Infrared recognizable label and method for manufacturing the same

Abstract

The present application relates to a kind of infrared identifiable label and its preparation method, it is related to micro-nano processing and infrared identification technical field.The present application selects aluminum metal as substrate, forms the thick porous anodic aluminum oxide layer of pattern area and the thin porous anodic aluminum oxide layer of background area on substrate surface using anodic oxidation treatment and controlling processing time, the difference of infrared emissivity of both, can realize clear infrared imaging;While the pattern area of high infrared emissivity is usually white or black, the background area of low infrared emissivity is different color due to also composite metal film, can also form visual contrast under visible light.In addition, the pattern area of the present application is directly grown from substrate by anodic oxidation treatment, and is integrated structure with substrate, reduces the risk of peeling and falling.The present application infrared identifiable label structure is solid, pattern and substrate integration, high infrared contrast, excellent weather resistance, and pattern precision is high, is suitable for traffic safety and other fields.

Description

Technical Field

[0001] This invention belongs to the field of signage technology and relates to an infrared identifiable sign and its preparation method. Background Technology

[0002] Traditional signage is manufactured using methods such as printing, spraying, or lamination. The functional layer is physically bonded to the substrate, making it susceptible to delamination and peeling under harsh environments (such as high and low temperatures, friction, and corrosion), leading to functional failure. For infrared recognition applications requiring high reliability, a more robust and durable pattern formation technology is needed. Existing technologies often create contrast by stacking layers of materials with different infrared properties on the substrate, resulting in complex processes and inconsistent interlayer adhesion. Therefore, developing a method for manufacturing visible-infrared dual-identifiable signage that integrates the pattern with the substrate, offers strong weather resistance, and provides high contrast is of great significance. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides an infrared identifiable sign and its manufacturing method. This invention uses aluminum metal as the substrate and employs anodizing treatment with controlled processing time to form a thick porous anodized aluminum layer in the pattern area and a thin porous anodized aluminum layer in the background area on the substrate surface. The difference in infrared emissivity between the two layers enables clear infrared imaging. Simultaneously, the pattern area with high infrared emissivity is typically white or black, while the background area with low infrared emissivity, due to the inclusion of a metal film, exhibits different colors, creating visual contrast even under visible light. Furthermore, the pattern area of ​​this invention is grown directly from the substrate through anodizing, forming an integral structure with the substrate, reducing the risk of peeling and detachment. This invention's infrared identifiable sign features a robust structure, integrated pattern and substrate, high infrared contrast, and excellent weather resistance, making it suitable for applications such as traffic safety.

[0004] The objective of this invention can be achieved through the following methods: In a first aspect, the present invention provides a method for preparing an infrared identifiable sign, comprising the following steps: S1. The aluminum substrate is anodized to generate a thick porous anodic aluminum oxide layer. S2. Using screen printing technology, a mask with the desired pattern is printed onto a thick porous anodized aluminum layer to obtain the printed sign. S3. After printing, the sign is heat-cured and then immersed in a chemical etching solution to remove the anodic oxide functional layer in the area not covered by the mask, forming a low infrared emissivity area. S4. Then, the sign is anodized to generate a thin porous anodic aluminum oxide layer in the low infrared emissivity area, and a metal film is sputtered on the surface of the thin anodic aluminum oxide layer to obtain a colored low emissivity area. S5. Remove the mask to obtain the final product.

[0005] In one embodiment of the present invention, in step S1, the aluminum substrate is an aluminum substrate that has undergone degreasing and cleaning treatment.

[0006] Furthermore, the degreasing and cleaning process includes: immersing the aluminum substrate in acetone (AR, >99.5%) and ethanol (AR, >99.7%) for 1-2 hours respectively, and then drying it at 55-65°C for 1-3 hours.

[0007] In one embodiment of the present invention, in step S1, the purity of the aluminum substrate is higher than 99.6%.

[0008] In one embodiment of the present invention, in step S1 or S4, the anodizing process includes: using an aluminum substrate as the anode and a carbon plate as the cathode, performing anodizing in an electrolyte, controlling the voltage at 100-200V, and the oxidation time at 2 min-10 h; the oxidation time in step S1 is 4-10 h, and the oxidation time in step S4 is 2-30 min. In step S1, the present invention generates a uniform porous anodic aluminum oxide (AAO) layer with high infrared emissivity (alumina thickness > 5 μm, infrared emissivity > 0.8) through long-term anodizing; in step S4, a thin porous anodic aluminum oxide layer (alumina thickness < 500 nm, infrared emissivity < 0.2) is generated through short-time anodizing.

