Lid material and method for manufacturing lid material

Abstract

The present invention aims to provide a lid material that does not contain metal materials such as aluminum foil and has excellent dead-hold properties, as well as a method for manufacturing the lid material. [Solution] The lid material 1 according to this embodiment is a lid material that seals the upper end opening of the container body, and comprises at least a paper substrate 11 and a sealant 122. Printing is performed on both sides of the paper substrate 11, and by leaving it to stand, a region with a high concentration of hydroxyl groups is formed where the density of hydroxyl groups is higher than in other parts where printing is not performed. The paper substrate 11 autonomously folds with one side facing inward at the printed area, creating multiple stable states.

Description

[Technical Field]

[0001] The present invention relates to a lid material and a method for manufacturing the lid material, and more specifically, to a lid material composed mainly of paper and resin, with metals such as aluminum foil removed from the constituent materials, and a method for manufacturing the lid material. [Background technology]

[0002] Conventionally, heat-sealable lids for cup-shaped food containers have generally been made of a laminated structure consisting of, for example, paper / polyethylene resin layer / aluminum foil / polyethylene resin layer / heat-sealable resin layer. In this type of lid, aluminum foil is used due to its rigidity, plastic deformability, and ability to prevent curling. Furthermore, lid materials that do not use aluminum foil are known to have a laminated structure such as paper / light-shielding ink layer / resin film layer / heat-sealable resin layer (Patent Document 1).

[0003] As mentioned above, lids made of aluminum foil can reduce curling due to the rigidity and plastic deformability inherent in aluminum foil. Furthermore, some products use this lid as a heat-sealing lid attached to cup-shaped containers. When consuming the food contained within, a portion of the lid is opened by rolling it up, hot water is poured in, and then the lid is closed to steam the food inside the container before consumption. In these products, the use of aluminum foil as part of the layer structure of the lid offers advantages such as excellent partial opening of the lid when pouring hot water and superior resealability when it is returned to its original position.

[0004] However, on the other hand, it is not possible to inspect for metal foreign objects using metal detectors after the contents are filled on the product manufacturing line, and consumers cannot use microwave cooking, which has recently gained attention, in addition to the cooking method of pouring hot water. Furthermore, the manufacturing cost of the lid material is high, and there are problems with disposal after use, such as residue remaining when incinerated and not decomposing when landfilled. Furthermore, while the latter lid material, which does not use aluminum foil, eliminates the drawbacks of using aluminum foil, it conversely loses the advantages of using aluminum foil, and sometimes becomes more prone to curling.

[0005] In contrast, a lid material is also known that uses a polyester film as the resin film layer, and has a laminated structure of paper / light-shielding ink layer / biaxially oriented polyester film layer / heat-sealable resin layer (Patent Document 2).

[0006] However, the biaxially oriented polyester film layer that makes up this lid material is stiff, which increases the resilience of the lid material. This results in a technical problem where the lid material has poor ability to maintain its open state (dead-hold property) once opened. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-310273 [Patent Document 2] Japanese Patent Application Publication No. 2003-137332 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Therefore, the present invention aims to provide a lid material that does not contain metal materials such as aluminum foil and has excellent dead-hold properties, as well as a method for manufacturing the lid material. [Means for solving the problem]

[0009] To solve the above problems, a lid material according to one aspect of the present invention is a lid material for sealing the upper end opening of a container body, comprising at least a paper substrate and a sealant, wherein printing is performed on both sides of the paper substrate, and by leaving it to stand, a region of high hydroxyl group concentration is formed in which the density of hydroxyl groups is higher than in other parts that are not printed, and the paper substrate autonomously folds with one side facing inward at the printed portion, creating multiple stable states.

[0010] Furthermore, in one aspect of the present invention, the lid material has a basis weight of 50 g / m² of the paper substrate before printing. 2 More than 150g / m 2 The following range is also acceptable. Furthermore, the lid material according to one aspect of the present invention may further include a protective layer on the side of the paper substrate opposite to the sealant side.

[0011] Furthermore, in one embodiment of the present invention, the lid material may have the printing using either an organic salt or an inorganic salt applied to at least a portion of both sides of the paper substrate. Furthermore, in one embodiment of the present invention, the lid material may have the printing using sodium chloride as a solute applied to at least a portion of both sides of the paper substrate.

[0012] Furthermore, in one aspect of the present invention, the lid material comprises a paper substrate having a straight bending portion for bending the paper substrate, a surface printing portion formed by printing on the surface of the paper substrate opposite to the sealant side, a trigger line printing portion formed by printing on the back surface of the paper substrate which is the sealant side, the surface printing portion being formed in a strip shape along the bending portion, and the trigger line printing portion being formed in a circular shape centered on a point virtually provided in the bending portion.

[0013] Furthermore, in one aspect of the present invention, the lid material comprises a paper substrate having a straight bending portion for bending the paper substrate, a surface printed portion formed by printing on the surface of the paper substrate opposite to the sealant side, a trigger line printed portion formed by printing on the back surface of the paper substrate which is the sealant side, the surface printed portion being formed in a strip shape along the bending portion, the trigger line printed portion comprising a composite trigger line having a curved portion in part of a V shape and a composite trigger line having a curved portion in part of an inverted V shape, formed symmetrically with respect to a second straight line perpendicular to a first straight line virtually provided along the bending portion, and the composite trigger line having a curved portion in part of a V shape and the composite trigger line having a curved portion in part of an inverted V shape may also be formed symmetrically with respect to the first straight line.

[0014] Furthermore, a method for manufacturing a lid material according to one aspect of the present invention is a method for manufacturing a lid material that seals the upper end opening of a container body, wherein the lid material comprises at least a paper substrate and a sealant, and comprises the steps of: printing an ink containing a substance containing hydroxyl groups from one side of the paper substrate and then leaving it to form a high-concentration hydroxyl group region on one side of the paper substrate where the density of the hydroxyl groups is higher than that of the area where the ink was not printed; and printing an ink containing a substance containing hydroxyl groups from the other side of the paper substrate and then leaving it to form a high-concentration hydroxyl group region on the other side of the paper substrate where the density of the hydroxyl groups is higher than that of the area where the ink was not printed, wherein the paper substrate is autonomously folded by using pressure as a trigger, with the printed ink on one side facing inward, or the printed ink on the other side facing inward, thereby creating a plurality of structurally stable states.

