JP4855844B2 - Polymer polymerization method and polymer polymerization apparatus - Google Patents

Description

  The present invention relates to a polymer polymerization method and a polymer polymerization apparatus for synthesizing a polymer from hydroxycarboxylic acid or an oligomer thereof, which is a polymer raw material in a molten state.

  In the synthesis of polymers synthesized by ring-opening polymerization reaction, degradation of quality such as partial thermal decomposition and coloration of the polymer becomes a problem due to prolonged temperature history and accumulation of reaction heat accompanying polymerization. There is.

  Polylactic acid, which is one of the polymers synthesized by ring-opening polymerization reaction, is a colorless and transparent polyester made from lactic acid, which is one of hydroxycarboxylic acids. One method for synthesizing polylactic acid from lactic acid is as follows. Lactic acid is condensed to form an oligomer, and a catalyst such as antimony oxide is added thereto to depolymerize to produce lactide (a dimer of lactic acid), which is a cyclic condensate. There is a method of ring-opening polymerization by adding a catalyst such as the above.

  Even in this case, during the ring-opening polymerization, the polylactic acid may be partly thermally decomposed and colored due to the temperature rise accompanying the heat of reaction. Since this coloration impairs the colorless transparency which is one of the characteristics of polylactic acid, it is desired to suppress it. The same applies to polyglycolic acid synthesized by ring-opening polymerization of glycolide, which is a cyclic dimer of glycolic acid.

  For this reason, in the invention described in Patent Document 1, a plurality of reaction tanks for ring-opening polymerization of lactide are prepared, and a continuous system in which these are connected in series to simultaneously supply a raw material and discharge a polymer is used. Adopted. And it is trying to reduce the thermal decomposition by a temperature history by changing and operating the temperature, catalyst amount, and residence time in each reaction tank. However, in this method, the following factors that increase coloring are not solved. (1) Longer temperature history due to dispersion of residence time due to mixing of a polymer having a low polymerization degree and viscosity and a polymer having a high polymerization degree and viscosity, and (2) ring-opening polymerization. There is a problem of acceleration of thermal decomposition accompanying accumulating reaction heat.

JP-A-8-259676

  An object of the present invention is to provide a polymerization method and a polymerization apparatus capable of synthesizing a high-quality polymer when synthesizing a polymer from a raw material in a molten state.

  The present invention relates to a method for producing a polymer by ring-opening polymerization of a cyclic condensate of hydroxycarboxylic acid as a raw material, and the raw material melt is added to the intermediate polymer in the reaction vessel and stirred. The present invention provides a polymer polymerization method characterized in that the polymerization reaction is advanced while mixing.

  In the present invention, the intermediate polymer is a product obtained by advancing the polymerization reaction of the raw material compound to some extent, and is neither an unreacted product nor a final polymer. However, since the polymerization partially proceeds, the molecular weight is larger than that of the raw material, and the viscosity of the polymerization reaction product is also increased. In the case of a polymerization apparatus using three or more reaction vessels, the polymer in the intermediate reaction vessel other than the first reaction vessel and the final reaction vessel corresponds.

  The present invention also relates to a polymer polymerization apparatus using a cyclic condensate of hydroxycarboxylic acid as a raw material, the polymerization apparatus comprising three or more reaction tanks connected in series, the first stage and the final stage. And a means for adding the raw material to an intermediate polymer in one or more intermediate reaction tanks excluding a stage reaction tank, and the reaction tank includes a stirring device. Is.

  According to the present invention, it is possible to synthesize a high-quality polymer of hydroxycarboxylic acid without quality deterioration.

  A more specific embodiment of the present invention is as follows.

  First, the raw material melt to be added is preferably kept at a temperature higher than the melting point of the raw material and lower than the temperature of the added intermediate polymer. In addition, this is a method of continuously producing a polymer by using a cyclic condensate of hydroxycarboxylic acid as a raw material and performing a ring-opening polymerization reaction in at least three stages. It is desirable that the raw material melt is added to the intermediate stage polymer between the first stage and the final stage, and the polymerization reaction proceeds while stirring and mixing.

  According to the present invention, the above raw materials are added to three or more reaction tanks connected in series and one or more intermediate reaction tanks other than the first and last reaction tanks. A polymer polymerization apparatus comprising means and a stirring device is provided.

  In the polymer polymerization apparatus, it is desirable that the first-stage reaction apparatus has a stirrer installed so that the rotation axis thereof is substantially horizontal. The final-stage reaction apparatus can be a vertical reaction tank having a stirrer installed so that the rotation axis thereof is substantially perpendicular to the horizontal plane.

  It is desirable to have a means for keeping the temperature of the raw material melt to be added higher than the melting point of the raw material and lower than the temperature of the added intermediate polymer.

  A more preferable polymer polymerization apparatus is a polymer polymerization apparatus using a cyclic condensate of hydroxycarboxylic acid as a raw material, and has the following requirements. That is, the polymerization apparatus comprises three or more reaction vessels connected in series, a means for supplying a cyclic condensate of hydroxycarboxylic acid to the reaction vessel, and first and final reaction vessels. And means for adding the raw material to an intermediate polymer in one or more intermediate reaction tanks. The reaction tank includes a stirring device, the intermediate reaction tank excluding the final reaction tank is a horizontal reaction tank having a substantially horizontal stirring rotation axis, and the final reaction tank is substantially vertical. It is a vertical reaction tank having a stirring rotation shaft.

  In the polymer polymerization apparatus, it is desirable to have means for keeping the temperature of the raw material melt to be added higher than the melting point of the raw material and lower than the temperature of the added intermediate polymer. Furthermore, it is desirable that the stirring device of the intermediate reaction tank is a biaxial type. Further, it is desirable that the interval between the stirring blades of the stirring device of the intermediate reaction tank is narrower than the spacing of the stirring blades of the stirring device of the horizontal reactor in the preceding stage.

  The inner wall surface of the vertical reactor is preferably at least non-smooth in the vertical direction. The stirring device of the vertical reactor is preferably a biaxial type. As described in Japanese Patent Laid-Open No. 6-218260, the horizontal reactor in the preceding stage of the intermediate reaction tank has a plurality of weirs arranged at appropriate intervals in the length direction, and penetrates under the weir. It is desirable to have holes. Moreover, it is desirable that each of the reaction vessels is equipped with a liquid level gauge.

  The present inventors have intensively studied to solve the above problems. As a result, in the initial stage of the reaction, by carrying out the ring-opening polymerization reaction in the stirring device installed so that the rotation axis thereof is substantially horizontal and in the reaction vessel having at least one weir. It was found that mixing of polymers having different polymerization degrees and viscosities can be suppressed.

  Further, it was found that by adding and mixing the raw material melt to the polymer in the intermediate stage, the heat of reaction can be absorbed as the enthalpy of the raw material melt and the temperature rise of the polymer can be suppressed. In the final stage of the reaction, the reaction heat removal efficiency is increased by carrying out a ring-opening polymerization reaction in a reaction vessel having a stirrer installed so that its rotation axis is substantially perpendicular to the horizontal plane. It has been found that the temperature rise can be suppressed. And it discovered that the coloring accompanying thermal decomposition of a polymer can be suppressed by the polymerization method including the process of adding and mixing the raw material melt to the polymer in an intermediate stage. The subject of this invention was able to be solved by performing a ring-opening polymerization reaction in the reaction apparatus which has one intermediate reaction tank in the front | former stage and back | latter stage each, and connected these in series. In addition, the said process can also be performed with at least 1 reaction tank.

  In one embodiment of the present invention, in a reactor for producing a polyester by ring-opening polymerization of a cyclic condensate of hydroxycarboxylic acid, a raw material is converted into a polymer (intermediate polymer) in an intermediate state between the raw material melt and the final polymer. It is characterized by adding the melt and stirring and mixing.

