Method for rubber / steel cord separation, recycling method for steel cords, and recycling method for rubber for tire

Abstract

A purpose of the present invention is to provide a method for rubber / steel cord separation, the method being capable of reducing the amount of a rubber adherent to steel cords without through any complicated step and enabling closed-loop recycling of the recovered steel.　Provided is a method for separating the rubber contained in a tire from the steel cords contained therein, the method being characterized by including a wet heat treatment step in which, prior to separation between the rubber and the steel cords, the tire is placed in a wet heat environment having a temperature of 60°C or higher and a humidity of 60% or higher.

Description

Rubber-steel cord separation method, steel cord recycling method, and tire rubber recycling method

[0001] The present invention relates to a method for separating rubber from steel cord, a method for recycling steel cord, and a method for recycling tire rubber.

[0002] From the perspective of contributing to a sustainable society, it is desirable to reuse tire products for a long period of time, and for example, there is a demand for recycling of scrap tires that can no longer be used. Here, the steel used in tire beads and steel cords has been collected and recycled as scrap iron. As a method for recovering steel, for example, a technology is known in which the beads are mechanically extracted from scrap tires and the rubber is mechanically crushed to extract the steel.

[0003] However, steel recovered using this technology often contains impurities such as rubber, and the sulfur and metal components contained in rubber can reduce the quality of the steel. Therefore, even if the steel is recycled, its use as wire (steel cord) for tires (horizontal recycling) is limited, and it often ends up being downcycled.

[0004] Therefore, Patent Document 1 discloses a technique in which the tread portion is heated by induction heating, and the portion expanded by the heating is cut open to remove and recover the steel wire. The technique disclosed in Patent Document 1 makes it possible to remove the steel cord from the tread portion of the tire with a relatively simple operation.

[0005] Japanese Patent Application Laid-Open No. 2003-260455

[0006] However, from the viewpoint of horizontal recycling of steel materials, the technology of Patent Document 1 does not sufficiently separate the steel cord from the rubber, and there has been a demand for the development of a technology that further promotes the separation of the steel cord from the rubber and enables the recovery of steel materials with higher purity.

[0007] Therefore, an object of the present invention is to provide a rubber-steel cord separation method that can reduce the amount of rubber adhering to the steel cord without going through complicated steps and enables horizontal recycling of the recovered steel. Another object of the present invention is to provide a steel cord recycling method that enables horizontal recycling of the recovered steel, and a tire rubber recycling method that enables various recycling of the recovered rubber.

[0008] The gist of the present invention, which solves the above-mentioned problems, is as follows: (1) A method for separating rubber and steel cords contained in a tire, the method comprising: a wet heat treatment step of placing the tire in a wet heat environment at a temperature of 60°C or higher and a humidity of 60% or higher prior to separating the rubber and the steel cords. The rubber-steel cord separation method having the above-mentioned configuration can reduce the amount of rubber adhering to the steel cords without going through complicated steps, and enables horizontal recycling of the recovered steel.

[0009] (2) A method for recycling a steel cord, characterized in that the steel obtained by the rubber-steel cord separation method according to (1) is reused as a steel cord. The steel cord recycling method having the above configuration enables horizontal recycling of the recovered steel.

[0010] (3) A method for recycling rubber for tires, characterized in that the rubber obtained by the rubber-steel cord separation method according to (1) is reused as rubber for tires. The steel cord recycling method having the above configuration can be applied to various recycling methods of recovered rubber.

[0011] According to the present invention, it is possible to provide a rubber-steel cord separation method that can reduce the amount of rubber adhering to the steel cord without going through complicated steps and that enables horizontal recycling of the recovered steel. Furthermore, according to the present invention, it is possible to provide a steel cord recycling method that enables horizontal recycling of the recovered steel, and a tire rubber recycling method that enables various recycling of the recovered rubber.

[0012] <Method for Separating Rubber from Steel Cord> One embodiment of the method for separating rubber from steel cord of the present invention will be specifically described below. The method for separating rubber from steel cord of the present invention is a method for separating rubber and steel cord contained in a tire. The present invention is characterized in that it includes a wet heat treatment step of placing the tire in a wet heat environment at a temperature of 60°C or higher and a humidity of 60% or higher prior to separation of the rubber from the steel cord.