[0015] Further, the method for producing a lid member according to one aspect of the present invention is the above-described method for producing a lid member, comprising: a step of printing an ink containing a hydroxyl group-containing substance from the front surface side, which is the surface of the paper base material opposite to the sealant side, followed by leaving the same to stand, thereby forming a high hydroxyl group concentration region in the front surface in which the hydroxyl group density is higher than that of a portion where the ink is not printed; and a step of printing an ink containing a hydroxyl group-containing substance from the back surface side, which is the surface of the paper base material on the sealant side, followed by leaving the same to stand, thereby forming a high hydroxyl group concentration region in the back surface in which the hydroxyl group density is higher than that of a portion where the ink is not printed, wherein with at least pressure as a trigger, the paper base material is deformed to bend autonomously with the front surface facing inward at the ink-printed portion on the front surface, or with the back surface facing inward at the ink-printed portion on the back surface, thereby creating a plurality of structurally stable states. Effects of the Invention

[0016] As described above, the lid member according to one aspect of the present invention and the lid member produced by the method for producing a lid member according to one aspect of the present invention do not contain a metal material such as an aluminum foil, and moreover have a property of excellent dead hold performance. Brief Description of the Drawings

[0017] [Figure 1] It is a schematic cross-sectional view showing the configuration of a lid member according to an embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view showing the configuration of a lid member according to another embodiment of the present invention. [Figure 3] It is a perspective view showing the overall configuration of a container sealed with a lid member according to an embodiment of the present invention. [Figure 4] It is a schematic plan view schematically showing a printed pattern (the printed pattern of the front surface printing portion) printed on the front surface of the lid member according to the embodiment of the present invention. [Figure 5] It is a schematic plan view schematically showing a printed pattern (the printed pattern of the trigger line printing portion) printed on the back surface of the lid member according to the embodiment of the present invention. [Figure 6] This is a schematic cross-sectional view illustrating a trigger mechanism that enables stepwise autonomous structure formation in a lid material according to an embodiment of the present invention. [Figure 7] This is a perspective view illustrating a trigger mechanism in a lid material according to an embodiment of the present invention that enables stepwise autonomous structure formation. [Figure 8] This is a perspective view illustrating the usage of the lid material according to an embodiment of the present invention. [Figure 9] This is a schematic cross-sectional view illustrating the rising angle β of the lid material according to an embodiment of the present invention. [Modes for carrying out the invention]

[0018] The lid material according to this embodiment is a lid material for sealing the upper opening of a container body, comprising at least a paper substrate and a sealant, wherein printing is performed on both sides of the paper substrate, and by leaving it to stand, a high-concentration hydroxyl group region is formed in which the density of hydroxyl groups is higher than in other parts that are not printed, and the paper substrate autonomously folds with one side facing inward at the printed area, creating multiple stable states. Specifically, on one side of the paper substrate, a first high-concentration hydroxyl group region is formed in which the density of hydroxyl groups is higher than in other parts of the paper substrate by impregnating a part of the paper substrate with a liquid (ink) consisting of water or an aqueous solution, and on the other side of the paper substrate, a second high-concentration hydroxyl group region is formed in which the density of hydroxyl groups is higher than in other parts of the other side. The embodiment will now be described in detail with reference to the drawings.

[0019] (Overall structure of lid material 1) As shown in Figure 1, the lid material 1 of this embodiment is composed of a laminate in which a paper layer (paper substrate) 11 and a sealant (heat-sealable resin layer) 122 constituting a multilayer resin layer 12 are essential constituent materials. In order to allow inspection for the presence or absence of metal foreign matter, it does not contain a metal layer such as aluminum foil. In addition, as shown in Figure 1, a light-shielding ink layer 13 can be provided between the paper layer 11 and the multilayer resin layer 12. Furthermore, a printed pattern layer (not shown) can be provided on the surface of the paper layer 11 (i.e., the side of the paper layer 11 opposite to the sealant 122 side).

[0020] The paper layer (paper substrate) 11 of this embodiment is a sheet made of paper itself (i.e., a paper sheet), or a sheet mainly composed of paper, and contains cellulose as its main component. As the paper sheet, for example, a relatively thick paper such as tracing paper is preferred, in which the cellulose fibers, bundled together, are compressed by strong pressing during the manufacturing process. A sheet primarily composed of paper may contain paper and other components. These other components can be arbitrarily selected according to the purpose, as long as they do not impair the effects of the present invention. Specific examples of these other components include resins, silica gel, cosmetic agents such as calcium carbonate and clay, glossing agents, and binders such as starch and PVA. Furthermore, as shown in Figure 2, the lid material 1 of this embodiment may also have a protective layer 14 provided on the surface of the paper layer 11.

[0021] In this embodiment, the protective layer 14 can be a protective layer according to the prior art, and examples include PET film (polyethylene terephthalate film), OPP film (oriented polypropylene film), PP film (polypropylene film), PVC film (polyvinyl chloride film), TPU film (thermoplastic polyurethane film), PE film (polyethylene film), OP varnish, or acrylic film.

[0022] Furthermore, as shown in the perspective view of the usage state in Figure 3, the lid material 1 of this embodiment is heat-sealed to the flange 2a on the periphery of the upper opening of the container body 2 to seal this opening. For this reason, among the multilayer resin layers 12, the sealant 122 in contact with the flange 2a, that is, the sealant 122 located on the outermost surface, needs to be a resin that can be heat-sealed to the flange 2a. In addition, the lid material 1 of this embodiment needs to be able to be opened by pressing and folding the surface printed portion (center line printed portion) A, which will be described later. For this reason, the sealant 122 needs to have easy-peel properties so that it can be peeled off from the flange 2a with this amount of force. As a sealant 122 having such easy-peel properties, a polyolefin resin or a resin having a component made of olefin and a component having an acidic group can be used. Examples of polyolefin resins include low-density polyethylene resin (LDPE) and polypropylene resin (PP). Examples of resins having a component made of olefin and a component having an acidic group include ethylene-vinyl acetate copolymer resin (EVA), ethylene-methacrylic acid copolymer resin (EMAA), and ethylene-acrylic acid copolymer resin (EAA).

[0023] Next, the multilayer resin layer 12 may also include a barrier resin layer 121 in addition to the sealant 122, which has excellent barrier properties against solvent vapors in the light-shielding ink layer 13 and odors from adjacent products. Furthermore, it is preferable that this barrier resin layer 121 has the property of retaining its folded shape (dead-hold property) without returning to its original flat state when folded and opened, and is preferably composed of an APET layer, a copolymerized PET layer, or an EVOH layer. Since these APET layers, copolymerized PET layers, and EVOH layers all have low crystallinity, their internal stress is small, and therefore they have excellent dead-hold properties.

