Easily-openable lid material and container with lid

Abstract

As shown in fig. 1, an easily-openable lid material (100) according to the present invention includes at least a base material layer (102), an inorganic particle-containing layer (104), and a sealant layer (106). The inorganic particle-containing layer (104) contains a polypropylene-based resin, and inorganic particles dispersed in the polypropylene-based resin. The percentage content of the inorganic particles is 25% by mass or more based on the mass of the inorganic particle-containing layer (104). The sealant layer (106) contains a polyethylene-based resin and a polypropylene-based resin. The polyethylene-based resin and the polypropylene-based resin are compatible with each other.

Description

Easy-open lids and containers with lids

[0001] The present invention relates to an easily openable lid material, and more particularly to an easily openable lid material having an inorganic particle-containing layer.

[0002] Conventionally, lid materials containing functional materials such as oxygen absorbers and desiccants, particularly inorganic particles, in the inner layer have been proposed. Such lid materials generally consist of a heat-seal layer, a resin layer containing functional materials such as oxygen absorbers, and a gas barrier layer, and these functional lid materials are tightly integrated with the upper surface of the flange portion of the container body by heat sealing. In such lid materials, achieving both airtightness and ease of opening is a challenge, and various proposals have been made to solve this problem.

[0003] Patent Document 1 discloses an oxygen-depleting sealed container comprising a gas barrier molded container and a lid material that is heat-sealed after an article is placed inside it. The gas barrier molded container has a container body and a flange portion. The lid material is an oxygen-depleting multilayer film in which at least a gas barrier layer made of a gas barrier material, an oxygen absorption layer made of an oxygen-absorbing resin composition containing an iron-based oxygen absorber, and a heat-seal layer made of an unstretched thermoplastic resin are laminated from the outside of the container. The surface layer of the gas barrier molded container and the heat-seal layer of the lid material are heat-sealed at the flange portion of the gas barrier molded container.

[0004] Japanese Patent Publication No. 2003-335367

[0005] While Patent Document 1 can achieve a certain degree of balance between airtightness and ease of opening, it was sometimes insufficient for packaging containers that required high-temperature sterilization. Specifically, in packaging containers requiring retort heat sterilization, it could not withstand the conditions, and unintended peeling of the lid material sometimes occurred.

[0006] The present invention provides a novel easy-open lid material that can suppress unintended peeling under harsh conditions, even when the inorganic particle content of the inorganic particle-containing layer is relatively high.

[0007] The present inventors, after diligent study, have found that the above problems can be solved by the following means, and have completed the present invention. That is, the present invention is as follows: <Aspect 1> An easy-open lid material having at least a base layer, an inorganic particle-containing layer, and a sealant layer, wherein the inorganic particle-containing layer contains a polypropylene resin and inorganic particles dispersed in the polypropylene resin, the content of the inorganic particles is 25% by mass or more with respect to the mass of the inorganic particle-containing layer, and the sealant layer contains a polyethylene resin and a polypropylene resin, and in the sealant layer, the polyethylene resin and the polypropylene resin are mutually compatible. <Aspect 2> The easy-open lid material according to Aspect 1, wherein the polypropylene resin contained in the sealant layer is block polypropylene. <Aspect 3> The easy-open lid material according to Aspect 1 or 2, wherein the inorganic particle-containing layer contains an oxygen absorber, and the base layer is a barrier base layer. <Aspect 4> The easy-open lid material according to Aspect 3, wherein the oxygen absorber contains iron powder. <Aspect 5> An easy-open lid material according to aspect 3 or 4, wherein the barrier substrate layer is composed of a substrate resin layer and a barrier layer. <Aspect 6> An easy-open lid material according to aspect 5, wherein the barrier layer is an inorganic vapor-deposited film or an organic coating film. <Aspect 7> An easy-open lid material according to any one of aspects 1 to 6, wherein the inorganic particle-containing layer has a skin layer on the substrate layer side. <Aspect 8> An easy-open lid material according to aspect 7, wherein the skin layer, the inorganic particle-containing layer, and the sealant layer are fused to each other. <Aspect 9> A container with a lid, comprising a container having a flange portion and a housing portion, and an easy-open lid material according to any one of aspects 1 to 8 heat-sealed to the flange portion of the container, wherein the surface of the container heat-sealed to the easy-open lid material is made of polypropylene resin. <Aspect 10> A container with a lid according to aspect 9, for retort heat sterilization. <Aspect 11> A lidded container containing contents, wherein the contents are contained in the storage section of the lidded container described in Aspect 9 or 10. <Aspect 12> A lidded container containing contents according to Aspect 11, wherein the contents are cooked rice.

