JP5259926B2 - Method for producing polylactic acid resin composition - Google Patents

Description

  The present invention relates to a method for producing a polylactic acid resin composition.

  Polylactic acid resin has been obtained by producing a large amount of L-lactic acid from saccharides obtained from corn, straw, etc. by fermentation, resulting in a low price. The resin is characterized by its high rigidity and good transparency, and its use is expected now. However, polylactic acid resins are easily hydrolyzed at high temperatures and high humidity, have poor durability, have no physical properties that can withstand actual use, and have limited applications.

In order to solve such a problem, Patent Document 1 discloses an aliphatic polyester resin in which a carboxyl group terminal is blocked with a monocarbodiimide compound having a 5% weight reduction temperature of 170 ° C. or more. Patent Document 2 discloses a biodegradable resin composition having improved hydrolysis resistance, which is obtained by blending a carbodiimide compound and an antioxidant with a biodegradable resin. However, even in these resin compositions, the hydrolysis resistance is not sufficiently satisfactory, and further improvement has been desired.
JP 2001-261797 A JP 2003-313436 A

  The subject of this invention is providing the manufacturing method of the polylactic acid resin composition excellent in hydrolysis resistance.

  The present invention provides a method for producing a polylactic acid resin composition, in which monocarbodiimide is blended with a polylactic acid resin, the carboxyl group terminal concentration of the resulting blend is 20 mmol / kg or less, and further polycarbodiimide is blended. .

  According to the present invention, a polylactic acid resin composition having excellent hydrolysis resistance can be obtained.

  Examples of the polylactic acid resin used in the present invention include polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic acid and the like, and glycolic acid and hydroxycaproic acid are preferable.

  A preferred molecular structure of polylactic acid is composed of 20 to 100 mol% of either L-lactic acid or D-lactic acid and 0 to 20 mol% of each enantiomer. The copolymer of lactic acid and hydroxycarboxylic acid is composed of 85 to 100 mol% of either L-lactic acid or D-lactic acid and 0 to 15 mol% of hydroxycarboxylic acid units.

  These polylactic acid resins can be obtained by dehydrating polycondensation using L-lactic acid, D-lactic acid and hydroxycarboxylic acid as a raw material by selecting those having the required structure. Preferably, it can be obtained by ring-opening polymerization by selecting a desired structure from lactide, which is a cyclic dimer of lactic acid, glycolide, which is a cyclic dimer of glycolic acid, and caprolactone. Lactide includes L-lactide which is a cyclic dimer of L-lactic acid, D-lactide which is a cyclic dimer of D-lactic acid, meso-lactide obtained by cyclic dimerization of D-lactic acid and L-lactic acid, and D-lactide. There is DL-lactide, which is a racemic mixture of lactide and L-lactide. Any lactide can be used in the present invention. However, the main raw material is preferably D-lactide or L-lactide.

  Examples of commercially available polylactic acid resins include Mitsui Chemicals, Inc., trade name Lacia series; Nature Works, trade name Nature works series; Toyota Motor Corporation, U'z series, and the like. .

  Among these polylactic acid resins, from the viewpoint of crystallization speed and physical properties, L-lactic acid is a high-purity product, particularly a grade of L-lactic acid, particularly LACEA H-400, LACEA H-100, LACEA H-440, manufactured by Mitsui Chemicals. A polylactic acid resin having an L-lactic acid purity of 95% or more, particularly, LACEA H-400, LACEA H-100, manufactured by Mitsui Chemicals, Inc. is more preferable.

  In the present invention, in order to obtain good hydrolysis resistance, first, monocarbodiimide is blended with the polylactic acid resin, and the carboxyl group terminal concentration of the resulting blend is 20 mmol / kg or less, preferably 15 mmol / kg or less. More preferably, it is 12 mmol / kg or less, and particularly preferably 10 mmol / kg or less.

  In addition, the carboxyl group terminal density | concentration of a compound can be measured with the following method.

<Measurement method of carboxyl group terminal concentration>
It is obtained by dissolving 3 g of the formulation in 100 mL of chloroform, adding 50 mL of benzyl alcohol and a small amount of phenolphthalein ethanol solution thereto, and titrating with 0.05 N potassium hydroxide ethanol solution. Here, chloroform is used as a solvent for dissolving polylactic acid resin, 0.05N potassium hydroxide ethanol solution is used as a titration solvent, benzyl alcohol is used as a compatibilizing agent, and phenolphthalein ethanol solution is used as an indicator.

