Additives for rubber compounds and methods for producing the same

Abstract

The present invention relates to an additive for improving electrical conductivity and physical and mechanical properties of rubber compounds, including modulus, tensile strength, tear resistance and abrasion resistance of composite elastomeric materials (rubbers), among others. The present invention proposes an additive containing 1-20% by weight of carbon nanotubes, 3-90% by weight of high viscosity organic rubber, and 8-95% by weight of low molecular weight organic dispersion medium. The present invention also proposes a method for producing the additive.

Description

[Technical Field]

[0001] The present invention relates, in particular, to composite elastomer materials (rubber) and additives for improving the conductivity and physical and mechanical properties of rubber compounds, including elastic modulus, tensile strength, tear resistance and abrasion resistance, and to composite elastomer materials (rubber). [Background technology]

[0002] Many fillers of various chemical properties and forms are known that, when added to rubber compounds, enhance the mechanical properties of rubber, namely its modulus of elasticity, tensile strength, tear resistance, etc. In this specification, “rubber compound” refers to rubber before curing or a mixture based on two or more rubbers. In this specification, “rubber” refers to the product obtained by curing a rubber compound. Some of these fillers enhance the conductivity of rubber, and the most popular such fillers are various types of carbon black. The disadvantage of using carbon black is that a large amount of carbon black (e.g., more than 30 parts per 100 parts of rubber) is required to obtain the desired conductivity. Adding such a significant amount of carbon black has detrimental effects on certain physical and mechanical properties, such as abrasion resistance. Carbon nanotubes are promising fillers that, due to the large length-to-diameter ratio typical of their forms, can enhance the conductivity and physical and mechanical properties of rubber when added in relatively small amounts. Among carbon nanotubes, those with the fewest walls (double-walled or single-walled carbon nanotubes) are most preferred because they have the largest length-to-diameter ratio and the largest specific surface area. By adding a very small amount of single-walled carbon nanotubes, such as 0.3% by weight, to the rubber, 10 4 Experimental data is available demonstrating that rubber volume resistivity of less than ohms·m can be obtained (e.g., Russian Patent No. 2731635, IPC:B60C11 / 00).

[0003] Adding carbon nanotubes, particularly single-walled or double-walled carbon nanotubes, to composite materials presents significant technical challenges. To achieve the desired technical results—that is, to improve the conductivity and physical and mechanical properties of rubber—it is necessary to reliably disperse the entangled aggregates of carbon nanotubes to the smallest possible size, preferably down to bundles of carbon nanotubes, without damaging or destroying them, and to uniformly distribute the carbon nanotubes throughout the bulk of the rubber compound. Adding carbon nanotubes to composite materials is extremely difficult for any material, but for rubber compounds, it becomes even more complex due to the combination of the viscoelastic properties of the rubber polymer and its high viscosity.

[0004] One approach disclosed for the dispersion of nano-sized additives in rubber-containing compounds utilizes a pre-dispersion in an aqueous rubber dispersion, i.e., latex. According to European Patent No. 2436720, 07 / 23 / 2014, IPC: C08J3 / 00, C08J3 / 215, C08J3 / 22, carbon nanotubes are first dispersed in an aqueous phase using ultrasound, then polymer latex is added, and then solidification is performed. The resulting masterbatch is further processed (dried). A drawback of this method is that a considerable amount of dispersant remains in the resulting masterbatch. This has detrimental effects on the rubber and the parts made therefrom (such as reducing the elasticity and / or strength of the rubber). Furthermore, when the manufacturing method disclosed in European Patent No. 2436720 is carried out, a large amount of water remains in the masterbatch after solidification, which requires costly drying.

[0005] Another publication [Russian Patent No. 2619782, 05 / 18 / 2017, IPC: C01B31 / 00, C08J3 / 22, C08J3 / 26, B82Y30 / 00, B29B7 / 34, B29B7 / 56] discloses a method for preparing a masterbatch containing carbon nanotubes in high-viscosity rubber, the method comprising mixing the nanotubes with at least one rubber latex, heating to 100°C to 200°C, evaporating the water, and then dispersing in a 3-roll mill, single-layer, multi-layer or double-layer carbon nanotubes used as nanoparticles, the masterbatch containing the carbon nanotubes being moved along the central roll into the gap between the central roll and the delivery roll, then dispersed therein, then removed from the delivery roll, the gap size being 5 to 120 μm, and the gap size being reduced by 1.5 times or more each time it passes through the gap. The evaporation of water is preferably carried out in a mixing unit such as an extruder, internal mixer, or press mixer. The masterbatch produced according to Russian Patent No. 2619782 disperses carbon nanotubes to an aggregate size of less than 10 μm in a high-viscosity rubber latex having a water content of less than 10% by weight, preferably less than 1% by weight. The drawbacks of this method are the complexity, duration, and energy consumption of the evaporation stage in the mixing process, and the example provided requires mixing for more than 20 minutes in an internal mixer. Such prolonged processing in a rubber mixer can result in substantial damage to both the rubber and the carbon nanotubes. Due to the high viscosity of the rubber, processing the mixture of carbon nanotubes and latex after water removal in a three-roll mill also requires high torque, and therefore conventional three-roll mills cannot be used for this purpose, requiring special equipment.

[0006] Another approach to the predispersion of nano-sized additives in rubber containing compounds is based on the predispersion of carbon nanotubes in a specific liquid dispersion medium having low elasticity. Such dispersion is more efficient than dispersion in high-viscosity and viscoelastic rubber or its latex. On the other hand, mixing of composite materials with additives that are dispersion systems containing nanotubes in this liquid dispersion medium is more efficient than mixing undispersed carbon nanotube powder and provides a more uniform distribution of nanotubes in the form of individual nanotubes or aggregates of those nanotubes of a smaller size. Dispersion of carbon nanotubes in such dispersion mediums can be achieved by a wide range of techniques, including processing by ultrasound, bead mills, high-pressure dispersers, 3-roll mills, and other known methods for dispersion and mixing. However, an obvious drawback of using CNT dispersions in liquid media is the introduction of a considerable amount of dispersion medium into the composite material.

[0007] This drawback is overcome in Russian Patent No. 2654959, 05 / 23 / 2018, IPC:С01B32 / 174,B82B1 / 00,B82B3 / 00,B82Y40 / 00, which provides a superconcentrate of carbon nanotubes, a dispersion system comprising carbon nanotubes as a dispersed phase and a dispersion medium, the dispersion system being obtained by mixing carbon nanotubes and the dispersion medium, the dispersion system containing at least 2 wt% of carbon nanotubes, and the dispersion system being obtained by mechanically treating the mixture of carbon nanotubes and the dispersion medium to a maximum size of carbon nanotube aggregates not exceeding 50 μm, the dispersion medium being a material having a contact angle to highly oriented pyrolysis graphite of 120° or less.

[0008] By using such "superconcentrates," i.e., highly concentrated CNT dispersions, the amount of dispersion medium introduced can be reduced to a relatively small amount (less than 49 of the mass of the introduced CNTs). If one of the components of the composite material (e.g., a plasticizer or epoxy reagent, or another component) is used, this allows for the addition of substantial amounts of carbon nanotubes, i.e., up to 1% by weight or more, pre-dispersed in the superconcentrate, to the composite material without the need to remove the dispersion medium from the composite material.

[0009] Regarding rubber compounds, a method is known for preparing them in liquid rubber according to European Patent No. 2607407, 08 / 20 / 2014, IPC:C08J3 / 22,C08K3 / 04,C08J5 / 00,C08J3 / 20,C08L9 / 02,C08L21 / 00, by dispersing a masterbatch containing carbon nanotubes on a 3-roll mill, which is employed as the prototype of the present invention. The method of the cited publication makes it possible to achieve a small size of carbon nanotube aggregates in the masterbatch by dispersing 5 to 50% by weight of carbon nanotubes in a dispersion medium containing liquid rubber with a mass-average molecular weight (MW) of 500 g / mol to 200 kg / mol (preferably 500 g / mol to 100 kg / mol, most preferably 500 g / mol to 20 kg / mol).

