Polylactic acid resin composition, molded product, and method of manufacturing polylactic acid resin composition

1. A polylactic acid resin composition comprising:

0.005 parts by weight to 1.2 parts by weight of a metal phosphate represented by Formula (1):

M x H y PO z   (1)

wherein M is an alkali metal atom or an alkaline earth metal atom, and x, y, and z are integers satisfying 1≦x≦2, 1≦y≦4, and 2≦z≦8, respectively, with respect to 100 parts by weight of a polylactic acid resin comprising a poly-L-lactic acid component and a poly-D-lactic acid component, and

wherein a crystallization enthalpy of crystals in the polylactic acid resin is not less than 5 J/g when a temperature of the polylactic acid resin composition is increased to 250° C., the temperature is kept constant for 3 minutes, followed by decreasing the temperature at a cooling rate of 20° C/min in differential scanning calorimetry, and the cooling crystallization temperature is 120° C. or higher,

the polylactic acid resin composition does not contain a polyfunctional compound other than the polylactic acid resin, and

the polylactic acid resin comprises a polylactic acid block copolymer composed of

poly-L-lactic acid segments containing L-lactic acid as a main component, and

poly-D-lactic acid segments containing D-lactic acid as a main component.

2. The composition according to claim 1 , wherein the metal phosphate is at least one selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, calcium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, calcium hydrogen phosphate, barium hydrogen phosphate, magnesium hydrogen phosphate, sodium hydrogen phosphite, potassium phosphite, calcium hydrogen phosphite, sodium hypophosphite, potassium hypophosphite, and calcium hypophosphite.

3. The composition according to claim 1 , wherein a weight loss percentage after the polylactic acid resin composition is heated at 240° C. for 30 minutes in a thermogravimetric analysis is less than 1.0%.

4. The composition according to claim 1 , wherein the polylactic acid block copolymer is obtained by mixing poly-L-lactic acid and poly-D-lactic acid under a condition of a combination 1 and/or a combination 2:

a combination 1, in which one of the poly-L-lactic acid and the poly-D-lactic acid has a weight average molecular weight of not less than 60,000 and not more than 300,000, and the other has a weight average molecular weight of not less than 10,000 and not more than 100,000,and/or

a combination 2, in which a ratio between the weight average molecular weight of the poly-L-lactic acid and the weight average molecular weight of the poly-D-lactic acid is not less than 2 and less than 30,

to obtain a mixture in which Sc satisfies Equation (3):

Sc=ΔHh /(Δ Hl+ΔHh )×100>60  (3)

where

ΔHh represents heat of fusion of stereocomplex crystals (J/g) by increasing a temperature at a heating rate of 20° C./min in differential scanning calorimetry, and

ΔHl represents heat of crystals (J/g) of poly-L-lactic acid alone or crystals (J/g) of poly-D-lactic acid alone by increasing a temperature at a heating rate of 20° C./min in differential scanning calorimetry, and that has a weight average molecular weight of not less than 90,000, followed by solid-state polymerization of the mixture at a temperature lower than a melting point of the mixture.

5. The composition according to claim 1 , wherein the polylactic acid block copolymer is obtained by mixing poly-L-lactic acid and poly-D-lactic acid under a condition of a combination 3 and/or a combination 4:

a combination 3, in which one of the poly-L-lactic acid and the poly-D-lactic acid has a weight average molecular weight of not less than 60,000 and not more than 300,000, and the other has a weight average molecular weight of not less than 10,000 and not more than 50,000, and/or

a combination 4, in which a ratio between the weight average molecular weight of the poly-L-lactic acid and the weight average molecular weight of the poly-D-lactic acid is not less than 2 and less than 30, to obtain a mixture in which Sc satisfies Equation (3):

Sc=ΔHh /(Δ Hl+ΔHh )×100>60  (3)

where

ΔHh represents heat of stereocomplex crystals (J/g) by increasing a temperature at a heating rate of 20° C./min in differential scanning calorimetry, and

ΔHl represents heat of fusion of crystals (J/g) of poly-L-lactic acid alone or crystals (J/g) of poly-D-lactic acid alone by increasing a temperature at a heating rate of 20° C./min in differential scanning calorimetry, and that has a weight average molecular weight of not less than 90,000, followed by solid-state polymerization of the mixture at a temperature lower than a melting point of the mixture.

