JP5555690B2 - Method for producing aliphatic polyester - Google Patents

Description

  The present invention relates to an improvement in a method for producing an aliphatic polyester by ring-opening polymerization of a cyclic ester such as glycolide.

  Aliphatic polyesters such as polyglycolic acid and polylactic acid have been attracting attention as biodegradable polymer materials that have a low environmental impact because they are degraded by water, microorganisms, or enzymes that exist in nature such as soil and sea.

  Among the aliphatic polyesters, polyglycolic acid has excellent barrier properties such as oxygen gas barrier properties, carbon dioxide gas barrier properties, and water vapor barrier properties, as well as excellent heat resistance and mechanical strength. Or, it is being used in combination with other resin materials.

  Aliphatic polyesters can be synthesized, for example, by dehydration polycondensation of α-hydroxycarboxylic acids such as glycolic acid and lactic acid, but it is difficult to produce high molecular weight aliphatic polyesters by this method. On the other hand, in order to efficiently produce a high molecular weight aliphatic polyester, a method of synthesizing a dimer cyclic ester of α-hydroxycarboxylic acid and subjecting the cyclic ester to ring-opening polymerization is employed. For example, when glycolide which is a dimer cyclic ester of glycolic acid is subjected to ring-opening polymerization, polyglycolic acid is obtained. Polylactic acid is obtained by ring-opening polymerization of lactide, which is a dimer cyclic ester of lactic acid. Aliphatic polyesters can also be obtained by ring-opening polymerization of lactones. Methods for producing aliphatic polyesters by ring-opening polymerization of these cyclic esters are known, for example, from Patent Documents 1 to 6 below. The present inventors also introduced a partial polymer in a solid pulverized state by continuously introducing a melt of a partial polymer into a biaxial agitator when ring-opening polymerization of a cyclic ester to produce an aliphatic polyester. Proposing a method for producing an aliphatic polyester (Patent Document 7) characterized in that it is continuously obtained, further subjected to solid-phase polymerization, and then the resulting polymer is melt-kneaded with a heat stabilizer and pelletized. doing.

In the method for producing an aliphatic polyester by ring-opening polymerization of these cyclic esters, initiators (molecular weight regulators) such as alcohols are used. Examples of the ring-opening polymerization catalyst include tin (Sn), titanium (Ti), aluminum (Al), antimony (Sb), germanium (Ge), zirconium (Zr), zinc (Zn) and other metal oxides, halogens Compounds such as compounds, carboxylates and alkoxides are used. Among these, tin dichloride (SnCl ₂ ) or a hydrate thereof is particularly preferably used because it has a relatively high catalytic activity compared to other metal compounds and is superior to tin tetrachloride in safety.

JP-A-7-126358 Japanese Patent Laid-Open No. 10-60101 JP 2005-220203 A WO2005 / 035623A JP-A-11-349670 JP-A-10-168171 WO2007 / 086563A

  However, when the present inventors industrially produce aliphatic polyesters by bulk ring-opening polymerization of cyclic esters using a tin dichloride catalyst, the activity of the tin dichloride catalyst varies from lot to lot. We faced the problem of destabilization. In particular, the problem of destabilization of the process due to the variation in the activity of the tin dichloride catalyst is caused by the specification of Patent Document 7 or Japanese Patent Application No. 2009-039675 (hereinafter referred to as “Patent Document 7” or “Japanese Patent Application No. 2009-039675”). It has also been found that it is manifested when continuously carried out as in the method of “Patent Document 8”.

  The present invention aims to improve the ring-opening polymerization process of the cyclic ester described in the above-mentioned patent document. In particular, by stabilizing the activity of the tin dichloride catalyst, it is possible to stabilize the aliphatic polyester by the ring-opening polymerization of the cyclic ester. The main purpose is to provide a simple manufacturing method.

According to the studies by the present inventors, the variation in the activity of the tin dichloride catalyst is due to the change in the oxidation state of the tin dichloride catalyst during storage, and the valence of tin changes from divalent to tetravalent. It has been found that the activity of the tin dichloride catalyst is stabilized by controlling the content of tetravalent tin contained in the range of 30 to 70%. That is, the method for producing an aliphatic polyester according to the present invention uses a tin dichloride catalyst that is in a solution state maintained in an inert gas atmosphere and contains 30 to 70% of tetravalent tin in a cyclic state. It is characterized by ring-opening polymerization.

In the present invention, although the change in the valence of tin in the tin dichloride catalyst is relatively difficult to occur in the solid state, for example, in order to make the production of the aliphatic polyester more efficient by continuing the polymerization process, When supplying the tin chloride catalyst in the solution state, it is likely to occur during storage, and in order to prevent the valence from changing suddenly during storage in the solution state, the dichloride in the solution state is supplied until it is supplied to the polymerization process. This is also based on the finding that it is preferable to keep the tin catalyst in an inert gas atmosphere .

1 is a schematic flow diagram of an example of an apparatus system suitable for carrying out the method of the present invention.

