JP2023001077A - Laminated sheet for lids, lid, food package and packaged food - Google Patents

Abstract

To provide a lid that is used in a food package, contains a paper substrate and has excellent piercing strength.SOLUTION: A laminated sheet for lids 10 is used in a lid of a food package, which has a package body having an opening and a lid covering the opening. The laminated sheet for lids 10 has a water-resistant functional layer 6, a printed layer 5, a paper substrate 4, a support layer 2, and a heat seal layer 1 in the stated order. The paper substrate 4 has a mass greater than the mass of any other layer included in the laminated sheet for lids 10. The support layer 2 contains at least one of polybutylene terephthalate and polyamide.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD 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 recent trend toward nuclear families, advances in distribution, freezing, and refrigeration technology have contributed to the spread of cooked or processed chilled foods sold at convenience stores and supermarkets. Demand for frozen foods is growing. At the same time, the demand for packaging containers containing chilled and frozen foods is also increasing.

On the other hand, as the reduction of plastic waste is progressing, there is a growing demand for food packaging containers that use paper as a base material, which has a low environmental impact and is a renewable resource. Packaging containers for chilled foods and frozen foods are also required to use paper-made packaging containers using paper as a base material.

For example, Patent Literature 1 discloses a food packaging material obtained by laminating two gas barrier layers using ethylene-modified polyvinyl alcohol resin on a paper substrate.

JP 2009-184138 A

An object of the present invention is to provide a lid which is used for a food packaging container, contains a paper substrate, and has excellent piercing strength.

According to one aspect of the present invention, there is provided a lid laminate sheet used for the lid of a food packaging container comprising a container body provided with an opening and a lid covering the opening, the laminated sheet having water resistance. A functional layer, a printed layer, a paper substrate, a support layer, and a heat seal layer are included in this order, and the mass of the paper substrate is equal to that of any other layer included in the lid laminated sheet. A laminated sheet for a lid is provided, which is larger than the mass, and the support layer includes at least one of polybutylene terephthalate and polyamide.

According to another aspect of the present invention, there is provided the laminated sheet for a lid according to the above aspect, wherein the support layer has a multilayer structure.

Alternatively, according to another aspect of the present invention, the support layer has a first layer and a second layer each containing at least one of polybutylene terephthalate and polyamide, and gas barrier properties, and the first layer and the A laminated sheet for a lid according to the above-described side surface including a gas barrier layer interposed between the second layer and the second layer is provided.

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

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any of the aspects above, wherein the weight ratio of the total weight of polybutylene terephthalate and polyamide to the weight of the support layer is 50% by weight or more. be done.

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any of the aspects above, wherein the support layer is a stretched film.

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any one of the aspects above, wherein the support layer has a thickness in the range of 3 to 60 μm.

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any of the aspects above, wherein the support layer has a breaking strength greater than the heat seal strength between the lid and the container body. .

According to still another aspect of the present invention, there is provided a laminated sheet for a lid according to any one of the above aspects, wherein the heat seal layer is formed of heat seal varnish.

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 other layers, the paper base material A laminated sheet for a lid according to any of the above aspects is provided, wherein the mass is greater than the total mass of the plastic layer and the total mass of the other layers.

According to still another aspect of the present invention, the paper substrate is a coated paper having a coat layer on one side, and the print layer is provided on the coat layer. A laminated sheet for a lid is provided.

According to still another aspect of the present invention, the paper substrate is a coated paper having a coat layer on one side, and the support layer is bonded to the paper substrate so as to face the coat layer. A laminated sheet for a lid according to any of the above-described side surfaces is provided.

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any of the aspects above, wherein the paper substrate is coated paper having coat layers on both sides.

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any of the above aspects, wherein the paper substrate has a basis weight in the range of 40 to 100 g/m ² .

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any one of the aspects above, wherein the heat seal layer is a sealant having easy peelability.

According to still another aspect of the present invention, there is provided the laminated sheet for a lid according to any of the aspects above, wherein the functional layer has a mass per area of 0.2 g/m ² or more.

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

According to still another aspect of the present invention, there is provided a food packaging container comprising a container body provided with an opening and a lid covering the opening and covering the side surface, wherein the support layer is the paper base material. and the interior space of the food packaging container.

According to still another aspect of the present invention, the container body has a flange around the opening, and the lid is heat-sealed to the flange via the heat-seal 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 the 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 one of the aspects described above and food contained in the food packaging container.

ADVANTAGE OF THE INVENTION According to this invention, it is used for the packaging container for foodstuffs, the lid|cover containing a paper base material and excellent in piercing strength is provided.

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. 11 is a partial cross-sectional view schematically showing a laminated sheet for a lid according to a modified example. FIG. 4 is a cross-sectional view schematically showing one step in the measurement of composite elastic modulus. Graph showing a load-displacement curve. Sectional drawing which shows roughly the packaging container for food which concerns on 3rd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings. Embodiments described below are more specific to any of the above aspects. Elements having the same or similar functions are denoted by the same reference numerals, and overlapping descriptions are 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.

A lid laminated sheet 10 shown in FIG. 1 is used as a lid in a food packaging container comprising a container body provided with an opening and a lid covering the opening. That is, the lid laminated sheet 10 is a lid material that is used as a lid itself or a portion cut out from it is used as a lid.

The lid laminate sheet 10 includes a heat seal layer 1, a support layer 2, a paper base material 4, a printed layer 5, and a water resistant functional layer (water resistant layer) 6 in this order. . Since this laminated sheet for lid 10 does not include a gas barrier layer, which will be described later, it is suitable for applications that do not require high gas barrier properties. Each layer included in the lid laminate sheet 10 will be described below.

(Paper substrate)
The lid laminate sheet 10 includes a paper base material 4 . The mass of the paper base material 4 is greater than the mass of any other layers included in the lid laminated sheet 10 . The ratio of the mass of the paper base material 4 to the mass of the lid laminated sheet 10 is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more. % is more preferred. According to one example, this proportion is less than or equal to 80%, according to another example less than or equal to 70%, and according to yet another example less than or equal to 65%.

When the layers other than the paper base material 4 included in the lid laminated sheet 10 are classified into a layer made of plastic and other layers, the mass of the paper base material 4 is the total mass of the layers made of plastic and It is preferably larger compared to the total mass of the other layers. In this case, in Japan, the lid laminate sheet 10 can be treated as paper under the Containers and Packaging Recycling Law.

Here, the above classification follows the "Explanatory material of the Containers and Packaging Recycling Law". In other words, "plastic" is a material that contains a polymer as an essential component and is shaped and manufactured by utilizing fluidity during processing. Paints and adhesives are not included in plastics, as they are irrelevant to the concept of "shaping". Therefore, in the example shown in FIG. 1, the support layer 2 and the heat seal layer 1 attached thereto are "layers made of plastic". In the example shown in FIG. 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."

The basis weight, ie the mass per area, of the paper substrate 4 is according to one example in the range of 20 to 500 g/m ² and according to another example in the range of 40 to 100 g/m ² . If the grammage of the paper base material 4 is increased, the lid becomes hard and the ease of opening the lid is lowered. If the grammage is reduced, the strength of the lid is reduced.

When the basis weight of the paper base material 4 is increased, the ratio of the mass of the paper base material 4 to the mass of the lid laminated sheet 10 also increases. However, when the basis weight of the paper base material 4 is increased, the amount of carbon dioxide emissions associated with the manufacture of the paper base material 4 and the disposal of the lid laminated sheet 10 increases.

