Multilayer film, and packaging material

Abstract

This multilayer film includes a first resin layer and a second resin layer, wherein: the first resin layer and the second resin layer each contain a poly(3-hydroxyalkanoate)-based resin; the ratio of the thickness of the first resin layer:the thickness of the second resin layer is 1.0:0.015 to 1.0:5.0; the heat quantity ∆H of the first resin layer is at least 30 J / g; and the heat quantity ∆H of the second resin layer is at most 25 J / g, provided that the heat quantity ∆H is a fusion heat quantity in the range of 130-190ºC.

Description

Technical Field

[0001] The present invention relates to a multilayer film having a resin layer containing a poly(3-hydroxyalkanoate) resin, and a packaging material using the same.

Background Art

[0002] Petroleum-derived plastics are discarded in large quantities every year, and the shortage of landfill sites and environmental pollution caused by these large amounts of waste have been taken up as serious problems. In recent years, microplastics have become a major problem in the marine environment.

[0003] Poly(3-hydroxyalkanoate) resins have excellent seawater degradability and are materials that can solve the environmental problems caused by discarded plastics. For example, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), which is one type of poly(3-hydroxyalkanoate) resin, can flexibly control mechanical properties by changing the composition ratio of 3-hydroxyhexanoate. In addition, among biodegradable resins, it has high gas barrier properties and is difficult to hydrolyze, so it is expected to be developed for a wide range of applications including packaging materials.

[0004] As a multilayer film containing a poly(3-hydroxyalkanoate) resin, for example, Patent Document 1 describes a multilayer film having a layer containing a poly(3-hydroxyalkanoate) resin and another biodegradable resin, and a layer having a poly(3-hydroxyalkanoate) resin content of less than 10% by weight.

[0005] Patent Document 2 describes a multilayer film including a layer composed of a composition containing a poly(3-hydroxyalkanoate) resin and unstructured starch, and a layer composed of a poly(3-hydroxyalkanoate) resin.

[0006] A multilayer film may be used as a heat-sealing film that is heat-sealed together to form a bag for enhancing airtightness and storage properties, for example, in food applications. However, Patent Documents 1 and 2 do not specifically discuss the use of a multilayer film for heat-sealing.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] When attempting to perform heat-sealing using the multilayer films described in Patent Documents 1 and 2, the heat-sealability was insufficient and good adhesiveness could not be obtained, or the base material layer might be deformed by the heating during heat-sealing.

[0009] In view of the above situation, an object of the present invention is to provide a multilayer film having a resin layer containing a poly(3-hydroxyalkanoate)-based resin, which has good heat-sealability and suppresses deformation of the base material layer during heat-sealing.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the inventors have found that in a multilayer film having two layers containing a poly(3-hydroxyalkanoate)-based resin, by setting the ratio of the thicknesses of the two layers within a specific range and setting the heat quantity ΔH of each layer within a specific range, the above problems can be solved, and the present invention has been completed.

[0011] That is, the present invention relates to a multilayer film including a first resin layer and a second resin layer, wherein the first resin layer and the second resin layer each contain a poly(3-hydroxyalkanoate) resin, the ratio of the thickness of the first resin layer to the thickness of the second resin layer is 1.0:0.015 to 1.0:5.0, the heat quantity ΔH of the first resin layer is 30 J / g or more, and the heat quantity ΔH of the second resin layer is 25 J / g or less. However, the heat quantity ΔH is represented by the following formula. Heat quantity ΔH = heat of fusion in the range from 130°C to 190°C Preferably, the thickness of the first resin layer is 10 μm or more and 300 μm or less. Preferably, the poly(3-hydroxyalkanoate) resin contains a copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit. Preferably, the poly(3-hydroxyalkanoate) resin contained in the first resin layer is a copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit in which the content ratio of the other hydroxyalkanoate unit is 1 to 7 mol%, and the poly(3-hydroxyalkanoate) resin contained in the second resin layer is a copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit in which the content ratio of the other hydroxyalkanoate unit is 7 to 20 mol%, and the content ratio of the other hydroxyalkanoate unit in the poly(3-hydroxyalkanoate) resin contained in the second resin layer is higher than the content ratio of the other hydroxyalkanoate unit in the poly(3-hydroxyalkanoate) resin contained in the first resin layer. Preferably, the other hydroxyalkanoate unit is a 3-hydroxyhexanoate unit. Preferably, the first resin layer and the second resin layer are integrated. Preferably, the thickness of the first resin layer is 10 μm or more and 300 μm or less, and the thickness of the second resin layer is 5 μm or more and 70 μm or less. Preferably, the first resin layer and / or the second resin layer further contains a crystallization nucleating agent. Preferably, the crystallization nucleating agent is at least one selected from the group consisting of poly(3-hydroxybutyrate) (P3HB), talc, fatty acid amides, nucleobases, and dipeptides. Preferably, the multilayer film is for heat sealing. The present invention also relates to a method for manufacturing a multilayer film, comprising: (A) a step of forming a first resin layer and a second resin layer by an inflation molding method or a T-die molding method, respectively; and (B) a step of integrating the first resin layer and the second resin layer obtained in (A) by a thermal lamination molding method, or a step of simultaneously molding the first resin layer and the second resin layer by a multilayer inflation molding method or a multilayer T-die molding method. The present invention also relates to a packaging material composed of the multilayer film. Preferably, the packaging form is a pillow package.

