Method for preparing recycled abs resin

Abstract

A method for manufacturing recycled ABS resin is provided, the method comprising: preparing an extrusion feed comprising an acrylonitrile-butadiene-styrene (ABS) base resin containing polyurethane, a metal carboxylate, and a polyol; and supplying the extrusion feed to an extruder to carry out a depolymerization reaction of the polyurethane and extruding the extrusion feed.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0036336, filed on March 23, 2022, the entire contents of which are incorporated herein as a part of this specification.

[0003] The present invention relates to a method for producing recycled resin (particularly, recycled ABS resin). Prior Art

[0004] The use of plastics has recently increased due to the development of plastics with desirable physical properties for various uses and purposes. Generally, the production of plastics, from crude oil extraction to production, consumes significant amounts of energy and emits significant carbon emissions. Furthermore, when the final product is discarded, along with the plastics contained within, the resulting environmental pollution from the plastics and their disposal incurs social costs. Therefore, recycling discarded plastics is essential to reduce energy consumption, carbon emissions, and environmental pollution. Plastics made from plastics discarded after final consumer use are known as post-consumer recycled (PCR) resins, and efforts to obtain PCR resins with the desired purity and physical properties continue.

[0005] Meanwhile, acrylonitrile butadiene styrene (ABS) resin, a copolymer of acrylonitrile, butadiene, and styrene, is more impact-resistant and heat-resistant than conventional plastics. It is also a plastic material that easily achieves aesthetically pleasing and diverse colors. As a result, it is widely used in products such as home appliances, office equipment, automotive interior and exterior materials, and toys. Due to the increasing number of products using ABS resin, the use of ABS resin has increased rapidly in recent years. Consequently, when products using ABS resin are discarded, the demand for recycling the waste ABS resin included in the products has also increased.

[0006] Methods for recycling waste plastics (resins) include mechanical recycling, chemical recycling, and thermal recycling. Mechanical recycling involves crushing and selecting collected waste plastics, separating them by type, melting them to form pellets, and then mixing them with new materials in specific proportions to produce resin products. Chemical recycling uses various chemical methods to extract only specific polymers from waste plastics, or to collect and repolymerize pure single molecules. Thermal recycling involves burning waste plastics to recover the plastics as heat energy.

[0007] When waste ABS resin is processed through mechanical recycling methods, it's difficult to separate waste plastics of a single type. Waste plastics are typically separated by type using a range of methods, such as gravity separation, optical selection / separation, fine selection, and step-by-step magnetic selection. However, the separated and selected plastics often contain 1 to 5% foreign matter. This foreign matter consists of various components, such as paper, ceramics, various types of plastics, carbides, metallic foreign matter, and dust. When waste ABS resin containing various impurities is melted at high temperatures and pelletized, the impurities can cause deformation of the recycled resin or the resulting PCR resin, or deterioration of physical properties, such as surface quality. In particular, in the case of recycled ABS resin obtained from large household appliances such as washing machines and refrigerators, adhesives such as urethane insulation materials cannot be separated, leading to deterioration of surface properties. Chemical recycling involves modifying the molecular structure of the recycled plastic itself to recover it as raw material. However, the reactions and methods involved in further modifying the already bonded molecular structure of terpolymer ABS resin are difficult.

[0008] Therefore, there has been a need to prepare recycled ABS resins whose physical properties are not deteriorated compared to virgin ABS resins before being used in products. Summary of the Invention

[0009] [Technical Issues] []

[0010] To solve the problems mentioned in the prior art, an object of the present invention is to provide a method for producing an improved recycled ABS resin, wherein the appearance characteristics of the recycled ABS resin are almost not deteriorated and deformation is minimized compared to new ABS resin.

[0011] That is, an object of the present invention is to provide a method for preparing recycled ABS resin from ABS base resin by an extruder, which can prevent the surface properties of the recycled ABS resin from being deteriorated by polyurethane and other impurities by utilizing the depolymerization of polyurethane contained in the ABS base resin. [Technical solution]

[0012] In a general aspect, a method for producing recycled ABS resin includes preparing an extrusion feed comprising an acrylonitrile butadiene styrene (ABS) base resin containing polyurethane, a metal carboxylate, and a polyol; and supplying the extrusion feed to an extruder to perform a depolymerization reaction of the polyurethane and extrude the extrusion feed. [Beneficial effects]

[0013] According to the method for producing recycled ABS resin of the present invention, a polyol that is stable under the high temperature and high pressure environment of an extruder is included in the extrusion feed supplied to the extruder, thereby stably performing the depolymerization reaction of the polyurethane contained in the ABS base resin.

