A stable-performance ink for watercolor pens and its preparation process

Abstract

The present invention relates to the technical field of ink, and specifically to an ink for watercolor pens with stable performance and its preparation process. It includes the following steps: Step 1: Mix itaconic acid and octylphenol polyoxyethylene ether OP-10 evenly; add sulfuric acid, and esterify at 90-95°C for 4-5 hours, neutralize and purify to obtain a dispersant; Step 2: Modify polyvinylpyrrolidone with acrylamide and itaconic acid monoester to obtain modified polyvinylpyrrolidone; Step 3: Disperse the organic pigment in deionized water, add the dispersant and stir evenly to obtain Solution A; Disperse titanium dioxide in deionized water, add the modified polyvinylpyrrolidone and stir evenly to obtain Solution B; Mix Solution B and Solution A evenly, add a cosolvent and an antifoaming agent, and homogenize to obtain a color paste; Step 4: Stir the color paste and the aqueous polymer emulsion evenly, add a cosolvent, a dispersant and an antifoaming agent, and homogenize to obtain the ink for watercolor pens.

Description

Technical Field

[0001] The present invention relates to the technical field of inks, and specifically to an ink for watercolor pens with stable performance and a preparation process thereof. Background Art

[0002] A watercolor pen is a stationery used for painting sketches, symbol marking, and engineering design. The key lies in the ink for watercolor pens, which mainly includes components such as dyes, solvents, and additives; at the same time, a water-based polymer resin is usually introduced as a binder to enhance the viscosity, adhesion, and color gloss of the ink.

[0003] In the prior art, there are the following problems. On the one hand, the performance of the color paste containing dyes is poor; on the other hand, the affinity between the color paste containing dyes and the introduced water-based polymer resin is poor; and the water-based polymer resin can only be partially dissolved in water, resulting in easy phase separation between the two, reducing the stability of the ink for watercolor pens, and thus causing a decrease in the painting smoothness during use, partial color accumulation during multiple depictions, uneven color painting, and paper penetration phenomenon.

[0004] In summary, solving the above problems, improving the stability of the water-based polymer resin, enhancing the affinity between the color paste and the resin, reducing the phase separation between the two, and preparing an ink for watercolor pens with stable performance are of great significance. Summary of the Invention

[0005] The purpose of the present invention is to provide an ink for watercolor pens with stable performance and a preparation process thereof to solve the problems raised in the above background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A preparation process of an ink for watercolor pens with stable performance, comprising the following steps:

[0008] Step 1: Mix itaconic acid and octylphenol polyoxyethylene ether OP-10 evenly; add sulfuric acid, and esterify at 90 - 95 °C for 4 - 5 hours, neutralize, and purify to obtain a dispersant;

[0009] Step 2: Dissolve polyvinylpyrrolidone in deionized water, add acrylamide and itaconic acid monoester, stir evenly, add ammonium cerium nitrate to obtain a reaction solution; carry out microwave reaction on it to obtain modified polyvinylpyrrolidone;

[0010] Step 3: Disperse organic pigments in deionized water, add a dispersant and stir evenly to obtain solution A; disperse titanium dioxide in deionized water, add modified polyvinylpyrrolidone and stir evenly to obtain solution B; mix solution B and solution A evenly, add a cosolvent and an antifoaming agent, and homogenize to obtain a color paste;

[0011] Step 4: Stir the color paste and the aqueous polymer emulsion evenly, add a cosolvent, a dispersant, and an antifoaming agent, and homogenize to obtain the ink for watercolor pens.

[0012] Preferably, the color paste comprises the following components: by weight, 10-14 parts of an organic pigment, 18-20 parts of deionized water, 3-4 parts of a dispersant, 0.5-0.7 parts of titanium dioxide, 2-3 parts of modified polyvinylpyrrolidone, 2-5 parts of a cosolvent, and 0.1-0.2 parts of an antifoaming agent; the cosolvent includes one or more of ethanol, ethylene glycol, propylene glycol, and butylene glycol.

