JP5573129B2 - Process for producing polylactic acid block copolymer - Google Patents

Description

  The present invention relates to a method for efficiently producing a polylactic acid block copolymer having a high molecular weight, a high melting point, and forming a highly crystalline polylactic acid stereocomplex.

  Polylactic acid is a polymer that can be melt-molded with excellent transparency and has biodegradable characteristics, so that it can be decomposed in the natural environment and converted into carbon dioxide and water after use. Development as a functional plastic has been promoted. On the other hand, in recent years, the characteristics of carbon neutral made from renewable resources (biomass) originating from carbon dioxide and water have attracted more attention than biodegradable characteristics, and the environmentally low load that does not increase carbon dioxide in the global environment. Use as a material is expected. Furthermore, since lactic acid, which is a monomer of polylactic acid, has been produced at low cost by fermentation using microorganisms, it has been studied as an alternative material for general-purpose polymers made of petroleum plastics. However, polylactic acid has lower heat resistance and durability than petroleum-based plastics, and its crystallization speed is low, so it is inferior in productivity, and the range of practical use is greatly limited. .

  As one means for solving such problems, the use of a polylactic acid stereocomplex has attracted attention. The polylactic acid stereocomplex is formed by mixing optically active poly-L-lactic acid (hereinafter referred to as PLLA) and poly-D-lactic acid (hereinafter referred to as PDLA), and this melting point is the melting point of the polylactic acid homopolymer. The temperature reaches 220 ° C., which is 50 ° C. higher than 170 ° C. For this reason, application as a high melting point and highly crystalline fiber, film, and resin molded product is tried.

  Conventionally, a polylactic acid stereocomplex is formed by mixing PLLA and PDLA in a solution state or by heat-melting and mixing PLLA and PDLA. However, the solution mixing of PLLA and PDLA has a problem that the manufacturing process becomes complicated because the solvent needs to be volatilized after mixing, resulting in high cost of the polylactic acid stereocomplex. In addition, in the case of heat-melt mixing of PLLA and PDLA, it is necessary to mix at a temperature at which the polylactic acid stereocomplex is sufficiently melted. At such a temperature, the thermal decomposition reaction of polylactic acid occurs at the same time. In some cases, there was a problem that the physical properties deteriorated. Furthermore, when high molecular weight PLLA and PDLA are heated and melted and mixed, the melting point of the polylactic acid homopolymer does not disappear even if the mixing composition ratio is 50:50, so a material having both heat resistance and durability can be obtained. The current situation is not possible.

  On the other hand, a polylactic acid block copolymer composed of a PLLA segment and a PDLA segment has been disclosed as a technique for forming a stereo complex even in a high molecular weight (Patent Documents 1 to 3).

  In Patent Document 1, a mixture is prepared by melt-kneading PLLA and PDLA prepared by ring-opening polymerization or direct polycondensation under heating, and then a polylactic acid block copolymer is obtained by solid-phase polymerization of the mixture. It has gained. In this technique, it is necessary to heat a temperature equal to or higher than the melting point of the polylactic acid stereocomplex during melt-kneading, and the molecular weight reduction of the mixture becomes a problem during melt-kneading. Further, improvement in productivity has also been desired in that a long-time reaction is required in solid phase polymerization.

  In Patent Document 2, a polylactic acid stereocomplex mixture is prepared by mixing PLLA oligomer and PDLA oligomer in the vicinity of the melting point, and a polylactic acid block copolymer is prepared by solid-phase polymerization of the mixture. ing. In this technique, since the formation of the stereocomplex is not uniform, the obtained polylactic acid block copolymer also varies in crystal characteristics. In addition, there is a problem in productivity because a long-time reaction is required in solid phase polymerization.

  In Patent Document 3, PLLA and PDLA are mixed in the vicinity of the melting point, and solid-phase polymerization is performed in the presence of polylactic acid homocrystals to produce a polylactic acid block copolymer. Also in this technique, the formation of the stereo complex is controlled only by the kneading temperature, and since partial melting is observed during kneading, there are variations in the crystal characteristics of the kneaded product. Further, the polylactic acid block copolymer obtained by solid-phase polymerization of the kneaded product also has a problem that the crystal characteristics are not uniform.

JP 2003-238672-A JP 2004-26876 A JP 2006-307071 A

  An object of the present invention is to solve the problems of the prior art and provide a method for producing a polylactic acid block copolymer that forms a polylactic acid stereocomplex having a high molecular weight and a high melting point.

  The present invention employs the following means as a result of intensive studies to solve the above problems.

That is, the method for producing the polylactic acid block copolymer of the present invention is as follows.
1. A method of mixing poly-L-lactic acid and poly-D-lactic acid and subjecting the mixture to solid phase polymerization, wherein at least one of poly-L-lactic acid and poly-D-lactic acid to be mixed is represented by the following formula: A method for producing a polylactic acid block copolymer satisfying (1) and having crystals remaining upon mixing, wherein the mixed poly-L-lactic acid and / or poly-D-lactic acid is sheared A method for producing a polylactic acid block copolymer, which is obtained by treatment at a temperature selected from the range of melting point -50 ° C to melting point + 20 ° C under application or pressure.
(ΔHm−ΔHc)> 20 (J / g) (1)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g)
2. 2. The polylactic acid block copolymer according to 1, wherein the poly-L-lactic acid and / or poly-D-lactic acid to be mixed is obtained by applying shear at a shear rate of 10 to 400 / sec. Production method.
3. 2. The method for producing a polylactic acid block copolymer according to 1 , wherein the poly-L-lactic acid and / or poly-D-lactic acid to be mixed is obtained by applying a pressure of 0.05 to 10 MPa. .
4). The polylactic acid block according to any one of 1 to 3, wherein the poly-L-lactic acid and / or poly-D-lactic acid to be mixed is obtained by treatment for a treatment time of 0.1 to 10 minutes. A method for producing a copolymer.
5. The method for producing a polylactic acid block copolymer according to any one of 1 to 4, wherein the treatment is carried out by either a single screw extruder or a twin screw extruder.
6). The polylactic acid block co-polymerization according to any one of 1 to 5, wherein both poly-L-lactic acid and poly-D-lactic acid to be mixed satisfy the following formula (1), and crystals remain upon mixing: Manufacturing method of coalescence.
(ΔHm−ΔHc)> 20 (J / g) (1)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g)
7). 7. The method for producing a polylactic acid block copolymer according to any one of 1 to 6, wherein at least one of poly-L-lactic acid and poly-D-lactic acid to be mixed satisfies the following formula (2): .
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm]> 80 (2)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g)
8). 8. The method for producing a polylactic acid block copolymer according to any one of 1 to 7, wherein the crystallinity of the mixture comprising poly-L-lactic acid and poly-D-lactic acid at the time of mixing is 10% or more.
9. 9. The method for producing a polylactic acid block copolymer according to 8, wherein the temperature at the time of mixing is in the range of the melting point −50 ° C. to the melting point + 20 ° C. of the mixture.
10. 10. The method for producing a polylactic acid block copolymer according to 8 or 9, wherein mixing is performed under shearing or under pressure.
11. The method for producing a polylactic acid block copolymer according to any one of 1 to 10, wherein a ratio of crystallization based on crystallization of the mixture after mixing satisfies the following formula (2).
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm]> 80 (2)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g)
12 12. The method for producing a polylactic acid block copolymer according to 11, wherein the stereocomplex formation rate of the mixture after mixing is 80% or less.
13. The method for producing a polylactic acid block copolymer according to any one of 1 to 12, wherein the polylactic acid block copolymer obtained has a weight average molecular weight of 100,000 or more.

  According to the present invention, a polylactic acid block copolymer that forms a polylactic acid stereocomplex having a high molecular weight and a high melting point can be efficiently produced. Since this polylactic acid block copolymer has a high molecular weight and a high melting point, it can be suitably used in fields requiring heat resistance, which was difficult to use with polylactic acid homopolymers.

  Hereinafter, the present invention will be described in detail.

  In the present invention, the polylactic acid block copolymer is a polylactic acid block copolymer composed of a segment composed of L-lactic acid units and a segment composed of D-lactic acid units.

  Here, the segment composed of L-lactic acid units is a polymer mainly composed of L-lactic acid, and preferably contains 70 mol% or more of L-lactic acid units, and contains 90 mol% or more. More preferably, it is more preferably 95 mol% or more, and particularly preferably 98 mol% or more.

  Moreover, the segment which consists of D-lactic acid units is a polymer which has D-lactic acid as a main component, It is preferable to contain 70 mol% or more of D-lactic acid units, and it contains 90 mol% or more. More preferably, it is more preferably 95 mol% or more, and particularly preferably 98 mol% or more.