  The blending amount of monocarbodiimide is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the polylactic acid resin from the viewpoint of obtaining good hydrolysis resistance and reducing the carboxyl group terminal concentration of the blend. 1 to 5 parts by weight is more preferable. Moreover, 0.1-3 weight part is further more preferable from a viewpoint of transparency, and 0.1-1 weight part is especially preferable.

  Examples of the monocarbodiimide used in the present invention include diphenylcarbodiimide, di-2,6-dimethylphenylcarbodiimide, di-2,6-diethylphenylcarbodiimide, di-2,6-diisopropylphenylcarbodiimide, di-2,6-di. tert-butylphenylcarbodiimide, di-o-tolylcarbodiimide, di-p-tolylcarbodiimide, di-2,4,6-trimethylphenylcarbodiimide, di-2,4,6-triisopropylphenylcarbodiimide, di-2,4 Aromatic monocarbodiimides such as 1,6-triisobutylphenylcarbodiimide; alicyclic monocarbodiimides such as di-cyclohexylcarbodiimide; aliphatic monocarbodiimides such as di-isopropylcarbodiimide and di-octadecylcarbodiimide From the viewpoint of obtaining good hydrolysis resistance and reducing the carboxyl group terminal concentration of the blend, aromatic monocarbodiimide is preferred, and di-2,6-diisopropylphenylcarbodiimide and di-2,6-dimethylphenylcarbodiimide are preferred. Is more preferable. These monocarbodiimides can be used alone or in combination of two or more.

  The temperature at which monocarbodiimide is added to the polylactic acid resin is preferably equal to or higher than the melting point (Tm) of the polylactic acid resin from the viewpoint of the reactivity between the polylactic acid resin and carbodiimide, and 250 ° C. from the viewpoint of not impairing the original physical properties of the resin. The following is preferable, and 230 ° C. or lower is more preferable. In addition, melting | fusing point (Tm) of a polylactic acid resin is a value calculated | required from the crystal melting endothermic peak temperature by the temperature rising method of differential scanning calorimetry (DSC) based on JIS-K7121. When the polylactic acid resin is Lacia H-400 (manufactured by Mitsui Chemicals, Inc.), Tm is 166 ° C. When such a polylactic acid resin having an L-lactic acid purity of 95% or more is used, 170 to 250 ° C is preferred, 170-230 ° C is more preferred, and 170-210 ° C is even more preferred.

  In this invention, after making the carboxyl group terminal density | concentration of the compound obtained by mix | blending a monocarbodiimide as mentioned above into 20 mmol / kg or less, a polycarbodiimide is further mix | blended. In addition, the timing which mix | blends polycarbodiimide determines and determines that the carboxyl group terminal density | concentration of the compound obtained by mix | blending monocarbodiimide is 20 mmol / kg or less by the said measuring method.

  Examples of the polycarbodiimide used in the present invention include poly (4,4′-diphenylmethanecarbodiimide), poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (diisopropylphenylenecarbodiimide), and poly (triisopropylphenylenecarbodiimide). Aromatic polycarbodiimides such as poly (4,4′-dicyclohexylmethanecarbodiimide), and aliphatic polycarbodiimides such as poly (diisopropylcarbodiimide), etc., and good hydrolysis resistance is obtained. From the viewpoint, aromatic polycarbodiimide and alicyclic polycarbodiimide are preferable. These polycarbodiimides can be used alone or in combination of two or more.

  The blending amount of the polycarbodiimide is preferably 0.1 to 10 parts by weight, more preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polylactic acid resin, from the viewpoint of obtaining good hydrolysis resistance. Moreover, 0.1-3 weight part is further more preferable from a transparency viewpoint, and 0.1-1 weight part is especially preferable.

  From the viewpoint of obtaining good hydrolysis resistance, the polycarbodiimide has a monocarbodiimide / polycarbodiimide blending ratio of monocarbodiimide / polycarbodiimide (weight ratio) = 1/9 to 9/1, more preferably 3/7 to It is preferable to mix | blend so that it may become 7/3.

