Preparation method of choline modified polyurethane aqueous dispersion

Abstract

The invention relates to the technical field of high polymer materials, in particular to a preparation method of choline modified polyurethane aqueous dispersion. The method comprises the following steps: carrying out a ring-opening reaction on choline and polyether diglycidyl ether which serve as raw materials under the action of a basic catalyst to prepare a quaternary ammonium type diol intermediate, carrying out a polymerization reaction on the quaternary ammonium type diol intermediate and a diisocyanate monomer to form a prepolymer, adding a micromolecule chain extender for chain extension, controlling an R value (OH / NCO) to be 1.05-1.2, finally adding pure water, and carrying out high-speed shearing dispersion, so as to obtain the polyurethane prepolymer. The stable hydroxyl-terminated polyurethane aqueous dispersion is obtained. A choline structure is covalently bonded to a polyurethane main chain through a one-step method to form an embedded quaternary ammonium cation hydrophilic center, post-neutralization is not needed, and the process is simple. The obtained product has excellent ink absorbency, color fastness and yellowing resistance, has excellent compatibility with transition metal ions, solves the problems of easy flocculation and poor stability of the traditional tertiary amine product, and is especially suitable for high-end textile ink-absorbing coatings.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a method for preparing a choline-modified polyurethane aqueous dispersion. Background Technology

[0002] Textile inkjet printing is a method of directly copying images from a computer onto fabric, enabling rapid image development and fixing. Despite its many advantages, inkjet printing also presents some technical challenges, such as poor image quality, ink smudging, poor water resistance, poor colorfastness, and yellowing in blank areas. The key factors affecting image quality and ink smudging are ink absorption and fixation, while poor water resistance and colorfastness are due to the coating's weak adhesion to the fibers. These problems are directly related to the ionicity of the coating. Significant efforts have been made in the market to improve these potential issues. Currently, using cationic treatment solutions to form a cationic ink-absorbing coating on the fabric surface is an effective solution.

[0003] Patent application CN104448116A discloses a cationic emulsion of acrylate polymers using hexadecyltrimethylammonium chloride as an emulsifier. This emulsion can improve the color fastness of dyed fabrics. To ensure the hand feel of the fabric, the glass transition temperature (Tg) of the acrylate polymer is usually between 0-10℃. However, acrylate polymers with low Tg often have the disadvantage of being tacky. Polyurethane can overcome the problem of tackiness caused by low Tg polymers. As an ink-absorbing coating for fabrics, polyurethane is applied in a cationic aqueous dispersion in the fabric treatment solution. Patent application CN103314025A discloses a cationic polyurethane aqueous dispersion that achieves water dispersion by neutralizing tertiary amine groups with acid. The bound tertiary amine groups described therein have better water dispersion performance. In the fabric treatment solution of the ink-absorbing coating, transition metal salts such as calcium chloride and zinc chloride are added to the ink-absorbing coating to synergistically improve the ink absorption performance. However, since the nitrogen atom in the tertiary amine group still has a lone pair of electrons, it will undergo a complexation reaction with transition metal ions, resulting in instability of the treatment solution. In addition, the lone pair of electrons of the nitrogen atom will also cause serious oxidative yellowing problems. Quaternary ammonium salt groups can effectively solve the problems of instability with transition metal ions and oxidative yellowing because the nitrogen atom does not have a lone pair of electrons. Although the invention mentions the quaternization reaction of the tertiary amine groups with organohalides, sulfates and ethylene oxide (epoxides), no specific examples are given. Patent application CN102701999A describes a method of quaternizing tertiary amine groups on the main chain with a quaternizing agent to obtain a cationic polyurethane aqueous dispersion. However, the quaternization reaction on the polyurethane main chain suffers from issues such as low conversion rates of tertiary amines to quaternary ammonium and residual small-molecule quaternizing agents. Furthermore, incomplete conversion of tertiary amines to quaternary ammonium leads to instability with transition metal ions and oxidative yellowing. In addition, patent application CN114144445A describes the preparation of a cationic polyurethane emulsion by adding a quaternary ammonium salt emulsifier to the polyurethane polymer. However, this externally emulsified emulsion exhibits significantly lower ink absorption and storage stability compared to self-emulsified polyurethane aqueous dispersions. Therefore, using quaternary ammonium chain extenders is a direct and effective method. Patent application CN114206971A proposes various quaternary ammonium diol chain extenders, mostly dihydroxyethyl quaternary ammonium salts. However, these are difficult to obtain, with almost no mass-produced products available on the market; only reagent-grade products are available, which are expensive and unsuitable for industrial-scale production of polyurethane aqueous dispersions.

