Paper container, top-seal paper container, and method for manufacturing paper container

Abstract

This paper container is mainly composed of the bottom part, a lateral wall part that is connected to the bottom part, a flange part that is connected to the upper end of the lateral wall part and that extends horizontally outward, and an edge wound part that is connected to the outer peripheral edge of the flange part. The flange part has a plurality of wrinkles (6) (including crushing wrinkles (7)) that are each formed, by press molding, to be folded in from the lower surface to the upper surface. Further, each of the wrinkles (6) (including the crushing wrinkles (7)) of the flange part is at least partially formed with a flat portion (28). With such a configuration, the flange part is flattened and the presence or absence of a fine gap (25) inside the wrinkle (6) does not affect top sealing, and thus a paper container which has improved top seal properties when performing top sealing by using a lid material such as a top seal film is achieved. Further, the strength is improved as compared with a conventional paper container in which wrinkles are not flattened.

Description

Paper container, top-sealed paper container, and method for manufacturing paper container

[0001] The present invention relates to a paper container, a top-seal paper container, and a method for manufacturing a paper container, and more particularly to a paper container formed from a single sheet of paperboard by press molding alone, a top-seal paper container, and a method for manufacturing a paper container.

[0002] A paper container formed solely by press molding from a single sheet of paperboard base paper is disclosed in Japanese Patent Application Laid-Open No. 10-43027.

[0003] FIG. 8 is a perspective view showing the external appearance of a conventional paper container disclosed in Japanese Patent Application Laid-Open No. 10-43027.

[0004] 8, the paper container 51 is composed of a substantially rectangular bottom 52 with rounded corners, a side wall 53 connected to the periphery of the bottom 52 and rising obliquely upward, a flange 54 connected to the upper end of the side wall 53 and extending horizontally, and a rolled-edge portion 55 connected to the outer periphery of the flange 54. The corners of the side wall 53 and the flange 54 are side wall corners 57 and curved flanges 58, each having a plurality of wrinkles 56 formed radially from the inside to the periphery.

[0005] FIG. 9 is a plan view showing the overall shape of the paperboard base paper for press-molding the paper container shown in FIG.

[0006] 9, the paperboard base paper 70 has a generally rectangular shape with rounded corners, with a central portion 72 corresponding to the bottom portion 52 of the paper container and an outer periphery 73 corresponding to the side wall portion 53, flange portion 54 and rolled-up portion 55 of the paper container 51. A plurality of radially extending ruled lines 71 are formed in the portions of the outer periphery 73 that correspond to the side wall corner portions 57 and curved flange portions 58 at the four corners of the outer periphery 73.

[0007] In the paper container 51 as described above in Japanese Patent Application Laid-Open No. 10-43027, irregular wrinkles that tend to occur at the corners during press molding are absorbed by the ruled lines 71 formed in the paperboard base paper 70, thereby preventing irregular wrinkles from occurring during molding.

[0008] However, because wrinkles 56 are formed in the press-molded paper container 51 as described above, even if the formation of wrinkles 56 can be controlled regularly by forming multiple ruled lines 71 in the paperboard base paper 70 and press-molding it, the wrinkles 56 themselves will end up being uneven. Therefore, in the case of a plastic container, it is possible to create a highly airtight top-sealed container by forming a flat flange on the container and top-sealing this flange with a plastic film that has top-sealing properties, but in the case of a paper container 51 in which wrinkles 56 are formed by press-molding, even if a flange 54 is formed and a plastic film is top-sealed, complete sealing is not possible due to the unevenness of the wrinkles 56. For this reason, it has been difficult to perform top sealing using a plastic film that has top-sealing properties.

[0009] Therefore, Japanese Patent Application Laid-Open Publication No. 2000-33927 discloses a technology relating to a deep-drawn paper container having a flange portion, which is press-molded using paperboard base paper in which a thermoplastic resin layer is laminated on one side of the paperboard, and then the flange portion is formed into a smooth surface by ultrasonic processing, and the flange portion is crushed using heat and pressure from the ultrasonic processing to form a smooth surface with few irregularities, resulting in a deep-drawn paper container with high airtightness due to the top seal.

[0010] Japanese Unexamined Patent Publication No. 10-43027 Japanese Unexamined Patent Publication No. 2000-33927

[0011] FIG. 10 is a diagram showing how the creases formed on the paperboard base paper change during the manufacture of paper containers, with (1) showing the state before the pressing process, (2) after the pressing process, (3) after the wrinkle pressing process using ultrasonic processing, and (4) after top-seal packaging.

[0012] 10(1), a resin layer (not shown) is formed on the inner surface of the paperboard base paper 80, and the paperboard base paper 80 is folded from the inner surface to the outer surface of the container to form a ruled line 81. That is, a recessed portion 82 and a protruding portion 83 of the ruled line 81 are formed on the inner surface and the outer surface of the container, respectively.

[0013] 10(2), when such paperboard base paper 80 is press-formed, wrinkles 86 are formed around convex portions 83 of the ruled lines 81 on the outer surface of the container. At this time, concave portions 82 of the ruled lines 81 formed on the inner surface of the container are compressed from both sides, and spaces 84 are formed inside the wrinkles 86.

[0014] 10(3), when the wrinkles 86 are pressed from above and below by ultrasonic processing, the resin layer on the surface of the wrinkles 86 on the inner surface of the container melts and forms a fusion layer that attempts to fuse together, thereby flattening the unevenness that has occurred in the wrinkles 86 of the flange portion to some extent.

[0015] However, in the paper container described in Patent Document 2, the wrinkles 86 formed in the sidewalls and flanges are formed by folding from the inner surface to the outer surface of the paper container. When wrinkles 86 are formed in this manner, even if the wrinkles 86 in the flanges are flattened by crushing them using heat and pressure from ultrasonic processing as in Patent Document 2, the minute spaces 84 inside the wrinkles 86 cannot be completely melted and fused, leaving voids 85 inside the wrinkles 86. Even if such a paper container contains a food (content) containing moisture and the flanges of the paper container are top-sealed with a plastic film 87, as shown in Figure 10 (4), moisture and other substances from the contents seep or leak through the minute voids 85 inside the wrinkles 86, making the top seal insufficient. This is presumably because liquids such as moisture are absorbed into the minute voids 85 inside the wrinkles 86 by capillary action. The same problem occurs with gases.

[0016] Furthermore, in order to eliminate such gaps 85, it is possible to increase the energy applied to the flange portion during ultrasonic processing or to extend the ultrasonic processing time, but if such measures are taken, problems will arise such as the wrinkles 86 becoming overheated and the resin or paper burning, making it difficult to control the processing.

[0017] The present invention has been made to solve the above-mentioned problems, and aims to provide a paper container with high top-sealing properties, a top-sealed paper container, and a method for manufacturing a paper container.

[0018] In order to achieve the above object, a paper container in a first aspect of the present invention is a paper container formed solely by press molding from a sheet of paperboard base paper having a resin layer formed on at least the surface that will become the inner surface of the container, and comprising a bottom, a side wall connected to the bottom, and a flange connected to the upper end of the side wall and extending horizontally outward, the side wall and flange having a plurality of wrinkles formed by press molding, the wrinkles in the flange being formed by folding from the lower surface to the upper surface of the flange, and the wrinkles that appear on the upper surface of the flange having at least a flat portion.

[0019] With this configuration, the flange portion is flattened, and the presence or absence of minute gaps on the inner side of the wrinkles does not affect the top seal, which is an effect 1.

