Manufacturing method for 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

[0006] , ,

[0005] , , ,

[0007] ,

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

Background Art

[0002] In recent years, the separation and recycling of food waste and composting have been promoted mainly in Europe, and plastic products that can be composted together with food waste are desired.

[0003] On the other hand, environmental problems caused by waste plastics have been spotlighted. In particular, it has been found that plastics that have flowed into the sea via ocean dumping or rivers are drifting in large quantities on a global scale in the ocean. Since such plastics maintain their shape over a long period of time, they are pointed out to have an impact on the ecosystem, such as so-called ghost fishing that restrains and captures marine organisms, or when marine organisms ingest them, they remain in the digestive tract and cause feeding disorders.

[0004] Furthermore, it has also been pointed out that microplastics formed by the disintegration and atomization of plastics by ultraviolet rays and the like adsorb harmful compounds in seawater, and when marine organisms ingest them, harmful substances are incorporated into the food chain.

[0005] Regarding such marine pollution caused by plastics, the use of biodegradable plastics is expected. However, in a report compiled by the United Nations Environment Programme in 2015, it is pointed out that plastics that can be biodegradable in compost, such as polylactic acid, cannot be expected to decompose in a short period in the actual ocean with a low temperature, and thus cannot be a countermeasure against marine pollution.

[0006] Among such circumstances, poly(3-hydroxybutyrate) resins are attracting attention as materials that can solve the above problems because they can undergo biodegradation even in seawater.

[0007] On the other hand, as a technique for producing a thin and high-strength film, a method of biaxially stretching a film is known. Patent Document 1 describes a method for producing a biaxially oriented film by melting a thermoplastic resin mainly composed of poly(3-hydroxybutyrate) resin, forming it into a film, allowing it to crystallize for a certain period of time, then performing primary stretching by rolling it between two rolls, and further performing secondary stretching at a temperature higher than the temperature at which it was rolled. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2006-168159 [Overview of the project] [Problems that the invention aims to solve]

[0009] According to the method described in Patent Document 1, a biaxially oriented film mainly composed of poly(3-hydroxybutyrate) resin can be manufactured. However, the manufacturing method described in the document requires an annealing process to crystallize the poly(3-hydroxybutyrate) resin before stretching. This annealing process is described as taking a long time, such as 12 hours, which prevents the film from being manufactured in a continuous process and results in poor productivity. Furthermore, since the primary stretching is carried out by roll rolling, which involves sandwiching the film between two rolls and applying pressure, there is a problem in that the film can stick to the rolls during this process.

[0010] In view of the above situation, the present invention aims to provide a method for producing a biaxially oriented film containing a poly(3-hydroxybutyrate) resin with high productivity. [Means for solving the problem]

[0011] As a result of diligent research to solve the above problems, the inventors of the present invention have found that by performing the stretching process by stretching the film instead of roll rolling, a biaxially oriented film containing a poly(3-hydroxybutyrate) resin can be manufactured with high productivity, and have completed the present invention.

[0012] In other words, the present invention relates to a method for producing a biaxially oriented film containing a poly(3-hydroxybutyrate) resin, comprising 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 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. Preferably, 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 the rolls that transport the film. Preferably, the manufacturing method further includes a step of cooling the molded film with a cooling roll while conveying it, after the molding step and before the stretching step. Preferably, the molding process to the stretching process is carried out as a continuous process. Preferably, 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. Preferably, the poly(3-hydroxybutyrate) resin contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Preferably, the film raw material further contains a filler, the filler content being 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. Furthermore, even more preferably, the filler is an organic filler. Preferably, the thickness of the biaxially oriented film is 10 to 200 μm. Preferably, the film formation is carried out by extruding the molten film material from a T-die. [Effects of the Invention]

[0013] According to the present invention, a method for producing a biaxially oriented film containing a poly(3-hydroxybutyrate) resin with high productivity can be provided. According to a preferred embodiment, a biaxially oriented film containing a poly(3-hydroxybutyrate) resin can be produced continuously and with high productivity. [Modes for carrying out the invention]

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

[0015] One embodiment relates to a method for producing a biaxially oriented film containing a poly(3-hydroxybutyrate) resin. The poly(3-hydroxybutyrate) resin is an aliphatic polyester resin that can be produced from microorganisms, and is a polyester resin in which 3-hydroxybutyrate is the repeating unit. The poly(3-hydroxybutyrate) resin may be a poly(3-hydroxybutyrate) in which only 3-hydroxybutyrate is the repeating unit, or it may be a copolymer of 3-hydroxybutyrate and other hydroxyalkanoates. Furthermore, the poly(3-hydroxybutyrate) resin may 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) resins include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvariate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Among these, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvariate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred because they are easy to produce industrially.

