Waterborne polyurethane and preparation method thereof

Abstract

The invention discloses waterborne polyurethane and a preparation method thereof. The preparation method comprises the following steps: preparing a prepolymer I of an isocyanate group-terminated prepolymer by taking alicyclic diisocyanate and oligomer polyester diol as main polymeric monomers; then adding a hydrophilic chain extender and a cyclopentanediol chain extender for reaction to obtain a prepolymer II; and finally, neutralizing and emulsifying the prepolymer II to obtain the waterborne polyurethane emulsion and the waterborne polyurethane emulsion. According to the technology provided by the invention, the waterborne polyurethane prepared by adopting cyclopentanediol as a chain extender has more excellent performances such as rigidity and heat resistance after film formation; belongs to the technical field of chemical synthesis.

Description

Technical Field

[0001] The invention relates to waterborne polyurethane and a preparation method thereof, and belongs to the technical field of chemical synthesis. Background Art

[0002] Waterborne polyurethane is an environmentally friendly polymer material that uses water as a dispersion medium. Its basic structure consists of a prepolymer formed by the polymerization of a soft segment, such as a polyether diol or polyester diol, with an isocyanate monomer, and then a chain extender.

[0003] Compared to traditional solvent-based polyurethanes, waterborne polyurethanes significantly reduce volatile organic compound (VOC) emissions and offer outstanding environmental advantages. During use, the polyurethane film formed after the water evaporates exhibits excellent physical and mechanical properties and chemical stability comparable to traditional solvent-based products. By flexibly adjusting the composition of the soft and hard segments, introducing functional monomers, or chemically modifying the structure, waterborne polyurethanes can be endowed with varying properties such as softness and hardness, chemical resistance, abrasion resistance, adhesion, and flexibility, enabling their widespread application in a wide range of fields, including wood coatings, textile coatings, synthetic leather, protective coatings for plastics and metals, personal care products, coating additives, adhesives, sealants, and water-based inks.

[0004] In the synthesis of waterborne polyurethane, chain extenders are key components for regulating its microscopic phase separation structure, hydrogen bond network and final performance. Currently commonly used chain extenders mainly include: 1. Bio-based chain extenders: such as diols or diamines derived from plant resources. 2. Diol chain extenders: mainstream traditional types, such as 1,4-butanediol (BDO), ethylene glycol (EG), diethylene glycol (DEG), neopentyl glycol (NPG), etc. 3. Diamine chain extenders: such as ethylenediamine (EDA), diethylenetriamine (DETA), etc., with high reactivity, are often used to prepare polyurethane urea (PUU) to improve hardness and strength. 4. Modified polyether / polyester polyols: have both soft segment and chain extension functions. Among them, diol chain extenders are the most commonly used.

[0005] Since traditional diol chain extenders are generally chain alicyclic diols, the current research on these diols has become a bottleneck. Since the functional groups of chain alicyclic diols are relatively simple, their use as chain extenders will result in poor tensile properties of polyurethanes. Summary of the Invention

[0006] In view of the above problems, the first object of the present invention is to provide an aqueous polyurethane emulsion, which has excellent tensile properties and hardness after film formation.

[0007] The second object of the present invention is to provide a method for preparing the aqueous polyurethane emulsion, which uses cyclopentanediol as a chain extender, so that the prepared aqueous polyurethane has better tensile properties and hardness after film formation.

[0008] To this end, the first technical solution provided by the present invention is as follows:

[0009] A method for preparing waterborne polyurethane comprises the following steps in sequence:

[0010] 1) Adding polypropylene glycol, a first hydrophilic chain extender, and a solvent to a reactor; heating to 50-70° C. and stirring until the polypropylene glycol and the first hydrophilic chain extender are dissolved; then adding isophorone diisocyanate; heating to 60-80° C.; adding a catalyst dropwise; and stirring and reacting at 60-80° C. for 1-3 hours to obtain prepolymer I;

[0011] 2) adding a second chain extender, cyclopentanediol, to the prepolymer I prepared in step 1), and stirring at 60-80° C. for 0.5-2.5 hours to obtain prepolymer II;

