JP2016060834A - Method for producing molding composed of polylactic acid composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a molding composed of a polylactic acid composition having a high stereocomplex crystallization degree and suppressed in hydrolysis.SOLUTION: There is provided a method for producing a molding composed of a polylactic acid composition by sequentially carrying out the following steps (a) to (f): (a) a step of supplying a poly-L-lactic acid and a poly-L-lactic acid in an extruder; (b) a step of injecting a supercritical fluid with pressure into the poly-L-lactic acid and the poly-L-lactic acid in the extruder; (c) a step of kneading the poly-L-lactic acid and the poly-L-lactic acid in the presence of a supercritical fluid to obtain a polylactic acid composition; (d) a step of removing (degassing) the supercritical fluid from the polylactic acid composition; (e) a step of obtaining an extruded product of the polylactic acid composition from the extruder; and (f) a step of impregnating the extruded product of the polylactic acid composition with a liquid additive as a hydrolysis inhibitor.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a molded article comprising a polylactic acid composition containing poly-L lactic acid and poly-D lactic acid which is an optical isomer thereof.

In recent years, for the purpose of protecting the global environment, resins that are easily decomposed in a natural environment have attracted attention and have been studied all over the world. Biodegradable polymers represented by aliphatic polyesters such as polylactic acid, polyglycolic acid, poly (3-hydroxybutyrate), and polycaprolactone are known as resins that are easily decomposed in a natural environment.
In particular, polylactic acid is a polymer material that is highly biosafe and environmentally friendly because it uses lactic acid obtained from plant-derived raw materials or derivatives thereof as raw materials. Therefore, the use as a general-purpose polymer is examined, and the use as a film, a fiber, an injection molded product, etc. is examined.

Paying attention to the easy decomposability of the resin and the water solubility of the decomposing monomer, its use in oil field excavation technology has been studied (see, for example, Patent Documents 1 to 3).
In this application, it is required to quickly decompose after holding the weight and shape of the resin for a certain period in hot water (see FIG. 1). However, aliphatic polyesters and the like are generally poor in hydrolysis resistance and can be used up to a medium temperature of about 120 ° C., but quickly decompose in high-temperature hot water (see FIG. 2). The problem is that the desired performance cannot be exhibited.

In addition, slow-degrading resins such as aromatic polyesters do not decompose quickly even in hot hot water (see FIG. 3), and the resulting decomposed monomer reacts with other components in this application and precipitates in water. This is a problem (Patent Document 7).
As for “high temperature”, 127 ° C. to 193 ° C. described in a report “US Shales Gas” issued by Halliburton in 2008, and “Oil” published by the Japan Oil, Gas and Metals National Corporation. Various definitions such as 149 ° C. or higher described in “Natural Gas Review” 2002/5 are made, and it is generally considered that the temperature is higher than 125 ° C. to 150 ° C. In the present invention, a temperature higher than 135 ° C. is defined as “high temperature”.

  In order to use polylactic acid so that the composition and the resin do not melt at such high temperatures, it is necessary to obtain a stereocomplex polylactic acid with a high melting point among the polylactic acids. As a means, a method of dissolving and mixing high optical purity poly L lactic acid and poly D lactic acid in a solvent, a method of melt kneading together with a plasticizer, and a method of imparting high shear during molding are conceivable. However, in order to knead without transesterification at a relatively low temperature, a method of forming a stereocomplex polylactic acid by bringing it into contact with a supercritical fluid and kneading (hereinafter referred to as supercritical method) is considered more useful (Patent Literature). 4).

In particular, in this supercritical method, when the supercritical fluid is vaporized at normal temperature and normal pressure, it becomes difficult to perform molding, so it is necessary to deaerate from kneading to the discharge port (Patent Document 5).
When the stereocomplex polylactic acid produced in this way is melted and extruded again, a homocrystal is simultaneously formed in addition to the stereocomplex crystal, causing problems such as fusion when actually used. After forming the stereocomplex polylactic acid by contacting with the resin, it is necessary to form a molded body without remelting.

Regarding the formation technology of stereocomplex polylactic acid using supercritical method, both homocrystal and stereocomplex crystal are formed by kneading poly L lactic acid and poly D lactic acid in supercritical fluid in Non-Patent Document 1. However, it is described that the formation of stereocomplex crystals is further promoted by low-temperature kneading and that more stereocomplex crystals are formed after heat treatment than when kneading without using a critical method.
However, even in the method described in Non-Patent Document 1, the molded product before heat treatment contains homocrystals, and even if heat treatment is performed to obtain stereocomplex polylactic acid having a stereocomplex crystallinity of 100%, sufficient crystallization is achieved. It was not possible to obtain a molded product of a stereocomplex polylactic acid of a certain degree.

Further, Patent Document 5 and Patent Document 6 only describe high-dispersion mixing of particles by supercriticality and mixtures (alloys) with various types of resins, and there is a description of polylactic acid, but a stereocomplex. No mention is made of the formation of polylactic acid.
Further, Patent Document 4 discloses a molded body having only a stereocomplex crystal having a high degree of crystallinity that does not produce a homocrystal, but does not specifically disclose a technique for applying an additive to the molded body.

On the other hand, in order to improve hydrolysis resistance of aliphatic polyester and the like, a hydrolysis regulator such as a carbodiimide compound is used, and hydrolysis is suppressed by sealing an acidic group generated by the initial stage and decomposition in the resin. Has already been proposed (Patent Documents 7 to 8).
Since acidic groups such as carboxyl groups generated by hydrolysis of aliphatic polyesters serve as autocatalysts and promote hydrolysis, they are immediately sealed with a carbodiimide compound or the like, so that they can be used in a humid heat environment of about 50 to 120 ° C. Improvement of hydrolysis resistance has been confirmed.
However, sufficient studies have not been made on the suppression of hydrolysis in hot water at a temperature higher than 135 ° C. from the viewpoint of a resin or a hydrolysis regulator.

  Incidentally, Patent Document 5 describes a method of adding a poly-L lactic acid or poly-D lactic acid before kneading and a mixture thereof by kneading or dry blending a hydrolysis-resistant agent into the mixture. If it is a low-hydrolytic agent, the effect is exhibited without problems, but if it is a liquid additive and highly volatile anti-hydrolyzer, it is necessary to deaerate the supercritical fluid. Since it volatilizes at the same time, it cannot be added by this supercritical method.

  As described above, in the oil field excavation technology, the resin composition that exhibits the desired performance as shown in FIG. 1 without causing melting or fusion between resins in hot water higher than 135 ° C. is a supercritical method. However, even in the method of forming stereocomplex polylactic acid by the supercritical method, the generation of homocrystals or sufficient stereocomplex crystallinity is insufficient, There were problems that volatilized, and the actual situation was not yet obtained.

JP 2009-114448 A US Pat. No. 7,267,170 US Pat. No. 7,228,904 JP 2013-252694 A Japanese Patent No. 5009876 JP2013-028751A US Pat. No. 7,275,596 JP 2012-012560 A

Tokyo Institute of Technology Graduate School of Science and Engineering Department of Materials Science Sumita-Asai Lab. Yukihiro Ikura Bachelor thesis March 2008

  An object of the present invention is to provide a method for producing a molded article made of a polylactic acid composition, which has not been achieved by the above prior art, and has a high stereocomplex crystallinity and suppressed hydrolyzability.

The inventors of the present invention have arrived at the present invention as a result of intensive studies in view of the above prior art.
That is, according to the present invention,
1. Provided is a method for producing a molded article comprising a polylactic acid composition, wherein the following steps (a) to (f) are sequentially performed.
(A) supplying poly-L-lactic acid and poly-D-lactic acid into an extruder;
(B) press-fitting a supercritical fluid into poly-L-lactic acid and poly-D-lactic acid in the extruder;
(C) a step of kneading poly-L-lactic acid and poly-D-lactic acid in the presence of a supercritical fluid to obtain a polylactic acid composition;
(D) removing (degassing) the supercritical fluid from the polylactic acid composition;
(E) obtaining an extruded product of the polylactic acid composition from the extruder;
(F) A step of impregnating the extruded product of the polylactic acid composition with a liquid additive as a hydrolysis inhibitor.

（式中、Ｒ_１〜Ｒ_４は各々独立に炭素数１〜２０の脂肪族基、３〜２０の脂環族基、炭素数５〜１５の芳香族基、またはこれらの組み合わせであり、ヘテロ原子を含んでいてもよい。Ｘ、Ｙは各々独立に水素原子、炭素数１〜２０の脂肪族基、３〜２０の脂環族基、炭素数５〜１５の芳香族基、またはこれらの組み合わせであり、ヘテロ原子を含んでいてもよい。各々の芳香環は置換基によって結合し環状構造を形成していてもよい。）
６．芳香族カルボジイミドとして、ビス（２，６−ジイソプロピルフェニル）カルボジイミドを用いる、上記５に記載の製造方法。
７．工程（ｄ）のステレオコンプレックスポリ乳酸からの超臨界流体除去（脱ガス）工程を、押し出し機に設けたベント口を用いて行う、上記１〜６のいずれか記載の製造方法。
８．工程（ｅ）の押出機から押し出し品を得る工程において、押出機に紡糸用ダイスを備え、押し出し紡糸する、上記１〜７のいずれか記載の製造方法。
９．上記１〜８のいずれか記載の製造方法によって得られたポリ乳酸組成物からなる成形品。 Moreover, the following 2-9 are also included by this invention.
2. The liquid additive in step (f) is a liquid additive obtained by melting or dissolving the additive in a solvent, and the content of the liquid additive is 3 in terms of additive based on the extruded product of the polylactic acid composition. 2. The production method according to 1 above, wherein the impregnation is performed so as to be not less than 20% by weight.
3. 3. The method according to 1 or 2 above, wherein the liquid additive in the step (f) has a boiling point of 20 ° C./100 kPa or more and 250 ° C./6 hPa or less.
4). 4. The production method according to any one of 1 to 3, wherein the liquid additive contains an aromatic carbodiimide compound having a hydrophobic functional group added around the carbodiimide group as a hydrolysis inhibitor.
5. 5. The production method according to 4 above, wherein a compound represented by the following formula (1) is used as the aromatic carbodiimide compound.

