Stretched film

Abstract

To provide a poly(3-hydroxyalkanoate) resin-containing film capable of achieving both high strength and suppression of elongation due to transport or residual elongation after transport.SOLUTION: A stretched film contains a modified poly(3-hydroxyalkanoate) resin (A), the modified poly(3-hydroxyalkanoate) resin (A) being a reaction product of a poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide, and has an elastic modulus of 1500 MPa or more and a breaking strength of 40 MPa or more in at least one direction. It is preferable that the creep elongation in at least one direction is 1% or less.SELECTED DRAWING: None

Description

[Technical field]

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

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

[0003] As a material having such compostable and marine degradable properties, poly(3-hydroxyalkanoate) resins, such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), have been attracting attention.

[0004] Meanwhile, a method of stretching a film is known as a technique for producing a thin and high-strength film. For example, in order to produce a stretched film from a general-purpose resin such as polypropylene, a molten resin is cooled and solidified by a cast roll to form a raw sheet, and then the raw sheet is preheated to a temperature at which it can be stretched and then stretched, thereby making it possible to continuously produce a stretched film with good productivity.

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

[0006] For example, Patent Document 1 describes a method for producing a biaxially oriented film by melting a film raw material containing a poly(3-hydroxybutyrate) resin in an extruder, forming it into a film, and then continuously stretching the film in both the MD and TD directions at a stretch ratio of 1.1 times 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 value by controlling the film temperature to a relatively low value, thereby realizing stretching at a high ratio. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2022-62759 [Patent Document 2] JP 2023-73820 A Summary of the Invention [Problem to be solved by the invention]

[0009] According to the method described in Patent Document 1, a biaxially stretched film containing a poly(3-hydroxybutyrate) resin can be produced, but the stretching ratio achieved in the examples was limited to about 1.5 to 1.6 times, and sufficient strength could not be achieved.

[0010] Furthermore, according to the method described in Patent Document 2, a high stretching ratio is achieved by controlling the temperature conditions during the production of a stretched film. However, it has been found that in such a stretched film made of a poly(3-hydroxybutyrate)-based resin, the film may be stretched due to stress applied during film transport in continuous production, and the stretch may remain after transport.

[0011] In view of the above-mentioned current situation, the present invention has an object to provide a poly(3-hydroxyalkanoate) resin-containing film that can achieve both high strength and suppression of elongation due to transport or residual elongation after transport. [Means for solving the problem]

[0012] As a result of intensive research aimed at solving the above-mentioned problems, the inventors have found that a stretched film using a poly(3-hydroxyalkanoate) resin modified by reacting it with an organic peroxide and controlling the elastic modulus and breaking strength of the film to above specific values ​​by film stretching has high strength and is less likely to break during transport, and further makes it possible to suppress elongation due to transport or residual elongation after transport, thereby completing the present invention.

[0013] That is, the present invention relates to a stretched film comprising a modified poly(3-hydroxyalkanoate) resin (A), which is a reaction product of a poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide, and having an elastic modulus in at least one direction of 1500 MPa or more and a breaking strength of 40 MPa or more. The present invention also relates to a laminate comprising the above-mentioned stretched film and a layer containing a poly(3-hydroxyalkanoate) resin (C) laminated on at least one surface of the stretched film. The present invention further relates to a method for producing a stretched film, comprising a step of stretching an original film in at least one direction at a ratio of 1.5 to 8 times, wherein the original film contains a modified poly(3-hydroxyalkanoate)-based resin (A), and the modified poly(3-hydroxyalkanoate)-based resin (A) is a reaction product of a poly(3-hydroxyalkanoate)-based copolymer (a) and an organic peroxide. Effect of the Invention

[0014] According to the present invention, it is possible to provide a poly(3-hydroxyalkanoate) resin-containing film that is capable of achieving both high strength and suppression of elongation due to transport or residual elongation after transport. The poly(3-hydroxyalkanoate) resin-containing film according to the present invention is resistant to breakage and is suppressed in elongation due to transportation and residual elongation, and can be suitably used as a packaging film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described, however, the present invention is not limited to the following embodiment. The present embodiment relates to a stretched film containing a modified poly(3-hydroxyalkanoate) resin (A) and having a specific elastic modulus and breaking strength in at least one direction. Hereinafter, the "stretched film" may be simply referred to as "film".

[0016] [Modified poly(3-hydroxyalkanoate) resin (A)] The modified poly(3-hydroxyalkanoate) resin (A) refers to a reaction product of the poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide. The reaction product is a modified resin in which a crosslinked structure has been introduced into the poly(3-hydroxyalkanoate) copolymer by reaction with an organic peroxide. By using a modified resin having a crosslinked structure as the poly(3-hydroxyalkanoate) resin and forming it into a stretched film, it is possible to provide a poly(3-hydroxyalkanoate) resin-containing film that has both high strength and suppression of elongation due to conveyance or residual elongation after conveyance.

[0017] [Poly(3-hydroxyalkanoate) copolymer (a)] The poly(3-hydroxyalkanoate) copolymer (a) refers to the poly(3-hydroxyalkanoate) copolymer before it is reacted with the organic peroxide. The poly(3-hydroxyalkanoate) copolymer (a) may be a single poly(3-hydroxyalkanoate) resin or a mixture of two or more poly(3-hydroxyalkanoate) resins.

[0018] The poly(3-hydroxyalkanoate) copolymer (a) is preferably a copolymer having a 3-hydroxyalkanoate unit, specifically a copolymer containing a unit represented by the following general formula (1). [-CHR-CH2-CO-O-] (1)

[0019] In the general formula (1), R is C p 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 1 to 10, and more preferably 1 to 8.

