Waterborne polyurethane curing agent as well as preparation method and application thereof

Abstract

The invention discloses a waterborne polyurethane curing agent as well as a preparation method and application thereof. The waterborne polyurethane curing agent is prepared from the following raw materials in parts by mass; based on the total amount of the raw materials being 100 parts, the raw materials comprise 30-32.5 parts of aromatic isocyanate; 2 to 2.3 parts of 2, 2-dimethylolpropionic acid; 25 to 27.5 parts of a nonionic hydrophilic monomer; 3 to 4.5 parts of trimethylolpropane; 23 parts to 25.5 parts of a solvent; 8 to 16.5 parts of an end-capping reagent; and 0.07 to 0.1 part of an organic tin catalyst. According to the invention, aromatic isocyanate, 2, 2-dimethylolpropionic acid, a nonionic hydrophilic monomer, trimethylolpropane, an end-capping reagent and an organic tin catalyst are selected as raw materials to prepare the curing agent, and through the synergistic effect of the raw materials, the performance balance of rapid curing, water dispersibility, stability and high mechanical strength is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of curing agents, in particular to a waterborne polyurethane curing agent, a preparation method and application thereof. BACKGROUND

[0002] In recent years, waterborne polyurethane curing agents have attracted extensive attention in the field of green functional materials. However, in order to improve water dispersibility, the existing waterborne polyurethane curing agents need to introduce a large amount of polyether structure, which will lead to a decrease in the curing rate of the curing agent, and a decrease in the crosslinking strength and durability. In addition, the high hydrophilicity of the polyether structure can also increase the viscosity of the system and increase the moisture absorption, thereby reducing the water resistance and drying efficiency of the coating.

[0003] Therefore, it is necessary to develop a waterborne polyurethane curing agent with high water dispersibility and high mechanical properties and stability. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present application provides a waterborne polyurethane curing agent, which has the characteristics of high water dispersibility, good stability and high mechanical properties.

[0005] The second aspect of the present application also provides a preparation method of a waterborne polyurethane curing agent.

[0006] The third aspect of the present application also provides an application of a waterborne polyurethane curing agent.

[0007] According to the first aspect of the present application, a waterborne polyurethane curing agent is provided, which is prepared from the following raw materials in parts by mass; the total amount of the raw materials is 100 parts:

[0008]

[0009] According to a preferred embodiment of the present application, the non-ionic hydrophilic monomer includes at least one of polyethylene glycol, polypropylene glycol, EO / PO block copolymer, hydroxyl-terminated polyether, and sugar polyol derivatives.

[0010] According to a preferred embodiment of the present application, the polyethylene glycol includes PEG-200, PEG-400, and PEG-600.

[0011] According to a preferred embodiment of the present application, the aromatic isocyanate includes at least one of toluene diisocyanate and diphenyl methane diisocyanate. Thus, when the aromatic isocyanate is selected from the above-mentioned substances, the crosslinking degree and cohesive energy of the polyurethane network can be significantly improved, so that the final coating film has higher hardness, tensile strength and water resistance.

[0012] According to a preferred embodiment of the present application, the end-capping agent comprises at least one of a phenolic end-capping agent or an alcoholic end-capping agent.

[0013] According to a preferred embodiment of the present application, the phenolic end-capping agent comprises at least one of phenol, p-chlorophenol, 2,4-dichlorophenol, 2-chloro-4-nitrophenol, p-bromophenol, p-nitrophenol. Further, when p-chlorophenol is selected, the heat resistance and film strength are improved.

[0014] According to a preferred embodiment of the present application, the alcoholic end-capping agent comprises at least one of 1,2-propanediol, methanol, ethanol, n-butanol, isopropyl alcohol, benzyl alcohol, 2-ethylhexanol, 2-hydroxymethylpyridine, 2-hydroxyethyl methacrylate. Further, when 1,2-propanediol is selected, the flexibility and workability can be adjusted.

[0015] According to a preferred embodiment of the present application, the solvent comprises at least one of acetone, methyl ethyl ketone or methyl isobutyl ketone.

[0016] According to a preferred embodiment of the present application, the organotin catalyst comprises at least one of dibutyltin dilaurate, dibutyltin dioctoate, dibutyltin dinonanoate.

