Preparation process of solvent-free waterborne polyurethane dry powder

Abstract

The invention relates to the technical field of polyurethane, and particularly discloses a preparation process of solvent-free waterborne polyurethane dry powder. According to the solvent-free waterborne polyurethane dry powder disclosed by the invention, the solvent is removed, so that leakage in a storage process does not need to be worried, and main transportation capacity does not need to be consumed in transportation of the solvent, so that the transportation cost performance and the storage stability of a waterborne polyurethane product can be effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of polyurethane, and more specifically, to a process for preparing solvent-free water-based polyurethane dry powder. Background Art

[0002] Polyurethane (PU), short for polyurethane, refers to a polymer material containing a carbamate (-NHCOO-) structure. Traditional polyurethanes are solvent-based, containing large amounts of organic solvents. These not only seriously pollute the environment but also pose a health risk. Furthermore, solvent recycling is difficult, resulting in a significant waste of resources. In recent years, with the improvement of environmental laws and regulations and the rise of public awareness, green, environmentally friendly, and low-pollution polyurethane products have garnered increasing attention, with water-based polyurethane being a key type.

[0003] Waterborne polyurethane (WPU) is a binary colloidal system with water as the dispersion medium and polyurethane as the dispersant. It is a block copolymer containing soft and hard segments and can be divided into polyether, polyester, and polyether-polyester hybrid types according to the different synthetic monomers. The synthesis of waterborne polyurethane can generally be divided into two stages. The first stage is the pre-polymerization stage, in which polyether or polyester diols, diisocyanates, chain extenders, hydrophilic monomers, etc. are pre-polymerized to form a prepolymer; the second stage is to disperse the prepolymer in water for emulsification. Waterborne polyurethane uses water as the dispersion medium instead of organic solvents. It not only has the key characteristics of solvent-based polyurethane, but also has the advantages of being non-toxic, non-flammable, pollution-free, energy-saving, and extremely easy to store and use. It is an environmentally friendly chemical material, and its application has extended from the traditional leather finishing industry to fields such as wood coatings and adhesives.

[0004] Regarding the above-mentioned related technologies, the inventors believe that the goods produced by water-based polyurethane manufacturers are water-based emulsions. For water-based emulsions with a solid content of 35%, their water content can reach 65%. On the one hand, there is a risk of leakage. On the other hand, a large amount of transportation capacity is spent on the transportation of water. The transportation cost-effectiveness and storage stability still need to be improved. Summary of the Invention

[0005] In the related art, the transportation cost-effectiveness and storage stability of waterborne polyurethane still need to be improved. In order to improve this defect, the present application provides a preparation process of solvent-free waterborne polyurethane dry powder.

[0006] The present application provides a process for preparing a solvent-free waterborne polyurethane dry powder, which adopts the following technical solution:

[0007] A process for preparing a solvent-free waterborne polyurethane dry powder comprises the following steps:

[0008] (1) mixing polyol raw materials to obtain a polyol mixture, preheating the polyol mixture, then adding diisocyanate, raising the heating temperature after heat preservation reaction, continuing heat preservation reaction, adding a chain extender and continuing temperature reaction, adding acetone to dilute after the isocyanate content reaches a theoretical value, cooling, adding triethylamine to neutralize, and standing to form a salt to obtain a polyurethane prepolymer; the polyol raw material includes polyether polyol;

[0009] (2) Deionized water and hydrazine hydrate are added to the polyurethane prepolymer, and after stirring, an aqueous polyurethane dispersion emulsion is obtained. The emulsion is evaporated under reduced pressure in a water bath, and after removing acetone, the remaining emulsion is freeze-dried to obtain a solvent-free aqueous polyurethane dry powder.

