Stretched film and method for manufacturing same

Abstract

Provided are: a stretched film in which wrinkles and tears hardly occur even after being wound onto a roll; and a method for manufacturing the same.　A stretched film according to the present invention includes a layer containing polylactic acid and has a loop stiffness value of 25 mN / 20 mm or less. A method for manufacturing the stretched film according to the present invention includes a step for stretching a sheet containing polylactic acid. Wrinkles and tears hardly occur in the stretched film of the present invention, even after the stretched film has been wound onto a roll.

Description

Stretched film and method for producing same

[0001] The present invention relates to a stretched film and a method for producing the same.

[0002] Stretched films are known to be produced, for example, by stretching a raw resin sheet, and known films include uniaxially stretched films formed by uniaxial stretching and biaxially stretched films formed by biaxial stretching.

[0003] Stretched films can exhibit various properties depending on the type of resin that constitutes the film, and are excellent in, for example, rigidity, heat resistance, oil resistance, chemical resistance, processability, etc. Because of these physical properties, stretched films are widely used as packaging materials such as food packaging materials, for piezoelectric applications, and as industrial materials such as adhesive tapes and release papers.

[0004] In recent years, biomass plastics have been attracting a great deal of attention for the purposes of reducing the amount of plastic material waste and the carbon dioxide generated by incineration. In light of this situation, many attempts have been made to produce stretched films using biomass plastics such as polylactic acid.

[0005] It is known that in order to maximize the physical properties of a stretched film, not only the selection of the type of resin but also the film-forming properties and the ease of winding the stretched film onto a roll during production are important for the physical properties of the stretched film. From this perspective, techniques for improving the winding properties of a stretched film have been widely studied (for example, Patent Document 1, etc.).

[0006] Japanese Patent Application Laid-Open No. 2021-133607

[0007] In the case of stretched films made using resins containing biomass plastics as a main component, such as the above-mentioned polylactic acid, the rolled body obtained by winding the stretched film on a roll has a problem in that wrinkles and cracks occur during storage. If wrinkles and cracks occur in the rolled body, it becomes unusable as a product.

[0008] The present invention has been made in view of the above, and aims to provide a stretched film that is less likely to wrinkle or crack even after being wound onto a roll, and a method for producing the same.

[0009] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that the above-mentioned object can be achieved by adjusting the loop stiffness value of the stretched film to a desired range, and have thus completed the present invention.

[0010] That is, the present invention encompasses, for example, the subject matter described in the following items. Item 1. A stretched film comprising a layer containing polylactic acid, having a loop stiffness value of 25 mN / 20 mm or less. Item 2. The stretched film according to item 1, in which the value of E1 / E2 is 1.5 or more, where E1 (GPa) is the maximum elastic modulus and E2 (GPa) is the minimum elastic modulus. Item 3. The stretched film according to item 1 or 2, having a thickness of 5 μm or more and 15 μm or less. Item 4. The stretched film according to any one of items 1 to 3, which is a uniaxially stretched film. Item 5. A method for producing the stretched film according to any one of items 1 to 4, comprising a step of stretching a sheet containing polylactic acid.

[0011] The stretched film of the present invention has a loop stiffness value within a predetermined range, so that wrinkles and cracks are less likely to occur even after being wound up on a roll.

[0012]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0013] 1. Stretched Film The stretched film of the present invention is a stretched film including a layer containing polylactic acid, and in particular has a loop stiffness value of 25 mN / 20 mm or less. This makes the stretched film of the present invention less susceptible to wrinkling and cracking even after being wound up on a roll. Therefore, the stretched film of the present invention is less susceptible to wrinkling and cracking even when stored for a long period of time in a wound up state on a roll, and can be stored for a long period of time.

[0014] When a conventional stretched film is wound onto a roll to form a roll, a force acts on the stretched film in the machine direction (stretching direction) while the roll is being stored, causing the film to shrink (because a force acts on the film to return to its original state). As a result, the film becomes too tightly wound after being wound onto the roll, causing wrinkles and cracks (so-called roll cracks) in the stretched film, making it difficult to use as a product.

[0015] In this regard, in the present invention, as described above, by setting the loop stiffness value of the stretched film within the desired range, shrinkage of the stretched film is suppressed even after it has been wound onto a roll, and as a result, wrinkles and cracks are less likely to occur even after it has been wound onto a roll.

