Multilayer film and packaging material

Abstract

A multilayer film comprising a first resin layer and a second resin layer, the first resin layer and the second resin layer each comprising a poly(3-hydroxyalkanoate)-based resin, the ratio of the thickness of the first resin layer: the thickness of the second resin layer being 1.0:0.015 to 1.0:5.0, the heat ΔH of the first resin layer being 30 J / g or more, and the heat ΔH of the second resin layer being 25 J / g or less. Here, the heat ΔH is the heat of fusion in the range of 130°C to 190°C.

Description

Technical Field

[0001] The present invention relates to a multilayer film having a resin layer comprising a poly(3-hydroxyalkanoate) resin and packaging materials using the multilayer film. Background Technology

[0002] Large quantities of petroleum-derived plastics are discarded every year, leading to a growing shortage of landfill space and environmental pollution. In addition, microplastics have become a significant problem in the marine environment in recent years.

[0003] Poly(3-hydroxyalkanoate) resins possess excellent seawater biodegradability, making them a promising material for addressing environmental problems caused by waste plastics. For example, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), a type of poly(3-hydroxyalkanoate) resin, allows for flexible control of its mechanical properties by varying the composition ratio of 3-hydroxyhexanoate. Furthermore, among biodegradable resins, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is expected to have broad applications, particularly in packaging materials, due to its high gas barrier properties and resistance to hydrolysis.

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

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

[0006] For example, in food applications, multilayer films are sometimes used as heat-sealing films to improve airtightness and preservation, forming bags by fusing the films together with heat. However, Patent Documents 1 and 2 do not specifically investigate the use of multilayer films for heat sealing.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-144553

[0010] Patent Document 2: Japanese Patent Publication No. 2005-507018 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] If heat sealing is to be performed using the multilayer film in Patent Documents 1 and 2, sometimes the heat sealing performance is insufficient and good adhesion cannot be obtained. In addition, sometimes the substrate layer will deform due to the heating during heat sealing.

[0013] In view of the above, the object of the present invention is to provide a multilayer film having a resin layer comprising a poly(3-hydroxyalkanoate) resin, having good heat-sealing properties, and suppressing deformation of the substrate layer during heat sealing.

[0014] Problem Solving Methods

[0015] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by setting the thickness ratio of the two layers in a multilayer film having two layers containing a poly(3-hydroxyalkanoate) resin within a specific range and setting the heat ΔH of each layer within a specific range, the above-mentioned problems can be solved, thereby completing the present invention.

[0016] That is, the present invention relates to a multilayer film comprising a first resin layer and a second resin layer, wherein the first resin layer and the second resin layer respectively comprise a poly(3-hydroxyalkanoate) resin, the thickness ratio of the first resin layer to the second resin layer is 1.0:0.015 to 1.0:5.0, the heat ΔH of the first resin layer is 30 J / g or more, and the heat ΔH of the second resin layer is 25 J / g or less.

[0017] The heat ΔH mentioned above is expressed by the following formula.

[0018] Heat of fusion ΔH = 130℃~190℃

[0019] Preferably, the thickness of the first resin layer is 10 μm or more and 300 μm or less.

[0020] Preferably, the above-mentioned poly(3-hydroxyalkanoate) resin comprises a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0021] Preferably, the poly(3-hydroxyalkanoate) resin contained in the first resin layer is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units is 1 to 7 mol%. The poly(3-hydroxyalkanoate) resin contained in the second resin layer is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units is 7 to 20 mol%. The content of other hydroxyalkanoate units in the poly(3-hydroxyalkanoate) resin contained in the second resin layer is higher than that in the poly(3-hydroxyalkanoate) resin contained in the first resin layer.

[0022] Preferably, the other hydroxyalkanoate unit mentioned above is a 3-hydroxyhexanoate unit.

[0023] Preferably, the first resin layer and the second resin layer are integrated.

[0024] 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.

[0025] Preferably, the first resin layer and / or the second resin layer further comprise a crystal nucleating agent. Preferably, the crystal nucleating agent is at least one selected from poly(3-hydroxybutyrate) (P3HB), talc, fatty acid amides, nucleic acid bases, and dipeptides.

[0026] Preferably, the multilayer film mentioned above is a heat-sealing multilayer film.

[0027] In addition, the present invention relates to a method for manufacturing a multilayer film, the method comprising (A) forming a first resin layer and a second resin layer respectively by blow molding or T-die molding; and (B) integrating the first resin layer and the second resin layer obtained in (A) by hot lamination molding; or comprising forming the first resin layer and the second resin layer simultaneously by multilayer blow molding or multilayer T-die molding.

[0028] In addition, the present invention relates to a packaging material formed from the above-mentioned multilayer film. The preferred packaging form is a pillow-shaped package.