[0017] Furthermore, by changing the composition ratio of the repeating unit, the melting point and crystallinity can be changed, and physical properties such as Young's modulus and heat resistance can be changed, and it is possible to impart physical properties between polypropylene and polyethylene. Also, from the viewpoint of being industrially easy to produce and being a physically useful plastic, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferable. In particular, among poly(3-hydroxybutyrate) - based resins having the property of being easily thermally decomposed under heating at 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is also preferable from the viewpoint that it can lower the melting point and enables molding processing at a low temperature.

[0018] Examples of commercially available poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) include "Kaneka Biodegradable Polymer PHBH" (registered trademark) of Kaneka Corporation.

[0019] The melting point, Young's modulus, etc. of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) change depending on the ratio of the 3-hydroxybutyrate component and the 3-hydroxyvalerate component. However, since both components co-crystallize, the crystallinity is as high as 50% or more. Compared with poly(3-hydroxybutyrate), it is flexible, but the improvement of brittleness is insufficient.

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

[0021] The average content ratio of each monomer unit in all the monomer units constituting the poly(3-hydroxybutyrate) 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 the monomer units constituting the poly(3-hydroxybutyrate) resin. When the poly(3-hydroxybutyrate) resin is a mixture of two or more poly(3-hydroxybutyrate) resins, it means the molar ratio of each monomer unit contained in the whole mixture.

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

[0023] Generally, the highly crystalline poly(3-hydroxybutyrate) resin has excellent productivity but poor mechanical strength, and the low-crystalline poly(3-hydroxybutyrate) resin has poor productivity but excellent mechanical properties. When both resins are used in combination, it is presumed that the highly crystalline poly(3-hydroxybutyrate) resin forms fine resin crystal particles, and the low-crystalline poly(3-hydroxybutyrate) resin forms tie molecules that crosslink these resin crystal particles. By using these resins in combination, the strength and productivity of the biaxially stretched film can be improved.

[0024] The content ratio of 3-hydroxybutyrate units contained in the highly crystalline poly(3-hydroxybutyrate) resin is preferably higher than the average content ratio of 3-hydroxybutyrate units in all the 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%, and 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, it is preferable that the content of 3-hydroxybutyrate units in the low-crystalline poly(3-hydroxybutyrate) resin is lower than the average content of 3-hydroxybutyrate units in the total 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 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 using a highly crystalline poly(3-hydroxybutyrate) resin and a low-crystalline poly(3-hydroxybutyrate) resin in combination, the proportion of each resin used relative to the total amount of both resins is not particularly limited, but it is preferable that the former is 10% to 60% by weight and the latter is 40% to 90% by weight, and more preferably that the former is 25% to 45% by weight and the latter is 55% to 75% by weight.

[0029] According to one preferred embodiment, it is preferable to use a combination of the highly crystalline poly(3-hydroxybutyrate) resin and the low-crystalline poly(3-hydroxybutyrate) resin, as well as a medium-crystalline poly(3-hydroxybutyrate) resin whose crystallinity is intermediate between that of 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%, even more preferably 6 mol% or more and 20 mol%, and preferably 6 mol% or more and 18 mol%.

[0031] The aforementioned 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 aforementioned medium-crystalline poly(3-hydroxybutyrate) resin is used in combination, the ratio of the medium-crystalline poly(3-hydroxybutyrate) resin to the total of the highly-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 by microbial production or by chemical synthesis. Alternatively, the blend may be obtained by melting and kneading two or more resins using an extruder, kneader, Banbury mixer, rolls, etc., or by dissolving two or more resins in a solvent, mixing and drying them.

[0034] The weight-average molecular weight of the poly(3-hydroxybutyrate) resin as a whole is not particularly limited, but from the viewpoint of achieving both strength and productivity of the biaxially oriented 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 a highly crystalline poly(3-hydroxybutyrate) resin and a low-crystalline poly(3-hydroxybutyrate) resin are used in combination, the weight-average molecular weight of the highly 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 the strength and productivity of the biaxially oriented 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 the strength and productivity of the biaxially oriented film. Furthermore, when using the aforementioned medium-crystalline poly(3-hydroxybutyrate) resin, 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 oriented film.

