Multilayer stretched film and production method for multilayer stretched film

Abstract

The present invention provides a multilayer stretched film that comprises a poly(3-hydroxyalkanoate)-based copolymer resin and that has good separability from a casting roll and a high stretchability.　Provided is a multilayer stretched film comprising a poly(3-hydroxyalkanoate)-based copolymer resin, said multilayer stretched film being provided with a first outer layer that contains a resin composition containing the poly(3-hydroxyalkanoate)-based copolymer resin, an inner layer that contains a resin composition containing the poly(3-hydroxyalkanoate)-based copolymer resin, and a second outer layer that contains a resin composition containing the poly(3-hydroxyalkanoate)-based copolymer resin in this order, wherein the crystallization speeds of the resin composition of the first outer layer and the resin composition of the second outer layer are faster than the crystallization speed of the resin composition of the inner layer.

Description

Multilayer stretched film and method for producing the same

[0001] The present invention relates to a multilayer stretched film and a method for producing the multilayer 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-hydroxyalkanoate) 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) resin at a high stretch ratio in a continuous process with good productivity.

[0008] JP 2023-073820 A

[0009] When a film primarily composed of a poly(3-hydroxyalkanoate) resin is used, for example, for packaging applications, a stretching process is required during film formation to achieve the required physical properties of strength and thickness. However, because it is difficult to control the crystallization rate of poly(3-hydroxyalkanoate) resins, it is difficult to achieve both releasability from a cast roll (hereinafter also referred to as CR) in the cooling process of the molten resin and stretchability in the subsequent stretching process. For example, when a raw material with a fast crystallization rate is used, the resin crystallizes and solidifies in the CR, resulting in good releasability from the CR, but difficulty in stretching due to the solidification. On the other hand, when a raw material with a slow crystallization rate is used, the resin does not solidify in the CR, resulting in poor releasability from the CR.

[0010] In view of the above-mentioned current situation, an object of the present invention is to provide a multilayer stretched film containing a poly(3-hydroxyalkanoate) copolymer resin that has good releasability from a casting roll and high stretchability.

[0011] The present invention relates to a multilayer stretched film containing a poly(3-hydroxyalkanoate)-based copolymer resin, the multilayer stretched film comprising, in this order: a first outer layer comprising a resin composition containing a poly(3-hydroxyalkanoate)-based copolymer resin; an inner layer comprising a resin composition containing a poly(3-hydroxyalkanoate)-based copolymer resin; and a second outer layer comprising a resin composition containing a poly(3-hydroxyalkanoate)-based copolymer resin, the multilayer stretched film being configured such that the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer.

[0012] According to the present invention, it is possible to provide a multilayer stretched film containing a poly(3-hydroxyalkanoate) copolymer resin, which has good releasability from a casting roll and high stretchability.

[0013] A conceptual diagram showing an example of the step (i) of forming into a film for producing a multilayer stretched film according to one embodiment of the present invention.

[0014] Although an embodiment of the present invention will be described below, the present invention is not limited to the following embodiment. The present embodiment relates to a multilayer stretched film containing a poly(3-hydroxyalkanoate)-based copolymer resin, the multilayer stretched film comprising, in this order, a first outer layer containing a resin composition containing the poly(3-hydroxyalkanoate)-based copolymer resin, an inner layer containing a resin composition containing the poly(3-hydroxyalkanoate)-based copolymer resin, and a second outer layer containing a resin composition containing the poly(3-hydroxyalkanoate)-based copolymer resin, the multilayer stretched film being configured such that the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer.

[0015] (Poly(3-hydroxyalkanoate)-based copolymer resin) In this embodiment, the resin composition of the first outer layer, the resin composition of the second outer layer, and the resin composition of the inner layer each contain a poly(3-hydroxyalkanoate)-based copolymer resin. Because the resin type is the same, delamination between the first outer layer and the inner layer and between the second outer layer and the inner layer is unlikely to occur.

[0016] The poly(3-hydroxyalkanoate) copolymer resin may be a single poly(3-hydroxyalkanoate) copolymer or a mixture of two or more poly(3-hydroxyalkanoate) copolymers. However, a mixture of at least two poly(3-hydroxyalkanoate) copolymers differing in the types of constituent monomers and / or the content ratios of the constituent monomers is preferred, as this not only achieves both film productivity and stretchability but also facilitates the achievement of good film properties (elongation, strength, etc.).

[0017] The poly(3-hydroxyalkanoate) copolymer resin is preferably a polymer having a 3-hydroxyalkanoate unit, specifically a polymer containing a unit represented by the following general formula (i): [—CHR—CH ２ -CO-O-] (i)

[0018] In the general formula (i), R is C ｐ H ２ｐ＋１ where p is an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. p is preferably an integer of 1 to 10, and more preferably an integer of 1 to 8.

[0019] As the poly(3-hydroxyalkanoate) copolymer resin, a poly(3-hydroxyalkanoate) copolymer produced by a microorganism is particularly preferred. In the poly(3-hydroxyalkanoate) copolymer produced by a microorganism, all of the 3-hydroxyalkanoate units are contained as (R)-3-hydroxyalkanoate units.

[0020] The poly(3-hydroxyalkanoate) copolymer resin preferably contains 3-hydroxyalkanoate units (particularly units represented by general formula (i)) in an amount of 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of the total structural units. The poly(3-hydroxyalkanoate) copolymer resin may contain only two or more types of 3-hydroxyalkanoate units as structural units of the polymer, or may contain other units (e.g., 4-hydroxyalkanoate units) in addition to one or more types of 3-hydroxyalkanoate units.

[0021] The poly(3-hydroxyalkanoate) copolymer resin is preferably a copolymer of 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units and other hydroxyalkanoate units (hereinafter also referred to as a "poly(3-hydroxybutyrate) copolymer"). In the copolymer, it is preferred that all of the 3-hydroxybutyrate units are (R)-3-hydroxybutyrate units.

[0022] Specific examples of poly(3-hydroxybutyrate) copolymers include poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), poly(3-hydroxy Examples of suitable poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), etc. In particular, from the viewpoints of film productivity, stretchability, mechanical properties, etc., poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred.

[0023] Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred from the viewpoints that by changing the composition ratio of the repeating units, it is possible to change the melting point 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 physically useful plastic. In particular, among poly(3-hydroxybutyrate)-based copolymers that tend to be thermally decomposed when heated to 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that it can lower the melting point and enable molding and processing at low temperatures.

[0024] Commercially available poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) products include Kaneka Biodegradable Polymer Green Planet (registered trademark) manufactured by Kaneka Corporation.

[0025] When the poly(3-hydroxyalkanoate) copolymer resin is a poly(3-hydroxybutyrate) copolymer, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the poly(3-hydroxyalkanoate) copolymer resin is preferably 3-hydroxybutyrate units / other hydroxyalkanoates = 99 / 1 to 80 / 20 (mol % / mol %), more preferably 97 / 3 to 82 / 18 (mol % / mol %), and even more preferably 95 / 5 to 85 / 15 (mol % / mol %), from the viewpoint of achieving both film productivity and stretchability and good film properties.

