JP2013082758A - Method for producing biodegradable aliphatic polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a biodegradable aliphatic polyester, which avoids blocking by coalescence of pellets in drying.SOLUTION: The method for producing a biodegradable aliphatic polyester includes: a crystallization step (S03) of heating and crystallizing a pellet 11 of a biodegradable aliphatic polyester that contains remaining monomers and has amorphous parts at a first predetermined temperature; and a drying step (S05) of drying the pellet 11 at a second predetermined temperature higher than the first predetermined temperature, wherein the first predetermined temperature is the glass transition temperature or higher and the melting point -40°C or lower.

Description

  The present invention relates to a method for producing a biodegradable aliphatic polyester, and more particularly to a method for producing a biodegradable aliphatic polyester that avoids blocking due to adhesion between pellets that occurs during drying.

  In the production process of the polyester, after the polymerization reaction, for example, flaky polyester is melt-extruded into a strand shape using a twin screw extruder or the like, and cut into a predetermined size into granular pellets. The pellets contain moisture, and moisture removal by drying is necessary for stable expression of physical properties and quality. Therefore, the pellet is subjected to a drying process. However, depending on the polyester, the pellets may adhere to the inner wall of the dryer during drying, or may cause so-called blocking, in which the pellets firmly adhere to each other and become agglomerated so as to prevent rotation of the rotating blades in the dryer. There is a problem that. This is because the crystallization is slow, and if the polyester has a large proportion of amorphous material, it will block during drying.

  As a conventional technique for avoiding blocking, the polyester granule is efficiently rubbed together, that is, the polyester granule is polished by a scrubbing action to roughen the surface and simultaneously crystallize the inner wall of the dryer. There is an anti-adhesion device that can provide a polyester granule that does not cause adhesion between the polyester granule and adhesion between the polyester granule (Patent Document 1, paragraph 0007).

Japanese Patent No. 2833459

However, resins (biodegradable aliphatic polyesters, etc.) that are susceptible to depolymerization due to thermal decomposition or heat are decomposed products produced by melt extrusion, such as glycolide (GL) and polylactic acid (PLA) in the case of polyglycolic acid (PGA). ) Contains lactide (LA), and in that state, even if heated at a relatively low temperature, blocking occurs due to the influence of GL and LA. This blocking is stronger than ordinary polyesters and has a problem that it cannot be easily crushed by conventional methods. When this blocking occurs, it becomes difficult to separate the pellets without destroying the pellet body.
Therefore, the present invention provides a method for producing a biodegradable aliphatic polyester that avoids blocking due to adhesion of granules (pellets) that occur during drying for a biodegradable aliphatic polyester that is susceptible to thermal decomposition and thermal depolymerization. The purpose is to do.

The method for producing a biodegradable aliphatic polyester according to the first aspect of the present invention for solving the above-described problem includes a remaining monomer, as shown in FIG. 1 (see FIG. 2 as appropriate), and an amorphous part. A crystallization step (S03) of crystallizing the biodegradable aliphatic polyester pellets 11 having a temperature at a first predetermined temperature; and a second step of the pellets 11 being higher than the first predetermined temperature. A drying step (S05) for drying at a predetermined temperature; the first predetermined temperature is not lower than the glass transition temperature and not higher than the melting point −40 ° C.
The “remaining monomer” means a monomer contained in the pellet during the crystallization step, and includes, for example, an unreacted monomer at the time of polymerization and a monomer generated by thermal decomposition or depolymerization by heat. The “glass transition temperature” refers to a temperature at which glass transition starts. “Melting point” refers to the temperature of the melting peak.

  With this configuration, the amorphous portion of the pellet is crystallized at the first predetermined temperature by the crystallization step. Since pellet crystallization proceeds to some extent in this way, blocking due to adhesion between pellets can be avoided even if heating and drying are performed in the subsequent manufacturing process. That is, in the heating / drying process, the pellets do not become a tightly bonded lump, and problems such as impeding the rotation of the rotating blades of the dryer can be avoided.

The method for producing a biodegradable aliphatic polyester according to the second aspect of the present invention is the same as the method for producing a biodegradable aliphatic polyester according to the first aspect of the present invention, as shown in FIG. A crushing step (S04) is provided between the crystallization step (S03) and the drying step (S05) to crush the adhesion between the pellets generated in the crystallization step (S03).
“Crushing” means separating pellets without destroying the pellet body.

  If comprised in this way, some adhesion produced between pellets in the crystallization process can be disintegrated. Crushing at this stage is easy, and the efficiency in the subsequent drying step and heat treatment step can be increased by crushing.

