US20030102361A1 - Resin box - Google Patents

Abstract

On a folding section of the thermoplastic sheet there is provided one or more thin-walled section, extending in a longitudinal direction of the folding section, whose minimum thickness is not less than {fraction (1/10)} and not more than ⅔ the thickness of the thermoplastic resin sheet. Thus, it is possible to provide a box in which rebound of the folding section is reduced and an operation efficiency upon setting up the box and putting goods into the box can be improved.

Description

FIELD OF THE INVENTION
• The present invention relates to a resin box, and in particular to a recursive resin box to be suitably used for a returnable box.[0001]
BACKGROUND OF THE INVENTION
• Conventionally, a resin box, such as a cardboard box, a plastic box, has been used for containers for transporting various products.[0002]
• However, a cardboard box is made of paper and therefore it is sensitive to water and is hardly recursive. Further, it causes a problem of paper dust, which is likely to get in the products.[0003]
• To provide a replacement of such a cardboard box, Japanese Unexamined Patent Publication No. 164933/1996 (Tokukaihei 8-164933, published on Jun. 25, 1996) and Japanese Unexamined Patent Publication No. 79940/2000 (Tokukai 2000-79940, published on Mar. 21, 2000) disclose a resin box, which is made of a folded resin sheet.[0004]
• However, the conventional resin box made of a folded resin sheet causes inefficiency during the fabrication of the box, as it requires some knack to deal with its repulsion force at the folding portion. Also the repulsion force at the cover sections interferes the work to put in the products in the box.[0005]
• Further, in the conventional resin box made of a folded resin sheet, when the box is sealed by folding flaps (cover sections), the upper flaps for covering over the lower flaps are lifted by the lower flaps beneath because of the compression strength in the thickness direction of the resin sheet. This causes deterioration of the appearance of the box after sealed, and also causes some difficulties when the sealing sections are sealed with tapes or the like.[0006]
• Further, in the conventional resin box made of a folded resin sheet, the connection section of each side is joined with metal stitches, metal rivets, or resin pins. In this joining method, the resin sheets are joined at portions having a certain area with arbitrary intervals by using pin-shaped components[0007]
• However, with this method, the resin box cannot be completely sealed, and may cause some gaps between the joining portions when a plurality of boxes is placed one on another. These gaps between the joining portions allow dust to get in the box.[0008]
• Further, the conventional resin box made of a folded resin sheet is harder than a cardboard box and therefore causes a difficulty of the folding work.[0009]
SUMMARY OF THE INVENTION
• In view of the foregoing problems, the object of the present invention is to provide a resin box showing reduced rebound of a folding section and being capable of improving operation efficiency upon setting up the box and putting goods into the box.[0010]
• As a result of earnest study performed by the inventors so as to solve the foregoing problems, they found that: as to a resin box constituted of a thermoplastic resin sheet, it is possible to reduce the rebound of the folding section and to improve the operation efficiency upon setting up the box and putting goods into the box by arranging as follows. According to this, they made the present invention.[0011]
• In order to achieve the foregoing object, the resin box of the present invention is constituted of a thermoplastic resin sheet including a folding section, wherein the folding section includes at least one thin-walled section, extending in a longitudinal direction of the folding section, whose minimum thickness is not less than {fraction (1/10)} and not more than ⅔ the thickness of the thermoplastic resin sheet.[0012]
• Further, in order to achieve the foregoing object, the resin box of the present invention is constituted of a thermoplastic resin sheet including a folding section, wherein the folding section includes at least one thin-walled section, extending in a longitudinal direction of the folding section, whose minimum thickness is not less than {fraction (1/10)} and not more than ⅔ the thickness of the thermoplastic resin sheet.[0013]
• Note that, it is more preferable to form two or more thin-walled sections in each folding section, and in the case where two or more thin-walled sections are formed in a folded section, the thin-walled sections are formed in parallel to each other.[0014]
• According to the invention, the folding section of the thermoplastic resin sheet includes a thin-walled section having a thickness of not less than {fraction (1/10)} and not more than ⅔ the sheet thickness, thereby improving operation efficiency upon setting up the box and putting goods into the box. Further, rebound of the folding section is reduced, thereby effectively preventing exfoliation and breakage of the connection section joined by pasting, etc.[0015]
• Therefore, it is possible to provide a resin box showing reduced rebound of the folding section and being capable of improving operation efficiency, upon setting up the box and putting goods into the box.[0016]
• Further, when each folding section includes two or more thin-walled sections parallel to each other, it is possible to fold the folding section more easily in comparison to the folding section including one thin-walled section, and to improve an upright property of the box.[0017]
• Another object of the present invention is to provide a resin box which shows reduced rebound between overlapping folded cover sections so as to improve an appearance of the box, and can be easily taped at the sealing point using a tape, etc., when the folded cover sections are overlapped and sealed.[0018]
• Further, another object of the present invention is to provide such a resin box that: when folded covers are overlapped with each other and are sealed, appearance of the box is improved by reducing repulsive force between the folding covers, and a sealing portion can be easily sealed with a tape etc.[0019]
• As a result of earnest study performed by the inventors so as to solve the foregoing problems, they found that: as to the resin box constituted of the thermoplastic resin sheet, by arranging the folded covers of the thermoplastic resin sheet as follows, the folded covers overlapped with each other do not repel each other, and the upper folded cover is not lifted by the lower folded cover, and the appearance of the box is improved, and it is easier to seal the sealing portion with tapes and the like. According to this, they made the present invention.[0020]
• In order to achieve the foregoing object, the resin box of the present invention is constituted by folding one or more thermoplastic resin sheet, wherein: the thermoplastic resin sheet is constituted of two or more side face sections, adjacent to each other, that are connected via folding sections to cover sections and bottom sections both of which are freely foldable, and each of the folding sections includes two or more thin-walled sections parallel to each other, and in one folding section, there is provided a level difference between the cover sections adjacent to each other, and in another folding section, there is another level difference between the bottom sections adjacent to each other, the level difference being 1 to 1.2 times the thickness of the thermoplastic resin sheet.[0021]
• According to the invention, the folding sections are provided between the side face sections adjacent to each other and the cover sections so as to have a level difference whose length is 1 to 1.2 times the thickness of the sheet in a depth direction of the box. For this reason, in a case where the cover sections adjacent to each other or the bottom sections adjacent to each other are folded at an angle of 90°, there exists the level difference whose length is 1 to 1.2 times the thickness of the sheet, so that the cover sections or the bottom sections overlap with each other with less strain. As a result, it is possible to prevent the rise of a cover sections or a bottom section caused by another cover section or the bottom section. Further, it is possible to reduce a gap between the overlapped portions, thereby preventing extraneous objects from coming into the box.[0022]
• Further, there are provided two thin-walled sections parallel to each other on a folding section, it is possible to fold the folding section more easily than the folding section having a single thin-walled section thereon. Thus, it is possible to obtain not only an advantage that an operation efficiency upon setting up the box and putting goods into the box is improved, but also an advantage that the rebound of the folding section is reduced.[0023]
• Therefore, it is possible to provide such a box that the rebound of the folding section is reduced and the operation efficiency upon setting up the box and putting goods into the box can be improved.[0024]
• Further, a further object of the present invention is to provided a resin box capable of enduring the repeated using, and capable of reducing a gap between the overlapped portions so as to prevent extraneous objects from coming into the box.[0025]
• As a result of earnest study performed by the inventors so as to solve the foregoing problems, they found that: a portion to which a connection portion of the side face section is bonded extends from the folding section on the side of the cover section to the folding section on the side of the bottom section, and there is no rift in bonded faces of the connection portion, so that an extraneous object such as a dust does not come into the box through the gap. According to this, they made the present invention.[0026]
• In order to achieve the foregoing object, the resin box of the present invention is constituted by folding one or more thermoplastic resin sheet, wherein: the thermoplastic resin sheet is constituted of two or more side face sections connected via folding sections, each of which has one or more thin-walled section, to cover sections and bottom sections both of which are freely foldable, and the thermoplastic sheet includes a connection portion connected to an opening side portion of at least one of the side face sections adjacent to each other, and the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least a foamed layer whose expansion ratio is 1.5 to 9 and at least a non-foamed layer, and the connection portion is welded to the side face section so that a length of the connection portion is substantially as long as a distance between a folding section along a cover section and a folding section along a bottom section extending from the side face section from which the cover section extends, and a bonded face of the connection portion extends from the folding section along the cover section to the other folding section along the bottom sections.[0027]
• According to the invention, a connection portion is welded on the side face section so as to have the same length as a distance between a folding section along a cover section and a folding section along a bottom section extending from the side face section from which the cover section extends.[0028]
• Thus, the bonded face is successively provided from the folding section along the cover section to the folding section along the bottom section. Thus, there is no rift in the bonded face on the connection section. Therefore, there is no possibility that dust comes through a gap into the box. Further, the resin sheet itself is bonded without using other adhesive, so that it is possible to efficiently recycle it.[0029]
• Meanwhile, the resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least one foamed layer whose expansion ratio is 1.5 to 9 for each layer and at least one non-foamed layer.[0030]
• In a case where the resin sheet is the monolayer resin sheet constituted of a foamed layer whose expansion ratio is less than 1.5, or in a case where the resin sheet is the multilayer resin sheet constituted of a non-foamed layer whose expansion ratio is less than 1.5 for all layers, the resin sheet becomes heavy in case of setting up the box. Meanwhile, the monolayer resin sheet constituted of a foamed layer whose expansion ratio is over 9 does not bring about sufficient rigidity.[0031]
• As a result, it is possible to provide the box that can endure the repetitive usages, and has no gap in the connection section, and can prevent extraneous objects such as dust from coming into the box.[0032]
• Yet another object of the present invention is to provide a resin box capable of being easily set up and folded with improving folding efficiency.[0033]
• As a result of earnest study performed by the inventors so as to solve the foregoing problem, they found that: as to the resin box constituted of the thermoplastic resin sheet, the thermoplastic resin sheet is arranged as follows, so that the operation efficiency upon setting up the box and putting goods into the box is improved. According to this, they made the present invention.[0034]
