Process for purification of waste polycarbonate-based resin and preparation method of monomer for synthesizing recycled plastic, monomer for synthesizing recycled plastic, recycled plastic and molded product, which use same

Abstract

The present invention relates to a process for purification of a waste polycarbonate-based resin and a preparation method of a monomer for synthesizing a recycled plastic, a monomer for synthesizing a recycled plastic, a recycled plastic and a molded product, which use same, the process comprising: a first step of introducing, into a filter, a precoat solution comprising a polycarbonate-based resin, a filtration aid and an organic solvent and filtering same; after the first step, a second step of introducing, into the filter, a waste polycarbonate-based resin solution comprising a waste polycarbonate-based resin, a filtration aid and an organic solvent and filtering same; and a third step of obtaining a purified polycarbonate-based resin solution that passed through the filter of the first step and the second step.

Description

Method for purifying waste polycarbonate-based resin, and method for producing a monomer for synthesizing recycled plastic using the same, monomer for synthesizing recycled plastic, recycled plastic, and molded article

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2025-0022484 dated February 20, 2025, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0003] The present invention relates to a method for purifying waste polycarbonate resin capable of producing a purified polycarbonate resin having high purity and improved color characteristics by removing impurities contained in the waste polycarbonate resin, a method for producing a monomer for synthesizing recycled plastic using the same, a monomer for synthesizing recycled plastic, recycled plastic, and a molded article.

[0004] Polycarbonate is a thermoplastic polymer and a plastic with excellent characteristics, such as excellent transparency, flexibility, and relatively low manufacturing costs.

[0005] Although polycarbonate is widely used for various purposes, concerns regarding the environment and health during waste disposal have been continuously raised.

[0006] Currently, physical recycling methods are being used, but this leads to quality degradation; therefore, research is being conducted on recycling waste polycarbonate through chemical decomposition.

[0007] Chemical decomposition of polycarbonate refers to obtaining an aromatic diol compound (e.g., bisphenol A (BPA)) which is a monomer through the decomposition of polycarbonate, and then utilizing it again in polymerization to obtain high-purity polycarbonate.

[0008] Meanwhile, waste polycarbonate contains various impurities, particularly solvent-insoluble impurities such as glass fibers and carbon black; therefore, a technology is used to remove these impurities as a pretreatment process before chemical decomposition by dissolving the waste polycarbonate in a solvent and then removing it through a filter.

[0009] However, when the waste polycarbonate pretreatment process is carried out on a large scale, there is a limitation in that as the impurity content increases, a large amount of impurities cover the filter surface, causing a sharp drop in flow rate and a shortened filter replacement cycle.

[0010] Accordingly, there is a need to develop technology that can further increase filtration efficiency during the filter purification of waste polycarbonate.

[0011] The present invention aims to provide a method for purifying waste polycarbonate resin that can produce a purified polycarbonate resin having high purity and improved color characteristics by removing impurities contained in the waste polycarbonate resin.

[0012] In addition, the present invention is intended to provide a method for manufacturing a monomer for synthesizing recycled plastic using the above-described method for purifying waste polycarbonate-based resin, a monomer for synthesizing recycled plastic, recycled plastic, and a molded article.

[0013] To solve the above problem, the present specification provides a method for purifying waste polycarbonate resin, comprising: a first step of introducing a precoat solution containing a polycarbonate resin, a filtration aid, and an organic solvent into a filter and filtering it; a second step of introducing a waste polycarbonate resin solution containing a waste polycarbonate resin, a filtration aid, and an organic solvent into the filter and filtering it after the first step; and a third step of obtaining a purified polycarbonate resin solution that has passed through the filters of the first and second steps.

[0014] The present specification also provides a method for producing a monomer for synthesizing recycled plastic, comprising the step of recovering an aromatic diol compound obtained by the depolymerization reaction of a purified polycarbonate resin solution obtained from the method for purifying waste polycarbonate resin.

[0015] In addition to this specification, a recycled plastic is provided comprising a reaction product of the monomer for synthesizing the recycled plastic and the comonomer.

[0016] In addition to the above, a molded article comprising the recycled plastic is provided.

[0017] The following describes in more detail a method for purifying waste polycarbonate-based resin according to specific embodiments of the invention, a method for manufacturing a monomer for synthesizing recycled plastic using the same, a monomer for synthesizing recycled plastic, recycled plastic, and a molded article.

[0018]

[0019] Unless explicitly stated otherwise in this specification, technical terms are used merely to refer to specific embodiments and are not intended to limit the invention.

[0020] The singular forms used in this specification include plural forms unless the phrases clearly indicate otherwise.

[0021] As used in this specification, the meaning of 'includes' specifies certain characteristics, regions, integers, steps, actions, elements, and / or components, and does not exclude the existence or addition of other specific characteristics, regions, integers, steps, actions, elements, components, and / or groups.

[0022] Also, in this specification, terms including ordinal numbers such as 'first' and 'second' are used for the purpose of distinguishing one component from another and are not limited by said ordinal numbers. For example, within the scope of the present invention, the first component may also be named the second component, and similarly, the second component may be named the first component.

[0023]

[0024] 1. Method for purifying waste polycarbonate-based resin

[0025] According to one embodiment of the invention, a method for purifying waste polycarbonate resin may be provided, comprising: a first step of introducing a precoat solution containing a polycarbonate resin, a filtration aid, and an organic solvent into a filter and filtering it; a second step of introducing a waste polycarbonate resin solution containing a waste polycarbonate resin, a filtration aid, and an organic solvent into the filter and filtering it after the first step; and a third step of obtaining a purified polycarbonate resin solution that has passed through the filters of the first and second steps.