The biodegradable aliphatic polyester production method according to the third aspect of the present invention is the biodegradable aliphatic polyester production method according to the first or second aspect of the present invention as shown in FIG. In addition, before the crystallization step (S03), a step (S02) of thinly laying the pellets in a container so as not to apply its own weight is provided.
Note that “thin so as not to apply its own weight” means not only the thickness of the pellet that does not apply its own weight but also the degree to which the pellet can be separated without destroying the pellet body after heating the pellet at the first predetermined temperature. Including the thinness that is subject to its own weight (load).

  If comprised in this way, since the pellet hardened | cured by adhesion | attachment in the case of crystallization becomes a shape when laid in a container, adhesion | attachment can be disintegrated easily. In addition, since the crushing simply makes the lump of pellets in a spread form fine, the waste of material (loss) does not occur due to the pellets being shaved or the like.

  The method for producing a biodegradable aliphatic polyester according to the fourth aspect of the present invention includes the drying step in the method for producing the biodegradable aliphatic polyester according to any one of the first to third aspects of the present invention. By (S05), the water content of the pellet is set to 100 ppm or less.

  If comprised in this way, the hydrolysis which arises when heat | fever is applied at the time of a process can be suppressed.

  The method for producing a biodegradable aliphatic polyester according to the fifth aspect of the present invention is the method for producing a biodegradable aliphatic polyester according to any one of the first to fourth aspects of the present invention. The biodegradable aliphatic polyester is a medical PGA resin or PGLLA resin.

  If comprised in this way, the blocking by the adhesion | attachment of the pellets which arise at the time of drying will be avoided, and manufacture of a medical PGA resin or PGLLA resin will be attained.

  The biodegradable aliphatic polyester production method according to the sixth aspect of the present invention is the biodegradable aliphatic polyester production method according to the fifth aspect of the present invention, wherein the resin is used as a suture. is there.

  If comprised in this way, in the manufacturing method of this application, since biodegradable aliphatic polyester is not shaved, all the materials can be utilized as a suture thread. In addition, with the technique of avoiding blocking by cutting the surface of the pellet or the like, the material (loss) that has been cut and separated cannot be reused for medical purposes, particularly for sutures.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of biodegradable aliphatic polyester which can avoid easily the blocking which pellets adhere firmly by heating at the time of drying etc. can be obtained.

It is a flowchart which shows the manufacturing method of the biodegradable aliphatic polyester which concerns on the 1st Embodiment of this invention. (A) is a figure and (b) is a figure explaining the bat which spreads a pellet. It is a figure explaining the heating apparatus used at a crystallization process. It is a figure explaining the flow of the air for drying of a heating apparatus. It is a figure which shows the table | surface regarding the measured value of Examples 1-2. It is a figure which shows the table | surface regarding the measured value of Examples 3-6.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same or similar reference numerals, and redundant description is omitted. Further, the present invention is not limited to the following embodiment.

In general, a biodegradable aliphatic polyester is molded into a pellet after polymerization, melt extrusion, cutting and the like. Then, it heats for drying, heat processing, etc. However, when heated for drying, heat treatment or the like, blocking occurs where the surfaces of the pellets firmly adhere to each other to form a lump.
In particular, a resin that easily undergoes thermal decomposition or thermal depolymerization, such as a biodegradable aliphatic polyester, generates a decomposition product during extrusion, and even when a resin containing such a decomposition product is heated at a relatively low temperature, Blocking occurs under the influence of decomposition products. This blocking is stronger than ordinary polyesters and cannot be easily crushed by conventional methods.
The present inventor lays the pellet in a thin plate shape so as not to apply its own weight, and when the pellet is heated at a predetermined temperature, the formed pellet thin plate can be easily crushed, and further, at least the surface of the pellet is crystallized by heating. As a result, it was found that blocking during subsequent drying and the like can be prevented by crystallization of the surface, and the present invention has been completed.

  With reference to the flowchart of FIG. 1, the manufacturing method of the biodegradable aliphatic polyester which concerns on the 1st Embodiment of this invention is demonstrated. It demonstrates using PGLLA as biodegradable aliphatic polyester. PGLLA is a polymer material used for barrier materials for sutures and PET bottles, and is a copolymer of polyglycolic acid (PGA) and poly L-lactic acid (PLLA). PGLLA is produced by mixing glycolide (GL) and L-lactide (LA) at a predetermined ratio and polymerizing them, and as a result, PGLLA, which is a copolymer of PGA and PLLA, is obtained. In addition, although demonstrated here using PLLA among polylactic acids, you may use poly D-lactic acid (PDLA). Moreover, as biodegradable aliphatic polyester, PGA or PLLA may be used instead of PGLLA, or a mixture of at least two of these may be used.