[0016] If the loop stiffness value of the stretched film of the present invention exceeds 25 mN / 20 mm, the flexibility of the stretched film will deteriorate and the rigidity will increase, which may result in the stretched film being more susceptible to wrinkling and cracking after being wound onto a roll.

[0017] A stretched film usually has an MD direction (the machine direction of the stretched film) and a TD direction (the direction perpendicular to the MD direction on the film surface), and the loop stiffness values ​​may differ between the MD and TD directions. Therefore, in the stretched film of the present invention, the loop stiffness values ​​are measured in both the MD and TD directions, and it is necessary that the loop stiffness values ​​in both directions be 25 mN / 20 mm or less.

[0018] In this specification, when the loop stiffness values ​​in the MD direction and the TD direction of a stretched film are different, the direction with the larger loop stiffness value may be referred to as the "maximum orientation direction," and the direction with the smaller loop stiffness value may be referred to as the "minimum orientation direction."

[0019] The loop stiffness value of the stretched film is preferably 15 mN / 20 mm or less, more preferably 10 mN / 20 mm or less, even more preferably 7.5 mN / 20 mm or less, and particularly preferably 5.0 mN / 20 mm or less. The lower limit of the loop stiffness of the stretched film is not particularly limited, and is preferably 0.5 mN / 20 mm or more, more preferably 1.5 mN / 20 mm or more, from the viewpoint of reducing the likelihood of wrinkling after storage.

[0020] The loop stiffness of the stretched film of the present invention is measured using a loop stiffness tester (manufactured by Toyo Seiki Co., Ltd.). The test piece for measuring the loop stiffness is 100 mm x 20 mm in size, and the loop stiffness is measured in both the long and short directions. In measuring the loop stiffness, the loop length is 50 mm, the load range is 200 mN or less, the pressing distance is 20 mm, and the compression speed is 3.3 mm / s.

[0021] The method for adjusting the loop stiffness value of the stretched film of the present invention is not particularly limited, and can be adjusted by various methods. For example, the loop stiffness value of the stretched film can be adjusted depending on the thickness of the stretched film, the elastic modulus of the stretched film, the stretching method, the stretching ratio, the type of material constituting the stretched film, etc. In particular, by adjusting the thickness, stretching method, and stretching ratio of the stretched film, it is easy to control the loop stiffness of the stretched film to a desired value.

[0022] The stretched film of the present invention includes a layer containing polylactic acid as a primary component. The type of polylactic acid is not particularly limited, and a wide variety of known polylactic acids can be used, including, for example, polylactic acid obtained by condensation polymerization of lactic acid as a raw monomer. The polylactic acid may contain either or both of the optical isomers L-lactic acid (L-form) and D-lactic acid (D-form). When the polylactic acid is primarily composed of L-lactic acid (L-form), the content of the D-form is preferably 5.0 mol% or less, more preferably 3.0 mol% or less, even more preferably 1.0 mol% or less, and particularly preferably 0.01 mol% or less. When the polylactic acid is primarily composed of D-lactic acid (D-form), the content of the L-form is preferably 5.0 mol% or less, more preferably 3.0 mol% or less, even more preferably 1.0 mol% or less, and particularly preferably 0.01 mol% or less. The glass transition temperature, crystallization temperature, molecular weight, etc. of the polylactic acid are not particularly limited.

[0023] The method for producing the polylactic acid used in the stretched film of the present invention is not particularly limited, and polylactic acid can be obtained, for example, by a known production method. Polylactic acid can also be obtained as a commercially available product. Representative commercially available polylactic acid products include "4032D" manufactured by NatureWorks and the Luminy series manufactured by Total Corbion, specifically "L175," "LX175," and "LX575."

[0024] In the stretched film of the present invention, the layer containing polylactic acid is formed from a resin component containing the polylactic acid. Such a resin component may also contain a resin other than polylactic acid. Examples of resins other than polylactic acid include various resins used in stretched films, such as various thermoplastic resins. Specific examples of thermoplastic resins include polyolefin resins such as polyethylene and polypropylene.

[0025] The resin component contained in the polylactic acid-containing layer preferably contains polylactic acid as a main component. For example, the content of polylactic acid relative to the total mass of the resin component contained in the polylactic acid-containing layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The resin component contained in the polylactic acid-containing layer may consist solely of polylactic acid.

