High-fluidity fast-curing silicone adhesive and preparation method thereof

Abstract

The invention relates to the field of sealants, in particular to a high-fluidity fast-curing silicone adhesive and a preparation method thereof.According to the high-fluidity fast-curing silicone adhesive and the preparation method thereof, an ethylene-vinyl acetate copolymer and lignin are combined, phenolic hydroxyl groups on the lignin are used for forming a micro-reaction environment system, and a crosslinking reaction system with a lignin molecular chain as the center is formed; the curing and damp-heat-resistant effects of the system are improved while the flowability is guaranteed, meanwhile, the compatibility and flowability of lignin are adjusted through the ethylene-vinyl acetate copolymer, the damp-proof performance of the system is further improved through the phenyl silicone oil, and then the effects of rapid curing and high flowability can be better considered.

Description

Technical Field

[0001] This application relates to the field of sealants, and in particular to a high-flow-rate, fast-curing silicone sealant and its preparation method. Background Technology

[0002] Neutral silicone sealant is a room-temperature, moisture-curing, elastic sealing material that releases neutral small molecules (such as alcohols and ketoximes) during curing. It is non-corrosive and suitable for various substrates including metal, stone, and glass. It is a mainstream adhesive for building curtain walls, home decoration sealing, and industrial assembly. The extruded polymer of neutral silicone sealant is typically α,ω-dihydroxypolydimethylsiloxane, which forms a cross-linked system during curing by adding catalysts and cross-linking agents, thus achieving curing.

[0003] Crosslinking agents for neutral silicone sealants include two types: deoxime-type and de-alcohol-type. The reaction mechanism of deoxime-type crosslinking agents involves the reaction of the ketoxime group (-ON=C(CH3)2) of the crosslinking agent with water molecules in the air to generate silanol (Si-OH) and release butanone oxime (or acetone oxime) as a byproduct. The generated silanol undergoes dehydration condensation with the terminal hydroxyl groups of the base polymer α,ω-dihydroxypolydimethylsiloxane (107 sealant) to form Si-O-Si crosslinking bonds. De-alcohol-type crosslinking agents are low-hydrolysis-activity crosslinking agents. They require the alkoxy group (-OCH3) to react with water to generate silanol, releasing methanol. The generated silanol then condenses and dehydrates with the terminal hydroxyl groups of the 107 sealant to form a three-dimensional network structure. Overall, de-alcohol-type crosslinking agents are more stable in storage due to their lower activity, but their reaction is also slower.

[0004] To improve the reaction rate of the alcohol-dehydrogenation process, fillers with higher specific surface area and greater hydroxyl content, such as ultrafine silica, are usually added to the system, or silica is modified, or materials with more hydroxyl content, such as cyclodextrin and polyether polyols, are introduced. However, these materials will affect the moisture resistance of the system. Under long-term use in high humidity environments, the high hydroxyl content makes it easier for water vapor to penetrate into the silicone sealant system, resulting in a significant loss of strength after long-term use in high humidity environments. At the same time, a higher hydroxyl content will also restrict the movement between molecules due to hydrogen bonds, which will lead to poor flowability of the silicone sealant during construction, making it unable to fill gaps well. Summary of the Invention

[0005] Based on the above problems, the purpose of this application is to provide a faster surface drying time and complete curing time in de-alcoholized silicone sealants while maintaining good flowability and waterproof performance.

[0006] First, this application provides a high-flow-rate, fast-curing silicone adhesive, comprising component A and component B, wherein component A contains α,ω-dihydroxy polydimethylsiloxane, and per 100 parts by weight of α,ω-dihydroxy polydimethylsiloxane, component A further comprises the following components in parts by weight: 5-10 parts of phenyl silicone oil; Based on 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, component B comprises the following parts by weight: 5-10 parts of crosslinking agent; 10-15 parts of ethylene-vinyl acetate copolymer; 5-10 parts of lignin; 1-5 parts of maleic anhydride-grafted EVA; 5-10 parts of hydroxyl-terminated polydimethylsiloxane; Component A and / or component B also contain inorganic fillers, wherein the total mass fraction of the inorganic fillers is 10 to 20 parts. Component A and / or component B also include a catalyst, wherein the total mass parts of the catalyst are 0.02 to 0.2 parts; In component A, the lignin is treated with a silane coupling agent, the amount of which is 2 to 5% of the total molar amount of hydroxyl groups in the lignin.

