JPH08169942A - Apparatus for producing polylactic acid - Google Patents

Abstract

PURPOSE: To provide an apparatus for industrially mass-producing polylactic acid. CONSTITUTION: After the first-step polymn. is carried out in a reactor 1, a valve V is opened to pour the formed polymer (polylactic acid) into a tray 7 at a cooling and molding section B. When the polymer in the tray exceeds a prescribed amt., it overflows and is sent to a grinding roll 10 through a conveyor belt 8 cooled with a cooling-water-spraying means 13. Polylactic acid ground with the roll 10 is fed into a reactor 16 to be subjected to the second- step polymn.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an apparatus for producing solid high molecular weight polylactic acid. The polylactic acid obtained by the apparatus of the present invention has a high molecular weight and has various forms such as a granular form, a pellet form and a plate form.

[0002]

2. Description of the Related Art Polylactic acid has high biosafety, and lactic acid, which is a decomposition product, is absorbed in vivo. As described above, polylactic acid is a highly biosafe polymer compound, and is also used for medical purposes such as surgical sutures, drug delivery (sustained release capsules), and reinforcing materials for fractures, and decomposes in natural environments. Therefore, it is attracting attention as a degradable plastic. It is also used for various applications as uniaxially and biaxially stretched films, fibers, release molded products and the like.

[0003] Such a method for producing polylactic acid includes a direct method for directly dehydrating and condensing lactic acid to obtain a desired product, and a method in which a cyclic lactide (dimer) is once synthesized from lactic acid and purified by a crystallization method or the like. Then, ring-opening polymerization is performed. Lactide synthesis, purification and polymerization procedures are described, for example, in US Pat.
57,537: Published European Patent Application No. 261,5
72: Polymer Bulletin, 14,491-495 (1985); and Makromol. Chem., 187, 1611-1628 (1986). In addition, Japanese Patent Publication Sho-56-146
In JP-A-88, two molecules of cyclic diester are used as intermediates,
It is disclosed that polylactic acid is produced by polymerizing this using tin octylate and lauryl alcohol as catalysts. The polylactic acid thus obtained is used in advance in order to facilitate the handling in the molding process, and in advance, spherical, cubic, columnar, crushed and other pellet-shaped products having a size of about rice grains to bean grains. Is done.

[0004]

However, the melting point of high molecular weight polylactic acid having a molecular weight of 100,000 to 500,000 is 175 to 175.
Conventionally, such a final polymer of polylactic acid was taken out of the reactor in a molten state at a high temperature of 200 ° C., and when it was heated to a temperature equal to or higher than the melting point, polylactic acid was decomposed or colored. Furthermore, at such temperatures, large amounts of lactide were generated in the polymer. This is probably because the equilibrium between the polymer and lactide is inclined toward the lactide side at such a temperature.

[0005] These lactides and decomposed products are raised during injection molding or spinning using polylactic acid pellets as a raw material, and adhere to dies or nozzles, thereby hindering operation. Furthermore, lactide and decomposed products lowered the glass transition temperature and melt viscosity of the polymer, and significantly deteriorated the moldability and heat stability.

[0006] Therefore, in order to solve such a problem, the applicant of the present invention, in the polymerization of polylactic acid, performs the first stage melt polymerization at a temperature lower than the melting point before obtaining the final product to form the polylactic acid into pellets. We have proposed a method in which it is molded and then made into the final polymer by the second-stage solid-state polymerization (Japanese Patent Application No. 6-83242).
22165).

However, in the past, there was no apparatus for industrially carrying out the above method, and polylactic acid could not be produced in a large amount.

An object of the present invention is to provide a production apparatus for industrially producing a large amount of polylactic acid.

[0009]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a reactor in which lactide is used as a main raw material to carry out a first stage polymerization to obtain solid polylactic acid by melt polymerization, and A cooling / molding unit that cools and conveys the solidified polylactic acid that has been polymerized and is molded during the conveying process, and the solid polylactic acid that has been molded in the cooling and molding unit is cooled in the second stage at a temperature lower than that in the first stage polymerization. Provided is a polylactic acid production apparatus including a reactor for performing eye polymerization.

