Laminated sheet for lid, lid body, packaging container for food and packaged food

Abstract

To provide a lid body which is used for a packaging container for food, which includes a paper base material, and which has excellent openability.SOLUTION: A laminated sheet for a lid body is used for the lid body of a packaging container for food, which includes a container body in which an opening is provided and a lid body covering the opening, and includes a paper base material, a coating layer, and a heat seal layer in this order. The ratio of the paper base material occupying the laminated sheet for the lid body is equal to or greater than 50 mass% with respect to the total mass of the laminated sheet for the lid body. In the coating layer, a composite elastic modulus of a cross section is within a range of 400 to 3600 MPa, and a stress relaxation degree is equal to or greater than 0.20.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 and freezing / refrigeration technology have led to an increase in demand for cooked or processed chilled foods sold at convenience stores and supermarkets, etc. At the same time, demand for packaging containers to store chilled foods is also growing.

[0003] Meanwhile, as efforts to reduce plastic waste progress, there is an increasing demand for food packaging containers that use paper, a renewable resource with a low environmental impact, as a base material. There is also a demand for paper packaging containers that use paper as a base material for packaging containers that store chilled foods (see, for example, Patent Document 1, etc.).

[0004] Although paper has excellent mechanical strength in the in-plane direction, its strength in the film thickness direction (peel strength) is weaker than that of plastic. For this reason, when a lid made of a laminate containing a paper substrate is used to cover an opening of a container body having an opening, there is a problem that the paper substrate is likely to break and peel when the lid is opened. Here, "paper peel" refers to the cohesive failure of the paper substrate when the lid is peeled from the container body, causing part of the lid to remain on the container body. When paper peel occurs, it can be difficult to remove the contents stored in the container body. [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 lid body for use in a food packaging container, which contains a paper base material and has excellent openability. [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 in a lid body of a food packaging container having a container body with an opening and a lid body covering the opening, the laminate sheet for a lid body comprising, in this order, a paper base material, a coating layer, and a heat seal layer, the proportion of the paper base material in the laminate sheet for a lid body being 50 mass% or more of the total mass of the laminate sheet for a lid body, and the coating layer having a cross-sectional composite elastic modulus in the range of 400 to 3600 MPa and a stress relaxation coefficient of 0.20 or more.

[0008] According to another aspect of the present invention, there is provided the laminate sheet for a lid according to the above aspect, wherein the coating layer has a thickness in the range of 3 to 20 μm.

[0009] According to yet another aspect of the present invention, the coating layer has a mass per area of ​​3.1 g / m 2 There is provided a laminate sheet for a lid according to any one of the above aspects.

[0010] 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.

[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 heat seal layer is a cured coating film of a heat seal varnish.

[0012] According to yet another aspect of the present invention, the heat seal layer has a mass per area of ​​0.5 to 15 g / m 2 The present invention provides a laminated sheet for a lid according to any one of the above aspects within the range of (a) to (c).

[0013] 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 comprising a printing layer and a water-resistant functional layer, in this order from the paper substrate side, on the side of the paper substrate opposite to the side having the coating layer.

[0014] 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.

[0015] 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.

[0016] 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 on the 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.

[0017] 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.

[0018] According to yet another aspect of the present invention, there is provided a 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.

[0019] According to yet another aspect of the present invention, there is provided a food packaging container according to any one of the above aspects, wherein the food packaging container is a packaging container for chilled food or a packaging container for frozen food.

[0020] 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]

[0021] According to the present invention, a lid body is provided which is used for a food packaging container, contains a paper base material, and has excellent openability. [Brief explanation of the drawings]

[0022] [Figure 1] 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. [Figure 2] FIG. 2 is a partial cross-sectional view schematically showing a laminated sheet for a lid according to one modified example. [Figure 3] FIG. 3 is a cross-sectional view schematically showing a food packaging container according to a third embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view schematically showing one step in the measurement of the composite elastic modulus and the stress relaxation rate. [Figure 5] FIG. 5 is a graph showing a load-displacement curve. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] [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.

[0027] 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.

[0028] 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.

[0029] (Paper base material) 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 layer included in the lid laminate sheet 10. The paper base material 4 accounts for 50% by mass or more of the total mass of the lid laminate sheet 10. In this case, the lid laminate sheet 10 can be treated as paper under the Containers and Packaging Recycling Act in Japan. The paper base material 4 accounts for preferably 70% by mass or more of the total mass of the lid laminate sheet 10. In addition, the paper base material 4 accounts for 90% by mass or less of the total mass of the lid laminate sheet 10, for example.

[0030] The basis weight of the paper substrate 4, i.e., the mass per area, is 40 to 160 g / m 2 and preferably in the range of 50 to 160 g / m 2 It is more preferable that the weight per area of ​​the paper base material 4 is within this range. If the weight 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 weight per area of ​​the paper base material 4 is small, the strength of the lid tends to decrease.

[0031] The thickness of the paper substrate 4 is preferably in the range of 40 to 160 μm, and more preferably in the range of 45 to 150 μm. As the thickness of the paper substrate 4 increases, the lid tends to become harder and less easy to open. On the other hand, as the thickness of the paper substrate 4 decreases, the strength of the lid tends to decrease. Here, when the paper substrate 4 is a coated paper having a coating layer described below, the mass and thickness per area described above are the mass and thickness per area of ​​the coated paper.

[0032] Increasing the mass per area of ​​the paper base material 4 also increases the proportion of the mass of the paper base material 4 in the total mass of the lid laminate sheet 10. However, increasing the mass per area of ​​the paper base material 4 increases the amount of carbon dioxide emissions associated with the production of the paper base material 4 and the disposal of the lid laminate sheet 10.