[0020] A paper container in a second aspect of the present invention has the same configuration as the invention in the first aspect, but has a rolled edge on the outer periphery of the flange, and the highest part of the rolled edge is located at the same height as or below the upper surface of the flange.

[0021] With this configuration, the second effect is obtained in that the rolled edge portion is not positioned on the outward extension of the mounting surface of the lid material.

[0022] A paper container in a third aspect of the present invention is one in which, in the configuration of the invention in the first or second aspect, the ratio (S1 / S2) of the cross-sectional thickness (S1) of the wrinkled paper container having a flat portion to the cross-sectional thickness (S2) of the wrinkled paper container having no flat portion is 0.7 or less.

[0023] With this configuration, effect 3 can be achieved, in which wrinkles having flat portions are more reliably flattened than wrinkles not having flat portions.

[0024] A paper container in a fourth aspect of the present invention has the configuration of the invention in the first or second aspect, wherein the wrinkles in the flange portion are formed based on a plurality of ruled lines formed in a portion of the paperboard base paper corresponding to the flange portion.

[0025] With this configuration, effect 4 can be achieved in that wrinkles that tend to occur irregularly during press molding are absorbed by the creases.

[0026] In a fifth aspect of the present invention, in the configuration of the invention of the first or second aspect, the wrinkles in the side wall portion are formed by folding from the inner surface to the outer surface of the side wall portion.

[0027] When configured in this manner, the recessed portions of the wrinkles are located on the inner surface of the side wall, and the wrinkles that are folded from the inner surface of the paper container to the outer surface extend only to the top of the side wall. Therefore, even if capillary action occurs due to tiny voids inside the wrinkles, moisture and the like absorbed by capillary action will only reach the top of the side wall and will not reach the flange portion, which is effect 5.

[0028] A top-seal paper container in a sixth aspect of the present invention is a top-seal paper container comprising the paper container in the first or second aspect and a lid material having top-sealing properties.

[0029] With this configuration, an effect 6 is obtained in which the flange portion is top-sealed without leakage.

[0030] A method for manufacturing a paper container in a seventh aspect of the present invention is a method for manufacturing a paper container comprising: a preparation step of preparing paperboard base paper; a pressing step of pressing the paperboard base paper to form a paper container having a bottom, side wall portions connected to the bottom, and flange portions connected to the upper ends of the side wall portions, extending horizontally outward, and having wrinkles formed on the upper surface by folding from the lower surface to the upper surface; and a wrinkle pressing step of forming flat portions in at least some of the wrinkles.

[0031] By configuring in this manner, effect 7 is achieved, in which the flange portion is flattened and a paper container is obtained in which the presence or absence of minute gaps inside the wrinkles does not affect the top seal.

[0032] In an eighth aspect of the present invention, there is provided a method for manufacturing a paper container according to the seventh aspect of the invention, wherein the wrinkle pressing step includes ultrasonic processing of the wrinkles.

[0033] With this configuration, an effect 8 can be obtained in which the flange portion can be easily flattened.

[0034] A method for manufacturing a paper container in a ninth aspect of the present invention is one in which, in the configuration of the invention in the eighth aspect, a resin layer is formed on at least the surface of the paperboard base paper that will become the inner surface of the container, and the resin layer is melted by ultrasonic processing.

[0035] By configuring in this manner, the inside of the wrinkles and the gaps around them are filled with the resin layer, and a paper container with a further flattened flange portion can be obtained, which is effect 9.

[0036] A tenth aspect of the present invention is a method for manufacturing a paper container, in the configuration of the ninth aspect of the invention, in which the wrinkle pressing step reduces the cross-sectional thickness of the wrinkled paper container having flat portions by ultrasonic processing to 70% or less of the cross-sectional thickness of the wrinkled paper container before ultrasonic processing, which is 100%.

[0037] By configuring in this manner, effect 10 can be achieved, that is, a paper container can be obtained in which the wrinkles in the flange portion are reliably flattened compared to the wrinkles before the ultrasonic processing.

[0038] A top-seal paper container in an eleventh aspect of the present invention is the same as the configuration of the sixth aspect of the invention, in which a resin layer having barrier properties is formed on the paper container and the lid material.

[0039] With this configuration, an effect 11 of top sealing the flange portion without leakage can be obtained.

[0040] As described above, the paper container according to the first aspect of the present invention achieves the above-mentioned effect 1, and therefore, when a lid material such as a top seal film is used for top sealing, the paper container has improved top sealing properties. Also, the strength is improved compared to conventional paper containers in which wrinkles are not flattened.

[0041] The paper container according to the second aspect of the present invention provides the above-mentioned effect 2 in addition to the effect of the first aspect of the invention, making it easier to attach the lid material and improving yield.

[0042] The paper container in the third aspect of the present invention has the above-mentioned effect 3 in addition to the effects of the invention in the first or second aspect, and therefore, when top sealing is performed using a top seal film, the top sealability is further improved.

[0043] The paper container in the fourth aspect of the present invention has the above-mentioned effect 4 in addition to the effects of the invention in the first or second aspect, so when top sealing is performed using a top seal film, there is less variation in the quality of the top sealability and the aesthetic appearance is improved.

[0044] The paper container in the fifth aspect of the present invention has the above-mentioned effect 5 in addition to the effects of the invention in the first or second aspect, thereby improving ease of eating, and when top sealing is performed using a top seal film, it is possible to achieve both good top sealing properties and ease of eating.

[0045] The top-seal paper container in the sixth aspect of the present invention achieves the above-mentioned effect 6, thereby improving the sealing performance of the top-seal paper container.

[0046] The method for manufacturing a paper container according to the seventh aspect of the present invention achieves the above-mentioned effect 7, and therefore when top sealing is performed using a top seal film, a paper container with improved top sealing properties can be obtained.

[0047] The method for manufacturing a paper container according to the eighth aspect of the present invention achieves the effect of the seventh aspect of the invention as well as the effect 8 above, thereby improving the productivity of paper containers.

[0048] The method for manufacturing a paper container in the ninth aspect of the present invention achieves the above-mentioned effect 9 in addition to the effect of the invention in the eighth aspect, and therefore when top sealing is performed using a top seal film, a paper container with further improved top sealability can be obtained.

[0049] The method for manufacturing a paper container in the tenth aspect of the present invention achieves the above-mentioned effect 10 in addition to the effect of the invention in the ninth aspect, and therefore when top sealing is performed using a top seal film, a paper container with further improved top sealability can be obtained.

[0050] The top-sealed paper container in the eleventh aspect of the present invention has the effect of the sixth aspect of the invention as well as the above-mentioned action 11, thereby improving the sealing property of the top-sealed paper container and making it a top-sealed paper container with high gas barrier properties.

[0051] 1 is a plan view showing the overall shape of a paper container according to an embodiment of the present invention. It is a cross-sectional view showing the overall structure of the paper container shown in FIG. 1. It is a plan view showing the overall shape of paperboard base paper for press-molding the paper container shown in FIG. 1. It is a diagram showing how the crease lines formed on the paperboard base paper shown in FIG. 3 change during the manufacture of a paper container, (1) before the press process, (2) after the press process, (3) after the wrinkle-pressing process by ultrasonic processing, and (4) after top-seal packaging. It is a schematic cross-sectional view showing the wrinkle-pressing process in the manufacturing method of the paper container shown in FIG. 1. It is a schematic diagram showing the state of a measurement test performed on the paper container shown in FIG. 1. It is a graph showing the results of the measurement test shown in FIG. 6, where (1) is in the longitudinal direction and (2) is in the lateral direction. It is a perspective view showing the external shape of a conventional paper container shown in Patent Document 1. It is a plan view showing the overall shape of paperboard base paper for press-molding the paper container shown in FIG. 8. 1A and 1B are diagrams showing how the creases formed on the paperboard base paper change during the manufacture of paper containers, in which (1) is the state before the pressing process, (2) is the state after the pressing process, (3) is the state after the wrinkle pressing process using ultrasonic processing, and (4) is the state after top-seal packaging.

