JPH09241494A - Lactic acid polymer composition improved in physical property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain a composition useful as a biodegradable plastic molding material excellent in flexibility at a low cost by refluxing a lactide generated as a by-product during the reaction process to the reaction system. SOLUTION: This lactic acid polymer composition containing lactic acid polymer of a weight-average mol.wt. of 50,000-200,000 and a solvent high in a vacuum boiling point is obtained by polycondensing lactic acid in the solvent, while a lactide generated as a by-product during the reaction process is refluxed to the reaction system. The solvent is the one having a boiling point of 250-350 deg.C under the atmospheric pressure, e.g. dibutyl phthalate, and is preferably added in an amount of 5-25 pts.wt. per 100 pts.wt. of the lactic acid oligomer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lactic acid polymer composition useful as a biodegradable plastic and a method for producing the same, and more particularly to a lactic acid polymer composition useful as a biodegradable plastic molding material having excellent flexibility and It relates to the efficient manufacturing method.

[0002]

2. Description of the Related Art Biodegradable plastics have recently attracted a great deal of attention as a material that is decomposed in the environment after fulfilling the purpose of use and is eventually reduced to the natural world in the form of a low molecular compound. . Among them, aliphatic polyesters are completely decomposed into monomers by microorganisms and water, and are eventually incorporated into the natural material cycle as carbon dioxide and water. Initially, recently, application development to general-purpose materials, which are expected to be discarded into the environment after use, is being considered.

As a representative of such aliphatic polyester-based biodegradable plastics, lactic acid polymer has excellent mechanical strength and transparency, and further has good compatibility with other polymers and is easily modified. Therefore, it can be easily decomposed into a monomer by heating operation or addition of a specific solvent.
Even as a material that can be recycled as a monomer, its application development is highly expected.

In addition to the above, since it has excellent decomposition characteristics, it can be efficiently reduced in volume and completely decomposed with low energy by enzymatic decomposition or hydrolysis by various microorganisms. Therefore, it is attracting attention as a material that significantly reduces the load on the environment during processing compared to conventional general-purpose plastics.

As described above, a method for producing a lactic acid polymer having excellent properties is to use lactide, which is a cyclic dimer of lactic acid, as a raw material, to perform ring-opening polymerization of this, and to conduct dehydration polycondensation of lactic acid. There are two ways to obtain the polymer directly.

Industrially, the former process via lactide is advantageous because the reaction proceeds in a chain by ionic polymerization, and the molecular weight of the obtained polymer is very high, ie, hundreds of thousands or more. , That process is already established.

However, in order to obtain such a polymer having a high molecular weight, a purification step (see Japanese Patent Publication No. 44-15789) in which the starting material lactide is recrystallized several times using a solvent such as ethyl acetate is required. In addition, since purified lactide has a property of absorbing moisture and deliquescent, it is necessary to store it under an atmosphere of diphosphorus pentoxide with the water completely removed. However, there are many points to be noted in handling, and there is an industrial disadvantage in the polymer production process.

As a solution to such a problem, in JP-A-7-304859, lactic acid is heated and polycondensed while a catalyst is added in a batchwise polymerization reaction tank, and (weight average molecular weight: Mw) is After obtaining 500 to 5,000 lactic acid prepolymer, this is fed to a twin-screw extruder to produce a lactic acid polymer having a weight average molecular weight of 10,000 or more, and the extruded polymer is molded and processed. Direct production methods for lactic acid polymers and molded articles have been proposed.

In addition, the inventors of the present invention, in the process of previously increasing the molecular weight of lactic acid by dehydration polycondensation reaction, positively introduce the lactide produced as a by-product during the reaction step into the reaction system together with the solvent by using a reflux device. By refluxing, the chemical equilibrium of the reaction solution is transferred to the polymer production side, and a technique for efficiently producing a high molecular weight having a weight average molecular weight Mw of 30,000 to 100,000 has been proposed (Japanese Patent Application No. 6-96). -306
No. 264).

