Polylactic acid-based films, food packaging films, fruit and vegetable packaging films

Abstract

To provide a film which reduces rigidity of a polylactic acid resin, and is suitably usable as a film for packaging a food product while having softness when being formed into a film.SOLUTION: A polylactic acid film has a layer (I) composed of a resin composition containing a polylactic acid resin (A) and a plasticizer (B), where the content of the plasticizer (B) with respect to the resin composition is 18 mass% or less, and a storage elastic modulus (E') at 22°C when the layer (I) is measured according to JIS K 7244-4 (1999) is 1.0 GPa or more and 4.0 GPa or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polylactic acid-based film having a layer composed of a resin composition containing a polylactic acid-based resin and a plasticizer, and a food packaging film and a fresh produce packaging film using the same.

Background Art

[0002] Plastics have penetrated into all fields of our lives, and the annual global production volume has reached more than 200 million tons. Most plastics are discarded after use, which is recognized as one of the causes of disturbing the global environment. Therefore, in recent years, effective utilization of petroleum-derived plastics, which are depleting resources, has been emphasized, and the use of renewable resources as substitutes for depleting resources has become important. Currently, the most notable use of renewable resources in plastics is the use of plant-derived plastics. Plant-derived plastics can utilize non-depleting resources and save depleting resources during plastic production. Among plant-derived plastics, particularly, polylactic acid-based resins are made from lactic acid obtained by fermentation of starch, can be mass-produced by chemical engineering, and have excellent transparency and rigidity. Therefore, their development as alternative materials to polystyrene, polyethylene terephthalate, etc. is expected.

[0003] For example, Patent Document 1 proposes using a polylactic acid-based resin to take advantage of properties similar to those of polyethylene terephthalate and using it as a film or sheet for use in molded product applications.

[0004] In addition, fresh produce such as vegetables and fruits continue to have a respiratory action even after being harvested. Therefore, during storage, distribution, and preservation after harvest, energy is consumed by the respiration of the fresh produce itself, causing deterioration of freshness. Therefore, as a method for maintaining the freshness of fresh produce, a method of appropriately suppressing the respiration of fresh produce to maintain freshness is known. Such a packaging bag used for maintaining the freshness of fresh produce is known as MA (Modified Atmosphere) packaging.

[0005] For example, Patent Document 2 discloses a packaging material for fruit and vegetable packaging, which consists of a low-rigidity section made of a synthetic resin layer and a high-rigidity section in which a paper layer is laminated on a part of the synthetic resin layer, wherein the area of ​​the high-rigidity section is 50-95%, and the low-rigidity section has through holes. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-219088 [Patent Document 2] Japanese Patent Publication No. 2022-10606 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the aforementioned Patent Document 1, polylactic acid resin is used for molded products. However, polylactic acid resin has a high modulus of elasticity at room temperature, and when formed into a film, it becomes very rigid, which can make it difficult to use in certain applications. For example, compared to soft films using polyolefin resins or polyamide resins, the rigidity of the film at room temperature is high, making it difficult to use.

[0008] Furthermore, Patent Document 2 proposes using a polyolefin resin as the low-rigidity part and providing through holes to improve gas (oxygen and water vapor) permeability for use as a film for fruits and vegetables. However, in this case, the appearance of the film is impaired, and there are concerns that hygiene problems may arise because the contents come into direct contact with the outside air.

[0009] The present invention aims to provide a film that reduces the rigidity of polylactic acid resins, while maintaining flexibility when formed into a film, and that can be suitably used as a packaging film for food and other products. [Means for solving the problem]

[0010] In view of the above circumstances, the inventors have solved the above problems and completed the present invention by setting the storage modulus of a layer made of a resin composition containing a polylactic acid resin and a specific amount of plasticizer to a specific range.

[0011] That is, the present invention has the following aspects. [1] A polylactic acid film having a layer (I) made of a resin composition containing a polylactic acid resin (A) and a plasticizer (B), The content of the plasticizer (B) in the resin composition is 18% by mass or less. A polylactic acid film wherein the aforementioned layer (I) has a storage modulus (E') at 22°C measured according to JIS K7244-4 (1999) of 1.0 GPa or more and 4.0 GPa or less. [2] The polylactic acid film according to [1], wherein the glass transition temperature of the layer (I), calculated from the peak temperature of the loss tangent (tanδ) measured in accordance with JIS K7244-4 (1999), is 65°C or less. [3] The polylactic acid-based film according to [1] or [2], wherein the polylactic acid-based resin (A) contains 0.1 to 60 mol% of D-lactic acid (D-isomer). [4] The polylactic acid film according to any one of [1] to [3], wherein the plasticizer (B) is a diester compound. [5] A polylactic acid film according to any one of [1] to [4], wherein the plasticizer (B) is a diester compound obtained by reacting an aromatic alcohol and / or a diethylene glycol monoalkyl ether with a dicarboxylic acid having 2 to 6 carbon atoms. [6] The polylactic acid film according to any one of [1] to [5], wherein the content of the plasticizer (B) in the resin composition is 4% by mass or more. [7] The polylactic acid film according to any one of [1] to [6], wherein the polylactic acid film is a polylactic acid film having at least two layers, layer (I) and layer (II), and layer (II) is made of a resin composition containing a thermoplastic resin other than the polylactic acid resin (A) and a plasticizer (B), and the content of the plasticizer (B) relative to the resin composition is less than 4% by mass. [8] The polylactic acid film according to [7], wherein the polylactic acid film has at least three layers in the order of layer (II) / layer (I) / layer (II). [9] A food packaging film using a polylactic acid-based film as described in any of [1] to [8].