[0013] Preferably, the ink comprises the following components: by weight, 20-25 parts of a color paste, 75-95 parts of an aqueous polymer emulsion, 5-10 parts of a cosolvent, 0.2-0.5 parts of a dispersant, and 0.2-0.5 parts of an antifoaming agent.

[0014] Preferably, the raw materials of the dispersant comprise the following components: by weight, 2-2.2 parts of itaconic acid, 10-11 parts of octylphenol polyoxyethylene ether OP-10, and 0.2-0.3 parts of sulfuric acid.

[0015] Preferably, the raw materials of the modified polyvinylpyrrolidone comprise the following components: by weight, 20 parts of polyvinylpyrrolidone, 1-2 parts of acrylamide, 1-2 parts of itaconic acid monoester, 0.2-0.5 parts of ammonium cerium nitrate, and 80-90 parts of deionized water; the itaconic acid monoester includes one or two of itaconic acid monomethyl ester and itaconic acid monoethyl ester.

[0016] Preferably, the conditions of the microwave reaction are: under a nitrogen atmosphere, the temperature is 60-65°C, the microwave power is 700-800W, and the time is 2-3 minutes.

[0017] Preferably, the preparation process of the aqueous polymer emulsion is: under a nitrogen atmosphere, stir poly(1,4-butanediol adipate) diol and dibutyltin dilaurate evenly, drop isophorone diisocyanate at 60-100°C, and react for 1.5-3 hours; add 1,4-butanediol and 2-(diethanolamino)ethanesulfonic acid sodium; and add an acrylic monomer mixture to reduce the viscosity; when the content of the NCO group in the reaction system is 2-8 wt%, add hydroxypropyl acrylate for end-capping to obtain an acrylate solution containing unsaturated polyurethane macromolecules; cool the unsaturated polyurethane macromolecules to 40-50°C, add an initiator and a surfactant solution; stir evenly, and react at 70-90°C for 2-4 hours under a nitrogen atmosphere, then cool down and add deionized water for dilution to obtain an aqueous polymer emulsion with a solid content of 25-30 wt%.

[0018] Preferably, the raw materials of the aqueous polymer emulsion include the following components: by weight, 100 parts of poly(1,4-butylene adipate) diol, 0.5 - 0.8 part of dibutyltin dilaurate, 85 - 90 parts of isophorone diisocyanate, 5 - 7 parts of 1,4-butanediol, 3 - 5 parts of 2-(diethanolamino)ethanesulfonic acid sodium salt, 130 - 155 parts of acrylic monomer mixture, 20 - 25 parts of hydroxypropyl acrylate, 1.5 - 2 parts of initiator, and 503.5 - 505 parts of surfactant solution.

[0019] Preferably, the acrylic monomer mixture includes the following components: 60 - 70 parts of butyl acrylate, 60 - 70 parts of methyl methacrylate, 7 - 10 parts of acrylic acid, and 3 - 5 parts of itaconic acid monoester; the surfactant solution includes the following components: 1 - 1.5 parts of dispersant, 1 - 1.5 parts of octylphenol polyoxyethylene ether OP-10, 1.5 - 2 parts of sodium dodecylbenzenesulfonate, and 500 parts of deionized water.

[0020] Preferably, an ink for watercolor pens prepared by a preparation process of an ink for watercolor pens with stable performance.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) A dispersant with a relatively large molecular weight is introduced into the color paste, which enhances the dispersion performance while increasing the consistency of the color paste and reducing its sedimentation and migration performance; thereby improving the stability of the color paste; the dispersant is based on octylphenol polyoxyethylene ether OP-10 (a non-ionic surfactant), and a dispersant with a relatively large molecular weight is prepared through its esterification reaction with itaconic acid; due to the presence of a hydrophobic spacer molecule (generated after grafting itaconic acid), the interfacial packing property is enhanced, which helps to reduce the molecular cross-sectional area and improve the adsorption of organic pigments, thereby improving the dispersion of organic pigments. At the same time, due to the relatively large molecular weight, the consistency of the color paste is increased, thereby improving the dispersion stability.

