A low-cost and high-efficiency transfer coating and its preparation method

Abstract

The present invention provides a low-cost, high-efficiency transfer coating and a preparation method thereof, belonging to the technical field of printing coatings. The transfer coating of the present invention is composed of the following components by weight: 5-40 parts modified functional starch; 2-10 parts nanocellulose hydrogel; 0-40 parts kaolin; and 10-100 parts water. The coating of the present invention has low viscosity, high solids content, good drying performance, and significant cost advantages. It meets the wet strength requirements of low-weight paper running on large, high-speed coating machines and is particularly suitable for industrial applications that pursue both high quality and cost-effectiveness.

Description

Technical Field

[0001] The present invention relates to the technical field of printing coatings, and in particular to a low-cost and high-efficiency transfer coating and a preparation method thereof. Background Art

[0002] Sublimation printing is an emerging printing process. It pre-prints a design onto transfer paper. A heat transfer machine then applies heat and pressure to transfer the delicate design onto the product surface. The resulting ink layer blends seamlessly with the product surface, creating a realistic and beautiful image with excellent reproducibility. This process can meet the designer's desired effect, significantly elevating product quality and making it suitable for mass production. It is also particularly well-suited for producing small quantities of diverse personalized and customized products, as well as for printing designs containing full-color images or photographs.

[0003] As the core medium for this technology, the performance of thermal sublimation transfer paper is directly related to the transfer effect. Currently, optimizing the paper surface coating formula to improve transfer efficiency is the future development trend in this field.

[0004] The most important component of thermal sublimation transfer paper is its surface coating. Existing coating formulation systems generally have low solid content, high viscosity, and poor drying performance, making it difficult to meet the wet strength requirements of low-weight paper running on large, high-speed coating machines. Moreover, with the trend towards lightweight paper, the functional requirements for transfer coatings are becoming increasingly stringent. The sublimated ink will diffuse outward from the back of the paper, affecting the transfer effect. Therefore, it is necessary to overcome the fluidity barriers caused by the high viscosity of the coating and the problem of downward penetration of low-viscosity inks, while also taking into account the adaptability of ultra-low-weight paper. In addition, as a process paper, thermal transfer paper is used in huge quantities. The higher the cost, the greater the waste. Reducing costs is also the goal pursued by this technology.

[0005] Therefore, it is very necessary to develop a thermal transfer coating with low cost, high transfer rate and suitable for fast transfer on ultra-low quantitative transfer paper. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-cost and high-efficiency transfer coating and a preparation method thereof, which are used to solve the technical problems that the high viscosity of the surface coating of thermal sublimation transfer paper easily leads to fluidity obstruction and the low viscosity leads to ink penetration.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a low-cost and high-efficiency transfer coating, which is composed of the following components in parts by mass:

[0009] 5-40 parts of modified functional starch;

[0010] 2-10 parts of nanocellulose hydrogel;

[0011] Kaolin 0-40 parts;

[0012] 10-100 parts water;

[0013] The preparation method of the modified functional starch comprises the following steps:

[0014] Mixing starch and alkali metal hydroxide and performing an esterification reaction to obtain esterified starch;

[0015] adding the acid anhydride solution to the esterified starch to react and obtain sulfonated precursor starch;

[0016] The sulfonating agent is added to the sulfonated precursor starch to carry out a sulfonation reaction, and the product is washed, dried and crushed in sequence to obtain the modified functional starch.

[0017] Furthermore, the molar ratio of the starch to the alkali metal hydroxide is 10:1-5, and the alkali metal hydroxide comprises sodium hydroxide;

[0018] The temperature of the esterification reaction is 30-80° C., and the time of the esterification reaction is 20-60 minutes.

[0019] Furthermore, the starch comprises one or more of wheat starch, corn starch, potato starch and bean starch;

[0020] When the acid anhydride solution is added to the esterified starch for reaction, the reaction temperature is 30-80° C. and the reaction time is 2-7 hours;

[0021] The molar ratio of acid anhydride to esterified starch in the acid anhydride solution is 1:1-1.5.

[0022] Furthermore, the molar ratio of the sulfonating agent to starch is 0.5-1.5:3, the temperature of the sulfonation reaction is 30-80° C., and the time of the sulfonation reaction is 2-4 hours;

[0023] The sulfonating agent comprises one or more of fuming sulfuric acid, chlorosulfonic acid, sulfur trioxide, aminosulfonic acid and sulfite.

