Preparation process of environment-friendly degradable heat-sensitive paper for food

Abstract

The application discloses a kind of preparation processes of food environment-friendly degradable heat-sensitive paper, it is related to heat-sensitive paper technical field.The application is beaten to wood pulp and polylactic acid fiber, and is backfilled using lignin, to enhance the interaction between fibers, with the increase of beating degree, the pore of paper is reduced, so that the substrate indirectly realizes the oil-proof effect, then, by vacuum freeze drying treatment, the substrate is porous, under the assistance of ultrasonic wave, starch composite zein solution is introduced, realizes easy degradation effect, at the same time, alkaline protease is used to hydrolyze zein, and glucose is reacted, so that the protein structure after drying becomes compact, to form a flexible film structure on the surface of substrate, reduce the permeability of water molecules and oil molecules, further improve the easy degradation and oil-proof effect.

Description

Technical Field

[0001] This invention relates to the field of thermal paper technology, specifically to a preparation process for an environmentally friendly biodegradable thermal paper for food use. Background Technology

[0002] Thermal paper is a heat-sensitive material that can be directly printed on after the surface coating of substrates such as paper and film has been processed, without the need for other consumables. The thermal printhead releases heat to the thermal coating of the thermal paper, causing the dye to develop color through the dissolution of the color developer in the coating. Since the invention of barcodes, thermal paper has been widely used in the logistics industry, and gradually, through its ability to print text, barcodes, and other images under the control of printing software, it has been adopted in various fields. With continuous technological advancements, the application areas of thermal paper continue to expand.

[0003] In the food industry, thermal paper is used not only for order taking and printing, but also for recording ingredients, printing recipes, and helping chefs record dishes more conveniently and quickly, while reducing error rates and improving efficiency. In the food delivery industry, it can print orders and receipts, facilitating order confirmation between delivery personnel and customers. Therefore, it is necessary to ensure that the printed labels or products do not become blurred due to grease or other substances, thus reducing work efficiency. To effectively prevent the adhesion of oil or dirt, the surface of the paper is often modified with substances with low surface energy, such as fluorinated compounds, to achieve an anti-oil effect. However, scientific research has proven that fluorides have carcinogenic effects on humans. Furthermore, thermal paper food labels are consumables in daily life. Therefore, it is particularly necessary to invent an environmentally friendly and biodegradable thermal paper for food. Summary of the Invention

[0004] The purpose of this invention is to provide a preparation process for an environmentally friendly biodegradable thermal paper for food use, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a preparation process for food-grade environmentally friendly biodegradable thermal paper, wherein the preparation method for food-grade environmentally friendly biodegradable thermal paper includes the following preparation steps: (1) Mix wood pulp, polylactic acid fiber, and deionized water, beat for 20-50 minutes, add lignin, continue beating for 30 minutes, and add lignin with a molecular weight of 6×10 6 Polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer are stirred at 500~1000 prm for 3~10 min and passed through a 60 mesh sieve to obtain a slurry with a beating degree of 50~80°SR. (2) The pulp is sequentially sheeted, molded, and dried to obtain the paper base; (3) The paper base is immersed in starch-composite corn gluten protein solution, 40wt% sodium hydroxide aqueous solution is added to adjust the pH of the solution to 9, the temperature is raised to 50℃, sonicated at 21kHz for 20~50min, the temperature is raised to 100℃, and left to stand for 5min. The paper base is then taken out and immersed in 10wt% glucose aqueous solution, the temperature is raised to 70℃, and sonicated for 10~20min. Then, it is washed with deionized water 1~3 times and dried at 40~60℃ for 4~8h to obtain biodegradable paper base. (4) A thermal coating and a protective layer are sequentially applied to the biodegradable paper base to obtain food-grade environmentally friendly biodegradable thermal paper.

[0006] Furthermore, the wood pulp in step (1) is prepared by mixing bleached softwood pulp board and bleached hardwood pulp board at a mass ratio of 7:3 and pulping to 37°SR.

[0007] Furthermore, the pulping pressure in step (1) is 3.5~8 kg.