[0024] Furthermore, even when using any of these APET layers, copolymerized PET layers, or EVOH layers as the barrier resin layer 121, if its thickness is too high, the dead-hold properties may be impaired. Conversely, if its thickness is too low, the barrier properties may be insufficient. The appropriate thickness is 2 to 5 μm.

[0025] Next, the multilayer resin layer 12 may include other resin layers 123 in addition to the sealant 122 and the barrier resin layer 121. For example, a polyolefin layer such as low-density polyethylene. As for the layer configuration, for example, one example is a laminate of "polyolefin 123 / barrier resin layer 121 / sealant 122" in that order from the paper layer 11 side (see Figure 2). Of course, it may also be a laminate of "barrier resin layer 121 / polyolefin 123 / sealant 122" in that order.

[0026] In addition, whether the multilayer resin layer 12 is composed of two layers, a sealant 122 and a barrier resin layer 121, or of three or more resin layers including other layers, if the total thickness of the multilayer resin layer 12 is too thick, the deadhold properties may be impaired. For this reason, the total thickness of the multilayer resin layer 12 is preferably 30 to 50 μm. Alternatively, instead of the multilayer resin layer 12 composed of multiple resin layers, a single-layer resin layer consisting only of sealant 122 (not shown) may be used.

[0027] Each resin layer constituting this multilayer resin layer 12 can be laminated via an adhesive or an adhesive resin layer. Preferably, it is formed integrally into a film by co-extrusion molding. The multilayer resin layer 12 thus integrally laminated into a film can then be bonded to the light-shielding ink layer 13 of the paper layer 11 using an adhesive. Alternatively, the multilayer resin layer 12 and the paper layer 11 may be laminated by so-called sand lamination. That is, molten resin is extruded between the multilayer resin layer 12 and the paper layer 11, and the layers are laminated using this molten resin.

[0028] Next, even if the barrier resin layer 121 has a thickness of 2 to 5 μm, if the basis weight of the paper layer 11 is small, excellent dead-hold properties may not be obtained. For this reason, the basis weight of the paper layer 11 should be 50 g / mm². 2 It is preferable to use the above, 90g / mm 2 It is preferable to use the above materials. However, if the basis weight is too high, it will take longer to heat seal the container body 2, and the interlayer strength of the paper will tend to decrease, so 150 g / mm² is preferable. 2 Preferably, it is 130 g / mm 2 The following is more preferable:

[0029] In this embodiment, the basis weight of the paper layer 11 mentioned above refers to the basis weight before the formation of the hydroxyl group high-concentration region, which will be described later. Basis weight 50g / mm 2 More than 150g / mm 2 The paper layer 11 within the following range may be single-sided coated paper having a coating layer on one side of the paper layer 11. For example, it may be single-sided coated paper in which the amount of coating agent applied is 20 to 30% by mass relative to the basis weight of the paper layer 11. If it is less than 20%, the effect of lamination of the coating layer will not be fully realized, and if it exceeds 30%, excessive rigidity will be imparted by the coating layer, which reduces the dead-hold property and is therefore undesirable.

[0030] The coating agent for the single-sided coated paper that constitutes the paper layer 11 consists of a pigment component and a resin component. As the pigment component, kaolin and heavy carbon can be used as the main component, and as the resin component, SBR (styrene-butadiene rubber) and starch can be used as the main component. The mass ratio of these components is within the range of pigment component / resin component = 90 / 10 to 60 / 40, and kaolin is contained as the main pigment component at a concentration of 70% or more of the pigment component, and SBR is contained as the main resin component at a concentration of 50% or more of the resin component. As a method of coating, such a coating agent can be applied to the outer side (one side) of the paper material to be made into single-sided coated paper by methods such as the air knife method or the blade method.

[0031] Note that the paper layer 11 of the present embodiment is not limited to the single-side coated paper described above, and may be a paper base material that does not include the coating layer of the paper layer 11. Even in that case, the basis weight of the paper layer 11 is 50 g / mm 2 or more and 150 g / mm 2 or less, which is preferable within the range. In addition, the light-shielding ink layer 13 can be printed on the paper layer 11, or can be printed on the multilayer resin layer 12. As the light-shielding ink layer 13, black ink can be preferably used, but it is also possible to perform overprinting of black ink and white ink to form the light-shielding ink layer 13 having a multilayer structure.

[0032] The lid material 1 according to the present embodiment can be manufactured by punching a laminate obtained by laminating at least the paper layer 11 and the sealant 122 constituting the multilayer resin layer 12 in this manner into an appropriate shape. For example, as shown in Figure 3, the shape is substantially the same as the shape of the upper end opening of the container body 2, and an unsealing tab 1a is provided on a part thereof. The unsealing tab 1a may be formed on a second straight line Y described later.

[0033] As shown in Figure 3, the lid material 1 according to the present embodiment is provided with a linear bent portion 1b for bending the lid material 1 (paper layer 11). The bent portion 1b may be provided so as to traverse the central portion of the lid material 1 (paper layer 11). For example, the bent portion 1b may be formed along a first straight line X passing through a point Z located at the center of the lid material 1 (paper layer 11). Note that the first straight line X and the second straight line Y shown in Figure 3 are virtually provided lines respectively, and the second straight line Y is a line orthogonal to the first straight line X.

[0034] (Print pattern of surface printing part) In this embodiment, at least a portion of the surface of the paper layer 11 is printed, and the printed area has a higher density of hydroxyl groups than the unprinted area. In this embodiment, the printed area on the surface of the paper layer 11 is conveniently referred to as the "surface printed area." In other words, the surface printed area formed by printing on the surface of the paper layer 11 has a higher density of hydroxyl groups than the area other than the surface printed area. Furthermore, the "surface printed area" formed along the first straight line X is conveniently referred to as the "centerline printed area."

[0035] Furthermore, the surface printed area may be formed using an ink containing a substance that contains hydroxyl groups. Furthermore, in this embodiment, the surface-printed area, which has a higher density of hydroxyl groups compared to other areas, is also referred to for convenience as the "first hydroxyl group high-concentration area." Figure 4 is a conceptual diagram showing an example of a printing pattern for the centerline printing area (surface printing area) A. As described above, the paper layer 11 in this embodiment is provided with a straight folding portion 1b for folding the paper layer 11. The center line printing portion A is formed in a strip shape along this folding portion 1b. In other words, the center line printing portion A may be provided so as to cross the central part of the lid material 1 (paper layer 11).

