Method for manufacturing methacrylic resins, method for recycling methacrylic resins

Abstract

Provided is a method for producing a methacrylic resin, which is low in cost and in which foreign matter can be sufficiently removed from a plastic including a methacrylic resin. This method for producing a methacrylic resin involves: a step (A) for mixing a plastic including a methacrylic resin with an alcohol to dissolve the methacrylic resin; a step (B) for removing an insoluble content included in the solution obtained in the step (A) by solid-liquid separation; a step (C) for producing the methacrylic resin from the solution after the solid-liquid separation by a phase separation method; and a step (D) for removing the alcohol remaining in the methacrylic resin produced in the step (C) by compression or centrifugation.

Description

Technical Field

[0001] The present invention relates to a method for producing a methacrylic resin, a method for recycling a methacrylic resin, a methacrylic resin, a monomer composition, and a methacrylic resin composition. This application claims priority based on Japanese Patent Application No. 2024-103856 filed in Japan on June 27, 2024, and incorporates the content herein.

Background Art

[0002] In the recycling of methacrylic resins such as polymethyl methacrylate, the quality of the raw material resin greatly affects the quality of the recycled product. Therefore, it is important to sufficiently remove foreign substances contained in waste materials containing methacrylic resins.

[0003] Patent Document 1 discloses a recycling method in which a recovered polymer containing a polymer containing acrylic acid esters or methacrylic acid esters is dissolved in a liquid containing an aliphatic alcohol containing an aliphatic hydrocarbon having 1 to 6 carbon atoms and water, and the polymer is precipitated from the solution to obtain a polymer.

[0004] Patent Document 2 discloses a method for recovering a methacrylic resin in which a resin composition containing a methacrylic resin and other thermoplastic resins is mixed with a monohydric alcohol having 2 to 4 carbon atoms and water to obtain a mixture of a solution in which the methacrylic resin is dissolved and a solid containing the thermoplastic resin, and then the mixture is separated into the solution and the solid.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the recycling of methacrylic resins, it is important to remove foreign matter from waste materials at low cost, and the technologies described in Patent Documents 1 and 2 need further improvement from this perspective. The primary object of the present invention is to provide a method for producing methacrylic resin and a method for recycling methacrylic resin that can sufficiently remove foreign matter from plastics containing methacrylic resin and is low-cost. Furthermore, the present invention aims to provide a methacrylic resin produced by the above-mentioned method for producing methacrylic resin, a monomer composition using the same, and a methacrylic resin composition. [Means for solving the problem]

[0007] In conventional techniques such as those described in Patent Documents 1 and 2, the methacrylic resin is precipitated and separated from the solution in which it is dissolved, and then the alcohol or other solvent used to dissolve the methacrylic resin is removed by heating and drying. In contrast, the present inventors have discovered that by separating the methacrylic resin from the solution and then removing the solvent remaining in the methacrylic resin by pressing or centrifugation, the energy required for removal can be reduced, thereby reducing costs, and thus the present invention has been completed.

[0008] In other words, the present invention includes the following embodiments. [1] A method for producing a methacrylic resin, comprising: (A) mixing a plastic containing a methacrylic resin with alcohol to dissolve the methacrylic resin; (B) removing insoluble matter from the solution obtained in step (A) by solid-liquid separation; (C) producing the methacrylic resin from the solution after solid-liquid separation by a phase separation method; and (D) removing the alcohol remaining in the methacrylic resin produced in step (C) by pressing or centrifugation. [2] The manufacturing method according to [1], wherein the plastic containing the methacrylic resin also contains a thermoplastic resin other than the methacrylic resin. [3] The manufacturing method according to [1] or [2], wherein in step (C), the methacrylic resin is produced from the solution after solid-liquid separation by a thermally induced phase separation method. [4] The manufacturing method according to any one of [1] to [3], wherein at least one of the alcohol separated from the methacrylic resin in step (C) and the alcohol separated from the methacrylic resin in step (D) is reused in step (A). [5] The manufacturing method according to any one of [1] to [4], wherein the alcohol comprises at least one selected from alcohols having 1 to 6 carbon atoms, and the alcohol concentration is 70% by volume or less in an aqueous solution. [6] A method for producing the methacrylic resin according to any one of [1] to [5], wherein in step (C), the solution after solid-liquid separation is brought into contact with a cooling surface at 20°C or lower to separate the phases. [7] The method for producing the methacrylic resin according to [6], wherein in step (C), the solution after solid-liquid separation is brought into contact with a cooling surface of 20°C or lower while being stretched and oriented. [8] The manufacturing method according to [6] or [7], wherein a long length of methacrylic resin is continuously produced by continuously bringing the solution after solid-liquid separation into contact with the cooling surface and peeling the precipitated methacrylic resin from the cooling surface. [9] A manufacturing method according to any one of [1] to [8], wherein the solution obtained by solid-liquid separation in step (B) is treated by adsorption and then supplied to step (C).

