Method for producing methacrylic resin, method for recycling methacrylic resin, methacrylic resin, monomer composition, and methacrylic resin composition

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

METHOD FOR PRODUCING METHACRYLIC RESIN, METHACRYLIC RESIN RECYCLING METHOD, METHACRYLIC RESIN, MONOMER COMPOSITION, AND METHACRYLIC RESIN COMPOSITION

[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 on June 27, 2024, the contents of which are incorporated herein by reference.

[0002] In the recycling of methacrylic resins such as polymethyl methacrylate, the quality of the raw resin significantly affects the quality of the recycled product, so it is important to thoroughly remove foreign matter contained in waste materials containing methacrylic resins.

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

[0004] Patent Document 2 discloses a method for recovering a methacrylic resin, which comprises mixing a resin composition containing a methacrylic resin and another thermoplastic resin 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 separating the mixture into the solution and the solid.

[0005] JP 2009-30017 A JP 2009-179690 A

[0006] In recycling methacrylic resins, it is important to inexpensively remove foreign matter from waste materials, and the techniques of Patent Documents 1 and 2 need further improvement in this regard. A primary object of the present invention is to provide a method for producing a methacrylic resin and a method for recycling a methacrylic resin that can sufficiently remove foreign matter from plastics containing a methacrylic resin and are low cost. Another object of the present invention is to provide a methacrylic resin produced by the method for producing a methacrylic resin, and a monomer composition and a methacrylic resin composition using the same.

[0007] In conventional techniques such as those described in Patent Documents 1 and 2, the methacrylic resin is separated by precipitating it from a solution in which it is dissolved, and then the alcohol or the like used to dissolve the methacrylic resin is removed by heating and drying. In contrast, the present inventors discovered that by separating the methacrylic resin from the solution and then removing the solvent remaining in the methacrylic resin by squeezing or centrifugation, it is possible to reduce the energy required for the removal and cut costs, and thus completed the present invention.

[0008] That is, the present invention includes the following aspects. [1] A method for producing a methacrylic resin, comprising: step (A) of mixing a plastic containing a methacrylic resin with an alcohol to dissolve the methacrylic resin; step (B) of removing an insoluble component contained in the solution obtained in step (A) by solid-liquid separation; step (C) of producing the methacrylic resin from the solution after solid-liquid separation by a phase separation method; and step (D) of removing the alcohol remaining in the methacrylic resin produced in step (C) by compression or centrifugation. [2] The production method according to [1], wherein the plastic containing a methacrylic resin contains a thermoplastic resin other than the methacrylic resin. [3] The production 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 is an aqueous solution having an alcohol concentration of 70% by volume or less. [6] The manufacturing method according to any one of [1] to [5], wherein in step (C), the methacrylic resin is produced by bringing the solution after solid-liquid separation into contact with a cooling surface at 20°C or less to cause phase separation. [7] The manufacturing method according to [6], wherein in step (C), the methacrylic resin is produced by bringing the solution after solid-liquid separation into contact with a cooling surface at 20°C or less while stretching and orienting it. [8] The manufacturing method according to [6] or [7], in which a long length of methacrylic resin is continuously manufactured by continuously bringing the solution after solid-liquid separation into contact with the cooling surface and peeling off the precipitated methacrylic resin from the cooling surface. [9] The manufacturing method according to any one of [1] to [8], in which the solution obtained by solid-liquid separation in step (B) is treated by an adsorption method and then supplied to step (C).

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

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

[12] A method for recycling a methacrylic resin, which comprises recycling the methacrylic resin manufactured by the manufacturing method according to any one of [1] to

[11] .

[13] A methacrylic resin manufactured by the manufacturing method according to any one of [1] to

[11] .

[14] A methacrylic resin stretched to two or more times its original length in the axial direction of the long length, which is manufactured by the manufacturing method according to any one of [1] to

[11] .

[15] A long methacrylic resin having an alcohol content of 75% by mass or less, which is manufactured by the manufacturing method according to any one of [1] to

[11] .

[16] A porous long methacrylic resin manufactured by the manufacturing method according to any one of [1] to

[11] .

[17] A monomer composition obtained by chemically recycling the methacrylic resin according to any one of

[13] to

[16] .

[18] A methacrylic resin composition obtained by polymerizing the monomer composition according to

[17] .

[0009] The present invention provides a method for producing a methacrylic resin, which can sufficiently remove foreign matter from plastics containing the methacrylic resin, and a low-cost method for recycling the methacrylic resin. The present invention also provides a methacrylic resin produced by the method for producing the methacrylic resin, and a monomer composition and a methacrylic resin composition using the same.