[0036] The printing width d of the centerline printing section A is not particularly limited, but for example, if the paper layer 11 is a circular substrate with a diameter of 141 mm that is used for general purposes, and the thickness of the paper layer 11 is in the range of 59 μm to 153 μm, then it is in the range of 14 mm to 22 mm. Furthermore, the upper limit of the printing width d of the centerline printing section A is correlated with the thickness of the paper layer 11, and tends to increase as the thickness of the paper layer 11 increases. Furthermore, as the printing width d of the center line printing section A increases, the autonomous folding angle of the lid material 1 (paper layer 11) tends to increase. The autonomous folding mechanism of the lid material 1 (paper layer 11) will be described later.

[0037] (Printing pattern for the trigger line area) In this embodiment, at least a portion of the back surface of the paper layer 11 (the surface of the paper layer 11 facing the sealant 122) is printed, and the printed area has a higher density of hydroxyl groups than the unprinted area. In this embodiment, the printed area on the back surface of the paper layer 11 is conveniently referred to as the "trigger line printed area." In other words, the trigger line printed area formed by printing on the back surface of the paper layer 11 has a higher density of hydroxyl groups than the area other than the trigger line printed area.

[0038] The trigger line printing area may be formed using the same ink containing a hydroxyl group as the ink used to form the center line printing area A, or it may be formed using a different ink. Furthermore, in this embodiment, the trigger line printing region, which has a higher density of hydroxyl groups compared to other regions, is also referred to for convenience as the "second hydroxyl group high concentration region."

[0039] Figure 5 is a conceptual diagram showing examples of various printing patterns for the trigger line printing section B. In Figure 5, the center line printing section A printed on the surface of the paper layer 11 is shown as a dashed line.

[0040] Figure 5(a) is a schematic plan view showing a configuration in which the trigger line printing section B is composed of a circular trigger line (circular trigger line) B1. The circular trigger line B1 is formed in a circular shape with a point Z virtually provided in the folded portion 1b as the center. If the paper layer 11 is a circular substrate with a diameter of 141 mm that is used for general purposes, and the thickness of the paper layer 11 is in the range of 59 μm to 153 μm, then the diameter g1 of the trigger line printing portion B (circular trigger line B1) is, for example, 40 mm.

[0041] Figure 5(b) is a schematic plan view showing that the trigger line printing section B is composed of a composite trigger line (V-shaped curve composite trigger line) B2, which has a curved section in part of its V-shape, and a composite trigger line (inverted V-shaped curve composite trigger line) B3, which has a curved section in part of its inverted V-shape. In this embodiment, the trigger line printing section B comprises a composite trigger line (V-shaped curve composite trigger line) B2 having a curved portion in part of its V shape, and a composite trigger line (inverted V-shaped curve composite trigger line) B3 having a curved portion in part of its inverted V shape, which are formed symmetrically with respect to a second straight line Y that is orthogonal to a first straight line X virtually provided along the folding section 1b. The composite trigger line (V-shaped curve composite trigger line) B2 and the composite trigger line (inverted V-shaped curve composite trigger line) B3 are each formed symmetrically with respect to the first straight line X, and the distance between the composite trigger line (V-shaped curve composite trigger line) B2 and the composite trigger line (inverted V-shaped curve composite trigger line) B3 is formed to be the shortest possible on the first straight line X.

[0042] Furthermore, if the paper layer 11 is a circular substrate with a diameter of 141 mm that is used for general purposes, and the thickness of the paper layer 11 is within the range of 59 μm to 153 μm, then the distance g2 between the composite trigger line (V-shaped curve composite trigger line) B2 and the composite trigger line (inverted V-shaped curve composite trigger line) B3 on the first straight line X is, for example, 40 mm. Furthermore, the angle θ formed by the straight sections that create the composite trigger line (V-shaped curve composite trigger line) B2 and the composite trigger line (inverted V-shaped curve composite trigger line) B3 is, for example, 46.1°.

[0043] Figure 5(c) is a schematic plan view showing the configuration in which the trigger line printing section B is composed of a V-shaped trigger line (V-shaped trigger line) B4 and an inverted V-shaped trigger line (inverted V-shaped trigger line) B5.

[0044] In this embodiment, the trigger line printing section B comprises a V-shaped trigger line (V-shaped trigger line) B4 and an inverted V-shaped trigger line (inverted V-shaped trigger line) B5, which are formed symmetrically with respect to a second straight line Y that is perpendicular to a first straight line X virtually provided along the folding section 1b. The V-shaped trigger line (V-shaped trigger line) B4 and the inverted V-shaped trigger line (inverted V-shaped trigger line) B5 are formed symmetrically with respect to the first straight line X, and the distance between the V-shaped trigger line (V-shaped trigger line) B4 and the inverted V-shaped trigger line (inverted V-shaped trigger line) B5 is formed to be the shortest possible on the first straight line X.

[0045] Furthermore, if the paper layer 11 is a circular substrate with a diameter of 141 mm that is used for general purposes, and the thickness of the paper layer 11 is within the range of 59 μm to 153 μm, then the distance g2 between the V-shaped trigger line (V-shaped trigger line) B4 and the inverted V-shaped trigger line (inverted V-shaped trigger line) B5 on the first straight line X is, for example, 40 mm. Furthermore, the angle θ formed by the straight sections that create the V-shaped trigger line (V-shaped trigger line) B4 and the inverted V-shaped trigger line (inverted V-shaped trigger line) B5 is, for example, 46.1°.

[0046] Figure 5(d) is a schematic plan view showing that the trigger line printing section B is composed of a U-shaped trigger line (U-shaped trigger line) B6, which is entirely composed of curves, and an inverted U-shaped trigger line (inverted U-shaped trigger line) B7, which is entirely composed of curves. In this embodiment, the trigger line printing section B comprises a U-shaped trigger line (U-shaped trigger line) B6 and an inverted U-shaped trigger line (inverted U-shaped trigger line) B7, which are formed symmetrically with respect to a second straight line Y that is orthogonal to a first straight line X virtually provided along the folding section 1b. The U-shaped trigger line (U-shaped trigger line) B6 and the inverted U-shaped trigger line (inverted U-shaped trigger line) B7 are formed symmetrically with respect to the first straight line X, and the distance between the U-shaped trigger line (U-shaped trigger line) B6 and the inverted U-shaped trigger line (inverted U-shaped trigger line) B7 is formed to be the shortest possible on the first straight line X.