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

[0021] The poly(3-hydroxyalkanoate) copolymer (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 constituent units. The poly(3-hydroxyalkanoate) copolymer (a) may contain only two or more kinds of 3-hydroxyalkanoate units as the constituent units of the polymer, or may contain other units (e.g., 4-hydroxyalkanoate units, etc.) in addition to one or more kinds of 3-hydroxyalkanoate units.

[0022] The poly(3-hydroxyalkanoate) copolymer (a) is preferably a copolymer of 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units and other hydroxyalkanoate units (hereinafter also referred to as "poly(3-hydroxybutyrate) copolymers"). In particular, it is preferable that all of the 3-hydroxybutyrate units are (R)-3-hydroxybutyrate units.

[0023] Specific examples of poly(3-hydroxybutyrate) copolymers include 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), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), Examples of the 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), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), etc. In particular, from the viewpoint of film productivity and mechanical properties, etc., 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 by changing the composition ratio of the repeating units, it is possible to change the melting point, the degree of crystallinity, and physical properties such as Young's modulus and heat resistance, and it is possible to impart physical properties between polypropylene and polyethylene, and that it is easy to produce industrially and is a physically useful plastic. In particular, among poly(3-hydroxybutyrate)-based copolymers that have the property of being easily thermally decomposed when heated at 180° C. or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that it is possible to lower the melting point and perform molding processing at low temperatures.

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

[0026] When the poly(3-hydroxyalkanoate) copolymer (a) contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the poly(3-hydroxyalkanoate) copolymer (a) is preferably 3-hydroxybutyrate units / other hydroxyalkanoates=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 film strength and productivity.

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

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

[0028] In this embodiment, the poly(3-hydroxyalkanoate)-based copolymer (a) preferably contains at least a copolymer (a-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of which is 1 mol% or more and 9 mol% or less. By modifying the copolymer (a-1) having a low content of other hydroxyalkanoate units and high crystallinity, it becomes easier to obtain a poly(3-hydroxyalkanoate)-based resin-containing film that has both high strength and suppression of elongation due to conveyance or residual elongation after conveyance.

[0029] In the copolymer (a-1), the content of the other hydroxyalkanoate units may be 1 mol% or more and less than 4 mol%, or 4 mol% or more and 9 mol% or less, preferably 4 mol% or more and 9 mol% or less, more preferably 5 to 8 mol%, and even more preferably 6 to 7 mol%.

[0030] As the copolymer (a-1), 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.

[0031] The poly(3-hydroxyalkanoate) copolymer (a) may be composed of only the copolymer (a-1), but may also contain, in addition to the copolymer (a-1), a copolymer (a-2) of 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of which exceeds 9 mol %.

[0032] In the copolymer (a-2), the content of the other hydroxyalkanoate units may be more than 9 mol % and less than 24 mol %, or may be 24 mol % or more and 99 mol % or less.

[0033] As 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] The weight proportion of copolymer (a-1) in the entire poly(3-hydroxyalkanoate)-based copolymer (a) is preferably 50% by weight or more and 100% by weight or less, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, from the viewpoint of suppressing elongation due to transport of the film or residual elongation after transport while maintaining high strength.

[0035] In the stretched film according to the present embodiment, the amount of copolymer (a-1) used is preferably 50% by weight or more and 100% by weight or less based on the total weight of the resin components contained in the stretched film, from the viewpoint of suppressing elongation due to transport of the film or residual elongation after transport while maintaining high strength. The lower limit is preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more. The upper limit is preferably 95% by weight or less, and more preferably 90% by weight or less.

[0036] The weight average molecular weight of the entire poly(3-hydroxyalkanoate) copolymer (a) is not particularly limited, but from the viewpoint of the elastic modulus and strength of the stretched 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. The weight average molecular weight of the copolymer (a-1) is also preferably within the ranges listed above.

[0037] The weight average molecular weight of the poly(3-hydroxyalkanoate) copolymer can be measured in terms of polystyrene using gel permeation chromatography (Shimadzu Corporation HPLC GPC system) using a chloroform solution. As a column for the gel permeation chromatography, a column suitable for measuring the weight average molecular weight may be used. The same applies to the following description.

[0038] The method for producing the poly(3-hydroxyalkanoate) copolymer is not particularly limited, and may be a production method by chemical synthesis or a production method using a microorganism. Among them, a production method using a microorganism is preferable. A known method can be applied to the production method using a microorganism. For example, Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB, are known as bacteria that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates. In particular, with regard to P3HB3HH, in order to increase the productivity of P3HB3HH, it is more preferable to use Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)) or the like, into which genes of P3HA synthase group have been introduced, and microbial cells in which P3HB3HH has been accumulated in the cells by culturing these microorganisms under appropriate conditions are 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 according to the poly(3-hydroxyalkanoate) resin to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0039] [Organic peroxide] The organic peroxide to be reacted with the poly(3-hydroxyalkanoate) copolymer (a) is not particularly limited, and examples thereof include diisobutyl peroxide, cumyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, bis(4-t-butylcyclohexyl) peroxydicarbonate, bis(2-ethylhexyl) peroxydicarbonate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, 1,1, Examples of the peroxyalkylene oxide include 3,3-tetramethylbutylperoxy-2-ethylhexanoate, disuccinic acid peroxide, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butylperoxy 2-ethylhexylcarbonate, t-butylperoxyisopropylcarbonate, 1,6-bis(t-butylperoxycarbonyloxy)hexane, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyacetate, t-butylperoxybenzoate, t-amylperoxy, 3,5,5-trimethylhexanoate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, and 2,2-di-t-butylperoxybutane. Among these, dibenzoyl peroxide, t-butylperoxy 2-ethylhexyl carbonate, and t-butylperoxy isopropyl carbonate are preferable. As the organic peroxide, one type may be used alone, or two or more types may be used in combination.

