JP2007062070A - Refining treatment method of waste plastic, manufacturing method of plastic molded product using waste plastic as a raw material and manufacturing method of plastic board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of stably manufacturing a plastic molded product of good quality from a waste plastic. <P>SOLUTION: In this refining treatment method of the waste plastic, the waste plastic 103 is charged in a first extruder 10 equipped with a vacuum means to be held to a vacuum state while heated to be melted. After the molten plastic is subjected to filtering treatment, the filtered melt is cooled and solidified to obtain a granular product 105 of the waste plastic. The granular product 105 is charged in a second extruder 20 equipped with a vacuum means and melted while held to a vacuum state under heating. Then, the obtained melt is subjected to extrusion molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a purification method for recycling waste plastic collected as general waste or industrial waste (hereinafter referred to as waste plastic) as a raw material for plastic molded products, and plastic using waste plastic as a raw material. The present invention relates to a method for manufacturing a molded article and a method for manufacturing a plastic board.

  Among the waste plastics, those discharged from general households are PE (polyethylene), PP (polypropylene), PS (polystyrene), PET (polyethylene terephthalate), PVC (polyvinyl chloride), PVDC (polyvinyl chloride). It is a mixture of many kinds of plastics. Moreover, the waste plastics of general waste contain foreign substances such as metals and papers in addition to plastics.

  Conventionally, general waste plastics collected in this state are treated with chlorine-free plastics such as PVC and PVDC that are not normally reused, and after removing foreign substances such as metal and paper, energy sources, etc. It was reused for the purpose.

  Methods for separating and removing foreign materials such as metals and plastics that are not reused include electrostatic separation and near-infrared methods that separate chlorine-containing plastics such as PVC and PVDC, magnetic separation that separates iron, and lightweight materials such as paper. Wind sorting for sorting, methods using a repulsive repulsion sorter for sorting solids, lightweights, and granules, various types of plastics with low specific gravity (PE, PP, etc.) and high specific gravity (PVC, There are wet specific gravity separation methods such as PVDC and PET. And when recycling waste plastic, the method which combined these some separation methods was implemented.

  However, when recycling waste plastic as a raw material for plastic molded products, it can be seen that if a material that has only been processed by a combination of the above conventional separation methods is used as a raw material, there will be a problem of clogging the die during molding, Technical improvements have been made for that purpose (for example, Patent Document 1). Patent Document 1 discloses a technique for removing foreign matter (solid matter) that could not be removed by the conventional separation method. In this technology, waste plastics separated by the above conventional separation method are heated to the molding temperature of plastic products and melted, and the melted material is filtered to leave residual metals, plastics with a high melting point, etc. This is due to the method of removing the solid matter.

As a technique for producing a plastic molded product from waste plastic as a raw material, Patent Document 2 discloses a method for producing a lightweight plastic board. A plastic board manufactured by this technology is formed in a three-layer structure by a main layer made of foamed waste plastic and a thermoplastic plastic layer covering both surfaces of the main layer.
JP 2003-191238 A Japanese Patent No. 3528841

  However, when the present inventors manufactured plastic board by extruding and molding the waste plastic separated by the same method as that of Patent Document 1 and using it as a raw material, Although solved, various new problems occurred.

  In other words, the surface of the extruded product can be swollen or dented, or the thickness of the product may fluctuate due to a thin part, resulting in stable quality plastic products. Could not be manufactured.

  Further, in the process after the heat-melting treatment with an extruder, there is a problem that a remarkable bad odor is generated from the waste plastic and the working environment is deteriorated, and the problem related to the bad odor has not been solved.

  As described above, even with the method of Patent Document 1, the clogging of the dies is eliminated, but a new problem that a high-quality plastic product cannot be stably produced occurs. In addition, problems related to bad odors are still not solved.

  An object of the present invention is to provide a method capable of stably producing a high-quality plastic molded product from waste plastic.

  In order to investigate the cause of the occurrence of the above problems, the present inventors examined the results of tests conducted in the past and conducted various tests. As a result, it was found that the cause of irregularities on the surface of the molded product and fluctuations in thickness was because bubbles were contained in the waste plastic melt introduced from the extruder to the die. It was. And it turned out that the bubble is produced | generated when gas is generated when waste plastic is heated.

