JP3098703B2 - Method for producing lactic acid polymer composition with improved physical properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a lactic acid polymer composition useful as a biodegradable plastic, and more particularly, to the efficiency of a lactic acid polymer composition useful as a biodegradable plastic molding material having excellent flexibility. Production method.

[0002]

2. Description of the Related Art Recently, biodegradable plastics have attracted a great deal of attention as materials that are decomposed in the environment after fulfilling the purpose of use, and finally reduced to the nature in the form of low molecular compounds. . Above all, aliphatic polyesters are completely decomposed into monomers by microorganisms and water, and eventually incorporated into the natural material cycle as carbon dioxide and water. At the beginning, recently, application development to general-purpose materials that are expected to be disposed of in the environment after use has been started.

[0003] As a representative of such aliphatic polyester-based biodegradable plastics, lactic acid polymers have excellent mechanical strength and transparency, as well as good compatibility with other polymers and are easily modified. Therefore, it is easily decomposed to monomer by heating operation or addition of specific solvent,
Even as a monomer-recyclable material, its use development is highly expected.

[0004] In addition, it has excellent decomposition characteristics in addition to the above, so that it is possible to efficiently reduce the volume and completely decompose at low energy by enzymatic decomposition or hydrolysis by various microorganisms. In addition, it has also attracted attention as a material that significantly reduces the burden on the environment during processing as compared with conventional general-purpose plastics.

[0005] As described above, a method for producing a lactic acid polymer having excellent properties includes a method in which lactide, which is a cyclic dimer of lactic acid, is used as a raw material and a ring-opening polymerization of lactide, and a method in which lactic acid is subjected to dehydration polycondensation. There are two ways to obtain the polymer directly.

Industrially, the former process using lactide is advantageous because the reaction proceeds in a chain by ionic polymerization and the resulting polymer has a very high molecular weight of several hundred thousand or more. , The process is already established.

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

In order to solve such a problem, Japanese Patent Application Laid-Open No. Hei 7-304859 discloses that lactic acid is heated and polycondensed while adding a catalyst in a batch polymerization reaction tank, and the weight-average molecular weight (Mw) is reduced. After obtaining a lactic acid prepolymer of 500 to 5,000, it is supplied to a twin-screw extruder to produce a lactic acid polymer having a weight average molecular weight of 10,000 or more, and to process the extruded polymer. Direct production methods for lactic acid polymers and molded articles have been proposed.

In addition, in the process of first increasing the molecular weight of lactic acid by a dehydration polycondensation reaction, the present inventors actively used a refluxing device to introduce lactide by-produced in the reaction step together with a solvent into the reaction system. By refluxing, the chemical equilibrium of the reaction solution is shifted to the polymer generation 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. Hei. −306
264).

[0010] These methods have the advantage that the production cost of the polymer can be greatly reduced since the polymer can be obtained directly from lactic acid without passing through lactide. While the establishment of the process has been progressing rapidly, on the other hand, the following problems have also been pointed out, which has hindered the industrialization of the process. (1) The dehydration / polycondensation reaction of lactic acid proceeds by forcibly distilling out elimination components such as free water and reaction by-product water out of the system under high temperature and high vacuum. Under such reaction conditions, The lactide formation reaction competing with the main reaction tends to proceed preferentially, in which case the rate of the polymer formation reaction is remarkably reduced and a high molecular weight product cannot be obtained. (2) Lactide generated by the side reaction of the above (1) is crystallized when cooled to 90 ° C. or less, so that the reaction system is blocked 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 main reaction of dehydration / polycondensation of lactic acid does not proceed. (3) When the viscosity of the polymer as the reaction solution increases with the progress of the reaction, the surface renewal effect becomes poor due to insufficient stirring power in a usual batch-type reaction tank, and the removal rate of by-product water decreases. Not only does it decrease, but the frequency of contact between the catalyst and the reaction terminal group of lactic acid decreases, preventing uniform progress of the reaction.

