JP5016801B2 - Polylactic acid composition - Google Patents

Description

  The present invention relates to a composition comprising polylactic acid. More specifically, the present invention relates to a composition in which another polylactic acid is blended with a random copolymer composed of L lactic acid units and D lactic acid units. Furthermore, this invention relates to the molded article excellent in the softness | flexibility, heat stability, and transparency which consist of this composition.

In recent years, bioplastics made from plants have attracted attention as biodegradable polymers that decompose in the natural environment and environmentally friendly plastics that effectively use renewable resources from the viewpoint of protecting the natural environment. A particularly active research and development is polylactic acid. Since polylactic acid has an asymmetric carbon in the main chain, even if it is a homopolymer consisting only of lactic acid units, crystalline poly L lactic acid and poly D lactic acid with an optical purity of 100%, and amorphous poly with an optical purity of 0% There is DL lactic acid and polylactic acid having an optical purity in between.
Since polylactic acid is excellent in transparency, mechanical properties, and heat resistance, research and development have been conducted for the purpose of application to various molded products such as films, sheets, tapes, fibers, nonwoven fabrics, and containers. However, polylactic acid having a relatively high optical purity is brittle and has a problem in workability such as bending. In addition, because of its high rigidity, it cannot be said that it is suitable alone for applications requiring flexibility such as films and packaging materials such as soft sheets, food packaging bags, and garbage bags. For this purpose, various techniques for softening by adding a plasticizer have been studied.
For example, a technique using lactic acid or a lactic acid oligomer as a plasticizer is known (Patent Document 1, Patent Document 2). However, such polylactic acid has a problem that its thermal stability during molding is low, it is easily hydrolyzed, and its strength decreases in a relatively short period of time.

  Since poly DL lactic acid is amorphous, it does not have a melting point itself, and its glass transition point is several degrees lower than poly L lactic acid and poly D lactic acid, and is inferior in heat resistance, but processability and flexibility Is excellent. However, compared with other polyesters, it is still difficult to say that they have sufficient heat resistance, processability and flexibility.

As a technique for softening a resin, methods such as (1) addition of a plasticizer, (2) blend of soft polymers, and (3) copolymerization are generally known.
(1) The addition of a general-purpose plasticizer has problems such as a decrease in heat resistance, a low workability during bending, a low strength of a bent portion, and a decrease in molecular weight during kneading. In addition, the flexibility and transparency may be reduced due to volatilization or exudation of the plasticizer.
(2) In the method of adding a soft polymer, the method of blending an aliphatic polyester has a low compatibility and may cause a problem in transparency. In addition, the heat-resistant temperature may be lowered or bleed out. In the method of blending polylactic acid and aliphatic polyester copolymer with polylactic acid, in order to maintain transparency, it is necessary to blend copolymer polyester having a high component ratio of polylactic acid, and the glass transition point is high. It rises and cannot keep flexibility.
(3) Regarding copolymerization, there is a system in which polylactic acid is copolymerized with polyester or polyether having a low melting point, and a copolymer or homopolymer having a similar structure is further added thereto, but a great effect is not obtained. .

An example of adding a polyester plasticizer having a glass transition temperature of 0 ° C. or higher (Patent Document 3) or a biodegradable polyester other than polylactic acid having a glass transition temperature of 10 ° C. or lower in order to give the resin flexibility. The example (patent document 4) etc. which are mixed are mention | raise | lifted. However, no example of adding a polylactic acid alone and having a glass transition temperature higher than the base polylactic acid cannot be found.
JP-A-6-306264 JP-A-4-335060 JP 2004-345208 A JP 2003-292642 A

  An object of the present invention is to provide a composition containing polylactic acid which is excellent in flexibility, heat resistance, transparency and processability. Another object of the present invention is to provide a molded article comprising the composition. A further object of the present invention is to provide a method for lowering the glass transition point of a random copolymer comprising L lactic acid units and D lactic acid units.

As a result of intensive studies to solve the above problems, the present inventors blend a specific polylactic acid (B) with polylactic acid (A) in which L lactic acid units and D lactic acid units are randomly arranged. As a result, it was found that the glass transition point of polylactic acid (A) can be lowered, and the present invention was completed. That is, in the present invention, polylactic acid (A) having L-lactic acid units and D-lactic acid units randomly arranged and having a weight average molecular weight of 50,000 or more, and L-lactic acid blocks and D-lactic acid blocks are randomly arranged to have a weight-average molecular weight of 20, It is a composition having a glass transition point (Tg) of 22.7 ° C. or more and 50 ° C. or less consisting of 000 or more polylactic acid (B).

