Film

Abstract

A film according to the present invention contains a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), wherein the polylactic acid resin (B) has a melting point peak with a peak temperature of less than 170°C when subjected to a differential scanning calorimetric analysis. The polylactic acid resin (B) content is preferably 10-60 wt% with respect to the total weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B).

Description

film

[0001] The present invention relates to a film containing a poly(3-hydroxyalkanoate)-based resin.

[0002] In recent years, the separate collection and composting of food waste has been promoted, particularly in Europe, and there is a demand for plastic products that can be composted together with food waste. Furthermore, there are hopes for marine-degradable plastics to solve the problem of marine pollution caused by plastics.

[0003] As a plastic material having such compost-degradability and marine-degradability, poly(3-hydroxyalkanoate) resins, typified by poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), have attracted attention.

[0004]

[0003] Meanwhile, a method of stretching a film is known as a technique for producing a thin, high-strength film. For example, to produce a stretched film from a general-purpose resin such as polypropylene, a molten resin is cooled and solidified using a cast roll to form a raw sheet, and the raw sheet is then preheated to a temperature at which it can be stretched, and then stretched, thereby enabling continuous production of a stretched film with good productivity.

[0005] However, poly(3-hydroxyalkanoate) resins are known to be difficult to stretch due to their properties, and therefore various techniques have been investigated for producing stretched films containing poly(3-hydroxyalkanoate) resins with good productivity.

[0006] For example, Patent Document 1 describes a method for efficiently producing a biaxially stretched film by melting a film raw material containing a poly(3-hydroxybutyrate) resin in an extruder, forming the film into a film, and then continuously stretching the film in both the MD and TD directions at a stretching ratio of 1.1 or more.

[0007] Furthermore, Patent Document 2 describes a method for producing a stretched film by melting a film raw material containing a poly(3-hydroxybutyrate) resin, extruding it onto a casting roll, peeling the film from the casting roll under conditions where the film temperature is 0 to 50° C., and then stretching the film in the MD direction under conditions where the film temperature is 10 to 65° C. This method controls the crystallinity of the poly(3-hydroxybutyrate) resin to a relatively low level by controlling the film temperature to a relatively low temperature, thereby realizing stretching at a high ratio.

[0008] JP 2022-62759 A JP 2023-73820 A

[0009] According to the method described in Patent Document 1, a biaxially stretched film containing a poly(3-hydroxybutyrate)-based resin can be produced, but the stretching ratio achieved in the examples was limited to about 1.5 to 1.6 times.

[0010] Furthermore, according to the method described in Patent Document 2, a high stretch ratio is achieved by controlling the temperature conditions during the production of the stretched film, but the film temperature during production needs to be controlled to a relatively low temperature around room temperature, and it is difficult to stabilize the production environment in such a temperature range, which makes it difficult to stably carry out continuous production of the stretched film.

[0011] As described above, Patent Documents 1 and 2 describe stretching a film containing a poly(3-hydroxyalkanoate) resin by controlling the production conditions of the stretched film, but have not fully investigated how to improve stretchability by changing the composition of the film raw material containing the poly(3-hydroxyalkanoate) resin.

[0012] In view of the above-mentioned current situation, an object of the present invention is to provide a poly(3-hydroxyalkanoate) resin-containing film having improved stretchability.

[0013] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors discovered that by blending a polylactic acid-based resin exhibiting specific physical properties with a poly(3-hydroxyalkanoate)-based resin to form a film, the stretchability of the film can be significantly improved, and thus completed the present invention.

[0014] That is, the present invention relates to a film containing a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), wherein the polylactic acid resin (B) has a melting point peak in differential scanning calorimetry analysis that has a peak temperature of less than 170° C. The present invention also relates to a laminate comprising a film and a layer containing a poly(3-hydroxyalkanoate) resin (C) laminated on at least one surface of the film. The present invention further relates to a method for producing a film comprising a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), wherein the polylactic acid resin (B) has a melting point peak whose peak temperature in differential scanning calorimetry is less than 170°C, the method comprising a step of stretching the film in an MD direction and / or a TD direction, wherein the film temperature in the stretching treatment is within a range of Tg - 25°C or more and Tg + 50°C or less, where Tg represents the glass transition temperature (°C) of the polylactic acid resin (B).

[0015] According to the present invention, it is possible to provide a poly(3-hydroxyalkanoate)-based resin-containing film with improved stretchability. According to the present invention, stretchability can be improved by adjusting the composition of the film raw materials. Therefore, there is no need to employ the specific temperature conditions described in Patent Document 2, and film stretching can be carried out even under temperature conditions that are easier to control and stabilize than the temperature conditions described in Patent Document 2. Therefore, it is possible to continuously and stably stretch a poly(3-hydroxyalkanoate)-based resin-containing film. As a result, the quality of the stretched film can be stabilized, and in particular, long stretched films can be stably produced. Furthermore, a high stretching ratio can be achieved. According to a preferred embodiment of the present invention, a uniaxially stretched film stretched in the MD direction or a biaxially stretched film stretched in both the MD and TD directions can be produced, and a high stretching ratio can be achieved in each direction.

[0016] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to the following embodiment. The present embodiment relates to a film containing a poly(3-hydroxyalkanoate)-based resin (A) and a polylactic acid-based resin (B).

[0017] [Poly(3-hydroxyalkanoate)-based resin (A)] The poly(3-hydroxyalkanoate) resin (A) may be a single poly(3-hydroxyalkanoate)-based resin or a mixture of two or more poly(3-hydroxyalkanoate)-based resins. However, in order to easily achieve both film strength and stretchability, a mixture of at least two poly(3-hydroxyalkanoate)-based resins that differ from each other in the type of constituent monomer and / or the content ratio of the constituent monomer is preferred.

[0018] The poly(3-hydroxyalkanoate) resin (A) is preferably a polymer having a 3-hydroxyalkanoate unit, specifically a polymer containing a unit represented by the following general formula (1): [—CHR—CH ２ -CO-O-] (1)

[0019] In the general formula (1), R is Cｐ H ２ｐ＋１ where p is an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. p is preferably an integer of 1 to 10, and more preferably an integer of 1 to 8.

