(12) United States Patent (10) Patent No.: US 9,023,953 B2 Nagano Et Al

USOO9023953B2

(12) United States Patent (10) Patent No.: US 9,023,953 B2 Nagano et al. (45) Date of Patent: *May 5, 2015

(54) PROCESS FOR PRODUCTION OF (58) Field of Classification Search POLY(LACTIC ACID)-TYPE RESIN, AND CPC ...... A61 K9/204; A61 K9/5153 POLY(LACTIC ACID)-TYPE PREPOLYMER USPC ...... 525/410, 415, 419,450 See application file for complete search history. (75) Inventors: Tatsuya Nagano, Tokai (JP); Tsuyoshi Tanaka, Nagoya (JP); Hiroyuki Ome, (56) References Cited Tokai (JP) U.S. PATENT DOCUMENTS (73) Assignee: Toray Industries, Inc. (JP) 8,173,753 B2 * 5/2012 Nagano et al...... 525/415 2011/0065871 A1* 3/2011 Nagano et al...... 525/450 (*) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 FOREIGN PATENT DOCUMENTS U.S.C. 154(b) by 148 days. CN 101805498 8, 2010 This patent is Subject to a terminal dis JP 8-183840 A T 1996 claimer. JP 8-193124 A T 1996 JP 8-23.1688 A 9, 1996 Appl. No.: 13/825,992 JP 11-106499. A 4f1999 (21) JP 2000-273.165 A 10, 2000 JP 2000-297143 A 10, 2000 (22) PCT Fled: Jun. 27, 2011 JP 2000-297145 A 10, 2000 JP 2000-302852 A 10, 2000 (86) PCT NO.: JP 2001-064375 A 3, 2001 JP 2001-192444 A T 2001 S371 (c)(1), JP 2009-144132 A T 2009 (2), (4) Date: Mar. 26, 2013 WO 2009,142.196 C 11, 2009 (87) PCT Pub. No.: WO2O12/042993 * cited by examiner PCT Pub. Date: Apr. 5, 2012 Primary Examiner — Gregory Listvoyb (74) Attorney, Agent, or Firm — DLA Piper LLP (US) (65) Prior Publication Data US 2013/O19718.6 A1 Aug. 1, 2013 (57) ABSTRACT A method of producing a poly(lactic acid) resin includes (30) Foreign Application Priority Data carrying out direct polycondensation using lactic acid as a main raw material to prepare a crystallized prepolymer hav Sep. 28, 2010 (JP) ...... 2010-216643 ing a weight average molecular weight of 5,000 to 25,000, an enthalpy of fusion AHm of 50 to 65 J/g, and an acid value A (51) Int. C. mol/ton satisfying (1) below: C08G 63/9. (2006.01) C08G 63/06 (2006.01) 450/(Mw/10,000-0.14):Zinc oxide and Zinc Sulfonic acid, trichloromethanesulfonic acid, methanedisul sulfate. Specific examples of the cobalt compounds include fonic acid, 1.2-ethanedisulfonic acid, 1,3-propanedisulfonic cobalt chloride, cobalt acetate, cobalt(II) octoate, cobalt(II) acid, 1,4-butanedisulfonic acid, pentanedisulfonic acid, hex 10 isooctoate, cobalt(II) isononanoate, cobalt(II) laurate, cobalt anedisulfonic acid, heptanedisulfonic acid, octanedisulfonic (II) oleate, cobalt(II) linoleate, cobalt naphthenate, cobalt(II) acid, nonanedisulfonic acid, decanedisulfonic acid, 1,11-un neodecanoate, cobalt(II) carbonate, cobalt(II) sulfate and decanedisulfonic acid, 12-dodecanedisulfonic acid, butane cobalt(II) oxide. Specific examples of the iron compounds Sulfonic acid, 2-hydroxyethanesulfonic acid, Sulfoacetic acid include iron(II) chloride, iron(II) acetate, iron(II) octoate, and taurine; and alicyclic sulfonic acids such as cyclopen 15 iron naphthenate, iron(II) carbonate, iron(II) sulfate and iron tanesulfonic acid, cyclohexanesulfonic acid and camphorsul (II) oxide. Specific examples of the lithium compounds fonic acid. In view of obtaining a poly(lactic acid) resin include lithium propoxide, lithium chloride, lithium acetate, having a high molecular weight or high melting point and, lithium octoate, lithium naphthenate, lithium carbonate, dil especially, excellent thermal stability, oxoacids of sulfur and ithium sulfate and lithium oxide. Specific examples of the Sulfonic acid group-containing compounds having two or rare earth compounds include triisopropoxyeuropium(III), more Sulfonic acid groups per one molecule are preferred. triisopropoxyneodymium(III), triisopropoxylanthanum, tri Among these, methanesulfonic acid, ethanesulfonic acid, isopropoxySamarium(III), triisopropoxyyttrium, isopro 1-propanesulfonic acid, Sulfuric acid, 1,3-propanedisulfonic poxyyttrium, dysprosium chloride, europium chloride, lan acid, 1.5-naphthalenedisulfonic acid and taurine are espe thanum chloride, neodymium chloride, Samarium chloride, cially preferred. A single type of catalyst may be used, or two 25 yttrium chloride, dysprosium(III) triacetate, europium(III) or more types of catalysts may be used in combination. triacetate, lanthanum acetate, neodymium triacetate, Further, metal catalysts and acid catalysts other than Sulfur Samarium acetate, yttrium triacetate, dysprosium(III) carbon containing compounds containing Sulfur having an oxidation ate, dysprosium(IV) carbonate, europium(II) carbonate, lan number of not less than +5 may also be preferably used as the thanum carbonate, neodymium carbonate, Samarium(II) car catalyst. 30 bonate, Samarium(III) carbonate, yttrium carbonate, Examples of the metal catalysts include metal compounds dysprosium Sulfate, europium(II) sulfate, lanthanum sulfate, such as tin compounds, titanium compounds, lead com neodymium sulfate, Samarium sulfate, yttrium sulfate, pounds, Zinc compounds, cobalt compounds, iron com europium dioxide, lanthanum oxide, neodymium oxide, pounds, lithium compounds and rare earth compounds, and samarium(III) oxide and yttrium oxide. Other examples of the preferred examples of the types of the compounds include 35 metal catalysts include potassium compounds Such as potas metal alkoxides, halogen metal compounds, organic carboxy sium isopropoxide, potassium chloride, potassium acetate, lates, carbonates, sulfates and oxides. Specific examples of potassium octoate, potassium naphthenate, potassium t-butyl the tin compounds include tinpowder, tin(II) chloride, tin(IV) carbonate, potassium Sulfate and potassium oxide; copper chloride, tin(II) bromide, tin(IV) bromide, ethoxytin(II), compounds such as copper(II) diisopropoxide, copper(II) t-butoxytin(IV), isopropoxytin(IV), tin(II) acetate, tin(IV) 40 chloride, copper(II) acetate, copper octoate, copper naphth acetate, tin(II) octanoate, tin(II) laurate, tin(II) myristate, tin enate, copper(II) sulfate and dicopper carbonate; nickel com (II) palmitate, tin(II) stearate, tin(II) oleate, tin(II) linoleate, pounds such as nickel chloride, nickel acetate, nickel Octoate, tin(II) acetylacetonate, tin(II) oxalate, tin(II) lactate, tin(II) nickel carbonate, nickel(II) sulfate and nickel oxide; Zirco tartrate, tin(II) pyrophosphate, tin(II) p-phenolsulfonate, tin nium compounds such as tetraisopropoxy Zirconium(IV), Zir (II) bis(methanesulfonate), tin(II) sulfate, tin(II) oxide, tin 45 conium trichloride, Zirconium acetate, Zirconium octoate, Zir (IV) oxide, tin(II) sulfide, tin(IV) sulfide, dimethyltin(IV) conium naphthenate, Zirconium(II) carbonate, Zirconium(IV) oxide, methylphenyltin(IV) oxide, dibutyltin(IV) oxide, dio carbonate, Zirconium sulfate and Zirconium(II) oxide; anti ctyltin(IV) oxide, diphenyltin(IV) oxide, tributyltin oxide, mony compounds such as triisopropoxyantimony, antimony triethyltin(IV) hydroxide, triphenyltin(IV) hydroxide, tribu (III) fluoride, antimony (V) fluoride, antimony acetate and tyltin hydride, monobutyltin(IV) oxide, tetramethyltin(IV), 50 antimony(III) oxide; magnesium compounds such as magne tetraethyltin(IV), tetrabutyltin(IV), dibutyldiphenyltin(IV), sium diisopropoxide, magnesium chloride, magnesium tetraphenyltin(IV), tributyltin(IV) acetate, triisobutyltin(IV) acetate, magnesium lactate, magnesium carbonate, magne acetate, triphenyltin(IV)acetate, dibutyltin diacetate, dibutyl sium sulfate and magnesium oxide; calcium compounds Such tin dioctoate, dibutyltin(IV) dilaurate, dibutyltin(IV) male as diisopropoxycalcium, calcium chloride, calcium acetate, ate, dibutyltin bis(acetylacetonate), tributyltin(IV) chloride, 55 calcium octoate, calcium naphthenate, calcium lactate and dibutyltin dichloride, monobutyltin trichloride, dioctyltin calcium Sulfate; aluminum compounds such as aluminum, dichloride, triphenyltin(IV) chloride, tributyltin sulfide, aluminum isopropoxide, aluminum chloride, aluminum tributyltin sulfate, tin(II) trifluoromethanesulfonate, ammo acetate, aluminum Octoate, aluminum sulfate and aluminum nium hexachlorostannate(IV), dibutyltin sulfide, diphenyltin oxide; germanium compounds such as germanium, tetraiso Sulfide, triethyltin Sulfate and tin(II) phthalocyanine. Among 60 propoxygermane and germanium(IV) oxide; manganese these, tin compounds other than tin(II) chloride are preferred. compounds such as triisopropoxymanganese(III), manga Specific examples of the titanium compounds include tita nese trichloride, manganese acetate, manganese(II) octoate, nium methoxide, titanium propoxide, titanium isopropoxide, manganese(II) naphthenate and manganese(II) sulfate; and titanium butoxide, titanium isobutoxide, titanium cyclohex bismuth compounds such as bismuth(III) chloride, bismuth ide, titanium phenoxide, titanium chloride, titanium diac 65 powder, bismuth(III) oxide, bismuth acetate, bismuth octoate etate, titanium triacetate, titanium