Methods for producing regenerated polymer material powder and molded body

Abstract

Provided is a method for producing a regenerated polymer material powder that includes a subcritical water treatment step in which a polymer material to be regenerated is brought into contact with subcritical water. The method for producing a regenerated polymer material powder includes a step for bringing the polymer material to be regenerated into contact with a treatment liquid containing a polar organic compound or a polar organic compound aqueous solution before the subcritical water treatment step or during the subcritical water treatment step and obtains a regenerated polymer material powder having an average particle diameter D50 of 500 μm or less.

Description

Method for manufacturing recycled polymer material powder and molded articles

[0001] The present invention relates to a method for obtaining recycled polymer material powder from a recycled polymer material, and to a method for producing a molded article using the recycled polymer material powder obtained by the method.

[0002] In recent years, there has been growing concern about global environmental issues, and the recognition that it is necessary to build a sustainable society is becoming widespread. These global environmental issues include global warming and resource depletion, and technologies related to the recycling and reuse of fossil resources such as plastics, and the reduction of greenhouse gas emissions, are becoming increasingly important in addressing these problems.

[0003] In particular, polyimide, which is used in large quantities in various fields such as automobiles and electrical and electronic applications, emits a relatively large amount of greenhouse gases during monomer production, making it desirable to reuse products containing polyimide.

[0004] For example, Patent Document 1 discloses a method for regenerating polymer materials such as polyimide, comprising the steps of: immersing the polymer material to be regenerated, which is solid at room temperature, in a first processing solution with an alkali ion concentration in the range of 0.5 to 20.0 mol / L; removing the polymer material in the critically decomposed state from the first processing solution when the hydrolysis of the polymer material to be regenerated has progressed to a critically decomposed state; immersing the removed polymer material in the critically decomposed state in a second processing solution with an alkali ion concentration of 0.0 to 0.5 mol / L to dissolve it and obtain a solution of the polymer material to be regenerated; and neutralizing the solution with acid to precipitate the dissolved product and recover it as a powder. However, the technology in Patent Document 1 has the problem of being inefficient in terms of productivity because it requires numerous steps such as neutralization, due to the need for operation under alkaline conditions.

[0005] Japanese Patent Publication No. 2021-46521

[0006] The present invention aims to provide a method for producing recycled polymer material powder that allows for the recovery of recycled polymer material powder, in which the average particle size is reduced to a predetermined value or less by pulverization, from a recycled polymer material with excellent productivity.

[0007] In order to achieve the above objective, the inventors conducted diligent research and discovered that by contacting the recycled polymer material with subcritical water in the presence of a polar organic compound, recycled polymer material powder, whose average particle size has been reduced to a predetermined value or less by pulverization, can be recovered with excellent productivity, thus completing the present invention.

[0008] In other words, the present invention provides the following [1] to [7]. [1] A method for producing recycled polymer material powder, comprising a subcritical water treatment step of contacting a polymer material to be recycled with subcritical water, wherein the method includes a step of contacting the polymer material to be recycled with a polar organic compound or a treatment liquid containing an aqueous solution of a polar organic compound before or during the subcritical water treatment step, and obtaining recycled polymer material powder having an average particle size D50 of 500 μm or less. [2] The method for producing recycled polymer material powder according to [1], wherein the polar organic compound is a polar organic compound containing a nitrogen atom. [3] The method for producing recycled polymer material powder according to [1] or [2], wherein the pKa of the polar organic compound is 3 to 30. [4] The method for producing recycled polymer material powder according to any one of [1] to [3], wherein the polymer material to be recycled is polyimide. [5] A method for producing recycled polymer material powder according to any one of [1] to [4], further comprising a grinding step of grinding the recycled polymer material before grinding after the subcritical water treatment step. [6] A method for producing a molded article comprising a step of obtaining recycled polymer material powder by the method for producing recycled polymer material powder according to any one of [1] to [5], and a step of molding the obtained recycled polymer material powder. [7] Use of recycled polymer material powder as a filler, wherein the recycled polymer material powder obtained by the method for producing recycled polymer material powder according to any one of [1] to [5] is used as a filler.