  In another embodiment of the present invention, the raw material melt is added to a polymer in an intermediate state between the raw material melt and the final polymer, and stirring and mixing are performed. The temperature of the raw material melt to be added is higher than the melting point of the raw material and lower than the temperature of the intermediate polymer to be added.

  In another embodiment, the polymer synthesizer comprises the following requirements: That is, it includes three or more reactors connected in series with the reactor, and in one or more intermediate reactors excluding the first and last reactors, the polymer raw material is added to the intermediate product. The polymer synthesizer is characterized in that the polymerization is carried out while being fed and stirred.

  In another embodiment of the present invention, the intermediate compound in one or more reactors, including three or more reactors connected in series, excluding the first and final reactors, is polymerized. The raw material is additionally supplied and a stirring means is provided. Further, the first-stage reaction tank relates to a polymer synthesizing apparatus having a stirrer installed so that its rotation axis is substantially horizontal and a weir installed in the tank.

  Another embodiment includes three or more reactors connected in series, and in one or more reactors excluding the first and last reactors, the polymer raw material is added to the intermediate product. Means for feeding and stirring. The last-stage reaction tank relates to the polymer synthesis apparatus having a stirring device installed so that a rotation axis thereof is substantially perpendicular to a horizontal plane.

  The polymer synthesizing method and apparatus of the present invention are suitably used for a polymerization reaction of a polymer that generates heat of reaction with a polymerization reaction. Such polymers include those produced by ring-opening polymerization reactions or addition polymerization reactions. About the polymer produced | generated by ring-opening polymerization reaction, it uses suitably for the polymer raw material of a cyclic condensate, especially the polymer synthesize | combined by the ring-opening polymerization reaction of a cyclic dimer, especially polyester. For example, polylactic acid, a copolymer containing lactic acid as a main component, polyglycolic acid, a copolymer containing glycolic acid as a main component, and the like can be given.

  The method and apparatus of the present invention are particularly preferably used for the synthesis of polylactic acid by ring-opening polymerization of lactide and polyglycolic acid by ring-opening polymerization of glycolide. Here, lactide used as a raw material for polylactic acid means a cyclic ester produced by dehydrating two molecules of water from two molecules of lactic acid. Polylactic acid means a polymer mainly composed of lactic acid. Poly L-lactic acid homopolymer, poly D-lactic acid homopolymer, poly L / D-lactic acid copolymer, and other ester bond formation on these polylactic acids. For example, it includes a copolymer component such as hydroxycarboxylic acid, lactone, copolymerized polylactic acid obtained by copolymerizing dicarboxylic acid and diol, and a mixture of additives as a secondary component.

  Glycolide means a cyclic ester formed by dehydrating two molecules of water from two molecules of glycolic acid, and polyglycolic acid means a polymer containing glycolic acid as a main component. Other ester bond-forming components such as hydroxycarboxylic acids, lactones, copolymerized polyglycolic acid obtained by copolymerizing dicarboxylic acid and diol, and those obtained by mixing additives as secondary components are included. Examples of hydroxycarboxylic acids other than lactic acid and glycolic acid include hydroxybutylcarboxylic acid and hydroxybenzoic acid. Examples of lactones include butyrolactone and caprolactone, and examples of dicarboxylic acids include aliphatic dicarboxylic acids having 4 to 20 carbon atoms, phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, and the like. Examples of the diol include aliphatic diols having 2 to 20 carbon atoms.

  Polyalkylene ether to oligomers and polymers such as polyethylene glycol, polypropylene glycol, polybutylene ether and the like are also used as copolymerization components. Similarly, oligomers and polymers of polyalkylene carbonate are also used as copolymerization components. Examples of additives include antioxidants, stabilizers, ultraviolet absorbers, pigments, colorants, inorganic particles, various fillers, mold release agents, plasticizers, and the like. The addition ratio of these copolymerization components and additives is arbitrary, but the main component is lactic acid or derived from lactic acid, and the copolymerization components and additives are preferably 50% by weight or less, particularly preferably 30% or less.

  The polymer synthesizing method and apparatus of the present invention are for polymerizing a polymer raw material in a molten state to synthesize a polymer continuously or intermittently. A reaction liquid containing a raw material and a catalyst in a molten state is reacted in the reactor. The polymerization reaction is performed by heating. A raw material means a monomer, a cyclic monomer, a cyclic condensate of a monomer, an oligomer, or the like, which is a component for synthesizing a polymer by a polymerization reaction. In the synthesis of polylactic acid, lactide is used as a raw material, a reaction liquid containing raw material lactide and a catalyst in a molten state is heated in a reaction apparatus, and lactide is polymerized in a molten state by performing a ring-opening polymerization reaction of lactide. To synthesize polylactic acid continuously or intermittently. In the synthesis of polyglycolic acid, glycolide is used as a raw material. The reaction solution containing the raw material glycolide and catalyst in a molten state is heated in a reaction apparatus and subjected to ring-opening polymerization reaction of glycolide to polymerize glycolide in a molten state to synthesize polyglycolic acid continuously or intermittently. . In the present specification, the reaction liquid refers to a molten polymer material, a mixture of a molten raw material and a catalyst, a mixture of a molten raw material, a catalyst, and a polymer having various degrees of polymerization, or a melt or product that circulates in the process of polymer synthesis. Etc. shall be included.

  In the present invention, continuous or intermittent synthesis has the meaning usually used in the art. This includes a case where the time zones for supplying the raw material and discharging the polymer as a product overlap at least partially, and supplying the raw material continuously or intermittently and discharging the polymer continuously or intermittently.

  When the raw material is in a molten state, the catalyst can be added to the molten raw material as it is and supplied to the reaction apparatus to be subjected to a polymerization reaction. However, if the raw material is in a solid form such as powder, the raw material melting apparatus The raw material is melted in advance by heating the raw material with The heating temperature in the raw material melting apparatus is not particularly limited as long as it is equal to or higher than the melting point of the raw material. Therefore, when the raw material is lactide, it is not particularly limited as long as it is 95 ° C. or higher, but it is usually 95 to 160 ° C., preferably 110 to 130 ° C. By setting the temperature to 160 ° C. or less, deterioration of lactide due to heat can be prevented. Moreover, when a raw material is glycolide, if it is 83 degreeC or more, it will not specifically limit, Usually, 83-160 degreeC, Preferably it is 90-130 degreeC. By setting the temperature to 160 ° C. or less, deterioration of glycolide due to heat can be prevented.

  As the catalyst for the polymerization reaction, a suitable catalyst can be appropriately selected depending on the polymer to be synthesized. For example, as a catalyst used for ring-opening polymerization of lactide or glycolide, conventionally known polylactic acid or polyglycolic acid polymerization catalysts can be used. For example, a catalyst containing at least one metal or metal compound selected from the group consisting of Group IA, Group IVA, Group IVB and Group VA of the periodic table can be used.

  Examples of those belonging to Group IVA include organotin catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate, α-tin naphthoate). , Β-tin naphthoate, tin octylate, etc.) and powdered tin.

  Examples of those belonging to Group IA include alkali metal hydroxides (for example, sodium hydroxide, potassium hydroxide, lithium hydroxide), alkali metal and weak acid salts (for example, sodium lactate, sodium acetate, sodium carbonate). Sodium octylate, sodium stearate, potassium lactate, potassium acetate, potassium carbonate, potassium octylate, etc.), alkali metal alkoxides (eg sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, etc.) Can be mentioned.

  Examples of those belonging to Group IVB include titanium compounds such as tetrapropyl titanate and zirconium compounds such as zirconium isopropoxide. Examples of those belonging to Group VA include antimony compounds such as antimony trioxide. Among these, an organotin catalyst or a tin compound is particularly preferable from the viewpoint of activity.

  The catalyst can be added to the molten raw material by a catalyst addition apparatus usually used in the art. The catalyst may be added to the molten raw material and then supplied to the reaction vessel, or the catalyst may be added directly to the reaction vessel.

