Method and apparatus for separating foreign matter from crushed rubber

Abstract

Various foreign materials such as metal, stone, sand, mud, wood, and plastic are separated from crushed rubber using simple equipment. [Solution] A method for separating foreign matter mixed in pulverized rubber having a specific gravity greater than 1, comprising: a high specific gravity foreign matter separation step in which the pulverized rubber is made to float on water by the surface tension of water acting upward, and high specific gravity foreign matter having a specific gravity greater than 1 that has sunk into the water; and a low specific gravity foreign matter separation step in which the pulverized rubber is made to sink in water by eliminating or reducing the surface tension of water acting upward, and low specific gravity foreign matter having a specific gravity less than 1 that has sunk into the water.

Description

Technical Field

[0001] The present invention relates to the separation of foreign substances from ground rubber.

Background Art

[0002] The importance of recycling rubber products such as used tires, seal parts, shock-absorbing parts, and hoses has been increasing. Various foreign substances such as metal, stone, sand, mud, wood, and plastic adhere to used rubber products. Although these foreign substances are less likely to cause problems when burned or thermally decomposed by thermal recycling or the like, they need to be separated from the rubber products because they can damage recycling equipment or degrade the quality of recycled rubber in non-combustion recycling. Therefore, conventionally, various methods for crushing rubber products and separating foreign substances from the ground rubber have been studied.

[0003] Patent Document 1 describes a method in which rubber products such as discarded old tires are crushed into rubber particles, these rubber particles are put into a perforated basket of a washing machine together with water, an alkali, and a surfactant, the basket is moved to stir the rubber particles, and contaminants are removed from the rubber particles during stirring for cleaning. Water, an alkali, a surfactant, and contaminants are discharged from the holes of the basket, and only the cleaned rubber particles remain in the basket. However, there is a problem that special baskets, alkalis, surfactants, etc. are essential.

[0004] Patent Document 2 describes a method for generating and recovering polyvinyl chloride / rubber pulverized material and iron powder by shredding automotive molding waste with a shredder, crushing it with a pulverizer, separating it with a vibrating sieve, separating it with an air separator, and further separating it by specific gravity with a specific gravity separator. The specific gravity separators described are (1) a water flow separator consisting of an inclined separation plate, a water supply trough, and a dust collection section, which aims to separate specific gravity by flow and water flow, and (2) a flotation separator consisting of a water tank, rollers, and a screw, which collects the polyvinyl chloride / rubber pulverized material that floats on the water surface in the water tank and removes the iron powder material that accumulates on the bottom of the water tank. However, there is a problem in that it is difficult to separate wood chips and the like with a specific gravity of less than 1 that float on the water surface together with the polyvinyl chloride / rubber pulverized material.

[0005] Patent Document 3 describes a method for producing high-purity rubber material, which includes a grinding step of crushing a rubber material containing impurities to make it finer, and a removal step of removing the impurities adhering to the finely ground rubber material. In the grinding step, the rubber material is crushed by sliding contact between a cylindrical screen and an inner blade that can rotate at high speed. In the removal step, before the finely ground rubber material adheres, the finely ground rubber material is washed with water using a pool equipped with a water jet device or water pump 16, or a washing machine with a dewatering function. However, there is a problem in that it requires large-scale water flow equipment.

[0006] Patent Document 4 describes a method for producing high-purity natural rubber, which includes a grinding step to obtain pulverized rubber by grinding natural rubber containing foreign matter, and a removal step to remove foreign matter adhering to the obtained pulverized rubber. In the grinding step, the natural rubber is pulverized to a size of 3 mm square or smaller. While there are no particular restrictions on the method of the removal step, it is stated that by installing a pool with circulating water directly below the grinder and washing the pulverized rubber in flowing water, impurities in the rubber can be removed easily and efficiently. However, this method has the problem of requiring equipment to create a strong water flow. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 8-509782 [Patent Document 2] Japanese Patent Application Publication No. 11-207312 [Patent Document 3] Japanese Patent Publication No. 2013-141825 [Patent Document 4] Japanese Patent Publication No. 2015-42712 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Therefore, the objective of the present invention is to enable the separation of various foreign substances such as metal, stone, sand, mud, wood, and plastic from crushed rubber using simple equipment. [Means for solving the problem]

[0009] The specific gravity of rubber varies depending on the type. Some types, such as natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), and ethylene propylene rubber (EPM, EPDM), have a specific gravity of less than 1, while others, such as chloroprene rubber (CR), nitrile rubber (NBR), acrylic rubber (ACM), urethane rubber (U), and fluororubber (FKM), have a specific gravity of more than 1.

