Preparation method and application of a yellowing-resistant modified amine epoxy curing agent

Abstract

This invention discloses a method for preparing a yellowing-resistant modified amine epoxy curing agent and its application, belonging to the technical field of epoxy curing agents. The yellowing-resistant modified amine epoxy curing agent, by weight, comprises the following components: 70-100 parts of an aminosiloxane-terminated diimine pyrrolidone compound and 5-10 parts of fumed silica; the aminosiloxane-terminated diimine pyrrolidone compound is formed by bonding an aldehyde pyrrolidone compound and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. This invention integrates the amino group (serving as the curing active center), the siloxane group (serving as a flexible regulating segment and weather-resistant barrier), the cyclic amide group (serving as a rigid reinforcing unit), and the imine bond into a single molecule through chemical bonds, avoiding compatibility problems that may arise from physical blending, and providing an epoxy resin curing agent with good yellowing resistance, good mechanical properties, and high curing efficiency.

Description

Technical Field

[0001] This invention belongs to the field of epoxy curing agent technology, specifically relating to a method for preparing a yellowing-resistant modified amine epoxy curing agent and its application. Background Technology

[0002] Epoxy resin itself is a linear thermoplastic polymer. Uncured epoxy resin completely lacks good mechanical properties, chemical resistance, and heat resistance. Linear epoxy resin needs to react with a suitable curing agent to form a three-dimensional cross-linked thermosetting network. This curing process is crucial for epoxy resin to obtain good mechanical properties, chemical resistance, and heat resistance. Therefore, the curing agent is the core component that enables epoxy resin to generate practical application value. Aging and yellowing of epoxy resin systems is a major obstacle to their application in high-value-added fields, such as high-end LED packaging, optical lenses, light-colored flooring, and outdoor weather-resistant coatings. The root cause of yellowing lies in the oxidation of the amine groups and adjacent hydrocarbon structures in the curing agent molecule under the action of ultraviolet light and oxygen, generating chromophores.

[0003] While traditional modified amine strategies have made some progress, they still face the following challenges: Although traditional aliphatic or cycloaliphatic amine curing agents improve initial color by avoiding benzene ring structures, the CN and CH bonds in their molecular skeletons are still targets of ultraviolet radiation, resulting in limited improvement in yellowing resistance; a single molecular structure cannot simultaneously achieve multiple properties; using ketoimine-terminated primary amine groups can greatly improve yellowing resistance during storage, but such latent curing agents are heavily dependent on environmental humidity for hydrolysis during application, with harsh curing conditions and the risk of incomplete hydrolysis, affecting the final performance. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention designs and synthesizes a novel aminosiloxane-terminated diimine pyrrolidone compound, and provides a method for preparing a yellowing-resistant modified amine epoxy curing agent and its application. The technical solution to achieve the purpose of this invention is as follows:

[0005] A yellowing-resistant modified amine epoxy curing agent, comprising the following components by weight: 70-100 parts of an aminosiloxane-terminated diimine pyrrolidone compound and 5-10 parts of fumed silica.

[0006] A method for preparing a yellowing-resistant modified amine epoxy curing agent includes the following steps:

[0007] S1. Synthesis of dialdehyde pyrrolidone compounds: 12.5 mmol of aliphatic diamine and 25.0 mmol of dimethyl itaconic acid in a molar ratio of 1:(2~2.1) were mixed with 1~2 mL of methanol and stirred at 300~400 rpm and heated to 85~90℃ for 15~20 h. The reaction endpoint was monitored by thin-layer chromatography. The reaction mixture was collected directly, and excess methanol was removed under reduced pressure. The residual solvent was further removed by passing the mixture through a high-vacuum device connected to a vacuum pump and a cold trap at a pressure of 2~4 mbar. Then, 1 eq of the obtained compound was dissolved in anhydrous tetrahydrofuran, dehydrated and deoxygenated, and the reactants were cooled to -78℃. Diisobutylaluminum hydride solution was slowly added dropwise through a dropping funnel while stirring in a glove box. The dropping rate was controlled to maintain the temperature below -70℃ and the addition was completed within 1 h. After the addition was completed, stirring was continued at -78℃ for 2~3 hours. h; After the reaction was completed, in a fume hood, 8-12 mL of saturated sodium potassium tartrate aqueous solution was slowly added to the reaction mixture at -78℃, and stirred until no bubbles were generated; then the temperature was naturally raised to 0℃, and 8-10 mL of 1 mol / L cold hydrochloric acid solution was slowly added, and the mixture was stirred for 20-30 min and gradually raised to room temperature. Ethyl acetate and deionized water were added for extraction and the mixture was separated. The organic phase was washed with saturated sodium bicarbonate solution and saturated brine, and then dried with anhydrous sodium sulfate. The dialdehyde pyrrolidone compound was purified by silica gel column chromatography, and its structure is shown in the following formula:

[0008] ;

[0009] S2. Synthesis of aminosiloxane-terminated diimine pyrrolidone: 1 eq of dialdehyde pyrrolidone was dissolved in anhydrous toluene, and water was removed by adding a molecular sieve. The mixture was stirred for 20–30 min under nitrogen protection. Then, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added in 2–2.1 times the molar amount of the dialdehyde pyrrolidone. A water separator was installed, and the mixture was stirred and heated to 100–110 °C until no more water was separated from the separator, corresponding to a reaction time of 5–8 h. After the reaction, the mixture was cooled to room temperature, and the molecular sieve was removed by filtration. The filter residue was thoroughly washed with a small amount of anhydrous toluene. The filtrate and washings were combined, and the solvent was removed under reduced pressure using a rotary evaporator to obtain the aminosiloxane-terminated diimine pyrrolidone compound, with the structure shown below.

[0010] ;

[0011] S3. Dry the fumed silica in an oven at 100~110℃ for 1~2 h, and immediately transfer it to a drying oven for later use after cooling; put the aminosiloxane-terminated diimine pyrrolidone compound into a planetary high-speed disperser, keep the temperature at 25~35℃, add 5~10 parts of fumed silica in two batches, with an interval of 10~15 min between each batch, and simultaneously shear at high speed of 2000~3000 rpm for 30~40 min, then switch to vacuum degassing mode, degas at 45~55℃ and 2~4 mbar pressure for 40~60 min to remove the bubbles introduced by stirring, cool to room temperature, and fill into dry and sealed containers to obtain the yellowing-resistant modified amine epoxy curing agent.

[0012] The amine hydrogen equivalent of the yellowing-resistant modified amine epoxy curing agent is 185~213 g / mol.

[0013] The dialdehyde pyrrolidone compound needs to be stored in a nitrogen atmosphere at -20 °C, protected from light, and the feeding should be completed within 24 hours.

[0014] The aliphatic diamine is selected from one or more of 1,4-butanediamine, 1,8-octanediamine, and 1,12-dodecanediamine.

[0015] The amount of diisobutylaluminum hydride solution added is 2 to 2.5 times the molar amount of dimethyl itaconic acid ester.

[0016] Another object of the present invention is to provide the application of the yellowing-resistant modified amine epoxy curing agent prepared by the above-mentioned method for preparing the yellowing-resistant modified amine epoxy curing agent in epoxy curing agents.

[0017] A dry-hanging adhesive includes component A and component B; by weight, component A includes: 100 parts epoxy resin, 5-15 parts epoxy diluent, and 100-150 parts silica powder; component B includes: 87-100 parts yellowing-resistant modified amine epoxy curing agent and 100-150 parts silica powder.

[0018] The epoxy resin is selected from one or two of bisphenol A type epoxy resin and bisphenol F type epoxy resin, and the epoxy equivalent is 180~190 g / mol.

[0019] The epoxy diluent is a C12-14 alkyl glycidyl ether.