[0029] The effects of the invention

[0030] According to the present invention, a multilayer film having a resin layer comprising a poly(3-hydroxyalkanoate) resin can be provided, the multilayer film having good heat-sealing properties and suppressing deformation of the substrate layer during heat sealing. Attached Figure Description

[0031] Figure 1 This is a graph illustrating the heat Δ in an example of a DSC curve measured on a resin layer. Detailed Implementation

[0032] One embodiment of the multilayer film of the present invention comprises a first resin layer and a second resin layer, wherein the first resin layer and the second resin layer each comprise a poly(3-hydroxyalkanoate) resin. This multilayer film can be used as a heat-sealing multilayer film. In this application, the first resin layer can function as a substrate layer, and the second resin layer can function as a heat-sealing layer.

[0033] The second resin layer, serving as the heat-sealing layer, can be laminated only on one side of the first resin layer, which serves as the substrate layer, or it can be laminated on both sides. Furthermore, the second resin layer can be laminated to the first resin layer in between other layers, or it can be laminated directly to the first resin layer without any other layers in between.

[0034] The first resin layer and the second resin layer each contain at least a poly(3-hydroxyalkanoate) resin.

[0035] The above-mentioned poly(3-hydroxyalkanoate) resin is preferably a polymer having 3-hydroxyalkanoate units, specifically a polymer containing units represented by the following general formula (1).

[0036] [-CHR-CH2-CO-O-](1)

[0037] In general formula (1), R represents C p H 2p+1 The alkyl group is represented by p, which is an integer from 1 to 15. Examples of R include straight-chain or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl. Preferably, p is 1 to 10, more preferably 1 to 8.

[0038] Of the above-mentioned poly(3-hydroxyalkanoate) resins, poly(3-hydroxyalkanoate) resins produced by microorganisms are particularly preferred. In poly(3-hydroxyalkanoate) resins produced by microorganisms, 3-hydroxyalkanoate units are contained as all (R)-3-hydroxyalkanoate units.

[0039] Poly(3-hydroxyalkanoate) resins preferably contain 50 mol% or more of 3-hydroxyalkanoate units (especially those represented by general formula (1)) of all constituent units, more preferably 60 mol% or more, and even more preferably 70 mol% or more. Poly(3-hydroxyalkanoate) resins may contain only one or two or more 3-hydroxyalkanoate units as constituent units of the polymer, or they may contain other units (e.g., 4-hydroxyalkanoate units, etc.) in addition to one or two or more 3-hydroxyalkanoate units.

[0040] Poly(3-hydroxyalkanoate) resins are preferably homopolymers or copolymers containing 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units. In particular, the 3-hydroxybutyrate units are preferably all (R)-3-hydroxybutyrate units. Furthermore, poly(3-hydroxyalkanoate) resins are preferably copolymers of 3-hydroxybutyrate units with other hydroxyalkanoate units. The copolymerization form is not particularly limited and can be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, etc.

[0041] Specific examples of poly(3-hydroxyalkanoate) resins include: poly(3-hydroxybutyrate) (abbreviated as P3HB), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviated as P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviated as 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), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as P3HB4HB). In particular, from the viewpoint of membrane productivity and mechanical properties, P3HB3HH, P3HB3HV, or P3HB4HB are preferred, and P3HB3HH or P3HB4HB are more preferred. It should be noted that P3HB, as a homopolymer, can also be used as a crystal nucleating agent as described later.

[0042] From the following perspectives, P3HB3HH is particularly preferred: by changing the composition ratio of repeating units, the melting point and crystallinity can be altered, resulting in changes to properties such as Young's modulus and heat resistance, and the ability to impart properties between polypropylene and polyethylene; it is also a plastic that is easy to produce industrially and useful in terms of physical properties, as described above. Furthermore, P3HB3HH has a lower melting point, making it preferred from the viewpoint of enabling low-temperature molding and processing.

[0043] According to a preferred embodiment, the first resin layer and the second resin layer preferably each comprise a copolymer of 3-hydroxybutyrate units and other hydroxyalkyl ester units, and particularly preferably comprise P3HB3HH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). When the first or second resin layer comprises the above-mentioned copolymers, each layer may contain only one of the above-mentioned copolymers, or it may contain at least two of the above-mentioned copolymers with different types and / or proportions of the constituent monomers. Additionally, each layer may contain at least one of the above-mentioned copolymers and P3HB.

[0044] The copolymers contained in the first resin layer and the copolymers contained in the second resin layer have different types and / or proportions of constituent monomers, thereby satisfying the heat ΔH condition described later. In this case, it is preferable that the proportion of other hydroxyalkanoate units (especially 3-hydroxyhexanoate units) in the copolymers contained in the second resin layer is greater than that in the copolymers contained in the first resin layer. Therefore, the second resin layer has a lower heat ΔH and a lower melting point compared to the first resin layer. Thus, the first resin layer is less prone to melting due to heating during heat sealing, while the second resin layer tends to melt easily. Therefore, while suppressing deformation of the substrate layer, the heat-sealing layer can exhibit good heat-sealing properties.

[0045] Specifically, in the copolymer contained in the first resin layer, the proportion 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.