  In the composition of the present invention, the ratio of polylactic acid (A) to polylactic acid (B) is preferably the former / the latter = 100/5 to 100/80. In the polylactic acid (B), the ratio of L lactic acid units to D lactic acid units is preferably the former / the latter = 80/20 to 20/80. The polylactic acid (B) preferably contains a stereocomplex crystal. It is preferable that the glass transition point (Tg) of a composition is 30-45 degreeC. The melting point (Tm) of the composition is preferably 150 ° C. or higher. The composition may further contain 0.01 to 30 parts of a plasticizer (C) with respect to 100 parts by weight of polylactic acid (A).

  Moreover, this invention includes the molded article which consists of a composition.

  In the present invention, 100 parts by weight of polylactic acid (A) having L-lactic acid units and D-lactic acid units randomly arranged and having a weight average molecular weight of 50,000 or more, L-lactic acid blocks and D-lactic acid blocks are randomly arranged, and weight average. This is a method for producing a composition comprising mixing 5 to 80 parts by weight of polylactic acid (B) having a molecular weight of 20,000 or more. The mixing is preferably melt mixing or solution mixing.

  Furthermore, in the present invention, the L lactic acid unit and the D lactic acid unit are randomly arranged, and the L lactic acid block and the D lactic acid block are randomly arranged in the polylactic acid (A) having a weight average molecular weight of 50,000 or more. And a method of adding 1,000 or more polylactic acid (B) to lower the glass transition point of polylactic acid (A).

According to the present invention, a composition having a low glass transition point can be obtained by adding a predetermined amount of polylactic acid (B) to polylactic acid (A) as compared to polylactic acid (A) alone. That is, in the present invention, polylactic acid (B) acts as a kind of plasticizer.
ADVANTAGE OF THE INVENTION According to this invention, the composition and molded article containing the polylactic acid excellent in the softness | flexibility, heat stability, and transparency are provided. Moreover, since the composition and molded article of the present invention consist essentially of polylactic acid, they have biodegradability. According to the production method of the present invention, the composition can be easily produced. Moreover, according to this invention, the method of reducing the glass transition point of polylactic acid (A) is provided.

<Composition>
(Polylactic acid (A))
Polylactic acid (A) is a random copolymer composed of L lactic acid units and D lactic acid units represented by the following structural formula (I). The ratio of the L lactic acid unit to the D lactic acid unit is preferably the former / the latter = 60/40 to 40/60, more preferably 55/45 to 45/55.

  The glass transition point (Tg) of polylactic acid (A) is preferably 45 to 60 ° C, more preferably 50 to 60 ° C. The polylactic acid (A) has a weight average molecular weight of 50,000 or more. Further, for ease of processing, those having a weight average molecular weight of 80,000 or more are preferable. On the other hand, the upper limit of the molecular weight is not particularly limited, but is generally 300,000 or less, and 200,000 or less for ease of use. Accordingly, the weight average molecular weight is preferably 50,000 to 300,000, more preferably 80,000 to 200,000.

Polylactic acid (A) can be obtained by, for example, (1) ring-opening polymerization method of lactide which is a cyclic dimer of lactic acid, (2) direct condensation polymerization method of lactic acid, (3) melt polymerization method and solid phase polymerization method. Can be manufactured. However, in the case of polylactic acid obtained by the lactide method, lactide contained in the polymer may adversely affect the thermal stability, hydrolyzability, strength, etc. of the composition. It is desirable that the lactide content is 1% by weight or less in advance.
The polylactic acid (A) may contain a copolymer component other than the L lactic acid unit and the D lactic acid unit represented by the structural formula (I) in a proportion of 10% by weight or less. As the copolymer component, units derived from dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone, etc. having a functional group capable of forming two or more ester bonds, various polyesters composed of these various components, various polyethers, Units derived from various polycarbonates and the like can be used alone or in combination. Examples of such dicarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid.

  Examples of the polyhydric alcohol include aliphatic polyvalents such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol. Examples thereof include aromatic polyhydric alcohols such as alcohols or the like obtained by adding ethylene oxide to bisphenol. Examples of the hydroxycarboxylic acid include glycolic acid and hydroxybutylcarboxylic acid. Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone, and the like.