[0026] The inventors confirmed through experiments that, as in the method for purifying waste polycarbonate-based resin of the above embodiment, when filtering waste polycarbonate-based resin with a filter, a precoat solution containing polycarbonate-based resin, a filtration aid, and an organic solvent is filtered first to form a precoat layer on the surface of a filter membrane, and then a waste polycarbonate-based resin solution containing waste polycarbonate-based resin, a filtration aid, and an organic solvent is filtered to suppress the phenomenon of membrane pores being clogged by impurities and to improve filter performance, and thus completed the invention.

[0027] In particular, since both the precoat solution and the waste polycarbonate resin solution contain polycarbonate resin, the change in the concentration of polycarbonate resin between the waste polycarbonate resin solution and the purified polycarbonate resin solution obtained after filter filtration is minimized. This allows the chemical decomposition process of the polycarbonate resin to be carried out using the purified polycarbonate resin solution without a separate concentration control process, thereby increasing process efficiency.

[0028] Specifically, the method for purifying waste polycarbonate-based resin according to one embodiment above may include a first step of introducing a precoat solution containing a polycarbonate-based resin, a filtration aid, and an organic solvent into a filter and filtering it. As in the first step, the precoat solution containing the polycarbonate-based resin, a filtration aid, and an organic solvent may be filtered first to form a precoat layer on the surface of a filter membrane. Accordingly, the precoat layer acts as a protective layer to suppress the phenomenon of membrane pores becoming clogged by impurities and can improve filter performance.

[0029] The thickness of the precoat layer may be 25 mm or less, or 1 mm to 25 mm. If the thickness of the precoat layer increases excessively beyond 25 mm, problems may occur such as a decrease in filtration speed or damage to the precoat layer causing it to detach.

[0030] The above precoat solution may include a polycarbonate-based resin, a filtration aid, and an organic solvent.

[0031] The above polycarbonate-based resin includes both homopolymers and copolymers containing polycarbonate repeating units, and collectively refers to reaction products obtained through the polymerization or copolymerization reaction of monomers including aromatic diol compounds and carbonate precursors. A homopolymer can be synthesized when containing one carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor. Additionally, a copolymer can be synthesized when containing two or more carbonates by using one aromatic diol compound and two or more carbonate precursors as monomers, using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor. The above homopolymer or copolymer may include low molecular weight compounds, oligomers, and high molecular weights according to the molecular weight range.

[0032] The above polycarbonate resin can be applied regardless of various forms or types, such as new polycarbonate resin produced through synthesis, recycled polycarbonate resin produced through a regeneration process, or polycarbonate resin waste. However, to give a specific example, the polycarbonate resin contained in the above precoat solution may be a new polycarbonate resin (neat PC) or a purified polycarbonate resin obtained from the purification method of waste polycarbonate resin of the above embodiment.

[0033] The mass ratio of the polycarbonate-based resin in the above precoat solution may be 10% to 20%. The mass ratio of the polycarbonate-based resin in the precoat solution can be determined by multiplying the value obtained by dividing the mass of the polycarbonate-based resin by the total mass of the precoat solution by 100.

[0034] Since both the above-mentioned precoat solution and the waste polycarbonate-based resin solution described below contain polycarbonate-based resin, the change in the concentration of polycarbonate-based resin between the waste polycarbonate-based resin solution and the purified polycarbonate-based resin solution obtained after filter filtration is minimized, thereby allowing the chemical decomposition process of the polycarbonate-based resin to be carried out using the purified polycarbonate-based resin solution without a separate concentration control process, which can increase the efficiency of the process.

[0035] The above filtration aid may include one or more compounds selected from the group consisting of diatomaceous earth, manganese sand, manganese zeolite, activated carbon, anthracite, ceramic sand, perlite, and cellulose. That is, the above filtration aid may include diatomaceous earth, manganese sand, manganese zeolite, activated carbon, anthracite, ceramic sand, perlite, cellulose, or a mixture of two or more of these.

[0036] The above filter aid may have an average particle size of 10 μm to 15 μm. If the average particle size of the above filter aid is reduced excessively, there is a problem that the filtration speed becomes very slow, and if the average particle size of the above filter aid is increased excessively, solid colorant among the impurities may pass through the filter and flow out.

[0037] In the above precoat solution, the content of the filtration aid may be 1 to 20 parts by weight, 10 to 20 parts by weight, 10 to 5 parts by weight, or 11 to 13 parts by weight, based on 100 parts by weight of the polycarbonate resin. If the content of the filtration aid is reduced excessively, it is difficult to sufficiently form a precoat layer on the surface of the filter membrane, making it difficult to achieve an effect that improves filter performance. On the other hand, if the content of the filtration aid is increased excessively, there is a problem that the filtration speed decreases.

[0038] The above organic solvent may further include one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0039] That is, the organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0040] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent, the solubility characteristics for polycarbonate-based resins or waste polycarbonate-based resins are improved, thereby improving the filter filtration performance through solid-liquid separation.

[0041] The above filter is equipment for separating solid components and filtrate by pressurized filtration. The specific type of filter, the method of inputting into the filter, and the method of filtration in the filter are not particularly limited, and various conventionally known filter technologies can be applied without restriction. However, as an example, a candle filter may be used.

