Paper lid

Abstract

[Problem] To provide a paper lid that can be molded into a so-called dome shape with a top sheet bulging upward and that can effectively suppress leakage of contents through a wrinkle or seam. [Solution] A paper lid 1 that fits onto a curled portion 28 of a paper container 2 having the curled portion 28 curved and formed at an upper end, the paper lid 1 comprising a top sheet part 11, a side wall section 12, and a peripheral edge part OEP. The peripheral edge part OEP comprises: an outer extension part 13 that extends to the outside along the outer periphery of the side wall section 12; and an annular recess 14 that can be fitted onto the curled portion 28 and is curved and formed so as to protrude upward along the outer periphery of the outer extension part 13. Before the annular recess 14 is fitted onto the curled portion 28, the curvature radius R1-1 of a curve extending from the top part of the annular recess 14 to the outside is smaller than the curvature radius R2 of a curve extending from the top part of the curled portion 28 to the outside.

Description

paper lid

[0001] The present invention relates to a paper lid.

[0002] Plastic and other resin lids are used as lids for paper containers such as paper cups. However, when discarding plastic lids, they must be separated from the paper cups and paper containers, which is a hassle for consumers. In particular, as a measure against global warming, there is a demand to reduce the amount of resin used and CO2 emissions, and there is an increasing shift from plastic lids to paper lids.

[0003] Lids can generally be broadly divided into two types: flat lids with a flat top and lids with a bulging top. Flat lids are used for cold drinks that are consumed with a straw, while hot drinks that are consumed directly from the container or that are topped with cream or other toppings often use dome-shaped lids with a bulging top.

[0004] Patent Document 1 describes a flat-shaped paper lid. The paper lid disclosed in Patent Document 1 allows a container to be fitted freely with an annular recess formed by an inner fitting portion, a top, and an outer fitting portion provided on the outer periphery of the top plate. However, this paper lid is configured so that the top plate is recessed into the inner surface of the container, and the annular recess is raised above the top plate. This poses a problem in that it is difficult to apply to types of drinks that are consumed directly from the container, such as hot beverages, or types that are topped with cream or other toppings.

[0005] Furthermore, such paper lids are manufactured by drawing, and wrinkles occur due to the compressive force applied to the paper during this drawing. If these wrinkles occur from the inner fitting portion to the top, there is a risk that the contents of the container will leak through the wrinkles. Furthermore, there is a risk that the contents of the container will leak through the seam where the blanks are overlapped when the paper container is formed into a cylindrical shape. Until now, no paper lids have been devised that can effectively prevent leakage of contents through such wrinkles and seams.

[0006] International Publication No. 2020 / 049769

[0007] The present invention was devised in consideration of the above-mentioned problems, and its purpose is to provide a paper lid that can be molded into a so-called dome shape with a top plate that bulges upward, and that can effectively prevent leakage of contents through wrinkles and seams.

[0008] The paper lid of the present invention is a paper lid that fits onto a curled portion of a paper container having a curled portion formed and curved at the upper end, and comprises: a top plate portion; a side wall portion that is arranged along the outer periphery of the top plate portion and extends downward, and is continuous with the top plate portion; and a peripheral portion that is arranged along the outer periphery of the side wall portion and extends outward, and is continuous with the side wall portion, and the peripheral portion has an extending portion that extends outward along the outer periphery of the side wall portion, and an annular recess that can fit onto the curled portion and is curved so as to be convex upward along the outer periphery of the extending portion, and is characterized in that before the annular recess is fitted onto the curled portion, the radius of curvature of the curve extending from the top of the annular recess to the outside is smaller than the radius of curvature of the curve extending from the top of the curled portion to the outside.

[0009] According to the present invention having the above-described configuration, the top plate can be molded into a so-called dome shape, bulging upward. Furthermore, before the annular recess is fitted to the curled portion, the radius of curvature of the curve extending from the top of the annular recess to the outside is smaller than the radius of curvature of the curve extending from the top of the curled portion to the outside. This allows the annular recess to be fitted to the curled portion, sandwiching the curled portion between the first and second contact portions, effectively preventing leakage of the contents of the paper container through wrinkles or seams.