[0020] As the poly(3-hydroxyalkanoate) resin (A), a poly(3-hydroxyalkanoate) resin produced by a microorganism is particularly preferred. In the poly(3-hydroxyalkanoate) resin produced by a microorganism, all of the 3-hydroxyalkanoate units are contained as (R)-3-hydroxyalkanoate units.

[0021] The poly(3-hydroxyalkanoate) resin (A) preferably contains 3-hydroxyalkanoate units (particularly units represented by general formula (1)) in an amount of 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of the total structural units. The poly(3-hydroxyalkanoate) resin (A) may contain only one or more types of 3-hydroxyalkanoate units as structural units of the polymer, or may contain one or more types of 3-hydroxyalkanoate units as well as other units (e.g., 4-hydroxyalkanoate units).

[0022] The poly(3-hydroxyalkanoate) resin (A) is preferably a homopolymer or copolymer containing 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units (hereinafter, both polymers are collectively referred to as "poly(3-hydroxybutyrate) resin"). In particular, it is preferable that all of the 3-hydroxybutyrate units are (R)-3-hydroxybutyrate units. Furthermore, the poly(3-hydroxyalkanoate) resin (A) preferably contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0023] Specific examples of poly(3-hydroxybutyrate)-based resins include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), Examples of such polyhydroxybutyrate include poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB). In particular, from the viewpoints of film stretchability and mechanical properties, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred.

[0024] Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred from the viewpoints that changing the composition ratio of the repeating units can change the melting point, degree of crystallinity, and physical properties such as Young's modulus and heat resistance, making it possible to impart physical properties between those of polypropylene and polyethylene, and that it is easy to produce industrially and is a physically useful plastic. In particular, among poly(3-hydroxybutyrate)-based resins that tend to be thermally decomposed when heated to 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that it can lower the melting point and enable molding and processing at low temperatures.

[0025] Commercially available poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) products include Kaneka Biodegradable Polymer Green Planet (registered trademark) manufactured by Kaneka Corporation.

[0026] When the poly(3-hydroxyalkanoate) resin (A) contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content ratio of the 3-hydroxybutyrate units and other hydroxyalkanoate units to all monomer units constituting the poly(3-hydroxyalkanoate) resin (A) is preferably 3-hydroxybutyrate units / other hydroxyalkanoate units=99 / 1 to 80 / 20 (mol % / mol %), more preferably 97 / 3 to 82 / 18 (mol % / mol %), and even more preferably 95 / 5 to 85 / 15 (mol % / mol %), from the viewpoint of achieving both strength and stretchability of the film.

[0027] The average content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate) resin (A) can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of WO 2013 / 147139. The average content ratio means the molar ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate) resin (A), and when the poly(3-hydroxyalkanoate) resin (A) is a mixture of two or more poly(3-hydroxyalkanoate) resins, it means the molar ratio of each monomer unit contained in the entire mixture.

[0028] As described above, the poly(3-hydroxyalkanoate) resin (A) may be a mixture of at least two poly(3-hydroxyalkanoate) resins that differ from each other in the types and / or content ratios of the constituent monomers. In this case, at least one highly crystalline poly(3-hydroxyalkanoate) resin and at least one lowly crystalline poly(3-hydroxyalkanoate) resin can be used in combination.

[0029] Generally, highly crystalline poly(3-hydroxyalkanoate) resins have excellent productivity but poor mechanical strength, while low-crystalline poly(3-hydroxyalkanoate) resins have poor productivity but excellent mechanical properties. By using both resins in combination, the strength and productivity of the film can be further improved.

[0030] The content of 3-hydroxybutyrate units in the highly crystalline poly(3-hydroxyalkanoate) resin is preferably higher than the average content of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin (A). On the other hand, the content of 3-hydroxybutyrate units in the low crystalline poly(3-hydroxyalkanoate) resin is preferably lower than the average content of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin (A).

[0031] When the poly(3-hydroxyalkanoate) resin (A) is a mixture of at least two types of poly(3-hydroxyalkanoate) resins, the resin (A) preferably contains the following copolymer (A-1) and copolymer (A-2). This embodiment makes it easy to achieve both strength and stretchability of the film. Copolymer (A-1): A copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of which is 24 mol % or more. Copolymer (A-2): A copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of which is 1 mol % or more and 9 mol % or less.

[0032] In copolymer (A-1), the content of other hydroxyalkanoate units is preferably 24 to 99 mol%, more preferably 24 to 50 mol%, even more preferably 24 to 35 mol%, and particularly preferably 24 to 30 mol%. In copolymer (A-2), the content of other hydroxyalkanoate units is preferably 2 to 8 mol%, more preferably 2 to 7 mol%.

[0033] As the copolymer (A-1) and the copolymer (A-2), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred.

[0034] When the resin (A) contains the copolymer (A-1) and the copolymer (A-2), the weight ratio (A-1 / A-2) of the copolymer (A-1) to the copolymer (A-2) is preferably 10 / 90 to 50 / 50, more preferably 20 / 80 to 40 / 60, and even more preferably 25 / 75 to 35 / 65, from the viewpoint of achieving both strength and stretchability of the film.

[0035] Copolymer (A-2) may be a mixture of at least two types of copolymers having different content ratios of constituent monomers. Specifically, it preferably contains the following copolymer (A-2-1) and copolymer (A-2-2). According to this embodiment, it is easier to achieve both strength and stretchability of the film. Copolymer (A-2-1): A copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, in which the content ratio of other hydroxyalkanoate units is 1 mol % or more and less than 4 mol %. Copolymer (A-2-2): A copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, in which the content ratio of other hydroxyalkanoate units is 4 mol % or more and 9 mol % or less.

[0036] In the copolymer (A-2-1), the content of the other hydroxyalkanoate units is preferably 1 to 3 mol %, more preferably 2 to 3 mol %, and in the copolymer (A-2-2), the content of the other hydroxyalkanoate units is preferably 5 to 8 mol %, more preferably 6 to 7 mol %.

[0037] As the copolymers (A-2-1) and (A-2-2), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred, with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) being particularly preferred.