The paper base material 4 is not particularly limited as long as it contains plant-derived pulp as a main component. Examples of the paper base material 4 include coated paper such as high quality paper, medium quality paper, lightly coated paper, single gloss paper, bleached and unbleached kraft paper (acidic paper or neutral paper).

The paper substrate 4 is preferably coated paper having a coat layer on at least one surface. That is, the paper substrate 4 is preferably single-sided coated paper or double-sided coated paper. The surface of the coated paper provided with the coat layer is superior in smoothness compared to the surface of the paper not provided with the coat layer.

When the paper substrate 4 is a coated paper having a coat layer on one side, the print layer 5 can be provided on the coat layer, for example. In this case, it is easy to display a high quality image on the print layer 5 . In addition, by providing the coat layer, the surface of the base of the functional layer 6 becomes smooth, so that the water resistance of the functional layer 6 is also improved.

When the paper base material 4 is a coated paper having a coat layer on one side, the support layer 2 may be attached to the paper base material 4 so as to face the coat layer. By doing so, for example, when the paper base material 4 and the support layer 2 are attached via an adhesive, the smoothness of the coat layer makes it easier to uniformly form an adhesive layer containing the adhesive. The adhesiveness of the support layer 2 to is improved, and the amount of adhesive used can be reduced.

When coated paper having coat layers on both sides is used as the paper base material 4, it becomes easy to display a high-quality image on the printing layer 5, and the water resistance of the functional layer 6 can be improved. Moreover, it becomes easy to achieve excellent adhesion between the paper substrate 4 and the support layer 2 .

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 copolymers, polypropylene, ethylene-vinyl acetate copolymers, ionomer resins, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-propylene copolymers , methylpentene polymer, acid-modified polyolefin resin obtained by modifying polyolefin resin such as polyethylene and polypropylene with unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic anhydride, and fumaric acid, polyethylene terephthalate resin, polybutylene terephthalate thermoplastic resins such as resins, nylon resins, and styrene-butadiene rubbers; 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 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.

(support layer)
The support layer 2 improves the strength of the lid laminate sheet 10 .
Support layer 2 contains at least one of polybutylene terephthalate and polyamide. The support layer 2 may have a single layer structure or a multilayer structure. 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. Here, as an example, the support layer 2 is assumed to be a layer made of polybutylene terephthalate or polyamide.

Polyamides, for example, contain an aliphatic backbone. Polyamides are, for example, nylons such as nylon 6, nylon 66, nylon 612, nylon 11, nylon 12, and nylon 46. According to one example, the polyamide is nylon 6 or nylon 66.

The support layer 2 may be a non-stretched film or a stretched film such as a biaxially stretched film. If it is a stretched film, it is preferred to utilize 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.

Support layer 2 may further comprise materials other than polybutylene terephthalate and polyamide. For example, the support layer 2 can further include additives such as curing agents, fillers, antiblocking agents, and antistatic agents. As the material for the support layer 2, a material that is cured by irradiation with active energy rays such as ultraviolet rays and electron beams can also be used.

The ratio of the total weight of polybutylene terephthalate and polyamide to the weight of the support layer 2 is preferably 50% by mass or more, more preferably 70% by mass or more. When the thickness of the support layer 2 is constant, increasing this ratio increases the piercing strength of the lid.

The thickness of the support layer 2 is preferably in the range of 3 to 60 μm, more preferably in the range of 10 to 30 μm. When the support layer 2 is thickened, it becomes easy to increase the piercing 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 lid.

The breaking strength of the support layer 2 is preferably greater than the heat sealing 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 MD (Machine Direction), the breaking strength of the support layer is greater than that between the lid and the container body. It means that the breaking strength of the supporting layer is greater than the heat sealing strength and that the breaking strength of the support layer is greater than the heat sealing strength between the lid and the container body in TD (Transverse Direction).

The breaking strength of the support layer 2 is a tensile force obtained by a measuring method specified in JIS Z1707:2019 "General Rules for Plastic Films for Food Packaging". The tensile force (N/15 mm) is a value obtained by converting the maximum force when the test piece breaks into a force (N/15 mm) corresponding to the width of the test piece of 15 mm. The heat seal strength between the lid and the container body will be described later.

When the breaking strength of the support layer 2 is greater than the heat seal strength between the lid and the container body, the paper is less likely to peel off when the lid is peeled off from the container body. For example, when the breaking strength of the support layer 2 is greater than 30 N/15 mm, paper peeling can be suppressed up to a heat seal strength of about 30 N/15 mm. Here, "paper peeling" means that when the lid is peeled off from the container body, cohesive failure of the paper base material occurs and part of the lid remains on the container body. If paper peeling occurs, it may become difficult to take out the contents accommodated in the container body.

The heat seal strength is adjusted according to the use and purpose of the packaging container. For example, the heat seal strength may be reduced in order to impart easy openability. Therefore, the breaking strength of the support layer 2 need not exceed 30 N/15 mm. Although the breaking strength of the support layer 2 is not particularly limited, it is preferably in the range of 10 to 100 N/15 mm, more preferably in the range of 25 to 85 N/15 mm. Increasing the above-mentioned breaking strength increases the effect of reinforcing the laminate in order to suppress paper peeling. However, if the thickness of the support layer 2 is increased in order to increase the breaking strength, the production of the support layer 2 and the disposal of the lid laminated sheet 10 increase the amount of carbon dioxide emissions and the cost.

The composite elastic modulus of the support layer 2 is preferably in the range of 2.0 to 4.2 GPa, more preferably in the range of 3.0 to 4.0 GPa. If the composite elastic modulus of the support layer 2 is excessively small, it will be easily broken by a relatively small external force, and therefore the puncture strength will be lowered. If the composite elastic modulus of the support layer 2 is excessively increased, the brittleness increases, resulting in a decrease in puncture strength. A method for measuring the composite elastic modulus will be described later with reference to the drawings.

As a means for forming the support layer 2, a method of laminating the paper base material 4 via an adhesive can be used. There are a sol lamination method and a sand lamination method using molten resin as an adhesive. Alternatively, the support layer 2 can be directly formed on the paper substrate 4 by extruding a melted composition, such as an extrusion lamination method. Also at this time, an adhesive layer may be formed on the paper substrate 4 as necessary.

(Print layer)
The printed layer 5 is a layer formed for practical use of the lid laminate sheet 10 or the lid as a commercial product. The printing layer 5 includes, for example, conventionally used ink binder resins such as urethane, acrylic, nitrocellulose, rubber, and vinyl chloride, various pigments, extenders, plasticizers, desiccants, and stabilizers. It is a layer composed of ink to which additives such as agents are added, and displays patterns such as letters and pictures. As a method for forming the printed layer 5, for example, known printing methods such as offset printing, gravure printing, and silk screen printing, and known coating methods such as roll coating, knife edge coating, and gravure coating are used. be able to.

The thickness of the print layer 5 is not particularly limited, and may be, for example, within the range of 0.1 to 5 μm, or within the range of 0.2 to 1 μm.

(Functional layer having water resistance)
The functional layer (water-resistant layer) 6 having water resistance suppresses the penetration of liquids outside the container such as moisture and oil due to dew condensation etc. into the lid in the packaged food described later, and the liquid is prevented from penetrating into the printed layer 5. It is a layer that suppresses reaching the layers such as the paper substrate 4 and the like. The functional layer 6 prevents the liquid outside the container from reaching the layers such as the printed layer 5 and the paper substrate 4, thereby preventing, for example, deterioration, breakage, or loss of adhesion of these layers.

