JP4693365B2 - Polylactic acid stretched film and method for producing the same - Google Patents

Description

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

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 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, it has been found that even if a composition obtained by simply melt-kneading PLLA and PDLA is stretched, a stretched film that easily forms a stereocomplex is difficult to obtain, and the stretched film obtained is also inferior in optical properties.

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 optical characteristics.

  As a result of various studies to achieve the above object, the present inventor has drawn a polylactic acid composition obtained by melt-kneading PLLA and PDLA in at least one direction under specific conditions, It was found that a stretched film having excellent heat resistance and optical characteristics can be obtained by heat treatment with the above, and the present invention has been 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 12 °. The present invention provides a stretched polylactic acid film characterized by being near 21 ° and around 24 °.

  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 180 to 220 ° C. for 1 minute or longer.

The stretched polylactic acid film of the present invention has excellent heat resistance and excellent optical properties even when a stereo complex is formed.
Moreover, according to the method of the present invention, a stretched polylactic acid film having a stereocomplex excellent in heat resistance and optical properties 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. When the weight average molecular weight is less than 60,000, the obtained stretched film may be inferior in strength. On the other hand, when the weight average molecular weight exceeds 1,000,000, the melt viscosity is large and the molding processability 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 diffraction peaks (2θ) by wide-angle X-ray diffraction are around 12 °, around 21 °, and around 24 ° [hereinafter, this region is detected. In some cases, these peaks are collectively referred to as ( _PSC ). ], Preferably a diffraction peak (2θ) near 16 ° by wide-angle X-ray diffraction [hereinafter, a peak detected in such a region may be referred to as (P _PL ). ] Is a stretched polylactic acid film that is not detected.
In such wide-angle X-ray diffraction, the peak around 16 ° is a peak (P _PL ) 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 polylactic acid stretched film of the present invention, that (P _SC ) is detected means that a stereocomplex is formed, and that (P _PL ) is not detected means that PLLA or PDLA It means that no crystals are formed.
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 ° .
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, the temperature was raised from 100 ° C. (starting temperature) at 5 ° C./min, and the temperature at which the test piece was extended by 10% was defined as the thermal deformation temperature (° C.). 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 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 base materials 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 a 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 preferably stretching 3 to 12 times is usually 140 to 220 ° C., preferably 150 to 200 ° C., preferably 1 second or more, preferably 3 seconds to 1 minute, under restraint. Is a method of heat-treating for 3 to 20 seconds and then heat-treating at 180 to 220 ° C. for 1 minute or more, preferably at 200 to 220 ° C. for 10 to 120 minutes to obtain a stretched polylactic acid film.
If the heat treatment conditions are less than 180 ° C. or less than 1 minute, conversion to a stereo complex structure may not proceed, and if the temperature is higher than 220 ° C., the stereo complex structure will melt and cool down when the stereo complex structure is cooled. May disappear. In addition, when the heat treatment is performed for more than 120 minutes, polylactic acid may be oxidized and yellowing or molecular weight may be reduced.
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 have poor 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. Although there is no problem even if the preheating time is long, it is preferably 1 minute or less in view of 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 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 heating is usually heated at 140 to 220 ° C., preferably 150 to 200 ° C. for 1 second or longer, preferably 3 seconds to 1 minute, more preferably 3 to 20 seconds. Under the constraint, it is a method of heat-treating at 180 to 220 ° C. for 1 minute or longer, preferably 200 to 220 ° C. for 10 to 120 minutes to obtain a stretched polylactic acid film. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

In the method for producing a stretched polylactic acid film of the present invention, it is preferable to use a sheet in which (P _PL ) and (P _SC ) by wide-angle X-ray diffraction are not detected as the sheet made of the polylactic acid composition. In particular, when a sheet in which a diffraction peak (2θ) by wide-angle X-ray diffraction is detected (P _SC ), that is, a sheet on which a stereocomplex is formed is used, depending on the amount of the formed stretched film, There is a possibility that transparency is inferior.
As a method for making a sheet made of a polylactic acid composition in a state where ( _PSC ) by wide-angle X-ray diffraction is not detected, for example, the polylactic acid composition is 220 ° C. or higher, preferably 230 to 250, which is the melting point of the stereocomplex. After melting in the range of ° C., cooling, preferably quenching into a sheet, or a polylactic acid composition in which PLLA and PDLA are mixed in the above range is 220 ° C. or higher, preferably 230- After melt-kneading in the range of 250 ° C., cooling, preferably quenching to form a sheet, and when using a polylactic acid composition having a melt-kneading temperature of less than 230 ° C., the above range is set when the sheet is molded. By adopting this method, formation of a stereo complex 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), Tm: 163.1 ° C. and Tg: 57.1.
(2) Poly-L-lactic acid (PLLA-2):
D form amount: 1.9% Mw: 222000 (g / mol), Tm: 162.9 ° C. and Tg: 58.1.
(3) Poly-D-lactic acid (manufactured by PURAC: PDLA-1):
D body amount: 100.0% Mw: 309000 (g / mol), Tm: 176.9 ° C and Tg: 57.0 ° C.
(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) 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 (Orientec Tensilon Universal Tester RTC-1225) 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.
(5) Thermal deformation temperature It was measured by the method described above.
(6) 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 vertically and horizontally 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 obtain a biaxially stretched film. It was. Next, the obtained biaxially stretched film was again heat-treated at 200 ° C. for 60 minutes in a state of being fixed to the metal frame with a clip, to obtain a polylactic acid biaxially stretched film.
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 (% by weight) 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 at 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.

