Multilayer film and method for producing same

Abstract

This multilayer film includes the following layers laminated in the stated order: a first outer layer that contains a poly(3-hydroxyalkanoate)-based resin (A1), a polylactic acid-based resin (B1), and, as an optional component, a sugar alcohol compound (C1); an inner layer that contains a poly(3-hydroxyalkanoate)-based resin (A0), a polylactic acid-based resin (B0), and a sugar alcohol compound (C0); and a second outer layer that contains a poly(3-hydroxyalkanoate)-based resin (A2), a polylactic acid-based resin (B2), and, as an optional component, a sugar alcohol compound (C2). The content of (C1) with respect to 100 parts by weight of (A1), and the content of (C2) with respect to 100 parts by weight of (A2) are each less than the content of (C0) with respect to 100 parts by weight of (A0) and are each 0-0.4 parts by weight.

Description

Multilayer film and method for producing the same

[0001] The present invention relates to a multilayer film containing a poly(3-hydroxyalkanoate)-based resin, and a method for producing the same.

[0002] In recent years, separate collection and composting of food waste have been promoted mainly in Europe, and plastic products that can be composted together with food waste have been desired. Further, in order to solve the problem of marine pollution caused by plastics, plastics having marine degradability are expected.

[0003] As a material having such compost degradability and marine degradability, poly(3-hydroxyalkanoate)-based resins represented by poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) have attracted attention.

[0004] However, poly(3-hydroxyalkanoate)-based resins are materials that crystallize slower than common thermoplastic resins, require time for solidification after heating and melting, and have the problem of impairing the productivity of molding processing such as film molding. To solve this problem, a technique of blending a poly(3-hydroxyalkanoate)-based resin with a sugar alcohol compound such as pentaerythritol as a crystal nucleating agent is known (see Patent Documents 1 and 2).

[0005] On the other hand, as a technique for producing a thin and high-strength film, a method of stretching the film is known. However, it is known that poly(3-hydroxyalkanoate)-based resins are materials that are difficult to stretch due to their properties.

[0006] WO 2014 / 020838 WO 2008 / 099586

[0007] According to the method of blending a sugar alcohol compound described in Patent Documents 1 and 2, the solidification property of a poly(3-hydroxyalkanoate)-based resin can be improved, and the productivity of a molded article containing the resin can be improved. Among these, pentaerythritol is excellent in the effect of improving the productivity of a film containing a poly(3-hydroxyalkanoate)-based resin.

[0008] However, it was found that when a film is formed by compounding a sugar alcohol compound with a poly(3-hydroxyalkanoate) resin, the sugar alcohol compound may sublimate during molding and adhere to and contaminate the cast roll used for film molding. Furthermore, it was found that the sugar alcohol compound may bleed onto the surface of the molded film, and that the bled compound may adversely affect subsequent processes such as film lamination.

[0009] However, formulations that do not include sugar alcohol compounds may result in decreased productivity of poly(3-hydroxyalkanoate) resin-containing films.

[0010] Furthermore, the poly(3-hydroxyalkanoate) resin-containing film needs to have excellent stretchability.

[0011] In view of the above situation, the present invention aims to provide a poly(3-hydroxyalkanoate) resin-containing film that can suppress the bleeding of sugar alcohol compounds while incorporating sugar alcohol compounds, and that has good stretchability.

[0012] As a result of diligent research to solve the above problems, the present inventors have found that by laminating a poly(3-hydroxyalkanoate) resin-containing film containing a sugar alcohol compound as a crystal nucleating agent with a poly(3-hydroxyalkanoate) resin-containing outer layer containing a reduced amount of sugar alcohol compound on both sides, the sugar alcohol compound is trapped in the inner layer by the outer layer, and by incorporating a polylactic acid resin into each layer, it is possible to provide a poly(3-hydroxyalkanoate) resin-containing film that suppresses the bleeding of the sugar alcohol compound while still containing it, and has good stretchability, thus completing the present invention.

[0013] That is, the present invention relates to a multilayer film comprising: a first outer layer containing a poly(3-hydroxyalkanoate) resin (A1), a polylactic acid resin (B1), and a sugar alcohol compound (C1) as an optional component; an inner layer containing a poly(3-hydroxyalkanoate) resin (A0), a polylactic acid resin (B0), and a sugar alcohol compound (C0); and a second outer layer containing a poly(3-hydroxyalkanoate) resin (A2), a polylactic acid resin (B2), and a sugar alcohol compound (C2) as an optional component, laminated in this order, wherein the content of the sugar alcohol compound (C1) per 100 parts by weight of resin (A1) and the content of the sugar alcohol compound (C2) per 100 parts by weight of resin (A2) are each less than the content of the sugar alcohol compound (C0) per 100 parts by weight of resin (A0), and are between 0 and 0.4 parts by weight. The present invention also relates to a method for producing the multilayer film, comprising the step of forming a film by co-extruding onto a cast roll while laminating in the following order: a molten first outer layer resin composition containing resin (A1), resin (B1), and a sugar alcohol compound (C1) as an optional component; a molten inner layer resin composition containing resin (A0), resin (B0), and a sugar alcohol compound (C0); and a molten second outer layer resin composition containing resin (A2), resin (B2), and a sugar alcohol compound (C2) as an optional component.

[0014] According to the present invention, it is possible to provide a poly(3-hydroxyalkanoate) resin-containing film that suppresses the bleeding of sugar alcohol compounds while incorporating them, and has good stretchability. According to the present invention, it is possible to suppress the adhesion and contamination of sugar alcohol compounds to the cast roll used in film molding. Furthermore, since the bleeding of sugar alcohol compounds to the film surface is suppressed, adverse effects on subsequent processes such as film lamination can be avoided.

[0015] According to the present invention, poly(3-hydroxyalkanoate) resin-containing films can be stretched effectively, suppressing film breakage and uneven stretching on the film surface. Furthermore, high stretching ratios can be achieved. According to a preferred embodiment of the present invention, uniaxially oriented films stretched in the MD direction, or biaxially oriented films stretched in both the MD and TD directions, can be manufactured. Additionally, the present invention provides a resin film with good biodegradability.

[0016] According to a preferred embodiment of the present invention, a poly(3-hydroxyalkanoate) resin-containing film with improved heat-sealability can be provided.

[0017] A conceptual diagram illustrating an example of the process (i) for forming a film for manufacturing the multilayer film according to this disclosure. A graph showing the results of measuring the heat seal strength of the multilayer stretched films obtained in Examples 7 and 8 (horizontal axis represents the heat sealing temperature).

[0018] Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and various modifications are possible within the scope defined in the claims. Furthermore, the configurations described below can be combined in any way, and such combinations may also constitute an embodiment of the present invention.

[0019] This embodiment relates to a multilayer film comprising a first outer layer, an inner layer, and a second outer layer, each containing a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B), laminated in that order. The multilayer film according to this disclosure has the advantage that delamination between the first or second outer layer and the inner layer is less likely to occur because the resin types of each layer are common.

[0020] [Poly(3-hydroxyalkanoate) resin (A)] In this application, the poly(3-hydroxyalkanoate) resin (A) contained in the first outer layer, inner layer, or second outer layer will be denoted as (A1), (A0), and (A2), respectively, and the description of (A) will apply to (A1), (A0), and (A2). However, resins (A1), (A0), and (A2) may have the same composition as each other, or they may have different compositions.

[0021] The poly(3-hydroxyalkanoate) resin (A) may be a single poly(3-hydroxyalkanoate) resin or a mixture of two or more poly(3-hydroxyalkanoate) resins. However, it is preferable that the mixture be of at least two poly(3-hydroxyalkanoate) resins in which the types of constituent monomers and / or the content ratios of the constituent monomers differ from each other, as this makes it easier to achieve both film strength and productivity, and can also improve the stretchability of the film.

[0022] The poly(3-hydroxyalkanoate) resin (A) is preferably a polymer having a 3-hydroxyalkanoate unit, specifically a polymer containing the unit shown in the following general formula (1): [-CHR-CH ２ -CO-O-] (1)

[0023] In general formula (1), R is C ｐ H ２ｐ＋１ R represents an alkyl group, where p is an integer from 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 groups. p is preferably 1 to 10, and more preferably 1 to 8.