[0013] The inventors of the present invention have investigated methods for separating rubber from steel cords. They found that in order to maintain the quality of the recovered steel material and enable horizontal recycling, it is necessary to reduce the amount of rubber adhering to the steel cords. They also noted that incorporating a process to reduce the adhesion between the rubber and steel cords during the typical recycling process for scrap tires would be effective. Further research led them to discover that a wet heat treatment process in which the tire is placed in a humid heat environment at a temperature of 60°C or higher and a humidity of 60% or higher prior to separation of the rubber from the steel cord reduces the adhesion between the rubber and steel cord, significantly reducing the amount of rubber adhering when the rubber and steel cord are separated. As a result, the rubber-steel cord separation method of the present invention does not require complicated processes, can reduce the amount of rubber adhering to the steel cords, and enables horizontal recycling of the recovered steel.

[0014] The tires used in the rubber-steel cord separation method of the present invention are usually used scrap tires. However, they do not necessarily have to be scrap tires, and when it is necessary to separate the rubber and the steel cords, new tires or tires currently in use can also be used. Furthermore, the type of tire and the configuration of the rubber and steel cords are not particularly limited, except that they are tires containing rubber and steel cords, and can be selected appropriately.

[0015] (Moist heat treatment step, decomposition step) As described above, the rubber-steel cord separation method of the present invention includes a moist heat treatment step of placing the tire in a moist heat environment at a temperature of 60°C or higher and a humidity of 60% or higher prior to separation of the rubber and the steel cord. The moist heat treatment step can reduce the adhesion between the rubber and the steel cord, thereby significantly reducing the amount of rubber adhering when the rubber and the steel cord are subsequently separated.

[0016] The reason for placing the tire in a humid and hot environment at a temperature of 60°C or higher and a humidity of 60% or higher is that the interface between the rubber and the steel cords can be efficiently deteriorated by the relatively high temperature and moisture. From the same perspective, the temperature in the humid and heat treatment step is preferably 60°C or higher, and more preferably 70°C or higher. On the other hand, if the temperature in the humid and heat treatment step is too high, it may cause deterioration of the rubber and steel cords, resulting in a decrease in the quality of the rubber and steel cords after recovery. Therefore, the temperature in the humid and heat treatment step is preferably 180°C or lower. Furthermore, the humidity in the humid and heat treatment step is preferably 60% or higher, and more preferably 70% or higher.

[0017] Furthermore, the wet heat treatment step is preferably carried out for 12 hours or more, although this depends on the exposure state of the steel cord, etc. This more reliably reduces the adhesion between the rubber and the steel cord, and further reduces the amount of rubber adhering when the rubber and the steel cord are separated. From the same viewpoint, the wet heat treatment step is preferably carried out for 12 hours or more, and more preferably for 36 hours or more.

[0018] In the wet heat treatment step, the oxygen concentration in the wet heat environment is preferably 20% or more, and more preferably 40% or more, because this promotes oxidation at the interface between the rubber and the steel cord, thereby more efficiently reducing adhesion.

[0019] In the wet heat treatment step, the atmospheric pressure in the wet heat environment can be high. In this case, the atmospheric pressure is preferably 100 kPa or more, more preferably 150 kPa or more, of atmospheric pressure. This is because it promotes deterioration of the interface between the rubber and the steel cord, and can more efficiently reduce adhesion.

[0020] Furthermore, the rubber-steel cord separation method of the present invention preferably further includes a disassembly step of cutting the tire at least one location to expose a tire cross section including the steel cord prior to the moist heat treatment step. By performing the moist heat treatment step while exposing the tire cross section including the steel cord and exposing it to oxygen, the adhesion between the rubber and the steel cord can be more efficiently reduced.

[0021] The conditions for cutting the tire in the disassembly step are not particularly limited as long as the tire can be cut in at least one location and the tire cross section including the steel cord can be exposed. For example, from the viewpoint of exposing more of the steel cord, it is preferable to increase the number of cutting locations of the tire, and from the viewpoint of reducing the effort and time required for the process, it is preferable to reduce the number of cutting locations.

[0022] Furthermore, from the viewpoint of more efficiently reducing the adhesion between the rubber and the steel cords, it is preferable to cut the tire so that all of the steel cords are exposed in at least one location in the longitudinal direction.

[0023] Furthermore, in the rubber-steel cord separation method of the present invention, in order to reduce the adhesion between the rubber and the steel cord by a certain percentage, the exposed amount of the steel cord in the tire cross section and the duration of the moist heat treatment step are inversely proportional to each other, so the duration of the moist heat treatment step can be reduced by increasing the exposed amount of the steel cord. In other words, by increasing the exposed amount of the steel cord, the adhesion between the rubber and the steel cord can be reduced more efficiently without carrying out the moist heat treatment step for a long time.

