An organic urea epoxy accelerator and its preparation method and application

Abstract

The present invention relates to the technical field of epoxy resin curing, and in particular to an organic urea epoxy accelerator and a preparation method and application thereof, wherein the organic urea epoxy accelerator is prepared by reacting N, N-dimethyldipropylenetriamine, thiourea and acrylonitrile, wherein the weight ratio of N, N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1: (0.25-0.8): (0.2-0.5), wherein the reaction temperature is 75-80°C; specifically, the organic urea epoxy accelerator is made of the following raw materials in parts by weight: 40-70 parts of N, N-dimethyldipropylenetriamine, 10-40 parts of thiourea, and 10-30 parts of acrylonitrile. The organic urea epoxy accelerator of the present invention has an excellent promoting effect on epoxy resin curing at low temperatures, and has antioxidant properties, has little effect on the apparent appearance of the cured product after epoxy resin curing, and has little change in its own appearance during long-term storage.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy resin curing, and in particular to an organic urea epoxy accelerator and a preparation method and application thereof. Background Art

[0002] Epoxy resin and curing agent system has been widely used in the field of industrial and civil coatings due to its excellent mechanical properties, bonding properties, electrical insulation properties, processing properties and corrosion resistance. In the epoxy resin and curing agent system, the overall curing performance is determined by the curing agent.

[0003] When the epoxy curing agent is expected to cure faster, an epoxy accelerator is usually added to it. DMP-30 is a commonly used epoxy accelerator on the market. It can promote epoxy ring opening, reduce the activation energy of the reaction, thereby accelerating the curing of the epoxy system, and also promote the film formation of the system. However, the molecular structure of DMP-30 contains phenolic hydroxyl groups, so it is easy to oxidize at high temperatures or when left for a long time, and the result is usually yellowing, and the promotion effect on epoxy resin curing is poor at low temperatures (less than or equal to 3°C). Summary of the invention

[0004] The purpose of the present invention is to provide an organic urea epoxy accelerator, which has an excellent promoting effect on the curing of epoxy resin at low temperature and is not easy to oxidize. At the same time, the accelerator can be prepared at a relatively low temperature, and the accelerator has good stability, no solid precipitation during long-term storage, little effect on the appearance of the cured product after the epoxy resin is cured, and little change in its own appearance during long-term storage.

[0005] In addition, the present invention also provides a preparation method and application of the organic urea epoxy accelerator.

[0006] The present invention is achieved through the following technical solutions:

[0007] An organic urea epoxy accelerator is prepared by reacting N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile, wherein the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.25-0.8):(0.2-0.5), and the reaction temperature is 75-80°C.

[0008] Preferably, the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.5-0.8):(0.2-0.5).

[0009] That is, the organic urea epoxy accelerator of the present invention is prepared by modifying N,N-dimethyldipropylenetriamine with thiourea and acrylonitrile, so that the prepared organic urea epoxy accelerator is more adaptable to the low-temperature curing of epoxy resin, that is, it has an excellent promoting effect on the curing of epoxy resin at low temperature, and effectively shortens the curing time of epoxy resin.

[0010] The low temperature in the present invention refers to 3°C or less.

[0011] The mechanism by which the urea epoxy accelerator of the present invention promotes the low-temperature curing of epoxy resin is:

[0012] Thiourea contains thiourea, so that the modified organic urea epoxy accelerator contains sulfur atoms. The sulfur atoms have greater nucleophilicity than the nitrogen atoms in various amines. Therefore, compared with N,N-dimethyldipropylenetriamine, the modified N,N-dimethyldipropylenetriamine can react with epoxy groups at a lower temperature or at a faster speed. During the reaction, the epoxy ring opens and releases heat, which increases the temperature of the nearby epoxy mixture, thereby promoting the reaction of the modified N,N-dimethyldipropylenetriamine with the epoxy group.

