JP2015044960A - Polylactic resin and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic resin containing no phosphorus compound.SOLUTION: There is provided a polylactic resin containing no phosphorus compound and having the temperature-falling crystallization temperature (Tc) observed by using differential scanning calorimeter (DSC) when raising the temperature from 30°C to 250°C at the rate of temperature raise of 20°C/min., holding at 250°C for 3 min. and then falling the temperature from 250°C to 30°C at the rate of temperature falling of 20°C/min. in the range of 145 to 175°C, and the weight loss rate by using thermogravimetry (TGA) when raising the temperature from 30°C to 240°C at the rate of temperature raise of 200°C/min. and then holding at 240°C for 30 min. in the range of 0.001 to 0.040 wt.%/min. The invention can provide a polylactic resin excellent in heat resistance and a molding cycle property during melt processing and further a low environmental load property.

Description

  The present invention relates to a polylactic acid resin that has high crystallization characteristics and has a low environmental burden and is metal-free and phosphorus-free, and a method for efficiently producing the same.

  In recent years, from the viewpoint of environmental conservation, polylactic acid resins made from plants have attracted attention. Polylactic acid is a polymer that can be melt-molded practically and has biodegradable characteristics. Therefore, it is a biodegradable polymer that decomposes in the natural environment and is released as carbon dioxide or water after use. Development has progressed. On the other hand, in recent years, polylactic acid itself is made from renewable resources (biomass) originating from carbon dioxide and water, so carbon that does not increase or decrease in the global environment even if carbon dioxide is released after use. Neutral properties have attracted attention and are expected to be used as environmentally friendly materials. Furthermore, since lactic acid, which is a monomer of polylactic acid, is being manufactured at low cost by fermentation using microorganisms, polylactic acid has been studied as an alternative material for general-purpose polymers made of petroleum-based plastics. .

  Because of these properties, polylactic acid has been widely used as a melt-molded product, but its heat resistance and durability are low compared to petroleum plastics, and its crystallization speed is low, so it is inferior in productivity. Currently, the scope of practical use is greatly limited. In addition, it is necessary to perform a crystallization treatment such as heat treatment for improving the heat resistance of the polylactic acid molded body, and there is a problem that the productivity is lowered. Therefore, a polylactic acid molded body having excellent heat resistance is desired. ing.

  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). The melting point of such a polylactic acid stereocomplex reaches 200 to 230 ° C., which is 30 to 60 ° C. higher than the melting point 170 ° C. of the polylactic acid homopolymer. Therefore, using this property, attempts have been made to apply polylactic acid stereocomplexes to high melting point and highly crystalline fibers, resin molded products, films and the like. In particular, a polylactic acid stereocomplex having a high crystallization rate is excellent in heat resistance and molding cycle property, and therefore development thereof has been demanded.

  On the other hand, there is a concern that these characteristics deteriorate due to the remaining catalyst during the production of the polylactic acid stereocomplex. Therefore, improvement of characteristics has been attempted by mixing a catalyst deactivator such as a phosphorus compound, a plasticizer, and a nucleating agent. However, the use of phosphorus compounds causes toxic phosphine gas at the time of combustion, shows strong biological harm in animal experiments, and phosphorus compounds flow into rivers by rainwater after incineration and landfill disposal. The load on the human body and the environment is also caused by contamination. Therefore, the polymer material is required to be phosphorus-free.

  In Patent Document 1, high crystallinity is achieved by melt-mixing PLLA and PDLA obtained by direct polymerization and then solid-phase polymerization. However, the remaining metal catalyst has a problem of poor melt residence stability during heat treatment and poor heat resistance and molding cycle performance.

  Further, Patent Document 2 discloses a method for obtaining a high molecular weight polylactic acid resin without containing a metal catalyst. However, it is not a stereocomplex polylactic acid resin and has a long production process time. Since the lactic acid resin cannot be produced, the heat resistance is poor and the application range is limited.

  On the other hand, Patent Documents 3 and 4 achieve high temperature-falling crystallization temperature and melt residence stability by using an additive such as a phosphoric acid ester metal salt and / or a phosphorus compound. The problem was that this caused an environmental load.

JP 2006-307071 A JP 2000-302852 A JP 2012-1618 A JP 2010-260899 A

  The polylactic acid resin can be molded and used for films, sheets, fibers, injection-molded products, and the like.

  When a production method that combines direct polycondensation and solid phase polymerization is used, a polylactic acid resin having a high molecular weight can be obtained, but a metal catalyst is required, and a polymer having excellent stability during melt processing. A lactic acid resin could not be obtained. On the other hand, when a phosphorus compound is used, the catalyst is deactivated and a polylactic acid resin having excellent stability during melt processing can be obtained. However, the inclusion of the phosphorus compound causes an environmental burden. It was.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a polylactic acid resin that is excellent in heat resistance and molding cycleability during melt processing, and further excellent in low environmental load, and has reached the present invention.

That is, the present invention is as follows.
(1) A polylactic acid resin containing a poly-L-lactic acid component and a poly-D-lactic acid component, and using a differential scanning calorimeter (DSC) at a temperature rising rate of 20 ° C./min. In the range of 145 to 175 ° C., the temperature-falling crystallization temperature (Tc) observed when the temperature is lowered from 250 ° C. to 30 ° C. at a rate of temperature reduction of 20 ° C./min. Then, using a thermogravimetric analyzer (TGA), the weight loss rate when the temperature was raised from 30 ° C. to 240 ° C. at a temperature rising rate of 200 ° C./min and then kept at 240 ° C. for 30 minutes was 0.001-0. A polylactic acid resin in a range of 0.040% by weight / min and containing no phosphorus compound.
(2) The weight average molecular weight is 100,000 to 300,000, and the temperature was raised from 30 ° C. to 250 ° C. at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter (DSC). Is maintained for 3 minutes, followed by a temperature decrease from 250 ° C. to 30 ° C. at a temperature decrease rate of 20 ° C./min, and then observed when the temperature is further increased from 30 ° C. to 250 ° C. at a temperature increase rate of 20 ° C./min. The stereocomplex crystal melting enthalpy (ΔHmsc) is in the range of 40 to 60 J / g, the polylactic acid resin as described in (1) above.
(3) The polylactic acid resin as described in (1) or (2) above, wherein the content of the sulfonic acid group-containing compound is 1 to 250 ppm relative to the polylactic acid resin in terms of sulfur atoms.
(4) The polylactic acid resin according to any one of (1) to (3) above, wherein the composition ratio of poly-L-lactic acid to poly-D-lactic acid is 80:20 to 20:80 .
(5) The polylactic acid resin according to any one of (1) to (4), wherein the polylactic acid resin is a polylactic acid block copolymer.
(6) (a) a step of obtaining poly-L lactic acid and poly-D-lactic acid by melt polymerization, (b) a step of mixing poly-L-lactic acid and poly-D-lactic acid, (c) a crystallization step and ( d) A method for producing a polylactic acid resin, comprising a solid phase polymerization step, wherein no phosphorus compound is added in any step.
(7) The method for producing a polylactic acid resin according to the above (6), wherein a metal compound is not added in the (a) melt polymerization step and the (b) mixing step.
(8) In the mixing step (b), the temperature condition for melt-kneading poly-L-lactic acid and poly-D-lactic acid is in the range of 190 to 250 ° C. (6) or (7 ) Manufacturing method of polylactic acid resin as described in 1).
(9) (d) The solid phase polymerization step is performed under multi-stage temperature conditions, and the final stage temperature conditions are in the range of 160 to 200 ° C. The manufacturing method of the polylactic acid resin in any one.