[0024] Furthermore, the preparation method of the nanocellulose hydrogel comprises the following steps:

[0025] The plant fibers are sequentially subjected to irradiation degradation, mechanochemical modification, and high-pressure homogenization to obtain nanocellulose hydrogels;

[0026] The nanocellulose hydrogel has a solid content of 1-5%, a diameter of 3-5 nm, and a length of 500-1000 nm.

[0027] Furthermore, the plant fiber comprises one or more of natural wood pulp, bamboo pulp or cotton pulp;

[0028] The radiation degradation dose of the plant fiber is 10-120 KGy;

[0029] Furthermore, the mechanochemical modification is specifically as follows: mixing the irradiated degraded plant fibers with water, then adding sodium hydroxide solution to adjust the pH to 11-12, performing a pulping process using a pulping machine, and stopping the pulping when the beating degree is 60-70°SR to obtain micron-sized cellulose fibers;

[0030] The high-pressure homogenization specifically comprises: mixing micron-sized cellulose fibers with water to obtain a suspension, and subjecting the suspension to high-pressure homogenization treatment at a flow rate of 2 to 20 L / h and a homogenization pressure of 200 to 1500 bar.

[0031] The present invention also provides a method for preparing a low-cost and high-efficiency transfer coating, comprising the following steps:

[0032] 1) Mixing the modified functional starch and water and gelatinizing the mixture to obtain a starch solution;

[0033] 2) Mix the remaining components with the starch solution to obtain the transfer coating.

[0034] Furthermore, the transfer coating has a solid content of 30-50% and a viscosity of 300-1000 mPa·s.

[0035] Beneficial effects of the present invention:

[0036] The coating of the present invention has low viscosity, high solid content, good drying performance and significant cost advantages. It meets the wet strength requirements of light-weight paper running on large, high-speed coating machines and is particularly suitable for industrial applications that pursue both high quality and cost-effectiveness.

[0037] The introduction of nanocellulose in the present invention is key. Nanocellulose has good film-forming properties and biocompatibility, and simultaneously exhibits a nanometer size effect. Its surface is rich in hydroxyl groups, allowing it to tightly bind to pulp fibers under the action of hydrogen bonds, thereby improving paper density and tensile strength and preventing ink from diffusing outward from the back of the paper, thereby affecting the transfer effect. Furthermore, nanocellulose acts as a dispersant, reinforcing agent, and adhesive in the coating, contributing to improved smoothness and fluidity, making it easy to level and spread on paper and improving the coating's application adaptability. Simultaneously, by introducing modifying groups into nanocellulose, the surface coating's adsorption capacity for ink is increased, thereby preventing ink from penetrating the back of the paper.

[0038] The modified functional starch in this invention is cationized and grafted with strongly electropositive groups. The high density of positively charged sites formed on its surface efficiently captures anionic ink particles, achieving targeted enrichment at the coating interface based on an electrostatic adsorption mechanism, significantly improving ink fixation efficiency. This property enables the cationic starch to form a dynamic adsorption layer in the printed coating. Through charge neutralization, it promotes interfacial anchoring of ink particles within 0.5-2 seconds, thereby improving heat transfer efficiency.

[0039] The nanocellulose and modified functional starch in the transfer coating of the present invention both contain cationic groups and have the effect of anion scavengers. They can effectively adsorb ink and prevent ink from seeping, thereby improving the quality of thermal transfer in the subsequent thermal transfer process and presenting clear and bright patterns. The combination of nanocellulose and modified starch can effectively adjust the viscosity of the coating and improve transfer efficiency. This further prevents the problem of excessive use of nanocellulose or starch alone, which leads to low or high viscosity of the coating, poor fluidity, and ineffective transfer.

[0040] The combined use of nanocellulose and modified starch in the present invention can also enhance the strength and durability of paper, enabling the thermal transfer paper to better maintain its shape and performance when subjected to high temperature and pressure, thereby improving the transfer effect; improving the smoothness and glossiness of the paper or coating surface, and increasing its ability to adsorb ink. During the thermal transfer process, the ink can adhere more evenly to the paper surface, presenting a clearer and more vivid pattern. DETAILED DESCRIPTION

[0041] The present invention provides a low-cost and high-efficiency transfer coating, which is composed of the following components in parts by mass:

[0042] 5-40 parts of modified functional starch;

[0043] 2-10 parts of nanocellulose hydrogel;

[0044] Kaolin 0-40 parts;

[0045] 10-100 parts water;

[0046] The preparation method of the modified functional starch comprises the following steps:

[0047] Mixing starch and alkali metal hydroxide and performing an esterification reaction to obtain esterified starch;

[0048] adding the acid anhydride solution to the esterified starch to react and obtain sulfonated precursor starch;

[0049] The sulfonating agent is added to the sulfonated precursor starch to carry out a sulfonation reaction, and the product is washed, dried and crushed in sequence to obtain the modified functional starch.

