Paper containers

Abstract

To increase the shape retention of an entire paper container formed by press molding by increasing the shape retention of the edge winding part of the straight part thereof.SOLUTION: A paper container 1 has a straight part L and a corner part R that are formed by press molding a paperboard. The ratio of the winding margin width against an edge winding diameter d2 of the edge winding part 5L of the straight part L is set larger than the ratio of the winding margin width against an edge winding diameter d1 of an edge winding part 5R of the corner part R. The edge winding part 5L of the straight part L that has no wrinkles results in a larger number of paperboard winding times, so the resistance against the winding back increases. In contrast, wrinkles on the edge winding part 5R of the corner part R increase the resistance against the winding back. As a result, the edge winding part 5L of the straight part L and the edge winding part 5R of the corner part R both can restrict the spring back equally, thereby enhancing the shape retention of the paper container 1.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a paper container obtained by press-molding a blank punched out from a sheet of paperboard, and in particular to a paper container having a rolled edge formed on the outer periphery. [Background technology]

[0002] Patent Documents 1 to 4 describe a technique for manufacturing paper containers with a rolled edge formed on the outer periphery by press-molding a blank punched out from a sheet of paperboard. Conventionally, in paper containers formed by press-molding, the rolled edge is formed by rolling in the outer periphery of the blank. The rolled edge increases the strength and shape retention of the container and also contributes to the airtightness when an outer-fitting lid is attached.

[0003] Patent Document 1 describes a technology for manufacturing a paper container that is approximately rectangular in plan view and has arc-shaped curved sections in areas corresponding to corners when viewed from above. In more detail, it describes that when a blank made by punching paperboard into a predetermined shape is press-molded, a plurality of ruled lines (also called lines) are formed in areas corresponding to the corners of the side wall that rises from the bottom of the paper container to intentionally create regular wrinkles, thereby preventing irregular wrinkles from occurring in areas other than the corners during press molding.

[0004] Patent Document 2 describes that in a paper container formed by press-molding paperboard, the number of times the rolled edge is rolled is 1.1 or more. This is said to prevent the rolled edge of the paper container from spreading or loosening after press-molding, thereby improving the shape retention of the container.

[0005] Patent Document 3 describes a technology for making the rolled edge uniform around the entire circumference of a paper container formed by press molding. Specifically, the technology anticipates a phenomenon in which the paper at the corners stretches more than other parts when the blank is ironed during press molding. To address this issue, a predetermined width of cut margin is provided in advance in the blank at the corners. As a result, the outer periphery of the blank at the corners is recessed slightly inward, making the rolled edge width at the corners slightly shorter than in other parts. Using a blank with this shape is said to absorb the stretch of the rolled edge that occurs at the corners during press molding, resulting in a uniform rolled edge.

[0006] Patent Document 4 describes a paper container having a bottom, a peripheral wall rising from the bottom, a flange extending outward from the upper end of the peripheral wall, and a rolled edge formed on the outer periphery of the flange, in which a portion of the rolled edge is gently curved in an arc toward the inside of the container. According to this technology, by forming the rolled edge so that it curves in an arc toward the inside of the container, it is possible to suppress a decrease in strength of the rolled edge due to unwinding over time. Furthermore, Patent Document 4 specifies that the amount of rolled edge at the corners is greater than the amount of rolled edge at other portions. This is the result of a design that prioritizes the formation of the rolled edge at corners, where it is relatively easy to form the rolled edge, in order to improve the formability of the container. Therefore, Patent Document 4 specifies that the rolled edge margin at the corners of the blank is larger than the rolled edge margin at other portions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3411951 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-080024 [Patent Document 3] Japanese Utility Model Application Publication No. 06-080615 [Patent Document 4] Patent No. 6785161 Summary of the Invention [Problem to be solved by the invention]

[0008] In the paper container described in Patent Document 1, regular wrinkles are formed in the corners due to multiple pre-defined lines on the paperboard, and the rolled edges formed in the corners also have wrinkles, which is thought to result in higher shape retention than other parts. This is because the multiple wrinkles at the corners of the paper container increase the paperboard's resistance to deformation, thereby suppressing loosening and opening (springback) of the rolled edges over time. Therefore, springback can be suppressed to a certain extent at the corners without increasing the amount of rolled edge.

[0009] On the other hand, in the portions of a paper container that are linear in plan view (linear portions), no wrinkles are formed during press molding, so the formation of the rolled edges is easier than in the corner portions. However, unlike the rolled edges in the corner portions, the rolled edges in the linear portions are prone to springback because no wrinkles are formed.

[0010] Therefore, it is conceivable to improve the shape retention of the rolled edge of the straight line sections by intentionally forming wrinkles in the areas of the paperboard corresponding to the straight line sections by forming multiple creases in advance, just as in the corner sections.However, unlike the corner sections, the straight line sections are not areas that are subject to strong horizontal compressive forces during press molding, making it difficult to form regular wrinkles.