[0052] FIG. 1 is a plan view showing the overall shape of a paper container according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the overall structure of the paper container shown in FIG.

[0053] Referring to Figures 1 and 2, the paper container 1 is composed of an oval bottom 2, a side wall 3 connected to the bottom 2, a flange 4 connected to the upper end of the side wall 3 and extending horizontally outward, and a rolled rim 5 connected to the outer periphery of the flange 4.

[0054] A plurality of wrinkles 6 (including crushed wrinkles 7, which will be described later) extending radially toward the outer periphery are formed all around the side wall 3, flange 4, and rolled edge 5 of the paper container 1. Details of the wrinkles 6 will be described later.

[0055] The rolled edge 5 is positioned downward from the outer periphery of the flange 4, and the end of the rolled edge 5 is formed so as to be rolled into the inside of the rolled edge 5 and is formed along the entire outer periphery of the flange 4, so that the cross section of the rolled edge 5 is formed in an annular shape. The highest part of the annular shape of the rolled edge 5 is formed so as to be flush with the upper surface of the flange 4.

[0056] By configuring it in this manner, when a lid material is used, the rolled edge portion 5 is not positioned so as to protrude above the upper surface of the flange portion 4 on the outward extension of the attachment surface of the lid material. Therefore, when top sealing is performed using a lid material, particularly a lid material such as a top seal film, the rolled edge portion 5 does not get in the way during top sealing, making top sealing easier, thereby facilitating attachment of the lid material and improving yield.

[0057] Next, the paperboard base paper used to press-mold the paper container 1 will be described.

[0058] FIG. 3 is a plan view showing the overall shape of the paperboard base paper for press-molding the paper container shown in FIG.

[0059] 3, the paperboard base paper 10 has an oval shape and is made by punching out a sheet body in which resin layers are formed on both sides of a paper base material by an extrusion lamination method. The central part of the paperboard base paper 10 is a bottom-corresponding part 12 that corresponds to the bottom 2 of the paper container 1, and on its outer periphery are side wall-corresponding parts 13, flange-corresponding parts 14, and curled-edge-corresponding parts 15 that correspond to the side wall 3, flange 4, and curled-edge part 5 of the paper container 1.

[0060] A plurality of radially extending creases 21 are formed on the side wall portion corresponding portion 13, the flange portion corresponding portion 14 and the curled edge portion corresponding portion 15.

[0061] Next, a method for manufacturing the paper container 1 will be described, focusing on the wrinkles 6 in the paper container 1.

[0062] FIG. 4 is a diagram showing how the crease lines formed on the paperboard base paper shown in FIG. 3 change during the manufacture of paper containers, with (1) showing the state before the pressing process, (2) after the pressing process, (3) after the wrinkle pressing process using ultrasonic processing, and (4) after top-seal packaging.

[0063] First, a paperboard base paper 10 is prepared. Referring to Fig. 4 (1), the ruled lines 21 formed on the paperboard base paper 10 are folded from the inner surface side of the container to the outer surface side of the container. That is, the convex portions 23 and the concave portions 22 of the ruled lines 21 are formed on the inner surface side and the outer surface side of the container, respectively.

[0064] Next, the paperboard base paper 10 is pressed from above and below by the mold members of the forming device to form a paper container 1. This forms the paperboard base paper 10, comprising a bottom 2, side wall portions 3 connected to the bottom 2, and flange portions 4 connected to the upper ends of the side wall portions 3, extending horizontally outward, and having wrinkles 6 formed by folding from the lower surface to the upper surface.

[0065] In this way, by forming the creases 21 in the side wall portion corresponding portion 13, the flange portion corresponding portion 14, and the curled edge corresponding portion 15 of the paperboard base paper 10, the creases 21 absorb and compress the irregular wrinkles that tend to occur during press molding, improving the aesthetic appearance of the paper container 1. Furthermore, by being able to prevent the occurrence of irregular wrinkles in the flange portion 4, when top sealing is performed on the flange portion 4 using a top seal film, variation in the quality of the top sealability is less likely to occur.

[0066] 4(2), wrinkles 6 are formed in the side wall 3 and flange 4 of the paper container 1 after the pressing process, centered on the convex portion 23 on the inner surface of the container. In the flange 4 of the paper container 1, the wrinkles 6 are formed by folding in a direction from the lower surface of the flange 4 to the upper surface.

[0067] The outer peripheral edge of the flange 4 is then rolled to form a rolled portion 5 around the entire periphery. The rolled portion 5 is formed in a ring shape on the outer peripheral edge of the flange 4, and the upper end (highest part) of the rolled portion 5 is located above the upper surface of the flange 4.

[0068] Next, after the pressing step, the wrinkles 6 in the flange portion 4 are further pressed by ultrasonic processing.

[0069] FIG. 5 is a schematic cross-sectional view showing a wrinkle pressing step in the method for manufacturing the paper container shown in FIG.

[0070] Referring also to Figure 5, after the pressing step, the paper container 1 is placed on the base 41 of the ultrasonic processing device, and an ultrasonic horn 42 is lowered from above the paper container 1, sandwiching the flange portion 4 of the paper container 1 between the base 41 and the ultrasonic horn 42. Then, pressure is applied from above and below while applying a predetermined ultrasonic vibration. This causes the resin layer of the flange portion 4 to be locally heated by the ultrasonic processing. Because the resin layer is thermoplastic, the folded portions along with the creases 21 melt and form a fused layer, which fuse together. Pressing in this state flattens the wrinkles 6 in the flange portion 4 overall.

[0071] Note that the portion of the base 41 of the ultrasonic processing device that corresponds to the rolled edge 5 is cut out, and the surface of the ultrasonic horn 42 that comes into contact with the paper container 1 is flat, including the portion that corresponds to the rolled edge 5. Therefore, when the ultrasonic horn 42 is lowered to the upper surface of the flange 4, the highest part of the rolled edge 5, which was located above the upper surface of the flange 4, is pressed downward by the ultrasonic horn 42. However, because the portion of the base 41 that corresponds to the rolled edge 5 is cut out, the rolled edge 5 is not crushed by the pressure of the ultrasonic horn 42, and as the ultrasonic horn 42 descends, the rolled edge 5 is pressed down to the same height as the upper surface of the flange 4. In this way, the paper container 1 shown in Figure 1 is manufactured. In the embodiment, ultrasonic processing was performed by placing the paper container 1 so that the ultrasonic horn 42 was in contact with the upper surface of the flange portion 4 as shown in Figure 5, but the same effect as the present invention can also be obtained by placing the paper container 1 in a direction so that the ultrasonic horn 42 is in contact with the lower surface of the flange portion 4 (i.e., so that the opening of the paper container 1 faces downward) and performing ultrasonic processing.

[0072] Next, the change in the wrinkles 6 in the flange portion 4 during the manufacture of paper containers will be described.

[0073] 4(2), as described above, when paperboard base paper 10 is press-formed, wrinkles 6 are formed around convex portions 23 of creases 21 on the container inner surface (upper surface of flange 4). At this time, a pair of gaps 26a, 26b are formed on both sides of convex portions 23 of creases 21 formed on the container inner surface (upper surface of flange 4). In addition, concave portions 22 of creases 21 formed on the container outer surface (lower surface of flange 4) are compressed from both sides, forming spaces 24 inside wrinkles 6.