  The biodegradable aliphatic polyester constituting the biodegradable aliphatic polyester pellets includes glycolic acid and glycolic acid containing glycolide (GL), which is a bimolecular cyclic ester of glycolic acid, lactic acid, and bimolecular cyclic of lactic acid. Lactic acid containing lactide which is an ester, ethylene oxalate (ie, 1,4-dioxane-2,3-dione), lactones (for example, β-propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, δ -Valerolactone, β-methyl-δ-valerolactone, ε-caprolactone, etc.), carbonates (eg, trimethylene carbonate, etc.), ethers (eg, 1,3-dioxane, etc.), ether esters (eg, dioxanone, etc.) , Cyclic monomers such as amides (ε caprolactam, etc.) -Hydroxycarboxylic acid such as 3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 6-hydroxycaproic acid, or an alkyl ester thereof; Aliphatic diol such as ethylene glycol or 1,4-butanediol And a substantially equimolar mixture of carboxylic acid such as succinic acid and adipylic acid or an alkyl ester thereof; homo- or copolymers of aliphatic ester monomers such as Among them, the formula: (—O—CH (R) —C (O) —) [R is a hydrogen atom or a methyl group. ] The biodegradable aliphatic polyester which has 70 mass% or more of the glycolic acid or lactic acid repeating unit represented by these is preferable, and those single, in the case of 2 or more types, a copolymer, Furthermore, the partially modified thing is also included. Specifically, PLA, that is, a homopolymer of L-lactic acid, a homopolymer of D-lactic acid, a copolymer having 70% by mass or more of a repeating unit of L-lactic acid or D-lactic acid, a mixture thereof, etc. Alternatively, PGA, that is, a homopolymer of glycolic acid, a copolymer having a glycolic acid repeating unit of 70% by mass or more, and a mixture of PLA and PGA are preferable. Particularly preferred are PGA, PLA, polycaprolactone, trimethylene carbonate, polydioxane or a copolymer of at least two of these from the viewpoints of decomposability, heat resistance and mechanical strength.

PGA particularly preferably used as a raw material for biodegradable aliphatic polyester pellets is a homopolymer of glycolic acid composed of glycolic acid repeating units represented by the formula: (—O—CH ₂ —C (O) —) In addition to (including a ring-opening polymer of glycolide (GL), which is a bimolecular cyclic ester of glycolic acid), a PGA copolymer containing 70% by mass or more of the glycolic acid repeating unit is included.

  The glycolic acid repeating unit in the PGA used as a raw material of the PGA pellet is 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more.

  PGA used as a raw material of PGA pellets is preferably PGA obtained by polymerizing 70 to 100% by mass of glycolide and 30 to 0% by mass of the other comonomer in order to efficiently produce a desired polymer. .

  In the method for producing a biodegradable aliphatic polyester, first, as shown in FIG. 1, PGLLA pellets as a biodegradable aliphatic polyester are produced (S01). The pellet manufacturing step (S01) includes a polymerization step (S11) and a pelletizing (extrusion) step (S12). The composition ratio of PGA and PLLA in the polymerization step (S11) varies depending on the polymerization conditions, that is, the apparatus used, polymerization temperature, polymerization time, raw material purity, and the like. Finally, it is preferable to carry out the polymerization so that the composition ratio of the copolymer of PGA and PLLA after polymerization is 70:30 to 100: 0% by mass. More preferably, it is 80: 20-99: 1 mass%, Most preferably, it is 85: 15-95: 5 mass%. As the polymerization method, a known method can be used.

  In the pelletizing (extrusion) step (S12), for example, a melt extrusion molding machine is used to form a strand, which is cut to obtain PGLLA granular pellets. As for the size of the pellet, the diameter d and the length l (see FIG. 2A) are, for example, 1 to 5 mm, preferably 2 to 4 mm, and more preferably 2.5 to 3 mm. The diameter d and the length l may be the same or different.

  As an example, a case where pellets of biodegradable aliphatic polyester are produced by bulk polymerization (S01) will be described. In bulk polymerization, raw materials glycolide (GL) and L-lactide (LA), initiator alcohol and catalyst are put in a dissolution tank and heated to dissolve. This solution is poured into a polymerization tank having a cylindrical hole and then polymerized by heating for a certain period of time. Thereafter, the polymerization tank is cooled, and a round bar polymer polymerized from each hole is extracted and pulverized to obtain a polymer pulverized product. This is melted and mixed with an extruder, then formed on a strand and cut with a pelletizer to obtain pellets. By forming with an extruder, problems such as (1) a pulverized product is not uniform in shape and (2) physical properties are not uniform. That is, it is melted and mixed by applying heat to make the shape and physical properties uniform as pellets.