(Wherein R _{1 to} R ₄ are each independently an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or a combination thereof, X and Y may each independently represent a hydrogen atom, an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or these (It is a combination and may contain a hetero atom. Each aromatic ring may be bonded by a substituent to form a cyclic structure.)
6). 6. The production method according to 5 above, wherein bis (2,6-diisopropylphenyl) carbodiimide is used as the aromatic carbodiimide.
7). 7. The production method according to any one of 1 to 6, wherein the supercritical fluid removal (degassing) step from the stereocomplex polylactic acid in step (d) is performed using a vent port provided in the extruder.
8). 8. The production method according to any one of 1 to 7 above, wherein in the step of obtaining an extruded product from the extruder in the step (e), the extruder is provided with a spinning die and subjected to extrusion spinning.
9. The molded article which consists of a polylactic acid composition obtained by the manufacturing method in any one of said 1-8.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a polylactic acid composition with high stereocomplex crystallinity and the suppression of hydrolyzability can be provided.
Moreover, the obtained polylactic acid composition can be made to have a crystal melting point of 220 ° C. or higher by being kneaded in a supercritical state.

When resin is used in hot water at a temperature higher than 135 ° C., it is an image diagram that quickly decomposes after maintaining the weight and shape of the molded body for a certain period, and is achieved in the molded body obtained by the manufacturing method of the present invention. It is a behavior. When resin is used in hot water of a temperature higher than 135 ° C., it is an image diagram in which decomposition rapidly proceeds from the initial stage, and is a behavior in a molded body made of a general aliphatic polyester. When resin is used in hot water at a temperature higher than 135 ° C., it is an image diagram in which decomposition rapidly proceeds from the initial stage, and is a behavior in a molded body made of a general aromatic polyester. When the resin is used in hot water at a temperature higher than 135 ° C., the molecular weight (m) and the acidic group amount (g) required to achieve the behavior of the resin weight (w) change as shown in FIG. It is the image figure showing change, Comprising: It is the behavior achieved in the molded object resin composition obtained by the manufacturing method of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, these description and Examples illustrate this invention, and do not restrict | limit the scope of the present invention.

  Here, polylactic acid consists of lactic acid units whose main chain is represented by the following formula (2). In this specification, “mainly” is preferably a ratio of 90 to 100 mol%, more preferably 95 to 100 mol%, and still more preferably 98 to 100 mol%.

  The lactic acid unit represented by the formula (2) includes an L-lactic acid unit and a D-lactic acid unit, which are optical isomers. The main chain of the polylactic acid is preferably mainly an L-lactic acid unit, a D-lactic acid unit or a combination thereof.

The polylactic acid is preferably poly D-lactic acid whose main chain is mainly composed of D-lactic acid units, and poly L-lactic acid whose main chain is mainly composed of L-lactic acid units. The proportion of other units constituting the main chain is preferably in the range of 0 to 10 mol%, more preferably 0 to 5 mol%, and still more preferably 0 to 2 mol%.
Examples of other units constituting the main chain include units derived from dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones and the like.

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

  The weight average molecular weight of polylactic acid is preferably 50,000 to 500,000, more preferably 80,000 to 350,000, and still more preferably 10 as the average weight average molecular weight in order to achieve both the mechanical properties and moldability of the molded product. It is in the range of ~ 250,000. The weight average molecular weight is a value measured by gel permeation chromatography (GPC) and converted to standard polystyrene.

  Polylactic acid is poly-D-lactic acid or poly-L-lactic acid, and crystal melting between 150 ° C. and 190 ° C. in a hydrolysis-resistant state with a hydrolysis-resistant agent in a differential scanning calorimeter (DSC) measurement It preferably has a peak (Tmh) and a heat of crystal melting (ΔHmsc) of 10 J / g or more. Heat resistance can be improved by satisfying the range of the crystal melting point and the crystal melting heat.

The main chain of polylactic acid is preferably stereocomplex polylactic acid including a stereocomplex phase formed by poly L-lactic acid units and poly D-lactic acid units.
The stereocomplex polylactic acid preferably has a degree of stereocomplexation (S) defined by the following formula (i) of 90 to 100%, more preferably 95 to 100%, and 98 to 100%. It is preferable.

[Equation 1]
S = [ΔHm _s / (ΔHm _h + ΔHm _s )] × 100 (i)
(However, .DELTA.Hm _s is the crystal melting enthalpy of stereocomplex-phase polylactic acid, .DELTA.Hm ^h represents the melting enthalpy of a polylactic acid homo-phase crystal.)

The crystallinity of stereocomplex polylactic acid, particularly the crystallinity by XRD measurement, is preferably at least 5%, more preferably 5-60%, even more preferably 7-60%, particularly preferably 10-60%. is there.
The crystal melting point of stereocomplex polylactic acid needs to be 220 ° C. or higher, preferably 220 to 250 ° C., more preferably 225 to 250 ° C., and further preferably 230 to 250 ° C. The crystal melting enthalpy by DSC measurement of stereocomplex polylactic acid is preferably 20 J / g or more, more preferably 20 to 80 J / g, still more preferably 30 to 80 J / g.

  When the crystalline melting point of stereocomplex polylactic acid is less than 220 ° C., the heat resistance is deteriorated. In particular, in order not to cause melting or fusion in high-temperature water, it is more preferable that the melting point is 220 ° C. or higher even in a state containing a hydrolysis agent. Furthermore, 222 degreeC or more is preferable. Moreover, when it exceeds 250 degreeC, it will be necessary to shape | mold at the high temperature of 250 degreeC or more, and it may become difficult to suppress thermal decomposition of resin. Therefore, it is preferable that the fiber composition of the present invention exhibits a crystal melting peak of 220 ° C. or higher as measured by a differential scanning calorimeter (DSC).

On the other hand, by measuring the melting point in water, melting and fusion in hot water can be directly evaluated.
In particular, in order to prevent fusion in hot water at 170 ° C. or higher, the melting point in water is preferably 190 ° C. or higher, more preferably 192 ° C. or higher, and further preferably 194 ° C. or higher.

In the stereocomplex polylactic acid, the weight ratio of poly D-lactic acid to poly L-lactic acid is preferably 90/10 to 10/90. More preferably, it is in the range of 80/20 to 20/80, more preferably 30/70 to 70/30, particularly preferably 40/60 to 60/40, and theoretically preferably as close to 1/1 as possible. .
The weight average molecular weight of the stereocomplex polylactic acid is preferably in the range of 70,000 to 500,000, more preferably 80,000 to 350,000, still more preferably 120,000 to 250,000, and particularly preferably 160,000 to 240,000. The weight average molecular weight is a value measured by gel permeation chromatography (GPC) and converted to standard polystyrene.

  Poly L-lactic acid and poly D-lactic acid can be produced by a conventionally known method. For example, it can be produced by ring-opening polymerization of L-lactide or D-lactide in the presence of a metal-containing catalyst. The low molecular weight polylactic acid containing a metal-containing catalyst is optionally crystallized or without crystallization, under reduced pressure or from normal pressure to increased pressure, in the presence or absence of an inert gas stream. It can also be produced by solid phase polymerization. Furthermore, it can be produced by a direct polymerization method in which lactic acid is subjected to dehydration condensation in the presence or absence of an organic solvent.

  The polymerization reaction can be carried out in a conventionally known reaction vessel. For example, in a ring-opening polymerization or direct polymerization method, a vertical reactor or a horizontal reactor equipped with a stirring blade for high viscosity, such as a helical ribbon blade, is used alone, or Can be used in parallel. Moreover, any of a batch type, a continuous type, a semibatch type may be sufficient, and these may be combined.

  Alcohol may be used as a polymerization initiator. Such alcohol is preferably non-volatile without inhibiting the polymerization of polylactic acid, such as decanol, dodecanol, tetradecanol, hexadecanol, octadecanol, ethylene glycol, trimethylolpropane, pentaerythritol, etc. Can be suitably used. It can be said that the polylactic acid prepolymer used in the solid-phase polymerization method is preferably crystallized in advance from the viewpoint of preventing resin pellet fusion. The prepolymer is in a solid state in a fixed vertical or horizontal reaction vessel, or in a reaction vessel (such as a rotary kiln) in which the vessel itself rotates, such as a tumbler or kiln, in the temperature range from the glass transition temperature of the prepolymer to less than the melting point. Polymerized.

  Metal-containing catalysts include alkali metals, alkaline earth metals, rare earths, transition metals, fatty acid salts such as aluminum, germanium, tin, antimony, titanium, carbonates, sulfates, phosphates, oxides, hydroxides , Halides, alcoholates and the like. Among them, fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides containing at least one metal selected from tin, aluminum, zinc, calcium, titanium, germanium, manganese, magnesium and rare earth elements Products, halides, and alcoholates are preferred.

