JP3301505B2 - Polylactic acid copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aliphatic polyester containing polylactic acid as a main component and having a melting point sufficiently lower than that of polylactic acid alone and suitable for molding.

[0002]

2. Description of the Related Art Conventionally, aliphatic polyesters represented by polylactic acid have been used as sustained-release polymers as biodegradable medical materials such as surgical sutures and microcapsules for injections and agricultural chemical compositions such as herbicides. Have been. In recent years, plastic pollution has become a problem, and biodegradable plastics, which are expected to be decomposed by enzymes and microorganisms, have attracted attention and research and development have been promoted.

[0003] Since polylactic acid has a melting point near 180 ° C, it can be formed into a thread, formed into a film, molded and melt-molded, and has excellent moldability even from the viewpoint of the production process. However, there is a problem in that the melting point and the thermal decomposition temperature are close to each other, and if the molding is performed at a high temperature or a melted state for a long time, the molecular weight is remarkably reduced, and the desired physical properties of the molded product cannot be obtained. Therefore, it is necessary to use a higher molecular weight polylactic acid as a raw material in consideration of the molecular weight reduction in the molding step from the beginning. In this method, a problem that the melt viscosity is remarkably high in the initial step of the molding step and a problem that the physical properties of the molded article are barracks occur, and it is hard to say that this method is preferable. In order to solve such a problem, it has been proposed to use melt molding or to stabilize the polymer by a terminal blocking method or the like, but a satisfactory solution has not yet been found.

[0004]

As described above, polylactic acid-based polyesters which do not cause significant decomposition, ie, decrease in molecular weight, during melt molding have not yet been obtained.

[0005]

Means for Solving the Problems In view of the above circumstances, the present inventors have intensively studied to obtain a polylactic acid-based polyester with a small decrease in molecular weight during melt molding, and finally completed the present invention. . That is, the present invention relates to lactic acid and 50 mol%
A polylactic acid copolymer obtained by copolymerizing the following (I) and (II) with an amount not exceeding 90.degree.
A polylactic acid copolymer having a temperature of 70 ° C. or lower. (I) Dicarboxylic acids having 4 to 42 carbon atoms (II) Glycols having 2 to 40 carbon atoms

[0006] The copolymerization in the present invention lowers the melting point and does not lower the decomposition temperature. That is, it is surprising that the difference between the melting point and the decomposition temperature is widened and a polylactic acid-based polyester which does not cause a decrease in molecular weight during molding can be obtained. The dicarboxylic acids (I) that can be copolymerized in the present invention are compounds having 4 to 42 carbon atoms. If the number of carbon atoms is 3 or less, a large amount of copolymerization is required to obtain the desired product, and characteristics other than thermal characteristics, such as mechanical characteristics, are remarkably deteriorated. On the other hand, if it is 43 or more, the mechanical properties and the like are remarkably deteriorated even in a small amount of copolymerization, which is not preferable. Specific examples include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, fumaric acid, and dimer acid. However, it is not limited to these. Particularly, succinic acid, adipic acid, fumaric acid, azelaic acid and dimer acid are preferred. These copolymerization components oxyacids or combinations of diols and dicarboxylic acids may be copolymerized alone or in combination of two or more.

The glycols (II) copolymerizable in the present invention are compounds having 2 to 40 carbon atoms. When the number of carbon atoms is 1 or less, a large amount of copolymerization is required to obtain a desired product, and characteristics other than thermal characteristics, such as mechanical characteristics, are remarkably deteriorated. On the other hand, if the ratio is 41 or more, the mechanical properties and the like are remarkably deteriorated even in a small amount of copolymerization, which is not preferable. Specifically, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,8-octanediol, 1,10-decanediol, 1,12-
Dodecanediol, propylene glycol, 2,3-butanediol, 1,3-butanediol, neopentyl glycol and the like can be mentioned. However, it is not limited to these. From the viewpoint of cost and decomposition product safety, ethylene glycol, 1,4-butanediol, and 2,3-butanediol are preferred. Combinations of these copolymerization components dicarboxylic acids (I) and diols (II) may be copolymerized singly or in combinations of two or more.

Further, in the present invention, α-α having 4 or more carbon atoms is used.
Oxy acids may be copolymerized. If the number of carbon atoms is 3 or less, a large amount of copolymerization is required to obtain the desired product, and characteristics other than thermal characteristics, such as mechanical characteristics, are remarkably deteriorated. Specifically, for example, α-hydroxybutyric acid,
α-hydroxyisobutyric acid, α-hydroxyvaleric acid, α-
Examples thereof include hydroxyisovaleric acid, α-hydroxy-α-methylbutyric acid, α-hydroxycaproic acid, α-hydroxyisocaproic acid, α-hydroxy-β-methylvaleric acid, and α-hydroxyheptanoic acid. But,
It is not limited to these. In the case of copolymerization, it is provided to the copolymerization system as an oxyacid or a corresponding cyclic diester.

Further, in the present invention, a cyclic compound having 7 or more carbon atoms is used.
Lactones may be copolymerized. If the number of carbon atoms is 6 or less, a large amount of copolymerization is required to obtain the desired product, and characteristics other than thermal characteristics, for example, mechanical characteristics, etc. are significantly reduced, which is not preferable. Specifically, for example, 7-heptanolide, 8
-Octanolide, 9-nonanolide, 10-decanolide,
Examples thereof include 11-undecanolide and 12-dodecanolide. However, it is not limited to these.

The polylactic acid-based polyester containing the above-mentioned copolymerization component can be synthesized from lactic acid or lactide and the above-mentioned copolymerization component by a known method such as dehydration polycondensation or ring-opening polymerization. Those having an asymmetric carbon in the polymer include optical isomers such as L-form, DL-form and D-form, and any of them may be used, or a mixture of these optical isomers may be used.

