JP3419609B2 - Polylactic acid demonomerization apparatus and demonomerization method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an apparatus and method for removing low molecular weight substances such as lactide in polylactic acid.

[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 purposes such as uniaxially or biaxially stretched films, fibers, and injection molded products.

[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. Polylactic acid thus obtained, in order to facilitate handling in the molding process, in advance of pellet-shaped products such as rice grain size to pea-sized spheres, cubes, cylinders, crushed shapes, etc. To be 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.
The temperature was as high as 200 ° C., and when such a final polymer of polylactic acid was taken out from the reactor in a molten state, a large amount of lactide was 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.

These lactides and decomposed products sublimate during injection molding or spinning using polylactic acid pellets and adhere to dies or nozzles, which hinders the 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.

Therefore, various methods for removing monomers from polylactic acid have been proposed, for example, JP-A-3-14829. This describes a method of removing residual monomers and low-molecular-weight volatiles by keeping the polyester in the range of the melting point or higher and 250 ° C. and reducing the pressure to 5 mmHg or lower. It is stated that it hardly volatilizes.

Further, in Japanese Patent Laid-Open No. 5-255488, 5
A method of increasing the molecular weight by polycondensation by a dehydration reaction by heating a low-molecular-weight lactic acid polymer having an individual particle size of μ to 5 mm at a temperature higher than the glass transition temperature and lower than its melting point is described. ing. However, this method requires 240 hours of operation according to the example, and is unlikely to be industrially feasible. Moreover,
This method is mainly intended for medical materials, and therefore is characterized by increasing the molecular weight without a catalyst, and is not focused on reducing low-molecular substances.

Further, JP-A-3-14829 describes a method for reducing the pressure while keeping glycolide and / or lactide in a molten state. However, in this specification, there is no description about a copolymer or a mixture other than a copolymer of glycolide and / or lactide, and no reference is made to the device.

Therefore, an object of the present invention is to efficiently remove volatile impurities such as low molecular weight substances such as unreacted monomers with a novel apparatus.

[0010]

In order to solve the above-mentioned problems, the present inventors have proposed a horizontal reactor in which at least one rotating shaft having a stirring blade is arranged in parallel in a vessel, and a horizontal reactor. Provided is a de-monomerization device for polylactic acid after completion of polymerization, which is provided with an inlet / outlet port for a reaction substance and a deaeration port.

Here, the horizontal reactor is not particularly limited as long as it has a structure in which stirring blades are arranged in parallel in the vessel.
For example, a single-screw or twin-screw extruder, a Sumitomo Heavy Industries byvolac, and a Hitachi glass wing polymerization machine can be used. Further, regardless of the shape of the screw or blade, a plurality of horizontal reactors may be connected in series.

The substance to be reacted is polylactic acid, which is not limited to polylactic acid homopolymer but is copolymerized with lactones such as β-propiolactone, δ-valerlactone, ε-caprolactone and δ-butyllactone. And copolymers with higher alcohols. Also, a mixture of polylactic acid and another resin may be used. The polylactic acid may be produced either by direct polymerization of lactic acid or ring-opening polymerization of lactide.

In the case of the production method by ring-opening polymerization of lactide,
The polymerization temperature is 140 to 210 ° C., preferably 150 to 18 in order to suppress racemization and decomposition coloring of L-lactide.
Perform at 0 ° C. By polymerization, polylactic acid having a weight average molecular weight of 50,000 to 300,000 can be obtained. However, the weight average molecular weight of polylactic acid in this specification means the weight average molecular weight of only the polymer portion in the GPC chromatogram.

As the catalyst used for the polymerization, tin compounds such as tin octylate, titanium compounds such as tetraisopropyl titanate, zirconium compounds such as zirconium isopropoxide, antimony compounds such as antimony trioxide are all used. A conventionally known catalyst can be used for the polymerization of lactic acid. Also, depending on the amount of catalyst added,
It is also possible to adjust the molecular weight of the final polymer. The lower the amount of catalyst, the slower the reaction rate, but the higher the molecular weight. A nucleating agent (talc, clay, titanium oxide, etc.) may be added.

The lactide used in the polymerization is D-, L-,
It can be copolymerized with lactones such as β-propiolactone, δ-barrel lactone, ε-caprolactone glycolide, δ-butyl lactone, etc., selected from DL- or a mixture of D- and L-. Further, the physical properties can be controlled by using a polyhydric alcohol such as glycerin. The polymerization reaction varies depending on the type of catalyst, but when tin octylate is used, it is 0.0001 relative to the weight of lactide.
-0.1 wt%, preferably 0.05-0.001 wt% of the catalyst is used, and usually heat-polymerized for 1.0-30 hours.
The reaction is preferably carried out in an atmosphere of an inert gas such as nitrogen or in an air stream.

