JP4570393B2 - Polylactic acid stretched film and method for producing the same - Google Patents

Description

  The present invention relates to a stretched film excellent in heat resistance and toughness comprising a composition of poly-L-lactic acid and poly-D-lactic acid, and a method for producing the same.

As biodegradable plastics, highly versatile aliphatic polyesters are attracting attention, and polylactic acid (PLA), polybutylene succinate (PBS), polyethylene succinate (PES), polycaprolactone (PCL), etc. are marketed. ing.
One of the uses of these biodegradable aliphatic polyesters is in the field of films for packaging, agriculture, food, etc., and high strength, heat resistance and biodegradability according to the use are required as basic performance.
Among the above-mentioned aliphatic polyesters, PLA has a melting point near 170 ° C. and has heat resistance, but is brittle. Therefore, many biaxially stretched PLA films have been proposed (for example, Patent Document 1, Patent Document). 2).
On the other hand, as a method for further improving the heat resistance of PLA, many methods for blending poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) to form a stereocomplex have been proposed (for example, Patent Documents). 3, Patent Document 4, Non-Patent Document 1).
However, even if a composition obtained by simply melt-kneading PLLA and PDLA is formed into a film, a stereocomplex is not easily formed, and the formed film is brittle, although its heat resistance is improved. It is difficult to use as a film.

JP-A-7-207041 Japanese Patent Laid-Open No. 8-198955 Japanese Patent Laid-Open No. 9-25400 JP 2000-17164 A Macromolecules, 20, 904 (1987)

  An object of this invention is to obtain the stretched film which consists of a polylactic acid composition of PLLA and PDLA excellent in heat resistance and toughness.

  As a result of various studies to achieve the above object, the present inventor has obtained heat resistance and toughness by stretching a polylactic acid composition obtained by melt-kneading PLLA and PDLA in at least one direction under specific conditions. As a result, it was found that a stretched film excellent in the above could be obtained, and the present invention was achieved.

That is, the present invention comprises a polylactic acid composition of 70 to 30 parts by weight of poly-L-lactic acid and 30 to 70 parts by weight of poly-D-lactic acid, and has a diffraction peak (2θ) by wide-angle X-ray diffraction around 16 °. And the total area (S _SC ) of diffraction peaks (2θ) around 12 °, around 21 ° and around 24 ° is the sum of the areas (S _PL ) and (S _SC ) of diffraction peaks around 16 ° The present invention provides a stretched polylactic acid film characterized by being less than 10% based on the amount.

  Further, the present invention provides a stretched film obtained by stretching a sheet comprising a polylactic acid composition of 70 to 30 parts by weight of poly-L-lactic acid and 30 to 70 parts by weight of poly-D-lactic acid in at least one direction. The present invention provides a method for producing a stretched polylactic acid film characterized by being heat-treated at 140 to 220 ° C. for 1 second or longer under restraint.

The stretched polylactic acid film of the present invention is superior in heat resistance and toughness as compared with a stretched polylactic acid film of the related art, and can sufficiently withstand even when heated to 200 ° C. in a microwave oven or the like.
Moreover, according to the method of the present invention, a stretched polylactic acid film having excellent heat resistance and toughness can be easily obtained.

Poly-L-lactic acid Poly-L-lactic acid (PLLA) according to the present invention is a polymer containing L-lactic acid as a main constituent, preferably 95 mol% or more. A polymer having a content of L-lactic acid of less than 95 mol% may be inferior in heat resistance of a stretched film obtained by stretching a polylactic acid composition obtained by melt-kneading with poly-D-lactic acid described later. .
The molecular weight of PLLA is not particularly limited as long as the polylactic acid composition mixed with poly-D-lactic acid described later has film-forming properties. Usually, the weight average molecular weight (Mw) is 60,000 to 1,000,000, preferably 20 It is in the range of 10,000 to 1,000,000. If the weight average molecular weight is less than 60,000, the strength of the obtained stretched film may be inferior. On the other hand, if it exceeds 1,000,000, the melt viscosity is large and the moldability may be inferior.