  In the present invention, the segment comprising L-lactic acid or D-lactic acid units may contain other component units as long as the performance of the resulting polylactic acid block copolymer is not impaired. Examples of component units other than L-lactic acid or D-lactic acid units include polycarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones, and the like. Specifically, succinic acid, adipic acid, sebacic acid, Polycarboxylic acids such as fumaric acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium sulfoisophthalic acid or their derivatives, ethylene glycol, propylene glycol, butane Ethylene oxide or propylene oxide was added to diol, pentanediol, hexanediol, octanediol, neopentyl glycol, glycerin, trimethylolpropane, pentaerythritol, trimethylolpropane or pentaerythritol Polyhydric alcohols, aromatic polyhydric alcohols obtained by addition reaction of ethylene oxide with bisphenol, polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol or their derivatives, glycolic acid, 3-hydroxybutyric acid, 4-hydroxy Hydroxycarboxylic acids such as butyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid, and glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and lactones such as δ-valerolactone.

The weight average molecular weight of the polylactic acid block copolymer obtained by the method of the present invention is not particularly limited, but is preferably 100,000 or more from the viewpoint of mechanical properties. 120,000 or more is more preferable, and 140,000 or more is particularly preferable in terms of moldability and mechanical properties. The weight average molecular weight is a value of weight average molecular weight in terms of standard polymethyl methacrylate as measured by gel permeation chromatography (GPC) using hexafluoroisopropanol or chloroform as a solvent. Moreover, it is preferable to obtain a polylactic acid block copolymer having a stereocomplex formation rate (Sc) of 50% or more, more preferably 70% or more, further preferably 75 to 100%, and more preferably 90 to 100%. % Is particularly preferred. Here, the stereocomplex formation rate is the ratio of the stereocomplex crystals in all the crystals in polylactic acid. Specifically, the amount of heat based on crystal melting of poly-L-lactic acid single crystal and poly-D-lactic acid single crystal measured by a differential scanning calorimeter (DSC) is ΔHl, and the amount of heat based on crystal melting of stereocomplex crystals. Can be calculated by the following equation (3).
Sc = ΔHh / (ΔHl + ΔHh) × 100 (3)

  Furthermore, in the present invention, the total number of segments consisting of L-lactic acid units and segments consisting of D-lactic acid units contained per molecule of the polylactic acid block copolymer is 3 or more, so that the high melting point polylactic acid It is preferable at the point from which the polylactic acid block copolymer which is easy to form a stereocomplex is obtained.

  In the present invention, the total weight ratio of the segment consisting of the L-lactic acid unit and the segment consisting of the D-lactic acid unit is preferably 90:10 to 10:90, and more preferably 75:25 to 25:75. More preferably, it is most preferably 60:40 to 40:60. When the weight ratio of the segments composed of L-lactic acid units is less than 10% by weight or more than 90% by weight, the increase in the melting point of the resulting polylactic acid block copolymer is reduced, forming a polylactic acid stereocomplex. It tends to be difficult to do.

(Polylactic acid production method)
In the present invention, the method for producing poly-L-lactic acid composed of L-lactic acid units and poly-D-lactic acid composed of D-lactic acid units is not particularly limited, and a general method for producing polylactic acid is used. Can be used. Specifically, using L-lactic acid or D-lactic acid as a raw material, L-lactide or D-lactide, which is a cyclic dimer, is once generated, and then ring-opening polymerization is performed. A one-step direct polymerization method in which a raw material is directly subjected to dehydration condensation in a solvent or a non-solvent is known, and any production method may be used.

  Here, poly-L-lactic acid is a polymer containing L-lactic acid as a main component and contains 70 mol% or more of L-lactic acid units, and 90 mol% or more. Is more preferably 95 mol% or more, and particularly preferably 98 mol% or more.

  Poly-D-lactic acid is a polymer containing D-lactic acid as a main component, contains 70 mol% or more of D-lactic acid units, and contains 90 mol% or more. More preferably, it is more preferably 95 mol% or more, and particularly preferably 98 mol% or more.

  The weight average molecular weight of poly-L-lactic acid or poly-D-lactic acid used in the present invention is preferably 100,000 or less, more preferably 70,000 or less, and particularly preferably 50,000 or less. The weight average molecular weight is preferably 5,000 or more, more preferably 10,000 or more.

  The amount of lactide and oligomer contained in poly-L-lactic acid or poly-D-lactic acid is preferably 5% or less, respectively. More preferably, it is 3% or less, and particularly preferably 1% or less. The amount of lactic acid contained in poly-L-lactic acid or poly-D-lactic acid is preferably 2% or less. More preferably, it is 1% or less, and particularly preferably 0.5% or less.