The melting point (Tm) of the copolymer, which is an important requirement of the present invention, is required to be 90 ° C. or more and 170 ° C. or less in order to impart the desired melt moldability. . If the temperature exceeds 170 ° C., it is difficult to lower the molding temperature remarkably as compared with the case of polylactic acid alone, so that a decrease in molecular weight cannot be suppressed. On the other hand, when the temperature is lower than 90 ° C., various physical properties such as heat resistance are remarkably reduced, which is not preferable. In order to obtain a polylactic acid-based copolymerized polyester having a melting point in such a range, the above-mentioned components are copolymerized. However, if the amount of the copolymerized components is too large, the melting point of the obtained polymer is less than 90 ° C. On the other hand, if the amount is too small, the melting point will not be 170 ° C. or less, and the object cannot be achieved. The optimum copolymerization amount varies depending on the components used, but does not exceed 50 mol%.

The polyester of the present invention has a reduced viscosity of 0.1.
It is 1 dl / g or more. If the reduced viscosity is less than 0.1 dl / g, the degree of polymerization is too low, and the desired thermal stability cannot be obtained. Preferably, it is 0.2 dl / g or more.

In the present invention, the polymer is melt-molded.
If necessary, it can be used by mixing with other polymers or inorganic substances. Further, as with ordinary polyesters, matting agents, pigments such as carbon black, antioxidants such as hindered phenol compounds, hindered amine compounds, phosphorus compounds, ultraviolet absorbers such as benzophenone compounds, benzotriazole compounds, salicylate compounds, etc., In some cases, a compound having a crosslinkable group may be contained.

The polyester of the present invention can be used in various fields because of its good melt moldability. For example, fishing fiber aggregates such as fishing lines and fish nets, aquaculture nets, ropes, sanitary fiber aggregates such as sanitary products, agricultural fiber aggregates such as bird nets and nurseries, waterproof sheets, temporary sheets, Civil fiber aggregates such as temporary nets, windbreak nets, temporary fixing ropes, drainage ropes, etc., agricultural films such as agricultural multi-films, greenhouse films, seedling cups, food packaging films, rice, fertilizers and garbage Such as bags, food container containers such as cups and trays, and drink pack paper laminates, bottles, trays, cups, pottings for seedlings and seedlings, eating and drinking utensils such as knives, forks, spoons, pipes, temporary fixing materials And other medical materials such as surgical products, surgical sutures, artificial joints, and microcapsules for injections, but are not limited thereto. No.

[0015]

【Example】

Example 1 20.0 g (0.106 mol) of azelaic acid, 14.5 g (0.234 mol) of ethylene glycol, Sb ₂
15.4 mg (5.3 × 10 ⁻⁵ mol) of O ₃ was charged into a polymerization tube equipped with a stirrer and a nitrogen inlet tube, and heated and heated from 170 ° C. to 240 ° C. under a nitrogen atmosphere to perform dehydration condensation. The resulting milky white solid is further gradually reduced to 0.3 mm at 240 ° C.
The pressure was reduced to Hg and the mixture was heated for 18 hours to distill off ethylene glycol produced by transesterification. The reduced viscosity of the obtained pale yellow solid (measurement: in chloroform at 25 ° C., 0.5
g / dl) was 1.73 dl / g. The obtained polymer was pulverized, 6.0 g was inserted into a polymerization tube, and 1
It dried under reduced pressure (0.5 mmHg) for 0 hours. Subsequently, 8.4 g (0.058 mol) of L-lactide and 2.5 mg (6.2 × 10 ⁻⁵ mol) of stannous octoate in toluene were dried under reduced pressure for 1 hour, and toluene was distilled off.
Heated at 00 ° C. for 1 hour. The reduced viscosity of the obtained polymer was 0.32 dl / g, and the melting point by DSC was 146.
° C (peak temperature). Its 10% weight loss temperature by TGA analysis was 280 ° C., which was almost the same as that of polylactic acid (see Comparative Example 1).

Comparative Example 1 A toluene solution of 10.0 g (0.069 mol) of L-lactide and 3 mg (7.4 × 10 ⁻⁵ mol) of stannous octylate was placed in a polymerization tube equipped with a stirrer and a nitrogen inlet tube. After being charged and dried under reduced pressure for 2 hours, it was heated at 200 ° C. for 1 hour under a nitrogen atmosphere. Reduced viscosity of the obtained polymer (measurement:
2.41 d at 25 ° C. in chloroform and 0.5 g / dl)
1 / g and the melting point by DSC was 181 ° C (peak temperature). Its 10% weight loss temperature by TGA analysis was 283 ° C.

[0017]

The polylactic acid-based copolymerized polyester of the present invention can lower the melting point without lowering the decomposition point of polylactic acid by copolymerizing the second component. Therefore, since it has a good melting point for melt molding, it is possible to easily bring out the excellent physical properties of the polymer without causing a decrease in molecular weight due to thermal decomposition during molding.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-215319 (JP, A) JP-A-5-177734 (JP, A) US Patent 4,481,353 (US, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C08G 63/00-63/91 WPI / L (QUESTEL)

Claims (1)

(57) [Claims] 1. A polylactic acid copolymer obtained by copolymerizing the following (I) and (II) in an amount not exceeding 50 mol% with lactic acid, and having a melting point in the range of 90 ° C. or more and 170 ° C. or less. Certain polylactic acid copolymers. (I) Dicarboxylic acids having 4 to 42 carbon atoms (II) Glycols having 2 to 40 carbon atoms