[0008] According to the present invention, a novel easy-open lid material that can suppress unintended peeling under severe conditions even when the content of inorganic particles in the inorganic particle-containing layer is relatively high can be provided.

[0009] Figure 1 is a side cross-sectional view of the easy-open lid material of the present invention. Figure 2(a) is a top view of the lidded container of the present invention. Figure 2(b) is a side cross-sectional view taken along line IIb-IIb in Figure 2(a).

[0010] <<Easy-open Lid Material>> The easy-open lid material of the present invention has at least a base material layer, an inorganic particle-containing layer, and a sealant layer, wherein the inorganic particle-containing layer contains a polypropylene-based resin and inorganic particles dispersed in the polypropylene-based resin, the content of the inorganic particles is 25% by mass or more based on the mass of the inorganic particle-containing layer, the sealant layer contains a polyethylene-based resin and a polypropylene-based resin, and in the sealant layer, the polyethylene-based resin and the polypropylene-based resin are mutually compatible.

[0011] In this specification, a polyethylene-based resin is a resin containing more than 50 mol%, 60 mol% or more, 70 mol% or more, or 80 mol% or more of repeating ethylene units in the main chain of the polymer, and is selected from the group consisting of, for example, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), derivatives thereof, and mixtures thereof.

[0012] In this specification, a polypropylene-based resin is a resin containing more than 50 mol%, 60 mol% or more, 70 mol% or more, or 80 mol% or more of repeating propylene units in the main chain of the polymer, and examples thereof include polypropylene (PP) homopolymer, random polypropylene (random PP), block polypropylene (block PP), chlorinated polypropylene, acid-modified polypropylene, derivatives thereof, and mixtures thereof.

[0013] Further, among the above "polypropylene-based resins", the "polypropylene homopolymer" means a homotype homopolymer polymerized only from propylene, "random polypropylene" means a random-type copolymer obtained by polymerizing propylene in the coexistence of a comonomer such as ethylene, and "block polypropylene" means a block-type copolymer obtained by polymerizing propylene and then further polymerizing in the coexistence of a comonomer such as ethylene.

[0014] When a lidded container using a lid material having an increased content of inorganic particles in the inorganic particle-containing layer is subjected to high-temperature high-pressure sterilization treatment (retort heat sterilization treatment), unintended peeling may occur during the retort heat sterilization treatment or during transportation of the lidded container. In contrast, the present inventors have found that the above configuration can achieve easy openability during use while suppressing unintended peeling of the lid material under severe conditions even when the content of inorganic particles in the inorganic particle-containing layer is relatively high.

[0015] While not wishing to be bound by theory, it is believed that when a sealant layer in which a polyethylene-based resin and a polypropylene-based resin are compatible is heat-sealed, particularly on the surface of a container formed of a polypropylene-based resin, under conditions that provide sufficient sealing strength, the sealant layer and the container are bonded via the portions formed of propylene monomers in the polypropylene-based resin. On the other hand, it is believed that sufficient adhesive strength can also be obtained between the inorganic particle-containing layer and the sealant layer via the polypropylene-based resin constituting the inorganic particle-containing layer and the polypropylene-based resin constituting the sealant layer.

[0016] Since the polyethylene-based resin and the polypropylene-based resin are compatible in the sealant layer, the sealant layer itself has sufficient strength, which makes the sealant layer itself less prone to breaking, and further good easy openability can be obtained. In addition, since the polyethylene-based resin and the polypropylene-based resin are compatible in the sealant layer, the sealant layer itself has sufficient heat resistance, which is believed to suppress the problem of unintended peeling during retort heat sterilization treatment or subsequent transportation.

