Heat-resistant ink and preparation method thereof

Abstract

The invention provides heat-resistant ink and a preparation method thereof, and belongs to the technical field of ink. The preparation method of the heat-resistant printing ink comprises the following steps: carrying out silanization modification on linen fibers after alkali treatment, and then grafting fluorosilane-acrylic acid copolymer to obtain modified fibers B; carrying out oxidation modification on the nanocellulose crystal to obtain a modified nanocellulose crystal; loading the modified nano cellulose crystal on the modified fiber B to obtain a modified fiber C; grafting an organic pigment to the modified fiber C to obtain a modified pigment; and mixing the modified pigment with waterborne polyurethane resin, a dispersing agent, zirconium phosphate nanosheets and deionized water to obtain the heat-resistant ink. The heat-resistant ink prepared by the preparation method shows excellent heat resistance, other mechanical properties of the ink are also improved, and the heat-resistant ink has a wide application range.

Description

Technical Field

[0001] The present invention relates to the technical field of inks, and particularly to a heat-resistant ink and a preparation method thereof. Background Art

[0002] Ink is an important material for printing, which shows patterns and words on a printing substrate through printing or spraying. Ink includes main components and auxiliary components, which are uniformly mixed and repeatedly rolled into a viscous colloidal fluid, and is commonly used in various fields such as books and periodicals, packaging and decoration, architectural decoration, and printed circuit boards.

[0003] However, traditional inks often have poor heat resistance and cannot meet the diverse needs of the market. Therefore, how to improve the heat resistance of inks is of great significance. Summary of the Invention

[0004] In order to solve the problems mentioned in the background art, the present invention provides a heat-resistant ink, which has heat resistance and excellent mechanical properties through special component formulations.

[0005] Specifically: A preparation method of a heat-resistant ink, comprising the following steps: Step 1: Subject flax fibers to alkali treatment, and then perform silanization modification to obtain modified fiber A; Step 2: Perform oxidation modification on nanocrystalline cellulose to obtain modified nanocrystalline cellulose; Step 3: Immerse modified fiber A in an ethanol solution containing acrylic acid, styrene, and 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-heptadecafluorodecyltrimethoxysilane, add an auxiliary agent, and react under nitrogen protection at 40 - 50 °C. Wash with water to remove unreacted monomers, and dry to obtain modified fiber B; Step 4: Add the modified nanocrystalline cellulose obtained in Step 2 and PEG2000 to MES buffer solution, add EDC and NHS, react at room temperature, centrifuge to separate the activated modified nanocrystalline cellulose, and then add it to MES buffer solution for ultrasonic dispersion to obtain a dispersion liquid containing modified nanocrystalline cellulose; Step 5: Immerse the modified fiber B obtained in Step 3 in MES buffer solution for pretreatment. Take out the pretreated modified fiber B and transfer it to the dispersion liquid containing modified nanocrystalline cellulose obtained in Step 4. Evacuate to -0.08 - 0 MPa, maintain the pressure for 0.5 - 1 h, centrifuge and filter to obtain modified fiber C; Step 6: Immerse the amino-functionalized organic pigment and the modified fiber C obtained in Step 5 in PBS buffer solution containing glutaraldehyde, react at 50 - 60 °C, wash and dry to obtain modified pigment; Step 7: After mixing the modified pigment obtained in Step 6 with aqueous polyurethane resin, dispersant, zirconium phosphate nanosheets, and deionized water, first treat it with an ultrasonic cell disruptor and then stir it with a high-speed shear mixer to obtain heat-resistant ink.

[0006] Further, in Step 1, the alkali treatment method for flax fiber is to immerse the flax fiber in a NaOH solution with a mass fraction of 5% - 5.5% at a solid-liquid ratio of 1 g : 20 - 25 mL, stir at 80 - 85 °C for 1 hour, wash with water until neutral, and dry. The silanization modification method is to immerse the alkali-treated flax fiber in an ethanol aqueous solution containing 3% - 3.5% KH550 silane coupling agent at a solid-liquid ratio of 1 g : 10 - 20 mL, react at 60 - 65 °C for 4 - 5 h, wash with water and dry; the volume ratio of ethanol to water in the ethanol aqueous solution is 9:1, and the pH is adjusted to 4 - 4.5 with acetic acid.

