Imidazolyl polyamide epoxy resin curing agent and preparation method thereof

Abstract

The invention discloses an imidazolyl polyamide epoxy resin curing agent and a preparation method thereof. The imidazolyl polyamide epoxy resin curing agent is prepared from 5-30% of imidazole substances, 5-30% of unsaturated binary acid (or acid anhydride), 0-60% of dimer acid and 25-55% of polyamine substances. Performance detection shows that the product is good in compatibility with epoxy resin, high in gloss after being cured, good in acid resistance and salt fog resistance and suitable for anticorrosive paint, and a very good technical effect is achieved.

Description

Technical Field

[0001] The invention relates to an epoxy resin curing agent, in particular to an imidazole polyamide epoxy resin curing agent suitable for anticorrosive coatings with good compatibility with epoxy resin, high cured gloss, good acid resistance and salt spray resistance, and a preparation method thereof, belonging to the technical field of polymer materials. Background Art

[0002] Low molecular weight polyamide is an important type of epoxy curing agent. Its cured products with epoxy resin have excellent flexibility and adhesion, good acid and salt spray resistance, and are widely used in anti-corrosion coatings, adhesives and other fields.

[0003] The typical polyamide synthesis process begins with the amidation reaction of dimer acid and polyamine at 150-160°C. The resulting polyamide has poor compatibility with epoxy resin, which results in uneven paint film, whitening and other appearance defects, as well as weakened adhesion, salt spray resistance and other protective functions during application. In response to this, the solution of polyamide manufacturers is to continue to raise the temperature to 200-250°C after the amidation reaction is completed, so that part of the polyamide is converted into an imidazoline structure, thereby improving the compatibility of the curing agent with the epoxy resin and solving a series of problems caused by poor compatibility.

[0004] Although this solution effectively solves some problems, it still has some shortcomings, mainly because the content of imidazoline in the final product is not easy to control. If the imidazoline content is too low, the compatibility of the product with the epoxy resin will not be improved; if the imidazoline content is too high, the curing speed will be seriously reduced. In actual production, multiple central control sampling and infrared testing are required to ensure stability between batches and achieve satisfactory performance. Secondly, this process has high energy consumption and does not conform to the concept of green development.

[0005] Imidazole is similar to imidazoline in structure, has good compatibility with epoxy resin, can provide electrons to metal empty d orbitals to generate covalent bonds, and can also accept existing electrons in metal empty orbitals to generate feedback π bonds, so it has good corrosion inhibition ability. The present invention uses imidazole substances as starting materials. First, the imidazole substances and unsaturated dibasic acids (or acid anhydrides) undergo Michael addition to obtain imidazole-based dibasic acids, which are then mixed with an appropriate amount of dimer acid, and amidation reaction with polyamine substances is performed to obtain the final product. The whole process does not require a high temperature of more than 200°C to generate polyamides with imidazole structures, and the imidazole content in the product can be directly controlled by the feed ratio, eliminating the step of infrared central control, and is more stable between batches. The final imidazole-based polyamide has good compatibility with epoxy resin, high gloss after curing, good acid and salt spray resistance, and is suitable for anticorrosive coatings. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an imidazole polyamide epoxy resin curing agent with good compatibility with epoxy resin, high gloss after curing, and good acid and salt spray resistance to meet the application needs of anti-corrosion coatings; another purpose of the present invention is to provide a method for preparing the epoxy resin curing agent.

[0007] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0008] An imidazole-based polyamide epoxy resin curing agent is prepared from the following raw materials in percentage by mass: 5-30% of imidazole substances, 5-30% of unsaturated dibasic acid (or anhydride), 0-60% of dimer acid and 25-55% of polyamine substances.

[0009] As a preferred embodiment, in the above-mentioned imidazole-based polyamide epoxy resin curing agent, the imidazole substance is one or a mixture of imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-benzylimidazole, 4-phenylimidazole, and benzimidazole.

[0010] As a preferred embodiment, in the above-mentioned imidazole-based polyamide epoxy resin curing agent, the unsaturated dibasic acid (or anhydride) is one or a mixture of maleic acid, itaconic acid, maleic anhydride, itaconic anhydride.