[0038] When the resin (A) contains the copolymer (A-2-2), the weight proportion of the copolymer (A-2-2) in the entire resin (A) is preferably 10 to 90% by weight, more preferably 20 to 70% by weight, even more preferably 25 to 60% by weight, and particularly preferably 30 to 50% by weight, from the viewpoint of achieving both strength and stretchability of the film.

[0039] The method for obtaining a blend of two or more poly(3-hydroxyalkanoate) resins is not particularly limited, and may be a method for obtaining a blend by microbial production or a method for obtaining a blend by chemical synthesis. Alternatively, a blend may be obtained by melt-kneading two or more resins using an extruder, kneader, Banbury mixer, roll, or the like, or by dissolving two or more resins in a solvent, mixing, and drying the resins.

[0040] Resin (A) may be composed of only one type of poly(3-hydroxyalkanoate) resin. In this case, resin (A) is preferably composed of only copolymer (A-2), and particularly preferably composed of only copolymer (A-2-2).

[0041] The weight average molecular weight of the entire poly(3-hydroxyalkanoate) resin (A) is not particularly limited, but from the viewpoint of achieving both strength and stretchability of the film, it is preferably 200,000 to 2,000,000, more preferably 300,000 to 1,500,000, and even more preferably 400,000 to 1,000,000.

[0042] Furthermore, when the poly(3-hydroxyalkanoate) resin (A) is a mixture of two or more poly(3-hydroxyalkanoate) resins, the weight-average molecular weight of each poly(3-hydroxyalkanoate) resin constituting the mixture is not particularly limited. However, from the viewpoint of achieving both film strength and stretchability, the weight-average molecular weight of copolymer (A-1) is preferably 200,000 to 1,000,000, more preferably 220,000 to 800,000, and even more preferably 250,000 to 600,000. On the other hand, from the viewpoint of achieving both film strength and stretchability, the weight-average molecular weight of copolymer (A-2) is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and even more preferably 300,000 to 2,000,000. Furthermore, from the viewpoint of achieving both film strength and stretchability, the weight-average molecular weight of copolymer (A-2-2) is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and even more preferably 300,000 to 2,000,000.

[0043] The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin can be measured in terms of polystyrene using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution. As the column for the gel permeation chromatography, a column appropriate for measuring the weight-average molecular weight may be used.

[0044] The method for producing poly(3-hydroxyalkanoate) resins is not particularly limited, and may be a production method using chemical synthesis or a production method using a microorganism. Among these, a production method using a microorganism is preferred. Known methods can be applied to the production method using a microorganism. For example, known bacteria that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, with regard to P3HB3HH, in order to increase the productivity of P3HB3HH, Alcaligenes eutrophus AC32 strain (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)) or the like into which genes encoding P3HA synthases have been introduced is more preferred, and microbial cells obtained by culturing these microorganisms under appropriate conditions and allowing P3HB3HH to accumulate within the cells can be used. In addition to the above, genetically modified microorganisms into which various poly(3-hydroxyalkanoate) resin synthesis-related genes have been introduced may be used depending on the poly(3-hydroxyalkanoate) resin to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0045] As the poly(3-hydroxyalkanoate) resin (A), an unmodified poly(3-hydroxyalkanoate) resin can be used. However, a resin obtained by modifying an unmodified poly(3-hydroxyalkanoate) resin with a raw material that reacts with the resin, such as a peroxide (hereinafter referred to as a "modifying raw material"), may also be used.

[0046] The modifying raw material is not particularly limited as long as it is a compound that can react with a poly(3-hydroxyalkanoate)-based resin, but organic peroxides are preferably used in terms of ease of handling and ease of controlling the reaction with a poly(3-hydroxyalkanoate)-based resin. Known compounds may be used as the organic compound.

[0047] [Polylactic acid resin (B)] The polylactic acid resin (B) is a polyester containing lactic acid as a constituent monomer. Polylactic acid resins typically have a glass transition temperature of around 60°C, and are difficult to crystallize when rapidly cooled from a molten state, becoming amorphous. Therefore, by incorporating the polylactic acid resin (B), the poly(3-hydroxyalkanoate) resin-containing film becomes more likely to soften, thereby improving its stretchability. The polylactic acid resin (B) is preferably a homopolymer of lactic acid, but may contain trace amounts of other monomers in addition to lactic acid.

[0048] The lactic acid constituting the polylactic acid-based resin (B) may be either the L- or D-form, or may contain both. In the latter case, the ratio of the L- and D-forms is not particularly limited. The polylactic acid-based resin (B) may be any of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin. It may also be a blend of these.

[0049] Examples of the other monomer that may be contained in the polylactic acid-based resin (B) include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, polyfunctional polysaccharides, etc. When the polylactic acid-based resin (B) is a copolymer of lactic acid and other monomers, from the viewpoint of crystallinity, the content of the other monomers is preferably about 0 to 3 mol %, more preferably 0 to 2 mol %, based on the total monomers contained in the polylactic acid-based resin (B).

[0050] The polylactic acid resin (B) used has a melting point peak of less than 170°C in differential scanning calorimetry. By using a polylactic acid resin having such a melting point in combination with the poly(3-hydroxyalkanoate) resin (A), the stretchability of the poly(3-hydroxyalkanoate) resin-containing film can be improved, resulting in a high-quality stretched film that does not break during stretching and has uniform stretching. Furthermore, the film can be continuously and stably stretched even under temperature conditions other than the specific temperature described in Patent Document 2. Furthermore, a high stretch ratio can be achieved.

[0051] In contrast, even if a polylactic acid-based resin having a melting point peak of 170°C or higher or an amorphous polylactic acid-based resin is used in combination with resin (A), the film does not have sufficient stretchability, and breakage or uneven stretching is likely to occur during stretching. Moreover, even if stretching is possible, it is difficult to perform continuous and stable stretching.

[0052] The peak temperature of the melting point peak of the polylactic acid resin (B) (hereinafter also referred to as "melting point peak temperature") is preferably 165° C. or lower, more preferably 160° C. or lower, from the viewpoint of enhancing the stretchability and strength of the film. The lower limit of the peak temperature is preferably 120° C. or higher, more preferably 130° C. or higher, and even more preferably 140° C. or higher, from the viewpoint of enhancing the stretchability of the film.