[0007] Further, in Step 2, the oxidation modification method for nanocrystalline cellulose is to disperse the nanocrystalline cellulose in a phosphate buffer solution with a pH of 6 - 6.3 at a solid-liquid ratio of 1 g : 20 - 25 mL. For every 1 g of nanocrystalline cellulose added, 2 - 2.2 mmol of TEMPO and 10 - 10.5 mmol of NaBr are added, and 5 - 5.2 mmol of NaClO is added dropwise, and the reaction is carried out at room temperature for 6 - 7 h, followed by centrifugation and washing until neutral.

[0008] Further, in Step 3, the solid-liquid ratio of the modified fiber A to the ethanol solution is 1 g : 15 - 20 mL; the ethanol solution contains 10% - 12% acrylic acid, 1.5% - 2% styrene, and 0.45% - 0.5% heptadecafluorodecyltrimethoxysilane. The auxiliaries selected are APS and TEMED initiators; the ethanol solution contains 0.05% - 0.1% APS and 0.04% - 0.05% TEMED initiators.

[0009] Further, in Step 4, the mass ratio of the modified nanocrystalline cellulose to PEG2000 added is 1 : 3 - 3.5; the solid-liquid ratio of the modified nanocrystalline cellulose to the MES buffer solution is 1 g : 40 - 45 mL; for every 1 g of the modified nanocrystalline cellulose added, 4.5 - 5 mmol of EDC and 2 - 2.5 mmol of NHS are added; the solid-liquid ratio of the activated modified nanocrystalline cellulose to the MES buffer solution is 1 g : 10 - 15 mL; the pH of the MES buffer solution is 5 - 5.5.

[0010] Further, in Step 5, the solid-liquid ratio of the modified fiber B to the MES buffer solution is 1 g : 20 - 25 mL; the pretreatment time is 6 - 12 h at room temperature; the pH of the MES buffer solution is 5 - 5.5; the solid-liquid ratio of the pretreated modified fiber B to the dispersion liquid containing the modified nanocrystalline cellulose is 1 g : 30 - 50 mL.

[0011] Further, in step 6, the mass ratio of the aminated organic pigment to the modified fiber C is 1:2; the solid-liquid ratio of the modified fiber C to the PBS buffer solution is 1 g: 25 - 30 mL; the PBS buffer solution contains 1% - 1.5% by mass of glutaraldehyde, and the pH = 7.4 - 7.5.

[0012] Further, in step 6, the organic pigment is selected from any one of azo pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, or isoindolinone pigments.

[0013] Further, in step 7, the formulation is in parts by mass: 12 - 15 parts of the modified pigment, 22 - 25 parts of the waterborne polyurethane resin, 0.8 - 1 part of the dispersant, 0.5 - 0.7 part of the zirconium phosphate nanosheets, and 55 - 60 parts of deionized water.

[0014] On the other hand, the present invention also provides a heat-resistant ink prepared by using the above-mentioned preparation method of the heat-resistant ink.

[0015] Compared with the prior art, the beneficial features of the present invention are as follows: 1. For the heat-resistant ink of the present invention, through special modification of the organic pigment, its heat resistance is improved, so that the color of the ink is not easily faded under high-temperature environments. The method is that after the flax fiber is silanized and modified, it can react with components such as acrylic acid, styrene, and heptadecafluorodecyltrimethoxysilane, and then a fluorosilane-acrylic acid copolymer is grafted on the surface of the flax fiber. The fluorosilane binds to the organic pigment through hydrophobic interaction, and the acrylic acid chain segment provides steric hindrance through electrostatic repulsion, thereby anchoring the organic fiber on the flax fiber. On the one hand, it can improve the thermal decomposition resistance of the pigment. On the other hand, the flax fiber is also grafted with a dispersant to avoid agglomeration of the organic pigment, and glutaraldehyde cross-linking can also reduce the migration of pigment molecules, improving the dispersion stability and wetting performance of the organic pigment; the surface modification of the organic pigment with amino groups can also enhance the binding with the dispersant; in addition, the flax fiber has natural grooves and cracks, and the grooves and silanized groups of the modified flax fiber capture nanocrystalline cellulose (NCC) through van der Waals forces and hydrogen bonds. Vacuum assistance forces the NCC to enter the internal porous structure of the fiber to form mechanical interlocking. The NCC is a natural spherical body, and when stressed, it can use the ball bearing effect to improve the abrasion resistance of the ink. The flexible spacer arm of the PEG chain allows the NCC to slightly displace when stressed, maintaining the ball bearing effect while avoiding shedding.