  ADVANTAGE OF THE INVENTION According to this invention, the polylactic acid resin excellent in the heat resistance at the time of melt processing and molding cycle property, and also excellent in the low load property to an environment can be obtained.

<Polylactic acid resin>
The polylactic acid resin of the embodiment of the present invention comprises a poly-L-lactic acid component and a poly-D-lactic acid component.

  In the present invention, when L-lactic acid is the main component, it is called poly-L-lactic acid, and when D-lactic acid is the main component, it is called poly-D-lactic acid. The main component of L-lactic acid is to contain more than 50 mol% of L-lactic acid units in the polymer, and the main component of D-lactic acid is to have D-lactic acid units in the polymer. It contains more than 50 mol%.

  Poly-L-lactic acid is a polymer mainly composed of L-lactic acid and has an optical purity of 99.0% e.e. e. From the viewpoint of heat resistance and molding processability, it is preferably 99.2% e.e. e. More preferably, it is 99.3% e.e. e. The above is particularly preferable. The upper limit of the optical purity is theoretically 100% e.e. e. However, in reality, 99.8e. e. It is.

  Poly-D-lactic acid is a polymer mainly composed of D-lactic acid and has an optical purity of 99.0% e.e. e. From the viewpoint of heat resistance and molding processability, it is preferably 99.2% e.e. e. More preferably, it is 99.3% e.e. e. The above is particularly preferable.

  In the present invention, the polylactic acid resin may be copolymerized with other components other than L-lactic acid or D-lactic acid as long as the performance of the obtained polylactic acid resin is not impaired. Examples of other components include polycarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, and lactones. Specifically, polyvalent carboxylic acids such as succinic acid, adipic acid, sebacic acid, fumaric acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, cyclohexanedicarboxylic acid and furandicarboxylic acid. Acids or their derivatives; ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, isosorbide, neopentylglycol, glycerin, trimethylolpropane, pentaerythritol, trimethylolpropane, pentaerythritol with ethylene oxide or propylene oxide Polyhydric alcohol with addition of bisphenol, aromatic polyhydric alcohol with addition reaction of ethylene oxide with bisphenol, diethylene glycol, triethylene glycol Polyhydric alcohols such as chol, polyethylene glycol, polypropylene glycol or derivatives thereof; hydroxycarboxylic acids such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid; glycolide, Examples include lactones such as ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and δ-valerolactone.

  In the present invention, the weight average molecular weight (Mw) of the polylactic acid resin is preferably 100,000 or more in view of mechanical properties, more preferably 120,000 or more, and molding processability of 140,000 or more. And particularly preferred in terms of mechanical properties. The weight average molecular weight (Mw) is preferably 300,000 or less, more preferably 280,000 or less, and 250,000 or less in terms of molding processability and mechanical properties. Is particularly preferable. Further, the degree of dispersion, which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), of the polylactic acid resin is preferably 1.5 or more from the viewpoint of mechanical properties, and is preferably 1.8 or more. Further, 2.0 or more is particularly preferable from the viewpoint of molding processability and mechanical properties. The degree of dispersion is preferably 3.0 or less, more preferably 2.7 or less, and preferably 2.4 or less in terms of molding processability and mechanical properties. Particularly preferred. The weight average molecular weight and dispersity are standard polymethylmethacrylate conversion values obtained by gel permeation chromatography (GPC) measurement using hexafluoroisopropanol as a solvent.

  The molecular weight of the poly-L-lactic acid component and the poly-D-lactic acid component used in the present invention is not particularly limited, but the weight average molecular weight of either poly-L-lactic acid or poly-D-lactic acid is not limited. Is preferably from 60,000 to 300,000, and the other weight average molecular weight is preferably from 10,000 to 50,000. More preferably, one weight average molecular weight is 100,000 to 270,000 and the other weight average molecular weight is 20,000 to 45,000. Particularly preferably, one weight average molecular weight is 150,000 to 240,000 and the other weight average molecular weight is 30,000 to 45,000. However, the weight average molecular weight of either one of poly-L-lactic acid or poly-D-lactic acid is less than 60,000 or more than 300,000, and the other weight average molecular weight is less than 10,000 or more than 50,000. Also good. Here, the weight average molecular weight is a standard polymethyl methacrylate conversion value obtained by gel permeation chromatography (GPC) measurement using hexafluoroisopropanol as a solvent.

  In the present invention, the ratio of the weight of the poly-L-lactic acid component to the total weight of the poly-L-lactic acid component and the poly-D-lactic acid component constituting the polylactic acid resin is preferably 20 to 80% by weight. In particular, it is desirable that the ratio of the weight of the poly-L-lactic acid component to the total weight is biased from the viewpoint of easy formation of a stereo complex. Specifically, it is desirable that the weight of the poly-L-lactic acid component and the weight of the poly-D-lactic acid component are different, and the difference between the two is larger. Therefore, the ratio of the weight of the poly-L-lactic acid component to the total weight is more preferably 60 to 80% by weight or 20 to 40% by weight, and 65 to 75% by weight or 25 to 35% by weight. Is most preferred. When the ratio of the weight of the poly-L-lactic acid component to the total weight of the poly-L-lactic acid component and the poly-D-lactic acid component constituting the polylactic acid resin is other than 50% by weight, It is preferable to blend a large amount of -L-lactic acid component or poly-D-lactic acid component.

  The polylactic acid resin of the embodiment of the present invention is composed of a segment composed of a poly-L-lactic acid component and a segment composed of a poly-D-lactic acid component in that the stereocomplex formation rate is high, and heat resistance and impact strength are excellent. The polylactic acid block copolymer is preferable. However, the polylactic acid resin of the embodiment of the present invention is obtained by heating and melt-mixing a poly-L-lactic acid component and a poly-D-lactic acid component without performing a special polymerization step for forming a block copolymer. May be manufactured.

  The polylactic acid resin of the present invention was heated from 30 ° C. to 250 ° C. at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter (DSC), and then kept at 250 ° C. for 3 minutes, and then the temperature falling rate of 20 The stereocomplex crystal melting point (Tmsc) is 215 ° C. observed when the temperature is lowered from 250 ° C. to 30 ° C. at a rate of 20 ° C./min and then further raised from 30 ° C. to 250 ° C. at a rate of temperature increase of 20 ° C./min. In view of excellent heat resistance, it is preferably 218 ° C. or higher, more preferably 220 ° C. or higher, and particularly preferably 222 ° C. or higher.

