JP3350606B2 - Method for producing polylactic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polymer containing lactic acid as a main component.

[0002]

2. Description of the Related Art Polymers that are biodegradable or decompose in the natural environment are attracting attention from the viewpoint of environmental protection. Lactic acid-based polymer is excellent in degradability, heat resistance, melt moldability, strength, etc., and the main raw material lactic acid is obtained from agricultural products, so it is also advantageous in resources, and One is expected. The polymer containing lactic acid as a main component can be obtained by polymerizing a polymerization raw material containing lactic acid and / or lactide as a main component. The method of direct polymerization of lactic acid requires (1) high-purity lactic acid, (2) high vacuum is required to remove water generated during polymerization (condensation), (3) reaction speed is slow and polymerization takes a long time. And the like, and there is a problem in economy and quality. On the other hand, polymerization from lactide, which is a cyclic dimer of lactic acid, can be achieved by (1) raw material lactide can be easily purified and high purity can be obtained, (2) ring-opening polymerization can be easily and quickly performed by heating and melting, (3) Therefore, there is an advantage that the quality of the polymer is excellent, which is extremely advantageous industrially.

[0003]

However, in melt ring-opening polymerization of lactide, there is a problem that ring-opening polymerization and its reverse reaction occur in equilibrium, and a certain amount of monomer (lactide) remains after polymerization. If a large amount of lactide remains in the polymer, it will leach or rise during molding, polluting the environment,
There are problems such as speeding up the decomposability of the polymer and deteriorating heat resistance and other quality and physical properties. To remove residual lactide from the polymer after polymerization, there are methods such as extraction with a solvent and removal by vacuum, but these are industrially and economically disadvantageous. An object of the present invention is to provide a new method for effectively producing a polymer having a small amount of residual monomers from a polymerization raw material containing lactide as a main component.

[0004]

The method of the present invention comprises:
A polymerization raw material containing L-lactide and / or D-lactide as a main component is melt-polymerized (hereinafter, referred to as a first step), and then the polymerized polymer is cooled and solidified into chips (hereinafter, referred to as a second step), Further, solid-phase polymerization of the chip is carried out (hereinafter referred to as “third polymerization”).
In this case, 0.1 to 3% by weight of alcohol or lactone with respect to the polymerization system is present in the chip at the beginning of the solid phase polymerization step.

[0005] In the present invention, the polymerization raw material containing L- and / or D-lactide as a main component is L- and / or D-lactide.
It is a polymerization raw material containing 50% by weight or more of lactide. Similarly, a polymer containing lactic acid as a main component means that 50% by weight or more of the constituent components of the polymer are derived from L and / or D-lactic acid components (segments).
-Lactic acid homopolymers, L / D-lactic acid copolymers, and those obtained by copolymerizing 50% by weight or less of an ester bond-forming polymerization raw material and those obtained by mixing other components at 50% by weight or less.

[0006] The melt polymerization in the first step of the present invention comprises L and / or
Or D-lactide as a main component, if necessary, a polymerization catalyst,
A polymerization raw material to which other copolymer components, stabilizers, additives, coloring agents, and the like are added is heated and melted at a temperature not lower than the melting point of the obtained polymer (for example, about 170 ° C. for an L-lactic acid homopolymer). It can be easily performed by performing operations such as stirring, supply and discharge of an inert gas, and vacuum. For example, the polymerization raw materials may be mixed in advance and supplied to a device capable of effectively reacting, for example, a twin-screw kneader (polymerization machine), or the polymerization raw materials may be separately supplied to the twin-screw kneader and stirred therein. The reaction may be carried out while mixing. The polymerization temperature is, for example, preferably from 180 to 230 ° C, particularly preferably from 190 to 220 ° C, and the polymerization time is preferably from 3 minutes to 2 hours, particularly preferably from 5 minutes to 60 minutes. The weight average molecular weight of the obtained polymer is preferably 50,000 or more, particularly preferably 80,000 to 300,000.