According to one example, the functional layer 6 is formed on the printed layer 5 to increase the water absorbency of the partially laminated sheet, which is the portion from the functional layer 6 to the paper substrate 4 in the lid laminated sheet 10. Control. The functional layer 6 preferably has water resistance such that the water absorbency of the laminated sheet for a lid formed by the Cobb method described below is 20 g/m ² or less.

Here, the water absorbency is defined in JIS P8140: 1998 "Paper and paperboard-Water absorbency test method-Cobb method", with the surface of the functional layer 6 as the measurement surface, and the contact time between the test piece and water. It is the water absorbency obtained when 300 seconds. As described above, the water absorbency 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 absorbency 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 6 is preferably an overprint varnish layer (hereinafter referred to as "OP varnish layer").

According to one example, the functional layer 6 contains a water-resistant resin. As the water-resistant resin, any resin capable of achieving the above-described water absorbency can be used without limitation. Examples of water-resistant resins include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and polyolefin resins such as vinyl chloride-vinyl acetate copolymers, silicone resins, acrylic resins, epoxy resins, Polyester-based resins, cellulose-based resins, or urethane-based resins can be used. The functional layer 6 can be obtained, for example, by applying a paint containing a water-resistant resin onto the paper substrate 4 having the printed layer 5 formed thereon 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, anti-blocking agents, and lubricating agents, solvents, and the like.

The functional layer 6 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 6 and the coating amount of the coating material thereof 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 content mass per area.

For example, in the lid laminated sheet 10 shown in FIG. 1, the paint for forming the functional layer 6 is preferably applied in an amount of 0.2 g/m ² or more. /m ² or more is more preferable. This paint is applied so that the coating amount is, for example, 10 g/m ² or less. The thickness of the functional layer 6 is preferably 0.2 μm or more, 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 be provided on the printed layer 5 by lamination.

(Heat seal layer)
The heat-seal layer 1 may be any material as long as it can heat-seal the lid 21 to the container body 22 of the food packaging container 20 shown in FIG. 5, which will be described later, and thereby seal the container. As the heat seal layer 1, for example, a film made of ethylene-vinyl acetate (EVA), ionomer resin, or other polyolefins is used. The heat seal layer 1 is preferably a layer containing at least one of linear low density polyethylene (LLDPE), very low density linear polyethylene (Very Low Density Polyethylene; VLDPE), or polypropylene. be.

A sealant layer having an easy peel function (simple peeling function) can also be used as the heat seal layer 1 . Easy peelability indicates excellent re-peelability and easy-openability. Means for bonding the heat seal layer 1 by lamination or the like include a dry lamination method using a solvent-based adhesive, a non-sol lamination method using a non-solvent-based adhesive, and a sand lamination method using a molten resin as an adhesive. . Moreover, when extruding the heat-seal layer from a molten resin, an extrusion lamination method can be used.

The heat seal layer 1 is provided on the support layer 2 by lamination, for example. The heat seal layer 1 can also be formed by applying a heat seal varnish. 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 as coating means.

The thickness of the heat seal layer 1 is not particularly limited. The thickness of the heat seal layer 1 is preferably in the range of 0.5 to 60 µm, more preferably in the range of 1 to 30 µm.

(adhesive layer)
The lid laminate sheet 10 may further include one or more adhesive layers.
For example, the lid laminate sheet 10 may include an adhesive layer between the heat seal layer 1 and the support layer 2 for bonding them. Alternatively, the lid laminate sheet 10 may include an adhesive layer between the support layer 2 and the paper substrate 4 for bonding them. Alternatively, the lid laminate sheet 10 includes an adhesive layer between the heat seal layer 1 and the support layer 2 for bonding them together, and between the support layer 2 and the paper base material 4 for bonding them together. may include an adhesive layer of

As the material of the adhesive layer, an adhesive resin or an adhesive that can obtain the required adhesive strength is appropriately selected and used according to the material of the layer to be adhered through the adhesive layer.

Examples of the adhesive resin include 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; Vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, 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 obtained by mixing a first composition containing a main agent and a solvent and a second composition containing a curing agent and a solvent. The adhesive layer obtained from this adhesive contains a cured product produced by the reaction of the main agent and the curing agent in the adhesive composition.

A polyol can be mentioned as an example of the main agent. Examples of curing agents include isocyanate compounds. Examples of adhesives include ether-based two-component reactive adhesives and ester-based two-component reactive adhesives.

The cured product of the ether-based two-component reactive adhesive is, for example, polyether polyurethane. A polyether polyurethane is produced by reacting a polyether polyol as a main agent with an isocyanate compound as a curing agent.

The cured product of the ester-based two-liquid reactive adhesive is, for example, polyester polyurethane and polyester. A polyester polyurethane is produced by reacting a polyester polyol as a main agent with an isocyanate compound as a curing agent.

Acrylic polyol may be used as the main agent in the two-component reactive adhesive. In addition, the above adhesive composition does not need to contain a solvent as long as it melts or lowers in viscosity when heated. 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 as coating means.

The mass per area of the lid laminated sheet 10 is preferably in the range of 50 to 160 g/m ² , more preferably in the range of 60 to 140 g/m ² , and more preferably 90 to 130 g/m 2 . It is more preferably in the range of ^m2 . Decreasing this value reduces the strength of the lid. If this value is increased, the lid body becomes harder and the ease of opening is lowered. Also, increasing this value increases the cost and carbon dioxide emissions associated with manufacturing and exhaust.

As described above, the lid laminate sheet 10 is used as a lid material for food packaging containers and includes the paper substrate 4 . When using a paper base material, it is difficult to achieve high puncture resistance, but by combining the structure and materials described above, a lid with excellent puncture resistance can be achieved.

Here, the "penetration strength" of the lid laminate sheet or lid is determined by the method specified in JIS Z1707:2019 "General Rules for Plastic Films for Food Packaging". This is a value obtained by piercing from the layer 6 side. Specifically, a needle having a diameter of 1 mm and a semi-circular tip is pierced into the lid laminated sheet or the lid at a speed of 50 mm / min from the functional layer 6 side until the needle penetrates. Measure maximum force. This measurement is performed multiple times and the arithmetic mean of the maximum force is obtained as the puncture strength. In addition, unless otherwise specified, the "penetration strength" means a value obtained when the laminate sheet for lid or the lid is pierced from the functional layer side.

The puncture strength of the lid laminated sheet 10 or the lid is preferably 5.5 N or more, more preferably 7.5 N or more. This piercing strength is, for example, 25 N or less.

In general, the piercing strength obtained when a needle is pierced from the heat-seal layer side of the lid laminated sheet or lid used in food packaging containers is It need not be as high as the puncture strength to be obtained. Moreover, the piercing strength obtained when a needle is pierced from the heat seal layer side is generally higher than the piercing strength obtained when a needle is pierced from the functional layer side.

[Modification]
Various modifications can be made to the laminated sheet for the lid. For example, as described below, the laminated lid sheet may further include a gas barrier layer. The matters described with reference to FIG. 1 can be applied singly or in combination to the laminated sheet for a lid according to the modified example described here.

FIG. 2 is a partial cross-sectional view schematically showing a laminated sheet for a lid according to a modified example.
The lid laminate sheet 11 shown in FIG. 2 is the same as the lid laminate sheet 10 described with reference to FIG. 1 except that the support layer 2 has the following structure. That is, in the lid laminated sheet 11, the support layer 2 includes the first layer 2a, the second layer 2b, and the gas barrier layer 2c.

(first layer and second layer)
The first layer 2 a and the second layer 2 b are interposed between the heat seal layer 1 and the paper substrate 4 . The first layer 2a and the second layer 2b are arranged in this order from the heat seal layer 1 side.