  Examples of the polymerization catalyst include a metal catalyst and an acid catalyst. Examples of the metal catalyst include tin compounds, titanium compounds, lead compounds, zinc compounds, cobalt compounds, iron compounds, lithium compounds, and rare earth compounds. The types of compounds include metal alkoxides, metal halogen compounds, organic carboxylates, Carbonates, sulfates, oxides and the like are preferable. Specifically, tin powder, tin (II) chloride, tin (IV) chloride, tin (II) bromide, tin (IV) bromide, ethoxy tin (II), t-butoxy tin (IV), isopropoxy Tin (IV), tin (II) acetate, tin (IV) acetate, tin (II) octylate, tin (II) laurate, tin (II) myristate, tin (II) palmitate, tin stearate (II) ), Tin (II) oleate, tin (II) linoleate, tin (II) acetylacetone, tin (II) oxalate, tin (II) lactate, tin (II) tartrate, tin (II) pyrophosphate, p- Phenol sulfonate tin (II), bis (methane sulfonate) tin (II), tin sulfate (II), tin oxide (II), tin oxide (IV), tin sulfide (II), tin sulfide (IV), oxidation Dimethyltin (IV), methylphenyltin (IV) oxide, dibuty oxide Tin (IV), dioctyl tin (IV) oxide, diphenyl tin (IV) oxide, tributyl tin oxide, triethyl tin hydroxide (IV), triphenyl tin hydroxide (IV), tributyl tin hydride, monobutyl tin (IV) Oxide, tetramethyltin (IV), tetraethyltin (IV), tetrabutyltin (IV), dibutyldiphenyltin (IV), tetraphenyltin (IV), tributyltin (IV) acetate, triisobutyltin (IV) acetate, Triphenyltin acetate (IV), dibutyltin diacetate, dibutyltin dioctanoate, dibutyltin (IV) dilaurate, dibutyltin (IV) maleate, dibutyltin bis (acetylacetonate), tributyltin chloride (IV), Dibutyltin dichloride, monobutyltin trichloride, dioctyltin dichloride, triphenyltin (IV) chloride, sulfide Examples thereof include tin compounds such as libutyltin, tributyltin sulfate, tin (II) trifluoromethanesulfonate, ammonium hexachlorotin (IV), dibutyltin sulfide, diphenyltin sulfide, triethyltin sulfate, and phthalocyanine tin (II). Also, titanium methoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide, titanium cyclohexyl, titanium phenoxide, titanium chloride, titanium diacetate, titanium triacetate, titanium tetraacetate, titanium (IV) oxide, etc. Titanium compounds, lead diisopropoxy (II), lead monochloride, lead acetate, lead (II) octylate, lead (II) isooctanoate, lead (II) isononanoate, lead (II) laurate, lead oleate (II), lead compounds such as lead (II) linoleate, lead naphthenate, lead (II) neodecanoate, lead oxide, lead (II) sulfate, zinc powder, methyl propoxy zinc, zinc chloride, zinc acetate, octylic acid Zinc (II), zinc naphthenate, zinc carbonate, zinc oxide, zinc sulfate and other zinc compounds, chloride Baltic, cobalt acetate, cobalt (II) octylate, cobalt (II) isooctanoate, cobalt (II) isononanoate, cobalt (II) laurate, cobalt (II) oleate, cobalt (II) linoleate, cobalt naphthenate , Cobalt compounds such as cobalt (II) neodecanoate, cobaltous carbonate, cobaltous sulfate, cobalt (II) oxide, iron (II) chloride, iron (II) acetate, iron (II) octylate, iron naphthenate Iron compounds such as iron carbonate (II), iron sulfate (II), iron oxide (II), propoxy lithium, lithium chloride, lithium acetate, lithium octylate, lithium naphthenate, lithium carbonate, dilithium sulfate, lithium oxide, etc. Lithium compounds, triisopropoxy europium (III), triisopropoxy neo (III), triisopropoxylantan, triisopropoxy samarium (III), triisopropoxy yttrium, isopropoxy yttrium, dysprosium chloride, europium chloride, lanthanum chloride, neodymium chloride, samarium chloride, yttrium chloride, dysprosium triacetate (III ), Europium triacetate (III), lanthanum acetate, neodymium triacetate, samarium acetate, yttrium triacetate, dysprosium carbonate (III), dysprosium carbonate (IV), europium carbonate (II), lanthanum carbonate, neodymium carbonate, samarium carbonate ( II), samarium carbonate (III), yttrium carbonate, dysprosium sulfate, europium (II) sulfate, lanthanum sulfate, neodymium sulfate, samarium sulfate, yttrium sulfate, yttrium dioxide Examples include rare earth compounds such as europium, lanthanum oxide, neodymium oxide, samarium (III) oxide, and yttrium oxide. Other potassium compounds such as potassium isopropoxide, potassium chloride, potassium acetate, potassium octylate, potassium naphthenate, tert-butyl potassium carbonate, potassium sulfate, potassium oxide, copper (II) diisopropoxide, copper chloride (II), copper acetate (II), copper octylate, copper naphthenate, copper sulfate (II), copper compounds such as dicopper carbonate, nickel chloride, nickel acetate, nickel octylate, nickel carbonate, nickel sulfate (II) Nickel compounds such as nickel oxide, tetraisopropoxyzirconium (IV), zirconium trichloride, zirconium acetate, zirconium octylate, zirconium naphthenate, zirconium carbonate (II), zirconium carbonate (IV), zirconium sulfate, zirconium oxide (II ) Zirconium etc. Compounds, antimony compounds such as triisopropoxyantimony, antimony fluoride (III), antimony fluoride (V), antimony acetate, antimony (III) oxide, magnesium, magnesium diisopropoxide, magnesium chloride, magnesium acetate, lactic acid Magnesium compounds such as magnesium, magnesium carbonate, magnesium sulfate and magnesium oxide, calcium compounds such as diisopropoxy calcium, calcium chloride, calcium acetate, calcium octylate, calcium naphthenate, calcium lactate and calcium sulfate, aluminum and aluminum isopropoxide Aluminum compounds such as aluminum chloride, aluminum acetate, aluminum octylate, aluminum sulfate, aluminum oxide, germanium, tetra Germanium compounds such as sopropoxygermane, germanium oxide (IV), triisopropoxymanganese (III), manganese trichloride, manganese acetate, manganese octylate (II), manganese naphthenate (II), manganese such as manganese sulfate Examples thereof include bismuth compounds such as compounds, bismuth (III) chloride, bismuth powder, bismuth oxide (III), bismuth acetate, bismuth octylate, and bismuth neodecanoate. Also, sodium stannate, magnesium stannate, potassium stannate, calcium stannate, manganese stannate, bismuth stannate, barium stannate, strontium stannate, sodium titanate, magnesium titanate, aluminum titanate, potassium titanate, Compounds composed of two or more metal elements such as calcium titanate, cobalt titanate, zinc titanate, manganese titanate, zirconium titanate, bismuth titanate, barium titanate and strontium titanate are also preferred. The acid catalyst may be a Bronsted acid as a proton donor, a Lewis acid as an electron pair acceptor, or an organic acid or an inorganic acid. Specifically, monocarboxylic acid compounds such as formic acid, acetic acid, propionic acid, heptanoic acid, octanoic acid, octylic acid, nonanoic acid, isononanoic acid, trifluoroacetic acid and trichloroacetic acid, oxalic acid, succinic acid, maleic acid, tartaric acid And dicarboxylic acid compounds such as malonic acid, tricarboxylic acid compounds such as citric acid and tricarivallic acid, benzenesulfonic acid, n-butylbenzenesulfonic acid, n-octylbenzenesulfonic acid, n-dodecylbenzenesulfonic acid, pentadecylbenzenesulfonic acid 2,5-dimethylbenzenesulfonic acid, 2,5-dibutylbenzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid , 5-amino-2 Methylbenzenesulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid, 2,4-dinitrobenzenesulfonic acid, p-chlorobenzenesulfonic acid, 2,5-dichlorobenzenesulfonic acid, p-phenol Sulfonic acid, cumene sulfonic acid, xylene sulfonic acid, o-cresol sulfonic acid, m-cresol sulfonic acid, p-cresol sulfonic acid, p-toluene sulfonic acid, 2-naphthalene sulfonic acid, 1-naphthalene sulfonic acid, isopropyl naphthalene sulfone Acid, dodecylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, 1,5-naphthalenedisulfonic acid, 2,7-naphthalenedisulfonic acid, 4,4-biphenyldisulfonic acid, anthraquinone-2-sulfonic acid, m- Benzene disulfonic acid, 2,5-diamino-1,3-benzenedisulfonic acid, aniline-2,4-disulfonic acid, anthraquinone-1,5-disulfonic acid, polystyrenesulfonic acid and other aromatic sulfonic acids, methanesulfonic acid, Aliphatic acids such as ethanesulfonic acid, 1-propanesulfonic acid, n-octylsulfonic acid, pentadecylsulfonic acid, trifluoromethanesulfonic acid, trichloromethanesulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid Sulfonic acid compounds such as alicyclic sulfonic acids such as sulfonic acid, cyclopentanesulfonic acid, cyclohexanesulfonic acid and camphorsulfonic acid, acidic amino acids such as aspartic acid and glutamic acid, ascorbic acid, retinoic acid, phosphoric acid, metaphosphoric acid, Phosphoric acid, hypochlorous Phosphoric acid, such as phosphoric acid, polyphosphoric acid, phosphoric acid monoesters such as monododecyl phosphate and monooctadecyl phosphate, phosphoric acid diesters such as didodecyl phosphate and dioctadecyl phosphate, phosphoric acid monoesters and phosphorous acid diesters Also included are compounds, boric acid, hydrochloric acid, sulfuric acid and the like. Further, the shape of the acid catalyst is not particularly limited, and any of a solid acid catalyst and a liquid acid catalyst may be used. For example, as the solid acid catalyst, acidic clay, kaolinite, bentonite, montmorillonite, talc, zirconium silicate and Natural minerals such as zeolite, oxides such as silica, alumina, titania and zirconia or oxide composites such as silica alumina, silica magnesia, silica boria, alumina boria, silica titania and silica zirconia, chlorinated alumina, fluorinated alumina, positive Examples thereof include ion exchange resins.

  In the present invention, when considering the molecular weight of the produced polylactic acid, tin compounds, titanium compounds, antimony compounds, rare earth compounds, and acid catalysts are preferred, and when considering the melting point of the produced polylactic acid, a tin compound, Titanium compounds and sulfonic acid compounds are more preferred. Furthermore, in consideration of the thermal stability of the polylactic acid produced, in the case of a metal catalyst, a tin-based organic carboxylate or a tin-based halogen compound is preferable, and in particular, tin (II) acetate, tin octylate (II ) And tin (II) chloride are more preferred, and in the case of an acid catalyst, mono- and disulfonic acid compounds are preferred, and methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, propanedisulfonic acid, and naphthalenedisulfonic acid are more preferred. Further, one type of catalyst may be used, or two or more types may be used in combination. However, in view of increasing the polymerization activity, it is preferable to use two or more types in combination, and coloring can be suppressed. In addition, it is preferable to use one or more selected from tin compounds and / or one or more selected from sulfonic acid compounds. Further, in terms of excellent productivity, tin (II) acetate and / or tin octylate ( II) and a combination of one or more of methanesulfonic acid, ethanesulfonic acid, propanedisulfonic acid, and naphthalenedisulfonic acid are more preferable. Tin (II) acetate and / or tin (II) octylate and methanesulfonic acid Further, the combined use of propanedisulfonic acid is more preferable.

  The addition amount of the polymerization catalyst is not particularly limited, and is preferably 0.001 part by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the raw material to be used (L-lactic acid, D-lactic acid, etc.). More preferred is 0.001 part by weight or more and 1 part by weight or less. If the amount of the catalyst is less than 0.001 part by weight, the effect of shortening the polymerization time is lowered, and if it exceeds 2 parts by weight, the molecular weight of the finally obtained polylactic acid block copolymer tends not to increase. In addition, when two or more types of catalysts are used in combination, the total addition amount is preferably within the above range, and one or more types selected from tin compounds and / or one or more types selected from sulfonic acid compounds are used in combination. In that case, it is preferable that the weight ratio of the tin compound and the sulfonic acid compound is 1: 1 to 1:30 in terms of maintaining high polymerization activity and suppressing coloration, and productivity. Is more preferably 1: 2 to 1:15.

  The addition timing of the polymerization catalyst is not particularly limited, but the acid catalyst is preferably added after dehydrating the raw material or the raw material in terms of excellent productivity, and the metal catalyst is added after dehydrating the raw material. It is preferable in view of increasing the polymerization activity.

(Polylactic acid treatment method)
Next, the process for treating polylactic acid will be described.

  In the present invention, the treatment of polylactic acid means that poly-L-lactic acid and poly-D-lactic acid are mixed, and the mixture is solid-phase polymerized to produce a polylactic acid block copolymer. This is a treatment for crystallizing at least one of L-lactic acid and poly-D-lactic acid.

