High-temperature-resistant stray light-eliminating ultra-black coating and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant stray light-eliminating inorganic super-black coating and a preparation method thereof, and belongs to the technical field of functional coatings and preparation thereof. The problem that an existing ultra-black coating cannot resist the extreme high temperature of 800 DEG C and cannot meet the coating requirements of precision parts at the same time is solved. According to the invention, self-made low-melting-point glass powder is used as an inorganic binder and is matched with high-temperature-resistant black pigments such as copper chromite black to construct a brand-new inorganic super-black coating system. The coating can be firmly attached to various substrates without harsh base material roughening treatment, the temperature resistance of the coating can reach 800 DEG C or above, space extreme temperature alternation and pneumatic thermal scouring can be effectively borne, and reliable full-spectrum stray light inhibition guarantee is provided for high-temperature working conditions of space optical systems such as high-precision star sensors and the like.

Description

Technical Field

[0001] This invention relates to a high-temperature resistant, anti-gloss, ultra-black coating and its preparation method, belonging to the field of functional coatings and their preparation technology. Background Technology

[0002] During on-orbit operation, the detection accuracy and imaging quality of space optical systems are highly susceptible to the severe impact of stray light. Stray light not only reduces the image signal-to-noise ratio but can also interfere with the normal operation of spacecraft, thus requiring effective suppression measures. As a key component of stray light suppression design for space optical systems, ultra-black coatings, applied to critical surfaces of optical payloads, efficiently absorb incident stray light and reduce internal reflections, thereby ensuring the imaging accuracy and sensitivity of the optical system. For high-precision attitude measurement equipment such as star sensors, the performance of ultra-black coatings directly affects the spacecraft's spatial positioning accuracy.

[0003] With the ever-increasing demands of space missions, space optical systems are placing more stringent requirements on the performance of ultra-black coatings. In low Earth orbit, satellites undergo tens of thousands of thermal cycles throughout their lifespan; while for missile-borne satellite sensors, they face aerodynamic thermal scouring environments lasting up to 3 hours and reaching temperatures as high as 800°C during atmospheric expulsion and reentry. This necessitates ultra-black coatings possessing extremely high thermal stability and resistance to thermal fatigue. However, existing high-absorption matting coating technologies are insufficient to meet these extreme operating conditions. Currently widely used organic resin-based ultra-black coatings, such as silicone or acrylic resin systems, typically have a temperature limit below 400°C. Under the extreme aerodynamic thermal environment of 800°C encountered by missile-borne satellite sensors during atmospheric expulsion / reentry, they may decompose, carbonize, or discolor, leading to permanent optical performance failure and failing to meet the requirements of high-temperature operation.

[0004] To address the high-temperature resistance issue, traditional inorganic super-black coatings use water-based silicates or phosphates as binders. While these improve temperature resistance, they have significant drawbacks when applied to the inner cavities of precision light shields made of high-temperature metal alloys. These inorganic binders exhibit poor wettability and weak adhesion on smooth alloy surfaces, necessitating pretreatment processes such as sandblasting or acid pickling to increase substrate surface roughness and enhance adhesion. However, with increasingly sophisticated light shield structures, particularly those requiring extremely high dimensional accuracy for the thin-walled cutting edge of the light-blocking ring, roughening processes like sandblasting or acid pickling alter the substrate's structural dimensions, rendering them unsuitable. This technological contradiction directly limits the application of traditional inorganic matte super-black coatings in precision star sensor light shields.

[0005] Therefore, in the current aerospace field, especially for missile-borne satellite sensors operating at temperatures up to 800°C and for precision optical components with complex structures, there is an urgent need for a full-spectrum ultra-high absorptivity matting coating that can withstand extreme temperatures and achieve firm adhesion on precision metal substrates. Existing technologies present an irreconcilable contradiction between temperature resistance, adhesion processes, and substrate adaptability. Developing a novel ultra-black coating system that can circumvent the stringent pretreatment requirements of traditional inorganic coatings and possesses both excellent high-temperature stability and high adhesion has become a key challenge in promoting the development of high-precision space optics technology. Summary of the Invention

[0006] This invention addresses the problem that existing ultra-black coatings cannot simultaneously withstand extreme high temperatures of 800℃ and meet the coating requirements of precision components, by providing a high-temperature resistant, anti-gloss ultra-black coating and its preparation method.