[0010] However, since rubber products contain a large amount of inorganic fillers such as carbon black and silica to improve performance, most rubber products, regardless of the type of rubber, have a specific gravity greater than 1. Therefore, most crushed rubber products also have a specific gravity greater than 1.0, and should therefore sink in water. However, experiments described later have shown that crushed rubber can either sink or be wiped in water, so further investigation led to the following approach.

[0011] [1] A method for separating foreign matter mixed in crushed rubber from crushed rubber with a specific gravity greater than 1, A high-density foreign matter separation process is performed in which the pulverized rubber is made to float on the water by the surface tension of the water acting upward, and high-density foreign matter with a specific gravity greater than 1 that sinks in the water is separated. A low-density foreign matter separation process is performed to separate low-density foreign matter that floats on the water by causing the surface tension of the water, which acts upward, to cause the crushed rubber to sink in the water, and to separate low-density foreign matter with a specific gravity of less than 1. A method for separating foreign matter from crushed rubber containing [specific material].

[0012] (action) As shown in Figures 6(a) and 7(a), when pulverized rubber is scattered in water, most of it floats. This is presumed to be because the surface of the pulverized rubber becomes hydrophobic due to the seepage of oil contained in the rubber, resulting in poor wetting to water. As a result, the contact angle θ > 90°, and the surface tension γ of the water acts upward, overpowering the weight w of the pulverized rubber. When the pulverized rubber floats in water in this way, low-density foreign matter with a specific gravity of less than 1 that was mixed in with the pulverized rubber floats with the pulverized rubber, but high-density foreign matter with a specific gravity greater than 1 that was mixed in with the pulverized rubber sinks in the water and can be separated from the pulverized rubber and removed (high-density foreign matter separation process).

[0013] As shown in Figures 6(b) and 7(b), when the upward surface tension is eliminated or reduced, the crushed rubber sinks in water, as shown in Figures 6(c) and 7(c). When the crushed rubber sinks in water in this way, low-density foreign matter with a specific gravity of less than 1 remains floating on the water and can be separated from the crushed rubber and removed (low-density foreign matter separation process).

[0014] [2] A method for eliminating or reducing the surface tension of water acting upward is to cover the crushed rubber with water. [1] A method for separating foreign matter from crushed rubber.

[0015] (action) As shown in Figure 6(b), when water is poured over the crushed rubber, as shown in Figure 6(c), the crushed rubber sinks in the water. This is because, although the oil is not removed from the surface of the crushed rubber when water is poured over it, the water temporarily hits the entire side surface of the crushed rubber, reducing the contact angle and eliminating the upward surface tension, causing the crushed rubber to sink due to its own weight.

[0016] As shown in Fig. 6(d), when the ground rubber that has once sunk in water is taken out of the water and scattered again in the water, it floats again in the water. This is presumably because almost no oil has been removed from the surface of the ground rubber even after it has sunk once in water, so the surface of the ground rubber taken out of the water remains hydrophobic, and the surface tension of water acts upward as in Fig. 6(a).

[0017] [3] A method for eliminating or reducing the upward acting surface tension of water is to add a surfactant to the water, which is the method for separating foreign substances in the ground rubber described in [1].

[0018] (Function) Fig. 7(a) shows the state where the ground rubber is floating in water, similar to Fig. 6(a).

[0019] As shown in Fig. 7(b), when a surfactant is added to the water, as shown in Fig. 7(c), the ground rubber sinks in the water. This is because the surfactant adsorbs on the surface of the ground rubber with the hydrophilic group facing outward, so the surface of the ground rubber becomes hydrophilic, the wettability improves, the contact angle becomes θ < 90°, the upward surface tension disappears, and the surface tension γ acts downward, so it is presumed that the ground rubber sinks in the water. The addition amount of the surfactant to the water is preferably 0.1 to 1.0% by mass, and more preferably 0.2 to 0.4% by mass.

[0020] As shown in Fig. 7(d), when the ground rubber that has once sunk in water is taken out of the water and scattered again in the water, this time it sinks in the water. This is because the surfactant remains on the surface of the ground rubber even after it is taken out of the water, so the surface of the ground rubber remains hydrophilic, and the surface tension of water acts downward as in Fig. 7(b). Therefore, it is difficult to remove high specific gravity foreign substances that have sunk in the water at this time.

[0021] [4] A method for eliminating or reducing the upward acting surface tension of water is to add alcohols to the water, which is the method for separating foreign substances in the ground rubber described in [1].

