Method for recovering polymer

Abstract

The present invention makes it possible to efficiently recover a polymer from an emulsion polymerization liquid. A method for recovering a polymer according to the present invention comprises the steps of: adding a solvent to an emulsion polymerization liquid that contains a polymer, an emulsifier, and a liquid medium, and forming coarse particles of the polymer to obtain a coarse polymer particle-containing liquid; and recovering coarse polymer particles from the coarse polymer particle-containing liquid. The absolute value of the difference between the dipole-dipole force term of the Hansen solubility parameter of the polymer and the dipole-dipole force term of the Hansen solubility parameter of a mixed liquid comprising the solvent and the liquid medium in the coarse polymer particle-containing liquid is preferably 3.0 MPa1 / 2 or more and 5.5 MPa1 / 2 or less.

Description

Polymer recovery method

[0001] The present invention relates to a method for recovering a polymer.

[0002] Conventionally, as a method for recovering a polymer from an emulsion polymerization liquid obtained by emulsion polymerization of a monomer composition containing a monomer, an emulsifier, and a solvent, a method has been known in which the emulsion polymerization liquid is dropped into a poor solvent in which the polymer has low solubility, and the precipitated polymer is filtered and dried.

[0003] Specifically, for example, in Patent Document 1, a small amount of tetrahydrofuran, which is a good solvent in which the polymer has high solubility, is added to an emulsion polymerization liquid obtained by emulsion polymerization of a monomer composition containing methyl α-chloroacrylate and α-methylstyrene as monomers, and the emulsion polymerization liquid is then dropped into methanol, which is a poor solvent, and the coagulated polymer is collected by filtration.

[0004] International Publication No. 2019 / 150966

[0005] However, the above-mentioned conventional methods have the problem that the filter medium such as filter paper becomes clogged during filtration, making it impossible to separate solids and liquids efficiently.

[0006] Therefore, there has been a demand for a method for recovering a polymer that enables efficient recovery of the polymer from an emulsion polymerization liquid.

[0007] The present inventors have conducted extensive research to solve the above problems, and have found that adding a solvent to an emulsion polymerization liquid so as to form coarse particles of the polymer makes it possible to efficiently separate the solid from the liquid and efficiently recover the polymer from the emulsion polymerization liquid, thereby completing the present invention.

[0008] That is, the present invention aims to advantageously solve the above-mentioned problems, and [1] the method for recovering a polymer of the present invention is characterized by comprising a step of adding a solvent to an emulsion polymerization liquid containing a polymer, an emulsifier, and a liquid medium, thereby coarsening the polymer into coarse particles to obtain a liquid containing coarse polymer particles, and a step of recovering the coarse polymer particles from the liquid containing coarse polymer particles.

[0009] Here, [2] the method for recovering a polymer of the present invention is characterized in that the absolute value of the difference between the dipole-dipole force term of the Hansen solubility parameter of the polymer and the dipole-dipole force term of the Hansen solubility parameter of the mixed liquid comprising the liquid medium and the solvent in the polymer coarse particle-containing liquid is 3.0 MPa or less. １／２ Over 5.5 MPa １／２ The polymer recovery method according to the above [1] is preferred. In the present invention, the "dipole-dipole term of the Hansen solubility parameter" can be determined using computer software (Hansen Solubility Parameters in Practice (HSPiP)). Specifically, for example, HSPiP version 5 may be used, and for substances registered in the database, the value may be used, and for substances not registered, an estimated value may be used.

[0010] [3] In the method for recovering a polymer of the present invention, the absolute value of the difference between the SP value of the polymer and the SP value of the solvent is 7.5 MPa. １／２ The method for recovering a polymer according to the above [1] or [2] is preferred. In the present invention, the "SP value" is a value defined by three-dimensional parameters of the Hansen solubility parameters (dD, dP, dH), and is expressed by the following formula (1). (SP value) ２ = (dD) ２ + (dP) ２ + (dH) ２ ... (1) (In formula (1), dD represents the dispersion term (also referred to as the London dispersion term), dP represents the dipole-dipole force term, and dH represents the hydrogen bond term.) The dD, dP, and dH used to calculate the SP value can be determined using computer software (Hansen Solubility Parameters in Practice (HSPiP)). Specifically, for example, HSPiP version 5 can be used, and for substances registered in the database, the values ​​can be used, and for substances not registered, estimated values ​​can be used.