[0042] Meanwhile, the method for purifying waste polycarbonate according to the above embodiment may include a second step after the first step, wherein a waste polycarbonate-based resin solution comprising a waste polycarbonate-based resin, a filtration aid, and an organic solvent is introduced into the filter and filtered. Through the second step, a large amount of impurities contained in the waste polycarbonate-based resin can be effectively removed to produce a purified polycarbonate-based resin having high purity and improved color characteristics.

[0043] The above waste polycarbonate-based resin solution may include waste polycarbonate-based resin, a filtration aid, and an organic solvent.

[0044] Waste polycarbonate resin refers to waste polycarbonate resin, and polycarbonate resin encompasses both homopolymers and copolymers containing polycarbonate repeating units, and collectively refers to reaction products obtained through the polymerization or copolymerization reaction of monomers including aromatic diol compounds and carbonate precursors. A homopolymer can be synthesized when containing one carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor. Additionally, a copolymer can be synthesized when containing two or more carbonates by using one aromatic diol compound and two or more carbonate precursors as the monomers, or using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor. The homopolymer or copolymer may include low molecular weight compounds, oligomers, and high molecular weights according to the molecular weight range.

[0045] The mass ratio of waste polycarbonate resin in the above waste polycarbonate resin solution may be 10% to 20%. A method for measuring the mass ratio of waste polycarbonate resin in the waste polycarbonate resin solution can be obtained by multiplying the value obtained by dividing the mass of waste polycarbonate resin by the total mass of the waste polycarbonate resin solution by 100.

[0046] If the mass ratio of waste polycarbonate resin in the above waste polycarbonate resin solution is excessively reduced, the amount of organic solvent used increases, which is not advantageous in terms of economic feasibility; conversely, if the mass ratio of waste polycarbonate resin in the above waste polycarbonate resin solution is excessively increased, there is a problem of reduced filtration speed.

[0047] The above filtration aid may include one or more compounds selected from the group consisting of diatomaceous earth, manganese sand, manganese zeolite, activated carbon, anthracite, ceramic sand, perlite, and cellulose. That is, the above filtration aid may include diatomaceous earth, manganese sand, manganese zeolite, activated carbon, anthracite, ceramic sand, perlite, cellulose, or a mixture of two or more of these.

[0048] The above filter aid may have an average particle size of 10 μm to 15 μm. If the average particle size of the above filter aid is reduced excessively, there is a problem that the filtration speed becomes very slow, and if the average particle size of the above filter aid is increased excessively, solid colorant among the impurities may pass through the filter and flow out.

[0049] In the above waste polycarbonate-based resin solution, the content of the filtration aid may be 1 to 20 parts by weight, 1 to 10 parts by weight, 1 to 5 parts by weight, or 2 to 3 parts by weight per 100 parts by weight of the polycarbonate-based resin. If the content of the filtration aid is reduced excessively, it is difficult to sufficiently form a filtration layer on the filter membrane, making it difficult to achieve an effect of improving filter performance. On the other hand, if the content of the filtration aid is increased excessively, there is a problem of the filtration life being shortened.

[0050] The above organic solvent may further include one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0051] That is, the organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0052] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent, the solubility characteristics for polycarbonate-based resins or waste polycarbonate-based resins are improved, thereby improving the filter filtration performance through solid-liquid separation.

[0053] Meanwhile, the above waste polycarbonate-based resin solution may further include an adsorbent. The adsorbent acts as a filtration aid and, by removing organic dyes that exhibit color, can realize a purified polycarbonate-based resin with high purity and improved color characteristics.

[0054] Examples of the above adsorbents may include activated carbon, charcoal, or mixtures thereof. The above activated carbon is a black carbon material with micropores manufactured by carbonizing the raw material at approximately 500°C and activating it at approximately 900°C. While the examples are not significantly limited, various types of activated carbon, such as plant-based, coal-based, petroleum-based, and waste-based activated carbon, can be applied without limitation depending on the type of raw material.

[0055] To give more specific examples, plant-based activated carbons include coconut activated carbon, wood activated carbon, and sawdust activated carbon. Additionally, coal-based activated carbons include lignite activated carbon, bituminous coal activated carbon, and anthracite activated carbon. Furthermore, petroleum-based activated carbons include petroleum coke activated carbon and oil carbon activated carbon. Additionally, waste-based activated carbons include synthetic resin activated carbon and pulp activated carbon.

[0056] The above adsorbent may include one or more types of activated carbon selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste material activated carbon. That is, the above adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste material activated carbon, or a mixture of two or more of these.

[0057] More specifically, the adsorbent may include one or more types of activated carbon selected from the group consisting of coconut activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous activated carbon. That is, the adsorbent may include coconut activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more of these.

[0058] The adsorption purification conditions using the above adsorbent are not specifically limited, and various conventionally known adsorption purification conditions can be used without limitation. However, for example, in the above waste polycarbonate-based resin solution, the content of the adsorbent may be 0.1 to 10 parts by weight, or 0.1 to 5 parts by weight, or 0.5 to 2 parts by weight, per 100 parts by weight of waste polycarbonate-based resin.

[0059] If the content of the above adsorbent is excessively reduced, colored organic dyes cannot be sufficiently removed, making it difficult to realize a purified polycarbonate-based resin with high purity and improved color characteristics. On the other hand, if the content of the above adsorbent is excessively increased, there are problems such as a decrease in filtration speed or an accelerated replacement cycle of the precoat.

