Isocyanate-modified phenalkamine curing agent, and preparation method and application thereof

Abstract

The application discloses an isocyanate-modified phenolic amine curing agent and a preparation method and application thereof, and the preparation method comprises the following steps: synthesizing a phenolic amine curing agent; adding a fatty acid to perform an amidation reaction; and isocyanate modification. In the preparation process, the unreacted small-molecule amine in the system is removed by using the fatty acid reaction, and then isocyanate modification treatment is performed, so that the activity of the reaction after the isocyanate is added is effectively reduced, the reaction condition is more moderate and controllable, no gel or explosive polymerization phenomenon is generated, the prepared curing agent not only has a low-temperature rapid curing performance, but also effectively improves the tensile strength and elongation at break of the cured epoxy resin and the flexibility and impact strength of an epoxy resin paint film, and has excellent use performance and strong practicability.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin curing agents, and in particular to an isocyanate-modified phenolic amine curing agent, its preparation method, and its application. Background Technology

[0002] Epoxy coatings are widely used in heavy-duty anti-corrosion, marine coatings, steel structure anti-corrosion, and bridge coatings due to their excellent adhesion and anti-corrosion properties. Phenolic amine curing agents are commonly used and offer superior performance in epoxy curing. In epoxy 2K systems, the use of phenolic amine curing agents not only meets the requirements for low surface preparation of the substrate but also satisfies the requirements for low-temperature curing.

[0003] However, existing phenolic amine curing agents have the following drawbacks after curing: the paint film surface is brittle and the adhesion is insufficient. In addition, fast-drying phenolic amine curing agents are often characterized by poor impact resistance and poor flexibility, which cannot meet the needs of coating customers. Summary of the Invention

[0004] This invention provides an isocyanate-modified phenolic amine curing agent, its preparation method, and its application, which can solve the above-mentioned problems existing in the curing of epoxy resins by existing phenolic amine curing agents.

[0005] To address the aforementioned technical problems, this invention provides an isocyanate-modified phenolic amine curing agent, comprising at least the following compounds:

[0006]

[0007] In the formula, R is a phenolic group;

[0008] R1 is -H,

[0009] R2 is an amine structure with two -NH2 residues removed;

[0010] R3 is

[0011] To address the aforementioned technical problems, this invention provides a method for preparing an isocyanate-modified phenolic amine curing agent, comprising the following steps:

[0012] (1) Synthesis of phenolic amine curing agent: A certain amount of phenolic compounds, amine compounds and aldehyde compounds are reacted in a reaction flask to generate phenolic amine curing agent;

[0013] (2) Amide reaction: Vacuum the mixture after the reaction in step (1) to remove water and small molecule amines, then add fatty acids to it, raise the temperature to carry out the amidation reaction, and further remove the small molecule amines in the system;

[0014] (3) Isocyanate modification: Isocyanate is added dropwise to the mixture after the amidation reaction in step (2). After the addition is complete, the mixture is heated and kept warm to carry out the isocyanate modification reaction, and the isocyanate-modified phenolic amine curing agent is obtained.

[0015] In a preferred embodiment of the present invention, in step (1), the molar ratio of the phenolic compound, the amine compound and the aldehyde compound is 1:1.0 to 2.2:1.05 to 2.05.

[0016] In a preferred embodiment of the present invention, in step (1), the reaction process conditions are: temperature 75-85°C, time 3-8h.

[0017] In a preferred embodiment of the present invention, in step (1), the phenolic compound includes at least one of cashew phenol, phenol, cresol, pentadecyl resorcinol, resorcinol, bisphenol A or bisphenol F;

[0018] The amine compounds include at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, m-phenylenediamine, or 1,3-cyclohexanedimethylamine;

[0019] The aldehyde compounds include at least one of paraformaldehyde, furfural, and benzaldehyde.

[0020] In a preferred embodiment of the present invention, in step (2), the amount of fatty acid added is 2 to 10% of the total mass of the phenolic compounds, amine compounds and aldehyde compounds.