Effects of the Invention

[0012] According to the present invention, there can be provided a multilayer film having a resin layer containing a poly(3-hydroxyalkanoate) - based resin, having good heat sealability, and suppressing deformation of the base material layer during heat sealing.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] The multilayer film according to an embodiment of the present invention includes a first resin layer and a second resin layer each containing a poly(3-hydroxyalkanoate) - based resin. The multilayer film can be used as a multilayer film for heat sealing. In this application, the first resin layer may correspond to the base material layer, and the second resin layer may correspond to the heat seal layer.

[0015] The second resin layer, which is the heat-sealing layer, may be laminated only on one side of the first resin layer, which is the base material layer, or may be laminated on both sides. Further, the second resin layer may be laminated on the first resin layer via another layer, or may be directly laminated on the first resin layer without passing through another layer.

[0016] The first resin layer and the second resin layer each contain at least a poly(3-hydroxyalkanoate)-based resin.

[0017] The poly(3-hydroxyalkanoate)-based resin is preferably a polymer having 3-hydroxyalkanoate units, specifically, a polymer containing units represented by the following general formula (1). [-CHR-CH2-CO-O-] (1)

[0018] In general formula (1), R represents an alkyl group represented by C p H 2p+1 and p represents an integer from 1 to 15. Examples of R include linear or branched alkyl groups such as a methyl group, an ethyl group, a propyl group, a methylpropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, and a hexyl group. As p, 1 to 10 is preferable, and 1 to 8 is more preferable.

[0019] As the poly(3-hydroxyalkanoate)-based resin, a poly(3-hydroxyalkanoate)-based resin produced particularly from microorganisms is preferable. In the poly(3-hydroxyalkanoate)-based resin produced from microorganisms, all 3-hydroxyalkanoate units are contained as (R)-3-hydroxyalkanoate units.

[0020] The poly(3-hydroxyalkanoate) resin preferably contains 3-hydroxyalkanoate units (particularly, the units represented by the general formula (1)) in an amount of 50 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more of all the constituent units. The poly(3-hydroxyalkanoate) resin may contain only one or more 3-hydroxyalkanoate units as the constituent units of the polymer, or may contain, in addition to one or more 3-hydroxyalkanoate units, other units (for example, 4-hydroxyalkanoate units, etc.).

[0021] The poly(3-hydroxyalkanoate) resin is preferably a homopolymer or copolymer containing 3-hydroxybutyrate (hereinafter may be referred to as 3HB) units. In particular, the 3-hydroxybutyrate units are preferably all (R)-3-hydroxybutyrate units. Further, the poly(3-hydroxyalkanoate) resin is preferably a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units. The form of copolymerization is not particularly limited and may be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, etc.

[0022] Specific examples of the poly(3-hydroxyalkanoate)-based resin include, for example, poly(3-hydroxybutyrate) (abbreviation: P3HB), 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-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), and the like. In particular, from the viewpoints of film productivity and mechanical properties, etc., P3HB3HH, P3HB3HV, or P3HB4HB is preferable, and P3HB3HH or P3HB4HB is more preferable. Note that P3HB, which is a homopolymer, can also be used as a crystallization nucleating agent described later.

[0023] By changing the composition ratio of the repeating units, the melting point and crystallinity can be changed, and as a result, physical properties such as Young's modulus and heat resistance can be changed, and it is possible to impart physical properties between those of polypropylene and polyethylene. From the viewpoint that it is industrially easy to produce and is a physically useful plastic as described above, P3HB3HH is particularly preferable. Also, P3HB3HH is preferable from the viewpoint that the melting point can be lowered and molding processing at low temperatures becomes possible.

[0024] According to a preferred embodiment, it is preferable that the first resin layer and the second resin layer each contain a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, and it is particularly preferable to contain P3HB3HH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). When the first resin layer or the second resin layer contains the copolymer, each layer may contain only one kind of the copolymer, or may contain at least two kinds of the copolymers having different types of constituent monomers and / or different content ratios of the constituent monomers. Further, each layer may contain at least one kind of the copolymer and P3HB.

[0025] The copolymer contained in the first resin layer and the copolymer contained in the second resin layer have different types of constituent monomers and / or different content ratios of the constituent monomers so as to satisfy the conditions of the heat quantity ΔH described later. At this time, the content ratio of other hydroxyalkanoate units (particularly 3-hydroxyhexanoate units) in the copolymer contained in the second resin layer is preferably higher than the content ratio of other hydroxyalkanoate units (particularly 3-hydroxyhexanoate units) in the copolymer contained in the first resin layer. Thereby, the second resin layer has a lower heat quantity ΔH and a lower melting point than the first resin layer. Therefore, while the deformation of the base material layer is suppressed, the heat seal layer can exhibit good heat sealability.

