WO2010137756A1 - Method and apparatus for recycling thermoplastic resin from a resin mixture - Google Patents

Method and apparatus for recycling thermoplastic resin from a resin mixture Download PDF

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Publication number
WO2010137756A1
WO2010137756A1 PCT/KR2009/002847 KR2009002847W WO2010137756A1 WO 2010137756 A1 WO2010137756 A1 WO 2010137756A1 KR 2009002847 W KR2009002847 W KR 2009002847W WO 2010137756 A1 WO2010137756 A1 WO 2010137756A1
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Prior art keywords
resin mixture
thermoplastic resins
rotary
impurities
liquid phase
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PCT/KR2009/002847
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French (fr)
Inventor
Byung Kyoo Park
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Byung Kyoo Park
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Priority to PCT/KR2009/002847 priority Critical patent/WO2010137756A1/en
Publication of WO2010137756A1 publication Critical patent/WO2010137756A1/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29BPREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B17/00Recovery of plastics or other constituents of waste material containing plastics
    • B29B17/02Separating plastics from other materials
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00Recovery or working-up of waste materials
    • C08J11/04Recovery or working-up of waste materials of polymers
    • C08J11/06Recovery or working-up of waste materials of polymers without chemical reactions
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29BPREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B17/00Recovery of plastics or other constituents of waste material containing plastics
    • B29B17/02Separating plastics from other materials
    • B29B2017/0203Separating plastics from plastics
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29BPREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B17/00Recovery of plastics or other constituents of waste material containing plastics
    • B29B17/02Separating plastics from other materials
    • B29B2017/0213Specific separating techniques
    • B29B2017/0217Mechanical separating techniques; devices therefor
    • B29B2017/0231Centrifugating, cyclones
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29KINDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/06Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
    • B29K2105/065Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts containing impurities
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29LINDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2007/00Flat articles, e.g. films or sheets
    • B29L2007/008Wide strips, e.g. films, webs
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29LINDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2009/00Layered products
    • B29L2009/003Layered products comprising a metal layer
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00Technologies for solid waste management
    • Y02W30/50Reuse, recycling or recovery technologies
    • Y02W30/62Plastics recycling; Rubber recycling

Abstract

Disclosed is a method and apparatus for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, and more particularly, a method and apparatus for recycling thermoplastic resins from an agricultural mulching film for covering soil or a multilayer film coated with a metal. A method for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, comprises the steps of heating the resin mixture to form a fluent liquid phase resin mixture, injecting the fluent liquid phase resin mixture to a rotary body, separating the thermoplastic resins and impurities from each other by floating the thermoplastic resins over the rotary body and permitting the impurities to fall beneath the rotary body, and collecting the thermoplastic resins.

Description

Description
METHOD AND APPARATUS FOR RECYCLING THERMOPLASTIC RESIN FROM A RESIN MIXTURE
Technical Field
[1] The present invention relates to a method and apparatus for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, and more particularly, to a method and apparatus for recycling thermoplastic resins from an agricultural mulching film used for covering soil or a multilayer film coated with a metal. Background Art
[2] Recently, petrochemical products made mainly from synthetic resins are used throughout a wide variety of fields, and the amount of synthetic resin waste is increasing more and more. Synthetic resin waste contaminates the soil when buried in the ground due to the fact that it does not decompose in the natural environment. Synthetic resin waste also contaminates the air when incinerated because heavy metals and noxious gas are released during incineration. In view of the above, there exists a strong need for recycling synthetic resin waste in an economically advantageous and environmentally safe manner.
[3] The disposal of mulching films made from synthetic resins after their use involves complex and costly operations. Agricultural mulching films are widely used throughout the world due to the many advantages they provide, including retention of moisture in the soil, retardation of weed growth, etc. However, significant amounts of mud, dirt and the like tend to strongly stick to used agricultural mulching films since the films are spread along the soil, and therefore it is not easy to remove mud, dirt and the like from the surfaces of mulching films.