(Polylactic acid (B))
Polylactic acid (B) is a block copolymer in which L lactic acid blocks and D lactic acid blocks are randomly arranged. The L lactic acid block and the D lactic acid block have an L lactic acid unit or a D lactic acid unit shown in the structural formula (I) as a basic unit. The average chain length of the L lactic acid block and the D lactic acid block is preferably 10 to 50, more preferably 15 to 45.
In the polylactic acid (B), the ratio of the L lactic acid unit and the D lactic acid unit represented by the structural formula (I) contained therein is preferably the former / the latter (weight ratio) = 80/20 to 20/80, More preferably, it is 70 / 30-30 / 70, More preferably, it is 60 / 40-40 / 60.

The polylactic acid (B) has a weight average molecular weight of 20,000 or more, preferably 20,000 to 200,000, more preferably 50,000 to 150,000. The glass transition point (Tg) of polylactic acid (B) is preferably 50 to 65 ° C, more preferably 50 to 60 ° C. The polylactic acid (B) preferably contains a stereocomplex crystal. The content of stereocomplex crystals is preferably 20 to 80%, more preferably 30 to 70%.
In the polylactic acid (B), in the differential scanning calorimeter (DSC) measurement, the ratio of the melting peak at 195 ° C. or higher is preferably 80% or higher, more preferably 90% or higher, among the melting peaks in the temperature rising process. . The ratio (%) of the melting peak at 195 ° C. or higher was calculated from the melting peak area at 195 ° C. or higher (high temperature) and the melting peak area at 140 to 180 ° C. (low temperature) by the following formula.
R _{195 or more} (%) = A _{195 or more} / (A _{195 or more} + A _{140 to 180} ) × 100
R _{195 or higher} : ratio of melting peak of 195 ° C. or _higher A _{195 or higher} : melting peak area of 195 ° C. or higher A _{140 to 180} : melting peak area of _{140 to} 180 ° C. The melting point of polylactic acid (B) is 190 to 240 ° C. The range is more preferably 192 to 230 ° C. The melting enthalpy is preferably 20 J / g or more, more preferably 30 J / g or more. Specifically, in the differential scanning calorimeter (DSC) measurement, the ratio of the melting peak at 195 ° C. or higher of the melting peak in the temperature rising process is 90% or higher, and the melting point is in the range of 190 to 250 ° C., It is preferable that the melting enthalpy is 20 J / g or more.

The polylactic acid (B) may contain a copolymer component other than the L lactic acid unit and the D lactic acid unit represented by the structural formula (I) in a proportion of 10% by weight or less. As the copolymer component, units derived from dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone, etc. having two or more functional groups capable of forming an ester bond described in the section of polylactic acid (A), and these various types Units derived from various polyesters, various polyethers, various polycarbonates and the like, which are constituent components, can be used alone or in combination.
Polylactic acid (B) can be produced by melt-mixing or solution-mixing poly-L lactic acid and poly-D lactic acid. After melt mixing or solution mixing, it is preferably solidified and further solid phase polymerized.

  The weight average molecular weight of poly L lactic acid and poly D lactic acid is preferably 500 to 1,000,000, more preferably 5,000 to 100,000. The optical purity of poly L lactic acid and poly D lactic acid is preferably 85% ee or more, more preferably 95% ee or more. The weight ratio of poly L lactic acid to poly D lactic acid is preferably the former / the latter = 80/20 to 20/80, more preferably 70/30 to 30/70, and even more preferably 60/40 to 40/60. .

Melt mixing refers to mixing poly L lactic acid and poly D lactic acid in a molten state. The temperature of the melt mixing may be any temperature condition in which poly L lactic acid and poly D lactic acid melt, but in order to suppress the decomposition reaction during melt mixing, the temperature should be lowered as much as possible so that the melt mixture does not solidify. preferable. Therefore, it is preferable that the melting point of poly-L lactic acid and poly-D lactic acid is the lower limit, and is melted within a range where the upper limit is 50 ° C., more preferably 30 ° C., particularly 10 to 20 ° C. higher than the lower limit. Specifically, it is preferable to perform melt mixing at 150 ° C. to 200 ° C.
The atmosphere at the time of melt mixing is not particularly limited, and it can be carried out under both normal pressure and reduced pressure conditions. In the case of normal pressure, it is preferably carried out under an inert gas flow such as nitrogen. Moreover, in order to remove the monomer which decomposes | disassembles at the time of melting, it is preferable to carry out under reduced pressure.