Poly-D-lactic acid Poly-D-lactic acid (PDLA) according to the present invention is a polymer containing D-lactic acid as a main constituent, preferably 95 mol% or more. A polymer having a D-lactic acid content of less than 95 mol% may be inferior in heat resistance of a stretched film obtained by stretching a polylactic acid composition obtained by melt-kneading with poly-L-lactic acid described later. .
The molecular weight of PDLA is not particularly limited as long as the polylactic acid composition mixed with the aforementioned PLLA has film-forming properties. Usually, the weight average molecular weight (Mw) is 60,000 to 1,000,000, preferably 200,000 to 1,000,000. It is in the range. If the weight average molecular weight is less than 60,000, the strength of the obtained stretched film may be inferior. On the other hand, if it exceeds 1,000,000, the melt viscosity is large and the moldability may be inferior.

In the PLLA and PDLA according to the present invention, a small amount of other copolymerization components such as polyvalent carboxylic acids or esters thereof, polyhydric alcohols, hydroxycarboxylic acids, lactones and the like are included within a range not impairing the object of the present invention. It may be copolymerized.
Specific examples of the polyvalent carboxylic acid include succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, suberic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, sebacic acid, diglycolic acid, ketopimelic acid, Examples thereof include aliphatic dicarboxylic acids such as malonic acid and methylmalonic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid.
Specific examples of the polyvalent carboxylic acid ester include dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, diethyl adipate, dimethyl pimelate, dimethyl azelate, and dimethyl suberate. , Aliphatic dicarboxylic acid diesters such as diethyl suberate, dimethyl sebacate, diethyl sebacate, dimethyl decanedicarboxylate, dimethyl dodecanedicarboxylate, dimethyl diglycolate, dimethyl ketopimelate, dimethyl malonate and dimethyl methylmalonate, and terephthalic acid And aromatic dicarboxylic acid diesters such as dimethyl and dimethyl isophthalate.
Specific examples of the polyhydric alcohol include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 2-methyl-propanediol, and 1,4-butanediol. , Neopentyl glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, decamethylene glycol, dodecamethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, dipropylene glycol, triethylene glycol , Tetraethylene glycol, pentaethylene glycol, polyethylene glycol having a molecular weight of 1000 or less, and the like.
Specific examples of the hydroxycarboxylic acid include glycolic acid, 2-methyllactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, Examples include 2-hydroxy-2-methylbutyric acid, 2-hydroxy-3-methylbutyric acid, hydroxypivalic acid, hydroxyisocaproic acid, and hydroxycaproic acid.
Specific examples of lactones include β-propiolactone, β-butyrolactone, γ-butyrolactone, β or γ-valerolactone, δ-valerolactone, δ-caprolactone, ε-caprolactone, and 4-methylcaprolactone. Various methylated caprolactones such as 3,5,5-trimethylcaprolactone and 3,3,5-trimethylcaprolactone; cyclic monomeric esters of hydroxycarboxylic acids such as β-methyl-δ-valerolactone, enanthlactone and laurolactone A cyclic dimer ester of the above hydroxycarboxylic acid such as glycolide, L-lactide, D-lactide and the like.
Further, PLLA and PDLA according to the present invention may each contain a small amount of D-lactic acid or L-lactic acid as long as it is within the above range.

Polylactic acid composition In the polylactic acid composition according to the present invention, the PLLA is 70 to 30 parts by weight, preferably 65 to 35 parts by weight and the PDLA is 30 to 70 parts by weight, preferably 35 to 65 parts by weight (PLLA + PDLA = 100 Part by weight). A composition having an amount of PLLA exceeding 70 parts by weight and a composition having less than 30 parts by weight may not yield a stretched film excellent in heat resistance even when stretched by a molding method described later.

