Method for producing polylactic acid resin composition and apparatus for producing polylactic acid resin composition

Abstract

To provide a method for producing a polylactic acid resin composition that enables stable and continuous production of a polylactic acid resin composition having a high molecular weight, superior biodegradability, and superior melt stability.SOLUTION: A method for producing a polylactic acid resin composition includes: a first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a ring-opening polymerizable monomer content of 15 mass% or more and 95 mass% or less; and a second polymerization step of adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step and polymerizing the lactide.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for producing a polylactic acid resin composition and an apparatus for producing a polylactic acid resin composition.

Background Art

[0002] In recent years, polylactic acid resins have been attracting attention in various fields. This is because polylactic acid is one of the few resins having both the characteristics of biodegradability as a biodegradable plastic and biomass plastic, and material development has been actively carried out in relation to the waste problem.

[0003] The polylactic acid is generally obtained by a ring-opening addition polymerization method of a cyclic dimer obtained by condensing lactic acid, which is generally called lactide. Since the polymerization reaction is an equilibrium reaction, it has a certain amount of ring-opening polymerizable monomer (unreacted monomer). When melt molding is performed with this lactide remaining in the polylactic acid resin composition, a small amount of water reacts with the hydroxyl group or carboxyl group at the end of the polylactic acid to cause hydrolysis, and lactic acid is generated. This lactic acid has a carboxylic acid and a hydroxyl group which is a hydrophilic group, and has an effect of promoting the hydrolysis of polylactic acid. Therefore, it is not preferable that lactide remains in the polylactic acid resin composition.

[0004] In addition, aliphatic polyesters such as polylactic acid have a larger decrease in viscosity after the melting point compared with polyesters having an aromatic ring, and non-Newtonian fluid characteristics (strain hardening property) required for molding processing cannot be exhibited, and also have insufficient melt strength, so that operation becomes unstable in blow molding etc., and it is regarded as a resin that is difficult to mold.

[0005] As a means for controlling the melt viscosity of this aliphatic polyester, in order to broaden the molecular weight distribution, a small amount of a high molecular weight resin is often added. In the case of polylactic acid, a high molecular weight body of polymethyl methacrylate having a relatively similar structure may be added in an amount of 10% by mass or more (see Patent Document 1).

[0006] When attempting to obtain the above-mentioned high-molecular-weight polylactic acid, after synthesizing low-molecular-weight polylactic acid by polycondensation of lactic acid, there is a method of increasing the molecular weight by solid-phase polymerization. However, industrially, the ring-opening addition polymerization method of lactide, which is the cyclic dimer of lactic acid, is generally used. However, even in this ring-opening addition polymerization method, side reactions such as transesterification reactions and molecular chain scissions tend to occur as the viscosity increases, and the molecular weight remains below 300,000. In addition, at that time, since the acid value increases due to the formation of carboxylic acid, there are inconveniences such as easy decomposition when remelted.

[0007] In response to the above problems, in the process of synthesizing polylactic acid from lactide, a method has been proposed in which a compressible fluid that functions as a plasticizer is added to lactide and polymerization is carried out while plasticizing (see Patent Document 2).

[0008] However, in this proposal, since monomers, catalysts, compounds having active hydrogen as initiators for adjusting the molecular weight, etc. dissolve in the compressible fluid, the reaction may become non-uniform. When the reaction becomes non-uniform, problems such as a slow reaction, an increase in the required amount of catalyst due to a decrease in the molecular weight distribution, control of the molecular weight, and a decrease in the polymerization rate occur. In addition, when the compressible fluid is added in the latter stage of the reaction, the plasticizing effect by the compressible fluid cannot be obtained, and side reactions accompanying the increase in viscosity occur simultaneously, resulting in problems such as no increase in the molecular weight or lack of melt stability.

[0009] On the other hand, a method has been proposed that has a first reaction section and a second reaction section and shares a compressible fluid between the first reaction section and the second reaction section (see Patent Document 3). This method has the advantage that the design of the entire equipment can be made economically in that the portion containing the compressible fluid in the entire polylactic acid production apparatus can be limited. However, in this proposal, there are problems such as a lack of melt stability of the obtained polylactic acid and instability of the quality such as the molecular weight in the continuous production of polylactic acid.

Summary of the Invention

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide a method for producing a polylactic acid resin composition that can stably and continuously produce a polylactic acid resin composition having a high molecular weight, excellent biodegradability, and excellent melt stability.

Means for Solving the Problems

[0011] The method for producing a polylactic acid resin composition of the present invention as a means for solving the above problems includes a first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less, and adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step, and a second polymerization step of polymerizing the lactide, and is characterized by including the above.

Effects of the Invention

[0012] According to the present invention, it is possible to provide a method for producing a polylactic acid resin composition that can stably and continuously produce a polylactic acid resin composition having a high molecular weight, excellent biodegradability, and excellent melt stability.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0014] (Method for Producing Polylactic Acid Resin Composition and Production Apparatus for Polylactic Acid Resin Composition) The method for producing a polylactic acid resin composition according to the first embodiment of the present invention includes a first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less, and a second polymerization step of adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step and polymerizing the lactide, and further includes other steps as necessary.

[0015] The production apparatus for a polylactic acid resin composition according to the first embodiment of the present invention has a first polymerization means for polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less, and a second polymerization means for adding a compressible fluid to the prepolymer-containing composition formed by the first polymerization means and polymerizing the lactide, and further has other means as necessary.

[0016] The method for producing a polylactic acid resin composition according to the first embodiment of the present invention is preferably carried out by the production apparatus for a polylactic acid resin composition according to the first embodiment of the present invention. Hereinafter, the production apparatus for a polylactic acid resin composition according to the first embodiment of the present invention will be described in detail together with the description of the method for producing a polylactic acid resin composition according to the first embodiment of the present invention. Note that the present invention is not limited to the embodiments shown below, and can be changed within the scope that those skilled in the art can conceive, such as other embodiments, additions, modifications, or deletions, and is included in the scope of the present invention as long as the functions and effects of the present invention are exhibited in any aspect.

[0017] <First Polymerization Step and First Polymerization Means> The first polymerization step (which may be referred to as the "prepolymerization step") is a step of polymerizing lactide (which may be referred to as "prepolymerization") in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less. The first polymerization means is a means for polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a ring-opening polymerizable monomer content of 15% by mass or more and 95% by mass or less. The first polymerization step is preferably carried out by the first polymerization means.

[0018] The first polymerization means is not particularly limited as long as it can form the prepolymer-containing composition. Examples include a tank that can be heated to a desired temperature. Further, it preferably has a stirring member such as a stirring blade in the tank, and more preferably has a measuring member that measures the rotational torque of the rotation axis of the stirring member.

[0019] At the initial stage of the reaction, it is important to quickly make the monomer, the catalyst, and, if necessary, the initiator, which are raw materials, into a uniform state. If stirring is insufficient and uniformity is not achieved, the reaction may proceed locally, which is not preferable. Also, since the ring-opening polymerization of lactide, which is a dimer of lactide, is an exothermic reaction, it is necessary to quickly remove the reaction heat.

[0020] <<Reaction raw materials>> In the method for producing the polylactic acid resin composition, as reaction raw materials, other components other than the lactide and the catalyst may be included. The other components are not particularly limited and can be appropriately selected according to the purpose. Examples include monomers other than the lactide, initiators, various additives, etc. These may be used alone or in combination of two or more.

[0021] -Lactide- As methods for polymerizing polylactic acid, generally, a direct melt polymerization method of lactic acid, a solid-phase polymerization method, a melt ring-opening polymerization method of lactide, which is a dimer of lactic acid (lactide method), etc. are used. In the present invention, from the viewpoint of a production process in which condensed water is not generated, it is easy to increase the molecular weight, and a high molecular weight polymer having a weight average molecular weight (Mw) of 300,000 or more can be preferably obtained, it is preferable to use a melt ring-opening polymerization method of lactide. Therefore, at least lactide is used as the monomer for the reaction raw material.

[0022] Examples of the lactide include the L-form of lactide (L-lactide), the D-form of lactide (D-lactide), and mixtures thereof (e.g., DL-lactide).

[0023] The optical purity of the lactide also directly affects the optical purity of the polylactic acid resin in the polylactic acid resin composition. The optical purity of the polylactic acid resin affects the crystallization rate and melting point and can be adjusted as appropriate. As the lactide, which is the monomer as the raw material of the polylactic acid resin composition, a mixture of about 0.01% by mass to 10% by mass of the D-form of lactide or the L-form of lactide may be used.

[0024] The amount of the lactide used is not particularly limited as long as the effects of the present invention are not impaired and can be appropriately selected according to the purpose. However, in consideration of recyclability, it is preferable that the lactide is 99% by mass or more based on all the monomer components in the reaction raw material.

[0025] Also, the acid value of the lactide is not particularly limited and can be appropriately selected according to the purpose, but is preferably 0.5 mg / g or less, and more preferably 0.1 mg / g or less. The acid value of the lactide can be measured by JIS K 0070-1992 or the like.

[0026] -Monomers other than lactide- By using monomers other than lactide as the reaction raw material, a polylactic acid resin composition containing a polymer blend can be produced.

[0027] The monomers other than lactide can be appropriately selected according to the application and desired physical properties of the resulting polylactic acid resin composition, and examples thereof include monomer components having biodegradability.

[0028] Specific examples of the monomers other than the lactide include monomer components having biodegradability such as raw material monomers of poly(3-hydroxybutyrate), poly(ε-caprolactone), or poly(butylene succinate); raw material monomers of polyalkylene resins for imparting flexibility; compounds having a carbodiimide group-containing moiety, a polysiloxane moiety, an aliphatic carboxylic acid amide moiety, an aliphatic carboxylic acid moiety, an aliphatic alcohol moiety, or an aliphatic carboxylic acid ester moiety as a transparent nucleating agent component; raw material monomers of a modified polylactide obtained by urethane-crosslinking (poly)ethylene oxide-added bisphenol A with an isocyanate compound in the presence of an amidation catalyst for improving heat resistance; raw material monomers of polyethylene (PET) resin or polybutylene (PBT) resin; raw material monomers of a resin alloy blended with a polysiloxane / acrylic composite rubber for improving impact resistance; and acrylate, polysiloxane, vinyl polyrolidone, sucrose, glycolic acid, glycolide, and the like. These may be used alone or in combination of two or more kinds. In addition to the above, monomer components in known polymer blends using polylactic acid can be appropriately used.

[0029] The amount of the monomers other than the lactide is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose. However, from the viewpoint of taking advantage of the recyclability of the lactide, it is preferable that the monomers other than the lactide are less than 1% by mass based on all monomer components in the reaction raw materials.

[0030] -Catalyst- The catalyst is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include organic catalysts and metal catalysts.

[0031] --Organic Catalyst-- The organic catalyst is not particularly limited and can be appropriately selected according to the purpose. For example, those that do not contain metal atoms, contribute to the ring-opening polymerization reaction of the ring-opening polymerizable monomer, form an active intermediate with the ring-opening polymerizable monomer, and then are eliminated and regenerated by reaction with alcohol are preferred.

[0032] For example, when polymerizing a ring-opening polymerizable monomer having an ester bond, as the organic catalyst, a (nucleophilic) compound that acts as a basic nucleophile is preferred, a compound containing a nitrogen atom is more preferred, and a cyclic compound containing a nitrogen atom is particularly preferred. Such compounds are not particularly limited and can be appropriately selected according to the purpose. For example, cyclic monoamines, cyclic diamines (for example, cyclic diamine compounds having an amidine skeleton, etc.), cyclic triamine compounds having a guanidine skeleton, heterocyclic aromatic organic compounds containing a nitrogen atom, N-heterocyclic carbenes, etc. can be mentioned. These may be used alone or in combination of two or more.

[0033] Examples of the cyclic monoamine include quinuclidine and the like.

[0034] Examples of the cyclic diamine include 1,4-diazabicyclo-[2.2.2]octane (DABCO), 1,5-diazabicyclo(4,3,0)-5-nonene, and the like.

[0035] Examples of the cyclic diamine compound having an amidine skeleton include 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), diazabicyclononene, and the like.

[0036] Examples of the cyclic triamine compound having a guanidine skeleton include 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), diphenylguanidine (DPG), and the like.

[0037] Examples of the nitrogen atom-containing heterocyclic aromatic organic compound include N,N-dimethyl-4-aminopyridine (DMAP), 4-pyrrolidinopyridine (PPY), pyrrocoline, imidazole, pyrimidine, purine, and the like.

[0038] Examples of the N-heterocyclic carbene include 1,3-di-tert-butylimidazole-2-ylidene (ITBU).

[0039] Among these, as the organic catalyst, 1,4-diazabicyclo-[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), diphenylguanidine (DPG), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), N,N-dimethyl-4-aminopyridine (DMAP), 4-pyrrolidinopyridine (PPY), 1,3-di-tert-butylimidazole-2-ylidene (ITBU) are preferred because they are less affected by steric hindrance and have high nucleophilicity, or because they have a boiling point that can be removed under reduced pressure.

[0040] Although cationic organic catalysts can also be used for ring-opening polymerization, in this case, since hydrogen is extracted (back-biting) from the main chain of the polylactic acid resin, the molecular weight distribution becomes wide and it is difficult to obtain a high molecular weight product.

