Preparation method of waterborne polyurethane, waterborne polyurethane and application

Abstract

The invention discloses a preparation method of waterborne polyurethane, which belongs to the field of polyurethane and comprises the following steps: step 1, obtaining sodium isobutoxide; 2, methanol amine and sodium isobutoxide are subjected to a contact reaction, and a first reactant is obtained; step 3, subjecting bromoisobutane and the first reactant to a contact reaction so as to obtain a second reactant, and removing impurities so as to obtain isobutoxy etherified methanol amine; 4, polyester polyol, polyether polyol or a mixture of the polyester polyol and the polyether polyol react with isocyanate to generate a third reactant of which the chain end is an isocyanate group, and the third reactant and isobutoxy etherified methanol amine are mixed and react to obtain a polyurethane prepolymer; step 5, emulsifying the polyurethane prepolymer to obtain waterborne polyurethane; the invention also discloses the polyurethane and application thereof.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular materials, in particular to a water-based polyurethane. BACKGROUND

[0002] As a representative of environmentally friendly polymer materials, water-based polyurethane (WPU) has become an important substitute for traditional solvent-based polyurethane. Its core advantage lies in using water as the dispersion medium, which greatly reduces the emission of volatile organic compounds (VOC), and has the characteristics of non-toxicity, non-flammability, and safe operation. At the same time, WPU has excellent flexibility, wear resistance, and good adhesion to various substrates, and is widely used in the fields of coatings, adhesives, leather finishing agents, textile finishing agents, etc., which meets the increasingly strict environmental protection regulations and sustainable development trend around the world.

[0003] However, in order to further improve the water resistance, chemical resistance, mechanical strength and heat resistance of the coating film, the conventional water-based polyurethane often needs to be compounded with an additional crosslinking agent (such as aziridine, carbodiimide, or epoxy crosslinking agent) before application. This method prepares the system into a two-component form, which improves the final performance to some extent, but also brings obvious application limitations: first, the two-component product needs to be accurately weighed and mixed before use, which not only increases the complexity of the operation steps and the requirement for the skills of the construction personnel, but also easily leads to unstable product performance or defects due to uneven mixing; secondly, and more importantly, once the two components are mixed, the system starts to crosslink, and the pot life is limited, which must be used within a few hours, otherwise it will be scrapped due to rapid viscosity increase and gelation, causing waste of raw materials and affecting construction efficiency.

[0004] In view of this industry pain point, the latest technical development focuses on solving this problem fundamentally by precise design of the molecular structure of water-based polyurethane. By introducing latent crosslinking functional groups (such as ketone carbonyl, acetoacetoxy, or blocked isocyanate, etc.) into the polyurethane molecular chain, a single-component post-crosslinkable water-based polyurethane can be successfully prepared. This product remains stable during the storage period, and the crosslinking reaction does not occur. After the film is formed by construction, through external conditions such as heating, these active groups can efficiently crosslink between molecules to form a three-dimensional network structure. This innovative single-component design not only perfectly avoids the inconvenience and waste of two-component systems, but also significantly improves the comprehensive performance of the coating film by building a denser crosslinking network, realizing the organic unity of convenient construction and high performance, and representing an important development direction of water-based polyurethane technology.

[0005] The nitrogen hydroxymethyl functional group (—NHCH2OH) is the key structural unit for the crosslinking and curing of amino resins (such as melamine formaldehyde resin). It is stable at room temperature, but exhibits high reactivity under heating conditions, and can form a crosslinked network through two main pathways: one is the dehydration condensation between nitrogen hydroxymethyl groups to form a methylene bridge (—CH2—); the other is the etherification reaction with active hydrogen-containing functional groups (such as hydroxyl groups, carboxyl groups, etc. in the resin), thereby constructing a dense three-dimensional network structure in the coating or adhesive layer. This mechanism endows the amino resin crosslinking system with high hardness, excellent chemical resistance and thermal stability, and is widely used in high-performance coatings and adhesives. To further optimize its performance and environmental friendliness, the nitrogen hydroxymethyl group is often etherified (such as using isobutanol for etherification), and the etherification reaction generates —NHCH2OR structure, which significantly reduces the free formaldehyde content in the resin, improves the storage stability, and still retains good thermal crosslinking reactivity. The etherified amino resin can be hydrolyzed in water to generate nitrogen hydroxymethyl groups, and further heating can still effectively achieve crosslinking, balancing the environmental requirements and final performance, and more in line with the development trend of modern green chemistry. SUMMARY

