Apparatus for cleaning waste plastic flakes and method for cleaning waste plastic flakes

Abstract

To provide a cleaning apparatus and a cleaning method for waste plastic flakes which can be performed in a shorter period of time than conventional methods and can suppress costs and environmental loads.SOLUTION: A cleaning apparatus 1 for waste plastic flakes according to the present disclosure includes a cleaning tank 10 having a storage space 11, a semi-closed passage 20 having an inlet 21, an outlet 22, and a cleaning region 23, and having at least the cleaning region being disposed in the storage space, a foam generator 30 of fine bubbles installed in the storage space, and a stirring and advancing mechanism 40 that generates a stirring flow of cleaning liquid L and a transport flow from the inlet side toward the outlet side in the cleaning region, where the storage space is partitioned by a partition wall 50 into a cleaning space that is a space inside the semi-closed passage and a non-cleaning space that is a space outside the semi-closed passage, at least a part of the non-cleaning space is present above the cleaning space, and at least a part of the partition wall is a perforated wall 51 having permeability to fine bubbles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a cleaning device for waste plastic flakes and a method for cleaning waste plastic flakes.

Background Art

[0002] In order to obtain flakes for recycling the collected waste plastics, pretreatment that does not introduce foreign substances into the recycling process is important in terms of improving the quality of the product plastics. Waste plastics are pretreated as crushed materials with a size of several millimeters square called waste plastic flakes. Conventionally, waste plastic flakes generally go through at least three steps: a step of removing foreign substances with a large specific gravity by cyclone separation, a step of removing foreign substances with a small specific gravity by specific gravity separation in water, and a step of removing firmly adhering foreign substances attached to the surface of the plastic by alkali cleaning, and then become recycled flakes and have been used as raw materials for recycled products (see, for example, Patent Document 1). Here, recycled flakes refer to flakes obtained by crushing, cleaning, and drying waste plastic flakes, and are distinguished from waste plastic flakes at the stage of simply crushing the collected waste plastics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conventional method for obtaining recycled flakes requires at least three steps of cyclone separation, specific gravity separation, and alkali washing, making it difficult to reduce costs. In addition, since alkali washing is usually performed with a high-temperature alkali washing solution, there are problems such as high utility costs for chemicals, heating steam, and neutralization treatment during drainage, and a large environmental burden. Furthermore, when alkali residues are mixed into the recycled flakes, the alkali residues function as decomposition catalysts during chemical recycling, making it difficult to control the decomposition reaction. Also, the inventors of the present invention discovered a new problem that when trying to obtain recycled flakes in a shorter time than the conventional method without spending much time on specific gravity separation, a certain number of heavy specific gravity plastic flakes with a specific gravity greater than that of water will float in water.

[0005] The present disclosure aims to solve the above problems and provide a cleaning device for waste plastic flakes and a cleaning method for waste plastic flakes that can achieve the cleaning in a shorter time than the conventional method and suppress costs and the environmental burden.

Means for Solving the Problems

[0006] The inventors of the present invention found that the above problems can be solved by performing fine bubble cleaning in a semi-closed environment, and completed the present invention. That is, the cleaning device for waste plastic flakes according to the present invention includes a cleaning tank having a storage space for storing a cleaning liquid, an inlet, an outlet, and a cleaning area, at least the cleaning area being a semi-closed passage disposed in the storage space, a fine bubble generator installed in the storage space, and a stirring and advancing mechanism for generating a stirring flow of the cleaning liquid and a conveying flow from the inlet side to the outlet side in the cleaning area. The storage space is partitioned by a partition wall into a cleaning space that is the space inside the semi-closed passage and a non-cleaning space that is the space outside the semi-closed passage. At least a part of the non-cleaning space exists above the cleaning space, and at least a part of the partition wall is a porous wall having permeability to the fine bubbles.

[0007] In the waste plastic flake cleaning device according to the present invention, it is preferable that the perforated wall includes an upper perforated wall that constitutes a part of the partition wall that partitions the cleaning space and a part of the non-cleaning space that exists above the cleaning space. Since the upper perforated wall discharges light specific gravity residues such as oil or dirt, which have a specific gravity smaller than that of water, to the outside of the semi-closed passage, the light specific gravity residues can be easily separated and removed.

[0008] In the waste plastic flake cleaning device according to the present invention, it is preferable that the semi-closed passage further has a floating and sinking separation region on the discharge port side of the cleaning region, and has an opening at the upper part in the floating and sinking separation region. Since the opening discharges light specific gravity plastic flakes such as olefin flakes, which have a specific gravity smaller than that of water, to the outside of the semi-closed passage, the light specific gravity plastic flakes can be easily separated and removed.

[0009] In the waste plastic flake cleaning device according to the present invention, it is preferable that the cleaning tank has an upper surface opening and an overflow pocket provided outside the storage space along the side of the upper surface opening. Since the overflow pocket discharges light specific gravity residues and light specific gravity plastic flakes floating on the liquid surface from the storage space, the cleanliness of the cleaning liquid in the storage space can be maintained.

[0010] In the waste plastic flake cleaning device according to the present invention, it is preferable that the perforated wall includes a lower perforated wall that constitutes a part of the partition wall that partitions the cleaning space and a part of the non-cleaning space that exists below the cleaning space. Since the lower perforated wall discharges heavy specific gravity residues such as sand or glass, which have a specific gravity larger than that of water, to the outside of the semi-closed passage, the heavy specific gravity residues can be easily separated and removed.

[0011] In the waste plastic flake cleaning device according to the present invention, it is preferable that the perforated wall is non-penetrable with respect to the waste plastic flakes. The waste plastic flakes can be kept in the semi-closed passage with less loss and can be washed more efficiently.

[0012] In the waste plastic flake cleaning device according to the present invention, it is preferable that the cleaning liquid is a neutral cleaning liquid, which can further reduce the environmental load.

[0013] The waste plastic flake cleaning method according to the present invention includes a cleaning step of bringing waste plastic flakes into contact with fine bubbles in a cleaning liquid in which fine bubbles are generated, separating light specific gravity residues from the waste plastic flakes, and separating the waste plastic flakes into light specific gravity plastic flakes having a specific gravity smaller than that of the cleaning liquid and heavy specific gravity plastic flakes having a specific gravity larger than that of the cleaning liquid. The cleaning step includes a step of performing cleaning while holding and restricting floating flakes that move in the liquid level direction of the cleaning liquid among the waste plastic flakes in the cleaning liquid.