[0007] In the above scheme, a two-component approach is adopted to separate hydroxyl polydimethylsiloxane from other reactive components. This firstly improves the overall stability, preventing it from reacting during storage. Overall, the system does not experience a decrease in fluidity due to long-term storage and exhibits strong weather resistance.

[0008] Based on the above, component A consists entirely of phenyl silicone oil and α,ω-dihydroxy polydimethylsiloxane, while component B contains various hydroxyl compounds. The crosslinking agent is generally a methyl-containing siloxane system. By separating the crosslinking agent, the hydroxyl-containing compound, and the catalyst from the hydroxyl polydimethylsiloxane, the reaction process can be separated. In use, components A and B are mixed and then reacted. Utilizing the larger number of hydroxyl structures, a faster reaction process is achieved, resulting in rapid curing. Simultaneously, two different flowability adjustment systems are used in the above system. One is an ethylene-vinyl acetate copolymer with relatively soft molecular chains, which can insert branches into the molecular chains of the system to improve flowability in the early stages of the reaction, and in the later stages of the reaction, it can better fill the pores between polymers. The other component is lignin, which contains both alcoholic hydroxyl groups and some phenolic hydroxyl groups. In the above system, under the action of a catalyst, a de-alcoholized crosslinking agent (such as alkyl-alkoxysilane) can react slightly with lignin to provide crosslinking performance between the silicone gum system and lignin. Phenolic hydroxyl groups, through their hydroxyl activity and easy ionization, can locally form a more reactive microenvironment. Furthermore, the crosslinking agent easily adheres to the periphery of lignin in the above system, forming a crosslinking system centered on lignin fibers. Simultaneously, the benzene ring has greater steric hindrance in this system. Due to the addition of a small amount of phenyl silicone oil in component A, although the above system contains a relatively large number of hydroxyl groups, the benzene ring more easily forms a water-blocking structure in the system after overall molding, thus exhibiting good weather resistance even in high humidity environments after the reaction. Adding single-hydroxyl-terminated polydimethylsiloxane can further improve the fluidity of the system, reduce the density of entanglement points, and act as a lubricant, while having no significant effect on the strength of the system. Meanwhile, in order to improve the overall dispersion performance, increase the dispersion uniformity and processing convenience, a certain amount of maleic anhydride-grafted EVA was added to component B. This system can provide good dispersibility for both lignin and ethylene-vinyl acetate copolymer, and improve the overall flowability, uniformity and processing performance.

[0009] To further mitigate the reduced flowability caused by the π-bond stacking between phenyl silicone oil and lignin, a silane coupling agent is used to partially couple the hydroxyl groups on the surface. This reduces the flowability loss caused by the mutual hindrance between benzene rings through steric hindrance, while also improving the overall adhesion performance and cohesive strength of the silicone sealant after curing. However, if too much silane coupling agent is applied, the amount of exposed hydroxyl groups on the surface will decrease, making it difficult for lignin to participate in the reaction of the silicone sealant. At the same time, the micro-reaction environment formed will also be interfered with by the coupling agent, resulting in a longer curing time.

[0010] It should be noted that the above equivalent refers to the total functionality of the silane coupling agent that can react with hydroxyl groups. For example, if some silane coupling agents can bind to hydroxyl groups in a molar ratio of 1:2, then 1 unit of substance is regarded as 2 equivalents in the above description.

[0011] Preferably, in component A, the lignin is treated with a silane coupling agent, wherein the equivalent amount of the silane coupling agent is 2 to 5% of the molar amount of the total hydroxyl groups in the lignin.

[0012] Preferably, the number-average molecular weight of the lignin is 5 to 10 kJ.

[0013] In the above scheme, lignin is controlled within a lower molecular weight range, which can provide better flowability and reduce its increase in raw material viscosity. Overall, compared with lignin with a larger molecular weight, this scheme improves flowability and provides better processing performance and uniformity.

