JP5323312B2 - Method for producing polylactide - Google Patents

Description

  The present invention relates to a method for producing polylactide. More specifically, the present invention relates to a method for producing a polylactide having an extremely small content of impurities, particularly volatile impurities, and having excellent thermal stability, hue stability, and hydrolysis resistance.

In recent years, for the purpose of protecting the global environment, biodegradable polymers that are decomposed in a natural environment have attracted attention and are being studied all over the world. As biodegradable polymers, polyhydroxybutyrate, polycaprolactone, aliphatic polyester, polylactide and the like are known.
Polylactide is made from lactide obtained from biologically derived raw materials, so it is highly biosafe and is not only used as an environmentally friendly polymer material but also as a general-purpose polymer. Uniaxial, biaxially stretched films, fibers As an injection-molded product, various uses such as a surgical suture, a sustained-release capsule, and a reinforcing material at the time of fracture are being studied.
However, polylactide is highly transparent and tough, but its melting point is about 170 ° C., so it cannot be said that heat resistance is sufficient for use as a general-purpose polymer. A polylactide stereocomplex obtained by mixing D- and L-polylactide in a solution or in a molten state has biodegradability and biocompatibility, and is a more severe environment as a material having higher heat resistance and stability than polylactide. It is expected as a material that can be used in

However, since polylactide and polylactide stereocomplex have an aliphatic polyester structure, it is necessary to increase the weight average molecular weight (Mw) to 100,000 or more in order to exert practical mechanical properties and thermal properties. It is well known that it is necessary to reduce the content of volatile impurities such as lactide that cause a decrease in stability.
Conventionally, for production of high molecular weight polylactide, direct melt polymerization method of lactide, solid phase polymerization method, melt ring-opening polymerization method of lactide and the like are well known, and among them, the melt ring-opening polymerization method of lactide has a production process. Simple, high production efficiency and high possibility of low manufacturing cost, good color tone of the resulting polylactide resin, relatively low impurity content, and production of polylactide with excellent stability It is considered a promising way to do.
However, since volatile impurities such as residual lactide are one of the causes of lowering the color tone and thermal stability of polylactide and polylactide stereocomplex produced therefrom, it is necessary to remove them to a sufficiently low level.

Further, the residual lactide causes a bad odor during the melt molding of polylactide and polylactide stereocomplex, and makes the molding atmosphere poor.
Solvent washing is typically used to reduce volatile impurities in high molecular weight polylactides, but extra materials such as solvents must be used, and in addition, the solvent can contaminate the polylactide, resulting in polylactide contamination. It may also cause a decrease in stability. Furthermore, an extra process such as drying is required, and the production efficiency is also reduced.

Patent Document 1 proposes a method of removing the lactide by vacuum suction of the obtained polylactide with a biaxial ruder vent. However, the simple vacuum suction method does not provide a satisfactory solution because the effect of reducing volatile impurities remains at a low level.
Patent Document 2 proposes a method of adding a phosphoric acid compound to polylactide obtained by polymerization and kneading and extruding lactide under vacuum using a horizontal extruder or the like. However, the addition of a small amount of a phosphoric acid compound sufficient to inactivate the catalyst does not achieve a non-uniform dispersion and does not sufficiently reduce the catalyst deactivation and volatile impurities. Further, when the catalyst deactivator is not sufficiently dispersed in the polylactide and the catalyst is not completely deactivated, there is a risk that hydrolysis is further promoted by adding water.
JP-A-10-120772 JP-A-9-104745

  An object of the present invention is to provide a method for producing polylactide having a very low content of impurities, particularly volatile impurities, and excellent in thermal stability, hue stability, and hydrolysis resistance. Moreover, this invention is providing the method of using the polylactide manufactured by this method for manufacture of a polylactide stereocomplex.

The present invention relates to a step (i) in which lactide is polymerized in the presence of an initiator and a metal catalyst to obtain polylactide, and polylactide is converted into water and a catalyst deactivator (provided that the group consists of a phosphate ester, a metal phosphate and an aluminum compound). In the presence of at least one deactivator selected from the group (1) above, followed by a reduced pressure treatment step (ii). The present invention also includes a method of using the polylactide produced by the method for producing a polylactide stereocomplex.

According to the method for producing polylactide of the present invention, polylactide having a very small content of impurities, particularly volatile impurities, can be produced in a simplified process. Further, according to the present invention, a polylactide having excellent thermal stability, hue stability, and hydrolysis resistance can be produced. That is, according to the present invention, since the catalyst can be deactivated in a short time, hydrolysis of polylactide can be efficiently suppressed. As a result, a polylactide having excellent thermal stability, hue stability, and hydrolysis resistance during molding can be produced.
According to the present invention, a polylactide stereocomplex with a high melting peak ratio of 200 ° C. or higher can be produced.

<Process (i)>
(Lactide)
The lactide used in the present invention is at least one selected from the group consisting of L-lactide, D-lactide, D / L-lactide and meso-lactide. L-lactide or D-lactide preferably has an optical purity of 90 to 100%, more preferably an optical purity of 95 to 100%. D / L-lactide has a D / L ratio of 0/100 to 100/0.
That is, L-lactide preferably contains 90 mol% or more, more preferably 95 mol% or more, and further preferably 98 mol% or more of L-lactide. Examples of other components include components other than D-lactide and lactide. Components other than D-lactide and lactide are preferably 10 mol% or less, more preferably 5 mol% or less, and still more preferably 2 mol% or less.
The D-lactide preferably contains 90 mol% or more, more preferably 95 mol% or more, and further preferably 98 mol% or more of D-lactide. Examples of other components include components other than L-lactide and lactide. Components other than L-lactide and lactide are preferably 10 mol% or less, more preferably 5 mol% or less, and still more preferably 2 mol% or less.
As components other than lactide, units derived from dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone, etc. having functional groups capable of forming two or more ester bonds, and various polyesters, various polyethers composed of these various components Examples are derived from various polycarbonates and the like.

  Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of polyhydric alcohols include aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol. Or aromatic polyhydric alcohol etc., such as what added ethylene oxide to bisphenol, etc. are mentioned. Examples of the hydroxycarboxylic acid include glycolic acid and hydroxybutyric acid. Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone, and the like.

Such a lactide usually contains water and an acid component as impurities, but polylactide is preferable if the acid value of the lactide is low. The acid value of lactide is preferably 5 to 20 eq / ton, more preferably 5 to 9 eq / ton, and further preferably 3 to 8 eq / ton.
Water is undesirable because it causes ring-opening degradation of lactide. The water content in lactide is preferably 0.5% by weight or less, more preferably 0.1% by weight or less.

(Initiator)
The initiator is preferably at least one selected from the group consisting of alcohols represented by the following formula (2), formula (3) and formula (4).

R ¹ —OH (2)
In the formula, R ¹ represents an aliphatic hydrocarbon group having 1 to 20 carbon atoms that may have a substituent. Examples of the aliphatic hydrocarbon group include an alkyl group having 1 to 20 carbon atoms. As the monohydric alcohol represented by the formula (2), methanol, ethanol, n-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, pentyl alcohol, n-hexyl alcohol, cyclohexyl alcohol, octyl alcohol, nonyl alcohol, 2 -Ethylhexyl alcohol, n-decyl alcohol, n-dodecyl alcohol, hexadecyl alcohol, lauryl alcohol, ethyl lactate, hexyl lactate and the like are exemplified.

R ^2- (OH) _n (3)
In the formula, R ² represents an n-valent hydrocarbon group having 2 to 20 carbon atoms, and n represents an integer of 2 to 5.
Examples of the hydrocarbon group include an alkane-diyl group having 2 to 20 carbon atoms, an alkane-triyl group, and an alkane-tetrayl group. Examples of the polyhydric alcohol represented by the formula (3) include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, trimethylolpropane, and pentaerythritol. .

HO— (R ³ —O) _m —H (4)
In the formula, R ³ represents an alkylene group having 2 to 5 carbon atoms, and m represents an integer of 2 to 100. Examples of the polyalkylene glycol represented by the formula (4) include diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, ethylene oxide adducts of other phenols, and ethylene glycol adducts of bisphenol.

From the viewpoint of reactivity and polylactide physical properties, stearyl alcohol, lauryl alcohol, ethylene glycol, propanediol, butanediol, hexanediol, polyethylene glycol, polypropylene glycol and the like are exemplified as preferable examples.
The amount of the initiator used is preferably 0.003 to 0.04 mol, more preferably 0.009 to 0.035 mol, and still more preferably 0.01 to 0.03 mol per kg of lactide.
As the initiator, those sufficiently dried and reduced are preferably used. The moisture content of the initiator is preferably 100 ppm or less, more preferably 50 ppm, and even more preferably 10 ppm or less.

(Polymerization catalyst)
As polymerization catalyst, fatty acid salts such as alkali metals, alkaline earth metals, rare earths, transition metals, aluminum, germanium, tin, antimony, carbonates, sulfates, phosphates, oxides, hydroxides, halides, Examples include alcoholates.
The metal catalyst is preferably tin, aluminum, zinc, calcium, titanium, germanium, manganese, magnesium, a rare earth element fatty acid salt, carbonate, sulfate, phosphate, oxide, hydroxide, halide, Examples include alcoholates.

For example, as a tin compound, stannous chloride, stannous bromide, stannous iodide, stannous sulfate, stannic oxide, tin myristate, tin octylate, tin stearate, tetraphenyltin, tin methoxide , Tin ethoxide, tin butoxide and the like.
Examples of the aluminum compound include aluminum oxide, aluminum acetylacetonate, aluminum isopropoxide, and an aluminum-imine complex.
Examples of the titanium compound include titanium tetrachloride, ethyl titanate, butyl titanate, glycol titanate, and titanium tetrabutoxide compound.

Further, zinc chloride, zinc oxide, diethyl zinc, antimony trioxide, antimony tribromide, antimony acetate, calcium oxide, germanium oxide, manganese oxide, manganese carbonate, manganese acetate, magnesium oxide, yttrium alkoxide and the like are exemplified.
In view of catalytic activity and few side reactions, a tin-containing catalyst, an aluminum-containing catalyst, and a titanium-containing catalyst are preferable.
In particular, tin-containing compounds such as stannous chloride, stannous bromide, stannous iodide, stannous sulfate, stannic oxide, tin myristate, tin octylate, tin stearate, tetraphenyltin and the like Examples thereof include aluminum-containing compounds such as aluminum acetylacetonate, aluminum butoxide, and aluminum-imine complex.
Of these, an aliphatic alkoxide having 1 to 22 carbon atoms of tin, a fatty acid salt having 2 to 22 carbon atoms and tin chloride are preferable. Accordingly, diethoxytin, dinonyloxytin, tin myristate, tin octylate, tin stearate, tin chloride, aluminum acetylacetonate, aluminum isopropoxide and the like are preferable.

The amount of the catalyst used is preferably 0.42 × 10 ^{−4 to} 100 × 10 ⁻⁴ mol per kg of lactide, and is more preferably 0.000 in view of reactivity, color tone of the obtained polylactide, and stability. The amount is 8 × 10 ^{−4 to} 42.1 × 10 ⁻⁴ mol, more preferably 1.1 × 10 ^{−4 to} 16.8 × 10 ⁻⁴ mol.
Therefore, it is preferable to use 0.002 to 0.04 mol of the initiator and 0.42 × 10 ^{−4 to} 100 × 10 ⁻⁴ mol of the metal catalyst in terms of metal element with respect to 1 kg of lactide.
As the metal catalyst, those sufficiently dried and reduced are preferably used. The moisture content is 100 ppm or less, preferably 50 ppm, more preferably 10 ppm or less.

