Modified dicyandiamide, single-component epoxy structural adhesive and preparation method thereof

Abstract

The application discloses a modified dicyandiamide, a single-component epoxy structural adhesive and a preparation method thereof. The modified dicyandiamide is obtained by the reaction of an epoxy group terminated polyether and dicyandiamide, and the epoxy group terminated polyether is obtained by the reaction of a polyether polyol and epichlorohydrin; the polyether polyol contains at least two hydroxyl groups. The single-component epoxy structural adhesive prepared by using the modified dicyandiamide as a curing agent, in combination with an epoxy resin and nano calcium carbonate and the like, has a relatively low curing temperature, and the elongation at break and the peeling strength are also significantly improved relative to a dicyandiamide system without modification, and the adhesive property between the material is better. Moreover, the single-component epoxy structural adhesive has a relatively high glass transition temperature and bulk strength while the above various properties are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of sealant technology, specifically to epoxy sealants, and particularly to a modified dicyandiamide, one-component epoxy structural adhesive and its preparation method. Background Technology

[0002] Dicyandiamide is a widely used one-component epoxy latent curing agent. One-component epoxy structural adhesives prepared by adding dicyandiamide have extremely high bulk strength and high glass transition temperature after curing, and are widely used.

[0003] However, existing dicyandiamide-cured one-component epoxy structural adhesives have the following drawbacks: on the one hand, the cured products are often hard and brittle, and toughening agents are usually added to improve the brittleness. However, using flexible toughening agents often significantly reduces the glass transition temperature of the cured adhesive, thereby reducing its bulk strength and other properties. On the other hand, the curing temperature of one-component epoxy structural adhesives with dicyandiamide as the curing agent is very high, often exceeding the range acceptable by the production process. Moreover, curing at high temperatures may damage the performance of the device.

[0004] How to improve the toughness and reduce the curing temperature of dicyandiamide-cured single-component epoxy structural adhesives while maintaining their high glass transition temperature and bulk strength is an urgent problem that needs to be solved in practical applications. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a one-component epoxy structural adhesive with a low curing temperature and high toughness, which also has a high glass transition temperature and bond strength.

[0006] To achieve the above objectives, the present invention includes the following technical solutions.

[0007] In a first aspect, the present invention provides a modified dicyandiamide obtained by reacting an epoxy-terminated polyether with dicyandiamide, wherein the epoxy-terminated polyether is obtained by reacting a polyether polyol with epichlorohydrin;

[0008] The polyether polyol contains at least two hydroxyl groups.

[0009] Secondly, the present invention provides a method for preparing the modified dicyandiamide, comprising the following steps:

[0010] The polyether polyol and catalyst are stirred evenly, heated to 30℃~50℃, and the epichlorohydrin is added dropwise. The reaction is carried out for 4~6 hours to obtain the epoxy-terminated polyether.

[0011] The modified dicyandiamide is obtained by refluxing the epoxy-terminated polyether and dicyandiamide at 130°C to 150°C for 3 to 5 hours.

[0012] Thirdly, the present invention provides a one-component epoxy structural adhesive, which, by weight, is obtained by mixing raw materials comprising the following components:

[0013]

[0014] Fourthly, the present invention provides a method for preparing the single-component epoxy structural adhesive, comprising the following steps:

[0015] The epoxy resin, modified dicyandiamide, organic urea, nano-calcium carbonate and heavy calcium carbonate are mixed evenly to obtain the single-component epoxy structural adhesive.

[0016] The present invention has the following beneficial effects:

[0017] This invention synthesizes epoxy-terminated polyethers of specific molecular weights using multifunctional polyether polyols and epichlorohydrin, and then modifies dicyandiamide using these epoxy-terminated polyethers to prepare a modified dicyandiamide containing polyether segments and hydroxyl groups. Using this modified dicyandiamide as a curing agent not only lowers the curing temperature of one-component epoxy structural adhesives but also acts as a toughening agent. Furthermore, it improves the toughness of one-component epoxy structural adhesives while maintaining high glass transition temperatures, storage stability, and bulk strength. In addition, the flexible segments and hydroxyl groups in this modified dicyandiamide can also improve the adhesion and peel strength between the one-component epoxy adhesive and the substrate.

