A nanocellulose-modified heat transfer paper and its preparation method

Abstract

This invention discloses a nanocellulose-modified heat transfer paper and its preparation method, belonging to the technical field of functional paper-based materials. The nanocellulose-modified heat transfer paper is obtained by coating a heat transfer base paper with a composite coating, wherein the composite coating comprises lignin nanocellulose filaments. The preparation method includes the following steps: compounding CS / CMC adhesive with inorganic micro / nano pigments, adding lignin nanocellulose filaments to obtain the composite coating, and then coating the composite coating onto the heat transfer base paper to obtain the nanocellulose-modified heat transfer paper. The nanocellulose-modified heat transfer paper provided by this invention has advantages such as high transfer rate, increased paper surface strength, reduced fuzzing and dust-related problems during printing, and fast drying speed. The raw materials used in this invention are all non-biotoxic, low in cost, with mild reaction conditions, safe and simple process, and meets environmental protection requirements.

Description

Technical Field

[0001] This invention belongs to the field of functional paper-based materials technology, and particularly relates to a nanocellulose-modified thermal transfer paper and its preparation method. Background Technology

[0002] The dyeing and printing industry is a traditionally high-pollution and high-energy-consumption industry, and environmental pressures are gradually forcing its transformation and upgrading. Digital printing uses computers to distribute ink "on demand," thereby significantly reducing dye usage and wastewater discharge, bringing new opportunities to the dyeing and printing industry. Digital printing can be further divided into digital direct-to-garment printing, heat transfer printing, and cold transfer printing. Among them, digital heat transfer printing has a short production time, high flexibility, does not require steaming or washing, and is environmentally friendly, significantly solving the threat of dyeing and printing wastewater to the ecological environment at the source, giving it a significant competitive advantage. As the "transfer station" in the digital heat transfer process, the performance of heat transfer paper plays a crucial role in the printing quality and transfer quality of the pattern.

[0003] Heat transfer paper generally consists of a base paper and a coating layer. The coating layer is a thin film formed by drying the coating material on the paper surface. Its main function is to provide excellent ink absorbency, prevent excessive ink absorption into the paper fibers, control dot gain, and create high-quality images and text. The coating material is generally composed of sizing agents, pigments, and functional additives. Heat transfer paper prepared with existing coating formulations suffers from problems such as easy scratching of the images and text and low transfer rates.

[0004] Nanocellulose (NC) is abundant and possesses high specific surface area, good biocompatibility, adjustable physical and chemical properties, and excellent rheological properties, dispersion stability, water retention, and film-forming properties. These superior properties make NC highly valuable for research and application in the field of composite materials. Cellulose nanofibers (CNFs), with diameters of 10-100 nm and lengths of several micrometers, have a large aspect ratio and easily form dense network structures. They can be used to improve the mechanical and barrier properties of membranes, generate porous coatings, improve the surface properties of coated paper, and overcome the strength reduction caused by filler content. The combined sizing of CNFs and cationic starch can give paper sheets smoothness and uniformity with controllable permeability and improve ink transfer rate. However, in existing technologies, composite coatings prepared using conventional CNFs, when used in transfer paper, produce unclear printed patterns and extremely poor printing effects, making them difficult to apply in practice.

[0005] Therefore, how to provide a method for improving the performance of transfer paper using nanocellulose is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a nanocellulose-modified thermal transfer paper and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A nanocellulose-modified heat transfer paper is obtained by coating a heat transfer base paper with a composite coating, wherein the composite coating includes lignin nanocellulose filaments (LCNFs).

[0009] Preferably, the lignin nanocellulose filaments have a diameter of 20-180 nm and a length of 2-5 μm.

[0010] Preferably, the lignin nanocellulose filaments are cationic lignin nanocellulose filaments (C-LCNFs) with a zeta potential of +15 to +30 mV.