(polymerization)
The polymerization is preferably performed in an inert gas atmosphere in order to prevent volatilization of the raw material lactide. The internal pressure is preferably 17.33 to 506.6 kPa, more preferably 111.5 to 202.7 kPa. The polymerization temperature is preferably 180 to 230 ° C, more preferably 185 to 220 ° C. When a plurality of polymerization tanks are used, it is preferable that the internal temperature of the polymerization tank on the downstream side is not lower than the internal temperature of the polymerization tank used on the upstream side. The polymerization time is preferably 0.1 to 10 hours, more preferably 0.3 to 8 hours, and further preferably 0.5 to 4 hours. The polymerization is preferably carried out while maintaining the reaction temperature at a relatively low temperature and suppressing side reactions of lactide.
The weight average molecular weight of the obtained polylactide is preferably 5 to 500,000, more preferably 70 to 300,000, and still more preferably 10 to 250,000. Mw / Mn of the polylactide obtained is preferably 1.3 to 2.4, more preferably 1.5 to 2.2, and still more preferably 1.7 to 2.1.

(Polymerization equipment)
For the polymerization, it is preferable to use a polymerization apparatus corresponding to the melt viscosity at each stage. For example, a polylactide containing 10 to 30% by weight of lactide has a significantly lower melt viscosity than a polylactide having a lactide content of less than 10% by weight, and thus is more suitable for production in a wider range of polymerization equipment. It has the advantage that a polymerization apparatus can be selected.
When the melt viscosity of the polymer does not exceed 3000 poise, a normal vertical polymerization tank can be used. Low-viscosity equipped with conventional well-known stirring blades such as vertical polymerization tank, inclined blade polymerization tank, spiral scraping blade polymerization tank, full zone blade polymerization tank, Max blend blade polymerization tank, log bone blade polymerization tank To medium viscosity melt polymerization equipment. Among them, there is a vertical polymerization tank equipped with a full zone blade capable of efficiently mixing lactide, an initiator and a metal catalyst and efficiently removing ring-opening polymerization heat, and a blade suitable for polymerizing a prepolymer having a relatively high melt viscosity. It is preferable to use them in series.

  When the melt viscosity exceeds 3000 poise, a polymerization apparatus suitable for producing a resin having a relatively high melt viscosity can be preferably used. For example, uniaxial and biaxial extruders, kneaders, non-axial vertical stirring tanks, Sumitomo Heavy Industries Vibo racks, Mitsubishi Heavy Industries N-SCR, Hitachi spectacles, lattice blades or Kenix type, or Sulzer type SMLX type static A mixer-equipped tubular polymerization tank or the like can be used. In view of the color tone of polylactide, a finisher, an N-SCR, a biaxial extrusion ruder or the like, which is a self-cleaning polymerization apparatus, can be preferably used. Among them, it is most preferable to use a finisher or N-SCR in view of production efficiency, color tone of polylactide, stability, heat resistance and the like.

The polymerization apparatus can adopt a continuous process or a batch process, but it is preferable to select a reaction process as appropriate in consideration of the efficiency of the apparatus. When a continuous polymerization process is employed, it is preferable to use a charging melting tank preceding the polymerization apparatus. As the preparation melting tank, it is preferable to use a full zone blade stirring tank capable of efficient stirring.
The charging and melting tank is preferably at an internal temperature of 130 to 170 ° C. and under an inert atmosphere and from a slightly reduced pressure to a slightly increased pressure. More preferably, the internal temperature is 135 to 170 ° C. and the internal pressure is 13.3 to 506.6 kPa. However, it is more preferable to use at 101.3 to 304 kPa so as not to take outside air, moisture and the like into the reaction system. In particular, the range where the internal pressure is 111.5 to 202.7 kPa is easy to handle, and the protective effect of moisture and outside air is sufficiently large and preferable.
When a batch process is employed, the product in each polymerization tank can be solidified and taken out as desired.

The above polymerization tanks can be used in appropriate combination in multiple stages or in one stage. That is, it is possible to use only a vertical polymerization tank, or an appropriate combination of a vertical polymerization tank and a horizontal polymerization tank. For example, the polymerization step is divided into several stages. In the initial stage of the reaction, the reaction is carried out at 180 to 195 ° C. for 1 to 4 hours with a full zone blade equipped stirrer to make the lactide reaction rate 30 to 60%. In, for example, a reaction vessel equipped with a log bone stirring blade and reacted at 190 to 210 ° C. for 1 to 4 hours, a reaction rate of 50 to 80%, and in the next stage, a non-axial cage type horizontal stirring vessel at 200 to 230 ° C. It is preferable to react for ˜4 hours to 70 to 90%.
Alternatively, from the beginning of the reaction, while monitoring the melt viscosity mechanically or with a motor stirring power, etc., in a stirring tank equipped with a vertical stirring blade, the initial stage of the reaction is 180 to 195 ° C., and then the reaction temperature as the reaction proceeds. It is also one of the preferred embodiments that the reaction temperature is raised and finally reacted at 220 to 230 ° C.

In order to improve production efficiency, the polylactide produced in each polymerization tank is preferably transferred to the next polymerization tank while maintaining a molten state without solidifying, but in some cases, as a predetermined shape, for example, as a chip It is also possible to transport after solidification. In particular, the prepolymer in the middle of the polymerization can be formed into chips and appropriately stored, and then transferred to the next polymerization tank. At this time, as usual in the melt polymerization method, it is necessary that the prepolymer absorbs moisture and prevents deterioration due to light, oxygen and the like.
In order to keep the polymerization activity in the next step at a sufficiently high level, the water content of polylactide is preferably 20 ppm by weight or less, preferably 10 ppm by weight or less, more preferably 5 ppm by weight or less.