[0010] FIG. 2 is an explanatory diagram of a method for producing a methacrylic resin according to an embodiment.

[0011] The following terms used in this specification have the following meanings. "(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 a methacrylic monomer, and may contain repeating units derived from an acrylic monomer in addition to repeating units derived from a methacrylic monomer. "Monomer" means a compound having one or more radically polymerizable double bonds in the molecule. "Repeating unit" means a unit derived from a monomer formed by polymerization of the monomer. The repeating unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a portion of the unit is converted into a different structure by treating the polymer after polymerization. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less.

[0012] [Method for producing methacrylic resin] The method for producing a methacrylic resin according to an embodiment includes the following steps (A) to (D). Step (A): A plastic containing a methacrylic resin is mixed with alcohol to dissolve the methacrylic resin. Step (B): Insoluble matter contained in the solution obtained in step (A) is removed by solid-liquid separation. Step (C): The methacrylic resin is produced from the solution after solid-liquid separation by a phase separation method. Step (D): The alcohol remaining in the methacrylic resin produced in step (C) is removed by squeezing or centrifugation.

[0013] (Step (A)) As shown in FIG. 1 , in step (A), for example, waste plastic containing methacrylic resin is mixed with alcohol, and the methacrylic resin is dissolved in the alcohol by stirring, shaking, etc. as necessary. In step (A), the solubility of methacrylic resin in alcohol is utilized to obtain a solution in which the methacrylic resin is dissolved in alcohol, and a mixture of a solid (foreign matter) containing components insoluble in alcohol. The solid foreign matter insoluble in alcohol is separated and removed in step (B) described below.

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

[0015] The methacrylic resin may be a homopolymer of MMA or a copolymer of MMA and a monomer 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. When the methacrylic resin contains a repeating unit derived from a monomer other than MMA, the repeating unit may be of one type or two or more types.

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

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

[0019] The thermoplastic resin other than the methacrylic resin is a thermoplastic resin insoluble in alcohol, and examples thereof include polycarbonate resin, styrene resin, polyolefin resin, polyvinyl chloride resin, polyester resin, and fluororesin. The thermoplastic resin other than the methacrylic resin contained in the plastic containing the methacrylic resin may be one type or two or more types.

[0020] The polycarbonate resin is not particularly limited, and examples thereof include resins obtained by polymerizing a dihydric phenol and a carbonylating agent by interfacial polycondensation or melt transesterification, resins obtained by polymerizing a carbonate prepolymer by solid-phase transesterification, and resins obtained by polymerizing a cyclic carbonate compound by ring-opening polymerization. Examples of dihydric 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 the carbonylating agent include phosgene, diphenyl carbonate, and dihaloformates of dihydric phenols.

[0021] A styrene-based resin is a polymer mainly composed of a styrene-based monomer. Here, "mainly composed of a styrene-based monomer" means that the proportion of repeating units derived from the styrene-based monomer to all repeating units of the styrene-based resin is 50 mass% or more. The styrene-based resin may be a homopolymer of a styrene-based monomer, or may be a copolymer of a styrene-based monomer and a monomer other than a styrene-based monomer.

[0022] Examples of styrene-based 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-based 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 alone or in combination of two or more.

[0023] Polyolefin resins are polymers primarily composed of α-olefin monomers. However, "primarily composed of α-olefin monomers" means that the proportion of repeating units derived from α-olefin monomers relative to all repeating units of the polyolefin resin is 50 mass% or more. The polyolefin resin may be a homopolymer of an α-olefin monomer, or 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 carboxylate esters such as vinyl acetate and vinyl propionate. These monomers may be used alone or in combination of two or more.

[0025] Polyvinyl chloride resin is a polymer mainly composed of vinyl chloride monomer. Here, "mainly composed of vinyl chloride monomer" means that the proportion of repeating units derived from vinyl chloride monomer to all repeating units of the polyvinyl chloride resin is 50 mass% or more. The polyvinyl chloride resin is not particularly limited, and examples thereof include soft vinyl chloride resin and hard vinyl chloride resin.

[0026] The polyester resin is a resin obtained by a condensation reaction of a carboxylic acid, an aromatic dicarboxylic acid, or an ester-forming derivative thereof, and an alkylene glycol. The polyester resin is not particularly limited, and examples thereof include polyethylene terephthalate, polybutylene terephthalate, and polylactic acid.

