Laminate sheet for lid, lid, food packaging container, and packaged food

Abstract

To provide a technique relating to a lid body including a paper base material and having excellent openability and durability.SOLUTION: A laminated sheet for a lid body used for a lid body of a packaging container including a container body provided with an opening and the lid body covering the opening, the laminated sheet comprising a paper base material, a coating layer, and a heat seal layer in this order, wherein a piercing strength measured from a side of the heat seal layer and a piercing strength measured from a side opposite to the heat seal layer are both 5N or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In addition to changes in household structure and lifestyles due to the recent trend toward nuclear families, advances in distribution, freezing, and refrigeration technologies have led to an increase in demand for cooked or processed chilled and frozen foods sold at convenience stores, supermarkets, etc. At the same time, demand for packaging containers for chilled and frozen foods is also increasing.

[0003] Meanwhile, as efforts to reduce plastic waste continue, there is growing demand for food packaging containers that use paper as a base material, a renewable resource with a low environmental impact. There is also a demand for packaging containers made of paper that use paper as a base material for packaging containers that hold chilled and frozen foods.

[0004] For example, Patent Document 1 discloses a food packaging material in which two gas barrier layers using ethylene-modified polyvinyl alcohol resin are laminated on a paper substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-184138 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a technology relating to a lid that includes a paper base material and has excellent openability and durability. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a laminate sheet for a lid body used for the lid body of a packaging container having a container body with an opening and a lid body that covers the opening, the laminate sheet for a lid body comprising, in that order, a paper base material, a coating layer, and a heat seal layer, and having a puncture strength of 5N or more when measured from the side of the heat seal layer and when measured from the side opposite the heat seal layer.

[0008] According to another aspect of the invention, the coating layer has a mass per area of ​​10 g / m 2 The laminate sheet for a lid body according to the above aspect is provided.

[0009] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to any one of the above aspects, wherein the coating layer is formed of a paint film containing a resin.

[0010] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to the above aspect, wherein the resin is a urethane resin.

[0011] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to any one of the above aspects, wherein the coating layer is in contact with the paper substrate.

[0012] According to yet another aspect of the present invention, there is provided a laminate sheet for a lid according to any of the above aspects, wherein the tensile strength of the paper base material in MD is 70 N / 15 mm or more, the tensile strength of the paper base material in TD is 35 N / 15 mm or more, and the tensile elongation at break in MD of the paper base material and the tensile elongation at break in TD of the paper base material are both 7% or more.

[0013] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to any one of the above aspects, wherein the paper base material is stretch paper.

[0014] According to yet another aspect of the present invention, there is provided a lid body laminate sheet according to any of the above aspects, wherein the tensile strength in MD of the lid body laminate sheet is 70 N / 15 mm or more, the tensile strength in TD of the lid body laminate sheet is 35 N / 15 mm or more, and the tensile elongation at break in MD of the lid body laminate sheet and the tensile elongation at break in TD of the lid body laminate sheet are both 7% or more.

[0015] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to any one of the above aspects, wherein the heat seal layer is formed by coating a heat seal varnish.

[0016] According to yet another aspect of the present invention, there is provided the laminate sheet according to the above aspect, wherein the heat seal varnish is a water-based emulsion.

[0017] According to yet another aspect of the present invention, there is provided a laminate sheet according to any of the above aspects, wherein the glass transition temperature of the solid content of the heat seal varnish is in the range of -40°C or higher and -10°C or lower, and the melting point of the solid content of the heat seal varnish is in the range of 40°C or higher and 100°C or lower.

[0018] According to yet another aspect of the present invention, there is provided a laminate sheet for a lid body according to any of the above aspects, in which, when layers other than the paper base material included in the laminate sheet for a lid body are classified into layers made of plastic and other layers, the mass of the paper base material is greater than the total mass of the layers made of plastic and the total mass of the other layers.

[0019] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to any one of the above aspects, further including a printed layer as a layer facing the coating layer with the paper substrate sandwiched therebetween.

[0020] According to yet another aspect of the present invention, there is provided a laminate sheet for a lid body according to any of the above aspects, further including a functional layer having water resistance as an outermost layer facing the coating layer with the paper substrate sandwiched therebetween.

[0021] According to yet another aspect of the present invention, there is provided the laminate sheet for a lid according to any one of the above aspects, further comprising a gas barrier layer between the coating layer and the heat seal layer.

[0022] According to yet another aspect of the present invention, there is provided a lid made of the lid-forming laminate sheet according to any one of the above aspects.

[0023] According to yet another aspect of the present invention, there is provided a food packaging container comprising a container body having an opening and a lid body relating to the above-mentioned side that covers the opening, wherein the coating layer is disposed between the paper base material and the internal space of the food packaging container.

[0024] According to yet another aspect of the present invention, there is provided a food packaging container 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-seal layer.

[0025] According to yet another aspect of the present invention, there is provided a packaged food product comprising the food packaging container according to any one of the above aspects and food contained in the food packaging container. [Effects of the Invention]

[0026] According to the present invention, a lid body is provided which includes a paper base material and has excellent openability and durability. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a partial cross-sectional view schematically showing an example of a laminate sheet for a lid according to a first embodiment of the present invention. [Figure 2] FIG. 10 is a partial cross-sectional view schematically showing an example of a laminated sheet for a lid according to a modified example. [Figure 3] FIG. 4 is a cross-sectional view schematically showing a food packaging container according to a third embodiment of the present invention. [Figure 4] Graph showing the relationship between load and elongation. [Figure 5]Graph showing the relationship between load and elongation. [Figure 6] Graph showing the relationship between puncture strength and needle movement. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific embodiments of any of the above aspects. The following items can be incorporated into each of the above aspects, either singly or in combination.

[0029] Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited by the materials, shapes, structures, etc. of the components described below. Various modifications can be made to the technical idea of ​​the present invention within the technical scope defined by the claims.

[0030] In the drawings, elements having the same or similar functions are denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, the drawings are schematic, and the relationship between dimensions in one direction and dimensions in another direction, and the relationship between the dimensions of one member and the dimensions of another member, etc. may differ from the actual relationship.

[0031] [First embodiment] FIG. 1 is a partial cross-sectional view schematically showing an example of a laminate sheet for a lid according to a first embodiment of the present invention.

[0032] The lid laminate sheet 10 shown in Fig. 1 is used as a lid in a food packaging container having a container body with an opening and a lid that covers the opening. That is, the lid laminate sheet 10 is a lid material that can be used as a lid itself or a portion cut out from the sheet can be used as a lid.

[0033] The lid laminate sheet 10 includes a heat seal layer 1, a coating layer 3, and a paper substrate 4, in this order. This lid laminate sheet 10 does not include a gas barrier layer, which will be described later, and is therefore suitable for applications that do not require high gas barrier properties. Each layer included in the lid laminate sheet 10 will be described below.

[0034] (Paper base material) The lid laminate sheet 10 includes a paper base material 4. The mass of the paper base material 4 is preferably greater than the mass of any other layer included in the lid laminate sheet 10. The mass ratio of the paper base material 4 to the mass of the lid laminate sheet 10 (hereinafter also referred to as the paper content ratio) is preferably greater than 50%, more preferably 60% or more, and even more preferably 70% or more. In one example, this ratio is 90% or less. The higher the ratio, the smaller the environmental impact of the lid laminate sheet 10.

[0035] When the layers other than the paper base material 4 included in the lid laminate sheet 10 are classified into layers made of plastic and other layers, it is preferable that the mass of the paper base material 4 is larger than the total mass of the layers made of plastic and 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 Act.