[0024] As the poly(3-hydroxyalkanoate) resin (A), poly(3-hydroxyalkanoate) resins produced from microorganisms are particularly preferred. In poly(3-hydroxyalkanoate) resins produced from microorganisms, all 3-hydroxyalkanoate units are contained as (R)-3-hydroxyalkanoate units.

[0025] The poly(3-hydroxyalkanoate) resin (A) preferably contains 50 mol% or more of 3-hydroxyalkanoate units (particularly units represented by general formula (1)) of the total constituent units, more preferably 60 mol% or more, and even more preferably 70 mol% or more. The poly(3-hydroxyalkanoate) resin (A) may contain only one or more types of 3-hydroxyalkanoate units as constituent units of the polymer, or it may contain one or more types of 3-hydroxyalkanoate units in addition to other units (for example, 4-hydroxyalkanoate units).

[0026] The poly(3-hydroxyalkanoate) resin (A) is preferably a homopolymer or copolymer containing 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units (hereinafter, both polymers are collectively referred to as "poly(3-hydroxybutyrate) resin"). In particular, it is preferable that all 3-hydroxybutyrate units are (R)-3-hydroxybutyrate units. Furthermore, it is preferable that the poly(3-hydroxyalkanoate) resin (A) contains copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0027] Specific examples of poly(3-hydroxybutyrate) resins include, for example, poly(3-hydroxybutyrate), 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), Examples include 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), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as P3HB4HB). In particular, from the viewpoint of film productivity and mechanical properties, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred.

[0028] Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred from the viewpoint that by changing the composition ratio of repeating units, the melting point and degree of crystallinity can be changed, thereby altering physical properties such as Young's modulus and heat resistance, and that it is possible to impart physical properties between those of polypropylene and polyethylene. Furthermore, it is easy to produce industrially and is a plastic with useful physical properties. In particular, among poly(3-hydroxybutyrate) resins that have the property of being easily thermally decomposed when heated at 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoint that its melting point can be lowered, enabling molding and processing at low temperatures.

[0029] Examples of commercially available poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) include Kaneka Corporation's "Kaneka Biodegradable Polymer Green Planet" (registered trademark).

[0030] When the poly(3-hydroxyalkanoate) resin (A) contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content ratio of 3-hydroxybutyrate units to other hydroxyalkanoate units in the total monomer units constituting the poly(3-hydroxyalkanoate) resin (A) is preferably 3-hydroxybutyrate units / other hydroxyalkanoates = 99 / 1 to 80 / 20 (mol% / mol%), more preferably 97 / 3 to 82 / 18 (mol% / mol%), and even more preferably 95 / 5 to 85 / 15 (mol% / mol%), from the viewpoint of achieving both film strength and productivity.

[0031] The average content ratio of each monomer unit to the total monomer units constituting the poly(3-hydroxyalkanoate) resin (A) can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of International Publication 2013 / 147139. The average content ratio means the molar ratio of each monomer unit to the total monomer units constituting the poly(3-hydroxyalkanoate) resin (A), and if the poly(3-hydroxyalkanoate) resin (A) is a mixture of two or more poly(3-hydroxyalkanoate) resins, it means the molar ratio of each monomer unit contained in the whole mixture.

[0032] As described above, the poly(3-hydroxyalkanoate) resin (A) may be a mixture of at least two poly(3-hydroxyalkanoate) resins having different types of constituent monomers and / or different content ratios of constituent monomers. In this case, at least one highly crystalline poly(3-hydroxyalkanoate) resin and at least one low-crystalline poly(3-hydroxyalkanoate) resin can be used in combination.

[0033] Generally, highly crystalline poly(3-hydroxyalkanoate) resins have excellent productivity but poor mechanical strength, while low-crystalline poly(3-hydroxyalkanoate) resins have poor productivity but excellent mechanical properties. By using both resins in combination, the strength and productivity of the film can be further improved.

[0034] The content of 3-hydroxybutyrate units in highly crystalline poly(3-hydroxyalkanoate) resins is preferably higher than the average content of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin (A). On the other hand, the content of 3-hydroxybutyrate units in low-crystalline poly(3-hydroxyalkanoate) resins is preferably lower than the average content of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin (A).

[0035] When the poly(3-hydroxyalkanoate) resin (A) is a mixture of at least two poly(3-hydroxyalkanoate) resins, it is preferable that the resin (A) specifically includes the following copolymer (A-a) and the following copolymer (A-b). According to this embodiment, it is easy to achieve both film strength and productivity, and it is also possible to further improve the stretchability of the film. Copolymer (A-a): A copolymer of 3-hydrokybtyrate units and other hydroxyalkanoate units in which the content of other hydroxyalkanoate units is 24 mol% or more. Copolymer (A-b): A copolymer of 3-hydrokybtyrate units and other hydroxyalkanoate units in which the content of other hydroxyalkanoate units is 1 mol% or more and 9 mol% or less.

[0036] In copolymer (A-a), the content of other hydroxyalkanoate units 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%. In copolymer (A-b), the content of other hydroxyalkanoate units is preferably 2 to 8 mol%, more preferably 2 to 7 mol%.

[0037] The copolymers (A-a) and (A-b) are preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) being particularly preferred.

[0038] In the multilayer film according to this embodiment, the content of copolymer (A-a) in each layer is preferably more than 0% by weight and 60% by weight or less, relative to the total weight of the poly(3-hydroxyalkanoate) resin (A) in each layer, from the viewpoint of film productivity and stretchability. The upper limit is preferably 50% by weight or less, and more preferably 40% by weight or less, from the viewpoint of film productivity. The lower limit is preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 15% by weight or more, from the viewpoint of film stretchability. However, embodiments that do not contain copolymer (A-a) are also possible.

[0039] Furthermore, from the viewpoint of film productivity and stretchability, the content of copolymer (A-b) in each layer is preferably more than 0% by weight and 90% by weight or less relative to the total weight of the poly(3-hydroxyalkanoate) resin (A) in each layer. The upper limit is preferably 80% by weight or less, and more preferably 70% by weight or less, from the viewpoint of film productivity and stretchability. The lower limit is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 30% by weight or more, and particularly preferably 40% by weight or more, from the viewpoint of film productivity.

[0040] When resin (A) contains copolymer (A-a) and copolymer (A-b), the weight ratio (A-a / A-b) of copolymer (A-a) to copolymer (A-b) in each layer is preferably 5 / 95 to 50 / 50, more preferably 10 / 90 to 40 / 60, even more preferably 15 / 85 to 30 / 70, and particularly preferably 20 / 80 to 30 / 70, from the viewpoint of achieving both film strength and productivity and further improving stretchability.

[0041] The copolymer (A-b) may be a mixture of at least two types of copolymers having different constituent monomer content ratios from each other. Specifically, it preferably comprises the following copolymer (A-b-1) and the following copolymer (A-b-2). According to this aspect, it becomes easier to achieve both the strength and productivity of the film, and the stretchability of the film can be further improved. Copolymer (A-b-1): a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content ratio of the other hydroxyalkanoate units is 1 mol% or more and less than 4 mol% Copolymer (A-b-2): a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content ratio of the other hydroxyalkanoate units is 4 mol% or more and 9 mol% or less

[0042] In the copolymer (A-b-1), the content ratio of the other hydroxyalkanoate units is preferably 1 to 3 mol%, more preferably 2 to 3 mol%. In the copolymer (A-b-2), the content ratio of the other hydroxyalkanoate units is preferably 5 to 8 mol%, more preferably 6 to 7 mol%.

[0043] As the copolymers (A-b-1) and (A-b-2), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred respectively, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred.

[0044] When the resin (A) comprises the copolymer (A-b-2), the weight ratio of the copolymer (A-b-2) to the total resin (A) in each layer is preferably 10 to 90% by weight, more preferably 20 to 70% by weight, still more preferably 25 to 60% by weight, and particularly preferably 30 to 50% by weight, from the viewpoint of improving the strength, productivity, or stretchability of the film.