  In the present invention, the reaction apparatus for polymerizing the raw material includes three or more reaction vessels connected in series, and the polymerization reaction is performed by heating the reaction liquid containing the molten raw material and the catalyst in the reaction vessel. Is what you do. The number of reaction vessels contained in the reaction apparatus may be 3 or more, and is usually 3 to 5, preferably 3 to 4, more preferably 3.

  Hereinafter, embodiments of the reaction method and apparatus for the polymerization reaction will be described.

  In one embodiment of the present invention, the raw material melt is additionally added to a polymer in an intermediate state between the raw material melt and the final polymer, and stirring and mixing are performed. The reaction apparatus for carrying out the polymerization reaction includes three or more intermediate reaction tanks connected in series. The intermediate reaction tank for additionally supplying and stirring the polymer raw material to the intermediate product is provided in the first stage and It is desirable to use an intermediate reaction tank installed at a position other than the final stage. However, if there is no particular problem, using a reactor composed of two or less reactors, additional addition of raw material between the polymer raw material supply port and the final polymer discharge port, and stirring and mixing with the intermediate polymer You can go.

  About the shape of a reaction tank etc., it does not restrict | limit in particular, What is normally used in this technical field can be used. The above-described embodiment is also included in the scope of the present invention when a reactor including a tank in which a polymerization reaction is not substantially performed in the previous stage is used. Here, the reaction apparatus for carrying out the polymerization reaction includes three reaction tanks connected in series, and additionally supplies and stirs the polymer raw material to the intermediate product in the second stage intermediate reaction tank. The case where a tank is used will be described.

  The reaction vessel in the first stage is not particularly limited, and those commonly used in this technical field can be used. However, the stirring device installed so that its rotating shaft is substantially horizontal and installed in the vessel. It is desirable to use a reaction vessel having at least one weir. Hereinafter, the reaction tank having a stirring device installed so that the rotation axis thereof is substantially horizontal is referred to as a horizontal reaction tank. The term “substantially horizontal” does not mean that the rotation axis of the stirring device is strictly horizontal, and the angle formed between the horizontal plane and the rotation axis is usually −5 ° to + 5 °, preferably −1 °. Means + 1 °, more preferably 0 °.

  The shape of the horizontal reaction vessel is not particularly limited as long as the stirring device can be installed so that the rotation axis thereof is substantially horizontal, and may be a tank type or a cylindrical shape, but is preferably substantially horizontal. A cylindrical shape having a central axis. The horizontal reaction tank has a supply port for supplying a reaction solution containing a molten raw material at one end in the rotation axis direction of the stirring device, and a discharge port for taking out the reaction solution at the other end. Accordingly, the supplied reaction solution moves substantially in the horizontal direction from the supply port to the discharge port. The supply port is preferably positioned below the axis of the stirring device, and the discharge port is preferably positioned below the rotation axis of the stirring device.

  The stirring device installed in the horizontal reaction tank is not particularly limited as long as the stirring is performed by rotation around a rotating shaft arranged substantially in the horizontal direction. For example, a mixer having two or more shafts in which two or more agitating blades such as a circle, an oval, a triangle, a quadrangle, and a multileaf blade are installed on the rotation axis with a space therebetween may be mentioned. . Two or more stirring devices that mesh with each other are preferable from the viewpoint of the self-cleaning action because they can prevent the reaction liquid from adhering to the rotating shaft of the stirring device and the reaction tank. In the case of using a biaxial mixer having a plurality of stirring blades, it is preferable that the stirring blades of the respective rotating shafts are installed alternately, and it is preferable to rotate the respective rotating shafts in the opposite directions. The rotation axis does not necessarily mean an actual rotation shaft member, but includes a rotation axis as a simple rotation center. Therefore, if the rotational center of the rotational motion of the stirring device is arranged substantially horizontally, the actual rotating shaft member does not necessarily have to exist.

  As a heating method in the horizontal reaction tank, a method usually used in this technical field can be used. For example, various methods such as installing a heat medium jacket on the outer periphery of the reaction tank and heating the reaction liquid by heat transfer through the reaction tank wall surface, or heating the reaction liquid through the heat medium inside the rotating shaft of the stirring device, etc. There are many ways. These may be used alone or in combination. It is preferred to heat the reaction vessel at a substantially constant temperature. The molten raw material supplied into the horizontal reaction tank is initially heated and polymerized by the above heating method. However, when the temperature of the reaction liquid becomes higher than that of the heat medium due to the temperature rise accompanying the heat of reaction, the heat medium from the reaction liquid is reversed. The heat will escape. That is, the heating method can also act as a cooling method. Therefore, in the case of a polymer in which reaction heat is generated by the polymerization reaction, heat can be effectively released, which is advantageous.

  If necessary, a heating method in which the inside of the reaction vessel is divided into a plurality of regions and the heat medium temperature can be changed for each of the divided regions may be used. Therefore, it is conceivable to use a plurality of heat medium jackets. The inside of the reaction vessel can be divided based on the area between the weirs, for example. Thereby, for example, the heating medium temperature is set high in a region where a low-temperature reaction liquid is heated, and conversely, the heating medium temperature is set low in a region where the reaction liquid temperature becomes high due to reaction heat and heat removal is required. It becomes possible. A temperature gradient can also be set inside the reaction tank by supplying the heating medium heated by the heating medium heating device to the vicinity of the supply port. When the temperature of the heating medium is lowered, a part of the melt may solidify and adhere to the inner surface of the reaction tank. In this case, the adhering substance can be peeled off by a stirring device installed in the reaction tank.

  The horizontal reaction tank desirably has a weir installed in the tank. This weir is installed so as to inhibit the reaction liquid from rapidly flowing from the reaction tank supply port toward the discharge port. The shape of the weir may be a shape that can inhibit the flow of the reaction solution, and can be determined based on the shape of the reaction tank, and preferably has a plate shape. The method for installing the weir is not particularly limited. For example, when the weir is plate-shaped, the weir is installed at an angle close to perpendicular to the horizontal plane. Moreover, it installs in the bottom inner wall of a reaction tank so that the lower side in the reaction tank cross section perpendicular | vertical to a stirring apparatus rotating shaft, for example, a lower half or 1/3 may be interrupted | blocked. Here, the angle close to perpendicular to the horizontal plane means that the angle formed by the horizontal plane and the plate-like weir is 85 to 95 °, preferably 89 to 91 °, more preferably 90 °. As the material of the weir, it is preferable to use a material having heat insulating properties.

  From the viewpoint of improving the flowability of the polymer, there may be a case where a through hole is provided in the weir, and the through hole is present at the boundary with the portion near the bottom of the reaction vessel, preferably the inner wall of the reaction vessel bottom. The number of through holes is usually 1 to 10, preferably 1 to 5. By providing the through hole as described above, the reaction solution can be circulated at an appropriate speed. A person skilled in the art can appropriately determine the installation position and interval of the weir based on reaction conditions and the like. For example, the installation position of the weir can be determined so as to divide the region where the viscosity distribution of the polymer is about the same. In addition, after deciding the position of the weir in the reaction tank, the resistance when the reaction liquid passes through the through hole at a predetermined flow rate penetrates so as to be smaller than the driving force due to the reaction liquid head difference before and after the weir. The hole diameter of the hole can be determined.

  The region between the two weirs acts in the same manner as a single mixing cell, and the reaction liquid is homogenized by being stirred by the stirring device. As a result, it is possible to suppress the influence of the raw material melt having a low viscosity and the low viscosity polymer having a low degree of polymerization flowing faster than the high viscosity polymer having a high degree of polymerization and being mixed in the final polymer. . The weir may be omitted when the viscosity of the polymer can be expected to some extent and the mixing effect is small.