[0016] 2. For the heat-resistant ink of the present invention, zirconium phosphate nanosheets are also added to its components. The layered structure of the zirconium phosphate nanosheets physically blocks the diffusion of heat and oxygen, which can not only improve the overall heat resistance of the ink but also reduce the oxidation rate of the pigment. Specific embodiments

[0017] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] In order to facilitate those skilled in the art to implement the present invention, some of the reagents used in the embodiments and comparative examples are now described: Flax fiber: Lanzhou Waterless Biotechnology; Nanocellulose crystals: Hubei Kemedi Chemical Industry; Acrylic acid: Jinan Juyang Chemical; Styrene: Jinan Zhengkang Chemical; Heptadecafluorodecyltrimethoxysilane: Wuhan Lanabai Chemical; PEG2000 (polyethylene glycol 2000): Jining Fangyu Chemical; MES buffer (2-(N-morpholino)ethanesulfonic acid buffer): Shanghai Shangbao Biotechnology; EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride): Wuhan Lanabai Chemical; NHS (N-hydroxysuccinimide): Wuhan Lanabai Chemical; Glutaraldehyde: Jinan Juyang Chemical; PBS buffer (phosphate buffered saline): Shanghai Shangbao Biotechnology; KH550 silane coupling agent: Shandong Qiyun Chemical; TEMPO (2,2,6,6-tetramethylpiperidinyl oxide): Wuhan Lanabai Chemical; NaBr: Jinan Zi'an Chemical Industry; NaClO: Jinan Zi'an Chemical Industry; APS (ammonium persulfate): Yunsheng Chemical; TEMED(Tetramethylethylenediamine):Shandong Haoshun Chemical Waterborne polyurethane resin: polyurethane emulsion, Jining Fangyu Chemical; Dispersant: BYK-190, Shandong Polychemical; Zirconium phosphate nanosheets: Wuhan Kemik Biomedical Technology; Organic pigment: Phthalocyanine blue, Shandong Polychemical; Amination process of phthalocyanine blue: Place phthalocyanine blue in a reaction vessel, add concentrated sulfuric acid five times the mass of phthalocyanine blue, and add fuming sulfuric acid equal to the amount of phthalocyanine blue. Heat to 90 °C, keep warm and stir for 4 h, cool and then introduce into an ice-water mixture for precipitation. After filtration, washing and drying, sulfonated phthalocyanine blue is obtained; Take the sulfonated phthalocyanine blue and disperse it in a borate buffer solution with pH = 8, and perform ultrasonic dispersion. The solid-liquid ratio of the sulfonated phthalocyanine blue to the borate buffer solution is 1 g:10 mL. Then add ethylenediamine three times the mass of the sulfonated phthalocyanine blue, heat in a water bath to 60 °C, adjust the pH to 8, stir and react for 12 h, perform centrifugal separation, wash and dry to obtain aminated phthalocyanine blue.