[0046] On the other hand, in the copolymer contained in the second resin layer, the proportion 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, further preferably 8 mol% or more and 15 mol% or less, and even more preferably 9 mol% or more and 13 mol% or less.

[0047] The proportion of other hydroxyalkanoate units in the poly(3-hydroxyalkanoate) resin contained in the second resin layer is higher than that in the poly(3-hydroxyalkanoate) resin contained in the first resin layer.

[0048] If the copolymer described above is used in each layer, the heat ΔH of the first resin layer and the heat ΔH of the second resin layer, which will be described later, can be easily achieved.

[0049] The proportion of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate) resin can be determined by methods known to those skilled in the art, such as those described in paragraph

[0047] of International Publication No. 2013 / 147139. It should be noted that when each layer contains a mixture of two or more poly(3-hydroxyalkanoate) resins, the above-mentioned proportion refers to the average proportion of each monomer unit contained in the mixture as a whole.

[0050] According to one embodiment, the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin contained in the first resin layer is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, further preferably 300,000 to 2,000,000, and particularly preferably 350,000 to 1,500,000. By ensuring that the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin contained in the first resin layer is within the above range, deformation of the first resin layer caused by heating during heat sealing can be more effectively suppressed.

[0051] According to one embodiment, the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin contained in the second resin layer is preferably 50,000 to 1,000,000, more preferably 100,000 to 800,000, further preferably 150,000 to 600,000, and particularly preferably 150,000 to 500,000. By ensuring that the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin contained in the second resin layer is within the above range, the second resin layer can exhibit higher adhesive strength upon heat sealing.

[0052] There are no particular limitations on the method for determining the weight-average molecular weight of poly(3-hydroxyalkanoate) resins. For example, it can be determined by using chloroform as the mobile phase, a Waters GPC system as the system, and a Showa Denko Shodex K-804 (polystyrene gel) column as the column, in the form of a weight-average molecular weight based on polystyrene.

[0053] The manufacturing method of poly(3-hydroxyalkanoate) resins is not particularly limited; it can be a chemical synthesis method or a microbial manufacturing method. The microbial manufacturing method is preferred. Known methods can be used as microbial manufacturing methods. For example, known bacteria that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates include *Aeromonas caviae* as a P3HB3HV and P3HB3HH producing bacterium, and *Alcaligenes eutrophus* as a P3HB4HB producing bacterium. In particular, regarding P3HB3HH, to improve the productivity of P3HB3HH, it is more preferable to use Alcaligenes eutrophus AC32 strain (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)) which has been introduced with genes for poly(3-hydroxyalkanoate) resin synthase. Microbial cells of these microorganisms can be used to accumulate P3HB3HH within the cells under appropriate conditions. In addition to the above, recombinant microorganisms that have been introduced with various poly(3-hydroxyalkanoate) resin synthesis-related genes in accordance with the desired poly(3-hydroxyalkanoate) resin can also be used, and the culture conditions, including the type of substrate, can be optimized.

[0054] Microbial-produced P3HB3HH is a random copolymer. The proportion of 3HH units in microbial-produced P3HB3HH can be adjusted, for example, by selecting the bacterial cells, selecting the carbon source used as raw material, blending two or more P3HB3HH with different proportions of 3HH units, or blending homopolymers of 3HB.

[0055] Commercially available products of P3HB3HH include, for example, Kaneka Corporation's "Kaneka Biodegradable Polymer PHBH (registered trademark)".

[0056] (Other resins)

[0057] Within the scope of the invention's effects, the first resin layer or the second resin layer may contain one or more resins other than poly(3-hydroxyalkanoate) resins. Among such other resins, biodegradable resins are preferred, and examples include aliphatic polyester resins such as polybutylene succinate, polybutylene adipate succinate, polycaprolactone, and polylactic acid, as well as aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebacic acid terephthalate, and polybutylene azelaic acid terephthalate.

[0058] Even if these other resins exhibit biodegradability, they do not show sufficient seawater degradability. Therefore, to ensure the seawater biodegradability of the aforementioned multilayer membrane, the lower the content of these other resins, the better. Specifically, when the total amount of the aforementioned multilayer membrane is 100 parts by weight, the content of the aforementioned other resins contained in the multilayer membrane is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, further preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less. The lower limit of the content of other resins is not particularly limited and can be 0 parts by weight.

[0059] (Crystal nucleating agent)

[0060] In one embodiment, to the extent that the invention achieves its effects, the first resin layer or the second resin layer may further contain a crystal nucleating agent. By containing a crystal nucleating agent in the first resin layer or the second resin layer, effects such as improved molding processability and manufacturability are achieved.

[0061] As a crystal nucleating agent, there are no particular limitations as long as the above-mentioned effects are achieved. Examples include: poly(3-hydroxybutyrate) (P3HB), talc, fatty acid amides, nucleic acid bases (e.g., adenine, guanine, thymine, cytosine, uracil, and their derivatives), dipeptides (e.g., glycylglycine, glycyl-L-leucine), pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, boron nitride, etc. Among these, pentaerythritol is preferred due to its particularly excellent effect on promoting the crystallization of poly(3-hydroxybutyrate) resins. These crystal nucleating agents can be used alone or in combination of two or more.