[4] Korean Patent Laid-Open Publication No. 2002-0034653 discloses a recycling method for mulching films. The conventional recycling method disclosed in the above Korean Patent Publication comprises the steps of shredding collected mulching films into pieces through the use of a film shredder, injecting the shredded mulching films along with water into a wash tub to remove mud, dirt and debris from the films, injecting the washed mulching films into a dehydrating tub to dehydrate the films, injecting the dehydrated films into a melt extruder and extruding the films while melting them with a heater, and cutting the films being extruded through the hole of the melt extruder into a reusable form, such as pellets, by using a cutter.
[5] However, the above-described recycling method for mulching films is undesirable because of the disposal of the contaminated water used for washing the films. In addition, it is not easy to completely remove mud, dirt and the like from the mulching film even after the washing process. This causes difficulty in producing pellets from the mulching film.
[6] In recent years, multilayer films have been widely used in the form of packing materials for various products including foods. To protect foods from moisture and ultraviolet ray, multilayer films for food packaging are made of films consisting of thermoplastic resins including polyethylene terephthalate (PET), polypropylene (PP) and polyethylene (PE), and thin metal (for example, aluminum) layer coated between the films.
[7] In order to use multilayer films as food packaging, a multi-stage layer laminating process and a printing process, for example, gravure printing, are carried out. Most of defective items generated during the layer laminating process or printing process are removed from the process and discarded. The discarded multilayer film can be partially reused without any special treatment. However, recycling of the discarded multilayer film is troublesome since the film is composed of PET, PP and PE mixed in a wide variety of ratios and coated with thin metal layer (i.e., thin aluminum layer). For this reason as well as due to inferior physical properties of the defective film, reuse of the defective film is limited to low grade plastics.
[8] In Korean Patent Registration No. 528646, there is disclosed a recycling method for multilayer packaging film comprising the steps of selective dissolution of an aluminum layer, separation of shredded waste films by using a difference of specific gravity, selective extrusion by using a melting temperature difference, and selective dissolution of components by using an organic solvent.
[9] However, the above-described recycling method is complex in process and costly since the method separates the aluminum layer by using a chemical solvent. Disclosure of Invention Technical Problem
[10] The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for easily separating one or more thermoplastic resins and impurities from a resin mixture containing one or more thermoplastic resins and impurities. Technical Solution
[11] The inventor of the present invention has studied methods of separating impurities including mud, pigment and metal extensively adhered to thermoplastic resins in a simple and economically advantageous way without using water or chemical solvents. As a result of extensive study to develop such methods, the inventor of the present invention has found that thermoplastic resins and impurities can be isolated if a resin mixture is heated to the level exceeding the melting temperature thereof and lower than the inflammation point thereof to provide the resin mixture with a fluidity, and the resin mixture in its fluent state (hereinafter, referred to as a "fluent liquid phase resin mixture") is subsequently centrifugally separated.
[12] In the present invention, impurities including mud, pigment and metal are still kept at a solid phase even at the temperature level exceeding the melting point of thermoplastic resin. In general, a thermoplastic resin is turned into a liquid having a high viscosity when molten. Hence, impurities uniformly distributed all over the resin mixture in a high viscosity state may not be easily separated from the resin mixture when a liquid cyclone method, i.e., a conventional solid-liquid separation method, is employed.
[13] The inventor of the present invention has found that thermoplastic resins and impurities are separated from each other in a solid phase by injecting the fluent liquid phase resin mixture to a rotary body which can be rotated at 20,000RPM or higher. From a experiment where the viscosity (poise) of a fluent liquid phase resin mixture changes in accordance with the change of temperature and the injection pressure (kgf / cm2) and/or injection quantity (L/min) of the fluent liquid phase resin mixture injected to the rotary body as well as the RPMs of the rotary body (i.e. centrifugal force (kgf)) are varied, the inventor has learned that, under certain conditions, the thermoplastic resin is turned into a powder or fibrous form and floats over the rotary body while impurities are turned into a fine powder form and fall beneath the rotary body, from among the fluent liquid phase resin mixture injected to the rotary body.