[0053] The melting point peak temperature refers to the peak top temperature Tm of the crystalline melting peak in a DSC curve obtained by differential scanning calorimetry (DSC measurement). The DSC curve was obtained by precisely weighing about 5 mg of the resin to be measured and heating it from 0°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter.

[0054] The polylactic acid-based resin (B) exhibiting the above-described melting point peak temperature is not particularly limited, and commercially available products can be used. Specific examples include polylactic acid-based resins having an L-isomer purity of lactic acid units of 88% or more and 98% or less.

[0055] From the viewpoint of enhancing the stretchability of the film, the melting peak temperature of the polylactic acid resin (B) is preferably close to the melting peak temperature of the poly(3-hydroxyalkanoate) resin (A). Specifically, the absolute value of the difference between the melting peak temperatures of the polylactic acid resin (B) and the poly(3-hydroxyalkanoate) resin (A) is preferably 40°C or less, more preferably 30°C or less, and even more preferably 20°C or less.

[0056] The melting peak temperature of the poly(3-hydroxyalkanoate) resin (A) is measured in the same manner as the melting peak temperature of the polylactic acid resin (B). When multiple melting peaks appear in the DSC curve measured for the poly(3-hydroxyalkanoate) resin (A), the peak temperature of the melting peak on the highest temperature side is taken as the melting peak temperature of the poly(3-hydroxyalkanoate) resin (A).

[0057] The molecular weight of the polylactic acid resin (B) is not particularly limited and may be set appropriately, but the number average molecular weight is preferably 1,000 to 700,000, and more preferably 10,000 to 300,000.

[0058] The lactic acid raw material for producing the polylactic acid resin (B) is not particularly limited, and examples thereof include L-lactic acid, D-lactic acid, DL-lactic acid, or a mixture thereof, or L-lactide, D-lactide, meso-lactide, or a mixture thereof. Lactic acid obtained by microbial fermentation from renewable plant-derived raw materials such as starch is preferably used. The method for producing the polylactic acid resin (B) is not particularly limited, and known methods such as dehydration condensation polymerization and ring-opening polymerization can be used.

[0059] In the film according to this embodiment, the content of the polylactic acid resin (B) is preferably 5% by weight or more and 60% by weight or less, and more preferably 10% by weight or more and 60% by weight or less, based on the total weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). By blending the polylactic acid resin (B) in such a weight ratio, the stretchability of the poly(3-hydroxyalkanoate) resin-containing film can be improved.

[0060] From the viewpoint of improving stretchability, a higher content of polylactic acid resin (B) is preferable, specifically 15% by weight or more is preferred, and more preferably 20% by weight or more, whereas from the viewpoint of increasing the biodegradability of the film (particularly biodegradability in compost and marine degradability), a lower content of polylactic acid resin (B) is preferable, specifically 50% by weight or less is preferred, more preferably 40% by weight or less, even more preferably 30% by weight or less, even more preferably 25% by weight or less, and particularly preferably 20% by weight or less.

[0061] The film according to this embodiment is a resin film mainly composed of a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B). The total proportion of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B) in the total amount of the film may be 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. It may also be 95% by weight or more, or 98% by weight or more.

[0062] (Other Resins) The film according to this embodiment may contain other resins in addition to the poly(3-hydroxyalkanoate)-based resin (A) and the polylactic acid-based resin (B), provided that the effects of the invention are not impaired. Examples of such other resins include aliphatic polyester-based resins such as polybutylene succinate adipate, polybutylene succinate, and polycaprolactone, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

[0063] The content of the other resin is not particularly limited, but is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 30 parts by weight or less, relative to 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). It may be 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight or more.

[0064] The film according to this embodiment may contain additives that can be used together with the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B), provided that the effects of the invention are not impaired. Examples of such additives include colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin and dextrin, fillers, plasticizers, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding properties improvers. Only one type of additive may be contained, or two or more types may be contained. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use. Crystal nucleating agents, lubricants, fillers, and plasticizers are described in more detail below.

[0065] (Crystal Nucleating Agent) The film according to this embodiment may contain a crystal nucleating agent. Examples of crystal nucleating agents include polyhydric alcohols such as pentaerythritol, galactitol, and mannitol; orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among these, pentaerythritol is preferred because of its particularly excellent effect of promoting the crystallization of the poly(3-hydroxyalkanoate) resin (A). One type of crystal nucleating agent may be used, or two or more types may be used, and the ratio of use can be appropriately adjusted depending on the purpose.

[0066] When a nucleating agent is used, the amount thereof is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B).

[0067] However, the film according to the present embodiment can achieve good productivity even without substantially blending a nucleating agent such as pentaerythritol. "Substantially no nucleating agent" means that the amount of nucleating agent blended is less than 0.1 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). It may also be less than 0.01 parts by weight. In an embodiment in which pentaerythritol is not substantially blended, the problem of contamination of the cast roll surface due to bleed-out of pentaerythritol can be avoided.

[0068] (Lubricant) The film according to this embodiment may contain a lubricant. Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide or erucamide is preferred because of its particularly excellent lubricating effect on the poly(3-hydroxyalkanoate) resin (A). One or more lubricants may be used, and the ratio of use can be adjusted appropriately depending on the purpose.

[0069] When a lubricant is used, the amount thereof is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, relative to 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). The film according to this embodiment preferably contains a lubricant, but does not necessarily need to contain one.

[0070] (Filler) The film according to this embodiment may contain a filler. By including a filler, a stretched film with higher strength can be obtained. The filler may be either an inorganic filler or an organic filler, or both may be used in combination. The inorganic filler is not particularly limited, but examples thereof include silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, and carbon black. Only one type of inorganic filler may be used, or two or more types may be used in combination.

[0071] When the filler is used, its content is not particularly limited, but is preferably 1 to 100 parts by weight, more preferably 3 to 80 parts by weight, even more preferably 5 to 70 parts by weight, and even more preferably 10 to 60 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). However, the film according to this embodiment may be substantially free of filler. "Substantially no filler" means that the amount of filler is less than 1 part by weight per 100 parts by weight of the resin (A) and the resin (B). It may also be less than 0.1 parts by weight.