[0050] In the present invention, the content of the modified functional starch is preferably 10 to 30 parts by mass, and more preferably 15 to 25 parts by mass.

[0051] In the present invention, the content of the nanocellulose hydrogel is preferably 2 to 8 parts by mass, more preferably 2 to 5 parts by mass.

[0052] In the present invention, the content of the kaolin is preferably 10 to 30 parts by mass, more preferably 15 to 25 parts by mass. In the present invention, the kaolin is kaolin commonly used in the papermaking industry on the market.

[0053] In the present invention, the water content is preferably 50 to 90 parts by mass, more preferably 60 to 80 parts by mass.

[0054] In the present invention, the molar ratio of starch to alkali metal hydroxide is 10:1 to 5, preferably 10:3; the alkali metal hydroxide comprises sodium hydroxide;

[0055] The temperature of the esterification reaction is 30-80° C., preferably 40-70° C., more preferably 50-60° C.; the time of the esterification reaction is 20-60 min, preferably 30-50 min, more preferably 40-45 min.

[0056] In the present invention, the starch comprises one or more of wheat starch, corn starch, potato starch and bean starch, preferably wheat starch and / or corn starch;

[0057] When the acid anhydride solution is added to the esterified starch for reaction, the reaction temperature is 30-80°C, preferably 40-70°C, more preferably 50-60°C; the reaction time is 2-7h, preferably 3-6h, more preferably 4-5h;

[0058] The molar ratio of acid anhydride to esterified starch in the acid anhydride solution is 1:1 to 1.5, preferably 1:1.

[0059] In the present invention, the molar ratio of the sulfonating agent to starch is 0.5-1.5:3, preferably 0.8-1.2:3, and more preferably 1.0:3; the temperature of the sulfonation reaction is 30-80°C, preferably 40-70°C, and more preferably 50-60°C; and the sulfonation reaction time is 2-4 hours, preferably 3 hours.

[0060] In the present invention, the sulfonating agent comprises one or more of fuming sulfuric acid, chlorosulfonic acid, sulfur trioxide, aminosulfonic acid and sulfite, preferably sulfite, more preferably sodium bisulfite.

[0061] In the present invention, the preparation method of the nanocellulose hydrogel comprises the following steps:

[0062] The plant fibers are sequentially subjected to irradiation degradation, mechanochemical modification, and high-pressure homogenization to obtain nanocellulose hydrogels;

[0063] The nanocellulose hydrogel has a solid content of 1-5%, a diameter of 3-5 nm, and a length of 500-1000 nm.

[0064] In the present invention, the solid content of the nanocellulose hydrogel is preferably 2-3%; the diameter is preferably 4 nm; and the length is preferably 600-900 nm, more preferably 700-800 nm.

[0065] In the present invention, the plant fiber comprises one or more of natural wood pulp, bamboo pulp or cotton pulp, preferably natural wood pulp.

[0066] The radiation degradation dose of the plant fiber is 10-120 KGy, preferably 20-100 KGy, and more preferably 50-80 KGy.

[0067] In the present invention, the mechanochemical modification is specifically as follows: mixing the irradiated degraded plant fiber with water, then adding sodium hydroxide solution to adjust the pH to 11-12, using a refiner to perform a refining treatment, and stopping the refining when the beating degree is 60-70°SR to obtain micron-sized cellulose fibers;

[0068] The high-pressure homogenization specifically comprises: mixing micron-sized cellulose fibers with water to obtain a suspension, and subjecting the suspension to high-pressure homogenization treatment at a flow rate of 2 to 20 L / h and a homogenization pressure of 200 to 1500 bar.

[0069] In the present invention, the mechanochemical modification is to add water to the irradiated plant fiber at a solid-liquid ratio (w:w) of 5% and stir, then add a 10% NaOH solution to adjust the pH value to 11-12, and then use a refiner to refine the plant fiber. When the beating degree of the pulp is 60-70°SR, the pulp is stopped, the pulp is taken out, and washed, separated and purified to produce micron-sized cellulose fibers.