In the present invention, it is important that at least one of the treated poly-L-lactic acid and poly-D-lactic acid satisfies the following formula (1).
(ΔHm−ΔHc)> 20 (J / g) (1)

  The value of (ΔHm−ΔHc) is preferably greater than 30 J / g, and particularly preferably greater than 40 J / g. Moreover, it is preferable that both poly-L-lactic acid and poly-D-lactic acid to be mixed satisfy the formula (1), preferably more than 30 J / g, particularly preferably more than 40 J / g.

  Here, ΔHm is the amount of heat (J / g) based on crystal melting when measured with a differential scanning calorimeter (DSC), and ΔHc is the amount of heat (J / g) based on crystallization at elevated temperature.

  Here, at least one of poly-L-lactic acid and poly-D-lactic acid to be mixed satisfies the formula (1), which means that either one, preferably both are crystallized. Yes.

It is also important that at least one of poly-L-lactic acid and poly-D-lactic acid to be mixed satisfies the following formula (2).
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm]> 80 (2)

  The proportion of crystallization is preferably greater than 85%, particularly preferably greater than 90%. Further, it is preferable that both poly-L-lactic acid and poly-D-lactic acid to be mixed satisfy the formula (2), the crystallization ratio is more preferably greater than 85%, and particularly preferably greater than 90%. .

  The molecular weight of poly-L-lactic acid or poly-D-lactic acid used in the present invention is preferably in the range of weight average molecular weight (Mw) of 5,000 to 100,000, and in the range of 7,000 to 80,000. It is more preferable that Further, the weight average molecular weight is preferably in the range of 10,000 to 60,000 from the relationship between the crystallinity of the obtained crystallized poly-L-lactic acid or poly-D-lactic acid and fluidity. When the weight average molecular weight is less than 5,000, the mechanical strength is low, which is not preferable. When the weight average molecular weight exceeds 100,000, the fluidity is low, particularly when the crystallinity is 10% or more. Is not preferable because it is extremely low. Further, when low molecular weight poly-L-lactic acid or poly-D-lactic acid is used, there is a problem in melt processability such as easy draw-down because the melt viscosity is usually low. The weight average molecular weight of poly-L-lactic acid or poly-D-lactic acid is measured by using hexafluoroisopropanol or chloroform as a solvent as a weight average molecular weight in terms of standard polymethyl methacrylate measured by gel permeation chromatography (GPC). be able to.

  With respect to the method for treating poly-L-lactic acid and poly-D-lactic acid according to the present invention, for example, a method of holding at a crystallization temperature in a gas phase or a liquid phase, poly-L-lactic acid and poly-D-lactic acid A method of volatilizing a solvent from a solution mixture, a method of retaining molten poly-L-lactic acid and poly-D-lactic acid in a melting machine having a melting point of −50 ° C. to a melting point + 20 ° C. while applying shear, and a molten poly- Examples thereof include a method of retaining L-lactic acid and poly-D-lactic acid while applying pressure in a melting machine having a melting point of −50 ° C. to a melting point + 20 ° C. Among them, from the viewpoint of easy operation and continuous supply to the process of mixing the treated poly-L-lactic acid and poly-D-lactic acid, molten poly-L-lactic acid and poly-D-lactic acid are used. A method of staying while applying shear or pressure in the melting machine is preferable. The melting machine at this time is not limited as long as shearing or pressure can be applied, and a polymerization can, a kneader, a Banbury mixer, a single screw extruder, a twin screw extruder, an injection molding machine, and the like can be used. They are a screw extruder and a twin screw extruder.

  The treatment temperature is preferably in the range of melting point −50 ° C. to melting point + 20 ° C. of poly-L-lactic acid and poly-D-lactic acid to be mixed. A more preferable range of the processing temperature is a melting point of −40 ° C. to a melting point, and a particularly preferable temperature range is a melting point of −30 ° C. to a melting point of −5 ° C. The temperature of the melting machine is usually set to a melting point + 20 ° C. or higher in order to melt the resin and develop good fluidity. However, if processing is performed at a temperature exceeding the melting point + 20 ° C., if crystals are generated, However, it is not preferred because it will be re-melted, and when it is crystallized by treatment at a melting point of -50 ° C. or lower, the fluidity is remarkably lowered. Here, the melting point is the crystal melting temperature when the temperature is raised from 30 ° C. to 240 ° C. at a rate of temperature rise of 20 ° C./minute using differential thermal scanning measurement.

  Moreover, it is preferable that processing time is 0.1 to 10 minutes, More preferably, it is 0.3 to 5 minutes, Most preferably, it is the range of 0.5 to 3 minutes. When the treatment time is 0.1 minutes or less, crystallization is insufficient, which is not preferable. When the treatment time is longer than 10 minutes, thermal decomposition is easily caused by the treatment, which is not preferable.

  By applying shear during the treatment, the molecules of the molten resin tend to be oriented, and as a result, the crystallization rate can be remarkably increased. The shear rate at this time is preferably in the range of 10 to 400 / second. A shear rate of less than 10 / sec is not preferred because the crystallization rate is reduced. On the other hand, when the shear rate exceeds 400 / sec, the resin temperature rises due to shear heat generation, and thermal decomposition tends to occur, which is not preferable.

  Even when a pressure is applied, crystallization tends to be promoted, and particularly in the range of 0.05 to 10 MPa, crystallized polylactic acid having both good fluidity and crystallinity can be obtained, which is preferable. When the pressure is less than 0.05 MPa and 10 MPa or more, the crystallization rate is low, which is not preferable.

  Furthermore, it is particularly preferable to perform treatment by simultaneously applying a shear rate of 10 to 400 / sec and a pressure of 0.05 to 10 MPa because the crystallization rate becomes higher.

(Polylactic acid mixing method)
Next, the process of mixing poly-L-lactic acid and poly-D-lactic acid will be described.
As a method of mixing poly-L-lactic acid and poly-D-lactic acid, poly-L-lactic acid and poly-D-lactic acid treated as described above are changed from poly-L-lactic acid and poly-D-lactic acid. The method of mixing so that the crystal | crystallization of this mixture may remain can be mentioned. Specifically, it is preferable to mix so that the crystallinity of the mixture composed of poly-L-lactic acid and poly-D-lactic acid is 10% or more. Regarding the degree of crystallinity, after freezing the crystal structure by cooling a mixture of poly-L-lactic acid and poly-D-lactic acid in an ice bath, wide-angle X-ray diffraction measurement was performed, and the halo region and crystal of the amorphous part were measured. It can be measured from the area ratio of the diffraction peak region of the part. Moreover, since the polymer turbidity in the melting machine changes with crystallization, crystallization can also be judged from the turbidity.

Specific examples of the mixing method include a method in which the treated poly-L-lactic acid and poly-D-lactic acid are mixed by a batch method or a continuous method. Of poly-L-lactic acid and poly-D-lactic acid in a melting machine having a melting point of −50 ° C. to melting point + 20 ° C. of polylactic acid having a lower melting point out of poly-L-lactic acid and poly-D-lactic acid. The method of staying while applying and the poly-L-lactic acid and poly-D-lactic acid in the molten state are melted at a melting point of polylactic acid having a lower melting point of poly-L-lactic acid and poly-D-lactic acid from −50 ° C. In particular, the method of staying while applying pressure in a melting point + 20 ° C. melter can control the crystallization ratio and stereocomplex formation rate of the mixture of poly-L-lactic acid and poly-D-lactic acid after mixing. preferable. The ratio of crystallization of the mixture of poly-L-lactic acid and poly-D-lactic acid after mixing here preferably satisfies the following formula (2).
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm]> 80 (2)

Moreover, the said stereocomplex formation rate is the ratio for which the stereocomplex crystal accounts in all the crystals in polylactic acid. Specifically, the amount of heat based on crystal melting of poly-L-lactic acid single crystal and poly-D-lactic acid single crystal measured by a differential scanning calorimeter (DSC) is ΔHl, and the amount of heat based on crystal melting of stereocomplex crystals. Can be calculated by the following equation (3).
Sc = ΔHh / (ΔHl + ΔHh) × 100 (3)

  The stereocomplex formation rate (Sc) can be calculated from the ratio of the polylactic acid single crystal and the stereocomplex crystal measured by X-ray diffraction, but in the present invention, from the crystal melting calorimetry measured by the DSC described above. Use the calculated value.

  In the present invention, it is important that the stereocomplex formation rate of the mixture after mixing is 80% or less. More preferably, it is 60% or less, further preferably 10 to 55%, and most preferably 20 to 45%.

  The apparatus used in the mixing step is not particularly limited, and examples thereof include a single-screw extruder, a twin-screw extruder, a plast mill, a kneader, and a stirred tank reactor equipped with a pressure reducing device. It is preferable to use a single screw extruder or a twin screw extruder.