[0027] The fluororesin is a resin containing fluorine atoms, and is not particularly limited, and examples thereof include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0028] The plastic containing a methacrylic resin may contain a copolymer of a vinyl cyanide monomer, butadiene, and a styrene monomer as a thermoplastic resin other than the methacrylic resin. Examples of the vinyl cyanide monomer include (meth)acrylonitrile. Examples of the styrene monomer include the same styrene monomers as those exemplified for the styrene resin. Specific examples of the copolymer of a vinyl cyanide monomer, butadiene, and a styrene monomer include an acrylonitrile-butadiene-styrene copolymer and an acrylonitrile-styrene-acrylic acid ester copolymer.

[0029] The plastic containing the methacrylic resin may contain additives such as an impact resistance agent, an antistatic agent, an antioxidant, a lubricant, a mold release agent, a dye, a pigment, etc. The additives contained in the plastic containing the methacrylic resin may be one type or two or more types.

[0030] As the alcohol, a monohydric alcohol having 1 to 6 carbon atoms is preferred. Specific 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. As the alcohol, ethanol, 1-propanol, isopropanol, and t-butanol are more preferred because they are inexpensively available and can be produced by thermally induced phase separation of the methacrylic resin after dissolution. One type of alcohol may be used alone, or two or more types may be used in combination.

[0031] The alcohol may be used as an aqueous alcohol solution. When used as an aqueous alcohol solution, the concentration of the alcohol in the aqueous alcohol solution is preferably 20% by volume or more, more preferably 25% by volume or more, even more preferably 50% by volume or more, and 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, relative to the total volume of the aqueous alcohol solution. The lower and upper limits of the alcohol concentration can be arbitrarily combined, and for example, 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 upper and lower limits of the alcohol concentration in the aqueous alcohol solution may be 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, or 20% by volume, based on the total volume of the aqueous alcohol solution. If the alcohol concentration is within a range between any two of these values, for example, 85 and 25, the alcohol concentration may be 25% by volume or more and 85% by volume or less. When the alcohol concentration is below the upper limit, only the methacrylic resin is dissolved, and the dissolved methacrylic resin can be easily produced by thermally induced phase separation. Furthermore, when the alcohol concentration is above the lower limit, the content of water, which has a larger latent heat of vaporization than alcohol, is reduced, thereby reducing the energy required to dry the methacrylic resin produced by phase separation, allowing for inexpensive production of the methacrylic resin.

[0032] The amount of alcohol or aqueous alcohol solution used can be adjusted appropriately 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, and even more preferably 10 parts by mass or more, and is 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 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, and are, for example, preferably 5 to 100 parts by mass, more preferably 7 to 50 parts by mass, and even more preferably 10 to 25 parts by mass.

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

[0034] The mixing time when dissolving the plastic containing the methacrylic resin in the alcohol or aqueous alcohol solution can be, for example, about 1 to 12 hours, and preferably 3 to 8 hours.

[0035] (Step (B)) In step (B), the solid insoluble matter contained in the solution containing the methacrylic resin obtained in step (A) is removed by solid-liquid separation. The solid-liquid separation method is not particularly limited, and examples thereof include filtration and decantation.

[0036] The dye and the like remaining in the solution after solid-liquid separation may be removed by an adsorption method, and the treated solution may then be supplied to step (C). Known adsorption methods can be used. Examples of adsorbents that can be used include activated carbon, activated alumina, silica gel, zeolite, titanium oxide, ion exchange resin, bentonite, diatomaceous earth, and activated clay. Examples of adsorption treatments that can be used include a method of passing the solution through a column packed with an adsorbent, and a method of adding an adsorbent to the solution and then removing the adsorbent again by solid-liquid separation.