  In the pelletizing step (S12), the molten PGLLA is extruded into a strand and rapidly cooled to room temperature. PGLLA is slow to crystallize, and as a result, after normal extrusion as described above, the PGLLA pellets are in a transparent amorphous state. As shown in FIG. 2B, the transparent pellets are thinly spread and spread over the entire surface of the flat bottom bat 21 as a container so as not to be subjected to its own weight (or weight) (S02), and the pellets 11 are arranged in a thin plate shape. The pellet 11 and the bat 21 will be described in detail later. It should be noted that “transparent” may be transparent regardless of being colorless or colored.

The bat 21 on which the pellets 11 are spread is heated at a first predetermined temperature lower than the temperature in the subsequent drying step (S05) to be crystallized (S03). The pellets before the crystallization step (S03) contain unreacted monomers at the time of polymerization, monomers generated by thermal decomposition or thermal depolymerization, and low molecular weight substances. Due to the influence of these monomers, blocking due to adhesion of pellets becomes stronger. Therefore, the crystallization step (S03) is performed before the drying step (S05) to promote crystallization of the pellets.
In addition, the effect of the manufacturing method of this application becomes higher that the quantity of the monomer which remain | survives in a pellet is 0.5 to 2 weight% with respect to a polymer. The “amount of remaining monomer” is the total amount of monomers constituting the homopolymer, and the total amount of the plurality of monomers constituting the copolymer.

  The first predetermined temperature in the crystallization step (S03) is a glass transition temperature or higher and a melting point −40 ° C. or lower, preferably a glass transition temperature + 10 ° C. or higher, a melting point −50 ° C. or lower, more preferably a glass transition temperature + 20 ° C. or higher. The melting point is −60 ° C. or lower. If the temperature is lower than the glass transition temperature, crystallization does not proceed, and if the melting point exceeds −40 ° C., there is a risk of melting if the temperature is not sufficiently controlled. Although heating time is based also on heating temperature or the thickness to spread, for example, when heating temperature is 80 degreeC, it is 1-2 hours. If the heating temperature is relatively low, the heating time is long, and if the heating temperature is relatively high, the heating time is short. For example, in the case of 50-60 degreeC, it is 5 to 10 hours, and in the case of 100 degreeC, it is 0.5 to 1.5 hours.

  As described above, the first predetermined temperature is preferably a melting point of −40 ° C. or lower. The higher the heating temperature, the easier the crystallization proceeds. However, the pellets just manufactured in the pellet manufacturing process (S01) adsorb a considerable amount of moisture. If the temperature exceeds the melting point of −40 ° C. in the presence of a large amount of moisture, the polymer is easily hydrolyzed by moisture, and the polymer is cut. For example, in the case of a suture thread, the cutting of the polymer causes a decrease in the strength of the thread. In addition, crystallization hardly proceeds at a temperature lower than the glass transition temperature. Even at the glass transition temperature or higher, the heating time tends to be longer than 2 hours at a relatively low temperature. For example, in the case of PGLLA having a melting point of 200 ° C., the first predetermined temperature is preferably the glass transition temperature or higher and the melting point 200 ° C.−40 ° C. = 160 ° C. or lower.

The heating time is sufficient to heat the pellet 11 at the first predetermined temperature and crystallize the pellet 11 to such an extent that the white turbidity of the surface of the pellet 11 can be visually confirmed. In the crystallization step (S03), the operator may cut the time while actually confirming the crystallinity by visual observation. However, in order to perform crystallization efficiently, it is preferable to experimentally determine the heating time and terminate the crystallization step (S03) when that time is reached. It is advisable to inform the operator of the passage of time with a timer. Alternatively, a heating device (such as a dryer described later) used for heating may be stopped by a timer.
Note that “white turbidity” refers to garlic appearing on the pellet surface due to crystallization of biodegradable aliphatic polyester. That is, it is not limited to the case of being completely white, but also includes the case where there is a slight coloration.

It is preferable to flow a dry gas, typically a gas such as air or nitrogen, in the heating apparatus used for heating. The term “dried” as used herein refers to a state in which the humidity of the gas can move the pellets in the drying direction by flowing them. A state where at least the water content is not increased.
By heating the pellet, moisture contained in PGLLA is discharged as vapor. PGA contained in PGLLA is very easy to absorb moisture, but by flowing air or the like, PGLLA can be prevented from being steamed with steam and starting to hydrolyze.
Note that “flowing” refers to circulating the gas inside the heating device in one embodiment. For example, you may blow in the dry air previously heated to preset temperature with the heating machine. A circulation system in which dry air heated to 80 ° C. is blown into a shelf dryer set at a set temperature (for example, 80 ° C.), air containing moisture from the discharge port is dehumidified and then returned again is preferable.
Alternatively, a vacuum dryer or a shelf dryer may be used to blow dry air at room temperature into the dryer and discharge it in one pass without circulation. Since air at room temperature is introduced, the temperature in the dryer decreases, but the dryer temperature is set to a higher value (for example, 100 ° C.) in anticipation of this. When room temperature air is put into this set dryer, the internal temperature becomes low (for example, about 80 ° C.), and the inner wall temperature is 100 ° C. It is preferable to put a thermometer in the dryer for checking the internal temperature so that the internal temperature is about 80 ° C. Since air is not circulated, it is possible to avoid steaming PGLLA with evaporated water.