[0006] The present application introduces this etherified nitrogen hydroxymethyl structure into the molecular chain of waterborne polyurethane, and also generates nitrogen hydroxymethyl structure on the polyurethane molecular chain by utilizing its hydrolysis performance, thereby developing a new type of one-component post-crosslinkable waterborne polyurethane. Firstly, its one-component characteristic avoids the cumbersome process of precise mixing before use and the pot life limitation of two-component systems, making the construction simple and free of gel rejection risk; secondly, during the heat treatment process after film formation, the nitrogen hydroxymethyl groups can crosslink with active groups in their own segments or other components, significantly improving the water resistance, wear resistance and mechanical strength of the coating film; finally, this strategy realizes the unification of environmental friendliness, process simplicity and high performance, providing a new direction for the development of the next generation of high-performance waterborne materials.

[0007] The purpose of the present application is to disclose a preparation method of waterborne polyurethane, which is aimed at solving the problems in the background art, and the steps are as follows: Step one, obtain sodium isobutoxide; Step two, contact methanolic amine and sodium isobutoxide to obtain a first reactant; Step three, contact bromoiso-butane and the first reactant to obtain a second reactant, remove impurities to obtain isobutoxy etherified methanolic amine; Step four, react polyester polyol, polyether polyol or their mixture with isocyanate to generate a third reactant with isocyanate group at the chain end, and mix the third reactant and isobutoxy etherified methanolic amine to obtain a polyurethane prepolymer; Step five, emulsify the polyurethane prepolymer to obtain a waterborne polyurethane.

[0008] In the preferred scheme, the method for obtaining sodium isobutoxide is as follows: under the protection of inert atmosphere, isobutanol is added into the reaction device, and sodium metal is added in batches at a temperature of 50-70°C.

[0009] In the preferred scheme, the molar ratio of isobutanol to sodium metal is 1.2-1.5:1, and the reaction is carried out for 1-3 hours.

[0010] In the preferred scheme, the method for obtaining the first reactant is as follows: methanolamine is slowly added into the sodium isobutoxide solution prepared in the foregoing step, and the temperature is controlled at 40-60°C, and the reaction is carried out for 4-8 hours.

[0011] In the preferred scheme, the method for obtaining the second reactant is as follows: bromoiso-butane is added into the first reactant, and the reaction is continued at 100-110°C for 6-10 hours.

[0012] In the preferred scheme, the molar ratio of bromoiso-butane to methanolamine is 1.05-1.2:1, In the preferred scheme, the method for obtaining isobutoxy etherified methanolamine is as follows: the second reactant is cooled to room temperature, and the generated sodium bromide solid is removed by filtration, and then unreacted isobutanol and bromoiso-butane are removed by distillation under reduced pressure at 40-80°C, to obtain isobutoxy etherified methanolamine.

[0013] In the preferred scheme, the emulsified polyurethane prepolymer is added into deionized water under high-speed dispersion conditions.

[0014] The application also discloses an aqueous polyurethane prepared by the method for preparing the aqueous polyurethane.

[0015] The application also discloses application of the aqueous polyurethane in a coating film.