[0018] The one-component epoxy structural adhesive prepared by using the modified dicyandiamide of this invention as a curing agent in combination with epoxy resin, nano-calcium carbonate, and other components not only has a lower curing temperature, facilitating applications in a wider range of situations, but also exhibits better toughness. The elongation at break is significantly improved compared to the unmodified dicyandiamide system, while the bond strength and peel strength are also significantly improved, resulting in better adhesion to materials. Furthermore, while achieving significant improvements in the aforementioned properties, the one-component epoxy structural adhesive of this invention also possesses a higher glass transition temperature and bulk strength. Attached Figure Description

[0019] Figure 1 It is the infrared spectrum of epoxy-terminated polyether.

[0020] Figure 2 This is the infrared spectrum of modified dicyandiamide. Detailed Implementation

[0021] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as limiting the invention.

[0022] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0023] The terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product, or device that includes a series of steps is not limited to the steps or modules listed, but may optionally include steps not listed, or may optionally include other steps inherent to such process, method, product, or device.

[0024] In this invention, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] Some embodiments of the present invention relate to a modified dicyandiamide obtained by reacting an epoxy-terminated polyether with dicyandiamide, wherein the epoxy-terminated polyether is obtained by reacting a polyether polyol with epichlorohydrin;

[0026] The polyether polyol contains at least two hydroxyl groups.

[0027] The polyether polyols described in this invention refer to polyether polymers containing two or more hydroxyl groups (-OH) at the end groups or side groups. They are prepared by addition polymerization of diols such as propylene glycol and ethylene glycol, triols such as glycerol and trimethylolpropane, or polyols such as pentaerythritol, with ethylene oxide, propylene oxide, etc. in the presence of a catalyst.

[0028] In some embodiments, the molar ratio of the epoxy-terminated polyether to dicyandiamide is 0.5 to 0.7:1.

[0029] In some embodiments, the molar ratio of the polyether polyol and epichlorohydrin is 1:1 to 3, preferably 1:1.5 to 2.3.

[0030] In some embodiments, the number average molecular weight of the polyether polyol is 300-2200, preferably 300-800, and more preferably 300-600.

[0031] In some embodiments, the number-average molecular weight of the epoxy-terminated polyether is 400 to 2300, preferably 400 to 900.

[0032] In some embodiments, the epoxy content of the epoxy-terminated polyether is 3-24%, preferably 12-20%.

[0033] In some embodiments, the modified dicyandiamide has an active hydrogen equivalent of 80-200, preferably 100-150, more preferably 110-120; and a hydroxyl content of 2-12%, preferably 5-9%, more preferably 7-8%.

[0034] In some embodiments, the polyether polyol is selected from any one polyether polyol of formula (I) or formula (II) or a combination of multiple polyether polyols:

[0035]

[0036] Where n = 2 - 25, x + y + z = 2 - 25.

[0037] In some of these embodiments, n is 4, 5, 6, 7, or 8.

[0038] In some embodiments, x+y+z = 4, 5, 6, 7, or 8.

[0039] In some embodiments, the polyether polyol is one or a combination of polyether polyol N204, polyether polyol N303F and polyether polyol N306.

[0040] In some embodiments, the polyether polyol is a combination of polyether polyol N303F and polyether polyol N306.

[0041] In some embodiments, the molar ratio of the polyether polyol N303F to the polyether polyol N306 is preferably 2 to 3:1.

[0042] In some embodiments, the polyether polyol and epichlorohydrin react in the presence of a catalyst, preferably boron trifluoride ethyl ether, and the molar ratio of the polyether polyol to the catalyst is preferably 1:0.1 to 0.3.