In addition to the various problems in the lactic acid polymer production process, the following drawbacks of the lactic acid polymer itself are factors that hinder the commercialization of the polymer. (1) Lactic acid polymer having optical activity (L- or D-
Lactic acid homopolymer) has a high stereoregularity, so when it becomes a high molecular weight product, it shows the property of being hard and brittle, and it can be applied to molded products that require flexibility such as films, coating materials, and laminate materials. Have difficulty. (2) Since lactic acid polymer has very low thermal stability, the molecular weight is remarkably reduced due to thermal deterioration during molding and phenomena such as coloring due to oxidative deterioration are apt to occur, and it is very difficult to control the quality of the polymer. (3) To solve the drawbacks of the physical properties of lactic acid polymer,
A process has been developed to copolymerize the raw material lactic acid or lactic acid oligomer with other monomer components.
Since OH groups have low reactivity, it is difficult to obtain high molecular weight polymers even if the reaction takes a long time, and secondary reactions (crosslinking reactions) etc. also easily proceed at the same time. Is difficult. (4) As in (3) above, in order to solve the drawbacks of lactic acid polymer, a technique has been developed in which lactide is added to the 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 the lactide is lost during the molding process, so that 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 or a laminate material, and a method for efficiently producing the same. It is in.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object. As a result, in the process of polycondensing lactic acid to obtain a high-molecular-weight lactic acid polymer, a secondary reaction was carried out during the reaction step. If the resulting lactide is refluxed into the reaction system, and the reaction is performed by adding a solvent having a high boiling point under reduced pressure,
The reaction efficiency is improved because the increase in the viscosity of the polymer as a reaction solution is suppressed with the progress of the polycondensation reaction, and the solvent having a high boiling point under reduced pressure uniformly present in the obtained lactic acid polymer composition is formed. Because it acts as a plasticizer during processing, this lactic acid polymer composition has excellent flexibility in film,
They have found that they are useful as molded articles such as coating materials and laminate materials, and have completed the present invention.

That is, according to the present invention, a solvent having a polycondensation reaction of lactic acid, in which lactide by-produced during the reaction step is refluxed to the reaction system, and having a boiling point of 250 to 350 ° C. under normal pressure, is mixed with 100 parts by weight of lactic acid oligomer. Weight-average molecular weight of 50,
An object of the present invention is to provide a method for producing a lactic acid polymer composition containing 000 to 200,000 lactic acid polymer and the solvent.

[0015]

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The lactic acid used in the present invention is a D-form,
Optically active substance such as L-form or D, L having no optical activity
And any of these compounds and mixtures thereof, preferably those having a purity of 85% or more. The reaction is carried out by a conventional method, that is, polycondensation under heating and reduced pressure in an inert atmosphere.

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 performed under heating and under reduced pressure. When producing a high molecular weight polymer having a weight average molecular weight of 100,000 or more, first, the weight average molecular weight is 1
After synthesizing a lactic acid prepolymer having a weight-average molecular weight of 100,000 to 50,000 to 50,000, it is further fed to an extruder having excellent stirring and kneading ability, and subjected to polycondensation under heating and reduced pressure conditions. The lactic acid polymer of 000 to 200,000 can be produced by a two-stage method.

The reaction temperature for the polycondensation reaction of lactic acid is 1
The temperature is preferably from 40 to 180C, more preferably from 150 to 175C. If the reaction temperature is too low, the reaction does not proceed sufficiently,
Conversely, if it is too high, a depolymerization reaction occurs and lactide production becomes significant, which is not preferable.

The reduced pressure level is preferably 0.1 to 100 mmHg, more preferably 1 to 50 mmHg in the reactor.
Set to be in the range of Hg. It is difficult to further reduce the pressure reduction level (<0.1 mmHg) in view of the structure of the reaction tank and the pumping capacity of the pump, and it is not preferable because lactic acid monomer is distilled off together with the distillation of water. Conversely, if the reduced pressure level is high (> 100 mmHg), it is not appropriate because free water and by-product water are difficult to be distilled off.

