Long-lasting stable silica for two-component epoxy systems and method for its preparation

Abstract

The application discloses long-acting stable silica for a two-component epoxy system and a preparation method thereof. Firstly, a silicon hydrogen group is introduced to the surface of fumed silica by treating the surface of the fumed silica with triethoxysilane; then, the silicon hydrogen group is subjected to a hydrosilylation addition reaction with vinyl-terminated polydimethylsiloxane (PDMS) to form a PDMS flexible steric hindrance layer; finally, the PDMS flexible steric hindrance layer is subjected to a hydrosilylation addition reaction with hexadecyldimethylhydrosilane to introduce a hexadecyl long chain as an anchoring arm. The long-acting stable silica obtained by the application exhibits excellent hydrophobicity and long-term compatibility in the two-component epoxy system, effectively solves the technical problems of viscosity reduction and sedimentation of the existing epoxy system, and has a wide application prospect in the fields of adhesives, coatings, electronic packaging and the like.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to a long-lasting stable silica for two-component epoxy systems and its preparation method. Background Technology

[0002] Silica, as an important inorganic nanomaterial, is widely used as a thickener, thixotropic agent, reinforcing agent, and functional filler in many industrial fields such as coatings, adhesives, composite materials, electronic packaging, and aerospace due to its high specific surface area, high strength, good chemical inertness, excellent optical properties, and low cost. Especially in two-component epoxy systems, the addition of silica can significantly regulate the rheological properties of the system, increase viscosity, impart excellent anti-sagging and anti-settling capabilities, and improve the mechanical properties and dimensional stability of the material.

[0003] However, existing silica applications generally present several technical challenges when used in two-component epoxy systems. First, unmodified silica contains a large number of silanol groups on its surface, exhibiting strong hydrophilicity. This results in poor dispersibility in hydrophobic organic polymer matrices (such as epoxy resins), leading to agglomeration and the formation of large secondary particles, which in turn affects the rheological properties of the system and the uniformity and stability of the final product. To improve its dispersibility, surface organic modification is typically performed.

[0004] Although existing technologies for surface modification of silica have been developed, most modified silica still face performance bottlenecks in practical applications. On the one hand, the grafting efficiency of many modifiers is low, resulting in uneven or incomplete modification layers on the silica surface, failing to completely solve the agglomeration problem in organic systems. This prevents the modified silica from achieving ideal initial thickening efficiency and thixotropic properties in epoxy systems. On the other hand, a more prominent problem is that even if some modified silica initially provides good rheological properties, their rheological properties, especially viscosity and thixotropic index, often show significant degradation during long-term storage in two-component epoxy systems. This performance degradation typically manifests as decreased viscosity, weakened thixotropy, and even severe sedimentation or agglomeration of the filler.

[0005] The aforementioned unstable and unsustainable properties pose significant challenges to the production, storage, and application of two-component epoxy systems. For example, in adhesives and coatings, the degradation of rheological properties leads to deterioration in application performance, such as sagging and delamination, ultimately affecting product quality and lifespan. This may be attributed to the continuous effect of complex components (such as curing agents, solvents, and additives) on the silica surface modification layer, as well as the insufficient stability of the modification layer's own structure. Existing modification methods have failed to effectively construct an interfacial structure capable of long-term resistance to erosion from the system's internal environment and maintaining stable dispersion.

[0006] Therefore, developing a silica modification technology that can achieve long-term stability and no performance degradation in two-component epoxy systems is a key technical problem that urgently needs to be solved in this field. It is of great significance for improving the storage stability, performance and market competitiveness of epoxy products. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a long-lasting stable silica for two-component epoxy systems and its preparation method. The present invention employs a one-pot method to sequentially construct a polysiloxane flexible segment and a long-chain alkyl bilayer modified structure on the surface of fumed silica, endowing the powder with excellent hydrophobicity and long-lasting compatibility with the epoxy system. This effectively solves the problems of filler sedimentation and poor storage stability in two-component epoxy systems, while simplifying the process flow and making it suitable for industrial production.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing long-lasting stable silica for a two-component epoxy system, comprising the following steps: (1) In toluene solvent, fumed silica powder is surface treated with triethoxysilane to obtain a suspension of hydrogen-silicon modified silica. (2) Add platinum catalyst and vinyl-terminated polydimethylsiloxane to the suspension of hydrogen-silicon modified silica obtained in step (1) to carry out hydrosilylation addition reaction to obtain a suspension containing intermediate; (3) Add hexadecyl dimethylhydrosilane to the suspension containing the intermediate obtained in step (2) to carry out hydrosilylation addition reaction. After the reaction is completed, filter, wash and vacuum dry in sequence to obtain the long-lasting stable silica for the two-component epoxy system.

