Method for producing stretched film

Abstract

Provided is a method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin having high stretchability and a small amount of heat shrinkage.　A method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin includes: a step for melting a film raw material containing the poly(3-hydroxyalkanoate) resin in an extruder and then shaping the film raw material into a film; a step for stretching the shaped film while heating the film; and a step for heat-treating the stretched film while relaxing the stretched film in the stretching direction. The heat treatment includes a treatment in which the stretched film is in a temperature range of the melting point of the poly(3-hydroxyalkanoate) resin of -50°C or higher and the melting point of the poly(3-hydroxyalkanoate) resin of -20°C or lower, the poly(3-hydroxyalkanoate) resin contains a copolymer (A), the copolymer (A) contains a 3-hydroxybutyrate unit and an additional hydroxyalkanoate unit, and the average content ratio of the 3-hydroxybutyrate unit and the additional hydroxyalkanoate unit in all monomer units constituting the copolymer (A) is 3-hydroxybutyrate unit / additional hydroxyalkanoate unit=76 / 24-50 / 50 (mol% / mol%).

Description

Stretched film manufacturing method

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

[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.

[0003] On the other hand, environmental problems caused by discarded plastics have been highlighted, and it has become clear that large amounts of plastic, particularly plastics dumped in the ocean or that have entered the ocean via rivers, are drifting in the ocean on a global scale. Because such plastics retain their shape for a long period of time, they can trap and capture marine organisms, a phenomenon known as ghost fishing, and if ingested by marine organisms, they can become trapped in the digestive tract, causing feeding disorders, and other problems have been pointed out as having an impact on the ecosystem.

[0004] Furthermore, it has been pointed out that microplastics, which are plastics that have broken down and become tiny particles due to ultraviolet rays and other factors, absorb harmful compounds in seawater, and when marine organisms ingest these, the harmful substances are absorbed into the food chain.

[0005] The use of biodegradable plastics is expected to address this type of marine pollution caused by plastics, but a report compiled by the United Nations Environment Programme in 2015 pointed out that plastics that can be biodegraded through compost, such as polylactic acid, cannot be expected to decompose in a short period of time in the cold ocean, and therefore cannot be used to combat marine pollution.In this context, poly(3-hydroxyalkanoate) resins are attracting attention as a material that can resolve the above issues, as they are capable of biodegrading even in seawater.

[0006]

[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 the stretched film with good productivity.

[0007] However, poly(3-hydroxybutyrate)-based resins are known to be difficult to stretch due to their properties. Patent Document 1 discloses a method for producing a stretched film containing a poly(3-hydroxybutyrate)-based resin at a high stretch ratio in a continuous process with good productivity.

[0008] JP 2023-073820 A

[0009] Although the stretchability of a film can be improved by adjusting the monomer composition of the repeating units constituting a poly(3-hydroxyalkanoate)-based resin, there is a problem in that the amount of shrinkage of the stretched film due to heating increases.When a stretched film containing a poly(3-hydroxyalkanoate)-based resin as a main component is used as a packaging film, for example, there is heat bonding between stretched films to seal contents, or heat fixing of ink after applying ink to the stretched film for printing, but such heating causes the stretched film to shrink, distorting the sealed portion and the printing.

[0010] In view of the above-mentioned current situation, an object of the present invention is to provide a method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin, which has high stretchability and a small amount of heat shrinkage.

[0011] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that a stretched film containing a poly(3-hydroxyalkanoate) resin that has high stretchability and little heat shrinkage can be produced by forming a film raw material containing a specific poly(3-hydroxyalkanoate) resin into a film, stretching the formed film while heating, and then heat-treating the film under specific conditions while relaxing it in the stretching direction, thereby completing the present invention.

[0012] That is, the present invention provides a method for producing a stretched film containing a poly(3-hydroxyalkanoate)-based resin, comprising the steps of melting a film raw material containing the poly(3-hydroxyalkanoate)-based resin in an extruder and then forming it into a film, stretching the formed film while heating it, and heat-treating the stretched film while relaxing it in the stretching direction, wherein the heat treatment is performed by heating the stretched film to a temperature of at least −50°C of the melting point of the poly(3-hydroxyalkanoate)-based resin and at least The present invention relates to a method for producing a stretched film, which includes a treatment at a temperature range of melting point −20°C or lower, wherein the poly(3-hydroxyalkanoate) resin contains a copolymer (A), the copolymer (A) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average content ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units in all monomer units constituting the copolymer (A) is 3-hydroxybutyrate units / other hydroxyalkanoate units = 76 / 24 to 50 / 50 (mol % / mol %).

[0013] According to the present invention, it is possible to provide a method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin, which has high stretchability and a small amount of heat shrinkage.

[0014] 1 is a conceptual diagram showing an example of a production line for carrying out a continuous process for producing a stretched film according to one embodiment of the present invention.

[0015] 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 method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin.

[0016] <Poly(3-hydroxyalkanoate)-based resin> The poly(3-hydroxyalkanoate)-based resin is an aliphatic polyester resin that can be produced from a microorganism and has 3-hydroxyalkanoate as a repeating unit. In the present disclosure, the poly(3-hydroxyalkanoate)-based resin contains a copolymer (A).

[0017] (Copolymer (A)) The copolymer (A) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average content ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units in all the monomer units constituting the copolymer (A) is 3-hydroxybutyrate units / other hydroxyalkanoate units = 76 / 24 to 50 / 50 (mol % / mol %). This allows the production method of the present disclosure to have high stretchability. If the ratio of 3-hydroxybutyrate units / other hydroxyalkanoate units is higher than 76 / lower than 24 (mol % / mol %), uneven stretching and breakage are likely to occur when a high stretch ratio is applied in the stretching step, and a stretched film cannot be obtained with good productivity.

[0018] The average content ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units in all monomer units constituting the copolymer (A) is preferably 3-hydroxybutyrate units / other hydroxyalkanoate units=76 / 24 to 60 / 40 (mol % / mol %), more preferably 76 / 24 to 70 / 30 (mol % / mol %).

[0019] The average content ratio of each monomer unit in all monomer units constituting the copolymer (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 copolymer (A).

[0020] Specific examples of the copolymer (A) include poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [hereinafter, may be referred to as P3HB3HV], poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [hereinafter, may be referred to as P3HB3HH], poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), and poly(3-hydroxybutyrate-co-3-hydroxyheptanoate). ate), 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-3-hydroxyoctadecanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [hereinafter, may be referred to as P3HB4HB].

[0021] Among these, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred because of ease of industrial production, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is more preferred.

