Isocyanate modified phenolic aldehyde amine curing agent as well as preparation method and application thereof

Abstract

The invention discloses an isocyanate modified phenolic aldehyde amine curing agent as well as a preparation method and application thereof. The preparation method comprises the following steps: synthesizing a phenolic aldehyde amine curing agent; fatty acid is added for an amidation reaction; and carrying out isocyanate modification. In the preparation process, fatty acid is firstly used for reaction to remove unreacted micromolecule amine in a system, then isocyanate is used for modification treatment, the reaction activity after isocyanate is added is effectively reduced, the reaction conditions are milder and more controllable, the gel or implosion phenomenon is not generated, and the prepared curing agent not only has low-temperature rapid curing performance, but also has good curing performance. The tensile strength and the elongation at break of the cured epoxy resin and the flexibility and the impact strength of an epoxy resin paint film are effectively improved, the use performance is excellent, and the practicability is high.

Description

Technical Field

[0001] The invention relates to the field of epoxy resin curing agents, in particular to an isocyanate-modified phenalkamine curing agent and a preparation method and application thereof. Background Art

[0002] Epoxy coating systems are widely used in heavy-duty anti-corrosion, ship coatings, steel structure anti-corrosion, bridges and other coating fields due to their good bonding and anti-corrosion properties. Phenolic amine curing agent is a commonly used epoxy curing agent with excellent performance. In epoxy 2K system, the use of phenolic amine curing agent can not only meet the low surface treatment of the substrate, but also meet the requirements of low temperature curing.

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

[0004] The present invention can solve the above-mentioned problems existing after the existing phenalkamine curing agent cures epoxy resin by providing an isocyanate-modified phenalkamine curing agent and a preparation method and application thereof.

[0005] In order to solve the above technical problems, the present invention provides an isocyanate-modified phenalkamine curing agent, which at least comprises a compound of the following structural formula:

[0006]

[0007] Wherein, R is a phenolic group;

[0008] R1 is -H,

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

[0010] R3 is

[0011] In order to solve the above technical problems, the present invention provides a method for preparing an isocyanate-modified phenalkamine curing agent, comprising the following steps:

[0012] (1) Synthesis of phenalkamine curing agent: reacting a certain amount of phenolic compound, amine compound and aldehyde compound in a reaction bottle to generate phenalkamine curing agent;

[0013] (2) amidation reaction: vacuumizing the mixture after the reaction in step (1) to remove water and small molecular weight amines, adding fatty acids thereto, and heating to carry out amidation reaction to further remove small molecular weight amines in the system;

[0014] (3) Isocyanate modification: adding isocyanate dropwise to the mixture after the amidation reaction in step (2), heating and keeping warm to carry out isocyanate modification reaction, and obtaining the isocyanate-modified phenalkamine curing agent.

[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 1:1.0-2.2:1.05-2.05.

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

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

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

[0019] The aldehyde compound includes at least one of paraformaldehyde, furfural and benzaldehyde.

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

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

[0022] In a preferred embodiment of the present invention, in step (3), the amount of the 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] In order to solve the above technical problems, the present invention also provides an application of an isocyanate-modified phenalkamine curing agent, which is used as a curing agent for epoxy resin.

[0025] The invention has the beneficial effects of: an isocyanate-modified phenolic amine curing agent and a preparation method and application thereof. In the preparation process, unreacted small molecule amines in the system are firstly removed by a fatty acid reaction, and then modified by isocyanate, thereby effectively reducing the reaction of free small molecule amines and isocyanate, making the reaction conditions milder and more controllable, and not generating gel or explosion. 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 epoxy resin after curing, as well as the flexibility and impact strength of the epoxy resin paint film, and has excellent use performance and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the infrared test spectrum of the isocyanate-modified phenalkamine curing agent prepared in a preferred embodiment 4 of the present invention. DETAILED DESCRIPTION

[0027] The preferred embodiments of the present invention are described in detail below in conjunction with 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 making a clearer and more definite definition of the protection scope of the present invention.