[0017] In this specification, "easy-open lid material" generally refers to a lid material that can be easily opened by hand when attached to a container, and may be referred to as "easy-peel lid material" by those skilled in the art. Whether or not a lid material is easy to open can be evaluated by sensory evaluation. Furthermore, the opening strength of a container with such an easy-open lid material can generally be 30 N / 15 mm or less, 25 N / 15 mm or less, 20 N / 15 mm or less, 15 N / 15 mm or less, or 10 N / 15 mm or less. This opening strength is, for example, measured at a temperature of 150°C and a pressure of 3 kgf / cm². －２ This can be obtained by heat-sealing a polypropylene film for 1.5 seconds, then using a measuring instrument to peel the portion corresponding to the heat-sealed area 180° at a rate of 300 mm / min and a peel length of 35 mm, and calculating the average peel strength at a peel length of 10 to 30 mm in the portion corresponding to the heat-sealed area.

[0018] In one aspect of the present invention, as shown in Figure 1, the easy-open lid material 100 of the present invention comprises at least a base layer 102, an inorganic particle-containing layer 104, and a sealant layer 106, wherein the inorganic particle-containing layer 104 contains a polypropylene resin and inorganic particles dispersed in the polypropylene resin, the inorganic particle content is 25% by mass or more with respect to the mass of the inorganic particle-containing layer 104, and the sealant layer 106 contains a polyethylene resin and a polypropylene resin, and the polyethylene resin and the polypropylene resin are mutually compatible.

[0019] Although not shown in Figure 1, the easy-open lid material of the present invention may have a skin layer on the side of the inorganic particle-containing layer facing the base material layer, i.e., the side opposite to the sealant layer. In this case, the skin layer, the inorganic particle-containing layer, and the sealant layer may be fused to each other.

[0020] In this case, the skin layer, inorganic particle-containing layer, and sealant layer can be manufactured by simultaneously forming and laminating the skin layer, inorganic particle-containing layer, and sealant layer using the three-layer T-die method and the three-layer inflation method. That is, the skin layer, inorganic particle-containing layer, and sealant layer may be a three-layer T-die film or a three-layer inflation film.

[0021] Although not shown in Figure 1, the easy-open lid material of the present invention may have a tab for pinching and pulling up when opening.

[0022] The easy-open lid material of the present invention may be a lid material for heat-sealing a polypropylene resin surface of a container.

[0023] The following describes each component of the present invention.

[0024] <Base Layer> The easy-open lid material has a base layer. The base layer may be a base layer having at least a barrier layer. In particular, when the inorganic particles are a gas absorbent, it is preferable that the base layer be a barrier base layer from the viewpoint of suppressing the absorption of gas from the outside.

[0025] The barrier substrate layer may have a substrate resin layer and a barrier layer. The substrate resin layer and the barrier layer may each consist of one or more layers, and these layers may be laminated via an adhesive layer.

[0026] In particular, the barrier substrate layer is preferably composed of a first substrate resin layer, a barrier layer, and a second substrate resin layer in that order, from the viewpoint of protecting the barrier layer. In particular, in this embodiment, it is preferable from the viewpoint of puncture resistance that at least one of the first and second substrate resin layers is a polyamide resin, especially nylon.

[0027] (Base resin layer) The base resin layer may be composed of a thermoplastic resin with excellent impact resistance, abrasion resistance, etc., such as vinyl resin, polyester resin, polyamide resin, polypropylene resin, etc. The base resin layer may be a single layer or a laminate.

[0028] Examples of vinyl resins include polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polychlorotrifluoroethylene, polytetrafluoroethylene, and polyacrylonitrile (PAN).

[0029] Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate.

[0030] Examples of polyamide resins include nylon (registered trademark) 6, nylon MXD6, and other types of nylon.

[0031] As for the polypropylene resin, the resins mentioned below can be used for the inorganic particle-containing layer.

[0032] From the viewpoint of mechanical strength of the packaging laminate, the thickness of the base resin layer is preferably 7 μm or more, or 10 μm or more. From the viewpoint of flexibility of the base resin layer, this thickness is preferably 55 μm or less, 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less. In other words, the base resin layer may be a flexible base resin layer.

[0033] The resins constituting the base resin layer may be not just one type, but a blend of two or more types, and additives to impart functionality may be included as needed.

[0034] Furthermore, it is preferable that the base resin layer be made from a pre-formed film. The film that becomes the base resin layer can be any film formed from the above-mentioned resin, and may be unstretched, uniaxially or biaxially stretched, or otherwise. Among these, a biaxially oriented film is preferred.

