A film-coated heat-sensitive material and a method for its production

Abstract

The application relates to the technical field of heat-sensitive materials, and discloses a film-coated heat-sensitive material and a preparation method thereof. The application is characterized by the following steps: preparing a base material, cutting the base material into a required shape and size, coating a heat-sensitive dye, uniformly spraying the heat-sensitive dye on the base material, drying the base material coated with the heat-sensitive dye, preparing a finished product, cutting the dried base material into a required final product shape and size, and obtaining the film-coated heat-sensitive material. The modified polyurethane and boron element in the phosphorus-containing flame retardant have good flame-retardant effects. In the combustion process, the phosphorus element in the phosphorus-containing flame retardant decomposes into a non-flammable liquid film of phosphoric acid, further generates metaphosphoric acid and poly-metaphosphoric acid, these substances form a protective layer on the material surface, isolate oxygen and high temperature, and have the flame-retardant effect. The quaternary ammonium salt in the quaternary ammonium chain extender has good antibacterial effect.

Description

Technical Field

[0001] The present invention relates to the technical field of thermosensitive materials, in particular to a film-coated thermosensitive material and a preparation method thereof. Background Art

[0002] A thermosensitive material is a material that responds to temperature changes and produces visible changes. The existing methods for making thermosensitive materials are as follows: (1) Thermosensitive dyes: Select suitable thermosensitive dyes that change color at different temperatures. (2) Substrate: Select a suitable substrate, such as PET polyester, polypropylene, polyvinyl chloride, polyethylene, etc. (3) Protective coating: Select a suitable transparent coating. (4) Production process: Prepare the substrate: Cut the substrate into the required shape and size. (5) Apply the thermosensitive dye: Use a suitable method (such as dipping, spraying or printing) to evenly apply the thermosensitive dye on the substrate. (6) Apply a transparent protective coating. (7) Drying: Dry the substrate coated with the thermosensitive dye to ensure that the dye is fully fixed on the substrate. (8) Prepare the finished product: Cut the dried substrate into the required final product shape and size to obtain a coated thermosensitive material.

[0003] Existing thermal materials can only be used on fixed substrates, limiting their use in specific scenarios. For example, thermal barcode wristbands for infants and young children require a high degree of material flexibility. The protective coatings on existing thermal materials also have poor abrasion resistance, and thermal information printed on them easily fades. Preventing this phenomenon is crucial to solving the problem. Summary of the Invention

[0004] (1) Technical problems solved

[0005] In view of the shortcomings of the existing technology, the present invention provides a coated thermosensitive material and a preparation method thereof, which has good flame retardant, antibacterial, waterproof and wear-resistant effects.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention provides the following technical solution: a coated thermosensitive material, comprising a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate is composed of the following components by weight: 20-30 parts by weight of a polyester film, 10-12 parts by weight of a modified polyurethane, 6-9 parts by weight of a phosphorus-containing flame retardant, 0.02-0.05 parts by weight of 2,4-dihydroxybenzophenone, 0.03-0.06 parts by weight of vitamin C, 0.01-0.03 parts by weight of benzimidazole, 1-2 parts by weight of tetrabutylammonium bromide, 5-12 parts by weight of polyethylene glycol, 8-10 parts by weight of polylactic acid, and 6-8 parts by weight of polycaprolactone.

[0008] Preferably, the preparation method of the modified polyurethane is:

[0009] (1) Add 4-methyl-5-thiazoleethanol to N,N-dimethylformamide solvent, stir and dissolve, continue to add boric acid, react at 105-120°C for 8-15 hours, and then remove the solvent by distillation under reduced pressure, wash and dry to obtain intermediate 1;

[0010] (2) adding 12-15 parts by weight of the intermediate 1 and 9-13 parts by weight of 2-bromoethanol to an isopropanol solvent, stirring and mixing, reacting at 75-90° C., rotary evaporating after the reaction, and recrystallizing from ethanol to obtain a quaternary ammonium chain extender;

[0011] (3) Hexamethylene diisocyanate and polyether polyol are added to a reactor, and then dibutyltin dilaurate is added, and a nitrogen atmosphere is introduced for protection to carry out prepolymerization. The reaction is carried out at 65-80°C for 3-5 hours, and then a quaternary ammonium chain extender is added thereto, and the chain extension reaction is carried out by stirring. After the reaction is completed, the mixture is naturally cooled and discharged to obtain a modified polyurethane.

