JPH0872058A - Method and apparatus for recycling plastic - Google Patents

Abstract

PURPOSE: To easily and simply obtain high purity plastic by bringing powdery plastic to a molten state in hot water and washing the molten plastic with hot water while separating impurities by specific gravity separation when the molten plastic is sedimented or floated in hot water. CONSTITUTION: Plastic 40 is ground by a jet of water to be thrown in a washing tank 12 in a slurry form along with water used in a jet of water and a stirrer 20 is operated to wash the powdery plastic 41 to mainly remove water-soluble impurities. Subsequently, the stirrer is stopped and the plastic slurry is allowed to stand to float insoluble impurities lighter than water to the vicinity of surface of water. Next, the powdery plastic 41 from which light impurities are removed and water are sent to a pressure-resistant melting tank 13 preliminarily filled with hot water and the steam sent from a boiler 31 and held to a high temp. and high pressure state under pressure by a pump 25. The dripped powdery plastic 41 is heated and melted to become molten plastic which is, in turn, washed while sedimented in hot water to be separated into a heavy impurity layer 44, a molten plastic layer 42 and a hot water layer 43 in the pressure- resistant melting tank 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently and inexpensively recovering plastic from a waste plastic molding or the like, and an apparatus used for the method.

[0002]

2. Description of the Related Art Plastic molded products have excellent characteristics, but they do not decompose in the natural world, harmful substances such as dioxin and hydrogen chloride are generated during incineration, and burnt residue adheres to the inner wall of the incinerator, resulting in incineration. The method of treating the waste has become a major social problem, such as damage to the furnace and a decrease in efficiency.

Therefore, in recent years, biodegradable plastics that can be decomposed in the natural world have been developed and researched, and some of them have been put into practical use. However, these are expensive and easily deteriorate physically or chemically. However, it could not be used as a substitute for existing plastic molded products. Therefore, it is considered promising to establish a method for collecting and recycling waste plastic moldings that cannot be used and are discarded.

As a method of collecting and recycling plastics, there is a method disclosed in Japanese Patent Application Laid-Open No. 49-112980. As shown in FIG. 3, a waste plastic molded product crushed into small pieces by a crusher (hereinafter abbreviated as small piece plastic) is washed in a water washing tank 1 and then drained to convey small piece plastic to a conveyor 2 At the specific gravity separation tanks 3 and 4 filled with a solvent having a desired specific gravity,
Dirt and impurities adhering to the small piece of plastic are separated by utilizing the difference in specific gravity, and only the plastic portion of the waste plastic molded product is recovered.

For example, when polystyrene is to be recovered, the first specific gravity separation tank 3 is filled with salt water having a specific gravity of about 1.1, and the small piece of plastic is charged therein.
Impure impurities such as aluminum foil and vinyl chloride,
It is sufficient to collect the small piece plastic containing polystyrene existing near the liquid surface.

In addition, the small piece plastic at this stage is
Since polyethylene, polypropylene, etc. may be contained in addition to polystyrene, the recovered small piece plastic is put into the second specific gravity separation tank 4 filled with water, and the polyethylene, polypropylene is then added. When polystyrene is floated and the sinking in the second specific gravity separation tank 4 is recovered, only polystyrene can be obtained.

However, in the above-mentioned method, in order to separate impurities, a plurality of specific gravity separation steps must be performed, and the specific gravity separation tanks 3 and 4 must be filled with solvents having different specific gravities. In order to keep the specific gravity of the solvent filled in the specific gravity separation tanks 3 and 4 that requires a specific gravity adjusting step, it is not possible to add small pieces of plastic that have been washed and have water adhering, and after washing, once The manufacturing process was complicated, for example, draining was required.

Further, a method has been proposed in which supercritical water is used to chemically decompose a plastic molded product into an oily low molecular weight material. However, this method has many treatment steps, which not only increases the cost but also decomposes the raw material stage.
Since it has to go through various processes, it is not practical from the viewpoint of recycling plastic.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of these circumstances, and a method of recycling a plastic for obtaining a high-purity plastic at a low cost with an easy and simple treatment process, and a method therefor. It is intended to provide a device used for.

