Manufacturing method of biaxially oriented film

Abstract

To provide a manufacturing method of a biaxially oriented film involving a poly(3-hydroxybutyrate)-based resin with good productivity.SOLUTION: A biaxially oriented film is obtained by melting a film raw material involving a poly(3-hydroxybutyrate)-based resin by using an extruder, followed by forming into a film shape and continuously drawing the formed film at a draw ratio of 1.1-fold or more in the MD direction and the TD direction both. Continuous drawing of the film in the MD direction can be run by differentiating roll rotational speeds between a plurality of rolls which are transporting the film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a biaxially stretched film containing a poly(3-hydroxybutyrate)-based resin. [Background technology]

[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, adsorb harmful compounds in seawater, and when marine organisms ingest these, harmful substances are introduced into the food chain.

[0005] The use of biodegradable plastics is expected to combat this type of marine pollution, 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.

[0006] In this context, poly(3-hydroxybutyrate) resins are attracting attention as a material that can solve the above problems because they are biodegradable even in seawater.

[0007] On the other hand, a method of biaxially stretching a film is known as a technique for producing a thin, high-strength film. Patent Document 1 describes a method for producing a biaxially stretched film by melting a thermoplastic resin containing a poly(3-hydroxybutyrate)-based resin as a main component, forming it into a film, crystallizing it over a certain period of time, sandwiching it between two rolls and rolling it to perform a primary stretching, and then performing a secondary stretching at a temperature higher than the temperature during the rolling. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-168159 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 as a main component can be produced. However, the production method described in this document requires an annealing step to crystallize the poly(3-hydroxybutyrate) resin before stretching. This annealing step is described as taking a long time, such as 12 hours, and therefore the film cannot be produced in a continuous process, resulting in poor productivity. Furthermore, the primary stretching is carried out by rolling the film between two rolls to apply pressure, which can cause the film to stick to the rolls. .

[0010] In view of the above-mentioned current situation, an object of the present invention is to provide a method for producing a biaxially stretched film containing a poly(3-hydroxybutyrate)-based resin with good productivity. [Means for solving the problem]

[0011] As a result of intensive research to solve the above problems, the inventors discovered that a biaxially oriented film containing a poly(3-hydroxybutyrate)-based resin can be produced with good productivity by performing the stretching step by stretching the film rather than by roll rolling, and thus completed the present invention.

[0012] That is, the present invention relates to a method for producing a biaxially stretched film containing a poly(3-hydroxybutyrate)-based resin, which comprises the steps of melting a film raw material containing the poly(3-hydroxybutyrate)-based resin in an extruder and then molding it into a film, and continuously stretching the molded film in both the MD direction and the TD direction at a draw ratio of 1.1 times or more to obtain a biaxially stretched film. Preferably, the continuous stretching of the film in the MD direction is carried out by varying the rotation speeds of the rolls that transport the film. Preferably, the production method further includes, after the forming step and before the stretching step, a step of cooling the formed film with a cooling roll while transporting the film. Preferably, the steps from the molding step to the stretching step are carried out in a continuous process. Preferably, from the time when the film raw material containing the poly(3-hydroxybutyrate)-based resin is melted in an extruder until the time when the biaxially stretched film is obtained, the temperatures of the film raw material and the film are within a range of a temperature 10°C lower than the glass transition temperature (Tg) of the poly(3-hydroxybutyrate)-based resin to 175°C. Preferably, the poly(3-hydroxybutyrate)-based resin includes poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Preferably, the film raw material further contains a filler, and the content of the filler is 1 to 100 parts by weight per 100 parts by weight of the poly(3-hydroxybutyrate) resin. More preferably, the filler is an inorganic filler, and even more preferably, the inorganic filler contains at least one selected from silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, and carbon black. Also, more preferably, the filler is an organic filler. Preferably, the thickness of the biaxially stretched film is 10 to 200 μm. Preferably, the forming into the film is carried out by extruding a molten film material through a T-die. [Effects of the Invention]