  The polylactic acid resin of the present invention was heated from 30 ° C. to 250 ° C. at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter (DSC), and then kept at 250 ° C. for 3 minutes, and then the temperature falling rate of 20 The stereocomplex crystal melting enthalpy (ΔHmsc) observed when the temperature was decreased from 250 ° C. to 30 ° C. at a rate of 20 ° C./min and then further increased from 30 ° C. to 250 ° C. at a rate of temperature increase of 20 ° C./min, In view of excellent heat resistance and molding processability, it is preferably 40 J / g or more, more preferably 45 J / g, and further preferably 50 J / g or more. The upper limit of ΔHmsc is theoretically 142 J / g, but is practically 100 J / g. ΔHmsc represents the value of the heat of crystal melting that appears at 190 ° C. or higher and lower than 240 ° C. when the polylactic acid resin is heated to 250 ° C. in DSC measurement.

  The polylactic acid resin of the present invention was heated from 30 ° C. to 250 ° C. at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter (DSC), and then kept at 250 ° C. for 3 minutes, and then the temperature falling rate of 20 It is necessary that the temperature-falling crystallization temperature (Tc) observed when the temperature is lowered from 250 ° C. to 30 ° C. at a rate of ° C./minute is in the range of 145 to 175 ° C. Moreover, it is preferable that it is 150-170 degreeC at the point which is excellent in molding cycle property, and it is further more preferable that it is 155-170 degreeC. When the temperature drop crystallization temperature (Tc) is less than 145 ° C., it is not preferable because excellent molding cycle properties cannot be exhibited. In addition, when the temperature-falling crystallization temperature (Tc) exceeds 175 ° C., it is in the vicinity of the melting temperature of the polylactic acid homocrystal, which is not preferable because decomposition proceeds with crystallization during molding.

  The polylactic acid resin of the present invention preferably has a cooling crystallization enthalpy (ΔHc) of 20 J / g or more in DSC measurement. The ΔHc is preferably 25 J / g or more from the viewpoint of heat resistance of a molded product made of polylactic acid resin, and more preferably 30 J / g or more from the viewpoint of moldability. By setting ΔHc to 20 J / g or more, the crystallization speed can be increased, the molding time can be shortened, and the molding processability can be improved. The upper limit of ΔHc is theoretically 142 J / g, but is practically 100 J / g.

  The polylactic acid resin of the present invention has a weight reduction rate when it is heated from 30 ° C. to 240 ° C. at a rate of temperature increase of 200 ° C./min using a thermogravimetric analyzer (TGA) and then kept at 240 ° C. for 30 minutes. It is necessary to be in the range of 0.001 to 0.040% by weight / min. In view of being hard to be thermally decomposed during molding, 0.030% by weight / minute or less is preferable, and 0.020% by weight / minute or less is more preferable. When the weight reduction rate exceeds 0.040% by weight / min, thermal decomposition during the molding process becomes remarkable, which leads to a decrease in mechanical properties of the molded product. The polylactic acid resin of the present invention is a polylactic acid resin that is in the range of the above-described weight reduction rate, exhibits high heat resistance, and is particularly excellent in moldability and mechanical properties.

  The polylactic acid resin of the present invention needs to contain no phosphorus compound. Here, it does not contain any phosphorus compound, but it is preferable that no phosphorus compound is contained, but it means that it is acceptable if it is a trace amount that may be mixed in from the raw material and the manufacturing process. A trace amount here means the range of 1-20 ppm with respect to polylactic acid resin in conversion of a phosphorus atom. It is preferably 1 to 10 ppm, and more preferably 1 to 5 ppm in that the crystallization characteristics are reduced by the phosphorus compound, the mechanical properties are reduced, and the influence on the environment is small.

  The polylactic acid resin of the present invention is preferably 1 to 250 ppm in terms of sulfur atom, more preferably 1 to 200 ppm relative to the polylactic acid resin, in terms of excellent hydrolysis resistance. Preferably, 1-150 ppm is more preferable. When the content of the sulfur-containing compound exceeds 250 ppm, hydrolysis resistance is lowered, which is not preferable.

  The polylactic acid resin of the present invention preferably contains no metal compound. The metal compounds here are tin compounds, titanium compounds, lead compounds, zinc compounds, cobalt compounds, iron compounds, lithium compounds, rare earth compounds, antimony compounds, bismuth compounds, manganese compounds, nickel compounds, copper compounds, molybdenum compounds and It means a metal salt comprising them. Moreover, it does not contain a metal compound at all, but it does not contain any metal compound, but it means that it is acceptable if it is a trace amount that may be mixed in from the raw material and the manufacturing process. A trace amount here means the range of 1-5 ppm with respect to polylactic acid resin in conversion of a metal atom. It is more preferably 3 ppm or less from the viewpoint that the influence of a decrease in crystallization characteristics, a decrease in mechanical properties and a load on the environment due to the metal compound is small.

<Method for producing polylactic acid resin>
As a method for producing the poly-L-lactic acid component and the poly-D-lactic acid component used in the embodiment of the present invention, any of a ring-opening polymerization method and a direct polymerization method can be used. However, it is preferable to manufacture by a direct polymerization method in terms of simplicity of the manufacturing process and raw material costs. The poly-L-lactic acid component and the poly-D-lactic acid component may be produced by the same production method, or one may be produced by a direct polymerization method and the other may be produced by a ring-opening polymerization method.

  As a method for obtaining a poly-L-lactic acid component and a poly-D-lactic acid component by a ring-opening polymerization method or a direct polymerization method, for example, either one of L-lactic acid and D-lactic acid is subjected to ring-opening polymerization in the presence of a catalyst. Or the method of performing direct polymerization can be mentioned.

  In the present invention, a polylactic acid prepolymer is produced by direct polycondensation using lactic acid as a raw material. As an impurity in lactic acid, lactic acid having a total of alcohols of 70 ppm or less, a total of organic acids of 800 ppm or less, a total of aldehydes of 50 ppm or less, and a total of esters of 400 ppm or less is used as a raw material. It is preferable.

  In addition, when obtaining a poly-L-lactic acid component and a poly-D-lactic acid component by a direct polymerization method, from the viewpoint of obtaining a high molecular weight product, the amount of water in the reaction system is the amount of L-lactic acid in the reaction system or It is preferable that it is 4 mol% or less with respect to the amount of D-lactic acid. More preferably, it is 2 mol% or less, and 0.5 mol% or less is particularly preferable. The water content is a value measured by a coulometric titration method using the Karl Fischer method.

  The production method of the prepolymer is not particularly limited, and can be produced by known direct polycondensation using lactic acid as a raw material. Either batch polymerization or continuous polymerization may be used, but continuous polymerization is preferred in that the amount of carboxyl end groups can be reduced and the effect of improving fluidity and hydrolysis resistance is increased. In the present invention, those obtained by melt polymerization are called prepolymers, those obtained by crystallizing the prepolymers are called crystallization prepolymers, and those obtained by solid-phase polymerization of the crystallized prepolymers are called polylactic acid resins. .