[0045] The method for obtaining a blend of two or more poly(3-hydroxyalkanoate)-based resins is not particularly limited; it may be a method of obtaining the blend by microbial production, or may be a method of obtaining the blend by chemical synthesis. Alternatively, a blend may be obtained by melt-kneading two or more resins using an extruder, kneader, Banbury mixer, roll or the like, or a blend may be obtained by dissolving two or more resins in a solvent, mixing and drying the mixture.

[0046] Further, the resin (A) may be composed of only one type of poly(3-hydroxyalkanoate)-based resin. In this case, the resin (A) is preferably composed only of the copolymer (A-b), and particularly preferably composed only of the copolymer (A-b-2).

[0047] The weight average molecular weight of the poly(3-hydroxyalkanoate)-based resin (A) is not particularly limited, but from the viewpoint of film strength and productivity, it is preferably 200,000 to 2,000,000, more preferably 300,000 to 1,500,000, and still more preferably 400,000 to 1,000,000.

[0048] Further, when the poly(3-hydroxyalkanoate)-based resin (A) is a mixture of two or more poly(3-hydroxyalkanoate)-based resins, the weight average molecular weight of each poly(3-hydroxyalkanoate)-based resin constituting the mixture is not particularly limited. However, from the viewpoint of film strength and productivity, the weight average molecular weight of the copolymer (A-a) is preferably 200,000 to 1,000,000, more preferably 220,000 to 800,000, and still more preferably 250,000 to 600,000. On the other hand, from the viewpoint of film strength and productivity, the weight average molecular weight of the copolymer (A-b) is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and still more preferably 300,000 to 2,000,000. Further, from the viewpoint of film strength and productivity, the weight average molecular weight of the copolymer (A-b-2) is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and still more preferably 300,000 to 2,000,000.

[0049] The weight-average molecular weight of poly(3-hydroxyalkanoate) resins can be measured using gel permeation chromatography with chloroform solution (HPLC GPC system manufactured by Shimadzu Corporation) and converted to polystyrene equivalent. For the gel permeation chromatography, any column suitable for measuring weight-average molecular weight should be used.

[0050] The method for producing poly(3-hydroxyalkanoate) 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 eutropus, 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, pp. 4821-4830 (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-hydroxyalkanoate) resin synthesis-related genes may be introduced according to the poly(3-hydroxyalkanoate) resin to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0051] As the poly(3-hydroxyalkanoate) resin (A), an unmodified poly(3-hydroxyalkanoate) resin can be used. However, a resin obtained by modifying an unmodified poly(3-hydroxyalkanoate) resin using a raw material that reacts with the resin, such as a peroxide (hereinafter referred to as "modification raw material"), may also be used.

[0052] The aforementioned modification raw material is not particularly limited as long as it is a compound that can react with poly(3-hydroxyalkanoate) resins, but organic peroxides are preferably used because of their ease of handling and ease of controlling the reaction with poly(3-hydroxyalkanoate) resins. Known compounds may be used as the organic compound.

[0053] [Polylactic acid resin (B)] In this application, the polylactic acid resin (B) contained in the first outer layer, inner layer, or second outer layer will be denoted as (B1), (B0), and (B2), respectively, and the description of (B) will apply to (B1), (B0), and (B2). However, resins (B1), (B0), and (B2) may have the same composition as each other, or they may have different compositions.

[0054] Polylactic acid resin (B) is a polyester whose constituent monomer is lactic acid. While poly(3-hydroxyalkanoate) resins have a glass transition temperature of around 0°C, polylactic acid resins typically have a glass transition temperature of around 60°C. Therefore, when polylactic acid resin (B) is incorporated, the polylactic acid resin solidifies below its glass transition temperature when the molten film material is cooled on a cast roll cooled to below 60°C. This makes it less likely to adhere to the cast roll, thereby increasing the productivity of poly(3-hydroxyalkanoate) resin-containing films. In practical processes, it is difficult to cool the molten resin to below the glass transition temperature of poly(3-hydroxyalkanoate) resin and maintain a temperature below 0°C.

[0055] Furthermore, since polylactic acid resins typically have a glass transition temperature of around 60°C and do not crystallize easily when rapidly cooled from a molten state, resulting in an amorphous state, the incorporation of polylactic acid resin (B) makes the film more flexible even at relatively low temperatures exceeding 60°C. Therefore, the incorporation of polylactic acid resin (B) can also improve the stretchability of poly(3-hydroxyalkanoate) resin-containing films. This makes it possible to obtain high-quality stretched films without breakage during stretching and without stretching unevenness. In addition, film stretching can be carried out continuously and stably. Moreover, high stretching ratios can be achieved.

[0056] The polylactic acid resin (B) is preferably a homopolymer of lactic acid, but may also contain trace amounts of other monomers in addition to lactic acid.

[0057] The lactic acid constituting the polylactic acid resin (B) may be either the L-isomer or the D-isomer, or it may contain both. In the latter case, the ratio of the L-isomer to the D-isomer is not particularly limited. The polylactic acid resin (B) may be any of the following: poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin. It may also be a blend of these.

[0058] Other monomers that may be included in the polylactic acid resin (B) include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polyhydric acids, and polyfunctional polysaccharides. When the polylactic acid resin (B) is a copolymer of lactic acid and other monomers, from the viewpoint of crystallinity, the content of the other monomers is preferably about 0 to 3 mol%, and more preferably 0 to 2 mol%, relative to the total monomers contained in the polylactic acid resin (B).

[0059] The polylactic acid resin (B) may be either crystalline or amorphous polylactic acid resin, but it is preferable to use a crystalline polylactic acid resin from the viewpoint of heat resistance, such as shrinkage during heating in post-processing steps like printing or vapor deposition.

[0060] The molecular weight of the polylactic acid resin (B) is not particularly limited and may be set as appropriate, but it is preferably 1,000 to 700,000 in number-average molecular weight, and more preferably 10,000 to 300,000 in number-average molecular weight.

[0061] The lactic acid raw material for producing polylactic acid resin (B) is not particularly limited, and L-lactic acid, D-lactic acid, DL-lactic acid, or mixtures thereof, or L-lactide, D-lactide, meso-lactide, or mixtures thereof can be used. Lactic acid obtained by microbial fermentation from plant-derived renewable raw materials such as starch can be suitably utilized. The method for producing polylactic acid resin (B) is not particularly limited and can be any known method such as dehydration condensation polymerization or ring-opening polymerization.

[0062] In the multilayer film according to this embodiment, the first outer layer, the inner layer, and the second outer layer each contain a poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B). By incorporating the poly(3-hydroxyalkanoate) resin (A) into each layer, the biodegradability of the multilayer film (particularly biodegradability in compost and marine biodegradability) can be enhanced. Furthermore, by incorporating the polylactic acid resin (B) into each layer, the stretchability of the multilayer film can be enhanced. In addition, the adhesion of the molten film material to the cast roll can be suppressed, thereby increasing the productivity of the multilayer film.

[0063] While the blending ratio of the two resins in each layer is not particularly limited, from the viewpoint of obtaining a good multilayer film by making the most of the properties of each resin, it is preferable that the weight ratio of resin (A1) / resin (B1) in the first outer layer, the weight ratio of resin (A0) / resin (B0) in the inner layer, and the weight ratio of resin (A2) / resin (B2) in the second outer layer be 20 / 80 to 90 / 10, respectively.

[0064] From the viewpoint of improving the biodegradability of the film, a higher proportion of poly(3-hydroxyalkanoate) resin (A) is preferable. From this viewpoint, the weight ratio of the two resins in each of the aforementioned layers may be 30 / 70 or more, 40 / 60 or more, 50 / 50 or more, 60 / 40 or more, or 70 / 30 or more.

[0065] On the other hand, from the viewpoint of improving the stretchability or productivity of the film, a higher proportion of polylactic acid resin (B) is preferable. From this viewpoint, the weight ratio of the two resins in each of the aforementioned layers may be 80 / 20 or less, or 70 / 30 or less.

[0066] Furthermore, the weight ratios of resin (A1) / resin (B1), resin (A0) / resin (B0), and resin (A2) / resin (B2) may be the same or different from each other.