[0062] When using P3HB as a crystal nucleating agent, in order to achieve the preferred range of viscosity and physical properties of the multilayer film during processing, the content of the crystal 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. The lower limit is not particularly limited and can be 0% by weight, but to promote the crystallization of the poly(3-hydroxyalkanoate) resin, it is preferably 1% by weight or more, more preferably 3% by weight or more.

[0063] When using a nucleating agent other than P3HB, in order to achieve the preferred range of viscosity and physical properties of the multilayer film during processing, the content of the 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. The lower limit is not particularly limited and can be 0% by weight. To promote the crystallization of the poly(3-hydroxyalkanoate) resin, it is preferably 0.1% by weight or more, more preferably 0.5% by weight or more.

[0064] When the above-mentioned multilayer film is applied to packaging materials, from the viewpoint of ensuring good heat-sealing properties, the second resin layer preferably does not contain crystal nucleating agents other than P3HB.

[0065] (additive)

[0066] Within the scope of the invention's effects, the first or second resin layer may contain additives commonly used in this technical field. Examples of such additives include: inorganic fillers such as talc, calcium carbonate, mica, silica, titanium dioxide, and alumina; organic fillers such as rice husks, wood flour, and waste paper such as newspapers; various starches and celluloses; colorants such as pigments and dyes; odor absorbers such as activated carbon and zeolite; fragrances such as vanillin and dextrin; plasticizers; antioxidants; weather-resistant modifiers; ultraviolet absorbers; lubricants; release agents; water-repellent agents; antibacterial agents; slip-modifying agents; tackifiers; fillers; crosslinking agents such as peroxides; and pharmaceuticals. The additive may contain only one type or more. Those skilled in the art can appropriately determine the content of these additives according to their intended use.

[0067] (Heat ΔH)

[0068] In one embodiment, by setting the ratio of the heat ΔH of the first resin layer to the thickness of the layer described later to a specific value or higher, and setting the heat ΔH of the second resin layer to a specific value or lower, the multilayer film can achieve both heat-sealing strength and suppression of substrate deformation during heat sealing. Specifically, the heat ΔH of the first resin layer is set to 30 J / g or higher, and the heat ΔH of the second resin layer is set to 25 J / g or lower. The aforementioned heat ΔH is expressed by the following formula.

[0069] Heat of fusion ΔH = 130℃~190℃

[0070] It should be noted that details related to the method for measuring the heat ΔH of each resin layer are described in Example 1.

[0071] By setting the heat values ​​ΔH of the first resin layer and the second resin layer to specific ranges as described above, the melting point of the second resin layer is lower than that of the first resin layer. Therefore, the first resin layer is less likely to melt due to heating during heat sealing, while the second resin layer tends to melt easily. Thus, while suppressing deformation of the substrate layer, the heat-sealing layer can exhibit good heat-sealing properties.

[0072] The heat 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. There is no particular upper limit, but it is generally 100 J / g or less, preferably 70 J / g or less, and more preferably 50 J / g or less.

[0073] The heat 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 can be 0 J / g or more, preferably 5 J / g or more, and more preferably 10 J / g or more.

[0074] For example, the heat ΔH of each layer can be controlled to the desired range by selecting the types and / or proportions of monomers in the poly(3-hydroxyalkanoate) resin that makes up each layer.

[0075] (Layer thickness)

[0076] In addition to the aforementioned heat ΔH, the ratio of the thickness of the first resin layer to the thickness of the second resin layer is controlled within a specific range. Therefore, the multilayer film can balance heat-sealing strength and suppression of substrate deformation during heat sealing. Specifically, 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. Particularly preferred is 1.0:0.1 to 1.0:3.3, more preferably 1.0:0.2 to 1.0:2.5, further preferably 1.0:0.3 to 1.0:2.0, and particularly preferably 1.0:0.5 to 1.0:1.5.

[0077] The thickness of the first resin layer is not particularly limited, but from the viewpoint of heat-sealing strength and suppression of substrate deformation 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. Furthermore, from the viewpoint of suppressing substrate deformation during high-temperature heat sealing, the thickness of the first resin layer is preferably 50 μm or more, more preferably 80 μm or more. Additionally, from the viewpoint of mechanical strength, the thickness of the first resin layer can be 10 μm or more, or 30 μm or more. Furthermore, from the viewpoint of productivity, it can be 300 μm or less, 100 μm or less, or 70 μm or less.

[0078] The thickness of the second resin layer is not particularly limited, but from the viewpoint of heat-sealing strength and suppression of substrate deformation 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. Furthermore, from a production efficiency perspective, the thickness of the second resin layer can be 70 μm or less, or 50 μm or less.