In the dehydration and polycondensation of lactic acid, it is important to quickly 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 the competitive reaction with lactide. Therefore, it is necessary to minimize the production of lactide. However, it is impossible to completely suppress such side reactions only by controlling the reaction conditions.Therefore, a reflux tube was installed in the reaction tank to recover the vaporized lactide and low-molecular-weight compounds of lactic acid, and again The chemical equilibrium is shifted to the polymer side by performing a reflux operation for returning the mixture into the reaction system. At this time, if the temperature in the reflux tube is set to be equal to or lower than the reduced pressure boiling point of lactide, only water is selectively distilled off.

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

At the time of refluxing lactide, if the inside of the reflux tube has a temperature lower than the melting point of lactide, crystallization occurs immediately and the inside of the tube is closed, so a solvent is used for the purpose of preventing this.
Examples of the lactide solvent include chloroform, acetone, xylene, benzene, lactic acid esters, ethyl acetate, tetrahydrofuran, dichlorobenzene, dipropyl ketone, and the like.
It is not a suitable solvent because it is liquefied in the reflux tube and distilled out of the reaction system without reflux with lactide.

In the present invention, in addition to the purpose of accelerating the lactide reflux operation in the reaction system, in order to impart plasticity to the produced lactic acid polymer, it has a high boiling point under reduced pressure and has compatibility with both lactide and the polymer. Use a solvent. More preferably, a solvent having a boiling point of 250 to 350 ° C. under normal pressure is used. As the type of the solvent, diphenyl ether (760 mmHg; 259 ° C., hereinafter all showing the boiling point at 760 mmHg), dimethylbenzyl ether (281
° C), benzyl phenyl ether (287 ° C), dibutyl phthalate (340 ° C), diethyl phthalate (30 ° C).
5 ° C.), dimethyl phthalate (284 ° C.) and the like. However, considering that the solvent finally remains in the molded article as a plasticizer, a non-toxic and highly safe one is desirable. In addition, the following properties are required for the solvent in the present invention.

(1) It is colorless and odorless. (2) Good plasticizing efficiency. (3) It is not eluted by water, acid, alkali or organic solvent. (4) It is thermally, light and chemically stable. (5) High electrical insulation.

As the solvent which satisfies 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 to be 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. If the addition amount is less than 5 parts by weight, the solvent does not sufficiently act on the reflux of lactide or lower the melt viscosity of the polymer. Conversely, if the addition amount exceeds 25 parts by weight, the resin is left as a plasticizer in the polymer. May cause a decrease in the molecular weight at the time of production and a decrease in the quality during storage of the molded article.

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

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

In the case of a metal catalyst, the amount of the catalyst is 0.00 0.00 parts by weight of the lactic acid oligomer as a reaction solution.
It is in the range of 1 to 0.5 part by weight, more preferably 0.05 to 0.1 part by weight. In the case of a non-metallic catalyst, the catalytic activity is lower than that of a metal-based catalyst. Therefore, the non-metallic catalyst is used in an amount of 0.05 to 1 part by weight, more preferably 0.1 to 0.5 part by weight, based on the lactic acid oligomer. Is preferred.

It is appropriate to add the catalyst after completion of the dehydration operation for removing free water of lactic acid as a raw material. This is because the catalyst used in the present invention is hydrolyzed and deactivated in a reaction system in which a large amount of water is present, and thus it is desirable to add the catalyst to the 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 the mixture is heated and polycondensed under reduced pressure. The polycondensation reaction is further performed while refluxing lactide as a by-product into the reaction system together with the solvent. If the weight average molecular weight is 50,000
A polymer composition comprising を 200,000 lactic acid polymer and a solvent having a high boiling point under reduced pressure is obtained.

The weight average molecular weight is from 50,000 to 200,
Reasons for synthesizing polymers with a range of 000
If the weight average molecular weight is less than 50,000, blown film molding, blow molding, biaxially stretched film molding,
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 an attempt is made to produce a polymer having a weight average molecular weight exceeding 200,000, not only a considerable amount of time is required until the completion of the reaction, but also quality deterioration such as coloring of the polymer and a decrease in the molecular weight is liable to occur during the reaction process. Therefore, it is difficult to establish a process industrially.