  Due to the heating, the crystallization of the PGLLA pellets is accelerated and the surface becomes cloudy. Further, the pellets are adhered to each other to some extent, and the pellets are formed into a single thin plate-like lump that is in a state of being laid on a bat. The term “adhesion to some extent” refers to adhesion to the extent that the pellets can be crushed, that is, adhesion to the extent that the pellets can be separated without destroying the pellet body in the crushing step (S04).

  The thin plate-shaped pellet is crushed (S04). Since the heating temperature in the crystallization process is relatively low as described above, hydrolysis of the pellet can be prevented. Furthermore, since the pellets are laid down so as not to have their own weight, the adhesion between the pellets is weak and can be easily crushed. For crushing, for example, it is broken by hand, and the size is reduced to a certain level by loosening. Ideally, separate the pellets one by one. In addition, it is preferable to make the pellet into a thin plate shape because it can be easily crushed.

The crushed pellets are dried at a second predetermined temperature higher than the first predetermined temperature using a dryer (S05). In the case of PGLLA, the second predetermined temperature is 80 ° C. or higher and 150 ° C. or lower. Preferably they are 100 degreeC or more and 140 degrees C or less, More preferably, they are 110 degreeC or more and 130 degrees C or less. Typically 120 ° C. The moisture contained in PGLLA is discharged by the drying process. The drying time is 1-2 hours at 120 ° C.
In addition, it is preferable to make the moisture content of a pellet into 100 ppm or less by a drying process (S05), More preferably, it is 50 ppm or less, More preferably, it is 30 ppm or less. When the water content is high, hydrolysis occurs when heat is applied during processing. Therefore, as the water content is lower, for example, a constant strength can be expressed without changing the spinning condition of the suture, and decomposition (= decrease in strength) during molding (spinning) can be avoided. When the water content is at least 100 ppm or more, if it is used as it is in the molding process, hydrolysis occurs, which may cause quality deterioration of the obtained molded product and trouble in molding operation.

The drying step may be performed by a later-described dryer used in the crystallization step, or may be performed separately by a dryer dedicated to the drying step. However, in the drying process, the dry air or nitrogen gas in the dryer may be circulated in the presence of a dehumidifier. Typically, dry air or nitrogen is used to remove air containing moisture in the dryer. It is preferable to discharge out of the dryer.
Note that a conical ribbon mixing dryer or the like may be used as the dryer. It is preferable to use an apparatus for drying and drying the drying chamber while drying and heat treatment described later, since the crushed pellets can be further finely separated.

After drying, the pellets are heat-treated at a third predetermined temperature higher than the second predetermined temperature (S06). For PGLLA, the third predetermined temperature is typically 170 ° C. The heat treatment time is typically 17 hours at 170 ° C.
Impurities (low molecular compounds such as remaining monomers and oligomers) contained in PGLLA are removed by heat treatment. That is, it is removed. Crystallization is completed in the heat treatment step.
The heat treatment step (S06) may be performed by a later-described dryer used in the crystallization step, or may be performed by a separate heating apparatus dedicated to the heat treatment step.

  The pellets for which the heat treatment process has been completed are filled into a shipping storage container, and the storage container is packed (S07). Thereafter, it is shipped (S08). The shipped pellets are processed into high value-added products such as sutures used in surgery.

In addition, it is preferable that the container which spreads a pellet is a flat bottom. However, the container is not limited to a flat bottom as long as it is a container in which the adhered pellets can be arranged thinly enough to break up. Similarly, the shape of the container is not particularly limited, such as a quadrangle and a circle. Further, as long as the adhered pellets can be crushed, the shape is not limited to a thin plate shape, and may be, for example, a lump having a plurality of cavities inside. That is, the shape of the pellets adhered in the crystallization process may be any shape that can be easily crushed.
In addition, the preferred thickness when the pellets are spread varies depending on the size of the pellets, but the thickness may be any thickness as long as a thin plate of pellets composed of weak adhesions can be easily crushed.