[0009] According to the present invention, it is possible to provide a method for producing recycled polymer material powder that can recover recycled polymer material powder, in which the average particle size has been reduced to a predetermined value or less by pulverization, with excellent productivity. Furthermore, according to the present invention, it is also possible to provide a method for producing molded articles using recycled polymer material powder obtained by such a method.

[0010] The present invention provides a method for producing recycled polymer material powder, comprising a subcritical water treatment step of contacting the polymer material to be recycled with subcritical water, wherein the method includes a step of contacting the polymer material to be recycled with a treatment liquid containing a polar organic compound or an aqueous solution of a polar organic compound before or during the subcritical water treatment step, thereby obtaining recycled polymer material powder having an average particle size D50 of 500 μm or less.

[0011] <Recyclable Polymer Materials> In the present invention, the polymer material to be recycled (recyclable polymer material) is not particularly limited, but condensed polymer materials are preferred from the viewpoint of achieving a higher recovery rate. Examples of condensed polymer materials include saturated polyester, polyimide, polyamide, polysaccharides, starches, phenolic resins, urea resin, melamine resin, epoxy resin, polycarbonate, unsaturated polyester, and polyether, but polyimide is particularly preferred.

[0012] Examples of polyimides include those mainly composed of aromatic polyimides and / or aliphatic polyimides, but it is preferable that the main component be an aromatic polyimide containing repeating units represented by the following formula (I).

[0013] (In formula (I), X １ Y is a tetravalent group obtained by removing a carboxyl group from a tetracarboxylic acid having an aromatic ring, and １ (This refers to one or more divalent groups obtained by removing the amino group from a diamine having an aromatic ring.)

[0014] X １ Preferably, the group is a tetravalent group without substituents on the aromatic ring, and in particular, a tetravalent group represented by the following formulas (II) to (VI) is preferred.

[0015] (In formula (III), Z １ (This is either a direct bond or a group represented by the following formula (VII).)

[0016] (In formula (VII), W １ W is a divalent organic group.２ , W ３ is each independently an amide bond, an ester bond, or a carbonyl bond, and W ４ is an organic group containing an aromatic ring.)

[0017] In formula (VII), W １ is preferably an aliphatic hydrocarbon group having 2 to 24 carbon atoms, or an aromatic hydrocarbon group having 6 to 24 carbon atoms. W ４ is preferably an aromatic hydrocarbon group having 6 to 24 carbon atoms.

[0018] As the compound for forming the tetravalent group represented by formulas (II) to (V), an aromatic tetracarboxylic acid compound having no substituent on the aromatic ring is preferred. Examples thereof include 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, diphenylsulfonetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, m-terphenyltetracarboxylic dianhydride and the like.

[0019] In addition, X １ as the compound for forming the same may be an aromatic tetracarboxylic acid compound having a substituent on the aromatic ring. Examples of the aromatic tetracarboxylic acid compound having a substituent on the aromatic ring include 5,5'-[2,2,2-trifluoro-1-[3-(trifluoromethyl)phenyl]ethylidene]diphthalic anhydride, 5,5'-[2,2,3,3,3-pentafluoro-1-(trifluoromethyl)propylidene]diphthalic anhydride, 1H-difuro[3,4-b:3',4'-i]xanthene-1,3,7,9(11H)-tetrone, 5,5'-oxybis[4,6,7-trifluoro-pyromellitic anhydride], 3,6-bis(trifluoromethyl)pyromellitic dianhydride, 4-(trifluoromethyl)pyromellitic dianhydride, 1,4-difluoropyromellitic dianhydride, 1,4-bis(3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene dianhydride and the like.

[0020] X １ The compound used to form the compound may be a single compound or a combination of two or more compounds.

[0021] Y １ Preferably, the group is a divalent group without substituents on the aromatic ring, and is a divalent group represented by the following formulas (VIII) and (IX). (In formula (IX), Z ２ (This is either a direct bond or a divalent group represented by the following formula (X) or formula (XI).)

[0022] (In formula (XI), W ５ ~W １３ These are either directly bonded independently, or are divalent groups represented by formula (X).

[0023] Suitable compounds for forming the groups represented by formulas (VIII) and (IX) are aromatic diamine compounds that do not have substituents on the aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenylmethane.

