Modified dicyandiamide curing agent, preparation method therefor and use thereof

Abstract

A modified dicyandiamide curing agent, a preparation method therefor, and a use thereof. The modified dicyandiamide curing agent is obtained by reacting dicyandiamide with a fatty acid. By modifying dicyandiamide with a flexible fatty acid, the curing temperature of the dicyandiamide curing agent during curing of epoxy resin is significantly reduced, the flexibility of the cured epoxy resin is improved, and while the flexibility of the epoxy resin is ensured, the glass transition temperature of the epoxy resin is not reduced, thereby avoiding the impact on the performance thereof.

Description

A modified dicyandiamide curing agent, its preparation method and application Technical Field

[0001] This invention relates to the field of curing agent technology, and in particular to a modified dicyandiamide curing agent, its preparation method, and its application. Background Technology

[0002] Dicyandiamide, as an epoxy resin curing agent, has excellent storage stability, extremely high bulk strength after curing, a high glass transition temperature, and its raw materials are widely available, stable, and inexpensive. It has long been widely used in commercial and industrial products, such as epoxy adhesives, composite materials, and electronic packaging materials.

[0003] Dicyandiamide, as an epoxy curing agent, has two main drawbacks. First, the cured product often exhibits hardness and brittleness. A common approach is to add toughening agents to the epoxy system to improve brittleness. However, using flexible toughening agents often lowers the glass transition temperature of the cured epoxy resin, reducing its strength and other defects. Second, due to the complexity of its curing mechanism and the presence of multiple reaction sites, its activity is relatively low. When used alone, it typically requires curing at high temperatures (150-170℃). Curing at high temperatures may damage the performance of precision components. While adding curing accelerators can lower the curing temperature to some extent, accelerators are expensive, and the addition of small-molecule accelerators can lead to migration within the epoxy resin over long-term use, affecting its lifespan.

[0004] Therefore, it is very meaningful to modify dicyandiamide epoxy resin curing agents to improve the performance of cured epoxy resins.

[0005] Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing dicyandiamide-cured epoxy resins, which cannot simultaneously improve properties such as curing temperature, glass transition temperature, and toughness. This invention provides a modified dicyandiamide curing agent for epoxy resins. By modifying dicyandiamide with fatty acids, this invention can significantly improve the curing temperature of the dicyandiamide curing agent and the properties of the cured resin.

[0007] Another object of the present invention is to provide a method for preparing the modified dicyandiamide curing agent.

[0008] Another object of the present invention is to provide the application of the modified dicyandiamide curing agent in the preparation of epoxy resins.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A modified dicyandiamide curing agent, wherein the modified dicyandiamide curing agent is obtained by reacting dicyandiamide with fatty acids.

[0011] This invention uses fatty acids to modify dicyandiamide. The carboxyl groups in the fatty acids undergo a substitution reaction with the amino groups in the dicyandiamide to form amide bonds. These amide bonds bind the flexible fatty acid chains and the dicyandiamide curing agent together, resulting in a modified dicyandiamide curing agent that simultaneously contains amino, amide, and cyano groups. The combined effect of these three groups enhances the reactivity of the dicyandiamide curing agent, enabling the curing of epoxy resin at lower temperatures. In this invention, the flexible fatty acid chain segments provide a certain degree of flexibility to the epoxy resin, thus playing a toughening role. Furthermore, the polar amide groups can promote the interaction between the flexible fatty acid chain segments and the epoxy resin chain segments, further increasing the glass transition temperature of the epoxy resin.

[0012] Preferably, the fatty acid includes straight-chain, branched-chain, or cyclic fatty acids with 16 or more carbon atoms. Specifically, it includes, but is not limited to, at least one of linoleic acid, tung oil acid, and hydrogenated dimer acid.

[0013] More preferably, the number of carbon atoms in the fatty acid is in the range of 16-50, and the length of the fatty acid chain segment is within the above-mentioned suitable range, which can simultaneously improve the flexibility and glass transition temperature of the cured epoxy resin.

[0014] Preferably, the fatty acid is a hydrogenated dimer acid, which includes at least one of the following structural formulas:

[0015] Preferably, the molar ratio of dicyandiamide to the carboxyl group in the fatty acid is (1-3):1, more preferably 2:1. Since the activity of the hydrogen atom in the amine group of the dicyandiamide molecule is influenced by the surrounding molecular structure, during the substitution reaction between dicyandiamide and fatty acid, only one hydrogen atom in the amine group undergoes a substitution reaction with the carboxyl group in the fatty acid. The slight excess of dicyandiamide ensures that the dicyandiamide curing agent is effectively modified.

[0016] The present invention also provides a method for preparing the modified dicyandiamide curing agent, comprising the following steps:

[0017] Dicyandiamide and fatty acids are dissolved in a solvent and subjected to an acylation reaction at 80-150°C. After the reaction is complete, the solvent is removed to obtain the modified dicyandiamide curing agent.

[0018] Preferably, the solvent includes, but is not limited to, at least one of good solvents such as N,N-dimethylformamide and N,N-dimethylacetamide.