tetraacetate and titanium and bismuth neodecanoate. Still other preferred examples of (IV) oxide. Specific examples of the lead compounds include the metal catalysts include compounds composed of two or US 9,023,953 B2 7 8 more kinds of metallic elements, such as sodium stannate, more selected from tin compounds and one or more selected magnesium Stannate, potassium Stannate, calcium Stannate, from Sulfur-containing compounds containing Sulfur having manganese stannate, bismuth Stannate, barium stannate, an oxidation number of not less than +5. strontium stannate, Sodium titanate, magnesium titanate, alu To efficiently obtain a poly(lactic acid) resin having a high minum titanate, potassium titanate, calcium titanate, cobalt molecular weight and a high melting point, the amount of the titanate, Zinc titanate, manganese titanate, Zirconium titanate, Sulfur-containing compound containing Sulfur having an oxi bismuth titanate, barium titanate and strontium titanate. dation number of not less than +5 to be added is preferably 30 The acid catalyst other than Sulfur-containing compounds to 3,000 ppm, more preferably 35 to 2,700 ppm, still more containing Sulfur having an oxidation number of not less than preferably 40 to 2,500 ppm, especially preferably 45 to 2,200 +5 may be either a Bronsted acid as a proton donor or a Lewis 10 ppm in terms of Sulfur atoms, with respect to the raw material acid as an electron-pair acceptor, and may be eitheran organic used (L-lactic acid, D-lactic acid and/or the like). acid or an inorganic acid. Examples of the acid catalyst The timing of addition of the Sulfur-containing compound include monocarboxylic acid compounds such as formic containing Sulfur having an oxidation number of not less than acid, acetic acid, propionic acid, heptanoic acid, octanoic +5 as a catalyst is preferably at the beginning of the melt acid, octylic acid, nonanoic acid, isononanoic acid, trifluoro 15 polymerization step or during the melt polymerization step in acetic acid and trichloroacetic acid; dicarboxylic acid com view of efficiently obtaining a poly(lactic acid) resin having a pounds such as oxalic acid, Succinic acid, maleic acid, tartaric high molecular weight and a high melting point. acid and malonic acid; tricarboxylic acid compounds such as The amount of other catalysts to be added is not restricted, citric acid and tricarballylic acid; acidic amino acids Such as and is preferably 0.0001 to 2 parts by weight, more preferably aspartic acid and glutamic acid; ascorbic acid; retinoic acid; 0.001 to 1 part by weight, still more preferably 0.005 to 0.5 phosphoric acid compounds such as phosphoric acid, meta part by weight, especially preferably 0.01 to 0.3 part by phosphoric acid, phosphorous acid, hypophosphorous acid, weight with respect to 100 parts by weight of the poly(lactic polyphosphoric acid, phosphoric acid monoesters including acid) resin. monododecyl phosphate and monooctadecyl phosphate, The reaction conditions for the melt polymerization step phosphoric acid diesters including didodecyl phosphate and 25 are not restricted, and the step may be carried out under dioctadecyl phosphate, phosphorous acid monoesters and various conditions. The melt polymerization step is prefer phosphorous acid diesters; boric acid; and hydrochloric acid. ably carried out continuously under conditions containing at The form of the acid catalyst other than sulfur-containing least the two stages described below: compounds containing Sulfur having an oxidation number of Melt polymerization conditions 1: 140°C. to 160° C., 13.3 not less than +5 is not restricted, and may be either a solid acid 30 to 66.6 kPa catalyst or a liquid acid catalyst. Examples of the Solid acid Melt polymerization conditions 2: 160° C. to 180° C., 1.3 catalyst include natural minerals such as acid clay, kaolinite, to 6.5 kPa. bentonite, montmorillonite, talc, Zirconium silicate and Zeo To efficiently obtain a poly(lactic acid) resin having a high lite; oxides such as silica, alumina, titania and Zirconia; oxide molecular weight, the melt polymerization step is carried out complexes such as silica alumina, silica magnesia, silica 35 preferably at a temperature of 140° C. to 180° C. and, to boria, alumina boria, silica titania and silica Zirconia; chlori efficiently obtain a poly(lactic acid) resin also having a high nated alumina; fluorinated alumina; and cation exchange res melting point and excellent hue, the melt polymerization step ins. is carried out preferably at a temperature of 145° C. to 175° In cases where polymerization of the poly(lactic acid) resin C., more preferably at a temperature of 140°C. to 170° C., in is carried out using a catalyst having stereoselective polymer 40 terms of the Substantial reaction temperature. The tempera izability and, as a raw material, a racemic body which is a ture during the melt polymerization step may be controlled mixture of the same amount of L-lactic acid and D-lactic acid, either by a single stage process wherein the temperature is poly-L-lactic acid and poly-D-lactic acid can be produced at kept constant, or by a multistage process with two or more the same time. stages wherein the temperature is changed stepwise. To effi To obtain a poly(lactic acid) resin having a high molecular 45 ciently obtain a poly(lactic acid) resin having a high molecu weight and a high melting point, tin compounds, titanium lar weight and a high melting point, the temperature is pref compounds, lead compounds, Zinc compounds, cobalt com erably controlled by a multistage process with two or more pounds, iron compounds, lithium compounds, rare earth stages. Examples of such a process include a method wherein compounds, antimony compounds, bismuth compounds, and the reaction is first allowed to proceed at a temperature of 140 Sulfur-containing compounds containing Sulfur having an 50 to 160° C. and then at a temperature of 160 to 180° C. oxidation number of not less than +5 are preferred and, in To efficiently obtain a poly(lactic acid) resin having a high view of achieving high productivity, tin compounds, titanium molecular weight, the melt polymerization step is carried out compounds, lead compounds, Zinc compounds, cobalt com preferably at a pressure of 0.13 to 130 kPa and, to efficiently pounds, iron compounds, lithium compounds, rare earth obtain a poly(lactic acid) resin also having excellent hue, the compounds, Sulfonic acid compounds, phosphorous com 55 melt polymerization step is preferably carried out at a pres pounds, and Sulfur-containing compounds containing Sulfur sure of 1 to 100 kPa, more preferably carried out at a pressure having an oxidation number of not less than +5 are more of 10 to 90 kPa, still more preferably carried out at a pressure preferred. Tin compounds, titanium compounds, rare earth of 10 to 80 kPa, especially preferably carried out at a pressure compounds, Sulfur-containing compounds containing Sulfur of 20 to 70 kPa, in terms of the substantial reaction pressure. having an oxidation number of not less than +5, and phos 60 The pressure during the melt polymerization step may be phorous compounds are still more preferred. Further, to controlled either by a single stage process wherein the pres obtain a poly(lactic acid) resin having also excellent thermal Sure is kept constant, or by a multistage process with two or stability and hue, the metal catalyst is still more preferably a more stages wherein the pressure is changed stepwise. To tin organic carboxylate having two ligands, and is especially efficiently obtain a poly(lactic acid) resin having a high preferably a tin(II) acetate or tin(II) octanoate. Two or more of 65 molecular weight and excellent hue, the pressure is preferably these may also be used in combination and, in cases where controlled by a multistage process with two or more stages. these are used in combination, it is preferred to use one or Examples of Such a process include a method wherein the US 9,023,953 B2 9 10 reaction is first allowed to proceed at a pressure of 13.3 to 66.6 merization step. Examples of the condenser constituting the kPa and then at a pressure of 1.3 to 6.5 kPa. The reaction is condensation section herein include those of the double-pipe also preferably carried out under the flow of an inert gas such type, multitubular type, coil type, plate type, plate fin type, as nitrogen. centrifugal type, spiral type and jacket type. The melt polymerization step is preferably carried out for a In the melt polymerization step, the method of removal of reaction time of 0.5 to 50 hours and, to efficiently obtain a the produced low-molecular-weight polymers from the reac poly(lactic acid) resin also having excellent hue, the melt tor after the reaction is not restricted, and examples of the polymerization step is preferably carried out for a reaction method include a method by extruding with an inert gas such time