[0021] In a preferred embodiment of the present invention, the fatty acid includes at least one of oleic acid, isooctanoic acid, butyric acid, heptanoic acid, caprylic acid, nonanoic acid, stearic acid, or lauric acid.

[0022] In a preferred embodiment of the present invention, in step (3), the amount of isocyanate added is 0.005 to 0.02 times the mass of the reaction product in step (2).

[0023] In a preferred embodiment of the present invention, the isocyanate includes at least one of toluene diisocyanate, diphenylmethane diisocyanate, or isophorone diisocyanate.

[0024] To address the aforementioned technical problems, this invention also provides an application of an isocyanate-modified phenolic amine curing agent, used as a curing agent for epoxy resins.

[0025] The beneficial effects of this invention are as follows: This invention provides an isocyanate-modified phenolic amine curing agent, its preparation method, and its application. In the preparation process, unreacted small molecule amines in the system are first removed by fatty acid reaction, and then modified with isocyanate. This effectively reduces the reaction between free small molecule amines and isocyanate, making the reaction conditions milder and more controllable, and preventing gelation or explosive polymerization. The prepared curing agent not only has low-temperature rapid curing performance, but also effectively improves the tensile strength and elongation at break of the cured epoxy resin, as well as the flexibility and impact strength of the epoxy resin film. It has excellent performance and strong practicality. Attached Figure Description

[0026] Figure 1 This is the infrared spectrum of the isocyanate-modified phenolic amine curing agent prepared in a preferred embodiment 4 of the present invention. Detailed Implementation

[0027] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0028] This invention discloses an isocyanate-modified phenolic amine curing agent, comprising at least compounds with the following structural formulas:

[0029]

[0030] In the formula, R is a phenolic group;

[0031] R1 is -H,

[0032] R2 is an amine structure with two -NH2 residues removed;

[0033] R3 is

[0034] The preparation method of the above-mentioned isocyanate-modified phenolic amine curing agent specifically includes the following steps:

[0035] (1) Synthesis of phenolic amine curing agent: Phenolic compounds and amines are added to a reaction flask at a molar ratio of 1:1.0 to 2.2. The temperature is raised to 30 to 70°C. Under the condition that the temperature does not exceed 75°C, aldehyde compounds are slowly added to the reaction flask. The molar ratio of phenolic compounds to aldehyde compounds is controlled to be 1:1.05 to 2.05. The temperature is kept below 75°C during the addition of aldehyde compounds. After the addition is complete, the temperature is raised to 75°C to 85°C and kept at this temperature for 3 to 8 hours to generate phenolic amine curing agent.

[0036] The phenolic compounds in the above reaction raw materials include at least one of cashew phenol, phenol, cresol, pentadecyl resorcinol, resorcinol, bisphenol A, or bisphenol F.

[0037] The amine compounds include at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, m-phenylenediamine, or 1,3-cyclohexanedimethylamine.

[0038] The aldehyde compounds include at least one of paraformaldehyde, furfural, benzaldehyde, or salicylaldehyde.

[0039] (2) Amide reaction: The mixture after the reaction in step (1) is evacuated for 1.5 to 4 hours under vacuum conditions of -0.095 to -0.098 MPa and temperature of 85 to 95°C to remove water and small molecule amines. Then fatty acids are added to it, the temperature is raised to 145 to 155°C, and the amide reaction is carried out for 2 to 3 hours. The fatty acids can react the unreacted small molecule amines in the reaction mixture, reduce the reaction between small molecule amines and isocyanates, and reduce the activity of the reaction system with isocyanates. This ensures that the reaction conditions are milder when the phenolic amine curing agent reacts with isocyanates, and it is not easy to produce gel or burst, thus improving the safety and controllability of the reaction.

[0040] The fatty acid includes at least one selected from oleic acid, isooctanoic acid, adipic acid, butyric acid, heptanoic acid, octanoic acid, nonanoic acid, stearic acid, or lauric acid. The amount of the fatty acid added is 2-10% of the total mass of the phenolic compounds, amine compounds, and aldehyde compounds.