[0014] Preferably, component B further comprises, per 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, 1 to 2.5 parts of polyethersulfone and 3 to 6 parts of polyether polyol.

[0015] The above scheme incorporates both polyethersulfone (PES) and polyether polyol systems. PES, being a highly polar system, significantly improves the strength properties of the system, particularly tensile strength. Furthermore, its rigid aromatic ring structure effectively blocks water molecules, enhancing the overall reaction rate and curing speed. After curing, the rigid molecules further reduce water penetration. During the reaction, the PES molecules themselves exist in a non-fixed system... With less obstruction to water vapor penetration, the overall reaction rate and curing efficiency are well guaranteed with the assistance of high hydroxyl content additives. However, polyethersulfone itself has a high melting point, making processing difficult. Furthermore, due to its intermolecular hindrance effect, it has a significant impact on the viscosity of the system. Therefore, a certain amount of polyether polyol is further introduced into the above system. The polyol system and polyethersulfone are improved through an interpenetrating network structure to enhance the compatibility between the two phases, while reducing the overall viscosity. Overall, this further ensures less loss of flowability and improves the weather resistance of silicone sealant in high humidity environments.

[0016] Preferably, the hydroxyl value of the polyether polyol is 50-100 mg KOH / g, and / or, The polyethersulfone has a number-average molecular weight of 30–50 kJ, and / or, The average particle size of the polyethersulfone particles is no greater than 50 μm, and / or, The polyethersulfone is first premixed with the polyether polyol at 180-220°C before being added to component A.

[0017] In the above scheme, polyether polyols and polyethersulfones with lower hydroxyl values ​​and smaller molecular weights were first used, which have a smaller overall impact on flowability. Furthermore, polyethersulfones with excessively large molecular weights can cause a significant water vapor barrier effect before the reaction, leading to a further extension of the reaction time and hindering the rapid curing effect. Further reducing the molecular weight of polyethersulfone, however, weakens the reinforcing and moisture-proof effects of the system. Additionally, polyethersulfones and polyether polyols need to be premixed before being added to the system. This is to further reduce the thickening effect of polyethersulfones on the system and improve the dispersion effect of the polyether polyol and polyethersulfone.

[0018] Preferably, the silane coupling agent is a fluorinated silane coupling agent.

[0019] In the above scheme, fluorine ions are introduced by using a fluorinated silane coupling agent to introduce a fluorinated silane interface on the lignin surface, which reduces lignin agglomeration and interparticle friction, thereby improving fluidity. The fluorinated silicon atoms embedded between the benzene rings work together to further improve the moisture resistance and weather resistance of the cured silicone sealant.

[0020] Preferably, the filler includes a first filler and a second filler. The first filler is selected from any number of titanium dioxide, alumina, zinc oxide, zirconium oxide, and calcium carbonate. The first filler is 5 to 10 parts by weight per 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, and the first filler is added to component A. The second filler includes at least silica particles with an average particle size of 100 to 500 nm. The second filler is 5 to 10 parts by weight per 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, and the second filler is added to component B.

[0021] In the aforementioned system, the addition of a second filler with an average particle size not exceeding 500 nm significantly impacts the reactivity of the silica in the system. A second filler with a particle size exceeding 500 nm leads to a marked decrease in reaction rate, resulting in a shorter curing time and a slight decrease in strength. In this application, the addition of a hydroxyl-containing compound maintains good overall reactivity. Therefore, appropriately larger silica particles can be used instead of fumed silica or other particles with an average particle size less than 100 nm, or even 30–50 nm, thus ensuring overall flowability without affecting reactivity. Furthermore, due to the hydroxyl structure on the silica surface, when components A and B are mixed, lignin and other systems in component B can adsorb onto the silica particle surface through bonding and participate in the reaction before silica. The silica particle size range used in this application balances system flowability with improved reaction contact, resulting in better reaction improvement and enhancing the reactivity of the silicone sealant.

[0022] Preferably, in the ethylene-vinyl acetate copolymer, the molar percentage of vinyl acetate monomer is 30-45%, and / or The weight-average molecular weight of the ethylene-vinyl acetate copolymer is 30-50 kDa.