The first-stage polymerization reaction is carried out at a relatively low temperature without decomposition or coloring, and pelletized solid polylactic acid is molded. The reaction temperature in the first step is 120 to 190 ° C, preferably 140 to 170 ° C, and the average molecular weight is 50,000 to 20.
In the meantime, polylactic acid having a lactide content of 10 to 50% by weight is obtained.
The polylactic acid obtained in the first stage has a viscosity of 1000 to 20,0.
00 pois, preferably 3000-7000 pois.
Such polylactic acid is easy to mold into pellets,
Moreover, fusion does not occur in the second-stage heat polymerization reaction.

The reactor for carrying out the first stage polymerization may be a vertical reactor or a horizontal reactor. When a vertical reactor is used, paddle blades, turbine blades, anchor blades, double-motion blades, helical ribbon blades and the like can be used as the stirring blades, but when the viscosity becomes high, helical ribbon blades are used. When a horizontal reactor is used, the stirring blade is 1
Axial and biaxial extruders can be used.

The polymer (polylactic acid) is taken out of the reactor by extrusion with an inert gas such as nitrogen when the viscosity is low, and by a gear pump when the viscosity is high.

The catalyst used for the polymerization includes tin compounds such as tin octylate, titanium compounds such as tetraisopropyl titanate, zirconium compounds such as zirconium isopropoxide, and antimony compounds such as antimony trioxide. In any case, a conventionally known catalyst can be mentioned for the polymerization of lactic acid. Further, the molecular weight of the final polymer can be adjusted by adjusting the amount of catalyst added.
The lower the amount of catalyst, the slower the reaction rate, but the higher the molecular weight. Nucleating agents (talc, clay, titanium oxide, etc.)
May be added.

The lactide used for the polymerization is D- or L.
It may be a mixture of-, DL- or D-, L-, and copolymerization with lactones such as β-propiolactone, δ-valerlactone, ε-caprolactone glycolide and δ-butyllactone is also possible. Further, the physical properties can be controlled by using a polyhydric alcohol such as glycerin.
The polymerization reaction is 0.0001 to 0.1 with respect to the weight of lactide.
The catalyst is used in an amount of 0.5% by weight, preferably 0.05 to 0.001% by weight, and usually heat-polymerized for 0.5 to 5 hours. The reaction is preferably carried out in an atmosphere of an inert gas such as nitrogen or in an air stream.

The cooling / molding unit cools and molds the polylactic acid taken out from the reactor in which the first-stage polymerization is carried out, and conveys it to the reactor in which the second-stage polymerization is carried out. For example, a belt cooler. , Or use a drum cooler. At the time of cooling, it is preferable to blow dehumidified air or nitrogen so as to prevent water from adhering to the polylactic acid so that the water content is 50 ppm or less on the cooling surface and in the gas phase. Cooling temperature is 1
It may be lower or higher than the crystallization temperature of the polylactic acid formed by the second-stage polymerization. Molding is carried out at the outlet side of the belt cooler or drum cooler, for example, by taking out in a strand form from a die having a diameter of 2 to 5 mm to cut into chips with a pelletizer, making into marble in a granulator, and taking out in a seal form. It is conceivable to arrange things to be crushed, but it is not limited to these.

A vertical reactor or a horizontal reactor is used as a reactor for carrying out the second-stage polymerization. In the reactor, it is left standing or fluidized and heated. When fluidized, it is preferable to blow it up with a conical dryer or an atmosphere of an inert gas such as nitrogen.

The temperature of the second-stage polymerization reaction is set to be not lower than the melting point of lactide and lower than the first-stage polymerization temperature by 5 ° C. or more, preferably 10 ° C. or more. Therefore, the reaction temperature in the second stage is 100 to 175 ° C, preferably 120 to 175 ° C.
It is 140 ° C. This makes it possible to prevent fusion in the second-stage polymerization reaction. Reaction time is 6-9
0 hours, preferably 20 to 40 hours. In order to shorten the reaction time, the reaction temperature may be increased as the second-stage polymerization proceeds. Final polymer melting point is 1
Since the temperature is from 70 to 180 ° C, the temperature can be raised to around 175 ° C. Here, in order to prevent the promotion of unreacted lactide, 0.1 to 1
0 kgf / cm ² preferably it may be the reaction under a pressure of 1~3kgf / cm ^2. A catalyst may be further added immediately before starting the second stage polymerization reaction. Further, finally, in order to remove a trace amount of low molecular weight, it may be heated to 70 to 185 ° C. under reduced pressure of 1 to 200 mgHg.

