JP2006342361A - Polylactic acid-based polymer composition and molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable polylactic acid-based polymer composition which can perfectly be degraded under the natural environments, has both excellent impact resistance/transparency, and has excellent elastic modulus, and to provide a molded article thereof. <P>SOLUTION: This polylactic acid-based polymer composition comprising (A) homopolylactic acid polymer and (B) a copolymer of polylactic acid with another aliphatic polyester in a (A)/(B) weight ratio of 30/70 to 80/20, wherein the copolymer (B) has only one glass transition temperature in a range of -20 to 40°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a biodegradable polylactic acid polymer composition which is suitable for fibers, films and other molded articles and has improved transparency, impact resistance and the like, and molded articles thereof.

  In recent years, biodegradable polymers that decompose in the natural environment and molded articles thereof have been demanded from the standpoint of protecting the natural environment, and research on natural degradable resins such as aliphatic polyesters has been actively conducted. In particular, a lactic acid polymer has a sufficiently high melting point of 170 to 180 ° C., is excellent in transparency, and has a high elastic modulus. However, polylactic acid has the disadvantage that it is inferior in impact resistance and brittle due to its rigid molecular structure, and improvement of this drawback in lactic acid polymers is desired.

  JP-A-7-173266 describes that a polymer having excellent transparency and flexibility can be obtained by copolymerizing polylactic acid and other aliphatic polyesters. It is difficult to control the polymerization and transesterification reaction, the polylactic acid segment size and the polyester segment size in the resulting copolymer cannot be guaranteed, and the physical properties of the resulting polymer are not stable. The impact resistance is improved by increasing the copolymerization ratio, but it is difficult to obtain a copolymer having excellent transparency due to the high crystallinity of the aliphatic polyester itself.

  Furthermore, JP-A-8-1557577 describes that a polymer having more transparency and flexibility can be obtained by copolymerizing with an aliphatic polyester having a branched chain. However, in order to improve impact resistance with these copolymers, copolymerization of several tens of percent or more is necessary, and a remarkable decrease in elastic modulus due to this is unavoidable.

That is, in reality, there is no known biodegradable polylactic acid polymer composition that is excellent in transparency and impact resistance and has an excellent elastic modulus.
JP-A-7-173266 JP-A-8-1557577

  An object of the present invention is to provide a biodegradable polylactic acid polymer composition that can be completely decomposed in a natural environment, has excellent impact resistance and transparency, and also has an excellent elastic modulus, and a molded article thereof. Is to provide.

In order to solve such problems, the present inventors have intensively studied and found that this can be achieved by the following biodegradable lactic acid copolymer composition and molded product thereof.

  That is, the gist of the present invention is that (A) a homopolylactic acid polymer and (B) a copolymer of polylactic acid and another aliphatic polyester are 30/70 to 80 by weight ratio of (A) / (B). / 20, and the copolymer (B) has only one glass transition temperature in the range of -20 to 40 ° C. It is.

  The different gist of the present invention is a polylactic acid polymer composition obtained by polymerizing lactide in the presence of an aliphatic polyester as a copolymer (B).

  A further subject matter of the present invention is a molded product selected from the group consisting of a film, a sheet, a plate, a pipe, a profile extrusion, a fiber, an injection molded product and a blow molded product, and a polylactic acid polymer composition is used. It is a molded product formed by

  The present invention provides a biodegradable polylactic acid-based polymer composition that is completely degradable in a natural environment, has excellent impact resistance and transparency, and has an excellent elastic modulus, and a molded product thereof. It became possible to do.

  The homopolylactic acid polymer (A) constituting the composition of the present invention is a polymer that is substantially composed only of monomer units derived from L-lactic acid and / or D-lactic acid. Here, “substantially” means that other monomer units not derived from L-lactic acid or D-lactic acid may be included as long as the effects of the present invention are not impaired. As a convenient measure, the glass transition temperature of the homopolylactic acid polymer (A) can be adopted.