[0033] There are no particular limitations on the paper base material 4 as long as it is made primarily of plant-derived pulp. Specific examples of the paper base material 4 include coated paper such as fine paper, medium-quality paper, and lightly coated paper, one-side glossy paper, bleached and unbleached kraft paper (acid paper or neutral paper), etc.

[0034] The paper substrate 4 is preferably a coated paper having a coating layer on at least one side. That is, the paper substrate 4 is preferably 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.

[0035] The coating layer contains a resin. Examples of the resin contained in the coating layer include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-α-olefin copolymers polymerized using a metallocene catalyst (single-site catalyst), polypropylene, ethylene-vinyl acetate copolymers, ionomer resins, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-propylene copolymers, methylpentene polymers, acid-modified polyolefin resins obtained by modifying polyolefin resins such as polyethylene and polypropylene with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic anhydride, and fumaric acid, polyethylene terephthalate resins, polybutylene terephthalate resins, nylon resins, and thermoplastic resins such as styrene-butadiene rubber. Two or more of these resins may be used in combination, or two or more may be copolymerized. The coating layer may further contain additives, such as fillers such as clay, kaolin, calcium carbonate, talc, mica, and titanium oxide. The coating layer may be glossed by calendering or the like to improve the surface smoothness.

[0036] The thickness of the coating layer is set appropriately depending on the desired quality, handling, etc. The thickness of the coating layer may be, for example, in the range of 0.5 to 15 μm. The weight ratio of the coating layer to the coated paper may be, for example, in the range of 0.5 to 15%.

[0037] (coating layer) The lid laminate sheet 10 has a coating layer 3 between a paper substrate 4 and a sealant layer 1. The coating layer 3 has specific tensile properties, and its presence between the paper substrate 4 and the sealant layer 1 contributes to preventing the paper from peeling.

[0038] The coating layer 3 has a cross-sectional composite elastic modulus in the range of 400 to 3600 MPa and a stress relaxation rate of 0.20 or more. The method for measuring the composite elastic modulus and stress relaxation rate will be described later with reference to the drawings.

[0039] By providing the heat seal layer 10 for the lid body with a coating layer 3 having the above composite elastic modulus and the above stress relaxation degree 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 body made of the heat seal layer 10 for the lid body is peeled off from the container body, making it less likely that the heat seal layer 1 will break and less likely that the paper substrate 4 will peel off.

[0040] 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 a force is also applied to the paper substrate 4 in the 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 due to its low composite modulus, which makes the paper substrate 4, which has weak strength in the thickness direction, prone to peeling. In contrast, if the coating layer 3 having the above composite modulus is interposed, the coating layer 3 mitigates the force and deformation applied to the heat-seal layer 1 during peeling (opening), preventing the heat-seal layer 1 from breaking and also mitigating the force applied to the paper substrate 4 in the thickness direction, enabling opening without peeling. In this case, the coating layer 3 having the above composite modulus will not break due to the force during peeling.

[0041] On the other hand, even if a coating layer 3 is present, if it does not have the above-mentioned composite elastic modulus and stress relaxation rate, the coating layer 3 cannot mitigate the force and deformation applied to the heat seal layer 1 and the paper base material 4 when peeling (opening), and paper peeling is not suppressed.

[0042] That is, when the heat seal layer 1 deforms during peeling (opening), the coating layer 3 also deforms. If the coating layer 3 has a low composite modulus, it cannot mitigate the force in the thickness direction applied to the paper substrate 4, and the paper substrate 4 must deal with the force solely through its strength in the thickness direction (peel strength). As a result, the paper substrate 4 is in the same state as if the coating layer 3 were not present, and paper peeling may occur. This tendency also occurs when the stress relaxation rate is too high. From this perspective, the composite modulus is 400 MPa or more, preferably 500 MPa or more. Furthermore, the stress relaxation rate is preferably 0.7 or less.

[0043] Furthermore, if the coating layer 3 has a high composite modulus or a low stress relaxation rate, the coating layer 3 has high strength and low elongation. Therefore, the coating layer 3 cannot relax the force applied to the paper substrate 4 in the thickness direction, and the paper substrate 4 must deal with the force solely through its strength in the thickness direction (peel strength). Furthermore, since the coating layer 3 is brittle in this case, it tends to break when the heat seal layer 1 is pulled by the heat seal layer 1 and deforms during peeling (opening). Coating defects, in particular, can easily lead to breakage of the coating layer 3, which can also be a manufacturing hurdle. From these perspectives, the composite modulus is 3600 MPa or less, preferably (3000) MPa or less. Furthermore, the stress relaxation rate is 0.20 or more.

[0044] 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 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 may be a cured film that has been further crosslinked as needed. The contact between the coating layer 3 and the paper substrate 4 facilitates the dispersion of the stresses described above during peeling (opening), thereby more effectively alleviating the force applied to the paper substrate 4 in the film thickness direction. Conventional techniques for preventing paper peeling include interposing a film such as a polyethylene terephthalate (PET) film or a nylon (Ny) film between the paper substrate and the heat-seal layer. However, PET films and the like are bonded to the paper substrate via an adhesive, which typically uses a two-component adhesive consisting of a polyol and an isocyanate. This requires aging for sufficient polymerization, posing a processing problem. Furthermore, the films generally used in the above-mentioned conventional technologies are only a few micrometers thick, and further thinning of the film to reduce the amount of resin poses the problem of making high-speed conveyance difficult, making this technology unsuitable for use in laminated sheets for lids that contain a high proportion of paper.

[0045] Resin composition (coating liquid) The coating layer 3 is a dried coating film formed using a coating liquid comprising the resin composition as described above, or a cured film obtained by further crosslinking the dried coating film. The resin components contained in the resin composition can be appropriately selected and used so that the cross-sectional composite elastic modulus and stress relaxation rate of the coating layer comprising the dried or cured film fall within the above-mentioned ranges.

