A wet-process silica adhesive for latex systems and its preparation method

Abstract

This invention discloses a wet-process silica rubber for latex systems and its preparation method, belonging to the field of rubber technology. The preparation method includes the following steps: physically coating silica with liquid silane in an alcohol liquid phase environment, then subjecting it to high-temperature treatment at 40-160°C, followed by mixing with water to obtain an aqueous silica slurry; mixing latex with the aqueous silica slurry to obtain a mixture, which is then coagulated to obtain a coagulated wet rubber; and drying the coagulated wet rubber to obtain the wet-process silica rubber. The equipment and process involved in this invention are simple, making it more suitable for industrial-scale production. In this invention, no external flocculant is required, and it can coagulate autonomously. Simultaneously, the dry wet-process masterbatch possesses good processing performance, thus avoiding the cost and post-processing problems caused by the introduction of flocculants in conventional wet mixing processes.

Description

Technical Field

[0001] This invention relates to the field of rubber technology, and in particular to a wet-process silica rubber for latex systems and its preparation method. Background Technology

[0002] In the tire manufacturing industry, silica reinforcement is an effective measure to reduce hysteresis loss in rubber compounds and improve tire rolling resistance. However, silica has poor affinity with the rubber matrix, and its particles are mainly at the nanoscale. Therefore, conventional dry mixing processes based on open mills or internal mixers are difficult to achieve uniform dispersion of silica in rubber, especially when the silica filler content is high. Poor dispersion of silica directly reduces its performance and degrades the physical properties of the rubber compound to some extent, thus affecting the performance of tire products.

[0003] The wet rubber compounding technology was first introduced to the rubber processing industry by Cabot Corporation in the United States and was the first to achieve industrialization. This technology achieves uniform nanoscale dispersion of filler particles in the matrix through full-liquid-phase mixing of rubber latex and nanofiller slurry. Finally, the mixture is flocculated and dried to obtain a dry rubber nanocomposite product. Wet technology also effectively addresses the drawbacks of dry compounding of silica. Currently, publicly reported wet compounding processes based on latex systems and silica typically involve thoroughly mixing a silica aqueous dispersion slurry with an aqueous latex, then flocculating it with acid or calcium chloride, and finally drying it to obtain a dry wet masterbatch.

[0004] However, existing wet compounding processes for latex and silica still have potential problems. For example, while flocculants such as acids or calcium chloride are effective at breaking down latex, they can cause rapid demulsification and coagulation in localized areas. Due to the increased viscosity of the system, the uniform diffusion of the flocculant within the system is somewhat restricted, resulting in uneven flocculation and curing of the rubber within the system, reducing the reinforcing properties of the rubber, and thus hindering its application. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a wet-process silica rubber for latex systems and its preparation method. The method of this invention can effectively ensure the processing and reinforcing properties of the rubber compound, is simple and easy to implement, and has good prospects for market application and industrialization.

[0006] This invention provides a method for preparing a wet-process silica adhesive for a latex system, comprising the following steps:

[0007] Silica is mechanically crushed to obtain crushed silica powder; a liquid silane alcohol solution is mixed with the crushed silica powder for physical coating to obtain silane-coated silica material; then it is subjected to high-temperature treatment at 40~160℃, and then mixed with water to obtain aqueous silica slurry.

[0008] The latex is mixed with the aqueous slurry of precipitated carbon black to obtain a mixture, which is then coagulated to obtain a coagulated wet adhesive.

[0009] The solidified wet adhesive is dried to obtain fumed silica wet adhesive.

[0010] In an embodiment of the present invention, the silica is precipitated silica with a nitrogen adsorption specific surface area of ​​70-230 m². 2 / g;

[0011] The liquid silane is one or more of alkoxysilane, phenylsilane, and sulfur-containing silane.

