JP2013203969A - Polylactic acid copolymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid copolymer excellent in hydrolysis resistance.SOLUTION: A polylactic acid copolymer includes a lactic acid unit and a hydroxypivalic acid unit, and has a weight average molecular weight of 30,000-300,000. The polylactic acid copolymer can be produced by (a) polymerizing lactide or lactic acid first, and then (b) adding pivalolactone or hydroxypivalic acid to polymerize, or by (b) polymerizing pivalolactone or hydroxypivalic acid first, and then (a) adding lactide or lactic acid to polymerize.

Description

  The present invention relates to a polylactic acid copolymer excellent in crystallinity and hydrolysis resistance.

  In recent years, from the viewpoint of environmental conservation, polylactic acid resin has attracted attention as a carbon-neutral material made from plants. Polylactic acid resin is expected to be a biomass plastic that can be substituted for a general-purpose plastic derived from petroleum raw materials because lactic acid, which is a monomer, has been produced at low cost by fermentation using microorganisms, and is gradually being used. However, when polylactic acid is used as a general-purpose plastic, it has problems such as a melting point as low as about 170 ° C. and a difficulty in development into a molded product due to a slow crystallization rate. In recent years, the melting point and crystallinity have been improved by studying high molecular weight polylactic acid using a raw material with high optical purity (for example, Non-patent Document 1) and stereocomplex polylactic acid (for example, Patent Document 1). However, the effect is still not enough.

  On the other hand, polypivalolactone obtained from hydroxypivalic acid is known as a polyhydroxycarboxylic acid other than polylactic acid. Polypivalolactone has a high melting point of 230 to 240 ° C. and a high crystallization rate, and has been studied for fiber applications and the like (for example, Patent Documents 2 to 4 and Non-Patent Document 2). However, polypivalolactone obtained by these conventional techniques is insufficient in high molecular weight, has poor hydrolysis resistance, and is not at a level that can be put into practical use as a general-purpose plastic. In Patent Document 5, polypivalolactone is mixed with aliphatic polyester for the purpose of improving crystallinity, but the characteristics are insufficient.

JP 2010-070589 A British Patent 766347 US Pat. No. 2,658,055 Japanese Patent Publication No.41-9810 JP 2002-212407 A

Development of industrial production method of high molecular weight poly-L-lactic acid from renewable resources. 6 2001 High Polymerization of β-Lactones with Acid and Base Catalysts Industrial Chemical Journal Vol. 67 No. 1 1964

  An object of the present invention is to provide a polylactic acid copolymer excellent in crystallinity and hydrolysis resistance.

  As a result of studying to solve the above problems, a polylactic acid copolymer excellent in hydrolysis resistance was found, and the present invention was achieved.

That is, the present invention is as follows.
1. A polylactic acid copolymer comprising a lactic acid unit and a hydroxypivalic acid unit and having a weight average molecular weight of 30,000 to 300,000.
2. 2. The polylactic acid copolymer according to 1, wherein the constituent ratio of the lactic acid unit (x) and the hydroxypivalic acid unit (y) is x / y = 99/1 to 1/99 (weight ratio).
3. 3. The polylactic acid copolymer according to 1 or 2, wherein the polylactic acid copolymer is a polylactic acid block copolymer having a lactic acid segment (A) and a hydroxypivalic acid segment (B).
4). 3. The weight average molecular weight of the lactic acid segment (A) is 50,000 to 200,000, and the weight average molecular weight of the hydroxypivalic acid segment (B) is 50,000 to 200,000. Polylactic acid copolymer.
5. Using a differential scanning calorimeter, the temperature was increased from 30 ° C. to 250 ° C. at a temperature increase rate of 20 ° C./min, held at 250 ° C. for 3 minutes, and then decreased from 250 ° C. to 30 ° C. at a temperature decrease rate of 20 ° C./min. Further, the crystal melting enthalpy (ΔHm) of the polylactic acid segment (A) observed at 2ndRun when the temperature is increased from 30 ° C. to 250 ° C. at a temperature increase rate of 20 ° C./min is 30 J / g or more. 5. The polylactic acid copolymer according to any one of 1 to 4, which is characterized.
6.1 A molded product obtained by molding the polylactic acid copolymer according to any one of 1 to 5.
7). (A) after first polymerizing lactide or lactic acid, then (b) polymerizing by adding pivalolactone or hydroxypivalic acid, or (b) after first polymerizing pivalolactone or hydroxypivalic acid, then (a) lactide Alternatively, the method for producing a polylactic acid copolymer according to any one of 1 to 6, wherein lactic acid is added for polymerization.

  It is a polylactic acid copolymer having a high molecular weight and excellent crystallinity and hydrolysis resistance.

  The polylactic acid copolymer of the present invention comprises a lactic acid unit and a hydroxypivalic acid unit, and the lactic acid unit is a polymer containing L-lactic acid and / or D-lactic acid as a main component, and L-lactic acid is the main component. In some cases, it is called poly-L-lactic acid, and when D-lactic acid is the main component, it is called poly-D-lactic acid.