  By providing a head difference between the supply port and the discharge port in the horizontal reaction tank, a driving force for moving the reaction solution from the supply port to the discharge port can be applied. The reaction liquid flows through the through-hole, or the reaction liquid at a position higher than the weir flows to the subsequent region due to the head difference, so that the horizontal reaction tank can flow toward the discharge port. In the horizontal reaction tank, the supply amount of the reaction liquid is not particularly limited, but is normally supplied in an amount of 10 to 70%, preferably 40 to 50% with respect to the capacity of the horizontal reaction tank. Moreover, it is preferable to supply with the quantity which does not exceed the height of a weir. This is because it is possible to effectively suppress the unreacted lactide from flowing rapidly. In the horizontal reaction tank, if necessary, a device for measuring the liquid level of the reaction liquid is installed, and the measurement signal is fed back to the liquid feed pump at the reaction tank supply port or the liquid feed pump at the reaction tank discharge port, etc. The transport amount of the reaction liquid can be adjusted so that the height of the liquid level becomes a predetermined value.

  As a method for measuring the liquid level, for example, there is a method in which a radioactive substance is installed in the upper part of a horizontal reaction tank and the amount of gamma rays generated therefrom is measured based on the permeation amount of the reaction liquid. There is also a method of measuring by emitting ultrasonic waves or electromagnetic waves from the upper part of the horizontal reaction tank and measuring the reflected waves. Furthermore, a method of measuring by placing a cylindrical capacitor in the upper part of the horizontal reaction tank, inserting it into the reaction solution, and measuring the change in the dielectric constant with the height of the reaction solution inside the tube can be mentioned.

  The reaction conditions in the first horizontal reaction tank can be appropriately determined by those skilled in the art, but the average reaction temperature in the reaction tank is usually 140 to 180 ° C., preferably 160 to 170 ° C., residence time. The time is usually 5 to 15 hours, preferably 7 to 10 hours. It is preferable to set the reaction conditions so that a polymer having a weight average molecular weight of usually 50,000 to 200,000, preferably 70,000 to 150,000 is obtained from the outlet of the first horizontal reaction tank.

  The first-stage reaction tank is a horizontal reaction tank, and the above-mentioned weir is provided in the first-stage reaction tank, so that the melted raw material having a low viscosity and the polymer having a low polymerization degree and viscosity are polymerized to some extent. Suppresses mixing with polymer which has progressed reaction. Thereby, the piston flow property in a reaction tank is securable. And it can prevent that a reaction liquid moves to the following process with unreacted, and can fully react in the 1st step | paragraph reaction tank. Therefore, since the prolonged temperature history resulting from the dispersion | variation in residence time is prevented, deterioration of the polymer by thermal decomposition is suppressed and a high quality polymer can be obtained.

  The intermediate reaction tank in the second stage is not particularly limited, and those commonly used in the art can be used. However, a horizontal reaction tank and a mixer having two rotating shafts having a plurality of stirring blades is preferable. . As for the form of the mixer, it is desirable that two or more stirring blades are installed at predetermined intervals on each rotating shaft. This prevents the polymer from adhering to the rotating shaft of the stirrer and the reaction vessel. From the viewpoint of the self-cleaning action, the subsequent reaction vessel in which the polymerization reaction proceeds and the viscosity of the polymer is increased. Is particularly effective. As for the rotation direction of the rotation shaft, as long as the stirring blades are engaged with each other, the rotation shaft may be rotated in the opposite direction or may be rotated in the same direction.

  Regarding the shape of the stirring blade, for example, general shapes such as a circle, an oval, a triangle, a quadrangle, and a multi-leaf shape can be used, and the shape is not particularly limited. The horizontal reaction tank has a supply port for supplying a reaction solution containing a molten raw material at one end in the rotation axis direction of the stirring device, and a discharge port for taking out the reaction solution at the other end. Accordingly, the supplied reaction solution moves substantially in the horizontal direction from the supply port to the discharge port. The supply port is preferably positioned below the axis of the stirring device, and the discharge port is preferably positioned below the rotation axis of the stirring device.

  In the second stage reaction vessel, the raw material melt is additionally added to the intermediate state polymer (hereinafter referred to as prepolymer) between the raw material melt and the final polymer, and the polymerization reaction proceeds while stirring and mixing. By mixing the raw material melt and the prepolymer, the reaction heat accumulated in the prepolymer is transferred to the raw material melt, the temperature of the prepolymer is lowered, and the thermal decomposition can be suppressed. At that time, the raw material melt receives heat from the prepolymer, so that the temperature required for the progress of the polymerization reaction can be obtained even if there is little heating from the outside such as a polymerization vessel. At that time, when the difference in viscosity between the raw material melt and the prepolymer is large, the mixing property by stirring may be lowered.

  In such a case, for example, in the invention disclosed in Japanese Patent Application Laid-Open No. 6-218260, the stirring blade installed on one rotating shaft is arranged with a small distance from the stirring blade on the other rotating shaft. The stirring device to be used becomes effective. This is because the gap between the blades is narrow, so that a large shearing force is applied to the raw material melt and the prepolymer between the blades by stirring, and the mixing property is improved. By increasing the mixability of the raw material melt and the prepolymer, the transfer heat of the reaction heat accumulated in the prepolymer is improved to a raw material melt having a temperature lower than that of the prepolymer, and the thermal decomposition inhibiting performance of the prepolymer is improved. The added raw material melt may contain a catalyst and a polymerization initiator, but these are usually not included in order to prevent the molecular weight distribution from widening and the stability of the final polymer from being impaired. Is preferred.

  The heating method in the horizontal reaction tank and the method of measuring the liquid level in the method of heating the reaction tank by dividing the inside of the reaction tank into a plurality of regions are handled in the same manner as in the first horizontal agitator. In addition, a weir may be installed in the tank to prevent the reaction liquid from rapidly flowing from the reaction tank supply port to the discharge port as necessary.

  The reaction conditions in the intermediate reaction tank in the second stage can be appropriately determined by those skilled in the art, but the average reaction temperature in the reaction tank is usually 140 to 200 ° C., preferably 160 to 180 ° C. The time is usually 0.5 to 15 hours, preferably 1 to 5 hours. It is preferable to set the reaction conditions so that a polymer having a weight average molecular weight of usually 70,000 to 300,000, preferably 100,000 to 200,000 is obtained from the outlet of the second stage reaction vessel.

  Addition of the raw material melt to the prepolymer in the second stage intermediate reaction tank, and advance the polymerization reaction while stirring and mixing, thereby suppressing degradation of the polymer due to thermal decomposition and obtaining a high quality polymer be able to.

  As the reaction vessel for the third stage, as a reaction apparatus for carrying out the polymerization reaction, at least the final stage of the reaction tank having a stirring device installed so that the rotation axis thereof is substantially perpendicular to the horizontal plane. The reactor included in is used. Hereinafter, the reaction tank having a stirring device installed so that the rotation axis thereof is substantially perpendicular to the horizontal plane is referred to as a vertical reaction tank. In this embodiment, the reaction apparatus has a vertical reaction tank at least in the final stage, but may further have a vertical reaction tank in a stage other than the final stage. The shape of the reaction vessel other than the final stage is not particularly limited, and those usually used in the art can be used. The above embodiment uses a reaction apparatus including a vertical reaction tank in the final stage, but uses a reaction tank including a tank in which the polymerization reaction is not substantially performed in the subsequent stages. Are also included within the scope of the present invention.

  “Substantially perpendicular to the horizontal plane” does not mean that the rotation axis of the stirring device is strictly perpendicular, and the angle between the horizontal plane and the rotation axis is usually 85 to 95 °, preferably 89 to 90 °. It means 91 °, more preferably 90 °. Similar to the horizontal reaction vessel, the rotation shaft does not necessarily mean an actual rotation shaft member, but also includes a rotation axis as a simple rotation center. Therefore, as long as the rotation center of the rotational movement of the stirring device is arranged substantially perpendicular to the horizontal plane, the actual rotating shaft member does not necessarily exist.