[0067] Each layer of the multilayer film according to this disclosure is a resin layer mainly composed of a poly(3-hydroxyalkanoate) resin (A) and a polylactic acid resin (B). Therefore, the total proportion of the poly(3-hydroxyalkanoate) resin (A1) and polylactic acid resin (B1) in the total amount of the first outer layer is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more. It may also be 95% by weight or more, or 98% by weight or more. The values ​​shown above also apply to the total proportion of resin (A0) and resin (B0) in the total amount of the inner layer, and the total proportion of resin (A2) and resin (B2) in the total amount of the second outer layer. Note that the total proportions of these three types may be the same or different.

[0068] (Sugar alcohol compound (C)) In this application, sugar alcohol compounds (C) contained in the first outer layer, inner layer, or second outer layer are denoted as (C1), (C0), and (C2), respectively, and the description of (C) applies to (C1), (C0), and (C2).

[0069] The sugar alcohol compound (C) is a component known to function as a crystal nucleating agent for poly(3-hydroxyalkanoate) resin (A). In the multilayer film according to this embodiment, the inner layer contains the sugar alcohol compound (C), while the first outer layer and the second outer layer have reduced sugar alcohol compound (C) content or do not contain sugar alcohol compound (C).

[0070] By including a sugar alcohol compound (C) in the inner layer, the crystallization rate of the inner layer is accelerated, thereby increasing the productivity of multilayer films. At the same time, since the amount of sugar alcohol compound (C) in the first and second outer layers is reduced, the bleeding of sugar alcohol onto the surface of the multilayer film can be suppressed.

[0071] As the sugar alcohol compound (C), compounds known as crystal nucleating agents for poly(3-hydroxyalkanoate) resins (A) can be used. Specifically, examples include pentaerythritol, erythritol, D-arabitol, ribitol, xylitol, galactitol, D-mannitol, L-mannitol, D-sorbitol, myo-inositol, scyllo-inositol, maltitol, lactitol, etc. Among these, pentaerythritol is preferred because of its excellent effect as a crystal nucleating agent.

[0072] The content of the sugar alcohol compound (C0) in the inner layer is not particularly limited and can be set appropriately from the viewpoint of promoting the crystallization of the poly(3-hydroxyalkanoate) resin (A0) contained in the inner layer. Specifically, it is preferably about 0.01 to 5 parts by weight, more preferably 0.1 to 3 parts by weight, and even more preferably 0.2 to 1.5 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin (A0).

[0073] On the other hand, the content of sugar alcohol compounds (C1) or (C2) in the first or second outer layer is set to be less than the content of sugar alcohol compound (C0) in the inner layer. This makes it possible to suppress the bleeding of sugar alcohols to the surface of the multilayer film while maintaining the productivity of the multilayer film. The content of sugar alcohol compound (C) in each layer is the value relative to 100 parts by weight of poly(3-hydroxyalkanoate) resin (A) contained in the same layer.

[0074] The content of sugar alcohol compound (C1) or (C2) in the first or second outer layer is set to 0 to 0.4 parts by weight, respectively, per 100 parts by weight of resin (A1) or resin (A2). The lower the content of sugar alcohol compound (C) in each outer layer, the less sugar alcohol bleeds onto the surface of the multilayer film.

[0075] From this viewpoint, the content is preferably 0.3 parts by weight or less, more preferably 0.2 parts by weight or less, and even more preferably 0.1 parts by weight or less. It may also be 0.05 parts by weight or less, or 0.01 parts by weight or less. It is most preferable that the first outer layer or the second outer layer does not contain sugar alcohol compound (C). The content of sugar alcohol compound (C1) in the first outer layer and the content of sugar alcohol compound (C2) in the second outer layer may be the same or different.

[0076] (Other Resins) In the multilayer film according to this embodiment, each layer may contain other resins other than the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B), to the extent that the effects of the invention are not impaired. Examples of such other resins include aliphatic polyester resins such as polybutylene succinate adipate, polybutylene succinate, and polycaprolactone, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be included, or two or more types may be included.

[0077] The content of the other resins is not particularly limited, but in each layer, it is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 30 parts by weight or less, relative to 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin (A) and polylactic acid resin (B) contained in each layer. It may also be 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less. The lower limit of the content of the other resins is not particularly limited and may be 0 parts by weight or more.

[0078] In the multilayer film according to this embodiment, each layer may contain additives that can be used together with the poly(3-hydroxyalkanoate) resin (A) and the polylactic acid resin (B), 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, fillers, plasticizers, antioxidants, weather-resistant modifiers, ultraviolet absorbers, 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 those skilled in the art depending on the intended use. The lubricants, fillers, and plasticizers will be described in more detail below.

[0079] (Lubricant) In the multilayer film according to this embodiment, each layer may contain a lubricant. By incorporating a lubricant, the multilayer film is given lubricity, and the film's release from the cast roll during film molding can be improved. Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearate, ethylenebisoleamide, ethylenebiserucamide, ethylenebislaurylamide, ethylenebiscaprate, p-phenylenebisstearate, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide or erucamide are preferred because they have a particularly excellent lubricating effect on poly(3-hydroxyalkanoate) resin (A). One type of lubricant may be used, or two or more types may be used, and the usage ratio can be appropriately adjusted depending on the purpose.

[0080] When using a lubricant, the amount used is not particularly limited, but 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, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin (A) and polylactic acid resin (B) contained in each layer. Each layer preferably contains a lubricant, but may not contain one.

[0081] In a preferred embodiment, it is preferable that the lubricant content in the first outer layer or the second outer layer be set to be less than the lubricant content in the inner layer. This makes it possible to improve the heat sealability of the multilayer film while achieving the effects of the lubricant formulation. The lubricant content in each layer is defined as the value relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin (A) contained in that layer.

[0082] From the viewpoint of improving heat sealability, the lubricant content in the first outer layer or the second outer layer is preferably 0 to 0.4 parts by weight per 100 parts by weight of resin (A1) or resin (A2), respectively. The lower the lubricant content in each outer layer, the better the heat sealability of the multilayer film can be.

[0083] From this viewpoint, the lubricant content is preferably 0.3 parts by weight or less, more preferably 0.2 parts by weight or less, and even more preferably 0.1 parts by weight or less. It may also be 0.05 parts by weight or less, or 0.01 parts by weight or less. It is most preferable that the first outer layer or the second outer layer does not contain a lubricant. The lubricant content in the first outer layer and the lubricant content in the second outer layer may be the same or different.

[0084] On the other hand, the amount of lubricant in the inner layer is not particularly limited and can be set appropriately from the viewpoint of the effect of the lubricant formulation. Specifically, it is preferably about 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 per 100 parts by weight of poly(3-hydroxyalkanoate) resin (A0).

[0085] (Filler) In the multilayer film according to this embodiment, each layer may contain a filler. By including a filler, a stretched film with higher strength can be made. 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.

[0086] When using the filler, its content is not particularly limited, but it 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 the total of the poly(3-hydroxyalkanoate) resin (A) and polylactic acid resin (B) contained in each layer. However, each layer may not contain substantially any filler. Substantially containing no filler means that the amount of filler contained in each layer is less than 1 part by weight per 100 parts by weight of the total of the resin (A) and resin (B) contained in each layer. It may also be less than 0.1 parts by weight.

[0087] (Plasticizer) In the multilayer film according to this embodiment, each layer may contain a plasticizer. Examples of plasticizers include glycerin ester compounds, citrate ester compounds, sebacate ester compounds, adipic acid ester compounds, polyether ester compounds, benzoic acid ester compounds, phthalate ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds. Among these, glycerin ester compounds, citrate ester compounds, sebacate ester compounds, and dibasic acid ester compounds are preferred because they have a particularly excellent plasticizing effect on the poly(3-hydroxyalkanoate) resin (A). Examples of glycerin ester compounds include glycerin diacetomolaurate. Examples of citrate ester compounds include tributyl acetylcitrate. Examples of sebacate ester compounds include dibutyl sebacate. Examples of dibasic acid ester compounds include benzylmethyldiethylene glycol adipate. One or more plasticizers may be used, and the ratio of use can be adjusted as appropriate depending on the purpose.