[10] [9] A film for packaging fresh produce using the food packaging film described above. [Effects of the Invention]

[0012] The polylactic acid-based film of the present invention, by incorporating a specific amount of plasticizer, is obtained to have a predetermined storage modulus. It possesses flexibility similar to that of a polyolefin-based film and can be suitably used as a packaging film for food and the like. [Modes for carrying out the invention]

[0013] The following describes, as an example of embodiments of the present invention, a polylactic acid-based film, a food packaging film, and a fruit and vegetable packaging film of the present invention. However, the scope of the present invention is not limited to the embodiments described below.

[0014] In this specification, "main component" refers to a component that accounts for 50% or more by mass when the total of the components constituting each layer is 100% by mass, preferably 60% or more by mass, more preferably 70% or more by mass, and particularly preferably 80% or more by mass. Furthermore, when written as "X~Y" (where X and Y are any numbers), unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as "preferably greater than X" and "preferably less than Y." Furthermore, "X and / or Y (where X and Y are any configuration)" means at least one of X and Y, and can mean X only, Y only, or X and Y. In addition, the upper and lower limits of numerical ranges in this specification shall be included within the equivalent range of the present invention even if they fall slightly outside the numerical range specified by the invention, as long as they have the same effects as those within the numerical range specified by the invention. In this specification, the longitudinal direction (MD) of the film refers to the flow direction in the film manufacturing process, and the transverse direction (TD) refers to the orthogonal direction thereto.

[0015] <Polylactic acid-based film> The polylactic acid-based film of the present invention (hereinafter also referred to as "the present film") is a polylactic acid-based film having a layer (I) composed of a resin composition containing a polylactic acid-based resin (A) and a specific amount of a plasticizer (B), wherein the storage elastic modulus (E') at 22°C measured for the layer (I) in accordance with JIS K7244-4 (1999) is 4.0 GPa or less. Hereinafter, each component contained in the resin composition forming the layer (I) will be described.

[0016] [Polylactic acid-based resin (A)] The polylactic acid-based resin (A) is a thermoplastic resin obtained by polymerizing lactic acid. Examples thereof include poly(L-lactic acid) having a structural unit of L-lactic acid, poly(D-lactic acid) having a structural unit of D-lactic acid, poly(DL-lactic acid) having structural units of L-lactic acid and D-lactic acid, or a mixed resin thereof, etc., which are homopolymers of lactic acid, and copolymers of lactic acid as a main monomer component and an aliphatic diol and / or an aliphatic dicarboxylic acid. Here, the main monomer component refers to a monomer component that occupies 50% by mass or more and 100% by mass or less in the resin. These may be used alone or in combination of two or more. Among them, a homopolymer of lactic acid is preferable, and poly(DL-lactic acid) is particularly preferable from the viewpoint of being able to adjust crystallinity.

[0017] Examples of the aliphatic diol include bifunctional aliphatic hydroxycarboxylic acids such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy n-butyric acid, 2-hydroxy 3,3-dimethylbutyric acid, 2-hydroxy 3-methylbutyric acid, 2-methyl lactic acid, 2-hydroxycaproic acid, etc., lactones such as caprolactone, butyrolactone, valerolactone, etc., ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, etc. These may be used alone or in combination of two or more.

[0018] Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanediic acid. These may be used individually or in combination of two or more.

[0019] Furthermore, polylactic acid resin (A) may be modified to include aromatic dicarboxylic acids such as terephthalic acid or aromatic diols such as ethylene oxide adducts of bisphenol A as copolymer components, in a range that does not impair the essential properties of polylactic acid resin (A) (for example, less than 10% by mass of polylactic acid resin (A)), in order to improve heat resistance and other properties. Furthermore, as copolymerization components, small amounts of chain extenders, such as diisocyanate compounds, epoxy compounds, or acid anhydrides, may be added to increase the molecular weight.

