Single-component epoxy structural adhesive as well as preparation method and application thereof

Abstract

The invention provides a single-component epoxy structural adhesive as well as a preparation method and application thereof. The single-component epoxy structural adhesive comprises specific parts of epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin and a curing agent, unmodified polyester resin and epoxy grafted polyester resin are introduced for toughening modification, so that the obtained single-component epoxy structural adhesive has excellent impact resistance and low-temperature resistance after being cured and still has good toughness at low temperature, and when the single-component epoxy structural adhesive is used as an automobile body structural adhesive, the impact resistance and the low-temperature resistance of the single-component epoxy structural adhesive are greatly improved. The automobile body material can still keep good bonding strength when being impacted by external force and bent, meanwhile, the automobile body material can be used for a long time at low temperature, and the safety is high.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and specifically relates to a one-component epoxy structural adhesive and a preparation method and application thereof. Background Art

[0002] Currently, automobiles are widely used. Considering the lightweight and safety of automobiles, the use of body structural adhesives is increasing, and the performance requirements are getting higher and higher. Compared with the performance requirements such as low temperature and collision safety, the demand for high impact resistance of structural adhesives is higher, so structural adhesives need to be toughened.

[0003] At present, the toughening of structural adhesives is mostly improved by toughening agents, such as using thermoplastic polyurethane (PPU) or fillers to improve toughness; on the one hand, the traditional dispersion method has certain shortcomings, and on the other hand, the introduction of too much toughening agents such as PPU will reduce the overall modulus, resulting in insufficient final strength of the structural adhesive.

[0004] CN103525352A discloses a room temperature curing epoxy vehicle body structural adhesive, which is mainly toughened by polyurethane. Although the structural adhesive obtained by this invention has good strength, during the baking process of electrophoretic paint, the polyurethane chain segments will crack at high temperatures, resulting in poor low-temperature toughening effect. At the same time, it has poor heat resistance and is not suitable for use in welding workshops.

[0005] CN101307214A discloses a hot melt adhesive and a preparation method thereof, which is mainly prepared by using synthetic thermoplastic styrene-butadiene rubber (SIS) as raw material, compounding with finished SIS on the market, introducing EVA and the like as auxiliary resins, and adding plasticizers as the main means of reducing viscosity. The adhesive system provided by the invention can have a certain high temperature resistance, and the melt viscosity can be reduced by introducing plasticizers. However, the adhesive provided by the invention has great low-temperature brittleness, and there are great problems in high and low temperature cycles in its application in the automotive field.

[0006] CN108753231A discloses a polyamide-modified epoxy resin structural adhesive for a vehicle body, which mainly achieves high-strength bonding through the polyamide-modified epoxy resin structural adhesive. However, its comprehensive modulus is too large, the glue hardness is large, and the toughness is poor. The function of the structural adhesive itself is to increase the toughness of the vehicle body. This type of direction does not meet current requirements.

[0007] CN111592845A discloses an automobile body structural adhesive and a method for making the same, which mainly improves the oxidation resistance of the adhesive, but does not specifically improve the impact resistance.

[0008] Therefore, in response to the above technical problems, it is urgent to develop a one-component epoxy structural adhesive that has high strength, high impact resistance and excellent low temperature resistance. Summary of the invention

[0009] In view of the deficiencies in the prior art, the object of the present invention is to provide a one-component epoxy structural adhesive and a preparation method and application thereof. The one-component epoxy structural adhesive has high strength, high impact resistance and excellent low-temperature properties. As a structural adhesive for automobile bodies, it can be used for a long time in a low temperature (-40°C) environment, and can ensure that the body still maintains good bonding strength when subjected to external force impact, and has higher safety.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a one-component epoxy structural adhesive, wherein the one-component epoxy structural adhesive comprises the following components in parts by weight:

[0012]