of 1 to 45 hours, more preferably carried out for a as nitrogen and a method by removing with a gearpump or the reaction time of 2 to 40hours, still more preferably carried out 10 like. From the viewpoint of ease of handling of the low for a reaction time of 3 to 35 hours, especially preferably molecular-weight polymers having low viscosity, the method carried out for a reaction time of 4 to 30 hours. In cases where by extruding with an inert gas such as nitrogen is preferred. the temperature and the pressure during the melt polymeriza The weight average molecular weight of the prepolymer tion step are controlled by a multistage process with two or produced by the melt polymerization step is 5,000 to 25,000, more stages, examples of Such a process include a method 15 preferably 10,000 to 20,000. Further, when the acid value of wherein the reaction is first allowed to proceed at a tempera the prepolymer is defined as a mol/ton, (2) below is preferably ture of 140 to 160° C. at a pressure of 13.3 to 66.6 kPa for a satisfied; (3) below is more preferably satisfied; and (4) below reaction time of 2 to 15 hours and then attemperature of 160 is still more preferably satisfied: to 180° C. at a pressure of 1.3 to 6.5 kPa for a reaction time of 2 to 15 hours. Even in the cases where the temperature and the 450/(Mw/10,000-0.14):titration with an alkaline solution. changed from normal pressure to the Substantial reaction The crystallization step is described below. pressure shown in the melt polymerization conditions 1 is To carry out the Solid-phase polymerization step, crystal preferably not more than 50%, more preferably not more than 35 lization of the prepolymer is necessary. Therefore, a crystal 40%, still more preferably not more than 30% of the length of lization treatment is carried out after completion of the melt time of the step. polymerization step before the beginning of the Solid-phase The melt polymerization step may be carried out by either polymerization step. a batch method or continuous method, and the reactor is not Examples of the method of crystallization include a restricted. Examples of the reactor which may be used include 40 method wherein heat treatment is carried out in a gas phase stirred tank reactors, mixer-type reactors, column reactors Such as nitrogen or air, or in a liquid phase Such as water or and extruder reactors. These reactors may be used as a com ethanol, at a crystallization treatment temperature; a method bination of two or more of them. In view of the productivity, wherein the prepolymer is dissolved in a solvent to prepare a the step is preferably carried out by a continuous method. solution, followed by evaporating the solvent; a method The melt polymerization step may be carried out using any 45 wherein the prepolymer is contacted with a solvent; and a reaction apparatus and, to efficiently obtain a poly(lactic acid) method wherein the prepolymer in the molten state is sub resin having a high molecular weight and a high melting point jected to an operation of extension or shear, followed by as well as excellent thermal stability and hue, an apparatus in cooling and Solidifying the prepolymer. Among the above which a reactor is connected to a reflux condenser is prefer methods, the method wherein heat treatment is carried out in ably used. 50 the nitrogen gas phase and the method wherein the prepoly The reactor may be constituted either by a single reaction mer in the molten state is subjected to an operation of exten chamber or by two or more reaction chambers separated by a sion or shear, followed by cooling and Solidifying the pre divider(s) and/or the like. To efficiently obtain a poly(lactic polymer are preferred. A plurality of the above methods may acid) resin having a high molecular weight, the reactor is also be used in combination. preferably constituted by two or more reaction chambers. 55 In the method wherein the prepolymer in the molten state is The reflux condenser preferably connects to the upper part subjected to an operation of extension or shear, followed by of the reactor and, more preferably, a vacuum pump connects cooling and Solidifying the prepolymer, the method of cool to the reflux condenser. The reflux condenser is used to sepa ing is preferably water cooling wherein the length of time of rate Volatile components, and any reflux condenser may be contacting with water is preferably not more than 10 minutes, used as long as it has a vaporization section having a function 60 more preferably not more than 5 minutes, still more prefer to remove a part of the volatile components to the outside of ably not more than 3 minutes, preferably not more than 1 the reaction system and a condensation section having a func minute, especially preferably not more than 30 seconds. In tion to return a part of the Volatile components into the reac cases where the length of time of contacting with water is tion system. More specifically, any reflux condenser may be within the preferred range described above, acidic com used as long as it removes water among the Volatile compo 65 pounds are unlikely to increase in the polymer. The length of nents and returns lactic acid and lactide and/or their low time from the cooling until the Solid-phase polymerization is molecular-weight polymers into the reactor in the melt poly preferably not more than 12 hours, more preferably not more US 9,023,953 B2 11 12 than 6 hours, still more preferably not more than 3 hours, to 10 mm, especially about 1.2 to 8 mm, and about 1.5 to 6 mm especially preferably not more than 1 hour. in most cases, with a ball shape, prolate spheroid shape, flat The crystallization treatment temperature herein is not ball shape, plate shape, rod shape, shape similar to these, restricted as long as the temperature is higher than the glass amorphous shape or another arbitrary shape. The pellet is also transition temperature and lower than the melting point of the called a “chip.” Examples of the method of pelletization prepolymer which can be obtained by the melt polymeriza include a method wherein the prepolymer in the molten state tion step. The crystallization treatment temperature is more is extruded into a strand-like shape and pelletized using a preferably between the heating crystallization temperature pelletizer, a method wherein the prepolymer is dropped in the and the cooling crystallization temperature as measured by form of a droplet using a drip nozzle and brought into contact differential scanning calorimetry (DSC) in advance. In cases 10 where the poly(lactic acid) resin is a poly(lactic acid) resin, to with a solid, gas or liquid to achieve pelletization, and a efficiently obtain a poly(lactic acid) resin having a high method wherein the prepolymer is extruded from a die into a molecular weight and a high melting point as well as excellent gas or liquid while the extruded prepolymer is cut. The pel hue, the crystallization treatment temperature is preferably 70 letization is preferably carried out under a dry atmosphere to 130° C., more preferably 75 to 130° C., most preferably 80 15 and, in cases where the prepolymer is brought into contact to 130° C. with moisture, the length of time of contact is preferably as The temperature during the crystallization step may also be short as possible. controlled by a single stage process wherein the temperature Examples of the method of forming the prepolymer into a is kept constant. However, the temperature is preferably con powder include a method wherein the prepolymer is pulver trolled by a multistage process with two or more stages ized using a mixer, blender, ball mill or hammer pulverizer. In wherein the temperature is changed stepwise, and the tem the case of a powder, in view of efficient crystallization, the perature is more preferably increased stepwise as the reaction average particle diameter is preferably 0.01 to 5 mm, more proceeds. Examples of Such a process include a method preferably 0.1 to 1 mm. wherein the reaction is first allowed to proceed at a tempera Industrially, the prepolymer is usually formed into a pellet. ture of 80 to 100° C. and then at a temperature of 100 to 130° 25 An excellent productivity and high effect can be achieved C. The amount of increase in the temperature at each stage is especially in cases where the crystallization treatment is car preferably not more than 30° C., more preferably not more ried out for a prepolymer in the form of a pellet. than 25°C., still more preferably not more than 20°C. The weight average molecular weight of the crystallized The length of time of crystallization is preferably 1 to 7 prepolymer is 5,000 to 25,000, preferably 10,000 to 20,000, hours, more preferably 1.5 to 5 hours, especially preferably 30 especially preferably 12,000 to 20,000. The weight average 1.5 to 3 hours. In terms of the pressure conditions during the molecular weight immediately