[0036] The weight-average molecular weight of poly(3-hydroxybutyrate) resins can be measured using gel permeation chromatography with chloroform solution (HPLC GPC system, Shimadzu Corporation) and converted to polystyrene equivalent. For this gel permeation chromatography, any column suitable for measuring weight-average molecular weight should be used.

[0037] The method for producing poly(3-hydroxybutyrate) resins is not particularly limited and may be by chemical synthesis or by microbial production. Among these, microbial production is preferred. Known methods can be applied to microbial production. For example, known microorganisms 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 respect to P3HB3HH, to increase the productivity of P3HB3HH, strains such as Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)) into which genes for the P3HA synthase group have been introduced are more preferable, and microbial cells that have accumulated P3HB3HH in their cells by culturing these microorganisms under appropriate conditions are used. In addition to the above, genetically modified microorganisms into which various poly(3-hydroxybutyrate) resin synthesis-related genes may be introduced according to 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 oriented film may not contain a filler, but it is preferable that it contains a filler. Including a filler makes it possible to produce a biaxially oriented film with 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, carbon black, etc. 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 still more preferably 10 to 60 parts by weight per 100 parts by weight of poly(3-hydroxybutyrate) resin.

[0040] As the film raw material, a resin can be used that has been modified from the poly(3-hydroxybutyrate) resin with a raw material that reacts with resins such as peroxides (modification raw material). When using a modified resin as a film raw material, the raw material may be formed into a film by reacting the resin with the modifying raw material in advance, or the modifying raw material may be mixed with the resin and reacted during film formation. Furthermore, when reacting the resin with the 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 then the remaining unmodified resin may 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) resin, but organic peroxides can be preferably used because they are easy to handle and their reaction with the poly(3-hydroxybutyrate) resin can be easily controlled.

[0042] Examples of the aforementioned 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, and 1,1,3,3-tetramethylbutyl peroxy-2 Examples include ethylhexanoate, disuccinate peroxide, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butylperoxy2-ethylhexyl carbonate, t-butylperoxyisopropyl 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-butylperoxycyclohexy)propane, and 2,2-di-t-butylperoxybutane. Among these, t-butyl peroxy-2-ethylhexyl carbonate and t-butyl peroxyisopropyl carbonate are preferred. Furthermore, combinations of two or more of these organic peroxides can also be used.

[0043] The organic peroxide can be used in various forms, such as solid or liquid, and may be a liquid diluted with a diluent. In particular, an organic peroxide in a form that can be easily mixed with the poly(3-hydroxybutyrate) resin (especially an organic peroxide that is liquid at room temperature (25°C)) is preferred because it can be dispersed more uniformly in the poly(3-hydroxybutyrate) resin and is more likely to suppress local modification reactions in the resin composition.

[0044] The film raw material or the biaxially oriented film may contain other resins besides poly(3-hydroxybutyrate) resins, to the extent that they do not impair the effects of the invention. Examples of such other resins include aliphatic polyester resins such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, and polybutylene azelate terephthalate. The other resin may consist of only one type or two or more types.

[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, per 100 parts by weight of the poly(3-hydroxybutyrate) 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] It is preferable that the film raw material or the biaxially oriented film does not contain additives that cause bleeding out when the film is stored at 80°C or above. International Publication No. 2015 / 052876 showed that a sample with pentaerythritol added did not bleed out after being stored for one month at 23°C and 50% humidity or less, but it may bleed out under storage conditions of 80°C or above. Therefore, it is preferable that the film raw material or the biaxially oriented film does not contain pentaerythritol. Furthermore, even without containing crystal nucleating agents such as pentaerythritol, biaxially oriented films can be manufactured with high productivity by employing the manufacturing method described later.

[0047] The film raw material or the biaxially oriented film may contain additives that can be used together with the poly(3-hydroxybutyrate) resin, to the extent that 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 zeolites, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather-resistant modifiers, ultraviolet absorbers, crystal nucleating agents, lubricants, mold release agents, water repellents, antibacterial agents, and sliding properties modifiers. Only one type of additive may be included, or two or more types may be included. The content of these additives can be appropriately determined by a person skilled in the art depending on the intended use.

[0048] Next, a method for manufacturing a biaxially oriented film according to one embodiment will be described. A method for producing a biaxially oriented 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 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.