[0046] 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.

[0047] A thermosetting resin is a resin that hardens when heated. Examples of thermosetting resins include acrylic resin, urethane resin, phenolic 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).

[0048] Alternatively, a resin may be dissolved or dispersed in a suitable solvent and then appropriately selected from those that can be dried to form the coating layer 3. For example, polyurethane dispersion, which is an aqueous dispersion of urethane resin, ethylene-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, polyvinylidene resin, polyacetal, polystyrene, and modified products thereof may also be used.

[0049] Among these, from the viewpoint of ease of control of the composite elastic modulus and stress relaxation rate, a urethane dispersion, which is an aqueous dispersion of a urethane resin, can be preferably used. Commercially available urethane dispersions may be used, such as Evaphanol (registered trademark) HA-55, HA-68, HA-170, HA-190, 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In one embodiment, the resin composition contains a urethane (meth)acrylate monomer (hereinafter referred to as "urethane (meth)acrylate compound A" or "compound A") having a molecular weight of less than 1500 and two or more (meth)acryloyl groups, thereby improving the strength and hardness of the coating layer 3.

[0054] The urethane (meth)acrylate compound A more preferably has a molecular weight of 100 or more and less than 1,500, and even more preferably has a molecular weight of 300 or more and less than 1,500.

[0055] The urethane (meth)acrylate compound A more preferably has two (meth)acryloyl groups, and more preferably contains an alicyclic skeleton such as tricyclodecane or trimethylcyclohexyl (IPDI type) or an aromatic ring in its structure.

[0056] The urethane (meth)acrylate compound A is preferably, for example, a urethane (meth)acrylate compound containing any one of the following cyclic structures and having two (meth)acryloyl groups. In the structural formula below, * indicates the bonding site to the rest of the compound. [ka]

[0057] The urethane (meth)acrylate compound A may be produced by a known method, or a commercially available product may be used. Examples of commercially available products that can be used include A-DCP, ABE-300, A-BPE300, and A-BPE-10 (all from Shin-Nakamura Chemical Co., Ltd.), BP-4EAL, DCP-A, and DCP-4EL (all from Kyoeisha Chemical Co., Ltd.).

[0058] In another embodiment, the resin composition preferably contains a urethane (meth)acrylate oligomer having a mass average molecular weight of 1,000 or more and two or more (meth)acryloyl groups, the urethane (meth)acrylate oligomer being selected from polyester-based urethane (meth)acrylate oligomers, polyether-based urethane (meth)acrylate oligomers, and polyol-based urethane (meth)acrylate oligomers (hereinafter referred to as "urethane (meth)acrylate compound B" or "compound B"). This improves the extensibility and flex resistance of the coating layer 3.

[0059] The urethane (meth)acrylate compound B more preferably has a mass average molecular weight of 1500 or more and 25000 or less, and further preferably 1500 or more and 20000 or less. Here, the mass average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0060] Furthermore, the urethane (meth)acrylate compound B more preferably has two or three (meth)acryloyl groups in one molecule.

[0061] The urethane (meth)acrylate compound B can be produced by a known method. For example, a urethane (meth)acrylate can be obtained by reacting a polyisocyanate such as a diisocyanate with a polyol to form a urethane bond, and then reacting the urethane bond with a hydroxy ester of (meth)acrylic acid or the like.

[0062] Examples of the polyol that can be used include polyester polyol, polycarbonate polyol, and polyether polyol.

[0063] Examples of polyisocyanates that can be used include hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), and dicyclohexylmethane diisocyanate.

[0064] As the urethane (meth)acrylate compound B, commercially available products may be used, such as UV-2000B, UV-2750B, UV-3000B, UV-3200B, UV-3300B, UV-3310B, UV-3700B, UV-6640B, UV-7000B, UV-3500BA, UV-3210EA, UV-3520EA (all Mitsubishi Chemical Corporation), UF-8001G (Kyoeisha Chemical Co., Ltd.), EBECRYL (registered trademark) 4491, EBECRYL 8411 (all Daicel-Allnex Corporation), and the like.

[0065] In another embodiment, the resin composition preferably contains a urethane (meth)acrylate compound A and a urethane (meth)acrylate compound B. By combining these two urethane (meth)acrylate compounds with different mechanical properties, it becomes easy to obtain a coating layer 3 that satisfies the above-mentioned tensile properties.

[0066] The mass ratio of the urethane (meth)acrylate compound A to the urethane (meth)acrylate compound B (compound A:compound B) contained in the resin composition is preferably within a range of 50:50 to 0:100, and more preferably within a range of 30:70 to 0:100.

[0067] The solvent is not particularly limited as long as it dissolves the ionizing radiation-curable compound and the photocuring initiator. For example, ethers such as dibutyl ether, dimethoxymethane, dimethoxyethane, diethoxyethane, propylene oxide, 1,4-dioxane, 1,3-dioxolane, 1,3,5-trioxane, tetrahydrofuran, anisole, and phenetole, ketones such as acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, and methylcyclohexanone, esters such as ethyl formate, propyl formate, n-pentyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, n-pentyl acetate, and γ-butyrolactone, and cellosolves such as methyl cellosolve, cellosolve, butyl cellosolve, and cellosolve acetate, dimethyl carbonate, water, etc. can be used. These solvents can be used alone or in combination of two or more.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] The coating layer 3 has a mass per area of ​​3.1 g / m 2 It is preferable that the content is 3.3 g / m or more. 2 More preferably, it is 4.4 g / m or more. 2 More preferably, it is 5.5 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, 22 g / m 2 The following is the result.