[0010] FIG. 1 is an exploded perspective view of a paper lid according to an embodiment of the present invention and a paper container to which the paper lid is fitted. FIG. 2(a) is a schematic plan view showing an example of a paper lid according to an embodiment of the present invention, and FIG. 2(b) is a schematic cross-sectional view taken along line IB-IB in FIG. 2(a). FIG. 3 is a schematic cross-sectional view showing an enlarged view of the area within the dashed frame II in FIG. 2(b). FIG. 4 is a schematic plan view showing the arrangement of the outer and inner convex portions of the paper lid. FIG. 5(a) is a schematic cross-sectional view of the side wall portion, and FIG. 5(b) is a schematic cross-sectional view of the annular recess portion. FIGS. 6(a) to 6(c) are diagrams illustrating the operation of fitting a paper lid to a paper container. FIG. 7 is a diagram showing X-ray cross-sectional views of paper lids in Example 1 and Comparative Example 1, as well as the results of a leakage test. FIGS. 8(a) and 8(b) are diagrams illustrating a clamping test. Fig. 9 shows X-ray cross-sections of paper lids in Example 2 of the present invention and Comparative Example 2, the materials, and the results of clamping pressure strength. Fig. 10 shows cross-sections of the ruled lines of blanks constituting paper lids in Example 3 of the present invention and Comparative Example 3, X-ray cross-sections of the paper lids, and the results of a leakage test. Fig. 11 is a diagram for explaining a method for calculating the void area in a cross-sectional view at a wrinkle. Fig. 12(a) is a diagram for explaining the measurement points of the void area in a cross-sectional view at a wrinkle in Example 4 of the present invention, and Fig. 12(b) is a diagram for explaining an X-ray cross-section of the paper lid in Example 4 of the present invention and the results of the void area in a cross-sectional view at a wrinkle.

[0011] Hereinafter, an embodiment of a paper lid to which the present invention is applied will be described in detail with reference to the drawings.

[0012] (Paper Lid) As shown in Figures 1, 2(a), 2(b), and 3, the paper lid 1 is made of a blank 10 mainly made of paper, and includes a top plate 11, a side wall 12, an extension 13, an annular recess 14, and a flange 15. The paper lid 1 has, for example, a circular shape when viewed from above. The paper container 2 is a cylindrical paper cup with a bottom that has an opening with a curled portion 28 at its top and is often used to hold and sell beverages 6 such as juice or coffee. The paper container 2 is made by forming blanks into a cylindrical shape, and a seam (not shown) is formed where the blanks overlap each other.

[0013] 2 and 3, the outer side (direction X1) refers to the outward direction from the paper container 2, for example, a paper cup, to be fitted, the lower side (direction X2) refers to the downward direction when the paper container 2 is placed via its bottom surface, and the upper side (direction X3) refers to the upward direction when the paper container 2 is placed via its bottom surface. Furthermore, the inner side (direction X4) refers to the inward direction from the paper container 2, for example, a paper cup, to be fitted. However, these lower side (direction X2) and upper side (direction X3) are not limited to completely vertically downward and vertically upward, but also include diagonally downward and diagonally upward directions that deviate from vertically downward and vertically upward directions.

[0014] Furthermore, the top plate portion 11 and the side wall portion 12 are responsible for the function of preventing the contents of the paper container 2 from scattering or leaking as the original lid of the paper lid 1, while the remaining peripheral portion OEP (extension portion 13, annular recess 14, flange portion 15) functions to fit into the paper container 2.

[0015] The top plate portion 11 extends outward (in the direction X1). The top plate portion 11 has a top surface and a container surface. The container surface of the top plate portion 11 is located on the reverse side of the top surface of the top plate portion 11. When the paper lid 1 is fitted to the paper container 2, the container surface of the top plate portion 11 faces the inner surface of the paper container 2. Although not shown in the drawings, a predetermined cut or the like may be formed in the top plate portion 11, and a drinking spout may be formed by pressing the cut or the like.