[0014] Furthermore, the inclusion of a metal carboxylate in the extrusion feed increases the reaction rate of the depolymerization reaction, thereby achieving the desired degree of depolymerization of the polyurethane despite a short residence time of the extrusion feed in the extruder. Furthermore, the short residence time prevents thermal degradation of the depolymerization reactants, including the ABS resin and additives, and allows for the production of recycled ABS resin with minimal deformation and physical properties equivalent to those of new ABS resin. [Best Mode] []

[0015] Based on the principle that the inventors are able to appropriately define the concepts of the terms in order to describe their own inventions in the best mode, the terms or words used in the disclosure and patent application of the present invention should not be restrictively interpreted as having the meanings defined in general or dictionaries, but should be interpreted as the meanings and concepts that are consistent with the technical concept of the present invention.

[0016] In the present invention, ABS resin or ABS (co)polymer is a general concept, which refers not only to a resin or (co)polymer including units derived from a conjugated diene compound, units derived from an aromatic vinyl compound, and units derived from a vinyl nitrile compound, but also to a resin composition or (co)polymer composition including such a resin or (co)polymer.

[0017] In the present invention, ABS base resin (which is ABS resin separated and recovered from waste products and pre-treated) refers to ABS resin containing impurities or foreign matter. The resin produced from this ABS base resin using the recycled resin production method of the present invention is defined as recycled ABS resin. Furthermore, ABS resin in the form of a mixture of recycled ABS resin and new materials for use in products, or ABS resin to which additives have been added to impart desired physical properties, is referred to as post-consumer recycled-ABS (PCR-ABS) resin.

[0018] Hereinafter, for a better understanding of the present invention, the present invention will be described in more detail.

[0019] A method for producing a recycled ABS resin according to an exemplary embodiment of the present invention may include: preparing an extrusion feed including an acrylonitrile butadiene styrene (ABS) base resin containing polyurethane, a metal carboxylate, and a polyol; and supplying the extrusion feed to an extruder to perform a depolymerization reaction of the polyurethane and extrude the extrusion feed.

[0020] The ABS resin according to the present invention may be a polymer comprising units derived from a conjugated diene compound, units derived from an aromatic vinyl compound, and units derived from a vinyl nitrile compound. For example, the ABS resin can be prepared by graft-polymerizing an aromatic vinyl compound and a vinyl nitrile compound onto a conjugated diene rubber polymer. In this case, the ABS resin may comprise 30 to 60 parts by weight of the aromatic vinyl compound and 10 to 30 parts by weight of the vinyl nitrile compound per 100 parts by weight of the rubber polymer.

[0021] The conjugated diene rubber polymer is preferably one or more selected from the group consisting of butadiene rubber polymers, isoprene rubber polymers, chloroisoprene rubber polymers, and any mixtures thereof. The aromatic vinyl compound is preferably one or more selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, and vinyltoluene, with styrene being more preferred. The vinyl nitrile compound is preferably one or more selected from the group consisting of acrylonitrile, methacrylonitrile, and ethacrylonitrile, with acrylonitrile being more preferred.

[0022] ABS resin possesses excellent properties such as impact strength, tensile strength, elastic modulus, and flame retardancy, and is widely used in household appliances such as refrigerators, automotive parts, and various electrical and electronic components. For example, when ABS resin is used as the material for the interior and exterior frames of refrigerators, a foam-filled polyurethane foam (PU foam) is typically provided in the enclosed space between the outer and inner frames to insulate the frames and maintain a cool temperature within the refrigerator. When products using both ABS resin and polyurethane are discarded and recycled ABS resin is prepared from waste ABS resin, the waste ABS resin and polyurethane are difficult to separate due to their strong adhesion. Foreign matter, such as polyurethane, remaining in the recycled ABS resin can degrade the physical properties of the recycled ABS resin or extruded products made from it. In particular, the product surface may exhibit degraded surface properties, such as uneven gelation or pitting.

