JP4530809B2 - Method for producing biaxially stretched polyester multilayer film - Google Patents

Description

The present invention relates to a biaxially stretched polyester multilayer film having biodegradability suitable for obtaining a packaging film having excellent oxygen barrier properties, transparency, interlayer adhesion strength, and also having low temperature heat sealability, and its It relates to a manufacturing method.

In order to facilitate the disposal of plastic films, biodegradable films have attracted attention, and various films have been developed. The biodegradable film undergoes hydrolysis and biodegradation in soil and water, and gradually collapses and breaks down the film. Finally, the biodegradable film is transformed into 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.

As one of the methods for improving the oxygen barrier property of a film made of an aliphatic polyester resin, a gas barrier composite film in which a polyglycolic acid film layer biaxially stretched on a thermoplastic resin film such as polylactic acid has been proposed. (For example, Patent Document 1). In Patent Document 1, a composite sheet obtained by co-extrusion of a thermoplastic resin, polyglycolic acid and an adhesive resin is stretched in the MD direction by a stretching roll or the like, and stretched in the TD direction by a tenter or the like as necessary. It is disclosed that composite films can be manufactured. However, when polylactic acid is used as the thermoplastic resin, it has been found that it is difficult to obtain a composite film by such a method because the stretching temperature of polylactic acid is different from the stretching temperature of polyglycolic acid.

Japanese Patent Laid-Open No. 10-80990 (claims, page 8)

An object of the present invention is to develop a method of biaxially stretching a multilayer sheet obtained by coextrusion using polylactic acid and polyglycolic acid.

In the present invention, a polyglycolic acid film obtained by coextrusion molding of polyglycolic acid and polylactic acid and a multilayer sheet obtained by laminating a polylactic acid film are longitudinally stretched at a temperature of 55 to 70 ° C. using a stretching roll. When stretching at least 1.5 times, the stretching point of the multilayer sheet is heated with infrared rays, and then stretched at least 1.5 times in the transverse direction at a temperature of 60 to 100 ° C. using a tenter. A method for producing an axially stretched polyester multilayer film is provided.

The present invention also provides a biaxially stretched polyester multilayer film in which an aliphatic polyester film having a melting point of 55 to 120 ° C. is laminated on the surface of a biaxially stretched polylactic acid film.

Furthermore, the present invention, when a multilayer sheet obtained by co-extrusion molding of polyglycolic acid and polylactic acid is stretched at least 1.5 times in the machine direction at a temperature of 55 to 70 ° C. using a stretching roll, A method for producing a biaxially stretched polyester multilayer film, characterized in that the stretching point of the multilayer sheet is heated and then stretched at least 1.5 times in the transverse direction at a temperature of 60 to 100 ° C. using a tenter. It is.

The biaxially stretched polyester multilayer film obtained by the present invention is excellent in oxygen barrier properties, as well as transparency and interlayer adhesion strength.
In addition, since the present invention can uniformly stretch a multilayer sheet obtained by coextrusion molding, a biaxially stretched polylactic acid film and a biaxially stretched polyglycolic acid film obtained in advance are combined with an adhesive or the like. A biaxially stretched polyester multilayer film having a simplified process and excellent appearance and interlayer adhesion strength can be obtained as compared with the method of using and laminating.

The requirements constituting the present invention will be described.
Polyglycolic acid The polyglycolic acid according to the present invention is a polymer (aliphatic polyester) obtained by polymerizing glycolic acid or a derivative thereof, and has the following formula (1)
_{(-O-CH 2 -CO-) ··········} (1)
The polymer having a repeating unit represented by the formula (1) is generally a repeating unit represented by the formula (1) 6
A polymer containing 0% by weight or more, more preferably 70% by weight or more, and still more preferably 80% by weight or more.
The molecular weight (melt viscosity) of the polyglycolic acid according to the present invention is not particularly limited as long as it has a film-forming ability, but is usually a temperature of (Tm + 20 ° C.) (that is, a temperature corresponding to a normal melt processing temperature) and shear. The melt viscosity η * measured at a speed of 100 / sec is 500-1
It is in the range of 00,000 Pa · s, more preferably 700 to 50,000 Pa · s, and still more preferably 800 to 20,000 Pa · s. A polymer having a melt viscosity η * of less than 500 Pa · s may be drawn down when melt-molded into a film, or a film melt-extruded from a T-die may be deformed during cooling and difficult to melt. Or, the toughness of the obtained film may be insufficient. A polymer having a melt viscosity η * exceeding 100,000 Pa · s requires a high temperature for melt processing, and polyglycolic acid may cause thermal deterioration during processing.
The polyglycolic acid according to the present invention is a crystalline polymer, and usually has a melting point of 150 ° C. or higher.
More preferably, it exists in the range of 180-225 degreeC, More preferably, it is the range of 210-225 degreeC. The heat of fusion (ΔHm) is usually in the range of 20 J / g or more, more preferably 30 to 75 J / g or more, and still more preferably 40 to 75 J / g. A polymer having a low melting point or ΔHm may have insufficient gas barrier properties, heat resistance, mechanical strength, and the like.