[0010] A manufacturing method according to any one of [1] to [9], wherein step (C) and step (D) are performed in the same apparatus.

[11] A manufacturing method according to any one of [2] to [9], which includes a step of recovering thermoplastic resins other than methacrylic resins in the insoluble matter separated by solid-liquid separation in step (B) above.

[12] A method for recycling methacrylic resin, wherein the methacrylic resin produced by any of the manufacturing methods described in [1] to

[11] is recycled.

[13] A methacrylic resin manufactured by any of the manufacturing methods described in [1] to

[11] .

[14] A methacrylic resin that has been stretched to more than twice its length in the axial direction, manufactured by the manufacturing method described in any of [1] to

[11] .

[15] A long methacrylic resin with an alcohol content of 75% by mass or less, manufactured by the manufacturing method described in any of [1] to

[11] .

[16] A porous, elongated methacrylic resin manufactured by any of the manufacturing methods described in [1] to

[11] . A monomer composition obtained by chemically recycling any of the methacrylic resins

[17]

[13] to

[16] . A methacrylic resin composition obtained by polymerizing the monomer compositions of

[18] and

[17] . [Effects of the Invention]

[0009] The present invention provides a method for producing a methacrylic resin and a method for recycling a methacrylic resin that can sufficiently remove foreign matter from plastics containing methacrylic resins and is low-cost. Furthermore, the present invention provides a methacrylic resin produced by the method for producing the methacrylic resin, a monomer composition using the same, and a methacrylic resin composition. [Brief explanation of the drawing]

[0010] [Figure 1] This is an explanatory diagram of a method for producing a methacrylic resin according to an embodiment. [Modes for carrying out the invention]

[0011] The following terms used in this specification have the meanings set forth below. "(Meth)acrylate" means at least one selected from "acrylate" and "methacrylate". "(Meth)acrylic acid" means at least one selected from "acrylic acid" and "methacrylic acid". (Meth)acrylonitrile means at least one selected from "acrylonitrile" and "methacrylonitrile". "Methacrylic resin" means a resin containing repeating units derived from methacrylic monomers, and may contain repeating units derived from acrylic monomers in addition to the repeating units derived from methacrylic monomers. "Monomer" means a compound having one or more radically polymerizable double bonds in the molecule. "Repeating unit" means a unit derived from the monomer formed by polymerization of the monomer. The repeating unit may be a unit directly formed by a polymerization reaction, or a unit in which a part of the unit is converted into another structure by treating the polymer after polymerization. A numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, and "A~B" means A or more and B or less.

[0012] [Method for producing methacrylic resin] The method for producing a methacrylic resin according to the embodiment includes the following steps (A) to (D). Step (A): Mix a plastic containing a methacrylic resin and an alcohol to dissolve the methacrylic resin. Step (B): Remove insoluble components contained in the solution obtained in step (A) by solid-liquid separation. Step (C): Produce the methacrylic resin from the solution after solid-liquid separation by a phase separation method. Step (D): Remove the alcohol remaining in the methacrylic resin produced in step (C) by pressing or centrifugation.