[0020] Another object of the present invention is to provide a method for preparing the dry-hanging adhesive as described above, comprising the following steps:

[0021] S1: Preparation of Component A: Add 100 parts epoxy resin and 5-15 parts epoxy diluent to a high-speed disperser and stir at 500-2000 rpm for 3-5 minutes until homogeneous; add 100-150 parts silica powder pre-dried at 100-110℃ in two batches, stirring at 500-2000 rpm for 5-8 minutes after each addition until the mixture is homogeneous, thus obtaining Component A;

[0022] S2: Preparation of Component B: Add 87-100 parts of yellowing-resistant modified amine epoxy curing agent to a high-speed disperser and stir at 500-2000 rpm for 3-5 minutes until uniformly mixed; add 100-150 parts of silica powder pre-dried at 100-110℃ in two batches, stirring at 500-2000 rpm for 5-8 minutes after each addition until the mixture is uniform, and then discharge to obtain Component B;

[0023] S3: Mix the above components A and B in a weight ratio of 1:(0.91~0.94) until uniform, stir at 500~800 rpm for 2~5 minutes until the color is uniform, and the dry-hanging adhesive is obtained. The obtained dry-hanging adhesive should be used up within 60~90 minutes at 25℃.

[0024] Beneficial effects

[0025] This invention designs and synthesizes an aminosiloxane-terminated diimine pyrrolidone compound, and provides a method for preparing a yellowing-resistant modified amine epoxy curing agent and its application, which includes the following beneficial effects:

[0026] 1. Synergistic effect of yellowing resistance and weather resistance: The silicon-oxygen bond introduced into the molecule constitutes the core weather resistance barrier. This bond has extremely high energy and stable chemical properties, and its resistance to ultraviolet light is much higher than that of traditional CC and CN bonds, eliminating the hidden danger of photodegradation at the molecular backbone level. The methyl group of the methyl silicon bond effectively blocks the contact between oxygen and ultraviolet light and the active site through steric hindrance around the amino group, thus delaying the process of oxidative yellowing. The imine bond stabilizes free radicals through conjugation effect, which helps to improve the molecule's resistance to yellowing. The rigid skeleton formed by the amide bond and the five-membered ring amide bond further enhances the overall stability of the molecule, making it difficult for the chain to break or rearrange due to light energy.

[0027] 2. A molecular chain design that combines rigidity and flexibility: The five-membered ring amide bond and imine bond provide the molecule with rigidity, thermal stability and creep resistance, ensuring good hardness and dimensional stability of the cured product; the siloxane segment gives the molecule flexibility and mobility, which can effectively absorb and disperse stress, thereby giving the cured product good toughness, impact resistance and adhesion to a variety of substrates, solving the inherent brittleness problem of epoxy materials.

[0028] 3. High-efficiency curing: The primary amines at the molecular ends ensure the activity of curing reaction with epoxy resin.

[0029] In summary, this invention integrates the amino group (serving as the curing active center), the siloxane (serving as the flexible regulating chain segment and weather-resistant barrier), the cyclic amide (serving as the rigid reinforcing unit), and the imine bond into a single molecule through chemical bonds, avoiding compatibility issues that may arise from physical blending. This provides an epoxy resin curing agent with good yellowing resistance, excellent mechanical properties, and high curing efficiency. Attached Figure Description

[0030] Figure 1 Synthetic routes for aminosiloxane-terminated diimine pyrrolidone compounds.

[0031] Figure 2 The 1H NMR spectrum of dialdehyde pyrrolidone compound 1.

