Multilayer film and polypropylene packaging

Abstract

The objective of the present invention is to provide a multilayer film and a polypropylene packaging with excellent airtightness, gas barrier properties, and strength, and which can be mechanically recycled after use.　To solve the problem, the present invention provides a multilayer film in which (a) at least one polypropylene resin is included, (b) the content ratio of the polypropylene resin is 90 wt% or more of the resin constituting the entire film, (c1) an ethylene vinyl alcohol copolymer which is 5 wt% or less of the resin constituting the entire film is included, and (d) the ethylene content of the ethylene vinyl alcohol copolymer is 32-45 mol%.

Description

Multilayer film and polypropylene packaging

[0001] The present invention relates to a multilayer film and a polypropylene-based packaging body.

[0002] Resin films have traditionally been used as packaging materials. For example, polyolefin resin films are widely used as sealant films because they have flexibility, transparency, and excellent heat-sealing properties. Resin films made of polyolefin generally cannot be used as substrates due to their lack of strength and heat resistance, and are therefore used in combination with polyester or nylon films. Therefore, typical packaging containers are made of laminated films in which the substrate and sealant film are made of different resin materials (see, for example, Patent Document 1).

[0003] Furthermore, with the growing demand for the creation of a recycling-oriented society, there is a demand for packaging containers that are highly recyclable, and the same can be said for containers made from the above-mentioned polyolefin materials. However, conventional packaging containers are made up of different types of resin materials, and because it is difficult to separate the resin materials, they are not currently recycled.

[0004] Therefore, from the viewpoint of creating a single material (mono-material) that allows mechanical recycling, for example, Patent Document 2 discloses a packaging container that is made of a single material, that is, a polypropylene, and is composed of a laminate having a stretched base material containing polypropylene and a sealant layer containing polypropylene.

[0005] JP 2009-202519 A JP 2023-051562 A

[0006] However, although the packaging container disclosed in Patent Document 2 is mechanically recyclable, it cannot be said that the container has sufficient performance as a package in terms of reducing airtightness due to shrinkage of the film (sealant layer) caused by residual stress after heat sealing, suppressing deformation of the container portion, film strength, etc., and there is room for further improvement.

[0007] Therefore, an object of the present invention is to provide a multilayer film and a polypropylene-based packaging material that have excellent airtightness, gas barrier properties and strength, and that can be mechanically recycled after use.

[0008]

[0006] The present inventors have conducted extensive research into multilayer films and polypropylene-based packaging materials used in packaging to solve the above-mentioned problems, and have found that by including a polypropylene-based resin as the main component in both the multilayer film and the container, and a small amount of a gas barrier resin, the entire container can be mechanically recycled and good gas barrier properties can be maintained. In addition, the present inventors have found that by satisfying specific conditions for the heat shrinkage rate and heat shrinkage stress of the multilayer film, it is possible to achieve excellent heat shrinkage rate and reduced heat shrinkage stress, as well as improved airtightness and strength, and have completed the present invention.

[0009] The present invention was made based on the above findings, and its gist is as follows: (1) A multilayer film comprising: (a) at least one polypropylene-based resin; (b) the content of the polypropylene-based resin is 90% by weight or more of the resin constituting the entire film; (c1) an ethylene-vinyl alcohol copolymer is 5% by weight or less of the resin constituting the entire film; and (d) the ethylene-vinyl alcohol copolymer has an ethylene content of 32 to 45 mol%, wherein the multilayer film has a heat shrinkage rate at 100°C of 10% to 30% in the machine direction (MD) and a heat shrinkage rate at 100°C of 10% to 30% in the transverse direction (TD), and wherein the multilayer film has a maximum heat shrinkage stress at 100°C of 4.0 MPa or less in the machine direction (MD) and a maximum heat shrinkage stress at 100°C of 4.0 MPa or less in the transverse direction (TD). (2) The multilayer film according to (1), characterized in that it is composed of at least five layers, with the heat seal layer being the innermost layer, and an inner intermediate layer, a core layer, an outer intermediate layer, and an outermost layer formed in that order toward the outermost layer. (3) The multilayer film according to (2), characterized in that the heat seal layer contains a polypropylene-based resin and an anti-fogging agent. (4) The multilayer film according to (2) or (3), characterized in that the outermost layer contains a polypropylene-based resin. (5) The multilayer film according to any one of (1) to (4), characterized in that the tear strength in the machine direction (MD) is 3.0 cN or more and 20.0 cN or less, and the tear strength in the transverse direction (TD) is 7.0 cN or more and 20.0 cN or less. (6) The multilayer film according to any one of (1) to (4), characterized in that the water vapor transmission rate at 40°C is 16 g / (m ２ (7) The multilayer film according to any one of (1) to (5), characterized in that the oxygen permeability at 23°C and 65% RH is less than 300 cc / (m ２(8) A polypropylene-based packaging body comprising a plastic container and a multilayer film serving as a lid for the container, wherein the container (a) comprises at least one polypropylene-based resin, (b) the content of the polypropylene-based resin is 90% by weight or more of the resin constituting the entire container, and (c) the container comprises a gas barrier resin in an amount of 5% by weight or less of the resin constituting the entire container, and the multilayer film is the multilayer film described in any of (1) to (7). (9) The polypropylene-based packaging body according to (8), wherein the gas barrier resin of the container is an ethylene-vinyl alcohol copolymer.

[0010] According to the present invention, it is possible to provide a multilayer film and a polypropylene-based packaging material that have excellent airtightness, gas barrier properties and strength, and that can be mechanically recycled after use.

[0011] 1 is a perspective view schematically illustrating an example of a container according to the present embodiment; FIG. 2 is a view schematically illustrating a cross section of an example of a multilayer film according to the present embodiment;

[0012] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be carried out with appropriate modifications within the scope of its gist.

[0013] Here, Fig. 1 is a schematic diagram of an example of a container according to the present embodiment, and Fig. 2 is a schematic diagram of an example of a multilayer film used in the container according to the present embodiment. Note that the dimensions and ratios of the components shown in Figs. 1 and 2 are different from the actual dimensions and ratios for the sake of convenience of explanation.

[0014] <Polypropylene-based packaging body> First, the polypropylene-based packaging body of this embodiment (hereinafter, sometimes simply referred to as "polypropylene-based packaging body") will be described. As shown in Fig. 1, the container of this embodiment is a polypropylene-based packaging body 100 including a container 20 made of plastic and a multilayer film 10 that serves as a lid for the container 20.