[0026] The average content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate) copolymer 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) copolymer resin, and when the poly(3-hydroxyalkanoate) copolymer resin is a mixture of two or more poly(3-hydroxyalkanoate) copolymers, it means the molar ratio of each monomer unit contained in the entire mixture.

[0027] In this embodiment, from the viewpoint of achieving better stretchability, the resin composition of the inner layer preferably contains 30% by weight or more, more preferably 35% by weight or more, and even more preferably 40% by weight or more of a poly(3-hydroxyalkanoate) copolymer resin having a weight-average molecular weight of 800,000 or more, based on 100% by weight of the poly(3-hydroxyalkanoate) copolymer resin. Alternatively, the content may be less than 50% by weight.

[0028] In this embodiment, the resin composition of the first outer layer and the resin composition of the second outer layer each preferably contain 50% by weight or more, more preferably 65% ​​by weight or more, and even more preferably 80% by weight or more of a poly(3-hydroxyalkanoate) copolymer resin having a weight-average molecular weight of 800,000 or more, based on 100% by weight of poly(3-hydroxyalkanoate) copolymer resin. Alternatively, the content may be 100% by weight or less. This provides better stretchability and makes it less likely for delamination to occur between the inner layer and the poly(3-hydroxyalkanoate) copolymer resin during the production of a multilayer stretched film.

[0029] The weight-average molecular weight of the poly(3-hydroxyalkanoate) copolymer resin can be measured in terms of polystyrene using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution. A column suitable for measuring the weight-average molecular weight may be used as the column for the gel permeation chromatography. The same applies to the following description.

[0030] (Polylactic acid) From the viewpoint of easily configuring the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer to be faster than the crystallization rate of the resin composition of the inner layer, it is preferable that the resin composition of the first outer layer and the resin composition of the second outer layer each contain polylactic acid.

[0031] Polylactic acid is a polymer containing a repeating unit represented by the following general formula (ii): [—CH(CH ３ )-CO-O-] (ii)

[0032] The polylactic acid used in this embodiment preferably contains repeating units represented by the general formula (ii) in an amount of 50 mol % or more of all repeating units, and may contain other repeating structures.

[0033] The polylactic acid used in this embodiment may be poly(D-lactic acid), poly(L-lactic acid), a copolymer of D-lactic acid and L-lactic acid, or a stereocomplex which is a blend of these.

[0034] The polylactic acid used in this embodiment is not particularly limited in terms of molecular weight or molecular weight distribution, as long as it can be molded. However, in order to obtain a molded article with an excellent balance between the physical properties and processability, the weight-average molecular weight is preferably 50,000 to 300,000, and more preferably 100,000 to 250,000.

[0035] The weight average molecular weight of polylactic acid can be measured in the same manner as the weight average molecular weight of poly(3-hydroxyalkanoate) copolymer resin.

[0036] The polylactic acid may have a melting point or may not have a clear melting point. However, the polylactic acid used in this embodiment is preferably one having a melting point. The presence or absence of a melting point of polylactic acid and the melting point can be evaluated and measured by differential scanning calorimetry (DSC). The same applies to various resin compositions and resins hereinafter.

[0037] Commercially available polylactic acid products include "Ingeo" (registered trademark) Biopolymer manufactured by NatureWorks, and "Luminy" (registered trademark) manufactured by Total Energies Corbion.

[0038] The content of polylactic acid in the resin composition for the first outer layer and the resin composition for the second outer layer is not particularly limited and may be 0 part by weight or more, but from the viewpoint of moldability, it is preferably 20 parts by weight or more, more preferably 30 parts by weight or more, and even more preferably 40 parts by weight or more, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) copolymer resin and polylactic acid. The upper limit is preferably 90 parts by weight or less, more preferably 80 parts by weight or less, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) copolymer resin and polylactic acid, in order to prevent delamination between the first outer layer and the second outer layer and the inner layer.

[0039] The content of polylactic acid in the resin composition of the inner layer is not particularly limited, but from the viewpoint of biodegradability, it is preferably 40 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 0 part by weight, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) copolymer resin and polylactic acid.

[0040] (Nucleating Agent) In the present embodiment, the resin composition of the first outer layer, the resin composition of the second outer layer, and the resin composition of the inner layer may or may not contain a nucleating agent. In other words, as long as the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are all faster than the crystallization rate of the resin composition of the inner layer, the content of the nucleating agent may be 0 parts by weight per 100 parts by weight of the total of the various resins in each of the first outer layer, the second outer layer, and the inner layer.

[0041] Examples of crystal nucleating agents include sugar alcohols such as pentaerythritol, galactitol, and mannitol; poly(3-hydroxybutyrate) homopolymer (abbreviated as P3HB); orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among these, poly(3-hydroxybutyrate) homopolymer is preferred because of its excellent biodegradability and the ability to avoid the problems of sugar alcohols bleeding out from the film and the resulting contamination of the cast roll surface. Sugar alcohols are preferred, and pentaerythritol is particularly preferred, because they are particularly effective in promoting the crystallization of poly(3-hydroxyalkanoate) copolymer resins. One or more crystal nucleating agents may be used, and the ratio of their use can be adjusted appropriately depending on the purpose.

[0042] The weight average molecular weight of the poly(3-hydroxybutyrate) homopolymer as a crystal nucleating agent is preferably 100,000 to 600,000, more preferably 150,000 to 500,000, and even more preferably 200,000 to 400,000, from the viewpoint of optimizing the crystallization rate.

[0043] From the viewpoint of easily configuring the resin composition of the first outer layer and the resin composition of the second outer layer so that their crystallization rates are both faster than that of the resin composition of the inner layer, it is preferred that the resin composition of the first outer layer and the resin composition of the second outer layer each contain a crystal nucleating agent. In this case, the contents of the crystal nucleating agent in the resin composition of the first outer layer, the resin composition of the second outer layer, and the resin composition of the inner layer are not particularly limited as long as the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than that of the resin composition of the inner layer, but it is preferred that the content of the crystal nucleating agent in the resin composition of the inner layer is less than the content of the crystal nucleating agent in the resin compositions of the first outer layer and the second outer layer.

[0044] The content of the poly(3-hydroxybutyrate) homopolymer in the resin composition for the first outer layer and the resin composition for the second outer layer is not particularly limited, but from the viewpoint of stretchability, it is preferably 70 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 35 parts by weight or less, and particularly preferably 30 parts by weight or less, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin in each outer layer. The lower limit may be 0 parts by weight or more.

[0045] Further, the cases where the resin composition of each outer layer does not contain polylactic acid and where it does contain polylactic acid will be described in detail below. When the resin composition of each outer layer does not contain polylactic acid [when the content of polylactic acid in the resin composition of each outer layer is not equivalent to 0 parts by weight (e.g., 5 parts by weight or more) per 100 parts by weight of the poly(3-hydroxyalkanoate)-based copolymer resin and polylactic acid combined], the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the first outer layer and the resin composition of the second outer layer is preferably 70 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 35 parts by weight or less, and particularly preferably 30 parts by weight or less, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based copolymer resin in each outer layer. The lower limit may be 0 parts by weight or more, but from the viewpoint of optimizing the crystallization rate of the resin composition of the first outer layer and the resin composition of the second outer layer, it is preferably 10 parts by weight or more, more preferably 15 parts by weight or more, and even more preferably 20 parts by weight or more.