[0020] Polylactic acid resin (A) can be polymerized using methods such as condensation polymerization, ring-opening polymerization, or other known polymerization methods. For example, in condensation polymerization, polylactic acid resin (A) with any composition can be obtained by directly dehydrating and condensing L-lactic acid or D-lactic acid, or a mixture thereof. Furthermore, in the ring-opening polymerization method, a polylactic acid-based resin (A) can be obtained using lactide, a cyclic dimer of lactic acid, with a selected catalyst, while using polymerization regulators as needed.

[0021] Examples of the lactides include L-lactide, which is a dimer of L-lactic acid; D-lactide, which is a dimer of D-lactic acid; and DL-lactide, which consists of L-lactic acid and D-lactic acid. In the ring-opening polymerization method, a polylactic acid-based resin (A) having any desired composition and crystallinity can be obtained by mixing and polymerizing these as needed.

[0022] The polylactic acid resin (A) obtained in this manner preferably has a D-lactic acid (D-isomer) content of 0.1 to 60 mol%, more preferably 0.2 to 40 mol%, and particularly preferably 0.3 to 20 mol%. By keeping the D-lactic acid content within the above range, it tends to be easier to suppress the decrease in molecular weight due to hydrolysis.

[0023] The heat of fusion (ΔHm) of the polylactic acid resin (A) is preferably 80 J / g or less, and more preferably 60 J / g or less. The lower limit is usually 0 J / g. By keeping the heat of fusion within the above range, there is a tendency for the film to have low crystallinity and not be rigid.

[0024] The mass-average molecular weight of the polylactic acid resin (A) is preferably 50,000 to 400,000, and more preferably 100,000 to 250,000. If the mass-average molecular weight of the polylactic acid resin (A) is above the lower limit of the above range, desirable practical physical properties tend to be obtained, and if it is below the upper limit, the melt viscosity does not become too high, and good moldability tends to be obtained.

[0025] The polylactic acid resin (A) is preferably included as the main component of the resin composition. Including it as the main component of the resin composition that forms layer (I) tends to make it easier to impart the appropriate heat resistance and rigidity of the polylactic acid resin (A) to the film.

[0026] Typical examples of polylactic acid resins (A) that are preferably used in the present invention include the "REVODE series" manufactured by Marine Biological Materials Co., Ltd. and the "NW series" manufactured by NatureWorks, Inc., which are commercially available.

[0027] [Plasticizer (B)] The plasticizer (B) is not particularly limited as long as it is a plasticizer used in thermoplastic resins, and examples include phthalate ester compounds, aliphatic monobasic acid ester compounds, aliphatic dibasic acid ester compounds, trimellitic acid ester compounds, polyester compounds, diester compounds, phosphate ester compounds, paraffin compounds, etc. These may be used individually or in combination of two or more. Among these, diester compounds are preferred because they lower the glass transition temperature of the polylactic acid resin (A) and give flexibility to the film.

[0028] [Diester compounds] The diester compound is an ester of an aliphatic polycarboxylic acid and an alcohol and / or ether alcohol, and has a biodegradable aliphatic chain. On the other hand, since the polylactic acid resin (A) is also an aliphatic polyester resin, it has good compatibility with the diester compound, and the diester compound tends not to leach out to the surface of the film. For this reason, the diester compound can be suitably used as a plasticizer for the polylactic acid resin (A).

[0029] Examples of the aliphatic polycarboxylic acid include divalent and trivalent linear aliphatic polycarboxylic acids. The number of carbon atoms in the aliphatic polycarboxylic acid is usually 2 to 20, preferably 4 to 10, and particularly preferably 2 to 6.

[0030] Specifically, examples include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These may be used individually or in combination of two or more. Among these, adipic acid and succinic acid are preferred, with adipic acid being particularly preferred.

[0031] Examples of the alcohol include straight-chain or branched saturated aliphatic alcohols and aromatic alcohols. The number of carbon atoms in the alcohol is usually 1 to 20, preferably 4 to 10.

[0032] Specifically, examples include linear saturated aliphatic alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, pentanol, hexanol, heptanol, and octanol; branched saturated aliphatic alcohols such as 2-methyl-1-propanol and 1,1-dimethyl-1-ethanol; and aromatic alcohols such as phenol, benzyl alcohol, and phenethyl alcohol. These may be used individually or in combination of two or more. Among these, aromatic alcohols are preferred, and benzyl alcohol is particularly preferred.

[0033] Examples of the ether alcohol include ethylene oxide adducts, propylene adducts, butylene adducts, etc., of the alcohol, which typically have 3 to 20 carbon atoms, preferably 3 to 10.

[0034] Specifically, ethylene oxide adducts such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, etc.; propylene glycol Examples include propylene oxide adducts such as ethylene oxide monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monophenyl ether, propylene glycol monobenzyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monophenyl ether, dipropylene glycol monobenzyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monophenyl ether, and tripropylene glycol monobenzyl ether. These may be used individually or in combination of two or more. Among these, ethylene oxide adducts are preferred, diethylene glycol monoalkyl ethers are more preferred, and diethylene glycol monomethyl ethers are particularly preferred.

