Electrically conductive, antistatic rubber compositions and vulcanizates and methods of making and using the same

Abstract

This invention relates to the field of rubber, and discloses a conductive and antistatic rubber composition, a vulcanized rubber, its preparation method, and its application. The rubber composition comprises a base rubber, a carbon-based filler, a vulcanizing agent, a vulcanization accelerator, a vulcanization activator, and an antioxidant. The base rubber is styrene-butadiene rubber (SBR); the carbon-based filler is graphene and / or graphene oxide; and the content of the carbon-based filler is 0.8-6.5 parts by weight relative to 100 parts by weight of the base rubber. The vulcanized rubber of this invention can meet the requirements of conductive rubber materials for flexible piezoresistive sensors in wearable devices (10...). 2 Ω·m to 10 6 The requirement for using (Ω·m) is to adjust the volume resistivity to 10. 6 Ω·m to 10 9 Between Ω·m, it can also be used as an antistatic rubber material.

Description

Technical Field

[0001] This invention relates to the field of rubber, specifically to a conductive and antistatic rubber composition and vulcanized rubber, as well as their preparation methods and applications. Background Technology

[0002] The volume resistivity of conductive rubber materials is in the range of 10. 2 ~10 6 Between Ω·m, conductive rubber materials are widely used in various types of pressure sensors. Piezoresistive sensors have attracted widespread attention due to their simple structure, low energy consumption, high sensitivity, and good frequency response. Among them, conductive rubber sensors, with their advantages of conductivity, low density, corrosion resistance, and adjustable conductivity within tens of orders of magnitude, often replace metal and inorganic conductive material piezoresistive sensors and are widely used in production and daily life. Meanwhile, antistatic rubber materials have a volume resistivity range of 10 Ω·m. 6 ~10 9 With an Ω·m content, it has wide applications in antistatic housings, antistatic conveyor belts, antistatic shoe soles, IC storage boxes, rubber rollers for photocopying and textiles, as well as antistatic rubber sheets and strips.

[0003] CN105670297A discloses a conductive rubber material for flexible sensors, its preparation method, and its application. This conductive rubber material for flexible sensors comprises the following components in parts by weight: 100 parts of silicone rubber matrix, 5-100 parts of conductive filler, 5-30 parts of modified silica, and 0.1-10 parts of coupling agent. The conductive rubber material is prepared by dispersing the conductive filler in a rubber material and then crosslinking it via electron beam or gamma-ray radiation. The silicone rubber matrix comprises a molecular backbone structure composed of alternating silicon and oxygen atoms. Further, the silicone rubber matrix is ​​at least one of dimethyl silicone rubber, methyl vinyl silicone rubber, methyl vinyl phenyl silicone rubber, phenylene silicone rubber, fluorosilicone rubber, nitrile silicone rubber, and borosilicate silicone rubber. The conductive filler is at least one of conductive carbon black, nano-graphite, carbon nanotubes, silver plating powder, nickel powder, and nickel plating powder. The resistivity of the conductive rubber material is in the range of 2.0 × 10⁻⁶. 3 Ω·m to 1.0×10 10 Ω·m. In this patent, the conductive rubber matrix is ​​made of expensive silicone rubber, the conductive filler is made of conductive carbon black, metal powder, etc., and the processing method is a melt composite method. The conductive filler is not easy to disperse efficiently in the rubber matrix, which affects the further improvement of conductivity.

[0004] With the widespread adoption of smart products, wearable electronic devices present a huge market prospect. However, achieving high sensitivity, high resolution, low-cost manufacturing, and complex signal detection in flexible electronic sensors remains a significant challenge. Conductive rubber materials, as one of the core component materials for sensors, will influence the future development of wearable devices due to factors such as the breadth of its adjustable resistivity range and manufacturing costs.

[0005] Therefore, there is a need to propose a method for preparing conductive rubber compositions that can solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem that conductive fillers are not easily dispersed efficiently in rubber matrices in the prior art, which affects the further improvement of conductivity. This invention provides a conductive and antistatic rubber composition and vulcanized rubber, as well as their preparation method and application. The vulcanized rubber has a wide volume resistivity and low cost.