Solution mixing is a method in which poly L lactic acid and poly D lactic acid are dissolved in a solvent and mixed, and then the solvent is removed. The solvent is not particularly limited as long as it dissolves poly L lactic acid and poly D lactic acid. For example, chloroform, methylene chloride, dichloroethane, tetrachloroethane, phenol, tetrahydrofuran, N-methylpyrrolidone, N, N-dimethylformamide, butyrolactone, acetonitrile, 1,4-dioxane, trioxane, hexafluoroisopropanol or the like, or a mixture of two or more of them is preferable.
The amount of the solvent is preferably 100 to 10,000 parts by weight, more preferably 200 to 4000 parts by weight with respect to 100 parts by weight of the total of poly L lactic acid and poly D lactic acid.

Mixing may be performed by dissolving poly L lactic acid and poly D lactic acid in a solvent and mixing them, or after dissolving one in a solvent, the other may be added and mixed. The solvent can be removed by heating.
It is preferable to perform solid phase polymerization after poly-L lactic acid and poly-D lactic acid are melt-mixed or solution-mixed and then solidified by cooling or the like. Solid-phase polymerization is a temperature not lower than the glass transition temperature (Tg) and not higher than the melting point (Tm), more preferably not lower than Tg and lower than Tm by 10 ° C., particularly not lower than Tg and lower than Tm by 50 ° C. Can be done. Tg and Tm can be measured by DSC.

  The solid phase polymerization is preferably performed under reduced pressure, for example, 0.01 to 20 hPa, preferably 0.1 to 2 hPa. Since poly-L lactic acid and poly-D lactic acid are chemically bonded by an ester reaction or a dehydration condensation reaction, water is by-produced as the reaction proceeds. By polymerizing under reduced pressure, this by-product water can be removed out of the system, and the reaction equilibrium can be shifted to the polymerization side. If it exceeds 20 hPa, such dehydration becomes insufficient. On the other hand, even if it falls below 0.01 hPa, no further dehydration effect is obtained, which is useless. The solid phase polymerization can also be performed in an inert gas atmosphere such as nitrogen. The time for solid phase polymerization is at least 5 hours, preferably 5 to 50 hours. It is preferable to increase the solid-state polymerization temperature in accordance with the degree of polymerization. The solid-state polymerization apparatus is not particularly limited, but a concentration drying apparatus or the like can be used. Moreover, a conical dryer, a drum-type heater, etc. can also be used.

The polylactic acid (B) may contain a catalyst involved in polymerization as long as the thermal stability of the resin is not impaired. As such a catalyst, various tin compounds, titanium compounds, calcium compounds, organic acids, inorganic acids and the like can be raised, and at the same time, a stabilizer that inactivates them may be present together.
The poly L lactic acid and poly D lactic acid used for the production of polylactic acid (B) are (1) ring-opening polymerization method of lactide, which is a cyclic dimer of lactic acid, (2) direct condensation polymerization method of lactic acid, (3) It can be produced by a combination of a melt polymerization method and a solid phase polymerization method. However, in the case of polylactic acid obtained by the lactide method, lactide contained in the polymer may adversely affect the thermal stability, hydrolyzability, strength, etc. of the composition. In addition, it is desirable to make the content 1% by weight or less in advance.

The glass transition point (Tg) of the composition of this invention is 22.7 degreeC or more and 50 degrees C or less. Preferably it is 25-45 degreeC, More preferably, it is 30-40 degreeC. Although the glass transition point of polylactic acid (A) is around 55 ° C., according to the present invention, 5 to 30 parts by weight of polylactic acid (B) is added to 100 parts by weight of polylactic acid (A). Thereby, the glass transition point of the whole composition falls. The glass transition point of the composition varies depending on the blending amount of polylactic acid (B). Therefore, the ratio of polylactic acid (A) and polylactic acid (B) in the composition can be determined from the glass transition point of the composition.

The melting point (Tm) of the composition of the present invention is preferably 150 ° C. or higher, more preferably 150 to 220 ° C., still more preferably 190 to 240 ° C., and even more preferably 192 to 210 ° C. In the differential scanning calorimeter (DSC) measurement of the composition of the present invention, the ratio of the melting peak at 195 ° C. or higher is preferably 70% or higher, more preferably 80% or higher, among the melting peaks in the temperature rising process. .
The melting enthalpy is preferably 10 J / g or more, more preferably 20 J / g or more. Specifically, in the differential scanning calorimeter (DSC) measurement, the ratio of the melting peak at 195 ° C. or higher is 80% or higher and the melting point is in the range of 190 to 250 ° C. It is preferable that the melting enthalpy is 10 J / g or more.

<Production of composition>
The composition of the present invention can be produced by mixing polylactic acid (A) and polylactic acid (B). The mixing ratio is 5 to 80 parts by weight, preferably 10 to 70 parts by weight, and more preferably 10 to 60 parts by weight with respect to 100 parts by weight of polylactic acid (A). Mixing can be performed by melt mixing or solution mixing.

