JP2008062586A - Polylactic acid type gas barrier film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid type gas barrier film which comprises a base material layer consisting of a polylactic acid composition layer having biodegradability and excellent heat resistance, and has barrier functionalities. <P>SOLUTION: The polylactic acid type gas barrier film is constituted by forming a gas barrier layer at least on one side of a polylactic acid type stretched film which is constituted of a polylactic acid type composition containing poly-L-lactic acid and poly-D-lactic acid and characterized in that the peak ratio (peak 1/peak 2) of the maximum endothermic peak (peak 1) of endothermic peak within a range of 150-200°C and the maximum endothermic peak (peak 2) of the endothermic peak within a range of 205-240°C in DSC measurement is 0.2 or below. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polylactic acid-based gas barrier film having a barrier property comprising a base layer composed of a polylactic acid composition layer having biodegradability and excellent heat resistance.

  In order to facilitate the disposal of plastic films, biodegradable films have attracted attention and various films have been developed. The biodegradable film is subject to hydrolysis and biodegradation in soil and water, gradually breaking down and decomposing the film, and finally changing to a harmless degradation product by the action of microorganisms. As such a film, a film formed from an aromatic polyester resin, an aliphatic polyester resin such as polylactic acid or polybutylene succinate, polyvinyl alcohol, cellulose acetate, starch or the like is known.

Biaxially stretched films made of polylactic acid, which is one of such biodegradable resins, are used in various applications including packaging films because of their excellent transparency. However, since the polylactic acid film is inferior in gas barrier properties, its use is limited as a packaging material for food. Examples of a method for imparting a barrier property to a polylactic acid film include a method of laminating polyvinyl alcohol on a polylactic acid film (for example, Patent Document 1; JP-A-8-244190), one side of a polylactic acid biaxially stretched film A method of forming a silicon oxide thin film layer on the substrate (for example, Patent Document 2; JP-A-10-138433) or a method of forming a layer made of an inorganic oxide, inorganic nitride, or the like (for example, Patent Document 3; (Kaihei 10-24518) or a method of forming a layer made of aluminum oxide, silicon oxide or the like (for example, Patent Document 4; JP 2000-94573 A) has been proposed.
However, since biodegradable polyesters such as polylactic acid have insufficient heat resistance compared to biaxially stretched polyethylene terephthalate films, their use is limited, and development of gas barrier films having heat resistance is desired.
JP-A-8-244190 JP 10-138433 A Japanese Patent Laid-Open No. 10-24518 JP 2000-94573 A

  An object of the present invention is to develop a polylactic acid-based gas barrier film having a barrier property comprising a base layer composed of a polylactic acid composition layer having biodegradability and excellent heat resistance.

  The present invention includes poly-L-lactic acid and poly-D-lactic acid, and a peak at cooling (10 ° C./min) after 10 minutes at 250 ° C. in DSC measurement is preferably 40 mJ / The present invention provides a polylactic acid-based gas barrier film characterized in that a gas barrier layer is formed on at least one surface of a polylactic acid-based stretched film of mg or more.

  The gas barrier film comprising the polylactic acid-based composition layer of the present invention can be used up to 180 ° C, whereas the conventional polylactic acid biaxially stretched film can be used up to 140 ° C, and Transparency, biodegradability and gas barrier properties

<Poly-L-lactic acid>
Poly-L-lactic acid (PLLA), which is one component of the polylactic acid composition layer according to the present invention, is a polymer containing L-lactic acid as a main component, preferably 95 mol% or more. A polymer having an L-lactic acid content of less than 95 mol% is obtained by stretching a layer composed of a polylactic acid-based composition obtained by melt-kneading with poly-D-lactic acid (PDLA) described later or the layer. There exists a possibility that the heat resistance of a stretched film may be inferior.

The molecular weight of PLLA is not particularly limited as long as the polylactic acid-based composition mixed with poly-D-lactic acid described later has formability as a layer such as a film. Usually, the weight average molecular weight (Mw) is 6,000 to 300. Poly-L lactic acid in the range of 10,000, preferably 6,000 to 2,000,000 is suitable. If the weight average molecular weight is less than 6,000, the strength of the resulting stretched film may be inferior. On the other hand, if it exceeds 3 million, the melt viscosity is large and the film processability may be inferior.
<Poly-D-lactic acid>
Poly-D-lactic acid (PDLA), which is one component of the polylactic acid composition layer 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% is a layer comprising a polylactic acid-based composition obtained by melt-kneading with the aforementioned poly-L-lactic acid or a stretched film obtained by stretching the layer. There is a possibility that heat resistance is inferior.