[0079] The overall thickness of the multilayer film can be appropriately set according to the application, etc. When the multilayer film is used in packaging materials, from the viewpoint 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. Furthermore, from an economic point of view, it is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less. Additionally, from an economic point of view, the overall thickness of the multilayer film can be 150 μm or less, or 100 μm or less.

[0080] (Other layers)

[0081] Depending on the requirements, the multilayer film may have layers other than the first and second resin layers at any location, such as between the first and second resin layers, on the outer side of the first resin layer (on the surface opposite to the side opposite to the second resin layer), or on the outer side of the second resin layer (on the surface opposite to the side opposite to the first resin layer). Examples of such other layers include barrier layers, vapor-deposited layers, printed layers, substrate layers, reinforcing layers formed from biodegradable resin, and adhesive layers. These other layers may be a single layer or multiple layers. However, to achieve heat sealing using the second resin layer, it is preferable that no other layers are present on the outer side of the second resin layer, which serves as the heat-sealing layer; that is, the second resin layer is the surface layer of the multilayer film.

[0082] (Integration)

[0083] Preferably, in the multilayer film of this embodiment, the first resin layer and the second resin layer are integrated. Therefore, the multilayer film can have high puncture strength.

[0084] In this application specification, "integration" refers to a state where the first resin layer and the second resin layer are directly bonded in an adjacent state, or indirectly bonded with other layers in between, or where a portion of the resin constituting at least one layer is bonded together with the adjacent layer by thermal fusion. Furthermore, in this application specification, "thermal fusion" refers to the process where resin is melted or softened by heating and bonded together with other substances. Therefore, a state where layers are bonded together by methods other than thermal fusion, such as pressing the first resin layer and the second resin layer together solely with a pressure-sensitive adhesive, does not constitute "integration." Additionally, "integration" can be evaluated using the "peel strength" described later.

[0085] In one embodiment, the first resin layer and the second resin layer are preferably integrated in such a way that the peel strength between them reaches 3N / 15mm or more, more preferably 5N / 15mm or more, and even more preferably 6N / 15mm or more. By achieving a peel strength of 3N / 15mm or more between the first resin layer and the second resin layer, higher puncture strength can be achieved. In this 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 contains 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 at the interface where peeling occurs.

[0086] In a preferred embodiment, the first resin layer and the second resin layer of the multilayer film are directly bonded in an adjacent state, and a portion of the resin constituting each layer is mixed with each other at the interlayer interface, thereby bonding the layers together. By making a portion of the resin constituting each layer mixed with each other at the interlayer interface, a higher puncture strength can be achieved.

[0087] (Manufacturing method of multilayer films)

[0088] According to one embodiment, multilayer films can be manufactured by multilayer blow molding, multilayer T-die molding, or extrusion lamination.

[0089] Multi-layer blow molding and multi-layer T-die molding can be carried out by co-extruding the resin composition that makes up each layer in a molten state using a multi-layer blow molding device or a multi-layer T-die molding device.

[0090] Extrusion lamination can be performed by forming at least one resin layer and extruding the composition constituting other resin layers onto the resulting film in a molten state. From the viewpoint of film-forming properties and extrusion properties, it is preferable to form a first resin layer with a low content of 3-hydroxyhexanoate constituent units, and then, as needed, extrude a second resin layer with a high content of 3-hydroxyhexanoate constituent units onto the resulting film in a molten state, with the other resin layers in between.

[0091] In multi-layer blow molding, multi-layer T-die molding, or extrusion lamination, the temperature during extrusion molding can be appropriately set according to the melting point and MFR of the resin composition constituting each layer. From the viewpoint of resin flowability and curing speed, it is preferably 150 to 180°C, and more preferably 155 to 170°C.

[0092] Preferably, the multilayer film can also be manufactured as follows: after forming the first resin layer and the second resin layer separately by blow molding or T-die molding, the two layers are integrated by hot lamination. If there are other layers between the first resin layer and the second resin layer, the first resin layer and the second resin layer can be integrated by hot lamination, with the other layers in between.

[0093] In the hot lamination molding method, the lamination temperature can be appropriately set according to the melting point and MFR of the resin composition constituting each layer. From the viewpoint of film dimensional stability, it is preferably 90 to 130°C, and more preferably 95 to 120°C.

[0094] In addition, multilayer membranes can also be manufactured as follows: at least one resin layer is formed into a membrane, an aqueous coating liquid constituting other resin layers is applied to one or both sides of the obtained membrane, and the membrane is heated / dried to form other resin layers.

[0095] (Packaging materials)

[0096] The heat value ΔH is lower than that of the first resin layer, and the melting point of the second resin layer is lower than that of the first resin layer. Therefore, it exhibits good heat-sealing properties. Thus, the above-described multilayer film can be appropriately used as a packaging material for applications requiring heat sealing.