  The shape of the vertical reaction tank is not particularly limited as long as the stirring device can be installed so that the rotation axis thereof is substantially perpendicular to the horizontal plane. The cylindrical shape has a central axis substantially parallel to the rotation axis of the stirring device. The vertical reaction tank has a supply port for supplying the reaction liquid from the previous reaction tank at one end in the direction of the rotating shaft of the stirring device, and a discharge port for taking out the reaction liquid at the other end. Accordingly, the supplied reaction solution moves in a substantially vertical direction from the supply port to the discharge port. The supply port is preferably present in the upper part of the reaction tank, and the discharge port is preferably present in the lower part of the reaction tank. Since the specific gravity of the polymer increases with the progress of the polymerization reaction, it is possible to prevent the polymer having a low polymerization degree from being mixed into the polymer having a high polymerization degree by providing a supply port in the upper part.

  The stirring device installed in the vertical reaction tank is not particularly limited as long as stirring is performed by rotation around a rotation axis that is arranged substantially perpendicular to the horizontal plane. For example, a mixer having two or more shafts in which two or more agitating blades such as a circle, an oval, a triangle, a quadrangle, and a multileaf blade are installed on the rotation axis with a space therebetween may be mentioned. . A two-shaft mixer having a plurality of stirring blades is preferably installed such that the stirring blades of the respective rotating shafts are staggered. Moreover, in this case, it is preferable to rotate each rotating shaft in the reverse direction. Two or more stirring devices that mesh with each other can prevent the adhesion of the polymer to the rotating shaft of the stirring device and the reaction vessel, and from the viewpoint of self-cleaning action, the polymerization reaction proceeds and the viscosity of the polymer increases. It is particularly advantageous to use it in a subsequent reaction vessel.

  As a heating method in the vertical reaction tank, a method usually used in this technical field can be used as in the case of the horizontal reaction tank. For example, various methods such as installing a heat medium jacket on the outer periphery of the reaction tank and heating the reaction liquid by heat transfer through the reaction tank wall surface, or heating the reaction liquid through the heat medium inside the rotating shaft of the stirring device, etc. There are many ways. These may be used alone or in combination.

  The molten raw material supplied into the vertical reaction tank is initially heated by the above heating method and the polymerization reaction proceeds. However, when the temperature of the reaction liquid becomes higher than that of the heating medium due to the temperature rise accompanying the reaction heat, the reaction liquid is reversed. Heat escapes from the heat medium. Therefore, as in the case of the horizontal reaction tank, if necessary, a heating method in which the inside of the reaction tank is divided into a plurality of regions and the heat medium temperature can be changed for each of the divided regions may be used. Thereby, for example, the heat medium temperature is set high in the region where the low temperature reaction liquid is heated, and the heat medium temperature is set low in the region where the reaction liquid temperature is high due to the reaction heat and heat removal is necessary. It becomes possible. If further heat removal is required, the heat removal efficiency can be further improved, for example, by installing fins (side irregularities in the reaction tank) inside the vertical reaction tank. Moreover, the aspect which keeps a polymer warm and prevents it cooling too much by supplying the heat medium heated with the heat medium heating apparatus to discharge port vicinity is also considered.

  Since it is preferable to perform the reaction at a high temperature in the latter stage of the polymerization reaction, degradation of the polymer accompanying the temperature rise becomes a problem, but by using a vertical reaction tank in the final stage, the temperature rise can be suppressed, The problem that the polymer is deteriorated and colored can be reduced.

  In the vertical reaction tank, the supply amount of the reaction liquid is not particularly limited, but is normally supplied in an amount of 20 to 100%, preferably 60 to 100% with respect to the capacity of the vertical reaction tank. Therefore, compared to a conventional horizontal reaction tank in which the reaction liquid is introduced only about half the normal capacity of the reaction tank, the area where the reaction liquid is in contact with the inner wall of the reaction tank is large, and the heat transfer area can be increased (FIG. 4). ).

  By removing the heat of reaction accompanying the polymerization of the raw material by heat transfer, the temperature rise of the reaction solution can be reduced, and in the latter stage of the polymerization reaction, the deterioration due to the thermal decomposition of the produced polymer is effectively suppressed, Coloring can be prevented. In particular, in the ring-opening polymerization of lactide, coloring of polylactic acid can be effectively prevented.

  Moreover, the heat transfer area can be further increased and the heat removal efficiency can be improved by making the inner surface shape of the vertical reaction tank into an uneven shape. In the above-described aspect in which the side surface is uneven, the high viscosity polymer stuck to the inner wall of the reaction tank can be scraped off by installing the stirring blade so as to mesh with the concave portion of the reaction tank (for example, FIG. 4). (See reaction vessel).

  In the vertical reaction tank, as in the horizontal reaction tank, an apparatus for measuring the liquid level of the reaction liquid is installed as necessary. Then, by feeding back the measurement signal to the liquid feed pump at the reaction tank supply port or the liquid feed pump at the reaction tank discharge port, the transport amount of the reaction liquid can be adjusted so that the height of the liquid level becomes a predetermined value. . As a method for measuring the liquid level, for example, there is a method in which a radioactive substance is installed in the upper part of a horizontal reaction tank and the amount of gamma rays generated therefrom is measured by the permeation amount of the reaction liquid. Further, there is a method of measuring by emitting ultrasonic waves or electromagnetic waves from the upper part of the vertical reaction tank and measuring the reflected waves. Furthermore, a method of measuring by installing a cylindrical capacitor in the upper part of the vertical reaction tank, inserting it into the reaction solution, and measuring the change in dielectric constant accompanying the height of the reaction solution inside the tube, etc. .

  The reaction conditions in the final vertical reaction tank can also be appropriately determined by those skilled in the art, but the average reaction temperature in the reaction tank is usually 180 to 220 ° C., preferably 190 to 210 ° C., residence time. Is usually 1 to 7 hours, preferably 3 to 5 hours. It is preferable to set the reaction conditions so that a polymer having a weight average molecular weight of usually 100,000 to 500,000, preferably 150 to 300,000 can be obtained from the outlet of the vertical reaction tank in the final stage.

  In the polymer synthesizing apparatus of the present invention, a residual raw material removing apparatus can be installed at the rear stage of the polymerization apparatus to remove unreacted raw materials from the reaction liquid discharged from the reaction apparatus. In the residual raw material removing apparatus, an unreacted raw material such as lactide is removed by creating a negative pressure environment while maintaining a molten state. Furthermore, although the polymer obtained through the synthesis method of the present invention is usually subjected to water cooling and pelletizing treatment with a chip cutter, these treatments can be omitted.

  Nitrogen gas supply for purging the interior with nitrogen gas to the raw material melting apparatus, catalyst supply apparatus, reaction apparatus including various reaction tanks, residual raw material removal apparatus, etc. used in the polymer synthesis apparatus of the present invention It is preferable that piping and an exhaust pipe are installed. And the operation of the synthesis process is basically preferably started after all the equipment in the process has been purged with nitrogen. Thereby, scorching of the reaction liquid due to the presence of oxygen can be prevented. In addition, the raw material melting apparatus, the catalyst supply apparatus, the raw material supply apparatus, various reaction vessels, and the like are preferably operated at a pressure of about atmospheric pressure. By doing so, volatilization of the molten raw material can be reduced.

  In another embodiment of the present invention, in the reactor, the raw material melt is additionally added to the prepolymer, stirring and mixing are performed, and for the raw material melt to be additionally added, the temperature is higher than the melting point of the raw material, The temperature is controlled to be lower than the temperature of the added prepolymer. When the temperature of the raw material melt to be added is higher than its melting point, it can be handled and supplied as a liquid, and the mixing property with the prepolymer can be improved. Moreover, by making the temperature lower than the temperature of the prepolymer, it is possible to absorb the heat of reaction of the prepolymer and contribute to the suppression of thermal decomposition through reducing the temperature of the entire mixture.