[0022] (Function) When alcohols are added to water, since the surface tension of alcohols is lower than that of water, the surface tension decreases compared to the state in Fig. 6(a), the contact angle becomes smaller, and the upward surface tension γ cannot overcome the self-weight w of the pulverized rubber, causing the pulverized rubber to sink in water. As a specific example, using the same container, sample 2, and water as in Experiment 1 described later, 50 g of water was placed in the container, 1 g of sample 2 was gently dropped from above and floated on the water, and then 4 mass% of ethanol was added to the water. As a result, 96% of the floating pulverized rubber (the ratio of the number of pulverized rubber particles. The same applies hereinafter) sank. The alcohols are not particularly limited, and examples thereof include methyl alcohol, ethyl alcohol, isopropyl alcohol, etc. The addition amount of alcohols to water is preferably 1.0 to 10.0 mass%, and more preferably 3.0 to 4.0 mass%.

[0023] [5] The method for disappearing or reducing the upward surface tension of water is to raise the temperature of water in the method for separating foreign substances of the pulverized rubber described in [1].

[0024] (Function) When the temperature of water is raised, the surface tension decreases compared to the state in Fig. 6(a), the contact angle becomes smaller, and the upward surface tension γ cannot overcome the self-weight w of the pulverized rubber, causing the pulverized rubber to sink in water. As a specific example, using the same container, pulverized rubber (sample 2), and water as in Experiment 1 described later, 50 g of water (about 35 °C) was placed in the container, 1 g of pulverized rubber was gently dropped from above and floated on the water, and then the temperature of the water was raised to 65 °C. As a result, 65% of the floating pulverized rubber sank. The temperature of water is preferably 40 °C or lower before raising (high specific gravity foreign substance separation step), and preferably raised to 60 °C or higher (more preferably 70 °C or higher).

[0025] [6] The method for disappearing or reducing the upward surface tension of water is to apply ultrasonic vibration to water in the method for separating foreign substances of the pulverized rubber described in [1].

[0026] (Function) When ultrasonic vibrations are applied to water, the surface tension decreases compared to the state shown in Figure 6(a), the contact angle becomes smaller, and the upward surface tension γ can no longer overcome the weight w of the crushed rubber, causing the crushed rubber to sink in the water. As a specific example, using the same container, crushed rubber (sample 2), and water as in Experiment 1 described later, 50g of water was placed in the container, and 1g of crushed rubber was gently added from above to float on the water. Then, the container was placed in an ultrasonic cleaner (EMERSON BRANSONIC M2800-J) and ultrasonic vibrations were applied, resulting in 38% of the floating crushed rubber (percentage of the number of crushed rubber particles; the same applies below) sinking.

[0027] [7] A method for separating foreign matter from pulverized rubber according to any one of the items [1] to [6], wherein a high-density foreign matter separation step is performed, followed by a low-density foreign matter separation step.

[0028] (action) In the high-density foreign matter separation process, the crushed rubber is floated in water, and the high-density foreign matter that sinks is separated. Then, in the low-density foreign matter separation process, the crushed rubber is submerged in water, and the low-density foreign matter that floats is separated. This eliminates the need to float the crushed rubber that has sunk in water again, making it efficient.

[0029] [8] A first water tank for floating the crushed rubber on the water using the surface tension of the water acting upward, and separating the high specific gravity foreign matter with a specific gravity greater than 1 that has sunk into the water, The system includes a second water tank for sinking crushed rubber in water by eliminating or reducing the surface tension of the water acting upward, and for separating low-density foreign matter with a specific gravity of less than 1 that floats in the water. A foreign matter separation device for crushed rubber, configured such that crushed rubber floating in the water in the first tank is sent to the second tank along with the overflowing water.

[0030] (action) The separation of high-density foreign matter in the first tank and low-density foreign matter in the second tank are performed simultaneously and continuously, resulting in high efficiency.

[0031] [9] The foreign matter separation apparatus for crushed rubber described above, wherein the first water tank is provided with a hopper for supplying crushed rubber onto the water and a first removal device for removing high-density foreign matter that has sunk into the water.[8]

[0032]

[10] The foreign matter separation apparatus for crushed rubber according to [8] or [9] is provided in the second water tank, which is equipped with a water stirring device that generates waves on the water surface and covers the crushed rubber floating on the water with the waves to sink the crushed rubber in the water, and a second removal device that removes low specific gravity foreign matter floating on the water.

[0033]

[11] A foreign matter separation apparatus for crushed rubber as described in any one of the items [8] to

[10] , wherein a surfactant is added to the water in the second tank.

[0034]

[12] A foreign matter separation apparatus for crushed rubber according to any one of the items [8] to

[11] , comprising a recovery device for recovering the crushed rubber removed from the second water tank.