The polyglycolic acid according to the present invention includes, for example, ethylene oxalate (that is, 1,4-dioxane-2,3-dione), lactide, lactones (for example, β-) as a copolymerization component.
Cyclic compounds such as propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone, β-methyl-δ-valerolactone, ε-caprolactone, trimethylene carbonate and 1,3-dioxane; lactic acid, Hydroxycarboxylic acids such as 3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 6-hydroxycaproic acid or alkyl esters thereof; ethylene glycol, trimethylene glycol, 1,4-butanediol, 1,4 -It may contain 1 type, or 2 or more types, such as aliphatic or alicyclic diols, such as cyclohexanediol; Aliphatic dicarboxylic acid, such as a succinic acid, adipic acid, and sebacic acid, or its alkylester.
By including such a copolymer component as polyglycolic acid, the melting point of the polyglycolic acid homopolymer can be lowered. Since the molding temperature can be lowered by lowering the melting point of polyglycolic acid, thermal decomposition during molding can be reduced. Moreover, the crystallization speed of polyglycolic acid can be controlled by copolymerization to improve extrusion processability and stretch processability.

The polyglycolic acid according to the present invention can be produced by various known methods. The specific polymerization method is:
For example, it is described in JP-A-10-80990 and JP-A-11-116666.

Polylactic acid according to the present invention includes poly (L-lactic acid) in which the structural unit of lactic acid is L-lactic acid, poly (D-lactic acid) in which the structural unit is D-lactic acid, and further L-lactic acid and D-lactic acid. Lactic acid mixture (racemic)
The main component is a lactic acid polymer such as poly (DL-lactic acid) and lactic acid, and a small amount of copolymerizable comonomer other than lactic acid, for example, less than 50% by weight of glycolic acid, preferably 30% by weight or less, more preferably It is a polymer mainly composed of lactic acid, such as a copolymer copolymerized at a ratio of 10% by weight or less, or a mixture thereof. Examples of the comonomer copolymerizable with lactic acid include 3-hydroxybutyrate, caprolactone, glycolic acid and the like.
As a method for polymerizing such polylactic acid, any known method such as a condensation polymerization method or a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, polylactic acid having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid or a mixture thereof.
Among these polylactic acids, a biaxially oriented film having a D-lactic acid content of less than 5% by weight, preferably less than 3% by weight, and a melting point of 150 to 170 ° C., preferably 160 to 170 ° C. is obtained. It is preferable because the transparency and rigidity of the film are excellent.
The molecular weight of polylactic acid is not particularly limited as long as it has film-forming properties, but usually the weight average molecular weight (Mw) is in the range of 60,000 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.
Polylactic acid melt flow rate (MFR: ASTM D-1238, 19) according to the present invention
The temperature of 0 ° C. and the load of 2160 g) is not particularly limited as long as it has a film-forming ability.
1 to 100 g / 10 min, preferably 0.2 to 50 g / 10 min, more preferably 0.5 to
It is in the range of 20 g / 10 minutes.

Aliphatic polyester The aliphatic polyester according to the present invention has a melting point of 55 to 120 ° C., preferably 70 to 115.
° C, more preferably an aliphatic polyester in the range of 80 to 115 ° C, such as aliphatic or alicyclic dihydroxy compounds and aliphatic or alicyclic dicarboxylic acids or derivatives thereof, and optionally aliphatic hydroxycarboxylic acids. Examples thereof include aliphatic polyesters obtained by condensation polymerization of acids or derivatives thereof or lactones, and polylactone aliphatic polyesters obtained by condensation polymerization of lactones. These aliphatic polyesters can be used alone or
You may use as a composition which consists of 2 or more types of aliphatic polyesters from which a composition differs. In particular, since the polylactone-based aliphatic polyester described below usually has a melting point of 55 to 75 ° C., which is lower than that of other aliphatic polyesters, it is used by mixing with an aliphatic polyester having a melting point of 75 to 120 ° C. It is preferable.
Melt flow rate of aliphatic polyester according to the present invention (MFR: ASTM D-1)
238, 190 ° C., load 2160 g) is not particularly limited as long as it has film-forming ability, but is usually 0.1 to 100 g / 10 minutes, preferably 0.2 to 50 g / 10 minutes, more preferably 0.5 to It is in the range of 20 g / 10 minutes.