[0013] Thiourea and acrylonitrile are both common fatty amine modifiers. However, in the prior art, thiourea and acrylonitrile are not used together to modify fatty amines. This is because: the reaction activity of fatty amines modified by thiourea is increased, which can improve the promotion effect of fatty amines on epoxy resin fixation and help shorten the low-temperature curing time of epoxy resin. However, acrylonitrile-modified fatty amines achieve cyanoethylation of fatty amines, which reduces the vapor pressure and reaction activity of fatty amines, and reduces the promotion effect of fatty amines on epoxy resin fixation, which is contrary to the basic goal of promoting epoxy resin curing.

[0014] However, if only thiourea is used to modify N,N-dimethyldipropylenetriamine, although the promotion effect of the modified N,N-dimethyldipropylenetriamine on the curing of epoxy resin can be improved, the stability of the prepared accelerator is poor. The test found that:

[0015] When the temperature of thiourea-modified N,N-dimethyldipropylenetriamine is 75-80°C, solid matter will precipitate out of the prepared accelerator after being placed for about 15 hours. As time goes by, the precipitation rate of the solid matter increases, that is, the stability of the prepared accelerator is extremely poor.

[0016] When the temperature of thiourea-modified N,N-dimethyldipropylenetriamine is 100-120°C, solid matter will precipitate out of the prepared accelerator after being placed for about 24 hours. As time goes by, the precipitation rate of the solid matter increases, that is, the stability of the prepared accelerator is very poor.

[0017] When the temperature of thiourea-modified N,N-dimethyldipropylenetriamine is 150-120°C, solid matter will precipitate out of the prepared accelerator after being placed for about 48 hours. As time goes by, the precipitation rate of the solid matter increases, that is, the stability of the prepared accelerator is poor.

[0018] In order to improve the stability of the accelerator prepared by thiourea-modified N,N-dimethyldipropylenetriamine, the present invention adds a certain amount of acrylonitrile to the reaction system to improve the stability of the accelerator. The experiment found that:

[0019] When the temperature of thiourea and acrylonitrile to modify N,N-dimethyldipropylenetriamine is 75-80°C, the prepared accelerator is placed for 7 days without solid precipitation, that is, the stability of the prepared accelerator is very good, and the accelerator is prepared at a lower temperature. In addition, the reaction of acrylonitrile and N,N-dimethyldipropylenetriamine can release heat, and the reaction temperature of acrylonitrile and thiourea to modify N,N-dimethyldipropylenetriamine is maintained, so that the reaction temperature can be adjusted in the system with acrylonitrile added without providing an additional heat source, which is conducive to reducing energy consumption.

[0020] Although the introduction of acrylonitrile will lead to a decrease in the reactivity of N,N-dimethyldipropylenetriamine, the applicant has found that the degree of reduction of the reactivity of acrylonitrile on N,N-dimethyldipropylenetriamine is lower than the promoting effect of thiourea on the reactivity of N,N-dimethyldipropylenetriamine. Therefore, by reasonably controlling the dosage ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile, it is ensured that the prepared promoter has excellent promoting effect on epoxy resin curing at low temperature and good stability. Among them, if the dosage of acrylonitrile is too small, the stability of the prepared promoter will be poor. If the dosage of acrylonitrile is too large, the promoting effect of thiourea on N,N-dimethyldipropylenetriamine will not be able to offset the weakening effect of acrylonitrile on N,N-dimethyldipropylenetriamine, which ultimately leads to the promoting effect of the prepared promoter on epoxy resin curing being lower than that of unmodified N,N-dimethyldipropylenetriamine.

[0021] Moreover, compared with the existing DMP-30 accelerator, the urea-based epoxy accelerator of the present invention does not contain phenolic hydroxyl groups, is not easily oxidized, has little effect on the appearance of the cured epoxy resin, and has little change in its appearance during long-term storage, so that the urea-based epoxy accelerator of the present invention can adapt to being placed at higher temperatures or for a long time.

[0022] In a preferred embodiment, the organic urea epoxy accelerator is made from the following raw materials in parts by weight:

[0023] 40-70 parts of N,N-dimethyldipropylenetriamine, 10-40 parts of thiourea, and 10-30 parts of acrylonitrile.

[0024] In a preferred embodiment, the organic urea epoxy accelerator is made from the following raw materials in parts by weight:

[0025] 40-70 parts of N,N-dimethyldipropylenetriamine, 25-35 parts of thiourea, and 20-25 parts of acrylonitrile.