[0013] According to the present invention, a method for producing a biaxially stretched film containing a poly(3-hydroxybutyrate)-based resin with high productivity can be provided. According to a preferred embodiment, a biaxially stretched film containing a poly(3-hydroxybutyrate)-based resin can be produced continuously with high productivity. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0015] One embodiment relates to a method for producing a biaxially oriented film comprising a poly(3-hydroxybutyrate) based resin. The poly(3-hydroxybutyrate)-based resin is an aliphatic poly(3-hydroxybutyrate) that can be produced from a microorganism. The poly(3-hydroxybutyrate)-based resin is an ester resin, specifically a polyester resin containing 3-hydroxybutyrate as a repeating unit. The poly(3-hydroxybutyrate)-based resin may be a poly(3-hydroxybutyrate) containing only 3-hydroxybutyrate as a repeating unit, or may be a copolymer of 3-hydroxybutyrate and another hydroxyalkanoate. The poly(3-hydroxybutyrate)-based resin may also be a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers.

[0016] Specific examples of the poly(3-hydroxybutyrate)-based resin include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), etc. Among these, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred because of ease of industrial production.

[0017] Furthermore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that changing the composition ratio of the repeating units can change the melting point, degree of crystallinity, and physical properties such as Young's modulus and heat resistance, making it possible to impart physical properties between those of polypropylene and polyethylene, and that it is easy to produce industrially and is a physically useful plastic. In particular, among poly(3-hydroxybutyrate)-based resins that tend to be thermally decomposed when heated to 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoint that it can lower the melting point and enable molding and processing at low temperatures.

[0018] Commercially available products of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) include Kaneka Biodegradable Polymer PHBH (registered trademark) manufactured by Kaneka Corporation.

[0019] The melting point, Young's modulus, etc. of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) vary depending on the ratio of the 3-hydroxybutyrate component to the 3-hydroxyvalerate component. However, because the two components co-crystallize, the degree of crystallinity is high at 50% or more, and although it is more flexible than poly(3-hydroxybutyrate), its brittleness is not sufficiently improved.

[0020] When the poly(3-hydroxybutyrate) resin contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units to all monomer units constituting the poly(3-hydroxybutyrate) resin is preferably 3-hydroxybutyrate units / other hydroxyalkanoates = 99 / 1 to 80 / 20 (mol % / mol %), more preferably 97 / 3 to 85 / 15 (mol % / mol %), from the viewpoint of achieving both strength and productivity of the biaxially stretched film.

[0021] The average content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxybutyrate)-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-hydroxybutyrate)-based resin, and when the poly(3-hydroxybutyrate)-based resin is a mixture of two or more poly(3-hydroxybutyrate)-based resins, the average content ratio of each monomer unit contained in the entire mixture The molar ratio of

[0022] The poly(3-hydroxybutyrate) resin is preferably a mixture of at least two poly(3-hydroxybutyrate) resins differing in the type and / or content of the constituent monomers. In this case, it is more preferable to use a combination of at least one highly crystalline poly(3-hydroxybutyrate) resin and at least one low-crystalline poly(3-hydroxybutyrate) resin.

[0023] Generally, highly crystalline poly(3-hydroxybutyrate)-based resins have excellent productivity but poor mechanical strength, while low-crystalline poly(3-hydroxybutyrate)-based resins have poor productivity but excellent mechanical properties. It is believed that when both resins are used in combination, the highly crystalline poly(3-hydroxybutyrate)-based resin forms fine resin crystal particles, while the low-crystalline poly(3-hydroxybutyrate)-based resin forms tie molecules that crosslink the resin crystal particles. Using these resins in combination can improve the strength and productivity of biaxially stretched films.

[0024] The content of 3-hydroxybutyrate units contained in the highly crystalline poly(3-hydroxybutyrate) resin is preferably higher than the average content of 3-hydroxybutyrate units in all monomer units constituting the mixture of poly(3-hydroxybutyrate) resins. When a highly crystalline poly(3-hydroxybutyrate) resin contains 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of the other hydroxyalkanoate units in the highly crystalline resin is preferably 1 to 5 mol %, more preferably 2 to 4 mol %.

