Method for treating recycled carbon black

Abstract

The present invention addresses the problem of providing a method for treating recycled carbon black that improves the reinforcing properties of the recycled carbon black when added to rubber. Provided is a method for treating recycled carbon black in which recycled carbon black is heat-treated in a vacuum.

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 various impurities remaining on its surface, which reduces its reactivity with rubber and other materials, resulting in a problem where it does not exhibit sufficient effects when compounded with rubber. Therefore, attempts have been made to remove the carbonized rubber (bituminous residue) on the surface of rCB by heat treatment or heat treatment combined with extraction using a medium-polar solvent. It has been proposed to heat-treat rCB at 550°C in a nitrogen atmosphere, or at 600°C in an argon atmosphere, a carbon dioxide atmosphere, or a water vapor atmosphere (see Patent Document 1). However, while Patent Document 1 states that heat treatment achieved a bituminous residue removal effect comparable to that of solvent extraction, it is shown that both heat treatment and solvent extraction are substantially necessary when processing rCB. Furthermore, although it is shown that the specific surface area increases by including heat treatment in the processing step, no effect on reinforcing properties when compounded with rubber is shown.

[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 a treatment method to improve the properties of recycled carbon black so that it could achieve 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 found that by heat-treating recycled carbon black in a vacuum, residual impurities on the surface could be removed, and the surface properties could be shaped to a suitable form. This allowed for improvement of the recycled carbon black's properties without multiple or complex processes, particularly improving its reinforcing effect when compounded into rubber. Thus, the present invention was completed.

[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 a vacuum. (2) The method for processing recycled carbon black according to (1), characterized in that the heat treatment temperature is 300 to 1000°C. (3) By performing the heat treatment of recycled carbon black in a vacuum, the N 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.

[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 method for treating recycled carbon black of the present invention is a method of heat-treating recycled carbon black in a vacuum. The recycled carbon black in the present invention is not particularly limited as long as it is carbon black obtained by pyrolysis from a material in which carbon black is blended in rubber such as used waste tires. In the present invention, vacuum means 0.1 MPa or less, preferably 0.095 MPa or less, more preferably 0.09 MPa or less, and still more preferably 0.01 MPa or less. The method for heat-treating the recycled carbon black in the present invention is not particularly limited as long as it can be heat-treated with the heat-treatment atmosphere in a vacuum state. For example, heat-treatment methods using various vacuum atmosphere furnaces, muffles, rotary kilns, etc. can be mentioned.

[0009] The heat-treatment temperature in the present invention is preferably 300 to 1000 °C, more preferably 350 to 970 °C, and still more preferably 370 to 930 °C. The heat-treatment time in the present invention can be appropriately selected. For example, 30 to 240 minutes, 60 to 180 minutes, etc. can be mentioned. 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 carried out 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 N ２ SA before the heat treatment (N ２ SA after the heat treatment / N ２ SA) 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 (m ２The 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 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 ２ The 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, in which heat treatment is performed in a vacuum, when removing the amount of organic residue adhering to the recycled carbon black, the N of the recycled carbon black after treatment is not increased without increasing the surface pores. ２SA / 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 after the gauge pressure was reduced to -0.01 MPa, heating was started. The heating rate was set to 20°C / min, and the temperature was raised to the predetermined temperature and held for 1 hour. After that, the temperature was lowered by circulating cooling water to room temperature, and the heat-treated rCB was removed from the sample case. The heating temperature was 300°C in Example 1, 500°C in Example 2, and 700°C in Example 3.

[0017] [Examples 4-6] 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 drawn down to a gauge pressure of -0.01 MPa, after which heating was started. The heating rate was set to 20°C / min, and the temperature was raised to 900°C and held for a predetermined time. After that, the temperature was lowered by circulating cooling water to room temperature and the heat-treated rCB was removed from the sample case. The holding time at 900°C was 1 hour in Example 4, 2 hours in Example 5, and 3 hours in Example 6.

[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 ２ The procedure was performed under a gas atmosphere, weighing approximately 20 mg of the sample and approximately 20 mg of alumina (for baseline) into a preheated platinum crucible, placing them in the autosampler of the measuring device, maintaining a temperature of 30°C for 30 minutes, increasing the temperature to 110°C at a rate of 10°C / min and maintaining it for 60 minutes, and then increasing the temperature to 920°C at a rate of 15°C / min. After the measurement was completed, the weight loss due to heating within the specified temperature range was calculated and the baseline was corrected with alumina.

[0021] The rubber composition used for measuring the M300 index was prepared according to a conventional method, containing 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), dibenzodithiazole disulfide (vulcanization accelerator: 1.5 parts by mass), and diphenylguanidine (vulcanization accelerator: 0.5 parts by mass). The M300 index was measured using the prepared rubber composition according to the method specified in JIS K6251:2023. The carbon black of Comparative Example 1 and Reference Example was also measured in the same manner as in Examples 1 to 6. The results of these measurements are shown in Table 1. ２ SA change rate, STSA change rate and N ２ The SA / STSA change rate is N for Comparative Example 1. ２ SA, STSA and N ２This represents the respective ratios when SA / STSA is set to 1. Furthermore, the M300 index for Examples 1-6 and Comparative Example 1 is expressed as a ratio when the measured value of the carbon black in the reference example is set to 100.

[0022]

[0023] The recycled carbon black after treatment in Examples 1 to 6 had a significantly higher M300 index compared to the recycled carbon black before treatment in Comparative Example 1. The recycled carbon black after treatment in Example 3 had an M300 that was almost the same as the reference example of virgin carbon black. Furthermore, the recycled carbon black after treatment in Examples 4 to 6 had an M300 that was equal to or greater than the reference example of virgin carbon black. This can be seen from the comparison of TGA between Examples 1 to 6 and Comparative Example 1, indicating that the organic residue adhering to the surface was removed by the treatment method of the present invention, reducing the amount of organic residue, and N ２ As shown in the SA / STSA change rate, the increase in pore size is suppressed when removing organic residue, N ２ The SA / STSA change rate can be made close to 1. ２ 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, which involves heat treatment of recycled carbon black in a vacuum.

2. The method for processing recycled carbon black according to claim 1, characterized in that the heat treatment temperature is 300 to 1000°C.

3. By performing the heat treatment of recycled carbon black in a vacuum, the N2 before heat treatment is reduced. 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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