JPH08157576A - Method for producing polylactic acid copolymer - Google Patents

Abstract

(57) [Summary] [Structure] A polylactic acid copolymer characterized in that a reaction product of a lactic acid oligomer having a number average molecular weight of 1,000 to 5,000 and an acid anhydride is copolymerized with an epoxy resin. Production method. [Effect] A copolymer can be obtained industrially advantageously,
The obtained copolymer has excellent physical properties and recyclability.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polylactic acid copolymer, and more particularly to a method for producing a polylactic acid copolymer having excellent physical properties and recyclability.

[0002]

2. Description of the Related Art Biodegradable plastics are plastics that are decomposed in the natural environment after fulfilling their purpose of use and are eventually reduced to the natural world in the form of low-molecular compounds.
It is a material that is rapidly gaining attention in recent years. 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.

Polylactic acid, which is one of such aliphatic polyester biodegradable plastics, has excellent decomposing characteristics and transparency, and further has good compatibility with other polymers and is easily modified. Since it is easily decomposed into a monomer by a heating operation or addition of a specific solvent, it is highly expected to be developed as a material that can be recycled as a monomer.

However, polylactic acid has the following drawbacks as a homopolymer. (1) High rigidity and brittleness (lack of flexibility and elasticity as a product) (2) Low heat resistance (prone to thermal decomposition and oxidative deterioration during molding) (3) High hydrolyzability (during storage) Is likely to decrease the molecular weight of

Therefore, it has been considered difficult to mold and process the homopolymer polylactic acid as it is to obtain a product.

On the other hand, the epoxy resin is a thermosetting plastic which is widely used as an adhesive for structures and an anticorrosive coating agent because it has excellent adhesiveness, mechanical properties and electrical properties. In addition, due to its high chemical resistance such as water resistance and chemical resistance, the reliability as a finished part is extremely high and it is possible to maintain the characteristics as a product for a long period of time. Is showing an increasing trend in the future.

On the other hand, however, having such excellent durability means that even if the product is disposed of after being used, it is not easily decomposed and remains in nature for a long time. In recent years, there has been a strong demand for recycling of waste plastics, and there has been a demand for urgent countermeasures for the same materials.

Further, since the epoxy resin is a material having a thermosetting property, it is impossible to heat melt the epoxy resin or reduce it to a monomer for reuse. Therefore, instead of recycling, a process of collecting and gasifying by thermal decomposition, that is, volume reduction is being considered (Japanese Patent Publication No. 6-
No. 126744). However, this process is only applicable when the epoxy resin is used as the sole material. The reason is that the same material is often used in the form of a composite with another thermoplastic resin, and the thermal decomposition temperature of both is very close to 300 to 400 ° C., so separation is difficult. Is. Although there is also a method of separating only the epoxy resin portion and recovering it, a large amount of solvent is required, which is not an industrially advantageous process. Therefore, these epoxy resins remain as impurities even in the thermoplastic resin after recycling, and as a result, they also contribute to the deterioration of the physical properties of the recycled material.

[0009]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method for industrially producing a plastic which can be recycled after use and is excellent in physical and chemical properties. .

[0010]

Means for Solving the Problems In view of such circumstances, the present inventors have conducted diligent research and found that a plastic obtained by carboxylating a lactic acid oligomer and chain-extending it with an epoxy resin as an esterifying agent is It has excellent physical properties such as mechanical strength and chemical properties, and after use, only polylactic acid component is thermally decomposed by heating at 200 to 250 ° C., and lactide which can be reused as a polymerization raw material can be produced and recovered, Further, when the remaining thermosetting epoxy resin is heated to 250 to 300 ° C. by an existing method, it can be thermally decomposed and the volume can be easily reduced, so that the present invention has been found to be excellent in recyclability. completed.

That is, the present invention has a number average molecular weight of 100
Provided is a method for producing a polylactic acid copolymer, which comprises copolymerizing a reaction product of 0 to 5,000 lactic acid oligomer and an acid anhydride with an epoxy resin.

