Method for producing purified regenerated carbon black

Abstract

One embodiment of the present invention provides a method for producing purified regenerated carbon black, the method being capable of extracting regenerated carbon black having a quality suitable for different applications from regenerated carbon black. In one embodiment, the present invention relates to a method for producing purified regenerated carbon black, the method comprising: a dispersion treatment step for subjecting regenerated carbon black to a dispersion treatment for imparting solvent dispersibility to the regenerated carbon black to obtain a regenerated carbon black dispersion liquid; and a centrifugal separation step for subjecting the regenerated carbon black dispersion liquid to a centrifugal separation treatment to obtain a rapidly settling particle component-containing substance and a slowly settling particle component-containing substance. In addition, another embodiment of the present invention provides a method for producing purified regenerated carbon black, the method removing a zinc compound from regenerated carbon black. In one embodiment, the present invention relates to a method for producing purified regenerated carbon black, the method including a step for bringing regenerated carbon black into contact with persulfate in a solvent.

Description

Method for producing refined and recycled carbon black

[0001] This invention relates to a processing technology for recycled carbon black.

[0002] In recent years, efforts to reduce the burden on the global environment have been actively pursued, including initiatives such as carbon neutrality and sustainability. The carbon black industry is also exploring the use of recycled carbon black, obtained by thermally decomposing rubber products such as waste tires, as part of its sustainability activities.

[0003] As a method for producing recycled carbon black by thermal decomposition of waste tires, for example, Patent Document 1 discloses a method of thermally decomposing waste tires at approximately 500°C by circulating nitrogen gas.

[0004] Japanese Patent Publication No. 5813985 WO2013 / 095145A1

[0005] This disclosure aims to solve the problems relating to the first invention and / or the problems relating to the second invention. A single tire has multiple parts with different performance requirements, such as the tread portion that contacts the ground, the shoulder portion that touches the shoulder of the tire, and the sidewall portion that protects the carcass on the side of the tire. Furthermore, the performance requirements differ for passenger cars, trucks, and buses. And the appropriate quality of carbon black differs for each of these applications.

[0006] However, because recycled carbon black is produced from a mixture of all these waste tires, it ends up being a mixture of carbon black of various qualities, making it unsuitable for any particular application and thus difficult to reuse.

[0007] Therefore, an object of one embodiment of the present invention (the first invention described later) is to provide a method for producing refined recycled carbon black that can extract recycled carbon black of a quality suitable for each application from recycled carbon black.

[0008] Another issue is that rubber products such as waste tires contain zinc compounds derived from vulcanization accelerators and other additives. When recycled carbon black containing a large amount of such zinc compounds is used again as a raw material for rubber products, it may have adverse effects such as reducing the reinforcing properties of the rubber. Therefore, the object of one embodiment of the present invention (the second invention described later) is to provide a method for producing purified recycled carbon black that can remove zinc compounds contained in recycled carbon black.

[0009] As a result of diligent study, the present inventors have found the following present invention and preferred embodiments thereof. The following (1) to (18) correspond to one embodiment of the first invention described below, and (19) to (21) correspond to one embodiment of the second invention described below. <First Invention> (1) A method for producing purified recycled carbon black, comprising: a dispersion treatment step of performing a dispersion treatment on recycled carbon black to impart dispersibility to a solvent to obtain a recycled carbon black dispersion; and a centrifugation step of centrifuging the recycled carbon black dispersion to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

[0010] (2) A method for producing purified recycled carbon black according to (1), comprising: a solvent addition step of adding a solvent to the high-settling-velocity particle component-containing material to obtain a solvent-added solution of the high-settling-velocity particle component; and a recentrifugation step of centrifuging the solvent-added solution of the high-settling-velocity particle component to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

[0011] (3) The method for producing purified recycled carbon black as described in (2), wherein the solvent addition step and the recentrifugation step are repeated two or more times.

[0012] (4) A method for producing purified recycled carbon black according to any one of (1) to (3), wherein the low-sedimentation-velocity particle component-containing material obtained in the centrifugal separation step is obtained as purified recycled carbon black.

[0013] (5) The method for producing purified recycled carbon black according to (2), wherein in the recentrifugation step, the low-sedimentation-velocity particle component-containing material obtained by the final recentrifugation treatment is obtained as purified recycled carbon black.

[0014] (6) The method for producing purified recycled carbon black according to (3) or (4), wherein in the re-centrifugation step, a low sedimentation rate particle component-containing material obtained by performing the final re-centrifugation treatment is obtained as the purified recycled carbon black.

[0015] (7) The method for producing purified recycled carbon black according to any one of (1) to (6), further comprising a pulverization step of pulverizing the recycled carbon black to obtain a pulverized product of the recycled carbon black before the dispersion treatment step, and in the dispersion treatment step, performing a dispersion treatment for imparting dispersibility in a solvent to the pulverized product of the recycled carbon black.

[0016] (8) The method for producing purified recycled carbon black according to any one of (1) to (7), wherein the recycled carbon black is derived from rubber products.

[0017] (9) The method for producing purified recycled carbon black according to any one of (1) to (8), wherein in the centrifugation step, a dispersion of recycled carbon black is continuously supplied to a centrifuge, and the obtained low sedimentation rate particle component-containing material and high sedimentation rate particle component-containing material are respectively discharged from the centrifuge continuously or intermittently.

[0018] (10) The method for producing purified recycled carbon black according to any one of (2) to (9), wherein in the re-centrifugation step, a dispersion of recycled carbon black is continuously supplied to a centrifuge, and the obtained low sedimentation rate particle component-containing material and high sedimentation rate particle component-containing material are respectively discharged from the centrifuge continuously or intermittently.

[0019] (11) The method for producing purified recycled carbon black according to any one of (1) to (10), comprising a solvent removal step of removing the solvent from the low sedimentation rate particle component-containing material to obtain the purified recycled carbon black.

[0020] (12) A method for producing purified recycled carbon black according to any one of (2) to (11), wherein in the centrifugal separation step and the recentrifugal step, n centrifugal separators are prepared, a solvent is added to the high-settling-velocity particle component-containing material discharged from the k-th centrifugal separator, and the liquid is sent to the k+1-th centrifugal separator (wherein k is an integer from 1 to n-1, and n is an integer of 2 or more).

[0021] (13) A method for producing purified recycled carbon black according to (12), comprising a solvent removal step of removing the solvent from the low-settling velocity particle component-containing material to obtain purified recycled carbon black.

[0022] (14) A method for producing purified recycled carbon black according to any one of (1) to (13), wherein the (d90-d10) / d50 in the DCP particle size distribution measurement of the purified recycled carbon black obtained is 1.2 or less.

[0023] (15) The STSA of the purified recycled carbon black obtained is 60 m ２ A method for producing purified recycled carbon black according to any one of (1) to (14), wherein the amount is 1 / g or more.

[0024] (16) A method for producing purified recycled carbon black according to any one of (1) to (15), wherein in the dispersion step, a recycled carbon black dispersion is obtained by contacting the recycled carbon black with an oxidizing agent in a solvent.

[0025] (17) The method for producing purified recycled carbon black according to (16), wherein the oxidizing agent is a persulfate.

[0026] (18) A method for producing purified recycled carbon black according to any one of (1) to (17), wherein the zinc content in the purified recycled carbon black is 1.0% by mass or less.

[0027] <Second Invention> (19) A method for producing purified recycled carbon black, comprising the step of contacting recycled carbon black with a persulfate in a solvent.

[0028] (20) The method for producing refined recycled carbon black according to (19), wherein the recycled carbon black is derived from rubber products.

[0029] (21) The method for producing purified recycled carbon black according to (19) or (20), wherein the zinc content in the purified recycled carbon black is 1.0% by mass or less.

[0030] According to one embodiment of the present invention (the first invention described below), a method for producing refined recycled carbon black is provided, which allows for the extraction of recycled carbon black of a quality suitable for each application from recycled carbon black.

[0031] Furthermore, according to one embodiment of the present invention (the second invention described later), a method for producing purified recycled carbon black is provided, which removes zinc compounds contained in recycled carbon black.

[0032] This graph plots the ASTM grade and the physical properties of Examples 1-7, with STSA on the horizontal axis and DBP absorption on the vertical axis.

[0033] Embodiments of the present invention will be described in detail below with reference to the drawings as appropriate. The following detailed description of the present invention is merely an example of an embodiment, and the present invention is not limited in any way to this embodiment. This specification describes the first and second inventions. The first invention is mainly aimed at obtaining recycled carbon black of a quality suitable for each application by wet classification. The second invention is mainly aimed at removing impurities (especially zinc compounds) using persulfates. In this specification, "wet classification" refers to a process in which recycled carbon black is dispersed in a solvent, and the difference in particle settling velocity caused by applying centrifugal force is used to separate the particles into a group having desired characteristics, as will be described later. In this specification, "method for producing purified recycled carbon black" is also simply referred to as "manufacturing method". In this specification, the upper and lower limits of each numerical range described in steps can be combined arbitrarily. Embodiments of the first invention and embodiments of the second invention will be described in order below.

[0034] <Embodiment of the First Invention> The method for producing purified recycled carbon black of the first invention comprises: a dispersion step of performing a dispersion treatment on recycled carbon black to impart dispersibility in a solvent to obtain a recycled carbon black dispersion; and a centrifugation step of centrifuging the recycled carbon black dispersion to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material. In a preferred embodiment, the method for producing purified recycled carbon black further comprises a grinding step of grinding recycled carbon black to obtain a recycled carbon black grinding product before the dispersion step, and in the dispersion step, a dispersion treatment is performed to impart dispersibility in a solvent to the recycled carbon black grinding product.

[0035] In a more preferred embodiment, the method for producing purified recycled carbon black is characterized by comprising: a grinding step of grinding recycled carbon black to obtain a recycled carbon black grinding product; a dispersion step of performing a dispersion treatment to impart water dispersibility to the recycled carbon black grinding product to obtain a recycled carbon black aqueous dispersion; and a centrifugation step of centrifuging the recycled carbon black aqueous dispersion to separate it into a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material. Each step will be described below.

[0036] <Grinding Process> In one embodiment, the method for producing purified recycled carbon black may optionally include a grinding step before the dispersion process to obtain a recycled carbon black pulverized product. The grinding step in the method for producing purified recycled carbon black is a step of grinding recycled carbon black to obtain a recycled carbon black pulverized product.