[0013] (Step (A)) As shown in Figure 1, in step (A), for example, a plastic containing methacrylic resin, which is waste material, is mixed with alcohol, and the mixture is stirred, shaken, etc., as needed to dissolve the methacrylic resin in the alcohol. Step (A) utilizes the property that methacrylic resin dissolves in alcohol to obtain a mixture of a solution in which methacrylic resin is dissolved in alcohol and a solid (foreign matter) containing components insoluble in alcohol. The solid foreign matter insoluble in alcohol is separated and removed in step (B) described later.

[0014] As the methacrylic resin, a polymer mainly composed of methyl methacrylate (MMA) (PMMA) is preferred. However, "mainly composed of methyl methacrylate" means that the proportion of repeating units derived from MMA to the total repeating units of the methacrylic resin is 50% by mass or more. Hereinafter, repeating units derived from MMA will also be referred to as "MMA units," and repeating units derived from other monomers will be referred to similarly. The proportion of MMA units in the methacrylic resin is preferably 70% by mass or more, and more preferably 90% by mass or more, relative to the total repeating units of the methacrylic resin. The proportion of MMA units is not particularly limited as long as the methacrylic resin is soluble in alcohol.

[0015] The methacrylic resin may be a homopolymer of MMA, or a copolymer of MMA and monomers other than MMA. The structure of the copolymer is not particularly limited and may be, for example, a random copolymer, a block copolymer, a graft copolymer, or an alternating copolymer.

[0016] Examples of monomers other than MMA include (meth)acrylic acid esters other than MMA, (meth)acrylic acid, and vinyl sulfonic acid. Examples of (meth)acrylic acid esters other than MMA include methyl acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. If the methacrylic resin contains repeating units derived from monomers other than MMA, there may be one type of repeating unit or two or more types.

[0017] Examples of foreign substances that may be contained in plastics containing methacrylic resins include thermoplastic resins other than methacrylic resins, phenolic resins, epoxy resins, melamine resins, thermosetting resins such as urethane, metals, and additives. The manufacturing method according to the embodiment is particularly useful as a method for producing methacrylic resin by separating and removing foreign substances from plastics containing methacrylic resins. Examples of thermosetting resins include phenolic resins, epoxy resins, melamine resins, and urea resins. The thermosetting resin contained in a plastic containing methacrylic resins may be one type or two or more types. The phenolic resin is not particularly limited, and examples include novolac-type phenolic resins and resol-type phenolic resins. The epoxy resin is not particularly limited as long as it has at least one epoxy group, and examples include bisphenol-type epoxy resins and novolac-type epoxy resins. The melamine resin is not particularly limited as long as it is a thermosetting resin obtained by the addition-condensation reaction of melamine and formaldehyde. The urea resin is not particularly limited as long as it is a thermosetting resin obtained by the addition-condensation reaction of urea and formaldehyde. Examples of metals include iron, steel, copper, aluminum, and titanium. The metal contained in plastics containing methacrylic resin may be one type or two or more types.

[0018] When a plastic containing methacrylic resin also contains thermoplastic resins other than methacrylic resin, its form is not particularly limited. For example, it may be a plastic in which methacrylic resin and other thermoplastic resins are uniformly mixed, or it may be a multilayer plastic consisting of a layer of methacrylic resin and a layer of thermoplastic resin other than methacrylic resin. Alternatively, it may be a PMMA molded board with a masking material such as a surface protection sheet (film) attached to it. The material of the surface protection sheet may be a resin such as polyethylene, or it may be paper.

[0019] Thermoplastic resins other than methacrylic resins are thermoplastic resins that are insoluble in alcohol, and examples include polycarbonate resins, styrene resins, polyolefin resins, polyvinyl chloride resins, polyester resins, and fluororesins. The thermoplastic resins other than methacrylic resins contained in plastics containing methacrylic resins may be one type or two or more types.

