Laminated sheets for lids, lids, food packaging containers, and packaged foods

Abstract

To provide a lid used in a packaging container for food, containing a paper substrate, and excellent in openability.SOLUTION: A lid laminated sheet 10 according to an embodiment of the present invention is a lid laminated sheet used for a lid of a food packaging container including a container body provided with an opening and the lid covering the opening. The lid laminated sheet 10 includes a water-resistant functional layer 6, a printed layer 5, a paper base material 4, a support layer 2, and a heat seal layer 1 in this order. The mass of the paper base 4 is larger than the mass of any other layer included in the lid laminated sheet 10, and the Young's modulus in MD and TD of the lid laminated sheet 10 are both in the range of 1.2 to 2.9 GPa, and the thickness of the lid laminated sheet is in the range of 80 to 205 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laminated sheet for a lid, a lid, a food packaging container, and packaged food.

Background Art

[0002] In addition to changes in household composition and lifestyle due to the recent trend of nuclear families, supported by the progress of distribution and refrigeration / frozen storage technologies, the demand for cooked or processed chilled foods and frozen foods sold at convenience stores and supermarkets has been increasing. At the same time, the demand for packaging containers for accommodating chilled foods and frozen foods has also been increasing.

[0003] On the other hand, while efforts are being made to reduce plastic waste, the demand for food packaging containers using paper, which has a small environmental impact and is a renewable resource, as a base material is increasing. It is also required to use paper-made packaging containers using paper as a base material for packaging containers for accommodating chilled foods.

[0004] For example, Patent Document 1 discloses a food packaging material formed by laminating two gas barrier layers using an ethylene-modified polyvinyl alcohol resin on a paper base material.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a lid that is used for a food packaging container, includes a paper base material, and has excellent opening properties.

Means for Solving the Problems

[0007] According to a first aspect of the present invention, there is provided a laminated sheet for a lid used for a lid of a food packaging container including a container body provided with an opening and a lid covering the opening, the laminated sheet for a lid including a functional layer having water resistance, a printing layer, a paper base material, a support layer, and a heat seal layer in this order, the mass of the paper base material being larger than the mass of any other layer included in the laminated sheet for a lid, the Young's modulus in the MD and TD of the laminated sheet for a lid being both within the range of 1.2 to 2.9 GPa, and the thickness of the laminated sheet for a lid being within the range of 80 to 205 μm.

[0008] According to a second aspect of the present invention, there is provided a lid made of the above laminated sheet for a lid.

[0009] According to a third aspect of the present invention, there is provided a food packaging container including a container body provided with an opening and the lid covering the opening, wherein the support layer is disposed between the paper base material and the internal space of the food packaging container.

[0010] According to a fourth aspect of the present invention, there is provided a packaged food including the above food packaging container and food accommodated in the food packaging container.

Advantages of the Invention

[0011] According to the present invention, there is provided a lid used for a food packaging container, including a paper base material and having excellent opening properties.

Brief Description of the Drawings

[0012] [Figure 1] A partial cross-sectional view schematically showing an example of a laminated sheet for a lid according to a first embodiment of the present invention. [Figure 2] A partial cross-sectional view schematically showing a laminated sheet for a lid according to a modified example. [Figure 3] A cross-sectional view schematically showing a food packaging container according to a third embodiment of the present invention.

Modes for Carrying Out the Invention

[0013] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific to any of the aspects described above. Elements having similar or identical functions will be given the same reference numerals, and redundant descriptions will be omitted.

[0014] [First Embodiment] Figure 1 is a schematic cross-sectional view showing an example of a laminated sheet for a lid according to the first embodiment of the present invention. The laminated sheet 10 for the lid shown in Figure 1 is used as the lid in a food packaging container that comprises a container body with an opening and a lid that covers the opening. In other words, the laminated sheet 10 for the lid is a lid material that is used either as the lid itself or as a portion cut from it.

[0015] The laminated sheet 10 for the lid includes a heat-seal layer 1, a support layer 2, a gas barrier layer 3, a paper substrate 4, a printed layer 5, and a water-resistant functional layer (water-resistant layer) 6 in this order. In this way, the laminated sheet 10 for the lid includes the gas barrier layer 3 between the paper substrate 4 and the support layer 2, but in the laminated sheet for the lid according to this embodiment, the gas barrier layer 3 may be included between the paper substrate 4 and the heat-seal layer 1. As a modification, the gas barrier layer 3 may be interposed between the support layer 2 and the heat-seal layer 1. Note that the gas barrier layer 3 may be omitted. Each layer included in the laminated sheet 10 for the lid is described below.

[0016] (Paper base material) The lid laminate sheet 10 contains a paper substrate 4. The mass of the paper substrate 4 is greater than the mass of any other layer contained in the lid laminate sheet 10. The ratio of the mass of the paper substrate 4 to the mass of the lid laminate sheet 10 is preferably 40% or more, more preferably 45% or more, even more preferably 50% or more, and even more preferably greater than 50%. This ratio is 80% or less in one example, 70% or less in another example, and 65% or less in yet another example.

[0017] When the layers other than the paper substrate 4 contained in the laminated lid sheet 10 are classified into layers made of plastic and other layers, it is preferable that the mass of the paper substrate 4 is greater than the total mass of the plastic layers and the total mass of the other layers. In this case, in Japan, the laminated lid sheet 10 can be treated as paper under the Container and Packaging Recycling Law.

[0018] Here, the above classification follows the "Explanatory Materials for the Container and Packaging Recycling Law." That is, "plastic" is a material that contains polymers as an essential component and is shaped and manufactured into a product using its fluidity during processing. Paints and adhesives are not included in plastic because they are unrelated to the concept of "shaping." Therefore, in the example shown in Figure 1, the support layer 2 and the heat-seal layer 1 bonded to it are "layers made of plastic." Also, in the example shown in Figure 1, the printing layer 5 formed from ink, the functional layer 6 formed by coating, and the adhesive layer (not shown) made of adhesive are "other layers."

[0019] On the other hand, the gas barrier layer 3 is classified according to the following cases. That is, in the example shown in Figure 1, if the gas barrier layer 3 is a layer formed on the paper substrate 4 by coating or vapor deposition, it can be treated as a "paper substrate" according to the explanatory materials above, but here it is treated as an "other layer". For example, if the paper substrate 4 is a barrier paper on which the gas barrier layer 3 is coated or vapor-deposited on one side, the gas barrier layer 3 is an "other layer". Also, if a polymer film made by melt molding such as extrusion is used for the barrier layer, it is a "layer made of plastic". In contrast, in the example shown in Figure 1, if the gas barrier layer 3 is a layer formed on the support layer 2 by coating, vapor deposition or melt molding, it is a "layer made of plastic" like the support layer 2. For example, if the support layer 2 is a gas barrier film on which the gas barrier layer 3 is formed on one side, the gas barrier layer 3 is a "layer made of plastic".

[0020] The basis weight of the paper substrate 4, i.e., the mass per unit area, is between 40 and 160 g / m². 2Preferably, it should be within the range of 50 to 160 g / m². 2 It is more preferable that it be within this range. Increasing the basis weight of the paper substrate 4 tends to make the lid harder and reduce its ease of opening. Decreasing the basis weight reduces the strength of the lid.

[0021] The thickness of the paper substrate 4 is preferably in the range of 40 to 160 μm, and more preferably in the range of 45 to 150 μm. If the paper substrate 4 is too thick, the lid tends to become hard and its ease of opening decreases. If the paper substrate 4 is too thin, the strength of the lid tends to decrease. For example, if the thickness of the heat seal layer 1 is in the range of 30 to 50 μm, the thickness of the paper substrate 4 is preferably in the range of 40 to 160 μm, and more preferably in the range of 45 to 150 μm.

[0022] Furthermore, increasing the basis weight of the paper substrate 4 increases the proportion of the paper substrate 4's mass to the total mass of the laminated lid sheet 10. However, increasing the basis weight of the paper substrate 4 increases the carbon dioxide emissions associated with the manufacture of the paper substrate 4 and the disposal of the laminated lid sheet 10.

[0023] The paper substrate 4 is not particularly limited as long as it is mainly composed of plant-derived pulp. Examples of paper substrate 4 include high-quality paper, medium-quality paper, coated paper such as lightly coated paper, glossy paper, bleached and unbleached kraft paper (acidic paper or neutral paper).

[0024] The paper substrate 4 is preferably coated paper having a coating layer on at least one side. That is, the paper substrate 4 is preferably single-sided coated paper or double-sided coated paper. The side of the coated paper with the coating layer has superior smoothness compared to the surface of paper without a coating layer.

[0025] If the paper substrate 4 is coated paper having a coating layer on one side, the printing layer 5 can be provided, for example, on the coating layer. In this case, it is easy to display high-resolution images on the printing layer 5. Furthermore, by providing a coating layer, the underlying surface of the functional layer 6 also becomes smooth, improving the water resistance of the functional layer 6. In addition, when a coating layer is provided, it is possible to suppress the seepage of the materials of the printing layer 5 and the functional layer 6 into the paper substrate 4.