[0011] Beneficial effects: The addition of lignin nanocellulose to the coating in this invention can enable the coating to form more micro-mesh, improve printing and transfer accuracy, and at the same time, the retention of lignin nanocellulose can reduce water absorption, thereby improving the ink drying speed. Furthermore, the cationic charge characteristics of lignin nanocellulose filaments can increase the adsorption performance of ink.

[0012] A method for preparing nanocellulose-modified thermal transfer paper includes the following steps:

[0013] The CS / CMC adhesive is compounded with inorganic micro-nano pigments to obtain an adhesive material. Then, lignin nanocellulose filaments (LCNFs) are added to obtain a composite coating. The composite coating is then applied to the heat transfer base paper to obtain the nanocellulose modified heat transfer paper.

[0014] Beneficial effects: Adding a small amount of inorganic micro / nano pigments and nanocellulose to CMC / CS adhesive forms a swelling coating. CMC / CS can quickly absorb most of the solvent in the ink droplets, resulting in fast drying. The inorganic micro / nano pigments and nanocellulose embedded in CMC / CS can form a large number of microporous mesh structures, which can effectively control the ink dots, form high-quality images, and improve printing and transfer accuracy.

[0015] Preferably, the preparation method of the CMC / CS adhesive includes the following steps:

[0016] The CMC / CS gel is obtained by heating the sodium carboxymethyl cellulose solution and then adding cationic starch and stirring to gelatinize it.

[0017] Preferably, the mass ratio of sodium carboxymethyl cellulose to cationic starch is 1:3 to 1:8.

[0018] Beneficial effects: CMC has good film-forming properties and good compatibility with pigments, improving printing quality and preventing ink migration into the coating and paper. Furthermore, starch is inexpensive and can quickly absorb water from the ink, accelerating its drying speed. However, a chemical bond inevitably exists between starch and ink, making ink separation relatively difficult. Therefore, a compound starch is used as the main component, with a small amount of CMC added.

[0019] Preferably, the mass ratio of the CMC / CS adhesive to the inorganic micro / nano pigment is 5:1 to 9:1;

[0020] More preferably, the inorganic micro / nano pigments include kaolin and / or nano-silica;

[0021] The kaolin is in flake form with a particle size of 1250 mesh.

[0022] The nano-silica is in the form of spherical particles with a particle size of 20-150 nm.

[0023] The mass ratio of kaolin to nano-silica is 4:1 to 9:1.

[0024] The lignin nanocellulose filaments account for 1% to 4% of the absolute mass of the adhesive.

[0025] Preferably, before coating, the heat transfer base paper is pre-dried to 70-80% dryness by infrared drying, and then dried to 92-96% dryness by double-row drying cylinders.

[0026] Preferably, during the coating process, the coating amount of the composite coating is 1.5-2.5 g / m³. 2 The paper pressure is designed to be 30-40 kN / m.

[0027] More preferably, the coating is applied using a film transfer coater.

[0028] Beneficial effects: The coating in this invention is based on CMC / CS, which has high fluidity and film-forming properties. The film transfer coating method can accurately control the coating amount and is conducive to forming a uniform and dense film layer.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] The nanocellulose-modified heat transfer paper provided by this invention combines CMC and CS, utilizing the interaction of hydroxyl-containing macromolecular chains of the two substances to form a network film, allowing ink particles to be quickly fixed on the paper coating surface, preventing their migration and improving the transfer rate. Cationic lignin nanocellulose and inorganic micro / nano pigments are introduced into the CMC / CS compound. The high aspect ratio and numerous hydrogen bonds of the lignin nanocellulose increase the surface strength of the paper, reducing fuzzing and dust-related problems during printing. Furthermore, the lignin nanocellulose reduces the water absorption of the coating, increasing the ink drying speed, and its cationic charge enhances the coating's ink adsorption capacity. In addition, the lignin nanocellulose and inorganic micro / nano pigments in this invention can be embedded in the CMC / CS to form a large number of microporous network structures, effectively controlling the dot gain of the printing ink, forming high-quality images, and improving printing and transfer accuracy. This invention uses raw materials that are non-biotoxic, has low cost, mild reaction conditions, and a safe and simple process, meeting environmental protection requirements. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0032] Figure 1 The following are trend graphs showing the effect of C-LCNFs addition amount on coating viscosity in Example 1 and Comparative Examples 1-4;