[0009] In a preferred embodiment of the present invention, in step (1), the specific surface area of ​​the fumed silica powder is 50~400m². 2 / g.

[0010] Specific surface area less than 50m²2 At a specific surface area of ​​ / g, silica exhibits poor thixotropic and thickening effects, failing to meet the rheological requirements of epoxy systems; 2 When the surface energy of the powder is too high, it is very easy for it to agglomerate, which leads to a significant deterioration in its dispersibility in toluene solvent and subsequent resin system.

[0011] As a preferred embodiment of the present invention, based on 100 parts of fumed silica powder in step (1), the amount of toluene solvent is 1000-3000 parts, and the amount of triethoxysilane is 5-25 parts; the surface treatment conditions are: under nitrogen protection, the reaction is carried out at 60-120°C for 2-6 hours.

[0012] The amount of toluene solvent used must be sufficient to ensure the system has a suitable viscosity for easy stirring and dispersion. Insufficient triethoxysilane dosage will result in an inadequate number of Si-H groups introduced onto the surface, failing to provide sufficient reaction sites for subsequent grafting; excessive dosage may lead to self-condensation or residue, increasing the burden of subsequent washing. Controlling the reaction temperature and time aims to ensure that the triethoxysilane is fully hydrolyzed and undergoes a condensation reaction with the silanol groups on the silica surface, chemically bonding the Si-H groups to the powder surface.

[0013] In a preferred embodiment of the present invention, in step (2), the number average molecular weight Mn of the vinyl-terminated polydimethylsiloxane is 500~2000 g / mol.

[0014] When the molecular weight is too low, the polymer chain segments are too short and cannot provide sufficient steric hindrance to prevent secondary agglomeration between silica particles; when the molecular weight is too high, the polymer chains are too long and will cause severe entanglement, resulting in a sharp increase in the viscosity of the system, which not only affects the grafting rate, but also has an adverse effect on the processing flowability of the final epoxy system.

[0015] As a preferred embodiment of the present invention, based on 100 parts of fumed silica powder in step (1), the amount of vinyl-terminated polydimethylsiloxane is 30-60 parts; the amount of platinum catalyst is 20-100 ppm of the total mass of fumed silica powder, triethoxysilane, toluene solvent and vinyl-terminated polydimethylsiloxane, based on the mass of platinum element.

[0016] In this invention, the platinum catalyst may be selected from homogeneous hydrosilylation catalysts commonly used in the art, such as Karstedt catalyst (i.e., platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex), chloroplatinic acid, or chloroplatinic acid-isopropanol solution (Speier catalyst), etc.

[0017] In a preferred embodiment of the present invention, in step (2), the temperature of the hydrosilylation addition reaction is 60~80℃ and the time is 4~12h, and the reaction is carried out under nitrogen or argon protection.

[0018] Inert gas protection can prevent oxidation of the system at high temperatures and interference from moisture in the air on the reaction. Step (2) utilizes the addition of vinyl groups to the Si-H on the surface of the product from step (1) to chemically anchor the polysiloxane segments to the powder surface.

[0019] As a preferred embodiment of the present invention, based on 100 parts of the mass of fumed silica powder in step (1), the amount of hexadecyl dimethylhydrosilane used is 10 to 30 parts.

[0020] Step (3) utilizes the Si-H groups in hexadecyl dimethylhydrosilane to undergo a secondary hydrosilylation addition reaction with the unreacted residual vinyl groups after grafting in step (2), introducing a long-chain alkyl group (hexadecyl). This long-chain alkyl group works together with the polydimethylsiloxane segments to greatly enhance the compatibility and long-term stability of silica in the two-component epoxy system.

[0021] In a preferred embodiment of the present invention, in step (3), the temperature of the hydrosilylation addition reaction is 60~80℃ and the time is 2~8h, and the reaction is carried out under nitrogen or argon protection.