  That is, in the present invention, it is important that the homopolylactic acid polymer has a glass transition temperature of 50 ° C. or higher. When the glass transition temperature is lower than 50 ° C., it can be obtained by blending with the copolymer (B) described later due to the influence of the molecular weight of the polymer, copolymerized monomer, residual monomer, additive, excessive water absorption and the like. The elastic modulus of the composition decreases, which is not preferable.

  In the present invention, “glass transition temperature” is defined using dynamic viscoelasticity measurement. That is, using the dynamic viscoelasticity measuring device VES-F-III manufactured by Iwamoto Seisakusho Co., Ltd., the main dispersion peak of the loss elastic modulus (E ″) in the dynamic viscoelasticity spectrum measured under the following conditions: The value was read and taken as the glass transition temperature.

Measurement condition
Sample thickness: 400 μm
Sample width: 4.5mm
Distance between chucks: 40mm
Measurement frequency: 10Hz
Distortion amount: 10 μm
Temperature increase rate: 1 ° C / min

  There is no other limitation on the homopolylactic acid polymer, and any known polymerization method can be adopted. Most representatively known is a method of ring-opening polymerization of lactide, which is an anhydrous cyclic dimer of lactic acid (lactide method), but lactic acid may be directly subjected to condensation polymerization. Moreover, as molecular weight, the range of 50,000-1,000,000 is preferable at a weight average molecular weight. Below this range, the mechanical properties and the like are not sufficiently expressed, and when it exceeds, the processability is inferior.

  When the homopolylactic acid polymer is composed only of monomer units derived from L-lactic acid and / or D-lactic acid, the polymer is crystalline and has a high melting point. In addition, the crystallinity and melting point can be freely adjusted by changing the ratio of monomer units derived from L-lactic acid and D-lactic acid (abbreviated as L / D ratio). Makes it possible to control. However, the glass transition temperature of the homopolylactic acid polymer is almost unchanged regardless of the L / D ratio if the molecular weight is sufficiently large, and is generally 55 to 65 ° C., generally 60, depending on the measurement method. ° C.

  Another polymer (B) constituting the composition of the present invention is a copolymer of polylactic acid and another aliphatic polyester.

  Thus, the aliphatic polyester is preferably a condensate of an aliphatic dicarboxylic acid and an aliphatic diol in consideration of ease of polymerization design and industrial costs. The condensate may contain a small amount of an alicyclic or aromatic monomer, but if the complete biodegradability and biodegradation rate are emphasized, the content is preferably 30 mol% or less. Further, it may be a condensate in which α-hydroxycarboxylic acid and its cyclic anhydride are copolymerized in an arbitrary ratio, or a homopolymer of α-hydroxycarboxylic acid and its cyclic anhydride is used together with the condensate. Alternatively, it may be replaced with the condensate. In any case, the aliphatic polyester desirably has a glass transition temperature of 0 ° C. or lower. If it is higher than 0 ° C., it is difficult to obtain an effect of improving impact resistance.

  As aliphatic dicarboxylic acid, what has a C4-C20 alkyl group is preferable, for example, succinic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid etc. are mentioned. The aliphatic diol preferably has an alkyl group having about 2 to 12 carbon atoms, and examples thereof include ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, and decanediol. The aliphatic diol includes a diol having an ether bond and a diol having a carbonate bond. The diol having an ether bond preferably has an alkyl group having about 2 to 8 carbon atoms, and examples thereof include diethylene glycol, triethylene glycol, dipropylene glycol, hydroxyethyl / hydroxypropyl ether, and bishydroxyethoxyhexane. The diol having a carbonate bond preferably has an alkyl group having about 4 to 8 carbon atoms, and examples thereof include bishydroxybutylene carbonate and bishydroxyhexane carbonate.