[0026] If the paper substrate 4 is coated paper having a coating layer on one side, the gas barrier layer 3 can be provided, for example, on the coating layer. This improves the adhesion of the gas barrier layer 3 to the paper substrate 4. Furthermore, the smoothness of the coating layer makes it easier to uniformly form an adhesive layer containing the adhesive, thus improving the adhesion of the gas barrier layer 3 to the paper substrate 4 and reducing the amount of adhesive used. In addition, the thickness of the gas barrier layer 3 required to exhibit barrier properties can be reduced.

[0027] Using coated paper with coating layers on both sides as the paper substrate 4 makes it easier to display high-quality images on the printing layer 5 and improves the water resistance of the functional layer 6. Furthermore, it becomes easier to achieve excellent adhesion between the paper substrate 4 and the gas barrier layer 3.

[0028] The coating layer contains a resin. Examples of resins included in the coating layer include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-α-olefin copolymer polymerized using a metallocene catalyst (single-site catalyst), polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, acid-modified polyolefin resins obtained by modifying polyolefin resins such as polyethylene and polypropylene with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic anhydride, and fumaric acid, polyethylene terephthalate resin, polybutylene terephthalate resin, nylon resin, and thermoplastic resins such as styrene-butadiene rubber. Two or more of these resins may be used in combination, or two or more may be copolymerized. The coating layer may further contain additives, such as fillers such as clay, kaolin, calcium carbonate, talc, mica, and titanium dioxide.

[0029] The thickness of the coating layer is preferably in the range of 0.5 to 50 μm, and more preferably in the range of 1 to 15 μm.

[0030] (Support layer) The support layer 2 improves the strength of the laminated sheet 10 for the lid. Support layer 2 includes, for example, polybutylene terephthalate (PBT), polyamide, polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer, polyacrylonitrile (PAN), polymethylpentene (PMP), polyvinyl alcohol resin, olefin resin, or unsaturated polyester resin. Support layer 2 may have a single-layer structure or a multi-layer structure.

[0031] The support layer 2 may be an unstretched film or a stretched film such as a biaxially oriented film. If it is a stretched film, it is preferable to use a biaxially oriented film. This is because biaxial stretching reduces the variation in various physical properties such as breaking strength in the direction within the film plane compared to uniaxial stretching.

[0032] Support layer 2 may further contain additives such as a curing agent, filler, antiblocking agent, and antistatic agent. Furthermore, the material used for support layer 2 may be one that hardens upon irradiation with active energy rays such as ultraviolet light and electron beams.

[0033] The support layer 2 preferably contains at least one of polybutylene terephthalate (PBT) and polyamide. For example, the support layer 2 is a layer made of polybutylene terephthalate, a layer made of polyamide, or a laminate containing at least one of them. The polyamide contains, for example, an aliphatic backbone. The polyamide is nylon such as nylon 6, nylon 66, nylon 612, nylon 11, nylon 12, and nylon 46.

[0034] When the support layer 2 contains at least one of polybutylene terephthalate (PBT) and polyamide, the ratio of the total mass of polybutylene terephthalate and polyamide to the mass of the support layer 2 is preferably 50% by mass or more, and more preferably 70% by mass or more. When the thickness of the support layer 2 is kept constant, increasing this ratio increases the puncture strength of the lid.

[0035] The thickness of the support layer 2 is preferably in the range of 3 to 60 μm, and more preferably in the range of 10 to 30 μm. Increasing the thickness of the support layer 2 makes it easier to increase the puncture strength of the lid, but it becomes difficult to increase the ratio of the mass of the paper substrate 4 to the mass of the laminated sheet 10 for the lid.

[0036] It is preferable that the breaking strength of the support layer 2 is greater than the heat seal strength between the lid and the container body. Here, the fact that the breaking strength of the support layer 2 is greater than the heat seal strength between the lid and the container body means that in the MD (Machine Direction), the breaking strength of the support layer is greater than the heat seal strength between the lid and the container body, and in the TD (Transverse Direction), the breaking strength of the support layer is greater than the heat seal strength between the lid and the container body.

[0037] The breaking strength of support layer 2 is the tensile force obtained by the measurement method specified in JIS Z1707:2019 "General Rules for Plastic Films for Food Packaging". This tensile force (N / 15mm) is the value obtained by converting the maximum force at which the test piece broke to a force (N / 15mm) equivalent to the width of the test piece (15mm). The heat seal strength between the lid and the container body will be described later.

[0038] If the breaking strength of support layer 2 is greater than the heat seal strength between the lid and the container body, paper peeling is less likely to occur when the lid is removed from the container body. For example, if the breaking strength of support layer 2 is greater than 30 N / 15 mm, paper peeling can be suppressed up to a heat seal strength of approximately 30 N / 15 mm. Here, "paper peeling" refers to the cohesive failure of the paper substrate that occurs when the lid is removed from the container body, resulting in a portion of the lid remaining on the container body. When paper peeling occurs, it can become difficult to remove the contents contained in the container body.

[0039] The heat seal strength is adjusted according to the application and purpose of the packaging container. For example, the heat seal strength may be reduced to provide easy opening. Therefore, the breaking strength of the support layer 2 does not need to exceed 30 N / 15 mm. The breaking strength of the support layer 2 is not particularly limited, but it is preferably in the range of 10 to 100 N / 15 mm, and more preferably in the range of 25 to 85 N / 15 mm. Increasing the breaking strength as described above enhances the effect of reinforcing the laminate to suppress paper peeling. However, if the support layer 2 is made thicker to increase the breaking strength, the carbon dioxide emissions and costs associated with the manufacture of the support layer 2 and the disposal of the laminate sheet 10 for the lid will increase.

[0040] (Gas barrier layer) The gas barrier layer 3 has gas barrier properties such as oxygen barrier and water vapor barrier properties. In packaged food described later, the gas barrier layer 3 suppresses the intrusion of gases such as oxygen, water vapor, and aroma components from outside the container into the container. As a result, the gas barrier layer 3 suppresses the deterioration of the food contents in packaged food. In addition, the gas barrier layer 3 suppresses the diffusion of odor components of the contents to the outside of the container in packaged food. For example, the gas barrier layer 3 has an oxygen permeability of 0.1 to 100 cc / m³ in an atmosphere of 30°C and 70% relative humidity. 2 It's / day / atm.

[0041] The gas barrier layer 3 is, for example, a metal layer, an inorganic oxide layer, a resin-containing layer, or a combination of two or more of these. When microwave heating by a microwave oven is anticipated, the gas barrier layer 3 is preferably an inorganic oxide layer, a resin-containing layer, or a combination of these.

[0042] The gas barrier layer 3 may be formed by coating, by melt molding, or by depositing an inorganic oxide. Alternatively, the gas barrier layer 3 may be a metal foil such as aluminum foil, or by depositing a metal such as aluminum.

[0043] Examples of inorganic oxides that can be used include silicon oxide, boron oxide, or metal oxides such as aluminum oxide, magnesium oxide, calcium oxide, potassium oxide, tin oxide, sodium oxide, titanium oxide, lead oxide, zirconium oxide, and yttrium oxide.

[0044] The resin-containing layer can be formed, for example, by coating. In this case, a coating solution containing resins such as polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, polyvinylidene chloride, polyacrylonitrile, and epoxy resin can be used. Additives such as organic or inorganic particles, layered compounds, and curing agents may be added to this coating solution.

[0045] When forming the resin-containing layer by melt molding, for example, extrusion molding techniques such as T-die or inflation can be used. In melt molding, for example, the above-mentioned resin or a mixture of the above-mentioned resin and additives is heated and melted, and the gas barrier layer 3 is processed into a film or sheet by T-die or inflation. This film or sheet is then laminated to at least one of the paper substrate 4 or the support layer 2.

[0046] The gas barrier layer 3 may be interposed between the paper substrate 4 and the support layer 2 of the laminated sheet 10 for the lid by using a gas barrier film consisting of a support layer 2 having the gas barrier layer 3 on one side. In this case, the gas barrier film is laminated to the paper substrate 4 so that the gas barrier layer 3 and the paper substrate 4 face each other. If the gas barrier layer 3 is a resin-containing layer, the gas barrier film may be formed together with the support layer 2 by co-extrusion.

[0047] The gas barrier layer 3 may be interposed between the paper substrate 4 and the support layer 2 of the lid laminate sheet 10 by using barrier paper made of a paper substrate 4 having the gas barrier layer 3 on one side. The paper substrate 4 constituting the barrier paper may be coated paper having a coating layer on at least one side. If the paper substrate 4 constituting the barrier paper has a coating layer on only one side, the gas barrier layer 3 may be provided on the coating layer or on the surface of the paper substrate 4 where the coating layer is not formed.