[0020] The polycarbonate resin is not particularly limited and includes, for example, a resin obtained by polymerizing a divalent phenol and a carbonylating agent by interfacial polycondensation or melt transesterification, a resin obtained by polymerizing a carbonate prepolymer by solid-phase transesterification, and a resin obtained by polymerizing a cyclic carbonate compound by ring-opening polymerization. Examples of divalent phenols include bisphenol A, 2,2-bis{(4-hydroxy-3-methyl)phenyl}propane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)-3-methylbutane, 2,2-bis(4-hydroxyphenyl)-3,3-dimethylbutane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and α,α'-bis(4-hydroxyphenyl)-m-diisopropylbenzene. Examples of carbonylating agents include phosgene, diphenyl carbonate, and dihaloformates of divalent phenols.

[0021] Styrene resins are polymers mainly composed of styrene monomers. However, "mainly composed of styrene monomers" means that the proportion of repeating units derived from styrene monomers to the total repeating units of the styrene resin is 50% by mass or more. The styrene-based resin may be a homopolymer of styrene-based monomers, or it may be a copolymer of a styrene-based monomer and a monomer other than a styrene-based monomer.

[0022] Examples of styrene monomers include styrene; halogenated styrenes such as chlorostyrene and bromostyrene; and alkyl-substituted styrenes such as vinyltoluene and α-methylstyrene. Examples of monomers other than styrene monomers include (meth)acrylonitrile, (meth)acrylic acid, maleic anhydride, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, divinylbenzene, and diallyl phthalate. These monomers may be used individually or in combination of two or more.

[0023] Polyolefin resins are polymers mainly composed of α-olefin monomers. However, "mainly composed of α-olefin monomers" means that the proportion of repeating units derived from α-olefin monomers to the total repeating units of the polyolefin resin is 50% by mass or more. The polyolefin resin may be a homopolymer of α-olefin monomers, or it may be a copolymer of an α-olefin monomer and a monomer other than an α-olefin monomer.

[0024] Examples of α-olefin monomers include ethylene, propylene, and 1-butylene. Examples of monomers other than α-olefin monomers include vinyl carboxylates such as vinyl acetate and vinyl propionate. These monomers may be used individually or in combination of two or more.

[0025] Polyvinyl chloride resin is a polymer mainly composed of vinyl chloride monomers. However, "mainly composed of vinyl chloride monomers" means that the proportion of repeating units derived from vinyl chloride monomers to the total repeating units of the polyvinyl chloride resin is 50% by mass or more. There are no particular limitations on the type of polyvinyl chloride resin; for example, flexible polyvinyl chloride resin and rigid polyvinyl chloride resin can be used.

[0026] Polyester resins are resins obtained by condensation reactions using carboxylic acids, aromatic dicarboxylic acids or their ester-forming derivatives, and alkylene glycols. Polyester resins are not particularly limited and include, for example, polyethylene terephthalate, polybutylene terephthalate, and polylactic acid.

[0027] Fluororesins are resins containing fluorine atoms and are not particularly limited; examples include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0028] Plastics containing methacrylic resins may also contain a copolymer of vinyl cyanide monomers, butadiene, and styrene monomers as a thermoplastic resin other than the methacrylic resin. Examples of vinyl cyanide monomers include (meth)acrylonitrile. Examples of styrene monomers include the same styrene monomers exemplified in the styrene resin. Specific examples of copolymers of vinyl cyanide monomers, butadiene, and styrene monomers include acrylonitrile-butadiene-styrene copolymers and acrylonitrile-styrene-acrylic acid ester copolymers.

[0029] Plastics containing methacrylic resins may contain additives such as impact absorbers, antistatic agents, antioxidants, lubricants, mold release agents, dyes, and pigments. The additives contained in plastics containing methacrylic resins may be one type or two or more types.

[0030] As the alcohol, monohydric alcohols having 1 to 6 carbon atoms are preferred. Specifically, examples include methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, t-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, cyclopentanol, and cyclohexanol. Ethanol, 1-propanol, isopropanol, and t-butanol are more preferred as alcohols because they are inexpensive and readily available, and the methacrylic resin after dissolution can be produced by thermally induced phase separation. One type of alcohol may be used alone, or two or more types may be used in combination.