The produced polylactic acid is continuously charged from the inlet of the substance to be reacted of the horizontal reactor to demonomerize it. During the demonomer operation, phosphoric acid or phosphorous acid compounds may be added to deactivate the catalyst. The addition amount is preferably 0.5 to 20 times mol of the catalyst used for the polymerization. This range is for completely deactivating the catalyst used for the polymerization. If it is less than 0.5 times by mole, the catalyst cannot be deactivated, and if it is more than 20 times by mole, there is no difference in effect. More specifically, when a tin compound is used as a catalyst for polymerization, the ratio of tin to phosphorus compound (provided that tin is divalent and phosphorus compound is tetravalent)
At 0.03 to less than 0.9, preferably 0.05 to 0.8
The range amount of is used. In addition, the addition of this catalyst caused the metal content in the catalyst during polymerization to be substantially 30 ppm. Below.

The types of phosphoric acid or phosphorous acid compounds include phosphoric acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, polyphosphoric acid monoester, polyphosphoric acid diethyl ester, triethyl phosphate and triphenyl phosphate. , Tetraethyl pyrophosphate, tetraphenyl pyrophosphate, triethyl phosphite, triphenyl phosphite, hexamethylpyrroamide pyrophosphate, ATP (adenosine triphosphate), tricalcium phosphate, calcium phosphinate, diphosphate Sodium or the like can be used.

In the horizontal reactor, heating is performed under reduced pressure to a temperature above the glass transition point of polylactic acid. The reduced pressure is preferably 500 mmHg or less, and the heating temperature is preferably 100 to 250 ° C.

The polylactic acid demonomerized in the horizontal reactor is, for example, a water tank or a Sandvik strip former, a funnel former, a double roll feeder, a Kaiser rotary drop former, and a piston drop former. By passing through a drum cooler made by Mitsubishi Kasei Engineering Co., Ltd., a steel belt cooler made by Nippon Belding Co., a hybrid former, etc., it is cooled to below the glass transition temperature and taken out. The depolymerized polylactic acid of the present invention has a weight average molecular weight of 100,000 to 500,000 and unreacted lactide of 1.0% or less.

The monomers removed in the present invention are mainly unreacted lactide. The removed lactide is recovered by a cooling condenser, cyclone, filter, lactic acid or molten lactide scrubber, etc.
Used again as a raw material. When a condenser is used, it can be considered whether the lactide is cooled and solidified and captured, or is captured in a liquid state, but the liquid state is preferable for continuous operation.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the demonomerizing apparatus of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a demonomerization apparatus, in which 1 is a horizontal reactor main body, and a stirring blade 6 is housed in the main body 1 in a direction parallel to the main body. The stirring blade 6 is rotated by the motor 5. Further, the main body 1 is provided with a reacting substance inlet 2 for supplying polylactic acid, which is a reacting substance, and a reacting substance outlet 3 for taking out the demomerized reacting substance, and above the reacting substance inlet 2. Is connected to a reactor (polymerizer) or raw material feeder not shown. The supply amount of polylactic acid is controlled by controlling the open / close valve 7.
Further, the main body 1 is provided with a deaeration port 4 for reducing the pressure inside the main body, and is connected to a vacuum pump P. Since the removed monomer is taken out from the degassing port 4, the vacuum pump P
A condenser (not shown) may be provided on the upper part of the column to collect and reuse the removed monomer. Although not shown,
A heating mechanism and a temperature sensor are also installed in the horizontal reactor main body 1 to control the temperature inside the main body 1. Further, the horizontal reactor main body 1 may be provided with an addition port for adding a catalyst for promoting depolymerization of polylactic acid into lactide.

With the above-mentioned constitution, the demonomer of polylactic acid is carried out as follows. First, polylactic acid is supplied to a raw material feeder (not shown), or polylactic acid in the reactor (polymerizer) is taken out by a pump, and an opening / closing valve 7 is opened to continuously construct the horizontal reactor main body 1
Polylactic acid is introduced into the inside. The vacuum pump P is operated to reduce the pressure in the horizontal reactor main body 1 through the degassing port 4, and the main body 1 is heated by a heating mechanism (not shown). The polylactic acid is melted and only the low molecular weight component, for example, lactide, is gasified and removed from the degassing port 4. The degassed low-molecular component is cooled by a condenser (not shown) and can be reused for polymerization.