[0012] 3) Cooling the prepolymer II prepared in step 2) to 40-60° C., adding a neutralizing agent, stirring for 10-50 minutes, transferring the prepolymer to a container filled with water, homogenizing and emulsifying the prepolymer in a homogenizer for 0.5-2.5 hours, and adding a third chain extender dropwise while homogenizing to obtain the target product, an aqueous polyurethane emulsion;

[0013] The mass ratio of the polypropylene glycol, the first hydrophilic chain extender, isophorone diisocyanate, and the catalyst is 31.91-42.93:2.94-3.47:21.69:0.05;

[0014] The mass fraction of the first hydrophilic chain extender in prepolymer II is 5.0%;

[0015] The mass fraction of the second chain extender cyclopentanediol in the prepolymer II is 2.0% to 4.0%;

[0016] The mass ratio of the prepolymer II, neutralizer, water, and third chain extender is 58.9-69.28:2.5:1.1;

[0017] Furthermore, in the above-mentioned method for preparing water-based polyurethane, the first hydrophilic chain extender is 2,2-dimethylolpropionic acid.

[0018] Furthermore, in the above-mentioned method for preparing water-based polyurethane, the solvent is N,N-dimethylformamide.

[0019] Furthermore, in the above-mentioned method for preparing waterborne polyurethane, the catalyst is stannous octoate.

[0020] Furthermore, in the above-mentioned method for preparing water-based polyurethane, the cyclopentanediol is trans-1,2-cyclopentanediol.

[0021] Furthermore, in the above-mentioned method for preparing water-based polyurethane, the neutralizing agent is triethylamine.

[0022] Furthermore, in the above-mentioned method for preparing waterborne polyurethane, the third chain extender is hydrazine hydrate.

[0023] Furthermore, in the above-mentioned method for preparing water-based polyurethane, the polypropylene glycol is a polypropylene glycol with a molecular weight of 2000.

[0024] Furthermore, in the above-mentioned method for preparing waterborne polyurethane, the homogenizing speed of the homogenizer is 1200-1600 rpm.

[0025] The second technical solution provided by the present invention is a waterborne polyurethane, which is prepared by the method described in the first technical solution.

[0026] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0027] 1. The emulsion prepared by the technical solution provided by the present invention has good stability and can be stored for a long time without the occurrence of stratification, precipitation or odor.

[0028] 2. After the water-based polyurethane emulsion prepared by the technical solution provided in the application is dried to form a cured film, it is tested that the tensile properties, hardness grade and other properties are better than those of the water-based polyurethane cured film prepared with pentanediol as the chain extender, and the application field is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a diagram of the aqueous polyurethane emulsion prepared in Example 1;

[0030] Figure 2 This is a diagram of a waterborne polyurethane cured film prepared in Example 1;

[0031] Figure 3 is a diagram of the aqueous polyurethane emulsion prepared in Example 2;

[0032] Figure 4 This is a diagram of a waterborne polyurethane cured film prepared in Example 2;

[0033] Figure 5 is a diagram of the aqueous polyurethane emulsion prepared in Example 3;

[0034] Figure 6 This is a diagram of a waterborne polyurethane cured film prepared in Example 3;

[0035] Figure 7is a diagram of the aqueous polyurethane emulsion prepared in Example 4;

[0036] Figure 8 This is a diagram of a waterborne polyurethane cured film prepared in Example 4;

[0037] Figure 9 is a diagram of the aqueous polyurethane emulsion prepared in Example 5;

[0038] Figure 10 This is a diagram of a waterborne polyurethane cured film prepared in Example 5;

[0039] Figure 11 This is a diagram of the aqueous polyurethane emulsion prepared in Comparative Example 1;

[0040] Figure 12 This is a diagram of a waterborne polyurethane cured film prepared in Comparative Example 1;

[0041] Figure 13 is a tensile strength and elongation at break curve of the waterborne polyurethane cured film prepared in Example 1;

[0042] Figure 14 is a tensile strength and elongation at break curve of the waterborne polyurethane cured film prepared in Example 2;

[0043] Figure 15 is a tensile strength and elongation at break curve of the waterborne polyurethane cured film prepared in Example 3;

