Water-based polyurethane resin for pyrography ink and preparation method of water-based polyurethane resin

Abstract

The invention belongs to the technical field of printing ink, and particularly relates to a preparation method of water-based polyurethane resin for pyrography ink. The preparation method comprises the following steps: (1) preparation of a prepolymer: mixing modified polycarbonate diol, a hydrophilic chain extender and a micromolecule chain extender, performing vacuum dehydration, cooling to 20-40 DEG C, adding diisocyanate, performing heat preservation reaction, cooling, adding acetone, stirring, heating to 75-80 DEG C, reacting for 4-6 hours, cooling, adding triethylamine and acetone, and stirring to obtain the prepolymer; (2) emulsifying process; and (3) a desolventizing process: heating the emulsion obtained in the step (2) to 40-45 DEG C, and removing acetone to obtain the water-based polyurethane resin for the pyrography ink. The waterborne polyurethane resin prepared by the invention can improve the fluency, stability, washing resistance and friction property of pyrography ink.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane, and particularly relates to a water-based polyurethane resin for heat transfer ink and a preparation method thereof. Background Art

[0002] Digital heat transfer (also known as thermal transfer or sublimation printing) is a process that transfers patterns to various substrates through heat and pressure. In this process, coatings (or inks, inks) play a vital role. Specific chemical components in coatings (such as resins, adhesives, etc.) can form a strong bond with the target substrate under the action of heat and pressure, which is very important to ensure that the pattern will not fall off or fade after long-term use. Water-based polyurethane resin is one of the important components of digital heat transfer ink. In the digital heat transfer printing process, it is necessary to first print the printed pattern on the transfer film using digital heat transfer ink, and then transfer the printed pattern on the transfer film to the printed fabric by pressing. However, many digital heat transfer inks currently have the disadvantages of insufficient fluidity and poor stability; and when applied to polyester-cotton blended fabrics, due to their poor adhesion to cotton materials, the adhesion and water washability of the heat transfer pattern are insufficient.

[0003] At present, the main types of waterborne polyurethane used in digital heat transfer are as follows: (1) Preparation by solvent method, mainly through chain extension of diol and isocyanate monomer, introduction of hydrophilic group, removal of solvent, self-emulsification and dispersion in water. However, this method needs to achieve comprehensive performance requirements such as good flexibility, high tensile strength, small particle size, no solvent, good hydrolysis resistance and heat stability, and the current domestic technology is still lacking. (2) Alkyd resin modification method: This method adjusts the performance of the coating by mixing waterborne resin with alkyd resin; the waterborne polyurethane coating prepared by this method has good physical properties and wear resistance, but poor water resistance. (3) Propylene glycol ether method: This method uses propylene glycol ether as solvent, and the preparation process does not require the addition of organic solvents, which reduces pollution to the environment. The prepared waterborne polyurethane has a high solid content and good corrosion resistance, but the shrinkage rate of the coating is large.

[0004] Therefore, there is an urgent need for a water-based polyurethane resin for heat transfer ink and a preparation method thereof. Summary of the invention

[0005] The invention aims to provide a water-based polyurethane resin for heat transfer ink and a preparation method thereof.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for preparing a water-based polyurethane resin for heat transfer ink comprises the following steps: (1) Preparation of prepolymer: 0.03-0.05 mol of modified polycarbonate diol, 0.01-0.02 mol of polyether diol, 0.02-0.03 mol of hydrophilic chain extender and 0.04-0.06 mol of small molecule chain extender are mixed, heated to 90-100°C, vacuum dehydrated at -0.1 MPa for 1.5-2.5 h, cooled to 20-40°C, added with 0.3-0.4 mol of diisocyanate, stirred and heated to 80-90°C, kept warm for reaction for 2-3 h, cooled to 45-65°C, added with 3-5 mol of acetone, stirred and heated to 75-80°C for reaction for 4-6 h, cooled to 10-20°C, added with 0.037-0.039 mol of triethylamine and 12-14 mol of acetone, stirred for 25-35 min, and obtained a prepolymer; (2) Emulsification process: Stir the prepolymer of step (1) at a speed of 1400-1500 r / min, add 27-30 mol of ice-water mixture, continue stirring for 15-20 min, then adjust the speed to 400-500 r / min, add ethylenediamine aqueous solution, and continue stirring for 3-5 h to obtain an emulsion; (3) Desolventization process: The emulsion of step (2) is heated to 40-45°C, and the acetone in the emulsion is removed under -0.09 MPa to obtain a water-based polyurethane resin for heat transfer ink.