Typical examples of the aliphatic or alicyclic dihydroxy compound used as a component of the aliphatic polyester according to the present invention include ethylene glycol, 1,3-propanediol,
1,4-butanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), cyclopentanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedi Examples include methanol and 1,4-cyclohexanedimethanol.
Representative examples of aliphatic or alicyclic dicarboxylic acids or derivatives thereof include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, fumaric acid, 2,2- Dicarboxylic acids such as dimethyl glutaric acid and suberic acid, dimethyl esters, diethyl esters, di-n-propyl esters, di-isopropyl esters, di-n-butyl esters, di-isobutyl esters, di-t-butyls of such dicarboxylic acids Examples thereof include ester-forming derivatives such as esters, di-n-pentyl esters, di-isopentyl esters or di-n-hexyl esters.
Representative examples of aliphatic hydroxycarboxylic acids or derivatives thereof include glycolic acid glycolic acid, L-lactic acid, D-lactic acid, D, L-lactic acid, 2-methyllactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid and Examples thereof include aliphatic hydroxycarboxylic acids such as hydroxypivalic acid, and aliphatic hydroxycarboxylic acid ester-forming derivatives such as methyl esters, ethyl esters, propyl esters, butyl esters, and cyclohexyl esters of such aliphatic hydroxycarboxylic acids.
Examples of lactones include ε-caprolactone, δ-valerolactone, γ-butyrolactone, and β-methyl-δ-valerolactone.
Specific examples of the aliphatic polyester include poly 1,4-butanediol / succinic acid ester, poly 1,4-butanediol / succinic acid / adipic acid ester, poly 1,4-butanediol / succinic acid / lactic acid ester Poly 1,4-butanediol, succinic acid, adipic acid, lactic acid ester, poly 1,4-butanediol, succinic acid, ε-caprolactone ester, and the like.
Among these aliphatic polyesters, poly 1,4-butanediol / succinic acid / adipic acid ester, poly 1,4-butanediol / succinic acid / lactic acid ester, poly 1,4-
Ternary copolyesters such as butanediol, succinic acid, adipic acid, lactic acid ester and poly 1,4-butanediol, succinic acid, ε-caprolactone ester have a melting point of 85-85.
It is preferable because it is in the range of 115 ° C. and is excellent in low temperature heat sealability.

Polylactone-based aliphatic polyester Specific examples of the polylactone-based aliphatic polyester according to the present invention include polyε-caprolactone.

The polyglycolic acid, polylactic acid and aliphatic polyester according to the present invention include a heat resistance stabilizer, a weather resistance stabilizer, an ultraviolet absorber, a lubricant, a slip agent, a nucleating agent, an antiblocking agent, an antistatic agent and an antifogging agent. Various additives usually used for thermoplastic resins such as pigments, dyes, inorganic or organic fillers, etc. may be added within a range not to impair the purpose of the present invention.

Biaxially stretched polyester multilayer film The biaxially stretched polyester multilayer film obtained by the present invention is formed by directly laminating a biaxially stretched polylactic acid film on at least one side, preferably both sides, of the above-described biglycolic acid film made of polyglycolic acid. It is a biaxially stretched polyester multilayer film.
Further, the biaxially stretched polyester multilayer film of the present invention comprises a biaxially stretched polylactic acid film directly laminated on at least one surface, preferably both surfaces of the biaxially stretched film made of the polyglycolic acid, and further the biaxially stretched polylactic acid. It is a biaxially stretched polyester multilayer film in which an aliphatic polyester film having a melting point of 55 to 120 ° C. is laminated on a film.
The thickness of the biaxially stretched polyester multilayer film of the present invention is appropriately determined according to the use and is not particularly limited, but is usually 2 to 20 μm for the biaxially stretched polyglycolic acid film. Preferably 2 to 15 μm, biaxially stretched polylactic acid film is in the range of 5 to 50 μm, preferably 5 to 20 μm, and 1 to 20 μm, preferably 1 to 10 μm, when the aliphatic polyester film is laminated. Is in range.

