Method for recycling of extruder filter for plastics

Abstract

The present invention relates to a method for regenerating a filter of an extruder that forms waste polymer into pellets, comprising the steps of: introducing the filter into a first high-temperature chamber; raising the temperature of the first high-temperature chamber to a first temperature; maintaining the first high-temperature chamber at the first temperature; cooling the first high-temperature chamber to room temperature and discharging the filter; introducing the discharged filter into a second high-temperature chamber; raising the temperature of the second high-temperature chamber to a second temperature; maintaining the second high-temperature chamber at the second temperature; cooling the second high-temperature chamber to room temperature and discharging the filter; and removing carbonized polymer attached to the discharged filter, wherein the first temperature is in the range of the melting point of the waste polymer to the melting point plus 100°C, and the second temperature is in the range of the ignition temperature of the waste polymer to the ignition temperature plus 100°C.

Description

Technology Field

[0001] The present invention relates to a method for regenerating a waste plastic extruder filter, and more specifically, to a method for regenerating a waste plastic extruder filter that enables the filter to be reused by opening through holes in an extruder filter that have been clogged with foreign substances. Background Technology

[0002] Recently, there has been growing interest in the recycling of waste polymers such as vinyl and PET bottles. The recycling and reuse of waste vinyl and plastics is very important from the perspectives of preventing the depletion of limited petroleum resources and preventing environmental pollution caused by waste resources.

[0003] In order for such waste polymers to be regenerated and for regeneration to be carried out efficiently, not only must waste resources be separated and disposed of, but the inclusion of foreign substances in the waste resources must also be minimized. The process of removing foreign substances from waste resources is carried out in various ways, and Figure 1 shows an example of a method for regenerating waste vinyl. Referring to Figure 1, raw materials such as waste vinyl are collected, and the collected waste materials are washed while floating in water. The washed waste materials are dried and compressed, and then regenerated into the form of plastic pellets through an extrusion molding process.

[0004] An extruder is used in this pellet-form recycling process. An extruder is a device that feeds plastic raw materials into a hopper, heats and melts the feedable materials, and forms them by applying pressure with a screw to extrude the molten material through a nozzle.

[0005] Korean Published Patent No. 2019-0056596 is a prior art regarding an extruder for producing recycled plastic. The aforementioned prior art discloses an extrusion die for producing recycled plastic raw materials, characterized by comprising: a support frame; a main body block installed on the upper part of the support frame through which molten resin is introduced and discharged; a sub-block coupled to the side of the main body block and having a connecting port formed therein through which molten resin passing through the main body block is introduced; a drum installed vertically through the sub-block and having a perforation formed on its side to allow molten resin passing through the connecting port to flow into it; a nozzle unit installed on one side of the support frame; a transfer unit that pressurizes the molten resin introduced into the interior of the drum and transfers it to the nozzle unit; a main filter unit for filtering out foreign substances in the molten resin introduced into the interior of the drum; a roll screen having a mesh structure installed to pass between the connecting port and the drum and covering one side of the perforation port; and a winding unit that winds one side of the roll screen and moves the roll screen by a certain length.

[0006] These plastic recycling extruders are equipped with a filter commonly referred to as a die mesh. This die mesh functions to filter out foreign substances contained in the recycled raw material, ensuring that the recycled pellets produced through molding do not contain such substances.

[0007] These die meshes have multiple through holes formed in a disc-shaped plate having a predetermined thickness; however, as usage time increases, foreign matter gets stuck in the through holes, and waste polymer hardens around the foreign matter, rendering the device unusable.

[0008] Through holes in die meshes are typically formed via laser processing; however, due to the high cost of laser processing, there is a great need to develop technology that allows worn-out die meshes to be regenerated and reused. The problem to be solved

[0009] Accordingly, the problem to be solved by the present invention is to provide a method for regenerating a waste polymer extruder filter that enables the reuse of the die mesh by removing foreign substances and / or solidified plastic attached to the filter penetration holes, which are the die mesh included in the waste plastic extruder. means of solving the problem

[0010] To achieve the above objective, the present invention provides a method for regenerating a filter of an extruder that forms waste polymer into pellets, comprising the steps of: introducing the filter into a first high-temperature chamber; raising the temperature of the first high-temperature chamber to a first temperature; maintaining the first high-temperature chamber at the first temperature; cooling the first high-temperature chamber to room temperature and discharging the filter; introducing the discharged filter into a second high-temperature chamber; raising the temperature of the second high-temperature chamber to a second temperature; maintaining the second high-temperature chamber at the second temperature; cooling the second high-temperature chamber to room temperature and discharging the filter; and removing carbonized polymer attached to the discharged filter, wherein the first temperature is in the range of the melting point of the waste polymer to the melting point plus 100°C, and the second temperature is in the range of the ignition temperature of the waste polymer to the ignition temperature plus 100°C.