[0023] Overall, when adding ethylene-vinyl acetate copolymer to the system, ethylene-vinyl acetate copolymer with medium or low molecular weight is still selected, and its vinyl acetate content is controlled within the range of 30-45%. Within this range, the activity of the molecular chains can be guaranteed, reducing the crystallization system caused by their flat arrangement, and further improving the fluidity of the system. Overall, it can also act as a solubilizer due to its relatively low molecular weight, and it has a significant improvement in the compatibility between different polymers. Compared with ethylene-vinyl acetate copolymer with a larger molecular weight, it provides good uniformity and reliability of silicone sealant system.

[0024] In addition, this application also relates to a method for preparing the above-mentioned high-flow-rate fast-curing silicone sealant. In component A, except for the catalyst, all components are mixed at 150-180°C under oxygen-free conditions, and then the catalyst is added for later use. In component B, except for the catalyst and crosslinking agent, it is first premixed at 100-150°C, then cooled to room temperature, the catalyst and crosslinking agent are added, and it is mixed evenly before use. Mix component A and component B, stir evenly, process to the desired position and shape, and then allow to stand and cure under natural conditions to obtain silicone sealant.

[0025] In the above scheme, components A and B are mixed and stored separately, which can extend the overall storage time. It should be noted that the catalyst can be added to components A and / or components B according to specific circumstances. Component A generally requires higher processing temperature, while component B needs to be mixed at a lower temperature, which can improve its overall storage time. Under light-proof and dry conditions, component B can usually be stored for about one year.

[0026] In summary, this application utilizes the combination of ethylene-vinyl acetate copolymer and lignin to create a micro-reaction environment system with phenolic hydroxyl groups on the lignin, forming a cross-linking reaction system centered on the lignin molecular chain. This improves the system's curing and resistance to damp heat while maintaining its fluidity. Furthermore, the hydroxyl groups in the lignin are modified to a certain extent, further enhancing the system's fluidity. Additionally, a combination of polyethersulfone and polyether polyol is added. Polyethersulfone further improves the system's strength and moisture resistance, while the addition of polyether polyol improves its fluidity and increases the reaction rate. Detailed Implementation

[0027] The technical solution of this application will be further described through the following specific embodiments.

[0028] For the following specific implementation method, component A and component B were mixed at 23±2℃ and 50% humidity, and the results were verified using the following experimental parameters.

[0029] 1. Surface drying time: Refer to Method B in GB / T13477.5-2002 Test Methods for Building Sealing Materials.

[0030] 2. Flowability: Refer to GB / T13477.3-2002 Test methods for building sealing materials - Part 3: Method for determining the extrudability of sealing materials using standard apparatus. Under the conditions of 23±2℃ and 50% humidity, use an extruder with a 2mm extrusion orifice and an extrusion pressure of 200kPa to determine the extrusion amount of the sample per unit time at room temperature.

[0031] 3. Mechanical properties: The tensile strength was measured after curing at 23±2℃ and 50% humidity for 24 hours in accordance with GB / T13477.8-2017 Test Methods for Building Sealing Materials.

[0032] 4. Adhesion: Refer to GB / T13477.10-2017 Test Methods for Building Sealing Materials Part 10: Determination of Adhesion at a Fixed Elongation. After curing at 23±2℃ and 50% humidity for 24 hours, the adhesion at a fixed elongation between the material and the aluminum alloy substrate is measured.

[0033] The mechanical properties and adhesion were measured by determining the tensile strength and adhesion at a given elongation after preparation and after the samples underwent hydrothermal treatment. The specific conditions for hydrothermal treatment are as follows: Temperature: 85℃; Processing time: 14 days; Humidity: 100%.

[0034] Preparation Example A: In this series of preparation examples, lignin underwent different modifications. Specifically, the lignin was modified through the following steps: In a solvent composed of water and ethanol (volume ratio 1:9), lignin was added at a mass concentration of 0.1 g / mL. After high-speed stirring to ensure complete swelling of the lignin, a small amount of glacial acetic acid was added dropwise to control the pH at 5. The temperature was then raised to 50°C, and a small amount of (3,3,3-trifluoropropyl)trimethoxysilane dissolved in toluene was added dropwise to the above system while stirring for 5 min. The temperature was then controlled at 50°C for a pre-hydrolysis reaction for 30 min. Dibutyltin dilaurate was then added as a catalyst at a mass concentration of 0.5 mg / mL, and the temperature was raised to 80°C for reflux reaction for 6 h. After the reaction was completed, ice water and triethylamine were added, the temperature was rapidly lowered, and the pH was adjusted to neutral. The mixture was then centrifuged at 5000 rpm, washed three times repeatedly with water and ethanol, and vacuum dried to obtain the modified lignin.