after melt polymerization crystallization step, any of the conditions of reduced pressure, hardly changes even through the crystallization step. In poly normal pressure and increased pressure may be employed. lactic acid, in contrast to findings for conventional polyesters, Among these, normal pressure is preferred. The crystalliza a high weight average molecular weight leads to low reactiv tion is preferably carried out under an anhydrous atmosphere 35 ity in Solid-phase polymerization and a low final molecular and, in cases where the crystallization is carried out under an weight, while a too low weight average molecular weight atmosphere containing moisture, the crystallization time is leads to requirement of a low solid-phase polymerization preferably as short as possible. temperature for prevention of melting during Solid-phase In cases where the temperature during the crystallization polymerization, resulting in decreased productivity. By using step is controlled by a multistage process with two or more 40 a prepolymer having a molecular weight within the above stages, examples of such a process include a method wherein described range, high productivity can be achieved. the first stage is carried out at a temperature of 70 to 100° C. The enthalpy offusion AHm of the crystallized prepolymer for 1 to 4 hours and the second stage is carried out at a is 50 to 65 J/g, more preferably 53 to 60. In conventional temperature of 100 to 130°C. for 1 to 4 hours. The process is Solid-phase polymerization, it has been suggested that a high more preferably carried out by a method wherein the first 45 degree of crystallinity, that is, high enthalpy offusion, leads to stage is carried out at a temperature of 70 to 90° C. for 1 to 3 low reactivity in the Solid-phase polymerization, but, in our hours, the second stage is carried out at a temperature of 90 to method, as the enthalpy of fusion increases, the reactivity in 110° C. for 1 to 3 hours, and the third stage is carried out at a the solid-phase polymerization increases. In cases where the temperature of 110 to 130° C. for 1 to 3 hours. Even in cases enthalpy of fusion AHm of the crystallized prepolymer is where the temperature is controlled by a multistage process 50 within the above-described preferred range, the reactivity in with two or more stages, the total reaction time of the crys the Solid-phase polymerization can be kept high while a high tallization step is preferably 1 to 7 hours. degree of crystallinity can be achieved. Instead of increasing the temperature stepwise as described The acid value A mol/ton of the crystallized prepolymer above by a multistage process wherein the temperature is kept needs to satisfy (1) below, preferably satisfies (5) below, more constant at each stage, the temperature may also be increased 55 preferably satisfies (6) below. In cases where the acid value is continuously. Examples of Such a process include a method too high, degradation is promoted during the Solid-phase wherein the temperature is first increased from 70° C. to 120° polymerization step, while in cases where the acid value is too C. for 2 hours, that is, at a rate of 25°C. per hour, and then kept low, the reactivity is low so that a high molecular weight and constant at 160°C. In cases where the temperature is continu a high melting point can be hardly achieved. The acid value is ously increased, the temperature increasing rate is preferably 60 derived from terminal carboxyl groups of the polymer and not more than 30° C. per hour. oligomers such as dimers, and acidic compounds such as The form of the prepolymer for the crystallization treat lactic acid, and the amount of terminal carboxyl groups of the ment is not restricted, and the prepolymer may be in the form polymer is dependent on the molecular weight. In particular, of any of a mass, film, pellet, powder and the like. The pre in cases where too much acidic compounds are contained, polymer is preferably in the form of a pellet or powder for 65 degradation occurs during the Solid-phase polymerization, so efficient crystallization. The pellet means a small molded that the acid value is preferably low, while in cases where the particle of a polymer having a maximum diameter of about 1 value is too low, the polymerization reactivity is low. We US 9,023,953 B2 13 14 discovered that high productivity can be obtained when the ably carried out for a reaction time of 3 to 80 hours, more following inequalities are satisfied: preferably carried out for a reaction time of 5 to 50 hours, still more preferably carried out for a reaction time of 10 to 30 450/(Mw/10,000-0.14):chromatography. 30 The pressure conditions in the Solid-phase polymerization The solid-phase polymerization step is described below. step are not restricted, and any of the conditions of reduced The solid-phase polymerization step is preferably continu pressure, normal pressure and increased pressure may be ously carried out under conditions including at least the fol employed. To efficiently obtain a poly(lactic acid) resin hav lowing two stages: ing a high molecular weight, the pressure conditions are Solid-phase polymerization conditions 1: 130° C. to 155° 35 preferably reduced pressure conditions or normal pressure C. conditions. In cases where the step is carried out under Solid-phase polymerization conditions 2: 155° C. to 165° reduced pressure conditions, the step is preferably carried out C. at a pressure of 0.13 to 1,300 Pa. Further, the step is preferably The solid-phase polymerization step is preferably carried carried out at a pressure of 1 to 1,000 Pa, more preferably out at a temperature of not more than the melting point of the 40 carried out at a pressure of 10 to 900 Pa, still more preferably prepolymer and, in view of efficiently obtaining a poly(lactic carried out at a pressure of 100 to 800 Pa, especially prefer acid) resin having a high molecular weight and a high melting ably carried out at a pressure of 500 to 700 Pa. The pressure point as well as excellent hue, the Solid-phase polymerization during the Solid-phase polymerization step may be controlled step is preferably carried out at a temperature of 130 to 165° either by a single stage process or by a multistage process C., more preferably carried out at a temperature of 135 to 165° 45 with two or more stages, and is preferably controlled by a C., still more preferably carried out at a temperature of 140 to multistage process with two or more stages. Examples of such 165°C. In particular, the final temperature is preferably 155 a process include a method wherein the reaction is first to 165° C., more preferably 160 to 165° C. allowed to proceed at a pressure of 700 to 1,300 Pa and then The temperature during the Solid-phase polymerization at a pressure of 0.13 to 700 Pa. In cases where the reaction is step may be controlled either by a single stage process or by 50 carried out under normal pressure conditions, the reaction is a multistage process with two or more stages and, in view of preferably carried out under the flow of an inert gas such as achieving a high molecular weight and excellent hue in a dry nitrogen. The flow rate is preferably 0.01 to 200 L/min. short time, the temperature is preferably controlled by a mul more preferably 0.1 to 150 L/min., especially preferably 0.5 tistage process with two or more stages, and the temperature to 100 L/min. per 1 kg of the prepolymer. is more preferably increased stepwise as the reaction pro 55 The form of the crystallized prepolymer used for the solid ceeds. Examples of Such a process include a method wherein phase polymerization step is not restricted, and the crystal the reaction is first allowed to proceed at a temperature of 130 lized prepolymer may be in the form of any of a mass, film, to 155° C. and then at a temperature of 155 to 165° C. The pellet, powder and the like. The form of a pellet or powder is amount of increase in the temperature at each stage is prefer preferred. The pellet means a small molded particle of a ably not more than 15°C., more preferably not more than 10° 60 polymer having a maximum diameter of about 1 to 10 mm, C., still more preferably not more than 5°C. especially about 1.2 to 8 mm, and about 1.5 to 6 mm in most To efficiently obtain a poly(lactic acid) resin having a high cases, with a ball shape, prolate spheroid shape, flat ball molecular weight and a high melting point as well as excellent shape, plate shape, rod shape, shape similar to these, amor thermal stability and hue, the Solid-phase polymerization step phous shape or another arbitrary shape. The pellet is also is preferably carried out for a reaction time of 1 to 100 hours 65 called a chip. In the case of a powder, in view of efficient and, to efficiently obtain a poly(lactic acid) resin also having Solid-phase polymerization, the average particle diameter is excellent hue, the solid-phase