Method for separating polyvinyl alcohol resin, and method for recycling polyvinyl alcohol resin

Abstract

To provide a method for separating PVA-based resins with small particle sizes from solutions containing PVA-based resins.SOLUTION: A method for separating PVA-based resin from a solution containing PVA-based resin (A), the solution comprising: one or more of a group consisting of polyhydric alcohol (B1), an ester (B2) containing structural units derived from polyhydric alcohol and structural units derived from monocarboxylic acid, and an ester (B3) containing structural units derived from monohydric alcohol and polycarboxylic acid; and an alcohol (C) different from the polyhydric alcohol (B1). The total content of the polyhydric alcohol (B1), the polyester (B2) containing structural units derived from polyhydric alcohol and monocarboxylic acid, and the ester (B3) containing structural units derived from monohydric alcohol and polycarboxylic acid in the solution is 0.001 mass% to 30 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for separating polyvinyl alcohol-based resins, and more specifically, to a method for separating polyvinyl alcohol-based resins from a solution containing polyvinyl alcohol-based resins. Further, the present invention relates to a method for recycling polyvinyl alcohol-based resins.

Background Art

[0002] Conventionally, polyvinyl alcohol-based resins (hereinafter also referred to as PVA-based resins) have been widely used industrially as water-soluble synthetic polymers, and are widely used as raw materials for synthetic fibers or films, fiber processing agents, paper processing agents, adhesives, binders for inorganic substances, polymerization stabilizers for vinyl chloride resins, and the like.

[0003] Among these applications, PVA-based resins are suitably used for applications such as support materials when manufacturing molded articles with a 3D printer by taking advantage of their water solubility, cores when manufacturing molded articles having hollow parts, and dispersants when manufacturing non-water-soluble resin fine particles. This is because support materials and cores are manufactured using PVA-based resins, non-water-soluble resin fine particles are dispersed by a dispersant containing PVA-based resins, and after manufacturing the target product, finally, by bringing a solvent such as water into contact with the support material, core, and dispersant, the support material, core, and dispersant can be separated from the manufactured molded article and fine particles.

[0004] On the other hand, when finally separating the PVA-based resin by bringing it into contact with water, waste liquid containing the PVA-based resin is generated. Regarding such waste liquid containing the PVA-based resin, from the viewpoint of reducing the environmental load, it is required to remove the PVA-based resin from the waste liquid. Also, if it becomes possible to recover the PVA-based resin from the waste liquid, the recovered PVA-based resin can be reused, which is also preferable in terms of cost.

[0005] As a method for recovering a PVA-based resin from an aqueous solution containing the PVA-based resin, for example, Patent Document 1 discloses a method in which a PVA-based resin molded body containing an inorganic filler is dissolved in water and then contacted with a precipitation solution mainly composed of an alcohol having 3 to 6 carbon atoms to precipitate a PVA-based resin containing the inorganic filler, and the precipitate is separated and recovered.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the method described in Patent Document 1, since the precipitated PVA-based resin is in the form of long fibers, the fibrous PVA-based resins may become entangled with each other to form a lump state, or the fibrous PVA-based resin may become entangled with the stirring shaft, which may cause operational difficulties. Therefore, it is necessary to use a device having a cutting function such as a cutter pump, and there is room for improvement in terms of ease of recovery and cost.

[0008] In addition, in the method described in Patent Document 1, when scaled up industrially, there is also a problem that when the precipitated PVA-based resin forms a large lump, it cannot be taken out from the reaction vessel or becomes difficult to take out.

[0009] Therefore, an object of the present invention is to provide a method for separating a PVA-based resin in which a PVA-based resin having a small particle size is separated from a solution containing the PVA-based resin.

Means for Solving the Problems

[0010] As a result of intensive studies by the present inventors, a solution containing a PVA-based resin contains at least one or more of an ester containing a polyhydric alcohol, a structural unit derived from the polyhydric alcohol, and a structural unit derived from a monocarboxylic acid, and an ester containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and further contains an alcohol different from the polyhydric alcohol. When the total content of the polyhydric alcohol (B1), the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from a polycarboxylic acid in the solution is 0.001% by mass to 30% by mass, the PVA-based resin is separated, and it has been found that the above problems can be solved, leading to the present invention.

[0011] That is, the present invention has the following aspects 1 to 13.

[0012] Aspect 1 of the present invention is a method for separating a polyvinyl alcohol-based resin from a solution containing a polyvinyl alcohol-based resin (A), wherein the solution further contains one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and an ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and an alcohol (C) different from the polyhydric alcohol (B1), and the total content of the polyhydric alcohol (B1), the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from a polycarboxylic acid in the solution is 0.001% by mass to 30% by mass, relating to a method for separating a polyvinyl alcohol-based resin.

[0013] Aspect 2 of the present invention relates to the method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the polyhydric alcohol (B1) is a di- to tetravalent alcohol, in the method for separating a polyvinyl alcohol-based resin according to aspect 1.

[0014] Aspect 3 of the present invention relates to a method for separating a polyvinyl alcohol-based resin in the method for separating the polyvinyl alcohol-based resin of Aspect 1 or 2, wherein the polyhydric alcohol (B1) is at least one selected from the group consisting of glycerin-based compounds and glycol-based compounds.

[0015] Aspect 4 of the present invention relates to a method for separating a polyvinyl alcohol-based resin in the method for separating any one of the polyvinyl alcohol-based resins of Aspects 1 to 3, wherein the polyhydric alcohol (B1) is at least one of glycerin and polyethylene glycol.

[0016] Aspect 5 of the present invention relates to a method for separating a polyvinyl alcohol-based resin in the method for separating any one of the polyvinyl alcohol-based resins of Aspects 1 to 4, in the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from the monocarboxylic acid, the polyhydric alcohol is a di- to tetravalent alcohol, and the monocarboxylic acid is an aliphatic monocarboxylic acid having 1 to 10 carbon atoms.

[0017] Aspect 6 of the present invention relates to a method for separating a polyvinyl alcohol-based resin in the method for separating any one of the polyvinyl alcohol-based resins of Aspects 1 to 5, wherein the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from the monocarboxylic acid is a glycerin fatty acid ester.

[0018] Aspect 7 of the present invention relates to a method for separating a polyvinyl alcohol-based resin in the method for separating any one of the polyvinyl alcohol-based resins of Aspects 1 to 6, in the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from the polycarboxylic acid, the monoalcohol is an alcohol having 1 to 5 carbon atoms, and the polycarboxylic acid is a carboxylic acid having 1 to 10 carbon atoms.