[0035] In the preparation examples, several lignins with different specifications were used, and the amount of silane coupling agent attached was adjusted by adding different masses of (3,3,3-trifluoropropyl)trimethoxysilane. At the same time, the effects of different lignins on the system were also explored. Specifically, the parameter differences between the different preparation examples are shown in Table 1.

[0036]

[0037] Preparation Example B: In this preparation example, compared to Preparation Example A, the silane coupling agent was replaced with KH550. Since KH550 does not require a catalyst to react, dibutyltin dilaurate was not added during the reaction. All other reaction conditions remained unchanged. Specifically, Preparation Example B includes the experimental groups shown in Table 2.

[0038]

[0039] Preparation Example C: In this preparation example, compared to Preparation Example A, the silane coupling agent is replaced with TESPT. In this system, a catalyst needs to be added. Therefore, the overall experimental procedure is the same as that of Preparation Example A. Specifically, Preparation Example C includes the experimental groups shown in Table 3.

[0040]

[0041] It is worth noting that in preparation example C, since TESPT is a bifunctional silane coupling agent, 1 mol of TESPT is equivalent to 2 mol of reaction sites. Therefore, when calculating the coupling agent equivalent / hydroxyl molar amount, it is necessary to compare twice the molar amount of coupling agent with the molar amount of hydroxyl.

[0042] Example 1: Based on the preparation example above, the following example is set up to verify the effect of the amount of lignin added and the selection of lignin on the performance of silicone sealant. The selection and amount of lignin added are shown in Table 4.

[0043] In this embodiment, the prepared silicone sealant has the components of AB sealant, wherein component A is the main silicone component, which contains α,ω-dihydroxypolydimethylsiloxane and has a viscosity of 80,000 MPa·s. Based on 100 parts by mass of α,ω-dihydroxypolydimethylsiloxane, component A also contains the following components. Phenyl silicone oil (viscosity 35Cst at 25℃, phenyl molar content 7.5%) Refer to Table 4 Tetrabutyl titanate (catalyst) 0.075 parts Titanium dioxide (average diameter 0.3μm) 10 parts Component B contains the following components per 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane: 8 parts of methyltriethoxysilane (crosslinking agent) Ethylene-vinyl acetate copolymer (vinyl acetate monomer molar content 45%, weight average molecular weight 40 kDa) 12.5 parts Diketoxime tin (catalyst) 0.075 parts 5 parts of silicon dioxide (spherical, average diameter 300 nm) Maleic anhydride-grafted EVA (grafting rate 1.2%, melt index 12.0 g / min at 190℃ and 2.16 kg) 3 portions Contains 8 parts of single-hydroxyl-terminated polydimethylsiloxane (viscosity 2000 MPa·s).

[0044] The preparation method of Example 1 is as follows: First, each component undergoes pre-dehydration treatment to ensure that the overall moisture content is below 0.05 wt%. Add all components of component A except the catalyst to a mixer, evacuate to a vacuum, heat to 170°C, mix at high speed for 30 minutes, then cool to room temperature, add the catalyst, and continue stirring for 10 minutes. Set aside. Except for the catalyst and crosslinking agent, component B is added to a mixer, evacuated to a vacuum, then heated to 120°C and stirred at high speed for 60 min. After cooling to room temperature, the catalyst and crosslinking agent are added to the above system, and stirring is continued for 15 min. The mixture is then ready for use. Add component A and component B to the mixer in the above-mentioned mass ratio, and stir thoroughly for 3 minutes until homogeneous before proceeding with construction or processing into the corresponding sample.

[0045] For comparison with Example 1, a Control Example 1 was also provided. In Control Example 1, no modified or unmodified lignin was added to component B, and the other preparation conditions were the same as in Example 1.

