Thermal treatment of recovered carbon black (RCB) to improve the electrical properties and use thereof in components made of an elastomer material

Abstract

The invention relates to a method for producing thermally post-treated recovered carbon black (rCB), comprising the thermal treatment of rCB at a temperature in the range of 1000 to 3000°C. The thermally post-treated rCB produced according to the invention has a high electrical conductivity and is suitable in particular as a sustainable filler or sustainable conductivity additive for components made of an elastomer material.

Description

[0001] Description

[0002] Thermal treatment of recovered carbon black (rCB) to improve electrical properties and its use in components made of an elastomer material

[0003] Field of the invention

[0004] The invention relates to a process for producing thermally post-treated recovered carbon black (rCB), the thermally post-treated rCB obtained therefrom with improved electrical properties and components made of an elastomer material which contain this thermally post-treated rCB.

[0005] State of the art

[0006] Industrial carbon blacks, especially standard carbon blacks, as they are currently used in technical elastomer materials, are often conductive due to their graphitic layer structure and these types almost always form the basis for electrical conductivity in elastomer materials at higher filler levels.

[0007] Commercially available "recovered carbon black" (rCB) has been discussed for some time as a sustainable alternative material. These materials are derived from the recycling of elastomer products and are manufactured using different processes than conventional industrial or standard carbon blacks.

[0008] Compared to industrial carbon black, rCBs exhibit particularly altered surface properties due to the presence of numerous functional groups and amorphous carbonaceous residues. Commercially available rCBs typically contain production-related impurities that can amount to, for example, 2 to 25 wt.%, frequently 5 to 10 wt.%, of the total weight of the rCB. The impurities are not carbon black. The impurities are usually inorganic material, e.g., zinc compounds, silicon dioxide, and / or silicates. This contamination is due to additives contained in rubber waste, especially scrap tires. The amount of impurity in an rCB can be easily determined analytically, e.g., by thermogravimetry.

[0009] The altered surface properties and impurities are clearly noticeable in the conductivity properties, which result in rCBs having only low electrical conductivity, while the physical / mechanical strengthening effects of rCBs are comparable to those of carbon black. In technical applications where electrical properties are not important, it is therefore possible to replace carbon black entirely or at least partially with rCBs.

[0010] The lack of electrical properties of rCB is due to the pyrolysis process used during production. Due to impurities in the starting material, the surface of the resulting rCB contains significantly more organic groups and inorganic impurities, which, under the conditions of the pyrolysis process, prevent the formation of a homogeneous graphite layer on the surface, which is responsible for the high electrical conductivity of carbon black.

[0011] When the electrical properties of carbon black, particularly its high electrical conductivity, are crucial, substitution with rCBs is only possible to a limited extent or not at all. Especially when high electrical conductivity requirements are placed on it, as in refueling hoses, it has therefore not yet been possible to replace carbon blacks as a filler with rCBs. The altered properties of rCBs, and in particular their reduced electrical conductivity compared to carbon blacks, is therefore a problem that limits the possible applications of rCBs. C. Roy et al., "Heat-treatment of carbon blacks obtained by pyrolysis of used tires.""Effect on the surface chemistry, porosity and electrical conductivity", Journal of Analytical and Applied Pyrolysis, Volume 67(1 ), pages 55 to 76, 2003, investigates the effects of thermal post-treatment on the surface properties, porosity, and electrical conductivity of rCBs. In this context, various pressures and temperatures ranging from 490 to 870 °C were tested for the thermal post-treatment of rCB.

[0012] A disadvantage of the current state of the art is that it has not yet been possible to provide rCBs with very high electrical conductivity. In particular, it has not yet been possible to provide rCBs with sufficiently high conductivity to replace carbon black in technical applications that place high demands on conductivity, especially in elastomer materials.

[0013] Description of the invention

[0014] Against this background, there is a need for sustainable carbon black types with high electrical conductivity. In particular, the object of the present invention was to provide a process by which rCBs with high electrical conductivity, e.g., with an electrical conductivity of more than 2.5 S / cm, can be obtained. A further object of the present invention was to provide components made of an elastomer material in which industrial carbon blacks used as fillers or conductivity additives can be completely or at least partially replaced by rCBs, yet which are nevertheless suitable for engineering elastomers with high conductivity requirements.