[0049] Generally, the MD direction is also called the machine direction, flow direction, or length direction, and the TD direction is perpendicular to the MD direction and is also called the vertical direction or width direction.

[0050] The aforementioned film formation may be carried out by sandwiching the molten film material between two or more rolls, i.e., by the calendering method; by extruding the molten film material from a circular die into a tube shape and inflating it with air, i.e., by the inflation molding method; or by extruding the molten film material from a T-die, i.e., by the extrusion molding method. The extrusion molding method is preferred for producing a film with uniform thickness.

[0051] It is preferable to perform a step of cooling the film with a cooling roll while transporting it after it has been formed into a film. By performing this cooling step, the crystallization of a portion of the poly(3-hydroxybutyrate) resin can be promoted before the stretching step is performed. This cooling step may be a step of cooling the film on one or more cooling rolls, or a step of cooling the film by sandwiching it between two cooling rolls. Note that this cooling roll step is not a step of rolling the film by applying pressure to it.

[0052] Generally, poly(3-hydroxybutyrate) resins crystallize much more slowly than other crystalline resins such as polypropylene. As a result, they tend not to crystallize and solidify sufficiently on the surface of the cooling roll, and are prone to sticking to the cooling roll. Therefore, the temperature of the cooling roll is preferably controlled at 40 to 100°C to allow the crystallization of the poly(3-hydroxybutyrate) resin to progress to a certain extent and to avoid adhesion to the cooling roll.

[0053] Subsequently, a biaxially oriented film can be obtained by continuously stretching the film in the MD direction and then in the TD direction. In this application, stretching a film refers to pulling the film in a specific planar direction. Stretching by applying pressure in the thickness direction of the film, such as roll rolling where 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. If performed sequentially, the order is not limited.

[0054] Stretching in the MD direction is not particularly limited, but can be performed, for example, by using a roll stretcher and creating a difference in the rotation speed of the rolls that transport the film. In this case, means of adjusting the temperature of the film to the desired stretching temperature include a method of adjusting the temperature of the roll with the slowest rotation speed to the stretching temperature, a method of adjusting 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 setting up an oven between the rolls and adjusting the temperature of the film in an oven that has been adjusted to the stretching temperature.

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

[0056] The stretching ratio in the stretching process 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. There is no particular upper limit to the stretching ratio, but it is preferably 3.0 times or less.

[0057] It is preferable to carry out the molding process to the stretching process in a continuous process. Here, a continuous process means that after the molding process, the stretching process is carried out without carrying out the crystallization process which takes a long time as described in Patent Document 1 (specifically, the process of rapidly cooling in ice water and then annealing at 40°C for 12 hours). However, the continuous process includes not only the case in which the molding process and the stretching process are carried out sequentially, but also the case in which the molding process, the cooling process using a cooling roll, and the stretching process 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. Performing the stretching step on such a film facilitates biaxial stretching, providing the advantage of making the film easier to stretch. At the same time, even without performing the crystallization step (annealing step) described in Patent Document 1, which can reduce productivity, the remaining crystals act as a starting point for the crystallization of the entire poly(3-hydroxybutyrate) resin during and after the stretching step.

[0059] From the above viewpoint, it is preferable to set the manufacturing conditions such that the temperature of the film raw material and the film, from the time the film raw material containing the poly(3-hydroxybutyrate) resin is melted in an extruder until the biaxially oriented film is obtained, is within the range of a temperature 10°C or higher than the glass transition temperature (Tg) of the poly(3-hydroxybutyrate) resin and 175°C or lower. If the temperature exceeds 175°C, it will not be possible to retain crystals in the poly(3-hydroxybutyrate) resin during the manufacturing process, and as a result, the crystallization of the entire poly(3-hydroxybutyrate) resin will not proceed easily, which may reduce the productivity of the biaxially oriented film. Furthermore, if the temperature is less than 10°C lower than the glass transition temperature (Tg) of the poly(3-hydroxybutyrate) resin, it may not be possible to adequately form it into a film or stretch it to a predetermined magnification. 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 oriented film to be manufactured is not particularly limited and can be set as appropriate by those skilled in the art, but from the viewpoint of uniform thickness, appearance, strength, and lightness of the film, it is preferably 10 to 200 μm, more preferably 15 to 150 μm, and even more preferably 20 to 100 μm.

[0061] Because the biaxially oriented film is thin yet strong, it can be suitably used as a heat-sealable film, twisted film, and other packaging film. [Examples]

[0062] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to these examples.