[0035] (Barrier Layer) As the barrier layer, a material can be used that prevents moisture, organic gases, and inorganic gases from permeating from the barrier substrate layer to the sealant layer, and / or, especially when the inorganic particles are oxygen absorbers, prevents oxygen from permeating from the outside and deactivating the inorganic particle-containing layer. Examples of such barrier layers include metal foil layers, inorganic vapor-deposited films, organic coating films, and barrier resin layers. In particular, when the contents are microwaveable food, an inorganic vapor-deposited film, an organic coating film, or a barrier resin layer can be used as the barrier layer.

[0036] As the metal foil layer, for example, a single metal foil layer such as copper foil or aluminum foil, or an alloy foil layer such as stainless steel foil can be used.

[0037] As the inorganic vapor-deposited film, for example, an aluminum vapor-deposited film, a silica vapor-deposited film, or a silica-alumina binary vapor-deposited film can be used. In particular, as such an inorganic vapor-deposited film, one that is commercially available in a vapor-deposited state on a film, such as "vapor-deposited PET," may be used.

[0038] As the organic coating film, for example, a polyvinylidene chloride coating film, a polychlorotrifluoroethylene coating film, or a polyvinylidene fluoride coating film can be used.

[0039] As the barrier resin layer, for example, ethylene-vinyl alcohol copolymer (EVOH), cyclic olefin polymer (COP), or cyclic olefin copolymer (COC) can be used.

[0040] When an inorganic vapor-deposited film or an organic coating film is used as the barrier layer, the thickness of the barrier layer is preferably 100 nm or more, 200 nm or more, 300 nm or more, 500 nm or more, 700 nm or more, or 1 μm or more from the viewpoint of ensuring strength and barrier properties, and is preferably 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less from the viewpoint of reducing the overall thickness of the easy-to-open lid material.

[0041] When a metal foil layer or a barrier resin layer is used as the barrier layer, the thickness of the barrier layer is preferably 5 μm or more, or 7 μm or more, from the viewpoint of ensuring strength and barrier properties. Furthermore, a thickness of 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less is preferable from the viewpoint of reducing the overall thickness of the easy-open lid material.

[0042] (Adhesive layer) For the adhesive layer, for example, a dry laminating adhesive or a hot laminating adhesive can be used.

[0043] <Inorganic Particle-Containing Layer> The inorganic particle-containing layer contains inorganic particles and polypropylene resin. The inorganic particle content is 25% by mass or more.

[0044] The inorganic particle-containing layer may contain an oxygen absorber. In this case, the oxygen absorber may contain iron powder as the main component of the oxygen absorber as inorganic particles.

[0045] The inorganic particle-containing layer may be fused to the sealant layer. Furthermore, if the easily removable lid material has a skin layer, the inorganic particle-containing layer may be fused to the skin layer.

[0046] The thickness of the inorganic particle-containing layer may be 5 to 100 μm. This thickness may be 5 μm or more, 7 μm or more, 10 μm or more, 12 μm or more, 15 μm or more, 18 μm or more, 20 μm or more, 23 μm or more, 25 μm or more, or 28 μm or more, and may also be 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, or 33 μm or less.

[0047] In particular, if the inorganic particles are iron powder, the inorganic particle-containing layer may further contain an oxidation accelerator.

[0048] In particular, if the inorganic particles are iron powder, the inorganic particle-containing layer may further contain other oxygen absorbers besides iron powder.

[0049] (Polypropylene resin) The polypropylene resins mentioned above can be used.

[0050] The density of the polypropylene-based resin is 0.900 g / cm ３ 3 or more and 0.950 g / cm ３ 3 or less, for example 0.840 g / cm ３ 3 or more, 0.845 g / cm ３ 3 or more, 0.850 g / cm ３ 3 or more, 0.855 g / cm ３ 3 or more, 0.860 g / cm ３ 3 or more, 0.870 g / cm ３ 3 or more, 0.880 g / cm ３ 3 or more, 0.885 g / cm ３ 3 or more, 0.890 g / cm ３ 3 or more, 0.900 g / cm ３ 3 or more, 0.905 g / cm ３ 3 or more, 0.910 g / cm ３ 3 or more, 0.915 g / cm ３ 3 or more, or 0.920 g / cm ３ 3 or more, and 0.950 g / cm ３ 3 or less, 0.945 g / cm ３ 3 or less, 0.940 g / cm ３ 3 or less, 0.935 g / cm ３ 3 or less, or 0.930 g / cm ３ 3 or less. In particular, a density of 0.930 g / cm ３ 3 or less is preferred from the viewpoint of heat seal strength.