[0019] Example 1 A heat-resistant ink, the preparation steps include: Step 1: Immerse flax fibers in a 5% NaOH solution by a solid-liquid ratio of 1 g:20 mL, stir at 80 °C for 1 hour, wash with water until neutral, and dry; Subsequently, immerse the alkali-treated flax fibers in an ethanol aqueous solution containing 3% KH550 silane coupling agent by a solid-liquid ratio of 1 g:10 mL. The volume ratio of ethanol to water in the ethanol aqueous solution is 9:1. Adjust the pH = 4 with acetic acid, react at 60 °C for 4 h, wash with water and dry to obtain modified fiber A; Step 2: Disperse nanocellulose crystals in a PBS buffer solution with pH = 6 by a solid-liquid ratio of 1 g:20 mL. For every 1 g of nanocellulose crystals added, add 2 mmol TEMPO and 10 mmol NaBr, and dropwise add 5 mmol NaClO. React at room temperature for 6 h, centrifuge and wash until neutral to obtain modified nanocellulose crystals; Step 3: Immerse modified fiber A in an ethanol solution containing 10% acrylic acid, 1.5% styrene, and 0.45% heptadecafluorodecyltrimethoxysilane by a solid-liquid ratio of 1 g:15 mL. Add 0.05% APS and 0.04% TEMED initiators, react under nitrogen protection at 40 °C, wash with water to remove unreacted monomers, and dry to obtain modified fiber B; Step 4: Add the modified nanocellulose crystals obtained in Step 2 and PEG2000 to a MES buffer solution by a mass ratio of 1:3. The solid-liquid ratio of the modified nanocellulose crystals to the MES buffer solution is 1 g:40 mL. Then, for every 1 g of modified nanocellulose crystals added, add 4.5 mmol EDC and 2 mmol NHS. After reacting at room temperature, centrifuge to separate the activated modified nanocellulose crystals, and then add them to a MES buffer solution with pH = 5 by a solid-liquid ratio of 1 g:10 mL for ultrasonic dispersion to obtain a dispersion liquid containing modified nanocellulose crystals; Step 5: Immerse the modified fiber B obtained in Step 3 into a pH = 5 MES buffer solution at a solid-liquid ratio of 1 g: 20 mL, and pretreat it at room temperature for 6 h. Take out the pretreated modified fiber B and transfer it to the dispersion liquid containing modified nanocrystalline cellulose obtained in Step 4 at a solid-liquid ratio of 1 g: 30 mL. Vacuumize to -0.08 MPa, keep the pressure for 0.5 h, and then perform centrifugal filtration to obtain modified fiber C; Step 6: Immerse the aminated organic pigment and the modified fiber C obtained in Step 5 into a PBS buffer solution containing 1% glutaraldehyde at a mass ratio of 1:2. The pH of the PBS buffer solution is 7.4, and the solid-liquid ratio of the modified fiber C to the PBS buffer solution is 1 g: 25 mL. React at 50 - 60 °C, wash and dry to obtain the modified pigment; Step 7: By mass parts, mix 12 parts of the modified pigment obtained in Step 6, 22 parts of waterborne polyurethane resin, 0.8 part of dispersant, 0.5 part of zirconium phosphate nanosheets, and 55 parts of deionized water. First, treat with an ultrasonic cell disruptor and then stir with a high-speed shear mixer to obtain heat-resistant ink.

[0020] Example 2 A heat-resistant ink, the preparation steps include: Step 1: Immerse flax fiber into a 5.5% NaOH solution by a solid-liquid ratio of 1 g: 25 mL, stir at 85 °C for 1 h, wash with water until neutral, and dry. Subsequently, immerse the alkali-treated flax fiber into an ethanol aqueous solution containing 3.5% KH550 silane coupling agent by a solid-liquid ratio of 1 g: 20 mL. The volume ratio of ethanol to water in the ethanol aqueous solution is 9:1, adjust the pH = 4.5 with acetic acid, react at 65 °C for 5 h, wash with water and dry to obtain modified fiber A; Step 2: Disperse nanocrystalline cellulose into a PBS buffer solution with a pH = 6.3 by a solid-liquid ratio of 1 g: 25 mL. For every 1 g of nanocrystalline cellulose added, add 2.2 mmol of TEMPO and 10.5 mmol of NaBr, and dropwise add 5.2 mmol of NaClO. React at room temperature for 7 h, and centrifuge and wash until neutral to obtain modified nanocrystalline cellulose; Step 3: Immerse the modified fiber A into an ethanol solution containing 12% acrylic acid, 2% styrene, and 0.5% heptadecafluorodecyltrimethoxysilane by a solid-liquid ratio of 1 g: 20 mL. Add 0.1% APS and 0.05% TEMED initiators, and react under nitrogen protection at 50 °C. Wash with water to remove unreacted monomers, and dry to obtain modified fiber B; Step 4: Add the modified nanocrystalline cellulose obtained in Step 2 and PEG2000 to the MES buffer solution at a mass ratio of 1:3.5. The solid-liquid ratio of the modified nanocrystalline cellulose to the MES buffer solution is 1 g:45 mL. Then, for every 1 g of the added modified nanocrystalline cellulose, add 5 mmol of EDC and 2.5 mmol of NHS. After reacting at room temperature, centrifuge and separate the activated modified nanocrystalline cellulose, and then add it to the MES buffer solution with pH = 5.5 at a solid-liquid ratio of 1 g:15 mL for ultrasonic dispersion to obtain a dispersion containing modified nanocrystalline cellulose; Step 5: Immerse the modified fiber B obtained in Step 3 in the MES buffer solution with pH = 5.5 at a solid-liquid ratio of 1 g:25 mL, and pretreat it at room temperature for 12 h. Take out the pretreated modified fiber B and transfer it to the dispersion containing modified nanocrystalline cellulose obtained in Step 4 at a solid-liquid ratio of 1 g:50 mL. Vacuumize to 0 MPa, keep the pressure for 1 h, centrifuge and filter to obtain modified fiber C; Step 6: Immerse the amino-functionalized organic pigment and the modified fiber C obtained in Step 5 in the PBS buffer solution containing 1.5% glutaraldehyde at a mass ratio of 1:2. The pH of the PBS buffer solution is 7.5, and the solid-liquid ratio of the modified fiber C to the PBS buffer solution is 1 g:30 mL. React at 60 °C, wash and dry to obtain the modified pigment; Step 7: By mass, mix 15 parts of the modified pigment obtained in Step 6, 25 parts of the waterborne polyurethane resin, 1 part of the dispersant, 0.7 part of the zirconium phosphate nanosheets, and 60 parts of deionized water. First, treat it with an ultrasonic cell disruptor and then stir it with a high-speed shear mixer to obtain the heat-resistant ink.