[0019] Aspect 8 of the present invention relates to a method for separating a polyvinyl alcohol-based resin according to any one of Aspects 1 to 7, wherein the total of the polyhydric alcohol (B1), the structural unit derived from the polyhydric alcohol, the ester (B2) containing the structural unit derived from the monocarboxylic acid, and the ester (B3) containing the structural unit derived from the monoalcohol and the structural unit derived from the polycarboxylic acid is 0.5 parts by mass or more with respect to 100 parts by mass of the polyvinyl alcohol-based resin (A).

[0020] Aspect 9 of the present invention relates to a method for separating a polyvinyl alcohol-based resin according to any one of Aspects 1 to 8, wherein the alcohol (C) contains one or more alcohols having 1 to 6 carbon atoms, and the solution contains the alcohol (C) as a main component.

[0021] Aspect 10 of the present invention relates to a method for separating a polyvinyl alcohol-based resin according to any one of Aspects 1 to 9, wherein in the solution, the mass ratio ((A) / (C)) of the content of the polyvinyl alcohol-based resin (A) to the content of the alcohol (C) is 0.2 / 99.8 to 50 / 50.

[0022] Aspect 11 of the present invention relates to a method for separating a polyvinyl alcohol-based resin according to any one of Aspects 1 to 10, wherein the polyvinyl alcohol-based resin (A) is a polyvinyl alcohol-based resin having a primary hydroxyl group in the side chain.

[0023] Aspect 12 of the present invention relates to a method for separating a polyvinyl alcohol-based resin according to any one of Aspects 1 to 11, wherein the average major axis length of the particles of the separated polyvinyl alcohol-based resin is 0.1 to 10 cm.

[0024] Aspect 13 of the present invention relates to a method for recycling a polyvinyl alcohol-based resin, which includes recovering the polyvinyl alcohol-based resin separated by any one of Aspects 1 to 12.

Advantages of the Invention

[0025] By the method for separating the PVA-based resin of the present embodiment, a PVA-based resin having a small particle size is separated from a solution containing the PVA-based resin.

Modes for Carrying Out the Invention

[0026] Hereinafter, embodiments of the present invention will be described in detail. However, these are merely examples of desirable embodiments and are not limited to these contents. The "~" in a numerical range includes the numerical values before and after it. For example, "0 mass% to 100 mass%" means a range that is 0 mass% or more and 100 mass% or less.

[0027] [1. Method for Separating Polyvinyl Alcohol-Based Resin] The method for separating the PVA-based resin of the present embodiment is a method for separating a PVA-based resin from a solution containing a PVA-based resin (A), wherein the solution further includes one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and an ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and an alcohol (C) different from the polyhydric alcohol (B1), and the total content of the polyhydric alcohol (B1), the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from a polycarboxylic acid in the solution is 0.001 mass% to 30 mass%.

[0028] A solution containing a PVA-based resin (A) further contains one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and an ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and an alcohol (C). After the separation of the PVA-based resin, the stickiness on the surface of the separated PVA-based resin particles can be suppressed, so that the aggregation of the particles can be suppressed. The reason why the stickiness on the surface of the particles can be suppressed is that the surface of the particles is covered with one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and an ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid. Thus, the surface of the particles is coated, and it is considered that moisture is repelled from the particles by the alcohol (C). Further, when the total content of the polyhydric alcohol (B1), the ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and the ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid in the above solution exceeds 30% by mass, the separation rate of the PVA-based resin may deteriorate.

[0029] The method for separating the PVA-based resin of this embodiment has a high degree of freedom in the separation process and is easy to manage the process. Further, since the particle size of the separated PVA-based resin is small, a pulverization process by a cutter pump or the like is unnecessary after separation. Therefore, the labor for the separation operation of the PVA-based resin is small, and the cost can also be suppressed. Furthermore, according to the method for separating the PVA-based resin of this embodiment, fibrous PVA-based resins do not get entangled with each other to form a lump state, and fibrous PVA-based resins do not get entangled with the stirring shaft. Therefore, the PVA-based resin can be separated even when industrially scaled up.

[0030] <Polyvinyl alcohol-based resin (A)> First, the PVA-based resin (A) used in this embodiment will be described. The PVA-based resin (A) is a resin mainly composed of vinyl alcohol structural units, obtained by saponifying a polyvinyl ester resin obtained by copolymerizing vinyl ester monomers, and is composed of vinyl alcohol structural units and vinyl ester structural units corresponding to the degree of saponification.

[0031] Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, isobutyl vinyl acetate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, etc. Among them, vinyl acetate is preferably used economically.

[0032] The average degree of polymerization of the PVA-based resin (A) used in this embodiment is preferably 100 to 2000, more preferably 200 to 1000, and even more preferably 250 to 800. When such an average degree of polymerization is 100 or more, sufficient strength of the resin can be obtained. Also, when such an average degree of polymerization is 2000 or less, decomposition of the resin due to shear heat generation during melt extrusion can be suppressed. The average degree of polymerization of the above PVA-based resin (A) is measured in accordance with JIS K6726:1994.

[0033] Also, the degree of saponification of the PVA-based resin (A) used in this embodiment is preferably 60 to 99.9 mol%, more preferably 80 to 99.5 mol%, and even more preferably 90 to 99.5 mol%. If such a degree of saponification is 60 mol% or more, water solubility is improved, and if it is 99.9 mol% or less, melt molding becomes easy. The degree of saponification of the above PVA-based resin is the average degree of saponification measured in accordance with JIS K6726:1994.

[0034] In addition to the unmodified PVA-based resin, the PVA-based resin (A) of this embodiment can use a modified PVA-based resin obtained by copolymerizing various monomers during the production of a polyvinyl ester-based resin and saponifying it, or various post-modified PVA-based resins obtained by introducing various functional groups into the unmodified PVA-based resin by post-modification, etc. Such modification can be carried out within a range where the water solubility of the PVA-based resin is not lost. Also, in some cases, the modified PVA-based resin may be further post-modified.