[0046] When the resin composition of each outer layer contains polylactic acid (when the content of polylactic acid in the resin composition of each outer layer is 0 parts by weight or so small as to be regarded as 0 parts by weight (for example, less than 5 parts by weight) per 100 parts by weight of the total of the poly(3-hydroxyalkanoate)-based copolymer resin and polylactic acid), the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the first outer layer and the resin composition of the second outer layer is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based copolymer resin in each outer layer. The lower limit may be 0 parts by weight or more.

[0047] The content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the inner layer is not particularly limited, but from the viewpoint of stretchability, it is preferably 15 parts by weight or less, more preferably less than 15 parts by weight, even more preferably 12 parts by weight or less, even more preferably 10 parts by weight or less, and particularly preferably 0 part by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin.

[0048] Further, cases where the resin composition of the inner layer does not contain polylactic acid and cases where it does contain polylactic acid will be described in detail below. When the resin composition of the inner layer does not contain polylactic acid [when the content of polylactic acid in the resin composition of the inner layer cannot be considered as 0 part by weight (for example, 5 parts by weight or more) per 100 parts by weight of the total of the poly(3-hydroxyalkanoate)-based copolymer resin and polylactic acid], the content of poly(3-hydroxybutyrate) homopolymer in the inner layer is preferably 15 parts by weight or less, more preferably less than 15 parts by weight, even more preferably 12 parts by weight or less, even more preferably 10 parts by weight or less, and particularly preferably 0 part by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based copolymer resin in the inner layer.

[0049] When the resin composition for the inner layer contains polylactic acid [when the content of polylactic acid in the resin composition for the inner layer is 0 parts by weight or so small as to be regarded as 0 parts by weight (for example, less than 5 parts by weight) per 100 parts by weight of the total of the poly(3-hydroxyalkanoate)-based copolymer resin and polylactic acid], the content of poly(3-hydroxybutyrate) homopolymer in the inner layer is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 0 part by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based copolymer resin in the inner layer.

[0050] When the resin composition for the first outer layer and the resin composition for the second outer layer contain pentaerythritol as a crystal nucleating agent, the content of pentaerythritol in the resin composition for the first outer layer and the resin composition for the second outer layer is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin, from the viewpoint of a balance between optimizing the crystallization rate and suppressing poor appearance due to precipitation of the crystal nucleating agent.

[0051] The content of pentaerythritol in the resin composition for the inner layer is preferably 3 parts by weight or less, more preferably 1 part by weight or less, even more preferably 0.5 parts by weight or less, and particularly preferably 0 part by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin, from the viewpoints of suppressing poor appearance due to precipitation of a crystal nucleating agent and of stretchability.

[0052] In this embodiment, the resin composition of the first outer layer, the resin composition of the second outer layer, and the inner layer may each contain, in addition to the polylactic acid, a resin other than the poly(3-hydroxyalkanoate) copolymer resin, within the range that does not impair the effects of the invention, and may also contain, in addition to the nucleating agent, an additive that can be used together with the poly(3-hydroxyalkanoate) copolymer resin.

[0053] The resin other than the poly(3-hydroxyalkanoate)-based copolymer resin is not particularly limited, but a biodegradable polyester resin is preferred. Examples of biodegradable polyester resins include aliphatic polyester resins such as poly(3-hydroxypropionate), poly(4-hydroxybutyrate), polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and the aforementioned polylactic acid (PLA); and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebate terephthalate, and polybutylene azelate terephthalate. Only one type of resin other than the poly(3-hydroxyalkanoate)-based copolymer resin may be contained, or two or more types may be contained. As the resin other than the poly(3-hydroxyalkanoate)-based copolymer resin, polylactic acid is preferred from the viewpoints of stretchability and mechanical strength.

[0054] Examples of additives other than the crystal nucleating agent 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, lubricants, release agents, water repellents, antibacterial agents, and sliding property improvers. Only one type of additive other than the crystal nucleating agent may be contained, or two or more types may be contained. The content of these additives can be appropriately determined by a person skilled in the art depending on the intended use.

[0055] The filler and lubricant will be described in more detail below. Examples of fillers include calcium carbonate, talc, alumina, and titanium oxide. Among these, talc is preferred because it improves film productivity by improving releasability from a casting roll, it can suppress the problem of films sticking together after being wound up, and it improves the elasticity of the multilayer stretched film. One type of filler may be used, or two or more types may be used, and the ratio of use can be appropriately adjusted depending on the purpose.

[0056] When the resin composition for the first outer layer and the resin composition for the second outer layer contain a filler, the content thereof is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 7 parts by weight, and even more preferably 1 to 5 parts by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin. In this embodiment, the resin composition for the first outer layer and the resin composition for the second outer layer preferably contain a filler, but do not necessarily need to contain one.

[0057] The content of the filler in the resin composition for the inner layer is not particularly limited, but in view of the fact that the resin composition for the inner layer is not directly involved in contact with the casting roll or the films themselves and in view of the stretchability of the multilayer stretched film, the content of the filler in the resin composition for the inner layer is preferably less than the content of the filler in the resin compositions for the first outer layer and the second outer layer. Furthermore, the content of the filler is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and even more preferably 0 part by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin.

[0058] Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide or erucamide is preferred because of its particularly excellent lubricating effect on poly(3-hydroxyalkanoate) copolymer resins. One or more lubricants may be used, and the ratio of use can be appropriately adjusted depending on the purpose.

[0059] When the resin composition for the first outer layer, the resin composition for the second outer layer, and the resin composition for the inner layer contain a lubricant, the content thereof is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin. In the present embodiment, the resin composition for the first outer layer, the resin composition for the second outer layer, and the resin composition for the inner layer preferably contain a lubricant, but do not necessarily need to contain one.

[0060] (Each Layer) The resin composition of the first outer layer and the resin composition of the second outer layer are configured so that their crystallization rates are faster than that of the resin composition of the inner layer. The crystallization rate of the resin composition of each layer can be adjusted by appropriately selecting one or more of the following means: the composition ratio of the monomer units constituting the poly(3-hydroxyalkanoate) copolymer resin, the molecular weight of the poly(3-hydroxyalkanoate) copolymer resin, the composition of the poly(3-hydroxyalkanoate) copolymer mixture, the presence / absence / content of polylactic acid, and the presence / absence / content of a crystal nucleating agent.

[0061] A faster crystallization rate of a resin composition means that the maximum line speed measured under the same conditions except for the resin composition is faster. The maximum line speed means the limit line speed at which the resin composition can be peeled off from the casting roll when the resin composition is extruded onto the casting roll using a T-die and the line speed (film conveying speed) is increased.