[0012] Preferably, the mass ratio of 4-methyl-5-thiazoleethanol to boric acid in (1) is 1:0.8-1.1.

[0013] Preferably, the reaction time in (2) is 25-30 hours.

[0014] Preferably, the mass ratio of hexamethylene diisocyanate, polyether polyol, dibutyltin dilaurate, and quaternary ammonium chain extender in (3) is 1.2-1.3:1:0.01-0.03:0.4-0.6.

[0015] Preferably, the preparation method of the phosphorus-containing flame retardant is:

[0016] S1. 4-8 parts by weight of acrylic acid and 5-10 parts by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to a reactor, nitrogen was introduced, and the reaction was carried out at 85-100 ° C for 8-12h. After completion, the reaction was cooled to room temperature, washed with acetone, filtered, and dried in vacuo to obtain intermediate 2;

[0017] S2. Add 6-9 parts by weight of intermediate 2 and 8-12 parts by weight of a quaternary ammonium chain extender to an N,N-dimethylformamide solvent, stir and dissolve, and continue to add 1-2 parts by weight of a p-toluenesulfonic acid catalyst thereto. React at 80-95°C for 7-10 hours, and then distill under reduced pressure, filter, wash and dry to obtain a phosphorus-containing flame retardant.

[0018] Preferably, the preparation method of the film-coated thermosensitive material is:

[0019] Prepare the substrate: Cut the substrate into the desired shape and size;

[0020] Coating with thermal dye: spraying thermal dye evenly on the substrate;

[0021] Drying: Dry the substrate coated with the heat-sensitive dye to ensure that the dye is fully fixed on the substrate;

[0022] Preparation of finished products: Cut the dried substrate into the desired final product shape and size to obtain the coated thermal material.

[0023] (3) Beneficial technical effects

[0024] The present invention comprises the following steps: preparing a substrate: cutting the substrate into a desired shape and size; coating a thermosensitive dye: spraying the thermosensitive dye evenly on the substrate; drying: drying the substrate coated with the thermosensitive dye to ensure that the dye is fully fixed on the substrate; and finally preparing a finished product: cutting the dried substrate into a desired final product shape and size to obtain a coated thermosensitive material.

[0025] The modified polyurethane and the boron element in the phosphorus-containing flame retardant of the present invention form a glassy covering layer during combustion, thereby sealing the surface of the burning material and isolating external oxygen and internal combustible gas, thereby achieving the purpose of flame retardancy. The intermediate 2 carboxyl groups in the phosphorus-containing flame retardant and a large number of hydroxyl groups in the quaternary ammonium chain extender undergo an esterification reaction, thereby increasing the substitution degree of the phosphorus element. During the combustion process of the phosphorus element, the phosphorus compound decomposes to generate a non-flammable liquid film of phosphoric acid, and further generates metaphosphoric acid and polymetaphosphoric acid. These substances form a protective layer on the surface of the material, isolating oxygen and high temperature, and achieving a flame retardant effect. The quaternary ammonium chain extender contains a large amount of quaternary ammonium salt, which has a good antibacterial effect. The polyurethane itself also has good wear resistance and waterproof effects.

[0026] Polyethylene glycol is a highly hydrophilic polymer. When added to the thermosensitive coating material, it can increase the hydrophilicity of the surface of the polyester film material, making the material easier to contact with biological tissues, thereby improving biocompatibility.

[0027] Polyurethane is an elastomer. Adding a thermosensitive coating material to polyurethane improves the elasticity of polyester film, making it more suitable for biomedical applications. This good elasticity reduces irritation and damage to biological tissues, thereby improving biocompatibility.

[0028] Polylactic acid and polycaprolactone are both biodegradable polymers. Their addition can make the polyester film material gradually degrade in the body, reducing the risk of long-term implantation in the body. At the same time, the released degradation products are harmless to the organism and help improve biocompatibility.

[0029] This invention improves the bonding sequence between the substrate and the thermosensitive dye. With the thermosensitive dye in the lower layer, unobstructed by other materials, it can be bonded to any other material simply by applying glue, thus embracing a wide range of applications. The transparent substrate on this material effectively protects the thermosensitive coating, making the printed thermosensitive information extremely waterproof and friction-resistant. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the layered structure of the finished product of the present invention. DETAILED DESCRIPTION

[0031] The heat-sensitive dye in the heat-sensitive dye layer is commercially available.