[0035] The diester compound is preferably a diester compound obtained by reacting an aromatic alcohol and / or a diethylene glycol monoalkyl ether with a C2-C6 dicarboxylic acid, in order to lower the glass transition temperature of the polylactic acid resin (A) and give flexibility to the film, and is particularly preferably a compound obtained by reacting adipic acid with benzyl alcohol and diethylene glycol monomethyl ether.

[0036] The number-average molecular weight of the diester compound is not particularly limited, but generally, the smaller the molecular weight, the greater the plasticizing effect, but the lower the stability, and the greater the possibility of blocking and contamination due to bleed-out to the film surface. For this reason, the number-average molecular weight of the diester compound is usually 200 to 1500, and preferably 300 to 1000.

[0037] Furthermore, the boiling point of the diester compound is usually 200°C or higher, preferably 250°C or higher, and more preferably 270°C or higher. The upper limit is usually 350°C.

[0038] The content of plasticizer (B) in the resin composition is 18% by mass or less, preferably 1 to 17% by mass, more preferably 2 to 16% by mass, and particularly preferably 4 to 15% by mass. By setting the content of plasticizer (B) within the above range, a film is obtained that has a balanced effect between plasticization and elution.

[0039] [Other ingredients] The resin composition may contain additives other than the polylactic acid resin (A), such as other thermoplastic resins, thermoplastic elastomers, inorganic particles, ultraviolet absorbers, light stabilizers, antioxidants, nucleating agents, lubricants, pigments, dyes, etc., to the extent that they do not impair the effects of the present invention. These may be used individually or in combination of two or more. In particular, it is preferable to include other thermoplastic resins because they can produce films with excellent transparency and flexibility.

[0040] The aforementioned other thermoplastic resins are not particularly limited as long as they are thermoplastic resins used for food packaging, but examples include polyamide resins, polyethylene resins, polypropylene resins, norbornene resins, polyester resins, vinyl alcohol resins, ethylene-vinyl alcohol resins, polystyrene resins, polyacrylic resins, cellulose acylate resins, etc., and at least one functional resin can be selected from among these. Among these, polyester resins and cellulose acylate resins are preferred.

[0041] The polyester resin is preferably a biodegradable polyester resin, and examples include polybutylene succinate resin obtained by polycondensation of 1,4-butanediol and succinic acid, polybutylene succinate adipate resin obtained by polycondensation of 1,4-butanediol, succinic acid and adipic acid, polybutylene adipate terephthalate resin obtained by polycondensation of 1,4-butanediol, adipic acid and terephthalic acid, polyethylene succinate resin obtained by polycondensation of ethylene glycol and succinic acid, polyglycolic acid resin obtained by polycondensation of polyglycolic acid, and 3-hydroxybutyric acid-5-hydroxycaproic acid copolymer obtained by polycondensation of 3-hydroxybutyric acid and 5-hydroxycaproic acid. These may be used individually or in combination of two or more.

[0042] In particular, as the biodegradable polyester resin, at least one selected from the group consisting of polybutylene succinate resin, polybutylene succinate adipate resin, polybutylene adipate terephthalate resin, and polyethylene succinate resin is preferred, with polybutylene succinate resin and polybutylene succinate adipate resin being more preferred, and the combined use of polybutylene succinate resin and polybutylene succinate adipate resin being particularly preferred. Using these biodegradable polyester resins tends to yield films with high transparency and low elastic modulus.

[0043] The content of biodegradable polyester resin in the resin composition is typically 4 to 55% by mass, preferably 6 to 45% by mass, and particularly preferably 8 to 30% by mass. By setting the content of biodegradable polyester resin within the above range, a film with high transparency and low elastic modulus tends to be obtained.

[0044] Furthermore, examples of the cellulose acylate resins include cellulose monoacetate, cellulose diacetate (DAC), cellulose triacetate (TAC), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB). These may be used individually or in combination of two or more. Among these, cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) are preferred from the viewpoint of improving the biodegradation rate of the resin molded article, and cellulose acetate propionate (CAP) is more preferred.

[0045] The content of cellulose acylate resin in the resin composition is usually 1 to 40% by mass, preferably 5 to 35% by mass, and particularly preferably 10 to 25% by mass. By setting the content of cellulose acylate resin within the above range, a film with high transparency and low elastic modulus tends to be obtained.

[0046] Layer (I) is obtained by forming a film from a resin composition containing these components using a method described later.

[0047] The thickness of layer (I) is typically 20 to 500 μm, preferably 30 to 400 μm, and more preferably 40 to 300 μm. Layers (I) with a thickness within the above range tend to exhibit excellent flexibility.

