Preparation method of rubber master batch for water-stop anti-skid sole

Abstract

The invention belongs to the technical field of shoe material pretreatment, and particularly relates to a preparation method of a rubber master batch for a water-stop anti-skid sole. Drying the precipitated silicon dioxide and the 3A type zeolite at high temperature; carrying out low-concentration atomization and slight moistening by using a deep eutectic solvent, and adjusting to proper water content; banburying at 145-155 DEG C to obtain a section of master batch; adding a coupling agent in two stages, and matching with tannic acid to complete low-temperature coupling; removing water, alcohol and other small molecules in a short time at 90-110 DEG C under negative pressure; and carrying out cold dry-type pelletizing on the strips and sealing with low-dew-point inert gas. The obtained master batch is low in moisture and residual volatilization, stable in white carbon black dispersion and small in reprocessing Mooney and vulcanization fluctuation, is suitable for a sole formula formed by a vulcanizable elastomer, replaces silicon dioxide raw powder and a coupling agent, is compatible with an environment-friendly low-zinc vulcanization activation system, and is beneficial to wet surface skid resistance and water resistance maintenance.

Description

A method for preparing a water-stopping and anti-slip rubber masterbatch for shoe soles Technical Field

[0001] This invention belongs to the field of shoe material pretreatment technology, specifically relating to a method for preparing a rubber masterbatch for water-stopping and anti-slip shoe soles. Background Technology

[0002] In scenarios such as restaurant back-of-house operations, supermarket wet areas, and medical logistics, shoe soles require a combination of properties including wet-surface slip resistance, abrasion resistance, water resistance, and environmental friendliness. The industry commonly uses precipitated silica combined with silane coupling agents to construct the interface, improving wet-surface friction and reinforcement. To improve dispersion and batch stability, the industry is gradually adopting a masterbatch approach, pre-preparing "silica, coupling agents, and interface additives" into masterbatches before using them in shoe sole formulations.

[0003] Chinese patent CN114437431A proposes a wet-process composite masterbatch for latex-polymerized styrene-butadiene rubber filled with silica: silica is first dispersed in an aqueous phase to form a mother liquor, which is then mixed with latex, coagulated, washed, and dried to obtain the masterbatch. This method improves initial dispersion and is suitable for rubber shoes. However, this route relies on latex and multiple wet-process steps, resulting in high energy consumption. Residual moisture, surfactants, and volatile components in the masterbatch are difficult to effectively reduce during the preparation stage, and cross-processing can easily cause Mooney and vulcanization fluctuations. Furthermore, it does not provide a complete set of controls for low-zinc activation systems and moisture regain during storage and transportation. Another patent, CN112250919A, proposes a dry-process formulation for shoe soles, which improves yellowing resistance and performance by directly adding silica and silane during internal mixing and open milling. However, this is still an in-situ coupling process, with high mixing temperatures and times, which can easily generate small molecules such as alcohols and bring VOC and scorch safety pressures. At the same time, it does not provide specific processes for the water content range of silica, the removal of small molecules, and the stability of subsequent granulation and packaging.

[0004] In summary, existing technologies cannot simultaneously satisfy the following requirements: moderately adjusting the water content of silica without relying on large amounts of solvents or wet processes, promoting interface formation under relatively mild conditions, and minimizing moisture and small molecules in the masterbatch stage to obtain a stable masterbatch that is easy to store and transport and compatible with low-zinc systems. Summary of the Invention

[0005] To address the aforementioned technical issues, a method for preparing rubber masterbatch is provided that does not rely on large amounts of organic solvents, allows for precise control of silica water content and small molecule residues, and is compatible with low-zinc activation, thereby obtaining a highly dispersed, low-VOC, and processing-stable masterbatch for waterproof and anti-slip shoe soles.

[0006] To achieve the above-mentioned technical objectives, the present invention provides the following technical solution.