[0007] To achieve the above objectives, a first aspect of the present invention provides a conductive and antistatic rubber composition, wherein the rubber composition comprises a base rubber, a carbon-based filler, a vulcanizing agent, a vulcanization accelerator, a vulcanization activator, and an antioxidant, wherein the base rubber is styrene-butadiene rubber; the carbon-based filler is graphene and / or graphene oxide; and the content of the carbon-based filler is 0.8-6.5 parts by weight relative to 100 parts by weight of the base rubber.

[0008] A second aspect of the present invention provides a vulcanized rubber, wherein the vulcanized rubber is obtained by mixing and vulcanizing the aforementioned conductive and antistatic rubber composition.

[0009] A third aspect of the present invention provides a method for preparing the aforementioned vulcanized rubber, wherein the method comprises:

[0010] (1) Disperse carbon-based materials in water to form a suspension containing carbon-based materials;

[0011] (2) Using a saturated NaCl aqueous solution as a flocculant, the base rubber is mixed with the suspension for co-coagulation, and the resulting co-coagulated solid is filtered, washed and dried to obtain the base rubber / carbon-based material masterbatch.

[0012] (3) The basic rubber / carbon-based material masterbatch, vulcanizing agent, vulcanization accelerator, vulcanization activator and antioxidant are mixed and vulcanized to obtain vulcanized rubber.

[0013] The fourth aspect of this invention provides an application of the aforementioned vulcanized rubber in the preparation of a flexible resistive sensor.

[0014] The fifth aspect of this invention provides an application of the aforementioned vulcanized rubber in the preparation of antistatic rubber materials.

[0015] Through the above technical solution, this invention efficiently disperses carbon-based materials in the base rubber using an emulsion compounding method, and reduces them in situ to highly conductive fillers during the compounding process, resulting in a vulcanized rubber composition with excellent electrical conductivity and a volume resistivity range of 10. 2 Ω·m to 10 9 Ω·m, which can meet the requirements of conductive rubber materials for flexible piezoresistive sensors in wearable devices (10 2 Ω·m to 10 6 The requirement for using (Ω·m) is to adjust the volume resistivity to 10. 6 Ω·m to 10 9 With a resistivity between Ω·m, it can also be used as an antistatic rubber material. Furthermore, the rubber composition matrix of this invention uses inexpensive styrene-butadiene rubber instead of the commonly used expensive silicone rubber or other rubber matrices. Due to the efficient dispersion technology of the conductive filler, a small amount of conductive filler can achieve a low volume resistivity, thus resulting in lower material costs. Attached Figure Description

[0016] Figure 1 The graph shows the relationship between the volume resistivity and graphene oxide content of the vulcanized rubber prepared in Examples 1-4 and Comparative Examples 1-3. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] As previously stated, the first aspect of the present invention provides a conductive and antistatic rubber composition, wherein the rubber composition comprises a base rubber, a carbon-based filler, a vulcanizing agent, a vulcanization accelerator, a vulcanization activator, and an antioxidant, wherein the base rubber is styrene-butadiene rubber; the carbon-based filler is graphene and / or graphene oxide; and the content of the carbon-based filler is 0.8-6.5 parts by weight relative to 100 parts by weight of the base rubber.

[0019] The inventors of this invention have discovered that efficient dispersion of conductive fillers is a crucial factor in significantly reducing the volume resistivity of rubber materials. If the dispersion effect of conductive fillers is not ideal, a large amount of expensive conductive fillers needs to be filled in order to prepare rubber materials with low resistivity, which undoubtedly increases the material cost and also affects the mechanical properties of rubber composite materials.

[0020] During their in-depth research, the inventors of this invention discovered that if carbon-based fillers (graphene and / or graphene oxide) are combined with styrene-butadiene rubber (SBR) latex, for example, due to the polarity of graphene oxide, it can interact with surfactants on the surface of SBR latex particles, effectively improving the dispersion effect of graphene oxide and SBR. This can reduce the volume resistivity of the rubber composite material with a lower amount of graphene oxide. Furthermore, graphene oxide contains a relatively high amount of surfactants. 3 Carbon atoms have relatively weak electrical conductivity. If a reducing agent is used in situ to reduce graphene oxide to graphene during the efficient dispersion of graphene oxide, sp... 3 A large number of carbon atoms are converted into sp 2 Carbon atoms, after reduction, have more freely moving electrons in graphene, which can significantly reduce the volume resistivity of rubber composites.