[0051] The melting point of the polypropylene-based resin may be 140°C or higher and 190°C or lower, for example, 140°C or higher, 145°C or higher, 150°C or higher, 155°C or higher, or 160°C or higher, and may be 190°C or lower, 185°C or lower, 180°C or lower, 175°C or lower, or 170°C or lower.

[0052] Here, in the present specification, the melting point means a melting point measured by differential scanning calorimetry (DSC) in accordance with JIS K7121:1987.

[0053] (Polypropylene resin: Polypropylene elastomer) Generally, thermoplastic elastomers are composed of plastic components (hard segments) and elastic components (soft segments), and thus are polymers that plasticize at high temperatures while exhibiting rubber-elastic properties at room temperature. In particular, polypropylene elastomers are thermoplastic elastomers that contain polypropylene as the hard segment.

[0054] The density of polypropylene elastomer is 0.900 g / cm³. ３ The following density may be used: 0.900 g / cm³ ３ Below, 0.895g / cm ３ Below, 0.890g / cm ３ Below, 0.885g / cm ３ Below, 0.880g / cm ３ Below, 0.875g / cm ３ The following, or 0.870 g / cm³ ３ It may be less than or equal to 0.840 g / cm³. ３ Above, 0.845g / cm ３ Above, 0.850g / cm ３ Above, 0.855g / cm ３ Above, or 0.860 g / cm³ ３ That's all.

[0055] (Polypropylene resins: Polypropylene resins other than polypropylene elastomers) Polypropylene resins other than polypropylene elastomers are resins obtained by removing the polypropylene elastomers from the above-mentioned polypropylene resins.

[0056] The density of polypropylene-based resins other than polypropylene elastomers is 0.900 g / cm³. ３ 0.950g / cm or more ３ The following may be true, for example, 0.900 g / cm³ ３ Above, 0.905g / cm ３ Above, 0.910g / cm ３ Above, 0.915g / cm ３ Above, or 0.920 g / cm³ ３ The above is sufficient, and also 0.950 g / cm³ ３Below, 0.945g / cm ３ Below, 0.940g / cm ３ Below, 0.935g / cm ３ The following, or 0.930 g / cm³ ３ The following is acceptable. In particular, the density is 0.930 g / cm³. ３ The following is preferable from the viewpoint of heat seal strength.

[0057] (Inorganic particles) Inorganic particles are inorganic particles dispersed in thermoplastic resins.

[0058] Examples of inorganic particles that can be used include gas absorbents and inorganic pigments.

[0059] As gas absorbents, the main component of oxygen absorbers such as iron powder, and organic gas absorbents such as hydrophobic zeolites can be used. As iron powder, for example, reduced iron powder, sprayed iron powder, activated iron powder, etc., can be used. Such iron powders can be those that are commercially available as masterbatches.

[0060] As inorganic pigments, for example, known inorganic coloring pigments, flaky metal pigments such as aluminum powder, and luminous pigments such as pearl pigments can be used.

[0061] The inorganic particle content in the inorganic particle-containing layer may be 25 to 80% by mass relative to the mass of the inorganic particle-containing layer. This content may be 25% or more by mass, 28% or more by mass, 30% or more by mass, 33% or more by mass, 35% or more by mass, 40% or more by mass, 45% or more by mass, 48% or more by mass, or 50% or more by mass, and may also be 80% or less by mass, 75% or less by mass, 70% or less by mass, or 65% or less by mass.

[0062] (Oxidation accelerators) As oxidation accelerators, alkali metal chlorides such as sodium chloride, alkaline earth metal oxides such as calcium chloride and magnesium chloride can be used.

[0063] The content of the oxidation accelerator may be 1 to 30% by mass relative to the mass of the iron powder. This content may be 1% or more by mass, 3% or more by mass, 5% or more by mass, 7% or more by mass, or 10% or more by mass, and may also be 30% or less by mass, 25% or less by mass, 20% or less by mass, or 15% or less by mass.