[0021] Example 3 A heat-resistant ink, the preparation steps include: Step 1: Immerse the flax fiber in a 5% NaOH solution by mass at a solid-liquid ratio of 1 g:25 mL, stir at 85 °C for 1 hour, wash with water until neutral, and dry. Then, immerse the alkali-treated flax fiber in an ethanol aqueous solution containing 3% KH550 silane coupling agent by mass at a solid-liquid ratio of 1 g:20 mL. The volume ratio of ethanol to water in the ethanol aqueous solution is 9:1, adjust the pH = 4 with acetic acid, react at 65 °C for 4 h, wash with water and dry to obtain modified fiber A; Step 2: Disperse the nanocrystalline cellulose in the PBS buffer solution with pH = 6 at a solid-liquid ratio of 1 g:25 mL. For every 1 g of added nanocrystalline cellulose, add 2 mmol of TEMPO and 10 mmol of NaBr, and dropwise add 5 mmol of NaClO. React at room temperature for 7 h, centrifuge and wash until neutral to obtain the modified nanocrystalline cellulose; Step 3: Immerse the modified fiber A in an ethanol solution containing 10% acrylic acid, 2% styrene, and 0.45% heptadecafluorodecyltrimethoxysilane at a solid-liquid ratio of 1 g: 15 mL. Add 0.1% APS and 0.04% TEMED initiators, and react under nitrogen protection at 40 - 50 °C. Wash with water to remove unreacted monomers, and obtain modified fiber B after drying; Step 4: Add the modified nanocrystalline cellulose obtained in Step 2 and PEG2000 to MES buffer at a mass ratio of 1:3. The solid-liquid ratio of the modified nanocrystalline cellulose to MES buffer is 1 g: 45 mL. Then, for every 1 g of the added modified nanocrystalline cellulose, add 5 mmol EDC and 2 mmol NHS. After reacting at room temperature, centrifuge to separate the activated modified nanocrystalline cellulose, and then add it to MES buffer with pH = 5 at a solid-liquid ratio of 1 g: 15 mL for ultrasonic dispersion to obtain a dispersion containing modified nanocrystalline cellulose; Step 5: Immerse the modified fiber B obtained in Step 3 in MES buffer with pH = 5 at a solid-liquid ratio of 1 g: 25 mL, and pretreat it at room temperature for 12 h. Take out the pretreated modified fiber B and transfer it to the dispersion containing modified nanocrystalline cellulose obtained in Step 4 at a solid-liquid ratio of 1 g: 30 mL. Vacuumize to -0.05 MPa, keep the pressure for 1 h, and then centrifuge and filter to obtain modified fiber C; Step 6: Immerse the amino-functionalized organic pigment and the modified fiber C obtained in Step 5 in PBS buffer containing 1% glutaraldehyde at a mass ratio of 1:2. The pH of the PBS buffer is 7.5, and the solid-liquid ratio of the modified fiber C to the PBS buffer is 1 g: 25 mL. React at 60 °C, wash, and dry to obtain the modified pigment; Step 7: Mix 14 parts of the modified pigment obtained in Step 6, 24 parts of waterborne polyurethane resin, 0.8 part of dispersant, 0.6 part of zirconium phosphate nanosheets, and 58 parts of deionized water by mass. First, treat with an ultrasonic cell disruptor and then stir with a high-speed shear mixer to obtain heat-resistant ink.