  About the temperature conditions to mix, the range of melting | fusing point-50 degreeC-melting | fusing point +20 degreeC of the mixture of poly-L-lactic acid and poly-D-lactic acid is preferable. A more preferable range of the mixing temperature is a melting point of −40 ° C. to a melting point, and a particularly preferable temperature range is a melting point of −30 ° C. to a melting point of −5 ° C. The temperature of the melting machine is usually set to a melting point + 20 ° C. or higher in order to melt the resin and develop good fluidity. However, if processing is performed at a temperature exceeding the melting point + 20 ° C., if crystals are generated, However, it is not preferred because it will be re-melted, and when it is crystallized by treatment at a melting point of -50 ° C. or lower, the fluidity is remarkably lowered. Here, the melting point refers to a crystal melting temperature when the temperature is raised from 30 ° C. to 240 ° C. at a rate of temperature rise of 20 ° C./min using a differential scanning calorimeter (DSC).

  The pressure condition for mixing is not particularly limited, and may be any condition under an air atmosphere or an inert gas atmosphere such as nitrogen.

  In the mixing step, the mixing weight ratio of poly-L-lactic acid composed of L-lactic acid units and poly-D-lactic acid composed of D-lactic acid units is preferably 90:10 to 10:90, and more preferably 80:20. -20: 80 is preferable, 70: 30-30: 70 is more preferable, and 60: 40-40: 60 is particularly preferable. When the weight ratio of the poly-L-lactic acid composed of L-lactic acid units is less than 10% by weight or more than 90% by weight, the increase in the melting point of the finally obtained polylactic acid block copolymer becomes small. This tends to make it difficult to form a polylactic acid stereocomplex.

  In this mixing step, a catalyst can be further added in order to efficiently proceed with the next solid phase polymerization.

  The addition amount of the catalyst is not particularly limited, and is preferably 0.001 part by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the mixture of poly-L-lactic acid and poly-D-lactic acid. 001 parts by weight or more and 1 part by weight or less are more preferable. If the amount of the catalyst is less than 0.001 part by weight, the effect of shortening the reaction time of the solid phase polymerization is reduced, and if it exceeds 2 parts by weight, the molecular weight of the finally obtained polylactic acid block copolymer tends not to increase.

  Further, in the mixing step, poly-L-lactic acid (segment consisting of L-lactic acid units) composed of L-lactic acid units and poly-D composed of D-lactic acid units in the finally obtained polylactic acid block copolymer. -In order to improve the alternation with lactic acid (segment consisting of D-lactic acid units), a polyfunctional compound may be mixed.

  The polyfunctional compound used here is not particularly limited, and polyvalent carboxylic acid anhydride, polyvalent carboxylic acid halide, polyvalent carboxylic acid, polyvalent isocyanate, polyvalent amine, polyhydric alcohol and Examples include polyhydric epoxy compounds, specifically 1,2-cyclohexanedicarboxylic acid anhydride, succinic acid anhydride, phthalic acid anhydride, trimellitic acid anhydride, 1,8-naphthalenedicarboxylic acid anhydride, Polycarboxylic acid anhydrides such as pyromellitic acid anhydride, polycarboxylic acid halides such as isophthalic acid chloride, terephthalic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, succinic acid, adipic acid, sebacic acid, fumaric acid , Polycarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hexamethylene Polyisocyanates such as isocyanate, 4,4'-diphenylmethane diisocyanate, toluene-2,4-diisocyanate, polyvalent amines such as ethylenediamine, hexanediamine, diethylenetriamine, ethylene glycol, propylene glycol, butanediol, hexanediol, glycerin, tri Polyhydric alcohols such as methylolpropane and pentaerythritol, terephthalic acid diglycidyl ester, naphthalene dicarboxylic acid diglycidyl ester, trimellitic acid triglycidyl ester, pyromellitic acid tetraglycidyl ester, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether , Cyclohexanedimethanol diglycidyl ether, glycerol triglycidyl Ether, trimethylolpropane triglycidyl ether, polyvalent epoxy compounds such as pentaerythritol polyglycidyl ether and the like. Of these, polyvalent carboxylic acid anhydrides, polyvalent isocyanates, polyhydric alcohols and polyvalent epoxy compounds are preferred, and polyvalent carboxylic acid anhydrides, polyvalent isocyanates and polyvalent epoxy compounds are particularly preferred. Moreover, these can be used combining 1 type (s) or 2 or more types.

  The mixing amount of the polyfunctional compound is not particularly limited, and is preferably 0.01 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight in total of poly-L-lactic acid and poly-D-lactic acid. Further, it is more preferably 0.1 parts by weight or more and 10 parts by weight or less. If the amount of the polyfunctional compound added is too large or too small, the effect of using the polyfunctional compound tends to be small.

  Further, when a polyfunctional compound is used, a catalyst may be added to promote the reaction of poly-L-lactic acid and poly-D-lactic acid with the polyfunctional compound. Examples of the catalyst include sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, potassium carbonate, lithium carbonate, sodium acetate, potassium acetate, lithium acetate, stearic acid. Sodium, potassium stearate, lithium stearate, sodium borohydride, lithium borohydride, sodium phenyl borohydride, sodium benzoate, potassium benzoate, lithium benzoate, disodium hydrogen phosphate, dihydrogen phosphate Alkali metal compounds such as potassium, dilithium hydrogen phosphate, disodium salt of bisphenol A, dipotassium salt, dilithium salt, sodium salt of phenol, potassium salt, lithium salt, cesium salt, calcium hydroxide , Hydroxide burr Alkaline earth such as sodium hydroxide, magnesium hydroxide, strontium hydroxide, calcium bicarbonate, barium carbonate, magnesium carbonate, strontium carbonate, calcium acetate, barium acetate, magnesium acetate, strontium acetate, calcium stearate, magnesium stearate, strontium stearate Metal compounds, triethylamine, tributylamine, trihexylamine, triamylamine, triethanolamine, dimethylaminoethanol, triethylenediamine, dimethylphenylamine, dimethylbenzylamine, 2- (dimethylaminomethyl) phenol, dimethylaniline, pyridine, picoline , Tertiary amines such as 1,8-diazabicyclo (5,4,0) undecene-7, 2-methylimidazole, 2-ethyl Imidazole compounds such as midazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, 4-phenyl-2-methylimidazole, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium bromide, trimethylbenzylammonium chloride, triethylbenzyl Quaternary ammonium salts such as ammonium chloride, tripropylbenzylammonium chloride, N-methylpyridinium chloride, phosphine compounds such as trimethylphosphine, triethylphosphine, tributylphosphine, trioctylphosphine, tetramethylphosphonium bromide, tetrabutylphosphonium bromide, tetra Phenylphosphonium bromide, ethylto Phosphonium salts such as triphenyl phosphonium bromide, triphenyl benzyl phosphonium bromide, trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl Phosphate esters such as phosphate, octyl diphenyl phosphate, tri (p-hydroxy) phenyl phosphate, tri (p-methoxy) phenyl phosphate, oxalic acid, p-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, dodecylbenzenesulfonic acid, etc. Organic acids and Lewis acids such as boron trifluoride, aluminum tetrachloride, titanium tetrachloride, tin tetrachloride And the like, which may be used alone or in combination of two or more.

  The addition amount of the catalyst is not particularly limited, and is preferably 0.001 part by weight or more and 1 part by weight or less with respect to 100 parts by weight of the total of poly-L-lactic acid and poly-D-lactic acid. If the amount of the catalyst is less than 0.001 part by weight, the effect of adding the catalyst is insufficient. Conversely, if the amount exceeds 1 part by weight, the molecular weight of the finally obtained polylactic acid block copolymer tends not to increase. Arise.

  The molecular weight of the mixture of poly-L-lactic acid and poly-D-lactic acid after mixing is preferably in the range of weight average molecular weight (Mw) of 5,000 to 100,000. The range of 7,000 to 80,000 is more preferable, and the range of 10,000 to 60,000 is particularly preferable.

  The amount of lactide and oligomer contained in poly-L-lactic acid or poly-D-lactic acid is preferably 5% or less, respectively. More preferably, it is 3% or less, and particularly preferably 1% or less. The amount of lactic acid contained in poly-L-lactic acid or poly-D-lactic acid is preferably 2% or less. More preferably, it is 1% or less, and particularly preferably 0.5% or less.

(Solid phase polymerization)
Next, a process for solid-phase polymerization of a mixture of poly-L-lactic acid and poly-D-lactic acid at a temperature lower than its melting point will be described.