The number average molecular weight used in the present invention is from 1,000 to
The 5,000 lactic acid oligomer can be obtained by a conventional method, that is, by subjecting lactic acid to a polycondensation reaction in an inert atmosphere under heating and reduced pressure.

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 polycondensation reaction is carried out under heating and under reduced pressure to give lactic acid. An oligomer is obtained.

The lactic acid may be any of an optically active substance such as D-form and L-form, a D, L-form having no optical activity, and a mixture thereof, and preferably a purity of 85% or more is used.

The heating temperature is preferably 90 to 180 ° C., 1
10-170 degreeC is more preferable. If the heating temperature is too low, the reaction does not proceed, and if it is too high, depolymerization occurs and the lactide formation reaction is promoted, which is not preferable. The decompression level is 0.1-100 mmHg, more preferably 1-10 mm
It is in the range of Hg. This is because when the inside of the reaction tank is in this reduced pressure range, the azeotropic temperature of lactic acid and water exists in the above-mentioned temperature range, and the reaction by-product water is easily distilled off efficiently. . It is difficult to make the decompression level lower than this (≤0.1 mmHg) considering the structure of the reaction tank and the exhaust capacity of the pump, and it is also possible that lactic acid, which is the reaction liquid, will boil off with water. It is not appropriate because it can happen. On the contrary, the decompression level is high (≧ 100mmHg)
In that case, the reaction by-product water is not easily distilled out of the reaction system, which is not preferable.

In the dehydration polycondensation of lactic acid, in order to increase the reaction rate, a reflux pipe is installed in the reaction tank to recover the vaporized lactide and the low-molecular-weight compound of lactic acid, and the reflux is returned to the reaction system. Do the operation. 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 and lactic acid as a reaction liquid, only water will be selectively distilled off.

This reflux pipe is made of SUS316 and has an outer diameter of 43.
It has a double cylindrical structure with a height of 400 mm and a height of 400 mm, and is used by being vertically attached to the upper lid of the reaction tank. A spiral resistor having a reverse screw direction is provided in the tube, and the temperature in the tube is controlled to 90 to 120 ° C, preferably 95 to 110 ° C by circulating a heating medium or using an electric heater. At this time, the degree of pressure reduction in the reflux pipe was 0.
Adjust to 1-100 mmHg.

In the reflux of lactide, when the inside of the reflux pipe becomes the melting point of lactide or less, it immediately crystallizes and clogs the pipe. Therefore, a suitable solvent may be used for the purpose of preventing this. Judging from the fact that the reflux operation is easy, the reduced pressure boiling point (10 mm
Hg; 146 ℃) diphenyl ether (10mmHg;
114 ° C), dimethylbenzyl ether (10 mmHg; 1
44 ° C), benzyl phenyl ether (10 mmHg; 14
4 ° C.) and the like are preferable. The amount of the solvent added at this time is 5 to 30% by weight, preferably 10 to 10% of the amount of the raw material charged.
A range of 20% by weight is suitable.

With these solvents, lactide is refluxed again into the reaction solution, but in order to completely carry out the reflux of the solvent, a dedicated glass cooling tube (outer diameter 40 mm, height 300 mm) is provided above the reflux tube. , Dimroth type), and cooling and recovery may be performed using cooling water, dry ice, or liquid nitrogen depending on the boiling point of the solvent to carry out the reflux operation.

A catalyst can be used in the reaction. Examples of this catalyst include stannous chloride, tin octylate, and antimony oxide. These catalysts include tetrahydrofuran, ethyl lactate, 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. If this catalyst addition operation is performed at a stage where the temperature of the reaction solution is high, it acts as a depolymerization catalyst for the lactic acid oligomer that is the reaction solution and causes a decrease in the molecular weight. It is necessary to go gradually.

Considering the high toxicity of the catalyst group, manganese acetate, acetoacetylaluminum,
Aluminum acetate, diethyl zinc, etc. can also be used as a catalyst. The above catalyst uses, for example, manganese acetate as a catalyst for accelerating the polycondensation reaction, as a catalyst for suppressing side reactions during the reaction and shifting the equilibrium state between the lactic acid polymer / monomer in the reaction solution to the polymer side. It is also possible to use an appropriate combination such as using antimony oxide. The amount of the catalyst used is preferably 0.01 to 1.0% by weight, more preferably 0.1 to 0.5% by weight, based on the lactic acid monomer as a raw material.