[0007] In traditional methods, in order to improve the hydrophilicity of polyurethane resin, a large amount of hydrophilic chain extenders (such as dimethylol propionic acid) are usually introduced. However, these ionic groups are prone to hydrolysis reaction in water, especially in high temperature or acid-base environment, resulting in decreased performance of the resin. The present invention uses non-ionic hydrophilic polyether-modified polycarbonate diol and polyether diol to carry out chain extension reaction with isocyanate monomer, thereby reducing the amount of hydrophilic chain extender, ensuring the hydrophilicity of waterborne polyurethane resin, and having a relatively low particle size when dispersed in water, while avoiding the problem of the introduction of a large number of ionic groups affecting the hydrolysis resistance and heat resistance of the resin.

[0008] Furthermore, the preparation method of the modified polycarbonate diol comprises the following steps: S1: Under a nitrogen atmosphere, 35-37 parts by weight of a mixed polyol, 10 parts by weight of diethylenetriamine and KOH are mixed, the temperature is raised to 135-140°C, 390-400 parts by weight of propylene oxide are added dropwise, and after the addition is completed, the reaction is continued at 135-140°C under a pressure of 0.2-0.3MPa for 3-4h, the temperature is lowered to 110-120°C, the temperature is kept for 1-1.5h, and the material is discharged by cooling to obtain a hydrophilic polyether; S2: adding water in an amount of 5-7% by weight of the hydrophilic polyether to the hydrophilic polyether, heating the mixture to 72-76° C., adjusting the pH to 4.5-5.0 with phosphoric acid, removing water under reduced pressure, filtering, and obtaining an acidified polyether; S3: Under nitrogen atmosphere, 10 parts by weight of NaOH, 1.2-1.4 parts by weight of CaCl 2 , 0.4-0.5 parts by weight of a phase transfer catalyst, and 90-93 parts by weight of an acidified polyether are mixed, 15-17 parts by weight of epichlorohydrin are added dropwise, after the addition is completed, the reaction is carried out at 30-35° C. for 6-8 hours, the solid salt is filtered out, phosphoric acid is used to neutralize the pH to 7, and the unreacted epichlorohydrin is removed under reduced pressure to obtain an epoxy-terminated hydrophilic polyether; S4: Evenly mix epoxy-terminated hydrophilic polyether, 3-aminopropane sulfonic acid and 0.1 mol / L hydrochloric acid aqueous solution in a weight ratio of 6: (22-25): (500-520), react at 80-90° C. for 2-3 h, neutralize to a neutral pH, and remove water by vacuum rotary evaporation to obtain a sulfonated polyether; S5: Mix polycarbonate diol, sulfonated polyether and toluene in a weight ratio of 20:(7-9):(400-420), react at 60-65°C for 6-8h, and after the reaction, wash and dry to obtain modified polycarbonate diol.

[0009] The present invention firstly causes a polyol and propylene oxide to undergo a ring-opening polymerization reaction under alkaline conditions to generate a hydrophilic polyether with a polyoxypropylene (PPG) structure. Diethylenetriamine, as a multifunctional compound, can introduce multiple amino groups to increase the branching degree and functionality of the polyether. The hydroxyl groups in the acidified polyether are deprotonated under alkaline conditions to form oxygen anions, which attack the epoxy groups of epichlorohydrin to initiate a ring-opening reaction and generate epoxy-terminated hydrophilic polyethers. The epoxy groups in the epoxy-terminated hydrophilic polyether undergo a ring-opening reaction with the amino groups in 3-aminopropane sulfonic acid, and the sulfonic acid groups on the surface of the sulfonated polyether can form hydrogen bonds or electrostatic interactions with the hydroxyl groups or other polar functional groups (such as ether bonds and ester bonds) in the polycarbonate diol. Such interactions can enhance the binding force between the two to obtain modified polycarbonate diols.