[0036] The above classification follows the "Container and Packaging Recycling Law Explanatory Materials." Specifically, "plastic" refers to materials that contain polymers as essential components and are shaped and manufactured using fluidity during processing. Paints and adhesives are not included in the category of plastics because they are unrelated to the concept of "shaping." Therefore, in the example shown in Figure 1, the heat-seal layer 1 formed by coating and the coating layer 3 formed by coating are "other layers." Also, in the example shown in Figure 2, if the gas barrier layer 2 is formed by coating or vapor deposition, the heat-seal layer 1 formed by coating, the gas barrier layer 2 formed by coating or vapor deposition, the coating layer 3 formed by coating, the printed layer 5 formed from ink, and the functional layer 6 formed by coating are all "other layers." However, if the gas barrier layer 2 is formed by melt molding, the gas barrier layer 2 is a "layer made of plastic." The lid laminate sheet shown in Figure 2 will be discussed later.

[0037] As such, the lid body laminate sheet 10 shown in Fig. 1 does not include a "layer made of plastic." Furthermore, the lid body laminate sheet 11 shown in Fig. 2 does not include a "layer made of plastic" when the gas barrier layer 2 is formed by coating or vapor deposition. Like these lid body laminate sheets, it is preferable that the lid body laminate sheet does not include a plastic film.

[0038] As the paper substrate 4, it is preferable to use paper having the following tensile properties (i) to (iv). (i) The tensile strength in MD is 70N / 15mm or more. (ii) The tensile force at TD is 35 N / 15 mm or more. (iii) The tensile elongation at break in the MD is 7% or more. (iv) The tensile elongation at break in the TD is 7% or more.

[0039] In this specification, MD is an abbreviation for machine direction, and TD is an abbreviation for transverse direction. In the paper substrate 4, most of the paper fibers are oriented in the MD. In the lid laminate sheet 10, the MD of the paper substrate 4 is aligned with the MD of the lid laminate sheet.

[0040] The tensile strength of the paper base material 4 in the MD is more preferably 80 N / 15 mm or more. The tensile strength of the paper base material 4 in the MD is, for example, 120 N / 15 mm or less. The tensile strength of the paper base material 4 in the TD is more preferably 40 N / 15 mm or more. The tensile strength of the paper base material 4 in the TD is, for example, 60 N / 15 mm or less.

[0041] The tensile breaking elongation in MD of the paper base material 4 is more preferably 10% or more. The tensile breaking elongation in MD of the paper base material 4 is, for example, 20% or less. The tensile breaking elongation in TD of the paper base material 4 is more preferably 10% or more. The tensile breaking elongation in TD of the paper base material 4 is, for example, 20% or less.

[0042] Here, the tensile strength and tensile elongation at break are measured using the method specified in JIS Z1707:2019 "General Rules for Food Packaging Plastic Films." In these measurements, the test specimen width is 15 mm, the length is 100 mm, the gauge length is 50 mm, and the test speed is 300 mm / min. The tensile strength is the maximum force (N) when the test specimen is pulled until it breaks, converted into the force equivalent to a 15 mm width of the test specimen (N / 15 mm).

[0043] It should be noted that JIS Z1707:2019 describes a measurement method specified for plastic films, but in this specification, this measurement method is applied to the paper base material 4 and the lid body laminate sheet including the paper base material 4.

[0044] An example of the paper substrate 4 having the above tensile properties (i) to (iv) is Clupak paper.

[0045] Alternatively, it is preferable to use stretched paper as the paper substrate 4. Stretched paper is paper with fine wrinkles on its surface and excellent elongation. Stretched paper is, for example, stretched kraft paper. Stretched kraft paper is kraft paper that has excellent impact resistance and stretchability imparted by finely shrinking the paper on a paper machine, as described in JIS P0001:1998. Stretched kraft paper is, for example, Kraft Paper Type 5 No. 1 or No. 2 described in JIS P3401:2000. Kraft Paper Type 5 No. 1 is kraft stretched paper that has been imparted MD (machine direction) stretchability by finely shrinking the paper on a paper machine. Kraft Paper Type 5 No. 2 is kraft stretched paper that has been imparted TD (transverse direction) stretchability by finely shrinking the paper on a paper machine. Stretched kraft paper may be made of unbleached kraft pulp or bleached kraft pulp.

[0046] Thus, the stretched paper may be stretched paper in which stretchability is imparted in the MD (machine direction) by creasing the paper in the MD, or stretched paper in which stretchability is imparted in the TD (transverse direction) by creasing the paper in the TD. Clupak paper is known as an example of the former stretched paper. Clupak paper is included in the category of kraft stretched paper. Fracto paper is known as an example of the latter stretched paper. Fracto paper is included in the category of kraft stretched paper. Alternatively, the stretched paper may be stretched paper in which stretchability is imparted in both the MD and TD by creasing the paper in both the MD and TD.

[0047] A paper substrate or stretched paper having the tensile properties (i) to (iv) above can have excellent puncture strength. The puncture strength here is preferably 5.0 N or more, more preferably 7.0 N or more, and even more preferably 8.0 N or more. The puncture strength here is, for example, 10.0 N or less. The method for measuring puncture strength will be described later.

[0048] Alternatively, the paper substrate 4 may be a coated paper having a coating layer on at least one side. That is, the paper substrate 4 may be a single-sided or double-sided coated paper. The surface of the coated paper having the coating layer is smoother than the surface of paper without the coating layer. Therefore, for example, when a coating layer 3 is applied on top of the coating layer, the coatability is improved.

[0049] The thickness of the paper substrate 4 is preferably in the range of 50 μm to 200 μm, and more preferably in the range of 50 μm to 150 μm. If the thickness of the paper substrate 4 is large, the lid tends to become hard and difficult to open. On the other hand, if the thickness of the paper substrate 4 is small, the strength of the lid tends to decrease.

[0050] The basis weight of the paper substrate 4, i.e., the mass per area, is 50 g / m 2 More than 100g / m 2 It is preferable that the thickness is within the range of 60 g / m 2 More than 90g / m 2 It is more preferable that the weight of the coated paper is within the following range: When coated paper is used as the paper substrate 4, the weight of the coated paper is 50 g / m 2 More than 100g / m 2 It is preferable that the thickness is within the range of 60 g / m 2 More than 100g / m 2 It is more preferable that the mass be within the following range: If the mass per area of ​​the paper base material 4 is large, the lid tends to become hard and become less easy to open. On the other hand, if the mass per area of ​​the paper base material 4 is small, the strength of the lid tends to decrease.

[0051] (coating layer) The lid laminate sheet 10 has a coating layer 3 between the paper substrate 4 and the heat seal layer 1. By providing the coating layer 3 between the paper substrate 4 and the heat seal layer 1, the stress applied to the heat seal layer 1 and the paper substrate 4 is dispersed when the lid made of the lid laminate sheet 10 is peeled off from the container body, making it less likely that the heat seal layer 1 will break and that the paper substrate 4 will peel off. In this specification, "peeling off" refers to a state in which a part of the lid made of the lid laminate sheet remains on the container body after it has been peeled off from the container body (including double lids).

[0052] That is, when the lid is peeled (opened) from the container body, a force is applied to the heat-seal layer 1 in the film thickness direction, causing it to begin to deform, and as a result, a force is also applied to the paper substrate 4 in the film thickness direction. If the coating layer 3 is not interposed between the paper substrate 4 and the heat-seal layer 1, the heat-seal layer generally breaks due to deformation, which makes the paper substrate 4, which has weak strength in the film thickness direction, prone to peeling. In contrast, if the coating layer 3 is interposed, the coating layer 3 alleviates the force and deformation applied to the heat-seal layer 1 during peeling (opening), preventing the heat-seal layer 1 from breaking and also alleviating the force applied to the paper substrate 4 in the film thickness direction, allowing the container to be opened without peeling. In this case, the coating layer 3 will not break due to the force during peeling.