[0023] Conventionally, waste ABS is filtered using a mesh to remove foreign matter, such as polyurethane. However, due to the inherent flexibility (flexibility) of polyurethane foam, foreign matter often passes through the mesh, making it impossible to produce highly reliable recycled ABS resin. Consequently, a large amount of new material must be mixed in to maintain the physical properties of the ABS resin, which can be degraded by foreign matter, and the recovery rate of the recycled ABS resin in products is limited.

[0024] Therefore, the present invention aims to provide a method in which a metal carboxylate and a polyol are supplied together to an extruder when an ABS base resin containing foreign substances such as polyurethane is supplied, thereby promoting an efficient depolymerization reaction of the polyurethane and minimizing the influence of the aggregation effect of other foreign substances such as polyurethane, and thus, producing a recycled ABS resin having highly reliable physical properties.

[0025] First, according to an exemplary embodiment of the present invention, an extrusion feed for reactive extrusion can be prepared in an extruder. The extrusion feed can include an acrylonitrile butadiene styrene (ABS) base resin containing polyurethane, a metal carboxylate, and a polyol. For example, the extrusion feed can be a composition comprising an acrylonitrile butadiene styrene (ABS) base resin, a metal carboxylate, and a polyol.

[0026] The ABS base resin is ABS resin in the form required for supply to the extruder. For example, it can be ABS resin in the form of flakes or particles (pellets or fine powder) of appropriate size, from which large foreign matter has been separated and removed. To this end, waste ABS resin can be pretreated as needed to first prepare ABS resin in the form of flakes or particles (pellets or fine powder).

[0027] Specifically, to produce ABS base resin, waste products containing waste ABS resin are first disassembled to separate the waste ABS resin, which is then washed and pulverized. To separate the waste ABS resin from other resins such as polypropylene (PP), polystyrene (PS), and high-impact polystyrene (HIPS), methods such as wet or dry separation using specific gravity, sieving and classification using near-infrared spectroscopy, and electrostatic separation using electrostatic properties can be used. Foreign matter other than the resin (such as metal or fiber components) can be separated from the pulverized waste ABS resin. This can be achieved by utilizing the material's magnetic properties or specific gravity differences. Consequently, large foreign matter in the waste ABS resin is removed, reducing the total foreign matter content.

[0028] Afterward, if necessary, the waste ABS resin, from which large foreign matter has been removed, is pulverized to produce a fine powder or flake phase. This pulverization can be performed using a pulverizing device such as a jaw crusher, impact crusher, cross-jet mill, roller mill, or rod mill. However, the waste ABS resin may still contain some foreign matter after pulverization.

[0029] Furthermore, in order to remove some fine foreign matter included in the waste ABS resin in a pulverized state, a device utilizing, for example, magnetic force, wind force, centrifugal force, gravity, etc. may be used to separate and remove the fine foreign matter.

[0030] Through the above-described pretreatment, an ABS base resin in a suitable state for supply to an extruder can be prepared from the waste ABS resin included in the waste product. Meanwhile, the pretreatment methods for the waste ABS exemplified above can be appropriately selected and modified as needed and are not particularly limited, as long as they provide an ABS base resin in a suitable state for supply to an extruder.

[0031] ABS base resins may contain trace amounts of foreign matter. For example, in addition to polyurethane, these foreign matter may also include various impurities such as trace amounts of fiber, resin, stone, and metal. The foreign matter content may be less than 0.5 wt% relative to the ABS base resin. When an ABS base resin containing even a small amount of foreign matter is supplied to an extruder and extruded without separate treatment, the physical properties of the recycled ABS resin, particularly its surface properties, may deteriorate. Specifically, surface degradation issues such as the appearance of colloids or indentations on the surface of the recycled ABS resin or molded articles made therefrom, may arise. This surface degradation may be directly caused by the polyurethane present on the surface of the ABS base resin, or may also be due to the effects of polyurethane-mediated impurities in the foreign matter.

[0032] In order to prevent the physical properties of the recycled ABS resin from being deteriorated due to foreign matter included in the ABS base resin, the extrusion composition of the present invention may include a polyol and a metal carboxylate.