[0025] The highly crystalline poly(3-hydroxybutyrate) resin is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0026] Furthermore, the content of 3-hydroxybutyrate units in the low-crystalline poly(3-hydroxybutyrate) resin is preferably lower than the average content of 3-hydroxybutyrate units in all monomer units constituting the mixture of poly(3-hydroxybutyrate) resins. When a low-crystalline poly(3-hydroxybutyrate) resin contains 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of the other hydroxyalkanoate units in the low-crystalline resin is preferably 24 to 99 mol%, more preferably 24 to 50 mol%, even more preferably 24 to 35 mol%, and particularly preferably 24 to 30 mol%.

[0027] The low-crystalline poly(3-hydroxybutyrate) resin is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0028] When a highly crystalline poly(3-hydroxybutyrate) resin and a low crystalline poly(3-hydroxybutyrate) resin are used in combination, the proportion of each resin relative to the total amount of both resins is not particularly limited, but it is preferable that the former be 10% by weight or more and 60% by weight or less, and the latter be 40% by weight or more and 90% by weight or less, and it is even more preferable that the former be 25% by weight or more and 45% by weight or less, and the latter be 55% by weight or more and 75% by weight or less.

[0029] According to a preferred embodiment, in addition to the high-crystalline poly(3-hydroxybutyrate)-based resin and the low-crystalline poly(3-hydroxybutyrate)-based resin, it is preferable to use a combination of a medium-crystalline poly(3-hydroxybutyrate)-based resin, whose crystallinity is intermediate between the two resins.

[0030] When a medium-crystalline poly(3-hydroxybutyrate) resin contains 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of other hydroxyalkanoate units in the medium-crystalline resin is preferably 6 mol% or more and less than 24 mol%, more preferably 6 mol% or more and 22 mol% or less, even more preferably 6 mol% or more and 20 mol% or less, and preferably 6 mol% or more and 18 mol% or less.

[0031] The medium-crystalline poly(3-hydroxybutyrate) resin is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0032] When the medium-crystalline poly(3-hydroxybutyrate) resin is further used in combination, the proportion of the medium-crystalline poly(3-hydroxybutyrate) resin to the total of the high-crystalline poly(3-hydroxybutyrate) resin, the low-crystalline poly(3-hydroxybutyrate) resin, and the medium-crystalline poly(3-hydroxybutyrate) resin is preferably 1% by weight or more and 99% by weight or less, more preferably 5% by weight or more and 90% by weight or less, and even more preferably 8% by weight or more and 85% by weight or less.

[0033] The method for obtaining a blend of two or more poly(3-hydroxybutyrate) resins is not particularly limited, and may be a method of obtaining a blend by microbial production or a method of obtaining a blend by chemical synthesis. Alternatively, a blend may be obtained by melt-kneading two or more resins using an extruder, kneader, Banbury mixer, roll, or the like, or by dissolving two or more resins in a solvent, mixing, and drying the resins.

[0034] The weight average molecular weight of the entire poly(3-hydroxybutyrate) resin is not particularly limited, but from the viewpoint of achieving both strength and productivity of the biaxially stretched film, it is preferably 200,000 to 2,000,000, more preferably 250,000 to 1,500,000, and even more preferably 300,000 to 1,000,000.

[0035] Furthermore, when the poly(3-hydroxybutyrate) resin is a mixture of two or more poly(3-hydroxybutyrate) resins, the weight-average molecular weight of each poly(3-hydroxybutyrate) resin constituting the mixture is not particularly limited. However, when the aforementioned high-crystalline poly(3-hydroxybutyrate) resin and low-crystalline poly(3-hydroxybutyrate) resin are used in combination, the weight-average molecular weight of the high-crystalline poly(3-hydroxybutyrate) resin is preferably 200,000 to 1,000,000, more preferably 220,000 to 800,000, and even more preferably 250,000 to 600,000, from the viewpoint of achieving both strength and productivity of the biaxially stretched film. On the other hand, the weight-average molecular weight of the low-crystalline poly(3-hydroxybutyrate) resin is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and even more preferably 300,000 to 2,000,000, from the viewpoint of achieving both strength and productivity of the biaxially stretched film. Furthermore, when the aforementioned medium-crystalline poly(3-hydroxybutyrate) resin is further used, the weight-average molecular weight of the medium-crystalline poly(3-hydroxybutyrate) resin is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and even more preferably 300,000 to 2,000,000, from the viewpoint of achieving both strength and productivity of the biaxially stretched film.