• In order to achieve the foregoing object, the resin box of the present invention is constituted so as to be a rectangular prism by folding at least one thermoplastic resin sheet, wherein: the at least one thermoplastic resin sheet is constituted of two or more side face sections connected via folding sections, each of which has one or more thin-walled section, to cover sections and bottom sections both of which are freely foldable, and the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least one foamed layer whose expansion ratio is 1.5 to 9 and at least one non-foamed layer, and two of the bottom sections adjacent to each other are partially bonded to each other as one pair, and a diagonally folding section is provided in a substantially 45° direction from a corner section on said one pair of the bottom sections that is externally positioned when the bottom sections are folded, and said one pair is opposite to another pair of the bottom sections. Note that, the foamed layer means a layer whose expansion ratio is not less than 1.5, and the non-foamed layer includes not only an absolute non-foamed layer whose expansion ratio is 1, but also a slightly foamed layer whose expansion ratio is not more than 1.5.[0035]
• According to the invention, the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least a foamed layer whose expansion ratio is 1.5 to 9 and at least a non-foamed layer[0036]
• According to this, at least one layer is constituted of the foamed layer, so that an end face that has been processed is not sharpened. This brings about not only the safety but also a hygienic advantage because an extraneous object does not come into the box through the end face. That is, in a thermoplastic resin sheet provided in a paper cardboard shape, the extraneous object comes into the box through the end face, but in the thermoplastic resin sheet having some thickness due to the foamed layer, the extraneous object is prevented from coming into the box through the end face.[0037]
• In the present invention, the resin box is arranged so that: the diagonally folding section is provided in a substantially 45° direction from a corner section on said one pair of the bottom sections that is externally positioned when the bottom sections are folded, and said one pair is opposite to another pair of the bottom sections.[0038]
• According to this, by folding the box along the diagonally folding sections, the box can be easily folded. Reversely, only by opening the folded resin box, the box can be obtained in a three-dimensional shape.[0039]
• As a result, it is possible to provide the box capable of being easily set up and folded with improving the folding efficiency.[0040]
• For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.[0041]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective diagram showing an embodiment of a resin box in the present invention.[0042]
• FIG. 2 is a development showing the resin box.[0043]
• FIG. 3([0044]a) is a sectional view showing a shape of a thin-walled section formed in a folding section of the resin box.
• FIG. 3([0045]b) is a sectional view showing another shape of the thin-walled section formed in the folding section of the resin box.
• FIG. 3([0046]c) is a sectional view showing a further shape of the thin-walled section formed in the folding section of the resin box.
• FIG. 4 is a perspective view showing the thin-walled section formed in the folding section of the resin box.[0047]
• FIG. 5([0048]a) is a sectional view showing a structure of a resin sheet of the resin box, which is a multilayer foamed sheet wherein a foamed layer is sandwiched with non-foamed layers on front and back surfaces.
• FIG. 5([0049]b) is a sectional view showing a structure of the resin sheet of the resin box, which is a multilayer foamed sheet wherein the non-foamed layer, a foamed layer with an expansion ratio of 1.5 through 9, and a foamed layer with an expansion ratio of 20 through 40 are sequentially layered from below.
• FIG. 5([0050]c) is a sectional view showing a structure of the resin sheet of the resin box, which is a multilayer foamed sheet wherein the non-foamed layer, the foamed layer with an expansion ratio of 1.5 through 9, a foamed layer with a expansion ratio of approximately 30 are sequentially layered from below.
• FIG. 5([0051]d) is a sectional view showing a structure of the resin sheet of the resin box, which is a multilayer sheet wherein the foamed layer with an expansion ratio of 1.5 through 9, the non-foamed layer, the non-foamed layer, and the foamed layer with an expansion ratio of 1.5 through 9 are sequentially layered from below.
• FIG. 6 is a development of another embodiment of the resin box of the present invention.[0052]
• FIG. 7 is an end view showing an arrangement of a folding section of the resin box.[0053]
• FIG. 8([0054]a) is an end view showing another arrangement of the folding section of the resin box.
• FIG. 8([0055]b) is an end view showing a further arrangement of the folding section of the resin box.
• FIG. 9 shows a side view showing a method of buckling strength evaluation.[0056]
• FIG. 10 is a perspective view showing chief members of the resin box.[0057]
• FIG. 11 is a development schematically showing the resin box.[0058]
• FIG. 12([0059]a) is a development showing one resin sheet of the resin box.
• FIG. 12([0060]b) is a development showing the other resin sheet of the resin box.
• FIG. 13 is a bottom view showing a back surface of the resin box when set up.[0061]
• FIG. 14([0062]a) is a sectional view showing a locking section and a locked section on a bottom section of the resin box.
• FIG. 14([0063]b) is a sectional view showing another locking section and another locked section on the bottom section of the resin box.
• FIG. 15([0064]a) is an exploded perspective view showing a further locking section and a further locked section on the bottom section of the resin box.
• FIG. 15([0065]b) is a plan view showing yet another locking section on the bottom section of the resin box.
DISCLOSURE OF INVENTION
• [Embodiment 1][0066]
• The following will explain an embodiment of the present invention with reference to FIGS. 1 through 5.[0067]
• A[0068]box1 in the present embodiment is a box capable of being folded, as shown in FIG. 1. Thebox1 is constituted of aresin sheet2 having a thickness of 2 mm through 10 mm. Thebox1 may be constituted of acontinuous resin sheet2, or may be composed of not less than tworesin sheets2 which have been joined together using proper means. However, at least oneresin sheet2 constituting thebox1 is provided with at least onefolding section3.
• The[0069]folding section3 may be aside section3abetween adjacent twofaces4 which are formed of thecontinuous resin sheet2, for example. Alternatively, thefolding section3 may be afolding section3bprovided along a boundary between (1) aface4 and (2) a connection section5 (a shaded section in FIG. 2), which is a continuous section of theface4, for joining theface4 with anotherface4, as shown in FIG. 2.
• In the[0070]box1, thefolding section3 of theresin sheet2 has a thin-walled section7 having a minimum thickness of not less than {fraction (1/10)} and not more than ⅔ the thickness of ageneral section6 of theresin sheet2, as shown in FIGS.3(a),3(b), and3(c). The thickness of the thin-walled section7 is more preferably not less than ⅕ and not more than ½ the thickness of thegeneral section6 of theresin sheet2. Namely, when the thin-walled section7 is less than {fraction (1/10)} the thickness of thegeneral section6, repetition of folding easily exfoliates and breaks the thin-walled section7. On the other hand, when the thin-walled section7 is not less than ⅔ the thickness of thegeneral section6, thefolding section3 has too much repulsive force as described later. Note that, a groove width of the thin-walled section7 is preferably not less than ½ the thickness of thegeneral section6 of theresin sheet2.
• In the[0071]box1 in the present embodiment, since thefolding section3 of theresin sheet2 is formed with the thin-walled section7 having the above-described size, the repulsive force (restitutive force) is reduced at thefolding section3 of theresin sheet2, thereby facilitating set-up of thebox1 as well as packing goods into thebox1. Further, since the repulsive force is reduced at thefolding section3 of theresin sheet2, the distortion of thebox1 itself is also reduced, thereby effectively preventing the breakage of thebox1 caused by the exfoliation of the connection section, etc.
• The thin-[0072]walled section7 in thefolding section3 of theresin sheet2 may be formed in such a manner that theresin sheet2 is heated and compressed using proper means, for example. The thin-walled section7 is preferably formed while stretching theresin sheet2, for achieving especially high durability to the repetition of folding and tearing. More specifically, the thin-walled section7 is preferably formed in the following manner. Theresin sheet2 is pressed on with a pressure jig (usually a bar-shaped jig) heated at a temperature which is 5° C. through 40° C. lower than the melting point of the resin, and is then pressured so that the pressured section of theresin sheet2 has a desirable thickness which is not less than {fraction (1/10)} and not more than ⅔ the initial thickness. Here, the temperature of the jig preferably ranges from 120° C. through 150° C. when theresin sheet2 mainly includes polypropylene.
• A cross-sectional shape, which is cut in a direction vertical to a longitudinal direction of the thin-[0073]walled section7, in a vicinity of the thin-walled section7 of theresin sheet2 is not limited. The cross-sectional shape may be a U-shape as shown in FIG. 3(a), a V-shape as shown in FIG. 3(b), or a rectangular shape having one opening side as shown in FIG. 3(c), but usually the U-shape is preferable because it is possible to effectively prevent stress concentration on the thin-walled section7. Further, in thebox1 which is formed by bonding one ormore resin sheet2 having the thin-walled section7, it is preferable that thebox1 is folded so that the thin-walled section7 is externally positioned, because thebox1 can stand upright more easily. Further, in view of the durability to tearing of the thin-walled section7, a thin-walled length Li of the thin-walled section7 is preferably shorter than a folding length L2 of thefolding section3 formed with the thin-walled section7, as shown in FIG. 4. Further, onefolding section3 is preferably formed with two or more thin-walled sections7 which are arranged in parallel to each other. The two or more thin-walled sections7 arranged in parallel may be internally provided, or may be externally provided as shown inEmbodiment 2 as described later.
• The[0074]box1 having the above-described arrangement can be manufactured by properly folding thefolding section3 and joining theconnection section5 with one ormore resin sheet2. Theresin sheet2 can be joined in accordance with tacking, screwing, welding, adhesion, but preferably in accordance with the welding or the adhesion. In accordance with the fusion or the adhesion, theresin sheet2 can be joined through not only a point but also an entire face, thereby achieving high withstand load.
• Further, when the[0075]resin sheet2 is joined to the entire face in accordance with the welding or the adhesion, it is possible to prevent an extraneous object from getting into thebox1 through the connection section. This is highly desirable in terms of security and hygiene. Further, it is most desirable to perform the foregoing joint in accordance with the welding because they can be strongly joined with each other. The welding may be performed in accordance with a method in which theresin sheet2 is subjected to pressure welding by heating theresin sheet2 after being contacted with a heat plate or brought in a vicinity of a pole of the heat plate. Alternatively, the fusion may be performed in accordance with methods such as ultrasonic welding and vibration welding. The ultrasonic welding is especially desirable, since it is hard to damage a material around the welded section because energy is concentrated in a vicinity of the welded section.
• Incidentally, the[0076]box1 desirably has high rigidity and thin sheet thickness. In order to satisfy these demands, thegeneral section6 of theresin sheet2 which constitutes thebox1 in the present embodiment preferably has a thickness of not less than 2 mm and not more than 10 mm. When thegeneral section6 of theresin sheet2 has a thickness of less than 2 mm, the wall surface of thebox1 has low rigidity, so that the box shape is hard to be retained while stored with the contents or applied with load. On the other hand, when theresin sheet2 has a thickness of more than 10 mm, thebox1 is too thick in terms of the sheet thickness and is inferior in terms of volume efficiency. Theresin sheet2 more preferably has a thickness of not less than 3 mm and not more than 5 mm.