[0010]

The object of the present invention is to recycle the plastics by separating the impurities from the powdered plastics obtained by crushing the plastics molded product, and the powdered plastics are melted in hot water. When the melt settles or floats in hot water, the problem can be solved by washing with the hot water and simultaneously separating the impurities by specific gravity separation. At this time, it is preferable to use steam as a heat source for melting the powdered plastic. Furthermore, in the above recycling method, powder plastic is melted in hot water, and when the melt sinks or floats in hot water, it is washed with the hot water and at the same time specific gravity separation is performed to separate impurities to separate impurities. It is preferable to use a recycling device equipped with a tank.

[0011]

In the plastic recycling method of the present invention, the powdered plastic is melted in hot water to form molten particles, which are allowed to settle or float in hot water.
Impurities are efficiently removed and separated by washing with hot water.

[0012]

EXAMPLES Next, as an example of the plastic recycling method of the present invention, the case where polystyrene foam is obtained by recycling expanded polystyrene will be described. FIG. 1 is a flow chart of main operations for explaining the polystyrene recycling method according to the present invention, and FIG. 2 is an example of an apparatus used for carrying out this recycling and polystyrene recycling when this apparatus is used. It is a schematic diagram which shows a process.

In FIG. 2, reference numeral 10 is a device for recycling, and this device 10 is roughly a crusher 11.
And a cleaning tank 12 and a pressure-resistant melting tank 13.
The crusher 11 crushes the expanded polystyrene 40 into a powdered polystyrene 41, and includes a jet port 15 through which a water jet is ejected and a fixing base 16 for fixing the expanded polystyrene 40 to be processed. The spout 15
Is connected to a high-pressure water supply device (not shown), and a fixing base 16 is arranged immediately below the jet port 15. Further, the fixed base 16 is provided with a horizontal movement mechanism (not shown), and the horizontal movement mechanism enables movement in the horizontal direction.

The powder polystyrene 41 produced by the crusher 11 is sent to the washing tank 12. The cleaning tank 12 is for cleaning the powdered polystyrene 41 with water, and has a hollow bottomed cylindrical shape. A stirrer 20 is attached to the washing tank 12 so that the powder polystyrene 41 can be washed while stirring. An oil separator 50 is connected to the washing tank 12,
Further, a water supply port 51 and a drain port 52 are provided so that the powder polystyrene 41 can be effectively washed while being rinsed.

The washed powder polystyrene 41 is
It is sent to the pressure-resistant melting tank 13. The pressure-resistant melting tank 13 includes a hollow bottomed cylindrical melting tank body 22 and the melting tank body 2
The cover 23 covers the second opening 24.
Further, one end of a connecting pipe A26 equipped with a pump A25 is inserted into the lid 23, and the connecting pipe A26 is inserted.
The other end of the cleaning tank 12 is inserted near the bottom of the cleaning tank 12 so that the contents of the cleaning tank 12 can be fed under pressure into the pressure-resistant melting tank 13.

Further, in the vicinity of the bottom of the melting tank body 22, a pipe B29 and a pipe C30 each having a valve B27 and a valve C28 are attached at positions whose heights from the bottom are different from each other. The contents inside can be discharged.

Further, in the vicinity of the central portion of the melting tank body 22, a water vapor jetting portion 32 having a hollow disk shape and having a small hole formed in a surface which is an upper surface when attached to the melting tank body 22.
Is built in. Then, one end of a pipe D33 for supplying water vapor is inserted into the water vapor jetting unit 32, and the other end of the pipe D33 is inserted into the upper surface of the boiler 31.

The boiler 31 generates steam, and the steam can be fed into the pressure-resistant melting tank 13 through the pipe D33 and the steam jetting section 32. In addition, this boiler 31 has a pump E35.
Is connected to one end of the connecting pipe E36, and the other end is connected to the vicinity of the central portion of the melting tank main body 22. Further, in addition to the connecting pipe E36, a pump F37 is provided, and one end of the pump F37 is provided with a refill water supply port 39.
The connection pipe F38 connected to the boiler 31 is also attached to the boiler 31.