[0026] A method for preparing an organic urea epoxy accelerator comprises the following steps:

[0027] S1. Introduce N,N-dimethyldipropylenetriamine into a reaction kettle, start a stirrer to stir; while stirring, add thiourea into the reaction kettle at a uniform speed;

[0028] S2, keep stirring, add acrylonitrile into the kettle, and maintain the temperature in the kettle;

[0029] S3. After adding acrylonitrile, continue stirring for 2-3 hours, cool down, and discharge to obtain an organic urea epoxy accelerator.

[0030] In a preferred embodiment, in step S1, the stirring speed is 800-1000 r / min.

[0031] In a preferred embodiment, in step S1, the reaction temperature is 75-80°C.

[0032] In a preferred embodiment, in step S3, the reaction kettle is cooled to below 65°C before discharging the material.

[0033] In a preferred embodiment, in step S3, acrylonitrile is added to the reactor in a dropwise manner.

[0034] The application of the above organic urea epoxy accelerator in low temperature curing of epoxy resin.

[0035] In a preferred embodiment, the amount of the organic urea epoxy accelerator is 0.5-0.8%.

[0036] As the amount of organic urea epoxy accelerator increases, the low-temperature curing speed of epoxy resin increases. However, as the curing speed increases, the brittleness of the cured product increases, the shear strength decreases, and the elongation at break first increases and then decreases. Therefore, it is necessary to reasonably control the amount of organic urea epoxy accelerator during the low-temperature curing of epoxy resin, so that the cured product has appropriate shear strength and elongation at break while ensuring a short fixing time.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] 1. The present invention adopts acrylonitrile and thiourea to modify N,N-dimethyldipropylenetriamine, so that the prepared accelerator has both the promoting effect and stability on epoxy resin at low temperature: the modified N,N-dimethyldipropylenetriamine can react with epoxy groups at a lower temperature or at a faster speed. During the reaction, the epoxy ring opens and releases heat, so that the temperature of the nearby epoxy mixture increases, thereby promoting the reaction of the modified N,N-dimethyldipropylenetriamine with the epoxy group, thereby achieving the modified N,N-dimethyldipropylenetriamine has an excellent promoting effect on the curing of epoxy resin at low temperature, greatly shortening the low-temperature curing time of epoxy resin, and the modified N,N-dimethyldipropylenetriamine has good stability and is not easy to oxidize, has little effect on the appearance of the cured product after the epoxy resin is cured, and has little change in its appearance during long-term storage.

[0039] 2. The present invention can ensure that the cured product has suitable shear strength and elongation at break under the premise of a short fixing time by reasonably controlling the amount of organic urea epoxy accelerator used during low-temperature curing of epoxy resin. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. The schematic implementation mode of the present invention and its description are only used to explain the present invention and are not intended to limit the present invention. The embodiments described below are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0041] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to those of ordinary skill in the art that these specific details do not have to be employed to practice the present invention. In other embodiments, in order to avoid confusing the present invention, known structures, materials or methods are not specifically described. The materials, instruments and reagents used in the following examples, unless otherwise specified, can be obtained from commercial sources. The technical means used in the examples, unless otherwise specified, are conventional means well known to those skilled in the art.

[0042] In order to promote the low-temperature curing of epoxy resin and shorten the low-temperature curing time of epoxy resin, the present embodiment provides an organic urea epoxy accelerator, which is prepared by reacting N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile, wherein the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.25-0.8):(0.2-0.5), and the reaction temperature is 75-80°C.

[0043] Preferably, the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.5-0.8):(0.2-0.5)

[0044] In this embodiment, acrylonitrile and thiourea are used to modify N,N-dimethyldipropylenetriamine, so that the modified N,N-dimethyldipropylenetriamine has an excellent promoting effect on the curing of epoxy resin at low temperature, greatly shortens the low-temperature curing time of epoxy resin, and the modified N,N-dimethyldipropylenetriamine has good stability and is not easy to oxidize, has little effect on the appearance of the cured epoxy resin, and has little change in its own appearance during long-term storage.