[0088] When using a plasticizer, its content is not particularly limited, but preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and even more preferably 3 to 10 parts by weight, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin (A) and polylactic acid resin (B) contained in each layer. However, each layer may not contain substantially any plasticizer. Substantially containing no plasticizer means that the plasticizer content in each layer is less than 1 part by weight per 100 parts by weight of the total of the resin (A) and resin (B) contained in each layer. It may even be less than 0.1 parts by weight.

[0089] [Multilayer Film] The multilayer film according to this embodiment may be an unstretched film that has not undergone stretching treatment, or a stretched film that has undergone stretching treatment in the MD direction and / or TD direction after film formation. The term "multilayer film" as used in this application may include both unstretched films and stretched films. From the viewpoint of strength, a stretched film is preferred.

[0090] The thickness of the multilayer film according to this embodiment is not particularly limited, but may be about 10 μm to 1 mm, preferably 15 μm to 500 μm, and more preferably 20 μm to 300 μm. In the case of a stretched film, its thickness is preferably 10 to 200 μm, more preferably 15 to 150 μm, and even more preferably 20 to 100 μm, from the viewpoint of uniform film thickness, appearance, strength, and lightness.

[0091] The thickness of the first outer layer and the second outer layer of the multilayer film are not particularly limited, but in the case of an unstretched film, they are preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, in order to improve the productivity of the multilayer film by providing good peelability from the cast roll. The upper limit may be 80 μm or less, or 50 μm or less.

[0092] In the case of stretched films, the thickness of the first outer layer and the thickness of the second outer layer are preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. The upper limit may be 40 μm or less, or 20 μm or less. The thickness of the first outer layer and the thickness of the second outer layer may be the same or different.

[0093] The ratio of the thickness of the first outer layer to the thickness of the inner layer (thickness of the first outer layer / thickness of the inner layer) is not particularly limited, but in terms of achieving both good peelability and stretchability on the cast roll, it is preferably 0.01 to 1, more preferably 0.05 to 0.5, even more preferably 0.08 to 0.3, and particularly preferably 0.1 to 0.2. The ratio of the thickness of the first outer layer to the thickness of the inner layer is common to both the unstretched film and the stretched film.

[0094] 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) is not particularly limited, but in terms of achieving both good peelability and stretchability on the cast roll, it is preferably 0.01 to 1, more preferably 0.05 to 0.5, even more preferably 0.08 to 0.3, and particularly preferably 0.1 to 0.2. The ratio of the thickness of the second outer layer to the thickness of the inner layer is common to both the unstretched film and the stretched film.

[0095] The multilayer film according to this embodiment is preferably a long film produced industrially, and is particularly preferably a strip-shaped film wound into a roll. The length of such a multilayer film is not particularly limited, but may be, for example, 50 m or more, or 100 m or more.

[0096] In the multilayer film according to this embodiment, it is preferable that the first outer layer and the second outer layer are in direct contact with both sides of the inner layer. The multilayer film may be a resin film composed only of the three layers described above, or it may be a film in which other layers are laminated on one or both sides of the three layers described above. Examples of these other layers include resin layers, inorganic layers, metal layers, metal oxide layers, and printing layers. These other layers may be laminate layers, coating layers, or vapor-deposited layers.

[0097] The multilayer film according to this embodiment can be suitably used as a packaging material, such as a packaging film for food products (including bottle labels), a heat-sealable film, a twisted film, and the like.

[0098] [Method for Manufacturing Multilayer Films] The method for manufacturing the multilayer film according to this disclosure is not particularly limited, but it can be suitably manufactured by co-extruding onto a cast roll and forming a film by laminating in the following order: a molten first outer layer resin composition containing resin (A1), resin (B1), and a sugar alcohol compound (C1) as an optional component; a molten inner layer resin composition containing resin (A0), resin (B0), and a sugar alcohol compound (C0); and a molten second outer layer resin composition containing resin (A2), resin (B2), and a sugar alcohol compound (C2) as an optional component. After this, a multilayer stretched film can also be manufactured by stretching the obtained multilayer film in at least one direction.

[0099] (Step (i) of forming into a film) 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 cast roll while stacking them in this order.

[0100] Co-extrusion may be carried out by feeding raw materials, including resins that constitute each layer, into an extruder, melting and kneading them, and then using the resulting pelletized resin composition for co-extrusion, or the pelletizing step may be omitted, and co-extrusion may be carried out continuously from the melting and kneading.

[0101] The melt-kneading described above can be carried out according to known or conventional methods, for example, using an extruder (single-screw or twin-screw extruder), a kneader, etc. The temperature of each resin composition during co-extrusion can be appropriately set according to the melting point and melt flow rate of each resin composition, but from the viewpoint of resin fluidity and solidification rate, for example, 160 to 190°C is preferred, and 165 to 180°C is more preferred.

[0102] The step (i) of forming the material into a film can be carried out using a T-die extrusion molding method. The T-die extrusion molding method is a molding method in which molten resin is extruded from a slit-shaped discharge port onto a cast roll in a film-like manner by an extruder to form a film. By extruding the molten resin onto the cast roll using an extruder, the molten resin comes into contact with the cast roll and moves along the surface of the cast roll, thereby being cooled, crystallized, and solidified.

[0103] According to this disclosure, since the content of sugar alcohol compounds (C) in the first outer layer resin composition and the second outer layer resin composition is reduced, contamination of the cast roll surface by sugar alcohol compounds can be suppressed. Furthermore, because the first outer layer resin composition and the second outer layer resin composition are less likely to adhere to the cast roll due to the incorporation of polylactic acid resin (B), the production speed can be increased despite the reduced content of sugar alcohol compounds (C).

[0104] The T-die is not particularly limited, and any T-die known for forming multilayer films can be used. The T-die preferably has an outlet shaped to extrude a molten resin composition in a film-like manner while layering it, but its shape is not particularly limited. The shape of the outlet is also not particularly limited.

[0105] In the T-die extrusion molding method described above, each molten resin composition is extruded in a film-like form from the discharge port of the T-die and laminated in a predetermined order. The laminate of molten resin compositions can be in the shape of a film, and its thickness and width are not particularly limited. The thickness is preferably 30 μm to 300 μm because it minimizes thickness variations and facilitates cooling after extrusion.

[0106] The melt viscosity of the molten resin composition extruded from the T-die nozzle is not particularly limited, but it is preferably 1500 Pa·sec or less, as this minimizes thickness variations and prevents the formation of die lines. This melt viscosity can be measured according to any known method.

[0107] The extrusion process may be a process of extruding molten material onto one or more cast rolls, or it may be a process of placing a touch roll opposite the cast rolls and sandwiching the molten material extruded onto the cast rolls with the touch roll.

[0108] Furthermore, an air knife or air chamber may be used to ensure stable contact of the molten material with the cast roll. To efficiently cool the opposite side of the contact surface with the cast roll, the cast roll may be placed in a water tank or an air chamber may be used.

[0109] The surface temperature of the cast roll is not particularly limited as long as it is the temperature at which the first outer layer resin composition and the second outer layer resin composition are cooled and solidified. However, from the viewpoint of good release from the cast roll and promotion of resin solidification, it is preferably 10 to 90°C, more preferably 20 to 80°C, and even more preferably 40 to 80°C. Note that the surface temperature of the cast roll refers to the temperature of the cast roll that the co-extruded molten resin composition first comes into contact with, regardless of whether there is one or two or more cast rolls.

[0110] Next, the multilayer film cooled on the cast roll is peeled off the cast roll by transporting it while the cast roll is rotating. This allows an unstretched multilayer film to be obtained.

[0111] (Stretching process (ii)) The multilayer film obtained in the film-forming process (i) can be subjected to a stretching process (ii) in the MD direction and / or the TD direction. This makes it possible to obtain a stretched film with high strength in the stretching direction. The terms MD direction and TD direction refer to the stretching direction of the film. The MD direction is also called the machine direction, conveying direction, flow direction, or length direction. The TD direction is perpendicular to the MD direction and is also called the vertical direction or width direction. The MD direction is preferred in terms of productivity.