[0013] The one-component epoxy structural adhesive provided by the present invention comprises a specific number of epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin and curing agent; on the one hand, by introducing the unmodified polyester resin and utilizing its long chain segment structure and high flexibility, it is ensured that good ductility and flexibility can be maintained in a low temperature environment, so that the obtained epoxy structural adhesive can well eliminate the stress mutation inside the material in a low temperature environment, thereby achieving excellent low temperature properties, and can be used as a vehicle body structural adhesive for a long time in a low temperature environment; on the other hand, by adding epoxy polyester resin, epoxy groups are introduced into the polyester structure, so that the hydroxyl group and the ether bond in the obtained epoxy polyester resin can also participate in the synthesis reaction, and finally the obtained epoxy structural adhesive has excellent toughness, and can be used as a vehicle body structural adhesive, so that the vehicle body material can still maintain good bonding strength when subjected to external force impact and bending, and the effect is better than that of mechanical blending;

[0014] In summary, the one-component epoxy resin structural adhesive provided by the present invention toughens and modifies the epoxy resin by introducing unmodified polyester resin and epoxy grafted polyester resin, so that the obtained epoxy structural adhesive has excellent impact resistance and low temperature resistance after curing, and still has good toughness at low temperatures. When used as a vehicle body structural adhesive, it can ensure that the vehicle body material still maintains good bonding strength when subjected to external force impact and bending, and at the same time can be used for a long time at low temperatures, with high safety.

[0015] Wherein, the content of the epoxy resin A can be 50 parts by weight, 52 parts by weight, 54 parts by weight, 56 parts by weight, 58 parts by weight or 60 parts by weight, etc.

[0016] The content of the unmodified polyester resin may be 10 parts by weight, 12 parts by weight, 14 parts by weight, 16 parts by weight, 18 parts by weight, or 20 parts by weight.

[0017] The content of the epoxy grafted polyester resin can be 20 parts by weight, 22 parts by weight, 24 parts by weight, 26 parts by weight, 28 parts by weight or 30 parts by weight.

[0018] The content of the curing agent can be 20 parts by weight, 22 parts by weight, 24 parts by weight, 26 parts by weight, 28 parts by weight or 30 parts by weight, etc.

[0019] Preferably, the epoxy resin A includes any one of glycidyl ether epoxy resin, glycidyl ester epoxy resin or alicyclic epoxy resin, or a combination of at least two thereof.

[0020] Preferably, the unmodified polyester resin is a saturated unmodified polyester resin.

[0021] Preferably, the glass transition temperature (Tg) of the unmodified polyester resin is 10-25°C, for example, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C or 25°C, etc.; by further limiting the Tg of the unmodified polyester resin to the above-mentioned specific range, it is ensured that it still has good ductility at low temperatures, thereby ensuring that the epoxy structural adhesive still has good toughness at a lower temperature, and is used for bonding automobile bodies, which can ensure the long-term usability of the body structural adhesive in a low temperature environment.

[0022] Preferably, the unmodified polyester resin is obtained by reacting an aliphatic long carbon chain dibasic acid and an aliphatic diol A under the action of a catalyst A.

[0023] Preferably, the carbon chain length of the aliphatic long carbon chain dibasic acid is ≥ 4, such as 4, 5, 6, 7, 8, 9 or 10, etc. By further controlling the carbon chain length of the aliphatic long carbon chain dibasic acid to be ≥ 4, it can be ensured that the obtained unmodified polyester resin has better ductility and flexibility at low temperatures.

[0024] Preferably, the aliphatic long carbon chain dibasic acid includes any one of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid or sebacic acid, or a combination of at least two thereof.

[0025] Preferably, the aliphatic diol A includes any one of neopentyl glycol, hexylene glycol, 1,7-heptanediol or 1,3-propylene glycol, or a combination of at least two thereof.

[0026] Preferably, the catalyst A comprises any one of cobalt acetate, tetrabutyl titanate, antimony trioxide, manganese acetate or germanium trioxide, or a combination of at least two thereof.

[0027] Preferably, the unmodified polyester resin is prepared by the following method, which comprises: subjecting an aliphatic long carbon chain dibasic acid, an aliphatic diol A and a catalyst to an esterification reaction, and then subjecting the reaction to a polycondensation reaction after vacuuming to obtain the unmodified polyester resin.