[0070] The high-pressure homogenization process first thoroughly washes the prepared micron-sized cellulose fibers with deionized water to remove residual impurities and chemical reagents. Subsequently, the washed micron-sized cellulose fibers are mixed with water in proportion to the desired solids content (e.g., 2%, or adjusted to other suitable solids contents depending on the specific application) to form a uniform suspension. Next, the suspension is treated using a high-pressure homogenizer. The flow rate during the homogenization process is controlled within the range of 2 to 20 L / h to ensure a balance between processing efficiency and quality. The homogenization pressure is set to 200 to 1500 bar, a pressure range designed to effectively disrupt the cellulose structure and promote uniform dispersion of the nanocellulose while avoiding damage to the fiber structure caused by excessive treatment. This precisely controlled high-pressure homogenization process further optimizes the morphology and properties of the nanocellulose to meet the high standards required for subsequent applications. The resulting nanocellulose hydrogel has a solids content of 2%.

[0071] The present invention also provides a method for preparing a low-cost and high-efficiency transfer coating, comprising the following steps:

[0072] 1) Mixing the modified functional starch and water and gelatinizing the mixture to obtain a starch solution;

[0073] 2) Mix the remaining components with the starch solution to obtain the transfer coating.

[0074] In the present invention, gelatinization is to mix the modified functional starch with an equal amount of water, and stir at a temperature of 70-100° C. for 1-10 minutes until the starch is completely gelatinized; preferably, stirring at 80-90° C. for 2-8 minutes.

[0075] In the present invention, the solid content of the transfer coating is 30-50%, preferably 35-45%, more preferably 40%; the viscosity is 300-1000 mPa·s, preferably 400-900 mPa·s, more preferably 500-800 mPa·s.

[0076] In the present invention, the transfer coating is applied by a knife on the base paper in a coating manner, with a coating amount of 2 to 4 g / m 2 , preferably 3g / m 2 .

[0077] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0078] Example 1

[0079] Preparation of modified functional starch:

[0080] Add sodium hydroxide in a molar ratio of 3:10 to corn starch, stir and knead in a kneader for 30 minutes, then add tetrahydrofuran and maleic anhydride and heat together (molar ratio: corn starch: maleic anhydride: tetrahydrofuran = 10:4:4), react at 60°C for 4 hours, then add sodium bisulfite and water (molar ratio: corn starch: sodium sulfite: water = 10:1:2) and react for 1 hour. Continue to react for 2 hours, then discharge, dry and crush the material.

[0081] Preparation of nanocellulose hydrogel:

[0082] Natural wood pulp was placed in an electron beam accelerator device for irradiation to degrade it to an appropriate viscosity with an irradiation dose of 100 KGy. The irradiated and degraded natural wood pulp was added with water at a solid-liquid ratio of 5% (w:w) and stirred. A 10% NaOH solution was then added to adjust the pH to 11. The pulp was then refined using a refiner. The refining was stopped when the beating degree of the pulp was 65°SR. The pulp was removed, washed, separated, and purified to produce micron-sized cellulose fibers. The micron-sized cellulose fibers were mixed with water (weight ratio: micron-sized cellulose fibers: water = 1:20) to obtain a suspension. The suspension was then subjected to high-pressure homogenization at a flow rate of 15 L / h and a homogenization pressure of 900 bar to obtain a nanocellulose hydrogel with a solid content of 5%, a diameter of 3-5 nm, and a length of 500-800 nm.

[0083] Prepare the following raw materials by weight: 30 parts modified functional starch (same as in Example 1), 2 parts nanocellulose hydrogel, and 68 parts water. After gelatinizing 30 parts modified functional starch and 30 parts water, add the nanocellulose hydrogel and the remaining water. Stir at high speed at 3000 rpm for 5 minutes or longer until the viscosity of the mixed solution drops below 1000 mPa·s. This results in a thermal transfer coating with a solids content of 30% ± 1% and a viscosity between 800 and 1000 mPa·s.

[0084] Then the coating was carried out at a speed of 1000m / min, and the coating was carried out on the coating base paper with a coating amount of 3g / m 2 .