[0023] (2) Titanium dioxide is introduced into the color paste, which can enhance the color vividness, improve the coloring ability, and at the same time; maliciously improve the ultraviolet resistance and water permeability; however, it also has aggregation; therefore, polyvinylpyrrolidone is used for modification to inhibit its aggregation; at the same time, due to the presence of pyrrolidone groups on the side chain of polyvinylpyrrolidone, acrylamide and itaconic acid monoester are grafted, making it have hydrophilic groups and certain ester groups, further promoting the dispersion and stability of the color paste.

[0024] (3) In the scheme, an aqueous polymer emulsion is prepared, which is a hybrid emulsion of polyurethane - polyacrylate; increasing its dispersion and stability, and at the same time enhancing the affinity with the color paste. Thereby ensuring the stability of the ink.

[0025] Among them, the aqueous polymer emulsion is prepared by using poly(butylene adipate) diol as a polyol, and at the same time, sodium 2-(diethanolamino)ethanesulfonate is introduced as a chain extender. The introduction of the amino sulfonate contained therein increases the urea bond content in the system, further increases the intramolecular hydrogen bond density, and can effectively inhibit feathering and water permeability; and it is capped with hydroxypropyl acrylate (added in excess, and the excess serves as a reaction monomer), and it is hybridized with the acrylic acid mixed monomer to form a polyurethane-polyacrylate hybrid emulsion.

[0026] Among them, sodium 2-(diethanolamino)ethanesulfonate can act as a surfactant during the subsequent copolymerization of polyacrylate. Among the surfactants, the prepared dispersant is introduced, which contains double bonds and can act as a reactive dispersant, thereby reducing the particle size of the polymer emulsion and improving the dispersibility of the aqueous polymer emulsion. At the same time, it has similarity with the dispersant in the color paste, thereby improving the affinity between the color paste and the aqueous polymer emulsion and reducing the interfacial separation. Specific embodiments

[0027] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] It should be noted that there are no special restrictions on the purchasing manufacturers of all raw materials involved in the present invention. Exemplarily, it includes: in the following embodiments, the average molecular weight of polyvinylpyrrolidone is 5500; the product number of titanium dioxide is N107, provided by Jinan Dehou Chemical Co., Ltd.; the organic pigment is Pigment Yellow 180; the CAS number of butyl acrylate is 141-32-2, the CAS number of methyl methacrylate is 80-62-6, acrylic acid 79-10-7, the CAS number of sodium 2-(diethanolamino)ethanesulfonate is 66992-27-6; the CAS number of isophorone diisocyanate is 16672-87-0; the CAS number of itaconic acid is 97-65-4; the sulfuric acid concentration is 98%, acrylamide 79-06-1; the CAS number of monoethyl itaconate is 57718-07-7; the product number of poly(butylene adipate) diol is YK0106, provided by Hubei Yongkuo Technology Co., Ltd.

[0029] Example 1: A preparation process of an ink for watercolor pens with stable performance, including the following steps:

[0030] Step 1: Mix 2 parts of itaconic acid and 10 parts of octylphenol polyoxyethylene ether OP-10 evenly; add 0.25 parts of sulfuric acid, esterify at 90 °C for 4 hours, add ammonia water to neutralize the pH, and purify to obtain a dispersant;

[0031] Step 2: Dissolve 20 parts of polyvinylpyrrolidone in 90 parts of deionized water, add 1 part of acrylamide and 1.5 parts of monoethyl itaconate, stir evenly, add 0.4 parts of ammonium cerium nitrate to obtain a reaction solution; carry out the reaction under a nitrogen atmosphere at a temperature of 60 °C and a microwave power of 800 W for 3 minutes; obtain modified polyvinylpyrrolidone;