The biaxially stretched polyester multilayer film obtained by the present invention may be subjected to surface treatment such as corona treatment or flame treatment on one or both sides as necessary. In addition, the biaxially stretched polyester multilayer film obtained by the present invention is a random co-polymer of high-pressure low-density polyethylene, linear low-density polyethylene, crystalline or low-crystalline ethylene and an α-olefin having 3 to 10 carbon atoms, depending on the application. A polymer or a random copolymer of propylene and ethylene or an α-olefin having 4 or more carbon atoms, a low melting point polymer such as polybutene, ethylene / vinyl acetate copolymer, etc. may be used alone or a composition thereof may be laminated. . Further, in order to further improve the gas barrier properties, an ethylene / vinyl alcohol copolymer, polyamide, polyester, vinylidene chloride polymer, etc. may be laminated by extrusion coating, film lamination, etc., or a metal or its oxide Further, silica or the like may be deposited. Of course, in order to improve the adhesion to other substances, the surface of the stretched film may be anchored with an adhesive such as imine or urethane, or maleic anhydride-modified polyolefin may be laminated.

Method for producing biaxially stretched polyester multilayer film The biaxially stretched polyester multilayer film of the present invention is obtained by stretching a multilayer sheet obtained by coextrusion molding of the polyglycolic acid, polylactic acid and, if necessary, aliphatic polyester. When stretching at least 1.5 times, preferably 2 to 4 times in the machine direction at a temperature of 55 to 70 ° C., preferably 60 to 70 ° C. using a roll, the stretching point of the multilayer sheet is heated with infrared rays, and then The film can be produced by stretching at least 1.5 times, preferably 2 to 10 times in the transverse direction at a temperature of 60 to 100 ° C., preferably 70 to 90 ° C., using a tenter.
When the multilayer sheet obtained by coextrusion molding is stretched in the longitudinal direction at a stretching temperature of less than 55 ° C., the multilayer sheet is not stretched uniformly, and the polyglycolic acid layer is cracked when stretched in the transverse direction. There is a possibility that a biaxially stretched polyester multilayer film cannot be obtained. Even if the stretching temperature in the machine direction exceeds 70 ° C, the multi-layer sheet can be stretched uniformly. However, when the multi-layer film stretched in excess of 70 ° C is stretched in the machine direction, the polyglycolic acid crystallizes and stretches in the transverse direction. In doing so, the polyglycolic acid crystallized may break, and uniform lateral stretching may not be possible.
The most important point in the production method of the biaxially stretched polyester multilayer film of the present invention is to heat the stretching point of the multilayer sheet with infrared rays when stretching the multilayer sheet obtained by coextrusion molding in the longitudinal direction. is there. When stretching the multilayer sheet, even when the stretching roll temperature is adjusted to the above range during longitudinal stretching, the multilayer sheet is not uniformly stretched when the stretching point of the multilayer sheet is not heated. When the sheet is whitened and the appearance is deteriorated and the sheet is stretched in the lateral direction, the multilayer sheet may be broken.
By heating the stretching point with infrared rays, particularly far infrared rays, the polymer compound such as polylactic acid and polyglycolic acid according to the present invention can be efficiently and instantaneously heated.
When the multilayer sheet is stretched in the longitudinal direction, even if the temperature of the stretching roll is adjusted to the above range, the multilayer sheet is not uniformly stretched in the longitudinal direction when the stretching point of the multilayer sheet is not heated with infrared rays. The film is whitened and the appearance is deteriorated, and the multilayer sheet may be broken when it is stretched in the lateral direction.
The multilayer sheets longitudinally stretched when transverse stretching, the temperature is less than 70 ° C. in the transverse stretching, the multilayer sheet is broken, or out from the tenter chuck may cormorants want, a possibility can not be performed uniform transverse stretching is there. On the other hand, when the temperature of transverse stretching exceeds 100 ° C., crystallization of polyglycolic acid proceeds and uniform transverse stretching cannot be performed.

EXAMPLES Next, although an Example is given and this invention is demonstrated further more concretely, this invention is not restrict | limited to these Examples, unless the summary is exceeded.

