Low-cobalt-salt adhesion promoter and preparation method thereof

Abstract

The invention relates to a low-cobalt-salt adhesion promoter and a preparation method thereof, and relates to the technical field of rubber adhesives, the low-cobalt-salt adhesion promoter is of a core-shell structure and comprises, by mass, 10-15 parts of core metal precursor powder, 15-20 parts of a shell SiO2 shell layer and 5-8 parts of long-chain alkylsilane grafted to the surface of the SiO2 shell layer; the metal precursor powder comprises cobalt hydroxide, manganese hydroxide and ferric hydroxide, and the molar ratio of the cobalt hydroxide to the manganese hydroxide to the ferric hydroxide is 1: (2-3): (1-1.5). According to the invention, the dispersibility of the low-cobalt salt adhesion promoter and the compatibility with rubber can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rubber adhesives, and particularly to a low-cobalt salt adhesion promoter, a preparation method thereof and an application thereof. Background Art

[0002] Cobalt salt adhesion promoters are direct-added adhesives for high-strength adhesion between rubber and metal, and are mainly used in rubber product industries such as steel radial tires, steel cord conveyor belts, steel braided rubber hoses and rubber rollers.

[0003] At present, both domestic and foreign-produced organic cobalt salt adhesion promoters are products obtained by reacting cobalt with different organic acids, belonging to organic acid cobalt mixtures. The cobalt content varies according to the product standards of different grades. However, when designing the formula of rubber products, the usage amounts of different organic cobalt salt adhesion promoters are calculated based on the cobalt content, that is, the amount of pure cobalt in every 100 parts of rubber. Because the principle of action of organic cobalt salt adhesion promoters during application is: the organic cobalt salt adhesion promoter is added during the rubber mixing process and evenly dispersed throughout the system. At this time, it is only physically dispersed. When the raw rubber is vulcanized, the organic cobalt salt adhesion promoter undergoes a displacement reaction with the coating surface on the metal surface at a certain temperature to generate free radical cobalt ions. The cobalt ions catalyze the formation of stable chemical bonds between the rubber, the metal and sulfur, achieving strong adhesion between the rubber and the metal, not only ensuring the high-speed driving performance of the tire, but also extending the service life of the tire.

[0004] The Chinese patent application with the publication number CN101481591A discloses a preparation method of an organic cobalt salt adhesion promoter. The method is to respectively prepare cobalt solutions, sodium hydroxide solutions and sodium carbonate solutions with certain concentrations; after heating the cobalt solution, slowly add the sodium hydroxide solution until the pH value of the reaction solution is 7, and then slowly add the sodium carbonate solution until the pH value of the reaction solution is 9.5; let the reaction solution stand, take the precipitate and rinse it with water; dehydrate the rinsed inorganic cobalt salt twice, and then react it with a weak organic acid in an organic solvent to obtain an organic cobalt salt adhesion promoter product.

[0005] This preparation method produces cobalt basic carbonate powder with high activity, which not only meets the requirements in terms of appearance, cobalt content, moisture content, trivalent cobalt content, impurity content, particle size, bulk density, etc., but more importantly, has good reaction activity. Then, through a neutralization reaction with a weak organic acid, a high-quality organic cobalt salt adhesion promoter product is obtained. However, cobalt in the organic cobalt salt adhesion promoter is a non-ferrous metal and a small variety among non-ferrous metals. The domestic cobalt production from raw ore is less than a thousand tons, and most of it relies on imported cobalt ore from abroad. Therefore, the price of cobalt has always been at a high level, and its cost accounts for 80% of the total raw material price in the cobalt salt adhesion promoter product. With the increasingly fierce market competition, the consumption of cobalt salt adhesion promoter will increase geometrically, but the price will not increase proportionally. Therefore, it is extremely necessary to research and develop new cobalt-free raw materials or new processes.

[0006] The Chinese invention patent application with the publication number CN103265726A discloses a preparation method of a high-performance and low-cobalt-content solid cobalt naphthenate adhesion promoter. Prepare a cobalt solution and a sodium hydroxide solution; add water to the reaction kettle, then add concentrated ammonia water to make the pH value of the water reach 9.5, then add an antioxidant, start stirring, and add the cobalt solution and the sodium hydroxide solution into the above reaction kettle simultaneously. Appropriately adjust the feeding flow rate according to the change of the pH meter to keep the pH value at 9.2 - 9.5 all the time; pump the reaction solution into a filter press for washing until the pH value of the washing liquid reaches 7; dehydrate the inorganic cobalt salt twice and then carry out a metathesis reaction with a weak organic acid in butyl acetate, and then distill out all the butyl acetate; then add hexamethylene-1,6-bis(thiosulfate) dihydrate and a high-performance rubber dispersant, and granulate after uniform dispersion to obtain a high-performance and low-cobalt-content solid cobalt naphthenate adhesion promoter.

[0007] In addition to the performance that the original cobalt salt adhesion promoter series products should have, the high-performance and low-content solid cobalt naphthenate adhesion promoter prepared by this preparation method has the outstanding advantage that while greatly reducing the cobalt consumption, it can still make the adhesion and corrosion resistance between rubber and metal better. Especially under different aging conditions (such as NaCl and FeCl3 salt aging, steam aging, aerobic and anaerobic aging), the retention rate of most physical properties is better than that of using pure cobalt salt adhesion promoter. However, the surface polarity of the low-cobalt salt adhesion promoter is relatively high, and its compatibility with non-polar rubbers (such as natural rubber NR and styrene-butadiene rubber SBR) is poor, and it is easy to aggregate in the matrix. It needs to rely on high-performance dispersants or high-shear mixing processes, which increases the processing complexity, and uneven dispersion is likely to cause local stress concentration, thereby affecting the adhesion performance. Summary of the Invention

[0008] To solve the problems of poor dispersibility and compatibility of low-cobalt salt adhesion promoters, the present invention provides a low-cobalt salt adhesion promoter and its preparation method, which can effectively improve the dispersibility of the low-cobalt salt adhesion promoter and its compatibility with rubber.

