Method for treating recycled carbon black

Abstract

The present invention addresses the problem of providing a method for treating recycled carbon black in order to improve reinforcement properties of the recycled carbon black when being blended in rubber. This method for treating recycled carbon black comprises heat-treating the recycled carbon black in an inert gas at a heat treatment temperature of 300-1000°C.

Description

Processing methods for recycled carbon black

[0001] This invention relates to a method for processing recovered carbon black (rCB) obtained by thermal decomposition of waste tires and the like.

[0002] In recent years, there has been research into using recycled carbon black (hereinafter also referred to as "rCB"), obtained by thermal decomposition from used tires and other waste materials, as a recyclable and sustainable material. However, rCB has a problem in that various impurities remain on its surface, reducing its reactivity with rubber and other materials, and thus failing to exhibit sufficient effects when compounded with rubber. Therefore, attempts have been made to purify rCB by performing heat treatment and extraction treatment using a medium-polar solvent to remove the carbonized rubber (bituminous residue) from the surface of the rCB (see Patent Document 1). However, the method in Patent Document 1 involves multiple steps, making the process complicated, and there are safety concerns due to the use of organic solvents. Furthermore, although Patent Document 1 shows that the bituminous residue is removed and the specific surface area increases, it does not show any effect on the reinforcing properties when compounded with rubber.

[0003] Special Publication No. 2023-504231

[0004] The object of the present invention is to provide a treatment method for recycled carbon black to improve the reinforcing properties of recycled carbon black when compounded into rubber.

[0005] The inventors began investigating treatment methods to improve the properties of recycled carbon black so that it could provide the same rubber reinforcing effect as virgin carbon black. During their investigation, the inventors discovered that not only the removal of residual impurities from the surface of recycled carbon black, as had been previously investigated, but also the surface properties, such as pore size, after the residual impurity removal treatment, significantly influence the improvement of the recycled carbon black's properties. They then discovered a treatment method and conditions that could remove residual impurities from the surface and achieve a suitable surface shape. This led to the completion of the present invention.

[0006] In other words, the present invention is defined by the following: (1) A method for processing recycled carbon black, comprising heat-treating recycled carbon black in an inert gas at a heat treatment temperature of 300 to 1000°C. (2) The method for processing recycled carbon black according to (1), characterized in that the inert gas is at least one selected from carbon dioxide, nitrogen, helium, and argon. (3) The method for processing recycled carbon black according to (2), characterized in that when the inert gas is carbon dioxide, the heat treatment temperature is 300 to 800°C, and when the inert gas is argon, the heat treatment temperature is 300 to 950°C. (4) By performing the heat treatment of recycled carbon black in an inert gas and setting the heat treatment temperature to 300 to 1000°C, the N ２ N after heat treatment for SA / STSA ２ N is the ratio of SA / STSA. ２ A method for processing recycled carbon black that controls the SA / STSA change rate to 0.95 to 1.3. Alternatively, the present invention is defined by the following: (5) The method for processing recycled carbon black according to (2) above, characterized in that when the inert gas is carbon dioxide, the heat treatment temperature is 300 to 500°C, and when the inert gas is argon, the heat treatment temperature is 650 to 950°C.

[0007] According to the method for processing recycled carbon black of the present invention, the reinforcing properties of recycled carbon black when compounded into rubber can be improved.

[0008] The present invention relates to a method for processing recycled carbon black, which involves heat-treating recycled carbon black in an inert gas at a heat treatment temperature of 300 to 1000°C. The recycled carbon black used in this invention is not particularly limited, as long as it is carbon black obtained by thermal decomposition from rubber materials such as used tires in which carbon black has been compounded. In this invention, the heat treatment of recycled carbon black is carried out in an inert gas. In this invention, the oxygen concentration in the inert gas used for heat-treating the recycled carbon black is preferably 1 volume% or less. In this invention, an inert gas refers to a gas with low reactivity with recycled carbon black during heat treatment, such as carbon dioxide (CO2). ２ ), nitrogen (N２ Examples include noble gases such as helium (He), neon (Ne), and argon (Ar). The method for heat-treating the recycled carbon black in the present invention is not particularly limited, and examples thereof include heat-treatment methods such as rotary kilns, small-scale vacuum atmosphere furnaces, and mufflers.

[0009] In the present invention, the heat-treatment temperature when heat-treating the recycled carbon black is 300 to 1000 °C. The heat-treatment temperature in the present invention is preferably 300 to 950 °C, more preferably 350 to 950 °C. Alternatively, the heat-treatment temperature in the present invention is preferably 300 to 500 °C, more preferably 300 °C or more and less than 500 °C, and even more preferably 330 to 480 °C. Alternatively, the heat-treatment temperature in the present invention is preferably 650 to 950 °C, more preferably 700 to 950 °C, more preferably more than 750 °C and ⅔ or less than 950 °C, and even more preferably 800 to 930 °C. In particular, when the inert gas is carbon dioxide, the heat-treatment temperature is preferably 300 to 800 °C, more preferably 300 to 500 °C or 300 °C or more and less than 500 °C. When the inert gas is argon, the heat-treatment temperature is preferably 300 to 950 °C, more preferably 650 to 950 °C, more preferably 730 to 950 °C, more preferably more than 750 °C and ⅔ or less than 930 °C. When the inert gas is carbon dioxide, the effects of the present invention can be achieved even at a relatively low temperature, and when the inert gas is argon, the effects of the present invention can be achieved even at a relatively high temperature. The heat-treatment time in the present invention can be appropriately selected, and examples thereof include 30 to 240 minutes, 60 to 180 minutes, and the like. In the present specification, A (numerical value) to B (numerical value) represents A or more and B or less.