[0016] The side wall portion 12 is provided along the outer periphery of the top plate portion 11 and extends downward (in the direction X2) beyond the top plate portion 11. This side wall portion 12 is configured to be continuous with the top plate portion 11. In this case, the side wall portion 12 may be molded so that its diameter gradually increases downward, in other words, so that it slopes outward in a side cross-sectional view. The side wall portion 12 is inclined, for example, by approximately 7° relative to the vertical direction. Furthermore, the continuous portion between the side wall portion 12 and the top plate portion 11 may be molded into a rounded, streamlined shape. The side wall portion 12 having such a shape allows the top plate portion 11 to be closed in a position spaced apart from the paper container 2. Furthermore, the top plate portion 11 and the side wall portion 12 can be molded into a dome shape that bulges upward, making it applicable to types that are consumed directly from the container, such as hot beverages, and types that are topped with cream or other toppings.

[0017] The extension portion 13 is provided on the peripheral edge portion OEP of the paper lid 1 along the outer periphery of the side wall portion 12 and extends outward (in the direction X1). This extension portion 13 is configured to be continuous with the side wall portion 12. The extension portion 13 is curved to be convex downward. In the direction X1, when the width X from the upper end of the side wall portion 12 to the end of the extension portion 13 on the annular recess 14 side is defined as X, and the radius of curvature Y of the bottom of the extension portion 13 is defined as Y, it is preferable that X > 2Y. In this case, the side wall portion 12 is molded so that its diameter gradually increases downward, in other words, so that it slopes outward in a side cross-sectional view. In this case, when the annular recess 14 is fitted into the curled portion 28 of the paper container 2, the extension portion 13 tends to flex and return, making it easier for the annular recess 14 to come into contact with the inner surface of the curled portion 28. Although not shown in the figure, the extension portion 13 may be provided on the peripheral portion OEP of the paper lid 1 along the outer periphery of the side wall portion 12 and extend horizontally outward (in the direction X1).

[0018] The annular recess 14 is provided on the peripheral edge portion OEP of the paper lid 1 along the outer periphery of the outward extending portion 13 and is curved so as to be convex upward. The annular recess 14 is configured to be continuous with the outward extending portion 13. The annular recess 14 can be fitted into the curled portion 28 of the paper container 2.

[0019] When the annular recess 14 is fitted to the curled portion 28 of the paper container 2, the annular recess 14 comes into contact with the curled portion 28 at a first contact portion P1 on the inner surface of the curled portion 28 and a second contact portion P2 located outside the first contact portion P1. A gap is formed between the annular recess 14 and the curled portion 28, between the first contact portion P1 and the second contact portion P2. The first contact portion P1 and the second contact portion P2 are located at different positions, on the inside and outside of the top of the curled portion 28. In this way, the annular recess 14 can be fitted to sandwich the curled portion 28 at the first contact portion P1 and the second contact portion P2, effectively preventing leakage of the contents of the paper container 2.

[0020] The flange portion 15 is provided on the peripheral edge portion OEP along the outer periphery of the annular recess 14 and extends downward. The flange portion 15 is configured to be continuous with the annular recess 14. The flange portion 15 has an under rib 16, an overlapping portion 17, and a protrusion 18.

[0021] The under-rib 16 is continuous with the annular recess 14 and extends downward beyond the annular recess 14. The under-rib 16 is disposed inside an outer edge end 14a on the outermost edge side of the annular recess 14.

[0022] The overlapping portion 17 is formed by folding back the blank 10 and overlapping it on itself. The overlapping portion 17 is formed continuous with the under-rib 16. The overlapping portion 17 has a first portion extending outward from the under-rib 16 and a second portion extending downward from the outwardly extending first portion. The overlapping portion 17 has an outer layer portion 17a disposed on the outside and an inner layer portion 17b bonded to the inner surface of the outer layer portion 17a.