[0022] After the reaction in step (3) is completed, the suspension contains unreacted silanes and small molecule impurities. The washing step can be performed by multiple centrifugation or filtration washing with conventional polar or nonpolar solvents (such as toluene, anhydrous ethanol, acetone or mixtures thereof) to thoroughly remove free small molecules. The vacuum drying is preferably carried out at 80~150℃ and an absolute pressure of less than 0.01MPa to thoroughly remove residual solvent.

[0023] In a second aspect, the present invention provides a long-lasting stable silica for a two-component epoxy system prepared by the method described in any of the above embodiments.

[0024] A third aspect of the invention provides the use of the aforementioned long-lasting stable silica in paints, coatings, adhesives, sealants, or resins. Preferably, the long-lasting stable silica is used as a rheology modifier or thixotropic agent in the aforementioned systems.

[0025] Compared with the prior art, the present invention has the following beneficial effects: This invention first utilizes triethoxysilane to treat fumed silica, which not only consumes the hydrophilic free silanol groups (-OH) on the powder surface that are prone to agglomeration, effectively reducing the surface energy and initial agglomeration tendency of the powder; more importantly, due to the small molecular size of triethoxysilane, it can form a high-density, highly reactive Si-H anchor layer on the powder surface, providing sufficient reaction sites for subsequent grafting of macromolecular chains, fundamentally overcoming the problem of low grafting rate caused by steric hindrance when directly grafting macromolecules.

[0026] Vinyl-terminated polydimethylsiloxane is grafted onto the silica surface via hydrosilylation, constructing a highly flexible polysiloxane macromolecular "buffer shell" around the particles. The PDMS segments possess extremely low surface tension and excellent flexibility, not only endowing silica with strong hydrophobic properties but also creating a powerful steric hindrance effect through the expansion of the macromolecular chains in solvents and resins. This effectively prevents particles from approaching each other, like a spring, completely eliminating the hardening and clumping of fillers during long-term storage.

[0027] Further hydrosilylation introduces hexadecyl dimethylhydrosilane, thereby introducing a C16 long-chain alkyl group onto the outermost periphery of the particles or the PDMS chain ends. Hexadecyl groups possess strong oleophilicity, and their polarity is highly compatible with the two-component epoxy resin system. This long carbon chain structure can easily extend and penetrate into the epoxy resin matrix, generating strong van der Waals forces and physical entanglement with the resin molecular chains, greatly improving the wettability, compatibility, and dispersion uniformity of the silica powder in the epoxy system.

[0028] The core breakthrough of this invention lies in the synergistic effect of the flexible PDMS chain and the rigid / oleophilic long C16 chain. In two-component epoxy systems, traditional modified silica often suffers irreversible collapse of the thixotropic network (i.e., thixotropic degradation or viscosity reduction) after several months of storage due to the gradual replacement of the adsorbed layer on its surface by polar curing agents or solvents within the system. This invention achieves this through the synergistic combination of PDMS and the long C16 chain: the inner PDMS layer provides dynamic repulsive force and completely shields residual polar sites, resisting the intrusion of polar molecules in the epoxy system; the outer hexadecyl group acts as an anchor, firmly locking the particles within the resin network, achieving long-term stability.

[0029] The combination of these two elements creates an interference-resistant and thermodynamically stable dispersed phase structure. This allows the silica to not only exhibit excellent rheological thickening and thixotropic anti-sagging properties in the initial stage of the two-component epoxy system, but also maintain its viscosity and thixotropic index with almost no degradation during storage periods of up to six months or even longer. This truly achieves the long-lasting, stable thickening and anti-sagging effect urgently needed in industrial applications. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some schematic diagrams of certain embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a microscopic photograph of the long-lasting stable silica prepared in Example 1 of the present invention; Figure 2 The infrared spectrum of the long-lasting stable silica prepared in Example 1 of this invention; Figure 3 This is a set of contact angle experimental data of long-lasting stable silica prepared in Example 1 of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0033] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0034] Fumed silica: Purchased from Hubei Huifu Nanomaterials Co., Ltd., HL series, such as HL-200 (specific surface area approximately 200m²). 2 / g), HL-50 (specific surface area approximately 50m²) 2 / g) and HL-380 (specific surface area approximately 380m²) 2 (g), etc.

[0035] Triethoxysilane: purchased from Saen Chemical Technology (Shanghai) Co., Ltd., purity ≥98%.