6. The composition according to claim 1 , wherein the polylactic acid block copolymer satisfies Equation (4):

1<( Tm−Tms )/( Tme−Tm )<1.8  (4)

where

Tm refers to a melting point attributed to stereocomplex crystals observed within a temperature range of not less than 190° C. and less than 250° C. when a temperature was increased at a heating rate of 40° C./min in differential scanning calorimetry,

Tms refers to a start of melting point derived from stereocomplex crystals observed within the temperature range of not less than 190° C. and less than 250° C. when the temperature was increased at a heating rate of 40° C./min in differential scanning calorimetry, and

Tme refers to an end of melting point of stereocomplex crystals observed within the temperature range of not less than 190° C. and less than 250° C. when the temperature was increased at a heating rate of 40° C./min in differential scanning calorimetry.

7. The composition according to claim 1 , wherein a weight average molecular weight of the polylactic acid resin is not less than 100,000 and not more than 300,000.

8. The composition according to claim 1 , wherein the metal phosphate is at least one selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, calcium dihydrogen phosphate, calcium hydrogen phosphate, barium hydrogen phosphate, magnesium hydrogen phosphate, sodium hydrogen phosphite, potassium phosphite, calcium hydrogen phosphite, sodium hypophosphite, potassium hypophosphite, and calcium hypophosphite.

9. A molded product made from a polylactic acid resin composition comprising:

0.005 parts by weight to 1.2 parts by weight of a metal phosphate represented by Formula (1):

M x H y PO z   (1)

wherein M is an alkali metal atom or an alkaline earth metal atom, and x, y and z are integers satisfying 1≦x≦2, 1≦y≦4, and 2≦z≦8, respectively, with respect to 100 parts by weight of a polylactic acid resin comprising a poly-L-lactic acid component and a poly-D-lactic acid component, and

wherein a crystallization enthalpy of crystals in the polylactic acid resin is not less than 5 J/g when a temperature of the polylactic acid resin composition is increased to 250° C., the temperature is kept constant for 3 minutes, followed by decreasing the temperature at a cooling rate of 20° C./min in differential scanning calorimetry, and the cooling crystallization temperature is 120° C. or higher,

the polylactic acid resin composition does not contain a polyfunctional compound other than the polylactic acid resin, and

the polylactic acid resin comprises a polylactic acid block copolymer composed of

poly-L-lactic acid segments containing L-lactic acid as a main component, and

poly-D-lactic acid segments containing D-lactic acid as a main component.

10. A method of manufacturing a polylactic acid resin composition including:

0.005 parts by weight to 1.2 parts by weight of a metal phosphate represented by Formula (1):

M x H y PO z   (1)

wherein M is an alkali metal atom or an alkaline earth metal atom, and x, y, and z are integers satisfying 1≦x≦2, 1≦y≦4, and 2≦z≦8, respectively, with respect to 100 parts by weight of a polylactic acid resin comprising a poly-L-lactic acid component and a poly-D-lactic acid component, and

wherein a crystallization enthalpy of crystals in the polylactic acid resin is not less than 5 J/g when a temperature of the polylactic acid resin composition is increased to 250° C., the temperature is kept constant for 3 minutes, followed by decreasing the temperature at a cooling rate of 20° C/min in differential scanning calorimetry, and the cooling crystallization temperature is 120° C. or higher,

the polylactic acid resin includes a polylactic acid block copolymer composed of

poly-L-lactic acid segments containing L-lactic acid as a main component,

poly-D-lactic acid segments containing D-lactic acid as a main component, and

the polylactic acid resin composition does not contain a polyfunctional compound other than the polylactic acid resin,

the method comprising:

obtaining the polylactic acid block copolymer; and

melt mixing the metal phosphate.