PROCESS FOR PRODUCING A LACTIC ACID-GLYCOLIC ACID COPOLYMER OR A SALT THEREOF TECHNICAL FIELD [0001] The present invention relates to processes for producing a lactic acid-glycolic acid copolymer or a salt thereof. BACKGROUND ART [0002] Lactic acid-glycolic acid copolymers or derivatives thereof such as salts are known as biodegradable polymers and are useful as, for example, materials for sustained release microcapsules for containing physiological active substances. If lactic acid-glycolic acid copolymers used as sustained release formulation materials contain large amounts of lactide and glycolide used as raw materials,-these residual materials are hydrolyzed to form acids, which promote the decomposition of the lactic acid-glycolic acid copolymers. Consequently, the sustained release formulations fail to achieve the desired sustained release period. For example, known techniques for producing purified lactic acid-glycolic acid copolymers suited for sustained release formulations are 1) to add water to a solution of a polyhydroxycarboxylic acid in a hydrophilic organic solvent to precipitate a copolymer (Patent Literature 1), 2) to treat a polyester solution in the presence of a precipitation solvent with a high-shear device to produce a copolymer as fine particles (Patent Literature 2) , 3) to supply a solution of a polyhydroxycarboxylic acid in an organic solvent and isopropyl alcohol to a device having a kneading mechanism, and to perform operations so as to produce a powdery copolymer (Patent Literature 3), and 4) to treat a lactic acid polymer in the presence of a solvent having a lactide solubility of not less than 4% while performing crushing and stirring with a mixer and thereby to extract residual lactide (Patent Literature 4) . However, the purified polymer obtained by the method 1) is a viscous liquid that contains a relatively large amount of the organic solvent remaining in the polymer, and the recovery of the polymer is difficult by filtration and entails a special decantation device. Further, vacuum drying for the purpose of removing the organic solvent and other residual substances encounters difficulties because the polymer is significantly expanded to a large volume by the evaporation of the residual substances such as the organic solvent. The purified polymer obtained during the method 2) , 3) or 4) is in the form of viscous liquid or mass even in the case where the polymer is precipitated by reprecipitation or the like. Thus, the direct drying of the polymer does not afford a polymer powder. In order to obtain the polymer as a powder, the method requires a special device such as a high-shear high-speed rotary device or a kneader to break the precipitated polymer by a shear force. [0003] Other known techniques include 5) to dissolve polylactic acid in a solvent followed by cooling to induce phase separation and fractionation {Patent Literature 5), 6) to dissolve polylactic acid into a water-miscible organic solvent and to add an aqueous alkali metal salt solution to the solution (Patent Literature 6), and 7) to hydrolyze a high-molecular weight lactic acid polymer to precipitate a target lactic acid polymer (Patent Literature 7). [0004] These conventional methods have difficulties in realizing industrial and simple production of a purified lactic acid-glycolic acid copolymer or a salt thereof in the form of powder, and are still susceptible to improvements. CITATION LIST PATENT LITERATURE [0005] Patent Literature 1: Japanese Patent No. 3902518 Patent Literature 2: JP-B-S63-254128 Patent Literature 3: JP-A-2000-26588 Patent Literature 4: JP-A-H08-245779 Patent Literature 5: JP-A-2007-534803 Patent Literature 6: JP-A-2012-508293 Patent Literature 7: Japanese Patent No. 5046447 SUMMARY OF INVENTION TECHNICAL PROBLEM [0006] An object of the invention is to produce a purified lactic acid-glycolic acid copolymer, preferably in the form of powder, having a reduced content of dimers such as residual lactide and glycolide by a simple industrial process without the use of any high-shear special device. Another object of the invention is to realize industrial simple production of a high-purity lactic acid-glycolic acid copolymer which has small amounts of dimers such as residual lactide and glycolide and small amounts of a low-molecular weight lactic acid-glycolic acid copolymer or a salt thereof and which has a small ratio of weight average molecular weight to number average molecular weight (Mw/Mn). SOLUTION TO PROBLEM [0007] The present inventors carried out extensive studies to achieve the above objects. As a result, the present inventors have developed a process in which a specific