[0064] (Other oxygen absorbers) Other oxygen absorbers besides iron powder include iron-based compounds such as ferrous oxide and ferrous salts, metal halides such as calcium chloride and magnesium chloride, and metal oxides such as cerium oxide.

[0065] The content of other oxygen absorbers may be 10% by mass or less, 7% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0% by mass, relative to the mass of the inorganic particle-containing layer.

[0066] <Sealant Layer> The sealant layer contains polyethylene resin and polypropylene resin. The polyethylene resin and polypropylene resin are mutually compatible. This compatibility may be achieved by a compatibilizer.

[0067] The thickness of the sealant layer may be greater than 10 μm and less than or equal to 100 μm. This thickness may be greater than 10 μm, 12 μm or more, or 15 μm or more, and may also be 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, less than 50 μm, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, or 23 μm or less.

[0068] (Polyethylene resin) As the polyethylene resin, the polyethylene resin described for the inorganic particle-containing layer can be used.

[0069] The polyethylene resin content may be 5% by mass or more and 45% by mass or less relative to the mass of the sealant layer. This content may be 5% by mass or more, or 7% by mass or more, and may also be 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, or 22% by mass or less.

[0070] (Polypropylene resin) As the polypropylene resin, the polypropylene resins listed for the inorganic particle-containing layer can be used.

[0071] In particular, polypropylene homopolymer and / or random PP and / or block PP may be used as the polypropylene resin, and the use of block PP is preferred from the viewpoint of easy opening.

[0072] From the viewpoint of adhesion, the polypropylene resin content is preferably 35% by mass or more and 85% by mass or less relative to the mass of the sealant layer. This content may be 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more, and may also be 85% by mass or less, 80% by mass or less, or 75% by mass or less.

[0073] The ratio of the mass of polypropylene resin in the sealant layer to the mass of polyethylene resin may be, for example, 0.5 or more and 8.0 or less. This ratio may be 0.5 or more, 0.6 or more, 0.8 or more, 1.0 or more, 1.5 or more, 2.0 or more, 2.5 or more, or 2.7 or more, and may also be 8.0 or less, 7.5 or less, 7.0 or less, 6.5 or less, 6.0 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, or 3.3 or less.

[0074] In particular, when the polypropylene resin is a polypropylene homopolymer and / or random PP and / or block PP, the density of the polypropylene resin is 0.880 g / cm³. ３ 0.920g / cm or more ３ The following may be the case, for example, 0.880 g / cm³ ３ Above, 0.885g / cm ３ Above, 0.890g / cm ３ Above, or 0.895 g / cm³ ３ The above, and also 0.920 g / cm³ ３ Below, 0.915g / cm ３ Below, 0.910g / cm ３ The following, or 0.905 g / cm³ ３ The following is acceptable:

[0075] The melting point of the polypropylene resin may be 120°C or higher and 180°C or lower, for example, 120°C or higher, 130°C or higher, 135°C or higher, 140°C or higher, 145°C or higher, 150°C or higher, or 155°C or higher, and may also be 180°C or lower, 175°C or lower, 170°C or lower, or 165°C or lower.

[0076] (Compatibilizer) As a compatibilizer, for example, it is preferable to use an α-olefin copolymer, because the repeating units of the α-olefin group contained therein include parts that provide affinity with polyethylene resins and parts that provide affinity with polypropylene resins, thereby making polyethylene resins and polypropylene resins compatible.

[0077] The compatibilizer content may be 5% by mass or more and 45% by mass or less relative to the mass of the sealant layer. This content may be 5% by mass or more, 7% by mass or more, 10% by mass or more, 15% by mass or more, or 18% by mass or more, and may also be 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, or 22% by mass or less.

[0078] The ratio of the mass of the compatibilizer in the sealant layer to the mass of the polyethylene resin may be, for example, 0.3 or more and 5.0 or less. This ratio may be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.8 or more, or 1.0 or more, and may also be 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. In particular, this ratio may be 1.0 or more.

[0079] <Skin Layer> The skin layer may be composed of a polyolefin resin. As the polyolefin resin, the polyolefin resins mentioned for the inorganic particle-containing layer, particularly polyethylene resins, can be used.

[0080] The thickness of the skin layer may be greater than 10 μm and less than or equal to 100 μm. This thickness may be greater than 10 μm, 12 μm or more, or 15 μm or more, and may also be 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, less than 50 μm, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, or 23 μm or less.