[0010] A common feature of the method for preparing the superconcentrate described in Russian Patent No. 2654959 and the masterbatch described in European Patent No. 2607407 is that the main technical result of the cited invention is the good dispersion of carbon nanotubes in the superconcentrate and masterbatch: there are no large aggregates of carbon nanotubes larger than 50 μm in the superconcentrate described in Russian Patent No. 2654959, while European Patent No. 2607407 mentions the absence of aggregates larger than 130 μm, preferably larger than 50 μm, and more preferably larger than 10 μm in the masterbatch. A common drawback of the superconcentrate described in Russian Patent No. 2654959 and the masterbatch described in European Patent No. 2607407 is that, despite the absence of large aggregates of carbon nanotubes in the superconcentrate or masterbatch, their addition to composite materials based on high-viscosity viscoelastic components such as rubber causes re-aggregation of carbon nanotubes, and therefore a uniform distribution and good dispersion of carbon nanotubes in the final composite material cannot be achieved. The process of carbon nanotube reaggregation is more pronounced for double-walled and single-walled carbon nanotubes, which can spontaneously bundle under the influence of van der Waals forces (π-π interactions). Since the disclosure and examples in European Patent No. 2607407 are limited to masterbatches containing multi-walled carbon nanotubes, the inventors failed to recognize this drawback of their proposed method, which becomes apparent when using single-walled carbon nanotubes.

[0011] There are two options for the dispersion medium for superconcentrates or masterbatches: (1) a dispersion medium soluble in one of the main components of the composite material (such as rubber), or (2) a dispersion medium insoluble in the main component of the composite material.

[0012] (1) When a soluble dispersion medium is used as one of the main components of a composite material, in the process of mixing the superconcentrate of Russian Patent No. 2654959 or the masterbatch of European Patent No. 2607407 with a rubber compound containing high-viscosity rubber, the dispersion medium dissolves in the rubber compound many times faster than the superconcentrate or masterbatch is mixed with the rubber compound, resulting in the absorption of the dispersion medium into the rubber compound, which leads to the formation of large aggregates from carbon nanotubes. As a result, the carbon nanotubes in the composite material are well distributed but poorly dispersed.

[0013] (2) When an insoluble dispersion medium is used as one of the main components of the composite material, in the process of mixing the superconcentrates of Russian Patent No. 2654959 and European Patent No. 2607407 with a composition containing a high viscosity viscoelastic component, the low viscosity superconcentrate or masterbatch (compared to rubber) behaves like a lubricant, resulting in a decrease in the mixing quality of the rubber compound, ultimately leading to the formation of an emulsion of the superconcentrate or masterbatch in the rubber compound and insufficient distribution of carbon nanotubes in the rubber compound. As the examples provided below show, the addition of the superconcentrate of Russian Patent No. 2654959 or the masterbatch of European Patent No. 2607407 to a rubber compound results in a low influence of the introduced carbon nanotubes on the physical and mechanical properties and conductivity, and in some cases, even a decrease in the physical and mechanical properties.

[0014] A significant drawback of the method for preparing the masterbatch described in European Patent No. 2607407 is that when such a masterbatch is subsequently added to a rubber compound, a large amount of liquid rubber is introduced into the rubber compound along with carbon nanotubes, i.e., relatively low molecular weight rubber. For example, if the average molecular weight (MW) of styrene-butadiene liquid rubber is 1000 Da, this means that while the monomer units of styrene and butadiene are present on average only 6 times each in the rubber molecule, a considerable proportion of the rubber molecules are present only 5 times or less each. Adding a significant amount of rubber oligomer alters the kinetics of the curing process, changes the post-curing structure of the polymer, and has detrimental effects on the physical and mechanical properties of the rubber. This drawback is an inherent characteristic of masterbatches produced by the method described in European Patent No. 2607407, and is caused by the use of liquid rubber as a dispersion medium rather than, for example, mineral oil or other low molecular weight solvents that do not alter the molecular weight distribution of the rubber polymer when introduced into the rubber.

[0015] Based on the above, the technical challenges are: to provide an additive for rubber compounds that contains carbon nanotubes and improves both the conductivity and physical and mechanical properties of the rubber; to provide a method for producing an additive for rubber compounds that contains carbon nanotubes and improves both the conductivity and physical and mechanical properties of the rubber; to provide a method for producing rubber with improved conductivity and physical and mechanical properties; and to provide rubber with improved conductivity and physical and mechanical properties that contains carbon nanotubes. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] Russian Patent No. 2731635 Specification [Patent Document 2] European Patent No. 2436720 [Patent Document 3] Russian Patent No. 2619782

Patent Document 4

Patent Document 5

Summary of the Invention

[0017] In one aspect, the present invention provides an additive for a rubber compound for improving the conductivity and physical and mechanical properties of rubber, which contains carbon nanotubes and comprises 1 to 20% by weight of carbon nanotubes, 3 to 90% by weight of a high-viscosity organic rubber (R), and 8 to 95% by weight of a low-molecular-weight organic dispersion medium capable of dissolving the high-viscosity organic rubber (R).

[0018] The presence of the high-viscosity rubber in the additive prevents the aggregation of carbon nanotubes during the process of the dispersion medium dissolving in the rubber compound when the additive and the rubber compound are mixed.

[0019] The technical result of using such an additive in a rubber compound is an improvement in the conductivity of the rubber, i.e., a decrease in the volume resistivity of the rubber, and an improvement in physical and mechanical properties including the rubber elastic modulus according to the standard [ISO 37:2017. Rubber, vulcanized or thermoplastic - Determination of tensile stress - strain properties], the rubber tear resistance according to the standard [ISO 34:1979. Rubber, vulcanized - Determination of tear strength (trouser, angle and crescent test pieces)], and the rubber hardness according to the standard [ISO 7619 - 1:2010 Rubber, vulcanized or thermoplastic - Determination of indentation hardness - Part 1: Durometer method (Shore hardness)].

[0020] Additional technical results achieved by using such additives may include, but not in all cases of use, increased rubber tensile strength, increased rubber thermal conductivity, increased rubber abrasion resistance, and improved rubber dynamic properties (including increased storage modulus and increased loss coefficient (mechanical loss tangent) of rubber at 0°C and 20°C). Compared with other conductive additives such as carbon black, additional technical results of using the provided additives for rubber compounds may include the possibility of producing lighter-colored rubber, the possibility of producing colored rubber when appropriate pigments are introduced, and the possibility of producing rubber that does not leave black marks on contact surfaces.

[0021] "High-viscosity organic rubber" refers to a Mooney viscosity of over 20 ML at 100°C. (1+4) This refers to synthetic or natural saturated or unsaturated rubber having the following properties. The mass-average molecular weight (M) of such rubber. wThe viscosity can reach over 1000 kg / mol (1 million daltons). Such rubber is sometimes called "solid" rubber, not because it is crystalline, but rather to contrast it with "liquid rubber," i.e., oligomers with lower average molecular weight and lower viscosity. As the examples of the present invention demonstrate, the presence of high viscosity or "solid" organic rubber in the additive ensures the formation of a considerable amount of bonded rubber therein, which in turn promotes good distribution and dispersion of carbon nanotubes in the rubber compound. Synthetic or natural saturated or unsaturated rubbers can be used as high-viscosity organic rubbers (R), including, but are not limited to, natural or synthetic isoprene rubber, styrene-butadiene rubber, nitrile-butadiene rubber, hydrogenated nitrile-butadiene rubber, butadiene rubber, butyl rubber, halobutyl rubber, ethylene-propylene rubber, ethylene-norbornene or ethylene-propylene-diene rubber containing 1,4-hexadiene or dicyclopentadiene as a third monomer, propylene oxide rubber, acrylate rubber, carboxylate rubber, chloroprene rubber, fluoroelastomer, polysulfide rubber, epichlorohydrin rubber, urethane rubber, chlorosulfonated rubber, or combinations thereof. Oil-applied rubber can be used as the high-viscosity rubber (R), i.e., synthetic rubber into which an organic plasticizer (oil) has been introduced during the manufacturing process. In contrast to high-viscosity "solid" organic rubbers, the presence of low-viscosity "liquid" rubber in additives is undesirable and should preferably be avoided for the reasons mentioned above.

