JP2023183296A - Lamination sheet for lid body, lid body, food packaging container, and packaged food - Google Patents

Abstract

To provide a lid body which is used in a food package container, includes a paper base material, and has excellent openability.SOLUTION: A lamination sheet 10 for a lid body according to an embodiment of the invention is used in a lid body of a food package container including a container body provided with an opening, and the lid body which covers the opening. The lamination sheet 10 for the lid body includes a function layer 7 having water resistance, a paper base material 5, a support layer 3, and a heat seal layer 1 in a written order. A mass of the paper base material 5 is larger than masses of any other layers included in the lamination sheet 10 for the lid body. The heat seal layer has a thickness ranging from 1 μm to 5.5 μm. A hardness of the heat seal layer is 12.0 MPa or lower.SELECTED DRAWING: Figure 1

Description

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

In addition to changes in household composition and lifestyles due to the trend toward nuclear families in recent years, advances in distribution, freezing, and refrigeration technologies have led to an increase in the number of cooked and processed chilled foods sold at convenience stores and supermarkets. Demand for frozen foods is increasing. At the same time, demand for packaging containers for chilled and frozen foods is also increasing.

On the other hand, as efforts are being made to reduce plastic waste, demand is increasing for food packaging containers that have a low environmental impact and use paper, a renewable resource, as a base material. There is also a demand for packaging containers for storing chilled foods to use paper packaging containers that use paper as a base material.

Furthermore, some packaging containers include a container body provided with an opening and a lid covering the opening.

For example, Patent Document 1 discloses, as a film used for a lid, a film including a base layer, a cohesive failure layer, and a heat seal layer in this order.

Japanese Patent Application Publication No. 2016-210063

An object of the present invention is to provide a lid body that is used for food packaging containers, includes a paper base material, and has excellent unsealability.

According to one aspect of the present invention, there is provided a laminated sheet for a lid used for the lid of a food packaging container, which includes a container main body provided with an opening and a lid covering the opening, and has water resistance. It includes a functional layer, a paper base material, a support layer, and a heat sealing layer in this order, and the mass of the paper base material is greater than the mass of any other layer included in the laminated sheet for lid body. There is provided a laminated sheet for a lid, wherein the heat seal layer has a thickness in a range of 1 μm or more and 5.5 μm or less, and a hardness of the heat seal layer is 12.0 MPa or less.

According to another aspect of the present invention, there is provided a laminated sheet for a lid body according to the above aspect, wherein the hardness is 6.5 MPa or more.

According to still another aspect of the present invention, there is provided a laminate sheet for a lid according to any of the above aspects, further including a printing layer between the functional layer and the paper base material.

According to still another aspect of the present invention, there is provided a laminate sheet for a lid according to the above aspect, further including a gas barrier layer having gas barrier properties between the printing layer and the heat sealing layer.

According to still another aspect of the present invention, there is provided a laminate sheet for a lid body according to the above aspect, in which the gas barrier layer includes at least one of an inorganic oxide layer and a resin-containing layer.

According to still another aspect of the present invention, when the layers other than the paper base material included in the lid laminated sheet are classified into a layer made of plastic and another layer, the paper base material There is provided a laminated sheet for a lid body according to any of the above aspects, wherein the mass is larger than the total mass of the plastic layers and the total mass of the other layers.

According to still another aspect of the present invention, there is provided a laminated sheet for a lid according to any of the above aspects, wherein the paper base material is coated paper having a coating layer on one side.

According to still another aspect of the present invention, the heat seal layer has a glass transition temperature in the range of 20 to 55° C. and is made of a heat seal varnish containing an ethylene-vinyl acetate copolymer. A laminated sheet for a lid body according to the present invention is provided.

According to still another aspect of the present invention, any of the above aspects further includes an anchor coat layer having a thickness of 0.5 μm or more and 2.5 μm or less between the support layer and the heat seal layer. A laminated sheet for a lid body according to the present invention is provided.

According to still another aspect of the present invention, there is provided a lid made of the laminated sheet for lids according to any of the above aspects.

According to still another aspect of the present invention, there is provided a food packaging container comprising a container main body provided with an opening and the lid covering the opening, wherein the support layer includes the paper base material and the food product. A food packaging container is provided which is disposed between the food packaging container and the interior space of the food packaging container.

According to still another aspect of the present invention, the food packaging according to the above aspect, wherein the container body has a flange around the opening, and the lid body is heat-sealed to the flange via the heat-sealing layer. A container is provided.

According to still another aspect of the present invention, the food packaging container according to any of the above aspects, wherein the internal space of the food packaging container is filled with a mixed gas containing oxygen gas, nitrogen gas, and carbon dioxide gas. provided.

According to still another aspect of the present invention, there is provided a food packaging container according to any of the above aspects, wherein the food packaging container is a chilled food packaging container or a frozen food packaging container.

According to still another aspect of the present invention, there is provided a packaged food comprising the food packaging container according to any of the above aspects and the food contained in the food packaging container.

According to the present invention, there is provided a lid that is used for food packaging containers, includes a paper base material, and has excellent unsealability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is 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. FIG. 3 is a cross-sectional view schematically showing one step in hardness measurement. Graph showing a load displacement curve. FIG. 3 is a cross-sectional view schematically showing a food packaging container according to a third embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific implementations of any of the above aspects. Note that elements having the same or similar functions are given the same reference numerals, and redundant explanations will be omitted.

[First embodiment]
FIG. 1 is a cross-sectional view schematically showing an example of a laminated sheet for a lid according to a first embodiment of the present invention.
The laminated sheet 10 for a lid shown in FIG. 1 is used as a lid in a food packaging container that includes a container body provided with an opening and a lid that covers the opening. That is, the laminated sheet for lid 10 is a lid material that itself is used as a lid, or a portion cut out from it is used as a lid.

The laminated sheet 10 for the lid includes a heat seal layer 1, an anchor coat layer 2, a support layer 3, a gas barrier layer 4, a paper base material 5, a printing layer 6, and a functional layer having water resistance (water resistance). layer) 7 in this order.

Each layer included in the lid laminated sheet 10 will be described below.

(Functional layer with water resistance)
The functional layer (water-resistant layer) 7 having water resistance suppresses liquids from outside the container, such as water and oil due to dew condensation, from penetrating into the lid body in packaged foods described later, and prevents this liquid from penetrating into the lid body. This is a layer that prevents the gas from reaching layers such as the paper base material 5 and the gas barrier layer 4. The functional layer 7 prevents liquid from outside the container from reaching layers such as the printing layer 6, paper base material 5, and gas barrier layer 4, thereby preventing, for example, deterioration, destruction, or reduction in adhesion of these layers. prevent.

According to one example, the functional layer 7 is formed on the printed layer 6 to control the water absorption of the partially laminated sheet that is the portion from the functional layer 7 to the gas barrier layer 4 of the laminated sheet 10 for the lid. do. The functional layer 7 preferably has water resistance that makes the water absorption of the laminated sheet for a lid body 20 g/m ² or less by the Cobb method described below.

Here, water absorption refers to the contact time of the test piece with water, using the measurement surface as the surface of the functional layer 7, in the method specified in JIS P8140:1998 "Paper and paperboard - Water absorption test method - Cobb method". This is the water absorption obtained when the time is 300 seconds. As mentioned above, 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 of this water absorption is ideally 0 g/m ² . According to one example, this water absorption is greater than or equal to 1 g/m ² .

The functional layer 7 is preferably an overprint varnish layer (hereinafter referred to as "OP varnish layer").
According to one example, the functional layer 7 contains a water-resistant resin. As the water-resistant resin, any resin that can achieve the above-mentioned water absorption can be used without any restriction. Examples of water-resistant resins include polyolefin resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and vinyl chloride-vinyl acetate copolymers, silicone resins, acrylic resins, epoxy resins, Polyester resins, cellulose resins, or urethane resins can be used. The functional layer 7 can be obtained, for example, by applying a paint containing a water-resistant resin onto the paper base material 5 on which the printing layer 6 is formed by a known method. In addition to the water-resistant resin, the paint may further contain additives such as pigments, dyes, curing agents, leveling agents, antiblocking agents, and lubricants, and solvents.