[0011] Furthermore, [4] the method for recovering a polymer of the present invention is preferably the method for recovering a polymer according to any one of the above [1] to [3], wherein the solvent is at least one selected from the group consisting of ketones, ethers, esters, hydrocarbons, alcohols, halogenated hydrocarbons, and water.

[0012] [5] The method for recovering a polymer of the present invention is preferably the method for recovering a polymer according to any one of the above [1] to [4], wherein the emulsifier is a fatty acid salt.

[0013] [6] The method for recovering a polymer according to any one of the above [1] to [5] may further include, before the step of obtaining the coarse polymer particle-containing liquid, a step of emulsion-polymerizing a monomer composition containing a monomer, an emulsifier, and a liquid medium to prepare the emulsion polymerization liquid.

[0014] According to the present invention, the polymer can be efficiently recovered from the emulsion polymerization liquid.

[0015] The present invention will be described in detail below. The method for recovering a polymer of the present invention can be used when recovering a polymer from an emulsion polymerization liquid.

[0016] (Polymer recovery method) The polymer recovery method of the present invention includes a step of coarsening a polymer contained in an emulsion polymerization liquid to obtain a liquid containing coarse polymer particles (hereinafter sometimes referred to as a "coarse particle generation step"), and a step of recovering coarse polymer particles from the liquid containing coarse polymer particles (hereinafter sometimes referred to as a "recovery step"). The polymer recovery method of the present invention may include a step of preparing an emulsion polymerization liquid (hereinafter sometimes referred to as a "preparation step") before the coarse particle generation step. The polymer recovery method of the present invention may also include a step of performing post-treatment such as drying on the coarse polymer particles after the recovery step.

[0017] <Preparation Step> In the preparation step, an emulsion polymerization liquid containing a polymer, an emulsifier, and a liquid medium, and optionally containing other components, is prepared. Specifically, in the preparation step, the emulsion polymerization liquid is prepared by emulsion polymerizing a monomer composition containing a monomer, an emulsifier, and a liquid medium, and optionally containing other components, or by purchasing a commercially available emulsion polymerization liquid, without any particular limitations. The prepared emulsion polymerization liquid is then subjected to the coarsening step.

[0018] [Polymer] Here, the polymer contained in the emulsion polymerization liquid is not particularly limited, and examples thereof include acrylic polymers such as polymethyl methacrylate; diene polymers and hydrogenated products thereof such as polybutadiene, polyisoprene, styrene-butadiene polymer (SBR), styrene-isoprene polymer, and acrylonitrile-butadiene polymer (NBR); nitrile polymers such as polyacrylonitrile; and other polymers.

[0019] In the present invention, "acrylic polymer" refers to a polymer having the highest content of (meth)acrylic acid ester units among all repeating units constituting the polymer. Furthermore, "diene polymer" refers to a polymer having the highest content of structural units derived from aliphatic conjugated dienes among all repeating units constituting the polymer. Furthermore, "nitrile polymer" refers to a polymer having the highest content of monomer units containing nitrile groups among all repeating units constituting the polymer. Here, "(meth)acrylic acid ester" refers to acrylic acid ester and / or methacrylic acid ester. Furthermore, "structural units derived from" a certain monomer include not only monomer units formed upon polymerization of the monomer, but also structural units formed by hydrogenating or crosslinking the formed monomer units.

[0020] Examples of other polymers include known polymers that do not fall under the category of acrylic polymers, diene polymers and hydrogenated products thereof, and nitrile polymers. [In formula (I), R １ is a halogen atom or an alkyl group substituted with a halogen atom, and R ２is an organic group, and R ３ and R ４ are each independently a hydrogen atom, a fluorine atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and may be the same or different from each other.] and a repeating unit (I) represented by the following formula (II): [In formula (II), R ５ , R ７ and R ８ are each independently a hydrogen atom, a halogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a halogen atom, and may be the same or different from each other; R ６ represents an organic group or a halogen atom, and n represents an integer of 0 to 5.

[0021] More specifically, the other polymers include at least one monomer unit selected from the group consisting of methyl α-chloroacrylate unit, ethyl α-chloroacrylate unit, benzyl α-chloroacrylate unit, 1-adamantyl α-chloroacrylate unit, 2,2,3,3,3-pentafluoropropyl α-chloroacrylate unit, 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate unit, 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate unit, and 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate unit, １ is a chlorine atom and R ３ and R ４ is a hydrogen atom, and a monomer unit derived from at least one monomer selected from the group consisting of α-methylstyrene (AMS) and its derivatives (for example, the following monomers (c-1) to (c-9)). ５ is a methyl group and R ７ and R ８ and a repeating unit represented by the above formula (II) in which R is a hydrogen atom.