[0031] Alcohol may also be used as an aqueous alcohol solution. When used as an aqueous alcohol solution, the concentration of alcohol in the aqueous solution is preferably 20% by volume or more, more preferably 25% by volume or more, even more preferably 50% by volume or more, preferably 90% by volume or less, more preferably 85% by volume or less, even more preferably 70% by volume or less, and particularly preferably 60% by volume or less, based on the total volume of the aqueous solution. The lower and upper limits of the alcohol concentration can be arbitrarily combined, for example, preferably 20% by volume or more and 90% by volume or less, more preferably 25% by volume or more and 85% by volume or less, even more preferably 25% by volume or more and 70% by volume or less, and particularly preferably 50% by volume or more and 60% by volume or less. The lower and upper limits of the alcohol concentration in the aforementioned aqueous alcohol solution can be 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, and 20 in relation to the total volume of the aqueous alcohol solution, and can be within the range of any two of these values, for example, if 85 and 25, then 25% by volume or more and 85% by volume or less. If the alcohol ratio is below the upper limit, it becomes easy to dissolve only the methacrylic resin and then produce the methacrylic resin after dissolution by thermally induced phase separation. Also, if the alcohol ratio is above the lower limit, the content of water, which has a higher latent heat of vaporization than alcohol, decreases, so the energy required to dry the methacrylic resin produced by phase separation is reduced, and the methacrylic resin can be produced at low cost.

[0032] The amount of alcohol or aqueous alcohol solution used can be appropriately adjusted within the range in which the methacrylic resin in the plastic containing the methacrylic resin dissolves. The amount of alcohol or aqueous alcohol solution used is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, even more preferably 10 parts by mass or more, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 25 parts by mass or less, per 1 part by mass of the plastic containing the methacrylic resin. The preferred lower and upper limits of the amount of alcohol or aqueous alcohol solution used can be arbitrarily combined, for example, 5 to 100 parts by mass is preferred, 7 to 50 parts by mass is more preferred, and 10 to 25 parts by mass is even more preferred.

[0033] When dissolving a plastic containing methacrylic resin in alcohol or an aqueous alcohol solution, the temperature of the alcohol or aqueous alcohol solution is preferably 40°C or higher, more preferably 50°C or higher, preferably 100°C or lower, and more preferably 90°C or lower, depending on the alcohol used. The preferred lower and upper limits of the temperature of the alcohol or aqueous alcohol solution can be arbitrarily combined, for example, preferably 40 to 100°C and more preferably 50 to 90°C.

[0034] The mixing time when dissolving plastics containing methacrylic resin in alcohol or an aqueous alcohol solution can be, for example, 1 to 12 hours, with 3 to 8 hours being preferable.

[0035] (Process (B)) In step (B), the insoluble solids contained in the solution of methacrylic resin obtained in step (A) are removed by solid-liquid separation. The solid-liquid separation method is not particularly limited and includes, for example, filtration and decantation.

[0036] The treated solution may be supplied to process (C) after removing any dyes or other substances remaining in the solution after solid-liquid separation by adsorption. Known methods can be used as the adsorption method. Examples of adsorbents include activated carbon, activated alumina, silica gel, zeolite, titanium dioxide, ion exchange resin, bentonite, diatomaceous earth, activated clay, etc. As for the adsorption treatment, for example, a method of passing the solution through a column packed with adsorbent or a method of adding the adsorbent to the solution and then removing the adsorbent again by solid-liquid separation can be used.

[0037] Furthermore, a separate step may be provided to recover thermoplastic resins other than methacrylic resins from the insoluble matter separated by solid-liquid separation in step (B). The recovered thermoplastic resins other than methacrylic resins can be recycled. Known methods can be used for recovering thermoplastic resins other than methacrylic resins.

[0038] (Process (C)) In step (C), a methacrylic resin is produced from the solution containing the dissolved methacrylic resin after solid-liquid separation in step (B) by a phase separation method. Examples of phase separation methods include thermally induced phase separation, which induces phase separation by temperature changes, and non-solvent-induced phase separation, which induces phase separation by contact of a non-solvent that does not dissolve the methacrylic resin or a poor solvent with the methacrylic resin. Thermally induced phase separation is preferred as the phase separation method. This is because phase separation can be induced by cooling alone without adding a non-solvent or poor solvent, and the composition of the alcohol does not change, allowing for inexpensive reuse of the alcohol.