[0032] The preparation method of the coated thermosensitive material is as follows:

[0033] Prepare the substrate: Cut the substrate into the desired shape and size;

[0034] Coating with thermal dye: spraying thermal dye evenly on the substrate;

[0035] Drying: Dry the substrate coated with the heat-sensitive dye to ensure that the dye is fully fixed on the substrate;

[0036] Preparation of finished products: Cut the dried substrate into the desired final product shape and size to obtain the coated thermal material.

[0037] Instructions attached Figure 1 The finished product of the present invention has a layered structure, improving the bonding sequence between the substrate and the thermosensitive dye. With the thermosensitive dye in the lower layer, unobstructed by other materials, it can be bonded to any other material simply by applying glue, thus embracing a wide range of applications. The transparent substrate on the surface of this material effectively protects the thermosensitive coating, making the printed thermosensitive information extremely waterproof and friction-resistant.

[0038] Example 1

[0039] A coated thermosensitive material comprises a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate comprises the following components by weight: 20 parts by weight of polyester film, 10 parts by weight of modified polyurethane, 6 parts by weight of a phosphorus-containing flame retardant, 0.02 parts by weight of 2,4-dihydroxybenzophenone, 0.03 parts by weight of vitamin C, 0.01 parts by weight of benzimidazole, 1 part by weight of tetrabutylammonium bromide, 5 parts by weight of polyethylene glycol, 8 parts by weight of polylactic acid, and 6 parts by weight of polycaprolactone.

[0040] (1) Add 4-methyl-5-thiazoleethanol to N,N-dimethylformamide solvent, stir and dissolve, and continue to add boric acid, wherein the mass ratio of 4-methyl-5-thiazoleethanol to boric acid is 1:0.8, and react at 105°C for 8 hours. After the reaction, remove the solvent by distillation under reduced pressure, wash and dry to obtain intermediate 1;

[0041] (2) adding 12 parts by weight of the intermediate 1 and 9 parts by weight of 2-bromoethanol to an isopropanol solvent, stirring and mixing, reacting at 75° C. for 25 h, and then rotary evaporating and recrystallizing from ethanol to obtain a quaternary ammonium chain extender;

[0042] (3) adding hexamethylene diisocyanate and polyether polyol to a reactor, then adding dibutyltin dilaurate, introducing nitrogen atmosphere for protection, performing prepolymerization, reacting at 65° C. for 3 h, then adding a quaternary ammonium chain extender, wherein the mass ratio of hexamethylene diisocyanate, polyether polyol, dibutyltin dilaurate, and quaternary ammonium chain extender is 1.2:1:0.01:0.4, stirring for chain extension reaction, waiting for the reaction to be completed, naturally cooling, discharging, and obtaining a modified polyurethane;

[0043] (4) 4 parts by weight of acrylic acid and 5 parts by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to a reactor, nitrogen was introduced, and the reaction was carried out at 85° C. for 8 h. After the reaction was completed, the mixture was cooled to room temperature, washed with acetone, filtered, and vacuum dried to obtain intermediate 2;

[0044] (5) Add 6 parts by weight of the intermediate 2 and 8 parts by weight of the quaternary ammonium chain extender to N,N-dimethylformamide solvent, stir and dissolve, continue to add 1 part by weight of p-toluenesulfonic acid catalyst, react at 80°C for 7 hours, and then distill under reduced pressure, filter, wash and dry to obtain a phosphorus-containing flame retardant.

[0045] Example 2

[0046] A coated thermosensitive material comprises a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate comprises the following components by weight: 30 parts by weight of polyester film, 12 parts by weight of modified polyurethane, 9 parts by weight of a phosphorus-containing flame retardant, 0.05 parts by weight of 2,4-dihydroxybenzophenone, 0.06 parts by weight of vitamin C, 0.03 parts by weight of benzimidazole, 2 parts by weight of tetrabutylammonium bromide, 12 parts by weight of polyethylene glycol, 10 parts by weight of polylactic acid, and 8 parts by weight of polycaprolactone.