[0010] [N ２ SA] N ２ SA is the specific surface area per unit weight (m ２ / g), and the measurement is performed by the method specified in JIS K6217-2:2017. N ２ SA preferably does not change significantly before and after the heat treatment, and the change rate is within ±10% with respect to the N ２ SA before the heat treatment (N ２ SA after the heat treatment / N ２ SA before the heat treatment) is preferable.

[0011] [STSA] STSA (Statistical Thickness Specific Surface Area) can be measured by the method specified in JIS K6217-7:2013, and is the specific surface area per unit weight (m²). ２ The value per g represents the external specific surface area, excluding the specific surface area inside the pores present on the carbon black surface. It is preferable that STSA does not change significantly before and after heat treatment, and that the change rate (STSA after heat treatment / STSA before heat treatment) is within ±10% of the STSA before heat treatment.

[0012] [N ２ SA / STSA] N ２ This is the value obtained by dividing SA by STSA. ２ SA represents the total specific surface area of ​​carbon black, including the specific surface area inside the pores present on the carbon black surface. On the other hand, STSA represents the external specific surface area, excluding the specific surface area inside the pores present on the carbon black surface. Therefore, N ２ An increase in SA / STSA indicates an increase in pore size, N ２ SA / STSA indicates the roughness of the carbon black surface. ２ Even if SA is large, if the proportion of the specific surface area inside the pores is large, the number of active sites on the carbon black surface that interact with rubber decreases, thus reducing the reinforcing effect when compounded with rubber. Therefore, simply N ２ A higher SA does not necessarily mean improved reinforcing properties when compounded with rubber. Therefore, from the perspective of maintaining the active sites on the carbon black surface that interact with rubber, N ２ It is preferable that SA / STSA does not change significantly before and after heat treatment, and N before heat treatment ２ N after heat treatment for SA / STSA ２ N is the ratio of SA / STSA. ２ The SA / STSA change rate is preferably 0.95 to 1.3, more preferably 0.95 to 1.2, and even more preferably 0.95 to 1.1. Also, the N after heat treatment ２The SA / STSA ratio is preferably 0.95 to 1.3, more preferably 0.98 to 1.2, and even more preferably 0.98 to 1.15. According to the processing method of the present invention, when removing the amount of organic residue adhering to the recycled carbon black, the N of the recycled carbon black after processing is obtained without increasing the surface pores. ２ SA / STSA can be set to the above preferred range.

[0013] [TGA (Loss at 110-550°C)] This value quantifies the components desorbed in the temperature range of 110-550°C when the temperature is raised from room temperature to 900°C under a nitrogen atmosphere. A smaller value indicates a smaller amount of organic residue adhering to the recycled carbon black after processing.

[0014] [M300 index (Measurement of tensile stress (M300) at 300% elongation)] The tensile stress (M300) of the rubber composition at 300% elongation is measured according to the method specified in JIS K6251:2023. The M300 index represents the ratio to the M300 of the reference rubber composition.

[0015] The present invention will be described in detail below with reference to examples of the present invention, but the technical scope of the present invention is not limited to these examples.

[0016] [Examples 1-3] 200g of rCB (PB365, manufactured by Enrestec) was placed in a sample case and placed in a small vacuum atmosphere furnace (KVA-70 / 120, manufactured by Kurata Giken), and the furnace lid was closed. Vacuum evacuation of the furnace was started and the vacuum was maintained until the gauge pressure was -0.01 MPa. Then, Ar gas (Ar: 99.99% or higher) was introduced into the furnace at a flow rate of 5 L / min to replace the inside of the furnace with Ar. After the replacement was complete, heating was started while flowing Ar gas (Ar: 99.99% or higher) into the furnace at a flow rate of 1 L / min. The heating rate was 20°C / min. In Example 1, the temperature was raised to 350°C and held for 1 hour. In Example 2, the temperature was raised to 750°C and held for 1 hour. In Example 3, the temperature was raised to 950°C and held for 1 hour. Subsequently, the temperature was lowered by circulating cooling water to room temperature, and the heat-treated rCB was removed from the sample case. The oxygen content in the furnace during heat treatment was approximately 0%. Note that the gas purity in Examples 1 to 6 is expressed as volume percent.