[0015] In the packaging body of this embodiment, the multilayer film satisfies the following conditions (a) and (b): (a) it contains at least one polypropylene-based resin, and (b) the content of the polypropylene-based resin is 90% by weight or more of the resin constituting the entire film. By satisfying the above conditions (a) and (b), the multilayer film contains a polypropylene-based resin as a main component (becoming a PP monomaterial), and therefore, mechanical recycling of the multilayer film becomes possible.

[0016] Furthermore, in the packaging body of this embodiment, the container satisfies the following conditions (a) and (b): (a) the container contains at least one polypropylene-based resin, and (b) the content ratio of the polypropylene-based resin is 90% by weight or more of the resin constituting the entire container. By satisfying the above conditions (a) and (b), the container contains a polypropylene-based resin as a main component (becoming a PP monomaterial), which makes it possible to mechanically recycle the entire packaging body and also maintain good gas barrier properties as a container.

[0017] (Condition (a) and Condition (b)) The multilayer film and the container both contain at least one polypropylene-based resin (condition (a)), and the content of the polypropylene-based resin is 90% by weight or more of the resin constituting the entire polypropylene-based packaging body (condition (b)). This means that the multilayer film and the container both contain polypropylene-based resin as the main component (PP monomaterial), which makes them highly recyclable and enables mechanical recycling.

[0018] Here, mechanical recycling in the present invention refers to the separation and decomposition of waste or used products using an appropriate processing method, extracting recyclable materials, and using them as raw materials for new products, such as when converting used plastic products into raw materials for reuse. On the other hand, material recycling refers to the appropriate processing of waste or used products and converting them into components for new products, such as when reusing plastic products as new plastic products, and is distinguished from the mechanical recycling. Therefore, in order to perform mechanical recycling on polypropylene-based packaging, the used polypropylene-based packaging must have a high purity (close to a monomaterial), and therefore the polypropylene-based packaging of this embodiment must satisfy the above conditions (a) and (b).

[0019] Here, the polypropylene-based resin is not particularly limited and can be appropriately selected depending on the required performance. Examples of the polypropylene-based resin include a propylene homopolymer and a copolymer of propylene with ethylene and another α-olefin (for example, an α-olefin having 4 to 20 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, or 1-eicosane, preferably an α-olefin having 4 to 8 carbon atoms).

[0020] The polypropylene may be one polymerized using a known catalyst such as a single-site catalyst or a multi-site catalyst, and from the viewpoint of achieving even better transparency, one polymerized using a single-site catalyst is preferred. The polypropylene may be a resin polymerized using a catalyst such as a Ziegler-Natta catalyst, or a resin polymerized using a metallocene catalyst. That is, for example, syndiotactic polypropylene, isotactic polypropylene, etc. can also be used as the polypropylene.

[0021] Furthermore, copolymers with propylene or ethylene can also be used. Examples of such copolymers include elastomers and plastomers containing structural units derived from propylene, elastomers and plastomers containing structural units derived from ethylene, elastomers and plastomers containing structural units derived from ethylene and structural units derived from propylene, and elastomers and plastomers containing structural units derived from ethylene, structural units derived from propylene, and structural units derived from other α-olefins (for example, α-olefins having 4 to 20 carbon atoms such as butene).

[0022] Acid-modified olefin resins can also be used. Examples of acid-modified olefin resins include polyolefins modified with carboxylic acids (including carboxylic anhydrides). The acid-modified olefin resins may be either homopolymers or copolymers, and preferably have repeating units derived from ethylene and / or α-olefins. Examples of the α-olefins include one selected from the group consisting of propylene, 1-butene, and 1-octene.

[0023] Examples of the olefin structure constituting the acid-modified olefin-based resin include homopolymers such as polyethylene, polypropylene, polybutene, and polyoctene, ethylene-propylene copolymers, ethylene-1-butene copolymers, propylene-1-butene copolymers, propylene-1-hexene copolymers, propylene-4-methyl-1-pentene copolymers, propylene-1-octene copolymers, propylene-1-decene copolymers, propylene-1,4-hexadiene copolymers, propylene-dicyclopentadiene copolymers, propylene-5-ethylidene-2-norbornene copolymers, propylene-2,5-norbornadiene copolymers, propylene-5-ethylidene-2-norbornene copolymers, 1-octene-ethylene copolymers, and 1-butene-propylene copolymers. Binary copolymers such as ethylene-propylene-1-butene copolymer, 1-butene-1-hexene copolymer, 1-butene-4-methyl-1-pentene copolymer, 1-butene-1-octene copolymer, 1-butene-1-decene copolymer, 1-butene-1,4-hexadiene copolymer, 1-butene-dicyclopentadiene copolymer, 1-butene-5-ethylidene-2-norbornene copolymer, 1-butene-2,5-norbornadiene copolymer, 1-butene-5-ethylidene-2-norbornene copolymer, ethylene-propylene-1-butene copolymer, ethylene-propylene-1-hexene copolymer, ethylene-propylene-1-octene copolymer, ethylene-propylene-1-octene copolymer, ethylene-propylene-1,4-hexadiene copolymer, ethylene-propylene-1,4-hexadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-5-ethylidene-2-norbornene copolymer, ethylene-propylene-5-ethylidene-2-norbornene copolymer, ethylene-propylene-2,5-norbornadiene copolymer, ethylene-propylene-2,5-norbornadiene copolymer, ethylene-propylene-5-ethylidene-2-norbornene copolymer, ethylene-propylene-5-ethylidene-2-norbornene copolymer, 1-butene-ethylene-propylene copolymer, 1-butene-ethylene-1-hexene copolymer, 1-butene-ethylene-1-octene copolymer, 1-butene-propylene - Multi-component copolymers such as 1-octene copolymer, 1-butene-ethylene-1,4-hexadiene copolymer, 1-butene-propylene-1,4-hexadiene copolymer, 1-butene-ethylene-dicyclopentadiene copolymer, 1-butene-propylene-dicyclopentadiene copolymer, 1-butene-ethylene-5-ethylidene-2-norbornene copolymer, 1-butene-propylene-5-ethylidene-2-norbornene copolymer, 1-butene-ethylene-2,5-norbornadiene copolymer, 1-butene-propylene-2,5-norbornadiene copolymer, 1-butene-ethylene-5-ethylidene-2-norbornene copolymer, 1-butene-propylene-5-ethylidene-2-norbornene copolymer, etc. Among these, ethylene-α-olefin copolymers such as polypropylene and ethylene-propylene copolymer are preferably used.