• Further, the above-described[0077]resin sheet2 is constituted of resin made mainly of thermoplastic resin such as propylene resin for example, and is constituted of a monolayer foamed sheet having only a single foamed layer whose expansion ratio is approximately 3, for example, as detailed later. Theresin sheet2 preferably has a density of not less than 0.1 g cm³and not more than 0.6 g/cm³. Namely, when theresin sheet2 has a density of more than 0.6 g/cm³, theresin sheet2 is too thick in proportion to its rigidity. On the other hand, when theresin sheet2 has a density of less than 0.1 g/cm³, theresin sheet2 has low rigidity so that the box shape is hard to be retained and thebox1 lacks shock resistance. Therefore, theresin sheet2 having the above-described density has high rigidity in proportion to its weight per unit area, and thebox1 composed of the above-describedresin sheet2 has high strength in proportion to its weight.
• Further, in terms of the expansion ratio, the[0078]resin sheet2 having only the single foamed layer preferably has an expansion ratio of 1.5 to 9. Namely, when theresin sheet2 has an expansion ratio of less than 1.5, theresin sheet2 is of too small weight per unit area in proportion to its rigidity. On the other hand, when theresin sheet2 has an expansion ratio of more than9, theresin sheet2 has low rigidity so that the box shape is hard to be retained and thebox1 lacks shock resistance.
• The[0079]resin sheet2 having the low density may be a resin sheet having a hollow structure formed with a rib and a liner, a resin sheet having a honeycomb core hollow structure, a resin sheet having a foamed layer, etc. Among the above-described resin sheets, theresin sheet2 having the foamed layer is preferable in view of manufacture cost of theresin sheet2 and tractability of theresin sheet2 when formed into thebox1.
• Further, in the present embodiment, the[0080]resin sheet2 may be preferably constituted of the monolayer foamed sheet having only the single foamed layer, as well as a multilayer foamed layer constituted of not less than two foamed layers, or a multilayer foamed layer constituted of at least one foamed layer and at least one non-foamed layer, as shown in FIGS.5(a) through5(d). When the multilayer foamed layer is constituted of not less than two foamed layers, materials and expansion ratios of the respective foamed layers may be the same, or may differ from one another.
• As the[0081]resin sheet2, thebox1 is preferably constituted of the foamed sheet having both of the foamed layer and the non-foamed layer, because lightness in weight and high strength can be simultaneously achieved. In concrete, it is preferable to use the foamed sheet constituted of the foamed layer whose expansion ratio is 1.5 to 9 and the non-foamed layer, for example, because lightness in weight and high rigidity can be easily achieved. The thickness ratio of the foamed layer and the non-foamed layer can be properly determined so as to achieve desired lightness in weight and desired strength.
• Here, in the present embodiment, the foamed layer is a layer whose expansion ratio is not less than 1.5, and is approximately 2 to 40, for example. On the other hand, the non-foamed layer includes a slightly foamed material whose expansion ratio is not more than 1.5, as well as an absolutely non-foamed layer whose expansion ratio is 1.[0082]
• In concrete, the[0083]resin sheet2 shown in FIG. 5(a), for example, is constituted of (1) a foamed layer having a thickness of 2 mm through 10 mm with an expansion ratio of 1.5 to 9, which is sandwiched in between (2) non-foamed layers respectively having a thickness of 100 μm through 1000 μm with an expansion ratio of less than 1.5 as the front and back surfaces. Note that, in FIG. 5(a), one of the non-foamed layers may be omitted. Further, theresin sheet2 as shown in FIG. 5(b), for example, is constituted of the non-foamed layer with an expansion ratio of less than 1.5, a foamed layer with an expansion ratio of 1.5 to 9, the non-foamed layer with an expansion ratio of less than 1.5, and a foamed layer with an expansion ratio of 20 through 40, which are sequentially layered from below. Note that, a small circle in FIG. 5(b) indicates a void. Further, as shown in FIG. 5(c), theresin sheet2 may be constituted of the non-foamed layer with an expansion ratio of less than 1.5, the foamed layer with an expansion ratio of 1.5 to 9, and the foamed layer with an expansion ratio of approximately 30, which are sequentially layered from below. Further, as shown in FIG. 5 (d), by using the non-foamed layer with an expansion ratio of less than 1.5 as a core material, theresin sheet2 may be constituted of the foamed layer with an expansion ratio of 1.5 to 9, the non-foamed layer with an expansion ratio of less than 1.5, the non-foamed layer with an expansion ratio of less than 1.5, the foamed layer with an expansion ratio of 1.5 to 9, which are sequentially layered from below.
• The monolayer foamed sheet can be manufactured in accordance with methods such as atmospheric pressure heating, extrusion foaming, pressure foaming, and injection foaming. On the other hand, the multilayer foamed sheet may be manufactured in accordance with methods such as multilayer extrusion foaming, or may be manufactured by layering the respectively manufactured layers in accordance with means such as adhesion and welding.[0084]
• Further, the material of the[0085]resin sheet2 constituting thebox1 in the present invention is not limited, but preferably resin including mainly propylene resin. This is because the propylene resin (polypropylene in particular) has high performance on integral molding, weldability, heat resistance, water resistance, oil resistance, chemical resistance, etc. The propylene resin may contain ethylene resin, elastomer, etc., as long as the characteristics of the propylene resin are not remarkably undermined.
• Further, the[0086]resin sheet2 constituting thebox1 in the present embodiment may contain inorganic fillers such as silica, mica and talc, reinforcing materials such as glass fiber, carbon fiber, aramid fiber and ultra-high molecular weight polyethylene fiber, additives such as heat stabilizers, ultraviolet absorbers and coloring agents, if necessary.
• The heat stabilizer may be Sumilizer BP101 (trade name, manufactured by Sumitomo Chemical Co., Ltd.), Ultranox 626 (trade name, manufactured by GE Specialty Chemicals), for example. Further, the ultraviolet absorber may be Sumisorb S577 (trade name, manufactured by Sumitomo Chemical Co., Ltd.), for example.[0087]
• Further, the[0088]box1 in the present embodiment is required to have fouling resistance when used as a returnable box. Generally, a box made of resin is easily charged, and thus easily fouled by adsorbing dust and the like. Thus, thebox1 is preferably provided with antistatic property. Theresin sheet2 can be provided with the antistatic property using an antistatic agent.
• The applicable antistatic agent may be amine compounds such as stearylethanolamine, stearyldiethanolamine, laurylamine and lauryldiethanolamine, amide compounds, ester compounds such as stearyl diethanolmonostearate and glycerin aliphatic ester, quaternary ammonium compounds, pyridine derivatives, and carboxylic derivatives, for example.[0089]
• The antistatic agent may be a single compound, or may be a mixture of not less than two compounds. Further, the antistatic agent may be not only low molecular weight antistatic agents as described above, but also polymer antistatic agents such as polyether resin and polyamide resin, for example.[0090]
• Further, among the above-described polymer antistatic agents, it is preferable to use polyether ester amide resin which is expressed in the following general equation;[0091]
• HO—[OC—R¹—NH]_x—(OC—(R²O)_z—)_y]_n—H
• (where n, x, y, and z are respectively independent integral numbers, and R[0092]¹and R²are respectively independent alkyl group, cyclic aliphatic group, or aromatic group).
• Incidentally, in a case where the[0093]box1 is made dirty, the dirt is wiped out or washed out. The low molecular type antistatic agent mentioned as an example has high affinity with respect to water, so that the antistatic agent is flown with water when thebox1 is washed with water. As a result, thebox1 loses the antistatic property. Then, this problem can be solved by using the polymer type antistatic agent as the antistatic agent.
• In order to concretely give the antistatic property to the[0094]resin sheet2, the following processes may be performed: the antistatic agent is kneaded into the resin before forming the resin sheet, or the antistatic agent is applied to the surface of theresin sheet2, or a film, having the antistatic property, that has been made in advance, is bonded to the surface of theresin sheet2.
• In the case where the antistatic agent is kneaded into the resin, the antistatic agent may be blended in an entire body of the[0095]resin sheet2, but it is preferable that, in theresin sheet2 constituted of at least two layers, only a layer having a surface on which the antistatic property is required contains the antistatic agent. For example, in a case where the antistatic property is required only on one surface of theresin sheet2, theresin sheet2 is constituted of at least two layers, and the antistatic agent is blended only in a layer having a surface on which the antistatic property is required, so that it is possible to efficiently achieve the desired antistatic property. Further, in a case where the antistatic property is required on both surfaces of theresin sheet2, the antistatic agent is blended in both outermost layers in theresin sheet2 constituted of at least three layers, so that it is possible to efficiently achieve the desired antistatic property.
• It is possible to manufacture the layered sheet having the antistatic property in accordance with an extrusion laminating process. In a case where the polymer type antistatic agent is used to kneading the antistatic agent into the resin, it is preferable that a blending amount of the antistatic agent is not less than 5 weight % with respect to the resin, and it is more preferable that the blending amount of the agent is not less than 10 weight % and not more than 20 weight %. This is because it is difficult to exhibit the sufficient antistatic property at less than 5 weight %.[0096]
• As described above, according to the[0097]box1 of the present embodiment, it is possible to providesuch box1 that: there occurs little rebound of thefolding section3, and the operation efficiency upon setting up thebox1 and putting goods into thebox1 is improved, and damages caused by internal distortion is hard to occur.
• Further, it is possible to preferably use the[0098]box1 of the present embodiment as a returnable box since thebox1 is superior in the durability.
• [Embodiment 2][0099]
• Another embodiment of the present invention is described as follows based on FIG. 6 through FIG. 8. Note that, the same reference signs are given to members having the same functions as the members shown in[0100]Embodiment 1 for convenience, and description thereof is omitted. Further, various characteristics described inEmbodiment 1 are applicable in combination with characteristics of the present embodiment.
• A[0101]box20 of the present embodiment is made by connecting tworesin sheets21, each of which is shown in FIG. 6, to each other. That is, theresin sheet21 includes: a front/backface constituting member21ahaving acover section8 and abottom section10; a sideface constituting member21b;and aconnection section22. Thus, a single sheet does not constitute four surfaces of a rectangular body as thebox20, so that it is possible to miniaturize a manufacturing device and to simplify a die.
• Meanwhile, in the present embodiment, thin-[0102]walled sections7 that are parallel to each other are provided on asingle folding section3, and thefolding section3 is folded so that the thin-walled sections7 are externally positioned. Further, the two thin-walled sections7 are such that: a thin-walled length L1 of each thin-walled section7 is shorter than a folding length L2 of thefolding section3 having the thin-walled portions7 thereon. Thus, both ends of each thin-walled section7 of the thin-walled length L1 is not thin-walled. Thus, even in a case where thebox20 is repeatedly folded in use, it is possible to prevent thefolding section3 from being torn off. Note that, although portions that are not thin-walled are provided on both ends of the thin-walled length L1 of each thin-walled section7 in the present embodiment, it is not necessary to limit the arrangement to this, for example, it is possible to provide one or plural portions that is/are not thin-walled at an arbitrary position of a central portion of each thin-walled section7.
• Further, in the present embodiment, as shown in FIG. 7, the two thin-[0103]walled sections7 are such that: supposing that a thickness of theresin sheet21 is t, 2D that is a sum of external surface opening lengths, that is, a sum of groove widths D, is set so as to satisfy the following expression.
• 1.4t≦2D≦1.7t  (Expression 1)
• That is, in order that tugging stress is not exerted on the external surface as much as possible upon folding the[0104]folding section3, it is ideal that a length of the external surface is shorter than a length of internal surface. Here, supposing that a curvature radius of the internal surface is X, a difference Δ between the length of the external surface and the length of the internal surface at thefolding section3 is expressed as follows.$\begin{array}{c}\Delta =2\pi \left(X+t\right)/4-2\pi X/4\\ =\pi t/2\\ =1.57t\end{array}$