[0026] Specifically, in the copolymer contained in the first resin layer, the content ratio of other hydroxyalkanoate units is preferably 1 mol% or more and 7 mol% or less, more preferably 3 mol% or more and 7 mol% or less, and even more preferably 5 mol% or more and 7 mol% or less. On the other hand, in the copolymer contained in the second resin layer, the content ratio of other hydroxyalkanoate units is preferably 7 mol% or more and 20 mol% or less, more preferably 8 mol% or more and 20 mol% or less, even more preferably 8 mol% or more and 15 mol% or less, and still more preferably 9 mol% or more and 13 mol% or less. However, the content ratio of other hydroxyalkanoate units in the poly(3-hydroxyalkanoate)-based resin contained in the second resin layer is higher than the content ratio of other hydroxyalkanoate units in the poly(3-hydroxyalkanoate)-based resin contained in the first resin layer. When the above copolymers are used in each layer, it is possible to easily realize the heat quantity ΔH of the first resin layer and the heat quantity ΔH of the second resin layer, which will be described later.

[0027] The content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate)-based resin can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of WO 2013 / 147139. Incidentally, the content ratio means the average content ratio of each monomer unit contained in the entire mixture when each layer contains a mixture of two or more poly(3-hydroxyalkanoate)-based resins.

[0028] According to one embodiment, the weight average molecular weight of the poly(3-hydroxyalkanoate)-based resin contained in the first resin layer is preferably from 200,000 to 2,500,000, more preferably from 250,000 to 2,300,000, still more preferably from 300,000 to 2,000,000, and particularly preferably from 350,000 to 1,500,000. When the weight average molecular weight of the poly(3-hydroxyalkanoate)-based resin contained in the first resin layer is within the above range, deformation of the first resin layer due to heating during heat sealing can be more effectively suppressed.

[0029] According to one embodiment, the weight average molecular weight of the poly(3-hydroxyalkanoate)-based resin contained in the second resin layer is preferably from 50,000 to 1,000,000, more preferably from 100,000 to 800,000, still more preferably from 150,000 to 600,000, and particularly preferably from 150,000 to 500,000. When the weight average molecular weight of the poly(3-hydroxyalkanoate)-based resin contained in the second resin layer is within the above range, the second resin layer can exhibit higher adhesive strength by heat sealing.

[0030] The method for measuring the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin is not particularly limited. For example, using chloroform as the mobile phase and a Waters GPC system as the system, and using Shodex K-804 (polystyrene gel) manufactured by Showa Denko K.K. for the column, it can be determined as the weight-average molecular weight in terms of polystyrene.

[0031] The method for producing the poly(3-hydroxyalkanoate) resin is not particularly limited and may be a production method by chemical synthesis or a production method by microorganisms. Among them, the production method by microorganisms is preferred. For the production method by microorganisms, known methods can be applied. For example, as copolymer-producing bacteria of 3-hydroxybutyrate and other hydroxyalkanoates, Aeromonas caviae, which is a P3HB3HV and P3HB3HH-producing bacterium, and Alcaligenes eutrophus, which is a P3HB4HB-producing bacterium, are known. In particular, regarding P3HB3HH, in order to increase the productivity of P3HB3HH, Alcaligenes eutrophus AC32 strain (Alcaligenes eutrophus AC32, FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)) into which the genes of the poly(3-hydroxyalkanoate) resin synthase group have been introduced is more preferred, and microbial cells in which P3HB3HH is accumulated in the cells by culturing these microorganisms under appropriate conditions are used. In addition to the above, depending on the poly(3-hydroxyalkanoate) resin to be produced, genetically modified microorganisms into which various poly(3-hydroxyalkanoate) resin synthesis-related genes have been introduced may be used, or the culture conditions including the type of substrate may be optimized.

[0032] Microbially produced P3HB3HH is a random copolymer. The adjustment of the content ratio of 3HH units in microbially produced P3HB3HH can be carried out, for example, by selection of the microbial cells, selection of the carbon source as the raw material, blending of two or more types of P3HB3HH having different content ratios of 3HH units, blending of a homopolymer of 3HB, etc.

[0033] Examples of commercially available products of P3HB3HH include "Kaneka Biodegradable Polymer PHBH (registered trademark)" of Kaneka Corporation, etc.

[0034] (Other resins) The first resin layer or the second resin layer may contain one or more resins other than poly(3-hydroxyalkanoate)-based resins within the scope where the effects of the invention are achieved. As such other resins, biodegradable resins are preferable, and examples thereof include aliphatic polyester-based resins such as polybutylene succinate, polybutylene succinate adipate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebacate terephthalate, and polybutylene azelate terephthalate.

[0035] Since these other resins show biodegradability but not sufficient seawater degradability, in order to ensure the seawater biodegradability of the multilayer film, it is preferable that the content of these other resins is less. Specifically, when the total amount of the multilayer film is 100 parts by weight, the content of the other resins contained in the multilayer film is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, still more preferably 10 parts by weight or less, and particularly preferably 5 parts 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.

[0036] (Nucleating agent) In one embodiment, the first resin layer or the second resin layer may further contain a nucleating agent within the scope where the effects of the invention are achieved. When the first resin layer or the second resin layer contains a nucleating agent, there is an effect of improving the moldability, productivity, etc.

[0037] The crystallization nucleating agent is not particularly limited as long as it exhibits the above effects. Examples include poly(3-hydroxybutyrate) (P3HB), talc, fatty acid amides, nucleobases (e.g., adenine, guanine, thymine, cytosine, uracil, and their derivatives, etc.), dipeptides (e.g., glycylglycine, glycyl-L-leucine, etc.), pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, boron nitride, and the like. Among them, pentaerythritol is preferred in that it particularly excellently promotes the crystallization of poly(3-hydroxyalkanoate)-based resins. These crystallization nucleating agents may be used alone or in combination of two or more.