[0033] The polyol is used as a reactant for the depolymerization reaction of the polyurethane included in the ABS base resin in the presence of a metal carboxylate in an extruder. The metal carboxylate may also be added to promote the depolymerization.

[0034] A depolymerization reaction may refer to a reaction that destroys some of the urethane bonds in a polyurethane. This depolymerization reaction may not completely decompose the polyurethane into its monomeric form, but may also refer to a reaction that decomposes a high-molecular-weight polyurethane into a low-molecular-weight polyurethane. Therefore, decomposition products of a polyurethane depolymerization reaction include polyurethanes having a molecular weight lower than that of the polyurethane used as a depolymerization reactant, and, if desired, may include monomers and oligomers that form the polyurethane.

[0035] As described below, the internal temperature of the extruder used to extrude the ABS base resin can be 200°C to 280°C or 230°C to 260°C. When the extrusion feed is subjected to this internal extruder temperature for an extended period of time, physical property degradation, such as heat-induced discoloration of the ABS base resin, can occur, and heat-induced side effects, such as decreased activity of the metal carboxylate, can occur. To minimize these heat-induced side effects, it is preferred that the extrusion feed remain in the extruder for only the minimum residence time required to extrude the ABS base resin. To this end, the depolymerization reaction must also be effectively performed over a short period of time.

[0036] From this perspective, the polyol according to one exemplary embodiment of the present invention may have a boiling point at or above the extruder internal temperature. Because the interior of the extruder is pressurized at or above atmospheric pressure, the boiling point of the polyol may increase. However, since the extruder internal temperature is similar to the boiling point of the polyol, evaporation of the polyol is promoted. Therefore, in order to stably carry out the depolymerization reaction at an extruder internal temperature of 200°C to 280°C, the boiling point of the polyol may be at least 200°C or higher, more specifically 230°C or higher. When the boiling point of the polyol is lower than 200°C, the amount of polyol that evaporates increases, reducing the amount of polyol that actually reacts, and thus, an efficient depolymerization reaction may be difficult. Furthermore, the evaporated polyol may cause backflow in the extruder inlet area, resulting in reduced productivity.

[0037] Specific examples of the polyol may be one or more of glycerol, erythritol, ethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol.

[0038] Specifically, referring to Table 1 below, it is found that among low-molecular-weight primary alcohols (e.g., methanol, ethanol, etc.) or secondary alcohols, ethylene glycol, etc. are alcohols having a boiling point lower than 200° C. When an alcohol having a low boiling point is used, as described above, the amount of alcohol evaporated in the extruder increases, resulting in a decrease in the amount of polyol participating in the actual reaction. As a result, an efficient depolymerization reaction may be difficult, or a reflux reaction may occur at the extruder inlet area, resulting in a decrease in productivity.

[0039] Meanwhile, even in the case of alcohols with slightly higher boiling points, high molecular weight primary alcohols (e.g., stearyl alcohol, etc.), diethylene glycol, triethylene glycol, or the like do not have a high OH group to mass ratio and, therefore, may have limited effects on the depolymerization reaction of polyurethane. That is, such alcohols may be preferred in terms of evaporation rate within the extruder, but may have limited effects on the depolymerization reaction efficiency of polyurethane.

[0040] Furthermore, since polyols such as arabitol, mannitol, sorbitol, xylitol, and maltitol are in a solid phase and have poor compatibility with ABS resin, they sometimes become another foreign matter and thus may be undesirable.

[0041] As described above, as the polyol, considering the boiling point (degree of evaporation in the extruder), the ratio of OH groups to mass (efficiency of the depolymerization reaction), the compatibility with the ABS resin, etc., among the above-mentioned alcohols, one or more of glycerin and erythritol can be preferably used.

[0042] Meanwhile, the content of the polyol in the extrusion feed may be 0.01 to 3 parts by weight, particularly 0.1 to 0.9 parts by weight, relative to 100 parts by weight of the ABS base resin.

[0043] When the content of the polyol is less than 0.01 parts by weight, the urethane decomposition reaction is insufficient, thereby reducing the foreign matter reduction effect, and when the content of the polyol is greater than 3 parts by weight, mechanical properties such as impact strength are deteriorated.