[0028] Preferably, the temperature of the esterification reaction is 180-200°C, for example, 180°C, 185°C, 190°C, 195°C or 200°C.

[0029] Preferably, the pressure of the esterification reaction is 0.01-0.5 MPa, for example, 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa or 0.5 MPa.

[0030] Preferably, the esterification reaction time is 1.5 to 2.5 h, for example, 1.5 h, 1.7 h, 1.9 h, 2.1 h, 2.3 h or 2.5 h.

[0031] Preferably, the temperature of the polycondensation reaction is 240-260°C, for example, 240°C, 245°C, 250°C, 255°C or 260°C.

[0032] Preferably, the vacuum degree of the polycondensation reaction is less than 50 Pa, for example, 49 Pa, 48 Pa, 46 Pa, 44 Pa, 42 Pa, 40 Pa, 38 Pa, 35 Pa, 30 Pa, 20 Pa, 25 Pa or 10 Pa, etc.

[0033] Preferably, the polycondensation reaction time is 1.5 to 2.5 h, for example, 1.5 h, 1.7 h, 1.9 h, 2.1 h, 2.3 h or 2.5 h.

[0034] Preferably, the epoxy grafted polyester resin is a saturated epoxy grafted polyester resin.

[0035] Preferably, the glass transition temperature (Tg) of the epoxy grafted polyester resin is 60-80°C, for example, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C.

[0036] Preferably, the epoxy grafted polyester resin is obtained by reacting a dibasic acid, an aliphatic diol B and an epoxy resin B under the action of a catalyst B.

[0037] Preferably, the dibasic acid comprises an aromatic dibasic acid.

[0038] Preferably, the dibasic acid further comprises an aliphatic dibasic acid and / or an alicyclic dibasic acid.

[0039] Preferably, the aromatic dibasic acid comprises terephthalic acid.

[0040] Preferably, the aliphatic dibasic acid comprises succinic acid.

[0041] Preferably, the alicyclic dibasic acid comprises 1,4-cyclohexanedicarboxylic acid.

[0042] Preferably, the aliphatic diol B includes any one of neopentyl glycol, hexylene glycol, 1,7-heptanediol or 1,3-propylene glycol, or a combination of at least two thereof.

[0043] Preferably, the epoxy resin B comprises a glycidyl ether type epoxy resin.

[0044] Preferably, the catalyst B comprises any one of cobalt acetate, tetrabutyl titanate, antimony trioxide, manganese acetate or germanium trioxide, or a combination of at least two thereof.

[0045] Preferably, the mass percentage of epoxy resin B in the raw materials for preparing the epoxy grafted polyester resin is 5-25%, for example, 5%, 10%, 15%, 20% or 25%.

[0046] Preferably, the epoxy grafted polyester resin is prepared by the following method, which comprises: subjecting a dibasic acid, an aliphatic diol B, an epoxy resin B and a catalyst B to an esterification reaction, and then subjecting the mixture to a condensation reaction after vacuuming and reducing the pressure to obtain the epoxy grafted polyester resin.

[0047] Preferably, the temperature of the esterification reaction is 200-220°C, for example, 200°C, 205°C, 210°C, 215°C or 220°C.

[0048] Preferably, the esterification reaction time is 1.5 to 2.5 h, for example, 1.5 h, 1.7 h, 1.9 h, 2.1 h, 2.3 h or 2.5 h.

[0049] Preferably, the pressure of the esterification reaction is 0.01-0.5 MPa, for example, 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa or 0.5 MPa.

[0050] Preferably, the temperature of the polycondensation reaction is 240-260°C, for example, 240°C, 245°C, 250°C, 255°C or 260°C.

[0051] Preferably, the vacuum degree of the polycondensation reaction is less than 50 Pa, for example, 49 Pa, 48 Pa, 46 Pa, 44 Pa, 42 Pa, 40 Pa, 38 Pa, 35 Pa, 30 Pa, 20 Pa, 25 Pa or 10 Pa, etc.