solvent having a low solubility for a lactic acid-glycolic acid copolymer or a salt thereof is added to a solution of a lactic acid-glycolic acid copolymer or a salt thereof in a specific organic solvent, and the resultant solution with a reduced solubility for the copolymer is added to a specific solvent having a low solubility for a lactic acid-glycolic acid copolymer or a salt thereof typically by dropwise addition and preferably under stirring conditions. In this manner, surprisingly, the copolymer may be precipitated easily as a solid or preferably as a powder without the use of a special high-shear device and the content of dimers such as residual lactide and glycolide in the copolymer is sufficiently low. Preferably, the process involves treating the lactic acid-glycolic acid copolymer or the salt thereof under specific conditions using liquid-liquid phase separation. These configurations have been found to achieve the aforementioned objects. The present invention has been completed based on the findings. Specifically, the present invention resides in the following [1] to [17]. [1] A process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof including the steps of: (1-1) dissolving a lactic acid-glycolic acid copolymer (Al) containing lactic acid units and glycolic acid units or a salt thereof into at least one organic solvent (Bl) having a solubility at 25°C of not less than 1 wt% to prepare a solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof; (1-2) adding at least one solvent (SI) selected from water and aliphatic alcohols (B2) to the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof to prepare a mixture liquid including the lactic acid-glycolic acid copolymer (Al) or the salt thereof; (2) adding the mixture liquid prepared in the step (1-2) to a solvent (S2') including at least one selected from water and aliphatic alcohols (B2) to precipitate a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof; and (3) recovering the precipitate of the purified lactic acid-glycolic acid copolymer (A2) or the salt thereof. [2] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in [1]/ wherein the lactic acid-glycolic acid copolymer (Al) contains 40 to 90 mol% of the lactic acid units and 60 to 10 mol% of the glycolic acid units (wherein the total of the lactic acid units and the glycolic acid units is 100 mol%). [3] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in [1] or [2], wherein the lactic acid-glycolic acid copolymer (Al) has a weight average molecular weight (Mw) in the range of 4,500 to 110,000. [4] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [1] to [3], wherein in the step (1-1), the lactic acid-glycolic acid copolymer (Al) or the salt thereof is dissolved into the organic solvent (Bl) with a concentration of 1 to 50 wt%. [5] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [1] to [4], wherein the organic solvent (Bl) used in the step (1-1) is an aprotic polar organic solvent. [6] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [1] to [5], wherein the addition in the step (2) is dropwise addition. [7] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [1] to [6], wherein in the step (2), the purified lactic acid-glycolic acid copolymer (A2) or the salt thereof is precipitated as a powder. [8] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in [1], wherein the process includes the steps of: (1-1) dissolving a lactic acid-glycolic acid copolymer (Al) or a salt thereof into at least one organic solvent (Bl) having a solubility at 25°C of not less than 1 wt% to prepare a 1-50 wt% solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof, the lactic acid-glycolic acid copolymer (Al) containing 40 to 90 mol% of lactic acid units and 60 to 10 mol% of glycolic acid units {wherein the total of the lactic acid units and the glycolic acid units is 100 mol%) and having a weight average molecular weight (Mw) in the range of 4,500 to 110,000; (1-2-A) adding at least one solvent (SI) selected from water and aliphatic alcohols (B2) to the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof to prepare a mixture solution including the lactic acid-glycolic acid copolymer (Al) or the salt thereof; (2) adding dropwise the mixture solution prepared in the step (1-2-A) to at least one solvent (S2) selected from water and aliphatic alcohols (B2) to precipitate a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof as a powder; and (3) recovering the precipitate of the purified lactic acid-glycolic acid copolymer (A2) or the salt thereof. [9] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [1] to [8], wherein the amount of the solvent (SI) SF-2785 9 used in