[0037] The recycled carbon black used as a raw material in this invention will be described below. This description also applies to recycled carbon black that is subjected to the dispersion process without going through the grinding process. The recycled carbon black used in the grinding process is obtained by thermally decomposing rubber products containing carbon black, such as waste tires, and removing all or part of the rubber component through thermal decomposition. In the manufacture and sale of recycled carbon black, the recycled carbon black is subjected to thermal decomposition of rubber products containing carbon black, and then either not ground, or ground to a certain size, or ground to a size according to the user's requirements. Therefore, in the grinding process in the method for producing refined recycled carbon black, recycled carbon black that has not been ground even once after thermal decomposition of rubber products containing carbon black may be used as the target for grinding. Alternatively, in the grinding process, recycled carbon black that has been ground once or two or more times after thermal decomposition of rubber products containing carbon black may be used as the target for grinding.

[0038] In the production of recycled carbon black, rubber components that could not be completely decomposed by thermal decomposition may remain on the surface. Therefore, recycled carbon black may contain carbon black with rubber residue, mainly composed of rubber carbides, attached to its surface. Normally, unused carbon black, that is, carbon black before being incorporated into rubber products after manufacturing, exists in the form of aggregates of primary particles (hereinafter also referred to as CB aggregates). Focusing on the carbon black component in recycled carbon black, some recycled carbon black has rubber residue attached to its surface. As a result, recycled carbon black may also contain multiple aggregates of CB aggregates (multiple aggregates of CB aggregates) where multiple CB aggregates are fixed via the rubber residue. When multiple aggregates of CB aggregates are included in rubber products such as tires, they reduce their reinforcing properties. Therefore, reducing multiple aggregates of CB aggregates is important for the reuse of recycled carbon black. Therefore, in one embodiment of the present invention for producing purified and recycled carbon black, the adhesion between multiple CB aggregates is released during the grinding process.

[0039] In the grinding step of the method for producing purified recycled carbon black of the present invention, commercially available products can be used as the material to be ground. Examples of commercially available recycled carbon black used in the grinding step include Enrestec's trade name PB365, Bolder Industries' trade name BolderBlack, Delta Energy's trade name DE-Black, and Ecolomondo's trade name MondoBlack. Such recycled carbon black may be recovered by any method and is not particularly limited, but examples include the method described in WO2013 / 095145A1.

[0040] The recycled carbon black that is pulverized in the pulverization process has a Raman spectrum of 1350 ± 20 cm² obtained by laser Raman spectroscopy at an excitation wavelength of 532 nm. －１When the peak intensity of a peak with its peak top within this range (hereinafter also referred to as D-band intensity) is set to 100, the result is 1580 ± 20 cm. －１ Examples of carbon black include those with a peak intensity (hereinafter also referred to as G-band intensity) of a peak having a peak top within the specified range, which is between 110 and 200, and those with a peak intensity between 112 and 190. The G-band intensity, when the D-band intensity of recycled carbon black is set to 100, serves as an indicator of the amount of rubber residue adhering to the carbon black surface. A G-band intensity within the above range indicates that the carbon black is recycled.

[0041] In this invention, the G-band intensity, with the D-band intensity set to 100, refers to the value calculated from the Raman spectrum obtained by measuring under the following measurement conditions (1) and then performing the data processing described in (2). (1) Using a HR-800 laser Raman spectrometer manufactured by Horiba, Ltd., several particles of the carbon black sample to be measured are placed on a glass slide, and the surface is flattened by rubbing it several times with a spatula. The sample is then measured under the following measurement conditions: YAG laser (excitation wavelength): 532 nm Line count: 600 gr / mm Filter: D0.6 Objective lens magnification: 100x Exposure time: 150 seconds Number of integrations: 2 (2) Measurement wavelength (Raman Shift) of the obtained spectrum: 2100 cm －１ The signal intensity at this point is set to 0, and the average value is calculated for every 39 adjacent data points that make up the spectrum. Then, smoothing is performed to obtain a spectral curve connecting these average values. Next, to facilitate comparison between samples, the measurement wavelength is set to 1350 ± 20 cm. －１ The peak top intensity observed within this range is set to 100. Next, 1580 ± 20 cm －１ Determine the peak top intensity of peaks whose peak tops fall within a certain range.

[0042] In the grinding process according to the method for producing purified recycled carbon black of the present invention, the Zn content of the recycled carbon black to be ground is preferably 1.0% by mass or more and 20% by mass or less, more preferably 1.5% by mass or more and 15% by mass or less. Zn in the recycled carbon black is derived from additives of rubber products such as vulcanization accelerator aids.

[0043] One of the purposes of the grinding process is to grind multiple aggregates of CB aggregates in the recycled carbon black, release the adhesion between CB aggregates, and reduce the multiple aggregates of CB aggregates (observed with a particle size of 10 μm or more) in the finally obtained purified recycled carbon black of the present invention as much as possible. For this purpose, it is preferable to grind until the volume-based particle size distribution of the recycled carbon black grinding product after grinding reaches a particle size of 50 μm or less at a cumulative volume frequency of 99%, more preferably until the particle size reaches 20 μm or less at a cumulative volume frequency of 99%, and even more preferably until the particle size reaches 10 μm or less at a cumulative volume frequency of 99%. The lower limit value of the particle size is not particularly limited, but may be 0.5 μm or more, or 1.0 μm or more. Thereby, the yield of the purified recycled carbon black can be increased.

[0044] The grinding device used in the grinding process according to the method for producing purified recycled carbon black of the present invention is not particularly limited as long as it can perform the above grinding. Examples of such grinding devices include roller mills, jet mills, hammer mills, pin mills, cutter mills, roll crushers, stamp mills, ring mills, etc. A jet mill is preferable in that it can reduce multiple aggregates more effectively.

[0045] The nitrogen adsorption specific surface area (N ２ SA) of the recycled carbon black grinding product is preferably 10 m ２ / g or more and 300 m ２ / g or less, more preferably 30 m ２ / g or more and 200 m ２ / g, more preferably 50 m ２ / g or more and 100 m ２ / g or less.

[0046] The external specific surface area (STSA) of the recycled carbon black pulverized material, excluding the specific surface area inside the pores, is preferably 10 m². ２ / g or more 200m ２ / g or less, more preferably 20m ２ / g or more 150m ２ / g, more preferably 40m ２ / g or more 90m ２ It is / g.

[0047] The amount of dibutyl phthalate absorbed (DBP absorbed) from the recycled carbon black pulverized product is preferably 40 ml / 100g or more and 200 ml / 100g or less, more preferably 60 ml / 100g or more and 150 ml / 100g or less, and more preferably 80 ml / 100g or more and 110 ml / 100g or less.

[0048] In the measurement of the disc centrifugal sedimentation particle size distribution (DCP particle size distribution measurement) of recycled carbon black pulverized material, the mode diameter Dst is preferably 30 nm to 300 nm, more preferably 50 nm to 200 nm, and more preferably 80 nm to 110 nm. The DCP particle size distribution can be measured by the method described in the examples.

[0049] In the DCP particle size distribution measurement of recycled carbon black pulverized material, the half-width ΔDst is preferably 40 nm to 250 nm, more preferably 60 nm to 180 nm, and more preferably 80 nm to 110 nm.

[0050] The ΔDst / Dst of the recycled carbon black pulverized product is preferably 0.6 to 1.4, more preferably 0.7 to 1.3, and more preferably 0.8 to 1.1.

[0051] In the DCP particle size distribution measurement of recycled carbon black pulverized material, (d90 - d10) / d50 is preferably 0.5 or more and 3.0 or less, more preferably 0.8 or more and 2.5 or less, and more preferably 1.1 or more and 2.0 or less.

[0052] <Dispersion Process> The dispersion process in the method for producing purified recycled carbon black of the present invention is a process of performing a dispersion process to impart solvent dispersibility to recycled carbon black and obtain a recycled carbon black dispersion. In a preferred embodiment, the dispersion process in the method for producing purified recycled carbon black of the present invention is a process of performing a dispersion process to impart water dispersibility to the recycled carbon black pulverized product obtained by the pulverization process and obtain a recycled carbon black aqueous dispersion.

[0053] In the present invention, the above-described grinding step is not an essential step. The recycled carbon black may be a ground recycled carbon black product obtained by the above-described grinding step, or it may not have undergone the grinding step. In one embodiment, it is preferable that it is a ground recycled carbon black product. In this specification, in the description of the dispersion step and subsequent steps, the term "ground recycled carbon black product" may be read as simply "recycled carbon black" in embodiments where the grinding step is not performed, and the same applies.

[0054] In this specification, "recycled carbon black dispersion" will also be referred to simply as "dispersion." In this specification, the case in which water is used as the solvent is described as a representative example, but the solvent in the present invention is not limited to water, and unless otherwise specified or unless there is a technical contradiction, the descriptions of "water," "water dispersion," etc., shall be read as "solvent," "dispersion," etc., respectively, and the same shall apply when a solvent other than water is used.

[0055] The dispersion process is not particularly limited as long as it is a method that imparts solvent dispersibility (preferably water dispersibility) to the recycled carbon black pulverized material to obtain a recycled carbon black dispersion (preferably a recycled carbon black aqueous dispersion). For example, (i) a method of performing a dispersion process to impart water dispersibility to the recycled carbon black pulverized material by oxidizing it, dispersing the recycled carbon black pulverized material in water to obtain a recycled carbon black aqueous dispersion, and (ii) a method of performing a dispersion process to impart water dispersibility to the recycled carbon black pulverized material by mixing a dispersant with the recycled carbon black pulverized material, dispersing the recycled carbon black pulverized material in water to obtain a recycled carbon black aqueous dispersion.

[0056] The solvent used in the dispersion process is not particularly limited as long as it is a commonly used solvent that does not impair the effects of the present invention, and may be an organic solvent or an aqueous solvent. From the viewpoint of being environmentally friendly and easy to handle, an aqueous solvent is preferred. Such an aqueous solvent may preferably be 100% by mass of water, but a mixed solvent of water and an organic solvent having water affinity, such as alcohols such as methanol, ethanol, and propanol, or ketones such as acetone, may also be used. From the viewpoint of being environmentally friendly and easy to handle, the water content is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to the total amount of the aqueous solvent, and may be 100% by mass, with 100% by mass being even more preferable.

[0057] The water used is not particularly limited and includes pure water, distilled water, deionized water, deaerated water, tap water, well water, etc. The solvent may also contain other additives such as dispersants, as long as they do not interfere with the effects of the present invention.