[0041] (4) Isocyanate modification: Heat the product after the reaction in step (2) to 25-50°C, and then add isocyanate accounting for 0.005-0.02 times the total mass of the product in step (2) dropwise. After the addition is complete, heat to 60-70°C and keep the reaction at this temperature for 1-2 hours to obtain the isocyanate-modified phenolic amine curing agent.

[0042] The isocyanate includes at least one of toluene diisocyanate, diphenylmethane diisocyanate, or isophorone diisocyanate.

[0043] The technical content of the present invention will be described in detail below through specific embodiments.

[0044] Example 1

[0045] Add 270g cashew phenol, 30g phenol and 70g ethylenediamine to a reaction flask and heat to 45°C; slowly add 35g paraformaldehyde in three portions, controlling the temperature not to exceed 60°C; after adding the paraformaldehyde, heat to 85°C and keep the reaction at that temperature for 3 hours.

[0046] After the heat preservation is completed, the vacuum is turned on and the pressure is controlled to -0.075 to -0.095 MPa. The vacuum is drawn at 85°C for 2 hours, 6g of oleic acid is added, and the temperature is raised to 145°C and kept for 2 hours.

[0047] The above 250g phenolic amine curing agent was heated to 35℃, and 2.5g toluene diisocyanate was slowly added dropwise. The addition was completed within 1 hour. After the addition was completed, the mixture was heated to 65℃ and kept at that temperature for 2 hours to obtain the isocyanate modified phenolic amine curing agent.

[0048] Its performance is as follows: viscosity at 25°C is 3500 mps; active hydrogen equivalent (AHEW) is 125.

[0049] Example 2

[0050] Add 300g pentadecylresorcinol, 30g ethylenediamine and 53g diethylenetriamine to a reaction flask and heat to 45°C; slowly add 35g paraformaldehyde in three portions, controlling the temperature not to exceed 65°C; after adding the paraformaldehyde, heat to 85°C and maintain the temperature for 3 hours.

[0051] After the heat preservation is completed, the vacuum is turned on and the pressure is controlled to -0.075 to -0.095 MPa. The vacuum is drawn at 85°C for 2 hours. Then, 5g of dimer acid is added and the temperature is raised to 150°C and kept for 2 hours.

[0052] The above 250g phenolic amine curing agent was heated to 40℃, and 3g toluene diisocyanate was slowly added dropwise. The addition was completed within 1 hour. After the addition was completed, the reaction was kept at 65℃ for 2 hours to obtain the isocyanate modified phenolic amine curing agent.

[0053] Its viscosity at 25°C was 4500 mps; its active hydrogen equivalent (AHEW) was 105.

[0054] Example 3

[0055] Add 300g pentadecylresorcinol, 30g ethylenediamine and 53g diethylenetriamine to a reaction flask and heat to 45°C; slowly add 35g paraformaldehyde in three portions, controlling the temperature not to exceed 70°C; after adding the paraformaldehyde, heat to 75°C and keep warm for 3 hours.

[0056] After the heat preservation is completed, the vacuum is turned on and the pressure is controlled to -0.075 to -0.095 MPa. The vacuum is drawn at 90°C for 2 hours, 6g of isooctanoic acid is added, and the temperature is raised to 150°C and kept for 3 hours.

[0057] Heat 250g of the above phenolic amine curing agent to 40℃, slowly add 4g of toluene diisocyanate, and keep the addition within 1 hour. After the addition is completed, keep the temperature at 65℃ for 2 hours to obtain the isocyanate modified phenolic amine curing agent.

[0058] Its viscosity at 25°C was tested to be 3000 mps; the active hydrogen equivalent (AHEW) was 115.

[0059] Example 4

[0060] Add 300g of cashew phenol, 30g of ethylenediamine and 53g of diethylenetriamine to a reaction flask and heat to 45°C; slowly add 35g of paraformaldehyde in three portions, controlling the temperature not to exceed 70°C; after adding the paraformaldehyde, heat to 75°C and keep warm for 3 hours.

[0061] After the heat preservation is completed, the vacuum is turned on and the pressure is controlled to -0.075 to -0.095 MPa. The vacuum is drawn at 90°C for 2 hours. 6g of dimer acid is added and the temperature is raised to 155°C and kept for 2 hours.