[0112] The specific method of stretching is not limited. For example, methods include stretching the film in the stretching direction, or stretching the film by applying pressure in the thickness direction, such as roll rolling, where the film is sandwiched between two rolls. In terms of productivity and the strength of the stretched film, the 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.

[0113] There are no particular limitations on the method of stretching the film in the stretching direction. The film can be stretched by grasping its end and pulling it in the stretching direction. Alternatively, a pair of rolls can be used, and the film can be stretched by creating a difference in the rotational speed of the rolls. In this case, the stretching ratio can be determined by the ratio of the rotational speed of the rolls before stretching to the rotational speed of the rolls after stretching. When stretching in a batch, the end of the film can be grasped and pulled in the stretching direction.

[0114] When stretching a film in the MD direction while continuously conveying it, for example, a roll stretcher can be used to stretch the film in the MD direction by using multiple rolls that convey the film, for example, a pair of rolls, and by creating a difference in the rotational speed of the rolls between the pair of rolls. The stretching ratio in the MD direction can be determined by the ratio of the rotational speed of the rolls before stretching to the rotational speed of the rolls after stretching.

[0115] By stretching in the MD direction followed by stretching in the TD direction, a biaxially oriented film with high strength in both the MD and TD directions can be obtained. When stretching in the TD direction, the film can be stretched by clamping both ends in the width direction of the film using a transverse stretching machine such as a clip-type tenter and pulling it in the TD direction. Stretching in the TD direction can be carried out continuously from the stretching process in the MD direction within a single manufacturing line.

[0116] The stretching ratio achieved in the process of stretching the multilayer film is not particularly limited, but is preferably 1.1 times or more, more preferably 1.3 times or more, even more preferably 1.5 times or more, and particularly preferably 2 times or more. The upper limit is not particularly limited and can be determined as appropriate, but may be, for example, 8 times or less, 7 times or less, 5 times or less, 3.5 times or less, or 3 times or less.

[0117] The stretching process is preferably carried out while heating the multilayer film. The heating temperature of the film at this time is preferably 35 to 110°C, more preferably 45 to 100°C, and even more preferably 55 to 90°C, from the viewpoint of softening the polylactic acid resin (B) to make it easier to stretch and from the viewpoint of avoiding breakage of the film during stretching.

[0118] The means for heating the film in the stretching process are not particularly limited, but examples include applying an airflow adjusted to a predetermined temperature to the film, controlling the film temperature by bringing the film into contact with a roll set to a predetermined temperature, using an auxiliary heating means such as an IR heater to heat the film and control the film temperature to a predetermined temperature, and passing the film through an oven that is temperature-controlled to a predetermined temperature. These may be used individually or in combination.

[0119] In a method in which a film is brought into contact with a heated roll, hot air may be applied to the film between the upstream stretching roll and the downstream stretching roll in the MD direction.

[0120] Figure 1 shows a conceptual diagram illustrating an example of the process (i) for forming a film using the T-die extrusion molding method. The arrows in the figure indicate the direction of film flow.

[0121] The resin composition constituting the first outer layer, the resin composition constituting the inner layer, and the resin composition constituting the second outer layer are melted by an extruder (not shown) and co-extruded from a die 11 to form a co-extruded product 31 on a cast roll 21, stacking the first outer layer 311, the inner layer 312, and the second outer layer 313 in that order. The formed co-extruded product 31 is conveyed and cooled by two cast rolls 21 and 22 to form a film, thereby obtaining a multilayer film 32 [film formation step (i)]. In Figure 1, the arrangement of the first outer layer 311 and the second outer layer 313 may be interchangeable.

[0122] The two cast rolls 21 and 22 are set so that the surface temperature of the rolls decreases in stages along the flow direction. When the molten co-extruded material 31 comes into contact with these cast rolls 21 and 22, it is cooled in stages, and a process (i) of forming it into a film is carried out. However, the number of cast rolls is not limited to the above.

[0123] A multilayer film 32 is transported along a predetermined path by multiple transport rolls (not shown) and undergoes a stretching process (ii) to obtain a multilayer stretched film. The stretching process (ii) is performed between a pair of stretching rolls. The rotational speed of the downstream stretching roll is controlled to be faster than that of the upstream stretching roll, and this difference in rotational speed stretches the multilayer film 32 in the MD direction. However, the number of stretching rolls is not limited to the above.

[0124] As described above, the film formed into a film shape (i) and the stretched film (ii) are wound onto a winding roll as a multilayer stretched film. In this way, multilayer stretched films can be manufactured continuously. However, the stretching process (ii) is an optional step and may be omitted.

[0125] The following sections list preferred embodiments of this disclosure, but the present invention is not limited to these sections. [Item 1] A multilayer film comprising: a first outer layer containing a poly(3-hydroxyalkanoate) resin (A1), a polylactic acid resin (B1), and a sugar alcohol compound (C1) as an optional component; an inner layer containing a poly(3-hydroxyalkanoate) resin (A0), a polylactic acid resin (B0), and a sugar alcohol compound (C0); and a second outer layer containing a poly(3-hydroxyalkanoate) resin (A2), a polylactic acid resin (B2), and a sugar alcohol compound (C2) as an optional component, laminated in this order, wherein the content of the sugar alcohol compound (C1) per 100 parts by weight of resin (A1) and the content of the sugar alcohol compound (C2) per 100 parts by weight of resin (A2) are each less than the content of the sugar alcohol compound (C0) per 100 parts by weight of resin (A0), and are between 0 and 0.4 parts by weight. [Item 2] A multilayer film according to Item 1, wherein the weight ratio of resin (A0) / resin (B0), the weight ratio of resin (A1) / resin (B1), and the weight ratio of resin (A2) / resin (B2) are 20 / 80 to 90 / 10. [Item 3] A multilayer film according to Item 1 or 2, wherein the content of sugar alcohol compound (C1) per 100 parts by weight of resin (A1), and the content of sugar alcohol compound (C2) per 100 parts by weight of resin (A2) are 0 to 0.1 parts by weight. [Item 4] A multilayer film according to any one of Items 1 to 3, wherein the sugar alcohol compounds (C0), (C1), and (C2) are pentaerythritol. [Item 5] A multilayer film according to any one of Items 1 to 4, wherein the content of the lubricant in the first outer layer per 100 parts by weight of resin (A1) and the content of the lubricant in the second outer layer per 100 parts by weight of resin (A2) are each less than the content of the lubricant in the inner layer per 100 parts by weight of resin (A0), and are between 0 and 0.4 parts by weight. [Item 6] A multilayer film according to any one of Items 1 to 5, wherein resins (A0), (A1), and (A2) contain copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units. [Item 7] A multilayer film according to Item 6, wherein the other hydroxyalkanoate units are 3-hydroxyhexanoate units.[Item 8] The multilayer film according to any one of Items 1 to 7, wherein the multilayer film is a stretched film. [Item 9] A method for producing the multilayer film according to any one of Items 1 to 8, comprising the step of forming a film by co-extruding onto a cast roll a molten first outer layer resin composition containing resin (A1), resin (B1), and a sugar alcohol compound (C1) as an optional component, a molten inner layer resin composition containing resin (A0), resin (B0), and a sugar alcohol compound (C0), and a molten second outer layer resin composition containing resin (A2), resin (B2), and a sugar alcohol compound (C2) as an optional component, in this order. [Item 10] The method for producing the multilayer film according to Item 9, further comprising the step of stretching the multilayer film in at least one direction.

[0126] 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.

[0127] In the examples and comparative examples, the following raw materials were used. (Poly(3-hydroxyalkanoate) resin (A)) As the P3HA resin (A), the following poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) resins A-1 to A-4 were used. 3HB represents a 3-hydroxybutyrate repeating unit, and 3HH represents a 3-hydroxyhexanoate repeating unit.