[0015] Surprisingly, the inventors have found that this problem can be solved by thermally post-treating commercially available rCB in a temperature range of 1000 to 3000°C. The invention thus relates to a process for producing thermally post-treated recovered carbon black (rCB), comprising the thermal treatment of rCB at a temperature in the range of 1000 to 3000°C.

[0016] The investigations have shown that the process according to the invention leads to a significant increase in the electrical conductivity of the rCBs treated according to the invention. Without being bound to any particular theory, it is assumed that the thermal post-treatment according to the invention at these high temperatures leads to a significant graphitization of the surface of the rCB, which can significantly increase the electrical conductivity of the rCB.

[0017] The rCBs obtainable by the process according to the invention can thus also be used for technical elastomer applications with high conductivity requirements. This was not possible in the past and represents a significant advantage of the invention.

[0018] This makes it possible to provide components made of an elastomer material that are suitable for elastomer applications with high conductivity requirements, while the mechanical properties of the component differ little or not at all from components containing conventional industrial carbon black.

[0019] The invention makes it possible to provide components made of an elastomer material with thermally post-treated rCBs that are sufficiently good electrical conductors to sufficiently reduce the risk of electrostatic discharges and thus to realize technical applications, e.g. as a tank hose, for which non-conductive components are not suitable.

[0020] Since the conventional carbon black in the components made of an elastomer material is partially or completely replaced by thermally post-treated rCB, these components are more sustainable, which is particularly important from an environmental perspective. The invention is described in detail below.

[0021] Recovered carbon black (rCB), also known in Germany as tire pyrolysis black or pyrolysis black, is a type of recovered carbon black. The recycled product rCB is typically obtained from rubber waste, especially scrap tires, usually through pyrolysis processes and is commercially available. Standard terminology for recovered carbon black (rCB) can be found in ASTM D8178:2022, which is referenced here.

[0022] Recovered carbon black is obtained from a recovery process and differs from so-called renewable fillers or soot ("renewable carbon black"), which are obtained from bio-based, renewable raw materials such as wood.

[0023] The process according to the invention produces a thermally post-treated recovered carbon black (rCB). The starting material used is rCB that has already been produced. The thermal post-treatment can, in principle, be carried out with any commercially available rCB. Since the production of rCB typically involves a pyrolysis process, the product produced by the process according to the invention is referred to as thermally post-treated recovered carbon black (rCB).

[0024] The process according to the invention comprises the thermal treatment of rCB at a temperature in the range of 1000 to 3000 °C. Preferably, the thermal treatment of rCB is carried out at a temperature in the range of 1000 to 1500 °C, particularly preferably at a temperature in the range of 1000 to 1200 °C. Below this temperature range, sufficient graphitization of the rCB, which is necessary for high conductivity requirements, cannot be achieved.

[0025] The thermal treatment of the rCB is usually carried out in a furnace. The furnace preferably has a closed chamber, also known as a reaction chamber, into which the rCB is introduced during the thermal treatment.

[0026] The furnace is preferably a pyrolysis reactor, a muffle furnace or a tube furnace.

[0027] The process according to the invention is, in particular, a pyrolysis process, meaning that the thermal treatment of the rCB is carried out largely or completely in the absence of oxygen. The rCB is thus, in particular, subjected to pyrolysis.

[0028] The thermal treatment is therefore usually carried out under an inert gas, preferably nitrogen. Therefore, the thermal treatment is preferably carried out under a nitrogen atmosphere. Applying an inert gas, such as nitrogen, to the rCB before the start of the thermal treatment or before the rCB is introduced into the furnace can also be advantageous.

[0029] The thermal treatment may include a heating period or take place at a constant temperature.

[0030] In a constant temperature thermal treatment, the furnace is brought to the desired temperature for the thermal treatment as specified above (target temperature) and then the rCB to be treated is introduced into the furnace.

[0031] Alternatively, the thermal treatment includes a heating period during which the rCB is introduced into the furnace at a temperature below the target temperature, e.g., ambient temperature. During the subsequent heating period, the furnace, containing the rCB, is heated to the target temperature. Heating can be gradual or stepwise. The heating rate during the heating period can be, for example, 2 to 20 K / min, preferably 5 to 10 K / min. The duration of the thermal treatment is generally not limited and can depend, for example, on the furnace type, the rCB type, and the temperature used.