[0081] As shown in Figures 2(a) and 2(b), the container with a lid 300 of the present invention comprises a container 200 having a flange portion 202 and a storage portion 204, and the above-mentioned easy-open lid material 100 which is heat-sealed to the flange portion 202 of the container 200, thereby sealing the container 200, and the surface of the container that is heat-sealed to the easy-open lid material is made of polypropylene resin.

[0082] The above-mentioned easy-open lid material may have a tab 110 for pinching and pulling up when opening.

[0083] The lidded container of the present invention may be a lidded container containing contents, having contents contained in the storage section of the lidded container described above.

[0084] The lidded container of the present invention may be used for retort heat sterilization.

[0085] <Container> The container has a flange portion and a storage portion. The surface of the container that is heat-sealed with an easy-open lid material is made of polypropylene resin.

[0086] The container is not particularly limited as long as it can be heat-sealed with an easy-open lid. Examples of containers that can be used include paper containers coated with a polypropylene resin, or containers made of polypropylene resin.

[0087] (Flange portion) The flange portion is the peripheral edge of the container's housing section and may be a flange-shaped portion. The shape of the outer circumference of the flange portion can be selected according to the shape of the lid material.

[0088] (Storage section) The storage section is the part in which the contents are stored. The shape of this section can be, for example, a roughly rounded square truncated pyramidal shape, a roughly rounded cone truncated pyramidal shape, a polygonal truncated pyramidal shape, a rectangular prism shape, a cube shape, etc.

[0089] <Contents> The contents are the items contained in the storage compartment. Examples of such contents include microwaveable foods that can be stored at room temperature, such as soup, instant noodles, and cooked rice; microwaveable foods such as chilled foods and frozen foods; and non-heated foods such as snacks and gummy candies.

[0090] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0091] <Preparation of containers with lids> <Example 1> A multilayer film consisting of a 20 μm thick skin layer, a 30 μm thick inorganic particle-containing layer, and a 20 μm thick sealant layer was prepared using a T-die film-making machine. The skin layer was made of block polypropylene (bPP1, density 0.900 g / cm³). ３ A polypropylene masterbatch with a melting point of 162°C and an MFR of 2.0 g / 10 min (230°C) was used as the inorganic particle-containing layer. The masterbatch used was a polypropylene-based masterbatch containing 60% by mass of iron powder (iron MB, density 2.76 g / cm³). ３ (melting point 109°C) and polypropylene elastomer (PP-el, density 0.866 g / cm³) ３ A blend of (MFR 6.0 g / 10 min (230°C)) and was used in a mass ratio of 50:50. Block polypropylene (bPP2, density 0.900 g / cm³) was used as the sealant layer. ３ (MFR 8.5 g / 10 min (230℃)) and low-density polyethylene (LDPE, density 0.920 g / cm³) ３ (melting point 107°C) and a compatibilizer (α-olefin copolymer, density 0.885 g / cm³). ３ A blend of (melting point 66°C) and (another substance) in a mass ratio of 60:20:20 was used.

[0092] Next, a biaxially oriented nylon film (15 μm thick) was dry-laminated to the aluminum vapor-deposited layer side of aluminum vapor-deposited polyethylene terephthalate (12 μm thick), and the skin layer side of the prepared multilayer film was dry-laminated to the other side of this biaxially oriented nylon film to obtain the laminate for lid material of Example 1.

[0093] <Examples 2-6 and Comparative Examples 1-4> Laminated lid materials for Examples 2-6 and Comparative Examples 1-4 were prepared in the same manner as in Example 1, except that the types and content of each component were changed as shown in Table 1. Details of each component shown in Table 1 are as follows: Random PP: Random polypropylene, density 0.900 g / cm³ ３ Melting point 132°C. HomoPP: Homopolypropylene, density 0.900 g / cm³. ３ Melting point 159°C EP sealant: Commercially available easy-peel resin film, 50 μm thick

[0094] 《Evaluation》 The resulting laminated material for the lid was cut to the size of the container to obtain the lid. Next, 45 g of water was filled into a 70 mm diameter polypropylene container. Then, this lid material was heat-sealed to the flange of the polypropylene container to obtain a container with a lid. The heat sealing of the lid material was performed under the following conditions, and multiple identical containers with lids were created: 170°C seal: temperature 170°C, pressure 189-193 kgf, time 1 second 175°C seal: temperature 175°C, pressure 189-193 kgf, time 1 second

[0095] <Peel Resistance> The lid material of the prepared lidded container was subjected to water-type retort heat sterilization at 125°C for 30 minutes, and after treatment, it was visually confirmed whether or not the lid material had peeled off.