[0011] According to one embodiment of the present invention, vibration can be applied to the filter in the step of maintaining the first high-temperature chamber at a first temperature.

[0012] According to another embodiment of the present invention, the filter has a through hole formed in a plate-shaped body in a direction penetrating the plate, and the vibration may consist of a first vibration application step applied in the thickness direction of the plate and a second vibration application step applied in the horizontal plane direction of the plate.

[0013] According to another embodiment of the present invention, the step of removing the carbonized polymer attached to the discharged filter can be performed in a sandblasting chamber. Effects of the invention

[0014] The method for regenerating waste plastic extruder filters of the present invention has the following effects.

[0015] 1. By heating the plastic material attached to the filter's through-hole along with foreign substances only to near the melting point and discharging it outside the through-hole, the plastic is prevented from carbonizing and adhering inside the through-hole.

[0016] 2. During the process of melting plastic raw materials and removing them from the through hole, vibration is applied to the filter so that foreign substances and plastic raw materials can be easily removed from the through hole.

[0017] 3. Vibrations applied to the filter are applied in stages in the thickness direction of the filter and in the direction perpendicular thereto, so that the removal of foreign substances and molten plastic can be easily achieved.

[0018] 4. Some of the plastic that is melted and removed remains at the bottom of the through hole. By heating the plastic raw material to a flash point and carbonizing it, the removal of carbonized material due to physical impact is made easier. Brief explanation of the drawing

[0019] Figure 1 shows the step-by-step process of recycling waste vinyl into plastic pellets. Figure 2 is a drawing illustrating the configuration of an extruder for pellet molding. Figure 3 shows the die mesh of an extruder. Figure 4 shows the cleaning process of a conventional die mesh. Figures 5 and 6 are drawings to explain the process of carbonized plastic remaining inside the through hole during a conventional die mesh cleaning process. FIGS. 7 and FIGS. 8 are drawings for explaining the die mesh cleaning process of the present invention. FIG. 9 is a diagram illustrating the process of carbonized plastic being formed outside the through hole during the die mesh cleaning process of the present invention. Specific details for implementing the invention

[0020] The present invention relates to a method for regenerating a filter of an extruder that forms waste polymer into pellets, comprising the steps of: introducing the filter into a first high-temperature chamber; raising the temperature of the first high-temperature chamber to a first temperature; maintaining the first high-temperature chamber at the first temperature; cooling the first high-temperature chamber to room temperature and discharging the filter; introducing the discharged filter into a second high-temperature chamber; raising the temperature of the second high-temperature chamber to a second temperature; maintaining the second high-temperature chamber at the second temperature; cooling the second high-temperature chamber to room temperature and discharging the filter; and removing carbonized polymer attached to the discharged filter, wherein the first temperature is in the range of the melting point of the waste polymer to the melting point plus 100°C, and the second temperature is in the range of the ignition temperature of the waste polymer to the ignition temperature plus 100°C.

[0021] The present invention will be described in detail below using the drawings.

[0022] Extruders used in the recycling process of waste plastics include filters to remove foreign substances contained in the waste raw materials. These filters are generally referred to as die meshes and are installed inside the extruder.

[0023] FIG. 2 is a diagram illustrating the configuration of an extruder for pellet molding. Referring to FIG. 2, raw materials such as waste plastic are fed into a hopper formed at one end of the extruder. The fed raw materials are heated above the melting point of the plastic and are conveyed by a rotating screw while under pressure in the direction in which pellet molding takes place. At this time, a filter is installed in the heating zone where extrusion takes place to remove foreign substances contained in the waste raw materials.

[0024] FIG. 3 illustrates a die mesh of an extruder. Referring to FIG. 3, a filter (100), referred to as a die mesh, comprises a disc-shaped body (110) having a predetermined thickness and a plurality of through holes (120) formed in the thickness direction of the body. The body may be made of steel and generally has a thickness of about 6.8 mm. The through holes may be configured with different diameters at the top and bottom; typically, the upper diameter d1 is 1.5 mm and the lower diameter d2 is 0.5 to 0.8 mm. The thickness of the body is sufficient to withstand the pressure inside the extruder, and the diameter of the through holes is sufficient for removing foreign substances. The through holes must be formed in multiple numbers for productivity and extruder durability, and preferably, they are formed at intervals with a pitch of 2 mm.