[0014] In the waste plastic flake cleaning method according to the present invention, it is preferable that the cleaning step includes performing cleaning in the cleaning area of a passage having an inlet, an outlet, and a cleaning area, and moving the waste plastic flakes in the cleaning area from the inlet side toward the outlet side. It can be cleaned more efficiently in a continuous manner.

[0015] In the waste plastic flake cleaning method according to the present invention, it is preferable that the cleaning step includes a step in which the light specific gravity residue separated from the waste plastic flakes moves to the liquid level of the cleaning liquid. By separating and removing the light specific gravity residue, the target plastic flakes can be submerged in the cleaning liquid according to their original specific gravity for separation and recovery. Also, the amount of foreign substances contained in the target plastic flakes can be reduced.

[0016] In the waste plastic flake cleaning method according to the present invention, it is preferable that the cleaning step includes a step of separating heavy specific gravity residues mixed in the waste plastic flakes from the waste plastic flakes. By separating and removing the heavy specific gravity residues, the amount of foreign substances contained in the target plastic flakes can be reduced.

[0017] In the method for cleaning waste plastic flakes according to the present invention, the cleaning step preferably includes a sedimentation separation step, and the sedimentation separation step preferably includes a step of moving the low specific gravity plastic flakes to the liquid surface and a step of precipitating the high specific gravity plastic flakes in the cleaning liquid. By separating and removing the low specific gravity plastic flakes, the amount of foreign matter contained in the target plastic flakes can be reduced.

[0018] In the method for cleaning waste plastic flakes according to the present invention, the cleaning step preferably includes a step of overflowing the low specific gravity residue or the low specific gravity plastic flakes floating on the liquid surface together with the cleaning liquid. The cleanliness of the cleaning liquid in the storage space can be maintained. In addition, the amount of foreign matter contained in the target plastic flakes can be reduced.

[0019] In the method for cleaning waste plastic flakes according to the present invention, the method for cleaning the waste plastic flakes further preferably includes a recovery step after the cleaning step, and the recovery step includes a step of taking out the high specific gravity plastic flakes from the cleaning liquid.

[0020] In the method for cleaning waste plastic flakes according to the present invention, the cleaning liquid is preferably a neutral cleaning liquid. The environmental impact can be further reduced.

Advantages of the Invention

[0021] According to the present disclosure, it is possible to provide a cleaning apparatus for waste plastic flakes and a method for cleaning waste plastic flakes that can suppress cost and environmental impact in a shorter time than conventional methods.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0023] Embodiments of the present invention will be described with reference to the drawings, but the present invention is not construed as being limited to these descriptions. As long as the effects of the present invention are achieved, the embodiments may be variously modified.

[0024] FIG. 1 is a schematic configuration diagram showing an example of a cleaning device according to the present embodiment. The cleaning device 1 for waste plastic flakes according to the present embodiment includes a cleaning tank 10 having a storage space 11 for storing a cleaning liquid, an inlet 21, an outlet 22, and a cleaning area 23, and at least the cleaning area 23 is arranged in the storage space 11. A semi-closed system passage 20, a fine bubble generator 30 installed in the storage space 11, and a stirring and advancing mechanism 40 for generating a stirring flow of the cleaning liquid L and a conveying flow from the inlet 21 side to the outlet 22 side in the cleaning area 23. The storage space 11 is partitioned by a partition wall 50 into a cleaning space 12 that is the space inside the semi-closed system passage 20 and a non-cleaning space 13 that is the space outside the semi-closed system passage 20. At least a part of the non-cleaning space 13 exists above the cleaning space 12, and at least a part of the partition wall 50 is a perforated wall 51 having permeability to fine bubbles.

[0025] The waste plastic flake cleaning device 1 is a device suitable for cleaning and separating and recovering heavy specific gravity plastic flakes with a specific gravity greater than that of water. Waste plastic flakes refer to crushed pieces obtained by crushing waste plastics including discarded, collected, and sorted PET bottles and the like, for example, with a side length of about 5 to 30 mm. Heavy specific gravity plastics with a specific gravity greater than that of water are not particularly limited, but for example, are polyester-based resins. Polyester-based resins include, for example, aromatic polyesters such as polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or polyethylene furanoate (PEF); wholly aromatic polyesters such as polyarylate or liquid crystal polymer; polycarbonate esters such as polycarbonate; aliphatic polyesters such as polylactic acid-based polymers, polybutylene succinate-based polymers, polyethylene adipate-based polymers, polyethylene succinate-based polymers, polycaprolactone-based polymers, polyhydroxyalkanoate-based polymers, aliphatic aromatic polyesters such as polybutylene adipate terephthalate, polyethylene adipate terephthalate, or polyethylene succinate terephthalate. Among these, the heavy specific gravity plastic is more preferably polyethylene terephthalate or polyethylene furanoate. Also, the heavy specific gravity plastic may be a virgin plastic material, a biodegradable plastic material, or a recycled plastic material.

[0026] The waste plastic flakes include plastic flakes of other materials in addition to the heavy specific gravity plastic flakes for recovery purposes. Further, the waste plastic flakes are mixed with foreign substances such as oil or dirt adhering to the surface of the waste plastic flakes, glass or sand. The inventors of the present invention have developed a cleaning device and a cleaning method for cleaning and separating and recovering heavy specific gravity plastic flakes for recovery purposes from waste plastic flakes in fewer steps and with a lower environmental impact than conventional cleaning methods for waste plastic flakes. As a result of the study, it was noted that the three conventional processes of a cyclone separation process, a specific gravity separation process, and an alkali cleaning process were combined into one process, and further that the process was carried out in a non-alkali environment. Therefore, the inventors of the present invention examined a cleaning device and a cleaning method for waste plastic flakes, taking as an example the case where the heavy specific gravity plastic flakes for recovery purposes are PET flakes. In the examination, it was found that the specific gravity of PET is about 1.4, and normally, waste PET flakes would sink in water, but a certain number of waste PET flakes may float on water immediately after being put into water. This phenomenon is considered to be caused by the surface tension, adhering dirt or adhering bubbles of the waste PET flakes. In the conventional cleaning method, in the specific gravity separation process, since a relatively long settling time is required, even if the waste PET flakes temporarily float due to surface tension or the like, they will sink within the settling time. Also, in the alkali cleaning process, the waste PET flakes sank in the alkali cleaning liquid. Therefore, the problem that a certain number of waste PET flakes float on water is a new problem that occurred for the first time when attempting to clean and separate and recover the waste PET flakes in one step and in a non-alkali environment. The inventors of the present invention have found that the above problems can be solved by performing fine bubble cleaning in a semi-closed system, and have completed the present invention.