[0016] Methanols are multifunctional compounds containing primary, secondary amino groups and hydroxymethyl groups. If directly used in the preparation of polyurethane, the primary, secondary amino groups and hydroxyl groups can all react with isocyanate, resulting in the consumption of hydroxymethyl groups and the inability to retain for subsequent crosslinking. To solve this problem, the principle of the preparation method is based on molecular design and step-by-step synthesis strategy, aiming to construct a one-component waterborne polyurethane system which is stable in storage and can be crosslinked by heating after use. The core is that the process uses a step-by-step reaction strategy to achieve high selectivity etherification of the hydroxyl group in methanolamine. The core principle is to construct a reactive center by an indirect method and accurately control the reaction path. First, isobutanol reacts with sodium metal to generate sodium isobutoxide, which aims to create a strong alkaline but moderately hindered alkoxide system. Then, methanolamine is added, and sodium isobutoxide can preferentially react with the hydroxyl group of methanolamine with stronger acidity to generate the key sodium methanolamine intermediate (H2N-CH2-O⁻Na⁺), while the amino group is retained. This step cleverly uses the alkalinity of sodium alkoxide to achieve the specific activation of the hydroxyl group, while avoiding side reactions of the amino group. Finally, this alcohol-oxygen anion intermediate, as a strong nucleophile, undergoes a bimolecular nucleophilic substitution reaction with bromoiso-butane, efficiently and specifically introducing the target ether chain on the hydroxyl group. The whole process successfully realizes the selective etherification of the hydroxyl group under mild conditions through the tandem design of step-by-step activation and nucleophilic substitution, thereby specifically making the hydroxyl group into isobutoxy, while completely retaining the original reactivity of the amino group, and finally synthesizing a new functional chain extender with both chain extension performance and latent crosslinking sites (reaction mechanism see Figure 1 ).

[0017] Subsequently, in the chain extension stage of the polyurethane prepolymer, the chain extender is introduced into the system together with the hydrophilic chain extender dimethylol propionic acid, so that ionizable carboxyl groups and etherified hydroxymethyl groups with potential crosslinking performance are embedded in the polymer molecular chain; after neutralization, the carboxyl groups impart excellent water dispersibility to the resin, and during the heat treatment process after drying and film formation, the etherified hydroxymethyl groups can be hydrolyzed to release active hydroxymethyl groups, which can further react with active groups such as hydroxymethyl groups on adjacent chain segments to form a dense three-dimensional network crosslinking structure. This method successfully realizes the unification of the single-component storage stability of the resin and the triggering of secondary crosslinking function after film formation by pre-embedding heat-sensitive crosslinking functional groups in the polyurethane main chain, significantly improving the mechanical strength, water resistance and durability of the material. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a schematic diagram of the result test. DETAILED DESCRIPTION

[0019] The present application will be described in detail below.

[0020] Example 1: (1) Preparation of chain extender: 10 g of isobutyl alcohol was added to a reactor, and 0.8 g, 0.8 g, and 0.8 g of sodium metal were sequentially added at an interval of 10 minutes at a temperature of 50°C, and stirred at the temperature for 1 hour. Then, 4.7 g of methanolamine was added dropwise, and the temperature was controlled at 50°C, and stirred for 4 hours. Then, 16 g of bromoiso-butane was added to the reaction system, and the reaction was continued at 100°C for 6 hours. After the reaction was completed, the system was cooled to room temperature, and the generated sodium bromide solid was removed by filtration. Then, the unreacted isobutyl alcohol and bromoiso-butane were removed by distillation under reduced pressure at 50°C and -0.09 MPa, to obtain the chain extender isobutoxy etherified methanolamine. The reaction principle is shown below: (2) Preparation of water-based polyurethane emulsion: 50 g of polypropylene glycol with a molecular weight of 1000 was first added to a reaction bottle, and dehydrated at 100°C for 1 hour under vacuum. Then, 33.3 g of isophorone diisocyanate and 0.1 g of a catalyst dibutyltin dilaurate were added, and stirred at 80°C for 3 hours. Then, 2.1 g of the above chain extender and 4 g of dimethylol propionic acid were dissolved in 10 g of N-methyl pyrrolidone, and added to the above reaction bottle, and reacted at 80°C for 3 hours to obtain a polyurethane prepolymer. Then, the temperature was lowered to 50°C, 3 g of triethylamine was added to the reaction bottle, and neutralized for 15 minutes. Then, 200 g of deionized water was added to the reaction bottle, and emulsified for 30 minutes to obtain the target water-based polyurethane product. The reaction principle is shown below: Example 2: (1) Preparation of a new chain extender: 9 g of isobutyl alcohol was added to a reactor, and 0.8 g, 0.8 g, and 0.8 g of sodium metal were sequentially added at an interval of 10 minutes at a temperature of 60°C, and stirred at the temperature for 1 hour. Then, 4.0 g of methanolamine was added dropwise, and the temperature was controlled at 55°C, and stirred for 4 hours. Then, 15 g of bromoiso-butane was added to the reaction system, and the reaction was continued at 100°C for 6 hours. After the reaction was completed, the system was cooled to room temperature, and the generated sodium bromide solid was removed by filtration. Then, the unreacted isobutyl alcohol and bromoiso-butane were removed by distillation under reduced pressure at 55°C and -0.09 MPa, to obtain the new chain extender isobutoxy etherified methanolamine.