polymerization step is prefer preferably 0.01 to 5 mm, more preferably 0.1 to 1 mm. Indus US 9,023,953 B2 15 16 trially, the prepolymer is usually formed into a pellet. An respect to the total molar amount of the metals after the excellent productivity and high effect can be achieved espe solid-phase polymerization is preferably 3.0 to 50 in view of cially in cases where the Solid-phase polymerization is car the interaction between the metal compounds and the sulfur ried out for a prepolymer in the form of a pellet. containing compound containing Sulfur having an oxidation The solid-phase polymerization step may be either a batch 5 number of not less than +5. The ratio is more preferably 4.0 to method or continuous method, and examples of the reactor 40. which may be used include stirred tank reactors, mixer-type To obtain an aliphatic polyester having excellent thermal reactors and column reactors. These reactors may be used as stability, a stabilizer is preferably added at the beginning of a combination of two or more of them. In view of the produc the melt polymerization step, during the melt polymerization tivity, the step is preferably carried out by a continuous 10 step or after the solid-phase polymerization. method. Examples of the stabilizer include Sulfur-containing com The weight average molecular weight of the poly(lactic pounds containing Sulfur having an oxidation number of less acid) resin obtained by the method is not restricted, and is than +5, phosphorous compounds, aromatic ketone com preferably not less than 100,000 in view of the mechanical pounds, hydrocarbon compounds having an aromatic ring(s), properties. In particular, for excellent moldability and 15 aliphatic dicarboxylic acids; aliphatic diols, alicyclic hydro mechanical properties, the weight average molecular weight carbon compounds, hindered phenol compounds, vitamin is preferably 100,000 to 1200,000, more preferably 120,000 compounds, triazole compounds and hydrazine derivative to 300,000, still more preferably 140,000 to 250,000. The compounds. These may also be used in combination. weight average molecular weight is the value of weight aver Specific examples of the Sulfur-containing compounds age molecular weight in terms of a poly(methyl methacrylate) 20 containing Sulfur having an oxidation number of less than +5 standard as measured by gel permeation chromatography include diphenyl sulfone, ditolyl sulfone, dibenzylsulfone, (GPC) using hexafluoroisopropanol as a solvent. methyl phenyl Sulfone, ethyl phenyl Sulfone, propyl phenyl The ratio of the weight average molecular weight with sulfone, methyl tolyl sulfone, ethyl tolyl sulfone, propyl phe respect to the number average molecular weight is preferably nyl sulfone, benzyl phenylsulfone, phenyl tolyl sulfone, ben 1.4 to 3 in view of uniformity of the physical properties of the 25 Zyl tolyl sulfone, bis(phenylsulfonyl)methane, bis(tolylsulfo polymer, and the ratio is more preferably 1.5 to 2.5. The rate nyl)methane, bis(benzylsulfonyl)methane, Sulfurous acid, of reduction in the weight after heating under nitrogen gas Sodium sulfite, potassium Sulfite, Sulfur, dilauryl thiodipropi flow at 200° C. for 20 minutes is preferably not more than onate, ditridecyl thiodipropionate, dimyristyl thiodipropi 0.6% in view of excellent heat resistance, and the rate is more onate, distearyl thiodipropionate, pentaerythritol-tetrakis(3- preferably not more than 0.4%. 30 laurylthiopropionate), pentaerythritol-tetrakis(3- The content of the Sulfur-containing compound containing dodecylthiopropionate), pentaerythritol-tetrakis(3- sulfur having an oxidation number of not less than +5 after the octadecylthiopropionate), pentaerythritol-tetrakis(3- solid-phase polymerization is preferably 10 to 4,000 ppm, myristylthiopropionate) and pentaerythritol-tetrakis(3- more preferably 30 to 3,000 ppm, still more preferably 40 to Stearylthiopropionate). Specific examples of trade names of 2,000 ppm, especially preferably 50 to 500 ppm in terms of 35 the Sulfur-containing compounds containing Sulfur having an Sulfur atoms, with respect to the produced polymer. oxidation number of less than +5 include "Adekastab’ The residual rate of the Sulfur-containing compound con AO-23, AO-4125 and AO-503A manufactured by ADEKA: taining Sulfur having an oxidation number of not less than +5 “Irganox' PS802 manufactured by Ciba Specialty Chemi after the solid-phase polymerization is preferably 0 to 90%, cals; “Sumilizer'TPL-R, TPM, TPS and TP-D manufactured more preferably 1 to 50%, especially preferably 5 to 30%. 40 by Sumitomo Chemical Co., Ltd.: DSTP, DLTP, DLTOIBand The residual rate (R) is an index of the difference between the DMTP manufactured by API Corporation: “Seenox” 412S concentrations, before and after the polymerization reaction, manufactured by Shipro Kasei; and “Cyanox' 1212 manu of the Sulfur-containing compound containing Sulfur having factured by Cyanamid Inc. an oxidation number of not less than +5, and is represented by Among the phosphorous compounds, examples of organic the Equations (7) to (9) below: 45 phosphorous compounds include phosphite compounds and phosphate compounds. Specific examples of Such phosphite R%=Cappm/Cbppm)x100 (7) compounds include tetrakis 2-t-butyl-4-thio(2'-methyl-4- (Cb, theoretical catalyst concentration calculated according hydroxy-5'-t-butylphenyl)-5-methylphenyl-1,6-hexameth to Equation (8), which is expected when all catalyst added is ylene-bis(N-hydroxyethyl-N-methylsemicarbazide)-diphos remaining in the polymer, Ca, actual concentration of the 50 phite, tetrakis 2-t-butyl-4-thio(2'-methyl-4-hydroxy-5'-t- catalyst remaining in the polymer after the polymerization butylphenyl)-5-methylphenyl-1,10-decamethylene-di reaction which is calculated according to Equation (9)) carboxylic acid-di-hydroxyethylcarbonylhydrazide diphosphite, tetrakis 2-t-butyl-4-thio(2'-methyl-4'-hydroxy 5'-t-butylphenyl)-5-methylphenyl)-1,10-decamethylene-di (Wb, weight of the catalyst added in the polymerization step; 55 carboxylic acid-di-Salicyloylhydrazide-diphosphite, tetrakis Wp, weight of the polymer after the polymerization reaction) 2-t-butyl-4-thio(2'-methyl-4'-hydroxy-5'-t-butylphenyl)-5- methylphenyl-di(hydroxyethylcarbonyl)hydrazide Cappm)= Wag/Wog)x10 (9) diphosphite and tetrakis 2-t-butyl-4-thio(2'-methyl-4- (Wb, weight of the catalyst in the polymer after the polymer hydroxy-5'-t-butylphenyl)-5-methylphenyl-N,N'-bis ization reaction; Wip, weight of the polymer after the poly- 60 (hydroxyethyl)oxamide-diphosphite. The phosphite merization reaction). compound preferably has at least one P O bond linked to an In cases where a tin compound(s), titanium compound(s), aromatic group. Specific examples of Such a compound lead compound(s), Zinc compound(s), cobalt compound(s), include tris(2,4-di-t-butyl-phenyl)phosphite, tetrakis(2,4-di iron compound(s), lithium compound(s) and/or rare earth t-butylphenyl)4,4'-biphenylenephosphonite, bis(2,4-di-t-bu compound(s) is/are used, the ratio of the molar amount of 65 tylphenyl)pentaerythritol-di-phosphite, bis(2,6-di-t-butyl-4- Sulfur atoms of the Sulfur-containing compound containing methylphenyl)pentaerythritol-di-phosphite, 2.2- sulfur having an oxidation number of not less than +5 with methylenebis(4,6-di-t-butylphenyl)octylphosphite, 4,4'- US 9,023,953 B2 17 18 butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecyl) propionate, n-octadecyl-3-(3'-methyl-5'-t-butyl-4'-hydrox phosphite, 1,1,3-tris(2-methyl-4-ditridecylphosphite-5-t- yphenyl)-propionate, n-tetradecyl-3-(3',5'-di-t-butyl-4-hy butyl-phenyl)butane, tris (mixed mono- and di-nonylphenyl) droxyphenyl)-propionate, 1.6-hexanediol-bis-3-(3,5-di-t- phosphite, tris(nonylphenyl)phosphite and 4,4'- butyl-4-hydroxyphenyl)-propionate, 1,4-butanediol-bis-3- isopropylidenebis(phenyl-dialkylphosphite). Tris(2,4-di-t- (3,5-di-t-butyl-4-hydroxyphenyl)-propionate, 2,2'- butylphenyl)phosphite, 2.2-methylenebis(4,6-di-t- methylenebis-(4-methyl-t-butylphenol), triethylene glycol butylphenyl)octylphosphite, bis(2,6-di-t-butyl-4- bis-3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate, methylphenyl)pentaerythritol-di-phosphite, tetrakis(2,4-di tetrakis methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl) t-butylphenyl)-4,4'-biphenylenephosphonite, 9,10-dihydro propionate methane, 3.9-bis(2-3-(3-t-butyl-4-hydroxy-5- 9-Oxa-10-phosphaphenanthrene-10-oxide, triisodecyl 10 methylphenyl)propionyloxy)-1,1-dimethylethyl2.4.8.10 phosphite and the like are preferably used. Specific examples tetraoxaspiro(5.5)undecane, N,N'-bis-3-(3',5'-di-t-butyl-4- of trade names of the phosphite compounds include Ade hydroxyphenyl)propionylhexamethylenediamine, N,N'- kastab” C, PEP-4C, PEP-8, PEP-11C, PEP-24G, PEP-36, tetramethylene-bis-3-(3'-methyl-5'-t-butyl-4- HP-10, 2112, 260, 522A, 329A, 1178, 1500, C, 135A, 3010 hydroxyphenol)propionyldiamine, N,N'-bis-3-(3,5-di-t- and