[0047] (1) Add 4-methyl-5-thiazoleethanol to N,N-dimethylformamide solvent, stir and dissolve, and continue to add boric acid, wherein the mass ratio of 4-methyl-5-thiazoleethanol to boric acid is 1:1.1, and react at 120°C for 15 hours. After the reaction, remove the solvent by distillation under reduced pressure, wash and dry to obtain intermediate 1;

[0048] (2) adding 15 parts by weight of the intermediate 1 and 13 parts by weight of 2-bromoethanol to an isopropanol solvent, stirring and mixing, reacting at 90° C. for 30 h, rotary evaporation after the reaction, and recrystallization from ethanol to obtain a quaternary ammonium chain extender;

[0049] (3) adding hexamethylene diisocyanate and polyether polyol to a reactor, then adding dibutyltin dilaurate, introducing nitrogen atmosphere for protection, performing prepolymerization, reacting at 80° C. for 5 h, then adding a quaternary ammonium chain extender, wherein the mass ratio of hexamethylene diisocyanate, polyether polyol, dibutyltin dilaurate, and quaternary ammonium chain extender is 1.3:1:0.03:0.6, stirring for chain extension reaction, waiting for the reaction to be completed, naturally cooling, discharging, and obtaining a modified polyurethane;

[0050] (4) 8 parts by weight of acrylic acid and 10 parts by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to a reactor, nitrogen was introduced, and the reaction was carried out at 100° C. for 12 h. After the reaction, the mixture was cooled to room temperature, washed with acetone, filtered, and dried in vacuo to obtain intermediate 2;

[0051] (5) Add 9 parts by weight of the intermediate 2 and 12 parts by weight of a quaternary ammonium chain extender to an N,N-dimethylformamide solvent, stir and dissolve, and then add 2 parts by weight of a p-toluenesulfonic acid catalyst. The mixture is reacted at 95° C. for 10 h, and then distilled under reduced pressure, filtered, washed, and dried to obtain a phosphorus-containing flame retardant.

[0052] Example 3

[0053] A coated thermosensitive material comprises a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate comprises the following components by weight: 25 parts by weight of polyester film, 11 parts by weight of modified polyurethane, 7.5 parts by weight of a phosphorus-containing flame retardant, 0.035 parts by weight of 2,4-dihydroxybenzophenone, 0.045 parts by weight of vitamin C, 0.02 parts by weight of benzimidazole, 1.5 parts by weight of tetrabutylammonium bromide, 8.5 parts by weight of polyethylene glycol, 9 parts by weight of polylactic acid, and 7 parts by weight of polycaprolactone.

[0054] (1) Add 4-methyl-5-thiazoleethanol to N,N-dimethylformamide solvent, stir and dissolve, and continue to add boric acid, wherein the mass ratio of 4-methyl-5-thiazoleethanol to boric acid is 1:9.5, and react at 112.5°C for 11.5 hours. After the reaction, remove the solvent by distillation under reduced pressure, wash and dry to obtain intermediate 1;

[0055] (2) adding 13.5 parts by weight of the intermediate 1 and 11 parts by weight of 2-bromoethanol to an isopropanol solvent, stirring and mixing, reacting at 82.5° C. for 27.5 hours, rotary evaporation after the reaction, and recrystallization from ethanol to obtain a quaternary ammonium chain extender;

[0056] (3) adding hexamethylene diisocyanate and polyether polyol to a reactor, then adding dibutyltin dilaurate, introducing nitrogen atmosphere for protection, performing prepolymerization, reacting at 72.5°C for 4h, then adding a quaternary ammonium chain extender, wherein the mass ratio of hexamethylene diisocyanate, polyether polyol, dibutyltin dilaurate, and quaternary ammonium chain extender is 1.25:1:0.02:0.5, stirring for chain extension reaction, waiting for the reaction to be completed, naturally cooling, discharging, and obtaining a modified polyurethane;

[0057] (4) 6 parts by weight of acrylic acid and 7.5 parts by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to a reactor, nitrogen was introduced, and the reaction was carried out at 92.5° C. for 10 h. After the reaction, the mixture was cooled to room temperature, washed with acetone, filtered, and dried in vacuo to obtain intermediate 2;

[0058] (5) Add 7.5 parts by weight of the intermediate 2 and 10 parts by weight of a quaternary ammonium chain extender to an N,N-dimethylformamide solvent, stir and dissolve, and then add 1.5 parts by weight of a p-toluenesulfonic acid catalyst. The mixture is reacted at 87.5° C. for 8.5 hours. After the reaction, the mixture is distilled under reduced pressure, filtered, washed and dried to obtain a phosphorus-containing flame retardant.

[0059] Comparative Example 1

[0060] A coated thermosensitive material comprises a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate comprises the following components by weight: 25 parts by weight of polyester film, 7.5 parts by weight of a phosphorus-containing flame retardant, 0.035 parts by weight of 2,4-dihydroxybenzophenone, 0.045 parts by weight of vitamin C, 0.02 parts by weight of benzimidazole, 1.5 parts by weight of tetrabutylammonium bromide, 8.5 parts by weight of polyethylene glycol, 9 parts by weight of polylactic acid, and 7 parts by weight of polycaprolactone.