[0009] In the first aspect, a low-cobalt salt adhesion promoter provided by the present invention has a core-shell structure by mass fraction, including: 10-15 parts of core metal precursor powder, 15-20 parts of outer shell SiO2 layer, and 5-8 parts of long-chain alkyl silane grafted onto the surface of the SiO2 layer; The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2-3:1-1.5.

[0010] In the above technical solution, Co in the core metal precursor powder 2+ reacts with sulfur (S8) in the rubber to form Co-S bonds, and coordinates with oxygen atoms of metal surface oxides (such as Fe3O4) to form stable Co-O bonds, accelerating the sulfur crosslinking reaction and enhancing the interfacial bonding between rubber and metal. Mn 2+ has a higher oxidation potential than cobalt ions and is preferentially oxidized to Mn 3+ during the high-temperature vulcanization process, consuming oxygen free radicals in the environment and delaying the oxidation of Co 2+ to inert Co 3+ and deactivation, maintaining the stability of the active center. Fe 3+ can replace part of Co 2+ , reducing the raw material cost, and at the same time can form secondary bonding with polar groups (such as carboxyl groups) in the rubber.

[0011] The outer shell SiO2 layer prevents direct contact between metal particles through steric hindrance effects, avoiding agglomeration caused by van der Waals forces during high-temperature mixing or vulcanization. The hydroxyl groups (-OH) on the surface of the SiO2 layer ionize in water to generate negative charges, maintaining the dispersion stability of nanoparticles through electrostatic repulsion. The SiO2 layer can also block direct contact between oxygen and the metal precursor powder, inhibiting the oxidation of Co 2+ to inert Co 3+ . The polarity of the SiO2 layer itself is between that of the highly polar metal precursor powder and the non-polar rubber, forming a polar transition layer and reducing the interfacial tension. At the same time, Fe 3+ forms Fe-O-Si bonds with oxygen in the SiO2 layer, enhancing the thermal stability of the core-shell structure.

[0012] Through the entanglement of the hydrophobic long-chain alkyl groups in the long-chain alkyl silane with the carbon chains of rubber molecules (such as natural rubber NR and styrene-butadiene rubber SBR), the interfacial polarity difference is reduced, and the compatibility between the adhesion enhancer and the rubber is improved.

[0013] Optionally, by mass fraction, the low-cobalt salt adhesion promoter further comprises 1-3 parts of bis-(γ-triethoxysilylpropyl)tetrasulfide grafted onto the surface of the SiO2 shell.

[0014] In the above technical solution, the tetrasulfide bond (-S4-) in bis-(γ-triethoxysilylpropyl)tetrasulfide crosslinks with the rubber vulcanization system to form a covalent bond connection. The ethoxy group (-Si-O-C2H5) at the end of the silane hydrolyzes into a silanol group (-Si-OH) in the presence of trace water and condenses with the hydroxyl group of the SiO2 shell to form a stable Si-O-Si bond, strengthening the interfacial bonding and enhancing the compatibility between the adhesion promoter and the rubber.

[0015] Optionally, by mass fraction, the low-cobalt salt adhesion promoter further comprises 0.5-1 part of an initiator, and the initiator is any one of benzoyl peroxide, dibenzoyl peroxide, and azobisisobutyronitrile.

[0016] In the above technical solution, the free radical in the initiator can cause the cleavage of the tetrasulfide bond in bis-(γ-triethoxysilylpropyl)tetrasulfide, promoting its homolytic cleavage to generate sulfur free radicals (·S-S·). The sulfur free radicals can react with the C=C double bond in the rubber molecular chain to form a covalent bond and embed into the rubber matrix.

[0017] Optionally, the long-chain alkyl silane includes any one of octadecyltrimethoxysilane and octadecyltrichlorosilane.

[0018] In the above technical solution, the outer surface of the SiO2 shell is modified to be low-polar by grafting a C18 alkyl chain. The C18 alkyl chain, as a flexible carbon chain, forms a physical entanglement with the rubber molecular chain through van der Waals forces. The siloxy group at the end of the alkyl chain is grafted onto the surface of the SiO2 shell through a chemical bond, which can enhance the compatibility between the adhesion promoter and the rubber by reducing the interfacial polarity difference.

[0019] In the second aspect, a preparation method of a low-cobalt salt adhesion promoter provided by the present invention includes the following steps: Preparation of metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5-1 mol / L. Pour the mixed solution into a NaOH solution with a concentration of 2-3 mol / L. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2-3:1-1.5:10-14. Stir at 50-60 °C, pH 9.5-10, and a rate of 500-600 rpm for 2-3 h, centrifuge to obtain a precipitate, wash it with deionized water until neutral, and dry it at 60-65 °C for 11-13 h to obtain the metal precursor powder; SiO2 shell coating: Disperse the metal precursor powder in a mixed solution of absolute ethanol and water with a volume ratio of 4 - 5:1, and ultrasonically treat it for 30 - 40 min until uniformly dispersed. Add sodium hydroxide solution to the mixed solution. Under the conditions of pH 9 - 10 and a stirring speed of 500 - 600 rpm, slowly add tetraethyl orthosilicate to the suspension, and then add ammonia water. The molar ratio of tetraethyl orthosilicate to ammonia water is 30 - 40:1. Stir at 40 - 50 °C for 5 - 7 h, centrifuge to obtain a precipitate, wash it with ethanol 2 - 3 times, and vacuum dry at 55 - 65 °C to obtain core - shell particles coated with SiO2; Graft modification on the surface of the SiO2 shell: Disperse the core - shell particles coated with SiO2 in a toluene solution with a concentration of 10 - 15 wt%, add long - chain alkyl silane, introduce nitrogen protection, reflux and react at 80 - 90 °C for 8 - 9 h, wash it with toluene 3 - 4 times, and vacuum dry at 60 - 70 °C to obtain a low - cobalt - salt adhesion promoter.