After the treatment for a predetermined time in the horizontal reactor main body, the polylactic acid from which the low molecular weight components have been removed is taken out from the reaction target substance outlet 3. This polylactic acid is introduced into, for example, a cooling device and cooled to near room temperature in the cooling device.
To be

[0024]

EXAMPLES The method of the present invention was confirmed by the following experiments. [Experimental Example 1] A reactor having a volume of 22 L (Sumitomo Heavy Industries Super Blend) was charged with 20 kg of in-house manufactured lactide,
After melting at 110 ℃, add 50ppm tin octylate and add 1
The temperature was raised to 70 ° C. At this time, the inner surface of the super blend was rotated at 80 rpm, and the outer double helical ribbon blade was rotated at 30 rpm in the opposite direction. After 8 hours, the polymer was taken out by a gear pump at 10 kg / hour, and the demonomerizing device Kurimoto twin-screw extruder (KEXN-3) was used.
0) (8 barrels), and phosphorous acid was added at 10 mg / min from the 3rd barrel. A vacuum was drawn from the vent port of the seventh barrel at 15 mmHg. At this time, the barrel temperature was 190 to 200 ° C. The molecular weight was 180,000 and unreacted lactide was 7% at the super blend outlet, but it was 1000 ppm at the extruder outlet.

[Experimental Example 2] In-house lactide 5 was placed in a reactor (Shinko Pantech's log horn blade) having a volume of 50 L.
Charge 0 kg, melt at 110 ° C, and stannous octylate 1
0 ppm was added and the temperature was raised to 190 ° C. At this time, the stirring speed was 60 rpm. After 24 hours, the polymer was taken out at 5 kg / hour by a gear pump, introduced into a high-viscosity horizontal biaxial reactor (Vivolac) manufactured by Sumitomo Heavy Industries, which is a demonomer, and phosphorous acid was added at 12 mg / min from the inlet. A vacuum was drawn from the vent port at 20 mmHg.
The molecular weight was 150,000 and unreacted lactide was 15% at the outlet of the reactor, but it was 800 ppm at the outlet of the extruder.

The analytical conditions of the experimental example are as follows. <Measurement of molecular weight; GPC measurement> Shimadzu Corporation detector; RID-6A pump; LC-9A column oven; CTO-6A column; Shim-pack GPC-801C, -804C, -806C, -8025C in series Analysis conditions Solvent: Chloroform Flow rate: 1 ml / min Sample amount: 200 μl (Sample 0.5 w / w% was dissolved in chloroform.) Column temperature: 40 ° C. <DSC measurement> Shimadzu Corporation DSC-50 heating rate; 10 ° C / min sample amount; 6-7 mg

[0027]

By using the demonomerizing apparatus of the present invention,
It is possible to produce polylactic acid that does not contain low-molecular components and has excellent moldability. Therefore, the polylactic acid treated by the method of the present invention is excellent in moldability of films, fibers, injection molded products and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the device of the present invention.

[Explanation of symbols]

1; Horizontal reactor main body 2; Reacted substance inlet 3; Reacted substance outlet 4; Degassing port 6; Stirring blade P; Vacuum pump

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Sawa 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto Shimazu Seisakujo Sanjo factory (72) Inventor Akiki Wasaki Nishinokyo Kuwabara-cho 1 Nakano-ku, Kyoto Shimadzu Sanjo Co., Ltd. In-house (72) Inventor Yasuhiro Fujii 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto Shimazu Manufacturing Sanjo Factory (72) Inventor Atsushi Atsushi Nishinokyo Kuwahara-cho 1, Nakagyo-ku, Kyoto Shimazu Manufacturing Sanjo Factory (72) Inventor Author Masahiro Ito 1 Kinohara Kuwahara-cho, Nishinokyo, Nakagyo-ku, Kyoto Inside Shimadzu Sanjo Factory (56) References JP-A-7-305228 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (2)

(57) [Claims] 1. A horizontal reactor having at least one rotating shaft having a stirring blade and arranged in parallel in a vessel, and a reactor after the completion of polymerization, which comprises a reactant inlet / outlet port and a degassing port provided in the reactor. De-monomerizer for polylactic acid. 2. A demonomerization method of polylactic acid after completion of polymerization, in which polylactic acid after completion of polymerization is continuously charged from an inlet of a substance to be reacted using the apparatus of claim 1 and depressurization is performed from a degassing port.