(Cyclic ester)
As the cyclic ester used in the present invention, α-hydroxycarboxylic acid dimer cyclic ester and lactone are preferable. Examples of the α-hydroxycarboxylic acid forming the dimer cyclic ester include glycolic acid, L- and / or D-lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid, and α-hydroxy. Examples include caproic acid, α-hydroxyisocaproic acid, α-hydroxyheptanoic acid, α-hydroxyoctanoic acid, α-hydroxydecanoic acid, α-hydroxymyristic acid, α-hydroxystearic acid, and alkyl-substituted products thereof. Can do.

  Examples of the lactone include β-propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone, β-methyl-δ-valerolactone, and ε-caprolactone. Examples of the cyclic ether ester include dioxanone.

  The cyclic ester having an asymmetric carbon may be any of D-form, L-form and racemate. These cyclic esters can be used alone or in combination of two or more. When two or more cyclic esters are used, any aliphatic copolyester can be obtained. The cyclic ester can be copolymerized with other copolymerizable comonomers, if desired. Examples of other comonomers include cyclic monomers such as trimethylene carbonate and 1,3-dioxolane.

  Among the cyclic esters, glycolide, which is a dimer cyclic ester of glycolic acid, L- and / or D-lactide, which is a dimer cyclic ester of L- and / or D-lactic acid, and a mixture thereof, are preferred. Is more preferable. Glycolide can be used alone, but it can also be used in combination with other cyclic monomers to produce a polyglycolic acid copolymer (copolyester). When producing a polyglycolic acid copolymer, the proportion of glycolide in the copolymer is preferably 70% by weight, more preferably 80% by weight, from the viewpoint of physical properties such as crystallinity and gas barrier properties of the resulting copolyester. As described above, it is particularly preferable that the content is 90% by weight or more. Further, as the cyclic monomer copolymerized with glycolide, lactide, ε-caprolactone, and trimethylene carbonate are preferable, and lactide is particularly preferable.

  The manufacturing method of cyclic ester is not specifically limited. For example, glycolide can be obtained by a method of depolymerizing glycolic acid oligomers. Examples of the depolymerization method of glycolic acid oligomers include, for example, a melt depolymerization method described in US Pat. No. 2,668,162, a solid-phase depolymerization method described in JP-A-2000-119269, and JP-A-9- The solution phase depolymerization method described in Japanese Patent No. 328881 and International Publication No. 02 / 14303A1 can be employed. K. Glycolide obtained as a cyclic condensate of chloroacetate as reported in Chujo et al., Die Makromolekule Cheme, 100 (1967), 262-266 can also be used.

  In order to obtain glycolide, the solution phase depolymerization method is preferable among the above depolymerization methods. In the solution phase depolymerization method, (1) a mixture containing a glycolic acid oligomer and at least one high-boiling polar organic solvent having a boiling point in the range of 230 to 450 ° C. is subjected to decomposition of the oligomer under normal pressure or reduced pressure. (2) the oligomer is dissolved in the solvent until the residual ratio (volume ratio) of the melt phase of the oligomer is 0.5 or less, and (3) further at the same temperature. The oligomer is depolymerized by continuing heating, (4) the dimer cyclic ester (that is, glycolide) formed is distilled together with the high-boiling polar organic solvent, and (5) glycolide is recovered from the distillate.

  Examples of the high boiling polar organic solvent include bis (alkoxyalkyl esters) phthalates such as di (2-methoxyethyl) phthalate, alkylene glycol dibenzoates such as diethylene glycol dibenzoate, and aromatic carboxyls such as benzylbutyl phthalate and dibutyl phthalate. Examples include acid esters, aromatic phosphate esters such as tricresyl phosphate, polyalkylene glycol ethers such as polyethylene dialkyl ether, etc., and usually 0.3 to 50 times (weight ratio) with respect to the oligomer. Use at a rate of. Along with the high-boiling polar organic solvent, tetraethylene glycol, polyethylene glycol, polypropylene glycol or the like can be used in combination as a solubilizer for the oligomer, if necessary. The depolymerization temperature of the glycolic acid oligomer is usually 230 ° C. or higher, preferably 230 to 320 ° C. Depolymerization is carried out under normal pressure or reduced pressure, but it is preferable to depolymerize by heating under reduced pressure of 0.1 to 90.0 kPa (1 to 900 mbar).

≪Production of aliphatic polyester≫
In the method of the present invention, the above cyclic ester is subjected to bulk ring-opening polymerization in the presence of an initiator (molecular weight regulator) and a tin dichloride catalyst.

(Initiator)
As the initiator (molecular weight regulator), monohydric alcohols such as water, butanol and dodecyl alcohol (lauryl alcohol), preferably higher alcohols; polyhydric alcohols such as butanediol, hexanediol and glycerin are used.

(catalyst)
In accordance with the present invention, the catalyst used is tin dichloride or a hydrate thereof containing 30 to 70% of tetravalent tin. A commercially available tin dichloride catalyst generally contains divalent tin at a ratio of almost 100%, and therefore, in the present invention, a commercially available tin dichloride catalyst is used in a more oxidized state. This oxidation proceeds relatively slowly even when the solid tin dichloride catalyst is stored in (dry) air (for example, 5% to 10% of tetravalent tin is allowed to stand for 1 day in dry air). However, in order to smoothly supply the polymerization apparatus as described above, the tetravalent tin in the tin dichloride catalyst stored in a solution state is in the range of 30 to 70%. It is preferable to prepare for supply to the polymerization apparatus by storing under controlled conditions. However, when a commercially available tin dichloride catalyst solution is stored in the air, the oxidation proceeds rapidly, and the tetravalent tin may exceed 70% even if stored for one day. After the catalyst is in solution, it is preferably stored in an inert gas atmosphere such as dry nitrogen. In general, tin in a tetravalent state can be increased to 30% or more even in about 1 day of storage in dry nitrogen (Example 1 described later), so storage in a dry nitrogen atmosphere is preferable, but some dry air is intentionally used. Can be introduced.