  Particularly suitable aliphatic polyesters include, for example, polyethylene suberate, polyethylene sebacate, polyethylene decanedicarboxylate, polybutylene succinate, polybutylene adipate, polybutylene sebacate, polybutylene succinate adipate. Polyester polyurethanes containing one or more urethane bonds in these polymer molecular chains can also be used. A branched structure can also be introduced into the aliphatic polyester, but the branched structure can be obtained by adding a polyfunctional compound such as a polyvalent carboxylic acid, a polyhydric alcohol, or a polyvalent isocyanate.

  On the other hand, the polylactic acid ester-bonded to the aliphatic polyester is usually composed only of monomer units derived from L-lactic acid and / or D-lactic acid. Moreover, the other monomer unit which does not originate in L-lactic acid or D-lactic acid may be included in the range which does not impair the effect of this invention.

  In the present invention, the copolymer (B) of polylactic acid and aliphatic polyester can be prepared by any method. For example, either one of polylactic acid or aliphatic polyester is separately prepared as a polymer, and the other constituent monomer is polymerized in the presence of the polymer.

  Usually, a copolymer (B) of polylactic acid and aliphatic polyester is obtained by polymerizing lactide in the presence of an aliphatic polyester prepared in advance. Basically, the polymerization can be carried out in the same manner as in the case of obtaining the homopolylactic acid polymer (A) by the lactide method, except that the aliphatic polyester is allowed to coexist. At this time, lactide polymerization proceeds, and at the same time, an appropriate transesterification reaction occurs between polylactic acid and the aliphatic polyester, and a copolymer (B) having relatively high randomness is obtained. When an aliphatic polyester urethane having a urethane bond is used as a starting material, ester-amide exchange is also generated.

  In the present invention, the glass transition temperature of the copolymer (B) needs to be -20 to 40 ° C. If it falls below this range, the transparency of the target composition is not good, whereas if it exceeds, the impact resistance is not good. The glass transition temperature of the copolymer (B) is appropriately controlled by the chemical composition of the starting aliphatic polyester, the copolymerization ratio with polylactic acid, the copolymerization reaction conditions, and the like. In the case of the above typical aliphatic polyesters such as polybutylene succinate, the glass transition temperature is generally in the range of −30 to −10 ° C., and when these are used, the copolymerization ratio depends on other conditions. However, it is adjusted in the range of polylactic acid / aliphatic polyester = 50/50 to 90/10.

  In the polylactic acid-based polymer composition of the present invention, the blending ratio of the polymer (A) and the copolymer (B) varies depending on the copolymer composition, but the weight ratio of (A) / (B) is 30 / It is necessary to make it the range of 70-80 / 20. When this weight ratio is less than 30/70, the tensile modulus and transparency are poor, while when it exceeds 80/20, the impact resistance is not sufficient.

  The composition of the present invention can be prepared by conventional means. That is, the mixing method and the mixing apparatus are not particularly limited, but those that can be continuously processed are advantageous and preferable from an industrial viewpoint. For example, the pellets of both polymers (A) and (B) are mixed at a predetermined ratio, melted with a single screw extruder or a twin screw kneading extruder, etc., and immediately injection-molded, film-formed or spun. Also good. Similarly, both polymers may be melted by separate extruders, mixed at a predetermined ratio by a static mixer or / and a mechanical stirring device, and immediately molded, or once pelletized. You may combine mixing by mechanical stirring, such as an extruder, and a static mixer. You may mix in a solution state using a solvent.

  In the melt mixing method, it is necessary to substantially prevent further copolymerization due to polymer deterioration, alteration, and transesterification reaction, and it is preferable to mix at a low temperature within a short time. For example, the temperature is preferably 230 ° C. or less, particularly preferably 210 ° C. or less, most preferably 190 ° C. or less, and the time is within 30 minutes, particularly within 20 minutes, most preferably within 10 minutes. In order to prevent alteration and transesterification due to melting, it is desirable to remove or reduce the hydroxyl group, carboxyl group, residual monomer and polymerization catalyst at the molecular end.