Further, the control of the polymerization conditions for the first-stage and second-stage polymerization, the driving of the cooling / molding section, etc. may be automatically controlled by a computer. Therefore, the present invention uses a lactide as a main raw material, a reactor for carrying out a first-stage polymerization to obtain solid polylactic acid by melt polymerization, and cool and convey the solid polylactic acid polymerized and molded in the reactor, and Cooling that is molded during the transfer process
A molding section, a reactor for carrying out the second-stage polymerization of the solid polylactic acid molded in the cooling / molding section at a temperature lower than the first-stage polymerization, and the first- and second-stage polymerization conditions, There is also provided a polylactic acid production apparatus including a control unit that controls the operation of the cooling / molding unit.

[0019]

In the present invention, the average molecular weight of 50,000 to 200,000 and the lactide content of 10 to 50 are obtained by the reactor for carrying out the first stage polymerization.
A polylactic acid of weight% is obtained, and while it is cooled in the cooling / molding section, it is conveyed to the reactor for carrying out the second-stage polymerization. The reactor for the second-stage polymerization is set at 5 ° C. or more, preferably 10 ° C. or more lower than the first-stage polymerization temperature, and the solid-phase polymerization is performed here.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the device according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a production apparatus according to the present invention, in which A is a reactor for the first-stage polymerization, B is a cooling / molding section,
C is a reactor for carrying out the second-stage polymerization.

The reactor A comprises a hollow cylindrical reaction tank 1 and a support base 2 for supporting the reaction tank 1. The reaction tank 1 is provided with openings for a raw material supply port 6 and a discharge port for the discharge port. A take-out nozzle 5 is connected to the opening. The nozzle 5 is provided with a valve V for controlling the amount of polylactic acid supplied to the next cooling / molding section B.

A helical ribbon blade 3 is housed in the reaction tank 1, and its drive source (motor) 4 is installed on the other opening side of the reaction tank 1. A nitrogen gas supply pipe (not shown) after the raw material is supplied is connected to the raw material supply port 6 of the reaction tank 1, and nitrogen gas is supplied into the tank 1 from a gas cylinder (not shown) through the pipe. Although not shown around the reaction tank 1, a heating mechanism (heater) for heating the reaction tank 1 is provided, and the temperature inside the reaction tank 1 is monitored by a temperature sensor (not shown). There is.

The cooling / molding section B is provided with a supply tray 7 disposed below the take-out nozzle 5, a conveyor belt 8 for conveying the polylactic acid overflowing from the supply tray 7, and a pulverizer for pulverizing the conveyed polylactic acid. It is composed of rolls 10. The supply tray 7 is separated from the conveyor belt 8 (without contact)
Is supported by a supporting member (not shown), and when polylactic acid in a range exceeding the capacity of the supply tray 7 is supplied,
The conveyor belt 8 overflows. In addition, the surface of the supply tray 7 that overflows toward the conveyor belt 8 is provided with an inclination so that the surface easily overflows.

The conveyor belt 8 is rotated by rotating rollers 9, 9 ', and a cooling water spraying mechanism 13 for cooling the conveyor belt 8 is installed on the back side of the conveyor belt 8. The cooling water spraying mechanism 13 is one in which a plurality of cooling water supply nozzles are attached to a panel having a width substantially the same as the lateral width of the conveyor belt, and the cooling water is sprayed directly on the back side of the conveyor belt. A blowing nozzle 14 for blowing dehumidified air or nitrogen is provided on the front side of the conveyor belt to prevent water from adhering to the polylactic acid. The nozzle 14 is supported by a support mechanism (not shown) at a distance from the conveyor belt, and the number of nozzles may be plural.