[0097] When the above-mentioned multilayer film is applied to packaging materials, from the viewpoint of handleability and heat-sealing, 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 formed from the above-mentioned multilayer film with the second resin layer as the innermost layer, it is possible to manufacture packaging bags and packaging containers with sufficient sealing strength. According to a particularly preferred embodiment, it is possible to provide a pillow-shaped package with the second resin layer as the heat-sealing layer.

[0098] (Heat-sealed)

[0099] The heat sealing of the aforementioned multilayer film can be performed, for example, as follows: the multilayer film is stacked with the second resin layers facing each other, and heat and pressure are applied from the first resin layer side to melt and bond the second resin layers. The heat sealing conditions, such as heating temperature, heating time, and pressure, are not particularly limited and can be achieved using general methods. For example, the preferred heating temperature for heat sealing is 100–150°C, more preferably 110–140°C.

[0100] Example

[0101] The following examples illustrate the invention in more detail, but the invention is not limited to these examples.

[0102] The following shows the substances used in Examples 1-4 and Comparative Examples 1-2.

[0103] [Poly(3-hydroxyalkanoate) resins]

[0104] P3HB3HH-1: P3HB3HH (average content ratio 3HB / 3HH = 93 / 7 (mol% / mol%), weight-average molecular weight is 740,000 g / mol)

[0105] It is manufactured according to the method described in Example 2 of International Publication No. 2010 / 13483.

[0106] P3HB3HH-2: P3HB3HH (average content ratio 3HB / 3HH = 91 / 9 (mol% / mol%), weight-average molecular weight is 720,000 g / mol)

[0107] It is manufactured according to the method described in Example 2 of International Publication No. 2010 / 13483.

[0108] P3HB3HH-3: P3HB3HH (average content ratio 3HB / 3HH = 91 / 9 (mol% / mol%), weight-average molecular weight is 420,000 g / mol)

[0109] It is manufactured according to the method described in Example 2 of International Publication No. 2010 / 13483.

[0110] [Crystal nucleating agent]

[0111] Behenic acid amide (manufactured by Nippon Seika Co., Ltd.: BNT-22H)

[0112] [Evaluation Method]

[0113] The evaluation methods implemented in Examples 1-4 and Comparative Examples 1-2 will be described below.

[0114] • Determination of the heat ΔH of the resin layer

[0115] Using the first or second layer monolayer film as a sample, measurements were performed using a DSC apparatus (NETZSCH DSC214 Polyma) at a temperature range of -20 to 190°C and a heating rate of 10°C / min. For each layer, the following results were obtained: Figure 1 The DSC curve is shown. In this DSC curve, a straight line connects the baseline before and after melting. Within the region enclosed by this straight line and the DSC curve, the area (heat of fusion) ranging from 130°C to 190°C is calculated as the heat ΔH for each layer. The heat ΔH is equivalent to... Figure 1 The value of the area of ​​the region marked with a diagonal line.

[0116] • Determination of heat seal strength

[0117] Two multilayer films were cut into 15mm × 8cm squares. With the two films overlapping, heat sealing was performed using a heat sealing tester (TESTER SANGYO CO.,LTD., TP-701-B) under the conditions of a gauge pressure of 0.2MPa, a sealing time of 1 second, and heating only through the upper sealing rod. Heat sealing was performed at temperatures of 110℃, 120℃, 130℃, or 140℃. During heat sealing, the sealing rods were positioned so that they contacted the first layer, and the second layers were positioned opposite each other.

[0118] For the heat-sealed samples, a T-shaped peel test (speed 100 mm / min) was performed using AUTOGRAPH (Shimadzu Corporation, AGS-X), and the heat seal strength was calculated by averaging N=3.

[0119] • Status confirmation of layer 1 (substrate layer)

[0120] After heat sealing, the condition of the first layer is confirmed. A condition in which the first layer has no wrinkles, breaks, or other damage is rated as 0, and a condition in which the above-mentioned damage is observed is rated as ×.

[0121] (Example 1)

[0122] In Table 1, 0.5 parts by weight of crystal nucleating agent were added to 100 parts by weight of resin P3HB3HH-1, which is recorded as the first layer. The mixture was compounded using a twin-screw extruder (TEM26 Toshiba Machinery) at a barrel temperature of 150°C, a screw speed of 100 rpm, and an ejection rate of 10 kg / h. The melt-mixed filament was taken out of the die and put into a water bath heated to 40°C to solidify it. The filament was then cut by a granulator to obtain resin composition granules.

[0123] Using a blow molding machine (manufactured by Hokushin Sangyo Co., Ltd.) equipped with a φ50mm single-screw extruder and a blow molding die (die diameter 100mm, die lip clearance 1.0mm), the above-mentioned resin composition granules were fed into the extruder, and a resin film (first layer) with a thickness of 35μm was obtained at an ejection rate of 10kg / h, a resin temperature of 165°C, a film fold width of 314mm (expansion ratio 2.0), and an extraction speed of 5m / min.

[0124] Next, using resin P3HB3HH-2, which is described as the second layer in Table 1, resin composition particles were obtained under the same conditions as described above, and a resin film (second layer) with a thickness of 35 μm was obtained under the same conditions.