[0074] Next, referring to FIG. 4 (3), after the pressing process, the wrinkles 6 are heated by ultrasonic processing while being pressed. This closes the gaps 26a and 26b, and the resin layers around the gaps 26a and 26b melt to form a fused layer that fuses to each other to fill the gaps 26a and 26b, forming a pair of gap marks 27a and 27b. This flattens the wrinkles 6, forming a flat portion 28 between the pair of gap marks 27a and 27b on the inner surface of the container (the upper surface of the flange 4). The flat portion 28 refers to the surface portion of the crushed wrinkles 7 formed on the inner surface of the container (the upper surface of the flange 4) after the wrinkles 6 are crushed through a wrinkle pressing process, such as ultrasonic processing. Furthermore, "flat" refers to a state in which there is no overall change in height, such as unevenness, to the extent that it does not interfere with the top seal. In this embodiment, a flat portion is formed on at least a portion of the upper portion of the wrinkles 6.

[0075] When the wrinkles 6 are heated by ultrasonic processing while being pressed, the resin layer on the surface of the wrinkles 6 on the outer surface of the container melts to form a fusion layer, and the adjacent surrounding resin layers fuse together, flattening the wrinkles 6 on the outer surface of the container to some extent. However, since the space 24 is considerably larger than the gaps 26a and 26b, the space 24 inside the wrinkles 6 cannot be completely eliminated, and a void 25 remains inside the wrinkles 6 (crushed wrinkles 7).

[0076] Next, referring to (4) in Figure 4, when such a paper container 1 contains a food (content) containing moisture and is top-sealed by a plastic film as a lid material 29 with top-sealing properties on the flange portion 4 of the paper container 1, the upper surface of the flange portion 4 has a flat portion 28 formed after the wrinkle pressing process using ultrasonic processing, flattening the flange portion and enabling leak-free top sealing of the flange portion 4. Furthermore, minute voids 25 on the inner side of the wrinkles 6 (crushing wrinkles 7) appear on the underside of the flange portion 4 and do not affect the top seal. This results in a paper container 1 with improved top-sealing properties. Furthermore, because the flange portion 4 is flattened, the strength is improved compared to conventional paper containers whose wrinkles are not flattened. In particular, because the wrinkle pressing process includes ultrasonic processing of the wrinkles, flattening the flange portion is easier, improving the productivity of paper containers.

[0077] In the above embodiment, the paper container has an oval outer edge, but the shape is not particularly limited as long as it has a flange. For example, the shape when viewed from above the container opening may be circular, rectangular, polygonal, or approximately elliptical with straight lines. The size of the container is also not particularly limited. Container shapes also include those with a partition on the inside.

[0078] Furthermore, in the above embodiment, the multiple wrinkles formed by press molding were formed based on the multiple lines formed on the paperboard base paper, but the same effects of improving strength and top sealing properties can be achieved even if the paperboard base paper does not have lines formed in advance.

[0079] Furthermore, in the above embodiment, the wrinkles appearing on the upper surface of the flange have flat portions from the end of the flange on the side wall side to the end of the rolled-up portion, but it is sufficient if a flat portion is formed on at least a portion of the area from the end on the side wall side to the end on the rolled-up portion side. Furthermore, it is also possible for only some of the wrinkles appearing on the upper surface of the flange to have flat portions, while the other wrinkles do not. For example, if the outer edge of a paper container is oval, forming flat portions only on the wrinkles of the flange in the longitudinal direction can improve the container's strength in the longitudinal direction, thereby making it possible to improve the strength in a specific direction or region.

[0080] Furthermore, in the above embodiment, the flat portion is formed around the entire circumference of the flange, but it may be formed on at least a part of the flange. It may also be formed on the side wall. In other words, ultrasonic processing may be performed on the side wall (wrinkles).

[0081] 4(2) and 4(3), in the above embodiment, it is preferable that the ratio of the cross-sectional thickness (S1) of the paper container at the wrinkles having flat portions to the cross-sectional thickness (S2) of the paper container at the wrinkles having no flat portions is 0.7 or less. By configuring in this way, the crushed wrinkles, which are wrinkles having flat portions, are reliably flattened compared to the wrinkles having no flat portions, further improving the top sealability. Note that S2 can also be measured as the cross-sectional thickness of the paper container at the wrinkles in the side wall portion that have not been subjected to ultrasonic processing.

[0082] Furthermore, in the above embodiment, the flanges extend horizontally, but the horizontal direction does not only refer to the horizontal direction when the paper container is placed on a horizontal surface, but also includes cases where the flanges extend diagonally upward or downward toward the horizontal direction. This also includes unavoidable errors due to the molding process and the characteristics of the paper.

[0083] Furthermore, in the above embodiment, the highest part of the rolled edge portion is located at the same height as the upper surface of the flange portion, but it may also be located above or below the upper surface of the flange portion.

[0084] Furthermore, in the above embodiment, the paper container has a rolled edge, but the paper container may not have a rolled edge.

[0085] Furthermore, in the above embodiment, the wrinkles in the side wall portion are formed by folding from the outer surface of the container to the inner surface of the container, but they may be formed by folding from the inner surface to the outer surface. In this case, the paperboard base paper may have a portion where the creases corresponding to the wrinkles in the side wall portion and the creases corresponding to the wrinkles in the flange portion are not connected to each other.

[0086] By configuring it in this way, the concave portions of the wrinkles are located on the inner side of the side wall. Then, when food is placed inside the container and eaten with a spoon or the like, there are no convex portions of the wrinkles on the inner side, so the spoon or the like does not get caught on the convex portions of the wrinkles on the inner side of the container. Furthermore, since the wrinkles that fold from the inner side to the outer side of the paper container only extend to the top of the side wall, even if capillary action occurs due to the minute voids inside the wrinkles, moisture absorbed by capillary action only reaches the top of the side wall and does not reach the flange. This allows for both good top sealing and ease of eating.

[0087] Furthermore, in the above embodiment, the top seal is performed using a lid material such as a top seal film, but a lid material made of paper, plastic, or metal such as aluminum may also be fitted. Also, shrink wrapping may be used.

[0088] When a top seal film is used, the type, configuration, and sealing mode are not particularly limited as long as the paper container can be sealed by sealing with the top seal film that serves as the lid material, and it does not matter whether the top seal film is a complete seal type or an easy peel type. Of course, a commonly used top seal film with known heat sealing properties can also be used. Therefore, the top seal film may be a film made of a single layer of resin as long as it has sealing properties, or it may be a film made of not only a single layer but also multiple layers of resin laminated together to provide heat resistance and barrier properties. In particular, when a top seal film with high gas barrier properties is used as the lid material for the paper container of the present invention, a top seal paper container with high gas barrier properties can be obtained.