[0033] Figure 2 This is a trend graph showing the effect of the amount of C-LCNFs added on smoothness and Cobb value in Example 1 and Comparative Examples 1-4;

[0034] Figure 3 The graph shows the effect of the amount of C-LCNFs added on the heat transfer paper transfer rate in Example 1 and Comparative Examples 1-4.

[0035] Figure 4 This is a four-color patch image of the heat transfer paper when 2% C-LCNFs were added in Example 1;

[0036] Where a represents the material before transfer, b represents the material after transfer, and c represents the substrate. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] This invention discloses a nanocellulose-modified heat transfer paper, which is obtained by coating the heat transfer base paper with a composite coating, wherein the composite coating includes lignin nanocellulose filaments (LCNFs).

[0040] In a preferred embodiment, the lignin nanocellulose filaments have a diameter of 20-180 nm and a length of 2-5 μm.

[0041] In a preferred embodiment, the lignin nanocellulose filaments are cationic lignin nanocellulose filaments (C-LCNFs) with a zeta potential of +15 to +30 mV. This invention adds lignin nanocellulose to coatings, enabling the formation of more fine meshes in the coating, improving printing and transfer accuracy. Simultaneously, retaining lignin in the nanocellulose reduces water absorption, thereby increasing ink drying speed. Furthermore, compared to ordinary nanocellulose, the cationic charge characteristics of the cationic lignin nanocellulose filaments in this invention enhance ink adsorption performance.

[0042] This invention also discloses a method for preparing nanocellulose-modified thermal transfer paper, comprising the following steps:

[0043] The CS / CMC adhesive is compounded with inorganic micro-nano pigments to obtain an adhesive material. Then, lignin nanocellulose filaments (LCNFs) are added to obtain a composite coating. The composite coating is then applied to the heat transfer base paper to obtain the nanocellulose modified heat transfer paper.

[0044] This invention adds a small amount of inorganic micro / nano pigments and lignin nanocellulose to CMC / CS adhesive to form a swelling coating. CMC / CS can quickly absorb most of the solvent in the ink droplets, resulting in fast drying. The inorganic micro / nano pigments and nanocellulose embedded in CMC / CS can form a large number of microporous mesh structures, which can effectively control the ink dots, form high-quality images, and improve printing and transfer accuracy.

[0045] In a preferred embodiment, the preparation method of the CMC / CS adhesive includes the following steps:

[0046] The CMC / CS gel is obtained by heating the sodium carboxymethyl cellulose solution and then adding cationic starch and stirring to gelatinize it.

[0047] In a preferred embodiment, the mass ratio of sodium carboxymethyl cellulose (CMC) to cationic starch is 1:3 to 1:8. CMC has good film-forming properties, good compatibility with pigments, and improves printing quality. It can prevent ink migration into the coating and paper, although ink drying takes a long time. Starch is inexpensive and can quickly absorb water from the ink, accelerating the drying speed. However, there is inevitably some chemical bond between starch and ink, making ink separation difficult. Therefore, a compound starch is used as the main component, with a small amount of CMC added.

[0048] In a preferred embodiment, the mass ratio of the CMC / CS adhesive to the inorganic micro / nano pigment is 5:1 to 9:1;

[0049] In a more preferred embodiment, the inorganic micro / nano pigment includes kaolin and / or nano-silica;

[0050] The kaolin is in flake form with a particle size of 1250 mesh.

[0051] The nano-silica is in the form of spherical particles with a particle size of 20-150 nm.

[0052] The mass ratio of kaolin to nano-silica is 4:1 to 9:1.