[0007] The composition of the polymerization raw material supplied to the first step of the present invention is such that L-lactide and / or D-lactide is 50% by weight or more. It can be freely selected within a range of 50% by weight or less. In general, a copolymer containing lactic acid as a main component tends to have reduced crystallinity and melting point, improved flexibility and toughness, and increased degradability due to copolymerization. Examples of the copolymer raw material include dicarboxylic acids having a functional group capable of forming an ester bond, diols, hydroxycarboxylic acids, and lactones.To obtain a copolymer having a high degree of polymerization, those having a large molecular weight, such as a terminal Polymers such as aliphatic polyesters having a hydroxyl group or a carboxyl group, polyesters containing an aromatic component having a melting point of 180 ° C. or lower, polyethers, and oligomers thereof are preferred. Preferred aliphatic polymers as the copolymer component include polyethylene adipate, polyhexamethylene adipate, polycaprolactone, polyglycolic acid, polyhydroxybutyrate, and the like.As the polyester containing an aromatic component, alkylene terephthalate or alkylene isophthalate or Copolymers of an aliphatic polyester with alkylene sulfoisophthalate and the like can be mentioned. Polyethers include polyethylene glycol, polypropylene glycol, polytetramethylene glycol and copolymers thereof. The copolymerization ratio and the mixing ratio of the third component for the above purpose are often 0.5 to 50%, particularly 1 to 30%.
%, Most often from 2 to 20%.

Third step At the beginning of the solid phase polymerization, the alcohol and / or lactone to be present in the polymerization system can be added to the polymerization system at the end of the first step. For example, the mixture may be supplied into the system from a vent hole or a supply hole provided near the outlet of the twin-screw kneader, or may be injected into the system immediately before the extrusion die, and extruded while being mixed with, for example, a static mixer. . The addition rate of the alcohol or lactone is preferably 1 to 30% by weight, particularly preferably 3 to 10% by weight, based on the residual monomer. 20 in the first step
The residual monomer (equilibrium value) at the time of polymerization at about 0 ° C. is about 10% by weight.
About 3 to 1% by weight is preferable.

The alcohol and / or lactone present at the early stage of solid phase polymerization functions as a polymerization initiator for lactide remaining in the polymer (chip). Since the solid-phase polymerization is preferably performed at a temperature between the melting point of lactide (98 ° C.) and the melting point of the polymer, that is, in the range of 100 to 170 ° C., the boiling points (atmospheric pressure) of the alcohol and lactone to be added are , 100 ° C or higher, particularly preferably 120 ° C or higher, and most preferably 170 ° C or higher. Examples of the alcohol include monoalcohols, glycols, polyhydric alcohols, oligomers and polymers having a hydroxyl group at a terminal, and the like, for example, butanol, hexanol, octanol,
Addition of ethylene oxide to aliphatic alcohols such as decanol, lauryl alcohol and stearyl alcohol, alicyclic alcohols such as cyclohexanol, hydroxycarboxylic acids such as glycolic acid, lactic acid and hydroxybutyl carboxylic acid, hydroxybenzoic acid, phenol and bisphenol Aromatic alcohols, such as
Polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, and neopentyl glycol; and ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol. Can be Similarly, examples of the lactone to be present during the solid phase polymerization include glycolide, ε-caprolactone, β-propiolactone, β or γ-butyrolactone, and pivalolactone. It is considered that these lactones are ring-opened by a very small amount of water present in the polymerization system to become a hydroxycarboxylic acid and function as a polymerization initiator.

The alcohol and / or lactone which is the polymerization initiator of the third step is attached to the chip at the beginning of the second and / or third step by, for example, spraying or the like,
It can also penetrate and diffuse inside.

After the completion of the melt polymerization in the first step, the polymer is cooled and solidified to form chips (pellets). The polymer is extruded through, for example, a slit having a width of 0.1 to 2 mm or a hole having a diameter of 2 to 5 mm, cooled and solidified, and cut into chips. Water can be used for cooling, but it is necessary to dry later, and it is extremely difficult to completely dehydrate.When heated or re-melted with water, the polymer is easily hydrolyzed and the molecular weight is significantly reduced. There are problems such as. Therefore, cooling is preferably performed in a non-aqueous system. For example, an extruded gut-like or sheet-like polymer is placed on a metal roll cooled from the inside.
It is preferable to cool and solidify by contacting once to a plurality of times and then cut with a cutter. In this case, the atmosphere is air without moisture,
Alternatively, an inert gas such as nitrogen is preferable.

The temperature of the solid-state polymerization in the third step is not lower than the melting point of lactide and not higher than the melting point of polylactic acid, that is, 100 to
170 ° C, particularly preferably 120 to 165 ° C, is preferred. In order to effectively carry out the solid-phase polymerization, it is preferable that the polymer be sufficiently crystallized and the residual monomer (lactide), the polymerization initiator and the polymerization catalyst are collected in the amorphous portion. For this reason, it is preferable that the polymer be sufficiently heated to be crystallized before the solid phase polymerization or at the early stage of the solid phase polymerization. Since the crystallization temperature of polylactic acid is about 80 to 100 ° C., the second step or the third step
It is desirable to crystallize by heating at 80 ° C. or higher, particularly 100 to 160 ° C., for 5 minutes to 10 hours, preferably 10 minutes to 2 hours at the beginning of the process.