  Tin compounds due to low catalytic activity and side reactions, specifically stannous chloride, stannous bromide, stannous iodide, stannous sulfate, stannic oxide, tin myristate, tin octylate Tin-containing compounds such as tin stearate and tetraphenyltin are exemplified as preferred catalysts. Among these, tin (II) compounds, specifically, diethoxytin, dinonyloxytin, tin (II) myristate, tin (II) octylate, tin (II) stearate, tin (II) chloride and the like are suitable. Illustrated.

The amount of the catalyst used is 0.42 × 10 ^{−4 to} 100 × 10 ⁻⁴ (mole) per 1 kg of lactide, and 1.68 × 10 ^{−4 in} consideration of reactivity, color tone and stability of the resulting polylactides. To 42.1 × 10 ⁻⁴ (mol), particularly preferably 2.53 × 10 ^{−4 to} 16.8 × 10 ⁻⁴ (mol).

  The metal-containing catalyst used for the polymerization of polylactic acid is preferably deactivated with a conventionally known deactivator prior to using polylactic acid. Examples of such a deactivator include an organic ligand having a group of chelate ligands having an imino group and capable of coordinating with a polymerized metal catalyst.

  Also, dihydridooxoline (I) acid, dihydridotetraoxodiphosphorus (II, II) acid, hydridotrioxoline (III) acid, dihydridopentaoxodiphosphoric acid (III), hydridopentaoxodi (II, IV) Acid, dodecaoxohexaphosphoric acid (III), hydridooctaoxotriphosphoric acid (III, IV, IV) acid, octaoxotriphosphoric acid (IV, III, IV) acid, hydridohexaoxodiphosphoric acid (III, V) acid, hexaoxodiacid Examples thereof include low oxidation number phosphoric acids having an acid number of 5 or less, such as phosphorus (IV) acid, decaoxotetraphosphoric (IV) acid, hendecaoxotetraphosphoric (IV) acid, and eneoxooxophosphorus (V, IV, IV) acid.

Further, orthophosphoric acid represented by the formula xH ₂ O · yP ₂ O ₅ and x / y = 3 may be mentioned. Moreover, polyphosphoric acid which is 2> x / y> 1, and is called diphosphoric acid, triphosphoric acid, tetraphosphoric acid, pentaphosphoric acid or the like based on the degree of condensation, and a mixture thereof can be mentioned. Moreover, the metaphosphoric acid represented by x / y = 1, especially trimetaphosphoric acid and tetrametaphosphoric acid are mentioned. Further, ultraphosphoric acid represented by 1> x / y> 0 and having a network structure in which a part of the phosphorus pentoxide structure is left (these may be collectively referred to as a metaphosphoric acid compound) may be mentioned. Moreover, the acid salt of these acids is mentioned. Moreover, the monovalent | monohydric and polyhydric alcohol of these acids, the partial ester of polyalkylene glycol, and complete ester are mentioned. Examples thereof include phosphono-substituted lower aliphatic carboxylic acid derivatives of these acids.

In view of the catalyst deactivation ability, orthophosphoric acid represented by the formula xH ₂ O · yP ₂ O ₅ and x / y = 3 is preferred. Moreover, 2> x / y> 1, and polyphosphoric acid referred to as diphosphoric acid, triphosphoric acid, tetraphosphoric acid, pentaphosphoric acid and the like, and a mixture thereof are preferable from the degree of condensation. Further, metaphosphoric acid represented by x / y = 1, particularly trimetaphosphoric acid and tetrametaphosphoric acid are preferable. Ultraphosphoric acid represented by 1> x / y> 0 and having a network structure in which a part of the phosphorus pentoxide structure is left (these may be collectively referred to as a metaphosphoric acid compound) is preferable. Moreover, the acidic salt of these acids is preferable. Further, monovalent or polyhydric alcohols of these acids or partial esters of polyalkylene glycols are preferred.

The metaphosphoric acid compound used in the present invention is a cyclic metaphosphoric acid in which about 3 to 200 phosphoric acid units are condensed, an ultra-region metaphosphoric acid having a three-dimensional network structure, or an alkali metal salt or an alkaline earth metal salt thereof. Onium salts). Among them, cyclic sodium metaphosphate, ultra-region sodium metaphosphate, phosphono-substituted lower aliphatic carboxylic acid derivative dihexylphosphonoethyl acetate (hereinafter sometimes abbreviated as DHPA) and the like are preferably used.
The polylactic acid preferably has a lactide content of 5,000 ppm or less. The lactide contained in the polylactic acid deteriorates the resin and deteriorates the color tone at the time of melt processing, and in some cases, it may be disabled as a product.

  Poly L-lactic acid and / or poly D-lactic acid immediately after melt ring-opening polymerization usually contains 1 to 5% by weight of lactide, but poly L-lactic acid and / or poly D-lactic acid is At any stage up to lactic acid molding, a conventionally known lactide weight loss method, that is, vacuum devolatilization with a single-screw or multi-screw extruder, or high vacuum treatment in a polymerization apparatus is carried out alone or in combination. In addition, lactide can be reduced to a suitable range.

  The smaller the lactide content, the better the melt stability and heat-and-moisture resistance of the resin, but there is also the advantage of lowering the resin melt viscosity, making it reasonable and economical to meet the desired purpose. is there. That is, it is reasonable to set it to 1,000 ppm or less, at which practical melt stability is achieved. More preferably, a range of 700 ppm or less, more preferably 500 ppm or less, particularly preferably 100 ppm or less is selected. By having a lactide content in such a range, the polylactic acid component improves the stability of the resin during the melt molding of the molded product of the present invention, and the advantage that the molded product can be efficiently manufactured and the heat-and-moisture stability of the molded product. , Low gas can be improved.

  The stereocomplex polylactic acid is prepared by bringing poly L-lactic acid and poly D-lactic acid into contact in a weight ratio of 10/90 to 90/10, preferably by melt contact, and more preferably melt kneading. Can be obtained. The contact temperature is preferably in the range of 200 to 290 ° C, more preferably 220 to 280 ° C, and even more preferably 225 to 275 ° C, from the viewpoint of improving the stability of polylactic acid when melted and the stereocomplex crystallinity.

When the molded article of the present invention is produced, poly L lactic acid and poly D lactic acid may be melt-kneaded with a twin screw extruder in the presence of a supercritical fluid while stretching and flowing.
Since the extension flow has a higher dispersion efficiency than the shear flow generally used at the time of melt kneading, kneading can proceed efficiently.
The screw shape of the twin-screw extruder is not particularly limited, and screws such as a fully meshed type, an incompletely meshed type, and a non-meshed type can be used. From the viewpoint of kneadability and reactivity, preferably a completely meshed type It is. Further, the rotation direction of the screw may be either in the same direction or in the reverse direction, but is preferably the same direction from the viewpoint of kneading property and reactivity.

In the present invention, the most preferable screw configuration is a co-rotation complete meshing type.
Moreover, in this invention, it is necessary for the inflow effect pressure drop before and behind the zone (extension flow zone) to melt-knead while extending and flowing to be 1 to 100 MPa (10 to 1000 kg / cm ² ).

The inflow effect pressure drop before and after the zone (extension flow zone) for melt kneading while stretching and flowing means the pressure difference (ΔP ₀ ) in the extension flow zone from the pressure difference (ΔP) before the extension flow zone. It can be obtained by subtracting. When the inflow effect pressure drop before and after the extension flow zone is less than 1 MPa (10 kg / cm ² ), the rate of formation of extension flow in the extension flow zone is low, and the pressure distribution is not uniform. Since it occurs, it is not preferable. Further, when the inflow effect pressure drop before and after the extension flow zone is larger than 100 MPa (1000 kg / cm ² ), the back pressure in the twin-screw extruder becomes too large, and it is not preferable because stable production becomes difficult. . In addition, the inflow effect pressure drop before and after the zone of melt kneading while stretching and flowing (extension and flow zone) is more preferably in the range of 5 to 60 MPa (50 to 600 kg / cm ² ), and more preferably 10 to 50 MPa (100 to 500 kg). / Cm ² ) is most preferable.

Further, in the present invention, if the length of one melt-kneading zone (extension flow zone) in the screw of the twin screw extruder is Lk and the screw diameter is D, from the viewpoint of kneadability and reactivity. Lk / D = 0.2-10 is preferable. More preferably, it is 0.3-9, More preferably, it is 0.5-8.
In the present invention, the zone (extension flow zone) in which the twin-screw extruder melts and kneads while stretching and flowing is preferably not disposed unevenly at a specific position in the screw.

Further, when producing the molded article of the present invention, it is necessary to melt and knead in the presence of a supercritical fluid while stretching and flowing with a twin-screw extruder. Here, "supercritical fluid" is in a state beyond the limit point (critical point) where gas and liquid can coexist, and has both properties as gas (diffusibility) and properties as liquid (solubility). It is a fluid.
Examples of the supercritical fluid include supercritical carbon dioxide, supercritical nitrogen, and supercritical water. The supercritical fluid used in the present invention is preferably supercritical carbon dioxide or supercritical nitrogen, and most preferably. Is supercritical carbon dioxide.