[0008] Furthermore, the wood pulp, polylactic acid fiber, deionized water, lignin, and molecular weight of 6×10 in step (1) are... 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 1~5:0.1~0.6:80~150:0.05:0.05:0.2~0.5:0.3.

[0009] Furthermore, the quantitative amount of the paper scraping in step (2) is 200~250g / m³. 2 .

[0010] Furthermore, the molding process parameters in step (2) are: temperature 168~175℃, pressure 6MPa, and time 2~5min.

[0011] Furthermore, the drying conditions described in step (2) are: vacuum degree of 10~50Pa, temperature of -56℃, and time of 24~48h.

[0012] Furthermore, the starch-complex corn gluten solution in step (3) is prepared by mixing corn gluten, alkaline protease, cationic starch, and deionized water in a mass ratio of 5~10:0.1:5~10:100~200.

[0013] Further, the coating of the heat-sensitive coating in step (4) is prepared by mixing silica, 3-(3-methylurea)phenyl-4-methylbenzenesulfonate, 1,2-diphenoxyethane, polyvinyl alcohol with a molecular weight of 20,000, 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane, and calcium stearate in a mass ratio of 7:15:10:3:6:2.5; the coating of the protective layer is prepared by mixing silica, polyvinyl alcohol with a molecular weight of 20,000, polyamide polyurea, and calcium stearate in a mass ratio of 8:6:3:3.

[0014] Furthermore, the coating amount of the heat-sensitive coating in step (4) is 5~12 g / m². 2 The application rate of the protective coating is 1~5 g / m². 2 .

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: The thermal paper of the present invention is made from wood pulp and polylactic acid fiber through pulping and freezing treatment to obtain a paper base, and then impregnated in a starch-composite corn gluten protein solution to achieve easy degradation and oil resistance.

[0016] First, this invention utilizes wood pulp as raw material and polylactic acid fiber as auxiliary material. During the pulping process, polylactic acid fiber can fill the gaps between fibers during paper forming, thereby enhancing the interaction between fibers and increasing the bonding area. Lignin is used for backfilling. As the degree of pulping increases, fiber fibrillation reduces the pore radius and increases the hydrogen bond content, increasing the bonding force between fibers. This reduces the porosity of the paper and the channels for oils, indirectly achieving an oil-resistant effect on the matrix. Next, freeze-drying is performed. By directly freezing the suspension into ice, a fine porous structure is formed to give the material surface sufficient roughness. Then, the solid solvent is sublimated by low-pressure vacuum, resulting in a porous morphology inside the matrix. At the same time, the fibers, after fibrillation treatment, remain in a fibrillated state to avoid keratinization and maintain the microfibrillated morphology of the surface.

[0017] Secondly, the paper is immersed in a starch-based corn gluten protein solution. With the aid of ultrasound, alkaline protease hydrolyzes the corn gluten protein, which then integrates with the starch into the porous structure of the matrix. The decomposition of the starch causes the material to break down into fine particles, thus making the paper base easily degradable. Next, the temperature is increased to gelatinize the starch solution, which then adheres to and fills the interior of the paper. At the same time, the active protease is eliminated, allowing the hydrolyzed amino acids to undergo Maillard reactions with glucose, promoting intermolecular forces and making the dried protein structure more compact. This forms a flexible film structure on the matrix surface, reducing the permeability of water and oil molecules, and further enhancing the easy degradation and oil-repellent effects. Detailed Implementation

[0018] 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.

[0019] 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 food-grade environmentally friendly biodegradable thermal paper prepared in the following embodiments are as follows: Oil resistance: Examples and comparative samples of the same size were tested for oil resistance according to Oil Kit Test-TAPPI 557, and the results were expressed as oil resistance ratings.

[0020] Easily degradable: Soil degradation was carried out on samples of the same size as the example and the comparative example. The degree of degradation of the samples was observed at 50 days and 150 days.