[0047] Furthermore, if the paper layer 11 is a circular substrate with a diameter of 141 mm that is used for general purposes, and the thickness of the paper layer 11 is within the range of 59 μm to 153 μm, then the distance g2 between the U-shaped trigger line (U-shaped trigger line) B6 and the inverted U-shaped trigger line (inverted U-shaped trigger line) B7 on the first straight line X is, for example, 40 mm.

[0048] In this embodiment, the line width of each trigger line printing section B is not particularly limited, but if the paper layer 11 is a circular substrate with a diameter of 141 mm that is used for general purposes, and the thickness of the paper layer 11 is in the range of 59 μm to 153 μm, then for example, it is 3 mm.

[0049] (Printing ink) The printing ink used in this embodiment may be an aqueous solution containing a salt as a solute. The salt contained as a solute in the aqueous solution may be either an organic salt or an inorganic salt, with an inorganic salt being more preferred.

[0050] Examples of inorganic salts include alkali metal chlorides such as lithium chloride (LiCl, hydration parameter: 7.1), sodium chloride (NaCl, hydration parameter: 3.5), potassium chloride (KCl, hydration parameter: 1.9), and rubidium chloride (RbCl, hydration parameter: 1.2); lithium bromide (LiBr, hydration parameter: 7.6), sodium bromide (NaBr, hydration parameter: 4.2), and potassium bromide (KBr, hydration parameter: 1.2). Alkali metal bromides such as sodium iodide (RbBr, hydration parameter: 0.9), rubidium bromide (2.1); alkali metal bromides such as lithium iodide (LiI, hydration parameter: 9.0), sodium iodide (NaI, hydration parameter: 5.5), potassium iodide (KI, hydration parameter: 2.5), rubidium iodide (RbI, hydration parameter: 0.6); magnesium chloride (MgCl2, hydration parameter: 13.7), calcium chloride Chlorides of Group 2 metals such as sodium (CaCl2, hydration parameter: 12.0) and strontium chloride (SrCl2, hydration parameter: 10.7); bromides of Group 2 metals such as magnesium bromide (MgBr2, hydration parameter: 17.0), calcium bromide (CaBr2, hydration parameter: 14.6), and strontium bromide (SrBr2, hydration parameter: 12.7); magnesium iodide (MgI2, hydration parameter: 19.0), yo Examples include iodides of Group II metals such as calcium iodide (CaI2, hydration parameter: 17.0) and strontium iodide (SrI2, hydration parameter: 15.5); and chlorides of transition metals such as manganese chloride (MnCl2, hydration parameter: 11.0), ferrous chloride (FeCl2, hydration parameter: 12.0), cobalt chloride (CoCl2, hydration parameter: 13.0), and nickel chloride (NiCl2, hydration parameter: 13.0).

[0051] In this embodiment, ink containing sodium chloride (NaCl, hydration parameter: 3.5) as the solute in the aqueous solution is most preferred.

[0052] For example, the solute is preferably one with a hydration parameter of 0.5 to 20.0, considering its availability and suitability for use. To facilitate the penetration of water in the aqueous solution into the paper layer 11, a solute with a hydration parameter of, for example, 0.5 to 9 can be selected. To suppress the penetration of water from the aqueous solution into the paper layer 11, a solute with a hydration parameter of, for example, 15-20 can be selected.

[0053] The concentration of the solute in the aqueous solution is not particularly limited, as long as it is below the saturation concentration. For example, the concentration of the solute in the aqueous solution may be 1 to 20 M (mol / L), but if it is 1 to 7 M, the printing process shown in Figure 6(a) and the drying process shown in Figure 6(b), which will be described later, can be carried out more stably.

[0054] [Method for measuring the density of hydroxyl groups] The concentration of hydroxyl groups in the high-hydroxyl group regions (first high-hydroxyl group region and second high-hydroxyl group region) formed by printing can be measured, for example, using the total internal reflection (ATR) method. The instrument used for the actual measurement was a Fourier transform infrared spectrophotometer, product name "IRAffinity-1S," manufactured by Shimadzu Corporation, and the measurement conditions were a resolution of 4 cm. -1 The apodized function (the function used during the Fourier transform) was set to Happ-Genzel, and the number of integration steps was set to 30.

[0055] (Method of manufacturing the lid material 1) The manufacturing method of the lid material 1 according to this embodiment will be briefly described below. The lid material 1 comprises at least a paper substrate 11 and a sealant 122. By printing an ink containing a hydroxyl group-containing substance onto one side (front) of the paper substrate 11 and then leaving it to stand, a high-hydroxyl group region (first high-hydroxyl group region) is formed on one side (front) of the paper substrate 11, where the density of hydroxyl groups is higher than in areas where ink was not printed. Furthermore, by printing an ink containing a hydroxyl group-containing substance onto the other side (back) of the paper substrate 11 and then leaving it to stand, a high-hydroxyl group region (second high-hydroxyl group region) is formed on the other side (back) of the paper substrate 11, where the density of hydroxyl groups is higher than in areas where ink was not printed.

[0056] In this way, a paper substrate 11 with the printing according to this embodiment is formed. Subsequently, a barrier resin layer 121, a sealant 122, other resin layers 123, a light-shielding ink layer 13, and a protective layer 14 are appropriately provided to manufacture the lid material 1 according to this embodiment. With the lid material 1 manufactured in this way, it is possible to autonomously fold the paper substrate 11 by using pressure as a trigger, so that at least the printed area on one side (front surface), namely the center line printed area A, faces inward, or the printed area on the other side (back surface), namely the trigger line printed area B, faces inward, thereby creating multiple structurally stable states.

[0057] (A trigger mechanism that enables gradual autonomous structure formation) The trigger mechanism that enables stepwise autonomous structure formation in this embodiment will be described below. Figure 6 is a schematic cross-sectional view illustrating the trigger mechanism in the lid material 1 according to this embodiment that enables stepwise autonomous structure formation. Figure 7 is a perspective view illustrating the trigger mechanism (particularly the "trigger ON" state and the "trigger OFF" state) in the lid material 1 according to this embodiment that enables stepwise and reversible autonomous structure formation.