  As the solvent for dissolving the tin dichloride catalyst, any organic solvent capable of dissolving the tin dichloride catalyst is used, but the concentration of the catalyst due to volatilization is not caused during storage and in the supply conditions to the polymerization apparatus. Those having a boiling point of 50 ° C. or higher are preferred. Examples of such organic solvents include ester solvents such as methyl acetate (boiling point 56.9 ° C.) and ethyl acetate (boiling point 77 ° C.); ether solvents such as dioxane (boiling point 101.1 ° C.); acetone (boiling point) 56.5 ° C.) and ketone solvents such as methyl ethyl ketone (boiling point 79.5 ° C.).

  The tin dichloride catalyst concentration in the tin dichloride catalyst solution is used at a relatively low concentration in order to reduce the residual amount in the product polymer, and is generally 0.1 g / mL or less, more preferably 0.05 g / mL. Hereinafter, it is more preferably about 0.001 to 0.02 g / mL.

  In addition, as the organic solvent, a liquid initiator having an action of dissolving a tin dichloride catalyst such as dodecyl alcohol is also used, and the quantity ratio with the catalyst according to the target product polymer molecular weight in relation to the molecular weight adjusting action. However, since no additional organic solvent is used, the remaining of the solvent in the product polymer can be avoided, and the process can be simplified.

  As described above, the tin dichloride catalyst preferably used in a solution state is generally 300 ppm or less, preferably 1 to 100 ppm, more preferably 10 to 60 ppm as tin dichloride on a weight basis with respect to the cyclic ester. Used.

  The ring-opening polymerization of the cyclic ester in the production method of the aliphatic polyester of the present invention (substantially bulk polymerization is used with almost no solvent other than the solvent used auxiliaryly for supplying an auxiliary agent such as a catalyst). The cyclic ester, the initiator and the tin dichloride catalyst described above can be accommodated in the polymerization apparatus and can be carried out batchwise (Examples 1 and 2 below). In order to produce stably, it is preferable to carry out at least the initial polymerization step continuously by using an apparatus system shown in FIG.

  Referring to FIG. 1, this apparatus system includes a monomer tank 1, a monomer liquefaction tank 2, a first reaction apparatus 3, a second reaction apparatus 4, and a solidification and pulverization apparatus 5 that are arranged almost in series as a schematic configuration. Thereafter, a plurality of (only one shown) solid-phase polymerization apparatuses 6 that can be switched are arranged. A catalyst dissolution tank CV1 for supplying a catalyst solution through the pipe L1 is disposed in the middle of the monomer transfer pipe L23 from the monomer liquefaction tank 2 to the first reactor 3. Here, the monomer liquefaction tank 2, the catalyst dissolution tank CV1, and the devices 3 to 6 each include a temperature control segment. Here, the temperature control segment is a jacket type using heat transfer oil, steam, hot water, cold water, etc. as a heat medium, a non-jacket type such as an electric heater, an infrared heater, an air cooling fan, or a combination type of these temperature control segments. Is included.

  Hereinafter, preferred embodiments of the method for producing an aliphatic polyester of the present invention will be described mainly with reference to production examples of polyglycolic acid by ring-opening polymerization of glycolide, which is a preferred embodiment of the present invention.

(Monomer tank 1, monomer liquefaction tank 2)
In the monomer tank 1, in order to promote the liquefaction (melting) of the cyclic ester monomer in the next monomer liquefaction tank 2, for example, a cyclic ester monomer having a diameter of 3 mm or less is held, and the monomer liquefaction is maintained. Depending on the residual amount of the liquefied monomer in the tank 2, it is supplied to the monomer liquefaction tank 2 through the pipe L12 in a timely manner.

  In the monomer liquefaction tank 2, the granular cyclic ester monomer supplied from the monomer tank 1 is heated to a temperature equal to or higher than its melting point, generally about 85 to 150 ° C., liquefied, and supplied to the first reactor 3. The

  The atmosphere in the monomer tank 1 and the monomer liquefaction tank 2 is arbitrary, and for example, an inert gas or air atmosphere is used. However, it has been confirmed that a moderately oxygen-containing atmosphere is preferable for improving a moderate polymerization rate, and a dry air atmosphere in which the oxygen concentration is adjusted to 10 to 21% is preferably used (patent) Reference 8).