[14] A significant point of the present invention is that the thermoplastic resin is turned into a powder or fibrous form and floats over the rotary body while impurities fall beneath the rotary body. If the thermoplastic resin fails to float over the rotary body, the thermoplastic resin, in a powder or fibrous form, and impurities are mixed together. If this occurs, it is nearly impossible to separate the thermoplastic resin and impurities or it costs a lot to separate them.
[15] The rotary body as used in the present invention means a device which allows the fluent liquid phase resin mixture injected thereto to be separated into solid phase thermoplastic resins and solid phase impurities at the moment when the resin mixture contacts the surface of the rotary body. The rotary body of the present invention takes one of shapes including a conical shape with a cut top end, a disc shape, a cup shape, and a multi-blade shape, etc.
[16] Accordingly, the present invention provides a method for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, comprising heating the resin mixture to form a fluent liquid phase resin mixture, injecting the fluent liquid phase resin mixture to a rotary body, separating the thermoplastic resins and impurities from each other by floating the thermoplastic resins over the rotary body and permitting the impurities to fall beneath the rotary body, and collecting the thermoplastic resins.
[17] The present invention provides an apparatus for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, comprising a melter for heating and stirring the thermoplastic resins and raising the temperature of the thermoplastic resins to a level higher than a melting point thereof in order to acquire a fluent liquid phase resin mixture, a centrifugal separator for separating the thermoplastic resins and the impurities from each other from the fluent liquid phase resin mixture by floating the thermoplastic resins over a rotary body and permitting the impurities to fall beneath the rotary body, a controller for controlling centrifugal force of the rotary body, viscosity of the fluent liquid phase resin mixture and injection quantity of the mixture to the rotary body, and a collector for collecting the thermoplastic resins, wherein the controller controls the centrifugal force, viscosity and quantity of the mixture to acquire thermoplastic resins in a powder or fibrous form.
[18]
Advantageous Effects
[19] The present invention has advantages in that the process for recycling thermoplastic resins from a resin mixture containing impurities is simple and economical because the impurities, such as mud, pigment and metal, can be separated from a fluent liquid phase resin mixture by injecting it to a rotary body, and thereby high purity thermoplastic resins are obtainable.
[20] Further, the present invention has an advantage effect in that the fluent liquid phase resin mixture is separated into one or more solid phase thermoplastic resins and impurities at the moment when the resin mixture contacts the surface of the rotary body, thus being a convenient and economically advantageous process. Brief Description of Drawings
[21] FIG. 1 schematically illustrates a process of separating thermoplastic resins and impurities from a resin mixture containing one or more thermoplastic resins and impurities according to the present invention.
[22] FIG. 2 illustrates the state in which thermoplastic resins and impurities are separated from each other in a centrifugal separator according to the present invention.
[23] FIG. 3,4 and 5 are perspective views illustrating a variety of forms of the rotary body of the centrifugal force, wherein Fig. 3 illustrates a disc type rotary body, Fig. 4 illustrates a multi-blade type rotary body, and Fig. 5 illustrates a cup type rotary body.
[24]
Best Mode for Carrying out the Invention [25] A method and apparatus for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities according to the present invention will be described hereinafter in detail with reference to the accompanying drawings.
[26] FIG. 1 schematically illustrates a process of separating thermoplastic resins and impurities from a resin mixture containing one or more thermoplastic resins and impurities according to the present invention, FIG. 2 illustrates the state in which thermoplastic resins and impurities are separated from each other in a centrifugal separator according to the present invention, and FIG. 3, 4 and 5 are perspective views illustrating a variety of forms of the rotary body of the centrifugal force, wherein Fig. 3 illustrates a disc type rotary body, Fig. 4 illustrates a multi-blade type rotary body, and Fig. 5 illustrates a cup type rotary body.