[0060] The content of the adsorbent in the above waste polycarbonate-based resin solution may be 20 to 500 parts by weight, or 40 to 200 parts by weight, or 20 to 80 parts by weight, or 40 to 80 parts by weight, based on 100 parts by weight of the filtration aid.

[0061] The above filter is equipment for separating solid components and filtrate by pressurized filtration. The specific type of filter, the method of inputting into the filter, and the method of filtration in the filter are not particularly limited, and various conventionally known filter technologies can be applied without restriction. However, as an example, a candle filter may be used.

[0062] The filter of the second stage above is identical to the filter of the first stage, and more specifically, the filter of the second stage above corresponds to a filter in which a precoat layer is formed on the surface of the filter membrane after the first stage is performed.

[0063] Meanwhile, in the second stage above, the filtration velocity according to the following mathematical formula 1 is 100 L / m 2 It can be more than h.

[0064] [Mathematical Formula 1]

[0065] Filtration rate (L / m) 2 h) = w - PC filtration volume (L) / [Filter filtration area (m²) 2 ) x Filter filtration time(h)].

[0066] The purification method for waste polycarbonate-based resin of the above embodiment suppressed the phenomenon in which impurities cover the filter surface and cause a rapid drop in flow rate, such that the filtration velocity according to Equation 1 is 100 L / m 2 It can increase above h. On the other hand, the filtration velocity according to the above Equation 1 is 100 L / m 2 If it decreases below h, it means that a problem has occurred where impurities derived from waste polycarbonate resin cover the filter surface, causing a sharp drop in flow rate.

[0067] In addition, in the second step above, the filtration life according to the following mathematical formula 2 is 50 kg / m 2 It could be more than that.

[0068] [Mathematical Formula 2]

[0069] Filtration life (kg / m²) 2 ) = Filtration speed of 50 L / m without filter replacement 2 Amount of w-PC capable of filtration while maintaining h or higher (kg) / Filter filtration area (m²) 2 ).

[0070] The purification method for waste polycarbonate-based resin of the above embodiment has a filtration life of 50 kg / m² according to the above Equation 2. 2As it increases above this level, a high filtration speed can be maintained for a long time relative to the same filtration area, thereby improving the filter replacement cycle. On the other hand, the filtration life according to the above Equation 2 is 50 kg / m 2 If it decreases below this level, it means that a problem has occurred where impurities derived from waste polycarbonate resin cover the filter surface, causing a sharp drop in flow rate.

[0071] In addition, the method for purifying waste polycarbonate-based resin of the above embodiment may have a change in polycarbonate concentration according to the following mathematical formula 3 of 2 weight% or less, or 1 weight% or less, or 0.1 weight% or less, or 0 weight% or more, or 0 weight% to 2 weight%, or 0 weight% to 1 weight%, or 0 weight% to 0.1 weight%.

[0072] [Mathematical Formula 3]

[0073] Change in Polycarbonate Concentration = (Percentage Concentration of Polycarbonate in Waste Polycarbonate (w-PC) Solution) - (Percentage Concentration of Polycarbonate in Refined Polycarbonate (r-PC) Solution).

[0074] In the purification method of the waste polycarbonate-based resin of the above embodiment, as the change in polycarbonate concentration according to Equation 3 is reduced to 2 weight% or less, the chemical decomposition process of the polycarbonate-based resin can be carried out using the purified polycarbonate-based resin solution without a separate concentration control process, thereby increasing the efficiency of the process. On the other hand, if the change in polycarbonate concentration according to Equation 3 increases to more than 2 weight%, the chemical decomposition process of the polycarbonate-based resin can be carried out after separately performing a process to additionally control the concentration of the purified polycarbonate-based resin solution, which results in poor process efficiency.

[0075] Meanwhile, the second step may include: a second step 2-1 of introducing and circulating a waste polycarbonate resin solution containing a waste polycarbonate resin, a filtration aid, and an organic solvent into a filter; and a second step 2-2 of introducing and filtration the circulated liquid obtained in the second step 2-1 into a filter. As described above, the second step 2-1, in which a waste polycarbonate resin solution containing a waste polycarbonate resin, a filtration aid, and an organic solvent is introduced and circulated into a filter, can be performed first to form a filtration layer on the filter membrane. Accordingly, the precoat layer formed in the first step and the filtration layer together act as a protective layer to suppress the phenomenon of membrane pores becoming clogged by impurities and to improve filter performance.

[0076] Step 2-1, which involves introducing and circulating a waste polycarbonate-based resin solution containing the waste polycarbonate-based resin, a filtration aid, and an organic solvent into a filter, can be performed for 30 to 60 minutes. If the time of Step 2-1 is reduced excessively, there is a problem in that it is difficult to sufficiently form a filtration layer on the filter membrane. On the other hand, if the time of Step 2-1 is increased excessively, the process time becomes longer, which may reduce the efficiency of the process.

[0077] Meanwhile, in the second step (2-2), in which the circulating liquid obtained in the second step (2-1) is introduced into a filter and filtered, the process may be repeated one or more times, two or more times, or three or more times as needed to ensure that impurities contained in the circulating liquid are sufficiently removed. The second step (2-2) may be performed for 30 to 60 minutes. If the time of the second step (2-2) is increased excessively, the process time becomes longer, which may reduce the efficiency of the process.

