Durable and non-cracking combustion-supporting adhesive label and preparation method thereof

Abstract

The application discloses a durable and non-cracking combustion-supporting self-adhesive label and a preparation method thereof, and relates to the technical field of labels. The paper material is subjected to plasma modification treatment to improve the roughness of the paper material, then a flame retardant prepared from boric acid, melamine and cyanuric acid is sprayed on the paper material by low pressure to achieve the effect of flame retardation, then the modified titanium dioxide is used to form an interconnected network structure in the polyurethane by using o-xylylene diisocyanate, so that the performance of anti-ultraviolet aging is realized; then, the modified nano-titanium dioxide-polyurethane is partially filled in the microcrystalline cellulose by the'shackles' effect of the microcrystalline cellulose, so that the mechanical strength of the paper material and the glue is enhanced, then, microwave-assisted low-temperature curing is performed on the paper material, so that the density of the glue is improved, and the effects of label aging resistance and non-cracking are improved. The self-adhesive label prepared by the application has the effects of flame retardation, aging resistance and non-cracking.

Description

Technical Field

[0001] This invention relates to the field of label technology, specifically to a durable, crack-resistant, and flame-retardant self-adhesive label and its preparation method. Background Technology

[0002] Labels are used to identify product targets and categories or content, acting like keywords to help oneself and others find and locate their targets. In the printing industry, labels are mostly printed materials used to identify relevant information about products, and most have adhesive backing, commonly known as "self-adhesive labels." Different industries have their own characteristics and usage requirements for self-adhesive labels, including resistance to acids, alkalis, high and low temperatures, and ultraviolet radiation. After being used under harsh conditions, the printed information on the label must remain clear and complete to guide consumers or serve as a warning. Currently, it is common to see permanent labels in daily use exhibiting obvious peeling and detachment. This is because the adhesive layer in the label ages under natural conditions, resulting in a significant decline in performance, or because the adhesive layer itself is of substandard quality or performance. If the label is destroyed, the item cannot be identified, especially when dealing with medical bottles and certain equipment. In the event of a fire, the label will burn, making it impossible to distinguish specific information. Therefore, inventing a durable, crack-resistant, and fire-retardant self-adhesive label is particularly necessary. Summary of the Invention

[0003] The purpose of this invention is to provide a durable, crack-resistant, and flame-retardant self-adhesive label and its preparation method, so as to solve the problems existing in the prior art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a durable, crack-resistant, and flame-retardant self-adhesive label, wherein the durable, crack-resistant, and flame-retardant self-adhesive label is made by coating flame retardant and modified adhesive onto modified paper.

[0005] Furthermore, the flame retardant is prepared by ultrasonic atomization spraying of boric acid, melamine, and cyanuric acid, followed by ultra-low temperature drying.

[0006] Furthermore, the modified adhesive is prepared from modified nano-titanium dioxide-polyurethane composite nanocrystalline cellulose.

[0007] Furthermore, the modified nano-titanium dioxide is prepared by modifying nano-titanium dioxide with phthalic acid diisocyanate.

[0008] Furthermore, the modified paper material is obtained by treating coated paper with low-temperature plasma.