[0028] The present invention discloses an isocyanate-modified phenalkamine curing agent, which comprises at least a compound of the following structural formula:

[0029]

[0030] Wherein, 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 phenalkamine curing agent specifically comprises the following steps:

[0035] (1) Synthesis of phenolic amine curing agent: Phenolic compound and amine substance are added into a reaction flask at a molar ratio of 1:1.0-2.2, and the temperature is raised to 30-70°C. Under the condition of not higher than 75°C, aldehyde compound is slowly added into the reaction flask, and the molar ratio of phenolic compound to aldehyde compound is controlled to be 1:1.05-2.05. The temperature is kept not higher than 75°C during the process of adding aldehyde compound. After the addition is completed, the temperature is raised to 75°C-85°C and kept warm for 3-8 hours to generate phenolic amine curing agent.

[0036] In the above-mentioned reaction raw materials, the phenolic compound includes at least one of cardanol, phenol, cresol, pentadecylresorcinol, resorcinol, bisphenol A or bisphenol F.

[0037] The amine compound includes at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, metaphenylenediamine or 1,3-cyclohexanedimethylamine.

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

[0039] (2) Amidation reaction: The mixture after the reaction in step (1) is evacuated for 1.5 to 4 hours at a vacuum degree of -0.095 to -0.098 MPa and a temperature of 85 to 95° C. to remove water and small molecular amines, and then fatty acids are added thereto. The temperature is raised to 145 to 155° C. and the amidation reaction is carried out for 2 to 3 hours. The fatty acids can react with unreacted small molecular amines in the reaction mixture, thereby reducing the reaction of small molecular amines with isocyanates and reducing the activity of the reaction system with isocyanates, thereby ensuring that the reaction conditions are milder when the phenolic amine curing agent reacts with isocyanates, and it is not easy to produce gel or explosion, thereby improving the safety and controllability of the reaction.

[0040] The fatty acid comprises at least one of oleic acid, isooctanoic acid, adipic acid, n-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 compound, the amine compound and the aldehyde compound.

[0041] (4) Isocyanate modification: The product after the reaction in step (2) is heated to 25-50° C., and then 0.005-0.02 times the total mass of the reaction product in step (2) is added dropwise thereto. After the addition is completed, the product is heated to 60-70° C. and kept warm for reaction for 1-2 hours to obtain the isocyanate-modified phenalkamine curing agent.

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

[0043] The technical contents of the present invention are described in detail below through specific embodiments.

[0044] Example 1

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

[0046] After the insulation is completed, turn on the vacuum, control the pressure to -0.075~-0.095MPa, evacuate at 85℃ for 2h, add 6g oleic acid, raise the temperature to 145℃ and keep it for 2h.

[0047] Heat the above 250g phenolic amine curing agent to 35°C, slowly drop 2.5g toluene diisocyanate, and keep the dropwise addition within 1 hour. After the dropwise addition is completed, heat to 65°C and keep the temperature for 2 hours to obtain the isocyanate-modified phenolic amine curing agent.

[0048] Performance: Its viscosity at 25°C is 3500 mps; its active hydrogen equivalent weight (AHEW) is 125.

[0049] Example 2

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

[0051] After the insulation is completed, the vacuum is turned on, the pressure is controlled to -0.075~-0.095MPa, and the vacuum is drawn at 85℃ for 2h; 5g of dimer acid is added thereto, and the temperature is raised to 150℃ and maintained for 2h.

[0052] Heat the above 250g phenolic amine curing agent to 40°C, slowly drop 3g toluene diisocyanate, and complete the dropwise addition within 1 hour. After the dropwise addition is completed, keep the temperature at 65°C for 2 hours to obtain the isocyanate-modified phenolic amine curing agent.

[0053] The viscosity at 25°C was tested to be 4500 mps; the active hydrogen equivalent weight (AHEW) was 105.

[0054] Example 3

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

[0056] After the insulation is completed, turn on the vacuum, control the pressure to -0.075~-0.095MPa, evacuate at 90℃ for 2h, add 6g of isooctanoic acid, and raise the temperature to 150℃ and keep it for 3h.