[0004] Therefore, developing a self-emulsifying polyurethane aqueous dispersion that uses readily available raw materials, has a simple process, and can achieve stable and efficient bonding of quaternary ammonium salt groups is of great practical significance for improving the overall performance of ink-absorbing coatings for high-end textiles and promoting industrial applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing choline-modified polyurethane aqueous dispersions to solve the aforementioned technical problems in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a choline-modified polyurethane aqueous dispersion, comprising the following steps: Step (1) Dehydrated polyether diglycidyl ether, choline, and the first catalyst are added to the reactor. After stirring and dissolving, the mixture is heated to the first reaction temperature and kept at the temperature to obtain a quaternary ammonium diol intermediate. In the above process, the hydroxyl groups of choline undergo a ring-opening addition reaction with the two epoxy groups of polyether diglycidyl ether to generate a quaternary ammonium diol with primary hydroxyl groups at both ends and quaternary ammonium cation centers on the side chain.

[0007] Step (2) Adjust to the second reaction temperature, add the second catalyst, and slowly add the diisocyanate monomer, and keep the reaction at the second reaction temperature; In the above process, the hydroxyl groups of the quaternary ammonium diol react with the isocyanate groups (-NCO) of the diisocyanate to form a polyurethane prepolymer with the quaternary ammonium diol as the soft segment.

[0008] Step (3) Slowly add the small molecule chain extender and slowly heat to the third reaction temperature to carry out the chain extension reaction; In the above process, the small molecule chain extender reacts with the -NCO groups at the end of the prepolymer chain to further extend the molecular chain and improve the molecular weight and mechanical properties of the polymer.

[0009] Step (4) Slowly add pure water and disperse it at high speed to obtain choline-modified polyurethane aqueous dispersion.

[0010] In the above process, the inherent quaternary ammonium cation hydrophilic centers in the polymer chain enable the polymer to spontaneously disperse in water without the addition of an external neutralizing agent, forming a uniform, stable, positively charged polyurethane aqueous dispersion.

[0011] Preferably, in step (1), the polyether diglycidyl ether is polyethylene glycol (PEG) diglycidyl ether. Preferably, in step (1), the structural formula of PEG diglycidyl ether is:

[0012] The molecular weight of PEG is Mw = 400-2000.

[0013] In the above process, the molecular weight range of PEG can balance the hydrophilicity, flexibility and water solubility of the dispersion.

[0014] Preferably, the choline in step (1) is either choline hydroxide or choline chloride.

[0015] Preferably, the choline is any one of the following structures: a) b)

[0016] Preferably, in step (1), the first catalyst is one of KOH, NaOH, and LiOH.

[0017] Preferably, the amount of the first catalyst used is 0.5-1% of the epoxy equivalent of polyethylene glycol diglycidyl ether.

[0018] Preferably, in step (1), the first reaction temperature is 90-120℃ and the heat preservation reaction time is 4-6h.

[0019] Preferably, in step (1), the structural formula of the quaternary ammonium diol intermediate is:

[0020] Preferably, the second reaction temperature in step (2) is 40-50℃; Preferably, the second catalyst in step (2) is at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate.

[0021] Preferably, the amount of the second catalyst is 0.01-0.1% of the total mass.