<Process (ii)>
In step (ii), the obtained polylactide is kneaded in the presence of water and a catalyst deactivator and then subjected to a reduced pressure treatment.
(Catalyst deactivator)
The catalyst deactivator is phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, glassy phosphoric acid, polyphosphoric acid, phosphoroxoacid, phosphoroxoacid ester, and organic phosphorus oxo represented by the following formula (1) It is preferably at least one selected from the group consisting of acid compounds.

R ⁵ -P (═O) _q (OH) _s (OR ⁴ ) _2-s (1)
In the formula, q is 0 or 1, s is 1 or 2, and R ⁴ and R ⁵ each independently represents a hydrocarbon group which may have a substituent having 1 to 20 carbon atoms. Examples of the hydrocarbon group include an alkyl group having 1 to 20 carbon atoms. These quenchers may be used alone or in combination.

  Examples of the phosphorus oxoacid include dihydridooxoline (I) acid, dihydridotetraoxodiphosphorus (II, II) acid, hydridotrioxoline (III) acid, dihydridopentaoxodiphosphoric acid (III), and hydridopentaoxodioxide. (II, IV) acid, dodecaoxohexaline (III) III, hydridooctaoxotriphosphate (III, IV, IV) acid, octaoxotriphosphate (IV, III, IV) acid, hydridohexaoxodiline (III, V) ) Low oxidation number phosphorus having an acid number of 5 or less, such as acid, hexaoxodiphosphorus (IV) acid, decaoxotetralin (IV) acid, hendecaoxotetralin (IV) acid, eneoxooxo triphosphoric acid (V, IV, IV) acid Examples include acids.

Also, the formula xH ₂ O. Polyphosphoric acid represented by yP ₂ O ₅ , x / y = 3 orthophosphoric acid, 2> x / y> 1, and referred to as diphosphoric acid, triphosphoric acid, tetraphosphoric acid, pentaphosphoric acid or the like based on the degree of condensation Acids and mixtures thereof, metaphosphoric acid represented by x / y = 1, especially trimetaphosphoric acid, tetrametaphosphoric acid and glassy phosphoric acid or glacial phosphoric acid and a mixture of linear polyphosphoric acid and cyclic metaphosphoric acid Ultraphosphoric acid represented by 1> x / y> 0 and having a network structure with a part of the phosphorus pentoxide structure, and monovalent, polyhydric alcohols, or polyalkylene glycols of these acids Examples of the partial ester and complete ester. From the catalyst deactivation ability, acids or acidic esters are preferably used.

  Although there is no restriction | limiting in particular regarding the alcohol which forms the ester of a phosphorus oxo acid, As monohydric alcohol, alcohol represented by following formula (5) is preferable.

Y-OH (5)
In formula, Y represents the C1-C22 hydrocarbon group which may have a substituent. Examples of the hydrocarbon group include an alkyl group having 1 to 22 carbon atoms. A C1-C10 alkyl group is mentioned as a substituent. Examples of the alcohol represented by the formula (5) include methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, 2-ethylhexyl alcohol, decanol, dodecanol, benzyl alcohol, cyclohexyl alcohol, hexyl alcohol, phenol, hexadecyl alcohol and the like. It is done.

  Examples of the polyhydric alcohol include polyhydric alcohols and sugar alcohols represented by the following formula (6).

X (—OH) _a (6)
In formula, X is a C2-C22 hydrocarbon group which may have a substituent, and a represents an integer of 2-6. Examples of the hydrocarbon group include an alkyl group having 2 to 22 carbon atoms. A C1-C10 alkyl group is mentioned as a substituent. Examples of the alcohol represented by the formula (6) include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, glycerin, pentaerythritol, trimethylolpropane, polyethylene glycol, and polypropylene glycol. , Myo-inositol, D-, L-inositol, scyllo-inositol and other inositols, cyclitol and the like.

  The amount of the catalyst deactivator is preferably 0.5 to 60 equivalents, more preferably 0.5 to 10 equivalents with respect to 1 equivalent of the metal element of the metal catalyst. The equivalent of the catalyst deactivator represents the number of sites present in one molecule of the catalyst deactivator and capable of reacting with one valence of the catalyst metal, and the relationship between the molar amount of the catalyst deactivator and the equivalent is represented by When one reaction site is present in one molecule, one mole is equal to one equivalent, and when two reaction sites are present, one mole is equal to two equivalents. For example, when the catalyst is octyltin (divalent) and the catalyst deactivator is phosphoric acid (one reaction site), the theoretical value of the catalyst deactivator necessary for 1 mol of the catalyst is 1 mol. The amount of the catalyst deactivator is preferably 0.01 to 500 ppm by weight, more preferably 1 to 350 ppm by weight, and still more preferably 10 to 100 ppm with respect to the polylactide.

  The amount of water is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 parts by weight, and still more preferably 0.3 to 2 parts by weight with respect to 100 parts by weight of polylactide. If the amount of water added is less than 0.1 parts by weight, removal of volatile impurities is insufficient, while if it exceeds 5 parts by weight, polylactide may be hydrolyzed to lower the molecular weight.

  Water and catalyst deactivator can be prepared in advance and added to polylactide. The composition of the mixed solution of water and the catalyst deactivator is preferably such that the catalyst deactivator is 0.5 to 50 parts by weight with respect to 100 parts by weight of water. The amount of the mixed solution of water and catalyst deactivator is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 parts by weight, and further preferably 0.3 to 2 parts by weight with respect to 100 parts by weight of polylactide. Part. By adding the catalyst deactivator as a liquid mixture with water, the uniform dispersibility in the polylactide is improved, so that the catalyst can be deactivated in a short time, so that the hydrolysis of the polylactide can be effectively suppressed.