  When an acid catalyst is used as the polymerization catalyst, a sulfur-containing compound having sulfur having an oxidation number of +5 or more is preferred in that a polylactic acid resin having a high molecular weight can be obtained. In addition, a monosulfonic acid compound is more preferable as the sulfur-containing compound having sulfur having an oxidation number of +5 or more in that a polylactic acid resin having excellent thermal stability can be obtained. In addition, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-bromoethanesulfonic acid, and 2-aminoethanesulfonic acid are more preferable because they can suppress coloring. P-Toluenesulfonic acid is particularly preferable in terms of excellent properties. Two or more kinds of catalysts can be used in combination.

  When a sulfur-containing compound having sulfur with an oxidation number of +5 or more is used as a catalyst, the amount added is a raw material to be used (L-lactic acid and L-lactic acid) in that a polylactic acid resin having a high molecular weight can be efficiently obtained. / Or D-lactic acid) is preferably 30 to 3,000 ppm in terms of sulfur atom, more preferably 35 to 2,700 ppm, further preferably 40 to 2,500 ppm, and 45 to 2,200 ppm. Particularly preferred.

  The catalyst is preferably added at the start of the melt polymerization process or during the melt polymerization process in that a high molecular weight polylactic acid resin can be efficiently obtained.

  The reaction conditions of the melt polymerization step are not particularly limited, but the melt polymerization step has a reaction temperature of 140 to 180 ° C. as a substantial reaction temperature in that a polylactic acid resin having a high molecular weight can be efficiently obtained. It is preferable to carry out at a temperature, and it is preferable to carry out at a temperature of 145-175 degreeC, and it is more preferable to carry out at a temperature of 140-170 degreeC at the point that the polylactic acid resin which is excellent also in hue can be obtained efficiently. . The temperature of the melt polymerization process may be a one-stage temperature condition maintained at a constant temperature, or may be a multi-stage temperature condition in which the temperature is changed in two or more stages. From the viewpoint that a lactic acid resin can be obtained efficiently, it is preferable to use two or more stages of temperature conditions. For example, after performing reaction at the temperature of 140-160 degreeC, the method of reacting at the temperature of 160-180 degreeC etc. are mentioned.

  In terms of efficiently obtaining a polylactic acid resin having a high molecular weight, the melt polymerization step is preferably performed at a pressure of 0.13 to 130 kPa as a substantial reaction pressure, and the polylactic acid also has excellent hue. It is preferable to carry out at a pressure of 1 to 100 kPa, more preferably at a pressure of 10 to 90 kPa, further preferably at a pressure of 10 to 80 kPa, in that the resin can be efficiently obtained. It is particularly preferable to carry out at a pressure of 70 kPa. Further, the pressure of the melt polymerization process may be a one-stage pressure condition that maintains a constant pressure, or may be a multi-stage pressure condition that changes the pressure stepwise to two or more stages, but it can increase the molecular weight and is excellent in hue. In this respect, it is preferable to set the pressure conditions in two or more stages. For example, after reacting at the pressure of 13.3-66.6 kPa, the method of reacting at the pressure of 1.3-6.5 kPa, etc. are mentioned. Moreover, it is also preferable to make it react under distribution | circulation of inert gas, such as nitrogen.

  Reaction conditions including a melt polymerization step including at least two stages of a temperature of 140 ° C. to 160 ° C., a pressure of 13.3 to 66.6 kPa, and a temperature of 160 ° C. to 180 ° C. and a pressure of 1.3 to 6.5 kPa. It is preferable to carry out continuously.

  The melt polymerization step is preferably performed with a reaction time of 0.5 to 50 hours, and can be performed with a reaction time of 1 to 45 hours in that a polylactic acid resin having an excellent hue can be efficiently obtained. The reaction time is preferably 2 to 40 hours, more preferably 3 to 35 hours, and particularly preferably 4 to 30 hours. Moreover, when performing the temperature and pressure of a melt-polymerization process on the conditions of 2 steps or more, for example, the reaction time of 2 to 15 hours at the temperature of 140-160 degreeC and the pressure of 13.3-66.6 kPa is sufficient. And a method of further reacting at a temperature of 160 to 180 ° C. and a pressure of 1.3 to 6.5 kPa for a reaction time of 2 to 15 hours. In addition, even if it is a case where temperature and pressure are performed on multistage conditions of two or more steps, the total reaction time of the melt polymerization step is preferably 0.5 to 50 hours.

  When the melt polymerization process is a batch process, the time required to reach the substantial reaction temperature from room temperature is preferably within 30% of the process time, more preferably within 20%, more preferably within 10%. More preferably it is. Further, the time required to reach a substantial reaction pressure from normal pressure is preferably within 50% of the process time, more preferably within 40%, and even more preferably within 30%.

  The reaction vessel used in the melt polymerization step 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. It is preferable to use an apparatus in which a reaction tank and a reflux apparatus are connected in that a polylactic acid resin having an excellent high molecular weight and hue can be obtained efficiently. The reflux device is preferably connected to the upper part of the reaction vessel, and more preferably a vacuum pump is connected to the reflux device. The reflux device is for separating volatile components, a vaporizing section that has a function of removing a part of the volatile components out of the reaction system, and a condensing section that has a function of returning a part of the volatile components into the reaction system. It is what has. Specifically, any volatile component can be used as long as it removes water and returns lactic acid and lactide or their low molecular weight polymer to the reaction vessel in the melt polymerization step. Here, as a system of the condenser constituting the condensing unit, for example, a double tube system, a multi-tube system, a coil system, a plate system, a plate fin system, a spiral system, a jacket system, and the like can be cited. The reaction tank may have one reaction chamber or may be composed of two or more reaction chambers divided by a partition plate or the like, but a polylactic acid resin having a high molecular weight can be obtained efficiently. In this respect, those composed of two or more reaction chambers are preferable.

  In the melt polymerization step, the method of taking out the produced prepolymer from the reaction vessel after completion of the reaction is not particularly limited, and examples thereof include a method of taking out by extrusion with an inert gas such as nitrogen, a method of taking out with a gear pump, and the like. . From the viewpoint of the handleability of the prepolymer having a low viscosity, a method of taking out by extrusion with an inert gas such as nitrogen is preferable.

  When producing the polylactic acid resin of the embodiment of the present invention, after the step of melt-kneading the poly-L-lactic acid component and the poly-D-lactic acid component, 70 to 90 ° C. under vacuum or nitrogen flow. It is preferable to perform a step of crystallization at 130 to 150 ° C. under vacuum or nitrogen flow. When the polylactic acid resin is a polylactic acid block copolymer composed of a segment composed of a poly-L-lactic acid component and a segment composed of a poly-D-lactic acid component, a vacuum is applied after the melt-kneading step. Crystallization is performed at 70 to 90 ° C. under a nitrogen flow or under a nitrogen flow, and then a devolatilization step is performed at 130 to 150 ° C. under a vacuum or a nitrogen flow. A step of phase polymerization may be performed.