[0007] The technical solution of the present invention: One of the objectives of this invention is to provide a low-melting-point glass powder, which, by weight percentage, is composed of CaO 5-15%, B2O3 15-20%, SiO2 45-55%, Na2O 0-5%, K2O 0-5%, Al2O3 2-4%, ZrO2 1-3%, Bi2O3 1-5%, and V2O5 1-5%.

[0008] Further specifying, the low-melting-point glass powder is prepared using CaCO3, H3BO3, SiO2, Al2O3, ZrO2, Bi2O3, V2O5, Na2CO3 and K2CO3 as raw materials and by a high-temperature melting-quenching method.

[0009] The second objective of this invention is to provide a method for preparing the aforementioned low-melting-point glass powder. The method comprises: mixing CaCO3, H3BO3, SiO2, Al2O3, ZrO2, Bi2O3, V2O5, Na2CO3 and K2CO3 evenly and placing them in a platinum crucible; melting and holding the mixture in a high-temperature furnace to form a homogeneous glass melt; rapidly pouring the glass melt into deionized water for water quenching to obtain shattered glass particles; drying, grinding, and passing the particles through a 100-mesh sieve to obtain low-melting-point glass powder.

[0010] Further specified, the melting and holding temperature is 1500℃, and the time is 1 h.

[0011] The third objective of this invention is to provide an application of the aforementioned low-melting-point glass powder, specifically as an inorganic binder for preparing a slurry for a high-temperature resistant, anti-glare, ultra-black coating.

[0012] The fourth objective of this invention is to provide a method for preparing a high-temperature resistant, anti-glare, ultra-black coating slurry, which is prepared by mixing the aforementioned low-melting-point glass powder, copper chromium black, and anhydrous ethanol as raw materials.

[0013] Further specifying, the mass ratio of low melting point glass powder to copper chromium black is (0.8~1.2):1.

[0014] Further specified, the mixed powder composed of low melting point glass powder and copper chromium black is dispersed in anhydrous ethanol at a concentration of 0.7~0.8 g / ml.

[0015] The fifth objective of this invention is to provide a method for preparing a high-temperature resistant, anti-gloss, ultra-black coating. Specifically, the above-mentioned slurry for preparing the high-temperature resistant, anti-gloss, ultra-black coating is applied to the surface of a clean substrate by scraping, brushing, or spraying. After drying in a ventilated environment at room temperature for 3 minutes, it is sintered to obtain the high-temperature resistant, ultra-black coating.

[0016] Further specifying the sintering process, it is as follows: heating to 580-620℃ at a heating rate of 35-45℃ / min, holding at that temperature for 0.5-1.5 min, and then cooling to room temperature with the furnace.

[0017] Further specified, the wet film thickness obtained by coating the slurry onto the surface of a clean substrate using a scraping method is 550 μm.

[0018] The sixth objective of this invention is to obtain a high-temperature resistant, anti-gravity, ultra-black coating prepared by the above method, which has a temperature resistance of over 800°C.

[0019] The seventh objective of this invention is to provide an application of the above-mentioned high-temperature resistant, stray light-suppressing ultra-black coating, specifically for stray light suppression in space optical systems.

[0020] Beneficial effects: This invention employs self-made low-melting-point glass powder as an inorganic binder, combined with high-temperature resistant black pigments such as copper chromium black, to construct a novel inorganic ultra-black coating system. This coating achieves strong adhesion to various substrates without requiring stringent substrate roughening treatment, and its temperature resistance reaches over 800℃, effectively withstanding extreme temperature variations and aerodynamic thermal erosion in space. It provides reliable full-spectrum stray light suppression for high-precision star sensors and other space optical systems operating under high-temperature conditions. Compared with existing technologies, it has at least the following advantages: (1) This invention uses self-made low-melting-point glass powder as an inorganic binder to overcome the insufficient temperature resistance of organic resin-based coatings and the process limitations of traditional inorganic coatings that must rely on pretreatment of damaged substrates due to poor wettability of binders. It can achieve a firmly attached high-temperature resistant and anti-glare super black coating and its preparation method without harsh roughening treatment, solving the problem that existing super black coatings cannot withstand extreme high temperature of 800℃ and meet the coating requirements of precision parts at the same time.