[0058] (i) is a method in which an oxidizing agent is brought into contact with the recycled carbon black pulverized material in a solvent (preferably water) to oxidize the recycled carbon black pulverized material, generating hydrophilic groups (-COOH, -OH) on the surface of the recycled carbon black pulverized material, thereby imparting water dispersibility to the recycled carbon black pulverized material, and the recycled carbon black pulverized material is dispersed in water to obtain a recycled carbon black aqueous dispersion.

[0059] The oxidizing agent for method (i-1) may be alkali metal salts such as persulfates, hypochlorites, chlorites, chlorates, persulfates, perborates, percarbonates, ammonium salts, hydrogen peroxide, ozone, ozonated water, or M ２ O ２ Examples of oxidizing agents include dichromates (where M is an alkali metal), dichromates, and permanganates. Of these, persulfates are preferred as oxidizing agents because they can impart water dispersibility to the recycled carbon black pulverized material through oxidation, and can also remove Zn, an impurity, from the recycled carbon black pulverized material, thereby reducing the Zn content. Examples of persulfates include alkali metal salts such as lithium persulfate, sodium persulfate, and potassium persulfate, or ammonia salts, with sodium persulfate being more preferred because it has a greater effect in reducing the Zn content.

[0060] In method (i-1), the amount of oxidizing agent used is selected as appropriate, but is preferably 1 to 40 mmol / g, more preferably 2 to 30 mmol / g, in terms of the amount of oxidizing agent per 1 g of recycled carbon black pulverized material.

[0061] In method (i-1), the proportion of recycled carbon black pulverized material in the water is appropriately selected within a range in which the oxidation reaction occurs favorably.

[0062] In method (i-1), recycled carbon black pulverized material and an oxidizing agent are added to water and stirred to perform oxidation treatment on the recycled carbon black pulverized material. The oxidation treatment temperature is appropriately selected depending on the oxidizing agent, preferably 40 to 100°C, more preferably 60 to 90°C, and the oxidation treatment time is appropriately selected depending on the oxidizing agent.

[0063] In method (i-1), when a peroxide salt such as a persulfate is used as the oxidizing agent, after the oxidation treatment, a desalting treatment can be performed to remove salts from the aqueous dispersion medium (solvent) of the regenerated carbon black aqueous dispersion, preferably using an ultrafiltration membrane, filter press, etc., and it is more preferable to use an ultrafiltration membrane. By performing the desalting treatment, unreacted oxidizing agents, reaction residues of oxidizing agents, and impurities such as Zn can be removed. This can improve the solvent dispersibility (preferably aqueous dispersibility) of the regenerated carbon black. When the solvent dispersibility of the regenerated carbon black is improved, the desired separation effect can be more favorably obtained in the subsequent centrifugation and recentrifugation steps.

[0064] In method (i-1), after desalination treatment, the pH of the recycled carbon black aqueous dispersion is adjusted to 4 to 14, preferably 5 to 12, using a base such as sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia. Then, a desalination treatment is performed to remove salts from the aqueous dispersion medium of the recycled carbon black aqueous dispersion using an ultrafiltration membrane, filter press, etc. In this specification, the treatment of adjusting the pH from an acidic state using a base is also referred to as "pH adjustment treatment" or "neutralization treatment".

[0065] Furthermore, as a method of (i), (i-2) a method is to oxidize the recycled carbon black pulverized material by contacting it with an oxidizing gas such as oxygen or ozone, thereby generating hydrophilic groups (-COOH, -OH) on the surface of the recycled carbon black pulverized material, thereby imparting water dispersibility to the recycled carbon black pulverized material, and then dispersing the oxidized recycled carbon black pulverized material in water to obtain a recycled carbon black aqueous dispersion.

[0066] In method (i-2), a method for contacting the recycled carbon black pulverized material with an oxidizing gas such as oxygen or ozone is, for example, to place the recycled carbon black pulverized material in an oxidation furnace, and then supply the oxidizing gas into the furnace while heating the furnace.

[0067] In method (i-2), the oxidation treatment conditions when the recycled carbon black pulverized material is brought into contact with an oxidizing gas such as oxygen or ozone, such as oxidation temperature, amount of oxidizing gas contact, supply rate of oxidizing gas, and pressure of oxidizing gas, are appropriately selected within a range that yields the desired dispersibility.

[0068] Method (ii) involves a dispersion treatment in which a dispersant is mixed with the recycled carbon black pulverized material to impart water dispersibility to the recycled carbon black pulverized material, and then the recycled carbon black pulverized material is dispersed in water to obtain a recycled carbon black aqueous dispersion.

[0069] The dispersant used in method (ii) can be any dispersant that can stably disperse the recycled carbon black pulverized material in water, and any dispersant suitable for dispersing ordinary carbon black can stably disperse the recycled carbon black pulverized material. Examples of dispersants include anionic dispersants, cationic dispersants, amphoteric dispersants, and nonionic dispersants, and can be a resin-type high molecular weight dispersant or a surfactant-type low molecular weight dispersant. Examples of commercially available products include DISPERBY K-2012, DISPERBY K-2013, DISPERBY K-2060, DISPERBY K-2061, and DISPERBY K-2096 from Bic Chemie; TEGO DISPERS 650, TEGO DISPERS 651, TEGO DISPERS 660C, TEGO DISPERS 750W, TEGO DISPERS 752W, TEGO DISPERS 755W, and TEGO DISPERS 760W from Evonik; the Demol series from Kao Corporation; and Nopco Spers 6150 from Sunopco Corporation.

[0070] In method (ii), the amount of dispersant used is selected as appropriate, but is preferably 0.5 to 50% by mass, more preferably 2.0 to 20% by mass, in terms of mass ratio per 1 g of recycled carbon black pulverized material.

[0071] In method (ii), the proportion of recycled carbon black pulverized material in the water is appropriately selected within a range in which dispersion treatment occurs effectively.

[0072] <Centrifugal Separation Process> The centrifugal separation process in the method for producing purified recycled carbon black of the present invention is a process in which a recycled carbon black dispersion (preferably a recycled carbon black aqueous dispersion) is subjected to centrifugal separation using the difference in sedimentation velocity due to differences in particle size, thereby obtaining a material containing high-settling-velocity particle components and a material containing low-settling-velocity particle components. This process is a wet classification, which has a higher classification capacity than dry classification and allows for more precise grading according to the application. In the description of this process and each of the associated processes, the case in which water is used as the solvent is described as an example, but unless otherwise specified, the descriptions of "water," "aqueous dispersion," "recycled carbon black aqueous dispersion," "water addition," etc. should be read as "solvent," "dispersion," "recycled carbon black dispersion," "solvent addition," etc., respectively, and the same applies when a solvent other than water is used.

[0073] In the method for producing purified recycled carbon black of the present invention, the high or low settling velocity refers to the relative high or low settling velocity of the recycled carbon black present in the recycled carbon black aqueous dispersion during the centrifugal separation step, and, if there is a recentrifugation step described later, it refers to the relative high or low settling velocity of the recycled carbon black present in the aqueous solution added to each high-settling-velocity particle component during each recentrifugation step. In other words, it is not a comparison between the centrifugal separation step and the recentrifugation step, nor is it a comparison between multiple recentrifugation steps if multiple recentrifugation steps are performed.

[0074] The main components of the recycled carbon black aqueous dispersion are recycled carbon black with a high settling velocity, recycled carbon black with a low settling velocity, and an aqueous solvent. In the recycled carbon black dispersion or the aqueous solution containing the high settling velocity particle component described later, recycled carbon black with a relatively large particle size has a relatively high settling velocity, and recycled carbon black with a relatively small particle size has a relatively low settling velocity. Therefore, in the centrifugal separation step, the difference in settling velocity is used to separate the recycled carbon black aqueous dispersion to obtain a high settling velocity particle component-containing material and a low settling velocity particle component-containing material. The high settling velocity particle component-containing material is an aqueous dispersion of recycled carbon black with a high settling velocity and / or a solid, water-containing material of recycled carbon black with a high settling velocity. The low settling velocity particle component-containing material is an aqueous dispersion of recycled carbon black with a low settling velocity. Note that the high settling velocity particle component-containing material and the low settling velocity particle component-containing material may also contain dissolved substances of the aqueous solvent.

[0075] The centrifugal separation of the recycled carbon black aqueous dispersion in the centrifugal separation process is a wet centrifugal separation process. By performing the process wet, the individual particles become stably dispersed, making it possible to extract recycled carbon black with physical properties suitable for each application.

[0076] In the centrifugal separation process, any method for centrifuging a recycled carbon black aqueous dispersion that utilizes the difference in sedimentation velocity to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material from the recycled carbon black aqueous dispersion is acceptable. Furthermore, the types of centrifugal separators used for centrifugal separation include batch-type centrifuges, separation plate-type centrifuges, and decanter-type centrifuges. Examples of batch-type centrifuges include the benchtop centrifuge manufactured by Kubota Manufacturing Co., Ltd. and the himac centrifuge manufactured by Eppendorf Himac Technologies. Examples of separation plate-type centrifuges include the TCS series disk-type centrifuge manufactured by Tomoe Engineering Co., Ltd., the Mitsubishi disk separator manufactured by Mitsubishi Chemical Machinery Co., Ltd., and the Saito separator manufactured by Saito Centrifuge Industry Co., Ltd. Examples of decanter-type centrifuges include the PTM type centrifuge manufactured by Tomoe Engineering Co., Ltd., the screw decanter type centrifuge manufactured by IHI Corporation, and the AD series manufactured by Kansai Centrifugal Separator Manufacturing Co., Ltd.

[0077] The inventors have found that carbon black with a large primary particle size and low primary particle aggregation is contained in regions of low mass distribution of aggregates of recycled carbon black, and have found that the low-settling-velocity particle component-containing material obtained by the centrifugation step in the method for producing purified recycled carbon black of the present invention contains CB aggregates with a large primary particle size and low primary particle aggregation without settling.

[0078] Furthermore, CB aggregates with a large primary particle size and low primary particle aggregation have low reinforcing properties when added to rubber products. Therefore, in one embodiment of the present invention for producing purified recycled carbon black, CB aggregates with a large primary particle size and low primary particle aggregation, i.e., CB aggregates with low reinforcing properties, are selectively removed, and separation treatment conditions in the centrifugal separation step and / or recentrifugal step are selected to obtain purified recycled carbon black with high reinforcing properties.

[0079] Furthermore, CB aggregates with a large primary particle size and low primary particle aggregation can be used in applications where strong reinforcement is not required, and can also be used in applications where airtightness is required, such as gas hoses. Therefore, in the method for producing purified recycled carbon black of the present invention, the centrifugal separation treatment conditions in the centrifugal separation step are selected in order to selectively obtain CB aggregates with a large primary particle size and low primary particle aggregation. As a result, the method for producing purified recycled carbon black of the present invention can be used in applications where strong reinforcement is not required, and it becomes easier to obtain purified recycled carbon black for applications where airtightness is required, such as gas hoses.