[0041] Among these organic catalysts, for example, DBU is liquid at room temperature and has a boiling point. When such an organic catalyst is selected, the organic catalyst can be almost quantitatively removed from the polylactic acid resin composition by subjecting the polylactic acid resin composition to a reduced pressure treatment. The type of the organic catalyst and the presence or absence of the removal treatment can be appropriately determined according to the purpose of use of the polylactic acid resin composition and the like.

[0042] --Metal catalyst-- The metal catalyst is not particularly limited and can be appropriately selected according to the purpose. For example, tin-based compounds, aluminum-based compounds, titanium-based compounds, zirconium-based compounds, antimony-based compounds, etc. can be mentioned.

[0043] Examples of the tin-based compound include tin dioctanoate, tin octanoate, tin dibutyrate, tin(II) 2-ethylhexanoate, etc.

[0044] Examples of the aluminum-based compound include aluminum acetylacetonate, aluminum acetate, etc.

[0045] Examples of the titanium-based compound include tetraisopropyl titanate, tetrabutyl titanate, etc.

[0046] Examples of the zirconium-based compound include zirconium isopropoxide, etc.

[0047] Examples of the antimony-based compound include antimony trioxide, etc.

[0048] Among the above catalysts, the metal catalyst is preferred, the tin-based compound is more preferred, and tin dioctanoate and tin(II) 2-ethylhexanoate are even more preferred because they are more likely to cause high molecular weight, and tin dioctanoate is particularly preferred.

[0049] The water content of the metal catalyst is not particularly limited and can be appropriately selected according to the purpose. However, those that are sufficiently dried to reduce the water content are preferred, more preferably 100 ppm or less, even more preferably 50 ppm, and particularly preferably 10 ppm or less.

[0050] The amount of the catalyst used is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably 50 ppm or more and 5,000 ppm or less, more preferably 100 ppm or more and 1,000 ppm or less, based on the monomer. When the amount of the catalyst used is 50 ppm or more based on the monomer, deactivation of the catalyst and the like are less likely to occur, and ring-opening addition polymerization of the lactide can proceed quantitatively. Further, when the amount of the catalyst used is 5,000 ppm or less based on the monomer, side reactions due to excessive reaction are less likely to cause a decrease in molecular weight, and it is less likely to function as a catalyst for depolymerization (decomposition) after the polymerization reaction, so a decrease in the molecular weight of the polylactic acid resin can be prevented.

[0051] -Initiator- The initiator is used to control the molecular weight of the polylactic acid resin obtained by the ring-opening addition polymerization reaction of the lactide.

[0052] The initiator is not particularly limited and can be appropriately selected according to the purpose. However, an initiator having active hydrogen is preferred, and examples thereof include alcohol-based initiators. The alcohol-based initiator may be either a monoalcohol of an aliphatic alcohol or a polyhydric alcohol, and may be either a saturated alcohol or an unsaturated alcohol.

[0053] Specific examples of the initiator include monoalcohol, polyhydric alcohol, lactic acid ester, and the like. These initiators may be used alone or in combination of two or more.

[0054] Examples of the monoalcohol include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, nonanol, decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, and the like.

[0055] Examples of the polyhydric alcohol include diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, nonanediol, tetramethylene glycol, and polyethylene glycol; glycerol, sorbitol, xylitol, ribitol, erythritol, triethanolamine, pentaerythritol, and the like.

[0056] Examples of the lactate ester include methyl lactate, ethyl lactate, and the like.

[0057] In addition, a polymer having a hydroxyl group may be used as the initiator. However, when a polyester is used, it is necessary to design considering the influence of the carboxylic acid contained in the polymer and side reactions such as transesterification.

[0058] The amount of the initiator used in the first polymerization step is not particularly limited and can be appropriately adjusted according to the target molecular weight. However, it is preferably 1 / 4,000 mol or more and 1 / 1,500 mol or less, more preferably 1 / 2,500 mol or more and 1 / 1,800 or less, and still more preferably 1 / 2,100 mol or more and 1 / 1,800 or less, per 1 mol of the lactide as the monomer.

[0059] The water content of the initiator is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably sufficiently dried to reduce the water content, more preferably 100 ppm or less, still more preferably 50 ppm, and particularly preferably 10 ppm or less.

[0060] In order to prevent non-uniform initiation of polymerization, it is preferable to mix the lactide and the initiator well in advance before the lactide comes into contact with the catalyst.

[0061] -Additive- The additive is not particularly limited and can be appropriately selected according to the purpose. For example, crosslinking agents, surfactants, antioxidants, stabilizers, anti-fogging agents, ultraviolet absorbers, pigments, colorants, fillers, heat stabilizers, light-resistant agents, flame retardants, crystal nucleating agents, antistatic agents, surface wetting improvers, incineration aids, lubricants, natural products, mold release agents, plasticizers, entrainers, and other similar substances can be mentioned. These can be used alone or in combination of two or more.

[0062] The amount of the additive used is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose of addition, the type of additive, etc. In the process of producing a high molecular weight polylactic acid resin, it is possible to ensure melt stability without using or minimizing the additive used in the polylactic acid resin composition. Therefore, from the viewpoints of biodegradability, melt stability, and moldability of the polylactic acid resin composition, it is preferable that the polylactic acid resin composition does not substantially contain the additive, more preferably 1 part by mass or less, and still more preferably 0.5 part by mass or less with respect to 100 parts by mass of the reaction raw material. By setting the amount of the additive used to 1 part by mass or less, the characteristics of the polylactic acid resin, which is a compostable resin, can be utilized.

[0063] --Crosslinking agent-- The crosslinking agent is not particularly limited and can be appropriately selected from known crosslinking agents. For example, epoxy-based crosslinking agents, organic acid halide-based crosslinking agents, isocyanate-based crosslinking agents, carbodiimide-based crosslinking agents, etc. can be mentioned. These can be used alone or in combination of two or more.

[0064] Examples of the epoxy-based crosslinking agent include those obtained by introducing an epoxy group into the side chain of a methacrylate-based resin (for example, Joncryl® ADR 4468, manufactured by BASF).

[0065] Examples of the organic acid halide-based crosslinking agent include 2,4,6-trimercapto-s-triazine (for example, ACTOR TSH, manufactured by Kawaguchi Chemical Industry Co., Ltd.).

[0066] Examples of the isocyanate-based crosslinking agent include polyisocyanates (e.g., BURNOCK DNW-5500, manufactured by DIC Corporation).

[0067] Examples of the carbodiimide-based crosslinking agent include polycarbodiimide compounds (e.g., bifunctional carbodiimide compounds such as Carbodilite (manufactured by Nisshinbo Chemical Inc.)).

[0068] When a polyfunctional crosslinking agent having three or more functional groups is used as the crosslinking agent, it may impair the biodegradability of the polylactic acid resin, or increase the reactive groups (e.g., hydroxyl groups) at the terminals of the polylactic acid resin that are prone to hydrolysis. In addition, an intramolecular three-dimensional crosslinked polymer (microgel) having a network structure formed locally may be formed, resulting in the occurrence of fish eyes in the molded body (e.g., film) of the polylactic acid resin composition, or troubles such as thread breakage in the fiber spinning process. Therefore, a bifunctional carbodiimide-based crosslinking agent is preferably used as the crosslinking agent.

[0069] The amount of the crosslinking agent used is not particularly limited and can be appropriately selected according to the purpose. Although it is generally recommended to use the crosslinking agent at 1% by mass or more, it is preferable that the polylactic acid resin in the polylactic acid resin composition has fewer active groups at the terminals of the polylactic acid resin. From this viewpoint, the amount of the crosslinking agent used is preferably 1% by mass or less based on the reaction raw materials.

[0070] --Filler-- The filler is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include inorganic fillers and organic fillers. These may be used alone or in combination of two or more.

[0071] Examples of the inorganic filler include talc, kaolin, calcium carbonate, layered silicate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate, boron nitride, graphite, glass fiber, carbon fiber, and the like. These inorganic fillers are suitable for improving the mechanical strength, heat resistance, and linear expansion coefficient of the molded article of the polylactic acid resin composition.

[0072] Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood powder, okara, sawdust, bran, and modified products thereof, sorbitol compounds, benzoic acid and metal salts of its compounds, metal salts of phosphate esters, rosin compounds, and the like.

[0073] The average particle size of the filler is not particularly limited and can be appropriately selected according to the purpose, but is preferably 7 nm to 100 nm.

[0074] The content of the filler is not particularly limited and can be appropriately selected according to the purpose, but is preferably 0.3% by mass to 5% by mass based on the total mass of the polylactic acid resin composition.

[0075] --Entrainer-- Generally, an entrainer means a substance that increases solubility (see Yoshio Iwai, Hirohisa Uchida, "Solubility of High-Boiling Compounds in Supercritical Fluids", Science and Technology of High Pressure, 1996, Vol. 5, No. 2, p. 71-77). In the present invention, it means a substance that increases the solubility of the polylactic acid resin composition or its raw materials. However, the compressible fluid is preferably not included in the entrainer as the other component and is a substance that assists the action of the compressible fluid. As the entrainer, there is no particular limitation as long as it is a substance having the above-described action, and it can be appropriately selected according to the purpose. For example, known solvents and the like can be mentioned.

[0076] The content of the entrainer is not particularly limited as long as the effects of the present invention are not impaired, and it can be appropriately selected according to the purpose. However, from the viewpoints of the biodegradability of the polylactic acid resin composition, as well as the melt stability and moldability, it is preferably substantially free of the entrainer, more preferably less than 1% by mass, and still more preferably 0.5% by mass or less, based on the total mass of the polylactic acid resin composition.

[0077] <<Prepolymer-containing composition>> The prepolymer-containing composition contains a prepolymer, a ring-opening polymerizable monomer, and the catalyst, and further contains the other components of the reaction raw materials as necessary. The content of the ring-opening polymerizable monomer in the prepolymer-containing composition is 15% by mass or more and 95% by mass or less.

[0078] -Prepolymer- In the present invention, the "prepolymer" is a polymer of the lactide or a polymer of the lactide and a monomer other than the lactide, and has an active hydrogen group such as a hydroxyl group at the prepolymer terminal in order for the lactide to react in the polymerization reaction of the present invention, and means a polymer having a smaller molecular weight than the polylactic acid resin obtained in the second polymerization step.

[0079] The weight average molecular weight (Mw) of the prepolymer is not particularly limited as long as it is smaller than the weight average molecular weight (Mw) of the polylactic acid resin obtained in the second polymerization step, and it can be appropriately selected according to the purpose. However, it is preferably 1,000 or more and 200,000 or less, and more preferably 5,000 or more and 100,000 or less. When the weight average molecular weight (Mw) of the prepolymer is 1,000 or more, unreacted initiators and the like are less likely to be contained, and the reaction proceeds uniformly in the compressible fluid. When it is 200,000 or less, a sufficient plasticizing effect by the compressible fluid can be obtained.

[0080] The molecular weight of the prepolymer can be measured by gel permeation chromatography (GPC). Specifically, a measurement sample is prepared by dissolving the prepolymer-containing composition in chloroform so that the concentration becomes 0.5% by mass. 1 mL of the prepared measurement sample is injected and measured under the following analysis conditions. Also, gel permeation chromatography is performed in the same manner using a monodisperse polystyrene standard sample, and a molecular weight calibration curve is created in advance. From the molecular weight distribution (Mw / Mn) of the prepolymer-containing composition, the number average molecular weight (Mn) and weight average molecular weight (Mw) of the polylactic acid resin in the prepolymer-containing composition can be calculated using the molecular weight calibration curve. [Analysis Conditions] · Apparatus: GPC-8020 (manufactured by Tosoh Corporation) · Column: TSKgel (registered trademark) G2000HXL and G4000HXL (manufactured by Tosoh Corporation) · Temperature: 40 °C · Solvent: Chloroform · Injection volume: 1 mL · Flow rate: 1.0 mL / min

[0081] The content of the prepolymer in the prepolymer-containing composition is not particularly limited and can be appropriately selected according to the purpose, but is preferably 2% by mass or more and 70% by mass or less, and more preferably 10% by mass or more and 33% by mass or less. When the content of the prepolymer in the prepolymer-containing composition is 2% by mass or more and 70% by mass or less, side reactions in the high molecular weight formation can be suppressed by the plasticizing effect of the polymer by the compressible fluid.

[0082] The weight average molecular weight (Mw) and content of the prepolymer can be adjusted by the reaction time in the first polymerization step, the amount of the catalyst, etc.

[0083] - Ring-opening polymerizable monomer - The ring-opening polymerizable monomer is the unreacted monomer in the prepolymer-containing composition, and may also be referred to as the "residual ring-opening polymerizable monomer".

[0084] The content of the ring-opening polymerizable monomer in the prepolymer-containing composition is 15% by mass or more and 95% by mass or less, preferably 30% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 60% by mass or less, based on the total mass of the prepolymer-containing composition. When the content of the ring-opening polymerizable monomer is less than 15% by mass, the plasticizing effect of the polymer by the compressible fluid becomes insufficient. When the ring-opening polymerizable monomer is less than 15% by mass, most of the polymerization reactions in the system proceed and it is in a state of high molecular weight. Since it takes time for the high molecular weight substance to be impregnated with the compressible fluid, the plasticization becomes non-uniform, and low molecular weight substances such as the ring-opening polymerizable monomer dissolve more in the compressible fluid, so it is considered that the polymerization process is completed without reacting with the high molecular weight substance which is the reaction active site. As a result, since the residual monomer contained in the obtained polylactic acid resin composition increases, there is a concern that the melt stability deteriorates. Also, when a compressible fluid is added in a state where the content of the ring-opening polymerizable monomer exceeds 95% by mass, the variation in the molecular weight of the polylactic acid resin obtained in continuous polymerization becomes large. The reason for this is not clear, but it is considered as follows.