[0044] Figure 16 is a tensile strength and elongation at break curve of the waterborne polyurethane cured film prepared in Example 4;

[0045] Figure 17 is a tensile strength and elongation at break curve of the waterborne polyurethane cured film prepared in Example 5;

[0046] Figure 18 This is a graph showing the tensile strength and elongation at break of the waterborne polyurethane cured film prepared in Comparative Example 1;

[0047] Figure 19 1 is a comparison chart of the hardness grades of the waterborne polyurethane emulsion cured films of Example 2 and Comparative Example 1;

[0048] Figure 20 1-5 is a comparison chart of the hardness grades of the waterborne polyurethane emulsion cured films of Examples 1-5. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0050] Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional in the art. Experimental methods in the following examples, where specific experimental conditions are not specified, are generally performed under conventional experimental conditions or according to the experimental conditions recommended by the manufacturer. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0051] Example 1

[0052] The present embodiment provides a method for preparing a waterborne polyurethane, comprising the following steps in sequence:

[0053] 1) In a four-necked flask connected to a nitrogen inlet and outlet tube and a mechanical stirring paddle, 42.93 g of polypropylene glycol with a molecular weight of 2000, 3.47 g of 2,2-dimethylolpropionic acid, and 3 g of N,N-dimethylformamide were added and mixed uniformly. The mixture was stirred at 400 rpm at 50°C. After 15 minutes, 21.69 g of isophorone diisocyanate and 50 mg of stannous octoate were added. The mixture was stirred at 60°C for 1 hour to obtain prepolymer I.

[0054] 2) To the prepolymer I prepared in step 1), 1.39 g of 1,2-cyclopentanediol and 3 g of N,N-dimethylformamide were added to prevent the prepolymer from becoming too viscous, and the mixture was stirred and reacted at 60° C. for 0.5 hour to obtain prepolymer II;

[0055] 3) 3 g of N, N-dimethylformamide was added to the prepolymer II of step 2), and after stirring, 2.62 g of triethylamine was added after the prepolymer II was cooled to 40°C, and the stirring was continued for 10 minutes; the prepolymer II was then slowly transferred to a container containing 130 g of water, and homogenized and emulsified in a homogenizer at a speed of 1200 rpm for 0.5 hours. During the homogenization process, 1.1 g of hydrazine hydrate was slowly added dropwise to obtain a 2.0 wt% aqueous polyurethane emulsion of cyclopentanediol. The emulsion had an appearance as shown in FIG. Figure 1 shown.

[0056] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube and centrifuged at 3000 r / min for 15 min. No precipitation was found, indicating that the emulsion had good stability and could be stored for a long time without stratification.

[0057] The waterborne polyurethane emulsion prepared in this example was evenly poured onto a silicone mold, placed horizontally, and dried naturally at room temperature for 1 day. After the water was basically evaporated and the film surface was basically formed, it was placed in a blast drying oven at 60°C and dried for 24 hours. It was then vacuum dried to constant weight to obtain a waterborne polyurethane cured film. The thickness was measured to be 0.52 mm. Figure 2 .

[0058] Example 2

[0059] The present embodiment provides a method for preparing a waterborne polyurethane, comprising the following steps in sequence:

[0060] 1) In a four-necked flask connected to a nitrogen inlet and outlet tube and a mechanical stirring paddle, 39.82 g of polypropylene glycol with a molecular weight of 2000, 3.32 g of 2,2-dimethylolpropionic acid, and 3 g of N,N-dimethylformamide were added to aid dissolution. The mixture was stirred at 55° C. at 400 rpm. After 15 minutes, 21.69 g of isophorone diisocyanate and 50 mg of stannous octoate as a catalyst were added. The mixture was stirred at 65° C. for 1.5 hours to obtain prepolymer I.

