US3750932A

US3750932A - Container having improved bellows closure and blank for making same

Info

Publication number: US3750932A
Application number: US00166921A
Authority: US
Inventors: D Ellison
Original assignee: Inland Container Corp
Current assignee: Inland Container Corp
Priority date: 1971-07-28
Filing date: 1971-07-28
Publication date: 1973-08-07
Anticipated expiration: 1990-08-07

Abstract

A corrugated fiberboard container having an improved bellows closure biased to remain in closed condition, once folded, and thereby eliminate the necessity of gluing closure flaps prior to filling. Illustrated is a container having a bellows bottom closure made up of four interconnected panels of equal length wherein diagonal score lines which do not meet provide trapezoidal closure flaps. The length of the closure panels provides an overlapping of the longer closure flaps in the closed condition with the edge of one flap nesting within the edge of the other. Slits are provided in the glue flap in the closure region which permit the glue flap to be hinged to the longer side wall and adhered to the shorter end wall thereby leaving the side wall unobstructed.

Description

United States Patent Ellison 3,750,932 Aug. 7, 1973 [75] Inventor: Donald E. Ellison, Clayton, Ind.

[73] Assignee: Inland Container Corporation,

Indianapolis, Ind.

[22] Filed: July 28, 1971 [21] Appl. No.: 166,921

[52] US. Cl. 229/37 R, 229/D1G. 2, 229/DIG. 4 [51] Int. Cl B65d 5/02 [58] Field of Search 2,29/17 R, 17 G, 37 R, 229/DIG. 2, DIG. 4

[56] References Cited UNITED STATES PATENTS 3,529,763 9/1970 229/37 R 2,470,789 S/l949 229/17 R 1,624,439 4/1927 229/37 R 3,343,750 9/1967 229/37 R R25,021 8/1961 229/17 G 2,195,922 4/1940 Gibson et al...... 229/17 R 3,341,104 9/1967 Loheed et al. 229/17 R 1,994,923 3/1935 Ross 229/17 R FOREIGN PATENTS OR APPLICATIONS 471,003 5/1969 Switzerland 229/DIG. 4

Primary ExaminerI-lerbert F. Ross Assistant Examiner-Stephen Marcus Attorney-Fitch, Even, Tabin & Luedeka [57] ABSTRACT A corrugated fiberboard container having an improved bellows closure biased to remain in closed condition, once folded, and thereby eliminate the necessity of gluing closure flaps prior to filling. Illustrated is a container having a bellows bottom closure made up of four interconnected panels of equal length wherein diagonal score lines which do not meet provide trapezoidal closure flaps. The length of the closure panels provides an overlapping of the longer closure flaps in the closed condition with the edge of one flap nesting within the edge of the other. Slits are provided in the glue flap in the closure region which permit the glue flap to be hinged to the longer side wall and adhered to the shorter end wall thereby leaving the side wall unobstructed.

15 Claims, 6 Drawing Figures Pmmwwv 1w 3.750.932

SNEH 1 0f 2 INVENTO DONALD E. E SON m, M, Tabm, $5M

ATTYS.

PAIENIEDAUB SHEET 2 BF 2 FIGS INVENTOR DONALD E. ELLISON PM 6 91, TIM,

ATTYS.

CONTAINER HAVING IMPROVED BELLOWS CLOSURE AND BLANK FOR MAKING SAME The present invention relates to containers adapted to be folded from a blank and, more particularly, to a container made of corrugated fiberboard having a bellows type closure and to a blank from which such a container may be folded.

Bellows-type closures have long been known and found to be usable for tubular containers including containers made of corrugated fiberboard and the like. In recent years, it has become desirable to employ large corrugated fiberboard containers for the shipment of bulk materials, for example, particulate chemical resins and other flowable materials, such as synthetic rubber and the like. Such bulk containers are fabricated of strong materials, such as double wall and sometimes even triple wall corrugated board, and they are often reinforced in various ways to effectively withstand the internal loads which may reach as high as two tones. The strength provided by the bellows-type closure, particularly for the bottoms of boxes, has been found to have application in the field of bulk containers.

However, the substantial thickness of the material from which the blanks for such bulk containers are fabricated gives rise to various problems which are simply not encountered in ordinary bellows closures employed on simple paperboard material, such as milk cartons presently used in the United States. For example, the strength and resiliency of double wall corrugated fiberboard creates an inherent biasing of the bellows closure to the open position; a problem in handling empty containers. Moreover, when a glue flap is provided to establish a manufacturers joint at one of the corners of the bulk container having a bellows-type closure, that flap has been hinged to one of the shorter end panels so that it is laminated to a side panel from which there depends a closure flap that is not scored to form triangular fold-back panels. This arrangement is illustrated in U.S. Pat. No. 3,523,635 and has limited the configuration of. such containers. Accordingly, improved bellows-type closures, particularly suited for use in bulk containers of corrugated fiberboard, are desired.