[0085] In the ring-opening polymerization of the ring-opening polymerizable monomer, the heat generation amount is large in the initial stage of polymerization. It is difficult to keep the reaction temperature constant. When a compressible fluid is added in this state, the density of the compressible fluid fluctuates with the temperature variation, and the solubility of the ring-opening polymerizable monomer, initiator, catalyst, or other materials also fluctuates. As a result, in continuous polymerization, the variation in the molecular weight of the polylactic acid resin obtained over time becomes large and the quality is not stable.

[0086] The content of the ring-opening polymerizable monomer in the prepolymer-containing composition may be a value obtained by subtracting the content of the prepolymer from 100% by mass, or the content of the ring-opening polymerizable monomer can also be adjusted by adding lactide as a raw material after the first polymerization step.

[0087] -Catalyst and Other Components- The content of the catalyst and other components of the prepolymer-containing composition is not particularly limited and can be appropriately selected according to the amount of the catalyst and other components used in the first polymerization step.

[0088] <Second Polymerization Step and Second Polymerization Means> The second polymerization step is a step of adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step and polymerizing the lactide. By polymerizing the monomer in the compressible fluid, heating at a high temperature can be avoided, which is preferable in that it is less likely to produce deteriorated products. The second polymerization means is a means of adding a compressible fluid to the prepolymer-containing composition formed by the first polymerization means and polymerizing the lactide. The second polymerization step is preferably carried out by the second polymerization means.

[0089] By the second polymerization step, a polylactic acid resin composition precursor containing the polylactic acid resin obtained by polymerizing the monomer and the compressible fluid is obtained.

[0090] In the second polymerization step, when adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step, the melt viscosity of the prepolymer-containing composition is not particularly limited and can be appropriately selected according to the purpose, but it is preferably 1 Pa·s or more and 3,000 Pa·s or less.

[0091] Also, due to the density of the compressible fluid, the plasticizing effect of the polylactic acid resin in the polylactic acid resin composition and the dissolving ability of low molecular weight components such as the monomer, the catalyst, and the initiator are different. Therefore, it is preferable to reduce the low molecular weight components from the prepolymer-containing composition and then add the compressible fluid.

[0092] As a method for reducing the low-molecular-weight component from the prepolymer-containing composition, there is no particular limitation, and it can be appropriately selected according to the purpose. For example, a method of separating the low-molecular-weight component from the prepolymer-containing composition in a vacuum state can be mentioned.

[0093] <<Precursor of polylactic acid resin composition>> The polylactic acid resin composition precursor contains lactide as a raw material monomer, a polylactic acid resin obtained by polymerizing monomers other than the lactide as required, the compressible fluid, and the catalyst, and may further contain a ring-opening polymerizable monomer, and further contains the other components of the reaction raw materials as required.

[0094] -Polylactic acid resin- There is no particular limitation on the weight average molecular weight (Mw) of the polylactic acid resin obtained in the second polymerization step, and it can be appropriately selected according to the purpose. However, it is preferably 270,000 or more and 5,000,000 or less, more preferably 300,000 or more and 5,000,000 or less, and still more preferably 350,000 or more and 2,000,000 or less.

[0095] There is no particular limitation on the content of the polylactic acid resin in the polylactic acid resin composition precursor, and it can be appropriately selected according to the purpose. However, it is preferably 90% by mass or more, and more preferably 95% by mass or more. When the content of the polylactic acid resin in the polylactic acid resin composition precursor is 90% by mass or more, the energy for separating the polylactic acid resin and other components from the polylactic acid resin composition precursor is small, and side reactions such as decomposition can be suppressed.

[0096] -Compressible fluid- The compressible fluid will be described with reference to FIGS. 1 and 2. FIG. 1 is a phase diagram showing the state of matter of the compressible fluid with respect to temperature and pressure used in the method for producing the polylactic acid resin composition. FIG. 2 is a phase diagram for defining the range of the compressible fluid used in the method for producing the polylactic acid resin composition.

[0097] The term "compressible fluid" means the state of a substance when it exists in any of the regions (1), (2), and (3) shown in Fig. 2 within the phase diagram represented by Fig. 1. In such regions, the substance is in a state of very high density and is known to exhibit behavior different from that at normal temperature and pressure. When the substance exists in region (1), it becomes a supercritical fluid.

[0098] The term "supercritical fluid" refers to a non-condensable high-density fluid that exists in a region of temperature (critical temperature) and pressure (critical pressure) beyond the limit (critical point) where gas and liquid can coexist, and does not condense even when compressed. When the substance exists in region (2), it becomes a liquid, but in this embodiment, it represents a liquefied gas obtained by compressing a substance that is in a gaseous state at normal temperature (25°C) and normal pressure (1 atm). When the substance exists in region (3), it is in a gaseous state, but in this embodiment, it represents a high-pressure gas with a pressure of 1 / 2 (1 / 2Pc) or more of the critical pressure (Pc). The compressible fluid is preferably a supercritical fluid at a pressure equal to or higher than the critical pressure and a temperature equal to or higher than the critical temperature.

[0099] There are no particular restrictions on the substance constituting the compressible fluid, and it can be appropriately selected according to the purpose. For example, carbon monoxide, carbon dioxide, nitrous oxide, nitrogen, methane, ethane, propane, 2,3-dimethylbutane, ethylene, dimethyl ether, etc. can be mentioned. These compressible fluids can be used alone or in combination of two or more. Among these, carbon dioxide is preferable in terms of having a critical pressure of about 7.4 MPa, a critical temperature of about 31°C, being able to easily create a supercritical state, and being easy to handle.

[0100] The pressure during polymerization, that is, the pressure of the compressible fluid, may be a pressure at which the compressible fluid becomes a liquefied gas ((2) in the phase diagram of Fig. 2) or a high-pressure gas ((3) in the phase diagram of Fig. 2), but a pressure at which it becomes a supercritical fluid ((1) in the phase diagram of Fig. 2) is preferable. By setting the compressible fluid to a supercritical fluid state, the dissolution or plasticization of the ring-opening polymerizable monomer of lactide is promoted, and the polymerization reaction can proceed uniformly and quantitatively.

[0101] When carbon dioxide is used as the compressible fluid, the pressure may be set according to the amount of carbon dioxide added to the prepolymer-containing composition. However, considering the reaction efficiency, polymer conversion rate, etc., the pressure is preferably 3.7 MPa or more, more preferably 5 MPa or more, and even more preferably 7.4 MPa or more of the critical pressure. In particular, when adding 5% by mass or more of carbon dioxide to the prepolymer-containing composition, it is preferably 7.4 MPa or more of the critical pressure.

[0102] Also, when carbon dioxide is used as the compressible fluid, considering the reaction efficiency, polymer conversion rate, etc., the temperature is preferably 25°C or more. Furthermore, when the tin-based compound is used as the catalyst, the temperature of the polymerization reaction has no particular limitation and can be appropriately selected according to the purpose, but is preferably 150°C or more, and more preferably 180°C or more.

[0103] The concentration of the compressible fluid is not particularly limited as long as it is a concentration capable of dissolving or plasticizing the ring-opening polymerizable monomer and the polymer produced from the ring-opening polymerizable monomer, and can be appropriately selected according to the purpose.

[0104] The amount of the compressible fluid used is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably within the saturated dissolution amount determined by the type, temperature, and pressure of the compressible fluid. More preferably, it is 3% by mass or more, still more preferably 8% by mass or more, and particularly preferably 18% by mass or more based on the total mass of the prepolymer-containing composition. Also, the upper limit of the amount of the compressible fluid used is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of economic rationality, it is preferably 30% by mass or less based on the total mass of the prepolymer-containing composition. The upper limit and the lower limit of the amount of the compressible fluid used can be appropriately combined. For example, it can be 3% by mass or more and 30% by mass or less, 8% by mass or more and 30% by mass or less, 18% by mass or more and 30% by mass or less, etc. based on the total mass of the prepolymer-containing composition. By setting the amount of the compressible fluid used to be 3% by mass or more and 30% by mass or less, the prepolymer-containing composition does not separate into a liquid phase and a gas phase, but becomes a single-layer state and the reaction proceeds uniformly.

[0105] The compressible fluid may be added in its entirety at once or in multiple portions to the prepolymer-containing composition. When the compressible fluid is added to the prepolymer-containing composition in multiple portions, the initial addition amount is preferably an amount such that the melt viscosity of the prepolymer-containing composition is 1 Pa·s or more and 3,000 Pa·s or less.

[0106] -Ring-opening polymerizable monomer- The content of the ring-opening polymerizable monomer in the polylactic acid resin composition precursor is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably 15% by mass or less, and more preferably 10% by mass or less.

[0107] In the method for producing the polylactic acid resin composition, it is preferable that the compressible fluid be removed in the compressible fluid removal step described below. Generally, when removing the monomer simultaneously with the compressible fluid, the molecular weight may decrease rapidly due to a rapid increase in viscosity and agitation for molecular chain scission and surface renewal. In contrast, in the method for producing the polylactic acid resin composition, since the ring-opening polymerizable monomer has the property of dissolving in the compressible fluid, the compressible fluid added in the second polymerization step removes the ring-opening polymerizable monomer, and a decrease in molecular weight can be suppressed. From the viewpoint of obtaining the above effects, the content of the ring-opening polymerizable monomer in the polylactic acid resin composition precursor is preferably 15% by mass or less, more preferably 10% by mass or less.

[0108] -Catalyst and Other Components- The content of the catalyst and the other components of the reaction raw materials in the polylactic acid resin composition precursor is not particularly limited and can be appropriately selected according to the amounts of the catalyst and the other components used in the first polymerization step.

[0109] <Other Processes and Other Means> The other processes are not particularly limited and can be appropriately selected according to the purpose, and examples include a catalyst deactivation process, a compressible fluid removal process, a hydrolysis inhibitor addition process, a molding process, and the like. The other means are not particularly limited and can be appropriately selected according to the purpose, and examples include a catalyst deactivation means, a compressible fluid removal means, a hydrolysis inhibitor addition means, a molding means, and the like.

[0110] <<Catalyst Deactivation Process and Catalyst Deactivation Means>> The catalyst deactivation process is a process for deactivating the activity of the catalyst. The catalyst deactivation process is preferably carried out after the polymerization process, more preferably after the second polymerization process and before the compressible fluid removal process. The catalyst deactivation means is a means for deactivating the activity of the catalyst. The catalyst deactivation process is preferably carried out by the catalyst deactivation means.

[0111] Since the catalyst also functions as a catalyst for the depolymerization (decomposition) reaction of the polylactic acid resin composition, it is not preferable to leave catalytic activity after the polymerization reaction. Since it is difficult to remove the catalyst materially, it is preferable to deactivate it. Further, by including the catalyst deactivation step, the melt stability of the polylactic acid resin composition can be further improved.

[0112] The method for deactivating the activity of the catalyst is not particularly limited and can be appropriately selected according to the purpose. For example, a method of adding a catalyst deactivator to the product obtained in the second polymerization step can be mentioned.

[0113] The catalyst deactivator is not particularly limited and can be appropriately selected according to the purpose, but it is preferably one that reacts with the hydroxyl group of the polylactic acid resin. For example, phosphorus compounds, carboxylic acid compounds, hydrochloric acid, or anhydrides thereof can be mentioned. These may be used alone or in combination of two or more. Examples of the phosphorus compound include triethyl phosphonoacetate, phosphoric acid, metaphosphoric acid, and the like. Examples of the carboxylic acid compound include benzoic acid, acetic acid, citric acid, lactic acid, and the like. In addition, the acid component as these catalyst deactivators also has the effect of stopping the polymerization reaction of the monomer. Among these, carboxylic acid compounds are preferable, and acetic anhydride and citric acid are more preferable in that they can react efficiently with the terminal hydroxyl group of the polylactic acid resin and can reduce the activity of the catalyst.

[0114] The amount of the catalyst deactivator used is not particularly limited and can be appropriately selected according to the purpose of addition, the type of the additive in the polylactic acid resin composition, etc. However, it is preferably 0.5 parts by mass or less based on 100 parts by mass of the polylactic acid resin composition. By setting the amount of the catalyst deactivator used to 0.5 parts by mass or less based on 100 parts by mass of the polylactic acid resin composition, the characteristics of the polylactic acid resin, which is a compostable resin, can be utilized.

[0115] The catalyst deactivator needs to react with the hydroxyl group of the polylactic acid resin, and an acid component such as a carboxylic acid is preferable. Therefore, the catalyst deactivation step also acts as a polymerization termination step for terminating the polymerization reaction of the monomer, and the catalyst deactivation means also functions as a polymerization termination means for terminating the polymerization reaction of the monomer.

[0116] <<Compressible fluid removal step and compressible fluid removal means>> The compressible fluid removal step is a step of removing the compressible fluid after the second polymerization step. When the method for producing the polylactic acid resin composition includes the polymerization termination step, it is preferably carried out after the polymerization termination step. The compressible fluid removal means is means for removing the compressible fluid. The compressible fluid removal step is preferably carried out by the compressible fluid removal means.

[0117] The method for removing the compressible fluid is not particularly limited and can be appropriately selected according to the purpose. For example, the method of subjecting the polylactic acid resin composition to a reduced pressure treatment with a vacuum pump or the like and removing it with a filter can be mentioned.