[0046] In Example 1, the types and amounts of lignin selected for each experimental group, the amount of phenyl silicone oil added, and the results of the control experiment compared with Control Example 1 are shown in Table 4.

[0047]

[0048] Example 2: The difference between this application and Example 1 is that no modification is performed when using different lignins. In Examples 2-1 to 2-4, the unmodified lignins corresponding to Preparation Example A1, Preparation Example A6, Preparation Example A8 and Preparation Example A9 in Preparation Example A were selected in turn, and the results are shown in Table 5.

[0049]

[0050] The experimental results in Tables 4 and 5 show that, compared to Examples 1 and 2, the modification of lignin significantly improved the flowability of the silicone sealant while still maintaining its effect of reducing surface drying time. Furthermore, the overall resistance to damp heat was noticeably improved. Clearly, without modification, the lignin surface has too many hydroxyl reaction sites, leading to rapid participation in the reaction at the initial stage and affecting moisture resistance. Comparing different silane coupling agents, under the same reaction conditions, the silicone sealant from Preparation Example A, compared to those from Preparation Examples B and C, provided better moisture resistance while maintaining a similar surface drying time. Under the same other conditions, the examples in Preparation Example A had a higher overall extrusion yield and better flowability, indicating that the introduction of fluorine atoms better balances flowability and moisture resistance, and under specific reaction conditions, it has no significant impact on the reaction rate and intensity, even showing a slight improvement. In selecting lignin, the fluidity generally increases and then decreases with increasing molecular weight. Using lignin with excessively large molecular weight leads to a significant decrease in system fluidity, and the reaction rate also decreases. Conversely, if the molecular weight of the lignin is too small, there will be a certain degree of weakening in strength, and smaller molecular weight lignin will also generate a larger specific surface area. Although this may improve the reaction rate, the overall fluidity will decrease to some extent. Furthermore, the surface modification of lignin needs to be controlled. It is important to note that since the number of reaction sites on the lignin surface is actually limited, the amount of lignin modification equivalent should only be within the range of 2-5% of the molar amount of phenolic hydroxyl groups in the lignin. Excessive modification will also lead to a decrease in the reaction rate and strength of the system.

[0051] By comparing Examples 1-22 to 1-24 with Examples 2-5 to 2-8, it can be seen that the addition of phenyl silicone oil, in the presence of lignin modified with a silane coupling agent, has virtually no adverse effect on the flowability of the system; on the contrary, it improves the system's resistance to damp heat. Experimental data from Example 2 show that, without the addition of phenyl silicone oil, the simple silane-modified lignin, while having a small impact on flowability, has a significant adverse effect on damp heat resistance due to the water vapor permeation channels formed by the lignin itself. In the environment using lignin without silane coupling agent modification, such as in Examples 2-5 to 2-8, a stronger π-π stacking structure forms between the lignin and phenyl silicone oil, resulting in a significant loss of flowability and an inability to guarantee the system's resistance to damp heat.

[0052] Example 3: Based on Experiment 1-1, this example further adds polyethersulfone and polyether polyol to the system. The following four types of polyethersulfone were selected: Polyethersulfone a1: molecular weight 48 kDa, ground to pass through a 50 μm sieve; Polyethersulfone a2: molecular weight 48 kDa, ground to pass through a 100 μm sieve; Polyethersulfone a3: molecular weight 65kDa, ground to pass through a 50μm sieve; Polyethersulfone a4: molecular weight 30 kDa, ground to pass through a 50 μm sieve; The following three polyether polyols are specifically selected: b1. Polypropylene glycol, molecular weight 1000da, hydroxyl value 110mg KOH / g; b2. Polypropylene glycol, molecular weight 2000da, hydroxyl value 55mg KOH / g; b3. Polytetrahydrofurandiol, molecular weight 1400 da, hydroxyl value 79 mg KOH / g.

[0053] In Example 3, polyether polyol and polyether sulfone were first mixed and then kneaded in a 200°C internal mixer for 10 minutes, and then mixed with α,ω-dihydroxypolydimethylsiloxane.