[0062] Conditions other than the resin composition that may affect the maximum line speed include the diameter of the casting roll, the surface material, the surface temperature of the casting roll that first comes into contact after extrusion, and the wrap angle with the resin composition. Specifically, for example, the maximum line speed can be measured under the following conditions: a casting roll diameter of 200 mm, a hard chrome-plated surface material, a surface temperature of 40 to 80°C of the casting roll that first comes into contact after extrusion, and a wrap angle of 210° with the resin composition. Under these conditions, the surface temperature of the casting roll that first comes into contact after extrusion can be adjusted depending on the type of resin contained in the resin composition (particularly the type of resin contained in the resin composition of the first outer layer and the resin composition of the second outer layer). For example, if the resin contained in the resin composition is only a poly(3-hydroxyalkanoate)-based copolymer resin, a temperature of 80°C or the like can be used; if the resin contains both a poly(3-hydroxyalkanoate)-based copolymer resin and polylactic acid, a temperature of 40°C or the like can be used.

[0063] When measuring the maximum line speed using two cast rolls, specifically, for example, two cast rolls are used (the upstream cast roll that first comes into contact is designated as CRA, and the downstream cast roll is designated as CRB), and the ideal state is one in which the film is peeled off from the CRA on a common tangent to the CRA and CRB.The line speed (film transport speed) is increased, and the maximum line speed can be determined as the limit line speed before the film deviates from the common tangent and begins to wrap around the CRA.

[0064] In the multilayer stretched film, it is preferable that the maximum line speed v1-1 measured for the resin composition of the first outer layer, the maximum line speed v1-2 measured for the resin composition of the second outer layer, and the maximum line speed v2 measured for the resin composition of the inner layer, all measured under the same conditions, satisfy the following relationship (1) and (2). This is to provide better releasability from the casting roll and higher stretchability. (1) Maximum line speed ratio N1 = v1-1 / v2 is 2 or more. (2) Maximum line speed ratio N2 = v1-2 / v2 is 2 or more. Maximum line speed v1-1: the maximum line speed at which the resin composition contained in the first outer layer can be extruded onto a casting roll using a T-die and peeled from the casting roll. Maximum line speed v1-2: the maximum line speed at which the resin composition contained in the second outer layer can be extruded onto a casting roll using a T-die and peeled from the casting roll. Maximum line speed v2: the maximum line speed at which the resin composition contained in the inner layer can be extruded onto a casting roll using a T-die and peeled from the casting roll.

[0065] The maximum line speed ratio N1 in the above relational expression (1) is more preferably 4 or more, and even more preferably 8 or more. In order to ensure uniform stretchability, it may be 15 or less.

[0066] The maximum line speed ratio N2 in the above relational expression (2) is more preferably 4 or more, and even more preferably 8 or more. In order to ensure uniform stretchability, it may be 15 or less.

[0067] The thickness of the first outer layer and the second outer layer of the multilayer stretched film is not particularly limited, but is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more, in terms of improving film productivity due to good peelability from the cast roll, and may be 30 μm or less, or may be 20 μm or less.

[0068] The ratio of the thickness of the first outer layer to the thickness of the inner layer of the multilayer stretched film (thickness of the first outer layer / thickness of the inner layer) is not particularly limited, but from the viewpoint of achieving both good releasability to a cast roll and good stretchability, it is preferably 0.01 to 2, more preferably 0.05 to 2, even more preferably 0.05 to 1, and particularly preferably 0.1 to 0.5.

[0069] The ratio of the thickness of the second outer layer to the thickness of the inner layer of the multilayer stretched film (thickness of the second outer layer / thickness of the inner layer) is not particularly limited, but from the viewpoint of achieving both good releasability to a cast roll and good stretchability, it is preferably 0.01 to 2, more preferably 0.05 to 2, even more preferably 0.05 to 1, and particularly preferably 0.1 to 0.5.

[0070] The ratio of the thickness of the first outer layer to the thickness of the inner layer of the multilayer stretched film (thickness of the first outer layer / thickness of the inner layer) and the ratio of the thickness of the second outer layer to the thickness of the inner layer (thickness of the second outer layer / thickness of the inner layer) are the same as those of the film before stretching, and are the same before and after the stretching step (ii) in the method for producing a multilayer stretched film described below.

[0071] The total thickness of the multilayer stretched film is not particularly limited, but is preferably 10 to 180 μm, more preferably 20 to 120 μm, and even more preferably 30 to 60 μm, from the viewpoint of designing it to have a product specification thickness after stretching.

[0072] The thickness of each layer and the total thickness of the film may be measured by observing the cross section.

[0073] The inner layer in the multilayer stretched film may be a single layer or multiple layers. When the inner layer is composed of multiple layers, the term "inner layer" in this disclosure refers to both the entire multiple layers that make up the inner layer and each individual layer.

[0074] The multilayer stretched film according to this embodiment is thin yet has high strength, and therefore can be suitably used as a packaging material, for example, a packaging film (including bottle labels) for food and the like that requires heat sealability.

[0075] [Method for producing a multilayer stretched film] The present embodiment relates to a method for producing a multilayer stretched film containing a poly(3-hydroxyalkanoate)-based copolymer resin, the method comprising: a step (i) of co-extruding a molten resin composition comprising a poly(3-hydroxyalkanoate)-based copolymer resin and a crystal nucleating agent or polylactic acid, which constitutes a first outer layer; a molten resin composition comprising a poly(3-hydroxyalkanoate)-based copolymer resin, which constitutes an inner layer; and a molten resin composition comprising a poly(3-hydroxyalkanoate)-based copolymer resin and a crystal nucleating agent or polylactic acid, which constitutes a second outer layer, in this order, onto a cast roll to form a film; and a step (ii) of stretching the film obtained in the forming step (i) in the MD direction, wherein the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer.

[0076] (Step (i) of forming into a film) The step (i) of forming into a film can be carried out by co-extruding the molten resin compositions constituting the first outer layer, the inner layer, and the second outer layer onto a casting roll while laminating them in this order.

[0077] Coextrusion may be carried out by feeding raw materials containing the poly(3-hydroxyalkanoate) copolymer resins constituting each layer into an extruder, melt-kneading the raw materials, and then coextruding the pelletized raw materials. Alternatively, the pelletizing step may be omitted, and coextrusion may be carried out immediately after the melt-kneading.

[0078] 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 temperature of the resin composition during co-extrusion can be appropriately set depending on the melting point and melt flow rate of the resin composition constituting each layer, and from the viewpoint of resin fluidity and curing speed, it is preferably, for example, 160 to 190°C, more preferably 165 to 180°C.

[0079] The step (i) of forming into a film can be performed using a T-die extrusion molding method. The T-die extrusion molding method refers to a molding method in which a molten resin is extruded from an extruder through a slit-shaped outlet onto a casting roll 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, crystallized, 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 molten resin composition to be extruded into a film while being laminated, but the shape of the outlet is not particularly limited. The shape of the outlet is also not particularly limited.

[0080] In the T-die extrusion molding method, a molten resin composition is extruded from the discharge port of a T-die into a film while being laminated. The shape of the laminate of the molten resin composition may be a film, and the thickness and width are not particularly limited. The thickness is preferably 30 μm to 300 μm, since this results in little thickness variation and allows for easy cooling after extrusion.

[0081] The melt viscosity of the molten resin composition 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 any known method.