[0019] Preferably, the reaction time is 1-24 hours, and from the perspective of curing performance and cost, the reaction time is further preferably 3-6 hours.

[0020] To further improve the utilization rate of raw materials, dicyandiamide and fatty acids can be dissolved in solvents to obtain reaction solutions. Then, under ultrasonic conditions, the reaction solution containing fatty acids is slowly added dropwise to the reaction solution containing dicyandiamide for reaction. The addition time is 0.5-6 hours, preferably 1-3 hours.

[0021] The present invention also protects the use of the modified dicyandiamide curing agent in the preparation of epoxy resin, specifically by crosslinking and curing an epoxy resin composition containing the modified dicyandiamide curing agent under heating conditions.

[0022] The epoxy resin composition comprises the following components in parts by weight:

[0023] 50-90 parts epoxy resin, 0-20 parts toughening agent, 5-20 parts modified dicyandiamide curing agent as described in any one of claims 1-4, 0-20 parts curing accelerator, and 0-50 parts filler.

[0024] Common epoxy resins, toughening agents, curing accelerators and fillers in the art can all be used to prepare epoxy resins in this invention.

[0025] The epoxy resin includes, but is not limited to, at least one of glycidyl ether bisphenol A, bisphenol F type epoxy resin, glycidyl ester, glycidyl amine, alicyclic epoxy resin, hydrogenated epoxy resin, and phenolic epoxy resin.

[0026] The toughening agent includes, but is not limited to, at least one of nitrile rubber, polyurethane, and acrylate reactive diluents.

[0027] The curing accelerator includes, but is not limited to, at least one of imidazole compounds, acid anhydride compounds, amine adducts, urea compounds, and aminoimide compounds.

[0028] The filler is used to enhance the mechanical strength of the epoxy resin, and includes, but is not limited to, at least one of silica, alumina, aluminum hydroxide, talc, and glass fiber.

[0029] The curing temperature is 60-120℃.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] This invention modifies dicyandiamide with flexible fatty acids, which significantly reduces the curing temperature of dicyandiamide curing agent in cured epoxy resin, improves the flexibility of cured epoxy resin, and ensures the flexibility of epoxy resin without reducing the glass transition temperature of epoxy resin and affecting its use. Attached Figure Description

[0032] Figure 1 shows the DSC test spectra of the epoxy resin compositions of Application Example 1 and Comparative Application Example 3. Detailed Implementation

[0033] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0034] Example 1

[0035] This embodiment provides a modified dicyandiamide curing agent, which is prepared according to a method including the following steps:

[0036] Weigh 0.2 mol of dicyandiamide (approximately 16.82 g) and dissolve it in 100 g of organic solvent N,N-dimethylacetamide to obtain reaction solution I; weigh 0.1 mol of hydrogenated dimer acid (35 g) as shown in formula I and dissolve it in 100 g of organic solvent N,N-dimethylacetamide to obtain reaction solution II;

[0037] Under ultrasonic conditions at 120℃, reaction solution II was added dropwise to reaction solution I over a period of 2 hours. After the addition was complete, the reaction was continued at this temperature for another 4 hours. After the reaction was complete, the solvent in the system was evaporated by rotary evaporation. The solid product was then filtered, washed, and dried to obtain the modified dicyandiamide curing agent, denoted as PD-1.

[0038] Example 2

[0039] This embodiment provides a modified dicyandiamide curing agent, which is prepared according to the method of Example 1, except that the organic acid is replaced with an equimolar amount of the hydrogenated dimer acid shown in Formula II;

[0040] The resulting modified dicyandiamide curing agent is designated PD-2.

[0041] Example 3

[0042] This embodiment provides a modified dicyandiamide curing agent, which is prepared according to the method of Example 1, except that the organic acid is replaced with an equimolar amount of the hydrogenated dimer acid shown in Formula II;

[0043] The resulting modified dicyandiamide curing agent is designated PD-3.

[0044] Example 4

[0045] This embodiment provides a modified dicyandiamide curing agent, which is prepared according to the method of Example 1. The difference from Example 1 is that the organic acid is replaced with an equimolar amount of linoleic acid. The resulting modified dicyandiamide curing agent is denoted as PD-4.

[0046] Example 5

[0047] This embodiment provides a modified dicyandiamide curing agent, which is prepared according to the method of Example 1. The difference from Example 1 is that the organic acid is replaced with an equimolar amount of tung oil acid. The resulting modified dicyandiamide curing agent is denoted as PD-5.

[0048] Example 6

[0049] This embodiment provides a modified dicyandiamide curing agent, which is prepared according to the method of Example 1. The difference from Example 1 is that the amount of dicyandiamide used is 0.4 mol, and the resulting modified dicyandiamide curing agent is denoted as PD-6.

[0050] Comparative Example 1

[0051] This comparative example provides a modified dicyandiamide curing agent, which was prepared according to the method of Example 1. The difference from Example 1 is that the fatty acid hydrogenated dimer acid was replaced with an equimolar amount of dihydroxy-terminated hexadecyl alcohol. The resulting modified dicyandiamide curing agent is denoted as PD-7.

