be irradiated by light in the coating raw materials can be completely removed. Therefore, the surface of the material is only an inorganic surface composed of carbon material, having an ultra-low fluorescence background and being resistant to deep ultraviolet light damage.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A preparation method of an ultraviolet-resistant light-absorbing coating based on photoresist and nano-carbon, characterized by comprising the following steps:

[0011] 1) Prepare a mixed suspension: fully mix and ultrasonically disperse the nano-carbon material and the photoresist to obtain a mixed suspension;

[0012] 2) Pretreat the substrate: treat the substrate to be coated with acetone, then clean the substrate with isopropanol or ethanol, and finally perform a drying treatment;

[0013] 3) Coating: Coating the mixed suspension on the surface of the cleaned substrate;

[0014] 4) Pre-baking: Heating the coating to remove most of the solvent;

[0015] 5) Photoresist stripping: Irradiating the coating with a large light field ultraviolet - deep ultraviolet light source to trigger the developer in the photoresist;

[0016] 6) Removing residual photoresist: Dissolving the developer transformed by deep ultraviolet light with a developer solution, and then removing the residual developer solution with deionized water;

[0017] 7) Post-baking: Further drying the coating to remove various liquids remaining on the coating, and finally obtaining an absorbent coating.

[0018] Further, in the above technical solution, the nano-carbon material is carbon particles or carbon nanotubes in the range of 10 μm to 50 nm.

[0019] Further, in the above technical solution, the photoresist is a photoresist, and its solubility changes under the irradiation of ultraviolet - deep ultraviolet light. The photoresist includes PCB wet film photoresist and su-8 photoresist.

[0020] Further, in the above technical solution, the developer includes aqueous solutions of tetramethylammonium hydroxide, n-butyl acetate, and potassium hydroxide.

[0021] Further, in the above technical solution, the mass fraction of the nano-carbon material in the mixed suspension is 2 - 20% wt.

[0022] Further, in the above technical solution, the temperature of the pre-baking process is 80°C to 100°C, and the heating time depends on the mass fraction of the carbon material in the suspension and is 70% of the complete drying time of the coating. The purpose is to leave some photoresist solvent in the coating so that a small amount of bubbles are generated in the subsequent photolithography step to form a mesoporous structure.

[0023] Further, in the above technical solution, in step 3), the coating is applied by brushing, spraying, spin-coating, or dipping the mixed suspension on the surface of the cleaned substrate.

[0024] Further, in the above technical solution, in step 4), the pre-baking is heating the coating using a hot plate or an oven.

[0025] Further, in the above technical solution, the method is used for the preparation of an absorbent coating for a fluorescence, absorbent detector, or sensor with a light source wavelength in the deep ultraviolet band.

[0026] Further, in the above technical solution, the large light field ultraviolet - deep ultraviolet light source is an LED, mercury lamp or deuterium lamp with a center wavelength in the range of 250 nm - 370 nm and a power ≥ 20 mW / mm 2 ².

[0027] The main difference between the present invention and the prior art is that most of the light - absorbing coatings based on carbon materials in the prior art obtain light - absorbing coatings by mixing carbon materials with adhesives and then further curing. However, there will be a certain amount of adhesive remaining on the surface of the coating obtained by this method. This adhesive - air interface will increase the material reflectivity and reduce the light - absorbing performance of the material. In addition, the organic components in the adhesive will produce fluorescence in the deep ultraviolet application environment, and even the chemical bonds therein will be damaged by deep ultraviolet light, leading to continuous changes in the light - absorbing performance of the material (resulting in an unstable baseline in the optical analysis system). Moreover, in the present invention, the pre - baking step ensures that part of the solvent is retained in the coating, which is used to generate a small number of holes in the subsequent photolithography etching step, and then in the subsequent photolithography and de - gluing steps, light - absorbing pores with multi - scales (pore diameter range of 0.1 μm - 100 μm) are generated, further improving the light - absorbing performance of the material.