[0022] Furthermore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that by changing the composition ratio of the repeating units, it is possible to change the melting point and degree of crystallinity, and thereby change 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 useful plastic in terms of physical properties such as film productivity, stretchability, and mechanical properties. In particular, among poly(3-hydroxyalkanoate) resins that tend to be thermally decomposed when heated to 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoint that it can lower the melting point and enable molding and processing at low temperatures.

[0023] The weight-average molecular weight of the entire copolymer (A) is not particularly limited, but from the viewpoint of extrusion moldability, it is preferably 200,000 to 2,000,000 g / mol, more preferably 250,000 to 1,500,000 g / mol, and even more preferably 300,000 to 1,000,000 g / mol. The weight-average molecular weight of the entire copolymer (A) can be measured by the same method as the method for measuring the weight-average molecular weight of a poly(3-hydroxyalkanoate) resin described below.

[0024] The content of the copolymer (A) in the stretched film of the present disclosure is preferably 5 to 40 parts by weight, and more preferably 8 to 30 parts by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin. If the content is less than 5 parts by weight, the effect of enhancing stretchability may be smaller than when the content is 5 parts by weight or more, and if the content is more than 40 parts by weight, the mechanical properties may be inferior to when the content is 40 parts by weight or less.

[0025] (Poly(3-hydroxyalkanoate)-based resin) The poly(3-hydroxyalkanoate)-based resin may contain the copolymer (A), and may be composed entirely of the copolymer (A), or may be composed of a mixture of the copolymer (A) and a homopolymer or a poly(3-hydroxyalkanoate)-based copolymer other than the copolymer (A).

[0026] The poly(3-hydroxyalkanoate) copolymer other than the copolymer (A) may also be a mixture of at least two poly(3-hydroxyalkanoate) copolymers differing from each other in the type and / or content ratio of the constituent monomers. Examples of the poly(3-hydroxyalkanoate) copolymer other than the copolymer (A) include the same copolymers as those listed as specific examples of the copolymer (A) above.

[0027] Furthermore, from the viewpoint of achieving both strength and productivity of the stretched film, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin is preferably 3-hydroxybutyrate units / other hydroxyalkanoates = 99 / 1 to 80 / 20 (mol % / mol %), and more preferably 97 / 3 to 85 / 15 (mol % / mol %).

[0028] The average content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate)-based resin 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)-based resin, and when the poly(3-hydroxyalkanoate)-based resin is a mixture of two or more poly(3-hydroxyalkanoate)-based resins, it means the molar ratio of each monomer unit contained in the entire mixture.

[0029] The weight average molecular weight of the entire poly(3-hydroxyalkanoate) resin is not particularly limited, but from the viewpoint of achieving both strength and productivity of the stretched film, it is preferably 200,000 to 2,000,000 g / mol, more preferably 250,000 to 1,500,000 g / mol, and even more preferably 300,000 to 1,000,000 g / mol.

[0030] 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.

[0031] 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 (poly(3-hydroxyalkanoate)) 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 also be used depending on the poly(3-hydroxyalkanoate) resin to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0032] In addition, even when a mixture of two or more poly(3-hydroxyalkanoate) resins is obtained, the method is not particularly limited, and may be a production method by chemical synthesis or a production method using a microorganism. Furthermore, a blend may be obtained by melt-kneading two or more poly(3-hydroxyalkanoate) resins using an extruder, kneader, Banbury mixer, roll, etc., or by dissolving two or more poly(3-hydroxyalkanoate) resins in a solvent, mixing, and drying them.

[0033] The poly(3-hydroxyalkanoate) resin may be an unmodified resin, or may be 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").

[0034] When a modified resin is used as a film raw material, a film raw material containing a poly(3-hydroxyalkanoate) resin that has been previously reacted with a modifying raw material may be formed into a film, or a film raw material containing an unmodified poly(3-hydroxyalkanoate) resin and a modifying raw material may be formed by reacting the resin with the modifying raw material. Furthermore, when reacting a resin with a modifying raw material, the entire resin may be reacted with the modifying raw material, or a portion of the resin may be reacted with the modifying raw material to obtain a modified resin, and the remaining unmodified resin may then be added to the modified resin.

[0035] The modifying raw material is not particularly limited as long as it is a compound that can react with the poly(3-hydroxyalkanoate)-based resin, but organic peroxides are preferably used in terms of ease of handling and ease of control of the reaction with the poly(3-hydroxyalkanoate)-based resin. Furthermore, by reacting the poly(3-hydroxyalkanoate)-based resin with an organic peroxide to introduce a crosslinked structure, the film becomes less likely to break even when stretched, making it possible to form a film with better stretchability.

[0036] Examples of the organic peroxides 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, 1,1,3,3-tetramethylbutylperoxy-2-methyl- t-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-ethylhexyl carbonate, t-butylperoxy isopropyl carbonate, 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, 2,2-di-t-butylperoxybutane, and the like. Among these, t-butylperoxy 2-ethylhexyl carbonate and t-butylperoxy isopropyl carbonate are preferred. Furthermore, a combination of two or more of these organic peroxides can also be used.

[0037] The organic peroxide is used in various forms such as solid or liquid, and may be in liquid form diluted with a diluent, etc. Among these, an organic peroxide in a form that can be easily mixed with the poly(3-hydroxyalkanoate)-based resin (particularly an organic peroxide that is liquid at room temperature (25°C)) is preferred because it can be more uniformly dispersed in the poly(3-hydroxyalkanoate)-based resin and is likely to suppress local modification reactions in the resin composition.

[0038] From the viewpoint of improving the stretchability of the film, the amount of 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) resin.

[0039] The modified poly(3-hydroxyalkanoate) resin can be obtained by adding a poly(3-hydroxyalkanoate) resin and an organic peroxide to an extruder and melt-kneading them. This allows the poly(3-hydroxyalkanoate) resin to be uniformly crosslinked. Furthermore, in addition to the poly(3-hydroxyalkanoate) resin and the organic peroxide, other components such as a crystal nucleating agent and a lubricant, as described below, may also be added to the extruder and melt-kneaded.

[0040] The content of the poly(3-hydroxyalkanoate) resin in the stretched film may be 50% by weight or more, 55% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 95% by weight or more. The upper limit of the content of the poly(3-hydroxyalkanoate) resin is not limited and may be 100% by weight or less. From the viewpoint of further enjoying the effects of high stretchability and reduced heat shrinkage achieved by the stretched film production method of the present disclosure, a content of 95% by weight or more is preferred.

[0041] The stretched film may contain additives that can be used with the poly(3-hydroxyalkanoate)-based resin, 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. The film may contain only one type of additive, or two or more types. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use. Even when the poly(3-hydroxyalkanoate)-based resin contains these additives, its melting point is approximately the same as that of the poly(3-hydroxyalkanoate)-based resin.