[0118] Since the ring-opening polymerizable monomer has the property of dissolving in the compressible fluid, the compressible fluid removal step also acts as a monomer removal step, and the ring-opening polymerizable monomer can be efficiently removed.

[0119] <<Hydrolysis inhibitor addition step and hydrolysis inhibitor addition means>> The hydrolysis inhibitor addition step is a step of adding the hydrolysis inhibitor to the product obtained in the second polymerization step. The hydrolysis inhibitor addition step is preferably carried out after the second polymerization step, and when the method for producing the polylactic acid resin composition includes the compressible fluid removal step, it is preferably carried out after the compressible fluid removal step. The hydrolysis inhibitor addition means is means for adding the hydrolysis inhibitor to the product obtained in the second polymerization step.

[0120] Lactic acid has two reactive groups, a hydroxyl group and a carboxyl group. The hydroxyl group of the lactic acid acts in the same manner as the alcohol of the initiator to reduce the molecular weight of the polylactic acid resin, and the carboxyl group of the lactic acid inhibits the polymerization reaction by impairing the activity of the catalyst. Therefore, it is preferable to remove these.

[0121] As a method for removing at least one of the hydroxyl group and the carboxyl group of the lactic acid, for example, in addition to the method of adding the hydrolysis inhibitor to the polylactic acid resin composition, if it is a low molecular compound, a method of performing a reduced pressure operation can be mentioned.

[0122] The amount of the hydrolysis inhibitor used is not particularly limited and can be appropriately selected according to the purpose. Generally, it is recommended to use the hydrolysis inhibitor at 1% by mass or more. However, as described above, in the polylactic acid resin in the polylactic acid resin composition, it is preferable that the number of reactive groups at the ends of the polylactic acid resin is small. From this viewpoint, the amount of the hydrolysis inhibitor used is preferably less than 1% by mass with respect to the product.

[0123] <<Molding step and molding means>> The molding step is a step of molding the finally obtained polylactic acid resin composition. The molding means is means for molding the finally obtained polylactic acid resin composition. The molding step is preferably carried out by the molding means.

[0124] The shaping means is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include molds such as dies. The shaping method is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include a method of extruding from the mold and further pelletizing with a pelletizer, a cutter, etc. as necessary.

[0125] The form of the shaping is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include pellets, sheets, films, etc.

[0126] <<<Manufacturing process>>> The manufacturing method of the polylactic acid resin composition can employ a continuous process or a batch process. Therefore, as the manufacturing apparatus for the polylactic acid resin composition, there is an advantage that a more suitable polymerization apparatus can be selected from a wider range of polymerization apparatuses. Specifically, in each step, it is preferable to use a polymerization apparatus corresponding to the melt viscosity of the prepolymer-containing composition, the polylactic acid resin composition precursor, or the polylactic acid resin composition. Among these, as the manufacturing method and the manufacturing apparatus for the polylactic acid resin composition, it is preferable to select a continuous polymerization process in consideration of apparatus efficiency, product characteristics, quality, etc.

[0127] Specifically, in the manufacturing method of the polylactic acid resin composition, the first polymerization step is preferably carried out by continuously supplying the lactide and the catalyst, and the second polymerization step is preferably a method of continuously adding the compressible fluid to the prepolymer-containing composition, continuously polymerizing the lactide, and continuously obtaining the polylactic acid resin composition. Here, in the present invention, "continuous" means that the raw materials such as the lactide enter each of the above steps at a constant flow rate, are converted into a polymer, and a certain amount of the polylactic acid resin composition as the final product is discharged from the final step of the manufacturing method. That is, it means repeating the first polymerization step, the second polymerization step, and, if necessary, the other steps two or more times. There is no particular limitation on the upper limit of the number of repetitions of each step, and it can be appropriately selected according to the amount of the target polylactic acid resin composition and the like.

[0128] In addition, in the step of mixing the raw material monomer and the catalyst of the polylactic acid resin composition, and, if necessary, other raw materials such as the initiator, and the polylactide containing 10% by mass or more and 30% by mass or less of the lactide, the melt viscosity is significantly reduced as compared with the polylactide containing less than 10% by mass of the lactide. It is preferable to adopt a continuous polymerization process according to the viscosity at that time.

[0129] When the melt viscosity of the prepolymer-containing composition, the polylactic acid resin composition precursor, or the polylactic acid resin composition does not exceed 600 Pa·s, a normal vertical polymerization tank can be used. Examples of the vertical polymerization tank include conventionally known low-viscosity to medium-viscosity melt polymerization apparatuses equipped with stirring blades such as a weight wing polymerization tank, an inclined wing polymerization tank, a spiral agitating wing polymerization tank, a full zone wing polymerization tank, a max blend wing polymerization tank, and a log bone wing polymerization tank. Among these, it is preferable to use in series a vertical polymerization tank equipped with a full zone wing that can efficiently mix the raw material monomer and the catalyst of the polylactic acid resin composition, and, if necessary, other raw materials such as the initiator, and can efficiently remove the ring-opening polymerization heat, and a weight wing suitable for polymerizing a prepolymer having a relatively high melt viscosity.

[0130] In addition, when the melt viscosity of the prepolymer-containing composition, the polylactic acid resin composition precursor, or the polylactic acid resin composition exceeds 600 Pa·s, a polymerization apparatus suitable for producing a resin with a relatively high melt viscosity can be preferably used. At this time, as side reactions occurring in the polymerization reaction of the monomer, it is necessary to remove the reaction heat while suppressing transesterification reactions and molecular chain scissions. For example, a single-screw extruder, a twin-screw extruder, a kneader, a shaftless cage-type stirring tank, a double-volute (manufactured by Sumitomo Heavy Industries, Ltd.), an N-SCR (manufactured by Mitsubishi Heavy Industries, Ltd.), a spectacle blade (manufactured by Hitachi, Ltd.), a lattice blade, a Kenics type, or a Sulzer type SMLX type static mixer-equipped tubular polymerization tank can be used. Also, a finisher, an N-SCR, a twin-screw extrusion extruder, etc., which are self-cleaning type polymerization apparatuses, can be preferably used. Among these, from the viewpoints of kneading property, production efficiency, stability, heat resistance, etc., it is particularly preferable to use a twin-screw extruder as the polymerization apparatus.

[0131] When adopting the continuous polymerization process, it is preferable to use a charging and melting tank preceding the polymerization apparatus. The charging and melting tank is not particularly limited, but it is preferable to use a full-zone blade stirring tank that can be efficiently stirred.

[0132] The conditions of the charging and melting tank are not particularly limited as long as they are higher than 100°C, the melting point of lactide, which is the raw material monomer, and can be appropriately selected according to the purpose. However, it is preferable that the internal temperature is 105°C to 150°C, under an inert atmosphere, and slightly pressurized. More preferably, the internal temperature is 110°C to 130°C, under an inert atmosphere, and the internal pressure is 12 kPa to 550 kPa. From the viewpoint of preventing the intake of outside air, moisture, etc. into the reaction system, it is more preferably 101.3 kPa to 304 kPa, and it is particularly preferable that the internal pressure is 111.5 kPa to 202.7 kPa because it is easy to handle and the protective effect against moisture and outside air is sufficiently large.

[0133] When adopting the batch process, the product in each polymerization tank can be solidified and taken out as desired. Alternatively, from the beginning of the reaction, in a stirring tank equipped with a pendulum-type stirring blade, while mechanically or electrically monitoring the stirring force moment and the melt viscosity with a motor stirring power or the like, in the initial stage of the reaction (i.e., the first polymerization step), for example, at a temperature of 190 ° C or lower, and then as the reaction progresses, the reaction temperature is raised, and finally (i.e., the second polymerization step), it is also a preferred embodiment to carry out the reaction at 190 ° C to 240 ° C. In order to suppress side reactions and increase the molecular weight, it is preferably set at 220 ° C or lower.

[0134] Next, a continuous polymerization process as an embodiment of the method for producing the polylactic acid resin composition using a continuous polymerization apparatus as an embodiment of the apparatus for producing the polylactic acid resin composition will be specifically described with reference to the drawings. However, the method for producing the polylactic acid resin composition and the apparatus for producing the polylactic acid resin composition of the present invention are not limited thereto.

[0135] [Embodiment 1 of Continuous Polymerization Apparatus] FIG. 3 is a diagram showing an example of a continuous polymerization apparatus suitably used in the method for producing a polylactic acid-containing composition of the present invention.

[0136] A. Raw Material Supply Step As shown in FIG. 3, in the continuous polymerization apparatus 100, the tank 1 (preferably the charging melting tank) is set to a temperature equal to or higher than the melting point of lactide, preferably set so that the internal temperature becomes 110 ° C to 130 ° C, and the melted lactide is supplied from the tank 1 to the prepolymerization tank 9 by the pump 2. Further, an initiator is supplied from the tank 3 to the prepolymerization tank 9 by the pump 4. Further, a catalyst is supplied from the tank 5 to the prepolymerization tank 9 by the pump 6. At this time, the prepolymerization tank 9 is set to 200 ° C. The raw materials are mixed and homogenized in the prepolymerization tank 9 with a stirring blade connected to the motor M. However, after mixing each raw material in the raw material mixing area a, it may be supplied to the prepolymerization tank 9. Also, the first raw material may be directly charged into the prepolymerization tank 9.

[0137] B. First Polymerization Step The first polymerization step is a step of mixing raw materials and homogenizing them to prepare a prepolymer-containing composition. At this time, it is preferable to make the melt viscosity of the prepolymer-containing composition in a viscosity state of 1 Pa·s or more and 3,000 Pa·s or less. Thereby, in the second polymerization step described later, by adding a compressible fluid to the prepolymer-containing composition having a melt viscosity of 1 Pa·s or more and 3,000 Pa·s or less, the polylactic acid resin can be suitably polymerized to a higher molecular weight.

[0138] In the raw material supply step, the lactide supplied by pump 2, the initiator supplied by pump 4, and the catalyst supplied by pump 6 are subjected to first polymerization in a prepolymerization tank 9 with a stirring blade connected to motor M. At this time, the flow rates of pump 15 and pump 16 are adjusted, and the average residence time in the prepolymerization tank 9 is set so that the content of the ring-opening polymerizable monomer in the prepolymer-containing composition is 15% by mass or more and 95% by mass or less. The prepolymerization tank 9 preferably has a stirring blade equipped with a torque meter. The prepolymer-containing composition containing lactide (monomer) sent by pump 15 is sent to the polymerization area b.

[0139] Here, the "average residence time" means the time required to replace all the contents of the prepolymerization tank 9 as long as the input amount of the raw material and the discharge amount from the prepolymerization tank 9 are the same.

[0140] The prepolymerization tank 9 is first heated to a temperature equal to or higher than the melting point of lactide, preferably 110°C to 130°C, and lactide and an initiator are charged. Then, while stirring, the temperature is raised to 200°C or lower, preferably up to 190°C, and after charging a catalyst, a first polymerization reaction is carried out while circulating with the pump 16. When the ring-opening polymerizable monomer (unreacted lactide) in the prepolymer-containing composition is 15% by mass or more and 95% by mass or less (for example, from 20 minutes to 40 minutes from the start of the first polymerization reaction), preferably further when the melt viscosity of the prepolymer-containing composition is 1 Pa·s or more and 3,000 Pa·s or less, the pump 15 is started, and the prepolymer-containing composition is sent to the polymerization area. At the same time, in such a form as to replenish the amount sent by the pump 15, the melted lactide from the tank 1 is fed by the pump 2, the initiator from the tank 3 is fed by the pump 4, and the catalyst from the tank 5 is fed by the pump 6 to the prepolymerization tank 9 continuously. At this time, by adjusting the flow rates of the pump 2, the pump 4, and the pump 6, fine adjustment may be carried out so that the liquid level of the raw materials in the prepolymerization tank 9 becomes constant.

[0141] Furthermore, when the continuous polymerization apparatus 100 has a stirring blade equipped with a torque meter in the prepolymerization tank 9, it may have a calculation unit that converts the rotational torque of the stirring blade into viscosity, and a detection unit that detects the melt viscosity of the prepolymer-containing composition calculated by the calculation unit, and the pump 15 may be configured to start in conjunction with the detection unit. The calculation unit may be, for example, a member that creates a data table in advance as a means for associating the rotational torque of the stirring blade with the melt viscosity of the prepolymer-containing composition, and can calculate the melt viscosity of the prepolymer-containing composition by comparing the rotational torque of the stirring blade measured by the torque meter with the data table.

[0142] C. Second polymerization step As an example of the second polymerization step, a method using a twin-screw extruder (for example, manufactured by Nippon Steel & Sumitomo Metal Corporation, JSW) can be mentioned. In the second polymerization step, a compressible fluid is added to the prepolymer-containing composition to reduce its viscosity, thereby suppressing side reactions of the polymerization reaction and completing the polymerization reaction of the polylactic acid resin to obtain a polylactic acid resin composition precursor. As a result, not only does the molecular weight of the polylactic acid resin increase, but it is also possible to reduce the residual monomer of lactide.

[0143] The compressible fluid is supplied as a liquid, for example, from a siphon-type cylinder 7 to a pressure regulating valve 8. In the extruder, the reactant of lactide is impregnated with the compressible fluid to complete the polymerization.

[0144] When adding additives such as a heat stabilizer and a light-resistant agent, as long as the polymerization reaction is not inhibited, they can be supplied and mixed in the raw material supply area a, added in the polymerization area b, added in the de-monomerization step described later, or added in one or more of these areas or process areas.