[0022] Here, without being particularly limited, the SP value of the polymer is 15.0 MPa１／２ Over 25.0 MPa １／２ In addition, the London dispersion term (dD Ｐ ) is 15.0 MPa １／２ Over 20.0 MPa １／２ Furthermore, the dipole-dipole force term (dP Ｐ ) is 5.0 MPa １／２ Over 12.0 MPa １／２ The hydrogen bonding strength term (dH Ｐ ) is 0.5 MPa １／２ Over 7.5 MPa １／２ It can be the following:

[0023] The polymer can be prepared by emulsion polymerization of the monomers in the presence of an emulsifier and a liquid medium, as described in detail below, using a known method. The concentration of the polymer in the emulsion polymerization liquid is not particularly limited, and can be, for example, from 15% by mass to 40% by mass.

[0024] [Emulsifier] Any emulsifier capable of emulsifying a monomer in a liquid medium during preparation of a polymer can be used. Specific examples of the emulsifier include anionic emulsifiers and nonionic emulsifiers.

[0025] Examples of the anionic emulsifier include fatty acid salts such as potassium tallow fatty acid, partially hydrogenated potassium tallow fatty acid, sodium decanoate, sodium laurate, potassium oleate, sodium oleate, potassium palmitate, potassium stearate, and potassium myristate; resin acid salts such as potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate; and alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate.

[0026] Examples of nonionic emulsifiers include polyethylene glycol ester emulsifiers and Pluronic (registered trademark) emulsifiers such as block copolymers of ethylene oxide and propylene oxide.

[0027] Among the above, from the viewpoint of suppressing the emulsifier from remaining in the recovered polymer, fatty acid salts are preferred as the emulsifier, fatty acid salts having 10 or more carbon atoms are more preferred, and saturated fatty acid salts having 10 or more carbon atoms such as sodium decanoate, sodium laurate, potassium palmitate, potassium stearate, potassium myristate, etc., and unsaturated fatty acid salts having 10 or more carbon atoms such as potassium oleate, sodium oleate, etc. are even more preferred.

[0028] The emulsifiers described above can be used alone or in combination of two or more. The amount of the emulsifier in the emulsion polymerization liquid is not particularly limited, and can be, for example, from 0.5 parts by mass to 30 parts by mass per 100 parts by mass of the polymer.

[0029] [Liquid medium] Water is usually used as the liquid medium. Note that, as long as emulsification with an emulsifier is possible, water alone or a mixture of water and an organic solvent may be used as the liquid medium. When a mixture of water and an organic solvent is used, the proportion of the organic solvent in the liquid medium can be, for example, 10% by volume or less, and preferably 5% by volume or less.

[0030] [Other Components] Examples of other components include known additives used in emulsion polymerization, such as polymerization initiators, chelating agents, oxygen scavengers, molecular weight modifiers, and pH adjusters.

[0031] <Coarse Particle Formation Step> In the coarse particle formation step, a solvent is added to the emulsion polymerization liquid to coarsely form the polymer contained in the emulsion polymerization liquid, thereby obtaining a liquid containing coarse polymer particles. Specifically, in the coarse particle formation step, the addition of a solvent causes the polymer contained in the emulsion polymerization liquid to aggregate or agglomerate and form coarse particles, thereby obtaining a liquid containing coarse polymer particles that have improved sedimentation properties compared to before the addition of the solvent. Note that the particle size of the coarse polymer particles is usually larger than the particle size of the polymer contained in the emulsion polymerization liquid.

[0032] [Solvent] The solvent used herein is not particularly limited, and may be any solvent capable of coarsening the polymer into coarse particles depending on the type of polymer and liquid medium contained in the emulsion polymerization liquid. Specific examples of the solvent include ketones such as acetone, methyl ethyl ketone, cyclohexanone, and diisobutyl ketone; ethers such as diethyl ether, dioxane, and tetrahydrofuran; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; hydrocarbons such as linear aliphatic hydrocarbons (e.g., hexane), cyclic aliphatic hydrocarbons (e.g., cyclopentane, cyclohexane), and aromatic hydrocarbons (e.g., toluene and xylene); alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol; halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, and chlorobenzene; and water. The above-mentioned solvents can be used alone or in combination of two or more kinds.