[0022] Preferably, in step (2), the diisocyanate monomer is at least one of isophorone diisocyanate, toluene 2,4-diisocyanate, dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, and 1,6-hexamethylene diisocyanate; the heat preservation reaction time is 1-1.5h; and the slow dropwise addition time is 0.5-1h.

[0023] Preferably, in step (3), the small molecule chain extender is one of ethylene glycol, propylene glycol, and 1,4-butanediol; the third reaction temperature is 75-85℃, and the chain extension reaction time is 2-4h.

[0024] Preferably, in step (4), the amount of pure water used is 60-70% of the total mass; the high-speed shear dispersion conditions are: the rotation speed of high-speed shear dispersion is 2500-3000 rpm, and the high-speed shear dispersion time is 0.5-1h.

[0025] The choline-modified polyurethane aqueous dispersion was prepared using the aforementioned method.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention utilizes inexpensive choline-p-polyether diglycidyl ether ring-opening polymerization to obtain a quaternary ammonium diol, followed by polyurethane polymerization. By controlling the R-value (OH / NCO) at 1.05-1.2, a stable hydroxyl-terminated quaternary ammonium polyurethane aqueous dispersion is obtained. The one-step synthesis of the quaternary ammonium diol monomer combines soft segments and hydrophilic centers, serving as both flexible segments for polyurethane and providing permanent, embedded cationic hydrophilic centers. This eliminates the post-neutralization step in traditional processes, simplifying the process and reducing costs.

[0027] 2. The choline-modified polyurethane aqueous dispersion prepared by this invention has a bulk cationic polyurethane dispersion with hydrophilic quaternary ammonium salt cations firmly bonded to the polyurethane molecular chain by covalent bonds. This results in more stable hydrophilicity, better hydrolysis resistance, and the coating is less prone to performance degradation due to the loss of hydrophilic groups. Its positive charge characteristic also gives it excellent compatibility with negatively charged pigments, fillers, and common transition metal ions. It can be stored stably for a long time when formulating ink-absorbing coating formulations containing metal ion fixing agents.

[0028] 3. The choline-modified polyurethane aqueous dispersion prepared by this invention has quaternary ammonium cations on the polymer chain that can generate strong ionic bonds and electrostatic adsorption with negatively charged dye molecules in inkjet ink, which significantly accelerates the ink absorption rate, improves the ink volume carrying capacity, and effectively prevents ink smudging.

[0029] 4. The choline-modified polyurethane aqueous dispersion polyurethane coating prepared by this invention is clear and transparent, has excellent light and weather resistance, is resistant to yellowing, and the coating is flexible and dense after film formation, with strong adhesion to various substrates (such as PET, PVC, and paper). Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is the infrared spectrum of the choline-modified polyurethane aqueous dispersion of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise specified, all reagents and raw materials used in the embodiments and comparative examples of this invention are purchased from the market. Example 1

[0034] This embodiment discloses a method for preparing a choline-modified polyurethane aqueous dispersion, including the following steps: Step (1) Add 51.2g of dehydrated PEG400 diglycidyl ether, 48.4g of choline hydroxide and 0.256g of KOH to the reaction vessel, stir to dissolve, heat to 110℃, keep warm for 5h to obtain quaternary ammonium diol intermediate; Step (2) Cool down to 45°C, add 0.077g of dibutyltin dilaurate, control the temperature at 45°C and slowly add isophorone diisocyanate monomer, complete the addition within 45min, and keep the temperature for 1h. After the reaction in step (3) is completed, add 9.9g of chain extender 1,4-butanediol, slowly raise the temperature to 80℃ and keep the reaction at that temperature for 2h; Step (4) Slowly add 285.81g of pure water to the system obtained in step (3) and stir at high speed at 3000rpm for 1h to obtain choline modified polyurethane aqueous dispersion.