[0128] A-1: P3HB3HH (average content ratio 3HB / 3HH = 97 / 3 (mol% / mol%)) A-1 was prepared according to the method described in Example 2 of International Publication No. 2019 / 142845, and adjusted to a weight-average molecular weight of 660,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0129] A-2: P3HB3HH (average content ratio 3HB / 3HH = 72 / 28 (mol% / mol%)) A-2 was prepared according to the method described in Example 9 of International Publication No. 2019 / 142845, and adjusted to a weight-average molecular weight of 660,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0130] A-3: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%)) A-3 was prepared according to the method described in Example 5 of International Publication No. 2019 / 142845, and adjusted to a weight-average molecular weight of 600,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0131] A-4: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%)) The PHBH-3 was prepared according to the method described in Example 1 of International Publication No. 2019 / 142845, and adjusted to a weight-average molecular weight of 400,000 g / mol by treatment with an aqueous sodium hydroxide solution.

[0132] (Polylactic acid resin (B)) B-1: Polylactic acid (Ingeo Corporation: PLA-4043D, melting point 160°C)

[0133] (Sugar alcohol compound (C)) C-1: Pentaerythritol (manufactured by Mitsubishi Chemical Corporation, Neurizer P)

[0134] (Lubricant) D-1: Behenamide (manufactured by Nippon Seika Co., Ltd.: BNT-22H)

[0135] (Weight-average molecular weight) The weight-average molecular weight of the resin was measured using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) and converted to polystyrene equivalent.

[0136] (Manufacturing of resin pellets containing P3HA resin (A)) Resin pellet P-1 As P3HA resin (A), A-1: ​​33 parts by weight, A-2: 27 parts by weight, A-3: 10 parts by weight, A-4: 30 parts by weight (total of 100 parts by weight of P3HA resin (A)) were dry blended with C-1: 1.0 part by weight as a crystal nucleating agent and D-1: 0.5 parts by weight as a lubricant. The obtained dry blend was put into a φ26 mm co-screw extruder hopper with the cylinder temperature and die temperature set to 150°C, melted and kneaded, extruded in strand form from the die, passed through a water bath filled with 45°C hot water to solidify the strand, and cut with a pelletizer to obtain resin pellet P-1.

[0137] Resin pellets P-2 were obtained by dry blending 33 parts by weight of A-1, 27 parts by weight of A-2, 10 parts by weight of A-3, and 30 parts by weight of A-4 (total of 100 parts by weight of P3HA resin (A)) with 0.5 parts by weight of C-1 as a crystal nucleating agent and 0.5 parts by weight of D-1 as a lubricant. The resulting dry blend was put into a φ26 mm co-screw extruder hopper with the cylinder temperature and die temperature set to 150°C, melted and kneaded, extruded in strand form from the die, passed through a water bath filled with 45°C water to solidify the strand, and cut with a pelletizer to obtain resin pellets P-2.

[0138] Resin pellet P-3 was obtained by dry blending a P3HA-based resin (A) consisting of A-1: ​​33 parts by weight, A-2: 27 parts by weight, A-3: 10 parts by weight, and A-4: 30 parts by weight (total of 100 parts by weight of P3HA-based resin (A)), with C-1: 0.25 parts by weight as a crystal nucleating agent and D-1: 0.5 parts by weight as a lubricant. The resulting dry blend was put into a φ26 mm co-direction twin-screw extruder hopper with the cylinder temperature and die temperature set to 150°C, melted and kneaded, extruded from the die in a strand shape, passed through a water bath filled with 45°C water to solidify the strand, and cut with a pelletizer to obtain resin pellet P-3.

[0139] For resin pellet P-4, a dry blend was prepared by adding 0.5 parts by weight of D-1 as a lubricant to P3HA resin (A), consisting of A-1: ​​33 parts by weight, A-2: 27 parts by weight, A-3: 10 parts by weight, and A-4: 30 parts by weight (total of 100 parts by weight of P3HA resin (A)). The resulting dry blend was put into a φ26 mm co-screw extruder hopper with the cylinder temperature and die temperature set to 150°C, melted and kneaded, extruded in strand form from the die, passed through a water bath filled with 45°C water to solidify the strand, and then cut with a pelletizer to obtain resin pellet P-4.

[0140] For resin pellet P-5, a dry blend of P3HA resin (A) was prepared by dry blending A-1: ​​33 parts by weight, A-2: 27 parts by weight, A-3: 10 parts by weight, and A-4: 30 parts by weight (totaling 100 parts by weight of P3HA resin (A)). The resulting dry blend was put into a φ26 mm co-direction twin-screw extruder hopper with the cylinder temperature and die temperature set to 150°C, melted and kneaded, extruded in strand form from the die, passed through a water tank filled with 45°C water to solidify the strand, and then cut with a pelletizer to obtain resin pellet P-5.

[0141] [Example 1] Two φ40 mm single-screw extruders, each connected to a 350 mm wide, 2-type, 3-layer multi-manifold die, had their cylinder and die temperatures set to 165°C. A dry blend of resin pellets P-1: 70 parts by weight and B-1: 30 parts by weight was fed into the hopper of the inner extruder, and a dry blend of resin pellets P-4: 60 parts by weight and B-1: 40 parts by weight was fed into the hopper of the outer extruder. Molten P-4 / B-1 = 60 / 40, molten P-1 / B-1 = 70 / 30, and molten P-4 / B-1 = 60 / 40 were stacked in this order, and the resulting film-like molten resin was extruded onto a φ200 mm cast roll (hard chrome plated) set to 35°C at a 180° angle to form it. After cooling to a film temperature of 35°C, the film was peeled off with a second cast roll (hard chrome plated) to obtain a three-layer multilayer film [process (i) for forming into a film]. The thicknesses of the first outer layer, inner layer, and second outer layer of the obtained multilayer film were 40 μm, 320 μm, and 40 μm, respectively. The obtained multilayer film was continuously transported and stretched three times in the MD direction using a pair of stretching rolls at a roll temperature of 60 to 90°C [process (ii) for stretching] to obtain a multilayer stretched film. The thickness of each layer was adjusted by adjusting the screw rotation speed of the outer and inner extruders.

[0142] (Calculation and Evaluation of ΔHz) Using a haze meter (NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.), the haze value was measured on a film piece cut from a film roll (after stretching) under conditions of a temperature of 23°C ± 2°C and a humidity of 50% ± 5%. After wiping both sides of the film with water and drying, the haze value was measured again. Based on these haze values, ΔHz = (Hz before wiping with water - Hz after wiping with water) was calculated. As a judgment criterion, a ΔHz of less than 5% was evaluated as "○", a ΔHz of 5% or more but less than 8% was evaluated as "△", and a ΔHz of 8% or more was evaluated as "×". The results are shown in Table 1.

[0143] Furthermore, a smaller ΔHz value indicates less bleeding of sugar alcohol compounds onto the film surface. When sugar alcohol compounds bleed onto the film surface, they are removed by wiping with water, which lowers the Hz value, resulting in a larger ΔHz value.

[0144] (Cast Roll Contamination) The method for evaluating cast roll contamination in the examples and comparative examples was as follows: The surface condition of the cast roll was visually observed after continuous film production for 30 minutes. If no contamination was observed on the surface of the cast roll, the cast roll contamination was evaluated as "○"; if contamination was observed on a part of the surface of the cast roll, the cast roll contamination was evaluated as "△"; and if contamination was observed on the entire surface of the cast roll, the cast roll contamination was evaluated as "×". The results are shown in Table 1.

[0145] (Stretchability Evaluation) When a multilayer film was stretched in the MD direction, if it was stretched uniformly without breakage or band-like uneven stretching, the stretchability was evaluated as "○". If breakage or uneven stretching occurred, the stretchability was evaluated as "×". The results are shown in Table 1.

[0146] (Overall Evaluation) In the evaluation of ΔHz, castroll contamination, and stretchability, if all items were evaluated as "○", the overall evaluation was evaluated as "○". If any item was evaluated as "△", the evaluation was "△". If any item was evaluated as "×", the evaluation was "×". The results are shown in Table 1.