[0039] The method for producing methacrylic resin by thermally induced phase separation is not particularly limited as long as it can cool the solution containing the dissolved methacrylic resin after solid-liquid separation. A preferred example is a method in which the solution after solid-liquid separation is brought into contact with a cooling surface of a cooling member, the solution is cooled to induce phase separation, and the methacrylic resin is precipitated for production. Any cooling component that can adjust the cooling surface to which the solution after solid-liquid separation comes into contact to a desired temperature is acceptable, and examples include cooling rolls, cooling plates, and cooling belts. Furthermore, while there are no particular limitations on the material of the cooling component, metals such as iron, stainless steel, aluminum, titanium, and copper, as well as those with a fluorine coating on their surface or a glass coating on their surface, can be used.

[0040] The temperature of the cooling surface is preferably 20°C or lower, more preferably 15°C or lower, and even more preferably 10°C or lower. If the temperature of the cooling surface is below the upper limit, phase separation is more easily induced, and methacrylic resin can be produced more efficiently. On the other hand, the temperature of the cooling surface is preferably -5°C or higher, more preferably 0°C or higher, and even more preferably 5°C or higher. If the temperature of the cooling surface is above the lower limit, the energy required to cool the cooling surface can be reduced, which is advantageous in terms of cost. The preferred lower and upper limits for the temperature of the cooling surface can be arbitrarily combined; for example, -5 to 20°C is preferred, 0 to 15°C is more preferred, and 5 to 10°C is even more preferred.

[0041] In process (C), it is preferable to continuously produce long lengths of methacrylic resin by continuously contacting the solution after solid-liquid separation with a cooling surface and peeling off the precipitated methacrylic resin from the cooling surface, since this allows for low-cost and efficient production of methacrylic resin. A specific example is a method of continuously manufacturing methacrylic resin using a cooling roll as a cooling component. For example, while rotating the cooling roll, the solution after solid-liquid separation is continuously brought into contact with the outer surface of the cooling roll, which is the cooling surface, at a certain point. Then, the methacrylic resin deposited on the outer surface of the rotating cooling roll is continuously peeled off before returning to the point where the solution after solid-liquid separation was in contact. This allows for continuous cooling of the solution after solid-liquid separation and continuous production of long lengths of methacrylic resin. In this case, it is necessary to impart toughness to the manufactured methacrylic resin, and in step (C), it is preferable to bring the solution after solid-liquid separation into contact with the cooling surface while stretching and oriented it, and it is preferable to continuously manufacture the methacrylic resin deposited on the cooling surface while stretching and oriented it to more than twice its length in the axial direction of the long length.

[0042] When stretching a methacrylic resin in the axial direction over a long length, the stretching ratio is preferably 2 times or more, preferably 10 times or less, and more preferably 5 times or less. If the stretching ratio is above the lower limit, the toughness of the methacrylic resin tends to improve. If the stretching ratio is below the upper limit, the methacrylic resin does not break and can be continuously recovered. The lower and upper limits of the stretching ratio can be arbitrarily combined; for example, 2 to 10 times is preferred, and 2 to 5 times is more preferred.

[0043] (Process (D)) In step (D), any alcohol remaining in the methacrylic resin produced in step (C) is removed by pressing or centrifugal force. The energy required for physical removal processes such as pressing and centrifugal separation is significantly less than the energy required for removal processes that involve evaporating alcohol by heating. Therefore, by performing process (D), energy savings are possible, and methacrylic resins can be manufactured at a low cost.

[0044] When removing residual alcohol from methacrylic resin by pressing or centrifugal separation, the operating temperature is preferably 40°C or higher, more preferably 60°C or higher, preferably 120°C or lower, and more preferably 100°C or lower. If the heating temperature is above the lower limit, the methacrylic resin is more likely to become porous. If the heating temperature is below the upper limit, handling during pressing is improved, and a large amount of solvent can be continuously removed. The lower and upper limits of the heating temperature can be arbitrarily combined; for example, 40 to 120°C is preferred, and 60 to 100°C is more preferred.