[0021] According to the present invention, preferably, the content of the carbon-based filler is 1-6.2 parts by weight, more preferably 1-5 parts by weight, relative to 100 parts by weight of the base rubber. In the present invention, if the content of the carbon-based filler is too low, the resistivity of the composition is very low, which does not meet the requirements for manufacturing a flexible resistance sensor; if the content of the carbon-based material is too high, the elasticity of the composition decreases, and the elongation at break is too low, which is also unsuitable as a material for a flexible resistance sensor.

[0022] According to the present invention, the base rubber is in the form of a base rubber emulsion; wherein the solid content of the base rubber emulsion is 10-30 wt%, preferably 15-30 wt%. Furthermore, it should be noted in the present invention that the base rubber emulsion refers to an emulsion in which an organic solution of the base rubber is the dispersed phase and water is the continuous phase; wherein the organic solution can be one or more of gasoline, cyclohexane, heptane, carbon tetrachloride, chloroform, dichloroethane, and chlorobenzene.

[0023] According to the present invention, relative to 100 parts by weight of styrene-butadiene rubber, the content of the vulcanizing agent is 1-3 parts by weight, the content of the vulcanizing activator is 3-6 parts by weight, the content of the vulcanizing accelerator is 0.5-2 parts by weight, and the content of the antioxidant is 0.5-2 parts by weight; preferably, relative to 100 parts by weight of styrene-butadiene rubber, the content of the vulcanizing agent is 1.25-2 parts by weight, the content of the vulcanizing activator is 3.5-6 parts by weight, the content of the vulcanizing accelerator is 1-2 parts by weight, and the content of the antioxidant is 1-2 parts by weight.

[0024] According to the present invention, in a preferred embodiment, the carbon-based material is graphene oxide. The number of graphene oxide layers dispersed in the rubber composition is 1-16 layers, preferably 9-16 layers. Furthermore, the number of graphene layers is preferably 9-16 layers.

[0025] In this invention, the basic structure of graphene and graphene oxide is a layer of carbon atoms, which can easily form a conductive network. After reduction, the conductivity of graphene oxide is further improved, and the resistivity of the rubber composition is further reduced.

[0026] According to the present invention, the vulcanizing agent is a sulfur donor, preferably, the vulcanizing agent is selected from one or more of ordinary sulfur S, oil-extended insoluble sulfur IS, and sulfur-based vulcanizing agents.

[0027] According to the present invention, the vulcanizing activator is an inorganic activator and / or an organic activator; wherein the inorganic activator includes one or more of indirect zinc oxide, direct zinc oxide and active zinc oxide; the organic activator includes one or more of stearic acid, lauric acid and octanoic acid; preferably, the vulcanizing activator is stearic acid.

[0028] According to the present invention, the vulcanization accelerator is selected from one or more of sulfenamide accelerators, thiazole accelerators, thiuram accelerators and guanidine accelerators; preferably, the vulcanization accelerator is accelerator CZ.

[0029] According to the present invention, the antioxidant is selected from one or more of amine antioxidants, quinoline antioxidants and benzimidazole antioxidants; preferably, the antioxidant is antioxidant 4010.

[0030] A second aspect of the present invention provides a vulcanized rubber, wherein the vulcanized rubber is obtained by mixing and vulcanizing the aforementioned conductive and antistatic rubber composition.

[0031] According to the present invention, the volume resistivity of the vulcanized rubber is 10. 2 Ω·m to 10 9 Ω·m.

[0032] A third aspect of the present invention provides a method for preparing the aforementioned vulcanized rubber, wherein the method comprises:

[0033] (1) Disperse carbon-based materials in water to form a suspension containing carbon-based materials;

[0034] (2) Using a saturated NaCl aqueous solution as a flocculant, the base rubber is mixed with the suspension for co-coagulation, and the resulting co-coagulated solid is filtered, washed and dried to obtain the base rubber / carbon-based material masterbatch.