[0073] (heat seal layer) The lid laminate sheet 10 includes a heat seal layer 1. 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. The heat seal layer 1 may be, for example, a film made of ethylene-vinyl acetate (EVA), an ionomer resin, or other polyolefins. 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.

[0074] A sealant layer with easy-peel functionality (simple peeling function) can also be used as the heat-seal layer 1. Easy-peel functionality means excellent re-peelability and ease of opening. Methods for attaching the heat-seal layer 1 by lamination include dry lamination using a solvent-based adhesive, non-solvent lamination using a solventless adhesive, and sand lamination using a molten resin as an adhesive. Furthermore, when the heat-seal layer is extruded using a molten resin, extrusion lamination can also be used.

[0075] The heat seal layer 1 is provided on the coating layer 3, for example, by lamination. The heat seal layer 1 can also be formed by applying a heat seal varnish. That is, the heat seal layer 1 may be a cured coating film of the 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.

[0076] 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.

[0077] The mass per area of ​​the heat seal layer 1 is 0.5 to 60 g / m 2 and preferably in the range of 1 to 30 g / m 2 For example, when the heat seal layer 1 is a sealant layer, the mass per area of ​​the heat seal layer 1 is preferably in the range of 10 to 60 g / m 2 and preferably in the range of 15 to 30 g / m 2 Alternatively, when the heat seal layer 1 is a cured coating of a heat seal varnish, the mass per area of ​​the heat seal layer 1 is preferably in the range of 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

[0078] [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.

[0079] 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.

[0080] (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.

[0081] 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.

[0082] When the paper substrate 4 is a coated paper having coated paper on one or both sides, the printing layer 5 can be provided on the coating layer. In this case, it is easy to display a high-quality image on the printing layer 5. Furthermore, by providing a coating layer, the underlying surface of the functional layer 6 becomes smooth, thereby improving the water resistance of the functional layer 6. Furthermore, when a coating layer is provided, it is possible to prevent the materials of the printing layer 5 and the functional layer 6 from seeping into the paper substrate 4.

[0083] 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.

[0084] (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.

[0085] 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.

[0086] 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.

[0087] The functional layer 6 is preferably an overprint varnish layer (hereinafter referred to as "OP varnish layer").

[0088] 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.

[0089] 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.

[0090] 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, for example, 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.

[0091] (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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] [Second embodiment] The lid body according to the second embodiment of the present invention is a lid body obtained from the lid body laminate sheet according to the first embodiment or the modified example described above. An example of the lid body according to the second embodiment is the lid body 21, which will be described later with reference to Fig. 3. As described in relation to the lid body laminate sheets 10 and 11, the lid body according to this embodiment is excellent in ease of opening, with paper peeling being suppressed.

[0101] [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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] [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.

[0108] As described above, in this packaged food, the heat seal strength between the lid 21 and the container body 22 is preferably smaller than the breaking strength of the coating layer 3 included in the lid 21. This heat seal strength is preferably in the range of 5 to 60 N / 15 mm, and more preferably in the range of 10 to 50 N / 15 mm. The difference between the breaking strength of the coating layer 3 and the heat seal strength between the lid 21 and the container body 22 is preferably in the range of 5 to 60 N / 15 mm, and more preferably in the range of 10 to 40 N / 15 mm. Here, the heat seal strength is a value obtained by the method specified in JIS Z0238:1998, "Test methods for heat-sealed flexible packaging bags and semi-rigid containers."

[0109] 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.

[0110] The lid included in this packaged food is designed to be easy to open and is less likely to peel off, so that when the lid is peeled off 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. [Example]

[0111] The following describes tests carried out in connection with the present invention. <1> Preparation of resin composition (coating liquid) <1.1> Resin component The resin components used to form the coating layer 3 in the lid laminate sheets 10 of Examples 1 to 34 and Comparative Examples 1 to 13 are shown below. As the base resin contained in the coating layer 3 of each lid laminate sheet 10, any one of the following resins A to F was used alone or in combination of two of them.

[0112] Resin A: Urethane (meth)acrylate compound A An oligomer represented by formula (1) [ka]

[0113] The urethane (meth)acrylate compound A was produced by the following method. A reaction vessel equipped with a condenser, stirrer, and thermometer was charged with 31.5 parts by mass of isophorone diisocyanate and 0.1 parts by mass of dibutyltin dilaurate and heated to 50°C. 68.4 parts by mass of ε-caprolactone 1 mol modified 2-hydroxyethyl acrylate (PLACCEL FA1DDM, Daicel Chemical Industries, Ltd.) was added dropwise over 1 hour, and the reaction was carried out with stirring at 90°C for 10 hours. Measurement of the amount of residual isocyanate in the reaction solution using FT-IR revealed that the urethanization reaction had proceeded quantitatively, ultimately resulting in the amount of isocyanate being nearly zero. 99.9 parts by mass of urethane (meth)acrylate compound A represented by the structural formula above was obtained.

[0114] Resin B: Urethane (meth)acrylate compound B1 UV-7000B (Mitsubishi Chemical Corporation, functional groups 2-3, Mw 3500) Resin C: Urethane dispersion Hydran HW-171 (DIC Corporation, non-volatile content (NV) 34-36% by mass) Resin D: Urethane dispersion Evaphanol HA-170 (Nicca Chemical Co., Ltd., NV 36.5% by mass) Resin E: Urethane (meth)acrylate compound B2 UV-3520EA (Mitsubishi Chemical Corporation, functional groups 2, Mw 14000) Resin F: Urethane dispersion Neo Sticker (registered trademark)-300 (Nicca Chemical Co., Ltd., NV 35% by mass)

[0115] <1.2> Coating liquid Coating liquid 1 Methyl ethyl ketone (MEK) was added to a mixture of 70 parts by mass of resin A (urethane (meth)acrylate compound A of formula (1)) and 30 parts by mass of resin B (urethane (meth)acrylate compound B1 UV-7000B) to obtain coating solution 1 with NV of 50% by mass.