Polylactic acid stretched film The polylactic acid stretched film of the present invention comprises the above-mentioned polylactic acid composition, and a diffraction peak (2θ) by wide-angle X-ray diffraction is around 16 ° [hereinafter, a peak detected in such a region (P _PL ) Sometimes called. ] And diffraction peaks (2θ) around 12 °, around 21 °, and around 24 ° [hereinafter, the peak detected in such a region may be collectively referred to as ( _PSC ). The total area of] _{(S SC)} is a stretched film of less than 10% relative to the total amount of surface area _{(S PL)} and _{(S SC)} of 16 ° around the diffraction peak _{(P PL).} The peak around 16 ° (P _PL ) in such wide-angle X-ray diffraction is a peak based on PLLA and PDLA crystals, and the peaks around 12 °, 21 ° and 24 ° are so-called co-crystals of PLLA and PDLA. This is a peak ( _PSC ) based on stereocomplex crystals.
That is, in the stretched polylactic acid film of the present invention, (S _SC ) is less than 10%, although it is a stretched film made of a polylactic acid composition in which PLLA and PDLA are mixed. Is not formed (not present: 0%) or, if formed, is small (less than 10%). A stretched film in which the amount of (S _SC ) with respect to the total amount of (S _PL ) and (S _SC ) exceeds 10% is excellent in heat resistance, but the tensile elongation at break in the stretching direction is less than 15%. Further, the breaking energy is less than 0.05 mJ, and the toughness may be inferior.
In the present invention, the diffraction peak (2θ) by wide-angle X-ray diffraction is Cu K-α as an X-ray target on the sheet or film, output using an X-ray diffractometer (automatic X-ray diffractometer RINT-2200 manufactured by Rigaku Corporation). : Diffraction peak angle (°) detected by irradiation with 1/40 kV × 40 mA, rotation angle: 4.0 ° / min, step: 0.02 °, scanning range: 10-30 ° . Each diffraction peak area is the diffraction peak (2θ) near 16 ° for (S _PL ), and the area of each diffraction peak (2θ) near 12 °, 21 ° and 24 ° for (S _SC ) chart paper. It was calculated by cutting out and measuring its weight. However, the area portion due to X-ray scattering in the air was deleted.
The stretched polylactic acid film of the present invention preferably has a heat deformation temperature of 180 ° C. or higher, more preferably in the range of 200 to 225 ° C. by thermomechanical analysis.
The thermal deformation temperature in the present invention is obtained by cutting a test piece having a width of 4 mm from a film using a thermal analyzer (thermal / application / strain measuring device TMA / SS120 manufactured by Seiko Instruments Inc.), and applying a load of 0 to the test piece with 5 mm between chucks. .25 MPa was applied, and the temperature was raised from 100 ° C. (starting temperature) at 5 ° C./min. In addition, when the test piece broke before elongating by 10%, the temperature was defined as the heat distortion temperature (° C.).
The stretched polylactic acid film of the present invention preferably has an elongation in the stretching direction (tensile elongation at break) of 15% or more, more preferably in the range of 10 to 100%, and the breaking energy in the stretching direction is preferably 0.00. 05 mJ or more, more preferably in the range of 0.1 to 2 mJ.
The breaking energy (mJ) in the present invention is determined by using a tensile tester (Orientec Co., Ltd., Tensilon Universal Tester RTC-1225) to pull a test piece having a length of 50 mm and a width of 15 mm with a distance between chucks of 20 mm. From the tensile stress-strain curve obtained by measuring at a speed of 300 mm / min, the area surrounded by the tensile stress-strain curve and the horizontal axis (strain) was cut out and the weight (W-1) was measured. Next, the area surrounded by the tensile stress (N) and the strain (elongation) (%) is cut out, the weight (W-2) is measured, and the breaking energy (W-1) and (W-2) are calculated from the ratio of (W-1) and (W-2). mJ). In addition, in order to obtain | require breaking energy (mJ), elongation (%) was converted into the distance (mm) required for destruction.