[0023] The protrusion 18 is formed continuously along the inner layer 17b of the overlapping portion 17. The protrusion 18 protrudes inward from the under-rib 16. The protrusion 18 is positioned on the same plane as the first portion extending outward from the inner layer 17b. This allows the protrusion 18 to come into contact with the curled portion 28 even if the paper lid 1 attempts to come off the paper container 2, thereby preventing the paper lid 1 fitted to the paper container 2 from coming off. The horizontal protrusion width of the protrusion 18 is preferably less than 1 mm, more preferably 0.4 mm to 0.8 mm. Although not shown in the drawings, in the present invention, the protrusion 18 may be omitted and the tip of the overlapping portion 17 may be positioned at the position of the under-rib 16.

[0024] By forming such a flange portion 15 , when the annular recess 14 is fitted to the paper container 2 , it is possible to guide the paper container 2 into the annular recess 14 via this flange portion 15 .

[0025] In a cross section of the paper lid 1, the paper lid 1 bends downward (in the direction X2) at the side wall portion 12, bends outward (in the direction X1) at the extension portion 13, curves so as to be convex upward at the annular recess 14, and bends outward (in the direction X1) and downward (in the direction X2) at the flange portion 15. In other words, the top plate portion 11, the side wall portion 12, the extension portion 13, the annular recess 14, and the flange portion 15 are each obtained from a single blank 10.

[0026] In a paper lid 1 having such a shape, the boundaries between the top plate portion 11 and the side wall portion 12, the boundary between the side wall portion 12 and the extension portion 13, the boundary between the extension portion 13 and the annular recess 14, and the boundary between the annular recess 14 and the flange portion 15 may be defined as, for example, the inflection points or the vicinity of the inflection points that occur when the blank 10 is extruded.

[0027] Wrinkles are formed outward at least on the peripheral edge portion OEP (extending portion 13, annular recess 14, flange portion 15) of the paper lid 1. These wrinkles are naturally generated by the compressive force applied to the blank 10 during the drawing process. Many of these wrinkles are present on both the inner and outer surfaces of the peripheral edge portion OEP, and are formed around the entire circumference of the paper lid 1.

[0028] As shown in Fig. 4, the inner surface of the side wall portion 12 has inner surface convex portions 102 that protrude toward the inner surface, and the outer surface of the peripheral edge portion OEP has outer surface convex portions 104 that protrude toward the outer surface. The inner surface convex portions 102 and the outer surface convex portions 104 are arranged radially. The outer surface convex portions 104 are arranged on the opposite side of the inner surface convex portions 102 on an extension line extending circumferentially outward.

[0029] As shown in Figure 5(a), the inner surface of the side wall 12 has inner convex portions 102 that protrude inward due to vertical outer ruling lines 101 formed on the outer surface of the blank 10. The outer surface of the side wall 12 is the part that comes into contact with the user's mouth when drinking the liquid contents in the paper container 2, so by having the inner convex portions 102 on the inner surface of the side wall 12, unevenness on the outer surface of the side wall 12 can be reduced, resulting in a better mouthfeel. Wrinkles S are formed on the inner surface of the side wall 12.

[0030] As shown in FIG. 5( b), the outer surface of the peripheral edge portion OEP has outer convex portions 104 that protrude outward due to vertical inner ruling lines 103 formed on the inner surface of the blank 10. Wrinkles S are formed on the inner surface side of the peripheral edge portion OEP. By providing the outer convex portions 104 on the outer surface of the peripheral edge portion OEP, the size of the wrinkles S that occur on the inner surface side can be reduced. As a result, the void area of ​​the wrinkles S can be reduced. The void area here indicates the cross-sectional area of ​​the wrinkles S and can be calculated from the relationship between the depth and width of the wrinkles S. This void area can be calculated by imaging the cross section with an optical microscope and then calculating the void area from the captured image.

[0031] Such outer surface convex portions 104 need only be provided at least on the annular recess 14. The annular recess 14 can be fitted into the curled portion 28 of the paper container 2 by contacting the curled portion 28. At this time, by forming the outer surface convex portions 104 on the outer surface of the annular recess 14, wrinkles S formed on the surface of the annular recess 14 that contacts the curled portion 28 can be reduced, and the liquid contents in the paper container 2 can be effectively prevented from leaking out along the wrinkles S.