[0026] The proportion of the resin component containing polylactic acid relative to the total mass of the stretched film of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0027] The layer containing polylactic acid may contain other additives in addition to the resin component, such as a heat stabilizer, an antioxidant, an organic or inorganic lubricant, a chlorine scavenger, an antistatic agent, an antifogging agent, a hydrolysis inhibitor, etc.

[0028] When the layer containing polylactic acid contains an additive, the content of the additive is not particularly limited. For example, the layer containing polylactic acid preferably contains the additive in an amount of 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0029] The stretched film of the present invention may be a so-called single layer formed only of a layer containing polylactic acid, or may be a multilayer film formed by laminating other layers on a layer containing polylactic acid.

[0030] When the stretched film of the present invention is multilayered, it may have a multilayer structure in which at least two layers containing the same or different polylactic acids are laminated, or at least one other layer is provided on one or both sides of a layer containing polylactic acid. In this case, the layer containing polylactic acid may be referred to as a "core layer." The core layer may have a multilayer structure in which at least two layers containing the same or different polylactic acids are laminated.

[0031] When the stretched film of the present invention is multilayered, the layers other than the core layer may include, for example, a heat-sealing layer having a heat-sealing function, a conductive layer having electrical conductivity, and a peeling layer having a peeling function. These other layers may be formed, for example, from the same materials as known layers, and may also be formed from polylactic acid, like the core layer. When the other layers are formed from polylactic acid, at least one or all of the other layers may be made of the same polylactic acid as the core layer. In other words, the stretched film may have a single-layer three-layer structure, etc. The thickness of the other layers is not particularly limited and is, for example, about 0.1 to 5 μm.

[0032] The thickness of the stretched film of the present invention is not particularly limited as long as the loop stiffness value is within the above-mentioned range. The thickness of the stretched film of the present invention can be, for example, less than 30 μm, and is preferably less than 25 μm, in order to facilitate adjustment of the loop stiffness value to 25 mN / 20 mm or less. The thickness of the stretched film of the present invention is preferably 5 μm or more and 15 μm or less, in order to facilitate adjustment of the loop stiffness value of the stretched film to 25 mN / 20 mm or less and to prevent wrinkles from occurring after storage. When the stretched film of the present invention is multilayered, the thickness of the stretched film refers to the sum of the thicknesses of the individual layers (i.e., the total thickness of the core layer and all other layers).

[0033] The thickness of the stretched film of the present invention is more preferably 6 μm or more, even more preferably 7 μm or more, from the viewpoint of being less prone to wrinkling after storage, and is more preferably 14 μm or less, even more preferably 13 μm or less.

[0034] The method for adjusting the thickness of the stretched film of the present invention is not particularly limited, and for example, a wide variety of known methods can be adopted in the present invention. For example, the thickness of the stretched film can be easily adjusted by adjusting the thickness of the raw sheet when producing the stretched film, adjusting the stretching conditions, etc.

[0035] The thickness of the stretched film of the present invention can be measured using a micrometer, and the measurement method conforms to JIS K 7130.

[0036] The stretched film of the present invention preferably has a maximum elastic modulus E1 (GPa) and a minimum elastic modulus E2 (GPa) such that the value of E1 / E2 is 1.5 or more, in which case the loop stiffness of the stretched film is easily adjusted to 25 mN / 20 mm or less, and the stretched film is less likely to wrinkle or crack even after being wound onto a roll.

[0037] The maximum elastic modulus E1 and minimum elastic modulus E2 of a stretched film can be measured as follows. First, the elastic modulus in the TD and MD directions of the stretched film of the present invention is measured, and the larger value is designated as the maximum elastic modulus E1, and the smaller value is designated as the minimum elastic modulus E2. In the stretched film of the present invention, for example, the elastic modulus in the TD direction is likely to have the maximum elastic modulus, and the elastic modulus in the MD direction is likely to have the minimum elastic modulus. The elastic modulus of the stretched film can be measured in accordance with JIS K 7127.

[0038] The value of E1 / E2 is preferably 1.6 or more, more preferably 1.7 or more, even more preferably 1.8 or more, and particularly preferably 1.9 or more. The value of E1 / E2 is preferably 4 or less, more preferably 3.5 or less, even more preferably 3 or less, and particularly preferably 2.5 or less.