[0010] By adopting the above technical solution, the process of the present application first prepares an aqueous polyurethane dispersion emulsion, then removes the acetone added to reduce the viscosity by reduced pressure evaporation, and then evaporates the water by freeze drying. After the remaining polyurethane is precipitated, a solvent-free aqueous polyurethane dry powder can be obtained. The aqueous polyurethane dry powder of the present application can be re-emulsified after mixing with water. There is no significant difference in performance between the polyurethane film prepared using the re-emulsified polyurethane emulsion and the polyurethane film directly prepared using the aqueous polyurethane emulsion before solvent removal. Since the solvent-free aqueous polyurethane dry powder of the present application has removed the solvent, there is no need to worry about leakage during storage, nor is it necessary to spend the main transportation capacity on the transportation of the solvent, thereby effectively improving the transportation cost-effectiveness and storage stability of the aqueous polyurethane product.

[0011] Preferably, the chain extender includes sodium N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate or 1,2-dihydroxy-3-propyl ester sulfonic acid.

[0012] By adopting the above-mentioned technical solution, the present application optimizes the type of chain extender. Since the present application selects a chain extender containing a sulfonic acid (sodium) group, the finished polyurethane will also contain a certain amount of sulfonic acid (sodium) groups. The sulfonic acid (sodium) group improves the hydrophilicity of the water-based polyurethane, alleviates the stress concentration phenomenon, helps to increase the bonding force inside the film, and improves the tensile strength of the film.

[0013] Preferably, the polyol raw material further comprises fumaric acid polyester polyol, and the fumaric acid polyester polyol is prepared according to the following method:

[0014] Fumaric acid, diol and zinc oxide are mixed and preheated under nitrogen protection. After all the raw materials are melted, the mixture is stirred and the temperature is increased to react. When the acid value is lower than 60 mg / g, vacuum is applied and the vacuum is continuously increased until the reaction is completed. The temperature is then lowered and the material is discharged to obtain fumaric acid polyester polyol.

[0015] By adopting the above technical solution, the present application uses fumaric acid and diol as the main raw materials to prepare fumaric acid polyester polyol under the catalysis of zinc oxide. The fumaric acid polyester polyol has a condensed polycyclic rigid structure, which helps to improve the tensile strength of the polyurethane film.

[0016] Preferably, the diol is one of ethylene glycol, 1,4-butanediol, diethylene glycol and triethylene glycol.

[0017] By adopting the above technical solution, ethylene glycol, 1,4-butanediol, diethylene glycol, and triethylene glycol can all react with fumaric acid, thereby realizing the preparation of fumaric acid polyester polyol.

[0018] Preferably, in the method for preparing the fumaric acid polyester polyol, the reaction temperature is 210-230°C.

[0019] By adopting the above technical solution, the present application optimizes the reaction temperature for preparing fumaric acid-based polyester polyols. When the reaction temperature is too low, the reaction is difficult to fully proceed, while when the reaction temperature is too high, the resulting fumaric acid-based polyester polyol is susceptible to degradation. However, within the above temperature range, fumaric acid and diols can fully react, and the resulting fumaric acid-based polyester polyol can effectively improve the tensile strength of polyurethane films.

[0020] Preferably, in the method for preparing the fumaric acid polyester polyol, the amount of zinc oxide used is 0.05-0.10% of the total weight of fumaric acid and diol.

[0021] By adopting the above technical solution, the present application optimizes the amount of catalyst used, promotes the reaction between fumaric acid and diol, and helps to improve the tensile strength of the polyurethane film.

[0022] Preferably, in step (2) of the method, after obtaining the aqueous polyurethane dispersion emulsion, acrylate, vinyl sulfonic acid and initiator are added to the aqueous polyurethane dispersion emulsion.

[0023] By adopting the above-mentioned technical solution, the present application adds acrylate, vinyl sulfonic acid and initiator to the aqueous polyurethane dispersion emulsion. Under the action of the initiator, the acrylate can form a copolymer with the vinyl sulfonic acid. The sulfonic acid group in the copolymer can synergistically improve the tensile strength of the polyurethane film with the sulfonic acid (sodium) group introduced into the polyurethane by the chain extender, and the hydrogen bonding effect between the copolymer and the polyurethane also makes a certain contribution to the tensile strength, thereby effectively improving the performance of the polyurethane film.

[0024] Preferably, the acrylic acid ester includes one of butyl acrylate and methyl methacrylate.