[0036] Vinyl-terminated polydimethylsiloxane: purchased from Wacker Chemie (China) Co., Ltd. or Dow Corning, with a number average molecular weight (Mn) ranging from 500 to 2000 g / mol.

[0037] Hexadecyldimethylsilane: purchased from Aladdin Reagent (Shanghai) Co., Ltd., purity ≥95%.

[0038] 1-Hexadecene: purchased from Maclean's Reagents (Shanghai) Co., Ltd., purity ≥98%.

[0039] Toluene: Purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade.

[0040] Platinum catalyst: usually refers to a platinum complex based on divinyltetramethyldisiloxane (Karstedt catalyst), with a platinum content of about 2%, purchased from Sigma-Aldrich; or chloroplatinic acid-isopropanol solution, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0041] Anhydrous ethanol: purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade.

[0042] Epoxy resin: Bisphenol A type epoxy resin, such as resin with an epoxy value of around 0.51 eq / 100g, purchased from Dow Chemical Company (model DER331) or other suppliers.

[0043] Curing agent: Polyetheramine curing agent, such as a curing agent with an amine value of around 450 mg KOH / g, purchased from Huntsman (model Jeffamine D230) or other suppliers.

[0044] This invention provides a long-lasting stable silica for two-component epoxy systems, the preparation steps of which are as follows: (1) In a reactor equipped with a mechanical stirrer, thermometer, reflux condenser and inert gas protection device, add 100 parts by weight of a specific surface area of ​​50~400m² 2 / g of fumed silica powder and 1000-3000 parts by weight of toluene solvent were mixed and stirred to fully disperse the powder. Then, 5-25 parts by weight of triethoxysilane were added. Under nitrogen protection, the temperature was raised to 60-120℃ and the reaction was maintained at this temperature for 2-6 hours. After the reaction was completed, the system was cooled to a suitable temperature to obtain a suspension of hydrogen-silicon modified silica.

[0045] (2) Maintaining an inert gas (nitrogen or argon) protection, add 30-60 parts by weight of vinyl-terminated polydimethylsiloxane (number average molecular weight Mn of 500-2000 g / mol) to the suspension of hydrosilicon-modified silica obtained in step (1), and add a platinum catalyst (such as Karstedt catalyst or chloroplatinic acid). The amount of platinum catalyst added, based on the mass of platinum element, is 20-100 ppm of the total mass of fumed silica powder, triethoxysilane, toluene solvent, and vinyl-terminated polydimethylsiloxane. Heat the system to 60-80℃ and carry out the hydrosilylation addition reaction at a constant temperature for 4-12 h to obtain a suspension containing the intermediate.

[0046] (3) After the reaction in step (2) above is completed, without separation, 10 to 30 parts by weight of hexadecyl dimethylhydrosilane are directly added to the suspension containing the intermediate. Under nitrogen or argon protection, the hydrosilylation addition reaction is continued at 60 to 80°C for 2 to 8 hours.

[0047] After the reaction is complete, the reaction solution is cooled to room temperature. The resulting suspension is filtered (or centrifuged), and the solid filter cake is washed multiple times with a suitable washing solvent (such as toluene, ethanol, etc.) to remove unreacted polymers, silane raw materials, and small molecule impurities. Finally, the washed solid is placed in a vacuum drying oven (e.g., at 80~150℃) and vacuum dried to constant weight. After pulverization, the long-lasting stable silica powder for the two-component epoxy system is obtained.

[0048] The present invention will be further described below through specific embodiments.

[0049] Example 1 A long-lasting stable silica for use in two-component epoxy systems, the preparation method of which includes the following steps: (1) Surface treatment: Weigh 100g of material with a specific surface area of ​​200m² 2 / g of fumed silica powder was added to a reaction vessel containing 2000g of toluene solvent and stirred to disperse it evenly. Under nitrogen protection, 15g of triethoxysilane was added, the temperature was raised to 90℃, and the reaction was stirred at a constant temperature for 4h to obtain a suspension of hydrogen-silicon modified silica.

[0050] (2) Grafted polysiloxane: Add 45g of vinyl-terminated polydimethylsiloxane (double-terminated vinyl) with a number average molecular weight of 1000g / mol to the suspension obtained in step (1), and add Karstedt platinum catalyst (the amount of platinum added is 50ppm of the total mass of the above materials); under nitrogen protection, adjust the temperature to 70℃ and carry out hydrosilylation addition reaction for 5h with constant temperature stirring to obtain a suspension containing intermediates.