[0032] Under a nitrogen atmosphere, stir 100 parts of poly(adipic acid-1,4-butanediol)diol and 0.6 parts of dibutyltin dilaurate evenly, dropwise add 85 parts of isophorone diisocyanate at 60 - 100 °C, and react for 1.5 - 3 hours; add 5 parts of 1,4-butanediol and 5 parts of 2-(diethanolamino)ethanesulfonic acid sodium; and add 145 parts of acrylic monomer mixture (65 parts of butyl acrylate, 65 parts of methyl methacrylate, 10 parts of acrylic acid, 5 parts of monoethyl itaconate) to reduce the viscosity; when the content of NCO groups in the reaction system is 6 wt%, add 25 parts of hydroxypropyl acrylate for capping to obtain an acrylate solution containing unsaturated polyurethane macromolecules; cool the unsaturated polyurethane macromolecules to 40 - 50 °C, add 1.8 parts of benzoyl peroxide and 504 parts of surfactant solution (1.5 parts of dispersant, 1 part of octylphenol polyoxyethylene ether OP-10, 1.5 parts of sodium dodecylbenzenesulfonate, 500 parts of deionized water); stir evenly, react at 80 °C for 3 hours under a nitrogen atmosphere, cool down, and add deionized water for dilution to obtain an aqueous polymer emulsion with a solid content of 25 wt%;

[0033] Step 4: Disperse 12 parts of organic pigment in 12 parts of deionized water, add 3.5 parts of dispersant and stir evenly to obtain solution A; disperse 0.5 parts of titanium dioxide in 8 parts of deionized water, add 2.5 parts of modified polyvinylpyrrolidone and stir evenly to obtain solution B; mix solution B and solution A evenly, add 4 parts of ethylene glycol and 0.2 parts of defoamer DF-114, and grind and homogenize to obtain a color paste;

[0034] Step 5: Stir 20 parts of the color paste and 80 parts of the aqueous polymer emulsion evenly, add 6 parts of ethylene glycol, 0.5 parts of dispersant, and 0.3 parts of defoamer DF-114, and homogenize to obtain the ink for watercolor pens.

[0035] Example 2: A preparation process of ink for watercolor pens with stable performance, including the following steps:

[0036] Step 1: Mix 2 parts of itaconic acid and 10 parts of octylphenol polyoxyethylene ether OP-10 evenly; add 0.25 parts of sulfuric acid, esterify at 90 °C for 4 hours, add ammonia water to neutralize the pH, and purify to obtain a dispersant;

[0037] Step 2: Dissolve 20 parts of polyvinylpyrrolidone in 90 parts of deionized water, add 1 part of acrylamide and 1.5 parts of monoethyl itaconate, stir evenly, add 0.4 parts of ammonium cerium nitrate to obtain a reaction solution; carry out the reaction under a nitrogen atmosphere at a temperature of 60 °C and a microwave power of 800 W for 3 minutes; obtain modified polyvinylpyrrolidone;

[0038] Under a nitrogen atmosphere, stir 100 parts of poly(adipic acid-1,4-butanediol)diol and 0.6 parts of dibutyltin dilaurate evenly, dropwise add 85 parts of isophorone diisocyanate at 60 - 100 °C, and react for 1.5 - 3 hours; add 5 parts of 1,4-butanediol and 5 parts of 2-(diethanolamino)ethanesulfonic acid sodium; and add 145 parts of acrylic monomer mixture (65 parts of butyl acrylate, 65 parts of methyl methacrylate, 10 parts of acrylic acid, 5 parts of monoethyl itaconate) to reduce the viscosity; when the content of NCO groups in the reaction system is 6 wt%, add 25 parts of hydroxypropyl acrylate for capping to obtain an acrylate solution containing unsaturated polyurethane macromolecules; cool the unsaturated polyurethane macromolecules to 40 - 50 °C, add 1.8 parts of benzoyl peroxide and 504 parts of surfactant solution (1.5 parts of dispersant, 1 part of octylphenol polyoxyethylene ether OP-10, 1.5 parts of sodium dodecylbenzenesulfonate, 500 parts of deionized water); stir evenly, react at 80 °C for 3 hours under a nitrogen atmosphere, cool down, and add deionized water for dilution to obtain an aqueous polymer emulsion with a solid content of 25 wt%;

[0039] Step 4: Disperse 10 parts of organic pigment in 10 parts of deionized water, add 3 parts of dispersant and stir evenly to obtain solution A; disperse 0.7 parts of titanium dioxide in 8 parts of deionized water, add 3 parts of modified polyvinylpyrrolidone and stir evenly to obtain solution B; mix solution B and solution A evenly, add 2 parts of ethylene glycol and 0.2 parts of defoamer DF-114, and grind and homogenize to obtain a color paste;

[0040] Step 5: Mix 25 parts of color paste and 75 parts of aqueous polymer emulsion evenly, add 10 parts of ethylene glycol, 0.2 parts of dispersant, and 0.3 parts of defoamer DF-114, and homogenize to obtain the ink for watercolor pens.