[0096] Further transport tests were conducted on lidded containers in which no lid material peeled off after retort heat sterilization. Specifically, all lidded containers using the same lid material and heat sealing conditions were placed in plastic bags, and these plastic bags were placed in cardboard boxes without cushioning material. These cardboard boxes were then transported by truck for 49 km, and afterwards, the cardboard boxes were opened and the extent of leakage of contents was visually checked.

[0097] The evaluation criteria are as follows: A: The lid did not peel off and the seal remained tight. B: The container was opened during transport and the contents leaked out. C: The container was opened during retort heat sterilization and therefore could not be transported.

[0098] <Ease of Opening> Among the lidded containers that were prepared, those whose lids did not peel off during the peel resistance evaluation were evaluated for ease of opening by sensory evaluation after being opened by hand. The evaluation criteria are as follows. In the evaluation below, a higher number indicates a higher opening strength, with "3" and "4", especially "3", being preferable, and "1" indicating that the lid peeled off during the peel resistance evaluation. 1: The seal strength was too weak, causing it to peel off during the peel resistance evaluation. 2: Although there was no unintended peeling, it could be opened with very little force. 3: It could be opened with moderate strength. 4: The opening strength was slightly strong, but it was easy to open. 5: The opening strength was too strong, resulting in significant stress when opening.

[0099] Table 1 shows the configurations and evaluation results of the examples and comparative examples.

[0100]

[0101] Table 1 shows that the easy-open lid material of the example, in which the inorganic particle-containing layer contains a polypropylene resin and the sealant layer contains a polyethylene resin and a polypropylene resin, and the polyethylene resin and the polypropylene resin are mutually compatible, can suppress unintended peeling under harsh conditions and achieve good easy-open properties, even when the inorganic particle content of the inorganic particle-containing layer is 25% by mass or more.

[0102] 100 Easy-open lid material 102 Base layer 104 Inorganic particle-containing layer 106 Sealant layer 110 Tab 200 Container 202 Flange portion 202a Flange seal portion 204 Storage portion 250 Contents

Claims

1. An easily openable lid material comprising at least a base layer, an inorganic particle-containing layer, and a sealant layer, wherein the inorganic particle-containing layer contains a polypropylene resin and inorganic particles dispersed in the polypropylene resin, the inorganic particle content is 25% by mass or more relative to the mass of the inorganic particle-containing layer, and the sealant layer contains a polyethylene resin and a polypropylene resin, and the polyethylene resin and the polypropylene resin are mutually compatible in the sealant layer.

2. The polypropylene resin contained in the sealant layer is block polypropylene, the easy-open lid material according to claim 1.

3. The easy-open lid material according to claim 1 or 2, wherein the inorganic particle-containing layer contains an oxygen absorber, and the base material layer is a barrier base material layer.

4. The easy-open lid material according to claim 3, wherein the oxygen absorbent contains iron powder.

5. The easy-open lid material according to claim 3, wherein the barrier substrate layer is composed of a substrate resin layer and a barrier layer.

6. The easy-open lid material according to claim 5, wherein the barrier layer is an inorganic vapor-deposited film or an organic coating film.

7. The easy-open lid material according to any one of claims 1 to 6, wherein the inorganic particle-containing layer has a skin layer on the surface facing the base material layer.

8. The easy-open lid material according to claim 7, wherein the skin layer, the inorganic particle-containing layer, and the sealant layer are fused to each other.

9. A container with a lid, comprising a container having a flange portion and a storage portion, and an easy-open lid material according to any one of claims 1 to 8, which is heat-sealed to the flange portion of the container, wherein the surface of the container that is heat-sealed to the easy-open lid material is made of polypropylene resin.

10. A lidded container according to claim 9, for use in retort heat sterilization.

11. A lidded container containing contents, having contents contained in the storage section of the lidded container according to claim 10.

12. The container with a lid containing contents according to claim 11, wherein the contents are cooked rice.

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