  The present invention, when producing stereocomplex polylactic acid by melt-kneading, melt-kneaded in the presence of a supercritical fluid while stretching and flowing, so that a contact interface between two types of polylactic acid can be obtained with a high dispersion efficiency. By realizing a state in which the amount is increased, and further allowing the presence of a supercritical fluid, the kneading speed between these two types of polylactic acid is dramatically increased while being a reaction in the melt, and in the solution. It is possible to react homogeneously as in the case of reaction, whereby stereocomplex crystallization is efficiently performed, and the stereocomplex crystallinity (sc degree) can be set to 100%.

In the production method of the present invention, the position where the supercritical fluid is introduced in the twin-screw extruder is sufficient to secure the introduction kneading portion of the supercritical fluid in the extruder, and the screw length L as the region from the root of the extruder. In terms of the ratio, it is preferably 0.2L to 0.9L, more preferably 0.25L to 0.85L, and still more preferably 0.3L to 0.8L. The root of the extruder is assumed to be the upstream end of the screw segment at the position (feed port) where the screw root raw material is supplied. Further, the position where the supercritical fluid is introduced in the twin-screw extruder is not limited to one, but may be two or more.
In the production method of the present invention, it is preferable to have a deaeration mechanism such as a vacuum vent on the downstream side of the position where the supercritical fluid is introduced in the twin-screw extruder. This is because the supercritical fluid kneaded in the extruder is degassed and removed by a vacuum vent or the like in a reduced pressure / vacuum state.

In the production method of the present invention, in order to maintain the supercritical state of the supercritical fluid in the twin-screw extruder, the upstream of the introduction position of the supercritical fluid and the upstream of the deaeration mechanism are held by a molten resin seal. It is preferable. The molten resin seal refers to a state in which the molten resin can fill and seal the clearance between the screw and the cylinder barrel (the inner wall surface of the cylinder that houses the screw) to maintain pressure without leaking gas. .
Such a molten resin seal is melted by a method of arranging a seal plate or by incorporating a screw segment with a reverse molten resin feed direction (a screw segment with a reverse spiral winding direction) into a predetermined position of the screw configuration. A pressure increasing region by a resin seal can be formed.

  In the production method of the present invention, when the length of the melt-kneaded region in the presence of the supercritical fluid is Ls, Ls / D is preferably 20 or more, more preferably 21 or more, and further preferably 22 or more. The upper limit is not particularly limited, and may extend to the tip of the screw. When Ls / D is less than 20, there may be a case where a region to be melt-kneaded in the presence of the supercritical fluid cannot be sufficiently secured, and the effect of miniaturizing the dispersed phase by the supercritical fluid tends not to be sufficiently exhibited. It is not preferable. The screw length melted and kneaded in the presence of the supercritical fluid in such a twin-screw extruder is a region where the pressure of the supercritical fluid is applied, and the molten resin seal disposed upstream of the position where the supercritical fluid is introduced. This is the length from the downstream end to the upstream end of the molten resin seal disposed upstream of the deaeration mechanism.

In the production method of the present invention, the amount of supercritical fluid introduced is preferably 0.1 to 200 parts by weight, more preferably 0.5 to 150 parts by weight, even more preferably 100 parts by weight of stereocomplex polylactic acid. Is 1 to 100 parts by weight. If the introduction amount of the supercritical fluid is less than the above range, fine dispersion of the molten resin by the supercritical fluid becomes insufficient, and if it exceeds the above range, the decrease in the melt resin viscosity by the supercritical fluid tends to increase. Yes, it is not preferable because sufficient shear cannot be imparted to the molten resin.
In the production method of the present invention, the temperature and pressure of the supercritical fluid introduced into the twin-screw extruder are not particularly limited as long as they are higher than the critical point of the fluid, but when supercritical carbon dioxide is used as the supercritical fluid. Requires a temperature of 31.3 ° C. or higher and a pressure of 7.4 MPa or higher.

In addition, the molten resin pressure in the extruder from the position where the supercritical fluid is introduced into the extruder to the position where the supercritical fluid is removed from the extruder by degassing etc. is maintained in order to maintain the supercritical state. There is no particular limitation as long as it is above the critical pressure of the fluid, but when supercritical carbon dioxide is used as the supercritical fluid, it is preferably 7.4 MPa or more, more preferably 8 to 50 MPa, and even more preferably 10 to 30 MPa. .
The rotational speed of the screw is not particularly limited as long as it is within the above range, but is usually 10 rpm or more, preferably 50 rpm or more, and more preferably 80 rpm or more. The amount of extrusion is not particularly limited as long as it is within the above range, but is usually 0.1 kg / h or more, preferably 0.15 kg / h or more, more preferably 0.2 kg / h or more.

  Moreover, in this invention, it is preferable that the residence time in the twin-screw extruder of stereocomplex polylactic acid is 1 to 30 minutes. The residence time is the position of the screw to which the raw material is supplied, and the colorant and the like are added together with the raw material. The stereocomplex polylactic acid is extruded from the discharge port of the twin screw extruder from the time when the colorant is supplied. It is the time until the maximum degree of coloration of the extrudate by the colorant. When the residence time is less than 1 minute, the reaction time in the twin-screw extruder is short, and the reaction is not sufficiently accelerated, which is not preferable. When the residence time is longer than 30 minutes, there is a problem that the resin is thermally deteriorated due to the long residence time. The residence time in the present invention is preferably 1.5 to 28 minutes, more preferably 2 to 25 minutes.

<Molded body>
The molded article of the present invention can be obtained by extruding a polylactic acid composition. For example, fibers obtained by melt spinning, films and sheets obtained by melt film formation can be raised.
That is, taking melt spinning as an example, the polylactic acid composition is measured by a gear pump without being cooled after being melted and kneaded in the presence of the supercritical fluid as described above and degassed the supercritical fluid, After being filtered in the pack, it is discharged as a monofilament, a multifilament or the like from a nozzle provided in the base.

  The shape of the base and the number of the bases are not particularly limited, and any of circular, irregular, solid, hollow and the like can be adopted. The discharged yarn is immediately cooled and solidified, then converged, applied with oil, and wound. The winding speed is not particularly limited, but when the one formed into a fiber shape is stereocomplex polylactic acid, a range of 100 m / min to 10,000 m / min is preferable because a stereocomplex crystal is easily formed. .

  The wound undrawn yarn can be used as it is, but can be used after being drawn. When used in an unstretched state, it is preferable that the heat treatment is performed at a temperature not lower than the melting point and higher than the glass transition temperature (Tg) of the stereocomplex polylactic acid composition after spinning and before winding. In addition to the hot roller, any method such as a contact heater or a non-contact hot plate can be adopted for the heat treatment. When stretching is performed, the spinning step and the stretching step are not necessarily separated from each other, and a direct spinning stretching method in which stretching is performed without winding once after spinning may be employed.

The stretching may be one-stage stretching or multi-stage stretching of two or more stages. From the viewpoint of producing a high-strength fiber, the stretching ratio is preferably 3 times or more, and more preferably 4 times or more. Preferably 3 to 10 times is selected. However, if the draw ratio is too high, the fiber is devitrified and whitened, the strength of the fiber is lowered, the elongation at break is too low, and it is not preferable for fiber use.
As a preheating method for stretching, in addition to the temperature rise of the roll, a flat or pin-like contact heater, a non-contact hot plate, a heat medium bath, and the like can be used, and a commonly used method may be used.

Following the stretching, it is preferable that the heat treatment is performed at a temperature not lower than the melting point and not lower than the glass transition temperature (Tg) of the polylactic acid composition before winding.
In addition to the hot roller, any method such as a contact heater or a non-contact hot plate can be adopted for the heat treatment.
The stretching temperature is, for example, selected from the glass transition temperature (Tg) to 170 ° C., preferably 60 ° C. to 140 ° C., particularly preferably 70 to 130 ° C.

When fibers are obtained as a molded product by the production method of the present invention, short fibers may be used. When producing short fibers, in addition to the method of drawing with long fibers, a step of cutting with a rotary cutter or the like into a predetermined fiber length according to the application, and if further crimping is required, constant length heat treatment and A step of imparting crimp with an indentation crimper or the like is added during the relaxation heat treatment. In that case, in order to improve crimp imparting property, it can be preheated before the crimper with steam, an electric heater or the like.
Moreover, after extending | stretching, it can also heat-set at 170 to 220 degreeC under tension.

The molded product obtained by the production method of the present invention may be used alone, or may be mixed with others depending on the purpose. In addition to various combinations with fiber structures composed of other types of fibers, mixed modes include mixed yarns with other fibers, composite false twisted yarns, mixed spun yarns, long and short composite yarns, fluid processed yarns, covering yarns, and twisted yarns. Examples thereof include union, union, pile, pile, mixed cotton, mixed non-woven fabric of long fibers and short fibers, and felt. When mixed, the mixing ratio is selected from the range of 1% by weight or more, more preferably 10% by weight or more, and further preferably 30% by weight or more in order to exhibit the characteristics of the resin composition.
Examples of other fibers used in combination include cellulose fibers such as cotton, hemp, rayon, and tencel, wool, silk, acetate, polyester, nylon, acrylic, vinylon, polyolefin, and polyurethane.
The same applies when the molded body is a film or sheet.

<Liquid additive>
In the production method of the present invention, the extruded product of the polylactic acid composition is impregnated with a liquid additive as a hydrolysis inhibitor. Here, the liquid additive is a substance that is liquid at room temperature, melts and liquefies when heated, or dissolves in a solvent, and seals polylactic acid end groups and acidic groups generated by decomposition. It is preferably an agent that stops.