[0010] These methods have the advantage that the production cost of the polymer can be significantly reduced because it is possible to obtain the polymer directly from lactic acid without passing through lactide. The establishment of the process has been progressing rapidly, but on the other hand, the following problems have been pointed out, which is a cause of hindering the industrialization of the process. (1) The dehydration polycondensation reaction of lactic acid proceeds by forcibly distilling off desorbed components such as free water and reaction by-product water from the system under high temperature and high vacuum, but under such reaction conditions The lactide production reaction that competes with the main reaction is likely to proceed preferentially, and in that case, the production reaction rate of the polymer is remarkably reduced and a high molecular weight product cannot be obtained. (2) The lactide produced by the side reaction of the above (1) is crystallized when cooled to 90 ° C. or lower, and thus the reaction system is closed by the precipitated lactide to maintain a desired reduced pressure state. become unable. As a result, the removal of free water and by-product water becomes insufficient, and the dehydration polycondensation reaction of lactic acid, which is the main reaction, does not proceed. (3) When the viscosity of the polymer, which is the reaction liquid, increases with the progress of the reaction, the surface renewal action becomes inferior due to lack of stirring force in a normal batch reaction tank, and the removal rate of by-product water is reduced. Not only does it decrease, but the frequency of contact between the catalyst and the reaction end groups of lactic acid decreases, which hinders the uniform progress of the reaction.

In addition to various problems in the lactic acid polymer production process, the following drawbacks of the lactic acid polymer itself are also factors that hinder the commercialization of the polymer. (1) Optically active lactic acid polymer (L- or D-
(Lactic acid homopolymer) has high stereoregularity, so it shows the characteristics of being hard and brittle when it becomes a high molecular weight substance, and can be applied to molded products requiring flexibility such as films, coating materials, and laminate materials. Have difficulty. (2) Since the lactic acid polymer has a very low thermal stability, it is very difficult to control the quality of the polymer because the molecular weight of the lactic acid polymer remarkably decreases due to heat deterioration during molding and coloring such as oxidative deterioration easily occurs. (3) In order to solve the physical property defects of lactic acid polymer,
A process for copolymerizing the raw material lactic acid or lactic acid oligomer with other monomer components has been developed.
Since the OH group has low reactivity, it is difficult to obtain a high molecular weight polymer even if the reaction takes a long time, and at the same time, secondary reactions (crosslinking reactions) easily proceed, so that the process and molded product quality can be controlled. Is difficult. (4) Similar to (3) above, in order to solve the drawbacks of lactic acid polymers, a technique has been developed in which lactide is added to the same polymer or oligomer to impart plasticity to the polymer during molding. In the molding temperature range (140 to 170 ° C.), lactide is vaporized and most of it is lost during the molding process, so a sufficient plasticizing effect cannot be expected.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lactic acid polymer composition which has good flexibility and can be used as a molded article such as a film, a coating material and a laminate material, and an efficient production method thereof. Especially.

[0013]

[Means for Solving the Problems] The inventors of the present invention have conducted diligent research in order to achieve the above-mentioned object. In the process of polycondensing lactic acid to obtain a high-molecular-weight lactic acid polymer, a secondary reaction is caused during the reaction step. If the lactide produced is refluxed in the reaction system, and a solvent having a high boiling point under reduced pressure is added to carry out the reaction,
The increase of the viscosity of the polymer as the reaction liquid due to the progress of the polycondensation reaction is suppressed, so that the reaction efficiency is improved, and the solvent with a high vacuum boiling point uniformly present in the obtained lactic acid polymer composition is molded. This lactic acid polymer composition has excellent flexibility because it acts as a plasticizer during processing.
They have found that they are useful as molded products such as coating materials and laminate materials, and have completed the present invention.

That is, according to the present invention, the polycondensation reaction of lactic acid is carried out by refluxing lactide produced as a by-product in the reaction step in the reaction system and in the presence of a solvent having a high reduced pressure boiling point. 50,000-200,000
A lactic acid polymer composition containing a lactic acid polymer of 0 and a solvent having a high boiling point under reduced pressure is provided.

Further, the present invention is characterized in that the polycondensation reaction of lactic acid is carried out in the presence of a solvent having a high boiling point under reduced pressure, by refluxing lactide produced as a by-product in the reaction step into the reaction system. It is intended to provide a method for producing a lactic acid polymer composition containing 50,000 to 200,000 lactic acid polymer and the solvent having a high vacuum boiling point.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Lactic acid used in the present invention is D-form,
Optically active substance such as L-form or D, L having no optical activity
It may be either a solid form or a mixture thereof, and preferably one having a purity of 85% or more is used. The reaction is carried out by polycondensation of these in an inert atmosphere under heating and reduced pressure in a conventional manner.

Specifically, for example, lactic acid as a raw material is charged into a batch-type reaction tank, the inside of the tank is replaced with nitrogen gas or argon gas, and then a polycondensation reaction is carried out under heating and under reduced pressure. When producing a high molecular weight polymer having a weight average molecular weight of 100,000 or more, the weight average molecular weight is 1
After synthesizing a lactic acid prepolymer of 50,000 to 50,000, the lactic acid prepolymer is further supplied to an extruder having excellent stirring and kneading ability, and polycondensed under heating and reduced pressure conditions to give a weight average molecular weight of 100, It can also be produced by a two-stage method in which 000 to 200,000 lactic acid polymers are produced.