[0042] The crystal nucleating agent, lubricant, filler, and plasticizer will be described in more detail below. (Crystal Nucleating Agent) Examples of crystal nucleating agents include polyhydric alcohols including sugar 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 poly(3-hydroxyalkanoate) resins. One or more crystal nucleating agents may be used, and the ratio of their use can be appropriately adjusted depending on the purpose.

[0043] When a nucleating agent is used, the amount used is not particularly limited, but is preferably 0.5 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, relative to 100 parts by weight of the total amount of the poly(3-hydroxyalkanoate) resin.

[0044] The stretched film may contain or may be substantially free of sugar alcohols such as pentaerythritol. In an embodiment in which the film contains substantially no sugar alcohols, the problem of sugar alcohols bleeding out from the film and the resulting contamination of the cast roll surface can be avoided. "Substantially free of sugar alcohols" means that the amount of sugar alcohols used is 0 parts by weight or more and less than 0.5 parts by weight, relative to 100 parts by weight of the total amount of poly(3-hydroxyalkanoate) resin. It may be less than 0.1 parts by weight, less than 0.01 parts by weight, or even 0 parts by weight.

[0045] When the composition is substantially free of sugar alcohols, it is preferable to contain talc as a filler and / or fatty acid amide as a lubricant, and it is more preferable to contain both talc as a filler and fatty acid amide as a lubricant.

[0046] (Lubricant) The inclusion of a lubricant can improve the sliding properties with an extruder or the like. In particular, when pelletized film raw materials are used for production, improved sliding properties with the extruder and die can enable efficient production of stretched films. Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and fatty acid amides such as polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide or erucamide is preferred because of its particularly excellent lubricating effect on poly(3-hydroxyalkanoate)-based resins. One or more lubricants may be used, and the ratio of use can be appropriately adjusted depending on the purpose.

[0047] When a lubricant is used, the amount used is not particularly limited, but is preferably 0.3 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.5 to 1.5 parts by weight, relative to 100 parts by weight of the total amount of poly(3-hydroxyalkanoate)-based resin. However, the stretched film may be substantially free of lubricant. "Substantially free of lubricant" means that the amount of lubricant used is 0 parts by weight or more and less than 0.3 parts by weight, relative to 100 parts by weight of the total amount of poly(3-hydroxyalkanoate)-based resin. It may be less than 0.1 parts by weight, less than 0.01 parts by weight, or even 0 parts by weight.

[0048] (Filler) By including a filler, a stretched film with higher strength can be obtained, and when the stretched film is produced using a roll, the peelability from the roll can be improved. 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 include silicates such as magnesium silicate, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, carbon black, etc. Only one type of inorganic filler may be used, or two or more types may be used in combination.

[0049] When a filler is used, its content is not particularly limited, but is preferably 0.1 to 100 parts by weight, more preferably 0.1 to 30 parts by weight, even more preferably 0.5 to 20 parts by weight, and even more preferably 1 to 10 parts by weight, relative to 100 parts by weight of the total amount of poly(3-hydroxyalkanoate)-based resin. However, the stretched film may be substantially free of fillers. "Substantially free of fillers" means that the amount of filler used is 0 parts by weight or more and less than 0.5 parts by weight, relative to 100 parts by weight of the total amount of poly(3-hydroxyalkanoate)-based resin. It may be less than 0.1 parts by weight, less than 0.01 parts by weight, or even 0 parts by weight.

[0050] (Plasticizers) Examples of plasticizers include glycerin ester compounds, citrate ester compounds, sebacate compounds, adipate 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, sebacate compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on poly(3-hydroxyalkanoate) resins. Examples of glycerin ester compounds include glycerin diacetomonolaurate. Examples of citrate ester compounds include acetyl tributyl citrate. Examples of sebacate 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.

[0051] 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 total amount of poly(3-hydroxyalkanoate) resin. However, the stretched film may be substantially free of plasticizer. "Substantially free of plasticizer" means that the amount of plasticizer used is 0 parts by weight or more and less than 0.5 parts by weight, per 100 parts by weight of the total amount of poly(3-hydroxyalkanoate) resin. It may be less than 0.1 parts by weight, less than 0.01 parts by weight, or even 0 parts by weight.

[0052] (Other Resins) The stretched film may contain other resins besides the poly(3-hydroxyalkanoate)-based resin, as long as the effects of the invention are not impaired. Examples of such other resins include aliphatic polyester-based resins such as poly(3-hydroxypropionate), poly(4-hydroxybutyrate), polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, 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.

[0053] The content of the other resin is not particularly limited, but may be 100 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, 50 parts by weight or less, 30 parts by weight or less, 20 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight or more.

[0054] Furthermore, when the other resin has a lower melting point than the poly(3-hydroxyalkanoate)-based resin, the lower limit may be 10 parts by weight or more, 20 parts by weight or more, 50 parts by weight or more, or 65 parts by weight or more relative to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin, and the upper limit may be 100 parts by weight or less relative to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin.

[0055] <Production of Stretched Film> A stretched film containing the poly(3-hydroxyalkanoate)-based resin of the present disclosure can be produced by the following production method. The production method includes the steps of melting a film raw material containing the poly(3-hydroxyalkanoate)-based resin in an extruder and then forming it into a film, stretching the formed film while heating it, and heat-treating the stretched film while relaxing it in the stretching direction, wherein the heat treatment includes heating the stretched film to a temperature range of at least the melting point of the poly(3-hydroxyalkanoate)-based resin minus 50°C and not more than the melting point of the poly(3-hydroxyalkanoate)-based resin minus 20°C. The poly(3-hydroxyalkanoate)-based resin contains the copolymer (A).

[0056] In the process of melting a film raw material containing a poly(3-hydroxyalkanoate) resin in an extruder and then molding it into a film, the film raw material containing the poly(3-hydroxyalkanoate) resin may be a film raw material that has been first melt-kneaded by adding the poly(3-hydroxyalkanoate) resin and the optional components described above to an extruder, and then pelletized. Alternatively, the pelletization process may be omitted, and the film molding process may be carried out immediately after the melt-kneading.

[0057] The melt-kneading can be carried out according to a known or conventional method, and can be carried out, for example, using an extruder (single-screw extruder or twin-screw extruder), a kneader, etc. The melt-kneading conditions are not particularly limited and can be set appropriately, but when an organic peroxide is added, it is preferable to set a resin temperature and residence time that can complete the reaction with the organic peroxide during melt-kneading, and a temperature and residence time that can uniformly disperse or melt other optional components. Specifically, for example, it is preferable to melt-knead at a resin temperature measured with a die thermometer in the range of 130°C to 190°C. It is also preferable to melt-knead so that the residence time in the extruder is 60 seconds to 300 seconds.