Each of the first layer 2a and the second layer 2b contains at least one of polybutylene terephthalate and polyamide. According to one example, the first layer 2a and the second layer 2b each consist of polybutylene terephthalate. According to another example, the first layer 2a and the second layer 2b each consist of polyamide.

The thickness of each of the first layer 2a and the second layer 2b is preferably within the range of 2 to 30 μm, more preferably within the range of 3 to 20 μm. The sum of the thickness of the first layer 2a and the thickness of the second layer 2b is preferably in the range of 4 to 60 µm, more preferably in the range of 7 to 40 µm.

(Gas barrier layer)
The gas barrier layer 2c is interposed between the first layer 2a and the second layer 2b. The gas barrier layer 2c has gas barrier properties such as oxygen barrier properties and water vapor barrier properties. The gas barrier layer 2c prevents gases such as oxygen, water vapor, and aromatic components outside the container from penetrating into the packaged food described later. Thereby, the gas barrier layer 2c suppresses the deterioration of the food, which is the content of the packaged food. In addition, the gas barrier layer 2c suppresses the diffusion of odorous components and the like in the contents of the packaged food to the outside of the container. According to one example, the gas barrier layer 2c has an oxygen permeability of 0.1 to 100 cc/m ² /day/atm in an atmosphere with a temperature of 30° C. and a relative humidity of 70%.

The gas barrier layer 2c 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 by a microwave oven is assumed, the gas barrier layer 2c is preferably an inorganic oxide layer, a resin-containing layer, or a combination thereof.

The gas barrier layer 2c may be formed by coating, may be formed by melt molding, or may be formed by depositing an inorganic oxide. Alternatively, the gas barrier layer 2c may be a metal foil such as an aluminum foil, or may be a vapor-deposited metal such as aluminum.

Examples of inorganic oxides include silicon oxide, boron oxide, and 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, 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 the coating liquid.

When the resin-containing layer is formed by melt molding, for example, the above resin or a mixture of the above resin and an additive can be used as the material. As melt molding, for example, extrusion molding techniques such as T-die and inflation can be used.

The resin-containing layer formed by melt-molding is attached to, for example, at least one of the first layer 2a and the second layer 2b. The resin-containing layer may be formed by co-extrusion together with at least one of the first layer 2a and the second layer 2b.

The thickness of the gas barrier layer 2c is in the range of 0.01 to 30 μm according to one example, and in the range of 0.1 μm to 12 μm according to another example.

The lid laminate sheet 11 has the same effect as the lid laminate sheet 10 described above. In addition to having gas barrier properties, the lid laminated sheet 11 is less likely to deteriorate 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 to prevent oxygen from entering from the outside, in order to suppress oxidation of the food packed therein. In such food packaging containers, the lid is also required to have oxygen barrier properties.

In order to impart gas barrier properties against oxygen and the like to a lid made of paper as a base material, for example, a metal foil or metal deposition film made of a metal such as aluminum is often provided as a gas barrier layer on a paper base material. However, food packaging containers with a lid containing a metal layer cannot be inspected for metallic foreign matter by a metal detector after filling, and cannot be incinerated as paper because they contain metal, and can be reused as waste paper There is a problem that it cannot be used for packaging containers such as chilled foods that are expected to be heated and cooked in a microwave oven.

As noted 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 MXD6, and resin such as polyacrylonitrile are often used. A metal layer-less lid can avoid the above problems.

Regarding the distribution and storage temperature of chilled food, an optimum temperature range is set for each food, but generally it is within the range of 0 to 10°C. Packaged foods, which are chilled foods contained in food packaging containers, are delivered to consumers through various distribution channels after production. 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 removes the packaged food from the refrigerator to the time the consumer starts cooking the packaged food. is placed in a normal temperature environment.

The present inventors have found that packaged foods in which chilled foods are accommodated in food packaging containers whose lids include a paper base material and a gas barrier layer, particularly packaged foods in which the gas barrier layer is a resin-containing layer are stored in a refrigerated state. It has been found that the gas barrier properties, particularly the oxygen barrier properties, of the lid are greatly reduced during the first few hours of exposure to the normal temperature environment. This is remarkable when the ratio of the mass of the paper substrate to the mass of the lid is large.

The inventors have found that the above problem is caused by dew condensation on the surface of the lid. That is, when the packaged goods under a refrigerated environment are 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 property of the lid is lowered.

The lid laminate sheet 11 includes a functional layer 6 having water resistance. Therefore, in a packaged food using this lid laminated sheet 11 as a lid material, moisture generated on the outer surface of the lid due to dew condensation hardly reaches the gas barrier layer 2c. Therefore, in a packaged food using this lid laminate sheet 11 as a lid material, the gas barrier layer 2c is less likely to be damaged due to dew condensation on the outer surface of the lid, and the oxygen barrier property is less likely to deteriorate.

In particular, the present inventors have found that when the lid contains a paper base material, paper peeling occurs when the lid is peeled off from the container body. I find it even easier. As described above, by making the breaking strength of the support layer 2 greater than the heat sealing strength between the lid and the container body, paper peeling can be made difficult to occur.

In addition, the problems described above regarding the case where the contents are chilled foods may also occur when the contents are frozen foods. The configuration described here can produce the same effect as described above for the case where the content is chilled food, even when the content is frozen food.

(Method for measuring composite elastic modulus)
The composite elastic modulus described above is obtained by a nanoindentation method. A method for measuring the composite elastic modulus will be described below. Here, as an example, the object to be measured is the support layer 2 of the lid laminate sheet 10 .

First, a strip-shaped sheet piece having a length of 3 mm and a width of 1 mm is cut out from the lid laminated sheet 10 . The sheet piece is cut so that its length direction is parallel to the MD. Next, the surface of the sheet piece on the side of the heat seal layer 1 and the surface on the side of the functional layer 6 are coated with a resin. Thereby, the sheet piece is embedded in the resin. By embedding the sheet piece in the resin, it is possible to prevent the heat seal varnish from dripping or coming off. 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 composite material of the sheet piece and the resin in which it is embedded is cut so that cross sections parallel to the thickness direction and width direction of the sheet piece are exposed. The finishing conditions are a cutting thickness of 300 nm and a cutting speed of 1 mm/sec. Further, the cutting is performed so as to expose the cross section of the paper base material 4 in which the embedding resin permeates the entire surface. This prevents frayed paper fibers and the like from interfering with the measurement results. In this way test pieces with a smooth cross section are obtained.

The specimen obtained is then placed in a nanoindenter. Here, the test piece is placed in the nanoindenter so that the indenter of the nanoindenter is in vertical contact with the cross section of the support layer 2 . A nanoindenter is used that allows surface detection at 1 μN. At the time of installation, the embedding resin may be trimmed if necessary.

Next, as shown in FIG. 3, an indenter 30 is pushed into the support layer 2. As shown in FIG. The indentation speed is 100 nm/sec. FIG. 3 is a cross-sectional view schematically showing a state in which the indenter 30 is pushed into the support layer 2 at the maximum depth. In FIG. 4, h _max indicates the maximum depth for indentation into the support layer 2, ie the maximum displacement. _Ac indicates the contact projected area. _hc indicates the contact depth. In the process of indenting the indenter 30, the load applied to the support layer 2 and the indentation depth are measured by a nanoindenter.