  The molecular weight of PDLA is not particularly limited as long as the polylactic acid composition mixed with the above-mentioned PLLA has formability as a layer such as a film. Usually, the weight average molecular weight (Mw) is 6,000 to 3,000,000, preferably Poly-D lactic acid in the range of 60 to 2 million is preferred. If the weight average molecular weight is less than 6,000, the strength of the resulting stretched film may be inferior. On the other hand, if it exceeds 3 million, the melt viscosity is large and the film processability may be inferior.

In the present invention, PLLA and PDLA contain a small amount of other copolymer components such as polycarboxylic acid or ester thereof, polyhydric alcohol, hydroxycarboxylic acid, lactone, etc. within the range not impairing the object of the present invention. It may be polymerized.
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-based stretched film>
A polylactic acid-based stretched film related to the polylactic acid-based gas barrier film of the present invention comprises a polylactic acid-based composition containing the poly-L-lactic acid and poly-D-lactic acid, and is in a range of 150 to 200 ° C. in DSC measurement. The peak ratio (peak 1 / peak 2) between the maximum endothermic peak of one endothermic peak (peak 1) and the maximum endothermic peak (peak 2) in the range of 205-240 ° C. is 0.2 or less, preferably 0 1. A polylactic acid-based stretched film characterized by being 1 or less.

  In addition to the above properties, the polylactic acid-based stretched film according to the present invention has an endothermic peak of 40 J / g or more, more preferably 50 J / g or more in the range of 205 to 240 ° C., and an endothermic peak in DSC measurement. After measurement, the amount of heat generated when the temperature is lowered is 40 J / g or more, more preferably 50 J / g or more.

In addition to the above properties, the stretched polylactic acid film according to the present invention has a total sum of peak areas (S _SC ) in the vicinity of 12 °, 21 °, and 24 ° in wide-angle X-ray measurement of 20% with respect to the entire area. As described above, it is preferably 25% or more, and the total peak area (S _PL ) of 2θ around 17 degrees and 19 degrees (S _PL ) is 5% or less, preferably 3% or less.

In such wide-angle X-ray measurement, peaks around 2 ° of 17 ° and 19 ° are peaks based on PLLA and PDLA crystals (P _PL ), and peaks around 12 °, 21 °, and 24 ° are the same for PLLA and PDLA. This is a peak ( _PSC ) based on crystal of so-called stereocomplex crystal.

The diffraction peak (2θ) by wide-angle X-ray in the present invention is the angle (degree) of the diffraction peak detected and measured by using an X-ray diffractometer (automatic X-ray diffractometer RINT-2200 or RINT-2500 manufactured by Rigaku Corporation). ). Each diffraction peak area based on a crystal is defined as a total area (total area) of 10 to 30 degrees of diffraction angle (2θ) surrounded by the base line (intensity; 0 cps) of the recording paper and the X-ray diffraction intensity curve. Cut out the areas of diffraction peaks (2θ) around 17 degrees and 19 degrees for (S _PL ) and 12 (21) and diffraction peaks (2θ) around 21 degrees and 24 degrees for (S _SC ) from the recording paper. It was calculated by measuring its weight. Moreover, the broad part resulting from an amorphous part was made into (amorphous part). When measuring (S _PL ) and (S _SC ), the diffraction curve associated with the amorphous portion was used as a baseline and the portion above it was measured.

  The heat melting characteristics of the polylactic acid-based stretched film in the present invention were measured using a Q100 manufactured by TA Instruments Inc. as a DSC (Differential Scanning Calorimeter), and approximately 5 mg of a sample was precisely weighed, and JIS K 7121 and JIS K In accordance with 7122, the DSC curve was obtained by raising the temperature from 0 ° C. to 250 ° C. at a heating rate of 10 ° C./min under the condition of nitrogen gas inflow rate: 50 ml / min. From the melting point (Tm) of the stretched film, the endothermic amount of the endothermic peak in the range of 205 to 240 ° C, the maximum endothermic peak (peak 1) of the endothermic peak in the range of 150 to 200 ° C, and the range of 205 to 240 ° C. The peak ratio (peak 1 / peak 2) of a certain endothermic peak to the maximum endothermic peak (peak 2) is obtained, and after maintaining at 250 ° C. for 10 minutes, the cooling rate is 0 ° C. at 10 ° C./min. The DSC curve at the time of temperature reduction was obtained by lowering the temperature at a temperature, and the calorific value (ΔHc) at the time of crystallization of the stretched film was determined from the obtained DSC curve.