  When performing this solid phase polymerization step, the shape of the mixture of poly-L-lactic acid and poly-D-lactic acid is not particularly limited, and any of a lump, a film, a pellet, and a powder may be used. From the viewpoint of efficiently proceeding with solid phase polymerization, it is preferable to use pellets or powder. Examples of the method for forming pellets include a method in which the mixture is extruded into a strand shape and pelletized. Moreover, as a method of making into powder, the method of grind | pulverizing using grinders, such as a mixer, a blender, a ball mill, and a hammer mill, is mentioned. The method for carrying out this solid phase polymerization step is not particularly limited, and may be a batch method or a continuous method. The reaction vessel may be a stirred tank reactor, a mixer reactor, a tower reactor, or the like. These reactors can be used in combination of two or more.

  When this solid phase polymerization step is carried out, it is preferable that a mixture of poly-L-lactic acid and poly-D-lactic acid is crystallized. In the present invention, when the mixture obtained in the mixing step of poly-L-lactic acid and poly-D-lactic acid is in a crystallized state, poly-L-lactic acid and poly-D are used when the solid phase polymerization step is performed. -Crystallization of a mixture of lactic acid is not particularly necessary, but the efficiency of solid-phase polymerization can be further increased by performing crystallization.

  The method for crystallization is not particularly limited, and a known method can be used. For example, a method of holding at a crystallization temperature in a gas phase or a liquid phase, a method of cooling and solidifying a molten mixture of poly-L-lactic acid and poly-D-lactic acid while performing an operation of stretching or shearing, etc. From the viewpoint of easy operation, a method of holding at the crystallization temperature in the gas phase or liquid phase is preferable.

  The crystallization temperature here is particularly higher as long as it is higher than the glass transition temperature and is lower than the melting point of polylactic acid having a low melting point among poly-L-lactic acid or poly-D-lactic acid mixed as described above. Although not limited, it is more preferable that the temperature is within the range of the temperature-rise crystallization temperature and the temperature-fall crystallization temperature measured in advance by a differential scanning calorimeter (DSC).

  When crystallizing, any of reduced pressure, normal pressure, and increased pressure may be used.

  Further, the time for crystallization is not particularly limited, but it is sufficiently crystallized within 3 hours, and preferably within 2 hours.

  The temperature condition for carrying out this solid phase polymerization step is a temperature not higher than the melting point of the mixture of poly-L-lactic acid and poly-D-lactic acid, and specifically, preferably 100 ° C. or higher and 220 ° C. or lower. Further, from the viewpoint of further promoting solid phase polymerization, it is more preferably 110 ° C. or more and 210 ° C. or less, and most preferably 120 ° C. or more and 200 ° C. or less.

  In order to shorten the reaction time of solid phase polymerization, it is preferable to raise the temperature stepwise or continuously as the reaction proceeds. As temperature conditions when the temperature is raised stepwise during solid phase polymerization, the first stage is 130 to 155 ° C. for 1 to 15 hours, the second stage is 160 to 175 ° C. for 1 to 15 hours, and the third stage is 180 degrees. It is preferable to raise the temperature at ~ 200 ° C for 10 to 30 hours. Furthermore, as the first step, 140 to 155 ° C for 2 to 12 hours, as the second step, 165 to 175 ° C for 2 to 12 hours, as the third step It is more preferable to raise the temperature at 185 to 195 ° C. for 15 to 25 hours. As a temperature condition when the temperature is continuously increased during solid-phase polymerization, it is preferable that the temperature is continuously increased from an initial temperature of 130 to 150 ° C. to 185 to 195 ° C. at a rate of 1 to 5 ° C./min. Further, combining stepwise temperature rise and continuous temperature rise is also preferable from the viewpoint of efficiently proceeding with solid phase polymerization.

  Moreover, when implementing this solid-phase polymerization process, it is preferable to carry out under vacuum or inert gas flow, such as dry nitrogen.

(Polylactic acid block copolymer)
By employing the production method of the present invention, it is preferable to obtain a polylactic acid block copolymer having a weight average molecular weight of 100,000 or more, more preferably 120,000 or more, and further preferably 140,000 or more. . Moreover, it is preferable to obtain a polylactic acid block copolymer having a stereocomplex formation rate (Sc) of 50% or more, more preferably 70% or more, further preferably 75 to 100%, and more preferably 90 to 100%. % Is particularly preferred.

  In the polylactic acid block copolymer obtained by the production method of the present invention, ordinary additives such as fillers (glass fiber, carbon fiber, metal fiber, natural fiber, organic fiber, and organic fiber) are used as long as the object of the present invention is not impaired. Fibers, glass flakes, glass beads, ceramic fibers, ceramic beads, asbestos, wollastonite, talc, clay, mica, sericite, zeolite, bentonite, montmorillonite, synthetic mica, dolomite, kaolin, fine silicic acid, feldspar powder, titanic acid Potassium, shirasu balloon, calcium carbonate, magnesium carbonate, barium sulfate, calcium oxide, aluminum oxide, titanium oxide, aluminum silicate, silicon oxide, gypsum, novaculite, dosonite or clay, ultraviolet absorbers (resorcinol, salicylate, base) Zotriazole, benzophenone, etc.), heat stabilizers (hindered phenols, hydroquinones, phosphites and their substitutes, etc.), lubricants, mold release agents (montanic acid and its salts, esters thereof, half esters, stearyl alcohol, Colorants including stearamide and polyethylene wax), dyes (such as nigrosine) and pigments (such as cadmium sulfide, phthalocyanine), anti-coloring agents (such as phosphite, hypophosphite), flame retardants (red phosphorus, phosphoric acid) Esters, brominated polystyrenes, brominated polyphenylene ethers, brominated polycarbonates, magnesium hydroxide, melamine and cyanuric acid or salts thereof, silicon compounds, etc., conductive agents or colorants (carbon black, etc.), slidability improvers (graphite) , Fluorine resin ), Crystal nucleating agents (inorganic nucleating agents such as talc, organic amide compounds such as ethylene bislauric acid amide, ethylene bis-12-dihydroxystearic acid amide and trimesic acid tricyclohexyl amide, copper phthalocyanine and pigment yellow 110) 1 type or 2 types or more of pigment type nucleating agent, organic carboxylic acid metal salt, zinc phenylphosphonate, etc.) and antistatic agent can be added.

  In addition, the polylactic acid block copolymer obtained by the production method of the present invention includes other thermoplastic resins (for example, polyethylene, polypropylene, acrylic resin, polyamide, polyphenylene sulfide resin, as long as the object of the present invention is not impaired). Polyether ether ketone resin, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyetherimide, etc.) or thermosetting resin (eg phenol resin, melamine resin, polyester resin, silicone resin, epoxy resin, etc.) or soft thermoplastic Resin (eg, ethylene / glycidyl methacrylate copolymer, polyester elastomer, polyamide elastomer, ethylene / propylene terpolymer, ethylene / butene-1 copolymer, etc.) It may further contain one or more.

  The polylactic acid block copolymer obtained by the production method of the present invention has a characteristic that it easily forms a high-melting polylactic acid stereocomplex even after it is once melted and solidified when it is processed into a molded product.

  The polylactic acid block copolymer obtained by the production method of the present invention can be widely used as a molded product. Molded products include, for example, films (non-stretched, uniaxially stretched, biaxially stretched), sheets, fibers / clothes, non-woven fabrics, injection molded products, extruded molded products, vacuum / pressure molded products, blow molded products, and other materials. These molded products include agricultural materials, horticultural materials, fishery materials, civil engineering / architectural materials, stationery, medical supplies, automotive parts, electrical / electronic components, optical films, and others. It is useful as an application.

  Hereinafter, the present invention will be described specifically by way of examples. Here, the number of parts in the examples indicates parts by weight. The physical properties were measured by the following method.

(1) Weight average molecular weight The weight average molecular weight is a standard polymethyl methacrylate conversion value measured by gel permeation chromatography (GPC). GPC measurement was performed using a WATERS differential refractometer WATERS410 as a detector, a WATERS MODEL510 as a pump, and a column in which Shodex GPC HFIP-806M and Shodex GPC HFIP-LG were connected in series. The measurement conditions were a flow rate of 0.5 mL / min, hexafluoroisopropanol was used as a solvent, and 0.1 mL of a solution having a sample concentration of 1 mg / mL was injected.

(2) Thermal characteristics The melting point, heat of fusion, crystallization temperature, and heat of crystallization were measured by a differential scanning calorimeter (DSC) from Perkin Elmer. A 5 mg sample was heated from 30 ° C. to 240 ° C. at a temperature rising rate of 20 ° C./min in a nitrogen atmosphere, and the resulting crystallization enthalpy (ΔHc) and crystal melting enthalpy (ΔHm) were measured. The ratio of crystallization was calculated from the following formula (4).
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm] (4)

(3) Polymer turbidity The turbidity of the polymer visually observed from the extruder vent port was judged according to the following criteria. In addition, it has shown that crystallization is progressing, so that turbidity is large.
A: It is white opaque and the screw surface cannot be seen at all.
B: Although it is white and turbid, the surface of the screw is visible.
C: Transparent and the screw surface of the extruder can be clearly seen.