[0072] (Plasticizer) The film according to this embodiment may contain a plasticizer. Examples of plasticizers include glycerin ester compounds, citrate ester compounds, sebacic ester compounds, adipate ester compounds, polyether ester compounds, benzoate ester compounds, phthalate ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds. Among these, glycerin ester compounds, citrate ester compounds, sebacic ester compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on the poly(3-hydroxyalkanoate) resin (A). Examples of glycerin ester compounds include glycerin diacetomonolaurate. Examples of citrate ester compounds include acetyl tributyl citrate. Examples of sebacic ester compounds include dibutyl sebacate. Examples of dibasic acid ester compounds include benzyl methyl diethylene glycol adipate. One type of plasticizer may be used, or two or more types may be used, and the ratio of use can be adjusted appropriately depending on the purpose.

[0073] When a plasticizer is used, the amount used is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and even more preferably 3 to 10 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). However, the film according to this embodiment may be substantially free of plasticizer. "Substantially free of plasticizer" means that the amount of plasticizer is less than 1 part by weight per 100 parts by weight of the resin (A) and the resin (B). It may also be less than 0.1 part by weight.

[0074] [Film] The film according to the present embodiment may be an unstretched film that has not been subjected to a stretching treatment, or may be a stretched film that has been stretched in the MD direction and / or TD direction after film formation. The term "film" as used herein may include both an unstretched film and a stretched film. From the viewpoint of strength, a stretched film is preferred.

[0075] The thickness of the film (particularly the stretched film) according to this embodiment is preferably 10 to 200 μm, more preferably 15 to 150 μm, and even more preferably 20 to 100 μm, from the viewpoints of uniform thickness, appearance, strength, lightness, and the like of the film.

[0076] The film according to the present embodiment is preferably an industrially produced long film, and more preferably a strip-shaped film wound into a roll. The length of such a film is not particularly limited, but may be, for example, 50 m or more, or 100 m or more. In the present embodiment, such a long film can be continuously and stably produced.

[0077] According to a preferred aspect, the stretched film according to one embodiment can exhibit an elastic modulus of 1500 MPa or more and a breaking strength of 40 MPa or more in at least the MD direction. It may also be a biaxially stretched film exhibiting an elastic modulus of 1500 MPa or more and a breaking strength of 40 MPa or more in both the MD and TD directions. The elastic modulus is preferably 2000 MPa or more, more preferably 2500 MPa or more. The breaking strength is preferably 60 MPa or more, more preferably 70 MPa or more. The elastic modulus and breaking strength are values ​​measured by the methods described in detail in the Examples section.

[0078] [Film Manufacturing Method] Next, an example of a method for manufacturing the film according to the present embodiment will be described, but the present invention is not limited to the following description. First, a film raw material containing the poly(3-hydroxyalkanoate) resin (A), the polylactic acid resin (B), and, if necessary, other components, is melted.

[0079] Although the melting method is not particularly limited, it is preferable to extrude the molten film raw material through a T-die, i.e., to carry out extrusion molding. By extrusion molding, a film with a uniform thickness can be easily produced. In extrusion molding, a single-screw extruder, a twin-screw extruder, etc. can be appropriately used.

[0080] The conditions for melting the film raw materials may be any conditions under which the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B) melt, and the temperature of the molten film raw materials may be, for example, about 140 to 210°C.

[0081] The molten film material is then extruded onto a casting roll to form a film. The molten film material comes into contact with the casting roll and moves along the surface of the casting roll, where it cools and solidifies.

[0082] This step may involve extruding the melt onto one or more casting rolls, or may involve placing a touch roll opposite the casting roll and sandwiching the melt extruded onto the casting roll between the touch rolls. An air knife or air chamber may be used to ensure stable contact of the melt with the casting roll. To efficiently cool the side opposite the contact surface with the casting roll, the casting roll may be placed in a water tank or an air chamber may be used.

[0083] The lower limit of the set temperature of the casting roll is preferably 0° C. or higher, more preferably 10° C. or higher, and even more preferably 15° C. or higher, in order to suppress the tackiness of the poly(3-hydroxyalkanoate) resin (A) and improve its releasability from the casting roll. The temperature is preferably a temperature higher than the glass transition temperature (Tg) of the poly(3-hydroxyalkanoate) resin (A) + 10° C.

[0084] The upper limit of the temperature setting of the cast roll is not particularly limited, but from the viewpoint of promoting solidification of the poly(3-hydroxyalkanoate) resin (A), it is preferably 80° C. or lower, more preferably 60° C. or lower.

[0085] Next, the film cooled on the casting roll is transported while the casting roll is rotated, and the film is peeled off from the casting roll, thereby obtaining an unstretched film.

[0086] The resulting film is then stretched in the MD direction to obtain a uniaxially stretched film with high strength in the MD direction. The MD direction is also called the machine direction, flow direction, or longitudinal direction. The TD direction, which will be described later, is the direction perpendicular to the MD direction and is also called the perpendicular direction or width direction.

[0087] The stretching step in the MD direction can be carried out continuously in one production line from the time of peeling from the casting roll. This step is not particularly limited, but can be carried out, for example, by using a roll longitudinal stretching machine and varying the rotation speed of multiple rolls that transport the film.

[0088] The MD stretching step is preferably carried out while heating the film. The heating method is not particularly limited, but examples thereof include a method of exposing the film to an air current adjusted to a predetermined temperature, a method of controlling the film temperature by setting a roll to a predetermined temperature, a method of heating the film using auxiliary heating means such as an IR heater to control the film temperature to a predetermined temperature, and a method of passing the film through an oven adjusted to a predetermined temperature. These methods may be used alone or in combination.

[0089] In Patent Document 2, in order to achieve film stretching by suppressing crystallization of the resin in the MD stretching step, a relatively low film temperature of 20° C. or 30° C. is employed in the examples. In contrast, in the present embodiment, the stretchability of the film is improved by the composition of the film raw materials, so there is no need to control the film temperature as described above, and MD stretching can be achieved even at a temperature higher than the aforementioned temperature.