[0022] High-viscosity organic rubber (R) has a viscosity of ML at 100°C. (1+4) It is preferable that the viscosity exceeds 20 Mooney units (MU) (the determination of rubber viscosity should be carried out according to the Russian standard GOST R 54552-2011 Rubbers and Rubber Compounds. Determination of Viscosity, Stress Relaxation and Pre-Vulcanization Characteristics by Mooney Viscometer, or the equivalent standard ASTM D 1646-2015). For certain applications, high-viscosity organic rubbers have a viscosity exceeding 40 Mooney units at 100°C (ML). (1+4)It is preferable to have the following. For other applications, the high-viscosity organic rubber has a viscosity of more than 60 Mooney units at 100°C (ML). (1+4) It is preferable that it has

[0023] "Low molecular weight dispersion medium" refers to a liquid low molecular weight organic compound having a molecular weight of less than 900 g / mol, or a solution of multiple low molecular weight organic compounds (i.e., compounds having a molecular weight of less than 900 g / mol). From the viewpoint of processability for both the manufacture and subsequent use of the additive, the flash point of the dispersion medium is preferably above 100°C, while the kinematic viscosity of the dispersion medium at temperatures below 100°C is preferably less than 0.1 Pa·s.

[0024] The dispersion medium may be a liquid phase containing mineral oil, such as naphthenic oil, paraffinic oil, or aromatic oil. For certain applications, the low molecular weight dispersion medium is preferably a mineral oil or other mineral oil with a composition similar to that of oils used for stretching organic synthetic rubbers (e.g., TDAE class aromatic oils used for stretching styrene-butadiene rubber). For such applications, the low molecular weight dispersion medium is preferably a mineral oil with a flash point above 200°C and a kinematic viscosity of less than 0.1 St at 100°C.

[0025] For certain applications, the low molecular weight dispersion medium is preferably a polar solvent with a dielectric constant greater than 5 at 25°C. The high polarity of the dispersion medium promotes good dispersion of carbon nanotubes in some cases. Most preferably, the dielectric constant of the dispersion medium is greater than 40 at 25°C. For example, the dispersion medium may, but is not limited to, more than 10% by weight of propylene carbonate, or 1,2-butylene carbonate, or 2,3-butylene carbonate, or mixtures thereof. For other applications, N,N-dimethyllactamide and / or N-formylmorpholine and / or other polar organic compounds can be used as components of the dispersion medium.

[0026] It should be noted that the technical results can also be achieved using low-polarity dispersion media. In certain applications, the dispersion media preferably contains, but is not limited to, at least 20% by weight of an ester or mixture of multiple esters of an aliphatic alcohol with an acid selected from phthalic acid, or terephthalic acid, or sebacic acid, or adipic acid, or cyclohexanedicarboxylic acid, such as dibutyl phthalate, dioctyl sebacate, dioctyl adipic acid, or cyclohexanoylcyclohexanoate. In certain other cases, polar dispersion media are undesirable because they may have adverse effects on the interactions of other components of the rubber compound.

[0027] "Carbon nanotube" refers to a cylindrical carbon nanostructure with a diameter of 0.7 nm to 50 nm, consisting of one or more carbon (graphene) layers. Single-walled carbon nanotubes and / or double-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used in the rubber compounds of the present invention. The surface of the carbon nanotube can be modified with functional groups such as carboxyl or hydroxyl, or organic groups such as one or more amino groups and / or sulfoxy groups and / or epoxy groups and / or peroxy groups and / or other groups, but is not limited to the examples listed. The structure of the carbon nanotube can include heteroatoms, such as nitrogen atoms. Single-walled carbon nanotubes with a diameter greater than 0.7 nm and less than 6 nm can be used as carbon nanotubes.

[0028] It is known that single-walled and double-walled nanotubes can be bundled due to van der Waals forces (π-π interactions). As nanotubes are bundled, both the diameter and length of the bundle increase, and the length / diameter ratio of the nanotube bundle increases as the number of nanotubes in the bundle increases. It is also known that the larger the length / diameter ratio of particles in the conductive filler, the lower the minimum concentration of conductive filler required to ensure the presence of connected conductive clusters (percolation threshold). Therefore, the number of nanotubes in the bundle, and thus the diameter of the nanotube bundle in the final rubber compound, is preferably as large as possible to achieve a lower percolation threshold, for example, greater than 300 nm, preferably greater than 1 μm, and preferably greater than 3 μm.

[0029] On the other hand, the presence of multiple thin nanotube bundles in the material is desirable to ensure the uniformity of the material, maintain its physical and mechanical properties (including strength and wear resistance), and reduce the contact resistance of the material. Therefore, additives in which nanotubes are combined into bundles having a broad bundle diameter distribution such as 10 nm to 500 nm, or more preferably 5 nm to 1 μm, or more preferably 3 nm to 3 μm are preferred.

[0030] Multiwalled nanotubes are typically assembled to form entangled aggregates, but they cannot be assembled into bundles. Entangled nanotube aggregates in the material are undesirable. Preferably, more than 25% by weight of carbon nanotubes in the additive are double-walled or single-walled, and most preferably more than 50% by weight of carbon nanotubes are single-walled. The characteristic of single-walled carbon nanotubes to be separated from other carbon allotropes is that they appear at approximately 1330 cm⁻¹ in the Raman spectrum. -1 Compared to the D band, it has a maximum range of approximately 1580cm. -1The G band has high intensity. Therefore, a larger G / D band intensity ratio in the Raman spectrum is preferable. Carbon nanotubes in the additive are preferably characterized by a Raman spectrum intensity ratio of greater than 10 at 532 nm. More preferably, carbon nanotubes in the additive are characterized by a Raman spectrum intensity ratio of greater than 40 at 532 nm. Most preferably, carbon nanotubes in the additive are characterized by a Raman spectrum intensity ratio of greater than 60 at 532 nm. However, it should be noted that in certain applications, technical results can also be achieved when the content of single-walled carbon nanotubes in the additive is low, and therefore the G / D band intensity ratio is low.

[0031] When the additive of the present invention is mixed with a rubber compound, a uniform network of well-dispersed carbon nanotubes and their bundles is formed within the rubber compound, increasing the conductivity, elastic modulus, tear resistance, and hardness of the rubber. To achieve this technical result, it is necessary not only to disperse the carbon nanotubes in a dispersion medium compatible with the target rubber compound and to include high-viscosity rubber in the carbon nanotube concentrate, but also to include high-viscosity rubber in the additive. This prevents the re-aggregation of carbon nanotubes during the mixing process of the rubber compound, maintains a high degree of dispersion of carbon nanotubes, and ensures a uniform distribution in the final composite material. Preferably, the fraction of high-viscosity rubber in the additive binds to the carbon nanotubes, forming a layer of binding rubber around the carbon nanotubes. In the following, the conventional term "bound rubber" (BdR) used in rubber technology refers to the rubber fraction that cannot be extracted from an uncured filled rubber mixture in a suitable solvent, i.e., a solvent in which the solubility of rubber is not restricted (see, for example, JLLeblanc, Elastomer-Filler Interactions and the Rheology of Filled Rubber Compounds, Journal of Applied Polymer Science, Vol. 78, 1541-1550 (2000)).

[0032] The residue (tail) after extracting rubber from an additive in a large amount (e.g., more than 100 times excess) of organic solvent, forming an unlimited series of organic rubber (R) solutions, for an extended period (e.g., more than 7 days), preferably contains more than 20% by weight of rubber, i.e., the additive preferably contains bound rubber, and the ratio of the mass fraction of carbon nanotubes to the rubber bound thereto is preferably less than 4. The polymer molecules in the bound rubber can be chemically bonded to the functional groups on the surface of the carbon nanotubes, but this is not essential, and the rubber interaction with the filler, and especially with the carbon nanotubes, may be due to van der Waals forces.