[0035] (3) The basic rubber / carbon-based material masterbatch, vulcanizing agent, vulcanization accelerator, vulcanization activator and antioxidant are mixed and vulcanized to obtain vulcanized rubber.

[0036] According to the present invention, in step (1), in the process of dispersing the carbon-based material into water to form a suspension containing the carbon-based material, preferably, the process is carried out under ultrasonic conditions, wherein the ultrasonic frequency is 20000-200000Hz.

[0037] According to the present invention, in step (2), the mixing conditions include: a stirring rate of 20-100 rpm, a temperature of 30-90°C, and a time of 5-600 min; preferably, the stirring rate is 40-90 rpm, the temperature is 40-80°C, and the time is 30-600 min.

[0038] According to the present invention, the conditions for co-coagulation include: a temperature of 40-90°C and a time of 1-20 min; preferably, a temperature of 40-80°C and a time of 2-20 min.

[0039] According to the present invention, a highly dispersed carbon-based filler is compounded with a base rubber (styrene-butadiene rubber) emulsion, which is efficiently dispersed in the base rubber and reduced in situ to a highly conductive filler during the compounding process. After flocculation and drying, a base rubber / carbon-based material masterbatch is obtained. Then, the base rubber / carbon-based material masterbatch is mixed with a vulcanizing agent, a vulcanization accelerator, a vulcanization activator, and an antioxidant to obtain a compound, which is then subjected to vulcanization treatment.

[0040] According to the present invention, the mixing process includes two methods: open mixing and closed mixing.

[0041] According to the present invention, the open milling method refers to mixing all components of the rubber composition in an open mill at 20-60°C for 5-30 minutes.

[0042] According to the present invention, the intensive mixing method refers to performing a first-stage intensive mixing of the components in the rubber composition other than the vulcanizing agent, followed by the addition of the vulcanizing agent for a second-stage intensive mixing. Specifically, the first-stage intensive mixing involves first adding the base rubber and high thermal conductivity filler at a mixing temperature of 145-150°C for 3-5 minutes, followed by adding the vulcanizing activator and other additives at a mixing temperature not exceeding 150°C for 1-3 minutes.

[0043] According to the present invention, the method for preparing vulcanized rubber is to vulcanize the above-mentioned compound under a pressure of 3-4 MPa and a temperature of 140-210°C for 5-50 min to obtain vulcanized rubber.

[0044] The fourth aspect of this invention provides an application of the aforementioned vulcanized rubber in the preparation of a flexible resistive sensor.

[0045] The fifth aspect of this invention provides an application of the aforementioned vulcanized rubber in the preparation of antistatic rubber materials.

[0046] In this invention, the volume resistivity of the vulcanized rubber meets the requirements of conductive rubber materials for flexible piezoresistive sensors in wearable devices (10). 2 Ω·m to 10 6 Requirements for use (Ω·m); adjusting volume resistivity to 10 6 Ω·m to 10 9 Between Ω·m, it can also be used as an antistatic rubber material.

[0047] The present invention will be described in detail below through embodiments.

[0048] In the following examples and comparative examples:

[0049] Experimental materials:

[0050] Styrene-butadiene latex: Solid content is 21%, produced by Chengdu Chuangwei New Materials Co., Ltd.

[0051] Graphene oxide: Produced by Xiamen Kaina Graphene Technology Co., Ltd.

[0052] Carbon black: N330 carbon black, produced by Tianjin Black Cat Carbon Black Company.

[0053] Hydrazine hydrate, antioxidant 4010, accelerator CZ, zinc oxide, stearic acid, and sulfur were purchased from Beijing Inokai Chemical Reagent Co., Ltd., and were chemically pure.

[0054] Internal mixer (model BR1600 BANBURY, manufactured by Farrell Company, USA, mixing chamber volume 1.5L);

[0055] Resistivity of vulcanized rubber

[0056] The resistivity of the vulcanized rubber was tested using a four-probe resistivity meter (model RTS-8, manufactured by Anhemeng Technology Development Co., Ltd.).

[0057] The volume resistivity parameter was measured by the voltmeter-ammeter method.