[0024] Also, Y １ The compound used to form the compound may be a diamine compound having substituents on the aromatic ring. Examples of diamine compounds having substituents on the aromatic ring include 2,4-toluenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis(4-amino-3-carboxyphenyl)methane, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,3,5,6-tetrafluoro-1,4-diaminobenzene, 2,4,5,6-tetrafluoro-1,3-diaminobenzene, 2,3,5,6-tetrafluoro-1,4-benzene(dimethanamine), 2,2'-difluoro(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, and 4,4'-oxybis(2,3,5,6-tetrafluoroaniline).

[0025] Y １The compound used to form the compound may be a single compound or a combination of two or more compounds.

[0026] The shape of the recycled polymer material is not particularly limited and may be in the form of a bulk material, film, or sheet having a predetermined shape. Furthermore, the size and thickness of the recycled polymer material are not particularly limited.

[0027] <Subcritical Water Treatment Process> The present invention provides a method for producing a recycled polymer material powder, comprising a subcritical water treatment process in which a polymer material to be recycled is brought into contact with subcritical water, and further comprising a step of bringing the polymer material to be recycled into contact with a treatment liquid containing a polar organic compound or an aqueous solution of a polar organic compound before or during the subcritical water treatment process.

[0028] According to the present invention, by using a polar organic compound and contacting the polymer material to be recycled with subcritical water in the presence of the polar organic compound, the polymer material to be recycled can be suitably reduced to a strength suitable for pulverization through such a simple process, and as a result, a pre-pulverization recycled polymer material with excellent crushability can be obtained. Furthermore, by pulverization, a recycled polymer material powder with an average particle size D50 of 500 μm or less can be obtained. For example, when the polymer material to be recycled is a condensed polymer material such as polyimide, a chemical reaction can be caused to at least a part of the condensation structure, such as imide bonds, to decompose, thereby suitably reducing the strength of the condensed polymer material such as polyimide to a strength suitable for pulverization. As a result, a pre-pulverization recycled condensed polymer material such as pre-pulverization recycled polyimide with excellent crushability can be obtained.

[0029] Furthermore, the recycled polymer material obtained by the present invention is highly pulverizable, and can be relatively easily reduced to powder form by pulverization. Specifically, it can be reduced to recycled polymer material powder with an average particle size D50 of 500 μm or less. The recycled polymer material powder obtained in this way can be suitably reused by forming it into various molded bodies. In particular, according to the present invention, by using a polar organic compound, the recycled polymer material can be easily pulverized even when the temperature of the subcritical water is relatively low. This suppresses the problem that occurs when the reaction is carried out under conditions of high subcritical water temperature, namely the decrease in recovery rate due to over-decomposition, and enables a high recovery rate. Moreover, when the recycled polymer material is a polymer material with excellent heat resistance, such as polyimide, the decrease in heat resistance due to over-decomposition can be suppressed, thereby enabling excellent heat resistance.

[0030] The polar organic compound can be any polar organic compound and is not particularly limited, but a polar organic compound that is water-soluble is preferred. The polar organic compound is preferably a basic organic compound, more preferably an organic compound containing a heteroatom, even more preferably an organic compound containing at least one selected from nitrogen, oxygen, and sulfur atoms, and even more preferably an organic compound containing a nitrogen atom.

[0031] Examples of polar organic compounds include amine compounds, nitrogen-containing heterocyclic compounds, cyclic amide compounds, sulfoxide compounds, and acetamide compounds. Among these, sulfoxide compounds and cyclic amide compounds are preferred, nitrogen-containing heterocyclic compounds are more preferred, and amine compounds are even more preferred.

[0032] Examples of the amine compound include monoamine compounds such as trimethylamine, triethylamine, aniline, 1-naphthylamine, 2-naphthylamine, 1-aminoanthracene, 2-aminoanthracene, 9-aminoanthracene, 9-aminophenanthracene, 2-aminobiphenyl, 3-aminobiphenyl, and 4-aminobiphenyl; and diamine compounds such as p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,4-toluenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis(4-amino-3-carboxyphenyl)methane, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,3,5,6-tetrafluoro-1,4-diaminobenzene, 2,4,5,6-tetrafluoro-1,3-diaminobenzene, 2,3,5,6-tetrafluoro-1,4-benzene(dimethanamine), 2,2'-difluoro(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, and 4,4'-oxybis(2,3,5,6-tetrafluoroaniline). Among these, diamine compounds are preferred, p-phenylenediamine, m-phenylenediamine, and 4,4'-diaminodiphenyl ether are more preferred, and p-phenylenediamine is even more preferred. Triethylamine as a monoamine compound is also suitable.