TPP manufactured by ADEKA: “Irgafos’ 168 manufac 15 butyl-4-hydroxyphenol)propionylhydrazine, N-salicyloyl tured by Ciba Specialty Chemicals; “Sumilizer P-16 manu N'-salicylidenehydrazine, 3-(N-salicyloyl)amino-1,2,4- factured by Sumitomo Chemical Co., Ltd.: “Sandostab' triazole, N,N'-bis(2-3-(3,5-di-t-butyl-4-hydroxyphenyl) P-EPQ manufactured by Clariant Ltd.: “Weston' 618, 619G. propionyloxyethylloxyamide, pentaerythrityl-tetrakis3-(3. and 624 manufactured by GE; and SANKO-HCA manufac 5-di-t-butyl-4-hydroxyphenyl)propionate and N,N'- tured by Sanko Co., Ltd. hexamethylenebis-(3,5-di-t-butyl-4-hydroxy Specific examples of the phosphate compounds include hydrocinnamide. Preferred examples of the hindered phenol monostearylacid phosphate, distearylacid phosphate, methyl compounds include triethylene glycol-bis-3-(3-t-butyl-5- acid phosphate, isopropyl acid phosphate, butyl acid phos methyl-4-hydroxyphenyl)-propionate, tetrakismethylene phate, octyl acid phosphate and isodecyl acid phosphate and, 3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate methane, among these, monostearyl acid phosphate and distearyl acid 25 1,6-hexanediol-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)- phosphate are preferred. Specific examples of trade names of propionate, pentaerythrityl-tetrakis3-(3,5-di-t-butyl-4-hy the phosphate compounds include “Irganox' MD 1024 manu droxyphenyl)propionate and N,N'-hexamethylenebis-(3.5- factured by Ciba Specialty Chemicals: “Inhibitor OABH di-t-butyl-4-hydroxy-hydrocinnamide). Specific examples of manufactured by Eastman Kodak Company; and Ade trade names of the hindered phenol compounds include Ade kastab’ CDA-1, CDA-6 and AX-71 manufactured by 30 kastab' AO-20, AO-30, AO-40, AO-50, AO-60, AO-70, ADEKA Corporation. AO-80 and AO-330 manufactured by ADEKA Corporation; Among the phosphorous compounds, examples of inor “Irganox” 245, 259, 565, 1010, 1035, 1076, 1098, 1222, ganic phosphorous compounds include phosphate com 1330, 1425, 1520, 3114 and 5057 manufactured by Ciba pounds, phosphite compounds and hypophosphite com Specialty Chemicals; “Sumilizer BHT-R, MDP-S, BBM-S, pounds. Specific examples of Such phosphate compounds 35 WX-R, NW, BP-76, BP-101, GA-80, GM and GS manufac include phosphoric acid, diphosphoric acid, triphosphoric tured by Sumitomo Chemical Co., Ltd.; and “Cyanox' acid, lithium phosphate, beryllium phosphate, sodium phos CY-1790 manufactured by Cyanamid Inc. phate, magnesium phosphate, aluminum phosphate, potas Specific examples of the vitamin compounds include natu sium phosphate and calcium phosphate; specific examples of ral compounds Such as d-C-tocopherol acetate, d-C-toco Such phosphite compounds include phosphorous acid, 40 pherol Succinate, d-C-tocopherol, d-f-tocopherol, d-y-toco lithium phosphite, beryllium phosphite, sodium phosphite, pherol, d-ö-tocopherol, d-C-tocotrienol, d-f-tocophetrienol, magnesium phosphite, aluminum phosphite, potassium phos d-y-tocophetrienol and d-Ö-tocophetrienol; and synthetic phite and calcium phosphite; and specific examples of Such compounds Such as dl-C-tocopherol, d1-C-tocopherol hypophosphite compounds include hypophosphorous acid, acetate, dl-O-tocopherol calcium Succinate and dl-C-toco lithium hypophosphite, beryllium hypophosphite, sodium 45 pherol nicotinate. Specific examples of trade names of the hypophosphite, magnesium hypophosphite, aluminum hypo vitamin compounds include “Tocopherol’ manufactured by phosphite, potassium hypophosphite and calcium hypophos Eisai Co., Ltd. and “Irganox' E201 manufactured by Ciba phite. Specialty Chemicals. Specific examples of the aromatic ketone compounds Specific examples of the triazole compounds include ben include 1,4-dibenzoylbenzene, benzophenone, acetophe 50 Zotriazole and 3-(N-salicyloyl)amino-1,2,4-triazole. none, propiophenone and benzoylnaphthalene. Specific examples of the hydrazine derivative compounds Specific examples of the hydrocarbon compounds having include decamethylenedicarboxylic acid-bis(N'-salicyloyl an aromatic ring(s) include triphenylmethane, diphenyl hydrazide), isophthalic acid bis(2-phenoxypropionylhy methane and toluene. drazide), N-formyl-N'-salicyloylhydrazine, 2.2-oxamidobis Specific examples of the aliphatic dicarboxylic acids 55 ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, include oxalic acid, Succinic acid, butanoic acid, adipic acid oxalyl-bis-benzylidene-hydrazide, nickel-bis(1-phenyl-3- and pentanoic acid. methyl-4-decanoyl-5-pyaZolate), 2-ethoxy-2-ethyloxanil Specific examples of the aliphatic diols include ethylene ide, 5-t-butyl-2-ethoxy-2-ethyl-oxanilide, N,N-diethyl-N', glycol, propanediol, butanediol, pentanediol, hexanediol. N'-diphenyloxamide, N,N'-diethyl-N,N'-diphenyloxamide, cyclohexanediol, spiroglycol and isosorbide. 60 oxalic acid-bis(benzylidenehydrazide), thiodipropionic acid Specific examples of the alicyclic hydrocarbon compounds bis(benzylidenehydrazide), bis(salicyloylhydrazine), N-sali include 1,2-dimethylcyclohexane, methylcyclohexane, 1.2, cylidene-N'-salicyloylhydrazone, N,N'-bis(3-(3,5-di-t-butyl 4-trimethylcyclohexane, 1,2-diethylcyclohexane, ethylcy 4-hydroxyphenyl)propionylhydrazine and N,N'-bis(2-3- clohexane, 1,2,4-triethylcyclohexane, 1,2-dipropylcyclohex (3,5-di-t-butyl-4-hydroxyphenyl)propionyloxyethyl ane, propylcyclohexane and 1,2,4-tripropylcyclohexane. 65 oxamide. Specific examples of the hindered phenol compounds Among the above examples, those having no t-butyl group include n-octadecyl-3-(3',5'-di-t-butyl-4-hydroxyphenyl)- are preferred. In particular, at least one selected from sulfur US 9,023,953 B2 19 20 containing compounds containing Sulfur having an oxidation cases where the stabilizer is added at the stages of both the number of less than +5, phosphorous compounds, aromatic melt polymerization conditions 1 and the melt polymeriza ketone compounds, hydrocarbon compounds having an aro tion conditions 2, the stabilizer is preferably added in an matic ring(s), aliphatic dicarboxylic acids, aliphatic diols and amount of 0.001 to 1 part by weight at each stage and, in view alicyclic hydrocarbon compounds is preferably contained. of achieving excellent productivity, the stabilizer is more Preferred Sulfur-containing compounds containing Sulfur preferably added in an amount of 0.01 to 0.5 part by weight at having an oxidation number of less than +5 are diphenylsul each stage, still more preferably added in an amount of 0.01 to fone, sulfurous acid, sodium sulfite and sulfur, and “Sum 0.1 part by weight at each stage with respect to 100 parts by ilizer” TPD (pentaerythritol tetrakis(B-laurylthio-propi weight of the poly(lactic acid) resin. onate)) manufactured by Sumitomo Chemical Co., Ltd. 10 To obtain a poly(lactic acid) resin having excellent thermal Among the phosphorous compounds, more preferred inor stability, the stabilizer may also be preferably added after the ganic phosphorous compounds are phosphoric acid com completion of the Solid-phase polymerization step. In this pounds and phosphorous acid compounds, and more pre case, the method of addition of the stabilizer is not restricted, ferred organic phosphorous compounds are phosphate and examples of the method include a method wherein melt compounds and phosphite compounds. More preferred spe 15 kneading is carried out at a temperature higher than the melt cific examples of the phosphorous compounds include inor ing point of the poly(lactic acid) resin and a method wherein ganic phosphorous compounds Such as phosphoric acid, the stabilizer is dissolved in a solvent and the resulting solu phosphorous acid, Sodium phosphate and sodium phosphite; tion is mixed, followed by removal of the solvent. For effi and organic phosphorous compounds such as "Adekastab' cient production, the method wherein melt kneading is car AX-71 (dioctadecylphosphate), PEP-8 (distearyl pentaeryth ried out at a temperature higher than the melting point of the ritol diphosphite), PEP-36 (cyclic neopentatetraylbis(2,6-t- poly(lactic acid) resin is preferred. The method of melt butyl-4-methylphenyl)phosphite), HP-10 (2,2'-methylenebis kneading may be either a batch method or continuous (4,6-di-t-butyl-1-phenyloxy)(2-ethylhexyloxy) method, and examples of the apparatus which may be used phosphorous), PEP-24G (bis(2,4-di-t-butylphenyl) include single screw extruders, twin screw extruders, multi pentaerythritol diphosphite), 3010 (triisodecyl phosphite) 25 screw extruders, plastomill, kneaders and stirred tank reactors and TPP (triphenyl phosphite) manufactured by ADEKA equipped with a pressure reducing device. For efficient uni Corporation: “Irgafos' 168 (tris(2,4-di-t-butylphenyl)phos form kneading, a single screw extruder or twin screw extruder phite) manufactured by Ciba Specialty Chemicals; and HCA is preferably used. The temperature at which the stabilizer is (9,10-dihydro-9-Oxa-10-phosphaphenanthrene-10-oxide) added is preferably a temperature of 180 to 250° C. and, to manufactured by Sanko Co., Ltd. In particular, phosphorous 30 achieve excellent mechanical properties, a temperature of compounds having a phosphorus atom(s) directly bound to a 190 to 230° C. is more preferred. The pressure at which the carbonatom(s) constituting an aromatic ring(s) are preferred, stabilizer is added may be any of a reduced pressure, normal and HCA (9,10-dihydro-9-Oxa-10-phosphaphenanthrene pressure and increased pressure. To remove gas generated 10-oxide) manufactured by Sanko Co., Ltd. is especially pre during melt kneading, the pressure is preferably a reduced ferred. 