[0012] In embodiments of the present invention, the alkoxysilane is one or more selected from n-octyltrimethoxysilane, n-octyltriethoxysilane, n-hexyltriethoxysilane, cyclohexyltrimethoxysilane, n-dodecyltrimethoxysilane, and n-hexadecyltrimethoxysilane.

[0013] The phenylsilane is phenyltrimethoxysilane and / or phenyltriethoxysilane;

[0014] The sulfur-containing silane is one or more of the following: bis-[3-(triethoxysilane)propyl]-tetrasulfide, bis-[3-(triethoxysilane)propyl]-disulfide, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, Si75, Si69, Si747, and NXT.

[0015] In an embodiment of the present invention, the high-temperature treatment is carried out in a forced-air drying oven at a temperature of 40~160°C for a duration of 20~240 min.

[0016] The mass fraction of silica in the aqueous silica slurry is 5~30wt%.

[0017] In embodiments of the present invention, the latex is natural latex or styrene-butadiene latex; the solid content of the latex is 20-80 wt%.

[0018] In an embodiment of the present invention, based on 100 parts of dry latex, the weight of silica in the aqueous silica slurry is 20-150 parts.

[0019] In an embodiment of the present invention, the solidification of the mixture is achieved autonomously under mechanical stirring, without the need to add flocculant, and the stirring speed is 120~2000 rpm.

[0020] In an embodiment of the present invention, the coagulated wet adhesive is pressed into a sheet with a thickness of less than 1 mm and dehydrated and dried at a temperature of 100~120°C to obtain a wet-process silica adhesive.

[0021] This invention provides a wet-process silica rubber obtained by the preparation method described above, for use in tire manufacturing.

[0022] For wet compounding technologies involving silica and latex, existing processes using flocculants tend to degrade rubber properties (as the flocculant remains as an impurity in the rubber). Furthermore, the introduction of flocculants (typically acids, divalent metal salts, or cationic polymers) not only increases production costs but also creates challenges in post-processing and environmental protection during industrialization. Additionally, some flocculants, such as divalent metal ions, may induce oxidative degradation of rubber macromolecules, leading to rapid deterioration of the compound's properties.

[0023] Due to insufficient affinity between silica and the rubber matrix, even in dry rubber compounds, silica particles can diffuse and aggregate, leading to a rapid increase in viscosity and deterioration in processing performance. To address this issue, a common approach is to mix the dry masterbatch with a specific silane coupling agent in an internal mixer. This silanization reaction inhibits silica flocculation and aggregation, thereby improving the compound's processing properties. However, this method also increases processing costs and can cause mechanical and thermal degradation of the rubber molecular chains due to the strong shearing action during mixing, affecting the final physical properties of the rubber composite.

[0024] The method for preparing wet-process precipitated silica rubber involved in this invention includes three main steps: obtaining aqueous precipitated silica slurry, mixing and coagulating latex and aqueous precipitated silica slurry, and drying the coagulated wet rubber. First, liquid silane is used to uniformly physical coat the precipitated silica in an alcoholic liquid phase environment, followed by solid-phase modification through high-temperature treatment, and then the aqueous slurry is prepared to form the aqueous slurry. This invention completes the silanization modification of precipitated silica in a dry environment before mixing the latex and precipitated silica slurry. Without additional mixing and silanization, the flocculation tendency of nanoparticles in the final precipitated silica-reinforced rubber composite material is significantly suppressed, thereby effectively ensuring the processing performance of the rubber compound and endowing the wet-process rubber with good processing properties. The equipment and process involved in this invention are simple and more conducive to industrial-scale production. In this invention, no external flocculant is required, and it can coagulate autonomously. Simultaneously, the dry wet-process masterbatch has good processing performance, thus avoiding the cost and post-processing problems caused by the introduction of flocculants in conventional wet mixing processes. Detailed Implementation

[0025] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] This invention provides a method for preparing a wet-process silica adhesive for a latex system, comprising the following steps:

[0027] Silica is mechanically crushed to obtain crushed silica powder; a liquid silane alcohol solution is mixed with the crushed silica powder for physical coating to obtain silane-coated silica material; then it is subjected to high-temperature treatment at 40~160℃, and then mixed with water to obtain aqueous silica slurry.