[0011] In Patent Document 2, the number of times the rolled edge portion is folded is set to 1.1 or more, but it is considered that the number of times the rolled edge portion is folded is the same for the corner portion and the straight portion, and this does not solve the problem that the shape retention of the rolled edge portion in the straight portion is inferior to that of the rolled edge portion in the corner portion.

[0012] Patent document 3 also merely describes making the rolled edge portion of the paper container uniform around the entire circumference after press molding, but does not solve the problem that the shape retention of the rolled edge portion in the straight section is inferior to that of the rolled edge portion in the corner section.

[0013] In Patent Document 4, the shape retention of the straight-line rolled edge portion is improved by curving the straight-line rolled edge portion. However, when a lid that is fitted onto the paper container is used, there are many areas where the lid and the rolled edge are not tightly fitted together in the curved parts of the rolled edge, which may reduce the airtightness of the lid.

[0014] Therefore, an object of the present invention is to improve the shape retention of the rolled edge portion of the straight portion in a paper container formed by press molding, and thereby improve the shape retention of the entire paper container. [Means for solving the problem]

[0015] In order to achieve the above object, the invention described in claim 1 is a paper container formed by press-molding paperboard, the shape of the outer edge portion when viewed in a plane having a straight portion that extends in a straight line and a curved portion that curves, a rolled edge portion on the outer edge, and regular wrinkles formed in the area including the curved portion, wherein the ratio of the rolled width to the rolled diameter of the rolled edge portion in the straight portion is set to be larger than the ratio of the rolled width to the rolled diameter of the rolled edge portion in the curved portion.

[0016] With this configuration, the ratio of the width of the wrapping allowance to the diameter of the wrapping in the wrapping portion is larger in the straight portions than in the curved portions, so the number of times the paperboard forming the wrapping portion in the straight portions is wrapped is greater than the number of times the paperboard is wrapped in the wrapping portion in the curved portions.

[0017] The invention described in claim 2 is the same as the invention described in claim 1, except that the area including the curved portion is formed by press-molding a paperboard having a plurality of regularly-spaced ruled lines in a predetermined area.

[0018] By configuring it in this manner, by pre-arranging multiple lines in a regular pattern in the area of ​​the paperboard corresponding to the area including the curved portion of the paper container, regular wrinkles can be formed in the curved area of ​​the paper container when the paperboard is press-molded.

[0019] The invention described in claim 3 is such that, in the configuration of the invention described in claim 1 or claim 2, the ratio of the width of the rolled portion to the rolled diameter is set to 4.00 to 4.15 in curved portions and 4.20 to 4.40 in straight portions.

[0020] With this configuration, the number of turns in the rolled hemming is greater in the straight sections. That is, the number of turns is approximately 1.27 to 1.32 in the curved sections and approximately 1.34 to 1.40 in the straight sections. In the curved sections, by setting the ratio of the rolled width to the rolled diameter to be 4.00 or more, the rolled hemming can be given sufficient resistance to loosening. If the ratio exceeds 4.15, it becomes difficult to achieve an improvement in resistance. In the straight sections, by setting the ratio of the rolled width to the rolled diameter to be 4.20 or more, the rolled hemming can be given sufficient resistance to loosening. If the ratio exceeds 4.40, it becomes difficult to achieve an improvement in resistance.

[0021] The invention described in claim 4 is the configuration of the invention described in any one of claims 1 to 3, in which the hemmed portion has a hemmed diameter that is designed to be the same over the entire circumference of the outer edge portion.

[0022] This configuration results in a hemmed portion with a uniform appearance all around.

[0023] The invention as set forth in claim 5 is the configuration of the invention as set forth in any one of claims 1 to 4, wherein the hemming diameter of the hemming portion is set in the range of 1.5 to 5.0 mm.

[0024] With this configuration, it is possible to provide a paper container having a rolled edge with a rolled edge diameter in the range of 1.5 to 5.0 mm.

[0025] The invention described in claim 6 is the configuration of the invention described in any one of claims 1 to 5, wherein the paperboard has an interlayer strength (T-peel method) of 500 mN / cm or more.

[0026] By configuring it in this way, the interlayer strength of the paperboard (T-peel method) is set to 500 mN / cm or more, making it less likely for delamination between the pulp layers that make up the paperboard or for the paperboard to buckle during press molding.

[0027] The invention described in claim 7 is the construction of the invention described in any one of claims 1 to 5, wherein the paperboard has an interlaminar strength (internal bond tester method) of 200 J / m 2 That's all.

[0028] By configuring it in this way, the interlaminar strength of the paperboard (internal bond tester method) can be increased to 200 mJ / m 2 The above settings make it less likely that delamination between the pulp layers constituting the paperboard or buckling of the paperboard will occur during press molding.