In order to promote crystallization of the polymer before or during solid phase polymerization, it is preferable to add a nucleating agent to the polymer in advance, for example, in the first step.
The crystal nucleating agent is an inorganic fine particle and / or a highly crystalline polymer, and is mixed and dispersed in a small amount in a polymer mainly composed of lactic acid. The nucleating agent may be added to the polymerization raw material in the first step, or may be added and mixed in the polymerization system at the end of the first step.

Examples of the inorganic compound fine particles used as a crystal nucleating agent include titanium oxide, zinc oxide, calcium sulfate,
Metal oxides and / or metal salts having a diameter of 1 nm to 2 μm, particularly 10 nm to 0.5 μm, such as barium sulfate, silica, zeolite, alumina, casium phosphate, kaolin, and calcium carbonate, which are white or almost non-toxic and have no toxicity. Is preferred. Similarly, examples of the highly crystalline polymer used as a crystal nucleating agent include polyethylene, polyolefins such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, aromatic polyesters such as polyhydroxybenzoic acid, and polyethers such as polyoxymethane. And a melting point of 80 ° C. or higher, particularly 100 ° C. or higher. These crystalline polymers are dispersed in a polymer containing lactic acid as a main component in the form of fine particles having a size similar to that of the inorganic particles (diameter: 10 nm to 10 μm),
It crystallizes (early after cooling) and acts as a crystal nucleating agent for polymers such as polylactic acid. The addition rate of these nucleating agents varies depending on the particle size, but is 1 ppm to 5% by weight,
Particularly, 10 ppm to 1% by weight is preferable. For example, diameter 10
If a particle of nm becomes the nucleus of a spherulite with a diameter of 1 μm,
The volume fraction of the nucleating agent is calculated as 1 ppm. In practice, all the particles are not completely dispersed and do not function effectively as a nucleating agent, so that an excess of nucleating agent of 10 times or more, sometimes 100 times or more of the calculated value is often added.

The solid-phase polymerization in the third step is performed by heating a polymer in the form of chips (pellets). The chips may be heated in an inert gas such as air or nitrogen, or may be heated in a vacuum to remove moisture and promote polymerization.
The heating temperature is 100 to 170 ° C. as described above, particularly 120 ° C.
To 165 ° C, and the heating time is preferably 1 to 100 hours, particularly preferably 5 to 50 hours. Industrially, for example, a cylindrical metal vertical tank is filled with chips, heated nitrogen gas is supplied from below and exhausted from above, chips are continuously supplied from above, and chips are continuously supplied from below. By taking it out, it can be done easily and efficiently. Further, the third step is divided into two parts. In the first half, a relatively low temperature (100 to 150 ° C.) and a normal pressure for a long time (20 to 50 hours) are performed at a relatively low temperature (100 to 150 ° C.) in order to crystallize the polymer and prevent lactide evaporation. It may be carried out at a slightly elevated temperature (160 ° C.) under reduced pressure for a short time (10 to 30 hours).

Third Step The molecular weight of the polymer after the solid phase polymerization is as follows:
It is preferably from 50,000 to 500,000, particularly from 80,000 to 300,000, and the content of the residual monomer (lactide) is preferably 5% by weight or less, particularly preferably 3% or less, most preferably 2% or less.

In the present invention, the average molecular weight of a polymer containing lactic acid as a main component is determined by the GPC (calibration using a polystyrene standard sample) analysis of a 0.1% by weight solution of a chloroform solution of a sample. ), And the weighted average value. Similarly, the residual monomer is measured by a GPC method calibrated using a known lactide or another liquid chromatography method. In the present invention, parts and percentages are by weight unless otherwise specified.