The stretched polylactic acid film of the present invention is preferably stretched twice or more in one direction, more preferably 2 to 12 times, and even more preferably 3 to 6 times. A stretched film with a draw ratio of less than 2 may not improve the heat resistance. On the other hand, the upper limit of the stretching ratio is not particularly limited as long as it can be stretched. However, if it exceeds 12 times, the film may be broken and may not be stably stretched.
The stretched polylactic acid film of the present invention is preferably 2 times or more in the longitudinal direction and 2 times or more in the transverse direction, more preferably 2 to 7 times in the longitudinal direction and 2 to 7 times in the transverse direction, further preferably in the longitudinal direction. It is stretched 2.5 to 5 times and 2.5 to 5 times in the transverse direction. A stretched film having a draw ratio of less than 2 may not improve the heat resistance. On the other hand, the upper limit of the stretching ratio is not particularly limited as long as it can be stretched. However, if it exceeds 7 times, the film may be broken and may not be stably stretched.
The thickness of the stretched polylactic acid film of the present invention can be variously determined depending on the use, but is usually in the range of 5 to 500 μm, preferably 10 to 100 μm.

  The polylactic acid stretched film of the present invention may be laminated with another substrate depending on various uses. Other substrates include, for example, polyolefins such as polyethylene, polypropylene, polybutene and polymethylpentene, polyesters such as polyethylene terephthalate and polycarbonate, nylon, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and ethylene / vinyl alcohol. Polymer, polymethyl methacrylate, ethylene / vinyl acetate copolymer, polylactic acid, film made of thermoplastic resin such as biodegradable polyester such as aliphatic polyester, sheet, cup, tray, or foam thereof, or Examples thereof include glass, metal, aluminum foil, and paper. The film made of the thermoplastic resin may be unstretched or may be a uniaxial or biaxially stretched film. Of course, the substrate may be a single layer or two or more layers.

Method for Producing Polylactic Acid Stretched Film In the method for producing a polylactic acid stretched film of the present invention, a sheet comprising the polylactic acid composition is usually at least 70 to 110 ° C., preferably 80 to 100 ° C., preferably twice or more in one direction. The stretched film obtained by stretching 3 to 12 times is usually 140 to 220 ° C., preferably 150 to 200 ° C. for 1 second or longer, preferably 3 seconds to 60 seconds, more preferably 3 to 20 seconds. In this way, a stretched polylactic acid film is obtained.
If the draw ratio is less than 2 times, a stretched film excellent in heat resistance may not be obtained. On the other hand, the upper limit of the draw ratio is not particularly limited, but if it exceeds 12 times, there is a possibility that it cannot be stably stretched. When the stretching temperature is less than 70 ° C., there is a possibility that the film cannot be stably stretched, and the obtained stretched film may be inferior in transparency and smoothness. On the other hand, when it exceeds 120 ° C., the film adheres to the heating roll, the film surface becomes dirty, and there is a possibility that the film cannot be stably stretched, and the toughness of the obtained stretched film may be inferior. If the heat treatment time is less than 1 second, heat may not be transmitted to the stretched film, and the effect of the heat treatment may not be exhibited. On the other hand, if it exceeds 60 seconds, the orientation of the stretched film is too relaxed, resulting in heat resistance, mechanical properties, etc. May decrease. Further, there is no problem even if the preheating time is long, but 60 seconds or less is preferable in the process.
In another aspect of the method for producing a stretched polylactic acid film of the present invention, the sheet comprising the polylactic acid composition is usually at a temperature of 70 to 110 ° C., preferably 80 to 100 ° C., preferably at least twice in the longitudinal direction and It is stretched 2 times or more in the transverse direction, more preferably 2 to 7 times in the longitudinal direction and 2 to 7 times in the transverse direction, further preferably 2.5 to 5 times in the longitudinal direction and 2.5 to 5 times in the transverse direction. The stretched film obtained by heat treatment is usually subjected to heat treatment at 140 to 220 ° C., preferably 150 to 200 ° C. for 1 second or longer, preferably 3 seconds to 60 seconds, more preferably 3 to 20 seconds. This is a method of making a stretched film. If the heat treatment time is less than 1 second, heat may not be transmitted to the stretched film, and the effect of the heat treatment may not be exhibited. On the other hand, if it exceeds 60 seconds, the orientation of the stretched film is too relaxed, resulting in heat resistance, mechanical properties, etc. May decrease. Further, there is no problem even if the preheating time is long, but 60 seconds or less is preferable in the process. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