Reference example 3
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 1
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. However, while the obtained biaxially stretched film was heat treated at 200 ° C. for 60 minutes, the biaxially stretched film was softened and melted, and a polylactic acid biaxially stretched film could not be obtained.
The results are shown in Table 1.

Comparative Example 2
It replaces with the composition-1 used in Example 1, and uses the polylactic acid composition which obtained PLLA-1: PDLA-1 by the mixing ratio of 80:20 (weight%) similarly to Example 1 went. However, while the obtained biaxially stretched film was heat treated at 200 ° C. for 60 minutes, the biaxially stretched film was softened and melted, and a polylactic acid biaxially stretched film could not be obtained.
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 biaxially stretched film before heat treatment at 200 ° C. obtained in Example 1 for 60 minutes was evaluated by the method described above.
The evaluation results are shown in Table 1.

As is apparent from Table 1, a stereocomplex was formed, that is, ( _PSC ) was detected by wide-angle X-ray diffraction, and ( _PPL ) was not detected, that is, no PLLA or PDLA crystal was formed. A polylactic acid biaxially stretched film is a film having a heat distortion temperature of 200 ° C. or more and excellent heat resistance (Examples 1 to 5 ).
Moreover, the biaxially stretched polylactic acid film obtained by using a sheet in which ( _PSC ) is detected as a sheet (press sheet) before forming the biaxially stretched polylactic acid film has a haze of 100% and parallel light transmittance. and There 0% (reference example 3), _{(P SC)} biaxially oriented polylactic acid film is obtained by using a sheet is not detected (examples 1-3: haze is 61-93% and the parallel light transmittance of 7 57%), it is clear that the resulting biaxially stretched polylactic acid film has reduced optical properties.
Further, as shown in Reference Example 1, neither (P _SC ) nor (P _PL ) was detected in the press sheet that was not biaxially stretched, and as shown in Reference Example 2, before being heat-treated at 200 ° C. for 60 minutes. (P _PL ) is detected in the biaxially stretched film, but (P _SC ) is not detected. In order to obtain a biaxially stretched film in which a stereocomplex is formed, the biaxially stretched film is subjected to certain conditions. It is clear that a heat treatment is necessary.

Example 7
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 treatment) for 10 seconds in an oven at 160 ° C., and then again fixed to the metal frame with a clip, After heat treatment at 200 ° C. for 60 minutes, it was sufficiently cooled at room temperature to obtain a polylactic acid uniaxially stretched film.
The obtained polylactic acid uniaxially stretched film was evaluated by the method described above. The evaluation results are shown in Table 2.

Example 8
The same procedure as in Example 7 was performed except that the press sheet used in Example 4 was used instead of the press sheet-1 used in Example 7.
The results are shown in Table 2.

Example 9
It carried out similarly to Example 7 except having used the press sheet used in Example 5 instead of the press sheet-1 used in Example 7.
The results are shown in Table 2.

Comparative Example 3
The same procedure as in Example 7 was performed except that the press sheet used in Comparative Example 1 was used instead of the press sheet-1 used in Example 7. However, while the obtained uniaxially stretched film was heat-treated at 200 ° C. for 60 minutes, the uniaxially stretched film was softened and melted, and a polylactic acid uniaxially stretched film could not be obtained.
The results are shown in Table 2.

As is clear from Table 2, the polylactic acid uniaxially stretched film was also formed with a stereo complex, that is, (P _SC ) by wide-angle X-ray diffraction was detected in the same manner as the polylactic acid biaxially stretched film. _PL ) is not detected, that is, a polylactic acid uniaxially stretched film in which PLLA or PDLA crystals are not formed is a film having a heat distortion temperature of 200 ° C. or more and excellent in heat resistance (Examples 7 to 9).

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 (1)

  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, which is heated and melted to 230 ° C. or higher, and then cooled to wide-angle X Stretching obtained by stretching a sheet whose diffraction peak due to line diffraction is not detected at around 12 °, around 21 ° and around 24 °, by stretching it twice or more in one direction, or stretching twice or more in the longitudinal direction and twice or more in the transverse direction. A method for producing a stretched polylactic acid film, comprising heat-treating a film at 140 to 220 ° C for 1 to 60 seconds in a state where the film is constrained, and then heat-treating at 180 to 220 ° C for 1 minute or more.