[0045] In step (D), after removing the alcohol remaining in the methacrylic resin by pressing or centrifugation, the methacrylic resin may be air-dried, or it may be heated and dried as needed. Performing pressing or centrifugation significantly reduces the energy required for drying compared to heating and drying without these processes. Therefore, energy savings are possible even when heating and drying are performed after pressing or centrifugation, allowing for the low-cost production of methacrylic resin.

[0046] The alcohol content of the methacrylic resin after pressing or stretching separation is preferably 75% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less, relative to the total mass of the methacrylic resin and alcohol. The lower the alcohol content after pressing or stretching separation, the less energy is required for subsequent drying.

[0047] When heat-drying methacrylic resins, the heating temperature is preferably 50 to 120°C, and more preferably 60 to 100°C. The drying time is preferably 0.5 to 12 hours, and more preferably 1 to 4 hours.

[0048] Furthermore, by providing a cooling unit within the apparatus used in process (D), the phase separation function of process (C) can be incorporated, allowing processes (C) and (D) to be performed in the same apparatus. For example, when using a press dewatering machine, a cooling unit can be provided within the press dewatering machine, and when using a centrifuge, the wetted parts of the centrifuge can be cooled to provide the phase separation function. Considering the time required for phase separation, it is preferable to have an apparatus structure that can hold the solution for a certain period of time.

[0049] As shown in Figure 1, in the manufacturing method according to the embodiment, it is preferable to reuse at least one of the alcohol separated from the methacrylic resin in step (C) and the alcohol separated from the methacrylic resin in step (D) in step (A). By reusing the alcohol recovered in steps (C) and (D) in step (A), the methacrylic resin can be manufactured at an even lower cost, and the environmental burden can also be reduced. Since the effects of cost reduction and environmental burden reduction are even greater, it is particularly preferable to reuse both the alcohol recovered in step (C) and the alcohol recovered in step (D) in step (A). Some additives and other components in plastics containing methacrylic resins may leach into alcohol in trace amounts. If the alcohol containing these leached additives is recovered and reused multiple times, these impurities may accumulate in the process, potentially adversely affecting the quality of the manufactured methacrylic resin. In such cases, the quality of the manufactured methacrylic resin can be maintained by replacing the alcohol with fresh alcohol or by separating and removing the additives and other impurities contained in the recovered alcohol through distillation or other means before reuse.

[0050] [Methacrylic resin] The methacrylic resin according to the embodiment is a methacrylic resin produced by the method for producing methacrylic resin described above. In the method for producing methacrylic resin described above, for example, methacrylic resins in the low molecular weight range of 30,000 or less remain dissolved in alcohol and are easily separated and removed, so the molecular weight distribution shifts to the higher molecular weight side. The methacrylic resin produced by the manufacturing method according to this embodiment can be a methacrylic resin that has been stretched to more than twice its length in the axial direction of a long length. The methacrylic resin produced by the manufacturing method according to this embodiment can be a long methacrylic resin with an alcohol content of 75% by mass or less. The methacrylic resin produced by the manufacturing method according to this embodiment can be a porous and elongated methacrylic resin.

[0051] The alcohol content of the methacrylic resin produced by the manufacturing method according to the embodiment is preferably 75% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less, based on the total mass of the methacrylic resin and alcohol. The lower the alcohol content, the better.

[0052] [Methacrylic resin recycling methods] The recycling method for methacrylic resin according to the embodiment is a method for recycling methacrylic resin produced by the manufacturing method according to the embodiment. The recycling method for the methacrylic resin according to the embodiment is not particularly limited other than using the methacrylic resin produced by the manufacturing method according to the embodiment. Examples include material recycling and chemical recycling, with chemical recycling being preferred.

[0053] One example of a chemical recycling method is to thermally decompose a methacrylic resin produced by the manufacturing method according to the embodiment to produce monomers as thermal decomposition products, and then use these monomers to produce recycled products. Polymethyl methacrylate is known to decompose thermally at relatively low temperatures of around 300°C. From the viewpoint of productivity and monomer purity, the thermal decomposition temperature is preferably 300 to 700°C, more preferably 300 to 500°C, and even more preferably 300 to 450°C.