[0027] The cleaning tank 10 may be any container capable of storing a cleaning liquid inside, for example, a container made of metal such as stainless steel. As shown in FIG. 1, the cleaning tank 10 is preferably a long tank arranged with the longitudinal direction X as the horizontal direction. The shape of the cleaning tank 10 is not particularly limited, and for example, it may be a rectangular tube shape or a cylindrical shape. The cleaning tank 10 is more preferably U-shaped in cross-section as shown in FIG. 2 in terms of ease of removing the heavy specific gravity residue accumulated at the bottom 16. The U-shaped cross-section includes, for example, a form in which the bottom 16 of the cleaning tank 10 has a round bottom shape. The upper surface 15 of the cleaning tank 10 may be open as shown in FIG. 2 or may be closed (not shown).

[0028] The storage space 11 is the space inside the cleaning tank 10 and is a space for storing the cleaning liquid L. The storage space 11 preferably has a raw material input section 11A, a cleaning section 11B, and a recovery section 11C along the longitudinal direction X. The raw material input section 11A is the area closer to the input port 21 than the bubble generator 30. In this area, mainly waste plastic flakes are introduced into the semi-closed passage 20. The cleaning section 11B is the area where the bubble generator 30 is provided. In this area, mainly waste plastic flakes are cleaned inside the semi-closed passage 20. The recovery section 11C is the area closer to the discharge port 22 than the bubble generator 30. In this area, mainly the cleaned heavy specific gravity plastic flakes are recovered.

[0029] In the waste plastic flake cleaning device 1 according to the present embodiment, the cleaning liquid L is preferably a neutral cleaning liquid, which can further reduce the environmental load. The neutral cleaning liquid is, for example, water. Various additives such as surfactants or bactericides may be added to the water. In the present embodiment, the cleaning liquid L is preferably water, but is not limited thereto, and a liquid in which an acidic component or an alkaline component is added to the water may also be used.

[0030] The semi-closed system passage 20 is a passage that is partially open. The semi-closed system passage 20 is surrounded by a partition wall 50, and a part of the partition wall 50 is a perforated wall 51 having permeability to fine bubbles, so that it becomes a semi-closed system that is partially open. As shown in FIG. 1, the semi-closed system passage 20 preferably has an elongated shape arranged with the longitudinal direction X as the horizontal direction. For example, it is preferably cylindrical, and more preferably cylindrical as shown in FIGS. 1 and 2. In the present embodiment, by performing cleaning within the semi-closed system, heavy specific gravity plastic flakes in the waste plastic flakes that float due to surface tension, adhered dirt, adhered bubbles, etc. are retained within the cleaning region 23, increasing the opportunity for the heavy specific gravity plastic flakes to contact the fine bubbles, and can be efficiently cleaned. The semi-closed system passage 20 may be a straight tubular shape that extends straight as shown in FIG. 1, or a curved tubular shape (not shown) having a bent portion.

[0031] The inlet 21 is an inlet for waste plastic flakes. In FIG. 1, as an example, a form is shown in which the inlet 21 is provided on a wall (hereinafter referred to as a side wall) 50a that forms the side surface of the cylindrical partition wall 50. However, the present invention is not limited to this, and the inlet 21 may be provided on a wall (hereinafter referred to as an end face wall) 50b that forms an end face closing one end of the side wall 50a of the cylindrical partition wall 50. It is preferable that an inlet guide (not shown) is connected to the inlet 21. The inlet guide may be connected to a crushing device for waste plastic.

[0032] The discharge port 22 is an outlet for the heavy specific gravity plastic flakes after cleaning. In FIG. 1, as an example, a form is shown in which the discharge port 22 is provided on an end face wall 50c that closes the other end of the side wall 50a of the cylindrical partition wall 50. However, the present invention is not limited to this, and the discharge port 22 may be provided on the side wall 50a of the cylindrical partition wall 50. It is preferable that a discharge guide (not shown) is connected to the discharge port 22. The discharge guide may be connected to a device for drying the plastic flakes after cleaning.

[0033] The cleaning area 23 is an area within the space in the semi-closed passage 20 where the waste plastic flakes are cleaned. The cleaning area 23 is preferably disposed within the storage space 11 and at a position below the liquid level of the cleaning liquid L during cleaning in the storage space 11. The cleaning area 23 may include, in order from the inlet 21 side, a first cleaning area where the waste plastic flakes and the cleaning liquid L are mixed, and a second cleaning area where the surface of the waste plastic flakes is cleaned in the first cleaning area and the heavy specific gravity plastic flakes among the waste plastic flakes precipitate in the semi-closed passage 20. In the first cleaning area, the light specific gravity plastic flakes move upward in the semi-closed passage 20, and a part of the heavy specific gravity plastic flakes move upward in the semi-closed passage 20 due to surface tension, adhered dirt, or adhered bubbles, etc. The heavy specific gravity residues such as glass or sand with a specific gravity greater than that of water move downward in the semi-closed passage 20, and the remaining heavy specific gravity plastic flakes with less influence of surface tension, adhered dirt, or adhered bubbles move downward in the semi-closed passage 20. In the second cleaning area, the heavy specific gravity plastic flakes that have moved upward in the semi-closed passage 20 together with the light specific gravity plastic flakes move downward in the semi-closed passage 20 according to their original specific gravity by removing the adhered dirt or adhered bubbles. The boundary between the first cleaning area and the second cleaning area does not need to be clearly separated, and in the vicinity of the boundary between the first cleaning area and the second cleaning area, it includes a form in which the amount of the heavy specific gravity plastic flakes that precipitate gradually increases as the cleaning of the waste plastic flakes progresses.

[0034] The bubble generator 30 may be any device that can generate fine bubbles and is not particularly limited. For example, it may be a super-high-speed swirling / shearing type bubble generator, a pressurized gas-liquid mixing type bubble generator, or an ultrasonic type bubble generator. The bubble generator 30 is preferably arranged such that the bubble discharge port 31 is located below the semi-closed passage 20. Fine bubbles refer to bubbles with a diameter of 100 μm or less, and include microbubbles with a diameter of 1 μm or more and 100 μm or less and nanobubbles with a diameter of less than 1 μm. The number average diameter or median diameter of the fine bubbles is preferably 50 μm or less.