[0145] The time of the polymerization reaction in the polymerization area b is not particularly limited and can be appropriately selected according to the molecular weight of the target polylactic acid resin, etc., but is preferably 15 minutes to 90 minutes. When the time of the polymerization reaction is 15 minutes or more, the conversion rate can be increased. Also, from the viewpoint of productivity, the time of the polymerization reaction is preferably 90 minutes or less. To obtain a predetermined degree of vacuum in the de-monomerization step described later, the conversion rate at the outlet of the polymerization area b is preferably 90% or more.

[0146] Here, the "conversion rate" means the ratio (%) obtained by subtracting the content (% by mass) of the ring-opening polymerizable monomer from the polylactic acid resin composition (100% by mass).

[0147] The reaction temperature in the overlapping area b is not particularly limited and can be appropriately selected according to the purpose. However, in order to prevent a decrease in the molecular weight of the obtained polylactic acid resin, 180°C to 230°C is preferable, 180°C to 210°C is more preferable, and 180°C to 200°C is even more preferable. When the reaction temperature is 230°C or lower, side reactions such as transesterification and molecular chain scission can be suppressed, and the polylactic acid resin can be more suitably polymerized to a higher molecular weight. When the reaction temperature is 210°C or lower, side reactions can be further suppressed in the polymerization reaction of the monomer, and the molecular weight can be further increased. Also, when the reaction temperature is 180°C or higher, it is possible to prevent the reaction time from becoming long and efficiently produce the polylactic acid resin composition. In addition, in the polymerization area b, in order to prevent a decrease in the molecular weight of the obtained polylactic acid resin, the temperature on the side and cylinder of the extruder during the process of raising the reaction temperature to 180°C to 230°C is preferably controlled within +20°C with respect to the temperature of the polylactic acid resin composition.

[0148] D. Compressible Fluid Removal Step Since the ring-opening addition polymerization of lactide is an equilibrium reaction, even after the polymerization reaction is sufficiently carried out, a certain amount of ring-opening polymerizable monomer (lactide) remains. In order to remove this, a process for removing the compressible fluid and the monomer is required. This process can be carried out by the vacuum pump 12 and the filter 13 of the continuous polymerization apparatus 100. Since the compressible fluid has the characteristic that the monomer lactide dissolves in it, the unreacted ring-opening polymerizable monomer can be efficiently removed together with the compressible fluid, which is advantageous for suppressing a decrease in molecular weight and side reactions. Therefore, the compressible fluid removal step is also a de-monomer step. In addition, in the method for producing the polylactic acid resin composition, the one obtained by removing the compressible fluid and the ring-opening polymerizable monomer from the polylactic acid resin composition precursor is defined as the "polylactic acid resin composition" which is the final product.

[0149] As described above, since the molecular weight of the polylactic acid resin after monomer removal decreases due to chain scission in the extruder, the time for the compressible fluid removal step is preferably 30 minutes or less, more preferably 10 minutes or less, in order to obtain a high molecular weight polymer.

[0150] E. Catalyst deactivation area The ring-opening polymerization reaction of lactide is an equilibrium reaction, and since the polylactic acid resin is likely to decompose when removing the monomer lactide, it is preferable to deactivate the catalyst before removing the unreacted ring-opening polymerizable monomer. In FIG. 3, the catalyst deactivator is stored in tank 17, and by pump 10, a three-fold to ten-fold equivalent amount relative to the initiator is supplied to acetylate the hydroxyl groups at the ends of the polylactic acid resin (polymer) and also deactivate the catalyst. Further, a hydrolysis inhibitor may be stored in tank 17 and introduced into the polylactic acid resin composition precursor by pump 10.

[0151] F. Molding process The polylactic acid resin composition P is discharged from the extrusion die (die) 14 in a strand shape and pelletized by a cutter.

[0152] [Embodiment 2 of the continuous polymerization apparatus] FIG. 4 is a diagram showing another example of a continuous polymerization apparatus suitably used for the method for producing a polylactic acid-containing composition of the present invention.

[0153] The continuous polymerization apparatus 100 according to Embodiment 1 was a twin-screw extruder in which the second polymerization step and the compressible fluid removal step could be continuously performed in the polymerization area b, whereas the continuous polymerization apparatus 200 according to Embodiment 2 is different from the continuous polymerization apparatus 100 according to Embodiment 1 in that the polymerization area b for performing the second polymerization step and the compressible fluid removal area c for performing the compressible fluid removal step are separated. Except for this point, the continuous polymerization apparatus 100 according to Embodiment 1 and the continuous polymerization apparatus 200 according to Embodiment 2 operate in the same manner. In the continuous polymerization apparatus 200 according to Embodiment 2, for the polymerization area b, for example, a tube-type polymerization tank equipped with a Sulzer type SMLX static mixer can be used.

[0154] <<Polylactic acid resin composition>> According to the method for producing the polylactic acid resin composition and the production apparatus for the polylactic acid resin composition, side reactions can be suppressed, and a polylactic acid resin composition containing a high molecular weight polylactic acid resin can be obtained.

[0155] The polylactic acid resin is one of the aliphatic polyester resins and is biodegradable by microorganisms, so it has attracted attention as an environmentally friendly polymer material with a low environmental load (see "Structure, Physical Properties, and Biodegradability of Aliphatic Polyesters", Yoshio Inoue, Polymer, 2001, Vol. 50, No. 6, p374 - 377).

[0156] The polylactic acid resin is not particularly limited and can be appropriately selected according to the type of monomer of the reaction raw materials used. For example, polylactic acid, a polymer blend of polylactic acid and a polymer other than polylactic acid, etc. can be mentioned.

[0157] Examples of the polylactic acid include one or more ring - opening polymers of lactide selected from the group consisting of the D - form of lactide (D - lactide), the L - form of lactide (L - lactide), and a copolymer of D - lactide and L - lactide (poly DL - lactide). When the polylactic acid is poly DL - lactide, the sequence pattern of the copolymer may be any of a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer.

[0158] Examples of the polymer blend include polylactic acid and copolymers of poly(3-hydroxybutyrate), poly(ε-caprolactone), poly(butylene succinate), or these monomers; copolymers of polylactic acid and polyalkylene resins for imparting flexibility; copolymers of polylactic acid and carbodiimide compounds as a transparent nucleating agent component; copolymers of polylactic acid and polysiloxane; copolymers of polylactic acid and aliphatic carboxylic acid amides; copolymers of polylactic acid and aliphatic carboxylic acids; copolymers of polylactic acid and aliphatic alcohols; copolymers of polylactic acid and aliphatic carboxylic acid esters; modified polylactic acid obtained by urethane crosslinking (poly)ethylene oxide-added bisphenol A for improving heat resistance with an isocyanate compound in the presence of an amidation catalyst; resin alloys obtained by blending polyethylene (PET) resin or polybutylene (PBT) resin into polylactic acid; resin alloys obtained by blending polylactic acid and polysiloxane / acrylic composite rubber for improving impact resistance; graft copolymers of polylactic acid-acrylate-polysiloxane; vinyl pyrrolidone / L-lactic acid copolymers; sucrose / L-lactic acid copolymers; glycolic acid / L-lactic acid copolymers; glycolide / L-lactide copolymers and the like. These may be used alone or in combination of two or more.

[0159] The content of the polylactic acid resin in the polylactic acid resin composition is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of recyclability, it is preferably 99% by mass or more, and more preferably 99.5% by mass or more.

[0160] [Ring-opening polymerizable monomer] The content of the ring-opening polymerizable monomer in the polylactic acid resin composition is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably 0.1% by mass or less, and more preferably 0.05% by mass or less. When the content of the ring-opening polymerizable monomer in the polylactic acid resin composition is 0.1% by mass or less, it can be compostable without impairing the crystallinity of the polylactic acid resin and can utilize the characteristics of materials such as bio-based materials.

[0161] [Optical purity] When using a ring-opening polymer of one or more monomers selected from the group consisting of D-lactide, L-lactide, and DL-lactide as the polylactic acid resin, as the amount of the less abundant optical isomer of the D-form and the L-form decreases, the crystallinity increases, the melting point and the crystallization rate increase, and the melting point and the glass transition point tend to increase. Also, as the amount of the less abundant optical isomer of the D-form and the L-form increases, the crystallinity decreases and eventually tends to become amorphous.

[0162] Since the content (optical purity) of either D-lactic acid or L-lactic acid as a constituent monomer unit of the polylactic acid resin in the polylactic acid resin composition is related to the heat resistance and the molding temperature of the molded article of the polylactic acid resin composition, it may be properly selected according to the application and is not particularly limited. However, the more L-lactic acid there is, the more preferable it is. It is more preferable that the content of L-lactic acid is 90 mol% or more, and it is still more preferable that it is 95 mol% or more.

[0163] The optical purity of the polylactic acid resin can be measured by liquid chromatography (HPLC; High Performance Liquid Chromatography). Specifically, the polylactic acid resin composition is cryogenically pulverized, 0.1 g of the powder is weighed, 5 mL of 1N aqueous sodium hydroxide solution is added, and hydrolysis is carried out by refluxing at room temperature (25 °C) for about 4 hours. The solution after reflux is neutralized with 1 mol / L sulfuric acid and used as a sample for measurement, which is subjected to HPLC analysis and measured under the following analysis conditions. Also, HPLC analysis is carried out in the same manner using a standard sample of L-lactic acid and a standard sample of D-lactic acid, and calibration curves are prepared in advance respectively. From the peak areas of L-lactic acid and D-lactic acid obtained by HPLC analysis, the respective contents are calculated from the calibration curves, and the optical purity of L-lactic acid can be calculated based on the following formula (1). Also, the optical purity of D-lactic acid can be calculated based on the following formula (2). Optical purity of L-lactic acid (%) = 100 × (amount of L-form - amount of D-form) / (amount of L-form + amount of D-form) ··· Formula (1) Optical purity of D-lactic acid (%) = 100 × (amount of D-form - amount of L-form) / (amount of L-form + amount of D-form) ··· Formula (2) However, in Formula (1) and Formula (2), "amount of L-form" indicates the content (% by mass) of L-lactic acid obtained by HPLC analysis, and "amount of D-form" indicates the content (% by mass) of D-lactic acid obtained by HPLC analysis. [Analysis conditions] · Apparatus: PU-2085plus series (manufactured by JASCO Corporation) · Column: Chromolith (registered trademark) coated with SUMICHIRAL OA-5000 (inner diameter: 4.6 mm, length: 150 mm, manufactured by Sumika Chemical Analysis Service, Ltd.) · Column temperature: 25 °C · Mobile phase: A mixture of 2 mM CuSO4 aqueous solution and 2-propanol (2 mM CuSO4 aqueous solution: 2-propanol = 95:5 (volume ratio)) · Flow rate: 1.0 mL / min · Detector: UV (254 nm) · Injection volume: 20 μL

[0164] There is no particular limitation on the content ratio of D-lactic acid and L-lactic acid in the constituent monomer units of the polylactic acid in the polylactic acid resin composition, and it can be appropriately selected according to the purpose.

[0165] [Molecular weight] The weight average molecular weight (Mw) of the polylactic acid resin in the polylactic acid resin composition is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably 270,000 or more and 5,000,000 or less, more preferably 300,000 or more and 5,000,000 or less, and even more preferably 350,000 or more and 2,000,000 or less. When the weight average molecular weight (Mw) of the polylactic acid resin is 270,000 or more and 5,000,000 or less, it can be suitably molded into a sheet, a thread, etc. When the weight average molecular weight (Mw) of the polylactic acid resin is 270,000 or more, when the polylactic acid resin composition is formed into a sheet, melt strength, strain hardening property, etc. can be sufficiently exhibited, and the target sheet molding, spinning, etc. can be suitably performed. When the weight average molecular weight (Mw) of the polylactic acid resin is 5,000,000 or less, the viscosity of the polylactic acid resin composition does not become too high, the equipment load during processing is low, and stable production can be achieved.

[0166] The molecular weight distribution (Mw / Mn) obtained by dividing the weight average molecular weight (Mw) of the polylactic acid resin by the number average molecular weight (Mn) is not particularly limited and can be appropriately selected according to the purpose. However, it is preferably 1.3 to 2.4, more preferably 1.5 to 2.2. A molecular weight distribution (Mw / Mn) of 1.3 to 2.4 is preferable because unintended side reactions in polymerization reactions such as decomposition and cross-linking reactions do not occur.

[0167] In addition, depending on the use of the molding process of the polylactic acid resin composition, it is possible to add a high molecular weight component or a low molecular weight component to broaden the molecular weight distribution. However, it is desirable to control within the above range in the manufacturing method of the polylactic acid resin composition.

[0168] The molecular weight of the polylactic acid resin in the polylactic acid resin composition can be measured by gel permeation chromatography (GPC). Specifically, the polylactic acid resin composition is dissolved in chloroform so that the concentration becomes 0.5 mass% to prepare a measurement sample. 1 mL of the prepared measurement sample is injected and measured under the same analysis conditions as those in the analysis of the molecular weight measurement of the prepolymer. Also, gel permeation chromatography is performed in the same manner using a monodisperse polystyrene standard sample, and a molecular weight calibration curve is created in advance. From the molecular weight distribution (Mw / Mn) of the polylactic acid resin composition, the number average molecular weight (Mn) and the weight average molecular weight (Mw) of the polylactic acid resin in the polylactic acid resin composition can be calculated using the molecular weight calibration curve.