[27] (Melter)
[28] A melter 10 of the present invention contains the resin mixture in a melting tub 11, and melts the resin mixture by heat transmitted from a hot thermal medium oil 12. The melter 10 of the present invention may use any device that can melt the resin mixture, including a device with a thermal medium oil, an electrical heating device, an extruder, and an induction heating device, etc.
[29] Inside the melter 10, there is provided a stirrer 13 for stirring the resin mixture. The stirrer 13 serves to assist melting of the resin mixture and break and mix evenly the impurities contained in the resin mixture. In the present invention, it is preferred that the impurities contained in the resin mixture are broken and distributed evenly since the impurities are strongly adhered to the thermoplastic resins.
[30] The resin mixture heated to a temperature level exceeding the melting temperature thereof is provided with a fluidity, and a resultant fluent liquid phase resin mixture is delivered to a storage tank 20 along a pipeline 14. Here, the fluidity of the fluent liquid phase resin mixture should be high enough so that the mixture can be pumped through the pipeline 14. The pipeline 14 is equipped with a heating element for fluidity retention of the fluent liquid phase resin mixture during delivery through the pipeline 14. The pipeline 14 is also equipped with a valve 15 for controlling flow of the fluent liquid phase resin mixture.
[31] (Storage tank)
[32] The storage tank 20 of the present invention temporarily stores and homogenizes the fluent liquid phase resin mixture. The storage tank 20 is also equipped with a heater for fluidity retention of the fluent liquid phase resin mixture.
[33] It would be desirable to keep stirring the fluent liquid phase resin mixture in the storage tank 20 with the stirrer 21 so as to prevent the impurities distributed all throughout the fluent liquid phase resin mixture from being agglomerated. Further, it would be desirable to control the temperature of the fluent liquid phase resin mixture in such a manner that the resin mixture has a viscosity appropriate to a centrifugal separation. The fluent liquid phase resin mixture in the storage tank 20 is delivered to a centrifugal separator 30 through a pipeline 22 equipped with a heating element.
[34] (Centrifugal separator)
[35] The centrifugal separator 30 of the present invention comprises, at least, a rotary body 32, a motor 33 for driving the rotary body 32, and a collector 31 for collecting thermoplastic resins in a powder or fibrous form. The fluent liquid phase resin mixture delivered to the centrifugal separator 30 through the pipeline 22 is injected to the rotary body 32 from a nozzle 34. In the present invention, the rotary body 32 is embodied into a conical form with a cut top end, however, a disc type rotary body 321, a multi- blade type rotary body 322, and a cup type rotary body 323 shown in Fig. 3, 4 and 5 can be also employed. The rotary body 32 can be made of any material that resists a high temperature, however, it would be preferable to make the rotary body 32 from stainless steel or ceramics.
[36] The fluent liquid phase resin mixture injected to the center of the rotary body 32 which rotates at a high speed is applied with centrifugal force. Whereby, impurities having a relatively larger specific gravity fall, in a powder form, beneath the rotary body, and the thermoplastic resins having a relatively smaller specific gravity float, in a powder or fibrous form, over the rotary body.
[37] The fluent liquid phase resin mixture has a high viscosity, and therefore, extremely large centrifugal force is required to separate impurities from the high viscosity resin mixture. The inventor of the present invention has devised a method of permitting impurities having a relatively larger specific gravity to fall beneath the rotary body and the thermoplastic resins having a relatively smaller specific gravity to float over the rotary body.
[38] The inventor of the present invention has studied methods of separating thermoplastic resins and impurities from a fluent liquid phase resin mixture with ease, and found that impurities will fall beneath a rotary body since the impurities having a sold phase in a fluent liquid phase resin mixture will keep the same phase even when they are separated from the resin mixture. The inventor also has discovered that thermoplastic resins in a powder or fibrous form will float over the rotary body if it is possible to control the viscosity of the fluent liquid phase resin mixture, injection pressure and/or injection quantity of the fluent liquid phase resin mixture from a nozzle, and centrifugal force of a rotary body.