[0010] In the process of preparing polyurethane emulsion using the above-mentioned modified polycarbonate diol and polyether diol, the hydrophobic part on the polyurethane macromolecular chain curls and gathers in the center of the latex, the hydrophilic groups are distributed on the surface of the latex particles and point to the peripheral water phase, and the splitting action of the ion complexes on the particle interface forms a double electric layer. The anions (cations) connected to the polyurethane skeleton by chemical bonds are retained and fixed on the particle surface, while the ions migrate to the water phase around the particles, forming a charge layer with N potential on the surface of the microspheres, thereby enhancing the stability of the aqueous dispersion.

[0011] Furthermore, the polycarbonate diol is a mixture of a polycarbonate diol with an average molecular weight of 2000, a polycarbonate diol with an average molecular weight of 3000 and a polycarbonate diol with an average molecular weight of 500 in a weight ratio of 1: (1.4-1.6): (0.3-0.5).

[0012] Furthermore, the polyether diol has a hydroxyl value of 36-39 KOH / g and a molecular weight of 3000. It is purchased from Jining Tangyi Chemical Co., Ltd., DL series products.

[0013] Furthermore, the mixed polyol comprises ethylene glycol, propylene glycol and 1,4-butanediol in a weight ratio of 1: (1.4-1.6): (0.3-0.5).

[0014] Furthermore, the phase transfer catalyst is tetraethylammonium chloride.

[0015] Furthermore, the amount of KOH added is 0.2-0.4% of the total weight of the materials in step (1).

[0016] Furthermore, the small molecule chain extender is 2,3,5,6-tetramethyl-1,4-dioxacyclo-2,5-diol.

[0017] Furthermore, the hydrophilic chain extender is dimethylol propionic acid.

[0018] Furthermore, the diisocyanate is selected from one or more of toluene diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate.

[0019] The invention also provides a water-based polyurethane resin for heat transfer ink prepared by the preparation method.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. The waterborne polyurethane prepared by the present invention has the characteristics of good flexibility, high tensile strength, small particle size, no solvent, good hydrolysis resistance and heat stability, etc. The hydrophilic polyether-modified polycarbonate diol and polyether diol are compounded, and the chain extension reaction is carried out with the isocyanate monomer to reduce the amount of dimethylol propionic acid or dimethylol butyric acid hydrophilic chain extension group, while ensuring the hydrophilicity of the resin and having a lower particle size when dispersed in water, avoiding the introduction of a large number of ionic groups to affect the hydrolysis resistance and heat resistance of the resin.

[0021] 2. The water-based polyurethane resin provided by the present invention can improve the transfer force of ink between different media such as PET materials and polyester-cotton blended fabrics, thereby obtaining a clear patterning effect, and can improve the adhesion and water-washing resistance of the heat transfer pattern. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0023] Example 1 This embodiment provides a method for preparing a water-based polyurethane resin for heat transfer ink, comprising the following steps: (1) Preparation of prepolymer: 0.04 mol of modified polycarbonate diol, 0.015 mol of polyether diol, 0.015 mol of hydrophilic chain extender and 0.05 mol of small molecule chain extender were mixed, heated to 95°C, vacuum dehydrated at -0.1 MPa for 2 h, cooled to 30°C, added with 0.35 mol of diisocyanate, stirred and heated to 85°C, kept warm for 2.5 h, cooled to 50°C, then added with 4 mol of acetone, stirred and heated to 77°C for 5 h, cooled to 15°C, added with 0.038 mol of triethylamine and 13 mol of acetone, stirred for 30 min, and obtained a prepolymer; the small molecule chain extender was 2,3,5,6-tetramethyl-1,4-dioxacyclo-2,5-diol. The hydrophilic chain extender was dimethylol propionic acid. The diisocyanate was toluene diisocyanate. The polyether diol has a hydroxyl value of 36-39KOH / g and a molecular weight of 3000; it is purchased from Jining Tangyi Chemical Co., Ltd., DL series products. The polycarbonate diol is a mixture of a polycarbonate diol with an average molecular weight of 2000, a polycarbonate diol with an average molecular weight of 3000, and a polycarbonate diol with an average molecular weight of 500 in a weight ratio of 1:1.5:0.4; it is purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0024] (2) Emulsification process: The prepolymer of step (1) was stirred at a high speed of 1450 r / min, and 28 mol of ice-water mixture was added. The stirring was continued for 18 min, and then the speed was adjusted to 450 r / min, and an ethylenediamine aqueous solution (the volume ratio of ethylenediamine to water was 1:7, and the molar number of ethylenediamine was 0.004 mol) was added. The stirring was continued for 4 h to obtain an emulsion.