  The method for melt-kneading the poly-L-lactic acid component and the poly-D-lactic acid component is not particularly limited. For example, among the poly-L-lactic acid component and the poly-D-lactic acid component, a method of melt kneading at or above the melting end temperature of the component having the higher melting point, a method of removing the solvent after mixing in the solvent, or a molten state At least one of the poly-L-lactic acid component and the poly-D-lactic acid component is retained in advance while being sheared in a melting machine within a temperature range of melting point −50 ° C. to melting point + 20 ° C., and then poly-L- Examples include a method of mixing so that crystals of a mixture of a lactic acid component and a poly-D-lactic acid component remain. Among these, the melt kneading method is preferable from the viewpoint of productivity.

  Examples of the method of melt-kneading at the melting end temperature or higher include a method of mixing the poly-L-lactic acid component and the poly-D-lactic acid component by a batch method or a continuous method, and any method may be used. Examples of the kneading apparatus 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. From the viewpoint that uniform and sufficient kneading can be performed, a single screw extruder or a twin screw extruder is used. It is preferable to use a machine.

  About the temperature conditions at the time of melt-kneading above the melting end temperature, it is preferable to carry out at or above the melting end temperature of the higher melting point component of the poly-L-lactic acid component and the poly-D-lactic acid component. Preferably it is 190 degreeC or more, More preferably, it is 210 degreeC or more, Most preferably, it is 220 degreeC or more. Moreover, it is preferably 250 ° C. or lower, more preferably 245 ° C. or lower, and particularly preferably 240 ° C. or lower. By setting the temperature at the time of melt kneading to 250 ° C. or lower, a decrease in the molecular weight of the mixture can be suppressed, and by setting it to 190 ° C. or higher, a decrease in the fluidity of the mixture can be suppressed.

  Moreover, about the time conditions for melt-kneading, 0.1 minutes or more are preferable, 0.3 minutes or more are more preferable, and 0.5 minutes or more are especially preferable. The time condition is preferably 10 minutes or less, more preferably 5 minutes or less, and particularly preferably 3 minutes or less. By setting the melt kneading time to 0.1 minutes or more, the uniformity of mixing of poly-L-lactic acid and poly-D-lactic acid can be improved. Moreover, the thermal decomposition by mixing can be suppressed by making melt-kneading time into 10 minutes or less.

  There are no particular limitations on the pressure conditions at the time of melt-kneading, and any conditions under an air atmosphere or an inert gas atmosphere such as nitrogen may be used.

  In the kneading using the extruder, the method for supplying the poly-L-lactic acid component and the poly-D-lactic acid component is not particularly limited, and the poly-L-lactic acid component and the poly-D-lactic acid component are collectively collected from the resin supply port. And a method of supplying the poly-L-lactic acid component and the poly-D-lactic acid component separately to the resin supply port and the side supply port, respectively, using a side supply port if necessary. Further, the supply of the poly-L-lactic acid component and the poly-D-lactic acid component to the kneader can also be performed in a molten state directly from the production process of the poly-L-lactic acid component and the poly-D-lactic acid component. .

  The screw element in the extruder is preferably provided with a kneading element in the mixing part so that the poly-L-lactic acid component and the poly-D-lactic acid component can be uniformly mixed to form a stereo complex.

  The shape after the melt-kneading of the poly-L-lactic acid component and the poly-D-lactic acid component is not particularly limited, and any of a lump shape, a film, a pellet, and a powder may be used. However, it is preferable to use pellets or powder from the viewpoint of efficiently proceeding with each step. As a method of making pellets, a method of extruding a pellet of a mixture of a poly-L-lactic acid component and a poly-D-lactic acid component and pelletizing, or a method of extruding the mixture into water and pelletizing using an underwater cutter Is mentioned. 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.

  For the purpose of increasing the molecular weight, solid phase polymerization may be further performed after direct polymerization. In the case of performing solid-phase polymerization, the shapes of poly-L-lactic acid and poly-D-lactic acid to be subjected to solid-phase polymerization are not particularly limited, and any of a lump shape, a film, a pellet, and a powder may be used. However, it is preferable to use pellets or powder from the viewpoint of efficiently proceeding with solid phase polymerization. As a method for forming pellets, poly-L-lactic acid or poly-D-lactic acid after direct polymerization is extruded into a strand shape and pelletized, or poly-L-lactic acid or poly-D-lactic acid after direct polymerization is submerged in water. And a method of pelletizing using an underwater cutter. 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 performed, it is preferable that poly-L-lactic acid or poly-D-lactic acid after direct polymerization is crystallized. In the embodiment of the present invention, when poly-L-lactic acid or poly-D-lactic acid after direct polymerization is in a crystallized state, poly-L-lactic acid or poly-D is used when the solid phase polymerization step is performed. -Crystallization of lactic acid is not always necessary. However, the efficiency of solid phase polymerization can be further increased by crystallizing poly-L-lactic acid or poly-D-lactic acid prior to the solid phase polymerization step.

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

  The temperature of the crystallization step after melt-kneading the poly-L-lactic acid component and the poly-D-lactic acid component is preferably 70 to 90 ° C. By setting the crystallization temperature to 70 ° C. or higher, crystallization can be sufficiently advanced, and it is possible to suppress the fusion of pellets or powders in the subsequent devolatilization step. Moreover, by setting the crystallization temperature to 90 ° C. or less, it is possible to suppress fusion of pellets or powders, and to suppress a decrease in molecular weight and generation of by-products due to thermal decomposition.

  The time for the crystallization step is preferably 3 hours or more, and more preferably 5 hours or more from the viewpoint of suppressing fusion of pellets or powders in the subsequent devolatilization step. By setting the crystallization time to 3 hours or longer, crystallization can be sufficiently advanced, and fusion of pellets or powders can be suppressed in the subsequent devolatilization step.

  When performing this crystallization process, it is preferable to carry out under vacuum or inert gas flow, such as dry nitrogen. The degree of vacuum when performing crystallization under vacuum is preferably 150 Pa or less, more preferably 75 Pa or less, and particularly preferably 20 Pa or less. The flow rate at the time of crystallization under an inert gas stream is preferably 0.1 ml / min or more, more preferably 0.5 ml / min or more, particularly preferably 1.0 ml / min or more with respect to 1 g of the mixture. The flow rate is preferably 2000 ml / min or less, more preferably 1000 ml / min or less, and particularly preferably 500 ml / min or less with respect to 1 g of the mixture.

  The temperature of the devolatilization step after the crystallization step is preferably 130 ° C. or higher, more preferably 135 ° C. or higher, more preferably 140 ° C. or higher, from the viewpoint of reducing the acid value by removing by-products. preferable. Moreover, it is preferable that the temperature of the said devolatilization process is 150 degrees C or less from the point of the acid value reduction by the removal of a by-product.

  About 3 hours or more is preferable about the time of a devolatilization process, It is more preferable that it is 4 hours or more from the point of the acid value reduction by removal of a by-product, and it is further more preferable that it is 5 hours or more.