[0048] The storage modulus (E') of layer (I) at 22°C, measured according to JIS K7244-4 (1999), is between 1.0 GPa and 4.0 GPa, preferably between 1.3 GPa and 3.8 GPa, and more preferably between 1.5 GPa and 3.6 GPa. By setting the storage modulus (E') of layer (I) within the above range, a flexible polylactic acid-based film can be obtained, which can be suitably used as a packaging film. The storage modulus (E') is calculated from the dynamic viscoelasticity measured using a viscoelastic spectrometer under the following conditions: vibration frequency of 10 Hz, strain of 0.1%, heating rate of 3°C / min, chuck distance of 1 cm, and measurement temperature of -100 to 200°C.

[0049] Furthermore, the glass transition temperature of layer (I) [resin composition] is preferably 65°C or lower, and more preferably 62°C or lower. The lower limit is usually 25°C. By setting the glass transition temperature of layer (I) within the above range, it tends to be possible to obtain a flexible polylactic acid-based film, which can be suitably used as a packaging film. The aforementioned glass transition temperature is calculated from the peak temperature of the loss tangent (tanδ) measured in accordance with JIS K7244-4 (1999).

[0050] This film may be a single-layer film consisting only of layer (I), a multilayer film in which multiple layers (I) are laminated, or a multilayer film in which layer (I) and layer (II) made of a resin composition containing another thermoplastic resin are laminated.

[0051] Other thermoplastic resins included in the resin composition forming layer (II) are not particularly limited as long as they are thermoplastic resins used for food packaging, but examples include polyolefin resins, polyamide resins, polyethylene resins, polypropylene resins, norbornene resins, polyester resins, vinyl alcohol resins, ethylene-vinyl alcohol resins, polystyrene resins, polyacrylic resins, etc., and at least one thermoplastic resin can be selected from among these.

[0052] The resin composition forming the layer (II) may contain additives such as thermoplastic elastomers, inorganic particles, ultraviolet absorbers, light stabilizers, antioxidants, plasticizers (B), nucleating agents, lubricants, pigments, and dyes.

[0053] If the resin composition forming the layer (II) contains a plasticizer (B), its content is preferably less than 4% by mass, and particularly preferably less than 3% by mass, relative to the resin composition. The lower limit is usually 0.1% by mass.

[0054] Layer (II) is obtained by forming a film of the resin composition containing the other thermoplastic resins described above using a method described later.

[0055] If this film has, for example, layer (I) and layer (II), in addition to a two-layer configuration of layer (I) / layer (II), it can also employ a two-type three-layer configuration such as layer (I) / layer (II) / layer (I), or layer (II) / layer (I) / layer (II). Furthermore, if the film has multiple layers, for example, layer (I) and layers (II) that contain different thermoplastic resins (hereinafter referred to as layer (II-1), layer (II-2), etc.), then configurations such as a 3-layer configuration of layer (I) / layer (II-1) / layer (II-2), a 3-type 5-layer configuration of layer (II-2) / layer (II-1) / layer (I) / layer (II-1) / layer (II-2), a 4-layer configuration of layer (I) / layer (II-1) / layer (II-2) / layer (II-3), or a 4-type 7-layer configuration of layer (II-3) / layer (II-2) / layer (II-1) / layer (I) / layer (II-1) / layer (II-2) / layer (II-3) can be adopted. In this film, there are no restrictions on the number of layers, the order of the layers, or the type and number of functional layers or other layers, but it is preferable to have at least three layers in the order of layer (II) / layer (I) / layer (II).

[0056] [Method of manufacturing this film] The method for manufacturing this film is not particularly limited and can be manufactured by known methods. For example, a resin composition can be obtained by melting it using an extruder, extruding it from a die into a film, and then cooling and solidifying it using a cooling roll, air cooling, or water cooling.

[0057] For example, if the film is a single-layer film consisting of only layer (I), the components constituting the film are mixed and kneaded, and then the resin composition is prepared by uniformly mixing each component using an extruder such as a single-screw extruder, an asymmetric twin-screw extruder, or a coaxial twin-screw extruder. Alternatively, before mixing each component in the extruder, they may be mixed beforehand in a mixer such as a tumbler mixer, mixing roll, Banbury mixer, ribbon blender, or super mixer, and then fed into the extruder. Alternatively, a strand die may be connected to the tip of another kneader, and the mixture may be pelletized by methods such as strand cutting or die cutting before the resulting pellets are fed into the extruder. Furthermore, some components may be pelletized first, and then the resulting pellets and the remaining components may be fed together into the extruder.

[0058] If the film is a laminated film having layer (II), the resin composition of layer (II) may be prepared according to the method for layer (I).

[0059] Subsequently, the resin composition melted by the extruder is formed into a film by connecting a die such as a T-die to the tip of the extruder, and then cooled and solidified using a cooling roll.