[0045] More specifically, the organic urea epoxy accelerator is made from the following raw materials in parts by weight:

[0046] 40-70 parts of N,N-dimethyldipropylenetriamine, 10-40 parts of thiourea, and 10-30 parts of acrylonitrile.

[0047] Preferably, the organic urea epoxy accelerator is made from the following raw materials in parts by weight:

[0048] 40-70 parts of N,N-dimethyldipropylenetriamine, 25-35 parts of thiourea, and 20-25 parts of acrylonitrile.

[0049] By reasonably controlling the dosage ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile, the promoting effect of the modified N,N-dimethyldipropylenetriamine on the low-temperature curing of epoxy resin can reach an optimal level without causing excessive use of thiourea and acrylonitrile.

[0050] The preparation method of the above-mentioned organic urea epoxy accelerator comprises the following steps:

[0051] S1. Introduce N,N-dimethyldipropylenetriamine into the reaction kettle, start the stirrer for stirring, and the stirring speed is 800-1000r / min; while stirring, add thiourea into the reaction kettle at a uniform speed, and the reaction temperature is 75-80°C;

[0052] S2, keep stirring, add acrylonitrile to the kettle, and maintain the temperature in the kettle;

[0053] S3. After the acrylonitrile is added dropwise, stirring is continued for 2-3 hours. The reaction kettle is cooled to below 65° C. and then the material is discharged to obtain an organic urea epoxy accelerator.

[0054] The invention discloses an application of an organic urea epoxy accelerator in low temperature curing of epoxy resin.

[0055] Preferably, the amount of the organic urea epoxy accelerator is 0.5-0.8% based on the weight of the epoxy resin.

[0056] The reaction process of this embodiment is:

[0057] The active hydrogen of N,N-dimethyldipropylenetriamine can undergo the following addition reaction on the double bond of acrylonitrile to achieve the cyanoethylation of N,N-dimethyldipropylenetriamine:

[0058]

[0059] The reaction process of N,N-dimethyldipropylenetriamine and thiourea is as follows:

[0060]

[0061] In order to better illustrate the technical effect of the organic urea epoxy accelerator of this embodiment, the following specific examples are used for illustration:

[0062] Embodiment 1:

[0063] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0064] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, and 25 parts of acrylonitrile. The weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.6:0.5.

[0065] The preparation method of the organic urea epoxy accelerator of this embodiment comprises the following steps:

[0066] S1. Introduce N,N-dimethyldipropylenetriamine into the reactor, start the stirrer for stirring, and the stirring speed is 1000r / min; while stirring, add thiourea into the reactor at a uniform speed, and the reaction temperature is 75°C;

[0067] S2, keep stirring at 1000r / min, add acrylonitrile dropwise into the kettle, and keep the temperature in the kettle at 75°C;

[0068] S3. After the acrylonitrile is added dropwise, stirring is continued for 2 hours. The reaction kettle is cooled to 50° C. and then the material is discharged and cooled to obtain an organic urea epoxy accelerator.

[0069] Embodiment 2:

[0070] This embodiment is based on embodiment 1, and the difference from embodiment 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0071] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0072] 60 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, and 30 parts of acrylonitrile. The weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.5:0.5.

[0073] Embodiment 3:

[0074] This embodiment is based on embodiment 1, and the difference from embodiment 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0075] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0076] 70 parts of N,N-dimethyldipropylenetriamine, 40 parts of thiourea, and 30 parts of acrylonitrile; the weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.57:0.43.

[0077] Embodiment 4:

[0078] This embodiment is based on embodiment 1, and the difference from embodiment 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0079] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0080] 40 parts of N,N-dimethyldipropylenetriamine, 25 parts of thiourea, and 20 parts of acrylonitrile; the weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.63:0.5.

[0081] Embodiment 5:

[0082] This embodiment is based on embodiment 1, and the difference from embodiment 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0083] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0084] 40 parts of N,N-dimethyldipropylenetriamine, 10 parts of thiourea, and 10 parts of acrylonitrile; the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:0.25:0.25.