  In addition, the peak height was calculated | required by the height from the base line obtained by connecting the base line near 65 to 75 degreeC and the base line near 240 to 250 degreeC.

  The thickness of the stretched polylactic acid film according to the present invention is usually in the range of 5 to 500 μm, preferably 10 to 100 μm.

The polylactic acid-based stretched film according to the present invention is subjected to primer coating, corona treatment, plasma treatment, flame treatment, etc., if necessary, in order to improve the adhesion with a gas barrier layer or other layer or printing layer described later. You may give it. In particular, when corona treatment is performed on the surface on which the gas barrier layer is to be formed, it is desirable to perform wet tone modification to 38 dynes or more.
<Polylactic acid-based composition>
In order to obtain a polylactic acid-based stretched film having the above-mentioned properties according to the present invention, a polylactic acid-based composition having the following heat melting properties as a polylactic acid-based composition containing poly-L-lactic acid and poly-D-lactic acid. It is preferable to prepare and stretch.

The polylactic acid composition according to the present invention preferably has a calorific value of 20 J / g or more when the temperature is lowered after melting the polylactic acid composition at 250 ° C. for 10 minutes in the DSC measurement (at the first temperature drop). It is desirable to have thermal properties that are
Furthermore, the polylactic acid-based composition according to the present invention was measured at the second temperature increase of the DSC (after 10 minutes at 250 ° C., the temperature was decreased at 10 ° C./minute, and then increased again from 0 ° C. at 10 ° C./minute. The peak ratio (peak) of the maximum endothermic peak (peak 10) of the endothermic peak in the range of 150 to 200 ° C. and the maximum peak of the endothermic peak (peak 20) in the range of 205 to 240 ° C. It is desirable to have a thermal characteristic that 10 / peak 20) is preferably 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less. This is presumably because this composition selectively forms stereocomplex crystals.
If the peak ratio (peak 10 / peak 20) is greater than 0.5, the amount of PLLA and PDLA single crystals formed after crystallization is large, and poly-L-lactic acid and poly-D-lactic acid are not sufficiently kneaded. Therefore, since the formation amount of α crystal (PLLA or PDLA single crystal) after crystallization is large, there is a possibility that the heat resistance is inferior even if it is stretched.
Moreover, it is preferable that the polylactic acid-type composition concerning this invention is 35 J / g or more in the endothermic peak of the endothermic peak of 205-240 degreeC in the time of the 2nd temperature rise of DSC.
The heat melting characteristics of the polylactic acid-based composition according to the present invention are the same as the methods for determining the heat-melting characteristics of the above-mentioned stretched polylactic acid film, and DSA (Differential Scanning Calorimeter) is used. About 100 mg of a sample was precisely weighed using Q100 manufactured by Ment Co., Ltd., and determined according to JIS K7121 and JIS K7122. In addition, the heat melting characteristic of the polylactic acid-type composition calculated | required the characteristic at the time of temperature fall and the time of the 2nd temperature rise.

  The polylactic acid composition according to the present invention is preferably 25 to 75 parts by weight of the PLLA, more preferably 35 to 65 parts by weight, particularly preferably 45 to 55 parts by weight, and particularly preferably 47 to 53 parts by weight. PDLA is preferably composed of 75 to 25 parts by weight, more preferably 65 to 35 parts by weight, particularly preferably 55 to 45 parts by weight, and most preferably 53 to 47 parts by weight (PLLA + PDLA = 100 parts by weight). That is, it is prepared.

  In the polylactic acid-based composition according to the present invention, the poly-L-lactic acid and the poly-D-lactic acid each have a weight average molecular weight in the range of 6,000 to 3,000,000, and It is desirable to prepare by kneading from poly-L-lactic acid and poly-D-lactic acid, each having a weight average molecular weight of 30,000 to 2,000,000.

The polylactic acid composition according to the present invention can be obtained, for example, by melt-kneading these PLLA and PDLA at 230 to 260 ° C. with a twin-screw extruder, twin-screw kneader, Banbury mixer, plast mill or the like. it can.
Even if a composition having an amount of PLLA outside the above range is kneaded by the above-described method, a film formed by stretching the obtained composition contains α-crystals and may have insufficient heat resistance.
The reason why the polylactic acid composition according to the present invention is excellent in heat resistance is that the composition forms a stereocomplex structure, and the stereocomplex structure is composed of equal amounts of PLLA and PDLA. .
In order to obtain the polylactic acid composition according to the present invention, the temperature at which PLLA and PDLA are melt-kneaded is preferably 230 to 260 ° C, more preferably 235 to 255 ° C. If the melt kneading temperature is lower than 230 ° C, the stereocomplex structure may be unmelted, and if it is higher than 260 ° C, polylactic acid may be decomposed.