  The optical purity of lactic acid used as a raw material constituting the lactic acid unit is not particularly limited, but it is preferably 95% or more, more preferably 98% or more in terms of excellent crystallinity, and 99 % Or more is particularly preferable.

  The impurity of hydroxypivalic acid used as a raw material constituting the hydroxypivalic acid unit is not particularly limited, but antimony is obtained in that polypivalolactone having good crystallinity and excellent hydrolysis resistance can be obtained. The tin, titanium, phosphorus, potassium, calcium, aluminum, iron, boron, nitrogen, and sulfur atom contents are each preferably 100 ppm or less.

  The polylactic acid copolymer of the present invention has a weight average molecular weight in the range of 3 to 300,000, preferably in the range of 5 to 300,000 in terms of excellent mechanical properties, and excellent in moldability and mechanical properties. In terms of the point, it is more preferably in the range of 100,000 to 300,000, and more preferably in the range of 150,000 to 300,000 in terms of excellent moldability, mechanical properties, and hydrolysis resistance. When the weight average molecular weight is less than 30,000, the mechanical properties are low and the hydrolysis resistance is also lowered, which is not preferable. 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 as a solvent.

  The polylactic acid copolymer of the present invention comprises lactic acid units and hydroxypivalic acid units, and the composition ratio of lactic acid units (x) and hydroxypivalic acid units (y) is x / y = 99/1 to 1/99 (weight ratio). X / y = 95/5 to 10/90 (weight ratio) in that a polylactic acid copolymer excellent in high molecular weight and hydrolysis resistance can be efficiently obtained. Preferably, x / y = 95/5 to 40/60 (weight ratio) is more preferable in that the constituent amount of the hydroxypivalic acid unit is small and the cost can be suppressed, and the decrease in crystallinity due to the copolymer structure can be suppressed. And x / y = 90/10 to 70/30 (weight ratio) is particularly preferable.

  The polylactic acid copolymer of the present invention preferably has a block structure from the viewpoint of obtaining more uniform characteristics. A random copolymer is not preferable because the characteristics of the highly crystalline hydroxypivalic acid unit are not sufficiently exhibited.

  The lactic acid segment (A) of the present invention preferably has a weight average molecular weight in the range of 0.5 to 200,000 in terms of excellent productivity, and in the range of 3 to 200,000 in terms of excellent mechanical properties. It is more preferable. A weight average molecular weight of less than 50,000 is not preferable because hydrolysis resistance decreases due to an increase in the amount of carboxyl end groups.

  Further, the hydroxypivalic acid segment (B) of the present invention is preferably in the range of 0.5 to 200,000 in view of excellent weight average molecular weight, and 3 to 200,000 in view of excellent crystallinity. More preferably, it is the range. A weight average molecular weight of less than 50,000 is not preferable because hydrolysis resistance decreases due to an increase in the amount of carboxyl end groups. In addition, the weight average molecular weight of the lactic acid segment (A) and the hydroxypivalic acid segment (B) is a weight average molecular weight in terms of standard polymethyl methacrylate measured by gel permeation chromatography (GPC) using hexafluoroisopropanol as a solvent. is there.

  The polylactic acid copolymer of the present invention is preferably 1 or more and 4 or less from the viewpoint of excellent hydrolysis resistance, and more preferably 1 or more and 3 or less from the viewpoint of uniform polymer properties. When the molecular weight distribution exceeds 4, it is not preferable because the polymer properties vary. When the molecular weight distribution is less than 1, it is not preferable because the melt viscosity is low and the molding processability is poor. In addition, molecular weight distribution is ratio of the weight average molecular weight with respect to the number average molecular weight of standard polymethylmethacrylate conversion by the gel permeation chromatography (GPC) measurement which uses hexafluoroisopropanol as a solvent.

  The polylactic acid copolymer of the present invention was heated from 30 ° C. to 250 ° C. at a rate of 20 ° C./min in a nitrogen atmosphere using a differential scanning calorimeter (DSC7) manufactured by PERKIN ELMER, and heated at 250 ° C. Crystal melting enthalpy of polylactic acid segment when held for 30 minutes, lowered from 250 ° C. to 30 ° C. at a rate of 20 ° C./min, held at 30 ° C. for 1 minute, and then raised from 30 ° C. to 250 ° C. at a rate of 20 ° C./min (ΔHm) is preferably 30 J / g or more, more preferably in the range of 40 to 150 J / g in terms of excellent hydrolysis resistance, and 50 to 150 J / g in terms of excellent crystallinity. More preferably, it is in the range. When ΔHm is less than 30 J / g, hydrolysis resistance is poor, which is not preferable. In the present invention, by making the copolymer of lactic acid segment and hydroxypivalic acid segment, and making the weight average molecular weight of the resulting polylactic acid copolymer in the range of 3 to 300,000, the crystallinity of polylactic acid is improved, A polylactic acid copolymer having excellent hydrolysis resistance in the range of ΔHm can be obtained. The crystal melting enthalpy (ΔHm) of the polylactic acid segment is the melting enthalpy corresponding to the melting point peak appearing at 130 ° C. or higher and 180 ° C. or lower, which is determined by the above measuring method.