[0035] As can be seen from the above, the present invention does not require equipment to create a strong water flow, and can therefore be carried out with simple equipment. However, the present invention does not exclude water flow, and can also be carried out by, for example, applying a weak water flow. [Effects of the Invention]

[0036] According to the present invention, various foreign substances such as metal, stone, sand, mud, wood, and plastic can be separated from crushed rubber using simple equipment. [Brief explanation of the drawing]

[0037] [Figure 1] Figure 1 is a photographic representation of Experiment 1 for an example. [Figure 2] Figure 2 is a photograph used as a diagram to illustrate Experiment 2. [Figure 3] Figure 3 is a photograph used as a diagram to illustrate Experiment 3. [Figure 4] Figure 4 is a photograph used as a substitute for a diagram, also illustrating Experiment 4. [Figure 5] Figure 5 is a photograph used as a diagram to illustrate Experiment 5. [Figure 6] Figure 6 is an explanatory diagram of the mechanism of action in Experiment 1. [Figure 7] Figure 7 is an explanatory diagram of the mechanism of action in Experiment 2. [Figure 8] Figure 8 is a schematic diagram of the apparatus used in Example 1. [Figure 9] Figure 9(a) is a schematic diagram of a portion of the apparatus used in Example 2, and (b) is a schematic diagram of a portion of the apparatus used in Example 3. [Figure 10] Figure 10 is a schematic diagram of the apparatus used in Example 4. [Modes for carrying out the invention]

[0038] <1> Crushed rubber Crushed rubber is rubber that has been crushed, and the crushing method is not limited to this. While there are no particular limitations on the type of crushed rubber, crushed used rubber products (tires, seals, cushioning parts, hoses, etc.) are preferable from a recycling standpoint. The type of rubber used for the crushed rubber is not particularly limited, but examples include NR, IR, SBR, BR, IIR, EPM, EPDM, CR, NBR, ACM, U, FKM, etc. The shape of the crushed rubber is not particularly limited, but examples include granular, flake, and linear forms. The dimensions of the crushed rubber are not particularly limited, but examples include those with a longest part measuring 1 to 10 mm.

[0039] <2> foreign object Foreign matter mixed into crushed rubber is not limited to, but examples include metal, stone, sand, mud, wood, and plastic. Examples of high-density foreign matter with a specific gravity greater than 1 include metals, stones, sand, and plastics (polyvinyl chloride, polystyrene, ABS, polyacetal, acrylic, polycarbonate, polyamide, polyurethane, fluorine-based materials, etc.). Examples of low-density foreign matter with a specific gravity of less than 1 include wood and plastics (polyethylene, polypropylene, EVA, etc.).

[0040] <3> water The type of water is not particularly limited, but examples include tap water, well water, rainwater, and distilled water. The water may contain additives that do not substantially affect the surface tension. The water temperature is not particularly limited, but 40°C or lower is preferable because of its high surface tension.

[0041] <3> High-density foreign matter separation process In the high-density foreign matter separation process, there are no particular limitations on the method of floating the pulverized rubber on water using the surface tension of water acting upward, but it is preferable to supply the pulverized rubber to the water such that water adheres to the bottom surface of the pulverized rubber, and water adheres to a part of the side of the pulverized rubber but not to the entire side. The method of supplying the pulverized rubber is not particularly limited, but the following methods can be given as examples. (a) The crushed rubber is scattered on the water from just above the water (preferably within 10 cm of the water surface, more preferably within 5 cm of the water surface). Specifically, although not particularly limited, examples include supplying the crushed rubber from a hopper onto the water and moving the hopper horizontally or moving the water surface. (i) After the crushed rubber has sunk into the water, lift it to the surface and expose it to the air, then scatter it in the same manner as in (a) above.

[0042] <4> Low specific gravity foreign matter separation process In the low-density foreign matter separation process, the method for eliminating or reducing the upward-acting surface tension is not particularly limited, but the following methods can be given as examples. (a) Cover the crushed rubber with water. Specifically, the following methods can be exemplified. • The crushed rubber is covered with waves created on the water surface. Examples of methods for creating waves include agitation and oscillating the water. Examples of agitation methods include using a water wheel to agitate the water surface, or installing a rotating body at the bottom of the water to agitate vigorously. • Spray water onto the crushed rubber. A watering device can be used for this purpose. • Press the crushed rubber into water. A pressing jig can be used for this. • Pour the crushed rubber into the water with force. (i) Add a surfactant to the water. (c) Add alcohols to water. (e) Raise the water temperature. (o) Apply ultrasonic vibrations to water.