  In the present invention, when deactivating the metal catalyst in polylactide, polylactide is kneaded in the presence of a catalyst deactivator and water. By simultaneously adding water and a catalyst deactivator, it is possible to simultaneously obtain the effect of deactivating the polymerization catalyst and the effect of removing volatile impurities. As a result, a part of the devolatilization process can be omitted, and a polylactide resin having a very low content of impurities, particularly volatile impurities, and having excellent thermal stability, hue stability, and hydrolysis resistance can be obtained in a simplified process. Can be manufactured.

The kneading temperature is preferably 180 to 300 ° C, more preferably 200 to 280 ° C. If the temperature of the polylactide is less than 180 ° C, it is difficult to knead water, the catalyst deactivator and the polylactide, while if it exceeds 300 ° C, the polylactide may thermally decompose.
The kneading pressure is preferably an absolute pressure of 0.3 to 10 MPa, more preferably 0.7 to 5.0 MPa, still more preferably 1.0 to 5.0 MPa, and particularly preferably 1.0 to 2.0 MPa. . When the kneading pressure is lower than 0.3 MPa, sufficient degassing performance cannot be obtained. When the kneading pressure is higher than 10 MPa, the manufacturing cost increases, which is economically disadvantageous. The kneading temperature is 180 to 240 ° C, preferably 190 to 220 ° C, more preferably 190 to 210 ° C. The kneading time is defined by the average residence time of polylactide in the kneading part, and is preferably 0.05 to 20 seconds.

(Decompression treatment)
After kneading polylactide, water, and a catalyst deactivator, pressure reduction treatment is performed in the vent portion. In the vent part, water added in the kneading part and volatile impurities present in the polylactide are removed by a vacuum pump or the like. It is preferable to install a full flight in the screw configuration of the vent portion. The pressure during the decompression treatment is preferably 1.333 × 10 Pa (0.1 mmHg) to 9.333 × 10 ⁴ Pa (700 mmHg), more preferably 1.333 × 10 ² Pa (1 mmHg) to 6.667 × 10. ⁴ Pa (500 mmHg). The residence time of the polylactide in the vent part which performs a pressure reduction process is about 0.1 to 10 seconds.
The reduced pressure treatment can effectively remove impurities remaining in the polylactide, particularly volatile impurities such as lactide, reaction by-products, and solvents. Further, when the catalyst deactivator contains a volatile compound, even if a thermal decomposition product is generated from the catalyst deactivator by thermal decomposition, it can be removed simultaneously by a reduced pressure treatment.

(Extruder with vent)
The kneading and decompression treatment is preferably performed with a vented extruder. The extruder with a vent is preferably a single screw or twin screw extruder. The extruder with a vent preferably has a unit treatment zone composed of a kneading part, a material seal part and a vent part. Although the number of unit processing zones may be one, it is preferable to have a plurality. The plurality is preferably about 2 to 10 pieces.
It is preferable to install neutral kneading, forward kneading, reverse kneading, or a combination thereof in the screw configuration of the kneading section. The supply port for water and the catalyst deactivator is preferably installed at the upstream side in the traveling direction of polylactide in the kneading section.
The material seal part is located between the kneading part and the vent part, and has a function of maintaining the reduced pressure state of the vent part. Moreover, it is preferable that a material seal part is comprised by any one or more types of reverse flight, a seal ring, or reverse kneading.
A vent port is installed in the vent part, and the inside of the vent part is maintained at a reduced pressure by a vacuum pump or the like.
Therefore, it is preferable that the extruder with a vent has a unit treatment zone composed of a kneading part, a material seal part and a vent part, and knead with polylactide by adding water and a catalyst deactivator to the kneading part.

(When there are multiple unit processing zones)
When the extruder with a vent has a plurality of unit treatment zones, it is preferable to add water and a catalyst deactivator and knead them in the first treatment zone. In the second treatment zone and after, it is preferable to carry out pressure reduction treatment after kneading polylactide and water. That is, after the step (ii), it is preferable to further include a step (iii) in which the polylactide is kneaded in the presence of water and then subjected to a reduced pressure treatment.
The conditions of the kneading and decompression treatment in the first treatment zone are as described above.
The amount of water in each zone after the second treatment zone is preferably 0.1 to 5 parts by weight, more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of polylactide.
The temperature at the time of kneading after the second treatment zone is preferably 190 to 300 ° C, more preferably 200 to 280 ° C.

The absolute pressure at the time of kneading the polylactide and water after the second treatment zone is preferably 0.3 to 10 MPa, more preferably 0.7 to 5.0 MPa, still more preferably 1.0 to 5.0 MPa, particularly preferably. Is 1.0 to 2.0 MPa. When the kneading pressure is lower than 0.3 MPa, sufficient degassing performance may not be obtained. When the kneading pressure is higher than 10 MPa, the production cost may increase, which may be economically disadvantageous.
The decompression condition after the second treatment zone is preferably 1.333 × 10 Pa (0.1 mmHg) to 9.333 × 10 ⁴ Pa (700 mmHg), more preferably 1.333 × 10 ² Pa (1 mmHg). ˜6.667 × 10 ⁴ Pa (500 mmHg).
As described above, using a vented extruder having a plurality of unit treatment zones comprising a kneading part, a material seal part and a vent part, the first treatment zone is kneaded in the presence of water and a catalyst deactivator and then decompressed. In the second treatment zone and thereafter, it is preferable to carry out decompression treatment after kneading in the presence of water.