[0078] In addition, the method for purifying waste polycarbonate of the above-described embodiment may include a third step of obtaining a purified polycarbonate-based resin solution that has passed through the filters of the first and second steps.

[0079] A mixture of the precoat solution passed through the filter in the first step and the waste polycarbonate-based resin solution passed through the filter in the second step can be obtained as a purified polycarbonate-based resin solution.

[0080] By including polycarbonate resin in a similar range of concentrations in both the precoat solution and the waste polycarbonate resin solution, the change in polycarbonate resin concentration between the waste polycarbonate resin solution and the purified polycarbonate resin solution obtained after filtration is minimized. This allows the chemical decomposition process of the polycarbonate resin to be carried out using the purified polycarbonate resin solution without a separate concentration control process, thereby increasing process efficiency.

[0081] The purity of the above-mentioned purified polycarbonate-based resin solution may be 99% or higher. Examples of methods for measuring the purity of the above-mentioned purified polycarbonate-based resin solution are not significantly limited, and, for example, GC-MS, NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc., can be used without limitation. Various previously known specific methods, conditions, equipment, etc. for the above-mentioned GC-MS, NMR, ICP-MS, HPLC, and UPLC can be applied without limitation.

[0082] In this way, the purity of the above-mentioned purified polycarbonate-based resin solution is increased to over 99%, and other impurities are minimized, thereby enabling the monomer recovered through chemical depolymerization using this solution to achieve excellent physical properties.

[0083] In addition, the color coordinate L* of the purified polycarbonate-based resin solution may be 98 or higher. In the present invention, "color coordinate" refers to a coordinate in the CIE Lab color space, which is a color value defined by the CIE (Commission International de l'Eclairage), and any position in the CIE color space can be expressed by three coordinate values: L*, a*, and b*.

[0084] Here, the L* value represents brightness, where L*=0 represents black and L*=100 represents white. Additionally, the a* value indicates whether the color with the corresponding color coordinates leans toward pure red or pure green, and the b* value indicates whether the color with the corresponding color coordinates leans toward pure yellow or pure blue.

[0085] If the color coordinate L* of the above purified polycarbonate-based resin solution decreases to less than 98, the color characteristics of the above purified polycarbonate-based resin solution become poor.

[0086] Examples of methods for measuring the color coordinate L* value of the above-mentioned purified polycarbonate-based resin solution are not significantly limited, and various color characteristic measurement methods in the field of plastics can be applied without restriction.

[0087] However, as an example of a method to measure the color coordinate L* value, it can be measured in transmission mode using the HunterLab UltraScan PRO Spectrophotometer.

[0088]

[0089] 2. Method for manufacturing monomers for synthesizing recycled plastics

[0090] According to another embodiment of the invention, a method for producing a monomer for synthesizing recycled plastic may be provided, comprising the step of recovering an aromatic diol compound obtained by the depolymerization reaction of a purified polycarbonate resin solution obtained in the method for purifying waste polycarbonate resin of the first embodiment.

[0091] The method for purifying waste polycarbonate-based resin of the above-mentioned embodiment and the purified polycarbonate-based resin solution obtained therefrom include all the details described above in the above-mentioned embodiment.

[0092] The specific reaction conditions for the depolymerization reaction of the above-mentioned purified polycarbonate-based resin solution are not particularly limited, and information known in conventional technologies related to the depolymerization of polycarbonate-based resins can be applied without limitation.

[0093] However, for example, when the depolymerization reaction of the purified polycarbonate-based resin solution is performed, the depolymerization reaction may be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction may proceed under basic (alkali) conditions. The type of base is not significantly limited, and examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The base acts as a base catalyst and has the advantage of being economical compared to organic catalysts mainly used under mild conditions. More specifically, when the depolymerization reaction of the purified polycarbonate-based resin solution is performed, the depolymerization reaction may proceed within a pH range of greater than 8 and less than 12.

[0094] In addition, the depolymerization reaction of the purified polycarbonate-based resin solution can be carried out under a solvent containing ethanol. By decomposing the purified polycarbonate-based resin solution with a solvent containing ethanol, high-purity monomer bisphenol A can be stably obtained, and there is an advantage of additionally obtaining high-value diethyl carbonate as a reaction byproduct.

[0095] The solvent in which the depolymerization reaction of the above purified polycarbonate-based resin solution proceeds may further include one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and dipropyl carbonate, in addition to ethanol.

[0096] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent mixed with the ethanol, the solubility characteristics for polycarbonate are improved, which has the advantage of improving reactivity.

[0097] Meanwhile, the temperature at which the depolymerization reaction of the purified polycarbonate-based resin solution is carried out is not significantly limited, but, for example, it can be carried out at 20°C to 100°C or 50°C to 70°C. In addition, the time for which the depolymerization reaction of the purified polycarbonate-based resin solution is carried out can be 1 hour to 30 hours or 4 hours to 6 hours.

[0098] Meanwhile, during the depolymerization reaction of the above-mentioned purified polycarbonate-based resin solution, an antioxidant may be added to the reaction solution. By adding the antioxidant, the aromatic diol compound recovered through recycling by the chemical decomposition of the polycarbonate-based resin can satisfy a low color coordinate b* value at a color level equivalent to that of a reagent commercially sold or used for PC polymerization.