[0058] After melt-kneading, the film raw material can be extruded into a strand shape and cut to obtain pellets having particle shapes such as cylindrical, elliptical, spherical, cubic, rectangular, etc. The produced pellets are preferably used after being thoroughly dried at 40 to 80°C to remove moisture.

[0059] (Molding step) In the step of melting a film raw material containing a poly(3-hydroxyalkanoate) resin in an extruder and then molding it into a film, the method of molding it into a film is not particularly limited, and known manufacturing methods can be used as appropriate. Specific examples include inflation molding, T-die extrusion molding using an extruder equipped with a T-die, calendar molding, rolling, and the like. Among these, inflation molding or T-die extrusion molding, particularly T-die extrusion molding, are preferred because they allow for the production of strip-shaped films with good productivity. Furthermore, the extruder can be a single-screw extruder (also called a single-screw extruder), a twin-screw extruder, or the like, as appropriate.

[0060] The molding temperature is not particularly limited as long as it is a temperature at which the resin can be properly melted, but for example, 130 to 200°C is preferable. The molding temperature here refers to the resin temperature from the extruder to the time when the resin is discharged from the die. The resin temperature can generally be measured, for example, by a thermometer installed in the adapter.

[0061] (T-die extrusion molding method) The T-die extrusion molding method refers to a molding method in which a molten resin is extruded by an extruder onto a casting roll through a slit-shaped outlet to form a film. When the molten resin is extruded onto the casting roll by the extruder, it comes into contact with the casting roll and moves along the surface of the casting roll, whereby it is cooled and solidified. The T-die is not particularly limited, and any known T-die can be used as appropriate. For example, the T-die preferably has an outlet shaped to allow the extrusion of a film-shaped raw material, but the shape is not particularly limited. Furthermore, the shape of the outlet is also not particularly limited.

[0062] In the T-die extrusion molding method, a film-shaped raw material is extruded from the discharge port of a T-die. The shape of the raw material may be a film, and the thickness and width are not particularly limited. The thickness is preferably about 20 μm to 600 μm, since this results in less thickness variation and allows for easy cooling after extrusion.

[0063] The melt viscosity of the raw material extruded from the discharge port of the T-die is not particularly limited, but is preferably 1500 Pa sec or less in order to minimize thickness unevenness and prevent the occurrence of die lines. The melt viscosity can be measured according to a known method as appropriate.

[0064] The set temperature of the casting roll is not particularly limited as long as the film is cooled and solidified, but from the viewpoint of transportability, it is preferably 0° C. or higher, more preferably 10° C. or higher, and even more preferably 20° C. or higher. From the viewpoint of improving the stretchability of the film, it is preferably 100° C. or lower, more preferably 80° C. or lower, and even more preferably 60° C. or lower.

[0065] The thickness of the film before stretching is not particularly limited and may be appropriately set in consideration of the desired thickness of the stretched film, the stretching ratio, strength, etc. For example, the thickness is preferably 20 to 600 μm, more preferably 40 to 500 μm, and even more preferably 50 to 300 μm. The thickness of the film can be measured using a vernier caliper.

[0066] (Stretching Step) In the step of stretching the formed film while heating it, the method is not particularly limited as long as it is possible to stretch the film, and known manufacturing methods can be used as appropriate.

[0067] The stretching direction in the stretching step is not particularly limited, and the film can be stretched in any direction in the plane direction of the film. When the film is a strip-shaped film, the stretching direction may be either the MD direction or the TD direction of the film, or both the MD and TD directions. Stretching in either the MD direction or the TD direction is called uniaxial stretching, and stretching in both the MD and TD directions is called biaxial stretching. Here, the MD direction is also called the machine direction, conveying direction, flow direction, or longitudinal direction. The TD direction is the direction perpendicular to the MD direction, and is also called the perpendicular direction or width direction.

[0068] Although the specific stretching method is not particularly limited, a method of stretching the film by stretching it in the stretching direction is preferred. Stretching the film in the stretching direction means pulling the film in the stretching direction. On the other hand, when stretching is performed by applying pressure in the thickness direction of the film, such as roll rolling in which the film is sandwiched between two rolls, the film tends to adhere to the rolling rolls, which may reduce the productivity of the stretched film.

[0069] The method for stretching the film in the stretching direction is not particularly limited. The film can be stretched by gripping the ends of the film and pulling it in the stretching direction. Stretching can be performed using a pair of rolls, with a difference in the rotation speed between the pair of rolls. In this case, the stretching ratio can be determined by the ratio of the rotation speed of the rolls before stretching to the rotation speed of the rolls after stretching. In particular, when stretching is performed in a batch system, the film can be stretched by gripping the ends of the film and pulling it in the stretching direction.

[0070] In the stretching step, when the stretching is performed while the formed film is being transported, the stretching direction is preferably the transport direction (MD direction) from the viewpoint of productivity.

[0071] When the film is stretched in the MD direction while being continuously transported, for example, a roll longitudinal stretching machine is used, and the film can be stretched in the MD direction by using a plurality of rolls, for example, a pair of rolls, which transport the film, and varying the rotation speed between the pair of rolls. The stretching ratio in the MD direction can be determined by the ratio of the rotation speed of the roll before stretching to the rotation speed of the roll after stretching.

[0072] When the film is stretched in the TD direction while being continuously transported, the film can be stretched in the TD direction by clamping both widthwise ends of the film using a transverse stretching machine such as a clip-type tenter and pulling the film in the TD direction. The stretch ratio in the TD direction can be determined by the ratio of the clamped width of the film before stretching to the clamped width of the film after stretching.

[0073] The stretching ratio achieved in the step of stretching the formed film is not particularly limited, but is preferably 1.1 times or more, more preferably 1.3 times or more, even more preferably 1.5 times or more, and particularly preferably 2 times or more. The upper limit is not particularly limited and may be determined appropriately, but may be, for example, 8 times or less, 7 times or less, 5 times or less, or 3 times or less.

[0074] The film temperature (also referred to as the film stretching temperature) due to heating in the stretching step is not particularly limited as long as it is a temperature at which the film can be appropriately stretched, and may be changed depending on the mechanical strength, surface properties, thickness accuracy, etc. required of the stretched film to be produced.

[0075] The film stretching temperature is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. The upper limit may be any temperature equal to or lower than the melting point of the poly(3-hydroxyalkanoate) resin, and is preferably 150°C or lower, more preferably 145°C or lower, even more preferably 140°C or lower, and may be lower than 130°C. When the stretching temperature is within the above temperature range, thickness unevenness of the resulting stretched film can be reduced, and mechanical properties such as elongation, tear propagation strength, and flexural fatigue resistance can be improved. Furthermore, problems such as the film sticking to the roll can be prevented.