[0028] Aiming at the problems existing in the prior art, the present invention designs a light - absorbing coating with low fluorescence background, low reflectivity and deep ultraviolet light aging resistance under deep ultraviolet conditions, using only photoresist and nano - carbon materials as raw materials. Compared with the prior art, the present invention has the following advantages:

[0029] 1. The surface of the obtained light - absorbing coating is a fully inorganic material, with extremely low background fluorescence and excellent deep ultraviolet light irradiation resistance. In a deep ultraviolet fluorescence detector, compared with the traditional organic glue + carbon material coating, the background noise can be reduced to 1 / 3 of the original, and the background drift is reduced to 1 / 5 of the original;

[0030] 2. Compared with the traditional method, the present method uses the method of etching the colloid in the surface pores with light to eliminate the adhesive - air interface, forming sub - micron - level pores and reducing the reflectivity of the material;

[0031] 3. By retaining part of the solvent as a foaming agent during the pre - baking process, micro - light traps with a pore diameter of 0.1 μm - 100 μm are formed, further reducing the reflectivity of the material. The light - absorbing structure formed thereby has a higher light - absorbing efficiency. Description of the Drawings

[0032] Figure 1 is a preparation flow chart of an ultraviolet - resistant light - absorbing coating based on photoresist and nano - carbon of the present invention;

[0033] Figure 2 is a comparison of deep ultraviolet fluorescence spectra of the coating of the present invention and various common light - absorbing materials in Example 1;

[0034] Figure 3 It is the fluorescence spectrum diagram of the material measured by the self-built evaluation system in Example 1;

[0035] Figure 4 It is the baseline change of the detector coated with the light-absorbing coating of the present invention under 255 nm deep ultraviolet light radiation for 12 h in Example 2. Detailed implementation manners

[0036] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] A preparation method of an ultraviolet-absorbing coating based on photoresist and nano-carbon, characterized by comprising the following steps:

[0038] 1) Prepare a mixed suspension: fully mix and ultrasonically disperse the nano-carbon material and the photoresist to obtain a mixed suspension;

[0039] 2) Substrate cleaning: Treat the substrate to be coated with acetone, then clean the substrate with isopropanol or ethanol, and finally perform a drying treatment;

[0040] 3) Coating: Coat the mixed suspension on the surface of the cleaned substrate by brushing, spraying, spin-coating or dipping;

[0041] 4) Pre-baking: Heat the coating using a hot plate or an oven to remove most of the solvent;

[0042] 5) Photoresist removal by etching: Irradiate the coating with a large light field ultraviolet-deep ultraviolet light source to trigger the developer in the photoresist;

[0043] 6) Residual photoresist removal: Dissolve the developer transformed by the deep ultraviolet light with a developer solution, and then remove the residual developer solution with deionized water;

[0044] 7) Post-baking: Further dry the coating to volatilize various liquids remaining on the coating and leave voids, and finally obtain the light-absorbing coating.

[0045] Further, the nano-carbon material is carbon particles or carbon nanotubes with a size ranging from 10 μm to 50 nm.

[0046] Further, the photoresist is a photoresist, and its solubility changes under the irradiation of ultraviolet-deep ultraviolet light.

[0047] Furthermore, the mass fraction of the nano-carbon material in the mixed suspension is 2-20wt%.

[0048] Furthermore, the temperature of the pre-baking process is 80° C. to 100° C., and the heating time depends on the mass fraction of the carbon material in the suspension, which is 70% of the complete drying time of the coating.

[0049] Furthermore, the method is used for fluorescence, absorption detectors or sensors whose light source wavelength is in the deep ultraviolet band.

[0050] Furthermore, the large light field ultraviolet-deep ultraviolet light source is a high-power LED, mercury lamp or deuterium lamp with a central wavelength in the range of 250nm-370nm.