the step (1-2) or (1-2-A) is 0.05 to 2.5 times by weight the amount of the organic solvent (Bl). [10] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described 5 in any of [1] to [9], wherein the temperature of the solvent (S2') used in the step (2) is from the solidification point of the solvent (S2') to 25°C. [11] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described 10 in any of [1] to [10], wherein the amount of the solvent (S2') used in the step (2) is 3 or more times by weight the amount of the organic solvent (Bl). [12] The process described in any of [1] to [7], wherein the step (1-2) includes the following steps {1-2-Bl} and 15 (1-2-B2): (1-2-Bl) adding at least one solvent (B2) selected from water and aliphatic alcohols to the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof and stirring the mixture to separate the mixture into two liquid 20 phases; and (1-2-B2) recovering one of the two phases which includes the lactic acid-glycolic acid copolymer or the salt thereof having a larger weight average molecular weight (Mw). [13] The process for producing a purified lactic SF-2785 10 acid-glycolic acid copolymer (A2) or a salt thereof described in [12], wherein the process includes the steps of: (1-1) dissolving a lactic acid-glycolic acid copolymer (Al) or a salt thereof into at least one organic solvent (Bl) 5 having a solubility at 25°C of not less than 10 wt% to prepare a 10-50 wt% solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof, the lactic acid-glycolic acid copolymer (Al) containing 40 to 90 mol% of lactic acid units and 60 to 10 mol% of glycolic acid units (wherein the total 10 of the lactic acid units and the glycolic acid units is 100 mol%) and having a weight average molecular weight (Mw) in the range of 4,500 to 105,000; (1-2-B1) adding at least one aliphatic alcohol £B2) to the solution of the lactic acid-glycolic acid copolymer (Al) 15 or the salt thereof and stirring the mixture to separate the mixture into two liquid phases; (1-2-B2) recovering one of the two phases which includes the lactic acid-glycolic acid copolymer or the salt thereof having a larger weight average molecular weight (Mw); 20 (2) adding dropwise the phase recovered in the step (1-2-B2) to a solvent including water to precipitate a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof; and (3) recovering the precipitate of the purified lactic SF-2785 11 acid-glycolic acid copolymer (A2) or the salt thereof. [14] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in [13], wherein the solvent to which the recovered phase is 5 added dropwise in the step (2) is water. [15] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [12] to [14] , wherein the phase recovered in the step (1-2-B2) is further subjected to one or more cycles of the steps 10 (1-2-Bl) and (1-2-B2) and thereafter subjected to the steps (2) and (3). [16] The process for producing a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof described in any of [12] to [15], wherein the organic solvent (Bl) is 15 added to the phase recovered in the step (1-2-B2) and thereafter the phase is further subjected to one or more cycles of the steps (1-2-Bl) and (1-2-B2) and thereafter subjected to the steps (2) and (3). [17] A sustained release formulation including a purified 20 lactic acid-glycolic acid copolymer (A2) or a salt thereof obtained by the production process described in any of [1] to [16]. ADVANTAGEOUS EFFECTS OF INVENTION [0008] SF-2785 12 According to the production processes of the invention, a powdery purified lactic acid-glycolic acid copolymer having a reduced content of dimers such as residual lactide and glycolide may be produced in a simple industrial manner without 5 the use of any high-shear special device. Further, the production processes of the invention realize industrial simple production of a high-purity lactic acid-glycolic acid copolymer which has small amounts of dimers such as residual lactide and glycolide and small amounts of low-molecular weight 10 lactic acid-glycolic acid polymers or salts thereof and which has a small ratio of weight average molecular weight to number average molecular weight (Mw/Mn). Lactic acid-glycolic acid copolymers produced by the processes are suited for applications such as sustained release formulations. 