The reaction temperature for carrying out the polycondensation reaction of lactic acid is 1
40-180 degreeC is preferable and 150-175 degreeC is more preferable. If the reaction temperature is too low, the reaction will not proceed sufficiently,
On the contrary, if it is too high, depolymerization reaction takes place and lactide is remarkably produced, which is not preferable.

The reduced pressure level in the reaction vessel is preferably 0.1 to 100 mmHg, more preferably 1 to 50 mm.
Set it within the range of Hg. It is difficult to make the decompression level lower than this (<0.1 mmHg) from the viewpoint of the structure of the reaction tank and the exhaust capacity of the pump, and it is not preferable because the lactic acid monomer is distilled off together with the water distillation. On the contrary, if the decompression level is high (> 100 mmHg), free water and reaction by-product water are hardly distilled off, which is not suitable.

In the dehydration polycondensation of lactic acid, it is also important to distill off by-product water out of the system in order to increase the reaction rate, but on the other hand, this reaction system is not suitable for competitive reaction with lactide. Therefore, it is necessary to suppress the production of lactide as much as possible. However, since it is not possible to completely suppress such side reactions only by controlling the reaction conditions, a reflux pipe is installed in the reaction tank to recover the vaporized lactide and low-molecular compounds of lactic acid, and to recover them again. The chemical equilibrium is transferred to the polymer side by performing a reflux operation for returning the reaction system. At this time, if the temperature in the reflux pipe is set to be equal to or lower than the reduced pressure boiling point of lactide, only water is selectively distilled off.

This reflux pipe has a double cylindrical structure and is used by being vertically attached to the upper lid of the reaction vessel. A spiral or screw type resistor in the reverse screw direction is provided in the tube to facilitate the reflux operation of lactide. The temperature in the tube is preferably 30 to 120 ° C., more preferably 40 ° C. by circulating cooling water or a heat medium or hot water.
Control to ~ 100 ° C. At this time, the degree of pressure reduction in the reflux pipe is preferably 0.1 to 50 mmHg, more preferably 1 to 50 mmHg.
Adjust to 30mmHg.

When the lactide is refluxed, if the inside of the reflux tube is below the melting point of lactide, crystallization will occur immediately and the tube will be blocked, so a solvent is used to prevent this.
Examples of the lactide solvent include chloroform, acetone, xylene, benzene, lactates, ethyl acetate, tetrahydrofuran, dichlorobenzene, and dipropyl ketone.
Since it is liquefied in the reflux tube and is distilled out of the reaction system without being refluxed together with lactide, it cannot be said to be an appropriate solvent.

In the present invention, in addition to the purpose of promoting the reflux operation of lactide in the reaction system, in order to impart plasticity to the produced lactic acid polymer, the boiling point under reduced pressure is high and the lactide and the polymer are compatible with each other. Use a solvent. More preferably, the solvent which has a boiling point of 250-350 degreeC under normal pressure is mentioned. Examples of the solvent include diphenyl ether (760 mmHg; 259 ° C., all showing boiling points at 760 mmHg) and dimethylbenzyl ether (281
℃), benzyl phenyl ether (287 ℃), dibutyl phthalate (340 ℃), diethyl phthalate (30
5 ° C.), dimethyl phthalate (284 ° C.), and the like, but in view of the fact that the solvent remains as a plasticizer in the molded product in the end, a non-toxic and highly safe one is desirable. In addition to these, the properties required for the solvent in the present invention include the following.

(1) Colorless and odorless. (2) Good plasticization efficiency. (3) It is not eluted with water, acid, alkali or organic solvent. (4) Heat, light and chemically stable. (5) High electrical insulation.

As the solvent satisfying all of these requirements, phthalic acid ester-based solvents such as dibutyl phthalate, diethylhexyl phthalate, diethyl phthalate and dimethyl phthalate are most suitable.

The amount of the solvent added is preferably 5 to 25 parts by weight, more preferably 7 to 20 parts by weight, based on 100 parts by weight of the lactic acid oligomer. When the addition amount is less than 5 parts by weight, the solvent does not sufficiently act on the reflux of lactide and the decrease in the melt viscosity of the polymer. On the contrary, when the addition amount is more than 25 parts by weight, the solvent remains in the polymer as a plastic material during the molding process. It may cause a decrease in the molecular weight and a decrease in the quality of the molded product during storage.