[0033] In addition to carbon nanotubes, dispersion media, and rubber, the additives of the present invention may include, but are not limited to, other components such as particles of metals from groups 8 to 11 of the periodic table, e.g., iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, silver, gold, or alloys thereof. Metal particles can be introduced into the additive along with carbon nanotubes as impurities by methods for producing carbon nanotubes. Metal particles or other components can be intentionally introduced into the additive to modify one or more properties of the rubber compound.

[0034] Variations in the carbon nanotube content, rubber content, and properties of the dispersion medium can alter the specific physical and chemical properties of the additive, such as its viscosity and conductivity. For certain applications, to ensure better mixing with the rubber compound, the additive should preferably not differ significantly in viscosity from the rubber compound, for example, within the range of 5 to 90 Mooney units at 100°C. For other specific applications, the additive may have low viscosity. In this case, its viscosity is preferably characterized by a needle penetration depth at 25°C over 5 seconds with a specified load of 100g, according to Russian standard GOST-11501-78 (or equivalent standard DIN EN1426:2015, ASTM D5). This property, in addition to characterizing the viscosity of the additive, also describes the uniformity of the dispersion and distribution of carbon nanotubes in the dispersion medium; in the case of a non-uniform additive, the needle penetration depth increases significantly. The needle penetration depth is preferably less than 20 mm (200 penetration units equal to 0.1 mm), most preferably less than 15 mm, and in certain applications, the penetration depth is preferably less than 10 mm (100 penetration units equal to 0.1 mm).

[0035] Furthermore, in certain applications, to ensure a better effect on the conductivity of the final rubber compound, the additive should preferably have a conductivity of at least 0.5 S / m, i.e., its volume resistivity at 25°C is 2 ohms·m or less, although in some other applications, a lower conductivity of the additive is sufficient.

[0036] The present invention also provides a method for producing the additive defined above, the method comprising the following sequential steps: step (I) - dissolving a high-viscosity rubber (R) in the dispersion medium, and step (II) - dispersing carbon nanotubes in the solution of step (I). The solution of step (I) may be a true solution or a colloidal solution of rubber in the dispersion medium. Even when a true rubber solution is produced in the dispersion medium in step (I), the rubber interacts with the carbon nanotubes after step (II) to form a bound rubber phase that is no longer dissolvable in the dispersion medium or when extracted with an organic solvent. The amount of this phase is preferably more than 25% by weight of the amount of carbon nanotubes in the additive. The carbon nanotubes can be dispersed in the rubber solution in the dispersion medium by using one of the known methods for slurry dispersion and homogenization, which include, but are not limited to, ball mills, planetary mills, twin-screw homogenizers, rotor-stator homogenizers, 3-roll mills, roller mills having 4 or more rolls, internal rubber mixers having various rotor shapes, and 2-roll rubber mills.

[0037] Since carbon nanotubes are a powder that poses a potential hazard to personnel and equipment, an additional step of pre-wetting and mixing the carbon nanotubes in the dispersion medium, in one of the components of the dispersion medium, or in the rubber solution in the dispersion medium is preferably performed between step (I) and step (II). This pre-wetting and mixing can be performed in any known type of mixer, including but not limited to uniaxial or twin-screw mixers, planetary mixers, kneaders, overhead stirrers with various impeller shapes, and rotary mixers. The quality of mixing in the pre-wetting and mixing stage does not play a significant role, as the main objectives of this process step are to wet the carbon nanotubes, facilitate their introduction, and ensure dust is absent during subsequent dispersion in step (II).

[0038] In some cases, it is preferable to further include a step after step (II) in which the resulting paste, containing carbon nanotubes, a dispersion medium, and high-viscosity organic rubber (R), is mixed with high-viscosity organic rubber (R2). The high-viscosity organic rubber (R2) may differ from high-viscosity organic rubber (R) in chemical and physical and chemical properties, but may be the same type of rubber (R) as rubber (R2). The resulting mixture can also be used as an additive to the rubber compound to enhance conductivity and physical and mechanical properties. The ratio of the weight of rubber (R2) to the weight of the slurry after step (II) is preferably 5 or less. The additional mixing of the slurry containing carbon nanotubes, a dispersion medium, and high-viscosity organic rubber (R) with high-viscosity organic rubber (R2) can be carried out using any known apparatus for rubber mixing, such as an internal mixer with tangent rotors, or an internal mixer with meshing rotors, or a two-roll rubber mill, but is not limited to the examples listed.

[0039] The present invention also provides a method for producing rubber having enhanced conductivity and physical and mechanical properties, comprising the step of adding an additive containing carbon nanotubes as defined above to a rubber compound. “Rubber compound” refers to uncured rubber or a mixture of two or more rubbers. Adding the additive to the rubber compound can be carried out as a separate process step, or in combination with, but not limited to, adding fillers and / or plasticizers, and / or antioxidants, and / or silane coupling agents, and / or curing agents, and / or curing accelerators, and / or curing retarders, and / or stabilizers, and / or dyes and / or pigments to the rubber mixture. The step of adding the additive containing carbon nanotubes to the rubber compound can be carried out by any known method of mixing the rubber mixture, including but not limited to, internal mixers having various geometric shapes of chambers and rotors, open mills (two-roll mills or rubber mixing rolls), twin-screw mixers, extruders, etc., and in a two-step or multi-step process using various combinations of mixing methods. In certain applications, the step of adding additives to the rubber compound in a preferred method of manufacturing rubber is carried out in an internal mixer. In certain other applications, the step of adding additives to the rubber compound in a preferred method of manufacturing rubber is carried out in a two-roll rubber mill. Mixing can be carried out at a higher temperature. After mixing and molding into a suitable shape, the rubber compound can be cured by one of the known methods to produce rubber.

[0040] The present invention also provides a rubber having enhanced conductivity and physical and mechanical properties, wherein the rubber contains 0.01 to 1% by weight of carbon nanotubes, and is manufactured by any of the methods defined above using additives containing the carbon nanotubes defined above.

[0041] The present invention is illustrated by the following examples and tables provided to better understand the essence of the invention, but the present invention is not limited to the examples provided.

[0042] A brief explanation of the table (Table 1) Table 1 shows the components of the additives in Examples 1 to 34, the properties of the TUBALL™ single-walled carbon nanotubes (SWCNTs) used in their manufacture, the properties of the dispersion medium and high-viscosity rubber used in their manufacture, and the ratio of the mass fraction of carbon nanotubes to the mass fraction of the rubber to which they are bound.

[0043] (Table 2) Table 2 shows data on the viscosity and conductivity of the additives in Examples 1 to 34.

[0044] (Table 3) Table 3 shows the components of the additives in Examples 35-41 and the properties of the carbon nanotubes used in their production.

[0045] (Table 4) Table 4 shows the components of the additives in Examples 42 to 45.

[0046] (Table 5) Table 5 shows the components of the rubber compound of Example 46, which is based on carbon black-free EPDM rubber and uses the additives of Examples 5 to 9, and the properties of the rubber after curing.

[0047] (Table 6) Table 6 shows the components of the rubber compound of Example 46, which is based on carbon black-free EPDM rubber and uses the additives of Examples 10 to 14, and the properties of the rubber after curing.

[0048] (Table 7) Table 7 shows the components of the rubber compound of Example 46, which is based on carbon black-free EPDM rubber using the additive of Example 9, and the properties of the cured rubber.

[0049] (Table 8) Table 8 shows the components of the rubber compound of Example 47, which is based on carbon black-free EPDM rubber using the additives of Examples 35-38, and the properties of the rubber after curing.

[0050] (Table 9) Table 9 shows the components of the rubber compound of Example 48, which is based on EPDM rubber containing carbon black N550, conductive filler, or conductive carbon powder Vulcan XC-72, using the additives of Example 9.

[0051] (Table 10) Table 10 shows the components of the rubber compound of Example 49, which is based on a colored (non-black) conductive rubber mixture based on EPDM rubber, using the additives of Example 9 and Example 42, and the properties of the rubber after curing.