[0085] Comparative Example 1:

[0086] This comparative example is based on Example 1, and the difference from Example 1 is that thiourea is directly used to modify N,N-dimethyldipropylenetriamine, specifically:

[0087] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0088] 50 parts of N,N-dimethyldipropylenetriamine and 30 parts of thiourea.

[0089] The preparation method of the organic urea epoxy accelerator of this comparative example comprises the following steps:

[0090] S1. Introduce N,N-dimethyldipropylenetriamine into the reactor, start the stirrer for stirring, and the stirring speed is 1000r / min; while stirring, add thiourea into the reactor at a uniform speed, and the reaction temperature is 75°C;

[0091] S2. Add thiourea at a uniform speed and continue stirring for 2 hours. Cool the reactor to 50°C, then discharge the material and cool to obtain an organic urea epoxy accelerator.

[0092] Comparative Example 2:

[0093] This comparative example is based on Example 1, and the difference from Example 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0094] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0095] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, 5 parts of acrylonitrile, and the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:0.6:0.125.

[0096] Comparative Example 3:

[0097] This comparative example is based on Example 1, and the difference from Example 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0098] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0099] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, and 10 parts of acrylonitrile. The weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.6:0.2.

[0100] Comparative Example 4:

[0101] This comparative example is based on Example 1, and the difference from Example 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0102] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0103] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, and 15 parts of acrylonitrile. The weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.6:0.3.

[0104] Comparative Example 5:

[0105] This comparative example is based on Example 1, and the difference from Example 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0106] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0107] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, and 20 parts of acrylonitrile. The weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.6:0.4.

[0108] Comparative Example 6:

[0109] This comparative example is based on Example 1, and the difference from Example 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0110] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0111] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, and 30 parts of acrylonitrile. The weight ratio of N,N-dimethyldipropylenetriamine, thiourea, and acrylonitrile is 1:0.6:0.6.

[0112] Comparative Example 7:

[0113] This comparative example is based on Example 1, and the difference from Example 1 is that the amounts of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile are different, specifically:

[0114] An organic urea epoxy accelerator is prepared from the following raw materials in parts by weight:

[0115] 50 parts of N,N-dimethyldipropylenetriamine, 30 parts of thiourea, 40 parts of acrylonitrile, and the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:0.6:0.8.

[0116] Comparative Example 8:

[0117] The accelerator used in this comparative example is DMP-30 accelerator.

[0118] The organic urea epoxy accelerators prepared in Examples 1 to 5, Comparative Examples 1 to 7, and the DMP-30 accelerator in Comparative Example 8 were placed at 60° C. and 100° C. for a period of time, respectively, and the apparent changes of each accelerator were observed. The results are shown in Tables 1 and 2:

[0119] Table 1 (60℃ storage)

[0120]

[0121] Table 2 (100℃ storage)

[0122]

[0123]

[0124] From the data in Table 1 and Table 2, we can see that:

[0125] The organic urea epoxy accelerator prepared by the present invention is not easy to be oxidized, and can maintain substantially no change in appearance after being placed at 60°C for 15 days; and can maintain substantially no change in appearance after being placed at 100°C for 5 days; while the DMP-30 accelerator containing phenolic hydroxyl groups turns slightly yellow after being placed at 60°C for 5 days, turns partially severely yellow and partially slightly yellow after being placed for 15 days; turns slightly yellow after being placed at 100°C for 2 days, turns partially severely yellow and partially slightly yellow after being placed for 5 days.

[0126] The organic urea epoxy accelerators prepared in Examples 1 to 5 and Comparative Examples 1 to 7 were placed at room temperature to observe the precipitation of solids. The results are shown in Table 3:

[0127] Table 3

[0128]

[0129] From the data in Table 3, we can see that:

[0130] 1) When thiourea is directly used to modify N,N-dimethyldipropylenetriamine, solid matter begins to precipitate after 15 hours. As time goes by, the amount of solid matter precipitated increases rapidly, and a large amount of solid matter precipitates after 24 hours.