In the batch reactor, the number average molecular weight is 1,0.
100-5,000 lactic acid oligomers are obtained. This is because it is difficult to obtain an oligomer having a number average molecular weight of more than 5,000 in a batch reaction tank in a short time. With an oligomer having a number average molecular weight of less than 1,000, the acid required for carboxylating both terminals in the next step is required. This is because not only the amount of the anhydride becomes too large, but also the reaction time to reach the target acid value becomes long, which is not practical as a process.

The reaction of the lactic acid oligomer thus obtained with the acid anhydride is preferably a melting reaction in a nitrogen gas atmosphere. By this reaction, a lactic acid prepolymer obtained by carboxylating both end groups of the lactic acid oligomer is obtained. As the acid anhydride used at this time, succinic anhydride, phthalic anhydride, maleic anhydride, tetrabromophthalic anhydride,
Tetrahydrophthalic anhydride, trimellitic anhydride, dodecyl succinic anhydride and the like can be mentioned, but in view of their low toxicity and high boiling point, which is less likely to be lost during the reaction, succinic anhydride (boiling point: 261 C.) and phthalic anhydride (boiling point; 285.degree. C.) are more preferable. The addition amount of these is adjusted to be equimolar to the charged amount of the lactic acid oligomer.

The reaction is carried out at 140 to 170 ° C., further 150 to 1
It is more preferable to carry out at 60 ° C. The reaction time is 1 to 5 hours, and the progress of the reaction is judged by measuring the acid value of the obtained carboxylated lactic acid oligomer. The reaction is completed when the acid value of the reaction solution reaches the theoretical value.
The method of measuring and calculating the acid value and the method of obtaining the theoretical value at that time are as follows.

<Method of measuring acid value> About 1 g of the produced polymer was weighed and dissolved in 20 ml of a toluene / methanol solution at room temperature, and a thymol blue / phenol red mixed indicator was added dropwise thereto, and 0.01 N KOH was added. Titrate with isopropyl alcohol solution.

[0026]

[Equation 1]

[0027]

[Equation 2]

In this reaction, the acid anhydride added for carboxylation loses sublimation due to heating during the reaction, so that a solvent such as toluene or xylene is contained in the reaction solution in an amount of 0.5 to 10% by weight, and more preferably. It is advisable to add 1 to 5% by weight to carry out an operation of sequentially returning to the reaction system while dissolving and liquefying.

The lactic acid prepolymer thus obtained has a number average molecular weight in the range of 2,000 to 7,000. At this time, when the number average molecular weight is less than 2,000, in the next step, the copolymerization reaction with the epoxy resin,
This is not suitable because the molecular chain of each lactic acid oligomer having both ends carboxylated is too short to obtain a sufficient high molecular weight product. Furthermore, when the number of reactive groups is large, the amount of heat generated by the reaction is large, and the crosslinking reaction is caused by the excessive supply of the amount of heat, so such a phenomenon must be avoided. Further, when trying to obtain a lactic acid prepolymer having a molecular weight of more than 7,000, it takes a long time in the molecular weight range of the lactic acid oligomer (1,000 to 5,000 in the number average molecular weight), so that it is not practical. Absent.

Thus, the copolymerization reaction of the lactic acid prepolymer having both terminal groups carboxylated with the epoxy resin is preferably carried out under heating in a screw type extruder.

The screw type extruder used in the present invention includes a screw, which is usually used for molding plastics,
A single-screw or twin-screw screw type extruder including a cylinder, a heating unit and a driving device can be used. Among these, a twin-screw extruder is preferable, and as the device, any of those in which the rotation directions of the screws are the same direction or different directions, those in which the flights of the screws are intermeshed or in which they are not intermeshed can be used. . In the present invention, a plurality of temperature control units are separately provided around the cylinder so that the temperature can be controlled individually, and the ratio (L / L) of the screw length (L) to the screw diameter (D) is provided.
It is preferable to use a meshing twin-screw extruder having a D ratio of 30 to 70. By using a twin-screw extruder with many temperature control units,
This is preferable because the temperature can be controlled according to the reaction stage for each zone of the extruder cylinder.