With reference to FIG. 2, a bat as an example of a pellet and a container in which the pellet is spread will be described. As shown in FIG. 2A, a typical PGLLA pellet 11 is formed in a small cylindrical shape, and both the diameter d and the length l (el) are 2.5 to 3.0 mm. Such pellets 11 are spread on the bat 21 as shown in FIG. In FIG. 2 (b), the bat 21 is shown partially broken. It is preferable that the thickness h spread on the bat 21 is a thickness that does not apply its own weight. For example, one layer is preferable, but two or more layers may be used from the viewpoint of productivity. For example, 2.5 mm or more, 5 mm or more, or 7 mm or more. Here, since the bottom of the bat 21 is a flat surface, the pellets 11 can be uniformly spread and spread thinly by placing the bat 21 so that the flat surface is horizontal. The thickness h of the thin plate at this time is, for example, 30 mm or less, and more preferably 15 mm or less. If it is 30 mm, the amount of production can be increased compared to 15 mm. If it is 15 mm or less, even if the pellets 11 are adhered, the thin plate can be crushed more easily. In addition, the minimum value of the thickness h is the size of one pellet, and the maximum value is 12 pellets or less as a guide, but it may be larger if it can be crushed. In addition, even if it is a pellet of the same magnitude | size, the pellet made from the material of lower density can make thickness h of a thin plate thicker.
The material of the bat may be anything as long as it has heat resistance and does not react with the pellets. However, Teflon (registered trademark) is preferable for a synthetic resin material, and austenitic stainless steel is preferable for a metal material.

  The dryer 26, which is a storage chamber for performing crystallization, will be described with reference to the illustration of the dryer in FIG. A shelf on which a plurality of bats 21 can be placed is provided in a dryer 26 which is a shelf dryer. The figure shows the case of four stages. The illustration of the door of the dryer 26 is omitted. Dryer 26 is supplied with dry air. The air flows so as to uniformly hit the plurality of bats 21 placed on the shelf.

  The relationship between the dryer 26 and the flow of dry air will be described with reference to the diagram showing the flow of dry air in FIG. Dry air is sent to the heat exchanger 28 by a fan 27 for flowing dry air to the dryer 26. The heating source of the heat exchanger 28 is an electric heater that is easy to turn on and off and has good operability. A gas heater may be used instead of the electric heater. The dry air 29 heated by the heat exchanger 28 is supplied to the dryer 26. The dried air after flowing around the bat 21 and heating the pellets 11 placed inside to advance the crystallization is slightly lowered in temperature and slightly raised in humidity and discharged outside the dryer 26. . Since the discharged dry air is still at a high temperature, heat exchange with the supplied dry air and the heat exchanger 30 has an advantage in terms of energy saving. When air supplied in this way is used as dry air and the used dry air is discarded, the pellets are not steamed by moisture evaporated from the pellets, and the decomposition of the polymer constituting the pellets can be suppressed. Therefore, it is preferable.

  As described above, in the crystallization step (S03), the heating time is visually monitored from the transparent heat-resistant glass viewing window provided on the door of the dryer, and the operator actually monitors the turbidity of the pellet 11 surface. Crystallization may be terminated while checking the degree. However, it is efficient and preferable to experimentally determine the heating time and complete the crystallization process at that time. It is advisable to inform the operator of the passage of time with a timer. Alternatively, the dryer is stopped by a timer. Turn off the heater when the dryer is stopped. At the same time or waiting for cooling inside the dryer, the blower fan may be stopped.

  In another embodiment, a dehumidifier that removes moisture in the dry air may be provided separately so that the dry air circulates in the dryer 26 (not shown). At this time, heat dissipation is small, so the energy saving effect is high.

  In the above embodiment, although the case where dry air was used was demonstrated, nitrogen gas may be sufficient. Since nitrogen gas is inert, it is preferable for maintaining the quality of the pellets 11. When nitrogen gas is used, it is preferable to provide a dehumidifier for removing moisture in the nitrogen gas so that the nitrogen gas circulates in the dryer 26. Since the heat exchanger 28 (see FIG. 4) heats the circulating nitrogen gas, the amount of heating is sufficient for heat radiation from the outer wall and conduit of the dryer 26 and heating of the pellets (including moisture).