[0058] Examples 1-7

[0059] (1) Graphene oxide was dispersed in water by ultrasound at an ultrasonic frequency of 30,000 Hz to form a suspension containing graphene oxide.

[0060] (2) Styrene-butadiene latex with a curing amount of 20 wt% was mechanically stirred at a stirring speed of 100 rpm and mixed with graphene oxide suspensions of different contents (1, 3, 4, 5, 0.8, 6.2, and 6.5 phr, where phr is relative to 100 parts by weight of the base rubber styrene-butadiene rubber). After stirring for 30 minutes, hydrazine hydrate was added. The ratio of hydrazine hydrate to graphene oxide was 30 mL of hydrazine hydrate per g of graphene oxide. The mixture was stirred in situ at 100 °C. After reduction for 24 hours, a saturated NaCl aqueous solution was added to the mixture for co-coagulation. The resulting co-coagulated solid was then filtered, washed with deionized water, and dried in a vacuum oven at 60°C for 48 hours to obtain styrene-butadiene rubber / graphene oxide masterbatch with different graphene oxide contents. The masterbatch codes for graphene oxide contents of 1, 3, 4, 5, 0.8, 6.2, and 6.5 phr are G1, G3, G4, G5, G0.8, G6.2, and G6.5, respectively.

[0061] (3) Next, the styrene-butadiene rubber / graphene oxide masterbatch is mixed in an internal mixer according to the rubber composition formula and the mixing steps of the internal mixer. Table 1 is the rubber composition formula and Table 2 is the mixing steps of the internal mixer, to obtain compound rubbers H1, H3, H4, H5, H0.8, H6.2 and H6.5.

[0062] H1, H3, H4, H5, H0.8, H6.2, and H6.5 were vulcanized in a flat vulcanizing machine at a pressure of 3.5 MPa and a temperature of 150 °C for 30 min to obtain sheet vulcanizates S1, S3, S4, S5, S0.8, S6.2, and S6.5 with a thickness of 2 mm.

[0063] Example 8

[0064] The vulcanized rubber was prepared using the same method as in Example 1, except that “graphene oxide” was replaced with “graphene”; and in step (2), hydrazine hydrate was not required for reduction treatment.

[0065] The masterbatch rubber is designated as GG1.

[0066] Compound rubber HH1.

[0067] The result was a 2mm thick sheet-like vulcanizate, SS1.

[0068] The results are shown in Tables 1 and 2.

[0069] Comparative Examples 1-3

[0070] Vulcanized rubber was prepared using the same method as in Examples 1-7, except that the content of graphene oxide was 0 parts by weight (Comparative Example 1), 9 parts by weight (Comparative Example 2), and 7 parts by weight (Comparative Example 3).

[0071] The masterbatch rubber codes are G0, G9, and G7, respectively.

[0072] Compound rubbers H0, H9, and H7.

[0073] The result was 2mm thick sheet-like vulcanizates S0, S9, and S7.

[0074] The results are shown in Tables 1 and 2.

[0075] Table 1

[0076]

[0077]

[0078] Note: phr represents the weight parts of each component relative to 100 parts by weight of base rubber. For example, 50 phr means that when the amount of base rubber is 100 grams, 50 grams of this substance should be added.

[0079] Table 2

[0080]

[0081]

[0082] *Note: The mixing was carried out using a 1.5L internal mixer manufactured by Valrell Company. The amount of raw materials was calculated as 7 times the formula, in grams.

[0083] Test case

[0084] The properties of the vulcanized rubbers prepared in Examples 1-8 and Comparative Examples 1-3 were tested, and the results are shown in Table 3, which shows the volume resistivity of the vulcanized rubbers.