[0033] Among the above-mentioned solvents, it is preferable to use a solvent in which the solubility of the polymer contained in the emulsion polymerization liquid at a temperature of 25° C. is 5 g / 100 g or more, and it is more preferable to use a solvent in which the solubility is 10 g / 100 g or more. When a solvent in which the solubility is equal to or more than the above-mentioned lower limit is used, the polymer can be successfully coarsened into large particles.

[0034] Furthermore, without being particularly limited, the SP value of the solvent is 17.0 MPa １／２ Over 23.0 MPa １／２ Below 19.0 MPa, preferably １／２ Over 20.0 MPa １／２ In addition, the London dispersion term (dD Ｓ ) is 12.0 MPa １／２ Over 18.0 MPa １／２ Below 15.0 MPa, preferably １／２ Over 17.0 MPa １／２Furthermore, the dipole-dipole force term (dP Ｓ ) is 3.0 MPa １／２ Over 12.0 MPa １／２ The hydrogen bonding strength term (dH Ｓ ) is 5.0 MPa １／２ More than 10.0 MPa １／２ Below 7.0 MPa, preferably １／２ Over 8.0 MPa １／２ It can be the following:

[0035] From the viewpoint of effectively coarsening the polymer particles, the solvent is preferably a solvent in which the absolute value of the difference between the SP value of the polymer contained in the emulsion polymerization liquid and the SP value of the solvent is 7.5 MPa. １／２ The solvent is preferably such that the absolute value of the difference between the SP value of the polymer and the SP value of the solvent is 5.0 MPa or less. １／２ A solvent in which the absolute value of the difference between the SP value of the polymer and the SP value of the solvent is 2.5 MPa or less is more preferred. １／２ The lower limit of the absolute value of the difference between the SP value of the polymer and the SP value of the solvent is not particularly limited, and is preferably 0 MPa or less. １／２ It can be more than that.

[0036] [Making the Polymer into Coarse Particles] The addition of a solvent to the emulsion polymerization liquid and the making of the polymer into coarse particles can be carried out at a temperature of, for example, 5°C or higher and 40°C or lower, without any particular limitation.

[0037] The solvent may be added in multiple stages, but is preferably added in one stage. The added solvent is not particularly limited, and can be mixed with the emulsion polymerization liquid using a known mixing method such as stirring. The mixture of the emulsion polymerization liquid and the solvent is then left to stand for a period of 30 seconds to 60 minutes, without any particular limitation, to allow the polymer to be sufficiently coarsened into particles.

[0038] The amount of the solvent added to the emulsion polymerization liquid can be, for example, 15% by mass or more and 85% by mass or less, and preferably 20% by mass or more and 80% by mass or less, where the total amount of the liquid medium and the amount of the solvent contained in the emulsion polymerization liquid is 100% by mass.

[0039] Furthermore, from the viewpoint of effectively coarsening the polymer particles, it is preferable that the type and amount of the solvent added to the emulsion polymerization liquid satisfy the following condition (1): Condition (1): The dipole-dipole term (dP Ｐ ) and the dipole-dipole term (dP Ｍ ) and the difference (dP Ｐ -dP Ｍ ) is 3.0 MPa １／２ Over 5.5 MPa １／２ below.

[0040] The coarse polymer particle-containing liquid obtained by adding a solvent to the emulsion polymerization liquid contains a coarse polymer (coarse polymer particles), an emulsifier, and a mixture of a liquid medium and a solvent, and optionally further contains other components.

[0041] <Recovery Step> In the recovery step, coarse polymer particles are recovered from the coarse polymer particle-containing liquid. As the recovery method, generally known solid recovery methods such as solid-liquid separation and distillation of liquid components can be used, but it is preferable to directly separate the coarse polymer particle-containing liquid obtained in the coarse particle formation step into solid-liquid separation.

[0042] [Solid-liquid separation] Here, the method for solid-liquid separation of a liquid containing coarse polymer particles is not particularly limited, and examples thereof include centrifugation, filtration, decantation, etc. These solid-liquid separation methods may be used alone or in combination of two or more. Among them, from the viewpoint of easily recovering the polymer, decantation is preferred as a method for solid-liquid separation of a liquid containing coarse polymer particles. Note that the coarse-particled polymer usually forms a mass at the bottom of the container, and solid-liquid separation can be easily performed by simply tilting the container without using tools such as filter paper or a dropper.