[0043] Some embodiments of the present invention involve a method for preparing the modified dicyandiamide, comprising the following steps:

[0044] The polyether polyol and catalyst are stirred evenly, heated to 30℃~50℃, and the epichlorohydrin is added dropwise. The reaction is carried out for 4~6 hours to obtain the epoxy-terminated polyether.

[0045] The modified dicyandiamide is obtained by refluxing epoxy-terminated polyether and dicyandiamide at 130℃~150℃ for 3~5 hours.

[0046] In some embodiments, the method for preparing the modified dicyandiamide includes the following steps:

[0047] The polyether polyol and catalyst are stirred evenly and heated to 35℃~45℃. Epichlorohydrin is added dropwise and reacted for 4~6 hours. The reaction product is separated by vacuum distillation. The reaction product is then washed with a saturated NaOH aqueous solution at a temperature of 25℃~35℃ to separate the oil layer and remove water, thus obtaining the epoxy-terminated polyether.

[0048] The modified dicyandiamide was obtained by reflux reaction of epoxy-terminated polyether and dicyandiamide at 135℃~145℃ for 3~5 hours and then separated by distillation.

[0049] Some embodiments of the present invention relate to a one-component epoxy structural adhesive, which, by weight, is obtained by mixing raw materials comprising the following components:

[0050]

[0051] In some embodiments, the one-component epoxy structural adhesive is obtained by mixing raw materials comprising the following components, in parts by weight:

[0052]

[0053] In some embodiments, the one-component epoxy structural adhesive is obtained by mixing raw materials comprising the following components, in parts by weight:

[0054]

[0055]

[0056] Some embodiments of the present invention relate to a method for preparing a one-component epoxy structural adhesive, comprising the following steps:

[0057] The epoxy resin, modified dicyandiamide, organic urea, nano-calcium carbonate and heavy calcium carbonate are mixed evenly to obtain the single-component epoxy structural adhesive.

[0058] The following are specific examples.

[0059] Unless otherwise specified, "parts" in the following embodiments refer to parts by weight.

[0060] Example 1

[0061] (1) Preparation of epoxy-terminated polyethers

[0062]

[0063] 1.6 mol of polyether polyol (N2O4, difunctional, number-average molecular weight 400) and 0.2 mol of boron trifluoride diethyl ether catalyst were weighed and added to a three-necked flask. The mixture was stirred until homogeneous, heated to 40°C, and 3 mol of epichlorohydrin was slowly added dropwise over 0.5 hours. The reaction was allowed to proceed for 5 hours, followed by vacuum distillation to separate the reaction product. The reaction product was washed with a saturated NaOH aqueous solution at 30°C, and the oil layer was separated. The water was removed by vacuum distillation to obtain an epoxy-terminated polyether with a number-average molecular weight of 508 and an epoxy content of 16.2%.

[0064] The infrared spectrum of the epoxy-terminated polyether is as follows: Figure 1 As shown: 3467cm -1 The characteristic absorption peak of hydroxyl groups is at 838 cm⁻¹. -1 The characteristic absorption peak of the epoxy group is at 2868 cm⁻¹. -1 The methylene absorption peak is at 1373 cm⁻¹. -1 The absorption peak for polyoxypropylene is at 1092 cm⁻¹. -1 The peak at this point represents a strong asymmetric stretching vibration of the COC bond.

[0065] (2) Preparation of modified dicyandiamide

[0066]

[0067] Weigh 1.2 mol of epoxy-terminated polyether and 2 mol of dicyandiamide (DYHARD 100S, active hydrogen equivalent 21, particle size 8.1-9.1 μm), and add them sequentially to a three-necked flask equipped with a condenser, stirrer, and heating mantle. Pour cooling water through the flask, turn on the stirrer and heating mantle, and reflux at 140°C for 4 hours. Then, replace the flask with a vacuum distillation apparatus, turn on the vacuum pump and heating mantle, and distill at an external temperature of 135°C until no liquid is drawn out. The product obtained is the modified dicyandiamide epoxy curing agent, with an active hydrogen equivalent of 108 and a hydroxyl content of 5.4%.