  
• Thus, although it is ideal that the value is set to be 1.57t≦2D, it is found that, as described above, the setting of 1.4t≦2D≦1.7t brings about no problem as to body swelling in a case where the[0105]resin sheet21 having no flexibility is folded. Further, the setting of 2D≦1.7t is based on such reason that: when 2D that is a sum of the groove widths D in the thin-walled sections7 is too large, theresin sheet21 tends to be torn at thefolding section3 upon using thebox20 repeatedly. Note that, it is preferable that the thin-walled sections7 are set to be in a rotation angle n/4 that is thefolding section3.
• Thus, it is not necessary to limit the number of the thin-[0106]walled sections7 of thefolding section3 to two, for example, it is possible to provide three or more grooves on the external surface as shown in FIG. 8(a). Further, as shown in FIG. 8(b), the foregoing relationship (Expression 1) is satisfied and two thin-walled sections7 are provided on the external surface, and a single thin-walled section7 can be provided on the internal surface for example. Thus, it is possible to improve an upright property of thebox20 when thebox20 is set up.
• Note that, description of the following arrangements is omitted since they are the same as in Embodiment 1: the arrangements other than the foregoing arrangement, for example, are (a) an arrangement in which each thin-[0107]walled section7 is not less than {fraction (1/10)} and not more than ⅔ the thickness of the sheet, (b) an arrangement in which theresin sheet2 is a multi-layered resin sheet including at least a foamed layer whose expansion ratio ranges from 1.5 to 9 for each layer and at least a non-foamed layer, (c) an arrangement in which theresin sheet2 is constituted of a single-layered resin sheet including at least a foamed layer whose expansion ratio ranges from 1.5 to 9 for each layer or of a multi-layered resin sheet, and at least an outermost layer contains an antistatic agent, and (d) an arrangement in which propylene resin is used as the resin.
• As described above, in the[0108]box20 of the present embodiment, there are provided two or more thin-walled sections7 parallel to each other in a longitudinal direction. Thus, it is possible to fold thefolding section3 more easily than thefolding section3 having a single thin-walled section7, so that it is possible to improve the upright property of thebox20.
• Further, in the[0109]box20 of the present embodiment, the thin-walled sections7 are externally positioned, so that tugging stress exerted on the external surface of thefolding section3 is reduced. Particularly in a case where there are provided two or more thin-walled sections7 on the external surface like the present embodiment, thebox20 has more durability with respect to repetition of folding compared with a box having a single thin-walled section7. That is, if thefolding section3 is repeatedly folded at the single thin-walled section7, a local portion is greatly damaged, so that thebox20 tends to be broken. However, in a case where two or more thin-walled section7 are provided on the external surface, thefolding section3 is folded in a curved manner in terms of a cross sectional view, so that thefolding section3 receives less damages compared with thefolding section3 having the single thin-walled section. Thus, it is possible to prevent the damages caused by the repetition of folding, so that it is possible to provide thebox20 that is preferable in using as a returnable box.
• Further, in the[0110]box20 of the present embodiment, the two or more thin-walled sections7 on thefolding section3 are provided so that 2D, the sum of the groove widths of the thin-walled sections7, is 1.4 to 1.7 times as thick as a thickness of the sheet.
• Thus, this value is theoretically a value at which the tugging stress exerted on the external surface of the[0111]folding section3 is reduced, so that the stress exerted on the external surface of thefolding section3 is reduced without fail, and rebound of thefolding section3 is reduced, and the body swelling of thebox20 is reduced. Thus, it is possible to secure the upright property of thebox20.
• Although the present invention is detailed as follows based on examples, a comparative example, and FIG. 9, the present invention is not limited to them.[0112]
EXAMPLE 1
• A foamed polypropylene sheet (Sumiceller (trade name) made by Sumika Plastech Co. Ltd., expansion ratio: 3) having a thickness of 4 mm was cut into a shape, shown in FIG. 2, that has been obtained by developing an A type box that is 400 mm in length, 300 mm in width, and 350 mm in height, as schematically shown in FIG. 1. Note that, the A type box is referred in accordance with JIS standard.[0113]
• Next, a[0114]U-shaped stick 5 mm wide that had been heated at 140° C. was pushed against a portion shown by a thick line in FIG. 2 until the minimum thickness of a sheet corresponding to the portion became 1.5 mm, so as to provide the thin-walled section7 (hinge section) as shown in FIG. 3(a). At this time, the thin-walled section7 was provided so that non-pressed portions, each of which had an approximately 1 to 3 mm length, remained at both ends of thefolding section3 as shown in FIG. 4. That is, (folding length L2−thin-walled length L1)/2=approximately 1 to 3 mm.
• Next, after the[0115]connection section5 of the foamed polypropylene sheet was made to adhere to a plate heated at 250° C. for 1 minute, theconnection section5 was connected to a receiving section11 (barred portion in FIG. 2) of the same sheet so as to obtain the A type box.
EXAMPLE 2
• A polypropylene film, having a 100 μm thickness, to which 20 weight % of a polyether ester amide resin-based antistatic agent (TPAE 10HP (trade name) made by Fuji Chemical Industry Co., Ltd.) has been added, was bonded, by using a hot melt type adhesive, to each of both surfaces of a foamed polypropylene sheet similar to the foamed polypropylene sheet used in Example 1. By using the obtained layered sheet, the A type box was obtained in the same way as in Example 1.[0116]
Comparative Example 1
• An A type box was obtained in the same manner as in Example 1 except that the minimum thickness of the thin-[0117]walled section7 in the sheet was set to 3 mm.
EXAMPLE 3
• A polypropylene film, having a 100 μm thickness, to which 0.5 weight % of a glycerin fatty acid ester antistatic agent (Denon 2220 (trade name) made by Marubishi Oil Chemical Co., Ltd.) has been added, was bonded, by using a hot melt type adhesive, to each of both surfaces of a foamed polypropylene sheet similar to the foamed polypropylene sheet used in Example 1. By using the obtained layered sheet, the A type box was obtained in the same way as in Example 1.[0118]
• (Evaluation)[0119]
• The[0120]box1 made in Examples 1 to 3 and Comparative Example 1 was evaluated in accordance with the following method. The result is shown in Table 1.
• (1) One of the[0121]cover sections8 of thebox1 was folded by manually pushing it over so that theside face section9 connected to thecover section8 has an angle of 90° with respect to thecover section8. After 30 seconds, thecover section8 is released from hand. After 30 seconds passed since thecover section8 had been released from hand, an angle α between thecover section8 and theside face section9 was measured. When α was not more than 135°, α was judged to be preferable. When α is not less than 135°, α was judged not to be preferable.
• (2) Water resistance of the antistatic agent[0122]
• A portion of 10 cm×10 cm was cut from the resin sheet. After the portion cut was soaked in water heated at 60° C. for 10 minutes, the portion was air-dried. The operation was performed three times. Surface resistivities of the sheet before and after the soaking process were measured. The surface resistivities were measured under the following conditions.[0123]
• Testing device: Ultra-super insulation meter SM-8210 Flat plate electrode SME8310 both of which are made by Toa Denpa Kogyo Kabushiki Kaisha.[0124]
• Testing environment: 23° C./50% RH[0125]
• Applied voltage: 500V[0126]
• Measuring operation: A voltage was applied to the foregoing portion for 10 seconds. After 1 minute passed since the application, a resistivity was measured.[0127]