[39] The inventor has demonstrated that impurities fall beneath the rotary body and the thermoplastic resins float over the rotary body because impurities, such as mud (specific gravity of approximately 2.8) and aluminum (specific gravity of ap- proximately 2.7) have a relatively larger specific gravity and thermoplastic resins, which are separated in a powder or fibrous form, have a relatively smaller specific gravity (say, 0.9 to 1.5 depending on the type of resin).
[40] The rotary body as used in the present invention means a device which allows the fluent liquid phase resin mixture injected thereto to be separated into solid phase thermoplastic resins and solid phase impurities at the moment when the resin mixture contacts the surface of the rotary body.
[41] Thermoplastic resins separated in a powder or fibrous form float over the rotary body which rotates at a high speed, and the floating thermoplastic resins can be collected by the collector 31, to thereby separate thermoplastic resins and impurities from the fluent liquid phase resin mixture in an efficient manner. The collector 31 shown in Fig. 1 collects thermoplastic resins through a vacuum collecting system using a vacuum suction means. However, the collector 31 is not limited to a specific type as long as it can collect thermoplastic resins in a powder or fibrous form. The collector 31 using a vacuum suction means collects thermoplastic resins through a suction port thereof at a vacuum state.
[42] Although the viscosity of the fluent liquid phase resin mixture is a function between the temperature and composition of the resin mixture, the viscosity of the resin mixture is adjusted through the control of the temperature of the resin mixture in the present invention. This is because it is difficult to control the composition of the resin mixture due to the properties of wastes. The temperature of the fluent liquid phase resin mixture can be controlled by a heating element installed in the melter 10, storage tank 20, or the pipeline 22, or by other well-known methods. In the present invention, the temperature of the resin mixture is controlled to adjust the viscosity of the resin mixture to 3 to lOcps, which falls to the viscosity level of the ink used in a fountain pen.
[43] The fluent liquid phase resin mixture is injected to the rotary body, and the injection pressure and/or injection quantity of the fluent liquid phase resin mixture can be adjusted through the control of a pump (not shown) or the nozzle 34. The centrifugal force of the rotary body is a function between the diameter and RPMs of the rotary body. However, the centrifugal force of the rotary body can be adjusted through the control of RPMs, since the diameter of the rotary body is generally fixed. The present invention uses a disc having a diameter of 200mm.
[44] Ambient temperature around the rotary body may affect the degree of crystallization of thermoplastic resins in a powder or fibrous form floating over the rotary body. Note that, ambient temperature around the rotary body is kept at room temperature since the present invention is focused on removing impurities from a thermoplastic resin mixture. [45] The viscosity of the fluent liquid phase resin mixture, the injection pressure and/or injection quantity of the resin mixture injected to the rotary body and the centrifugal force of the rotary body can be controlled through a controller 38. In the present invention, the controller 38 may be provided to each member to individually control the viscosity, injection pressure and/or injection quantity, and centrifugal force, or a integrated controller can be installed for the whole system. Control operation of the present invention includes manual adjustment of the injection pressure and/or injection quantity.
[46] The present invention may include a surveillance camera 37 and a monitor (not shown) for monitoring separation of thermoplastic resins and impurities. If the monitoring results in a poor separation of the thermoplastic resins and impurities, the controller 38 controls the separation.
[47] The thermoplastic resin in a powder or fibrous form floating over the rotary body 32 may include a plurality of thermoplastic resins which are collected by the collector 31. In addition, a valve 36 arranged below the centrifugal separator 30 collects impurities in a powder form falling at a high speed beneath the rotary body 32.