[0025] (3) Desolventization process: The emulsion of step (2) is heated to 42°C, and the acetone in the emulsion is removed under -0.09 MPa to obtain a water-based polyurethane resin for heat transfer ink.

[0026] The preparation method of the modified polycarbonate diol comprises the following steps: S1: Under a nitrogen atmosphere, 36 parts by weight of a mixed polyol, 10 parts by weight of diethylenetriamine and KOH are mixed, wherein the amount of KOH added accounts for 0.3% of the total weight of the materials in step (1); the temperature is raised to 138°C, and 395 parts by weight of propylene oxide are added dropwise. After the addition is completed, the reaction is continued at 140°C for 3.5 hours under a pressure of 0.2 MPa, the temperature is lowered to 115°C, the temperature is kept for 1.2 hours, and the material is discharged after cooling to obtain a hydrophilic polyether; the mixed polyol comprises ethylene glycol, propylene glycol and 1,4-butanediol in a weight ratio of 1:1.5:0.4; S2: adding water (6% by weight of the hydrophilic polyether) to the hydrophilic polyether, heating to 74° C., adjusting the pH to 4.7 with phosphoric acid, removing water under reduced pressure, filtering, and obtaining an acidified polyether; S3: Under a nitrogen atmosphere, 10 parts by weight of NaOH and 1.3 parts by weight of CaCl 2 , 0.45 parts by weight of tetraethylammonium chloride, a phase transfer catalyst, and 92 parts by weight of an acidified polyether are mixed, 16 parts by weight of epichlorohydrin are added dropwise, after the addition is completed, the reaction is carried out at 32° C. for 7 hours, the solid salt is filtered out, phosphoric acid is used to neutralize the pH to 7, and the unreacted epichlorohydrin is removed under reduced pressure to obtain an epoxy-terminated hydrophilic polyether; S4: Evenly mix epoxy-terminated hydrophilic polyether, 3-aminopropane sulfonic acid and 0.1 mol / L hydrochloric acid aqueous solution in a weight ratio of 6:23:510, react at 85° C. for 2.5 h, neutralize to a neutral pH, and remove water by vacuum rotary evaporation to obtain a sulfonated polyether; S5: Mix polycarbonate diol, sulfonated polyether and toluene in a weight ratio of 20:8:415, react at 62°C for 7 hours, and after the reaction, recover toluene by rotary evaporation under reduced pressure, wash with anhydrous ethanol, and dry to obtain modified polycarbonate diol.