[0058] Figure 6(a) is a schematic cross-sectional view showing the state of the paper substrate 11 immediately after printing. Figure 6(b) is a schematic cross-sectional view showing the state of the paper substrate 11 after it has been dried. Following the printing process shown in Figure 6(a), the drying process shown in Figure 6(b) dries the paper layer 11, which has a water concentration gradient (more precisely, a hydroxyl group concentration gradient). As a result, for example as shown in Figure 6(a), the paper layer 11 begins to fold so that one surface (surface) 11a becomes concave in the area with the water concentration gradient, that is, in the centerline printed area A, which is an area with a higher density of hydroxyl groups compared to the unprinted area. As drying (in other words, removal of water 9) progresses, the angle of folding increases, and for example as shown in Figure 6(b), stress is generated in the target paper layer 11 when drying is complete. In this embodiment, by drying the paper layer 11 which has a water concentration gradient (in other words, a region in which the density of hydroxyl groups is higher than in the unprinted region), the paper layer 11 is autonomously folded at the folded portion 1b, which was the part that had the water concentration gradient.

[0059] In the paper layer 11, cellulose molecules are initially bonded together by hydrogen bonds. In the printing process, when water 9 is impregnated into the paper layer 11, one side (surface) 11a expands. It is presumed that within the paper layer 11, water molecules break the hydrogen bonds between cellulose molecules, creating a state where water molecules are interposed between cellulose molecules, and thus forming intermolecular bonds between cellulose molecules, water molecules, and cellulose molecules.

[0060] On the other hand, the paper layer 11 is manufactured in a state where it is strained by external forces due to its manufacturing method. When a drying process is performed on such a paper layer 11 after the printing process, as the water 9 in the paper layer 11 is reduced by drying, the cellulose molecules in the paper layer 11 bond together again by hydrogen bonds. At this time, the paper layer 11 becomes more stable than its initial state, with reduced or eliminated strain, and is presumed to shrink compared to before the penetration of water 9. Due to the shrinkage force generated at this time, the paper layer 11 is presumed to autonomously fold at the folded portion 1b, which is the part that had a water concentration gradient (more precisely, a hydroxyl group concentration gradient), as shown in Figure 6(b).

[0061] In the drying process, the paper layer 11 is autonomously folded so that the side with the higher concentration of water 9 contained in the printing ink (i.e., one side 11a) faces inward (i.e., the other side 11b faces outward).

[0062] When the paper layer 11 is folded autonomously, the folded portion 1b does not necessarily have a clear crease, and the surface of the folded portion 1b on which the center line printed portion A is formed is often curved.

[0063] Figure 7(a) shows a lid material 1 (paper layer 11) having a center line printed section A formed by printing on the surface, and a U-shaped trigger line B6 and an inverted U-shaped trigger line B7 formed by printing on the back surface. In the lid material 1 (paper layer 11) as shown in Figure 7(a), stress is generated in a way that causes the surface of the lid material 1 (paper layer 11) to fold inward, due to the center line printing area A. In addition, in the lid material 1 (paper layer 11) as shown in Figure 7(a), folds are formed by a U-shaped trigger line B6 and an inverted U-shaped trigger line B7 to counteract the stress caused by the center line printing area A. In other words, in the lid material 1 (paper layer 11) as shown in Figure 7(a), the stress generated by the center line printing area A is accumulated by the U-shaped trigger line B6 and the inverted U-shaped trigger line B7. In this embodiment, this state of accumulated stress is conveniently referred to as "trigger ON".

[0064] When pressure is applied from the surface side of the lid material 1 (paper layer 11) in the form shown in Figure 7(a), where stress has accumulated, the inhibiting force due to the fold formed in the lid material 1 (paper layer 11) is overcome by the stress generated by the center line printing area A, causing the lid material 1 (paper layer 11) to fold inward with its surface facing inward, as shown in Figure 7(b). This shape (structurally stable state) is then maintained. In this embodiment, the state in which this stress is released is conveniently referred to as "trigger OFF".

[0065] Next, when pressure is applied from the surface side of the lid material 1 (paper layer 11) in the form shown in Figure 7(b), which represents the stress-released state, to the portion of the lid material 1 (paper layer 11) other than the centerline printed area A, the stress generated by the centerline printed area A is overcome by the inhibiting force created by the folds formed in the lid material 1 (paper layer 11), and the lid material 1 (paper layer 11) is flattened as shown in Figure 7(a). This shape (structurally stable state) is then maintained. In this way, the "trigger ON" state is formed again.

[0066] In this way, by forming the center line printed section A, which is formed by printing, on the surface of the lid material 1 (paper layer 11), and forming the trigger line printed section B, which is formed by printing, on the back surface of the lid material 1 (paper layer 11), it becomes possible to form an autonomous structure in stages and in a reversible manner, triggered by pressure.

[0067] (Usage of lid material 1) The following describes an example of how the lid material 1 is used in this embodiment. Figure 8 is a perspective view illustrating an example of how the lid material 1 is used according to this embodiment. Figure 8(a) shows the state in which the lid material 1 in the form shown in Figure 7(a), which represents a state where stress has accumulated, i.e., the "trigger ON" state, is heat-sealed to the flange 2a on the periphery of the upper opening of the container body 2, thereby sealing the opening. Next, when pressure (trigger) is applied from the surface side of the lid material 1 to the center line printed area A of the lid material 1, which is in the "trigger ON" state, the stress generated by the center line printed area A is released, and as shown in Figure 8(b), a part of the lid material 1 folds and opens.

[0068] Next, as shown in Figure 8(c), pour hot water into the lid material 1 while it is partially folded and opened. Next, as shown in Figure 8(d), a stress is manually applied to the partially bent lid material 1, which is in the "trigger OFF" state. In this way, as shown in Figure 8(e), the lid material 1 is flattened and returned to the "trigger OFF" state. Finally, pressure (trigger) is applied again to the centerline printed area A of the lid material 1, which is in the "trigger ON" state, from the surface side of the lid material 1, as shown in Figure 8(f). In this way, the stress generated by the centerline printed area A is released, and a part of the lid material 1 is bent, as shown in Figure 8(g), to bring it to the "trigger OFF" state.

[0069] Thus, with the lid material 1 of this embodiment, it is possible to open and close the lid material 1 with easy operation. In other words, with the lid material 1 of this embodiment, high usability can be achieved by utilizing a structural change triggered by pressure.

[0070] [Examples] The lid material 1 according to this embodiment will be described below with reference to examples. Note that the lid material 1 according to this embodiment is not limited to these examples.