[0076] The means for adjusting the stretching temperature is not particularly limited, and examples thereof include non-contact heating methods such as a method of applying hot air heated to within the above temperature range to the film being stretched, a method of heating the film being stretched using an auxiliary heating means such as an infrared heater, and a method of stretching the film in a heating furnace whose temperature is adjusted to within the above temperature range; and contact heating methods such as a method of bringing the film into contact with a roll heated to within the above temperature range. These methods may be used alone or in combination.

[0077] In the method of bringing the film into contact with rolls heated to within the above temperature range, hot air may be applied to the film between the upstream stretching roll and the downstream stretching roll in the MD direction.

[0078] From the viewpoint of heating efficiency, it is preferable to use a floating heating method as a method for applying hot air heated to within the above temperature range to the film during stretching. Floating heating is a method in which hot air is blown onto both sides of the film from upper and lower nozzles. Multiple upper nozzles and multiple lower nozzles are arranged alternately toward the film surface, and the film can be heated by the hot air blown from each of the upper and lower nozzles without the film coming into contact with either the upper or lower nozzle.

[0079] In the method of using an auxiliary heating means such as an infrared heater to heat the film during stretching, the temperature of the film surface and inside can be raised to the same temperature in a short period of time, enabling uniform stretching throughout the entire film.

[0080] The infrared rays to be irradiated can be electromagnetic waves in the general infrared region, and may be any of near infrared rays: wavelength 0.74 μm to 1.5 μm, mid infrared rays: wavelength 1.5 μm to 3.0 μm, and far infrared rays: wavelength 3.0 μm to 1 mm.

[0081] In the method of bringing the film into contact with rolls heated to the above temperature range, when the film is stretched using a pair of stretching rolls while being continuously transported, the upstream stretching roll in the MD direction may be heated to the above temperature range. In this case, the stretching temperature can be controlled by setting the roll temperature to the desired stretching temperature.

[0082] In the production method of the present disclosure, a method of adjusting the film temperature during stretching is preferably a method of bringing the film into contact with rolls heated to the above temperature range, from the viewpoint of excellent productivity and easy heating particularly in mass production. This method is suitable for uniaxial stretching, particularly when stretching in the MD direction using multiple rolls of a roll longitudinal stretching machine.

[0083] From the viewpoint of avoiding the problem of the film sticking to the heating tool, a non-contact heating method in which the heating tool heated to the above temperature range does not come into contact with the film is preferred.

[0084] (Heat Treatment Step) The step of heat treating the stretched film involves heat treating the stretched film while relaxing it in the stretching direction, and the heat treatment includes a treatment of heating the stretched film to a temperature range of the melting point of the poly(3-hydroxyalkanoate) resin −50° C. or more and the melting point of the poly(3-hydroxyalkanoate) resin −20° C. or less. This makes it possible to reduce the amount of heat shrinkage of the stretched film containing the poly(3-hydroxyalkanoate) resin.

[0085] If the melting point of the poly(3-hydroxyalkanoate) resin is higher than -20°C, the film may have poor appearance such as wrinkles or surface roughness after heat treatment.

[0086] If the melting point of the poly(3-hydroxyalkanoate) resin is lower than −50° C., the amount of heat shrinkage of the resulting stretched film in the stretching direction may increase.

[0087] The temperature range for the heat treatment is preferably the melting point of the poly(3-hydroxyalkanoate) resin minus 40° C. or more, and more preferably the melting point of the poly(3-hydroxyalkanoate) resin minus 30° C. or more, because this makes it possible to further reduce the amount of heat shrinkage in the stretching direction.

[0088] The melting point of the poly(3-hydroxyalkanoate) resin refers to the apex temperature of the melting point peak in a DSC curve obtained by differential scanning calorimetry. Details of differential scanning calorimetry will be described in the Examples section.

[0089] The film temperature due to the heat treatment in the heat treatment step is preferably higher than the film temperature due to heating in the stretching step, in order to efficiently remove residual stress due to stretching and reduce the amount of heat shrinkage in the stretching direction.

[0090] When the stretched film produced by the production method of the present disclosure is heated at 100°C for 10 minutes, the heat shrinkage in the stretching direction is preferably 8% or less, more preferably 7% or less, even more preferably 6% or less, and particularly preferably 4% or less. The smaller the heat shrinkage, the better, but it may be 0% or more, or 1% or more. Details of the method for measuring the heat shrinkage are as described in the Examples section.

[0091] In the step of heat-treating the stretched film while relaxing it in the stretching direction, the amount of relaxation in the stretching direction may be greater than 0%, preferably 10% to 25%, more preferably 10% to 20%.

[0092] The relaxation amount can be calculated by the following formula (1): Relaxation amount [%] = {(film dimension in the stretching direction before heat treatment) - (film dimension in the stretching direction during heat treatment)} / (film dimension in the stretching direction before heat treatment) × 100 (1)

[0093] Here, relaxation refers to reducing the film dimension in the stretching direction to remove the stress present in the film in the stretching direction. Furthermore, film dimension refers to the length from one end of the film to the other. When the film is a strip-shaped film, the film dimension in the MD direction can be adjusted by adjusting the ratio of the rotation speeds of two adjacent rolls, and the film dimension in the TD direction can be adjusted by changing the width of the clamped film. When slack occurs in the film during heat treatment, the film dimension is the linear distance from one end of the film to the other.

[0094] In the heat treatment step, the method for relaxing the stretched film is not particularly limited, but from the viewpoint of productivity, it is preferable to use a pair of rolls and to differentiate the rotation speeds of the rolls in the pair.

[0095] In particular, when the film is a strip-shaped film and the film dimension in the MD direction is adjusted using the ratio of the rotation speeds of a pair of rolls, the relaxation amount can be calculated by the following formula (2): Relaxation amount [%] = {(Rotation speed of the upstream roll of the pair of rolls) - (Rotation speed of the downstream roll of the pair of rolls)} / (Rotation speed of the upstream roll of the pair of rolls) × 100 (2)

[0096] The time for the heat treatment of the stretched film is not particularly limited, but from the viewpoint of productivity, it is preferably 0.5 to 30 seconds, more preferably 0.5 to 10 seconds, and even more preferably 0.5 to 5 seconds.

[0097] The means for adjusting the film temperature in the heat treatment is not particularly limited, and examples thereof include non-contact heating methods such as a method of applying hot air heated to within the above-mentioned temperature range to the film, a method of heating the film using an auxiliary heating means such as an infrared heater, and a method of heating the film by placing it in a heating furnace whose temperature is adjusted to within the above-mentioned temperature range; and contact heating methods such as a method of bringing the film into contact with a roll heated to within the above-mentioned temperature range. These methods may be used alone or in combination.