[0024] The content of the acid-modified component in the acid-modified olefin resin is preferably 1% by mass or more and 10% by mass or less, preferably 1% by mass or more and 8% by mass or less, and more preferably 2% by mass or more and 7% by mass or less, from the viewpoint of adhesion between the adhesive layer and the adjacent layer. Examples of the acid-modified component include unsaturated carboxylic acids. Specific examples include maleic acid, fumaric acid, acrylic acid, crotonic acid, methacrylic acid, itaconic acid, and acid anhydrides of these acids. Of these, it is preferable to use maleic anhydride, maleic acid, or acrylic acid. The acid-modified olefin resin is preferably a polyolefin modified with maleic anhydride, and particularly preferably maleic anhydride-modified polyethylene.

[0025] The acid-modified olefin resin may be produced by a conventional method, for example, by graft polymerizing an unsaturated carboxylic acid onto the polyolefin under conventional conditions, for example, stirring under heating, or may be a commercially available product, such as a polymer obtained by grafting maleic anhydride onto LDPE, HDPE, LLDPE, PS, or PP.

[0026] The polypropylene resin may contain at least one type of polypropylene resin, and may be composed of only one type or a plurality of types.

[0027] The reason why the content ratio of the polypropylene-based resin is 90% by weight or more of the resin constituting the entire polypropylene-based packaging body is that if the content ratio of the polypropylene-based resin is less than 90% by weight of the resin constituting the entire polypropylene-based packaging body, the purity of the polypropylene in the used polypropylene-based packaging body may be insufficient, making it impossible to perform mechanical recycling.

[0028] The method for making the content of the polypropylene-based resin 90% by weight or more of the resin constituting the entire polypropylene-based packaging body is not particularly limited. For example, the multilayer film and the container can be made of a polypropylene-based resin composition whose content is adjusted so that the polypropylene-based resin is the main component, or the multilayer film and the container can be made of a member (layer) made of the polypropylene-based resin and a member (layer) made of a resin other than the polypropylene-based resin, and the content of the polypropylene-based resin in the resin constituting the entire polypropylene-based packaging body can be controlled by adjusting the ratio of each member (layer).

[0029] (Conditions (c), (c1)) The multilayer film contains an ethylene-vinyl alcohol copolymer in an amount of 5% by weight or less of the resin constituting the entire film (condition (c1)). Furthermore, the container contains a gas barrier resin in an amount of 5% by weight or less of the resin constituting the entire container (condition (c)). By containing small amounts of a gas barrier resin such as an ethylene-vinyl alcohol copolymer in both the multilayer film and the container, the gas barrier properties required for polypropylene-based packaging can be maintained without impairing the above-mentioned recyclability.

[0030]

[0023] From the viewpoint of maintaining a high content of the polypropylene-based resin, the content of the ethylene-vinyl alcohol copolymer in the multilayer film and the content of the gas barrier resin in the container must each be 5% by weight or less of the resin constituting the entire multilayer film and the entire container. That is, in the polypropylene-based packaging body of this embodiment, the content of the gas barrier resin is 5% by weight or less of the entire packaging body. Furthermore, from the viewpoint of more reliably maintaining the gas barrier properties required for the multilayer film and the container, it is preferable that the content of the ethylene-vinyl alcohol copolymer in the multilayer film and the content of the gas barrier resin in the container are both 1% by weight or more of the resin constituting the entire multilayer film and the entire container.

[0031] The gas barrier resin contained in the container is not particularly limited as long as it can impart gas barrier properties, and can be appropriately selected depending on the required performance. Examples of the gas barrier resin include ethylene-vinyl alcohol copolymer (EVOH), polyamide-based resins, polyester-based resins, and polyvinylidene chloride-based resins. Among these, ethylene-vinyl alcohol copolymer (EVOH) or polyamide-based resins are preferred from the viewpoint of being particularly excellent in gas barrier properties and stretch moldability and suitable for mechanical recycling, and more preferably ethylene-vinyl alcohol copolymer (EVOH), as with the multilayer film. The gas barrier resin may be one type, or multiple types may be used in combination.

[0032] Furthermore, the ethylene-vinyl alcohol copolymer tends to have better stretchability because the crystallinity and melting point decrease as the content of structural units derived from ethylene (sometimes referred to as the ethylene content in this specification) increases. Generally, the melting point is 183°C when the ethylene content is 32 mol%, 173°C when it is 38 mol%, and 163°C when it is 44 mol%. On the other hand, the gas barrier property per unit thickness of the ethylene-vinyl alcohol copolymer tends to improve as the ethylene content decreases. Therefore, in the multilayer film of this embodiment, the ethylene content of the ethylene-vinyl alcohol copolymer is 32 mol% or more and 45 mol% or less (condition (d)). An ethylene content within the above range allows for the production of a film with excellent stretchability and gas barrier properties. When the container contains an ethylene-vinyl alcohol copolymer, the ethylene content of the ethylene-vinyl alcohol copolymer is preferably 30 mol% or more and 60 mol% or less, more preferably 31 mol% or more and 50 mol% or less, and even more preferably 32 mol% or more and 45 mol% or less.

[0033] The gas barrier property tends to be better as the interaction between molecular chains increases, and ethylene-vinyl alcohol copolymers in particular have high gas barrier property due to their high intermolecular interaction. However, because the interaction between molecular chains is high, heat shrinkage stress is large, and when used as a shrink (heat-shrinkable) film, container deformation of polypropylene-based packaging materials is likely to occur.

[0034] By controlling the crystal structure, the ethylene-vinyl alcohol copolymer can achieve both a melting point of 180°C or less (preferably 170°C or less) and an ethylene content of 45 mol% or less. Furthermore, by using a saponified ethylene-vinyl alcohol copolymer having a larger supercooling temperature difference, which is the difference between the melting point and the crystallization temperature by cooling, compared to a typical ethylene-vinyl alcohol copolymer, the lamella thickness becomes small and the crystals become more uniform. In the case of a core layer containing such an ethylene-vinyl alcohol copolymer, stress concentration is reduced, and container deformation during gas pack packaging can be suppressed.

[0035] Furthermore, the supercooling temperature difference is preferably 25°C or higher, more preferably 26°C or higher, and even more preferably 27°C or higher. The reason for this effect is not entirely clear, but is thought to be as follows. The heat shrinkage properties of a multilayer film are exhibited when the amorphous portions, which have been stretched due to the molecular orientation of the constituent resins, relax and attempt to return to a non-oriented state, and the crystalline portions serve to prevent the shrinkage of the amorphous portions up to near the melting temperature. Generally, ethylene-vinyl alcohol copolymers have strong intermolecular interactions and large heat shrinkage stress, which tends to dominate the heat shrinkage stress of the entire multilayer film. However, by controlling the crystalline structure, it is thought that stress concentration due to relaxation of the orientation of the amorphous and crystalline portions can be suppressed, and a multilayer film with excellent barrier properties can be provided.