The physical property values and the like in Examples and Comparative Examples were obtained by the following evaluation methods.
<Evaluation method>
(1) Tensile properties:
A strip-shaped test piece (length: 150 mm, width: 15 mm) is taken from the biaxially stretched polyester multilayer film in the MD direction and TD direction, and a tensile test is performed using a chuck distance of 100 mm (name of the tensile tester). The strength (stress) (MPa), elongation (%), and Young's modulus (MPa) at the breaking point were determined. Elongation (%) was defined as a change in the distance between chucks.
(2) Oxygen permeability:
Using OX-TRAN 2/20 manufactured by Mocon, temperature 20 according to JIS K 7126
The measurement was performed under the conditions of ° C. and humidity 80% RH.
(3) Heat shrinkage rate:
A sample having a length of 120 mm and a width of 15 mm was cut out from the biaxially stretched polyester multilayer film, and marked lines were drawn at intervals of 100 mm. Subsequently, the film is subjected to a predetermined temperature (80 ° C.
, 100 ° C., 120 ° C.), left for 15 minutes in an oven, then taken out, left at room temperature for 15 minutes or longer, and then measured the length (L: mm) between the marked lines. [(100-L) / 10
The value of 0] × 100 (%) was defined as the heat shrinkage rate (%).
(4) Melting characteristics:
Based on JIS K7121 and K7122, it calculated | required on condition of the following using DSC (differential scanning calorimeter).
About 5 mg of a sample is precisely weighed and packed in an aluminum pan. As DSC, Q100 manufactured by TA Instruments Co., Ltd. is used, and 250 ° C. at a rate of 20 ° C. to 10 ° C./min in a nitrogen atmosphere of 50 ml / min.
The temperature is raised to 50 ° C. and once melted, then maintained at 250 ° C. for 10 minutes and 20 ° C. at a rate of 10 ° C./min.
The solution was cooled down to crystallization, maintained at 10 ° C. for 5 minutes, and then again at a rate of 10 ° C./min.
The temperature was raised to 0 ° C. to obtain a thermal melting curve, and the heat of fusion and melting point (endothermic peak temperature) of the sample were determined from the obtained thermal melting curve.
(5) Heat seal test:
After overlapping the biaxially stretched polyester multilayer film, it is sandwiched between 12 μm thick biaxially stretched polyethylene terephthalate films (trade name “Lumirror 12μ” manufactured by Toray Industries, Inc.), and using TP-701-B HEATSEALTESTER manufactured by Tester Sangyo Co., Ltd. Then, heat sealing was performed at a predetermined temperature under conditions of a seal surface pressure of 1 kg / cm ² and a time of 0.5 seconds. The heating was performed only on the upper side. Next, the heat-fused biaxially stretched polyester multilayer film was peeled off at 15 mm wide with a tensile rate of 300 mm / min using a Tensilon universal testing machine RTC-1225 manufactured by Orientec Co. The heat fusion strength was used.

The polymers used in Examples and Comparative Examples are shown below.
(1) Polyglycolic acid (PGA):
Melt viscosity η *: 1,000-1,500 Pa · sec, melting point: 220 ° C., heat of fusion: 64
J / g.
(2) Polylactic acid (PLA):
Polylactic acid (trade name: “Lacia H100E” sold by Mitsui Chemicals, Inc.), glass transition temperature: 56 ° C., melting point: 164 ° C., MFR: 10 g / 10 min.
(3) Aliphatic polyester (PBSL):
1,4-Butanediol / succinic acid / lactic acid copolymer (Mitsubishi Chemical Corporation, trade name: “
Gs Pla AZ91T ”) lactic acid content: 2 mol%, melting point: 112 ° C., MFR: 4.5
g / 10 minutes.
(4) Polylactic acid copolymer (PLAC):
D-lactic acid content: 12.6% by weight, specific gravity: 1.3, Tg: 56.9 ° C., MFR (temperature 1
90 ° C., load 2160 g): 2.6 g / 10 min.