[0032] Preferably, the thermal treatment is carried out for a duration of 10 minutes to 5 hours, preferably 1 to 2 hours.

[0033] The thermal treatment is carried out, for example, at a temperature in the range of 1000 to 3000 °C for a duration of 10 minutes to 5 hours, preferably at a temperature in the range of 1000 to 1500 °C or 1000 to 1200 °C for a duration of 1 to 2 hours.

[0034] The specified duration of the thermal treatment refers only to the time during which the temperature required for the thermal post-treatment, between 1000 and 3000°C, prevails. The time required during a heating period to reach the required temperature is not included in the heat treatment duration.

[0035] The thermal treatment of the rCB can be carried out in the presence of one or more additives, wherein the additive is preferably selected from an oxidizing agent and / or a hydrocarbon-based additive.

[0036] The additive is essentially unlimited and primarily serves to promote the graphitization of rCB during thermal treatment. Such additives are also referred to as graphitization additives. In particular, the oxidizing agents used as additives are generally used in small quantities, so the process is still considered pyrolysis.

[0037] The oxidizing agent is preferably air, O2, O3, an oxygen-containing acid, water vapor, CO2, or combinations thereof. The hydrocarbon-based additive is preferably natural gas, petroleum, acetylene, or combinations thereof.

[0038] Combinations of the above-mentioned additives or, if necessary, the addition of a catalyst are also possible.

[0039] The thermal treatment of rCB is preferably carried out at atmospheric pressure, which allows for simple process control. However, the thermal treatment can also be carried out at overpressure or underpressure.

[0040] The present invention also relates to a thermally post-treated rCB obtainable by the process according to the invention.

[0041] The rCB according to the invention exhibits exceptionally high electrical conductivity. The thermally post-treated rCB according to the invention preferably exhibits an electrical conductivity of more than 2.5 S / cm, preferably more than 2.6 S / cm.

[0042] The electrical conductivity of the thermally post-treated rCB can be determined using the following measurement protocol, which was taken from the above-cited publication by C. Roy et al.

[0043] Electrical conductivity was determined at room temperature by impedance spectroscopy in the frequency range from 10 to 200 Hz at a voltage of 1 V using a computer-controlled impedance-Z gain phase analyzer SI 1260 from Solartron (Farnborough, Hampshire, UK). A sample of approximately 2 g of thermally post-treated rCB, dried overnight at 100 °C, was compressed in a hollow glass cylinder with an inner diameter of 11 mm between two metal pistons at a pressure of 0.009 to 1.7 MPa. These pressures were achieved by placing metal parts of different masses on the upper piston. The very small changes in sample height were measured using a cathometer from Gaertner Scientific Corporation (Chicago, IL, USA). Electrical conductivity (α) is determined by the following relationship: α 1 ~ α α

[0044] Where / is the change in sample height, R is the resistance in ohms and A is the surface area of ​​the bulb.

[0045] The present invention also relates to a component made of an elastomer material, comprising at least one elastomer and recovered carbon black (rCB), wherein the rCB is an rCB thermally post-treated at a temperature of 1000 to 3000°C.

[0046] Preferably, the rCB thermally treated at a temperature of 1000 to 3000°C is thermally post-treated rCB obtainable by the process according to the invention as described above. The thermally post-treated rCB according to the invention is further described above, to which reference is made.

[0047] Since the thermally post-treated rCBs according to the invention have a very high electrical conductivity, the components according to the invention are particularly suitable for applications with high requirements on electrical conductivity.

[0048] The electrical conductivity of an elastomer material can be determined by measuring the volume resistance according to DIN EN 62631-3-1. In general, an electrically conductive component made of an elastomer material is understood to be a component that has an electrical volume resistance of less than 10*10 3Q, measured according to DIN EN 62631-3-1:2017. The term electrical volume resistance is defined in DIN EN 62631-3-1:2017. The unit for electrical volume resistance is ohms. The electrical volume resistance, measured according to DIN EN 62631-3-1:2017, was determined on vulcanized elastomer materials with a thickness of 6 mm and a diameter of 60 mm. As suggested in DIN EN 62631-3-1:2017, conductive silver ink was applied to the top and bottom of the samples as a contact material. For the conductive samples, the volume resistance between the top and bottom was then determined according to DIN EN 62631-3-1:2017 at a measuring voltage of 6 V.