That is, it has an effect of suppressing the autocatalytic action of polylactic acid and delaying hydrolysis, that is, it is preferably a hydrolysis inhibitor.
In particular, when a liquid additive having a boiling point of 20 ° C./100 kPa or more and 190 ° C./4 hPa or less is applied, the production method of the present application exhibits its effect.

Examples of the acidic group include at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfinic acid group, a phosphonic acid group, and a phosphinic acid group. In the present invention, a carboxyl group is particularly exemplified.
Since the use conditions are hot water higher than 135 ° C., the polylactic acid composition preferably has a water resistance at 120 ° C. of 95% or more and a reactivity with acidic groups at 190 ° C. of 50% or more.

  Here, water resistance at 120 ° C. means, for example, 1) When 2 g of water is added to a system in which 1 g of a sample is dissolved in 50 ml of dimethyl sulfoxide, and the mixture is stirred at reflux for 5 hours at 120 ° C. Approximate amount of the agent that remains unchanged after 5 hours of treatment calculated from the analysis of the portion present, or 2) If the sample does not dissolve in dimethyl sulfoxide, the sample can be dissolved and a hydrophilic solvent Is a value represented by the following formula (iii) using an approximate amount obtained by performing the same process as in 1) above. In 2), when the boiling point of the solvent used was less than 120 ° C., dimethyl sulfoxide was mixed with the solvent in a range where at least a part of the polylactic acid composition was dissolved, and 50 ml of the mixed solvent was used. The mixing ratio is usually selected from the range of (1: 2) to (2: 1), but is not particularly limited as long as the above conditions are satisfied. The solvent used in 2) is usually soluble if selected from tetrahydrofuran, N, N-dimethylformamide, and ethyl acetate.

[Equation 2]
Water resistance (%) = [Amount after 5 h treatment / initial amount] × 100 (iii)

In addition, the water resistance may be expressed by an equivalent evaluation.
When the water resistance of an unstable agent is evaluated, a part of the agent is denatured by hydrolysis, and the acidic group sealing ability is lowered. When such an agent is used in hot hot water, it is deactivated by water, so that the ability to seal the target acidic group is significantly reduced. From the above, the water resistance at 120 ° C. is more preferably 97% or more, further preferably 99% or more, and particularly preferably 99.9% or more. When it is 99.9% or more, that is, stable in high-temperature hot water, the reaction with acidic groups can be carried out selectively and efficiently.

  Moreover, the reactivity with an acidic group at 190 ° C. means, for example, that a group that reacts with a carboxyl group of a hydrolysis modifier is 1. It is obtained by adding an amount of an agent equivalent to 5 times equivalent and melt-kneading for 1 minute at a resin temperature of 190 ° C. and a rotation speed of 30 rpm under a nitrogen atmosphere using a lab plast mill (Toyo Seiki Seisakusho). With respect to the resin composition, the carboxyl group concentration was measured, and the value given by the following formula (iv).

[Equation 3]
Reactivity (%) = [(carboxyl group concentration of polylactic acid for evaluation−carboxyl group concentration of resin composition) / carboxyl group concentration of polylactic acid for evaluation] × 100 (iv)

The polylactic acid for evaluation preferably has a MW of 120,000 to 200,000 and a carboxyl group concentration of 10 to 30 equivalents / ton. As such polylactic acid, for example, polylactic acid “NW3001D” (MW is 150,000, carboxyl group concentration is 22.1 equivalent / ton) manufactured by Nature Works can be suitably used. Add the amount of the agent that makes the group that reacts with the carboxyl group of the adjusting agent 33.15 equivalents / ton, and use Labo Plast Mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) under a nitrogen atmosphere under a resin temperature of 190 ° C. About the resin composition obtained by melt-kneading for 1 minute at the rotation speed of 30 rpm, the value of reactivity can be calculated | required by measuring a carboxyl group density | concentration.
In addition to this, the reactivity with an acidic group may be given by an equivalent evaluation.

When the reactivity of a stable agent is evaluated, the carboxyl group concentration of the resin composition hardly changes even when kneaded under the above conditions. Such an agent, when used in high-temperature hot water, hardly exhibits the ability to seal the target acidic group, and thus cannot suppress the degradation of the stereocomplex polylactic acid.
From the above, the reactivity with acidic groups at 190 ° C. is more preferably 60% or more, further preferably 70% or more, and particularly preferably 80% or more. When the reactivity with acidic groups in high-temperature hot water is 80% or more, the reaction with acidic groups can be carried out efficiently.

It is important that the liquid additive of the present invention has a water resistance at 120 ° C. of 95% or more and a reactivity with acidic groups at 190 ° C. of 50% or more. That is, a very stable agent has a high water resistance, but a low reactivity with acidic groups. In that case, the ability to seal the target acidic groups in hot hot water is almost manifested. do not do. In addition, a very unstable agent has a high reactivity with an acidic group, but has a low water resistance. In that case, it is deactivated by water in high-temperature hot water. The ability to seal is significantly reduced.
From the above, the hydrolysis regulator having high water resistance and high reactivity with acidic groups is preferably used in the present invention.

Among the additives to be liquefied, examples of the hydrolysis resistance inhibitor include addition reaction type compounds such as carbodiimide compounds, isocyanate compounds, epoxy compounds, oxazoline compounds, oxazine compounds, and aziridine compounds. Two or more of these compounds can be used in combination. From the viewpoint of water resistance and reactivity with acidic groups, a carbodiimide compound is preferably exemplified.
Examples of the carbodiimide compound include those having the basic structures of the following general formulas (I) and (II).

Wherein R and R ′ are each independently an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or a combination thereof, and a hetero atom R and R ′ may be bonded to form a cyclic structure, or two or more cyclic structures may be formed by a spiro structure or the like)

(In the formula, each R ″ is independently an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or a combination thereof. (N may be an integer from 2 to 1000.)

  From the viewpoints of stability and ease of use, an aromatic carbodiimide compound is more preferable. For example, aromatic carbodiimide compounds such as the following formulas (1) and (3) are exemplified.

(Wherein R _{1 to} R ₄ are each independently an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or a combination thereof, X and Y may each independently represent a hydrogen atom, an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or these It is a combination and may contain hetero atoms, and each aromatic ring may be bonded by a substituent to form a cyclic structure, or two or more cyclic structures may be formed by a spiro structure or the like. )

(Wherein R _{5 to} R ₇ are each independently an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or a combination thereof, (It may contain an atom. N is an integer of 2 to 1000.)

Specific examples of such aromatic carbodiimide compounds include polysynthesized by decarboxylation condensation reaction of bis (2,6-diisopropylphenyl) carbodiimide and 1,3,5-triisopropylbenzene-2,4-diisocyanate. Examples thereof include carbodiimide and a combination of the two.
In particular, when an aromatic carbodiimide compound is added with a hydrophobic functional group around the carbodiimide group, the reactivity between hot water and the carbodiimide group can be reduced, and the ability of the carbodiimide compound to inhibit hydrolysis is reduced. This is particularly preferable.

<Molded body>
The molded body of the present invention satisfies any of the following A1 to A3.
A1: In hot water at an arbitrary temperature of 135 ° C. to 160 ° C., after 3 hours, the acidic group derived from the polylactic acid composition is 30 equivalents / ton or less and the weight of the non-water-soluble content of the polylactic acid composition is 50% or more and After 24 hours, the water-insoluble content of the polylactic acid composition is 50% or less.
A2: In hot water at an arbitrary temperature of 160 ° C. to 180 ° C., the acidic group derived from the polylactic acid composition is 30 equivalents / ton or less after 2 hours, and the weight of the non-water-soluble component of the polylactic acid composition is 50% or more After 24 hours, the water-insoluble content of the polylactic acid composition is 50% or less.
A3: In hot water at an arbitrary temperature of 180 ° C. to 220 ° C., the acidic group derived from the polylactic acid composition is 30 equivalents / ton or less after 1 hour, and the weight of the non-aqueous component of the polylactic acid composition is 50% or more and After 24 hours, the water-insoluble content of the polylactic acid composition is 50% or less.

In order to exhibit the desired performance, it is important to control the molded body of the present invention so that it quickly disintegrates after maintaining the weight and shape of the molded body in hot water at a temperature higher than 135 ° C. for a certain period of time. is there.
The fixed period is determined depending on the application, but is preferably any one of 10 minutes to 12 hours. Moreover, from a viewpoint of exhibiting desired performance, any of 30 minutes to 6 hours is more preferable, and any of 30 minutes to 4 hours is more preferable.

  Preserving the weight and shape of the molded body preferably means that the weight of the non-aqueous component of the molded body is 50% or more, and the volume change representing the shape is 50% or less. For example, even if the weight of the non-aqueous component of the molded body is 50% or more, it cannot be said that the weight and shape of the molded body are maintained in a completely hydrolyzed state. From the viewpoint of exhibiting desired performance, the weight of the non-aqueous component of the molded body is more preferably 70% or more, and further preferably 90% or more. Further, the volume change amount representing the shape is more preferably 30% or less, and further preferably 10% or less.

Here, the weight of the molded body and the volume change amount of the shape are values given by the following evaluation, for example.
300 mg of the molded product and 12 ml of distilled water were charged in a sealed melting crucible preheated to 110 ° C. (OM-Labtec Co., Ltd., MR-28, internal volume of 28 ml), sealed, and dried in hot air previously maintained at a predetermined temperature. Place the crucible in the machine (KLO-45M, manufactured by Koyo Thermo System Co., Ltd.).