A windshield panel 11 for preventing the conveyed polylactic acid from scattering is provided near the rotary roller 9 ', and the above-mentioned crushing roll 10 is provided below the panel 11. . The crushing roll 10 is rotated by a rotating mechanism (not shown), and the protrusion thereof crushes the polylactic acid. The crushed polylactic acid is
Enter the discharge tray 12. A crusher (not shown) for further crushing the crushed polylactic acid is housed in the discharge tray 12, and the re-crushed polylactic acid is stored in the discharge tray 12.
Via a nozzle 15 connected to the lower opening of the reactor C into the reactor C for the second stage polymerization. The nozzle 15 has a reactor C
A valve may be provided to control the amount of polylactic acid supplied to the.

Similar to the reactor A, the reactor C comprises a hollow cylindrical reaction tank 16 and a support 17 for supporting the same, and the reaction tank 16 is connected to the above-mentioned nozzle 15 and molded into A supply port 18 for supplying lactic acid is provided. Although not shown, a heating mechanism for heating the reaction tank 16 is provided around the reaction tank 16. The temperature inside the reaction tank 16 is a temperature sensor (not shown).
Is being monitored by. A paddle blade 19 is housed in the reaction tank 16, and its drive source (motor) is installed on the supply port 18 side. Further, the reaction tank 16 is provided with circulation ports 20 and 21 for circulating the nitrogen gas, and the nitrogen gas is blown from the circulation port 20 by the blower 22. The nitrogen gas is heated by the heater 23 so that the temperature inside the reactor C does not decrease due to the nitrogen gas. Further, numeral 24 indicates a punching board so that the product obtained as a result of the second stage polymerization reaction does not block the circulation port 20.

With the above constitution, polylactic acid is produced as follows. First, L-lactide and a catalyst (tin octylate, 0.01% by weight) are put into the reaction tank 1 through the raw material supply port 6. At this time, the valve V is closed. The raw material supply port 6 is closed, a nitrogen gas supply pipe is connected to perform nitrogen substitution, and then a heating mechanism (not shown) and the helical ribbon blade 3 are operated to perform the first-stage polymerization. At this time, the polymerization temperature is monitored and controlled within a certain range.

When the first stage polymerization reaction proceeds after a certain period of time, the valve V is opened and the polymer (polylactic acid) is supplied from the nozzle 5 to the tray 7. At this time, driving of the conveyor belt 8 and operation of the cooling water spraying mechanism 13 and the spraying nozzle 14 are started, and if polylactic acid overflows from the tray 7, it can be transported to the crushing roll 10. When the valve V is opened, the nitrogen gas is still supplied, so that the valve 7 is pushed out, and the polylactic acid is easily supplied to the tray 7.

The polylactic acid conveyed to the crushing roll 10 is
Here, it is roughly crushed and enters the discharge tray 12. After being pulverized again in the discharge tray 12, the polylactic acid is added to the reaction tank 16
to go into. When entering the reaction tank 16, the paddle blade 19, the heating mechanism (not shown), and the blower 22 are operated to perform the second-stage polymerization while blowing up the nitrogen gas. After a lapse of a predetermined time, the polymer is taken out from the reaction tank 16.

The polymerization temperature of the first and second stages of polymerization,
The polymerization time, the opening / closing operation of the valve V, etc. are automatically controlled by a computer (not shown).

[0031]

According to the production apparatus of the present invention, a high molecular weight polylactic acid molded article (pellet) having a molecular weight of 200,000 to 500,000, which is free from coloring and decomposition products, can be produced.

[Brief description of drawings]

FIG. 1 is a schematic view of a manufacturing apparatus of the present invention.

[Explanation of symbols]

A ... Reactor for first-stage polymerization B ... Cooling / molding section C ... Reactor for second-stage polymerization 1, 16 ... Reaction tank 3 ... Helical ribbon blade 8 ... Conveyor belt 10 ... Grinding roll 13 ... Cooling Water spray mechanism 19 ... Paddle wings

Claims (1)

[Claims] 1. A reactor in which lactide is used as a main raw material and a first-stage polymerization for obtaining solid polylactic acid by melt polymerization, and solid polylactic acid polymerized and molded in the reactor are cooled and conveyed,
In addition, a cooling / molding unit for molding in the conveying process and a reactor for carrying out the second-stage polymerization of the solid polylactic acid molded in the cooling / molding unit at a temperature lower than the first-stage polymerization Lactic acid production equipment.