[0035] The stirring and advancing mechanism 40 is a mechanism that stirs the cleaning liquid and conveys the waste plastic flakes from the inlet 21 side toward the outlet side. The direction F from the inlet 21 side toward the outlet side is the cleaning direction. The stirring flow and the conveying flow are preferably swirling flows that swirl in a spiral shape within the cleaning region 23. As shown in FIGS. 1 and 2, the stirring and advancing mechanism 40 is preferably a screw conveyor disposed within the semi-closed passage 20, but may also be a mechanism (not shown) including a device that stirs the cleaning liquid L by sending large bubbles and a device that extrudes the waste plastic flakes with a plunger, or a mechanism (not shown) that conveys while stirring with a water flow. The plunger is, for example, an extrusion member having a size corresponding to the inner diameter of the semi-closed passage 20. In the mechanism using the plunger, the semi-closed passage 20 is preferably straight tubular. As the plunger moves within the semi-closed passage 20, the waste plastic flakes within the semi-closed passage 20 are pushed and conveyed from the inlet 21 side toward the outlet side. The large bubbles are preferably generated by a bubble generator different from the bubble generator 30 to generate bubbles with a size of millimeter order or more. The installation location of the bubble generator for large bubbles is not particularly limited, but is below the semi-closed passage 20, above the semi-closed passage 20, on the side of the semi-closed passage 20, or a combination thereof. Also, for the mechanism that conveys while stirring with a water flow, it is preferable to dispose a pipe such as a hose within the storage space 11 and inject cleaning water from the pipe. The injection direction of the cleaning water may be the same as the cleaning direction F, an inclined direction with respect to the cleaning direction F, or a combination thereof. For example, it is preferable to inject the cleaning water in the same direction as the cleaning direction F and also in an inclined direction from the lower side of the semi-closed passage 20 toward the cleaning direction F side.

[0036] The partition wall 50 constitutes the outer wall of the semi-closed passage 20. The partition wall 50 preferably has an elongated shape arranged with the longitudinal direction X as the horizontal direction, for example, preferably has a cylindrical shape, and more preferably has a cylindrical shape as shown in FIGS. 1 and 2. The partition wall 50 preferably has a cylindrical side wall 50a, and more preferably further has end walls 50b and 50c that close both ends of the side wall 50a in addition to the side wall 50a. The cleaning space 12 is a space where waste plastic flakes are cleaned. The non-cleaning space 13 is a space other than the cleaning space 12 in the storage space 11. At least a part of the non-cleaning space 13 exists above the cleaning space 12. In this specification, in the depth direction D of the storage space 11, the direction in which the water depth becomes shallower and approaches the liquid surface of the cleaning liquid L is referred to as "upward" or "upper direction", and the direction in which the water depth becomes deeper and away from the liquid surface of the cleaning liquid L is referred to as "downward" or "lower direction". In FIGS. 1 and 2, as an example, a form is shown in which the non-cleaning space 13 exists over the entire circumference of the cleaning space 12 including a portion 13B existing below and a portion 13C existing laterally in addition to a portion 13A existing above the cleaning space 12, but the present invention is not limited to this, and the non-cleaning space 13 may be a form in which only the portion 13A existing above the cleaning space 12 (not shown), a form in which only the portion 13A existing above the cleaning space 12 and the portion 13B existing below (not shown), or a form in which only the portion 13A existing above the cleaning space 12 and the portion 13C existing laterally (not shown).

[0037] The perforated wall 51 is a wall having through holes with a pore diameter through which fine bubbles can pass. By the perforated wall 51, the semi-closed passage 20 becomes a semi-closed system, and fine bubbles can travel between the non-cleaning space 13 and the cleaning space 12 to efficiently clean waste plastic flakes.

[0038] FIG. 3 is a schematic plan view showing an example of a perforated wall, where (a) shows a form in which the perforated wall is a mesh material, and (b) shows a form in which the perforated wall is a punching material. The perforated wall 51 may be, for example, a mesh material that is a fabric of wire rods such as made of metal as shown in FIG. 3(a), or a punching material in which through holes are provided in a plate material such as made of metal as shown in FIG. 3(b). The mesh material as shown in FIG. 3(a) or the punching material as shown in FIG. 3(b) is an exemplification of the perforated wall 51, and the present invention is not limited thereto. In the present invention, various forms of walls can be adopted as long as they are effective. In this embodiment, the entire partition wall 50 may be the perforated wall 51, or a part of the partition wall 50 may be the perforated wall 51 and the remaining part may be a non-perforated wall. Also, the perforated wall 51 may be in the same form as a whole or a combination of different forms. For example, the perforated wall 51 may be a mesh material as shown in FIG. 3(a) or a punching material as shown in FIG. 3(b) as a whole, or a combination of a mesh material as shown in FIG. 3(a) and a punching material as shown in FIG. 3(b). The lower perforated wall 51b described later is preferably a punching material as shown in FIG. 3(b). Since the punching material has less unevenness on the wall surface other than the through holes in the perforated wall 51, clogging of heavy specific gravity residues can be suppressed.

[0039] In the waste plastic flake cleaning device 1 according to this embodiment, as shown in FIG. 1, the perforated wall 51 preferably includes an upper perforated wall 51a that constitutes a part of the partition wall 50 that partitions the cleaning space 12 and a portion 13A of the non-cleaning space 13 that exists above the cleaning space 12. Since the light specific gravity residue having a specific gravity smaller than that of water such as oil or dirt is discharged outside the semi-closed passage 20, for example, as indicated by the arrow s in FIG. 1, the light specific gravity residue can be easily separated and removed. The upper perforated wall 51a is preferably provided in a portion of the partition wall 50 that is disposed in a region above the position that bisects the semi-closed passage 20 in the depth direction D. For example, taking the case where the semi-closed passage 20 is cylindrical as shown in FIGS. 1 and 2 as an example, as shown by the dotted line in FIG. 2, the perforated wall 51 provided in a part or all of the partition wall 50 in the upper region E1 of the regions E1 and E2 that bisect the height h of the semi-closed passage 20 in the depth direction D is defined as the upper perforated wall 51a. The light specific gravity residue discharged outside the semi-closed passage 20 preferably floats on the liquid surface of the cleaning liquid L and is removed by an overflow pocket 17 (shown in FIGS. 6 and 7) described later.