[0040] The organic peroxide is used in various forms such as solid and liquid, and may be a liquid form diluted with a diluent, etc. Among them, an organic peroxide in a form that can be mixed with the poly(3-hydroxyalkanoate)-based copolymer (a) (particularly, an organic peroxide that is liquid at room temperature (25° C.)) is preferred because it can be uniformly dispersed in the poly(3-hydroxyalkanoate)-based copolymer (a) and makes it easier to suppress localized modification reactions.

[0041] The amount of the organic peroxide used is preferably 0.01 to 1 part by weight, more preferably 0.03 to 0.5 parts by weight, and even more preferably 0.05 to 0.3 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer (a), from the viewpoint of realizing high-strength stretching by modifying the poly(3-hydroxyalkanoate) resin and thereby realizing high strength of the film.

[0042] The modified poly(3-hydroxyalkanoate) resin (A) can be obtained by feeding the poly(3-hydroxyalkanoate) copolymer (a) and the organic peroxide into an extruder and melt-kneading them. This allows the poly(3-hydroxyalkanoate) copolymer (a) to be uniformly crosslinked. In addition to the poly(3-hydroxyalkanoate) copolymer (a) and the organic peroxide, other components such as a crystal nucleating agent and a lubricant, as described below, may also be fed into the extruder to perform melt-kneading.

[0043] The melt-kneading can be carried out according to a known or conventional method, for example, using an extruder (single-screw extruder or twin-screw extruder), a kneader, etc. The conditions for melt-kneading are not particularly limited and can be set appropriately, but it is preferable to set a resin temperature and residence time that can complete the reaction with the organic peroxide during melt-kneading. Specifically, it is preferable to melt-knead at a resin temperature measured with a die thermometer in the range of 130°C to 175°C. It is also preferable to melt-knead so that the residence time in the extruder is 60 seconds to 300 seconds.

[0044] After melt kneading, the resin material is extruded into a strand shape and cut to obtain pellets having a particle shape such as a cylindrical shape, an elliptical cylinder shape, a spherical shape, a cubic shape, or a rectangular parallelepiped shape. The produced pellets are preferably used after being thoroughly dried at 40 to 80°C to remove moisture. However, the pelletizing process may be omitted, and other resins or components may be further mixed as necessary following the melt kneading to form a film.

[0045] In the stretched film according to the present embodiment, the content of the modified poly(3-hydroxyalkanoate)-based resin (A) is preferably 40% by weight or more and 100% by weight or less based on the total weight of the resin components contained in the stretched film, from the viewpoint of suppressing elongation due to transport of the film or residual elongation after transport while maintaining high strength. The lower limit is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and particularly preferably 80% by weight or more. The upper limit is preferably 95% by weight or less, more preferably 90% by weight or less.

[0046] [Poly(3-hydroxyalkanoate) resin (B)] The resin component contained in the stretched film according to this embodiment may be composed only of the modified poly(3-hydroxyalkanoate) resin (A), but may further contain an unmodified poly(3-hydroxyalkanoate) resin (B) in addition to the modified resin (A). The unmodified resin is different from the modified resin (A) and refers to a resin that has not been reacted with an organic peroxide. By blending the unmodified resin (B), it may be possible to further increase the strength of the film and further suppress elongation due to conveyance or residual elongation.

[0047] As the poly(3-hydroxyalkanoate)-based resin (B), in addition to the above-mentioned poly(3-hydroxyalkanoate)-based copolymer (a), a poly(3-hydroxyalkanoate)-based homopolymer can be used. Specific examples are as described above, so detailed description is omitted.

[0048] From the viewpoint of suppressing elongation due to conveyance of the film or residual elongation after conveyance while having high strength, the poly(3-hydroxyalkanoate) resin (B) preferably contains a copolymer (B-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units, the weight average molecular weight of which is 700,000 or more and the content of other hydroxyalkanoate units is 4 mol% or more and less than 24 mol%. By using the copolymer (B-1) having low to medium crystallinity and high molecular weight in combination with the modified resin (A), the strength of the film can be further increased and the elongation due to conveyance or residual elongation can be further suppressed.

[0049] In the copolymer (B-1), the content of the other hydroxyalkanoate units may be 4 mol% or more and less than 10 mol%, or may be 10 mol% or more and less than 24 mol%, but is preferably 10 mol% or more and less than 24 mol%, more preferably 10 to 20 mol%, more preferably 10 to 17 mol%, and even more preferably 10 to 14 mol%.

[0050] As the copolymer (B-1), 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.

[0051] The weight average molecular weight of the copolymer (B-1) is 700,000 or more, preferably 750,000 or more. The upper limit is not particularly limited, but from the viewpoint of productivity, it is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less.

[0052] The weight proportion of the copolymer (B-1) in the entire poly(3-hydroxyalkanoate) resin (B) is preferably 50% by weight or more and 100% by weight or less, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, from the viewpoint of the elastic modulus and strength of the stretched film.

[0053] When a poly(3-hydroxyalkanoate)-based resin (B) is used, the content of the resin (B) in the stretched film according to the present embodiment is preferably 5% by weight or more and 60% by weight or less of the total weight of the modified resin (A) and the resin (B), from the viewpoint of suppressing elongation due to transport of the film or residual elongation after transport while maintaining high strength. The lower limit is preferably 10% by weight or more, since the effect obtained by blending the resin (B) is easily achieved. Moreover, the upper limit is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less, from the viewpoint of maintaining the effect of the modified resin (A).

[0054] The stretched film according to this embodiment is a resin film mainly composed of modified poly(3-hydroxyalkanoate) resin (A) and optional poly(3-hydroxyalkanoate) resin (B). The proportion of modified resin (A) in the total amount of the film, or the total proportion of modified resin (A) and resin (B) in the total amount of the film when resin (B) is included, is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more, from the viewpoint of enhancing the biodegradability of the film. It may be 95% by weight or more, or 98% by weight or more.