[0011] As a preferred embodiment, the above-mentioned imidazole-based polyamide epoxy resin curing agent, the polyamine substance is one or a mixture of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, pentamethylenediamine, hexamethylenediamine, 2-methylpentamethylenediamine, isophoronediamine, 1,3-cyclohexyldimethylamine, meta-xylylenediamine, cyclohexyldiamine, cyclopentamethylenediamine, diaminodicyclohexylmethane, and diaminodiphenylmethane.

[0012] The preparation method of the imidazole-based polyamide epoxy resin curing agent of the present invention comprises the following steps:

[0013] (1) adding imidazole substances, unsaturated dibasic acids or acid anhydrides into a reactor according to mass percentage, and stirring to make the materials uniformly mixed;

[0014] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C;

[0015] (3) Add dimer acid and polyamines, stir at 60-70°C and then heat to 150-160°C;

[0016] (4) Keep the reaction at 150-160°C;

[0017] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0018] (6) Cooling and filtration.

[0019] As a preferred embodiment, the method for preparing the imidazole-based polyamide epoxy resin curing agent of the present invention comprises the following steps:

[0020] (1) adding imidazole substances and unsaturated dibasic acids (or acid anhydrides) into a reactor according to mass percentage, and stirring to make the materials uniformly mixed;

[0021] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0022] (3) Add dimer acid and polyamines, stir at 60-70°C for 15 minutes, and then heat to 150-160°C;

[0023] (4) Keep the reaction at 150-160°C for 3 hours;

[0024] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0025] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0026] The representative reaction process of the present invention is as follows Figure 1 .:

[0027] The present invention mainly improves the deficiencies of the prior art through the following solutions:

[0028] 1. The product of the present invention has a novel structure. No epoxy curing agent with this structure has been reported. The novel structure gives it unique properties.

[0029] 2. The present invention uses imidazoles as raw materials to improve the compatibility of polyamide and epoxy resin, thereby improving various properties and avoiding the high energy consumption and difficult to control process of high temperature cyclization of traditional polyamide to imidazoline above 200°C.

[0030] 3. Imidazole has multiple active sites and can slow down acid corrosion. Therefore, imidazole-based polyamide epoxy curing agent has better acid resistance than traditional polyamide epoxy curing agent.

[0031] 4. The present invention can achieve diversity in product molecular structure through raw material selection, thereby designing products suitable for different usage requirements.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0033] The present invention designs a novel epoxy curing agent, which uses imidazole substances as starting materials to obtain imidazole-based polyamide through two-step reactions, and has the following advantages: 1. It does not require the traditional polyamide high-temperature process; 2. The imidazole content in the product can be controlled by the feed ratio, eliminating the steps of multiple infrared central control of imidazoline content in the traditional process; 3. The imidazole-based polyamide structure has a corrosion inhibition effect. The curing agent has good compatibility with epoxy resin, high gloss after curing, good acid and salt spray resistance, and is suitable for anti-corrosion coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a representative reaction equation of the present invention. DETAILED DESCRIPTION

[0035] Example 1

[0036] 1. An imidazole-based polyamide epoxy resin curing agent, which is made of the following raw materials in percentage by mass: 15.47% of benzimidazole, 15.20% of maleic acid, 30.67% of dimer acid, and 38.66% of diethylenetriamine.

[0037] 2. A method for preparing an imidazole-based polyamide epoxy resin curing agent, comprising the following steps:

[0038] (1) 118 g of benzimidazole and 116 g of maleic acid were added into a reactor and stirred to mix the materials evenly;

[0039] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0040] (3) Add 234 g of dimer acid and 295 g of diethylenetriamine in sequence, stir at 60-70° C. for 15 minutes, and then heat to 150-160° C.;

[0041] (4) Keep the reaction at 150-160°C for 3 hours;

[0042] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0043] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0044] Example 2

[0045] 1. An imidazole-based polyamide epoxy resin curing agent, which is made of the following raw materials in percentage by mass: 21.61% of benzimidazole, 21.25% of maleic acid, 14.28% of dimer acid, and 42.86% of diethylenetriamine.