  Melt mixing is a method in which polylactic acid (A) and polylactic acid (B) are mixed in a molten state. The melting temperature may be any temperature at which polylactic acid (A) and polylactic acid (B) melt, but in order to suppress the decomposition reaction during melt mixing, the temperature should be lowered as much as possible so that the molten mixture does not solidify. Is preferred. Therefore, the higher of the melting points of polylactic acid (A) and polylactic acid (B) is set as the lower limit, and the upper limit is set to 50 ° C., more preferably 30 ° C., particularly 10 to 20 ° C. higher than the lower limit value. It is preferable to melt in the range. Specifically, it is preferable to perform melt mixing at 150 ° C. to 210 ° C.

The atmosphere at the time of melt mixing is not particularly limited, and it can be carried out under both normal pressure and reduced pressure conditions. In the case of normal pressure, it is preferably carried out under an inert gas flow such as nitrogen. Moreover, in order to remove the monomer which decomposes | disassembles at the time of melting, it is preferable to carry out under reduced pressure.
The order in which polylactic acid (A) and polylactic acid (B) are charged into an apparatus or the like during melt mixing is not limited. Therefore, the two components may be charged simultaneously into the mixing apparatus. For example, after the polylactic acid (A) is melted, the polylactic acid (B) may be charged and mixed. At this time, each component may have any shape such as powder, granule, or pellet. The mixing may be performed by heating and kneading using a mill roll, a mixer, a single or twin screw extruder, a heatable batch container, and the like.

Solution mixing is a method in which polylactic acid (A) and polylactic acid (B) are dissolved and mixed in a solvent, and then the solvent is removed. The solvent is not particularly limited as long as it dissolves polylactic acid (A) and polylactic acid (B). For example, chloroform, methylene chloride, dichloroethane, tetrachloroethane, phenol, tetrahydrofuran, N-methyl Pyrrolidone, N, N-dimethylformamide, butyrolactone, acetonitrile, 1,4-dioxane, trioxane, hexafluoroisopropanol, etc., alone or in combination of two or more are preferred.
The amount of the solvent is preferably 100 to 4000 parts by weight, more preferably 200 to 3000 parts by weight with respect to 100 parts by weight of the total of polylactic acid (A) and polylactic acid (B). Mixing may be performed by dissolving polylactic acid (A) and (B) in a solvent and mixing them, or after dissolving one in a solvent, the other may be added and mixed. The solvent can be removed by heating or reduced pressure.

(Plasticizer (C))
The composition of the present invention preferably further contains 0.01 to 30 parts, more preferably 0.1 to 25 parts of the plasticizer (C) with respect to 100 parts by weight of the polylactic acid (A). In general, increasing the amount of plasticizer increases flexibility, but volatilization, leaching, and extraction from the system may adversely affect quality and storage stability. There is.

  As plasticizers, phthalates such as diethyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, di-1-butyl adipate, di-n-octyl adipate, di-n-butyl sebacate, azelaic acid di- Aliphatic dibasic acid esters such as 2-ethylhexyl, diphenyl-2-ethylhexyl phosphate, phosphate esters such as diphenyloctyl phosphate, tributyl acetylcitrate, tri-2-ethylhexyl acetylcitrate, citric acid Hydroxy polycarboxylic esters such as tributyl, fatty acid esters such as methyl acetylricinoleate and amyl stearate, polyhydric alcohol esters such as glycerin triacetate and triethylene glycol dicaprylate, epoxidized soybean oil, epoxy stearic acid Epoxy plasticizers such as corruptible, polypropylene glycol adipic acid ester, polyester plasticizers such as polypropylene glycol sebacic acid ester. Since the composition of the present invention is composed of polylactic acid having biodegradability, the plasticizer is also preferably biodegradable. It is preferable that the glass transition point of the composition containing the plasticizer of this invention is 30-40 degreeC. Moreover, melting | fusing point (Tm) becomes like this. Preferably it is 150 degreeC or more, More preferably, it is 160-220 degreeC.

  The composition of the present invention may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include ultraviolet absorbers, heat stabilizers, lubricants, mold release agents, anti-coloring agents, flame retardants, and antioxidants.

<Molded product>
The present invention includes a molded article having excellent flexibility, thermal stability and transparency, comprising the above-described composition. Examples of the molded product include films and sheets. Films and sheets can be produced by casting a solvent solution containing the composition. Moreover, a film and a sheet | seat can be manufactured by melt-casting a composition. Films and sheets can be stretched in the machine and / or transverse direction.