[0051] (3) End-capping grafting of long-chain alkyl groups: 20g of hexadecyl dimethylhydrosilane was added to the suspension obtained in step (2). Under nitrogen protection, the temperature was adjusted to 70℃ and the mixture was stirred at a constant temperature for 5h to carry out a secondary hydrosilylation addition reaction. After the reaction was completed, the resulting suspension was centrifuged and filtered, and the filter cake was washed three times alternately with an appropriate amount of toluene and anhydrous ethanol to remove unreacted free matter. Finally, the filter cake was placed in a vacuum drying oven at 120℃ (vacuum degree <0.01MPa) and dried for 6h. After pulverization, the long-term stable silica was obtained. Its microscopic photograph is shown below. Figure 1 As shown, the infrared spectrum is as follows Figure 2 As shown, the contact angle experimental data are as follows: Figure 3 As shown.

[0052] Example 2 A method for preparing long-lasting stable silica for two-component epoxy systems, comprising the following steps: (1) In a reactor equipped with a mechanical stirrer, thermometer and reflux condenser, add 100g of fumed silica powder (specific surface area of ​​50m²) 2 Add 1000g of toluene solvent and stir to disperse evenly. Then add 5g of triethoxysilane, purge the air in the reactor with nitrogen and maintain nitrogen protection, raise the temperature to 120℃, and stir the reaction at a constant temperature for 2h to obtain a suspension of hydrogen-silicon modified silica.

[0053] (2) Maintaining nitrogen protection, add 30g of vinyl-terminated polydimethylsiloxane (number average molecular weight Mn of 500g / mol) to the suspension obtained in step (1) above, and add Karstedt platinum catalyst (the amount added is 30ppm of the total mass of the powder, triethoxysilane, toluene and polydimethylsiloxane, based on the mass of platinum element). Heat the system to 60℃ and carry out the hydrosilylation addition reaction at a constant temperature for 12h to obtain a suspension containing the intermediate.

[0054] (3) Add 10g of hexadecyl dimethylhydrosilane to the suspension containing the intermediate obtained in step (2) above, keep the nitrogen protection, and carry out the hydrosilylation addition reaction at 60°C for 8h.

[0055] After the reaction was complete, the system was cooled to room temperature, filtered, and the filter cake was washed three times with a mixed solvent of anhydrous ethanol and toluene to remove unreacted free components. Finally, the washed product was dried to constant weight in a vacuum drying oven at 100°C, and then pulverized to obtain long-lasting stable silica.

[0056] Example 3 A method for preparing long-lasting stable silica for two-component epoxy systems, comprising the following steps: (1) Add 100g of fumed silica powder (specific surface area of ​​380m²) to the reactor. 2 The mixture was stirred and dispersed with 3000g of toluene solvent, and then 25g of triethoxysilane was added. Under nitrogen protection, the temperature was raised to 120℃ and stirred for 2 hours to obtain a suspension of hydrogen-silicon modified silica.

[0057] (2) Maintaining nitrogen protection, add 60g of vinyl-terminated polydimethylsiloxane (number-average molecular weight Mn of 1500g / mol) to the suspension obtained in step (1), and add chloroplatinic acid-isopropanol solution (the amount added is 100ppm of the total mass of the above materials, calculated as platinum). Heat the system to 80℃ and react at a constant temperature for 4h to obtain a suspension containing the intermediate.

[0058] (3) Add 30g of hexadecyl dimethylhydrosilane to the obtained suspension containing the intermediate and continue the reaction at 80°C for 2h.

[0059] After the reaction was completed, the mixture was cooled and filtered. The filter cake was washed multiple times with toluene and then vacuum dried at 120°C to constant weight. After pulverization, long-lasting stable silica was obtained.

[0060] Comparative Example 1 This comparative example aims to verify the role of long-chain alkyl groups. The specific steps are as follows: (1) The steps are exactly the same as in Example 1 (1), and a suspension of hydrogen-silicon modified silica is obtained.

[0061] (2) The same as step (2) in Example 1 was performed, with the addition of vinyl-terminated polydimethylsiloxane and platinum catalyst to carry out a hydrosilylation addition reaction. After the reaction was completed, the resulting suspension was centrifuged and filtered, and the filter cake was washed repeatedly with large amounts of toluene and anhydrous ethanol. Then it was placed in a vacuum drying oven to dry thoroughly to completely remove residual platinum catalyst and unreacted free matter, and intermediate powder was obtained.