[0053] In this way, the coating layer 3 is interposed between the paper substrate 4 and the heat seal layer 1, thereby contributing to the prevention of paper peeling.

[0054] Preferably, no other layer is interposed between the coating layer 3 and the paper substrate 4, and these two layers are in contact with each other. The coating layer 3 is preferably formed from a coating film containing a resin. The coating layer 3 may be a dried film formed by applying a resin composition (coating liquid) described below to the paper substrate 4 and then drying the coating film, or a cured film formed by applying a resin composition (coating liquid) described below to the paper substrate 4 and then drying and crosslinking the coating film. The contact between the coating layer 3 and the paper substrate 4 makes it easier to distribute the stress described above when peeling (opening), and more effectively alleviates the force applied to the paper substrate 4 in the film thickness direction.

[0055] As mentioned above, the paper substrate 4 is preferably stretched paper, but stretched paper may have different smoothness between the front and back sides because it has been subjected to a wrinkle-imparting treatment. In this case, it is preferable to provide the coating layer 3 on the side of the paper substrate 4 that is smoother.

[0056] Resin composition (coating liquid) The coating layer 3 is a dried film of a coating film formed using a coating liquid comprising the resin composition as described above, or a cured film obtained by further crosslinking the dried film.

[0057] The resin composition may be selected as appropriate from those prepared by dissolving or dispersing a resin in an appropriate solvent and drying it to form the coating layer 3. For example, an aqueous dispersion of a urethane resin (i.e., polyurethane dispersion), an ethylene-vinyl alcohol copolymer resin, a vinyl chloride-vinyl acetate copolymer, an ethylene-vinyl acetate copolymer, a polyvinylidene resin, polyacetal, polystyrene, and modified products thereof may also be used.

[0058] Among these, polyurethane dispersions, which are aqueous dispersions of urethane resins, are preferred because they allow for easy control of the effect of the coating layer 3 (i.e., the effect of dispersing stress applied to the heat seal layer 1 and the paper substrate 4). Commercially available polyurethane dispersions may be used, such as Evaphanol (registered trademark) HA-55, HA-68, HA-170, HA-190, HA-207, and HA-560 manufactured by Nicca Chemical Co., Ltd., Hydran (registered trademark) HW-171 manufactured by DIC Corporation, and UW-5502D-C1, UW-3039E, UW-3018, and UW-1053D manufactured by Ube Industries, Ltd., or mixtures thereof.

[0059] For example, the resin composition may contain one or more curable resins. The resin composition may contain, as the curable resin, a thermosetting resin, an ionizing radiation curable resin, or both.

[0060] A thermosetting resin is a resin that hardens when heated. Examples of thermosetting resins include acrylic resin, urethane resin, phenol resin, urea melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. When the resin composition contains a thermosetting resin, one or more thermosetting resins can be used as the base resin in combination with a curing agent such as a melamine resin, a urea resin, or a polyisocyanate compound (including a blocked compound).

[0061] Ionizing radiation curable resins are resins that are cured by ionizing radiation. Here, ionizing radiation refers to electromagnetic waves or charged particle beams that have an energy quantum capable of polymerizing or crosslinking molecules, and typically ultraviolet (UV) rays or electron beams (EB) are used. However, other types of radiation, such as electromagnetic waves like X-rays and gamma rays, and charged particle beams like alpha rays and ion beams, can also be used.

[0062] When the resin composition contains an ionizing radiation-curable resin, the resin composition contains a compound having an ionizing radiation-curable functional group (hereinafter also referred to as "ionizing radiation-curable compound"). As the ionizing radiation-curable compound, either a monomer or an oligomer can be used. Examples of the ionizing radiation-curable functional group include ethylenically unsaturated bond groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, epoxy groups, and oxetanyl groups.

[0063] The ionizing radiation-curable compound contained in the resin composition is preferably a compound having an ethylenically unsaturated bond group, more preferably a compound having two or more ethylenically unsaturated bond groups. Among these, a urethane (meth)acrylate compound having two or more (meth)acryloyl groups is preferred, and a urethane (meth)acrylate compound having two or three (meth)acryloyl groups is more preferred. If the urethane (meth)acrylate compound has one (meth)acryloyl group per molecule, there is a risk of insufficient curing. If the urethane (meth)acrylate compound has a large number of (meth)acryloyl groups per molecule, stress increases and elongation tends to decrease. The (meth)acryloyl group means an acryloyl group and a methacryloyl group, and the urethane (meth)acrylate means a urethane acrylate and a urethane methacrylate.

[0064] As a coating method for applying a coating liquid made of a resin composition to a substrate, various coating methods such as gravure coating, die coating, blade coating, knife coating, and bar coating can be used.

[0065] After the resin composition is applied, the coating film can be dried by a known method, such as hot air, infrared rays, a heating cylinder, or a combination of these. The drying temperature may be, for example, within the range of 80° C. to 150° C. When curing of the coating film is not required, a coating layer can be formed by drying alone.

[0066] When the coating film needs to be cured, if the curable resin is a thermosetting resin, it is cured by heating, whereas if the curable resin is an ionizing radiation curable resin, it is cured by irradiating it with ionizing radiation such as ultraviolet light or an electron beam.

[0067] The thickness of the coating layer 3 is preferably 3 μm or more, more preferably 4 μm or more, and even more preferably 5 μm or more. It is preferable that the thickness of the coating layer 3 is not too thin in order to prevent coating defects such as missing coating layers from leading to paper peeling. The thickness of the coating layer 3 is, for example, 20 μm or less.

[0068] The coating layer 3 has a mass per area (i.e., coating amount) of 10 g / m 2 It is preferable that the content is 20 g / m or more. 2 More preferably, it is 30 g / m or more. 2 More preferably, it is 35 g / m or more. 2 It is more preferable that the mass per area of ​​the coating layer 3 is not too small, from the viewpoint of preventing coating defects such as missing coating layers from leading to paper peeling. The mass per area of ​​the coating layer 3 is, for example, 40 g / m 2 The following is the result.

[0069] (heat seal layer) The heat seal layer 1 may be any material that enables heat sealing of the lid 21 to the container body 22 of the food packaging container 20 shown in Fig. 3 (described later), thereby sealing the container. For example, a film made of ethylene-vinyl acetate (EVA), an ionomer resin, or other polyolefins is used as the heat seal layer 1. The heat seal layer 1 is preferably a layer containing at least one of linear low density polyethylene (LLDPE), very low density linear polyethylene (VLDPE), or polypropylene.

[0070] The heat seal layer 1 is preferably formed by a coating of heat seal varnish. For example, the heat seal layer 1 is a cured coating of heat seal varnish. Various coating methods, such as gravure coating, die coating, blade coating, knife coating, and bar coating, can be used to apply the heat seal varnish. When heat seal varnish is used, adhesives can be omitted, thereby reducing the environmental impact. Furthermore, in this case, the thickness of the heat seal layer 1 can be reduced compared to when the heat seal layer 1 is formed by lamination. In this case, the proportion of the mass of the paper substrate 3 in the mass of the lid laminate sheet 10 can be increased.

[0071] The heat seal varnish is preferably an aqueous emulsion. The glass transition temperature of the solid content of the heat seal varnish is preferably in the range of -40°C to -10°C. The melting point of the solid content of the heat seal varnish is preferably in the range of 40°C to 100°C. The glass transition temperature refers to a value measured using a DSC (differential scanning calorimeter) in accordance with JIS K7271:2012. When the solid content of the heat seal varnish has a glass transition temperature and a melting point within the above-mentioned temperature ranges, the heat seal layer 1 formed from such a heat seal varnish can exhibit excellent heat sealing performance even in packaging containers for chilled or frozen foods.