[0021] First, 100g of polycarbonate with a molecular weight of 2000 was added to a reaction flask and dehydrated under vacuum at 100℃ for 1 hour. Then, 52.4g of dicyclohexylmethane diisocyanate and 0.15g of dibutyltin dilaurate were added, and the mixture was stirred and reacted at 85℃ for 3 hours. Next, 3.1g of the above-mentioned novel chain extender and 7g of dimethylolpropionic acid were dissolved in 10g of N-methylpyrrolidone and added to a reaction vessel. The mixture was reacted at 85℃ for 3 hours to obtain a prepolymer with isocyanate groups at the molecular chain ends. The temperature was then lowered to 50℃, and 5.5g of triethylamine was added to the reaction vessel and neutralized for 15 minutes. Finally, 240g of deionized water was added to the reaction flask and emulsified for 30 minutes to obtain the target waterborne polyurethane product.

[0022] Example 3: (1) Preparation of novel chain extender: 14g of isobutanol was added to the reactor, and 1.0g, 1.0g and 1.0g of sodium metal were added sequentially at 60℃ for 10 minutes. The reaction was stirred at this temperature for 1 hour. Then 6.2g of methanolamine was added dropwise, and the temperature was controlled at 50℃ and stirred for 4 hours. Then 20g of bromoisobutane was added to the reaction system, and the reaction was stirred at 105℃ for 5 hours. After the reaction was completed, the system was cooled to room temperature, the generated sodium bromide solid was removed by filtration, and then the unreacted isobutanol and bromoisobutane were removed by vacuum distillation at 60℃ and -0.09MPa to obtain the novel chain extender - isobutoxy etherified methanolamine.

[0023] First, 100g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to the reaction flask and dehydrated under vacuum at 100°C for 1 hour. Then, 44.4g of isophorone diisocyanate and 0.1g of [unclear text - possibly a specific ingredient or product] were added. Dibutyltin dilaurate The mixture was stirred and reacted at 85°C for 3 hours. Then, 4.0 g of ethylene glycol and 6.7 g of dimethylolpropionic acid were dissolved in 10 g of N-methylpyrrolidone and added to the reactor. The mixture was reacted at 85°C for 3 hours to obtain a prepolymer with isocyanate groups at the ends of the molecular chain. The temperature was then lowered to 50°C, and 5.5 g of triethylamine was added to the reactor and neutralized for 15 minutes. Then, 220 g of deionized water was added to the reaction flask and emulsified for 30 minutes to obtain the target waterborne polyurethane product.

[0024] Application testing: Pigment printing is a widely used printing process. Its principle involves using polymeric compounds (i.e., binders) to firmly adhere insoluble organic or inorganic pigments to the fabric surface. Since pigments themselves lack affinity for fibers and cannot directly bond, the binder plays a crucial role. Through physical anchoring and chemical bonding, it encapsulates and fixes the pigment particles onto the fibers, thus forming a durable pattern. During drying and high-temperature curing, the polymer chains within the binder cross-link and coalesce into a continuous, transparent, and tough film. This film completely encapsulates the pigment particles and effectively prevents them from detaching.

[0025] Waterborne polyurethane as a kind of pigment printing adhesive can give the printed fabric excellent softness, elasticity and color fastness. However, the conventional waterborne polyurethane is difficult to form an effective three-dimensional network structure in the film forming process due to the lack of cross-linkable functional groups in its molecular structure, resulting in poor wash resistance of the printed fabric, and the printed pattern is easily damaged under external mechanical brushing. This patent aims to solve the above problems. Three modified waterborne polyurethanes (Examples 1, 2 and 3) are used as adhesives to compare and evaluate the wash resistance and pattern fastness with conventional waterborne polyurethane.