[0035] Examples of monomers copolymerizable with vinyl ester-based monomers include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene; hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 3,4-dihydroxy-1-butene and derivatives such as their acylates; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid; their salts, monoesters, or dialkyl esters; nitriles such as acrylonitrile, methacrylonitrile; amides such as diacetoneacrylamide, acrylamide, methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid or their salts; alkyl vinyl ethers; dimethylallyl vinyl ketone; N-vinylpyrrolidone; vinyl chloride; vinyl ethylene carbonate; 2,2-dialkyl-4-vinyl-1,3-dioxolane; glycerin monoallyl ether; 3,4-diacetoxy-1-butene and other vinyl compounds; substituted vinyl acetates such as isopropenyl acetate, 1-methoxyvinyl acetate; vinylidene chloride; 1,4-diacetoxy-2-butene; vinylene carbonate, etc.

[0036] In addition, examples of the modified PVA-based resin having a functional group introduced by a post-reaction include those having an acetoacetyl group by reaction with diketene, those having a polyalkylene oxide group by reaction with ethylene oxide, those having a hydroxyalkyl group by reaction with an epoxy compound or the like, or those obtained by reacting an aldehyde compound having various functional groups with PVA.

[0037] When the PVA-based resin is a modified PVA-based resin, the modification species in such a modified PVA-based resin, that is, the structural units derived from various monomers in the copolymer, or the content (modification amount) of the functional group introduced by a post-reaction, cannot be generally stated because the characteristics vary greatly depending on the modification species, but 0.1 to 20 mol% is preferable, and a range of 0.5 to 12 mol% is more preferable.

[0038] Among these various modified PVA-based resins, in the present embodiment, a PVA-based resin having a hydrophilic modification group is preferably used. Examples of the hydrophilic modification group include a hydroxyl group, a carboxyl group, an amino group, and the like. Particularly from the viewpoint of water solubility, a polyvinyl alcohol-based resin having a primary hydroxyl group in the side chain is preferable, and a PVA-based resin containing a structural unit having a 1,2-diol modification group is particularly preferable.

[0039] Among the PVA-based resins containing a structural unit having such a 1,2-diol modification group, it is preferable to use a PVA-based resin containing a 1,2-diol structural unit in the side chain represented by the following formula (1) (hereinafter, may be referred to as "PVA-based resin containing a side-chain 1,2-diol structural unit"). Since the PVA-based resin is a PVA-based resin containing a side-chain 1,2-diol structural unit, the melting point can be lowered, so that the temperature range during melt molding can be widened. In addition, the portion other than the 1,2-diol structural unit is a vinyl alcohol structural unit and a vinyl ester structural unit of the un-saponified portion, similar to a normal PVA-based resin.

[0040]

Chemical formula

[0041] (In formula (1), R 1 ~R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and X represents a single bond or a linking chain.)

[0042] In the above formula (1), R 1 ~R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. R 1 ~R 6 are preferably all hydrogen atoms, but may be alkyl groups having 1 to 5 carbon atoms as long as the resin properties are not significantly impaired. The alkyl group is not particularly limited, and for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, etc. are preferable, and the alkyl group may have substituents such as a halogeno group, a hydroxyl group, an ester group, a carboxylic acid group, a sulfonic acid group, etc. as necessary.)

[0043] Also, X in the 1,2-diol structural unit represented by formula (1) is most preferably a single bond in terms of thermal stability and stability under high temperature or acidic conditions, but may be a linking chain as long as the effects of the present invention are not inhibited. Such linking chains include hydrocarbons such as an alkylene group, an alkenylene group, an alkynylene group, a phenylene group, a naphthylene group (these hydrocarbons may be substituted with halogen atoms such as a fluorine atom, a chlorine atom, a bromine atom, etc.), and in addition, -O-, -(CH2O)m-, -(OCH2) m -, -(CH2O) m CH2-, -CO-, -COCO-, -CO(CH2) mCO-, -CO(C6H4)CO-, -S-, -CS-, -SO-, -SO2-, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO4-, -Si(OR)2-, -OSi(OR)2-, -OSi(OR)2O-, -Ti(OR)2-, -OTi(OR)2-, -OTi(OR)2O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O-, etc. (where each R is independently an arbitrary substituent, preferably a hydrogen atom or an alkyl group, and m is an integer from 1 to 5). Among them, an alkylene group having 6 or fewer carbon atoms, particularly a methylene group, or -CH2OCH2- is preferred in terms of stability during production or use.

[0044] A particularly preferred structure in the 1,2-diol structural unit represented by the above formula (1) is R 1 ~R 6 All being hydrogen atoms, and X being a single bond, is a structural unit represented by the following formula (1a).

[0045] [Chemical formula]

[0046] When the PVA-based resin is a PVA-based resin containing a 1,2-diol structural unit in the side chain, the content (modification amount) of the structural unit represented by the formula (1) contained in the PVA-based resin containing a 1,2-diol structural unit in the side chain is preferably 0.1 to 10 mol%, more preferably 0.5 to 9 mol%, and even more preferably 1 to 8 mol%. When such a content is 0.1 mol% or more, the effect of the 1,2-diol structure in the side chain can be sufficiently obtained. Also, when such a content is 10 mol% or less, the melt moldability is improved.

[0047] Note that the content (modification amount) of the 1,2-diol structural unit in the PVA-based resin is that of the completely saponified PVA-based resin 1It can be determined from the 1H-NMR spectrum (solvent: DMSO-d6, internal standard: tetramethylsilane). Specifically, it may be calculated from the peak areas derived from the hydroxyl protons, methine protons, and methylene protons in the 1,2-diol structural unit, the methylene protons in the main chain, and the protons of the hydroxyl groups linked to the main chain.

[0048] In addition, when using a PVA-based resin having a 1,2-diol structural unit in the side chain, the preferred degree of saponification is preferably 80 to 99.9 mol%, more preferably 98.5 to 99.5 mol%. If the degree of saponification is 80 mol% or more, it is difficult to decompose and deformation at high temperatures can be suppressed.

[0049] As a method for producing a PVA-based resin having a 1,2-diol structural unit in the side chain, it can be produced by a known production method. For example, (i) a method of saponifying a copolymer of a vinyl ester monomer and a compound represented by the following formula (2), (ii) a method of saponifying and decarboxylating a copolymer of a vinyl ester monomer and a compound represented by the following formula (3), or (iii) a method of saponifying and deketalizing a copolymer of a vinyl ester monomer and a compound represented by the following formula (4) is preferably used.