  The heating temperature of the waste plastic by the extruder is generally about 180 ° C. to 250 ° C. However, when the waste plastic is heated to the above temperature, evaporation of the attached water, volatilization of the deposit such as food, Decomposition, decomposition of some plastic components, etc. occur, and some substances in waste plastic are gasified. The generated gas becomes bubbles and is discharged from the extruder while being contained in the waste plastic melt and introduced into the die, causing various problems as described above.

  The present invention has been made on the basis of the above-mentioned knowledge, and a method for refining waste plastic that solves the above-mentioned problem is to melt the waste plastic while holding it in a reduced pressure state while heating it, and then melting the melt. It is characterized by filtering.

  Moreover, the manufacturing method of the plastic molded product which uses waste plastics as a raw material is charged with the waste plastics in a first extruder equipped with a decompression means, kept under reduced pressure while being heated, and melted. After performing the filtration process, the product is cooled and solidified to obtain a granular product of waste plastic. The granular product is charged into a second extruder equipped with a decompression means, and kept under reduced pressure while being heated. It is characterized by melting and extruding the melt.

  Furthermore, a method for producing a plastic board using waste plastic as a raw material is a method for producing a plastic board having a three-layer structure in which a main layer made of thermoplastic waste plastic and a surface layer made of thermoplastic plastic are provided on both sides of the main layer. The waste plastic is charged into a first extruder equipped with a pressure reducing means, heated and melted while being held in a reduced pressure state, and the melt is filtered and then cooled and solidified. A step of obtaining a granular product of waste plastic, and charging the granular product into a second extruder equipped with a decompression means, holding the molten product in a reduced pressure state while heating, and blowing a gas into the melt A step of including bubbles in the melt, and forming the main layer by forming a waste plastic melt containing the bubbles into a flat plate shape, and separately heating and melting the thermoplastic plastic; A step of forming the surface layer by dissolving and integrating on both sides of the main layer, a step of extruding the formed main layer and the surface layer into a strip shape, and then cooling and solidifying It is characterized by having.

  In the present invention, when manufacturing a product such as plastic board using waste plastic as a raw material, the waste plastic is subjected to a purification process, and the purified waste plastic is subjected to extrusion molding. Can be obtained because it has the following structure. In the refining process, not only is the solid removal process (filtering process) that melts and filters the waste plastic, but also a process (degassing process) that removes the gas in the heated and melted waste plastic is added. Furthermore, also in the molding process, when extruding the refined waste plastic, the waste plastic that has been heated and melted in the extruder is again deaerated.

  First, in the purification process, a two-stage purification process consisting of a filtration process and a deaeration process is performed, but the gas generated here is derived from deposits such as moisture and food contained in the waste plastic. However, since the waste plastic to be collected is miscellaneous that is discharged from ordinary households, it cannot be removed by the above-described separation process, and is mixed in, so the mixing must be allowed. Absent. For this reason, it is necessary to remove the gas components generated in the extruder, but it is necessary to treat the gas generated in the extruder simply by exhausting it, for example, by attaching a fan to the extruder, In such a procedure that the gas accumulated in the gas is exhausted, bubbles contained in the waste plastic that is only in a softened state cannot be removed. For this reason, in the present invention, a degassing process is performed in which a predetermined portion in the extruder is held at a high pressure reduced state by a pressure reducing means such as a vacuum pump, and the gas existing in the molten waste plastic is sucked and removed. .

  In the refining process, the molten waste plastic discharged from the extruder is stretched in water, cooled and solidified, and then cut into a granular material. However, if the degassing treatment has not been performed, bubbles may be contained in the molten waste plastic, and the stretched waste plastic may be interrupted. Must. Moreover, even if the granulation treatment can be continued, an irregularly shaped granular material containing a large amount of moisture is generated, which adversely affects the next molding step. In this refining treatment step, the molten waste plastic discharged from the extruder may be cut with a cutter or the like and dropped into water to form a granular material.