[0026] 1. Pulp preparation formula: 2. Process: pulp preparation (viscosity adjusted to about 25000 mpa.s) → printing → drying (100℃ x 3min) → setting (150℃ x 3min) → comparison of brushing fastness.

[0027] 3. Test of wash resistance: The wash resistance of textiles is mainly based on the national standard GB / T 3921-2008 "Textile color fastness to soaping and washing".

[0028] The specific test process is as follows: 1. Prepare the sample: cut a certain size of sample from the textile to be tested and mark it.

[0029] 2. Washing treatment: put the sample into a container containing a specific concentration of soap solution or detergent, and wash according to the specified conditions.

[0030] 3. Drying and rating: dry the washed sample and evaluate the color stability by mechanical brushing, i.e. the ability of the textile color to resist being brushed off.

[0031] As shown in Figure 1 , the conventional waterborne polyurethane film is easily damaged under brushing due to the lack of cross-linking structure, resulting in the printed pattern falling off and the fabric surface becoming obviously white. In contrast, the waterborne polyurethane in Examples 1, 2 and 3 introduces a post-crosslinking structure, which can undergo crosslinking reaction at a setting temperature of 150℃, thereby forming a firm combination with the fabric and effectively resisting brushing to maintain the printed pattern almost without falling off.

Claims

1. A process for the preparation of an aqueous polyurethane, characterized in that, The steps are as follows: Step one, obtaining sodium isobutoxide; Step two, contacting methanolic amine and sodium isobutoxide to obtain a first reactant; Step three, contacting bromo-isobutane and the first reactant to obtain a second reactant, removing impurities to obtain isobutoxy etherified methanolic amine; Step four, reacting polyester polyol, polyether polyol or mixture thereof with isocyanate to obtain a third reactant with isocyanate group at the chain end, mixing the third reactant and isobutoxy etherified methanolic amine to obtain polyurethane prepolymer; Step five, emulsifying the polyurethane prepolymer to obtain waterborne polyurethane.

2. The process for the preparation of waterborne polyurethane according to claim 1, characterized in that, The method for obtaining sodium isobutoxide is as follows: in a reaction device protected by inert atmosphere, isobutanol is added, and metal sodium is added in batches at a temperature of 50-70°C.

3. The process for the preparation of waterborne polyurethane according to claim 2, characterized in that, The molar ratio of isobutanol to metal sodium is 1.2-1.5:1, and the reaction is carried out for 1-3 hours.

4. The method of preparing a waterborne polyurethane according to claim 2, characterized in that, The method for obtaining the first reactant is as follows: methanolic amine is slowly added dropwise into the sodium isobutoxide solution prepared in the foregoing step, and the temperature is controlled at 40-60°C for 4-8 hours.

5. The method of preparing a waterborne polyurethane according to claim 4, characterized in that, The method for obtaining the second reactant is as follows: bromo-isobutane is added into the first reactant, and the reaction is continued at 100-110°C for 6-10 hours.

6. The method of preparing a waterborne polyurethane according to claim 5, characterized in that, The molar ratio of bromo-isobutane to methanolic amine is 1.05-1.2:

1.

7. The method of preparing a waterborne polyurethane according to claim 4, characterized in that, The method for obtaining isobutoxy etherified methanolic amine is as follows: the second reactant is cooled to room temperature, and the generated sodium bromide solid is removed by filtration, and then unreacted isobutanol and bromo-isobutane are removed by distillation under reduced pressure at 40-80°C to obtain isobutoxy etherified methanolic amine.

8. The method of preparing a waterborne polyurethane according to claim 1, characterized in that, The polyurethane prepolymer is emulsified in deionized water under high-speed dispersion conditions.

9. An aqueous polyurethane, characterized in that The waterborne polyurethane is prepared by the method described in any one of claims 1-8.

10. The use of the waterborne polyurethane described in claim 9 in a coating film.

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