[0050]

Chemical formula

[0051] (In formula (2), R 1 ~R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, X represents a single bond or a bonding chain, and R 7 and R 8 each independently represents a hydrogen atom or R 9 -CO- (wherein R 9 is an alkyl group having 1 to 6 carbon atoms).)

[0052]

Chemical formula

[0053] (In formula (3), each of R 1 ~R 6 independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and X represents a single bond or a linking chain.)

[0054] [Chemical formula]

[0055] (In formula (4), each of R 1 ~R 6 independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, X represents a single bond or a linking chain, and each of R 10 and R 11 independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.)

[0056] For R 1 ~R 6 and X in the above formulas (2) to (4), specific examples and preferred examples are the same as those in the case of the above formula (1). Also, each of R 7 and R 8 is independently a hydrogen atom or R 9 -CO- (wherein R 9 is an alkyl group having 1 to 6 carbon atoms). Each of R 10 and R 11 is independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and specific examples and preferred examples of the alkyl group having 1 to 5 carbon atoms are the same as those in the case of formula (1).

[0057] For the methods (i), (ii), and (iii), for example, the methods described in JP-A-2006-95825 can be used. Among the above methods, from the viewpoint of excellent copolymerization reactivity and industrial handleability, the method (i) is preferred. In particular, as the compound represented by the above formula (2), when R 1 ~R 6 are hydrogen atoms, X is a single bond, R 7 , R 8 are R 9 -CO-, and R 9It is preferable to use 3,4-diasyloxy-1-butene in which R is an alkyl group having 1 to 4 carbon atoms. Among them, 3,4-diacetoxy-1-butene in which R 9 is a methyl group is preferably used.

[0058] Further, the PVA-based resin (A) used in the present embodiment may be a single type or a mixture of two or more types. In that case, the above-mentioned unmodified PVAs, an unmodified PVA and a PVA-based resin having a structural unit represented by the formula (1), PVAs having different saponification degrees, average polymerization degrees, modification amounts, etc. and having a structural unit represented by the formula (1), unmodified PVA, or a combination such as a PVA-based resin having a structural unit represented by the formula (1) and another modified PVA-based resin can be used.

[0059] 〔Other components〕 As long as the effects of the present invention are not impaired, lubricants such as magnesium stearate and magnesium 12-hydroxystearate may be added as additives to the PVA-based resin (A). Furthermore, plasticizers such as glycerin, diglycerin, polyglycerin, ethylene oxide adducts of glycerin, and glycerin fatty acids may be contained as necessary.

[0060] <Polyhydric alcohol (B1)> The polyhydric alcohol (B1) is not particularly limited as long as it is a polyvalent organic compound having two or more hydroxyl groups. Specific examples of the polyhydric alcohol (B1) include dihydric alcohols such as propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, polyethylene glycol, and butanediol; trihydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, and trimethylolbutane; tetrahydric alcohols such as diglycerin, pentaerythritol, erythritol, and sorbitan; pentahydric alcohols such as xylitol and triglycerin; and hexahydric or higher alcohols such as sorbitol, mannitol, polyglycerin, sucrose, glucose, fructose, mannose, xylose, saccharose, trehalose, and lactitol. Due to the balance of miscibility with alcohols and water, di- to tetravalent alcohols are preferred as the polyhydric alcohol (B1), glycerin-based compounds, glycol-based compounds, etc. are more preferred, and from the perspective of alcohol miscibility, glycerin and polyethylene glycol are particularly preferred.

[0061] <Ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid> The ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid is obtained by esterifying a polyhydric alcohol and a monocarboxylic acid. Hereinafter, the ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid is also referred to as "ester (B2)".

[0062] The preferred polyhydric alcohol in the ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid is the same as the above-described preferred polyhydric alcohol (B1).

[0063] In the ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid, preferable monocarboxylic acids include aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, enanthic acid, caproic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, sorbic acid, eicosenoic acid, erucic acid, and aromatic monocarboxylic acids such as benzoic acid, traumatic acid, biphenylcarboxylic acid, naphthalenecarboxylic acid, tetralinecarboxylic acid, cumic acid, hemellitic acid, mesitylenic acid. Preferably, they are aliphatic monocarboxylic acids having 1 to 10 carbon atoms, and more preferably aliphatic monocarboxylic acids having 2 to 8 carbon atoms.

[0064] Examples of the ester (B2) containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid include the esters containing a structural unit derived from a polyhydric alcohol and a structural unit derived from a monocarboxylic acid described above. In the ester (B2), it is preferable that the polyhydric alcohol is a di- to tetravalent alcohol and the monocarboxylic acid is an aliphatic monocarboxylic acid having 1 to 10 carbon atoms. Examples of the ester (B2) include fatty acid esters of ethylene glycol such as ethylene glycol diacetate, fatty acid esters of propylene glycol such as propylene glycol diacetate, propylene glycol monobutyrate, and propylene glycol dibutyrate, fatty acid esters of glycerin such as monoacetin, diacetin, triacetin, monobutyrylin, dibutyrylin, and tributyrylin, fatty acid esters of butanediol such as 1,3-butanediol diacetate and 1,4-butanediol diacetate, and fatty acid esters of hexanediol such as 1,6-hexanediol diacetate. Preferably, they are fatty acid esters of glycerin, and particularly preferably triacetin.

[0065] <Ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid> The ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid is obtained by esterifying a monoalcohol and a polycarboxylic acid. Hereinafter, the ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid is also referred to as "ester (B3)".

[0066] Preferred monoalcohols in the ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid include methanol, ethanol, n-propyl alcohol, isopropyl alcohol (IPA), n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, 1-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 2,2-dimethyl-1-propanol, 2-pentanol, 3-methyl-2-butanol, 3-pentanol, 2-methyl-2-butanol, 1-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, 3,3-dimethyl-1-butanol, 2-ethyl-1-butanol, 2-hexanol, 3-hexanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3,3-dimethyl-2-butanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 2,3-dimethyl-2-butanol, etc. Alcohols having 1 to 5 carbon atoms are preferred, and alcohols having 1 to 3 carbon atoms are particularly preferred.

[0067] Preferred polycarboxylic acids in the ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, fumaric acid, and sebacic acid, polycarboxylic acids having a hydroxyl group such as citric acid, tartaric acid, and malic acid, and aromatic polycarboxylic acids such as phthalic acid and biphenyldicarboxylic acid. Polycarboxylic acids having 1 to 10 carbon atoms are preferred, aliphatic polycarboxylic acids having 1 to 10 carbon atoms are more preferred, and citric acid is particularly preferred.