[0062] Heat 250g of the above phenolic amine curing agent to 40℃, slowly add 4g of diphenylmethane diisocyanate, and keep the addition within 1 hour. After the addition is completed, keep the temperature at 65℃ for 2 hours to obtain the isocyanate modified phenolic amine curing agent.

[0063] Its viscosity at 25°C was tested to be 3000 mps; the active hydrogen equivalent (AHEW) was 115.

[0064] Comparative Example 1

[0065] Add 300g of cashew phenol, 30g of ethylenediamine and 53g of diethylenetriamine to a reaction flask and heat to 45°C; slowly add 35g of paraformaldehyde in three portions, controlling the temperature not to exceed 70°C; after adding the paraformaldehyde, heat to 75°C and keep warm for 3 hours.

[0066] After the heat preservation is completed, the vacuum is turned on and the pressure is controlled to -0.075 to -0.095 MPa. The vacuum is drawn at 90°C for 2 hours. 6g of dimer acid is added and the temperature is raised to 155°C and kept for 2 hours.

[0067] Heat 250g of the above phenolic amine curing agent to 40°C, and slowly add 15g of diphenylmethane diisocyanate. The addition should be completed within 3 hours. After the addition is complete, the substance will turn into a gel-like substance within 5 minutes and become unusable.

[0068] Comparative Example 2

[0069] Add 300g of cashew phenol, 30g of ethylenediamine and 53g of diethylenetriamine to a reaction flask and heat to 45°C; slowly add 35g of paraformaldehyde in three portions, controlling the temperature not to exceed 65°C; after adding the paraformaldehyde, heat to 75°C and keep warm for 3 hours.

[0070] After the heat preservation is completed, the vacuum is turned on and the pressure is controlled to -0.075 to -0.095 MPa. The vacuum is drawn at 90°C for 2 hours. 6g of oleic acid is added and the temperature is raised to 145°C and kept for 2 hours.

[0071] Its viscosity at 25°C was tested to be 2500 mps; the active hydrogen equivalent (AHEW) was 100.

[0072] Comparative Example 3

[0073] Add 300g of cashew phenol, 30g of ethylenediamine and 53g of diethylenetriamine to a reaction flask and heat to 45°C; slowly add 35g of paraformaldehyde in three portions, controlling the temperature not to exceed 70°C; after adding the paraformaldehyde, heat to 75°C and keep warm for 3 hours.

[0074] After the heat preservation is completed, turn on the vacuum and control the pressure to -0.075 to -0.095 MPa, and evacuate at 90°C for 2 hours.

[0075] Heat 250g of the above phenolic amine curing agent to 40℃, slowly add 4g of diphenylmethane diisocyanate, and keep the addition within 1 hour. After the addition is completed, keep the temperature at 65℃ for 2 hours.

[0076] The material contains a large number of small particulate substances that are immiscible with the system.

[0077] Performance testing:

[0078] The isocyanate-modified phenolic amine curing agent prepared in Example 4 was subjected to infrared spectroscopy, and its infrared spectrum is shown in the attached figure. Figure 1 As shown.

[0079] The infrared spectrum shows that the wavelength is 2270 cm⁻¹. -1 The characteristic peak of NCO is no longer present at 1636 cm⁻¹. -1 The appearance of a urea peak indicates that the isocyanate has reacted sufficiently with the phenolic amine curing agent, resulting in an isocyanate-modified phenolic amine curing agent.

[0080] The isocyanate-modified phenolic amine curing agents prepared in Examples 1-4 and Comparative Example 2 were mixed with epoxy resin respectively, and stirred in a ratio of 1:1 between the active hydrogen equivalent AHEW in the curing agent and the epoxy equivalent (EEW=195) in the epoxy resin.

[0081] The above mixture was used to prepare a 200 μm wet film. After natural drying at 25 °C for 7 days, the flexibility and impact properties of the film were tested. The obtained performance data are shown in Table 1 below.