  The temperature when blending the polycarbodiimide is preferably not less than the melting point (Tm) of the polylactic acid resin from the viewpoint of sufficiently dispersing the polycarbodiimide in the polylactic acid resin, and not more than 250 ° C. from the viewpoint of not impairing the original physical properties of the resin. Is preferable, and 230 degrees C or less is more preferable. In addition, melting | fusing point (Tm) of a polylactic acid resin is a value calculated | required from the crystal melting endothermic peak temperature by the temperature rising method of differential scanning calorimetry (DSC) based on JIS-K7121. When the polylactic acid resin is Lacia H-400 (manufactured by Mitsui Chemicals, Inc.), Tm is 166 ° C. When such a polylactic acid resin having an L-lactic acid purity of 95% or more is used, 170 to 250 ° C is preferred, 170-230 ° C is more preferred, and 170-210 ° C is even more preferred.

  The present invention is a method for producing a polylactic acid resin composition in which monocarbodiimide is blended with a polylactic acid resin, the carboxyl group terminal concentration of the resulting blend is 20 mmol / kg or less, and then polycarbodiimide is further blended. By using this method, the hydrolysis resistance of the polylactic acid resin composition can be effectively improved.

  The reason why the hydrolysis resistance is improved by the method of the present invention is not clear, but is probably based on the following reason. Monocarbodiimide reacts with the terminal carboxyl group of the polylactic acid resin, so that the carboxyl group end is blocked, and then even if polycarbodiimide is blended, most of them do not react with the terminal carboxyl group of the polylactic acid resin, and in a free state It can exist. Due to the synergistic effect of quickly and effectively blocking the carboxyl group end of monocarbodiimide and the chain extending effect of polycarbodiimide, it is not possible to give excellent hydrolysis resistance with a lower amount of carbodiimide. It is thought.

You may mix | blend a plasticizer, a crystal nucleating agent, etc. with the polylactic acid resin composition of this invention further.
The plasticizer is not particularly limited, and for example, glycerin diacetomonolaurate, diglycerin tetraacetate, tributyl acetylcitrate, etc. used in general biodegradable resins, and having two or more ester groups in the molecule Examples include ethylene oxide adducts. Among these, from the viewpoint of flexibility and transparency of the polylactic acid resin, a compound having 2 or more ester groups in the molecule and an average added mole number of ethylene oxide of 2 to 9, particularly 3 to 9 is preferable. . Examples of such compounds include esters of polyvalent carboxylic acids such as succinic acid, adipic acid, 1,3,6-hexanetricarboxylic acid and polyethylene glycol monoalkyl ether, and alkyl ethers of polyhydric alcohols such as glycerin and polyethylene glycol. Examples include esters. These plasticizers may be used alone or in combination of two or more.

  The blending amount of the plasticizer is preferably 5 to 70 parts by weight, more preferably 10 to 50 parts by weight, from the viewpoint of expressing the effect of the plasticizer and not impairing the properties of the resin with respect to 100 parts by weight of the polylactic acid resin. .

  In the present invention, as the crystal nucleating agent, either an organic nucleating agent or an inorganic nucleating agent can be used. The organic nucleating agent preferably has a melting point of 65 ° C. or higher, more preferably 70 ° C. to 220 ° C., from the viewpoint of improving the crystallization speed of the polylactic acid resin. Examples of the organic nucleating agent include aliphatic esters, aliphatic amides, fatty acid metal salts and the like. From the viewpoint of improving the crystallization speed of polylactic acid resin, 12-hydroxystearic acid triglyceride, behenic acid monoglyceride, ethylene bis 12- Hydroxy stearic acid amide, hexamethylene bis 12-hydroxy stearic acid amide, 12-hydroxy stearic acid monoethanol amide, ethylene biscaprylic acid amide, ethylene biscapric acid amide and the like are preferable.

  The inorganic nucleating agent is not particularly limited, but silicates such as talc, smectite, bentonite, dolomite, sericite, feldspar powder, kaolin, mica, montmorillonite are used from the viewpoint of improving heat resistance, moldability and crystallinity. preferable.

  When an organic nucleating agent is used as the crystal nucleating agent, the blending amount of the organic nucleating agent is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polylactic acid resin from the viewpoint of manifesting the effect as the crystal nucleating agent. More preferred is 3 to 5 parts by weight. Moreover, when using an inorganic nucleating agent, the blending amount of the inorganic nucleating agent is preferably 0.1 to 150 parts by weight, based on 100 parts by weight of the polylactic acid resin, from the viewpoint of manifesting the effect as a crystal nucleating agent, and 3 to 80 parts by weight. Part by weight is more preferred.