[0061] 2) Adding 1.66 g of 1,2-cyclopentanediol and 3 g of N,N-dimethylformamide to the prepolymer I prepared in step 1) to prevent the prepolymer from being too viscous, and continuing the reaction at 65° C. with stirring for 1 hour to obtain prepolymer II;

[0062] 3) Add 3g of solvent N,N-dimethylformamide to the prepolymer II prepared in step 2), stir until the temperature drops to 45°C, then add 2.50g of neutralizing agent triethylamine, and continue stirring for 20 minutes; then slowly transfer it to a container filled with 130g of water, homogenize and emulsify it in a homogenizer at a speed of 1300rpm for 1 hour, and slowly add 1.1g of hydrazine hydrate dropwise during the homogenization process to finally obtain a 2.5wt% cyclopentanediol waterborne polyurethane emulsion; the emulsion has an appearance as shown Figure 3 shown.

[0063] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube and centrifuged at 3000 r / min for 15 min. No precipitation was found, indicating that the emulsion had good stability and could be stored for a long time without stratification.

[0064] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube, evenly poured onto a silica gel mold, placed horizontally, and dried naturally at room temperature for 1 day. After the water was basically evaporated and the film surface was basically formed, it was placed in a blast drying oven at 60°C for 24 hours, and then vacuum dried to constant weight to obtain a waterborne polyurethane cured film. The thickness was measured to be 0.65 mm; see the appearance diagram for details. Figure 4 .

[0065] Example 3

[0066] 1) In a four-necked flask connected to a nitrogen inlet and outlet tube and a mechanical stirring paddle, 36.96 g of polypropylene glycol with a molecular weight of 2000, 3.19 g of 2,2-dimethylolpropionic acid, and 3 g of N,N-dimethylformamide were added to facilitate dissolution, and the mixture was stirred at 60°C at 400 rpm. After 15 minutes, 21.69 g of isophorone diisocyanate and 50 mg of stannous octoate as a catalyst were added, and the mixture was stirred at 70°C for 2 hours to obtain prepolymer I;

[0067] 2) Adding 1.91 g of 1,2-cyclopentanediol and 3 g of N,N-dimethylformamide to the prepolymer I prepared in step 1) to prevent the prepolymer from being too viscous, and continuing the reaction at 70° C. with stirring for 1.5 hours to obtain prepolymer II;

[0068] 3) Add 3g of solvent N,N-dimethylformamide to the prepolymer II prepared in step 2), stir until it cools to 50°C, then add 2.41g of neutralizing agent triethylamine, and continue stirring for 30 minutes; then slowly transfer it to a container containing 130g of water, homogenize and emulsify it in a homogenizer at a speed of 1400rpm for 1.5 hours, and slowly add 1.1g of chain extender hydrazine hydrate during the homogenization process to finally obtain a 3.0wt% cyclopentanediol water-based polyurethane emulsion, the appearance of the emulsion is as follows: Figure 5 shown.

[0069] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube and centrifuged at 3000 r / min for 15 min. No precipitation was found, indicating that the emulsion had good stability and could be stored for a long time without stratification.

[0070] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube, evenly poured onto a silica gel mold, placed horizontally, and dried naturally at room temperature for 1 day. After the water was basically evaporated and the film surface was basically formed, it was placed in a blast drying oven at 60°C for 24 hours, and then vacuum dried to constant weight to obtain a waterborne polyurethane cured film. The measured thickness was 0.75 mm; see the appearance diagram for details. Figure 6 .

[0071] Example 4

[0072] 1) In a four-necked flask connected to a nitrogen inlet and outlet tube and a mechanical stirring paddle, 34.33 g of polypropylene glycol with a molecular weight of 2000, 3.06 g of 2,2-dimethylolpropionic acid, and 3 g of N,N-dimethylformamide solvent were added to aid dissolution, and stirred at 65°C at 400 rpm. After 15 minutes, 21.69 g of isophorone diisocyanate and 50 mg of stannous octoate catalyst were added, and the mixture was stirred at 75°C for 2.5 hours to obtain prepolymer I;

[0073] 2) Adding 2.14 g of 1,2-cyclopentanediol and 3 g of N,N-dimethylformamide to the prepolymer I prepared in step 1) to prevent the prepolymer from being too viscous, and continuing the reaction at 75° C. with stirring for 2 hours to obtain prepolymer II;

[0074] 3) Continue to add 3g of solvent N,N-dimethylformamide as in step 2), stir until it cools to 55°C, then add 2.31g of neutralizing agent triethylamine, and continue stirring for 40 minutes; then slowly transfer it to a container filled with 130g of water, homogenize and emulsify it in a homogenizer at a speed of 1500rpm for 2 hours, and slowly add 1.1g of hydrazine hydrate dropwise during the homogenization process to finally obtain a 3.5wt% cyclopentanediol water-based polyurethane emulsion, the appearance of the emulsion is as follows: Figure 7 shown.