[0085] The transfer rate and other items of the above embodiment were tested, and the test results are shown in the following table:

[0086] Table 1 High transfer rate thermal transfer formula

[0087]

[0088] Table 2 Physical indicators of the coating

[0089]

[0090] Table 3 Coated paper sample test data

[0091]

[0092] Conclusion: The high transfer rate thermal transfer coating provided by the present invention has low viscosity, good leveling and good ink transfer rate.

[0093] Example 2

[0094] Prepare the following raw materials by weight: 15 parts modified functional starch (same as in Example 1), 2 parts nanocellulose hydrogel (same as in Example 1), 15 parts kaolin, and 68 parts water. After gelatinizing 15 parts of the modified functional starch and 50 parts of water, add the nanocellulose hydrogel, kaolin, and the remaining water. Stir at high speed at 3000 rpm for 5 minutes or longer until the viscosity of the mixed solution drops below 1000 mPa·s. This results in a thermal transfer coating with a solids content of 30% ± 1% and a viscosity controlled between 300 and 600 mPa·s.

[0095] Then the coating was carried out at a speed of 1000m / min, and the coating was carried out on the coating base paper with a coating amount of 4g / m 2 .

[0096] The transfer rate and other items of the above embodiment were tested, and the test results are shown in the following table:

[0097] Table 4 High transfer rate thermal transfer formula

[0098]

[0099] Table 5 Physical indicators of the coating

[0100]

[0101] Table 6 Coated paper sample test data

[0102]

[0103] Conclusion: The high transfer rate thermal transfer coating provided by the present invention has low viscosity, good leveling, high ink transfer rate and fast ink drying speed.

[0104] Comparative Example 1

[0105] Prepare the following raw materials by weight: 10 parts modified functional starch (same as in Example 1), 20 parts kaolin, and 70 parts water. After gelatinizing 10 parts modified functional starch and 50 parts water, add the kaolin and the remaining water. Stir at high speed at 3000 rpm for 5 minutes or longer until the viscosity of the mixed solution drops below 1000 mPa·s. This results in a thermal transfer coating with a solids content of 30 ± 1% and a viscosity controlled between 400 and 1000 mPa·s.

[0106] Then the coating was carried out at a speed of 1000m / min, and the coating was carried out on the coating base paper with a coating amount of 4g / m 2 .

[0107] The transfer rate and other items of the above embodiment were tested, and the test results are shown in the following table:

[0108] Table 7 High transfer rate thermal transfer formula

[0109]

[0110] Table 8 Physical indicators of the coating of Comparative Example 1

[0111]

[0112] Table 9 Coated paper sample test data

[0113]

[0114] Comparative Example 2

[0115] Prepare the following raw materials by weight: 10 parts nanocellulose hydrogel, 20 parts kaolin, and 70 parts water. Add 10 parts nanocellulose hydrogel to 70 parts water and ultrasonically disperse until evenly dispersed. Then, add 20 parts kaolin and stir at 3000 rpm for 5 minutes or longer until the solution is uniformly mixed. The resulting thermal transfer coating has a solids content of 20 ± 1% and a viscosity of 100 mPa·s or less.

[0116] Then the coating is carried out at a speed of 1000m / min, and the coating base paper is coated with a knife, and the coating amount is 2~3g / m 2 .

[0117] The transfer rate and other items of the above embodiment were tested, and the test results are shown in the following table:

[0118] Table 10 High transfer rate thermal transfer formula

[0119] Table 11 Physical indicators of the coating of Comparative Example 2

[0120]

[0121] Table 12 Coated paper sample test data

[0122]

[0123] Comparative Example 3

[0124] Prepare the following raw materials by weight: 15 parts conventional corn starch, 2 parts nanocellulose hydrogel (same as in Example 1), 15 parts kaolin, and 68 parts water. After gelatinizing 15 parts conventional corn starch and 60 parts water, add the nanocellulose hydrogel, kaolin, and remaining water. Stir at a high speed of 3000 rpm for 5 minutes or longer until the solution is uniformly mixed, resulting in a thermal transfer coating with a solids content of 30 ± 1%.

[0125] Then the coating was carried out at a speed of 1000m / min, and the coating was carried out on the coating base paper with a coating amount of 4g / m 2 .

[0126] The transfer rate and other items of the above embodiment were tested, and the test results are shown in the following table:

[0127] Table 13 High transfer rate thermal transfer formula

[0128]

[0129] Table 14 Physical indicators of coatings of Comparative Example 3

[0130]

[0131] Table 15 Coated paper sample test data

[0132]

[0133] Conclusion: The use of nanocellulose hydrogel and modified functional starch alone cannot improve the ink transfer efficiency, and the ink drying rate is slow; when nanocellulose hydrogel and modified functional starch are used in combination, the obtained coating has a lower transfer efficiency and viscosity, a high ink transfer rate, and a fast ink drying speed.