[0038] When using P3HB as the crystallization nucleating agent, the content of the crystallization nucleating agent in the first resin layer or the second resin layer is preferably 10% by weight or less, more preferably 7% by weight or less, in order to make the viscosity during processing and the physical properties of the multilayer film within a suitable range. The lower limit is not particularly limited and may be 0% by weight, but in order to promote the crystallization of the poly(3-hydroxyalkanoate)-based resin, it is preferably 1% by weight or more, more preferably 3% by weight or more.

[0039] When using a crystallization nucleating agent other than P3HB as the crystallization nucleating agent, the content of the crystallization nucleating agent in the first resin layer or the second resin layer is preferably 5% by weight or less, more preferably 3% by weight or less, in order to make the viscosity during processing and the physical properties of the multilayer film within a suitable range. The lower limit is not particularly limited and may be 0% by weight, but in order to promote the crystallization of the poly(3-hydroxyalkanoate)-based resin, it is preferably 0.1% by weight or more, more preferably 0.5% by weight or more.

[0040] When applying the multilayer film to a packaging material, from the viewpoint of ensuring good heat sealability, the second resin layer preferably does not contain a crystallization nucleating agent other than P3HB.

[0041] (Additive) The first resin layer or the second resin layer may contain additives commonly used in the art within the scope where the effects of the invention can be achieved. Such additives include, for example, inorganic fillers such as talc, calcium carbonate, mica, silica, titanium oxide, and alumina; organic fillers such as wood chips, wood powder, waste paper such as newsprint, various starches, and cellulose; colorants such as pigments and dyes; odor absorbers such as activated carbon and zeolite; fragrances such as vanillin and dextrin; plasticizers, antioxidants, oxidation inhibitors, weather resistance improvers, ultraviolet absorbers, lubricants, mold release agents, water repellents, antibacterial agents, sliding property improvers, tackifiers, fillers, crosslinking agents such as peroxides, and drugs. As the additive, only one kind may be contained, or two or more kinds may be contained. The content of these additives can be appropriately set by those skilled in the art according to the purpose of use.

[0042] (Heat quantity ΔH) In one embodiment, by setting the heat quantity ΔH of the first resin layer to be equal to or greater than a specific value and the heat quantity ΔH of the second resin layer to be equal to or less than a specific value together with the ratio of the thicknesses of the layers described later, the multilayer film can achieve both high heat seal strength and suppression of deformation of the substrate during heat sealing. Specifically, the heat quantity ΔH of the first resin layer is set to be 30 J / g or more, and the heat quantity ΔH of the second resin layer is set to be 25 J / g or less. Here, the heat quantity ΔH is represented by the following formula. Heat quantity ΔH = Heat of fusion in the range from 130°C to 190°C Note that details regarding the measurement method of the heat quantity ΔH of each resin layer are described in the section of Examples.

[0043] By setting the heat quantity ΔH of the first resin layer and the heat quantity ΔH of the second resin layer within specific ranges as described above, since the melting point of the second resin layer is lower than that of the first resin layer, the first resin layer is less likely to melt during heating for heat sealing, while the second resin layer tends to melt easily. Therefore, while suppressing the deformation of the substrate layer, the heat seal layer can exhibit good heat sealability.

[0044] The heat quantity ΔH of the first resin layer is preferably 32 J / g or more, more preferably 35 J / g or more, and even more preferably 38 J / g or more. The upper limit is not particularly limited, but is usually 100 J / g or less, preferably 70 J / g or less, and more preferably 50 J / g or less.

[0045] The heat quantity ΔH of the second resin layer is preferably 24 J / g or less, more preferably 22 J / g or less, even more preferably 20 J / g or less, and particularly preferably 18 J / g. The lower limit is not particularly limited and may be 0 J / g or more, but is preferably 5 J / g or more, and more preferably 10 J / g or more.

[0046] The heat quantity ΔH of each layer can be controlled within a desired range, for example, by selecting the type and / or content ratio of the constituent monomers of the poly(3-hydroxyalkanoate)-based resin constituting each layer.

[0047] (Thickness of the layer) In addition to the heat quantity ΔH, by controlling the ratio of the thickness of the first resin layer to the thickness of the second resin layer within a specific range, the multilayer film can achieve both heat seal strength and suppression of deformation of the base material during heat sealing. Specifically, the ratio of the thickness of the first resin layer: the thickness of the second resin layer is 1.0:0.015 to 1.0:5.0. In particular, it is preferably 1.0:0.1 to 1.0:3.3, more preferably 1.0:0.2 to 1.0:2.5, even more preferably 1.0:0.3 to 1.0:2.0, and particularly preferably 1.0:0.5 to 1.0:1.5.

[0048] The thickness of the first resin layer is not particularly limited, but from the viewpoints of heat seal strength and suppression of deformation of the base material during heat sealing, it is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 30 μm or more and 150 μm or less. Further, from the viewpoint of suppressing deformation of the base material during heat sealing at high temperature, the thickness of the first resin layer is preferably 50 μm or more, and more preferably 80 μm or more. Also, from the viewpoint of mechanical strength, the thickness of the first resin layer may be 10 μm or more, or may be 30 μm or more. Also, from the viewpoint of productivity, it may be 300 μm or less, may be 100 μm or less, or may be 70 μm or less.