[0040] In the waste plastic flake cleaning device 1 according to this embodiment, as shown in FIG. 1, the perforated wall 51 preferably includes a lower perforated wall 51b that constitutes a part of the partition wall 50 that partitions the cleaning space 12 and a portion 13B of the non-cleaning space 13 that exists below the cleaning space 12. Since the heavy specific gravity residue having a specific gravity larger than that of water such as sand or glass is discharged outside the semi-closed passage 20, for example, as indicated by the arrow t in FIG. 1, the heavy specific gravity residue can be easily separated and removed. The lower perforated wall 51b is preferably provided in a portion of the partition wall 50 that is disposed in a region below the position that bisects the semi-closed passage 20 in the depth direction D. For example, taking the case where the semi-closed passage 20 is cylindrical as shown in FIGS. 1 and 2 as an example, as shown by the dotted line in FIG. 2, the perforated wall 51 provided in a part or all of the partition wall 50 in the lower region E2 of the regions E1 and E2 that bisect the height h of the semi-closed passage 20 in the depth direction D is defined as the lower perforated wall 51b.

[0041] In this embodiment, it is preferable that the entire surface of the partition wall 50 is a perforated wall 51. Such a form is, for example, a form in which the partition wall 50 is a cylindrical wire mesh. In this embodiment, as shown in FIGS. 1 and 2, the partition wall 50 is preferably a cylindrical wire mesh. Thereby, fine bubbles are distributed throughout the semi-closed passage 20, and cleaning can be performed more efficiently.

[0042] In the waste plastic flake cleaning device 1 according to this embodiment, the perforated wall 51 preferably has non-penetrability with respect to the waste plastic flakes. The waste plastic flakes can be more reliably retained in the semi-closed passage 20 and cleaned more efficiently. The pore diameter of the perforated wall 51 is more preferably such that the light specific gravity residue and / or the heavy specific gravity residue, which are foreign substances mixed in the waste plastic flakes, can pass through, and the heavy specific gravity plastic flakes, which are the objects to be recovered, cannot pass through. The pore diameter of the perforated wall 51 is not particularly limited, but is preferably 1 to 10 mm in mesh size, and more preferably 1.5 to 5.0 mm in mesh size.

[0043] FIGS. 4 and 5 are schematic views showing a modified example of the semi-closed passage, FIG. 4 is a schematic front view, and FIG. 5 is a schematic plan view. The cleaning device 1 shown in FIGS. 4 and 5 has the same basic structure as the cleaning device 1 shown in FIGS. 1 and 2 except that the semi-closed passage 20 is different. In the waste plastic flake cleaning device 1 according to this embodiment, as shown in FIG. 4, the semi-closed passage 20 preferably further has a floating and sinking separation region 14 on the discharge port 22 side rather than the cleaning region 23, and has an opening 55 upward in the floating and sinking separation region 14.

[0044] The floating and sinking separation region 14 is a region where oil and dirt adhering to the surface of the waste plastic flakes are removed by washing in the washing region 23, and the heavy specific gravity plastic flakes, which are the objects with a specific gravity greater than that of water, move downward in the washing liquid L and are separated by specific gravity from the light specific gravity plastic flakes such as olefin flakes with a specific gravity smaller than that of water. The light specific gravity plastic flakes are, for example, olefin flakes such as PP derived from the caps of bottles. The opening 55 is an opening provided in the partition wall 50. For example, when the partition wall 50 is cylindrical, the opening 55 may be a hole formed by cutting out a part of the side wall 50a of the cylinder on the side closer to the discharge port 22. As described above, even if the specific gravity of the waste plastic flakes is greater than that of water, a certain number of them may float in the water immediately after being put into the water due to surface tension or the like. Therefore, when the cleanliness of the waste plastic flakes immediately after being put into the semi-closed passage 20 is low, it is difficult to separate the heavy specific gravity plastic flakes and the light specific gravity plastic flakes contained in the waste plastic flakes. As the waste plastic flakes move in the washing direction F while being washed in the washing region 23, the cleanliness of the waste plastic flakes increases, and among the waste plastic flakes, the heavy specific gravity plastic flakes move downward along the semi-closed passage 20 according to their specific gravity and are separated from the light specific gravity plastic flakes that have moved above the semi-closed passage 20. By providing the opening 55, the light specific gravity plastic flakes that have moved above the semi-closed passage 20 are discharged outside the semi-closed passage 20, so that the light specific gravity plastic flakes can be easily separated and removed. The light specific gravity plastic flakes discharged outside the semi-closed passage 20 preferably float on the liquid surface of the washing liquid L and are removed by an overflow pocket 17 (shown in FIGS. 6 and 7) described later.

[0045] In addition, the semi-closed passage 20 may further have a charging area (not shown) on the inlet 21 side rather than the cleaning area 23 in addition to the cleaning area 23. The charging area is the area before the waste plastic flakes are cleaned after being charged into the semi-closed passage 20. For example, it is an area where the fine bubbles generated by the bubble generator 30 do not reach or reach in a small amount, or an area upstream of the area where the stirring and advancing mechanism 40 is arranged in the cleaning direction F. In such an area, the waste plastic flakes may be immersed in the cleaning liquid L in a non-stirred state.

[0046] FIGS. 6 and 7 are schematic views showing a modified example of the cleaning tank. FIG. 6 is a schematic plan view, and FIG. 7 is a schematic end view taken along line B-B of FIG. 6. In the waste plastic flake cleaning device 1 according to the present embodiment, as shown in FIG. 1, the cleaning tank 10 preferably has an upper surface opening 15a and an overflow pocket 17 provided outside the storage space 11 along the side of the upper surface opening 15a. The overflow pocket 17 discharges the low specific gravity residue and the low specific gravity plastic flakes that have moved in the liquid level direction from the storage space 11, so that the cleanliness of the cleaning liquid in the storage space 11 can be maintained.