  According to the present invention, after adding and kneading the catalyst deactivator, the step of adding and kneading the catalyst deactivator can be omitted as compared with the method of removing the volatile impurities, and the impurities, in particular, can be simplified. A polylactide having an extremely low content of volatile impurities and excellent in heat stability, hue stability, and hydrolysis resistance can be produced. In addition, the quality of the polylactide molded product thus produced is significantly improved.

  In the present invention, the time for kneading the polylactide is defined by the average residence time of the polylactide in the kneading part. The kneading time per unit treatment zone is preferably 0.05 to 20 seconds. The kneading time in the case of an extruder having a plurality of unit treatment zones is expressed as the total time for kneading polylactide in the plurality of unit treatment zones, and is preferably 0.1 to 100 seconds. When the kneading time is shorter than this, the effect of removing impurities is lowered, and the catalyst deactivator is not sufficiently kneaded, which is not preferable. On the other hand, when the kneading time is longer than this, polylactide may be hydrolyzed to lower the degree of polymerization. Accordingly, the kneading time per processing zone after the first processing zone and the second processing zone is preferably 0.05 to 20 seconds. The kneading time of the first treatment zone and the total treatment zone after the second treatment zone is preferably 0.1 to 100 seconds.

(Polylactide)
The weight average molecular weight (Mw) of the polylactide obtained by the present invention is preferably 5 to 500,000, more preferably 100 to 300,000.
The lactide concentration of polylactide is preferably 0.08% or less, more preferably 0.05% or less.
The polylactide obtained by the present invention preferably has a weight loss after holding at 260 ° C. for 1 hour of less than 10% by weight. If the polylactide is washed with a solvent and the catalyst concentration is less than 0.1 ppm, the weight loss after holding at 260 ° C. for 1 hour is about 5% by weight. It can be considered that the closer to this value, the more the catalyst activity is lost. When polylactide is actually used as a molded article, it can be used without any problem if the weight reduction is less than 10% by weight.

(Filler)
The polylactide obtained by the present invention can contain various fillers as desired. The filler is preferably an organic filler or an inorganic filler.
Examples of inorganic fillers include glass fiber, graphite fiber, carbon fiber, metal fiber, potassium titanate whisker, aluminum borate whisker, magnesium-based whisker, silicon-based whisker, wollastonite, sepiolite, zonolite, elestadite, gypsum fiber, silica fiber ,silica. Alumina fiber, zirconia fiber, silicon nitride fiber, boron fiber, glass flake, non-swellable mica, graphite, metal foil, talc, clay, mica, sericite, bentonite, kaolin, magnesium carbonate, magnesium sulfate, aluminum hydroxide, acid Valent magnesium, hydrotalcite, magnesium hydroxide, gypsum, dosonite and the like.

Examples of the organic filler include natural fiber, para-type aramid fiber, polyazole fiber, polyarylate, polyoxybenzoic acid whisker, polyoxynaphthoic acid whisker, and cellulose whisker.
These fillers can be used in the form of fibers, plates, or needles. Among these fillers, fibrous inorganic fillers are preferable, and glass fibers are particularly preferable.
Further, the aspect ratio of these fillers is preferably 5 or more, and more preferably 10 or more. Particularly preferred is 100 or more.
The straight aspect ratio is a value obtained by dividing the fiber length by the fiber diameter in the case of a fibrous filler, and is a value obtained by dividing the length in the long period direction by the thickness in the case of a plate-like filler. The elastic modulus of the filler is preferably 50 GPa or more.
The filler is also preferably coated or focused with a thermoplastic resin or a thermosetting resin. For example, it may be treated with a coupling agent such as aminosilane or epoxysilane, or treated with various organic substances. The filler may be used alone or in combination of two or more.

The natural fiber has a strength as a single fiber of preferably 200 MPa or more, more preferably 300 MPa or more. This is because, within this range, sufficient mechanical properties can be exhibited as a composite, and the amount of the filler mixed can be reduced, so that the shape of the surface of the molded body can produce better results.
Natural fibers have a fiber diameter in the range of 0.1 μm to 1 mm, preferably in the range of 1 μm to 500 μm. Moreover, it is preferable to have asmect ratio 50 or more. Such fibers can be well mixed with the resin and can be made into a composition having excellent physical properties by compounding. The aspect ratio is more preferably 100 to 500, and still more preferably 100 to 3000.
Natural fibers can be used effectively regardless of their types as long as they satisfy the above conditions. Among these, plant fibers such as kenaf, bamboo, flax, hemp, wood pulp, and cotton can be preferably used. In particular, wood pulp obtained from waste materials, pulp obtained from waste paper, and fibers made from kenaf are very preferable because they have a low environmental load and high regeneration ability.

Any natural fiber produced by any method can be suitably used as long as its form and strength are maintained within an appropriate range.
For example, (i) fiberization by chemical pulping, (ii) fiberization by biopulping, (iii) explosion, (iv) mechanical disintegration and the like can be mentioned.
The surface of the natural fiber may be modified. It is more preferable when the interface strength between the resin and the fiber is increased by modifying the surface of the natural fiber and the durability is further increased. Such modification methods include: (i) a method of chemically introducing a functional group, (ii) a method of mechanically densifying the surface, or (iii) a method of smoothing (iv) a surface modifier. Examples thereof include a method of reacting by mechanical stimulation. The natural fiber may be a single fiber or a fiber assembly.

The weight ratio of polylactide to natural fiber is the former / the latter = 98/2 to 1/99. The former / the latter is preferably 85/15 to 40/60, and more preferably 70/30 to 50/50.
In addition to the fillers described above, polylactide does not impair the object of the present invention, and various additives such as plasticizers, antioxidants, light stabilizers, ultraviolet absorbers, heat stabilizers, lubricants, mold release agents, antistatic agents , Flame retardant, foaming agent, filler, antibacterial. One kind or two or more kinds of colorants including anti-epileptics, nucleation goods, dyes and pigments can be contained.