  	TABLE 1
  	Rebound of	Surface resistance ratio (Ω)

  	folding	Before			Three
  	section	soaking	Once	twice	times

  Example 1	Preferable	1016	1016	1016	1016
  Example 2	Preferable	109	109	1010	1010
  Example 3	Preferable	1010	1013	1015	∞
  Comparative	Not	1016	1016	1016	1016
  Example 1	preferable

EXAMPLES 4 and 5
• Here, buckling strength evaluation that was performed by using the[0128]box1 ofEmbodiment 1 and thebox2 ofEmbodiment 2 is described.
• The[0129]box1 internally provided with two thin-walled sections7 and thebox20 externally provided with two thin-walled sections7 were evaluated for the degree of the difference therebetween in buckling strength.
• Concretely, the[0130]box1 internally provided with two thin-walled sections7 and thebox20 externally provided with two thin-walled sections7 were subjected to compression test in which, as shown in FIG. 9, holding plates were brought into contact with the side faces of the boxes and then load was applied downward. In this manner, the box were evaluated for buckling strength.
• Each of the[0131]boxes1 and2 was 325 mm in width×405 mm in depth×295 mm in height. Further, DSS-2000 autograph (trade name)(made by Shimadzu Corporation Ltd.) was used as a compression tester, and compression speed was set to be 10 mm/min. Further, both theresin sheets2 and21 had an expansion ratio of three times and a thickness of 4 mm. Further, a U-shaped groove was provided as the thin-walled section7, and the depth thereof was set to be 1.5 mm. Further, a length of both ends in thefolding section3 except for the thin-walled section7 was set to be 2 mm. Note that, a temperature at which the stick for providing the thin-walled section7 was heated was 140° C. upon forming the thin-walled section7.
• Table 2 shows the results of the tests performed in Example 4 in which the[0132]box1 was internally provided with two thin-walled sections7 and in Example 5 in which thebox20 was externally provided with two thin-walled sections7.