[0022] Comparative Example 1 An ink, the preparation steps of which include: Mix 12 parts of phthalocyanine blue, 22 parts of waterborne polyurethane resin, 0.8 part of dispersant, 0.5 part of zirconium phosphate nanosheets, and 55 parts of deionized water by mass. First, treat with an ultrasonic cell disruptor and then stir with a high-speed shear mixer to obtain the ink.

[0023] The inks obtained in Examples 1 - 3 and Comparative Example 1 were respectively tested as follows: 1. Thermogravimetric analysis: Use a thermogravimetric analyzer to test the thermogravimetric performance of the cured ink film for the cured ink specimens, with nitrogen as the test atmosphere and a heating rate of 10 °C / min.

[0024] 2. Thermal environment chromaticity test: Place the aluminum plate with an ink film (thickness 1 μm) in an environment at 250 °C for 120 h, and observe the degree of color change.

[0025] 3. Abrasion resistance test: Uniformly scrape the ink on A4 paper as a sample. Use an ink abrasion tester. Cut the sample into 25 cm × 6 cm and fix it on the test device. Cut the blank A4 paper into 20 cm × 5 cm and fix it on the friction slider. Add weights to increase the weight, with a pressure of 4 pounds. Set the number of friction times to 100 times. After the test, observe the floating color on the surface of the blank A4 paper and the decolorization on the surface of the sample.

[0026] 4. Pigment dispersibility test: Use screen printing equipment to coat the ink on an ABS board (thickness 10 μm). After the paint film dries, observe its color uniformity and check for the existence of spots or areas with uneven color; make 10 samples in each group. If there is uneven chromaticity in the samples, it is considered unqualified.

[0027] The test results are as follows: From the above test results, it can be seen that the test results of Examples 1 - 4 are all better than those of Comparative Example 1.

[0028] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a heat-resistant ink, characterized in that, It includes the following steps: Step 1: Alkali-treat the flax fiber, and then carry out silanization modification to obtain modified fiber A; Step 2: Oxidatively modify the nanocellulose crystal to obtain a modified nanocellulose crystal; Step 3: Immerse the modified fiber A in an ethanol solution containing acrylic acid, styrene, and 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-heptadecafluorodecyltrimethoxysilane, add an auxiliary agent, react under nitrogen protection at 40 - 50 °C, wash with water to remove unreacted monomers, and dry to obtain modified fiber B; Step 4: Add the modified nanocellulose crystal obtained in Step 2 and PEG2000 to MES buffer solution, add EDC and NHS, react at room temperature, centrifuge to separate the activated modified nanocellulose crystal, and then add it to the MES buffer solution for ultrasonic dispersion to obtain a dispersion liquid containing the modified nanocellulose crystal; Step 5: Immerse the modified fiber B obtained in Step 3 in MES buffer solution for pretreatment, take out the pretreated modified fiber B and transfer it to immerse in the dispersion liquid containing the modified nanocellulose crystal obtained in Step 4, evacuate to -0.08 - 0 MPa, keep the pressure for 0.5 - 1 h, centrifuge and filter to obtain modified fiber C; Step 6: Immerse the amino-functionalized organic pigment and the modified fiber C obtained in Step 5 in PBS buffer solution containing glutaraldehyde, react at 50 - 60 °C, wash and dry to obtain a modified pigment; Step 7: Mix the modified pigment obtained in Step 6 with waterborne polyurethane resin, a dispersant, zirconium phosphate nanosheets, and deionized water, first treat with an ultrasonic cell disruptor and then stir with a high-speed shear mixer to obtain a heat-resistant ink.