[0032] In conventional paper lids made by drawing, the size of the wrinkles increases toward the outside in the circumferential direction, so the gap area of ​​the wrinkles in the annular recess is larger than the gap area of ​​the wrinkles in the side wall 12. In this regard, in the present invention, since the outer surface of the annular recess 14 has the outer surface-side convex portion 104, the gap area of ​​the wrinkles S in the annular recess 14 is smaller than the gap area of ​​the wrinkles S in the side wall 12.

[0033] Next, a method for fitting the paper lid 1 to the paper container 2 will be described.

[0034] As shown in Figure 6(a), first, the paper lid 1 is placed above the paper container 2. Before the annular recess 14 is fitted into the curled portion 28, the radius of curvature R1-1 of the curve extending from the top of the annular recess 14 to the outside is smaller than the radius of curvature R2 of the curve extending from the top of the curled portion 28 to the outside.

[0035] As shown in Fig. 6(b), the paper lid 1 is moved downward toward the paper container 2. As a result, the protruding piece 18 formed by the blank 10 comes into contact with the curled portion 28, and the protruding piece 18 is bent upward.

[0036] As shown in Figure 6 (c), the paper lid 1 is moved further downward toward the paper container 2. This allows the annular recess 14 to fit around the curled portion 28 at the first contact portion P1 and the second contact portion P2. When the annular recess 14 is fitted to the curled portion 28, the protruding piece 18, which had been bent upward, returns to its original position, and the protruding piece 18 is positioned on the same plane as the first portion extending outward from the inner layer portion 17b. A sound is generated when the protruding piece 18, which had been bent upward, returns to its original position, making it easy to know that the annular recess 14 has been fitted around the curled portion 28.

[0037] When the annular recess 14 formed by the blank 10 is fitted into the curled portion 28, the annular recess 14 deforms so as to expand on both sides of its apex. Therefore, after the annular recess 14 is fitted into the curled portion 28, the radius of curvature R1-2 of the curve extending outward from the apex of the annular recess 14 becomes larger than the radius of curvature R1-1 of the curve extending outward from the apex of the annular recess 14 before fitting. Furthermore, the radius of curvature R1-2 of the curve extending outward from the apex of the annular recess 14 becomes equal to or larger than the radius of curvature R2 of the curve extending outward from the apex of the curled portion 28.

[0038] This completes the method for fitting the paper lid 1 to the paper container 2.

[0039] One example of a method for calculating the radius of curvature is to take an X-ray cross-sectional view of the paper lid 1 and create a CAD drawing from the X-ray cross-sectional view. Then, based on the CAD drawing of the paper lid 1, the radius of curvature R1-1, radius of curvature R1-2, radius of curvature R2, etc. can be calculated.

[0040] According to this embodiment, before the annular recess 14 is fitted into the curled portion 28, the radius of curvature of the curve extending from the top of the annular recess 14 to the outside is smaller than the radius of curvature of the curve extending from the top of the curled portion 28 to the outside. As a result, when the annular recess 14 is fitted into the curled portion 28, the annular recess 14 can be fitted to sandwich the curled portion 28 at the first contact portion P1 and the second contact portion P2, thereby effectively preventing leakage of the contents of the paper container 2 through wrinkles or seams.

[0041] According to this embodiment, the side wall portion 12 is inclined outward from the outer periphery of the top plate portion 11. As a result, when the annular recess 14 is fitted into the curled portion 28 of the paper container 2, the outward extending portion 13 tends to bend and return to its original position (to expand in the outward direction X1), making it easier for the annular recess 14 to come into contact with the inner surface of the curled portion 28.

[0042] According to this embodiment, the extending portion 13 is curved so as to be convex downward. As a result, when the annular recess 14 is fitted into the curled portion 28 of the paper container 2, the curved extending portion 13 bends and returns to its original shape more strongly, making it easier for the annular recess 14 to come into contact with the inner surface of the curled portion 28. Furthermore, by curving the extending portion 13 so as to be convex downward, it is possible to reduce the amount of content that accumulates between the extending portion 13 and the inner surface of the container when, for example, the paper container 2 is tilted, thereby reducing the amount of remaining liquid in the content.