[0052] Comparative Example 2

[0053] This comparative example provides a modified dicyandiamide curing agent, which was prepared according to the method of Example 1. The difference from Example 1 is that the fatty acid hydrogenated dimer acid was replaced with an equimolar amount of phosphonic acid. The resulting modified dicyandiamide curing agent is denoted as PD-8.

[0054] Application examples

[0055] Application examples of the present invention also provide a series of epoxy resins comprising the modified dicyandiamide curing agents prepared in the above embodiments and comparative examples, prepared according to the raw material formulations (parts by weight) in Table 1 and a method comprising the following steps:

[0056] According to the raw material formula (parts by weight) in Table 1, epoxy resin, toughening agent, curing agent, curing accelerator and filler are mixed and stirred evenly. After degassing the obtained mixed raw material, it is poured into a mold and cured under heating conditions (curing temperature and time, see Table 1). After curing, epoxy resin is obtained, and the performance of the prepared epoxy resin is tested.

[0057] Table 1. Formulation and curing conditions of epoxy resin

[0058] Table 2. Formulation and curing conditions of epoxy resin

[0059] Performance testing

[0060] The properties of the epoxy resins prepared in the above application examples were characterized. The specific test items, test methods, and results are as follows:

[0061] 1. Tensile properties: The tensile strength and elongation at break of the epoxy resin after curing were obtained by testing according to the method in the standard GB / T16421-1996, where the test temperature was room temperature (25℃) and the tensile rate was 5 mm / min. The tensile strength and elongation at break of the epoxy resin after curing were calculated by the stress-strain diagram of the tensile test.

[0062] 2. Impact resistance (toughness): Tested according to the method in standard GB / T2571-1995, with a test temperature of room temperature (25℃). Impact specimens with dimensions of 80mm*10mm*4mm were prepared according to the standard V-notch small specimen. The notch of the specimen was machined. The speed of the pendulum impacting the center of the specimen was 2.9m / s. The mass of the pendulum was selected based on the actual energy consumption of approximately 50%. The impact strength of the cured epoxy resin was calculated.

[0063] 3. Glass transition temperature: obtained through DSC analysis;

[0064] 4. Initial curing temperature (°C): The epoxy resin composition (uncured) was analyzed by DSC test. The heating rate was 3°C / min, from room temperature (about 25°C) to 250°C. The DSC test spectrum is shown in Figure 1 (comparison between Application Example 1 and Comparative Application Example 3). As can be seen from Figure 1, the curing reaction temperature of the epoxy resin with the modified dicyandiamide curing agent of the present invention (103°C in Application Example 1) decreased by 70°C compared with the unmodified dicyandiamide curing agent in Comparative Application Example 3 (173°C). The test spectra of epoxy resins in other application examples are similar to those in Figure 1. The specific results are shown in Table 3.

[0065] Table 3 Performance Test Results

[0066] The results above show that:

[0067] This invention modifies dicyandiamide with flexible fatty acids, which significantly reduces the curing temperature of dicyandiamide curing agent in cured epoxy resin, improves the flexibility of cured epoxy resin, and ensures the flexibility of epoxy resin without reducing the glass transition temperature of epoxy resin and affecting its use.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A modified dicyandiamide curing agent, characterized in that, The modified dicyandiamide curing agent is obtained by reacting dicyandiamide with fatty acids, wherein the fatty acids include at least one of linoleic acid, tung oil acid, and hydrogenated dimer acid, and the hydrogenated dimer acid includes at least one having the following structural formula:

2. The modified dicyandiamide curing agent according to claim 1, characterized in that, The molar ratio of dicyandiamide to the carboxyl group in the fatty acid is (1-3):

1.

3. The method for preparing the modified dicyandiamide curing agent according to any one of claims 1-2, characterized in that, Includes the following steps: Dicyandiamide and fatty acids are dissolved in a solvent and subjected to an acylation reaction at 80-150°C. After the reaction is complete, the solvent is removed to obtain the modified dicyandiamide curing agent.

4. The preparation method of the modified dicyandiamide curing agent according to claim 3, characterized in that, The solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide.

5. The method for preparing the modified dicyandiamide curing agent according to claim 3, characterized in that, The reaction time is 1-24 hours.

6. The application of the modified dicyandiamide curing agent according to any one of claims 1-2, characterized in that, The modified dicyandiamide curing agent is used to prepare epoxy resin.

7. The application of the modified dicyandiamide curing agent according to claim 6, characterized in that, The epoxy resin composition used to prepare epoxy resin includes the following components in parts by weight: 50-90 parts epoxy resin, 0-20 parts toughening agent, 5-20 parts modified dicyandiamide curing agent as described in any one of claims 1-2, 0-20 parts curing accelerator, and 0-50 parts filler.

8. The application of the modified dicyandiamide curing agent according to claim 6, characterized in that, The curing temperature of the epoxy resin is 60-120℃.

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