[0041] Example 3: A preparation process of an ink for watercolor pens with stable performance, including the following steps:

[0042] Step 1: Mix 2 parts of itaconic acid and 10 parts of octylphenol polyoxyethylene ether OP-10 evenly; add 0.25 part of sulfuric acid, esterify at 90 °C for 4 hours, add ammonia water to neutralize the pH, and purify to obtain a dispersant;

[0043] Step 2: Dissolve 20 parts of polyvinylpyrrolidone in 90 parts of deionized water, add 1 part of acrylamide and 1.5 parts of monoethyl itaconate, stir evenly, add 0.4 part of ammonium cerium nitrate to obtain a reaction solution; carry out the reaction under a nitrogen atmosphere at a temperature of 60 °C and a microwave power of 800 W for 3 minutes; obtain modified polyvinylpyrrolidone;

[0044] Step 3: Under a nitrogen atmosphere, stir 100 parts of poly(adipic acid-1,4-butanediol) diol and 0.6 part of dibutyltin dilaurate evenly, dropwise add 85 parts of isophorone diisocyanate at 60 - 100 °C, and react for 1.5 - 3 hours; add 5 parts of 1,4-butanediol and 5 parts of 2-(diethanolamino)ethanesulfonic acid sodium; and add 145 parts of acrylic monomer mixture (65 parts of butyl acrylate, 65 parts of methyl methacrylate, 10 parts of acrylic acid, 5 parts of monoethyl itaconate) to reduce the viscosity; when the content of NCO groups in the reaction system is 6 wt%, add 25 parts of hydroxypropyl acrylate for capping to obtain an acrylate solution containing unsaturated polyurethane macromolecules; cool the unsaturated polyurethane macromolecules to 40 - 50 °C, add 1.8 parts of benzoyl peroxide and 504 parts of surfactant solution (1.5 parts of dispersant, 1 part of octylphenol polyoxyethylene ether OP-10, 1.5 parts of sodium dodecylbenzenesulfonate, 500 parts of deionized water); stir evenly, react at 80 °C for 3 hours under a nitrogen atmosphere, cool down, and add deionized water for dilution to obtain an aqueous polymer emulsion with a solid content of 25 wt%;

[0045] Step 4: Disperse 14 parts of organic pigment in 15 parts of deionized water, add 4 parts of dispersant and stir evenly to obtain solution A; disperse 0.5 part of titanium dioxide in 5 parts of deionized water, add 2 parts of modified polyvinylpyrrolidone and stir evenly to obtain solution B; mix solution B and solution A evenly, add 5 parts of ethylene glycol and 0.2 part of defoamer DF-114, and grind and homogenize to obtain a color paste;

[0046] Step 5: Mix 20 parts of the color paste and 95 parts of the aqueous polymer emulsion evenly, add 5 parts of ethylene glycol, 0.5 part of dispersant, and 0.3 part of defoamer DF-114, and homogenize to obtain the ink for watercolor pens.

[0047] Comparative Example 1: Replace the dispersant in Example 1 with an equal mass of octylphenol polyoxyethylene ether OP-10, and the other steps are the same as in Example 1 to obtain the ink for watercolor pens.

[0048] Comparative Example 2: The polyvinyl pyrrolidone in Example 1 was replaced by polyvinyl pyrrolidone of equal mass, and the rest of the steps were the same as in Example 1 to obtain ink for watercolor pens.