[0035] Figure 1 The infrared spectrum of the choline-modified polyurethane aqueous dispersion prepared in Example 1 is shown at 3571.22 cm⁻¹. -1 The broad peak at 2924.22 cm⁻¹ includes characteristic peaks of water and terminal hydroxyl groups in the polyurethane aqueous dispersion. -1 The peak is a characteristic peak of the methylene group in the carbon chain, at 1719.82 cm⁻¹. -1 and 1638.83cm -1 This is a characteristic peak for carbon-based polyurethanes, specifically at 1558.55 cm⁻¹. -1 These are characteristic peaks of the three methyl groups on the quaternary ammonium salt. Example 2

[0036] The difference from Example 1 is that the feed ingredients are 12.6g of 1,4-butanediol, 0.078g of dibutyltin dilaurate, and 290.83g of water, while the remaining steps and material quantities are exactly the same. Example 3

[0037] The difference from Example 1 is that the feed ingredients are 111.2g PEG2000 diglycidyl ether, 0.556g KOH, 0.107g dibutyltin dilaurate, and 397.24g water, while the remaining steps and material amounts are exactly the same. Example 4

[0038] The difference from Example 1 is that the catalyst is 0.256g NaOH, while the rest of the steps and material amounts are exactly the same. Example 5

[0039] The difference from Example 1 is that choline chloride is used instead of choline hydroxide. Specifically, the feed consists of 55.6g of choline chloride, 0.081g of dibutyltin dilaurate, and 299.19g of water. The remaining steps and material quantities are exactly the same.

[0040] Comparative Example 1 This comparative example discloses a method for preparing a tertiary amine-modified polyurethane aqueous dispersion, comprising the following steps: Add 40g PEG400 and 0.157g dibutyltin lauryl ester catalyst to a reactor, heat to 45℃, add 44.4g isophorone diisocyanate monomer dropwise over 45min, maintain the temperature for 1h, slowly add 5.95g N-methyldiethanolamine and 5.4g 1,4-butanediol mixture as hydrophilic chain extender, slowly heat to 75-85℃ and maintain the temperature for 2h, then add 6g glacial acetic acid for neutralization, and finally slowly add 355.64g pure water and disperse at high speed of 3000rpm for 1h to obtain tertiary amine modified polyurethane aqueous dispersion.

[0041] Comparative Example 2 The difference from Example 1 is that the feed ingredients are 211.2g PEG4000 diglycidyl ether, 0.157g dibutyltin dilaurate, 1.056g KOH, and 582.96g water. The remaining steps and material quantities are exactly the same.

[0042] Comparative Example 3 The difference from Example 1 is that the feed ingredients are 9g of 1,4-butanediol, 0.077g of dibutyltin dilaurate, 0.256g of KOH, and 284.14g of water. The remaining steps and material quantities are exactly the same.

[0043] Performance testing: The polyurethane aqueous dispersions prepared in Examples 1-5 and Comparative Examples 1-3 were tested using the following methods: 1. Transition metal ion stability test: Add 10g of 50% calcium chloride solution to 100g of sample, stir well and let stand for 24h to observe the stability of the mixture.

[0044] 2. Ink absorption performance test: The ink absorption coating process is as follows: white polyester and nylon materials are coated separately, with 60g / L of the samples prepared in Examples 1-5 and Comparative Examples 1-3 and 10g / L of water-based blocked isocyanate crosslinking agent, dipped and rolled, and baked at 160℃ for 120s. Ink absorption: Use a capillary tube to drop printing ink onto the treated fabric and observe whether the ink smudges.

[0045] 3. Color fastness test: Print an image on the treated fabric using an inkjet printer. After drying, wash the fabric 10 times according to GB / T8629-2001 "Home Washing and Drying Procedures for Textile Testing". Observe the clarity of the printed image and whether the color fades.