[0090] Specifically, in the production of the film according to this embodiment, the film temperature during stretching in the MD direction is preferably Tg-25°C or higher, more preferably Tg-15°C or higher, and even more preferably Tg-5°C or higher, where Tg is the glass transition temperature (°C) of the polylactic acid-based resin (B). Furthermore, the film temperature is preferably 35°C or higher, more preferably 45°C or higher, and even more preferably 55°C or higher. Polylactic acid-based resins typically have a glass transition temperature of around 60°C, and are less likely to crystallize when rapidly cooled from a molten state, resulting in an amorphous state. Therefore, even if the temperature is below the melting point of the poly(3-hydroxyalkanoate)-based resin, the film according to this embodiment is likely to soften in the above temperature range, enabling good stretching. Furthermore, the temperature is easily controlled and stabilized. Therefore, film stretching can be carried out continuously and stably, enabling the stable production of long stretched films.

[0091] The upper limit of the film temperature during stretching in the MD direction is not particularly limited, but from the viewpoint of avoiding breakage of the film during stretching, it is preferably Tg + 50°C or less, more preferably Tg + 40°C or less, and even more preferably Tg + 30°C or less. Here, Tg is the glass transition temperature (°C) of the polylactic acid resin (B), as described above. The upper limit of the film temperature is preferably 110°C or less, preferably 100°C or less, and more preferably 90°C or less.

[0092] The stretching ratio in the MD direction is not particularly limited, but is preferably 2 times or more, more preferably 2.5 times or more, and even more preferably 3 times or more. The composition of the film raw material according to this embodiment makes it possible to achieve such a high stretching ratio. The upper limit of the stretching ratio is not particularly limited and may be determined appropriately, but may be, for example, 8 times or less.

[0093] Next, by stretching in the MD direction followed by stretching in the TD direction, a biaxially stretched film with high strength in both the MD and TD directions can be obtained. The TD stretching step can be carried out continuously from the MD stretching step in a single production line. This step is not particularly limited, but can be carried out, for example, by clamping both widthwise ends of the film using a transverse stretching machine such as a clip-type tenter and pulling it in the TD direction.

[0094] The stretching step in the TD direction is also preferably carried out while heating the film. The heating method is not particularly limited, and examples thereof include those described above for the stretching step in the MD direction.

[0095] The temperature conditions in the TD stretching step do not need to be controlled to the specific temperature disclosed in Patent Document 2. Specifically, the film temperature during TD stretching may be the same as the film temperature during MD stretching described above, and is preferably Tg-25°C or higher and Tg+50°C or lower, more preferably Tg-15°C or higher and Tg+40°C or lower, and even more preferably Tg-5°C or higher and Tg+30°C or lower. Furthermore, the temperature is preferably 35°C or higher and 110°C or lower, preferably 45°C or higher and 100°C or lower, and more preferably 55°C or higher and 90°C or lower.

[0096] The stretching ratio in the TD direction is not particularly limited, but is preferably 2 times or more, more preferably 3 times or more, and even more preferably 4 times or more. The composition of the film raw material according to this embodiment makes it possible to achieve such a high stretching ratio. The upper limit of the stretching ratio is not particularly limited and may be determined appropriately, but may be, for example, 8 times or less.

[0097] After the MD stretching step or the TD stretching step, it is preferable to carry out a heat setting step in which the stretched film is heated to a temperature at which high-melting-point crystals grow, thereby increasing the crystallinity of the stretched film, increasing its strength, and stabilizing its physical properties.

[0098] The heating temperature during heat setting is preferably 80 to 150°C, more preferably 90 to 135°C, and most preferably 100 to 130°C. If the heating temperature is 80°C or higher, the crystallinity of the stretched film increases, and the formed crystals may have a high melting point. If the heating temperature is 150°C or lower, breakage due to melting of the film can be avoided.

[0099] This heating can be carried out, for example, by stretching the film in the TD direction using a transverse stretching machine such as a clip-type tenter, and then heating the film while maintaining the stretched state. At this time, since heat shrinkage occurs in the direction opposite to the stretching direction, it is preferable to relax the film to prevent breakage. Relaxation is an operation of releasing tension in the direction opposite to the stretching direction, and the amount of relaxation is preferably adjusted appropriately between 5 and 30%.

[0100] Thereafter, a step of cooling the film may be carried out as appropriate, and then, a step of winding the stretched film on a winding roll is preferably carried out.

[0101] The film manufacturing method according to this embodiment is preferably carried out while continuously transporting the film from melt extrusion to the final step. This makes it possible to produce the film with high productivity through an industrially simple process. The manufacturing method according to this embodiment can be carried out while continuously winding up the produced film on a winding roll.

[0102] When the film is continuously transported, the transport speed is not particularly limited, but from the viewpoint of film productivity, it is preferably 5 m / min or more at the stage before the start of stretching, and from the viewpoint of production stability, it is preferably 50 m / min or less at the stage before the start of stretching.

[0103] [Laminate] The film according to this embodiment may be a resin film composed of an independent single layer, or may be a laminate formed by laminating other layers on one or both sides of the film. Such a laminate also constitutes one aspect of the present invention. Examples of such other layers include a resin layer, an inorganic layer, a metal layer, a metal oxide layer, a printed layer, etc. These other layers may be laminate layers, coating layers, or vapor-deposited layers.

[0104] The resin layer, which is one of the other layers in the laminate, is not particularly limited, but from the viewpoint of enhancing the biodegradability of the entire laminate, it is preferably a layer containing a poly(3-hydroxyalkanoate)-based resin (C). As the poly(3-hydroxyalkanoate)-based resin (C), those described above for the poly(3-hydroxyalkanoate)-based resin (A) can be used as appropriate, but are not particularly limited. The components other than the poly(3-hydroxyalkanoate)-based resin (C) are also not particularly limited, and known components as additives to resin layers can be used as appropriate. This resin layer may function as a heat seal layer.

[0105] [Applications of Film] The film according to this embodiment can be suitably used as a packaging film, a heat-sealable film, a twist film, or the like.