[0025] By adopting the above technical solution, the present application preferably selects the type of acrylate, wherein methyl methacrylate is a hard monomer, and the hard segment introduced by it can more effectively improve the tensile strength of the polyurethane film.

[0026] Preferably, in step (1) of the method, polybutadiene diol is added to the polyol mixture before adding diisocyanate to the polyol mixture.

[0027] By adopting the above technical solution, polybutadiene diol can react with diisocyanate, thereby introducing non-polar rubber segments into water-based polyurethane. The double bonds in polybutadiene diol can also copolymerize with acrylate and vinyl sulfonic acid under the action of an initiator, thereby enhancing the bonding force between the polyurethane segments and the acrylic copolymer segments, and helping to improve the tensile strength of the polyurethane film.

[0028] Preferably, the initiator is at least one of ammonium persulfate and azobisisobutylcyanide.

[0029] By adopting the above technical solution, when the two initiators are used in combination, the monomer conversion rate is relatively high, which helps to improve the tensile strength of the polyurethane film.

[0030] In summary, this application has the following beneficial effects:

[0031] 1. The solvent-free waterborne polyurethane dry powder of the present application has been freed of solvent, so there is no need to worry about leakage during storage, nor is it necessary to expend major transportation capacity on the transportation of solvents, thereby effectively improving the transportation cost-effectiveness and storage stability of waterborne polyurethane products.

[0032] 2. This application uses a chain extender containing a sulfonic acid (sodium) group, so the finished polyurethane will also contain a certain amount of sulfonic acid (sodium) groups. The sulfonic acid (sodium) group improves the hydrophilicity of the water-based polyurethane, alleviates the stress concentration phenomenon, helps to increase the bonding force inside the film, and improves the tensile strength of the film.

[0033] 3. In the present application, acrylate, vinyl sulfonic acid and initiator are added to the aqueous polyurethane dispersion emulsion. Under the action of the initiator, acrylate can form a copolymer with vinyl sulfonic acid. The sulfonic acid group in the copolymer can synergistically improve the tensile strength of the polyurethane film with the sulfonic acid (sodium) group introduced into the polyurethane by the chain extender, and the hydrogen bonding effect between the copolymer and the polyurethane also makes a certain contribution to the tensile strength, thereby effectively improving the performance of the polyurethane film. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a comparison chart of the infrared spectra of Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0035] The present application is further described in detail below with reference to the Examples, Preparation Examples and Comparative Examples. The raw materials involved in the present application can all be obtained commercially.

[0036] Preparation Example of Fumaropimaric Acid Polyester Polyol

[0037] The following is an explanation using Preparation Example 1.

[0038] Preparation Example 1

[0039] In this preparation example, ethylene glycol is used as diol, the molar ratio of fumaric acid to diol is 1:1.2, and the amount of zinc oxide used is 0.03% of the total weight of fumaric acid and diol.

[0040] In this preparation example, fumaric acid polyester polyol was prepared according to the following method:

[0041] Fumaric acid, diol, and zinc oxide were mixed, preheated under nitrogen protection, and heated to 160°C at a rate of 10°C / h. The mixture was then kept warm until all the raw materials were melted, stirred, and the temperature was raised to 200°C (reaction temperature). When the acid value of the reaction reached less than 60 mg / g, vacuum was applied. The vacuum was continuously increased until the reaction was completed, and the mixture was cooled to 160°C for discharging to obtain fumaric acid polyester polyol.

[0042] Preparation Example 2

[0043] The difference between this Preparation Example and Preparation Example 1 is that the diol is 1,4-butanediol.

[0044] Preparation Example 3

[0045] The difference between this Preparation Example and Preparation Example 1 is that the diol is diethylene glycol.

[0046] Preparation Example 4

[0047] The difference between this Preparation Example and Preparation Example 1 is that the diol is triethylene glycol.

[0048] Preparation Example 5

[0049] The difference between this preparation example and preparation example 4 is that in the method for preparing fumaric pimaric acid polyester polyol, the reaction temperature is 210°C.

[0050] Preparation Example 6

[0051] The difference between this preparation example and preparation example 4 is that in the method for preparing fumaric acid polyester polyol, the reaction temperature is 220°C.