[0009] Furthermore, a method for preparing a durable, crack-resistant, and flame-retardant self-adhesive label includes the following preparation steps: (1) Place the coated paper in an environment with a vacuum of 3~5Pa, introduce ammonia gas at 30L / min for 10~20min, then evacuate the vacuum, repeat the above operation until the vacuum is 30Pa, and process it at 200W discharge power for 15min to obtain modified paper. (2) Mix boric acid, melamine, cyanuric acid and deionized water at 90°C in a mass ratio of 1:1:0.5:4.5~1:2:1:6.5, and ultrasonically atomize the mixture into deionized water at 5~10°C with a mass of 18~25 times that of boric acid. Filter the mixture, take the solid, and dry it at -40~-50°C and a vacuum of 10~100Pa for 5~8 hours to obtain a flame retardant. Spray the flame retardant onto modified paper at low pressure to obtain a base material. (3) Mix hydroxyl-rich titanium dioxide with N,N-dimethylformamide at a mass ratio of 3:90~5:130, sonicate at 21~25kHz for 10~20min, add 0.5~1 times the mass of hydroxyl-rich titanium dioxide with o-phthalic diisocyanate, continue sonicating for 20~25min, raise the temperature to 70~80℃, add 0.01~0.02 times the mass of hydroxyl-rich titanium dioxide with dibutyltin dilaurate under a nitrogen atmosphere, react for 12~16h, centrifuge at 5000~7000rpm for 10~20min, filter, take the solid, wash with toluene 5~8 times, dry at 85~120℃ and vacuum degree of 0.2~1kPa for 6~12h to obtain modified nano titanium dioxide; (4) Mix the modified nano-titanium dioxide, phthalic diisocyanate, and acetone-xylene mixed solvent, sonicate at 21-25 kHz for 25-40 min, add PPG-2000, heat to 50-60 ℃, stir at 70-100 rpm for 50-80 min, cool to room temperature, add nano-microcrystalline cellulose, sonicate at 21-25 kHz for 10-20 min, add nonylphenol polyoxyethylene ether and anhydrous ethanol, stir evenly to obtain the modified adhesive; (5) The modified adhesive is coated on the base material with a thickness of 0.1~0.5mm. After low-temperature curing, it is laminated with silicone backing paper to obtain a durable, crack-resistant, and flame-retardant self-adhesive label.

[0010] Furthermore, the process parameters for ultrasonic atomization spraying in step (2) are: ultrasonic spraying frequency 100kHz, nozzle diameter 0.5mm; and the process parameters for low-pressure spraying are: spray gun pressure 0.1~0.3MPa, spraying distance 10~20cm.

[0011] Further, the preparation method of the hydroxyl-rich titanium dioxide in step (3) is as follows: urea and 0.5 mol / L titanium sulfate aqueous solution are mixed at a mass ratio of 1:1, heated to 180℃, reacted for 6 h, filtered, the solid is taken, washed with deionized water until the filtrate is neutral, dried at 80℃ for 8 h, and the product is obtained; the product is mixed with deionized water at a mass ratio of 3:25, sonicated at 21 kHz for 30 min, 2.5 times the mass of the product is added to a 10 wt% sodium hydroxide aqueous solution, stirred at 70~100 rpm for 7 days, and hydroxyl-rich titanium dioxide with a particle size of 20~30 nm is obtained.

[0012] Further, the preparation method of the acetone-xylene mixed solvent in step (4) is as follows: acetone and xylene are mixed at a mass ratio of 1:2; the mass ratio of the modified nano titanium dioxide, phthalic diisocyanate, acetone-xylene mixed solvent, PPG-2000, nano-microcrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 1:4.2:25:55:3:2:10~1.7:8.5:35:60:5:2.5:30.

[0013] Furthermore, the process parameters for low-temperature curing in step (5) are: temperature 10~15℃, microwave power 100~200W, and curing time 5~8h.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: The self-adhesive label of the present invention is made by coating flame retardant and modified adhesive onto modified paper to achieve flame retardant, aging resistant and crack-resistant effects.

[0015] First, this invention performs low-temperature plasma modification treatment on the paper material to etch its surface, thereby increasing the roughness of the paper material. Then, a flame retardant is sprayed onto the paper material under low pressure, followed by a layer of modified adhesive to produce a self-adhesive label, achieving the effects of flame retardancy, aging resistance, and crack resistance. The flame retardant is made by ultrasonic atomization spraying of boric acid, melamine, and cyanuric acid, followed by ultra-low temperature drying. With the assistance of ultrasonic vibration, it can obtain chemically uniform nanoparticles, which are then sprayed onto the paper material under low pressure, thereby improving the safety of using boric acid and achieving the flame retardant effect.