[0082] The above mixture was prepared into resin strips measuring 10cm*5cm*2cm. After natural drying at 25℃ for 7 days, the tensile strength and elongation at break were tested. The obtained performance data are shown in Table 1 below.

[0083] Table 1

[0084] project Example 1 Example 2 Example 3 Example 4 Comparative Example 2 25℃ for surface drying 1h / 1.5h 1.2h / 1.8h 1.5h / 2h 1h / 2h 3h / 5h Flexibility, mm 1mm 1mm 1mm 1mm 10mm Impact performance (kg·CM) 90 100 95 100 30 Tensile strength (MPa) 60 65 60 65 20 Elongation at break % 10 15 10 12 5

[0085] As can be seen from the above performance data, the isocyanate-modified phenolic amine curing agent prepared in this invention can significantly reduce the surface drying time and actual drying time when used for epoxy resin curing. The cured paint film has good flexibility and its impact performance is more than 3 times higher than that before modification. The cured epoxy resin has higher tensile strength and elongation at break, with tensile strength reaching more than 60 MPa and elongation at break reaching more than 10%, both of which far exceed the level of existing curing agents.

[0086] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An isocyanate-modified phenolic amine curing agent, characterized in that, Compounds that include at least the following structural formulas: In the formula, R is at least one of cashew phenol, phenol, cresol, pentadecylresorcinol, resorcinol, bisphenol A or bisphenol F. R1 is -H, R2 is a group formed by removing two -NH2 groups from at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, m-phenylenediamine, or 1,3-cyclohexanedimethylamine. R3 is .

2. A method for preparing an isocyanate-modified phenolic amine curing agent as described in claim 1, characterized in that, Includes the following steps: (1) Synthesis of phenolic amine curing agent: A certain amount of phenolic compounds, amine compounds and aldehyde compounds are reacted in a reaction flask to generate phenolic amine curing agent; The phenolic compounds include at least one of cashew phenol, phenol, cresol, pentadecyl resorcinol, resorcinol, bisphenol A or bisphenol F; The amine compounds include at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, m-phenylenediamine, or 1,3-cyclohexanedimethylamine; The aldehyde compounds include at least one of paraformaldehyde, furfural, and benzaldehyde; (2) Amide reaction: Vacuum the mixture after the reaction in step (1) to remove water and small molecule amines, then add fatty acids to it, raise the temperature to carry out the amidation reaction, and further remove the small molecule amines in the system; (3) Isocyanate modification: Isocyanate is added dropwise to the mixture after the amidation reaction in step (2). After the addition is complete, the mixture is heated and kept warm to carry out the isocyanate modification reaction, and the isocyanate-modified phenolic amine curing agent is obtained.

3. The method for preparing an isocyanate-modified phenolic amine curing agent according to claim 2, characterized in that, In step (1), the molar ratio of the phenolic compound, amine compound and aldehyde compound is 1:1.0~2.2:1.05~2.

05.

4. The method for preparing an isocyanate-modified phenolic amine curing agent according to claim 2, characterized in that, In step (1), the reaction process conditions are: temperature 75-85℃, time 3-8h.

5. The method for preparing an isocyanate-modified phenolic amine curing agent according to claim 2, characterized in that, In step (2), the amount of fatty acid added is 2 to 10% of the total mass of the phenolic compounds, amine compounds and aldehyde compounds.

6. The method for preparing an isocyanate-modified phenolic amine curing agent according to claim 5, characterized in that, The fatty acids include at least one of oleic acid, isooctanoic acid, butyric acid, heptanoic acid, caprylic acid, nonanoic acid, stearic acid, or lauric acid.

7. The method for preparing an isocyanate-modified phenolic amine curing agent according to claim 2, characterized in that, In step (3), the amount of isocyanate added is 0.005 to 0.02 times the mass of the reaction product in step (2).

8. The method for preparing an isocyanate-modified phenolic amine curing agent according to claim 7, characterized in that, The isocyanate includes at least one of toluene diisocyanate, diphenylmethane diisocyanate, or isophorone diisocyanate.

9. The application of an isocyanate-modified phenolic amine curing agent as described in claim 1, characterized in that, Used as a curing agent for epoxy resins.

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