[0049] The component according to the invention preferably has an electrical volume resistance of less than 1000 ohms, preferably less than 500 ohms, measured according to DIN EN 62631-3-1:2017.

[0050] The elastomer material of the component according to the invention comprises at least one elastomer. The at least one elastomer can be a single elastomer or a mixture of two or more elastomers.

[0051] Elastomer materials based on at least one elastomer are formed by vulcanizing a compound comprising one or more unvulcanized elastomers or rubbers. The compound also typically contains vulcanizing agents, e.g., sulfur-based vulcanizing agents or peroxide vulcanizing agents, and may contain one or more additives commonly used in rubber technology. The compound for the elastomer material contains the thermally post-treated rCB as described above.

[0052] The at least one elastomer of the elastomer material can be, for example, a vulcanized rubber selected from the group consisting of acrylonitrile-butadiene rubber (NBR), carboxyl group-containing nitrile rubber (XNBR), ethylene-vinyl acetate copolymer (EVAC), ethylene-vinyl acetate rubber (EVM), hydrogenated acrylonitrile-butadiene rubber (HNBR), perfluorocarbon rubber (FFKM), ethylene-acrylate rubber (AEM), polyacrylate rubber (ACM), chloropolyethylene rubber (CM), chlorosulphonyl polyethylene rubber (CSM), ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), fluorocarbon rubber (FKM), epichlorohydrin rubber (CO), epichlorohydrin copolymer rubber (ECO), epichlorohydrin terpolymer (GECO), polydimethylsiloxane (PDMS), propylene oxide copolymer rubber (GPO), butadiene rubber (BR), chloroprene rubber (CR), isobutene-isoprene rubber (HR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), isoprene rubber (IR), natural rubber (NR),Styrene-butadiene rubber (SBR), fluorosilicone rubber (FVMQ), methylphenylsilicone rubber (PMQ), methylphenylvinylsilicone rubber (PVMQ), methylsilicone rubber (MQ), methylvinylsilicone rubber (VMQ), polyester urethanes (AU), polyether urethanes (EU) and combinations thereof.

[0053] The elastomer material may contain one or more other additives commonly used in the art. Examples of such additives include plasticizers, additional fillers other than the thermally post-treated rCB according to the invention, such as carbon black, silica, or calcium carbonate, processing aids, anti-aging agents, or combinations thereof.

[0054] In a preferred embodiment, the amount of thermally post-treated rCB in the elastomer material is 10 to 80 phr, preferably 20 to 50 phr. The unit phr is customary in the art and means parts by weight per 100 parts by weight of rubber or elastomer.

[0055] The component according to the invention can preferably be a component of a hose, in particular a refueling hose, a tire, an EMC shielding material, a non-visible marking, a belt, a shoe sole, a drive belt, an air spring, a conveyor belt, an elastomer-coated fabric, a vibration damper element, a heatable elastomer application, or an electronic component. EMC is an abbreviation for electromagnetic compatibility and refers to the ability of an EMC shielding material to protect devices or equipment from unwanted electrical or electromagnetic effects.

[0056] An invisible marking, preferably a security marking, can be achieved, for example, by a patterned arrangement of an electrically conductive component made of an elastomer material and / or an electrically non-conductive component made of an elastomer material. A marking formed by the pattern is not visible but can be read by measuring the different electrical conductivities.

[0057] The component can be, for example, a component of an electrically conductive refueling hose, a conductive tire, or an antistatic belt. Preferred examples of an electronic component are a capacitor, preferably an elastic capacitor, a sensor component, or an electrical switching element. The capacitor, in particular the elastic capacitor, is preferably a film capacitor.

[0058] The present invention also relates to the use of the thermally post-treated rCB according to the invention as a filler or conductivity additive for a component made of an elastomer material. Due to the high electrical conductivity of the rCB according to the invention, it is particularly suitable as a sustainable replacement for the otherwise conventional industrial carbon blacks in components made of an elastomer material with high electrical conductivity requirements, such as the aforementioned examples for the component.