[48] (Resin storage tank)
[49] Thermoplastic resin in a powder or fibrous form is collected by a collector 31 and delivered to a resin storage tank 40 through a pipeline 35. The collected thermoplastic resin is used as a raw material in the form of a powder or fiber for producing plastics or films in accordance with an injection molding system. Therefore, thermoplastic resin collected in a powder or fibrous form according to the present invention can be used as recycling material without any additional treatment.
[50] (Melt extruder and etc.)
[51] In the case where a material in pellet form is needed, resin in a powder or fibrous form is delivered to a melt extruder 50 through a pipeline 42. Resin extruded by the melt extruder 50 passes through a cooler 60, and is cut into a reusable form, for example, pellets, by a cutter 70. Thus-produced pellets are delivered to a pellet storage tank 80 through a pipeline 71, and stored therein. Here, reference numeral 41 denotes a valve.
[52] Hereinafter, a method of separating one or more thermoplastic resins and impurities from a resin mixture by using the recycling apparatus of the present invention will be discussed in detail.
[53] Embodiment 1
[54] In general, agricultural film is made from low density polyethylene (LDPE), however, mulching film is made from high density polyethylene (HDPE) in many cases. In addition, high density polyethylene (HDPE) is typically black, due to the use of carbon as pigment. Mulching film is arranged to cover the soil, and therefore, mud adheres strongly to the surface of the mulching film as if the film is coated with mud. Further, mulching film is mixed with sand, iron debris, water, and the like during collection.
[55] The collected mulching film is cut into a predetermined size, and a pre-process is performed to remove sand, iron debris and the like from the film. Iron debris can be removed by using a magnet, and sand can be removed by disposing the film on a rack and vibrating the rack. The pre-process can be omitted in accordance with the condition of the collected mulching film.
[56] Subsequent to the pre-process, the mulching film is injected in the melter 10 and melted therein. In embodiment 1, the mulching film is put inside the melter and melted by the raised temperature in the melter while being stirred by the stirrer 13. Here, the mulching film is melted into a liquid, and mud on the film is crushed and mixed with the liquid mulching film.
[57] Polyethylene which constitutes a mulching film has a melting temperature of approximately 100°C to 1350C, however, it is preferred that the heating temperature of the film is as high as possible within the range lower than the inflammable point thereof so as to provide the molten film with a fluidity.
[58] The molten mulching film with a fluidity (hereinafter, referred to as a "fluent liquid phase resin mixture") is delivered to the centrifugal separator 30 and centrifugally separated.
[59] In embodiment 1, the temperature of the fluent liquid phase resin mixture constituted mainly by polyethylene is adjusted to the range of 1450C to 200°C. Although the fluent liquid phase resin mixture is constituted mainly by polyethylene, it can be mixed with polypropylene or polyethylene terephthalate film because they may be collected from wastes. In this case, the upper limit of the temperature range needs to be raised since the melting temperature of polyethylene terephthalate is higher than that of polyethylene.
[60] In embodiment 1, the temperature of the fluent liquid phase resin mixture is adjusted such that the viscosity thereof becomes 3 to lOcps. The resin mixture is more suited to a centrifugal separation when the viscosity of the fluent liquid phase resin mixture becomes lower. However, since molten resin has a high viscosity, and the temperature of the resin mixture should be raised in order to lower the viscosity of the fluent liquid phase resin mixture, it is desirable that the lower limit of the viscosity is 3cps. Meanwhile, it is desirable that the upper limit of the viscosity is set to lOcps because it is difficult to separate impurities from the resin mixture or increased RPMs (centrifugal force) of the rotary body is required for separating impurities from the resin mixture if the viscosity of the resin mixture is high.