[0049] The thickness of the second resin layer is not particularly limited, but from the viewpoints of heat seal strength and suppression of deformation of the base material during heat sealing, it is preferably 5 μm or more and 200 μm or less, more preferably 10 μm or more and 150 μm or less, and even more preferably 20 μm or more and 100 μm or less. Also, from the viewpoint of productivity, the thickness of the second resin layer may be 70 μm or less, or may be 50 μm or less.

[0050] The thickness of the entire multilayer film can be appropriately set according to the application and the like. When the multilayer film is applied as a packaging material, from the viewpoints of mechanical strength and barrier properties, it is preferably 15 μm or more, more preferably 30 μm or more, and even more preferably 50 μm or more. Also, from the viewpoint of economy, it is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less. Also, from the viewpoint of economy, the thickness of the entire multilayer film may be 150 μm or less, or may be 100 μm or less.

[0051] (Other layers) The multilayer film may, if necessary, have other layers other than the first resin layer and the second resin layer at any position such as between the first resin layer and the second resin layer, outside the first resin layer (on the surface opposite to the surface facing the second resin layer), outside the second resin layer (on the surface opposite to the surface facing the first resin layer), and the like. Examples of such other layers include a barrier layer, a vapor deposition layer, a printing layer, a base material layer, a reinforcing layer made of a biodegradable resin, an adhesive layer, and the like. The other layer may be one layer or a plurality of layers. However, in order to realize heat sealing by the second resin layer, it is preferable that there is no other layer outside the second resin layer which is the heat-sealing layer, that is, the second resin layer is the surface layer of the multilayer film.

[0052] (Integrated) In the multilayer film according to the present embodiment, it is preferable that the first resin layer and the second resin layer are integrated. Thereby, the multilayer film can have high puncture strength.

[0053] In the present specification, "integrated" means that the first resin layer and the second resin layer are directly or indirectly joined in an adjacent state, and a part of the resin constituting at least one layer is heat-fused to the adjacent layer, so that the layers are adhered to each other. Also, in the present specification, "heat fusion" means that the resin is melted or softened by heating and adheres to other substances. Therefore, a state in which the layers are adhered to each other by an adhesion mode other than heat fusion, for example, a state in which the first resin layer and the second resin layer are only pressure-bonded via a pressure-sensitive adhesive, is excluded from "integrated". Also, "integrated" can be evaluated by the "peel strength" described later.

[0054] In one embodiment, the first resin layer and the second resin layer are preferably integrated such that the peel strength between them is 3 N / 15 mm or more, more preferably integrated such that the peel strength is 5 N / 15 mm or more, and even more preferably integrated such that the peel strength is 6 N / 15 mm or more. By the peel strength between the first resin layer and the second resin layer being 3 N / 15 mm or more, higher piercing strength can be achieved. In the present specification, the peel strength between the first resin layer and the second resin layer is a value measured by the measurement method described in the examples below. When the test piece includes other layers between the first resin layer and the second resin layer, the peel strength between the first resin layer and the second resin layer refers to the peel strength of the interface where peeling occurred.

[0055] In a preferred embodiment, in the multilayer film, the first resin layer and the second resin layer are directly joined in an adjacent state, and a part of the resin constituting each layer mixes with each other at the interface between the layers, whereby the layers are adhered to each other. By a part of the resin constituting each layer mixing with each other at the interface between the layers, higher piercing strength can be achieved.

[0056] (Method for manufacturing a multilayer film) According to one embodiment, the multilayer film can be manufactured by a multilayer inflation molding method, a multilayer T-die molding method, or an extrusion lamination method.

[0057] The multilayer inflation molding method and the multilayer T-die molding method can each be performed by co-extruding while laminating the resin compositions constituting each layer in a molten state using a multilayer inflation molding apparatus or a multilayer T-die molding apparatus.

[0058] The extrusion lamination method can be carried out by forming at least one resin layer into a film and extruding a composition constituting another resin layer in a molten state onto the obtained film. From the viewpoints of film-forming property and extrudability, etc., a first resin layer having a low content of structural units derived from 3-hydroxyhexanoate is formed into a film, and on the obtained film, through an additional resin layer if necessary, a second resin layer having a high content of structural units derived from 3-hydroxyhexanoate is preferably extruded in a molten state.

[0059] In the multilayer inflation molding method, multilayer T-die molding method or extrusion lamination method, the temperature during extrusion molding can be appropriately set according to the melting point, MFR, etc. of the resin composition constituting each layer. From the viewpoints of resin fluidity and curing rate, for example, it is preferably 150 to 180°C, more preferably 155 to 170°C.

[0060] Preferably, the multilayer film can also be produced by forming the first resin layer and the second resin layer by the inflation molding method or the T-die molding method respectively, and then integrating the two layers by the thermal lamination molding method. When other layers are included between the first resin layer and the second resin layer, the first resin layer and the second resin layer may be integrated by the thermal lamination molding method through the other layers.

[0061] In the thermal lamination molding method, the lamination temperature can be appropriately set according to the melting point, MFR, etc. of the resin composition constituting each layer. From the viewpoint of film dimension stability, for example, it is preferably 90 to 130°C, more preferably 95 to 120°C.