[0072] There is no particular limitation on the thickness of the heat seal layer 1. In one example, the thickness of the heat seal layer 1 is in the range of 0.5 to 60 μm, and in another example, in the range of 1 to 30 μm.

[0073] The mass per area of ​​the heat seal layer 1 (i.e., the amount of coating) is 0.5 to 15 g / m 2 and preferably in the range of 1 to 10 g / m 2 It is more preferable that the temperature is in the range of

[0074] (Laminated sheet for lid) The puncture strength of the above-described lid laminate sheet 10 is 5 N or more when measured from the heat seal layer 1 side and when measured from the side opposite the heat seal layer 1. The puncture strength when measured from the heat seal layer 1 side and when measured from the side opposite the heat seal layer 1 are both preferably 7.0 N or more, and more preferably 8.0 N or more. These puncture strengths are, for example, both 15.0 N or less.

[0075] In this specification, "puncture strength" refers to a value measured according to the method specified in JIS Z1707:2019 "General Rules for Food Packaging Plastic Films." The puncture strength is measured when a needle is pierced from the heat seal layer 1 side, and when the needle is pierced from the side opposite the heat seal layer 1. Specifically, a needle with a diameter of 1 mm and a semicircular tip is pierced from the top or bottom side of the lid laminate sheet at a speed of 50 mm / min, and the maximum force required for the needle to penetrate is measured. This measurement is performed multiple times, and the arithmetic average of the maximum forces is taken as the puncture strength.

[0076] The above-mentioned laminated sheet for a lid 10 preferably has the following tensile properties (i) to (iv). (i) The tensile strength in MD is 70N / 15mm or more. (ii) The tensile force at TD is 35 N / 15 mm or more. (iii) The tensile elongation at break in the MD is 7% or more. (iv) The tensile elongation at break in the TD is 7% or more.

[0077] The methods for measuring the "tensile strength" and "tensile elongation at break" are as described above.

[0078] The tensile strength of the lid laminate sheet 10 in MD is more preferably 80 N / 15 mm or more. The tensile strength of the lid laminate sheet 10 in MD is, for example, 120 N / 15 mm or less. The tensile strength of the lid laminate sheet 10 in TD is more preferably 40 N / 15 mm or more. The tensile strength of the lid laminate sheet 10 in TD is, for example, 60 N / 15 mm or less.

[0079] The tensile breaking elongation in MD of the lid body laminate sheet 10 is more preferably 10% or more. The tensile breaking elongation in MD of the lid body laminate sheet 10 is, for example, 20% or less. The tensile breaking elongation in TD of the lid body laminate sheet 10 is more preferably 10% or more. The tensile breaking elongation in TD of the lid body laminate sheet 10 is, for example, 20% or less.

[0080] The above-described lid laminate sheet contains paper, but when used as a lid for a packaging container, it can achieve excellent openability and durability. Specifically, as demonstrated in the openability test in the Examples below, when used as a lid for a packaging container, the above-described lid laminate sheet is less likely to cause paper peeling upon opening. Furthermore, as demonstrated in the transportation test in the Examples below, when used as a lid for a packaging container, the above-described lid laminate sheet is less likely to be damaged by collisions with the contents or other packaging containers due to vibrations during transportation of the packaging container. The mechanism by which excellent openability is achieved is thought to be that the coating layer interposed between the paper substrate and the heat-seal layer distributes the stress applied to the heat-seal layer and the paper substrate when the lid made of the lid laminate sheet is peeled from the container body, thereby making it less likely for the heat-seal layer to break and for the paper to peel. The mechanism by which excellent durability is achieved is thought to be that the high puncture strength of the lid laminate sheet increases the packaging container's durability against impacts that may occur during transportation.

[0081] The background to the invention of this laminate sheet for lids is described below. The inventors used stretched paper as the paper substrate of the laminate sheet for lids, and discovered that while it was possible to improve the impact resistance (i.e., durability against impact) of the lid, it was difficult to maintain the integrity of the stretched paper and the heat-seal layer, resulting in a new problem: the paper was prone to peeling when the lid was opened. The present invention is based on the solution to this new problem by providing a coating layer between the stretched paper and the heat-seal layer. However, as explained above, the paper substrate usable in this invention is not limited to stretched paper, and can be expanded to any paper substrate that can achieve the same effect.

[0082] [Variations] The lid laminate sheet can be modified in various ways. For example, the lid laminate sheet may further include one or more of a printed layer, a water-resistant functional layer, and a gas barrier layer. Hereinafter, with reference to FIG. 2, a modified lid laminate sheet further including a printed layer, a water-resistant functional layer, and a gas barrier layer will be described. The matters described with reference to FIG. 1 can be applied singly or in combination to the lid laminate sheet according to the modified example described herein.

[0083] FIG. 2 is a partial cross-sectional view schematically showing a laminated sheet for a lid according to one modified example. The lid body laminate sheet 11 shown in Figure 2 includes, in this order, a heat seal layer 1, a gas barrier layer 2, a coating layer 3, a paper substrate 4, a printing layer 5, and a water-resistant functional layer (water-resistant layer) 6. The lid body laminate sheet 11 is similar to the lid body laminate sheet 10 described with reference to Figure 1, except that it further includes, in this order from the paper substrate 4 side, a printing layer 5 and a water-resistant functional layer 6 on the side of the paper substrate 4 opposite to the side having the coating layer 3, and further includes a gas barrier layer 2 between the coating layer 3 and the heat seal layer 1.

[0084] (Printing layer) The printed layer 5 is a layer formed to prepare the lid laminate sheet 11 or the lid for practical use as a commercial product. The printed layer 5 is a layer made of ink containing additives such as various pigments, extender pigments, plasticizers, desiccants, and stabilizers added to a conventionally used ink binder resin, such as urethane, acrylic, nitrocellulose, rubber, or vinyl chloride, and displays patterns such as letters and pictures. The printed layer 5 may be omitted.

[0085] The printing layer 5 can be formed by known printing methods such as offset printing, gravure printing, and silk screen printing, or known coating methods such as roll coating, knife edge coating, and gravure coating.

[0086] When the paper substrate 4 is stretched paper, the stretched paper may have been subjected to a wrinkle-imparting treatment, resulting in differences in smoothness between the front and back surfaces. In this case, the coating layer 3 is preferably provided on the smoother side of the paper substrate 4, and the printing layer 5 is provided on the opposite side (the less smooth side).

[0087] When the paper substrate 4 is coated paper, the printing layer 5 can be provided on the coating layer of the coated paper. In this case, it is easy to display a high-quality image on the printing layer 5. Furthermore, when the printing layer 5 is provided on the coating layer, the underlying surface of the functional layer 6 is also smooth, thereby improving the water resistance of the functional layer 6. Furthermore, when the printing layer 5 is provided on the coating layer, it is possible to prevent the materials of the printing layer 5 and the functional layer 6 from seeping into the paper substrate 4.

[0088] The thickness of the printed layer 5 is not particularly limited, and may be, for example, in the range of 0.1 to 5 μm, or in the range of 0.2 to 1 μm.

[0089] (Water-resistant functional layer) The water-resistant functional layer (water-resistant layer) 6 is a layer that, in packaged foods described below, prevents liquids outside the container, such as water and oil caused by condensation, from penetrating the lid and prevents these liquids from reaching layers such as the printed layer 5 and the paper base material 4. By preventing liquids outside the container from reaching layers such as the printed layer 5 and the paper base material 4, the functional layer 6 prevents, for example, deterioration, destruction, or a decrease in adhesion of these layers.