  In this invention, the other component unit may be included in the range which does not impair the performance of a polylactic acid copolymer. 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 Diol, hexanediol, octanediol, neopentylglycol, glycerin, trimethylolpropane, pentaerythritol, trimethylolpropane, or polyhydric alcohol obtained by adding ethylene oxide or propylene oxide to pentaerythritol, Aromatic polyhydric alcohols obtained by addition reaction of phenol with ethylene oxide, polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol or their derivatives, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4 -Hydroxycarboxylic acids such as hydroxy valeric acid and 6-hydroxycaproic acid, and glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, δ-valerolactone, etc. Lactones and the like.

  Next, the manufacturing method of the polylactic acid copolymer in this invention is demonstrated.

  In the polylactic acid copolymer of the present invention, (a) lactide or lactic acid is polymerized first, and then (b) pivalolactone or hydroxypivalic acid is added to polymerize, or (b) pivalolactone or hydroxypivalic acid is first polymerized. Then, (a) lactide or lactic acid can be added and polymerized.

  In the present invention, in the ring-opening polymerization method using lactide as a starting material and using a known polymerization catalyst, the starting material lactide is not particularly limited but is commercially available. Higher purity is preferable, but it usually contains some impurities, and these may be contained.

  In the present invention, in a direct polymerization method in which lactic acid is used as a starting material and is produced by direct polycondensation, the total amount of alcohols as impurities in lactic acid is 70 ppm or less, the total of organic acids is 800 ppm or less, and aldehydes It is preferable to use lactic acid having a total of 50 ppm or less and a total of esters of 400 ppm or less as a main raw material.

  The method for producing the lactic acid segment of the present invention is not particularly limited when lactide or lactic acid is polymerized first, but ring-opening polymerization using lactide as a starting material and using a known polymerization catalyst, or lactic acid There is a direct polymerization method in which is used as a starting material to produce by direct polycondensation. Either batch polymerization or continuous polymerization may be used.

  In the method for producing a lactic acid segment of the present invention, when pivalolactone or hydroxypivalic acid is first polymerized and then polymerized by adding lactide or lactic acid, decomposition of the hydroxypivalic acid segment by the monomer can be suppressed. More preferably, lactide is used.

  In the case of using lactic acid, the addition amount is preferably 90 parts by weight or less, more preferably 60 parts by weight or less, in terms of the ability to suppress decomposition with respect to 100 parts by weight of the total of polypivalolactone and lactic acid. Preferably, it is 30 parts by weight or less. Moreover, the addition amount in the case of using lactide is not specifically limited.

  The weight average molecular weight of polypivalolactone in the case of using lactic acid is preferably 40,000 or more, more preferably 80,000 or more in that a high molecular weight polylactic acid copolymer is obtained. More preferably, it is 10,000 or more. A weight average molecular weight of less than 40,000 is not preferable because the hydrolysis resistance of the resulting polylactic acid copolymer is lowered. Moreover, the weight average molecular weight of polypivalolactone when using lactide is not particularly limited.

  In the present invention, a catalyst may coexist in order to promote polymerization of the polylactic acid segment. Tin compounds, titanium compounds, lead compounds, zinc compounds, cobalt compounds, iron compounds, lithium compounds, rare earth compounds, antimony compounds, bismuth compounds, and sulfur-containing compounds having sulfur with an oxidation number of +5 or more are preferred and are said to be excellent in productivity. In terms of tin compounds, titanium compounds, lead compounds, zinc compounds, cobalt compounds, iron compounds, lithium compounds, rare earth compounds, sulfonic acid compounds, phosphorus compounds, and sulfur-containing compounds having sulfur with an oxidation number of +5 or more are more preferable. Tin compounds, titanium compounds, rare earth compounds, sulfur-containing compounds having sulfur with an oxidation number of +5 or more, and phosphorus compounds are more preferable. In addition, as the metal catalyst, a tin-based organic carboxylate having two ligands is more preferable in that a polylactic acid-based resin having excellent thermal stability and hue can be obtained. II) or tin (II) octylate is particularly preferred. Also, two or more kinds can be used in combination. When used together, one or more kinds selected from tin compounds and one or more kinds selected from sulfur-containing compounds having sulfur having an oxidation number of +5 or more are used. preferable.

  The addition amount of the catalyst is not particularly limited, but is 0.0001 to 2 parts by weight in that the polymerization can proceed efficiently with respect to 100 parts by weight of lactide and polylactic acid which are raw materials for the polylactic acid segment. Preferably, it is more preferably 0.001 to 1 part by weight, more preferably 0.005 to 0.5 part by weight, and 0.01 to 0.3 part by weight in that the amount of remaining metal can be reduced. It is particularly preferred that

  In the method for producing a lactic acid segment of the present invention, the reaction temperature when performing melt polymerization is preferably higher than the melting point of the reaction product. More preferably, it is performed at a temperature of 50 to 300 ° C, and more preferably 100 to 250 ° C. Further, the temperature of melt polymerization may be one step or may be two or more steps.