[0082] The surface temperature of the casting roll is not particularly limited as long as it is a temperature at which the resin composition of the first outer layer and the resin composition of the second outer layer are cooled and solidified, but from the viewpoint of achieving both good releasability and stretchability from the casting roll, it is preferably 10 to 90° C., more preferably 20 to 80° C., and even more preferably 40 to 80° C. The surface temperature of the casting roll refers to the temperature of the casting roll that the co-extruded molten resin composition first comes into contact with, regardless of whether the number of casting rolls is one or two or more.

[0083] The thickness of the first outer layer and the second outer layer of the film obtained in the molding step (i) before the stretching step (ii) is not particularly limited, but is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, from the viewpoint of improving film productivity due to good peelability from the cast roll, and may also be 40 μm or less, or may be 30 μm or less.

[0084] The ratio of the thickness of the first outer layer to the thickness of the inner layer of the film obtained in the molding step (i) prior to the stretching step (ii) (thickness of the first outer layer / thickness of the inner layer) is not particularly limited, but is preferably 0.01 to 2, more preferably 0.05 to 2, even more preferably 0.05 to 1, and particularly preferably 0.1 to 0.5, from the viewpoint of achieving both good releasability to a cast roll and good stretchability.

[0085] The ratio of the thickness of the second outer layer to the thickness of the inner layer of the film obtained in the molding step (i) prior to the stretching step (ii) (thickness of the second outer layer / thickness of the inner layer) is not particularly limited, but is preferably 0.01 to 2, more preferably 0.05 to 2, even more preferably 0.05 to 1, and particularly preferably 0.1 to 0.5, from the viewpoint of achieving both good releasability to a cast roll and good stretchability.

[0086] The thickness (total thickness) of the film obtained in the forming step (i) before the stretching step (ii) is not particularly limited and may be appropriately set in consideration of the desired thickness of the multilayer stretched film, the stretching ratio, strength, etc. For example, it is preferably 30 to 300 μm, more preferably 45 to 200 μm, and even more preferably 60 to 120 μm. The film thickness can be measured using a vernier caliper.

[0087] (Stretching step (ii)) In the step (ii) of stretching the film obtained in the molding step (i) in the MD direction, the method is not particularly limited as long as stretching is possible, and known manufacturing methods can be used as appropriate. The stretching direction of a film is referred to as the MD direction and the TD direction. 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. The MD direction is preferred in terms of productivity.

[0088] The specific stretching method is not particularly limited. For example, a method of stretching the film in the stretching direction, and a method of stretching the film by applying pressure in the thickness direction of the film, including roll rolling in which the film is sandwiched between two rolls, are mentioned. From the viewpoint of productivity and strength of the stretched film, a method of stretching the film by stretching it in the stretching direction is preferred. Note that stretching the film in the stretching direction means pulling the film in the stretching direction.

[0089] 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.

[0090] 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.

[0091] The stretching ratio achieved in the step of stretching the film is not particularly limited, but is preferably 1.1 or more, more preferably 1.3 or more, even more preferably 1.5 or more, and particularly preferably 2 or more. The upper limit is not particularly limited and may be determined appropriately, but may be, for example, 8 or less, 7 or less, 5 or less, 3.5 or less, or 3 or less.

[0092] The film temperature in the stretching step (also referred to as the film stretching temperature) 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 for the multilayer stretched film to be produced.

[0093] The stretching temperature of the film is preferably (melting point of the resin composition of the inner layer - 60) ° C. to (melting point of the resin composition of the inner layer) ° C., more preferably (melting point of the resin composition of the inner layer - 50) ° C. to (melting point of the resin composition of the inner layer - 5) ° C., and even more preferably (melting point of the resin composition of the inner layer - 40) ° C. to (melting point of the resin composition of the inner layer - 10). When the stretching temperature is within the above temperature range, thickness unevenness of the obtained multilayer stretched film can be reduced, and further, mechanical properties such as elongation, tear propagation strength, and flexural fatigue resistance can be improved.

[0094] 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 the stretching temperature to the film during stretching, a method of heating the film during stretching 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 the stretching temperature; and contact heating methods such as a method of bringing the film into contact with a roll heated to the stretching temperature. These methods may be used alone or in combination.

[0095] In the method of bringing the film into contact with rolls heated to the stretching temperature, hot air may be applied to the film between the upstream stretching roll and the downstream stretching roll in the MD direction.

[0096] In the method of bringing a film into contact with rolls heated to the stretching temperature, when a pair of stretching rolls is used to stretch the film while continuously transporting the film, the upstream stretching roll may be heated to the stretching temperature. The downstream stretching roll may be heated to a temperature equal to or lower than the upstream stretching roll, for example, (the temperature of the upstream stretching roll) to (upstream stretching roll -30°C) or (the temperature of the upstream stretching roll) to (upstream stretching roll -20°C). In this case, the stretching temperature can be controlled by setting the roll temperature to the desired stretching temperature.

[0097] As a means for adjusting the stretching temperature in the method for producing a multilayer stretched film according to this embodiment, a method in which the film is brought into contact with rolls heated to the stretching temperature is preferred, from the viewpoint of excellent productivity and easy heating, particularly in the case of mass production.

[0098] 1 is a conceptual diagram showing an example of the film-forming step (i) of a production line for continuously carrying out the film-forming step (i) and the stretching step (ii) while conveying a film using a T-die extrusion molding method. The arrow in the figure indicates the flow direction of the film.

[0099] The resin composition 311 constituting the first outer layer, the resin composition 312 constituting the inner layer, and the resin composition 313 constituting the second outer layer, which are film raw materials containing a poly(3-hydroxyalkanoate) copolymer resin, are each melted in an extruder 11, and the resin composition 311 constituting the first outer layer, the resin composition 312 constituting the inner layer, and the resin composition 313 constituting the second outer layer are laminated in this order on a casting roll 21. The resulting co-extrudate 31 is cooled and formed into a film by two casting rolls 21 and 22, yielding a molded film 32 [film-forming step (i)]. The molded film 32 is transported through a predetermined path by multiple transport rolls (not shown) and undergoes predetermined processes, including a stretching step (ii), to obtain a multilayer stretched film. The stretching step (ii) is performed using a pair of stretching rolls. However, the arrangement of the resin composition 311 constituting the first outer layer and the resin composition 313 constituting the second outer layer may be interchanged, and the number of casting rolls and the number of stretching rolls are not limited to the above.

[0100] The two casting rolls 21, 22 are set so that the roll surface temperature gradually decreases along the flow direction. When the coextrudate 31 molten in the extruder comes into contact with the casting rolls 21, 22, it is gradually cooled and formed into a film (step (i)).

[0101] The stretching step (ii) is carried out between a pair of stretching rolls. The rotation speed of the downstream stretching roll is controlled to be faster than the rotation speed of the upstream stretching roll, and the formed film 32 is stretched in the MD direction due to this difference in rotation speed.

[0102] The film that has been subjected to the film-forming step (i) and the stretching step (ii) as described above is wound up on a take-up roll as a multilayer stretched film. In this way, multilayer stretched films can be continuously produced.