  The cyclic ester monomer in the monomer tank 1 can be directly supplied to the first reactor 3 by using a dry feed device without going through the monomer liquefaction tank 2. Further, the initiator and the catalyst can be directly supplied to the first reactor 3. However, in order to uniformly disperse these auxiliaries in the monomer before polymerization, it is preferable that the monomer is previously melted in the monomer liquefaction tank 2 and dispersed in the liquefied monomer before being supplied to the first reactor 3. That is, it is preferable to supply the initiator in the monomer liquefaction tank 2 or in the middle of the supply pipe L23 to the first reactor 3, for example, through the pipe L1. The catalyst is preferably supplied in the form of a paste, melt or solution, more preferably in the form of a solution, for example, in the middle of the monomer supply path L23 supplied in a molten state through the pipe L2. Generally, the initiator is added to the monomer prior to the catalyst, or is added simultaneously with the catalyst on the monomer feed path. In order to further improve the dispersibility of these auxiliaries, a mixer such as a static mixer can be provided in the supply line L23 after the supply.

(Catalyst dissolution tank CV1)
According to a particularly preferred embodiment of the present invention, the tin dichloride catalyst is dissolved in an organic solvent such as ethyl acetate at a concentration of 0.001 to 0.02 g / mL, for example, in a dry nitrogen atmosphere supplied from the gas pipe GL3. The retained catalyst dissolution tank CV1 is provided close to the monomer liquefaction tank 2 → the monomer supply pipe L23 to the first reactor 3. As a result, a tin dichloride catalyst solution containing tetravalent tin in a proportion of 30 to 70% is held in the catalyst dissolution tank CV1 and supplied in the middle of the supply pipe L23 to the first reactor 3. . As dry nitrogen as a preferable example of the inert gas, it is preferable to use a dry nitrogen having a dew point of -10 ° C or lower, particularly -30 ° C or lower.

  As described above, in the catalyst dissolution tank CV1, a solution obtained by dissolving the tin dichloride catalyst in the initiator alone or in a mixed solvent with another organic solvent may be retained, and the supply of the initiator from the pipe L1 may be omitted. it can.

(First reactor 3)
In the 1st reactor 3, the polymerization temperature controlled by the heat medium which goes in and out of the jacket divided | segmented into two or more as needed is set to 100-240 degreeC, Preferably it is 120-220 degreeC, and the molten state of a content is maintained. However, the reaction rate is preferably 10 to 40%, more preferably 20 to 35%, still more preferably 25 to 35%, and 1 to 30 minutes, preferably 3 to 3 to obtain the reaction rate. Set residence time within 15 minutes. If the reaction rate is excessively high, the coloring of the partial polymer increases and the agitation load in the first reactor 3 is increased, so that there is a limitation.

  As the stirring device, a multi-stage paddle blade, a helical ribbon blade, a helical screw blade, etc. suitable for stirring high-viscosity contents, or a vertical or horizontal twin-screw type stirring as disclosed in JP-A-11-279267. An apparatus is preferably used.

  Moreover, it prevents the adhesion of the space of the stirring tank to the tank wall and the like due to the fluctuation of the liquid level in the stirring layer, and the spatial gas phase atmosphere (if present, it is necessary to provide a dry air atmosphere with a reduced oxygen concentration. In order to eliminate the necessity of control of (), it is preferable to use a full-liquid type stirring tank 3 (in this example, equipped with a biaxial multistage paddle blade stirring device) as shown in FIG.

(Second reactor 4)
In the second reactor 4, the partial polymer from the first reactor 3 (that is, the mixture of the polymer and the residual monomer) is in a molten state through the pipe L 34 and the connecting portion 41 that is preferably in a dry nitrogen atmosphere. Introduced in The connection part 41 is a box-shaped space for receiving the flowing viscous reaction mixture and flowing it down to the hopper of the second reaction apparatus 4, and the inside is held in a dry nitrogen atmosphere introduced from the pipe GL4. The internal temperature of the second reactor 4 is controlled to a temperature of 120 to 240 ° C., preferably 140 to 220 ° C., preferably 50 to 90 by a heating medium entering and exiting the jacket divided into two or more as necessary. %, More preferably 60 to 87%. In order to process such a highly viscous content while giving a necessary residence time, for example, 5 to 20 minutes, a vertical or horizontal biaxial stirring device is preferably used as the stirring device of the second reactor 4. In particular, a horizontal biaxial agitator as shown in FIG. 1 is preferable because it has transportability and self-cleaning property. The residence time can also be adjusted by the inclination of the installation angle of the stirrer or the outlet diameter of the stirrer. Although it is desirable that the reaction rate at this stage is also high, increasing the polymerization rate has a limitation that the coloring of the resulting partial polymer also tends to increase.