[0051] Example 1

[0052] like Figure 1 As shown, a preparation method of an anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon, the specific steps are: 1) preparing a mixed suspension: using carbon particles with an average diameter of 300 μm as a light absorber, using PCB wet film photoresist as the photoresist, taking 5 g of carbon particles and 100 mL of photoresist to fully mix the two, and ultrasonically disperse them for 20 minutes before use; 2) substrate pretreatment: the substrate material is an aluminum alloy plate with a thickness of 5 mm, after cleaning with acetone, and then using a water / isopropanol solution with a volume ratio of 1:1 to ultrasonically clean the aluminum alloy plate for 10 minutes, and blow dry the surface liquid; 3) coating: applying the mixed suspension by brushing The good paint is brushed on the surface of the substrate; 4) Pre-baking: put the coated substrate into the oven, set the temperature to 80℃ and heat for 10 minutes (the time required for complete drying is 14 minutes); 5) Photo-etching and degumming: take the nearly completely dried substrate out of the oven, and use a high-power 255nm deep ultraviolet LED with a light power of 42mW to irradiate the coating until the substrate is completely cooled; 6) Remove residual glue: soak the obtained substrate in the developer (n-butyl acetate) for 3 minutes, stir the developer continuously during the process, and rinse off the residual developer on the surface of the material with deionized water; 7) Post-baking: dry the surface of the material to obtain a light-absorbing coating.

[0053] The prepared light-absorbing coating was tested for reflectivity at different wavelengths in a diffuse reflectance spectrometer. The result showed that the reflectivity was less than 1% in the wavelength range of 300-800 nm, and the three-dimensional fluorescence spectrum of the coating at Ex: 200-500 nm / Em: 250-700 nm was measured using a fluorescence spectrophotometer, and the fluorescence intensity value of the material was lower than 10 times the blank noise of the photometer.

[0054] The coating is exposed to a radiation intensity of 10mW / mm 2 After 12h irradiation with 254nm light, Figure 3 As shown, the reflectance and fluorescence intensity of the material changed by -0.5%.

[0055] Application Examples

[0056] Using a self-built material fluorescence evaluation system (the evaluation system adopts a colinear optical path structure, consisting of a 24mW (300mA) 255nm deep ultraviolet LED light source and a fiber optic spectrometer with a pre-placed bandpass filter with a transmission band of 300nm-800nm), the fluorescence spectrum of the material at 300-700nm under 255nm excitation conditions was evaluated. The results were compared with the commercial light-absorbing material FINESHUT (Wuxi Guangye Electronics Co., Ltd.) and the commonly used blackening process - fluorocarbon blackening coating (Dalian Aosong Technology Co., Ltd.). Figure 2 As shown. This shows that the coating has excellent resistance to deep ultraviolet aging and extremely low fluorescence background while having extremely low reflectivity.

[0057] Example 2

[0058] A method for preparing an anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon, the specific steps are as follows: 1) preparing a mixed suspension: using carbon particles with an average diameter of 100 μm as a light absorber, using SU-8 photoresist as the photoresist, taking 10 g of carbon particles and 100 mL of photoresist, mixing the two thoroughly, and ultrasonically dispersing them for 20 minutes before use; 2) substrate pretreatment: selecting a fluorescence detector cell seat processed by 3D printing of PLA material as the substrate, using a water / isopropanol solution with a volume ratio of 1:1 to ultrasonically clean the cell seat for 10 minutes, and then cleaning it with deionized water to blow dry the liquid on the inner and outer surfaces; 3) coating: applying the cell seat by dipping The seat is vertically immersed in the mixed coating and stays for 3 minutes, then it is vertically taken out and left to stand for 1 minute; 4) Pre-baking: the pool seat coated with the coating is placed in an oven, set the temperature to 80°C and heat for 10 minutes (the time required for complete drying is 14 minutes); 5) Photo-etching and de-gumming: the pool seat that is almost completely dried is taken out of the oven, and a high-power mercury lamp is used to directly irradiate the inner wall from each light hole of the pool seat; 6) Removal of residual glue: the obtained substrate is immersed in a developer (tetramethylammonium hydroxide) for 3 minutes, the developer is constantly stirred during the process, and the residual developer on the surface of the material is rinsed off with deionized water; 7) Post-baking: the surface of the dried material is obtained to obtain a light-absorbing coating.