[0080] And, DBP absorption amount, N ２ The higher the SA and STSA values, and the sharper the particle size distribution, the higher the reinforcing properties of the rubber product. Also, DBP absorption amount, N ２ The lower the SA and STSA values, the lower the viscosity when compounded into rubber products, thus improving the processability of the rubber products. Therefore, the method for producing refined recycled carbon black according to the present invention makes it possible to produce refined recycled carbon black with physical properties suitable for each application.

[0081] In the present invention's method for producing purified recycled carbon black, a low-sedimentation-velocity particle component-containing material obtained by centrifugal separation can be obtained as purified recycled carbon black. Such purified recycled carbon black is in the form of an aqueous dispersion.

[0082] <Solvent Removal Step> Furthermore, in the method for producing purified recycled carbon black of the present invention, a water removal step can be performed to remove water from the low-settling-velocity particle component-containing material obtained by the centrifugal separation step (i.e., the purified recycled carbon black aqueous dispersion) to obtain powdered purified recycled carbon black. When a solvent other than water is used, "water" in this step should be read as "solvent" ("water removal step" should be read as "solvent removal step").

[0083] In the water removal process, methods for removing water from the low-settling-velocity particle component-containing material obtained by centrifugal separation include, for example, heating under atmospheric or reduced pressure to evaporate the water and dry it, or spray drying. Alternatively, the solid content can be increased before evaporation to improve drying efficiency by methods such as filtration, centrifugal concentration, or treatment with a coagulant such as acid. Furthermore, purified and recycled carbon black can be obtained by granulating the slurry after filtration or centrifugal concentration and then drying it. Alternatively, rubber latex can be added before drying, and the resulting wet masterbatch can be recovered.

[0084] In the present invention's method for producing purified recycled carbon black, after the water removal step, the obtained purified recycled carbon black can be subjected to granulation or the like.

[0085] <Solvent Addition Step and Recentrifugation Step> In the method for producing purified and recycled carbon black of the present invention, a solvent addition step (preferably a water addition step) and a recentrifugation step can be performed on the high-settling velocity particle component-containing material obtained by the centrifugal separation step. The solvent used in the solvent addition step is the same as the solvent used in the dispersion treatment step described above, with aqueous solvents being preferred and water being more preferred. In the following, the water addition step is described as an example, but unless otherwise specified, if a solvent other than water is used, "water" should be read as "solvent" and the same procedure should be applied.

[0086] In the method for producing purified recycled carbon black of the present invention, by performing a water addition step and a recentrifugation step, it is possible to obtain purified recycled carbon black with more limited physical properties, or purified recycled carbon black with higher performance, or purified recycled carbon black that is more specialized for a particular application.

[0087] The water addition step involves adding water to a material containing high-settling-velocity particle components to obtain a solution containing high-settling-velocity particle components with added water.

[0088] In the water addition process, the high-settling-velocity particle component-containing material to which water is added is the high-settling-velocity particle component-containing material obtained by the centrifugal separation process.

[0089] In the water addition step, the amount of water added to the high-settling-velocity particulate material is appropriately selected, and in the recentrifugation step, the amount of water added to the high-settling-velocity particulate material is adjusted so that the desired separation effect is obtained.

[0090] In the water addition process, a disperser may be used when adding water to a material containing high-settling velocity particle components. Examples of dispersers include high-pressure homogenizers, sand mills, dyno mills, ball mills, paint shakers, ultrasonic dispersers, and dispersers that disperse by cavitation effect in a high-pressure chamber. Alternatively, dispersion may be performed using a conventional agitator with a stirring blade, a high-speed disperser, an emulsifier, etc.

[0091] The recentrifugation step is a process in which the water-added solution of high-settling-velocity particle components obtained in the water-addition step is separated into a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material by centrifugal separation using the difference in sedimentation velocity, thereby obtaining the high-settling-velocity particle component-containing material and the low-settling-velocity particle component-containing material, respectively.

[0092] The centrifugal separation method and apparatus in the recentrifugation process are the same as those in the centrifugal separation process.

[0093] Then, a water addition step is performed by adding water to the high-settling-velocity particle component-containing material obtained by centrifugal separation to obtain a water-added solution of the high-settling-velocity particle component. Subsequently, the water-added solution of the high-settling-velocity particle component is subjected to a centrifugal separation step to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

[0094] Furthermore, in the method for producing purified recycled carbon black of the present invention, the water addition step and the recentrifugation step may be repeated until purified recycled carbon black having desired physical properties suitable for each application is obtained. When the water addition step and the recentrifugation step are repeated two or more times, the high-settling-velocity particle component-containing material to which water is added in the water addition step is the high-settling-velocity particle component-containing material obtained by the previous centrifugal separation treatment.

[0095] In the method for producing purified and recycled carbon black of the present invention, when the water addition step and the recentrifugation step are repeated two or more times, the water addition step and the recentrifugation step are the same as the water addition step and the recentrifugation step when the water addition step and the recentrifugation step are performed once, except that the substance to which water is added in the water addition step is the substance containing high settling velocity particles obtained in the recentrifugation step, instead of the substance containing high settling velocity particles obtained in the centrifugal separation step.

[0096] For example, if the water addition step and the recentrifugation step are performed twice, the water addition step is performed by adding water to the high-settling-velocity particle component-containing material obtained by the centrifugal separation step to obtain a water-added solution of the high-settling-velocity particle component, and then the obtained water-added solution of the high-settling-velocity particle component is subjected to centrifugal separation to perform a recentrifugation step to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material. Next, the water addition step is performed by adding water to the obtained high-settling-velocity particle component-containing material to obtain a water-added solution of the high-settling-velocity particle component, and then the obtained water-added solution of the high-settling-velocity particle component is subjected to centrifugal separation to perform a recentrifugation step to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

[0097] When the water addition step and the recentrifugation step are performed n times (where n is an integer of 2 or more), the water addition step is performed by adding water to the high-settling-velocity particle component-containing material obtained by the centrifugal separation step to obtain a water-added solution of the high-settling-velocity particle component. Then, the water-added solution of the high-settling-velocity particle component obtained is subjected to centrifugal separation to perform a recentrifugation step to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material. Thereafter, the water addition step and recentrifugation step are repeated for the high-settling-velocity particle component-containing material obtained in the previous recentrifugation step, and the water addition step and recentrifugation step are performed n times to obtain the final high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

[0098] In the method for producing purified recycled carbon black of the present invention, by repeating the water addition step and the recentrifugation step two or more times, it is possible to obtain purified recycled carbon black with more limited physical properties, or purified recycled carbon black with even higher performance, or purified recycled carbon black that is even more specialized for a particular application, compared to when the water addition step and recentrifugation step are performed only once.

[0099] In the method for producing purified recycled carbon black of the present invention, when a water addition step and a recentrifugation step are performed, the low-settling-velocity particle component-containing material obtained by the final recentrifugation step can be obtained as purified recycled carbon black, that is, as an aqueous dispersion of purified recycled carbon black. Furthermore, in the method for producing purified recycled carbon black of the present invention, when a water addition step and a recentrifugation step are performed, the low-settling-velocity particle component-containing material obtained by any recentrifugation step other than the final one can be obtained as purified recycled carbon black, that is, as an aqueous dispersion of purified recycled carbon black.

[0100] In one embodiment, in the centrifugal separation and recentrifugal separation processes, from the viewpoint of industrial continuous production, it is preferable to use, for example, a disc separator type centrifugal separator. A disc separator type centrifugal separator has a structure in which a number of conical separation plates (disks) are stacked at predetermined intervals inside a rotating body. In the centrifugal separation process using this apparatus, it is preferable to continuously supply the regenerated carbon black dispersion into the rotating body. The supplied regenerated carbon black dispersion is classified by centrifugal force as it passes through the gaps between the separation plates. The centrifugal separator may be of a type that separates the regenerated carbon black dispersion into two components (also called "light liquid" and "heavy liquid" in order of increasing sedimentation velocity), or it may be of a type that separates into three or more components (also called "light liquid," "heavy liquid," and "sludge" in order of increasing sedimentation velocity). In one embodiment, the component containing many particles with low sedimentation velocity (also called "light liquid") moves in the direction of the rotation axis and is discharged from the top continuously or intermittently (preferably continuously), and this is obtained as "low sedimentation velocity particle component containing material." On the other hand, components containing many particles with high settling velocities move towards the outer circumference of the rotating body. For example, when separated into three components, the light liquid may be designated as the "low settling velocity particle component," and the other components ("heavy liquid" and "sludge") may be combined to form the "high settling velocity particle component-containing material." This "low settling velocity particle component" and the "high settling velocity particle component-containing material" are discharged continuously or intermittently from a nozzle or the like, respectively. In this way, productivity can be improved by using a separation plate type centrifugal separator.

[0101] In a separation plate type centrifugal separator, there are no limited methods for adjusting the properties of the resulting particles (e.g., particle size distribution, structure, etc.), but examples include adjusting the rotation speed of the rotating body (centrifugal force), the delivery rate of the recycled carbon black dispersion (supply rate), and the solid content concentration of the recycled carbon black dispersion. In some industrial centrifugal separators, the rotation speed is set to a constant value from the viewpoint of structural stability and load on the discharge mechanism. In such cases, the residence time in the apparatus can be changed by adjusting the delivery rate of the recycled carbon black dispersion, thereby controlling the particle size, structure, etc., contained in the low-settling-velocity particle component material. For example, lowering the delivery rate (i.e., increasing the residence time) allows particles with lower sedimentation velocities to be separated by sedimentation, so the diameter of the particles recovered as light liquid (low-settling-velocity particle component material) becomes smaller. Conversely, increasing the delivery rate (i.e., shortening the residence time) results in a larger diameter of particles recovered as low-settling-velocity particle component material.

[0102] In the case of performing a centrifugal separation step and one or more recentrifugation steps, a preferred embodiment is to prepare n centrifugal separators, add a solvent to the high-settling-velocity particle component-containing material discharged from the k-th centrifugal separator, and send it to the k+1-th centrifugal separator (where k is an integer from 1 to n-1, and n is an integer of 2 or more). In the case of such multi-stage processing, a preferred embodiment is a process in which a plurality of centrifugal separators (preferably separation plate type centrifugal separators) are connected in series to perform centrifugal separation. Specifically, n centrifugal separators (n is an integer of 2 or more) are prepared and connected in series, and the "high-settling-velocity particle component-containing material" obtained from the first centrifugal separator (k=1) is mixed with a solvent (preferably water) using a line mixer, stirring tank, etc. to redisperse it, and this is sent to the second centrifugal separator (k=2). In this way, the high-settling-velocity particle component-containing material discharged from the k-th device may be sequentially mixed with a solvent and processed in the k+1-th device.