  This devolatilization step is preferably performed under vacuum or an inert gas stream such as dry nitrogen. The degree of vacuum when performing devolatilization under vacuum is preferably 150 Pa or less, more preferably 75 Pa or less, and particularly preferably 20 Pa or less. The flow rate during devolatilization under an inert gas stream is preferably 0.1 ml / min or more, more preferably 0.5 ml / min or more, and particularly preferably 1.0 ml / min or more with respect to 1 g of the mixture. The flow rate is preferably 2000 ml / min or less, more preferably 1000 ml / min or less, and particularly preferably 500 ml / min or less with respect to 1 g of the mixture.

  In the method for producing a polylactic acid resin according to an embodiment of the present invention, a solid phase polymerization step is further performed after the devolatilization step, thereby comprising a segment composed of a poly-L-lactic acid component and a poly-D-lactic acid component. You may manufacture the polylactic acid block copolymer comprised from a segment.

  The final temperature condition for carrying out the solid phase polymerization step after the direct polymerization is preferably in the range of 160 to 200 ° C. in that the solid phase polymerization proceeds efficiently. Moreover, it is more preferable that it is the range of 165-190 degreeC at the point that a high molecular weight and highly crystalline polylactic acid resin is obtained, and it is the range of 170-180 degreeC from the point that coloring can be suppressed. Is more preferable. When the final temperature condition of the solid phase polymerization step is less than 160 ° C., the condensed water generated in the solid phase polymerization is not sufficiently distilled off, and the progress of the solid phase polymerization is slowed down to obtain a highly crystalline polylactic acid resin. It is not preferable because it is not possible. Moreover, when the final temperature condition of a solid phase polymerization process exceeds 200 degreeC, since a stereocomplex crystal melt | dissolves, a pellet is easy to fuse | melt and a yield falls, and is unpreferable.

  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 110 to 130 ° C. for 1 to 15 hours, the second stage is 135 to 155 ° C. for 1 to 30 hours, and the third stage is 160 It is preferable to raise the temperature at ~ 200 ° C for 10 to 30 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 ° C. to 150 ° C. to 160 to 200 ° C. at a rate of 1 to 5 ° C./hour. 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. The degree of vacuum when performing solid-phase polymerization under vacuum is preferably 150 Pa or less, more preferably 75 Pa or less, and particularly preferably 20 Pa or less. The flow rate when solid-phase polymerization is performed under an inert gas stream is preferably 0.1 ml / min or more, more preferably 0.5 ml / min or more, and 1.0 ml with respect to 1 g of the mixture. / Min or more is particularly preferable. Further, it is preferably 2000 ml / min or less, more preferably 1000 ml / min or less, and particularly preferably 500 ml / min or less.

  The shape of the crystallization prepolymer used in the solid phase polymerization step is not particularly limited, and any of a lump shape, a film, a pellet, and a powder may be used, but the shape of a pellet or a powder is preferable. For example, the maximum diameter is about 1 to 10 mm, particularly about 1.2 to 8 mm, most often about 1.5 to 6 mm, spherical, oblong, flat sphere, plate, rod, and the like A shape, irregular shape, or any other shape, also called a chip. In the case of powder, the average particle diameter is preferably 0.01 to 5 mm, more preferably 0.1 to 1 mm, in that solid-phase polymerization can be efficiently performed. The pellet shape is excellent in productivity and highly effective particularly in solid phase polymerization.

  The solid phase polymerization step may be a batch method or a continuous method. Moreover, a stirring tank type reaction tank, a mixer type reaction tank, a tower type reaction tank, etc. can be used for the reaction tank, These reaction tanks can be used in combination of 2 or more types. It is preferable to carry out by a continuous method from the point of productivity.

  A filler and other additives can be added to the polylactic acid resin of the present invention as long as the characteristics of the present invention are not impaired. It does not specifically limit as a filler, Any fillers, such as fibrous form, plate shape, a powder form, a granular form, can be used. Specific examples of the filler include glass fiber, carbon fiber, potassium titanate whisker, zinc oxide whisker, calcium carbonate whisker, wollastonite whisker, aluminum borate whisker, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, Fibrous fillers such as stone fiber and metal fiber; or silicates such as talc, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, asbestos, alumina silicate; silicon oxide, magnesium oxide Metal oxides such as alumina, zirconium oxide, titanium oxide and iron oxide; carbonates such as calcium carbonate, magnesium carbonate and dolomite; metal sulfates such as calcium sulfate and barium sulfate; glass beads, ceramic beads, boron nitride , Metal hydroxides such as silicon carbide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide; glass flakes, glass powder, carbon black and silica, non-fibrous fillers such as graphite; and montmorillonite, beidellite, nontronite, Smectite clay minerals such as saponite, hectorite, and soconite; various clay minerals such as vermiculite, halloysite, kanemite, and kenyanite; A layered silicate typified by swellable mica is used.

  Other additives include antioxidants (eg hindered phenolic antioxidants), UV absorbers (eg resorcinol, salicylate), anti-coloring agents, lubricants and mold release agents (stearic acid, montanic acid and metal salts thereof) , Its esters, its half esters, stearyl alcohol, stearamide and polyethylene wax), colorants (dyes, pigments, etc.), conductive agents or colorants such as carbon black, crystal nucleating agents, plasticizers, flame retardants (bromine flame retardants) , Silicone flame retardants, etc.), flame retardant aids, and antistatic agents.

  Further, the polylactic acid resin of the present invention can be mixed with other resins as long as the object of the present invention is not impaired. Examples of other resins include heat such as polyethylene, polypropylene, acrylic resin, styrene resin, polyamide, polyphenylene sulfide resin, polycarbonate resin, polyether ether ketone resin, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. Plastic resin; thermosetting resin such as phenol resin, melamine resin, polyester resin, silicone resin, epoxy resin; or ethylene / glycidyl methacrylate copolymer, polyester elastomer, polyamide elastomer, ethylene / propylene terpolymer, ethylene / butene-1 At least one selected from soft thermoplastic resins such as copolymers can be used.

  The polylactic acid resin composition of the present invention can be widely used as a molded product. Examples of the molded products include films, sheets, fibers / clothes, nonwoven fabrics, injection molded products, extrusion molded products, vacuum / pressure molded products, blow molded products, and composites with other materials. The article is useful for agricultural materials, horticultural materials, fishery materials, civil engineering / architectural materials, stationery, medical supplies, automotive parts, electrical / electronic components or other uses. The polylactic acid resin composition of the present invention is particularly suitable for processing into a film or sheet.

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

(1) Weight average molecular weight, number average molecular weight, molecular weight distribution Prepolymer and polylactic acid resin are measured by gel permeation chromatography (GPC), and values of weight average molecular weight and number average molecular weight in terms of standard polymethyl methacrylate are obtained. It was. The molecular weight distribution is a value represented by the ratio of the weight average molecular weight to the number average molecular weight. GPC measurement is 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 such that the flow rate was 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 as a measurement sample.