[0068] Examples of the ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polyvalent carboxylic acid include the esters containing a structural unit derived from a monoalcohol and a structural unit derived from a polyvalent carboxylic acid described above. In the ester (B3), it is preferable that the monoalcohol is an alcohol having 1 to 5 carbon atoms and the polyvalent carboxylic acid is a carboxylic acid having 1 to 10 carbon atoms. Examples of the ester (B3) include dimethyl oxalate, diethyl oxalate, dibutyl oxalate, diisopropyl oxalate, dipentyl oxalate, dimethyl succinate, diethyl succinate, dibutyl succinate, dipentyl succinate, dipropyl succinate, trimethyl citrate, triethyl citrate, tripropyl citrate, tributyl citrate, tripentyl citrate, acetyl tributyl citrate, dimethyl maleate, diethyl maleate, dibutyl maleate, diisopropyl maleate, dipentyl maleate, dimethyl fumarate, diethyl fumarate, dibutyl fumarate, diisopropyl fumarate, dipentyl fumarate, etc., and triethyl citrate is particularly preferable.

[0069] <Alcohol (C)> In the method for separating the PVA-based resin of the present embodiment, the solution containing the PVA-based resin (A) contains one or more selected from the group consisting of the polyhydric alcohol (B1), the ester (B2), and the ester (B3), and the alcohol (C). The alcohol (C) is an alcohol different from the polyhydric alcohol (B1). When the alcohol (C) is present in the solution, the alcohol (C) is miscible with one or more selected from the group consisting of the polyhydric alcohol (B1), the ester (B2), and the ester (B3), and it becomes easier to separate the PVA-based resin (A) from the solution.

[0070] Alcohol (C) is not particularly limited, but preferably contains an alcohol having 1 to 6 carbon atoms, and more preferably contains one or more alcohols having 1 to 6 carbon atoms. Further, it is preferable that the solution containing the PVA-based resin (A) contains alcohol (C) as a main component. Here, containing as a main component means that the solution containing the PVA-based resin (A) contains 50% by mass or more of alcohol (C) with respect to the total amount of the solution.

[0071] Examples of alcohol (C) include, specifically, methanol, ethanol, n-propyl alcohol, isopropyl alcohol (IPA), n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, 1-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 2,2-dimethyl-1-propanol, 2-pentanol, 3-methyl-2-butanol, 3-pentanol, 2-methyl-2-butanol, 1-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, 3,3-dimethyl-1-butanol, 2-ethyl-1-butanol, 2-hexanol, 3-hexanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3,3-dimethyl-2-butanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 2,3-dimethyl-2-butanol, etc. These may be used alone or in combination of two or more. From the viewpoint of the separation rate of PVA, as alcohol (C), an alcohol having 3 or less carbon atoms is preferably used, and particularly methanol and IPA are preferable.

[0072] <Solution containing PVA-based resin (A)> In the method for separating the PVA-based resin (A) of this embodiment, the PVA-based resin (A) is separated from the solution containing the PVA-based resin (A). The solution containing the PVA-based resin (A) is preferably a waste liquid containing the PVA-based resin (A). The waste liquid containing the PVA-based resin (A) is generated, for example, when manufacturing an object with a 3D printer, by laminating and solidifying a model material and a support material containing the PVA-based resin (A) in a molten state to produce a laminated molded object, and then removing the support material by bringing the laminated molded object into contact with water (solvent). It is also generated by an operation such as filtering out the solvent from the object after mixing a dispersion obtained by thermally melting and kneading a dispersoid and a dispersant containing PVA together in an extruder such as a twin-screw extruder with water (solvent). The waste liquid containing the PVA-based resin (A) may contain components contained in the object, residues of those used in the production of the object, for example, components added for the purpose of blending into the object. Examples of the above object include 3D printer molded objects and fine particles such as water-insoluble resins.

[0073] The solution containing the PVA-based resin (A) may contain various additives such as thermoplastic resins, pigments, inorganic fillers, surfactants, lubricants, plasticizers, chain transfer agents, antioxidants, ultraviolet absorbers, thickeners, crosslinking agents, etc.

[0074] Examples of the inorganic filler include kaolin, talc, light calcium carbonate, aluminum hydroxide, amorphous silica, etc.

[0075] Examples of the surfactant include anionic surfactants such as carboxylic acid type surfactants, sulfate ester type surfactants, sulfonic acid type surfactants, and nonionic surfactants such as alkyl ether type surfactants, alkyl phenyl ether type surfactants, alkyl ester type surfactants, alkyl amine type surfactants, alkyl amide type surfactants, polypropylene glycol ether type surfactants, alkanolamide type surfactants, allyl phenyl ether type surfactants, etc.

[0076] Examples of the lubricant include paraffin waxes, fatty acid waxes, aliphatic amide waxes, fatty acid lower alcohol esters, metal soaps such as zinc stearate, magnesium stearate, calcium stearate, and rosin zinc, etc.

[0077] Examples of the plasticizer include epoxy plasticizers and phosphate plasticizers.

[0078] Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol and dodecyl mercaptan; and organic halides such as carbon tetrachloride, trichloroethylene, and perchloroethylene.

[0079] Examples of the antioxidant include sulfites such as sodium sulfite, potassium sulfite, calcium sulfite, and ammonium sulfite, tartaric acid, ascorbic acid, sodium thiosulfate, techol, and Rongalit, etc.

[0080] Examples of the ultraviolet absorber include organic ultraviolet absorbers such as cyclic iminoester-based, benzotriazole-based, and benzophenone-based ultraviolet absorbers, and inorganic ultraviolet absorbers such as titanium oxide, zinc oxide, indium oxide, tin oxide, talc, kaolin, calcium carbonate, titanium oxide-based composite oxides, zinc oxide-based composite oxides, ITO (tin-doped indium oxide), ATO (antimony-doped tin oxide), etc.

[0081] Examples of crosslinking agents include monoaldehyde compounds, aldehyde compounds, amine compounds, methylol compounds, reaction products of ammonia and formaldehyde such as hexamethylenetetramine, boron compounds such as boric acid and borax, zirconium compounds, titanium orthoesters; titanium chelates, titanium compounds, aluminum compounds such as aluminum organic acid chelates, organoalkoxysilane compounds having organic reactive groups such as silane coupling agents, polyvalent epoxy compounds, various isocyanate compounds, polyamide polyamine-epichlorohydrin resins, and the like.