[0068] The infrared spectrum of the modified dicyandiamide is as follows: Figure 2 As shown, in the infrared spectrum of this modified dicyandiamide, 3469 cm⁻¹ -1 The characteristic absorption peak of hydroxyl groups is at 2865 cm⁻¹. -1 The methylene absorption peak is at 2187 cm⁻¹. -1 The absorption peak for cyano is at 1373 cm⁻¹. -1 The absorption peak for polyoxypropylene is at 1094 cm⁻¹. -1 The peak at 1565 cm⁻¹ represents a strong asymmetric stretching vibration of the COC bond. -1 The absorption peaks are for nitrogen and hydrogen groups.

[0069] (3) Preparation of one-component epoxy structural adhesive

[0070] Weigh out 43 parts of epoxy resin (NPEL-128), 25 parts of modified dicyandiamide (active hydrogen equivalent 108), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano calcium carbonate (CCS-25i, 70nm), and 21.75 parts of heavy calcium carbonate (1250 mesh), mix them evenly, and obtain a one-component epoxy structural adhesive.

[0071] Example 2

[0072] (1) Preparation of epoxy-terminated polyethers

[0073]

[0074] Where x + y + z = 4.

[0075] 1.6 mol of polyether polyol (N303F, trifunctional, number-average molecular weight 340) and 0.2 mol of boron trifluoride diethyl ether catalyst were weighed and added to a three-necked flask. The mixture was stirred until homogeneous, heated to 40°C, and 3 mol of epichlorohydrin was slowly added dropwise over 0.5 hours. The reaction was allowed to proceed for 5 hours, followed by vacuum distillation to separate the reaction product. The reaction product was washed with a saturated NaOH aqueous solution at 30°C, and the oil layer was separated. The water was removed by vacuum distillation to obtain epoxy-terminated polyether. The number-average molecular weight was measured to be 451, and the epoxy content was 19.1%.

[0076] (2) Preparation of modified dicyandiamide

[0077]

[0078] Where x + y + z = 4.

[0079] Weigh 1.2 mol of epoxy-terminated polyether and 2 mol of dicyandiamide (DYHARD 100S, active hydrogen equivalent 21, particle size 8.1-9.1 μm), and add them sequentially to a three-necked flask equipped with a condenser, stirrer, and heating mantle. Pour cooling water through the flask, turn on the stirrer and heating mantle, and reflux at 140°C for 4 hours. Then, replace the flask with a vacuum distillation apparatus, turn on the vacuum pump and heating mantle, and distill at an external temperature of 135°C until no liquid is drawn out. The product obtained is the modified dicyandiamide epoxy curing agent, with an active hydrogen equivalent of 102 and a hydroxyl content of 8.1%.

[0080] (3) Preparation of one-component epoxy structural adhesive

[0081] Weigh out 43 parts of epoxy resin (NPEL-128), 24 parts of modified dicyandiamide (active hydrogen equivalent 102), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano calcium carbonate (CCS-25i, 70nm) and 22.75 parts of heavy calcium carbonate (1250 mesh), mix them evenly to obtain a one-component epoxy structural adhesive.

[0082] Example 3

[0083] (1) Preparation of epoxy-terminated polyethers

[0084]

[0085] Where x + y + z = 8.

[0086] 1.6 mol of polyether polyol (N306, trifunctional, number-average molecular weight 600) and 0.2 mol of boron trifluoride diethyl ether catalyst were weighed and added to a three-necked flask. The mixture was stirred until homogeneous, heated to 40°C, and 3 mol of epichlorohydrin was slowly added dropwise over 0.5 hours. The reaction was allowed to proceed for 5 hours, followed by vacuum distillation to separate the reaction product. The reaction product was washed with a saturated NaOH aqueous solution at 30°C, and the oil layer was separated. The water was removed by vacuum distillation to obtain epoxy-terminated polyether. The number-average molecular weight was measured to be 708, and the epoxy content was 12.1%.