[0054] As the pyrolysis apparatus, known apparatuses can be used, such as microwave decomposition apparatuses, extruders, kneaders, and fluidized bed heaters. An extruder is a device that uses a screw located inside a cylindrical member (cylinder) to rotate, melting the raw material fed from the upstream side of the cylinder and transporting it downstream. An example of a kneader is the device described in U.S. Patent No. 1,0301,235. An example of a fluidized bed heater is the device described in Japanese Patent Application Publication No. 2009-112902.

[0055] [Monomer composition] The monomer composition according to the embodiment is a monomer composition obtained by subjecting a methacrylic resin produced by the above-described manufacturing method to chemical recycling. Compared to conventional monomer compositions derived from fossil fuels, the monomer composition obtained by the above-described recycling method can be manufactured while suppressing carbon dioxide emissions, is obtained at low cost, and has high purity.

[0056] [Methacrylic resin composition] Furthermore, a methacrylic resin composition can be obtained by polymerizing the monomer composition obtained by the chemical recycling described above. Polymerization may also be carried out by adding monomers produced by other known methods to the monomer composition obtained by the chemical recycling described above. Polymerization methods include, for example, bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization. Among these polymerization methods, bulk polymerization and suspension polymerization are preferred from the viewpoint of superior productivity, and bulk polymerization is more preferred. The methacrylic resin composition obtained in this way can be manufactured while suppressing carbon dioxide emissions, is obtained at low cost, and has high purity compared to conventional methacrylic resin compositions derived from fossil fuels.

[0057] The present invention is not limited to the embodiments described above, and it is possible to replace components with well-known components as long as it does not depart from the spirit of the invention, and the above-described modifications may be combined as appropriate.

Claims

1. A method for producing a methacrylic resin, comprising: (A) mixing a plastic containing a methacrylic resin with alcohol to dissolve the methacrylic resin; (B) removing insoluble matter from the solution obtained in step (A) by solid-liquid separation; (C) producing the methacrylic resin by phase separation by contacting the solution after solid-liquid separation with a cooling surface at 20°C or lower; and (D) removing the alcohol remaining in the methacrylic resin produced in step (C) by pressing or centrifugal separation.

2. The manufacturing method according to claim 1, wherein the plastic containing the methacrylic resin also contains a thermoplastic resin other than the methacrylic resin.

3. The manufacturing method according to claim 1, wherein in step (C), the methacrylic resin is produced from the solution after solid-liquid separation by a thermally induced phase separation method.

4. The manufacturing method according to claim 1, wherein at least one of the alcohol separated from the methacrylic resin in step (C) and the alcohol separated from the methacrylic resin in step (D) is reused in step (A).

5. The manufacturing method according to claim 1, wherein the alcohol comprises at least one selected from alcohols having 1 to 6 carbon atoms, and is an aqueous solution with an alcohol concentration of 70% by volume or less.

6. The manufacturing method according to claim 1, wherein in step (C), the methacrylic resin is produced by phase separation by bringing the solution after solid-liquid separation into contact with a cooling surface at 20°C or lower while stretching and oriented.

7. The manufacturing method according to claim 1, wherein a long length of methacrylic resin is continuously produced by continuously bringing the solution after solid-liquid separation into contact with the cooling surface and peeling the precipitated methacrylic resin from the cooling surface.

8. The manufacturing method according to claim 1, wherein the solution obtained by solid-liquid separation in step (B) is treated by an adsorption method and then supplied to step (C).

9. The manufacturing method according to claim 1, wherein step (C) and step (D) are performed in the same apparatus.

10. The manufacturing method according to claim 2, further comprising a step of recovering thermoplastic resins other than methacrylic resins in the insoluble matter separated by solid-liquid separation in step (B) above.

11. A method for recycling a methacrylic resin, comprising recycling a methacrylic resin produced by a manufacturing method described in any one of claims 1 to 10.

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