[0106] The following items enumerate preferred embodiments of the present disclosure, but the present invention is not limited to each of them. [Item 1] A film containing a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), wherein the polylactic acid resin (B) has a melting point peak with a peak temperature of less than 170°C in differential scanning calorimetry. [Item 2] The film according to item 1, wherein the content of the polylactic acid resin (B) is 10% by weight or more and 60% by weight or less, based on the total weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). [Item 3] The film according to item 1 or 2, wherein the peak temperature is 120°C or more. [Item 4] The film according to any one of items 1 to 3, wherein the poly(3-hydroxyalkanoate) resin (A) is a poly(3-hydroxybutyrate) resin. [Item 5] The film according to item 4, wherein the poly(3-hydroxybutyrate)-based resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). [Item 6] The film according to any one of items 1 to 5, wherein the absolute value of the difference between the peak melting point temperature of the polylactic acid-based resin (B) and the peak melting point temperature of the poly(3-hydroxyalkanoate)-based resin (A) is 40°C or less. [Item 7] The film according to any one of items 1 to 6, wherein the film is a stretched film. [Item 8] The film according to item 7, wherein the stretched film exhibits an elastic modulus of 1500 MPa or more and a breaking strength of 40 MPa or more, at least in the MD direction. [Item 9] A laminate comprising the film according to any one of items 1 to 8, and a layer containing a poly(3-hydroxyalkanoate)-based resin (C) laminated on at least one side of the film.[Item 10] A method for producing a film containing a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), wherein the polylactic acid resin (B) has a melting point peak whose peak temperature in differential scanning calorimetry is less than 170°C, the method comprising stretching the film in an MD direction and / or a TD direction, wherein the film temperature in the stretching treatment is in the range of Tg - 25°C or more and Tg + 50°C or less, where Tg represents the glass transition temperature (°C) of the polylactic acid resin (B). [Item 11] The method for producing a film according to Item 10, wherein the film temperature is in the range of 35°C or more and 110°C or less.

[0107] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0108] In the examples, the following raw materials were used. (Poly(3-hydroxyalkanoate)-based resin (A)) As the P3HA-based resin, the following poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) resins PHBH-1 to PHBH-3 were used. 3HB represents a 3-hydroxybutyrate repeating unit, and 3HH represents a 3-hydroxyhexanoate repeating unit. PHBH-1:P3HB3HH (average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight average molecular weight 660,000 g / mol) These resins were produced in accordance with the method described in Example 9 of WO 2019 / 142845. PHBH-2: P3HB3HH (average content ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol%), weight average molecular weight is 660,000 g / mol) Produced in accordance with the method described in Example 2 of WO 2019 / 142845. PHBH-3: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%), weight average molecular weight is 600,000 g / mol) Produced in accordance with the method described in Example 1 of WO 2019 / 142845.

[0109] (Polylactic acid resin (B)) B-1: PLA (LX175 grade, manufactured by Total Corbion PLA, peak melting point temperature 155°C) B-2: PLA (LX575 grade, manufactured by Total Corbion PLA, peak melting point temperature 165°C) B-3: PLA (L175 grade, manufactured by Total Corbion PLA, peak melting point temperature 173°C)

[0110] (Nucleating Agent) C-1: Pentaerythritol (manufactured by Mitsubishi Chemical Corporation, Neuraizer P)

[0111] (Lubricant) D-1: Behenic acid amide (manufactured by Nippon Fine Chemical Co., Ltd.: BNT-22H)

[0112] The following evaluations were performed for each example and comparative example. [Measurement of Melting Point Peak Temperature (Crystalline Melting Temperature: Tm) of Resin Component] The melting point peak temperature of the resin component was measured by differential scanning calorimetry (DSC measurement). For differential scanning calorimetry, approximately 5 mg of the resin component in each example and comparative example was precisely weighed, and the temperature was raised from 0°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter (Seiko Instruments Inc., SSC5200). From the obtained DSC curve, the peak top temperature of the crystalline melting peak was taken as the melting point peak temperature (Tm). The melting point peak temperature of the poly(3-hydroxyalkanoate) resin (A) was a value measured for a mixture of each component (PHBH-1 to PHBH-3) of the P3HA resin (A) in the examples and comparative examples.

[0113] [Film stretchability] A film was produced from each resin composition using a T-die and continuously stretched 3 times in the MD direction (the flow direction of T-die film production) using a roll stretching machine at a temperature range of 60°C to 70°C, and the stretchable range (stretching ratio) was evaluated according to the following evaluation criteria. In addition, the film stretched in the MD direction was fixed at both MD end portions and stretched 5 times in the TD direction (direction perpendicular to the MD direction) at a temperature range of 70°C to 80°C, and the stretchable range (stretching ratio) was evaluated according to the following evaluation criteria.

[0114] <Evaluation criteria> ◯: The film was not broken during stretching, and a stretched film was obtained, and no stretching unevenness (uneven stretching portions such as uneven film thickness) was observed visually in the obtained stretched film. ×: The film was broken during stretching, or the obtained stretched film had stretching unevenness (uneven stretching portions such as uneven film thickness) observed visually.

[0115] [Film Properties] <Elastic Modulus, Breaking Strength, and Breaking Elongation of Film> The stretched film was stored for one week in an atmosphere of 23°C and 50% humidity, and then ten dumbbells (small test pieces, size 2(1 / 3)) in the MD and / or TD directions were punched out in accordance with JIS K7113. The elastic modulus, breaking strength, and breaking elongation were measured and calculated five times using a tensile tester ("AUTOGRAPH AG2000A" manufactured by Shimadzu Corporation) at a test speed of 100 mm / min. The average values ​​were then reported in Table 1 as the elastic modulus, breaking strength, and breaking elongation.

[0116] <Film Tear Strength> After storing the stretched film in an atmosphere of 23°C and 50% humidity for one week, the tear strength was measured using the Elmendorf tear method based on JIS K 1281. The measurement was carried out five times, and the average value was recorded as the tear strength in Table 1.

[0117] [Biodegradability] The degree of biodegradability was calculated as the ratio of biological oxygen demand (BOD) to theoretical oxygen demand (ThOD) and evaluated according to the following evaluation criteria: Specifically, for home compostability, a biodegradation test was conducted at 28±2°C in accordance with ISO 14855-1 (28±2°C) and JIS K 6953-1, and the degree of biodegradability was calculated as the ratio of the amount of carbon dioxide generated to the theoretical amount of carbon dioxide generated.