As described above, the biodegradable aliphatic polyester production method of the present application includes a crystallization process in which pellets are spread in a thin plate shape and heated as a pretreatment for the drying process.
In addition, in the manufacturing method of normal biodegradable aliphatic polyester, it is necessary to dry the pellet by the drying step (S05) after the step of manufacturing the pellet (S01), but when the pellet is transferred to the drying step as it is, Due to the heating during drying, the pellets are blocked in the dryer, and the pellets are firmly bonded to form a lump or firmly attached to the inner wall of the dryer.
However, in the method for producing a biodegradable aliphatic polyester of the present application, as a pretreatment of the drying process, each process of a thin laying process (S02), a crystallization process (S03), and a crushing process (S04) so as not to apply its own weight. Is provided. Therefore, the pellet is heated at a predetermined temperature before being put into the dryer, and the pellet is crystallized to some extent. At the same time, in order to cope with the slight adhesion between the pellets caused by heating, the pellets are fused so as to have a shape that can be easily crushed. By these steps, blocking in the drying step which is a subsequent step is prevented. Thus, by providing each process of S02-S04, it becomes the manufacturing method of biodegradable aliphatic polyester which prevents blocking easily.
Moreover, in the conventional adhesion prevention apparatus as shown in patent document 1, since the polyester granule is grind | polished by a scorching action, powder generate | occur | produces from a polyester granule. For this reason, a separator for separating the powder is required, and at the same time, waste (loss) occurs in the polyester granular material (material). However, in the method for producing a biodegradable aliphatic polyester of the present application, since the biodegradable aliphatic polyester is not scraped, all of the material can be used as a product without causing material loss. In particular, since the biodegradable resin used for the suture thread such as PGLLA cannot reuse the scraped material, the manufacturing method of the present application that does not waste the material is beneficial. Thus, it is preferable that the resin used for the medical suture is manufactured using the biodegradable aliphatic polyester manufacturing method of the present application, because no material is wasted.

  Examples 1 to 6 will be described. In Examples 1 to 6, the amorphous PGLLA resin (transparent) was subjected to the step shown in FIG. 1 (S02), the crystallization step (S03), and the crushing step (S04). A drying step (S05) and a heat treatment step (S06) were performed.

[Examples 1-2]
Each condition of Examples 1-2 is shown.
Resin used: Amorphous pellets (PGLLA, diameter approximately 2.5 mm, length approximately 2.5 mm)
Resin composition: PGA: PGLLA = 90: 10% by mass
Residual monomer amount: GL; 0.73% by weight, LA; 0.92% by weight
Heating time in the crystallization step (S03): 80 ° C., 2 hours Heating time in the drying step (S05): 120 ° C., 1 hour Heating time in the heat treatment step (S06): 170 ° C., 17 hours Air injection: Air volume, 300L / min
・ Heater: Hot air circulation dryer ・ Container: Vat (SUS, approximately 42cm in length × approximately 20cm in width)
Using a vacuum dryer, room-temperature dry air was blown at an air volume of 300 L / min to crystallize under the above conditions (S03). Then, after crushing (S04), the pellet was transferred to a glass small bottle, and dried (S05) and heat-treated (S06) using a hot-air circulating dryer blown with nitrogen. The set values for the vacuum dryer were 105 ° C. (internal temperature was 80 ° C.), and the set values for the hot-air circulating dryer were 120 ° C. and 170 ° C., respectively.

The measured value about Examples 1-2 is shown in the table | surface of FIG.
“Thickness” is the thickness of the pellet when the bat is laid with pellets.
“Air injection” indicates whether or not heating was performed while injecting dry Air in the crystallization step (S03).
“MV” indicates the melt viscosity of the pellets after the heat treatment step (S06). The melt viscosity correlates with the molecular weight, and the lower the value, the more the polymer is decomposed. That is, it can be said that it is an index indicating how much higher the molecule is. The numerical values in FIG. 5 are melt viscosities measured at 240 ° C. and a shear rate of 122 sec ⁻¹ .
“Moisture” indicates the amount of water contained in the pellets after the heat treatment step (S06).
“Crushing” indicates whether or not the thin plate-like pellets after the crystallization step (S03) could be crushed by hand. “◯” indicates that it could be finely crushed by hand. “X” indicates that it could not be finely crushed.
“Adhesion” indicates whether blocking has occurred in the drying step (S05) or the heat treatment step (S06). “O” indicates that it occurred. “X” indicates that it did not occur.

[Measuring method of melt viscosity]
The melt viscosity of PGLLA was measured using a 140-SAS2002 semiautocapillary rheometer manufactured by Yasuda Seiki Seisakusho with a die (1 mmΦ × 10 mmL) as a melt viscosity measuring device. More specifically, about 8.2 g of a pellet sample was introduced into a measuring apparatus heated to 240 ° C., held at 240 ° C. for 5 minutes, and then melt viscosity was measured at a shear rate of 122 sec ⁻¹ .

[Measurement method of water content]
The pellet content was measured using a Karl Fischer moisture meter with a vaporizer [CA-100 manufactured by Mitsubishi Chemical Corporation; attached vaporizer VA-100]. Specifically, after wiping off moisture adhering to the wet polymer surface, about 2 g of pellet sample precisely weighed was placed in a vaporizer heated to a temperature of 220 ° C. Dry nitrogen gas was allowed to flow from the vaporizer to the Karl Fischer moisture meter. After the approximate polymer sample was put into the vaporizer, the water vaporized from the approximate polymer sample was introduced into the Karl Fischer liquid in the Karl Fischer moisture measuring device in association with the dry nitrogen gas. The end point was determined when the electric conductivity of the Karl Fischer liquid decreased to +0.1 μg / S from the background by the coulometric titration method.