[0090] According to one example, the functional layer 6 is formed on the printing layer 5 to control the water absorbency of the partial laminate sheet, which is the portion of the lid laminate sheet 11 from the functional layer 6 to the paper substrate 4. The functional layer 6 controls the water absorbency of the lid laminate sheet by the Cobb method described below to 20 g / m 2 It is preferable that the material has the following water resistance.

[0091] Here, the water absorbency is the water absorbency obtained by the method specified in JIS P8140:1998 "Paper and paperboard - Water absorbency test method - Cobb method" when the measurement surface is the surface of the functional layer 6 and the contact time between the test piece and water is 300 seconds. This water absorbency is 20 g / m as described above. 2 Preferably, it is 10 g / m or less. 2 More preferably, it is 5 g / m or less. 2 The lower limit of the water absorbency is ideally 0 g / m 2 According to one example, this water absorption is 1 g / m 2 That's all.

[0092] The functional layer 6 is preferably an overprint varnish layer (hereinafter referred to as "OP varnish layer").

[0093] According to one example, the functional layer 6 contains a water-resistant resin. Any resin capable of achieving the above-mentioned water absorbency can be used without limitation as the water-resistant resin. Examples of water-resistant resins that can be used include polyolefin-based resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, and vinyl chloride-vinyl acetate copolymers, silicone-based resins, acrylic resins, epoxy-based resins, polyester-based resins, cellulose-based resins, and urethane-based resins. The functional layer 6 can be obtained, for example, by applying a paint containing the water-resistant resin to the paper substrate 4 on which the printing layer 5 has been formed, using 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, as well as solvents.

[0094] The functional layer 6 preferably has high abrasion resistance and scratch resistance so as to maintain sufficient water resistance. From this perspective, the thickness of the functional layer 6 and the amount of paint applied, which is its material, are preferably greater than the thickness and amount of paint applied of a typical OP varnish layer. Here, the "amount applied" refers to the mass of solids per area.

[0095] For example, in the lid laminate sheet 11 shown in FIG. 2, the coating amount of the paint for forming the functional layer 6 is 0.2 g / m 2 It is preferable to coat the coating amount so that it is 2.0 g / m or more. 2 It is more preferable to apply the coating material so that the coating amount is 10 g / m or more. 2 The coating is performed so that the thickness of the functional layer 6 is as follows: The thickness of the functional layer 6 is preferably 0.2 μm or more, and more preferably 2.0 μm or more. The thickness of the functional layer 6 is, for example, 10 μm or less. The functional layer 6 may be provided on the printing layer 5 by lamination. The functional layer 6 may be omitted.

[0096] (gas barrier layer) The gas barrier layer 2 has gas barrier properties such as oxygen barrier property and water vapor barrier property. In a packaged article described below, the gas barrier layer 2 prevents gases such as oxygen, water vapor, and aroma components from outside the container from penetrating into the container. As a result, the gas barrier layer 2 prevents food deterioration when the contents of the packaged article are, for example, food. Furthermore, when the contents are, for example, food, the gas barrier layer 2 prevents odor components and the like from the contents from diffusing to the outside of the container. According to one example, the gas barrier layer 2 has an oxygen permeability of 0.1 to 100 cc / m in an atmosphere at a temperature of 30°C and a relative humidity of 70%. 2 / day / atm.

[0097] The gas barrier layer 2 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 expected, the gas barrier layer 2 is preferably an inorganic oxide layer, a resin-containing layer, or a combination thereof.

[0098] The gas barrier layer 2 may be formed by coating, by melt molding, or by vapor deposition of an inorganic oxide. Alternatively, the gas barrier layer 2 may be a metal foil such as aluminum foil, or may be vapor deposited with a metal such as aluminum.

[0099] Examples of inorganic oxides that can be used 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.

[0100] 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, or epoxy resin can be used. Additives such as organic or inorganic particles, layered compounds, and curing agents may also be added to the coating liquid.

[0101] When the resin-containing layer is formed by melt molding, the material may be, for example, the above-mentioned resin or a mixture of the above-mentioned resin and an additive. For melt molding, for example, an extrusion molding technique such as a T-die or inflation molding can be used.

[0102] The thickness of the gas barrier layer 2 is, for example, in the range of 0.01 to 30 μm, and in another example, in the range of 0.1 to 12 μm.

[0103] The position of the gas barrier layer 2 is not limited to that shown in Fig. 2. For example, the gas barrier layer 2 may be included between the printed layer 5 and the paper substrate 4. The gas barrier layer 2 may be omitted.

[0104] (Other variations) Another example of a lid laminate sheet according to a modification is a lid laminate sheet including, in this order, a heat seal layer 1, a coating layer 3, a paper substrate 4, a printing layer 5, and a water-resistant functional layer (water-resistant layer) 6. Another example of a lid laminate sheet according to a modification is a lid laminate sheet including, in this order, a heat seal layer 1, a gas barrier layer 2, a coating layer 3, and a paper substrate 4.

[0105] [Second embodiment] The 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 modified example. An example of the lid according to the second embodiment is the lid 21, which will be described later with reference to Fig. 3. As described in relation to the laminated sheet for a lid, the lid according to this embodiment has excellent openability and durability.

[0106] [Third embodiment] Fig. 3 is a cross-sectional view showing a food packaging container according to a third embodiment of the present invention. The food packaging container 20 shown in Fig. 3 comprises a container body 22 having an opening, and a lid 21 that covers the opening.

[0107] The container body 22 is, for example, a cylindrical shape with a bottom. Here, the container body 22 includes a bottom, a body (or a side wall), and a flange 22a. The flange 22a widens outward at the position of the upper opening of the body.

[0108] The container body 22 contains, for example, an olefin-based resin such as polypropylene. The container body 22 may further contain a component such as an ethylene-vinyl alcohol copolymer to enhance its gas barrier properties. The container body 22 may also further contain additives, for example, additives for improving processability, designability, and chemical durability.

[0109] 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 multi-layer 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.

[0110] The container body 22 can also be made of paper. When the contents include a liquid, the container body 22 can have a multilayer structure including a paper base material and a layer of resin or the like provided on the surface facing the contents to prevent the liquid from seeping into the paper base material. Examples of materials that can be used for the container body 22 containing a paper base material include paper sheets, paper powder, pulp, and recycled paper. The container body 22 can be formed using general-purpose techniques, such as folding and pasting sheets including paper sheets, as is done in the manufacture of paper cartons, press molding of sheets using a mold, and pulp molding. Using paper for the container body 22 can reduce carbon dioxide emissions associated with the manufacture and disposal of the entire food packaging container 20, thereby reducing the environmental impact.

[0111] The lid 21 is one of the lid laminate sheets 10 and 11, or is a cut-out of one of them. After the contents are placed in the container body 22, the lid 21 is heat-sealed to the flange 22a via the heat-seal layer 1. In this heat-sealing, the sealing temperature, sealing pressure, and sealing time can be set as appropriate.