[0032] Figure 3 The infrared spectrum of aminosiloxane-terminated diimine pyrrolidone compound 1. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0035] Dialdehyde pyrrolidone compound 1: prepared in-house, as follows:

[0036] 12.5 mmol of 1,8-octanediamine and 25.0 mmol of dimethyl itaconic acid were mixed with 2 mL of methanol in a molar ratio of 1:2. The mixture was stirred at 350 rpm and heated to 85 °C for 18 h. The reaction endpoint was monitored by thin-layer chromatography. The reaction mixture was collected directly, and excess methanol was removed under reduced pressure. The residual solvent was further removed by passing the mixture through a high-vacuum apparatus equipped with a vacuum pump and a cold trap at 3 mbar. Then, 1 eq of the obtained compound was dissolved in anhydrous tetrahydrofuran, dehydrated and deoxygenated, and the reactants were cooled to -78 °C. Diisobutylaluminum hydride solution was slowly added dropwise through a dropping funnel while stirring in a glove box, controlling the dropping rate to maintain the temperature below -70 °C and completing the addition within 1 h. After the addition was complete, stirring was continued at -78 °C for 2.5 h. After the reaction was complete, 10 mL of saturated sodium potassium tartrate aqueous solution was slowly added to the reaction mixture at -78 °C in a fume hood, stirring until no bubbles were generated. The mixture was then allowed to warm naturally to 0 °C, and 10 mL of 1... The mixture was stirred in a cold hydrochloric acid solution at mol / L for 25 min, then gradually brought to room temperature. Ethyl acetate and deionized water were added for extraction, and the mixture was separated. The organic phase was washed with saturated sodium bicarbonate solution and saturated brine, then dried over anhydrous sodium sulfate. The resulting product was purified by silica gel column chromatography to obtain a dialdehyde pyrrolidone compound in 78% yield. The 1H NMR spectrum is attached. Figure 2 As shown, the structure is as follows:

[0037] ;

[0038] Dialdehyde pyrrolidone compound 2: prepared in-house, the preparation method is the same as that of dialdehyde pyrrolidone compound 1, except that 1,8-octanediamine is replaced with 1,4-butanediamine, while other conditions remain unchanged, to obtain dialdehyde pyrrolidone compound 2 with a yield of 80%, the structure of which is shown below:

[0039] ;

[0040] Dialdehyde pyrrolidone compound 3: prepared in-house, the preparation method is the same as that of dialdehyde pyrrolidone compound 1, except that 1,8-octanediamine is replaced with 1,12-dodecanediamine, while other conditions remain unchanged, to obtain dialdehyde pyrrolidone compound 3 with a yield of 77%, the structure of which is shown below:

[0041] ;

[0042] Epoxy resin: Bisphenol A type epoxy resin, model YD-127, purchased from Shanghai Gongcheng Chemical Co., Ltd.

[0043] Epoxy diluent: C12-14-alkyl glycidyl ether, product number D838088, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0044] Silica powder: particle size 0.5~20 μm, purchased from Jiangsu Jingshengyuan New Material Technology Co., Ltd.;

[0045] Fumed silica: Product number S104600, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0046] 1,5-Diaminopentane: Product No. B010145, purchased from Anhui Zesheng Technology Co., Ltd.;

[0047] Dimethyl itaconic acid: Product No. 1069406, purchased from Shanghai Haohong Biomedical Technology Co., Ltd.;

[0048] Diisobutylaluminum hydride: a 1 mol / L diisobutylaluminum hydride hexane solution, product number D807153, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0049] 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane: Product No. 1228769, purchased from Shanghai Haohong Biomedical Technology Co., Ltd.;

[0050] Preparation Example

[0051] Preparation Example 1

[0052] Aminosiloxane-terminated bisimine pyrrolidone compound 1: prepared in-house, the preparation method is as follows:

[0053] The newly prepared 1 eq dialdehyde pyrrolidone compound 1 was dissolved in anhydrous toluene, and water was removed by adding a molecular sieve. The mixture was stirred for 25 min under nitrogen protection. 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added in a molar amount equal to that of dialdehyde pyrrolidone compound 1, and a water separator was installed. The mixture was stirred and heated to 110 °C until no more water was separated from the water separator. After the reaction was completed, the mixture was cooled to room temperature, the molecular sieve was removed by filtration, and the filter residue was thoroughly washed with a small amount of anhydrous toluene. The filtrate and washing liquid were combined, and the solvent was removed by rotary evaporator under reduced pressure to obtain aminosiloxane-terminated diimine pyrrolidone compound 1.