[0103] In another embodiment, the recovered high-sedimentation-velocity particle component-containing material may be dispersed in a solvent using a single centrifuge and then returned to the same apparatus for a recentrifugation process.

[0104] As described above, when performing multi-stage processing in the centrifugal separation and recentrifugation processes, it is preferable to gradually change the centrifugal separation conditions (centrifugal force, residence time, etc.) at each stage. In processing using a centrifugal separator (preferably a separation plate type centrifugal separator), although not limited to these, the centrifugal force may be adjusted to 3,000 to 20,000 G, the liquid delivery rate (supply rate) of the dispersion to 30 to 30,000 L / hr, the residence time to 0.1 to 3 minutes, and the solid content concentration of the dispersion to 1 to 25% by mass.

[0105] In one embodiment, for example, it is preferable to operate under relatively strong conditions (e.g., high centrifugal force and / or long residence time due to low liquid flow rate) in the first stage (upstream) of centrifugal separation, and to gradually reduce the conditions to relatively weaker conditions (e.g., low centrifugal force and / or short residence time due to high liquid flow rate) as the number of stages increases (downstream). By controlling the centrifugal separation conditions in this way, purified and recycled carbon black of different grades can be efficiently recovered in stages. This method is particularly preferable because it allows for the high yield of low-settling-velocity particles with desired characteristics.

[0106] In another embodiment, conversely to the above, the centrifugation conditions may be changed in stages from relatively weak conditions to strong conditions, and multiple centrifugation processes may be performed. In this embodiment, for example, in the first stage (upstream) of centrifugation, the process may be operated under relatively weak conditions (e.g., low centrifugal force and / or short residence time due to high liquid flow rate), and the obtained low-settling-velocity particulate material may be recovered and subjected to the next stage of recentrifugation. As the number of stages increases (downstream), the process may be carried out under relatively stronger conditions (e.g., high centrifugal force and / or long residence time due to low liquid flow rate). This makes it possible to recover high-settling-velocity particulate material of different grades in stages as purified recycled carbon black.

[0107] In one embodiment, when manufacturing on a laboratory scale or in batch production, a batch-type centrifuge such as a benchtop centrifuge may be used. In this case, when the recycled carbon black dispersion placed in a container (centrifuge tube, etc.) is centrifuged with a predetermined centrifugal force and time, the components that settle at the bottom of the container (solid phase or concentrated slurry) are separated from the upper liquid phase. The centrifugation conditions at this time are not particularly limited, but for example, the solid content concentration of the recycled carbon black dispersion may be adjusted as appropriate within the range of 1 to 25% by mass, the centrifugal force may be 1,000 to 20,000 G, and the processing time may be 1 to 300 minutes. The upper liquid phase (also called the "supernatant") may be collected by means of decantation (tilting method), pipette aspiration, etc. to obtain a "low settling velocity particle component-containing material." Alternatively, the precipitated components remaining at the bottom may be collected to obtain a "high settling velocity particle component-containing material."

[0108] <Solvent Removal Step> Furthermore, in the method for producing purified recycled carbon black of the present invention, when the water addition step and the recentrifugation step are repeated once or two or more times, a water removal step can be performed to remove water from the low-settling-velocity particulate matter obtained by the final recentrifugation step to obtain powdered purified recycled carbon black. Alternatively, a water removal step can be performed to remove water from the low-settling-velocity particulate matter obtained by any recentrifugation step other than the final one to obtain powdered purified recycled carbon black. In this step as well, the water removal step when water is used as the solvent is described as an example, but unless otherwise specified, when a solvent other than water is used, "water" should be read as "solvent" and the same procedure should be applied.

[0109] In the water removal process, methods for removing water from the low-settling-velocity particle component-containing material obtained by the recentrifugation process include, for example, heating under atmospheric or reduced pressure to evaporate the water and dry it, or spray drying. Alternatively, the solid content concentration can be increased before evaporation to improve drying efficiency by methods such as filtration, centrifugal concentration, or treatment with a coagulant such as acid. Furthermore, purified and recycled carbon black can be obtained by granulating the slurry after filtration or centrifugal concentration and then drying it. Alternatively, rubber latex can be added before drying, and the resulting material can be recovered as a wet masterbatch.

[0110] In the present invention's method for producing purified recycled carbon black, after the water removal step, the obtained purified recycled carbon black can be subjected to granulation or the like.

[0111] Furthermore, the refined recycled carbon black obtained by the manufacturing method of this embodiment may be sold as a product on its own, or it may be blended with other types of carbon black to create a product that suits the desired application and required characteristics. The properties of the recycled carbon black used as raw material may vary depending on its origin (type of waste tire, manufacturing date, etc.), and there may be differences in quality between lots. In such cases, the quality of the product may be made uniform or adjusted to the desired physical properties by appropriately adjusting and blending refined recycled carbon black obtained from different lots.

[0112] In the method for producing purified recycled carbon black of the present invention, recycled carbon black (in one embodiment, recycled carbon black pulverized product obtained by pulverizing in a pulverization step) is subjected to wet centrifugation treatment in a centrifugation step, or a centrifugation step and a recentrifugation step, and the conditions are selected to separate the material into a material containing high settling velocity particles and a material containing low settling velocity particles by utilizing the difference in settling velocity, thereby obtaining purified recycled carbon black with different physical properties. Therefore, in the method for producing purified recycled carbon black of the present invention, the conditions of centrifugation in the centrifugation step or the recentrifugation step are selected so that purified recycled carbon black with physical properties suitable for each application is obtained. For example, in the method for producing purified recycled carbon black of the present invention, in order to obtain purified recycled carbon black with physical properties suitable for each application, wet centrifugation is performed in a centrifugation step, or a centrifugation step and a recentrifugation step, and the conditions of the wet centrifugation treatment are selected so that recycled carbon black with physical properties suitable for each application is obtained. Conditions for wet centrifugation include the centrifugal force applied to the material to be separated (e.g., rotation speed and diameter of the centrifugation apparatus), the processing time for one centrifugation cycle (processing time, residence time, liquid transfer rate), the solid content concentration of recycled carbon black in the recycled carbon black aqueous dispersion, and the number of centrifugation cycles. Note that the appropriate conditions vary depending on the centrifugation apparatus used; therefore, the desired N2 should be determined for each centrifugation apparatus. ２ Select conditions that yield purified recycled carbon black having SA and DBP absorption levels.

[0113] In the present invention's method for producing refined recycled carbon black, N is involved in wear resistance, heat generation, and processability. ２ Regarding the amount of DBP absorbed, which is related to SA, wear resistance and machinability, in the centrifugal separation process of the centrifugal separation process and / or recentrifugal separation process, the desired N ２ Select separation treatment conditions that yield purified and recycled carbon black with SA and DBP absorption levels.

[0114] Furthermore, in the method for producing purified recycled carbon black of the present invention, with respect to Dst, which is involved in wear resistance, and DBP absorption, which is involved in wear resistance and processability, separation treatment conditions are selected in the centrifugal separation step and / or recentrifugal separation step to obtain purified recycled carbon black having the desired Dst and DBP absorption amounts.

[0115] Furthermore, in the method for producing refined and recycled carbon black of the present invention, N is involved in wear resistance, heat generation, and processability. ２ For SA and STSA, in the centrifugal separation process of the centrifugal separation step and / or recentrifugal separation step, the desired N ２ Select separation treatment conditions that yield purified and recycled carbon black containing SA and STSA.

[0116] Furthermore, in the method for producing purified recycled carbon black of the present invention, with respect to ΔDst / Dst, which is involved in wear resistance and heat generation, separation treatment conditions are selected in the centrifugal separation step and / or recentrifugal separation step to obtain purified recycled carbon black having the desired ΔDst / Dst.

[0117] Thus, according to the method for producing purified recycled carbon black of the present invention, it is possible to extract purified recycled carbon black having physical properties suitable for each application from recycled carbon black, which was a mixture of various types of carbon black.

[0118] The purified recycled carbon black obtained by the method for producing purified recycled carbon black of the present invention exhibits a Raman spectrum of 1350 ± 20 cm⁻¹ obtained by laser Raman spectroscopy at an excitation wavelength of 532 nm. －１ When the peak intensity of a peak with its peak top within this range is set to 100, the range is 1580 ± 20 cm. －１ The carbon black has a peak intensity of 90 to 200, preferably 100 to 190, where the peak top is within the specified range.

[0119] In the method for producing purified recycled carbon black of the present invention, N ２ SA is 40m ２ / g or more 140m ２It is possible to selectively produce refined and recycled carbon black within a range of less than / g.

[0120] The present invention provides a method for producing purified recycled carbon black, which allows for the selective production of purified recycled carbon black with DBP absorption levels ranging from 50 ml / 100 g to 150 ml / 100 g.

[0121] In the present invention's method for producing purified and recycled carbon black, STSA is 35m ２ / g or more 90m ２ It is possible to selectively produce refined and recycled carbon black within a range of less than / g.

[0122] The present invention's method for producing purified recycled carbon black allows for the selective production of purified recycled carbon black with a Dst (disk centrifugal sedimentation particle size distribution) in the range of 50 nm to 250 nm.

[0123] The present invention's method for producing purified recycled carbon black allows for the selective production of purified recycled carbon black with a DCP particle size distribution measurement of a full width at half maximum (ΔDst) in the range of 30 nm to 250 nm.

[0124] The present invention's method for producing purified recycled carbon black makes it possible to selectively produce purified recycled carbon black with a ΔDst / Dst ratio in the range of 0.6 to 1.2.

[0125] In the present invention's method for producing purified recycled carbon black, it is possible to selectively produce purified recycled carbon black in a range of 0.6 to 1.2 for (d90-d10) / d50 in DCP particle size distribution measurement.

[0126] The present invention's method for producing purified recycled carbon black can reduce the Zn content of the purified recycled carbon black to preferably 1.0% by mass or less, and more preferably 0.5% by mass or less.

[0127] The present invention's method for producing purified recycled carbon black makes it possible to selectively produce purified recycled carbon black with physical properties equivalent to ASTM grades such as N762, N550, N326, N330, and N351.