[0021] Example 1; (1) Bleached softwood pulp board and bleached hardwood pulp board were mixed at a mass ratio of 7:3 and pulped to 37°SR to obtain wood pulp; wood pulp, polylactic acid fiber and deionized water were mixed and pulped for 20 min at a pulping pressure of 3.5 kg, lignin was added, and pulping was continued for 30 min, and lignin with a molecular weight of 6×10 was added. 6 Polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer were stirred at 500 rpm for 3 minutes and passed through a 60-mesh sieve to obtain a pulp with a freeness of 50°SR; the wood pulp, polylactic acid fiber, deionized water, lignin, and a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 1:0.1:80:0.05:0.05:0.2:0.3. (2) The slurry is sheeted, with a quantitative amount of 200g / m³. 2 Next, it is molded at 168℃ and 6MPa for 2 minutes, and finally dried at -56℃ and 10Pa vacuum for 24 hours to obtain paper base. (3) Mix zein protein, alkaline protease, cationic starch and deionized water in a mass ratio of 5:0.1:5:100 to obtain a starch-composite zein protein solution; immerse the paper base in the starch-composite zein protein solution, add 40wt% sodium hydroxide aqueous solution to adjust the pH of the solution to 9, heat to 50℃, sonicate at 21kHz for 20min, heat to 100℃, let stand for 5min, take it out, immerse it in 10wt% glucose aqueous solution, heat to 70℃, continue sonicating for 10min, then wash once with deionized water, dry at 40℃ for 4h to obtain a biodegradable paper base; (4) Mix silica, 3-(3-methylurea)phenyl-4-methylbenzenesulfonate, 1,2-diphenoxyethane, polyvinyl alcohol with a molecular weight of 20,000, 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane, and calcium stearate in a mass ratio of 7:15:10:3:6:2.5 to obtain a heat-sensitive coating; mix silica, polyvinyl alcohol with a molecular weight of 20,000, polyamide polyurea, and calcium stearate in a mass ratio of 8:6:3:3 to obtain a protective coating; apply the coating at a rate of 5 g / m². 2 and 1g / m 2 A biodegradable paper base is coated with a thermal coating and a protective coating to obtain an environmentally friendly biodegradable thermal paper for food use.

[0022] Example 2; (1) Bleached softwood pulp board and bleached hardwood pulp board were mixed at a mass ratio of 7:3 and pulped to 37°SR to obtain wood pulp; wood pulp, polylactic acid fiber and deionized water were mixed and pulped for 35 min at a pulping pressure of 5.5 kg, lignin was added, and pulping was continued for 30 min, and lignin with a molecular weight of 6×10 was added. 6 Polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer were stirred at 750 rpm for 6 minutes and passed through a 60-mesh sieve to obtain a pulp with a freeness of 65°SR; the wood pulp, polylactic acid fiber, deionized water, lignin, and a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 3:0.4:120:0.05:0.05:0.35:0.3; (2) The slurry is sheeted, with a quantitative amount of 225 g / m³. 2 Next, it is molded at 170℃ and 6MPa for 3.5 minutes, and finally dried at -56℃ and 20Pa vacuum for 36 hours to obtain paper base. (3) Mix zein protein, alkaline protease, cationic starch and deionized water in a mass ratio of 8:0.1:8:170 to obtain a starch-composite zein protein solution; immerse the paper base in the starch-composite zein protein solution, add 40wt% sodium hydroxide aqueous solution to adjust the pH of the solution to 9, heat to 50℃, sonicate at 21kHz for 35min, heat to 100℃, let stand for 5min, take it out, immerse it in 10wt% glucose aqueous solution, heat to 70℃, continue sonicating for 15min, then wash twice with deionized water, dry at 50℃ for 6h to obtain a biodegradable paper base; (4) Mix silica, 3-(3-methylurea)phenyl-4-methylbenzenesulfonate, 1,2-diphenoxyethane, polyvinyl alcohol with a molecular weight of 20,000, 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane, and calcium stearate in a mass ratio of 7:15:10:3:6:2.5 to obtain a heat-sensitive coating; mix silica, polyvinyl alcohol with a molecular weight of 20,000, polyamide polyurea, and calcium stearate in a mass ratio of 8:6:3:3 to obtain a protective coating; apply the coating at a rate of 8 g / m². 2 and 3g / m 2 A biodegradable paper base is coated with a thermal coating and a protective coating to obtain an environmentally friendly biodegradable thermal paper for food use.