  Moreover, when preparing the polylactic acid-type composition concerning this invention, it is desirable to melt-knead PLLA and PDLA fully. The melt-kneading time is usually 5 minutes or longer, although it depends on the melt-kneader used. The longer the melt kneading time of PLLA and PDLA is, for example, 20 minutes or more, or 30 minutes or more, the resulting polylactic acid-based composition has a temperature of 205 to 240 at the second temperature increase of DSC. The endothermic amount (ΔHm) of the endothermic peak at 45 ° C. is 45 J / g or more, or 50 J / g or more, and the endothermic amount of the endothermic peak in the range of 150 to 200 ° C. is 3.5 J / g or less, or 0 J / g, It is possible to obtain a polylactic acid-based composition in which steric complex crystallization is quicker and PLLA or PDLA single crystal (α crystal) is less likely to be formed.

  The polylactic acid-based composition according to the present invention is considered to be difficult to produce a single crystal (α crystal) of PLLA or PDLA because the stereocomplex is rapidly crystallized and the stereocomplex crystallizable region is large.

  As described above, the polylactic acid-based composition according to the present invention has a peak due to crystallization of 20 J / g or more as measured by DSC at the time of temperature decrease after 10 minutes at 250 ° C. (10 ° C./minute). Crystallization of the polylactic acid-based composition occurs rapidly.

  On the other hand, if the peak due to crystallization is less than 20 J / g, the crystallization rate is low and the kneading may not be sufficient.

  The weight average molecular weight of the polylactic acid composition according to the present invention is not particularly limited. However, the polylactic acid composition according to the present invention preferably has a weight average molecular weight in the range of 10,000 to 1,500,000, and more preferably in the range of 50,000 to 500,000. If the weight average molecular weight deviates from the above range to the polymer side, stereocomplexation may not be sufficient and heat resistance may not be obtained, and if it deviates to the low molecular side, the strength of the polylactic acid composition layer obtained is sufficient There is a possibility that it is not.

<Method for producing a polylactic acid-based stretched film>
The polylactic acid-based stretched film according to the present invention is a film or sheet obtained by extrusion molding using the polylactic acid-based composition containing poly-L-lactic acid and poly-D-lactic acid, preferably in one direction. A stretched film having excellent heat resistance and transparency can be obtained by stretching 2 times or more, more preferably 2 to 12 times, and even more preferably 3 to 6 times. 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 or the film may not be stably stretched.

  Further, the film or sheet obtained by extrusion molding is preferably at least 2 times in the vertical direction and at least 2 times in the horizontal direction, more preferably 2 to 7 times in the vertical direction and 2 to 7 times in the horizontal direction, still more preferably. Is stretched 2.5 to 5 times in the longitudinal direction and 2.5 to 5 times in the lateral direction, whereby a stretched film (biaxially stretched film) having excellent heat resistance and transparency is obtained. 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 stretched polylactic acid film according to the present invention, after being stretched, is preferably 140-220 ° C, more preferably 150-200 ° C, preferably 1 second or longer, more preferably 3-60 seconds, Furthermore, heat resistance is improved.
<Gas barrier layer>
Various known gas barrier materials can be used as the gas barrier material for forming the gas barrier layer of the polylactic acid-based gas barrier film of the present invention. These gas barrier materials include, for example, vinyl alcohol polymers such as polyvinyl alcohol and ethylene / vinyl alcohol copolymers; vinylidene chloride polymers such as polyvinylidene chloride and vinylidene chloride / vinyl chloride copolymers; (meth) acrylic acid Polymers made of unsaturated carboxylic acid polyvalent metal salts such as zinc and magnesium (meth) acrylate; polymer compound gas barrier materials such as silicon, aluminum, titanium, zirconium, tin, magnesium, indium and zinc Inorganic compound-based barrier materials such as elements; or oxides, nitrides, fluorides thereof; or composites thereof; Among these inorganic compound-based barrier materials, aluminum oxide is preferable because of its excellent transparency.

  Among these gas barrier materials, the vinyl alcohol polymer and the inorganic compound barrier material do not impair the biodegradability of the polylactic acid gas barrier film, and the vinyl alcohol polymer and aluminum oxide are excellent in transparency. Particularly preferred.