The method for producing a stretched polylactic acid film of the present invention is not detected in the vicinity of 12 °, 21 ° and 24 ° by wide-angle X-ray diffraction as a sheet made of the polylactic acid composition [( _PSC ) is not detected]. It is preferable to use a sheet. When using a sheet in which a diffraction peak (2θ) by wide-angle X-ray diffraction is detected around 12 °, around 21 °, and around 24 °, that is, a sheet on which a stereo complex is formed, it depends on the amount of formation. The obtained stretched film has poor transparency and may have poor toughness.
As a method for bringing a sheet made of a polylactic acid composition into a state where a diffraction peak (2θ) by wide-angle X-ray diffraction is not detected around 12 °, around 21 ° and around 24 ° ((P _SC ) is not detected), For example, the polylactic acid composition is melted at a melting point of stereo complex of 220 ° C. or higher, preferably in the range of 230 to 250 ° C., and then cooled, preferably rapidly cooled to form a sheet, or PLLA and PDLA The polylactic acid composition mixed in the range is melt-kneaded in the range of 220 ° C. or higher, preferably 230-250 ° C., which is the melting point of the stereo complex, and then cooled, preferably rapidly cooled to form a sheet. When using a polylactic acid composition having a temperature of less than 0 ° C., a stereoconformer can be obtained by adopting the above-mentioned method when forming a sheet. Formation of plexes can be suppressed.

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.
The polylactic acid used in the examples and comparative examples is as follows.
(1) Poly-L-lactic acid (PLLA-1):
D body amount: 2.0% Mw: 122000 (g / mol), melting point (Tm): 163.1 ° C. and glass transition temperature (Tg): 57.1 ° C.
(2) Poly-L-lactic acid (PLLA-2):
D body amount: 1.9% Mw: 222000 (g / mol), Tm: 162.9 ° C and Tg: 58.1 ° C.
(3) Poly-D-lactic acid (manufactured by PURAC: PDLA-1):
D-form amount: 100.0% Mw: 309000 (g / mol), Tm: 176.9 ° C and Tg: 57.0.
(4) Poly-D-lactic acid (manufactured by PURAC: PDLA-2):
D body amount: 100.0% Mw: 404000 (g / mol), Tm: 178.4 ° C and Tg: 59.2 ° C

The measurement method in the present invention is as follows.
(1) Weight average molecular weight (Mw)
To 20 mg of the sample, 10 ml of GPC eluent was added, and the mixture was allowed to stand overnight and then gently stirred by hand. This solution was filtered through an amphiphilic 0.45 μm-PTFE filter (ADVANTEC DISMIC-25HP045AN) to obtain a GPC sample solution.
Measuring device Shodex GPC SYSTEM-21
Analysis device Data analysis program: SIC480 data station II
Detector Differential refraction detector (RI)
Column Shodex GPC K-G + K-806L + K-806L
Column temperature 40 ° C
Eluent Chloroform Flow rate 1.0 ml / min Injection volume 200 μL
(2) Thermal transition temperature Using Q100 manufactured by TA Instruments as a differential scanning calorimeter (DSC), approximately 5 mg of a sample is precisely weighed, and in accordance with JIS K 7121, nitrogen gas inflow: 50 ml / min After the sample was melted by heating from 0 ° C. to 250 ° C. at a heating rate of 10 ° C./min under the conditions of the above, it was maintained at 250 ° C. for 10 minutes and the cooling rate: 0 ° C. at 10 ° C./min After cooling and crystallizing, the heating rate was increased to 250 ° C. at a heating rate of 10 ° C./min to obtain a thermal melting curve. From the obtained thermal melting curve, the melting point (Tm) of the sample and the glass transition point (Tg) was determined.
(3) Transparency The haze (HZ) and parallel light ray transmittance (PT) of the film were measured using a haze meter 300A manufactured by Nippon Denshoku Industries Co., Ltd.
(4) Surface roughness The center surface average roughness (SRa) of the film surface was measured using a three-dimensional surface roughness measuring instrument SE-30K manufactured by Kosaka Laboratory.
(5) Tensile test A strip-shaped test piece (length: 50 mm, width: 15 mm) is taken from the film in the MD direction, and a tensile tester (Tensilon Universal Tester RTC-1225 manufactured by Orientec Co., Ltd.) is used. The distance between chucks: 20 mm, the crosshead speed: 300 mm / min (however, the Young's modulus is measured at 5 mm / min), the tensile test is performed, the tensile strength (MPa), the elongation (%) and the Young's modulus ( MPa) was determined.
The breaking energy (mJ) was determined by the method described above.
(6) Thermal deformation temperature It was measured by the method described above.
(7) Crystal diffraction peak A crystal diffraction peak was determined by the method described above.