[0052] (Table 11) Table 11 shows the components of the rubber compound of Example 50, which is based on a mixture of natural rubber and butadiene rubber, using the additives of Examples 9, 15-17 and 43-44, and the properties of the cured rubber.

[0053] (Table 12) Table 12 shows the components of the rubber compound of Example 51, which is based on a mixture of natural rubber and butadiene rubber without oil plasticizers, using the additives of Examples 16, 17, and 25, and the properties of the rubber after curing.

[0054] (Table 13) Table 13 shows the components of the rubber compound of Example 52, based on carbon black-filled nitrile butadiene rubber, using the additives of Examples 18-20, 25-26, and 44, and the properties of the cured rubber.

[0055] (Table 14) Table 14 shows the components and properties of the rubber compound of Example 53, which is based on silicon dioxide-filled nitrile butadiene rubber, using the additives of Examples 21-23, 25, 29, and 31, and the rubber after curing.

[0056] (Table 15) Table 15 shows the components and properties of the rubber compound of Example 53, which is based on silicon dioxide-filled nitrile butadiene rubber and uses the additives of Examples 32-34 and 39-41, as well as the properties of the cured rubber.

[0057] (Table 16) Table 16 shows the components of the rubber compound of Example 54, which is based on a mixture of styrene-butadiene rubber and butadiene rubber, using the additives of Examples 9, 22, and 26-28, and the properties of the rubber after curing.

[0058] (Table 17) Table 17 shows the components of the rubber compound of Example 54, which is based on a mixture of styrene-butadiene rubber and butadiene rubber, using the additives of Examples 24, 25, and 45, and the properties of the cured rubber. [Modes for carrying out the invention]

[0059] Herein, preferred embodiments of the present invention will be referred to in detail. [Examples]

[0060] In the examples and tables shown below, the numerical values ​​for physical and chemical properties were experimentally determined according to the methods described in the following standards: Russian GOST R 54552-2011 Rubbers and Rubber Compounds. Standard Test Methods for Viscosity, Stress Relaxation, and Pre-Vulcanization Characteristics by Mooney Viscometer (and ASTM D 1646-2015); Russian GOST R 54547-2011 Rubber Compounds. Standard Test Method for Property-Vulcanization Using Rotorless Cure Meters (and ASTM D 5289-2012); Russian GOST R 54553-2011 Vulcanized Rubber and Thermoplastic Elastomers. Standard Test Method for Tensile Stress-Strain Properties (and ASTM D 412); Russian GOST 262-79 Rubber. Standard Test Method of Tear Strength (and ASTM D 624);Russian GOST R ISO 7619-1-2009 Rubber,Vulcanized or Thermoplastic.Determination of Indentation Hardness.Part 1.Durometer Method(Shore Hardness)(and ISO 7619-1:2004);ASTM D 991-Standard Test Method for Rubber Property-Volume Resistivity Of Electrically Conductive and Antistatic Products;Russian GOST-11501-78 Petroleum Bitumens.Standard Test Method for Determination of Depth of Needle Penetration(and DIN EN1426:2015, ASTM D 5).

[0061] The following symbols and abbreviations are used in the following table: NPD - needle penetration depth expressed in penetration units equal to 0.1 mm (according to Russian GOST-11501-78), ρ V - volume resistivity, ρ S - surface resistivity, M50 - stress at a given elongation of 50%, M100 - stress at a given elongation of 100%, M200 - stress at a given elongation of 200%, M300 - stress at a given elongation of 300%, TS - maximum tearing stress, EB - maximum breaking elongation, CrTear - crescent-shaped sample tear resistance, AnTear - angular-shaped sample tear resistance, H - hardness, λ - thermal conductivity.

[0062] Examples 1 to 34. Examples 1 to 4 are comparative examples by prototype, that is, single-walled carbon nanotubes and a dispersion medium containing a low molecular weight solvent with an average molecular weight of less than 1000 daltons (hydrogenated extract of gasoline-derived aromatic hydrocarbons having a viscosity of about 0.02 Pa·s at 100°C and a flash point of 220°C, aromatic oil TDAE Norman 346) or a liquid rubber oligomer (liquid having a viscosity of 6 Pa·s at 38°C, butadiene Kuraray LBR-352 with MW = 9000 Da; liquid having a viscosity of 20 - 30 Pa·s, nitrile butadiene Nipol1312 (Zeon Chemicals); or liquid having a viscosity of 350 Pa·s at 38°C, styrene butadiene - Kuraray LSBR-820 with MW = 8500 g / mol). Table 1 shows the composition of these additives, the properties of the TUBALL (trademark) single-walled carbon nanotubes (SWCNT) used in their production, and the properties of the dispersion medium (or liquid rubber oligomer).

[0063] Examples 5-34 illustrate additives of the present invention for improving the conductivity and physical and mechanical properties of rubber containing carbon nanotubes, wherein the additive comprises 1-20% by weight of carbon nanotubes, 3-90% of high-viscosity organic rubber(R), and 8-95% by weight of a low molecular weight organic dispersion medium capable of dissolving the high-viscosity organic rubber(R). In each of the provided examples, the additive has an average diameter (d) greater than 1.4 nm and less than 1.8 nm, and 300 m 2 / g over 600m 2 The TUBALL® single-walled carbon nanotubes contain a specific surface area (S) of less than 1 / g and a Raman spectrum intensity ratio of greater than 40 at 532 nm. The TUBALL® single-walled carbon nanotubes contain iron impurities in the form of nanoparticles of iron, iron carbide, and small amounts of iron oxide.

[0064] TUBALL(trademark)(m Fe The iron impurity content in the nanotubes is less than 15% by weight. An exception is Examples 15 and 24, which use TUBALL® single-walled carbon nanotubes that have been further purified from iron impurities to a content of 0.65% by weight. These single-walled carbon nanotubes are 1230m 2 It is characterized by a larger specific surface area of ​​ / g, which is due to the opening of internal channels in the carbon nanotubes during the purification process. Actual values ​​of the parameters of TUBALL® single-walled carbon nanotubes in the additive are shown in Table 1. In each example provided, the additive comprises a low molecular weight dispersion medium and a high viscosity organic rubber. The chemical composition, viscosity (η), and flash point (t) of the dispersion medium are also shown. fl Table 1 shows the following abbreviations: TDAE - Processed distillate aromatic extract, aromatic oil produced by hydrogenation of gasoline distillates, using Norman 346 oil (JSC Orgkhim), P460 - paraffinic oil type Petronas Process Oil P 460 (Petronas), DBP - dibutyl phthalate, PC - propylene carbonate, BC - butylene carbonate, DOA - dioctyl adipate, DOS - dioctyl sebacate, DINP - diisononyl phthalate.

[0065] Each coating (ML (1+4) Table 1 shows the chemical composition, trademark, and viscosity in Mooney units of the high-viscosity organic rubber used in the product. The following abbreviations are used in the table: NR - natural rubber, NBR - nitrile butadiene rubber, EPDM - ethylene propylene diene monomer rubber. Table 1 also shows the weight % ratio (m³) of TUBALL (trademark) to the weight of the additives. CNT ), the weight % ratio of the weight of high viscosity organic rubber (R) to the weight of rubber (R) solution in the dispersion medium (m R ), and the ratio of the weight of SWCNTs to the weight of the rubber bound to them, as determined by extraction in a solvent (m CNT / BdR ) indicates.

[0066] The additives in Examples 5 to 34 were prepared by sequentially performing the steps of (I) dissolving a high-viscosity organic rubber (R) in a dispersion medium, followed by (II) dispersing single-walled carbon nanotubes in the solution from step (I). To prevent dust formation in the work area during dispersion, the single-walled carbon nanotubes were pre-moistened between steps (I) and (II) by the dispersion medium (oil P460) in Examples 5 to 14, and by the rubber solution in the dispersion medium in Examples 15 to 34.