In addition to this reaction being an exothermic reaction, the amount of heat supplied from the inside of the cylinder and the shearing heat generated as the reaction progresses also add to this, so that the polymer produced with care is thermally decomposed. There is a possibility that it will end up.
Therefore, in order to avoid such a phenomenon, it is necessary to strictly control the temperature of the cylinder so that it is within the above temperature range. Regarding the temperature control in the cylinder, a temperature sensor insertion port is installed in the cylinder part, and the material temperature inside the cylinder is measured over time by an infrared sensor without contact.

The material temperature inside the cylinder is 100 to 160.
C is preferable, and 110 to 150 C is more preferable. When the material temperature is less than 100 ° C, the reaction rate becomes too slow, and when it exceeds 160 ° C, the active hydrogen of the hydroxyl group generated by the reaction between the carboxyl groups at both ends of the lactic acid oligomer and the epoxy resin is epoxy. It is not preferred because it preferentially reacts with the groups, resulting in the progress of a crosslinking reaction that causes gelation.

A reaction time of about 5 to 15 minutes is sufficient. If the reaction time is long, a cross-linking reaction easily occurs between the hydroxyl group and the epoxy group remaining after the copolymerization reaction, so care must be taken.

The epoxy resin used is not particularly limited, but examples thereof include Epicoat (made by Yuka Shell), Araldite (made by Ciba-Geigy), Epolite (made by Kyoei Chemical), D.I. E. FIG. R. (Dow Chemical Japan), Epomic (Mitsui Petrochemical), Sumiepoxy (Sumitomo Chemical Co., Ltd.), Epiclon (Dainippon Ink and Chemicals Co., Ltd.), etc., depending on the intended use, the type and grade can be selected arbitrarily. To do. These vary from liquid to paste and solid powder. Depending on the shape, they are supplied from the hopper by a feeder or by a rotary pump etc. from the solvent injection port provided in the cylinder. To do.

At this time, the charging weight ratio (compounding ratio) of the epoxy resin and the lactic acid prepolymer is adjusted so that the chemical equivalent is the same as the epoxy group in the epoxy resin. The method of determining the charged amount at that time is as follows.

[0037]

[Equation 3] Epoxy resin charging amount (g) = number of moles of COOH group of carboxylated lactic acid oligomer x epoxy equivalent (g
/ Equiv. ) ³⁾ Note 3) Average molecular weight of epoxy resin ÷ number of epoxy groups per molecule

The epoxy resin can be diluted with a solvent as required, or can be heated to reduce the viscosity and improve the accuracy of quantitative supply. As the solvent, a solvent having an oxygen atom in the molecule, for example, a suitable solvent selected from ketones, esters, ethers, alcohols and the like can be used. The alcohol is preferably used in the form of a mixed solution with toluene or xylene. In the addition operation at this time, if the epoxy resin is not quantitatively supplied and is mixed nonuniformly with the lactic acid oligomer, the crosslinking reaction partially proceeds,
Care must be taken as the polymer gels and loses its value as a product.

In the reaction, a catalyst can be used for the purpose of bonding the epoxy group and the active hydrogen of the terminal carboxyl group of the lactic acid prepolymer. Examples of this catalyst include benzyldimethylamine (BDMA), triethylbenzylammonium chloride (TEBAC), tetramethylammonium chloride (TMAC), and triphenylphosphine (TPP). The addition amount is 0.005 to 0.2% by weight, and further 0.01 to
A range of 0.1% by weight is preferred.

Further, in the present invention, the screw rotation speed of the screw type extruder is also very important in the sense that it promotes the epoxidation reaction and suppresses the three-dimensional cross-linking reaction caused by the nonuniform progress of the reaction. Therefore, the rotation speed is 10
It is preferably set in the range of 0 to 300 rpm, particularly 150 to 250 rpm.