[0043] <5> Steps of the process The order of the high-density foreign matter separation process and the low-density foreign matter separation process is not particularly limited, but the following order can be exemplified. (a) A high-density foreign matter separation process is performed, followed by a low-density foreign matter separation process. (i) A low-density foreign matter separation process is performed, followed by a high-density foreign matter separation process. (c) A high-density foreign matter separation process is performed, followed by a low-density foreign matter separation process, and then the high-density foreign matter separation process is performed again.

[0044] <4> Ripple effect By separating various foreign substances from crushed rubber, the following ripple effects can be obtained. • This prevents problems such as clogging or screw breakage in the subsequent rubber recycling process. • The quality of recycled rubber has improved, and even when recycled rubber is mixed with virgin rubber in products, the tensile strength and elongation do not decrease. [Examples]

[0045] Next, embodiments of the present invention (including experiments) will be described. Note that the materials, conditions, structure, shape, and dimensions of the embodiments are illustrative and can be modified as appropriate without departing from the spirit of the invention.

[0046] [Experiment 1] As Experiment 1, we conducted buoyancy and sinking experiments on various rubber scraps in water, as shown in Figure 1. Sample 1 is pulverized rubber obtained by crushing a new rubber compound formulated by the applicant. The particle size is approximately 6 mm, and the specific gravity is 1.04. No foreign matter is present. Sample 2 is crushed rubber obtained by crushing the tread surface portion of a tire recalled from the market. The particle size is approximately 6 mm and the specific gravity is 1.07. Foreign matter was removed beforehand. Sample 3 is crushed rubber obtained by crushing the entire tire that was recalled from the market. The particle size is 1-3 mm, and the specific gravity is greater than 1, although it is difficult to measure precisely due to its fineness. Foreign matter was removed beforehand.

[0047] Three glass containers, each with an opening diameter of 45 mm and a height of 50 mm, were used as containers. A stainless steel spatula with a 20mm dish length and a 140mm handle length was used as a stirring tool. Tap water was used as the water source. The water temperature was approximately 35°C.

[0048] (1) When 50g of water was placed in each container and 1g of each sample was gently added from above, as shown in the upper part of Figure 1, samples 1 and 2 floated almost entirely, while sample 3 floated almost entirely, with about 1% (the percentage of the number of crushed rubber particles; the same applies below) sinking. As shown in Figure 6(a) and mentioned above, it was estimated that samples 1-3 floated because the surface tension γ of the water acted upward. The reason why some of sample 3 sank is thought to be because it contains different rubber components from various parts of the tire, resulting in differences in the oil it contains and the amount of oil it seeps out.

[0049] (2) Subsequently, when a stirring operation was performed by inserting the spatula halfway into the water and moving it back and forth horizontally at a rate of 2 back-and-forth movements per second for 1 minute, waves were created on the water surface, as shown in the middle of Figure 1. Almost all of samples 1 to 3 sank into the water, with approximately 1% of sample 1, 2% of sample 2, and 5% of sample 3 remaining floating. As shown in Figures 6(b) and 6(c) and mentioned above, it is presumed that samples 1, 2, and 3 sank because the waves on the water surface covered the pulverized rubber with water, causing the upward surface tension to disappear. It is thought that a relatively large amount of sample 3 remained floating because it contained a mixture of different rubber components from various parts of the tire.

[0050] (3) Afterwards, each of the submerged samples was lifted above the water surface using a spatula and then gently lowered back into the water. As shown in the lower part of Figure 1, samples 1 and 2 floated almost entirely, while sample 3 floated almost entirely, with about 4% remaining submerged. As shown in Figure 6(d) and mentioned earlier, it is presumed that samples 1-3 floated again because the oil was hardly removed from the surface of the crushed rubber, causing the surface tension of the water to act upward. It is thought that some of sample 3 remained submerged because it contained a mixture of different rubber components from various parts of the tire.

[0051] [Experiment 2] In Experiment 2, we tested the effects of adding a surfactant to water, as shown in Figure 2. The same sample 2, container, spatula, and water as in Experiment 1 were used. A detergent containing 16% alkyl ether sulfate sodium was used as the surfactant.

[0052] (1) When 50g of water was placed in a container and 1g of sample 2 was gently added from above, sample 2 floated almost entirely in the water, as shown in the upper part of Figure 2.

[0053] (2) Next, 0.1 g of surfactant was added to the water. Then, with the spatula inserted halfway into the water, a stirring operation was performed by moving it back and forth horizontally at a rate of 2 back and forth per second for 10 seconds. As shown in the middle of Figure 2, Sample 2 was completely submerged in the water. As shown in Figures 7(b) and 7(c) and as described above, it is presumed that Sample 2 submerged in the water because the surfactant made the surface of the crushed rubber hydrophilic, causing the upward surface tension to disappear.