[0116] Coating liquid 2 MEK was added to a mixture of 50 parts by mass of Resin A and 50 parts by mass of Resin B to obtain Coating Solution 2 with NV content of 50% by mass.

[0117] Coating liquid 3 MEK was added to a mixture of 30 parts by mass of Resin A and 70 parts by mass of Resin B to obtain Coating Solution 3 with NV content of 50% by mass.

[0118] Coating liquid 4 MEK was added to Resin B to obtain Coating Solution 4 with NV content of 50% by mass.

[0119] Coating liquid 5 MEK was added to Resin E (urethane (meth)acrylate compound B2 UV-3520EA) to obtain Coating Solution 5 with an NV content of 30% by mass.

[0120] Coating liquid 6 Water was added to resin C (urethane dispersion Hydran HW-171) to obtain coating solution 6 with an NV content of 30% by mass.

[0121] Coating liquid 7 Water was added to Resin D (urethane dispersion Evaphanol HA-170) to obtain Coating Solution 7 with an NV content of 30% by mass.

[0122] Coating liquid 8 Water was added to resin F (urethane dispersion Neo Sticker-300) to obtain coating solution 8 with an NV content of 30% by mass.

[0123] <2> Manufacturing of laminated sheets for lids (Example 1) The lid laminate sheet 10 shown in FIG. 1 was produced by the following method. First, the paper substrate 4 has a mass per area of ​​52.3 g / m 2 A single-sided coated paper was prepared. Coating solution 2 was applied to the coating layer of this paper substrate 4 to form a coating film. This coating film was dried at 100°C for 1 minute and then cured with an electron beam at an irradiation dose of 3.2 Mrad to form coating layer 3. Coating solution 2 was applied using a bar coater to a dry film thickness of 3 μm and a dry mass per area of ​​3.3 g / m 2 The coating layer 3 was then coated with a heat seal varnish, 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 -35°C and a melting point of 40 to 100°C. The heat seal varnish was printed by gravure printing to a dry mass per area of ​​3 g / m 2 In this manner, a lid laminate sheet 10 shown in FIG. 1 was obtained.

[0124] (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 2 was applied using a bar coater to a coating film having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0125] (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 2 was applied using a bar coater to a coating film having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0126] (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 2 was applied using a bar coater to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0127] (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, coating liquid 3 was used instead of coating liquid 2.

[0128] (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 3 was applied using a bar coater to a coating solution having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0129] (Example 7) 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 3 was applied using a bar coater to a coating solution having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0130] (Example 8) 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 3 was applied using a bar coater to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0131] (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, coating liquid 4 was used instead of coating liquid 2.

[0132] (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 4 was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0133] (Example 11) 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 4 was applied using a bar coater to a coating solution having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0134] (Example 12) 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 4 was applied using a bar coater to a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0135] (Example 13) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, Coating Liquid 6 was used instead of Coating Liquid 2, and the coating film was dried at 140°C for 10 minutes to form a coating layer 3. Electron beam curing was not performed.

[0136] (Example 14) A lid laminate sheet 10 was produced in the same manner as in Example 13, except for the following points: In this example, the coating solution 6 was applied using a bar coater to a coating film having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0137] (Example 15) A lid laminate sheet 10 was produced in the same manner as in Example 13, except for the following points: In this example, the coating solution 6 was applied using a bar coater to a coating film having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0138] (Example 16) A lid laminate sheet 10 was produced in the same manner as in Example 13, except for the following points: In this example, the coating solution 6 was applied using a bar coater to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0139] (Example 17) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, Coating Liquid 7 was used instead of Coating Liquid 2, and the coating film was dried at 140°C for 10 minutes to form a coating layer 3. Electron beam curing was not performed.

[0140] (Example 18) A lid laminate sheet 10 was produced in the same manner as in Example 17, except for the following points: In this example, the coating solution 7 was applied using a bar coater to a coating film having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0141] (Example 19) A lid laminate sheet 10 was produced in the same manner as in Example 17, except for the following points: In this example, the coating solution 7 was applied using a bar coater to a coating film having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0142] (Example 20) A lid laminate sheet 10 was produced in the same manner as in Example 17, except for the following points: In this example, the coating solution 7 was applied using a bar coater to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0143] (Example 21) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: In this example, coating liquid 5 was used instead of coating liquid 2.

[0144] (Example 22) A lid laminate sheet 10 was produced in the same manner as in Example 21, except for the following points: In this example, the coating solution 5 was applied using a bar coater to a coating film having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0145] (Example 23) A lid laminate sheet 10 was produced in the same manner as in Example 21, except for the following points: In this example, the coating liquid 5 was applied using a bar coater to a coating film having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0146] (Example 24) A lid laminate sheet 10 was produced in the same manner as in Example 21, except for the following points: In this example, the coating solution 5 was applied using a bar coater to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0147] (Example 25) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points. That is, in this example, coating liquid 6 was used instead of using coating liquid 2. Furthermore, instead of applying the coating liquid onto the coating layer of paper substrate 4, which is single-sided coated paper, coating liquid 6 was applied to the surface of the paper substrate 4 on the side where no coating layer was provided. Furthermore, coating liquid 6 was applied using a bar coater to a thickness of 5 μm on dry film and a dry mass per area of ​​5.5 g / m. 2 The coating film was dried at 140° C. for 10 minutes to form a coating layer 3. No electron beam curing was performed.