Thus, the number average molecular weight is 30,000 to 10
50,000 copolymers of polylactic acid and epoxy resin are obtained.

An example of the method for producing the polylactic acid copolymer according to the present invention will be introduced below with reference to FIG. 1 attached to the application.

Lactic acid is supplied to the batch-type polymerization reaction tank 1, the temperature of the reaction solution is set to a predetermined temperature, and an inert gas is supplied to the cylinder 2.
The dehydration polycondensation reaction is carried out while supplying more. At this time, the inside of the reaction tank is depressurized using the vacuum pump 4, and the produced low molecular weight lactide or lactic acid is recovered by the reflux pipe 5 and refluxed into the reaction tank to produce a lactic acid oligomer. At this time, the by-product water not collected in the reflux pipe is cooled / collected by the trap 6.

Next, an acid anhydride is added to the lactic acid oligomer 7 in a heated and melted state to carry out a carboxyl group-forming reaction. The acid anhydride sublimated in the unreacted state is dissolved in the reflux pipe 5 by adding a solvent such as toluene,
It will be returned to the system again.

The reaction is terminated when the acid value of the reaction solution reaches the theoretical value, and the obtained lactic acid prepolymer 8 is supplied to the hopper 11 of the twin-screw extruder 10 which is the next step by the plunger pump 9. Supply a fixed amount.

At the same time, the rotary pump 12
More epoxy resin is quantitatively supplied from the supply port 13. At this time, a catalyst can be added if necessary.

The lactic acid prepolymer supplied to the inside of the extruder is copolymerized with the epoxy resin heated at different temperatures for each zone by a plurality of temperature control units while advancing inside the cylinder while being kneaded by the screw. .

Thus, the copolymerization reaction between the epoxy resin and the lactic acid prepolymer in the extruder is carried out so as to be completed within the residence time of the apparatus. The molten copolymer 14 produced after the reaction is extruded by the screw, passes through the screen 15, and then through the die 16. These are stored in the storage tank 17 and formed into a final product such as a film or a container.

The copolymer of the epoxy resin and the lactic acid prepolymer obtained as described above is 200 to 250 after use.
When heated to ° C, only the polylactic acid component is thermally decomposed and can be recovered as lactide that can be reused as a polymerization raw material. Further, if the remaining epoxy resin is heated to 250 to 300 ° C., it is thermally decomposed and the volume can be easily reduced.

[0050]

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 10 kg of L-lactic acid was charged into a batch polymerization reactor having a capacity of 14 liters, which was equipped with a stirrer, a thermocouple, a nitrogen gas introducing tube, and a reflux tube, and stannous chloride was used as a catalyst for the raw material. It was added at a rate of 0.3% by weight. Next, 5 to 7 mm
The reaction temperature was set to 120 to 170 ° C. under reduced pressure of Hg, and the polycondensation reaction was performed for about 8 hours to give a number average molecular weight of 4,650.
A lactic acid oligomer of To 7 kg of this oligomer, 0.15 kg of succinic anhydride was added in an equimolar amount, and a carboxylation reaction was carried out at 150 ° C. under normal pressure so as to approximate 24 which is the theoretical acid value. When the acid value of the carboxylated lactic acid oligomer obtained after the reaction for about 1.5 hours was examined, it was 23 and the number average molecular weight was 5,220.
At this time, the succinic anhydride sublimated during the reaction was continuously dissolved in the reaction system by adding toluene at a ratio of 5% by weight with respect to the charged amount of the lactic acid oligomer in the reaction solution while dissolving it in the reflux tube. I put it back in. Next, this was supplied as a lactic acid prepolymer to a twin-screw extruder,
A copolymerization reaction with an epoxy resin was performed. The extruder used at that time was a meshing type co-rotating twin-screw extruder with L / D42 and screw diameter of 32 mm. As shown in Fig. 2, a total of 12 zones of the cylinder could be set to different temperatures. Is to have. The term "zone" used here means that different positions of the cylinder can be set to different temperatures, and is not limited to the meaning that the zones are separated from each other. The operating conditions at that time are as follows.