[0027] Example 2 This embodiment provides a method for preparing a water-based polyurethane resin for heat transfer ink, comprising the following steps: (1) Preparation of prepolymer: 0.03 mol of modified polycarbonate diol, 0.01 mol of polyether diol, 0.02 mol of hydrophilic chain extender and 0.04 mol of small molecule chain extender were mixed, heated to 100°C, vacuum dehydrated at -0.1 MPa for 1.5 h, cooled to 40°C, added with 0.4 mol of diisocyanate, stirred and heated to 90°C, kept warm for 2 h, cooled to 45°C, then added with 5 mol of acetone, stirred and heated to 75°C for 6 h, cooled to 10°C, added with 0.039 mol of triethylamine and 14 mol of acetone, stirred for 25 min, and obtained a prepolymer; the small molecule chain extender was 2,3,5,6-tetramethyl-1,4-dioxacyclo-2,5-diol. The hydrophilic chain extender was dimethylol propionic acid. The diisocyanate was isophorone diisocyanate. The polyether diol has a hydroxyl value of 36-39KOH / g and a molecular weight of 3000. It is purchased from Jining Tangyi Chemical Co., Ltd., DL series products. The polycarbonate diol is a mixture of a polycarbonate diol with an average molecular weight of 2000, a polycarbonate diol with an average molecular weight of 3000, and a polycarbonate diol with an average molecular weight of 500 in a weight ratio of 1:1.4:0.3; it is purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0028] (2) Emulsification process: add 27 mol of ice-water mixture to the prepolymer prepared in step (1) at a high speed of 1500 r / min, continue stirring for 20 min, then adjust the speed to 400 r / min, add ethylenediamine aqueous solution (the volume ratio of ethylenediamine to water is 1:8, and the molar number of ethylenediamine is 0.004 mol), and continue stirring for 3 h to obtain an emulsion;

[0029] (3) Desolventization process: The emulsion of step (2) is heated to 45°C, and the acetone in the emulsion is removed under -0.09 MPa to obtain a water-based polyurethane resin for heat transfer ink.

[0030] The preparation method of the modified polycarbonate diol comprises the following steps: S1: Under a nitrogen atmosphere, 35 parts by weight of a mixed polyol, 10 parts by weight of diethylenetriamine and KOH are mixed, wherein the amount of KOH added accounts for 0.4% of the total weight of the materials in step (1); the temperature is raised to 140°C, 390 parts by weight of propylene oxide are added dropwise, and after the addition is completed, the reaction is continued at 135°C for 4 hours under a pressure of 0.3 MPa, the temperature is lowered to 120°C, the temperature is kept for 1.5 hours, and the material is discharged after cooling to obtain a hydrophilic polyether; the mixed polyol comprises ethylene glycol, propylene glycol and 1,4-butanediol in a weight ratio of 1:1.4:0.3; S2: adding water which accounts for 7% of the weight of the hydrophilic polyether to the hydrophilic polyether, heating to 76° C., adjusting the pH to 4.5 with phosphoric acid, removing water under reduced pressure, filtering, and obtaining an acidified polyether; S3: Under a nitrogen atmosphere, 10 parts by weight of NaOH and 1.4 parts by weight of CaCl 2 , 0.5 parts by weight of tetraethylammonium chloride, a phase transfer catalyst, and 90 parts by weight of an acidified polyether are mixed, 17 parts by weight of epichlorohydrin are added dropwise, after the addition is completed, the reaction is carried out at 35° C. for 8 hours, the solid salt is filtered out, phosphoric acid is used to neutralize the pH to 7, and the unreacted epichlorohydrin is removed under reduced pressure to obtain an epoxy-terminated hydrophilic polyether; S4: Evenly mix epoxy-terminated hydrophilic polyether, 3-aminopropane sulfonic acid and 0.1 mol / L hydrochloric acid aqueous solution in a weight ratio of 6:25:500, react at 90° C. for 3 h, neutralize to a neutral pH, and remove water by vacuum rotary evaporation to obtain a sulfonated polyether; S5: Mix polycarbonate diol, sulfonated polyether and toluene in a weight ratio of 20:7:420, react at 65°C for 6 hours, and after the reaction, recover toluene by rotary evaporation under reduced pressure, wash with anhydrous ethanol, and dry to obtain modified polycarbonate diol.

[0031] Comparative Example 1 The difference between this comparative example and Example 1 is that the modified polycarbonate diol is replaced by polycarbonate diol.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is that the mixed polyol includes ethylene glycol, propylene glycol and 1,4-butanediol in a weight ratio of 1:1:1.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that the polyether diol is replaced by modified polycarbonate diol.