  In the method for producing a lactic acid segment of the present invention, the pressure at which melt polymerization is performed is not particularly limited, and may be any of a reduced pressure condition, a normal pressure condition, and a pressurized condition, but a pressure of 0.13 to 130 kPa. It is preferable to carry out with. Moreover, the pressure of melt polymerization may be one step or may be two or more steps. When performing melt polymerization under normal pressure conditions, the inside of the reaction system is preferably under an inert gas stream such as nitrogen or argon.

  In the method for producing a lactic acid segment of the present invention, the melt polymerization is preferably performed in a reaction time of 1 to 1000 minutes. When the reaction time is 5 to 500 minutes, it is more preferable in that the hydrolysis resistance of the obtained lactic acid segment is good.

  The method for producing the hydroxypivalic acid segment of the present invention is not particularly limited when pivalolactone or hydroxypivalic acid is polymerized first, but it is not limited, but a method of ring-opening polymerization using pivalolactone as a starting material, or hydroxypivalin There is a direct polymerization method in which an acid is used as a starting material and is produced by direct polycondensation. It is preferable to use a production method that undergoes melt polymerization in that polypivalolactone can be efficiently obtained in a high yield. In addition, it is preferable to use a production method that undergoes solid phase polymerization in that polypivalolactone having a high molecular weight can be obtained. Moreover, it is preferable to use the manufacturing method which passes through ring-opening polymerization at the point that molecular weight distribution can be made small. Either batch polymerization or continuous polymerization may be used.

  In the production method of the hydroxypivalic acid segment of the present invention, when lactide or lactic acid is first polymerized and then polymerized by adding pivalolactone or hydroxypivalic acid, decomposition of the lactic acid segment by the monomer can be suppressed. It is more preferable to use pivalolactone.

  In the case of using hydroxypivalic acid, the amount added is preferably 90 parts by weight or less, and preferably 60 parts by weight or less, in terms of being able to suppress decomposition with respect to 100 parts by weight of the total of polylactic acid and hydroxypivalic acid. Is more preferable, and it is further more preferable that it is 30 parts weight or less. Moreover, the addition amount in the case of using pivalolactone is not particularly limited.

  The weight average molecular weight of polylactic acid when hydroxypivalic acid is used is preferably 40,000 or more, more preferably 80,000 or more in that a high molecular weight polylactic acid copolymer is obtained. More preferably, it is 10,000 or more. A weight average molecular weight of less than 40,000 is not preferable because the hydrolysis resistance of the resulting polylactic acid copolymer is lowered. Moreover, the weight average molecular weight of polylactic acid in the case of using pivalolactone is not particularly limited.

  In the present invention, in order to promote the polymerization of the hydroxypivalic acid segment, although not particularly limited, a catalyst may coexist. Using hydroxypivalic acid as a starting material, a polymerization catalyst such as an antimony compound such as antimony trioxide, a phosphorus compound such as phosphoric acid or triphenyl phosphite, or a tin compound such as dibutyltin dilaurate can be used.

  In addition, using pivalolactone as a starting material, no catalyst or titanium compounds such as titanium-n-butyl titanate, aluminum compounds such as aluminum chloride, iron compounds such as iron chloride, potassium compounds such as potassium acetate and potassium hydroxide, calcium acetate Polymerization catalysts such as calcium compounds such as calcium hydroxide, boron compounds such as boron trifluoride diethyl ether complex, nitrogen compounds such as hexamethylenetetramine and dimethylaniline, and acidic compounds such as sulfuric acid can be used.

  The addition amount in the case of adding a catalyst is not particularly limited, but is 0.0001 in that the polymerization can proceed efficiently with respect to 100 parts by weight of hydroxypivalic acid which is a raw material of the hydroxypivalic acid segment. It is preferably ˜2 parts by weight, more preferably 0.001 to 1 part by weight, further preferably 0.005 to 0.5 part by weight in that the amount of remaining metal can be reduced. It is particularly preferable that the amount is 0.01 to 0.3 parts by weight.

  In the method for producing a hydroxypivalic acid segment of the present invention, the reaction temperature when performing melt polymerization is preferably a temperature equal to or higher than the melting point of the reaction product. More preferably, it is performed at a temperature of 50 to 300 ° C, and more preferably 100 to 250 ° C. Further, the temperature of melt polymerization may be one step or may be two or more steps.

  In the method for producing a hydroxypivalic acid segment of the present invention, the pressure at which melt polymerization is performed is not particularly limited, and may be any of a reduced pressure condition, a normal pressure condition, and a pressurized condition, but is 0.13 to 130 kPa. It is preferable to carry out at the pressure of. Moreover, the pressure of melt polymerization may be one step or may be two or more steps. When performing melt polymerization under normal pressure conditions, the inside of the reaction system is preferably under an inert gas stream such as nitrogen or argon.