[0052]

[Table 1] (Operating conditions) Raw material supply rate: 2.83 kg / h Screw rotation speed: 150 rpm Cylinder temperature: Zone 1, 2 = 110 ° C Zone 3-11 = 120-140 ° C Zone 12, die = 120 ° C

Also mounted in zone 2 of the cylinder
Araldite at a rate of 0.19kg / h
(Epoxy equivalent; 168) was supplied. At the same time,
TEBAC is used as a catalyst in 0.01% of epoxy resin.
The copolymerization reaction was carried out while adding it in a weight percentage. So
Reaction time in the extruder (at the time of average residence in the extruder)
It was about 15 minutes. After the reaction,
The basic characteristics of the copolymer discharged from the extruder were investigated.
The number average molecular weight was 52,640. This polymer
Heat press to form a film,
The tensile strength was 1.82 kgf / mm.
²The elongation was 185%. The film after use
Is heated to 220 ℃ and pyrolyzed, polylactic acid component
Theoretically, it is decomposed into lactide at a rate of almost 100%, and the remaining
The existing epoxy resin component was also thermally decomposed at 260-280 ℃.
If so, it became clear that the volume can be reduced significantly.
Was.

Example 2 One batch of L-lactic acid was added to a batch-wise polymerization reaction tank having a capacity of 14 liters equipped with a stirrer, a thermocouple, a nitrogen gas introducing tube and a reflux tube.
0 kg was charged, and tin octylate as a catalyst was added thereto at a ratio of 0.25% by weight based on the raw material. Next, 2-8
The reaction temperature is set to 120 to 170 ° C. under reduced pressure of mmHg,
The polycondensation reaction was carried out for about 8 hours and the number average molecular weight was 1,300.
A lactic acid oligomer of 0.56 kg of succinic anhydride was added to 7.3 kg of this oligomer so as to be equimolar,
The carboxylation reaction was carried out at 150 ° C. under normal pressure so as to approximate 80 which is the theoretical acid value. When the acid value of the carboxylated lactic acid oligomer obtained after the reaction for about 3 hours was examined, it was 81, and the number average molecular weight was 2,220.
At this time, the succinic anhydride sublimated during the reaction was mixed with toluene in the reaction solution at 2.5% with respect to the charged amount of the lactic acid oligomer.
By adding it in a weight percentage, it was continuously returned to the reaction system while being dissolved in the reflux tube. Next, this was supplied as a lactic acid prepolymer to the same twin-screw extruder as in Example 1 to carry out a copolymerization reaction with an epoxy resin. The operating conditions at that time are as follows.

[0055]

[Table 2] (Operating conditions) Raw material supply rate: 2.65 kg / h Screw rotation speed: 200 rpm Cylinder temperature: Zone 1, 2 = 110 ° C Zone 3-11 = 130-150 ° C Zone 12, die = 120 ° C

Also mounted in zone 2 of the cylinder
From the supply port, the rate of 0.52 kg / h
Poxy equivalent; 135) was fed. At the same time, the catalyst
As TMAC 0.02% by weight to epoxy resin
The copolymerization reaction was carried out while adding at a ratio of. then
Reaction time in the extruder (depending on the average residence time in the extruder)
It was about 14 minutes. After the reaction is completed, the extruder
When the basic characteristics of the discharged polymer were examined,
The average molecular weight was 34,530. This polymer is
Hot press to form a film and measure its mechanical strength.
When determined, the tensile strength is 1.12 kgf / mm ², Shin
Was 192%. After using the film at 225 ℃
When heated and pyrolyzed, the polylactic acid component theoretically becomes almost
Epoxy that was decomposed into lactide at a rate of 100% and remained
Volume reduction if the resin component is also pyrolyzed at 260-280 ° C
It became clear that the chemical treatment can be performed.