(Solidification / Crushing device 5)
In the solidification and pulverization apparatus 5 which is a biaxial stirring apparatus used in a preferred embodiment of the present invention, the partial polymer from the second reaction apparatus 4 is introduced in a molten state through a connecting part 51 in a dry nitrogen atmosphere. . At least in the subsequent stage of the solidification / pulverization apparatus 5, the partial polymer is solidified and continuously discharged in a pulverized state using the solid pulverization force of the biaxial stirring apparatus. For this purpose, it is necessary to set the partial polymer temperature at the outlet of the apparatus 5 to be equal to or lower than the melting point of the produced aliphatic polyester, and the heat medium temperature entering and exiting the jacket divided into two or more as required is usually set. It will be adjusted below the melting point. The melting point and the crystallization temperature from the molten state change depending on the reaction rate of the partial polymer. Generally, the higher the reaction rate, the higher the melting point and the crystallization temperature. As the heat medium temperature approaches the melting point of the partial polymer, the partial polymer discharged from the solidification / pulverization apparatus 5 is likely to be fused and become a large granular material. As the heat medium temperature is too low with respect to the crystallization temperature of the partial polymer, the partial polymer discharged from the solidification / pulverization apparatus 5 is not crystallized due to rapid cooling and becomes amorphous and easily adheres. Therefore, the heat medium temperature of the solidification / pulverization apparatus 5 is appropriately determined depending on the reaction rate of the supplied partial polymer. That is, the main function of the solidification / pulverization apparatus 5 is solidification and pulverization of the partial polymer. Further polymerization of the partial polymer is based on the heat capacity of the partial polymer introduced from the second reactor 4 and the melt. This is a subordinate function depending on the heat capacity associated with the change during solidification and the allowable residence time (for example, 1 to 10 minutes) in the solidification / pulverization apparatus 5. Therefore, although depending on the outlet reaction rate of the second stage reactor, the reaction rate in the solidification / pulverization device 5 is usually 5% or less, particularly about 0 to 3%. In order to suppress coloring of the polymer, the final reaction rate is preferably 50 to 95%, particularly preferably 60 to 90%. As the solidification / pulverization apparatus 5, a vertical or horizontal biaxial stirring apparatus in different directions or the same direction is used, but a same direction biaxial stirring apparatus with good transportability of the partial polymer is preferable, and for the same reason. A horizontal biaxial stirring device is more preferable. As the pulverized product, a granular material containing fine powder and having a particle size of more than 30 mm is obtained. From the viewpoint of operability, the average particle size is preferably about 1 to 20 mm. In order to obtain uniformity of the degree of polymerization in the subsequent solid phase polymerization step, it is preferable to make the particle diameter as uniform as possible.

(Solid phase polymerization)
The partial polymer solid pulverized product obtained by using the solidification / pulverization apparatus 5 as described above is preferably melted below its melting point, preferably at a temperature within the range of -100 ° C to -20 ° C for a predetermined time. And a reaction rate of 98% or more, preferably 99 to 100% is achieved, and the residual monomer amount is preferably 2% or less, more preferably 1% or less. As the apparatus, only for a predetermined time required to achieve the above reaction rate, for example, 0.5 to 10 hours, preferably 1 to 5 hours, the partial polymer is placed in a predetermined temperature and an inert gas atmosphere such as nitrogen. Arbitrary batch or continuous transfer type devices such as inverted conical conduction heat transfer devices, drum type devices, groove type conduction heat transfer devices, fluidized bed dryers, air flow dryers, conveyors, etc. can be used. When a continuous transfer type apparatus is used, the amount of residual cyclic ester in the produced polymer can be further reduced by setting the subsequent stage as a reduced pressure atmosphere. In the example shown in FIG. 1, an inverted conical conduction heat transfer device 6 having a powder stirring blade 61 is used. Since this apparatus 6 is basically operated in a batch system, a plurality of the apparatuses 6 are provided and can be switched between receiving and accumulating a solid pulverized product of a partial polymer from a polymerization / pulverization system and for solid-phase polymerization. Is preferred.

(Modification)
In the above, although the manufacturing method of the aliphatic polyester of this invention was demonstrated about the preferable one aspect, referring FIG. 1, a various deformation | transformation is possible within the scope of the present invention. For example, it is possible to proceed the first stage reaction with a stirring batch reactor and charge the produced partial polymer into a batch type tube-type stationary polymerization apparatus to proceed with the second stage reaction.

(Pelletized)
The pulverized polymer obtained as described above, that is, the aliphatic polyester, is preferably melt-kneaded together with a heat stabilizer and pelletized.

  Preferred examples of the heat stabilizer include cyclic neopentanetetrayl bis (2,6-di-tert-butyl-4-methylphenyl) phosphite, cyclic neopentanetetrayl bis (2,4-di-tert). Phosphoric acid ester having a pentaerythritol skeleton structure such as -butylphenyl) phosphite and cyclic neopentanetetraylbis (octadecyl) phosphite; mono- or di-stearyl acid phosphate or a mixture thereof is preferable. Are alkyl phosphates or phosphite alkyl esters having 8 to 24 alkyl groups; metal carbonates such as calcium carbonate and strontium carbonate; and bis [2- (2- Hydroxybenzoyl) hydrazine] Hydrazine compounds having a -CONHNH-CO- unit such as cannic acid, N, N'-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine; 3- (N- Salicyloyl) triazole compounds such as amino-1,2,4-triazole, and triazine compounds. The structure of these heat stabilizers is shown in WO2003 / 037956A1, if necessary. These heat stabilizers are used in an amount of preferably 3 parts by weight or less, more preferably 0.003 to 1 part by weight, and most preferably 0.01 to 0.05 part by weight, based on 100 parts by weight of the aliphatic polyester. It is done.

  Furthermore, the water resistance (hydrolysis resistance) of the obtained pellet-shaped aliphatic polyester can be improved by adding a carboxyl group-capping agent in addition to the heat stabilizer.