  After allowing the crucible to stand, let the crucible stand in the hot air dryer, and then the time for the temperature inside the crucible to reach the specified test temperature is the starting point of the test. Remove from the hot air dryer. The crucible taken out from the hot air dryer is air-cooled for 20 minutes and then cooled to room temperature by water cooling for 10 minutes, and then the crucible is opened to collect the internal sample and water.

The inner sample and water were filtered using filter paper (JIS P3801: 1995, 5 types A standard), and the composition remaining on the filter paper was dried at 60 ° C. under a vacuum of 133.3 Pa for 3 hours, and then molded. The volume of the shape and the volume of the shape is measured, and the volume change amount of the weight and the shape from the following formulas (v) and (vi) is obtained.
[Equation 4]
Weight (%) = [weight of the molded product after treatment for a certain period / weight of the initial molded product] × 100 (v)
[Equation 5]
Volume change in shape (%) = [volume of composition after treatment for a certain period / volume of initial composition] × 100 (vi)

Here, the volume of the shape is a value obtained by measuring the compact with a stereomicroscope.
As the stereomicroscope, for example, M205C manufactured by Leica Microsystems, Inc. can be used.
In this evaluation, as the size of the molded body, particularly the fiber-shaped molded body, for example, a fiber diameter of 1 μm to 1000 μm and a fiber length of 1 mm to 40 mm can be usually used.
In addition to this, the volume change of the weight and shape of the molded body may be given by an equivalent evaluation.

  Rapid decomposition means a state in which hydrolysis of polylactic acid is promoted by autocatalysis, and the concentration of acidic groups increases exponentially. On the other hand, polylactic acid is gradually decomposed while the acidic group concentration is kept low. Therefore, the concentration of acidic groups derived from the polylactic acid composition is preferably 30 equivalents / ton or less while trying to maintain the weight and shape of the molded body.

When the amount is more than 30 equivalents / ton, hydrolysis of polylactic acid is promoted by autocatalysis, and the effect of the liquid additive is not sufficiently exhibited. Since the lower the concentration of acidic groups, the smaller the weight and shape of the molded body can be suppressed, the polylactic acid composition is maintained while maintaining the weight and shape of the molded body from the viewpoint of exerting desired performance. The concentration of the acidic group derived from the product is more preferably 20 equivalent / ton or less, further preferably 10 equivalent / ton or less, and particularly preferably 3 equivalent / ton or less.
Here, the concentration of the acidic group derived from the polylactic acid composition is, for example, a composition obtained by preparing a composition in the same manner as the evaluation used for obtaining the volume change amount of the weight and shape of the molded body described above. It can be determined by measuring the product by ¹ H-NMR.

  Moreover, the molded object of this invention can be used conveniently in the hot water of arbitrary temperatures of 135 to 220 degreeC. Below 135 ° C., the desired performance can be exhibited only by adding a hydrolysis inhibitor, and the significance of the present invention is diminished. Further, at a temperature higher than 220 ° C., the molded article of the present invention may be immediately decomposed and may not exhibit desired performance. Therefore, the molded article of the present invention can be used more suitably in hot water at any temperature from 150 ° C. to 220 ° C., and more preferably in hot water at any temperature from 170 ° C. to 210 ° C. It can be used more suitably at 190 to 210 ° C.

The molded body of the present invention satisfies any of the following A1 to A3.
A1: In hot water at an arbitrary temperature of 135 ° C. to 160 ° C., after 3 hours, the acid groups derived from the polylactic acid composition are 30 equivalents / ton or less and the weight of the non-aqueous component of the molded product is 50% or more and 24 hours. Later, the weight of the non-water content of the molded product is 50% or less.
A2: In hot water at an arbitrary temperature of 160 ° C. to 180 ° C., after 2 hours, the acid groups derived from the polylactic acid composition are 30 equivalents / ton or less and the weight of the non-aqueous component of the molded product is 50% or more and 24 hours. Later, the weight of the non-water content of the molded product is 50% or less.
A3: In hot water at an arbitrary temperature of 180 ° C. to 220 ° C., the acidic group derived from the polylactic acid composition is 30 equivalents / ton or less after 1 hour, and the weight of the non-aqueous component of the molded product is 50% or more and 24 hours. Later, the weight of the non-water content of the molded product is 50% or less.

  The range in which the molded article of the present invention can be suitably used varies depending on the temperature. Further, in A1 to A3, the time earlier than the specified fixed period (1 hour, 2 hours, 3 hours) is that the acidic group derived from the polylactic acid composition is 30 equivalents / ton or less and the weight of the non-water-soluble content of the molded product is It is preferable that it is 50% or more.

  In A1, the fixed period is 3 hours, and during this time, the weight and shape of the compact are retained. In addition, from the viewpoint of exerting desired performance in an oil field drilling technique or the like, polylactic acid after a certain period longer than 2 hours defined in the present invention in hot water at an arbitrary temperature of 135 ° C. to 160 ° C. The acidic group derived from the composition may be 30 equivalent / ton or less and the weight of the non-water-soluble component of the molded body may be 50% or more.

  In A2, the fixed period is 2 hours, and during this time, the weight and shape of the molded body are maintained. In addition, from the viewpoint of exerting desired performance in an oil field drilling technique or the like, polylactic acid after a certain period longer than 2 hours defined in the present invention in hot water at an arbitrary temperature of 160 ° C. to 180 ° C. The acidic group derived from the composition may be 30 equivalent / ton or less and the weight of the non-water-soluble component of the molded body may be 50% or more.

  In A3, the fixed period is 1 hour, and during this time, the weight and shape of the molded body are maintained. A polylactic acid composition after a certain period longer than 1 hour defined in the present invention in hot water at an arbitrary temperature of 180 ° C. to 220 ° C. from the viewpoint of exerting desired performance in an oil field drilling technique or the like The derived acidic group may be 30 equivalents / ton or less, and the weight of the non-aqueous component of the molded body may be 50% or more.

After a certain period of time defined in A1 to A3 (1 hour, 2 hours, 3 hours), the effect of sealing the acidic group of the liquid additive disappears, and the decomposition of the resin is promoted by the autocatalytic action of the acidic group. The concentration of acidic groups increases exponentially. Further, as the decomposition proceeds, the polylactic acid composition in the molded body becomes a water-soluble monomer and dissolves in water. That the phenomenon occurs as soon as possible after maintaining the weight and shape of the compact for a certain period of time is suitable when using the compact of the present invention in oil field excavation technology or the like.
Therefore, it is preferable that the weight of the non-aqueous component of the molded body is 50% or less after 24 hours. For the above reasons, it is more preferable that the weight of the water-insoluble portion of the molded body after 18 hours is 50% or less, and the weight of the water-insoluble portion of the molded body after 12 hours is more preferably 50% or less, and 6 hours. It is more preferable that the weight of the non-water content of the molded body is 50% or less later.

  The molded product of the present invention preferably has a weight of non-water-soluble content of the molded product of 10% or less after 100 hours in hot water at an arbitrary temperature of 135 ° C. to 220 ° C. For example, when using the composition of the present invention in oil field drilling technology, etc., the molded body can work effectively by dissolving in water quickly after holding the weight and shape of the composition for a certain period of time. it can. Therefore, it is preferable that the weight of the non-aqueous component of the molded body is 10% or less after 100 hours in hot water at an arbitrary temperature of 135 ° C. to 220 ° C. Further, from the viewpoint of performing treatment in water after use and exhibiting desired performance, the less water-insoluble content is better, and the weight of the water-insoluble content of the composition is more preferably 5% or less after 100 hours. More preferably, it is% or less.

  The heat distortion temperature of the polylactic acid composition of the present invention is preferably 135 ° C to 300 ° C. Here, the heat distortion temperature refers to the melting point or softening point of the resin composition. Since the use of the molded body assumes hot water having a temperature higher than 135 ° C., the higher the heat distortion temperature of the polylactic acid composition, the wider the temperature range. On the other hand, when the temperature exceeds 300 ° C., the process cost for maintaining the molding temperature increases, so the heat distortion temperature of the polylactic acid composition is more preferably 150 ° C. to 300 ° C., and 165 ° C. to 300 ° C. More preferably, it is more preferably 170 ° C to 300 ° C, still more preferably 175 ° C to 285 ° C, and particularly preferably 180 ° C to 285 ° C.

  In the molded article of the present invention, the impregnation amount of the liquid additive is 1 to 30 parts by weight with respect to 100 parts by weight of the total of the polylactic acid composition and the liquid additive. When the amount is less than 1 part by weight, a sufficient acidic group sealing effect may not be exhibited in hot water at a temperature higher than 135 ° C. On the other hand, if the amount is more than 30 parts by weight, the additive may bleed out from the molded body, the moldability may be deteriorated, and the characteristics of the substrate may be denatured. From this viewpoint, the addition amount of the liquid additive is preferably 1.5 to 20 parts by weight, more preferably 2 to 15 parts by weight with respect to 100 parts by weight of the total of the polylactic acid composition and the liquid additive. 0.5 to 12.5 parts by weight is more preferable, and 3.0 to 10 parts by weight is particularly preferable.