[0039] In the stretched film of the present invention, the method for adjusting the E1 / E2 value is not particularly limited. For example, the E1 / E2 value can be adjusted by the stretching conditions when producing the stretched film. In particular, as described below, when the stretched film is produced by uniaxial stretching, it is easier to adjust the E1 / E2 value to the desired range.

[0040] The stretching ratio of the stretched film of the present invention is not particularly limited. In order to prevent wrinkles and cracks from occurring even after being wound up on a roll, the stretching ratio is preferably 3.5 or more, more preferably 4.0 or more, and even more preferably 4.5 or more, and is preferably 6.0 or less, more preferably 5.5 or less, and even more preferably 5.0 or less.

[0041] The stretching ratio of the stretched film means the stretching ratio in the maximum orientation direction, based on the raw sheet described below for obtaining the stretched film.

[0042] The stretched film of the present invention may be a uniaxially stretched film formed by uniaxial stretching, or a biaxially stretched film formed by biaxial stretching. Preferably, the stretched film of the present invention is a uniaxially stretched film. In this case, the loop stiffness value of the stretched film of the present invention can be easily adjusted to a desired range, and the stretched film of the present invention is particularly resistant to wrinkling and cracking even after being wound up on a roll.

[0043] The stretched film of the present invention is not limited to a specific stretching direction, and may be stretched in any of the TD direction, MD direction, and other directions (for example, an oblique direction such as a 45° angle). In any case, the stretched film of the present invention has a loop stiffness value that can be easily adjusted to a desired range, and is particularly resistant to wrinkling and cracking even after being wound onto a roll.

[0044] 2. Method for Producing Stretched Film The method for producing the stretched film of the present invention is not particularly limited, and for example, a wide variety of known methods can be employed. For example, the stretched film of the present invention can be produced by a production method including a step of stretching a sheet containing polylactic acid.

[0045] More specifically, a resin sheet containing at least polylactic acid is extruded to produce the stretched film of the present invention, and the resin sheet is then stretched. This production method is abbreviated as "Production Method A."

[0046] The resin raw material used in Production Method A is primarily composed of polylactic acid and may contain other resins as needed. The resin raw material may further contain various additives as needed. The resin raw material may be prepared using known preparation methods, such as dry blending polylactic acid pellets or powder using a batch mixer such as a tumbler or mixer, or a continuous metering mixer; or feeding polylactic acid pellets or powder, together with other resin pellets or powder and / or additives as needed, into a kneader and melt-kneading to obtain a melt-blend resin composition. Among these, melt-kneading is preferred for preparing the resin raw material.

[0047] As the kneader used for melt kneading, a known kneader can be used, and a single-screw type, a twin-screw type, or a multi-screw type having more than two screws can be used. Furthermore, in the case of a twin or more screw type, either a co-rotating or counter-rotating kneading type can be used.

[0048] The kneading temperature for melt kneading is preferably in the range of 200°C to 300°C, more preferably 220°C to 280°C. To prevent deterioration of the resin during melt kneading, an inert gas such as nitrogen can be purged. The melt-kneaded resin can be pelletized to an appropriate size using a commonly known granulator to obtain melt blend resin composition pellets.

[0049] In production method A, a resin sheet can be obtained using the resin raw material obtained as described above. Specifically, the resin raw material is supplied to an extruder, heated and melted, and, if necessary, fine foreign matter and the like is removed using a filter or the like, and then the melt is extruded into a sheet shape through a T-die, thereby obtaining a resin sheet.

[0050] The extruder used to obtain the resin sheet can be, for example, a wide variety of known extruders. There are no limitations on the screw type of the extruder, and a single-screw type, twin-screw type, or multi-screw type with more than one screw may be used. When the resin raw materials are prepared by dry blending, using a twin-screw type or multi-screw type with more than one screw tends to provide excellent mixing and dispersion. The extrusion temperature is preferably in the range of 200°C to 300°C, more preferably 220°C to 280°C. To prevent thermal degradation of the resin during extrusion, an inert gas such as nitrogen can be purged.

[0051] The melt-extruded resin sheet is formed into a sheet by a known method, for example, by adhering it to at least one metal drum set at a temperature of 25 to 120°C using an air knife or other rolls, or by static electricity, etc., and the resin sheet is obtained as a so-called raw sheet. The temperature of the metal drum is more preferably 30 to 80°C.