  In the method for producing a hydroxypivalic acid segment of the present invention, the melt polymerization is preferably carried out in a reaction time of 1 to 1000 minutes. When the reaction time is 5 to 500 minutes, the hydrolysis resistance of the resulting hydroxypivalic acid segment is more preferable. The reaction time is more preferably 10 to 300 minutes, and particularly preferably 15 to 240 minutes.

  In the present invention, in order to produce a polylactic acid copolymer having a higher block property and a high molecular weight, a solid phase polymerization reaction or a chain extension reaction can also be performed.

  In the method for producing a polylactic acid copolymer of the present invention, the reaction temperature when performing solid-phase polymerization is preferably a temperature not higher than the melting point of the reaction product. More preferably, it is performed at a temperature of 50 to 250 ° C, and more preferably 100 to 230 ° C. Further, the temperature of the solid phase polymerization may be one step or may be two or more steps.

  In the method for producing a polylactic acid copolymer of the present invention, the pressure at which solid phase polymerization is performed is not particularly limited, and may be any of a reduced pressure condition, a normal pressure condition, and a pressurized condition. It is preferable to carry out at a pressure of ˜130 kPa. Further, the pressure of the solid phase polymerization may be one step or may be two or more steps. When solid phase polymerization is carried out under normal pressure conditions, the reaction system is preferably under an inert gas stream such as nitrogen or argon.

  In the method for producing a polylactic acid copolymer of the present invention, the solid phase polymerization is preferably performed in a reaction time of 1 to 5000 minutes. It is more preferable to carry out with a reaction time of 5 to 2000 minutes in that a polylactic acid copolymer having good hydrolysis resistance is obtained. The reaction time is more preferably 10 to 1000 minutes, and particularly preferably 15 to 600 minutes.

  The chain extender of the present invention is not particularly limited, but a compound having two or more functional groups and capable of reacting is preferable. Examples of the chain extender include compounds such as isocyanate, epoxy, acid anhydride, acid chloride, oxazoline, and phenols.

Specific examples of the chain extender include tolylene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, naphthylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, methylene biscyclohexyl diisocyanate, norbornane diisocyanate, bisisocyanatomethylcyclohexane and other diisocyanates. Resorcinol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, diglycidyl terephthalic acid, diglycidyl isophthalic acid, etc. diglycidyl ether, naphthalene tetracarboxylic anhydride, dioxo Tetrahydrofuranylmethylcyclo Xenedicarboxylic anhydride, pyromellitic anhydride, oxydiphthalic anhydride, biphenyltetracarboxylic anhydride, benzophenonetetracarboxylic anhydride, diphenylsulfonetetracarboxylic anhydride, tetrafluoroisopropylidenediphthalic anhydride, terphenyl Acid anhydrides such as tetracarboxylic anhydride, cyclobutanetetracarboxylic anhydride, carboxymethylcyclopentanetricarboxylic anhydride, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid And alicyclic carboxylic acids such as sebacic acid and cyclohexanedicarboxylic acid and acid chlorides thereof, and bisoxazolines such as 2,2 ′-(1,3-phenylene) bis-2-oxazoline. Of these, diisocyanate, diglycidyl ether, and bisoxazoline are preferable because of high reactivity and easy handling. If the amount is small, a compound containing 3 or more functional groups may be used in combination.

  The amount of chain extender added is such that the ratio (chain extender / polylactic acid copolymer) between the functional group amount of the chain extender and the terminal functional group amount of the polylactic acid copolymer to be chain extended is 0.8 to 1. Is preferably in the range of .5. When the ratio of the added amount exceeds 1.5, it is not preferable because the physical properties are lowered and coloring occurs due to side reaction of the chain extender. When the ratio of the added amount is less than 0.8, the increase in block property is small, and a high molecular weight polylactic acid copolymer cannot be obtained, which is not preferable.

  The reaction temperature of the chain extension reaction is preferably in the range of the melting start temperature of the polylactic acid copolymer from −20 ° C. to the melting start temperature of + 40 ° C., from the point that the chain extension reaction proceeds favorably, and the solution starting temperature −10 More preferably, it is in the range of from ° C to melting start temperature + 30 ° C, and more preferably in the range of solution starting temperature to melting start temperature + 20 ° C. When the reaction temperature is lower than the melting start temperature −20 ° C., the chain extension reaction does not proceed well, which is not preferable. When the reaction temperature exceeds the melting start temperature + 40 ° C., it is not preferable because physical properties are lowered and coloring occurs due to side reaction of the chain extender.

  The reaction time of the chain extension reaction is preferably 1 minute to 2 hours, and more preferably 3 minutes to 1 hour. A reaction time of less than 1 minute is not preferable because the chain extension reaction does not proceed well. If it exceeds 2 hours, it is not preferable because the physical properties are lowered and coloring occurs due to side reaction of the chain extender.

  In the present invention, in order to promote the chain extension reaction, although not particularly limited, a catalyst may coexist. Examples of the catalyst include metals such as tin, zinc, lead, titanium, bismuth, zirconium, germanium, antimony, aluminum, magnesium, and derivatives thereof. Examples of the metal derivatives include metal alkoxides, carboxylates, carbonates, oxides, and halides.