Next, a recycling method using such an apparatus 10 will be described with reference to FIGS. 1 and 2. First, the expanded polystyrene 40 to be treated is set on the fixed base 16. Then, a water jet is jetted onto the expanded polystyrene 40 to pulverize the expanded polystyrene 40 into powder polystyrene 41. At this time, the horizontal movement mechanism is operated so that the water jet is applied to the entire expanded polystyrene 40. At this time, the jet pressure of the water jet is 30 to 500 kg / cm ² G,
Especially 50-200kg / cm ² G, and even 100-150kg
Although it is preferably / cm ² G, it may be out of the above range depending on the thickness, size and hardness of the expanded polystyrene 40 to be treated.

At this time, 1 of the powder polystyrene 41
It is necessary to grind so that no bubbles remain in one particle. The particle size of the pulverized powder polystyrene 41 is 0.1
100 μm, especially 1 to 50 μm, further 10 to 30 μm
It is preferably m. This is 0.1-100 μm
Within the range, no bubbles remain in the particles, and it is possible to prevent the powder polystyrene 41 from floating during the separation of the specific gravity and to prevent the recovery rate from decreasing, and in comparison with the surface area of the expanded polystyrene 40, This is because the total surface area of the obtained powdery polystyrene 41 is much increased, and the subsequent washing and melting steps effectively proceed.

Next, the powdered polystyrene 41 is made into a slurry with the water used for the water jet, and is put into the cleaning tank 12. Then, operate the stirrer 20,
The powder polystyrene 41 is washed to mainly remove water-soluble impurities. At this time, in addition to the water used as the water jet, water is supplied from the water supply port 51 to the cleaning tank 12 and the waste water is discharged from the drain port 52 for more effective cleaning. You can The washing time is preferably 5 to 30 minutes, particularly preferably 10 to 20 minutes, but depending on the amount of the powder polystyrene 41, the rotating force of the stirrer 20, the degree of contamination of the expanded polystyrene 40, etc. You can also do it.

Then, the stirrer 20 is stopped and left for several minutes. By this standing, water-insoluble impurities lighter than water (hereinafter, abbreviated as light impurities) such as various oils attached to the expanded polystyrene 40 float near the liquid surface. here,
An appropriate means, for example, water is further added to cause the light impurities to overflow, and this is removed, but this can be omitted depending on the degree of contamination of the expanded polystyrene.
At this time, the oil separation device 50 may be operated to remove oil components floating on the liquid surface.

Then, the powder polystyrene 41 from which the light impurities have been removed and the water are stirred again, and the pump A25 is operated, and this is pressure-fed to the pressure-resistant melting tank 13, and the upper portion of the pressure-resistant melting tank 13 is heated. Drop from. Pressure-resistant melting tank 1
Inside 3 is hot water and the pipe 31 from the boiler 31 in advance.
3 and the steam ejected from the steam ejecting section 32, and is in a high temperature and high pressure state. Then, the dropped powdery polystyrene 41 is heated by steam and hot water, melted to become molten polystyrene, and is washed while settling in the hot water.

At this time, the powder polystyrene 4
Impurities that are mixed in 1 and could not be removed in the previous step are easily and surely separated by melting the powder polystyrene 41 into molten polystyrene. The main impurities separated here are metal fragments, gravel, branches, seeds,
Examples thereof include water-insoluble impurities (hereinafter, abbreviated as heavy impurities) that are heavier than the molten polystyrene, such as skins, leaves, fish scales, bones, and other solid substances. And the heavy impurities are
It settles faster than the molten polystyrene, and the content in the pressure-resistant melting tank 13 is large and is separated into three layers, a heavy impurity layer 44, a molten polystyrene layer 42, and a hot water layer 43.

At this time, the temperature inside the pressure-resistant melting tank 13 is preferably slightly higher than the melting temperature of the plastic to be treated, and the temperature of the steam is adjusted to such a temperature. Further, the pressure and temperature of the water vapor have a close relationship, and the pressure inevitably rises as the temperature of the water vapor rises. For example, since the melting temperature of the expanded polystyrene 40 used in this example is about 140 to 170 ° C.,
It is only necessary to feed steam into the pressure-resistant melting tank 13 at a temperature slightly higher than the above 140 to 170 ° C., specifically, about 150 to 180 ° C. And the pressure of steam in this state is about 4.5.
It is about 15 atm.