  In the polylactic acid resin composition of the present invention, an antioxidant, a lubricant, an antistatic agent, an antifogging agent, a light stabilizer, an ultraviolet absorber, a pigment, an inorganic filler, and an antifungal agent are included as components other than those described above. Antibacterial agents, foaming agents, flame retardants, and the like can be blended within a range that does not hinder the achievement of the object of the present invention.

Synthesis example 1
In a flask equipped with a stirring motor, a nitrogen gas bubbling tube and a cooling tube, 100 g of 2,6-dimethylphenyl isocyanate, 1 g of carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) and triethylene glycol 250 mL of dimethyl ether was added and carbodiimidization reaction was performed at 100 ° C. for 6 hours to obtain di-2,6-dimethylphenylcarbodiimide. NCO% of the obtained product was 0, and it was confirmed that carbodiimidization was completed.

Synthesis example 2
In a flask equipped with a stirring motor, a nitrogen gas bubbling tube and a cooling tube, 100 g of 4,4′-diphenylmethane diisocyanate, 1 g of carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) and triethylene glycol 250 mL of dimethyl ether was added and a carbodiimidization reaction was performed at 100 ° C. for 3 hours to obtain poly (4,4′-diphenylmethanecarbodiimide). The obtained product had an NCO% of 18 and a degree of polymerization of 5.

Examples 1-3
Monocarbodiimide shown in Table 1 was added to polylactic acid resin (manufactured by Mitsui Chemicals, Ltd., LACEA H-400) (hereinafter referred to as PLA) at a ratio shown in Table 1, and a test kneader (laboplast mill 40C, Toyo Seiki ( The product was melt-mixed in a temperature range of 180 to 200 ° C. Table 1 shows the carboxyl group terminal concentration of the blend at this time. Subsequently, the polycarbodiimide shown in Table 1 was added in the ratio shown in Table 1, and it melt-mixed in the temperature range of 180-200 degreeC, and obtained the resin composition.

Example 4
In Example 1, after adding polycarbodiimide and melt mixing in a temperature range of 180 to 200 ° C., a plasticizer and a crystal nucleating agent shown in Table 1 are further added, and melt mixing in a temperature range of 180 to 200 ° C. Thus, a resin composition was obtained.

Comparative Example 1
Monocarbodiimide shown in Table 1 is added to PLA in the ratio shown in Table 1, and melt mixed in a temperature range of 180 to 200 ° C. using a test kneader (Laboplast Mill 40C, manufactured by Toyo Seiki Co., Ltd.). A composition was obtained. Table 1 shows the carboxyl group terminal concentration of the blend at this time.

Comparative Examples 2-3
To the PLA, polycarbodiimide shown in Table 1 was added in the ratio shown in Table 1, and melt mixed in a temperature range of 180 to 200 ° C. using a test kneader (laboplast mill 40C, manufactured by Toyo Seiki Co., Ltd.). Table 1 shows the carboxyl group terminal concentration of the blend at this time. Subsequently, the monocarbodiimide shown in Table 1 was added in the ratio shown in Table 1, and it melt-mixed in the temperature range of 180-200 degreeC, and obtained the resin composition.

Comparative Example 4
Mono-carbodiimide and polycarbodiimide shown in Table 1 are simultaneously added to PLA in the proportions shown in Table 1, and melted in a temperature range of 180 to 200 ° C. using a test kneader (laboplast mill 40C, manufactured by Toyo Seiki Co., Ltd.). The resin composition was obtained by mixing. Table 1 shows the carboxyl group terminal concentration of the blend at this time.

Comparative Example 5
To the PLA, polycarbodiimide shown in Table 1 was added in the ratio shown in Table 1, and melt mixed in a temperature range of 180 to 200 ° C. using a test kneader (laboplast mill 40C, manufactured by Toyo Seiki Co., Ltd.). Table 1 shows the carboxyl group terminal concentration of the blend at this time. Subsequently, a plasticizer and a crystal nucleating agent shown in Table 1 were further added and melt-mixed in a temperature range of 180 to 200 ° C. to obtain a resin composition.