[0147] [Examples 2-3] In Example 1, the ratio of P-4 and B-1 used in the dry blend material fed into the outer layer extruder was changed, thereby altering the content of P3HA-based resin (A) and polylactic acid-based resin (B) in the first and second outer layers as shown in Table 1. Otherwise, multilayer films and multilayer stretched films were obtained and evaluated in the same manner as in Example 1. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0148] [Examples 4-5] In Example 1, multilayer films and multilayer stretched films were obtained and evaluated in the same manner as in Example 1, except that the type of resin pellet in the dry blend material fed into the inner layer extruder was changed to P-2 or P-3 as shown in Table 1, thereby changing the content of sugar alcohol (C) in the inner layer. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0149] [Example 6] In Example 1, the type of resin pellets in the dry blend material fed into the outer layer extruder was changed to P-3 as shown in Table 1, thereby changing the sugar alcohol (C) content in the first and second outer layers. A multilayer film and a multilayer stretched film were obtained and evaluated in the same manner as in Example 1. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0150] [Example 7] In Example 7, the resin pellets in the dry blend material fed into the outer layer extruder were changed to P-5 as shown in Table 1 to ensure that the first and second outer layers did not contain lubricant, and the usage ratio of P-5 and B-1 was changed to alter the content of P3HA-based resin (A) and polylactic acid-based resin (B) in the first and second outer layers as shown in Table 1. Otherwise, multilayer films and multilayer stretched films were obtained and evaluated in the same manner as in Example 1. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0151] [Example 8] In Example 8, the only difference was that the ratio of P-4 and B-1 used in the dry blend material fed into the outer layer extruder was changed, thereby altering the content of P3HA-based resin (A) and polylactic acid-based resin (B) in the first and second outer layers as shown in Table 1. A multilayer film and a multilayer stretched film were obtained and evaluated in the same manner as in Example 1. The results of the evaluation of ΔHz, cast roll contamination, and stretchability are shown in Table 1.

[0152] [Comparative Example 1] In the same manner as in Example 1, a multilayer film and a multilayer stretched film were obtained and evaluated, except that the type of resin pellet in the dry blend material fed into the outer layer extruder was changed to P-1 as shown in Table 1, thereby changing the content of sugar alcohol (C) in the first and second outer layers. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0153] [Comparative Examples 2-3] In Comparative Example 1, the usage ratio of P-1 and B-1 in the dry blend material fed into the outer layer extruder was changed, thereby altering the content of P3HA-based resin (A) and polylactic acid-based resin (B) in the first and second outer layers as shown in Table 1. Otherwise, multilayer films and multilayer stretched films were obtained and evaluated in the same manner as in Comparative Example 1. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0154] [Comparative Example 4] In Comparative Example 1, the only difference was that the type of resin pellet in the dry blend material fed into the outer layer extruder was changed to P-2 as shown in Table 1, thereby changing the sugar alcohol (C) content in the first and second outer layers. Multilayer films and multilayer stretched films were obtained and evaluated in the same manner as in Comparative Example 1. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0155] [Comparative Example 5] In the same manner as in Example 1, multilayer films and multilayer stretched films were obtained and evaluated, except that only P-1 was put into the hoppers of the inner and outer extruders, and polylactic acid resin (B) was not used in either case. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0156] [Comparative Example 6] In the same manner as in Example 1, a multilayer film and a multilayer stretched film were obtained and evaluated, except that only P-1 was put into the hopper of the inner layer extruder and only P-4 was put into the hopper of the outer layer extruder, and polylactic acid resin (B) was not used in either case. The results of ΔHz, cast roll contamination, and stretchability evaluation are shown in Table 1.

[0157]

[0158] Table 1 shows that in Examples 1 to 8, the ΔHz value was small, the amount of sugar alcohol compound bleeding onto the film surface was small, the cast roll contamination was minimal, and the stretchability evaluation was good.

[0159] On the other hand, in Comparative Examples 1 to 5, the first and second outer layers contained 0.5 parts by weight or more of sugar alcohol compounds per 100 parts by weight of P3HA resin (A), resulting in a large ΔHz value, a large amount of sugar alcohol compounds bleeding onto the film surface, and contamination of the cast roll was also observed.

[0160] Furthermore, in Comparative Examples 5 and 6, the stretchability was insufficient because polylactic acid resin (B) was not included in each layer.

[0161] (Evaluation of Heat Sealability) A 15 mm wide test piece was cut from the multilayer stretched film obtained in Example 7 or Example 8. The test piece was folded and held so that the first outer layers were in contact with each other, and heat sealing was performed by heating and pressing from both sides using a heat seal tester (Tester Industries Co., Ltd., model TP-701-B) at a pressure of 0.3 MPa, a pressing time of 1 second, and a predetermined temperature in the range of 60 to 140°C. The heat seal strength was measured by performing a tensile test on the multilayer stretched film after heat sealing using a precision universal testing machine (Shimadzu Corporation, model AZ-LX) at a tensile speed of 300 mm / min. The results obtained in the heating temperature range of 80 to 130°C during heat sealing are shown in Figure 2.

[0162] Example 7 contains no lubricant in the first and second outer layers, while Example 8 contains 0.5 parts by weight of lubricant in both the first and second outer layers. Figure 2 shows that, in the heat sealing temperature range of 90 to 130°C, the heat seal strength of Example 7 is generally higher than that of Example 8. From the above, it can be seen that the heat seal strength of a multilayer film can be improved by reducing the amount of lubricant in the first and second outer layers.

[0163] The heating temperature at which the heat seal strength reaches 1 N / 15 mm is called the seal start temperature (SIT). The SIT calculated from the results in Figure 2 was 82°C in Example 7 and 88°C in Example 8. From these results, it can be seen that the SIT of a multilayer film can be lowered by reducing the amount of lubricant in the first and second outer layers.

[0164] 11 Die 21, 22 Cast roll 31 Co-extruded product 311 First outer layer 312 Inner layer 313 Second outer layer 32 Multilayer film

Claims

1. A multilayer film comprising: a first outer layer containing a poly(3-hydroxyalkanoate) resin (A1), a polylactic acid resin (B1), and a sugar alcohol compound (C1) as an optional component; an inner layer containing a poly(3-hydroxyalkanoate) resin (A0), a polylactic acid resin (B0), and a sugar alcohol compound (C0); and a second outer layer containing a poly(3-hydroxyalkanoate) resin (A2), a polylactic acid resin (B2), and a sugar alcohol compound (C2) as an optional component, laminated in this order, wherein the content of the sugar alcohol compound (C1) per 100 parts by weight of resin (A1) and the content of the sugar alcohol compound (C2) per 100 parts by weight of resin (A2) are each less than the content of the sugar alcohol compound (C0) per 100 parts by weight of resin (A0), and are between 0 and 0.4 parts by weight.

2. The multilayer film according to claim 1, wherein the weight ratio of resin (A0) / resin (B0), the weight ratio of resin (A1) / resin (B1), and the weight ratio of resin (A2) / resin (B2) are 20 / 80 to 90 / 10.

3. The multilayer film according to claim 1, wherein the content of sugar alcohol compound (C1) per 100 parts by weight of resin (A1) and the content of sugar alcohol compound (C2) per 100 parts by weight of resin (A2) are 0 to 0.1 parts by weight.

4. The multilayer film according to claim 1, wherein the sugar alcohol compounds (C0), (C1), and (C2) are pentaerythritol.

5. The multilayer film according to claim 1, wherein the content of the lubricant in the first outer layer per 100 parts by weight of resin (A1) and the content of the lubricant in the second outer layer per 100 parts by weight of resin (A2) are each less than the content of the lubricant in the inner layer per 100 parts by weight of resin (A0), and are between 0 and 0.4 parts by weight.

6. The multilayer film according to claim 1, wherein the resins (A0), (A1), and (A2) comprise copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units.

7. The multilayer film according to claim 6, wherein the other hydroxyalkanoate unit is a 3-hydroxyhexanoate unit.

8. The multilayer film according to claim 1, wherein the multilayer film is a stretched film.

9. A method for producing a multilayer film according to any one of claims 1 to 8, comprising the step of forming a film by co-extruding onto a cast roll while laminating in this order a molten first outer layer resin composition containing resin (A1), resin (B1), and a sugar alcohol compound (C1) as an optional component, an inner layer resin composition containing resin (A0), resin (B0), and a sugar alcohol compound (C0), and a second outer layer resin composition containing resin (A2), resin (B2), and a sugar alcohol compound (C2) as an optional component.

10. The method for producing a multilayer film according to claim 9, further comprising the step of stretching the multilayer film in at least one direction.

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