Further, since the water dropped together with the powdery polystyrene 41 is heated in the pressure-resistant melting tank 13 to become hot water, the pump E35 is arranged so that the amount of hot water in the pressure-resistant melting tank 13 does not exceed a certain level. Is operated to supply hot water to the boiler 31 via the connecting pipe E36. Then, the hot water sent to the boiler 31 is further heated to become steam,
It is again sent into the pressure-resistant melting tank 13 via the pipe D33 and the water vapor jetting section 32 to prevent the temperature and pressure in the pressure-resistant melting tank 13 from decreasing. Further, when the hot water in the boiler 31 is insufficient, the pump F37 is operated to feed water from the replenishment water supply port 39 through the connection pipe F38,
Adjust so that the amount of water is constant.

Then, the valve B27 is opened and the pipe B2 is opened.
The molten polystyrene is discharged from 9 and collected. Furthermore, the collected polystyrene is cooled, and the injection molding machine,
A recycled plastic molded product can be obtained by carrying it to an extrusion molding machine or the like and performing a new molding process.

The plastic recycling method of the present invention and the apparatus 10 used for the method are not limited to the above examples. For example, recycled plastic molded products are not limited to expanded polystyrene, but expanded thermoplastic resins such as expanded polyethylene and expanded polyvinyl chloride, and non-expanded foam such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, ABS resin, and methacrylic resin. Any material may be used as long as it is composed of the thermoplastic resin.

Further, the temperature in the pressure-resistant melting tank 13 (temperature of hot water) is preferably slightly higher than the melting temperature of the plastic to be treated, and is appropriately set according to the type of plastic to be recovered. be able to. Specifically, in the case of low density polyethylene, 130 to 200
C., 150 to 230.degree. C. for high density polyethylene, 170 to 220.degree. C. for polypropylene, and 160 to 220.degree. C. for methacrylic resin. Further, in order to keep the temperature of the hot water within the above range, it is preferable that the temperature of the steam supplied into the pressure-resistant melting tank 13 is slightly higher than the temperature of each hot water.

Further, thermoplastic resins include those having a specific gravity lighter than water and those having a higher specific gravity. Polystyrene, which is a raw material of the expanded polystyrene in the above example, has a specific gravity of about 1.06 to
Since it is 1.08, since it precipitates below the hot water in the pressure-resistant melting tank 13, pipes B29 and C30 were attached near the bottom of the melting tank main body 22.
Since polypropylene and other materials having a lower specific gravity than water are stacked on top of hot water, impurities and hot water are discharged first, and then the plastic is recovered or the plastic recovery pipe B29 is installed in the melting tank main body 22. It is recommended to attach it in the center or near the top.

The layers of the molten plastic and the impurities in the pressure-resistant melting tank 13 are not always one layer at a time. When the treated plastic molded article is composed of a plurality of plastics, the respective plastics may be separated and the molten plastic layer may be two or more layers.
The same applies to the case of impurities, and if the impurities are not a single kind, there may be two or more layers of impurities. In this case, a small amount of sample may be extracted from each layer, an appropriate qualitative analysis may be performed to identify the substance forming the layer, and only the useful layer may be collected.

Further, light impurities may be separated and removed after the powdered plastic is made into molten plastic.

Further, the crushing can be carried out by a water jet as in the above-mentioned example as long as it is a foamed thermoplastic resin.
If it is a non-foaming thermoplastic resin, it is necessary to use a mechanical grinding method such as a hammer mill.

In such a plastic recycling method, a plastic molding is pulverized by a water jet into a powder plastic by using a recycle device having a pressure-resistant melting layer for melting the powder plastic, and then the above-mentioned. The granular plastic is washed with water to remove water-soluble impurities, and light impurities are separated and removed by preliminary specific gravity separation.
Next, in the pressure-resistant melting tank, the powdered plastic is melted in hot water to obtain molten plastic, and when the molten plastic settles in hot water, the molten plastic is washed with the hot water at the same time, the specific gravity is separated, Since the heavy impurities are separated and removed, the impurities can be efficiently removed and separated, so that a high-purity plastic can be obtained easily and inexpensively.
It is possible to obtain products that are comparable in quality and appearance.