  And if a deaeration process is performed at a refinement | purification process process, while being able to continue a refinement | purification process stably, malodorous gas is removed from waste plastics. The generation of malodorous gas is thought to be due to components that have been volatilized or decomposed by heating foods that have adhered to waste plastics, but the odorous gas affects even the presence of trace amounts. It is difficult to remove the odor-generating substance adhering to the waste plastic to the extent that it does not generate odor before the refining process. For example, even if the waste plastic separation process performed in the previous stage of the purification process is wet specific gravity separation in which water washing is performed at the same time, water-soluble substances can be removed, but sticky deposits and the like are removed. It is not possible.

Further, in the molding process, the heated and melted waste plastic is degassed. The reason for this degassing treatment is as follows. Oxidized components and the like are removed from the granular waste plastic obtained in the refining treatment process, but it contains moisture taken up when granulated in the refining treatment process in addition to moisture. Although this moisture is a small amount, it cannot be ignored in the molding of plastics. For example, when refined waste plastic containing 0.5 mass% of moisture is charged into an extruder at a flow rate of 500 kg / hr and heated to 200 ° C., a large amount of about 5.4 m ³ / hr from the melted waste plastic Gas will be generated. When such a large amount of gas is generated, the bubbles inflate the surface at the time of molding or blow out to the surface to create a dent, thereby deteriorating the quality of the molded product. Thus, even if the waste plastic used for the molding process contains only 0.5 mass% of water, a good molded product cannot be obtained.

  In addition, since the amount of gas generating substances contained in waste plastic varies, the amount of gas in the waste plastic after foaming fluctuates, especially when producing porous molded products by foaming. Therefore, it cannot be maintained at a predetermined value, and a product with good quality cannot be obtained.

  According to the present invention, when waste plastic is heated and melted in both the purification process of waste plastic and the process of molding the refined product, it is kept in a reduced pressure state. The generated gas is sucked and removed. For this reason, the molded product can be prevented from being swollen or the surface can be dented, and a plastic molded product with good quality can be stably produced. In the purification process, the odor generating substance is removed, and the purification process can be continued stably.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example of a method for producing a plastic molded product using waste plastic as a raw material. This method comprises a processing step A for purifying waste plastic and a molding step B for processing the purified waste plastic into a molded product. The raw material waste plastic to be supplied to the refining process step A is, for example, subjected to a separation process for removing PVC and iron from the recovered waste plastic by the method shown in FIG. Polyolefin type. The classification processing method shown in FIG. 4 will be described later.

  In FIG. 1, the first extruder 10 and the second extruder 20 have electric heating means, and are connected to a vacuum pump for maintaining a part of the machine in a highly depressurized state. It has a function of heating and a function of degassing the charged material.

  In the refining process step A, the waste plastic 103 subjected to the separation process is charged into the first extruder 10 and heated to melt. The heating temperature of the waste plastic varies depending on the type of plastic to be collected, and is in the range of about 180 ° C to 250 ° C. However, when a non-target plastic with a high melting point is mixed, the melting temperature of the non-target plastic Set to a lower temperature.

  In the extruder 10, as described above, the moisture contained in the charged waste plastic evaporates, the organic matter such as attached food is volatilized or decomposed, and the plastic A part of the gas is decomposed or gasified, and a non-negligible amount of gas is generated. However, since the inside of the extruder 10 is sucked by the vacuum pump 14 and is in a highly reduced pressure state, the generated gas is sucked and exhausted without remaining in the molten waste plastic. Since the exhausted gas contains a component that emits a bad odor, it is introduced into the deodorizing device 15 filled with the adsorbent and subjected to a deodorizing process.

  Next, the melt discharged from the extruder 10 is press-fitted into a filtration device 12 equipped with a screen by a gear pump 11 and filtered. By this filtration treatment, the solid matter 104 such as non-target plastic or aluminum foil having a high melting point that could not be removed by the separation process in the previous step is removed. In this filtration process, it is preferable to reduce the clogging of the screen by arranging a plurality of screens having different mesh sizes in series in the order of large and small to perform multi-stage filtration.

  The melt from which the solid material 104 has been removed is introduced into the granulator 13, stretched in water, cooled and solidified, and then cut into refined granular waste plastic 105. The refined granular waste plastic 105 does not contain a metal or a plastic having a high melting point that existed in a solid state when melted, and further, a malodorous substance is removed. For this reason, if this refined granular waste plastic 105 is used as a raw material of a plastic molded product, a high-quality plastic product can be manufactured.