[0036] Examples of polyamide resins used as the gas barrier resin include polyamides with a head group of polyamide 6, polyamide 66, polyamide 610, polyamide 11, polyamide 12, polyamide 6 / 66, polyamide 6 / 12, polyamide 6 / 610, polyamide 6 / 66 / 12, polyamide 6 / 66 / 610, and polyamide 6 / 66 / 612.

[0037] <Multilayer film> In addition to satisfying the above-mentioned conditions (a) to (c1), the multilayer film of this embodiment has a heat shrinkage rate of 10% or more and 30% or less in the machine direction (MD) at 100°C and a heat shrinkage rate of 10% or more and 30% or less in the width direction (TD) at 100°C, a maximum heat shrinkage stress of 4.0 MPa or less in the machine direction (MD) at 100°C and a maximum heat shrinkage stress of 4.0 MPa or less in the width direction (TD) at 100°C.

[0038] By setting the heat shrinkage rate of the multilayer film of this embodiment at 100°C in both the longitudinal direction (MD) and the transverse direction (TD) to 10% or more and 30% or less, and setting the maximum heat shrinkage stress at 100°C in both the longitudinal direction (MD) and the transverse direction (TD) to 4.0 MPa or less, it is possible to suppress a decrease in airtightness and strength due to the seal coming off or the container being deformed due to residual stress caused by shrinkage of the film after the multilayer film is heat-sealed to the container.

[0039] The reason why the heat shrinkage percentages of the multilayer film of this embodiment in both the machine direction (MD) and the width direction (TD) at 100°C are specified as 10% to 30% is that a heat shrinkage percentage of 10% or more can suppress excessive shrinkage of the multilayer film and improve conformability, while a heat shrinkage percentage of 30% or less can suppress deterioration of sealing performance and deformation of the container. From the same perspective, the heat shrinkage percentages of the multilayer film in both the machine direction (MD) and the width direction (TD) at 100°C are preferably 12% to 28%, and more preferably 15% to 25%. The heat shrinkage percentage can be measured in accordance with ASTM D-2732. A film cut into a square measuring 100 mm in both directions was placed in a thermostatic chamber set at an ambient temperature of 100°C for 30 minutes, and the heat shrinkage percentage was calculated using the following formula. Two tests were performed. Heat shrinkage rate (%) = 100 x (100 - W) / 100 W: Dimensions of the film after removal from the thermostatic chamber

[0040] The maximum heat shrinkage stress at 100°C in both the machine direction (MD) and the width direction (TD) of the multilayer film of this embodiment is set to 4.0 MPa or less because a maximum heat shrinkage stress of 4.0 MPa or less enhances the conformability of the multilayer film and suppresses deterioration of sealability and deformation of the container. From the same perspective, the maximum heat shrinkage stress at 100°C in both the machine direction (MD) and the width direction (TD) of the multilayer film is preferably 3.5 MPa or less, and more preferably 3.0 MPa or less. The maximum heat shrinkage stress can be measured in accordance with ASTM-D2838. The film was sampled into a strip measuring 90 mm in the machine direction / width direction (50 mm measurement length + 40 mm zipper grip), and 10 mm in the width direction / length direction. The maximum heat shrinkage stress was measured after immersion in an oil bath at 100°C for 3 minutes. Five tests were performed.

[0041] Furthermore, the multilayer film of this embodiment preferably has a tear strength in the machine direction (MD) of 3.0 cN or more and 20.0 cN or less, and a tear strength in the transverse direction (TD) of 7.0 cN or more and 20.0 cN or less. By setting the tear strengths in both the machine direction (MD) and the transverse direction (TD) of the multilayer film to 7.0 cN or more, the strength of the multilayer film can be better maintained, and by setting them both to 20.0 cN or less, the multilayer film can be imparted with flexibility and improved conformability. From the same viewpoint, the tear strength in the machine direction (MD) of the multilayer film is preferably 3.5 cN or more and 19.5 cN or less, and more preferably 4.0 cN or more and 19.0 cN or less. The tear strength in the transverse direction (TD) is preferably 7.5 cN or more and 19.5 cN or less, and more preferably 8.0 cN or more and 19.0 cN or less. The tear strength can be measured in accordance with JIS-K-7128 using a light-load tear tester (manufactured by Toyo Seiki Co., Ltd.). The film was sampled into a rectangular shape measuring 63.5 mm in the length direction / or width direction and 50.0 mm in the width direction / or length direction, and the tear strength was measured in an atmosphere at a temperature of 23°C and a relative humidity of 50%. The number of tests was n=5.

[0042] 2, the multilayer film 10 of this embodiment is preferably composed of at least five layers, with the heat seal layer 11 as the innermost layer, and the following layers formed in this order toward the outermost layer: an inner intermediate layer 12, a core layer 13, an outer intermediate layer 14, and an outermost layer 15. By having the multilayer film 10 have such a layer structure, the conformability and strength of the multilayer film can be improved, and deterioration of the sealability can be suppressed, and good gas barrier properties can also be maintained.

[0043] Heat Seal Layer The heat seal layer is the innermost layer of the multilayer film (the layer closest to the container), and as its name suggests, is a layer formed to adhere to the container by heat and seal the polypropylene-based packaging body.

[0044] The resin used in the heat seal layer is not particularly limited. For example, polypropylene-based resins, polyethylene-based resins, etc. can be used. Examples of the polyethylene-based resin include ethylene homopolymers, ethylene-α-olefin copolymers, and ethylene-vinyl acetate copolymers. The thermoplastic resins may be used alone or in combination of two or more. They may be selected from polyethylene, ethylene copolymers such as ethylene-α-olefin copolymers and ethylene-vinyl acetate copolymers, or mixtures thereof. Among these, the polypropylene-based packaging body of this embodiment preferably contains at least a polypropylene-based resin from the viewpoint of satisfying the above-mentioned condition (b). The composition of the polypropylene-based resin is as described above.

[0045] The polyethylene resin used in the heat seal layer may be polymerized using a known catalyst such as a single-site catalyst or a multi-site catalyst, and from the viewpoint of achieving even better transparency, strength, and heat sealability of the film, it is preferable to polymerize using a single-site catalyst.