[0055] (Other resins) The stretched film according to the present embodiment may contain other resins other than the modified poly(3-hydroxyalkanoate)-based resin (A) and the poly(3-hydroxyalkanoate)-based resin (B) within the scope of the invention. Examples of such other resins include aliphatic polyester-based resins such as polylactic acid, 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.

[0056] The content of the other resin is not particularly limited, but from the viewpoint of enhancing the biodegradability of the film (particularly biodegradability in compost and marine degradability) relative to a total of 100 parts by weight of the modified poly(3-hydroxyalkanoate)-based resin (A) and the optional poly(3-hydroxyalkanoate)-based resin (B), it 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. 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.

[0057] The stretched film according to the present embodiment may contain additives that can be used together with the modified poly(3-hydroxyalkanoate) resin (A) within a range that does not impair the effects of the invention. Examples of such additives include colorants such as pigments and dyes, odor absorbents such as activated carbon and zeolite, fragrances such as vanillin and dextrin, fillers, plasticizers, antioxidants, weather resistance improvers, ultraviolet absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding 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 set by a person skilled in the art depending on the purpose of use. The crystal nucleating agent, lubricant, filler, and plasticizer will be described in more detail below.

[0058] (Nucleating agent) The stretched film according to the present embodiment may contain a crystal nucleating agent. Examples of the crystal nucleating agent include polyhydric alcohols such as pentaerythritol, galactitol, and mannitol; orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among them, pentaerythritol is preferred because of its particularly excellent effect of promoting the crystallization of the modified poly(3-hydroxyalkanoate) resin (A). The crystal nucleating agent may be used alone or in combination with two or more other agents, and the ratio of use may be appropriately adjusted depending on the purpose.

[0059] When a crystal nucleating agent is used, its amount 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 combined weight of the modified poly(3-hydroxyalkanoate) resin (A) and the optional poly(3-hydroxyalkanoate) resin (B).

[0060] However, the stretched film according to the present embodiment can achieve good productivity even if a crystal nucleating agent such as pentaerythritol is not substantially blended. "Substantially no crystal nucleating agent" means that the amount of crystal nucleating agent is less than 0.1 parts by weight per 100 parts by weight of the total of the modified poly(3-hydroxyalkanoate) resin (A) and the optional poly(3-hydroxyalkanoate) resin (B). It may be less than 0.01 parts by weight. In the embodiment in which pentaerythritol is not substantially blended, the problem of contamination of the cast roll surface due to bleeding out of pentaerythritol can be avoided.

[0061] (lubricant) The stretched film according to the present embodiment may contain a lubricant. Examples of the lubricant include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauramide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among them, behenamide or erucamide is preferred because of its particularly excellent lubricant effect on the modified poly(3-hydroxyalkanoate) resin (A). One or more types of lubricants may be used, and the ratio of use may be appropriately adjusted depending on the purpose.

[0062] 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 in total of the modified poly(3-hydroxyalkanoate) resin (A) and the optional poly(3-hydroxyalkanoate) resin (B). The stretched film according to this embodiment preferably contains a lubricant, but does not necessarily need to contain one.

[0063] (filling material) The stretched film according to the present embodiment may contain a filler. By containing 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, and 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.

[0064] When the filler is used, the 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 total of the modified poly(3-hydroxyalkanoate) resin (A) and the optional poly(3-hydroxyalkanoate) resin (B). However, the stretched film according to the present embodiment may not substantially contain a filler. "Substantially no filler" means that the amount of filler is less than 1 part by weight per 100 parts by weight of the total of the resin (A) and the resin (B). It may be less than 0.1 part by weight.

[0065] (Plasticizer) The stretched film according to the present embodiment may contain a plasticizer. Examples of the plasticizer include glycerin ester compounds, citrate compounds, sebacic acid ester compounds, adipate compounds, polyether ester compounds, benzoic acid ester compounds, phthalic acid ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds. Among them, glycerin ester compounds, citrate compounds, sebacic acid ester compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on the modified poly(3-hydroxyalkanoate) resin (A). Examples of the glycerin ester compounds include glycerin diacetomonolaurate. Examples of the citrate compounds include acetyl tributyl citrate. Examples of the sebacic acid ester compounds include dibutyl sebacate. Examples of the dibasic acid ester compounds include benzyl methyl diethylene glycol adipate. The plasticizer may be used alone or in combination of two or more kinds, and the ratio of use can be appropriately adjusted depending on the purpose.

[0066] When a plasticizer is used, the amount of the plasticizer 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 modified poly(3-hydroxyalkanoate) resin (A) and the optional poly(3-hydroxyalkanoate) resin (B). However, the stretched film according to the present 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 be less than 0.1 part by weight.

[0067] [Stretched film] The stretched film according to this embodiment is a stretched film that has been subjected to a stretching treatment in the MD direction and / or the TD direction after film formation.

[0068] The thickness of 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, light weight, and the like of the film.

[0069] The stretched film according to the present embodiment is preferably a long stretched film produced industrially, and more preferably a strip-shaped stretched film wound into a roll. The length of such a stretched 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 stretched film can be continuously and stably produced.

[0070] The stretched film according to this embodiment has an elastic modulus of 1500 MPa or more and a breaking strength of 40 MPa or more in at least one direction (particularly the MD direction). By using the modified resin (A) and by having the film have high elastic modulus and breaking strength, the stretched film is less likely to break during transport, and elongation due to transport and residual elongation after transport can be suppressed. A film satisfying such elastic modulus and breaking strength can be obtained by stretching a film containing the modified poly(3-hydroxyalkanoate)-based resin (A) at a high ratio. The stretched film according to this embodiment may 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 1700 MPa or more, more preferably 1900 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 method described in detail in the Examples section.