[0067] The dispersion medium in the additives of Examples 5-16 contains mineral oil having a flash point above 200°C and a viscosity of less than 0.1 St at 100°C (21 cSt for TDAE Normal 346 and 36 cSt for Petronas P460). The dispersion medium in the additives of Examples 18-31 contains nitrile butadiene rubber and a polar solvent having a dielectric constant greater than 5 at 25°C (DBP: 6.4; butylene carbonate: 56; propylene carbonate: 64). In Example 30, the dispersion medium is Solution 1 with a weight ratio of propylene carbonate to butylene carbonate of 9:1 (the isomer composition of butylene carbonate is unknown). In Example 31, the dispersion medium is Solution 2 with a weight ratio of propylene carbonate to butylene carbonate of 1:9 (the isomer composition of butylene carbonate is unknown). The dispersion medium in the additives of Examples 32-34 includes a polar solvent having a lower dielectric constant (DOS: 4.0; DINP: 4.6).

[0068] Table 2 shows the viscosity and conductivity data for the additives of Examples 1 to 34 at a temperature of 25°C.

[0069] Examples 35-41. The additives in Examples 35-38 were prepared in the same manner as the additive in Example 9, and the additives in Examples 39-41 were prepared in the same manner as in Example 26, but different carbon nanotubes with the properties shown in Table 3 were used. Examples 35 and 39 used carbon nanotubes that mostly consisted of double-walled carbon nanotubes, which was confirmed by high-resolution transmission electron microscopy, with a mass fraction of single-walled carbon nanotubes of approximately 30% by weight. Examples 36, 37, and 40 used multi-walled carbon nanotubes, but in Example 37, they were pre-mixed with TUBALL® single-walled carbon nanotubes in a 3:1 weight ratio. Examples 38 and 41 used so-called "multi-layered" carbon nanotubes, i.e., multi-walled carbon nanotubes with 2-5 graphene layers in the wall, and the carbon nanotubes mostly contained 3-4 graphene layers.

[0070] Examples 42-45. The additive was prepared in the same manner as the additives in Examples 9, 17, and 26, but after step (II), a further step was performed in which the resulting slurry containing carbon nanotubes, dispersion medium, and high-viscosity organic rubber (R) was mixed with high-viscosity organic rubber (R2) at a ratio of the weight of rubber (R2) to the weight of the slurry after step (II) of 5 or less. The composition and type of rubber (R2) used, the weight ratio of the weight of rubber (R2) to the weight of the slurry after step (II), and the final composition of the additive and the weight ratio of carbon nanotubes to the bound rubber are shown in Table 4.

[0071] Example 46. This example demonstrates the production of rubber mixtures and rubber based on EPDM rubber without carbon black using the additives of Examples 5-14. The additives of Comparative Example 2 were used for comparison with the prototype. The rubber was mixed in two stages using an internal mixer WSM SKI-3.5L and then homogenized in a 2-roll rubber mill 200 / 400 with a diameter of 200 mm, a length of 400 mm, and a friction coefficient of 1:1.2. In the first stage, rubber, oil P460, PEG4000, CaCO3, white carbon (SiO2), kaolin, TiO2, and ZnO were mixed for 5 minutes at a maximum mixing temperature of 150°C. In the second stage, additives including the curing agents triallyl isocyanurate (TAIC) and bis(tert-butylperoxyisopropyl)benzene (BIPB-40-GR), as well as carbon nanotubes, were introduced into the rubber compound over 2 minutes at a maximum mixing temperature of 90°C. The rubber compounding process includes the step of adding an additive containing carbon nanotubes to the rubber compound, and the addition of this additive to the rubber compound is combined with the addition of a curing agent to the rubber compound.

[0072] Tables 5 and 6 show the results of testing cured rubber samples regarding the rubber mixture formulation, conductivity, and physical and mechanical properties. These data indicate that the additives in Examples 5-14 provide technical results, namely significantly improved conductivity and mechanical properties (coefficients M50-M200 and tear resistance), while the effect of the additive in Comparative Example 2 on conductivity and tear resistance is much lower, and is actually negative in the M50-M200 range.

[0073] The effect of the amount of additive introduced is shown in Table 7, which provides data for various amounts of additive in Example 9. When the concentration of carbon nanotubes in the rubber was changed from 0.04 to 1%, the technical results were: significantly improved conductivity and mechanical properties (coefficients M50-M200 and tear resistance) were achieved, and some rubber samples also showed significantly increased tensile strength and maximum elongation at break.

[0074] Example 47. This example demonstrates the production of rubber mixtures and rubber based on EPDM rubber without carbon black using the additives of Examples 35-38. The additives of Comparative Example 2 were used for comparison with the prototype. The rubber was mixed in two stages using an internal mixer WSM SKI-3.5L, as in Example 48, and then homogenized in a two-roll rubber mill Zamak LM 200 / 400 with a diameter of 200 mm, a length of 400 mm, and a friction coefficient of 1:1.2.

[0075] Table 8 shows the results of testing cured rubber samples regarding the rubber mixture formulation, conductivity, and physical and mechanical properties. These data indicate that the additives of Examples 35-38 provide technical results, namely improved conductivity and mechanical properties (coefficients M50-M200 and tear resistance), but the greatest effect is achieved when using single-walled and / or double-walled carbon nanotubes (additives of Examples 9 and 35). Therefore, additives containing single-walled and / or double-walled carbon nanotubes are preferred.

[0076] Example 48. This example demonstrates the production of rubber mixtures and rubber based on EPDM rubber containing carbon black N550, conductive filler, or conductive carbon powder Vulcan XC-72, using the additives of Example 9. The additives of Comparative Example 2 were used for comparison with the prototype. The rubber was mixed in two stages: the first stage was performed using an internal mixer VSM SKI-3.5L, and the second stage was performed in a two-roll rubber mill Zamak 200 / 400 with a diameter of 200 mm, a length of 400 mm, and a friction coefficient of 1:1.2, at a maximum temperature of 90°C for 2 minutes. The additive containing carbon nanotubes was introduced into the two-roll rubber mill, and the addition of this additive to the rubber compound was combined with the addition of a curing agent (2-mercaptobenzothiazole (MBT), tetramethylthiuram disulfide (TMTD), and sulfur) to the rubber compound.

[0077] Table 9 shows the results of testing cured rubber samples regarding the rubber mixture formulation, conductivity, and physical and mechanical properties. These data demonstrate that, despite the fact that the rubber was already conductive without the additive, the additive in Example 9 provides technical results, namely significantly enhanced mechanical properties (coefficients M50-M200 and tear resistance), as well as a very significant increase in conductivity. At the same time, the effect of the additive in Comparative Example 2 on physical and mechanical properties is remarkably low, within the range of measurement uncertainty, although the conductivity of rubber containing this additive actually decreases.

[0078] Example 49. This example demonstrates that further technical results can be achieved by using the additives of the present invention, i.e., by producing colored (non-black) conductive rubber mixtures and rubber based on EPDM rubber. The rubber formulations are shown in Table 10. For coloring, the organic dye phthalocyanine blue pigment was added to the rubber mixture. The rubber was whitened by increasing the titanium dioxide content. This example also demonstrates the possibility of adding carbon nanotubes to the rubber mixture as part of an additive containing a high-concentration, high-viscosity organic rubber according to Example 42. The base rubber without additives was mixed in two stages: the first stage was carried out using an internal mixer VSM SKI-3.5L, and all components except the curing system (TAIC and peroxide) were added to the rubber. The second stage, including the addition of the curing agent, was carried out using a 2-roll rubber mill Zamak 200 / 400 with a diameter of 200 mm, a length of 400 mm, and a friction coefficient of 1:1.2, at a maximum temperature of 90°C for 2 minutes. The additive containing carbon nanotubes was introduced into the rubber using an internal mixer before adding the other components of the rubber mixture. The resulting rubber has a deep blue color along with sufficient conductivity to dissipate static charge. The data in Table 10 demonstrate that the addition of the additives in both Examples 9 and 42 resulted in improvements to the physical and mechanical properties of the rubber.