[0075] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube and centrifuged at 3000 r / min for 15 min. No precipitation was found, indicating that the emulsion had good stability and could be stored for a long time without stratification.

[0076] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube, evenly poured onto a silica gel mold, placed horizontally, and dried naturally at room temperature for 1 day. After the water was basically evaporated and the film surface was basically formed, it was placed in a blast drying oven at 60°C for 24 hours, and then vacuum dried to constant weight to obtain a waterborne polyurethane cured film. The thickness was measured to be 0.55 mm; see the appearance diagram for details. Figure 8 .

[0077] Example 5

[0078] 1) In a four-necked flask connected to a nitrogen inlet and outlet tube and a mechanical stirring paddle, 31.91 g of polypropylene glycol with a molecular weight of 2000, 2.94 g of 2,2-dimethylolpropionic acid, and 3 g of N,N-dimethylformamide were added to aid dissolution. The mixture was stirred at 70°C at 400 rpm. After 15 minutes, 21.69 g of isophorone diisocyanate and 50 mg of stannous octoate as a catalyst were added. The mixture was stirred at 80°C for 3 hours to obtain prepolymer I.

[0079] 2) Adding 2.36 g of 1,2-cyclopentanediol and 3 g of N,N-dimethylformamide to the prepolymer I prepared in step 1) to prevent the prepolymer from being too viscous, and continuing the reaction at 80° C. with stirring for 2.5 hours to obtain prepolymer II;

[0080] 3) Continue to add 3g of solvent N,N-dimethylformamide to step 2), stir until it cools to 60°C, then add 2.22g of neutralizing agent triethylamine, and continue stirring for 50 minutes; then slowly transfer it to a container containing 130g of water, homogenize and emulsify it in a homogenizer at a speed of 1600rpm for 2.5 hours, and slowly add 1.1g of chain extender hydrazine hydrate dropwise during the homogenization process to finally obtain a 4.0wt% cyclopentanediol water-based polyurethane emulsion, the appearance of the emulsion is as follows: Figure 9 shown.

[0081] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube and centrifuged at 3000 r / min for 15 min. No precipitation was found, indicating that the emulsion had good stability and could be stored for a long time without stratification.

[0082] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube, evenly poured onto a silica gel mold, placed horizontally, and dried naturally at room temperature for 1 day. After the water was basically evaporated and the film surface was basically formed, it was placed in a blast drying oven at 60°C and dried for 24 hours, and then vacuum dried to constant weight to obtain a waterborne polyurethane cured film. The measured thickness was 0.84 mm; see the appearance diagram for details. Figure 10 .

[0083] Comparative Example I

[0084] 1) In a four-necked flask connected to a nitrogen inlet and outlet tube and a mechanical stirring paddle, 40.09 g of polypropylene glycol with a molecular weight of 2000, 3.34 g of 2,2-dimethylolpropionic acid, and 3 g of N,N-dimethylformamide were added to aid dissolution, and stirred at 55°C at 400 rpm. After 15 minutes, 21.69 g of isophorone diisocyanate and 50 mg of stannous octoate as a catalyst were added, and the mixture was stirred at 65°C for 1.5 hours to obtain prepolymer I;

[0085] 2) Adding 1.67 g of 1,5-pentanediol and 3 g of N,N-dimethylformamide to the prepolymer I prepared in step 1) to prevent the prepolymer from being too viscous, and continuing the reaction at 65° C. with stirring for 1 hour to obtain prepolymer II;

[0086] 3) Continue to add 3g of solvent N,N-dimethylformamide as in step 2), stir until it cools to 45°C, then add 2.52g of neutralizing agent triethylamine, and continue stirring for 20 minutes; slowly transfer to a container containing 130g of water, homogenize and emulsify in a homogenizer at a speed of 1300rpm for 1 hour, and slowly add 1.1g of post-chain extender hydrazine hydrate dropwise to finally obtain a 4.0wt% cyclopentanediol waterborne polyurethane emulsion, the appearance of the emulsion is as follows: Figure 9 shown.