  Further, the composition of the present invention can be subjected to various modifications by adding secondary additives. Examples of secondary additives include stabilizers, antioxidants, UV absorbers, pigments, colorants, various fillers, electrostatic agents, mold release agents, plasticizers, perfumes, antibacterial agents, nucleating agents, etc. The similar thing is mentioned.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Various physical properties were measured on the sheets obtained in Examples and Comparative Examples under the following conditions.

(1) Glass transition temperature It was performed by the method described in the text. When two or more peaks of E ″ of the copolymer (B) are clearly present, the glass transition temperature was determined on the side close to homopolylactic acid, that is, on the high temperature side.

(2) Impact resistance It measured using the Shimadzu Corporation hydro-shot impact tester. A sample cut out to 100 mm × 100 mm from the sheet is fixed with a clamp, an impact is applied to the center of the film with a falling weight, and the energy (unit: Kgf · mm) is read. The measurement temperature is 23 ° C., and the falling speed of the falling weight is 3 m / second.

(3) Transparency Using a sample cut out from the sheet, haze (unit%) was measured according to JIS K-7105.

(4) Tensile modulus In accordance with JIS K-6732, a sample that was long in parallel with the sheet extrusion direction and cut into a strip of 5 mm width × 50 mm was left in an atmosphere conditioned at 23 ° C. for 2 days. Thereafter, a tensile test was performed using a Tensilon II type machine manufactured by Toyo Seiki Co., Ltd. with a chuck distance of 25 mm and a tensile speed of 5 mm / min. From the initial slope of the obtained stress-strain curve, the tensile modulus (unit: Kgf / mm) ² ) was calculated.

(Reference Example 1)
Synthesis of aliphatic polyester (PE1) 236 g of succinic acid and 216 g of 1,4-butanediol were mixed at 210 ° C. in a nitrogen gas atmosphere, esterified to give an acid value of 7.9, and then tetrabutyl titanate was added to the mixture as a catalyst. .2 g was added and the reaction was allowed to proceed. Finally, the pressure was reduced to 0.05 torr and the deglycolization reaction was performed for about 10 hours to synthesize an aliphatic polyester (PE1) having a weight average molecular weight of 82,000. The glass transition temperature was -26 ° C.

  In addition, as other aliphatic polyester (PE2), a commercially available product (Showa High Polymer Co., Ltd .: Bionore 3010), an aliphatic compound comprising adipic acid, succinic acid, 1,4-butanediol, and hexamethylene diisocyanate. Polyester urethane (PE2) was used. The glass transition temperature was −30 ° C.

(Reference Example 2)
Synthesis of crystalline aliphatic branched polyester polyurethane (PE3) 300 g of 1,4-butanediol, 300 g of succinic anhydride, 7 g of trimethylolpropane (about 1.5 mol% based on succinic anhydride), 0.6 g of tetraisopropyl titanate Was mixed in a nitrogen gas atmosphere at 205 to 210 ° C., esterified to an acid value of 7.1, and finally, the pressure was reduced to 0.5 torr and the reaction was allowed to proceed at 215 to 220 ° C. for about 5 hours. A deglycolization reaction was performed to synthesize a polyester having a weight average molecular weight of 70,000. Subsequently, at a temperature of 205 ° C., 4 g of hexamethylene diisocyanate was added and urethane crosslinking was carried out to obtain a polyester polyurethane (PE3) having a branched structure with a weight average molecular weight of 176,000 and a polydispersity (Mw / Mn) of 4.89. The glass transition temperature was -28 ° C.

(Reference Example 3)
Synthesis of various aliphatic polyester copolymers (CP1 to CP6)
To 28 parts by weight of the aliphatic polyester (PE1) obtained in Reference Example 1, 72 parts by weight of L-lactide was added, melted and mixed in an inert gas atmosphere, and 0.10 parts by weight of tin octylate as a ring-opening polymerization catalyst. The mixture was added and polymerized at 190 ° C. for 15 minutes while stirring with a biaxial kneader, and then extruded through a nozzle with a diameter of 2 mm, cooled with water, and cut to obtain an aliphatic polyester copolymer chip C1. The chip C1 was treated in nitrogen at 120 ° C. and a pressure of 1.5 kg / cm ² for 12 hours to remove unreacted monomer (lactide) to obtain a chip CP1. The weight average molecular weight of the chip CP1 is 155,000. Residual monomer (lactide) was 0.1%. From the NMR analysis, the polylactic acid component was 70% by weight and the aliphatic polyester component other than polylactic acid was 30% by weight. Only one glass transition temperature was observed, 30 ° C.