  In the molding step B, the purified granular waste plastic 105 obtained in the previous step is charged into the second extruder 20 and melted. Although the refined granular waste plastic 105 to be charged contains water, the vacuum pump 24 is also connected to the second extruder 20, and a part of the inside of the machine is in a highly decompressed state. The generated gas is sucked and exhausted without remaining in the molten waste plastic.

  The melted waste plastic is introduced into the die 22 by the gear pump 21, formed into a predetermined shape, and cooled and solidified to become a plastic molded product 106. In this molding step B, since the molten waste plastic introduced into the die 22 does not contain bubbles, a plastic molded product with a smooth surface can be obtained without causing the molded product to bulge or dent.

  FIG. 2 is a diagram showing an example of a method for producing a plastic board using waste plastic as a raw material. The method of FIG. 2 includes a processing step A for purifying waste plastic and a molding step C for processing the purified waste plastic into a molded product. According to this method, as shown in FIG. 3, a plastic board having a three-layer structure including a main layer 108a in which a large number of cavities 109 are formed and a surface layer 108b provided on both surfaces thereof is manufactured. This plastic board is reduced in weight and can be used for applications such as concrete form panels, wall and ceiling members. Hereinafter, a method for manufacturing the lightweight plastic board having the three-layer structure shown in FIG. 3 will be described.

  In FIG. 2, as in FIG. 1, the first extruder 30 and the second extruder 40 have electrothermal heating means, and a vacuum pump for maintaining a part of the machine in a highly decompressed state. It is connected and has the function of heating the charge and the function of degassing the charge. In the description of FIG. 2, the waste plastic refining process is a process for performing the same processing operation as the refining process of FIG.

  In the molding step C, the refined granular waste plastic 105 obtained in the refinement treatment step A is charged into the second extruder 40 that forms the main layer and melted. The refined granular waste plastic 105 also contains moisture, but the second extruder 40 has a highly decompressed state inside the machine, so that the generated gas remains in the molten waste plastic. Instead, it is aspirated and removed. The second extruder 40 is provided with a gas blowing means for forming a hollow portion in the main layer, and a gas such as nitrogen gas adjusted to a predetermined flow rate is blown. By this gas blowing, the blown gas is dispersed in the melt, and a melt containing bubbles is formed. The melt containing bubbles is introduced into a T-die 42 for forming three layers by a gear pump 41 to form a plate, and a main layer is formed. Bubbles are contained in the main layer, and these bubbles become cavities of a plastic board to be formed later.

  Note that the ratio of the voids formed in the main layer is determined by the amount of gas blown, but if the waste plastic supplied to the second extruder 40 contains a gas generating substance, Since the amount of bubbles in the layer increases, the amount of blown gas must be reduced by an amount corresponding to the amount of gas generated. However, for example, even if the waste plastic supplied contains only 0.5 mass% of water, the amount of gas generated by this is equivalent to several to ten times the amount of nitrogen gas or the like blown. The target plastic board cannot be manufactured. In addition, even if the water content of the waste plastic to be supplied is even smaller, the properties of the waste plastic are not constant, and the amount of gas generating substance always fluctuates. By doing so, the amount of bubbles cannot be kept constant.

  With respect to this point, in the present invention, the inside of the second extruder 40 is maintained in a highly decompressed state, and the gas generated from the waste plastic is sucked and removed, so that the gas blowing amount is controlled. Thus, the amount of bubbles present in the melt can be uniquely determined. For this reason, the production | generation ratio of the cavity part in a main layer can be maintained in a predetermined range.

  In parallel with the formation of the main layer, a polyolefin-based plastic that does not contain foreign substances and the like is charged into a surface layer extruder 45 equipped with electrothermal heating means and melted. This melt is introduced into the T-die 42 by the gear pump 46, and is dissolved and integrated on both sides of the melt of the main layer containing bubbles to form a surface layer.

  Next, the material extruded from the T-die 42 is introduced into a modeling cooling device 43 in which metal rolls are arranged, and cooled and solidified, whereby a main layer in which a large number of cavities are formed and a polyolefin-based plastic on both surfaces thereof. Thus, a lightweight plastic board 108 having a three-layer structure in which a surface layer made of is formed is obtained.