[0036] The weight average molecular weight of poly(3-hydroxybutyrate) resin is measured by chloroform solution. The weight average molecular weight can be measured in terms of polystyrene using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a liquid. As a column for the gel permeation chromatography, a column suitable for measuring the weight average molecular weight may be used.

[0037] The method for producing poly(3-hydroxybutyrate) resins is not particularly limited, and may be a production method by 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, as a microorganism that produces a copolymer of 3-hydroxybutyrate and other hydroxyalkanoates, Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alkalige, which produces P3HB4HB, are examples. Ness eutrophus (Alcaligenes eutrophus) and others are known. In particular, in order to increase the productivity of P3HB3HH, we have developed Alcaligenes eutrophus AC32 (Alcaligenes eutrophus AC32), which has been transformed with genes encoding the P3HA synthase group. More preferred are E. coli L. eutrophus AC32, FERM BP-6038 (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), and microbial cells obtained by culturing these microorganisms under appropriate conditions and allowing P3HB3HH to accumulate within the cells are used. In addition to the above, genetically modified microorganisms into which various poly(3-hydroxybutyrate) resin synthesis-related genes have been introduced may be used depending on the poly(3-hydroxybutyrate) resin to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0038] The film raw material or the biaxially stretched film may not contain a filler, but preferably contains a filler. By including a filler, the biaxially stretched film can have higher strength. 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, 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.

[0039] The content of the filler 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, relative to 100 parts by weight of the poly(3-hydroxybutyrate) resin.

[0040] As the raw material for the film, a resin obtained by modifying the poly(3-hydroxybutyrate) resin with a raw material (modifying raw material) that reacts with the resin, such as peroxide, can be used. When a modified resin is used as a film raw material, the resin may be reacted with the modifying raw material in advance and the resulting raw material may be molded into a film, or the modifying raw material may be mixed with the resin and reacted during film molding. When reacting the resin with the modifying raw material, the entire resin may be reacted with the modifying raw material, or a part 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.

[0041] The modifying raw material is not particularly limited as long as it is a compound that can react with the poly(3-hydroxybutyrate)-based resin. However, organic peroxides are preferably used in terms of ease of handling and ease of controlling the reaction with the poly(3-hydroxybutyrate)-based resin.

[0042] 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-ethylhexanoate, disuccinic acid peroxide, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethyl Examples of organic peroxides include tert-butylperoxy-2-ethylhexyl carbonate, tert-butylperoxyisopropyl carbonate, 1,6-bis(tert-butylperoxycarbonyloxy)hexane, tert-butylperoxy-3,5,5-trimethylhexanoate, tert-butylperoxyacetate, tert-butylperoxybenzoate, tert-amylperoxy-3,5,5-trimethylhexanoate, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, and 2,2-di-tert-butylperoxybutane. Among these, tert-butylperoxy-2-ethylhexyl carbonate and tert-butylperoxyisopropyl carbonate are preferred. Furthermore, combinations of two or more of these organic peroxides can also be used.

[0043] 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-hydroxybutyrate)-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-hydroxybutyrate)-based resin and is likely to suppress local modification reactions in the resin composition.

[0044] The film raw material or the biaxially stretched film may contain other resins besides poly(3-hydroxybutyrate)-based resins, provided that the effects of the invention are not impaired. Examples of such other resins include aliphatic polyester-based resins such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

[0045] The content of the other resin is not particularly limited, but is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, relative to 100 parts by weight of the poly(3-hydroxybutyrate)-based resin. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight or more.

[0046] The film raw material or the biaxially stretched film preferably does not contain an additive that bleeds out when the film is stored at 80°C or higher. International Publication No. 2015 / 052876 reveals that a sample containing added pentaerythritol did not bleed out after storage for one month at 23°C and humidity of 50% or less. However, bleed-out may occur under storage conditions of 80°C or higher. Therefore, the film raw material or the biaxially stretched film preferably does not contain pentaerythritol. Furthermore, even if a crystal nucleating agent such as pentaerythritol is not contained, a biaxially stretched film can be produced with high productivity by employing the production method described below.