15 DESCRIPTION OF EMBODIMENTS [0009] In the invention, a lactic acid-glycolic acid copolymer (Al) or a salt thereof is used as a raw material. The lactic acid-glycolic acid copolymer (Al) is a polymer containing 20 lactic acid units and glycolic acid units. The lactic acid-glycolic acid copolymer (Al) usually contains the lactic acid units at 40 to 90 mol%, and preferably 50 to 85 mol% and the glycolic acid units at 60 to 10 mol%, and preferably 50 to 15 mol% (wherein the total of the lactic acid units and the SF-2785 13 glycolic acid units is 100 mol%). The lactic acid-glycolic acid copolymer (Al) may contain ester derivative units. Examples of the ester derivative units include monool residues, diol residues and polyol residues. These residues are derived 5 from initiators (C) described later. [0010] The weight average molecular weight (Mw) of the lactic . acid-glycolic acid copolymer (Al) is usually 4,500 to 110,000, preferably 4,500 to 105,000, more preferably 5,000 to 90,300, 10 still more preferably 5,000 to 80,000, and further preferably 8,000 to 80,000. The molecular weight distribution, namely, the weight average molecular weight/number average molecular weight (Mw/Mn) of the lactic acid-glycolic acid copolymer (Al) is usually 1.5 to 7.0, and preferably 1.8 to 6.0. It is also 15 preferable that the Mw/Mn be 1.5 to 5.0, and particularly preferably 1.8 to 4 . 7 . In the invention, the weight average molecular weight (Mw) and the weight average molecular weight/number average molecular weight (Mw/Mn) are values determined by gel permeation chromatography (GPC) relative to 20 polystyrene standards. [0011] For example, the lactic acid-glycolic acid copolymer (Al) may be produced by ring-opening polymerization of lactide that is a cyclic dirtier of lactic acid and glycolide that is a cyclic SF-2785 14 dimer of glycolic acid as raw materials while optionally using additives such as an initiator (C) and a catalyst. Alternatively, the lactic acid-glycolic acid copolymer (Al) may be produced by copolymerizing lactic acid and glycolic acid 5 optionally in the presence of a catalyst. [0012] The initiator (C) may be a hydroxycarboxylic acid such as lactic acid or glycolic acid, in which case the obtainable molecule of the lactic acid-glycolic acid copolymer (Al) is 10 terminated with a carboxyl group. [0013] The initiator (C) may be a monool such as hexanol, octanol or dodecanol, in which case the obtainable lactic acid-glycolic acid copolymer (Al) has an ester derivative unit at an end of 15 the molecule. [0014} The initiator (C) may be a diol such as ethylene glycol or propylene glycol, in which case the obtainable lactic acid-glycolic acid copolymer (Al) includes an ester derivative 20 unit in the inside of the molecule. [0015] The initiator (C) may be a polyol such as glycerol, mannitol, pentaerythritol, sorbitol, xylitol, fructose, glucose or cyclodextrin, in which case the obtainable lactic SF-2785 15 acid-glycolic acid copolymer (Al) has a branched structure including an ester derivative unit in the inside of the molecule. [0016] 5 The lactic acid-glycolic acid copolymer (Al) produced as described above typically has a lactic acid content of 40 to 90 mol%, and more typically 50 to 85 mol%. In the lactic acid-glycolic acid copolymer (Al), the glycolic acid content is typically 60 to 10 mol%, and more typically 50 to 15 mol%. 10 The lactic acid-glycolic acid copolymer (Al) may be a commercial product. [0017} The lactic acid-glycolic acid copolymer (Al) may be in the form of salt. For example, the salt may be a salt of an 15 inorganic metal, for example, an alkali metal such as sodium or potassium, or an alkaline earth metal such as calcium or magnesium, or may be a salt of a basic organic compound such as triethylamine. [0018] 20 [Step (1-1)3 In the step (1-1), the lactic acid-glycolic acid copolymer (Al) or the salt thereof is dissolved into at least one organic solvent (Bl) having a solubility at 25°C of not less than 1 wt% to give a solution of the lactic acid-glycolic SF-2785 16 acid copolymer or the salt thereof. Here, the term solubility means the solubility at 25°C for a lactic acid-glycolic acid copolymer (containing 85 mol% lactic acid units and 15 mol% glycolic acid units) having a weight average molecular weight 5 (Mw) of 76,000 and a number average molecular weight (Mn) of 14,100. In a preferred embodiment, the lactic acid-glycolic acid copolymer (Al) or the salt thereof is dissolved into at least one organic solvent (Bl) having a solubility at 25°C of not less than 10 wt% to give a solution of the lactic 10 acid-glycolic acid copolymer or the salt thereof. Here, the term solubility in the phrase "solubility of not less than 10 wt%" means the solubility at 25°C for a lactic acid-glycolic acid copolymer (containing 73 mol% lactic acid units and 27 mol% glycolic acid units) having a weight average molecular 15 weight (Mw) of 11,300 and a number average molecular weight (Mn) of 5,300. [0019] Examples of the organic solvents (Bl) include aprotic