[0043] According to this embodiment, the blank 10 has a flange portion 15 that is provided along the outer periphery of the annular recess 14, extends downward, and is continuous with the annular recess 14, and the flange portion 15 has an overlapping portion 17 where the blank 10 is folded back and overlapped on top of each other. This improves the clamping strength of the paper lid 1 compared to a paper lid that does not have an overlapping portion 17. If the clamping strength is low, the lid will bend and the handleability (ease of gripping the lid) will be reduced. However, because the clamping strength of the paper lid 1 can be improved, the paper lid 1 is less likely to bend when gripped, and the handleability of the paper lid 1 can be improved.

[0044] According to this embodiment, the overlapping portion 17 has an outer layer portion 17a arranged on the outside and an inner layer portion 17b bonded to the inner surface of the outer layer portion 17a, and the flange portion 15 further has an under-rib 16 continuous with the annular recess 14 and the outer layer portion 17a, the under-rib 16 being arranged inwardly of the outer edge end portion 14a arranged on the outermost side of the annular recess 14, and the flange portion 15 further has a protrusion 18 continuous with the inner layer portion 17b and protruding inwardly of the under-rib 16.

[0045] As a result, when the annular recess 14 is fitted into the curled portion 28, the protruding piece 18 that was bent upward returns to its original position, and the protruding piece 18 is positioned on the same plane as the first portion that extends outward from the inner layer portion 17b. Because a sound is generated when the protruding piece 18 that was bent upward returns to its original position, it is easy to know that the annular recess 14 has been fitted into the curled portion 28. Furthermore, even if the paper lid 1 tries to come off the paper container 2, the protruding piece 18 can be brought into contact with the curled portion 28, which prevents the paper lid 1 from coming off the paper container 2.

[0046] According to this embodiment, the inner surface of the side wall 12 has an inner surface convex portion 102 that protrudes inward due to an outer ruled line 101 in the vertical direction formed on the outer surface of the blank 10. The outer surface of the side wall 12 is the part that comes into contact with the user's mouth when drinking the liquid contents in the paper container 2, so by having the inner surface convex portion 102 on the inner surface of the side wall 12, it is possible to reduce the unevenness of the outer surface of the side wall 12, resulting in a better mouthfeel.

[0047] According to this embodiment, the outer surface of the annular recess 14 has an outer convex portion 104 that protrudes outward due to an inner ruled line 103 in the vertical direction formed on the inner surface of the blank 10. This reduces the wrinkles S formed on the surface of the annular recess 14 that contacts the curled portion 28, effectively preventing the liquid content in the paper container 2 from leaking out along the wrinkles S.

[0048] In Example 1, a leakage test was conducted to confirm leakage of the content liquid. In the leakage test, hot coffee at 80°C was poured into the paper container as the content liquid. The content volume of the content liquid was 80% of the full pour volume. For the test, the paper container containing the content liquid was covered with a lid and tilted at a 45° angle, and left for 3 minutes to confirm the presence or absence of leakage. The test was conducted on both the general portion where the blank constituting the paper container is single-layered and the seam portion where the blanks overlap.

[0049] In Example 1 of the present invention, before the annular recess was fitted to the curled portion of the paper container, the radius of curvature of the curve extending from the top of the annular recess to the outside was 1.13 mm, which was smaller than the radius of curvature of the curve extending from the top of the curled portion of the paper container to the outside, which was 1.27 mm.In Comparative Example 1, before the annular recess was fitted to the curled portion of the paper container, the radius of curvature of the curve extending from the top of the annular recess to the outside, which was 1.78 mm, which was larger than the radius of curvature of the curve extending from the top of the curled portion of the paper container to the outside, which was 1.27 mm.