<Method of reducing glass transition point>
The present invention includes a method of reducing the glass transition point of polylactic acid (A) by adding polylactic acid (B) to polylactic acid (A). The glass transition point of polylactic acid (A) is around 55 ° C. According to the present invention, 5 to 80 parts by weight of polylactic acid (B) is added to 100 parts by weight of polylactic acid (A). Thereby, the glass transition point of the whole composition falls. The glass transition point of polylactic acid (B) is around 57 ° C., and the addition of polylactic acid (B) having a high glass transition point has the effect of lowering the glass transition point of the composition. Polylactic acid (B) acts as a kind of plasticizer. Since polylactic acid (B) is composed of the same L lactic acid unit and D lactic acid unit as polylactic acid (A), the biodegradability of polylactic acid (A) is not inhibited.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by a following example. The physical properties in the examples are values measured by the following method.

(1) Weight average molecular weight It converted into the standard polystyrene value by exclusion chromatography (SEC) (it is also called a gel permeation chromatography, GPC). The measuring instrument used was a detector; differential refractometer Shimadzu RID-6A, pump; Shimadzu LC-10AT, column; Tosoh TSKgel G2000HXL, TSKgel G3000HXL and TSKguardcolumn HXL-L connected in series. Chloroform was used as an eluent, and 10 μl of a sample having a temperature of 40 ° C., a flow rate of 1.0 ml / min, and a concentration of 1 mg / ml was injected.
(2) Residual lactide amount Using triethylene glycol (concentration 20 mg / ml) as an internal standard substance, the amount was measured by gas chromatography (GC) (calibration curve method). Sample concentration is 50 mg / ml. Measuring instrument is Shimadzu GC-14B, detection method: FID, column; glass column 4MG3 1.0 m, column temperature: 175 ° C., injection part and detection part temperature; 200 ° C., carrier gas; helium (50 kg / cm ² ), Combustion gas: hydrogen 0.6 kg / cm ² , air 0.5 kg / cm ² .
(3) Thermal characteristics A Shimadzu DSC-69 differential scanning calorimeter (DSC) was used. Measurement conditions were as follows: 10 mg of a sample was heated from 0 ° C. to 250 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere.
(4) Measurement of average chain length of block
Of the carbon peaks attributed to carbonyl carbon (C═O), the peak (a) (around 170.1-170.3 MHz) is found in the homosequence (LLLLLL or DDDDDDD) by ¹³ C-NMR measurement. b) (around 170.0-169.8 MHz) belongs to the racemic chain (LLLDDD...). From the integrated values of these peaks, the average chain length was calculated by the following formula.
v = integral value of peak (a) / integral value of peak (b)
¹³ CNMR instrument: BURKER ARX-500 manufactured by Nippon Bruker
Sample: 50mg / 0.7ml
Measurement solvent: 10% HFIP-containing deuterated chloroform Internal standard: Tetramethylsilane (TMS) 1% (v / v)
Measurement temperature: 27 ° C (300K)
Measurement frequency: 125 MHz
(5) Stereocomplex content rate Stereocomplex content rate was computed by the following formula | equation.
Content (%) = (ΔHmc / ΔHmh + ΔHmc) × 100
ΔHmc: heat of fusion of stereocomplex in DSC ΔHmh: heat of fusion of homopolymer in DSC Polylactic acid (A), polylactic acid (B) and plasticizer (C) used in this example were obtained as follows.

Production Example 1 (polylactic acid (A))
100 parts by weight of water at 20 ° C. is added to 100 parts by weight of DL lactide (manufactured by Musashino Chemical Laboratory, trade name Novaracto, optical purity 0% ee), and pulverized with a homogenizer for 2 minutes while maintaining the temperature at 20 ° C. While washing with water, a creamy slurry was obtained. The slurry was subjected to centrifugal filtration to obtain a cake, and then 100 parts by weight of water was sprayed on the cake to wash the crystals, and centrifugal filtration was performed again to separate purified DL lactide crystals.
Next, 0.1 parts by weight of octylic acid is added to 100 parts by weight of the purified DL lactide obtained, sealed in a nitrogen atmosphere, reacted at 180 ° C. for 1 hour, and further reacted at 100 ° C. for 10 hours. It was. After opening, it was chipped to obtain a polymer. After dissolving 10 parts by weight of this polymer in chloroform, it was reprecipitated in 10 times the volume of methanol in chloroform, and the deposited precipitate was recovered and further dried at 50 ° C. under reduced pressure for 24 hours to obtain polylactic acid ( A) was obtained. The resulting polylactic acid (A) had a weight average molecular weight of 140,000, an optical purity of 0% ee, a glass transition point (Tg) of 55.3 ° C., and a residual lactide content of 0.3% by weight.