[0103] The following items list preferred aspects of the present disclosure, but the present invention is not limited to them. [Item 1] A multilayer stretched film containing a poly(3-hydroxyalkanoate)-based copolymer resin, the multilayer stretched film comprising, in this order: a first outer layer containing a resin composition containing a poly(3-hydroxyalkanoate)-based copolymer resin, an inner layer containing a resin composition containing a poly(3-hydroxyalkanoate)-based copolymer resin, and a second outer layer containing a resin composition containing a poly(3-hydroxyalkanoate)-based copolymer resin, the multilayer stretched film being configured such that the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer. [Item 2] The multilayer stretched film according to Item 1, wherein the ratio of the thickness of the first outer layer to the thickness of the inner layer (thickness of first outer layer / thickness of inner layer) is 0.01 to 2, and the ratio of the thickness of the second outer layer to the thickness of the inner layer (thickness of second outer layer / thickness of inner layer) is 0.01 to 2. [Item 3] The multilayer stretched film according to Item 1 or 2, wherein a maximum line speed v1-1 measured for the resin composition of the first outer layer, a maximum line speed v1-2 measured for the resin composition of the second outer layer, and a maximum line speed v2 measured for the resin composition of the inner layer are all measured under the same conditions and satisfy the following relational expressions (1) and (2): (1) The maximum line speed ratio N1 = v1-1 / v2 is 2 or more. (2) The maximum line speed ratio N2 = v1-2 / v2 is 2 or more. Maximum line speed v1-1: the maximum line speed at which the resin composition contained in the first outer layer is extruded onto a casting roll using a T-die and can be peeled off from the casting roll. Maximum line speed v1-2: the maximum line speed at which the resin composition contained in the second outer layer is extruded onto a casting roll using a T-die and can be peeled off from the casting roll. Maximum line speed v2: the maximum line speed at which the resin composition contained in the inner layer is extruded onto a casting roll using a T-die and can be peeled off from the casting roll. [Item 4] The multilayer stretched film according to any one of Items 1 to 3, wherein the resin composition of the first outer layer and the resin composition of the second outer layer further contain polylactic acid.[Item 5] The multilayer stretched film according to Item 4, wherein the content of polylactic acid in the resin composition of the first outer layer and the resin composition of the second outer layer is 40 to 80 parts by weight per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) copolymer resin and polylactic acid. [Item 6] The multilayer stretched film according to any one of Items 1 to 5, wherein the resin compositions of the first outer layer and the second outer layer further contain a nucleating agent. [Item 7] The multilayer stretched film according to Item 6, wherein the content of nucleating agent in the resin composition of the inner layer is less than the content of nucleating agent in the resin compositions of the first outer layer and the second outer layer. [Item 8] The multilayer stretched film according to Item 6 or 7, wherein the nucleating agent contained in the resin composition of the first outer layer and the resin composition of the second outer layer is poly(3-hydroxybutyrate) homopolymer. [Item 9] The multilayer stretched film according to any one of Items 1 to 8, wherein the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the first outer layer is 70 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin, and the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the second outer layer is 70 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin. [Item 10] The multilayer stretched film according to any one of Items 1 to 9, wherein the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the inner layer is less than 15 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin. [Item 11] The multilayer stretched film according to any one of Items 1 to 10, wherein the resin composition of the first outer layer contains 50% by weight or more of a poly(3-hydroxyalkanoate) copolymer resin having a weight-average molecular weight of 800,000 or more based on 100% by weight of poly(3-hydroxyalkanoate) copolymer resin, and the resin composition of the second outer layer contains 50% by weight or more of a poly(3-hydroxyalkanoate) copolymer resin having a weight-average molecular weight of 800,000 or more based on 100% by weight of poly(3-hydroxyalkanoate) copolymer resin.[Item 12] A method for producing a multilayer stretched film containing a poly(3-hydroxyalkanoate)-based copolymer resin, comprising: a step (i) of co-extruding a molten resin composition comprising a poly(3-hydroxyalkanoate)-based copolymer resin and a crystal nucleating agent or polylactic acid, which constitutes a first outer layer; a molten resin composition comprising a poly(3-hydroxyalkanoate)-based copolymer resin, which constitutes an inner layer; and a molten resin composition comprising a poly(3-hydroxyalkanoate)-based copolymer resin and a crystal nucleating agent or polylactic acid, which constitutes a second outer layer, onto a cast roll while laminating them in this order to form a film; and a step (ii) of stretching the film obtained in the forming step (i) in the MD direction, wherein the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer. [Item 13] The method for producing a multilayer stretched film according to item 12, wherein the thickness of the first outer layer of the film obtained in the molding step (i) is 5 μm or more, and the thickness of the second outer layer of the film obtained in the molding step (i) is 5 μm or more. [Item 14] The method for producing a multilayer stretched film according to item 12 or 13, wherein the surface temperature of the cast roll in the molding step (i) is in the range of 10 to 90°C. [Item 15] The method for producing a multilayer stretched film according to any one of items 12 to 14, wherein the stretching step (ii) involves stretching the film in the MD direction under conditions where the temperature of the film is in the range of (melting point of the resin composition of the inner layer - 60)°C to (melting point of the resin composition of the inner layer)°C. [Item 16] The method for producing a multilayer stretched film according to any one of items 12 to 15, wherein the stretching ratio in the MD direction in the stretching step (ii) is 1.5 to 3.5 times. [Item 17] A packaging material comprising the multilayer stretched film according to any one of items 1 to 11.

[0104] 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.

[0105] The following raw materials were used in the examples and comparative examples. Resins A-1 to A-3 were used as poly(3-hydroxyalkanoate) copolymer resins, polylactic acid was used as a resin other than poly(3-hydroxyalkanoate) copolymer resins, B-1 was used as a lubricant, and C-1 was used as a filler. In the following, 3HB represents a 3-hydroxybutyrate repeating unit, and 3HH represents a 3-hydroxyhexanoate repeating unit.

[0106] (Resin) Poly(3-hydroxyalkanoate) copolymer resin A-1: ​​P3HB3HH (average content ratio 3HB / 3HH=94 / 6 (mol% / mol%)) Resin A-1 was produced in accordance with the method described in Example 1 of WO 2019 / 142845, and the weight average molecular weight was adjusted to 830,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0107] Poly(3-hydroxyalkanoate) copolymer resin A-2: P3HB3HH (average content ratio 3HB / 3HH=89 / 11 (mol% / mol%)) Resin A-2 was produced in accordance with the method described in Example 5 of WO 2019 / 142845, and the weight-average molecular weight was adjusted to 830,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0108] Poly(3-hydroxyalkanoate) copolymer resin A-3: P3HB3HH (average content ratio 3HB / 3HH=94 / 6 (mol% / mol%)) Produced in accordance with the method described in Example 1 of WO 2019 / 142845, the weight-average molecular weight was adjusted to 630,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0109] The following polylactic acid products were used: PLA: Ingeo (registered trademark) Biopolymer (melting point: 145 to 160°C)

[0110] (Lubricant) B-1: Behenic acid amide (manufactured by Nippon Fine Chemical Co., Ltd.: BNT-22H)

[0111] (Filler) C-1: Hydrous magnesium silicate (manufactured by Nippon Talc Co., Ltd.: SG-200N15)

[0112] (Nucleating Agent) D-1: P3HB Produced according to the method described in Comparative Example 1 of WO 2004 / 041936, the weight-average molecular weight was adjusted to 350,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0113] (Method for producing resin composition) Resin composition P-1 Poly (3-hydroxyalkanoate) copolymer resin, A-1: ​​25 parts by weight, A-2: 75 parts by weight, for a total of 100 parts by weight, B-1: 1.25 parts by weight as a lubricant, C-1: 1.25 parts by weight as a filler, D-1: 25 parts by weight as a crystal nucleating agent 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 150 ° C to 180 ° 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 resin pellets (resin composition) P-1. The melting point of the resin pellets (resin composition) P-1 was 163 ° C.