[0060] The extrusion temperature is preferably around 160 to 240°C, and more preferably 170 to 220°C. Optimizing the extrusion temperature and shear conditions is effective in achieving desired values ​​for various physical and mechanical properties.

[0061] If this film is a laminated film, it can be laminated by co-extrusion, extrusion lamination, heat lamination, dry lamination, etc. For example, a laminated film can be manufactured by using multiple extruders to combine and co-extrude each resin composition through a feed block and a multi-manifold die.

[0062] This film may be an unstretched film or a stretched film stretched in at least one direction, but stretching in at least one direction is preferable because it imparts mechanical strength and makes it a durable packaging film.

[0063] There are no particular restrictions on the method of stretching this film, but it is stretched in at least one direction, such as by roll stretching in the direction of film flow (hereinafter sometimes referred to as the longitudinal direction or MD) or by tenter stretching in a direction perpendicular to the direction of film flow (hereinafter sometimes referred to as the transverse direction or TD). Alternatively, the unstretched film may be cut and stretched in at least one direction using a batch-type stretcher.

[0064] Furthermore, when this film is biaxially stretched in the longitudinal and transverse directions, it may be stretched longitudinally first, then transversely, or transversely first, then longitudinally. Also, if it has been stretched longitudinally and transversely, it may be stretched two or more times in the same direction. Furthermore, it may be stretched longitudinally, then transversely, and then longitudinally again. In addition, it may be stretched simultaneously longitudinally and transversely using a simultaneous biaxial stretching machine.

[0065] The stretching temperature is typically 60 to 95°C, preferably 62 to 90°C, and more preferably 65 to 85°C. If the stretching temperature is above the lower limit of the applicable range, it tends to prevent the film from breaking during stretching. On the other hand, if the stretching temperature is below the upper limit of the applicable range, the polylactic acid resin (A) does not crystallize during stretching, allowing for sufficient stretching and making film breakage less likely.

[0066] The film is preferably stretched at an area stretching ratio of 20 times or less, more preferably 16 times or less, and particularly preferably 9 times or less. The lower limit is not particularly limited, but is usually 2 times or more. By setting the area stretching ratio within the above range, it tends to become easier to impart appropriate rigidity and strength to the film.

[0067] Furthermore, after the stretching process, it is preferable to perform heat treatment (heat setting) while the stretched film is held in place to suppress thermal shrinkage. Typically, in the roll method, heat treatment is performed by bringing the stretched film into contact with a heated roll, while in the tenter method, heat treatment is performed while the film is held in place with clips. The heat treatment temperature depends on the compounding ratio and type of resin used, but it is preferable to set it in the range of 100°C to 150°C. By performing such heat treatment, it is possible to impart better heat resistance and mechanical properties.

[0068] The surface of this film may have a coating layer coated with an anti-fogging agent, an antistatic agent, a mold release agent, etc. The coating layer can be formed by coating the film surface using a known method after extrusion from a die into a film shape, cooling and solidifying with a cooling roll, air cooling, or water cooling, or after stretching the film. Alternatively, the film surface may be subjected to corona treatment using a known method before forming the coating layer.

[0069] The thickness of this film is typically 20 to 500 μm, preferably 30 to 400 μm, and more preferably 40 to 300 μm. When the thickness of this film is within the above range, it tends to have excellent flexibility.

[0070] Furthermore, if the film is a laminated film having layer (I) and layer (II), the ratio of the thickness of layer (I) to the thickness of the film is usually 50% or less, preferably 40% or less. The lower limit is usually 10%.

[0071] The haze of this film, as measured according to JIS K7136 (2000), is typically 60% or less, preferably 40% or less, and more preferably 20% or less. The lower limit is typically 0%. By setting the haze of this film within the above range, a highly transparent polylactic acid-based film can be produced, which tends to be suitable for use as a packaging film.

[0072] The storage modulus (E') of this film at 22°C, measured according to JIS K7244-4 (1999), is typically between 1.0 GPa and 4.0 GPa, preferably between 1.3 GPa and 3.8 GPa, and more preferably between 1.5 GPa and 3.6 GPa. By setting the storage modulus (E') of this film within the above range, a flexible polylactic acid-based film can be obtained, making it suitable for use as a packaging film.

[0073] Furthermore, the elution rate of the plasticizer (B) in this film is typically less than 4.0% by mass, preferably less than 3.0% by mass, and more preferably less than 1.5% by mass. The aforementioned elution rate can be measured under the measurement conditions described in the examples below.

[0074] This film has an oxygen permeability of 300 cc / m² as measured according to JIS K7126-2 (2006). 2 Preferably, it should be 400cc / m 2 It is more preferable that the current rate is 500cc / m² or higher. 2 A rate of / day / atm or higher is preferable. The upper limit is usually 2000cc / m 2 While a value of / day / atm or less is acceptable, a higher value is preferable, especially when used for packaging food products such as fresh produce.