[0052] Preferably, the polycondensation reaction time is 2 to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours.

[0053] Preferably, the curing agent comprises dicyandiamide and / or organic hydrazide.

[0054] Preferably, the one-component epoxy structural adhesive also includes fillers.

[0055] Preferably, the content of filler in the one-component epoxy structural adhesive is 20 to 30 parts by weight, for example, 20 parts by weight, 22 parts by weight, 24 parts by weight, 26 parts by weight, 28 parts by weight or 30 parts by weight.

[0056] Preferably, the filler includes any one of calcium carbonate, silica powder or alumina, or a combination of at least two of them.

[0057] Preferably, the one-component epoxy structural adhesive also includes a diluent.

[0058] Preferably, the content of the diluent in the one-component epoxy structural adhesive is 10 to 20 parts by weight, for example, 10 parts by weight, 12 parts by weight, 14 parts by weight, 16 parts by weight, 18 parts by weight or 20 parts by weight.

[0059] Preferably, the diluent comprises a diepoxy reactive diluent.

[0060] Preferably, the one-component epoxy structural adhesive also includes an antioxidant.

[0061] Preferably, the content of the antioxidant in the one-component epoxy structural adhesive is 1 to 2 parts by weight, for example, 1 part by weight, 1.2 parts by weight, 1.4 parts by weight, 1.6 parts by weight, 1.8 parts by weight or 2 parts by weight.

[0062] Preferably, the antioxidant includes antioxidant 1010.

[0063] Preferably, the one-component epoxy structural adhesive also includes carbon black.

[0064] Preferably, the content of carbon black in the one-component epoxy structural adhesive is 0.5 to 1.5 parts by weight, for example, 0.5 parts by weight, 0.7 parts by weight, 0.9 parts by weight, 1.1 parts by weight, 1.3 parts by weight or 1.5 parts by weight.

[0065] In a second aspect, the present invention provides a method for preparing the one-component epoxy structural adhesive as described in the first aspect, the preparation method comprising: mixing epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin, curing agent, optional filler, optional diluent, optional antioxidant and optional carbon black to obtain the one-component epoxy structural adhesive.

[0066] Preferably, the preparation method specifically comprises: mixing epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin, optional filler, optional diluent and optional antioxidant at 60-90°C (for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, etc.) for 60-90min (for example, 60min, 65min, 70min, 75min, 80min, 85min or 90min, etc.), and then adding a curing agent and optional carbon black and mixing for 20-40min (for example, 20min, 22min, 24min, 26min, 28min, 30min, 32min, 34min, 36min, 38min or 40min, etc.) to obtain the one-component epoxy structural adhesive.

[0067] In a third aspect, the present invention provides a use of the one-component epoxy structural adhesive as described in the first aspect in bonding automobile bodies.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] The one-component epoxy structural adhesive provided by the present invention comprises specific portions of epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin and curing agent; by introducing unmodified polyester resin and epoxy grafted polyester resin for toughening modification, the obtained one-component epoxy structural adhesive has excellent impact resistance and low temperature resistance after curing, and still has good toughness at low temperature (-40°C). When used as a vehicle body structural adhesive, it can ensure that the vehicle body material still maintains good bonding strength when subjected to external force impact and bending, and can be used for a long time at low temperature, with high safety. DETAILED DESCRIPTION

[0070] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0071] Unless otherwise specified, the raw materials involved in the following specific embodiments are all conventional materials in the art and can be purchased from commercial products; in particular, the information of some raw materials involved is as follows:

[0072] (1) Glycidyl ether epoxy resin: Phoenix brand epoxy resin, brand number E51;

[0073] (2) Diluent: Bis-epoxy reactive diluent, brand LS-622;

[0074] (3) Antioxidant: purchased from BYK, brand 1010;

[0075] (4) Carbon black: specifically Cabot carbon black, brand BLACK PEARLS 4350;

[0076] (5) PPU resin: purchased from Covestro, brand number 3378A.