[0048] The thickness of the gas barrier layer 3 is, in one example, in the range of 0.01 to 30 μm, and in another example, in the range of 0.1 to 12 μm.

[0049] (Printing layer) The printed layer 5 is a layer formed to make the lid laminate sheet 10 or the lid a commercially usable product. The printed layer 5 is a layer composed of ink in which various pigments, extender pigments, plasticizers, desiccants, and stabilizers are added to conventionally used ink binder resins such as urethane, acrylic, nitrocellulose, rubber, and vinyl chloride, and displays patterns such as characters and images. As a method for forming the printed layer 5, well-known printing methods such as offset printing, gravure printing, and silkscreen printing, or well-known coating methods such as roll coating, knife-edge coating, and gravure coating can be used.

[0050] The thickness of the printed layer 5 is not particularly limited, and in one example it is in the range of 0.1 to 5 μm, and in another example it is in the range of 0.2 to 1 μm.

[0051] (Water-resistant functional layer) The water-resistant functional layer (water-resistant layer) 6 suppresses the penetration of liquids outside the container, such as moisture and oil due to condensation, etc., into the lid in the packaged food described later, and suppresses this liquid from reaching layers such as the printing layer 5 and the paper base material 4. The functional layer 6 suppresses the liquid outside the container from reaching layers such as the printing layer 5 and the paper base material 4, thereby preventing, for example, deterioration, destruction or reduction in adhesion of these layers.

[0052] According to one example, the functional layer 6 is formed on the printing layer 5 to control the water absorption of the partial laminated sheet, which is the part of the laminated sheet for the lid 10 from the functional layer 6 to the paper base material 4. The functional layer 6 preferably has water resistance such that the water absorption of the laminated sheet for the lid by the Cobb method described below is 20 g / m 2 or less.

[0053] Here, the water absorption is the water absorption obtained when the measurement surface is the surface of the functional layer 6 and the contact time between the test piece and water is 300 seconds in the method defined in JIS P8140:1998 "Paper and Paperboard - Test Method for Water Absorption - Cobb Method". This water absorption is preferably 20 g / m 2 or less, more preferably 10 g / m 2 or less, and even more preferably 5 g / m 2 or less. The lower limit value of this water absorption is ideally 0 g / m 2 According to one example, this water absorption is 1 g / m 2 or more.

[0054] The functional layer 6 is preferably an overprint varnish layer (hereinafter referred to as the "OP varnish layer"). The functional layer 6, for example, contains a water-resistant resin. Any resin capable of achieving the above-mentioned water absorption level can be used without limitation. Examples of water-resistant resins include polyolefin resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and vinyl chloride-vinyl acetate copolymers, as well as silicone resins, acrylic resins, epoxy resins, polyester resins, cellulose resins, or urethane resins. The functional layer 6 can be obtained, for example, by coating a coating containing a water-resistant resin onto a paper substrate 4 on which the printed layer 5 is formed, using a known method. In addition to the water-resistant resin, the coating may further contain additives such as pigments, dyes, curing agents, leveling agents, anti-blocking agents, and lubricants, as well as solvents.

[0055] The functional layer 6 preferably has high abrasion resistance and scratch resistance so as to maintain sufficient water resistance. From this viewpoint, the thickness of the functional layer 6 and the amount of paint applied to it are preferably greater than the thickness of a normal OP varnish layer and the amount of normal OP varnish applied. Here, "amount applied" refers to the mass of solids per unit area.

[0056] For example, in the laminated sheet 10 for the lid shown in Figure 1, the amount of paint used to form the functional layer 6 is 0.2 g / m². 2 It is preferable to coat the area in such a manner as described above, with a density of 2.0 g / m². 2 It is more preferable to apply the coating in such a manner as described above. The coating amount should be, for example, 10 g / m². 2 The coating is carried out as follows: The thickness of the functional layer 6 is preferably 0.2 μm or more, and more preferably 2.0 μm or more. The thickness of the functional layer 6 is, for example, 10 μm or less. The functional layer 6 may also be provided on the printed layer 5 by lamination.

[0057] (Heat seal layer) The heat seal layer 1 only needs to enable the heat sealing of the lid 21 to the container body 22 of the food packaging container 20 shown in Figure 3, which will be described later, thereby sealing the container. The ease with which the lid can be peeled off from the container body can be adjusted, for example, according to the peeling mechanism of the heat seal layer, such as interfacial peeling or cohesive failure, or the heat seal strength, which will be described later. As the heat seal layer 1, for example, a film made of ethylene-vinyl acetate copolymer (EVA), ionomer resin, or other polyolefins can be used. Preferably, the heat seal layer 1 is a layer containing at least linear low-density polyethylene (LLDPE), very low-density linear polyethylene (VLDPE), or polypropylene.

[0058] As the heat seal layer 1, a sealant layer with an easy-peel function (simple peeling function) can also be used. Easy-peel properties refer to excellent re-peelability and ease of opening.

[0059] The heat seal layer 1 is provided on the support layer 2, for example, by lamination. The heat seal layer 1 can also be formed by applying a heat seal varnish to the support layer 2.

[0060] The thickness of the heat seal layer 1 is not particularly limited. In one example, the thickness of the heat seal layer 1 may be in the range of 0.5 to 60 μm, and in another example, it may be in the range of 1 to 30 μm.

[0061] (adhesive layer) The laminated sheet 10 for the lid may further include one or more adhesive layers. For example, the laminated lid sheet 10 may include an adhesive layer between the heat seal layer 1 and the support layer 2 to bond them together. Alternatively, the laminated lid sheet 10 may include an adhesive layer between the support layer 2 and the gas barrier layer 3 to bond them together. Alternatively, the laminated lid sheet 10 may include an adhesive layer between the gas barrier layer 3 and the paper substrate 4 to bond them together. Alternatively, the laminated lid sheet 10 may include two or more of the above-described adhesive layers.

[0062] The adhesive layer material should be appropriately selected and used, depending on the material of the layer to be bonded via it, to obtain the required adhesive strength.

[0063] As adhesive resins, one or more resins selected from polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and copolymers with ethylene-α-olefin polymerized using a metallocene catalyst; ethylene-unsaturated carboxylic acid copolymers such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-maleic acid copolymer; and ionomer resins can be used.

[0064] The adhesive is, for example, an adhesive composition obtained by mixing a first composition containing a main component and a solvent with a second composition containing a curing agent and a solvent. The adhesive layer obtained from this adhesive includes a cured product formed by the reaction of the main component and the curing agent in the adhesive composition.

[0065] Examples of main components include polyols. Examples of curing agents include isocyanate compounds. Examples of adhesives include ether-based two-component reactive adhesives or ester-based two-component reactive adhesives.

[0066] The cured product of an ether-based two-component reactive adhesive is, for example, polyether polyurethane. Polyether polyurethane is produced by the reaction of a polyether polyol as the main component and an isocyanate compound as the curing agent.

[0067] The cured products of ester-based two-component reactive adhesives are, for example, polyester polyurethane and polyester. Polyester polyurethane is produced by the reaction of a polyester polyol as the main component and an isocyanate compound as the curing agent.

[0068] In two-component reactive adhesives, an acrylic polyol may be used as the main component. Furthermore, the above adhesive composition does not need to contain a solvent, as long as it melts or becomes less viscous upon heating.

[0069] This laminated sheet 10 for the lid has a mass per unit area of ​​50 to 160 g / m². 2 It is preferable that it be within the range of 60 to 140 g / m². 2 It is more preferable that it be within the range of 90 to 130 g / m². 2 It is preferable for the value to be within this range. If this value is too small, the strength of the lid decreases. If this value is too large, the lid tends to become hard and difficult to open. In addition, if this value is too large, the cost will increase, as well as the carbon dioxide emissions associated with manufacturing and exhaust.

[0070] The laminated sheet 10 for the lid described above has a Young's modulus in both the medium diameter (MD) and the torso diameter (TD) that is within the range of 1.2 GPa to 2.9 GPa. Preferably, the Young's modulus of the laminated sheet 10 for the lid is within the range of 1.2 to 2.6 GPa. Preferably, the difference between the Young's modulus in the MD and the Young's modulus in the TD is small.

[0071] Here, the Young's modulus of the laminated sheet 10 for the lid or the lid is the value obtained by dividing the tensile stress obtained by the method specified in JIS K7161-1:2014 "Plastics - Determination of tensile properties - Part 1: General rules" by the tensile strain obtained by the above method.

[0072] The Young's modulus of the laminated sheet 10 for the lid can be adjusted, for example, according to the material of each layer included in the laminated sheet 10 for the lid.

[0073] Furthermore, the laminated sheet 10 for the lid described above has a thickness in the range of 80 μm to 205 μm. Preferably, the thickness of the laminated sheet 10 for the lid is in the range of 80 μm to 180 μm, and more preferably in the range of 90 μm to 150 μm.