[0075] This film has a water vapor transmission rate of 10 g / m², as measured according to JIS K7129-2 (2008). 2 Preferably 30 g / m² or more per day. 2 It is more preferable that it be 50 g / m² or more per day. 2 A value of / day / atm or higher is preferable. The upper limit is usually 500g / m². 2 While the value should be less than / day, a larger value is preferable, especially when used for packaging food products such as fresh produce.

[0076] Because this film is flexible, it can be suitably used as a food packaging film. In particular, because this film has oxygen permeability and water vapor permeability within the aforementioned ranges, it can be suitably used as a fruit and vegetable packaging film for packaging fruits and vegetables. Fruit and vegetables continue to respire even after being harvested, and it is known that during storage, distribution, or preservation after harvest, the fruits and vegetables consume energy through their own respiration, causing deterioration of freshness. Therefore, this film, which has appropriate oxygen permeability and water vapor permeability, is suitable. Therefore, it is particularly preferable that the oxygen permeability measured according to JIS K7126-2 (2006) and the water vapor permeability measured according to JIS K7129-2 (2008) of the film of the present invention are both within the above range. [Examples]

[0077] The present invention will be specifically described below with reference to examples. However, the present invention is not limited in any way by the following examples.

[0078] The raw materials used in each example and comparative example are as follows. In the examples, the longitudinal direction (MD) of the film refers to the flow direction in the film manufacturing process, and the transverse direction (TD) refers to the direction perpendicular to it. Furthermore, the storage modulus and glass transition temperature, described later, were measured in the longitudinal direction (MD) of the film.

[0079] <Polylactic acid resin (A)> A1: D-lactic acid content = 0.9 mol%, L-lactic acid content = 99.1 mol%, mass-average molecular weight = 190,000, ΔHm = 33.5 J / g (manufactured by Marine Biological Materials Co., Ltd.) A2: D-lactic acid content = 2.8 mol%, L-lactic acid content = 97.2 mol%, mass-average molecular weight = 200,000, ΔHm = 12.2 J / g (manufactured by Marine Biological Materials Co., Ltd.)

[0080] The heat of fusion (ΔHm) of polylactic acid resin (A) was measured according to JIS K7121 (2012). A sample of approximately 10 mg was shaved off and heated from -70 to 220°C at a rate of 10°C / min using a thermal analyzer (PerkinElmer "DSC-7"). The heat of fusion (ΔHm) was then read from the resulting thermogram.

[0081] <Plasticizer (B)> B1: A diester compound formed by the reaction of benzyl alcohol, diethylene glycol monomethyl ether, and adipic acid; boiling point 293°C (DAIFATTY-101, manufactured by Daihachi Chemical Industry Co., Ltd.)

[0082] [Examples 1-3, Comparative Examples 1-2] Each raw material was prepared in the proportions shown in Table 1 below. These raw materials were placed in a laboplast mill (Toyo Seiki Seisakusho Co., Ltd. "4C150") and melt-kneaded at 200°C, 60 rpm, for 5 minutes to obtain a resin composition. The obtained resin composition was press-molded at 200°C using a heated press (Imoto Seisakusho Co., Ltd. "IMC-18DA type") to obtain films with a thickness of 100 μm or 48 μm.

[0083] [Examples 4-8, Comparative Example 3] Each raw material was prepared in the proportions shown in Table 1 below. These raw materials were fed into a co-rotating twin-screw extruder (φ25mm), melted and kneaded at 210°C and 120 rpm, and extruded to obtain an unstretched film. The discharge rate of molten resin from the extruder and the line speed were adjusted so that the thickness of the unstretched film averaged 350 μm. The unstretched film obtained thereafter was sequentially stretched to 2.7 times its MD ratio and 2.7 times its TD ratio using a biaxial stretcher (manufactured by Island Industries Co., Ltd.) at a temperature of 70°C, and then heat-treated in a heat treatment oven at a temperature of 130°C to obtain a stretched film. The stretched area ratio of the obtained stretched film was 7.29 times, and the film thickness was 48 μm.

[0084] [Reference example] As a reference example, a commercially available stretched polypropylene film (film thickness 50 μm) was prepared.

[0085] The polylactic acid-based films obtained from Examples 1-8 and Comparative Examples 1-3, as well as the stretched polypropylene film from Reference Example 1, were used for the following evaluations. The results are shown in Table 1 below.