[0033]

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

Example 1 L-lactic acid was charged into a 15-L batch polymerization reactor equipped with a stirrer, a thermocouple, a nitrogen gas inlet tube, and a reflux tube.
The reaction temperature was set to 120 ° C. under a reduced pressure of 5 to 20 mmHg to perform a lactic acid dehydration reaction. After the lactic acid dehydration reaction is completed, tin octylate is added as a catalyst in a ratio of 0.1 part by weight to 100 parts by weight of the lactic acid oligomer as a reaction solution, and the reaction temperature is set to 170 ° C. to perform a polycondensation reaction. Advanced.

At this time, dibutyl phthalate is used as a solvent in an amount of 7.5 parts by weight based on 100 parts by weight of the lactic acid oligomer in order to reflux lactide as a by-product and reduce the melt viscosity of the polymer to promote the surface renewal effect of the reaction solution. It was added in parts by weight. In addition, the inside of the reaction tank at that time is 10-20.
The pressure was reduced to mmHg. The temperature of the reflux tube was set at 85 ° C.

After the completion of the reaction, the polymer composition obtained was subjected to gel filtration permeation chromatography (manufactured by Tosoh, model: HL
C-8020, column; TSK-G1000 x 1, G
5000 × 1 tube, GMH × 2 tube, total of 4 tubes, solvent: chloroform, column temperature: 35 ° C., detector: differential refractometer, molecular weight was calculated as relative molecular weight to polystyrene). 101,
500. This is heat pressed to a thickness of 25 μm
Strength of the film molded into JIS K 7113
The tensile strength was measured in accordance with the following formula: 150 kgf /
It became clear that the polymer had a physical property comparable to that of polyethylene, that is, cm ² and an elongation of 182%, and it was possible to solve the hard and brittle physical properties of the lactic acid polymer.

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

At this time, diethyl phthalate is used as a solvent in an amount of 10 parts by weight with respect to 100 parts by weight of the lactic acid oligomer in order to reflux lactide as a by-product and reduce the melt viscosity of the polymer to promote the surface renewal effect of the reaction solution. At a rate of In addition, 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 completion of the reaction was examined by gel filtration permeation chromatography.
The weight average molecular weight was 97,500. When the mechanical strength of the film formed by heat pressing to a thickness of 30 μm was measured in accordance with JIS K 7113, the tensile strength was 142 kgf / cm ² , the elongation was 180% and the physical properties were as good as polyethylene. It was found that the lactic acid polymer had a hard and brittle physical property defect.

[0040]

The effects of the present invention include the following items. 1. By leaving the solvent as a plasticizer in the lactic acid polymer composition, the disadvantage of the polymer being hard and brittle is solved, and the physical properties of the molded product are significantly improved. 2. Since a solvent having a high boiling point under reduced pressure is used for refluxing lactide, the solvent is not distilled out of the reaction system even under reduced pressure conditions during the polycondensation reaction of lactic acid. It is not necessary to replenish or to provide a large number of cooling traps for collecting the solvent in the reaction path, so that the number of steps can be considerably reduced. 3. Since the step of devolatilizing 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 low cost.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noriaki Hashimoto 1-6-1 Funakoshi Minami, Aki-ku, Hiroshima City, Hiroshima Prefecture Inside Japan Steel Works Co., Ltd. (72) Kunihiko Koyanagi 1-6-1 Minami Funakoshi, Aki-ku, Hiroshima City, Hiroshima Prefecture -1 Japan Steel Works, Ltd. (56) References JP-A-7-257660 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G08G 63/06-63/08 G08G 63 / 78-63/87

Claims (1)

(57) [Claims] 1. The polycondensation reaction of lactic acid is carried out by refluxing lactide, which is a by-product during the reaction step, to the reaction system and under normal pressure for 250 minutes.
Solvent having a boiling point of about 350 ° C.
A weight average molecular weight of 50,000 to 200,000, wherein the addition is carried out by adding 5 to 25 parts by weight to 0 parts by weight.
And a method for producing a lactic acid polymer composition containing the solvent.