[0047] The film raw material or the biaxially stretched film may contain additives that can be used together with the poly(3-hydroxybutyrate) resin, as long as they do not impair the effects of the invention. 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, plasticizers, antioxidants, weather resistance improvers, UV absorbers, and the like. Examples of additives include a nucleating agent, a lubricant, a release agent, a water repellent, an antibacterial agent, and a sliding property improver. Only one type of additive may be contained, or two or more types may be contained. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use.

[0048] Next, a method for producing a biaxially stretched film according to one embodiment will be described. A method for producing a biaxially stretched film according to one embodiment includes the steps of melting a film raw material containing the poly(3-hydroxybutyrate) resin in an extruder and then forming it into a film, and continuously stretching the formed film in both the MD and TD directions at a stretch ratio of 1.1 or more to obtain a biaxially stretched film.

[0049] Generally, the MD direction is also called the machine direction, flow direction, or longitudinal direction, and the TD direction is a direction perpendicular to the MD direction and is also called the perpendicular direction or cross direction.

[0050] The forming into the film may be carried out by sandwiching the molten film raw material between two or more rolls, i.e., by a calendar method, or by extruding the molten film raw material through a round die into a tubular shape and inflating it with air, i.e., by an inflation method, or by extruding the molten film raw material through a T-die, i.e., by an extrusion method. In order to produce a film with a uniform thickness, the extrusion method is preferred.

[0051] After forming into a film, it is preferable to carry out a step of cooling the film with cooling rolls while transporting the film. By carrying out this cooling step, it is possible to promote partial crystallization of the poly(3-hydroxybutyrate) resin before carrying out the stretching step. The cooling step may be a step of cooling the film on one or more cooling rolls, or a step of cooling by sandwiching the film between two cooling rolls. Note that the cooling roll step is not a step of applying pressure to the film to perform rolling.

[0052] Generally, poly(3-hydroxybutyrate) resins have an extremely slow crystallization rate compared to other crystalline resins such as polypropylene. Therefore, they tend not to fully crystallize and solidify on the surface of the chill roll, and tend to stick to the chill roll. Therefore, the temperature of the chill roll is preferably adjusted to 40 to 100°C in order to allow the crystallization of the poly(3-hydroxybutyrate) resin to proceed to a certain extent and prevent it from sticking to the chill roll.

[0053] The film is then continuously stretched in the MD direction and continuously stretched in the TD direction to obtain a biaxially stretched film. In this application, stretching a film refers to pulling the film in a specific plane direction. Stretching by applying pressure in the thickness direction of the film, such as roll rolling in which the film is sandwiched between two rolls, is excluded. Stretching in the MD direction and stretching in the TD direction may be performed sequentially or simultaneously. When performing the stretching sequentially, the order is not limited.

[0054] Stretching in the MD direction can be performed, for example, by using a roll longitudinal stretching machine and varying the rotation speed of multiple rolls that transport the film. The means for controlling the temperature of the film to the desired stretching temperature include a method of controlling the temperature of a roll with a slower rotation speed to the stretching temperature, a method of controlling the temperature of the film to the stretching temperature using auxiliary heating means such as an IR heater between the rolls, and a method of providing an oven between the rolls and controlling the temperature of the film in an oven that is controlled to the stretching temperature.

[0055] The stretching in the TD direction is not particularly limited, but for example, it can be performed by clamping both widthwise ends of the film using a transverse stretching machine such as a clip-type tenter and pulling it in the TD direction. In the case of a tenter-type transverse stretching machine, the temperature of the film can be controlled in an oven controlled to a desired stretching temperature.

[0056] The stretching ratio in the stretching step is preferably 1.1 times or more, more preferably 1.2 times or more, even more preferably 1.3 times or more, and particularly preferably 1.4 times or more. The upper limit of the stretching ratio is not particularly limited, but is preferably 3.0 times or less.

[0057] It is preferable to carry out the steps from the molding step to the stretching step in a continuous process. Here, the continuous process refers to carrying out the stretching step after the film-forming step without carrying out the crystallization step that requires a long time as described in Patent Document 1 (specifically, a step of quenching in ice water and then annealing at 40°C for 12 hours). However, the continuous process includes not only a case where the molding step and the stretching step are carried out sequentially, but also a case where the molding step, the cooling step using a cooling roll, and the stretching step are carried out sequentially in this order.