[0082] <Method for Separating Polyvinyl Alcohol-Based Resin> This embodiment is a method for separating a PVA-based resin from a solution containing the PVA-based resin (A), wherein the solution further contains one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3), and an alcohol (C) different from the polyhydric alcohol (B1), and the total content of the polyhydric alcohol (B1), the ester (B2), and the ester (B3) in the solution is 0.001% by mass to 30% by mass.

[0083] Here, the solution containing the PVA-based resin (A) is preferably the above-mentioned solution containing the PVA-based resin (A), and more preferably an aqueous solution containing the above-mentioned PVA-based resin (A) (also referred to as a PVA-based resin aqueous solution). The PVA-based resin aqueous solution is obtained by bringing the PVA-based resin (A) into contact with water and dissolving the PVA-based resin (A) (dissolving step).

[0084] The method for bringing the PVA-based resin into contact with water is not particularly limited and can be carried out by a known method. For example, normal pressure and normal temperature dissolution method, high pressure and normal temperature dissolution method, normal pressure hot water dissolution method, high pressure hot water dissolution method, etc. can be mentioned, and as the apparatus, an ultrasonic homogenizer, a three-one motor, a homomixer, etc. can be used. In such a high-pressure hot water dissolution method, the water temperature is preferably 0 to 200°C, more preferably 50 to 150°C, and even more preferably 80 to 120°C. If the water temperature is 50°C or higher, the solubility of the PVA-based resin is improved, and if it is 150°C or lower, the decomposition of the PVA-based resin can be suppressed. Also, the dissolution time, that is, the contact time between the PVA-based resin and water, is preferably 0.5 to 50 hours, more preferably 1 to 25 hours, and even more preferably 1.5 to 5 hours. If such a dissolution time is 0.5 hours or longer, the remaining undissolved PVA-based resin can be suppressed, and if it is 50 hours or shorter, it is economically preferable.

[0085] When the PVA-based resin is brought into contact with water, it is preferably stirred. The stirring speed is preferably 1 to 2000 rpm, more preferably 1 to 1000 rpm.

[0086] The concentration of the PVA-based resin in this embodiment slightly varies depending on its type, dissolution apparatus, etc., but is preferably 1 to 40% by mass, more preferably 5 to 35% by mass, and even more preferably 10 to 30% by mass. When the concentration of the PVA-based resin in the PVA-based resin aqueous solution is 1% by mass or more, the number of repetitions of the recovery process described later can be reduced, which is efficient. Also, if the concentration is 40% by mass or less, the solubility becomes high and the efficiency of the dissolution process can be sufficiently increased.

[0087] One or more selected from the group consisting of polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from polyhydric alcohol and a structural unit derived from monocarboxylic acid, and an ester (B3) containing a structural unit derived from monoalcohol and a structural unit derived from polycarboxylic acid may be included in the PVA resin (A) before contact with water, or may be mixed simultaneously when the PVA-based resin is contacted with water. One or more selected from the group consisting of polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from polyhydric alcohol and a structural unit derived from monocarboxylic acid, and an ester (B3) containing a structural unit derived from monoalcohol and a structural unit derived from polycarboxylic acid may be mixed in a solution containing the PVA-based resin (A). Alternatively, one or more selected from the group consisting of polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from polyhydric alcohol and a structural unit derived from monocarboxylic acid, and an ester (B3) containing a structural unit derived from monoalcohol and a structural unit derived from polycarboxylic acid may be mixed with alcohol (C) and then further mixed with a solution containing the PVA-based resin (A). In a solution containing the PVA-based resin (A), one or more selected from the group consisting of polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from polyhydric alcohol and a structural unit derived from monocarboxylic acid, and an ester (B3) containing a structural unit derived from monoalcohol and a structural unit derived from polycarboxylic acid, by setting the total content to 0.001% by mass to 30% by mass, the PVA-based resin can be preferably separated. By setting the above content to 0.001% by mass to 30% by mass, the PVA-based resin is flexible and has a small particle size, so it is not necessary to cut it using a cutter pump or the like during transportation, and recovery becomes easy.

[0088] When separating the PVA-based resin (A), the method of making the solution containing the PVA-based resin (A) further contain one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and an ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and an alcohol (C) is not particularly limited and can be carried out by a known method.

[0089] For example, a method of adding one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3) to the PVA-based resin (A) before contacting with water, a method of adding one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3) to the solution containing the PVA-based resin (A), a method of adding the PVA-based resin to one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3), a method of mixing the PVA-based resin aqueous solution and one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3) at once, etc. can be mentioned. Among them, a method of gradually adding one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3) to the PVA-based resin aqueous solution is preferable in terms of enabling efficient separation of the PVA-based resin.

[0090] A typical mixing method is a method of filling the PVA-based resin aqueous solution into a tank and gradually adding one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3) to the circulating PVA-based resin aqueous solution, or a method of adding them at once. When adding gradually, the total addition amount per unit time of the polyhydric alcohol (B1), the ester (B2), and the ester (B3) is not particularly limited, but 0.1 to 800 kg / min is preferable, and 0.3 to 400 kg / min is more preferable. The PVA-based resin is separated from the PVA-based resin aqueous solution containing one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2), and an ester (B3) and an alcohol (C), and a mixed solution and the separated PVA-based resin are obtained.

[0091] When mixing the aqueous PVA resin solution with one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3), the liquid temperature is not particularly limited, but it is preferably adjusted to be 5 to 80°C, more preferably 10 to 60°C. By setting the temperature during mixing within the above range, evaporation and freezing of water can be prevented.

[0092] Further, the separation method of the present embodiment preferably includes mixing a solution containing a PVA resin (A), one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3), and alcohol (C).

[0093] The total amount of the solution containing the PVA resin (A), the total amount of one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3), and the total amount of alcohol (C) may be mixed at once. The solution containing the PVA resin (A) and one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3) may be mixed first, and then alcohol (C) may be mixed later. First, one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3) and alcohol (C) may be mixed, and then the solution containing the PVA resin (A) may be mixed later.

[0094] Regardless of the above order, a part of one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3) may be first mixed with the solution containing the PVA resin (A) or alcohol (C), and then the remaining one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3) may be gradually added. Alcohol (C) may be mixed with the solution at once, or after mixing a part of alcohol (C) with the solution, the remaining alcohol (C) may be added dropwise. From the perspective of cost, a method of mixing at once the total amount of the solution containing the PVA-based resin (A), the total amount of one or more selected from the group consisting of the polyhydric alcohol (B1), the ester (B2), and the ester (B3), and the total amount of the alcohol (C) is preferred.