Example 3 1 batch of L-lactic acid was added to a batch-wise polymerization reaction tank having a capacity of 14 liters equipped with a stirrer, a thermocouple, a nitrogen gas introduction tube, and a reflux tube.
0 kg was charged, and tin octylate as a catalyst was added thereto at a ratio of 0.3% by weight based on the raw material. Next, 1-10
The reaction temperature is set to 120 to 170 ° C. under reduced pressure of mmHg,
The polycondensation reaction was carried out for about 8 hours and the number average molecular weight was 3,400.
A lactic acid oligomer of 0.31 kg of phthalic anhydride was added to 7.2 kg of this oligomer so as to be equimolar,
The carboxylation reaction was carried out at 160 ° C. under normal pressure for about 2 hours so as to approximate to the theoretical acid value of 32. When the acid value of the carboxylated lactic acid oligomer obtained after the reaction was examined, it was 32, and the number average molecular weight was 3,840. At this time, the phthalic anhydride sublimed during the reaction was mixed with xylene in the reaction solution in an amount of 3% by weight based on the charged amount of the lactic acid oligomer.
Was added to the reaction system while continuously dissolving it in the reflux tube and returning it to the reaction system. Next, this was supplied as a lactic acid prepolymer to the same twin-screw extruder as in Example 1 to carry out a copolymerization reaction with an epoxy resin. The operating conditions at that time are as follows.

[0058]

[Table 3] (Operating conditions) Raw material supply rate: 3.00 kg / h Screw rotation speed: 200 rpm Cylinder temperature: Zone 1, 2 = 110 ° C Zone 3-11 = 130-150 ° C Zone 12, die = 120 ° C

Also mounted in zone 2 of the cylinder
Epolite (E) at a rate of 0.32 kg / h
Poxyequivalent; 188) was fed. At the same time, the catalyst
0.01% by weight of TPP with respect to the epoxy resin
The copolymerization reaction was carried out while adding in a ratio. At that time
Reaction time in the extruder (depending on the average residence time in the extruder)
Calculation) was about 13 minutes. After the reaction, the extruder
The basic characteristics of the polymer discharged from the
The average molecular weight was 40,350. This polymer
Toppress to form a film and measure its mechanical strength
As a result, the tensile strength is 1.64 kgf / mm ², Stretch
Was 186%. The film after use is heated to 225 ° C.
When heated and pyrolyzed, the polylactic acid component is theoretically about 1
Epoxy remaining after being decomposed into lactide at a rate of 00%
Volume reduction if the resin component is also pyrolyzed at 260-280 ℃
It became clear that it could be processed.

[0060]

Industrial Applicability According to the method of the present invention, a copolymer can be industrially produced from inexpensive lactic acid as a raw material.
Further, the copolymer obtained by the method of the present invention has excellent physical properties such as mechanical strength and weather resistance, and can be easily decomposed after use, so that it has excellent recyclability.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of an apparatus used in the manufacturing method of the present invention.

FIG. 2 is a diagram showing an example of a screw type extruder.

[Explanation of symbols]

 1. Polymerization reaction tank 2. Inert gas cylinder 3. Stirrer 4. Vacuum pump 5. Reflux tube 6. Trap (water) 7. Lactic acid oligomer 8. Lactic acid prepolymer 9. Plunger pump 10. Twin screw type extruder 11. Hopper 12. Rotary pump 13. Supply port 14. Polylactic acid copolymer 15. Screen 16. Die 17. Storage tank

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kayoko Yokota, 1-1, Funakoshi Minami, Aki-ku, Hiroshima City, Hiroshima Prefecture, Japan 6-1 Japan Steel Works, Ltd. (72) Inventor, Yukihiro Sumihiro 1-chome, Funakoshi South, Aki-ku, Hiroshima City 6-1 Inside Japan Steel Works, Ltd.

Claims (3)

[Claims] 1. A method for producing a polylactic acid copolymer, which comprises copolymerizing a reaction product of a lactic acid oligomer having a number average molecular weight of 1,000 to 5,000 and an acid anhydride with an epoxy resin. 2. The method for producing a polylactic acid copolymer according to claim 1, wherein the copolymerization reaction is carried out in a screw type extruder. 3. The method for producing a polylactic acid copolymer according to claim 1, wherein the reaction between the lactic acid oligomer having a number average molecular weight of 1,000 to 5,000 and the acid anhydride is carried out in a batch reaction tank.