<Impregnation of liquid additive>
In general, various methods for adding a liquid additive to a polylactic acid composition have been adopted, but when added during the melt-kneading process, the liquid additive is subsequently used for degassing and removing the supercritical fluid. Volatilizes and sublimates, so there is a limit to what is called dry blending or side feed addition.
If the supercritical fluid is not degassed or removed in order to prevent volatilization or sublimation of the liquid additive, the supercritical fluid remains in the molten resin, resulting in defects in the molded body.

In the method for producing a molded body of the present invention, these problems are solved by impregnating the molded body with a liquid additive.
As an impregnation method, a liquid in which a liquid additive is dissolved, dispersed, or melted is contacted (applied or sprayed) or immersed in a molded body to be infiltrated with the liquid additive.
The acidic group sealing reaction of the stereocomplex polylactic acid composition with the liquid additive can be performed at a temperature of room temperature (25 ° C.) to about 300 ° C., but from the viewpoint of reaction efficiency, 50 to 280 ° C., more preferably 100 It is more accelerated in the range of ˜280 ° C. The polylactic acid composition is more likely to react at a melting temperature, but is preferably reacted at a temperature lower than 300 ° C. in order to suppress volatilization and decomposition of a liquid additive such as a hydrolysis modifier. . It is also effective to apply a solvent to lower the melting temperature of the polylactic acid composition and increase the stirring efficiency.

  Although the reaction proceeds sufficiently rapidly without a catalyst, a catalyst that accelerates the reaction can also be used. As a catalyst, the catalyst generally used with liquid additives, such as a hydrolysis regulator, is applicable. These can be used alone or in combination of two or more. The addition amount of the catalyst is not particularly limited, but is preferably 0.001 to 1 part by weight, more preferably 0.01 to 0.1 part by weight, more preferably 100 parts by weight of the resin composition. Most preferred is 0.02 to 0.1 parts by weight.

  In the present invention, two or more liquid additives as hydrolysis regulators may be used in combination. For example, a liquid such as a hydrolysis regulator that performs an initial acidic group blocking reaction of a polylactic acid composition. You may use a separate thing about liquid additives, such as a hydrolysis control agent which performs the sealing reaction of the acidic group produced in an additive and hot water higher than 135 degreeC.

  Further, it is preferable to use a hydrolysis adjusting agent assistant, that is, an agent for assisting the effect in order to delay the hydrolysis. As such an agent, any known agent can be used. For example, at least selected from hydrotalcite, alkaline earth metal oxide, alkaline earth metal hydroxide, and alkaline earth metal carbonate. One compound is exemplified. The content of the auxiliary agent is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 20 parts by weight, and further preferably 0.7 to 10 parts by weight per 100 parts by weight of the liquid additive such as a hydrolysis modifier. Part.

As a solvent in the above, what is inactive with respect to a polylactic acid composition and a liquid additive can be used. In particular, a solvent that has affinity for both and at least partially dissolves both is preferable.
As the solvent, for example, hydrocarbon solvents, ketone solvents, ester solvents, ether solvents, halogen solvents, amide solvents and the like can be used.

  Examples of the hydrocarbon solvent include hexane, cyclohexane, benzene, toluene, xylene, heptane, decane and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, and isophorone.

  Examples of ester solvents include ethyl acetate, methyl acetate, ethyl succinate, methyl carbonate, ethyl benzoate, and diethylene glycol diacetate. Examples of the ether solvent include diethyl ether, dibutyl ether, tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, triethylene glycol diethyl ether, diphenyl ether and the like. Examples of the halogen solvent include dichloromethane, chloroform, tetrachloromethane, dichloroethane, 1,1 ', 2,2'-tetrachloroethane, chlorobenzene, dichlorobenzene and the like. Examples of the amide solvent include formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. These solvents may be used alone or as a mixed solvent as desired.

In the present invention, the solvent is applied in the range of 1 to 1,000 parts by weight per 100 parts by weight of the polylactic acid composition. If the amount is less than 1 part by weight, there is no significance in applying the solvent. The upper limit of the amount of solvent used is not particularly limited, but is about 1,000 parts by weight from the viewpoints of operability and reaction efficiency.
The resin composition of the present invention can be used by adding all known additives and fillers as long as the effects of the invention are not lost. For example, a stabilizer, a crystallization accelerator, a filler, a mold release agent, an antistatic agent, a plasticizer, an impact resistance improver, a terminal blocking agent, and the like can be given.

  In addition, with respect to the additive, from the viewpoint of not losing the effect of the invention, it is decomposed in a component that promotes the decomposition of a resin having an autocatalytic action mainly composed of a water-soluble monomer, such as a phosphoric acid component or a resin composition Thus, it is important to reduce the influence by a method such as not using a phosphite-based additive that generates a phosphoric acid component, reducing the amount of the phosphoric acid as much as possible, or deactivating it. For example, the method of using together the component which deactivates or suppresses them with a hydrolysis regulator can be taken suitably.

Hereinafter, the present invention will be further described by examples. Each physical property was measured by the following methods.
(1) Weight average molecular weight (Mw) and number average molecular weight (Mn):
The weight average molecular weight and number average molecular weight of the polymer were measured by gel permeation chromatography (GPC) and converted to standard polystyrene.
For GPC measurement, 10 μl of a sample of 1 mg / ml (chloroform containing 1% hexafluoroisopropanol) at a temperature of 40 ° C. and a flow rate of 1.0 ml / min was used with the following detector and column. Injected and measured.
Detector: Differential refractometer (manufactured by Shimadzu Corporation) RID-6A.
Column: Toso-Co., Ltd. TSKgelG3000HXL, TSKgelG4000HXL, TSKgelG5000HXL and TSKguardcolumnHXL-L connected in series, or Toso- Co., Ltd. TSKgelG2000HXL, TSKgelG3000HXL, TSKumHXL

(2) DSC measurement of stereocomplex crystallinity [S (%)], crystal melting temperature, etc .:
Using DSC (TA Instrument, TA-2920), the sample was heated to 250 ° C. at 10 ° C./min under a nitrogen stream in the first cycle, and the glass transition temperature (Tg), stereocomplex phase poly Lactic acid crystal melting temperature (Tm *), stereocomplex phase polylactic acid crystal melting enthalpy (ΔHm _s ) and homophase polylactic acid crystal melting enthalpy (ΔHmh) were measured.
In addition, the crystallization start temperature (Tc *) and the crystallization temperature (Tc) were measured by rapidly cooling the measurement sample and then performing a second cycle measurement under the same conditions. The stereocomplex crystallinity (S) is a value obtained by the following formula (a) from the stereocomplex phase and homophase polylactic acid crystal melting enthalpy obtained by the above measurement.
[Equation 6]
S = [ΔHm _s / (ΔHm _h + ΔHm _s )] × 100 (a)
(Where ΔHm _s is the melting enthalpy of stereocomplex phase crystals, ΔHm _h is the melting enthalpy of homophase polylactic acid crystals)

(3) Evaluation of hydrolysis resistance in high-temperature hot water:
300 mg of sample and 12 ml of distilled water were charged in a sealed melting crucible (O-M Labotech Co., Ltd., MR-28, internal volume 28 ml) preheated to 110 ° C. and sealed, and predetermined temperatures (150 ° C., 170 ° C., 190 ° C.) in advance. The crucible was allowed to stand in a hot-air dryer (manufactured by Koyo Thermo System Co., Ltd., KLO-45M).
After leaving the crucible to stand in a hot air dryer, the time for the temperature inside the crucible to reach the specified test temperature is taken as the test start time, and when a certain period of time has elapsed from the start of this test, Removed from the dryer.
The crucible taken out from the hot air dryer was air-cooled for 20 minutes and then cooled to room temperature by water cooling for 10 minutes, and then the crucible was opened to collect the internal sample and water. The internal sample and water were filtered using a filter paper (JIS P3801: 1995, 5 types A standard), and the composition remaining on the filter paper was dried at 60 ° C. under a vacuum of 133.3 Pa for 3 hours. The weight and the carboxyl group concentration were measured. The weight was determined from the following formula (v).
[Equation 7]
Weight (%) = [weight of composition after treatment for a certain period / weight of initial composition] × 100 (v)
Moreover, the state of the composition after the hot water treatment at 190 ° C. for 2 hours was evaluated according to the following criteria.
Fusion:
(Double-circle): It is a state with favorable dispersion | distribution of a slurry without fusion | melting by microscope observation.
○: The state of good dispersion of the slurry without fusing by visual observation.
X: State in which lumps melted or fused are visually observed.
Bleed out:
A: Good bleed-out state by microscopic observation.
○: The bleed-out state is good by visual observation.
X: State in which bleed out is seen visually.

Hereinafter, the compounds used in this example will be described.
<Polylactic acid>
The following was manufactured and used as polylactic acid.

[Production Example 1] Poly L-lactic acid resin (A1):
To 100 parts by weight of L-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity 100%), 0.005 parts by weight of tin octylate was added, and 180 ° C. in a reactor equipped with a stirring blade in a nitrogen atmosphere. The mixture was reacted at 0 ° C. for 2 hours, phosphoric acid equivalent to 1.2 times the amount of tin octylate was added, and then the remaining lactide was removed at 13.3 Pa to obtain chips, thereby obtaining a poly L-lactic acid resin.
The obtained poly L-lactic acid resin had a weight average molecular weight of 200,000, a melting point (Tmh) of 175 ° C., and a glass transition point (Tg) of 55 ° C.