polar organic solvents, in particular, aprotic polar organic 20 solvents having 2 to 5 carbon atoms. [0020] Examples of the aprotic polar organic solvents include ketones having 2 to 5 carbon atoms such as acetone; organic cyanides having 2 to 5 carbon atoms such as acetonitrile; cyclic SF-2785 17 ethers having 2 to 5 carbon atoms such as tetrahydrofuran; carboxylate esters having 2 to 5 carbon atoms such as ethyl acetate; amide compounds having 2 to 5 carbon atoms such as N,N-dimethylformamide; and sulfur-containing organic 5 compounds having 2 to 5 carbon atoms such as dimethyl sulfoxide. [0021] Of the organic solvents (Bl) , acetone, tetrahydrofuran and N,N-dimethylformamide are preferable from viewpoints such as easy handling. Acetone, tetrahydrofuran and 10 N, N-dimethylf ormamide have a solubility at 25°C of 30 wt% or above as measured with respect to a lactic acid-glycolic acid copolymer (containing 85 mol% lactic acid units and 15 mol% glycolic acid units) having a weight average molecular weight (Mw) of 76,000 and a number average molecular weight (Mn) of 15 14,100. [0022] Of the organic solvents (Bl), acetone and acetonitrile are particularly preferable from viewpoints such as easy handling. Acetone and acetonitrile have a solubility at 25°C 20 of 40 wt% or above as measured with respect to a lactic acid-glycolic acid copolymer (containing 73 mol% lactic acid units and 27 mol% glycolic acid units) having a weight average molecular weight (Mw) of 11,300 and a number average molecular weight (Mn) of 5,300. SF-2785 18 [0023] Of the organic solvents (Bl), acetone is particularly preferable from the viewpoint of toxicity in the event that the solvent remains in the purified lactic acid-glycolic acid 5 copolymer (A2). [0024] The concentration of the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof may be controlled appropriately in accordance with factors such as 10 the weight average molecular weight (Mw) and the molar ratio of the lactic acid units to the glycolic acid units of the lactic acid-glycolic acid copolymer (Al) that is used, so that the desired purified copolymer will be obtained, preferably in the form of powder. The concentration is usually in the range of 15 1 to 50 wt%, and may be, for example, 5 to 40 wt%. In an embodiment, the concentration of the solution of the lactic acid-glycolic acid copolymer or the salt thereof is usually in the range of 10 to 50 wt%. In a preferred embodiment, the concentration is preferably in the range of 20 to 40 wt% from 20 viewpoints such as easy purification. [0025] The copolymer or the salt thereof may be dissolved in the step (1-1) usually at a temperature of about 15 to 35°C, and preferably about 20 to 30°C. Where necessary, heating may be SF-2785 19 performed during the dissolution. [0026] [Step (1-2)] In the step (1-2) , at least one solvent (SI) selected from 5 water and aliphatic alcohols (B2) is added to the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof obtained in the step (1-1), and a mixture liquid including the lactic acid-glycolic acid copolymer (Al) or'the salt thereof is prepared. The mixture liquid may be formed by mixing the 10 mixture of the solution from the step (1-1) and the solvent (SI) by stirring. [0027] Examples of the aliphatic alcohols (B2) used in the step (1-2) include linear or branched aliphatic alcohols, in 15 particular, those alcohols having 1 to 4 carbon atoms. Specif ic examples include methanol, ethanol, isopropyl alcohol, propyl alcohol and butyl alcohol. [0028] The amount of the solvent (SI) used in the step (1-2) is 20 preferably 0.05 to 2.5 times by weight, and more preferably 0.15 to 1.5 times by weight the amount of the organic solvent (Bl). [0029] The step (1-2-A), and the steps (1-2-Bl) and (1-2-B2) SF-2785 20 described below represent preferred embodiments of the step (1-2). [0030] [Step (1-2-A)] 5 In the step (1-2-A), at least one solvent (SI) selected from water and aliphatic alcohols (B2) is added to the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof obtained in the step (1-1), and a mixture solution including the lactic acid-glycolic acid copolymer (Al) or the 10 salt thereof is prepared. The mixture solution may be formed by mixing the mixture of the solution from the step (1-1) and the solvent (SI) by stirring. [0031] Examples of the aliphatic alcohols (B2) used in the step 15 (1-2-A) include the aliphatic alcohols mentioned in the section of the step (1-2) . Of the aliphatic alcohols (B2) , methanol, ethanol and isopropyl alcohol are preferable from viewpoints such as economic efficiency and odor. The aliphatic alcohols may be used singly or in combination with water, or