[0016] Secondly, the isocyanate groups of phthalic diisocyanate react with hydroxyl-rich titanium dioxide to generate urethane groups, which enhance the compatibility between the nano-titanium dioxide particles and polyurethane. As the amount of phthalic diisocyanate increases, it grafts with amino groups to form urea-formate, creating an interconnected network structure that blocks ultraviolet light and achieves anti-UV aging properties. Then, relying on the "locking" effect of microcrystalline cellulose, the adhesive formed by the modified nano-titanium dioxide-polyurethane is partially filled into the hollow structure inside the microcrystalline cellulose, preventing leakage and significantly optimizing the moisture retention of the adhesive. This enhances the mechanical strength of the paper and the adhesive, making the label less prone to cracking and improving aging resistance. Finally, it is cured at low temperature on the paper, and with the assistance of microwaves, the molecular chains are induced to achieve dense packing, thereby increasing the adhesive density and further improving the label's aging resistance and crack resistance. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The test methods for various indicators of the durable, crack-resistant, and flame-retardant self-adhesive labels produced in the following embodiments are as follows: Flame retardancy: LOI tests were conducted on the same size of the example and comparative samples.

[0019] Not prone to cracking: When the same size of the example and comparative examples were placed in a natural environment for 1 month, 6 months and 12 months, their cracking status was observed.

[0020] Aging resistance: Example samples and comparative samples of the same size were tested for 180° peel strength according to GB / T2792, and the samples were placed in an accelerated UV aging chamber with an irradiation intensity of 1.5 kWh / m². 2 Peel strength at 180° after 15 days of UV irradiation at 65°C. Example 1:

[0021] (1) Place the coated paper in an environment with a vacuum degree of 3Pa, introduce ammonia gas at 30L / min for 10min, then evacuate the vacuum, repeat the above operation until the vacuum degree is 30Pa, and process it at a discharge power of 200W for 15min to obtain modified paper. (2) Boric acid, melamine, cyanuric acid and deionized water at 90°C are mixed in a mass ratio of 1:1:0.5:4.5 and ultrasonically atomized and sprayed onto deionized water at 5°C with a mass of 18 times that of boric acid. The process parameters are: ultrasonic spraying frequency 100kHz, nozzle diameter 0.5mm, drying at -40°C and vacuum degree of 10Pa for 5h to obtain flame retardant; low-pressure spraying on modified paper at spray gun pressure of 0.1MPa and spraying distance of 10cm to obtain base material. (3) Mix urea and 0.5 mol / L titanium sulfate aqueous solution at a mass ratio of 1:1, heat to 180℃, react for 6 h, filter, take the solid, wash with deionized water until the filtrate is neutral, dry at 80℃ for 8 h to obtain the product; mix the product with deionized water at a mass ratio of 3:25, sonicate at 21 kHz for 30 min, add 2.5 times the mass of the product in 10 wt% sodium hydroxide aqueous solution, stir at 70 rpm for 7 days to obtain hydroxyl-rich titanium dioxide with a particle size of 20 nm; mix the hydroxyl-rich titanium dioxide with N, N Dimethylformamide was mixed at a mass ratio of 3:90 and sonicated at 21 kHz for 10 min. Phthalic diisocyanate (0.5 times the mass of hydroxyl-rich titanium dioxide) was added, and sonication was continued for 20 min. The temperature was raised to 70 °C, and dibutyltin dilaurate (0.01 times the mass of hydroxyl-rich titanium dioxide) was added under a nitrogen atmosphere. The reaction was carried out for 12 h, centrifuged at 5000 rpm for 10 min, filtered, and the solid was washed 5 times with toluene. The solid was dried at 85 °C and a vacuum of 0.2 kPa for 6 h to obtain modified nano-titanium dioxide. (4) Mix modified nano-titanium dioxide, phthalic diisocyanate, and acetone-xylene mixed solvent. The mass ratio of acetone to xylene in the acetone-xylene mixed solvent is 1:2. Sonicate at 21 kHz for 25 min. Add PPG-2000. Heat to 50 ℃ and stir at 70 rpm for 50 min. Cool to room temperature. Add nano-microcrystalline cellulose. Sonicate at 21 kHz for 10 min. Add nonylphenol polyoxyethylene ether and anhydrous ethanol. Stir evenly to obtain modified adhesive. The mass ratio of modified nano-titanium dioxide, phthalic diisocyanate, acetone-xylene mixed solvent, PPG-2000, nano-microcrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 1:4.2:25:55:3:2:10. (5) The modified adhesive is coated on the base material with a thickness of 0.1 mm, cured at a low temperature of 10℃ and microwave power of 100W for 5 hours, and then combined with silicone oil backing paper to obtain durable, crack-resistant, and flame-retardant self-adhesive labels. Example 2:

[0022] (1) Place the coated paper in an environment with a vacuum degree of 4 Pa, introduce ammonia gas at 30 L / min for 15 min, then evacuate the vacuum, repeat the above operation until the vacuum degree is 30 Pa, and process it at a discharge power of 200 W for 15 min to obtain modified paper. (2) Boric acid, melamine, cyanuric acid and deionized water at 90°C are mixed in a mass ratio of 1:1.5:0.75:5 and ultrasonically atomized and sprayed onto deionized water at 7°C with a mass of 21 times that of boric acid. The process parameters are: ultrasonic spraying frequency 100kHz, nozzle diameter 0.5mm, drying at -45°C and vacuum degree of 55Pa for 7h to obtain flame retardant; low-pressure spraying on modified paper at spray gun pressure of 0.2MPa and spraying distance of 15cm to obtain base material. (3) Urea and 0.5 mol / L titanium sulfate aqueous solution were mixed at a mass ratio of 1:1, heated to 180℃, reacted for 6 h, filtered, and the solid was taken. The solid was washed with deionized water until the filtrate was neutral and dried at 80℃ for 8 h to obtain the product. The product was mixed with deionized water at a mass ratio of 3:25, sonicated at 21 kHz for 30 min, and 2.5 times the mass of the product was added to a 10 wt% sodium hydroxide aqueous solution. The mixture was stirred at 85 rpm for 7 days to obtain hydroxyl-rich titanium dioxide with a particle size of 25 nm. The hydroxyl-rich titanium dioxide was then reacted with N,N-di(2,3 ... Methylformamide was mixed at a mass ratio of 4:110 and sonicated at 23 kHz for 15 min. Phthalic diisocyanate with a mass of 0.75 times that of hydroxyl-rich titanium dioxide was added, and sonication was continued for another 23 min. The temperature was raised to 75 °C, and dibutyltin dilaurate with a mass of 0.015 times that of hydroxyl-rich titanium dioxide was added under a nitrogen atmosphere. The reaction was carried out for 14 h, centrifuged at 6000 rpm for 15 min, filtered, and the solid was taken. It was washed 7 times with toluene and dried at 103 °C and a vacuum of 0.6 kPa for 9 h to obtain modified nano-titanium dioxide. (4) Mix modified nano-titanium dioxide, phthalic diisocyanate, and acetone-xylene mixed solvent. The mass ratio of acetone to xylene in the acetone-xylene mixed solvent is 1:2. Sonicate at 23 kHz for 33 min. Add PPG-2000. Heat to 55 ℃ and stir at 85 rpm for 65 min. Cool to room temperature. Add nano-microcrystalline cellulose. Sonicate at 23 kHz for 15 min. Add nonylphenol polyoxyethylene ether and anhydrous ethanol. Stir evenly to obtain modified adhesive. The mass ratio of modified nano-titanium dioxide, phthalic diisocyanate, acetone-xylene mixed solvent, PPG-2000, nano-microcrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 1.4:6.5:30:57:4:2.3:20. (5) The modified adhesive is coated on the base material with a thickness of 0.3 mm, and cured at a low temperature of 12℃ and microwave power of 170W for 6.5 h. The composite silicone backing paper is then used to obtain a durable, crack-resistant, and flame-retardant self-adhesive label. Example 3:

[0023] (1) Place the coated paper in an environment with a vacuum degree of 5 Pa, introduce ammonia gas at 30 L / min for 20 min, then evacuate the vacuum, repeat the above operation until the vacuum degree is 30 Pa, and process it at a discharge power of 200 W for 15 min to obtain modified paper. (2) Boric acid, melamine, cyanuric acid and deionized water at 90°C are mixed in a mass ratio of 1:2:1:6.5 and ultrasonically atomized and sprayed onto deionized water at 10°C with a mass of 25 times that of boric acid. The process parameters are: ultrasonic spraying frequency 100kHz, nozzle diameter 0.5mm, drying at -50°C and vacuum degree of 100Pa for 8h to obtain flame retardant; low-pressure spraying on modified paper at spray gun pressure of 0.3MPa and spraying distance of 20cm to obtain base material. (3) Urea and 0.5 mol / L titanium sulfate aqueous solution were mixed at a mass ratio of 1:1, heated to 180℃, reacted for 6 h, filtered, and the solid was taken. The solid was washed with deionized water until the filtrate was neutral, and dried at 80℃ for 8 h to obtain the product. The product was mixed with deionized water at a mass ratio of 3:25, sonicated at 21 kHz for 30 min, and 2.5 times the mass of the product was added to a 10 wt% sodium hydroxide aqueous solution. The mixture was stirred at 100 rpm for 7 days to obtain hydroxyl-rich titanium dioxide with a particle size of 30 nm. The hydroxyl-rich titanium dioxide was then reacted with N, N-Dimethylformamide was mixed at a mass ratio of 5:130 and sonicated at 25 kHz for 20 min. Phthalic diisocyanate with a mass ratio of 1:1 that of hydroxyl-rich titanium dioxide was added, and sonication was continued for another 25 min. The temperature was raised to 80 °C, and dibutyltin dilaurate with a mass ratio of 0.02:1 that of hydroxyl-rich titanium dioxide was added under a nitrogen atmosphere. The reaction was carried out for 16 h, centrifuged at 7000 rpm for 20 min, filtered, and the solid was collected. The solid was washed 8 times with toluene and dried at 120 °C and a vacuum of 1 kPa for 12 h to obtain modified nano-titanium dioxide. (4) Mix modified nano-titanium dioxide, phthalic diisocyanate, and acetone-xylene mixed solvent. The mass ratio of acetone to xylene in the acetone-xylene mixed solvent is 1:2. Sonicate at 25 kHz for 40 min. Add PPG-2000. Heat to 60 ℃ and stir at 100 rpm for 80 min. Cool to room temperature. Add nano-microcrystalline cellulose. Sonicate at 25 kHz for 20 min. Add nonylphenol polyoxyethylene ether and anhydrous ethanol. Stir evenly to obtain modified adhesive. The mass ratio of modified nano-titanium dioxide, phthalic diisocyanate, acetone-xylene mixed solvent, PPG-2000, nano-microcrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 1.7:8.5:35:60:5:2.5:30. (5) The modified adhesive is coated on the base material with a thickness of 0.5 mm, and cured at a low temperature of 15℃ and microwave power of 200W for 8 hours. The composite silicone backing paper is then used to obtain a durable, crack-resistant, and flame-retardant self-adhesive label.

[0024] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that step (1) is omitted. The remaining steps are the same as in Example 2.

[0025] Comparative Example 2 The difference between Comparative Example 2 and Example 2 lies in step (2). Step (2) is changed to: mixing boric acid, melamine, cyanuric acid and deionized water at 90°C in a mass ratio of 1:1.5:0.75:5, and spraying the mixture onto the modified paper material at a low pressure of 0.2 MPa and a spraying distance of 15 cm to obtain the base material. The remaining steps are the same as in Example 2.

[0026] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that step (2) is omitted. The remaining steps are the same as in Example 2.