[0062] (3) The dried intermediate powder was redispersed in 1500g of toluene, and 20g of hexadecyl dimethylhydrosilane was added without adding platinum catalyst. The mixture was stirred at 70°C for 5h under nitrogen protection.

[0063] After the reaction was completed, the resulting suspension was centrifuged and filtered, dried in a vacuum drying oven at 120°C for 6 hours, and then pulverized to obtain comparative silica.

[0064] Comparative Example 2 This comparative example aims to verify the role of PDMS as a spatial steric hindrance layer. The specific steps are as follows: (1) The steps are exactly the same as in Example 1 (1), and a suspension of hydrogen-silicon modified silica is obtained.

[0065] (2) Add 20g of 1-hexadecene (to provide double bonds for addition to the underlying Si-H) and castor platinum catalyst (the amount of platinum added is 50ppm of the total mass of the above materials) to the suspension obtained in step (1), and react at a constant temperature of 70℃ for 5h. After the reaction is completed, the suspension is centrifuged and filtered, washed repeatedly with toluene and anhydrous ethanol, and thoroughly dried under vacuum to remove residual platinum catalyst, and intermediate powder is obtained.

[0066] (3) The dried intermediate powder was redispersed in 1500g of toluene, and 45g of vinyl-terminated polydimethylsiloxane with a number average molecular weight of 1000g / mol was added. No platinum catalyst was added, and the mixture was stirred at 70°C for 5h.

[0067] After the reaction was completed, the suspension was centrifuged, filtered, and vacuum dried to obtain comparative silica.

[0068] Comparative Example 3 This comparative example aims to provide a basic modification control, retaining only step (1), the specific steps of which are as follows: (1) Add 100g of fumed silica powder (specific surface area of ​​200m² / g), 2000g of toluene solvent and 15g of triethoxysilane to the reactor. Under nitrogen protection, heat to 90℃ and react for 4h.

[0069] After the reaction was completed, no further grafting was performed. The system was directly cooled to room temperature, filtered, the filter cake was washed repeatedly with toluene, and then vacuum dried at 100°C to constant weight. After pulverization, the control silica powder was obtained.

[0070] This experiment will comprehensively evaluate the superior performance of the long-lasting stable silica of this invention by performing physicochemical characterization of the prepared samples, rheological property testing in a two-component epoxy system, and long-term storage stability testing.

[0071] 1. Physicochemical characterization Carbon content: The carbon content in the silica sample, i.e. the amount of organic modifier grafted, was determined using an infrared high-frequency sulfur and carbon analyzer to assess the modification efficiency.

[0072] Contact angle measurement: Using a contact angle meter and the seated drop method with deionized water as the probe solution, the static contact angle of the silica powder tablet surface was measured. Five points were measured for each sample, and the average value was taken to evaluate the surface hydrophobicity. The higher the hydrophilicity, the smaller the contact angle.

[0073] 2. Rheological properties Epoxy system formulation: Use general-purpose bisphenol A type epoxy resin (model E51) with an epoxy equivalent of 185 g / eq and polyamide curing agent with an amine equivalent of 65 g / eq.

[0074] Silica addition: The silica samples prepared in Examples 1-3 and Comparative Examples 1-3 were added to epoxy resin (component A) containing fillers (talc, calcium carbonate) at a dosage of 3.0% (mass percentage). The silica was dispersed for 15 minutes using a high-speed disperser (2500 rpm) to ensure uniform dispersion, followed by vacuum degassing for 10 minutes.

[0075] Rheological performance testing: The tests were conducted using a rotational rheometer under constant temperature conditions of 25°C.

[0076] Initial viscosity: Using steady-state shear mode, at a shear rate of 10 r / min (approximately 0.95 s). -1 The viscosity of the system was measured under these conditions.

[0077] Thixotropic index: Measured at a shear rate of 100 r / min (approximately 9.5 s). -1 ) and 10 r / min (approximately 0.95 s)-1 The viscosity at TI is the ratio of the two values. The higher the TI value, the better the thixotropy of the system.