[0087] (2) Preparation of modified dicyandiamide

[0088]

[0089] Where x + y + z = 8.

[0090] Weigh 1.2 mol of epoxy-terminated polyether and 2 mol of dicyandiamide (DYHARD 100S, active hydrogen equivalent 21, particle size 8.1-9.1 μm), and add them sequentially to a three-necked flask equipped with a condenser, stirrer, and heating mantle. Pour cooling water through the flask, turn on the stirrer and heating mantle, and reflux at 140°C for 4 hours. Then, replace the flask with a vacuum distillation apparatus, turn on the vacuum pump and heating mantle, and distill at an external temperature of 135°C until no liquid is drawn out. The product obtained is the modified dicyandiamide epoxy curing agent, with an active hydrogen equivalent of 142 and a hydroxyl content of 5.9%.

[0091] (3) Preparation of one-component epoxy structural adhesive

[0092] Weigh out 43 parts of epoxy resin (NPEL-128), 33 parts of modified dicyandiamide (active hydrogen equivalent 142), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano calcium carbonate (CCS-25i, 70nm) and 13.75 parts of heavy calcium carbonate (1250 mesh), mix them evenly to obtain a one-component epoxy structural adhesive.

[0093] Example 4

[0094] (1) Preparation of modified dicyandiamide

[0095] Weigh 0.8 mol of the epoxy-terminated polyether prepared in Example 2, 0.4 mol of the epoxy-terminated polyether prepared in Example 3, and 2 mol of dicyandiamide, and add them sequentially to a three-necked flask equipped with a condenser, stirrer, and heating mantle. Pour cooling water through the flask, turn on the stirrer and heating mantle, and reflux at 140°C for 4 hours. Then replace the vacuum distillation apparatus, turn on the vacuum pump and heating mantle, and distill at an external temperature of 135°C until no liquid is drawn out. The product obtained is the modified dicyandiamide epoxy curing agent, with an active hydrogen equivalent of 113 and a hydroxyl content of 7.1%.

[0096] (2) Preparation of one-component epoxy structural adhesive

[0097] Weigh out 43 parts of epoxy resin (NPEL-128), 30 parts of modified dicyandiamide (active hydrogen equivalent 113), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano calcium carbonate (CCS-25i, 70nm) and 16.75 parts of heavy calcium carbonate (1250 mesh), mix them evenly to obtain a one-component epoxy structural adhesive.

[0098] Comparative Example 1: Preparation of a one-component epoxy structural adhesive

[0099] Weigh out 43 parts of epoxy resin (NPEL-128), 4.3 parts of dicyandiamide (DYHARD 100S, active hydrogen equivalent 21, particle size 8.1-9.1μm), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano calcium carbonate (CCS-25i, particle size 70nm), and 42.45 parts of heavy calcium carbonate (1250 mesh), mix them evenly, and obtain a one-component epoxy structural adhesive.

[0100] Comparative Example 2: Preparation of One-Component Epoxy Structural Adhesive

[0101] Weigh out 43 parts of epoxy resin (NPEL-128), 19.7 parts of epoxy-terminated polyether (prepared in Example 1), 4.3 parts of dicyandiamide (DYHARD 100S, active hydrogen equivalent 21, particle size 8.1-9.1μm), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano-calcium carbonate (CCS-25i, particle size 70nm), and 22.75 parts of heavy calcium carbonate (1250 mesh), mix them evenly, and obtain a one-component epoxy structural adhesive.