[0046] In addition, the polyethylene resin has a density of 860 kg / m from the viewpoint of further improving the heat sealability at low temperatures. ３ More than 960kg / m ３ It is preferable that the value is equal to or less than 870 kg / m ３ More than 955kg / m ３ More preferably, it is 875 kg / m or less. ３ More than 950kg / m ３ The lower the density of the polyethylene resin, the more improved the heat sealability at low temperatures. ３ If it is less than this, the heat sealability tends to be improved.

[0047] Furthermore, from the viewpoint of low-temperature heat sealing properties and stretch moldability, the melting point (Tm) of the resin constituting the heat seal layer is preferably 60°C or higher but lower than 160°C, more preferably 65 to 150°C, and even more preferably 70 to 140°C. The melting point can be measured, for example, using differential scanning calorimetry (DSC). 5 mg of resin was weighed, and in order to cancel the thermal history of the resin, the temperature was first increased at a rate of 10°C / min, and then decreased at a rate of 10°C / min. The temperature was then increased again at a rate of 10°C / min, and the resulting curve was taken as a DSC curve. This DSC curve can be analyzed according to a method in accordance with JIS K7122 to determine the melting point and glass transition point.

[0048] Furthermore, the heat seal layer preferably further contains an anti-fogging agent in addition to the polypropylene-based resin. This suppresses fogging of the multilayer film and achieves better appearance. The anti-fogging agent is not particularly limited. Examples include mono-, di-, tri-, and poly-fatty acid esters of glycerin, as well as monoglycerin esters, diglycerin esters, triglycerin esters, and tetraglycerin esters of saturated or unsaturated fatty acids having 8 to 18 carbon atoms. Among these, those primarily composed of diglycerin oleate, diglycerin laurate, glycerin stearate, glycerin monooleate, or a mixture thereof are preferred because they are less likely to impair the film's slipperiness and optical properties. Furthermore, the addition of an ethylene oxide adduct can impart good anti-fogging properties by reducing the surface tension of water droplets. Examples of ethylene oxide adducts include polyoxyethylene alkyl ethers. The heat seal layer may also contain components other than the thermoplastic resin and the anti-fogging agent. For example, any additives such as thermoplastic resins, various surfactants, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, colorants, and inorganic fillers may be contained within the range that does not impair the properties of the composition.

[0049] Core layer: The core layer is the central layer of the multilayer film and is formed to impart gas barrier properties and water vapor barrier properties. Therefore, the core layer contains an ethylene-vinyl alcohol copolymer in order to satisfy the above-mentioned condition (c1). The composition of the ethylene-vinyl alcohol copolymer is as described above.

[0050] The gas barrier properties of the entire multilayer film including the core layer are as follows: oxygen permeability at 23°C and 65% RH is 300 cc / (m ２ The oxygen permeability can be measured, for example, in accordance with JIS K7126-1 (differential pressure method) under conditions of 23° C. and 65% RH.

[0051] Furthermore, the water vapor barrier property of the entire multilayer film including the core layer is such that the water vapor permeation amount of the multilayer film at 40°C is 16 g / (m ２ The water vapor permeability can be measured, for example, in accordance with ASTM F1249 under conditions of 40°C and 90% RH.

[0052] The oxygen permeability and water vapor permeability can be appropriately adjusted by, for example, the composition of the resin constituting the core layer, the thickness of the core layer, and the like.

[0053] Outermost layer: The outermost layer is a layer that constitutes the outer surface of the multilayer film. Here, from the viewpoint of satisfying the above-mentioned condition (b), the outermost layer preferably contains at least a polypropylene-based resin. The composition of the polypropylene-based resin is as described above.

[0054] The outermost layer is preferably composed solely of a polypropylene-based resin from the viewpoint of satisfying the above-mentioned condition (b). However, a small amount of a polyamide resin may also be contained from the viewpoint of a balance between heat resistance, transparency, stretchability, etc. Examples of the polyamide resin include aliphatic amide resins such as nylon-6 and nylon-12, aliphatic amide copolymers such as nylon-6,66 and nylon-6,12, and aliphatic terpolymers such as nylon-6,66,12. Of these, nylon-6,66 is preferred because it provides high heat shrinkability. The outermost layer may also contain components other than the thermoplastic resin. For example, the outermost layer may contain any additives such as known crystal nucleating agents, thermoplastic resins, various surfactants, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, UV absorbers, colorants, and inorganic fillers, provided that the properties of the outermost layer are not impaired.

[0055] Inner Intermediate Layer, Outer Intermediate Layer The inner intermediate layer and outer intermediate layer are layers for imparting adhesion between the core layer, the heat seal layer, and the outermost layer. The inner intermediate layer and outer intermediate layer contain at least a resin and may further contain additives. Examples of resins constituting the inner intermediate layer and outer intermediate layer include thermoplastic resins. Examples of the thermoplastic resin include acid-modified olefin-based resins, modified olefin-based resins such as modified LLDPE, and olefin-based resins. The composition of the acidic olefin-based resin is as described above.

[0056] Examples of the olefin (olefin monomer) constituting the olefin-based resin include ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Among these, it is preferable to use propylene (containing a polypropylene-based resin) from the viewpoint of satisfying the above-mentioned condition (b). The constitution of the polypropylene-based resin is as described above.

[0057] The melt flow rate (MFR) of the resin contained in the inner intermediate layer and the outer intermediate layer is preferably 1 to 20 g / 10 min, more preferably 1.5 to 10 g / 10 min, and even more preferably 2 to 8 g / 10 min, from the viewpoints of adhesive strength with adjacent layers and stretch moldability. The melt flow rate can be measured, for example, in accordance with JIS K7210 or ASTM D1238, at a temperature of 190°C or 230°C and a load of 2.16 kg. It is preferable that at least one of the resins contained in the inner intermediate layer and the outer intermediate layer satisfies the above MFR, and it is more preferable that all of the resins satisfy the above MFR.

[0058] The melting points (Tm) of the resins contained in the inner intermediate layer and the outer intermediate layer can be measured by the same method as that for measuring the melting point (Tm) of the resin constituting the heat seal layer.

[0059] (Method for producing multilayer film) The method for producing the multilayer film is not particularly limited, but the following method can be mentioned in this example. The method for producing a multilayer film according to this embodiment preferably includes a step of laminating a laminate having at least five resin layers (hereinafter sometimes referred to as "unstretched raw sheet") by a co-extrusion method and heat-stretching the laminate. The co-extrusion method will be described below.