[0148] (Example 26) 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 mass per area of ​​52.3 g / m 2 Instead of using single-sided coated paper with a mass per area of ​​60 g / m 2A single-sided coated paper of the same composition was used. Furthermore, instead of using Coating Solution 2, Coating Solution 6 was used. Furthermore, Coating Solution 6 was used to coat a single-sided coated paper having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m2 using a bar coater. 2 The coating film was dried at 140° C. for 10 minutes to form a coating layer 3. No electron beam curing was performed.

[0149] (Example 27) 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 mass per area of ​​52.3 g / m 2 Instead of using single-sided coated paper with a mass per area of ​​65g / m 2 A single-sided coated paper of the same composition was used. Furthermore, instead of using Coating Solution 2, Coating Solution 6 was used. Furthermore, Coating Solution 6 was used to coat a single-sided coated paper having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m2 using a bar coater. 2 The coating film was dried at 140° C. for 10 minutes to form a coating layer 3. No electron beam curing was performed.

[0150] (Example 28) 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 mass per area of ​​52.3 g / m 2 Instead of using single-sided coated paper with a mass per area of ​​73.3 g / m 2 A single-sided coated paper of the same composition was used. Furthermore, instead of using Coating Solution 2, Coating Solution 6 was used. Furthermore, Coating Solution 6 was used to coat a single-sided coated paper having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m2 using a bar coater. 2 The coating film was dried at 140° C. for 10 minutes to form a coating layer 3. No electron beam curing was performed.

[0151] (Example 29) 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 2 was applied using a bar coater to a coating solution having a dry film thickness of 20 μm and a dry mass per area of ​​22 g / m 2 The coating was applied so that

[0152] (Example 30) A lid laminate sheet 10 was produced in the same manner as in Example 29, except for the following points: In this example, coating liquid 3 was used instead of coating liquid 2.

[0153] (Example 31) A lid laminate sheet 10 was produced in the same manner as in Example 29, except for the following points: In this example, coating liquid 4 was used instead of coating liquid 2.

[0154] (Example 32) A lid laminate sheet 10 was produced in the same manner as in Example 29, except for the following points. That is, in this example, Coating Liquid 6 was used instead of Coating Liquid 2. The coating film was dried at 140°C for 10 minutes to form a coating layer 3. Electron beam curing was not performed.

[0155] (Example 33) A lid laminate sheet 10 was produced in the same manner as in Example 29, except for the following points. That is, in this example, Coating Liquid 7 was used instead of Coating Liquid 2. The coating film was dried at 140°C for 10 minutes to form a coating layer 3. Electron beam curing was not performed.

[0156] (Example 34) A lid laminate sheet 10 was produced in the same manner as in Example 29, except for the following points: In this example, coating liquid 5 was used instead of coating liquid 2.

[0157] (Comparative Example 1) A lid laminate sheet 10 was produced in the same manner as in Example 1, except for the following points: That is, in this example, the coating layer 3 was not provided.

[0158] (Comparative Example 2) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 1, except for the following points: In this example, the paper substrate 4 had a mass per area of ​​52.3 g / m 2 Instead of using single-sided coated paper with a mass per area of ​​60 g / m 2Single-sided coated paper was used.

[0159] (Comparative Example 3) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 1, except for the following points: In this example, the paper substrate 4 had a mass per area of ​​52.3 g / m 2 Instead of using single-sided coated paper with a mass per area of ​​65g / m 2 Single-sided coated paper was used.

[0160] Comparative Example 4 A lid laminate sheet 10 was produced in the same manner as in Comparative Example 1, except for the following points: In this example, the paper substrate 4 had a mass per area of ​​52.3 g / m 2 Instead of using single-sided coated paper with a mass per area of ​​73.3 g / m 2 Single-sided coated paper was used.

[0161] (Comparative 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, Coating Liquid 1 was used instead of Coating Liquid 2.

[0162] (Comparative Example 6) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 5, except for the following points: In this example, the coating solution 1 was applied to a coating film having a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m using a bar coater. 2 The coating was applied so that

[0163] (Comparative Example 7) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 5, except for the following points: In this example, the coating solution 1 was applied to a coating film having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m using a bar coater. 2 The coating was applied so that

[0164] (Comparative Example 8) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 5, except for the following points: In this example, the coating solution 1 was applied to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m using a bar coater. 2 The coating was applied so that

[0165] (Comparative 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, Coating Liquid 8 was used instead of Coating Liquid 2. The coating film was dried at 140°C for 10 minutes to form a coating layer 3. Electron beam curing was not performed.

[0166] (Comparative Example 10) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 9, except for the following points: In this example, the coating solution 8 was applied using a bar coater to a dry film thickness of 5 μm and a dry mass per area of ​​5.5 g / m 2 The coating was applied so that

[0167] (Comparative Example 11) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 9, except for the following points: In this example, the coating solution 8 was applied using a bar coater to a coating solution having a dry film thickness of 10 μm and a dry mass per area of ​​11 g / m 2 The coating was applied so that

[0168] (Comparative Example 12) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 9, except for the following points: In this example, the coating solution 8 was applied using a bar coater to a coating film having a dry film thickness of 15 μm and a dry mass per area of ​​16.5 g / m 2 The coating was applied so that

[0169] (Comparative Example 13) A lid laminate sheet 10 was produced in the same manner as in Comparative Example 9, except for the following points: In this example, the coating solution 8 was applied using a bar coater to a coating film having a dry film thickness of 20 μm and a dry mass per area of ​​22 g / m 2 The coating was applied so that

[0170] <3> Measurement method for composite elastic modulus and stress relaxation rate The method for measuring the composite elastic modulus and stress relaxation rate of the coating layer of the above-mentioned lid laminate sheet will be described below. Except for Comparative Examples 1 to 3 in which no coating layer 3 was formed, the composite elastic modulus and stress relaxation rate of the coating layer 3 of each of the lid body laminate sheets 10 prepared above were obtained by the nanoindentation method described below.