Production Example 2 (poly L lactic acid and poly D lactic acid)
A dehydration reaction was performed to oligomerize 100 parts by weight of an aqueous L lactic acid solution having a concentration of 90% by weight with stirring at 150 ° C. under a reduced pressure of 30 mmHg for 6 hours. To this oligomer, 0.1 part by weight of stannous chloride and 0.1 g of p-toluenesulfonic acid were added and melt polymerized at 180 ° C. for 6 hours under a reduced pressure of 10 mmHg. After cooling, the solid was pulverized to obtain a low molecular weight poly-L lactic acid having a weight average molecular weight of 15,000 and a melting point (Tm) of 154 ° C. Subsequently, this low molecular weight poly-L lactic acid was subjected to solid phase polymerization under reduced pressure at 110 ° C. for 2 hours and further at 150 ° C. for 24 hours to obtain a poly L having a weight average molecular weight of 96,000, a melting point of 173 ° C., and an optical purity of 98% ee. Lactic acid was obtained. In the same manner, poly-D-lactic acid having a weight average molecular weight of 99,000, a melting point of 177 ° C., an optical purity of 99% ee, and a residual lactide amount of 0.3% by weight was obtained from a D lactic acid raw material.

Production Example 3 (Polylactic acid (B))
10 parts by weight of poly-L lactic acid produced in Production Example 2 and 10 parts by weight of poly-D lactic acid were mixed, and 0.02 parts by weight of stannous chloride and 0.02 parts by weight of p-toluenesulfonic acid were added as catalysts. After drying, purging with nitrogen, it was heated at normal pressure. When it was uniformly melted, the heating was stopped, the temperature was returned to room temperature, and the solidified product was pulverized into a powder of 100 to 400 mm. The powder was heated at 120 ° C. under reduced pressure of 0.5 hpa for 1 hour for crystallization, then heated to 150 ° C. and subjected to solid phase polymerization for 24 hours to obtain polylactic acid (B). The stereocomplex crystal content of polylactic acid (B) was 76.9%. The polylactic acid (B) had a weight average molecular weight of 63,000, a melting point of 169, 207 ° C., and a residual lactide amount of 0.1% by weight or less (undetected). The average chain length of the L lactic acid block and the D lactic acid block was 41.3, and the glass transition point (Tg) was 58.7 ° C.
As the plasticizer (C), Riquemal P-019 (manufactured by Riken Vitamin Co., Ltd.) was used.

<Example 1>
Polylactic acid (A) and polylactic acid (B) were mixed at a mixing ratio (A) / (B) = 100/10 so that the total weight was 500 mg, and dissolved in 10 ml of methylene chloride. At this time, a small amount of hexafluoroisopropanol was used to dissolve the polylactic acid (B). This solution was transferred to a petri dish having a diameter of 90 mm and left at room temperature for 24 hours to remove the solvent. Furthermore, the cast film was manufactured by drying for 24 hours at 50 ° C. under reduced pressure to completely remove the solvent. A DSC chart of the obtained film is shown in FIG. 1 (1 in FIG. 1). Residual solvent was not observed by ¹ HNMR and IR. This film had a glass transition temperature (Tg) of 39.6 ° C. and a melting point (Tm) of 194.5 ° C.

<Example 2>
A film was produced in the same manner as in Example 1 except that the mixing ratio (A) / (B) of polylactic acid (A) and polylactic acid (B) was changed to 100/20. A DSC chart of the obtained film is shown in FIG. 1 (2 in FIG. 1). This film had a glass transition temperature (Tg) of 31.0 ° C. and a melting point (Tm) of 194.5 ° C.

<Example 3>
A film was produced in the same manner as in Example 1 except that the mixing ratio (A) / (B) of polylactic acid (A) and polylactic acid (B) was changed to 100/50. A DSC chart of the obtained film is shown in FIG. 1 (3 in FIG. 1). This film had a glass transition temperature (Tg) of 33.0 ° C. and a melting point (Tm) of 201.4 ° C.

<Comparative Example 1>
A film was produced in the same manner as in Example 1 except that polylactic acid (B) was not added and only polylactic acid (A) was added. A DSC chart of the obtained film is shown in FIG. 1 (7 in FIG. 1). The glass transition temperature (Tg) of this film was 55.3 ° C., and the melting point (Tm) did not appear.