[0060] In the co-extrusion method, each material is melt-extruded from a separate extruder, laminated in a multi-layer die, melt-co-extruded, and quenched to obtain an unstretched raw sheet. Here, the melt-co-extrusion method is not particularly limited, and examples thereof include a method using a multi-layer T-die or a multi-layer circular die (annular die). Among these, a method using a multi-layer circular die is preferred. The use of a multi-layer circular die is advantageous in terms of the required space and investment amount for equipment, is suitable for small-lot production of a wide variety of products, and makes it easier to obtain the desired heat shrinkage rate.

[0061] As the refrigerant used for rapid cooling, water at 60°C or less is usually suitably used. The refrigerant can be brought into direct contact with the molten resin or can be used indirectly as an internal refrigerant for the metal roll. When used as an internal refrigerant, other known refrigerants such as oil can be used in addition to water, and in some cases, it can also be used in combination with blowing cold air.

[0062] In the stretching step, the unstretched raw sheet obtained is heated, for example, to a temperature equal to or higher than the softening temperature of the resin constituting the unstretched raw sheet, and stretched, for example, in the MD (machine direction: longitudinal direction (length direction)) by 1.5 times or more and in the TD (transverse direction: transverse direction (width direction)) by 1.5 times or more. By such a stretching step, the above-mentioned multilayer film can be easily obtained.

[0063] The stretching ratio is appropriately selected depending on the purpose, and if necessary, a heat treatment (thermal relaxation treatment) can be performed after stretching. The thermal relaxation treatment relaxes the molecular orientation of the multilayer film, thereby further suppressing dimensional changes during transportation and / or storage.

[0064] The stretching step can also be carried out by a direct inflation method, in which air or nitrogen is blown into a tube immediately after melt extrusion to perform stretching. This method also makes it easy to obtain a multilayer film with a predetermined heat shrinkage rate. However, to more reliably achieve an appropriate heat shrinkage rate, a biaxial stretching method is preferred, and a tubular method (also known as a double bubble method) in which an unstretched raw sheet obtained using the circular die described above is heated and biaxially stretched is more preferred. That is, the multilayer film of this embodiment is preferably a biaxially stretched multilayer film produced by a tubular method involving biaxial stretching.

[0065] The above-mentioned production method may include a crosslinking step of crosslinking the resin before or after stretching. When crosslinking is performed, it is preferable to perform the crosslinking treatment by irradiating with energy rays before heating and stretching the resin. This increases the melt tension of the laminate during heat stretching, making it possible to further stabilize the stretching. The laminate after stretching may also be irradiated with energy rays to crosslink the resin. Examples of energy rays that can be used include ionizing radiation such as ultraviolet rays, electron beams, X-rays, and gamma rays. Of these, electron beams are preferred.

[0066] <Container> The container constituting the polypropylene-based packaging body of this embodiment is a container 20 adhered to the multilayer film 10 as shown in FIG.

[0067] For example, the polypropylene-based resin composition used for the container may contain any additives such as known crystal nucleating agents, thermoplastic resins, various surfactants, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, colorants, and inorganic fillers, as long as the effects of the present invention are not impaired.

[0068] Furthermore, the container may be formed of a polyethylene sheet or a multilayer sheet including a barrier layer, if necessary, from the viewpoint of stain resistance, heat sealing properties with a multilayer film, gas barrier properties, etc.

[0069] The method for producing the container is not particularly limited and can be appropriately selected depending on the shape of the container and the required performance. For example, the container can be obtained by molding the polypropylene resin composition using various molding machines such as a known extrusion molding machine, an injection molding machine, a direct blow molding machine, a stretch blow molding machine, a film molding machine, or a fiber molding machine.

[0070] The use of the polypropylene-based packaging material of this embodiment including the container is not particularly limited, but is preferably used for storing goods, such as a container for storing goods, a lid for the container, or a bag for storing goods.More specifically, food containers (rice containers, side dish containers, meat and fish containers, processed food containers, soup containers, pudding containers, jelly containers, yogurt containers, chawanmushi containers, instant ramen containers, retort containers, lunch box containers, microwave heating containers, microwave cooking containers, Ziploc® containers, etc.), bags (zipper bags, slider bags, Ziploc® bags, chuck bags, bread bags, snack bags, plastic shopping bags, eco-bags, various packaging bags, etc.), films (tobacco films, various packaging films, sealant films, multi-layer films, single-layer films, barrier films, etc.), food wraps, plastic wraps, beverage containers (drink bottles, coffee containers, juice containers, other beverage containers, etc.), caps (PET bottle caps, condiment caps, cosmetic container caps, etc.), pharmaceutical containers (infusion bags, blood bags, pre-filled syringes, kit preparations, eye drop containers, drug solution containers, pharmaceutical containers, long-term liquid storage containers, PTP sheets, etc.), medical devices (disposable disposable syringes and their parts, catheter tubes, vacuum blood collection tubes, surgical nonwoven fabrics, blood filters, disposable instruments such as blood circuits, parts for artificial organs such as artificial lungs and artificial anus, dialyzers, test tubes, centrifuge tubes, sutures, compress base materials, dental material parts, orthopedic material parts, contact lens cases, etc.), various other containers (ink bottles, cosmetic containers, etc.), daily necessities (wardrobe cases, buckets, washbasins, writing implements, containers, toys, cooking utensils, zipper bags, Ziploc bags (regular (registered trademark) containers, Ziploc® bags, and various other cases), automotive parts (instrument panels, bumpers, lighting fixtures, etc.), storage boxes (wrap boxes, Saran Wrap® boxes, returnable boxes, shipping boxes, beer cases, sake cases, etc.), fillers, stationery, insulation boards, insulation materials, insulated containers, electric and electronic parts (members and housings for various electric devices, semiconductor transport containers, optical parts, various information media cases, solar cell encapsulants, etc.), water purification materials, electric wire coating materials, various coating materials, films, fibers, sheets, etc.