[0098] The means for adjusting the film temperature during heat treatment can be the same as the means for adjusting the film temperature during stretching, so a description of each method will be omitted.

[0099] As a means for adjusting the film temperature in the heat treatment in the production method of the present disclosure, a method of bringing the film into contact with a roll heated to within the above temperature range is preferred from the viewpoint of excellent productivity, particularly in terms of easy heating in mass production. This is suitable for uniaxial stretching, particularly when stretching in the MD direction of the film using multiple rolls of a roll longitudinal stretching machine, because it allows the film to be continuously transported and is therefore excellent in productivity.

[0100] The manufacturing method of the present disclosure may include a step of cooling the film after the step of heat-treating the film. The film temperature in the step of cooling the film may be 60°C or lower, preferably 40°C or lower. As long as the film temperature can be lowered to a temperature lower than the heat treatment temperature, there are no particular limitations on the means for doing so, and examples include a method of bringing the film into contact with rolls cooled to 60°C or lower, preferably 40°C or lower. More specifically, the film may be cooled on one or more rolls, or by sandwiching the film between two rolls.

[0101] From the viewpoint of productivity, the production method of the present disclosure is preferably carried out in a continuous process from the step of melting the film raw material in an extruder, forming it into a film, to the step of heat-treating it, and further to obtaining a stretched film. Here, the continuous process refers to the step of melting the film raw material in an extruder, forming it into a film, to the step of stretching the formed film, to the step of heat-treating the stretched film, and further to the step of cooling the film as necessary, in order to obtain a stretched film.

[0102] <Preferred embodiment of a method for producing a stretched film by a continuous process> The method for producing a stretched film according to this embodiment may be carried out batchwise, but is preferably carried out continuously from the viewpoint of the productivity of the stretched film. When carried out continuously, it is preferable to carry out each step while continuously transporting the film. Specifically, it is preferable to carry out the stretching step and the heat treatment step sequentially while continuously transporting the film formed by melting a film raw material containing the poly(3-hydroxyalkanoate) resin in an extruder and extruding it onto a cast roll. Furthermore, it is preferable to continuously wind up the stretched film that has undergone each step on a winding roll.

[0103] 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.

[0104] FIG. 1 shows an example of a production line for continuously carrying out the film forming step (i), stretching step (ii), and heat treatment step (iii) using a T-die extrusion molding method while transporting the film. The arrows in the figure indicate the flow direction of the film. A film raw material containing a poly(3-hydroxyalkanoate) resin is melted by an extruder 11, extruded onto a cast roll 21, and cooled by cast rolls 21 and 22 while being formed into a film [forming step (i)]. The formed film 31 is transported through a predetermined route by multiple transport rolls, undergoes predetermined treatments including the stretching step (ii) and heat treatment step (iii), and is then taken up around a take-up roll 51 as a stretched film 32.

[0105] The multiple transport rolls are composed of, in order from the casting roll 21 side along the flow direction, two casting rolls 21 and 22, a pair of stretching rolls 41 and 42, and a pair of heat treatment rolls 61 and 62. However, the numbers of casting rolls, stretching rolls, and heat treatment rolls are not limited to those mentioned above.

[0106] The casting rolls 21 and 22 are set so that the roll surface temperature gradually decreases along the flow direction. When a film raw material containing a poly(3-hydroxyalkanoate) resin melted in an extruder comes into contact with the casting rolls 21 and 22, it is gradually cooled and formed into a film (step (i)). Because the casting rolls 21 and 22 have relatively low set temperatures, film sticking to the rolls is suppressed.

[0107] The film is stretched between a pair of stretching rolls 41 and 42. The rotation speed of the downstream stretching roll 42 is controlled to be faster than the rotation speed of the upstream stretching roll 41, and the formed film 31 is stretched in the MD direction due to this difference in rotation speed.

[0108] Of the pair of stretching rolls 41 and 42, the surface temperature of the upstream stretching roll 41 is controlled to a desired stretching temperature, thereby making it possible to adjust the film temperature during stretching.

[0109] The stretched film is heat-treated between a pair of heat-treatment rolls 61 and 62. The rotation speed of the downstream heat-treatment roll 62 is controlled to be slower than the rotation speed of the upstream heat-treatment roll 61, and due to this difference in rotation speed, the stretched film is heat-treated while being relaxed in the stretching direction.

[0110] Of the heat treatment rolls 61 and 62, the surface temperature of the heat treatment roll 61 located on the upstream side can be controlled to a desired heat treatment temperature, thereby adjusting the film temperature during heat treatment.

[0111] The film that has been subjected to the forming step (i), stretching step (ii), and heat treatment step (iii) as described above is taken up around the take-up roll 51 as a stretched film 32. In this manner, stretched films can be continuously produced.

[0112] <Stretched Film> The thickness of the stretched film is not particularly limited and may be appropriately set to the desired thickness. From the viewpoints of the uniform thickness, appearance, strength, lightness, etc. of the film, the thickness is preferably 10 to 200 μm, more preferably 15 to 150 μm, and even more preferably 20 to 100 μm. The thickness of the film can be measured using a vernier caliper.

[0113] The stretched film of the present disclosure is thin yet has high strength, and therefore can be suitably used as a packaging film, for example, a packaging film (including bottle labels) for food and the like that requires heat sealability.

[0114] The following items are preferred embodiments of the present disclosure, but the present invention is not limited to them. [Item 1] A method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin, comprising the steps of melting a film raw material containing the poly(3-hydroxyalkanoate) resin in an extruder and then forming it into a film, stretching the formed film while heating it, and heat-treating the stretched film while relaxing it in the stretching direction, wherein the heat treatment includes heating the stretched film to a temperature range of at least the melting point of the poly(3-hydroxyalkanoate) resin minus 50°C and not more than the melting point of the poly(3-hydroxyalkanoate) resin minus 20°C, A method for producing a stretched film, wherein the poly(3-hydroxyalkanoate) resin contains a copolymer (A), the copolymer (A) contains 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average content ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units in all monomer units constituting the copolymer (A) is 3-hydroxybutyrate units / other hydroxyalkanoate units = 76 / 24 to 50 / 50 (mol % / mol %). [Item 2] A method for producing a stretched film according to Item 1, wherein the copolymer (A) is contained in an amount of 5 to 40 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin. [Item 3] A method for producing a stretched film according to Item 1 or 2, wherein the film temperature due to heat treatment in the heat treatment step is higher than the film temperature due to heating in the stretching step. [Item 4] The method for producing a stretched film according to any one of items 1 to 3, wherein the relaxation in the heat treatment step is carried out using a pair of rolls by varying the rotation speed of the pair of rolls. [Item 5] The method for producing a stretched film according to any one of items 1 to 4, wherein the amount of relaxation in the stretching direction in the heat treatment step is 10% or more and 25% or less. [Item 6] The method for producing a stretched film according to any one of items 1 to 5, wherein the stretched film contains 95% by weight or more of a poly(3-hydroxyalkanoate) resin.[Item 7] The method for producing a stretched film according to any one of items 1 to 6, wherein the copolymer (A) is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate). [Item 8] The method for producing a stretched film according to any one of items 1 to 7, wherein in the stretching step, the stretching is performed while transporting the formed film, and the stretching direction is the transport direction. [Item 9] The method for producing a stretched film according to any one of items 1 to 8, wherein the stretched film is a uniaxially stretched film.