Comparative Example 6
Monocarbodiimide shown in Table 1 was added to PLA at a ratio shown in Table 1, and melt mixed in a temperature range of 180 to 200 ° C. using a test kneader (Laboplast Mill 40C, manufactured by Toyo Seiki Co., Ltd.). Table 1 shows the carboxyl group terminal concentration of the blend at this time. Subsequently, the polycarbodiimide shown in Table 1 was added in the ratio shown in Table 1, and it melt-mixed in the temperature range of 180-200 degreeC, and obtained the resin composition.

  About the resin composition obtained in Examples 1-4 and Comparative Examples 1-6, the hydrolysis resistance was evaluated by the following method. The results are shown in Table 1.

<Evaluation method of hydrolysis resistance>
(1) sandwiched between two metal plates with mold thickness 0.5mm to create a resin composition sample for durability test, after pre-load for 3 minutes 5 kg / cm ² at 180 ° C., further 200 kg / cm ² A sample sheet having a thickness of 0.5 mm was prepared by pressing for 1 minute.

(2) Evaluation of hydrolysis resistance The obtained sample sheet was put in a thermo-hygrostat (Platinus series PSL-2, manufactured by Tabay Espec Co., Ltd.) at 80 ° C./95% Rh, and a weight average after 72 hours. The molecular weight (Mw) was measured, and the molecular weight retention rate (%) was determined from the following formula.

Molecular weight retention (%) = (Mw after 72 hours / initial Mw) × 100
The weight average molecular weight (Mw) was measured by GPC (gel permeation chromatography) under the following conditions, and the sample was prepared by dissolving 30 mg of the sample in 10 mL of chloroform.
Column: GMH _HR -H x 2
Column temperature: 40 ° C
Detector: RI or UV (210 nm)
Eluent: Chloroform flow rate: 1.0 mL / min
Injection volume: 0.1 mL
Standard: Polystyrene

* 1 PLA: Polylactic acid resin (manufactured by Mitsui Chemicals, LACEA H-400)
* 2 Di-2,6-diisopropylphenylcarbodiimide: Stabuxol I (Rhein Chemie)
* 3 Di-2,6-dimethylphenylcarbodiimide: prepared in Synthesis Example 1
* 4 Poly (4,4′-dicyclohexylmethanecarbodiimide): Carbodilite LA-1 (Nisshinbo Industries, Ltd.)
* 5 Poly (4,4′-diphenylmethanecarbodiimide): prepared in Synthesis Example 2
* 6 Bismethyl triglycol succinate: Diester of succinic acid and triethylene glycol monomethyl ether
* 7 Ethylene bis 12-hydroxystearic acid amide: Nippon Kasei Co., Ltd., SLIPAX H
* 8 Examples 1-4 and Comparative Examples 1 and 6 are carboxyl group terminal concentrations when monocarbodiimide is blended, Comparative Examples 2-3 and 5 are carboxyl group terminal concentrations when polycarbodiimide is blended, and Comparative Example 4 is The carboxyl group terminal density | concentration at the time of mix | blending monocarbodiimide and polycarbodiimide is shown.

Claims (6)

0.1-3 parts by weight of monocarbodiimide is added to polylactic acid resin with respect to 100 parts by weight of polylactic acid resin , and after the carboxyl group terminal concentration of the obtained composition is 10 mmol / kg or less, polycarbodiimide is further added. A method for producing a polylactic acid resin composition. Amount of polycarbodiimide The process of claim 1 polylactic acid resin composition wherein 0.1 to 10 parts by weight per 100 parts by weight of the polylactic acid resin. The method for producing a polylactic acid resin composition according to claim 1 or 2, wherein the monocarbodiimide is at least one selected from the group consisting of aromatic monocarbodiimides. The method for producing a polylactic acid resin composition according to any one of claims 1 to 3 , wherein the polycarbodiimide is at least one selected from the group consisting of an aromatic polycarbodiimide and an alicyclic polycarbodiimide. The method for producing a polylactic acid resin composition according to any one of claims 1 to 4, wherein the temperature when the monocarbodiimide is blended with the polylactic acid resin is equal to or higher than the melting point (Tm) of the polylactic acid resin. The method for producing a polylactic acid resin composition according to any one of claims 1 to 5 , wherein a temperature at which the polycarbodiimide is blended is equal to or higher than a melting point (Tm) of the polylactic acid resin.