[0061] (1) 6 parts by weight of acrylic acid and 7.5 parts by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to a reactor, nitrogen was introduced, and the reaction was carried out at 92.5° C. for 10 hours. After the reaction, the mixture was cooled to room temperature, washed with acetone, filtered, and dried in vacuo to obtain intermediate 2;

[0062] (2) Add 7.5 parts by weight of the intermediate 2 and 10 parts by weight of a quaternary ammonium chain extender to an N,N-dimethylformamide solvent, stir and dissolve, and then add 1.5 parts by weight of a p-toluenesulfonic acid catalyst. The mixture is reacted at 87.5° C. for 8.5 hours. After the reaction, the mixture is distilled under reduced pressure, filtered, washed and dried to obtain a phosphorus-containing flame retardant.

[0063] Comparative Example 2

[0064] A coated thermosensitive material comprises a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate comprises the following components by weight: 25 parts by weight of polyester film, 11 parts by weight of modified polyurethane, 0.035 parts by weight of 2,4-dihydroxybenzophenone, 0.045 parts by weight of vitamin C, 0.02 parts by weight of benzimidazole, 1.5 parts by weight of tetrabutylammonium bromide, 8.5 parts by weight of polyethylene glycol, 9 parts by weight of polylactic acid, and 7 parts by weight of polycaprolactone.

[0065] (1) Add 4-methyl-5-thiazoleethanol to N,N-dimethylformamide solvent, stir and dissolve, and continue to add boric acid, wherein the mass ratio of 4-methyl-5-thiazoleethanol to boric acid is 1:9.5, and react at 112.5°C for 11.5 hours. After the reaction, remove the solvent by distillation under reduced pressure, wash and dry to obtain intermediate 1;

[0066] (2) adding 13.5 parts by weight of the intermediate 1 and 11 parts by weight of 2-bromoethanol to an isopropanol solvent, stirring and mixing, reacting at 82.5° C. for 27.5 hours, rotary evaporation after the reaction, and recrystallization from ethanol to obtain a quaternary ammonium chain extender;

[0067] (3) Hexamethylene diisocyanate and polyether polyol are added to a reactor, and then dibutyltin dilaurate is added, and a nitrogen atmosphere is introduced for protection to carry out prepolymerization. The reaction is carried out at 72.5°C for 4 hours, and then a quaternary ammonium chain extender is added thereto, wherein the mass ratio of hexamethylene diisocyanate, polyether polyol, dibutyltin dilaurate, and quaternary ammonium chain extender is 1.25:1:0.02:0.5. The chain extension reaction is carried out by stirring. After the reaction is completed, the product is naturally cooled and discharged to obtain a modified polyurethane.

[0068] Use an oxygen index meter to test the limiting oxygen index of the material, and use a horizontal and vertical combustion instrument to test the combustion grade of the material.

[0069] Table 1: Flame retardancy test.

[0070] Item Limiting oxygen index (%) Flame class Example 1 30 V-0 Example 2 33 V-0 Example 3 32 V-0 Comparative Example 1 20 V-1 Comparative Example 2 21 V-1

[0071] As can be seen from Table 1, the film-coated thermosensitive materials prepared in the present invention, Examples 1-3, have better flame retardant effects than Comparative Examples 1-2.

[0072] Pipette 1 mL of a 108 CFU / mL of Staphylococcus aureus was added to PBS buffer, and then diluted 10-fold to 10 5 CFU / mL, then add the coated thermosensitive material sample (1cm×1cm×0.2cm), and then culture it in a constant temperature incubator at 37℃ with shaking for 24h. After culture, add PBS buffer and dilute the bacterial solution 10 times in sequence. Then, transfer 0.5mL of the bacterial solution to the agar medium and continue to culture it at 37℃ with shaking for 24h. After culture, count the colonies and calculate the inhibition rate.

[0073] Table 2: Antibacterial performance test.

[0074] Item Bacteriostatic rate (%) Example 1 99.1 Example 2 99.9 Example 3 99.5 Comparative Example 1 85.7 Comparative Example 2 84.6

[0075] As can be seen from Table 2, the film-coated thermosensitive materials prepared in the present invention, Examples 1-3 have better antibacterial effects than Comparative Examples 1-2.

[0076] The Akron abrasion test of the coated heat-sensitive material was carried out using the Akron test method.

[0077] Table 3: Wear resistance test.