[0017] The waterborne polyurethane curing agent according to the embodiment of the present application has at least the following beneficial effects:

[0018] The present application firstly takes aromatic isocyanate as the only isocyanate source, adds 2,2-dimethylol propionic acid and non-ionic hydrophilic monomer. The combination of the above can not only ensure good water dispersion, but also significantly improve the stability and reactivity of the system. This is because the non-ionic hydrophilic monomer and 2,2-dimethylol propionic acid can maintain electrostatic repulsion when the pH changes, ensuring dispersion stability. At the same time, the steric hindrance generated by the non-ionic segment and the anionic electrostatic repulsion synergistically prevent particle agglomeration and prolong the storage time of the dispersion system.

[0019] The combination further introduces a trifunctional crosslinking agent trimethylolpropane (TMP) to further improve the crosslinking density of the system and speed up the curing process. The introduction of an end-capping agent in the system can further improve the storage stability of the curing agent while maintaining excellent water dispersion. The synergistic effect of the above strategies achieves a balance between fast curing, water dispersibility, stability and high mechanical strength.

[0020] According to a second aspect of the present application, a method for preparing the waterborne polyurethane curing agent of the first aspect of the present application is provided, comprising the following steps:

[0021] S1, mixing aromatic isocyanate, 2,2-dimethylol propionic acid, non-ionic hydrophilic monomer and organic tin catalyst to carry out prepolymerization to obtain intermediate I;

[0022] S2, adding trimethylolpropane to the reaction system of step S1 to continue the reaction to obtain intermediate II;

[0023] S3, adding a blocking agent to the reaction system of step S2 to continue the reaction; thus, the water-based polyurethane curing agent is obtained.

[0024] According to a preferred embodiment of the present application, the temperature of the prepolymerization is 65-70℃.

[0025] According to a preferred embodiment of the present application, the time of the prepolymerization is 3-5h.

[0026] According to a preferred embodiment of the present application, in step S2, the temperature of the reaction is 50-60℃.

[0027] According to a preferred embodiment of the present application, in step S2, the time of the reaction is 3-4h.

[0028] According to a preferred embodiment of the present application, in step S3, the temperature of the reaction is 50-60℃.

[0029] According to a preferred embodiment of the present application, in step S3, the time of the reaction is 1.5h-2h.

[0030] The third aspect of the present application provides an application of the above-mentioned water-based polyurethane curing agent in preparing water-based paint and adhesive.

[0031] Other features and advantages of the present application will be illustrated in the following description, and some will become apparent from the description, or will be understood by those skilled in the art through implementation of the present application. DETAILED DESCRIPTION

[0032] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in combination with the embodiments, but the present application is not limited to these embodiments.

[0033] The reagents, methods and equipment used in the present application are all conventional reagents, methods and equipment in the technical field, unless otherwise specified.

[0034] Some raw materials in the examples and comparative examples of the present application are as follows:

[0035] Aromatic isocyanate: toluene diisocyanate (TDI); purchased from Anjie Chemical, CAS: 584-84-9;

[0036] Nonionic hydrophilic monomer: polyethylene glycol (PEG-400); purchased from Shanghai Macklin Biochemical Technology Co., Ltd., CAS: 25322-68-3;

[0037] Solvent: acetone; purchased from Anjieji Chemical;

[0038] End-capping agent: p-chlorophenol and 1,2-propanediol; purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.;

[0039] Organotin catalyst: dibutyltin dilaurate; purchased from Anjieji Chemical;

[0040] 2,2-dimethylol propionic acid, trimethylolpropane, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.

[0041] Example 1

[0042] This example provides a water-based polyurethane curing agent, the raw materials are shown in Table 1, and the preparation method is as follows:

[0043] S1, in a 250 mL four-necked flask equipped with a reflux condenser, a stirrer, a constant pressure dropping funnel and a N2 protection device, toluene diisocyanate (TDI), 2,2-dimethylol propionic acid (DMPA), polyethylene glycol (PEG-400) and dibutyltin dilaurate were added, and the reaction was carried out at 65-70°C for 4h to obtain intermediate I;

[0044] S2, in the reaction system of step S1, trimethylolpropane (TMP) was added, and the reaction was carried out at 60°C for 3-4h to obtain intermediate II;

[0045] S3, in the reaction system of step S2, 1,2-propanediol was added under the condition of keeping 50-60°C, and the reaction was continued for 1.5-2h, then the temperature was lowered and the reaction was stopped when the -NCO content was unchanged, to obtain the curing agent.