  In order to confirm that the temperature of the raw material melt to be added is higher than the melting point, the temperature of the raw material melt in the storage tank or the temperature of the raw material melt in the supply pipe to the reaction tank is set in the tank or the pipe. Measure with the inserted thermocouple. The result may be fed back to a tank / pipe heating / heat-retaining device and controlled to reach a predetermined temperature. In order to make the temperature lower than that of the prepolymer, it is necessary to measure not only the raw material melt but also the temperature of the prepolymer. For this purpose, a thermocouple is inserted into the reaction vessel or the prepolymer supply pipe, and the temperature is measured, and the result is fed back to the raw material melt tank and the raw material supply pipe heating / warming device, What is necessary is just to control so that it may become temperature.

  Furthermore, in any of the above-described embodiments, it is preferable that the temperature in the reaction vessel included in the reaction apparatus is set higher as it becomes later, and the residence time in the reaction vessel is set shorter as it becomes later. In the initial stage of the reaction, the polymerization reaction is advanced as much as possible by carrying out the polymerization reaction at a low temperature where the influence of thermal decomposition is relatively small. In the latter stage, where the progress of the polymerization reaction has slowed down, the high-quality polymer with less coloration can be achieved by advancing the polymerization reaction under higher temperature conditions, thereby shortening the reaction time under high temperature conditions and suppressing degradation of the polymer. Can be obtained. In this embodiment, for example, the temperature in the first reaction vessel is 140 to 180 ° C., preferably 160 to 170 ° C., and the temperature in the final reaction vessel is 180 to 220 ° C., preferably 190 to 170 ° C. The temperature is set to 210 ° C., and the temperature is set so that the temperature gradually increases from the first stage to the final stage.

  The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto.

Example 1
FIG. 1 shows an embodiment of a polylactic acid polymerization apparatus as an embodiment of the polymer polymerization apparatus of the present invention. In this embodiment, lactide supply devices 1 to 3, lactide melting devices 4 to 6, catalyst supply devices 7 to 9, polymerization initiator supply devices 10 to 12, lactide supply devices 13 to 15, horizontal reaction tank 16, and additional additive raw materials Polymerization of polylactic acid is performed by an apparatus including a mixing tank 17, a vertical reaction tank 18, a residual lactide removing device 19, a liquid feed pump 20 to 35, and valves 36 to 51. In this example, three reactors, a horizontal reaction tank 16, an additional additive raw material mixing tank 17, and a vertical reaction tank 18 are connected in series as reaction apparatuses, and two additional raw material additions to the additional additive raw material mixing tank 17 are performed. It is an example using the reactor implemented by. The number of systems for additional material addition to the additional material mixture tank 17 can be increased or decreased as necessary. About the liquid feeding pumps 20-35, the viscosity of the liquid to be transported is low, and the case where the liquid can be fed using gravity can be partially omitted. Further, the valves 36 to 51 can be omitted as necessary.

  The lactide supply devices 1 to 3 supply solid or powdery lactide to the lactide melting devices 4 to 6. As a transportation method of the lactide supply devices 1 to 3, there are methods such as transportation by a screw feeder, transportation by ultrasonic vibration, transportation by a gas flow, and the like. In the lactide melting devices 4 to 6, the sent lactide is heated and melted. The temperature at that time is not less than the melting point of lactide, and preferably not more than 160 ° C. so as not to cause deterioration due to heat.

  When the raw material lactide is supplied in liquid form instead of solid or powder, the lactide supply devices 1 to 3 serve as liquid feed pumps, and the lactide melting devices 4 to 6 function as buffer tanks. The melted lactide produced by the lactide melting devices 4 to 6 is opened by the valves 36 to 38 and then discharged by the liquid feed pumps 20 to 22. The valves 39 to 44 are opened and the pumps 23 to 28 are used to supply the catalyst supply device 7. The catalyst and the polymerization initiator are supplied to the lactide supply devices 13 to 15 after the molten lactide is supplied from ˜9 and the polymerization initiator supply devices 10 to 12.

  The flow rate of the molten lactide discharged from the liquid feed pumps 20 to 22, the ratio of the catalyst amount supplied from the catalyst supply devices 7 to 9 to the molten lactide flow rate, and the polymerization supplied from the polymerization initiator supply devices 10 to 12 The ratio of initiator to molten lactide flow need not be the same. They can be changed as needed. Furthermore, when it is not necessary to add a catalyst or a polymerization initiator to the additionally added molten lactide, valves 40 to 41, 43 to 44, pumps 24 to 25, 27 to 28, catalyst supply devices 8 to 9, and polymerization start The agent supply devices 11 to 12 can be omitted.

  In the lactide supply devices 13 to 15, the temperature of the molten lactide is maintained in the range of the melting point of lactide or higher and desirably 160 ° C. or lower. The lactide supply devices 13 to 15 are essentially buffers to tanks and may be omitted if not necessary. The molten lactide in the lactide supply device 13 opens the valve 45 and is continuously supplied to the horizontal reaction tank 16 by the liquid feed pump 29. When the lactide supply device 13 is omitted, the liquid feed pump 29 is also omitted. The liquid supply pipes before and after the liquid supply pumps 20 to 29 and 31 to 32 are all over the melting point of lactide by heating and heat retention, preferably 160 ° C. or less, in order to avoid lactide coagulation and blockage due to temperature drop. Is kept in the range.

  Thermocouples are inserted in the pipes before and after the lactide melting devices 4 to 6, the lactide supply devices 13 to 15, and the liquid feed pumps 20 to 22, 29, and 31 to 32, and the temperature of the molten raw material is measured at each position. To do.

  In the horizontal reaction tank 16, molten lactide flows due to the head difference between the supply port and the discharge port, and the polymerization reaction proceeds. In the horizontal reaction tank 16, the reaction solution is heated by a heat medium jacket on the outer periphery of the reaction tank.

  FIG. 2 shows an enlarged view of the horizontal reaction tank 16 having a weir. Stirring blades 84 are provided on the rotating shaft 83 of the stirring device at regular intervals. A weir 53 having a through hole 52 is installed inside the horizontal reaction tank 16. In the region 54 between the weirs, the reaction liquid is homogenized by the stirring blade 84 (this region can be regarded as a single mixing cell). And only the reaction liquid in a position higher than the weir can flow into the subsequent mixing cell due to the head difference. The reaction liquid in the horizontal reaction tank 16 is transported to the additional addition raw material mixing tank (intermediate reaction tank) 17 by gravity and the liquid feed pump 30 with the valve 48 opened. As for the liquid feed pump 30, a screw for extraction, a gear pump, or the like can be selected according to the viscosity of the reaction liquid.

  Further, when the reaction liquid can be extracted from the horizontal reaction tank 16 by gravity, the liquid feeding pump 30 can be omitted. The transport piping around the liquid feed pump 30 needs to be heated and kept warm in order to avoid clogging due to the solidification of the internal reaction liquid. The temperature at that time is preferably 200 ° C. or lower so that the reaction solution does not thermally decompose. In the horizontal reaction tank 16, an apparatus (a liquid level meter 55) for measuring the liquid level of the reaction liquid is installed as necessary, and a measurement signal is sent to the liquid feed pump 29 or the liquid level so that the liquid level becomes a predetermined value. It feeds back to the liquid feed pump 30 to adjust the transport amount of the reaction liquid. 2 and 3, it is preferable to install the level gauges 55 and 58 in the reaction tank.

  In the additional additive raw material mixing tank 17, the prepolymer flows due to the head difference between the supply port and the discharge port, and the polymerization reaction proceeds. In the additional addition raw material mixing tank 17, the reaction liquid is heated by the jacket of the heat medium at the outer periphery of the reaction tank.