[0071] The present invention will be described in detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0072] [Examples 1 to 9, Reference Examples, and Comparative Examples 1 to 12] (1) Preparation of Multilayer Films Each sample of the multilayer film in the Examples and Comparative Examples was prepared under the conditions shown in Tables 1 and 2. While the method for producing the multilayer film is not particularly limited, in these Examples, each sample was prepared by coextrusion. The melt coextrusion conditions included a multilayer circular die and water at 60°C or less as the refrigerant. The stretching process employed a tubular method in which the unstretched raw fabric obtained using the circular die was biaxially stretched. Each multilayer film was prepared by sequentially forming an inner intermediate layer, a core layer, an outer intermediate layer, and an outermost layer, starting with the heat seal layer as the innermost layer and moving toward the outermost layer. The polypropylene resin content of each multilayer film sample is shown in Tables 1 and 2. (2) Preparation of Polypropylene-Based Packaging Each sample of the obtained multilayer film was sealed in a container using a "Traysealer T100 (manufactured by Multivac Japan Co., Ltd.)" at a temperature of 125°C for 1.5 seconds to prepare each sample of polypropylene-based packaging. The container used was a cold-resistant PP (polypropylene) M-100-50H (100mm x 100mm x 50mm, manufactured by Akamatsu Chemical Industry Co., Ltd.) laminated with an LLDPE (low-density polyethylene) film "LL-XMTN (manufactured by Futamura Chemical Co., Ltd.)." The polypropylene resin content and gas barrier resin content in each polypropylene-based packaging sample are shown in Tables 1 and 2.

[0073] The resins and additives used in each example and comparative example are as follows: PP1: propylene homopolymer, density 900 kg / m ３ , MFR 3.5 g / 10 min (230 ° C) PP2: ethylene-propylene copolymer, density 900 kg / m ３ , MFR 5.3 g / 10 min (230 ° C) PP3: ethylene-propylene copolymer, density 876 kg / m ３ , MFR 2.0 g / 10 min (230 ° C) PP4: ethylene-propylene copolymer, density 876 kg / m ３, MFR 8.0 g / 10 min (230 ° C) PP5: Propylene-α-olefin copolymer, MFR 7.0 g / 10 min (230 ° C) PP6: Ethylene-propylene copolymer, density 900 kg / m ３ , MFR 7.5 g / 10 min (230 ° C) LLDPE1: ethylene-α-olefin copolymer, density 903 kg / m ３ , MFR 1.2 g / 10 min (190 ° C) LLDPE2: ethylene-α-olefin copolymer, density 903 kg / m ３ , MFR 3.8 g / 10 min (190 ° C) LLDPE3: ethylene-α-olefin copolymer, density 904 kg / m ３ , MFR 2.0 g / 10 min (190 ° C) LLDPE4: ethylene-α-olefin copolymer, density 937 kg / m ３ , MFR 2.3 g / 10 min (190 ° C) PPGL1: modified polypropylene polymer, density 896 kg / m ３ , MFR 7.7 g / 10 min (230 ° C) PPGL2: modified polypropylene polymer, density 901 kg / m ３ , MFR 3.0 g / 10 min (230 ° C) PEGL1: Modified ethylene-α-olefin copolymer, density 907 kg / m ３ , MFR 2.3 g / 10 min (190 ° C) PEGL2: modified ethylene-α-olefin copolymer, density 910 kg / m ３ , MFR 6.2 g / 10 min (190 ° C) EVOH1: ethylene vinyl alcohol copolymer, density 1210 kg / m ３ , MFR 4.0 g / 10 min (210 ° C), ethylene content 27 mol% EVOH2: ethylene vinyl alcohol copolymer, density 1210 kg / m ３ , MFR 3.8 g / 10 min (210 ° C), ethylene content 29 mol% EVOH3: ethylene vinyl alcohol copolymer, density 1190 kg / m ３ , MFR 3.8 g / 10 min (210 ° C), ethylene content 32 mol% EVOH4: ethylene vinyl alcohol copolymer, density 1160 kg / m ３, MFR 4.0 g / 10 min (210 ° C), ethylene content 38 mol%) EVOH5: ethylene vinyl alcohol copolymer, density 1140 kg / m ３ , MFR 3.5 g / 10 min (210 ° C), ethylene content 44 mol% EVOH6: ethylene vinyl alcohol copolymer, density 1120 kg / m ３ , MFR 6.4 g / 10 min (210 ° C), ethylene content 48 mol% NY1: Polyamide 6 / 66 copolymer, density 1140 kg / m ３ NY2: Polyamide 6, density 1140 kg / m ３ SEBS1: Hydrogenated styrene-based thermoplastic elastomer, density 890 kg / m ３ , MFR 13.0 g / 10 min (230°C) EVA1: ethylene-vinyl acetate copolymer, MFR 2.3 g / 10 min (190°C), vinyl acetate content = 15% EVA2: ethylene-vinyl acetate copolymer, MFR 2.5 g / 10 min (190°C), vinyl acetate content = 18% AF1: mixture of 67 mass% of glycerin monooleate (HLB = 4.3) and 33 mass% of diglycerin laurate (HLB = 7.3) SL1: sodium calcium aluminosilicate hydrate

[0074] <Evaluation> The multilayer film samples and polypropylene packaging samples obtained as described above were evaluated as follows. The evaluation results are shown in Tables 1 and 2.

[0075] (1) Heat Shrinkage of Multilayer Film A multilayer film sample was cut into a square measuring 100 mm in both length and width, and then left to stand in a thermostatic chamber set at an atmospheric temperature of 100°C for 30 minutes, and the heat shrinkage was calculated using the following formula. Note that the number of tests was n=2, and the calculated average value was taken as the heat shrinkage. Heat shrinkage (%)=100×(100−W) / 100 W: Dimensions of the film after removal from the thermostatic chamber

[0076] (2) Maximum Heat Shrinkage Stress of Multilayer Film The maximum heat shrinkage stress of a multilayer film sample was measured in accordance with ASTM-D2838. Specifically, the film was sampled into a strip measuring 90 mm in the machine direction (MD) / or transverse direction (TD) (measurement length 50 mm + chuck grip 40 mm) and 10 mm in the transverse direction (TD) / or machine direction (MD), and the maximum heat shrinkage stress after immersion in an oil bath at 100°C for 3 minutes was measured. The number of tests was n=5, and the calculated average value was taken as the maximum heat shrinkage stress.

[0077] (3) Tear Strength of Multilayer Film The tear strength of a multilayer film sample was measured using a light-load tear tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.) in accordance with JIS-K-7128. Specifically, the film was sampled into a rectangular shape measuring 63.5 mm in the machine direction (MD) / or width direction (TD) and 50.0 mm in the width direction / or machine direction, and the tear strength was measured in an atmosphere at a temperature of 23°C and a relative humidity of 50%. The number of tests was n=5, and the calculated average value was taken as the tear strength.

[0078] (4) Water Vapor Barrier Properties of Multilayer Films For multilayer film samples, the water vapor transmission rate (%) was measured under conditions of 40°C and 90% RH using a water vapor transmission rate measuring device PERMATRAN W3-98 (manufactured by MOCON Corporation) in accordance with ASTM F1249. The measured water vapor transmission rates were evaluated according to the following criteria: ◯ (Excellent water vapor barrier): Water vapor transmission rate of 16 g / (m ２ × (poor water vapor barrier properties): Water vapor permeation rate is less than 16 g / (m ２ ・day) or more.