[0089] The resin used for the top seal film is not particularly limited, but examples thereof include thermoplastic resins such as polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin resins such as polypropylene, polyethylene, and polymethylpentene; polyamide resins such as nylon; acrylic (methacrylic) resins; diene resins such as polybutadiene; and polycarbonate resins. To make the paper container more environmentally friendly, for example, the above-mentioned thermoplastic resins produced as biomass resins derived from living organisms, or biodegradable resins such as polybutylene succinate (PBS), polylactic acid (PLA), and cellophane can also be used. Among these, particularly when used as a top seal film for food packaging containers, a resin with heat resistance that can withstand high temperatures in an oven or microwave oven is more preferable. Furthermore, when it is desired to impart barrier properties to the paper container that block or suppress the permeation of gases such as oxygen and water vapor, a resin with such barrier properties can be laminated as a film or coating. The type of resin with barrier properties is not particularly limited, and examples include polyvinyl alcohol resin, ethylene-vinyl alcohol copolymer resin, polyvinylidene chloride resin, etc. Furthermore, polyethylene terephthalate or polypropylene films having a metal vapor-deposited film such as aluminum or an inorganic vapor-deposited film such as silica or alumina formed on the surface thereof can also be used for the purpose of imparting barrier properties. Furthermore, a top seal film may be formed by combining and laminating a plurality of the above-mentioned various resins. For example, a top seal film may be formed by laminating at least a polyolefin resin such as polypropylene or polyethylene, or a polyester resin such as polyethylene terephthalate or polybutylene terephthalate with a resin having high gas barrier properties such as an ethylene-vinyl alcohol copolymer resin or a polyvinyl alcohol resin. In particular, the use of a top seal film formed by laminating at least an ethylene-vinyl alcohol copolymer resin on polyethylene terephthalate is preferred, since it can impart high gas barrier properties and produce a top-sealed paper container with high heat resistance when top-sealed to the paper container of the present invention.Of course, this does not preclude laminating other resins (for example, a sealant layer in the case of heat sealing) or other components (for example, paper or metal foil such as aluminum foil) in this configuration. Furthermore, the sealant layer may be formed from a known sealant film or an adhesive such as a lacquer-type adhesive, an easy-peel adhesive, or a hot-melt adhesive. The thickness of such a top seal film is not particularly limited, but examples include those with a thickness of about 5 μm to 200 μm. A thickness of about 20 μm to 80 μm is preferred.

[0090] Furthermore, the type of paper used for the paperboard base paper of the present invention is not particularly limited, and examples thereof include 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. Furthermore, depending on the intended use, a paperboard with a resin film attached thereto, a paperboard extruded by extrusion lamination, or a paperboard coated with a resin can also 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 more preferable to use a paperboard with resin layers formed on both sides.

[0091] Furthermore, the thickness of the paperboard base paper is not particularly limited, but is preferably 0.1 to 0.5 mm (basis weight: 100 to 500 g / m ２ ) can be preferably used. When the wrinkles in the flange portion of the paper container of the present invention are flattened by ultrasonic processing or the like, the strength of the flange portion is improved, and the resistance of the entire container to deformation is therefore increased. Therefore, it is possible to form the container using paperboard base paper that is thinner than conventional paperboard, and even when such a thin paperboard is used, it is possible to ensure strength that is comparable to conventional paperboard.

[0092] Furthermore, the interlayer strength of the paperboard base paper is preferably 500 mN / cm or more, more preferably 700 mN / cm or more, in the case of the T-peel method. ２ It is preferable that the saturation is 290 J / m or more. ２ Since the paperboard base paper 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. It is more preferable that the interlayer strength of the paperboard base paper is 500 mN / cm or more in the case of the T-peel method or 200 J / m or more in the case of the internal bond tester method. ２ If the interlaminar strength is equal to or greater than 1500 mN / cm, it is preferable that the interlaminar strength be 1500 mN / cm or less, and more preferably 1000 mN / cm or less, in the case of the T-peel method. ２ Preferably, 500 J / m or less ２ It is more preferable that the interlayer strength is not more than the above-mentioned upper limit. If the interlayer strength exceeds the above-mentioned upper limit, the rigidity of the paperboard base paper becomes too high, which may result in a decrease in formability or a tendency for springback to occur 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 setting the interlayer strength within the above-mentioned range, it is possible to suppress peeling between layers, and it is possible to improve the formability, particularly of the edge wrapping portion. Note that when the paperboard base paper is composed of multiple pulp layers, such as three or five layers, it is more preferable that the interlayer strength be within the above-mentioned range for all of the layers.

[0093] Furthermore, it is desirable that the paperboard base paper has a predetermined folding endurance. In the case of a paper container obtained by press-molding a single sheet of paperboard base paper, the paper is prone to tearing in the side wall of the paper container, especially in the corners where many wrinkles are concentrated. This is because the corners of the paperboard base paper 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 base paper 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 base paper with a folding endurance of less than 800 times may tear during press-molding of the side wall of the paper container, especially in the corners. Paperboard base paper with a folding resistance of more than 2,000 times has too strong folding properties, so springback is likely to occur in the rolled edge after press molding, which may reduce the shape retention of the paper container.

[0094] Furthermore, a resin film or coating may be laminated on the surface of the paperboard base paper. When a resin layer is formed on at least one side of the paperboard base paper, the type of resin is not particularly limited, and examples include thermoplastic resins such as polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate, polyolefin-based resins such as polypropylene, polyethylene, and polymethylpentene, acrylic (methacrylic) resins, diene-based resins such as polybutadiene, and polycarbonate resins. To make the paper container more environmentally friendly, for example, the above-mentioned thermoplastic resins produced as biomass resins derived from living organisms, or biodegradable resins such as polybutylene succinate (PBS) and polylactic acid (PLA) can also be used. Among these, thermoplastic resins suitable for ultrasonic processing after paper container formation are preferred, and particularly thermoplastic resins with heat resistance sufficient to withstand high temperatures in an oven or microwave oven when used as a food packaging container are more preferred. Furthermore, when it is desired to impart barrier properties to the paper container that block or suppress the permeation of gases such as oxygen or water vapor, resins with such barrier properties can be laminated as a film or coating. The type of resin with barrier properties is not particularly limited, and examples include polyvinyl alcohol resin (PVA), ethylene-vinyl alcohol copolymer resin (EVOH), polyvinylidene chloride resin (PVDC), etc. Furthermore, polyethylene terephthalate or polypropylene films with a metal vapor-deposited film such as aluminum or an inorganic vapor-deposited film such as silica or alumina formed on the surface can also be used to impart barrier properties. Furthermore, a combination of the above-mentioned resins may be laminated on the surface of the paperboard base paper. For example, a plurality of resins may be laminated in this order from the surface of the paperboard base paper: a first resin layer made of a polyolefin-based resin such as polypropylene or polyethylene, or a polyester-based resin such as polyethylene terephthalate or polybutylene terephthalate; a second resin layer made of a resin with high gas barrier properties such as an ethylene-vinyl alcohol copolymer resin or a polyvinyl alcohol resin; and a third resin layer made of a polyolefin-based resin or polyester-based resin similar to the first layer.In particular, a laminated structure in which, from the surface of the paperboard base paper, the first resin layer is polypropylene, the second resin layer is an ethylene-vinyl alcohol copolymer resin, and the third resin layer is polypropylene is preferable because it can impart high gas barrier properties to the paper container, has high heat resistance, is easy to process, and allows for a low raw material cost configuration. Of course, this does not exclude laminating other resins or other components (e.g., metal foil such as aluminum foil) in this configuration. Examples of methods for forming the resin layer include extrusion lamination, dry lamination, wet lamination, and resin solution coating. The resin lamination can impart properties such as heat resistance, water resistance, and gas / liquid permeability resistance to the molded paper container. Furthermore, when it is desired to impart high gas barrier properties to the paper container described above, a method can be adopted in which a gas barrier resin film is prepared in advance and then laminated on top of another resin layer when the other resin layer is extrusion laminated on the surface of the paperboard base paper.