  In the above method, the amount of lactide charged or the type of aliphatic polyester was changed to obtain aliphatic polyester copolymer chips CP2 to CP6 as shown in Table 1. In the table, the amount of the polylactic acid component is a value obtained by measuring the amount of the polylactic acid component in the copolymer (B) by NMR analysis and expressing the result in wt%. In the synthesis of the chips CP5 to CP6, 0.14 parts by weight of di-n-butyltin dilaurate was added together with the ring-opening polymerization catalyst as a transesterification and / or ester amide exchange catalyst for the carbamate.

  Examples 1-6, Comparative Examples 1-7 In these Examples and Comparative Examples, the homopolylactic acid polymer (A) was a poly L-lactic acid “Lacty” manufactured by Shimadzu Corporation having a weight average molecular weight of 210,000. 1000 "was used. The glass transition temperature was 60 ° C. The number of revolutions of the polymer (A) and the various copolymers (B) using a same-direction twin-screw extruder (Mitsubishi Heavy Industries, 40 mmφ) in the ratios shown in Table 2 or Table 3 below. The mixture was mixed at 80 rpm and a temperature of 210 ° C. to obtain a polylactic acid polymer composition.

  This composition was extruded using a single-screw T-die extruder (manufactured by Mitsubishi Heavy Industries, 30 mmφ) equipped with a full flight screw at an extrusion temperature of 200 ° C. and a thickness of 400 μm, and rapidly cooled with a water-cooled cast roll to obtain a sheet. . The obtained sheet was subjected to measurement and evaluation of various physical properties and comprehensive judgment, and the results are also shown in the same table. In the table, “◎”, “・”, “Δ”, and “×” are relative evaluations, which indicate that they have good physical properties in this order. Depending on the application, ○ means that it is a practical property.

  As is clear from the above examples, the polylactic acid-based polymer composition of the present invention uses CP1, 3, 5, 6 which are copolymers (B) having an appropriate glass transition temperature, It can be seen that when the polymer composition has a weight ratio of A) / (B), the impact resistance, transparency, and tensile modulus are excellent, and a comprehensive judgment that the properties are practical in general can be obtained.

  On the other hand, when using CP2,4 which is a copolymer (B) having an inappropriate glass transition temperature, or an inappropriate (A) / (B) weight ratio, as seen in Comparative Examples Is extremely inferior in any of impact resistance, transparency and tensile elastic modulus, which causes a problem in practical use. Further, as seen in Comparative Examples 4 and 6, in order to sufficiently improve the impact resistance of polylactic acid using only the copolymer (B) alone, at least 20%, preferably 30% or more aliphatic polyester. However, as the copolymerization ratio increases, the copolymer becomes cloudy and the elastic modulus significantly decreases, which is a practical problem.

Claims (3)

  (A) A composition in which a homopolylactic acid polymer and (B) a copolymer of polylactic acid and other aliphatic polyester are blended at a weight ratio of (A) / (B) at a ratio of 30/70 to 80/20. The polylactic acid polymer composition is characterized in that the copolymer (B) has only one glass transition temperature in the range of -20 to 40 ° C.   The polylactic acid-based polymer composition according to claim 1, wherein the copolymer (B) described in the previous item is obtained by polymerizing lactide in the presence of an aliphatic polyester.   A molded product selected from the group consisting of a film, a sheet, a plate, a pipe, a profile extrusion product, a fiber, an injection molded product, and a blow molded product, and the polylactic acid polymer composition according to claim 1 or 2 is used. Molded product characterized by being molded.