[0112] The lid 21 typically has a tab (not shown) on a portion of its outer edge, and the user opens the food packaging container 20 by pulling this tab. The relationship between the opening direction of the lid 21 and the fiber direction of the paper base material 4 is not particularly limited, but it is preferable that the opening direction of the lid 21 is approximately parallel to the MD of the paper base material 4 (i.e., the MD of the lid laminate sheet). The opening direction of the lid 21 may change from the start to the end of the opening operation depending on the shape of the lid 21 and the position of the tab. In such cases, the "opening direction of the lid 21" refers to the opening direction at any point during the opening operation of the lid 21. In this way, when the lid 21 is positioned so that the opening direction of the lid 21 is approximately parallel to the MD (i.e., the fiber direction) of the paper base material 4, the tensile force in the MD of the paper base material 4 is greater than the tensile force in the TD, making it less likely for the paper base material 4 to peel off during opening. For example, if the lid body 21 is substantially rectangular and has tabs at the corners of the lid body 21, the lid body 21 is opened substantially in the diagonal direction of the lid body 21 at the start of the opening operation, and peeling continues in substantially the same direction, and in the latter half of the opening operation, the lid body 21 is opened along the longitudinal direction of the lid body 21. In the case of such a lid body 21, it is preferable that the diagonal direction of the lid body 21 is substantially parallel to the MD of the paper base material 4 (i.e., the MD of the lid body laminate sheet), or that the longitudinal direction of the lid body 21 is substantially parallel to the MD of the paper base material 4 (i.e., the MD of the lid body laminate sheet).

[0113] [Fourth embodiment] The packaged food product according to the fourth embodiment of the present invention is obtained by packaging food in the food packaging container according to the third embodiment described above. The food packaged 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 dishes.

[0114] As described above, in this packaged food, the heat seal strength between lid 21 and container body 22 is preferably smaller than the breaking strength of coating layer 3 included in lid 21. Here, the heat seal strength is a value obtained by the method specified in JIS Z0238:1998 "Test methods for heat-sealed flexible packaging bags and semi-rigid containers."

[0115] In producing this packaged food, the gas inside the container body 22 may be replaced by a known method before heat-sealing the lid 21 to the container body 22, for example, after the contents have been placed inside the container body 22 and before heat-sealing the lid 21 to the container body 22. For example, the container body 22 may be filled with an inert gas. By appropriately changing the gas composition inside the container, it is possible to suppress bacterial growth and extend the shelf life, to prevent oxidation and thereby maintain the flavor, color, etc. of the food, and to prevent vitamin loss. The replacement gas is selected appropriately depending on the type of food contained therein. A mixed gas of oxygen gas, nitrogen gas, and carbon dioxide gas is preferably used as the replacement gas.

[0116] The lid 21 included in this packaged food is one of the lid laminate sheets 10 and 11, or is a cut-out of one of them. Therefore, as described above, this packaged food is easy to open, with the paper not peeling off when opened. Therefore, when the lid is peeled off from the container body to open the packaged food, the paper does not peel off, making it difficult to remove the contents contained in the container body.

[0117] Furthermore, packaged foods are packed in boxes prior to transportation. During packaging, packaged foods are often laid out at the bottom of the box, with other packaged foods stacked on top of the packaged foods. Therefore, during transportation, the lid may be damaged by vibrations that cause it to collide with the contents or other packaging containers. However, as described above, the lid included in this packaged food has excellent resistance to impacts. Therefore, this packaged food is less likely to experience deterioration of the contents due to damage to the lid. [Example]

[0118] The following describes tests carried out in connection with the present invention.

[0119] <1> Manufacturing of laminated sheets for lids (Example 1) The lid laminate sheet 10 shown in FIG. 1 was produced by the following method. First, as the paper substrate 4, a paper sheet having a basis weight of 70 g / m 2 As the stretched paper, unbleached kraft Clupak paper (specifically, Taioh Atlas (registered trademark) Clupak paper (manufactured by Daio Paper Co., Ltd.)) was used.

[0120] A printing layer 5 and a functional layer 6 were sequentially formed on the Clupak-treated surface (the surface with less smoothness) of this paper substrate 4 using a gravure multicolor printer. The printing layer 4 was formed using a normal printing ink. The coating amount of the printing ink was 1.0 g / m. 2 The functional layer 5 was formed using an OP varnish whose main components were a nitrocellulose resin and polyethylene granular wax. The amount of OP varnish applied was 0.6 g / m 2 It was decided.

[0121] A coating liquid was applied to the side of this paper substrate 4 that did not have the printing layer 5 and functional layer 6, i.e., the side that had not been subjected to Clupak treatment (the side with high smoothness), and the coating film was dried at 140°C for 10 minutes to form a coating layer 3. The coating liquid used was a polyurethane dispersion (specifically, Hydran HW-171 (DIC Corporation)). The coating liquid was applied using a bar coater to a dry film thickness of 4 μm and a dry mass per area (coating amount) of 10.2 g / m. 2 The coating was applied so that

[0122] Next, a heat seal varnish was applied to the coating layer 3, and the coating was dried to form the heat seal layer 1. The heat seal varnish used was an aqueous emulsion containing ethylene-vinyl acetate copolymer as the main component and water and isopropanol as the solvent or dispersion medium. The solid content of this heat seal varnish had a glass transition temperature of -27°C and a melting point of 50 to 90°C. The heat seal varnish was applied using a bar coater to a thickness of 3.0 g / m2. 2 In this manner, a lid laminate sheet 10 shown in FIG. 1 was obtained.

[0123] (Example 2) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area (coating amount) of 12.9 g / m 2 The coating was applied so that

[0124] (Example 3) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 10 μm and a dry mass per area (coating amount) of 18.6 g / m 2 The coating was applied so that

[0125] (Example 4) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 25.3 g / m 2 The coating was applied so that

[0126] (Example 5) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points. In this example, a polyurethane dispersion, Evaphanol HA-560 (Nicca Chemical Co., Ltd.), was used as the coating liquid for forming the coating layer 3, instead of Hydran HW-171 (DIC Corporation). In this example, this coating liquid was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area (coating amount) of 13.5 g / m. 2 The coating was applied so that

[0127] (Example 6) A lid laminate sheet 10 was produced in the same manner as in Example 5, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 25.7 g / m 2 The coating was applied so that

[0128] (Example 7) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points. In this example, a polyurethane dispersion, Evaphanol HA-170 (Nicca Chemical Co., Ltd.), was used as the coating liquid for forming the coating layer 3, instead of Hydran HW-171 (DIC Corporation). In this example, this coating liquid was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area (coating amount) of 12.3 g / m. 2 The coating was applied so that

[0129] (Example 8) A lid laminate sheet 10 was produced in the same manner as in Example 7, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 26.8 g / m 2 The coating was applied so that

[0130] (Example 9) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points. In this example, a polyurethane dispersion, Evaphanol HA-207 (Nicca Chemical Co., Ltd.), was used as the coating liquid for forming the coating layer 3, instead of Hydran HW-171 (DIC Corporation). In this example, this coating liquid was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area (coating amount) of 13.5 g / m. 2 The coating was applied so that

[0131] (Example 10) A lid laminate sheet 10 was produced in the same manner as in Example 9, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 32.1 g / m 2 The coating was applied so that

[0132] (Example 11) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the paper substrate 4 had a basis weight of 70 g / m 2 Instead of stretched paper, the basis weight is 73.3 g / m 2 The coating layer 3 was formed on the coating layer of the single-sided coated paper. In this example, the coating liquid for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 23.9 g / m. 2 The coating was applied so that

[0133] (Comparative Example 1) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the heat seal layer 1 was formed on the side of the paper substrate 4 that had not been subjected to Clupak treatment (i.e., the side with high smoothness), without providing a coating layer 3.

[0134] (Comparative Example 2) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the paper substrate 4 had a basis weight of 70 g / m 2 Instead of stretched paper, the basis weight is 52.3 g / m 2 In this example, the coating layer 3 was not provided, and the heat seal layer 1 was formed on the coating layer of the single-sided coated paper.