[0050] As shown in Figure 7, no leakage was confirmed for 180 seconds in either the general portion or the seam portion in Example 1 of the present invention. Furthermore, as shown in the X-ray cross section, in Example 1 of the present invention, when the annular recess is fitted into the curled portion of the paper container, there are two contact portions in the cross section.

[0051] In contrast, in Comparative Example 1, no leakage was observed in the general portion for 180 seconds, but leakage was observed in the seam portion after 75 seconds. Also, as shown in the X-ray cross section, in Comparative Example 1, when the annular recess was fitted into the curled portion of the paper container, there was one contact portion in the cross section.

[0052] From the above, in Example 1 of the present invention, before the annular recess is fitted to the curled portion, the radius of curvature of the curve extending from the apex of the annular recess to the outside is smaller than the radius of curvature of the curve extending from the apex of the curled portion to the outside. As a result, when the annular recess is fitted to the curled portion, the annular recess can sandwich the curled portion at the first contact portion and the second contact portion and thereby effectively suppress leakage of the contents of the paper container. In contrast, in Comparative Example 1, before the annular recess is fitted to the curled portion, the radius of curvature of the curve extending from the apex of the annular recess to the outside is larger than the radius of curvature of the curve extending from the apex of the curled portion to the outside. As a result, when the annular recess is fitted to the curled portion, the annular recess has only one contact portion in cross section and cannot sandwich the curled portion, which is thought to have caused leakage of the contents of the paper container.

[0053] In Example 2, a clamping test was conducted to measure the clamping strength. In the clamping test, the flange of the paper lid was clamped from both sides using a load cell as shown in Figure 8(a), and the strength when it was pressed down 9.5 mm as shown in Figure 8(b) was taken as the clamping strength. The clamping test was performed five times for each of Inventive Example 2 and Comparative Example 2.

[0054] As shown in Figure 9, in Example 2 of the present invention, the flange portion had an overlapping portion where the blank was folded over and overlapped on top of each other. The blank material of the paper lid in Example 2 of the present invention was PE / base paper / PE. In Comparative Example 2, the flange portion was a single layer without the blank being folded over. The blank material of the paper lid in Comparative Example 2 was PP / base paper / PP.

[0055] As a result, the clamping pressure strength of Inventive Example 2 was 3.2 to 3.7N, whereas the clamping pressure strength of Comparative Example 2 was 2.6 to 2.7N.

[0056] From the above, in Example 2 of the present invention, the flange portion has an overlapping portion where the blanks are folded over and overlapped with each other. This improves the clamping strength of the paper lid compared to the paper lid of Comparative Example 2, which does not have an overlapping portion. If the clamping strength is low, the lid will bend and the handleability, or ease of gripping the lid, will be reduced. However, by improving the clamping strength, the paper lid is less likely to bend when gripped, improving the handleability of the paper lid.

[0057] As shown in Figure 10, in Example 3, a similar leakage test was conducted to confirm leakage in a case where a convex portion was formed on the surface of the annular recess that contacts the paper container (Comparative Example 3) and a case where a convex portion was formed on the surface of the annular recess opposite the surface that contacts the cup (Invention Example 3). In Comparative Example 3, a convex portion was formed on the surface of the annular recess that contacts the paper container, so the ruled line was positioned on the outside of the blank. In Invention Example 3, a convex portion was formed on the surface of the annular recess opposite the surface that contacts the paper container, so the ruled line was positioned on the inside of the blank. The white line in the X-ray cross section in Figure 10 indicates the contact area between the lid (annular recess) and the paper container (curled portion).

[0058] In Comparative Example 3, leakage was confirmed in the seam area at 152 seconds, but not in the general area at 180 seconds. In Comparative Example 3, the convex portion of the annular recess contacts the curled portion, reducing the contact area between the annular recess and the curled portion. This is thought to be why leakage occurred in the seam area.

[0059] In Example 3, no leakage was observed in the seam portion or the general portion for 180 seconds. In Example 3, the surface of the annular recess opposite to the surface on which the protrusion is formed contacts the curled portion, increasing the contact area between the annular recess and the curled portion. This is thought to be why no leakage was observed.