[0047] The overflow pocket 17 is a tank that receives the cleaning liquid L that has overflowed beyond the upper surface opening 15a of the cleaning tank 10. In FIGS. 6 and 7, as an example, the overflow pocket 17 is shown in a form of a gutter protruding outside the storage space 11. However, the present invention is not limited to this. The overflow pocket 17 may be an overflow space adjacent to the storage space 11 via the side wall of the cleaning tank 10 in the storage space 11, and the overflow space and the storage space 11 may communicate with each other through a horizontal hole provided in the side wall of the cleaning tank 10 (not shown). As shown in FIG. 6, the overflow pocket 17 is more preferably provided along the longitudinal direction X of the cleaning tank 10. The overflow pocket 17 may be provided over the entire region in the longitudinal direction X of the cleaning tank 10, or may be provided in a part of the longitudinal direction X of the cleaning tank 10 (not shown). The form of providing the overflow pocket 17 in a part of the longitudinal direction X of the cleaning tank 10 is not particularly limited. For example, the overflow pocket 17 may be provided from the middle stream to the downstream in the cleaning direction F, or the overflow pocket 17 may be provided only in the cleaning part 11B. In FIGS. 6 and 7, as an example, the form of providing the overflow pocket 17 on both sides in the short side direction Y of the cleaning tank 10 is shown. However, the present invention is not limited to this, and the overflow pocket 17 may be provided only on either one of the short side directions Y of the cleaning tank 10.

[0048] The cleaning device 1 for waste plastic flakes according to the present embodiment may further include a filtering device (not shown) for the cleaning liquid L containing the light specific gravity residue and the light specific gravity plastic flakes collected in the overflow pocket 17, and a circulation device (not shown) for returning the cleaning liquid L from which the light specific gravity residue and the light specific gravity plastic flakes have been removed through the filtering device to the cleaning tank 10.

[0049] In FIGS. 1 and 2, the entire semi-closed passage 20 including the inlet 21, the outlet 22, and the cleaning area 23 is shown to be disposed in the cleaning liquid L in the storage space 11. However, the present invention is not limited to this. For example, the inlet 21 may be in a form (not shown) that protrudes from the liquid level of the cleaning liquid L. In the form where the inlet 21 protrudes from the liquid level of the cleaning liquid L, the semi-closed passage 20 may be disposed with its longitudinal direction inclined with respect to the horizontal direction. Further, in FIGS. 1 and 2, the partition wall 50 is shown to be disposed away from the inner wall of the cleaning tank 10 and the semi-closed passage 20 extends to the central portion of the storage space 11. However, the present invention is not limited to this. The partition wall 50 may be disposed so as to vertically bisect the cleaning tank 10, and the lower half region of the cleaning tank 10 may be in the form of the semi-closed passage 20 (not shown).

[0050] The waste plastic flake cleaning device 1 according to the present embodiment may further include a mechanism (not shown) in which the semi-closed passage 20 rotates about an axis extending in the longitudinal direction X within the storage space 11. By rotating the semi-closed passage 20, it is possible to prevent the semi-closed passage 20 from being clogged by substances accumulated at the bottom of the semi-closed passage 20, such as waste plastic flakes or heavy specific gravity residues.

[0051] The waste plastic flake cleaning device 1 according to the present embodiment includes a form (not shown) in which the partition wall 50 has only the upper perforated wall 51a as the perforated wall 51, and the portion other than the upper perforated wall 51a of the partition wall 50 is a non-perforated wall having no holes. In this form, it is preferable that the non-perforated wall has a protruding groove at the bottom, and a perforated member having a through-hole with a hole diameter that does not allow waste plastic flakes to pass through and allows heavy specific gravity residues to pass through is provided between the space in the protruding groove and the space in the semi-closed passage 20. By adopting such a form, the heavy specific gravity residues move into the protruding groove through the perforated member, so that the waste plastic flakes and the heavy specific gravity residues can be separated.

[0052] Next, the method for cleaning waste plastic flakes according to the present embodiment will be described. The cleaning method can be preferably carried out by using the cleaning device 1 shown in FIGS. 1 to 7. However, the cleaning device is not limited to the continuous cleaning device 1 as shown in FIGS. 1 to 7, and the cleaning method may be carried out using a modified form of the cleaning device 1 or a batch-type cleaning device (not shown) such as a cleaning device. Also, components with the same terms in the description of the cleaning device 1 and the description of the cleaning method shall be regarded as the same as each other.

[0053] The method for cleaning waste plastic flakes according to the present embodiment includes a cleaning step of bringing the waste plastic flakes into contact with fine bubbles in a cleaning liquid in which fine bubbles are generated, separating light specific gravity residues from the waste plastic flakes, and separating the waste plastic flakes into light specific gravity plastic flakes having a specific gravity smaller than that of the cleaning liquid and heavy specific gravity plastic flakes having a specific gravity larger than that of the cleaning liquid. The cleaning step includes a step of cleaning while restraining floating flakes that move in the direction of the liquid surface of the cleaning liquid among the waste plastic flakes in the cleaning liquid.

[0054] The method for cleaning waste plastic flakes according to the present embodiment preferably further includes a charging step of charging the waste plastic flakes into the cleaning liquid. The method of charging the waste plastic flakes into the cleaning liquid is not particularly limited. However, the waste plastic flakes may be charged into a cleaning tank storing the cleaning liquid, or the cleaning liquid may be injected into the cleaning tank after charging the waste plastic flakes into the cleaning tank. As shown in FIG. 1, the charging step is preferably a step of charging the waste plastic flakes from the charging port 21 into the semi-closed system passage 20 before the cleaning step.

[0055] By using fine bubbles for cleaning, the amount of use of alkaline cleaning agents or the like can be reduced to zero or reduced. In the method for cleaning waste plastic flakes according to the present embodiment, the cleaning liquid is preferably a neutral cleaning liquid. The environmental load can be further reduced. The temperature of the cleaning liquid L is not particularly limited, but is preferably room temperature. Room temperature means a natural temperature without performing heat treatment or cooling treatment, etc., for example, a temperature not exceeding the outside air temperature.

[0056] The substances introduced into the cleaning liquid are a mixture of waste plastic flakes including heavy specific gravity plastic flakes and light specific gravity plastic flakes, light specific gravity residues such as oil or dirt adhering to the waste plastic flakes, and heavy specific gravity residues such as sand or glass mixed in the waste plastic flakes.