[0074] Incidentally, packaging materials with a paper base are often used because they have a low environmental impact. However, when packaging materials with a paper base are used as lids for packaging containers, paper peeling sometimes occurs when opening. To create a lid that is less prone to this paper peeling, it is conceivable to provide a support layer containing plastic between the paper base and the heat-seal layer. However, in a lid with such a support layer, if the mass of the paper base relative to the mass of the packaging material is increased, the rigidity of the lid tends to increase as the rigidity of the paper increases. If the rigidity of the lid is high, that is, if the flexibility of the lid is low, it may feel like it is catching when opening, or force may be required to open it, resulting in poor openability. Also, if the rigidity of the lid is too low, the aforementioned paper peeling may occur, the lid may stretch, or part of the lid may tear. Thus, if the rigidity of the lid is too low, it may also result in poor openability.

[0075] As described above, the rigidity of the lid contributes to its ease of opening. Furthermore, the rigidity of the lid is proportional to the Young's modulus of the lid. However, the inventors have found that Young's modulus alone does not contribute to ease of opening. For example, even if the Young's modulus is within the range described above, if the lid is too thick, it may feel sticky when opening, or require force to open, resulting in poor openability. Also, even if the Young's modulus is within the range described above, if the lid is too thin, the paper may peel off, the lid may stretch, or a part of the lid may tear. The rigidity of the lid can be rephrased as the stiffness of the lid. Examples of stiffness include bending stiffness, Clark stiffness, and pure bending stiffness.

[0076] On the other hand, in the laminated sheet 10 for the lid described above, the Young's modulus in both the MD and TD is within the range described above, and the thickness of the laminated sheet 10 for the lid is also within the range described above. For this reason, such a laminated sheet 10 for the lid has excellent openability.

[0077] Furthermore, in the laminated sheet 10 for the lid described above, if the support layer 2 contains at least one of polybutylene terephthalate and polyamide, a lid with particularly excellent puncture strength can be realized.

[0078] Here, the "puncture strength" of the lid laminate sheet or lid is the value obtained by piercing the lid laminate sheet or lid from the functional layer 6 side, according to the method specified in JIS Z1707:2019 "General Rules for Plastic Films for Food Packaging". Specifically, a needle with a diameter of 1 mm and a semicircular tip is pierced into the lid laminate sheet or lid from the functional layer 6 side at a speed of 50 mm / min, and the maximum force until the needle penetrates is measured. This measurement is performed multiple times, and the arithmetic mean of the maximum forces is obtained as the puncture strength. Unless otherwise specified, "puncture strength" refers to the value obtained by piercing the lid laminate sheet or lid from the functional layer side.

[0079] The puncture strength of the laminated sheet 10 for the lid or the lid itself is preferably 5.5N or higher, and more preferably 7.5N or higher. This puncture strength is, for example, 25N or lower.

[0080] Furthermore, for laminated sheets or lids used in food packaging containers, the puncture strength obtained when a needle is inserted from the heat-seal layer side does not generally need to be as high as the puncture strength obtained when a needle is inserted from the functional layer side. Also, the puncture strength obtained when a needle is inserted from the heat-seal layer side is usually higher than the puncture strength obtained when a needle is inserted from the functional layer side.

[0081] Furthermore, when the aforementioned laminated sheet 10 for the lid includes a gas barrier layer 3, it not only offers excellent openability but also possesses high gas barrier properties. Moreover, such a laminated sheet 10 for the lid is less prone to a decrease in gas barrier properties, particularly oxygen barrier properties. This will be explained below.

[0082] Food packaging containers are sometimes required to have excellent oxygen barrier properties to prevent oxygen from entering from the outside, in order to suppress the oxidation of the food they contain. In such food packaging containers, the lid also needs to have oxygen barrier properties.

[0083] To impart gas barrier properties against oxygen and other gases to paper-based lids, a metal foil or metal-deposited film made of a metal such as aluminum is often provided on the paper substrate as a gas barrier layer. However, food packaging containers with lids containing a metal layer have several problems: they cannot be inspected for the presence of metal foreign objects using a metal detector after the contents are filled; they cannot be incinerated as paper because they contain metal and cannot be recycled as waste paper; and they cannot be used as packaging containers for chilled foods that are expected to be heated in a microwave oven.

[0084] As mentioned above, some gas barrier layers do not contain a metal layer. Such gas barrier layers often contain polyamides such as polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, and nylon MXD-6, as well as resins such as polyacrylonitrile. A lid without a metal layer can avoid the above-mentioned problems.

[0085] The optimal temperature range for distribution and storage of chilled foods is set for each type of food, but it is generally within the range of 0 to 10°C. Packaged foods, which contain chilled foods in food packaging containers, reach consumers through various distribution channels after their manufacture. During this process, for example, from the time a consumer purchases the packaged food at a store until they store it in their refrigerator at home, and from the time a consumer takes the packaged food out of the refrigerator until they start cooking it, the packaged food is kept in a room temperature environment.

[0086] The inventors have found that packaged foods containing chilled food in a food packaging container whose lid comprises a paper substrate and a gas barrier layer, particularly packaged foods in which the gas barrier layer is a resin-containing layer, experience a significant decrease in the gas barrier properties, especially the oxygen barrier properties, of the lid during the first few hours after being exposed from a refrigerated state to a room temperature environment. This is particularly noticeable when the proportion of the paper substrate's mass to the lid's mass is large.

[0087] The inventors have determined that the above problem is caused by condensation occurring on the surface of the lid. Specifically, when packaged goods that have been in a refrigerated environment are exposed to a room temperature environment, condensation occurs on the outer surface of the lid, and this moisture reaches the gas barrier layer, damaging it. As a result, the oxygen barrier properties of the lid decrease.

[0088] The laminated lid sheet 10 described above includes a water-resistant functional layer 6. Therefore, in packaged foods using this laminated lid sheet 10 as the lid material, moisture generated on the outer surface of the lid due to condensation is less likely to reach the gas barrier layer 3. Consequently, in packaged foods using this laminated lid sheet 10 as the lid material, damage to the gas barrier layer 3 due to condensation on the outer surface of the lid is less likely to occur, and a decrease in oxygen barrier performance is less likely to occur.

[0089] The inventors have further discovered that, in particular, when chilled food is contained in a food packaging container, if the lid contains a paper base material, the paper is prone to peeling when the lid is removed from the container body. As described above, by making the breaking strength of the support layer 2 greater than the heat seal strength between the lid and the container body, the paper peeling can be made less likely to occur.

[0090] Furthermore, the problems described above regarding chilled foods can also occur when the contents are frozen foods. The configuration described here can produce the same effects as described above when the contents are frozen foods, even when the contents are chilled foods.

[0091] <Variation> The laminated sheet for the lid can be modified in various ways. As described above, the laminated sheet for the lid according to this embodiment may include a gas barrier layer between the paper substrate and the heat seal layer, or, as will be explained below with reference to Figure 2, it may include a gas barrier layer between the support layer and the heat seal layer. The matters described with reference to Figure 1 can be applied individually or in combination to the laminated sheet for the lid according to the modified examples described herein.

[0092] Figure 2 is a schematic partial cross-sectional view showing a laminated sheet for a lid according to one modified example. The laminated sheet 11 for the lid shown in Figure 2 is the same as the laminated sheet 10 for the lid described with reference to Figure 1, except that the gas barrier layer 3 is interposed between the support layer 2 and the heat seal layer 1.

[0093] In other words, the laminated sheet 11 for the lid includes a heat seal layer 1, a gas barrier layer 3, a support layer 2, a paper substrate 4, a printed layer 5, and a water-resistant functional layer (water-resistant layer) 6 in this order. This laminated sheet 11 for the lid provides the same effects as the laminated sheet 10 for the lid described above.

[0094] [Second Embodiment] The lid according to the second embodiment of the present invention is a lid obtained from the laminated sheet for lids according to the first embodiment or a modified example described above. An example of the lid according to the second embodiment is lid 21, which will be described later with reference to Figure 3. The lid according to this embodiment has excellent openability, as described in relation to the laminated sheets for lids 10 and 11.

[0095] [Third Embodiment] Figure 3 is a schematic cross-sectional view showing a food packaging container according to a third embodiment of the present invention. The food packaging container 20 shown in Figure 3 comprises a container body 22 having an opening and a lid 21 covering the opening.

[0096] The container body 22 is, for example, a bottomed cylindrical shape. In this case, the container body 22 comprises a bottom, a body (or side wall), and a flange 22a. The flange 22a widens outward at the upper opening of the body.

[0097] The container body 22 includes, for example, an olefin resin such as polypropylene. The container body 22 may further contain components such as an ethylene-vinyl alcohol copolymer to enhance its gas barrier properties. The container body 22 may also further contain additives, such as additives aimed at improving processability, design, and chemical durability.

[0098] The container body 22 may have a single-layer structure or a multilayer structure. This multilayer structure may be a two-layer structure or may include three or more layers. In the latter case, the multilayer structure may include an intermediate layer containing a gas barrier layer, such as the ethylene-vinyl alcohol copolymer mentioned above.