(4) Crystallinity After freezing the crystal structure by cooling a polymer having a temperature selected from the range of melting point −50 ° C. to melting point + 20 ° C. in an ice bath, wide-angle X-ray diffraction measurement was performed, It was measured from the area ratio of the diffraction peak region between the halo region and the crystal part.

(5) Stereo complex formation rate in the mixture (Sc)
The stereo complex formation rate (Sc) was calculated from the following formula (3).
Sc = ΔHh / (ΔHl + ΔHh) × 100 (3)
However, the heat quantity based on the crystal melting of the poly-L-lactic acid single crystal and the poly-D-lactic acid single crystal that appears at 150 ° C. or higher and lower than 190 ° C. when the temperature of the differential scanning calorimeter (DSC) is raised is ΔH1, 190 ° C. or higher and 250 ° C. Let ΔHh be the amount of heat based on crystal melting of the stereocomplex crystal that appears below.

(6) Stereo complex formation rate in polymer (Sc)
The stereo complex formation rate (Sc) was calculated from the following formula (3).
Sc = ΔHh / (ΔHl + ΔHh) × 100 (3)

  However, the amount of heat based on the crystal melting of the poly-L-lactic acid single crystal and the poly-D-lactic acid single crystal that appears at 150 ° C. or higher and lower than 190 ° C. at the second temperature rise of the differential scanning calorimeter (DSC) is ΔH1, 190 ° The amount of heat based on the crystal melting of the stereocomplex crystal appearing at a temperature lower than 250 ° C. is ΔHh.

[Reference Example 1]
In a reaction vessel equipped with a stirrer and a reflux device, 50 parts of a 90% L-lactic acid aqueous solution was placed, the temperature was adjusted to 150 ° C., and the reaction was carried out for 3.5 hours while gradually reducing the pressure to distill off water. Thereafter, the pressure was increased to normal pressure in a nitrogen atmosphere, 0.05 parts of tin (II) acetate was added, and then a polymerization reaction was performed for 7 hours while gradually reducing pressure to 170 Pa at 13 ° C. to obtain poly-L-lactic acid ( PLA1) was obtained. PLA1 had a weight average molecular weight of 18,000 and a melting point of 149 ° C.

[Reference Example 2]
The PLA 1 obtained in Reference Example 1 was subjected to crystallization treatment at 110 ° C. for 1 hour in a nitrogen atmosphere, and then a solid phase under a pressure of 60 Pa for 3 hours at 140 ° C., 3 hours at 150 ° C., and 6 hours at 160 ° C. Polymerization was performed to obtain poly-L-lactic acid (PLA2). PLA2 had a weight average molecular weight of 52,000 and a melting point of 160 ° C.

[Reference Example 3]
The PLA 1 obtained in Reference Example 1 was subjected to crystallization treatment at 110 ° C. for 1 hour in a nitrogen atmosphere, and then solid phase under a pressure of 60 Pa for 3 hours at 140 ° C., 3 hours at 150 ° C., and 9 hours at 160 ° C. Polymerization was performed to obtain poly-L-lactic acid (PLA3). PLA3 had a weight average molecular weight of 84,000 and a melting point of 170 ° C.

[Reference Example 4]
In a reaction vessel equipped with a stirrer and a reflux device, 50 parts of a 90% D-lactic acid aqueous solution was put, the temperature was raised to 150 ° C., and the mixture was reacted for 3.5 hours while gradually reducing the pressure to distill off water. Thereafter, the pressure was increased to normal pressure in a nitrogen atmosphere, 0.05 parts of tin (II) acetate was added, and then a polymerization reaction was performed for 7 hours while gradually reducing the pressure to 170 Pa at 13 ° C. to obtain poly-D-lactic acid ( PDA1) was obtained. PDA1 had a weight average molecular weight of 15,000 and a melting point of 148 ° C.

[Reference Example 5]
The PDA 1 obtained in Reference Example 4 was crystallized at 110 ° C. for 1 hour in a nitrogen atmosphere, and then solid-phased at a pressure of 60 Pa for 3 hours at 140 ° C., 3 hours at 150 ° C., and 6 hours at 160 ° C. Polymerization was performed to obtain poly-D-lactic acid (PDA2). PDA2 had a weight average molecular weight of 49,000 and a melting point of 158 ° C.

[Reference Example 6]
The PDA 1 obtained in Reference Example 4 was crystallized at 110 ° C. for 1 hour in a nitrogen atmosphere, and then solid-phased at a pressure of 60 Pa for 3 hours at 140 ° C., 3 hours at 150 ° C., and 9 hours at 160 ° C. Polymerization was performed to obtain poly-D-lactic acid (PDA3). PDA3 had a weight average molecular weight of 81,000 and a melting point of 167 ° C.

(Examples 1-14, Comparative Examples 1-3)
(1) Process for treating poly-L-lactic acid and poly-D-lactic acid As shown in Tables 1 and 2, poly-L-lactic acid was mixed with TEX30 type twin screw extruder (L / D manufactured by Nippon Steel Works). = 45.5), and treatment by shear crystallization was performed. The twin screw extruder was provided with a plasticized portion set at a temperature of 180 ° C. at a portion of L / D = 10 from the resin supply port, and then provided with a crystallization portion set at the temperature shown in Tables 1 and 2. . The screw element of the crystallization part was equipped with a kneading disk to provide a screw capable of imparting shear.
On the other hand, poly-D-lactic acid was crystallized by heating in a nitrogen atmosphere. The treatment temperature and time at this time are as shown in Tables 1 and 2.

  In addition, the ratio of crystallization and (ΔHm−ΔHc) upon treatment for poly-L-lactic acid and poly-D-lactic acid are as shown in Tables 1 and 2, respectively. In Examples 1 to 13 and Comparative Example 2, the ratio of crystallization and (ΔHm−ΔHc) were high due to the treatment, and the crystallization characteristics were excellent. In contrast, Example 14 and Comparative Example 1 were ratios of crystallization. And (ΔHm−ΔHc) was high only for PDA, and in Comparative Example 3, the proportion of crystallization and (ΔHm−ΔHc) were low for both PLA and PDA.

(2) Step of mixing poly-L-lactic acid and poly-D-lactic acid Part of L / D = 30 from the resin supply port with respect to poly-L-lactic acid sheared and crystallized by the above-mentioned twin screw extruder The poly-D-lactic acid that had been subjected to the heat treatment was added and mixed from the side supply port provided on the side. The screw element of the mixing part was equipped with a kneading disk to provide a screw that could be sheared, and mixing was performed under shearing. Table 1 and Table 2 show the temperature settings during mixing, and the polymer turbidity and crystallinity during mixing. Further, the ratio of crystallization of the mixture after mixing and the stereocomplex formation rate (Sc) are also as described in Tables 1 and 2.

  From the results of Tables 1 and 2, in Examples 1 to 13, high melting point of the mixture was observed at the time of mixing and after mixing, and the crystallization characteristics such as crystallinity and crystallization ratio were excellent. In addition, the stereo complex formation rate was 80% or less. In Example 14, although the mixture at the time of mixing and after mixing was crystallized, the crystallization characteristics were low. The stereo complex formation rate was as high as 87%. In Comparative Examples 1 to 3, a high melting point of the mixture was observed, and the stereocomplex formation rate was 80% or more, but the crystallization characteristics such as crystallinity and crystallization ratio were all low values. It was.

(3) Step of solid-phase polymerization of a mixture of poly-L-lactic acid and poly-D-lactic acid. The mixture obtained in (2) is placed in a vacuum dryer, and the solid phase is obtained at 140 ° C. and a pressure of 13.3 Pa for 4 hours. Polymerization was carried out, and then the temperature was raised to 150 ° C. for 4 hours, and further to 160 ° C. for 10 hours to carry out solid phase polymerization. As shown in Tables 1 and 2, for Examples 1 to 13, the molecular weight was increased to 100,000 or more after solid-phase polymerization, and a high melting point and a stereo complex formation rate of 70% or more were observed. It was done. On the other hand, in Example 14 and Comparative Examples 1 to 3, the melting point was increased and the stereocomplex formation rate was also observed to be 70% or more, but the molecular weight after solid phase polymerization did not increase to 100,000 or more.