The functional layer 7 preferably has high abrasion resistance and scratch resistance so as to maintain sufficient water resistance. From this point of view, it is preferable that the thickness of the functional layer 7 and the coating amount of the paint that is its material are larger than the thickness of the normal OP varnish layer and the coating amount of the normal OP varnish. Here, the "coating amount" is the solid mass per area.

For example, in the lid laminated sheet 10 shown in FIG. 1, the paint for forming the functional layer 7 is preferably applied in an amount of 0.2 g/m ² or more, and 2.0 g/m 2 or more. It is more preferable to apply the coating in such a manner that the coating thickness is at least /m ² . This paint is applied in such a manner that the coating amount is, for example, 10 g/m ² or less. The thickness of the functional layer 7 is preferably 0.2 μm or more, more preferably 2.0 μm or more. The thickness of the functional layer 7 is, for example, 10 μm or less. Note that the functional layer 7 may be provided on the printing layer 6 by lamination.

(Printing layer)
The printed layer 6 is a layer formed in order to put the lid laminate sheet 10 or the lid into practical use as a commercial product. The printing layer 6 is made of, for example, a conventional ink binder resin such as urethane-based, acrylic-based, nitrocellulose-based, rubber-based, or vinyl chloride-based, and various pigments, extender pigments, plasticizers, drying agents, and stabilizers. This layer is made of ink to which additives such as agents are added, and displays patterns such as letters and pictures. As a method for forming the printing layer 6, for example, well-known printing methods such as offset printing, gravure printing, and silk screen printing, and well-known coating methods such as roll coating, knife edge coating, and gravure coating are used. be able to.

The thickness of the printed layer 6 is not particularly limited, and according to one example is within the range of 0.1 to 5 μm, and according to another example is within the range of 0.2 to 1 μm.

(Paper base material)
The lid laminated sheet 10 includes a paper base material 5. The mass of the paper base material 5 is larger than the mass of any other layer included in the lid laminated sheet 10. The ratio of the mass of the paper base material 5 to the mass of the laminated sheet 10 for lid body is preferably 40% or more, more preferably 45% or more, even more preferably 50% or more, and 50% or more. It is more preferable that it exceeds %. In one example, this percentage is 80% or less, in another example 70% or less, and in yet another example 65% or less.

When the layers other than the paper base material 5 included in the lid laminated sheet 10 are classified into layers made of plastic and other layers, the mass of the paper base material 5 is equal to the total mass of the layers made of plastic and It is preferable that the mass is larger than the total mass of the other layers. In this case, in Japan, the lid laminated sheet 10 can be treated as paper under the Containers and Packaging Recycling Law.

The above classification is based on the "Containers and Packaging Recycling Law Explanatory Materials." That is, "plastic" is a material that contains a polymer as an essential component and is shaped and manufactured using fluidity during processing. Paints and adhesives are not included in plastics because they are unrelated to the concept of "forming." Therefore, in the example shown in FIG. 1, the support layer 3 is a "layer made of plastic." Further, in the example shown in FIG. 1, a heat seal layer 1, an anchor coat layer 2, a printing layer 6 formed from ink, a functional layer 7 formed by coating, and an adhesive layer (not shown) formed from an adhesive. is the "other layer".

On the other hand, the gas barrier layer 4 is classified according to the following cases. That is, in the example shown in FIG. 1, if the gas barrier layer 4 is a layer formed by coating or vapor deposition on the paper base material 5, it can be treated as a "paper base material" according to the above explanatory material. However, it is treated as "other layers" here. For example, when the paper base material 5 is a barrier paper on which the gas barrier layer 4 is coated or vapor-deposited on one side, the gas barrier layer 4 is the "other layer". Moreover, when the gas barrier layer 4 is a layer formed on the support layer 3 by coating or vapor deposition, it is treated as an "other layer" here. Moreover, when a polymer film produced by at least melt molding such as extrusion processing is used for the gas barrier layer 4, it is a "layer made of plastic".

The basis weight, ie, the mass per area, of the paper substrate 5 is in the range of 20 to 500 g/m ² according to one example, and in the range of 40 to 100 g/m ² according to another example. When the basis weight of the paper base material 5 is increased, the lid becomes hard and the opening property tends to deteriorate. When the basis weight is reduced, the strength of the lid is reduced.

In addition, when the basis weight of the paper base material 5 is increased, the ratio of the mass of the paper base material 5 to the mass of the laminated sheet for lid 10 also increases. However, when the basis weight of the paper base material 5 is increased, the amount of carbon dioxide emitted during manufacturing of the paper base material 5 and disposal of the lid laminated sheet 10 increases.

The paper base material 5 is not particularly limited as long as it has plant-derived pulp as its main component. Examples of the paper base material 5 include coated paper such as high-quality paper, medium-quality paper, and lightly coated paper, glossy paper, and bleached and unbleached kraft paper (acidic paper or neutral paper).

The paper base material 5 is preferably coated paper having a coating layer on at least one surface. That is, it is preferable that the paper base material 5 is a single-sided coated paper or a double-sided coated paper. The surface of coated paper provided with a coating layer has excellent smoothness compared to the surface of paper not provided with a coating layer.

When the paper base material 5 is coated paper having a coat layer on one side, the printing layer 6 can be provided on the coat layer, for example. In this case, excellent adhesion can be achieved between the paper base material 5 and the printed layer 6.

When the paper base material 5 is coated paper having a coat layer on one side, the gas barrier layer 4 can be provided on the coat layer, for example. By doing so, the adhesion of the gas barrier layer 4 to the paper base material 5 is improved. Furthermore, the thickness of the gas barrier layer 4 required to exhibit barrier properties can be reduced.

When coated paper having coating layers on both sides is used as the paper base material 5, excellent adhesion between the paper base material 5 and the printing layer 6 can be achieved. Moreover, it becomes easy to realize excellent adhesion between the paper base material 5 and the gas barrier layer 4.

The coat layer contains resin. Examples of the resin contained in the coating layer include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ethylene-α polymerized using a metallocene catalyst (single-site catalyst). -Olefin copolymer, 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 resins, and polybutylene terephthalate. Examples include thermoplastic resins such as resin, nylon resin, and styrene-butadiene rubber. These resins may be used in combination of two or more, or may be used by copolymerizing two or more. The coating layer may further contain additives, such as fillers such as silica, clay, kaolin, calcium carbonate, talc, mica, and titanium oxide.

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

(Gas barrier layer)
The gas barrier layer 4 has gas barrier properties such as oxygen barrier properties and water vapor barrier properties. The gas barrier layer 4 suppresses gases such as oxygen, water vapor, and aroma components from outside the container from entering the container in the packaged food described later. Thereby, the gas barrier layer 4 suppresses deterioration of the food contents in the packaged food. Moreover, the gas barrier layer 4 suppresses the diffusion of odor components of the contents to the outside of the container in the packaged food. According to one example, the gas barrier layer 4 has an oxygen permeability of 0.1 to 100 cc/m ² /day/atm under an atmosphere of a temperature of 30° C. and a relative humidity of 70%.

The gas barrier layer 4 is, for example, a metal layer, an inorganic oxide layer, a resin-containing layer, or a combination of two or more thereof. When microwave heating using a microwave oven is assumed, the gas barrier layer 4 is preferably an inorganic oxide layer, a resin-containing layer, or a combination thereof.

The gas barrier layer 4 may be formed by coating, melt molding, or vapor-deposited inorganic oxide. Alternatively, the gas barrier layer 4 may be a metal foil such as an aluminum foil, or may be formed by vapor-depositing a metal such as aluminum.