[0115] 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.

[0116] The following raw materials were used in the examples and comparative examples. Resins A-1 to A-4 were used as poly(3-hydroxyalkanoate) resins, B-1 was used as a lubricant, and C-1 to C-3 were used as additives. In the following, 3HB represents a 3-hydroxybutyrate repeating unit, and 3HH represents a 3-hydroxyhexanoate repeating unit.

[0117] (Resin) Poly(3-hydroxyalkanoate) resin A-1: ​​P3HB3HH (average content ratio 3HB / 3HH=97.2 / 2.8 (mol% / mol%)) Resin A-1 was produced in accordance with the method described in Example 2 of WO 2019 / 142845, and the weight average molecular weight was adjusted to 660,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0118] Poly(3-hydroxyalkanoate) resin A-2: P3HB3HH (average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%)), which corresponds to the copolymer (A). Resin A-2 was produced in accordance with the method described in Example 9 of WO 2019 / 142845, and the weight-average molecular weight was adjusted to 660,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0119] Poly(3-hydroxyalkanoate) resin A-3: P3HB3HH (average content ratio 3HB / 3HH=94 / 6 (mol% / mol%)). Resin A-3 was produced in accordance with the method described in Example 1 of WO 2019 / 142845, and the weight-average molecular weight was adjusted to 630,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0120] Poly(3-hydroxyalkanoate) Resin A-4: P3HB (Poly(3-hydroxybutyrate)) Resin A-4 was produced in accordance with the method described in Comparative Example 1 of WO 2004 / 041936, and the weight-average molecular weight was adjusted to 350,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0121] (Lubricant) B-1: Behenic acid amide (manufactured by Nippon Fine Chemical Co., Ltd.: BNT-22H)

[0122] (Additives) C-1: Hydrous magnesium silicate (manufactured by Nippon Talc Co., Ltd.: SG-200N15) C-2: t-butylperoxyisopropyl carbonate (manufactured by NOF Corporation: Perbutyl I) C-3: Pentaerythritol (manufactured by Mitsubishi Chemical Corporation, Neuraizer P)

[0123] (Method for producing resin composition) Resin composition P-1 Poly (3-hydroxyalkanoate) resin, A-1: ​​37.5 parts by weight, A-2: 37.5 parts by weight, A-3: 5 parts by weight, A-4: 20 parts by weight, for a total of 100 parts by weight, B-1: 1 part by weight as a lubricant, C-1: 1 part by weight as an additive, C-2: 0.2 parts by weight were dry blended. The obtained dry blend was put into a φ26 mm co-rotating twin-screw extruder hopper with the cylinder temperature and die temperature set to 160 ° C, melt-kneaded, extruded into a strand shape from the die, passed through a water tank filled with hot water at 45 ° C to solidify the strand, and cut with a pelletizer to obtain a pellet-shaped resin composition P-1. The melting point of the resin composition P-1 was 153 ° C.

[0124] Resin composition P-2 Poly (3-hydroxyalkanoate) resin, A-1: ​​30 parts by weight, A-2: 30 parts by weight, A-3: 20 parts by weight, A-4: 20 parts by weight, for a total of 100 parts by weight, B-1: 1 part by weight as a lubricant, C-1: 1 part by weight as an additive, C-2: 0.2 parts by weight were dry blended. The obtained dry blend was put into a φ26 mm co-rotating twin-screw extruder hopper with the cylinder temperature and die temperature set to 160 ° C, melt-kneaded, extruded into strands from the die, passed through a water tank filled with hot water at 45 ° C to solidify the strands, and cut with a pelletizer to obtain a pellet-shaped resin composition P-2. The melting point of the resin composition P-2 was 153 ° C.

[0125] Resin composition P-3 Poly (3-hydroxyalkanoate) resin: A-1: ​​7.5 parts by weight, A-2: 7.5 parts by weight, A-3: 65 parts by weight, A-4: 20 parts by weight, a total of 100 parts by weight of B-1: 1 part by weight as a lubricant, C-1: 1 part by weight as an additive, C-2: 0.2 parts by weight were dry blended. The obtained dry blend was put into a φ26 mm co-rotating twin-screw extruder hopper with the cylinder temperature and die temperature set to 160 ° C, melt-kneaded, extruded into strands from the die, passed through a water bath filled with hot water at 45 ° C to solidify the strands, and cut with a pelletizer to obtain a pellet-shaped resin composition P-3. The melting point of the resin composition P-3 was 153 ° C.

[0126] Resin composition P-4: 100 parts by weight of poly(3-hydroxyalkanoate) resin A-3 was dry-blended with 0.5 parts by weight of B-1 as a lubricant and 1 part by weight of C-3 as an additive. The resulting dry blend was placed in a hopper of a φ26 mm co-rotating twin-screw extruder with the cylinder temperature and die temperature set to 150 ° C, melt-kneaded, extruded into strands from the die, passed through a water bath filled with hot water at 45 ° C to solidify the strands, and cut with a pelletizer to obtain pellet-shaped resin composition P-4. The melting point of resin composition P-4 was 146 ° C.

[0127] (Weight Average Molecular Weight) The weight average molecular weight of the resin was measured in terms of polystyrene using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation).

[0128] (Film Heat Shrinkage) The film to be measured was cut into a square of 5 cm in the MD direction x 5 cm in the TD direction, and heated in an oven set to 100°C for 10 minutes. Furthermore, the dimensions of the film in the MD direction before and after heating were measured, and the heat shrinkage in the MD direction was calculated using the following formula: Heat shrinkage [%] = (1 - (dimension after heating) / (dimension before heating)) x 100

[0129] (Evaluation of Film Appearance) The appearance of the obtained film was observed with the naked eye to check for the presence or absence of irregularities and wrinkles. Films for which no irregularities or wrinkles were observed were rated as ○ (good), and films for which irregularities or wrinkles were observed were rated × (bad).