[0062] Furthermore, the multilayer film can also be produced by forming at least one resin layer into a film, applying an aqueous coating liquid constituting another resin layer to one or both sides of the obtained film, and heating and drying to form another resin layer.

[0063] (Packaging material) The second resin layer with a heat quantity ΔH value lower than that of the first resin layer can exhibit good heat sealability because its melting point is lower than that of the first resin layer. Therefore, the multilayer film can be suitably used as a packaging material for applications where heat sealing is performed.

[0064] When applying the multilayer film as a packaging material, from the viewpoints of handleability and heat sealability, it is preferable that the first resin layer is located on the outer layer side and the second resin layer is located on the inner layer side. By heat-sealing the packaging material made of the multilayer film so that the second resin layer becomes the innermost layer, a packaging bag and a packaging container having sufficient seal strength can be manufactured. According to a particularly preferred embodiment, a pillow packaging using the second resin layer as a heat-sealing layer can be provided.

[0065] (Heat seal) The heat seal of the multilayer film can be carried out, for example, by laminating the multilayer film with the second resin layers facing each other, and applying heat and pressure from the first resin layer side to melt and bond the second resin layer. The heat seal implementation conditions such as heating temperature, heating time, and pressure are not particularly limited and may be according to conventional methods. For example, the heating temperature during heat sealing is preferably 100 to 150°C, and more preferably 110 to 140°C.

Examples

[0066] Examples are shown below to more specifically explain the present invention, but the present invention is not limited to these examples in any way.

[0067] The substances used in Examples 1 to 4 and Comparative Examples 1 to 2 are shown below. [Poly(3-hydroxyalkanoate) - based resin] P3HB3HH - 1: P3HB3HH (average content ratio 3HB / 3HH = 93 / 7 (mol% / mol%), weight average molecular weight is 740,000 g / mol) Manufactured according to the method described in Example 2 of International Publication No. 2010 / 13483. P3HB3HH-2: P3HB3HH (average content ratio 3HB / 3HH = 91 / 9 (mol% / mol%), weight average molecular weight is 720,000 g / mol) It was produced according to the method described in Example 2 of International Publication No. 2010 / 13483. P3HB3HH-3: P3HB3HH (average content ratio 3HB / 3HH = 91 / 9 (mol% / mol%), weight average molecular weight is 420,000 g / mol) It was produced according to the method described in Example 2 of International Publication No. 2010 / 13483.

[0068] [Nucleating agent] Behenic acid amide (manufactured by Nippon Fine Chemical Co., Ltd.: BNT-22H)

[0069] [Evaluation method] Regarding the evaluation methods carried out in Examples 1 to 4 and Comparative Examples 1 and 2, they will be described below. ·Measurement of the heat quantity ΔH of the resin layer Using the single-layer film of the first layer or the second layer as a sample, and using a DSC measuring device (NETZSCH, DSC214 Polyma), measurement was carried out under the conditions of a temperature range: -20 to 190 °C and a heating rate: 10 °C / min. For each layer, a DSC curve as shown in Figure 1 was obtained. In the DSC curve, the baseline before the start of melting and after the end of melting was connected by a straight line, and in the region surrounded by the straight line and the DSC curve, the area in the range of 130 °C to 190 °C (heat of fusion) was determined as the heat quantity ΔH of each layer. The heat quantity ΔH is a value corresponding to the area of the hatched region in Figure 1.

[0070] ·Measurement of heat seal strength Two pieces of the multilayer film were cut out into a 15 mm × 8 cm square. Using a heat seal tester (Tester Sangyo Co., Ltd., TP-701-B), heat sealing was carried out under the conditions of a gauge pressure of 0.2 MPa, a seal time of 1 second, and only the upper seal bar was heated. The heat seal temperature was carried out at each temperature of 110 °C, 120 °C, 130 °C, or 140 °C. During heat sealing, the seal bar was set to touch the first layer, and the second layers were set to face each other. The heat-sealed samples were subjected to a T-peel test (speed: 100 mm / min) using an autograph (Shimadzu Corporation, AGS-X), and the heat-sealing strength was determined from the average of N = 3.

[0071] · Confirmation of the state of the first layer (substrate layer) After heat-sealing, the state of the first layer was confirmed. When there was no damage such as wrinkles or tears in the first layer, it was evaluated as ○, and when such damage was observed, it was evaluated as ×.

[0072] (Example 1) To 100 parts by weight of the resin P3HB3HH-1 described as the first layer in Table 1, 0.5 part by weight of a crystal nucleating agent was added, and the mixture was kneaded using a twin-screw extruder (TEM26 manufactured by Toshiba Machine Co., Ltd.) under the conditions of a barrel temperature of 150°C, a screw rotation speed of 100 rpm, and a discharge rate of 10 kg / h. The molten kneaded strands were discharged from the die and introduced into a water bath heated to 40°C to solidify, and then cut with a pelletizer to obtain resin composition pellets.

[0073] Using an inflation molding machine (manufactured by Hokushin Sangyo Co., Ltd.) having a φ50 mm single-screw extruder and an inflation molding die (die diameter: 100 mm, lip clearance: 1.0 mm), the resin composition pellets were charged into the extruder, and a resin film (first layer) with a thickness of 35 μm was obtained at a discharge rate of 10 kg / h, a resin temperature of 165°C, a film folding width of 314 mm (blow-up ratio: 2.0), and a take-up speed of 5 m / min.