[0027] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that step (3) is omitted, and step (4) is changed to: mixing titanium dioxide and acetone-xylene mixed solvent, with the mass ratio of acetone to xylene in the acetone-xylene mixed solvent being 1:2, sonicating at 23 kHz for 33 min, adding PPG-2000, heating to 55 ℃, stirring at 85 rpm for 65 min, cooling to room temperature, adding nanocrystalline cellulose, sonicating at 23 kHz for 15 min, adding nonylphenol polyoxyethylene ether and anhydrous ethanol, stirring evenly to obtain the modified adhesive; the mass ratio of titanium dioxide, acetone-xylene mixed solvent, PPG-2000, nanocrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 1.4:30:57:4:2.3:20. The remaining steps are the same as in Example 2.

[0028] Comparative Example 5 The difference between Comparative Example 5 and Example 2 is that step (3) is omitted, and step (4) is changed to: mixing PPG-2000 with nanocrystalline cellulose, sonicating at 23 kHz for 15 min, adding nonylphenol polyoxyethylene ether and anhydrous ethanol, and stirring evenly to obtain a modified adhesive; the mass ratio of PPG-2000, nanocrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 57:4:2.3:20. The remaining steps are the same as in Example 2.

[0029] Comparative Example 6 The difference between Comparative Example 6 and Example 2 lies in step (4). Step (4) is changed to: mixing modified nano-titanium dioxide, phthalic acid diisocyanate, and acetone-xylene mixed solvent, with a mass ratio of acetone to xylene of 1:2 in the acetone-xylene mixed solvent, sonicating at 23 kHz for 33 min, adding PPG-2000, heating to 55°C, and stirring at 85 rpm for 65 min to obtain the adhesive; the mass ratio of modified nano-titanium dioxide, phthalic acid diisocyanate, acetone-xylene mixed solvent, and PPG-2000 is 1.4:6.5:30:57. The remaining steps are the same as in Example 2.

[0030] Comparative Example 7 The difference between Comparative Example 7 and Example 2 lies in step (5). Step (5) is changed to: coating the modified adhesive onto the base material with a thickness of 0.3 mm, curing at 12°C for 6.5 h, and then bonding it with silicone backing paper to obtain a durable, crack-resistant, and flame-retardant self-adhesive label. The remaining steps are the same as in Example 2.

[0031] Example of effect Table 1 below presents the performance analysis results of the durable, crack-resistant, and flame-retardant self-adhesive labels produced using Examples 1 to 3 and Comparative Examples 1 to 7 of the present invention.