[0125] After the obtained membrane was cured at 50°C for 1 week, the first and second layers were stacked and bonded together using a vacuum laminating device (Module Laminator LM-50x50-S manufactured by NPC Co., Ltd.) at a temperature of 100°C and a pressure of 2 atmospheres to obtain a multilayer membrane.

[0126] For the obtained multilayer film, the heat seal strength was measured and the condition of the first layer was confirmed as described above. The evaluation results are summarized in Table 1.

[0127] (Examples 2-4, Comparative Examples 1-2)

[0128] The types of resins used were changed as shown in Table 1. Additionally, the thicknesses of each resin film were changed as shown in Table 1. Otherwise, multilayer films were obtained in the same manner as in Example 1, and their evaluation was conducted. The evaluation results are summarized in Table 1.

[0129]

[0130] The following information is available from Table 1. In Example 1, heat sealing was achieved without damaging the substrate layer within a heat sealing temperature range of 110–130°C. Good results were obtained in Example 2 within a heat sealing temperature range of 130–140°C, in Example 3 at 130°C, and in Example 4 within a heat sealing temperature range of 110–130°C.

[0131] On the other hand, in Comparative Example 1, heat sealing could not be achieved without damaging the substrate layer at any heat sealing temperature. In Comparative Example 2, although heat sealing could be achieved without damaging the substrate layer at a heat sealing temperature of 140°C, the sealing strength was not high enough.

[0132] Next, the substances used in Example 5 and Comparative Examples 3 to 6 are shown below.

[0133] [Poly(3-hydroxyalkanoate) resins]

[0134] P3HB3HH-4: The copolymer composition ratio is (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 93.8 / 6.2 (mol / mol), and the weight average molecular weight is 600,000 for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0135] P3HB3HH-5: The copolymer composition ratio is (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 92.3 / 7.7 (mol / mol), and the weight average molecular weight is 600,000 for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0136] [Crystal nucleating agent]

[0137] P3HB and betaine amide were used.

[0138] [Evaluation Method]

[0139] The evaluation methods implemented in Example 5 and Comparative Examples 3 to 6 will be described below.

[0140] • Determination of the heat ΔH of the resin layer

[0141] The above methods were used to determine the results of Examples 1-4 and Comparative Examples 1-2.

[0142] ·Puncture strength

[0143] The test piece is fixed with a clamp, and a semi-circular needle with a diameter of 1.0 mm and a front-end radius of 0.5 mm is used to puncture it at a test speed of 50 ± 5 mm / min. The integral of the test force (N) until the needle penetrates the needle relative to the stroke is obtained and calculated in mJ.

[0144] Peel strength

[0145] Two appropriately sized films were overlapped, with one end serving as the peel strength measurement area, and then integrated (thermal lamination described later). A 15mm wide test piece was cut from this sample, and the test piece was opened 180° so that the peel strength measurement area was centered in the clamp. Both ends were mounted on the clamps of the tensile testing machine, and the sample was stretched until peeling or failure. The maximum force (N) was determined and recorded as the peel strength. The test speed was set to 300mm / min.

[0146] Heat-sealing properties

[0147] Two appropriately sized films are overlapped and heat-sealed at one end using a lamination temperature of 110℃ and a pressure of 0.1MPa. A 15mm wide test piece is cut from the resulting specimen. The test piece is opened 180° with the heat-sealed portion centered in the clamps. Both ends are mounted on the clamps of the tensile testing machine, and the test is stretched until the heat-sealed portion fails. The maximum force (N) is then determined. The clamp spacing at the start of the test is set to at least 50mm. The test speed is set to 300mm / min.

[0148] [Example 5]

[0149] (The formation of the first layer)

[0150] A dry blending process was performed, incorporating 3 parts by weight of P3HB (as a crystal nucleating agent) and 0.5 parts by weight of betaine amide, relative to 100 parts by weight of P3HB3HH-4. The resulting resin material (resin mixture) was extruded at an extrusion temperature of 160°C using a single-layer blow molding apparatus to produce a single-layer film with a thickness of 30 μm.

[0151] (The formation of the second layer)

[0152] A dry blending process was performed, incorporating 3 parts by weight of P3HB (as a crystal nucleating agent) and 0.5 parts by weight of betaine amide, relative to 100 parts by weight of P3HB3HH-5. The resulting resin material (resin mixture) was extruded at an extrusion temperature of 155°C using a single-layer blow molding apparatus to produce a single-layer film with a thickness of 30 μm.

[0153] (Layered)

[0154] The first and second layers obtained above were bonded together using a hot lamination method at a lamination temperature of 110°C and a pressure of 0.1 MPa, thereby obtaining a laminated film (60 μm thick) with a layer structure of first layer (30 μm thick) / second layer (30 μm thick). The puncture strength, peel strength, and heat-sealing properties of the obtained laminated film were measured using the methods described above. The results are shown in Table 2.