[0028] The latex is mixed with the aqueous slurry of precipitated carbon black to obtain a mixture, which is then coagulated to obtain a coagulated wet adhesive.

[0029] The solidified wet adhesive is dried to obtain fumed silica wet adhesive.

[0030] The method of this invention can effectively ensure the processing and reinforcing properties of the rubber compound, without the need to add flocculants. The process is simple and easy to implement, with low cost and relatively environmentally friendly characteristics, making it suitable for industrial production and widespread application.

[0031] This invention first prepares a silica aqueous slurry (or aqueous paste), the preferred process of which includes four main steps: mechanical crushing of silica, physical coating of silica with liquid silane, high-temperature treatment of silica material, and preparation of the aqueous slurry. The specific process details are as follows:

[0032] 1) First, use the mechanical crushing action of the pulverizer to break up the granular silica into a loose silica powder.

[0033] 2) Dissolve liquid silane in an alcohol solvent to form a silanol solution, and mix the silanol solution with the crushed silica powder in proportion to form a physical coating. Then spread the silane-coated silica material in an open container and air dry it at room temperature in a ventilated environment.

[0034] 3) The dried silica powder can be placed in a metal tray and put into a forced-air drying oven for high-temperature treatment at 40°C or above;

[0035] 4) After the high-temperature treated silica powder cools to room temperature, add it to water according to the weight ratio and stir manually or mechanically to obtain a high-viscosity silica water slurry.

[0036] In embodiments of the present invention, the granular silica can be precipitated silica commonly used in the tire industry, with a nitrogen adsorption specific surface area (BET) of 70~230 m². 2 / g, for example, 100~200 m 2 / g. In this embodiment of the invention, the silica raw material is mechanically crushed, facilitating subsequent silane modification. The particle size of precipitated silica used in the rubber industry is between micrometers and millimeters; therefore, this invention does not require limitation on particle size, and all precipitated silica used in the rubber industry is applicable to this invention.

[0037] In embodiments of the present invention, the liquid silane is one or more selected from alkoxysilanes, phenylsilanes, and sulfur-containing silanes. Preferably, the alkoxysilane is one or more selected from n-octyltrimethoxysilane, n-octyltriethoxysilane, n-hexyltriethoxysilane, cyclohexyltrimethoxysilane, n-dodecyltrimethoxysilane, and n-hexadecyltrimethoxysilane, and more preferably n-octyltrimethoxysilane, n-octyltriethoxysilane, or n-dodecyltrimethoxysilane. Furthermore, the phenylsilane may be one of phenyltrimethoxysilane and phenyltriethoxysilane.

[0038] The sulfur-containing silane may be one or more of the following: bis-[3-(triethoxysilane)propyl]-tetrasulfide, bis-[3-(triethoxysilane)propyl]-disulfide, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, or commonly used silane coupling agents in the tire industry: Si75, Si69, Si747, and NXT. Silane coupling agent Si69 has a silane coupling group as its functional group and a sulfur mass fraction of 0.2462, and is widely used. Silane coupling agent NXT has sterically hindered silane coupling groups and organic plasticizing groups as its functional groups and a sulfur mass fraction of 0.0879.

[0039] In some embodiments of the present invention, one type of silane may be used, or two or three types of compound silane may be used, such as Si69 and n-dodecyltrimethoxysilane compounded (the compound mass ratio may be 1:1, 1:2, 2:1, etc.), or NXT, phenyltriethoxysilane and n-octyltriethoxysilane compounded.

[0040] In a preferred embodiment of the present invention, a silane / ethanol solution is prepared to achieve uniform physical coating of silane molecules on the surface of silica in a liquid phase environment, laying the foundation for improving the efficiency of subsequent solid-phase modification. Preferably, the silane / ethanol solution has a mass concentration of 10-50 wt%, more preferably 20-40 wt%.