[0044] Meanwhile, according to an exemplary embodiment of the present invention, the extrusion feed may include a metal carboxylate. The metal carboxylate can be used to accelerate the depolymerization reaction rate between the polyurethane and polyol contained in the ABS base resin. As mentioned above, in order to produce a recycled ABS resin with minimal changes in physical properties, it is necessary to minimize the heat exposure time of the ABS base resin. Although the addition of the metal carboxylate shortens the residence time of the extrusion feed in the extruder, the depolymerization reaction of the polyurethane in the ABS base resin can proceed rapidly and fully.

[0045] The metal element of the metal carboxylate may be potassium and zinc. Carboxylates of metal elements such as sodium and magnesium do not cause sufficient urethane decomposition reaction to reduce the effect of foreign matter reduction.

[0046] The amount of the metal carboxylate salt included in the extrusion feed can be 0.05 to 3 parts by weight, particularly 0.1 to 2 parts by weight, and more particularly 0.3 to 1 part by weight, relative to 100 parts by weight of the ABS base resin. The desired effect of promoting the depolymerization reaction of the polyurethane can be achieved by adding the metal carboxylate salt only when the amount of the metal carboxylate salt is at least 0.05 parts by weight or greater relative to 100 parts by weight of the ABS base resin. Furthermore, the effect of the metal carboxylate salt on the physical properties of the recycled ABS resin, such as color, during the extrusion process, as well as the deterioration of the physical properties caused by the metal carboxylate salt remaining in the recycled ABS resin, can be reduced only when the amount of the metal carboxylate salt is 3 parts by weight or less relative to 100 parts by weight of the ABS base resin.

[0047] The carboxylate anion of the metal carboxylate may be an aliphatic or aromatic carboxylate having 2 to 18 carbon atoms, preferably 2 to 12 carbon atoms. Specifically, the metal carboxylate may be an aliphatic zinc carboxylate, such as zinc acetate, zinc propionate, zinc butyrate, zinc octoate, zinc decanoate, zinc laurate, and zinc stearate. Furthermore, the metal carboxylate may be an aliphatic potassium carboxylate, such as potassium acetate, potassium propionate, potassium butyrate, potassium octoate, potassium decanoate, potassium laurate, and potassium stearate. More specifically, the metal carboxylate may be zinc acetate and potassium acetate.

[0048] Metal carboxylates have an excellent effect of accelerating the depolymerization reaction rate of polyurethane of polyol, and particularly, among metal carboxylates, zinc acetate and potassium acetate have less structural hindrance and excellent fluidity in the depolymerization reaction due to their simple structures and thus may be preferable.

[0049] Furthermore, according to an exemplary embodiment of the present invention, the mass ratio of the metal carboxylate to the polyol in the extrusion feed can be 1:10 to 1:0.1, particularly 1:0.3 to 1:1. Within this numerical range, the surface properties of the resin improve with increasing glycerol content.

[0050] Meanwhile, the extrusion feed may be supplied to the inlet of the extruder in the form of one composition, and one or more of the components included in the extrusion feed may be supplied through separate supply lines.

[0051] A method for producing a recycled ABS resin according to an exemplary embodiment of the present invention may include supplying an extrusion feed to an extruder to perform a depolymerization reaction of polyurethane and extruding the extrusion feed.

[0052] The extruder melts, kneads, and extrudes the ABS base resin. It also depolymerizes the polyurethane contained in the ABS base resin and uniformly disperses the decomposition products of the depolymerized polyurethane. Specifically, the extruder can be a twin-screw extruder.

[0053] Meanwhile, an extruder according to an exemplary embodiment of the present invention may include a supply port to which an extrusion feed is supplied, an outlet located at the other end of the supply port, through which the extrudate is discharged, a barrel in the housing of the extruder (in which the extrusion feed is extruded), a screw located in the barrel and pushing the extrusion feed or extrudate in the direction of the outlet, and a heating device provided outside the barrel and heating the barrel.