[0054] Example 4: In this example, the same combination of polyethersulfone and polyether polyol as in Example 3 was used. However, the difference is that in Example 4, the polyether polyol and polyethersulfone were not first subjected to a mixing process. Instead, the polyether polyol and polyethersulfone were directly added to the α,ω-dihydroxypolydimethylsiloxane system and mixed together.

[0055] The addition mass and selection of polyethersulfone and polyether polyol used in different experimental groups in Examples 3 and 4 are shown in Table 6.

[0056]

[0057] The experimental results for each experimental group are shown in Table 7.

[0058]

[0059] The above experiments show that adding polyethersulfone and polyether polyol to the system can further improve the system's resistance to damp heat without significantly affecting the curing time. Overall, only the experimental group using polyethersulfone a3 showed a significant impact on the extrusion performance of the system. However, the amount of polyethersulfone added should not be excessive. For example, in Examples 3-4, the excessive addition of polyethersulfone led to a significant decrease in the system's fluidity and tensile strength. Furthermore, grinding the polyethersulfone is also crucial, as it helps form a better blend with the polyether polyol and improves its dispersion performance in silicone sealant. Polyether polyol provides better dispersion; in experimental groups 3-7, the absence of polyether polyol resulted in a significant weakening of the system's extrusion performance and a marked deterioration in strength, due to the excessive rigidity of the polyethersulfone. Furthermore, the hydroxyl value of the polyether polyol is crucial. Choosing b1, i.e., polyoxypropylene glycol with a higher hydroxyl value, will result in a slight increase in the viscosity of the system, leading to a decrease in extrusion performance and a deterioration in moisture resistance. Additionally, excessive addition of polyether polyol, due to its high hydroxyl content, will also reduce the system's resistance to damp heat.

[0060] In addition, comparing Example 4 with Example 3, it can be found that without premixing, the overall dispersion performance of polyethersulfone is worse, which leads to the flowability approaching that of experimental groups 3-7.

[0061] Example 5: In this example, based on experimental group 3-3, the effects of different ethylene-vinyl acetate copolymers and their addition amounts on the system were further studied. Specifically, the ethylene-vinyl acetate copolymers selected were as follows: c1: Vinyl acetate monomer molar content 45%, weight-average molecular weight 40 kDa c2: Vinyl acetate monomer molar content 58%, weight-average molecular weight 45kDa. c3: Vinyl acetate monomer molar content 30%, weight average molecular weight 50kDa c4: Vinyl acetate monomer molar content 22%, weight-average molecular weight 30kDa Wherein, c1 is the ethylene-vinyl acetate copolymer used in other prior embodiments.

[0062] In addition, a control example 3 was set up in which no ethylene-vinyl acetate copolymer was added.

[0063] The experimental results of Example 5 are shown in Table 8.

[0064]

[0065] The experimental results show that the addition of ethylene-vinyl acetate copolymer significantly improves the flowability of the system. Through the acetate ester structure on the branched chains and the overall soft structure, it forms an interpenetrating system with silane molecules, thus improving overall flowability. Simultaneously, the ethylene-vinyl acetate copolymer should ideally have a vinyl acetate monomer molar percentage of 30–45% and a weight-average molecular weight of 30–50 kDa. Excessively high or low vinyl acetate content will lead to poorer flowability and a certain loss of strength. Furthermore, it should be noted that ethylene-vinyl acetate copolymer will slightly reduce the system's moisture resistance. This may be because ethylene-vinyl acetate copolymer weakens the close packing of molecules, creating gaps that allow water molecules to enter and thus impair adhesion. However, the effect is minimal when its mass fraction is no higher than 15 parts. In the control example, the absence of ethylene-vinyl acetate copolymer results in poor overall flowability and poor compatibility between the lignin and silicone adhesive system, leading to a significant loss of adhesion.

[0066] Example 6: In this example, based on experimental group 3-3, the amount of phenyl silicone oil and the amount of single-hydroxyl polydimethylsiloxane added to the system were further studied. Specifically, the amount of phenyl silicone oil and the amount of single-hydroxyl polydimethylsiloxane added, as well as the experimental results of the corresponding experimental groups, are shown in Table 9.