Examples of inorganic oxides 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. can use things.

The resin-containing layer can be formed, for example, by coating. In this case, a coating liquid containing a resin 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 liquid. As a coating method, various coating methods such as a gravure coating method, a die coating method, a blade coating method, a knife coating method, and a bar coating method can be used.

When forming the resin-containing layer by melt molding, for example, extrusion molding techniques such as T-die and inflation can be used. In melt molding, for example, the resin or a mixture of the resin and additives is heated and melted, and the gas barrier layer 4 is processed into a film or sheet using a T-die, inflation, or the like. This film or sheet is bonded to the paper base material 5. Examples of bonding methods include a dry lamination method using a solvent-based adhesive, a non-sol lamination method using a solvent-free adhesive, and a sand lamination method using a molten resin as an adhesive. Alternatively, it can be formed directly on the paper base material by extrusion lamination or the like, and in this case, an adhesive layer may also be formed on the paper base material if necessary.

The gas barrier layer 4 may be interposed between the paper base material 5 and the support layer 3 by forming it on one surface of the support layer 3 . Alternatively, the gas barrier layer 4 can be interposed between the paper base material 5 and the support layer 3 of the laminated sheet for lid 10 by using a barrier paper consisting of the paper base material 5 having the gas barrier layer 4 on one side. You may let them. The paper base material 5 constituting the barrier paper may be a coated paper having a coating layer on at least one surface. When the paper base material 5 constituting the barrier paper has a coat layer on only one side, the gas barrier layer 4 may be provided on the coat layer, or on the surface of the paper base material 5 on which the coat layer is not formed. It may be provided above.

The thickness of the gas barrier layer 4 is in the range 0.01 to 30 μm according to one example, and in the range 0.1 μm to 12 μm according to another example.

(Support layer)
The support layer 3 improves the strength of the lid laminated sheet 10.
The support layer 3 is made of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide, ethylene/vinyl alcohol copolymer, polyacrylonitrile (PAN), polymethylpentene (PMP), polyvinyl alcohol resin, olefin resin, or unsaturated Contains polyester resin. The support layer 3 may have a single layer structure or a multilayer structure.

The support layer 3 may be an unstretched film or a stretched film such as a biaxially stretched film. In the case of a stretched film, it is preferable to use a biaxially stretched film. This is because biaxial stretching reduces variations in physical properties such as breaking strength in the in-plane direction of the film compared to uniaxial stretching.

The support layer 3 may further include additives such as a curing agent, a filler, an antiblocking agent, and an antistatic agent. Moreover, as a material for the support layer 3, a material that can be cured by irradiation with active energy rays such as ultraviolet rays and electron beams can also be used.

The thickness of the support layer 3 is preferably in the range of 3 to 60 μm, more preferably in the range of 10 to 30 μm. If the support layer 3 is too thick, it will be difficult to increase the ratio of the mass of the paper base material 5 to the mass of the laminated sheet for lid 10.

The support layer can be formed by laminating it on a paper base material using an adhesive, such as a dry lamination method using a solvent-based adhesive, a non-sol lamination method using a solvent-free adhesive, or a method using molten resin. There is a sand lamination method that is used as an agent. Alternatively, the supporting layer composition can be directly formed on the paper base material by extruding a molten state of the support layer composition using an extrusion lamination method, and an adhesive layer may also be formed on the paper base material if necessary.

(Anchor coat layer)
Anchor coat layer 2 is a layer for improving the adhesion between heat seal layer 1 and support layer 3.
For the material of the anchor coat layer 2, an adhesive resin or an adhesive that provides the necessary adhesive strength is appropriately selected and used depending on the material of the layer to be bonded therethrough.

Examples of the adhesive resin include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, and polyethylene such as a copolymer of ethylene-α olefin polymerized using a metallocene catalyst; Vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-maleic acid copolymer, etc. One or more resins selected from ethylene-unsaturated carboxylic acid copolymers; and ionomer resins can be used.

The adhesive is, for example, an adhesive composition formed by mixing a first composition containing a base agent and a solvent and a second composition containing a curing agent and a solvent. The adhesive layer obtained from this adhesive includes a cured product produced by the reaction between the main agent and the curing agent in the adhesive composition.

An example of the main ingredient is a polyol. Examples of curing agents include isocyanate compounds. Examples of the adhesive include ether-based two-component reactive adhesives and ester-based two-component reactive adhesives.

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

Examples of cured ester-based two-component adhesives include polyester polyurethane and polyester. Polyester polyurethane is produced by the reaction of a polyester polyol as a main ingredient and an isocyanate compound as a curing agent.

In a two-component reactive adhesive, an acrylic polyol may be used as the main ingredient. Moreover, the above-mentioned adhesive composition does not need to contain a solvent as long as it can be melted by heating and its viscosity can be lowered.

The thickness of the anchor coat layer 2 is preferably in the range of 0.5 μm or more and 2.5 μm or less, and more preferably in the range of 0.8 to 2.0 μm. When the thickness of the anchor coat layer 2 is within the above range, it is possible to achieve high adhesion even though the thickness of the anchor coat layer 2 is thin.

The dry mass per area of the anchor coat layer 2, that is, the coating amount is preferably within the range of 0.5 to 2.5 g/ ^m2 , and preferably within the range of 0.8 to 2.0 g/ ^m2 . It is more preferable that the amount is within the range of 1.0 to 1.8 g/m ² . As a coating method, various coating methods such as a gravure coating method, a die coating method, a blade coating method, a knife coating method, and a bar coating method can be used.

(heat seal layer)
The heat-sealing layer 1 enables the lid 21 to be heat-sealed to the container body 22 of the food packaging container 20 shown in FIG. 4, which will be described later.

According to one example, the heat-sealing layer 1 can be provided on the anchor coat layer 2 by lamination. In this case, the heat-sealing layer 1 is made of, for example, an easy-peel sealant. Methods for bonding the heat seal layer to the anchor coat layer by lamination or the like include dry lamination using a solvent-based adhesive, non-sol lamination using a solvent-free adhesive, and sand lamination using a molten resin as an adhesive. There is. Moreover, when extrusion-molding a heat-sealing layer with a molten resin, an extrusion lamination method can also be used.

According to another example, the heat-sealing layer 1 can also be formed on the anchor coat layer 2 by coating. In this case, the heat seal layer 1 is made of heat seal varnish, for example. When the heat seal layer 1 is made of heat seal varnish, a thin heat seal layer can be obtained more easily than when the heat seal layer 1 is made of an easy peel sealant. This is because the easy-peel sealant has a multilayer structure. When the heat seal layer 1 is thin, it is easy to reduce the amount of petroleum-derived compounds used. Furthermore, when the heat seal layer 1 made of heat seal varnish is used, the cost can be reduced compared to the case where the heat seal layer 1 is made of easy peel sealant. Here, as an example, it is assumed that the heat seal layer 1 is made of heat seal varnish. As a coating method, various coating methods such as a gravure coating method, a die coating method, a blade coating method, a knife coating method, and a bar coating method can be used.

The heat sealing layer 1 is made of, for example, ethylene-vinyl acetate (EVA), ionomer resin, polypropylene, linear low density polyethylene (LLDPE), or ultra-low density straight polyethylene. Contains polyolefins such as chain polyethylene (Very Low Density Polyethylene; VLDPE). The heat seal layer 1 may contain additives such as ultraviolet absorbers.

The heat-sealing layer 1 is preferably a layer containing an ethylene-vinyl acetate copolymer, more preferably a layer containing an ethylene-vinyl acetate copolymer as a main component, and still more preferably a layer containing an ethylene-vinyl acetate copolymer. This layer is made of a copolymer.