[0020] In the above technical solution, under alkaline conditions, the ethoxy group (-OC2H5) in tetraethyl orthosilicate is replaced by a hydroxyl group (-OH) to form silicic acid (Si(OH)4). The surface of the metal precursor powder is rich in hydroxyl groups (-OH), and the hydroxyl groups of the metal precursor powder and silicic acid form M - O - Si bonds (M is a metal) through hydrogen bonds or dehydration. The M - O - Si bond can ensure that the SiO2 shell is tightly anchored on the metal surface. At the same time, the alkaline condition with a pH of 9 - 10 can promote the deprotonation of the hydroxyl groups on the metal surface (-O - ), enhancing the electrostatic attraction with Si(OH)4 and enabling it to preferentially deposit on the surface of metal particles. Silicic acid molecules form Si - O - Si bonds through a condensation reaction, and this process continues on the metal surface, finally forming an amorphous SiO2 shell. In this way, tetraethyl orthosilicate and ammonia water form an SiO2 shell on the surface of the metal precursor powder through a sol - gel reaction.

[0021] Long - chain alkyl silane (such as C 18 H 37 -Si(OCH3)3) hydrolyzes in a trace - water or humid environment, and the methoxy group (-OCH3) hydrolyzes to form silanol groups (-Si - OH) and methanol (CH3OH). The silanol groups (-Si - OH) generated by hydrolysis undergo dehydration condensation with the hydroxyl groups on the surface of the SiO2 shell to form stable Si - O - Si bonds, grafting the silane onto the SiO2 surface.

[0022] Optionally, in the graft modification step on the surface of the SiO2 shell, after reflux reaction at 80 - 90 °C for 8 - 9 h, the product is centrifuged to obtain a precipitate, and then the precipitate is dispersed in a toluene solution with a concentration of 5 - 10 wt%. Bis-(γ-triethoxysilylpropyl)tetrasulfide is added, and the reaction is carried out at 65 - 75 °C under nitrogen protection for 6 - 7 h. Ice ethanol is added to terminate the reaction, and the precipitate is centrifuged again. When washing the precipitate, it is washed with toluene 3 - 4 times, and then washed with ethanol 2 - 3 times each, and vacuum dried at 40 - 50 °C.

[0023] In the above technical solution, bis-(γ-triethoxysilylpropyl)tetrasulfide is added. The tetrasulfide bond (-S4-) in bis-(γ-triethoxysilylpropyl)tetrasulfide crosslinks with the rubber vulcanization system to form a covalent bond connection. The ethoxy group (-Si-O-C2H5) at the end of the silane hydrolyzes into a silanol group (-Si-OH) in the presence of trace water, and condenses with the hydroxyl group on the metal surface or the SiO2 shell to form a stable Si-O-Si bond, strengthening the interfacial bonding. One end of the grafted bis-(γ-triethoxysilylpropyl)tetrasulfide molecule is fixed on the surface of the SiO2 shell through the Si-O-Si bond, and the other end is embedded in the rubber matrix through a covalent bond, forming a stable chemical bridge, improving the compatibility between the adhesion enhancer and the rubber.

[0024] Optionally, in the graft modification step on the surface of the SiO2 shell, an initiator is added simultaneously with bis-(γ-triethoxysilylpropyl)tetrasulfide.

[0025] In the above technical solution, the free radicals in the initiator can cause the cleavage of the tetrasulfide bond in bis-(γ-triethoxysilylpropyl)tetrasulfide. For example, azobisisobutyronitrile decomposes at 60 - 80 °C to generate isobutyronitrile radicals (·C(CH3)CN) and nitrogen, promoting its homolytic cleavage to generate sulfur radicals (·S-S·). The sulfur radicals can react with the C=C double bond in the rubber molecular chain to form a covalent bond and be embedded in the rubber matrix.

[0026] In the third aspect, the present invention provides an application of a low-cobalt salt adhesion promoter and a low-cobalt salt adhesion promoter prepared by the preparation method of the low-cobalt salt adhesion promoter in the manufacture of steel radial tires, steel wire reinforced conveyor belts, steel braided rubber hoses, and rubber rollers.

[0027] In summary, the present invention includes at least one of the following beneficial technical effects: Co in the metal precursor powder 2+ reacts with sulfur (S8) in the rubber to form Co-S bonds, undergoes a coordination reaction with oxygen atoms of the metal surface oxide (such as Fe3O4) to form stable Co-O bonds, accelerates the sulfur crosslinking reaction, and enhances the interfacial bonding between the rubber and the metal. Mn2+ has a higher oxidation potential than cobalt ions and is preferentially oxidized to Mn oxide during high-temperature vulcanization 3+ , consuming oxygen free radicals in the environment and delaying the oxidation of Co 2+ to inert Co 3+ from being deactivated by oxidation and maintaining the stability of the active center. Fe 3+ can replace part of Co 2+ , reducing the raw material cost. At the same time, it can form secondary bonds with polar groups (such as carboxyl groups) in the rubber.

[0028] Tetraethyl orthosilicate and ammonia form a SiO2 shell on the surface of the metal precursor powder through a sol-gel reaction. The steric hindrance effect prevents direct contact between metal particles, avoiding agglomeration caused by van der Waals forces during high-temperature mixing or vulcanization. The hydroxyl groups (-OH) on the surface of SiO2 ionize in water to generate negative charges, maintaining the dispersion stability of nanoparticles through electrostatic repulsion. The formed SiO2 shell can also block the direct contact between oxygen and the metal precursor powder, inhibiting the oxidation of Co 2+ to inert Co 3+ . The polarity of the formed SiO2 shell itself is between that of the highly polar metal precursor powder and the non-polar rubber, forming a polar transition layer, reducing the interfacial tension. At the same time, Fe 3+ forms Fe-O-Si bonds with oxygen in the SiO2 shell, enhancing the thermal stability of the core-shell structure.

[0029] By adding long-chain alkyl silanes, the hydrophobicity of the long-chain alkyls is intertwined with the carbon chains of rubber molecules (such as natural rubber NR and styrene-butadiene rubber SBR), reducing the interfacial polarity difference and improving the compatibility between the adhesion enhancer and the rubber. Specific Embodiments

[0030] The present invention will be further described in detail below with reference to the embodiments.