[0102] Preparation of one-component epoxy structural adhesive in Comparative Example 3

[0103] Weigh out 43 parts of epoxy resin (NPEL-128), 19.7 parts of modified nitrile rubber (WD-510), 4.3 parts of dicyandiamide (DYHARD100S, active hydrogen equivalent 21, particle size 8.1-9.1μm), 0.25 parts of organic urea accelerator (DYHARD UR500, particle size 8.5-9.5μm), 10 parts of nano calcium carbonate (CCS-25i, particle size 70nm), and 22.75 parts of heavy calcium carbonate (1250 mesh), mix them evenly, and obtain a one-component epoxy structural adhesive.

[0104] The following performance tests were performed on the one-component epoxy structural adhesives prepared in Examples 1-4 and Comparative Examples 1-3:

[0105] 1. Glass transition temperature: The glass transition temperature shall be determined in accordance with the provisions of GB / T 19466.2-2004 Differential Scanning Calorimetry (DSC) for Plastics - Part 2: Determination of Glass Transition Temperature.

[0106] 2. Tensile shear strength test: The test shall be conducted in accordance with GB / T 7124 (aluminum-aluminum).

[0107] 3. Peel strength: The test shall be conducted in accordance with the requirements of GB / T 2791-1995 Test Method for Peel Strength of Adhesives.

[0108] 4. Tensile modulus of elasticity and elongation at break: determined in accordance with GB / T 1040.2-2006.

[0109] 5. Storage stability test: Place the sample in a constant temperature control chamber at 40±2℃ and maintain for 168 hours. Then, remove the sample and measure its viscosity and tensile shear strength. The viscosity shall be measured according to the provisions of GB / T 2794-2013 Adhesives - Determination of Viscosity - Single Cylindrical Rotation Viscometer Method. The tensile shear strength shall be measured according to GB / T 7124 (aluminum-aluminum).

[0110] Among them, the single-component epoxy structural adhesive test sample prepared in Comparative Example 1 was cured at 170℃ for 20 min, and the single-component epoxy structural adhesive test samples prepared in Examples 1-4 and Comparative Examples 2-3 were cured at 150℃ for 20 min. The samples were tested after returning to room temperature.

[0111] The test results are shown in Table 1:

[0112] Table 1. Performance parameters of the one-component epoxy structural adhesives prepared in Examples 1-4 and Comparative Examples 1-3.

[0113]

[0114] Based on the above results, the single-component epoxy structural adhesives of Examples 1-4 prepared using the modified dicyandiamide synthesized in this invention all have low curing temperatures, high glass transition temperatures, and good tensile shear strength, T-peel strength, tensile modulus of elasticity, and elongation at break. They also have good storage stability and excellent overall performance.

[0115] Compared to Example 1, Comparative Example 1 did not use a modified dicyandiamide curing agent and did not add a toughening agent. The peel strength and elongation at break of the resulting one-component epoxy structural adhesive were significantly lower than those of Example 1. Compared to Example 1, Comparative Example 2 added the epoxy-terminated polyether (a flexible toughening agent) prepared in Example 1. The glass transition temperature of the resulting one-component epoxy structural adhesive decreased significantly, and its peel strength and elongation at break were improved compared to Comparative Example 1, but not as good as Example 1. Comparative Example 3 used modified nitrile rubber as a toughening agent. The glass transition temperature of the resulting one-component epoxy structural adhesive also decreased significantly, while its peel strength and elongation at break were significantly lower than those of Example 1.

[0116] Compared with Example 1, Example 2 uses trifunctional polyether polyol to prepare epoxy-terminated polyether, and dicyandiamide modified with it increases the hydroxyl content. The resulting single-component epoxy structural adhesive has improved tensile shear strength and T-peel strength compared with Example 1. Compared with Example 1, the flexible chain segment is slightly shorter and the elongation at break is decreased.

[0117] Compared with Example 2, Example 3 uses a longer-chain 3-functional polyether polyol to prepare an epoxy-terminated polyether, and uses it to modify dicyandiamide. The hydroxyl content is similar to that of Example 2. The resulting one-component epoxy structural adhesive has similar tensile shear strength and T-peel strength to Example 2, and the elongation at break is improved.