An object of the present invention is to provide a container having an improved bellows-type closure.

Another object of the invention is to provide a container having a bellows closure which when folded into a closed position is biased to remain closed.

A further object is to provide a blank for a tubular container having a bellows-type closure which is adapted to facilitate the folding of such a closure even though the blank is fabricated from strong, stiff fiberboard.

Still another object of the invention is to provide a container having a bellows-type bottom closure which when set up will rest flat upon a supporting surface even though empty,\vithout gluing the closure panels to one another.

These and other objects of the invention shouldbe-v come clear upon a reading of the following detailed description, while making reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a container having a bellows-type bottom closure embodying various features of the present invention;

FIG. 2 is a plan view of the blank from which the container shown in FIG. 1 is formed;

FIG. 3 is a perspective view of the container illustrated in FIG. 1 shown in inverted position with the bottom closure in a partially closed condition;

FIG. 4 is a perspective view similar to FIG. 3 illustrating the container with the bottom closure in a fully closed position;

FIG. 5 is an enlarged, fragmentary sectional view taken along the line 5-5 of FIG. 3; and

FIG. 6 is an enlarged fragmentary sectional view taken along line 6--6 of FIG. 4.

Illustrated in the drawings are a container 11 and a blank 13 from which the container 11 is formed. The illustrated container 11 is designed] particularly for the transport of bulk materials, and the blank 13 is accordingly formed from double wall corrugated fiberboard. The container 11 has four upstanding vertical walls which are referred to in the following description as

side walls

15a and 15b and

end walls

16a and 16b; however, it should be understood that the terminology is employed for ease of reference only and, insofar as the concept of the invention is concerned, the terms should be considered interchangeable. The blank may also be part of a total container containing a laminated 7 liner or liners, or it may be part of a multicell container containing one or more of such blanks. In the blank 13, the end walls and the side walls are defined by four longitudinally extending,

parallel score lines

17a, 17b, 17c and 17d, by a transverse upper score line 19a and by a transverse lower score line 19b. The blank is preferably made from corrugated fiberboard having flutes which run parallel to the lines 17 and extends longitudinally both above and below the transverse score lines 19. Thefour parallel score lines 17 extend to the lower edge of the blank, thereby defining a first pair of

closure flaps

23a and 23b which are hinged to the side walls 15 and a second pair of closure flaps 25a and 251) which are hinged to the end walls 16.

As can be seen from FIG. 2, the lower and upper edges of the blank 13 are straight. At its upper end,the blank 13 is slotted at what would otherwise be extensions of the four parallel score lines l7.above the transverse score line. These slots create four separate un connected

upper flaps

27a, 27b, 27c and 27d. Although the container 11 is illustrated as having such separate flaps 27 of the type sometimes employed as a part of an interlocking cap arrangement, it should be understood that the illustrated upper portion of the container 11 forms no part of the present invention. Accordingly, the upper portion of the container 11 could be fabricated with any type of an upper closure, or no closure at all with the blank 13 simply ending at what is illustrated as the upper transverse score line 19a. Likewise, it should be understood that the improved bellows clo sure, as hereinafter discussed in detail, which is provided by the interconnected closure flaps23a, 23b, 25a and 25b could equally well be providedat both the top and bottom of a container, or it might conceivably be only provided at the top of the container while a standard bottom construction i s used. V,

In the illustrated embodiment, a glue flap 29 for creating a manufacturers joint at one corner of the container 11 is hinged to the side wall 15a along the vertical score line 17a. The glue flap 29 extends from the upper transverse score line 19a to the lower edge of the blank and is designed to be attached by adhesive or by stitching to the outersurface of the end wall panel 16b and thereby form the flat blank 13 into a tube. Other types of manufacturers joints may also be used in different embodiments of containers wherein the improved closure is included. For example, in a multicell container a tapped, butt joint in one of the side walls might be employed.

As best seen in FIG. 2, the first pair of

panels

23a and 23b are provided with pairs of converging score lines 31a and 31b, respectively, which extend from the intersections of the score lines 17 with the transverse score line 19b and which along with the lower transverse score line 19b and the lower edge of the blank define

first closure flaps

33a and 33b that are trapezoidal in shape. The four parallel score lines 17 and the upper and lower transverse score lines 19 are all formed upon what eventually becomes the inner surface of the container 11, whereas the score lines 31 are preferably formed on the outer surface of the blank for a purpose to be explained hereinafter.