[0031] The materials used in the following embodiments can all be obtained by purchasing in the market.

[0032] Example 1: This example discloses a low-cobalt salt adhesion promoter #1 and its preparation method.

[0033] By mass, the low-cobalt salt adhesion promoter includes: 10 parts of metal precursor powder, 15 parts of SiO2 shell, and 5 parts of long-chain alkyl silane grafted onto the surface of the SiO2 shell.

[0034] The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2:1.

[0035] In this embodiment, the long-chain alkylsilane is selected as octadecyltrimethoxysilane. In other embodiments, octadecyltrichlorosilane can also be selected.

[0036] The preparation method of the low-cobalt salt adhesion promoter #1 includes the following steps: S1. Preparation of metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5 mol / L. Pour the mixed solution into a 2 mol / L NaOH solution. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2:1:10. Stir at 50 °C, pH 9.5, and a rate of 500 rpm for 2 h, then centrifuge to obtain a precipitate. Wash the precipitate with deionized water until it is neutral, and dry it at 60 °C for 12 h to obtain the metal precursor powder. S2. SiO2 shell coating: Disperse the metal precursor powder in a mixed solution with a volume ratio of anhydrous ethanol to water of 4:1, and perform ultrasonic treatment for 30 min until it is uniformly dispersed. Add a sodium hydroxide solution to the mixed solution. Slowly add tetraethyl orthosilicate to the suspension under the conditions of pH 9.5 and a stirring speed of 500 rpm, and then add ammonia water. The molar ratio of tetraethyl orthosilicate to ammonia water is 35:1. Stir at 45 °C for 6 h, centrifuge to obtain a precipitate, wash the precipitate with ethanol three times, and dry it in vacuum at 60 °C to obtain core-shell particles coated with SiO2. S3. Graft modification on the surface of the SiO2 shell: Disperse the core-shell particles coated with SiO2 in a 10 wt% toluene solution, add long-chain alkylsilane, and introduce nitrogen for protection. Carry out reflux reaction at 80 °C for 8 h, wash with toluene three times, and dry in vacuum at 60 °C to obtain the low-cobalt salt adhesion promoter #1.

[0037] Example 2: This example discloses a low-cobalt salt adhesion promoter #2 and its preparation method.

[0038] By mass, the low-cobalt salt adhesion promoter includes: 15 parts of metal precursor powder, 20 parts of SiO2 shell, and 8 parts of octadecyltrichlorosilane grafted onto the surface of the SiO2 shell. The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide. The molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:3:1.5.

[0039] In the preparation method of the low-cobalt salt adhesion promoter #2, except that the feeding ratio of each material is adjusted correspondingly according to the ratio of the product of this example, other preparation methods are the same as those in Example 1.

[0040] Example 3: This example discloses a low-cobalt salt adhesion promoter #3 and its preparation method.

[0041] By mass fraction, the low-cobalt salt adhesion promoter includes: 13 parts of metal precursor powder, 18 parts of SiO2 shell, and 6 parts of octadecyltrimethoxysilane grafted onto the surface of the SiO2 shell.

[0042] The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2.5:1.2.

[0043] In the preparation method of the low-cobalt salt adhesion promoter #3, except that the feeding ratio of each material is adjusted correspondingly according to the ratio of the product of this embodiment, other preparation methods are the same as those in Example 1.

[0044] Example 4: This example discloses a low-cobalt salt adhesion promoter #4 and its preparation method.

[0045] By mass fraction, the low-cobalt salt adhesion promoter includes: 13 parts of metal precursor powder, 18 parts of SiO2 shell, 6 parts of octadecyltrimethoxysilane grafted onto the surface of the SiO2 shell, and 2 parts of bis-(γ-triethoxysilylpropyl) tetrasulfide.

[0046] The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2.5:1.2.

[0047] The preparation method of the low-cobalt salt adhesion promoter #4 includes the following steps: S1. Preparation of metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5 mol / L. Pour the mixed solution into a 2 mol / L NaOH solution. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2.5:1.2:12. Stir at 50 °C, pH 9.5, and a rate of 500 rpm for 2 h, centrifuge to obtain a precipitate, wash it with deionized water until neutral, and dry it at 60 °C for 12 h to obtain the metal precursor powder; S2. SiO2 shell coating: Disperse the metal precursor powder in a mixed solution with a volume ratio of anhydrous ethanol to water of 4:1, ultrasonically treat it for 30 min until uniformly dispersed. Add sodium hydroxide solution to the mixed solution. Slowly add tetraethyl orthosilicate to the suspension under the conditions of pH 9.5 and a stirring speed of 500 rpm, and then add ammonia water. The molar ratio of tetraethyl orthosilicate to ammonia water is 35:1. Stir at 45 °C for 6 h, centrifuge to obtain a precipitate, wash it with ethanol 3 times, and dry it in vacuum at 60 °C to obtain core-shell particles coated with SiO2; S3. Graft modification of the SiO2 shell surface: The core-shell particles coated with SiO2 are dispersed in a toluene solution with a concentration of 10 wt%, long-chain alkylsilane is added, nitrogen is introduced for protection, and the reaction is refluxed at 80 °C for 8 h. The precipitate is obtained by centrifugation. Then the precipitate is dispersed in a toluene solution with a concentration of 10 wt%, bis-(γ-triethoxysilylpropyl)tetrasulfide is added, and the reaction is carried out at 70 °C under nitrogen protection for 6 h. Ice ethanol is added to terminate the reaction, and the precipitate is taken by centrifugation. When washing the precipitate, it is washed 3 times with toluene and then 2 times with ethanol, and vacuum dried at 40 - 50 °C to obtain the low cobalt salt adhesion promoter #4.

[0048] Example 5: This example discloses a low cobalt salt adhesion promoter #5 and its preparation method.

[0049] By mass, the low cobalt salt adhesion promoter includes: 13 parts of metal precursor powder, 18 parts of SiO2 shell, 6 parts of octadecyltrimethoxysilane grafted onto the surface of the SiO2 shell, and 0.8 part of initiator.