[0053] The lignin nanocellulose filaments account for 1% to 4% of the absolute mass of the adhesive.

[0054] In a preferred embodiment, the heat transfer base paper is first pre-dried to 70-80% dryness by infrared drying before coating, and then dried to 92-96% dryness by double-row drying cylinders.

[0055] In a preferred embodiment, during the coating process, the coating amount of the composite coating is 1.5-2.5 g / m³. 2 The paper pressure is designed to be 30-40 kN / m.

[0056] In a more preferred embodiment, the coating is applied using a film transfer coater. The coating in this invention is based on CMC / CS, exhibiting high fluidity and film-forming properties. The film transfer coating method allows for precise control of the coating amount and facilitates the formation of a uniform and dense film layer.

[0057] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels;

[0058] In this embodiment of the invention, the cationic lignin nanocellulose (C-LCNFs) was purchased from Zhongshan Nanofiber New Material Co., Ltd., and its length was 0.2-0.4 μm, its diameter was 20 nm, and its crystallinity was 78.67%.

[0059] Sodium carboxymethyl cellulose was purchased from Nanjing Liangyou Chemical Co., Ltd., with industrial grade purity, viscosity of 39 cP, and degree of polymerization of 1.2 Mmol / g.

[0060] The cationic starch was purchased from Hangzhou Zhiyou Technology Co., Ltd., and its purity was industrial grade.

[0061] The kaolin was purchased from Chenxing Industrial Co., Ltd., with a particle size of 1250 mesh.

[0062] The nano-silica was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a particle size of 50 nm.

[0063] The thermal transfer base paper was purchased from a specialty paper company in Quzhou, with a basis weight of 80 g / m³. 2 ;

[0064] Unless otherwise specified, the glue-pigment ratio described in the embodiments of the present invention is the mass ratio of CS / CMC adhesive to inorganic micro / nano pigments.

[0065] Example 1

[0066] A method for preparing nanocellulose-modified thermal transfer paper includes the following steps:

[0067] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, kaolin was added to the obtained CS / CMC adhesive solution at a mass ratio of 4:1 to obtain an adhesive. Then, 2% of C-LCNFs by mass of the adhesive was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0068] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure was designed to be 30 kN / m. After coating and drying, the paper sample was used to obtain nanocellulose modified heat transfer paper.

[0069] Comparative Example 1

[0070] A method for preparing heat transfer paper, differing from Example 1 in that 1% C-LCNFs by weight of the adhesive is added, specifically including the following steps:

[0071] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, kaolin was added to the obtained CS / CMC adhesive solution at a mass ratio of 4:1 to obtain an adhesive. Then, 1% of the absolute mass of C-LCNFs was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0072] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure is designed to be 30kN / m. After coating, the paper sample is dried to obtain heat transfer paper.

[0073] Comparative Example 2

[0074] A method for preparing heat transfer paper, differing from Example 1 in that 3% C-LCNFs by weight of the adhesive is added, specifically including the following steps:

[0075] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, kaolin was added to the obtained CS / CMC adhesive solution at a mass ratio of 4:1 to obtain an adhesive. Then, 3% of the absolute mass of C-LCNFs was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0076] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure is designed to be 30kN / m. After coating, the paper sample is dried to obtain heat transfer paper.

[0077] Comparative Example 3

[0078] A method for preparing heat transfer paper, differing from Example 1 in that 4% (by weight) of C-LCNFs is added, specifically including the following steps:

[0079] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, kaolin was added to the obtained CS / CMC adhesive solution at a mass ratio of 4:1 to obtain an adhesive. Then, 4% of the absolute mass of C-LCNFs was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0080] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure is designed to be 30kN / m. After coating, the paper sample is dried to obtain heat transfer paper.