[0007] A method for preparing a water-stopping and anti-slip rubber masterbatch for shoe soles includes the following steps: S1 Raw material pre-drying: Precipitated silica and type 3A zeolite are dried at 250-300℃ for 2-4 hours until the silica moisture content is ≤1.0wt%; S2 Silica powder micro-wetting pre-activation: A 0.1-0.5wt% aqueous solution is prepared using a deep eutectic solvent composed of choline chloride and glycerol, and the silica pre-dried in S1 is atomized and sprayed for 10-30 seconds to reduce its apparent moisture content to 0.6-1.2wt%, thus obtaining pre-activated silica; S3 First-stage internal mixing and sheet preparation: Elastomer, the pre-activated silica, type 3A zeolite, and a softener are added sequentially to an internal mixer at 145-155℃, and after mixing for 6-8 minutes, the mixture is sheeted to obtain a first-stage masterbatch sheet; S4 Second-stage open mixing and coupling: The first-stage masterbatch sheet is subjected to a temperature of ≤110℃. S5. Controlled devolatilization: The two-stage masterbatch is treated at 90-110℃ and -0.06--0.09MPa for 2-6 minutes until the total volatile matter is ≤300 mg / kg, to obtain devolatilized masterbatch; S6. Cooling, granulation and sealing: The devolatilized masterbatch is dried and granulated after strip cooling, and sealed in a nitrogen environment with a dew point ≤-20℃, so that the moisture content of the masterbatch in the package is ≤0.5wt%.

[0008] Preferably, the mass ratio of choline chloride to glycerol in the deep eutectic solvent is (1.1 to 1.3):1, and the amount introduced is 1.0 to 2.0 parts per 100 parts of rubber, and it is applied by atomized spraying in step S2.

[0009] Preferably, step S4 uses a low-zinc vulcanization activation system, i.e., the total amount of zinc oxide is ≤1.0 part / 100 parts of rubber, and is used in combination with organic zinc-calcium compound soap.

[0010] Preferably, in step S4, the bis[triethoxysilylpropyl]tetrasulfide is added in two stages: first, 40-60% of the amount is added at 60-80°C and passed through for 1-2 minutes; then, the remaining amount is added at 80-100°C to complete the coupling.

[0011] Preferably, the amount of tannic acid used in step S4 is 0.5 to 1.5 parts per 100 parts of rubber.

[0012] Preferably, the 3A type zeolite is a molecular sieve with an average pore size of about 0.3 nm, and its dosage is 1 to 3 parts per 100 parts of rubber. It is added in the same stage as silica in step S3 to selectively adsorb moisture and inhibit excessive hydrolysis.

[0013] Preferably, during step S5, the volatile matter in the exhaust gas is monitored online until the total volatile matter is ≤300 mg / kg, at which point the volatile matter removal process ends.

[0014] Preferably, before dry pelletizing in step S6, an anti-sticking powder is lightly sprinkled on the surface of the rubber strip. The anti-sticking powder is ultrafine silica, and the specific surface area of ​​the ultrafine silica is ≥150m² / g, with an average particle size D. 50 3~8μm, dosage is 0.05~0.20 parts / 100 parts rubber.

[0015] Preferably, the sealed packaging uses an aluminum-plastic composite barrier bag filled with an inert gas with a dew point ≤ -40℃.

[0016] Preferably, the masterbatch is used in a shoe sole formulation composed of a vulcanizable elastomer, wherein the elastomer is selected from one or more of solution-polymerized styrene-butadiene rubber, emulsion-polymerized styrene-butadiene rubber, butadiene rubber, natural rubber, and isoprene rubber; the masterbatch replaces all or part of the silica raw powder and silane coupling agent.

[0017] This invention involves thoroughly drying precipitated silica and type 3A zeolite at high temperatures, then atomizing and micro-wetting the silica powder with an extremely low concentration aqueous solution of choline chloride / glycerol eutectic solvent. This adjusts the surface moisture of the particles to a narrow window conducive to hydrolysis-condensation. The type 3A zeolite, added in the same stage as the silica, selectively adsorbs moisture but does not adsorb ethanol, allowing silanes to undergo controllable "semi-silanization" at a lower temperature. Under the action of tannic acid, a dense and stable "silicon interface layer" is first formed, which then chemically and physically anchors with the rubber chain segments, thereby weakening the filler-filler network and enhancing the filler-rubber interaction. Subsequently, the second-stage masterbatch is subjected to medium-temperature vacuum short-time devolatilization to preferentially remove small molecules such as water and alcohol. Finally, dry granulation is used and sealed with a low dew point inert gas to maintain the final state of the masterbatch with low water content and low residual volatility, and to ensure compatibility with the low-zinc activation system to guarantee subsequent vulcanization efficiency and processing window.