[0033] Examples of nitrogen-containing heterocyclic compounds include five-membered nitrogen-containing heterocyclic compounds such as imidazole, 2-methylimidazole, 1,2-dimethylimidazole, pyrrole, methylpyrrole, thiazole, oxazole, pyrazole, isoxazole, and pyrrolidine; and six-membered nitrogen-containing heterocyclic compounds such as pyridine, 4-dimethylaminopyridine, pyrazine, pyrimidine, pyridazine, triazine, 2,6-lutidine, piperidine, and piperazine; Examples include condensed nitrogen-containing heterocyclic compounds such as noline, isoquinoline, quinoxaline, quinazoline, sinnoline, purine, indole, isoindole, benzimidazole, benzoxazole, benzoisoxazole, 1,8-diazabicyclo[5.4.0]unde-7-cene (DBU), 1,5-diazabicyclo[4.3.0]no-5-nene, and 1,4-diazabicyclo[2.2.2]octane (DABCO). Among these, five-membered nitrogen-containing heterocyclic compounds and six-membered nitrogen-containing heterocyclic compounds are preferred, and imidazole, 2-methylimidazole, 1,2-dimethylimidazole, 4-dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]unde-7-cene (DBU), and 1,4-diazabicyclo[2.2.2]octane (DABCO) are more preferred.

[0034] Examples of cyclic amide compounds include azetidinone compounds such as 2-azetidinone, N-methylazetidinone, and N-ethylazetidinone; pyrrolidone compounds such as 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone, N-isopropylpyrrolidone, N-butylpyrrolidone, N-cyclohexylpyrrolidone, N-octylpyrrolidone, N-phenylpyrrolidone, and vinylpyrrolidone; piperidone compounds such as 2-piperidone, N-methylpiperidone, and N-ethylpiperidone; and imidazolidinone compounds such as 2-imidazolidinone, 1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-dipropyl-2-imidazolidinone, and 1,3-dibutyl-2-imidazolidinone. Among these, pyrrolidone compounds and imidazolidinone compounds are preferred, and N-methylpyrrolidone and 1,3-dimethyl-2-imidazolidinone are more preferred.

[0035] Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, and diphenyl sulfoxide, and among these, dimethyl sulfoxide is preferred.

[0036] Examples of the acetamide compound include N-methylacetamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N,N-diphenylacetamide, and among these, N,N-dimethylacetamide is preferred.

[0037] The polar organic compound may be used alone, or two or more thereof may be used in combination.

[0038] The pKa of the polar organic compound is preferably 3 to 30, more preferably 4 to 20, still more preferably 5 to 15, even more preferably 5.5 to 13, and particularly preferably 5 to 7. By setting the pKa of the polar organic compound within the above range, a regenerated polymer material before pulverization having excellent friability can be recovered at a higher recovery rate, and consequently, a regenerated polymer material powder can be obtained at a higher recovery rate. The pKa value can be easily searched through SciFinder (registered trademark), which is known as a search service based on databases such as Chemical Abstracts. Here, the value calculated by Advanced Chemistry Development (ACD / Labs) Software V11.02 (Copyright 1994-2011 ACD / Labs) can be adopted.

[0039] The melting point of the polar organic compound is not particularly limited, but is preferably -130 to 230°C, more preferably -50 to 200°C, and still more preferably 0 to 160°C. The boiling point of the polar organic compound is, for example, 100 to 400°C.

[0040] The amount of polar organic compound used is preferably 0.0001 to 10,000 moles, more preferably 0.001 to 1,000 moles, and even more preferably 0.01 to 100 moles per mole of monomer units contained in the recycled polymer material. Furthermore, the amount of polar organic compound used is preferably 0.01 to 1,000,000 parts by weight, more preferably 0.1 to 1,000,000 parts by weight, even more preferably 1 to 10,000 parts by weight, even more preferably 5 to 100 parts by weight, especially preferably 8 to 50 parts by weight, and particularly preferably 20 to 40 parts by weight per 100 parts by weight of the recycled polymer material. By setting the amount of polar organic compound used within the above range, a recycled polymer material with excellent crushability before pulverization can be obtained with a higher recovery rate, and consequently, recycled polymer material powder can be obtained with a higher recovery rate.

