JP2004034437A - Method for repelletizing waste plastics and its system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently reprocess for a pellet with high merchandise value using waste plastics. <P>SOLUTION: This method for repelletizing waste plastics comprises a vented extruder 1 which melts the grinds of sorted/cleaned waste plastics and molds the melt into strands, a belt conveyor 2 which cools the surface of the molten strands discharged from the die of the extruder 1 by spraying cooling water to the strands and a strand cutter 3 which receives the strands with a solidified surface and continuously cuts the strands into pellets while spraying the cooling water to a cutting part. Consequently, it is possible to minimize the rupture or crushing of the strands which occurs significantly during cutting in repelletizing the waste plastics. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for repelletizing waste plastic recovered from waste and a system thereof. More specifically, pellets are used in the material recycling process for recycling waste plastics, excluding PET bottles, which are mainly used for containers and packaging, etc., into molding material pellets. And a device therefor.
[0002]
In the present invention, "waste plastic" mainly refers to plastic belonging to "8" in the table described in Article 2 of the "Ministry Ordinance on Separated Collection of Containers and Packaging Waste" promulgated in 1995. However, the present invention is not limited to this, but refers to waste plastics including waste plastics and mixed plastic bottles and the like.
[0003]
[Prior art]
Recycling of waste plastic is broadly divided into thermal recycling, in which waste plastic is burned and recovered as an energy source, and material recycling, which is reused as a substance.The latter is broken down into raw materials such as hydrocarbons and recycled as chemical raw materials. There are chemical recycling to be used, a method of reclaiming waste plastics by pressurizing and melting them into piles and blocks, and a method of re-pelletizing and regenerating them as raw materials for forming according to the present invention.
[0004]
Since waste plastic cannot be recycled as it is at the time of collection, foreign substances are generally separated by appropriately selecting, crushing, washing and the like according to the purpose of use. It would be desirable if waste plastic could be repelletized and widely used as a raw material for molding, because it could be economically reused as a relatively high quality processed product. For example, plastic bottles that are being recycled are collected as a single resin, distinguished from other plastics, and are crushed, washed, etc. to remove adhering substances, labels, aluminum caps, and other foreign substances such as other plastics. They are carefully separated and removed, finally melted and re-pelletized to form molding raw materials, and then molded again as products with relatively high added value.
[0005]
In addition to plastic bottles, households and other sources emit a large amount of plastics such as polyolefins, polystyrene, and polyvinyl chloride. Waste plastics used for containers and packaging other than PET bottles, including waste plastics used for other than containers and packaging, are collected as so-called "other plastics" and recycled. These "other plastics" are rarely separated and collected as a single waste plastic except for a part, and physical properties, such as various plastics with different melting points and plastic bottles that have been separated and collected, are not separated. Have been collected. Therefore, the application is limited, and conventionally, the separation, washing, and pulverization of foreign matters have been moderately heated and pressed to form a simple shape, which has been processed into a blast furnace reducing agent or horticultural product which does not require high physical properties.
[0006]
[Problems to be solved by the invention]
However, recycling of the above-mentioned "other plastics" (hereinafter simply referred to as waste plastics) is not proceeding smoothly. In order to make recycling effective, it is necessary to recycle waste plastic as the raw material for the molding process, improve the commercial value and diversify the recycled products. One of the important means for that is to perform a necessary and sufficient treatment such as sorting, washing, and pulverization of the waste plastic to be reused, and then to pelletize it so that it can be easily used as various molded products. However, unlike pelletization of virgin plastic, in addition to a relatively small lot, a lot of plastics are included at a constantly changing ratio, and contamination of foreign matter cannot be avoided. There are many obstacles to transformation. The present invention has been completed as a result of studying means for easily and stably pelletizing waste plastic in recycling waste plastic.
[0007]
[Means for Solving the Problems]
As a means for pelletizing virgin plastic, several methods have been developed based on conditions such as the form of a polymerization product, the amount of residual monomer and the amount of water. As a result of studying pelletization of waste plastic, considering that the main component is thermoplastic resin, fluctuation of constituent components, contamination of foreign matter, versatility, processing amount, vaporization products, etc., the extruder tip A perforated die was attached, the molten plastic was continuously extruded into strands, and the strands were cooled and completely solidified by running through a cooling water tank, and then cut into pellets using a strand cutter. However, when it was actually carried out in the waste plastic recycling process, strand breakage, die clogging at the start of operation, etc. occurred frequently, and it was difficult to perform the pelletizing operation normally. As a solution to this, washing and separation / removal of foreign matter were strengthened, but the effect was limited. As a result of further research, the present invention was completed as a means for solving the above-mentioned problems. The present invention will be described with reference to the drawings.