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

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

[0039] The method for producing a methacrylic resin by thermally induced phase separation is not particularly limited as long as it can cool the solution in which the methacrylic resin has been dissolved after solid-liquid separation. A suitable example is a method in which the solution after solid-liquid separation is brought into contact with the cooling surface of a cooling element, the solution is cooled to induce phase separation, and the methacrylic resin is precipitated. The cooling element may be any element that can adjust the cooling surface that contacts the solution after solid-liquid separation to the desired temperature, and examples of such elements include a cooling roll, a cooling plate, and a cooling belt. The material of the cooling element is not particularly limited, and metals such as iron, stainless steel, aluminum, titanium, and copper, and those with a fluorine-coated surface or a glass-coated 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 equal to or lower than the upper limit, phase separation is easily induced, and the 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 equal to or higher than the lower limit, the energy required for cooling the cooling surface can be reduced, which is advantageous in terms of cost. The preferred lower and upper limits of the temperature of the cooling surface can be arbitrarily combined, and 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 step (C), since methacrylic resin can be produced efficiently at low cost, it is preferable to continuously produce a long length of methacrylic resin by continuously contacting the solution after solid-liquid separation with a cooling surface and peeling the precipitated methacrylic resin from the cooling surface. A specific example is a method of continuously producing a methacrylic resin using a cooling roll as a cooling member. For example, while rotating the cooling roll, the solution after solid-liquid separation is continuously brought into contact with the outer peripheral surface of the cooling roll, which is the cooling surface, at a certain point. Then, the methacrylic resin precipitated on the outer peripheral surface of the rotating cooling roll is continuously peeled off until it returns to the contact point with the solution after solid-liquid separation. This allows the solution after solid-liquid separation to be continuously cooled, thereby continuously producing a long length of methacrylic resin. In this case, it is necessary to impart toughness to the methacrylic resin produced, and in step (C), it is preferable to bring the solution after solid-liquid separation into contact with a cooling surface while stretching and orienting it, and it is preferable to continuously produce the methacrylic resin while stretching and orienting it in the axial direction of the long length by at least two times.

[0042] When stretching a methacrylic resin in the axial direction of the long length, the stretching ratio is preferably 2 times or more, and preferably 10 times or less, and more preferably 5 times or less. If the stretching ratio is equal to or greater than the lower limit, the toughness of the methacrylic resin is likely to be improved. If the stretching ratio is equal to or less than 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, and for example, 2 to 10 times is preferred, and 2 to 5 times is more preferred.

[0043] (Step (D)) In step (D), the alcohol remaining in the methacrylic resin produced in step (C) is removed by squeezing or centrifugation. The energy required for physical removal processes such as squeezing and centrifugation is much smaller than the energy required for removal processes that involve evaporating the alcohol by heating. Therefore, by performing step (D), energy savings are possible, and the methacrylic resin can be produced at low cost.

[0044] The operating temperature when removing the alcohol remaining in the methacrylic resin by squeezing or centrifugation is preferably 40°C or higher, more preferably 60°C or higher, and preferably 120°C or lower, more preferably 100°C or lower. If the heating temperature is above the lower limit, the methacrylic resin is likely to become porous. If the heating temperature is below the upper limit, handling during squeezing 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), the alcohol remaining in the methacrylic resin is removed by squeezing or centrifugation, and the methacrylic resin may be naturally dried, or may be dried by heating as needed. If a treatment by squeezing or centrifugation is performed, the energy required for drying is significantly reduced compared to when the resin is heated and dried without undergoing such treatment. Therefore, energy saving is possible even when heat drying is performed after squeezing or centrifugation, and the methacrylic resin can be produced at low cost.

[0046] The alcohol content of the methacrylic resin after separation by squeezing or stretching 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 after separation by squeezing or stretching, the more energy required for subsequent drying can be reduced.

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

[0048] Furthermore, by providing a cooling section within the apparatus used in step (D), the phase separation function of step (C) can be imparted, and steps (C) and (D) can also be performed in the same apparatus. For example, when a press dehydrator is used, a cooling section can be provided within the press dehydrator, and when a centrifuge is used, the phase separation function can be imparted by cooling the liquid-contacting parts of the centrifuge. Taking into account the time required for phase separation, it is preferable to use an apparatus structure that can hold the solution for a certain period of time.

[0049] As shown in FIG. 1 , in the production method according to the embodiment, it is preferable to reuse in step (A) 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). By reusing the alcohol recovered in step (C) or step (D) in step (A), the methacrylic resin can be produced at lower cost and the environmental impact can be reduced. Because of the greater cost and environmental impact reduction effects, it is particularly preferable to reuse both the alcohol recovered in step (C) and the alcohol recovered in step (D) in step (A). Some components, such as additives, contained in plastics containing methacrylic resins may leach into the alcohol in small amounts. Multiple recovery and reuse of alcohol containing eluted additives may cause these impurities to accumulate during the process, adversely affecting the quality of the methacrylic resin produced. In such cases, the quality of the methacrylic resin produced can be maintained by replacing the alcohol with new alcohol or separating and removing impurities, such as additives, contained in the recovered alcohol by distillation or the like before reusing it.