[0099] The container body 22 can also be made of paper. If the contents include a liquid, the container body 22 can have a multilayer structure that includes a paper base material and a layer made of resin or the like, provided on the side facing the contents, to prevent the liquid from seeping into it. As materials for the container body 22 that includes the paper base material, for example, paper leaves, paper dust, pulp, or recycled paper can be used. For molding the container body 22, general-purpose technologies such as folding and gluing sheets containing paper leaves, as used in the manufacture of paper cartons, press molding of sheets using molds, and pulp molding can be used. By using paper for the container body 22, it is possible to reduce the amount of carbon dioxide emissions associated with the manufacture and disposal of the food packaging container 20 as a whole, and therefore the environmental burden is reduced.

[0100] The lid 21 is either one of the laminated sheets 10 and 11 for lids, or a piece cut from one of them. After the contents are placed inside the container body 22, the lid 21 is heat-sealed to the flange 22a via the heat-seal layer 1. In this heat sealing, the sealing temperature, sealing pressure, and sealing time can be set as appropriate.

[0101] [Fourth Embodiment] A packaged food according to the fourth embodiment of the present invention is a food packaging container according to the third embodiment described above, in which food is contained. The food contained is not particularly limited, but it is preferably a chilled food or a frozen food. Chilled foods and frozen foods are, for example, cooked or processed foods. Chilled foods and frozen foods are, for example, grilled fish, boiled fish, or prepared foods.

[0102] In this packaged food, as described above, it is preferable that the heat seal strength between the lid 21 and the container body 22 is less than the breaking strength of the support layer 2 contained in the lid 21. This heat seal strength is preferably in the range of 5 to 60 N / 15 mm, and more preferably in the range of 10 to 50 N / 15 mm. The difference between the breaking strength of the support layer 2 and the heat seal strength between the lid 21 and the container body 22 is preferably in the range of 5 to 60 N / 15 mm, and more preferably in the range of 10 to 40 N / 15 mm. Here, the heat seal strength is a value obtained by the method specified in JIS Z0238:1998 "Test method for heat-sealable flexible packaging bags and semi-rigid containers".

[0103] In the manufacture of this packaged food, the gas inside the container body 22 may be replaced by a known method before heat-sealing the lid 21 to the container body 22, for example, after the contents have been placed inside the container body 22 but before heat-sealing the lid 21 to the container body 22. For example, an inert gas may be filled into the container body 22. By appropriately changing the gas composition inside the container, it is possible to suppress bacterial growth and extend the shelf life, maintain the flavor and color of the food for a longer period by preventing oxidation, and prevent the loss of vitamins. The replacement gas is appropriately selected according to the type of food contents. A mixture of oxygen gas, nitrogen gas, and carbon dioxide gas is preferably used as the replacement gas.

[0104] The lid included in this packaged food is easy to open. Therefore, this packaged food is less likely to cause the contents to spill when opened. [Examples]

[0105] The tests conducted in connection with the present invention are described below. <1> Manufacturing of laminated sheets for lids (Example 1) The laminated sheet 10 for the lid shown in Figure 1 was manufactured by the following method. First, as paper substrate 4, the basis weight is 52.3 g / m². 2A single-sided coated paper was prepared. A printing layer 5 and a functional layer 6 were sequentially formed on the coating layer of this paper substrate 4 using a gravure multi-color printing press. The printing layer 5 was formed using conventional printing ink. The amount of printing ink applied was 1.0 g / m². 2 The functional layer 6 was formed using an OP varnish agent mainly composed of nitrocellulose resin and polyethylene granular wax. The application amount of the OP varnish agent was 0.5 g / m². 2 The single-sided coated paper has a basis weight of 37.3 g / m². 2 On the imitation paper, the coating solution is applied at a mass of 15 g / m² per unit area. 2 This is paper obtained by coating it in the manner described above. The coating layer solution mainly contains polyvinyl alcohol (PVA) and styrene-butadiene rubber (SBR), and further contains silica and layered silicate. The thickness of the single-sided coated paper was 48 μm. Next, the support layer 2 has a thickness of 12 μm and a mass per unit area of ​​16.8 g / m². 2 A biaxially oriented polyethylene terephthalate (PET) film was prepared. By depositing alumina as an inorganic oxide onto one surface of this support layer 2, a gas barrier film was obtained comprising a support layer 2 made of PET film and a gas barrier layer 3 made of an inorganic oxide layer.

[0106] Next, the gas barrier film was bonded to the laminate consisting of a paper substrate 4, a printing layer 5, and a functional layer 6 by dry lamination. For dry lamination, first, a dry laminating agent was applied to the surface of the gas barrier layer 3 of the gas barrier film using a gravure coater to form an adhesive layer. A two-component reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used as the dry laminating agent. The amount of dry laminating agent applied was 3.0 g / m². 2 Next, with this adhesive layer in between, the laminate and the support layer 2 were bonded together so that the gas barrier layer 3 faced the paper substrate 4.

[0107] Subsequently, a heat-seal layer 1 was bonded to the laminate, which included a support layer 2, a gas barrier layer 3, a paper substrate 4, a printing layer 5, and a functional layer 6, by dry lamination. The heat-seal layer 1 included a support layer and an easy-peel layer, and had a mass of 27.6 g / m². 2 A film with a thickness of 30 μm and corona treatment on the side opposite the easy-peel layer was used to provide easy-peel properties. For dry lamination, first, a dry laminating agent was applied to the surface of support layer 2 using a gravure coater to form an adhesive layer. A two-component reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used as the dry laminating agent. The application amount of dry laminating agent was 3.0 g / m². 2 Next, the laminate and the heat seal layer 1 were bonded together with this adhesive layer in between, so that the corona-treated surface of the heat seal layer 1 faced each other.

[0108] Subsequently, this was aged at 40°C. In this manner, the laminated sheet 10 for the lid shown in Figure 1 was obtained.

[0109] (Example 2) The laminated sheet 10 for the lid was manufactured in the same manner as in Example 1, except for the following point. That is, in this example, instead of using a biaxially oriented polyethylene terephthalate (PET) film as the support layer 2, a film with a thickness of 15 μm and a mass per unit area of ​​17.4 g / m² was used. 2 The material used was a biaxially oriented nylon (Ny) film with an easy-adhesion treatment applied to one side and corona treatment applied to both sides. The support layer 2 was configured so that the side with the easy-adhesion treatment faced the heat-seal layer 1.

[0110] (Example 3) The laminated sheet 10 for the lid was manufactured in the same manner as in Example 1, except for the following point. That is, in this example, instead of using polyethylene terephthalate (PET) film as the support layer 2, the support layer 2 had a thickness of 15 μm and a mass per unit area of ​​20.9 g / m². 2Therefore, a biaxially oriented polybutylene terephthalate (PBT) film that has been corona-treated on both sides was used.

[0111] (Example 4) The laminated sheet 10 for the lid was manufactured in the same manner as in Example 1, except for the following points. Specifically, in this example, instead of using single-sided coated paper as the paper base material 4, the thickness was 93 μm and the basis weight was 80 g / m². 2 I used kraft paper.

[0112] (Example 5) The laminated sheet 10 for the lid was manufactured in the same manner as in Example 1, except for the following point. In this example, instead of using single-sided coated paper as the paper base material 4, the thickness was 137.1 μm and the basis weight was 120 g / m². 2 I used kraft paper.

[0113] (Example 6) The laminated sheet 10 for the lid shown in Figure 1 was manufactured by the following method. First, as the paper base material 4, the basis weight is 50 g / m². 2 Kraft paper was prepared. A gas barrier layer 3 was formed by coating one main surface of this paper substrate 4 with a coating solution containing polyvinyl alcohol (PVA) as the main component and a layered compound (synthetic mica) as an inorganic oxide. This resulted in a structure consisting of the gas barrier layer 3 and the kraft paper substrate 4, with a mass per unit area of ​​65 g / m². 2 A barrier paper was obtained. On the coating layer of this barrier paper, a printed layer 5 and a functional layer 6 were sequentially formed using a gravure multicolor printing press in the same manner as in Example 1.

[0114] Next, a support layer 2 was bonded to the laminate, which consisted of a gas barrier layer 3, a paper substrate 4, a printing layer 5, and a functional layer 6, by dry lamination. The support layer 2 had a thickness of 12 μm and a mass per unit area of ​​16.8 g / m². 2A biaxially oriented polyethylene terephthalate (PET) film was used. For dry lamination, first, a dry laminating agent was applied to one side of the support layer 2 using a gravure coater to form an adhesive layer. A two-component reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used as the dry laminating agent. The application amount of the dry laminating agent was 3.0 g / m². 2 Next, with this adhesive layer in between, the laminate and the support layer 2 were bonded together so that the support layer 2 faced the gas barrier layer 3.