  As the carboxyl group-capping agent, those known as water resistance improvers for aliphatic polyesters such as polylactic acid can be generally used. For example, monocarbodiimides such as N, N-2,6-diisopropylphenylcarbodiimide And carbodiimide compounds including polycarbodiimide compounds, 2,2'-m-phenylenebis (2-oxazoline), 2,2'-p-phenylenebis (2-oxazoline), 2-phenyl-2-oxazoline, styrene-iso Oxazoline compounds such as propenyl-2-oxazoline; Oxazine compounds such as 2-methoxy-5,6-dihydro-4H-1,3-oxazine; Epoxy compounds such as N-glycidylphthalimide, cyclohexene oxide and triglycidyl isocyanurate Etc. Of these, carbodiimide compounds and epoxy compounds are preferred. These carboxyl group-capping agents can be used in combination of two or more as required. 0.01 to 10 parts by weight, and further 0.1 to 2 parts by weight with respect to 100 parts by weight of the aliphatic polyester. Parts, particularly 0.2 to 1 part by weight.

  The above-mentioned aliphatic polyester pulverized product and heat stabilizer, and further, a carboxyl group blocking agent added as necessary, have a melting point of the aliphatic polyester of +5 to + 60 ° C., for example, when the aliphatic polyester is polyglycolic acid (PGA), It is preferably melted (mixed) by heating to a temperature range of 230 to 280 ° C, more preferably 240 to 270 ° C. The melting (mixing) means is basically arbitrary, and a stirrer, a continuous kneader, etc. are also used, but an extruder that can be processed in a short time and can be smoothly transferred to the subsequent cooling step ( For example, heating and melting (mixing) in a co-rotating twin-screw kneading extruder is preferable. For example, in the case of PGA, if the heat melting temperature is less than 230 ° C., the effect of additives such as a heat stabilizer and a carboxyl group sealing agent tends to be insufficient. On the other hand, when it exceeds 280 ° C., the PGA resin composition tends to be colored. When using an extruder and adding a carboxyl group sealant in addition to the heat stabilizer, the heat stabilizer is supplied from the extruder inlet hopper together with the aliphatic polyester, and the carboxyl group sealant is supplied from the middle stage of the extruder. By doing so, the additive effect can be maximized. Further, if necessary, a reduced pressure can be applied to the melt in the middle stage of the extruder to further reduce the residual cyclic ester.

  In order to impart mechanical strength and other properties to the aliphatic polyester, it is possible to use a filler, the type of which is not particularly limited, but fibrous, plate-like, powdery, Granular fillers can be used. Specifically, organic fibers such as glass fibers, PAN and pitch carbon fibers, stainless fibers, metal fibers such as aluminum fibers and brass fibers, natural fibers such as chitin / chitosan, cellulose and cotton, and aromatic polyamide fibers. Fiber, gypsum fiber, ceramic fiber, asbestos fiber, zirconia fiber, alumina fiber, silica fiber, titanium oxide fiber, silicon carbide fiber, rock wool, potassium titanate whisker, barium titanate whisker, aluminum borate whisker, silicon nitride whisker, etc. Fibrous or whisker-like fillers; natural inorganic minerals such as mica, talc, kaolin, silica, sand, calcium carbonate, glass beads, glass flakes, glass microballoons, clay, molybdenum disulfide, wollastonite, montmorillonite, oxidation Tan, zinc oxide, polyphosphoric acid calcium, powdery such as graphite, include particulate or plate-like filler. The kind of glass fiber is not particularly limited as long as it is generally used for reinforcing resin, and can be selected from, for example, long fiber type, short fiber type chopped strand, milled fiber, and the like. Two or more kinds of the above fillers can be used in combination. The surface of the filler can also be used by treating the surface with a known coupling agent (for example, a silane coupling agent, a titanate coupling agent, etc.) or other surface treatment agents. The glass fibers may be coated or bundled with a thermoplastic resin such as an ethylene / vinyl acetate copolymer or a thermosetting resin such as an epoxy resin. The addition amount of the filler is 0.1 to 100 parts by weight, particularly preferably 1 to 50 parts by weight with respect to 100 parts by weight of the PGA resin.

  Hereinafter, the present invention will be described more specifically with reference to examples in which PGA is produced as an aliphatic polyester. Including the following description, the physical properties (values) described in the present specification are based on measured values by the following method.

(1) Reaction rate:
The glycolide content in the reaction mixture was measured and calculated as the conversion rate of glycolide. In order to measure the glycolide content, a special grade dimethyl sulfoxide (Kanto Chemical Co., Ltd.) was prepared by dissolving an internal standard substance 4-chlorobenzophenone (manufactured by Kanto Chemical Co., Ltd.) at a concentration of 0.2 g / L in about 100 mg of a sample. 2) 2mL was added, heated at 150 ° C for about 5 minutes to dissolve, cooled to room temperature, and then filtered. 1 μL of the filtrate was collected and injected into a gas chromatography (GC) apparatus for measurement.

<GC conditions>
Equipment: “GC-2010” manufactured by Shimadzu Corporation
Column: “TC-17”, 0.25 mmφ × 30 m
Column temperature: 150 ° C. held for 5 minutes, heated to 270 ° C. at 20 ° C./min, 270 ° C. held for 3 minutes Injection temperature: 180 ° C.
Detector: FID (hydrogen flame ionization detector), temperature: 300 ° C.