[0077] Preparation Examples 1-1 to 1-6

[0078] Preparation Examples 1-1 to 1-6 respectively provide an unmodified polyester resin, whose number average molecular weight, glass transition temperature and the amount of each component in the preparation raw material are shown in Table 1:

[0079] Table 1

[0080]

[0081]

[0082] The preparation method of the unmodified polyester resin provided in Preparation Examples 1-1 to 1-6 includes: heating aliphatic long-chain dibasic acid, aliphatic diol and a catalyst to 190°C after mixing, and conducting an esterification reaction for 2 hours under nitrogen protection, the pressure of the esterification reaction is 0.1MPa, the rotation speed is 50rpm, and after the esterification reaction is completed, the temperature is continued to be raised to 250°C, and the pressure is reduced by vacuum to conduct co-condensation, the vacuum degree during the condensation reaction is controlled to be less than 50Pa, and the condensation time is 2h to obtain the unmodified polyester resin.

[0083] Preparation Examples 2-1 to 2-7

[0084] Preparation Examples 2-1 to 2-7 respectively provide an epoxy grafted polyester resin, whose number average molecular weight, glass transition temperature and the amount of each component in the preparation raw material are shown in Table 2:

[0085] Table 2

[0086]

[0087]

[0088] The preparation method of the epoxy grafted polyester resin provided in Preparation Examples 2-1 to 2-7 includes: heating the dibasic acid, diol, epoxy resin and catalyst to 210°C in the system for esterification reaction for 2 hours, the pressure of the esterification reaction is 0.1MPa, and after the esterification reaction is completed, the temperature is continued to rise to 250°C, and the pressure is reduced by vacuum to carry out co-condensation, the vacuum degree during the condensation reaction is controlled to be less than 50Pa, and the condensation time is 3 hours to obtain the epoxy grafted polyester resin.

[0089] Examples 1 to 12 and Comparative Examples 1 to 6

[0090] Examples 1 to 12 and Comparative Examples 1 to 6 respectively provide a one-component epoxy structural adhesive, the components and amounts thereof are shown in Table 3 and Table 4;

[0091] In Tables 3 and 4, the dosage units of each component are all "parts by weight";

[0092] Table 3

[0093]

[0094] Table 4

[0095]

[0096] The preparation method of the one-component epoxy structural adhesive provided in Examples 1 to 12 and Comparative Examples 1 to 6 includes: adding epoxy resin, unmodified polyester resin, epoxy grafted polyester resin (or PPU resin), diluent, calcium carbonate, silicon powder and antioxidant to a double planetary power mixer, stirring and dispersing at 80° C. for 90 minutes to uniformly disperse the components, subsequently adding a curing agent and carbon black, stirring for 30 minutes to form a uniform mixture, and obtaining the one-component epoxy structural adhesive.

[0097] Performance Testing:

[0098] The obtained one-component epoxy structural adhesive was cured at 180°C for 20 min and then subjected to the following tests;

[0099] (1) Shear strength: The shear strength was measured at a tensile rate of 10 mm / min in accordance with the provisions of GB / T 7124-2008.

[0100] (2) Tensile strength / elongation at break: The tensile strength and elongation at break were measured at a speed of 10 mm / min in a standard test environment in accordance with the provisions of GB / T 1040-2006.

[0101] (3) Impact strength (23℃ / -40℃): The specimen is placed in a standard test environment for 24 hours and the impact peel strength is tested at a rate of 2m / s under standard test environment. The test process is required to comply with ISO 11343-2005.