[0071] The stretched film according to the present embodiment preferably exhibits a creep elongation of 1% or less in at least one direction (particularly the MD direction). Creep elongation is a physical property value indicating stress resistance, and it is understood that the smaller the value, the better the stress resistance. A film satisfying such physical property value can sufficiently suppress elongation due to conveyance and residual elongation after conveyance. Such creep elongation can be achieved by forming the stretched film using the modified poly(3-hydroxyalkanoate)-based resin (A). The creep elongation is preferably 0.5% or less, more preferably 0.4% or less.

[0072] The creep elongation is the amount of strain obtained by subtracting the amount of strain that occurs from zero to 16 MPa from the amount of strain that occurs after a film-like test piece (JIS dumbbell) is held under a load of 16 MPa for 3 minutes. Specifically, it can be measured by the method described in detail in the Examples section.

[0073] [Manufacturing method of stretched film] The stretched film of this embodiment can be produced by producing a raw film from a film raw material containing the modified poly(3-hydroxyalkanoate) resin (A), an optional poly(3-hydroxyalkanoate) resin (B), and, as necessary, other components, and stretching the raw film at least in one direction by a factor of 1.5 to 8.

[0074] Hereinafter, an example of a method for producing a stretched 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 modified poly(3-hydroxyalkanoate) resin (A), any poly(3-hydroxyalkanoate) resin (B), and other components as required, is melted.

[0075] The melting method is not particularly limited, but it is preferable to extrude the molten film raw material from a T-die, that is, to carry out an extrusion molding method. By the extrusion molding method, a film with a uniform thickness can be easily produced. In the extrusion molding, a single screw extruder, a twin screw extruder, etc. can be appropriately used.

[0076] The conditions for melting the film raw material may be any conditions that melt the resin components including the modified poly(3-hydroxyalkanoate) resin (A), and the temperature of the molten film raw material may be, for example, about 140 to 210°C.

[0077] The molten film material is then extruded onto a casting roll to be formed into a film. The molten film material comes into contact with the casting roll and moves along the surface of the casting roll, whereby it is cooled and solidified.

[0078] This step may be a step of extruding the molten material onto one or more casting rolls, or a step of opposing a touch roll to a casting roll and sandwiching the molten material extruded onto the casting roll between the touch rolls. In order to bring the molten material into stable contact with the casting roll, an air knife or an air chamber may be used. In order to efficiently cool the opposite side of the contact surface with the casting roll, the casting roll may be placed in a water tank or an air chamber may be used.

[0079] 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 adhesion of the modified poly(3-hydroxyalkanoate) resin (A) and improve the peelability from the casting roll. In addition, the temperature is preferably a temperature exceeding the glass transition temperature (Tg) of the poly(3-hydroxyalkanoate) copolymer (a) + 10° C.

[0080] The upper limit of the temperature set for the cast roll is not particularly limited, but from the viewpoint of promoting solidification of the modified poly(3-hydroxyalkanoate) resin (A), it is preferably 80° C. or lower, more preferably 60° C. or lower.

[0081] Next, the film cooled on the casting roll is transported while rotating the casting roll, and the film is peeled off from the casting roll, thereby obtaining an unstretched film.

[0082] Next, the obtained film is 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.

[0083] The stretching process in the MD direction can be carried out continuously from the peeling off from the cast roll in one production line. This process is not particularly limited, but can be carried out, for example, by using a roll longitudinal stretching machine and varying the rotation speed of the rolls that transport the film.

[0084] In order to perform the stretching, it is desirable to soften the film material containing the modified poly(3-hydroxyalkanoate) resin (A) to a degree that allows stretching. Therefore, it is desirable to perform the stretching in the MD direction while heating the film to a temperature close to the melting point of the poly(3-hydroxyalkanoate) resin. Specifically, the heating temperature is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher. Since the poly(3-hydroxyalkanoate) resin used in this embodiment is modified using an organic peroxide, it is difficult to break even when stretched at such a high temperature, and stretching at a high ratio is possible. The upper limit of the heating temperature is preferably lower than the melting point of the poly(3-hydroxyalkanoate) resin.

[0085] 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 an auxiliary heating means such as an IR heater to control the film temperature to a predetermined temperature, a method of passing the film through an oven adjusted to a predetermined temperature, etc. These methods may be used alone or in combination.

[0086] The stretching ratio in the MD direction is desirably 1.5 times or more in order to achieve the above-mentioned breaking strength. It is preferably 2 times or more, more preferably 2.5 times or more, and further preferably 3 times or more. Such a high stretching ratio can be realized by using a poly(3-hydroxyalkanoate)-based resin modified by reaction with an organic peroxide. The upper limit of the stretching ratio is usually 8 times or less, but may be 6 times or less.

[0087] Next, by stretching in the MD direction and then stretching in the TD direction, a biaxially stretched film with high strength in both the MD and TD directions can be obtained. The stretching step in the TD direction can be carried out in one production line, continuously from the stretching step in the MD direction. This step is not particularly limited, but can be carried out, for example, by clamping both ends of the film in the width direction using a transverse stretching machine such as a clip-type tenter and pulling it in the TD direction.

[0088] The stretching step in the TD direction is also preferably performed while heating the film. The heating method is not particularly limited, and may be the same as that described above for the stretching step in the MD direction.

[0089] The temperature in the TD stretching step may be the same as the temperature in the MD stretching step described above, but when the MD stretching step and the TD stretching step are performed successively, the temperature may be lower than the temperature in the MD stretching step. Such a temperature is preferably 35 to 110°C, more preferably 45 to 100°C, and more preferably 55 to 90°C.