[0029] The invention described in claim 8 is the construction of the invention described in any one of claims 1 to 7, wherein the paperboard has a resin layer formed on at least one surface thereof.

[0030] When configured in this manner, the manufactured paper container has a resin layer on at least one surface.

[0031] The invention described in claim 9 is a configuration of the invention described in any one of claims 1 to 8, which comprises a bottom portion, a side wall portion connected to the bottom portion, and a flange portion connected to the side wall portion and extending horizontally, wherein a rolled edge portion is formed on the outer peripheral edge of the flange portion, and the width dimension of the curved portion of the flange portion is set larger than the width dimension of the straight portion.

[0032] With this configuration, the width dimension of the flange portion of the curved portion is set larger than the width dimension of the flange portion of the straight portion, so that long wrinkles are formed in the curved portion, and when compressed in that state, the compressed area expands, thereby suppressing the return of wrinkles due to changes over time.

[0033] The invention described in claim 10 is the same as the invention described in claim 9, in which the wrinkles formed in the side wall portion, flange portion and rolled edge portion in the area including the curved portion are formed so as to extend radially from the outer edge of the bottom toward the outer peripheral edge.

[0034] With this configuration, the wrinkles are not irregular but are regular radial wrinkles.

[0035] The invention described in claim 11 is the structure of the invention described in claim 10, in which the wrinkles are formed based on a plurality of radial lines that are provided in advance on the paperboard.

[0036] With this configuration, wrinkles are formed based on a plurality of radially arranged lines on the paperboard in advance, which prevents irregular wrinkles from occurring during press molding and allows regular wrinkles to be formed. [Effects of the Invention]

[0037] According to the invention described in claim 1, the number of turns in the rolled edge of the straight section is set to be greater than the number of turns in the rolled edge of the curved section, thereby increasing the contact area between the paperboard sheets in the rolled edge of the straight section and improving resistance to unwinding. Meanwhile, in the rolled edge of the curved section, the wrinkles formed increase resistance to unwinding, allowing shape retention to be achieved even with fewer turns. As a result, springback can be suppressed equally in both the rolled edge of the straight section and the rolled edge of the curved section, improving the shape retention of the paper container. Furthermore, this eliminates the need to curve the outer periphery of the straight section as in Patent Document 4, thereby improving the sealing performance with the lid that is fitted over the container.

[0038] In addition to the effect of the invention of claim 1, the invention of claim 2 makes it possible to regularize the wrinkles formed by press molding, thereby stabilizing the quality of paper containers that are repeatedly manufactured.

[0039] The invention of claim 3 has the effect of the invention of claim 1 or 2, and in addition, it makes it easy to design a curled edge portion that is less likely to become loose and does not waste material.

[0040] The invention of claim 4 can provide a paper container that is excellent in appearance in addition to the effect of the invention of any one of claims 1 to 3.

[0041] In addition to the effects of any one of claims 1 to 4, the invention of claim 5 has the following advantages: if the rolled edge diameter is less than 1.5 mm, it may be difficult to form the rolled edge by press molding; if the rolled edge diameter is more than 5.0 mm, the rolled edge may easily loosen or widen; therefore, by setting the rolled edge diameter within the above range, it is possible to provide a paper container that is excellent in formability, has excellent shape retention, and exhibits reliable resistance to loosening.

[0042] In addition to the effects of the inventions of any of claims 1 to 5, the inventions of claims 6 and 7 can suppress buckling of the paperboard, particularly buckling at the rolled edge, during the production of paper containers, thereby improving the formability of the paper containers.

[0043] The invention described in claim 8 has the effects of any of the inventions described in claims 1 to 7, and can also impart properties such as heat resistance, water resistance, and gas / liquid permeability resistance to paper containers depending on the properties of the laminated resin.

[0044] The invention of claim 9 has the effect of the invention of any one of claims 1 to 8, and in addition, the shape retention of the paper container is improved as a result of wrinkles being less likely to return to their original shape due to changes over time.

[0045] The invention of claim 10 provides the effect of the invention of claim 9 as well as a paper container with a highly designed design.

[0046] The invention of claim 11 has the same effect as the invention of claim 10, but also makes it possible to control wrinkles that occur, thereby improving the shape retention of paper containers. [Brief explanation of the drawings]

[0047] [Figure 1] 1 is a perspective view showing a paper container according to an embodiment of the present invention. [Figure 2] FIG. 1 is a plan view of a paper container according to an embodiment of the present invention. [Figure 3] 1 is a plan view showing a blank for forming a paper container according to an embodiment of the present invention. FIG. [Figure 4] 4 is an enlarged plan view of a portion of the blank shown in FIG. 3. FIG. [Figure 5] 3A and 3B are enlarged cross-sectional views showing the rolled edge portion of the paper container according to the embodiment of the present invention, where FIG. 3A is a cross-sectional view taken along line AA in FIG. 2, and FIG. 3B is a cross-sectional view taken along line BB in FIG. [Figure 6] FIG. 1 is a schematic diagram showing the implementation status of a test to measure the shape retention of a paper container. DETAILED DESCRIPTION OF THE INVENTION