(2) Molecular weight:
After heating at 275 ° C. for 90 seconds and further pressing at 2 MPa for 60 seconds and then rapidly cooling in ice water, an amorphous polymer sheet is formed, and 10 mg of the polymer sample cut out from this is dissolved in the following GPC eluent. 10 mL of the sample solution. The solution was filtered through a PTFE 0.1 μm membrane filter, and injected into a gel permeation chromatography (GPC) apparatus for molecular measurement. The time from dissolution to injection was set to be within 30 minutes. Based on the measured molecular weight distribution, the weight average molecular weight and the number average molecular weight were determined, and the polydispersity (= weight average molecular weight / number average molecular weight) was further determined therefrom.

<GPC conditions>
Equipment: “Shodex GPC-104” manufactured by Showa Denko K.K.
Column: “HFIP-606M” (2), pre-column: “HFIP-G” (1) in series connection Column temperature: 40 ° C.
Eluent: Solution flow rate in 5 mM sodium trifluoroacetate / HFIP (hexafluoroisopropanol): 0.6 mL / min
Detector: RI (differential refractive index detector)
Reference substance for determining molecular weight: Standard polymethyl methacrylate (manufactured by Showa Denko KK, molecular weights 195,000, 65,990, 218,000, 50,000, 21,000, 7,000 and 0 .20,000).

(3) Tin valence measurement in tin catalyst:
An accurately weighed tin dichloride catalyst sample containing 50 to 100 mg of tin was dissolved in 5 mL of ethyl acetate in the case of a solid to prepare a solution catalyst sample. In the case of a tin dichloride catalyst solution prepared in advance, the sample was used as it was. Subsequently, 10 mL of dimethyl sulfoxide was added. Iodine solution was added dropwise as an oxidizing agent, and iodine titration was performed with the point that the solution exhibited yellow color due to unreacted iodine as a result of completion of oxidation of contained tin. From divalent tin contained to tetravalent tin. The amount of iodine required for oxidation was determined, and the amount of divalent tin in the sample was determined. Next, the amount of tetravalent tin in the sample was determined as the amount of tin in the sample minus the amount of divalent tin in the sample.

[Catalyst Preparation Example 1]
100 mL of ethyl acetate was added to 1.5 g of tin dichloride dihydrate and dissolved completely, and then stored in a nitrogen atmosphere for 1 day to obtain a solution catalyst (1). The proportion of tetravalent tin in the catalyst (1) was 36%.

[Catalyst Preparation Example 2]
2 L of ethyl acetate was added to 30.0 g of tin dichloride dihydrate and dissolved completely, and then stored in a nitrogen atmosphere for 7 days to obtain a solution catalyst (2). The proportion of tetravalent tin in the catalyst (2) was 67%.

[Catalyst Preparation Example 3]
Commercially available tin dichloride dihydrate was used as the catalyst (3) in the solid state after opening. The proportion of tetravalent tin in the catalyst (3) was less than 1%.

[Catalyst Preparation Example 4]
2 L of ethyl acetate was added to 30.0 g of tin dichloride dihydrate and dissolved completely, and then stored in an air atmosphere for 7 days to obtain a solution catalyst (4) in which some cloudiness was observed. The ratio of tetravalent tin in the catalyst (4) was 97%.

Example 1
To 100 g of glycolide at 100 ° C. (oxygen content of about 2 vol.%) Completely melted in a dry air atmosphere, 0.25 mol% of 1-dodecanol and 0.1 mL of solution catalyst (1) (dichloride dichloride) 30 mg) was added as tin dihydrate, and after sufficient stirring, this was transferred to a test tube made of Teflon and immersed in an oil bath heated to 200 ° C. to perform partial ring-opening polymerization. After 5 minutes, the test tube was taken out and immersed in liquid nitrogen. When the physical properties of the obtained polymer were evaluated after pulverization, the reaction rate was 30% and the weight average molecular weight was 100,000.

(Example 2)
The same operation as in Example 1 was performed except that the solution catalyst (2) was used. When the physical properties of the polymer obtained after pulverization were evaluated, the reaction rate was 32% and the weight average molecular weight was 110,000.

(Example 3)
The partial ring-opening polymerization of glycolide was performed using the apparatus system shown in FIG. That is, glycolide stored in a dry air atmosphere and melted in the monomer liquefaction tank 2 in a dry air atmosphere (water content of less than 30 ppm, oxygen content of about 2 vol.%) Is passed through a pipe L23 by a biaxial multistage paddle blade. Under stirring, the mixture was continuously supplied at 30 kg / h to the bottom of a vertical cylindrical full liquid first reactor 3 having an internal volume of 1.8 L set at an internal temperature of 200 ° C. At the same time, in the middle of the pipe L23, the catalyst (1) in the catalyst dissolution tank CVI maintained in a dry nitrogen atmosphere so that 1-dodecyl alcohol (initiator) is 0.25 mol% with respect to glycolide through the pipe L1. 2) was supplied to the bottom of the apparatus 3 continuously through the pipe L2 so as to be 30 ppm (based on the weight of tin dichloride) with respect to glycolide. The content discharged from the upper part of the first reactor 3 with an average residence time of about 5 minutes has a glycolide reaction rate of about 30% as a result of analysis of a part thereof in a steady state, and the weight average molecular weight of the produced polymer is about It was confirmed that it was 100,000.