[0025] Considering the filter body material and the aspect ratio of the through holes, the through holes must be machined by laser processing rather than physical drilling. However, the process of forming multiple through holes in a steel body is costly and causes the price of the die mesh to rise.

[0026] If foreign matter gets stuck in the through holes during the process of using the die mesh in the extruder, the molten plastic material solidifies along with the foreign matter and fills the inside of the through holes; if such clogging of the through holes becomes frequent, the die mesh can no longer be used.

[0027] A conventional method for regenerating a die mesh is illustrated in FIG. 4. Referring to FIG. 4, the cleaning process for regenerating the die mesh consists of a first cleaning, a second cleaning, and a third cleaning. In the first cleaning, the die mesh is placed in a first high-temperature chamber, heated to approximately 500°C and left for 4 hours, cooled to room temperature, and discharged. The outer surface of the die mesh is then physically cleaned by wire brushing or grinding. In the second cleaning, the die mesh cleaned in the first cleaning is placed in a second high-temperature chamber and heated to 470°C. The second high-temperature chamber contains sand particles, and cleaning is performed as the moving sand particles collide with the die mesh. The third cleaning includes a chemical treatment such as hydrochloric acid and a final cleaning step using high-pressure water.

[0028] This conventional die mesh cleaning process has the problem that plastic raw materials remain carbonized inside the through holes. This problem is because the heating temperature of the first high-temperature chamber is close to the ignition point of general waste plastics; commonly used waste vinyl materials, such as polyethylene, have an ignition temperature of 349°C, polypropylene 570°C, polyvinyl chloride 454°C, and polystyrene 491°C. Therefore, the heating temperature of 500°C in the first cleaning process of the conventional technology exceeds the ignition point of most waste vinyl materials.

[0029] When plastic reaches a temperature above its ignition point under air conditions, it ignites, and some of it is blown away in the form of carbon dioxide and water, while some is carbonized and remains on the die mesh in the form of charcoal. If the carbonized material adheres to the surface of the die mesh body, it is easy to remove, but if the carbonized material remains inside the through hole, it becomes very difficult to remove.

[0030] Figures 5 and 6 are diagrams illustrating the process of carbonized plastic remaining inside the through hole during a conventional die mesh cleaning process. Although Figure 5 shows the diameter of the through hole decreasing as it goes down, cleaning can also be performed by flipping the through hole upside down to facilitate the discharge of foreign matter.

[0031] Referring to FIG. 5 (a), the polymer foreign material (200) discharged into the through hole (120) formed in the body (110) of the filter may be formed such that the plastic, formed by melting and cooling together with contaminants attached to the waste material, is trapped inside the through hole by the foreign material. Referring to FIG. 5 (b), the foreign material heated in the first high-temperature chamber is discharged outside the through hole in the form of molten polymer (210) as the plastic melts, but some remains inside the through hole in the form of carbonized polymer (220). Although this carbonized polymer may not completely block the through hole, it may cause problems such as reducing the diameter of the through hole and allowing some of the carbonized polymer to mix in toward the nozzle, and consequently shortening the lifespan of the die mesh.

[0032] Figure 6 is a diagram illustrating the process occurring in the first high-temperature chamber. When the first high-temperature chamber begins to heat up at room temperature, it reaches α°C, the melting point of the plastic raw material, at some point, and then, as it is further heated, it reaches a temperature exceeding β°C, the ignition point of the plastic raw material. Therefore, the first high-temperature chamber passes through a section where the plastic material melts and a section where carbonization occurs along with melting as time progresses. At this time, the plastic material that is not discharged outside the through-hole during the melting section ignites or carbonizes inside the through-hole and becomes firmly bonded to the inner wall.

[0033] The die mesh cleaning process of the present invention is characterized by a configuration in which, during the first cleaning process, the temperature of the first high-temperature chamber is limited to the range of the melting point of the waste polymer to the melting point plus 100°C, thereby ensuring that only the plastic melts and does not undergo carbonization. Additionally, a characteristic feature is a configuration in which vibration is applied to the die mesh in the first high-temperature chamber to facilitate the easy discharge of the molten plastic to the outside of the through hole. Furthermore, a characteristic feature is a configuration in which the vibration is applied stepwise in the thickness direction and the horizontal direction of the die mesh. The plastic that is melted and discharged to the outside of the through hole during the first cleaning process remains partially at the bottom; the remaining plastic is carbonized during the second cleaning process and can be easily removed by physical methods such as wire brushing, sandblasting, or grinding. More preferably, the heating temperature of the first high-temperature chamber may be the melting point plus 50°C. From another perspective, the heating temperature of the first high-temperature chamber may be from the melting point to the ignition point, and more preferably from the melting point + 50°C to the ignition point, and the heating temperature of the second high-temperature chamber may be from the ignition point to the ignition point + 100°C.