[0079] Example 50. This example demonstrates the production of rubber compounds and rubber based on a mixture of rubber, namely natural rubber (using SMR10 rubber) and butadiene rubber (using BR-22 rubber), using any of the additives from Examples 9, 15-17, and 43-44. The additives from Comparative Example 1 were used for comparison with the prototype. The composition of the rubber mixture is shown in Table 11. This composition emulates the composition of the rubber mixture in the treads of agricultural tires and truck tires. Rubber without additives was mixed in two stages using an internal mixer WSM SKI-3.5L and then homogenized in a two-roll rubber mill Zamak 200 / 400 with a friction coefficient of 1:1.2. In the first stage, rubber, oil Nytex 4700, carbon black N234, stearic acid, ZnO, and N-(1,3-dimethyl)-N'-phenyl-1,4-phenyldiamine (6PPD) antioxidant were mixed for 5 minutes at a maximum mixing temperature of 130°C. In the second stage, the curing agent 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ); N-cyclohexyl-2-benzothiazole sulfenamide (Sulsenamide C) (CBS); diphenylguanidine (DPG); pre-vulcanization inhibitor (PVI); and sulfur were introduced into the rubber compound at a maximum mixing temperature of 100°C for 2 minutes. The addition of additives including carbon nanotubes was performed between the first and second stages of mixing the base rubber mixture using a Zamak 200 / 400 two-roll rubber mill with a friction coefficient of 1:1.2. The volume resistivity and physical and mechanical properties of the cured rubber samples are shown in Table 11, and pre-cut crescent-shaped samples were used for tear resistance testing. These data show that adding the additives of Examples 15-17, 43, 9, and 42 to the rubber compound significantly reduces the volume resistivity of the rubber and increases the stress value, tensile strength, and tear resistance at a given elongation of 100-300%, without adversely affecting the maximum elongation at break. At the same time, the addition of the additives of Comparative Example 1, shown herein for comparison with the prototype, does not result in any significant improvement in the rubber properties.

[0080] Example 51. This example demonstrates the production of rubber mixtures and rubber based on a mixture of rubber, i.e., natural rubber (using SVR-3L rubber) and butadiene rubber (using Buna CB 24 rubber), without the use of plasticizer oil, using any of the additives from Examples 16, 17, and 25. The additives of Comparative Example 1 were used for comparison with the prototype. The composition of the rubber mixtures is shown in Table 12. Rubber without additives was mixed in two stages using an internal mixer WSM SKI-3.5L and then homogenized in a two-roll rubber mill Zamak 200 / 400 with a friction coefficient of 1:1.2. In the first stage, rubber, carbon black N330, stearic acid, ZnO, and N-(isopropyl)-N'-phenyl-1,4-phenyldiamine (iPPD) antioxidant were mixed for 5 minutes at a maximum mixing temperature of 130°C. In the second stage, a curing agent of benzothiazole sulfenamide (CBS), diphenylguanidine (DPG), sulfur, and additives were introduced into the rubber compound at a maximum temperature of 100°C for 2 minutes. Therefore, the step of adding additives containing carbon nanotubes is combined with the step of adding the curing system.

[0081] Table 12 shows the volume resistivity and physical and mechanical properties of the cured rubber samples, and pre-cut crescent-shaped samples were used for tear resistance testing. Adding the additives of Examples 16, 17, and 25 to the rubber compound significantly reduced the rubber's volume resistivity, increased the stress value at a given elongation of 100-300%, and increased the tear resistance, without significantly adversely affecting the maximum elongation at break and tensile strength. Furthermore, adding the additives of Examples 16, 17, and 25 to the rubber compound improved the rubber hardness. Simultaneously, the addition of the additives of Comparative Example 1, shown herein for comparison with the prototype, did not result in any significant improvement in rubber properties.

[0082] Example 52. This example demonstrates the production of rubber mixtures and rubber based on carbon black-filled nitrile butadiene rubber using the additives of Examples 18-20, 25-26, and 44. For comparison with the prototype, the additive of Comparative Example 3 was used (dispersion of single-walled carbon nanotubes in liquid nitrile butyl rubber oligomer Nipol 1213). The rubber was mixed in two stages using an internal mixer WSM SKI-3.5L and then homogenized in a 2-roll rubber mill 200 / 400 with a diameter of 200 mm, a length of 400 mm, and a friction coefficient of 1:1.2. In the first stage, the rubber, carbon black, ZnO, stearic acid, dibutyl phthalate (DBP), and N-(isopropyl)-N'-phenyl-1,4-phenyldiamine (iPPD) antioxidant were mixed for 5 minutes at a maximum mixing temperature of 120°C. In the second stage, N-cyclohexyl-2-benzothiazole sulfenamide (CZ) and a sulfur curing agent were added over a period of 2 minutes at a maximum mixing temperature of 90°C. The step of adding the additive containing carbon nanotubes was carried out using an internal mixer. The addition of this additive to the rubber compound was combined with the addition of the curing agent to the rubber compound.

[0083] Table 13 shows the results of testing cured rubber samples regarding the rubber mixture formulation, conductivity, and physical and mechanical properties. These data indicate that the additives in Examples 18-20, 25-26, and 46 resulted in technical improvements, namely improvements in mechanical properties (coefficients M50-M200 and tear resistance) and conductivity, while the effect of the additive in Comparative Example 3 on conductivity was remarkably low, and there was no effect on physical and mechanical properties.

[0084] Example 53. This example demonstrates the production of rubber mixtures and rubbers based on silicon dioxide-filled nitrile butadiene rubber using the additives of Examples 21-23, 25, 29, 31-34, and 39-41. For comparison with the prototype, the additive of Comparative Example 3 was used (dispersion of single-walled carbon nanotubes in liquid nitrile butyl rubber oligomer Nipol 1213). The rubber was mixed in two stages using an internal mixer WSM SKI-3.5L and then homogenized in a 2-roll rubber mill 200 / 400 with a diameter of 200 mm, a length of 400 mm, and a friction coefficient of 1:1.2.

[0085] In the first stage, rubber, carbon black, ZnO, stearic acid, silicon dioxide, silane coupling agent TESPT (Si-69), titanium dioxide, and N-(isopropyl)-N'-phenyl-1,4-phenyldiamine (iPPD) antioxidant were mixed at a maximum mixing temperature of 150°C for 5 minutes. In the second stage, mercaptobenzothiazole disulfide (MBTS), tetramethylthiuram disulfide (TMTD), and sulfur curing agents were introduced into the rubber compound at a maximum temperature of 90°C for 2 minutes. The addition of additives containing carbon nanotubes was carried out using an internal mixer. The addition of these additives to the rubber compound was combined with the addition of the curing agents to the rubber compound.

[0086] Tables 14 and 15 show the results of testing cured rubber samples regarding the rubber mixture formulation, conductivity, and physical and mechanical properties. These data indicate that the additives in Examples 21-23, 25, 29, 31-34, and 39-41 produce sufficient technical results, namely improvements in the mechanical properties (coefficients M50-M200 and tear resistance) and conductivity of the rubber to dissipate static charge, but that larger amounts of additives 40-41 (including multi-walled carbon nanotubes) are required to achieve these technical results, while the effect of the additives in Comparative Example 3 on conductivity and tear resistance is not significant.

[0087] Example 54. This example demonstrates the production of rubber mixtures and rubber based on a mixture of rubber, namely styrene-butadiene rubber (solution SBR Buna VSL 4526-2HM expanded with TDAE oil) and butadiene rubber (using Buna CB 24 rubber), using any of the additives from Examples 9, 22, 24-28, and 45. For comparison with the prototype, the additive from Comparative Example 4, in which single-walled carbon nanotubes were dispersed in a liquid oligomer of styrene-butadiene rubber Kuraray LSBR-820, was used. The composition of the rubber mixture is shown in Tables 16 and 17. This composition emulates the composition of a rubber mixture for automotive tire treads. Note that the rubber mixture does not contain carbon black or any other conductive fillers, apart from the additives containing carbon nanotubes. The additive-free rubber was mixed in three stages using an internal mixer WSM SKI-3.5L and then homogenized after mixing in a two-roll rubber mill Zamak 200 / 400 with a friction coefficient of 1:1.2.