[0050] [Methacrylic Resin] The methacrylic resin according to the embodiment is a methacrylic resin produced by the above-described method for producing a methacrylic resin. In the above-described method for producing a methacrylic resin, for example, a methacrylic resin in the low molecular weight range having a molecular weight of 30,000 or less remains dissolved in alcohol and is easily separated and removed, so the molecular weight distribution shifts to the higher molecular weight side. The methacrylic resin produced by the production method according to the embodiment can be a methacrylic resin stretched to two or more times its original length in the axial direction of the long length. The methacrylic resin produced by the production method according to the embodiment can be a long methacrylic resin having an alcohol content of 75% by mass or less. The methacrylic resin produced by the production method according to the embodiment can be a porous long methacrylic resin.

[0051] The alcohol content of the methacrylic resin produced by the production 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 Method] The methacrylic resin recycling method according to the embodiment is a method of recycling the methacrylic resin produced by the production method according to the embodiment. The methacrylic resin recycling method according to the embodiment is not particularly limited except that the methacrylic resin produced by the production method according to the embodiment is used. Examples of the recycling method include material recycling and chemical recycling, with chemical recycling being preferred.

[0053] An example of a chemical recycling method is to thermally decompose the methacrylic resin produced by the production method according to the embodiment, produce a monomer as a pyrolysis product, and use the monomer to produce a recycled product. Polymethyl methacrylate is known to thermally decompose at a relatively low temperature of about 300°C. From the viewpoints of productivity and monomer purity, the pyrolysis temperature is preferably 300 to 700°C, more preferably 300 to 500°C, and even more preferably 300 to 450°C.

[0054] As the thermal decomposition device, known devices can be used, such as a microwave decomposition device, an extruder, a kneader, and a fluidized bed heater. An extruder is a device equipped with a mechanism that rotates a screw disposed inside a cylindrical member (cylinder) to melt raw materials introduced from the upstream side of the cylinder and transport them downstream. An example of a kneader is the device described in U.S. Pat. No. 10,301,235. An example of a fluidized bed heater is the device described in JP-A-2009-112902.

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

[0056] [Methacrylic Resin Composition] Furthermore, a methacrylic resin composition can be obtained by polymerizing the monomer composition obtained by the above-mentioned chemical recycling. Monomers produced by other known methods may be added to the monomer composition obtained by the above-mentioned chemical recycling, and polymerization may be carried out. Examples of polymerization methods include bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization. Among these polymerization methods, bulk polymerization and suspension polymerization are preferred from the viewpoint of excellent productivity, and bulk polymerization is more preferred. The methacrylic resin composition obtained in this manner can be produced while reducing 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 above-described forms, and it is possible to replace components with well-known components as appropriate within the scope of the present invention, and the above-described modified examples may be combined as appropriate.

Claims

1. A method for producing a methacrylic resin, comprising: step (A) of mixing a plastic containing a methacrylic resin with alcohol to dissolve the methacrylic resin; step (B) of removing insoluble matter contained in the solution obtained in step (A) by solid-liquid separation; step (C) of producing the methacrylic resin from the solution after solid-liquid separation by a phase separation method; and step (D) of removing the alcohol remaining in the methacrylic resin produced in step (C) by squeezing or centrifugation.

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

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

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

6. The method according to claim 1, wherein in step (C), the solution after solid-liquid separation is brought into contact with a cooling surface at 20°C or less to cause phase separation, thereby producing the methacrylic resin.

7. The method according to claim 6, wherein in step (C), the solution after solid-liquid separation is stretched and oriented while being brought into contact with a cooling surface at 20°C or less to cause phase separation, thereby producing the methacrylic resin.

8. The method according to claim 6, wherein the solution after solid-liquid separation is continuously brought into contact with the cooling surface while the precipitated methacrylic resin is peeled off from the cooling surface, thereby continuously producing a long length of methacrylic resin.

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

10. The manufacturing method according to claim 1, wherein the steps (C) and (D) are carried out in the same apparatus.

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

12. A method for recycling a methacrylic resin, comprising recycling a methacrylic resin produced by the method according to any one of claims 1 to 11.

13. A methacrylic resin produced by the method of claim 1.

14. A methacrylic resin stretched in the axial direction of a long length by at least two times its original length, produced by the method of claim 1.

15. A continuous length of methacrylic resin having an alcohol content of 75% by mass or less, produced by the production method described in claim 1.

16. A porous, elongated methacrylic resin produced by the method of claim 1.

17. A monomer composition obtained by chemically recycling the methacrylic resin according to any one of claims 13 to 16.

18. A methacrylic resin composition obtained by polymerizing the monomer composition of claim 17.

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