[0048] Figure 1 is an oblique view showing a paper container according to an embodiment of the present invention, Figure 2 is a plan view of a paper container according to an embodiment of the present invention, Figure 3 is a plan view showing a blank for forming a paper container according to an embodiment of the present invention, Figure 4 is a plan view showing an enlarged portion of the blank shown in Figure 3, and Figure 5 is a cross-sectional view showing an enlarged edge roll portion of a paper container according to an embodiment of the present invention, where (A) is a cross-sectional view along line AA in Figure 2 and (B) is a cross-sectional view along line BB in Figure 2.

[0049] Referring to FIG. 1, a paper container 1 according to this embodiment is formed by press-molding a blank, which is made by punching out a paperboard into a predetermined shape, into a three-dimensional shape. The paper container 1 of this example includes a bottom 2, a side wall 3 that connects to the outer edge 2a of the bottom 2 and stands upright, a flange 4 that connects to the upper end 3a of the side wall 3 and extends horizontally outward, and a rolled-edge portion 5 formed on the outer edge of the flange 4. Referring to FIG. 2, this paper container 1 has, in a plan view, a shape in which the outer edge 1a has a rectangular shape with its corners chamfered into an arc, and has a straight portion L that extends linearly and a corner portion R that is curved into an arc. Therefore, in this example, the corner portion R corresponds to a curved portion. Furthermore, this example is designed so that no wrinkles are formed in the area including the straight portion L, and regular wrinkles 6 are formed in the area including the corner portion R.

[0050] 3, blank 10 for forming paper container 1 is formed by punching out paperboard so that the shape of outer peripheral edge 10a approximates the planar shape of paper container 1. In the figure, dash-dotted line 12a represents the outline of the bottom, dash-dotted line 13a represents the boundary between the side wall and the flange, and dash-dotted line 14a represents the boundary between the flange and the rolled edge. Therefore, area 12 surrounded by dash-dotted line 12a corresponds to the bottom of paper container 1, area 13 between dash-dotted lines 12a and 13a corresponds to the side wall, area 14 between dash-dotted lines 13a and 14a corresponds to the flange, and the area outside dash-dotted line 14a is a winding allowance 15 for forming the rolled edge.

[0051] Because the paper container 1 is made by press-molding a flat blank 10 into a three-dimensional shape, it is inevitable that some wrinkles will occur in the paperboard. However, depending on the design of the blank 10, it is possible to clearly distinguish between areas where no wrinkles will be formed and areas where wrinkles are intentionally formed.

[0052] Referring to Figure 4, region r of blank 10, which includes arc-shaped outer peripheral edge 10a, corresponds to corner R of paper container 1. Therefore, in region r of blank 10, a plurality of creases 16 are formed in advance in a regular pattern, with point P set at an appropriate position in region 12 corresponding to the bottom as the center, extending radially from dash-dot-dot line 12a representing the outline of the bottom toward arc-shaped outer peripheral edge 10a. When blank 10 with such creases 16 is press-molded, wrinkles are generated in the paperboard along creases 16 when the paperboard is compressed to form the corners, so that regular wrinkles 6 can be formed in corner R of paper container 1. As a result, a paper container 1 can be obtained in which straight line portion L is an area where no wrinkles are formed and corner portion R is an area where wrinkles are formed.

[0053] By press-molding paperboard with pre-lined lines, a paper container 1 having the shape shown in Figure 1, i.e., a bottom 2, a side wall 3, a flange 4, and a rolled-up edge 5 on the outer peripheral edge 1a, with wrinkles 6 formed only in the corners R, can be formed using the techniques described in Patent Documents 1 to 4 and other known techniques.

[0054] 1 and 2, when a paper container 1 having a rolled edge 5 at its outer periphery 1a is formed by press-molding paperboard, regular wrinkles 6 are formed at the corners R due to multiple creases pre-formed in the paperboard, resulting in the rolled edge 5R formed at the corners R also having wrinkles. Among the rolled edges 5 provided at the outer periphery 1a of a paper container 1, the rolled edge 5R having wrinkles 6 at the corners R generally has high shape retention, while the rolled edge 5L having no wrinkles at the straight portions L tends to be more susceptible to springback. This is because the multiple wrinkles 6 at the corners R of the paper container 1 increase the paperboard's resistance to deformation, thereby suppressing loosening and opening (springback) of the rolled edge 5R over time. Therefore, springback can be suppressed to a certain extent at the corners R without increasing the amount of rolled edge 5R. On the other hand, since wrinkles do not form in the straight portions L of the paper container 1 during press molding, the formation of the rolled edge 5L itself is easier than in the corner portions R. However, unlike the rolled edge 5R of the corner portions R, the rolled edge 5L of the straight portions L is prone to springback because wrinkles are not formed therein.