[0078] Shear thinning behavior: within a shear rate range of 0.1 s⁻¹ -1 up to 100s -1 Logarithmic scanning was performed to record the viscosity change curve with shear rate, and the shear-thinning properties of the system were evaluated.

[0079] Yield stress: Using steady-state shear mode, gradually increasing shear stress is applied until the system begins to flow, and the yield stress value at this point is recorded.

[0080] 3. Long-term storage stability Sample preparation: The prepared epoxy resin component A (without curing agent) containing silica was dispensed into transparent wide-mouth glass bottles with an inner diameter of 20 mm and a height of 100 mm, with approximately 50 g of sample in each bottle. The sample surface was ensured to be flat, and the bottles were sealed tightly. All samples were stored at 25°C in the dark.

[0081] Visual inspection: On days 0, 30, 90 and 180 of storage, visually inspect the sample vials for any sedimentation, clumping, stratification or oil separation.

[0082] Rheological properties were measured periodically: at the above storage time points (day 0, day 30, day 90 and day 180), the corresponding sample bottles were taken out and the initial viscosity and thixotropic index were measured again.

[0083] Key indicators: Calculate viscosity retention rate (%) and thixotropic index retention rate (%) based on measurement results, and combine with visual observation to comprehensively evaluate its long-term storage stability.

[0084] Viscosity retention rate = (viscosity at time T / viscosity at time 0) × 100%; TI retention rate = (TI at time T / TI at time 0) × 100%.

[0085] Table 1 Physicochemical characterization data Examples 1-3: The carbon content results show that the silica samples prepared in the examples of this invention have a significant amount of organic grafting, indicating that PDMS and hexadecyl groups were successfully grafted onto the silica surface. Their contact angles are all much greater than 125°, reaching a maximum of 135.0°, exhibiting strong hydrophobic properties, verifying that the modifier effectively imparts extremely strong hydrophobicity to the silica surface.

[0086] Comparative Example 1: The amount of organic grafting and the initial contact angle were both high, which is consistent with the expectation that PDMS has been chemically grafted. However, its contact angle was slightly lower than that of the Example, which may indicate that the physically adsorbed C16 was initially present but not as neatly arranged as the chemical bonds, or that some of it was removed by subsequent washing.

[0087] Comparative Example 2: The amount of organic grafting and the initial contact angle were also high, which is consistent with the expectations of C16 chemical grafting and the initial presence of physically adsorbed PDMS. However, the contact angle was slightly lower than in the Example, which may suggest that the physically adsorbed PDMS was not ideally arranged.

[0088] Comparative Example 3: The amount of organic grafting was the lowest, only 1.1%, with a contact angle of 95.3°, which is at the hydrophilic or ordinary hydrophobic level. This confirms that Si-H modification alone failed to introduce macromolecular chains with strong hydrophobic effects.

[0089] Table 2 Rheological performance test data (3.0% addition amount) Examples 1-3: The product exhibits a significant thickening effect in epoxy resin, with an initial viscosity much higher than that of epoxy resin component A without silica. Simultaneously, it displays high yield stress, a large thixotropic index (both greater than 4.5), and a steep shear-thinning curve, indicating that the product can form a stable three-dimensional network structure in a static state, effectively preventing sagging and settling. Under shear stress (such as during application), it can rapidly reduce viscosity, demonstrating excellent workability.

[0090] Comparative Example 1: The initial viscosity, yield stress, and thixotropic index showed good performance, similar to those of the Examples. This is consistent with the expectation that PDMS chemical grafting can provide good initial rheological properties. However, the slight difference from the Examples may suggest insufficient initial contribution from physically adsorbed C16, or partial detachment during sample preparation (e.g., dispersion).

[0091] Comparative Example 2: The initial viscosity, yield stress, and thixotropic index also showed good performance, similar to those of the Example. This is consistent with the expectation that C16 chemical grafting provides good dispersibility, and that physically adsorbed PDMS can also provide some steric hindrance in the initial stage.

[0092] Comparative Example 3: It only provides a weak thickening effect, has low yield stress, a thixotropic index close to that of pure resin, and shows little shear thinning. This indicates that Si-H modification alone cannot construct an effective rheological network in an epoxy system.