[0115] Subsequently, using the same method as in Example 1, the heat seal layer 1 was bonded to the laminate containing the support layer 2, the gas barrier layer 3, the paper substrate 4, the printing layer 5, and the functional layer 6, with the adhesive layer in between, so that the support layer 2 faced the heat seal layer 1.

[0116] Subsequently, this was aged at 40°C. In this manner, the laminated sheet 10 for the lid shown in Figure 1 was obtained.

[0117] (Comparative Example 1) A laminated sheet for the lid was manufactured using the same method as in Example 1, except that the paper substrate 4 and the barrier paper used in Example 6 were used as the gas barrier layer 3, and the support layer was omitted.

[0118] (Comparative Example 2) A laminated sheet for the lid was manufactured in the same manner as in Example 1, except for the following point. That is, in this comparative example, instead of using single-sided coated paper as the paper substrate 4, a basis weight of 186 g / m² was used. 2 Art paper with a thickness of 183 μm was used.

[0119] (Comparative Example 3) A laminated sheet for the lid was manufactured in the same manner as in Example 1, except for the following point. That is, in this comparative example, instead of using single-sided coated paper as the paper substrate 4, a basis weight of 25 g / m² was used. 2 The thin paper used has a thickness of 28 μm, and the heat seal layer 1 includes a support layer and an easy-peel layer, with a mass per unit area of ​​46.0 g / m².2 The film used had a thickness of 50 μm and was corona-treated on the side opposite the easy-peel layer, giving it easy-peel properties.

[0120] <2> evaluation (Measurement of Young's modulus) The Young's modulus of the laminated sheets for lids according to Examples 1 to 6 and Comparative Examples 1 to 3 was measured using the method described above. Specifically, first, three test pieces with their length parallel to the MD direction and three test pieces with their length parallel to the TD direction were cut from the laminated sheet for lids. Each test piece was in the shape of a strip with a width of 15 mm and a length of 100 mm. Next, using a Tensilon universal testing machine, one end and the other end of each test piece in the length direction were gripped by the machine's grips, and these grips were moved away from each other. The relative movement speed of the grips, i.e., the tensile speed, was set to 300 mm / min. The distance between the gauge marks was set to 50 mm. The movement of the grips was continued until each test piece fractured. Next, the tensile stress was obtained by dividing the tensile force by the initial cross-sectional area within the gauge marks. The tensile strain was obtained by dividing the increase in the distance between the gauge marks by the distance between the gauge marks. Next, the Young's modulus was obtained by dividing the resulting tensile stress by the tensile strain.

[0121] (Opening test) Lids were cut from laminated sheets for lids according to Examples 1 to 6 and Comparative Examples 1 to 3. Using these lids, multiple food packaging containers 20, as shown in Figure 3, were manufactured. Here, a container body 22 made by molding a resin sheet into a tray shape was used. The container body 22 had a roughly rectangular opening with a length of 120 mm in the long side direction and a length of 90 mm in the short side direction, and a height of 30 mm. Heat sealing of the lid 21 to the flange 22a was performed by using a 5 mm wide sealing bar manufactured to conform to the shape of the flange 22a, and applying a temperature of 160°C and a pressure of 0.2 MPa for 1.5 seconds.

[0122] Here, a three-layer sheet was used as the resin sheet, comprising a pair of polypropylene layers and a layer interposed between them consisting of a mixture of polypropylene and 4% by mass of ethylene-vinyl alcohol copolymer.

[0123] Next, for each laminated sheet for the lid, the lid 21 was manually peeled off from the corner of the container body 22 of any 10 of the manufactured food packaging containers 20. After that, the presence or absence of paper peeling and the ease of opening were evaluated. The results of the above measurements and tests are summarized in the table below.

[0124] [Table 1]

[0125] [Table 2]

[0126] In the "Openability" column in Table 1 above, "A" indicates that the user did not experience any of the following: feeling resistance when opening, feeling that force was required to open, or the lid stretching or tearing when opening. "B" indicates that the user experienced at least one of the following: feeling resistance when opening, feeling that force was required to open, or the lid stretching or tearing when opening.

[0127] In the column labeled "Paper Peeling" in Table 1 above, "A" indicates that cohesive failure occurred in the heat-seal layer, but no paper peeling occurred. "B" indicates that paper peeling occurred, but only a portion of the lid material remained on the container body in or around the sealed area. In the case of "B", the contents can be removed from the container body. "C" indicates that paper peeling occurred, and the lid material remained on the container body in areas other than the sealed area and its surroundings. Specifically, in the case of "C", it indicates that a double lid was created or the lid was torn. Here, a double lid occurs when cohesive failure of the paper substrate occurs, and a portion of the lid, mainly consisting of the paper substrate and the heat-seal layer, remains on the container body, covering the entire or almost all of the opening of the container body. In the case of "C", removing the contents from the container body and separating the lid from the container body is time-consuming.

[0128] In the column labeled "Paper Mark" in Table 2 above, "A" indicates that the paper mark under the Container Recycling Law can be displayed, meaning that when the layers other than the paper substrate contained in the lid laminate sheet are classified into layers made of plastic and other layers, the mass of the paper substrate is greater than the total mass of the layers made of plastic and the total mass of the other layers. "B" indicates that the above paper mark cannot be displayed, meaning that when the layers other than the paper substrate contained in the lid laminate sheet are classified into layers made of plastic and other layers, the mass of the paper substrate is less than the total mass of the layers made of plastic and the total mass of the other layers.

[0129] In Table 2 above, "mass" refers to the mass per unit area. The classifications of "paper," "plastic," and "other" in the column labeled "mass ratio" follow the "Explanatory Materials for the Container and Packaging Recycling Law," as explained above.

[0130] As shown in Table 1 above, when the laminated lid sheets according to Examples 1 to 6 were used, the opening performance was excellent and no paper peeling occurred. On the other hand, when the laminated lid sheets according to Comparative Examples 1 to 3 were used, the opening performance was poor.

[0131] <3> Evaluation of oxygen barrier properties <Reference example 1> Glossy paper as a paper base material (basis weight 65g / m²) 2 A coating film mainly composed of polyvinyl alcohol (coating amount 13g / m²) is applied to the main non-gloss surface of the ) 2 A laminated sheet was prepared, consisting of a gas barrier layer with a thickness of 10 μm.

[0132] On the main surface of the paper substrate opposite to the main surface where the gas barrier layer is formed, printing ink is applied by gravure printing at a rate of 1 g / m². 2 The coating was applied, and a printed layer was laminated. On top of the printed layer, an OP varnish agent mainly composed of nitrocellulose resin was applied using the gravure coating method, with an application rate of 10 g / m². 2 A functional layer consisting of an OP varnish layer (in a dry state) was laminated.

[0133] Next, an adhesive composition containing a polyester-based main component and an aliphatic isocyanate-based curing agent is applied to the gas barrier layer by gravure coating, with a coating amount of 2 g / m². 2 A dry adhesive layer was laminated. A heat seal layer with a thickness of 30 μm and a density of 27 g / m² was applied on top of the adhesive layer. 2 A laminated sheet for a lid was obtained by laminating an unstretched film mainly composed of linear low-density polyethylene (LLDPE).

[0134] <Comparative Example 4> A laminated sheet for the lid was manufactured using the same method as in Reference Example 1, except that a functional layer consisting of an OP varnish layer was not provided.

[0135] (Preparation of test specimens for oxygen permeability measurement) The laminated sheets for the lids obtained from Reference Example 1 and Comparative Example 4 were cut into 4cm x 4cm shapes to serve as test specimens. Two test specimens were prepared for each of Reference Example 1 and Comparative Example 4. The test specimens were sandwiched between two aluminum films, each having a 25mm diameter hole in the center, and fixed with adhesive so that the two holes overlapped. By laminating these films, an aluminum laminate (hereinafter also referred to as the "aluminum laminate") was obtained to hold the laminated sheets for the lids. This aluminum laminate was used as the lid for an aluminum cup in the oxygen permeability measurement test described later.

[0136] For the aluminum cups, we prepared cups that conformed to the aluminum moisture-permeable cups specified in JAPAN TAPPI Paper and Pulp Test Method No. 7:2000 Paper and Cardboard - Moisture Permeability Test Method B. By placing the aluminum laminate containing the test specimens into the opening of these cups, we closed the lids and secured them with fasteners, thereby creating a total of four test specimens for environmental storage to be used in the tests described below.

[0137] (Environmental storage of test specimens and measurement of oxygen permeability) Each test specimen obtained above was first stored for 12 hours in a refrigerated environment at 5°C and humidity-free. Next, one of the two test specimens in each of Reference Example 1 and Comparative Example 4 was subjected to environmental storage for 1 hour in a high-temperature, high-humidity environment at 40°C and 90% relative humidity, thereby forcibly inducing condensation on the surface of the test specimen located on the outside of the cup. Then, as a static adjustment before measuring oxygen permeability, each test specimen was stored for 24 hours in an environment at 24°C and 55% relative humidity, after which oxygen permeability was measured (Condition 2). Furthermore, for the other test specimen in each of Reference Example 1 and Comparative Example 4, after being stored in the refrigerated environment as described above, the static adjustment was performed without the above-described environmental storage in the high-temperature, high-humidity environment, and then oxygen permeability was measured (Condition 1).