[0009] Further, the electrolyte is selected from one of oxalic acid solution and phosphoric acid solution; wherein the concentration of oxalic acid solution is 0.3~0.6 mol / L, and the concentration of phosphoric acid solution is 0.2~0.4 mol / L; the temperature of the electrolyte is 2~4℃. The electrolyte is prepared using deionized water and ethanol (AR, >99.7%) in a volume ratio of 1:1 as solvent.

[0010] In one embodiment of the present invention, step S2, the printing includes: selecting a polymer resin solution as ink, using a screen template with the desired pattern, and printing the ink onto the surface of a porous anodized aluminum layer; wherein the polymer resin solution includes Paraaloid B72. In some embodiments, the polymer resin solution is a solution formed by dissolving 20% ​​by mass of acrylic resin (such as Paraaloid B72) in methanol or acetone.

[0011] In one embodiment of the present invention, in step S3, the temperature for thermal curing is 55-65°C, and the time is 15-30 minutes. Thermal curing can enhance the mask's ability to protect against subsequent etching.

[0012] In one embodiment of the present invention, in step S3, the chemical etching solution includes a phosphoric acid solution, and the chemical etching temperature is 30~60℃ for 1-2 hours. The AAO layer not protected by the resin mask will be etched away, exposing the original smooth aluminum substrate surface, while the AAO layer in the protected area remains intact.

[0013] As one embodiment of the present invention, in step S4, the sputtering method includes DC ion sputtering, and the sputtering time is 15~30 s.

[0014] In one embodiment of the present invention, in step S4, the metal film includes one of gold, platinum, silver, and chromium.

[0015] As one embodiment of the present invention, in step S5, the method for removing the mask includes: soaking in acetone (AR, >99.5%) for 1 to 2 hours, and then placing it in a vacuum drying oven at 60°C for drying time of not less than 1 hour.

[0016] As one embodiment of the present invention, the thickness of the thick porous anodic aluminum oxide layer is 5-10 μm, and its infrared emissivity is 0.8-0.95; the thickness of the thin porous anodic aluminum oxide layer is <500 nm, and its infrared emissivity is <0.2.

[0017] Secondly, the present invention provides an infrared identifiable sign obtained by the preparation method described above.

[0018] This invention creates an AAO pattern area with high infrared emissivity and a colored aluminum substrate background area with low infrared emissivity, thereby generating a strong difference in infrared radiation that can be clearly identified by infrared devices. Simultaneously, the sign exhibits visible differences from conventional signs, allowing it to be identified by video surveillance systems commonly used by traffic management departments under normal lighting conditions.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention is the first to discover that the infrared emissivity of porous anodic aluminum is related to its thickness. Therefore, by constructing regions of porous anodic aluminum with different emissivity on a high-reflectivity substrate, the infrared identifiable sign prepared utilizes the high infrared reflection of the aluminum substrate and the wide range of infrared emissivity (0.1-0.95) of porous anodic aluminum affected by its thickness, thus achieving clear infrared imaging.

[0020] 2. The present invention also unexpectedly discovered that the metal film can only be made to exhibit different colors when it is laminated on the surface of the thin porous anodic aluminum oxide layer. Therefore, by laminating the metal film onto the thin porous anodic aluminum oxide layer, low infrared emissivity areas with different colors are formed, while high infrared emissivity areas are usually white or black, thus forming a visual contrast under visible light.

[0021] 3. The infrared - recognizable sign prepared by the present invention has the same identification characteristics in visible light and infrared, and at the same time has the advantage of integrated structure. The pattern (AAO layer) grows directly from the substrate and is an integral structure with the substrate, reducing the risk of peeling and falling off. Combining with the precision of screen printing, complex and delicate patterns can be prepared.