[0041] Regarding the weight ratio of silane in the silica and silane ethanol solution, the total amount of silane is 2-20 parts per 100 parts of silica, preferably 5-10 parts.

[0042] After physical coating, the high-temperature treatment of the silica described in this embodiment of the invention is carried out in a forced-air drying oven. The preferred temperature for the high-temperature treatment in the forced-air drying oven is 40~160℃, further preferably 60~120℃, such as 80℃, 100℃, 105℃, 115℃, 120℃, etc. The treatment time can be 20~240 min, preferably 40~120 min. This embodiment of the invention modifies silica (solid-phase modification) in a dry environment through high-temperature treatment in an oven. Compared with conventional liquid-phase modification, the solid-phase modification involved in this invention can significantly increase the temperature and shorten the modification time, and the equipment and process are simple, making it more suitable for industrial production.

[0043] In this embodiment of the invention, high-temperature treated silica powder is mixed with water to form a slurry (the slurry should be fluid according to the process flow and the required silica mass fraction); the silica mass fraction in the aqueous silica slurry can be 5~30wt%, preferably 10~20wt%.

[0044] Subsequently, in this embodiment of the invention, the obtained aqueous precipitate of silica is mixed with latex to obtain a mixture of latex and silica precipitate; it can solidify on its own under mechanical stirring to obtain a solidified wet adhesive.

[0045] In embodiments of the present invention, the latex is natural latex or styrene-butadiene latex; natural latex is generally a viscous, milky-white liquid, while styrene-butadiene latex is a synthetic latex formed by emulsion polymerization of butadiene and styrene. The solid content of the latex can be 20-80 wt%, preferably 30-70 wt%, further 40-60 wt%, and can be 30 wt%, 40 wt%, 60 wt%, etc. The latex is a common latex system in the rubber industry and is applicable to the present invention without special requirements.

[0046] Regarding the mixing ratio of the latex and the aqueous slurry of silica, based on 100 parts by dry weight of the latex, the weight of silica in the aqueous slurry is preferably 20-150 parts, more preferably 30-100 parts, and further preferably 40-90 parts, for example 45 parts, 50 parts, 55 parts, 60 parts, 70 parts, 80 parts, 85 parts, 90 parts, etc.

[0047] The solidification of the mixture described in this embodiment of the invention is achieved autonomously under mechanical stirring, without the need to add flocculants, and the flocculation or solidification of the latex can be completed; the speed of the mechanical stirring can be 120~2000 rpm, or more specifically 120~1000 rpm, and conventional stirring equipment can be used.

[0048] Finally, the preferred drying process for the solidified wet adhesive described in this embodiment of the invention includes: pressing the fully solidified, soft wet adhesive after stirring into a thin sheet with a thickness of less than 1 mm using a thinning machine, and then placing it in a forced-air drying oven for dehydration and drying, preferably at 120°C for 3 hours, to obtain the final product.

[0049] This invention provides a wet-process silica adhesive prepared by the method described above, which can be used as a tire compound in tire manufacturing, etc. In some embodiments of this invention, the Mooney viscosity (MS) of the wet-process silica adhesive is... 1+4 (100℃) is 85~99.

[0050] Furthermore, the application formula of the silica wet-process adhesive includes: the silica wet-process adhesive, activator, antioxidant, accelerator, and sulfur. Each component can be a conventional material. For example, the activator is zinc oxide and stearic acid; the antioxidant is an amine, specifically antioxidant 6PPD (i.e., N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine); the accelerator is accelerator TBBS and / or accelerator D. Accelerator TBBS is N-tert-butyl-2-benzothiazole sulfenamide; accelerator D is N,N'-diphenylguanidine. For example, based on 100 phr of raw rubber in wet-process rubber, the components are: zinc oxide 3-5 phr, stearic acid 0.5-1.5 phr, antioxidant 6PPD 1-2 phr, accelerator TBBS 1-1.5 phr, accelerator D 0.5-1.5 phr, and sulfur 0.8-1.5 phr.