[0021] (2) This invention utilizes a composite structure of graded light trapping and chemical bonding constructed during the sintering process of a heat-resistant inorganic glass binder phase and a high-dullness black pigment, resulting in an ultra-black coating that combines heat resistance, adhesion, and high absorption rate. Specifically, during the hot sintering process, the low-melting-point glass powder binder softens to form a continuous liquid phase with excellent wettability and fluidity (softening point 400~700℃), achieving sufficient wetting and coating of spinel pigments such as copper chromium black to form a stable bond. Simultaneously, under an oxidizing atmosphere, it chemically bonds / interdiffused (e.g., MO-Si bridging or ionic bonding) with the oxide film on the surface of precision-machined metal substrates (such as titanium alloys and stainless steel light shields), forming strong chemical bonds and physical anchoring. This achieves a breakthrough in obtaining firm adhesion on precision components without destructive roughening treatment, perfectly adapting to the coating needs of complex structures such as the inner cavity of precision light shields with high dimensional accuracy requirements, and completely avoiding the impact of traditional processes on the dimensional accuracy of the substrate. After cooling, the glass solidifies into a continuous three-dimensional skeleton, firmly embedding the pigment particles and constructing a graded light trapping structure.

[0022] (3) The high light absorption performance of the coating prepared by this invention is contributed by the intrinsic absorption of the pigment and the scattering of the microstructure. Copper chromium black pigment itself has a wide-spectrum strong absorption characteristic. During the coating forming process, by precisely controlling the ratio of glass powder to pigment and the sintering process, while ensuring that the overall temperature resistance of the coating reaches above 800℃, the microstructure inside the coating is optimized. In the solid skeleton formed by the glass binder phase, the random stacking of pigment particles and the filling of the glass phase will form multi-scale micro-nano pores and rough interfaces. These structures constitute light traps. When incident light enters the coating, multiple diffuse reflections will occur between these micro-nano interfaces, and the optical path will be significantly extended, so that it will be fully and gradually absorbed by the pigment particles, ensuring that the coating can achieve a stable high absorption rate in the full spectrum and under wide angle incident conditions, significantly improving the imaging signal-to-noise ratio and detection accuracy of the optical system.

[0023] (4) Based on the CaO-B2O3-SiO2 system, this invention introduces 1~5 wt% Bi2O3 / V2O5 to replace part of the CaO, enabling it to form strong chemical bonds with the surface oxides of the substrate (such as Cr2O3 of stainless steel and TiO2 of titanium alloy). Simultaneously, increasing the Al2O3 content can slightly increase the glass transition temperature (T0). g The viscosity is reduced to prevent excessive flow of glass powder during sintering, thus forming a stronger binder layer. Further, the SiO2 content is increased based on the CaO-B2O3-SiO2 system. SiO2 is the strongest network former; the higher its content, the better the thermal and chemical stability of the glass. 1-3 wt% ZrO2 is added. ZrO2 is an extremely strong network former / intermediate, which can significantly improve the thermal stability of the glass. gThis improves hardness, chemical stability, and resistance to crystallization. Reducing the Na2O / K2O content can decrease thermal expansion of the coating and improve its temperature resistance. Attached Figure Description

[0024] Figure 1 The surface SEM image of the ultra-black coating prepared in Example 1; Figure 2 A cross-sectional SEM image of the ultra-black coating prepared in Example 1; Figure 3 The image shows the solar absorptivity test results of the ultra-black coating prepared in Example 1. Figure 4 The cross-cut test pattern of the ultra-black coating prepared in Example 1; Figure 5 Comparison of macroscopic optical photographs of the ultra-black coating prepared in Example 1 before and after high-temperature testing at 800℃; Figure 6 SEM image of the surface of the ultra-black coating prepared in Example 1 after a high-temperature test at 800°C; Figure 7 Comparison of solar absorptivity test results before and after the ultra-black coating prepared in Example 1 was tested at 800℃; Figure 8 The cross-cut test pattern of the ultra-black coating prepared in Example 1 after being tested at 800°C. Figure 9 The cross-cut test pattern is shown for the ultra-black coating prepared in Comparative Example 1. Figure 10 The image shows a comparison of the solar absorptivity test results of the ultra-black coating prepared in Comparative Example 1 before and after a high-temperature test at 800℃. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] Example 1: Step 1: Prepare low-melting-point glass powder using a high-temperature melting-quenching method: Low-melting-point glass powder was prepared, consisting of CaO 15%, B2O3 19%, SiO2 47%, Na2O 1%, K2O 1%, Al2O3 4%, ZrO2 3%, Bi2O3 5%, and V2O 55%.