[0138] Oxygen permeability was measured using a MOCON OX-TRAN2 / 20 oxygen permeability analyzer under conditions of 30°C and 70% relative humidity. The results are shown in Table 3. Lower oxygen permeability indicates superior oxygen barrier properties.

[0139] [Table 3]

[0140] As shown in the measurements in Table 3, lids using laminated sheets for lids that have both a gas barrier layer and a functional layer show controlled degradation of barrier performance due to condensation even when exposed from a refrigerated environment to a high-temperature, high-humidity environment, and the degradation of oxygen barrier performance is dramatically improved. Considering that the time between consumers purchasing packaged chilled food at a store and storing it in their home refrigerator, and the time between consumers taking the packaged food out of the refrigerator and cooking it, lids using laminated sheets for lids that have both a gas barrier layer and a functional layer are extremely effective as lids for chilled food packaging containers.

[0141] <4> Measurement of puncture strength, heat seal strength, and breaking strength <Reference example 2> The laminated sheet for the lid according to Reference Example 2 was manufactured by the following method. First, as a paper base material, the basis weight is 52.3 g / m². 2 A single-sided coated paper was prepared. A printable layer and a functional layer were sequentially formed on the coated layer of this paper substrate using a gravure multi-color printing press. The printable layer was formed using conventional printing ink. The ink application rate was 1.0 g / m². 2 The functional layer 6 was formed using an OP varnish agent mainly composed of nitrocellulose resin and polyethylene granular wax. The application amount of the OP varnish agent was 0.5 g / m². 2 That's what I decided.

[0142] Next, a biaxially oriented polybutylene terephthalate (PBT) film with a thickness of 15 μm was prepared as a support layer. Silica was deposited as an inorganic oxide on one surface of this support layer, and then a coating solution mainly composed of polyvinyl alcohol (PVA) was applied onto this deposited layer to obtain a gas barrier film comprising a support layer made of PBT film and a gas barrier layer made of an inorganic oxide layer and a PVA layer. The mass per unit area of ​​this gas barrier film was 22.2 g / m². 2 That was the case.

[0143] Next, the gas barrier film was bonded to the laminate, which consisted of a paper substrate, a printed layer, and a functional layer, by dry lamination. For dry lamination, first, a dry laminating agent was applied to the gas barrier layer surface of the gas barrier film using a gravure coater to form an adhesive layer. A two-component reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used as the dry laminating agent. The application amount of the dry laminating agent was 3.0 g / m². 2 Next, the laminate and the gas barrier film were bonded together with this adhesive layer in between, so that the gas barrier layer faced the paper substrate.

[0144] Subsequently, a heat-seal layer was bonded to the laminate, which included a support layer, a gas barrier layer, a paper substrate, a printed layer, and a functional layer, by dry lamination. The heat-seal layer included a support layer and an easy-peel layer, with a mass per unit area of ​​26.0 g / m². 2 Therefore, an easy-peel film was used, which had corona treatment applied to the side opposite the easy-peel layer. For dry lamination, first, a dry laminating agent was applied to the surface of the support layer using a gravure coater to form an adhesive layer. A two-component reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used as the dry laminating agent. The amount of dry laminating agent applied was 3.0 g / m². 2 Next, the laminate and the heat seal layer were bonded together with this adhesive layer in between, so that the corona-treated surface of the heat seal layer faced each other.

[0145] Subsequently, this was aged at 40°C. In this manner, a laminated sheet for the lid according to Reference Example 2 was obtained.

[0146] (Reference example 3) A laminated sheet for the lid was manufactured in the same manner as in Reference Example 2, except for the following point. Specifically, in this example, instead of using a biaxially oriented polybutylene terephthalate (PBT) film as the support layer, a biaxially oriented nylon (Ny) film with a thickness of 15 μm was used, and a gas barrier layer containing the inorganic oxide layer and the PVA layer was formed on it, resulting in a mass per unit area of ​​18.6 g / m². 2 A gas barrier film was formed.

[0147] (Reference example 4) The laminated sheet for the lid was manufactured by the following method. First, as a paper base material, the basis weight is 52.3 g / m². 2 A single-sided coated paper was prepared. A gas barrier layer was formed by applying a coating solution containing polyvinyl alcohol (PVA) as the main component and synthetic mica (a layered compound) as an inorganic oxide to the side of this paper substrate that did not have a coating layer. This resulted in a structure consisting of a gas barrier layer and the single-sided coated paper substrate, with a mass per unit area of ​​67.3 g / m². 2 A barrier paper was obtained. On the coating layer of this barrier paper, a printed layer and a functional layer were sequentially formed using a gravure multi-color printing press in the same manner as in Reference Example 2.

[0148] Next, a support layer was bonded to the laminate, which consisted of a gas barrier layer, a paper substrate, a printed layer, and a functional layer, by dry lamination. The support layer had a thickness of 15 μm and a mass per unit area of ​​20.9 g / m². 2A biaxially oriented polybutylene terephthalate (PBT) film, corona-treated on both sides, was used. For dry lamination, a dry laminating agent was first applied to one side of the support layer 2 using a gravure coater to form an adhesive layer. A two-component reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used as the dry laminating agent. The application amount of the dry laminating agent was 3.0 g / m². 2 Next, with this adhesive layer in between, the laminate and the support layer were bonded together so that the support layer faced the gas barrier layer.

[0149] Subsequently, using the same method as in Reference Example 2, a heat seal layer was bonded to a laminate containing a support layer, a gas barrier layer, a paper substrate, a printed layer, and a functional layer, with the adhesive layer in between, so that the support layer faced the heat seal layer.

[0150] Subsequently, this was aged at 40°C. In this manner, a laminated sheet for the lid according to Reference Example 4 was obtained.

[0151] (Reference example 5) The laminated sheet for the lid was manufactured in the same manner as in Reference Example 4, except for the following point. In this example, instead of using a biaxially oriented polybutylene terephthalate (PBT) film as the support layer, a sheet with a thickness of 15 μm and a mass per unit area of ​​17.4 g / m² was used. 2 The material used was a biaxially oriented nylon (Ny) film with an easy-adhesion treatment applied to one side and corona treatment applied to both sides. The support layer was configured so that the side with the easy-adhesion treatment faced the heat-seal layer 1.

[0152] (Comparative Example 5) A laminated sheet for the lid was manufactured in the same manner as in Reference Example 2, except for the following points. Specifically, in this comparative example, instead of using a biaxially oriented polybutylene terephthalate (PBT) film as the support layer, a biaxially oriented polyethylene terephthalate (PET) film with a thickness of 12 μm was used, and a gas barrier layer containing the inorganic oxide layer and the PVA layer was formed on it, resulting in a mass per unit area of ​​17.6 g / m².2 A gas barrier film was formed.

[0153] (Comparative Example 6) The laminated sheet for the lid was manufactured using the same method as in Reference Example 2, except that the support layer and gas barrier layer were omitted.

[0154] (Measurement of breaking strength) The rupture strength of the support layers used in Reference Examples 2 to 5 and Comparative Example 5 was measured by the method described above.

[0155] Here, three test specimens with their longitudinal direction parallel to the medium-density (MD) and three test specimens with their longitudinal direction parallel to the horizontal (TD) were cut from each support layer. Each test specimen was in the shape of a strip with a width of 15 mm and a length of 100 mm.

[0156] The gauge line distance was set to 50 mm, and the test speed was set to 1000 mm / min. The fracture strength was measured using a Tensilon universal tester.

[0157] The fracture strength at MD was obtained by arithmetic mean of the measurements obtained using specimens whose length direction was parallel to MD. Similarly, the fracture strength at TD was obtained by arithmetic mean of the measurements obtained using specimens whose length direction was parallel to TD.

[0158] (Measurement of heat seal strength) The heat seal (HS) strength of the laminated sheets for lids according to Reference Examples 2 to 5 and Comparative Examples 5 and 6 was measured against the resin sheet described above using the method described above.

[0159] Each lid laminate sheet and resin sheet were heat-sealed using a TP-701-B heat seal tester manufactured by Tester Sangyo Co., Ltd. The heat seal tester used here had a sealing bar width of 5 mm. The length of the sealing bar was perpendicular to the median diameter (MD). Heat sealing was performed by applying a temperature of 190°C and a pressure of 0.2 MPa for 2 seconds to the laminate of the lid laminate sheet and resin sheet at each heat sealing position. From each laminate partially heat-sealed in this way, strips with a width of 15 mm, a length parallel to the MD, one end unsealed, and the other end 30 to 50 mm long were obtained. Three heat-sealed test pieces were cut out.