[0088] In the first stage, rubber, oil TDAE Normal 346, silicon dioxide, silane coupling agent bis(triethoxysilylpropyl)tetrasulfide (Si-69), and stearic acid were mixed at a maximum mixing temperature of 150°C for 5 minutes. The amount of plasticizer (TDAE oil) was reduced by the amount of low molecular weight dispersion medium introduced along with the additives. In the second stage, the mixture was homogenized, and zinc oxide and the antioxidant N-(1,3-dimethyl)-N'-phenyl-1,4-phenyldiamine (iPPD) were added over 2 minutes at a maximum mixing temperature of 110°C. In the third stage, sulfur, the curing agents N-tert-butyl-2-benzothiazole sulfenamide (TBBS) and diphenylguanidine (DPG) were introduced into the rubber compound over 2 minutes at a maximum mixing temperature of 110°C. The additives were introduced in the second stage, while the addition of additives was combined with the homogenization of the mixture and the addition of zinc oxide and antioxidants. The exception is that the additives in Example 45 are added to the styrene-butadiene rubber at separate stages in the two-roll rubber mill prior to step 1. The volume resistivity and physical and mechanical properties of the cured rubber samples are shown in Tables 16 and 17, and pre-cut crescent-shaped samples were used for tear resistance testing.

[0089] This data shows that when the additives of Examples 9, 22, 24-28, and 45 are added to the rubber compound, the volume resistivity and surface resistance of the rubber are significantly reduced, while conductive rubber is provided even in the absence of other conductive fillers, and stress values, tensile strength, and tear resistance at a given elongation of 100-300% are increased without adversely affecting the maximum elongation at break. At the same time, the addition of the additives of Comparative Example 4, shown herein for comparison with the prototype, does not result in any significant improvement in the rubber properties.

[0090] As shown in Table 17, the addition of the additives in Examples 24-25 and 45 significantly increased the loss tangent (tan(δ)) in dynamic mechanical tests at 0°C, which characterizes the friction coefficient and traction of the tire tread. Therefore, tire quality can be greatly improved by adding the additives to the rubber mixture for the manufacture of tire treads. It should be noted that this addition of the additives has only a very slight effect on (tan(δ)) at high temperatures (e.g., 60°C), meaning it does not increase the rolling resistance of the tire.

[0091] It should also be noted that this example further demonstrates that the addition of 0.38 wt% carbon nanotubes achieves further technical benefits, namely a 10% increase in the thermal conductivity of the cured rubber. The thermal conductivity data is shown in Table 17. [Table 1] JPEG0007898249000002.jpg254122JPEG0007898249000003.jpg254122 [Table 2] [Table 3] [Table 4] [Table 5] [Table 6] [Table 7] [Table 8] [Table 9] [Table 10] [Table 11] [Table 12] [Table 13] [Table 14] [Table 15] [Table 16] [Table 17] [Industrial applicability]

[0092] The present invention provides rubber that can be used in the manufacture of rubber compounds and has improved conductivity and physical and mechanical properties.

Claims

1. An additive to rubber compounds for improving the conductivity and physical and mechanical properties of rubber, 1-20% by weight of carbon nanotubes; High-viscosity organic rubber in a concentration of 3 to 90% by weight; and The high-viscosity organic rubber (R) comprises 8 to 95% by weight of a low molecular weight dispersion medium capable of dissolving it. (a) an oil having a flash point greater than 200°C and a kinematic viscosity of less than 1 St at 100°C, (b) a polar solvent having a dielectric constant greater than 5 at 25°C, and (c) an ester or mixture of one or more esters of an aliphatic alcohol and an acid selected from the group consisting of (1) phthalic acid, (2) terephthalic acid, (3) sebacic acid, (4) adipic acid, and (5) cyclohexanedicarboxylic acid. Carbon nanotubes exceeding 25% by weight are single-walled or double-walled carbon nanotubes. The carbon nanotube has a G / D band intensity ratio of more than 10 in the Raman spectrum at 532 nm. Additives.

2. The additive according to claim 1, wherein the high-viscosity organic rubber is selected from the group consisting of natural rubber, synthetic isoprene rubber, styrene-butadiene rubber, nitrile-butadiene rubber, hydrogenated nitrile-butadiene rubber, butadiene rubber or butyl rubber, halobutyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber containing ethylene norbornene or dicyclopentadiene as a third monomer, propylene oxide rubber, acrylate rubber, carboxylate rubber, chloroprene rubber, fluoroelastomer, and mixtures of two or more of these rubbers.

3. The aforementioned high-viscosity organic rubber has a viscosity exceeding 20 Mooney units at 100°C. （１＋４） The additive according to claim 1, having the following characteristics.

4. The aforementioned high-viscosity organic rubber has a viscosity exceeding 40 Mooney units at 100°C. （１＋４） The additive according to claim 3, having the following characteristics.

5. The aforementioned high-viscosity organic rubber has a viscosity exceeding 60 Mooney units at 100°C. （１＋４） The additive according to claim 4, having the following characteristics.

6. The additive according to claim 1, wherein the dispersion medium is a polar solvent having a relative permittivity of more than 40 at 25°C.

7. The additive according to claim 6, wherein the dispersion medium comprises at least 10% by weight of propylene carbonate.

8. The additive according to claim 6, wherein the dispersion medium comprises at least 10% by weight of 1,2-butylene carbonate, 2,3-butylene carbonate, or a mixture thereof.

9. The additive according to claim 1, wherein the carbon nanotube has a G / D band intensity ratio of more than 40 in the Raman spectrum at 532 nm.

10. The additive according to claim 1, wherein the carbon nanotube has a G / D band intensity ratio of more than 60 in the Raman spectrum at 532 nm.

11. The additive according to claim 1, wherein the ratio of the mass fraction of the carbon nanotube to the mass fraction of the rubber bonded to the carbon nanotube is less than 4.

12. The additive according to claim 1, wherein at least a portion of the carbon nanotubes are bundled together.

13. The additive according to claim 12, wherein the thickness of at least a portion of the carbon nanotube bundle is greater than 300 nm.

14. The additive according to claim 1, further comprising one or more metal particles or alloys thereof derived from Groups 8 to 11.

15. The additive according to claim 1, wherein the additive has a volume resistivity of 2 ohms·m or less at a temperature of 25°C.

16. The additive according to claim 1, wherein the additive has a viscosity of more than 5 and less than 90 Mooney units at a temperature of 100°C.

17. The additive according to claim 1, wherein the viscosity of the additive is characterized by a needle penetration depth of less than 15 mm at a temperature of 25°C for 5 seconds under a specified load of 100 g.

18. A method for producing the additive according to claim 1, comprising the following sequential steps: A method comprising the steps of (I) dissolving the high-viscosity rubber (R) in the dispersion medium, and (II) dispersing carbon nanotubes in the solution of step (I).

19. The method according to claim 18, further comprising an additional step between step (I) and step (II) of pre-wetting and mixing carbon nanotubes in the dispersion medium or one of the components of the dispersion medium, or in a solution of rubber (R) in the dispersion medium.

20. The method according to claim 19, further comprising step (III) of mixing the obtained carbon nanotube slurry, dispersion medium, and high viscosity organic rubber (R) with high viscosity organic rubber (R2) after step (II), wherein the ratio of the weight of rubber (R2) to the weight of slurry after step (II) is 5 or less.

21. A method for producing rubber, comprising adding the additive described in claim 1 to the rubber.

22. The method according to claim 21, further comprising adding a filler, and / or a plasticizer, and / or an antioxidant, and / or a silane coupling agent, and / or a curing agent, and / or a curing accelerator, and / or a curing retarder, and / or a stabilizer, and / or a dye, and / or a pigment to the rubber.

23. The method according to claim 21, wherein the addition is performed using an internal mixer.

24. The method according to claim 21, wherein the addition is performed using a two-roll rubber mill.

25. A rubber having improved conductivity and physical and mechanical properties, comprising 0.01 to 1% by weight of carbon nanotubes, and manufactured by the method of claim 21.

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