[0090] The stretching ratio in the TD direction is not particularly limited, but in order to achieve the above-mentioned breaking strength in the TD direction, it is desirable that it is 1.5 times or more. It is preferably 2 times or more, more preferably 2.5 times or more, and even more preferably 3 times or more. The upper limit of the stretching ratio is usually 8 times or less, but may be 6 times or less.

[0091] 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 crystals grow, thereby increasing the crystallinity of the stretched film, increasing its strength, and stabilizing its physical properties.

[0092] 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 crystals formed 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.

[0093] This heating can be carried out, for example, by stretching in the TD direction using a transverse stretching machine such as a clip-type tenter, and then heating 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 so as not to break. Relaxation is an operation of returning tension in the direction opposite to the stretching direction, and it is preferable to appropriately adjust the amount of relaxation between 5 and 30%.

[0094] Thereafter, a step of cooling the film may be carried out as appropriate, and then, preferably, a step of winding the stretched film on a winding roll is carried out.

[0095] The method for producing a stretched film according to the present embodiment is preferably carried out while continuously transporting the stretched film from the melt extrusion to the final step. This makes it possible to produce a stretched film with good productivity through an industrially simple process. The production method according to the present embodiment can be carried out while continuously winding up the produced stretched film on a winding roll.

[0096] When the stretched film is continuously transported, the transport speed is not particularly limited, but from the viewpoint of productivity of the stretched film, it is preferably 5 m / min or more before the start of stretching, and from the viewpoint of production stability, it is preferably 50 m / min or less before the start of stretching.

[0097] [Laminate] The stretched film according to the present embodiment may be a resin film composed of an independent single layer, but may also be a laminate in which another layer is laminated on one or both sides of the stretched film. Such a laminate also constitutes one aspect of the present invention. Examples of the other layer 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 deposition layers.

[0098] The resin layer, which is one of the other layers in the laminate, is not particularly limited, but is preferably a layer containing a poly(3-hydroxyalkanoate) resin (C) from the viewpoint of enhancing the biodegradability of the entire laminate. As the poly(3-hydroxyalkanoate) resin (C), those described above for the poly(3-hydroxyalkanoate) resin (B) can be appropriately used, but are not particularly limited. There are also no particular limitations on the components other than the poly(3-hydroxyalkanoate) resin (C), and known components can be appropriately used as additives to the resin layer. This resin layer may function as a heat seal layer.

[0099] [Uses of oriented film] The stretched film according to this embodiment can be suitably used as a packaging film, a heat-sealable film, a twist film, and the like.

[0100] The following items enumerate preferred aspects of the present disclosure, but the present invention is not limited to the following items. [Item 1] Contains a modified poly(3-hydroxyalkanoate) resin (A), the modified poly(3-hydroxyalkanoate) resin (A) is a reaction product of a poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide; A stretched film having an elastic modulus in at least one direction of 1500 MPa or more and a breaking strength of 40 MPa or more. [Item 2] 2. The stretched film according to item 1, having a creep elongation of 1% or less in at least one direction. Creep elongation: The amount of strain obtained by subtracting the amount of strain that occurs from zero strain to 16 MPa from the amount of strain after a film-shaped test piece (JIS dumbbell) is held under a load of 16 MPa for 3 minutes. [Item 3] 3. The stretched film according to item 1 or 2, wherein the poly(3-hydroxyalkanoate)-based copolymer (a) comprises a copolymer (a-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of which is 1 mol% or more and 9 mol% or less of the other hydroxyalkanoate units. [Item 4] 4. The stretched film according to item 3, wherein the content of the other hydroxyalkanoate units in the copolymer (a-1) is 50% by weight or more based on the total weight of the resin components contained in the stretched film. [Item 5] Further comprising a poly(3-hydroxyalkanoate)-based resin (B), The stretched film according to any one of items 1 to 4, wherein the poly(3-hydroxyalkanoate) resin (B) comprises a copolymer (B-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units having a weight average molecular weight (here, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene as determined by gel permeation chromatography using chloroform as a solvent) of 700,000 or more and a content of other hydroxyalkanoate units of 4 mol% or more and less than 24 mol%. [Item 6] Item 6. The stretched film according to item 5, wherein the content of the poly(3-hydroxyalkanoate) resin (B) is 5 to 60% by weight of the total weight of the modified poly(3-hydroxyalkanoate) resin (A) and the poly(3-hydroxyalkanoate) resin (B). [Item 7] 7. The stretched film according to any one of items 3 to 6, wherein the other hydroxyalkanoate units include 3-hydroxyhexanoate units. [Item 8] 8. A laminate comprising the stretched film according to any one of items 1 to 7, and a layer containing a poly(3-hydroxyalkanoate) resin (C) laminated on at least one surface of the stretched film. [Item 9] A method for producing a stretched film, comprising a step of stretching an original film at least in one direction at a magnification of 1.5 times or more and 8 times or less, The raw film contains a modified poly(3-hydroxyalkanoate) resin (A), The method for producing a stretched film, wherein the modified poly(3-hydroxyalkanoate) resin (A) is a reaction product of a poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide. [Item 10] The raw film further contains a poly(3-hydroxyalkanoate)-based resin (B), Item 10. The method for producing a stretched film according to item 9, wherein the poly(3-hydroxyalkanoate) resin (B) comprises a copolymer (B-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units having a weight average molecular weight (here, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene as determined by gel permeation chromatography using chloroform as a solvent) of 700,000 or more and a content of other hydroxyalkanoate units of 4 mol% or more and less than 24 mol%. EXAMPLES

[0101] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0102] In the examples, the following raw materials were used: (Poly(3-hydroxyalkanoate) resin) The P3HA-based resins used were the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) resins PHBH-1 to PHBH-4 shown below, where 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 is 660,000 g / mol) It was 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) It was 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) It was produced in accordance with the method described in Example 1 of WO 2019 / 142845. PHBH-4: P3HB3HH (average content ratio of 3HB / 3HH = 94 / 11 mol% / mol%, weight average molecular weight is 800,000 g / mol) It was produced according to the method described in the Examples (raw material A-3) of WO 2013 / 147139.