[0049] Comparative Example 3: The preparation process of the aqueous polymer emulsion is changed to: under a nitrogen atmosphere, 65 parts of butyl acrylate, 65 parts of methyl methacrylate, 10 parts of acrylic acid, 5 parts of monoethyl itaconate, 25 parts of hydroxypropyl acrylate, and 5 parts of sodium 2-sulfonate ethyl undec-10-enoate are mixed evenly, and 1.8 parts of benzoyl peroxide and 204 parts of a surfactant solution (1.5 parts of a dispersant, 1 part of octylphenol polyoxyethylene ether OP-10, 1.5 parts of sodium dodecylbenzene sulfonate, and 200 parts of deionized water) are added; the mixture is stirred evenly, reacted at 80° C. for 3 hours under a nitrogen atmosphere, cooled, and deionized water is added for dilution to obtain an aqueous polymer emulsion with a solid content of 25wt%; the remaining steps are the same as in Example 1 to obtain ink for a watercolor pen.

[0050] Comparative Example 4: The monoethyl itaconate in Example 1 was replaced by an equal amount of itaconic acid; the sodium 2-(diethanolamino)ethanesulfonate was replaced by an equal amount of diethanolamine; the remaining steps were the same as in Example 1 to obtain ink for watercolor pens.

[0051] Experiment: The properties of the watercolor pen ink in the embodiment and the comparative example were tested. (1) Stability test: The watercolor pen ink was added to a centrifuge tube and centrifuged at 3000r / min for 30 minutes. After centrifugation, it was allowed to stand for 5 minutes. The maximum absorbance of the sample before and after centrifugation was tested, recorded as A0 and A1. The relative absorbance R% = A1 / A0×100% was then calculated and used as the centrifugal stability index. (2) Usability test: 2g of watercolor pen ink was made into a watercolor pen. It was placed on 70g of copy paper and a 5cm straight line was overlapped 12 times to see if the following problems occurred: paper damage, partial accumulation of color, and uneven color. The data obtained are shown below:

[0052] Stability % Surface condition Example 1 98.3 No damage, no color accumulation Example 2 97.5 No damage, no color accumulation Example 3 96.9 No damage, no color accumulation Comparative Example 1 90.3 Slight damage, color accumulation Comparative Example 2 91.4 No damage, color accumulation Comparative Example 3 88.1 No damage, color accumulation Comparative Example 4 90.6 Slight damage, color accumulation

[0053] Conclusion: According to the data in the above table, it is shown that the present invention effectively increases the dispersibility of the color paste by introducing the prepared dispersant and modified polyvinyl pyrrolidone into the color paste. At the same time, the aqueous polymer emulsion that is compatible with the color paste is synergistically used to increase the dispersibility and fluidity, thereby improving the color uniformity of the ink.

[0054] Comparisons of the data in Comparative Examples 1 to 4 with those in Example 1 show the following conclusions: As can be seen from Comparative Example 1, compared with directly using octylphenol polyoxyethylene ether OP-10, the dispersant prepared in the solution can effectively enhance the dispersion stability and improve the paintability. From Comparative Example 2, it can be seen that using modified polyvinylpyrrolidone can effectively increase the dispersibility and improve the affinity with the aqueous polymer emulsion, thereby enhancing the stability and paintability. From Comparative Example 3, it can be seen that using acrylic emulsion alone leads to a decrease in stability. From Comparative Example 4, it can be seen that monoethyl itaconate and 2-(diethanolamino)ethanesulfonic acid effectively increase the dispersibility and paint performance of the ink.