[0099] Specific examples of the above aromatic diol compounds include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (Bisphenol Z), 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, and 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane. Examples include 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, or a mixture of two or more of these. Preferably, the aromatic diol compound of the monomer for synthesizing recycled plastic in the above embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0100]

[0101] 3. Monomers for the synthesis of recycled plastics

[0102] According to another embodiment of the invention, a monomer for synthesizing recycled plastic comprising an aromatic diol compound obtained in the method for manufacturing a monomer for synthesizing recycled plastic of the other embodiment may be provided.

[0103] That is, the monomer for synthesizing recycled plastic of the above-mentioned other embodiment may be obtained by the method for manufacturing the monomer for synthesizing recycled plastic. The details regarding the method for manufacturing the monomer for synthesizing recycled plastic include all the details described above in the above-mentioned other embodiment.

[0104] The above aromatic diol compound is characterized by being obtained in the method for preparing a monomer for recycled plastic synthesis of the above other embodiment. That is, the above aromatic diol compound is characterized by being recovered from the purified polycarbonate-based resin used for recovering the monomer for recycled plastic synthesis. Accordingly, cases in which a novel aromatic diol compound is added externally, separate from the recovery from the purified polycarbonate-based resin, to prepare the monomer for recycled plastic synthesis of the above other embodiment are not included in the scope of the aromatic diol compound of the present invention.

[0105] Specifically, the term "recovered from the polycarbonate-based resin" means that it was obtained through the depolymerization reaction of the polycarbonate-based resin. The depolymerization reaction can be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction can be carried out under basic (alkali) conditions. In particular, as described below, it is preferable that the depolymerization reaction be carried out in an ethanol solvent.

[0106] The monomer for synthesizing recycled plastic of the above other embodiment can be used as a raw material for manufacturing various recycled plastics (e.g., polycarbonate (PC)) described below.

[0107] The monomer for synthesizing recycled plastic of the above other embodiment may further include some small amounts of other additives and solvents, and the specific types of additives or solvents are not significantly limited, and various materials widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate-based resins can be applied without limitation.

[0108]

[0109] 4. Recycled plastic

[0110] According to another embodiment of the invention, a recycled plastic comprising a reaction product of a monomer for synthesizing recycled plastic and a comonomer of the other embodiment may be provided.

[0111] The details regarding the monomer for synthesizing recycled plastic in the other embodiment above include all the details described above in the other embodiment.

[0112] Examples corresponding to the above recycled plastics are not significantly limited, and various plastics synthesized using aromatic diol compounds such as bisphenol A and carbonate precursors such as dimethyl carbonate, diethyl carbonate, or ethylmethyl carbonate as monomers can be applied without limitation, and more specific examples include polycarbonate resins.

[0113] More specifically, in a recycled plastic comprising the reaction product of the monomer and comonomer for the synthesis of the recycled plastic, a carbonate precursor may be used as the comonomer. Specific examples of the carbonate precursor include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditoryl carbonate, bis(chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate, or bishaloformate.

[0114] Examples of reaction processes for the monomers and comonomers used to synthesize the above-mentioned polycarbonate-based resin are not significantly limited, and various previously known methods for manufacturing polycarbonate can be applied without restriction.

[0115] However, as an example of the above-mentioned method for manufacturing polycarbonate, a method for manufacturing polycarbonate may be used that includes the step of polymerizing a composition comprising a monomer for synthesizing recycled plastic and a comonomer. In this case, the polymerization may be performed as interfacial polymerization, and during interfacial polymerization, the polymerization reaction is possible at atmospheric pressure and low temperature, and molecular weight control is easy.

[0116] The polymerization temperature may be 0 to 40°C, and the reaction time may be 10 minutes to 5 hours. In addition, the pH during the reaction may be maintained at 9 or higher or 11 or higher.

[0117] The solvent that can be used for the above polymerization is not particularly limited as long as it is a solvent used in the industry for the polymerization of polycarbonates, and for example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0118] In addition, the polymerization can be carried out in the presence of an acid binder, and an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine, can be used as the acid binder.

[0119] In addition, to control the molecular weight of the polycarbonate during the above polymerization, polymerization may be carried out in the presence of a molecular weight regulator. An alkylphenol having 1 to 20 carbon atoms may be used as the molecular weight regulator, and specific examples thereof include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, or triacontylphenol. The molecular weight regulator may be added before, during, or after the start of polymerization. The molecular weight regulator may be used in an amount of 0.01 to 10 parts by weight or 0.1 to 6 parts by weight per 100 parts by weight of the aromatic diol compound, and a desired molecular weight can be obtained within this range.

[0120] In addition, to promote the polymerization reaction, reaction promoters such as tertiary amine compounds, quaternary ammonium compounds, and quaternary phosphonium compounds, such as triethylamine, tetra-n-butylammonium bromide, tetra-n-butylphosphonium bromide, etc., may be additionally used.

[0121]

[0122] 5. Molded product

[0123] According to another embodiment of the invention, a molded article comprising recycled plastic of the other embodiment may be provided. The details regarding the recycled plastic include all details described above in the other embodiment.

[0124] The above-mentioned molded article may be obtained by applying various known plastic molding methods to the above-mentioned recycled plastic without limitation, and examples of the above-mentioned molding methods include injection molding, foam injection molding, blow molding, or extrusion molding.

[0125] Examples of the above-mentioned molded articles are not significantly limited and can be applied without restriction to various molded articles using plastic. Examples of the above-mentioned molded articles include automotive parts, electrical and electronic products, communication products, household goods, building materials, optical components, exterior materials, etc.

