A thermosensitive film based on modified cellulose and its preparation method

Abstract

This invention relates to the field of thermal printing materials technology, specifically to a thermal film based on modified cellulose and its preparation method. To improve the waterproof and moisture-proof performance of the thermal film, this invention uses tetrafluorophthalic acid, containing a large amount of fluorine, as a raw material to undergo an esterification reaction with 1,3-di(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane, thereby generating a hydroxyl-terminated fluorine intermediate containing fluorine and silicon elements. This improves the hydrophobic properties of the protective layer against water vapor and reduces the surface energy of the protective layer, reducing friction with other objects and reducing adhesion between thermal films. Based on this, this invention mixes the hydroxyl-terminated fluorine intermediate with polyether polyol and carboxymethyl cellulose, thereby grafting the polyether polyol and the hydroxyl-terminated fluorine intermediate into the cellulose carbon chain and crosslinking it with isocyanate to form a network crosslinked structure, achieving protection of the thermal imaging layer in the thermal film.

Description

Technical Field

[0001] This invention relates to the field of thermal printing materials technology, specifically to a thermal film based on modified cellulose and its preparation method. Background Technology

[0002] Thermal film is a type of film commonly used in medical imaging. It works by using thermal dyes to excite the film and then develop it, thereby preserving medical images.

[0003] However, existing thermal films have problems such as poor waterproof performance, susceptibility to moisture, and high friction, which often affect their color development effect and even damage thermal imaging equipment during use. Summary of the Invention

[0004] The purpose of this invention is to provide a thermosensitive film based on modified cellulose and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a thermal film based on modified cellulose, having the following technical features: the thermal film comprises, from top to bottom, a protective layer, a thermal imaging layer, a polyester substrate layer, and a back layer;

[0006] The protective layer, by weight, is formed by uniformly mixing 21-28 parts of modified cellulose polyol, 9-14 parts of isophorone diisocyanate, and 1-3.5 parts of nano-silica, coating it onto the thermal imaging layer, and then drying and curing it.

[0007] The thermal imaging layer is prepared by uniformly mixing 20-25 parts of cellulose, 30-40 parts of bisphenol A, 10-20 parts of fluorane dye and 50-60 parts of deionized water, coating it onto the surface of a polyester substrate, and then drying it.

[0008] The backing layer is prepared by uniformly mixing 7-10 parts of polyethyleneimine and 7-15 parts of deionized water, coating it onto the underside of a polyester substrate layer, and then drying it.

[0009] Furthermore, the method for preparing the modified cellulose polyol is as follows:

[0010] a. Disperse tetrafluorophthalic acid in deionized water and sonicate for 35-60 min. Then add 4,4-dimethylaminopyridine and continue stirring for 15-30 min. Under nitrogen atmosphere, add it dropwise to 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane while stirring continuously. After the addition is complete, heat the mixture to 150-160℃ and reflux and stir for 2-18 h. Remove excess solvent by rotary evaporation, wash 2-3 times with deionized water at 0-4℃, and then vacuum dry to constant weight to obtain the hydroxyl-terminated fluorine intermediate.

[0011] b. Mix the hydroxyl-terminated fluorine intermediate with the polyether polyol, heat to 105-110℃, heat for 20-60 min, cool to room temperature, add concentrated sulfuric acid and pentaerythritol, sonicate for 15-30 min, then under nitrogen atmosphere protection, heat to 158-162℃, stir for 40-80 min, add carboxymethyl cellulose, continue stirring and mixing for 2-4 h, then stop heating to obtain the modified cellulose polyol.

[0012] Further, in step a, the mass ratio of tetrafluorophthalic acid, 4,4-dimethylaminopyridine and 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane is 1:(0.05-0.08):(1.9-2.4).

[0013] Furthermore, in step b, the mass ratio of the terminal hydroxyl fluorine intermediate, the polyether polyol, and concentrated sulfuric acid is 1:

[0014] (2-4): (0.08-0.15).

[0015] Furthermore, in step b, the mass ratio of the terminal hydroxyl fluorine intermediate, pentaerythritol, and carboxymethyl cellulose is 1:(0.4-0.8):(0.5-1.2).

[0016] Furthermore, in step b, the carboxymethyl cellulose has a molecular weight of 80,000-100,000, a degree of substitution of 0.65-0.75, and a viscosity of 50-100 mPa·s.

[0017] Furthermore, in step b, the polyether polyol is any one or more of polytetrahydrofuran diol and polyethylene adipate diol.

[0018] Furthermore, a method for preparing a thermosensitive film based on modified cellulose includes the following steps:

[0019] S1. Mix polyethyleneimine with deionized water, stir evenly and defoam, then coat it on the lower surface of the polyester substrate layer. After drying and setting, it forms the back layer of the thermal film.