[0103] (Nucleating agent) C-1: Pentaerythritol (Mitsubishi Chemical, NeuRizer P)

[0104] (lubricant) D-1: Behenamide (Nippon Fine Chemicals: BNT-22H)

[0105] (organic peroxide) E-1: NOF Corp. Perbutyl I (t-butylperoxyisopropyl carbonate, 1-minute half-life temperature: 159°C)

[0106] In each of the Examples and Comparative Examples, the following evaluations were carried out. [Film properties] <Film elasticity and breaking strength> The films obtained in each Example and Comparative Example were stored for one week at 23°C and 50% humidity, and then ten dumbbells (small test pieces, size 2(1 / 3)) were punched out in the MD and / or TD directions based on JIS K7113. The elastic modulus and breaking strength were measured and calculated five times at a test speed of 100 mm / min using a tensile tester (Shimadzu Corporation, "AUTOGRAPH AG2000A"), and the average values ​​were listed in Table 1 as the elastic modulus and breaking strength.

[0107] <Film creep elongation> The films obtained in each Example and Comparative Example were stored for one week at 23°C and 50% humidity, and then, based on JIS K7113, a dumbbell (small test piece No. 2 (1 / 3) type) was punched out in the MD and / or TD directions to prepare a test piece. Both ends of the test piece were clamped with the chucks of a tensile tester (Shimadzu Corporation "AUTOGRAPH AG2000A") so as not to loosen, and the test piece length between the chucks was taken as the reference value (Y0). The test piece was pulled until the tensile stress reached 16 MPa, and the tensile tester was stopped. The test piece length (chuck distance) at that time was taken as the initial value (Y1), and the test piece length (chuck distance) 3 minutes after stopping while maintaining the stress was taken as the strain value (Y2). The creep elongation (%) was calculated using the following formula. (Formula) Creep elongation (%) = (Y2-Y1) / Y0 x 100

[0108] [Film practicality evaluation] <Transport elongation, residual elongation> The films obtained in each Example and Comparative Example were cut out in a TD direction with a width of 50 mm and 1 m long, and lines (reference lines) were drawn on both ends to define a length (L0) of 300 mm in the MD direction. Weights were attached to both ends of the film in the MD direction so that the stress of the film strip was 16 MPa, and the film was held for 3 minutes. The length (L1) between the reference lines in the stressed state after the holding was measured, and the value (L1-L0) obtained by subtracting the initial length between the reference lines (L0=300 mm) from L1 was taken as the transport elongation. Furthermore, the weights were removed, and the length (L2) of the reference line was measured after the stress was eliminated, and the value (L2-L0) obtained by subtracting the initial length between the reference lines (L0=300 mm) from L2 was taken as the residual elongation. For practical use, it is preferable that the transport elongation is less than 5 mm, and the residual elongation is less than 1 mm.

[0109] <Break> The films obtained in each Example and Comparative Example were slit into 100 m long pieces with a width of 50 mm in the TD direction, set in a film rewinding machine, and transported at a speed of 50 m / min while applying a tension of 16 MPa. At this time, it was evaluated whether the film broke. In addition, it was evaluated whether the 50 mm wide film broke when it was set in the rewinding machine. If it broke in any of these cases, it was marked with ×, and if it did not break in any of these cases, it was marked with ◯.

[0110] Example 1 (Method of producing resin composition) 100 parts by weight of poly(3-hydroxyalkanoate) resin PHBH-3, 1 part by weight of C-1 as a crystal nucleating agent, 0.5 parts by weight of D-1 as a lubricant, and 0.2 parts by weight of E-1 as an organic peroxide were dry-blended. The obtained resin material was put into a hopper of a φ26 mm co-rotating twin-screw extruder with a cylinder temperature and die temperature set to 150 ° C, melt-kneaded, extruded from the die in the form of a strand, passed through a water tank filled with hot water at 45 ° C to solidify the strand, and cut with a pelletizer to obtain resin pellets P-1. In addition, during the melt-kneading process, the reaction between P3HA and the organic peroxide proceeded to form a modified resin (A).

[0111] (Manufacturing of stretched films) Furthermore, the resin pellets P-1 were put into a single-screw extruder 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, and continuously stretched 3 times in the MD direction at 140°C using a roll longitudinal stretching machine, and then heated to 120°C with a roll for heat setting. The film was then cooled to 50°C to obtain a uniaxially stretched film with a width of 1200 mm and a thickness of 40 μm. The above process was carried out continuously. The elastic modulus, breaking strength, creep elongation, and practicality (transport elongation, residual elongation, and breaking) of the obtained stretched film were evaluated. The evaluation results are shown in Table 1.

[0112] Example 2 The resin pellets P-1 were fed into a single-screw extruder and extruded into a film shape through a T-die. The formed film was cooled with a cooling roll set at 50°C, then taken up with a take-up roll, and continuously stretched 3 times in the MD direction at 140°C using a roll longitudinal stretching machine, and continuously stretched to a stretch ratio of 5 times in the TD direction at a stretching temperature of 60°C using a clip-type tenter transverse stretching machine. Subsequently, the stretching was relaxed by 15% while heating to 130°C for heat setting. The biaxially stretched film was cooled to 50° C., and the widthwise end portion was slit to obtain a biaxially stretched film having a width of 1200 mm and a thickness of 20 μm. The above process was carried out continuously. The elastic modulus, breaking strength, creep elongation, and practicality (transport elongation, residual elongation, and breaking) of the obtained stretched film were evaluated. The evaluation results are shown in Table 1.