[0128] The purified recycled carbon black obtained by the method for producing purified recycled carbon black of the present invention is preferably one in which (d90 - d10) / d50 in DCP particle size distribution measurement is 1.2 or less, in terms of tensile strength and abrasion resistance of rubber.

[0129] The refined recycled carbon black obtained by the method for producing refined recycled carbon black of the present invention has STSA of 60m in terms of tensile strength and abrasion resistance of rubber. ２ It is preferable that the amount is 1 / g or more.

[0130] The following are examples of the physical properties of the purified recycled carbon black produced by the method for producing purified recycled carbon black of the present invention. <Purified Recycled Carbon Black 1> N ２ SA(m) ２ / g): 37-47 STSA (m ２ ( / g): 32-42 DBP absorption (ml / 100g): 53-63 Dst (nm): 51-61 ΔDst: 31-41 <Purified recycled carbon black 2> N ２ SA(m) ２ / g): 68-78 STSA(m ２ ( / g): 57-67 DBP absorption (ml / 100g): 66-76 Dst (nm): 73-83 ΔDst: 64-74 <Purified recycled carbon black 3> N ２ SA(m) ２ / g):74-84 STSA(m ２ ( / g): 65-75 DBP absorption (ml / 100g): 95-105 Dst (nm): 76-86 ΔDst: 55-65 <Purified recycled carbon black 4> N ２ SA(m) ２ / g):63-73 STSA(m ２ ( / g): 56-66 DBP absorption (ml / 100g): 113-123 Dst (nm): 97-107 ΔDst: 73-83 <Purified recycled carbon black 5> N ２ SA(m) ２ / g):50-60 STSA(m ２( / g): 43-53 DBP absorption (ml / 100g): 116-126 Dst (nm): 123-133 ΔDst: 139-149 <Purified recycled carbon black 6> N ２ SA(m) ２ / g):43-53 STSA(m ２ ( / g): 37-47 DBP absorption (ml / 100g): 121-131 Dst (nm): 202-212 ΔDst: 205-215

[0131] The above-mentioned uses and corresponding physical properties are illustrative examples, and the method for producing purified and recycled carbon black of the present invention is not limited to the production of carbon black used in these exemplified uses.

[0132] Conventionally, recycled carbon black was recognized as having limited reuse applications because it is a mixture of various types of carbon black. However, the present invention's method for producing refined recycled carbon black makes it possible to produce refined recycled carbon black with physical properties suitable for various applications from recycled carbon black, which is a mixture of various types of carbon black, thereby expanding the applications of recycled carbon black.

[0133] For example, Figure 1 shows a graph plotting the ASTM grade and Examples 1 to 7, described later, with STSA on the horizontal axis and DBP absorption on the vertical axis. In Figure 1, the plot for the recycled carbon black pulverized product is near the center of the graph, and its physical properties can only be used for this purpose. In contrast, it can be seen that the physical properties of the refined recycled carbon black can be brought closer to N762 in Example 1, closer to N326 in Examples 2 and 3, closer to N330 in Example 4, and closer to N550 in Examples 5, 6, and 7.

[0134] According to one embodiment of the present invention for producing purified recycled carbon black, in the grinding step, the amount of multiple aggregates of CB aggregates contained in the recycled carbon black can be reduced by grinding. As a result, the amount of CB aggregates that are not multiplely attached, which are useful components of carbon black, can be increased in the ground recycled carbon black, thereby increasing the yield of purified recycled carbon black with excellent physical properties.

[0135] According to one embodiment of the present invention for producing purified recycled carbon black, in the dispersion treatment step, dispersion is performed by oxidation treatment, and by using a persulfate as the oxidizing agent at that time, dispersibility can be imparted to the recycled carbon black and the Zn content, which is an impurity in the recycled carbon black, can be reduced.

[0136] In the manufacturing method of the present invention, the high-settling-velocity particle component-containing material obtained by the centrifugal separation step, and the high-settling-velocity particle component-containing material obtained by the final recentrifugation step when a recentrifugation step is performed, may be recycled carbon black products, taking into consideration the relationship between their physical properties and performance. Alternatively, the high-settling-velocity particle component-containing material may be mixed with the raw material (in one embodiment, the recycled carbon black to be crushed) and reused in the manufacturing method of the present invention using recycled carbon black from a different lot.

[0137] <Embodiment of the Second Invention> A method for producing purified recycled carbon black according to one embodiment of the second invention includes a step of contacting recycled carbon black with a persulfate in a solvent. This step makes it possible to efficiently remove impurities (particularly zinc compounds) contained in the recycled carbon black.

[0138] Generally, a known method for removing zinc from recycled carbon black involves dissolving it using acids such as hydrochloric acid and sulfuric acid. However, this method has the problem that if zinc sulfide or other impurities are present, toxic hydrogen sulfide gas is generated as a by-product. Furthermore, Patent Document 3 (Japanese Patent Application Publication No. 2024-006106) describes a method for producing purified carbon black with reduced ash content, which includes a step of contacting recovered carbon black from used tires with organic acids such as hydrogen peroxide and formic acid. However, the method in Patent Document 3 lacks sufficient solvent dispersibility and has room for improvement. Moreover, the method in Patent Document 3 is insufficient in suppressing the generation of hydrogen sulfide gas, and also has room for improvement.

[0139] In response to this, the present inventors have found that by performing an oxidation reaction using persulfates, zinc compounds can be dissolved and removed more safely without generating hydrogen sulfide gas. Thus, according to the manufacturing method of this embodiment, zinc compounds can be removed safely and efficiently, and when the resulting purified recycled carbon black is incorporated into rubber products, an improvement in the properties of the rubber products (e.g., reinforcing properties) can be expected. Furthermore, by using persulfates, hydrophilic groups can be efficiently introduced to the surface of recycled carbon black, making it possible to impart excellent solvent dispersibility.

[0140] In this specification, the term "zinc compound" to be removed refers to all substances containing zinc atoms, and unless otherwise specified, it includes all components containing zinc atoms, such as elemental zinc (metallic zinc), zinc oxide, zinc sulfide, zinc existing in an ionic state, or zinc components physically or chemically bonded or adsorbed with other components (the same applies in the first invention). In one embodiment, the impurities to be removed are mainly zinc compounds derived from additives (vulcanization accelerators, etc.) in rubber products (waste tires, etc.) that are raw materials for recycled carbon black. The zinc compound content of recycled carbon black is not limited, but the zinc (Zn) content (Zn content) is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less. The Zn content of recycled carbon black and purified recycled carbon black can be measured by the method described in the examples.

[0141] In the manufacturing method according to the second invention, the description of recycled carbon black in the first invention described above applies similarly to the recycled carbon black used as a raw material (the material from which impurities are removed). That is, the recycled carbon black in the second invention may be recycled carbon black pulverized product obtained through the pulverization process described above, or it may be recycled carbon black that has not undergone the pulverization process. Furthermore, the description of the origin of the recycled carbon black (waste tires, etc.) and its physical properties (Raman spectrum, etc.) also applies similarly to the description in the first invention.

[0142] In the step of contacting recycled carbon black and persulfate in a solvent in the second invention, the explanation of (i-1) of the dispersion treatment step of the first invention described above can be applied by replacing "oxidizing agent" with "persulfate".

[0143] The oxidation reaction that occurs when recycled carbon black is brought into contact with persulfate in a solvent introduces hydrophilic groups to the surface of the recycled carbon black, thereby imparting solvent dispersibility (preferably water dispersibility) to the recycled carbon black. Furthermore, by using persulfate, zinc compounds, which are impurities, can be dissolved and removed from the recycled carbon black, thereby reducing the Zn content. The Zn in recycled carbon black originates, for example, from additives in rubber products such as vulcanization accelerators.

[0144] Examples of persulfates include alkali metal salts such as lithium persulfate, sodium persulfate, and potassium persulfate, as well as ammonia salts. Sodium persulfate is more preferred because it has a higher effect in reducing Zn content.

[0145] The amount of persulfate used is selected as appropriate and is not limited. The amount of persulfate per gram of recycled carbon black is, for example, preferably 0.5 mmol / g or more, more preferably 1 mmol / g or more, and in one embodiment, it may be 2 mmol / g or more, or 3 mmol / g or more. Furthermore, the amount of persulfate per gram of recycled carbon black is preferably 40 mmol / g or less, more preferably 30 mmol / g or less, even more preferably 20 mmol / g or less, and even more preferably 11 mmol / g or less.

[0146] Examples of solvents include those used in the dispersion process of the first invention described above, preferably aqueous solvents, and more preferably water. The proportion of recycled carbon black in the solvent (preferably water) is appropriately selected within a range in which the oxidation reaction occurs favorably.

[0147] The recycled carbon black (preferably pulverized recycled carbon black) and persulfate are added to the solvent and stirred to perform oxidation treatment of the recycled carbon black. The conditions for the oxidation treatment are not limited, but the oxidation treatment temperature is preferably 40 to 100°C, more preferably 60 to 90°C, and the oxidation treatment time is appropriately selected depending on the oxidizing agent.

[0148] After oxidation treatment with persulfate, a desalting treatment may be performed to remove salts from the dispersion medium of the regenerated carbon black dispersion using an ultrafiltration membrane, filter press, etc., and it is preferable to use an ultrafiltration membrane. By performing the desalting treatment, unreacted persulfate, reaction residue of persulfate, impurities such as Zn can be removed, thereby improving the solvent dispersibility (preferably water dispersibility) of the regenerated carbon black. When the solvent dispersibility of the regenerated carbon black is improved, the desired separation effect can be more favorably obtained in the subsequent centrifugation and recentrifugation steps.

[0149] After desalting, the pH of the recycled carbon black dispersion may be adjusted to 4 to 14, preferably 5 to 12, using a base such as sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia (pH adjustment treatment). Then, a desalting treatment may be performed to remove salts from the dispersion medium of the recycled carbon black dispersion using an ultrafiltration membrane, filter press, or the like.

[0150] The manufacturing method of the second invention makes it possible to lower the Zn content in the obtained purified recycled carbon black to, for example, preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less (it may even be 0% by mass).

[0151] The dispersion of purified recycled carbon black obtained by contacting recycled carbon black with persulfate in a solvent, and optionally by subsequent desalting, pH adjustment, etc., may be used as a product by removing the solvent as is, or it may be subjected to the "centrifugation step," "recentrifugation step," etc., described above in the first invention.