two or more 20 may be used in combination. In a preferred embodiment, water alone is used as the solvent (SI) from the viewpoints of econoraic efficiency and nontoxicity. The solvent (SI) should be miscible with the organic solvent (Bl) used in the step (1-1) . [0032] SF-2785 21 In the step (1-2-A) , the solvent (Si) maybe mixed together with the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof obtained in the step (1-1), usually at a temperature of about 15 to 35°C, and preferably about 20 5 to 30°C. Where necessary, heating may be performed during the mixing. [0033] The amount of the solvent (SI) used in the step (1-2-A) is preferably 0.05 to 2.5 times by weight, and more preferably 10 0.15 to 1.5 times by weight the amount of the organic solvent (Bl) . [0034] Mixing of the solvent (SI) with the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof obtained 15 in the step (1-1) results in a decrease of the solubility of the copolymer in the solution. As the solvent (SI) is added in small portions to the solution obtained in the step (1-1), the mixture gradually becomes white turbid. At the addition of this amount which causes the onset of the occurrence of white 20 turbidity, the mixture is in such a state that the copolymer is present in the solvent relatively stably while its solubility has been decreased to a degree. This configuration forms a relatively preferred embodiment of the mixture solution prepared in the step (1-2-A) of the invention. The addition SF-2785 22 of any larger amount of the solvent (SI) may result in the occurrence of liquid-liquid phase separation. Even in this case, the mixture may be used as such when heating of the mixture gives a uniform solution. 5 [0035] Hereinbelow, there will be described the steps (1-2-Bl) and (1-2-B2) that represent another preferred embodiment of the step (1-2). [0036] 10 [Step (1-2-B1)] In the step (1-2-Bl) , at least one aliphatic alcohol (B2) is added to the solution of the lactic acid-glycolic acid copolymer (Al) or the salt thereof obtained in the step (1-1), and stirring is performed to separate the mixture into two 15 liquid phases. [0037] Examples of the aliphatic alcohols (B2) used in the step (1-2-Bl) include the aliphatic alcohols mentioned in the section of the step (1-2). Of the aliphatic alcohols (B2), 20 ethanol and isopropyl alcohol are preferable for reasons such as that the purified lactic acid-glycolic acid copolymer or the salt thereof may be recovered in the form of powder. The aliphatic alcohols may be used singly, or two or more may be used in combination. SF-2785 23 [0038] Separate liquid phases are formed in the step (1-2-B1) . The solvent added in the step (1-2-B1) to induce the liquid-liquid phase separation may be selected appropriately 5 in accordance with factors such as, for example, the weight average molecular weight (Mw) and the molar ratio of the lactic acid units to the glycolic acid units of the lactic acid-glycolic acid copolymer (Al) or the salt thereof used as the raw material, or the desired ratio of weight average 10 molecular weight to number average molecular weight (Mw/Mn) of the purified lactic acid-glycolic acid copolymer (A2) or the salt thereof. [0039] Preferably, the liquid phases formed in the step (1-2-B1) 15 are clearly separate from each other with little intermediate phase. When, for example, the organic solvent (Bl) used in the step (1-1) is acetone, the aliphatic alcohol (B2) in the step (1-2-B1) is preferably isopropyl alcohol or ethanol. When, for example, the organic solvent (Bl) used in the step (1-1) is 20 acetonitrile, the aliphatic alcohol (B2) is preferably isopropyl alcohol. [0040] The weight ratio of the aliphatic alcohol (B2) to the organic solvent (Bl) is not particularly limited as long as SF-2785 24 the liquid-liquid phase separation occurs in the step (1-2-Bl) , and may be determined appropriately in accordance with factors such as the weight average molecular weight (Mw) and the molar ratio of the lactic acid units to the glycolic acid units of 5 the lactic acid-glycolic acid copolymer (Al) or the salt thereof When, for example, the organic solvent (Bl) is acetone and the aliphatic alcohol (B2) is isopropyl alcohol or ethanol, the weight ratio is usually not less than 0.6, and preferably not less than 0. 70, and is usually not more than 3 . 5, and preferably 10 not more than 2.5. When the organic solvent (Bl) is acetonitrile and the aliphatic alcohol (B2) is isopropyl alcohol, the weight ratio is usually not less than 0.6, and preferably not less than 0.70, and is usually not more than 3.5, and preferably not more than 3.0. 