The glass transition temperature of the heat seal layer 1 is preferably within the range of 20 to 55°C, more preferably within the range of 25 to 50°C. If the glass transition temperature is too low, blocking tends to occur. If the glass transition temperature is too high, damage may occur to other layers when heat sealing the lid to the container body.

The thickness of the heat seal layer 1 is within the range of 1 μm or more and 5.5 μm or less. The thickness of the heat seal layer 1 is preferably in the range of 1.2 μm or more and 5.0 μm or less, and more preferably in the range of 1.5 μm or more and 4.5 μm or less. When the thickness of the heat seal layer 1 is less than 1 μm, it is difficult to achieve high heat seal strength between the lid and the container body. That is, it is difficult to achieve high sealing performance. If the thickness of the heat seal layer 1 is greater than 5.5 μm, fluffing and stringiness are likely to occur when the lid is peeled off from the container body. Fluffing and stringiness will be discussed later. Furthermore, if the heat seal layer 1 is too thick, it takes a long time to dry, which tends to reduce productivity.

The dry mass per area of the heat-sealing layer 1, that is, the coating amount is preferably within the range of 0.5 to 5.0 g/ ^m2 , and preferably within the range of 1.0 to 4.5 g/ ^m2 . It is more preferable that the amount is within the range of 1.5 to 4.0 g/m ² .

The hardness of the heat seal layer 1 is 12.0 MPa or less. The hardness of the heat seal layer 1 is preferably 11.7 MPa or less, more preferably 11.5 MPa or less. The hardness of the heat seal layer 1 is preferably 6.5 MPa or more, more preferably 6.7 MPa or more, and even more preferably 7 MPa or more.

If the hardness of the heat seal layer 1 is too small, blocking is likely to occur. If the hardness of the heat seal layer 1 is greater than 12.0 MPa, fluffing and stringiness are likely to occur when the lid is peeled off from the container body.

The hardness of the heat seal layer 1 is preferably in the range of 6.5 to 12.0 MPa, more preferably in the range of 6.7 to 11.7 MPa, and more preferably in the range of 7 to 11.5 MPa. It is more preferable that the

Hardness is obtained by nanoindentation method. The method for measuring hardness will be described below.

First, a rectangular sheet piece having a length of 3 mm and a width of 1 mm is cut out from the laminated sheet 10 for a lid. Next, the surface of the obtained sheet piece on the heat seal layer 1 side and the surface on the functional layer 7 side are coated with resin. This embeds the sheet piece in resin. As the resin, a photocurable resin such as an ultraviolet curable resin and a visible light curable resin is used.

Next, using a microtome, the resin-embedded sheet piece is cut in a direction parallel to the thickness direction of the lid laminated sheet 10 and parallel to the width direction. Conditions during finishing include a cutting thickness of 300 nm and a cutting speed of 1 mm/sec. This process makes the cross section uniform. Moreover, according to this treatment, it is possible to suppress the heat seal varnish from dripping or falling off. Further, cutting is performed so that the portion of the paper base material 5 soaked with the embedding resin is exposed. This prevents frayed paper fibers from interfering with the measurement results. A test piece is thus obtained.

Next, the obtained test piece is placed in a nanoindenter. Here, the test piece is placed in the nanoindenter so that the indenter included in the nanoindenter contacts the cross section of the heat seal layer 1 perpendicularly. As the nanoindenter, one that is capable of surface detection at 1 μN is used. Note that during installation, the embedding resin may be trimmed if necessary.

Next, as shown in FIG. 2, the indenter 30 is pushed into the heat seal layer 1. The pushing speed is 100 nm/sec. FIG. 2 is a cross-sectional view schematically showing a state in which the indenter 30 is pushed into the heat seal layer 1 at the maximum depth. In FIG. 2, hmax indicates the maximum depth of indentation into the heat seal layer 1, that is, the maximum displacement. Ac indicates the projected contact area. hc indicates the contact depth. During the process of pushing in the indenter 30, the load applied to the heat seal layer 1 and the pushing depth are measured using a nanoindenter.

As the indenter 30, a Berkovich indenter made of diamond is used. The tip of the Berkovich indenter consists of three surfaces, each having a triangular shape. Each triangle has the position of one of its vertices coincident with the position of one of the vertices of each of the other two triangles. Further, in these triangles, the angles formed by the two sides extending from the above-mentioned vertices are equal to each other. That is, these three surfaces form a substantially regular triangular pyramid. In the indenter 30 used here, the angle of each triangle is 115°. Further, the angle between the center line of the indenter 30 and a plane including one of the above triangles is 65.27°. The nanoindenter is set so that the indenter 30 further presses the surface of the heat seal layer 1 by 200 nm after the surface detection load reaches 1 μN. When set in this way, the actual indentation depth is approximately 260 nm. The holding time at maximum depth is 2 seconds.

Next, the indenter 30 is pulled out from the heat seal layer 1. The drawing speed is 100 nm/sec. In this process as well, the load applied to the heat seal layer 1 and the depth of indentation are measured using a nanoindenter. In addition, in FIG. 2, Pmax indicates the maximum load of the unloading curve.

According to the above-described operation, the graph shown in FIG. 3 is obtained. FIG. 3 is a graph showing a load displacement curve. The vertical axis in FIG. 3 is the load applied to the heat seal layer 1, and the horizontal axis is the indentation depth of the indenter 30, that is, the displacement. In FIG. 3, a load of 0N indicates a state in which the indenter 30 is not in contact with the heat seal layer 1. Further, the position where the displacement is 0 is the position where the load applied to the heat seal layer 1 starts to increase from 0N. In FIG. 3, a curve that starts at a load of 0 μN and ends at about 13 μN shows the relationship between load and displacement during the process of pushing the indenter 30 into the heat seal layer 1. The curve starting at a load of about 9 μN and ending at about −1 μN is the unloading curve. The unloading curve shows the relationship between load and displacement during the process of pulling out the indenter 30 from the heat seal layer 1.

Next, the contact depth hc is determined by analysis using the Oliver-Pharr method.

The contact depth hc can be determined by the following equation (1).

Here, ε is a constant related to the shape of the indenter. For Berkovich indenters, this constant is 0.75. The maximum load Pmax and maximum displacement hmax of the unloading curve can be determined based on the graph shown in FIG. 3. S is the contact stiffness. The contact stiffness S is the slope of the unloading curve in FIG. 3 immediately after pulling out, of an approximated curve obtained by fitting the range of 60 to 95% of the maximum load with the function of the following formula (2). . Here, P is the load and h is the indentation depth. Furthermore, A, h _f and m are fitting parameters during fitting.

Next, the projected contact area Ac is determined based on the shape of the indenter and the contact depth hc. The projected contact area Ac can be expressed as a function of the contact depth hc, as shown in equation (3) below. Note that Equation (3) includes a term including C1 to C5 called a correction term in order to correct the influence of the indenter shape. C ₁ to C ₅ were measured using fused quartz as a test piece at a maximum load of 20 μN to 10 mN, and the composite modulus at each maximum load was 69.6 GPa, which is the composite modulus of elasticity Er of fused silica. This is the specified value.

Next, the hardness H is determined based on the projected contact area Ac and the maximum load Pmax. The hardness H can be determined by the following equation (4).

The hardness H is measured at a plurality of locations, for example, 25 locations on one test piece, and the average value of the obtained hardness H is determined as the hardness.
The method for measuring hardness has been described above.

(Adhesive layer)
The lid laminated sheet 10 can further include one or more adhesive layers.
For example, the lid laminated sheet 10 may include an adhesive layer between the gas barrier layer 4 and the paper base material 5 to bond them together. Alternatively, the lid laminated sheet 10 may include an adhesive layer between the support layer 3 and the gas barrier layer 4 to bond them together. Alternatively, the lid laminated sheet 10 may include two or more of the adhesive layers described above.