[0171] First, a rectangular sheet piece measuring 3 mm in length and 1 mm in width is cut from the lid laminate sheet 10. The sheet piece is cut so that its length is parallel to the MD (machine direction). Next, the surface of the sheet piece facing the heat seal layer 1 and the surface facing the paper substrate 4 are coated with resin. This embeds the sheet piece in resin. Embedding the sheet piece in resin can prevent the heat seal varnish from dripping or falling off. A photocurable resin such as an ultraviolet-curable resin or a visible-light-curable resin is used as the resin. When a thermosetting resin is used as the resin, it is sufficient to perform the curing process under heating conditions that do not cause changes in the physical properties of each layer before and after heating. Here, visible-light-curable embedding resin D-800 (Nissin EM Co., Ltd.) was used.

[0172] Next, a microtome is used to cut the composite of the sheet piece and the resin in which it is embedded so that a cross section parallel to the thickness and width of the sheet piece is exposed. The finishing conditions are a cutting thickness of 100 nm and a cutting speed of 1 mm / sec. However, if sagging occurs in the test piece when the cutting thickness is 100 nm (for example, when it contains LLDPE), the cutting thickness is reduced to 3 μm.

[0173] Next, the obtained test piece is placed in a nanoindenter. Here, the test piece is placed in the nanoindenter so that the indenter provided in the nanoindenter contacts the cross section of the coating layer 3 perpendicularly. The nanoindenter used is one that is capable of surface detection at 1 μN. Although this was not done in this example, trimming of the embedding resin may be performed when placing the test piece, if necessary.

[0174] Next, as shown in Figure 4, the indenter 30 is pressed into the cross section of the coating layer 3. The pressing speed is 100 nm / sec. Figure 4 is a cross-sectional view that schematically shows the state in which the indenter 30 is pressed into the cross section of the coating layer 3 to the maximum depth. In Figure 4, hmax indicates the maximum depth of pressing into the cross section of the coating layer 3, i.e., the maximum displacement. Ac indicates the contact projected area. hc indicates the contact depth. During the pressing process of the indenter 30, the load applied to the cross section of the coating layer 3 and the pressing depth are measured using a nanoindenter.

[0175] The indenter 30 is a diamond Berkovich indenter. The tip of the Berkovich indenter has three triangular faces. One of the vertices of each triangle coincides with one of the vertices of the other two triangles. The two sides extending from the vertices of these triangles form equal angles. In other words, these three faces form an approximately equilateral triangular pyramid. The indenter 30 used here has an angle of 115° for each triangle. 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 presses 300 nm into the cross section of the coating layer 3 after the surface detection load reaches 1 μN. The holding time for the displacement h to remain constant at the maximum depth is 3 seconds.

[0176] Next, the indenter 30 is withdrawn from the cross section of the coating layer 3. The withdrawal speed is set to 100 nm / sec. During this process, the load applied to the cross section of the coating layer 3 and the indentation depth are measured by the nanoindenter.

[0177] The above-described operation can produce the relationship shown in FIG. 5, for example. FIG. 5 is a graph showing a load-displacement curve. In FIG. 5, the vertical axis represents the load P applied to the coating layer 3, and the horizontal axis represents the indentation depth of the indenter 30, i.e., the displacement h. In FIG. 5, when the load P is 0, the indenter 30 is not in contact with the coating layer 3. The position where the displacement h is 0 is the starting point where the load P applied to the cross section of the coating layer 3 increases from 0. In FIG. 5, the solid curve (legend: indentation) in which the load P increases steadily from 0 as the displacement h increases shows the relationship between the load P and the displacement H during the process of indenting the indenter 30 into the cross section of the coating layer 3. The maximum load at this time is designated P1. The dashed curve (legend: hold) in which the load decreases while the displacement remains constant shows the relationship between the load P and the displacement H during the process of holding the indenter 30 at the maximum depth into the coating layer 3 for 3 seconds while the displacement h remains constant. The load after holding for 3 seconds is designated P2. The curve indicated by the dashed dotted line, in which the load P decreases downward to a negative value as the displacement h decreases, is the unloading curve. The unloading curve shows the relationship between the load and the displacement during the process of pulling the indenter 30 out of the coating layer 3. Pmax (=P2) indicates the maximum load on the unloading curve, and hmax is the maximum displacement.

[0178] Next, the contact depth hc is calculated by analysis using the Oliver-Pharr method. The contact depth hc can be calculated using the following formula (1).

[0179]

number

[0180] Here, ε is a constant related to the indenter shape. For a Berkovich indenter, this constant is 0.75. The maximum load Pmax and maximum displacement hmax of the unloading curve can be determined based on the graph shown in Figure 5. S is contact stiffness. Contact stiffness S is the slope of the approximate curve immediately after withdrawal, which is obtained by fitting the range of 20 to 95% of the maximum load of the unloading curve in Figure 5 with the function of the following equation (2). Here, P is the load, and h is the indentation depth. Furthermore, A, hf, and m are fitting parameters used in the fitting.

[0181]

number

[0182] Next, the contact projected area Ac is calculated based on the shape of the indenter and the contact depth hc. The contact projected area Ac can be expressed as a function of the contact depth hc, as shown in the following equation (3).

[0183]

number

[0184] Equation (3) includes terms called correction terms, C1 to C5, to correct for the influence of the indenter shape. C1 to C5 are values ​​determined by using fused silica as a test piece and performing measurements under maximum loads of 20 μN to 10 mN, so that the composite elastic modulus Er at each maximum load is 69.6 GPa, which is the composite elastic modulus of fused silica.

[0185] Next, the composite elastic modulus Er is calculated based on the contact projected area Ac and the contact stiffness S. The composite elastic modulus Er can be calculated by the following formula (4).