[0041] In the subcritical water treatment process, the polymer material to be recycled is brought into contact with subcritical water in the presence of the polar organic compound described above. The method for bringing the polymer material to be recycled into contact with subcritical water in the presence of the polar organic compound is not particularly limited, but one method is to bring the polymer material to be recycled into contact with a treatment solution containing the polar organic compound or an aqueous solution of the polar organic compound before or during the subcritical water treatment process. For example, the polymer material to be recycled and the treatment solution containing the polar organic compound or an aqueous solution of the polar organic compound may be brought into contact beforehand before the subcritical water treatment process, and the subcritical state can be achieved by raising the temperature while maintaining this state. Alternatively, the polymer material to be recycled and water may be brought into contact beforehand before the subcritical water treatment process, and the subcritical state can be achieved by raising the temperature while maintaining this state, and then the treatment solution containing the polar organic compound may be added during the subcritical water treatment process. One example of a method for performing a subcritical water treatment process is to place water containing a dissolved polar organic compound and the polymer material to be recycled in a pressure-resistant sealed container such as a reaction tube, heat the sealed container from the outside to raise the temperature of the water containing the dissolved polar organic compound to 101°C or higher and less than 375°C to create a subcritical state, and maintain the subcritical state for a predetermined time. In addition, in the subcritical water treatment process, the polymer material to be recycled may be subjected to a pre-treatment such as coarse grinding to a size below a predetermined size before contact with the subcritical water.

[0042] In the subcritical water treatment process, the temperature of the subcritical water is preferably 101°C or higher and less than 375°C, more preferably 150°C or higher and less than 350°C, even more preferably 200°C or higher and less than 350°C, even more preferably 230°C or higher and less than 300°C, and particularly preferably 230°C or higher and less than 280°C. When the temperature of the subcritical water is within the above range, a recycled polymer material with excellent crushability before pulverization can be obtained with a high recovery rate, and consequently, recycled polymer material powder can be obtained with an even higher recovery rate. Furthermore, when the polymer material to be recycled is a polymer material with excellent heat resistance, such as polyimide, the decrease in heat resistance due to degradation can be effectively suppressed, and the recycled polymer material powder obtained thereby can have excellent heat resistance. If the temperature of the subcritical water is too low, the resulting pre-pulverization recycled polymer material will have poor crushability. Conversely, if the temperature of the subcritical water is too high, the recovery rate of the pre-pulverization recycled polymer material will decrease, or excessive decomposition will reduce the heat resistance of the resulting pre-pulverization recycled polymer material, ultimately leading to a decrease in the heat resistance of the recycled polymer material powder.

[0043] In the subcritical water treatment process, the contact time (reaction time), which is the time the polymer material to be recycled is in contact with the subcritical water, is not particularly limited, but is preferably 1 to 720 minutes, more preferably 3 to 480 minutes, even more preferably 5 to 300 minutes, even more preferably 20 to 200 minutes, especially preferably 30 to 150 minutes, and particularly preferably 45 to 75 minutes. By setting the contact time within the above range, the recycled polymer material before pulverization, which has excellent crushability, can be recovered at a higher recovery rate, and consequently, the recycled polymer material powder can be obtained at a higher recovery rate.

[0044] In the subcritical water treatment process, the pressure at which the polymer material to be recycled is brought into contact with the subcritical water is not particularly limited, but can be, for example, the saturated water vapor pressure.

[0045] In the subcritical water treatment process, the amount of subcritical water used is preferably 200 to 5000 parts by weight, more preferably 400 to 3000 parts by weight, even more preferably 600 to 2000 parts by weight, even more preferably 700 to 1500 parts by weight, and particularly preferably 800 to 1200 parts by weight, per 100 parts by weight of the polymer material to be recycled.

[0046] After subcritical water treatment, the regenerated polymer material after subcritical water treatment can be separated from the water containing dissolved polar organic compounds by filtration or other means, and dried as needed to obtain the regenerated polymer material before pulverization.