[0081] Comparative Example 4

[0082] A method for preparing thermal transfer paper, which differs from Example 1 in that C-LCNFs are not added, specifically includes the following steps:

[0083] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, kaolin was added to the obtained CS / CMC adhesive solution at a mass ratio of 4:1 to obtain an adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0084] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure is designed to be 30kN / m. After coating, the paper sample is dried to obtain heat transfer paper.

[0085] Example 2

[0086] A method for preparing nanocellulose-modified thermal transfer paper includes the following steps:

[0087] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, kaolin was added to the obtained CS / CMC adhesive solution at a mass ratio of 9:1 to obtain an adhesive. Then, 2% of C-LCNFs by mass of the adhesive was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0088] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure was designed to be 30 kN / m. After coating and drying, the paper sample was used to obtain nanocellulose modified heat transfer paper.

[0089] Example 3

[0090] A method for preparing nanocellulose-modified thermal transfer paper includes the following steps:

[0091] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, nano-silica was added to the obtained CS / CMC adhesive solution at a glue-to-pigment ratio of 4:1 to obtain an adhesive. Then, 2% of C-LCNFs by mass of the adhesive was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0092] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure was designed to be 30 kN / m. After coating and drying, the paper sample was used to obtain nanocellulose modified heat transfer paper.

[0093] Comparative Example 5

[0094] A method for preparing heat transfer paper includes the following steps:

[0095] Sodium carboxymethyl cellulose and cationic starch were mixed at a mass ratio of 1:4 to prepare a CS / CMC adhesive solution with a mass concentration of 20%. Then, nano-silica was added to the obtained CS / CMC adhesive solution at a glue-to-pigment ratio of 10:1 to obtain an adhesive. Then, 2% of C-LCNFs by mass of the adhesive was added to the adhesive. After stirring and standing to remove bubbles, a composite coating was obtained.

[0096] Before coating, the heat transfer base paper is pre-dried using infrared technology to 70-80% dryness, and then dried to 92-96% dryness using a double-row drying cylinder. Then, the composite coating is applied to the heat transfer base paper using a film transfer coater, with the coating amount controlled at 1.5 g / m². 2 The paper pressure is designed to be 30kN / m. After coating, the paper sample is dried to obtain heat transfer paper.

[0097] The nanocellulose-modified heat transfer paper prepared in this embodiment becomes too smooth, making it difficult for ink to adhere and thus affecting printing quality. This demonstrates that adding an appropriate amount of nano-silica can improve the ink transfer rate of the paper and enhance printing quality to some extent. However, adding too much will reduce the ink transfer rate of the paper.

[0098] Comparative Example 6

[0099] A method for preparing heat transfer paper differs from Example 1 in that lignin nanocellulose is replaced with ordinary nanocellulose, the nanocellulose having a particle size of 1-100 nanometers and an aspect ratio of 7-10:1.

[0100] The nanocellulose-modified heat transfer paper prepared in this comparative example has high water absorption, which causes the ink to be quickly absorbed and diffused on the paper surface, affecting the details and clarity of the printed pattern and thus reducing the quality of the printing effect. The high water absorption of the heat transfer paper means that the ink may take longer to dry after being absorbed, which will prolong the printing operation time and reduce production efficiency.

[0101] As can be seen, compared with ordinary nanocellulose, the lignin nanocellulose in this invention has reduced water absorption, thereby improving the ink drying speed; lignin nanocellulose usually has higher mechanical strength and stability, making the paper more durable and less prone to deformation and tearing, thereby improving the printing quality and stability of heat transfer paper.

[0102] Comparative Example 7

[0103] A method for preparing heat transfer paper differs from Example 1 in that the preparation method involves directly mixing all raw materials evenly, coating the heat transfer base paper with a laboratory film transfer coater, and drying the coated paper sample to obtain the heat transfer paper.

[0104] The adhesive obtained by directly mixing all raw materials uniformly has poor stability and low rheological properties. It can be seen that by first preparing the CS / CMC adhesive in this invention, the adhesive exhibits better stability because the CS and CMC adhesives can act as carriers for nano-silica, allowing for better and more uniform dispersion.