For the material of the adhesive layer, an adhesive resin or an adhesive that provides the necessary adhesive strength is appropriately selected and used depending on the material of the layer to be adhered through the adhesive layer. For example, the same material that can be used for the anchor coat layer 2 can be used for the adhesive layer. As a coating method, various coating methods such as a gravure coating method, a die coating method, a blade coating method, a knife coating method, and a bar coating method can be used.

The thickness of the lid laminated sheet 10 is preferably within the range of 40 to 170 μm, more preferably within the range of 45 to 160 μm.

The mass per area of the lid laminated sheet 10 is preferably within the range of 45 to 160 g/m ² , more preferably within the range of 50 to 150 g/m ² . If this value is reduced, the strength of the lid will be reduced. When this value is increased, the lid becomes hard and the opening performance tends to decrease. Furthermore, increasing this value not only increases the cost but also increases the amount of carbon dioxide emissions associated with manufacturing and exhaust.

By the way, in order to suppress the deterioration of the contents during storage and the peeling of the lid during transportation, high heat seal strength is required between the lid and the container body. However, increasing the heat sealing strength increases the load applied to the lid and the container body when the container is opened. If this load is too large, problems are likely to occur when opening the package. For example, when the container is opened, a portion of the lid may remain on the container body, causing fuzz or stringiness.

Fuzzing refers to the fact that the layers constituting the lid, such as the heat seal layer 1, remain in the form of a film on the container body when the container is opened. Stringing means that the layers constituting the lid, such as the heat seal layer 1, remain in the container body in the form of strings when the container is opened.

According to one example, fuzzing and stringing may cause a portion of the lid to protrude into the opening of the container body. In this case, it may be difficult to remove the contents, and a portion of the lid may get mixed into the contents. Since such a packaging container has an unfavorable appearance, it may lead to a poor impression on consumers.

Fuzzing and stringing occur at the boundary between heat-sealed and non-heat-sealed portions of the packaging container. It is thought that fluffing and stringiness occur when a part of the lid, such as the heat seal layer 1, does not break instantaneously at the above-mentioned boundary when the package is opened, but instead stretches into a film or string shape and then breaks. Therefore, in order to suppress fuzzing and stringiness, for example, it is conceivable to break the heat seal layer 1 before stretching it.

In addition, it is considered that the heat-seal layer is less likely to break, especially in lids where delamination is likely to occur. Therefore, in order to suppress fuzzing and stringiness, it is considered preferable that the two adjacent layers forming the lid have high adhesion.

In the lid laminated sheet 10 described above, the thickness of the heat seal layer 1 is within the above range, and the hardness of the heat seal layer 1 is within the above range, so that the heat seal layer 1 does not break. Cheap. Therefore, the above-described laminated sheet 10 for a lid is less likely to cause fuzzing or stringiness. Therefore, the lid laminated sheet 10 described above has excellent unsealability.

Further, the above-described laminated sheet 10 for a lid can achieve high heat seal strength between the container body and the lid, and therefore has excellent sealing performance.

In addition, in the above-described laminated sheet for lid 10, the mass of the paper base material 5 is larger than the mass of any other layer included in the laminated sheet for lid 10, so the amount of petroleum-derived compounds used can be reduced. can do. Therefore, according to the above-described laminated sheet for lid 10, the environmental load can be reduced.

Moreover, this laminated sheet 10 for a lid has excellent gas barrier properties in addition to being excellent in opening properties. Furthermore, this laminated sheet for lid 10 is unlikely to cause a decrease in gas barrier properties, particularly oxygen barrier properties. This will be explained below.

Food packaging containers are sometimes desired to have excellent oxygen barrier properties that prevent oxygen from entering from the outside in order to suppress the oxidation of the packed food. In such food packaging containers, the lid is also required to have oxygen barrier properties.

To impart gas barrier properties against oxygen and the like to a paper-based lid, a metal foil or a metal-deposited film made of a metal such as aluminum is often provided as a gas barrier layer on the paper base material, for example. However, food packaging containers whose lids include metal layers cannot be inspected for metal foreign matter using a metal detector after filling, and cannot be incinerated as paper because they contain metal, so they can be recycled as waste paper. There are problems in that it cannot be used in packaging containers for chilled foods that are expected to be cooked in a microwave oven.

As mentioned above, some gas barrier layers do not include a metal layer. As such a gas barrier layer, those containing polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, polyamide such as nylon MXD-6, and resin such as polyacrylonitrile are often used. A metal layer-less lid can avoid the above problems.

The optimum temperature range for distribution and storage of chilled foods is set for each food, but generally it is within the range of 0 to 10 degrees Celsius. After production, packaged foods made by housing chilled foods in food packaging containers reach consumers through various distribution channels. During this process, for example, from the time a consumer purchases a packaged food at a store until it is stored in the refrigerator at home, or from the time the consumer takes the packaged food out of the refrigerator until the time the consumer starts cooking, the packaged food is placed in a room temperature environment.

The present inventors have discovered that a packaged food in which a chilled food is housed in a food packaging container whose lid body includes a paper base material and a gas barrier layer, particularly a packaged food in which the gas barrier layer is a resin-containing layer, is stored in a refrigerated state. It has been found that the gas barrier properties, particularly the oxygen barrier properties, of the lid body decrease significantly during the first few hours of exposure to a room temperature environment. This is remarkable when the proportion of the mass of the paper base material to the mass of the lid is large.

The present inventors have found that the above problem is caused by dew condensation occurring on the surface of the lid. That is, when a packaged article that has been in a refrigerated environment is exposed to a room temperature environment, dew condensation occurs on the outer surface of the lid, and the moisture reaches the gas barrier layer, damaging the gas barrier layer. As a result, the oxygen barrier properties of the lid decrease.

The above laminated sheet 10 for a lid includes a functional layer 7 having water resistance. Therefore, in a packaged food using this lid laminated sheet 10 as a lid material, moisture generated on the outer surface of the lid due to dew condensation does not easily reach the gas barrier layer 4. Therefore, in a packaged food using this lid laminated sheet 10 as a lid material, the gas barrier layer 4 is less likely to be damaged due to dew condensation on the outer surface of the lid, and the oxygen barrier properties are less likely to deteriorate.

The lid laminated sheet 10 has been described above.
In FIG. 1, the gas barrier layer 4 is provided between the paper base material 5 and the support layer 3, but the gas barrier layer 4 may be provided at any position between the functional layer 7 and the heat seal layer 1. Good too. For example, the gas barrier layer 4 may be provided at any position between the print layer 6 and the heat seal layer 1. Moreover, the anchor coat layer 2, the gas barrier layer 4, and the printing layer 6 may be omitted.

[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 described above. An example of the lid according to the second embodiment is a lid 21 that will be described later with reference to FIG. 4. The lid according to this embodiment has excellent unsealability, as described in relation to the laminated sheet for lid 10.

[Third embodiment]
FIG. 4 is a cross-sectional view schematically showing a food packaging container according to a third embodiment of the present invention. The food packaging container 20 shown in FIG. 4 includes a container body 22 provided with an opening, and a lid 21 that covers the opening.

The container body 22 has, for example, a cylindrical shape with a bottom. The container body 22 here includes a bottom portion, a body portion (or side wall portion), and a flange 22a. The flange 22a widens outward at the upper opening of the body.

The container body 22 contains, for example, olefin resin such as polypropylene. The container body 22 may further contain a component such as an ethylene-vinyl alcohol copolymer in order to improve its gas barrier properties. Further, the container body 22 may further contain additives, for example, additives intended to improve processability, design, and chemical durability.

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 a gas barrier layer, for example a layer containing a component such as the above-mentioned ethylene-vinyl alcohol copolymer, as an intermediate layer.