(2) Thermal characteristics The thermal characteristics of the polylactic acid resin were measured using a differential scanning calorimeter (DSC7) manufactured by PERKIN ELMER. When 10 mg of a sample was heated from 30 ° C. to 250 ° C. at a rate of 20 ° C./min in a nitrogen atmosphere, held at 250 ° C. for 3 minutes, and then cooled from 250 ° C. to 30 ° C. at a rate of 20 ° C./min. The temperature-falling crystallization temperature of the lactic acid resin was Tc, and the temperature-falling crystallization enthalpy was ΔHc. When the temperature was further raised from 30 ° C. to 250 ° C. at a rate of 20 ° C./min, the stereocomplex crystal melting point appearing at 190 ° C. or higher and lower than 240 ° C. was defined as Tmsc, and the stereocomplex crystal melting enthalpy was defined as ΔHmsc.

(3) Weight reduction rate during melt residence The weight reduction rate during melt residence of the polylactic acid resin was measured using a thermogravimetric analyzer (TGA7) manufactured by PERKIN ELMER. 10 mg of the sample was calculated from the weight loss after 30-minute residence after raising the temperature from 30 ° C. to 240 ° C. at a rate of 200 ° C./min in a nitrogen atmosphere.

(4) Content of phosphorus compound and tin compound After 1.0 g of a polylactic acid resin was precisely weighed, nitric acid, sulfuric acid, perchloric acid, and hydrofluoric acid were added, followed by thermal decomposition under conditions of 550 ° C./8 hours. After heating, 20 ml of 1.2 M dilute nitric acid solution was added to obtain a sample solution for ICP measurement. The luminescence intensity was measured using an ICP emission spectroscopic analyzer (manufactured by SII Nanotechnology, SPS-4000), and the phosphorus atom and tin atom contents were quantified. In addition, the detection lower limit density | concentration by the measuring method used this time is 1.0 ppm.

(5) Heat resistance ◎, when the weight reduction rate during melt residence is 0.001 wt% / min to 0.020 wt% / min, exceeding 0.020 wt% / min to 0.030 wt% The case where it was% / min or less was marked with ○, the case where it exceeded 0.030 wt% / min to 0.040 wt% / min or less, Δ, and the case where it exceeded 0.040 wt% / min, where x.

(6) Hydrolysis resistance Using a constant temperature and humidity chamber manufactured by Espec, 50 mg of polylactic acid resin was subjected to wet heat treatment under conditions of a temperature of 80 ° C. and a relative humidity of 95% for 24 hours, and the weight average molecular weight of the polylactic acid resin before and after treatment was determined. It measured by the method of said (1). The case where the weight average molecular weight retention of the polylactic acid resin after the treatment based on the weight average molecular weight of the polylactic acid resin before the treatment is 95% or more is ◎, the case where it is less than 95% to 85% or more, The case of less than 85% to 75% or more was judged as Δ, and the case of less than 75% was judged as ×.

(7) Molding cycle (cooling time for molding)
Using the injection molding machine (Sumitomo Heavy Industries, Ltd. SG75H-MIV), injection molding is performed at a cylinder temperature of 220 ° C and a mold temperature of 70 ° C, and the shortest cooling that gives a solid molded product (tensile test piece) without deformation. Time (cooling time for molding) was measured. The case where the cooling time was less than 40 seconds was judged as ◎, the case where it was 40 seconds or more but less than 45 seconds, ◯, the case where it was 45 seconds or more but less than 50 seconds, Δ, and the case where it was 50 seconds or more, was judged as ×. . It can be said that the shorter the molding cycle time, the better the moldability.

(8) Environmental impact property The thing which does not contain 1.0 ppm or more of phosphorus compounds or a metal compound in a polylactic acid resin was set as (circle), and the thing which contains it was set as x.

(Production Example 1)
In a reaction vessel equipped with a stirrer and a reflux device, 100 parts by weight of a 90% aqueous solution of L-lactic acid and 0.6 parts by weight of p-toluenesulfonic acid monohydrate as a catalyst were added, and then the temperature was raised to 150 ° C. After that, the reaction was continued for 3.5 hours while the pressure was gradually reduced and water was distilled off. Thereafter, a polymerization reaction was carried out for 7 hours while gradually reducing the pressure at 170 ° C. until reaching 13 Pa. Thereafter, crystallization treatment is performed at 80 ° C. for 5 hours under a nitrogen atmosphere, and after devolatilization at 140 ° C. for 6 hours and 150 ° C. for 6 hours under a pressure of 60 Pa, 160 ° C. for 20 hours and 170 ° C. for 10 hours. Solid phase polymerization was performed to obtain poly-L-lactic acid (a-1).

(Production Example 2)
Poly-L-lactic acid (a-2) was obtained in the same manner as in Production Example 1 except that the catalyst used was changed to 0.6 parts by weight of benzenesulfonic acid.

(Production Example 3)
Poly-L-lactic acid (a-3) was obtained in the same manner as in Production Example 1 except that the catalyst used was changed to 1.5 parts by weight of methanesulfonic acid.

(Production Example 4)
After adding 100 parts by weight of a 90% aqueous solution of D-lactic acid and 0.6 parts by weight of p-toluenesulfonic acid monohydrate in a reaction vessel equipped with a stirrer and a reflux device, the temperature was raised to 150 ° C. The reaction was continued for 3.5 hours while the pressure was gradually reduced and water was distilled off. Thereafter, a polymerization reaction was carried out for 7 hours while gradually reducing the pressure at 170 ° C. until reaching 13 Pa. Thereafter, crystallization treatment was performed at 80 ° C. for 5 hours in a nitrogen atmosphere, devolatilization was performed at 140 ° C. for 6 hours and 150 ° C. for 6 hours under a pressure of 60 Pa, and then solid phase polymerization was performed at 160 ° C. for 3 hours. Poly-D-lactic acid (b-1) was obtained.

(Production Example 5)
Poly-D-lactic acid (b-2) was obtained in the same manner as in Production Example 4 except that the catalyst amount of p-toluenesulfonic acid used was changed to 0.3 parts by weight.

(Production Example 6)
Poly-D-lactic acid (b-3) was obtained in the same manner as in Production Example 4 except that the catalyst amount of p-toluenesulfonic acid used was changed to 1.2 parts by weight.

(Production Example 7)
Poly-D-lactic acid (b-4) was obtained in the same manner as in Production Example 4 except that the catalyst amount of p-toluenesulfonic acid used was changed to 1.8 parts by weight.

(Production Example 8)
Poly-D-lactic acid (b-5) was obtained in the same manner as in Production Example 4 except that the catalyst amount of p-toluenesulfonic acid used was changed to 2.4 parts by weight.

(Production Example 9)
Poly-D-lactic acid (b-6) was obtained in the same manner as in Production Example 4 except that the catalyst used was changed to 0.6 parts by weight of benzenesulfonic acid.

(Production Example 10)
A poly-D-lactic acid (b-7) was obtained in the same manner as in Production Example 4 except that the catalyst used was changed to 1.5 parts by weight of methanesulfonic acid.

(Production Example 11)
Poly-L-lactic acid (c-1) was obtained in the same manner as in Production Example 1 except that the catalyst used was changed to 0.02 part by weight of stannous chloride and 0.02 part by weight of p-toluenesulfonic acid.