As the indenter 30, a Berkovich indenter made of diamond is used. The tip of the Berkovich indenter consists of three faces each having a triangular shape. Each triangle has one position of its vertices coinciding with one position of the vertices of each of the other two triangles. Also, in these triangles, the angles formed by the two sides extending from the above vertices are equal to each other. That is, these three faces form a substantially equilateral triangular pyramid. In the indenter 30 used here, the angle of each triangle is 115°. The angle between the center line of the indenter 30 and the plane containing one of the triangles is 65.27°. The nanoindenter is set so that the indenter 30 pushes the cross-section of the support layer 2 further by 100 nm after the surface detection load reaches 1 μN. With this setting, the actual indentation depth is approximately 110 nm. The holding time at maximum depth shall be 1 second.

Next, the indenter 30 is pulled out from the support layer 2 . The drawing speed is 100 nm/sec. Also in this process, the load applied to the support layer 2 and the indentation depth are measured by the nanoindenter. In addition, in FIG. 3, P _max indicates the maximum load of the unloading curve.

According to the operation described above, for example, the relationship shown in FIG. 4 is obtained. FIG. 4 is a graph showing load-displacement curves. In FIG. 4, the vertical axis represents the load P applied to the support layer 2, and the horizontal axis represents the indentation depth of the indenter 30, that is, the displacement h. In FIG. 4, the indenter 30 is not in contact with the support layer 2 when the load P is zero. Further, the position where the displacement h is 0 is the position of the starting point where the load P applied to the support layer 2 increases from 0. In FIG. 4, the curve in which the load P increases upward from 0 as the displacement h increases shows the relationship between the load P and the displacement H in the process of pressing the indenter 30 into the support layer 2. . The curve in which the load P decreases to a negative value as the displacement h decreases is the unloading curve. The unloading curve shows the relationship between load and displacement in the process of pulling out the indenter 30 from the support layer 2 .

Next, the contact depth _hc is determined by analysis using the Oliver-Pharr method. The contact depth _hc can be obtained by the following formula (1).

where ε is a constant related to the indenter shape. For Berkovich indenters, this constant is 0.75. The maximum load P _max and maximum displacement h _max of the unloading curve can be obtained based on the graph shown in FIG. S is the contact stiffness. The contact stiffness S is the slope of the approximation curve obtained by fitting the range of 20% to 95% of the maximum load in the unloading curve in FIG. 4 with the function of the following formula (2) immediately after extraction. . where P is the load and h is the indentation depth. Also, A, _hf and m are fitting parameters for fitting.

Next, the projected contact area A _c is obtained based on the shape of the indenter and the contact depth h _c . The contact projected area A _c can be expressed as a function of the contact depth h _c as shown in Equation (3) below. Equation (3) includes terms including C1 to C5 called correction terms in order to correct the influence of the shape of the indenter. For C1 to C5, fused silica was used as a test piece, and a maximum load of 20 _μN to ₁₀ mN was measured. It is a defined value.

Next, based on the contact projected area Ac and the contact stiffness S, the composite elastic modulus Er is obtained. The composite elastic modulus Er can be obtained by the following formula (4).

The composite elastic modulus Er is measured at a plurality of points, for example 10 to 20 points, on one test piece. An average value of these composite elastic moduli Er is obtained as the above composite elastic modulus.

[Second embodiment]
A lid according to the second embodiment of the present invention is a lid obtained from the laminated sheet for a lid according to the first embodiment or the modification described above. An example of the lid according to the second embodiment is lid 21, which will be described later with reference to FIG. The lid according to the present embodiment has excellent piercing strength, as described in relation to the lid laminated sheets 10 and 11 .

[Third Embodiment]
FIG. 5 is a cross-sectional view schematically showing a food packaging container according to a third embodiment of the present invention. A food packaging container 20 shown in FIG. 5 includes a container body 22 having an opening, and a lid 21 covering the opening.

The container main body 22 is, for example, in the shape of a cylinder 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 barrel.

The container body 22 contains, for example, an olefin resin such as polypropylene. The container body 22 may further contain a component such as an ethylene-vinyl alcohol copolymer in order to enhance its gas barrier properties. Moreover, the container body 22 may further contain additives, for example, additives for the purpose of improving workability, designability, and chemical durability.

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

Paper can also be used for the container body 22 . When the contents contain a liquid material, the container body 22 includes a paper base material and a layer made of resin or the like provided on the surface facing the contents in order to prevent the liquid material from penetrating into the paper base material. A multi-layer structure including and can be adopted. As the material of the container body 22 containing the paper substrate, for example, paper leaves, paper dust, pulp, or used paper can be used. For molding into the container body 22, it is possible to use general-purpose techniques such as a method of folding and pasting a sheet containing paper leaves as in the manufacture of a paper pack, sheet press molding using a mold, and pulp molding. is. By using paper for the container body 22, it is possible to reduce the amount of carbon dioxide emitted during the manufacture and disposal of the food packaging container 20 as a whole, thus reducing the burden on the environment.

The lid 21 is one of the lid laminated sheets 10 and 11, or one of them cut out. The lid body 21 is heat-sealed to the flange 22a via the heat-seal 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 appropriately set.

[Fourth Embodiment]
A packaged food according to the fourth embodiment of the present invention is obtained by accommodating food in the food packaging container according to the third embodiment. Foods to be accommodated are not particularly limited, but are preferably chilled foods or frozen foods. Chilled and frozen foods are, for example, cooked or processed foods. Chilled and frozen foods are, for example, grilled fish, boiled fish, or side dishes.

In this packaged food, as described above, the heat seal strength between the lid 21 and the container body 22 is preferably smaller than the breaking strength of the support layer 2 included in the lid 21 . The heat seal strength is preferably in the range of 5N/15mm to 60N/15mm, more preferably in the range of 10N/15mm to 50N/15mm. The difference between the breaking strength of the support layer 2 and the heat sealing strength between the lid 21 and the container body 22 is preferably within the range of 5 to 60 N/15 mm, and within the range of 10 to 40 N/15 mm. It is more preferable to have 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".

In the production of this packaged food, the lid 21 is heat-sealed to the container body 22 before the lid 21 is heat-sealed to the container body 22, for example, after the contents are accommodated in the container body 22. Previously, the gas within container body 22 may be replaced by known methods. For example, the container body 22 may be filled with an inert gas. By appropriately changing the gas composition in the container, it is possible to suppress the growth of bacteria and extend the quality preservation period, to maintain the flavor and color of food for a long time by preventing oxidation, and to prevent the loss of vitamins. be able to. The replacement gas is appropriately selected according to the type of food that is the content. As the replacement gas, a mixed gas of oxygen gas, nitrogen gas and carbon dioxide gas is preferably used.

The lid contained in this packaged food has excellent piercing strength. Therefore, this packaged food is less likely to cause defects such as pinholes and holes in the lid, and thus less likely to cause deterioration of the contents.

The following describes tests conducted in relation to the present invention.

<1> Test 1
<1.1> Production of laminated sheet for lid (Example 1)
A laminate sheet 10 for a lid shown in FIG. 1 was manufactured by the following method.
First, a single-sided coated paper having a basis weight of 52.3 g/m ² was prepared as the paper base material 4 . A print layer 5 and a functional layer 6 were sequentially formed on the coat layer of the paper substrate 4 using a gravure multicolor printer. The printing layer 5 was formed using normal printing ink. The amount of printing ink applied was 1.0 g/m ² . The functional layer 6 was formed using an OP varnish containing nitrocellulose-based resin and polyethylene-based granular wax as main components. The coating amount of the OP varnish was 0.5 g/m ² .