[0034] Comparative Example 4 The difference between this comparative example and Example 1 is that the polycarbonate diol is a mixture of a polycarbonate diol with an average molecular weight of 2000, a polycarbonate diol with an average molecular weight of 3000 and a polycarbonate diol with an average molecular weight of 500 in a weight ratio of 1:1:1; the polycarbonate diol is purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0035] Comparative Example 5 The difference between this comparative example and Example 1 is that the modified polycarbonate diol is replaced by polyether diol.

[0036] Comparative Example 6 The difference between this comparative example and Example 1 is that the water-based polyurethane resin used for heat transfer ink is a commercially available product purchased from Shanghai MacLean Biochemical Technology Co., Ltd., item number A909856.

[0037] Performance Testing The digital heat transfer ink was prepared according to the following weight percentage formula: 18% of the aqueous polyurethane resin prepared in Examples 1-2 and Comparative Examples 1-6, 3% of oxidized starch, 25% of pigment paste, 2% of nonionic surfactant (fatty alcohol polyoxyethylene ether AEO-9), 2% of propylene glycol, and the balance was deionized water. The preparation method is: under stirring conditions, the pigment paste, propylene glycol and other components are sequentially added to the deionized water, stirred and mixed evenly, and filtered through a 0.45 μm microporous filter membrane to obtain the digital heat transfer ink.

[0038] (1) Fluency test. Load the digital heat transfer ink into the printer, clean the nozzle before printing, ensure that there is no needle or thread breakage during printing, and continuously print color blocks on the PET transfer film under the same normal printing conditions. The printing length is 5 meters. After printing, print a test strip to observe whether there is any needle or thread breakage.

[0039] (2) Standby test. After the digital heat transfer ink completes the continuous printing task in test (1), clean the nozzle and wait for 3 hours. Then perform the same regular printing task to observe whether there is any broken needle or thread.

[0040] (3) Stability test: Place the digital heat transfer ink in a sealed aging test bottle and bake it in a 60°C constant temperature oven for 14 days. Then load the aged ink into the printer for a fluidity test to check for broken needles and threads.

[0041] (4) Color fastness test. Use a heat press machine to heat-print the heat transfer sample obtained in test (2) onto a polyester-cotton blended fabric (polyester:cotton blend ratio 50 / 50) at 220°C for 20 seconds. Use the hot-printed polyester-cotton blended fabric as the test sample and measure the color fastness to rubbing in accordance with GB / T3920-2008 and the color fastness to washing in accordance with GB / T 5713-2013.

[0042] Table 1 Performance test results

[0043] It can be seen from the above performance test results that the heat transfer ink prepared by the water-based polyurethane of Examples 1-2 has good high temperature resistance, hydrolysis resistance and high fluidity.

[0044] However, the comparative examples are obviously inferior to the embodiments in the corresponding performance tests because they do not adopt the necessary technical solutions. In comparative example 1, the polycarbonate diol is not modified, and it can be seen that the high temperature resistance and hydrolysis resistance effects are reduced. In comparative example 2, the ratio of the mixed polyol is changed, and the wet rubbing color fastness is reduced. In comparative example 3, no polyether diol is added, and the wet rubbing color fastness and hydrolysis resistance are reduced. In comparative example 4, the composition of the polycarbonate diol is different, and the wet rubbing color fastness and hydrolysis resistance are reduced. In comparative example 5, only polyether diol is used, and the smoothness is reduced. In comparative example 6, commercially available water-based polyurethane is used, and the comprehensive effect is worse than the product prepared by the present invention. The above experimental results further prove the importance of the technical solution defined in the present invention for its technical effect.

[0045] The above is 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 the scope of protection of the present invention.