[0086] [Storage modulus] The storage modulus (E') of the polylactic acid-based films of Examples 1-8 and Comparative Examples 1-3, and the stretched polypropylene film of Reference Example 1, was calculated by measuring dynamic viscoelasticity in accordance with JIS K7244-4 (1999) using a viscoelastic spectrometer (IT Measurement Co., Ltd. "DVA-200") under the conditions of a vibration frequency of 10 Hz, strain of 0.1%, heating rate of 3°C / min, and chuck spacing of 1 cm, within a measurement temperature range of -100 to 200°C. The obtained storage modulus (E') was evaluated according to the following criteria. (Evaluation Criteria) ◎: 1.0 GPa or higher, 3.0 GPa or lower ○: Over 3.0 GPa and 4.0 GPa or less ×: Less than 1.0 GPa or greater than 4.0 GPa

[0087] [Hayes] The haze was measured for the polylactic acid-based films of Examples 1-8 and Comparative Examples 1-3, and the stretched polypropylene film of Reference Example 1, in accordance with JIS K7136 (2000).

[0088] [Glass transition temperature] The glass transition temperatures of the polylactic acid-based films of Examples 1-8 and Comparative Examples 1-3, and the stretched polypropylene film of Reference Example 1, were calculated from the peak temperature of the loss tangent (tanδ) measured using a viscoelastic spectrometer (model number: "DVA-200", manufactured by IT Keisoku Co., Ltd.) in accordance with JIS K7244-4 (1999).

[0089] [Dissolution test] Test specimens measuring 10 cm x 15 cm were cut from the polylactic acid-based films of Examples 1-3, Comparative Examples 1 and 2, and the stretched polypropylene film of Reference Example 1, and aged for 24 hours in a constant temperature and humidity environment of 60°C and 70% RH. After that, the specimens were wiped with ethanol, and the elution rate of the plasticizer was calculated by measuring the mass before and after wiping, and evaluated according to the following criteria. Dissolution rate (mass%) = (mass before wiping - mass after wiping) / mass before wiping × 100 (Evaluation Criteria) ◎: Less than 1.5% by mass ○: 1.5% by mass or more and less than 3.0% by mass △: 3.0% by mass or more and less than 4.0% by mass ×: 4.0% by mass or more

[0090] [Oxygen permeability, water vapor permeability] The oxygen permeability of the polylactic acid-based films of Example 6 and Comparative Example 2, and the stretched polypropylene film of Reference Example 1 was measured in accordance with JIS K7126-2 (2006). In addition, the water vapor permeability of the polylactic acid-based films of Examples 4-8, Comparative Examples 2 and 3, and the stretched polypropylene film of Reference Example 1 was measured in accordance with JIS K7129-2 (2008).

[0091] [Table 1]

[0092] The results in Table 1 show that the polylactic acid-based films of Examples 1-8 had low storage modulus and flexibility equivalent to that of stretched polypropylene films. On the other hand, the film of Comparative Example 1 had a large amount of plasticizer (B) added, making it too flexible and difficult to handle, and there was also significant plasticizer leaching, which posed a hygiene problem. The films of Comparative Examples 2 and 3, which consisted only of polylactic acid-based resin, had high glass transition temperatures and high storage modulus. As a result, they were highly rigid and lacked flexibility. Furthermore, based on the oxygen permeability and water vapor permeability results of the polylactic acid film in Example 6, it can be said that the polylactic acid films of Examples 1 to 8 have good oxygen permeability and water vapor permeability for use as food packaging and fruit and vegetable packaging films. [Industrial applicability]

[0093] This film is highly transparent and flexible, and possesses appropriate oxygen and water vapor permeability, making it suitable for use as a food packaging film, and particularly useful as a film for packaging fresh produce.

Claims

1. A polylactic acid film having a layer (I) made of a resin composition containing only a polylactic acid resin (A) and a plasticizer (B), The polylactic acid resin (A) contains 0.1 to 2.8 mol% of D-lactic acid (D-isomer). The plasticizer (B) is a diester compound obtained by the reaction of an aromatic alcohol and a diethylene glycol monoalkyl ether with a dicarboxylic acid having 2 to 6 carbon atoms. The content of the plasticizer (B) in the resin composition is 10% by mass or more and 15% by mass or less. A polylactic acid film wherein the aforementioned layer (I) has a storage modulus (E') at 22°C measured according to JIS K7244-4 (1999) of 1.0 GPa or more and 4.0 GPa or less.

2. The polylactic acid film according to claim 1, wherein the glass transition temperature of the layer (I), calculated from the peak temperature of the loss tangent (tanδ) measured in accordance with JIS K7244-4 (1999), is 65°C or less.

3. The polylactic acid film according to claim 1 or 2, wherein the polylactic acid film is a polylactic acid film having at least two layers, layer (I) and layer (II), and layer (II) is made of a resin composition containing a thermoplastic resin other than the polylactic acid resin (A) and a plasticizer (B), and the content of the plasticizer (B) in relation to the resin composition is less than 4% by mass.

4. The polylactic acid film according to claim 3, wherein the polylactic acid film has at least three layers in the order of layer (II) / layer (I) / layer (II).

5. A food packaging film using a polylactic acid-based film according to any one of claims 1 to 4.

6. A film for packaging fresh produce using the food packaging film described in claim 5.

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