[0078] Item <![CDATA[阿克隆磨耗量cm 3 / 1.61km]]> Example 1 0.41 Example 2 0.38 Example 3 0.39 Comparative Example 1 0.48 Comparative Example 2 0.49

[0079] As can be seen from Table 3, the coated thermosensitive materials prepared in Examples 1-3 of the present invention have better wear resistance than those in Comparative Examples 1-2.

[0080] The waterproof performance of the coated thermosensitive material was tested using a contact angle meter.

[0081] Table 4: Waterproof performance test.

[0082] Item Example 1 Example 2 112 Example 3 114 Comparative Example 1 113 Comparative Example 2 101 Item Water contact angle (°) Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 103

[0083] As can be seen from Table 4, the film-coated thermosensitive materials prepared in the present invention, Examples 1-3 have better waterproof properties than Comparative Examples 1-2.

[0084] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A coated thermosensitive material, characterized in that: The invention comprises a substrate and a thermosensitive dye layer arranged in sequence from top to bottom; the substrate is composed of the following components by weight: 20-30 parts by weight of a polyester film, 10-12 parts by weight of a modified polyurethane, 6-9 parts by weight of a phosphorus-containing flame retardant, 0.02-0.05 parts by weight of 2,4-dihydroxybenzophenone, 0.03-0.06 parts by weight of vitamin C, 0.01-0.03 parts by weight of benzimidazole, 1-2 parts by weight of tetrabutylammonium bromide, 5-12 parts by weight of polyethylene glycol, 8-10 parts by weight of polylactic acid, and 6-8 parts by weight of polycaprolactone; The preparation method of the modified polyurethane is: (1) Add 4-methyl-5-thiazoleethanol to N,N-dimethylformamide solvent, stir and dissolve, continue to add boric acid, react at 105-120°C for 8-15 hours, and then remove the solvent by distillation under reduced pressure, wash and dry to obtain intermediate 1; (2) adding 12-15 parts by weight of the intermediate 1 and 9-13 parts by weight of 2-bromoethanol to an isopropanol solvent, stirring and mixing, reacting at 75-90° C., rotary evaporating after the reaction, and recrystallizing from ethanol to obtain a quaternary ammonium chain extender; (3) adding hexamethylene diisocyanate and polyether polyol to a reactor, then adding dibutyltin dilaurate, introducing nitrogen atmosphere for protection, and performing prepolymerization, reacting at 65-80° C. for 3-5 hours, then adding a quaternary ammonium chain extender, stirring to perform a chain extension reaction, and after the reaction is completed, naturally cooling and discharging to obtain a modified polyurethane; The preparation method of the phosphorus-containing flame retardant is: S1. 4-8 parts by weight of acrylic acid and 5-10 parts by weight of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to a reactor, nitrogen was introduced, and the reaction was carried out at 85-100 ° C for 8-12h. After completion, the reaction was cooled to room temperature, washed with acetone, filtered, and dried in vacuo to obtain intermediate 2; S2. Add 6-9 parts by weight of intermediate 2 and 8-12 parts by weight of a quaternary ammonium chain extender to an N,N-dimethylformamide solvent, stir and dissolve, and continue to add 1-2 parts by weight of a p-toluenesulfonic acid catalyst thereto. React at 80-95°C for 7-10 hours, and then distill under reduced pressure, filter, wash and dry to obtain a phosphorus-containing flame retardant.

2. The film-coated thermosensitive material according to claim 1, characterized in that: The mass ratio of 4-methyl-5-thiazoleethanol to boric acid in (1) is 1:0.8-1.

1.

3. The film-coated thermosensitive material according to claim 1, characterized in that: The reaction time in (2) is 25-30h.

4. The film-coated thermosensitive material according to claim 1, characterized in that: The mass ratio of hexamethylene diisocyanate, polyether polyol, dibutyltin dilaurate and quaternary ammonium chain extender in (3) is 1.2-1.3:1:0.01-0.03:0.4-0.

6.

5. A method for preparing a film-coated thermosensitive material according to any one of claims 1 to 4, characterized in that: The preparation method of the film-coated thermosensitive material is as follows: Prepare the substrate: Cut the substrate into the desired shape and size; Coating with thermal dye: spraying thermal dye evenly on the substrate; Drying: Dry the substrate coated with the heat-sensitive dye to ensure that the dye is fully fixed on the substrate; Preparation of finished products: Cut the dried substrate into the desired final product shape and size to obtain the coated thermal material.

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