  In the present invention, a transesterification catalyst may be added as necessary. Examples of the transesterification catalyst include tin octylate, tetrabutyl titanate, tetraisopropyl titanate, antimony trioxide, germanium dioxide, and the like. The addition amount of the transesterification catalyst is preferably 0.001 to 0.1 parts by weight with respect to 100 parts by weight of the polylactic acid copolymer. If the addition amount is less than 0.001 part by weight, the effect of addition is poor, and if it exceeds 0.1 part by weight, the thermal stability of the polylactic acid copolymer is lowered, which is not preferable.

  In the present invention, the reaction vessel is not particularly limited, and for example, a stirring vessel type reaction vessel, a mixer type reaction vessel, a tower type reaction vessel, an extruder type reaction vessel, and the like can be used. Two or more types can be used in combination.

  In the present invention, a stabilizer may be added to obtain a polylactic acid copolymer having excellent thermal stability.

  Examples of the stabilizer used in the present invention include sulfur-containing compounds having sulfur with an oxidation number of less than +5, phosphorus compounds, aromatic ketone compounds, hydrocarbon compounds having aromatic rings, aliphatic dicarboxylic acids, aliphatic diols, and fats. Examples thereof include cyclic hydrocarbon compounds, hindered phenol compounds, vitamin compounds, triazole compounds, hydrazine derivative compounds, and the like, and these may be used in combination. Among them, selected from sulfur-containing compounds having sulfur with an oxidation number of less than +5, phosphorus compounds, aromatic ketone compounds, hydrocarbon compounds having aromatic rings, aliphatic dicarboxylic acids, aliphatic diols, and alicyclic hydrocarbon compounds. It is preferable to contain at least one kind. Examples of sulfur-containing compounds having sulfur with an oxidation number of less than +5 include diphenyl sulfone, sulfurous acid, sodium sulfite, sulfur, “Sumizer” TPD (pentaerythritol tetrakis (β-lauryl-thio-propionate)) manufactured by Sumitomo Chemical Co., Ltd. Is preferred. Among the phosphorus compounds, the inorganic phosphorus compound is preferably a phosphoric acid compound or a phosphorous acid compound, and the organic phosphorus compound is more preferably a phosphate compound or a phosphite compound. More preferable examples of specific examples include phosphoric acid, phosphorous acid, sodium phosphate, and sodium phosphite as the inorganic phosphorus compound, and “ADEKA STAB” AX-71 (manufactured by ADEKA) as the organic phosphorus compound. Octadecyl phosphate), PEP-8 (distearyl pentaerythritol diphosphite), PEP-36 (cyclic neopentatetraylbis (2,6-t-butyl-4-methylphenyl) phosphite), HP-10 ( 2,2'-methylenebis (4,6-di-t-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus), PEP-24G (bis (2,4-di-t-butylphenyl) pentaerythritol Diphosphite), 3010 (triisodecyl phosphite), TPP (triphenyl phosphite), Ciba spe "Irgaphos" 168 (Tris (2,4-di-t-butylphenyl) phosphite) manufactured by Jalty Chemicals Co., Ltd., HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene manufactured by Sanko Co., Ltd.) -10-oxide). Among them, a phosphorus compound in which a phosphorus atom is directly bonded to a carbon atom constituting an aromatic ring is preferable. Among them, HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 manufactured by Sanko Co., Ltd.) -Oxide) is preferred. Particularly preferred as the aromatic ketone compound are 1,4-dibenzoylbenzene and benzophenone, the hydrocarbon compound having an aromatic ring is triphenylmethane, the aliphatic dicarboxylic acid is oxalic acid, and the aliphatic diol is hexane. As the diol and alicyclic hydrocarbon compound, 1,2-dimethylcyclohexane is particularly preferable.

  The addition amount of the stabilizer is not particularly limited, but is preferably 0.001 to 2 parts by weight with respect to 100 parts by weight of the polylactic acid copolymer in terms of excellent thermal stability, 0.01 to The amount is more preferably 1 part by weight, further preferably 0.05 to 0.5 part by weight, and most preferably 0.08 to 0.3 part by weight.

  In the polylactic acid copolymer of the present invention, ordinary additives such as fillers (glass fiber, carbon fiber, metal fiber, natural fiber, organic fiber, glass flake, glass, and the like are included within the range not impairing the object of the present invention. Beads, ceramic fibers, ceramic beads, asbestos, wollastonite, talc, clay, mica, sericite, zeolite, bentonite, montmorillonite, synthetic mica, dolomite, kaolinite, finely divided silicic acid, feldspar powder, potassium titanate, shirasu balloon , Calcium carbonate, Magnesium carbonate, Barium sulfate, Calcium oxide, Aluminum oxide, Titanium oxide, Aluminum silicate, Silicon oxide, Gypsum, Novacurite, Dawsonite or clay, UV absorber (resorcinol, salicylate, benzotriazole, benzo Enones, etc.), lubricants, mold release agents (such as montanic acid and its salts, its esters, their half esters, stearyl alcohol, stearamide and polyethylene wax), dyes (such as nigrosine) and pigments (such as cadmium sulfide, phthalocyanine) Agent, anti-coloring agent (phosphite, hypophosphite, etc.), flame retardant (red phosphorus, phosphate ester, brominated polystyrene, brominated polyphenylene ether, brominated polycarbonate, magnesium hydroxide, melamine and cyanuric acid or Salts thereof), conductive agents or colorants (carbon black, etc.), slidability improvers (graphite, fluororesins, etc.), crystal nucleating agents (inorganic nucleating agents such as talc, ethylene bislauric acid amide, ethylene bis- 12-dihydroxystearic amide and Organic amide compounds such as rimesic acid tricyclohexylamide, pigment nucleating agents such as copper phthalocyanine and pigment yellow 110, organic carboxylic acid metal salts, zinc phenylphosphonates, etc.), antistatic agents, antioxidants, etc. Two or more kinds can be added.