[0118] Example 4 uses a trifunctional polyether polyol with a reasonable combination of long and short chains to prepare an epoxy-terminated polyether. The single-component epoxy structural adhesive prepared by modifying dicyandiamide with this polyether has the best overall performance compared to other examples.

[0119] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0120] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A modified dicyandiamine characterized in that, The modified dicyandiamine is obtained by reacting an epoxy-terminated polyether and dicyandiamine, wherein the epoxy-terminated polyether is obtained by reacting a polyether polyol and epichlorohydrin; The polyether polyol is selected from any one of the polyether polyols of the general formula (I) or (II) or a combination of a plurality of polyether polyols: (I) (II) wherein n=2-25; x+y+z=2-25; The molar ratio of the epoxy-terminated polyether and dicyandiamine is 0.5-0.7:1; The molar ratio of the polyether polyol and epichlorohydrin is 1:1.5-2.

3.

2. The modified dicyandiamide according to claim 1, characterized in that The epoxy group content of the epoxy-terminated polyether is 12-20%.

3. The modified dicyandiamide of claim 1, wherein n is 4, 5, 6, 7 or 8; x+y+z=4, 5, 6, 7 or 8.

4. The modified dicyandiamide according to claim 3, characterized in that, The polyether polyol is one of polyether polyol N204, polyether polyol N303F and polyether polyol N306 or a combination of a plurality of the polyether polyols.

5. The modified dicyandiamide of claim 4, wherein, The polyether polyol is a combination of polyether polyol N303F and polyether polyol N306, and the molar ratio of polyether polyol N303F and polyether polyol N306 is 2-3:

1.

6. The modified dicyandiamide of claim 1, wherein The hydroxyl group content of the modified dicyandiamine is 2-12%.

7. The modified dicyandiamide according to claim 6, characterized in that The hydroxyl group content of the modified dicyandiamine is 5-9%.

8. The modified dicyandiamide of claim 7, wherein, The hydroxyl group content of the modified dicyandiamine is 7-8%.

9. The modified dicyandiamide according to any one of claims 1 to 8, characterized in that, The polyether polyol and epichlorohydrin are reacted in the presence of a catalyst, and the catalyst is boron trifluoride etherate.

10. The modified dicyandiamide of claim 9, wherein, The molar ratio of the polyether polyol and catalyst is 1:0.1-0.

3.

11. A process for the preparation of the modified dicyandiamide according to any one of claims 1 to 10, characterized in that The method comprises the following steps: The polyether polyol and catalyst are stirred uniformly, heated to 30-50°C, and the epichlorohydrin is added dropwise, and the reaction is carried out for 4-6 hours to obtain the epoxy-terminated polyether; The epoxy-terminated polyether and dicyandiamine are refluxed at 130-150°C for 3-5 hours to obtain the modified dicyandiamine.

12. A one-part epoxy structural adhesive, characterized by, The raw materials are mixed to obtain the following components by weight: Epoxy resin 30-60 parts The modified dicyandiamine of any one of claims 1-10 20-40 parts Organic urea 0.1-0.5 parts Nano calcium carbonate 8-15 parts Heavy calcium carbonate 10-45 parts.

13. The one-part epoxy structural adhesive of claim 12, wherein, The raw materials are mixed to obtain the following components by weight: Epoxy resin 40-45 parts The modified dicyandiamine 24-33 parts Organic urea 0.2-0.3 parts Nano calcium carbonate 10-12 parts Heavy calcium carbonate 13-25 parts.

14. The method for preparing the one-component epoxy structural adhesive according to claim 12 or 13, characterized in that, The method comprises the following steps: The epoxy resin, modified dicyandiamine, organic urea, nano calcium carbonate and heavy calcium carbonate are mixed uniformly to obtain the single-component epoxy structural adhesive.

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