Claims

1. A method for preparing a water-based polyurethane resin for heat transfer ink, characterized in that: The following steps are involved: (1) Preparation of prepolymer: 0.03-0.05 mol of modified polycarbonate diol, 0.01-0.02 mol of polyether diol, 0.015-0.02 mol of hydrophilic chain extender and 0.04-0.06 mol of small molecule chain extender are mixed, heated to 90-100°C, vacuum dehydrated, cooled to 20-40°C, added with 0.3-0.4 mol of diisocyanate, stirred and heated to 80-90°C, kept warm for reaction for 2-3 hours, cooled to 45-65°C, added with 3-5 mol of acetone, stirred and heated to 75-80°C for reaction for 4-6 hours, cooled to 10-20°C, added with 0.037-0.039 mol of triethylamine and 12-14 mol of acetone, stirred for 25-35 minutes, and obtained a prepolymer; (2) Emulsification process: Stir the prepolymer of step (1) at a speed of 1400-1500 r / min, add 27-30 mol of ice-water mixture, continue stirring for 15-20 min, then adjust the speed to 400-500 r / min, add ethylenediamine aqueous solution, and continue stirring for 3-5 h to obtain an emulsion; (3) Desolventization process: The emulsion of step (2) is heated to 40-45°C to remove acetone to obtain a water-based polyurethane resin for heat transfer ink.

2. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 1, characterized in that: The preparation method of the modified polycarbonate diol comprises the following steps: S1: Under a nitrogen atmosphere, 35-37 parts by weight of a mixed polyol, 10 parts by weight of diethylenetriamine and KOH are mixed, the temperature is raised to 135-140° C., 390-400 parts by weight of propylene oxide are added dropwise, and after the addition is completed, the reaction is continued at 135-140° C. for 3-4 hours, the temperature is lowered to 110-120° C., the temperature is kept for 1-1.5 hours, and the material is discharged by cooling to obtain a hydrophilic polyether; S2: adding water in an amount of 5-7% by weight of the hydrophilic polyether to the hydrophilic polyether, heating to 72-76° C., adjusting the pH to 4.5-5.0, removing water under reduced pressure, filtering, and obtaining an acidified polyether; S3: Under a nitrogen atmosphere, 10 parts by weight of NaOH, 1.2-1.4 parts by weight of CaCl2, 0.4-0.5 parts by weight of a phase transfer catalyst, and 90-93 parts by weight of an acidified polyether are mixed, and 15-17 parts by weight of epichlorohydrin are added dropwise. After the addition is completed, the reaction is carried out at 30-35° C. for 6-8 hours, and the pH value is neutralized to 7. Unreacted epichlorohydrin is removed under reduced pressure to obtain an epoxy-terminated hydrophilic polyether; S4: Evenly mix epoxy-terminated hydrophilic polyether, 3-aminopropane sulfonic acid and hydrochloric acid aqueous solution in a weight ratio of 6: (22-25): (500-520), react at 80-90° C. for 2-3 hours, neutralize to a neutral pH, and remove water by vacuum rotary evaporation to obtain a sulfonated polyether; S5: Mix polycarbonate diol, sulfonated polyether and toluene in a weight ratio of 20:(7-9):(400-420), react at 60-65°C for 6-8h, and after the reaction, wash and dry to obtain modified polycarbonate diol.

3. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 2, characterized in that: The mixed polyol comprises ethylene glycol, glycerol and 1,4-butanediol in a weight ratio of 1:(1.4-1.6):(0.3-0.5).

4. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 2, characterized in that: The volume ratio of ethylenediamine to water in the ethylenediamine aqueous solution is 1:(6-8).

5. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 2, characterized in that: The phase transfer catalyst is tetraethylammonium chloride.

6. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 2, characterized in that: The polycarbonate diol is a mixture of a polycarbonate diol with an average molecular weight of 2000, a polycarbonate diol with an average molecular weight of 3000 and a polycarbonate diol with an average molecular weight of 500 in a weight ratio of 1: (1.4-1.6): (0.3-0.5).

7. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 2, characterized in that: The polyether diol has a hydroxyl value of 36-39 KOH / g and a molecular weight of 3000.

8. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 1, characterized in that: The hydrophilic chain extender is dimethylol propionic acid.

9. The method for preparing water-based polyurethane resin for heat transfer ink according to claim 1, characterized in that: The diisocyanate is selected from one or more of toluene diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate.

10. A water-based polyurethane resin for heat transfer ink prepared by the preparation method according to any one of claims 1 to 9.

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