Moreover, you may add at least 1 type, such as another thermoplastic resin, a thermosetting resin, and a soft thermoplastic resin, to a polylactide.
The mixing of polylactide and filler can be performed by the following method, for example.
(I) A method in which polylactide is heated and melted, blended with, for example, natural fiber, and uniformly dispersed:
(Ii) A method in which a polylactide film is prepared in advance, and a plurality of natural fibers, for example, are stacked on top of each other, and a polylactide film is further stacked thereon. :
(Iii) A method in which powdered polylactide is adhered to, for example, natural fibers that have been shaped in advance, and then heated to a temperature equal to or higher than the melting point of polylactide to be compounded:
(Iv) A method in which polylactide is processed into a fibrous form, for example, a yarn is formed with natural fibers, given a predetermined shape, and then heated to a temperature higher than the glass transition temperature of polylactide to form a composite.

  The composite obtained in this way exhibits good biodegradability and sufficient strength, and both polylactide and natural fibers do not give an environmental load, and therefore can be suitably used as various molded articles. In particular, it is suitable not only for structural members and building materials that require strength, but also for joinery materials and construction temporary materials. The biodegradable composite of the present invention has a heat distortion temperature of preferably 240 ° C. or lower, more preferably 200 ° C. or lower, more preferably 170 ° C. or lower. The composition of the present invention can be used for various applications as molded articles such as sheets and mats.

  Using the polylactide obtained in the present invention, an injection molded product, an extrusion molded product, a vacuum / pressure molded product, a blow molded product, a film, a sheet, a sheet nonwoven fabric, a fiber, a cloth, a composite with other materials, an agricultural material, Fishery materials, civil engineering. Building materials, stationery, medical supplies or other molded articles can be obtained by a conventionally known method.

  Examples will be described below. In the examples, “%”, “parts” and “ppm” are “% by weight”, “parts by weight” or “parts by weight” unless otherwise specified.

1. The physical properties of the polylactide obtained in the examples were measured as follows.
(1) Weight average molecular weight (Mw), number average molecular weight Mn:
Comparison with polystyrene standard samples was also performed by gel permeation chromatography (GPC). GPC measuring instrument
Detector: Differential refractometer RID-6A manufactured by Shimadzu Corporation
Pump: LC-9A manufactured by Shimadzu Corporation
Column: Tosoh Corporation TSKgelG3000HXL, TSKgelG4000HXL, TSKgelG5000HXL and TSKguardcocumHXL-L were connected in series.
Chloroform eluent was used and flowed at a column temperature of 40 ° C. and a flow rate of 1.0 ml / min, and 10 μl of a sample having a concentration of 1 mg / ml (chloroform) was injected.
(2) Catalyst deactivation characteristics:
The weight of the sample before and after holding at 260 ° C. for 1 hour in a nitrogen atmosphere was measured, and the catalyst deactivation characteristics = (weight before holding−weight after holding) / weight before holding × 100.
(3) Lactide concentration:
The lactide concentration of the polylactide was determined by using a JEOL nuclear magnetic resonance apparatus JNM-EX270 spectrometer in deuterated chloroform, and a lactide-derived quadruple with respect to the polylactide-derived quadruple peak area ratio (5.10 to 5.20 ppm). Calculated as a line peak area ratio (4.98 to 5.05 ppm).

2. Apparatus The apparatus consists of a charging tank, a polymerization tank, a devolatilizer, and a pelletizer.
(1) The charging tank is a vertical stirring tank (capacity 250 L) provided with a vacuum pipe, a nitrogen gas pipe, a heating / cooling device, and anchor blades.
(2) The polymerization tank is a vertical stirring tank (120 L) equipped with a vacuum pipe, a nitrogen gas pipe, a catalyst / lactide solution addition pipe, an initiator addition pipe, a cooling device, and a spiral blade. A pelletizer was disposed at the outlet of the polymerization tank.
(3) The devolatilizer is a uniaxial rudder (type A) or a biaxial rudder (type B), and includes a hopper tip insertion device, a deactivator mixed liquid addition precision pump, and a two-stage vacuum vent. Both types A and B have first to fourth unit processing zones comprising a kneading part, a material seal part and a vent part. A pelletizer was placed at the outlet of the devolatilizer.

3. Raw materials L-lactide and D-lactide used lactide manufactured by Musashino Chemical Laboratory. Commercially available special grades were used as they were for tin octylate, stearyl alcohol, and phosphoric acid.

<Example 1>
(Manufacture of polylactide)
(1) Charge tank The amount and type of lactide, metal catalyst and initiator shown in Table 1 were charged into the charge tank, and the internal pressure was maintained at 130 ° C. and nitrogen gas at 111.5 kPa and stirred.
(2) Polymerization tank The solution in the charging tank was transferred to the polymerization tank and reacted at the residence time shown in Table 1 while stirring at an internal temperature of 180 to 210 ° C and an internal pressure of nitrogen gas of 111.5 kPa. The resulting polylactide was pelletized. Table 1 shows the physical properties of the resulting polylactide.

(Devolatilization)
(1) First Zone In both the single-screw extruder (type A) and the twin-screw extruder (type B), the mixture of the catalyst deactivator and water listed in Tables 2 to 6 is continuously added to the kneading section of the first zone. Added and kneaded with polylactide. Kneading and depressurization were performed at the temperatures and pressures shown in Tables 2 to 6, and volatiles in the polylactide were removed.
(2) Second to fourth treatment zones In the second to fourth treatment zones, water in the amounts shown in Tables 2 to 6 was continuously added to the kneading part and kneaded with polylactide. Kneading and depressurization were performed at the temperatures and pressures shown in Tables 2 to 6, and volatiles in the polylactide were removed.
(3) Pelletizer Polylactide was extruded from a die through a gear pump and pelletized by a pelletizer. The physical properties of the obtained polylactide were measured. The results are shown in Tables 2-6.