15 [0041] If the weight ratio exceeds the upper limit, one of the separated phases, typically the lower phase tends to exhibit poor fluidity and the separation operation for the recovery of the phase may be difficult. If the weight ratio is less than 20 the lower limit, the formation of separate liquid phases tends to be difficult. [0042] In the step (1-2-Bl), the formation of separate liquid phases usually takes place at a temperature of about 0 to 40°C, SF-2785 25 and preferably about 5 to 30°C, although variable depending on factors such as the weight average molecular weight (Mw) and the molar ratio of the lactic acid units to the glycolic acid units of the lactic acid-glycolic acid copolymer (Al) or 5 the salt thereof used as the raw material. [0043] The steps (1-1) and (1-2-Bl) may be performed by simultaneously adding to the lactic acid-glycolic acid copolymer (Al) or the salt thereof the organic solvent (Bl) 10 in such an amount that the concentration prescribed in the step (1-1) is obtained and the aliphatic alcohol (B2) in such an amount that a desired weight ratio of the aliphatic alcohol (B2) to the organic solvent (Bl) described in the step (1-2-Bl) is obtained. 15 [0044] [Step (1-2-B2)] In the step (1-2-B2), one of the two phases formed in the step (1-2-Bl) which includes the lactic acid-glycolic acid copolymer or the salt thereof having a larger weight average 20 molecular weight (Mw) is recovered. Of the two phases formed in the step (1-2-Bl), the one which includes the lactic acid-glycolic acid copolymer or the salt thereof having a larger weight average molecular weight (Mw) may be easily identified by sampling the solutions of the respective phases and SF-2785 26 determining the weight average molecular weights (Mw) of the lactic acid-glycolic acid copolymer present in the respective phases. [0045] 5 Because the mixture has been separated into two liquid phases in the step (1-2-Bl) , the phase which includes the lactic acid-glycolic acid copolymer or the salt thereof having a larger weight average molecular weight (Mw) may be easily recovered by separation using a separatory funnel or the like. 10 [0046] In the case where one pass through the steps (1-1) and (1-2-Bl) is insufficient for the lactic acid-glycolic acid copolymer or the salt thereof to attain desired properties, for example, a desired weight average molecular weight (Mw) 15 and a desired weight average molecular weight/number average molecular weight (Mw/Mn), one or more cycles of the steps (1-2-Bl) and (1-2-B2) may be performed after the step (1-2-B2) . Alternatively, the organic solvent (Bl) may be added to the recovered phase which includes the lactic acid-glycolic acid 20 copolymer or the salt thereof having a larger weight average molecular weight (Mw) , and thereafter the phase may be subjected to one or more cycles of the steps (1-2-Bl) and (1-2-B2). [0047] The step (1-2-B2) is usually performed at a temperature SF-2785 27 of about 0 to 30°C, and preferably about 5 to 25°C. [0048] [Step (2)] In the step (2), the mixture liquid prepared in the step 5 (1-2) is added to a solvent (S2') including at least one selected from water and aliphatic alcohols (B2) to precipitate a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof, preferably in the form of powder. [0049] 10 The solvent (S2' ) may include an organic solvent (B3) other than the aliphatic alcohols (B2). Examples of the organic solvents (B3) include aprotic polar organic solvents, in particular, aprotic polar organic solvents having 2 to 5 carbon atoms. Examples of the aprotic polar organic solvents 15 include ketones having 2 to 5 carbon atoms such as acetone; organic cyanides having 2 to 5 carbon atoms such as acetonitrile; cyclic ethers having 2 to 5 carbon atoms such as tetrahydrofuran; carboxylate esters having 2 to 5 carbon atoms such as ethyl acetate; amide compounds having 2 to 5 carbon 20 atoms such as N,N-dimethylformamide; and sulfur-containing organic compounds having 2 to 5 carbon atoms such as dimethyl sulfoxide. [0050] The addition to the solvent (S2') may be performed SF-2785 28 continuously or intermittently. The addition is preferably dropwise addition. Particularly preferably, the mixture liquid is added as droplets. The addition time is not particularly limited, but is, for example, 0.05 to 20 hours, 5 and preferably 0.3 to 3 hours. The rate of addition is not particularly limited. For example, the rate of addition, typically the dropping rate in the case of dropwise addition per unit amount of the solvent (S2') is 100 to 10000 g/hr/kg, and preferably 300 to 6000 g/hr/kg. The dropping rate in the 10 case of the dropwise addition in droplets per unit amount of the solvent