[0055] Therefore, in this example, as shown in FIGS. 4 and 5, the ratio of the wrap width t2 to the wrap diameter d2 of the edge wrap portion 5L in the straight portion L where no wrinkles are formed is set to be larger than the ratio of the wrap width t1 to the wrap diameter d2 of the edge wrap portion 5R in the corner portion R where wrinkles are formed. Here, the wrap widths t1 and t2 of the edge wrap portion in the blank 10 refer to the shortest distance between the outer peripheral edge portion 10a defining the wrap allowance 15 of the blank 10 and the two-dot chain line 14a. In FIG. 5, if d1 = d2, then in FIG. 4, t1 < t2 may be set. With such a configuration, the number of winding times of the edge wrap portion 5L in the straight portion L becomes larger than the number of winding times of the edge wrap portion 5R in the corner portion R. That is, if the number of winding times of the edge wrap portion 5R is 1 + α and the number of winding times of the edge wrap portion 5L is 1 + β, then α < β. As a result, the area where the cardboard sheets contact each other in the edge wrap portion 5L becomes larger, so that the resistance to unwinding increases accordingly. Consequently, springback can be suppressed in the edge wrap portion 5L of the straight portion L as much as or more than in the edge wrap portion 5R of the corner portion R, and thus the shape retention of the entire paper container 1 is improved.

[0056] Specifically, the ratios of the wrap widths t1 and t2 to the wrap diameters d1 and d2 of the edge wrap portions 5R and 5L are preferably both 3.45 or more. Thereby, the number of winding times of the cardboard in the edge wrap portion can be 1.1 or more, so that the resistance to springback can be surely imparted to the edge wrap portion.

[0057] Furthermore, it is recommended to set the ratio of the width of the rolled edge t1 to the diameter of the rolled edge 5R at the corners R, t1 / d1, between 4.00 and 4.15, and the ratio of the width of the rolled edge t2 to the diameter of the rolled edge 5L at the straight sections L, t2 / d2, between 4.20 and 4.40. This setting results in a number of turns for the rolled edge 5R at the corners R of approximately 1.27 to 1.32, while the number of turns for the rolled edge 5L at the straight sections L is even larger, at approximately 1.34 to 1.40. This configuration provides sufficient resistance to springback for both the rolled edge 5R and 5L while maintaining good formability, facilitating the design of rolled edge sections with excellent shape retention and formability. Below the lower limit of the above setting, sufficient resistance to springback may not be obtained. If the upper limit of the above set value is exceeded, it becomes difficult to improve the resistance, which may cause the edge to open or hinder the shape retention of the paper container.

[0058] Furthermore, when the straight portion L has a long side portion and a short side portion, as in the paper container 1 of this example, the ratio of the width of the rolled edge portion to the diameter of the rolled edge portion on the short side portion needs to be equal to or greater than the ratio on the corner portion R, and may be set to be equal to or less than the ratio on the long side portion.

[0059] The curled edge diameters d1 and d2 of both the curled edge portions 5R and 5L may be designed to be the same around the entire outer rim 1a, i.e., d1 = d2. This gives the curled edge portion 5 a uniform appearance around the entire periphery of the paper container 1, making it possible to provide a paper container 1 with excellent aesthetics. However, as long as it is within the scope of the specified configuration of the present invention, the curled edge diameters d1 and d2 do not have to be the same.

[0060] Furthermore, the rolled edge diameters d1 and d2 of the rolled edge portions 5R and 5L should be set in the range of 1.5 to 5.0 mm, more preferably in the range of 2.0 to 4.0 mm. If the rolled edge diameter is less than 1.5 mm, it may be difficult to form the rolled edge portion by press molding. If the rolled edge diameter exceeds 5.0 mm, springback is likely to occur. Therefore, by setting the rolled edge diameter within the above range, it is possible to provide a paper container that has good formability, excellent shape retention, and reliable resistance to loosening.

[0061] The paper container 1 of this example includes a bottom 2, a sidewall 3 connected to the bottom 2, a flange 4 connected to the sidewall 3 and extending horizontally, and a rolled edge 5 formed on the outer periphery of the flange 4. Regular wrinkles 6 are formed at the corners R. In this case, the width of the flange 4 at the corners R where the wrinkles 6 are formed may be set larger than the width of the flange 4 at the straight portions L where no wrinkles are formed. Specifically, the width of the flange 4 at the corners R is preferably set to 1.1 to 5 times, and more preferably 1.5 to 3 times, the width of the flange 4 at the straight portions L. The wrinkles 6 formed at the corners R are formed by compressing the paperboard, and therefore, the shape may return to its original shape over time. Therefore, with the above-described configuration, the wrinkles are formed longer in the wrinkled areas, and compression in this state expands the compressed area. This prevents the wrinkles from returning to their original shape over time, thereby improving the shape retention of the paper container.