[0008]
First, as a means for solving the above-mentioned problem, the present invention supplies a crushed piece of sorted and washed waste plastic to a vent type extruder 1 to melt it, and extrudes a molten strand 8 from a die onto a belt conveyor 2. The cooling water 10 is sprayed to convey the strand surface to the strand cutter 3 while solidifying the strand surface, and the solidified surface is taken up by the strand cutter 3 to continuously cut and pelletize while spraying the cooling water 11. A method for repelletizing waste plastic is provided.
[0009]
The present invention also provides a vent-type extruder 1 for melting and sorting a crushed piece of waste plastic that has been sorted and washed into a strand, and spraying cooling water on a molten strand 8 discharged from a die of the extruder. Conveyor 2, which conveys to the strand cutter 3 while cooling and solidifying the surface, and a strand cutter which takes the above-mentioned strand whose surface has solidified, and continuously cuts and pelletizes while spraying the cooling water 11 to the cutting portion. (3) A waste plastic repelletizing system characterized by comprising
[0010]
In the re-pelletizing system, it is preferable to use the net belt 4 as the belt of the conveyor, and it is desirable to mount an exchange device for the screen pack 5 at the tip of the extruder. More preferably, a centrifugal dehydrator 6 for dehydrating and separating water adhering to the pellets pelletized by the strand cutter 3 is attached. Further, it is preferable to add a continuous vibrating sieve sorting device 7 for separating powdery substances mixed in the dehydrated pellets.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Further, the present invention will be specifically described with reference to the drawings and exemplifying embodiments. FIG. 1 is a system diagram illustrating a waste plastic repelletizing system according to the present invention.
[0012]
The waste plastic separately collected from general households and the like is compressed and packed in a pail for recycling as a raw material for recycling and delivered to a recycler. The recycler cuts the pail with a cutting machine and sorts it by hand. Metals, glasses, ceramics mixed in waste plastic by using a vibrator, magnet roll, crusher, wind separator, washing machine, dehydrator, etc. as appropriate Remove foreign matter such as sand, deposits and paper and dehydrate. In addition, if necessary, for example, polyvinyl chloride or high melting point PET which generates chlorine gas is separated by specific gravity.
[0013]
In the present invention, the waste plastic stored in the stock hopper 9 in the present embodiment, which is obtained by sufficiently pulverizing, removing foreign substances, and separating unnecessary components as described above, is pelletized. The waste plastic generally contains a large amount of film-like waste, has a low bulk specific gravity, and contains considerable moisture even after dehydration. In general, the water content is about 20% by weight and the bulk specific gravity is about 0.2, depending on the preceding treatment method and the disposal source. First, the waste plastic is heated and melted and kneaded by using a vented extruder 1, formed into a molten strand 8 through a porous die at the tip, and extruded. A single-screw or twin-screw extruder with a high compression ratio capable of performing a stable extrusion operation, compressing and melting a bulky supply waste plastic, and releasing generated steam and decomposed gaseous substances outside the machine is used.
[0014]
In the system of the present invention, it is preferable to mount a screen changer for exchanging a clogged screen pack in the mounted state at the end of the extruder 1 and on the upstream side of the breaker plate. Since the supplied waste plastic contains a relatively large amount of solid foreign matter and is frequently clogged, it is very effective in facilitating the operation of replacing the screen pack and continuing the continuous operation.
[0015]
Next, in the conventional pelletizing system, the melt-discharged strand was immediately immersed in a cooling water tank, rapidly cooled, solidified to the core, taken off by a strand cutter, and cut into pellets. In the waste plastic pelletizing system according to the present invention, instead of quenching in a cooling water tank as in the conventional method, the extruded molten strand 8 is discharged onto the belt conveyor 2, and the cooling water 10 is sprayed on the belt. It is cooled on the conveyor 2 and conveyed to the strand cutter 3 while solidifying the surface. In the method of spraying the cooling water, the cooling water is sprayed and made into a shower shape or a water film shape, and the cooling water is brought into contact with the strand to solidify the strand surface. There is no need to solidify to the core. The belt is preferably, but not limited to, a net belt, usually a wire mesh, so that excess spray water can easily fall under the belt and be collected easily.
[0016]
The reason why the cooling water is sprayed on the belt conveyor 2 will be described. Extrusion of waste plastic to form strands is unavoidable, foreign matter is unavoidable, screen pads are frequently replaced, and multiple plastics with a large difference in melting point are mixed, so the progress of cooling and solidification is complicated, and the content ratio Because of the fact that the content and the variation of the content state are often large, compared with the pelletization of virgin plastic, the discharged strand is interrupted and the number of breaks due to rapid cooling after the discharge is large.