[0046] 2. A method for preparing an imidazole-based polyamide epoxy resin curing agent, comprising the following steps:

[0047] (1) 118 g of benzimidazole and 116 g of maleic acid were added into a reactor and stirred to mix the materials evenly;

[0048] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0049] (3) Add 78 g of dimer acid and 234 g of diethylenetriamine in sequence, stir at 60-70° C. for 15 minutes, and then heat to 150-160° C.;

[0050] (4) Keep the reaction at 150-160°C for 3 hours;

[0051] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0052] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0053] Example 3

[0054] 1. An imidazole-based polyamide epoxy resin curing agent, which is made of the following raw materials in percentage by mass: 8.42% of benzimidazole, 8.28% of maleic acid, 50.11% of dimer acid, and 33.19% of diethylenetriamine.

[0055] 2. A method for preparing an imidazole-based polyamide epoxy resin curing agent, comprising the following steps:

[0056] (1) 118 g of benzimidazole and 116 g of maleic acid were added into a reactor and stirred to mix the materials evenly;

[0057] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0058] (3) Add 702 g of dimer acid and 465 g of diethylenetriamine in sequence, stir at 60-70° C. for 15 minutes, and then heat to 150-160° C.;

[0059] (4) Keep the reaction at 150-160°C for 3 hours;

[0060] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0061] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0062] Example 4

[0063] 1. An imidazole-based polyamide epoxy resin curing agent, which is made of the following raw materials in percentage by mass: 12.97% of 2-methylimidazole, 15.51% of maleic anhydride, 28.48% of dimer acid, and 43.04% of diethylenetriamine.

[0064] 2. A method for preparing an imidazole-based polyamide epoxy resin curing agent, comprising the following steps:

[0065] (1) 82 g of 2-methylimidazole and 98 g of maleic anhydride were added to a reactor and stirred to mix the materials uniformly;

[0066] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0067] (3) Add 180 g of dimer acid and 272 g of diethylenetriamine in sequence, stir at 60-70° C. for 15 minutes, and then heat to 150-160° C.;

[0068] (4) Keep the reaction at 150-160°C for 3 hours;

[0069] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0070] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0071] Example 5

[0072] 1. An imidazole-based polyamide epoxy resin curing agent, which is made of the following raw materials in percentage by mass: 12.87% of benzimidazole, 14.18% of itaconic acid, 27.04% of dimer acid, and 45.91% of triethylenetetramine.

[0073] 2. A method for preparing an imidazole-based polyamide epoxy resin curing agent, comprising the following steps:

[0074] (1) 118 g of benzimidazole and 130 g of itaconic acid were added into a reactor and stirred to mix the materials evenly;

[0075] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0076] (3) Add 248 g of dimer acid and 421 g of triethylenetetramine in sequence, stir at 60-70° C. for 15 minutes, and then heat to 150-160° C.;

[0077] (4) Keep the reaction at 150-160°C for 3 hours;

[0078] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0079] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0080] Comparative Example 1

[0081] 1. In the formula of Example 1, dimer acid is eliminated and the formula is made of the following raw materials in percentage by mass: 26.82% of benzimidazole, 26.36% of maleic acid, and 46.82% of diethylenetriamine.

[0082] 2. A method for preparing an imidazole-based polyamide epoxy resin curing agent, comprising the following steps:

[0083] (1) 118 g of benzimidazole and 116 g of maleic acid were added into a reactor and stirred to mix the materials evenly;

[0084] (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours;

[0085] (3) Add 206 g of diethylenetriamine, stir at 60-70° C. for 15 minutes, then heat to 150-160° C.;

[0086] (4) Keep the reaction at 150-160°C for 3 hours;

[0087] (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0088] (6) Cooling and filtering, and packaging to obtain the finished product: imidazole polyamide epoxy resin curing agent.

[0089] Comparative Example 2

[0090] 1. In the formula of Example 1, benzimidazole and maleic acid are eliminated to prepare a dimer acid type polyamide, which is made of the following raw materials in percentage by mass: 73.11% dimer acid and 26.89% diethylenetriamine.