[0018]

【Example】

(Example 1) For L-lactide having an optical purity of 99.9% or more, 0.1% of tin octylate as a polymerization catalyst, 0.1% of Irganox 1010 manufactured by Ciba-Geigy as an antioxidant, and fluidity. 0.3% of magnesium stearate as an improver, 0.5% of titanium oxide having a diameter of 0.1 μm or 1.0% of powdery high-density polyethylene having a molecular weight of 50,000 as a nucleating agent are mixed and supplied to a twin-screw kneader. And at 190 ° C
Polymerized for 2 minutes, extruded from a hole with a hole diameter of 2 mm, solidified in contact with five cooling metal rolls (5 ° C.) in nitrogen, and cut with a cutter to obtain a chip having a diameter of 3.2 mm and a length of 2.5 mm. Was. From the final vent hole of the twin screw kneader of the first step, glycerin 0.1%, lauryl alcohol 0.2%, triethylene glycol 0.1%, molecular weight 4 as a polymerization initiator
The experiment was carried out by mixing 0.2% of polyethylene glycol 0.2% each. Each of the obtained chips was heat-treated (crystallization and initial solid-phase polymerization) at 120 ° C. in a nitrogen atmosphere for 10 hours.
Solid phase polymerization was carried out at 60 ° C. for 20 hours. For comparison, an experiment in which the nucleating agent and the polymerization initiation were not added was also performed in the same manner. Table 1 shows the average molecular weight and residual monomer content of the polymer obtained in each experiment.

[0019]

[Table 1] As shown in Table 1, the nucleating agent and the polymerization initiator have an effect of increasing the molecular weight and an effect of reducing the residual monomer.

(Embodiment 2) In substantially the same manner as in Embodiment 1,
However, as a main polymerization raw material, the diameter of L-lactide is 10 n.
m is mixed and metered and supplied to a twin-screw kneader, while tin octylate, an antioxidant Irganox 1010, a fluidity improver magnesium stearate, Diameter 10 as nucleating agent
of silica particles having a molecular weight of 8000 as a copolymer component.
The melted and mixed product of polyethylene glycol (PEG) is calculated and supplied to a twin-screw kneader. Tin octylate, Irganox 1010, magnesium stearate, silica particles, and PEG were 0.3 to L-lactide, respectively.
%, 0.1%, 0.3%, 0.1%, and 2%. In the same manner as in Example 1, oligomers of hexanediol, ε-caprolactone, and hexaneadipate having hydroxyl groups at both ends and an average degree of polymerization of 4 from the final vent hole of the twin-screw kneader were 0.1% each. , 0.2%,
0.3% was mixed. Table 2 shows the results of cooling, solidification, chipping, and solid-phase polymerization of the polymer. As can be seen from Table 2, Experiment No. 1 according to the present invention was compared with Comparative Example. 9-11
It is recognized that the polymer has a high molecular weight and a low residual monomer.

[0021]

[Table 2]

[0022]

According to the present invention, a polymer containing lactic acid as a main component having a high degree of polymerization and a small amount of residual monomers can be easily and effectively produced at low cost. The resulting polymer has less coloration and other excellent quality, molded products, films,
It can be used for various applications as sheets, fibers, knitted fabrics, nonwoven fabrics, papers and other products, and can utilize excellent moldability, workability, thermoplasticity and decomposability.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitomi Ohara 1 Shiwazu Works, Shimanzu Seisakusho Co., Ltd., Shigazu, Nakagyo-ku, Kyoto, Japan Inside the plant (72) Inventor Seiji Sawa 1 Nishinokyo Kuwaharacho, Nakagyo-ku, Kyoto Shimazu Works Sanjo Plant (72) Inventor Yasuhiro Fujii 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto Shimazu Works Sanjo Factory (56) Reference Reference JP-A-63-17929 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (5)

(57) [Claims] 1. A polymerization raw material containing L-lactide and / or D-lactide as a main component is melt-polymerized (first step), and then the polymerized polymer is cooled and solidified into chips (second step). When the solid phase polymerization of the chip is performed (third step) , a polymerization system is added to the chip at the beginning of the solid phase polymerization step.
A method for producing a polymer, characterized in that 0.1 to 3% by weight of alcohol or lactone is present. 2. The method according to claim 1, wherein the alcohol and / or lactone present at the beginning of the third step is added between the end of the first step and the beginning of the third step. Wherein the alcohol and / or lactone initially present in the third step, the method according to any one of claims 1-2, characterized in that is more than the boiling point 100 ° C.. 4. A nucleating agent composed of fine particles of an inorganic compound and / or a highly crystalline polymer is added to a polymerization system in advance, and while the lactic acid-based polymer is crystallized or after crystallization, The method according to any one of claims 1 to 3, wherein solid phase polymerization is performed. 5. The solid-phase polymerization of the third step is carried out at 100 to 170.
The method according to any one of claims 1 to 4, characterized in that 1 to 100 hours at a temperature of ° C..