[0062] The paperboard used to form the paper container of this embodiment preferably has the materials, properties, and configuration described below.

[0063] Types of paperboard include, for example, pure white roll paper, kraft paper, coated cardboard, parchment paper, ivory paper, Manila paper, cardboard, cup paper, glassine paper, etc., as well as paperboard or synthetic paper that has been treated to be water-resistant or oil-resistant, and the desired material can be selected depending on the application. Depending on the intended use, a resin film may be attached to the paperboard, or a resin may be extruded by extrusion lamination, or a resin-coated paperboard may be used in combination. Particularly when used for food storage, it is preferable that a resin layer be formed by extrusion lamination on at least one side of the paperboard (the side that comes into contact with food), and it is even more preferable to use paperboard with resin layers formed on both sides.

[0064] The thickness of the paperboard (paper substrate) is not particularly limited, but is preferably 0.2 to 0.5 mm (basis weight: 150 to 500 g / m 2 ) can be preferably used.

[0065] The interlaminar strength of the paperboard is preferably 500 mN / cm or more in the case of the T-peel method, and more preferably 700 mN / cm or more. In the case of the test method according to the internal bond tester method (JAPAN TAPPI No. 18-2 "Paper and paperboard - Internal bond strength test method - Part 2: Internal bond tester method"), it is 200 J / m 2 It is preferable that the value is equal to or greater than 290 J / m 2 It is more preferable that the interlayer strength of the paperboard is 500 mN / cm or more when measured by the T-peel method or 200 J / m or more when measured by the internal bond tester method. Since the paperboard normally used for forming paper containers is composed of multiple pulp layers produced by papermaking, if the interlayer strength is low, delamination between the pulp layers is likely to occur and buckling is likely to occur during forming. 2 If the strength is above this, buckling of the paperboard during the formation of paper containers, particularly during the formation of the rolled edges, can be suppressed. There is no particular upper limit to the interlaminar strength of the paperboard, but in the case of the T-peel method, it is preferably 1500 mN / cm or less, and more preferably 1000 mN / cm or less. In the case of the internal bond tester method, it is 800 J / m 2 Less than 500 J / m is preferable. 2 It is more preferable that the interlayer strength is not more than the above upper limit. If the interlayer strength exceeds the above upper limit, the rigidity of the paperboard may become too high, which may result in reduced formability or increased springback after forming. Here, the interlayer strength refers to the peel resistance strength between each of the first and second layers and between the second and third layers. By keeping the interlayer strength within the above range, it is possible to suppress peeling between layers, and it is possible to improve the formability, particularly of the curled edge portion. Furthermore, when the paperboard is composed of multiple pulp layers, such as three or five layers, it is more preferable that the interlayer strength be within the above range for all of the layers.

[0066] A resin layer may be formed on at least one side of the paperboard. In this case, the type of synthetic resin used is not particularly limited, and examples include polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyolefin resins such as polypropylene, polyethylene, and polymethylpentene, acrylic (methacrylic) resins, diene resins such as polybutadiene, and thermoplastic resins such as polycarbonate resins. Furthermore, to make the paper container more environmentally friendly, biodegradable resins such as polylactic acid (PLA) can also be used.

[0067] Furthermore, so-called bio-PET, as described below, can also be used. When polyethylene terephthalate resin (PET) is used, the PET is preferably a copolymerized polyethylene terephthalate resin obtained by copolymerization with isophthalic acid, the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin being 1 mol % or more but less than 10 mol %, and the melting point being 235°C or more and 250°C or less. Furthermore, the copolymerized polyethylene terephthalate resin is preferably a biologically derived (biomass resource-derived) biomass polyethylene terephthalate resin with a bio-based carbon content of 5% or more. Generally, polyethylene terephthalate resin is a synthetic resin obtained by polycondensation of ethylene glycol and terephthalic acid as its main components, but most of it is derived from fossil resources. Therefore, replacing these with biomass polyethylene terephthalate resin obtained from biological raw materials such as sugarcane can reduce the amount of fossil resource-derived raw materials used and improve carbon neutrality, thereby increasing sustainability and contributing to environmental conservation.

[0068] When implementing the above, the bio-based carbon content, which is an index showing the proportion of biologically derived raw materials in the copolymerized polyethylene terephthalate resin, is preferably 5% or more, and more preferably 15% or more. The higher the bio-based carbon content, the lower the proportion of fossil-derived raw materials, resulting in a paper container that is more environmentally friendly. However, since a high bio-based carbon content may also increase costs, it is more preferable to keep it within an appropriate range.