[0059] Preferably, the rCB thermally treated at a temperature of 1000 to 3000°C is thermally post-treated rCB obtainable by the process according to the invention.

[0060] The present invention also relates to the use of the component according to the invention as described above as a component of a hose, in particular a refueling hose, a tire, an EMC shielding material, an invisible marking, a belt, a shoe sole, a drive belt, an air spring, a conveyor belt, an elastomer-coated fabric, a vibration damper element, a heatable elastomer application or an electronic component.

[0061] For the uses according to the invention, all information given above for the elastomer article according to the invention applies in the same way, so that reference is made thereto.

Claims

Patent claims 1. A process for producing thermally post-treated recovered carbon black (rCB), comprising thermally treating rCB at a temperature in the range of 1000 to 3000 °C.

2. The process according to claim 1, wherein the thermal treatment of rCB is carried out at a temperature in the range of 1000 to 1500 °C, preferably 1000 to 1200 °C.

3. The method according to claim 1 or 2, wherein the thermal treatment is carried out for a period of 10 minutes to 5 hours, preferably 1 to 2 hours.

4. Process according to one of the preceding claims, wherein the thermal treatment is carried out under inert gas, preferably under nitrogen.

5. Method according to one of the preceding claims, wherein the thermal treatment comprises a heating period or takes place at a constant temperature.

6. The process according to any one of the preceding claims, wherein the thermal treatment of the rCB is carried out in the presence of one or more additives, wherein the additive is preferably selected from an oxidizing agent and / or a hydrocarbon-based additive.

7. Process according to one of the preceding claims, wherein the thermal treatment takes place in a pyrolysis reactor, a muffle furnace or a tube furnace.

8. Component made of an elastomer material comprising at least one elastomer and recovered carbon black (rCB), wherein the rCB is an rCB thermally post-treated at a temperature of 1000 to 3000°C.

9. Component according to claim 8, wherein the thermally post-treated rCB was obtained by a process according to any one of claims 1 to 7.

10. Component according to claim 8 or 9, wherein the at least one elastomer is a vulcanized rubber selected from the group consisting of acrylonitrile-butadiene rubber (NBR), carboxyl-containing nitrile rubber (XNBR), ethylene-vinyl acetate copolymer (EVAC), ethylene-vinyl acetate rubber (EVM), hydrogenated acrylonitrile-butadiene rubber (HNBR), perfluorocarbon rubber (FFKM), ethylene-acrylate rubber (AEM), polyacrylate rubber (ACM), chloropolyethylene rubber (CM), chlorosulphonyl polyethylene rubber (CSM), ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), fluorocarbon rubber (FKM), Epichlorohydrin rubber (CO), epichlorohydrin copolymer rubber (ECO), epichlorohydrin terpolymer (GECO), polydimethylsiloxane (PDMS), propylene oxide copolymer rubber (GPO), butadiene rubber (BR), chloroprene rubber (CR), isobutene-isoprene rubber (HR), bromobutyl rubber (BIIR), chlorobutyl rubber (CIIR), isoprene rubber (IR), natural rubber (NR),Styrene-butadiene rubber (SBR), fluorosilicone rubber (FVMQ), methylphenylsilicone rubber (PMQ), methylphenylvinylsilicone rubber (PVMQ), methylsilicone rubber (MQ), methylvinylsilicone rubber (VMQ), polyester urethanes (AU), polyether urethanes (EU) and combinations thereof.

11. Component according to one of claims 8 to 10, wherein the amount of thermally post-treated rCB in the elastomer material is 10 to 80 phr, preferably 20 to 50 phr.

12. Component according to one of claims 8 to 11, wherein the component is a component of a hose, in particular a refueling hose, a tire, an EMC shielding material, a non-visible marking, a belt, a shoe sole, a drive belt, an air spring, a conveyor belt, an elastomer-coated fabric, a vibration damper element, a heatable elastomer application or an electronic component.

13. Thermally post-treated rCB, obtainable by a process according to any one of claims 1 to 7.

14. Thermally post-treated rCB according to claim 13, which has an electrical conductivity greater than 2.5 S / cm.

15. Use of thermally post-treated rCB according to claim 13 or 14 as a filler or conductivity additive for a component made of an elastomer material.