[0034] The die mesh cleaning process of the present invention is described in detail below using the drawings.

[0035] FIGS. 7 and FIGS. 8 are drawings illustrating the die mesh cleaning process of the present invention. Although FIG. 7 shows the diameter of the through hole decreasing as it goes down, cleaning may also be performed by flipping the through hole upside down to facilitate the discharge of foreign substances.

[0036] Referring to FIG. 7(a), the polymer foreign substance (200) discharged into the through hole (120) formed in the body (110) of the filter may be formed in a manner where plastic, formed by melting and cooling together with contaminants attached to the waste material, is trapped inside the through hole by the foreign substance. Referring to FIG. 7(b), the waste polymer is melted and discharged outside the through hole in a first high-temperature chamber heated to a range of the melting point of the waste polymer to the melting point plus 100°C. At this time, vibration may be applied to the die mesh to facilitate the discharge of the molten polymer. As can be seen in FIG. 8, the first high-temperature chamber is heated only to the melting point of the waste polymer, α°C, or to a temperature of the melting point plus 100°C (not shown in the drawing), so only the melting of the polymer occurs and carbonization does not occur.

[0037] An additional component that facilitates the easy discharge of molten plastic to the outside of the through-hole is vibration applied to the die mesh. Vibration can be applied in stages along the thickness direction of the die mesh and in a direction perpendicular thereto; the former vibration facilitates the removal of contaminants trapped inside the through-hole, while the latter vibration facilitates the downward discharge of molten plastic within the through-hole. Vibration can be implemented through various methods, such as connection with an eccentric rotating body or the application of ultrasonic waves.

[0038] FIG. 9 is a diagram illustrating the process of carbonized plastic being formed outside the through hole during the die mesh cleaning process of the present invention.

[0039] The plastic that is melted in the first high-temperature chamber and discharged outside the through hole adheres to the bottom of the through hole due to surface tension. When this plastic is carbonized, it is transformed into a material that crumbles easily under physical impact and can be easily removed by physical cleaning methods such as wire brushing, sandblasting, and grinding. Figures 9 (a) and 9 (b) respectively show the polymer attached to the bottom of the through hole after melting and the carbonized polymer.

[0040] The above description explains the technical concept of the present invention using one embodiment, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiment described in the present invention is intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiment. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0041] 100 : Filter 110 : Body 120 : Through hole 200 : Polymer foreign substance 210: Molten polymer 220: Carbonized polymer

Claims

Claim 1 A method for regenerating a filter of an extruder that forms waste polymer into pellets, comprising the steps of: introducing a filter, having a plurality of through holes formed in the thickness direction in a disc-shaped body made of steel, into a first high-temperature chamber; raising the temperature of the first high-temperature chamber to a range of the melting point of the waste polymer to the melting point plus 100°C; maintaining the first high-temperature chamber at the range of the melting point of the waste polymer to the melting point plus 100°C to melt the waste polymer attached inside the through holes and discharging it from the through holes; cooling the first high-temperature chamber to room temperature and discharging the filter; introducing the discharged filter into a second high-temperature chamber; raising the temperature of the second high-temperature chamber to a second temperature of the ignition temperature of the waste polymer plus 100°C; maintaining the second high-temperature chamber at the second temperature of the ignition temperature of the waste polymer plus 100°C to carbonize the waste polymer attached to the filter; cooling the second high-temperature chamber to room temperature and discharging the filter. A method for regenerating a waste polymer extruder filter comprising: a step of removing carbonized polymer attached to the discharged filter by wire brushing, sandblasting, or grinding; and a step of maintaining the first high-temperature chamber in the range of the melting point of the waste polymer to the melting point + 100°C to melt the waste polymer attached inside the through hole and discharge it from the through hole, wherein the diameter of the through hole decreases along the thickness direction of the plate, and the melted waste polymer is discharged along the direction in which the diameter of the through hole decreases. Claim 2 A method for regenerating a waste polymer extruder filter according to claim 1, characterized by applying vibration to the filter in the step of maintaining the first high-temperature chamber at a first temperature. Claim 3 A method for regenerating a waste polymer extruder filter according to claim 2, characterized in that the vibration comprises a first vibration application step applied in the thickness direction of the plate and a second vibration application step applied in the horizontal plane direction of the plate. Claim 4 A method for regenerating a waste polymer extruder filter according to claim 1, characterized in that the step of removing the carbonized polymer attached to the discharged filter is performed in a sandblasting chamber.

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