[0018] The beneficial technical effects of this invention are as follows: the silica in the masterbatch is more fully wetted and depolymerized, and interfacial coupling can be effectively carried out under mild conditions, thus reducing mixing energy consumption and torque fluctuations and improving batch stability; the stable "silicon-silane-rubber" interface improves reinforcement efficiency and viscoelastic response without significantly increasing hardness, making the water-stopping and anti-slip shoe soles maintain friction for longer under wet conditions and have stronger resistance to water absorption, whitening, and hydrolysis; the reduction of small molecule residues results in lower VOC and odor load, while improving scorch safety and vulcanization flatness, and making the process easier to control; dry granulation and low dew point sealing reduce moisture regain during storage and transportation and drift during reprocessing, facilitating consistent application across workshops and factories; and when combined with low zinc activation, it helps reduce the risk of zinc leaching, achieving a comprehensive improvement in performance, processing stability, and environmental compliance. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0020] I. Main Raw Materials: Precipitated silica (specific surface area 170–200 m² / g), type 3A zeolite molecular sieve (average pore size approximately 0.3 nm, D...) 50 3–8μm), solution-polymerized styrene-butadiene rubber, butadiene rubber, natural rubber, softener (low aromatic environmentally friendly oil), bis[triethoxysilylpropyl]tetrasulfide (TESPT), tannic acid, zinc oxide (if low zinc is required, organic zinc-calcium complex soap is added), antioxidants, etc.

[0021] II. General preparation process of rubber masterbatch S1 Raw material pre-drying: Precipitated silica and type 3A zeolite are placed together in a circulating air furnace at 270℃ for 3 hours. After cooling to room temperature, the silica moisture content is ≤1.0wt%.

[0022] S2 Silica Powder Interface Micro-wetting Pre-activation: Prepare a 0.3 wt% aqueous solution with choline chloride: glycerol = 1.2:1, and spray it onto S1 treated silica via atomization for 20s to make the apparent moisture content 0.6-1.2 wt%, thus obtaining pre-activated silica.

[0023] S3 One-stage internal mixing sheet production: The feeding sequence of the internal mixer is: elastomer → pre-activated silica and type 3A zeolite → softener; 145~155 ℃, 6~8 min to produce sheet, resulting in a one-stage masterbatch sheet; the elastomer refers to vulcanizable rubber, including one or more of solution styrene-butadiene rubber (S-SBR), emulsion styrene-butadiene rubber (E-SBR), butadiene rubber (BR), natural rubber (NR), and isoprene rubber (IR).

[0024] S4 Two-stage open mill coupling: Open mill at ≤110 ℃, add TESPT and tannic acid in sequence, and pass through a thin stream to obtain two-stage masterbatch; if necessary, a vulcanization activation system can be added at this step.

[0025] S5 Controlled Volatilization: The second-stage masterbatch is placed at 90-110 ℃, -0.06--0.09 MPa for 2-6 min until the total volatile matter is ≤300 mg / kg.

[0026] S6 Cooling Granulation and Sealing: After strip cooling, dry pelleting is performed, nitrogen gas with a dew point ≤ -20 ℃ is introduced, and the pellets are sealed in aluminum-plastic composite bags. The moisture content of the masterbatch is ≤ 0.5wt%.

[0027] III. Examples and Comparative Examples To verify the necessity and synergistic effect of each step in the process of this invention, the examples and comparative examples were designed according to the single-factor isolation and overall comparison approach: Example 1 serves as the baseline of the complete process, reflecting the comprehensive effect and processing stability of the technical solution of this application; Example 2 only changed the activation system to low zinc to test the compatibility of the process with environmentally oriented formulations; Comparative Example A removed the micro-wetting step to examine the impact of missing water content control on dispersion and wet slip retention; Comparative Example B replaced 3A molecular sieve with 4A molecular sieve to compare the impact of changes in molecular sieve pore size selectivity on water control and interfacial reaction; Comparative Example C did not add tannic acid to examine the contribution of interfacial synergy. The downstream formulations and sulfidation conditions of all samples were kept consistent. Evaluation indicators covered the final state of the masterbatch (water content, total volatiles, masterbatch appearance), processing stability (viscosity, t5 / t90), functional performance (DIN abrasion, wet ceramic tile μ and water immersion μ), and environmental friendliness (VOC, zinc leaching) to ensure that performance differences could be attributed to the investigated factors, proving that the absence of each step would lead to performance degradation, while the complete combination would produce significant gains.

[0028] The preparation steps of the examples and comparative examples are general preparation processes for rubber masterbatches, differing only in the proportions and a few individual steps.

[0029] Unless otherwise stated, "parts" refers to 100 parts of rubber.

[0030] 1) Example 1 (Standard operating conditions, conventional zinc activation) Masterbatch composition: elastomer (solution polystyrene-butadiene 60 parts, butadiene 20 parts, natural rubber 20 parts), silica 85 parts, type 3A zeolite 2.0 parts, softener 5.0 parts, TESPT 4.5 parts, tannic acid 1.0 part, zinc oxide 2.5 parts.