[0023] Example 3; (1) Bleached softwood pulp board and bleached hardwood pulp board were mixed at a mass ratio of 7:3 and pulped to 37°SR to obtain wood pulp; wood pulp, polylactic acid fiber and deionized water were mixed and pulped for 50 min at a pulping pressure of 8 kg, lignin was added, and pulping was continued for 30 min, and lignin with a molecular weight of 6×10 was added. 6 Polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer were stirred at 1000 rpm for 10 minutes and passed through a 60-mesh sieve to obtain a pulp with a freeness of 80°SR; the wood pulp, polylactic acid fiber, deionized water, lignin, and a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer is 5:0.6:150:0.05:0.05:~0.5:0.3; (2) The slurry is sheeted, with a quantitative amount of 250 g / m³. 2 Next, it is molded at 175℃ and 6MPa for 5 minutes, and finally dried at -56℃ and 50Pa for 48 hours to obtain the paper base. (3) Mix zein protein, alkaline protease, cationic starch and deionized water in a mass ratio of 10:0.1:10:200 to obtain a starch-composite zein protein solution; immerse the paper base in the starch-composite zein protein solution, add 40wt% sodium hydroxide aqueous solution to adjust the pH of the solution to 9, heat to 50℃, sonicate at 21kHz for 50min, heat to 100℃, let stand for 5min, take it out, immerse it in 10wt% glucose aqueous solution, heat to 70℃, continue sonicating for 20min, then wash with deionized water 3 times, dry at 60℃ for 8h to obtain a biodegradable paper base; (4) Mix silica, 3-(3-methylurea)phenyl-4-methylbenzenesulfonate, 1,2-diphenoxyethane, polyvinyl alcohol with a molecular weight of 20,000, 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane, and calcium stearate in a mass ratio of 7:15:10:3:6:2.5 to obtain a heat-sensitive coating; mix silica, polyvinyl alcohol with a molecular weight of 20,000, polyamide polyurea, and calcium stearate in a mass ratio of 8:6:3:3 to obtain a protective coating; apply the coating at a rate of 12 g / m². 2 and 5g / m 2 A biodegradable paper base is coated with a thermal coating and a protective coating to obtain an environmentally friendly biodegradable thermal paper for food use.

[0024] Comparative Example 1; The difference between Comparative Example 1 and Example 2 is that step (1) is different. Step (1) is changed to: bleached softwood pulp board and bleached hardwood pulp board are mixed at a mass ratio of 7:3 and pulped to 37°SR to obtain wood pulp; the wood pulp and deionized water are mixed and pulped for 35 min at a pulping pressure of 5.5 kg, lignin is added, and pulping is continued for 30 min, and lignin with a molecular weight of 6×10 is added. 6 Polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer were stirred at 750 rpm for 6 minutes and passed through a 60-mesh sieve to obtain a pulp with a freeness of 65°SR; the wood pulp, deionized water, lignin, and a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 3:120:0.05:0.05:0.35:0.3; the remaining steps are the same as in Example 2.