[0051] In this embodiment of the invention, precipitated silica wet-process rubber is used as the wet-process masterbatch. After mixing and vulcanization according to the aforementioned formula, the resulting rubber compound exhibits good physical properties. The vulcanization process can be performed using conventional industry methods, with a vulcanization temperature of 140-160℃ and a vulcanization time determined based on vulcanization characteristic test results. This is a commonly used method in the industry.

[0052] The present invention provides a dry masterbatch of silica wet-process without flocculant flocculation, wherein the silica has undergone sufficient silanization solid-phase modification before slurry preparation, resulting in good processing performance of the rubber compound and ensuring or improving its mechanical properties; the process technology route involved in the present invention has better prospects for market application and industrialization promotion.

[0053] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention. The substances used in the embodiments of this invention are commercially available; the silica involved is precipitated silica commonly used in the tire industry.

[0054] Example 1

[0055] Preparation of silica slurry:

[0056] 1) First, use the mechanical crushing action of the pulverizer to break up the granular silica into a loose silica powder.

[0057] 2) Dissolve liquid silane in ethanol to form a silane / ethanol solution, and mix the silane / ethanol solution with the crushed silica powder in proportion to form a physical coating. Then spread the silane-coated silica material in an open container and air dry it at room temperature in a ventilated environment.

[0058] 3) Place the dried silica powder in a metal tray and put it in a forced-air drying oven for high-temperature treatment;

[0059] 4) After the high-temperature treated silica powder cools to room temperature, add it to water according to the weight ratio and stir mechanically to obtain silica water slurry.

[0060] The obtained aqueous precipitate of silica is mixed with latex to obtain a mixture of latex and silica precipitate; it then solidifies spontaneously under mechanical stirring to obtain a solidified wet adhesive.

[0061] The wet adhesive, which has been fully solidified and has a soft texture after stirring, is pressed into a sheet with a thickness of less than 1 mm using a thinning machine. Then, it is placed in a forced-air drying oven and dehydrated at 120℃ for 3 hours to obtain wet silica adhesive.

[0062] The process conditions are shown in Table 1.

[0063] Examples 2-4

[0064] Following the operating steps of Example 1, wet-process silica adhesives were obtained respectively; the specific process conditions are shown in Table 1.

[0065] For Examples 1-4, Mooney tests were first conducted on the raw rubber / fumed silica binary masterbatch, and then the physical properties of the rubber compound were evaluated using the same formulation.

[0066] Table 1. Technical solutions and process conditions used in Examples 1-4

[0067]

[0068] The raw materials in this evaluation formulation include raw rubber, silica, zinc oxide, stearic acid, antioxidant 6PPD, accelerator TBBS, accelerator D, and sulfur. The raw rubber and silica are presented together in the form of wet-process rubber. The proportions of zinc oxide, stearic acid, antioxidant 6PPD, accelerator TBBS, accelerator D, and sulfur, based on 100 phr of raw rubber in the wet-process rubber, are 4 phr, 1 phr, 1.5 phr, 1.2 phr, 1.0 phr, and 1.2 phr, respectively.

[0069] The viscosity test results of the wet-process masterbatch are shown in the table below:

[0070] Table 2 Viscosity test results of wet-process masterbatch

[0071]

[0072] Table 3. Physical property test results of wet-process masterbatch after mixing and vulcanization according to the above formula.