[0093] Table 3 Long-term storage stability test data Examples 1-3: After 180 days of long-term storage, the epoxy system of the product of this invention maintained a viscosity retention rate and thixotropic index retention rate of over 97%. More importantly, no sedimentation, clumping, or stratification was observed in the sample vials by the naked eye, and the system remained uniform and stable throughout. This fully demonstrates that the long-lasting stable silica prepared by this invention can effectively resist the erosion and swelling effects of complex components in the epoxy system on the surface, thus providing excellent long-term storage stability and solving the core technical problem of viscosity reduction and sedimentation of traditional rheology modifiers in two-component systems.

[0094] Comparative Example 1: Although Comparative Example 1 exhibited good initial rheological properties, after 180 days of storage, both viscosity retention and TI retention decreased significantly (to 60% and 52.1%, respectively), and obvious sedimentation and stratification were observed. This strongly demonstrates that even if PDMS chemical grafting provides initial stability, if the long-chain alkyl group (C16) fails to be chemically anchored, the physically adsorbed C16 will gradually detach or become ineffective during long-term storage, failing to provide durable anchoring and stabilization, resulting in poor long-term stability of the system.

[0095] Comparative Example 2: Storage stability was even worse, with a significant decrease in viscosity retention and TI retention (to 44.4% and 41.9%, respectively). Obvious sedimentation was observed, with soft nodules forming at the bottom. This confirms that even though C16 chemical grafting provides good initial compatibility, if PDMS acts as a steric hindrance layer and is only physically adsorbed, PDMS will desorb during long-term storage, losing its steric hindrance effect, leading to particle re-aggregation and sedimentation, resulting in extremely poor system stability.

[0096] Comparative Example 3: The sample exhibited the worst stability, with a viscosity retention rate of only 61.5% and a TI retention rate of less than 70%. Severe sedimentation occurred, forming a dense deposit layer at the bottom, severely disrupting the system's homogeneity. This indicates that Si-H modification alone cannot provide sufficient interfacial compatibility and steric hindrance, and therefore cannot effectively maintain the long-term dispersion stability of silica in the epoxy system.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing long-lasting stable silica for two-component epoxy systems, characterized in that, Includes the following steps: (1) In toluene solvent, fumed silica powder is surface treated with triethoxysilane to obtain a suspension of hydrogen-silicon modified silica. (2) Add platinum catalyst and vinyl-terminated polydimethylsiloxane to the suspension of hydrogen-silicon modified silica obtained in step (1) to carry out hydrosilylation addition reaction to obtain a suspension containing intermediate; (3) Add hexadecyl dimethylhydrosilane to the suspension containing the intermediate obtained in step (2) to carry out hydrosilylation addition reaction. After the reaction is completed, filter, wash and vacuum dry in sequence to obtain the long-lasting stable silica for the two-component epoxy system.

2. The method according to claim 1, characterized in that, In step (1), the specific surface area of ​​the fumed silica powder is 50~400m². 2 / g.

3. The method according to claim 1, characterized in that, Based on 100 parts of fumed silica powder in step (1), the amount of toluene solvent is 1000~3000 parts, and the amount of triethoxysilane is 5~25 parts; the surface treatment conditions are: under nitrogen protection, the reaction is carried out at 60~120℃ for 2~6 hours.

4. The method according to claim 1, characterized in that, In step (2), the number average molecular weight Mn of the vinyl-terminated polydimethylsiloxane is 500~2000 g / mol.

5. The method according to claim 1, characterized in that, Based on 100 parts of the mass of fumed silica powder in step (1), the amount of vinyl-terminated polydimethylsiloxane is 30-60 parts; the amount of platinum catalyst is 20-100 ppm of the total mass of fumed silica powder, triethoxysilane, toluene solvent and vinyl-terminated polydimethylsiloxane, based on the mass of platinum element.

6. The method according to claim 1, characterized in that, In step (2), the hydrosilylation addition reaction is carried out at a temperature of 60~80℃ for 4~12h under nitrogen or argon protection.

7. The method according to claim 1, characterized in that, Based on 100 parts of fumed silica powder in step (1), the amount of hexadecyl dimethylhydrosilane used is 10 to 30 parts.

8. The method according to claim 1, characterized in that, In step (3), the hydrosilylation addition reaction is carried out at a temperature of 60~80℃ for 2~8h, and the reaction is carried out under nitrogen or argon protection.

9. A long-lasting stable silica for use in two-component epoxy systems, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The use of the long-lasting stable silica for two-component epoxy systems according to claim 9 in paints, coatings, adhesives, sealants or resins.

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