[0017] [Examples 4-6] 200g of rCB, the same as in Examples 1-3, was placed in a sample case and placed in a batch-type atmosphere rotary kiln (volume: 24.5L, heating coil: fibrotal type, manufactured by Takasago Kogyo), and the kiln lid was closed. CO2 was used inside the kiln. ２ It was purged with gas. CO ２ Gas purging is CO ２ Gas (CO ２ CO2 (over 99.5%) was introduced into the kiln at a flow rate of 15 L / min for 15 minutes. ２ After purging with gas, CO ２ Gas (CO ２ While flowing 99.5% or higher into the kiln at a rate of 2 L / min, the temperature was increased at a rate of 4°C / min. In Example 4, the temperature was raised to 350°C and held for 1 hour, in Example 5, the temperature was raised to 450°C and held for 1 hour, and in Example 6, the temperature was raised to 750°C and held for 1 hour. After the holding time, the temperature was lowered to room temperature, and the heat-treated rCB was removed from the sample case in each case. CO2 was used during the cooling process. ２ Replace gas with N ２ The temperature was lowered using a cooling fan while gas was flowed into the kiln. The kiln's rotation speed was 1 rpm, and the oxygen level inside the furnace during heat treatment was 0.5% or less.

[0018] [Comparative Example 1] The rCB used in Examples 1 to 6 before heat treatment was used as the carbon black for Comparative Example 1.

[0019] [Reference Example] Virgin carbon black (Asahi #65, manufactured by Asahi Carbon), which is not recycled, was used as the carbon black in the reference example.

[0020] Regarding the heat-treated samples obtained in Examples 1 to 6, N ２ SA, STSA, N ２ SA / STSA, TGA, and M300 index measurements were performed. These measurements were carried out based on the above description of these measurement items. Note that the TGA measurement was performed using a differential thermal-thermogravimetric simultaneous measurement device (TG-DTA8122), N ２Performed under a gas atmosphere, approximately 20 mg of the sample and approximately 20 mg of alumina (for baseline) were weighed into a platinum crucible that had been pre-baked, placed into the auto-sampler of the measuring device, held at 30°C for 30 minutes, heated to 110°C at 10°C / min and held for 60 minutes, heated to 920°C at 15°C / min, and after the measurement was completed, the loss on ignition in the specified temperature range was calculated and baseline corrected with alumina. This was carried out using this method.

[0021] The rubber composition used for the measurement of M300 index was prepared according to a conventional method with the following formulation: SBR (#1723) (137.5 parts by mass), carbon black (50 parts by mass), stearic acid (1 part by mass), zinc oxide (3 parts by mass), sulfur (1.5 parts by mass), dibenzothiazole disulfide (vulcanization accelerator: 1.5 parts by mass), diphenylguanidine (vulcanization accelerator: 0.5 parts by mass). Using the prepared rubber composition, the M300 index was measured by the method specified in JIS K6251:2023. For the carbon black in Comparative Example 1 and the Reference Example, the same measurements as in Examples 1 to 6 were also carried out. The results of these measurements are shown in Table 1. The N of Examples 1 to 6 ２ SA change rate, STSA change rate and N ２ SA / STSA change rate is that of N in Comparative Example 1 ２ SA, STSA and N ２ They represent the respective ratios when SA / STSA is taken as 1. Also, the M300 index of Examples 1 to 6 and Comparative Example 1 is represented by the ratio when the measured value of the carbon black in the Reference Example is taken as 100.

[0022]

[0023] The regenerated carbon black after the treatment in Examples 1 to 6 had a larger M300 index compared to the regenerated carbon black before the treatment in Comparative Example 1 and had an M300 almost equivalent to that of Reference Example 1 which is virgin carbon black. As can be seen from the comparison of TGA between Examples 1 to 6 and Comparative Example 1, the organic residues adhering to the surface were removed by the treatment method of the present invention and the amount of organic residues decreased, and as shown by the N ２ SA / STSA change rate, the increase in pores was suppressed during the removal of organic residues, and the N ２ SA / STSA change rate could be made close to 1 and N２ This is thought to be due to the ability to suppress changes in SA / STSA. Thus, by processing recycled carbon black using the processing method of the present invention, it was possible to convert recycled carbon black into carbon black with excellent rubber reinforcing properties.

[0024] The processing method of the present invention can improve the properties of recycled carbon black and enhance its reinforcing properties when compounded into rubber, making it suitable for use when recycling carbon black contained in used waste tires and the like for reuse as a filler in rubber and the like.

Claims

1. A method for processing recycled carbon black, comprising heat-treating recycled carbon black in an inert gas at a heat treatment temperature of 300 to 1000°C.

2. The method for treating recycled carbon black according to claim 1, characterized in that the inert gas is at least one selected from carbon dioxide, nitrogen, helium, and argon.

3. The method for processing recycled carbon black according to claim 2, characterized in that the heat treatment temperature is 300 to 800°C when the inert gas is carbon dioxide, and 300 to 950°C when the inert gas is argon.

4. By performing heat treatment of recycled carbon black in an inert gas and setting the heat treatment temperature to 300 to 1000°C, the N2 before heat treatment is obtained. ２ N after heat treatment for SA / STSA ２ N is the ratio of SA / STSA. ２ A method for processing recycled carbon black that controls the SA / STSA change rate to 0.95 to 1.3.

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