[0052] Preparation Example 7

[0053] The difference between this preparation example and preparation example 4 is that in the method for preparing fumaric pimaric acid polyester polyol, the reaction temperature is 230°C.

[0054] Preparation Example 8

[0055] The difference between this preparation example and preparation example 4 is that in the method for preparing fumaric acid polyester polyol, the reaction temperature is 240°C.

[0056] Preparation Example 9

[0057] The difference between this preparation example and preparation example 6 is that in the method for preparing the fumaric acid polyester polyol, the amount of zinc oxide used is 0.05% of the total weight of fumaric acid and diol.

[0058] Preparation Example 10

[0059] The difference between this preparation example and preparation example 6 is that in the method for preparing fumaric acid polyester polyol, the amount of zinc oxide used is 0.07% of the total weight of fumaric acid and diol.

[0060] Preparation Example 11

[0061] The difference between this preparation example and preparation example 6 is that in the method for preparing the fumaric acid polyester polyol, the amount of zinc oxide used is 0.10% of the total weight of fumaric acid and diol.

[0062] Preparation Example 12

[0063] The difference between this preparation example and preparation example 6 is that in the method for preparing the fumaric acid polyester polyol, the amount of zinc oxide used is 0.15% of the total weight of fumaric acid and diol.

[0064] Example

[0065] Examples 1-5

[0066] The following description will be given using Example 1 as an example.

[0067] Example 1

[0068] In this embodiment, the polyol mixture is prepared by mixing PTMG-2000 and GY-3010E in a weight ratio of 4:1, IPDI is selected as the diisocyanate, and dimethylol propionic acid is selected as the chain extender.

[0069] This embodiment provides a process for preparing a solvent-free waterborne polyurethane dry powder, comprising the following steps:

[0070] (1) PTMG-2000 and GY-3010E were mixed to obtain 75 kg of a polyol mixture, which was preheated at 70°C, and then 35 kg of diisocyanate was added. After 30 minutes of heat preservation reaction, the temperature was increased to 80°C and the heat preservation reaction was continued for 30 minutes. After 7.5 kg of a chain extender was added, the temperature was increased to 85°C and the heat preservation reaction was continued. After the isocyanate content reached the theoretical value, the mixture was cooled to 60°C, 48 kg of acetone was added for dilution, and 5.3 kg of triethylamine was added to neutralize the mixture when the mixture continued to cool to 30°C. The mixture was allowed to stand for 15 minutes to form a salt, thereby obtaining a polyurethane prepolymer.

[0071] (2) 160 kg of deionized water and 1.7 kg of hydrazine hydrate were added to the polyurethane prepolymer, and the mixture was stirred for 30 min to obtain an aqueous polyurethane dispersion emulsion. The mixture was kept warm at 80° C. for 5 h, then cooled to 35° C., and heated in a 35° C. water bath while maintaining a vacuum degree within the range of 0.3-0.4 atm. The emulsion was evaporated under reduced pressure, and after removing acetone, the remaining emulsion was freeze-dried to obtain a solvent-free aqueous polyurethane dry powder.

[0072] Example 2

[0073] In this embodiment, the polyol mixture is prepared by mixing PTMG-2000 and polycarbonate diol 980R in a weight ratio of 5:2, IPDI is selected as the diisocyanate, and 1,4-butanediol and dimethylolpropionic acid are selected as the chain extender.

[0074] This embodiment provides a process for preparing a solvent-free waterborne polyurethane dry powder, comprising the following steps:

[0075] (1) PTMG-2000 and polycarbonate diol 980R were mixed to obtain 70 kg of a polyol mixture, which was preheated at 60 ° C, and then 39 kg of diisocyanate was added. After 30 minutes of heat preservation reaction, the temperature was increased to 70 ° C and the heat preservation reaction was continued for 30 minutes. After 5 kg of 1,4-butanediol was added, the temperature was increased to 80 ° C and the heat preservation reaction was continued for 30 minutes. 5 kg of dimethylol propionic acid was added and the heat preservation reaction was continued. After the isocyanate content reached the theoretical value, the mixture was cooled to 60 ° C, 40 kg of acetone was added for dilution, and 3.2 kg of triethylamine was added to neutralize the mixture when it continued to cool to 30 ° C. The mixture was allowed to stand for 15 minutes to form a salt, thereby obtaining a polyurethane prepolymer.