[Production Example 6] Poly-D-lactic acid resin (B1):
A poly D-lactic acid resin is obtained in the same manner as in Production Example 1 except that D-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity 100%) is used instead of L-lactide in Production Example 1. It was. The obtained poly-D-lactic acid resin had a weight average molecular weight of 180,000, a melting point (Tmh) of 172 ° C., and a glass transition point (Tg) of 55 ° C.

<Liquid additive>
The following additives were used as liquid additives.
D1: DIPC (carbodiimide compound, manufactured by Kawaguchi Chemical Industry Co., Ltd.): boiling point 210 ° C./6 hPa
D2: “Celoxide (registered trademark)” 2021P (epoxy compound, manufactured by Daicel Corporation): boiling point 188 ° C./4 hPa

[Examples 1 to 4, Comparative Example 1, Comparative Example 6]
Poly-L-lactic acid (PLLA) having a melting point of 175 ° C. and a weight average molecular weight of 200,000 is used, and poly-D-lactic acid (PDLA) having a melting point of 172 ° C. and a weight average molecular weight of 180,000 is used. Then, PLLA and PDLA were mixed at a weight ratio of 1: 1, charged into a hopper of a twin screw extruder, and a screw diameter of 37 mm and a L / D = 40 co-rotating fully meshed twin screw extruder (manufactured by Toshiba Machine Co., Ltd., TEM-37) and melt-kneaded.
At that time, supercritical carbon dioxide is introduced and melt-kneaded in the region of L / D = 8 to 32, and supercritical carbon dioxide is degassed in a reduced pressure state by a vacuum vent at positions L / D = 32 and 35. After removal, the melt-kneaded resin is weighed by a gear pump, filtered in a pack, and then discharged and spun as a filament from a nozzle provided in the base.
That is, DIPC (carbodiimide compound, Kawaguchi, which was discharged at 4 kg / hr from a spinning cap set at 220 ° C. with 48 holes of 0.25φ, set at 220 ° C., then preheated 90 ° C. and then melted at 150 ° C. (Chemical Industry Co., Ltd.) It was immersed in the melt and impregnated, and simultaneously heat set.
Furthermore, it wash | cleaned with the DIPC methanol solution of a predetermined density | concentration, and adjusted to the predetermined density | concentration.
As shown in Table 1, the hydrolysis resistance in the high-temperature hot water at 190 ° C. for 2 hours in the evaluation of hydrolysis resistance tends to decrease when the amount of impregnation of the liquid additive decreases, and hydrolysis is promoted. When the impregnation amount of DIPC is 2% as in Comparative Example 1, the weight of the stereocomplex polylactic acid fiber is reduced. On the other hand, when the amount of impregnation of the liquid additive is increased, hydrolysis hardly occurs and the weight of the stereocomplex polylactic acid fiber is maintained, but when the amount of impregnation is excessive, the amount of impregnation of DIPC as in Comparative Example 6 is 25%. In this case, DIPC bleeds out to the fiber surface, which is not preferable.

[Example 5]
Spinning of stereocomplex polylactic acid fiber in Example 2 and stretching to 4 times, followed by heat setting at 150 ° C., followed by dipping in a 5% methanol solution (25 ° C.) of DIPC and drying to obtain stereocomplex polylactic acid fiber It was. The results are shown in Table 1, and were satisfactory, showing characteristics almost similar to Example 2 when immersed in molten DIPC.

[Example 6]
Stereocomplex polylactic acid fiber in the same manner as in Example 5 except that liquid “Celoxide (registered trademark)” 2021P (epoxy compound, manufactured by Daicel Corporation) is used instead of DIPC as a liquid additive in Example 5. Got. The results are shown in Table 1. Although the weight loss was slightly large in the hydrolysis resistance evaluation at 190 ° C. for 2 hours, it was almost satisfactory.

[Comparative Example 2]
After melting, kneading, and spinning in the same manner as in Example 1 and stretching 4 times, heat treatment was performed with hot air at 150 ° C. without impregnating the liquid additive to obtain a stereocomplex polylactic acid fiber. The evaluation results are shown in Table 1, but the hydrolysis resistance was inferior, and in the evaluation of hydrolysis resistance, the weight loss of the stereocomplex polylactic acid fiber was large and the molecular weight was also greatly reduced.

[Comparative Example 3]
Poly-L-lactic acid (PLLA) having a melting point of 175 ° C. and a weight average molecular weight of 200,000 is used, and poly-D-lactic acid (PDLA) having a melting point of 172 ° C. and a weight average molecular weight of 180,000 is used. Then, PLLA and PDLA are mixed at a weight ratio of 50 parts by weight: 50 parts by weight. Further, metal phosphate (“ADEKA STAB (registered trademark)” NA11: 0.04 parts by weight manufactured by ADEKA Co., Ltd.) is added and biaxial The mixture was introduced into a hopper of an extruder, led to a co-rotating fully meshed twin screw extruder (TEM-37, manufactured by Toshiba Machine Co., Ltd.) having a screw diameter of 37 mm and L / D = 40, and melt kneaded.
At that time, without adding a liquid additive or the like, the mixture was melt-kneaded, weighed by a gear pump, filtered in a pack, and then discharged and spun as a filament from a nozzle provided in the base.
Thereafter, in the same manner as in Example 2, it was immersed in DIPC stretched and melted 4 times, heat-set, and washed with a methanol solution of DIPC having a predetermined concentration to obtain a stereocomplex polylactic acid fiber adjusted to a predetermined concentration. The evaluation results are shown in Table 1. The melting point was low, and therefore, in the evaluation of hydrolysis resistance, fusion in hot water occurred although the weight loss was relatively small. Judged to be unbearable for use in hot hot water.

[Comparative Example 4]
Phosphoric acid metal salt (“ADEKA STAB (registered trademark)” NA11 manufactured by ADEKA Co., Ltd.) NA11: A stereocomplex polylactic acid fiber was obtained in the same manner as in Comparative Example 3 except that 0.04 part by weight was not added. As described in No. 1, the sc conversion degree is low, and in the evaluation of hydrolysis resistance, although the weight loss is relatively small, the melting point is lowered because DIPC works as a plasticizer. It was judged that it could not withstand use in hot hot water.

[Comparative Example 5]
In Comparative Example 2, except that poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) are mixed at a weight ratio of 50 parts by weight: 50 parts by weight, and further 5 parts by weight of DIPC is added and supplied. In the same manner as in Example 2, a stereocomplex polylactic acid fiber was obtained.
The evaluation results are shown in Table 1. However, the hydrolysis resistance is inferior because DIPC is removed together with the degassing / removal of supercritical carbon dioxide. The molecular weight was greatly reduced.

The molded product obtained by the production method of the present invention has a high melting point of 220 ° C. or higher, high heat resistance, and high hydrolysis resistance. Therefore, the molded product in hot water at a temperature higher than 135 ° C. for a certain period of time. It is possible to show the characteristics of quickly decomposing after maintaining the weight and shape.
In addition, since the molded product is derived from polylactic acid, it dissolves efficiently after being decomposed in high-temperature hot water, and precipitation due to reaction with other components, which is a problem with some aromatic polyesters, is greatly increased. It is possible to reduce it.

Claims (9)

The manufacturing method of the molded article which consists of a polylactic acid composition which implements the process of following (a)-(f) sequentially.
(A) supplying poly-L-lactic acid and poly-D-lactic acid into an extruder;
(B) press-fitting a supercritical fluid into poly-L-lactic acid and poly-D-lactic acid in the extruder;
(C) a step of kneading poly-L-lactic acid and poly-D-lactic acid in the presence of a supercritical fluid to obtain a polylactic acid composition;
(D) removing (degassing) the supercritical fluid from the polylactic acid composition;
(E) obtaining an extruded product of the polylactic acid composition from the extruder;
(F) A step of impregnating the extruded product of the polylactic acid composition with a liquid additive as a hydrolysis inhibitor.   The liquid additive in step (f) is a liquid additive obtained by melting or dissolving the additive in a solvent, and the content of the liquid additive is 3 in terms of additive based on the extruded product of the polylactic acid composition. The production method according to claim 1, wherein the impregnation is performed so as to be not less than 20% by weight.   The manufacturing method according to claim 1 or 2, wherein the liquid additive in the step (f) has a boiling point of 20 ° C / 100kPa to 250 ° C / 6hPa.   The production method according to any one of claims 1 to 3, wherein the liquid additive contains an aromatic carbodiimide compound having a hydrophobic functional group added around the carbodiimide group as a hydrolysis inhibitor. The manufacturing method of Claim 4 using the compound represented by following formula (1) as an aromatic carbodiimide compound.

(Wherein R _{1 to} R ₄ are each independently an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or a combination thereof, X and Y may each independently represent a hydrogen atom, an aliphatic group having 1 to 20 carbon atoms, an alicyclic group having 3 to 20 carbon atoms, an aromatic group having 5 to 15 carbon atoms, or these (It is a combination and may contain a hetero atom. Each aromatic ring may be bonded by a substituent to form a cyclic structure.)   The production method according to claim 5, wherein bis (2,6-diisopropylphenyl) carbodiimide is used as the aromatic carbodiimide.   The production method according to any one of claims 1 to 6, wherein the supercritical fluid removal (degassing) step from the stereocomplex polylactic acid in step (d) is performed using a vent port provided in the extruder.   The production method according to claim 1, wherein in the step of obtaining an extruded product from the extruder in the step (e), the extruder is provided with a spinning die and subjected to extrusion spinning.   The molded article which consists of a polylactic acid composition obtained by the manufacturing method in any one of Claims 1-8.

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