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

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

[0059] Example 4

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

[0061] After the insulation is completed, the vacuum is turned on, the pressure is controlled to -0.075~-0.095MPa, and the vacuum is drawn at 90℃ for 2h; 6g of dimer acid is added, and the temperature is raised to 155℃ and maintained for 2h.

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

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

[0064] Comparative Example 1

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

[0066] After the insulation is completed, the vacuum is turned on, the pressure is controlled to -0.075~-0.095MPa, and the vacuum is drawn at 90℃ for 2h; 6g of dimer acid is added, and the temperature is raised to 155℃ and maintained for 2h.

[0067] 250g of the above-mentioned phenolic amine curing agent was heated to 40°C, and 15g of diphenylmethane diisocyanate was slowly added dropwise. The addition was completed within 3 hours. After the addition was completed, it turned into a gel-like substance in 5 minutes and could not be used.

[0068] Comparative Example 2

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

[0070] After the insulation is completed, open the vacuum, control the pressure to -0.075~-0.095MPa, and evacuate at 90℃ for 2h; add 6g oleic acid, raise the temperature to 145℃ and keep it for 2h.

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

[0072] Comparative Example 3

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

[0074] After the insulation is completed, turn on the vacuum, control the pressure to -0.075~-0.095MPa, and evacuate at 90℃ for 2h.

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

[0076] A large amount of small granular substances appear in the material, which are immiscible with the system.

[0077] Performance Test:

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

[0079] From the infrared spectrum, we can see that: 2270cm -1 There is no characteristic peak of NCO at 1636cm -1 The appearance of the urea peak indicates that the isocyanate has fully reacted with the phenalkamine curing agent to obtain an isocyanate-modified phenalkamine curing agent.

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

[0081] The above mixture was prepared into a 200 μm wet film, and 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 a resin strip of 10 cm*5 cm*2 cm, and after natural drying at 25°C 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℃ surface dry 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] It can be seen from the above performance data that the isocyanate-modified phenolic amine curing agent prepared by the present invention can significantly reduce the surface drying time and the actual drying time when used for epoxy resin curing. The paint film has good flexibility after curing, and the impact performance is improved by more than 3 times compared with that before modification. The cured epoxy resin has higher tensile strength and elongation at break, among which the tensile strength reaches more than 60MPa and the elongation at break reaches more than 10%, both of which are far higher than the level of existing curing agents.

[0086] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An isocyanate-modified phenalkamine curing agent, characterized in that: A compound comprising at least the following structural formula: Wherein, R is a phenolic group; R1 is -H, R2 is an amine structure with two -NH2 residues removed; R3 is 2. A method for preparing the isocyanate-modified phenalkamine curing agent according to claim 1, characterized in that: The steps include: (1) Synthesis of phenalkamine curing agent: reacting a certain amount of phenolic compound, amine compound and aldehyde compound in a reaction bottle to generate phenalkamine curing agent; (2) amidation reaction: vacuumizing the mixture after the reaction in step (1) to remove water and small molecular weight amines, adding fatty acids thereto, and heating to carry out amidation reaction to further remove small molecular weight amines in the system; (3) Isocyanate modification: adding isocyanate dropwise to the mixture after the amidation reaction in step (2), heating and keeping warm to carry out isocyanate modification reaction, and obtaining the isocyanate-modified phenalkamine curing agent.

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

05.

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

5. The method for preparing an isocyanate-modified phenalkamine curing agent according to claim 2, characterized in that: In step (1), the phenolic compound includes at least one of cardanol, phenol, cresol, pentadecylresorcinol, resorcinol, bisphenol A or bisphenol F; The amine compound includes at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, m-phenylenediamine or 1,3-cyclohexanedimethylamine; The aldehyde compound includes at least one of paraformaldehyde, furfural and benzaldehyde.

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

7. The method for preparing an isocyanate-modified phenalkamine curing agent according to claim 6, characterized in that: The fatty acid includes at least one of oleic acid, isooctanoic acid, n-butyric acid, heptanoic acid, octanoic acid, nonanoic acid, stearic acid or lauric acid.

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

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

10. A use of the isocyanate-modified phenalkamine curing agent as claimed in claim 1, characterized in that: Used as a curing agent for epoxy resins.

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