[0135] (Comparative Example 3) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the paper substrate 4 had a basis weight of 70 g / m 2 Instead of stretched paper, the basis weight is 52.3 g / m 2 The coating layer 3 was formed on the coat layer of the single-sided coated paper. In this example, the coating liquid for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area (coating amount) of 6.8 g / m. 2 The coating was applied so that

[0136] Comparative Example 4 A lid laminate sheet 10 was produced in the same manner as in Comparative Example 3, except for the following points: In this example, the coating liquid for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 10 μm and a dry mass per area (coating amount) of 12.7 g / m 2 The coating was applied so that

[0137] (Comparative Example 5) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 3, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 23.9 g / m2 The coating was applied so that

[0138] (Comparative Example 6) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, the paper substrate 4 had a basis weight of 70 g / m 2 Instead of stretched paper, the basis weight is 41.3 g / m 2 In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area (coating amount) of 10.1 g / m 2 The coating was applied so that

[0139] (Comparative Example 7) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 6, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 10 μm and a dry mass per area (coating amount) of 15.3 g / m 2 The coating was applied so that

[0140] (Comparative Example 8) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 3, except for the following points: In this example, the coating solution for forming the coating layer 3 was applied using a bar coater to a dry film thickness of 20 μm and a dry mass per area (coating amount) of 24.2 g / m 2 The coating was applied so that

[0141] <2> Evaluation method The lid laminate sheets of Examples 1 to 11 and Comparative Examples 1 to 8 were evaluated as follows.

[0142] (Paper conversion rate) The paper content rate was calculated by calculating the percentage of the mass of the paper substrate in the mass of the lid laminate sheet. The mass of the lid laminate sheet and the paper substrate was calculated by directly measuring the mass. Specifically, the mass of each sample measuring 200 mm x 250 mm was measured, and the measured value was expressed as g / m 2 was converted to.

[0143] (Tensile properties) The tensile properties of the lid laminate sheet were measured according to the method specified in JIS K7127:1999.

[0144] 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 out from the lid laminate sheet. Each test piece was a strip with a width of 15 mm and a length of 100 mm. The gauge length was 50 mm, and the test speed was 300 mm / min.

[0145] Tensile strength measurements were performed using a Tensilon universal testing machine. The "tensile strength in MD" was calculated by arithmetically averaging the measurements obtained using specimens whose length direction was parallel to the MD. The "tensile strength in TD" was calculated by arithmetically averaging the measurements obtained using specimens whose length direction was parallel to the TD.

[0146] The tensile elongation at break was calculated by dividing the increase in the gauge length when the test specimen broke in the tensile force measurement by the original gauge length. The "tensile elongation at break in MD" was obtained by arithmetically averaging the values ​​calculated using test specimens whose length direction was parallel to MD. The "tensile elongation at break in TD" was also obtained by arithmetically averaging the values ​​calculated using test specimens whose length direction was parallel to TD.

[0147] (Puncture strength) The "puncture strength" of the lid laminate sheet was measured according to the method specified in JIS Z1707:2019 "General Rules for Plastic Films for Food Packaging." The puncture strength was measured when a needle was pierced into the lid laminate sheet from the paper substrate 4 side, and when a needle was pierced into the lid laminate sheet from the heat seal layer 1 side. Each puncture strength was obtained by arithmetically averaging the values ​​obtained from five measurements.

[0148] Specifically, a needle having a diameter of 1 mm and a semicircular tip was pierced into the lid laminate sheet at a speed of 50 mm / min, and the maximum force required for the needle to penetrate was measured.

[0149] (Transportation Test) The contents were filled into the container body 22, and the lid 21 was heat-sealed to the container body 22 to produce a packaged food. A predetermined number of packaged foods were packed into an outer box, stored frozen, and then transported in a frozen state. After transportation, the package was opened, and the presence or absence of tears in the lid 21 was visually confirmed.

[0150] The detailed procedure for the transportation test is described below. (1) Preparation of the lid and container body First, a substantially rectangular lid 21 was cut out from the lid laminate sheet of Examples 1 to 11 and Comparative Examples 1 to 8. A resin sheet containing polypropylene resin as a main component, molded into a tray shape, was used as the container body 22. The container body 22 had a flange 22a around the opening to seal the lid 21. The opening of the container body 22 had a substantially rectangular shape.

[0151] The dimensions of the container body 22 were as follows: Opening: 8cm x 13cm Flange: Width 1cm Bottom: 7.5cm x 12.5cm Height: 3cm.

[0152] (2) Preparation of packaged foods The contents were filled into the container body 22. Approximately 110 g of commercially available frozen processed food (grilled beef innards) was used as the contents. Next, the lid body 21 was heat-sealed to the container body 22. During heat sealing, the lid body 21, which had a substantially rectangular shape, was positioned so that the longitudinal direction of the lid body 21 was substantially parallel to the MD of the paper base material 4 (i.e., the MD of the lid body laminate sheet). Heat sealing was performed using a ring-shaped seal bar that conformed to the shape of the flange 22a, with the container body 22 fitted into a jig. A receiving base hollowed out so that the container body 22 would be embedded was used as the jig. Heat sealing was performed using a 4 mm wide seal bar, applying a temperature of 190°C and a pressure of 0.2 MPa for 1 second. Packaged foods were produced in this manner. 36 packaged foods were produced for each type of lid.

[0153] (3) Packaging and transportation Thirty-six packaged foods were packed into an outer box (cardboard). Specifically, six packaged foods were placed on the bottom of the outer box (cardboard), and the packaged foods were stacked six layers high, for a total of 36 packaged foods in the outer box (cardboard). The packed packaged foods were then stored at -20°C for two hours.

[0154] The packaged food was then loaded onto a vehicle while still frozen and transported a distance of approximately 650 km.

[0155] (4) Evaluation After transportation, the packages were opened, and the 36 packaged foods were visually inspected for tears in the lids 21. The number of packaged foods with torn lids 21 among the 36 packaged foods was counted and evaluated according to the following evaluation criteria.

[0156] Evaluation criteria A: There were no packaged foods with broken lids 21. B: The number of packaged foods with broken lids 21 was 1 to 3 C: The number of packaged foods with torn lids 21 was four or more.

[0157] (Openability test) The food packaging container 20 shown in Figure 3 was produced by sealing the lid 21 to the container body 22 without filling it with contents. The food packaging container 20 was produced using the same procedure as for producing the packaged food in the transportation test, except that the contents were not filled. The lid 21 was prepared from the lid laminate sheet of Examples 1 to 11 and Comparative Examples 1 to 8.

[0158] For each food packaging container 20, the lid 21 was peeled off by hand from the corner (grip) of the container body 22. The state of opening, including the presence or absence of paper peeling, was visually confirmed and evaluated according to the following evaluation criteria. "Paper peeling" refers to the situation where a part of the lid (including double lids) remains on the container body after the lid made of the lid laminate sheet is peeled off from the container body.

[0159] Evaluation criteria A: No peeling of the paper occurred. B: Paper peeling occurred, but part of the lid remained on the container body only at the seal or its periphery. The remaining part was smaller than the width of the flange. C: Paper peeling occurred, and the lid remained on the container body in areas other than the sealed area and its surroundings. The remaining area was large enough to come into contact with the contents, or a double lid was formed.

[0160] <3> Evaluation results The results of the above measurements and tests are shown in Tables 1 and 2 below.