<Polylactic acid gas barrier film>
The polylactic acid-based gas barrier film of the present invention is a film in which a gas barrier layer made of the gas barrier material is formed on at least one surface of the polylactic acid-based stretched film.

The thickness of each layer of the polylactic acid-based gas barrier film of the present invention can be variously determined depending on the application, but the thickness of the polylactic acid-based stretched film is usually in the range of 5 to 500 μm, preferably 10 to 100 μm. Is a layer formed from a polymer compound-based gas barrier material, usually 1 to 50 μm, preferably 5 to 30 μm, and a layer formed from an inorganic compound-based barrier material is usually 5 to 500 nm, Preferably it exists in the range of 10-200 nm.
The polylactic acid-based gas barrier film of the present invention may be laminated with other layers depending on the application. Other layers 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, ethylene / vinyl alcohol copolymer Films, sheets, cups, trays, foams, or glass made of thermoplastic resins such as coalesced polymers, polymethyl methacrylate, ethylene / vinyl acetate copolymers, polylactic acid, and biodegradable polyesters such as aliphatic polyesters , Metal, aluminum foil, paper and the like. The film made of a thermoplastic resin may be unstretched or may be a uniaxial or biaxially stretched film. Of course, the other layers may be one layer or two or more layers.
<Method for producing polylactic acid-based gas barrier film>
The polylactic acid-based gas barrier film of the present invention is formed by laminating the previously obtained polylactic acid-based stretched film and the previously obtained polymer compound-based gas barrier layer when a polymer compound-based gas barrier material is used as the gas barrier material. (Bonding) method, method of extrusion laminating or extrusion coating a polymer compound-based gas barrier material on at least one surface of the polylactic acid-based stretched film; when an inorganic compound-based barrier material is used as the gas barrier material, An inorganic compound-based barrier material is deposited on a polylactic acid-based stretched film by chemical vapor deposition (CVD), low-pressure CVD and plasma CVD, vacuum vapor deposition (reactive vacuum vapor deposition), sputtering (reactive sputtering), and ion plating. Physical vapor deposition (PV) such as coating (reactive ion plating) ), Capable of forming by using a plasma spray method such as low pressure plasma spraying and plasma spraying.

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 Examples and Comparative Examples is as follows.
(A) Poly-L-lactic acid (PLLA-1):
D body amount: 1.9% Mw: 220,000 (g / mol), Tm: 163 ° C.
(B) Poly-D-lactic acid (manufactured by PURAC: PDLA-2):
D body amount: 100.0% Mw: 1.35 million (g / mol), Tm: 180 ° C.
Inherent viscosity (solvent: chloroform, measurement temperature: 25 ° C., concentration: 0.1 g / dl): 7.04 (dl / g)
The measuring method in the present invention is as follows.
(1) Weight average molecular weight (Mw)
Poly-L-lactic acid and poly-D-lactic acid were measured by the following methods.

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
Molecular weight calibration; monodisperse polystyrene (2) DSC measurement: Measured by the method described above.
(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: 150 mm, width: 15 mm) was sampled from the film in the MD direction and TD direction, respectively, and a tensile tester (Tensilon Universal Tester RTC-1225 manufactured by Orientec Co., Ltd.) ), A tensile test is performed at a distance between chucks: 100 mm, a crosshead speed: 300 mm / min (however, Young's modulus is measured at 5 mm / min), tensile strength (MPa), elongation (%) And Young's modulus (MPa) was calculated | required.
(6) Heat resistance A test piece with a width of 4 mm is cut out from the film using a thermal analyzer (thermal / application / strain measuring device TMA / SS120 manufactured by Seiko Instruments Inc.), and a load of 0.25 MPa is applied to the test piece with a gap of 5 mm between chucks. The temperature was raised from 100 ° C. (starting temperature) at 5 ° C./min, and the deformation (elongation or shrinkage) of the test piece at each temperature was measured.
(7) Wide-angle X-ray measurement Measuring device: X-ray diffractometer (automatic X-ray diffractometer RINT-2200 manufactured by Rigaku Corporation)
Reflection method X-ray target; Cu K-α
Output: 40 kV x 40 mA
Rotation angle: 4.0 degrees / minute step; 0.02 degrees Scanning range: 10-30 degrees (8) Moisture permeability (water vapor permeability)
It calculated | required based on JISZ0208. The film was collected to make a bag having a surface area of about 100 cm ² , and after putting an appropriate amount of calcium chloride, it was sealed. This was left in an atmosphere of 40 ° C. and 90% RH (relative humidity) for 3 days, and the moisture permeability (water vapor permeability) was determined from the weight increase.
(9) Oxygen permeability Based on JIS K7126, the oxygen permeability was measured using an oxygen permeation measuring instrument (manufactured by MOCON, OXTRAN2 / 21 ML) under the conditions of 20 ° C. and 0% RH (relative humidity).
Reference example 1
PLLA-1: PDLA-2 was weighed in a ratio of 50:50 (parts by weight), and melted and kneaded at a melting temperature of 250 ° C. and a kneading time of 6 minutes using a twin-screw kneading extruder, and a polylactic acid composition. After obtaining the product, a sheet made of a polylactic acid-based composition having a thickness of about 300 μm was obtained with a T-die sheet molding machine. The heat melting characteristics of the polylactic acid composition were measured by the method described above.
Next, the sheet was stretched in a longitudinal direction by a biaxial stretching machine manufactured by Bruckner; 3 times at 65 ° C., a stretching temperature in the transverse direction; 3 times at 70 ° C., and about 180 ° C. in a tenter. Heat setting was performed for 40 seconds to obtain a polylactic acid-based stretched film. The physical properties of the obtained polylactic acid-based stretched film were measured by the method described above. The measurement results are shown in Table 1, and the thermal melting characteristics are shown in FIGS.