[0102] The one-component epoxy structural adhesives provided in Examples 1 to 12 and Comparative Examples 1 to 6 were tested according to the above test method, and the test results are shown in Table 5;

[0103] Table 5

[0104]

[0105] According to the data in Table 5, we can see that:

[0106] (1) The one-component epoxy structural adhesive provided in Examples 1 to 5 and Example 9 has a shear strength of up to 30 to 33 MPa, a tensile strength of up to 30 to 33 MPa, an elongation at break of 10 to 12%, an impact peel strength of 39 to 45 N / mm at 23°C, and an impact peel strength of 31 to 35 N / mm at -40°C, and has high strength, high toughness and excellent low temperature resistance;

[0107] (2) Comparison of the data of Example 1 and Comparative Examples 1 to 6 shows that:

[0108] ① Compared with Comparative Example 1, it can be seen that compared with the traditional PPU resin, the epoxy grafted polyester resin has a better toughening effect and better low temperature resistance;

[0109] ② Compared with Comparative Example 2, it can be seen that without adding unmodified polyester resin, the low-temperature impact resistance and impact peel strength of the structural adhesive will decrease.

[0110] ③ Compared with Comparative Example 3, it can be seen that without adding epoxy grafted polyester resin, the structural adhesive will have stronger rigidity and poorer toughness, and the performance in terms of impact resistance will be obviously insufficient;

[0111] ④ Compared with Comparative Example 4, it can be seen that the structural adhesive obtained by using only epoxy resin without adding unmodified polyester resin and epoxy grafted polyester resin will also be brittle, strong in rigidity, poor in toughness and no impact resistance;

[0112] ⑤ Compared with Comparative Example 5, the addition amount of the unmodified polyester resin is too high, while the addition amount of the epoxy grafted polyester resin is insufficient, resulting in a softer structure of the obtained structural adhesive, a significant reduction in toughness, and reduced tensile properties and impact resistance;

[0113] ⑥ Compared with Comparative Example 6, the addition amount of epoxy grafted polyester resin is too high, and the addition amount of unmodified polyester resin is insufficient, resulting in the obtained structural adhesive having strong rigidity. Although it can ensure high strength, it has poor toughness and increases the brittleness of the structure, resulting in poor impact resistance.

[0114] (3) Comparing the data of Example 1 and Examples 6 to 12, it can be seen that:

[0115] ① If the unmodified polyester resin has a low Tg (Preparation Example 1-4), the entire structural adhesive will be too soft, which can improve the elongation at break to a certain extent and have excellent impact resistance. However, the rigidity of the entire structure is insufficient, which will lead to a decrease in shear strength and tensile strength;

[0116] ② If the unmodified polyester resin has a higher Tg (Preparation Example 1-5), although the overall strength of the structural adhesive can be improved to a certain extent, the flexibility of the entire structural adhesive will be deteriorated and the impact resistance will be reduced;

[0117] ③ If the chain length of the unmodified polyester resin used is too short (Preparation Example 1-6), the Tg of the unmodified polyester resin obtained will be too high, which will also reduce the flexibility of the structural adhesive and reduce the impact resistance.

[0118] ④ If the Tg of the epoxy grafted polyester resin used is low (Preparation Examples 2-5 and 2-6), the entire structural adhesive will have better flexibility and impact resistance, but will lead to insufficient rigidity, reduced strength, and reduced shear strength and tensile strength;

[0119] ⑤ If the Tg of the epoxy grafted polyester resin used is too high (Preparation Example 2-7), the entire structural adhesive will have greater rigidity, reduced flexibility, easy brittleness, and significantly reduced impact resistance.

[0120] The applicant declares that the present invention illustrates a one-component epoxy structural adhesive and its preparation method and application through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A one-component epoxy structural adhesive, characterized in that: The one-component epoxy structural adhesive comprises the following components in parts by weight:

2. The one-component epoxy structural adhesive according to claim 1, characterized in that: The epoxy resin A includes any one of glycidyl ether epoxy resin, glycidyl ester epoxy resin or alicyclic epoxy resin, or a combination of at least two of them.