[0057] In the initial stage of the cleaning process, for example, immediately after being introduced into the cleaning liquid, a certain number of heavy specific gravity plastic flakes among the waste plastic flakes become floating flakes together with the light specific gravity plastic flakes and move in the direction of the liquid surface of the cleaning liquid, and the heavy specific gravity residue moves downward in the cleaning liquid according to its specific gravity. At this time, in the cleaning method according to the present embodiment, the movement in the liquid surface direction is restricted so that the floating flakes do not reach the liquid surface of the cleaning liquid, and the floating flakes are kept in the cleaning liquid. Thereby, the opportunity for fine bubbles to contact the waste plastic flakes is increased, and cleaning can be performed efficiently.

[0058] In the method for cleaning waste plastic flakes according to the present embodiment, the cleaning process preferably includes a step of separating the heavy specific gravity residue mixed in the waste plastic flakes from the waste plastic flakes. By separating and removing the heavy specific gravity residue, the amount of foreign substances contained in the target heavy specific gravity plastic flakes can be reduced.

[0059] The method for separating the heavy specific gravity residue is not particularly limited, and examples thereof include a screening method or a filtering method. The screening method and the filtering method are methods for separating the heavy specific gravity residue and the waste plastic flakes by utilizing, for example, the specific gravity difference and the size. More specifically, it is a method of separating using a perforated wall sized to allow the heavy specific gravity residue to pass through and not allow the waste plastic flakes to pass through.

[0060] In the method for cleaning waste plastic flakes according to the present embodiment, it is preferable that the cleaning step includes a step in which the heavy specific gravity residue separated from the waste plastic flakes passes through the lower perforated wall 51b and precipitates in the non-cleaning space 13B below the semi-closed passage 20, as shown in FIG. 1.

[0061] In the middle stage of the cleaning step, as the fine bubbles come into contact with the waste plastic flakes and the cleaning progresses, the light specific gravity residue adhering to the surface of the waste plastic flakes is separated from the surface of the waste plastic flakes and moves in the direction of the liquid surface of the cleaning liquid. Then, among the waste plastic flakes from which the light specific gravity residue has been removed, the heavy specific gravity plastic flakes move downward in the cleaning liquid according to a specific gravity greater than that of the original water and are separated from the light specific gravity plastic flakes moving in the direction of the liquid surface of the cleaning liquid.

[0062] In the method for cleaning waste plastic flakes according to the present embodiment, it is preferable that the cleaning step includes a step in which the light specific gravity residue separated from the waste plastic flakes moves to the liquid surface of the cleaning liquid. By separating and removing the light specific gravity residue, the heavy specific gravity plastic flakes can be submerged in the cleaning liquid according to their original specific gravity and separated and recovered. In addition, the amount of foreign matter contained in the recovered heavy specific gravity plastic flakes can be reduced.

[0063] The method for separating the low specific gravity residue is not particularly limited, and for example, it is a physical separation method or a chemical separation method. The physical separation method is, for example, a method of providing holes of a size that allows the low specific gravity residue to pass through and does not allow the waste plastic flakes to pass through in a member that restricts the movement of the waste plastic flakes in the liquid surface direction. The chemical separation method is, for example, a method of adsorbing and removing the low specific gravity residue that has moved in the liquid surface direction of the waste plastic flakes to an adsorbent or an adsorption sheet.

[0064] In the method for cleaning waste plastic flakes according to the present embodiment, it is preferable that the cleaning step includes a step in which the low specific gravity residue separated from the waste plastic flakes passes through the upper perforated wall 51a and floats in the non-cleaning space 13A above the semi-closed passage 20, as shown in FIG. 1.

[0065] In the method for cleaning waste plastic flakes according to the present embodiment, it is preferable that the cleaning step includes a step of performing cleaning in the cleaning area 23 of a passage having an inlet 21, an outlet 22, and a cleaning area 23, and moving the waste plastic flakes in the cleaning area 23 from the inlet 21 side toward the outlet 22 side. It can be cleaned more efficiently in a continuous manner.

[0066] As shown in FIG. 1, the cleaning step is preferably a step of stirring and advancing the waste plastic flakes in the cleaning area 23 while supplying the cleaning liquid L to the cleaning tank 10 so that the liquid level of the cleaning liquid L is at least above the cleaning area 23, generating a stirring flow and a conveying flow of the cleaning liquid L by the stirring and advancing mechanism 40, and generating fine bubbles by the bubble generator 30.

[0067] In the method for cleaning waste plastic flakes according to the present embodiment, the cleaning step preferably includes a floating and sinking separation step, and the floating and sinking separation step preferably includes a step of moving the low specific gravity plastic flakes to the liquid surface and a step of precipitating the high specific gravity plastic flakes in the cleaning liquid. By separating and removing the low specific gravity plastic flakes, the amount of foreign substances contained in the high specific gravity plastic flakes can be reduced.

[0068] The floating and sinking separation step is preferably a step of releasing the regulation of the upward movement of the floating flakes. As described above, as the cleaning progresses, among the waste plastic flakes from which the light specific gravity residues have been removed, the heavy specific gravity plastic flakes move downward in the cleaning liquid according to a specific gravity greater than that of the original water. When the regulation of the upward movement of the light specific gravity plastic flakes is released, they move to the liquid surface.

[0069] In the method for cleaning waste plastic flakes according to the present embodiment, as shown in FIGS. 4 and 5, the floating and sinking separation step is preferably a step of discharging the light specific gravity plastic flakes from the open port 55 provided in the semi-closed passage 20 to the outside of the semi-closed passage 20.

[0070] In the method for cleaning waste plastic flakes according to the present embodiment, the cleaning step preferably includes a step of overflowing the light specific gravity residues or light specific gravity plastic flakes floating on the liquid surface together with the cleaning liquid. The cleanliness of the cleaning liquid in the storage space can be maintained. Also, the amount of foreign matter contained in the heavy specific gravity plastic flakes can be reduced.

[0071] The method of overflowing is not particularly limited. For example, it is a method of supplying the cleaning liquid in an amount exceeding the capacity of the cleaning tank. The overflowed cleaning liquid may be allowed to overflow directly outside the cleaning tank, or may be collected once. The method of collecting once is not particularly limited. For example, as shown in FIGS. 6 and 7, an overflow pocket 17 is provided, and the light specific gravity residues or light specific gravity plastic flakes are discharged from the storage space 11 to the overflow pocket 17 together with the cleaning liquid. The cleaning liquid containing the overflowed light specific gravity residues or light specific gravity plastic flakes may be returned to the cleaning tank again after removing the light specific gravity residues or light specific gravity plastic flakes.