[0030] Using CaCO3, H3BO3, SiO2, Al2O3, ZrO2, Bi2O3, V2O5, Na2CO3 and K2CO3 as raw materials, the raw materials are weighed according to the above weight percentages: 15% CaO (provided by the thermal decomposition of CaCO3), 19% B2O3 (derived from H3BO3), 47% SiO2, 4% Al2O3, 3% ZrO2, 5% Bi2O3, 5% V2O5, 1% Na2O (derived from Na2CO3) and 1% K2O (derived from K2CO3).

[0031] The above raw materials were mixed in a drum ball mill for 24 hours to ensure uniform mixing. The uniformly mixed batch was then placed in a platinum crucible and melted in a high-temperature furnace at 1500°C for 1 hour to form a homogeneous glass melt. The glass melt was then rapidly poured into deionized water for quenching to obtain fragmented glass particles. After drying, the glass particles were ground in a planetary ball mill for at least 12 hours and finally passed through a 100-mesh sieve to obtain low-melting-point glass powder of the desired particle size.

[0032] Step 2: Preparation of coating slurry: Low-melting-point glass powder and high-temperature resistant black pigment copper chromium black (CuCr2O4) powder were accurately weighed at a mass ratio of 1:1. The mixed powder was dispersed in anhydrous ethanol at a concentration of 0.75 g / ml and stirred continuously with a magnetic stirrer for 2 h, followed by ultrasonic dispersion for 30 min to obtain a uniform and stable coating slurry.

[0033] Step 3: Preparation of wet film: Stainless steel sheets were selected as the substrate and ultrasonically cleaned with acetone and anhydrous ethanol for 10 minutes in sequence to remove surface oil. After drying with nitrogen, they were ready for use.

[0034] The above slurry was applied to the surface of a clean substrate using a precision scraping method, and the wet film thickness was controlled at approximately 550 μm.

[0035] Step 4: Coating preparation: After coating, the sample was placed in a fume hood and dried at room temperature for 3 minutes to allow the ethanol to evaporate completely. Then, the sample was transferred to a box muffle furnace and heated to 600°C at a heating rate of 40°C / min, held at that temperature for 1 minute, and then cooled to room temperature with the furnace to complete the preparation of the super black coating.

[0036] The structure and properties of the ultra-black coatings prepared in the above embodiments were characterized: (1) The surface and cross-sectional morphology of the coating were observed using a scanning electron microscope (SEM), and the results are as follows: Figure 1 and Figure 2 As shown. Figure 1 As shown, the coating surface exhibits a uniform and dense microstructure formed by copper chromium black pigment particles encapsulated and bonded by a low-melting-point glass phase, with no obvious macroscopic cracks. Figure 2 The coating shown is tightly bonded to the metal substrate, with no gaps at the interface, and has a uniform thickness of approximately 300 μm.

[0037] (2) Using a UV-Vis-NIR spectrophotometer with an integrating sphere attachment, the spectral reflectance of the coating in the 200-2500 nm wavelength range was tested, and its solar absorptivity was calculated. The test results are as follows: Figure 3 As shown in the figure, the solar absorptivity of the prepared original coating is ≥0.96.

[0038] (3) According to GB / T 9286-1998 standard, the coating was subjected to a cross-cut adhesion test (3 mm spacing). The adhesion was observed using an optical microscope. Figure 4 As shown, the edges of the coating in the gridded area are smooth and flat, with no peeling. The adhesion level is 1, indicating that the coating is extremely firmly bonded to the substrate.

[0039] (4) The ultra-black coating prepared in this embodiment was placed in a muffle furnace and heated to 800°C in an air atmosphere and held for 3 h to simulate the extreme high-temperature conditions encountered by the missile-borne satellite sensor. After the sample cooled to room temperature, its morphology and performance were compared with those of the original coating before treatment.

[0040] Macroscopic optical images before and after the ultra-black coating was tested at 800℃. Figure 5 As shown, a is a photo before the 800℃ high-temperature test, and b is a photo after the 800℃ high-temperature test. The comparison shows that after heat treatment at 800℃ for 3 hours, the coating surface has a uniform color, and no discoloration, blistering, or peeling is observed.

[0041] SEM images of the ultra-black coating after a high-temperature test at 800℃ are as follows. Figure 6As shown in the figure, after the coating has undergone heat treatment at 800℃ for 3 hours, its microstructure remains intact, and the glass binder phase and pigment particles are still well bonded together. No microcracks or interface debonding caused by the mismatch of thermal expansion coefficients have appeared.