[0087] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube and centrifuged at 3000 r / min for 15 min. No precipitation was found, indicating that the emulsion had good stability and could be stored for a long time without stratification.

[0088] The aqueous polyurethane emulsion prepared in this example was transferred to a centrifuge tube, evenly poured onto a silica gel mold, placed horizontally, and dried naturally at room temperature for 1 day. After the water was basically evaporated and the film surface was basically formed, it was placed in a blast drying oven at 60°C for 24 hours, and then vacuum dried to constant weight to obtain a waterborne polyurethane cured film. The thickness was measured to be 0.53 mm; see the appearance diagram for details. Figure 12 .

[0089] In order to verify the performance of the waterborne polyurethane prepared in this application, the performance test experiment of the waterborne polyurethane prepared in this application is given below.

[0090] 1. Tensile performance test:

[0091] The tensile strength and elongation at break of the WPU cured films were tested according to the standard GB / T 528-2009, "Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties." The cured films prepared in Examples 1-5 and Comparative Example 1 were cut into 25 mm x 4 mm dumbbell-shaped strips using a mold. Tensile tests were performed on the strips using an Inspekt Table Bliue electronic universal testing machine at a rate of 100 mm / min. Each sample was tested three times at room temperature. The test results are shown in Table 1.

[0092] Table 1

[0093] Test samples Tensile strength (MPa) Elongation at break (%) The waterborne polyurethane cured film provided in Example 1 36.98 802.85 The waterborne polyurethane cured film provided in Example 1 47.97 788.83 The waterborne polyurethane cured film provided in Example 1 46.56 632.59 The waterborne polyurethane cured film provided in Example 1 45.41 627.31 The waterborne polyurethane cured film provided in Example 1 53.81 594.88 The waterborne polyurethane cured film provided in Example 1 22.23 619.09

[0094] The tensile properties of the waterborne polyurethane cured film provided in Example 1 are shown in FIG. Figure 13 ; Example 2 provides a waterborne polyurethane cured film tensile properties diagram for reference Figure 14 ; Example 3 provides a waterborne polyurethane cured film tensile properties diagram for reference Figure 15 Example 4 provides a waterborne polyurethane cured film tensile properties diagram for reference Figure 16 Example 5 provides a waterborne polyurethane cured film tensile properties diagram for reference Figure 17 Comparative Example 1 provides a waterborne polyurethane cured film tensile properties diagram for reference Figure 18 .

[0095] The tensile strength and elongation at break of the waterborne polyurethane cured film provided by Examples 1-5 and Comparative Example 1 can be seen as the increase of the mass fraction of cyclopentanediol as a chain extender, and the tensile strength is increased to 53.81MPa from 36.98MPa, and the elongation at break drops to 594.09% from 802.85%. This illustrates that the increase of the mass fraction of cyclopentanediol leads to a progressive improvement in its tensile strength, and a reduction in its elongation at break. Compared with Example 2, the tensile strengths of cyclopentanediol and pentanediol using the same mass fractions as chain extenders are 47.97MPa and 22.23MPa, respectively, and the elongation at break is 788.83% and 619.09%, respectively. It can be seen that the waterborne polyurethane cured film prepared by cyclopentanediol as a chain extender is far better than the waterborne polyurethane cured film prepared by pentanediol as a chain extender in terms of tensile properties.

[0096] 2. Pencil hardness test

[0097] The cyclopentanediol aqueous polyurethane emulsions obtained in Examples 1-5 and the 2.5 wt% pentanediol aqueous polyurethane emulsion prepared in Comparative Example 1 were uniformly coated on the surface of the tinplate sheet with a thickness of 200 μm using a knife. After the emulsions were dried and cured to form films, the hardness of the cured films was tested according to GB / T 6739-2006 "Paints and varnishes - Determination of film hardness by pencil method".