[0069] The biobased carbon content can be expressed as the C14 content obtained by radiocarbon (C14) measurement in accordance with ISO-16620-2 (equivalent to the ASTM-D6866 standard). Fossil resources contain very little C14, while biological resources contain a certain percentage (105.5 pMC). Therefore, if the C14 content in copolymerized polyethylene terephthalate resin is designated PC14, the biobased carbon content can be calculated based on this value using the following formula (X): (X) Biobased carbon content (%) = PC14 / 105.5 x 100 The thickness of the resin layer formed on the paperboard is not particularly limited, but may be, for example, in the range of 10 to 50 μm, and particularly preferably in the range of 20 to 30 μm. Examples of methods for forming the resin layer include extrusion lamination, dry lamination, wet lamination, and coating with a resin solution.

[0070] By laminating the resin, the molded paper container is endowed with properties such as heat resistance, water resistance, and gas / liquid permeability resistance depending on the type of synthetic resin.

[0071] As mentioned above, when a resin layer is formed on at least one side (preferably both sides) of the paperboard, heating during or after press molding can cause the resin on the surface of the paperboard in the rolled-up portion to melt partially or completely, welding the paperboard together at the rolled-up portion. In this case, if the rolled-up portion has a length that allows it to be sufficiently rolled up within the rolled-up portion, the area over which the paperboard is welded together by heating will be expanded, further suppressing springback in the rolled-up portion and further improving shape retention.

[0072] It is desirable for paperboard to have a predetermined folding endurance. In the case of paper containers obtained by press-molding a single sheet of paperboard, the paper is prone to tearing in the sidewalls of the paper container, especially in the corners where numerous wrinkles are concentrated. This is because the corners of the paperboard are folded three-dimensionally in the vertical direction by a mold during press-molding, and external forces act from multiple directions to form multiple wrinkles. Therefore, the paperboard used in this example must be able to withstand folding times of 800 to 2000 in both the longitudinal and transverse directions, as measured in accordance with JIS P8115 (2001) "Test Method for Folding Endurance of Paper and Paperboard Using an MIT Tester." More preferably, the folding endurance is 1000 to 1800. Paperboard with a folding endurance of fewer than 800 times may tear during press-molding of the sidewalls, especially the corners, of the paper container. Paperboard with a folding resistance of more than 2,000 times has excessively strong folding properties, which can easily cause springback in the rolled edges after press molding, potentially reducing the shape retention of the paper container.

[0073] The relationship between the folding endurance (number of times folded) of paperboard and the formability and shape retention of paper containers was confirmed by the following tests. (Paperboard) The paperboard used for the test is approximately 0.3 mm thick and has a basis weight of approximately 300 g / m 2 Each of the paperboards in Examples 1 to 6 had an interlaminar strength (T-peel method) in the range of 500 mN / cm to 1500 mN / cm, and an interlaminar strength (internal bond tester method) in the range of 200 J / m2 More than 800J / m 2 It was within the following range: (Paper container) The above paperboard was press-molded to produce a paper container of the form shown in Figure 1. When viewed in plan, this paper container had a long side length of approximately 177 mm (including the flange), a short side length of approximately 123 mm (including the flange), a height from the bottom to the flange of approximately 27 mm, a rim diameter of approximately 3 mm, and a flange width of approximately 7 mm (including the rim). (Moldability test) 1,000 paper containers were produced by press molding for each paperboard having the number of folding times shown in Table 1. Of the 1,000 paper containers obtained, the number of paper containers that had tears in even one of the four corners was visually counted. The evaluation method was that if even one of the 1,000 paper containers produced had a tear in a corner, it was judged to be defective. (Shape retention test: Part 1) The width dimension in the short direction of five randomly selected paper containers was measured immediately after press molding, 30 minutes after press molding, and 24 hours after press molding. Based on these, the following value (Y) was obtained and the average value was calculated. (Y) Degree of opening due to springback over time (%) = Width of the paper container in the short direction after aging (mm) ÷ Width of the paper container in the short direction immediately after molding (mm) × 100 (Shape Retention Test: Part 2) The compressive strength of the paper containers in the longitudinal direction was measured using a method similar to that described in JP 2018-043753 A. Paper containers were prepared by press-molding paperboard with the folding endurance counts listed in Table 1. Figure 6 is a schematic diagram showing the state of the paper container shape retention measurement test. The measurement device used was the "Autograph" material testing machine (manufactured by Shimadzu Corporation: registered trademark) and the company's data processing software "TRAPEZIUM" (registered trademark), and the test was conducted in accordance with the circumferential direction test adopted by "TRAPEZIUM." The switching stroke value was changed from 10 mm to 20 mm. Referring to Figure 6, the test method involved placing a paper container 1 with its bottom end fixed as shown, and then pressing the paper container 1 in the direction indicated by arrow F using the measuring device 30 described above to measure the stress and deformation. The test was carried out on three of each type of paper container, and the deformation amount of the paper container was read when a stress of 1N was applied, and the arithmetic average of the three readings was calculated as the measurement test result. The evaluation method was that paper containers that deformed by 5mm or less when a stress of 1N was applied were judged as good, and anything else was judged as bad. The test results are shown in Table 1 below.