[0073]

[0074] To highlight the effects of this invention, Comparative Examples 1-4, with formulations identical to Examples 1-4, were used to prepare formulated rubbers via dry mixing, followed by vulcanization and property characterization under the same conditions. During dry mixing, the silane did not need to be dissolved in ethanol but was added to the internal mixer along with the silica. The silica did not require high-temperature treatment or preparation into a slurry but was added to the internal mixer in its original powder state to mix with the rubber. Comparative Examples 1-4 used natural rubber, styrene-butadiene rubber, styrene-butadiene rubber, and dry natural rubber, respectively, instead of latex, and the dry rubber / silica ratio in the mixed rubber was the same as in Examples 1-4.

[0075] The performance of comparative examples 1-4 is shown below:

[0076] Table 4 Performance results of Comparative Examples 1-4

[0077]

[0078] The data shows that the 100% tensile stress and hardness of the comparative rubber compound are higher than those of the corresponding embodiment, while the 300% tensile stress and the ratio of 300% tensile stress to 100% tensile stress are lower than those of the corresponding embodiment. The fundamental reason for this is that there is significant aggregation of silica during dry mixing.

[0079] As can be seen from the above embodiments, this invention completes the silanization modification of silica in a dry environment before mixing the latex and silica slurry, thus imparting good processing properties to the wet-process rubber without additional mixing and silanization. The equipment and process involved in this invention are simple, making it more conducive to industrial-scale production. In this invention, no external flocculant is required, and it can solidify autonomously. Simultaneously, the dry wet-process masterbatch possesses good processing properties, thereby avoiding the cost and post-processing problems caused by the introduction of flocculants in conventional wet mixing processes.

[0080] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only for the purpose of helping to understand the method and core ideas of the present invention. The above descriptions are only preferred embodiments of the present invention. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of the present invention.

Claims

1. A method for preparing wet-process silica adhesive for latex systems, characterized in that, Includes the following steps: Silica is mechanically crushed to obtain crushed silica powder; a liquid silane alcohol solution is mixed with the crushed silica powder for physical coating to obtain silane-coated silica material; then, it is subjected to high-temperature treatment at 40~160℃, and then mixed with water to obtain an aqueous silica slurry; the silica is precipitated silica with a nitrogen adsorption specific surface area of ​​70~230 m². 2 / g; the liquid silane is one or more of alkoxysilane, phenylsilane, and sulfur-containing silane; the high-temperature treatment is carried out by a forced-air drying oven, and the high-temperature treatment time is 20~240min; the mass fraction of silica in the aqueous silica slurry is 5~30wt%; The latex and the aqueous slurry of silica are mixed to obtain a mixture, which is then coagulated to obtain a coagulated wet rubber. The coagulation of the mixture is achieved autonomously under mechanical stirring without the addition of flocculants. The stirring speed is 120~2000 rpm. The latex is natural latex or styrene-butadiene latex. Based on 100 parts of dry rubber in the latex, the weight of silica in the aqueous slurry is 20~150 parts. The solidified wet adhesive is dried to obtain fumed silica wet adhesive.

2. The method for preparing wet-process silica adhesive according to claim 1, characterized in that, The alkoxysilane is one or more selected from n-octyltrimethoxysilane, n-octyltriethoxysilane, n-hexyltriethoxysilane, cyclohexyltrimethoxysilane, n-dodecyltrimethoxysilane, and n-hexadecyltrimethoxysilane. The phenylsilane is phenyltrimethoxysilane and / or phenyltriethoxysilane; The sulfur-containing silane is one or more of the following: bis-[3-(triethoxysilane)propyl]-tetrasulfide, bis-[3-(triethoxysilane)propyl]-disulfide, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, Si75, Si69, Si747, and NXT.

3. The method for preparing wet-process silica adhesive according to any one of claims 1-2, characterized in that, The latex solid content is 20~80wt%.

4. The method for preparing wet-process silica adhesive according to any one of claims 1-2, characterized in that, The solidified wet adhesive is pressed into a sheet with a thickness of less than 1 mm and dehydrated and dried at a temperature of 100~120℃ to obtain wet precipitated silica.

5. The wet-process silica rubber obtained by the preparation method according to any one of claims 1-4 is used to prepare tires.

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