[0169] [Acid value] The acid value of the polylactic acid in the polylactic acid resin composition is a numerical value associated with lactic acid (residual ring-opening polymerizable monomer) generated in the process of ring-opening addition polymerization of the lactide. Since the lactic acid has both a hydroxyl group that reduces the molecular weight by hydrolysis and a carboxyl group that deactivates the catalytic activity, the presence of lactic acid is not preferable in the reaction process of ring-opening addition polymerization of lactide. Therefore, the acid value of the polylactic acid resin is preferably 0.5 mgKOH / g or less, and more preferably 0.1 mgKOH / g or less. The acid value of the polylactic acid can be measured according to JIS K 0070-1992 or the like.

[0170] [Biodegradability] The polylactic acid resin composition is excellent in biodegradability, particularly compostability. Here, "biodegradability" means the property of being able to be decomposed by the action of organisms such as microorganisms in nature. Also, "compostability" means having biodegradability at 58°C. The biodegradability of the polylactic acid resin composition can be confirmed in accordance with ISO 14855-1 or ISO 14855-2.

[0171] [Melt stability] The polylactic acid resin composition is excellent in melt stability. The melt stability of the polylactic acid resin composition can be confirmed by measuring the complex viscosity η*. In the present invention, the complex viscosity η* of the polylactic acid resin composition is a numerical value measured under the following measurement conditions using a parallel plate type rotational viscometer (ARES-G2, manufactured by TA Instruments). [Measurement conditions] · Parallel plates: diameter 20 mm, gap: 1.00 mm · Temperature: 200 °C · Frequency: 1 Hz (6.28 rad / s) · Atmosphere: under nitrogen atmosphere · Measurement sample size: strip shape with thickness 30 μm, width 7 mm, and length 35 mm

[0172] The measurement sample for the complex viscosity η* can be prepared as follows. The pelletized polylactic acid resin composition is dried at 80 °C for about 12 hours, placed on a measurement jig at the melting point of the polylactic acid resin in the polylactic acid resin composition + 20 °C for 3 to 5 minutes to melt it, and then pressed until the gap between the parallel plates becomes 1.05 mm. Next, the polylactic acid-containing composition protruding from the outer periphery of the parallel plates is scraped off with a spatula or the like, pressed again until the gap between the parallel plates becomes 1.00 mm, and left standing for 3 to 5 minutes to remove the residual stress, and it can be prepared into the above measurement sample size.

[0173] - Complex viscosity η* (30) - Using a parallel plate type rotational viscometer for the polylactic acid resin composition, measurement was started under the above measurement conditions, and the result of measuring the complex viscosity after 30 minutes was taken as the complex viscosity η* (30) When regarded as (30) There are no particular restrictions on the complex viscosity η* 4 and it can be appropriately selected according to the purpose. However, 1×10 4 Pa·s or more is preferable, 1.5×10 4 Pa·s or more is more preferable, and 2×10 (30) Pa·s or more is even more preferable. When the complex viscosity η* 4 is 1×10 (30) Pa·s or more, the melt strength required for molding the polylactic acid resin composition can be ensured. Also, as the upper limit value of the complex viscosity η* 4 There are no particular restrictions and it can be appropriately selected according to the purpose. However, from the viewpoint of good fluidity and moldability, 5×10 4It is more preferable that it is below Pa·s.

[0174] -Ratio [η* (30) / η* (5) - Using a parallel plate type rotational viscometer for the polylactic acid resin composition, the measurement was started under the above measurement conditions, and the complex viscosity after 5 minutes was measured. The result is the complex viscosity η* (5) When this is done, the complex viscosity η* (5) For the complex viscosity η* (30) Ratio of [η* (30) / η* (5) is not particularly limited and can be appropriately selected according to the purpose, but 0.45 or more is preferable, 0.5 or more is more preferable, 0.6 or more is still more preferable, and 0.8 or more is particularly preferable. The ratio [η* (30) / η* (5) is 0.45 or more, it is possible to prevent variations and defects in the quality of the molded product of the polylactic acid resin composition. Also, since the higher the ratio [η* (30) / η* (5) is, the more preferable it is, the upper limit value thereof is not particularly limited and can be appropriately selected according to the purpose.

[0175] -Ratio [η* (60) / η* (5) - Using a parallel plate type rotational viscometer for the polylactic acid resin composition, the measurement was started under the above measurement conditions, and after 60 minutes (that is, 30 minutes after the measurement of the complex viscosity η* (30) ), the complex viscosity was measured. The result is the complex viscosity η* (60) When this is done, the complex viscosity η* (5) For the complex viscosity η* (60) Ratio of [η* (60) / η* (5) is not particularly limited and can be appropriately selected according to the purpose, but 0.7 or more is preferable, 0.8 or more is more preferable. When the ratio [η* (60) / η* (5) is 0.7 or more, it is possible to suppress variations in the quality of the molded product of the polylactic acid resin composition and also suppress decomposition due to abnormal retention of the polylactic acid resin such as process troubles. On the contrary, the ratio [η*(60) / η* (5) When it is less than 0.7, it means that the decomposition of the polylactic acid resin has progressed, and the low molecular weight components generated by the decomposition also function as a plasticizer for the polylactic acid resin composition. Therefore, not only does the strength of the polylactic acid resin composition decrease rapidly, but it may also cause process troubles. The ratio [η* (60) / η* (5) is preferably as high as possible. Therefore, there is no particular limitation on its upper limit value, and it can be appropriately selected according to the purpose.

[0176] The melting point of polylactic acid is generally in the range of 140°C to 175°C. As described above, when at least one of the complex viscosity η* (30) of the polylactic acid resin composition, the ratio [η* (30) / η* (5) , and the ratio [η* (60) / η* (5) is within the preferred range, the viscosity reduction above the melting point of the polylactic acid resin is small, the non-Newtonian fluid characteristics (expression of strain hardening) required for molding processing can be expressed, and the melt stability is excellent. Further, thereby, the operation is stable in blow molding etc., and the moldability is excellent.

[0177] Here, the melting point of the polylactic acid resin is determined from a differential scanning calorimetry (DSC) measurement in accordance with JIS K 7122-1987 (Method for Measuring Transition Heat of Plastics). Specifically, for the DSC measurement of the melting point of the polylactic acid resin, for example, a differential scanning calorimeter device (for example, Q-2000 type, manufactured by TA Instruments) can be used. 5 mg to 10 mg of a measurement sample obtained by cutting the pellet-shaped polylactic acid resin composition with scissors, nippers, etc. is placed in a dedicated pan manufactured by TA Instruments and used for measurement. It is placed in the container of the differential scanning calorimeter device and heated from 10°C to 200°C at a heating rate of 10°C / min. The melting point of the polylactic acid resin refers to the peak top temperature of the endothermic peak observed in the temperature range above the glass transition point when scanning again from 25°C to 200°C at a heating rate of 10°C / min after the 1st cooling.

[0178] According to the present invention, by suppressing side reactions associated with an increase in viscosity during the production process of the polylactic acid resin composition, a high molecular weight polylactic acid resin composition can be obtained. Further, in the process of producing a high molecular weight polylactic acid resin composition, it is possible to ensure melt stability while not using or minimizing the additives used in the polylactic acid resin composition, so that it can be suitably used for melt molding applications.

[0179] The polylactic acid resin composition produced by an embodiment of the method for producing a polylactic acid resin composition of the present invention and the production apparatus for the polylactic acid resin composition of the present invention can be formed into, for example, particles, films, sheets, foamed sheets, molded articles, fibers, etc., and can be used, for example, for daily necessities, industrial materials, agricultural supplies, sanitary materials, pharmaceuticals, cosmetics, electrophotographic toners, packaging materials, electrical equipment materials, home appliance housings, automotive materials, etc. It can be widely used without impairing the biodegradable and bio-based material characteristics of polylactic acid.

[0180] The method for performing the molding is not particularly limited, and the polylactic acid resin composition can be preferably applied by using a conventionally known sheet production method, foamed sheet molding method, foamed bead molding method, fiber molding method, etc. used for thermoplastic resins such as sheet processing. Specific examples thereof include the T-die method, inflation method, calendar method, etc.

[0181] (Method for Producing Polylactic Acid Resin Composition and Production Apparatus for Polylactic Acid Resin Composition) The method for producing a polylactic acid resin composition according to the second embodiment of the present invention includes a first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a melt viscosity of 1 Pa·s or more and 3,000 Pa·s or less at a temperature of 180°C and a shear rate of 6.28 rad / s, and adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step to polymerize the lactide, and further includes other steps as necessary.

[0182] The manufacturing apparatus of the polylactic acid resin composition according to the second embodiment of the present invention forms a prepolymer-containing composition having a melt viscosity of 1 Pa·s or more and 3,000 Pa·s or less at a temperature of 180°C and a shear rate of 6.28 rad / s. It has a first polymerization means for polymerizing lactide in the presence of a catalyst, and a second polymerization means for adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step to polymerize the lactide, and further has other means as required.

[0183] The manufacturing method of the polylactic acid resin composition according to the second embodiment and the manufacturing apparatus of the polylactic acid resin composition according to the second embodiment are the same as the manufacturing method of the polylactic acid resin composition according to the first embodiment and the manufacturing apparatus of the polylactic acid resin composition according to the first embodiment, except that the characteristics of the prepolymer-containing composition in the first polymerization step and the first polymerization means are different. Hereinafter, the differences between the manufacturing method of the polylactic acid resin composition according to the second embodiment and the manufacturing apparatus of the polylactic acid resin composition according to the second embodiment and the manufacturing method of the polylactic acid resin composition according to the first embodiment and the manufacturing apparatus of the polylactic acid resin composition according to the first embodiment will be described.

[0184] <<Melt Viscosity of Prepolymer-Containing Composition>> The melt viscosity of the prepolymer-containing composition is 1 Pa·s or more and 3,000 Pa·s or less, preferably 10 Pa·s or more and 2,500 Pa·s or less, more preferably 10 Pa·s or more and 1,000 Pa·s or less, still more preferably 10 Pa·s or more and 600 Pa·s or less, and particularly preferably 100 Pa·s or more and 600 Pa·s or less. When the melt viscosity of the prepolymer-containing composition is 1 Pa·s or more and 3,000 Pa·s or less, by adding a compressible fluid in the following second polymerization step, in the ring-opening addition polymerization of the lactide, the molecular weight can be determined by the ratio of the lactide as the monomer and the initiator. When the melt viscosity of the prepolymer-containing composition is less than 1 Pa·s, the catalyst forms a complex with the initiator, and it is the stage where the ring-opening reaction with the lactide as the monomer does not start. It is difficult to control the reaction because the initiator, the monomer, and the catalyst dissolve in the compressible fluid. Also, when the melt viscosity of the prepolymer-containing composition exceeds 3,000 Pa·s, the compressible fluid does not penetrate into the produced polymer, the plasticizing effect cannot be obtained, and since the lactide as the monomer is preferentially dissolved, it becomes difficult to control the reaction.

[0185] In the present invention, the melt viscosity of the prepolymer-containing composition is the viscosity at a temperature of 180 °C and a shear rate of 6.28 rad / s. In the first polymerization step, the prepolymer-containing composition can be extracted and measured by a known rheometer (for example, ARES-G2, manufactured by TA Instruments, etc.) as a measurement sample, but as long as the melt viscosity of the prepolymer-containing composition can be measured, the measurement method is not limited to this.

[0186] The melt viscosity of the prepolymer-containing composition changes as the polymerization of the monomer proceeds. For example, in the manufacturing apparatus of the polylactic acid resin composition, when the tank (for example, the prepolymerization tank) for synthesizing the prepolymer-containing composition has a stirring blade, the stirring torque of the rotation axis of the stirring blade also changes according to the change in the viscosity of the prepolymer-containing composition. Utilizing this, in the manufacturing apparatus of the polylactic acid resin composition, a stirring blade with a torque meter attached is provided in the tank for synthesizing the prepolymer-containing composition, and the torque applied to the rotation axis of the stirring blade is measured at a temperature of 180°C. Separately, in the tank for synthesizing the prepolymer-containing composition in the manufacturing apparatus of the polylactic acid resin composition, a standard sample having a known viscosity is accommodated instead of the prepolymer-containing composition, and the torque applied to the rotation axis of the stirring blade is measured at a temperature of 180°C respectively. Further, in the tank for synthesizing the prepolymer-containing composition in the manufacturing apparatus of the polylactic acid resin composition, the torque in the empty state without putting the measurement sample is measured (the viscosity at this time is regarded as zero). A calibration curve (for example, vertical axis: viscosity (Pa·s), horizontal axis: torque (N·m)) is created from the torque and the viscosity in the state without the standard sample and the measurement sample. The melt viscosity of the prepolymer-containing composition may be obtained by conversion from the torque applied to the rotation axis of the stirring blade in the tank for synthesizing the prepolymer-containing composition using the calibration curve. In this case, it is desirable that the measurement sample in the tank is put in until the entire stirring blade is completely immersed in the measurement sample.

[0187] The standard sample is not particularly limited as long as it has a known viscosity, and can be appropriately selected according to the purpose. For example, silicone oil (for example, KF-96 series, manufactured by Shin-Etsu Chemical Co., Ltd.) can be used.

[0188] Since the torque applied to the rotating shaft of the tank equipped with the stirring blades is specific to the device, the torque will change if the device changes. Therefore, for each device to be used, a calibration curve between torque and viscosity may be created by the above method. In this way, for any device, the melt viscosity of the prepolymer-containing composition can be determined by measuring the torque applied to the rotating shaft.