[0043] <Post-treatment step> The coarse particles of the polymer obtained in the recovery step are in the form of coarse agglomerates, and since polymers are generally stored in powder form, in an optional post-treatment step, the recovered polymer can be dissolved in a good solvent and reprecipitated by dropping the solution into a poor solvent, followed by filtration and drying to convert the polymer into a powder form.

[0044] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the following examples.

[0045] Example 1 Preparation Step: 10.00 g of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ester and 3.55 g of α-methylstyrene were placed in a bottle as monomers, and 0.10 g of azobisisobutyronitrile (AIBN) as an initiator. A previously prepared aqueous sodium laurate solution (a mixture of 3.39 g of sodium laurate as an emulsifier and 22.10 g of purified water as a liquid medium) was then added and emulsified with vigorous stirring. The atmosphere in the bottle was replaced with nitrogen, and the mixture was stirred at 75°C for 3 hours. After completion of the reaction, the temperature was returned to room temperature, and the glass container was opened to the atmosphere to obtain an emulsion polymerization liquid containing 13.55 g of polymer A (a polymer composed of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ester units and α-methylstyrene units). <Coarse particle formation step> 19.0 g of tetrahydrofuran as a solvent was added to the obtained emulsion polymerization liquid, and after stirring, the mixture was left to stand for 5 minutes. At this time, the amount of tetrahydrofuran added was an amount such that the proportion of tetrahydrofuran was 46 mass%, assuming that the total of the amount of water contained in the emulsion polymerization liquid and the amount of tetrahydrofuran added was 100 mass%. <Recovery step> Finally, the mixture after standing was decanted, and the polymer was recovered.

[0046] Example 2 The preparation step, the coarse-particle formation step, and the recovery step were carried out in the same manner as in Example 1, except that 1.82 g of KORR-18 (trade name; manufactured by Kao Corporation, an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 17.5 to 18.5%) was used instead of sodium laurate as the emulsifier in the preparation step, and the amount of tetrahydrofuran added in the coarse-particle formation step was changed to 33.0 g (an amount such that the proportion of tetrahydrofuran was 60 mass %, assuming that the total of the amount of water contained in the emulsion polymerization liquid and the amount of tetrahydrofuran added was 100 mass %). As a result, the mixed liquid could be decanted well, and the polymer could be recovered.

[0047] (Example 3) The preparation step, coarsening step, and recovery step were carried out in the same manner as in Example 1, except that 2.40 g of sodium decanoate was used instead of sodium laurate as the emulsifier in the preparation step. As a result, the mixed liquid could be decanted well, and the polymer could be recovered.

[0048] Example 4 The preparation step, the coarse-particle formation step, and the recovery step were carried out in the same manner as in Example 1, except that 83.0 g of acetone (an amount such that the proportion of acetone was 79 mass %, assuming that the total of the amount of water contained in the emulsion polymerization liquid and the amount of acetone added was 100 mass %) was used instead of tetrahydrofuran as the solvent to be added to the emulsion polymerization liquid in the coarse-particle formation step. As a result, the mixed liquid could be satisfactorily decanted, and the polymer could be recovered.

[0049] Example 5 Preparation Step: 61.1 g of pure water as a liquid medium, 3.0 g of sodium carbonate, and 5.0 g of KORR-18 (trade name; manufactured by Kao Corporation, an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solids content of 17.5 to 18.5%) as an emulsifier were placed in a separable flask and dissolved. 10.0 g of methyl α-chloroacrylate and 24.1 g of α-methylstyrene were added as monomers, and the mixture was emulsified with vigorous stirring. After replacing the atmosphere in the flask with nitrogen, 0.4 g of sodium dithionite, 0.003 g of tetrasodium ethylenediaminetetraacetate trihydrate, 0.008 g of tetrasodium ethylenediaminetetraacetate tetrahydrate, 0.005 g of sodium formaldehyde sulfoxylate, and 0.017 g of cumene hydroperoxide were added in this order, followed by stirring at 5°C for 48 hours. 0.17 g of 2,6-di-tert-butyl-4-methylphenol was added to stop the reaction, and the mixture was then returned to room temperature and opened to the atmosphere to obtain an emulsion polymerization liquid containing polymer B (a polymer composed of methyl α-chloroacrylate units and α-methylstyrene units). <Coarse Particle Formation Step> 15.3 g of tetrahydrofuran was added as a solvent to the obtained emulsion polymerization liquid, and after stirring, the mixture was allowed to stand for 5 minutes. The amount of tetrahydrofuran added was such that the proportion of tetrahydrofuran was 20% by mass, with the total of the amount of water contained in the emulsion polymerization liquid and the amount of tetrahydrofuran added being 100% by mass. <Recovery Step> Finally, the mixture after standing was decanted to recover the polymer.