  	TABLE 2
  	Example 4	Example 5

  		Com-		Com-
  	Body swelling	pression	Body swelling	pression
  	amount (mm)	load (kg)	amount (mm)	load (kg)

  Initial stage	3.5	0	1.8	0
  (upon setting
  up the box)
  Upon flexing	12.0	148	2.0	53
  by 10 mm
  Upon flexing	22.5	293	15.0	183
  by 20 mm
  Buckling yield	—	311	—	409
  point

• Table 2 shows the following facts.[0133]
• {circle over (1)} According to the conditions of the[0134]box1 and thebox20 at an initial stage (upon setting up the box), the body swelling amount of thebox1 at the initial stage (upon setting up the box) was 3.5 mm. On the other hand, the body swelling amount of thebox20 at the initial stage (upon setting up the box) was 1.8 mm. Thus, a swelling ratio of thebox1 upon setting up the box was as large twice as that of thebox20. That is, this means that the body swelling amount of thebox20 externally provided with two thin-walled sections7 is small upon setting up the box.
• {circle over (2)} The body swelling amount of the[0135]box1 when the box flexed by 10 mm was 12.9 mm. On the other hand, the body swelling amount of thebox20 when the box flexed by 10 mm was 2.0 mm. This means that: merely by giving a small transverse load to thebox1, the body swelling amount becomes large. That is, the following result is found: in a case where a load is given from the side to the box, the body swelling amount that is naturally large at the side face vertical to the loading direction becomes larger.
• {circle over (3)} The compression load at the buckling yield point of the[0136]box1 was 311 kg. On the other hand, the compression load at the buckling yield point of thebox20 was 409 kg. Thus, it is found that the buckling strength of thebox20 was larger than that of thebox1. Further, as to the buckling condition at this time, thebox1 buckled so as to externally swell. On the other hand, thebox20 buckled so as to slightly cave in.
• According to the evaluation, it is found that: the[0137]box20 externally provided with two thin-walled sections7 has a smaller body swelling amount at the initial stage and a larger buckling strength than thebox1 internally provided with two thin-walled sections7.
• [Embodiment 3][0138]
• Another embodiment of the present invention is described as follows based on FIG. 10. Note that, the same reference signs are given to members having the same functions as the members described in[0139]Embodiments 1 and 2, and description thereof is omitted.
• The[0140]box1 of the present embodiment, as shown in FIG. 2, is made by folding the singlethermoplastic resin sheet2 constituted of fourside face sections9 adjacent to each other that are connected via thefolding sections3 to thecover section8 and thebottom section9 both of which are freely foldable.
• Further, it is possible to provide two thin-[0141]walled sections7 parallel to each other on thefolding section3 as shown in FIG. 10. While, thefolding sections3 are provided respectively on theside face sections9 adjacent to each other so as to have a level difference Z between thecover sections8, and the length of the level difference Z is 1 to 1.2 times the thickness of the sheet in a depth direction of thebox1. Note that, although not shown, as to thefolding sections3 connected to thebottom section10, there is provided the level difference Z whose length is 1 to 1.2 times the thickness of the sheet in the depth direction of thebox1. Further, in the drawing, there is formed the level difference Z whose length is 1 to 1.2 times the thickness of the sheet in the case where the two thin-walled sections7 parallel to each other are externally provided, but the arrangement is not necessarily limited to this. It is also possible to provide the level difference Z whose length is 1 to 1.2 times the thickness of the sheet in the case where two thin-walled sections7 parallel to each other are externally provided. Further, it is also possible to provide the level difference Z whose length is 1 to 1.2 times the thickness of the sheet in the case where a single thin-walled section7 is provided on thefolding section3 regardless of whether the thin-walled section7 is provided internally or externally.
• According to the foregoing arrangement, in a case where the[0142]cover sections8 adjacent to each other or thebottom sections10 adjacent to each other are folded at an angle of 90°, there exists the level difference Z whose length is 1 to 1.2 times the thickness of the sheet, so that thecover sections8 or thebottom sections10 overlap with each other with less strain. As a result, it is possible to prevent the rise of thecover sections8 or thebottom sections10 caused by theother cover section8 or thebottom section10.
• That is, in a case where there is not provided the level difference Z, the one[0143]cover section8 or the onebottom section10 is raised by theother cover section8 or theother bottom section10 at a portion where thecover sections8 or the bottom sections are overlapped with each other, so that the onecover section8 or thebottom section10 rises higher than the case where the level difference Z is provided, but this problem is solved by the level difference Z in theresin sheet2.
• Further, in the[0144]resin sheet2, the level difference Z causes thecover sections8 or thebottom sections10 not to be overlapped with each other in a curved manner, so that it is possible to reduce a gap in the overlapping portion. Thus, it is possible to prevent extraneous objects from coming into the box. Note that, as to a conventional cardboard box made of paper, paper is so flexible that the overlapping portions are flexibly united, thus bringing about no gap. Further, the level difference Z is 1 to 1.2 times the thickness of the sheet. That is, when the level difference is too large, the gap becomes large in the overlapping portions. Thus, it is preferable that the level difference is 1 to 1.2 times the thickness of the sheet.
• Further, in a case where there are provided the two thin-[0145]walled sections7 parallel to each other on thefolding section3, it is possible to fold thefolding section3 more easily than thefolding section3 having the single thin-walled section7 thereon.
• Thus, it is possible to obtain not only an advantage that an operation efficiency upon setting up the box and putting goods into the box is improved, but also an advantage that the rebound of the[0146]folding section3 is reduced. Thus, it is possible to provide thebox1 in which the rebound of thefolding section3 is reduced and the operation efficiency upon setting up the box and putting goods into the box can be improved.
• As described above, the level difference Z is provided in the[0147]box1 of the present embodiment, so that it is possible to provide thebox1 in which the rebound of thefolding section3 is reduced and the operation efficiency upon setting up the box and putting goods into the box is improved, and damages caused by the internal distortion is hard to occur.
• Further, it is possible to preferably use the[0148]box1 of the present embodiment as a returnable box since thebox1 is superior in the durability.
• Note that, the[0149]box1 of the present embodiment is made by folding thesingle resin sheet2 constituted of fourside face sections9 adjacent to each other that are connected via thefolding sections3 to thecover section8 and thebottom section9. However, thebox1 is not necessarily limited to this arrangement, but thebox1 may be arranged by providing theside face sections9 adjacent to each other so as to be connected via thefolding section3 to thecover section8 and the bottom section that are freely foldable.
• Thus, it is possible to make the[0150]box1 by folding fourresin sheets2 containing theside face sections9 connected via thefolding section3 to thecover section8 and thebottom section10. On the other hand, thebox1 may be arranged by joining tworesin sheets21 and2 to each other like thebox20 described inEmbodiment 2.
• Further, in the present embodiment, the[0151]box1 is a rectangular, so that theside face section9 exist in four surfaces, but thebox1 may be provided in a polygonal manner such as a triangle plane shape in which threeside face sections9 exist or a pentagonal plane shape in which fiveside face sections9 exist.
• Note that, as to other arrangements, it is possible to use the characteristics of[0152]Embodiments 1 and 2.
• [Embodiment 4][0153]
• Another embodiment of the present invention is described as follows based on FIG. 11. Note that, the same reference signs are given to members having the same functions as the members shown in figures corresponding to[0154]Embodiments 1 to 3, and description thereof is omitted.
• In the present embodiment, as shown in FIG. 11, a[0155]connection section5 as a connection portion is laminated on theside face section9 so as to have the same length as a distance from a connection point of thecover section8 and thefolding section3 to a connection point of thebottom section10 and thefolding section3. Concretely, not less than 80% area of theconnection section5 is to be bonded to theside face section9. Thus, it is possible to provide thebox1 that is strong with respect to exfoliation and compression in a box shape. That is, when abonding face5aoccupies not less than 80% area of theconnection section5, it is possible to substantially use the entire surface of theconnection section5 as thebonding face5a.
• Further, in the present invention, the[0156]bonding face5ais successively provided from the connection portion of thecover section8 and thefolding section3 to the connection portion of thebottom section10. Thus, there is no rift in thebonding face5aon theconnection section5. Therefore, there is no possibility that dust comes through a gap into the box. Further, theresin sheet2 itself is bonded without using other adhesive, so that it is possible to efficiently recycle it.
• Further, as described above, the[0157]resin sheet2 is the monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or the multilayer resin sheet constituted of at least a foamed layer whose expansion ratio is 1.5 to 9 for each layer and at least a single non-foamed layer.
• That is, in a case where the[0158]resin sheet2 is the monolayer resin sheet constituted of a foamed layer whose expansion ratio is less than 1.5, or in a case where theresin sheet2 is the multilayer resin sheet constituted of a non-foamed layer whose expansion ratio is less than 1.5 for all layers, theresin sheet2 becomes heavy in case of setting up the box. Meanwhile, the monolayer resin sheet constituted of a foamed layer whose expansion ratio is over 9 does not bring about sufficient rigidity.
• As a result, it is possible to provide the[0159]box1 than can endure the repetitive usages, and has no gap in the connection section, and can prevent extraneous objects such as dust from coming into the box.
• As described above, it is possible to preferably use the[0160]box1 of the present embodiment as a returnable box since thebox1 is superior in the durability.
• Note that, as to other arrangements, it is possible to use the characteristics of[0161]Embodiments 1 through 3.
• [Embodiment 5][0162]
• The following will explain another embodiment of the present invention with reference to FIGS. 12 through 15. Note that, for ease of explanation, members having the same functions as those shown in the drawings pertaining to the first through fourth embodiments above will be given the same reference symbols, and explanation thereof will be omitted here.[0163]
• A[0164]box1 in the present embodiment is a box able to be folded, as shown in FIG. 1. Thebox1 is constituted of aresin sheet2 having a thickness of 2 mm through 10 mm. Thebox1 may be constituted of acontinuous resin sheet2, or may be constituted of two ormore resin sheets2 which have been joined together using proper means. However, at least oneresin sheet2 composing thebox1 is provided with at least onefolding section3.
• The[0165]folding section3 may be aside section3abetween adjacent twofaces4 which are formed with thecontinuous resin sheet2, for example. Alternatively, thefolding section3 may be afolding section3bprovided at a boundary between (1) aface4 and (2) a connection section5 (a shaded section in FIG. 2), which is a continuous section of theface4, for joining theface4 withconnected sections12 of anotherface4, as shown in FIGS.12(a) and12(b).
• Here, in the present embodiment, as shown in FIGS.[0166]12(a) and12(b), thebox1 shown in FIG. 1 is completed in such a manner that thethermoplastic resin sheets2 are joined together and folded so as to be formed into a rectangular parallelepiped shape. Thethermoplastic resin sheets2 are composed of twoadjacent side sections9 in which a freely openable andclosable cover section8 and abottom section10, or thecover section8 and abottom section11 are respectively connected via thefolding section3.