[0131] 2) When thiourea and acrylonitrile are used to modify N,N-dimethyldipropylenetriamine, the addition of acrylonitrile can improve the compatibility of thiourea and N,N-dimethyldipropylenetriamine and improve the stability of the accelerator. However, the amount of acrylonitrile used needs to be reasonably controlled. If the amount of acrylonitrile added is too little, the accelerator will begin to precipitate solid matter in a relatively short period of time. As the amount of acrylonitrile increases, the time for solid matter to precipitate is prolonged, and the precipitation speed will also be relatively slow. When the weight ratio of thiourea to acrylonitrile is less than or equal to 1.5:1, the accelerator will not precipitate solid matter even after being placed for a week.

[0132] The organic urea epoxy accelerators prepared in Examples 1 to 5 and Comparative Examples 1 to 7, and the DMP-30 accelerator in Comparative Example 8 are applied to the low-temperature curing of epoxy resin. The specific application process is: epoxy resin E-446101, low-temperature curing agent (polythiol 309) and accelerator are mixed in proportion, evenly coated on a tinplate to form a film with a thickness of 50 μm, and then the mold is placed in a refrigerator at -5°C, wherein the weight ratio of epoxy resin E-446101 to polythiol 309 is 4:1, and the amount of accelerator added is 0.5% based on the weight of the epoxy resin. According to GB / T 6739-2006, the hardness of the sample after actual drying was tested; according to GB / T7124-2008 and GB / T1042-1992 standards, a universal material testing machine (Shenzhen Wanchuang Testing Equipment Co., Ltd., TSE305D, microcomputer-controlled electronic universal testing machine) was used to test the shear strength and tensile strength of the sample after actual drying (tensile rate was 5mm / min, each group was tested 5 times in parallel, and the average value was taken). The surface drying time refers to the time from the beginning of film formation of the sample until the surface of the sample is touched with a finger, and it feels a little sticky but there is no water on the hand. The actual drying time refers to the time required for the sample to form a film until it is completely solid and the surface is completely dry. The thumb or glass rod can be pressed on the surface of the sample without leaving any marks. The results are shown in Table 4:

[0133] Table 4 (-5℃ curing)

[0134] Surface drying time / min Drying time / h hardness Shear strength / MPa Elongation at break / % Example 1 45 4.0 3H 16.5 24.8 Example 2 60 7.6 3H 19.6 20.8 Example 3 42 3.5 3H 16.1 25.2 Example 4 40 3.2 3H 15.6 25.9 Example 5 80 10.0 3H 21.7 17.8 Comparative Example 1 30 1.7 3H 13.8 23.4 Comparative Example 2 35 2.6 3H 14.6 24.9 Comparative Example 3 38 2.9 3H 15.1 25.8 Comparative Example 4 40 3.3 3H 15.6 26.0 Comparative Example 5 43 3.6 3H 16.3 25.0 Comparative Example 6 50 5.3 3H 18.2 22.6 Comparative Example 7 60 7.4 3H 19.3 20.2 Comparative Example 8 95 12.5 3H 23.5 15.6

[0135] From the data in Table 4, we can see that:

[0136] 1) The organic urea epoxy accelerator prepared by the present invention is used for curing epoxy resin at -5°C, with a surface drying time of less than 80 minutes and a practical drying time of less than 10 hours, and can meet higher hardness, shear strength and elongation at break.

[0137] 2) Under the premise that the weight ratio of N,N-dimethyldipropylenetriamine to thiourea remains unchanged, as the amount of acrylonitrile added increases, the surface drying time increases. Using the data in Tables 3 and 4, when the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.25-0.8):(0.2-0.5), the prepared accelerator has both stability and low-temperature acceleration effect on epoxy resin. When the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.5-0.8):(0.2-0.5), the effect is better. Not only is there no precipitation in one week, but the surface drying time is within 60 minutes and the actual drying time is within 7.6 hours. More preferably, the weight ratio of thiourea to acrylonitrile is greater than 1, preferably greater than or equal to 1.2.