35 pressure. In terms of the atmospheric conditions during the As the aromatic ketone compound, 1,4-dibenzoylbenzene melt kneading, the melt kneading may be carried out either in and benzophenone are especially preferred; as the hydrocar the air or under an atmosphere of an inert gas Such as nitrogen. bon compound having an aromatic ring(s), triphenylmethane To reduce the amount of gas generated during the melt knead is especially preferred; as the aliphatic dicarboxylic acid, ing, the melt kneading is preferably carried out under an oxalic acid is especially preferred; as the aliphatic diol, hex 40 atmosphere of an inert gas. anediol is especially preferred; and, as the alicyclic hydrocar In cases where the mixing is carried out in a solvent, a bon compound, 1,2-dimethylcyclohexane is especially pre Solvent that dissolves the polymer and monomers is used. ferred. Examples of the solvent which may be used include chloro The amount of the stabilizer to be added is not restricted form, methylene chloride and acetonitrile. In cases where the and, in view of achieving excellent thermal stability, the 45 solvent needs to be removed after the mixing, the method of amount is preferably 0.001 to 2 parts by weight, more pref removing the Solvent is not restricted, and examples of the erably 0.01 to 1 part by weight, still more preferably 0.05 to method which may be used include a method wherein the 0.5 part by weight, most preferably 0.08 to 0.3 part by weight Solvent is evaporated at room temperature and a method with respect to 100 parts by weight of the poly(lactic acid) wherein the solvent is evaporated under reduced pressure at a resin. The timing of addition of the stabilizer is not restricted, 50 temperature higher than the boiling point of the solvent. and may be either before the beginning or after the comple To further improve hydrolysis resistance, at least one tion of either the melt polymerization step or the solid-phase selected from amine compounds, alkali metal compounds polymerization step. In cases where the stabilizer is added at and alkaline earth metal compounds is preferably added at the the stage of the melt polymerization step in view of obtaining beginning of the melt polymerization step or after the comple a poly(lactic acid) resin having a high melting point and a 55 tion of the Solid-phase polymerization step, or at any stage high molecular weight, the stabilizer is preferably added therebetween. By this, in cases where a polymerization cata immediately before the completion of the above-described lyst, especially a catalyst having an acid, is remaining, melt polymerization conditions 1 (140°C. to 160°C., 13.3 to hydrolysis of the poly(lactic acid) resin during the melt 66.6 kPa) or at the beginning of the above-described melt kneading and the melt molding by the remaining catalyst can polymerization conditions 2 (160° C. to 180° C., 1.3 to 6.5 60 be suppressed and the hydrolysis resistance can thus be kPa), more preferably added both immediately before the increased. completion of the melt polymerization conditions 1 and at the Specific examples of the amine compounds include meth beginning of the melt polymerization conditions 2 from the ylethylamine, triethylamine, dimethylpropylamine, ethy viewpoint of achieving excellent productivity. In cases where lamine, isoamylamine, butylamine, propylamine, ethylenedi the stabilizer is added at the beginning of the melt polymer 65 amine, butanediamine, hexamethylenediamine, 1,2,3- ization conditions 2, the catalyst for Solid-phase polymeriza triaminopropane, tetraethylammonium hydroxide, aniline, tion is preferably added after the addition of the stabilizer. In naphthylamine, naphthalenediamine, cyclohexanediamine, US 9,023,953 B2 21 22 benzenediamine, benzidine, diaminodiphenylether, diamino Stearate, potassium naphthenate, potassium t-butyl carbon diphenylmethane, dibenzylamine, didodecylamine, pyrimi ate, potassium sulfate and potassium oxide. In particular, dine, 2-aminopyrimidine, 2-amino-4-methyl-6-methoxypy least one of organic carboxylic acid alkali metal compounds rimidine, pyrimidine-2,4,6-triamine, N-(2-aminoethyl)-N- having not less than 4 carbon atoms is preferably contained. pyrimidine-2-ylamine, 6-t-butylpyrimidine-4-amine, 4.6- Examples of the alkaline earth metal compounds include dimethoxy-5-phenylpyrimidine-2-amine, magnesium compounds such as magnesium diisopropoxide, 2-ethoxypyrimidine-4,6-diamine, 5-phenylpyrimidine-4- magnesium chloride, magnesium acetate, magnesium lactate, amine3.9-bis(2-(3,5-diamino-2,4,6-triazaphenyl)ethyl-2,4, magnesium Stearate, magnesium carbonate, magnesium Sul 8,10-tetraoxaspiro5.5undecane, ethylenediamine-tetraace fate and magnesium oxide; calcium compounds such as cal tic acid, alkali metal (Li, Na, K) salts of ethylenediamine 10 cium diisopropoxide, calcium chloride, calcium acetate, cal tetraacetic acid, N,N'-disalicylidene-ethylenediamine, N,N'- cium octoate, calcium naphthenate, calcium lactate, calcium disalicylidene-1,2-propylenediamine, N,N'-disalicylidene Stearate and calcium Sulfate; barium compounds such as N'-methyl-dipropylenetriamine, 3-salicyloylamino-1,2,4- barium diisopropoxide, barium chloride, barium acetate, triazole and N.N.N'-trimethylethylenediamine; hindered barium octoate, barium naphthenate, barium lactate, barium amine compounds such as 4-acetoxy-2.2.6,6-tetramethylpip 15 Stearate and barium Sulfate. In particular, at least one of eridine, 4-stearoyloxy-2.2.6,6-tetramethylpiperidine, 4-acry organic carboxylic acid alkaline earth metal compounds hav loyloxy-2.2.6,6-tetramethylpiperidine, 4-(phenylacetoxy)-2, ing not less than 4 carbon atoms is preferably contained. 2.6,6-tetramethylpiperidine, 4-benzoyloxy-2.2.6.6- The amount of the amine compound(s), alkali metal(s) tetramethylpiperidine, 4-methoxy-2.2.6.6- and/or alkaline earth metal(s) to be added is not restricted and, tetramethylpiperidine, 4-stearyloxy-2.2.6.6- in view of achieving excellent hydrolysis resistance, the tetramethylpiperidine, 4-cyclohexyloxy-2.2.6.6- amount is preferably 0.001 to 2 parts by weight, more pref tetramethylpiperidine, 4-benzyloxy-2.2.6.6- erably 0.01 to 1 part by weight, still more preferably 0.05 to tetramethylpiperidine, 4-phenoxy-2.2.6.6- 0.5 part by weight, most preferably 0.08 to 0.3 part by weight tetramethylpiperidine, 4-(ethylcarbamoyloxy)-2.2.6.6- with respect to 100 parts by weight of the poly(lactic acid) tetramethylpiperidine, 4-(cyclohexylcarbamoyloxy)-2.2.6.6- 25 resin. In cases where an amine compound is used, the ratio of tetramethylpiperidine, 4-(phenylcarbamoyloxy)-2.2.6.6- the molar amount of nitrogenatoms of the amine compound tetramethylpiperidine, bis(2.2.6,6-tetramethyl-4-piperidyl)- with respect to the molar amount of sulfur atoms of the carbonate, bis(2.2.6.6-tetramethyl-4-piperidyl)oxalate, bis Sulfur-containing compound containing Sulfur having an oxi (2.2.6,6-tetramethyl-4-piperidyl)-malonate, bis(2.2.6.6- dation number of not less than +5 as a catalyst in the polymer tetramethyl-4-piperidyl)-sebacate, bis(2.2.6,6-tetramethyl 30 after solid-phase polymerization is preferably 0.3 to 0.9, more 4-piperidyl)-adipate, bis(2.2.6.6-tetramethyl-4-piperidyl)- preferably 0.4 to 0.8. The timing of addition of the amine terephthalate, 1,2-bis(2.2.6,6-tetramethyl-4-piperidyloxy)- compound(s), alkali metal(s) and/or alkaline earth metal(s) is ethane, C.C.'