[0054] (3) Afterwards, the submerged sample 2 was lifted above the water surface with a spatula and then gently lowered again from above. As shown in the lower part of Figure 2, sample 2 sank in the water (without floating). As shown in Figure 7(d) and as previously mentioned, sample 2 sank in the water because the surfactant remained on the surface of the crushed rubber even after it was removed from the water, so the surface of the crushed rubber remained hydrophilic.

[0055] [Experiment 3] As Experiment 3, we investigated the behavior when the container size was increased, as shown in Figure 3. The same sample 2, spatula, and water as in Experiment 1 were used. A plastic container with an opening of 130mm x 75mm and a height of 95mm was used as the container.

[0056] (1) When 500g of water was placed in a container and 6g of sample 2 was gently added from above, as shown in the upper part of Figure 3, most of sample 2 floated in the water, and about 2% sank.

[0057] (2) Subsequently, when the spatula was inserted partway into the water and stirred back and forth horizontally at a rate of 1 back and forth per second for 1 minute, as shown in the middle left of Figure 3, most of Sample 2 sank into the water, with about 15% remaining floating. When this stirring operation was performed for an additional minute, as shown in the middle right of Figure 3, a portion of Sample 2 sank into the water, with about 10% remaining floating.

[0058] (3) After that, sample 2, which had sunk, was lifted above the water surface with a spatula and then gently lowered again from above. As shown in the lower part of Figure 3, most of sample 2 floated again, while about 3% remained submerged.

[0059] These results show that even when the container (opening area) is larger than in Experiment 1, the same phenomenon as in Experiment 1 was observed. However, since it tends to take longer to submerge Sample 2 in water than in Example 1, it is preferable to consider the stirring method. For example, stirring the water surface using gears or installing a rotating body at the bottom of the water to stir vigorously could be considered.

[0060] [Experiment 4] As Experiment 4, as shown in Figure 4, an experiment was conducted to separate the crushed rubber from wood chips, which are low-density foreign matter. The same sample 2, spatula, and water as in Experiment 1, and the same container as in Experiment 3 were used. For the wood pieces, I used toothpicks cut to a length of 5 mm.

[0061] (1) When 500g of water was placed in a container and 6g of Sample 2 was gently added from above, as shown in the upper left and right of Figure 4, most of the rubber powder floated on the water, and about 3% sank. When 30 pieces of wood (0.4g) were then gently added from above, all of the wood pieces floated.

[0062] (2) After that, with the spatula inserted halfway into the water, a stirring operation was performed by moving it back and forth horizontally at a rate of 1 back and forth per second for 1 minute. As shown in the middle left and lower left of Figure 4, all of the wood chips remained floating, while most of Sample 2 sank in the water, with about 10% remaining floating. When this stirring operation was performed for an additional minute, as shown in the middle right and lower right of Figure 4, all of the wood chips remained floating, and a portion of Sample 2 sank further, with about 8% remaining floating. The floating wood chips and Sample 2 were removed, dried, and weighed. The wood chips weighed 0.4g and Sample 2 weighed 0.5g.

[0063] These results confirm that objects with a low specific gravity (mostly 0.2-0.7), such as wood chips, float in water regardless of whether they are stirred in step (2), and separate from the sunk rubber, making it easy to remove the floating wood chips. However, depending on the part of the rubber product recovered from the market, there may be particles in the sunk rubber that float strongly, so care must be taken with the yield.

[0064] [Experiment 5] As Experiment 5, as shown in Figure 5, an experiment was conducted to separate the rubber pulverized material from the high-density foreign matter, which is stone. The same sample 2, spatula, and water as in Experiment 1, and the same container as in Experiment 3 were used. For the stones used, we selected pieces of maifan stone manufactured by Daiso Industries, with a diameter of approximately 5 mm.

[0065] (1) When 500g of water was placed in a container and 6g of sample 2 was gently added from above, as shown in the upper left and right of Figure 5, most of the rubber powder floated on the water, and about 3% sank. When 30 stones (5.8g) were then gently added from above, all of the stones sank.

[0066] (2) After that, when the spatula was inserted halfway into the water and stirred back and forth horizontally at a rate of 1 back and forth per second for 1 minute, as shown in the middle left of Figure 5, all of the stones remained submerged, and most of Sample 2 sank in the water, with about 4% remaining floating. When this stirring operation was performed for an additional minute, as shown in the middle right and bottom right of Figure 5, all of the stones remained submerged, and a portion of Sample 2 sank further, with about 3% remaining floating.