[0160] Separately, each lid laminate sheet and resin sheet were heat-sealed in the same manner as described above, except that the length direction of the sealing bar was perpendicular to the TD. From each laminate partially heat-sealed in this way, three test pieces were cut out, each having a strip shape with a width of 15 mm, a length parallel to the TD, and one end not heat-sealed, while the other end was heat-sealed over a length of 30 to 50 mm.

[0161] Next, the heat seal strength of each test specimen was measured using the method described above. Specifically, a Tensilon universal tester was used to measure the heat seal strength. The unheat-sealed laminated sheet portion and resin sheet portion of each test specimen were gripped by the grips of the tester, and these grips were moved away from each other. The relative movement speed of these grips, i.e., the peeling speed, was set to 1000 mm / min. For each test specimen, the maximum tensile load applied until fracture occurred was recorded.

[0162] For each laminated sheet for the lid, the heat seal strength at MD was obtained by arithmetic mean of the maximum tensile loads obtained from three test specimens whose length direction was parallel to MD. Similarly, for each laminated sheet for the lid, the heat seal strength at TD was obtained by arithmetic mean of the maximum tensile loads obtained from three test specimens whose length direction was parallel to TD.

[0163] (Measurement of puncture strength) The puncture strength of the laminated sheets for lids according to Reference Examples 2 to 5 and Comparative Example 5 was measured using the method described above. Here, the puncture strength when a needle was inserted into the laminated sheet for lids from the functional layer side and the puncture strength when a needle was inserted into the laminated sheet for lids from the heat seal layer side were determined. Each puncture strength was obtained by arithmetic mean of the values ​​obtained from three measurements.

[0164] (Cup seal test) Lids were cut from the laminated sheets for lids according to Reference Examples 2 to 5 and Comparative Examples 5 and 6. Using these lids, a food packaging container 20 as shown in Figure 3 was manufactured. Here, the container body 22 was made by molding the aforementioned resin sheet into a tray shape. The container body 22 had a roughly rectangular opening with a length of 120 mm in the long side direction and a length of 90 mm in the short side direction, and a height of 30 mm. Heat sealing of the lid 21 to the flange 22a was performed by using a 5 mm wide sealing bar manufactured to conform to the shape of the flange 22a, and applying a temperature of 160°C and a pressure of 0.2 MPa for 1.5 seconds.

[0165] Next, for each food packaging container 20, the lid 21 was peeled off by hand from the corner of the container body 22. After that, it was checked whether any paper peeling had occurred. The results of the above measurements and tests are summarized in Table 4 below.

[0166] [Table 4]

[0167] In Table 4 above, "mass" refers to the mass per unit area. The classifications of "paper," "plastic," and "other" in the column labeled "mass ratio" follow the "Explanatory Materials for the Container and Packaging Recycling Law," as explained above. The column labeled "difference" shows the value obtained by subtracting the heat seal strength between the lid laminate sheet and the resin sheet from the breaking strength of the support layer.

[0168] In the column labeled "Paper Peeling" in Table 4 above, "A" indicates that cohesive failure occurred in the heat-seal layer, but no paper peeling occurred. "B" indicates that paper peeling occurred, but only a portion of the lid material remained on the container body in or around the sealed area. In the case of "B", the contents can be removed from the container body. "C" indicates that paper peeling occurred, and the lid material remained on the container body in areas other than the sealed area and its surroundings. Specifically, in the case of "C", it indicates that a double lid was created or the lid was torn. Here, a double lid occurs when cohesive failure of the paper substrate occurs, and a portion of the lid, mainly consisting of the paper substrate and the heat-seal layer, remains on the container body, covering the entire or almost all of the opening of the container body. In the case of "C", removing the contents from the container body and separating the lid from the container body is time-consuming.

[0169] In the column labeled "Puncture Strength" in Table 4 above, "Upper Surface" represents the penetration strength when the needle is inserted into the laminated lid sheet from the functional layer side, and "Lower Surface" represents the penetration strength when the needle is inserted into the laminated lid sheet from the heat seal layer side. In the column labeled "Upper Surface" or "Lower Surface", "A" indicates that the penetration strength was twice or more than that obtained for the laminated lid sheet of Comparative Example 6. "B" indicates that the penetration strength was more than 1.5 times but less than 2 times that of the laminated lid sheet of Comparative Example 6. "C" indicates that the penetration strength was 1.5 times or less that of the laminated lid sheet of Comparative Example 6.

[0170] As shown in Table 4 above, the laminated sheets for covers according to Reference Examples 2 to 5 exhibited high puncture strength when the needle was inserted into the laminated sheet for covers from both the functional layer side and the heat seal layer side. In contrast, the laminated sheet for covers according to Comparative Example 6 exhibited low puncture strength when the needle was inserted into the laminated sheet for covers from both the functional layer side and the heat seal layer side. The laminated sheet for covers according to Comparative Example 5 exhibited high puncture strength when the needle was inserted into the laminated sheet for covers from the heat seal layer side, but low puncture strength when the needle was inserted into the laminated sheet for covers from the functional layer side.

[0171] Furthermore, as shown in Table 4 above, when the laminated lid sheets according to Reference Examples 2 to 5 and Comparative Example 5 were used, no paper peeling occurred. On the other hand, when the laminated lid sheet according to Comparative Example 6 was used, paper peeling occurred.

[0172] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of symbols]

[0173] 1...Heat seal layer, 2...Support layer, 3...Gas barrier layer, 4...Paper substrate, 5...Printed layer, 6...Water-resistant functional layer, 10, 11...Laminated sheet for lid, 20...Food packaging container, 21...Lid, 22...Container body, 22a...Flange.

Claims

1. A laminated sheet for a lid used in the lid of a food packaging container comprising a container body having an opening and a lid covering the opening, comprising, in this order, a water-resistant functional layer, a printing layer, a paper substrate, a support layer, and a heat-seal layer. The mass of the paper substrate is greater than the mass of any other layer included in the laminated sheet for the lid. The aforementioned functional layer is an overprint varnish layer. The Young's modulus of the laminated sheet for the lid is in the range of 1.2 to 2.9 GPa in both the MD and TD directions. The laminated sheet for the lid has a thickness in the range of 80 to 205 μm.

2. The laminated sheet for a lid according to claim 1, wherein the Young's modulus is in the range of 1.2 to 2.6 GPa.

3. The laminated sheet for the lid according to claim 1 or 2, wherein the thickness of the laminated sheet for the lid is in the range of 90 to 150 μm.

4. The support layer comprises at least one of polybutylene terephthalate and polyamide, as described in any one of claims 1 to 3, for a laminated sheet for a lid.

5. The laminated sheet for a lid according to any one of claims 1 to 4, wherein, when the layers other than the paper substrate included in the laminated sheet for a lid are classified into layers made of plastic and other layers, the mass of the paper substrate is greater than the total mass of the layers made of plastic and the total mass of the other layers.

6. The laminated sheet for a lid according to any one of claims 1 to 5, further comprising a gas barrier layer having gas barrier properties between the paper substrate and the heat seal layer.

7. The laminated sheet for a lid according to claim 6, wherein the gas barrier layer comprises at least one of an inorganic oxide layer and a resin-containing layer.

8. The laminated sheet for a lid according to claim 6 or 7, wherein the gas barrier layer is included between the paper substrate and the support layer.

9. The laminated sheet for a lid according to any one of claims 6 to 8, wherein the paper substrate is a barrier paper having the gas barrier layer on one side.

10. The laminated sheet for a lid according to any one of claims 1 to 9, wherein the paper substrate is coated paper having a coating layer on one side, and the printing layer is provided on the coating layer.

11. The aforementioned paper substrate has a basis weight of 40 to 160 g / m². ２ A laminated sheet for a lid according to any one of claims 1 to 10 within the range of [the specified range].

12. The laminated sheet for a lid according to any one of claims 1 to 11, wherein the heat-seal layer is a sealant having easy-peel properties.

13. The functional layer has a mass of 0.2 g / m² per unit area. ２ The laminated sheet for a lid according to any one of claims 1 to 12.

14. A lid made of a laminated sheet for lids according to any one of claims 1 to 13.

15. A food packaging container comprising a container body having an opening and a lid according to claim 14 that covers the opening, wherein the support layer is disposed between the paper substrate and the internal space of the food packaging container.

16. The food packaging container according to claim 15, wherein the container body has a flange around the opening, and the lid is heat-sealed to the flange via the heat-seal layer.

17. The food packaging container according to claim 15 or 16, wherein the internal space of the food packaging container is filled with a mixed gas containing oxygen gas, nitrogen gas, and carbon dioxide gas.

18. The food packaging container according to any one of claims 15 to 17, wherein the food packaging container is a chilled food packaging container or a frozen food packaging container.

19. The food packaging container according to any one of claims 15 to 18, wherein the breaking strength of the support layer is greater than the heat seal strength between the lid and the container body.

20. A packaged food comprising a food packaging container according to any one of claims 15 to 19, and food contained in the food packaging container.

Images