  The reaction product (melt) at about 180 ° C. from the first reactor 3 was continuously divided into four in the longitudinal direction through the pipe L34 and independently set at 200 ° C., 210 ° C., 210 ° C., and 210 ° C. It was supplied to a device connecting part (hopper) 41 of a second reactor 4 having the same direction and rotating biaxial horizontal type having a jacket (“KRC kneader S5 type” manufactured by Kurimoto Iron Works). The inside of the device connecting portion 41 was maintained in a dry nitrogen atmosphere supplied from the pipe GL4. The dry nitrogen supplied to the pipe GL3 is designed so that the space generated in the upper part of the apparatus 4 is also maintained in a dry nitrogen atmosphere. The reactant discharged under stirring with an average residence time of about 12 minutes showed a reaction rate of 78% and a monomer weight average molecular weight of about 200,000.

  The reaction product discharged from the second reactor 4 at a temperature of about 215 ° C. passes through the connecting portion 51, and has a jacket set at a temperature of about 80 ° C. Incorporated by Kurimoto Iron Works “KRC Kneader S4”). The connecting portion 51 has an airtight structure that covers the hopper of the device 5, and the dry nitrogen introduced from the pipe GL 5 keeps the connecting portion 51 in a dry nitrogen atmosphere and also makes the internal space of the device 5 have a dry nitrogen atmosphere. Designed. The average residence time in the apparatus 5 was about 2 minutes, and a granular reaction product having an average particle size (major axis reference) of about 5 mm was discharged from the discharge section at about 30 kg / h. The increase in the reaction rate in the apparatus 5 is about 2 to 3%, and there is substantially no role as a polymerization apparatus.

  After reaching the steady state, the continuous operation of the devices 3 to 5 could be stably continued for 30 hours.

(Comparative Example 1)
The same operation as in Example 1 was performed except that 30 mg of the solid catalyst (3) was used instead of 0.2 mL of the solution catalyst (1). When the physical properties of the polymer obtained after pulverization were evaluated, the reaction rate was 5% or less and the weight average molecular weight was 50,000 or less.

(Comparative Example 2)
The same operation as in Example 1 was performed except that the solution catalyst (4) was used instead of the solution catalyst (1). When the physical properties of the polymer obtained after pulverization were evaluated, the reaction rate was 45% and the weight average molecular weight was 150,000, which was empirically applied to the first stage reactor of the continuous polymerization apparatus as shown in FIG. Therefore, it was determined to be unfavorable from the viewpoint of control of the reaction, which is excessive as compared with a target reaction rate of 30% and a target molecular weight of 100,000 in a reaction at 200 ° C. for 5 minutes.

(Comparative Example 3)
The same operation as in Example 3 was performed except that the solution catalyst (4) in the dissolution tank CV1 held in a dry air atmosphere was used instead of the solution catalyst (2), but before the steady state was reached (about 30 The reaction temperature of the second reaction device 4 becomes unstable after the elapse of minutes), the discharge amount from the solidification / pulverization device 5 becomes unstable, and the reaction mixture is blocked in the second reaction device 4. Could not continue. The physical properties of the polymer obtained in the discharge part of the second reactor 4 (or the solidification / pulverization device 5) before the operation was stopped fluctuated with a reaction rate of 82 to 96% and a weight average molecular weight of 20 to 220,000. It was not stable.

Table 1 below summarizes the outlines of the above Examples and Comparative Examples.

  According to the results of the above Examples and Comparative Examples, when producing an aliphatic polyester by ring-opening polymerization of a cyclic ester according to the present invention, a tin dichloride catalyst containing tetravalent tin in a proportion of 30 to 70% is obtained. It can be seen that a favorable coexistence of improvement in polymerization activity and stabilization can be obtained.

Claims (10)

An aliphatic polyester obtained by subjecting a cyclic ester to bulk ring-opening polymerization using a tin dichloride catalyst which is in a solution state maintained in an inert gas atmosphere and contains 30 to 70% of tetravalent tin. Manufacturing method. The manufacturing method of Claim 1 using the tin dichloride catalyst melt | dissolved in the organic solvent whose boiling point is 50 degreeC or more . The manufacturing method of Claim 1 using the tin dichloride catalyst melt | dissolved in the liquid initiator. The production method according to claim 3, wherein the liquid initiator is dodecyl alcohol. The production method according to claim 1, wherein the inert gas is nitrogen. The production method according to any one of claims 1 to 5 , wherein ring-opening polymerization is performed by supplying a liquefied cyclic ester mixed with a liquid initiator and a tin dichloride catalyst in advance to a polymerization apparatus. The manufacturing method of Claim 6 which mixes a liquefied cyclic ester, a liquid initiator, and a tin dichloride catalyst in the supply pipe | tube of the liquefied cyclic ester to a superposition | polymerization apparatus. The manufacturing method in any one of Claims 1-7 including the serial continuous superposition | polymerization process of at least 2 steps | paragraphs. The production method according to claim 8 , further comprising a solid phase polymerization step after the at least two stages of serial continuous polymerization step. The production method according to any one of claims 1 to 9 , wherein the cyclic ester is glycolide alone or a mixture of glycolide and lactide containing 70% by weight or more of glycolide.

Images