[0046] Examples 2-6

[0047] Examples 2-6 provide a series of water-based polyurethane curing agents, the raw material usage is shown in Table 1, and the preparation method is the same as example 1.

[0048] Table 1 Examples 1-6 (weight parts)

[0049]

[0050] Comparative examples 1-2

[0051] Comparative examples 1-2 provide a series of water-based polyurethane curing agents, the raw material usage is shown in Table 2, and the preparation method is the same as example 5.

[0052] Table 2 Comparative examples 1-2 (weight parts)

[0053]

[0054] Performance test

[0055] The waterborne polyurethane curing agents of Examples 1-6 and Comparative Examples 1-2 of the present application were subjected to the following tests; the results are shown in Table 3:

[0056] 1. Unblocking temperature test: According to GB / T 19466.3-2004 / ISO 11357-3:1999 "Differential scanning calorimetry - Part 3: Determination of the glass transition temperature", the unblocking temperature of the sample was determined using a differential scanning calorimeter (DSC). The test conditions were nitrogen atmosphere, heating rate of 10℃ / min, and the onset temperature and peak temperature of the endothermic and exothermic peaks corresponding to the unblocking reaction of isocyanate groups in the heat flow curve were recorded.

[0057] 2. NCO content test after synthesis: According to GB / T 12009.4-2016 "Determination of free isocyanate content of polyurethane prepolymers", the free NCO mass fraction in the sample was determined using diphenylamine-toluene titration method. A certain amount of sample was taken, dissolved in toluene, and titrated with standard formic acid solution using diphenylamine as an indicator, and the NCO content was calculated.

[0058] 3. Change rate of free NCO content after 180 days of storage: The sample was sealed and stored in an environment of (25±2)℃ for 180 days, and the free NCO content was determined periodically according to GB / T 12009.4-2016. The change rate of NCO content after 180 days was calculated based on the initial NCO content, reflecting the storage stability.

[0059] 4. Thermogravimetric analysis (5% weight loss temperature): According to GB / T 19466.6-2004 / ISO 11358:1997 "Plastics - Thermogravimetric analysis - General method", the thermal decomposition behavior of the sample was determined using a thermogravimetric analyzer. The test conditions were nitrogen atmosphere, heating rate of 10℃ / min, and the temperature corresponding to a 5% mass loss of the sample was recorded as the 5% weight loss temperature.

[0060] 5. Stability evaluation: visual observation; "best" means no delamination, no precipitation, and the change rate of free NCO after 180 days of storage is less than 1%; "good" means no delamination, no precipitation, and the change rate of free NCO after 180 days of storage is greater than 1% and less than 5%; "medium" means there is flocculation; "very poor" means there is gel and flocculation.

[0061] Table 3 Performance data of Examples 1-6 and Comparative Examples 1-2

[0062]

[0063] After synthesis, Fourier infrared detection was performed, and no peak of the NCO functional group was found in Examples 1 to 6 of the present invention, indicating that the end-capping reaction was sufficient under the present process conditions, the end-capping agent reacted completely with NCO, and there was no detectable free isocyanate group in the system, which had good initial stability. Although the free NCO content of the end-blocking curing agent synthesized by the present invention was 0% after the reaction was completed, during storage, some systems may still have very small amounts of incompletely stabilized isocyanate structures or latent NCO groups. These groups are affected by trace amounts of moisture or residual hydroxyl groups in the system during storage, and may react slowly, resulting in a slight decrease in the NCO content during detection. Setting the "180-day NCO decrease rate" as a stability indicator can reflect the end-capping effect and the chemical stability of the system during storage.