Paper can also be used for the container body 22. When the contents include a liquid substance, the container body 22 includes a paper base material and a layer made of resin or the like provided on the surface of the content side to prevent the liquid substance from seeping into the paper base material. A multilayer structure including the following can be adopted. As the material for the container body 22 containing the paper base material, for example, paper leaves, paper powder, pulp, or waste paper can be used. For forming the container body 22, general-purpose techniques such as folding and pasting of sheets containing paper leaves as used in the production of paper packs, press molding of sheets using molds, and pulp molding can be used. It is. By using paper for the container body 22, it is possible to reduce the amount of carbon dioxide emitted during the manufacturing and disposal of the food packaging container 20 as a whole, thereby reducing the burden on the environment.

The lid 21 is the lid laminated sheet 10 or a cutout thereof. The lid 21 is heat-sealed to the flange 22a via the heat-sealing layer 1 after the contents are contained in the container body 22. In this heat sealing, the sealing temperature, sealing pressure, and sealing time can be set as appropriate.

[Fourth embodiment]
The packaged food according to the fourth embodiment of the present invention is obtained by accommodating a food product in the food packaging container according to the third embodiment described above. The food to be accommodated is not particularly limited, but 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.

In this packaged food, the heat seal strength between the lid 21 and the container body 22 is preferably 5 N/15 mm or more. Here, the heat seal strength is a value obtained by the method specified in JIS Z0238:1998 "Test method for heat seal flexible packaging bags and semi-rigid containers".

In manufacturing this packaged food, before the lid 21 is heat-sealed to the container body 22, for example, after the contents have been accommodated in the container body 22, the lid 21 is heat-sealed to the container body 22. Before this, the gas in the container body 22 may be replaced by a known method. For example, the container body 22 may be filled with an inert gas. By appropriately changing the gas composition inside the container, we can suppress the growth of bacteria and extend the quality retention period, maintain the flavor and color of food for a long time by preventing oxidation, and prevent the loss of vitamins. be able to. The replacement gas is appropriately selected depending on the type of food contained therein. As the replacement gas, a mixed gas of oxygen gas, nitrogen gas, and carbon dioxide gas is suitably used.

The lid included in this packaged food has excellent opening properties. Therefore, this packaged food is less likely to become fluffy or stringy when opened.

Tests conducted in connection with the present invention will be described below.
<1> Manufacture of laminated sheet for lid (Example 1)
The laminated sheet 10 for a lid shown in FIG. 1 was manufactured by the following method.
First, as the paper base material 5, single-sided coated paper with a basis weight of 52.3 g/m ² was prepared. This single-sided coated paper contains polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), silica, and layered silicate as main components in an imitation paper with a mass per area of 37.3 g/ ^m2 . , was obtained by coating a coating liquid containing water as the main solvent. The resulting coat layer had a solid mass per area of 15 g/m ² .

Next, a printed layer 6 and a functional layer 7 were sequentially formed on the surface of the paper base material 5 on which the coat layer was formed using a gravure multicolor printing machine. The printing layer 6 was formed using normal printing ink. The amount of printing ink applied was 1.0 g/m ² . The functional layer 7 was formed using an OP varnish agent containing nitrocellulose resin and polyethylene granular wax as main components. The coating amount of the OP varnish agent was 0.6 g/m ² .

Next, as the support layer 3, a polyethylene terephthalate (PET) film having a thickness of 12 μm and a mass per area of 16.8 g/m ² was prepared. An inorganic oxide film was formed on one surface of this support layer 3, and then a coating liquid containing polyvinyl alcohol (PVA) as a main component was applied to form a gas barrier layer 4. A gas barrier film was thus obtained. The mass per area of this gas barrier film was within the range of 17.0 to 17.4 g/m ² .

Next, the above gas barrier film was attached to the laminate consisting of the paper base material 5, the printed layer 6, and the functional layer 7 by dry lamination. For dry lamination, first, a dry laminating agent was applied to the surface of the gas barrier layer 4 of the gas barrier film using a gravure coater to form an adhesive layer. As the dry laminating agent, a two-component reactive adhesive containing a polyester base agent and an isocyanate curing agent was used. The amount of dry laminating agent applied was 3.0 g/m ² . Next, the above laminate and the above gas barrier film were bonded together with this adhesive layer in between so that the gas barrier layer 4 faced the paper base material 5.

Thereafter, heat seal varnish A is applied by gravure printing onto the support layer 3 of the laminate including the support layer 3, the gas barrier layer 4, the paper base material 5, the printed layer 6, and the functional layer 7. A sealing layer 1 was formed. Heat seal varnish A was applied so that the mass per area was 3.2 g/m ² in a dry state. Heat seal varnish A is an aqueous emulsion containing ethylene-vinyl acetate copolymer as a main component. The solvents contained in heat seal varnish A are water and isopropyl alcohol (IPA). Further, the glass transition temperature of the solid content contained in the heat seal varnish A is 35°C. Further, the melting point of heat seal varnish A is within the range of 70 to 100°C.
In the manner described above, a laminated sheet for a lid was obtained.

(Example 2)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish C was used instead of heat seal varnish A, and heat seal varnish C was applied so that the mass per area in a dry state was 3.3 g/m ² . Heat seal varnish C is a mixture of heat seal varnish A and heat seal varnish B described above. In this mixture, the solid content mass ratio of heat seal varnish A and heat seal varnish B is 7:3. Heat seal varnish B is an aqueous emulsion containing an ethylene-vinyl acetate copolymer as a main component. The solvents contained in heat seal varnish B are water and isopropyl alcohol (IPA). Moreover, the glass transition temperature of the solid content contained in the heat seal varnish B is 50°C. Further, the melting point of heat seal varnish B is within the range of 70 to 100°C.

(Example 3)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish D is used instead of heat seal varnish A, and heat seal varnish D is applied so that the mass per area in a dry state is 3.3 g/m ² . An anchor coat layer 2 was provided between layer 1 and support layer 3. Heat seal varnish D is a mixture of heat seal varnish A and heat seal varnish B described above. In this mixture, the solid content mass ratio of heat seal varnish A and heat seal varnish B is 3:7. The anchor coat layer 2 is formed by applying a solvent-based coating liquid containing an ester resin as a main component and further containing an isocyanate curing agent onto the support layer 3 using a gravure printing method. It was formed by coating so that the amount was 1.5 g/m ² . The thickness of anchor coat layer 2 was 1.3 μm.

(Example 4)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish B is used instead of heat seal varnish A, and heat seal varnish B is applied so that the mass per area in a dry state is 2.5 g/m ² . The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3.

(Example 5)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish E is used instead of heat seal varnish A, and heat seal varnish E is applied so that the mass per area in a dry state is 3.7 g/m ² . The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3. Heat seal varnish E is an aqueous emulsion containing ethylene-vinyl acetate copolymer as a main component. The solvents contained in heat seal varnish E are water and isopropyl alcohol (IPA). Moreover, the glass transition temperature of the solid content contained in the heat seal varnish E is 52°C. Further, the melting point of heat seal varnish E is within the range of 80 to 110°C.

(Example 6)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, the mass per area of heat seal varnish A in a dry state was changed from 3.2 g/m ² to 4.5 g/m ² .

(Example 7)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish C was used instead of heat seal varnish A, and heat seal varnish C was applied so that the mass per area in a dry state was 4.2 g/m ² .

(Example 8)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish D is used instead of heat seal varnish A, and heat seal varnish D is applied so that the mass per area in a dry state is 4.1 g/m ² . The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3.

(Example 9)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish B is used instead of heat seal varnish A, and heat seal varnish B is applied so that the mass per area in a dry state is 4.1 g/m ² . The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3.

(Example 10)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, the mass per area of heat seal varnish A in a dry state was changed from 3.2 g/m ² to 1.1 g/m ² .

(Example 11)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish B was used instead of heat seal varnish A, and heat seal varnish B was applied so that the mass per area in a dry state was 1.1 g/m ² .