Comparative Example 1
Instead of PLLA-1 and PDLA-1 used in Example 1, PLLA-1 is used alone, except that heat setting of the biaxially stretched film is performed at 150 ° C. for about 40 seconds, and performed in the same manner as in Example 1. A sheet of PLLA-1 and a biaxially stretched film were obtained. The measurement results are shown in Table 1, and the thermal melting characteristics are shown in FIGS.

表１から明らかなように、参考例１で得られたポリ乳酸系組成物からなる二軸延伸フィルムは、熱融解特性において、１５０〜２００℃の範囲の吸熱ピーク（吸熱量）は僅かで、２０５〜２４０℃の範囲の吸熱ピークは大きく、吸熱量（ΔＨｍ）も６６．１Ｊ／ｇと多く、降温した際の発熱量（ΔＨｃ）も４９．７Ｊ／ｇある。また、二軸延伸フィルムの素材となるポリ乳酸系組成物（シート）の熱融解特性は、第１回降温時の発熱量（ΔＨｃ）が２０．３Ｊ／ｇと２０Ｊ／ｇ以上であり、第２回昇温時には、１５０〜２００℃の範囲には吸熱ピークはみられず、２０５〜２４０℃の範囲の吸熱ピークの吸熱量（ΔＨｍ）は５１．０Ｊ／ｇと３５Ｊ／ｇ以上である。さらに、参考例１で得られたポリ乳酸系組成物からなる二軸延伸フィルムは、透明性、耐熱性に優れ、透湿度及び酸素透過度も低く、バリア性能を有し、広角Ｘ線測定における回折ピークは２θが１２、２１、２４度近辺にのみ有し、２θが１７、１９度近辺には回折ピークは現れなかった。また１７、１９度近辺のピーク面積（Ｓ_ＰＬ）が全体の面積に対して０％と５％未満であり、２θが１２、２１、２４度近辺のピーク面積（Ｓ_ＳＣ）が全体の面積に対して５１％と２０％以上であった。

As is clear from Table 1, the biaxially stretched film made of the polylactic acid composition obtained in Reference Example 1 has a slight endothermic peak (endothermic amount) in the range of 150 to 200 ° C. in the heat melting characteristics. The endothermic peak in the range of 205 to 240 ° C. is large, the endothermic amount (ΔHm) is as large as 66.1 J / g, and the calorific value (ΔHc) when the temperature is lowered is 49.7 J / g. The heat melting characteristics of the polylactic acid composition (sheet) that is the raw material of the biaxially stretched film are as follows. The calorific value (ΔHc) at the first temperature drop is 20.3 J / g and 20 J / g or more. When the temperature is raised twice, no endothermic peak is observed in the range of 150 to 200 ° C, and the endothermic amounts (ΔHm) of the endothermic peak in the range of 205 to 240 ° C are 51.0 J / g and 35 J / g or more. Furthermore, the biaxially stretched film made of the polylactic acid composition obtained in Reference Example 1 is excellent in transparency and heat resistance, has low moisture permeability and oxygen permeability, has barrier performance, and is used in wide-angle X-ray measurement. The diffraction peak was only in the vicinity of 2θ of 12, 21 and 24 degrees, and no diffraction peak appeared in the vicinity of 2θ of 17 and 19 degrees. Also, the peak area (S _PL ) around 17 and 19 degrees is 0% and less than 5% with respect to the entire area, and the peak area (S _SC ) around 12, 21 and 24 degrees is 2θ. On the other hand, it was 51% and 20% or more.