[0063] The following raw materials were used in the examples and comparative examples. (Poly(3-hydroxybutyrate) resin) A-1: P3HB3HH (Average content ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol%), weight-average molecular weight is 660,000 g / mol, glass transition temperature is 6°C) It was manufactured in accordance with the method described in Example 2 of International Publication No. 2019 / 142845. A-2:X131A (Kaneka Biodegradable Polymer PHBH®) (Average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%), weight-average molecular weight is 600,000 g / mol, glass transition temperature is 6°C) A-3: P3HB3HH (Average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight-average molecular weight is 660,000 g / mol, glass transition temperature is 1°C) It was manufactured in accordance with the method described in Example 9 of International Publication No. 2019 / 142845.

[0064] (Evaluation of film thickness) The thickness of the film was measured at 10 points, 10 cm apart, along the TD direction, using calipers. The arithmetic mean of the 10 thicknesses was calculated and used 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, first, approximately 5 mg of the resin to be measured was accurately weighed, and the temperature was increased from -20°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter (SSC5200, manufactured by Seiko Electronics Industries, Ltd.) to obtain a DSC curve. Next, in the obtained DSC curve, the baseline before and after the change was extended in the portion where the baseline changed in a step-like manner due to the glass transition, 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 step-like change due to the glass transition was defined as the glass transition temperature (Tg).

[0066] [Manufacturing of poly(3-hydroxybutyrate) resin pellets P-1] A-1 (8 parts by weight), A-2 (80 parts by weight), A-3 (12 parts by weight), and 0.5 parts by weight of behenamide (manufactured by Nippon Seika Co., Ltd.: BNT-22H) as a lubricant were dry-blended. The resulting resin material was fed into a φ26 mm co-screw extruder with the cylinder and die temperatures set to 150°C and extruded. The strands were solidified by passing the extruder through a water bath filled with 45°C water, and then cut with a pelletizer to obtain resin pellets P-1. The glass transition temperature of resin pellets P-1 was 5°C.

[0067] [Manufacturing of poly(3-hydroxybutyrate) resin pellets P-2] 36 parts by weight of A-1, 54 parts by weight of A-3, 0.15 parts by weight of t-butylperoxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I) as an organic peroxide, and 0.5 parts by weight of behenamide (manufactured by Nippon Seika Co., Ltd.: BNT-22H) as a lubricant were dry-blended. The resulting resin material was fed into a φ26 mm co-screw extruder with the cylinder temperature and die temperature 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 water, and then cut with 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 φ65mm single-screw extruder connected to a 1400mm wide T-die were both set to 160°C. The resin pellets P-1 were fed into the single-screw extruder and extruded into a film using a T-die. The formed film was cooled on a cooling roll at a set temperature of 50°C, then taken up by a take-up roll and continuously stretched in a roll longitudinal stretcher at a stretching temperature of 100°C to a stretch ratio of 1.5 times in the longitudinal (MD) direction. Subsequently, it was continuously stretched in a clip-type tenter transverse stretcher at a stretching temperature of 100°C to a stretch ratio of 1.5 times in the transverse (TD) direction. The biaxially stretched film was cooled to 50°C, and the widthwise ends were slit to obtain a biaxially stretched film with a width of 1500 mm and a thickness of 30 μm. 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 for the resin pellets and the stretching temperature during longitudinal stretching was set to 90°C and the stretching temperature during transverse stretching was set to 90°C, to obtain a biaxially oriented film with 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 (excluding a porous film containing 100 parts by weight of an aliphatic polyester biodegradable resin and 30 to 500 parts by weight of an inorganic filler), 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. 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. A method for producing the aforementioned film raw material, wherein the content of resins other than poly(3-hydroxybutyrate) resin is 0 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the poly(3-hydroxybutyrate) resin.

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 molding step to the stretching step is carried out in a continuous process.

5. The manufacturing method according to any one of claims 1 to 4, wherein the temperature of the film raw material and the film is within the range of 40°C to 170°C 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.

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 poly(3-hydroxybutyrate) resin is a mixture of at least two poly(3-hydroxybutyrate) resins having different types of constituent monomers and / or different content ratios of constituent monomers.

8. The manufacturing method according to any one of claims 1 to 7, 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.

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

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

11. The manufacturing method according to claim 8, wherein the filler is an organic filler.

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

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