[0189] Further, in the production apparatus of the polylactic acid resin composition, a capillary type online viscometer may be installed in the tank for synthesizing the prepolymer-containing composition, and the melt viscosity of the prepolymer-containing composition may be directly measured during the first polymerization step under the conditions of a temperature of 180°C and a shear rate of 6.28 rad / s. Also, in the production apparatus of the polylactic acid resin composition, when the tank for synthesizing the prepolymer-containing composition is a loop reactor composed of pipes, a method of converting viscosity from the pressure loss of the prepolymer-containing composition may be used. In that case, pressure gauges may be provided at the inlet and outlet of the loop reactor, and control may be performed with the pressure difference. In that case, as an example, it is preferable to obtain a calibration curve with a fluid having a known viscosity.

[0190] In the present invention, it does not prevent the melt viscosity of the prepolymer-containing composition in the method for producing a polylactic acid resin composition according to the first embodiment and the production apparatus of the polylactic acid resin composition according to the first embodiment from being 1 Pa·s or more and 3,000 Pa·s or less. Also, in the present invention, it does not prevent the content of the ring-opening polymerizable monomer in the method for producing a polylactic acid resin composition according to the second embodiment and the production apparatus of the polylactic acid resin composition according to the second embodiment from being 15% by mass or more and 95% by mass or less.

[0191] The manufacturing method of the polylactic acid resin composition according to the first embodiment, the manufacturing apparatus of the polylactic acid resin composition according to the first embodiment, the manufacturing method of the polylactic acid resin composition according to the second embodiment, and the manufacturing apparatus of the polylactic acid resin composition according to the second embodiment can all stably and continuously manufacture a polylactic acid resin composition having a high molecular weight, excellent biodegradability, and excellent melt stability.

[0192] (Molded article and method for manufacturing the molded article) The molded article of the present invention is formed by molding the polylactic acid resin composition obtained by the manufacturing method of the polylactic acid resin composition of the present invention or the manufacturing apparatus of the polylactic acid resin composition of the present invention. The molded article is not particularly limited and can be appropriately selected according to the purpose. Examples include films, sheets, foamed sheets, foamed beads, fibers, and the like.

[0193] The manufacturing method of the molded article of the present invention includes a step of molding the polylactic acid resin composition obtained by the manufacturing method of the polylactic acid resin composition of the present invention or the manufacturing apparatus of the polylactic acid resin composition of the present invention, and further includes other steps as necessary. The molding method is not particularly limited and can be appropriately selected from known methods according to the shape of the target molded article. For example, for the manufacture of a sheet-shaped molded article, a conventionally known sheet manufacturing method used for thermoplastic resins such as sheet processing can be used.

[0194] Specific examples of the manufacturing method of the molded article include the T-die method, the inflation method, the calendar method, and the like.

[0195] When processing the polylactic acid resin composition into a sheet shape, the processing conditions can be appropriately determined based on the type of the polylactic acid resin in the polylactic acid resin composition, the apparatus, etc. For example, when processing the polylactic acid resin composition by the T-die method, the temperature is preferably 160 °C or higher and 250 °C or lower by heating the polylactic acid resin composition with an extruder having a T-die attached to the outlet, and then extruding it from the T-die to perform sheet-shaped molding processing.

[0196] In addition, in the manufacturing apparatus for the polylactic acid resin composition, a molding area may be further provided, and the production of the polylactic acid resin composition and the production of the molded article may be integrated.

[0197] (Product and method for manufacturing a product) The product of the present invention includes the molded article of the present invention, and further includes other components as necessary. There are no particular restrictions on the other components, and they can be appropriately selected from those used in ordinary resin products.

[0198] The method for manufacturing the product of the present invention includes a processing step of processing the molded article obtained by the method for manufacturing the molded article of the present invention, and further includes other steps as necessary. There are no particular restrictions on the method for processing the molded article, and it can be appropriately selected from known manufacturing methods of the target product.

[0199] The concept of the product includes, as an intermediate for processing the product, for example, not only a raw fabric obtained by rolling a sheet as the molded article, or a single product, but also parts made of products such as handles of trays, and products equipped with products such as trays with handles attached.

[0200] Examples of the product (also referred to as "consumer goods") include daily necessities such as bags, packaging containers, trays, tableware, cutlery, stationery, and cushioning materials. Further, the product may be applied to uses other than the daily necessities, and can be widely applied to, for example, industrial materials, daily necessities, agricultural supplies, food, pharmaceuticals, cosmetics, etc., such as sheets and packaging materials.

[0201] Examples of the bag include plastic shopping bags, shopping bags, and garbage bags.

[0202] Examples of the stationery include clear files, seals, etc.

Examples

[0203] Examples and comparative examples are given below to more specifically explain the present invention, but the present invention is not limited in any way by these examples. In the following examples and comparative examples, unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass".

[0204] (Example 1) Using the continuous polymerization apparatus 100 shown in FIG. 3, a polylactic acid resin composition was obtained as follows. The polymerization area b in the continuous polymerization apparatus 100 was a twin-screw extruder (manufactured by JSW Corporation, Japan Steel Works, Ltd.) (shown as "Type A" in Tables 1 to 4 below). The production conditions of the polylactic acid resin composition are summarized in Tables 1 to 4 below.

[0205] <Raw material supply step and first polymerization step> The prepolymerization tank 9 (capacity 2 L) equipped with a stirring blade to which a torque meter is attached was heated to 110°C, and 1 kg of molten L-lactide (a ring-opening polymerizable monomer) melted separately at 120°C as a raw material of the polylactic acid resin composition and 0.355 g of hexanol (1 / 2,000 mol relative to lactide) as an initiator were charged therein. Then, while stirring, the temperature of the prepolymerization tank 9 was raised to 180°C, 0.1 g of tin dioctylate (100 ppm relative to lactide) as a catalyst was charged, and at the same time as starting the first polymerization reaction, circulation was carried out with the pump 16 to obtain a prepolymer-containing composition. 30 minutes after the start of the reaction, the pump 15 was started, and the prepolymer-containing composition was fed to the reaction tank 11 at a flow rate of 1 kg / hour. At the same time, L-lactide melted in the tank 1 set so that the internal temperature became 120°C was supplied at a flow rate of 1 kg / hour with the pump 2 in such a manner as to replenish the amount fed by the pump 15, hexanol as an initiator was supplied from the tank 3 at a flow rate of 0.32 g / hour with the pump 4, and tin dioctylate as a catalyst was supplied from the tank 5 at a flow rate of 0.10 g / hour with the pump 6 to start continuous supply. At this time, fine adjustment was performed so that the liquid level in the prepolymerization tank 9 became constant. Also, the flow rates of the pump 15 and the pump 16 were adjusted so that the average residence time of the prepolymer-containing composition in the prepolymerization tank 9 became 25 minutes.

[0206] <Second polymerization step> In the continuous polymerization apparatus 100, a twin-screw extruder (manufactured by Japan Steel Works, Ltd.) was used in the polymerization area b. Into the polymerization area b containing the prepolymer-containing composition formed in the first polymerization step, carbon dioxide as a compressible fluid was supplied from the siphon cylinder 7 through the pressure regulating valve 8 at a flow rate of 100 g / hour (10% by mass with respect to the prepolymer-containing composition). At this time, the pressure regulating valve 8 was adjusted to supply the compressible fluid (carbon dioxide) so that the pressure inside the polymerization area b became 10 MPa. Since the polymerization reaction of lactide proceeds by maintaining a high temperature state, finally, the polymer polylactic acid resin and the monomer lactide reached an equilibrium state, and the polymerization reaction was completed. As a result, a polylactic acid resin composition precursor containing a polylactic acid resin, a ring-opening polymerizable monomer (unreacted lactide), and carbon dioxide as a compressible fluid was obtained.

[0207] <Compressible Fluid Removal Step> After the second polymerization step, a vacuum was applied using the pump 12 and the filter 13 to remove the compressible fluid from the polylactic acid resin composition precursor and separate the ring-opening polymerizable monomer (unreacted lactide), thereby obtaining a polylactic acid resin composition.

[0208] <Molding Step> After the de-monomer step, the polylactic acid resin composition was discharged in a strand shape through the extrusion die 14 and pelletized with a cutter to obtain a pelletized polylactic acid resin composition P.

[0209] Six hours after the start of the discharge of the polylactic acid resin composition P from the extrusion die (die) 14 and thereafter, the polylactic acid composition P was sampled 24 times at 30-minute intervals.

[0210] (Example 2) In Example 1, in the raw material supply step, except that the use of 100% by mass of L-lactide as lactide (ring-opening polymerizable monomer) was changed to 90% by mass of L-lactide and 10% by mass of D-lactide, a polylactic acid resin composition was obtained in the same manner as in Example 1.

[0211] (Example 3) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the initiator species in the raw material supply step was changed from hexanol to 1,6 - hexanediol.

[0212] (Example 4) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the initiator species in the raw material supply step was changed from hexanol to pentaerythritol.

[0213] (Example 5) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the amount of the initiator in the raw material supply step was changed from 1 / 2,000 mol to 1 / 4,000 mol based on the monomer lactide.

[0214] (Example 6) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the amount of the initiator in the raw material supply step was changed from 1 / 2,000 mol to 1 / 1,500 mol based on the monomer lactide.

[0215] (Example 7) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the average residence time of the prepolymer - containing composition in the prepolymerization tank 9 in the first polymerization step was changed from 25 minutes to 7 minutes.

[0216] (Example 8) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the average residence time of the prepolymer - containing composition in the prepolymerization tank 9 in the first polymerization step was changed from 25 minutes to 60 minutes.

[0217] (Example 9) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the supply amount of carbon dioxide as the compressible fluid in the second polymerization step to the prepolymer - containing composition was changed from 10% by mass to 5% by mass.

[0218] (Example 10) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the supply amount of carbon dioxide as a compressible fluid in the second polymerization step to the prepolymer-containing composition was changed from 10% by mass to 20% by mass.

[0219] (Example 11) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the average residence time of the prepolymer-containing composition in the prepolymerization tank 9 in the first polymerization step was changed from 25 minutes to 17 minutes.

[0220] (Example 12) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the average residence time of the prepolymer-containing composition in the prepolymerization tank 9 in the first polymerization step was changed from 25 minutes to 40 minutes.

[0221] (Example 13) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that the average residence time of the prepolymer-containing composition in the prepolymerization tank 9 in the first polymerization step was changed from 25 minutes to 12 minutes.

[0222] (Example 14) In Example 1, the continuous polymerization apparatus 100 shown in FIG. 3 was changed to the continuous polymerization apparatus 200 shown in FIG. 4, and the polymerization area b in the continuous polymerization apparatus 200 was a tube-type polymerization tank equipped with a Sulzer type SMLX static mixer (shown as "Type B" in Table 4 below). The same operation as in Example 1 was performed to obtain a polylactic acid resin composition.

[0223] (Comparative Example 1) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that in the first polymerization step, the average residence time of the prepolymer-containing composition in the prepolymerization tank 9 was changed from 25 minutes to 5 minutes.

[0224] (Comparative Example 2) In Example 1, a polylactic acid resin composition was obtained in the same manner as in Example 1, except that in the first polymerization step, the average residence time of the prepolymer-containing composition in the prepolymerization tank 9 was changed from 25 minutes to 100 minutes.

[0225] <Evaluation of Physical Properties> For the polylactic acid resin compositions obtained in Examples 1 to 14 and Comparative Examples 1 and 2, the molecular weight of polylactic acid and the content of the remaining ring-opening polymerizable monomer in the polylactic acid resin composition were measured by the following method. Also, for the prepolymer-containing compositions, which are intermediate products of the polylactic acid resin compositions obtained in Examples 1 to 14 and Comparative Examples 1 and 2, the molecular weight of the prepolymer and the content of the remaining ring-opening polymerizable monomer in the prepolymer-containing composition were measured by the following method, and the melt viscosity was further measured by the following method. These results are shown in Tables 1 to 4 below.