[0054] The internal temperature of the extruder may be 200°C to 280°C, particularly 230°C to 260°C, and more particularly 240°C to 260°C. In the case of an extruder having a barrel within the extruder housing, the internal temperature of the extruder may refer to the internal temperature of the barrel. This internal temperature range of the extruder is equal to or higher than the melting point and equal to or lower than the thermal degradation temperature of the ABS base resin. However, this temperature range is higher than the extrusion temperature used in conventional production of recycled ABS resin. When the ABS base resin remains in an extruder within this temperature range for an extended period of time, it is susceptible to thermal degradation and discoloration, which directly correlates to the deterioration of the physical properties of the recycled ABS resin. Furthermore, when the reaction feed remains in the extruder for an extended period of time, the amount of thermally inactivated metal carboxylates increases, as does the amount of evaporated polyols, resulting in reduced efficiency in the depolymerization reaction of the polyurethane. That is, as the temperature inside the extruder increases, the depolymerization reaction of the polyurethane occurs more easily. However, when the extruded feed is exposed to high temperatures for a long time, the aforementioned problem arises, and as a result, the efficiency of the depolymerization reaction may deteriorate. Therefore, when the internal temperature of the extruder is maintained at 200°C to 280°C, it is important to minimize the adverse effects caused by heat by shortening the residence time of the extruded feed in the extruder. In addition, in order to allow the depolymerization reaction of the polyurethane to proceed to the desired extent within a short period of time, the use of the metal carboxylate and polyol of the present invention is essential.

[0055] According to the method for producing recycled ABS resin of the present invention, the residence time of the extrusion feed in the extruder can be 0.5 to 10 minutes, particularly 1 to 5 minutes. The residence time herein refers to the time during which the depolymerization reaction of the polyurethane with the metal carboxylate and the polyol proceeds in the extruder.

[0056] Such a short residence time minimizes the time during which the ABS base resin, metal carboxylate, and polyol supplied to the extruder are exposed to heat, thereby preventing degradation of physical properties such as heat-induced discoloration of the recycled ABS resin, decreased activity due to degradation of the metal carboxylate, and reduced reaction efficiency due to excessive evaporation of the polyol. Furthermore, since both the metal carboxylate and the polyol are used for reactive extrusion, the polyurethane in the ABS can be efficiently depolymerized even with a short residence time. Furthermore, since the depolymerization products include polyurethane with a sufficiently reduced molecular weight, the decomposition products can be uniformly distributed throughout the melted and kneaded recycled resin. Consequently, it is possible to produce recycled ABS resin with excellent physical properties (e.g., good surface properties).

[0057] Meanwhile, the pressure inside the extruder according to one exemplary embodiment of the present invention can range from atmospheric pressure to 100 bar or less. Within this pressure range, the temperature inside the extruder is easily controlled, and the ABS base resin can be melted and kneaded optimally. In particular, within this pressure range, polyurethane can be efficiently depolymerized.

[0058] According to an exemplary embodiment of the present invention, the extruded composition discharged from the extruder is supplied to a pelletizer for pelletization. For example, the extruded composition discharged from the extruder outlet is molded into a desired size using an underwater pelletizer, ultimately producing recycled ABS resin.

[0059] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are provided for the purpose of illustrating the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto. Implementation Method

[0060] [[] [Example] []] [Example] [1]

[0061] Waste ABS resin recovered from refrigerators was crushed and classified, with large foreign matter removed by separation, and then crushed to produce an ABS base resin with an average particle size (D50) of 15 mm. 100 kg of the ABS base resin, 300 g of zinc acetate as a metal carboxylate, and 600 g of glycerin as a polyol were supplied to a mixer and mixed to prepare an extrusion feed, which was then supplied to the extruder via the extruder supply port.

[0062] As the extruder, a twin-screw extruder including a barrel having an inner diameter of 25 mm and having a screw length of 800 mm was used.

[0063] While the internal temperature of the extruder is maintained at 260° C., the ABS base resin is melted and kneaded in the extruder, and a depolymerization reaction of the polyurethane included in the ABS base resin is carried out.