[0118] <Evaluation criteria> XXX: BOD 75% or more XXX: BOD 70% or more but less than 75% 〇: BOD 65% or more but less than 70% △: Less than 65%

[0119] (Example 1) (Method of producing resin composition) 30 parts by weight of poly(3-hydroxyalkanoate) resins PHBH-1, 30 parts by weight of PHBH-2, and 40 parts by weight of PHBH-3 were dry-blended with 1.0 part by weight of C-1 as a crystal nucleating agent and 0.5 parts by weight of D-1 as a lubricant. The resulting resin material was charged into the hopper of a φ26 mm co-rotating twin-screw extruder with the cylinder temperature and die temperature set to 150°C, melt-kneaded, and extruded from the die in the form of strands. The strands were solidified by passing them through a water tank filled with hot water at 45°C, and then cut with a pelletizer to obtain resin pellets P-1.

[0120] (Production of biaxially stretched film in MD and TD directions) Furthermore, the resin pellets P-1 and B-1 were charged into a single-screw extruder in a weight ratio of 80:20 and extruded into a film shape using a T-die. The formed film was cooled with a cooling roll set at 50 ° C., then taken up with a take-up roll. It was continuously stretched 3 times in the MD direction at 60-70 ° C. using a roll longitudinal stretching machine, and then continuously stretched in the TD direction at a stretching temperature of 70-80 ° C. using a clip-type tenter transverse stretching machine to a stretching ratio of 5 times. It was then heated to 130 ° C. while relaxing the stretching by 15% and heat-set. The biaxially stretched film was cooled to 50 ° C., and the width direction end was slit to obtain a biaxially stretched film with a width of 1200 mm and a thickness of 20 μm. The above process was carried out continuously. The film was observed after stretching in the MD direction and after stretching in the TD direction to evaluate the stretchability of the film. The elastic modulus, breaking strength, breaking elongation, tear strength and biodegradability of the obtained stretched film were evaluated. The evaluation results are shown in Table 1.

[0121] (Examples 2 to 7) Resin pellets P-2 to P-7 were produced in the same manner as in Example 1, except that the formulation was changed as shown in Table 1. Furthermore, films were produced in the same manner as in Example 1, and the stretchability of the films, the elastic modulus of the stretched films, tensile strength, breaking strength, breaking elongation, tear strength, and biodegradability were evaluated. The evaluation results are shown in Table 1.

[0122] (Comparative Example 1) Only the resin pellets P-1 were loaded into a single-screw extruder and extruded into a film form through a T-die. The formed film was cooled on a cooling roll set at 50°C, then taken up on a take-up roll. It was continuously stretched in the MD direction at 60-70°C using a roll longitudinal stretching machine, and then continuously stretched in the TD direction at a stretching temperature of 70-80°C using a clip-type tenter transverse stretching machine. It was then heated to 130°C and heat-set while relaxing the stretching by 15%. The biaxially stretched film was cooled to 50°C, and the widthwise end was slit to obtain a biaxially stretched film with a width of 1200 mm and a thickness of 20 μm. The above process was carried out continuously. When stretched at the same ratio as in Example 1, significant stretching unevenness was observed, and a high-quality stretched film could not be obtained; therefore, the film stretchability was evaluated as ×. However, when the stretching ratio was changed to 2x in the MD direction and 4x in the TD direction, a stretched film could be obtained, and this was used for evaluation. The elastic modulus, breaking strength, breaking elongation, tear strength and biodegradability of the obtained stretched film were evaluated. The evaluation results are shown in Table 1.

[0123] Comparative Examples 2 and 3 Resin pellets P-9 and 10 were produced in the same manner as in Example 1, except that the formulation was changed as shown in Table 1. An attempt was made to produce a film in the same manner as in Example 1, but the film broke during stretching, and a stretched film could not be obtained.

[0124]

[0125] As can be seen from Table 1, in Examples 1 to 7, in which a polylactic acid resin (B) having a melting point peak temperature of less than 170°C was blended with a poly(3-hydroxyalkanoate) resin (A), biaxially stretched films stretched at high ratios in both the MD and TD directions were obtained. On the other hand, in Comparative Examples 1 and 3, in which no polylactic acid resin was blended, uneven stretching was observed or the film broke during the stretching process, making it impossible to obtain a stretched film. Furthermore, in Comparative Example 2, in which a polylactic acid resin having a high melting point peak temperature of 173°C was used, the film broke during the stretching process, making it impossible to obtain a stretched film.

Claims

1. It contains a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), The polylactic acid resin (B) has a melting point peak with a peak temperature of less than 170°C in differential scanning calorimetry. A film in which the absolute value of the difference between the melting point peak temperature of the polylactic acid resin (B) and the melting point peak temperature of the poly(3-hydroxyalkanoate) resin (A) is 20°C or less.

2. The film according to claim 1, wherein the content of the polylactic acid resin (B) is 10% by weight or more and 60% by weight or less with respect to the total weight of the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B).

3. The film according to claim 1 or 2, wherein the peak temperature is 120°C or higher.

4. The film according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate) resin (A) is a poly(3-hydroxybutyrate) resin.

5. The film according to claim 4, wherein the poly(3-hydroxybutyrate) resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

6. The film according to claim 1 or 2, wherein the film is a stretched film.

7. The film according to claim 6, wherein the stretched film exhibits an elastic modulus of 1500 MPa or more and a breaking strength of 40 MPa or more in at least the MD direction.

8. A laminate comprising a film according to claim 1 or 2, and a layer containing a poly(3-hydroxyalkanoate) resin (C) laminated on at least one side of the film.

9. A method for producing a film comprising a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), wherein the polylactic acid resin (B) has a melting point peak with a peak temperature of less than 170°C in differential scanning calorimetry, The process includes stretching the film in the MD direction and / or the TD direction. The film temperature during the stretching process is within the range of Tg -25°C or higher and Tg +50°C or lower, where Tg represents the glass transition temperature (°C) of the polylactic acid resin (B). A method for producing a film, wherein the absolute value of the difference between the melting point peak temperature of the polylactic acid resin (B) and the melting point peak temperature of the poly(3-hydroxyalkanoate) resin (A) is 20°C or less.

10. The method for manufacturing a film according to claim 9, wherein the film temperature is within the range of 35°C to 110°C.