[0020] S2. After mixing cellulose, fluorane dye and deionized water evenly, add bisphenol A, continue mixing for 5-8 minutes, and then coat the mixture onto the upper surface of the polyester substrate layer to obtain the thermal imaging layer of the thermal film.

[0021] S3. Mix the modified cellulose polyol with nano silica, ultrasonically disperse for 30-60 min, add isophorone diisocyanate, continue mixing for 3-5 min, coat it on the upper surface of the thermal imaging layer, dry and set it to form a protective layer for the thermal film, and then roll it up to obtain the thermal film based on modified cellulose.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0023] In order to improve the waterproof and moisture-proof performance of thermal films, this invention improves the protective layer of thermal films;

[0024] This invention first uses tetrafluorophthalic acid, which contains a large amount of fluorine, as a raw material. Then, under the catalysis of 4,4-dimethylaminopyridine, the hydroxyl groups contained therein undergo an esterification reaction with the hydroxyl groups in 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane, thereby generating a fluorine intermediate with terminal hydroxyl groups containing fluorine and silicon elements.

[0025] Both fluorine and silicon have high electronegativity. Adding them to the protective layer material can effectively improve the hydrophobicity of the protective layer to water vapor, thereby avoiding the influence of water vapor on the dye in the thermal imaging layer of the thermal film. Furthermore, the introduction of fluorine and silicon can further reduce the surface energy of the protective layer, thereby reducing friction with other objects, reducing adhesion between thermal films, and reducing printing problems during the thermal film printing process.

[0026] Furthermore, based on this, this application mixes a hydroxyl-terminated fluorine intermediate with a polyether polyol, and then mixes it with concentrated sulfuric acid and carboxymethyl cellulose. Under the catalysis of concentrated sulfuric acid, the hydroxyl groups on the carbon chain of carboxymethyl cellulose undergo dehydration condensation with the hydroxyl-terminated fluorine intermediate and the hydroxyl groups in the polyether polyol, thereby grafting the polyether polyol and the hydroxyl-terminated fluorine intermediate onto the carbon chain of cellulose. At the same time, this invention also strictly limits the amount of hydroxyl-terminated fluorine intermediate, polyether polyol, and carboxymethyl cellulose added, thereby ensuring that after dehydration condensation, the hydroxyl-terminated fluorine intermediate, polyether polyol, and carboxymethyl cellulose still retain sufficient hydroxyl groups to crosslink with isocyanate, thereby forming a network crosslinked structure and achieving protection of the thermal imaging layer in the thermal film. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In this application, the coating method used for the backing layer, thermal imaging layer, and protective layer is drop-coating, with a coating amount of 20 g / m², respectively. 2 100g / m 2 25g / m 2 ;

[0029] The cellulose used in this application is hydroxypropyl methylcellulose with a viscosity of 4000-6500 mPa·s; the nano-silica used is AEROSIL R972 hydrophobic silica; and the polyether polyol used is polytetrahydrofuran diol, M w The molecular weight is 2000; the carboxymethyl cellulose used has a molecular weight of 90,000, a degree of substitution of 0.7, and a viscosity of 50-100 mPa·s.

[0030] Example 1. A method for preparing a thermosensitive film based on modified cellulose, comprising the following steps:

[0031] S1. By weight, 8 parts of polyethyleneimine and 12 parts of deionized water are mixed, stirred evenly and defoamed, and then coated on the lower surface of the polyester substrate layer. After drying and shaping, the back layer of the thermal film is formed.

[0032] S2. By weight, 25 parts cellulose, 15 parts fluorane dye and 55 parts deionized water are mixed evenly, then 30 parts bisphenol A are added and mixed for 5 minutes. The mixture is then coated on the upper surface of the polyester substrate layer to obtain the thermal imaging layer of the thermal film.

[0033] S3. By weight, 21 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0034] The method for preparing the modified cellulose polyol is as follows:

[0035] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for 15 min. Under nitrogen atmosphere protection, the mixture was added dropwise to 1.9 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixed solution was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0036] b. By weight, mix 1 part of terminal hydroxyl fluorine intermediate with 2 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 0.5 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0037] Example 2. A method for preparing a thermosensitive film based on modified cellulose, comprising the following steps:

[0038] Compared with Example 1, this example increases the amount of modified cellulose polyol added in step S3;

[0039] S3. By weight, 28 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0040] The method for preparing the modified cellulose polyol is as follows:

[0041] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for 15 min. Under nitrogen atmosphere protection, the mixture was added dropwise to 1.9 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixed solution was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0042] b. By weight, mix 1 part of terminal hydroxyl fluorine intermediate with 2 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 0.5 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0043] Example 3. A method for preparing a thermosensitive film based on modified cellulose, comprising the following steps:

[0044] Compared with Example 1, this example increases the amount of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane added in step a;

[0045] S3. By weight, 28 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0046] The method for preparing the modified cellulose polyol is as follows:

[0047] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for another 15 min. Under nitrogen atmosphere, the mixture was added dropwise to 2.4 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixture was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0048] b. By weight, mix 1 part of terminal hydroxyl fluorine intermediate with 2 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 0.5 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0049] Example 4. A method for preparing a thermosensitive film based on modified cellulose, comprising the following steps:

[0050] Compared with Example 1, this example increases the amount of polyether polyol added in step b;

[0051] S3. By weight, 28 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0052] The method for preparing the modified cellulose polyol is as follows:

[0053] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for another 15 min. Under nitrogen atmosphere, the mixture was added dropwise to 2.4 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixture was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0054] b. By weight, mix 1 part of the terminal hydroxyl fluorine intermediate with 3 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 0.5 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0055] Example 5. A method for preparing a thermosensitive film based on modified cellulose, comprising the following steps:

[0056] Compared with Example 4, this example increases the amount of polyether polyol added in step b;

[0057] S3. By weight, 28 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0058] The method for preparing the modified cellulose polyol is as follows:

[0059] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for another 15 min. Under nitrogen atmosphere, the mixture was added dropwise to 2.4 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixture was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0060] b. By weight, mix 1 part of the terminal hydroxyl fluorine intermediate with 4 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 0.5 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0061] Example 6. A method for preparing a thermosensitive film based on modified cellulose, comprising the following steps:

[0062] Compared with Example 1, this example increases the amount of carboxymethyl cellulose added in step b;

[0063] S3. By weight, 28 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0064] The method for preparing the modified cellulose polyol is as follows:

[0065] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for another 15 min. Under nitrogen atmosphere, the mixture was added dropwise to 2.4 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixture was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0066] b. By weight, mix 1 part of the terminal hydroxyl fluorine intermediate with 2 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 1.2 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0067] Comparative Example 1. A method for preparing a thermal film based on modified cellulose, comprising the following steps:

[0068] Compared with Example 1, this comparative example did not use modified cellulose polyols, but directly used equal parts by mass of polyether polyols;

[0069] S1. By weight, 8 parts of polyethyleneimine and 12 parts of deionized water are mixed, stirred evenly and defoamed, and then coated on the lower surface of the polyester substrate layer. After drying and shaping, the back layer of the thermal film is formed.

[0070] S2. By weight, 25 parts cellulose, 15 parts fluorane dye and 55 parts deionized water are mixed evenly, then 30 parts bisphenol A are added and mixed for 5 minutes. The mixture is then coated on the upper surface of the polyester substrate layer to obtain the thermal imaging layer of the thermal film.

[0071] S3. By weight, 21 parts of polyether polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0072] Comparative Example 2. A method for preparing a thermal film based on modified cellulose, comprising the following steps:

[0073] Compared with Example 1, this comparative example increased the amount of carboxymethyl cellulose added in step b;

[0074] S3. By weight, 21 parts of modified cellulose polyol and 2.5 parts of nano silica are mixed and ultrasonically dispersed for 30 min. Then, 12 parts of isophorone diisocyanate are added and mixed for another 3 min. The mixture is then coated onto the surface of the thermal imaging layer. After drying and setting, a protective layer for the thermal film is formed. The film is then rolled up to obtain a thermal film based on modified cellulose.

[0075] The method for preparing the modified cellulose polyol is as follows:

[0076] a. By weight, 1 part of tetrafluorophthalic acid was dispersed in deionized water and ultrasonically dispersed for 45 min. Then, 0.08 parts of 4,4-dimethylaminopyridine were added and stirred for 15 min. Under nitrogen atmosphere protection, the mixture was added dropwise to 1.9 parts of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. The mixture was stirred continuously during the dropwise addition. After the dropwise addition was completed, the mixed solution was heated to 155°C and refluxed and stirred for 12 h. The excess solvent was removed by rotary evaporation. The mixture was washed twice with deionized water at 4°C and then vacuum dried to constant weight to obtain the terminal hydroxyl fluorine intermediate.

[0077] b. By weight, mix 1 part of the terminal hydroxyl fluorine intermediate with 2 parts of polyether polyol, heat to 105°C, heat for 30 min, cool to room temperature, add 0.15 parts of concentrated sulfuric acid and 0.4 parts of pentaerythritol, sonicate for 15 min, under nitrogen atmosphere protection, heat to 160°C, stir for 40 min, add 2.5 parts of carboxymethyl cellulose, continue stirring and mixing for 2 h, then stop heating to obtain modified cellulose polyol.