Further, since the water jet is used for crushing the plastic molded product, there is no generation of noise and dust, the water can be easily processed, and the water used for the water jet is the whole process of recycling. There is no waste of being circulated in and utilized. In addition, water is easy to handle, has no effect on the human body, and is nonflammable, so it is not subject to the Fire Defense Law.
The recycling process can proceed safely. Therefore, even when the powdered plastic is transported, it is possible to put it in an appropriate container together with water and transport it safely and easily by a truck or the like. Since it is easy to transport, the plastic molded products are only crushed at any factory, and the crushed powdered plastic is transported to another factory where it is only washed with water and further cleaned. It is possible to easily carry out centralized processing of each process, such as transporting the powdered plastic to another factory and performing the melting process of the powdered plastic, the specific gravity separation process, and the recovery process of the plastic there. Since the plastic molded article can be processed efficiently, the processing cost can be further reduced.

Further, since the pressure-resistant melting tank 13 is always filled with water vapor, there is no concern that the molten plastic will come into contact with air and deteriorate. Further, even in the case of a plastic molded product made of a plurality of plastics, the respective plastics can be separated and collected at the same time.

[0037]

As described above, the plastic recycling method of the present invention is a plastic recycling method in which impurities are separated from powder plastic obtained by crushing a plastic molded product. In the molten state, when the melt settles or floats in hot water, it is washed with the hot water and at the same time, the specific gravity is separated to separate the impurities. Since it is well removed and separated, high-purity plastic can be easily obtained at low cost.
It is comparable in quality and appearance. further,
There is no waste because water is circulated and used in all recycling processes. Also, water is easy to handle and has no effect on the human body,
The recycling process can proceed safely. Further, even in the case of a plastic molded product made of a plurality of plastics, the respective plastics can be separated and collected at the same time.

Furthermore, the recycling apparatus of the present invention melts the powdered plastic in hot water, and when the melt settles or floats in the hot water, it is washed with the hot water and at the same time the specific gravity is separated to remove impurities. Since the pressure-resistant melting tank for separation is provided, melting of the above-mentioned powdered plastic in hot water and separation of specific gravity proceed smoothly. In addition, since the pressure-resistant melting tank is always filled with water vapor, there is an effect that there is no concern that the molten plastic will come into contact with air and deteriorate.

[Brief description of drawings]

FIG. 1 is a flow chart showing steps of a plastic recycling method of the present invention.

FIG. 2 is a schematic view showing an example of an apparatus used for recycling plastics of the present invention and an example of a recycling method using this apparatus.

FIG. 3 is a schematic configuration diagram showing an embodiment of a conventional recycling device used for recycling plastics.

[Explanation of symbols]

11 ... Crusher, 12 ... Washing tank, 13 ... Pressure-resistant melting tank, 20
... Stirrer, 22 ... Melting tank main body, 23 ... Lid, 31 ... Boiler, 32 ... Steam ejection part, 40 ... Expanded polystyrene, 4
1. Powder polystyrene

Claims (6)

[Claims] 1. A method of recycling a plastic for separating impurities from a powdered plastic obtained by crushing a plastic molded product, wherein the powdered plastic is melted in hot water, and the melt sinks in the hot water. Alternatively, when floating, a method for recycling plastics is characterized in that the impurities are separated by specific gravity separation while washing with the hot water. 2. The method of recycling plastic according to claim 1, wherein steam is used as a heat source when melting the powdered plastic. 3. The plastic recycling method according to claim 1, wherein the powder plastic is pretreated by washing with water as a pretreatment. 4. The method for recycling a plastic according to claim 1 or 2, wherein as a pretreatment of the powdered plastic, the powdered plastic is washed with water, and impurities are separated and removed by at least one preliminary gravity separation. Characteristic plastic recycling method. 5. A recycling apparatus for recovering plastic from a plastic molded product, wherein powdered plastic is melted in hot water, and when the melt sinks or floats in the hot water, it is washed with the hot water and at the same time has a specific gravity. A plastic recycling apparatus comprising a pressure-resistant melting tank for separating impurities by separation. 6. The plastic recycling apparatus according to claim 5, further comprising a crusher for crushing a plastic molded product into powder plastic, a cleaning tank for cleaning the powder plastic, and steam in the pressure-resistant melting tank. A plastic recycling device comprising a boiler for supplying the.