(Example 12)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, the mass per area of heat seal varnish A in a dry state was changed from 3.2 g/m ² to 4.5 g/m ² and the printed layer was omitted.

(Comparative example 1)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this comparative example, the mass per area of heat seal varnish A in a dry state was changed from 3.2 g/m ² to 5.4 g/m ² .

(Comparative example 2)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish B is used instead of heat seal varnish A, and heat seal varnish B is applied so that the mass per area in a dry state is 5.4 g/m ² . The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3.

(Comparative example 3)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this comparative example, the mass per area of heat seal varnish A in a dry state was changed from 3.2 g/m ² to 0.4 g/m ² .

(Comparative example 4)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish E is used instead of heat seal varnish A, and heat seal varnish E is applied so that the mass per area in a dry state is 5.6 g/m ² . The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3.

(Comparative example 5)
A laminated sheet for a lid was manufactured in the same manner as in Example 1 except for the following points. That is, in this example, heat seal varnish E is used instead of heat seal varnish A, heat seal varnish E is applied so that the mass per area in a dry state is 2.3 g/m ² , and heat seal varnish E is used instead of heat seal varnish A. The anchor coat layer 2 described above was provided between the layer 1 and the support layer 3.

<2> Evaluation (measurement of hardness)
The hardness of the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5 was measured by the method described above. As a nanoindenter, TI Premier (manufactured by Bruker Japan Co., Ltd.) was used. Further, as the resin for embedding the sheet pieces, a visible light curable resin (trade name "Aronix (registered trademark) LCR D-800" (manufactured by Toagosei Co., Ltd.)) was used. For curing this resin, a halogen lamp light source device (trade name "KTX-100R", manufactured by Kenko Tokina Co., Ltd.) was used. The resin was cured by irradiating the resin with light for 1.5 minutes at the maximum light intensity of this light source device. Further, as a microtome, an ultramicrotome (trade name "Leica EM UC7", manufactured by Leica Microsystems Co., Ltd.) equipped with a diamond knife was used. In addition, cutting was performed after the sheet piece was fixed in advance to a holder for fixing it so that the indenter entered perpendicularly to the cross section during measurement.

(Measurement of anchor coat layer thickness)
First, test pieces having lengths within the range of 5 to 10 mm were cut out from each of the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5. Next, the outermost surface of the obtained test piece was coated with an ultraviolet curable resin. Next, the laminated sheet for lid 10 coated with resin was cut in the thickness direction of the laminated sheet for lid using a microtome. Next, five arbitrary locations on the obtained cross section were imaged using a scanning electron microscope (SEM). Next, in each of the five obtained images, the thickness of the anchor coat layer was measured at five arbitrary locations, and the average value of the obtained values was taken as the thickness of the anchor coat layer. Note that the thickness was measured using a scale written on the obtained image.

(Measurement of heat seal layer thickness)
For each of the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5, the thickness of the heat seal layer was measured by the same method as the method for measuring the thickness of the anchor coat layer described above.

(Measurement of heat seal strength)
Regarding the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5, the heat seal (HS) strength against the resin sheet was measured by the method described above.

Here, the resin sheet used is a sheet with a three-layer structure including a pair of polypropylene layers and a layer made of a mixture of polypropylene and 4% by mass ethylene-vinyl alcohol copolymer interposed between them. did.

Each lid laminated 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 seal bar width of 5 mm. The length direction of the seal bar was perpendicular to the MD. Heat sealing was performed by applying a temperature of 210° C. and a pressure of 0.2 MPa for 2 seconds to the laminate of the lid laminate sheet and the resin sheet at each heat sealing position. Each laminate partially heat-sealed in this way has a strip shape with a width of 15 mm, the length direction is parallel to the MD, one end is not heat-sealed, and the other end is 30 mm. Three heat-sealed specimens were cut out over a length of 50 mm.

Separately, each lid laminated sheet and resin sheet were heat-sealed in the same manner as above except that the length direction of the seal bar was perpendicular to the TD. Each laminate partially heat-sealed in this way has a strip shape with a width of 15 mm, the length direction is parallel to TD, one end is not heat-sealed, and the other end is 30 mm. Three heat-sealed specimens were cut out over a length of 50 mm.

Next, the heat seal strength of each test piece was measured by the method described above. Specifically, a Tensilon universal testing machine was used to measure the heat seal strength. The non-heat-sealed lid laminated sheet portion and resin sheet portion of each test piece were gripped by the gripping tools of the testing machine, and the gripping tools were moved in a direction away from each other. The relative moving speed of these gripping tools, ie, the peeling speed, was 300 mm/min. For each specimen, the maximum tensile load applied until it broke was recorded. The interval between the grips was 50 mm.

For each lid laminated sheet, the heat seal strength in MD was obtained by arithmetic averaging the maximum values of the tensile loads obtained for three test pieces whose length direction was parallel to MD. In addition, for each lid laminated sheet, the heat seal strength in TD was obtained by arithmetic averaging the maximum values of the tensile loads obtained for three test pieces whose length direction was parallel to TD.

(Opening test)
Lids were cut out from the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5. A food packaging container 20 shown in FIG. 4 was manufactured using these lids. Here, as the container body 22, one formed by molding the resin sheet used for measuring the heat seal strength into a tray shape was used. The container main body 22 had a substantially rectangular opening with a long side dimension of 120 mm and a short side dimension of 90 mm, and a height of 30 mm. Heat sealing of the lid body 21 to the flange 22a is performed by applying a temperature of 210° C. and a pressure of 0.2 MPa for 1.5 seconds using a seal bar with a width of 5 mm that is made to follow the shape of the flange 22 a. This was done by

Next, in each of the food packaging containers 20, the lids 21 of ten arbitrary containers were peeled off from the corners of the container body 22 by hand. Thereafter, it was checked whether fluffing or stringiness had occurred. It was also confirmed whether paper peeling occurred. Here, "paper peeling" means that when the lid is peeled off from the container body, cohesive failure of the paper base material occurs and a portion of the lid remains on the container body.

(Water absorption)
The water absorption of the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5 was measured by the method described above.

The results of the above measurements and tests are summarized in Tables 1 and 2 below.

In Tables 1 and 2 above, "mass" is mass per area. The classification of "paper," "plastic," and "other" in the column labeled "mass percentage" is in accordance with the "Containers and Packaging Recycling Law Explanatory Materials" and is as explained above. The column labeled "Difference" lists the value obtained by subtracting the heat seal strength between the lid laminated sheet and the resin sheet from the breaking strength of the support layer.

In the column labeled "Opening Test" in Tables 1 and 2 above, "A" indicates that no visible fluffing or stringiness occurred. "B" indicates that at least one of visible fuzzing and stringing occurred locally, but no part of the lid protruded into the opening of the container body due to fuzzing and stringing. ing. "C" indicates that at least one of fuzzing and stringing occurred, and a portion of the lid protruded into the opening of the container body due to the fuzzing and stringing. In the case of "C", there is a possibility that fluff and stringiness may be mixed into the contents.

In the column labeled "Heat seal strength" in Tables 1 and 2 above, "A" indicates that the heat seal strength in both MD and TD was 5 N/15 mm or more. "C" indicates that at least one of the heat seal strengths in MD and TD was less than 5 N/15 mm.

As shown in Tables 1 and 2 above, when the laminated sheets for lids according to Examples 1 to 12 were used, no fluffing or stringiness occurred. On the other hand, when the laminated sheets for lids according to Comparative Examples 1, 2, 4, and 5 were used, at least one of fluffing and stringiness occurred.

Furthermore, as shown in Tables 1 and 2 above, the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1, 2, 4, and 5 achieved high heat seal strength. That is, high sealing performance could be achieved. On the other hand, the laminated sheet for a lid according to Comparative Example 3 could not achieve high heat seal strength.