[0067] From these results, it was confirmed that objects with a high specific gravity, such as stones (mostly 1.5-3), sink almost entirely and separate from the floating crushed rubber in stage (1), making it easy to remove the sunken stones. However, if the crushed rubber sinks in stage (2), separation becomes difficult, so a system in which the stones sink first and then the wood pieces float is considered preferable.

[0068] [Example 1] Example 1, based on the above experiments, will be explained with reference to Figure 8. Note that the configuration of each part of the example is illustrative and can be modified as appropriate without departing from the spirit of the invention.

[0069] The foreign matter separation device for crushed rubber in this embodiment comprises a first water tank 1 for storing water, a second water tank 2 located next to the first water tank 1 for storing water that overflows from the first water tank 1, a recovery device 3 for recovering the crushed rubber sent out from the second water tank 2 along with the water, and a water circulation device 4 for circulating the water that flows out of the recovery device 3 back to the first water tank 1.

[0070] The first water tank 1 is equipped with a hopper 5 for supplying crushed rubber onto the water, a water transfer device 6 that moves the water surface toward the second water tank 2, thereby sending the floating crushed rubber to the second water tank 2 along with the overflowing water, and a first removal device (not shown) for removing high-density foreign matter with a specific gravity greater than 1 that has sunk into the water.

[0071] The second water tank 2 is equipped with a water stirring device 8 that creates waves on the water surface and covers the pulverized rubber floating on the water with these waves, thereby sinking the pulverized rubber into the water; an underwater screw 9 that sends the pulverized rubber that has sunk into the water out of the second water tank 2 from the bottom along with the water; and a second removal device (not shown) that removes low-density foreign matter with a specific gravity of less than 1 that floats in the water.

[0072] The recovery device 3 consists of a conveyor 11 that inclines and transports the crushed rubber sent out with water by the underwater screw 9, and a recovery container 12 that receives the crushed rubber and water transported by the conveyor 11. The recovery container 12 has a bottom plate 13 that stores the crushed rubber and allows water to pass through and fall, and a water collection plate 14 that collects the water that falls from the bottom plate 13.

[0073] The water circulation device 4 consists of a circulation pipe 15 and a pump 16 that circulate the water collected by the water collection plate 14 back to the first water tank 1.

[0074] Using the apparatus configured as described above, foreign matter is separated from the pulverized rubber in the following manner. (1) High-density foreign matter separation process The crushed rubber, which contains both high-density and low-density foreign matter, is supplied by dropping it from the hopper 5 onto the water in the first tank 1. At this time, the water surface is moving towards the second tank 2 by the water transfer device 6, so the crushed rubber is dispersed and scattered on the moving water (without clumping together in a narrow area). In this way, the surface tension of the water acting upward as described above causes the crushed rubber to float on the water, and the water transfer device 6 sends the floating crushed rubber to the second tank 2 along with the overflowing water. Then, the high-density foreign matter that has sunk into the water in the first tank 1 and separated is removed by the first removal device.

[0075] (2)Low specific gravity foreign matter separation process Waves are generated on the water surface of the second tank 2 by the water agitator 8. As a result, the crushed rubber sent from the first tank 1 to the second tank 2 is covered with water by the waves on the water surface. In this way, the surface tension of the water acting upward as described above is eliminated, causing the crushed rubber to sink into the water, and the submerged screw 9 sends the submerged crushed rubber out of the second tank 2 along with the water flowing out from the bottom. Then, the low-density foreign matter that floats and separates in the water of the second tank 2 is removed by the second removal device.

[0076] (3) Collection of crushed rubber and water circulation The crushed rubber, sent out with water by the underwater screw 9, is transported by the conveyor 11 of the recovery device 3 and received in the recovery container 12. The crushed rubber accumulated on the bottom plate 13 is recovered, and the water collected after falling onto the water collection plate 14 is circulated back to the first water tank 1 by the water circulation device 4.

[0077] According to this embodiment, various foreign materials such as metal, stone, sand, mud, wood, and plastic can be separated from crushed rubber using simple equipment. Furthermore, since the above processes are carried out simultaneously and continuously, the efficiency is high.

[0078] [Example 2] Embodiment 2, shown in Figure 9(a), differs from Embodiment 1 in that the hopper 5 is provided with a sinking prevention section 5a that receives the crushed rubber just below the water surface and prevents the crushed rubber from sinking into the water due to the force of its fall from the hopper 5. Otherwise, it is the same as Embodiment 1.