[0022] 4. The infrared - recognizable sign prepared by the present invention has excellent weather resistance and wear resistance, extremely strong adhesion, and high pattern precision. Alumina itself has high hardness, stable chemical properties, and far exceeds ordinary paints or films in terms of wear resistance, corrosion resistance, and anti - ultraviolet aging ability, and is applicable to fields such as traffic safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] By reading the following detailed description of the non - restrictive embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent: Figure 1 is the spectral emissivity in the long - wave infrared of the high - emissivity region and the low - emissivity region in the visible - infrared dual - recognizable sign in Example 1; Figure 2 is the spectral reflectivity in the visible of the high - emissivity region and the low - emissivity region in the visible - infrared dual - recognizable sign in Example 1; <( Figure 3 is the photo of the infrared - recognizable license plate prepared in Example 1 under a visible camera and an infrared camera; Figure 4 is the photo of the anodic titanium oxide film layer peeling off from the titanium substrate in Comparative Example 1; Figure 5 is the spectral emissivity in the long - wave infrared region of the titanium oxide layers with different oxidation times in Comparative Example 1 (the thicker anodic titanium oxide layer oxidized for about 1 hour and the thin anodic titanium oxide layer oxidized for 10 minutes); Figure 6 is the photo of the titanium substrate logo under an infrared camera in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are implemented on the premise of the technical solution of the present invention, providing detailed implementation manners and specific operation processes, which will help those skilled in the art to further understand the present invention. It should be noted that the protection scope of the present invention is not limited to the following embodiments. Several adjustments and improvements made on the premise of the concept of the present invention all belong to the protection scope of the present invention.

[0025] Example 1 Taking the infrared - recognizable sign prepared with the license plate number "Hu A·88888" as the identification template as an example, the specific steps are as follows: (1) Pretreat the substrate: First, take a high-purity aluminum substrate (99.9%) with a thickness of 3 mm, soak it in acetone and ethanol for 1 hour respectively to remove the surface grease, and dry it in a vacuum drying oven at 60°C for 1 hour.

[0026] (2) Conduct an anodic oxidation reaction on the pretreated substrate: Use the pretreated substrate as the anode and a carbon plate as the cathode, and conduct anodic oxidation treatment in a 0.3M phosphoric acid electrolyte solution (2 - 4°C), control the voltage at 180V, and the oxidation time is up to 8 hours to grow a thick porous anodic aluminum oxide layer with uniform density and high infrared emissivity on the aluminum sheet surface (the thickness of aluminum oxide is 5.19 μm).

[0027] (3) Conduct a protective mask printing on the anodized substrate: Prepare a 20wt% acetone solution of Paraloid B72 acrylic resin as the screen printing "ink". Use a customized screen template with the encoding pattern of "Shanghai A·88888" to print this resin solution on the surface of the anodic aluminum oxide layer.

[0028] (4) Cure the mask on the printed substrate: Put the printed substrate into an oven at 60°C and heat it for 15 minutes to completely cure the resin mask, which tightly adheres to the substrate surface.

[0029] (5) Conduct selective chemical etching on the cured substrate: Immerse the substrate with the cured mask completely into a 5wt% phosphoric acid solution and etch it for 1 hour in a constant temperature water bath at 60°C. During this process, the anodic aluminum oxide layer not covered by the resin mask is completely dissolved, exposing the underlying metal aluminum substrate, while the anodic aluminum oxide layer in the "Shanghai A·88888" pattern area protected by the mask remains intact.

[0030] (6) Conduct an anodic oxidation reaction on the etched substrate: Use the etched substrate as the anode and a carbon plate as the cathode, and conduct anodic oxidation treatment in a 0.3M phosphoric acid electrolyte solution (2 - 4°C), control the voltage at 180V, and the oxidation time is 10 minutes to grow a thin porous anodic aluminum oxide layer on the surface of the etched low-emissivity area (the thickness of aluminum oxide is 306 nm).

[0031] (7) Ion sputter deposit a metal film on the surface of the thin anodic aluminum oxide area: Use a gold target, the central distance between the target and the substrate holder is 10 cm, and the sputtering time is 15 seconds.

[0032] (8) Remove the mask on the substrate: Take out the substrate from the etching solution, rinse it thoroughly with deionized water, then soak it in acetone for 1 hour to completely dissolve and remove the resin mask, and place it in a vacuum drying oven at 60°C for drying, and the drying time is not less than 1 hour.