[0114] Resin composition P-2: Poly(3-hydroxyalkanoate) copolymer resin: A-2: 40 parts by weight, A-3: 60 parts by weight, a total of 100 parts by weight, and B-1: 0.5 parts by weight as a lubricant were dry-blended. The obtained dry blend was charged into a φ26 mm co-rotating twin-screw extruder hopper with the cylinder temperature and die temperature set to 130 ° C 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 resin pellets (resin composition) P-2. The melting point of the resin pellets (resin composition) P-2 was 143 ° C.

[0115] Resin composition P-3: Poly(3-hydroxyalkanoate) copolymer resins, A-2: 24 parts by weight, A-3: 36 parts by weight, polylactic acid, PLA: 40 parts by weight, a total of 100 parts by weight, B-1: 0.5 parts by weight as a lubricant, were dry blended. The obtained dry blend was charged into a φ26 mm co-rotating twin-screw extruder hopper with cylinder temperature and die temperature set to 150 ° C to 180 ° 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 resin pellets (resin composition) P-3. The melting point of the resin pellets (resin composition) P-3 was 147 ° C.

[0116] Resin composition P-4: Resin pellets (resin composition) P-4 were obtained in the same manner as in resin composition P-3, except that the blending amounts of poly(3-hydroxyalkanoate) copolymer resin and polylactic acid were changed to 16 parts by weight for A-2, 24 parts by weight for A-3, and 60 parts by weight for PLA, totaling 100 parts by weight. The melting point of resin pellets (resin composition) P-4 was 149°C.

[0117] Resin composition P-5: Resin pellets (resin composition) P-5 were obtained in the same manner as in resin composition P-3, except that the blending amounts of poly(3-hydroxyalkanoate) copolymer resin and polylactic acid were changed to 8 parts by weight of A-2, 12 parts by weight of A-3, and 80 parts by weight of PLA, totaling 100 parts by weight. The melting point of resin pellets (resin composition) P-5 was 151°C.

[0118] (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).

[0119] [Example 1] The cylinder temperature and die temperature of two φ40 mm single-screw extruders connected to a 350 mm wide, two-type, three-layer multi-manifold die were each set to 165 ° C. The resin pellets (resin composition) P-1 were placed in the hopper of the outer layer extruder, and the resin pellets (resin composition) P-2 were placed in the hopper of the inner layer extruder. Molten resin composition P-1, molten resin composition P-2, and molten resin composition P-1 were laminated in this order, and the resulting film-like molten resin was extruded onto a φ200 mm cast roll (hard chrome plated, hereinafter CR1) set at 80 ° C. at a wrap angle of 210 ° to form a film. After cooling to a film temperature of 80 ° C., the film was peeled off with a second cast roll (hard chrome plated, hereinafter CR2) to obtain a molded film [Process (i) of forming into a film]. The thicknesses of the first outer layer, inner layer, and second outer layer of the obtained molded film were 10 μm, 40 μm, and 10 μm, respectively. The obtained molded film was continuously transported and stretched twice in the MD direction using a pair of stretching rolls at a roll temperature of 100 to 120°C [stretching step (ii)] to obtain a multilayer stretched film. The thickness of each layer was adjusted by adjusting the screw rotation speed of the outer layer extruder and the inner layer extruder.

[0120] Furthermore, for the resin composition of the first outer layer and the resin composition of the second outer layer P-1, the maximum line speeds v1-1 and v1-2 measured under the same conditions as when the molded film in Example 1 was obtained were both 5.0 m / min, and the maximum line speed v2 measured for the resin composition of the inner layer was 0.5 m / min. Therefore, the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer were faster than that of the resin composition of the inner layer, and the maximum line speed ratios N1 and N2 defined as above were both calculated to be 10.

[0121] (Evaluation of Roll Releasability) When obtaining a cast film, the ideal state was when the film was peeled from CR1 on the common tangent line between CR1 and CR2. The limit line speed before the film deviated from the common tangent line and began to wrap around CR1 was measured, and roll releasability was evaluated. When the limit line speed was 1.0 m / min or more and productivity was good, it was evaluated as ○, and when it was less than 1.0 m / min, it was evaluated as ×. The results are shown in Table 2. The limit line speed corresponds to the maximum line speed at which the film can be peeled from the cast roll.

[0122]

[0123]

[0124] (Evaluation of stretchability) The molded film was evaluated for its ability to be stretched. If the film could be stretched uniformly without unevenness, it was marked as ◯, and if uneven stretching occurred or the film broke, it was marked as x. The results are shown in Table 2.

[0125] (Measurement of thickness of each layer and total thickness) The obtained molded film or multilayer stretched film was cut into cross sections with a cutter knife and observed. The observation was performed using a microscope (Keyence VHX-5000) to measure the thickness of each layer and the total thickness. The results are shown in Tables 1 and 2.

[0126] [Examples 2 to 5] Multilayer stretched films were obtained and evaluated in the same manner as in Example 1, except that the screw rotation speeds of the outer layer extruder and the inner layer extruder were adjusted so that the thicknesses of the outer layers (first outer layer and second outer layer) and the inner layer were as shown in Table 1. The evaluation results of roll peelability and stretchability, and the measurement results of the thickness of each layer and the total thickness are shown in Table 2.

[0127] [Examples 6 to 8] Multilayer stretched films were obtained and evaluated in the same manner as in Example 1, except that the type of resin composition was changed, the screw rotation speeds of the outer layer extruder and the inner layer extruder were adjusted, and the cast roll temperature was changed to 40°C so that the resin compositions and thicknesses of the outer layers (first outer layer and second outer layer) and the thickness of the inner layer would be as shown in Table 1. The results of the evaluation of roll peelability and stretchability, and the measurement of the thickness of each layer and the total thickness are shown in Table 2.

[0128] Comparative Example 1 A multilayer stretched film was obtained and evaluated in the same manner as in Example 1, except that resin pellets (resin composition) P-1 were fed into the hoppers of the outer layer extruder and the inner layer extruder, and the screw rotation speeds of the outer layer extruder and the inner layer extruder were adjusted so that the thicknesses of the outer layers (first outer layer and second outer layer) and the inner layer would be as shown in Table 1.