[0079] (5) Oxygen Gas Barrier Property of Multilayer Film For multilayer film samples, oxygen permeability (%) was measured under conditions of 23°C and 65% RH in accordance with JIS K7126-1 (differential pressure method) using differential pressure gas / vapor permeability measuring devices [GTR-30XAD2, G2700T.F] and [GTR-30XAD, G6800T.F(S)] (manufactured by GTR Tech Co., Ltd. and Yanaco Technical Science Co., Ltd.). The measured oxygen permeability was evaluated according to the following criteria. ◯ (Excellent oxygen gas barrier property): Oxygen permeability of 300 cc / (m ２ × (poor oxygen gas barrier properties): oxygen permeation rate is less than 300 cc / (m ２ ·day·MPa) or more.

[0080] (6) Container Deformation The dimension (X) of each polypropylene packaging sample was measured, the deformation rate was calculated as follows, and the container deformation was evaluated according to the following criteria: Deformation rate (%) = 100 x (100 - X) / 100 Good (small container deformation): Both the vertical and horizontal deformation rates of the polypropylene packaging were less than 10%. Bad (large container deformation): At least one of the vertical and horizontal deformation rates of the polypropylene packaging was 10% or more.

[0081] (7) Airtightness A sample of a polypropylene-based package prepared by putting 100 g of water into it was left standing horizontally in a room at 20°C, and the amount of moisture immediately after packaging and after 24 hours (Y = weight of polypropylene-based package immediately after packaging - weight of polypropylene package after 24 hours) was measured, and the moisture loss rate was calculated as follows and evaluated according to the following criteria: Moisture loss rate (%) = 100 x (100 - Y) / 100 Good (excellent airtightness): Moisture loss rate is 99.5% or more Poor (poor airtightness): Moisture loss rate is less than 99.5%

[0082] (8) Anti-Fogging Properties A sample of a polypropylene-based package prepared by putting 100 g of water in it was placed horizontally in a refrigerator at 5°C, and the state of the water film and water droplets on the inside of the film was visually observed immediately after being placed and after 24 hours had passed, and the anti-fogging properties were evaluated according to the following criteria: ○ (Excellent): A uniform water film was formed on the inside surface of the film, or the formed water film was slightly patchy but free of water droplets. △ (Good): One to three or fewer water droplets were present over the entire surface of the film. × (Poor): A large water droplet was present in the center of the film.

[0083] (9) Stretchability The unstretched raw fabric sample obtained with the circular die was cut into a square of 100 mm lengthwise and widthwise, and then preheated to 90°C for 1 minute. Using a biaxial stretching tester EX10 (manufactured by Toyo Seiki Seisaku-sho, Ltd.), the sample was stretched 3.0 times lengthwise and widthwise at a speed of 1,000 mm / min, and the stretchability was evaluated according to the following criteria. The number of tests was n=5. ◯ (Excellent stretchability): No breakage of the multilayer film occurred during stretching. Δ (Good stretchability): Breakage of the multilayer film occurred once during stretching. × (Poor stretchability): Breakage of the multilayer film occurred two or more times during stretching.

[0084] From the results in Tables 1 and 2, it can be seen that each sample of the Examples showed well-balanced and good results in all evaluation items. On the other hand, it can be seen that each sample of the Comparative Examples showed inferior results compared to the Examples in at least one evaluation item. Furthermore, it can be seen that the polypropylene-based packaging bodies of each sample of the Examples also have excellent recyclability, since the content ratio of polypropylene-based resin in each sample is 90% by weight or more.

[0085] According to the present invention, it is possible to provide a multilayer film and a polypropylene-based packaging material that have excellent airtightness, gas barrier properties and strength, and that can be mechanically recycled after use.

[0086] REFERENCE SIGNS LIST 10 Multilayer film 11 Heat seal layer 12 Inner intermediate layer 13 Core layer 14 Outer intermediate layer 15 Outermost layer 20 Container 100 Polypropylene-based packaging body

Claims

1. A multilayer film comprising: (a) at least one polypropylene-based resin; (b) the content of said polypropylene-based resin is 90% by weight or more of the resin constituting the entire film; (c1) an ethylene-vinyl alcohol copolymer is 5% by weight or less of the resin constituting the entire film; and (d) the ethylene content of said ethylene-vinyl alcohol copolymer is 32 to 45 mol%, wherein the multilayer film has a heat shrinkage rate of 10% or more and 30% or less in the machine direction (MD) at 100°C and a heat shrinkage rate of 10% or more and 30% or less in the transverse direction (TD) at 100°C; and wherein the multilayer film has a maximum heat shrinkage stress of 4.0 MPa or less in the machine direction (MD) and a maximum heat shrinkage stress of 4.0 MPa or less in the transverse direction (TD) at 100°C.

2. The multilayer film according to claim 1, characterized in that it is composed of at least five layers, with the heat seal layer being the innermost layer, followed by an inner intermediate layer, a core layer, an outer intermediate layer and an outermost layer in that order.

3. The multilayer film according to claim 2, wherein the heat seal layer contains a polypropylene-based resin and an anti-fogging agent.

4. The multilayer film according to claim 2, wherein the outermost layer comprises a polypropylene-based resin.

5. The multilayer film according to claim 1, characterized in that the tear strength in the machine direction (MD) is 3.0 cN or more and 20.0 cN or less, and the tear strength in the transverse direction (TD) is 7.0 cN or more and 20.0 cN or less.

6. Water vapor permeability at 40°C is 16 g / (m ２ 2. The multilayer film of claim 1, wherein the film has a viscosity of less than 1000 saturations per minute (day).

7. Oxygen permeability at 23°C and 65% RH is 300cc / (m ２ 2. The multilayer film according to claim 1, wherein the modulus of elasticity is less than 1 / 2 day / MPa.

8. A polypropylene-based packaging body comprising a plastic container and a multilayer film that serves as a lid for the container, wherein the container: (a) comprises at least one polypropylene-based resin; (b) the content of the polypropylene-based resin is 90% by weight or more of the resin that constitutes the entire container; and (c) the container contains a gas barrier resin in an amount of 5% by weight or less of the resin that constitutes the entire container; and the multilayer film is a multilayer film as defined in any one of claims 1 to 7.

9. The polypropylene-based packaging material according to claim 8, wherein the gas barrier resin of the container is an ethylene-vinyl alcohol copolymer.

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