[0031] Key parameters: S2 atomizes 0.3 wt% DES aqueous solution for 20 s; S4 adds 50% TESPT at 70 ℃ and passes through for 1.5 min, then adds the remainder at 95 ℃; S5 100 ℃ / −0.08 MPa×4 min.

[0032] Downstream outer bottom adhesive (verifying masterbatch compatibility): 180 parts masterbatch, 20 parts solution-polymerized styrene-butadiene, 1.0 part antioxidant, 1.5 parts sulfur, 1.0 part N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts diphenylguanidine; the sample was pressed at 170 ℃ for 10 min.

[0033] 2) Differences in Example 2 (low zinc activation): S4 uses low zinc activation: 0.8 parts zinc oxide and 0.7 parts organic zinc-calcium compound soap; the rest is the same as in Example 1.

[0034] Downstream outsole: Same vulcanization system as in Example 1.

[0035] 3) Comparative Example A (without S2 micro-lubrication): S2 was not implemented, and the silica entered S3 directly without micro-lubrication; the rest was the same as in Example 1.

[0036] 4) Comparative Example B (different specifications of adsorption phase): The adsorption phase 3A type zeolite was replaced with an equal amount of 4A type (average pore size of about 0.4 nm); the rest is the same as in Example 1.

[0037] 5) Comparative Example C (without tannic acid): S4 does not contain tannic acid; the rest is the same as Example 1.

[0038] All samples in the examples and comparative examples were prepared and tested according to a standardized process of "masterbatch → downstream outsole".

[0039] IV. Test Methods and Results 4.1 Test Methods: Moisture (Karl Fischer): according to GB / T 6283; Total Volatile Matter of Masterbatch: according to GB / T 24131.1; Processing Indicators: Mooney Viscosity, according to GB / T 1232.1, ML (1+4), 100 ℃; Vulcanization Characteristics (t5, t90): determined according to GB / T 16584; Outer Base Rubber Performance: DIN Volumetric Abrasion, according to GB / T 9867; Dynamic Friction Coefficient μ of Wet Tiles, according to GB / T 3903.6; 24h Water Immersion Water Absorption Rate (Gross Method), according to GB / T 1690; VOC (Finished Rubber): Thermal Desorption-GC / MS (as toluene equivalent), refer to ISO 16000-6; Zinc Leaching: Leaching Conditions: Soaking in deionized water at 25 ℃ for 24 h; Zinc content in the leachate was determined according to GB / T 5750.6.

[0040] 4.2 Test Results Table 1 Key Indicators of Masterbatch Stage

[0041] As shown in Table 1, in Examples 1 and 2, with the combination of S2 micro-lubrication and 3A zeolite, the moisture content of the masterbatch was stable at approximately 0.45 wt%, and the total volatile matter was ≤250 mg / kg. After dry granulation and low dew point sealing, there were no signs of agglomeration or moisture regain. In Comparative Example A, due to the lack of S2 micro-lubrication, the silica was too dry, leading to insufficient wetting and increased agglomeration during the mixing stage, resulting in slight agglomeration of the masterbatch particles. In Comparative Example B, although the moisture content and total volatile matter were similar after replacing 3A zeolite with 4A zeolite, the subsequent release and interface homogenization were not ideal due to the stronger adsorption of small molecules by 4A zeolite. In Comparative Example C, lacking the assistance of tannic acid, the masterbatch exhibited a certain degree of viscosity and decreased fluidity.

[0042] Table 2 Downstream outsole performance (standardized vulcanization conditions)

[0043] As shown in Table 2, the Mooney viscosity fluctuation of the masterbatch prepared using the process of this invention, when used in the outer bottom rubber, significantly converged (±2), and the vulcanization times t5 and t90 fell within a narrow range, indicating that the processing and vulcanization process was more stable. The dynamic friction coefficient μ of the wet ceramic tile (initial and after water immersion) was higher than that of the comparative examples, and μ was better maintained after water immersion, indicating that interface construction and low water absorption are beneficial to maintaining the water-stopping and anti-slip performance. The DIN volumetric wear was reduced, showing improved reinforcement efficiency. The VOC was significantly lower than that of the comparative examples, indicating that small molecules were fully eliminated in the masterbatch stage, reducing the volatile load entering the downstream mixing. In Example 2, when using a low-zinc activation system, the overall mechanical and wet slip properties were comparable to those of Example 1, while zinc leaching was reduced to 0.45 mg / L, showing that the masterbatch process and the low-zinc system have good compatibility.