[0047] <Grinding Process> In addition, in the present invention, a grinding process may be performed to obtain a recycled polymer material powder having an average particle size D50 of 500 μm or less by grinding the recycled polymer material before grinding after the subcritical water treatment process described above.

[0048] According to the present invention, the recycled polymer material obtained by subcritical water treatment before pulverization is highly easily crushable, so even when using a relatively simple pulverization method, a powdered recycled polymer material suitable for molding can be obtained, thereby making it possible to obtain a recycled polymer material powder with an average particle size D50 of 500 μm or less.

[0049] The grinding method in the grinding process is not particularly limited, but can be dry or wet. In the case of dry grinding, examples include using dry grinding equipment such as an attritor, blade grinder, jet mill, hammer mill, pin mill, or ball mill. In the case of wet grinding, examples include mixing the regenerated polymer material before grinding with water and / or an organic solvent to form a slurry in which the regenerated polymer material before grinding is dispersed in water and / or an organic solvent, and then using wet grinding equipment such as a ball mill or bead mill. Among these, the method using dry grinding equipment is preferred, and the method using a ball mill as the dry grinding equipment is more preferred.

[0050] In the grinding process, the average particle size D50 of the recycled polymer material powder obtained by grinding is the cumulative 50% volume particle size measured by laser diffraction / scattering, and the average particle size D50 of the recycled polymer material powder is 500 μm or less, preferably 0.1 to 200 μm, and more preferably 1 to 100 μm. Having the average particle size D50 within this range makes it possible to achieve good moldability.

[0051] The recycled polymer material powder obtained through the pulverization process can be used, for example, as a polymer material for obtaining molded articles, or mixed with various resins and rubbers to be used as a filler.

[0052] <Molded article> The molded article of the present invention is obtained by molding a recycled polymer material powder having an average particle size D50 of 500 μm or less.

[0053] The shape of the molded body is not particularly limited and can be any shape, such as a sheet, cylinder, or cube.

[0054] The molding method for obtaining a molded body is not particularly limited, but examples include filling a mold with recycled polymer material powder and applying pressure and heat simultaneously or separately. Specifically, examples include a method of heat compression molding at a molding temperature of 350 to 600°C and a molding pressure of 30 to 2000 MPa, or a method of obtaining a pre-molded body at a molding temperature of 25 to 350°C and a molding pressure of 30 to 2000 MPa, followed by post-sintering at 350 to 600°C under non-compression conditions.

[0055] Furthermore, since the recycled polymer material powder obtained by the present invention can be molded even under relatively mild conditions, for example, when the recycled polymer material powder is recycled polyimide powder, a molded body with excellent compressive strength can be obtained by methods such as heat compression molding at a molding temperature of 350 to 550°C and a molding pressure of 30 to 500 MPa, or by obtaining a pre-molded body at a molding temperature of 25 to 350°C and a molding pressure of 30 to 500 MPa, followed by post-sintering at 350 to 550°C under non-compression conditions.

[0056] Furthermore, when manufacturing molded articles, any filler can be mixed with recycled polymer material powder and used. The filler is not particularly limited, but examples of inorganic fillers such as glass fibers, ceramic fibers, boron fibers, glass beads, whiskers, diamond powder, alumina, silica, natural mica, synthetic mica, alumina, carbon black, silver powder, copper powder, aluminum powder, nickel powder, metal fibers, ceramic fibers, whiskers, silicon carbide, silicon oxide, alumina, magnesium powder, titanium powder, carbon fibers, and graphite, or organic fillers such as fluororesins and aramid fibers can be used. These fillers may be used alone or in combination of two or more fillers.

[0057] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0058] (Evaluation) The recycled polyimide and recycled polyimide powder obtained in each example and comparative example were evaluated for the following items using the method described below.