Further, when the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5 were used, paper peeling did not occur. Moreover, the water absorption of the laminated sheets for lids according to Examples 1 to 12 and Comparative Examples 1 to 5 was 20 g/m ² or less.

<3> Evaluation of oxygen barrier property <Reference example>
A gas barrier consisting of a coating film mainly composed of polyvinyl alcohol (coating amount 13 g/m ² , thickness 10 μm) on the main non-glossy surface of single gloss paper (basis weight 65 g/m ² ) as a paper base material. A laminated sheet in which layers were laminated was prepared.

On the main surface of the paper base opposite to the main surface on which the gas barrier layer was formed, printing ink was applied at a coating amount of 1 g/m ² by gravure printing, and a printed layer was laminated. On the printed layer, an OP varnish agent containing nitrocellulose resin as a main component was applied by a gravure coating method, and a functional layer consisting of an OP varnish layer with a coating amount of 10 g/m ² (dry state) was laminated.

Next, on the gas barrier layer, an adhesive composition containing a polyester base agent and an aliphatic isocyanate curing agent was applied by gravure coating to form an adhesive layer with a coating amount of 2 g/m ² (dry state). A laminate sheet for a lid was obtained by laminating a non-stretched film mainly composed of linear low density polyethylene (LLDPE) with a thickness of 30 μm and 27 g/m ² as a heat seal layer on the adhesive layer. .

<Comparative example 6>
A laminated sheet for a lid was produced in the same manner as in Reference Example 1 except that the functional layer consisting of the OP varnish layer was not provided.

(Preparation of test specimen for oxygen permeability measurement)
Each of the laminated sheets for lids of Reference Example and Comparative Example 6 obtained above was cut into a shape of 4 cm x 4 cm and used as a test piece. Two test pieces were prepared for each of Reference Example and Comparative Example 6. By sandwiching the test piece between two aluminum films that have a hole with a diameter of 25 mm in the center, fixing them with adhesive so that the two holes overlap, and stacking them together, the laminated sheet for the lid is sandwiched between the aluminum sheets. A body (hereinafter also referred to as "aluminum laminate") was obtained. This aluminum laminate was used as a lid for an aluminum cup in an oxygen permeability measurement test described below.

The aluminum cup meets JAPAN TAPPI Paper Pulp Test Method No. 7:2000 Paper and Paperboard - Moisture Permeability Test Method A cup conforming to the aluminum moisture permeable cup specified in Method B was prepared. By placing the aluminum laminate sandwiching the test piece in the opening of this cup, the cup is covered with a lid, and secured with a fastener, a total of 4 test pieces for environmental storage will be used in the tests described below. Created.

(Environmental storage of test specimen and oxygen permeability measurement test)
Each of the test specimens obtained above was first stored for 12 hours in a humidity-free refrigerated environment at a temperature of 5°C. Next, one of the two test specimens in each of Reference Example 1 and Comparative Example 6 was stored in a high temperature and high humidity environment of 40° C. and 90% relative humidity for 1 hour to remove the outside of the cup. Condensation was forced to form on the surface of the test piece located on the side. Next, as a static adjustment before oxygen permeability measurement, each test specimen was stored in an environment with a temperature of 24° C. and a relative humidity of 55% for 24 hours, and then the oxygen permeability was measured (condition 2). In addition, for the other test specimen in each of Reference Example and Comparative Example 6, after being stored in the above-mentioned refrigerated environment, the above-mentioned static adjustment was carried out without carrying out environmental storage in the above-mentioned high temperature and high humidity environment. After that, the oxygen permeability was measured (condition 1).

The oxygen permeability was measured using an oxygen permeability measuring device OX-TRAN2/20 manufactured by MOCON under conditions of a temperature of 30° C. and a relative humidity of 70%. The results are shown in Table 3. The lower the oxygen permeability, the better the oxygen barrier property.

From the measured values shown in Table 3, the lid using the laminated sheet for the lid, which has both a gas barrier layer and a functional layer, exhibits poor barrier performance due to condensation even when exposed from a refrigerated environment to a high-temperature, high-humidity environment. It can be seen that the decrease in oxygen barrier performance is controlled and the decrease in oxygen barrier performance is dramatically improved. The time from when a consumer purchases a packaged product containing chilled food at a store until it is stored in the refrigerator at home, and from the time the consumer takes the packaged product out of the refrigerator to the time it is cooked is usually about one hour. In view of the above, it can be seen that a lid using a laminated sheet for lids having both a gas barrier layer and a functional layer is extremely effective as a lid for packaging containers for chilled foods.

Note that the present invention is not limited to the above-described embodiments, and can be variously modified at the implementation stage without departing from the gist thereof. Moreover, each embodiment may be implemented in combination as appropriate, and in that case, the combined effect can be obtained. Furthermore, the embodiments described above include various inventions, and various inventions can be extracted by combinations selected from the plurality of constituent features disclosed. For example, if a problem can be solved and an effect can be obtained even if some constituent features are deleted from all the constituent features shown in the embodiment, the configuration from which these constituent features are deleted can be extracted as an invention.

DESCRIPTION OF SYMBOLS 1... Heat seal layer, 2... Anchor coat layer, 3... Support layer, 4... Gas barrier layer, 5... Paper base material, 6... Printing layer, 7... Functional layer having water resistance, 10... Laminated sheet for lid, 20... Food packaging container, 21... Lid, 22... Container body, 22a... Flange.

Claims (15)

A laminated sheet for a lid used for the lid of a food packaging container comprising a container body provided with an opening and a lid covering the opening, the sheet comprising: a functional layer having water resistance; and a paper base material. , comprising a support layer and a heat-sealing layer in this order, the mass of the paper base material is greater than the mass of any other layer included in the laminated sheet for lid, and the heat-sealing layer has a thickness of A laminated sheet for a lid, wherein the heat seal layer has a hardness of 12.0 MPa or less, and a hardness of the heat seal layer is in the range of 1 μm or more and 5.5 μm or less. The laminated sheet for a lid according to claim 1, wherein the hardness is 6.5 MPa or more. The laminated sheet for a lid according to claim 1, further comprising a printing layer between the functional layer and the paper base material. The laminated sheet for a lid according to claim 3, further comprising a gas barrier layer having gas barrier properties between the printing layer and the heat sealing layer. The laminated sheet for a lid body according to claim 4, wherein the gas barrier layer comprises at least one of an inorganic oxide layer and a resin-containing layer. When the layers other than the paper base material included in the lid laminated sheet are classified into layers made of plastic and other layers, the mass of the paper base material is the sum of the layers made of plastic. The laminated sheet for a lid body according to claim 1, which is larger than the total mass of the mass and the other layers. The laminated sheet for a lid body according to claim 1, wherein the paper base material is coated paper having a coating layer on one side. 2. The laminated sheet for a lid body according to claim 1, wherein the heat seal layer is made of a heat seal varnish having a glass transition temperature in the range of 20 to 55° C. and containing an ethylene-vinyl acetate copolymer. The laminated sheet for a lid body according to claim 1, further comprising an anchor coat layer having a thickness of 0.5 μm or more and 2.5 μm or less between the support layer and the heat seal layer. A lid made of the laminated sheet for lids according to any one of claims 1 to 9. A food packaging container comprising a container body provided with an opening and a lid according to claim 10 that covers the opening, wherein the support layer is formed between the paper base material and the inside of the food packaging container. A food packaging container placed between the space. 12. The food packaging container according to claim 11, wherein the container body has a flange around the opening, and the lid is heat-sealed to the flange via the heat-sealing layer. The food packaging container according to claim 11, wherein the internal space of the food packaging container is filled with a mixed gas containing oxygen gas, nitrogen gas, and carbon dioxide gas. The food packaging container according to claim 11, wherein the food packaging container is a chilled food packaging container or a frozen food packaging container. A packaged food comprising the food packaging container according to claim 11 and a food contained in the food packaging container.