[0024] In the disassembly step, the device used to cut the tire is not particularly limited, and a commercially available tire cutting machine can be appropriately selected.

[0025] (Dielectric Heating Step) The rubber-steel cord separation method of the present invention preferably further includes a dielectric heating step of heating the steel cord portion in the tire to 100 to 180° C. by dielectric heating prior to the wet heat treatment step. By increasing the temperature of the steel cord, the adhesion between the rubber and the steel cord can be more efficiently reduced, and the amount of rubber adhering when the rubber and the steel cord are separated can be significantly reduced.

[0026] In the dielectric heating step, the steel cord portion is heated to 100°C or higher to more effectively reduce the adhesion between the rubber and the steel cord, and the steel cord portion is heated to 180°C or lower to prevent deterioration of the steel cord and the rubber due to excessive heating. From the same perspective, it is more preferable to heat the steel cord portion by dielectric heating to 120 to 160°C.

[0027] The heating device used for the induction heating is not particularly limited, and commercially available products can be used as appropriate. For example, a device having a movable high-frequency induction coil is preferably used as the induction heating means. However, this is not limited to this, and any other suitable type of induction heating means, including one having a fixed high-frequency induction coil, can also be used. Furthermore, the induction heating means can be, for example, a high-frequency hardening device having a frequency of 50 kHz and an output of several tens of kW. The shape of the heating coil is also not limited. The method of heating the tread portion using the high-frequency induction coil may be any suitable method, such as fixing the high-frequency induction coil and bringing the rotating tread portion close to it, or bringing the high-frequency induction coil close to the tread portion fixed to a fixing means, but the method is not particularly limited.

[0028] Here, the dielectric heating step is carried out prior to the moist heat treatment step, but may be carried out before or after the decomposition step. From the viewpoint of more effectively promoting the reduction in adhesion between the rubber and the steel cord, the dielectric heating step is preferably carried out after the decomposition step, i.e., between the decomposition step and the moist heat treatment step.

[0029] The heating time in the dielectric heating step is not particularly limited and can be adjusted appropriately depending on the heating conditions of the steel cord. For example, the heating time can be set to 1 second to 1,000 minutes. When the heating time of the dielectric heating is 10 seconds or longer, the adhesion between the rubber and the steel cord can be more reliably reduced, and when the heating time of the dielectric heating is 100 minutes or shorter, deterioration of the steel cord and rubber due to heating can be more reliably prevented.

[0030] (Inner liner removal step) Preferably, the rubber-steel cord separation method of the present invention further includes an inner liner removal step of removing the inner liner from the tire prior to the moist heat treatment step. The inner liner makes it difficult for air to pass through, so if it remains in the tire, it tends to inhibit deterioration of the adhesive strength between the rubber and the steel cord when the moist heat treatment step is carried out. Therefore, by removing the inner liner from the tire prior to the moist heat treatment step, the adhesion between the rubber and the steel cord can be more efficiently reduced, and the amount of rubber adhering when the rubber and the steel cord are separated can be significantly reduced.

[0031] Here, the inner liner removal step is carried out prior to the wet heat treatment step, and is preferably carried out prior to the decomposition step and the dielectric heating step. By carrying out the inner liner removal step before the decomposition step and the dielectric heating step, the adhesion between the rubber and the steel cord can be more efficiently reduced, and the amount of rubber adhering when the rubber and the steel cord are separated can be further reduced.

[0032] (Magnetic Separation Step) In addition, the rubber-steel cord separation method of the present invention preferably further includes a magnetic separation step of finely cutting the tire after the wet heat treatment step and extracting steel by magnetic separation. By selecting and extracting steel by the magnetic separation, it is possible to efficiently recover steel.

[0033] The device used for the magnetic separation is not particularly limited, and a commercially available magnetic separator can be appropriately selected depending on the required performance.

[0034] In the magnetic separation step, the tire after the wet heat treatment step is cut into small pieces, and the cut size can be appropriately selected depending on the time for the wet heat treatment step, the performance of the magnetic separator, etc. For example, from the viewpoint of more efficient magnetic separation and ease of recycling of the rubber after separation of the steel cords, it is preferable to cut the tire into pieces of 2 inches square or less, and more preferably into pieces of 1 inch square or less.