[0226] <<Measurement of Molecular Weight>> The molecular weight of the prepolymer in each prepolymer-containing composition in the prepolymerization tank 9 obtained in the first polymerization step of Examples 1 to 14 and Comparative Examples 1 and 2, and the molecular weight of polylactic acid in each polylactic acid resin composition obtained in 24 portions in the molding step were measured by gel permeation chromatography (GPC) under the following analysis conditions. Specifically, each prepolymer-containing composition or each polylactic acid resin composition was dissolved in chloroform to a concentration of 0.5% by mass to prepare a measurement sample. 1 mL of the prepared measurement sample was injected and measured under the following analysis conditions. Also, gel permeation chromatography was performed in the same manner using a monodisperse polystyrene standard sample (manufactured by Tosoh Corporation), and a molecular weight calibration curve was prepared in advance. From the molecular weight distribution of the polymer or polylactic acid resin in the prepolymer-containing composition, the number average molecular weight (Mn) and weight average molecular weight (Mw) of polylactic acid in the prepolymer-containing composition or the polylactic acid resin composition were calculated using the molecular weight calibration curve. The molecular weight of polylactic acid in each polylactic acid resin composition obtained in 24 portions in the molding step was further calculated as the average value of 24 times. The molecular weight distribution is the value (Mw / Mn) obtained by dividing Mw by Mn. The results of the weight average molecular weight (Mw) are shown in Tables 1 to 4 below. [Analysis Conditions] · Apparatus: GPC-8020 (manufactured by Tosoh Corporation) · Columns: TSKgel® G2000HXL and G4000HXL (manufactured by Tosoh Corporation) · Temperature: 40 °C · Solvent: chloroform · Injection volume: 1 mL · Flow rate: 1.0 mL / min

[0227] [Measurement of Content of Residual Ring-Opening Polymerizable Monomer] In Examples 1 to 14, and Comparative Examples 1 and 2, the content of the residual ring-opening polymerizable monomer in each prepolymer-containing composition (the prepolymer-containing composition obtained at each average residence time described in Tables 1 to 4) in the prepolymerization tank 9 and each finally obtained polylactic acid resin composition was determined by the following method. 0.1 g of each prepolymer-containing composition or each polylactic acid resin composition was weighed as a sample, added to 3 mL of methylene chloride, and uniformly dissolved to prepare a methylene chloride solution of the sample. Next, 5 mL of acetonitrile was taken in a beaker, and while irradiating with ultrasonic waves, the methylene chloride solution was dropped into the acetonitrile over 1 minute. The obtained solution was transferred to a volumetric flask and made up to the mark with acetonitrile. The volume for making up to the mark was 200 mL for each prepolymer-containing composition and 10 mL for each polylactic acid resin composition. The solution made up to the mark was filtered through a membrane filter, and the obtained filtrate was analyzed by HPLC under the following analysis conditions. Separately, based on the calibration curve of the ring-opening polymerizable monomer prepared, the content of the ring-opening polymerizable monomer in each prepolymer-containing composition or each polylactic acid resin composition was determined. [Analysis Conditions] · Apparatus: Preparative HPLC system (manufactured by JASCO Corporation) · Analytical column: Inertsil ODS-3 (particle size: 5 μm, inner diameter 4.6 mm, length 250 mm, manufactured by GL Sciences Inc.) · Mobile phase: 100% acetonitrile · Flow rate: 1.0 mL / min · Column temperature: 40 °C ·Detector: UV210nm

[0228] <<Measurement of melt viscosity>> For the melt viscosities of the prepolymer-containing compositions in the prepolymerization tank 9 obtained in the first polymerization steps of Examples 1 to 14 and Comparative Examples 1 and 2, the torque applied to the rotating shaft of the stirring blade was measured by a torque meter attached to the stirring blade in the prepolymerization tank 9, and it was determined by conversion from the torque value based on a calibration curve prepared in advance. The calibration curve was prepared as follows. First, the prepolymerization tank 9 was filled with a standard sample (KF-96 series, manufactured by Shin-Etsu Chemical Co., Ltd.) having a known viscosity instead of the prepolymer-containing composition, and the torque applied to the rotating shaft of the stirring blade was measured at a temperature of 180°C. Next, the torque in the empty state with no measurement sample in the prepolymerization tank 9 was measured, and the viscosity at this time was taken as zero. Using the torque (N·m) as the horizontal axis and the viscosity (Pa·s) as the vertical axis, the torques of the three points of the standard sample and the viscosity calibration liquid, and the torque in the empty state with no measurement sample were plotted to prepare a calibration curve. Tables 1 to 4 below show the results of the melt viscosity.

[0229] <Evaluation of polylactic acid resin composition> For the polylactic acid resin compositions obtained in Examples 1 to 14 and Comparative Examples 1 and 2, the complex viscosity (melt stability) and continuous polymerization stability were evaluated by the following method. Table 5 below shows the evaluation results.

[0230] <<Evaluation of complex viscosity (melt stability)>> The complex viscosities of the pellets of the polylactic acid resin compositions finally obtained in Examples 1 to 14 and Comparative Examples 1 and 2 were measured using a parallel plate type rotational viscometer (ARES-G2, manufactured by TA Instruments). Specifically, the pellets of each polylactic acid resin composition were dried at 80°C for 12 hours, melted by placing them at 200°C for 5 minutes on a measuring jig, and then pressed until the gap between the parallel plates reached 1.05 mm. Next, the polylactic acid-containing composition protruding from the outer peripheral part of the parallel plates was scraped off with a spatula, pressed again until the gap between the parallel plates reached 1.00 mm, left standing for 5 minutes to remove residual stress, and a measurement sample was prepared in the form of a strip with a thickness of 30 μm, a width of 7 mm, and a length of 35 mm. Using this measurement sample, the complex viscosity η* (5) and the complex viscosity η* (30) 30 minutes after the start of measurement were measured. [Measurement conditions] · Parallel plate: diameter 20 mm, gap: 1.00 mm · Temperature: 200°C · Frequency: 1 Hz (6.28 rad / s) · Atmosphere: under nitrogen atmosphere · Measurement sample size: strip with a thickness of 30 μm, a width of 7 mm, and a length of 35 mm

[0231] From the measured values, the ratio [η* (5) of the complex viscosity η* (30) to the complex viscosity η* (30) / η* (5) was determined.

[0232] Based on the ratio [η* (30) / η* (5) , the melt stability was evaluated according to the following evaluation criteria. In the case of "×", it indicates that the quality of the polylactic acid resin is significantly deteriorated during melt processing, and it was judged not to be practical. - Evaluation criteria for melt stability - ◎: 0.60 or more 〇: 0.50 or more and less than 0.60 △: 0.40 or more and less than 0.50 ×: less than 0.40

[0233] <<Continuous polymerization stability>> The weight-average molecular weight (Mw) of polylactic acid in the polylactic acid resin composition sampled 24 times was measured by the same method as the <<Measurement of Molecular Weight>> described above, and the coefficient of variation was calculated. Based on the coefficient of variation, the continuous polymerization stability was evaluated according to the following evaluation criteria. In the case of "×", it was determined that the variation in the weight-average molecular weight of polylactic acid in the obtained polylactic acid resin composition was large, and it was not practical as a production method and production apparatus for the polylactic acid resin composition. - Evaluation Criteria for Continuous Polymerization Stability - ◎: Coefficient of variation is less than 0.030 〇: Coefficient of variation is 0.030 or more and less than 0.045 △: Coefficient of variation is 0.045 or more and less than 0.060 ×: Coefficient of variation is 0.060 or more

[0234] [Table 1]

[0235] [Table 2]

[0236] [Table 3]

[0237] [Table 4]

[0238] [Table 5]

[0239] Examples of the aspects of the present invention include, for example, the following. <1> A first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less, Add a compressible fluid to the prepolymer-containing composition formed in the first polymerization step, and a second polymerization step of polymerizing the lactide. A method for producing a polylactic acid resin composition, characterized by comprising <2> The method for producing a polylactic acid resin composition according to <1>, wherein the lactide is polymerized in the presence of the catalyst so as to form a prepolymer-containing composition in which the content of the ring-opening polymerizable monomer is 30% by mass or more and 70% by mass or less. <3> The method for producing a polylactic acid resin composition according to any one of <1> to <2>, wherein the lactide is polymerized in the presence of the catalyst so as to form a prepolymer-containing composition in which the content of the ring-opening polymerizable monomer is 40% by mass or more and 60% by mass or less. <4> The method for producing a polylactic acid resin composition according to any one of <1> to <3>, wherein the compressible fluid is carbon dioxide. <5> The method for producing a polylactic acid resin composition according to any one of <1> to <4>, wherein the compressible fluid is a supercritical fluid at a pressure equal to or higher than the critical pressure and a temperature equal to or higher than the critical temperature. <6> The method for producing a polylactic acid resin composition according to any one of <1> to <5>, wherein the addition amount of the compressible fluid is 3% by mass or more and 30% by mass or less based on the prepolymer-containing composition. <7> The method for producing a polylactic acid resin composition according to any one of <1> to <6>, wherein the catalyst is a tin-based compound. <8> The first polymerization step is carried out by continuously supplying the lactide and the catalyst. <9> The second polymerization step is to continuously add the compressible fluid to the prepolymer-containing composition, continuously polymerize the lactide, and continuously obtain the polylactic acid resin composition. The method for producing a polylactic acid resin composition according to any one of <1> to <7>. <9> The content of the polylactic acid resin in the polylactic acid resin composition is 99% by mass or more. The weight average molecular weight of the polylactic acid resin is 300,000 or more. The content of the ring-opening polymerizable monomer in the polylactic acid resin composition is 0.1% by mass or less. It is a method for producing the polylactic acid resin composition according to any one of <1> to <8>. <10> A first polymerization means for polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a ring-opening polymerizable monomer content of 15% by mass or more and 95% by mass or less, A second polymerization means for adding a compressible fluid to the prepolymer-containing composition formed by the first polymerization means and polymerizing the lactide, It is a manufacturing apparatus of the polylactic acid resin composition characterized by having. <11> A first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a melt viscosity of 1 Pa·s or more and 3,000 Pa·s or less at a temperature of 180°C and a shear rate of 6.28 rad / s, A second polymerization step of adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step and polymerizing the lactide, It is a method for producing a polylactic acid resin composition characterized by including. <12> A first polymerization means for polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a melt viscosity of 1 Pa·s or more and 3,000 Pa·s or less at a temperature of 180°C and a shear rate of 6.28 rad / s, A second polymerization means for adding a compressible fluid to the prepolymer-containing composition formed by the first polymerization means and polymerizing the lactide, It is a manufacturing apparatus of the polylactic acid resin composition characterized by having. <13> It is a method for producing a molded article characterized by including a molding step of molding the polylactic acid resin composition obtained by the method for producing the polylactic acid resin composition according to any one of <1> to <9> or the method for producing the polylactic acid resin composition according to <11>. <14> The method for producing a molded article according to <13>, wherein the molded article is at least any one of particles, films, sheets, foamed sheets, foamed beads, and fibers. <15> A manufacturing method of a product, characterized by including a processing step of processing a molded body obtained by the manufacturing method of the molded body according to any one of <13> to <14>. <16> The manufacturing method of the product according to <15>, wherein the product is at least any one of a bag, a packaging container, a tray, tableware, cutlery, stationery, and a cushioning material.

[0240] The manufacturing method of the polylactic acid resin composition according to any one of <1> to <9>, the manufacturing apparatus of the polylactic acid resin composition according to <10>, the manufacturing method of the polylactic acid resin composition according to <11>, the manufacturing apparatus of the polylactic acid resin composition according to <12>, the manufacturing method of the molded body according to any one of <13> to <14>, and the manufacturing method of the product according to any one of <15> to <16> can solve the above-mentioned various problems in the prior art and achieve the object of the present invention.

Explanation of reference numerals

[0241] a Raw material mixing area b Polymerization area c Compressible fluid removal area 1 Tank 2 Pump 3 Tank 4 Pump 5 Tank 6 Pump 7 Cylinder 8 Pressure regulating valve 9 Prepolymerization tank 10 Pump 12 Vacuum pump 13 Filter 14 Extrusion die 15 Pump 16 Pump 17 Tank 100 Continuous polymerization apparatus P Polylactic acid resin composition M Motor

Prior art documents

Patent documents

[0242] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2015-063583 [Patent Document 2] Japanese Patent No. 6024299 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2016-98320

Claims

1. A first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less; A second polymerization step of adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step and polymerizing the lactide; A method for producing a polylactic acid resin composition, comprising:

2. The method for producing a polylactic acid resin composition according to claim 1, wherein the lactide is polymerized in the presence of the catalyst so as to form a prepolymer-containing composition having a content of the ring-opening polymerizable monomer of 30% by mass or more and 70% by mass or less.

3. The method for producing a polylactic acid resin composition according to claim 1, wherein the lactide is polymerized in the presence of the catalyst so as to form a prepolymer-containing composition having a content of the ring-opening polymerizable monomer of 40% by mass or more and 60% by mass or less.

4. The method for producing a polylactic acid resin composition according to claim 1, wherein the compressible fluid is carbon dioxide.

5. The method for producing a polylactic acid resin composition according to claim 1, wherein the compressible fluid is a supercritical fluid having a pressure equal to or higher than the critical pressure and a temperature equal to or higher than the critical temperature.

6. The method for producing a polylactic acid resin composition according to claim 1, wherein the addition amount of the compressible fluid is 3% by mass or more and 30% by mass or less based on the prepolymer-containing composition.

7. The method for producing a polylactic acid resin composition according to claim 1, wherein the catalyst is a tin-based compound.

8. The first polymerization step is carried out by continuously supplying the lactide and the catalyst, The second polymerization step is carried out by continuously adding the compressible fluid to the prepolymer-containing composition, continuously polymerizing the lactide, and continuously obtaining the polylactic acid resin composition. The method for producing a polylactic acid resin composition according to claim 1.

9. The content of the polylactic acid resin in the polylactic acid resin composition is 99% by mass or more, The weight average molecular weight of the polylactic acid resin is 300,000 or more, The content of the ring-opening polymerizable monomer in the polylactic acid resin composition is 0.1% by mass or less, The method for producing a polylactic acid resin composition according to claim 1.

10. A first polymerization means for polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a content of a ring-opening polymerizable monomer of 15% by mass or more and 95% by mass or less; A second polymerization means for adding a compressible fluid to the prepolymer-containing composition formed by the first polymerization means and polymerizing the lactide; An apparatus for producing a polylactic acid resin composition, characterized by having the same. **Claim 11** A first polymerization step of polymerizing lactide in the presence of a catalyst so as to form a prepolymer-containing composition having a melt viscosity of 1 Pa·s or more and 3,000 Pa·s or less at a temperature of 180°C and a shear rate of 6.28 rad / s; A second polymerization step of adding a compressible fluid to the prepolymer-containing composition formed in the first polymerization step and polymerizing the lactide; A method for producing a polylactic acid resin composition, characterized by including the same.

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