Example 1
<Production of polylactic acid composition>
PLLA-1: PDLA-1 was weighed at a ratio of 50:50 (% by weight) at 80 g and melted at 200 ° C. and 60 rpm for 3 minutes using a Toyo Seiki Laboplast Mill C model (biaxial kneader). The mixture was kneaded to obtain a polylactic acid composition (Composition-1).
<Manufacture of press sheets>
After sandwiching the composition-1 with a polyimide film having a thickness of 50 μm (trade name: Upilex 50S manufactured by Ube Industries), the composition-1 was put into a stainless steel rectangular metal frame having a thickness of 0.5 mm and 270 mm × 270 mm, and a press temperature: 230 ° C., initial pressure: 3 minutes (pressure 0), degassing: 5 times, press time: 4 minutes (pressure 100 kgf), cooling temperature: 18 ° C. (water temperature), cooling time: 5 minutes (pressure 20 kgf) Press molding was performed to obtain a press sheet (press sheet-1).
<Manufacture of biaxially stretched film>
Press sheet 1 was preheated with hot air at 95 ° C. for 30 seconds using a pantograph batch biaxial stretching device (Toyo Seiki Seisakusho, Heavy type), and then 3.0 mm in the vertical and horizontal directions at a speed of 5 m / min. Double-stretching (simultaneous biaxial stretching) was performed, and immediately after stretching, the stretched film was cooled with a fan to obtain a biaxially stretched film having a thickness of about 50 μm. Next, the obtained biaxially stretched film (250 mm × 250 mm) was fixed to a metal frame with a clip, heat-set (heat treated) for 10 seconds in an oven at 160 ° C., and then sufficiently cooled at room temperature to be a polylactic acid biaxially stretched film Got.
The obtained polylactic acid biaxially stretched film was evaluated by the method described above. The evaluation results are shown in Table 1.

Example 2
In place of the composition-1 used in Example 1, except that a polylactic acid composition (composition-2) obtained by mixing PLLA-1: PDLA-1 with a mixing ratio of 60:40 (% by weight) was used. The same operation as in Example 1 was performed.
The results are shown in Table 1.

Example 3
Implemented except that instead of the composition-1 used in Example 1, a polylactic acid composition (composition-3) obtained by melt-kneading at 230 ° C was used, and the press sheet was produced at 240 ° C. Performed as in Example 1.
The results are shown in Table 1.

Example 4
In place of the composition-3 used in Example 3, except that a polylactic acid composition (composition-4) obtained by mixing PLLA-1: PDLA-2 at a mixing ratio of 50:50 (wt%) was used. The same operation as in Example 3 was performed.
The results are shown in Table 1.

Example 5
In place of the composition-3 used in Example 3, except that a polylactic acid composition (composition-5) obtained by mixing PLLA-2: PDLA-2 with a mixing ratio of 50:50 (% by weight) was used. The same operation as in Example 3 was performed.
The results are shown in Table 1.

Comparative Example 1
It replaced with the press sheet-1 used in Example 1, and performed similarly to Example 1 except using the press sheet (press sheet-2) manufactured with the press temperature: 220 degreeC.
The results are shown in Table 1.

Comparative Example 2
It replaced with the composition-1 used in Example 1, and it carried out like Example 1 except using PLLA-1 single-piece | unit without melt-kneading and making extending | stretching temperature 80 degreeC.
The results are shown in Table 1.