[0076] (2) Add 190 kg of deionized water and 1.9 kg of hydrazine hydrate to the polyurethane prepolymer, stir for 30 minutes to obtain an aqueous polyurethane dispersion emulsion, continue to keep the temperature at 80 ° C for 5 hours, then cool to 35 ° C, and maintain the vacuum degree in the range of 0.3-0.4 atm under the condition of heating in a water bath at 35 ° C., evaporate the emulsion under reduced pressure, remove acetone, and freeze-dry the remaining emulsion to obtain a solvent-free aqueous polyurethane dry powder.

[0077] Example 3

[0078] The difference between this embodiment and embodiment 2 is that sodium N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate is used as the chain extender.

[0079] Example 4

[0080] The difference between this embodiment and embodiment 2 is that 1,2-dihydroxy-3-propyl sulfonic acid is used as the chain extender.

[0081] Example 5

[0082] The difference between this embodiment and embodiment 4 is that the polycarbonate diol 980R is replaced by the fumaric acid polyester polyol of preparation example 1.

[0083] As shown in Table 1, the difference between Examples 5-16 is that the preparation examples of polyester polyols are different.

[0084] Table 1 Preparation example of polyester polyol

[0085] sample Preparation Example Example 5 Preparation Example 1 Example 6 Preparation Example 2 Example 7 Preparation Example 3 Example 8 Preparation Example 4 Example 9 Preparation Example 5 Example 10 Preparation Example 6 Example 11 Preparation Example 7 Example 12 Preparation Example 8 Example 13 Preparation Example 9 Example 14 Preparation Example 10 Example 15 Preparation Example 11 Example 16 Preparation Example 12

[0086] Example 17

[0087] The difference between this embodiment and Example 15 is that, in step (2) of preparing the solvent-free aqueous polyurethane dry powder, after obtaining the aqueous polyurethane dispersion emulsion, acrylate, vinyl sulfonic acid and initiator are further added to the aqueous polyurethane dispersion emulsion, the acrylate is butyl acrylate, the initiator is ammonium persulfate, the amount of acrylate is 25% of the total weight of the polyurethane prepolymer, the amount of vinyl sulfonic acid is 5% of the total weight of the polyurethane prepolymer, and the amount of initiator is 0.3% of the total weight of the polyurethane prepolymer.

[0088] Example 18

[0089] The difference between this embodiment and embodiment 17 is that methyl methacrylate is used as the acrylic acid ester.

[0090] Example 19

[0091] The difference between this embodiment and Example 18 is that, in step (1) of preparing the solvent-free water-based polyurethane dry powder, polybutadiene diol is also added to the polyol mixture before adding diisocyanate to the polyol mixture. The number average molecular weight of the polybutadiene diol is 2000, and the amount of the polybutadiene diol is 10% by weight of the polycarbonate diol 980R.

[0092] Example 20

[0093] The difference between this embodiment and embodiment 19 is that the initiator is prepared by mixing ammonium persulfate and azobisisobutyronitrile in a weight ratio of 2:1.

[0094] Comparative Example

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 1 is that after obtaining the aqueous polyurethane dispersion emulsion, no subsequent operation is performed, and the aqueous polyurethane dispersion emulsion is used as the final product.

[0097] Comparative Example 2

[0098] The difference between this comparative example and Example 2 is that after obtaining the aqueous polyurethane dispersion emulsion, no subsequent operation is performed, and the aqueous polyurethane dispersion emulsion is used as the final product.

[0099] Performance testing methods

[0100] Prior to formal testing, acetone recovered from the reduced-pressure evaporation process was added to the dry polyurethane powders of each example. After stirring, the same amount of deionized water as used in the preparation process was added. After shear stirring and dispersion for 30 minutes, a re-emulsified aqueous polyurethane emulsion was obtained. The re-emulsified aqueous polyurethane emulsions corresponding to Examples 1-20 and the aqueous polyurethane dispersions of Comparative Examples 1-2 served as the test subjects in the following tests. Each test subject was coated onto mirror-finished release paper and dried in a 120°C forced-air oven to obtain a polyurethane coating film (film thickness 0.09 mm).