Next, the support layer 2 was adhered to the laminate composed of the paper substrate 4, the printed layer 5 and the functional layer 6 by dry lamination. As the support layer 2, a biaxially oriented polybutylene terephthalate film having a thickness of 15 μm, a mass per area of 20.9 g/m ² and both surfaces of which were subjected to corona treatment was used. For the dry lamination, first, a dry laminating agent was applied to one surface of the support layer 2 using a gravure coater to form an adhesive layer. As the dry laminating agent, a two-liquid reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used. The coating amount of the dry laminating agent was 3.0 g/m ² . Next, with the adhesive layer interposed therebetween, the laminate and the support layer 2 were bonded together so that the support layer 2 faced the surface of the paper substrate 4 on which the coat layer was not provided.

After that, the heat seal layer 1 was attached to the laminate including the support layer 2, the paper substrate 4, the print layer 5 and the functional layer 6 by dry lamination. The heat seal layer 1 includes a support layer and an easy peel layer, has a mass per area of 26.0 g/m ² , and has easy peel properties in which the surface opposite to the easy peel layer is corona-treated. A film with In the dry lamination, first, a dry laminating agent was applied to two surfaces of the support layer using a gravure coater to form an adhesive layer. As the dry laminating agent, a two-liquid reactive adhesive containing an ester-based polyol and an isocyanate-based curing agent was used. The coating amount of the dry laminating agent was 3.0 g/m ² . Next, the laminate and the heat seal layer 1 were bonded together with the adhesive layer interposed therebetween such that the corona-treated surface of the heat seal layer 1 faced the support layer 2 .

It was then aged at 40°C. As described above, the laminate sheet 10 for a lid shown in FIG. 1 was obtained.

(Example 2)
A laminate sheet 10 for a lid was produced in the same manner as in Example 1, except for the following points. That is, in this example, instead of using a biaxially oriented polybutylene terephthalate film as the support layer 2, it has a thickness of 15 μm, a mass per area of 17.4 g/m ² , and is easily coated on one side. A biaxially oriented nylon film that had been subjected to adhesion treatment and had been subjected to corona treatment on both sides was used. The support layer 2 was arranged so that the surface to which the easy-adhesion treatment was applied faced the heat seal layer 1 .

(Example 3)
A laminated sheet 11 for a lid shown in FIG. 2 was manufactured by the following method. That is, the same method as described above for the lid laminate sheet 10 in Example 1, except that a multilayer film having a three-layer structure was used as the support layer 2 instead of using a biaxially stretched polybutylene terephthalate film. A laminated sheet 11 for a lid was manufactured by the above. This multilayer film is obtained by a multilayer coextrusion method, and consists of a pair of layers mainly composed of nylon and a layer mainly composed of ethylene-vinyl alcohol copolymer interposed between them. A biaxially stretched film with a 15 μm, a weight per area of 17.4 g/m ² and corona treated on both sides was used.

(Comparative example 1)
Example except that instead of using a biaxially oriented polybutylene terephthalate film as the support layer, a biaxially oriented polyethylene terephthalate film having a thickness of 12 μm and a weight per area of 16.4 g/m ² was used. A laminated sheet for a lid was produced in the same manner as in 1.

(Comparative example 2)
A laminate sheet for a lid was produced in the same manner as in Example 1, except that the support layer was omitted.

<1.2> Evaluation (measurement of breaking strength)
The breaking strength of the support layers used in Examples 1-3 and Comparative Example 1 was measured by the method described above.

Here, from each support layer, three test pieces with the length direction parallel to the MD and three test pieces with the length direction parallel to the TD were cut. Each test piece had a strip shape with a width of 15 mm and a length of 100 mm.

The distance between gauge lines was 50 mm, and the test speed was 1000 mm/min. The breaking strength was measured using a Tensilon universal testing machine.

The breaking strength in the MD was obtained by arithmetically averaging the measurements obtained using specimens with the length direction parallel to the MD. Moreover, the breaking strength in TD was obtained by arithmetically averaging the measured values obtained using a test piece whose length direction was parallel to TD.

(Measurement of heat seal strength)
The heat sealing strength to the resin sheet was measured by the method described above for the laminated sheets for lids according to Examples 1 to 3 and Comparative Examples 1 and 2.

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

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 seal bar width of 5 mm. The length direction of the seal bar was perpendicular to MD. Heat sealing was performed by applying a temperature of 190° C. and a pressure of 0.2 MPa to the laminate of the lid laminated sheet and the resin sheet for 2 seconds at each heat sealing position. From each laminate partially heat-sealed in this way, a strip having a width of 15 mm, the length direction parallel to the MD, one end not heat-sealed and the other end 30 mm Three heat-sealed specimens were cut over a length of ∼50 mm.

Separately from this, each lid laminated sheet and the resin sheet were heat-sealed by the same method as described above, except that the length direction of the seal bar was perpendicular to the TD. From each laminate partially heat-sealed in this way, a strip having a width of 15 mm, the length direction parallel to the TD, one end not heat-sealed and the other end 30 mm Three heat-sealed specimens were cut 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 tester 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 grippers of the tester, and the grippers were moved away from each other. The relative movement speed of these grippers, that is, the peeling speed, was 1000 mm/min. The maximum tensile load applied to each specimen until it broke was recorded.

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

(Measurement of piercing strength)
The puncture strength of the laminated sheets for lids according to Examples 1 to 3 and Comparative Example 1 was measured by the method described above. Here, the piercing strength when a needle is pierced into the laminated lid sheet from the functional layer side and the piercing strength when the needle is pierced into the laminated lid sheet from the heat seal layer side were determined. . Each puncture strength was obtained by arithmetically averaging the values obtained from three measurements.

(Cup seal test)
Lids were cut out from the laminated sheets for lids according to Examples 1 to 3 and Comparative Examples 1 and 2. A food packaging container 20 shown in FIG. 5 was manufactured using these lid bodies. Here, as the container body 22, the resin sheet used for measuring the heat seal strength was formed into a tray shape. The container 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 21 to the flange 22a is performed by using a seal bar with a width of 5 mm, which is made along the shape of the flange 22a, and applying a temperature of 160° C. and a pressure of 0.2 MPa for 1.5 seconds. It was done by

Next, for each food packaging container 20, the lid 21 was peeled off from the corner of the container body 22 by hand. After that, it was confirmed whether or not the paper peeled off.

Table 1 below shows the physical properties and the like of the support layer included in the lid laminate sheet. Also, the results of the above measurements and tests are summarized in Table 2 below.

In Tables 1 and 2, "PBT", "Ny", "EVOH", and "PET" represent polybutylene terephthalate, nylon, ethylene-vinyl alcohol copolymer, and polyethylene terephthalate, respectively. In Tables 1 and 2, "mass" is mass per area. In Table 2, the classification of "Paper", "Plastic" and "Others" in the column labeled "Mass ratio" conforms to the "Container and Packaging Recycling Law Explanatory Material". The column labeled "difference" describes 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 "paper peeling" in Table 2, "A" indicates that cohesive failure occurred in the heat seal layer and no paper peeling occurred. "B" indicates that although the paper was peeled off, a portion of the lid material remained in the container body only at or around the seal portion. In the case of "B", the contents can be taken out from the container body. "C" indicates that the paper was peeled off and the lid material remained on the container body in areas other than the seal portion and its surroundings. Specifically, "C" indicates that a double lid was formed or the lid was torn. Here, the double lid means that a part of the lid mainly including the paper substrate and the heat seal layer covers the entire opening of the container body or most of it due to cohesive failure of the paper substrate. It is to remain in the container body as much as possible. In the case of "C", it takes time and effort to take out the contents from the container body and separate the lid from the container body.