A catalyst can be used in the reaction. Examples of this catalyst include metal acid catalysts such as stannous chloride, tin octylate, and antimony oxide. These catalysts include tetrahydrofuran, butyl lactate, chloroform, acetone, xylene, ethanol,
It is desirable to add it to the reaction solution after completely dissolving it in a solvent such as benzene. It should be noted that this operation of adding a catalyst acts as a depolymerization catalyst of the lactic acid oligomer as a reaction solution and promotes the formation of lactide if it is performed at a stage where the temperature of the reaction solution is high.

Considering the high toxicity of the catalyst group, manganese acetate, zinc acetate, aluminum acetate,
A non-metal acid catalyst such as diethyl zinc can also be used.
These catalysts use, for example, manganese acetate for promoting the polycondensation reaction, and suppress side reactions during the reaction,
Appropriate combinations such as zinc acetate used as a catalyst for shifting the equilibrium state between the lactic acid polymer / monomer in the reaction solution to the polymer side can be used as a mixed system.

In the case of a metal catalyst, the amount of the catalyst used is 0.00 based on 100 parts by weight of the lactic acid oligomer which is the reaction liquid.
The amount is in the range of 1 to 0.5 parts by weight, preferably 0.05 to 0.1 parts by weight. Further, in the case of a non-metal catalyst, since the catalytic activity is lower than that of a metal catalyst, it is used in the range of 0.05 to 1 part by weight, and further 0.1 to 0.5 part by weight with respect to the lactic acid oligomer. Preferably.

The catalyst is preferably added after the dehydration operation for removing the free water of lactic acid as a raw material is completed. This is because the catalyst used in the present invention is hydrolyzed and inactivated in a reaction system in which a large amount of water exists, and therefore it is desirable to add it to a lactic acid oligomer from which free water has been completely removed. The weight average molecular weight of the lactic acid oligomer at that time is in the range of 1,000 to 3,000.

As described above, the polycondensation catalyst is added to the lactic acid oligomer and heated under reduced pressure for polycondensation, and the lactide by-produced is refluxed into the reaction system together with the solvent to further advance the polycondensation reaction. Then, the weight average molecular weight is 50,000.
A polymer composition is obtained which comprises ˜200,000 lactic acid polymer and a solvent having a high vacuum boiling point.

The weight average molecular weight is 50,000 to 200,
The reason for synthesizing a polymer having a range of 000 is as follows.
If the weight average molecular weight is less than 50,000, inflation film molding, blow molding, biaxially stretched film molding,
This is because it is not suitable because it does not have the melt viscosity required as a raw material for various molding processes such as injection molding.
Further, when it is attempted to produce a polymer having a weight average molecular weight of more than 200,000, it not only takes a considerable amount of time until the reaction is completed, but also the quality of the polymer is likely to deteriorate during the reaction step such as coloring of the polymer and reduction of the molecular weight. Therefore, it is difficult to establish a process industrially.

[0033]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 L-lactic acid was charged into a batch polymerization reaction tank of 15 L capacity equipped with a stirrer, a thermocouple, a nitrogen gas introduction tube, and a reflux tube,
The reaction temperature was set to 120 ° C. under a reduced pressure of 5 to 20 mmHg to carry out the dehydration reaction of lactic acid. After completion of the dehydration reaction of lactic acid, 0.1 part by weight of tin octylate as a catalyst was added to 100 parts by weight of the lactic acid oligomer as a reaction liquid, and the reaction temperature was set at 170 ° C. to carry out the polycondensation reaction. Advanced.

At this time, at the same time as refluxing the by-produced lactide, dibutyl phthalate is used as a solvent in an amount of 7.5 with respect to 100 parts by weight of the lactic acid oligomer in order to lower the melt viscosity of the polymer and promote the surface renewal action in the reaction solution. Added in parts by weight. In addition, the inside of the reaction tank at that time is 10 to 20.
The pressure was reduced to mmHg. The temperature of the reflux tube was set to 85 ° C.

The polymer composition obtained after completion of the reaction was subjected to gel permeation chromatography (manufactured by Tosoh Corporation, model: HL).
C-8020, column; TSK-G1000 x 1, G
5000 x 1 bottle, GMH x 2 bottles in total, 4 connections, solvent; chloroform, column temperature; 35 ° C, detector; differential refractometer, molecular weight calculated as relative molecular weight to polystyrene) 101,
500. Heat press this to a thickness of 25 μm
The mechanical strength of the film molded into JIS K 7113
The tensile strength is 150 kgf /
It was clarified that the polymer had the same physical properties as polyethylene with a cm ² and an elongation of 182%, and it was possible to solve the drawback of the lactic acid polymer that was hard and brittle.