[0064] As can be seen from the data in Table 3, the present invention not only significantly improves the water dispersion stability of the waterborne polyurethane curing agent (no obvious precipitation within 180 days, and the free NCO change rate is less than 5%), but also exhibits excellent mechanical strength, ductility, and heat resistance in terms of application performance.

[0065] Furthermore, the waterborne polyurethane curing agent of Example 2 of the present invention, the waterborne polyurethane curing agent of Example 4 and a commercially available curing agent (Guangdong Huaguoshan Environmental Protection Technology Co., Ltd.; modified polyurethane dispersion 5420; acrylic modified polyurethane dispersion) was used to prepare a waterborne two-component polyurethane coating, and the corresponding properties were tested; the preparation method is as follows:

[0066] A water-based hydroxylated acrylic dispersion (component A; hydroxyl content: 3%, solid content: 40%) and a curing agent (component B, selected from Example 5, Example 2, or a commercially available curing agent) were mixed at an NCO / OH ratio of 1.5 and stirred until uniform. The mixture was then evenly coated on the surface of an aluminum plate to a wet film thickness of approximately 100 μm and baked at 60°C for 60 min. Paint Films I, II, and III were obtained, respectively.

[0067] The tensile strength, elongation at break, adhesion, and water resistance of paint films I, II, and III were tested, respectively. The results are shown in Table 4.

[0068] Tensile strength: GB / T 528-2009 “Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties”, 2009.

[0069] Elongation at break: GB / T 528-2009 “Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties”, 2009.

[0070] Adhesion: GB / T 9286-2021 "Scratch test for paint and varnish films" 2021.

[0071] Water resistance; GB / T 1733-2021 "Determination of water resistance of paint, varnish and varnish coating" 2021.

[0072] Table 4

[0073]

[0074] From the data in Table 4, the waterborne polyurethane curing agent according to the embodiments of the present application is used to prepare a waterborne polyurethane paint film, which has good mechanical properties and water resistance.

[0075] The above is a detailed description of the embodiments of the present application, but the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application.

Claims

1. A waterborne polyurethane curing agent, characterized in that The following raw materials are prepared in parts by weight; the total amount of raw materials is calculated as 100 parts:

2. The waterborne polyurethane curing agent according to claim 1, characterized in that The nonionic hydrophilic monomer includes at least one of polyethylene glycol, polypropylene glycol, EO / PO block copolymer, terminal hydroxylated polyether, and sugar polyol derivatives.

3. The waterborne polyurethane curing agent according to claim 1, characterized in that The aromatic isocyanate includes at least one of toluene diisocyanate and diphenylmethane diisocyanate.

4. The waterborne polyurethane curing agent according to claim 1, characterized in that The end-capping agent includes at least one of a phenol end-capping agent and an alcohol end-capping agent.

5. The waterborne polyurethane curing agent according to claim 4, characterized in that The alcohol capping agent includes at least one of 1,2-propylene glycol, methanol, ethanol, n-butanol, isopropanol, benzyl alcohol, 2-ethylhexanol, 2-hydroxymethylpyridine or 2-hydroxyethyl methacrylate.

6. The waterborne polyurethane curing agent according to claim 1, characterized in that The solvent includes at least one of acetone, methyl ethyl ketone or methyl isobutyl ketone.

7. The waterborne polyurethane curing agent according to claim 1, characterized in that The organic tin catalyst includes at least one of dibutyltin dilaurate, dibutyltin dioctoate or dibutyltin dipelargonate.

8. A method for preparing the waterborne polyurethane curing agent according to any one of claims 1 to 7, characterized in that: The steps include: S1, mixing aromatic isocyanate, 2,2-dimethylol propionic acid, a nonionic hydrophilic monomer and an organotin catalyst to perform a prepolymerization reaction to obtain an intermediate I; S2. Add trimethylolpropane to the reaction system of step S1 and continue the reaction to obtain intermediate II; S3. Add a blocking agent to the reaction system of step S2 and continue the reaction to obtain a waterborne polyurethane curing agent.

9. The preparation method according to claim 8, characterized in that The temperature of the prepolymerization reaction is 65°C to 70°C.

10. Use of the waterborne polyurethane curing agent according to any one of claims 1 to 7 in the preparation of waterborne coatings and adhesives.

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