[0095] In a solution containing the PVA-based resin (A), one or more selected from the group consisting of the polyhydric alcohol (B1), the ester (B2), and the ester (B3), and the alcohol (C), the total content of the polyhydric alcohol (B1), the ester (B2), and the ester (B3) is 0.001% by mass to 30% by mass, preferably 0.005% by mass to 20% by mass, more preferably 0.01% by mass to 10% by mass, and still more preferably 0.03% by mass to 7.5% by mass.

[0096] In a solution containing the PVA-based resin (A), one or more selected from the group consisting of the polyhydric alcohol (B1), the ester (B2), and the ester (B3), and the alcohol (C), based on 100 parts by mass of the PVA-based resin (A), the total of the polyhydric alcohol (B1), the ester (B2), and the ester (B3) is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, still more preferably 1.5 part by mass or more, and particularly preferably 2.0 part by mass or more from the perspective of the separation rate. In the mixed solution, based on 100 parts by mass of the PVA-based resin (A), the total of the polyhydric alcohol (B1), the ester (B2), and the ester (B3) is more preferably 0.5 part by mass to 30 parts by mass, and still more preferably 1 part by mass to 25 parts by mass.

[0097] In a solution containing the PVA-based resin (A), one or more selected from the group consisting of the polyhydric alcohol (B1), the ester (B2), and the ester (B3), and the alcohol (C), the mass ratio ((A) / (C)) of the content of the PVA-based resin (A) to the content of the alcohol (C) is preferably 0.2 / 99.8 to 50 / 50 from the perspective of the separation rate. In the above solution, (A) / (C) is more preferably 0.5 / 99.5 to 30 / 70, and still more preferably 1 / 99 to 15 / 85.

[0098] Also, as a combination of one or more selected from the group consisting of polyhydric alcohol (B1), ester (B2), and ester (B3) and alcohol (C), preferably, glycerin and methanol, glycerin and isopropyl alcohol, triacetin and methanol, triacetin and isopropyl alcohol, polyethylene glycol and methanol, polyethylene glycol and isopropyl alcohol, triethyl citrate and methanol, triethyl citrate and isopropyl alcohol can be mentioned. Among them, the combination of triacetin and methanol or triacetin and isopropyl alcohol is particularly preferable.

[0099] Further, in the present embodiment, the ratio (separation rate) of the mass of the PVA-based resin separated by the above separation method to the mass of the PVA-based resin in the PVA-based resin aqueous solution is preferably 50% or more. If the separation rate is 50% or more, the PVA-based resin in the solution can be sufficiently recovered. The higher the separation rate, the more preferable it is, 70% or more is more preferable, 80% or more is further preferable, 85% or more is particularly preferable, and the upper limit is 100%.

[0100] Here, the separation rate can be calculated by the following method. The PVA-based resin separated by the above separation method is dried at 140 °C for 3 hours using a dryer (for example, SPH-102 manufactured by ESPEC). Measure the mass of the dried PVA-based resin, and calculate the separation rate based on the following formula. Separation rate (%) = {mass of PVA-based resin after drying (g) / mass of charged PVA-based resin (g)} × 100

[0101] Examples of the particle shape of the separated PVA-based resin include spherical, fibrous, etc. From the viewpoint of the convenience of reuse, spherical is preferable.

[0102] Further, the average major axis length of the separated PVA-based resin particles is preferably 0.1 to 10 cm, more preferably 0.3 to 5 cm. Here, the major axis length corresponds to the maximum diameter of the PVA-based resin particles. The maximum diameter of the PVA-based resin particles is, for example, the particle diameter at the site where the distance between two parallel plates becomes the largest when the PVA-based resin is sandwiched between the two parallel plates. The above range is preferable because it prevents the particles from being entangled with each other to form lumps or being entangled with the stirring shaft, and eliminates the need for a pulverization step during the recovery of the PVA-based resin.

[0103] The particle size of the PVA-based resin particles may be measured by a conventionally known method. For example, it can be measured using calipers.

[0104] [2. Recycling method of polyvinyl alcohol-based resin] The recycling method according to the present embodiment includes recovering the PVA-based resin separated by the separation method according to the present embodiment (recovery step).

[0105] The method for recovering the PVA-based resin separated by the separation method according to the present embodiment is not particularly limited and can be performed by a known method. Specifically, for example, the separated PVA-based resin can be filtered from the mixed solution, centrifuged, and then dried by a vibration fluidized dryer, a vacuum dryer, or the like to obtain the PVA-based resin. The drying time is preferably 2 to 24 hours, more preferably 3 to 15 hours. The drying temperature is not particularly limited, but is preferably 150°C or lower.

Examples

[0106] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, "parts" and "%" mean mass basis unless otherwise specified.

[0107] (Example 1) <Production of PVA-based resin> A PVA-based resin having a 1,2-diol structural unit represented by the above formula (1a) (saponification degree: 99.2 mol%, degree of polymerization: 350, content of 1,2-diol structural unit: 6 mol%) was pelletized by melt extrusion using a twin-screw extruder. Such pellets are cylindrical with a total length of 3 mm and an outer diameter of 2 mm.

[0108] (A) Dissolution step (preparation of waste liquid) Water was put into a container (volume: 450 cc) equipped with a stirring blade (propeller blade), and the above-mentioned pellets were added while stirring at 500 rpm. After raising the temperature to 85°C, stirring was continued for 60 minutes to completely dissolve the above-mentioned pellets in water, and an aqueous PVA-based resin solution of about 27 mass% was obtained. Thereafter, the solid content was calculated by the volatile matter method (mass of solid after drying / mass of aqueous solution × 100), and a 25 mass% PVA resin aqueous solution was prepared by adding water.

[0109] (B) Separation step The 25 mass% PVA aqueous solution prepared in the dissolution step was put into a reaction kettle (tank diameter: 0.13 m) equipped with a stirring blade (edged turbine, blade diameter: 0.1 m), and the amount was adjusted to 20 mass parts of the 25 mass% PVA-based resin aqueous solution obtained in the above dissolution step with respect to 100 mass parts of methanol. Further, 1 mass part of triacetin (Triacetin manufactured by Tokyo Chemical Industry Co., Ltd.) was added with respect to 100 mass parts of methanol, and the mixture was stirred for 10 minutes to prepare a mixed solution, which was then allowed to stand to separate the PVA-based resin. Note that the separation of the PVA-based resin started before stirring, and more PVA-based resin was separated by stirring and standing. The composition in the mixed solution is shown in Table 1.