[0152] In other words, by using a dispersion containing recycled carbon black with reduced impurity (zinc compound) content according to the manufacturing method of the second invention as the "recycled carbon black dispersion" in the first invention, and subjecting it to centrifugal separation, a material containing high-settling-velocity particle components and a material containing low-settling-velocity particle components can be obtained. Furthermore, the specific procedures and conditions for this centrifugal separation step and any subsequent steps (solvent addition step and recentrifugation step for the material containing high-settling-velocity particle components, and solvent removal step for the material containing low-settling-velocity particle components, etc.) are as described in the first invention above.

[0153] In this way, by combining the second invention (zinc removal) and the first invention (wet classification), high-quality refined recycled carbon black can be obtained that has a reduced zinc content and physical properties such as particle size distribution suitable for each application.

[0154] The present invention will be described using the following examples, but the present invention is not limited to these examples. Of the examples described below, Examples 1 to 7 are examples included in the first invention, and Examples 1 to 8 are examples included in the second invention.

[0155] (Example 1) (Grinding Process) 10 kg of recycled carbon black (Enrestec, PB365) was ground using a jet mill (Nisshin Engineering, SJ-100) under the conditions of a high-pressure air pressure of 0.6 MPa and a supply speed of 3 kg / hour to obtain ground recycled carbon black material. The particle size distribution of the obtained ground recycled carbon black material was measured using the laser diffraction scattering method described below.

[0156] (Measurement of particle size distribution of recycled carbon black pulverized material by laser diffraction scattering method) The particle size distribution was measured using a wet method with a HORIBA LA-960V2 laser diffraction scattering machine. As a pretreatment, 40 g of ion-exchanged water and β-naphthalene sulfonic acid formalin condensate sodium salt (Kao Demol NL) as a surfactant were added to 0.4 g of powder, and ultrasonic treatment was performed for 1 minute at 150 W using an ultrasonic homogenizer (Nippon Seiki US-300E). The measurement conditions were a refractive index of 1.92-0.552i for the sample and a dispersion medium (water) of 1.33.

[0157] The particle size distribution measurement described above revealed that the particle size (d99) at which the cumulative volume frequency of the recycled carbon black pulverized material reached 99% was 4.4 μm.

[0158] (Dispersion Process) In a 65 L reflux tubing reaction vessel, 45 L of pure water, 3.6 kg of the obtained recycled carbon black pulverized material, and 8.7 kg of sodium persulfate were added. The mixture was heated to 90°C and held for 3 hours while stirring at a stirring speed of 100 rpm, and then allowed to cool naturally to 25°C to perform oxidation treatment (dispersion treatment). Next, the oxidation treatment solution containing the oxidized recycled carbon black was desalted using an ultrafiltration membrane (Asahi Kasei Chemicals, AHV-3010 (molecular weight cutoff 50,000)). Then, sodium hydroxide was added to the desalted oxidation treatment solution until the pH reached 12.0, and the solution was neutralized by treating it at 100°C for 3 hours to obtain a neutralized treatment solution containing the oxidized recycled carbon black (solid content concentration 3% by mass). Next, the neutralization solution containing the obtained oxidized recycled carbon black was desalted using an ultrafiltration membrane (AHV-3010 (molecular weight cutoff 50,000) manufactured by Asahi Kasei Chemicals Corporation) to remove any remaining salts, thereby obtaining an aqueous dispersion of the dispersed recycled carbon black (solid content concentration 10% by mass).

[0159] (Centrifugal Separation Process) A benchtop centrifuge S500T (manufactured by KUBOTA Corporation) was used for centrifugal separation. The aqueous dispersion of recycled carbon black obtained above and pure water were added to a centrifuge tube to a total volume of 60 mL, and a recycled carbon black aqueous dispersion was prepared with a solid content concentration in the range of 4-5% by mass. Next, the mixture was processed at a rotation speed of 3,500 rpm for 180 minutes, and the supernatant was separated and recovered as a low-settling velocity particulate matter.

[0160] (Water Removal Process) The separated supernatant liquid (containing low-settling-velocity particle components) was dried at 110°C to evaporate and remove the water, thereby obtaining purified recycled carbon black.

[0161] (Analysis) The following analysis was performed on the obtained purified recycled carbon black. Unless otherwise specified, the same analytical methods were used for other examples, comparative examples, and reference examples.

[0162] <N ２ SA > Nitrogen adsorption specific surface area N ２ SA refers to the multi-point nitrogen specific surface area (NSA) as defined in JIS K6217-7 2013 "Basic properties of carbon black for rubber - Part 7: Rubber compounding - Method for determining multi-point nitrogen specific surface area (NSA) and statistical thickness specific surface area (STSA)," and was measured in accordance with the specified method.

[0163] <STSA> STSA refers to the statistical thickness specific surface area as defined in JIS K6217-7 2013 "Carbon black for rubber - Basic properties - Part 7: Rubber compound - Method for determining multi-point nitrogen specific surface area (NSA) and statistical thickness specific surface area (STSA)," and was measured in accordance with the specified method.

[0164] <DBP Absorption Amount> The DBP absorption amount refers to the oil absorption amount (OAN) as defined in JIS K6217-4 2017 "Basic properties of carbon black for rubber - Part 4: Method for determining oil absorption amount," and was measured in accordance with the specified method.

[0165] <Zn Content> The Zn content was measured using a Rigaku Supermini 200 X-ray fluorescence analyzer. 2 g of powder was placed in a polyethylene container lined with ProLene film, and elemental species F to U were measured under vacuum conditions. The Zn content (weight %) in the powder was calculated using standardless analysis (SQX analysis) with the fundamental parameter method.

[0166] <Measurement of Aggregate Distribution by DCP Method> The particle size was measured using disk centrifugal sedimentation particle size distribution (DCP method) as follows. The particle size obtained by this measurement method is not the primary particle size of carbon black, but the equivalent spherical diameter of the aggregates after dispersion treatment. A BI-DCP Particle Sizer manufactured by Brookhaven Instruments was used as the measuring device. The measurement sample was prepared by mixing a dry carbon black sample with a 20% ethanol solution containing a small amount of surfactant to create a dispersion with a carbon black concentration of 1000 mg / L, and then thoroughly dispersing it by sonication. The specific gravity of carbon black used to calculate the equivalent spherical diameter in disk centrifugal sedimentation particle size distribution measurement was 1.75 g / cm³. ３ The value was adopted. Based on the distribution curve of the equivalent sphere diameter of the aggregates obtained by this measurement, the following indices were calculated.

[0167] <(i) Dst, ΔDst> Dst and ΔDst refer to the mode diameter and half-width (mode diameter and half-width of the above distribution curve) as defined in JIS K6217-6 2019 "Basic properties of carbon black for rubber - Part 6: Method for determining aggregate distribution by disk centrifugal photoprecipitation," and were determined in accordance with the specified method. Next, the value of ΔDst / Dst was calculated based on the obtained values ​​of Dst and ΔDst.

[0168] <(ii) d10, d50, d90> d10, d50, and d90 represent the particle sizes at 10%, 50%, and 90% of the cumulative mass in the above distribution curve according to JIS K6217-6 2019 "Basic properties of carbon black for rubber - Part 6: Method for determining aggregate distribution by disk centrifugal photoprecipitation," and were determined in accordance with the specified method. Next, the value of (d90 - d10) / d50 was calculated based on the obtained values ​​of d10, d50, and d90.

[0169] <Yield> The yield is calculated based on the solid content of carbon black and is determined by the following formula: Yield (%) = 100 × (Dry mass of recovered purified recycled carbon black / Dry mass of recycled carbon black introduced into the dispersion process)

[0170] (Example 2) The procedure was the same as in Example 1, except that the centrifugal treatment time was changed from 180 minutes to 60 minutes.

[0171] (Example 3) The procedure was the same as in Example 1, except that the centrifugal treatment time was changed from 180 minutes to 30 minutes.

[0172] (Example 4) (Water addition step and recentrifugation step) In the centrifugal separation step of Example 1, after separating and recovering the supernatant liquid, pure water was added to the remaining precipitate (containing high-settling velocity particle components) so that the solid content concentration was 4-5% by mass, and ultrasonic treatment was performed for 1 minute to prepare a water-added solution for high-settling velocity particle components. Next, 60 mL of the water-added solution for high-settling velocity particle components was added to a centrifuge tube and treated at a rotation speed of 3,500 rpm for 60 minutes, and the supernatant liquid was separated and recovered as a low-settling velocity particle component. (Water removal step) The separated and recovered supernatant liquid (containing low-settling velocity particle components) was dried at 110°C to evaporate and remove the water, and purified recycled carbon black was obtained.

[0173] (Example 5) (Water addition step and recentrifugation step) In the recentrifugation step of Example 4, after separating and recovering the supernatant, pure water was added to the remaining precipitate so that the solid content concentration was 4-5% by mass, and ultrasonic treatment was performed for 1 minute to prepare a water-added solution of high-settling-velocity particle components. Next, 60 mL of the water-added solution of high-settling-velocity particle components was added to a centrifuge tube and treated at a rotation speed of 3,500 rpm for 30 minutes, and the supernatant was separated and recovered as a low-settling-velocity particle component-containing material. (Water removal step) The separated and recovered supernatant (low-settling-velocity particle component-containing material) was dried at 110°C to evaporate and remove the water, and purified recycled carbon black was obtained.

[0174] (Example 6) (Water addition step and recentrifugation step) In the recentrifugation step of Example 5, after separating and recovering the supernatant, pure water was added to the remaining precipitate so that the solid content concentration was 4-5% by mass, and ultrasonic treatment was performed for 1 minute to prepare a water-added solution of high-settling-velocity particle components. Next, 60 mL of the water-added solution of high-settling-velocity particle components was added to a centrifuge tube and treated at a rotation speed of 3,500 rpm for 10 minutes, and the supernatant was separated and recovered as a low-settling-velocity particle component-containing material. (Water removal step) The separated and recovered supernatant (low-settling-velocity particle component-containing material) was dried at 110°C to evaporate and remove the water, and purified recycled carbon black was obtained.

[0175] (Example 7) (Water addition step and recentrifugation step) In the recentrifugation step of Example 6, after separating and recovering the supernatant, pure water was added to the remaining precipitate so that the solid content concentration was 4-5% by mass, and ultrasonic treatment was performed for 1 minute to prepare a water-added solution of high-settling-velocity particle components. Next, 60 mL of the water-added solution of high-settling-velocity particle components was added to a centrifuge tube and treated at a rotation speed of 3,500 rpm for 3 minutes, and the supernatant was separated and recovered as a low-settling-velocity particle component-containing material. (Water removal step) The separated and recovered supernatant (low-settling-velocity particle component-containing material) was dried at 110°C to evaporate and remove the water, and purified recycled carbon black was obtained.