[0105] Technical effects:

[0106] The transfer rate was tested according to standard T / ZZB 0241-2017. The formula is shown in Equation 1. The average value was taken. In this experiment, the transfer rate was the average value of the transfer rates of the four color blocks: cyan (100% C), magenta (100% M), yellow (100% Y), and black (100% K).

[0107] (1)

[0108] In the formula: T—transfer rate, %; A1—color density value of paper before transfer; A2—density value of color blocks on paper after transfer.

[0109] The heat transfer rates of Examples 1-3, Comparative Examples 1-7, and the base paper and control paper samples were tested using the above method. The base paper was the heat transfer base paper from Example 1 without composite coating. The control paper sample was purchased from a coated paper company in Hangzhou and had a basis weight of 84 g / m³. 2The paper has a width of 0.48m and a thickness of 0.2mm. The final heat transfer rates of Examples 1-3 are 85.41%, 82.97%, and 83.74%, respectively, while those of Comparative Examples 1-7 are 82.04%, 84.29%, 83.71%, 81.48%, 69.45%, and 78.62%, respectively. The heat transfer rates of the base paper and the control paper are 56.95% and 69.45%, respectively. It can be seen that the nanocellulose modified heat transfer paper obtained in Example 1 is 28.46%, 15.96%, and 3.93% higher than that of the base paper, the control paper, and the paper without C-LCNFs, respectively. This indicates that adding an appropriate amount of C-LCNFs to the composite coating can effectively improve the ink transfer rate of the heat transfer paper. This study is of great significance for promoting the localization of high-grade heat transfer paper and narrowing the gap with the world's advanced level. The transfer rate of the heat transfer paper obtained in Comparative Example 1 was 25.09%, 12.59%, and 0.56% higher than that of the original paper, the control paper, and the paper without C-LCNFs, respectively. However, it was 3.37% lower than that when the C-LCNFs addition was 2%, indicating that appropriately increasing the amount of C-LCNFs in the composite coating can effectively improve the ink transfer rate of the heat transfer paper. The transfer rate of the heat transfer paper obtained in Comparative Example 2 was 27.34%, 14.84%, and 2.81% higher than that of the original paper, the control paper, and the paper without C-LCNFs, respectively. However, it was 1.12% lower than that when the C-LCNFs addition was 2%, indicating that the effect of the amount of C-LCNFs in the composite coating on the ink transfer rate of the heat transfer paper shows a trend of first increasing and then decreasing. The transfer rate of the nanocellulose-modified heat transfer paper obtained in Example 2 was higher than that of the original paper, the control paper, and the paper without C-LCNFs, indicating that a pigment-to-particle ratio of 9:1 in the composite coating can still effectively improve the ink transfer rate of the heat transfer paper. The heat transfer rate results obtained in Example 3 show that the addition of nano-silica can also effectively improve the ink transfer rate of the heat transfer paper.

[0110] Figure 1The graphs showing the effect of C-LCNFs addition on coating viscosity in Examples 1 and Comparative Examples 1-4 demonstrate that coating viscosity initially decreases and then increases with CNFs addition. When 1% CNFs are added, the coating viscosity is at its lowest, decreasing by 6.30% compared to no CNFs. This is because CNFs themselves, and CNFs and water molecules, form a network structure through hydrogen bonds, containing the pigments and restricting their migration. Furthermore, the water absorption of the pigments and the swelling capacity of CNFs rapidly increase the diameter and volume of this structure, increasing the internal friction of the liquid flow and hindering the flow of water molecules. This results in a more uniform and stable distribution of coating components, thus reducing viscosity to some extent. However, as CNFs increase, the number of vacancies in the aqueous phase of the coating system decreases, further restricting the flow of water molecules, and therefore, the coating viscosity increases accordingly. The amount of C-LCNFs added has a significant impact on the viscosity of the coating. When the amount of C-LCNFs added is 1-2%, the viscosity of the coating can be significantly reduced. However, as the amount of C-LCNFs added increases, the viscosity of the coating gradually increases, making it difficult to coat the surface of heat transfer paper in practical applications.