[0071] <Example 1> First, an ink containing a substance with hydroxyl groups was printed on one side (surface) of the paper substrate 11, and then left to stand. This formed a central line printed area A (surface printed area A) on one side (surface) of the paper substrate 11, which is a high-concentration hydroxyl group region (first high-concentration hydroxyl group region) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. Next, an ink containing a hydroxyl group-containing substance was printed on the other side (back side) of the paper substrate 11, and then left to stand. This formed a trigger line printing area B (circular trigger line B1) on the other side (back side) of the paper substrate 11, which is a high-hydroxyl group concentration area (second high-hydroxyl group concentration area) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. In this way, the lid material 1 according to Example 1 was formed.

[0072] <Example 2> First, an ink containing a substance with hydroxyl groups was printed on one side (surface) of the paper substrate 11, and then left to stand. This formed a central line printed area A (surface printed area A) on one side (surface) of the paper substrate 11, which is a high-concentration hydroxyl group region (first high-concentration hydroxyl group region) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. Next, an ink containing a substance containing hydroxyl groups was printed on the other side (back side) of the paper substrate 11, and then left to stand. This formed a trigger line printing area B (V-shaped curve composite trigger line B2 and inverted V-shaped curve composite trigger line B3) on the other side (back side) of the paper substrate 11, which is a high-hydroxyl group concentration area (second high-hydroxyl group concentration area) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. In this way, the lid material 1 according to Example 2 was formed.

[0073] <Example 3> First, an ink containing a substance with hydroxyl groups was printed on one side (surface) of the paper substrate 11, and then left to stand. This formed a central line printed area A (surface printed area A) on one side (surface) of the paper substrate 11, which is a high-concentration hydroxyl group region (first high-concentration hydroxyl group region) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. Next, an ink containing a hydroxyl group-containing substance was printed on the other side (back side) of the paper substrate 11, and then left to stand. This formed a trigger line printing area B (V-shaped trigger line B4 and inverted V-shaped trigger line B5) on the other side (back side) of the paper substrate 11, which is a high-hydroxyl group concentration area (second high-hydroxyl group concentration area) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. In this way, the lid material 1 according to Example 3 was formed.

[0074] <Example 4> First, an ink containing a substance with hydroxyl groups was printed on one side (surface) of the paper substrate 11, and then left to stand. This formed a central line printed area A (surface printed area A) on one side (surface) of the paper substrate 11, which is a high-concentration hydroxyl group region (first high-concentration hydroxyl group region) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. Next, an ink containing a hydroxyl group-containing substance was printed on the other side (back side) of the paper substrate 11, and then left to stand. This formed a trigger line printing area B (U-shaped trigger line B6 and inverted U-shaped trigger line B7) on the other side (back side) of the paper substrate 11, which is a high-hydroxyl group concentration area (second high-hydroxyl group concentration area) where the density of hydroxyl groups is higher than in the areas where the ink was not printed. In this way, the lid material 1 according to Example 4 was formed.

[0075] (Confirmation of deadhold capability) In this embodiment, the presence or absence of deadhold properties was determined by measuring the "rise angle β" of the lid material 1 according to Examples 1 to 4. In this embodiment, the "rising angle β" refers to the bending angle of the lid material 1 placed on the mounting base 3 when it changes from the "trigger ON" state (see Figure 7(a)) to the "trigger OFF" state (see Figure 7(b)), as shown in Figure 9.

[0076] In this example, it was determined that if the rising angle β of the lid material 1 is "90°" or greater, there are no problems in use and it is evaluated as having excellent dead-hold properties. In all of the lid materials 1 in Examples 1 to 4 of this embodiment, the rising angle β was "90°" or greater. Thus, the lid material 1 according to Examples 1 to 4 of this embodiment has excellent dead-hold properties.

[0077] Furthermore, the lid material 1 according to Examples 1 and 2 of this embodiment had a larger rising angle β than the lid material 1 according to Examples 3 and 4 of this embodiment. Thus, with the lid material 1 according to Examples 1 to 4 of this embodiment, when pressure is applied to close the lid material 1, the trigger on the back surface is activated, and the lid material 1 returns to a flat state. Furthermore, it was confirmed that in all of Examples 1 to 4, the lid material 1 does not return in the opening direction, and that the sealing function is sufficient. In particular, it was confirmed that the lid material 1 according to Examples 1 and 2 can maintain better flatness than the lid material 1 according to Examples 3 and 4.

[0078] Furthermore, for example, the present invention can take the following configuration. (1) A lid material that seals the upper opening of the container body, It comprises at least a paper substrate and a sealant, A lid material characterized by printing on both sides of the aforementioned paper substrate and leaving it to stand, thereby forming a region with a high density of hydroxyl groups compared to other unprinted areas, and by autonomously folding the paper substrate with one side facing inward at the printed area, creating multiple stable states. (2) The basis weight of the paper substrate before printing is 50 g / m². 2 More than 150g / m 2 The lid material described in (1) above, characterized in that it is within the following range. (3) The lid material according to (1) or (2) above, further comprising a protective layer on the side of the paper substrate opposite to the sealant side. (4) The lid material according to any one of (1) to (3) above, characterized in that the paper substrate is printed on both sides using a solute that is either an organic salt or an inorganic salt. (5) The lid material according to any one of (1) to (3) above, characterized in that the printing using sodium chloride as a solute is applied to both sides of the paper substrate. (6) The paper substrate is provided with a straight folding portion for folding the paper substrate, On the surface of the paper substrate opposite to the sealant side, a surface printing portion is formed by the printing. On the back surface of the paper substrate, which is the sealant side, a trigger line printing area is formed by the printing. The surface printed portion is formed in a strip shape along the folded portion, The lid material according to any one of (1) to (5) above, characterized in that the trigger line printing portion is formed in a circular shape with respect to a point virtually provided in the folding portion. (7) The paper substrate is provided with a straight folding portion for folding the paper substrate, On the surface of the paper substrate opposite to the sealant side, a surface printing portion is formed by the printing. On the back surface of the paper substrate, which is the sealant side, a trigger line printing area is formed by the printing. The surface printed portion is formed in a strip shape along the folded portion, The trigger line printing section comprises a composite trigger line having a curved portion in part of a V-shape, formed symmetrically with respect to a second straight line perpendicular to a first straight line virtually provided along the bending section, and a composite trigger line having a curved portion in part of an inverted V-shape. The cover material according to any one of (1) to (5) above, characterized in that the composite trigger line having a curved portion in part of the V-shape and the composite trigger line having a curved portion in part of the inverted V-shape are each formed symmetrically with respect to the first straight line. (8) A method for manufacturing a lid material that seals the upper opening of a container body, The aforementioned lid material comprises at least a paper substrate and a sealant, A step of printing an ink containing a substance containing hydroxyl groups onto one side of the paper substrate, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on one side of the paper substrate where the density of hydroxyl groups is higher than in the area where the ink was not printed. The process includes printing an ink containing a substance containing hydroxyl groups onto the other side of the paper substrate, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on the other side of the paper substrate where the density of hydroxyl groups is higher than in the areas where the ink was not printed. A method for manufacturing a lid material, characterized by autonomously folding the paper substrate by using pressure as a trigger, so that in the area where the ink is printed on one surface, the one surface faces inward, or in the area where the ink is printed on the other surface, the other surface faces inward, thereby creating multiple structurally stable states. (9) A method for manufacturing a lid material as described in any one of the above items (1) to (7), A step of printing an ink containing a substance containing hydroxyl groups onto the surface side of the paper substrate, which is the side opposite to the sealant side, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on the surface where the density of hydroxyl groups is higher than in the areas where the ink was not printed. The process includes printing an ink containing a substance containing hydroxyl groups onto the back side of the paper substrate, which is the sealant side, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on the back side where the density of hydroxyl groups is higher than in the areas where the ink was not printed. A method for manufacturing a lid material, characterized in that, at least triggered by pressure, the paper substrate is autonomously folded by deforming it so that the printed surface of the ink on the surface faces inward, or the printed back surface of the ink on the back surface faces inward, thereby creating multiple structurally stable states. [Explanation of symbols]