Example 2 L-lactic acid was charged in a batch polymerization reaction tank of 15 L capacity equipped with a stirrer, a thermocouple, a nitrogen gas introduction tube, and a reflux tube,
The reaction temperature was set to 120 ° C. under a reduced pressure of 5 to 20 mmHg to carry out the dehydration reaction of lactic acid. After the dehydration reaction of lactic acid was completed, zinc acetate and manganese acetate as catalysts were added at a ratio of 0.5 parts by weight to 100 parts by weight of the lactic acid oligomer as a reaction liquid, and the reaction temperature was set to 165 ° C. The polycondensation reaction proceeded.

At this time, at the same time as refluxing the lactide produced as a by-product, at the same time, in order to lower the melt viscosity of the polymer and promote the surface renewal action of the reaction solution, diethyl phthalate is used as a solvent in an amount of 10 parts by weight per 100 parts by weight of the lactic acid oligomer. Was added. The inside of the reaction tank at that time is 10 to 20 mm.
The pressure was reduced to Hg. The temperature of the reflux tube was set to 80 ° C.

The polymer composition obtained after the reaction was examined by gel filtration permeation chromatography.
The weight average molecular weight was 97,500. The mechanical strength of the film heat-pressed to a thickness of 30 μm was measured according to JIS K 7113. Tensile strength: 142 kgf / cm ² , elongation: 180% It became clear that the lactic acid polymer was hard and brittle in terms of physical properties.

[0040]

The effects of the present invention include the following items. 1. By allowing the solvent to remain as a plasticizer in the lactic acid polymer composition, the drawback of the polymer being hard and brittle is solved, and the physical properties of the molded product are significantly improved. 2. Since a solvent with a high reduced pressure boiling point is used for lactide reflux, even under reduced pressure conditions during the polycondensation reaction of lactic acid, the solvent is not distilled out of the reaction system, and the solvent loss during the reaction step is reduced. Since it is not necessary to replenish or to provide a large number of cooling traps for collecting the solvent in the reaction path, the number of steps can be considerably reduced. 3. Since the step of devolatilizing the solvent or purifying the solvent after the production of the lactic acid polymer can be omitted, the cost required for the process can be minimized, and the polymer can be provided at a low cost.

Front page continued (72) Inventor Yukihiro Sumihiro 1-1-1, Funakoshi Minami, Aki-ku, Hiroshima City, Hiroshima Prefecture Japan Steel Works, Ltd. (72) Inventor Noriaki Hashimoto 1-1-1, Funakoshi-minami, Aki-ku, Hiroshima City, Hiroshima Prefecture Inside Japan Steel Works, Ltd. (72) Inventor Kunihiko Koyanagi 1-1-1, Funakoshi Minami, Aki-ku, Hiroshima City, Hiroshima Prefecture Inside Japan Steel Works, Ltd.

Claims (6)

[Claims] 1. A weight average molecular weight of 50,000 to 50,000, which is obtained by carrying out the polycondensation reaction of lactic acid in the presence of a solvent having a high vacuum boiling point by refluxing lactide, which is a by-product in the reaction step, in the reaction system. A lactic acid polymer composition containing 200,000 lactic acid polymer and the solvent having a high vacuum boiling point. 2. The solvent having a high reduced pressure boiling point is 250 at normal pressure.
The lactic acid polymer composition according to claim 1, which is a solvent having a boiling point of ˜350 ° C. 3. The lactic acid polymer composition according to claim 1, wherein the added amount of the solvent having a high reduced pressure boiling point is 5 to 25 parts by weight with respect to 100 parts by weight of the lactic acid oligomer. 4. A weight-average molecular weight of 5, characterized in that the polycondensation reaction of lactic acid is carried out in the presence of a solvent having a high vacuum boiling point, with lactide produced as a by-product in the reaction step being refluxed in the reaction system.
A method for producing a lactic acid polymer composition containing 10,000 to 200,000 lactic acid polymer and a solvent having a high boiling point under reduced pressure. 5. The solvent having a high reduced pressure boiling point is 250 at normal pressure.
The method for producing a lactic acid polymer composition according to claim 4, which is a solvent having a boiling point of 350 ° C. 6. The method for producing a lactic acid polymer composition according to claim 4, wherein the added amount of the solvent having a high reduced pressure boiling point is 5 to 25 parts by weight with respect to 100 parts by weight of the lactic acid oligomer.