[0059] <Recovery Rate> The recovery rate was calculated using the obtained pre-pulverized recycled polyimide according to the following formula. The results are shown in Table 1. Recovery Rate [%] = (Weight of pre-pulverized recycled polyimide [g] / Weight of crushed polyimide film before subcritical water treatment and contact with polar compounds [g]) × 100

[0060] <Ease of Crushing> A small sample of the recycled polyimide before crushing was taken and crushed using a mortar and pestle. The state of the resulting pulverized material was observed, and its ease of crushing was evaluated according to the following criteria. In the following, recycled polyimide powder refers to material with a long axis diameter of 500 μm or less, and crushed film fragments refer to material with a long axis diameter greater than 500 μm and less than 0.1 cm. ◎: All pulverized material was recycled polyimide powder. 〇: The pulverized material contained recycled polyimide powder and film fragments from crushed material. △: The pulverized material did not contain recycled polyimide powder but contained film fragments from crushed material. ×: The material contained neither recycled polyimide powder nor film fragments from crushed material (there was no change from the crushed polyimide film before critical water treatment and before contact with polar compounds).

[0061] <Average Particle Size> For recycled polyimide powder, the average particle size D50 (cumulative 50% volume particle size) was calculated using the laser diffraction / scattering method with a laser diffraction / scattering particle size distribution analyzer (product name "Mastersizer 3000", manufactured by Malvern).

[0062] <Example 1> A polyimide film (1) (UPIREX®-S (manufactured by UBE)) was used as the recycled polymer material, and crushed material was prepared by crushing this polyimide film (1) to a size of 0.1 cm x 0.1 cm or less. Then, 1 part by weight of polyimide film (1), 10 parts by weight of degassed water (water degassed by nitrogen bubbling), and p-phenylenediamine (pKa: 6.5, melting point: 142°C) were charged into a pressure-resistant reaction tube. The amount of p-phenylenediamine used was 0.3 parts by weight per 1 part by weight of polyimide film (1).

[0063] Then, the reaction tube containing the polyimide film (1), degassed water, and p-phenylenediamine was placed in a salt bath set to a temperature of 300°C while being held in place by a holder, and subcritical water treatment was performed by holding the temperature inside the reaction tube at 300°C for 60 minutes. At this time, the pressure inside the reaction tube was at the saturated water vapor pressure, and the degassed water inside the reaction tube was in a subcritical state (the same applies to Examples 2 to 5 and Comparative Examples 1 to 3 described later). After 60 minutes, the reaction tube was removed from the salt bath and cooled to room temperature, and the reaction product inside the reaction tube was filtered and dried to obtain regenerated polyimide before grinding. The obtained regenerated polyimide before grinding was then crushed for 5 minutes using a planetary ball mill (product name: "Premium Line PL-7", manufactured by Fritsch) to obtain regenerated polyimide powder with an average particle size D50 (cumulative 50% volume particle size) of 17 μm. Furthermore, the pulverization process using a planetary ball mill was performed using the recycled polyimide before pulverization, after the above-mentioned recovery rate and ease of pulverization measurements had been taken (the same applies to Examples 2 to 16, Reference Example 1, and Comparative Examples 1 and 2 described later).

[0064] <Examples 2-4, 7, 8> Except for changing the holding temperature and holding time in the subcritical water treatment to those shown in Table 1, the subcritical water treatment and pulverization treatment were carried out in the same manner as in Example 1 to obtain regenerated polyimide before pulverization and regenerated polyimide powder, and were evaluated in the same manner. The results are shown in Table 1.

[0065] <Examples 5 and 6> Except for using polyimide film (2) (Kapton® 100H (manufactured by Toray DuPont)) instead of polyimide film (1) in Example 1, and using crushed material obtained by crushing this polyimide film (2) to a size of 0.1 cm × 0.1 cm or less, and changing the holding temperature and holding time in the subcritical water treatment to those shown in Table 1, the subcritical water treatment and pulverization treatment were carried out in the same manner as in Example 1 to obtain regenerated polyimide before pulverization and regenerated polyimide powder, and were evaluated in the same manner. The results are shown in Table 1. In Examples 5 and 6, the amount of p-phenylenediamine used was 0.3 parts by weight per 1 part by weight of polyimide film (2).

[0066] <Reference Example 1> Except for changing the holding temperature and holding time in the subcritical water treatment to those shown in Table 1, the subcritical water treatment and pulverization treatment were carried out in the same manner as in Example 1 to obtain regenerated polyimide before pulverization and regenerated polyimide powder, and were evaluated in the same manner. The results are shown in Table 1.