Comparative Example 3
Instead of the composition-1 used in Example 1, the same procedure as in Example 1 was used except that a polylactic acid composition obtained by mixing PLLA-1: PDLA-1 with a mixing ratio of 80:20 (wt%) was used. went.
The results are shown in Table 1.

Reference example 1
The press sheet-1 used in Example 1 was evaluated by the method described above without stretching.
The evaluation results are shown in Table 1.

Reference example 2
The polylactic acid biaxially stretched film obtained in Example 1 was heat-treated in an oven heated to 200 ° C. for 1 hour.
The evaluation results are shown in Table 1.

As is apparent from Table 1, a polylactic acid biaxially stretched film obtained by stretching a press sheet in which ( _PSC ) is not detected, that is, a stereocomplex is not formed, comprises a polylactic acid composition of PLLA and PDLA. Even in a polylactic acid biaxially stretched film, (P _PL ) is detected, that is, crystals based on PLLA and PDLA are formed, but (P _SC ) is not detected, that is, crystals based on stereo complex ( ), Or even when formed, the polylactic acid biaxially stretched film having an (S _SC ) of less than 10% has an elongation of 15% or more (19% or more in the examples), and the breaking energy. Is also excellent in heat resistance with a heat distortion temperature of 200 ° C. or more while having toughness of 0.1 mJ or more (0.17 mJ or more in the examples) (施例 1-5).
In addition, the polylactic acid biaxially stretched film (Example 5) obtained from PLLA-2 and PDLA-2 having molecular weights exceeding 200,000, respectively, was superior in transparency (low haze), small in surface roughness, and excellent in appearance. It is a stretched film.
In contrast, (P _SC) polylactic acid biaxially stretched film obtained by stretching a pressed sheet detected (Comparative Example 1), the biaxially stretched polylactic acid film (P _SC) exists and (S _SC ) Is 10%, the haze is 100%, the parallel light beam transmittance is 0%, which is inferior in optical properties, the elongation is 9%, the breaking energy is 0.04 mJ, and the film is inferior in toughness. I understand.
On the other hand, the polylactic acid biaxially stretched film obtained by stretching a press sheet obtained from a polylactic acid composition containing 100% by weight of PLLA and 80% by weight of PLLA has a heat deformation temperature of 180 ° C. and is heat resistant. It is a film inferior in property (Comparative Examples 2 and 3).
Further, as shown in the reference example, the press sheet itself has no heat resistance (Reference Example 1), and the polylactic acid biaxially stretched film obtained in Example 1 was heat-treated in an oven heated to 200 ° C. for 1 hour. Thus, the polylactic acid biaxially stretched film in which only the stereocomplex is formed is slightly improved in heat resistance, but may become a film (reference example 2) inferior in toughness with an elongation of 2% and a breaking energy of 0.01 mJ. it is obvious.

Example 6
After preheating the press sheet-1 obtained in Example 1 with hot air of 95 ° C. × 30 seconds using a pantograph batch biaxial stretching apparatus (Toyo Seiki Seisakusho, Heavy type), at a speed of 5 m / min, The film was stretched 4.0 times in the machine direction (uniaxial stretching), and immediately after stretching, the stretched film was cooled with a fan to obtain a uniaxially stretched film having a thickness of about 120 μm. Next, the obtained uniaxially stretched film (90 mm × 330 mm) was fixed to a metal frame with a clip, heat-set (heat treated) for 10 seconds in an oven at 160 ° C., and then sufficiently cooled at room temperature to obtain a polylactic acid uniaxially stretched film. It was.
The obtained polylactic acid uniaxially stretched film was evaluated by the method described above. The evaluation results are shown in Table 2.

Example 7
It replaced with the press sheet-1 used in Example 6, and performed similarly to Example 6 except using the press sheet used in Example 4. FIG.
The results are shown in Table 2.

Example 8
It replaced with the press sheet-1 used in Example 6, and performed similarly to Example 6 except using the press sheet used in Example 5.
The results are shown in Table 2.