[0025] Comparative Example 2; The difference between Comparative Example 2 and Example 2 is that step (1) is different. Step (1) is changed to: bleached softwood pulp board and bleached hardwood pulp board are mixed at a mass ratio of 7:3 and pulped to 37°SR to obtain wood pulp; wood pulp, polylactic acid fiber, and deionized water are mixed and pulped for 65 minutes at a pulping pressure of 5.5 kg, and a molecular weight of 6×10 is added. 6 Polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer were stirred at 750 rpm for 6 minutes and passed through a 60-mesh sieve to obtain a pulp with a freeness of 65°SR; the wood pulp, polylactic acid fiber, deionized water, and a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 3:0.4:120:0.05:0.35:0.3; 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 (1) is different. Step (1) is changed to: bleached softwood pulp board and bleached hardwood pulp board are mixed at a mass ratio of 7:3 and pulped to 37°SR to obtain wood pulp; wood pulp, polylactic acid fiber, and deionized water are mixed and pulped for 10 minutes at a pulping pressure of 2.5 kg; lignin is added and pulping is continued for 10 minutes; lignin with a molecular weight of 6×10 is added. 6 Polyacrylamide, polyamide-epoxychloropropane resin, and alkyl ketene dimer were stirred at 750 rpm for 6 minutes and passed through a 60-mesh sieve to obtain a pulp with a freeness of 40°SR; the wood pulp, polylactic acid fiber, deionized water, lignin, and a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 3:0.4:120:0.05:0.05:0.35:0.3; 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 (2) is different. Step (2) is changed to: the slurry is sheeted, and the quantitative amount is 225g / m 2 Next, it is molded at 170°C and 6MPa for 3.5 minutes, and finally dried at 50°C for 5 hours to obtain the paper base; 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 different. Step (3) is changed to: mixing zein protein, alkaline protease, cationic starch and deionized water in a mass ratio of 8:0.1:8:170 to obtain a starch-composite zein protein solution; immersing the paper base in the starch-composite zein protein solution, adding 40wt% sodium hydroxide aqueous solution to adjust the pH of the solution to 9, heating to 50℃, reacting for 35 min, heating to 100℃, standing for 5 min, taking it out, immersing it in 10wt% glucose aqueous solution, heating to 70℃, reacting for 15 min, then washing it twice with deionized water, drying it at 50℃ for 6 h to obtain a biodegradable paper base; the remaining steps are the same as in Example 2.

[0029] Comparative Example 6; The difference between Comparative Example 6 and Example 2 is that step (3) is different. Step (3) is changed to: mixing zein protein, alkaline protease and deionized water in a mass ratio of 8:0.1:8:170 to obtain a zein protein solution; immersing the paper base in the zein protein solution, adding 40wt% sodium hydroxide aqueous solution to adjust the pH of the solution to 9, heating to 50°C, sonicating at 21kHz for 35min, heating to 100°C, letting stand for 5min, taking it out, immersing it in 10wt% glucose aqueous solution, heating to 70°C, continuing to sonicate for 15min, then washing twice with deionized water, drying at 50°C for 6h to obtain a biodegradable paper base; the remaining steps are the same as in Example 2.

[0030] Comparative Example 7; The difference between Comparative Example 7 and Example 2 is that step (3) is different. Step (3) is changed to: mix cationic starch and deionized water at a mass ratio of 8:170 to obtain a starch solution; immerse the paper base in the starch solution, sonicate at 21 kHz for 35 min, heat to 100 ℃, let stand for 5 min, take it out, wash it twice with deionized water, and dry it at 50 ℃ for 6 h to obtain a biodegradable paper base; the remaining steps are the same as in Example 2.

[0031] Comparative Example 8; The difference between Comparative Example 8 and Example 2 is that step (3) is different. Step (3) is changed to: mixing corn gluten protein, cationic starch and deionized water in a mass ratio of 8:0.1:8:170 to obtain a starch-composite corn gluten protein solution; immersing the paper base in the starch-composite corn gluten protein solution, sonicating at 21 kHz for 35 min, heating to 100 ℃, letting stand for 5 min, taking it out, washing it twice with deionized water, and drying it at 50 ℃ for 6 h to obtain a biodegradable paper base; the remaining steps are the same as in Example 2.

[0032] Example of effect Table 1 below shows the performance analysis results of the food-grade environmentally friendly biodegradable thermal paper used in Examples 1 to 3 and Comparative Examples 1 to 8 of the present invention.