[0050] Comparative Example 1 The preparation step and the coarse-particle formation step were carried out in the same manner as in Example 1, except that 2.40 g of sodium decanoate was used instead of sodium laurate as the emulsifier in the preparation step, and the amount of tetrahydrofuran added in the coarse-particle formation step was changed to 9.93 g (an amount such that the proportion of tetrahydrofuran was 31 mass % when the total of the amount of water contained in the emulsion polymerization liquid and the amount of tetrahydrofuran added was 100 mass %), and an attempt was made to carry out the recovery step, but the polymer did not become coarse particles, and decantation was not possible.

[0051] Comparative Example 2 The preparation step and the coarse-particle formation step were carried out in the same manner as in Example 1, except that 9.93 g of acetone (an amount such that the proportion of acetone was 31 mass % when the total of the amount of water contained in the emulsion polymerization liquid and the amount of acetone added was taken as 100 mass %) was used instead of tetrahydrofuran as the solvent to be added to the emulsion polymerization liquid in the coarse-particle formation step, and an attempt was made to carry out the recovery step, but the polymer did not become coarse particles, and decantation was not possible.

[0052] Comparative Example 3 The preparation step and the coarse-particle formation step were carried out in the same manner as in Example 5, except that the amount of tetrahydrofuran added in the coarse-particle formation step was changed to 66.7 g (an amount such that the proportion of tetrahydrofuran was 52 mass %, assuming that the total of the amount of water contained in the emulsion polymerization liquid and the amount of tetrahydrofuran added was 100 mass %), and an attempt was made to carry out the recovery step; however, the addition of tetrahydrofuran caused the polymer to dissolve, resulting in a homogeneous solution, and decantation was not possible.

[0053] Comparative Example 4: An attempt was made to decant the emulsion polymerization liquid prepared in the preparation step of Example 1, but the polymer did not precipitate even after leaving it to stand for a day and night, making decantation impossible. Furthermore, when the emulsion polymerization liquid was subjected to vacuum filtration, the filter paper became clogged, and it took more than 16 hours to completely complete the filtration.

[0054] Comparative Example 5 An attempt was made to decant the emulsion polymerization liquid prepared in the preparation step of Example 5, but the polymer did not precipitate even after leaving it to stand for a day and night, making decantation impossible. Furthermore, when the emulsion polymerization liquid was subjected to vacuum filtration, the filter paper became clogged, and it took more than 16 hours to completely complete the filtration.

[0055]

[0056] According to the present invention, the polymer can be efficiently recovered from the emulsion polymerization liquid.

Claims

1. A method for recovering a polymer, comprising: a step of adding a solvent to an emulsion polymerization liquid containing a polymer, an emulsifier, and a liquid medium, thereby coarsening the polymer into particles to obtain a liquid containing coarse polymer particles; and a step of recovering the coarse polymer particles from the liquid containing coarse polymer particles.

2. The absolute value of the difference between the dipole-dipole force term of the Hansen solubility parameter of the polymer and the dipole-dipole force term of the Hansen solubility parameter of the mixed liquid consisting of the liquid medium and the solvent in the polymer coarse particle-containing liquid is 3.0 MPa. １／２ Over 5.5 MPa １／２ 2. The method for recovering a polymer according to claim 1, wherein:

3. The absolute value of the difference between the SP value of the polymer and the SP value of the solvent is 7.5 MPa. １／２ The method for recovering a polymer according to claim 1 or 2, wherein:

4. The method for recovering a polymer according to claim 1 or 2, wherein the solvent is at least one selected from the group consisting of ketones, ethers, esters, hydrocarbons, alcohols, halogenated hydrocarbons and water.

5. The method for recovering a polymer according to claim 1 or 2, wherein the emulsifier is a fatty acid salt.

6. The method for recovering a polymer according to claim 1 or 2, further comprising, before the step of obtaining the liquid containing the coarse polymer particles, a step of emulsion-polymerizing a monomer composition containing a monomer, an emulsifier, and a liquid medium to prepare the emulsion polymerization liquid.

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