[0074] Next, using the resin P3HB3HH-2 described as the second layer in Table 1, resin composition pellets were obtained under the same conditions as above, and then a resin film (second layer) with a thickness of 35 μm was obtained under the same conditions.

[0075] After the obtained films were cured at 50°C for one week, the first layer and the second layer were laminated and bonded together using a vacuum laminator (manufactured by NPC Co., Ltd., Module Laminator LM-50x50-S) under the conditions of a temperature of 100°C and a pressure of 2 atmospheres to obtain a multilayer film.

[0076] Regarding the obtained multilayer film, the heat seal strength was measured and the state of the first layer was confirmed according to the above. The obtained evaluation results are summarized in Table 1.

[0077] (Examples 2 to 4, Comparative Examples 1 to 2) A multilayer film was obtained in the same manner as in Example 1 except that the type of resin used was changed as shown in Table 1 and the thickness of each resin film was changed as shown in Table 1, and the evaluation was performed. The obtained evaluation results are summarized in Table 1.

[0078] [Table 1]

[0079] It can be seen from Table 1 that in Example 1, heat sealing could be realized in the heat seal temperature range of 110 to 130 °C without damaging the base material layer. In Example 2, good results were obtained in the heat seal temperature range of 130 to 140 °C, in Example 3 at 130 °C, and in Example 4 in the range of 110 to 130 °C.

[0080] On the other hand, in Comparative Example 1, heat sealing could not be realized without damaging the base material layer at any heat seal temperature. In Comparative Example 2, although heat sealing could be realized without damaging the base material layer at a heat seal temperature of 140 °C, the seal strength was not sufficiently high.

[0081] Next, the substances used in Example 5 and Comparative Examples 3 to 6 are shown below. [Poly(3-hydroxyalkanoate) - based resin] P3HB3HH - 4: Poly(3-hydroxybutyrate - co - 3-hydroxyhexanoate) with a copolymer component composition ratio of (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 93.8 / 6.2 (mol / mol) and a weight average molecular weight of 600,000 P3HB3HH-5: Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with a composition ratio of the copolymer components of (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 92.3 / 7.7 (mol / mol) and a weight average molecular weight of 600,000

[0082] [Nucleating agent] P3HB and behenic acid amide were used.

[0083] [Evaluation method] The evaluation methods carried out in Example 5 and Comparative Examples 3 to 6 will be described below. · Measurement of the heat quantity ΔH of the resin layer It was determined by the method described above for Examples 1 to 4 and Comparative Examples 1 to 2. · Puncture strength The test piece was fixed with a jig, and a semi-circular needle with a diameter of 1.0 mm and a tip shape radius of 0.5 mm was punctured at a test speed of 50 ± 5 mm / min. The integral of the test force (N) versus the stroke until the needle penetrated was taken and calculated as mJ.

[0084] · Peel strength Two films of appropriate size were overlapped, and integral processing (thermal laminating molding described later) was carried out with one end as the peel strength measurement area. A test piece with a width of 15 mm was cut out from the sample. With the peel strength measurement area of the test piece at the center of the gripping tool, it was opened at 180°, and both ends were attached to the gripping tools of a tensile testing machine. It was pulled until peeling or breaking, and the maximum force (N) was obtained and recorded as the peel strength. The test speed was 300 mm / min.

[0085] · Heat sealability Two films of appropriate size were overlapped, and one end was heat-sealed at a lamination temperature of 110 °C and a pressure of 0.1 MPa. From the sample thus obtained, a test piece with a width of 15 mm was cut out. The test piece was opened at 180° so that the heat-sealed part was at the center of the gripper, and both ends were attached to the grippers of a tensile testing machine, and pulled until the heat-sealed part was broken to obtain the maximum force (N). The distance between the grippers at the start of the test was set to 50 mm or more. The test speed was set to 300 mm / min.

[0086] [Example 5] (Molding of the first layer) To 100 parts by weight of P3HB3HH-4, 3 parts by weight of P3HB and 0.5 parts by weight of behenic acid amide were blended as a crystal nucleating agent and dry-blended. The obtained resin material (resin mixture) was extrusion-molded at an extrusion temperature of 160 °C using a single-layer inflation molding apparatus to produce a single-layer film with a thickness of 30 μm.

[0087] (Molding of the second layer) To 100 parts by weight of P3HB3HH-5, 3 parts by weight of P3HB and 0.5 parts by weight of behenic acid amide were blended as a crystal nucleating agent and dry-blended. The obtained resin material (resin mixture) was extrusion-molded at an extrusion temperature of 155 °C using a single-layer inflation molding apparatus to produce a single-layer film with a thickness of 30 μm.

[0088] (Lamination) The first layer and the second layer obtained above were laminated by a thermal lamination molding method at a lamination temperature of 110 °C and a pressure of 0.1 MPa to obtain a laminated film (60 μm thick) having a layer structure of the first layer (30 μm thick) / the second layer (30 μm thick). For the obtained laminated film, the puncture strength, peel strength, and heat sealability were measured by the above method. The results are shown in Table 2.