  Next, an example of a separation processing method when supplying waste plastic to the purification processing step will be described with reference to FIG. The collected waste plastic 100 of general waste is subjected to magnetic separation or the like as necessary, and then crushed to an appropriate size by the crusher 50. The crushed waste plastic is separated by a wet specific gravity separator 51 into one having a small specific gravity and one having a large specific gravity, and a low specific gravity is recovered. The wet specific gravity separator used in this embodiment is of a centrifugal separation type, and its structure is shown in FIG.

  The specific gravity separation processing method will be described with reference to FIG. In FIG. 5, water 66 in which waste plastic is dispersed is charged into a main body 60 configured to be rotatable. When the main body 60 rotates, a structure having a specific gravity greater than that of water (high specific gravity) 101 gathers on the outer peripheral portion of the main body 60 and a structure having a specific gravity smaller than that of water (low specific gravity) 102 gathers on the water surface (inside). ing. And what was gathered in the outer peripheral part and what gathered in the water surface part (inner side) are separately extracted with a screw, respectively, and the waste plastics charged are separated into those having a small specific gravity and those having a large specific gravity. In FIG. 5, 62 is an inlet for water in which waste plastic is dispersed, 63 is a screw for scraping high and low specific gravity components in left and right directions, 64 is a discharge port for high specific gravity, and 65 is a low specific gravity component. It is a discharge port.

  By this specific gravity separation treatment, PVC, PVDC, PET, and the like are removed from the charged waste plastic as a high specific gravity, and plastics mainly made of polyolefin such as PE and PP are recovered as a low specific gravity. The drained waste plastic 102 having a low specific gravity is drained and then charged into the granulator 52 to become a granular waste plastic 103. The separated polyolefin-based plastic can be sent to the next process as it is for purification, but its state is very bulky, so it is granulated to reduce storage volume and to facilitate handling. It is preferable to do.

It is a figure which shows an example of the manufacturing method of the plastic molded product which uses a waste plastic as a raw material. It is a figure which shows an example of the manufacturing method of the plastic board which uses waste plastics as a raw material. It is a figure which shows the cross section of the lightweight plastic board of the 3 layer structure manufactured by the method of FIG. It is a figure which shows an example of the method of classifying a waste plastic. It is a figure which shows the structure of a centrifugation system wet specific gravity separator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 1st extruder 12 Filtration apparatus 13 Granulator 14 Vacuum pump 20 2nd extruder 22 Die 24 Vacuum pump 30 1st extruder 32 Filtration apparatus 33 Granulator 34 Vacuum pump 40 2nd extruder 42 T-die 45 Surface layer extruder 51 Wet specific gravity separator 100 Recovered waste plastic 102 Low specific gravity 103 Waste plastic 104 subjected to separation treatment Solid 105 Purified granular waste plastic 106 Plastic molded product 107 Polyolefin plastic 108 Lightweight plastic board 108a Main layer 108b Surface layer 109 Cavity

Claims (3)

  A method for purifying waste plastic, characterized in that the waste plastic is melted while being heated under reduced pressure and then the melt is filtered.   The waste plastic is charged into a first extruder equipped with a decompression means, heated and melted while being kept in a reduced pressure state, and the melt is filtered and then cooled and solidified. Waste obtained by obtaining a granular product, charging the granular product into a second extruder equipped with a decompression means, holding the molten product in a reduced pressure state while heating, and extruding the melt. A method for manufacturing plastic molded products made of plastic.   A method of manufacturing a plastic board having a three-layer structure in which a main layer made of thermoplastic waste plastic and a surface layer made of thermoplastic plastic are provided on both sides of the main layer, wherein the waste plastic is provided with a pressure reducing means. A process of charging into an extruder, holding and melting in a reduced pressure state while heating, filtering the melt, cooling and solidifying to obtain a granular product of waste plastic, and this granular product , Charging into a second extruder equipped with a decompression means, holding the melt in a decompressed state while heating, blowing a gas into the melt to include bubbles in the melt, and And forming the main layer by forming a waste plastic melt into a flat plate, and separately melting and integrating the thermoplastic plastic that has been separately heated and melted to integrate the surface layer. Forming process and shape After the strip has been what the main layer and the surface layer are integrated extruded to method of manufacturing a plastic board for waste plastics characterized by having a step of cooling and solidifying the raw material.

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