[0033] The long-wave infrared spectral emissivity of the infrared identifiable sign obtained above is as follows: Figure 1 As shown. Fourier transform infrared spectroscopy revealed that the infrared emissivity of the sign's characteristic infrared pattern (high emissivity region) in the long-wave infrared region (8–14 μm) is 0.83, while the background region (low emissivity region) has an infrared emissivity of 0.11 in the long-wave infrared region, resulting in a difference of 0.72. The spectral reflectance in the visible band is as follows. Figure 2 As shown, the background area has a distinct characteristic peak in the visible band, appearing blue, while the infrared feature pattern is black with low reflectivity in the visible band. The sign was hung at the actual license plate location, and photos were taken using both a visible camera and an infrared camera, resulting in the following images. Figure 3 As shown, both the visible and infrared photographs exhibit a clear template pattern with high contrast.

[0034] Comparative Example 1 To verify the impact of substrate material selection on the performance of infrared-identifiable signs, this comparative example uses a titanium substrate instead of the aluminum substrate in Example 1 to examine its applicability in the infrared band. The specific steps are as follows: (1) Take a high-purity titanium substrate with a thickness of 1 mm (purity 99.6%, TA1 grade), soak it in acetone and ethanol for 1 hour to remove surface grease, and dry it in a vacuum drying oven at 60°C for 1 hour.

[0035] (2) Using the pretreated titanium substrate as the anode and a platinum sheet as the cathode, anodizing was performed in an ethylene glycol electrolyte containing 3 wt% NH4F and 1.6 wt% H2O, with the voltage controlled at 20 V. When the oxidation time reached 1 hour, the anolyzed titanium layer detached from the surface of the titanium substrate (e.g., Figure 4 As shown in the figure, growth could not continue. This is because during the anodizing of titanium in a fluorine-containing electrolyte, fluoride ions accumulate at the metal / oxide interface, forming a fluorine-rich layer. This results in insufficient adhesion between the titanium oxide film and the substrate, causing the film to peel off under internal stress. In contrast, in Example 1, the aluminum substrate was oxidized for 8 hours under the same anodizing conditions, and the AAO layer maintained a strong, integrated bond with the aluminum substrate.

[0036] (3) The emissivity of titanium oxide layers obtained at different oxidation times in the long-wave infrared region (8~14 μm) was measured using a Fourier transform infrared spectrometer (e.g., Figure 5 (As shown). The results show that the infrared emissivity of the thicker anodic titanium oxide layer formed before nearing detachment (approximately 1 hour) in the long-wave infrared region is 0.58; the infrared emissivity of the thinner anodic titanium oxide layer formed after 10 minutes of oxidation is 0.23. The difference in infrared emissivity between the two is only 0.35.

[0037] (4) Take another titanium substrate that has undergone the same pretreatment and try to prepare an infrared identifiable sign according to the complete process flow of Example 1. After anodizing (oxidation time controlled within 30 minutes to avoid film peeling), screen printing mask, and curing, immerse the sign in a 5 wt% phosphoric acid solution for etching.

[0038] Observe the above signs under an infrared camera (e.g.) Figure 6 As shown), although the sign pattern can be vaguely discerned, the infrared contrast of the pattern is significantly lower than in Example 1 because the intrinsic infrared emissivity difference between the high / low emissivity regions in the TiO2 system (Δε = 0.35) is much smaller than that in the aluminum system (Δε = 0.72), resulting in a smaller radiation temperature difference. Figure 3 In contrast, aluminum substrate signs exhibit clear patterns with high contrast under infrared cameras, while titanium substrate signs have low pattern contrast, making it difficult to meet the needs of actual infrared recognition.

[0039] In summary, the results of Comparative Example 1 indicate that there are the following problems with using titanium as a substrate material to prepare infrared identifiable signs: (1) Poor film-substrate adhesion: During the anodic oxidation of titanium in a fluorine-containing electrolyte, fluoride ions accumulate at the metal / oxide interface, causing the titanium oxide film to detach from the substrate after 1 hour of oxidation. Figure 4 The aluminum substrate used in this invention has an integrated structure with the aluminum substrate, making it impossible to form a stable structure that is integrated with the substrate. Even after oxidation for more than 8 hours, the film layer remains firmly attached and has excellent durability.