[0067]

[0068] The experimental data above show that phenyl silicone oil has a certain impact on the strength of the system and also significantly improves its resistance to humid heat. Overall, due to its soft main chain and rigid branches, it can provide overall moisture resistance without affecting the overall curing effect, resulting in minimal change before and after humid heat treatment. However, increasing the amount of phenyl silicone oil added leads to a decrease in system uniformity and fluidity. Excessive stacking of phenyl groups in the system causes a significant loss of fluidity, affecting not only surface drying time but also overall tensile strength. Single-hydroxyl-terminated polydimethylsiloxane can effectively improve the viscosity of the system and has a significant impact on fluidity; however, excessive addition will prolong the surface drying time.

[0069] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-flowability, fast-curing silicone adhesive, characterized in that, It comprises component A and component B, wherein component A contains α,ω-dihydroxypolydimethylsiloxane, and per 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, component A further comprises the following components in parts by weight: 5-10 parts of phenyl silicone oil; Based on 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, component B comprises the following parts by weight: 5-10 parts of crosslinking agent; 10-15 parts of ethylene-vinyl acetate copolymer; 5-10 parts of lignin; 1-5 parts of maleic anhydride-grafted EVA; 5-10 parts of hydroxyl-terminated polydimethylsiloxane; Component A and / or component B also contain inorganic fillers, wherein the total mass fraction of the inorganic fillers is 10 to 20 parts. Component A and / or component B also include a catalyst, wherein the total mass parts of the catalyst are 0.02 to 0.2 parts; In component A, the lignin is treated with a silane coupling agent, the amount of which is 2 to 5% of the total molar amount of hydroxyl groups in the lignin.

2. The high-flowability, fast-curing silicone adhesive according to claim 1, characterized in that, The number-average molecular weight of the lignin is 5–10 kJ.

3. The high-flowability, fast-curing silicone adhesive according to claim 1, characterized in that, The silane coupling agent is a fluorinated silane coupling agent.

4. The high-flow-rate, fast-curing silicone adhesive according to claim 1, characterized in that, Component A further comprises, per 100 parts by weight of α,ω-dihydroxypolydimethylsiloxane, 1 to 2.5 parts of polyethersulfone and 3 to 6 parts of polyether polyol.

5. The high-flowability, fast-curing silicone adhesive according to claim 4, characterized in that, The hydroxyl value of the polyether polyol is 50–100 mg KOH / g, and / or, The polyethersulfone has a number-average molecular weight of 30–50 kJ, and / or, The average particle size of the polyethersulfone particles is no greater than 50 μm, and / or, The polyethersulfone is first premixed with the polyether polyol at 180-220°C before being added to component A.

6. The high-flowability, fast-curing silicone adhesive according to claim 1, characterized in that, The filler includes a first filler and a second filler. The first filler is selected from any number of titanium dioxide, aluminum oxide, zinc oxide, zirconium oxide, and calcium carbonate. The first filler is 5 to 10 parts by mass per 100 parts by mass of α,ω-dihydroxypolydimethylsiloxane. The first filler is added to component A. The second filler comprises at least silica particles with an average particle size of 100-500 nm. The second filler is 5-10 parts by mass per 100 parts by mass of α,ω-dihydroxypolydimethylsiloxane, and the second filler is added to component B.

7. The high-flow-rate, fast-curing silicone adhesive according to claim 1, characterized in that, In the ethylene-vinyl acetate copolymer, the molar percentage of vinyl acetate monomer is 30-45%, and / or The weight-average molecular weight of the ethylene-vinyl acetate copolymer is 30-50 kDa.

8. A method for preparing the high-flow-rate, fast-curing silicone adhesive according to any one of claims 1 to 7, characterized in that, In component A, except for the catalyst, all components are mixed at 150–180°C under oxygen-free conditions, and then the catalyst is added for later use. In component B, except for the catalyst and crosslinking agent, all components are premixed at 100-150°C under oxygen-free conditions, then cooled to room temperature, the catalyst and crosslinking agent are added, and the mixture is further mixed evenly before use. Mix component A and component B, stir evenly, process to the desired position and shape, and then allow to stand and cure under natural conditions to obtain silicone sealant.

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