In the column labeled "Penetration strength" in Table 2, "Upper surface" represents the piercing strength when a needle is pierced from the functional layer side into the lid laminated sheet, and "Lower surface" represents the needle. shows the piercing strength when the laminated sheet for lid is pierced from the heat seal layer side. In the column labeled "upper surface" or "lower surface", "A" has a piercing strength that is at least twice as high as the piercing strength obtained for the laminated sheet for a lid according to Comparative Example 2. indicates that "B" indicates that the piercing strength was more than 1.5 times and less than 2 times the piercing strength obtained for the laminated sheet for a lid according to Comparative Example 2. "C" indicates that the laminate sheet for a lid according to Comparative Example 2 had a puncture strength 1.5 times or less than the puncture strength obtained for the lid laminate sheet.

As shown in Table 2, the laminated sheets for lids according to Examples 1 to 3 were pierced with needles from the functional layer side and from the heat seal layer side. , had a high puncture strength. On the other hand, the laminated sheet for a lid according to Comparative Example 2 had a low piercing strength when the needle was pierced into the laminated sheet for a lid from the functional layer side and the needle was pierced from the heat seal layer side. had a The laminated sheet for a lid according to Comparative Example 1 had a high piercing strength when a needle was pierced into the laminated sheet for a lid from the heat-seal layer side, but the needle did not function in the laminated sheet for a lid. The piercing strength when pierced from the layer side was low.

Moreover, as shown in Table 2, when the laminated sheets for lids according to Examples 1 to 3 and Comparative Example 1 were used, no paper peeling occurred. On the other hand, when the laminate sheet for a lid according to Comparative Example 2 was used, paper peeling occurred.

<2> Test 2
<2.1> Production of laminated sheet for lid (Example 4)
A laminate sheet 10 for a lid was manufactured in substantially the same manner as in Example 1, except for the following points. That is, in this example, the heat seal layer 1 used in Example 1 was the same as that used in Example 1 except that the mass per unit area was 27.6 g/m ² , and the coating amount of the OP varnish was 0.6 g/m 2 . 6 g/m ² .

(Example 5)
A laminate sheet 10 for a lid was manufactured in substantially the same manner as in Example 2, except for the following points. That is, in this example, the heat seal layer 1 used in Example 1 was the same as that used in Example 1 except that the mass per unit area was 27.6 g/m ² , and the coating amount of the OP varnish was 0.6 g/m 2 . 6 g/m ² .

(Example 6)
A laminate sheet 10 for a lid was manufactured in substantially the same manner as in Example 3, except for the following points. That is, in this example, the heat seal layer 1 used in Example 1 was the same as that used in Example 1 except that the mass per unit area was 27.6 g/m ² , and the coating amount of the OP varnish was 0.6 g/m 2 . 6 g/m ² .

(Example 7)
A laminate sheet 10 for a lid was manufactured in substantially the same manner as in Example 4, except for the following points. That is, in this example, the heat seal layer 1 is formed by applying a heat seal varnish to the support layer 2 instead of laminating a film including a support layer and an easy peel layer to the support layer 2 via a dry laminating agent. It was formed by drying the coating film. As the heat seal varnish, an aqueous emulsion containing an ethylene-vinyl acetate copolymer as a main component and containing water and isopropanol as a solvent or dispersion medium was used. The solid content of this heat seal varnish had a glass transition temperature of 35°C and a melting point of 70 to 100°C. The heat seal varnish was applied by gravure printing so that the dry mass per area was 3 g/m ² .

(Example 8)
A laminate sheet 10 for a lid was manufactured in substantially the same manner as in Example 5, except for the following points. That is, in this example, the heat seal layer 1 is formed by applying a heat seal varnish to the support layer 2 instead of laminating a film including a support layer and an easy peel layer to the support layer 2 via a dry laminating agent. It was formed by drying the coating film. As the heat seal varnish, an aqueous emulsion containing an ethylene-vinyl acetate copolymer as a main component and containing water and isopropanol as a solvent or dispersion medium was used. The solid content of this heat seal varnish had a glass transition temperature of 35°C and a melting point of 70 to 100°C. The heat seal varnish was applied by gravure printing so that the dry mass per area was 3 g/m ² .

(Example 9)
A laminate sheet 10 for a lid was manufactured in substantially the same manner as in Example 6, except for the following points. That is, in this example, the heat seal layer 1 is formed by applying a heat seal varnish to the support layer 2 instead of laminating a film including a support layer and an easy peel layer to the support layer 2 via a dry laminating agent. It was formed by drying the coating film. As the heat seal varnish, an aqueous emulsion containing an ethylene-vinyl acetate copolymer as a main component and containing water and isopropanol as a solvent or dispersion medium was used. The solid content of this heat seal varnish had a glass transition temperature of 35°C and a melting point of 70 to 100°C. The heat seal varnish was applied by gravure printing so that the dry mass per area was 3 g/m ² .

(Comparative Example 3)
A laminate sheet for a lid was produced in substantially the same manner as in Comparative Example 1, except for the following points. That is, in this example, the heat seal layer 1 used in Example 1 was the same as that used in Example 1 except that the mass per unit area was 27.6 g/m ² , and the coating amount of the OP varnish was 0.6 g/m 2 . 6 g/m ² .

(Comparative Example 4)
A laminate sheet for a lid was produced in substantially the same manner as in Comparative Example 3, except for the following points. That is, in this example, the heat seal layer is formed by applying a heat seal varnish to the support layer instead of laminating the film including the support layer and the easy peel layer to the support layer via the dry laminating agent. A membrane was formed by drying. As the heat seal varnish, an aqueous emulsion containing an ethylene-vinyl acetate copolymer as a main component and containing water and isopropanol as a solvent or dispersion medium was used. The solid content of this heat seal varnish had a glass transition temperature of 35°C and a melting point of 70 to 100°C. The heat seal varnish was applied by gravure printing so that the dry mass per area was 3 g/m ² .

(Comparative Example 5)
A laminate sheet for a lid was produced in substantially the same manner as in Comparative Example 2, except for the following points. That is, in this example, the heat seal layer 1 used in Example 1 was the same as that used in Example 1 except that the mass per unit area was 27.6 g/m ² , and the coating amount of the OP varnish was 0.6 g/m 2 . 6 g/m ² .

<2.2> Evaluation (Measurement of heat seal strength)
For the lid laminated sheets according to Examples 4 to 9 and Comparative Examples 3 to 5, the heat sealing strength to the resin sheet was measured by the same method as in <1.2> Evaluation.

However, in the case where the heat seal layer is a sealant layer, heat sealing is performed by applying a temperature of 190° C. and a pressure of 0.2 MPa to the laminate of the lid laminate sheet and the resin sheet at each heat seal position. Seconds were added. On the other hand, in the case where the heat seal layer is made of heat seal varnish, the heat seal is performed by applying a temperature of 210° C. and a pressure of 0.1 MPa to the laminate of the lid laminate sheet and the resin sheet at each heat seal position. This was done by adding for 5 seconds.

(Measurement of piercing strength)
The puncture strength of the laminated sheets for lids according to Examples 4 to 9 and Comparative Examples 3 to 5 was measured by the same method as in <1.2> Evaluation.

(Cup seal test)
The same cup seal test as in <1.2> Evaluation was performed on the laminated sheets for lids according to Examples 4 to 9 and Comparative Examples 3 to 5.

However, when the heat seal layer was the sealant layer, heat sealing of the cover 21 to the flange 22a was performed by applying a temperature of 160° C. and a pressure of 0.2 MPa for 1.5 seconds. On the other hand, when the heat seal layer was made of heat seal varnish, heat sealing of the cover 21 to the flange 22a was performed by applying a temperature of 210° C. and a pressure of 0.2 MPa for 1.5 seconds.