[0050] The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2.5:1.2.

[0051] In this example, azobisisobutyronitrile is selected as the initiator. In other examples, benzoyl peroxide or dibenzoyl peroxide can also be selected as the initiator.

[0052] The preparation method of the low cobalt salt adhesion promoter #5 includes the following steps: S1. Preparation of the metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5 mol / L. Pour the mixed solution into a 2 mol / L NaOH solution. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2.5:1.2:12. Stir at 50 °C, pH 9.5, and a rate of 500 rpm for 2 h. The precipitate is obtained by centrifugation, washed with deionized water until neutral, and dried at 60 °C for 12 h to obtain the metal precursor powder. S2. SiO2 shell coating: Disperse the metal precursor powder in a mixed solution with a volume ratio of anhydrous ethanol to water of 4:1, and ultrasonically treat for 30 min until uniformly dispersed. Add sodium hydroxide solution to the mixed solution. Slowly add tetraethyl orthosilicate to the suspension under the conditions of pH 9.5 and a stirring speed of 500 rpm, and then add ammonia water. The molar ratio of tetraethyl orthosilicate to ammonia water is 35:1. Stir at 45 °C for 6 h. The precipitate is obtained by centrifugation, washed 3 times with ethanol, and vacuum dried at 60 °C to obtain the core-shell particles coated with SiO2. S3. Graft modification on the surface of the SiO2 shell: Disperse the core-shell particles coated with SiO2 in a toluene solution with a concentration of 10 wt%, add long-chain alkyl silane, introduce nitrogen for protection, reflux and react at 80 °C for 8 h, centrifuge to obtain a precipitate, then disperse the precipitate in a toluene solution with a concentration of 10 wt%, add azobisisobutyronitrile, react at 70 °C under nitrogen protection for 6 h, add ice ethanol to terminate the reaction, centrifuge to collect the precipitate, when washing the precipitate, wash it 3 times with toluene and then 2 times with ethanol, and vacuum dry at 40 - 50 °C to obtain the low-cobalt salt adhesion promoter #5.

[0053] Example 6: This example discloses a low-cobalt salt adhesion promoter #6 and its preparation method.

[0054] By mass parts, the low-cobalt salt adhesion promoter includes: 13 parts of metal precursor powder, 18 parts of SiO2 shell, 6 parts of octadecyltrimethoxysilane grafted onto the surface of the SiO2 shell, 2 parts of bis-(γ-triethoxysilylpropyl) tetrasulfide, and 0.8 part of azobisisobutyronitrile.

[0055] The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2.5:1.2.

[0056] The preparation method of the low-cobalt salt adhesion promoter #6 includes the following steps: S1. Preparation of the metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5 mol / L. Pour the mixed solution into a 2 mol / L NaOH solution. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2.5:1.2:12. Stir at 50 °C, pH 9.5, and a rate of 500 rpm for 2 h, centrifuge to obtain a precipitate, wash it with deionized water until neutral, and dry at 60 °C for 12 h to obtain the metal precursor powder; S2. SiO2 shell coating: Disperse the metal precursor powder in a mixed solution with a volume ratio of anhydrous ethanol to water of 4:1, ultrasonically treat for 30 min until uniformly dispersed, add sodium hydroxide solution to the mixed solution, slowly add tetraethyl orthosilicate to the suspension under the conditions of pH 9.5 and a stirring speed of 500 rpm, then add ammonia water. The molar ratio of tetraethyl orthosilicate to ammonia water is 35:1. Stir at 45 °C for 6 h, centrifuge to obtain a precipitate, wash it 3 times with ethanol, and vacuum dry at 60 °C to obtain the core-shell particles coated with SiO2; S3. Grafting modification on the surface of the SiO2 shell: The core-shell particles coated with SiO2 are dispersed in a toluene solution with a concentration of 10 wt%, long-chain alkyl silane is added, nitrogen is introduced for protection, and the reaction is refluxed at 80 °C for 8 h. The precipitate is obtained by centrifugation. Then the precipitate is dispersed in a toluene solution with a concentration of 10 wt%, bis-(γ-triethoxysilylpropyl) tetrasulfide and azobisisobutyronitrile are added, and the reaction is carried out at 70 °C under nitrogen protection for 6 h. Ice ethanol is added to terminate the reaction, and the precipitate is taken by centrifugation. When washing the precipitate, it is washed 3 times with toluene and then 2 times with ethanol, and vacuum dried at 40 - 50 °C to obtain the low-cobalt salt adhesion promoter #6.

[0057] Comparative Example 1: This comparative example provides a comparative low-cobalt salt adhesion promoter D1, which is the same as Example 6, except that: the metal precursor powder includes zinc hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of zinc hydroxide, manganese hydroxide, and iron hydroxide is 1:2.5:1.2.

[0058] The preparation method of the comparative low-cobalt salt adhesion promoter D1 is as follows: S1. Preparation of the metal precursor powder: Weigh zinc nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5 mol / L. Pour the mixed solution into a 2 mol / L NaOH solution. The molar ratio of zinc nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2.5:1.2:10. Stir at 50 °C, pH 9.5, and a rate of 500 rpm for 2 h. The precipitate is obtained by centrifugation, washed with deionized water until neutral, and dried at 60 °C for 12 h to obtain the metal precursor powder; S2. SiO2 shell coating: Disperse the metal precursor powder in a mixed solution of anhydrous ethanol and water with a volume ratio of 4:1, and ultrasonically treat for 30 min until evenly dispersed. Add sodium hydroxide solution to the mixed solution. Slowly add tetraethyl orthosilicate to the suspension at pH 9.5 and a stirring speed of 500 rpm, and then add ammonia water. The molar ratio of tetraethyl orthosilicate and ammonia water is 35:1. Stir at 45 °C for 6 h. The precipitate is obtained by centrifugation, washed 3 times with ethanol, and vacuum dried at 60 °C to obtain the core-shell particles coated with SiO2; S3. Graft modification on the surface of the SiO2 shell: Disperse the core-shell particles coated with SiO2 in a toluene solution with a concentration of 10 wt%, add long-chain alkylsilane, introduce nitrogen for protection, reflux and react at 80 °C for 8 h, centrifuge to obtain a precipitate, then disperse the precipitate in a toluene solution with a concentration of 10 wt%, add bis-(γ-triethoxysilylpropyl)tetrasulfide and azobisisobutyronitrile, react at 70 °C under nitrogen protection for 6 h, add ice ethanol to terminate the reaction, centrifuge to take the precipitate, when washing the precipitate, wash it 3 times with toluene, and then wash it 2 times with ethanol, dry it under vacuum at 40 - 50 °C to obtain the low-cobalt salt adhesion promoter D1.