[0126] In addition to the recycled plastic of the other embodiment above, the molded article may additionally include one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent whitening agents, ultraviolet absorbers, pigments, and dyes, as needed.

[0127] As an example of a method for manufacturing the above-mentioned molded product, the method may include the step of thoroughly mixing the recycled plastic and additive of the above-mentioned other embodiment using a mixer, then extruding them into pellets using an extruder, drying the pellets, and then injecting them using an injection molding machine.

[0128] According to the present invention, a method for purifying waste polycarbonate capable of producing purified polycarbonate having high purity and improved color characteristics by removing impurities contained in waste polycarbonate, a method for producing a monomer for synthesizing recycled plastic using the same, a monomer for synthesizing recycled plastic, recycled plastic, and a molded article may be provided.

[0129] The invention is described in more detail in the following examples. However, the following examples are merely illustrative of the invention, and the scope of the invention is not limited by the following examples.

[0130]

[0131] <Examples and Comparative Examples>

[0132] Example 1

[0133] A w-PC solution was prepared by dissolving 0.6 kg of waste polycarbonate (w-PC), 12 g of diatomaceous earth (average particle size 13 μm), and 6 g of charcoal in 3.4 kg of methylene chloride (MC).

[0134] A pre-coat solution was prepared by dissolving 0.3 kg of clear polycarbonate (neat PC) and 36 g of diatomite (average particle size 13 μm) in 1.7 kg of methylene chloride (MC).

[0135] A pre-coat solution was introduced into a candle filter using a pump, and filtered in the filter at room temperature for 30 minutes to form a pre-coat layer on the surface of the filter membrane.

[0136] Afterwards, the w-PC solution was placed into a candle filter and pre-filtration was performed by filtering it inside the filter for 30 minutes.

[0137] Afterwards, the filtered solution was circulated back into the candle filter and filtered within the filter for 30 minutes to perform main-filtration.

[0138] Afterwards, the purified polycarbonate (r-PC) solution, which is a filtrate, was recovered.

[0139] In addition, the inside of the candle filter was drained to recover the residual solution and the filtercake was recovered.

[0140]

[0141] Example 2

[0142] A purified polycarbonate (r-PC) solution was recovered in the same manner as in Example 1, except that the w-PC solution of Example 1 above was prepared by dissolving 0.6 kg of waste polycarbonate (w-PC) and 18 g of diatomite (average particle size 13 μm) in 3.4 kg of methylene chloride (MC).

[0143]

[0144] Comparative Example 1

[0145] A purified polycarbonate (r-PC) solution was recovered in the same manner as in Example 1, except that a solution prepared by dissolving 36 g of diatomite (average particle size 13 μm) in 2 kg of methylene chloride (MC) was used as the pre-coat solution.

[0146]

[0147] <Experimental Example>

[0148] The physical properties of the purified polycarbonate (r-PC) solutions obtained in the above examples and comparative examples were measured by the following method, and the results are shown in Table 1.

[0149]

[0150] 1. Purity

[0151] 1 g of the purified polycarbonate (r-PC) solution obtained in the above examples and comparative examples was dissolved in 10 mL of chloroform, and 20 mL of methanol was added to the solution to precipitate the polymer components. Afterward, the solution was completely precipitated using a centrifuge, and 10 mL of the supernatant was transferred to a vial and completely dried under N2 purge. 1 mL of a chloroform:acetone = 1:2 mixed solvent was added to the vial to completely dissolve the solution, and after filtering, a gas chromatography-mass spectrometry (GC-MS) spectrum was obtained using a GC / MS instrument under the following conditions, and the purity of the purified polycarbonate (r-PC) was analyzed.

[0152] <Gas Chromatography (GC) Conditions>

[0153] ① Column: HP-5MS(L:30m, ID:0.25mm, film:0.25μm)

[0154] ② Injection volume: 0.2 µl

[0155] ③ Inlet, Temp.: 300 ℃, spill ratio: 20:1

[0156] ④ Column flow: (He) 1ml / min

[0157] ⑤ Oven temp.: 50℃ / 5min-10℃ / min-320℃ / 15min (Total 47min)

[0158] ⑥ Detector Temp.: 300℃

[0159] ⑦ GC Model: Agilent 7890

[0160]

[0161] 2. Color coordinates (L*)

[0162] For the purified polycarbonate (r-PC) solution obtained in the above example and the purified polycarbonate (r-PC) solution obtained in the above comparative example, the color coordinates (L*) were measured in transmission mode using a HunterLab UltraScan PRO Spectrophotometer.

[0163]

[0164] 3. Filtration performance

[0165] (1) Filtration rate (L / m 2 h)

[0166] In the above main-filtration process, the filtration amount (L) of w-PC, filter filtration area (m²) 2 The filtration speed was calculated by measuring the filter filtration time (h) and using the following mathematical formula 1.

[0167] [Mathematical Formula 1]

[0168] Filtration rate (L / m)2 h) = w - PC filtration volume (L) / [Filter filtration area (m²) 2 ) x Filter Filtration Time (h)]

[0169] (2) Filtration life (kg / m²) 2 )

[0170] In the above main-filtration process, a filtration speed of 50 L / m without filter replacement 2 Amount of w-PC (kg) capable of filtration while maintaining h or more, filter filtration area (m²) 2 The filtration life was calculated by measuring ) and using the following mathematical formula 2.