[0054] Preparation Example 2

[0055] Aminosiloxane-terminated diimine pyrrolidone compound 2: prepared in-house. The preparation method is the same as that of aminosiloxane-terminated diimine pyrrolidone compound 1, except that dialdehyde pyrrolidone compound 1 is replaced with aldehyde pyrrolidone compound 2, while other conditions remain unchanged, to obtain aminosiloxane-terminated diimine pyrrolidone compound 2.

[0056] Preparation Example 3

[0057] Aminosiloxane-terminated diimine pyrrolidone compound 3: prepared in-house. The preparation method is the same as that of aminosiloxane-terminated diimine pyrrolidone compound 1, except that dialdehyde pyrrolidone compound 1 is replaced with aldehyde pyrrolidone compound 3, while other conditions remain unchanged, to obtain aminosiloxane-terminated diimine pyrrolidone compound 3.

[0058] Preparation Example 4

[0059] Amino-terminated diimine pyrrolidone compound 4: prepared in-house. The preparation method is the same as that of aminosiloxane-terminated diimine pyrrolidone compound 1, except that 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is replaced with 1,5-diaminopentane, while other conditions remain unchanged, to obtain amino-terminated diimine pyrrolidone compound 4.

[0060] The raw materials and equipment used in the embodiments and comparative examples are described below:

[0061] Example

[0062] Example 1

[0063] Yellowing-resistant modified amine epoxy curing agent 1: Self-made, preparation method as follows:

[0064] Fumed silica was dried in an oven at 105°C for 2 hours and immediately transferred to a drying oven after cooling. 85 parts of aminosiloxane-terminated diimine pyrrolidone compound 1 were fed into a planetary high-speed disperser and the temperature was maintained at 30°C. A total of 7.5 parts of fumed silica were added in two batches, with an interval of 13 minutes between each batch. At the same time, the mixture was sheared at 2500 rpm for 30 minutes. Then, the mixture was switched to vacuum degassing mode and degassed at 50°C and 3 mbar for 50 minutes to remove the bubbles introduced by stirring. The mixture was cooled to room temperature and filled into a dry and sealed container to obtain yellowing-resistant modified amine epoxy curing agent 1.

[0065] Example 2

[0066] Yellowing-resistant modified amine epoxy curing agent 2: self-made. The preparation method is the same as that of yellowing-resistant modified amine epoxy curing agent 1, except that the total amount of fumed silica is replaced with 5 parts, and the amount of aminosiloxane-terminated diimine pyrrolidone compound 1 is replaced with 70 parts. All other conditions remain unchanged to obtain yellowing-resistant modified amine epoxy curing agent 2.

[0067] Example 3

[0068] Yellowing-resistant modified amine epoxy curing agent 3: self-made. The preparation method is the same as that of yellowing-resistant modified amine epoxy curing agent 1, except that the total amount of fumed silica is replaced with 10 parts, and the amount of aminosiloxane-terminated diimine pyrrolidone compound 1 is replaced with 100 parts. All other conditions remain unchanged to obtain yellowing-resistant modified amine epoxy curing agent 3.

[0069] Example 4

[0070] Yellowing-resistant modified amine epoxy curing agent 4: self-made. The preparation method is the same as that of yellowing-resistant modified amine epoxy curing agent 1, except that aminosiloxane-terminated diimine pyrrolidone compound 1 is replaced with aminosiloxane-terminated diimine pyrrolidone compound 2, while other conditions remain unchanged, to obtain yellowing-resistant modified amine epoxy curing agent 4.

[0071] Example 5

[0072] Yellowing-resistant modified amine epoxy curing agent 5: self-made. The preparation method is the same as that of yellowing-resistant modified amine epoxy curing agent 1, except that aminosiloxane-terminated diimine pyrrolidone compound 1 is replaced with aminosiloxane-terminated diimine pyrrolidone compound 3, while other conditions remain unchanged, to obtain yellowing-resistant modified amine epoxy curing agent 5.