[0101] 1. Mechanical properties test

[0102] Tensile strength tests were performed using a universal materials testing machine (Meters microcomputer-controlled CMT6104 electronic universal testing machine) (instrument operating speed: 400 mm / min; dumbbell-shaped test film thickness: 0.09 mm). Each sample was tested three times, and the average value was taken. The results are shown in Table 2.

[0103] 2. Infrared test

[0104] The polyurethane coating films corresponding to Example 1 and Comparative Example 1 were subjected to infrared testing, and the results were as follows: Figure 1 shown.

[0105] Table 2

[0106]

[0107] Combining Examples 1-2 with Comparative Examples 1-2 and Table 2, it can be seen that the tensile strengths measured in Example 1 and Comparative Example 1 are relatively close, and the tensile strengths measured in Example 2 and Comparative Example 2 are relatively close, indicating that the solvent-free waterborne polyurethane dry powder of the present application is more convenient to transport while maintaining its original mechanical properties. While maintaining substantially all of the mechanical properties, the solvent-free waterborne polyurethane dry powder of the present application, since the solvent is removed, does not need to worry about leakage during storage, and does not require the primary transportation capacity to be expended on transporting the solvent. This effectively improves the transportation cost-effectiveness and storage stability of the waterborne polyurethane product.

[0108] Combined with Example 1 and Comparative Example 1 Figure 1 It can be seen that the infrared signals of the two are consistent. -1 There is a strong absorption peak near 1741cm, which is the stretching vibration of -NH; -1 There is a strong absorption peak near 1558cm, which is the C=O group stretching vibration absorption. Due to its large number in the polymer chain, the absorption intensity is large, and the intensity does not change much before and after freeze drying; -1 There is an absorption peak near the -NH bending vibration, indicating the presence of -NHCOO-. Figure 1 It can be seen that only physical changes occur during the freeze-drying process, only water is evaporated and removed, and the structure of the water-based polyurethane product does not undergo chemical changes.

[0109] From Examples 2-4 and Table 2, it can be seen that since Examples 3-4 selected a chain extender containing a sulfonic acid (sodium) group, the finished polyurethane will also contain a certain amount of sulfonic acid (sodium) groups. The sulfonic acid (sodium) group improves the hydrophilicity of the water-based polyurethane, alleviates the stress concentration phenomenon, and helps to increase the bonding force inside the film, thereby improving the tensile strength of the film.

[0110] Combining Example 4 and Example 5 with Table 2, it can be seen that the tensile strength measured in Example 5 is higher. This is because the fumaric acid polyester polyol has a fused polycyclic rigid structure, which helps to improve the tensile strength of the polyurethane film.

[0111] Combining Examples 5-8 with Table 2, it can be seen that the tensile strengths measured in Examples 7-8 are relatively high. This is because the molecular weight of the fumaric acid polyester polyol prepared using diethylene glycol and triethylene glycol is relatively large, which enhances the intermolecular force and thus hinders the occurrence of tensile failure.

[0112] As can be seen from Examples 8-12 and Table 2, in the method for preparing fumaric acid-based polyester polyols, the tensile strength of the polyurethane film first increases and then decreases with increasing reaction temperature. This is because when the reaction temperature is too low, the reaction is difficult to fully proceed, while when the reaction temperature is too high, the resulting fumaric acid-based polyester polyol is susceptible to degradation. However, within the range of 210-230°C, fumaric acid and diols react fully, and the resulting fumaric acid-based polyester polyol can effectively improve the tensile strength of the polyurethane film.

[0113] It can be seen from Example 10, Examples 13-16 and Table 2 that in the method for preparing fumaric acid polyester polyol, when the amount of zinc oxide is 0.05-0.10% of the sum of the weight of fumaric acid and diol, the tensile strength of the polyurethane film increases significantly with increasing the amount of zinc oxide.