[0064] At this time, the screw speed was set to 300 rpm to control the residence time to 120 seconds, and the extrusion composition after the reaction extrusion was discharged through the outlet of the extruder. The extrusion composition was supplied to a pelletizer to prepare a recovered ABS resin having a diameter of 2 mm. [Example] [2] [to] [twenty one] [Comparative Example] [1] [to] [4] []

[0065] Recycled ABS resin was prepared in the same manner as in Example 1, except that the temperature inside the barrel of the extruder, the metal carboxylate included in the extrusion feed, and the content of the polyol were as listed in Tables 2 to 5.

[0066] Specifically, in Examples 9, 10, and 21, recovered ABS resins were prepared in the same manner as in Example 1, except that potassium acetate (Example 9), zinc stearate (Example 10), or sodium acetate (Example 21) was used as the metal carboxylate instead of zinc acetate in Example 1.

[0067] Meanwhile, in Examples 13 and 14, recovered ABS resins were prepared in the same manner as in Example 1, except that ethylene glycol (Example 13) or polyethylene glycol having a molecular weight of 4,000 (Example 14) was used as the polyol instead of the glycerol in Example 1, and in Comparative Example 4, recovered ABS resins were prepared in the same manner as in Example 1, except that stearyl alcohol was used instead of the polyol. [Experimental example]

[0068] The physical properties of the recovered ABS resins prepared in Examples and Comparative Examples were measured and evaluated by the following methods, and the results are shown in Tables 2 to 5. 1. Number of film colloids (film foreign matter fraction)

[0069] The recycled ABS resin pellets were blended with a styrene-acrylonitrile (SAN) copolymer at a mass ratio of 1:9, and then extruded using a separate extruder to produce a film sample with a thickness of 0.02 mm. The SAN copolymer resin was prepared by mixing 70 parts by weight of styrene, 30 parts by weight of acrylonitrile, 20 parts by weight of ethylbenzene as a solvent, and 0.15 parts by weight of di-tert-dodecanethiol as a molecular weight modifier. This mixture was then continuously added to a reaction vessel for polymerization at a reaction temperature of 148°C.

[0070] The number of colloids in the film was then counted using Collin's Q-Film software. Colloids and fibers with a diameter of 100 μm or greater were identified as colloids in the film sample prepared above and counted. The colloids were categorized into those with a colloid diameter of 100 μm or greater and less than 300 μm, those with a diameter of 300 μm or greater and less than 500 μm, and those with a diameter of 500 μm or greater. The number of colloids in each size fraction was counted and displayed in Tables 2 to 5.

[0071] Furthermore, depending on the number of colloids measured, the film foreign matter score was calculated by evaluating 100 μm or more and less than 300 μm as 0.03 points, 300 μm or more and less than 500 μm as 0.05 points, and 500 μm or more as 0.1 points. 2. Number of injected pits (injected foreign body fraction)

[0072] The prepared recycled ABS resin pellets were injected to produce block specimens measuring 5 cm x 10 cm. A high-resolution camera was used to count the number of pits on the surface of the block specimens. Pits in the prepared block specimens were identified as shadows with a diameter of 100 μm or greater on the surface and counted. The pits were categorized into those with a diameter of 100 μm or greater and less than 300 μm, those with a diameter of 300 μm or greater and less than 500 μm, and those with a diameter of 500 μm or greater. The number of pits in each size range was counted and displayed in Tables 2 to 5.

[0073] Furthermore, depending on the number of measured pits, 100 μm or more and less than 300 μm was evaluated as 0.03 points, 300 μm or more and less than 500 μm was evaluated as 0.05 points, and 500 μm or more was evaluated as 0.1 points to calculate the foreign matter score. 3. Whiteness index and yellowness index

[0074] Whiteness and yellowness were measured using a Hunter Lab colorimeter (supplied by Hunter Lab, USA) using 5 cm x 10 cm block specimens to measure the number of injected dimples. Whiteness was measured according to ASTM E313-73, and yellowness was measured according to ASTM E313-15. The results are shown in Tables 2 to 5.

[0075] From the above results, it is confirmed that the recycled ABS resin prepared according to the embodiment of the present invention has a good film foreign matter fraction and injection foreign matter fraction.