[0074] [Table 1] The results show that paper containers press-formed using paperboards with a folding resistance of 800 to 2000 times in both the longitudinal and transverse directions (Examples 1 to 6) exhibit good results in both formability and shape retention. Therefore, the paperboards used for the paper containers of this example are preferably those with a folding resistance of 800 to 2000 times in both the longitudinal and transverse directions, and it is clear that using paperboards with a folding resistance of 1000 to 1800 times in particular (Examples 3 to 5) provides better compression resistance. When paperboards with a folding resistance of less than 800 times (Comparative Examples 1 and 2) are used, springback is less likely to occur, but the compression resistance of the paper container decreases. Conversely, when paperboards with a folding resistance of more than 2000 times (Comparative Example 3) are used, springback increases and shape retention decreases.

[0075] In the above embodiment, the straight portions of the paper container are regions where no wrinkles are formed, but by providing relatively sparse regular creases in advance in the locations of the blank that correspond to the straight portions, the straight portions of the paper container formed by press molding may be regions where sparse regular wrinkles are formed. Even in such a case, the same effect can be obtained by setting the ratio of the roll allowance width to the roll diameter of the rolled edge portion in the straight portions to be larger than the ratio of the roll allowance width to the roll diameter of the rolled edge portion in the curved portions.

[0076] Although the paper container in the above embodiment has a substantially rectangular shape in plan view, the shape is not particularly limited as long as the outer peripheral edge has straight and curved portions, and may be, for example, a square, polygonal, or substantially elliptical shape including straight portions in plan view. Furthermore, the straight portions are not limited to being strictly straight, and may include shapes in which the outer peripheral edge is gently curved. Furthermore, the size of the paper container is not particularly limited. Furthermore, the paper container may have a shape with a partition on the inside.

[0077] Furthermore, the surface of the paperboard base paper may be printed, which can improve the design. [Explanation of symbols]

[0078] 1...Paper containers 1a...Outer periphery 2…Bottom 2a...outer edge 3...Side wall 3a…Top end 4...Flange 5...Edge wrapping 5L...Hemming 5R...Hemming 6...Wrinkles 10...Blank 10a...Outer periphery 15...Rolling allowance 16...Rounded line 30...Measuring device F...arrow L…Straight section R... Corner section (curved section) d1...Hemming diameter d2...Hemming diameter r…area t1...winding width t2...winding width In addition, the same reference numerals in each drawing indicate the same or corresponding parts.

Claims

1. A paper container formed by press-molding a paperboard, the shape of the outer periphery of which, when viewed in plan, has a straight portion that extends linearly and a curved portion that curves, the outer periphery is provided with a rolled edge portion, and regular wrinkles are formed in an area including the curved portion, A paper container, wherein the ratio of the width of the rolled edge portion to the diameter of the rolled edge in the straight portion is set to be larger than the ratio of the width of the rolled edge portion to the diameter of the rolled edge in the curved portion.

2. The paper container according to claim 1, wherein the region including the curved portion is formed by press-molding the paperboard having a plurality of regularly-spaced creases in a predetermined region.

3. The paper container according to claim 1 or claim 2, wherein the ratio of the winding allowance width to the winding diameter of the wound edge portion is set to 4.00 to 4.15 in the curved portion and 4.20 to 4.40 in the straight portion.

4. The paper container according to any one of claims 1 to 3, wherein the rolled edge portion has a rolled edge diameter that is set to be uniform over the entire circumference of the outer periphery.

5. The paper container according to any one of claims 1 to 4, wherein the diameter of the folded edge portion is set in the range of 1.5 to 5.0 mm.

6. The paper container according to any one of claims 1 to 5, wherein the paperboard has an interlaminar strength (T-peel method) of 500 mN / cm or more.

7. The paperboard has an interlaminar strength (internal bond tester method) of 200 J / m ２ The paper container according to any one of claims 1 to 5.

8. The paper container according to any one of claims 1 to 7, wherein a resin layer is formed on at least one surface of the paperboard.

9. a bottom portion, a side wall portion connected to the bottom portion, and a flange portion connected to the side wall portion and extending horizontally; The curled portion is formed on the outer peripheral edge of the flange portion, The paper container according to any one of claims 1 to 8, wherein the width dimension of the flange portion at the curved portion is set larger than the width dimension of the straight portion.

10. The paper container according to claim 9, wherein in the region including the curved portion, the wrinkles formed in the side wall portion, the flange portion, and the rolled edge portion are formed so as to extend radially from the outer edge of the bottom portion toward the outer peripheral edge portion.

11. The paper container according to claim 10, wherein the wrinkles are formed based on a plurality of radially formed lines on the paperboard.

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