[0067] <Comparative Example 1> Except for not using p-phenylenediamine, the same subcritical water treatment and pulverization treatment were carried out as in Example 1 to obtain regenerated polyimide before pulverization and regenerated polyimide powder, and the same evaluation was performed. The results are shown in Table 1. In Comparative Example 1, although the pulverization treatment was carried out as in Example 1, the ease of pulverization was poor, and it was not possible to obtain regenerated polyimide powder with an average particle size D50 of 500 μm or less.

[0068] <Comparative Example 2> Except for not using p-phenylenediamine, the same subcritical water treatment and pulverization treatment were carried out as in Example 5 to obtain regenerated polyimide before pulverization and regenerated polyimide powder, and the same evaluation was performed. The results are shown in Table 1. In Comparative Example 2, although the pulverization treatment was carried out as in Example 1, the ease of pulverization was poor, and it was not possible to obtain regenerated polyimide powder with an average particle size D50 of 500 μm or less.

[0069]

[0070] <Examples 9-16> Except for using the polar organic compounds shown in Table 2 instead of p-phenylenediamine, the same subcritical water treatment and grinding treatment were carried out as in Example 4 to obtain regenerated polyimide before grinding and regenerated polyimide powder, and were evaluated in the same manner. The results are shown in Table 2.

[0071]

[0072] As shown in Tables 1 and 2, by contacting a polyimide film, as the polymer material to be recycled, with subcritical water in the presence of a polar organic compound, pre-pulverized recycled polyimide with excellent crushability and heat resistance was obtained with excellent productivity. Furthermore, due to its excellent crushability, recycled polyimide powder with an average particle size D50 of 500 μm or less could be easily obtained (Examples 1 to 16). On the other hand, the pre-pulverized recycled polyimide obtained in Comparative Examples 1 and 2 had poor crushability, and it was not possible to obtain recycled polyimide powder with an average particle size D50 of 500 μm or less. Incidentally, when small samples of the pre-pulverized recycled polyimide obtained in Examples 1 to 8, 12, and 15 were lightly pressed with a spatula, they were found to be pulverizable.

[0073] <Example 17> Using the recycled polyimide powder obtained in Example 4, a pre-molded body was obtained by molding using a mold having a cylindrical cavity under the conditions of a molding pressure of 300 MPa, a molding temperature of 300°C, and a molding time of 60 minutes. Then, the obtained pre-molded body was subjected to post-sintering under non-compression conditions at a post-sintering temperature of 500°C and a post-sintering time of 120 minutes to obtain a cylindrical recycled polyimide molded body of 7 mmφ × 5 mm.

[0074] <Compressive Strength> The compressed strength of the obtained recycled polyimide molded body was measured using a compression tester (product name: "5582", manufactured by Instron) at a strain rate of 1 mm / min. The results are shown in Table 3.

[0075]

[0076] As is clear from the results in Table 3, the recycled polyimide molded article obtained using recycled polyimide powder obtained by the manufacturing method specified in the present invention had sufficiently high compressive strength (Example 17).

[0077] The recycled polymer material powder obtained by the manufacturing method of the present invention is suitably used in various molded articles and various fillers.

Claims

1. A method for producing recycled polymer material powder, comprising a subcritical water treatment step of contacting a polymer material to be recycled with subcritical water, wherein the method includes a step of contacting the polymer material to be recycled with a treatment liquid containing a polar organic compound or an aqueous solution of a polar organic compound before or during the subcritical water treatment step, and obtaining recycled polymer material powder having an average particle size D50 of 500 μm or less.

2. The method for producing a recycled polymer material powder according to claim 1, wherein the polar organic compound is a polar organic compound containing a nitrogen atom.

3. The method for producing a recycled polymer material powder according to claim 1, wherein the pKa of the polar organic compound is 3 to 30.

4. The method for producing a recycled polymer material powder according to claim 1, wherein the recycled polymer material is polyimide.

5. A method for producing a recycled polymer material powder according to claim 1, comprising a grinding step of grinding the recycled polymer material before grinding after the subcritical water treatment step.

6. A method for producing a molded article comprising the steps of obtaining recycled polymer material powder by the method for producing recycled polymer material powder described in any one of claims 1 to 5, and molding the obtained recycled polymer material powder.

7. Use of recycled polymer material powder as a filler, wherein recycled polymer material powder obtained by the method for producing recycled polymer material powder according to any one of claims 1 to 5 is used as a filler.

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