[0073] Comparative Example 1

[0074] Yellowing-resistant modified amine epoxy curing agent 6: self-made. The preparation method is the same as that of yellowing-resistant modified amine epoxy curing agent 1, except that aminosiloxane-terminated diimine pyrrolidone compound 1 is replaced with amino-terminated diimine pyrrolidone compound 4, while other conditions remain unchanged, to obtain yellowing-resistant modified amine epoxy curing agent 6.

[0075] Comparative Example 2

[0076] Commercially available epoxy curing agent: Select diamine, with an effective ingredient content of 99%, purchased from Hunan Qilu New Material Technology Co., Ltd.

[0077] Application examples

[0078] Application Examples 1-7 and Comparative Application Examples 1-2

[0079] Dry-hanging adhesive 1-9 is prepared from the following raw materials in parts by weight:

[0080] S1: Preparation of Component A: Add 100 parts of epoxy resin and 5-15 parts of epoxy diluent to a high-speed disperser and stir at 1000-2000 rpm for 3-5 minutes until homogeneous; add 100-150 parts of silica powder pre-dried at 100-110℃ in two batches, stirring at 1800-2000 rpm for 5-8 minutes after each addition until the mixture is homogeneous to obtain Component A;

[0081] S2: Preparation of component B: Add 87-100 parts of yellowing-resistant modified amine epoxy curing agent to a high-speed disperser and stir at 1500 rpm for 5 min until the mixture is uniform; add 100-150 parts of silica powder pre-dried at 105℃ in two batches, stirring at 1500 rpm for 6 min after each addition until the mixture is uniform, and then discharge to obtain component B.

[0082] S3: Mix the above components A and B in a weight ratio of 1:(0.91~0.94) until uniform, stir at 650 rpm for 5 min until the color is uniform, and the dry-hanging adhesive is obtained. The obtained dry-hanging adhesive should be used within 25℃ and 90 min.

[0083] Table 1. Formulations of Application Examples 1-7 and Comparative Application Examples 1-2 (by weight)

[0084]

[0085] The above-mentioned dry-hanging adhesives 1 to 9 need to be applied within 60 to 90 minutes. After application, they should be cured at 25°C and 50% relative humidity for 24 hours. Performance testing should be conducted after they are fully dry.

[0086] The following are the test methods for performance parameters involved in this invention:

[0087] 1. Proton NMR spectroscopy: Compound 1, a dialdehyde pyrrolidone, was characterized using a Bruker AM-600, Advance 600 NMR spectrometer. The results are shown in the attached figure. Figure 2 As shown: proton hydrogens of the aldehyde matrix are visible at 9.4 ppm, corresponding to number 1; proton hydrogens of the alkyl chain are visible at 1.1~1.6 ppm, corresponding to numbers 6~8; proton hydrogens of the five-membered ring are visible at 2.6~3.6 ppm, some of which overlap with the proton hydrogen signals of the alkyl chain, corresponding to numbers 2~5. The above proves the successful synthesis of dialdehyde pyrrolidone compound 1.

[0088] 2. Fourier Transform Infrared Spectroscopy (FT-IR): FT-IR analysis of aminosiloxane-terminated diimine pyrrolidone compound 1 was performed using a Thermo Nicolet IS10 Fourier Transform Infrared Spectrometer. The results are shown in the attached figure. Figure 3 As shown: in the range of 3250~3300 cm -1 The strong double peak of the primary amine is visible at 1650 cm⁻¹. -1 The C=O bond of the visible amide is 1620 cm⁻¹. -1 The characteristic peak of imine appears at 1100 cm⁻¹. -1 The characteristic Si-O-Si peak appears at 1260 cm⁻¹. -1 The presence of Si-C characteristic peaks confirms the successful synthesis of aminosiloxane-terminated bisimine pyrrolidone compound 1.

[0089] 3. Impact strength test: Refer to GB / T 2571-1995.