(Production Example 12)
Poly-D-lactic acid (d-1) was obtained in the same manner as in Production Example 4 except that the catalyst used was changed to 0.02 part by weight of stannous chloride and 0.02 part by weight of p-toluenesulfonic acid.

(Production Example 13)
Poly-L-lactic acid (c-2) was obtained in the same manner as in Production Example 1 except that the catalyst used was changed to 0.08 parts by weight of tin acetate and 0.22 parts by weight of methanesulfonic acid.

(Production Example 14)
Poly-D-lactic acid (d-2) was obtained in the same manner as in Production Example 4 except that the catalyst used was changed to 0.08 parts by weight of tin acetate and 0.22 parts by weight of methanesulfonic acid.

(Production Example 15)
In a reaction vessel equipped with a stirrer and a reflux device, 100 parts by weight of L-lactide was placed and dissolved uniformly at 120 ° C. in a nitrogen atmosphere. By adding 04 parts by weight and reacting for 2 hours, poly-L-lactic acid (c-3) was obtained.

(Production Example 16)
Poly-D-lactic acid (d-3) was obtained in the same manner as in Production Example 15 except that the L-lactide used was D-lactide and the reaction time was changed to 30 minutes.

(Example 1)
After 70 parts by weight of poly-L-lactic acid (a-1) and 30 parts by weight of poly-D-lactic acid (b-1) were dry blended, they were melt kneaded in a twin screw extruder having a vent. The twin-screw extruder is provided with a plasticizing portion set at a temperature of 240 ° C. at a portion of L / D = 10 from a resin supply port, and a screw having a kneading disk at a portion of L / D = 30 under shearing. It has a structure that can be mixed. The melt-kneading of poly-L-lactic acid and poly-D-lactic acid was performed at a kneading temperature of 240 ° C. under reduced pressure. The mixture obtained by melt kneading was pelletized.

  Crystallization was performed on 1 g of the pellets of the obtained mixture at 80 ° C. for 9 hours under a nitrogen flow of 20 ml / min. Next, devolatilization was performed at 140 ° C. for 5 hours under a nitrogen flow of 20 ml / min with respect to 1 g of the pellets of the mixture. Furthermore, by raising the temperature from 150 ° C. to 170 ° C. at a rate of 3 ° C./hour under a nitrogen flow of 20 ml / min with respect to 1 g of the pellets of the mixture, followed by solid phase polymerization at 170 ° C. for 20 hours. A polylactic acid resin was obtained. The properties of the obtained polylactic acid resin are shown in Table 1.

(Examples 2-14, Comparative Examples 1-3)
The same procedure as in Example 1 was conducted except that poly-L-lactic acid and poly-D-lactic acid used and the production conditions were as shown in Tables 1 and 2. In Comparative Examples 1 and 2, it can be seen that the molding cyclability is inferior due to the low temperature-falling crystallization temperature. In the comparative example 3, it turns out that the weight reduction rate at the time of a melt | dissolution residence is high, and it is inferior to heat resistance.

(Comparative Example 4)
The same procedure as in Example 1 was carried out except that 0.2 parts by weight of dioctadecyl phosphate was mixed as a stabilizer, poly-L-lactic acid and poly-D-lactic acid used, and the production conditions shown in Table 2. In Comparative Example 4, it can be seen that, due to the low temperature-falling crystallization temperature, the molding cycle property is inferior, and the inclusion of the phosphorus compound increases the burden on the environment.

(Comparative Examples 5 and 6)
Poly-L-lactic acid and poly-D-lactic acid used by mixing 0.03 part by weight of phenylphosphonic acid as a stabilizer and 0.1 part by weight of phosphate ester metal salt ADK STAB NA-71 as a nucleating agent, and solid phase Without polymerization, 1 g of the mixture pellets after melt-kneading was crystallized at 80 ° C. for 9 hours under a nitrogen stream of 20 ml / min. Thereafter, the mixture pellets were further devolatilized at 140 ° C. for 5 hours under a nitrogen flow of 20 ml / min with respect to 1 g of the mixture pellets, and the production conditions were as shown in Table 2, as in Example 1. went. In Comparative Examples 5 and 6, it can be seen that the inclusion of the phosphorus compound increases the environmental load.

ADVANTAGE OF THE INVENTION According to this invention, the polylactic acid resin excellent in the heat resistance at the time of melt processing and molding cycle property, and also excellent in the low load property to an environment can be obtained.

Claims (9)

A polylactic acid resin containing a poly-L-lactic acid component and a poly-D-lactic acid component, which is heated from 30 ° C. to 250 ° C. at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter (DSC). Then, after holding at 250 ° C. for 3 minutes, the temperature drop crystallization temperature (Tc) observed when the temperature is lowered from 250 ° C. to 30 ° C. at a temperature drop rate of 20 ° C./min is in the range of 145 to 175 ° C., Using a thermogravimetric analyzer (TGA), the weight reduction rate when the temperature was raised from 30 ° C. to 240 ° C. at a temperature rising rate of 200 ° C./min and then kept at 240 ° C. for 30 minutes was 0.001 to 0.040 wt. % Poly (lactic acid) resin, characterized in that it contains no phosphorus compound. Using a differential scanning calorimeter (DSC) with a weight average molecular weight of 100,000 to 300,000, the temperature was raised from 30 ° C. to 250 ° C. at a heating rate of 20 ° C./min, and then at 250 ° C. for 3 minutes. A stereocomplex crystal that is observed when the temperature is lowered from 250 ° C. to 30 ° C. at a temperature lowering rate of 20 ° C./min, and then further increased from 30 ° C. to 250 ° C. at a temperature rising rate of 20 ° C./min. The polylactic acid resin according to claim 1, wherein the melting enthalpy (ΔHmsc) is in the range of 40 to 60 J / g. The polylactic acid resin according to claim 1 or 2, wherein the content of the sulfonic acid group-containing compound is 1 to 250 ppm with respect to the polylactic acid resin in terms of sulfur atoms. The polylactic acid resin according to any one of claims 1 to 3, wherein a weight ratio of the poly-L-lactic acid component and the poly-D-lactic acid component is 80:20 to 20:80. The polylactic acid resin according to any one of claims 1 to 4, wherein the polylactic acid resin is a polylactic acid block copolymer. (A) a step of obtaining poly-L lactic acid and poly-D-lactic acid by melt polymerization, (b) a step of mixing poly-L-lactic acid and poly-D-lactic acid, (c) a crystallization step and (d) a solid A method for producing a polylactic acid resin, comprising a phase polymerization step, wherein no phosphorus compound is added in any step. The method for producing a polylactic acid resin according to claim 6, wherein no metal compound is added in the (a) melt polymerization step and the (b) mixing step. The polylactic acid according to claim 6 or 7, wherein in the mixing step (b), a temperature condition for melt-kneading poly-L-lactic acid and poly-D-lactic acid is in a range of 190 to 250 ° C. Manufacturing method of resin. (D) The solid phase polymerization step is performed under multi-stage temperature conditions, and the final-stage temperature condition is in the range of 160 to 200 ° C. A method for producing a lactic acid resin.