[Measurement method of GL and LA content]
To about 100 mg of sample PGLLA, 2 ml of dimethyl sulfoxide containing the internal standard substance 4-chlorobenzophenone at a concentration of 0.2 g / l was added, dissolved by heating at 150 ° C. for about 5 minutes, cooled to room temperature, and then 6 ml of acetone was added. In addition, filtration is performed. 1 μl of the solution was sampled and injected into a gas chromatography (GC) apparatus for measurement. From the numerical value obtained by this measurement, the amount of GL or the amount of LA was calculated as the weight percentage contained in the polymer. The GC analysis conditions are as follows.
・ Equipment: Shimadzu GC-2010
Column: TC-17 (0.25mmΦ × 30m)
Column temperature: held at 150 ° C. for 5 minutes, then heated to 270 ° C. at 20 ° C./minute and held at 270 ° C. for 3 minutes. Vaporization chamber temperature: 180 ° C.
Detector: FID (hydrogen flame ionization detector), temperature: 300 ° C

  As shown in the table of FIG. 5, the 20 mm thick pellet thin plates of Examples 1 and 2 could be easily crushed by hand. Moreover, since the pellet surface was crystallized, blocking did not occur in the subsequent drying step and heat treatment step. As shown by the MV value in Example 2, it is preferable to perform crystallization while injecting Air since the decomposition of the polymer can be suppressed.

[Examples 3 to 6]
Each condition of Examples 3-6 is shown.
-Resin used: Amorphous pellets (PGLLA, diameter: about 2.5 mm, length: about 2.5 mm)
Resin composition: PGA: PGLLA = 90: 10% by mass
Residual monomer amount: GL; 0.87% by weight, LA; 1.01% by weight
Heating time in the crystallization step (S03): 80 ° C., 2 hours Heating time in the drying step (S05): 120 ° C., 1 hour Heating time in the heat treatment step (S06): 170 ° C., 17 hours Air injection: Air volume, 300L / min
-Heater: Hot air circulation dryer-Container: Vat (SUS, stainless steel, length approx. 42 cm x width approx. 20 cm)
Using a vacuum dryer, room-temperature dry air was blown at an air volume of 300 L / min to crystallize under the above conditions (S03). Then, after crushing (S04), the pellet was transferred to a glass small bottle, and dried (S05) and heat-treated (S06) using a hot-air circulating dryer blown with nitrogen. The set values for the vacuum dryer were 105 ° C. (internal temperature was 80 ° C.), and the set values for the hot-air circulating dryer were 120 ° C. and 170 ° C., respectively.

The measured value about Examples 3-6 is shown in the table | surface of FIG.
“Container” indicates the material of the bat used. Other items are the same as those in FIG.

  As shown in the table of FIG. 6, when the thickness of the thin plate-like pellets of Examples 3 to 5 was 15 mm to 30 mm, the thin plate of pellets could be easily crushed by hand. In addition, in the case of 30 mm, although some force was required for crushing compared with other thickness, it was able to crush enough. Moreover, since the pellet surface was crystallized, blocking did not occur in the subsequent drying step and heat treatment step. Further, as shown in Examples 3 and 6, even when the material of the container was different, the pellet thin plate could be easily crushed by hand, and no blocking occurred in the subsequent drying step and heat treatment step.

11 Pellet 21 Container, vat 26 Dryer 27 Fan
28 heat exchanger 29 air 30 heat exchanger

Claims (6)

A crystallization step of crystallizing the biodegradable aliphatic polyester pellets containing the remaining monomer and having an amorphous portion by heating at a first predetermined temperature;
Drying the pellet at a second predetermined temperature higher than the first predetermined temperature;
The first predetermined temperature is a glass transition temperature or higher and a melting point of −40 ° C. or lower.
A method for producing a biodegradable aliphatic polyester. A crushing step of crushing the adhesion between the pellets generated in the crystallization step between the crystallization step and the drying step;
The manufacturing method of the biodegradable aliphatic polyester of Claim 1. Prior to the crystallization step, comprising a step of thinly laying the pellet in a container so as not to apply its own weight;
The manufacturing method of the biodegradable aliphatic polyester of Claim 1 or Claim 2. By the drying step, the moisture content of the pellets is set to 100 ppm or less.
The method for producing a biodegradable aliphatic polyester according to any one of claims 1 to 3. The biodegradable aliphatic polyester is a medical PGA resin or PGLLA resin.
The manufacturing method of the biodegradable aliphatic polyester of any one of Claim 1 thru | or 4. The use of the resin is a suture,
The manufacturing method of the biodegradable aliphatic polyester of Claim 5.

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