[0032] Table 1

[0033] A comparison of the test data of the embodiments and comparative examples in Table 1 reveals that the present invention first performs low-temperature plasma modification treatment on the paper to improve its roughness; then, a flame retardant is prepared by ultrasonic atomization spraying of boric acid, melamine, and cyanuric acid, followed by ultra-low temperature drying, and then sprayed onto the paper surface under low pressure to achieve a flame retardant effect; next, titanium dioxide is modified using phthalic diisocyanate to enhance the compatibility of nano-titanium dioxide particles in polyurethane. As the amount of phthalic diisocyanate increases, it grafts with amino groups to form an interconnected network structure, achieving anti-UV aging performance; then, the adhesive formed by the modified nano-titanium dioxide-polyurethane is partially filled into the hollow structure inside the microcrystalline cellulose, which can maintain the moisture retention of the self-adhesive for a long time, thereby enhancing the mechanical strength of the paper and the adhesive, making the label less prone to cracking and improving its aging resistance; finally, it is cured on the paper at low temperature, and with the assistance of microwaves, the adhesive density is increased, thereby improving the label's aging resistance and crack resistance.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a durable, crack-resistant, and flame-retardant self-adhesive label, characterized in that, The durable, crack-resistant, flame-retardant self-adhesive label is made by coating flame retardants and modified adhesives onto modified paper, and includes the following preparation steps: (1) Place the coated paper in an environment with a vacuum of 3~5Pa, introduce ammonia gas at 30L / min for 10~20min, then evacuate the vacuum, repeat the above operation until the vacuum is 30Pa, and process it at 200W discharge power for 15min to obtain modified paper. (2) Mix boric acid, melamine, cyanuric acid and deionized water at 90°C in a mass ratio of 1:1:0.5:4.5~1:2:1:6.5, and ultrasonically atomize the mixture into deionized water at 5~10°C with a mass of 18~25 times that of boric acid. Filter the mixture, take the solid, and dry it at -40~-50°C and a vacuum of 10~100Pa for 5~8 hours to obtain a flame retardant. Spray the flame retardant onto modified paper at low pressure to obtain a base material. (3) Mix hydroxyl-rich titanium dioxide with N,N-dimethylformamide at a mass ratio of 3:90~5:130, sonicate at 21~25kHz for 10~20min, add 0.5~1 times the mass of hydroxyl-rich titanium dioxide with o-phthalic diisocyanate, continue sonicating for 20~25min, raise the temperature to 70~80℃, add 0.01~0.02 times the mass of hydroxyl-rich titanium dioxide with dibutyltin dilaurate under a nitrogen atmosphere, react for 12~16h, centrifuge at 5000~7000rpm for 10~20min, filter, take the solid, wash with toluene 5~8 times, dry at 85~120℃ and vacuum degree of 0.2~1kPa for 6~12h to obtain modified nano titanium dioxide; (4) Mix the modified nano-titanium dioxide, phthalic diisocyanate, and acetone-xylene mixed solvent, sonicate at 21-25 kHz for 25-40 min, add PPG-2000, heat to 50-60 ℃, stir at 70-100 rpm for 50-80 min, cool to room temperature, add nano-microcrystalline cellulose, sonicate at 21-25 kHz for 10-20 min, add nonylphenol polyoxyethylene ether and anhydrous ethanol, stir evenly to obtain the modified adhesive; (5) The modified adhesive is coated on the base material with a thickness of 0.1~0.5mm. After low-temperature curing, it is laminated with silicone backing paper to obtain a durable, crack-resistant, and flame-retardant self-adhesive label.

2. The method for preparing a durable, crack-resistant, and flame-retardant self-adhesive label according to claim 1, characterized in that, The process parameters for ultrasonic atomization spraying in step (2) are: ultrasonic spraying frequency 100kHz, nozzle diameter 0.5mm; the process parameters for low-pressure spraying are: spray gun pressure 0.1~0.3MPa, spraying distance 10~20cm.

3. The method for preparing a durable, crack-resistant, and flame-retardant self-adhesive label according to claim 1, characterized in that, The preparation method of the hydroxyl-rich titanium dioxide in step (3) is as follows: urea and 0.5 mol / L titanium sulfate aqueous solution are mixed at a mass ratio of 1:1, heated to 180℃, reacted for 6 h, filtered, the solid is taken, washed with deionized water until the pH of the filtrate is 7, dried at 80℃ for 8 h to obtain the product; the product is mixed with deionized water at a mass ratio of 3:25, sonicated at 21 kHz for 30 min, 2.5 times the mass of the product is added to a 10 wt% sodium hydroxide aqueous solution, stirred at 70~100 rpm for 7 days to obtain hydroxyl-rich titanium dioxide with a particle size of 20~30 nm.

4. The method for preparing a durable, crack-resistant, and flame-retardant self-adhesive label according to claim 1, characterized in that, The preparation method of the acetone-xylene mixed solvent in step (4) is as follows: acetone and xylene are mixed at a mass ratio of 1:2; the mass ratio of the modified nano titanium dioxide, phthalic diisocyanate, acetone-xylene mixed solvent, PPG-2000, nano-microcrystalline cellulose, nonylphenol polyoxyethylene ether, and anhydrous ethanol is 1:4.2:25:55:3:2:10~1.7:8.5:35:60:5:2.5:

30.

5. The method for preparing a durable, crack-resistant, and flame-retardant self-adhesive label according to claim 1, characterized in that, The process parameters for low-temperature curing in step (5) are: temperature 10~15℃, microwave power 100~200W, and curing time 5~8h.

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