[0006] When this method is used, multiple resin layers can be formed on the surface of the paperboard base paper without using a separate adhesive. For example, as described above, in the case where multiple resins are laminated in the following order from the surface of the paperboard base paper, starting from the surface, such as a first resin layer made of a polyolefin resin such as polypropylene or polyethylene, or a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, a second resin layer made of a resin with high gas barrier properties such as an ethylene-vinyl alcohol copolymer resin or a polyvinyl alcohol resin, and a third resin layer made of a polyolefin resin or polyester resin similar to the first layer, a gas barrier resin film in which the second and third resin layers are laminated together is prepared in advance, and when a polyolefin resin such as polypropylene or polyethylene, or a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, is extrusion-laminated onto the surface of the paperboard base paper as the first resin layer, this gas barrier resin film can be laminated on top of the first resin layer, thereby easily imparting gas barrier properties to a paper container.Therefore, known gas barrier resin films that are commercially available as gas barrier resin films can also be used.

[0095] Furthermore, the thickness of the resin on the surface of the paperboard base paper is not particularly limited, but may be, for example, in the range of 10 μm to 50 μm. A thickness in the range of 20 μm to 30 μm is particularly preferred. However, as described above, when multiple resin layers are laminated as the resin layer, the thickness may exceed this range. For example, when multiple resin layers are laminated, the total thickness may be in the range of 10 μm to 200 μm, particularly preferably 30 μm to 100 μm, and even more preferably 50 μm to 70 μm. Within this range, the desired effect of forming the resin layer can be achieved. Furthermore, by using a thick resin layer, paper irregularities are less likely to appear on the flange surface when the flange is flattened, which contributes to further flattening the flange. If the resin layer thickness is below this range, the desired effect of forming the resin layer may not be achieved, while if the resin layer thickness exceeds this range, costs will increase. Furthermore, if the total thickness of a plurality of laminated resin layers exceeds 200 μm, the resulting container may no longer be considered a paper container due to the thickness or weight of the paperboard base paper.

[0096] Furthermore, the surface of the paperboard base paper may be printed, thereby improving the design.

[0097] Furthermore, although the paperboard base paper has been described above with creases formed around the entire periphery of the portions corresponding to the side wall portions, flange portions, and curled edges, it is sufficient that the creases are formed around at least a portion of the side wall portions and flange portions. Also, the creases do not have to be formed.

[0098] 4(2) and 4(3), it is more preferable that in the wrinkle pressing step, the cross-sectional thickness of the wrinkled paper container having flat portions due to ultrasonic processing is 70% of the cross-sectional thickness of the wrinkled paper container before ultrasonic processing, compared to 100% of the cross-sectional thickness of the wrinkled paper container before ultrasonic processing. By configuring in this way, the wrinkles in the flange portion are reliably flattened compared to the wrinkles before ultrasonic processing, resulting in a paper container with further improved top sealing properties.

[0099] Furthermore, although the paper containers according to the embodiments of the present invention are manufactured by a specific manufacturing method, they may be manufactured by other manufacturing methods.

[0100] Furthermore, the flange portion of the paper container according to the embodiment of the present invention is manufactured by pressing wrinkles using ultrasonic processing to form a flat portion, but the manufacturing method may also be such that the flat portion is formed by pressing using a method other than ultrasonic processing.

[0101] The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited to these examples.

[0102] Test specimens for the examples and comparative examples of the present invention were prepared, and a test for measuring the thickness of the cross section of the wrinkled paper container was conducted on these test specimens to compare the thickness of the cross section of the wrinkled paper container, an air leakage test to evaluate the adhesion of the top seal, and a strength measurement test to measure the strength of the paper container. <Test specimen preparation> Example 1 First, a paperboard base paper with resin layers formed on both sides and with ruled lines formed in the parts corresponding to the side wall parts, the flange parts, and the rolled edge parts was prepared (preparation step), and this paperboard base paper was press-molded to form a paper container (pressing step). The paperboard base paper had a thickness of about 0.3 mm and a basis weight of about 260 g / m ２ The paper container had a planar long-side length of approximately 179 mm (including the flange), a short-side length of approximately 120 mm (including the flange), a height from the bottom to the flange of approximately 30 mm, and a rolled-edge diameter of approximately 3 mm. Furthermore, because the lines in the paperboard base paper were folded from the outer surface of the container to the inner surface of the container, wrinkles were formed in the sidewalls and flanges of the paper container after press molding, folding from the outer surface of the container (the lower surface of the flange) to the inner surface of the container (the upper surface of the flange) (hereinafter, the state in which wrinkles are formed so as to fold from the outer surface of the container to the inner surface of the container is referred to as "reverse grain").