<Examples 2 to 14>
Examples 2 and 3 vary the amount of water added, Examples 4 and 5 vary the kneading time, Examples 6 and 7 vary the amount of catalyst deactivator, and Examples 8, 9, and 10 knead. Polylactide was produced in the same manner as in Example 1 except that the temperature was changed, Examples 11 and 12 were changed to vent pressure, and Examples 13 and 14 were changed to the quencher type. Tables 2 and 3 show the measurement results of lactide concentration, weight average molecular weight and catalyst deactivation characteristics of the obtained polylactide.

<Examples 15 to 19>
Example 1 except that the kneading temperature was 230 ° C., Examples 15 and 16 were different in the type of polylactide and the corresponding deactivator amount, Examples 17 and 18 were the amount of water added, and Example 19 was changed in the kneading time. Polylactide was produced in the same manner as described above. Table 4 shows the measurement results of lactide concentration, weight average molecular weight, and catalyst deactivation characteristics of the obtained polylactide.

<Examples 20 to 23>
In Example 20, polylactide was produced in the same manner as in Example 1 except that Luder A was used and the kneading temperature was changed. Example 21 changed the quencher type, and Examples 22 and 23 produced polylactide in the same manner as in Example 20 except that PL4 and 5 were used as polylactide. Table 5 shows the measurement results of lactide concentration, weight average molecular weight and catalyst deactivation characteristics of the obtained polylactide.

<Comparative Examples 1-3>
Comparative Examples 1 and 2 kneaded without adding the catalyst deactivator, and Comparative Example 3 produced polylactide in the same manner as in Example 1 except that water was not added together with the catalyst deactivator. Table 6 shows the measurement results of lactide concentration, weight average molecular weight and catalyst deactivation characteristics of the obtained polylactide.

<Example 24>
Production of Polylactide Stereo Complex An equal amount of the polylactide obtained in Examples 21 and 22 was added to the flask, and after nitrogen substitution, the temperature was raised to 260 ° C., and melt blending was performed at 260 ° C. for 10 minutes. The weight average molecular weight of the obtained resin was 160,000. DSC measurement was performed on this resin. As a result, a melting peak with a melting point of 201 ° C. was observed on the DSC chart, and the melting enthalpy was 34 J / g. The melting peak at 140 to 180 ° C. was not observed, and the ratio of the melting peak at 200 ° C. or higher (R _{200 or higher} ) was 100%. The crystallization point was 111 ° C.

  Since the polylactide obtained by the present invention is excellent in thermal stability, hue stability, and hydrolysis resistance, the polylactide obtained in the present invention is used for various moldings for agriculture, fishery, civil engineering, medical use, etc. Goods can be obtained.

Claims (14)

A step (i) in which lactide is polymerized in the presence of an initiator and a metal catalyst to obtain polylactide, and polylactide is selected from the group consisting of water and a catalyst deactivator (provided that a phosphate ester, a metal phosphate, and an aluminum compound) A method for producing polylactide, which comprises a step (ii) of kneading in the presence of at least one kind of deactivator) and then subjecting to a reduced pressure treatment. The method according to claim 1, wherein the initiator is used in an amount of 0.003 to 0.04 mol and the metal catalyst is converted into a metal element in an amount of 0.42 × 10 ^{−4 to} 100 × 10 ⁻⁴ mol per 1 kg of lactide. The method according to claim 1, wherein the kneading is performed at 180 to 300 ° C. The method according to claim 1, wherein the decompression treatment is performed at 1.333 × 10 to 9.333 × 10 ⁴ Pa. The catalyst deactivator is phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, glassy phosphoric acid, polyphosphoric acid, phosphoroxoacid, phosphoroxoacid ester, and organic phosphorus oxo represented by the following formula (1) It is at least 1 type chosen from the group which consists of an acid compound, The method as described in any one of Claims 1-4.
R ⁵ -P (═O) _q (OH) _s (OR ⁴ ) _2-s (1)
(In the formula, q is 0 or 1, s is 1 or 2, and R ⁴ and R ⁵ each independently represents a hydrocarbon group optionally having a substituent having 1 to 20 carbon atoms.) The method according to claim 1, wherein the catalyst deactivator is used in an amount of 0.5 to 60 equivalents relative to 1 equivalent of the metal element of the metal catalyst. The method according to claim 1, wherein 0.1 to 5 parts by weight of water is used per 100 parts by weight of polylactide. The method according to claim 1, wherein the kneading is performed using an extruder with a vent. The method according to claim 8, wherein the extruder with a vent has a unit treatment zone composed of a kneading part, a material seal part and a vent part, and kneads with polylactide by adding water and a catalyst deactivator to the kneading part. The method according to claim 1, further comprising a step (iii) of step (ii) wherein the polylactide is kneaded in the presence of water and then subjected to a reduced pressure treatment. Using an extruder with a vent having a plurality of unit treatment zones comprising a kneading part, a material seal part and a vent part, the first treatment zone is kneaded in the presence of water and a catalyst deactivator, and then subjected to a reduced pressure treatment. The method according to claim 10, wherein after the treatment zone, the mixture is kneaded in the presence of water and then decompressed. The method according to claim 11, wherein the kneading time per unit treatment zone is 0.05 to 20 seconds and the kneading time in the total treatment zone is 0.1 to 100 seconds. The method according to claim 11, wherein 0.1 to 5 parts by weight of water is added to 100 parts by weight of polylactide in each zone after the second treatment zone. The method to use the polylactide manufactured by the method as described in any one of Claims 1-13 for manufacture of a polylactide stereocomplex.