(water absorption)
The water absorbency of the lid laminated sheets according to Examples 4 to 9 and Comparative Examples 3 to 5 was measured by the method described above.

(Measurement of composite elastic modulus)
The composite modulus of elasticity of the support layers of the laminated sheets for lids according to Examples 4 to 9 and Comparative Examples 3 to 5 was measured by the method described above. As a nanoindenter, TI Premier (manufactured by Bruker Japan) was used. As the resin for embedding the sheet piece, an ultraviolet curable resin was used. As the microtome, an ultramicrotome (trade name: "Leica EM UC7", manufactured by Leica Microsystems) to which a diamond knife was attached was used. Moreover, the cutting was performed after fixing the sheet piece to a holder for fixing it in advance so that the indenter could enter the cross section perpendicularly at the time of measurement.

The results of the above measurements and tests are summarized in Tables 3 and 4 below.

Abbreviations and item names in Tables 3 and 4 have the same meanings as those in Table 2.

In the column labeled "Water Absorbency" in Tables 3 and 4, "A" indicates that the water absorbency was 20 g/ ^m2 or less, and "B" indicates that the water absorbency was greater than 20 g/ ^m2 . indicates that

In the column labeled "Paper Peeling" in Tables 3 and 4, "A" indicates that cohesive failure occurred in the heat seal layer and no paper peeling occurred. "B" indicates that although the paper was peeled off, a portion of the lid material remained in the container body only at or around the seal portion. In the case of "B", the contents can be taken out from the container body. "C" indicates that the paper was peeled off and the lid material remained on the container body in areas other than the seal portion and its surroundings. Specifically, "C" indicates that a double lid was formed or the lid was torn.

In the column labeled "Puncture strength" in Tables 3 and 4, "upper surface" represents the piercing strength when a needle is pierced from the functional layer side of the laminated lid sheet, and "lower surface". represents the piercing strength when a needle is pierced from the heat-seal layer side of the lid laminated sheet. In the column labeled "upper surface" or "lower surface", for those in which the heat-sealing layer is a sealant layer, "A" is the piercing strength obtained for the laminated sheet for a lid according to Comparative Example 3. "B" is more than 1.0 times the piercing strength obtained for the laminated sheet for a lid according to Comparative Example 3. 0.7 times or more the puncture strength obtained for the laminated sheet for a lid according to Comparative Example 3. "D" indicates that the piercing strength was less than 0.7 times the piercing strength obtained for the lid laminated sheet according to Comparative Example 3. It shows that it had In addition, in the column labeled "upper surface" or "lower surface", for those in which the heat-seal layer is made of heat-seal varnish, "A" is the piercing strength obtained for the laminated sheet for lid according to Comparative Example 4. "B" is 1.0 times the piercing strength obtained for the laminated sheet for a lid according to Comparative Example 4. It shows that it had a piercing strength of more than 1.5 times and less than 1.5 times, and "C" is 1.0 times or less than the piercing strength obtained for the laminated sheet for lid according to Comparative Example 4. It shows that it had a piercing strength of

As shown in Table 3, the laminated sheets for lids according to Examples 4 to 9 were pierced with a needle from the functional layer side and from the heat seal layer side. , had a high puncture strength. On the other hand, as shown in Table 4, the laminated sheets for lids according to Comparative Examples 3 to 5 were pierced with a needle from the functional layer side and from the heat seal layer side. In both cases it had a low puncture strength. In particular, the laminated sheet for a lid according to Comparative Example 5 has extremely low piercing strength when a needle pierces the laminated sheet for a lid from the functional layer side and from the heat seal layer side. had

Moreover, as shown in Tables 3 and 4, when the laminated sheets for lids according to Examples 4 to 9 and Comparative Examples 3 and 4 were used, no paper peeling occurred. On the other hand, when the laminate sheet for a lid according to Comparative Example 5 was used, paper peeling occurred.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the scope of the invention. In addition, each embodiment may be implemented in combination as appropriate, in which case the combined effect can be obtained. Furthermore, various inventions are included in the above embodiments, and various inventions can be extracted by combinations selected from a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiments, if the problem can be solved and effects can be obtained, a configuration in which these constituent elements are deleted can be extracted as an invention.

DESCRIPTION OF SYMBOLS 1... Heat seal layer, 2... Support layer, 2a... First layer, 2b... Second layer, 2c... Gas barrier layer, 4... Paper substrate, 5... Printing layer, 6... Functional layer, 10... Laminate for lid body Sheet 11 Laminated sheet for lid, 20 Food packaging container, 21 Lid, 22 Container body, 22a Flange, 30 Indenter.

Claims (22)

A lid laminated sheet used for the lid of a food packaging container comprising a container body provided with an opening and a lid covering the opening, comprising a functional layer having water resistance, a printed layer, A paper base material, a support layer, and a heat-seal layer are included in this order, the mass of the paper base material being greater than the mass of any other layer included in the laminated lid sheet, and the support layer is a laminated sheet for a lid containing at least one of polybutylene terephthalate and polyamide. The laminate sheet for a lid according to claim 1, wherein the support layer has a multilayer structure. The support layer includes a first layer and a second layer each containing at least one of polybutylene terephthalate and polyamide, and a gas barrier layer having gas barrier properties and interposed between the first layer and the second layer. The laminated sheet for a lid according to claim 1, comprising: The laminated sheet for a lid according to claim 3, wherein the gas barrier layer comprises at least one of an inorganic oxide layer and a resin-containing layer. 2. The laminated sheet for a lid according to claim 1, wherein the ratio of the total mass of polybutylene terephthalate and polyamide to the mass of said support layer is 50% by mass or more. The laminate sheet for a lid according to claim 1, wherein the support layer is a stretched film. 2. The laminated sheet for a lid according to claim 1, wherein the support layer has a thickness in the range of 3 to 60 [mu]m. The laminate sheet for lid according to claim 1, wherein the breaking strength of the support layer is greater than the heat seal strength between the lid and the container body. The laminate sheet for a lid according to claim 1, wherein the heat seal layer is formed of heat seal varnish. When the layers other than the paper base material included in the lid laminated sheet are classified into a layer made of plastic and other layers, the mass of the paper base material is the sum of the layers made of plastic. The laminate sheet for a lid according to claim 1, which is larger than the total mass of the mass and the other layers. The laminate sheet for a lid according to claim 1, wherein the paper substrate is coated paper having a coat layer on one surface, and the printed layer is provided on the coat layer. The laminate for a lid according to claim 1, wherein the paper substrate is a coated paper having a coat layer on one surface, and the support layer is bonded to the paper substrate so as to face the coat layer. sheet. 2. The laminated sheet for a lid according to claim 1, wherein the paper substrate is coated paper having coat layers on both sides. The laminate sheet for a lid according to claim 1, wherein the paper base material has a basis weight in the range of 40 to 100 g/ ^m2 . 2. The laminated sheet for a lid according to claim 1, wherein the heat seal layer is a sealant having an easy peel property. The laminated sheet for a lid according to claim 1, wherein the functional layer has a mass per area of 0.2 g/ ^m2 or more. A lid comprising the laminated sheet for a lid according to any one of claims 1 to 16. A food packaging container comprising: a container body provided with an opening; and the lid according to claim 17 covering the opening, wherein the support layer covers the paper substrate and the inside of the food packaging container A food packaging container that is placed between the space. 19. The food packaging container according to claim 18, wherein said container body has a flange around said opening, and said lid is heat-sealed to said flange via said heat-seal layer. 19. The food packaging container according to claim 18, wherein said internal space of said 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 18, 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 18 and a food contained in the food packaging container.

Images