-bis(2.2.6.6-tetramethyl-4-piperidyloxy)-p- not restricted, and may be either before the beginning or after Xylene, bis(2.2.6,6-tetramethyl-4-piperidyltolylene-2,4- the completion of either the melt polymerization step or the dicarbamate, bis(2.2.6,6-tetramethyl-4-piperidyl)- 35 Solid-phase polymerization step. To obtain a poly(lactic acid) hexamethylene-1,6-dicarbamate, tris(2.2.6.6-tetramethyl-4- resin having a high melting point and a high molecular piperidyl)-benzene-1,3,5-tricarboxylate, tris(2.2.6.6- weight, the compound(s) is/are preferably added at the stage tetramethyl-4-piperidyl)-benzene-1,3,4-tricarboxylate, 1-2- of the melt polymerization step and, to achieve excellent {3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxybutyl-4- productivity, the compound(s) is/are more preferably added 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy|2.2.6,6- 40 immediately before completion of the above-described melt tetramethylpiperidine, condensates of 1,2,3,4- polymerization conditions 1 (140°C. to 160°C., 13.3 to 66.6 butanetetracarboxylic acid, 1.2.2.6,6-pentamethyl-4- kPa) or at the beginning of the above-described melt poly piperidinol and B.B.B.B'-tetramethyl-3,9-24.8.10 merization conditions 2 (160° C. to 180° C., 1.3 to 6.5 kPa), tetraoxaspiro(5.5)undecane diethanol, and polycondensates still more preferably added both immediately before the of succinic acid dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2, 45 completion of the melt polymerization conditions 1 and at the 2.6,6,-tetramethylpiperidine; and polyamines Such as 3.9-bis beginning of the melt polymerization conditions 2. Further, 2-(3,5-diamino-2,4,6-triazaphenyl)ethyl-2,4,8,10-tetraox similarly, to achieve excellent productivity, the compound(s) aspiro5.5undecane, ethylenediamine-tetraacetic acid, is/are preferably added after addition of the sulfur-containing alkali metal (Li, Na, K) salts of ethylenediamine-tetraacetic compound containing Sulfur having an oxidation number of acid, N,N'-disalicylidene-ethylenediamine, N,N'-disali 50 not less than +5 as a catalyst. In cases where the compound(s) cylidene-1,2-propylenediamine, N,N'-disalicylidene-N'-me is/are added at the beginning of the melt polymerization con thyl-dipropylenetriamine and 3-salicyloylamino-1,2,4-triaz ditions 2, the catalyst for Solid-phase polymerization is pref ole. Among these, at least one of aromatic amine compounds, erably added after the addition of the amine compound(s), alkylamine compounds having not less than 4 carbon atoms, alkali metal(s) and/or alkaline earth metal(s). In cases where and amine compounds having a pyrimidine skeleton is pref 55 the compound(s) is/are added at the stages of both the melt erably contained. polymerization conditions 1 and the melt polymerization Specific examples of the alkali metal compounds include conditions 2, the compound(s) is/are preferably added in an lithium compounds such as lithium isopropoxide, lithium amount of 0.001 to 1 part by weight at each stage and, in view chloride, lithium acetate, lithium lactate, lithium octoate, of achieving excellent productivity, the compound(s) is/are lithium stearate, lithium naphthenate, lithium t-butyl carbon 60 more preferably added in an amount of 0.01 to 0.5 part by ate, lithium Sulfate and lithium oxide; sodium compounds weight at each stage, still more preferably added in an amount Such as Sodium isopropoxide, Sodium chloride, sodium of 0.01 to 0.1 part by weight at each stage with respect to 100 acetate, sodium lactate, Sodium octoate, Sodium Stearate, parts by weight of the poly(lactic acid) resin. To obtain a Sodium naphthenate, Sodium t-butyl carbonate, Sodium Sul poly(lactic acid) resin having excellent hydrolysis resistance, fate and sodium oxide; and potassium compounds such as 65 the compound(s) may also be preferably added after comple potassium isopropoxide, potassium chloride, potassium tion of the solid-phase polymerization step. The method of acetate, potassium lactate, potassium octoate, potassium addition of the amine compound(s), alkali metal(s) and/or US 9,023,953 B2 23 24 alkaline earth metal(s) is not restricted, and examples of the 1.2 to 3 in view of the uniformity of the physical properties of method include a method wherein melt kneading is carried the polymer, and the ratio is more preferably 1.4 to 2.5. out at a temperature higher than the melting point of the The weight average molecular weight and the number aver poly(lactic acid) resin and a method wherein the age molecular weight mean the values of weight average compound(s) is/are dissolved in a solvent and the resulting 5 molecular weight and number average molecular weight in solution is mixed, followed by removal of the solvent. For terms of a poly(methyl methacrylate) standard as measured efficient production, the method wherein melt kneading is by gel permeation chromatography (GPC) using hexafluor carried out at a temperature higher than the melting point of oisopropanol as a solvent; the enthalpy of fusion AHm means the poly(lactic acid) resin is preferred. The method of melt the enthalpy of the melting peak upon temperature increase as kneading may be either a batch method or continuous 10 measured by differential scanning calorimetry (DSC); the method, and examples of the apparatus which may be used acid value Ameans the amount of terminal carboxyl groups as include single screw extruders, twin screw extruders, multi measured by neutralization titration with an alkaline solution; screw extruders, plastomill, kneaders and stirred tank reactors the lactide content means the content in the prepolymer as equipped with a pressure reducing device. For efficient uni measured by proton NMR; and the D-lactic acid content dand form kneading, a single screw extruder or twin screw extruder 15 the L-lactic acid content 1 mean the contents in the total lactic is preferably used. The temperature at which the amine com acid component as measured by liquid chromatography. pound(s), alkali metal(s) and/or alkaline earth metal(s) is/are To the poly(lactic acid) resin obtained by the production added is preferably a temperature of 180 to 250° C. and, to method, one or more of normal additives may be added as achieve excellent mechanical properties, a temperature of long as the product is not adversely affected. Examples of 190 to 230° C. is more preferred. The pressure at which the such additives include fillers (glass fibers, carbon fibers, amine compound(s), alkali metal(s) and/or alkaline earth metal fibers, natural fibers, organic fibers, glass flakes, glass metal(s) is/are added may be any of a reduced pressure, nor beads, ceramic fibers, ceramic beads, asbestos, wollastonite, mal pressure and increased pressure. To remove gas gener talc, clay, mica, sericite, Zeolite, bentonite, montmorillonite, ated during melt kneading, the pressure is preferably a synthetic mica, dolomite, kaolinite, silicic acid fine powder, reduced pressure. In terms of the atmospheric conditions 25 feldspar powder, potassium titanate, shirasu balloon, calcium during the melt kneading, the melt kneading may be carried carbonate, magnesium carbonate, barium sulfate, calcium out either in the air or under an atmosphere of an inert gas Such oxide, aluminum oxide, titanium oxide, aluminum silicate, as nitrogen. To reduce in the amount of gas generated during silicon oxide, plaster, novaculite, dawsonite, white clay and the melt kneading, the melt kneading is preferably carried out the like), ultraviolet absorbers (resorcinol, salicylate, benzo under an atmosphere of an inert gas. 30 triazole, benzophenone and the like), lubricants, releasing In cases where the mixing is carried out in a solvent, a agents (montanic acid and salts thereof, esters thereof and solvent that dissolves the polymer and monomers is used. half esters thereof, stearyl alcohol, stearamide, polyethylene Examples of the solvent which may be used include chloro wax and the like), coloring agents including dyes (nigrosine form, methylene chloride and acetonitrile. In cases where the and the like) and pigments (cadmium Sulfide, phthalocyanine solvent needs to be removed after the mixing, the method for 35 and the like), anti-coloring agents (phosphites, hypophosphi removing the Solvent is not restricted, and examples of the tes and the like), flame retardants (red phosphorus, phospho method which may be used include a method wherein the ric acid esters, brominated polystyrene, brominated polyphe Solvent is evaporated at room temperature and a method nylene ether, brominated polycarbonate, magnesium wherein the solvent is evaporated under reduced pressure at a hydroxide, melamine, cyanuric acid and salts thereof, and the temperature higher than the boiling point of the solvent. 40 like), electrically conducting agents or coloring agents (car The crystallized poly(lactic acid) prepolymer prepared has bon black and the like), tribological property improving a weight average molecular weight of 5,000 to 25,000, and the agents (graphite, fluorine resins and the like), nuclear agents weight average molecular weight is preferably 10,000 to (inorganic nucleating agents including talc, organic amide 20,000. The enthalpy of fusion AHm is 50 to 65 J/g, more compounds including ethylenebislauric acid amide, ethyl preferably 53 to 60. 45 enebis-12-dihydroxy Stearic acid amide and trimesic acid tri The acid value A mol/ton of the crystallized prepolymer cyclohexylamide, pigment nucleating agents including cop needs to satisfy (1) below, preferably satisfies (5) below, more per phthalocyanine and Pigment Yellow 110; organic preferably satisfies (6) below: carboxylic acid metal salts; phenylphosphonic acid Zinc, and the like) and antistatic agents. 450/(Mw/10,000-0.14):