[0085] Table 3

[0086]

[0087] in addition, Figure 1 This is a schematic diagram showing the relationship between the volume resistivity and graphene oxide content of the vulcanized rubbers prepared in Examples 1-4 and Comparative Examples 1-3; from Table 3 and... Figure 1 It can be seen that the volume resistivity of the vulcanizate prepared from the graphene oxide / SBR composition initially decreases significantly with increasing graphene oxide content, then increases slightly. The lowest volume resistivity corresponds to a graphene oxide content of 7 phr. Compared with pure SBR, the volume resistivity of the vulcanizate with a graphene oxide content of 7 phr is reduced by 12-13 orders of magnitude. When the graphene oxide content is 1 phr, the volume resistivity of the vulcanizate composite material reaches the antistatic standard (10⁻⁶). 6Ω·m~10 9 When the graphene oxide content is above 3 phr, the vulcanized rubber composite material can be used as a conductive rubber composite material (10 Ω·m). 2 Ω·m~10 6 (Ω·m) is used. The rapid decrease in volume resistivity is because graphene oxide is reduced to graphene in situ by a reducing agent (hydrazine hydrate). At graphene content greater than the percolation threshold, the graphene oxide sheets come into contact with each other to form a conductive network. That is, when the graphene oxide content is low (below the percolation threshold), the graphene oxide sheets are isolated and do not come into contact with each other, making it difficult to conduct electricity effectively. When the content is high (above the percolation threshold), there are enough graphene oxide sheets in the rubber material, and the sheets have the opportunity to come into contact with each other to form an interconnected network, and the resistivity of the material will decrease significantly.

[0088] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing vulcanized rubber for use in flexible resistive sensors, characterized in that, The method includes: (1) Dispersing carbon-based filler in water to form a suspension containing carbon-based filler; wherein the carbon-based filler is graphene oxide; (2) The base rubber is mixed with the suspension for co-coagulation, and then hydrazine hydrate is added for in-situ reduction; then saturated NaCl aqueous solution is added as a flocculant for co-coagulation; and the obtained co-coagulated solid is filtered, washed and dried to obtain base rubber / carbon-based filler masterbatch; wherein the base rubber is styrene-butadiene rubber, and the content of carbon-based filler is 3 parts by weight, 4 parts by weight, 5 parts by weight, 6.2 parts by weight and 6.5 parts by weight relative to 100 parts by weight of the base rubber; (3) The base rubber / carbon-based filler masterbatch, vulcanizing agent, vulcanization accelerator, vulcanization activator and antioxidant are mixed and vulcanized to obtain vulcanized rubber; The volume resistivity of the vulcanized rubber is 2.5 × 10⁻⁶. 4 Ω·m, 1.8×10 3 Ω·m, 1.0×10 2 Ω·m, 2.1×10 2 Ω·m, 2.7×10 2 Ω·m.

2. The method according to claim 1, wherein, The base rubber is in the form of a base rubber emulsion. And / or, the solid content of the base rubber latex is 10-30 wt%; And / or, the number of layers of the carbon-based filler is 1-16 layers.

3. The method according to claim 1, wherein, Relative to 100 parts by weight of styrene-butadiene rubber, the content of the vulcanizing agent is 1-3 parts by weight, the content of the vulcanizing activator is 3-6 parts by weight, the content of the vulcanizing accelerator is 0.5-2 parts by weight, and the content of the antioxidant is 0.5-2 parts by weight.

4. The method according to claim 3, wherein, Relative to 100 parts by weight of styrene-butadiene rubber, the content of the vulcanizing agent is 1.25-2 parts by weight, the content of the vulcanizing activator is 3.5-6 parts by weight, the content of the vulcanizing accelerator is 1-2 parts by weight, and the content of the antioxidant is 1-2 parts by weight.

5. The method according to claim 1 or 4, wherein, The vulcanizing agent is a sulfur donor; And / or, the vulcanizing activator is an inorganic activator and / or an organic activator; And / or, the vulcanization accelerator is selected from one or more of sulfenamide accelerators, thiazole accelerators, thiuram accelerators, and guanidine accelerators; And / or, the antioxidant is selected from one or more of amine antioxidants, quinoline antioxidants, and benzimidazole antioxidants.

6. The method according to claim 5, wherein, The vulcanizing agent is selected from one or more of ordinary sulfur S, oil-extended insoluble sulfur IS, and sulfur-based vulcanizing agents.

7. The method according to claim 1, wherein, The mixing conditions include: a stirring rate of 20-100 rpm, a temperature of 30-90℃, and a time of 5-600 min; And / or, the conditions for co-condensation include: a temperature of 40-90°C and a time of 1-20 min.

8. A vulcanized rubber prepared by the method according to any one of claims 1-7.

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