[0046] 4. Yellowing Test: The treated fabric was placed in a 120℃ oven for 72 hours, and the yellowing was observed. The test results are shown in Table 1. Table 1

[0047] As shown in Table 1, Examples 1-5 prepared stable quaternary ammonium polyurethane aqueous dispersions through choline ring-opening modification and R-value control (1.05-1.2). Due to the strong cationicity of the quaternary ammonium group, it exhibits excellent ink absorption and color fastness. Furthermore, the absence of lone pairs of electrons on its nitrogen atom makes the choline-modified polyurethane aqueous dispersions prepared in Examples 1-5 stable in the presence of transition metal ions and exhibiting low yellowing at high temperatures, demonstrating excellent stability. Comparative Example 1 used a tertiary amine as the hydrophilic end of the cationic group, which has slightly weaker cationicity than the quaternary ammonium group, resulting in inferior ink absorption performance. The lone pairs of electrons on its nitrogen atom make it unstable when mixed with transition metal ions, leading to complexation and flocculent formation, and severe yellowing during high-temperature storage. Comparative Example 2 used a high molecular weight polyether diglycidyl ether, which resulted in excessive viscosity during solvent-free polymerization, making it difficult to react uniformly to the end. Comparative Example 3 had an R-value of 1, with a theoretically infinite molecular weight, but gelation occurred in the later stages of polymerization, preventing hydration.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a choline-modified polyurethane aqueous dispersion, characterized in that, Includes the following steps: (1) Dehydrated polyether diglycidyl ether, choline and the first catalyst are added to the reactor, stirred and dissolved, and then heated to the first reaction temperature for heat preservation reaction to obtain quaternary ammonium diol intermediate. (2) Adjust the system temperature to the second reaction temperature, add the second catalyst, then slowly add the diisocyanate monomer, and keep the reaction at the second reaction temperature; (3) Slowly add small molecule chain extender to the system and slowly heat to the third reaction temperature to carry out chain extension reaction; (4) Slowly add pure water to the reaction system and perform high-speed shear dispersion to obtain choline-modified polyurethane aqueous dispersion.

2. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 1, characterized in that, In step (1), the first reaction temperature is 90-120℃; the heat preservation reaction time is 4-6h; the polyether diglycidyl ether is polyethylene glycol (PEG) diglycidyl ether; the choline is choline hydroxide or choline chloride; the first catalyst is KOH, NaOH, or LiOH; the amount of the first catalyst is 0.5-1% of the epoxy equivalent of the polyether diglycidyl ether.

3. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 2, characterized in that, The structural formula of the polyethylene glycol (PEG) diglycidyl ether is: ； The molecular weight (Mw) of PEG is 400-2000.

4. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 2, characterized in that, The choline is any one of the following structures: a) b) 。 5. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 1, characterized in that, The structural formula of the quaternary ammonium diol intermediate is: 。 6. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 1, characterized in that, In step (2), the second reaction temperature is 40-50℃; the heat preservation reaction time is 1-1.5h; the second catalyst includes at least one of dibutyltin dilaurate, stannous octoate or dibutyltin diacetate; the amount of catalyst used is 0.01-0.1% of the total mass of the reaction system.

7. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 1, characterized in that, In step (2), the diisocyanate monomer is one or more of isophorone diisocyanate, toluene-2,4-diisocyanate, dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, or 1,6-hexamethylene diisocyanate.

8. The method for preparing the choline-modified polyurethane aqueous dispersion according to claim 1, characterized in that, In step (3), the third reaction temperature is 75-85℃; the small molecule chain extender is one of ethylene glycol, propylene glycol or 1,4-butanediol; the chain extension reaction time is 2-4h; in step (4), the amount of pure water is 60-70% of the total mass of the reaction system before dispersion; high-speed shear dispersion conditions: the high-speed shear dispersion speed is 2500-3000rpm, and the high-speed shear dispersion time is 0.5-1h.

9. A choline-modified polyurethane aqueous dispersion prepared by the method according to any one of claims 1-10.

10. The choline-modified polyurethane aqueous dispersion according to claim 9, characterized in that, The aqueous dispersion has an R value (OH / NCO) of 1.05-1.2, the polymer chain ends with hydroxyl groups, and the chain segments contain quaternary ammonium cationic groups derived from choline.

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