<Comparative example 2>
A film was produced in the same manner as in Example 1 with the mixing ratio of polylactic acid (A) and poly-L-lactic acid being the former / the latter = 100/10. A DSC chart of the obtained film is shown in FIG. 1 (8 in FIG. 1). The glass transition temperature (Tg) of this film was 55.0 ° C.

<Example 4>
Film in the same manner as in Example 1 except that the mixing ratio of polylactic acid (A), polylactic acid (B), and plasticizer (C) was changed to (A) / (B) / (C) = 100/10/5 Manufactured. A DSC chart of the obtained film is shown in FIG. 1 (4 in FIG. 1). This film had a glass transition temperature (Tg) of 23.0 ° C. and a melting point (Tm) of 192.7 ° C.

<Example 5>
Film in the same manner as in Example 1 except that the mixing ratio of polylactic acid (A), polylactic acid (B), and plasticizer (C) was changed to (A) / (B) / (C) = 100/20/5 Manufactured. A DSC chart of the obtained film is shown in FIG. 1 (5 in FIG. 1). This film had a glass transition temperature (Tg) of 22.7 ° C. and a melting point (Tm) of 193.8 ° C.

<Example 6>
Film in the same manner as in Example 1 except that the mixing ratio of polylactic acid (A), polylactic acid (B) and plasticizer (C) was changed to (A) / (B) / (C) = 100/20/10 Manufactured. A DSC chart of the obtained film is shown in FIG. 1 (6 in FIG. 1). This film had a glass transition temperature (Tg) of 25.0 ° C. and a melting point (Tm) of 194.6 ° C.

  The composition of the present invention is suitable for food / confectionery packaging films, food wrap films, cosmetic wrap films, pharmaceutical wrap films, agricultural / horticultural films, stationery wrap films, electronic / electrical parts wrap films, etc. Can be used.

It is a DSC chart of the film manufactured in Examples 1-6 and Comparative Examples 1 and 2.

Explanation of symbols

1 is a DSC chart of the film produced in Example 1.
2 DSC chart of the film produced in Example 2.
3 is a DSC chart of the film produced in Example 3.
4 is a DSC chart of the film produced in Example 4.
5 is a DSC chart of the film produced in Example 5. FIG.
6 is a DSC chart of the film produced in Example 6.
7 is a DSC chart of the film produced in Comparative Example 1.
8 is a DSC chart of the film produced in Comparative Example 2.

Claims (12)

Polylactic acid (A) having L-lactic acid units and D-lactic acid units randomly arranged and having a weight average molecular weight of 50,000 or more, and polylactic acid having L-lactic acid blocks and D-lactic acid blocks randomly arranged and having a weight-average molecular weight of 20,000 or more A composition comprising (B) and having a glass transition point (Tg) of 22.7 ° C. or higher and 50 ° C. or lower.   2. The composition according to claim 1, wherein the ratio of polylactic acid (A) to polylactic acid (B) is the former / the latter = 100/5 to 100/80.   The composition according to claim 1, wherein the polylactic acid (B) has a ratio of L lactic acid units to D lactic acid units of the former / the latter = 80/20 to 20/80.   The composition according to claim 1, wherein the polylactic acid (B) contains a stereocomplex crystal.   2. The composition according to claim 1, wherein the polylactic acid (A) has a ratio of L lactic acid units to D lactic acid units of the former / the latter = 60/40 to 40/60.   The composition according to claim 1, wherein the glass transition point (Tg) is 30 to 45 ° C.   The composition according to claim 1, which has a melting point (Tm) of 150 ° C or higher.   The composition according to claim 1, further comprising 0.01 to 30 parts of a plasticizer (C) with respect to 100 parts by weight of the polylactic acid (A).   A molded article comprising the composition according to claim 1.   100 parts by weight of polylactic acid (A) having L-lactic acid units and D-lactic acid units randomly arranged and having a weight average molecular weight of 50,000 or more, and L-lactic acid blocks and D-lactic acid blocks are randomly arranged to have a weight average molecular weight of 20,000. A method for producing a composition comprising mixing 5 to 80 parts by weight of the above polylactic acid (B).   The manufacturing method according to claim 10, comprising melt mixing or solution mixing. Polylactic acid (A) having L-lactic acid units and D-lactic acid units randomly arranged and having a weight average molecular weight of 50,000 or more, and polylactic acid having L-lactic acid blocks and D-lactic acid blocks randomly arranged and having a weight average molecular weight of 20,000 or more. A method in which lactic acid (B) is added to lower the glass transition point of polylactic acid (A).

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