In each of the second pair of

closure panels

250 and 25b attached to the

end panels

16a and 16b are provided another pair of converging diagonal score lines 35a and 35b, respectively, which extend from the intersections of the score lines 17 with the transverse score line 19b and form in those panels two smaller

trapezoidal flaps

37a and 37b,'which are nearly triangularin shape as a result of the very short lower side. The score lines 31 and 35 alternately define pairs of triangular fold-

back panels

39a and 39b located mainly in the end closure panels 25 but extending slightly past the respective parallel vertical score lines, as seen in FIG. 2. These triangular fold-back panels include the angle A which should be slightly less than the angle D (between the transverse score line 19 and the diagonal lines 35) in order to obtain the over-center closing action described hereinafter. The angle A is also less than 45, and the angle D is usually between 46 and 54.

As illustrated in FIG. 3, the folding of the bottom bellows closure is carried out by first bending the larger closure flaps 33a and 33b, hinged to the side panels of the container, inward after the blank 13 has been set up from its knockdown shipping condition to an open tube. Because the score lines 31 and 35 are preferably printed on the exterior surface of the blank, the

panels

37a and 37b are first pushed inward to initially break the score lines 35a and 35b. Then, the side closure flap 33a is folded first, followed by the other flap 33b, causing the slight outward displacement of the end trapezoidal flaps 37a and 37b as shown in FIG. 3. As can be seen, the length of the flaps 33 is sufficient so that they overlap by at least a predetermined distance.

As shown in FIG. 5, in this intermediate position, both of the flaps 33 are oriented at an angle slightly above the horizontal plane defined by the hinge line 19b, i.e., slightly exterior of the cavity of the container 11. The folding of the closure is completed by grasping the generally triangular end closure flaps 37 and swinging them and the attached fold-back panels 39 inwardly until the flaps 37 are aligned substantially in the horizontal plane of the hinge line 19b.

At the end of this swinging movement, the bellows closure actually snaps into closed position as a result of the movement of the side flaps over center. This over center action is best seen by comparing FIGS. and 6 which show sectional views of the container closure in the intermediate position and in the closed position. The over center action results from the location of the score lines 31 and 35 so that, as seen in FIG. 5, the

angle A between score lines 35a and 31b is less than the angle D between score lines 35a and 19b.

There is some latitude in the angular orientation of these score lines 31a and 31b depending upon the relative widths of the side panels and the end panels and upon the strength and thickness of the material from which the blank is fabricated. In order for the flap 23b to nest inside the flap 23a (FIG. 3), the angle B at which the score lines 31b are oriented relative to the transverse line 19b should be less than the angle C at which the lines 31a are oriented. For a container of this type to have a satisfactory over-center action in the closing of the bellows-type closure, the angle A between the score lines 35 and the score lines 31b on the panel 23b to be folded inward second, and thusnest within the other, should be between about 2 and about 9 less than angle D formed by score lines 35 and hinge line 19. Variables include size, amount of overlap if used, and rigidity of container material. Thus, the precise angular orientation of the score lines 35 is dependent partially upon the location of the line 31; however, the angle D is greater than 45 for meeting or overlap flaps. In general, the angles B and C will be between about 82 and 89 degrees. However, so far as the angle C is concerned, it can approach 90, and in some containers it is possible toeliminate the lines 31a and only employ six diagonal score lines, i.e., 3lb,.35a and 35b. Thus, because it might be eliminated, the angle between the diagonal lines 31a and 35a is labeled A. Also, slots or slit cuts, particularly on the panel 23a to be folded first, can be used to further provide for ease of folding while retaining all advantages of this improved bellows closure.

As previously indicated, the longitudinal length of the side closure panels 23 should be such that there is a sufficient overlap of the side flaps 33 in the closed position so that the outer edges 43 of these flaps do not interengage. The closed position is illustrated in FIG. 6, and it can be seen that the necessary amount of overlap will be dependent upon the width of the end panels 16 and upon the angle which the flaps are disposed interiorly of the end plane of the container 11 in this closed position, which angles are indicated by the reference letter B in FIG. 6. As a general rule, it is preferred that the longitudinal length of the closure panels 23 be at least equal to about percent of the width of the end panel 15; however, dependent upon other variables in the construction, there may be sufficient overlapping when the length is only 52 percent of the end panel width.