• Further, in the[0167]box1 of the present embodiment, as shown in FIGS.12(a) and12(b), respective portions of the twoadjacent bottom sections10 and11 are welded viawelding sections10aand11a.Further, as also shown in FIG. 13, diagonally foldingsections10brespectively in a substantially 45° direction fromcorner sections1aare formed on a pair ofbottom sections10 which are folded to be externally positioned among two pairs of thebottom sections10 and thebottom sections11 which respectively face one another.
• With this, by folding the[0168]box1 along thediagonally folding sections10b,thebox1 can be easily folded. Reversely, only by opening the foldedbox1, thebox1 can be obtained in a three-dimensional shape.
• As a result, it is possible to provide the[0169]box1 capable of being easily set up and folded with improving the folding efficiency.
• Further, in the[0170]box1 of the present embodiment, among the two pairs of thebottom sections10 and thebottom sections11 which respectively face one another, the pair ofbottom sections11 which are folded to be internally positioned are overlapped with each other when folded, as shown in FIG. 14(a).
• In other words, when the pair of[0171]bottom sections11 which are folded to be internally positioned, among the two pairs of thebottom sections10 and thebottom sections11 which respectively face one another, have the same length in their facing directions, the goods are managed to be put into thebox1 while thebox1 is open. However, when the goods are heavy to some extent, the goods may drop off through a butted section of the bothbottom sections11.
• In the present embodiment, however, among the two pairs of the[0172]bottom sections10 and thebottom sections11 which respectively face one another, the pair ofbottom sections11 which are folded to be internally positioned are overlapped with each other when folded, as described above. Further, one of thebottom sections11 is longer than theother bottom section11 in their facing directions.
• With this, it is possible to prevent the goods from being dropped off from the bottom, when storing somewhat heavy goods in the[0173]box1.
• Note that, the[0174]bottom section11 preferably has the substantially same length as the width length of thebox1. This surely prevents the goods from being dropped off from the bottom.
• Further, in the[0175]box1 of the present embodiment, as shown in FIG. 13, among the two pairs of thebottom sections10 and thebottom sections11 which respectively face one another, the pair ofbottom sections11 which are folded to be internally folded are provided with (1) a bump-shapedlatching section13 on one of the overlappingbottom sections11, and (2) a latchedsection14 on the other overlappingbottom section11, being constituted of a hole that allows the bump-shapedlatching section13 to come into the latchedsection14, as shown in FIG. 14(a).
• This surely prevents the goods from being dropped off from the bottom when storing somewhat heavy goods in the[0176]box1.
• Incidentally, the latching[0177]section13 is not limited to a “fungiform” bump as shown in FIG. 14(a), but may be an L-shaped bump as shown in FIG. 14(b). Further, the latchingsections13 shown in FIGS.14(a) and14(b) may be provided by forming a bump on thebottom section11, or by newly providing a bump with adhesion, etc. Further, as shown in FIG. 15(a), a substantially T-shaped cut13ais cut on one of thebottom sections11, and the substantially T-shaped cut13ais folded at a right angle so as to stand upright. Then, while the T-shaped head section is pressured so as to be bent in an arrow direction in FIG. 15(a), the substantially T-shaped cut13ais come into the latchedsection14 constituted of the hole on theother bottom section11. The pressure is then released so that the latchingsection13 formed with the substantially T-shaped cut13ais latched with the latchedsection14 on theother bottom section11. With these steps, the latchingsection13 can be integrally formed with theresin sheet2.
• Note that, the substantially T-shaped cut[0178]13ahaving a flat head section is explained above, but the shape of the head section is not limited to this. The head section may have a semicircle shape, as shown in FIG. 15(b).
• Further, the respective numbers of the latching[0179]section13 and the latchedsection14 are not limited to one, but a plurality of latchingsections13 and a plurality of the latchedsections14 may be provided. If the bump becomes an obstacle, the bump may be provided at the corner section or in a vicinity of the side section.
• As described above, it is possible to preferably use the[0180]box1 of the present embodiment as a returnable box since thebox1 is superior in the durability.
• Further, according to the[0181]box1 of the present embodiment, it is possible to providesuch box1 that: there occurs little rebound of thefolding section3, and the operation efficiency upon setting up thebox1 and putting goods into thebox1 is improved, and damages caused by internal distortion is hard to occur.
• Note that, as to other arrangements, it is possible to use the characteristics of[0182]Embodiments 1 through 4.
• As described, the resin box of the present invention has the arrangement such that the thin-walled section is made to be shorter than the folding section. Thus, durability in the folding can be improved compared to the case where the thin-walled section is made to be the same length as that of the folding section, thus preventing the folding section from being easily torn and broken.[0183]
• Further, the thin-walled section is externally provided in the resin box of the present invention. This reduces tensility affecting the external surface of the folding section. Particularly, by forming two or more thin-walled sections on the external surface of the folding section, the durability in the folding can be further improved compared to the case where only one thin-walled section is provided even when the folding is repeated many times. More specifically, repetitive folding with respect to one folding section greatly damages the folding section and may cause breakage of the section; however, when two or more thin-walled sections are formed on the external surface, the damage of the folding section can be reduced for each folding section, as the folding sections are bent rather than folded. As a result, the damage due to the repetitive folding can be prevented, and it becomes possible to provide a resin box can suitably be used as a returnable box.[0184]
• In the resin box of the present invention, in a case where two or more thin-walled sections are provided on the folding section, a total width of the thin-walled sections is 1.4 to 1.7 times the thickness of the thermoplastic resin sheet.[0185]
• This value can theoretically reduce the tensility affecting the external surface of the folding section. Thus, it certainly reduces the tensility affecting the external surface of the folding section, and reduces the repulsion force in the folding section, and also reduces body swelling of the resin box, and further, ensures upright property of the resin box.[0186]
• Further, in the resin box of the present invention, the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least a foamed layer whose expansion ratio is 1.5 to 9 and at least a non-foamed layer. Note that, the forming layer refers to a layer whose forming expansion ratio is not less than 1.5. Also, the non-foamed layer includes not only absolutely non-foamed layer having an expansion ratio of 1, but also slightly foamed body having an expansion ratio of less than 1.5.[0187]
• In the foregoing arrangement, the thermoplastic resin sheet may be a monolayer resin sheet, or may be a multilayer resin sheet. However, in the case of a monolayer resin sheet, its foamed layer preferably has an expansion ratio of 1.5 to 9. Further, in the case of a multilayer resin sheet, its foamed layer preferably includes at least a foamed layer having an expansion ratio of 1.5 to 9, and includes at least a non-foamed layer.[0188]
• With this arrangement, it is possible to reduce the body swelling of the resin box, and to ensure the upright property of the resin box. Particularly, the multilayer resin sheet including at least a non-foamed layer can further improve the upright property of the resin box, as a non-foamed layer has a higher strength than that of a foamed layer. Further, a multilayer resin sheet can improve lightness in weight and crashproof of the box by stacking a plurality of foamed layers respectively having different expansion ratio. This realizes two compatible effects: lightness in weight and strength of the resin box.[0189]
• Further, in the resin box of the present invention, an antistatic additive is blended in the monolayer resin sheet or at least an outermost layer of the multilayer resin sheet. Therefore, it reduces adsorption of dust or the like, and can keeps the resin box clean.[0190]
• Further, in the resin box of the present invention, resin constituting the thermoplastic resin sheet is propylene resin. Therefore, it is possible to provide a resin box ensuring superior performance in weldability, heat-resistance, water-resistance, oil-resistance, chemical resistance and the like.[0191]
• Further, in the resin box of the present invention, in one folding section, there is provided a level difference between the cover sections adjacent to each other, and in an other folding section, there is another level difference between the bottom sections adjacent to each other, the level difference being 1 to 1.2 times the thickness of the thermoplastic resin sheet.[0192]
• With these level differences of 1 to 1.2 times the thickness of the thermoplastic resin sheet, the adjacent cover sections and the adjacent bottom sections do not directly clash with each other when they are folded at an angle of 90°. As a result, the cover sections and the bottom sections are not lifted by clashing with each other. Further, the gap in the portions where each cover section and each bottom section overlap can be reduced, thus keeping extraneous objects out of the box.[0193]
• Further, the folding section having at least two thin-walled sections is easier to fold than that having only one thin-walled section. This ensures efficiencies during the composition of the box and the work for putting the products in the box. Also, it reduces repulsion force in the folding section.[0194]
• With the foregoing arrangement, it is possible to provide a resin box capable of keeping extraneous objects such as dust out of the box, and ensuring efficiencies during the composition of the box and the work for putting the products in the box, by reducing repulsion force in the folding section.[0195]
• Further, in the resin box of the present invention, a pair of the bottom sections is internally positioned when the bottom sections are folded, and the bottom sections of the pair are overlapped with each other when the bottom sections are folded.[0196]
• Namely, when each of the bottom sections of the pair internally positioned when the bottom sections are folded have the same length in each opposing direction, though it is possible to put a product while the box is opened, it may go through the juncture of the bottom sections when the product have some weight.[0197]
• However, in the present invention, a pair of the bottom sections is internally positioned when the bottom sections are folded, and the bottom sections of the pair are overlapped with each other when the bottom sections are folded. Thus, it is possible to prevent the product having some weight from being gone through the juncture of the bottom sections.[0198]
• Further, in the resin box of the present invention, there is provided a latching section in a protruding manner on one of the bottom sections overlapped with each other, and on an other bottom section, there is provided a latched section constituted of a hole that allows the latching section to come into the latched section.[0199]
• Thus, it is possible to surely prevent the product having some weight from being gone through the juncture of the bottom sections.[0200]
• The embodiments and concrete examples of implementation discussed in the foregoing detailed explanation serve solely to illustrate the technical details of the present invention, which should not be narrowly interpreted within the limits of such embodiments and concrete examples, but rather may be applied in many variations within the spirit of the present invention, provided such variations do not exceed the scope of the patent claims set forth below.[0201]