[0098] According to the standard, handle the pencil tip and install the device. When testing, the pencil tip should just touch the surface of the cured film. Then start pushing the test plate. Finally, observe whether there is a scratch on the cured film and record the pencil model that caused the scratch. Each cured film is measured for hardness three times and the average value is taken. When recording the hardness grade, first convert it to a number, round down the average value, and then convert it back to a hardness grade (the lowest hardness grade "6B" corresponds to the number "1", the highest hardness grade "6H" corresponds to the number "13", and the other hardness grades are converted in the same way). The test results are referred to Figure 19 、 Figure 20 and Table 2.

[0099] Table 2

[0100] 1

[0102] pass Figure 19 、 Figure 20As can be seen from Table 1, the hardness of the cured films gradually increases with increasing cyclopentanediol mass fraction. Cured films prepared with 2.0wt% and 2.5wt% cyclopentanediol achieve a hardness rating of 4H, while the cured film prepared with 2.5wt% cyclopentanediol only achieves a hardness rating of 3H. This indicates that the cyclic structure of cyclopentanediol imparts higher hardness and deformation resistance to the cured films. As the cyclopentanediol mass fraction continues to increase, the cured film prepared with 3.0wt% cyclopentanediol achieves a hardness rating of 5H, while the films prepared with 3.5wt% and 4.0wt% cyclopentanediol achieve the highest hardness rating of 6H.

[0103] The above is merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing waterborne polyurethane, characterized in that: The method includes the following steps in sequence: 1) Adding polypropylene glycol, a first hydrophilic chain extender, and a solvent to a reactor; heating to 50-70° C. and stirring until the polypropylene glycol and the first hydrophilic chain extender are dissolved; then adding isophorone diisocyanate; heating to 60-80° C.; adding a catalyst dropwise; and stirring and reacting at 60-80° C. for 1-3 hours to obtain prepolymer I; 2) adding a second chain extender, cyclopentanediol, to the prepolymer I prepared in step 1), and stirring at 60-80° C. for 0.5-2.5 hours to obtain prepolymer II; 3) Cooling the prepolymer II prepared in step 2) to 40-60° C., adding a neutralizing agent, stirring for 10-50 minutes, transferring the prepolymer to a container filled with water, homogenizing and emulsifying the prepolymer in a homogenizer for 0.5-2.5 hours, and adding a third chain extender dropwise while homogenizing to obtain the target product, an aqueous polyurethane emulsion; The mass ratio of the polypropylene glycol, the first hydrophilic chain extender, isophorone diisocyanate, and the catalyst is 31.91-42.93:2.94-3.47:21.69:0.05; The mass fraction of the first hydrophilic chain extender in prepolymer II is 5.0%; The mass fraction of the second chain extender cyclopentanediol in the prepolymer II is 2.0% to 4.0%; The mass ratio of the prepolymer II, the neutralizer, water and the third chain extender is 58.9-69.28:2.5:1.

1.

2. The method for preparing waterborne polyurethane according to claim 1, wherein The first hydrophilic chain extender is 2,2-dimethylol propionic acid.

3. The method for preparing waterborne polyurethane according to claim 1, wherein The solvent is N,N-dimethylformamide.

4. The method for preparing waterborne polyurethane according to claim 1, wherein The catalyst is stannous octoate.

5. The method for preparing waterborne polyurethane according to claim 1, wherein The cyclopentanediol is trans-1,2-cyclopentanediol.

6. The method for preparing waterborne polyurethane according to claim 1, wherein The neutralizing agent is triethylamine.

7. The method for preparing waterborne polyurethane according to claim 1, wherein The third chain extender is hydrazine hydrate.

8. The method for preparing waterborne polyurethane according to claim 1, wherein The polypropylene glycol is a polypropylene glycol with a molecular weight of 2000.

9. The method for preparing waterborne polyurethane according to claim 1, wherein The homogenizing speed of the homogenizer is 1200-1600 rpm.

10. A waterborne polyurethane, characterized in that It is prepared by the method described in any one of claims 1 to 7.

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