[0060] In Example 4, the void area in the cross section of the wrinkles corresponding to the position of the paper lid (Example 4 of the present invention) was measured. As shown in Figure 11, the cross section of the paper lid was imaged with an optical microscope, and the void area was calculated from the image. In Example 4, the area of ​​the portion surrounded by the reference plane of the wrinkles due to the drawing in the paper lid (the shaded portion in Figure 11) was taken as the void area.

[0061] As shown in Figure 12(a), the cross-sectional gap area of ​​the wrinkles was measured at the A-A portion of the side wall 12 of the paper lid 1, the B-B portion of the annular recess 14 of the paper lid 1, and the C-C portion of the flange 15 of the paper lid 1. In the paper lid 1, the inner surface of the side wall 12 having the A-A portion had an inner surface convex portion that protruded toward the inner surface due to the vertical outer ruled line formed on the outer surface of the blank. In addition, the annular recess 14 having the B-B portion had an outer surface convex portion that protruded toward the outer surface due to the vertical inner ruled line formed on the inner surface of the blank.

[0062] As shown in FIG. 12(b), the void area in the cross section of the wrinkle is 5993 μm at the A-A portion. 2 / mm, and 680 μm at the B-B portion 2 / mm, and 33236 μm at the CC portion 2 The white line in the X-ray cross-sectional view of part B in Fig. 12 indicates the contact portion between the lid (annular recess) and the paper container (curl portion).

[0063] As described above, the inner surface of the side wall portion 12 having the A-A portion has an inner surface convex portion that protrudes inward due to the vertical outer crease formed on the outer surface of the blank. Also, the annular recess 14 having the B-B portion has an outer surface convex portion that protrudes outward due to the vertical inner crease formed on the inner surface of the blank. For this reason, it is believed that the gap area in the B-B portion is smaller than the gap area in the A-A portion.

[0064] In the above Examples 3 and 4, the outer surface of the annular recess has an outer convex portion that protrudes outward due to the vertical inner ruled line formed on the inner surface of the blank. This reduces wrinkles formed on the surface of the annular recess that contacts the curled portion, effectively preventing liquid contents from leaking out of the paper container along these wrinkles.

[0065] 1: Paper lid 2: Paper container 10: Blank 11: Top plate portion 12: Side wall portion 13: Outer extension portion 14: Annular recess 14a: Outer edge end portion 15: Flange portion 16: Under-rib 17: Joint portion 17a: Outer layer portion 17b: Inner layer portion 18: Projection piece 28: Curl portion 6: Beverage 101: Outer ruled line 102: Inner convex portion 103: Inner ruled line 104: Outer convex portion OEP: Peripheral portion P1: First contact portion P2: Second contact portion R1-1: Radius of curvature R1-2: Radius of curvature R2: Radius of curvature S: Wrinkle

Claims

1. A paper lid that fits onto a curled portion of a container having a curved portion formed at the top end, comprising: a top plate portion; a side wall portion that is provided along the outer periphery of the top plate portion and extends downward, continuous with the top plate portion; and a peripheral edge portion that is provided along the outer periphery of the side wall portion and extends outward, continuous with the side wall portion, wherein the peripheral edge portion has an extending portion that extends outward along the outer periphery of the side wall portion, and an annular recess that is capable of fitting onto the curled portion and is curved so as to be convex upward along the outer periphery of the extending portion, and wherein before the annular recess is fitted onto the curled portion, the radius of curvature of the curve extending from the top of the annular recess to the outside is smaller than the radius of curvature of the curve extending from the top of the curled portion to the outside.

2. The paper lid according to claim 1, wherein the side wall portion is inclined outward from the outer periphery of the top plate portion.

3. The paper lid according to claim 2, wherein the outer extension is curved so as to be convex downward.

4. A paper lid as described in claim 1 or 2, characterized in that when the annular recess is fitted into the curled portion, the annular recess and the curled portion come into contact at a first contact portion and a second contact portion located at a position different from the first contact portion, and there is a gap between the annular recess and the curled portion between the first contact portion and the second contact portion.

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