[0017]
In the present invention, since the strand is moved without being pulled by the adoption of the belt conveyor 2 and the spraying of the cooling water 10, the breakage due to rapid solidification up to the strand core is reduced, and the discharge of the strand is interrupted or the cooling / cooling is stopped. Even if it breaks during solidification, the re-discharged or broken strand is sent again on the belt, so it is basically unnecessary or extremely easy to take measures against strand breakage during operation, and it is possible to form waste plastic strands. Specific problems can be solved.
[0018]
Although the present invention does not require that the core portion of the strand is not solidified, the cutting ratio is generally smaller when the surface is solidified and not solidified until the core, and the length of the cooling device is shortened. It is advantageous. The present invention has an advantage that the cooling state can be controlled by adjusting the distribution of the cooling water 10. The breakage of the strand during cooling is largely related to the composition of the waste plastic and the cooling conditions, as in the case of avoiding the crushing phenomenon at the time of cutting by the strand cutter 3. It is desirable to maintain the best operating conditions by adjusting.
[0019]
Further, the above-mentioned strand is fed by a take-up roll composed of two rolls of a strand cutter 3 onto a take-off fixed blade, and is rotated on the circumference to rotate between a rotary blade attached at a right angle to the rotation direction. While the cooling water 11 is being sprayed to cool the pellets and the cutting blade, the strands are continuously cut and re-pelletized. By spraying the cooling water 11, the cut waste plastic pellets are solidified to the core. Also in this step, it is advantageous that the strand to be cut is not solidified up to the core portion, and the ratio of the strand being cut without being cut at the time of cutting is smaller than that of the solidified strand.
[0020]
Then, using a dehydrator, preferably a continuous centrifugal dehydrator 6, dewaters the spray water accompanying the pellets, and further passes through a loader such as a continuous vibrating sieve 7 to separate and remove powdery plastic. It is desired that the commercial value of the pellets be improved.
[0021]
【The invention's effect】
By utilizing the present invention, foreign matter is mixed in, and a strand is easily extruded from a crushed piece of waste plastic having a large volume and a large water content, and the formed strand is adjusted under cooling conditions under no tension load. Thus, it is possible to reduce strand breakage, which is a problem of re-pelletizing waste plastic. Even if the strand breaks, no special measures are required or easy. Also, equipment costs are reduced. It is possible to avoid reduction in grinding in the strand cutter and to reprocess into pellets having high commercial value.
[Brief description of the drawings]
FIG. 1 is a system diagram illustrating a waste plastic repelletizing system of the present invention.
1: Vent-type extruder 2: Belt conveyor 3: Strand cutter 4: Net belt 5: Screen pack 6: Centrifugal dewatering machine 7: Continuous vibrating sieve sorting device 8: Melting strand 9: Stock hopper 10: Belt conveyor cooling water (Spray device)
11: strand cutter cooling water (spraying device)

Claims (6)

The sorted and washed waste plastic crushed pieces are supplied to a vent-type extruder and melted, and the molten strand is extruded from a die onto a belt conveyor, and cooled water is sprayed to convey the strand surface to a strand cutter while solidifying the strand surface. A method for re-pelleting waste plastic, wherein the strand whose surface has solidified is taken up by a strand cutter, and continuously cut and pelletized while spraying cooling water. A vent-type extruder (1) that melts and sorts the crushed and crushed waste plastic into a strand, and cools the surface by spraying cooling water on the molten strand discharged from the die of the extruder. A belt conveyor (2) for conveying the solidified solid to the strand cutter (3), and a strand cutter for taking the above-mentioned solidified solid and continuously cutting it into pellets while spraying cooling water on the cutting portion. A re-pelletizing system for waste plastics, comprising: The system according to claim 2, characterized in that a net belt (4) is used for the conveyor belt. 4. The re-pelletizing system for waste plastic according to claim 2, wherein an exchanging device for the screen pack (5) is mounted at the tip of the extruder. The method according to any one of claims 2 to 4, further comprising a centrifugal dehydrator (6) for dehydrating and separating water adhering to the pellets pelletized by the strand cutter (3). 2. The re-pelletizing system for waste plastic according to 1. The waste plastic according to any one of claims 2 to 5, further comprising a continuous vibrating sieve sorting device (7) for separating powdery substances mixed in the dehydrated pellets. Re-pelletizing system.

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