Claims (22)

What is claimed is:

1. A resin box constituted of a thermoplastic resin sheet including a folding section, wherein

the folding section includes at least one thin-walled section, extending in a longitudinal direction of the folding section, whose minimum thickness is not less than {fraction (1/10)} and not more than ⅔ the thickness of the thermoplastic resin sheet.

2. A resin box constituted by folding at least one thermoplastic resin sheet, wherein:

the thermoplastic resin sheet is constituted of two or more side face sections, adjacent to each other, that are connected via folding sections to cover sections and bottom sections both of which are freely foldable, and

each of the folding sections includes two or more thin-walled sections parallel to each other, and

in one folding section, there is provided a level difference between the cover sections adjacent to each other, and in an other folding section, there is another level difference between the bottom sections adjacent to each other, the level difference being 1 to 1.2 times the thickness of the thermoplastic resin sheet.

3. A resin box constituted by folding at least one thermoplastic resin sheet, wherein:

the thermoplastic resin sheet is constituted of two or more side face sections connected via folding sections, each of which has one or more thin-walled section, to cover sections and bottom sections both of which are freely foldable, and the thermoplastic sheet includes a connection portion connected to an opening side portion of at least one of the side face sections adjacent to each other, and

the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least one foamed layer whose expansion ratio is 1.5 to 9 and at least one non-foamed layer, and

the connection portion is bonded to the side face section so that a length of the connection portion is substantially as long as a distance between a folding section along a cover sections and a folding section along a bottom section extending from the side face section from which the cover section extends, and a bonding face of the connection portion extends from said one folding section on the side of the cover sections to said other folding section on the side of the bottom sections.

4. The resin box as set forth inclaim 3, wherein in one folding section, there is provided one level difference between cover sections adjacent to each other, and in an other folding section, there is provided an other level difference between the bottom sections adjacent to each other.

5. A resin box constituted so as to be a rectangular prism by folding at least one thermoplastic resin sheet, wherein:

the thermoplastic resin sheet is constituted of two or more side face sections connected via folding sections, each of which has one or more thin-walled section, to cover sections and bottom sections both of which are freely foldable, and

the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least one foamed layer whose expansion ratio is 1.5 to 9 and at least one non-foamed layer, and

two of the bottom sections adjacent to each other are partially bonded to each other as one pair, and a diagonally folding section is provided in a substantially 45° direction from a corner section on said one pair of the bottom sections that is externally positioned when the bottom sections are folded, said one pair being opposite to another pair of the bottom sections.

6. The resin box as set forth inclaim 5, wherein said another pair of the bottom sections is internally positioned when the bottom sections are folded, and the bottom sections of said another pair are overlapped with each other when the bottom sections are folded.

7. The resin box as set forth inclaim 6, wherein there is provided a latching section in a protruding manner on one of the bottom sections overlapped with each other, and on an other bottom section, there is provided a latched section constituted of a hole that allows the latching section to come into the latched section.

8. The resin box as set forth inclaim 1, wherein the thin-walled section is shorter than the folding section.

9. The resin box as set forth inclaim 2, wherein each of the thin-walled sections is shorter than each of the folding sections.

10. The resin box as set forth inclaim 3, wherein the thin-walled section is shorter than each of the folding sections.

11. The resin box as set forth inclaim 1, wherein the thin-walled section is externally provided.

12. The resin box as set forth inclaim 2, wherein each of the thin-walled sections is externally provided.

13. The resin box as set forth inclaim 3, wherein the thin-walled section is externally provided.

14. The resin box as set forth inclaim 1, wherein in a case where two or more thin-walled sections are provided on the folding section, a total width of the thin-walled sections is 1.4 to 1.7 times the thickness of the thermoplastic resin sheet.

15. The resin box as set forth inclaim 2, wherein the two or more thin-walled sections are provided on the folding section so that a total width of the thin-walled sections is 1.4 to 1.7 times the thickness of the thermoplastic resin sheet.

16. The resin box as set forth inclaim 3, wherein in a case where two or more thin-walled sections are provided on the folding section, a total width of the thin-walled sections is 1.4 to 1.7 times the thickness of the thermoplastic resin sheet.

17. The resin box as set forth inclaim 1, wherein the thermoplastic resin sheet is a monolayer resin sheet constituted of a foamed layer whose expansion ratio is 1.5 to 9, or a multilayer resin sheet constituted of at least a foamed layer whose expansion ratio is 1.5 to 9 and at least one non-foamed layer.

18. The resin box as set forth inclaim 17, wherein an antistatic agent is blended in the monolayer resin sheet or at least one outermost layer of the multilayer resin sheet.

19. The resin box as set forth inclaim 1, wherein resin constituting the thermoplastic resin sheet is propylene resin.

20. The resin box as set forth inclaim 2, wherein resin constituting the thermoplastic resin sheet is propylene resin.

21. The resin box as set forth inclaim 3, wherein resin constituting the thermoplastic resin sheet is propylene resin.

22. The resin box as set forth inclaim 5, wherein resin constituting the thermoplastic resin sheet is propylene resin.

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