[0114] Combining Examples 15 and 17-18, it can be seen that the tensile strength measured in Examples 17-18 is relatively high. This is because, under the action of the initiator, the acrylate can form a copolymer with the vinyl sulfonic acid. The sulfonic acid groups in the copolymer can synergistically improve the tensile strength of the polyurethane film with the sulfonic acid (sodium) groups introduced into the polyurethane by the chain extender. In addition, the hydrogen bonding between the copolymer and the polyurethane also contributes to the tensile strength, thereby effectively improving the performance of the polyurethane film. Of the two preferred acrylates in this application, methyl methacrylate has a higher effect on tensile strength.

[0115] Combining Examples 18 and 19, it can be seen that the tensile strength of the film measured in Example 19 is higher. This is because polybutadiene diol can react with diisocyanate, thereby introducing non-polar rubber segments into the water-based polyurethane. The double bonds in polybutadiene diol can also copolymerize with acrylate and vinyl sulfonic acid under the action of an initiator, thereby enhancing the bonding force between the polyurethane segments and the acrylic copolymer segments, which helps to improve the tensile strength of the polyurethane film.

[0116] Combining Examples 19 and 20, it can be seen that the tensile strength of the film measured in Example 19 is higher. This is because when the two initiators are used in combination, the monomer conversion rate is relatively high, which helps to improve the tensile strength of the polyurethane film.

[0117] The above embodiments are merely explanations of the present application and are not limitations of the present application. After reading this specification, those skilled in the art may make modifications to the embodiments of the present application as needed without any creative contribution. However, as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A process for preparing a solvent-free waterborne polyurethane dry powder, characterized in that: The following steps are involved: (1) mixing polyol raw materials to obtain a polyol mixture, preheating the polyol mixture, then adding diisocyanate, raising the heating temperature after heat preservation reaction, continuing heat preservation reaction, adding a chain extender and continuing temperature reaction, adding acetone to dilute after the isocyanate content reaches a theoretical value, cooling, adding triethylamine to neutralize, and standing to form a salt to obtain a polyurethane prepolymer; the polyol raw material includes polyether polyol; (2) Deionized water and hydrazine hydrate are added to the polyurethane prepolymer, and after stirring, an aqueous polyurethane dispersion emulsion is obtained. The emulsion is evaporated under reduced pressure in a water bath, and after removing acetone, the remaining emulsion is freeze-dried to obtain a solvent-free aqueous polyurethane dry powder.

2. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 1, wherein: The chain extender includes sodium N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate or 1,2-dihydroxy-3-propyl ester sulfonic acid.

3. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 1, wherein: The polyol raw material further includes fumaric acid polyester polyol, and the fumaric acid polyester polyol is prepared according to the following method: Fumaric acid, diol and zinc oxide are mixed and preheated under nitrogen protection. After all the raw materials are melted, the mixture is stirred and the temperature is increased to react. When the acid value is lower than 60 mg / g, vacuum is applied and the vacuum is continuously increased until the reaction is completed. The temperature is then lowered and the material is discharged to obtain fumaric acid polyester polyol.

4. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 3, wherein: The diol is one of ethylene glycol, 1,4-butanediol, diethylene glycol and triethylene glycol.

5. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 3, wherein: In the method for preparing the fumaric acid polyester polyol, the reaction temperature is 210-230°C.

6. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 3, wherein: In the method for preparing the fumaric acid polyester polyol, the amount of zinc oxide used is 0.05-0.10% of the total weight of fumaric acid and diol.

7. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 1, characterized in that: In step (2) of the method, after obtaining the aqueous polyurethane dispersion emulsion, acrylate, vinyl sulfonic acid and initiator are added to the aqueous polyurethane dispersion emulsion.

8. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 7, characterized in that: The acrylic acid ester includes one of butyl acrylate and methyl methacrylate.

9. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 8, characterized in that: In step (1) of the method, polybutadiene diol is added to the polyol mixture before adding diisocyanate to the polyol mixture.

10. The process for preparing the solvent-free waterborne polyurethane dry powder according to claim 7, characterized in that: The initiator is at least one of ammonium persulfate and azobisisobutylcyanide.

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