[0040] (2) Insufficient infrared emissivity contrast: In the titanium system, the infrared emissivity of a thicker TiO2 layer is only 0.58, and the infrared emissivity of a thinner TiO2 layer is 0.23. Figure 5 The difference in infrared emissivity Δε between the two is only 0.35. In contrast, the infrared emissivity of the AAO layer in the aluminum system of Example 1 is 0.83, and only 0.11 in the low emissivity region, with a Δε as high as 0.72, which is twice that of the titanium system. The titanium system is not high enough at the high emissivity end (0.60 vs 0.83) and not low enough at the low emissivity end (0.20 vs 0.11), and is inferior to the aluminum system at both ends, resulting in insufficient overall infrared contrast. Figure 6 This makes it difficult to meet the reliable infrared recognition requirements in scenarios such as traffic safety.

[0041] Therefore, it can be seen that the present invention selects an aluminum metal substrate and utilizes the inherent large emissivity difference (Δε = 0.72) between the porous anodic aluminum oxide (AAO) layer and the pure aluminum substrate in the long-wave infrared band. Combined with the high bonding force of the integrated structure of AAO and aluminum substrate, it is a key technology choice to achieve high contrast and high durability of visible-infrared dual identifiable signs, and has irreplaceable technical advantages.

[0042] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an infrared-identifiable sign, characterized in that, The steps include the following: S1. The aluminum substrate is anodized to generate a thick porous anodic aluminum oxide layer. S2. Using screen printing technology, a mask with the desired pattern is printed onto a thick porous anodized aluminum layer to obtain the printed sign. S3. After printing, the sign is heat-cured and then immersed in a chemical etching solution to remove the anodic oxide functional layer in the area not covered by the mask, forming a low infrared emissivity area. S4. Then, the sign is anodized to generate a thin porous anodic aluminum oxide layer in the low infrared emissivity area, and a metal film is sputtered on the surface of the thin anodic aluminum oxide layer to obtain a colored low emissivity area. S5. Remove the mask to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step S1, the aluminum substrate is an aluminum substrate that has undergone degreasing and cleaning treatment; the degreasing and cleaning treatment includes: immersing the aluminum substrate in acetone and ethanol for 1-2 hours respectively, and then drying it at 55-65℃ for 1-3 hours.

3. The preparation method according to claim 1, characterized in that, In step S1 or S4, the anodizing process includes: using an aluminum substrate as the anode and a carbon plate as the cathode, performing anodizing in an electrolyte, controlling the voltage at 100-200V, and the oxidation time at 2min-10h; the oxidation time in step S1 is 4-10h, and the oxidation time in step S4 is 2-30min.

4. The preparation method according to claim 3, characterized in that, The electrolyte is selected from one of oxalic acid solution and phosphoric acid solution; wherein the concentration of oxalic acid solution is 0.3~0.6 mol / L, and the concentration of phosphoric acid solution is 0.2~0.4 mol / L; the temperature of the electrolyte is 2~4℃.

5. The preparation method according to claim 1, characterized in that, In step S2, the printing includes: selecting a polymer resin solution as ink, using a screen template with the desired pattern, and printing the ink on the surface of a porous anodized aluminum layer; wherein the polymer resin solution includes Paraaloid B72.

6. The preparation method according to claim 1, characterized in that, In step S3, the temperature for thermal curing is 55-65℃ and the time is 15-30 min; the chemical etching solution includes a phosphoric acid solution, and the temperature for chemical etching is 30-60℃ and the time is 1-2 h.

7. The preparation method according to claim 1, characterized in that, In step S4, the sputtering method includes direct current ion sputtering, with a sputtering time of 15-30 s; the metal film includes one of gold, platinum, silver, and chromium.

8. The preparation method according to claim 1, characterized in that, In step S5, the method for removing the mask includes: soaking in acetone for 1 to 2 hours, and then drying in a vacuum drying oven.

9. The preparation method according to claim 1, characterized in that, The thickness of the thick porous anodic aluminum oxide layer is 5-10 μm, and its infrared emissivity is 0.8-0.95; the thickness of the thin porous anodic aluminum oxide layer is <500 nm, and its infrared emissivity is <0.

2.

10. An infrared identifiable sign obtained by the preparation method according to any one of claims 1-9.

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