[0091] 2. A method for preparing a dimer acid type polyamide epoxy resin curing agent, comprising the following steps:

[0092] (1) Add 560 g of dimer acid and 206 g of diethylenetriamine to a reaction flask, stir at 60-70° C. for 15 minutes, and then heat to 150-160° C.;

[0093] (2) Keep the reaction at 150-160°C for 3 hours;

[0094] (3) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure;

[0095] (4) Cooling and filtering, and packaging to obtain the finished product: dimer acid type polyamide epoxy resin curing agent.

[0096] Example 8 Performance Test

[0097] Epoxy resin (epoxy resin 828 produced by Jiangsu Sanmu Chemical Co., Ltd.) was mixed evenly with the epoxy resin curing agent prepared in Examples 1-7, and evenly coated on the tinplate to form a film with a thickness of 40 μm. The basic properties of the finished product after curing were measured as shown in the following table.

[0098]

[0100] The above performance test results show that the imidazole-based polyamide curing agent has good compatibility with epoxy resin, which is intuitively manifested in the high gloss of the paint film. The paint film of the dimer acid type polyamide (Example 7) that has not been modified by imidazole is basically glossless. Due to the introduction of the imidazole rigid ring, the hardness of the imidazole-based polyamide is improved and the flexibility is significantly reduced, but the addition of an appropriate amount of dimer acid can produce an epoxy curing agent with balanced properties such as hardness, adhesion and flexibility. Due to the electronic effect of imidazole and metal, the adhesion, acid resistance and salt spray resistance of the imidazole-based polyamide curing agent on metal substrates are improved. Overall, the imidazole-based polyamide epoxy curing agent obtained by the present invention has good comprehensive performance and is suitable for anti-corrosion coatings. In addition, compared with Examples 1 to 5, the imidazole-based polyamide curing agent prepared in Example 2 has the best performance in all aspects and has achieved very good technical effects.

[0101] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An imidazole-based polyamide epoxy resin curing agent, characterized in that: The invention is prepared from the following raw materials in the following mass percentages: 5-30% of imidazole substances, 5-30% of unsaturated dibasic acid or acid anhydride, 0-60% of dimer acid and 25-55% of polyamine substances.

2. The imidazole-based polyamide epoxy resin curing agent according to claim 1, characterized in that: The imidazole substance is one or a mixture of imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-benzylimidazole, 4-phenylimidazole and benzimidazole.

3. The imidazole-based polyamide epoxy resin curing agent according to claim 1, characterized in that: The unsaturated dibasic acid or anhydride is one or a mixture of maleic acid, itaconic acid, maleic anhydride and itaconic anhydride.

4. The imidazole-based polyamide epoxy resin curing agent according to claim 1, characterized in that: The polyamine substance is one or a mixture of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, pentanediamine, hexanediamine, 2-methylpentanediamine, isophoronediamine, 1,3-cyclohexanedimethylamine, meta-xylylenediamine, cyclohexanediamine, cyclopentanediamine, diaminodicyclohexylmethane, and diaminodiphenylmethane.

5. The method for preparing the imidazole-based polyamide epoxy resin curing agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) adding imidazole substances, unsaturated dibasic acids or acid anhydrides into a reactor according to mass percentage, and stirring to make the materials uniformly mixed; (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C; (3) Add dimer acid and polyamines, stir at 60-70°C and then heat to 150-160°C; (4) Keep the reaction at 150-160°C; (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure; (6) Cooling and filtration.

6. The method for preparing the imidazole-based polyamide epoxy resin curing agent according to claim 5, characterized in that: The following steps are involved: (1) adding imidazole substances, unsaturated dibasic acids or acid anhydrides into a reactor according to mass percentage, and stirring to make the materials uniformly mixed; (2) raising the temperature of the reactants to 60-70°C and keeping the temperature at 60-70°C for 3 hours; (3) Add dimer acid and polyamines, stir at 60-70°C for 15 minutes, then heat to 150-160°C; (4) Keep at 150-160°C for 3 hours; (5) removing the water generated by the reaction and a small amount of unreacted raw materials under reduced pressure; (6) Cooling and filtration.

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