[0089] [Comparative Example 3] For 100 parts by weight of P3HB3HH-4, 3 parts by weight of P3HB and 0.5 parts by weight of behenic acid amide were blended as a crystal nucleating agent and dry blended. The obtained resin material (resin mixture) was extrusion molded at an extrusion temperature of 160 °C using a single-layer inflation molding apparatus to form a single-layer film with a thickness of 60 μm. For the obtained single-layer film, the puncture strength was measured by the above method. The results are shown in Table 2.

[0090] [Comparative Example 4] For 100 parts by weight of P3HB3HH-5, 3 parts by weight of P3HB and 0.5 parts by weight of behenic acid amide were blended as a crystal nucleating agent and dry blended. The obtained resin material (resin mixture) was extrusion molded at an extrusion temperature of 155 °C using a single-layer inflation molding apparatus to form a single-layer film with a thickness of 60 μm. For the obtained single-layer film, the puncture strength was measured by the above method. The results are shown in Table 2.

[0091] [Comparative Example 5] For 100 parts by weight of P3HB3HH-4, 3 parts by weight of P3HB and 0.5 parts by weight of behenic acid amide were blended as a crystal nucleating agent and dry blended. The obtained resin material (resin mixture) was extrusion molded at an extrusion temperature of 160 °C using a single-layer inflation molding apparatus to form a single-layer film with a thickness of 30 μm. For the obtained single-layer film, the puncture strength was measured by the above method. The results are shown in Table 2.

[0092] [Comparative Example 6] For 100 parts by weight of P3HB3HH-5, 3 parts by weight of P3HB and 0.5 parts by weight of behenic acid amide were blended as a crystal nucleating agent and dry blended. The obtained resin material (resin mixture) was extrusion molded at an extrusion temperature of 155 °C using a single-layer inflation molding apparatus to form a single-layer film with a thickness of 30 μm. For the obtained single-layer film, the puncture strength was measured by the above method. The results are shown in Table 2.

[0093]

Table 2

[0094] As shown in Table 2, the laminated film of Example 5 including the first layer and the second layer was found to have a high puncture strength while having the same thickness as the single-layer films of Comparative Example 3 and Comparative Example 4 each consisting of only one of the layers. Further, as shown in Table 2, the laminated film of Example 5 had a puncture strength twice or more as high as that of the single-layer films of Comparative Example 5 and Comparative Example 6 having a thickness of 30 μm, which was half of that of Example 5. From these results, it was found that the puncture strength increased synergistically by integrating the first layer and the second layer.

Claims

1. A multilayer film comprising a first resin layer and a second resin layer, wherein the first resin layer and the second resin layer each contain a poly(3-hydroxyalkanoate) resin, the ratio of the thickness of the first resin layer to the thickness of the second resin layer is 1.0:0.015 to 1.0:5.0, the heat quantity ΔH of the first resin layer is 30 J / g or more, and the heat quantity ΔH of the second resin layer is 25 J / g or less, and the multilayer film. However, the heat quantity ΔH is represented by the following formula. Heat quantity ΔH = heat of fusion in the range of 130°C to 190°C

2. The multilayer film according to claim 1, wherein the thickness of the first resin layer is 10 μm or more and 300 μm or less.

3. The multilayer film according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate) resin contains a copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit.

4. The poly(3-hydroxyalkanoate) resin contained in the first resin layer is a copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit, and the content ratio of the other hydroxyalkanoate unit is 1 to 7 mol%, the poly(3-hydroxyalkanoate) resin contained in the second resin layer is a copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit, and the content ratio of the other hydroxyalkanoate unit is 7 to 20 mol%, The multilayer film according to any one of claims 1 to 3, wherein the content ratio of the other hydroxyalkanoate unit in the poly(3-hydroxyalkanoate) resin contained in the second resin layer is higher than the content ratio of the other hydroxyalkanoate unit in the poly(3-hydroxyalkanoate) resin contained in the first resin layer.

5. The multilayer film according to claim 3 or 4, wherein the other hydroxyalkanoate unit is a 3-hydroxyhexanoate unit.

6. The multilayer film according to any one of claims 1 to 5, wherein the first resin layer and the second resin layer are integrated.

7. The thickness of the first resin layer is 10 μm or more and 300 μm or less, The multilayer film according to any one of claims 1 to 6, wherein the thickness of the second resin layer is 5 μm or more and 70 μm or less.

8. The multilayer film according to any one of claims 1 to 7, wherein the first resin layer and / or the second resin layer further contains a crystallization nucleating agent.

9. The multilayer film according to claim 8, wherein the crystal nucleating agent is at least one selected from the group consisting of poly(3-hydroxybutyrate) (P3HB), talc, fatty acid amides, nucleobases, and dipeptides.

10. The multilayer film according to any one of claims 1 to 9, which is for heat sealing.

11. A method for producing the multilayer film according to any one of claims 1 to 10, comprising: (A) a step of molding the first resin layer and the second resin layer by an inflation molding method or a T-die molding method, respectively; and (B) a step of integrating the first resin layer and the second resin layer obtained in (A) by a thermal lamination molding method. A manufacturing method comprising:

12. A method for producing the multilayer film according to any one of claims 1 to 10, comprising: a step of simultaneously molding the first resin layer and the second resin layer by a multilayer inflation molding method or a multilayer T-die molding method.

13. A packaging material composed of the multilayer film according to any one of claims 1 to 10.

14. The packaging material according to claim 13, which is used for pillow packaging.

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