[0155] [Comparative Example 3]

[0156] A dry blend was performed with 3 parts by weight of P3HB (as a crystal nucleating agent) and 0.5 parts by weight of betaine amide, relative to 100 parts by weight of P3HB3HH-4. The resulting resin material (resin mixture) was extruded at an extrusion temperature of 160°C using a single-layer blow molding apparatus to produce a single-layer film with a thickness of 60 μm. The puncture strength of the obtained single-layer film was measured using the method described above. The results are shown in Table 2.

[0157] [Comparative Example 4]

[0158] A dry blend was performed with 3 parts by weight of P3HB (as a crystal nucleating agent) and 0.5 parts by weight of betaine amide, relative to 100 parts by weight of P3HB3HH-5. The resulting resin material (resin mixture) was extruded at an extrusion temperature of 155°C using a single-layer blow molding apparatus to produce a single-layer film with a thickness of 60 μm. The puncture strength of the obtained single-layer film was measured using the method described above. The results are shown in Table 2.

[0159] [Comparative Example 5]

[0160] Relative to 100 parts by weight of P3HB3HH-4, 3 parts by weight of P3HB (as a crystal nucleating agent) and 0.5 parts by weight of betaine amide were dry-blended. The resulting resin material (resin mixture) was extruded at an extrusion temperature of 160°C using a single-layer blow molding apparatus to produce a single-layer film with a thickness of 30 μm. The puncture strength of the obtained single-layer film was measured using the method described above. The results are shown in Table 2.

[0161] Relative to 100 parts by weight of P3HB3HH-5, 3 parts by weight of P3HB (as a crystal nucleating agent) and 0.5 parts by weight of betaine amide were dry-blended. The resulting resin material (resin mixture) was extruded at an extrusion temperature of 155°C using a single-layer blow molding apparatus to produce a single-layer film with a thickness of 30 μm. The puncture strength of the obtained single-layer film was measured using the method described above. The results are shown in Table 2.

[0162] [Table 2]

[0163]

[0164] As shown in Table 2, the laminated film of Example 5, which includes both the first and second layers, exhibits higher puncture strength compared to the single-layer films of Comparative Examples 3 and 4, which are formed from only one layer, even though they have the same thickness. Furthermore, as shown in Table 2, the laminated film of Example 5 has more than twice the puncture strength compared to the single-layer films of Comparative Examples 5 and 6, which have a thickness of half 30 μm. Based on these results, it can be concluded that by integrating the first and second layers, the puncture strength is synergistically increased.

Claims

1. A multilayer film comprising a first resin layer and a second resin layer, The first resin layer and the second resin layer each comprise 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 ΔH of the first resin layer is above 30 J / g, and the heat ΔH of the second resin layer is below 25 J / g. in, The heat ΔH is expressed by the following formula. Heat of fusion ΔH = 130℃~190℃ The multilayer film is a heat-sealing multilayer film, wherein the first resin layer is a substrate layer and the second resin layer is a heat-sealing layer.

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

3. The multilayer film according to claim 1 or 2, wherein, The poly(3-hydroxyalkanoate) resin comprises a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units.

4. The multilayer film according to claim 1 or 2, wherein, The poly(3-hydroxyalkanoate) resin contained in the first resin layer is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units is 1-7 mol%. The poly(3-hydroxyalkanoate) resin contained in the second resin layer is a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units is 7-20 mol%. The proportion of other hydroxyalkanoate units in the poly(3-hydroxyalkanoate) resin contained in the second resin layer is higher than that in the poly(3-hydroxyalkanoate) resin contained in the first resin layer.

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

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

7. The multilayer film according to claim 1 or 2, wherein the first resin layer and the second resin layer are integrally formed.

8. The multilayer film according to claim 1 or 2, wherein, The thickness of the first resin layer is greater than 10 μm and less than 300 μm. The thickness of the second resin layer is greater than 5 μm and less than 70 μm.

9. The multilayer film according to claim 1 or 2, wherein, The first resin layer and / or the second resin layer further contain a crystal nucleating agent.

10. The multilayer film according to claim 9, wherein, The crystal nucleating agent is selected from at least one of poly(3-hydroxybutyrate) (P3HB), talc, fatty acid amide, nucleic acid bases and dipeptides.

11. A method for manufacturing a multilayer film according to any one of claims 1 to 10, the method comprising: (A) The process of forming the first resin layer and the second resin layer by blow molding or T-die molding respectively; as well as (B) A process of integrating the first resin layer and the second resin layer obtained by (A) by hot lamination molding.

12. A method for manufacturing a multilayer film according to any one of claims 1 to 10, the method comprising: The process of simultaneously forming the first resin layer and the second resin layer using a multi-layer blow molding method or a multi-layer T-die molding method.

13. A packaging material formed from a multilayer film according to any one of claims 1 to 10.

14. The packaging material according to claim 13, wherein, The packaging is in the form of a pillow shape.

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