[0058] In a preferred embodiment, the poly(3-hydroxybutyrate) resin subjected to the stretching step is not completely crystallized. However, some crystals remain in the film without melting, resulting in a mixture of resin crystals and molten material. By performing the stretching step on such a film, biaxial stretching becomes easier, which has the advantage of making the film more easily stretched. At the same time, even though the crystallization step (annealing step) described in Patent Document 1, which can reduce productivity, is not performed, the remaining crystals act as starting points to facilitate crystallization of the entire poly(3-hydroxybutyrate) resin during and after the stretching step.

[0059] From these perspectives, it is preferable to set production conditions so that the temperature of the film raw material and the film, from the time the poly(3-hydroxybutyrate)-based resin is melted in an extruder until the biaxially stretched film is obtained, is within a range of at least 10°C lower than the glass transition temperature (Tg) of the poly(3-hydroxybutyrate)-based resin and not higher than 175°C. If the temperature exceeds 175°C, crystals in the poly(3-hydroxybutyrate)-based resin cannot remain during the production process, which may result in poor crystallization of the poly(3-hydroxybutyrate)-based resin as a whole, reducing the productivity of the biaxially stretched film. Furthermore, if the temperature is less than 10°C lower than the glass transition temperature (Tg) of the poly(3-hydroxybutyrate)-based resin, it may be difficult to sufficiently form the film into a film or stretch it to a predetermined ratio. The temperature is more preferably 40°C or higher and 170°C or lower, and even more preferably 60°C or higher and 165°C or lower.

[0060] The thickness of the biaxially stretched film to be produced is not particularly limited and can be appropriately determined by a person skilled in the art. From the viewpoint 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.

[0061] The biaxially stretched film is thin yet has high strength, and therefore can be suitably used as a heat-sealable film, a twist film, or other packaging film. [Example]

[0062] 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.

[0063] In the examples and comparative examples, the following raw materials were used. (Poly(3-hydroxybutyrate) resin) A-1: P3HB3HH (average content ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol) (%), weight average molecular weight 660,000 g / mol, glass transition temperature 6°C) It was produced in accordance with the method described in Example 2 of WO 2019 / 142845. A-2: X131A (Kaneka Biodegradable Polymer PHBH (registered trademark)) (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%), weight average molecular weight 600,000 g / mol, glass transition temperature 6°C) A-3: P3HB3HH (average content ratio of 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight average molecular weight of 660,000 g / mol, glass transition temperature of 1°C) Produced in accordance with the method described in Example 9 of WO 2019 / 142845.

[0064] (Film thickness evaluation) The thickness was measured at 10 points at 10 cm intervals along the TD direction of the film using a vernier caliper, and the arithmetic mean value of the thicknesses at the 10 points was calculated as the film thickness.

[0065] (Method for measuring glass transition temperature) The glass transition temperature (Tg) of each resin was determined by differential scanning calorimetry in accordance with JIS K-7121. Specifically, about 5 mg of the resin to be measured was weighed out and heated from -20°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter (Seiko Instruments Inc., SSC5200) to obtain a DSC curve. Next, in the obtained DSC curve, the baseline before and after the stepwise change due to the glass transition was extended, and a center line was drawn equidistant from these two lines in the vertical direction. The temperature at the point where this center line intersects with the curve of the stepwise change due to the glass transition was determined to be the glass transition temperature (Tg).

[0066] [Production of poly(3-hydroxybutyrate) resin pellets P-1] A dry blend of 8 parts by weight of A-1, 80 parts by weight of A-2, 12 parts by weight of A-3, and 0.5 parts by weight of behenamide (Nippon Fine Chemicals Co., Ltd.: BNT-22H) as a lubricant was performed. The resulting resin material was fed into a φ26 mm co-rotating twin-screw extruder with cylinder and die temperatures set to 150°C, extruded, passed through a water bath filled with hot water at 45°C to solidify the strands, and cut with a pelletizer to obtain resin pellets P-1. The glass transition temperature of the resin pellets P-1 was 5°C.