3. The one-component epoxy structural adhesive according to claim 1 or 2, characterized in that: The unmodified polyester resin is a saturated unmodified polyester resin; Preferably, the glass transition temperature of the unmodified polyester resin is 10 to 25°C; Preferably, the unmodified polyester resin is obtained by reacting an aliphatic long carbon chain dibasic acid and an aliphatic diol A under the action of a catalyst A; Preferably, the carbon chain length of the aliphatic long carbon chain dibasic acid is ≥ 4; Preferably, the aliphatic long carbon chain dibasic acid includes any one of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid or sebacic acid, or a combination of at least two thereof; Preferably, the aliphatic diol A comprises any one or a combination of at least two of neopentyl glycol, hexylene glycol, 1,7-heptanediol or 1,3-propylene glycol; Preferably, the catalyst A comprises any one of cobalt acetate, tetrabutyl titanate, antimony trioxide, manganese acetate or germanium trioxide, or a combination of at least two thereof.

4. The one-component epoxy structural adhesive according to any one of claims 1 to 3, characterized in that: The epoxy grafted polyester resin is a saturated epoxy grafted polyester resin; Preferably, the glass transition temperature of the epoxy grafted polyester resin is 60 to 80°C; Preferably, the epoxy grafted polyester resin is obtained by reacting a dibasic acid, an aliphatic diol B and an epoxy resin B under the action of a catalyst B; Preferably, the dibasic acid comprises an aromatic dibasic acid; Preferably, the dibasic acid further comprises an aliphatic dibasic acid and / or an alicyclic dibasic acid; Preferably, the aromatic dibasic acid comprises terephthalic acid; Preferably, the aliphatic dibasic acid comprises succinic acid; Preferably, the alicyclic dibasic acid comprises 1,4-cyclohexanedicarboxylic acid; Preferably, the aliphatic diol B includes any one or a combination of at least two of neopentyl glycol, hexylene glycol, 1,7-heptanediol or 1,3-propylene glycol; Preferably, the epoxy resin B comprises a glycidyl ether type epoxy resin; Preferably, the catalyst B comprises any one or a combination of at least two of cobalt acetate, tetrabutyl titanate, antimony trioxide, manganese acetate or germanium trioxide; Preferably, the mass percentage of epoxy resin B in the raw materials for preparing the epoxy grafted polyester resin is 5-25%.

5. The one-component epoxy structural adhesive according to any one of claims 1 to 4, characterized in that: The curing agent includes dicyandiamide and / or organic hydrazide.

6. The one-component epoxy structural adhesive according to any one of claims 1 to 5, characterized in that: The one-component epoxy structural adhesive also includes fillers; Preferably, the content of filler in the one-component epoxy structural adhesive is 20 to 30 parts by weight; Preferably, the filler comprises any one of calcium carbonate, silica powder or alumina, or a combination of at least two thereof; Preferably, the one-component epoxy structural adhesive further includes a diluent; Preferably, the content of the diluent in the one-component epoxy structural adhesive is 10 to 20 parts by weight; Preferably, the diluent comprises a diepoxy reactive diluent.

7. The one-component epoxy structural adhesive according to any one of claims 1 to 6, characterized in that: The one-component epoxy structural adhesive also includes an antioxidant; Preferably, the content of the antioxidant in the one-component epoxy structural adhesive is 1 to 2 parts by weight; Preferably, the antioxidant comprises antioxidant 1010; Preferably, the one-component epoxy structural adhesive further comprises carbon black; Preferably, the content of carbon black in the one-component epoxy structural adhesive is 0.5 to 1.5 parts by weight.

8. A method for preparing the one-component epoxy structural adhesive according to any one of claims 1 to 7, characterized in that: The preparation method comprises: mixing epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin, curing agent, optional filler, optional diluent, optional antioxidant and optional carbon black to obtain the one-component epoxy structural adhesive.

9. The preparation method according to claim 8, characterized in that: The preparation method specifically comprises: mixing epoxy resin A, unmodified polyester resin, epoxy grafted polyester resin, optional filler, optional diluent and optional antioxidant at 60-90° C. for 60-90 minutes, then adding curing agent and optional carbon black and mixing for 20-40 minutes to obtain the one-component epoxy structural adhesive.

10. Use of the one-component epoxy structural adhesive as claimed in any one of claims 1 to 7 in bonding automobile bodies.

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