[0059] Comparative Example 2: This comparative example provides a comparison. The preparation of the low-cobalt salt adhesion promoter D2 is the same as that in Example 6, except that: long-chain alkylsilane is missing.

[0060] The preparation method of the low-cobalt salt adhesion promoter D2 is as follows: S1. Preparation of metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5 mol / L. Pour the mixed solution into a NaOH solution with a concentration of 2 mol / L. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2.5:1.2:12. Stir at 50 °C, pH 9.5, and a rate of 500 rpm for 2 h, centrifuge to obtain a precipitate, wash it with deionized water until neutral, and dry it at 60 °C for 12 h to obtain the metal precursor powder; S2. SiO2 shell coating: Disperse the metal precursor powder in a mixed solution of anhydrous ethanol and water with a volume ratio of 4:1, ultrasonically treat for 30 min until uniformly dispersed, add a sodium hydroxide solution to the mixed solution, slowly add tetraethyl orthosilicate to the suspension under the conditions of pH 9.5 and a stirring speed of 500 rpm, then add ammonia water. The molar ratio of tetraethyl orthosilicate and ammonia water is 35:1. Stir at 45 °C for 6 h, centrifuge to obtain a precipitate, wash it 3 times with ethanol, and dry it under vacuum at 60 °C to obtain the core-shell particles coated with SiO2; S3. Graft modification on the surface of the SiO2 shell: Disperse the core-shell particles coated with SiO2 in a toluene solution with a concentration of 10 wt%, add bis-(γ-triethoxysilylpropyl)tetrasulfide and azobisisobutyronitrile, react at 70 °C under nitrogen protection for 6 h, add ice ethanol to terminate the reaction, centrifuge to take the precipitate, when washing the precipitate, wash it 3 times with toluene, and then wash it 2 times with ethanol, dry it under vacuum at 40 - 50 °C to obtain the low-cobalt salt adhesion promoter D2.

[0061] Comparative Example 3: This comparative example provides a comparative low cobalt salt adhesion promoter D3 and its preparation method, which is the same as Example 6, except that dodecyltrichlorosilane is used instead of octadecyltrimethoxysilane.

[0062] Comparative Example 4: This comparative example provides a comparative low cobalt salt adhesion promoter D4 and its preparation method, which is the same as Example 6, except that propyl orthosilicate is used instead of ethyl orthosilicate.

[0063] Comparative Example 5: This comparative example provides a comparative low cobalt salt adhesion promoter D5 and its preparation method, which is the same as Example 6, except that bis-(γ-triethoxysilylpropyl) disulfide is used instead of bis-(γ-triethoxysilylpropyl) tetrasulfide.

[0064] Comparative Example 6: This comparative example provides a comparative low cobalt salt adhesion promoter D6 and its preparation method, which is the same as Example 6, except that azobisisoheptanenitrile is used instead of azobisisobutyronitrile.

[0065] The low cobalt salt adhesion promoters #1-#6 of Examples 1-6 and the low cobalt salt adhesion promoters D1-D6 of Comparative Examples 1-6 were subjected to tensile shear strength test, interface peel strength test, adhesion retention rate test after wet heat aging test and Payne effect test. The tensile shear strength of the adhesion promoter was measured according to GB7124-1986 "Method for Determination of Tensile Shear Strength of Adhesives (Metal to Metal)" (tensile shear strength indicates the adhesion performance, and the greater the tensile shear strength, the better the adhesion performance).

[0066] The test steps of interfacial peel strength and adhesion retention after wet heat aging are as follows: 1. Add low cobalt salt promoters #1-#6 and comparative examples 1-6 to low cobalt salt adhesion promoters D1-D6 into rubber-metal bonding test pieces prepared according to ASTM D429 standard and number them 1-12; 2. Use a tensile testing machine to perform 180° peel tests according to ASTM D429-14 standard, with a peel speed of 50 mm / min and an effective peel length of ≥50 mm, record the peel force curve, exclude the data of the first 10 mm and the last 5 mm, and calculate the average peel strength: σ 初始 =F avg / b (unit: kN / m), in the formula: F avgis the average force value in the effective range, b is the sample width of 25mm; 3. Set the temperature of the wet heat test chamber to 85℃, relative humidity 85%RH, and aging time to 168h to simulate a high temperature and high humidity environment. Hang the vulcanized adhesive specimens in the test chamber to avoid contact with the chamber wall or overlap to ensure uniform heating; 4. After the wet heat aging, use a tensile testing machine to perform a 90° peel test according to the ASTMD429 standard, with a peel speed of 50mm / min and an effective peel length of ≥50mm. Record the peel force curve, exclude the first 10mm and the last 5mm data, and calculate the average peel strength: σ 老化后 =F avg / b (unit: kN / m), in the formula: F avg is the average force value in the effective range, b is the sample width of 25mm; 5. Compare the peel strength before and after aging and calculate the adhesion retention rate: Adhesion retention rate = σ 老化后 / σ 初始 ×100%.

[0067] The Payne effect test uses a dynamic mechanical analyzer in shear mode, with a frequency of 1 Hz, a temperature of 25°C, and a strain amplitude range of 0.1%-100%. The G' values of the low strain area (0.1%-1%) and the high strain area (10%-100%) are recorded, and the Payne effect intensity is calculated: ΔG'=G'0.1%-G'100%.