  In addition, the polylactic acid copolymer of the present invention includes other thermoplastic resins (for example, polyethylene, polypropylene, acrylic resins, styrene resins, polyamides, polyphenylene sulfide resins, polycarbonate resins) within the range that does not impair the object of the present invention. , 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 heat Plastic resin (for example, ethylene / glycidyl methacrylate copolymer, polyester elastomer, polyamide elastomer, ethylene / propylene terpolymer, ethylene / butene-1 copolymer, etc.) It may further contain at least one or more kinds.

  Since the polylactic acid copolymer of the present invention has good hydrolysis resistance, it can be widely used as a molded article. Examples of molded articles include fibers, films, sheets, injection molded articles, extruded molded articles, blow molded articles, and composites with other materials. These molded articles are used for clothing such as woven and knitted fabrics, insect repellents, and the like. Agricultural uses such as heat insulation, frost prevention, shading, grass protection film, sheet, fishery use such as fishing nets, fishing line, various aquaculture ropes, medical hygiene use including suture thread, sanitary products, It is useful for automobile applications such as car seats, floor mats and interiors of cars, electrical / electronic components, and other applications.

  Hereinafter, the present invention will be described specifically by way of examples. The number of parts in the examples indicates parts by weight.

  The measurement method and determination method used in the present invention are shown below.

(1) Weight average molecular weight, number average molecular weight, molecular weight distribution Standard polymethyl methacrylate conversion weight average molecular weight and number average molecular weight measured by gel permeation chromatography (GPC), and the molecular weight distribution is relative to the number average molecular weight. It is a value represented by the ratio of weight average molecular weight. GPC measurement was performed using a WATERS differential refractometer WATERS410 as a detector, a MODEL510 high performance liquid chromatography as a pump, and a column with Shodex GPC HFIP-806M and Shodex GPC HFIP-LG connected in series. It was. 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 10 mg of a sample was heated from 30 ° C. to a rate of 20 ° C./min at a rate of 20 ° C./min in a nitrogen atmosphere by a differential scanning calorimeter (DSC7) manufactured by PERKIN ELMER. Crystals of polylactic acid copolymer when held for 30 minutes, lowered from 250 ° C. to 30 ° C. at a rate of 20 ° C./min, held at 30 ° C. for 1 minute, and then raised from 30 ° C. to 250 ° C. at a rate of 20 ° C./min The melting enthalpy was ΔHm.

(3) Hydrolysis resistance In a constant temperature and humidity chamber manufactured by Espec, 50 mg of polylactic acid copolymer after solid phase polymerization was subjected to wet heat treatment for 24 hours under conditions of a temperature of 60 ° C. and a relative humidity of 95%, and the weight before and after the treatment. Those having a molecular weight retention from the average molecular weight of 95% or more are ◎, those having a molecular weight of less than 95% to 85% or more are ◯, those having a molecular weight retention of 85% to 75% or more are Δ, and those having a molecular weight retention of less than 75% Is indicated by x.

[Production Example 1]
In a reaction vessel equipped with a stirrer and a reflux device, 100 parts by weight of a 90% L-lactic acid aqueous solution was put, the temperature was raised to 150 ° C., and the pressure was gradually reduced to 800 Pa, and 3.5 hours while removing water. After the reaction, 0.08 parts by weight of tin (II) acetate and 0.22 parts by weight of methanesulfonic acid were added as catalysts, and a prepolymer subjected to a polymerization reaction at a temperature of 170 ° C. and a pressure of 400 Pa for 6 hours was obtained at 100 ° C. For 2 hours. The obtained crystallized prepolymer was continuously heated from 110 ° C. to 160 ° C. for 20 hours under a pressure of 50 Pa (temperature increase rate 2.5 ° C. per hour), and subjected to solid state polymerization at 160 ° C. for 10 hours, Polylactic acid (A-1) having a weight average molecular weight of 132,000 was obtained.

[Production Example 2]
Except changing the time of solid-phase polymerization to 30 hours, it carried out similarly to manufacture example 1, and obtained the polylactic acid (A-2) of the weight average molecular weight 163000.

[Production Example 3]
Except changing the time of solid-phase polymerization to 35 hours, it carried out similarly to manufacture example 1, and obtained the polylactic acid (A-3) of the weight average molecular weight 189000.