[0110] (Example 2) The PVA-based resin was separated in the same manner as in Example 1, except that the blending amounts of various components in the mixed solution were changed as shown in Table 1.

[0111] (Example 3) The PVA-based resin was separated in the same manner as in Example 1, except that the blending amounts of various components in the mixed solution were changed as shown in Table 1.

[0112] (Example 4) The stirring blade installed in the reaction vessel was changed to a stirring blade (edged turbine, blade diameter 0.06 m), and the PVA-based resin was separated in the same manner as in Example 1 except that the blending amounts of various components in the mixed solution were changed as shown in Table 1.

[0113] (Example 5) The stirring blade installed in the reaction vessel was changed to a stirring blade (paddle, blade diameter 0.1 m), and the PVA-based resin was separated in the same manner as in Example 1 except that the blending amounts of various components in the mixed solution were changed as shown in Table 1.

[0114] (Example 6) The stirring blade installed in the reaction vessel was changed to a stirring blade (edged tabine, blade diameter 0.06 m), and the PVA-based resin was separated in the same manner as in Example 1 except that the rotation speed during stirring was changed to 550 rpm.

[0115] (Example 7) The PVA-based resin was separated in the same manner as in Example 1 except that methanol was changed to IPA.

[0116] (Example 8) The PVA-based resin was separated in the same manner as in Example 1 except that triacetin was changed to glycerin.

[0117] (Example 9) The PVA-based resin was separated in the same manner as in Example 1 except that triacetin was changed to PEG.

[0118] (Example 10) The PVA-based resin was separated in the same manner as in Example 1 except that triacetin was changed to triethyl citrate.

[0119] (Comparative Example 1) The PVA-based resin was separated in the same manner as in Example 1 except that triacetin was not blended.

[0120] 《Evaluation Method》 <Particle Size of the Separated PVA-Based Resin> Ten arbitrary PVA-based resins were collected from the PVA-based resin obtained in the above process, and the value of the maximum diameter (also referred to as the major axis) of each resin was measured using calipers. The average value of the diameters of the ten PVA-based resins was calculated from the major axis of each resin. The results are shown in Table 2.

[0121] <Particle shape> The shape of the separated PVA-based resin was visually confirmed. The results are shown in Table 2.

[0122] <Separation rate> The PVA-based resin obtained in the above process was dried at 140 °C for 3 hours using an explosion-proof dryer (SPH-102 manufactured by ESPEC). The mass of the dried PVA-based resin was measured, and the separation rate was calculated based on the following formula. The results are shown in Table 2. Separation rate (%) = {mass of PVA-based resin after drying (g) / mass of charged PVA-based resin (g)} × 100

[0123]

Table 1

[0124]

Table 2

[0125] In Examples 1 to 10, spherical or fibrous PVA-based resins with small major axes of the particles could be separated. Furthermore, Examples 1 to 10 showed high separation rates. On the other hand, in Comparative Example 1, since the PVA-based resin precipitated in the system agglomerated, the major axis of the particles could not be measured.

[0126] From this, it was shown that by including in the solution containing the PVA-based resin at least one or more of an ester containing a predetermined amount of polyhydric alcohol, a structural unit derived from the polyhydric alcohol, and a structural unit derived from a monocarboxylic acid, and an ester containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and an alcohol different from the above polyhydric alcohol, a PVA-based resin with a small particle diameter can be separated.

Claims

1. A method for separating a polyvinyl alcohol-based resin from a solution containing a polyvinyl alcohol-based resin (A), wherein the solution further contains one or more selected from the group consisting of a polyhydric alcohol (B1), an ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and an ester (B3) containing a structural unit derived from a monoalcohol and a structural unit derived from a polycarboxylic acid, and further contains an alcohol (C) different from the polyhydric alcohol (B1), in the solution, the total content of the polyhydric alcohol (B1), the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from a polycarboxylic acid is 0.001% by mass to 30% by mass, A method for separating a polyvinyl alcohol-based resin.

2. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the polyhydric alcohol (B1) is a di- to tetravalent alcohol.

3. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the polyhydric alcohol (B1) is one or more selected from the group consisting of glycerin-based compounds and glycol-based compounds.

4. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the polyhydric alcohol (B1) is at least one of glycerin and polyethylene glycol.

5. In the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, the polyhydric alcohol is a di- to tetravalent alcohol, and the monocarboxylic acid is an aliphatic monocarboxylic acid having 1 to 10 carbon atoms. The method for separating a polyvinyl alcohol-based resin according to claim 1.

6. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid is a glycerin fatty acid ester.

7. In the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from a polycarboxylic acid, the monoalcohol is an alcohol having 1 to 5 carbon atoms, and the polycarboxylic acid is a carboxylic acid having 1 to 10 carbon atoms. The method for separating a polyvinyl alcohol-based resin according to claim 1.

8. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the total amount of the polyhydric alcohol (B1), the ester (B2) containing a structural unit derived from the polyhydric alcohol and a structural unit derived from a monocarboxylic acid, and the ester (B3) containing a structural unit derived from the monoalcohol and a structural unit derived from a polycarboxylic acid is 0.5 parts by mass or more with respect to 100 parts by mass of the polyvinyl alcohol-based resin (A).

9. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the alcohol (C) contains one or more alcohols having 1 to 6 carbon atoms, and the solution contains the alcohol (C) as a main component.

10. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the mass ratio ((A) / (C)) of the content of the polyvinyl alcohol-based resin (A) to the content of the alcohol (C) in the solution is 0.2 / 99.8 to 50 / 50.

11. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the polyvinyl alcohol-based resin (A) is a polyvinyl alcohol-based resin having a primary hydroxyl group in a side chain.

12. The method for separating a polyvinyl alcohol-based resin according to claim 1, wherein the average major axis of the particles of the separated polyvinyl alcohol-based resin is 0.1 to 10 cm.

13. A method for recycling a polyvinyl alcohol-based resin, comprising recovering the polyvinyl alcohol-based resin separated by the method according to any one of claims 1 to 12.

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