[0052] Production method A may further include a lamination step as necessary. For example, when the aforementioned multilayer stretched film is to be obtained, production method A preferably includes a lamination step. In the lamination step, for example, a wide variety of conventional lamination methods can be used, including films obtained by laminating using a coextrusion method, a lamination method, a heat sealing method, etc.

[0053] When producing a multilayer stretched film, two or more dry-blended and / or melt-blended resin compositions (each resin composition may have the same or different composition) can be co-extruded to obtain a resin sheet having a laminated structure. Alternatively, a multilayer stretched film can be produced by laminating a monolayer stretched film with another film. Alternatively, a multilayer stretched film can be produced by stretching a multilayer unstretched film (each layer may have the same or different resin composition) obtained by laminating two or more layers of unstretched film extruded as a single layer together.

[0054] Examples of coextrusion methods include a pre-die lamination method in which molten resins are brought into contact in a feed block before a die, an in-die lamination method in which they are brought into contact within a path inside a die, such as a multi-manifold die, and an out-die lamination method in which they are discharged from multiple concentric lips and brought into contact, etc. For example, in the in-die lamination method, a multi-layer die such as a three-layer multi-manifold die can be used.

[0055] Examples of lamination methods include extrusion lamination, which uses equipment for melt extrusion molding used in the T-die method to directly extrude a film of molten resin onto another film to form a laminated film.

[0056] Examples of heat sealing methods include an external heating method in which a heated metal body is pressed against multiple bonded films from the outside of the films, and the conducted heat melts and bonds the films, and an internal heating method in which high-frequency radio waves or ultrasound are used to generate heat in the films and bond them.

[0057] In production method A, the above lamination methods can be used alone or in combination. When production method A includes a lamination step, the resin sheet can have a laminated structure, and when production method A does not include a lamination step, the resin sheet has a single-layer structure. By using a resin sheet having a single-layer structure and stretching it as described below, a stretched film consisting of a layer containing polylactic acid can be obtained.

[0058] In manufacturing method A, a resin sheet (raw sheet) having the above-described single-layer or laminated structure is stretched. As the stretching method, known methods such as stretching between rolls with different peripheral speeds, a tenter method, a tubular method, etc. can be used. As the stretching direction, uniaxial stretching, biaxial stretching, and biaxial stretching in an oblique direction can be used, and in the case of biaxial or more stretching, both sequential stretching and simultaneous stretching can be applied. Of these, uniaxial stretching is preferably used because it is easier to obtain the desired stretched film. When uniaxial stretching is used, for example, the temperature during stretching can be 100°C to 140°C, and the stretching speed can be 10 to 20 m / min.

[0059] In the production method A, the resin sheet (raw sheet) can be stretched according to the desired stretching ratio described above.

[0060] The stretching direction of the resin sheet (raw sheet) is not limited, and it may be stretched in any of the TD direction, MD direction, and other directions (for example, an oblique direction such as a 45° direction).

[0061] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0062] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0063] Example 1: Polylactic acid "Luminy L-175" manufactured by Total Corbion PLA was prepared and fed from a hopper into a screw-type extruder, melted, and extruded through a single-layer die. The extruded resin layer was placed on a cooling drum controlled at 45°C to obtain a raw sheet, which was then stretched. The stretching was performed at a stretching temperature of 100-140°C and a stretching speed of 15.0 m / min, with the stretching direction being the same as the maximum orientation direction. This resulted in a stretched film with a stretch ratio of 4.9 and a thickness of 10.3 μm.

[0064] Examples 2 to 4 As shown in Table 1, stretched films were obtained in the same manner as in Example 1, except that the thickness of the stretched film and the stretching ratio were changed.

[0065] Example 5: Polylactic acid "Luminy L-175" manufactured by Total Corbion PLA was prepared and fed from a hopper into a screw-type extruder, melted, and extruded through a three-layer die. The extruded resin layer was placed on a cooling drum controlled at 45°C to obtain a raw sheet, which was then stretched. The stretching was performed at a stretching temperature of 100-140°C and a stretching speed of 15.0 m / min, with the stretching direction being the same as the maximum orientation direction. This resulted in a stretched film with a stretch ratio of 5.2 and a thickness of 10 μm.