[0072] In the method for cleaning waste plastic flakes according to this embodiment, the method for cleaning waste plastic flakes further includes a recovery step after the cleaning step, and the recovery step includes a step of taking out the heavy specific gravity plastic flakes from the cleaning liquid.

[0073] The method for recovering the heavy specific gravity plastic flakes is not particularly limited. For example, the method of moving the heavy specific gravity plastic flakes submerged in the cleaning liquid to the drying tank through the connecting pipe leading to the next drying tank, or the method of scooping up the heavy specific gravity plastic flakes submerged in the cleaning liquid.

[0074] In the method for cleaning waste plastic flakes according to this embodiment, as shown in FIG. 1, the recovery step preferably includes a step of recovering the heavy specific gravity plastic flakes submerged at the bottom of the semi-closed passage 20 from the discharge port 22. It is more preferable to connect a connecting pipe (not shown) leading to the next drying tank to the discharge port 22 and convey it from the discharge port 22 to the dehydration drying tank through the connecting pipe.

[0075] In the method for cleaning waste plastic flakes according to this embodiment, before the cleaning step, a step of removing foreign matters having a size equal to or larger than that of the waste plastic flakes may be included. By having such a step, it is possible to prevent foreign matters having a size equal to or larger than that of the waste plastic flakes from being mixed into the cleaning step, and to more efficiently separate and recover the waste plastic flakes.

Explanation of symbols

[0076] 1 Cleaning device 10 Cleaning tank 11 Storage space 11A Raw material input section 11B Cleaning section 11C Recovery section 12 Cleaning space 13, 13A, 13B, 13C Non-cleaning space 14 Flotation and sedimentation separation region 15 Upper surface of the cleaning tank 15a Upper surface opening 16 Bottom of the cleaning tank 17 Overflow Pocket 20 Semi-closed Passage 21 Inlet 22 Outlet 23 Washing Area 30 Bubble Generator 40 Stirring and Forward Mechanism 50 Partition Wall 50a Side Wall 50b, 50c End Walls 51 Perforated Wall 51a Upper Perforated Wall 51b Lower Perforated Wall 55 Opening L Cleaning Liquid D Depth Direction F Cleaning Direction X Longitudinal Direction Y Transverse Direction

Claims

1. A cleaning tank having a storage space for storing a cleaning liquid, An inlet, an outlet, and a cleaning area, and a semi-closed passage in which at least the cleaning area is disposed within the storage space, A fine bubble generator installed in the storage space, A stirring and advancing mechanism for generating a stirring flow of the cleaning liquid and a conveying flow from the inlet side toward the outlet side in the cleaning area, and comprising: The storage space is partitioned by a partition wall into a cleaning space that is the space within the semi-closed passage and a non-cleaning space that is the space outside the semi-closed passage, At least a part of the non-cleaning space exists above the cleaning space, At least a part of the partition wall is a perforated wall having permeability to the fine bubbles, and a cleaning device for waste plastic flakes is characterized thereby.

2. The cleaning device for waste plastic flakes according to claim 1, wherein the perforated wall includes an upper perforated wall that constitutes a part of the partition wall partitioning the cleaning space and a part of the non-cleaning space that exists above the cleaning space among the non-cleaning space.

3. The cleaning device for waste plastic flakes according to claim 1, wherein the semi-closed passage further has a floating and separating area on the outlet side of the cleaning area, and has an opening at the upper part in the floating and separating area.

4. The cleaning device for waste plastic flakes according to claim 2 or 3, wherein the cleaning tank has an upper surface opening and an overflow pocket provided outside the storage space along the side of the upper surface opening.

5. The cleaning device for waste plastic flakes according to claim 1, wherein the perforated wall includes a lower perforated wall that constitutes a part of the partition wall partitioning the cleaning space and a part of the non-cleaning space that exists below the cleaning space among the non-cleaning space.

6. The cleaning device for waste plastic flakes according to claim 1, wherein the perforated wall has non-permeability to waste plastic flakes.

7. The cleaning device for waste plastic flakes according to claim 1, wherein the cleaning liquid is a neutral cleaning liquid.

8. In a cleaning liquid in which fine bubbles are generated, waste plastic flakes are brought into contact with the fine bubbles to separate light specific gravity residues from the waste plastic flakes and separate the waste plastic flakes into light specific gravity plastic flakes having a specific gravity smaller than that of the cleaning liquid and heavy specific gravity plastic flakes having a specific gravity larger than that of the cleaning liquid, including a cleaning step. The cleaning method of waste plastic flakes is characterized in that the cleaning step includes a step of performing cleaning in a state where floating flakes that move in the liquid surface direction of the cleaning liquid among the waste plastic flakes are retained in the cleaning liquid.

9. The cleaning step is characterized in that cleaning is performed in the cleaning area of a passage having an inlet, an outlet, and a cleaning area, and the step of moving the waste plastic flakes in the cleaning area from the inlet side toward the outlet side is included. The cleaning method of waste plastic flakes according to claim 8.

10. The cleaning step is characterized in that the cleaning method of waste plastic flakes according to claim 8 includes a step in which the light specific gravity residue separated from the waste plastic flakes moves to the liquid surface of the cleaning liquid.

11. The cleaning step is characterized in that the cleaning method of waste plastic flakes according to claim 8 includes a step of separating heavy specific gravity residues mixed in the waste plastic flakes from the waste plastic flakes.

12. The cleaning step includes a flotation and sedimentation separation step. The flotation and sedimentation separation step is characterized in that the flotation and sedimentation separation step according to claim 8 includes a step of moving the light specific gravity plastic flakes to the liquid surface and a step of precipitating the heavy specific gravity plastic flakes in the cleaning liquid.

13. The cleaning step is characterized in that the cleaning method of waste plastic flakes according to claim 10 or 12 includes a step of overflowing the light specific gravity residue or the light specific gravity plastic flakes floating on the liquid surface together with the cleaning liquid.

14. The cleaning method of waste plastic flakes further includes a recovery step after the cleaning step. The recovery step is characterized in that the recovery step according to claim 8 includes a step of taking out the heavy specific gravity plastic flakes from the cleaning liquid.

15. The cleaning method of waste plastic flakes according to claim 8, wherein the cleaning liquid is a neutral cleaning liquid.

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