[0138] In order to verify the optimal dosage of organic urea epoxy accelerator in promoting low-temperature curing of epoxy resin, the following experiments were conducted:

[0139] The organic urea epoxy accelerator prepared in Example 1 is applied to the low-temperature curing of epoxy resin. The specific application process is: epoxy resin E-446101, low-temperature curing agent (polythiol 309) and accelerator are mixed in proportion, and then the mixture is poured into a mold, and then the mold is placed in a refrigerator at -5°C, wherein the weight ratio of epoxy resin E-446101 and polythiol 309 is 4:1, and the amount of accelerator added is set to 0.3%, 0.4%, 0.5%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1.0% in sequence based on the weight of epoxy resin. The results are shown in Table 5:

[0140] Table 5

[0141] Surface drying time / min Drying time / h hardness Shear strength / MPa Elongation at break / % 0.3％ 50 5.2 3H 18.0 22.8 0.4％ 48 4.5 3H 17.2 23.6 0.5％ 45 4.0 3H 16.5 24.8 0.6％ 42 3.5 3H 16.0 25.4 0.7％ 39 3.0 3H 15.4 26.2 0.8％ 35 2.5 3H 14.8 25.1 0.9％ 30 1.8 3H 13.6 23.6 1.0％ 25 1.2 2H 11.5 19.8

[0142] From the data in Table 4, we can see that:

[0143] 1) As the amount of organic urea epoxy accelerator increases, the low-temperature curing speed of epoxy resin increases. However, as the curing speed increases, the brittleness of the cured product increases and the shear strength decreases; the elongation at break first increases and then decreases. Therefore, it is necessary to reasonably control the amount of organic urea epoxy accelerator during the low-temperature curing of epoxy resin, so that the cured product has appropriate shear strength and elongation at break while ensuring a short fixing time.

[0144] 2) When the amount of organic urea epoxy accelerator added during low-temperature fixation of epoxy resin is 0.5%-0.8%, the surface drying time is 35-45min, and the actual drying time is 2.5-4.0, which can achieve low-temperature curing of epoxy resin and have high hardness, shear strength and elongation at break; when the amount of organic urea epoxy accelerator added during low-temperature fixation of epoxy resin is greater than or equal to 1.0%, the hardness drops to 2H, and the shear strength and elongation at break are greatly reduced. When the addition amount is less than 0.5%, although it has high hardness, shear strength and elongation at break, the surface drying time and actual drying time are increased.

[0145] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An organic urea epoxy accelerator, characterized in that: It is prepared by reacting N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile, wherein the weight ratio of N,N-dimethyldipropylenetriamine, thiourea and acrylonitrile is 1:(0.25-0.8):(0.2-0.5), wherein the reaction temperature is 75-80°C, and the weight ratio of thiourea to acrylonitrile is less than or equal to 1.5:

1.

2. An organic urea epoxy accelerator according to claim 1, characterized in that: Made from the following raw materials in parts by weight: 40-70 parts of N,N-dimethyldipropylenetriamine, 10-40 parts of thiourea, and 10-30 parts of acrylonitrile.

3. An organic urea epoxy accelerator according to claim 2, characterized in that: Made from the following raw materials in parts by weight: 40-70 parts of N,N-dimethyldipropylenetriamine, 25-35 parts of thiourea, and 20-25 parts of acrylonitrile.

4. The method for preparing the organic urea epoxy accelerator according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Introduce N,N-dimethyldipropylenetriamine into a reaction kettle, start a stirrer to stir; while stirring, add thiourea into the reaction kettle at a uniform speed; S2, keep stirring, add acrylonitrile into the kettle, and maintain the temperature in the kettle; S3. After adding acrylonitrile, continue stirring for 2-3 hours, cool down, and discharge to obtain an organic urea epoxy accelerator.

5. The preparation method according to claim 4, characterized in that: In step S1, the stirring speed is 800-1000 r / min.

6. The preparation method according to claim 4, characterized in that: In step S1, the reaction temperature is 75-80°C.

7. The preparation method according to claim 4, characterized in that: In step S3, the reaction kettle is cooled to below 65° C. before discharging the material.

8. The preparation method according to claim 4, characterized in that: In step S3, acrylonitrile is added into the reaction kettle in a dropwise manner.

9. Use of the organic urea epoxy accelerator according to any one of claims 1 to 3 in low-temperature curing of epoxy resin.

10. The use according to claim 9, characterized in that the amount of the organic urea epoxy accelerator is 0.5-0.8% based on the weight of the epoxy resin.

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