[0067] [Production of poly(3-hydroxybutyrate) resin pellets P-2] A dry blend of 36 parts by weight of A-1, 54 parts by weight of A-3, 0.15 parts by weight of t-butylperoxyisopropyl carbonate (NOF Corp., Perbutyl I) as an organic peroxide, and 0.5 parts by weight of behenamide (Nippon Fine Chemicals Co., Ltd., BNT-22H) as a lubricant was used. The resulting resin material was fed into a 26 mm diameter co-rotating twin-screw extruder with cylinder and die temperatures set to 150°C. 10 parts by weight of A-2 was then added to the extruder via a side feeder and extruded. The strands were solidified by passing them through a water bath filled with 45°C hot water and then cut into pellets using a pelletizer to obtain resin pellets P-2. The glass transition temperature of the resin pellets P-2 was 3°C.

[0068] Example 1 The cylinder temperature and die temperature of a φ65 mm single-screw extruder connected to a 1400 mm wide T-die were set to 160°C. The resin pellets P-1 were fed into the single-screw extruder and extruded into a film shape through a T-die. The formed film was cooled on a cooling roll set at 50°C, then taken up on a take-up roll. The film was continuously stretched in the machine direction (MD) at a stretching temperature of 100°C in a roll longitudinal stretching machine to a stretching ratio of 1.5 times, and then further continuously stretched in the transverse direction (TD) at a stretching temperature of 100°C in a clip-type tenter transverse stretching machine to a stretching ratio of 1.5 times. The biaxially stretched film was cooled to 50°C and slit at the width direction end to obtain a film having a width of 1500 mm. A biaxially stretched film having a thickness of 30 μm was obtained. The above process was carried out continuously.

[0069] <Example 2> The process was carried out continuously in the same manner as in Example 1, except that P-2 was used as the resin pellets, the stretching temperature during longitudinal stretching was 90°C, and the stretching temperature during transverse stretching was 90°C, to obtain a biaxially stretched film having a width of 1500 mm and a thickness of 30 μm.

Claims

1. A method for producing a biaxially oriented film containing a poly(3-hydroxybutyrate) resin, The process involves melting the film raw material containing the aforementioned poly(3-hydroxybutyrate) resin in an extruder and then forming it into a film, and The process includes obtaining a biaxially oriented film by continuously stretching the formed film in the MD direction and the TD direction at a stretching ratio of 1.1 times or more. The poly(3-hydroxybutyrate) resin comprises at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). A manufacturing method comprising carrying out the molding process to the stretching process in a continuous process.

2. The manufacturing method according to claim 1, wherein the continuous stretching of the film in the MD direction is carried out by creating a difference in the rotational speed of the rolls between a plurality of rolls that transport the film.

3. The manufacturing method according to claim 1 or 2, further comprising a step of cooling the molded film with a cooling roll while conveying it after the molding step and before the stretching step.

4. The manufacturing method according to any one of claims 1 to 3, wherein the poly(3-hydroxybutyrate) resin includes a poly(3-hydroxybutyrate) resin modified with a peroxide.

5. The manufacturing method according to any one of claims 1 to 4, wherein, from the time the film raw material containing the poly(3-hydroxybutyrate) resin is melted in an extruder until a biaxially oriented film is obtained, the temperature of the film raw material and the film is within a range of 10°C or more below the glass transition temperature (Tg) of the poly(3-hydroxybutyrate) resin and 175°C or less.

6. The manufacturing method according to any one of claims 1 to 5, wherein the poly(3-hydroxybutyrate) resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

7. The manufacturing method according to any one of claims 1 to 6, wherein the film raw material further contains a filler, and the amount of the filler is 1 to 100 parts by weight per 100 parts by weight of the poly(3-hydroxybutyrate) resin.

8. The manufacturing method according to claim 7, wherein the filler is an inorganic filler.

9. The manufacturing method according to claim 8, wherein the inorganic filler comprises at least one selected from silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, and carbon black.

10. The manufacturing method according to claim 7, wherein the filler is an organic filler.

11. The manufacturing method according to any one of claims 1 to 10, wherein the thickness of the biaxially oriented film is 10 to 200 μm.

12. The manufacturing method according to any one of claims 1 to 11, wherein the molding into a film is carried out by extruding molten film raw material from a T-die.