[0042] The solar absorptivity test results of the ultra-black coating after being tested at 800℃ are as follows: Figure 7 As shown in the figure, after the coating has undergone heat treatment at 800℃ for 3 hours, the solar absorptivity still remains at a high level of ≥0.96, with minimal performance degradation, proving its excellent thermal stability.

[0043] The cross-cut adhesion test was performed on the ultra-black coating after it had been subjected to a high temperature test of 800℃. The results are as follows: Figure 8 As shown, the coating still maintains Grade 1 adhesion after heat treatment at 800℃ for 3 hours, with no peeling observed, proving that the 800℃ high-temperature exposure did not damage the bonding interface between the coating and the substrate.

[0044] Comparative Example 1: The difference between this comparative example and Example 1 is that commercially available low-melting-point glass powder was used instead of the low-melting-point glass powder prepared in step 1. The remaining process steps and parameter settings are the same as in Example 1. Specifically, the commercially available low-melting-point glass powder mainly consists of a CaO-B2O3-SiO2 system and was purchased from Xiamen Baijiaxiang Microcrystalline Materials Technology Co., Ltd., model number RW070.

[0045] The ultra-black coating prepared in this comparative example was subjected to cross-cut adhesion testing according to GB / T 9286-1998 standard. The test results are as follows: Figure 9 As shown, the adhesion level is only level 2, with a large area of ​​coating peeling off at the intersection of the grid lines, and obvious powder shedding on the surface, proving that the interfacial bonding between traditional glass powder and the substrate is poor.

[0046] The super-black coating prepared in this comparative example was further placed in a muffle furnace and heated to 800°C in air atmosphere, and held at that temperature for 3 hours to simulate the extreme high-temperature conditions encountered by the missile-borne satellite sensor. After the sample cooled to room temperature, its optical properties were compared with those of the original coating before treatment. The solar absorptivity test results were compared... Figure 10 As shown in the figure, after the coating underwent heat treatment at 800℃ for 3 hours, the solar absorptivity dropped sharply from the initial approximately 0.96 to below 0.94.

[0047] In summary, traditional commercial low-melting-point glass powders, due to their insufficient thermal stability and low reactivity with the substrate, cannot meet the stringent requirements for coating adhesion and optical performance stability under extreme high-temperature conditions of 800℃.

[0048] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A low melting point glass powder, characterized by, CaO 5-15%, B2O3 15-20%, SiO2 45-55%, Na2O 0-5%, K2O 0-5%, Al2O3 2-4%, ZrO2 1-3%, Bi2O3 1-5%, V2O5 1-5% by weight percentage.

2. The low melting point glass powder according to claim 1, characterized by, The low-melting-point glass powder is prepared by using CaCO3, H3BO3, SiO2, Al2O3, ZrO2, Bi2O3, V2O5, Na2CO3 and K2CO3 as raw materials and by adopting a high-temperature melting-quenching method.

3. A method of producing a low melting point glass powder as claimed in claim 1 or 2, characterized by, CaCO3, H3BO3, SiO2, Al2O3, ZrO2, Bi2O3, V2O5, Na2CO3 and K2CO3 are uniformly mixed and then placed in a platinum crucible to be melted and kept at high temperature to form a uniform glass liquid, the glass liquid is rapidly poured into deionized water for water quenching, the glass particles are obtained by crushing, drying, grinding and passing through a 100-mesh sieve.

4. The production method according to claim 3, characterized by, The melting and keeping temperature is 1500 DEG C and the time is 1 h.

5. Use of a low melting point glass powder according to claim 1 or 2, characterized in that, The slurry of claim 6 is coated on the surface of a clean substrate by means of scraping, brushing or spraying, and then sintered after being dried at room temperature for 3 min, to obtain a high-temperature-resistant super-black coating.

6. A slurry for preparing a high-temperature-resistant light-scattering ultra-black coating, characterized in that, The sintering process is as follows: heating at a rate of 35-45 DEG C / min to 580-620 DEG C, keeping for 0.5-1.5 min, and then cooling to room temperature in the furnace.

7. A method for preparing a high-temperature-resistant stray light eliminating superblack coating, characterized in that, The temperature resistance is up to 800 DEG C or above.

8. The method of use of claim 7, wherein, The slurry is used for suppressing stray light in a space optical system.

9. The high temperature resistant light eliminating super black coating prepared by the method of claim 7 or 8, characterized in that, The slurry is used for suppressing stray light in a space optical system.

10. Use of the high-temperature-resistant, light-scattering, superblack coating according to claim 9, characterized in that ​

Images