[0103] Next, the press-molded paper container (after the pressing process) was placed on the base of an ultrasonic processing device as shown in Figure 5, and an ultrasonic horn was lowered from above the paper container to sandwich the flange of the paper container between the base and the ultrasonic horn, and ultrasonic vibrations of 3.0 kW were applied to the flange for 0.5 seconds, resulting in a vibration of 0.4 MPa / cm. ２ The wrinkles were crushed from above and below by applying a pressure of 0.4 MPa / cm. This paper container was designated as Example 1. Example 2: A paper container press-molded in the same manner as in Example 1 was subjected to ultrasonic vibration of 3.0 kW for 1.0 second on the flange portion using the same ultrasonic processing device as in Example 1, and the pressure was reduced to 0.4 MPa / cm. ２ The wrinkles were crushed from above and below by applying a pressure of 0.4 MPa / cm. This paper container was designated as Example 2. Example 3: A paper container was press-molded in the same manner as in Example 1, and ultrasonic vibrations of 3.0 kW were applied to the flange portion for 1.5 seconds using the same ultrasonic processing device as in Example 1, to crush the wrinkles from above and below. ２ The paper container was designated as Example 3. Example 4: Instead of the paperboard base paper used in Example 1, a paperboard having a thickness of about 0.3 mm and a basis weight of about 260 g / m ２ The paper container was press-molded in the same manner as in Example 1, except that a paperboard base paper was used in which approximately 20 μm of polypropylene resin was extrusion-laminated on one side of the paperboard base paper and approximately 20 μm of polypropylene resin as a first resin layer, approximately 20 μm of ethylene-vinyl alcohol copolymer resin as a second resin layer, and approximately 20 μm of polypropylene resin as a third resin layer, in that order from the surface of the paperboard base paper, was used, with the side of the paperboard base paper on which only the polypropylene resin was formed facing the outer surface of the container.Using the same ultrasonic processing device as in Example 1, ultrasonic vibrations of 3.0 kW were applied to the flange portion for 1.0 second, resulting in a vibration of 0.4 MPa / cm. ２The wrinkles were crushed from above and below by applying a pressure of 100 psi. This paper container was designated Example 4. The first to third resin layers were formed on the paperboard base paper by preparing in advance a composite film (gas barrier resin film) in which the second and third resin layers were laminated, and laminating this gas barrier resin film on the first resin layer when extrusion laminating polypropylene resin onto the surface of the paperboard base paper as the first resin layer. Example 5: Instead of the paperboard base paper used in Example 1, a paperboard with a thickness of about 0.3 mm and a basis weight of about 260 g / m ２ The paper container was press-molded in the same manner as in Example 1, except that a paperboard base paper was used in which approximately 20 μm of polypropylene resin was extrusion-laminated on one side of the paperboard base paper and approximately 20 μm of polypropylene resin as a first resin layer, approximately 20 μm of ethylene-vinyl alcohol copolymer resin as a second resin layer, and approximately 20 μm of polypropylene resin as a third resin layer, in that order from the surface of the paperboard base paper, was used, with the side of the paperboard base paper on which only the polypropylene resin was formed facing the inner surface of the container.Using the same ultrasonic processing device as in Example 1, ultrasonic vibrations of 3.0 kW were applied to the flange portion for 1.5 seconds, resulting in a vibration of 0.4 MPa / cm. ２ The wrinkles were crushed from above and below by applying a pressure of 0.4 MPa / cm. This paper container was designated as Example 5. The first to third resin layers were formed on the paperboard base paper in the same manner as in Example 4. Example 6 A paper container was press-molded in the same manner as in Example 1, except that the formation of the creases on the paperboard base paper in the preparation step of Example 1 was performed in the manner described below. The flange portion of the paper container was subjected to ultrasonic vibration of 3.0 kW for 1.0 second using the same ultrasonic processing device as in Example 1, and the pressure was 0.4 MPa / cm. ２A pressure of 1000 kJ / cm was applied to crush the wrinkles from above and below. This paper container was designated Example 6. Here, in obtaining the paper container of Example 6, the creases in the paperboard base paper in the portion corresponding to the side wall portion of the paper container after press molding were formed so as to be folded from the inner surface of the container to the outer surface of the container, and the creases in the portion corresponding to the flange portion of the paper container after press molding were formed so as to be folded from the outer surface of the container to the inner surface of the container, and there were portions where the creases corresponding to the wrinkles in the side wall portion and the creases corresponding to the wrinkles in the flange portion were not connected. As a result, the paper container after the pressing step and before the wrinkle pressing step using the ultrasonic processing device has wrinkles formed in its side wall portion as if folded from the inner surface of the container to the outer surface of the container (hereinafter, the state in which wrinkles are formed as if folded from the inner surface of the container to the outer surface of the container is referred to as "with the grain") and has wrinkles formed in its flange portion with the grain crossed, and the wrinkles in the flange portion are crushed by the wrinkle pressing step using the ultrasonic processing device. Example 7 A paper container was press-molded in the same manner as in Example 6. The flange portion was subjected to ultrasonic vibration of 3.0 kW for 1.5 seconds using the same ultrasonic processing device as in Example 6, and the pressure was reduced to 0.4 MPa / cm. ２ The wrinkles were crushed from above and below by applying a pressure of 0.4 MPa / cm to the flange portion of the paper container. This paper container was designated as Example 7. Comparative Example 1 A paper container press-molded in the same manner as in Example 1 was designated as Comparative Example 1. In other words, this paper container was not subjected to the wrinkle pressing process using an ultrasonic processing device. Comparative Example 2 A paper container press-molded in the same manner as in Example 1 was simply pressed at 0.4 MPa / cm to the flange portion without performing the wrinkle pressing process using an ultrasonic processing device. ２ The wrinkles were crushed by applying only pressure of 0.3 mm. This paper container was designated Comparative Example 2. That is, it is a paper container that was not subjected to the wrinkle pressing process using an ultrasonic processing device. Comparative Example 3 A paper container was formed by press-molding a paperboard base paper on which resin layers were formed on both sides and on which ruled lines were formed in the portions corresponding to the side wall portions, the flange portions, and the rolled-edge portions. The paperboard base paper had a thickness of about 0.3 mm and a basis weight of about 260 g / m ２The paper container had a planar long-side length of approximately 179 mm (including the flange), a short-side length of approximately 120 mm (including the flange), a height from the bottom to the flange of approximately 30 mm, and a rolled-edge diameter of approximately 3 mm. Furthermore, since the ruled lines of the paperboard base paper were formed by folding from the inner surface of the container to the outer surface of the container, wrinkles along the grain were formed on the side walls and flanges of the paper container after press molding. This paper container was designated Comparative Example 3. That is, this paper container differs from Example 1 in the wrinkle formation direction and was not subjected to a wrinkle pressing process using an ultrasonic processing device. Comparative Example 4: A paper container press-molded in the same manner as Comparative Example 3 was subjected to ultrasonic vibrations of 3.0 kW for 1.0 second on the flanges using the same ultrasonic processing device as Example 1, resulting in a 0.4 MPa / cm ２ The wrinkles were crushed by applying a pressure of 0.4 MPa / cm. This paper container was designated Comparative Example 4. That is, this paper container has wrinkles formed in a different direction from Example 1, and was subjected to a wrinkle pressing process using an ultrasonic processing device under the same conditions as Example 2. Comparative Example 5 A paper container press-molded in the same manner as Comparative Example 3 was subjected to ultrasonic vibrations of 3.0 kW for 1.5 seconds on the flange portion using the same ultrasonic processing device as Example 1, resulting in a pressure of 0.4 MPa / cm. ２ The wrinkles were crushed by applying a pressure of 1000 kJ / cm. This paper container was designated Comparative Example 5. That is, this paper container had wrinkles formed in a different direction from Example 1, and was subjected to a wrinkle pressing process using an ultrasonic processing device under the same conditions as Example 3. Comparative Example 6 A paper container press-molded in the same manner as Example 4 was designated Comparative Example 6. That is, this paper container was not subjected to a wrinkle pressing process using an ultrasonic processing device. <Thickness measurement test of paper container cross section with wrinkles, air leakage test, and strength measurement test> Test 1-1. Thickness measurement test of paper container cross section with wrinkles The cross-sectional thickness of the paper container at the wrinkles at four points on the flange was measured using a micrometer.

[0104] The micrometer used was manufactured by Mitutoyo Corporation, product number: M110-25.

[0105] Referring to FIG. 1, the measurement points were two points on both sides of the flange in the longitudinal direction (measurement points A and C) and two points on both sides of the flange in the lateral direction (measurement points B and D).

[0106] The results are shown in Table 1 below.

[0107] Next, the thickness (S2) of the cross section of the paper container at the wrinkles in the side wall portion connected below the measurement points A to D of each example and comparative example was measured.

[0108] Then, to compare the cross-sectional thickness of the wrinkled paper container before and after ultrasonic processing of the flange portion, the cross-sectional thickness of the wrinkled paper container at the flange portion (S1) / the cross-sectional thickness of the wrinkled paper container at the side wall portion (S2) was calculated. Note that, since the side wall portion was not subjected to ultrasonic processing in this test, the cross-sectional thickness of the wrinkled paper container at the side wall portion was used as the cross-sectional thickness of the wrinkled paper container at the flange portion before ultrasonic processing.

[0109] The results are shown in Table 2 below.

[0110] Referring to Table 2, the four-point average for Examples 1 to 7, which were subjected to ultrasonic processing, was S1 / S2 < 0.7. Furthermore, the four-point average for Examples 2 to 7, which were subjected to ultrasonic processing for 1.0 second or more, was S1 / S2 ≦ 0.59. From the above measurement results, it was found that ultrasonic processing reliably flattens wrinkles. Furthermore, the four-point average for Comparative Examples 4 and 5, which were subjected to ultrasonic processing, was S1 / S2 ≦ 0.57. Test 1-2. Air Leakage Test A sample for the test to measure the thickness of the cross section of a wrinkled paper container was top-sealed, and 0.1 MPa of compressed air was enclosed and the sample was submerged, and air leakage from the sealed surface was visually confirmed. The sealing conditions were a heating temperature of 180°C, a heating time of 2 seconds, and a pressure of 0.5 MPa / cm. ２ The sealing was performed once.

[0111] Furthermore, the evaluation was made as follows: no air leakage was indicated by ⊚; air leakage was reduced to a small amount compared to the case without ultrasonic processing or compression and was indicated by ◯; and air leakage was observed and was unsatisfactory, indicated by x.