[Production Example 4]
In a reaction vessel equipped with a stirrer and a reflux apparatus, 10 parts by weight of L-lactide was added, 0.1 mol% of tin octylate as a polymerization catalyst was added to L-lactide, and the reaction temperature was adjusted under a nitrogen stream. The reaction system was heated to 150 ° C., and the ring-opening polymerization reaction was started in the molten state. Residual lactide was removed from the resulting reaction product with a biaxial stirring and devolatilizer at a reduced pressure of 200 Pa to obtain polylactic acid (B-1) having a weight average molecular weight of 135,000.

[Production Example 5]
136 parts by weight of 3-chloropivalic acid was dissolved in chloroform, a 2N aqueous sodium hydroxide solution was added, and the mixture was reacted at 40 ° C. for 3 hours. The organic layer was washed with water, the solvent was distilled off, and the residue was distilled under reduced pressure to obtain 50 parts by weight of pivalolactone.

[Production Example 6]
10 parts by weight of pivalolactone obtained in Production Example 5 was placed in a reaction vessel equipped with a stirrer and a reflux device, and the reaction temperature was heated to 150 ° C. under a nitrogen stream to start a ring-opening polymerization reaction in a molten state. . After 10 minutes, since the reaction product started to solidify, the stirring was stopped, and the reaction was continued for another 50 minutes in the solid phase to obtain polypivalolactone (C-1) having a weight average molecular weight of 161,000.

[Production Example 7]
In a reaction vessel equipped with a stirrer and a reflux device, 10 parts by weight of hydroxypivalic acid is placed, and the reaction temperature is raised from 150 ° C. to 240 ° C. over 180 minutes in a nitrogen atmosphere, and then at 240 ° C. for 60 minutes. The polymerization reaction was performed in the molten state. After that, the reflux apparatus was removed, and the pressure inside the reaction vessel was gradually reduced to 200 Pa over 60 minutes. At the same time, the reaction temperature was raised to 240 ° C. over 60 minutes, and then melted at 240 ° C. and 200 Pa for 180 minutes. The polymerization reaction was carried out. When the obtained reaction product was subjected to a polymerization reaction at 200 ° C. and 200 Pa in a solid phase for 1000 minutes, polypivalolactone (D-1) having a weight average molecular weight of 46500 was obtained.

[Example 1]
In a reaction vessel equipped with a stirrer and a reflux device, 90 parts by weight of polylactic acid (A-1) obtained in Production Example 1 and 10 parts by weight of pivalolactone obtained in Production Example 5 were placed, and the reaction temperature was measured under a nitrogen stream. The polylactic acid copolymer having a weight average molecular weight of 151000 and a crystal melting enthalpy of 51 J / g with good hydrolysis resistance is obtained by heating the mixture at 200 ° C. for 2 hours and then reducing the pressure to 200 Pa. Obtained. The results are shown in Table 1.

[Examples 2 to 10, Comparative Examples 1 to 4]
The same procedure as in Example 1 was carried out except that the types of polylactic acid, lactic acid monomer, polypivalolactone, hydroxypivalic acid monomer used, their composition ratio, and polymerization conditions were changed as shown in Table 1. The results are shown in Table 1.

Claims (7)

A polylactic acid copolymer comprising a lactic acid unit and a hydroxypivalic acid unit and having a weight average molecular weight of 30,000 to 300,000. The polylactic acid copolymer according to claim 1, wherein the constituent ratio of the lactic acid unit (x) and the hydroxypivalic acid unit (y) is x / y = 99/1 to 1/99 (weight ratio). . The polylactic acid copolymer according to claim 1 or 2, wherein the polylactic acid copolymer is a polylactic acid block copolymer having a lactic acid segment (A) and a hydroxypivalic acid segment (B). The weight average molecular weight of the lactic acid segment (A) is 50,000 to 200,000, and the weight average molecular weight of the hydroxypivalic acid segment (B) is 50,000 to 200,000. The polylactic acid copolymer as described. Using a differential scanning calorimeter, the temperature was increased from 30 ° C. to 250 ° C. at a temperature increase rate of 20 ° C./min, held at 250 ° C. for 3 minutes, and then decreased from 250 ° C. to 30 ° C. at a temperature decrease rate of 20 ° C./min. Further, the crystal melting enthalpy (ΔHm) of the polylactic acid segment (A) observed at 2ndRun when the temperature is increased from 30 ° C. to 250 ° C. at a temperature increase rate of 20 ° C./min is 30 J / g or more. The polylactic acid copolymer according to any one of claims 1 to 4, wherein A molded product formed by molding the polylactic acid copolymer according to any one of claims 1 to 5. (A) after first polymerizing lactide or lactic acid, then (b) polymerizing by adding pivalolactone or hydroxypivalic acid, or (b) after first polymerizing pivalolactone or hydroxypivalic acid, then (a) lactide Alternatively, lactic acid is added for polymerization, and the method for producing a polylactic acid copolymer according to any one of claims 1 to 6.