2. The preparation method of the heat-resistant ink according to claim 1, characterized in that, The alkali treatment method of the flax fiber in Step 1 is to immerse the flax fiber in a NaOH solution with a mass fraction of 5% - 5.5% at a solid-liquid ratio of 1 g : 20 - 25 mL, stir at 80 - 85 °C for 1 hour, wash with water until neutral, and dry; The silanization modification method is to immerse the alkali-treated flax fiber in an ethanol aqueous solution containing a KH550 silane coupling agent with a mass fraction of 3% - 3.5% at a solid-liquid ratio of 1 g : 10 - 20 mL, react at 60 - 65 °C for 4 - 5 h, wash and dry; the volume ratio of ethanol to water in the ethanol aqueous solution is 9:1, and the pH is adjusted to 4 - 4.5 with acetic acid.

3. The preparation method of the heat-resistant ink according to claim 1, wherein, The oxidative modification method of the nanocellulose crystal in Step 2 is to disperse the nanocellulose crystal in PBS buffer solution with a pH of 6 - 6.3 at a solid-liquid ratio of 1 g : 20 - 25 mL, add 2 - 2.2 mmol TEMPO and 10 - 10.5 mmol NaBr for every 1 g of nanocellulose crystal added, dropwise add 5 - 5.2 mmol NaClO, react at room temperature for 6 - 7 h, and centrifuge and wash until neutral.

4. The preparation method of the heat-resistant ink according to claim 1, characterized in that, In Step 3, the solid-liquid ratio of the modified fiber A to the ethanol solution is 1 g : 15 - 20 mL; the ethanol solution contains acrylic acid with a mass fraction of 10% - 12%, styrene with a mass fraction of 1.5% - 2%, and 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-heptadecafluorodecyltrimethoxysilane with a mass fraction of 0.45% - 0.5%; The auxiliary agent selects APS and TEMED initiators; the ethanol solution contains APS with a mass fraction of 0.05% - 0.1% and TEMED initiator with a mass fraction of 0.04% - 0.05%.

5. The preparation method of the heat-resistant ink according to claim 1, characterized in that, In step 4, the mass ratio of the modified nanocrystalline cellulose to PEG2000 is 1:3 - 3.5; the solid-liquid ratio of the modified nanocrystalline cellulose to the MES buffer solution is 1 g:40 - 45 mL; for every 1 g of the added modified nanocrystalline cellulose, 4.5 - 5 mmol of EDC and 2 - 2.5 mmol of NHS are added; the solid-liquid ratio of the activated modified nanocrystalline cellulose to the MES buffer solution is 1 g:10 - 15 mL; the pH of the MES buffer solution is 5 - 5.

5.

6. The preparation method of the heat-resistant ink according to claim 1, wherein, In step 5, the solid-liquid ratio of the modified fiber B to the MES buffer solution is 1 g:20 - 25 mL; the pretreatment time is 6 - 12 h at room temperature; the pH of the MES buffer solution is 5 - 5.5; the solid-liquid ratio of the pretreated modified fiber B to the dispersion liquid containing the modified nanocrystalline cellulose is 1 g:30 - 50 mL.

7. The preparation method of the heat-resistant ink according to claim 1, characterized in that, In step 6, the mass ratio of the aminated organic pigment to the modified fiber C is 1:2; the solid-liquid ratio of the modified fiber C to the PBS buffer solution is 1 g:25 - 30 mL; the PBS buffer solution contains 1% - 1.5% by mass of glutaraldehyde and has a pH of 7.4 - 7.

5.

8. The preparation method of the heat-resistant ink according to claim 1, characterized in that, In step 6, the organic pigment is selected from any one of azo pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments or isoindolinone pigments.

9. The preparation method of the heat-resistant ink according to claim 1, wherein, In step 7, the formulation is made in parts by mass: 12 - 15 parts of the modified pigment, 22 - 25 parts of the waterborne polyurethane resin, 0.8 - 1 part of the dispersant, 0.5 - 0.7 part of the zirconium phosphate nanosheets, and 55 - 60 parts of deionized water.

10. A heat-resistant ink, characterized in that, Prepared by using the preparation method of the heat-resistant ink according to any one of claims 1 to 9.

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