[0033] Table 1

[0034] A comparison of the experimental results of the embodiments and comparative examples in Table 1 reveals that this invention utilizes wood pulp as raw material, uses polylactic acid fibers to fill the gaps between fibers during pulping, enhances the interaction between fibers, and utilizes lignin for backfilling. As the degree of pulping increases, fiber fibrillation reduces the pore radius and increases the hydrogen bond content, increasing the bonding force between fibers, thereby reducing the channels for oils and indirectly achieving an oil-resistant effect on the matrix. Next, vacuum freeze-drying is performed, directly freezing the suspension into ice to form a fine porous structure, giving the material surface sufficient roughness and making the matrix interior porous. With the assistance of ultrasound, a starch-based corn gluten protein solution is introduced, and alkaline protease is used to hydrolyze the corn gluten protein, thereby making the paper base easily degradable. Then, the hydrolyzed amino acids undergo a Maillard reaction with glucose, making the dried protein structure compact, thus forming a flexible film structure on the matrix surface, reducing the permeability of water and oil molecules, and further improving the oil-resistant effect.

[0035] 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 preparation process for an environmentally friendly biodegradable thermal paper for food use, characterized in that, The preparation steps include the following: (1) Mix wood pulp, polylactic acid fiber, and deionized water, beat for 20-50 minutes at a beating pressure of 3.5-8 kg, add lignin, continue beating for 30 minutes, and add lignin with a molecular weight of 6×10 6 Polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer are stirred at 500-1000 rpm for 3-10 minutes and passed through a 60-mesh sieve to obtain a slurry with a beating degree of 50-80°SR. (2) The pulp is sequentially subjected to sheet forming, molding and drying to obtain paper base; the drying conditions are a vacuum degree of 10~50Pa, a temperature of -56℃ and a time of 24~48h; (3) The paper base is immersed in starch-composite corn gluten protein solution, 40wt% sodium hydroxide aqueous solution is added to adjust the pH of the solution to 9, the temperature is raised to 50℃, sonicated at 21kHz for 20~50min, the temperature is raised to 100℃, and left to stand for 5min. The paper base is then taken out and immersed in 10wt% glucose aqueous solution, the temperature is raised to 70℃, and sonicated for 10~20min. Then, it is washed with deionized water 1~3 times and dried at 40~60℃ for 4~8h to obtain biodegradable paper base. (4) A thermal coating and a protective layer are sequentially applied to the biodegradable paper base to obtain food-grade environmentally friendly biodegradable thermal paper; The wood pulp in step (1) is prepared by mixing bleached softwood pulp board and bleached hardwood pulp board at a mass ratio of 7:3 and pulping to 37°SR; The wood pulp, polylactic acid fiber, deionized water, and lignin mentioned in step (1) have a molecular weight of 6×10 6 The mass ratio of polyacrylamide, polyamide epichlorohydrin resin, and alkyl ketene dimer is 1~5:0.1~0.6:80~150:0.05:0.05:0.2~0.5:0.3; The starch-complex corn gluten solution in step (3) is prepared by mixing corn gluten, alkaline protease, cationic starch, and deionized water in a mass ratio of 5~10:0.1:5~10:100~200.

2. The preparation process of an environmentally friendly biodegradable thermal paper for food use according to claim 1, characterized in that, The quantitative amount of the paper scraping in step (2) is 200~250g / m 2 .

3. The preparation process of an environmentally friendly biodegradable thermal paper for food use according to claim 1, characterized in that, The molding process parameters in step (2) are: temperature 168~175℃, pressure 6MPa, and time 2~5min.

4. The preparation process of an environmentally friendly biodegradable thermal paper for food use according to claim 1, characterized in that, The coating for the heat-sensitive coating in step (4) is prepared by mixing silica, 3-(3-methylurea)phenyl-4-methylbenzenesulfonate, 1,2-diphenoxyethane, polyvinyl alcohol with a molecular weight of 20,000, 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane, and calcium stearate in a mass ratio of 7:15:10:3:6:2.5; the coating for the protective layer is prepared by mixing silica, polyvinyl alcohol with a molecular weight of 20,000, polyamide polyurea, and calcium stearate in a mass ratio of 8:6:3:

3.

5. The preparation process of an environmentally friendly biodegradable thermal paper for food use according to claim 1, characterized in that, The coating amount of the heat-sensitive coating in step (4) is 5~12g / m². 2 The application rate of the protective coating is 1~5 g / m². 2 .

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