[0186]

number

[0187] The composite elastic modulus Er is measured at multiple locations per test piece, for example, 10 to 20 locations, and the average value of these composite elastic moduli Er is obtained as the composite elastic modulus.

[0188] In this measurement, the rate of decrease in load P due to holding at the maximum depth was calculated as the degree of stress relaxation. If the load before holding is P1 and the load after holding is P2 (=Pmax), the degree of stress relaxation is given by equation (5).

[0189]

number

[0190] <4> Openability evaluation The lid laminate sheets 10 according to Examples 1 to 34 and Comparative Examples 1 to 13 were subjected to the following two heat seal tests, and the presence or absence of paper peeling was visually confirmed to evaluate the openability. Here, "paper peeling" refers to, as described above, when the lid is peeled off, cohesive failure of the paper base occurs, and part of the lid remains on the container body (including double lids and membrane breaks).

[0191] (Heat seal test 1) Here, the resin sheet used as the adherend was a three-layer polypropylene resin sheet (PP / PP+EVOH4% / PP) consisting of a pair of polypropylene (PP) layers and a layer of a mixture of polypropylene and 4% by mass of ethylene-vinyl alcohol copolymer (EVOH) sandwiched between them. Such resin sheets are generally used for tray containers.

[0192] 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. Heat sealing was performed by applying a temperature of 170°C and a pressure of 0.1 MPa to the laminate of the lid laminate sheet and the resin sheet for 5 seconds. From each heat-sealed laminate, a 15 mm wide strip-shaped test piece was cut out.

[0193] A peel test was carried out on each test piece in accordance with JIS Z 0238:1998 using a Tensilon under the conditions of a chuck distance of 50 mm, a peel speed of 300 mm / min, and 180-degree peeling, and the openability was evaluated based on the following criteria. A: Peeled off without peeling off the paper. B: The paper peeled off without peeling, but some damage was observed to the paper base material. C: The paper peeled off without peeling, but significant damage to the paper substrate was observed. D: The paper peeled off.

[0194] (Heat seal test 2 / Cup seal test) Lids were cut out from the lid laminate sheets 10 according to Examples 1 to 34 and Comparative Examples 1 to 13. These lids were used to manufacture food packaging containers 20 shown in Fig. 3. Here, the container body 22 was formed from the resin sheet used in Heat Sealing Test 1 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 was 30 mm high.

[0195] The lid 21 was heat-sealed to the flange 22a using a cup sealer equipped with a receiving stand and a seal bar. The receiving stand has a recess on its upper surface into which the bottom and barrel of the container body 22 fit. The seal bar used was made 5 mm wide to fit the shape of the flange 22a. The heat sealing was performed by applying a temperature of 210°C and a pressure of 0.2 MPa to the lid 21 and flange 22a for 1.5 seconds.

[0196] Next, for each food packaging container 20, the lid 21 was peeled off by hand from a corner of the container body 22, and the openability was evaluated based on the following criteria. A: Cohesive failure occurred in the heat seal layer, and no paper peeling occurred. B: Although the paper peeled off, part of the lid material remained on the container body only at the seal or around it, and this did not affect removal of the contents. C: Paper peeling occurred, and the lid material remained on the container body in areas other than the seal area and its surroundings. For example, the double lid or the lid itself was torn.

[0197] The results of the above measurements and tests are summarized in Table 1 below.

[0198] [Table 1]

[0199] [Table 2]

[0200] [Table 3] [Explanation of symbols]

[0201] 1...heat seal layer, 2...gas barrier layer, 3...coating layer, 4...paper base material, 5...printed layer, 6...water-resistant functional layer, 10...laminated sheet for lid, 11...laminated sheet for lid, 20...food packaging container, 21...lid, 22...container body, 22a...flange, 30...indenter

Claims

1. A lid laminate sheet used for a lid of a food packaging container having a container body with an opening and a lid covering the opening, A paper substrate, a coating layer, and a heat-seal layer, in this order; The proportion of the paper base material in the lid body laminate sheet is 50% by mass or more with respect to the total mass of the lid body laminate sheet, The coating layer has a cross-sectional composite elastic modulus in the range of 400 to 3600 MPa and a stress relaxation coefficient of 0.20 or more.

2. 2. The lid laminate sheet according to claim 1, wherein the coating layer has a thickness in the range of 3 to 20 [mu]m.

3. The coating layer has a mass per area of ​​3.1 g / m ２ The laminate sheet for a lid according to claim 1, wherein the laminate sheet is as described above.

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

5. 2. The lid laminate sheet according to claim 1, wherein the heat seal layer is a cured coating film of heat seal varnish.

6. The heat seal layer has a mass per area of ​​0.5 to 15 g / m ２ The laminated sheet for a lid according to claim 5, wherein the range is 1000 to 15000.

7. The laminated sheet for a lid body according to claim 1, further comprising a printed layer and a water-resistant functional layer in this order from the paper substrate side on the side of the paper substrate opposite to the side having the coating layer.

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

9. A lid body comprising the laminate sheet for lid bodies according to any one of claims 1 to 8.

10. A food packaging container comprising a container body having an opening and a lid body as described in claim 9 that covers the opening, wherein the coating layer is disposed between the paper base material and the internal space of the food packaging container.

11. 11. The food packaging container according to claim 10, 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.

12. 11. The food packaging container according to claim 10, wherein the internal space of the food packaging container is filled with a mixed gas containing oxygen gas, nitrogen gas, and carbon dioxide gas.

13. The food packaging container according to claim 10, wherein the food packaging container is a chilled food packaging container or a frozen food packaging container.

14. A packaged food product comprising the food packaging container according to claim 10 and food contained in the food packaging container.

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