[61] In embodiment 1, the rotary body 32 having a diameter of 200mm is employed, and the centrifugal force generated from the rotary body is a function of RPMs. In embodiment 1, the RPMs of the rotary body range from 2,000 to 20,000RPMs, desirably 5,000 to 20,000RPMs, and more desirably 10,000 to 20,00OsRPM. The RPMs of the rotary body are adjusted in such a manner that impurities are separated from the fluent liquid phase resin mixture and the thermoplastic resin in a powder or fibrous form floats over the rotary body. Although polyethylene in a fine powder form can be obtained as the RPMs of the rotary body increases, it is desirable to set the upper limit of the RPMs of the rotary body to 20,000RPMs in consideration of safety and maintenance of the rotary body.
[62] In embodiment 1, the fluent liquid phase resin mixture is injected to the rotary body
32 from the nozzle 34, and the injection pressure ranges from 3 to 5kgf/cm2. The nozzle 32 has a diameter that is not specifically limited, however, it is preferable that the diameter of the nozzle is 10 to 40mm considering that the diameter of the rotary body is 200mm. The injection quantity of the fluent liquid phase resin mixture injected to the rotary body is set to 5 to 20L/min, since the injection quantity is a function between the diameter of the nozzle and the injection pressure and directly affects the yield of the thermoplastic resin.
[63] In embodiment 1, ambient temperature around the rotary body is kept at room temperature so as to obtain the thermoplastic resin in a powder or fibrous form.
[64] Embodiment 2
[65] In general, multilayer film is made of film consisting of thermoplastic resins including polyethylene terephthalate, polypropylene and polyethylene, and a thin metal (for example, aluminum) layer coated between the films. The multilayer film can be mixed with foodstuff, sand, iron debris as well as mud during collection.
[66] The pre-process and the melting process are substantially identical with those of embodiment 1, and the description thereof will be omitted.
[67] Polyethylene terephthalate, polypropylene and polyethylene which constitute the multilayer film have respective melting temperatures of approximately 100°C to 1350C, approximately 1550C to 165°C, and approximately 2450C to 275°C, however, it is preferred that the melting temperature is as high as possible within the range lower than the inflammable point thereof so as to provide the molten film with a fluidity. The multilayer films collected from wastes may be mixed with a variety of types of films. In a case where diverse films are mixed together, the film mixture should be heated at the temperature higher than that of the film with the highest melting temperature.
[68] The molten multilayer film with a fluidity (hereinafter, referred to as a "fluent liquid phase resin mixture") is delivered to the centrifugal separator 30 by a pump and is then centrifugally separated.
[69] In embodiment 2, the temperature of the fluent liquid phase resin mixture constituted mainly by polyethylene is adjusted to the range of 1450C to 200°C. If the resin mixture is constituted mainly by polypropylene, the temperature of the resin mixture is adjusted to the range of 18O0C to 22O0C. If the resin mixture is constituted mainly by polyethylene terephthalate, the temperature of the resin mixture is adjusted to the range of 280°C to 320°C. If the resin mixture is mixed with PE, PP and PET, the temperature range is adjusted to a suitable level.
[70] The rest of the process is substantially the same as that of embodiment 1, and description thereof will be omitted.
[71] Although the description of the present invention has been provided according to the above-described embodiments, various modifications and changes may be made as would be obvious to a person skilled in the art.
[72] That is to say, although the invention described above is embodied in mulching films, other equivalents, for example, agricultural film or industrial film can be recycled by the present invention. In addition, although the invention is embodied in multilayer films, it is obvious that the present invention is also applicable to single layer films and films coated with no metals. Further, the present invention is applicable to products in which metals are coated to thermoplastic resins in a plate form, sheet form or agglomerate form.
[73] Although the present invention has been explained in relation to one or more thermoplastic resins that melt at a high temperature, however, it can also be explained in relation to thermosetting resins that are not thermally decomposed at the melting point of thermoplastic resins. In addition, it is obvious that the present invention is applicable to thermoplastic resins in an agglomerate form.