Comparative Example 4
The same procedure as in Example 6 was performed except that the press sheet used in Comparative Example 2 was used instead of the press sheet-1 used in Example 6.
The results are shown in Table 2.

As is clear from Table 2, similarly to the above-mentioned polylactic acid biaxially stretched film, the polylactic acid uniaxially stretched film is obtained by longitudinally stretching a press sheet in which ( _PSC ) is not detected, that is, a stereocomplex is not formed. Even if the polylactic acid uniaxially stretched film is a polylactic acid uniaxially stretched film made of a polylactic acid composition of PLLA and PDLA, (P _PL ) is detected, that is, crystals based on PLLA and PDLA are formed. However, a polylactic acid uniaxially stretched film in which ( _PSC ) is not detected, i.e., a stereocomplex (crystal based on) is not formed or ( _SSC ) is less than 10% is not stretched in the machine direction. In either case, the breaking energy is 15% or more (18% or more in the example), and the breaking energy is 0.1 mJ or more (in the example, 0. While having 1mJ higher) and toughness, heat distortion temperature is superior to 200 ° C. or higher and heat resistance (Examples 6-8).

The stretched polylactic acid film of the present invention is superior in heat resistance and toughness as compared to a conventional stretched polylactic acid film. For example, a single layer or a laminated film formed by laminating a stretched polylactic acid film and paper is used as a tray or the like. Even if the container is heated to 200 ° C. with a microwave oven or the like, it can be sufficiently tolerated.
Moreover, according to the method of the present invention, a stretched polylactic acid film having excellent heat resistance and toughness can be easily obtained.

Claims (11)

It consists of a polylactic acid composition of 70 to 30 parts by weight of poly-L-lactic acid and 30 to 70 parts by weight of poly-D-lactic acid, and has a diffraction peak (2θ) by wide-angle X-ray diffraction around 16 ° and 12 ° The total area (S _SC ) of diffraction peaks (2θ) around 21 °, around 21 ° and around 24 ° is 10% with respect to the total amount of the diffraction peaks around 16 ° (S _PL ) and (S _SC ). A polylactic acid stretched film, characterized by being less than.   The stretched polylactic acid film according to claim 1, which has a heat deformation temperature of 200 ° C. or higher by thermomechanical analysis.   The stretched polylactic acid film according to claim 1 or 2, wherein an elongation in the stretching direction is 15% or more.   The stretched polylactic acid film according to claim 1 or 2, wherein the breaking energy in the stretching direction is 0.05 mJ or more.   Surface stretch (SRa) is 1.0 micrometer or less, The polylactic acid stretched film of any one of Claims 1-4.   The polylactic acid biaxially stretched film according to any one of claims 1 to 5, which is stretched twice or more in one direction.   The stretched polylactic acid film according to any one of claims 1 to 5, which is stretched twice or more in the longitudinal direction and twice or more in the transverse direction.   While restraining a stretched film obtained by stretching a sheet made of a polylactic acid composition of 70 to 30 parts by weight of poly-L-lactic acid and 30 to 70 parts by weight of poly-D-lactic acid in one direction at least twice, A method for producing a stretched polylactic acid film, comprising heat treatment at 140 to 220 ° C. for 1 second or longer.   A sheet comprising a polylactic acid composition of 70 to 30 parts by weight of poly-L-lactic acid and 30 to 70 parts by weight of poly-D-lactic acid is obtained by stretching at least twice in the longitudinal direction and at least twice in the transverse direction. A method for producing a stretched polylactic acid film, wherein the biaxially stretched film is heat-treated at 140 to 220 ° C. for 1 second or longer under restraint.   The method for producing a stretched polylactic acid film according to claim 8 or 9, wherein the sheet made of the polylactic acid composition is a sheet in which a diffraction peak by wide-angle X-ray diffraction is not detected around 12 °, around 21 °, and around 24 °.   The method for producing a stretched polylactic acid film according to any one of claims 8 to 10, wherein the sheet made of the polylactic acid composition is a sheet formed by being heated and melted at 230 ° C or higher and then cooled.