[0044] In summary, the masterbatch preparation process of "strict drying of silica → micro-wetting of DES to a suitable moisture content → selective adsorption of 3A → low-temperature two-stage coupling with the addition of tannic acid → medium-temperature vacuum short-time devolatilization → dry granulation and low dew point sealing" can stably obtain well-dispersed rubber masterbatch with low moisture and low residual volatility without relying on a large amount of organic solvents. When this masterbatch is used in the formulation of water-stopping and anti-slip shoe soles, it can provide higher and more durable friction performance under wet conditions, while taking into account wear resistance and environmental protection indicators, which fully proves the effectiveness of the technical solution of this invention.

[0045] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A method for preparing a rubber masterbatch for waterproof and anti-slip shoe soles, characterized in that, Includes the following steps: S1 Raw material pre-drying: Precipitated silica and type 3A zeolite are dried at 250-300℃ for 2-4 hours until the silica moisture content is ≤1.0wt%; S2 Silica powder micro-moistening pre-activation: A 0.1-0.5wt% aqueous solution is prepared using a deep eutectic solvent composed of choline chloride and glycerol, and the silica pre-dried in S1 is atomized and sprayed for 10-30 seconds to reduce its apparent moisture content to 0.6-1.2wt%, thus obtaining pre-activated silica; S3 First-stage internal mixing and sheet forming: Elastomer, the pre-activated silica, type 3A zeolite, and softener are added sequentially to an internal mixer at 145-155℃, and after mixing for 6-8 minutes, the mixture is sheeted out to obtain a first-stage masterbatch sheet; S4 Second-stage open mixing and coupling: The first-stage masterbatch sheet is subjected to a temperature of ≤110℃. S5. Controlled devolatilization: The two-stage masterbatch is treated at 90-110℃ and -0.06--0.09MPa for 2-6 minutes until the total volatile matter is ≤300 mg / kg, to obtain devolatilized masterbatch; S6. Cooling, granulation and sealing: The devolatilized masterbatch is dried and granulated after strip cooling, and sealed in a nitrogen environment with a dew point ≤-20℃, so that the moisture content of the masterbatch in the package is ≤0.5wt%.

2. The method according to claim 1, characterized in that, The mass ratio of choline chloride to glycerol in the deep eutectic solvent is (1.1-1.3):1, and the amount introduced is 1.0-2.0 parts per 100 parts of rubber, and it is applied by atomized spraying in step S2.

3. The method according to claim 1, characterized in that, Step S4 also involves adding a low-zinc vulcanization activation system, i.e., a total zinc oxide content ≤ 1.0 part / 100 parts of rubber, and using it in conjunction with an organic zinc-calcium compound soap.

4. The method according to claim 1, characterized in that, In step S4, the bis[triethoxysilylpropyl]tetrasulfide is added in two stages: first, 40-60% of the amount is added at 60-80 °C and passed through for 1-2 minutes; then, the remaining amount is added at 80-100 °C to complete the coupling.

5. The method according to claim 1, characterized in that, In step S4, the amount of tannic acid used is 0.5 to 1.5 parts per 100 parts of rubber.

6. The method according to claim 1, characterized in that, The 3A type zeolite is a molecular sieve with an average pore size of about 0.3 nm. Its dosage is 1 to 3 parts per 100 parts of rubber, and it is added in the same stage as silica in step S3 to selectively adsorb moisture and inhibit excessive hydrolysis.

7. The method according to claim 1, characterized in that, During step S5, online monitoring of volatile matter in the exhaust gas is conducted until the total volatile matter content is ≤300 mg / kg, at which point the volatilization process ends.

8. The method according to claim 1, characterized in that, Before dry pelletizing in step S6, a non-sticking powder is lightly sprinkled on the surface of the rubber strip. The non-sticking powder is ultrafine silica with a specific surface area ≥150 m² / g and an average particle size D. 50 3~8μm, dosage is 0.05~0.20 parts / 100 parts rubber.

9. The method according to claim 1, characterized in that, The sealed packaging uses an aluminum-plastic composite barrier bag, filled with an inert gas with a dew point ≤ -40 ℃.

10. The method according to any one of claims 1 to 9, characterized in that, The masterbatch is used in shoe sole formulations made of vulcanizable elastomers, wherein the elastomers are selected from one or more of solution-polymerized styrene-butadiene rubber, emulsion-polymerized styrene-butadiene rubber, butadiene rubber, natural rubber, and isoprene rubber; the masterbatch replaces all or part of the silica raw powder and silane coupling agent.

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