[0090] 4. Anti-yellowing test method: Refer to HG / T 3862-2006.

[0091] 5. Storage stability test method: Prepare 10 kg of sample according to the sample preparation plan, let it stand naturally for six months, and then weigh the exudate.

[0092] Table 2 Performance test results of dry-hanging adhesives 1-9

[0093]

[0094] As shown in Table 2, the impact strength of dry-hanging adhesives 1-7 ranges from 5.2 to 7.9 kJ / m. 2 This is because the flexibility of the siloxane chain segments in the molecule and the rigid skeleton of the five-membered ring amide bond work together to effectively disperse stress and improve impact strength; dry-hanging adhesive 8 lacks flexible siloxane chain segments, has poor molecular chain mobility, and reduces impact strength; dry-hanging adhesive 9 uses commercially available hexamethylenediamine curing agent, which has high crosslinking density but weak impact resistance, verifying the key role of siloxane chain segments in impact strength.

[0095] In terms of yellowing resistance, dry-hanging adhesive 3 has the lowest yellowing coefficient, indicating that increasing the amount of silica powder can help improve yellowing resistance. Dry-hanging adhesive 8, lacking the siloxane weather barrier, has its amino groups directly exposed to ultraviolet light, resulting in an increased yellowing coefficient. The CN bond in the dry-hanging adhesive 8 molecule is easily oxidized to form chromophores, proving that the siloxane end-capping structure is a key component for yellowing resistance. In addition, the conjugation effect of imine bonds and the rigid skeleton formed by amide bonds and five-membered ring amide bonds further enhance the overall stability of the molecule, making it difficult for chain breakage or rearrangement to occur due to light energy.

[0096] Regarding storage stability, dry-hanging adhesives 1-7 showed only trace amounts of oil seepage after six months of storage. This is because the aminosiloxane-terminated diimine pyrrolidone compound crosslinks with the epoxy resin through chemical bonds, rather than physical blending, thus avoiding small molecule migration. Dry-hanging adhesive 8, due to its short molecular chain and low crosslinking density, is prone to phase separation during storage. Dry-hanging adhesive 9 showed a higher amount of oil seepage, reflecting the phase separation problem caused by the migration or moisture absorption of traditional curing agents. This demonstrates the dual optimization of storage stability by silane segments and fumed silica.

[0097] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A yellowing resistant modified amine epoxy curing agent characterized in that, By weight, it includes the following components: The compound comprises 70-100 parts of an aminosiloxane-terminated diimine pyrrolidone compound and 5-10 parts of fumed silica; the aminosiloxane-terminated diimine pyrrolidone compound is formed by bonding a dialdehyde pyrrolidone compound with 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane; the structure of the aminosiloxane-terminated diimine pyrrolidone compound is shown in the following formula. 。 2. A process for the preparation of a yellowing resistant modified amine epoxy curing agent, characterized in that, Includes the following steps: S1. Synthesis of dialdehyde pyrrolidone compounds: Aliphatic diamine and dimethyl itaconic acid were mixed with methanol, stirred and heated, and the reaction mixture was collected directly to remove residual solvent; the obtained compound was dissolved in anhydrous tetrahydrofuran, dehydrated and deoxygenated, and the reactants were cooled. Diisobutylaluminum hydride solution was added dropwise while stirring in a glove box. After the addition was completed, stirring was continued at a cooling temperature; after the reaction was completed, saturated sodium potassium tartrate aqueous solution and hydrochloric acid solution were slowly added to the reaction mixture at a cooling temperature in a fume hood, and the mixture was stirred and gradually raised to room temperature to obtain dialdehyde pyrrolidone compounds. The aliphatic diamine was selected from one or more of 1,4-butanediamine, 1,8-octanediamine, and 1,12-dodecanediamine. S2. Synthesis of aminosiloxane-terminated diimine pyrrolidone compounds: Dehydrated and deoxygenated dialdehyde pyrrolidone compounds were mixed in anhydrous toluene, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added. A water separator was installed, and the mixture was stirred and heated to 100-110°C. After the reaction was completed, the mixture was cooled to room temperature and purified to obtain aminosiloxane-terminated diimine pyrrolidone compounds. S3. Dry the fumed silica in an oven, and immediately transfer it to a drying oven after cooling. Put the aminosiloxane-terminated diimine pyrrolidone compound into a planetary high-speed disperser, keep the temperature at 25~35℃, add 5~10 parts of fumed silica in two batches, and simultaneously shear at high speed. Then switch to vacuum degassing mode to remove the air bubbles introduced by stirring. Cool to room temperature and fill into a dry and sealed container to obtain the yellowing-resistant modified amine epoxy curing agent.