On the other hand, the biaxially stretched film made of PLLA-1 obtained in Comparative Example 1 has only an endothermic peak in the range of 150 to 200 ° C, no endothermic peak in the range of 205 to 240 ° C, and exotherm when the temperature is lowered. The amount (ΔHc) is 0.4 J / g, which is smaller than the biaxially stretched film made of the polylactic acid composition obtained in Reference Example 1. In addition, the thermal melting characteristics of PLLA-1 (sheet), which is a material of the biaxially stretched film, has a calorific value (ΔHc) of 0 at the first temperature drop, and a range of 205 to 240 ° C. at the second temperature rise. No endothermic peak was observed, only a peak in the range of 150 to 200 ° C., and the endothermic amount (ΔHm) was 32.1 J / g. Furthermore, the biaxially stretched film made of PLLA-1 obtained in Comparative Example 1 is excellent in transparency, but is inferior in heat resistance and barrier performance, and the diffraction peak in wide-angle X-ray measurement is 2θ of around 17 and 19 degrees. No diffraction peak appeared in the vicinity of 2, 21 and 24 degrees. Moreover, the peak area (S _PL ) around 17 and 19 degrees exceeds 57% and 5% with respect to the entire area, and the peak area (S _SC ) around 12, 21 and 24 degrees with 2θ is the entire area. And 0% and less than 20%.

Example 1
<Manufacture of polylactic acid-based gas barrier film>
On the corona-treated surface of the polylactic acid-based biaxially stretched film of Reference Example 1, an electron beam heating type vacuum deposition apparatus is used, aluminum oxide is used as a deposition source, and the vacuum chamber is maintained at a vacuum degree of 0.001 Torr or less. Then, a vapor barrier treatment was performed to form a gas barrier layer composed of an aluminum oxide film having a thickness of 100 mm to obtain a polylactic acid-based gas barrier film. The results are shown in Table 2.

Example 2
Using the polylactic acid-based biaxially stretched film obtained in Reference Example 1 and forming a gas barrier layer made of an aluminum oxide film having a thickness of 300 mm on its corona-treated surface, a polylactic acid-based gas barrier property is performed in the same manner as in the examples. A film was obtained. The results are shown in Table 2.

Example 3
Using the polylactic acid biaxially stretched film obtained in Reference Example 1, using an electron beam heating type vacuum deposition apparatus on the corona-treated surface of the film, and using a mixture of SiO: SiO ₂ = 1: 2 as a deposition source. Then, vapor deposition was performed while maintaining the vacuum inside the vacuum vessel at 0.001 Torr or less, and a gas barrier layer made of a silicon oxide film having a thickness of 100 mm was formed to obtain a polylactic acid-based gas barrier film. The results are shown in Table 2.

Example 4
Using the polylactic acid-based biaxially stretched film obtained in Reference Example 1, a 12% by weight aqueous solution of polyvinyl alcohol (degree of saponification: 98.5%, average degree of polymerization: 500) on the corona-treated surface of the film, After coating using a Mayer bar, water was evaporated using a dryer to form a gas barrier layer comprising a polyvinyl alcohol layer having a thickness of 2 μm to obtain a polylactic acid-based gas barrier film. The results are shown in Table 2.

The polylactic acid-based gas barrier film of the present invention has biodegradability, is excellent in heat resistance and gas barrier performance, and also has transparency and high mechanical strength required as a packaging material.
Taking advantage of these properties, the polylactic acid-based gas barrier film of the present invention requires heat resistance and barrier properties, and can be used for food packaging such as microwave-compatible packaging bags that could only be used with conventional polyolefins. This makes it easy to collect and process compost waste, including the use of biodegradable plastic products. As other forms of use of the invention, food packaging bags, especially those requiring heat resistance such as for microwave ovens, and compost containers for food or disposal by laminating the polylactic acid gas barrier film of the present invention and paper Etc.