  Enlarged views of the additional additive raw material mixing tank or the intermediate layer reaction tank 17 are shown in FIGS. 3 (a), 3 (b), and 3 (c). In this case, as shown in FIG. 3C, the rotating shaft 57 of the stirring blade 56 rotates in the same direction. Each stirring blade is installed so as to rotate away from the stirring blade and the rotating shaft of the adjacent shaft by a small distance. When a mixture of a prepolymer having a relatively high viscosity and an additional supply of molten raw material having a low viscosity is inserted in a minute space between the stirring blades, the viscosity of the mixture is subjected to a large shearing force due to the rotation of the blades at the front and rear positions. Decreases, the homogenization of the mixture proceeds.

  In the additional additive raw material mixing tank 17, a plurality of regions in which a region having a predetermined number of stirring blades can be regarded as a substantially complete mixing vessel are generated according to the viscosity of the mixture of the prepolymer and the additionally supplied molten raw material at each position. To do. This region is a single mixing cell where there is no local back-flow phenomenon of the mixture to the subsequent region. The number of complete mixing tanks is desirably equal to or greater than the number of additional raw material addition lines in the additional additive raw material mixing tank 17.

  The melted lactide of the lactide supply devices 14 to 15 is continuously supplied to the additional additive raw material mixing tank 17 by the liquid feed pumps 31 to 32 by opening the valves 46 to 47. In addition, when the lactide supply apparatuses 14 and 15 are omitted, the liquid feed pumps 31 and 32 are also omitted. At the position of the additional additive raw material supply port in the direction of prepolymer flow in the additional additive raw material mixing tank 17, the temperature of the mixture of the prepolymer and the additional supplied molten raw material is measured. The measurement is performed by inserting a thermocouple at the above position. The melt lactide flow rate of the lactide supply devices 14 to 15 is controlled so that the temperature of the mixture of the prepolymer in the additional additive raw material mixing tank 17 and the additional supplied molten raw material becomes a predetermined value.

  The reaction liquid in the additional additive raw material mixing tank 17 is transported to the vertical reaction tank 18 by gravity and the liquid feed pump 33 with the valve 49 opened. As for the liquid feed pump 33, a screw for extraction and a gear pump can be selected according to the viscosity of the reaction liquid. Further, when the reaction liquid can be extracted from the additional additive raw material mixing tank 17 by gravity, the liquid feed pump 33 can be omitted.

  The transport piping before and after the liquid feed pump 33 needs to be heated and kept warm in order to avoid clogging due to the solidification of the internal reaction liquid. The temperature at that time is preferably 200 ° C. or lower so that the reaction solution does not thermally decompose. An apparatus (a liquid level gauge 58) for measuring the liquid level of the reaction liquid is installed in the additional additive raw material mixing tank 17 as necessary, and a measurement signal is sent to the liquid feed pump 30 so that the height of the liquid level becomes a predetermined value. To adjust the transport volume of the reaction solution. Alternatively, when the additional additive raw material mixing tank 17 is operated in a full liquid state, the liquid level gauge 58 can be removed unless particularly necessary, and the liquid feed pump 33 is adjusted in accordance with the flow rates of the liquid feed pumps 30 to 32. Is done.

  The reaction liquid is transported to a supply port installed at the upper part of the vertical reaction tank 18, flows toward the discharge port at the lower part of the vertical reaction tank 18 by gravity, and the polymerization reaction proceeds. Thereby, it can prevent that the polymer with a low polymerization degree mixes in the polymer with a high polymerization degree. In the vertical reaction tank 18, the reaction solution is heated by a heat medium jacket on the outer periphery of the reaction tank, or is removed when the heat medium temperature is lower than that of the polymer.

  Since the vertical reaction tank 18 shown in FIGS. 4A and 4B has a larger heat transfer area than the horizontal reaction tank 16, the efficiency of heating and heat removal is high. For this reason, by using the vertical reaction tank 18 in the final stage, it is possible to reduce the deterioration of the polymer due to the temperature rise accompanying the reaction heat. In the vertical reaction vessel 18, a stirrer (hereinafter referred to as a biaxial stirrer) having two rotating shafts 57 ′ provided with a stirring blade 56 ′, which is suitable for stirring a high-viscosity polymer, is used. Since this reaction tank has a shape with irregularities on the inner side surface, the heat transfer surface 60 can be made larger. Therefore, when the temperature of the polymer is higher than that of the heat medium, the amount of heat removal is increased, and the polymerization is performed. It is possible to further reduce the effect of thermal degradation of the object. In addition, when it is not necessary to take large heat removal amount, it is not necessary to set it as such an uneven | corrugated side surface. The nitrogen gas flow valves 61 to 80 prevent the reactants in the reaction tank from being deteriorated by oxygen or the like.

  The reaction liquid inside the vertical reaction tank 18 is continuously discharged by gravity and the liquid feed pump 34 with the valve 50 opened, and is transported to the residual lactide removing device 19 shown in FIG. As the liquid feed pump 34, an extraction screw, a gear pump, or the like can be selected according to the viscosity of the reaction liquid. The transportation piping before and after the liquid feeding pump 34 needs to be heated and kept warm in order to avoid clogging due to the solidification of the internal reaction liquid. The temperature at that time is preferably 200 ° C. or lower so that the polymer is not thermally decomposed. Inside the vertical reaction tank 18, as in the case of the horizontal reaction tank 16, an apparatus (a liquid level gauge 59) for measuring the liquid level of the reaction liquid is installed if necessary, and the height of the liquid level is a predetermined value. The measurement signal is fed back to the liquid feed pump 33 or the liquid feed pump 34 so as to adjust the transport amount of the reaction liquid.

  The residual lactide removing device 19 creates a negative pressure environment while maintaining a molten state, and removes unreacted lactide. The treated reaction liquid is continuously discharged by the liquid feed pump 35 with the valve 51 opened. As the liquid feed pump 35, an extraction screw, a gear pump, or the like can be selected according to the viscosity of the reaction liquid. The discharged polymer is usually subjected to water cooling and pelletizing with a chip cutter.

  The preferable temperature ranges at the entrances and exits of the above reaction vessels are summarized as follows. It is preferable to control so that the temperature of the raw material monomer at the raw material inlet a in FIG. 2 is 100 to 140 ° C. and the temperature of the outlet b is 150 to 210 ° C. The temperature of the inlet c in the intermediate reaction tank is controlled to 150 to 210 ° C., and the temperature of the outlet d is controlled to 150 to 210 ° C. Furthermore, it is preferable to control the temperature at the inlet e of the final stage reaction tank to 150 to 210 ° C. and the temperature at the outlet f to 170 to 220 ° C.

  In the embodiment shown in FIG. 1, lactide supply devices 1 to 3, lactide melting devices 4 to 6, catalyst supply devices 7 to 9, polymerization initiator supply devices 10 to 12, lactide supply devices 13 to 15, and horizontal reaction tank 16. , An additional additive raw material mixing tank 17 and a vertical reaction tank 18 are provided. The residual lactide removing device 19 is provided with nitrogen gas supply pipes and exhaust pipes 61 to 80 for purging the inside with nitrogen gas. This is to prevent scorching of the reaction solution due to the presence of oxygen. The operation of the process should basically be started after a nitrogen purge of all equipment in the process. Also, lactide supply devices 1 to 3, lactide melting devices 4 to 6, catalyst supply devices 7 to 9, polymerization initiator supply devices 10 to 12, lactide supply devices 13 to 15, horizontal reaction tank 16, and additional additive raw material mixing tank 17 The vertical reaction tank 18 is operated at a pressure of about atmospheric pressure. This is to reduce the volatilization of the molten lactide.