[0111] Figure 2 The graphs showing the effects of C-LCNFs addition on smoothness and Cobb value in Example 1 and Comparative Examples 1-4 show that the smoothness of the heat transfer paper first increases and then decreases with the increase of CNFs. When the addition amount is 2%, the smoothness of the heat transfer paper is the highest, which is 3.33% higher than the paper sample without CNFs and 6.90% higher than the control paper sample.

[0112] Figure 3 The graph shows the effect of C-LCNFs addition amount on the heat transfer paper transfer rate in Example 1 and Comparative Examples 1-4. The results show that the heat transfer paper transfer rate first increases and then decreases with the addition of CNFs. When the CNFs addition amount is 2%, the heat transfer paper transfer rate reaches the highest value (85.41%), which is 28.46%, 15.96%, and 3.93% higher than that of the original paper, the control paper, and the paper without CNFs, respectively. This indicates that the coating of the composite coating can significantly improve the ink transfer rate.

[0113] Figure 4 The four-color block diagrams of the heat transfer paper with 2% C-LCNFs added in Example 1 (a before transfer, b after transfer, c substrate) show that the optical density and transfer effect of cyan (C), magenta (M), yellow (Y), and black (K) are significantly improved before and after transfer.

[0114] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A nanocellulose modified heat transfer paper, which is obtained by coating a heat transfer base paper with a composite coating material, characterized in that, The composite coating comprises lignin nanocellulose filaments; The preparation method of the composite coating comprises the following steps: The CMC / CS glue solution is compounded with inorganic micro-nano pigments to obtain glue, and then lignin nanocellulose filaments are added to obtain the composite coating. The preparation method of the CMC / CS glue solution comprises the following steps: The sodium carboxymethyl cellulose solution is heated, cationic starch is added, and stirring and gelatinization are performed to obtain the CMC / CS glue solution. The lignin nanocellulose filaments are cationic lignin nanocellulose filaments. The mass ratio of the CMC / CS glue solution to the inorganic micro-nano pigments is 5:1-9:

1. The addition amount of the lignin nanocellulose filaments is 2% of the absolute mass of the glue.

2. The nanocellulose modified heat transfer paper according to claim 1, characterized in that, The diameter of the lignin nanocellulose filaments is 20-180nm.

3. The nanocellulose modified heat transfer paper according to claim 2, characterized in that, The zeta potential of the lignin nanocellulose filaments is +15 to +30mv.

4. A method for producing a nanocellulose-modified heat transfer paper according to any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: The CMC / CS glue solution is compounded with inorganic micro-nano pigments to obtain glue, and then lignin nanocellulose filaments are added to obtain the composite coating, and then the composite coating is coated on the thermal transfer base paper to obtain the nanocellulose modified thermal transfer paper. The preparation method of the CMC / CS glue solution comprises the following steps: The sodium carboxymethyl cellulose solution is heated, cationic starch is added, and stirring and gelatinization are performed to obtain the CMC / CS glue solution.

5. The method for preparing nanocellulose-modified thermal transfer paper according to claim 4, characterized in that, The mass ratio of the sodium carboxymethyl cellulose to the cationic starch is 1:3-1:

8.

6. The method for preparing nanocellulose-modified thermal transfer paper according to claim 4, characterized in that, Before coating, the thermal transfer base paper is pre-dried by infrared to a dryness of 70-80%, and then dried by a double-cylinder dryer to a dryness of 92-96%.

7. The method for preparing nanocellulose-modified thermal transfer paper according to claim 4, characterized in that, The coating process, the coating amount of the composite coating is 1.5-2.5g / m 2 , the design paper pressure is 30-40kN / m.

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