(Examples 15 to 33, Comparative Example 4)
(1) Process for treating poly-L-lactic acid and poly-D-lactic acid As shown in Tables 3 and 4, poly-L-lactic acid was mixed with TEX30 type twin screw extruder (L / D manufactured by Nippon Steel Works). = 45.5), and treatment by shear crystallization was performed. The twin-screw extruder was provided with a plasticized portion set at a temperature of 180 ° C. at a portion of L / D = 10 from the resin supply port, and then provided a crystallization portion set at a temperature described in Tables 3 and 4. . The screw element of the crystallization part was equipped with a kneading disk to provide a screw capable of imparting shear.
Similarly to poly-L-lactic acid, poly-D-lactic acid was treated by shear crystallization using a TEX30 twin screw extruder (L / D = 45.5) manufactured by Nippon Steel Works. The screw arrangement of the twin screw extruder is the same as that in the case of shear crystallization of poly-L-lactic acid, and the temperature setting of the crystallized portion is as described in Tables 3 and 4.

  Tables 3 and 4 show the ratio of crystallization and (ΔHm−ΔHc) when poly-L-lactic acid and poly-D-lactic acid were treated, respectively. In Examples 15 to 31 and Comparative Example 4, the ratio of crystallization and (ΔHm−ΔHc) were high by the treatment, and the crystallization characteristics were excellent, while Examples 32 and 33 were the ratio of crystallization and (ΔHm -ΔHc) was higher only for PDA.

(2) Step of mixing poly-L-lactic acid and poly-D-lactic acid With respect to poly-L-lactic acid shear-crystallized by the above twin screw extruder, L / D = 30 from the resin supply port. From the side supply port provided in the part, the poly-D-lactic acid subjected to the shear crystallization treatment was added and mixed. The screw element of the mixing part was equipped with a kneading disk to provide a screw that could be sheared, and mixing was performed under shearing. Table 3 and Table 4 show the temperature settings during mixing and the polymer turbidity and crystallinity during mixing. Further, the crystallization ratio and the stereo complex formation rate (Sc) of the mixture after mixing are as described in Tables 3 and 4.

  From the results of Tables 3 and 4, in Examples 15 to 31, a high melting point of the mixture was observed during and after mixing, and crystallization characteristics such as crystallinity and crystallization ratio were excellent. In addition, the stereo complex formation rate was 80% or less. In Examples 32 and 33, although the mixture during and after mixing was crystallized, the crystallization characteristics were low, but the stereocomplex formation rate was as high as 80% or more. In Comparative Example 4, an increase in the melting point of the mixture was observed, and the stereocomplex formation rate was 80% or more, but the crystallization characteristics such as the degree of crystallization and the ratio of crystallization were all low values.

(3) Step of solid-phase polymerization of a mixture of poly-L-lactic acid and poly-D-lactic acid. The mixture obtained in (2) is placed in a vacuum dryer, and the solid phase is obtained at 140 ° C. and a pressure of 13.3 Pa for 4 hours. Polymerization was carried out, and then the temperature was raised to 150 ° C. for 4 hours, and further to 160 ° C. for 10 hours to carry out solid phase polymerization. As shown in Tables 3 and 4, all of Examples 15 to 31 have a molecular weight of 100,000 or more after solid-phase polymerization, and a high melting point and a stereo complex formation rate of 70% or more are observed. It was done. In contrast, in Examples 32 and 33 and Comparative Example 4, the melting point and the formation rate of the stereocomplex were also observed to be 70% or more, but the molecular weight after solid phase polymerization did not increase to 100,000 or more.

(Examples 34 to 47, Comparative Example 5)
(1) Process of treating poly-L-lactic acid and poly-D-lactic acid As shown in Tables 5 and 6, crystals are obtained by heating poly-L-lactic acid and poly-D-lactic acid in a nitrogen atmosphere, respectively. Processing was performed. The treatment temperature and time at this time are as shown in Tables 5 and 6. As shown in Tables 5 and 6, the thermal characteristics after the treatments were high in crystallization ratio and (ΔHm−ΔHc) in Examples 34 to 46 and Comparative Example 5, and excellent in crystallization characteristics. On the other hand, in Example 47, the ratio of crystallization and (ΔHm−ΔHc) were high only with PDA.

(2) Step of mixing poly-L-lactic acid and poly-D-lactic acid The heat-crystallized poly-L-lactic acid and poly-D-lactic acid are mixed with TEX30 type twin screw extruder manufactured by Nippon Steel Works ( L / D = 45.5) was added and mixed from the side supply ports provided in the portion of L / D = 30. The screw element of the mixing part was equipped with a kneading disk to provide a screw that could be sheared, and mixing was performed under shearing. Table 5 and Table 6 show the temperature settings during mixing and the polymer turbidity and crystallinity during mixing. In addition, the crystallization ratio and stereocomplex formation rate (Sc) of the mixture after mixing are as described in Tables 5 and 6.

  From the results of Tables 5 and 6, in Examples 34 to 46, high melting point of the mixture was observed during and after mixing, and the crystallization characteristics such as crystallinity and crystallization ratio were excellent. In addition, the stereo complex formation rate was 80% or less. On the other hand, in Example 47 and Comparative Example 5, a high melting point of the mixture was observed, and the stereocomplex formation rate was 80% or more, but the crystallization characteristics such as crystallinity and crystallization ratio. All were low values.

(3) Step of solid-phase polymerization of a mixture of poly-L-lactic acid and poly-D-lactic acid. The mixture obtained in (2) is placed in a vacuum dryer, and the solid phase is obtained at 140 ° C. and a pressure of 13.3 Pa for 4 hours. Polymerization was carried out, and then the temperature was raised to 150 ° C. for 4 hours, and further to 160 ° C. for 10 hours to carry out solid phase polymerization. As shown in Table 3, in each of Examples 34 to 46, the molecular weight was increased to 100,000 or more after solid phase polymerization, and a high melting point and a stereocomplex formation rate of 70% or more were observed. In contrast, in Example 47 and Comparative Example 5, the melting point and the stereo complex formation rate were also observed to be 70% or more, but the molecular weight after solid phase polymerization did not increase to 100,000 or more.

Claims (13)

A method of mixing poly-L-lactic acid and poly-D-lactic acid and subjecting the mixture to solid phase polymerization, wherein at least one of poly-L-lactic acid and poly-D-lactic acid to be mixed is represented by the following formula: A method for producing a polylactic acid block copolymer satisfying (1) and having crystals remaining upon mixing, wherein the mixed poly-L-lactic acid and / or poly-D-lactic acid is sheared A method for producing a polylactic acid block copolymer, which is obtained by treatment at a temperature selected from the range of melting point -50 ° C to melting point + 20 ° C under application or pressure.
(ΔHm−ΔHc)> 20 (J / g) (1)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g) 2. The polylactic acid block copolymer according to claim 1, wherein the poly-L-lactic acid and / or poly-D-lactic acid to be mixed is obtained by applying shear at a shear rate of 10 to 400 / sec. Manufacturing method of coalescence. Mixed poly -L- lactic acid and / or poly -D- lactic acid, polylactic acid block copolymer according to claim 1, wherein a is obtained by applying a pressure of 0.05~10MPa Production method. The poly-L-lactic acid and / or poly-D-lactic acid to be mixed is obtained by treatment with a treatment time of 0.1 to 10 minutes. A method for producing a lactic acid block copolymer. The method for producing a polylactic acid block copolymer according to any one of claims 1 to 4, wherein the treatment is performed by either a single screw extruder or a twin screw extruder. The polylactic acid block according to any one of claims 1 to 5, wherein both the poly-L-lactic acid and poly-D-lactic acid to be mixed satisfy the following formula (1), and crystals remain during mixing. A method for producing a copolymer.
(ΔHm−ΔHc)> 20 (J / g) (1)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g) The polylactic acid block copolymer according to any one of claims 1 to 6, wherein at least one of poly-L-lactic acid and poly-D-lactic acid to be mixed satisfies the following formula (2). Production method.
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm]> 80 (2)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g) The production of a polylactic acid block copolymer according to any one of claims 1 to 7, wherein the crystallinity of the mixture comprising poly-L-lactic acid and poly-D-lactic acid at the time of mixing is 10% or more. Method. The method for producing a polylactic acid block copolymer according to claim 8, wherein the temperature during mixing is in the range of the melting point of the mixture to -50 ° C to the melting point + 20 ° C. The method for producing a polylactic acid block copolymer according to claim 8 or 9, wherein mixing is performed under shearing or under pressure. The method for producing a polylactic acid block copolymer according to any one of claims 1 to 10, wherein a ratio of crystallization based on crystallization of the mixture after mixing satisfies the following formula (2).
Ratio of crystallization (%): [(ΔHm−ΔHc) / ΔHm]> 80 (2)
ΔHm: Crystal melting enthalpy (J / g)
ΔHc: Crystallization enthalpy at elevated temperature (J / g) The method for producing a polylactic acid block copolymer according to claim 11, wherein the stereocomplex formation rate of the mixture after mixing is 80% or less. The weight average molecular weight of the obtained polylactic acid block copolymer is 100,000 or more, The manufacturing method of the polylactic acid block copolymer in any one of Claims 1-12 characterized by the above-mentioned.