(Example 2)
Polylactic acid was polymerized by the apparatus shown in Example 1. The temperature of the lactide melting devices 2 to 4 was set to 120 ° C., and molten lactide (molecular weight 144) in which the catalyst and the polymerization initiator were dispersed was supplied to the horizontal reaction tank 16 at 120 ° C. In the horizontal reaction tank 16, the reaction solution was maintained at an average temperature of 160 ° C. and a residence time of 10 hours. In the first half of the residence time, it is heated by heat conduction from the jacket on the outer periphery of the reaction vessel, and in the second half, the temperature of the polymer itself increases with the reaction heat accompanying the polymerization, but some reaction heat is It was removed by heat conduction through the inner wall. The polylactic acid discharged from the horizontal reaction tank has a polymerization reactivity (conversion) of 30% (polymerization reactivity = 1-calculated as residual lactide concentration / initial lactide concentration), a weight average molecular weight of 70,000, and a viscosity of about 100 Pa · s. Met.

  This polymer was then supplied to the additional additive raw material mixing tank 17. In the additional addition raw material mixing tank 17, the polymer was maintained at an average temperature of 190 ° C. and a residence time of 2 hours, and during that time, additional addition of the molten raw material at 100 ° C. was performed from two locations. The additional addition amount was 50% of the prepolymer flow rate. During the residence time, the temperature of the polymer itself increased with the heat of reaction accompanying the polymerization, but part of the heat of reaction was absorbed by the temperature increase of the additional added monomer, and was removed by heat conduction through the inner wall of the reaction vessel. It was. As the polymerization reaction progresses, the heat generation rate per unit volume decreases, so while the heat generation rate exceeds the heat removal rate by heat conduction, the temperature of the polymer itself rises, but when it becomes lower, the polymer product Its temperature drops. The polylactic acid discharged from the additional additive raw material mixing tank 17 had a polymerization reactivity of 60%, a weight average molecular weight of 140,000, and a viscosity of about 1000 Pa · s.

  This polymer was then fed to the vertical reactor 18. In the vertical reaction vessel 18, the polymer was maintained at an average temperature of 190 ° C. and a residence time of 3 hours. During the residence time, the temperature of the polymer itself increased with the reaction heat accompanying the polymerization, but a part of the reaction heat was removed by heat conduction through the inner wall of the reaction vessel. As the polymerization reaction progresses, the heat generation rate per unit volume decreases, so while the heat generation rate exceeds the heat removal rate by heat conduction, the temperature of the polymer itself rises, but when it becomes lower, the polymer product Its temperature drops. The polylactic acid discharged from the vertical reaction tank 18 had a polymerization reactivity of 85%, a weight average molecular weight of 200,000, and a viscosity of about 2500 Pa · s.

When the hue (b) of the obtained polylactic acid was measured with a chromaticity meter, b = 4. From the above, it has been clarified that the method of the present invention yields high-quality polylactic acid with little b = 4 or less coloring.

It is a diagram which shows one Example of the polymerization method of the polylactic acid of this invention. It is a figure side surface cross-section figure which shows the horizontal type | mold reaction tank which has a weir used by this invention. It is sectional drawing which shows the intermediate reaction tank which has a biaxial stirring apparatus used by this invention, (a) is an upper surface top sectional view, (b) is the side surface sectional view, (c) is a front sectional drawing. It is sectional drawing which shows the vertical reaction tank which has the heat-transfer surface of a shape which has an unevenness | corrugation in the inner wall surface used by this invention, and a biaxial stirring apparatus, (a) is side surface sectional drawing, (b) is upper surface top sectional drawing. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1-3 ... Lactide supply apparatus, 4-6 ... Lactide melting apparatus, 7-9 ... Catalyst supply apparatus, 10-12 ... Polymerization initiator supply apparatus, 13-15 ... Lactide supply apparatus, 16 ... Horizontal reaction tank, 17 ... Additional addition raw material mixing tank, 18 ... vertical reaction tank, 19 ... residual lactide removal device, 20-35 ... liquid feed pump, 36-51 ... valve, 52 ... through hole, 53 ... weir, 54 ... area between weirs, 55, 58, 59 ... liquid level gauge, 56 ... stirring blade, 57 ... rotating shaft, 60 ... uneven heat transfer surface, 61-80 ... nitrogen gas flow valve, 81 ... vacuum pump, 83 ... rotating shaft, 84 ... stirring Wings.

Claims (14)

In a method for producing a polymer by ring-opening polymerization of a cyclic condensate of hydroxycarboxylic acid as a raw material, the cyclic condensate of hydroxycarboxylic acid is divided into at least three stages and opened using a plurality of reaction vessels. A method of continuously producing a polymer by carrying out a ring polymerization reaction, wherein the melt of the raw material is added to the intermediate polymer in the reaction vessel in the other intermediate stage excluding the reaction vessel in the first stage and the final stage. A polymer polymerization method characterized in that the polymerization reaction is carried out while adding, stirring and mixing. 2. The polymer polymerization method according to claim 1, wherein the raw material melt to be added is kept at a temperature higher than the melting point of the raw material and lower than the temperature of the added intermediate polymer. A polymer polymerization apparatus using a cyclic condensate of hydroxycarboxylic acid as a raw material, the polymerization apparatus excluding three or more reaction tanks connected in series and reaction tanks in the first and last stages Means for adding a melt of the raw material to an intermediate polymer in one or more intermediate reaction tanks, and the intermediate reaction tank includes a stirrer. 4. The polymer polymerization apparatus according to claim 3, wherein the first-stage reaction apparatus has a stirring apparatus installed so that a rotation axis thereof is −5 ° to + 5 ° with respect to a horizontal plane . 5. The polymer polymerization apparatus according to claim 3, wherein the final-stage reaction apparatus has a stirrer installed so that an angle formed between the rotation axis and a horizontal plane is 85 ° to 95 ° . 6. The polymer according to claim 3, further comprising means for maintaining the temperature of the raw material melt to be added at a temperature higher than the melting point of the raw material and lower than the temperature of the intermediate polymer to be added. Polymerization equipment. A polymer polymerization apparatus using a hydroxycarboxylic acid cyclic condensate as a raw material, wherein the polymerization apparatus comprises three or more reaction vessels connected in series, and a reaction product of a hydroxycarboxylic acid cyclic condensate melt. Means for supplying to the tank, and means for adding the raw material to an intermediate polymer in one or more intermediate reaction tanks excluding the first and final stage reaction tanks, The reaction tank provided with a stirrer and excluding the final reaction tank is a horizontal reaction tank having a stirring rotation axis of −5 ° to + 5 ° with respect to the horizontal plane , and the final reaction tank has an angle of 85 with the horizontal plane. A polymer polymerization apparatus, characterized in that it is a vertical reaction tank having a stirring rotation axis of from 0 to 95 ° . 8. The polymer polymerization apparatus according to claim 7, further comprising means for keeping the temperature of the raw material melt to be added at a temperature higher than the melting point of the raw material and lower than the temperature of the added intermediate polymer. The polymer polymerization apparatus according to claim 7, wherein the stirring apparatus of the intermediate reaction tank is a biaxial type. 8. The polymer polymerization apparatus according to claim 7, wherein the interval between the stirring blades of the stirring device of the intermediate reaction tank is narrower than the spacing of the stirring blades of the stirring device of the horizontal reactor in the preceding stage. The polymer polymerization apparatus according to claim 7, wherein the inner wall surface of the vertical reaction vessel is non-smooth at least in the vertical direction. The polymer polymerization apparatus according to claim 7, wherein the stirring device of the vertical reaction tank is a biaxial type. The horizontal reactor in the preceding stage of the intermediate reaction tank has a plurality of weirs arranged at appropriate intervals in the length direction, and has a through hole in the lower part of the weir. The polymer polymerization apparatus as described. The polymer polymerization apparatus according to claim 7, wherein each of the intermediate reaction tanks is provided with a liquid level gauge.

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