[0113] (Examples 3 and 4) Resin pellets P-2 and 3 were produced in the same manner as in Example 1, except that the formulation was changed as shown in Table 1, P3HA(a) and each additive were first charged into a twin-screw extruder hopper, and the crosslinking reaction was allowed to proceed and be completed in the extruder, after which P3HA(B) was charged from the side feeder of the extruder. In addition, uniaxially stretched films were produced in the same manner as in Example 1, except that the stretching conditions were changed as shown in Table 1. The elastic modulus, breaking strength, creep elongation, and practicality (transport elongation, residual elongation, and breaking) of the obtained stretched film were evaluated. The evaluation results are shown in Table 1.

[0114] Comparative Example 1 The resin pellets P-1 were fed into a single screw extruder and extruded into a film shape through a T-die. The formed film was cooled with a cooling roll set at a temperature of 50° C. and then taken up with a take-up roll to obtain an unstretched film. The unstretched film thus obtained was evaluated for its elastic modulus, breaking strength, creep elongation, and practicality (transport elongation, residual elongation, and breaking). The evaluation results are shown in Table 1.

[0115] Comparative Example 2 A resin pellet P-4 was produced in the same manner as in Example 1, except that no organic peroxide was used. An attempt was made to produce a stretched film in the same manner as in Example 1, but the film broke during stretching, and a stretched film could not be obtained.

[0116] Comparative Example 3 Resin pellets P-5 were produced in the same manner as in Example 1, except that the composition was changed as shown in Table 1. In addition, a uniaxially stretched film was produced in the same manner as in Example 1, except that the stretching conditions were changed as shown in Table 1. The elastic modulus, breaking strength, creep elongation, and practicality (transport elongation, residual elongation, and breaking) of the obtained stretched film were evaluated. The evaluation results are shown in Table 1.

[0117] [Table 1]

[0118] As shown in Table 1, in Examples 1 to 4, a stretched film having a high elastic modulus and breaking strength at least in the MD direction was obtained by using the modified poly(3-hydroxyalkanoate) resin (A) obtained by reacting the poly(3-hydroxyalkanoate) copolymer (a) with an organic peroxide. The stretched film did not break in the practical evaluation, and had a small conveying elongation and residual elongation. On the other hand, the film of Comparative Example 1, which was not stretched, had a lower breaking strength than that of Example 1, and broke in the practical use evaluation. In Comparative Example 2, in which the same poly(3-hydroxyalkanoate) copolymer (a) as in Example 1 was used but was not modified with an organic peroxide, the film broke during stretching, and a stretched film could not be obtained. In Comparative Example 3, which used PHBH-1, a low-crystalline poly(3-hydroxyalkanoate) copolymer with a 3HH ratio of 28 mol%, a stretched film could be obtained without modification with an organic peroxide. However, compared with Example 1, the elastic modulus was lower and the creep elongation was larger, and the conveying elongation and residual elongation were larger in the practical evaluation.

Claims

1. Contains a modified poly(3-hydroxyalkanoate) resin (A), the modified poly(3-hydroxyalkanoate) resin (A) is a reaction product of a poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide; A stretched film having an elastic modulus in at least one direction of 1500 MPa or more and a breaking strength of 40 MPa or more.

2. 2. The stretched film of claim 1, having a creep elongation of 1% or less in at least one direction. Creep elongation: The amount of strain obtained by subtracting the amount of strain that occurs from zero to 16 MPa from the amount of strain after a film-like test piece (JIS dumbbell) is held under a load of 16 MPa for 3 minutes.

3. The stretched film according to claim 1, wherein the poly(3-hydroxyalkanoate)-based copolymer (a) comprises a copolymer (a-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of which is 1 mol % or more and 9 mol % or less of the other hydroxyalkanoate units.

4. The stretched film according to claim 3, wherein the content of the copolymer (a-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units, in which the content ratio of the other hydroxyalkanoate units is 1 mol% or more and 9 mol% or less, is 50% by weight or more based on the total weight of the resin components contained in the stretched film.

5. Further comprising a poly(3-hydroxyalkanoate)-based resin (B), The stretched film according to claim 1, wherein the poly(3-hydroxyalkanoate) resin (B) comprises a copolymer (B-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units having a weight average molecular weight (here, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene as determined by gel permeation chromatography using chloroform as a solvent) of 700,000 or more and a content of other hydroxyalkanoate units of 4 mol% or more and less than 24 mol%.

6. The stretched film according to claim 5, wherein the content of the poly(3-hydroxyalkanoate) resin (B) is 5 to 60% by weight of the total weight of the modified poly(3-hydroxyalkanoate) resin (A) and the poly(3-hydroxyalkanoate) resin (B).

7. The stretched film of claim 3 or 5, wherein the other hydroxyalkanoate units include 3-hydroxyhexanoate units.

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

9. A method for producing a stretched film, comprising a step of stretching an original film at least in one direction at a magnification of 1.5 times or more and 8 times or less, The raw film contains a modified poly(3-hydroxyalkanoate)-based resin (A), The method for producing a stretched film, wherein the modified poly(3-hydroxyalkanoate) resin (A) is a reaction product of a poly(3-hydroxyalkanoate) copolymer (a) and an organic peroxide.

10. The raw film further contains a poly(3-hydroxyalkanoate)-based resin (B), The method for producing a stretched film according to claim 9, wherein the poly(3-hydroxyalkanoate) resin (B) comprises a copolymer (B-1) of 3-hydroxybutyrate units and other hydroxyalkanoate units having a weight average molecular weight (here, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene as determined by gel permeation chromatography using chloroform as a solvent) of 700,000 or more and a content of other hydroxyalkanoate units of 4 mol% or more and less than 24 mol%.

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