[0079] 1 Lid material 1a Opening tab 1b Folded section 11 paper layer 11a One side (surface) 11b The other side (back side) 12 Multilayer resin layer 121 Barrier resin layer 122 Heat-sealable resin layer (sealant) 123 Other resin layers 13 Light-blocking ink layer 14 Protective layer A Surface printing section (center line printing section) B Trigger line printing section B1 Trigger line printing area (circular trigger line) B2 Trigger line printing area (V-shaped curve composite trigger line) B3 Trigger line printing area (reverse V-shaped curve composite trigger line) B4 Trigger line printing area (V-shaped trigger line) B5 trigger line printing area (inverted V-shaped trigger line) B6 Trigger line printing area (U-shaped trigger line) B7 Trigger line printing area (inverted U-shaped trigger line) 2. Container body 2a Flange 3 Installation stand X is a first hypothetical straight line. Y is a second hypothetical straight line. Z is a virtually defined center point. d Printing width of the surface printing area g1 Diameter of the trigger line printing area g2 Distance between trigger line printing areas

Claims

1. A lid material that seals the upper opening of the container body, It comprises at least a paper substrate and a sealant, A lid material characterized by printing on both sides of the aforementioned paper substrate and leaving it to stand, thereby forming a region with a high density of hydroxyl groups compared to other unprinted areas, and by autonomously folding the paper substrate with one side facing inward at the printed area, creating multiple stable states.

2. The basis weight of the paper substrate before printing is 50 g / m². ２ 150g / m or more ２ The lid material according to claim 1, characterized in that it is within the following range.

3. The lid material according to claim 1, further comprising a protective layer on the side of the paper substrate opposite to the sealant side.

4. The lid material according to claim 1, characterized in that the printing using a solute that is either an organic salt or an inorganic salt is applied to both sides of the paper substrate.

5. The lid material according to claim 1, characterized in that the printing using sodium chloride as a solute is applied to both sides of the paper substrate.

6. The paper substrate is provided with a straight folding portion for folding the paper substrate, On the surface of the paper substrate opposite to the sealant side, a surface printing portion is formed by the printing. On the back surface of the paper substrate, which is the sealant side, a trigger line printing area is formed by the printing. The surface printed portion is formed in a strip shape along the folded portion, The lid material according to claim 1, characterized in that the trigger line printing portion is formed in a circular shape with respect to a point virtually provided in the folding portion.

7. The paper substrate is provided with a straight folding portion for folding the paper substrate, On the surface of the paper substrate opposite to the sealant side, a surface printing portion is formed by the printing. On the back surface of the paper substrate, which is the sealant side, a trigger line printing area is formed by the printing. The surface printed portion is formed in a strip shape along the folded portion, The trigger line printing section comprises a composite trigger line having a curved portion in a part of a V shape, formed symmetrically with respect to a second straight line perpendicular to a first straight line virtually provided along the bending section, and a composite trigger line having a curved portion in a part of an inverted V shape. The cover material according to claim 1, characterized in that the composite trigger line having a curved portion in part of the V-shape and the composite trigger line having a curved portion in part of the inverted V-shape are each formed symmetrically with respect to the first straight line.

8. A method for manufacturing a lid material that seals the upper opening of a container body, The aforementioned lid material comprises at least a paper substrate and a sealant, A step of printing an ink containing a substance containing hydroxyl groups onto one side of the paper substrate, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on one side of the paper substrate where the density of hydroxyl groups is higher than in the area where the ink was not printed. The process includes printing an ink containing a substance containing hydroxyl groups onto the other side of the paper substrate, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on the other side of the paper substrate where the density of hydroxyl groups is higher than in the areas where the ink was not printed. A method for manufacturing a lid material, characterized by autonomously folding the paper substrate by using pressure as a trigger, so that in the area where the ink is printed on one surface, the one surface faces inward, or in the area where the ink is printed on the other surface, the other surface faces inward, thereby creating multiple structurally stable states.

9. A method for manufacturing a lid according to any one of claims 1 to 7, A step of printing an ink containing a substance containing hydroxyl groups onto the surface side of the paper substrate, which is the side opposite to the sealant side, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on the surface where the density of hydroxyl groups is higher than in the areas where the ink was not printed. The process includes printing an ink containing a substance containing hydroxyl groups onto the back side of the paper substrate, which is the sealant side, and then leaving it to stand, thereby forming a high-concentration region of hydroxyl groups on the back side where the density of hydroxyl groups is higher than in the areas where the ink was not printed. A method for manufacturing a lid material, characterized in that, at least triggered by pressure, the paper substrate is autonomously folded by deforming it so that the printed surface of the ink on the surface faces inward, or the printed back surface of the ink on the back surface faces inward, thereby creating multiple structurally stable states.

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