[0055] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation process of ink for watercolor pens with stable performance, characterized in that: It includes the following steps: Step 1: Mix itaconic acid and octylphenol polyoxyethylene ether OP-10 evenly; add sulfuric acid, esterify at 90-95°C for 4-5 hours, neutralize and purify to obtain a dispersant. Step 2: Dissolve polyvinylpyrrolidone in deionized water, add acrylamide and itaconic acid monoester, stir evenly, add ammonium cerium nitrate to obtain a reaction solution; carry out microwave reaction on it to obtain modified polyvinylpyrrolidone. Step 3: Disperse organic pigment in deionized water, add dispersant and stir evenly to obtain solution A; disperse titanium dioxide in deionized water, add modified polyvinylpyrrolidone and stir evenly to obtain solution B; mix solution B and solution A evenly, add cosolvent and defoamer, and homogenize to obtain a color paste. Step 4: Mix the color paste and aqueous polymer emulsion evenly, add cosolvent, dispersant and defoamer, and homogenize to obtain the ink for watercolor pen. The raw materials of the modified polyvinylpyrrolidone include the following components: by weight, 20 parts of polyvinylpyrrolidone, 1-2 parts of acrylamide, 1-2 parts of itaconic acid monoester, 0.2-0.5 parts of ammonium cerium nitrate, 80-90 parts of deionized water; the itaconic acid monoester includes one or two of methyl itaconate and ethyl itaconate. The preparation process of the aqueous polymer emulsion is as follows: under a nitrogen atmosphere, stir poly(1,4-butanediol adipate) diol and dibutyltin dilaurate evenly, dropwise add isophorone diisocyanate at 60-100°C, and react for 1.5-3 hours; add 1,4-butanediol and 2-(diethanolamino)ethanesulfonic acid sodium; and add a mixture of acrylic monomers to reduce the viscosity; when the content of NCO groups in the reaction system is 2-8 wt%, add hydroxypropyl acrylate for capping to obtain an acrylate solution containing unsaturated polyurethane macromolecules; cool the acrylate solution containing unsaturated polyurethane macromolecules to 40-50°C, add initiator and surfactant solution; stir evenly, under a nitrogen atmosphere, react at 70-90°C for 2-4 hours, cool down, and add deionized water for dilution to obtain an aqueous polymer emulsion with a solid content of 25-30 wt%.

2. The preparation process of an ink for watercolor pens with stable performance according to claim 1, characterized in that: The color paste includes the following components: by weight, 10-14 parts of organic pigment, 18-20 parts of deionized water, 3-4 parts of dispersant, 0.5-0.7 parts of titanium dioxide, 2-3 parts of modified polyvinylpyrrolidone, 2-5 parts of cosolvent, 0.1-0.2 parts of defoamer; the cosolvent includes one or more of ethanol, ethylene glycol, propylene glycol and butanediol.

3. The preparation process of an ink for watercolor pens with stable performance according to claim 1, characterized in that: The ink includes the following components: by weight, 20-25 parts of color paste, 75-95 parts of aqueous polymer emulsion, 5-10 parts of cosolvent, 0.2-0.5 parts of dispersant, 0.2-0.5 parts of defoamer.

4. The preparation process of an ink for watercolor pens with stable performance according to claim 1, characterized in that: The raw materials of the dispersant include the following components: by weight, 2-2.2 parts of itaconic acid, 10-11 parts of octylphenol polyoxyethylene ether OP-10, 0.2-0.3 parts of sulfuric acid.

5. The preparation process of an ink for watercolor pens with stable performance according to claim 1, characterized in that: The conditions of the microwave reaction are: under a nitrogen atmosphere, the temperature is 60-65°C, the microwave power is 700-800W, and the time is 2-3 minutes.

6. The preparation process of an ink for watercolor pens with stable performance according to claim 1, characterized in that: The raw materials of the aqueous polymer emulsion include the following components: by weight, 100 parts of poly(1,4-butylene adipate)diol, 0.5 - 0.8 part of dibutyltin dilaurate, 85 - 90 parts of isophorone diisocyanate, 5 - 7 parts of 1,4-butanediol, 3 - 5 parts of 2-(diethanolamino)ethanesulfonic acid sodium salt, 130 - 155 parts of acrylic monomer mixture, 20 - 25 parts of hydroxypropyl acrylate, 1.5 - 2 parts of initiator, and 503.5 - 505 parts of surfactant solution.

7. The preparation process of an ink for watercolor pens with stable performance according to claim 1, characterized in that: The acrylic monomer mixture includes the following components: 60 - 70 parts of butyl acrylate, 60 - 70 parts of methyl methacrylate, 7 - 10 parts of acrylic acid, and 3 - 5 parts of monoester of itaconic acid; the surfactant solution includes the following components: 1 - 1.5 parts of dispersant, 1 - 1.5 parts of octylphenol polyoxyethylene ether OP-10, 1.5 - 2 parts of sodium dodecylbenzenesulfonate, and 500 parts of deionized water.

8. An ink for watercolor pens prepared by the preparation process of an ink for watercolor pens with stable performance according to any one of claims 1 - 7.