[0176] (Comparative Example 1) Recycled carbon black used as a raw material.

[0177] (Example 8) The dispersion process of Example 1 was carried out, and the material was dried at 110°C without centrifugation to remove moisture and obtain purified recycled carbon black. The physical properties of the obtained purified recycled carbon black were measured in the same manner as in Example 1. In addition, the particle size distribution of the recycled carbon black after the dispersion process and before the removal of moisture was measured using the "Particle size distribution measurement by laser diffraction scattering method without surfactants" described later, and the dispersion performance in the solvent was evaluated. This measurement evaluates the solvent dispersibility of the carbon black itself after the dispersion process without using surfactants or performing sonication. Furthermore, the amount of hydrogen sulfide gas generated during the reaction process was measured using the method described later, and the safety of the process was evaluated. This example corresponds to an example of the second invention.

[0178] (Particle size distribution measurement by laser diffraction scattering method without surfactants) Particle size distribution measurement by laser diffraction scattering was performed using a HORIBA LA-960V2 and the wet method. To evaluate the dispersibility in water, no surfactants were used, and no sonication was performed; the dispersion liquid was measured directly before drying. The measurement conditions were a refractive index of 1.92–0.552i for the sample and a dispersion medium (water) of 1.33i.

[0179] (Confirmation of hydrogen sulfide generation) A hydrogen sulfide concentration meter (Riken Keiki Portable Hydrogen Sulfide Gas Monitor HS-04) was installed at the reflux tubing outlet of the reaction vessel in the dispersion process to confirm the concentration of hydrogen sulfide generated during the reaction.

[0180] (Reference Example 7) 50 g of recycled carbon black obtained in the (grinding process) of Example 1 and 250 mL of 1.2 mol / L hydrochloric acid were added to a 500 mL reactor with a reflux tube and stirred with a magnetic stirrer at 98 °C for 6 hours. The resulting slurry was filtered under reduced pressure using filter paper of type 5C as specified in JIS P 3801 to separate the solids, then washed with 500 mL of distilled water and filtered under reduced pressure. A small amount of the filtered recycled carbon black was placed in a beaker containing pure water to check its dispersibility, but the recycled carbon black precipitated and showed no dispersibility whatsoever, making it impossible to measure its dispersibility. Next, the crudely purified solid was dried at 110 °C to remove the water by evaporation, thereby obtaining purified recycled carbon black. The zinc content of the obtained purified recycled carbon black and the amount of hydrogen sulfide gas generated during the reaction process were measured using the same method as in Example 8.

[0181] (Reference Example 8) 50 g of recycled carbon black obtained in the (grinding process) of Example 1 and 500 g of an aqueous solution containing 2.5 wt% hydrogen peroxide and 5.0 wt% formic acid were added to a 2 L reflux condenser reactor and stirred at 60°C for 1 hour at a stirring speed of 200 rpm. The resulting treatment solution was desalted using an ultrafiltration membrane (Asahi Kasei Chemicals, SLP-0053 (molecular weight cutoff 10,000)). To confirm the dispersibility of the dispersion after desalting, the particle size distribution was measured by the aforementioned surfactant-free laser diffraction scattering method. Next, the desalted solution was dried at 110°C to evaporate and remove the water, thereby obtaining purified recycled carbon black. The zinc content of the obtained purified recycled carbon black and the amount of hydrogen sulfide gas generated during the reaction process were measured using the same method as in Example 8.

[0182] For reference, the following carbon black (fresh) samples were prepared and their physical properties were measured. (Reference Example 1) Seast 7HM, ASTM Grade: N234 (Reference Example 2) Seast 7KH, ASTM Grade: N339 (Reference Example 3) Seast 300, ASTM Grade: N326 (Reference Example 4) Seast 3, ASTM Grade: N330 (Reference Example 5) Seast SO, ASTM Grade: N550 (Reference Example 6) Seast S, ASTM Grade: N762

[0183] Table 1 shows the measurement results of the physical properties for Examples 1 to 8 and Comparative Example 1. Table 2 shows the measurement results of the physical properties for Reference Examples 1 to 6. Table 3 shows the measurement results for Example 8 and Reference Examples 7 to 8.

[0184]

[0185]

[0186]

[0187] Examples 1-7, Comparative Example 1, and Reference Examples 1-6 were plotted on a graph with STSA on the horizontal axis and DBP absorption on the vertical axis. The graph is shown in Figure 1.

[0188] As shown in Table 3, in Example 8, which used persulfate, the amount of hydrogen sulfide gas generated in the reaction process was suppressed to less than 1 ppm (below the detection limit) while sufficiently reducing the zinc content. Furthermore, in Example 8, particle size distribution measurements under conditions without surfactants and sonication showed that the cumulative volume frequency 50% particle size was small, indicating that the purified recycled carbon black had excellent solvent dispersibility.

[0189] In contrast, in Reference Example 7, which used hydrochloric acid, although zinc was removed, a high concentration of hydrogen sulfide gas exceeding 100 ppm was generated during the reaction process. Furthermore, the purified recycled carbon black obtained in Reference Example 7 precipitated in the solvent and did not exhibit dispersibility. In Reference Example 8, which used hydrogen peroxide and formic acid, 4 ppm of hydrogen sulfide gas was also generated. In addition, the solvent dispersibility of the purified recycled carbon black obtained in Reference Example 8 was inferior to that of Example 8.

[0190] This application claims priority based on Japanese Patent Application No. 2025-023936, filed on 18 February 2025, and incorporates all of its disclosures herein. While the present invention has been described above with reference to embodiments, the present invention is not limited to these embodiments. Various modifications to the structure and details of the present invention are possible, as can be understood by those skilled in the art within the scope of the present invention.

[0191] According to the present invention (first invention), it is possible to selectively produce refined recycled carbon black of various qualities from recycled carbon black. Furthermore, according to the present invention (second invention), it is possible to safely and efficiently reduce impurities (zinc compounds) in recycled carbon black and obtain refined recycled carbon black with improved properties such as rubber reinforcing properties. Therefore, according to the present invention, it is possible to provide refined recycled carbon black of optimal quality according to the required characteristics, thereby broadening the range of applications for recycled carbon black, which was previously limited due to quality variability and / or impurity issues.

Claims

1. A method for producing purified recycled carbon black, comprising: a dispersion step of performing a dispersion treatment to impart dispersibility to recycled carbon black in a solvent to obtain a recycled carbon black dispersion; and a centrifugation step of performing a centrifugation treatment of the recycled carbon black dispersion to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

2. A method for producing purified recycled carbon black according to claim 1, comprising: a solvent addition step of adding a solvent to the high-settling-velocity particle component-containing material to obtain a solvent-added solution of the high-settling-velocity particle component; and a recentrifugation step of centrifuging the solvent-added solution of the high-settling-velocity particle component to obtain a high-settling-velocity particle component-containing material and a low-settling-velocity particle component-containing material.

3. A method for producing purified and recycled carbon black according to claim 2, wherein the solvent addition step and the recentrifugation step are repeated two or more times.

4. The method for producing purified recycled carbon black according to claim 1, wherein the low-sedimentation-velocity particle component-containing material obtained in the centrifugal separation step is obtained as purified recycled carbon black.

5. The method for producing purified recycled carbon black according to claim 2, wherein in the recentrifugation step, the product containing low settling velocity particles obtained by the final recentrifugation treatment is obtained as purified recycled carbon black.

6. The method for producing purified recycled carbon black according to claim 3, wherein in the recentrifugation step, the product containing low settling velocity particles obtained by the final recentrifugation treatment is obtained as purified recycled carbon black.

7. A method for producing purified recycled carbon black according to claim 1, further comprising a grinding step of grinding recycled carbon black to obtain a recycled carbon black pulverized product before the dispersion step, and a dispersion treatment in the dispersion step of imparting dispersibility in a solvent to the recycled carbon black pulverized product.

8. The method for producing refined recycled carbon black according to claim 1, wherein the recycled carbon black is derived from rubber products.

9. The method for producing purified recycled carbon black according to claim 1, wherein in the centrifugal separation step, a recycled carbon black dispersion is continuously supplied to the centrifugal separator, and the obtained low-settling-velocity particle component-containing material and high-settling-velocity particle component-containing material are continuously or intermittently discharged from the centrifugal separator, respectively.

10. The method for producing purified recycled carbon black according to claim 2, wherein in the recentrifugation step, the recycled carbon black dispersion is continuously supplied to the centrifuge, and the obtained low-settling-velocity particle component-containing material and high-settling-velocity particle component-containing material are continuously or intermittently discharged from the centrifuge, respectively.

11. A method for producing purified recycled carbon black according to any one of claims 1 to 10, comprising a solvent removal step of removing the solvent from the low-settling-velocity particle component-containing material to obtain purified recycled carbon black.

12. A method for producing purified recycled carbon black according to claim 2 or 3, wherein, in the centrifugal separation step and the recentrifugal separation step, n centrifugal separators are prepared, a solvent is added to the high-settling-velocity particle component-containing material discharged from the k-th centrifugal separator, and the liquid is sent to the k+1-th centrifugal separator (where k is an integer from 1 to n-1, and n is an integer of 2 or more).

13. A method for producing purified recycled carbon black according to claim 12, comprising a solvent removal step of removing the solvent from the low-settling velocity particle component-containing material to obtain purified recycled carbon black.

14. The method for producing purified recycled carbon black according to claim 1, wherein the (d90-d10) / d50 in the DCP particle size distribution measurement of the obtained purified recycled carbon black is 1.2 or less.

15. The STSA of the obtained purified recycled carbon black is 60 m ２ A method for producing purified recycled carbon black according to claim 1, wherein the amount is 1 / g or more.

16. The method for producing purified recycled carbon black according to claim 1, wherein in the dispersion step, a recycled carbon black dispersion is obtained by contacting the recycled carbon black with an oxidizing agent in a solvent.

17. The method for producing purified recycled carbon black according to claim 16, wherein the oxidizing agent is a persulfate.

18. The method for producing purified recycled carbon black according to claim 16 or 17, wherein the zinc content in the purified recycled carbon black is 1.0% by mass or less.

19. A method for producing purified recycled carbon black, comprising the step of contacting recycled carbon black with a persulfate in a solvent.

20. The method for producing purified recycled carbon black according to claim 19, wherein the recycled carbon black is derived from rubber products.

21. The method for producing purified recycled carbon black according to claim 19 or 20, wherein the zinc content in the purified recycled carbon black is 1.0% by mass or less.

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