FIG. 1 is a diagram showing a DSC measurement chart of the first temperature increase of the stretched film of Reference Example 1. FIG. 2 is a chart showing a DSC measurement chart of the first temperature drop of the stretched film of Reference Example 1. FIG. FIG. 3 is a diagram showing a DSC measurement chart of the second temperature increase of the stretched film of Reference Example 1. 4 is a diagram showing a DSC measurement chart of the first temperature increase of the stretched film of Comparative Example 1. FIG. FIG. 5 is a diagram showing a DSC measurement chart of the first temperature drop of the stretched film of Comparative Example 1. 6 is a chart showing a DSC measurement chart of the second temperature increase of the stretched film of Comparative Example 1. FIG. 7 is a chart showing a DSC measurement chart of the first temperature drop of a sheet (unstretched) made of the polylactic acid-based composition of Reference Example 1. FIG. FIG. 8 is a diagram showing a DSC measurement chart of the second temperature increase of a sheet (unstretched) made of the polylactic acid-based composition of Reference Example 1. FIG. 9 is a chart showing a DSC measurement chart of the first temperature drop of a sheet (unstretched) made of the polylactic acid-based composition of Comparative Example 1. FIG. 10 is a diagram showing a DSC measurement chart of the second temperature rise of a sheet (unstretched) made of the polylactic acid-based composition of Comparative Example 1. FIG. 11 is a diagram showing the results of wide-angle X-ray diffraction measurement of the stretched film of Reference Example 1. FIG. 12 is a view showing a wide-angle X-ray diffraction measurement result of the stretched film of Comparative Example 1.

Claims (13)

  It consists of a polylactic acid-based composition containing poly-L-lactic acid and poly-D-lactic acid, and has a maximum endothermic peak (peak 1) in the range of 150 to 200 ° C. and a range of 205 to 240 ° C. in the DSC measurement. A gas barrier layer is formed on at least one side of a polylactic acid-based stretched film having a peak ratio (peak 1 / peak 2) of a certain endothermic peak to a maximum endothermic peak (peak 2) of 0.2 or less. Polylactic acid gas barrier film.   2. The polylactic acid-based gas barrier film according to claim 1, wherein the polylactic acid-based stretched film has an endothermic amount of an endothermic peak in the range of 205 to 240 ° C. of 40 J / g or more.   2. The polylactic acid-based gas barrier film according to claim 1, wherein the polylactic acid-based stretched film has a calorific value of 40 J / g or more when the temperature is lowered after measuring the endothermic peak in DSC measurement. In the polylactic acid-based stretched film, 2θ in wide-angle X-ray measurement is 12 °, 21 °, and the sum of peak areas in the vicinity of 24 ° (S _SC ) is 20% or more with respect to the entire area, and 2θ is 17 °. 4. The polylactic acid-based gas barrier film according to claim 1, wherein a sum of peak areas around 19 degrees (S _PL ) is 5% or less with respect to the entire area.   The polylactic acid-based stretched film is obtained by stretching a polylactic acid-based composition having a calorific value of 20 J / g or more when the temperature is lowered after a lapse of 10 minutes at 250 ° C in DSC measurement. Polylactic acid gas barrier film.   In the DSC measurement, the polylactic acid-based stretched film has a maximum endothermic peak (peak 10) in the range of 150 to 200 ° C. and a maximum endothermic peak in the range of 205 to 240 ° C. at the second temperature increase. The polylactic acid-based gas barrier film according to any one of claims 1 to 4, which is obtained by stretching a polylactic acid-based composition having a peak ratio (peak 10 / peak 20) to (peak 20) of 0.5 or less.   The polylactic acid-based stretched film is formed by stretching a polylactic acid-based composition having an endothermic peak of 35 J / g or more in the range of 205 to 240 ° C at the time of second temperature increase in DSC measurement. 4. The polylactic acid-based gas barrier film according to any one of 4 above.   A polylactic acid-based composition is prepared from 75 to 25 parts by weight of poly-L-lactic acid and 25 to 75 parts by weight of poly-D-lactic acid (a total of 100 parts by weight of poly-L-lactic acid and poly-D-lactic acid). The polylactic acid-based gas barrier film according to any one of claims 1 to 7.   The polylactic acid-based gas barrier film according to any one of claims 1 to 4, wherein the polylactic acid-based stretched film is a layer composed of a stretched film stretched at least twice in one direction.   The polylactic acid-based gas barrier film according to any one of claims 1 to 4, wherein the polylactic acid-based stretched film is a stretched film that is stretched twice or more in the longitudinal direction and twice or more in the transverse direction.   The polylactic acid-based gas barrier film according to claim 9 or 10, wherein the polylactic acid-based stretched film is heat-treated at 140 to 220 ° C for 1 second or longer.   The polylactic acid gas barrier film according to any one of claims 1 to 8, wherein the gas barrier layer is a vinyl alcohol polymer layer. The polylactic acid gas barrier film according to any one of claims 1 to 8, wherein the gas barrier layer is an inorganic compound layer.

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