[0076] Meanwhile, in Example 10, which used zinc stearate as the metal carboxylate, the film foreign matter fraction and the injected foreign matter fraction were slightly inferior compared to the other Examples using zinc acetate or potassium acetate. This is believed to be due to the fact that zinc acetate or potassium acetate, due to their simple structures, have less structural hindrance during the depolymerization reaction and excellent fluidity. In Examples 13 and 14, which used ethylene glycol or polyethylene glycol, respectively, as the polyol, the film foreign matter fraction and the injected foreign matter fraction were slightly inferior compared to the other Examples. This suggests that ethylene glycol has a lower boiling point than glycerol, making the depolymerization reaction of polyurethane inefficient. Furthermore, polyethylene glycol has a low OH equivalent to mass (the number of OH groups per molecule divided by the molecular weight), making it difficult to depolymerize polyurethane efficiently.

[0077] Meanwhile, in Comparative Examples 1 to 4, which did not use metal carboxylates or polyols, both the film foreign matter score and the injected foreign matter score were significantly poor. In particular, in Comparative Example 4, which used a primary alcohol, it was found that the expected surface property improvement compared to a polyol was not achieved.

[0078] Furthermore, in Example 15, where the extruder temperature was lower than in the other examples, the improvement in the film foreign matter fraction and the injected foreign matter fraction was minimal, indicating that sufficient depolymerization of the polyurethane at low temperatures in the extruder was difficult. However, in Example 16, where the extruder temperature was high at 300°C, the surface foreign matter fraction was good, but the color properties of the yellowness index deteriorated. This confirms that excessively high extruder temperatures can lead to degradation of physical properties, such as heat-induced discoloration of the recovered ABS resin.

[0079] Furthermore, referring to Examples 17 and 18, it was confirmed that when the mass ratio of the metal carboxylate to the polyol in the extrusion feed was too low or too high, color properties such as the yellowness index were deteriorated, or surface properties such as the foreign matter fraction were deteriorated.

[0080] Meanwhile, in Example 19 using a low content of metal carboxylate, it was found that the improvement effects of the film foreign matter fraction and the injected foreign matter fraction were not significant, whereas in Example 20 using a high content of metal carboxylate, it was found that the color properties were deteriorated.

[0081] In addition, referring to Example 21, when sodium acetate was used as the metal carboxylate, the surface property improvement effect was not significant compared to the case of other examples using zinc acetate.

Claims

1. A method for manufacturing recycled ABS resin, the method comprising: preparing an extrusion feed comprising an acrylonitrile-butadiene-styrene (ABS) base resin containing polyurethane, a metal carboxylate, and a polyol; and supplying the extrusion feed to an extruder to carry out a depolymerization reaction of the polyurethane and extruding the extrusion feed, wherein the content of the metal carboxylate in the extrusion feed is 0.05 parts by weight to 3 parts by weight relative to 100 parts by weight of the ABS base resin, and wherein the content of the polyol in the extrusion feed is 0.01 parts by weight to 3 parts by weight relative to 100 parts by weight of the ABS base resin.

2. The method for manufacturing the recycled ABS resin as claimed in claim 1, wherein the metal carboxylate is one or more of zinc acetate, zinc stearate, and potassium acetate.

3. The method for manufacturing recycled ABS resin as claimed in claim 1, wherein the content of the metal carboxylate in the extrusion feed is 0.1 to 2 parts by weight relative to 100 parts by weight of ABS base resin.

4. The method for manufacturing the recycled ABS resin as claimed in claim 1, wherein the polyol has a boiling point of 200°C or higher.

5. The method for manufacturing the recycled ABS resin as claimed in claim 1, wherein the polyol is one or more of glycerol and erythritol.

6. The method for manufacturing recycled ABS resin as claimed in claim 1, wherein the internal temperature of the extruder is 200°C to 280°C.

7. The method for manufacturing recycled ABS resin as claimed in claim 1, wherein the residence time of the extruded feed in the extruder is 0.5 minutes to 10 minutes.

8. The method for manufacturing recycled ABS resin as claimed in claim 1, wherein the mass ratio of the metal carboxylate in the extrusion feed to the polyol is 1:0.3 to 1:

1.

9. The method for manufacturing the recycled ABS resin as claimed in claim 1, further comprising: After the polyurethane undergoes depolymerization and the extrusion feed is extruded, the extruded composition discharged from the extruder is supplied to a granulator for granulation.