[0059] The prepared light-absorbing coating was measured for the reflectance of the material at different wavelengths in a diffuse reflectance spectrometer, and the result was that the reflectance was less than 1% in the wavelength range of 300 - 800 nm. A patch-type LED with a divergence angle of 60° at 255 nm was used as the light source, a PD with a light window of 12 mm was used as the photodetector, an interference filter with a central wavelength of 255 nm and a bandwidth of 20 mm was used as the excitation filter, and an interference filter with a central wavelength of 430 nm and a bandwidth of 30 nm was used as the emission filter. The optical path structure was collinear. The dichroic mirror had high reflectivity at 200 - 400 nm and high transmittance at 400 - 700 nm, and the angles with the excitation and emission optical paths were both 45°. The baseline change of the detector before and after irradiating the material with deep ultraviolet light at 255 nm for 12 h was tested, as Figure 4 , and the baseline change amplitude was 0.4%.

[0060] A control group was set up. A fluorescence detector cell holder made of PLA material 3D printed without the light-absorbing coating of the present invention with the same structure was used, and the internal optical components were the same as in Example 2. A light-absorbing coating made of nano-carbon and epoxy resin (nano-carbon mass fraction 10%, coating thickness 100 μm) was applied to its inner surface, and the baseline noise and drift of the system in both cases were tested.

[0061] Experimental results: The noise of the detector with the light-absorbing coating of the present invention was 25 μV, only 1 / 2 of that of the control group (50 μV). The baseline drift value of the detector using the coating of the present invention was -5 μV / min, 1 / 4 of that of the control group (-20 μV / min), indicating that the coating has a low fluorescence background under the excitation conditions of deep ultraviolet light and can reduce the baseline noise and stabilize the baseline in a fluorescence detector using deep ultraviolet light as the excitation light source.

Claims

1. A preparation method of an anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon, characterized in that, It includes the following steps: 1) Prepare a mixed suspension: fully mix and ultrasonically disperse the nano-carbon material and the photoresist to obtain a mixed suspension; 2) Substrate pretreatment: clean the surface of the substrate to be coated and perform a drying treatment; 3) Coating: coat the mixed suspension on the surface of the cleaned substrate; 4) Pre-baking: heat the coating to remove most of the solvent; 5) Photolithographic degluing: irradiate the coating with a large light field ultraviolet-deep ultraviolet light source to trigger the developer in the photoresist; 6) Remove residual glue: dissolve the developer transformed by the deep ultraviolet light with a developer solution, and then use deionized water to remove the residual developer solution; 7) Post-baking: further dry the coating to remove various liquids remaining on the coating, and finally obtain an absorbent coating.

2. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, The nano-carbon material is carbon particles or carbon nanotubes in the range of 10μm to 50nm.

3. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, The photoresist is a photoresist, and its solubility changes under the irradiation of ultraviolet-deep ultraviolet light.

4. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, In step 1), the mass fraction of the nano-carbon material in the mixed suspension is 2-20wt%.

5. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, In step 4), the temperature of the pre-baking process is 80°C to 100°C, and the heating time is 70% of the complete drying time of the coating, depending on the mass fraction of the carbon material in the mixed suspension.

6. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, In step 3), the coating is applied by brushing, spraying, spin-coating or dipping the mixed suspension on the surface of the cleaned substrate.

7. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, In step 4), the pre-baking is to heat the coating using a hot plate or an oven.

8. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, The method is used for the preparation of an absorbent coating for a fluorescence, absorbent detector or sensor with a light source wavelength in the deep ultraviolet band.

9. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, The large light field ultraviolet - deep ultraviolet light source is an LED, mercury lamp or deuterium lamp with a center wavelength in the range of 250 nm - 370 nm and a power ≥ 20 mW / mm 2 .

10. The preparation method of the anti-ultraviolet light-absorbing coating based on photoresist and nano-carbon according to claim 1, characterized in that, The surface pore size range of the absorbent coating is 0.1μm to 100μm.

Images