[0130] [Example 1] (Film molding process) The cylinder temperature and die temperature of a φ40 mm single-screw extruder connected to a 350 mm wide T-die were each set to 165 ° C. The resin composition P-1 was charged into the single-screw extruder, melted, and the molten resin at a temperature of 165 ° C. was extruded into a film using a T-die. The film-like molten resin was extruded onto a cast roll CR1 set at 60 ° C., and molded at a take-up speed of 10 m / min with cast rolls CR1 and CR2 (CR2 is the roll downstream of CR1), and cooled to a film temperature of 40 ° C. (the set temperature of the cast roll CR2). The film was peeled off from the cast roll CR2 (molding process). The set temperatures of the cast rolls CR1 and CR2 in this molding process are as shown in Table 1.

[0131] (Film Stretching Step) The formed film was continuously transported and stretched in the film transport direction while being heated by a pair of stretching rolls R2 and R3 (R3 is a roll downstream of R2) (stretching step). The set temperatures of the pair of stretching rolls R2 and R3 and the stretch ratio in the MD direction in this stretching step are as shown in Table 1.

[0132] (Film Heat Treatment Step) The stretched film was continuously transported and heat-treated while being relaxed in the stretching direction by a pair of heat treatment rolls R4 and R5 (R5 is a roll downstream of R4) (heat treatment step), to obtain a stretched film. The set temperatures and relaxation amounts (%) of the pair of heat treatment rolls R4 and R5 in the heat treatment step are as shown in Table 1, and the relaxation amounts (%) were calculated using the above formula (2). Note that when the rotational speeds of the heat treatment roll R4 and the heat treatment roll R5 are substituted into the above formula (2), the following is obtained: Relaxation amount [%] = {(Rotational speed of heat treatment roll R4) - (Rotational speed of heat treatment roll R5)} / (Rotational speed of heat treatment roll R4) x 100

[0133] The heat shrinkage in the MD direction of the obtained stretched film and the evaluation results of the appearance are shown in Table 1.

[0134]

[0135] [Examples 2 to 3, Comparative Examples 1 to 5] Stretched films were obtained in the same manner as in Example 1, except that the roll temperature (set temperature), MD stretch ratio, and relaxation amount were set as shown in Table 1. The evaluation results of the heat shrinkage in the MD and appearance of the obtained stretched films are shown in Table 1.

[0136] [Examples 4 to 6, Comparative Examples 6 to 10] Stretched films were obtained using resin composition P-2. Stretched films were obtained in the same manner as in Example 1, except that the resin composition was changed, and the roll temperature (set temperature), MD stretch ratio, and relaxation amount were each set as shown in Table 2. The evaluation results of the heat shrinkage in the MD and appearance of the obtained stretched films are shown in Table 2.

[0137]

[0138] [Examples 7 to 8, Comparative Examples 11 to 14] Stretched films were obtained using resin composition P-3. At this time, stretched films were obtained in the same manner as in Example 1, except that the resin composition was changed, and the roll temperature (set temperature), MD stretch ratio, and relaxation amount were each set as shown in Table 3. The evaluation results of the heat shrinkage in the MD direction and appearance of the obtained stretched films are as shown in Table 3.

[0139]

[0140] Comparative Example 15: An attempt was made to obtain a stretched film using resin composition P-4. The procedure was the same as in Example 1, except that the resin composition was changed, and the roll temperature (set temperature), MD stretch ratio, and relaxation amount were each set as shown in Table 3.

[0141] The stretched films of Examples 1 to 8 were obtained by molding a film raw material containing a poly(3-hydroxyalkanoate) resin (specific resin) containing a copolymer (A) containing 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the average content ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units among all the monomer units constituting the copolymer (A) is 3-hydroxybutyrate units / other hydroxyalkanoate units = 76 / 24 to 50 / 50 (mol % / mol %), stretching the formed film while heating, and heat-treating the film under specific heat-treatment conditions while relaxing in the stretching direction. The films could be stretched at least 2 to 2.5 times, had a small heat shrinkage of 8.0% or less, were free from unevenness and wrinkles, and had a good appearance evaluation.

[0142] On the other hand, the stretched films of Comparative Examples 1 to 14, which were obtained without relaxation or without specific heat treatment conditions in the heat treatment step, could be stretched 2 to 2.5 times, but had large amounts of heat shrinkage or wrinkles, and were evaluated as poor in appearance. Furthermore, the film of Comparative Example 15, which was molded using a film raw material containing P3HB but not the specific resin, experienced uneven stretching during the stretching step, and a stretched film could not be obtained.

[0143] 31 Molded film 32 Stretched film (i) Molding step (ii) Stretching step (iii) Heat treatment step

Claims

1. A method for producing a stretched film containing a poly(3-hydroxyalkanoate) resin, comprising the steps of melting a film raw material containing the poly(3-hydroxyalkanoate) resin in an extruder and then forming it into a film; stretching the formed film while heating it; and heat-treating the stretched film while relaxing it in the stretching direction, wherein the heat treatment includes heating the stretched film to a temperature within the range of the melting point of the poly(3-hydroxyalkanoate) resin minus 50°C or more and the melting point of the poly(3-hydroxyalkanoate) resin minus 20°C or less. The method for producing a stretched film, wherein the poly(3-hydroxyalkanoate) resin comprises a copolymer (A), the copolymer (A) comprises 3-hydroxybutyrate units and other hydroxyalkanoate units, and the average content ratio of the 3-hydroxybutyrate units to the other hydroxyalkanoate units in all monomer units constituting the copolymer (A) is 3-hydroxybutyrate units / other hydroxyalkanoate units = 76 / 24 to 50 / 50 (mol % / mol %).

2. The method for producing a stretched film according to claim 1, wherein the copolymer (A) is contained in an amount of 5 to 40 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin.

3. The method for producing a stretched film according to claim 1 or 2, wherein the film temperature due to the heat treatment in the heat treatment step is higher than the film temperature due to heating in the stretching step.

4. The method for producing a stretched film according to claim 1 or 2, wherein the relaxation in the heat treatment step is carried out by using a pair of rolls and varying the rotation speed of the rolls in the pair.

5. The method for producing a stretched film according to claim 1 or 2, wherein the amount of relaxation in the stretching direction in the heat treatment step is 10% or more and 25% or less.

6. The method for producing a stretched film according to claim 1 or 2, wherein the stretched film contains 95% by weight or more of a poly(3-hydroxyalkanoate) resin.

7. The method for producing a stretched film according to claim 1 or 2, wherein the copolymer (A) is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

8. The method for producing a stretched film according to claim 1 or 2, wherein in the stretching step, the stretching is performed while the formed film is being transported, and the stretching direction is the transport direction.

9. The method for producing a stretched film according to claim 1 or 2, wherein the stretched film is a uniaxially stretched film.

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