[0171] [Mathematical Formula 2]

[0172] Filtration life (kg / m²) 2 ) = Filtration speed of 50 L / m without filter replacement 2 Amount of w-PC capable of filtration while maintaining h or higher (kg) / Filter filtration area (m²) 2 )

[0173]

[0174] 4. Change in polycarbonate concentration

[0175] The difference between the percentage concentration (weight%) of polycarbonate in the waste polycarbonate (w-PC) solution and the percentage concentration (weight%) of polycarbonate in the purified polycarbonate (r-PC) solution was calculated using the following Equation 3.

[0176] [Mathematical Formula 3]

[0177] Change in Polycarbonate Concentration = (Percentage Concentration of Polycarbonate in Waste Polycarbonate (w-PC) Solution) - (Percentage Concentration of Polycarbonate in Refined Polycarbonate (r-PC) Solution)

[0178]

[0179] Experimental Example Measurement Results Classification Purity (%) Color Coordinates (L*) Filtration Rate (L / m 2 h) Filtration life (kg / m²) 2Change in PC Concentration (Weight%) Example 1: 99.99.79 120 50 or more 0 Example 2: 99.99.89 120 50 or more 0 Comparative Example 1: 99.99.79 150 50 or more 4.5

[0180] According to Table 1 above, the purified polycarbonate obtained in the example exhibited high purity, excellent color properties, and filtration characteristics equivalent to or better than those of the comparative example, while having the advantage of being applicable to the polycarbonate depolymerization process without a separate concentration control process due to minimal change in polycarbonate concentration.

Claims

1. A first step of introducing a precoat solution containing a polycarbonate-based resin, a filter aid, and an organic solvent into a filter and filtering it; After the first step above, a second step of introducing a waste polycarbonate resin solution containing waste polycarbonate resin, a filtration aid, and an organic solvent into the filter and filtering it; and A method for purifying waste polycarbonate resin, comprising: a third step of obtaining a purified polycarbonate resin solution that has passed through the filters of the first and second steps above.

2. In Paragraph 1, In the second step above, The filtration velocity according to the following Equation 1 is 100 L / m 2 Method for purifying waste polycarbonate resins with h or higher: [Mathematical Formula 1] Filtration rate (L / m) 2 h) = w - PC filtration volume (L) / [Filter filtration area (m²) 2 ) x Filter filtration time(h)].

3. In Paragraph 1, In the second step above, Filtration life according to the following Mathematical Formula 2 is 50 kg / m 2 Method for purifying waste polycarbonate resins, above [Mathematical Formula 2] Filtration life (kg / m²) 2 ) = Filtration speed of 50 L / m without filter replacement 2 Amount of w-PC capable of filtration while maintaining h or higher (kg) / Filter filtration area (m²) 2 ).

4. In Paragraph 1, A method for purifying waste polycarbonate-based resin, wherein the change in polycarbonate concentration according to the following mathematical formula 3 is 2 weight% or less: [Mathematical Formula 3] Change in Polycarbonate Concentration = (Percentage Concentration of Polycarbonate in Waste Polycarbonate (w-PC) Solution) - (Percentage Concentration of Polycarbonate in Refined Polycarbonate (r-PC) Solution).

5. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein the purity of the purified polycarbonate resin solution is 99% or higher.

6. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein the color coordinate L* of the purified polycarbonate resin solution is 98 or higher.

7. In Paragraph 1, The above second step is, Step 2-1 of introducing a waste polycarbonate resin solution containing waste polycarbonate resin, a filtration aid, and an organic solvent into a filter and circulating it; and A method for purifying waste polycarbonate-based resin, comprising: a second step of introducing the circulating liquid obtained in the above second-1 step into a filter and filtering it.

8. In Paragraph 1, A method for purifying waste polycarbonate-based resin, wherein the organic solvent is methylene chloride.

9. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein the mass ratio of waste polycarbonate resin in the above waste polycarbonate resin solution is 10% to 20%.

10. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein the mass ratio of the polycarbonate resin in the above precoat solution is 10% to 20%.

11. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein in the above waste polycarbonate resin solution, the content of a filtration aid is 1 to 20 parts by weight per 100 parts by weight of polycarbonate resin.

12. In Paragraph 1, A method for purifying waste polycarbonate-based resin, wherein the above-mentioned filtration aid comprises one or more compounds selected from the group consisting of diatomaceous earth, manganese sand, manganese zeolite, activated carbon, anthracite, ceramic sand, perlite, and cellulose.

13. In Paragraph 1, The above filtration aid is a method for purifying waste polycarbonate-based resin having an average particle size of 10 μm to 15 μm.

14. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein in the above precoat solution, the content of the filtration aid is 1 to 20 parts by weight per 100 parts by weight of the polycarbonate resin.

15. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein the above-mentioned waste polycarbonate resin solution further comprises an adsorbent.

16. In Paragraph 1, A method for purifying waste polycarbonate resin, wherein the adsorbent comprises charcoal or activated carbon.

17. A method for producing a monomer for synthesizing recycled plastic, comprising the step of recovering an aromatic diol compound obtained by the depolymerization reaction of a purified polycarbonate resin solution obtained in the method for purifying waste polycarbonate resin of claim 1.

18. A monomer for synthesizing recycled plastic, comprising an aromatic diol compound obtained in the method for manufacturing a monomer for synthesizing recycled plastic according to claim 17.

19. Recycled plastic comprising the reaction product of the monomer and comonomer for the synthesis of recycled plastic of paragraph 18.

20. A molded article comprising recycled plastic of paragraph 19.