[0066] (Example 6) A stretched film having a stretch ratio of 3.5 and a thickness of 15 μm was obtained in the same manner as in Example 1, except that a batch-type biaxial stretching machine KARO manufactured by Bruckner was used instead of the uniaxial stretching device.

[0067] Comparative Examples 1 and 2 As shown in Table 1, stretched films were obtained in the same manner as in Example 1, except that the thickness of the stretched film and the stretching ratio were changed.

[0068] Comparative Example 3 A stretched film having a draw ratio of 4.8 and a thickness of 30 μm was obtained in the same manner as in Example 1 except that the discharge conditions were changed.

[0069] Comparative Example 4 A stretched film having a thickness of 16 μm was obtained in the same manner as in Example 1, except that the stretching ratio was changed to 5.7 times.

[0070] (Evaluation of Physical Properties) The stretched films obtained in each of the Examples and Comparative Examples were evaluated for loop stiffness, modulus of elasticity, presence or absence of cracks in the wound body after storage, and presence or absence of wrinkles in the wound body after storage as described below.

[0071] <Loop Stiffness> A stretched film specimen measuring 20 mm in width and 100 mm in length was placed in a loop stiffness tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.) set to a pressing distance of 20 mm and a load cell of 200 mN, and measurement was initiated. The specimen was bent into a loop (loop length 50 mm), and the measured value when the loop was crushed (compression speed 3.3 mm / s) was taken as the loop stiffness value. Loop stiffness values ​​were measured in both the width direction and the length direction, with the larger value being taken as the "maximum orientation direction" and the smaller value being taken as the "minimum orientation direction."

[0072] <Elastic Modulus> The elastic modulus of the stretched film was measured in both the MD and TD directions in accordance with JIS K 7127, with the higher value being the maximum elastic modulus and the lower value being the minimum elastic modulus.

[0073] <Presence or Absence of Cracks in the Rolled Body After Storage> The stretched film obtained in each Example and Comparative Example was wound around a roll at a winding speed of 15.0 m / min to obtain a rolled body. This rolled body was stored in an environment of 20°C and 50% RH. Six months after this storage, the rolled body was visually inspected for cracks, and the presence or absence of cracks after storage was judged based on the following evaluation criteria. <Evaluation Criteria> ⊚: No cracks or seaming marks were found, and the storage condition was extremely good. ◯: Seaming of several millimeters was observed, but no cracks were found, and the storage condition was good. Δ: Cracks were found, and the seaming was also found to be several centimeters long, and the storage condition was poor. ×: Linear cracks were found, and the storage condition was extremely poor.

[0074] <Presence or absence of wrinkles in the roll after storage> The stretched film obtained in each example and comparative example was wound around a roll at a winding speed of 15.0 m / min to obtain a roll. This roll was stored in an environment of 20°C and 50% RH. Six months after this storage, the roll was visually inspected for the presence or absence of wrinkles, and cracks after storage were judged based on the following evaluation criteria. <Evaluation criteria> ○: No wrinkles, storage condition was extremely good. △: Wrinkles of about several centimeters were observed, but were at a level that was not problematic for practical use. ×: Wrinkles of about several tens of centimeters were observed, storage condition was extremely poor.

[0075] Table 1 shows the layer structure (single layer or multilayer), stretching ratio, thickness, loop stiffness value, maximum elastic modulus E1 (GPa), minimum elastic modulus E2 (GPa), E1 / E2 value, and evaluation results for the presence or absence of cracks and wrinkles after storage of the wound body of the stretched film obtained in each Example and Comparative Example.

[0076] From Table 1, it can be seen that stretched films having loop stiffness values ​​of 25 mN / 20 mm or less in both the maximum and minimum orientation directions are less likely to wrinkle or crack even after being wound up on a roll.

[0077]

Claims

1. A stretched film comprising a layer containing polylactic acid, the loop stiffness value being 25 mN / 20 mm or less.

2. The stretched film according to claim 1, wherein the maximum elastic modulus is E1 (GPa) and the minimum elastic modulus is E2 (GPa), and the value of E1 / E2 is 1.5 or more.

3. The stretched film according to claim 1, having a thickness of 5 μm or more and 15 μm or less.

4. The stretched film of claim 1 which is a uniaxially stretched film.

5. A method for producing the stretched film according to any one of claims 1 to 4, comprising the step of stretching a sheet containing polylactic acid.

Images