[0068] The data obtained from the above test are shown in Table 1.

[0069] Table 1

[0070] It can be seen from the data of Examples 1-3 in Table 1, especially the data of Example 3, that through the reasonable proportion of the low-cobalt salt adhesion promoter, the tensile shear strength, interfacial peel strength, adhesion retention rate after wet heat aging, and ΔG' of the low-cobalt salt adhesion promoter of the present application are relatively excellent.

[0071] Compared with Example 3, Example 4 adds bis-(γ-triethoxysilylpropyl)tetrasulfide to the low cobalt salt adhesion promoter #4 of Example 4, and the various properties of low cobalt salt adhesion promoter #4 are better than those of low cobalt salt adhesion promoter #3. Compared with Example 3, Example 5 adds an initiator to the low cobalt salt adhesion promoter #5 of Example 5, and the various properties of low cobalt salt adhesion promoter #5 are better than those of low cobalt salt adhesion promoter #3. Compared with Example 4 and Example 5, Example 6 adds bis-(γ-triethoxysilylpropyl)tetrasulfide and an initiator to the low cobalt salt adhesion promoter #6 of Example 6, and the various properties of low cobalt salt adhesion promoter #6 are better than those of low cobalt salt adhesion promoter #4 and low cobalt salt adhesion promoter #5.

[0072] Comparing Comparative Example 1 with Example 6, in Comparative Example 1, zinc nitrate was selected instead of cobalt nitrate as the metal precursor powder in the comparative low-cobalt salt adhesion promoter D1. The tensile shear strength, interfacial peel strength, adhesion retention rate after damp heat aging, ΔG’, and other properties of the obtained low-cobalt salt adhesion promoter D1 were far inferior to those of the low-cobalt salt adhesion promoter #6. This is because Co 2+ in the metal precursor powder reacts with sulfur (S8) in the rubber to form Co-S bonds, and undergoes a coordination reaction with the oxygen atoms of the metal surface oxide (such as Fe3O4) to form stable Co-O bonds, accelerating the sulfur crosslinking reaction and enhancing the interfacial bonding between the rubber and the metal. While Zn 2+ has weak coordination ability and low interfacial chemical bonding strength, and Zn 2+ can be used as a vulcanization activator, but cannot directly participate in interfacial bonding like Co 2+ does, which easily leads to a decrease in the bonding strength and thermal stability of the adhesion promoter.

[0073] Comparing Comparative Example 2 with Example 6, in Comparative Example 2, the long-chain alkylsilane was missing in the comparative low-cobalt salt adhesion promoter D2. The properties of the obtained comparative low-cobalt salt adhesion promoter D2 were poor. This is because the hydrophobicity of the long-chain alkyl in the long-chain alkylsilane entangles with the carbon chain of the rubber molecule, reducing the interfacial polarity difference and enhancing the compatibility between the adhesion enhancer and the rubber.

[0074] Comparing Comparative Example 3 with Example 6, in Comparative Example 3, dodecyltrichlorosilane was selected instead of octadecyltrimethoxysilane in the comparative low-cobalt salt adhesion promoter D3. The properties of the obtained comparative low-cobalt salt adhesion promoter D3 were far inferior to those of the low-cobalt salt adhesion promoter #6. This is because by grafting the C18 alkyl chain, the outer surface of the SiO2 shell was further modified to be low-polar. The C18 alkyl chain, as a flexible carbon chain, forms physical entanglement with the rubber molecular chain through van der Waals forces, and the siloxane group at the end of the alkyl chain is grafted onto the surface of the SiO2 shell through chemical bonds. While grafting the C12 short chain is prone to hydrolysis, is extremely susceptible to moisture, and has poor hydrophobicity, and cannot be closely entangled with the carbon chain.

[0075] Comparing Comparative Example 4 with Example 6, in Comparative Example 4, propyl orthosilicate was selected instead of ethyl orthosilicate in the comparative low-cobalt salt adhesion promoter D4. The properties of the obtained comparative low-cobalt salt adhesion promoter D4 were far inferior to those of the low-cobalt salt adhesion promoter #6. This is because ethyl orthosilicate and ammonia form a SiO2 shell on the surface of the metal precursor powder through a sol-gel reaction. The steric hindrance effect prevents the direct contact between metal particles, avoiding agglomeration caused by van der Waals forces during high-temperature mixing or vulcanization. The hydroxyl groups (-OH) on the SiO2 surface ionize in water to generate negative charges, maintaining the dispersion stability of nanoparticles through electrostatic repulsion. The formed SiO2 shell can also block the direct contact between oxygen and the metal precursor powder, inhibiting Co2+ Oxidized to inert Co 3+ The polarity of the formed SiO2 shell itself is between that of the highly polar metal precursor powder and the non-polar rubber, forming a polar transition layer to reduce the interfacial tension. At the same time, Fe 3+ forms Fe-O-Si bonds with the oxygen in the SiO2 shell, enhancing the thermal stability of the core-shell structure. Although propyl orthosilicate and ethyl orthosilicate are both tetraalkoxysilanes, its hydrolysis rate is too slow to form a dense SiO2 shell under mild conditions, which is likely to cause uneven coating.

[0076] Comparing Comparative Example 5 with Example 6, in Comparative Example 5, the comparative low-cobalt salt adhesion promoter D5 uses bis-(γ-triethoxysilylpropyl) disulfide instead of bis-(γ-triethoxysilylpropyl) tetrasulfide. The performance of the obtained comparative low-cobalt salt adhesion promoter D5 is inferior to that of the low-cobalt salt adhesion promoter #6. That is because the tetrasulfide bond (-S4-) in bis-(γ-triethoxysilylpropyl) tetrasulfide crosslinks with the rubber vulcanization system to form a covalent bond connection. The ethoxy group (-Si-O-C2H5) at the end of the silane hydrolyzes into a silanol group (-Si-OH) in the presence of trace water and condenses with the hydroxyl group on the metal surface or the SiO2 shell to form a stable Si-O-Si bond, strengthening the interfacial bonding. While the sulfur chain of bis-(γ-triethoxysilylpropyl) disulfide is short, less sulfur is released during the vulcanization process, making it difficult to form a strong interfacial bond with the metal, and it has poor flexibility and low crosslinking density.