Example 1
<Manufacture of multilayer sheets>
Using a 40mmφ three-type three-layer single-screw extruder equipped with a T-die at the tip, PLA / PGA /
PLA was extruded at a thickness ratio of 70/70/70 / and quenched with a casting roll at 30 ° C. to obtain a three-layer multilayer sheet having a thickness of 210 μm.
The extrusion temperatures of PLA and PGA were 230 ° C. and 270 ° C., respectively.
<Manufacture of biaxially stretched polyester multilayer film>
The obtained multilayer sheet was stretched 3 times in the longitudinal direction using a stretching roll heated to 60 ° C. In addition, an infrared heater (WC) installed between the low-speed roll and the high-speed roll during longitudinal stretching.
The stretching point of the laminated sheet was heated using eraeus (2400 W / 200 V). Subsequently, the laminated sheet longitudinally stretched by a tenter-type lateral stretching apparatus at 3.5 ° C. at 80 ° C. in the lateral direction.
The film was stretched twice, and heat-fixed at 160 ° C. for 3 seconds and wound up to obtain a biaxially stretched polyester multilayer film.
The evaluation results of the obtained biaxially stretched polyester multilayer film are shown in Table 1.

Example 2
<Production of aliphatic polyester composition>
As an aliphatic polyester composition, PLAC and PBSL were weighed at a ratio of 10:90 (% by weight), and silica having an average particle diameter of 3 μm (trade name “Siricia 730”, Fuji Silysia Chemical Co., Ltd.)
0.1 parts by weight) was added and melt-kneaded at 180 ° C. using a 40 mmφ single screw extruder to prepare an aliphatic polyester composition (APES).
<Manufacture of multilayer sheets>
APES / PLA using a 40mmφ three-kind five-layer single-screw extruder equipped with a T-die at the tip
/ PGA / PLA / APES is extruded at a thickness ratio of 50/50/50/50/50, 30
Quenching was performed with a casting roll at 0 ° C. to obtain a multi-layered sheet having a thickness of 250 μm. In addition,
The extrusion temperatures of PLA, PGA and APES were 230 ° C, 270 ° C and 230 ° C, respectively.
<Manufacture of double-stretched polyester multilayer film>
The resulting five-layer multilayer sheet was stretched in the longitudinal and transverse directions in the same manner as in Example 1 to obtain a biaxially stretched polyester multilayer film.
The evaluation results of the obtained biaxially stretched polyester multilayer film are shown in Table 1.

Example 3
It replaced with the aliphatic polyester composition (APES) used in Example 2, and it carried out similarly except using PBSL independently.
The evaluation results of the obtained biaxially stretched polyester multilayer film are shown in Table 1.

Comparative Example 1
When the multilayer sheet obtained in Example 1 was not heated by an infrared heater when it was stretched in the machine direction using a stretching roll, the multilayer sheet was whitened during the longitudinal stretching, and uniform stretching could not be performed.

Comparative Example 2
When the multilayer sheet obtained in Example 1 was stretched in the longitudinal direction using a stretching roll, stretching was performed at a stretching temperature (roll temperature) of 80 ° C., and then lateral stretching was performed. Cracked and uniform stretching was not possible.

Reference example 1
<Manufacture of non-stretched sheet>
Using a 40 mmφ single-screw extruder equipped with a T-die at the tip, PLA was extruded and quenched with a casting roll at 30 ° C. to obtain an unstretched sheet having a thickness of 210 μm.
The extrusion temperature of PLA was 230 ° C.
<Manufacture of biaxially stretched film>
The obtained unstretched sheet was guided to a roll heated to 60 ° C., and roll-stretched three times in the longitudinal direction. Infrared rays were placed between the rolls and heated indirectly. This longitudinally stretched sheet was stretched 3.5 times at 80 ° C. in the transverse direction by a tenter-type lateral stretching apparatus, heat-fixed at 160 ° C. for 3 seconds, and wound to obtain a biaxially stretched film.
The evaluation results of the obtained biaxially stretched film are shown in Table 1.

A biaxially stretched multilayer film in which a biaxially stretched polylactic acid film is directly laminated on at least one surface of the biaxially stretched polyglycolic acid film of the present invention has excellent oxygen barrier properties, transparency, interlayer adhesion strength, rigidity, and flexibility. Therefore, it can be suitably used as a packaging film for various items to be packaged such as foods and pharmaceuticals.

Claims (1)

A multilayer sheet obtained by laminating a polyglycolic acid film and a polylactic acid film obtained by coextrusion molding of polyglycolic acid and polylactic acid is at least 1.5 in the longitudinal direction at a temperature of 55 to 70 ° C. using a stretching roll. The biaxially stretched polyester multilayer is characterized in that, when stretched, the stretching point of the multilayer sheet is heated with infrared rays and then stretched at least 1.5 times in the transverse direction at a temperature of 60 to 100 ° C. using a tenter. A method for producing a film.