[0161] [Table 1]

[0162] [Table 2]

[0163] In Tables 1 and 2, "HS layer" refers to the heat-seal layer. In Table 1, "other layers" refers to the mass of layers classified as other layers according to the "Container and Packaging Recycling Law Explanatory Materials." In the "MD" column of Table 2, the "Tensile Strength" and "Tensile Breaking Elongation" columns indicate the tensile strength and tensile breaking elongation obtained for test specimens whose length direction is parallel to MD. In the "TD" column of Table 2, the "Tensile Strength" and "Tensile Breaking Elongation" columns indicate the tensile strength and tensile breaking elongation obtained for test specimens whose length direction is parallel to TD. In the "Puncture Strength" column of Table 2, the "Paper Substrate Side" column indicates the puncture strength when a needle is pierced into the lid laminate sheet from the paper substrate side, and the "HS Layer Side" column indicates the puncture strength when a needle is pierced into the lid laminate sheet from the heat-seal layer side.

[0164] The results of measuring the tensile properties of the lid laminate sheets of Example 4, Comparative Example 5, and Comparative Example 8 are shown in Figure 4. Figure 4 is a graph showing the relationship between load and elongation. In Figure 4, "Example 4-MD" shows the results of a test piece cut out from the lid laminate sheet of Example 4 with its length direction parallel to MD, and "Example 4-TD" shows the results of a test piece cut out from the lid laminate sheet of Example 4 with its length direction parallel to TD. In Figure 4, "Comparative Example 5-MD," "Comparative Example 5-TD," "Comparative Example 8-MD," and "Comparative Example 8-TD" also have the same meanings.

[0165] Furthermore, the results of the tensile properties and puncture strength measured on the paper substrate are shown in Figures 5 and 6, respectively. The measured samples in Figures 5 and 6 are shown below.

[0166] Reference Example 1: The stretched paper used in Examples 1 to 10 (thickness: 102 μm, basis weight: 70 g / m 2 ) Reference Example 2: Coated paper used in Comparative Examples 2 to 5 (thickness: 48 μm, basis weight: 52.3 g / m 2 ) Reference Example 3: The same parchment paper (thickness: 48 μm, basis weight: 41.3 g / m) as used in Comparative Examples 6 to 8 2 ) Reference Example 4: Biaxially oriented polyethylene terephthalate film with a gas barrier layer (thickness: 12 μm, mass: 16.4 g / m 2 ) Reference Example 5: Laminate of the coating layer and the heat seal layer contained in the lid laminate sheet of Example 4 (thickness: 23 μm, mass: 42.6 g / m 2 ).

[0167] Figure 5 is a graph showing the relationship between load and elongation. Figure 6 is a graph showing the relationship between puncture strength and needle movement. In Figure 5, "Reference Example 1-MD" shows the results when a test piece with its length parallel to MD was cut out from the stretched paper of Reference Example 1, and "Reference Example 1-TD" shows the results when a test piece with its length parallel to TD was cut out from the stretched paper of Reference Example 1. In Figure 5, "Reference Example 2-MD," "Reference Example 2-TD," "Reference Example 3-MD," and "Reference Example 3-TD" also have the same meaning.

[0168] The results in Tables 1, 2, and Figure 4 show that when a lid laminate sheet has a coating layer between the paper substrate and the heat seal layer and the puncture strength of the lid laminate sheet is excellent, it is possible to achieve both ease of opening the lid and durability of the lid during transportation. Specifically, the coating layer contributes to preventing paper peeling upon opening, and increasing the thickness of the coating layer further prevents paper peeling upon opening. Furthermore, when the puncture strength of the lid laminate sheet is excellent, the durability of the lid during transportation can be increased, and when the puncture strength of the lid laminate sheet is increased, the durability of the lid during transportation can be further increased. A lid laminate sheet that combines these effects also had excellent tensile properties (tensile strength and tensile elongation at break).

[0169] Furthermore, the results in Tables 1, 2, Figures 4 and 5 show that the excellent tensile properties of the lid laminate sheet of the present invention are attributable to the tensile properties of the paper substrate used. Furthermore, the results in Tables 1, 2 and Figure 6 show that the excellent puncture strength of the lid laminate sheet of the present invention is attributable to the puncture strength of the paper substrate used. The puncture strength of the paper substrate used was higher than that of a PET film with a gas barrier layer (Reference Example 4) and a laminate of a coating layer and a heat seal layer (Reference Example 5). [Explanation of symbols]

[0170] 1...heat seal layer, 2...gas barrier layer, 3...coating layer, 4...paper base material, 5...printed layer, 6...functional layer, 10...laminated sheet for lid, 11...laminated sheet for lid, 20...food packaging container, 21...lid, 22...container body, 22a...flange

Claims

1. A lid laminate sheet used for a lid of a packaging container having a container body with an opening and a lid body that covers the opening, A paper substrate, a coating layer, and a heat-seal layer, in this order; The laminated sheet for a lid body has a puncture strength of 5N or more when measured from the heat seal layer side and when measured from the side opposite to the heat seal layer.

2. The coating layer has a mass per area of ​​10 g / m ２ The laminate sheet for a lid according to claim 1, wherein the laminate sheet is as described above.

3. The lid laminate sheet according to claim 1 , wherein the coating layer is formed of a paint film containing a resin.

4. The lid laminate sheet according to claim 3, wherein the resin is a urethane resin.

5. The lid laminate sheet according to claim 1 , wherein the coating layer is in contact with the paper substrate.

6. The laminated sheet for lids according to claim 1, wherein the tensile strength of the paper substrate in the MD is 70 N / 15 mm or more, the tensile strength of the paper substrate in the TD is 35 N / 15 mm or more, and the tensile breaking elongation of the paper substrate in the MD and the tensile breaking elongation of the paper substrate in the TD are both 7% or more.

7. The lid laminate sheet according to claim 1, wherein the paper substrate is a stretched paper.

8. 2. The lid body laminate sheet according to claim 1, wherein the tensile strength in the MD of the lid body laminate sheet is 70 N / 15 mm or more, the tensile strength in the TD of the lid body laminate sheet is 35 N / 15 mm or more, and the tensile breaking elongation in the MD of the lid body laminate sheet and the tensile breaking elongation in the TD of the lid body laminate sheet are both 7% or more.

9. 2. The lid laminate sheet according to claim 1, wherein the heat seal layer is formed by coating a heat seal varnish.

10. 10. The laminated sheet according to claim 9, wherein the heat seal varnish is a water-based emulsion.

11. The laminate sheet according to claim 9, wherein the glass transition temperature of the solid content of the heat seal varnish is in the range of -40°C or higher and -10°C or lower, and the melting point of the solid content of the heat seal varnish is in the range of 40°C or higher and 100°C or lower.

12. 2. The lid body laminate sheet according to claim 1, wherein when the layers other than the paper base material included in the lid body laminate sheet are classified into layers made of plastic and other layers, the mass of the paper base material is greater than the total mass of the layers made of plastic and the total mass of the other layers.

13. The lid laminate sheet according to claim 1, further comprising a printed layer as a layer facing the coating layer with the paper substrate sandwiched therebetween.

14. The lid laminate sheet according to claim 1, further comprising a water-resistant functional layer as an outermost layer facing the coating layer with the paper substrate sandwiched therebetween.

15. The lid laminate sheet according to claim 1, further comprising a gas barrier layer between the coating layer and the heat seal layer.

16. A lid body comprising the laminate sheet for lid bodies according to any one of claims 1 to 15.

17. A food packaging container comprising a container body having an opening and a lid body as described in claim 16 that covers the opening, wherein the coating layer is disposed between the paper base material and the internal space of the food packaging container.

18. 18. The food packaging container according to claim 17, wherein the container body has a flange around the opening, and the lid body is heat-sealed to the flange via the heat-seal layer.

19. A packaged food product comprising the food packaging container according to claim 17 and food contained in the food packaging container.

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