[0035] The steel removed after the magnetic separation process has a small amount of rubber attached, specifically, the amount of rubber attached is 10% by mass or less when the mass of the steel is 100% by mass. When the amount of rubber attached is as low as 10% by mass or less, horizontal recycling of the recovered steel is possible.

[0036] In the rubber-steel cord separation method of the present invention, after the steel is removed by the magnetic separation step, it is possible to appropriately carry out a known secondary processing step.

[0037] <How to recycle steel cord and tire rubber>

[0038] The steel cord recycling method of the present invention is characterized in that the steel obtained by the above-mentioned rubber-steel cord separation method of the present invention is reused as a steel cord. Since the steel obtained by the rubber-steel cord separation method of the present invention is of a quality that allows horizontal recycling, the quality of the original steel cord can be maintained even for the steel cord obtained by recycling.

[0039] Furthermore, the steel cord recycling method of the present invention is characterized in that the rubber obtained by the above-mentioned rubber-steel cord separation method of the present invention is reused as tire rubber. The rubber recovered by the rubber-steel cord separation method of the present invention is recyclable, and can therefore be used as tire rubber.

[0040] [Examples 1 to 3, Comparative Example 1, Conventional Example] For tires containing steel cords under the same conditions, the steel cords were separated and recovered under the conditions shown in Table 1. The processes were carried out in the following order: inner liner removal process, decomposition process, dielectric heating process, moist heat treatment process, and magnetic separation process. For the decomposition process in Table 1, the tire was cut using a cutter. For the induction heating process in Table 1, the steel was heated at a temperature of 120°C for 1 minute. For the moist heat treatment process in Table 1, the temperature was 70-90°C and the humidity was 50-90% for 24 hours. For the magnetic separation process in Table 1, the tire after moist heat treatment was crushed into 1-inch cubes.

[0041] <Evaluation> The amount of residual rubber contained in the obtained steel was estimated from a steel peeling test (exposing the steel surface with a knife and peeling it off in a 90° direction from the exposed surface at a speed of 50 mm / min) under various humidity and heat conditions, and the percentage (mass%) was calculated. The calculation results are shown in Table 1.

[0042]

[0043] The results in Table 1 show that Examples 1 to 3 have a smaller amount of residual rubber and have achieved higher quality steel than the Comparative Example and Conventional Example. Furthermore, Example 3, which involves the dielectric heating process, has a particularly small amount of residual rubber.

[0044] According to the present invention, it is possible to provide a rubber-steel cord separation method that can reduce the amount of rubber adhering to the steel cord without going through complicated steps and that enables horizontal recycling of the recovered steel. Furthermore, according to the present invention, it is possible to provide a steel cord recycling method that enables horizontal recycling of the recovered steel, and a tire rubber recycling method that enables various recycling of the recovered rubber.

Claims

1. A method for separating rubber and steel cords contained in a tire, the method comprising, prior to separation of the rubber and steel cords, a wet heat treatment step of placing the tire in a wet heat environment at a temperature of 60°C or higher and a humidity of 60% or higher.

2. The rubber-steel cord separation method according to claim 1, further comprising a disassembly step of cutting the tire in at least one location to expose a cross section of the tire including the steel cord prior to the wet heat treatment step.

3. The method for separating rubber and steel cord according to claim 1 or 2, wherein the wet heat treatment process is carried out for 12 hours or more.

4. The rubber-steel cord separation method according to claim 1 or 2, further comprising a dielectric heating step of heating the steel cord portion in the tire to 100 to 180°C by dielectric heating prior to the wet heat treatment step.

5. The method for separating rubber and steel cords according to claim 1 or 2, further comprising an inner liner removing step of removing an inner liner from the tire prior to the wet heat treatment step.

6. The method for separating rubber and steel cords according to claim 1 or 2, further comprising a magnetic separation step of finely shredding the tire after the wet heat treatment step and extracting the steel by magnetic separation.

7. The method for separating rubber and steel cord according to claim 6, wherein the steel removed after the magnetic separation process has an amount of rubber adhering to it of 10% by mass or less.

8. A method for recycling steel cords, comprising reusing the steel obtained by the method for separating rubber from steel cords according to claim 1 or 2 as steel cords.

9. A method for recycling rubber for tires, comprising reusing the rubber obtained by the method for separating rubber and steel cord according to claim 1 or 2 as tire rubber.

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