[0112] The results are shown in Table 3 below.

[0113] Referring to Table 3, it was confirmed that in all of Examples 1 to 7, air leakage was reduced and top sealing performance was improved.

[0114] Furthermore, it was confirmed that in Examples 2 to 7, where S1 / S2 was less than 0.7, there was no air leakage and the top sealability was further improved. - Test 1-3. Oxygen gas permeability measurement test 1. Preparation of measurement samples The paper containers of Examples 4 and 5 were prepared as measurement samples. Furthermore, as Example 5-2, a paper container was prepared in the same manner as in Example 5, except that in the paper container of Example 5, the second resin layer was an ethylene-vinyl alcohol copolymer resin with a thickness of approximately 10 μm. All paper containers had undergone a wrinkle pressing process. Next, a laminated film (manufactured by Mitsubishi Chemical Corporation, product name Diamiron VM60) having a total thickness of 50 μm and comprising an EVOH (ethylene vinyl alcohol copolymer resin) / nylon / PP (polypropylene resin) easy-peel sealant layer was dry laminated with a 12 μm PET (polyethylene terephthalate resin) film to produce a top-sealable lid material comprising a PET / EVOH / nylon / easy-peel sealant layer. The paper containers of Examples 4, 5, and 5-2 were top-sealed to the flanges of the paper containers by heat sealing, with the easy-peel sealant layer of the lid material facing the paper container, thereby preparing the top-sealed paper containers of the present invention. 2. Measurement test using measurement samples The oxygen gas permeability of the top-sealed paper containers of Examples 4, 5, and 5-2 obtained in 1 above was measured using a method in accordance with JIS K7126-2.

[0115] The measurement equipment and conditions were as follows, and the top-sealed paper container itself was used as the measurement sample. Measurement equipment: OX-TRAN2 / 21 (manufactured by MOCON) Temperature and humidity: 23°C, 50% RH air (outside, test gas), 23°C, dry nitrogen (inside, carrier gas) Permeating gas: air (21% oxygen) Permeation direction: permeation from outside to inside The results are shown in Table 4 below.

[0116] Referring to Table 4, it was confirmed that the top-sealed paper containers of Examples 4, 5, and 5-2 obtained in 1 above all had good oxygen gas permeability. It was also confirmed that Examples 4 and 5, in which the second resin layer was an ethylene-vinyl alcohol copolymer resin of approximately 20 μm, had better oxygen gas permeability than Example 5-2, in which the second resin layer was an ethylene-vinyl alcohol copolymer resin of approximately 10 μm. Test 2. Strength Measurement Test I. Preparation for Measurement Test As examples, Examples 1 to 3 described above were prepared.

[0117] As a comparative example, the above-mentioned comparative example 1 was prepared.

[0118] Using these examples and comparative examples, the circumferential strength (longitudinal direction, lateral direction) of each was measured.

[0119] The measurement device used was a material testing machine "Autograph" (registered trademark) manufactured by Shimadzu Corporation and its data processing software "TRAPEZIUM" (registered trademark).

[0120] The measurement test was conducted in accordance with the circumferential test of the above-mentioned "TRAPEZIUM" (registered trademark), but the switching stroke was changed from 10 mm to 20 mm. II. Longitudinal Measurement Test Figure 6 is a schematic diagram showing the state of the measurement test conducted on the paper container shown in Figure 1.

[0121] Referring to FIG. 6, paper container 1 was pressed in the direction indicated by the arrow in the figure while the lower end was fixed by measuring device 30, and the resulting stress was measured by measuring device 30.

[0122] The measurement test was carried out on three pieces each of the example and the comparative example, and the arithmetic mean of the three measurements was calculated to be the result of the measurement test.

[0123] FIG. 7 is a graph showing the results of the measurement test shown in FIG. 6, where (1) is the longitudinal direction and (2) is the transverse direction.

[0124] 7(1), when the same test force [N] was applied in the longitudinal direction to the paper containers of the Example and Comparative Example, it was found that the Example had a smaller deformation amount [mm] than the Comparative Example. Furthermore, among Examples 1 to 3, it was found that Example 3, which had the longest ultrasonic processing time, had the smallest deformation amount [mm]. III. Measurement test in the transverse direction The measurement method was the same as the longitudinal measurement test described above, except that the paper container was placed at a 90-degree angle.

[0125] 7(2), when the same test force was applied in the short direction to the paper containers of the Example and the Comparative Example, it was found that the Example had a smaller deformation amount than the Comparative Example. Furthermore, it was found that, among Examples 1 to 3, Example 3, which had the longest ultrasonic processing time, had the smallest deformation amount [mm].

[0126] From the results of the above measurement tests, it was confirmed that the ultrasonically processed paper container of the present invention has improved strength.

[0127] As described above, the paper container, top-seal paper container, and paper container manufacturing method according to the present invention are suitable for containing, for example, food products.

Claims

1. A paper container (1) formed solely by press molding from a sheet of paperboard base paper (10) having a resin layer formed on at least the surface that will become the inside surface of the container, and comprising a bottom (2), a side wall (3) connected to the bottom, and a flange (4) connected to the upper end of the side wall and extending horizontally outward, wherein the side wall and the flange have a plurality of creases (6) formed by press molding, the creases in the flange are formed by folding from the lower surface to the upper surface of the flange, and the creases appearing on the upper surface of the flange have at least a flat portion (28) formed in at least a portion of the paper container.

2. The paper container according to claim 1, wherein the outer periphery of the flange portion is provided with a rolled edge portion (5), and the highest part of the rolled edge portion is located at the same height as or below the upper surface of the flange portion.

3. A paper container as described in claim 1 or claim 2, wherein the ratio (S1 / S2) of the cross-sectional thickness (S1) of the paper container at the wrinkles having the flat portion to the cross-sectional thickness (S2) of the paper container at the wrinkles not having the flat portion is 0.7 or less.

4. A paper container according to claim 1 or 2, wherein the wrinkles in the flange portion are formed based on a plurality of creases (21) formed in a portion (14) of the paperboard base paper that corresponds to the flange portion.

5. A paper container according to claim 1 or 2, wherein the wrinkles in the side wall portion are formed by folding from the inner surface to the outer surface of the side wall portion.

6. A top-sealed paper container comprising the paper container according to claim 1 or 2 and a lid material (29) having top-sealing properties.

7. A method for manufacturing a paper container comprising: a preparation step of preparing paperboard base paper (10); a pressing step of pressing the paperboard base paper to form a paper container (1) having a bottom (2), a side wall portion (3) connected to the bottom, and a flange portion (4) connected to the upper end of the side wall portion, extending horizontally outward, and having wrinkles (6) formed on its upper surface by folding from the bottom to the top; and a wrinkle pressing step of forming a flat portion (28) in at least a portion of the wrinkles.

8. The method for manufacturing a paper container according to claim 7, wherein the wrinkle pressing step includes subjecting the wrinkles to ultrasonic processing.

9. The method for manufacturing a paper container according to claim 8, wherein a resin layer is formed on at least the surface of the paperboard base paper that will become the inner surface of the container, and the resin layer is melted by the ultrasonic processing.

10. A method for manufacturing a paper container as described in claim 9, wherein the wrinkle pressing process reduces the cross-sectional thickness of the wrinkled paper container having the flat portion by the ultrasonic processing to 70% or less, compared to 100% of the cross-sectional thickness of the wrinkled paper container before the ultrasonic processing.

11. The top-sealed paper container according to claim 6, wherein the paper container and the lid are provided with a resin layer having barrier properties.

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