3. The preparation method of the yellowing-resistant modified amine epoxy curing agent as described in claim 2, characterized in that, In step S1, the molar ratio of the aliphatic diamine to dimethyl itaconic acid is 1:(2~2.1); the amount of methanol added is 1~2 mL; the stirring and heating temperature is 85~90℃; the cooling temperature is -78℃; the amount of diisobutylaluminum hydride solution added is 2~2.5 times the molar amount of dimethyl itaconic acid; the diisobutylaluminum hydride solution must be added dropwise while maintaining the temperature below -70℃ and completed within 1 hour.

4. The preparation method of the yellowing-resistant modified amine epoxy curing agent as described in claim 2, characterized in that, In step S2, the molar ratio of the dialdehyde pyrrolidone compound and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 1:(2~2.1); the endpoint for determining the end of the reaction is when no more water is separated from the water separator.

5. The preparation method of the yellowing-resistant modified amine epoxy curing agent as described in claim 2, characterized in that, In step S3, the drying conditions for the fumed silica are drying in an oven at 100~110℃ for 1~2 h; the time interval for adding the fumed silica is 10~15 min; the parameters for the high-speed shearing are stirring at 2000~3000 rpm for 30~40 min; and the parameters for the vacuum degassing are degassing at 45~55℃ and 2~4 mbar for 40~60 min.

6. The application of the yellowing-resistant modified amine epoxy curing agent prepared by the preparation method of the yellowing-resistant modified amine epoxy curing agent according to claim 1 or any one of claims 2 to 5 in epoxy curing agents.

7. A dry-hanging adhesive, characterized in that, Includes component A and component B; By weight, component A comprises: 100 parts epoxy resin, 5-15 parts epoxy diluent, and 100-150 parts silica powder; component B comprises: 87-100 parts of the yellowing-resistant modified amine epoxy curing agent prepared by the preparation method of the yellowing-resistant modified amine epoxy curing agent according to claim 1 or any one of claims 2-5, and 100-150 parts silica powder.

8. The method for preparing a dry-hanging adhesive as described in claim 7, characterized in that, Includes the following steps: S1: Preparation of component A: Add 100 parts of epoxy resin and 5-15 parts of epoxy diluent to a high-speed disperser and stir until uniform; add 100-150 parts of pre-dried silica powder in two batches, stirring evenly after each addition to obtain component A; S2: Preparation of component B: Add 87-100 parts of yellowing-resistant modified amine epoxy curing agent to a high-speed disperser and stir evenly; add 100-150 parts of pre-dried silica powder in two batches, stirring evenly after each addition, and then discharge to obtain component B; S3: Mix the above components A and B in a weight ratio of 1:(0.91~0.94) until uniform in color, and stir until the dry-hanging adhesive is obtained.

9. The method for preparing dry-hanging adhesive as described in claim 8, characterized in that, The pre-dried silica powder needs to be dried in an oven at 100~110℃; the stirring speeds in step S1 are 500~2000 rpm and 500~2000 rpm respectively; the stirring speeds in step S2 are 500~2000 rpm and 500~2000 rpm respectively; the stirring speed in step S3 is 500~800 rpm; the dry-hanging adhesive should be used up within 60~90 minutes at 25℃.

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