[0134] As can be seen from the above examples, the present invention provides a low-cost, high-efficiency transfer coating and its preparation method. The coating of the present invention has low viscosity, high solids content, excellent drying performance, and significant cost advantages. It meets the wet strength requirements of low-weight paper running on large, high-speed coating machines and is particularly suitable for industrial applications that pursue both high quality and cost-effectiveness.

[0135] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A low-cost and high-efficiency transfer coating, characterized in that: It is composed of the following components in parts by mass: 5-40 parts of modified functional starch; 2-10 parts of nanocellulose hydrogel; Kaolin 0-40 parts; 10-100 parts water; The preparation method of the modified functional starch comprises the following steps: Mixing starch and alkali metal hydroxide and performing an esterification reaction to obtain esterified starch; adding the acid anhydride solution to the esterified starch to react and obtain sulfonated precursor starch; The sulfonating agent is added to the sulfonated precursor starch to carry out a sulfonation reaction, and the product is washed, dried and crushed in sequence to obtain the modified functional starch; The preparation method of the nanocellulose hydrogel comprises the following steps: The plant fibers are sequentially subjected to irradiation degradation, mechanochemical modification, and high-pressure homogenization to obtain nanocellulose hydrogels; The radiation degradation dose of the plant fiber is 10 to 120 KGy; The mechanochemical modification specifically comprises: mixing the irradiated degraded plant fibers with water, then adding a sodium hydroxide solution to adjust the pH to 11-12, performing a pulping process using a pulping machine, and stopping the pulping when the beating degree reaches 60-70°SR to obtain micron-sized cellulose fibers; The high-pressure homogenization specifically comprises: mixing micron-sized cellulose fibers with water to obtain a suspension, and subjecting the suspension to high-pressure homogenization treatment at a flow rate of 2 to 20 L / h and a homogenization pressure of 200 to 1500 bar.

2. The low-cost and high-efficiency transfer coating according to claim 1, characterized in that: The molar ratio of the starch to the alkali metal hydroxide is 10:1-5, and the alkali metal hydroxide comprises sodium hydroxide; The temperature of the esterification reaction is 30-80° C., and the time of the esterification reaction is 20-60 minutes.

3. The low-cost and high-efficiency transfer coating according to claim 1 or 2, characterized in that: The starch comprises one or more of wheat starch, corn starch, potato starch and bean starch; When the acid anhydride solution is added to the esterified starch for reaction, the reaction temperature is 30 to 80° C. and the reaction time is 2 to 7 hours; The molar ratio of acid anhydride to esterified starch in the acid anhydride solution is 1:1 to 1.

5.

4. The low-cost and high-efficiency transfer coating according to claim 1, characterized in that: The molar ratio of the sulfonating agent to starch is 0.5-1.5:3, the temperature of the sulfonation reaction is 30-80° C., and the time of the sulfonation reaction is 2-4 hours; The sulfonating agent comprises one or more of fuming sulfuric acid, chlorosulfonic acid, sulfur trioxide, aminosulfonic acid and sulfite.

5. The low-cost and high-efficiency transfer coating according to claim 1, characterized in that: The nanocellulose hydrogel has a solid content of 1-5%, a diameter of 3-5 nm, and a length of 500-1000 nm.

6. The low-cost and high-efficiency transfer coating according to claim 5, characterized in that: The plant fiber comprises one or more of natural wood pulp, bamboo pulp or cotton pulp.

7. The method for preparing the low-cost and high-efficiency transfer coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: 1) mixing the modified functional starch and water and gelatinizing the mixture to obtain a starch solution; 2) Mixing the remaining components with the starch solution to obtain the transfer coating.

8. The method for preparing a low-cost and high-efficiency transfer coating according to claim 7, characterized in that: In step 2), the mixing is performed under high-speed stirring at a speed of 2000 to 8000 r / min for ≥5 min until the viscosity of the solution drops below 1000 mPa·s.

9. The method for preparing a low-cost and high-efficiency transfer coating according to claim 7 or 8, characterized in that: The transfer coating has a solid content of 30-50% and a viscosity of 300-1000 mPa·s.

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