[74] It should be noted that although the present invention employs centrifugal separation using a rotary body in order to separate thermoplastic resins and impurities in a convenient and economically advantageous manner, other types of centrifugal separation used for separating materials into solid phase material and solid phase impurities belong to the claimed scope of the present invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example and that it should not be taken as limiting the present invention as defined by the following claims.
[75]

Claims (7)

  1. Claims
    [1] A method for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, the method comprising: heating the resin mixture to form a fluent liquid phase resin mixture; injecting the fluent liquid phase resin mixture to a rotary body; separating the thermoplastic resins and impurities from each other by floating the thermoplastic resins over the rotary body and permitting the impurities to fall beneath the rotary body; and collecting the thermoplastic resins.
    [2] The method of claim 1, wherein the separating is carried out by adjusting the centrifugal force of the rotary body, viscosity of the fluent liquid phase resin mixture, and injection quantity of the resin mixture injected to the rotary body.
    [3] The method of claim 1 or claim 2, wherein the viscosity of the fluent liquid phase resin mixture is 3 to lOcps.
    [4] The method of claim 1 or claim 2, wherein the thermoplastic resins separated and collected are in a powder or fibrous form.
    [5] The method of claim 1 or claim 2, wherein the rotary body has one of shapes comprising a conical shape with a cut top end, a disc shape, a cup shape, and a multi-blade shape.
    [6] An apparatus for recycling one or more thermoplastic resins from a resin mixture containing one or more thermoplastic resins and impurities, the apparatus comprising: a melter for heating and stirring the thermoplastic resins and raising the temperature of the thermoplastic resins to a level higher than a melting point thereof in order to acquire a fluent liquid phase resin mixture; a centrifugal separator for separating the thermoplastic resins and the impurities from each other from the fluent liquid phase resin mixture by floating the thermoplastic resins over a rotary body and permitting the impurities to fall beneath the rotary body; a controller for controlling the centrifugal force of the rotary body, viscosity of the fluent liquid phase resin mixture, and injection quantity of the mixture injected to the rotary body; and a collector for collecting the thermoplastic resins, wherein the controller controls the centrifugal force, viscosity and quantity of the mixture to acquire thermoplastic resins in a powder or fibrous form.
    [7] The apparatus of claim 6, wherein the rotary body has one of shapes comprising a conical shape with a cut top end, a disc shape, a cup shape, and a multi-blade shape.
PCT/KR2009/002847 2009-05-28 2009-05-28 Method and apparatus for recycling thermoplastic resin from a resin mixture WO2010137756A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111361051A (en) * 2020-03-23 2020-07-03 杭州帮贡科技有限公司 Plastic part recycling density grading device based on centrifugal principle

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH09220721A (en) * 1995-12-13 1997-08-26 Ain Eng Kk Method for recovery and pelletizing of discarded resin packaging container and apparatus therefor
KR100245206B1 (en) * 1992-03-31 2000-02-15 오노 알버어스 Process for the removal of foreign materials from a post-consumer polyethylene terephthalate feed stream
JP2002180068A (en) * 2000-12-14 2002-06-26 Hoshun Tei Apparatus for forming waste plastic into oil
JP2004188695A (en) * 2002-12-10 2004-07-08 Tanaka:Kk Method for recycling waste polyolefins and system therefor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100245206B1 (en) * 1992-03-31 2000-02-15 오노 알버어스 Process for the removal of foreign materials from a post-consumer polyethylene terephthalate feed stream
JPH09220721A (en) * 1995-12-13 1997-08-26 Ain Eng Kk Method for recovery and pelletizing of discarded resin packaging container and apparatus therefor
JP2002180068A (en) * 2000-12-14 2002-06-26 Hoshun Tei Apparatus for forming waste plastic into oil
JP2004188695A (en) * 2002-12-10 2004-07-08 Tanaka:Kk Method for recycling waste polyolefins and system therefor

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111361051A (en) * 2020-03-23 2020-07-03 杭州帮贡科技有限公司 Plastic part recycling density grading device based on centrifugal principle

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