[0129] Since the resin composition of the first outer layer, the resin composition of the second outer layer, and the resin composition of the inner layer were all P-1, the maximum line speed ratio N1 and the maximum line speed ratio N2 defined as above were all calculated to be 1. The evaluation results of the roll releasability and stretchability, and the measurement results of the thickness of each layer and the total thickness are shown in Table 2.

[0130] Comparative Example 2 A multilayer stretched film was obtained and evaluated in the same manner as in Example 1, except that resin pellets (resin composition) P-2 were fed into the hoppers of the outer layer extruder and the inner layer extruder, and the screw rotation speeds of the outer layer extruder and the inner layer extruder were adjusted so that the thicknesses of the outer layers (first outer layer and second outer layer) and the inner layer were as shown in Table 1.

[0131] Since the resin composition of the first outer layer, the resin composition of the second outer layer, and the resin composition of the inner layer were all P-2, the maximum line speed ratio N1 and the maximum line speed ratio N2 defined as above were all calculated to be 1. The evaluation results of the roll releasability and stretchability, and the measurement results of the thickness of each layer and the total thickness are shown in Table 2.

[0132] Multilayer stretched films (Comparative Examples 1 and 2) in which the resin composition of the outer layers (first outer layer and second outer layer) was the same as the resin composition of the inner layer and the crystallization rate of the resin composition of the outer layers (first outer layer and second outer layer) was the same as the crystallization rate of the resin composition of the inner layer were poor in evaluation of releasability to a cast roll or stretchability of the formed film. On the other hand, multilayer stretched films (Examples 1 to 8) in which the crystallization rate of the resin composition of the outer layers (first outer layer and second outer layer) was faster than the crystallization rate of the resin composition of the inner layer were found to have good releasability to a cast roll and high stretchability of the formed film.

[0133] 21, 22 Cast roll 311 Resin composition constituting first outer layer 312 Resin composition constituting inner layer 313 Resin composition constituting second outer layer

Claims

1. A multilayer stretched film comprising a poly(3-hydroxyalkanoate) copolymer resin, the multilayer stretched film comprising, in this order: a first outer layer comprising a resin composition containing a poly(3-hydroxyalkanoate) copolymer resin; an inner layer comprising a resin composition containing a poly(3-hydroxyalkanoate) copolymer resin; and a second outer layer comprising a resin composition containing a poly(3-hydroxyalkanoate) copolymer resin, the multilayer stretched film being configured so that the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer.

2. The multilayer stretched film according to claim 1, wherein the ratio of the thickness of the first outer layer to the thickness of the inner layer (thickness of first outer layer / thickness of inner layer) is 0.01 to 2, and the ratio of the thickness of the second outer layer to the thickness of the inner layer (thickness of second outer layer / thickness of inner layer) is 0.01 to 2.

3. The multilayer stretched film according to claim 1, wherein the maximum line speed v1-1 measured for the resin composition of the first outer layer, the maximum line speed v1-2 measured for the resin composition of the second outer layer, and the maximum line speed v2 measured for the resin composition of the inner layer are all measured under the same conditions and satisfy the following relationship (1) and (2): (1) maximum line speed ratio N1 = v1-1 / v2 is 2 or more (1) maximum line speed ratio N2 = v1-2 / v2 is 2 or more (2) maximum line speed v1-1: the maximum line speed at which the resin composition contained in the first outer layer can be extruded onto a casting roll using a T-die and peeled from the casting roll; maximum line speed v1-2: the maximum line speed at which the resin composition contained in the second outer layer can be extruded onto a casting roll using a T-die and peeled from the casting roll; and maximum line speed v2: the maximum line speed at which the resin composition contained in the inner layer can be extruded onto a casting roll using a T-die and peeled from the casting roll.

4. The multilayer stretched film according to claim 1, wherein the resin composition of the first outer layer and the resin composition of the second outer layer further contain polylactic acid.

5. The multilayer stretched film according to claim 4, wherein the content of polylactic acid in the resin composition of the first outer layer and the resin composition of the second outer layer is 30 to 90 parts by weight per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) copolymer resin and polylactic acid.

6. The multilayer stretched film according to claim 1, wherein the resin compositions of the first outer layer and the second outer layer further contain a nucleating agent.

7. The multilayer stretched film according to claim 6, wherein the content of the nucleating agent in the resin composition of the inner layer is less than the content of the nucleating agent in the resin compositions of the first outer layer and the second outer layer.

8. The multilayer stretched film according to claim 6, wherein the nucleating agent contained in the resin composition of the first outer layer and the resin composition of the second outer layer is poly(3-hydroxybutyrate) homopolymer.

9. The multilayer stretched film according to claim 1, wherein the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the first outer layer is 70 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin, and the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the second outer layer is 70 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin.

10. The multilayer stretched film according to claim 1, wherein the content of poly(3-hydroxybutyrate) homopolymer in the resin composition of the inner layer is less than 15 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) copolymer resin.

11. The multilayer stretched film according to claim 1, wherein the resin composition of the first outer layer contains 50% by weight or more of a poly(3-hydroxyalkanoate) copolymer resin having a weight-average molecular weight of 800,000 or more out of 100% by weight of poly(3-hydroxyalkanoate) copolymer resin, and the resin composition of the second outer layer contains 50% by weight or more of a poly(3-hydroxyalkanoate) copolymer resin having a weight-average molecular weight of 800,000 or more out of 100% by weight of poly(3-hydroxyalkanoate) copolymer resin.

12. A method for producing a multilayer stretched film containing a poly(3-hydroxyalkanoate) copolymer resin, comprising: step (i) of co-extruding a molten resin composition comprising a poly(3-hydroxyalkanoate) copolymer resin and a nucleating agent or polylactic acid, which constitutes a first outer layer; a molten resin composition comprising a poly(3-hydroxyalkanoate) copolymer resin, which constitutes an inner layer; and a molten resin composition comprising a poly(3-hydroxyalkanoate) copolymer resin and a nucleating agent or polylactic acid, which constitutes a second outer layer, in this order, onto a cast roll to form a film; and step (ii) of stretching the film obtained in the forming step (i), in the machine direction, wherein the crystallization rates of the resin composition of the first outer layer and the resin composition of the second outer layer are both faster than the crystallization rate of the resin composition of the inner layer.

13. The method for producing a multilayer stretched film according to claim 12, wherein the thickness of the first outer layer of the film obtained in the forming step (i) is 5 μm or more, and the thickness of the second outer layer of the film obtained in the forming step (i) is 5 μm or more.

14. The method for producing a multilayer stretched film according to claim 12 or 13, wherein in the forming step (i), the surface temperature of the casting roll is in the range of 10 to 90°C.

15. A method for producing a multilayer stretched film according to claim 12 or 13, wherein in the stretching step (ii), the film is stretched in the machine direction under conditions where the temperature of the film is in the range of (melting point of the resin composition of the inner layer - 60)°C to (melting point of the resin composition of the inner layer)°C.

16. A method for producing a multilayer stretched film according to claim 12 or 13, wherein in the stretching step (ii), the stretching ratio in the MD direction is 1.5 to 3.5 times.

17. A packaging material comprising the multilayer stretched film according to any one of claims 1 to 11.

Images