[0077] Comparing Comparative Example 6 with Example 6, in Comparative Example 6, the comparative low-cobalt salt adhesion promoter D6 uses azobisisoheptonitrile instead of azobisisobutyronitrile. The performance of the obtained comparative low-cobalt salt adhesion promoter D6 is inferior to that of the low-cobalt salt adhesion promoter #6. That is because the isobutyronitrile radical generated by the decomposition of azobisisobutyronitrile can cause the cleavage of the tetrasulfide bond in bis-(γ-triethoxysilylpropyl) tetrasulfide, promoting its homolytic cleavage to generate sulfur radicals (·S-S·). The sulfur radicals can react with the C=C double bond in the rubber molecular chain to form a covalent bond and embed into the rubber matrix. While azobisisoheptonitrile is prone to decompose to produce nitrogen-containing by-products at high temperature or under light, which is likely to damage the stability of the core-shell structure of the low-cobalt salt promoter. The polar group (-CN) of azobisisoheptonitrile has poor compatibility with non-polar rubbers (such as natural rubber NR / styrene-butadiene rubber SBR), which may cause uneven dispersion of the promoter in the rubber matrix, resulting in differences in local crosslinking density and a decrease in interfacial peel strength.

[0078] The above are all the preferred embodiments of the present invention, and the protection scope of the present invention is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-cobalt salt adhesion promoter, characterized in that, By mass parts, the low-cobalt salt adhesion promoter has a core-shell structure and includes: 10-15 parts of core metal precursor powder, 15-20 parts of outer shell SiO2 shell layer, and 5-8 parts of long-chain alkylsilane grafted onto the surface of the SiO2 shell layer; The metal precursor powder includes cobalt hydroxide, manganese hydroxide, and iron hydroxide, and the molar ratio of cobalt hydroxide, manganese hydroxide, and iron hydroxide is 1:2-3:1-1.

5.

2. The low-cobalt salt adhesion promoter according to claim 1, characterized in that, By mass fraction, the low-cobalt salt adhesion promoter further includes 1-3 parts of bis-(γ-triethoxysilylpropyl) tetrasulfide grafted onto the surface of the SiO2 shell layer.

3. The cobalt salt-free adhesion promoter according to claim 2, wherein, By mass fraction, the low-cobalt salt adhesion promoter further includes 0.5-1 part of initiator, and the initiator is any one of benzoyl peroxide, dibenzoyl peroxide, and azobisisobutyronitrile.

4. A low-cobalt salt adhesion promoter according to any one of claims 1-3, characterized in that The long-chain alkylsilane is any one of octadecyltrimethoxysilane and octadecyltrichlorosilane.

5. A method for preparing the low-cobalt salt adhesion promoter according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: Preparation of metal precursor powder: Weigh cobalt nitrate, manganese nitrate, and iron nitrate and dissolve them in water to prepare a mixed solution with a total metal ion concentration of 0.5-1 mol / L. Pour the mixed solution into a NaOH solution with a concentration of 2-3 mol / L. The molar ratio of cobalt nitrate, manganese nitrate, iron nitrate, and sodium hydroxide is 1:2-3:1-1.5:10-14. Stir at 50-60 °C, pH 9.5-10, and a rate of 500-600 rpm for 2-3 h. Centrifuge to obtain a precipitate, wash it with deionized water until neutral, and dry it at 60-65 °C for 11-13 h to obtain the metal precursor powder; SiO2 shell coating: Disperse the metal precursor powder in a mixed solution with a volume ratio of anhydrous ethanol to water of 4-5:1, and ultrasonically treat it for 30-40 min until evenly dispersed. Add a sodium hydroxide solution to the mixed solution. Slowly add tetraethyl orthosilicate to the suspension under the conditions of pH 9-10 and a stirring speed of 500-600 rpm, and then add ammonia water. The molar ratio of tetraethyl orthosilicate to ammonia water is 30-40:

1. Stir at 40-50 °C for 5-7 h, centrifuge to obtain a precipitate, wash it with ethanol 2-3 times, and dry it under vacuum at 55-65 °C to obtain core-shell particles coated with SiO2; Graft modification on the surface of the SiO2 shell layer: Disperse the core-shell particles coated with SiO2 in a toluene solution with a concentration of 10-15 wt%, add long-chain alkylsilane, introduce nitrogen protection, reflux and react at 80-90 °C for 8-9 h, wash it with toluene 3-4 times, and dry it under vacuum at 60-70 °C to obtain the low-cobalt salt adhesion promoter.

6. The preparation method of a low-cobalt salt adhesion promoter according to claim 5, characterized in that, In the graft modification step on the surface of the SiO2 shell, after reflux reaction at 80-90 °C for 8-9 h, the product is centrifuged to obtain a precipitate, and then the precipitate is dispersed in a toluene solution with a concentration of 5-10 wt%, bis-(γ-triethoxysilylpropyl)tetrasulfide is added, and the reaction is carried out at 65-75 °C under nitrogen protection for 6-7 h. Ice ethanol is added to terminate the reaction, and the precipitate is centrifuged again. When washing the precipitate, it is washed with toluene 3-4 times, and then washed with ethanol 2-3 times each, and dried under vacuum at 40-50 °C.

7. The preparation method of a low-cobalt salt adhesion promoter according to claim 6, characterized in that, In the graft modification step on the surface of the SiO2 shell, an initiator is added simultaneously with the addition of bis-(γ-triethoxysilylpropyl)tetrasulfide.

8. Application of a low-cobalt salt adhesion promoter in the manufacture of steel radial tires, steel cord conveyor belts, steel braided rubber hoses, and rubber rollers, characterized in that, A low-cobalt salt adhesion promoter prepared by using the low-cobalt salt adhesion promoter according to any one of claims 1-4, or the preparation method of the low-cobalt salt adhesion promoter according to any one of claims 5-7.

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