[0079] According to this embodiment, in addition to the same effects as in Example 1, the recovery rate of crushed rubber can be increased.

[0080] [Example 3] Example 3, shown in Figure 9(b), differs from Example 1 in that, considering that some of the crushed rubber sinks in the water due to the force of falling from the hopper 5, a re-introduction device 17 is provided in the first water tank 1 to bring the crushed rubber that has sunk back to the surface and re-introduce it. Otherwise, it is the same as Example 1.

[0081] According to this embodiment, in addition to the same effects as in Example 1, the recovery rate of crushed rubber can be increased.

[0082] [Example 4] Example 4, shown in Figure 10, differs from Example 1 in that 0.2% or more of a surfactant is added to the water in the second tank 2 to make the surface of the crushed rubber hydrophilic, thereby eliminating the upward surface tension and ensuring that the crushed rubber sinks in the water, and that the circulation of the surfactant-containing water to the first tank 1 is not performed because circulating the water in the first tank 1 would prevent the crushed rubber from floating in the water. Otherwise, it is the same as Example 1. Note that the water stirring device 8 from Example 1 may also be used in combination.

[0083] According to this embodiment, in addition to the same effects as in Example 1, the recovery rate of crushed rubber can be increased.

[0084] It should be noted that the present invention is not limited to the embodiments described above, and can be appropriately modified and implemented without departing from the spirit of the invention. [Explanation of Symbols]

[0085] 1. Tank No. 1 2. Second Tank 3. Recovery device 4 Water circulation device 5 Hoppa 5a Settlement prevention section 6 Water transfer device 8. Water stirring device 9. Underwater propeller 11 Conveyor 12 Collection containers 13 Bottom plate 14 Water collection board 15 Reflux tube 16 pumps 17 Reloading device

Claims

1. A method for separating foreign matter mixed in crushed rubber having a specific gravity greater than 1, A high-density foreign matter separation process is performed in which the pulverized rubber is made to float on the water by the surface tension of the water acting upward, and high-density foreign matter with a specific gravity greater than 1 that sinks in the water is separated. A low-density foreign matter separation process is performed to separate low-density foreign matter that floats on the water by causing the surface tension of the water acting upward to disappear or decrease, thereby submerging the crushed rubber in water, and separating the low-density foreign matter with a specific gravity of less than 1. A method for separating foreign matter from crushed rubber containing [unspecified].

2. The method for removing foreign matter from crushed rubber according to claim 1, wherein the method for eliminating or reducing the surface tension of water acting upward is to cover the crushed rubber with water.

3. The method for separating foreign matter from pulverized rubber according to claim 1, wherein the method for eliminating or reducing the upward-acting surface tension of water is to add a surfactant to the water.

4. The method for separating foreign matter from pulverized rubber according to claim 1, wherein the method for eliminating or reducing the upward-acting surface tension of water is to add alcohols to the water.

5. The method for separating foreign matter from pulverized rubber according to claim 1, wherein the method for eliminating or reducing the upward-acting surface tension of water is to raise the temperature of the water.

6. The method for separating foreign matter from pulverized rubber according to claim 1, wherein the method for eliminating or reducing the upward-acting surface tension of water is to apply ultrasonic vibrations to the water.

7. A method for separating foreign matter from pulverized rubber according to any one of claims 1 to 6, comprising performing a high-density foreign matter separation step, followed by a low-density foreign matter separation step.

8. A first water tank is used to separate high-density foreign matter with a specific gravity greater than 1 that sinks to the water, by using the surface tension of water acting upward to float the crushed rubber on the water. The system includes a second water tank for sinking crushed rubber in water by eliminating or reducing the surface tension of the water acting upward, and for separating low-density foreign matter with a specific gravity of less than 1 that floats in the water. A foreign matter separation device for crushed rubber, configured such that crushed rubber floating in the water in the first tank is sent to the second tank along with the overflowing water.

9. The foreign matter separation apparatus for crushed rubber according to claim 8, wherein the first water tank is provided with a hopper for supplying crushed rubber onto the water and a first removal device for removing high-density foreign matter that has sunk into the water.

10. The foreign matter separation apparatus for crushed rubber according to claim 8, wherein the second water tank is provided with a water stirring device that generates waves on the water surface and covers the crushed rubber floating on the water with the waves to sink the crushed rubber into the water, and a second removal device that removes low-density foreign matter floating on the water.

11. The foreign matter separation apparatus for crushed rubber according to claim 8, wherein a surfactant is added to the water in the second tank.

12. A foreign matter separation device for crushed rubber according to any one of claims 8 to 11, further comprising a recovery device for recovering the crushed rubber removed from the second water tank.

Images