[0078] Test: The thermal films prepared in Examples 1-6 and Comparative Examples 1-2 were placed in an environment with 100% humidity and 100°C for 30 days. After 30 days, they were taken out, the water stains on their surface were removed, and then they were subjected to color development printing to observe the color development performance.

[0079] The thermal films prepared in Examples 1-6 and Comparative Examples 1-2 were placed in deionized water at an ambient temperature of 40°C for 4 hours. After soaking, the thermal films were removed and the protective layer was rubbed with an eraser to observe whether any material fell off.

[0080] The thermal films prepared in Examples 1-6 and Comparative Examples 1-2 were printed, and after printing, the surface of the protective layer was checked for scratches.

[0081] The test results are shown in the table below;

[0082]

[0083]

[0084] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermal film based on modified cellulose, characterized in that: The thermal film comprises, from top to bottom, a protective layer, a thermal imaging layer, a polyester substrate layer, and a backing layer; The protective layer, by weight, is formed by uniformly mixing 21-28 parts of modified cellulose polyol, 9-14 parts of isophorone diisocyanate, and 1-3.5 parts of nano-silica, coating it onto the thermal imaging layer, and then drying and curing it. The thermal imaging layer is prepared by uniformly mixing 20-25 parts of cellulose, 30-40 parts of bisphenol A, 10-20 parts of fluorane dye and 50-60 parts of deionized water, coating it onto the surface of a polyester substrate, and then drying it. The backing layer is prepared by uniformly mixing 7-10 parts of polyethyleneimine and 7-15 parts of deionized water, coating it onto the lower surface of a polyester substrate layer, and then drying it. The method for preparing the modified cellulose polyol is as follows: a. Disperse tetrafluorophthalic acid in deionized water and sonicate for 35-60 min. Then add 4,4-dimethylaminopyridine and continue stirring for 15-30 min. Under nitrogen atmosphere, add it dropwise to 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane while stirring continuously. After the addition is complete, heat the mixture to 150-160℃ and reflux and stir for 2-18 h. Remove excess solvent by rotary evaporation, wash 2-3 times with deionized water at 0-4℃, and then vacuum dry to constant weight to obtain the terminal hydroxyl fluorine intermediate. b. Mix the hydroxyl-terminated fluorine intermediate with the polyether polyol, heat to 105-110℃, heat for 20-60 min, cool to room temperature, add concentrated sulfuric acid and pentaerythritol, sonicate for 15-30 min, then under nitrogen atmosphere protection, heat to 158-162℃, stir for 40-80 min, add carboxymethyl cellulose, continue stirring and mixing for 2-4 h, then stop heating to obtain the modified cellulose polyol.

2. The thermal film based on modified cellulose according to claim 1, characterized in that: In step a, the mass ratio of tetrafluorophthalic acid, 4,4-dimethylaminopyridine and 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane is 1:(0.05-0.08):(1.9-2.4).

3. The thermal film based on modified cellulose according to claim 1, characterized in that: In step b, the mass ratio of the terminal hydroxyl fluorine intermediate, polyether polyol, and concentrated sulfuric acid is 1:(2-4):(0.08-0.15).

4. The thermal film based on modified cellulose according to claim 1, characterized in that: In step b, the mass ratio of the terminal hydroxyl fluoride intermediate, pentaerythritol, and carboxymethyl cellulose is 1:(0.4-0.8):(0.5-1.2).

5. The thermal film based on modified cellulose according to claim 1, characterized in that: In step b, the carboxymethyl cellulose has a molecular weight of 80,000-100,000, a degree of substitution of 0.65-0.75, and a viscosity of 50-100 mPa·s.

6. The thermal film based on modified cellulose according to claim 1, characterized in that: In step b, the polyether polyol is any one or more of polytetrahydrofuran diol and polyethylene adipate diol.

7. A method for preparing a cellulose-based thermal film as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Mix polyethyleneimine with deionized water, stir evenly and defoam, then coat it on the lower surface of the polyester substrate layer. After drying and setting, it forms the back layer of the thermal film. S2. After mixing cellulose, fluorane dye and deionized water evenly, add bisphenol A, continue mixing for 5-8 minutes, and then coat the mixture onto the upper surface of the polyester substrate layer to obtain the thermal imaging layer of the thermal film. S3. Mix the modified cellulose polyol with nano silica, ultrasonically disperse for 30-60 min, add isophorone diisocyanate, continue mixing for 3-5 min, coat it on the upper surface of the thermal imaging layer, dry and set it to form a protective layer for the thermal film, and then roll it up to obtain the thermal film based on modified cellulose.

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