As shown in FIG. 2, all of the bottom closure flaps 23, 25 are of the same length which permits economical fabrication because die cutting is rendered unnecessary. Although the length of the bottom flaps could be extended up to a point where interference between the

flaps

37a and 37b was encountered, such extension is not considered to achieve any useful purpose and is disadvantageous because it would increase the cost of the corrugated board. Thus, it is unlikely that the length of the bottom panels would exceed about percent of the width of the side panels.

In the illustrated embodiment, .the container 11 is provided with a manufacturers joint at the corner which is formed by the glue flap 29, the interior surface of which is coated with adhesive and then laminated to the outer surface of the end panel 16b and the end closure panel 25b. When the container blank 13 is made from a strong, thick material, such as a doublewall corrugated fiberboard or a laminated construction, the two thicknesses which are created at the location where the glue flap is laminated have been found to exert a considerable restraint to bending. As can be seen in FIGS. 3 and 4, one bend of 90 is required and one bend of substantially 180 is required when the glue flap 29 is laminated to an end panel 16 to leave the side panels free from obstruction. It has been found that by slitting glue flap 29, immediate relief from this restraint is provided.

As seen in FIG. 2, a horizontal slit 45 is provided in the glue flap 29 located at the extension of the lower hinge line 1%. Moreover, a second slit 47 is provided at an angle generally the same as the angle of the score line 35b. The second slit facilitates the 180 bend at the point of hinging to the fold-back flaps 39. As can be seen in FIG. 4, the

slits

45 and 47 define a small triangular panel 49 at the edge of the blank. If desired, this panel can be removed by extending both slits all the way to the intersection between the vertical score line 17a and the hinge line 19b. However removal of the small panel 49 is not required, and to facilitate fabrication it may be desirable to terminate the

slits

45, 47 short of the intersection.

In summary, the scored blank 13 is fabricated as shown in FIG. 2, with the score lines 17 and 19 being located on what will be the interior surface of the container 11 and with the diagonal score lines 31 and 35 printed on the exterior surface. Adhesive is applied to the glue flap 29, and the end panel 16b and the side panel 15a are folded about the

parallel score lines

17d and 17b, respectively. Compression is then applied to the blank to form the manufacturers joint. The container 11 is shipped to the place of ultimateuse in this flat or knocked down condition.

To set up the box for filling, the flattened, seamed blank is inverted and formed into a tubular shape by squeezing at the score lines 17b and 17d. The score lines 35 are then broken by momentary inward application of pressure to the panels 25. The side closure flaps 33 are then folded inward to the relatively stable position shown in FIG. 3. The end generally triangular closure flaps 37 are then swung about their hinge lines inward until they are aligned substantially in the end plane of the container, defined by the peripheral hinge line 19b. In reaching this position an over-center action occurs as the side closure flaps 23a and 23b snap interiorly into the location shown in FIG. 6. In this position, the closure is stable as a result of the over-center action. Accordingly, the container 11 can be turned right side up and will set flat upon a level surface, such as the floor. However, because of the weighjt of the filled bulk container, it is usually disposed upon a pallet, such as that depicted in FIG. 1 to facilitate its handling by mechanical lift equipment.

As a result of the stable, over-center position, the empty container 11 can be moved without gluing the bottom closure to the filling location. Once the container is filled with hundreds of pounds of contents, the bottom closure is of course compressed between the contents and the upper surface of the pallet 51, and it thereafter remains tightly closed until it is emptied or removed from the pallet. Accordingly, if it is the intention to employ the container either with an associated pallet, or perhaps by disposing it inside ofa bottom cap, the bottom flaps of the bellows-type closure need not be glued to one another. Of course, if desired, total sealing of the bottom closure may be achieved by applying a glue pattern to the triangular fold-back panels 39 and optionally along the lower exterior edgev of the underlying side closure flap 33b. The containerr 11 may advantageously be used without gluing the bottom closure, as by strapping it to a pallet, because it then remains succeptible to being knocked down to its flattened condition and transported for reuse.

In the illustrated container 11, the

slits

45 and 47 provided in the glue flap 29 are particularly advantageous because of the over-center action incorporated in the closure. However, the employment of these slits, which alleviates the tendency of the two-layer thickness of corrugated material to resist bending, is advantageous even if the over-center lock-action is not incorporated because it facilitates the folding operation to form a standard bellows closure. The arrangement also allows the glue flap to be hinged to a side panel, thus leaving the container sidewalls unobstructed.

Although the invention has been illustrated with respect to a preferred embodiment, it should be understood that various modifications, other than those hereinbefore stated, such as would be obvious to one having the ordinary skill in the art, may be made without departing from the scope of the invention which is defined in the appended claims. For example,-if a completely die cut container blank is used, it may be desirable to offset slightly upward the portions of the lower hinge line 19b which define the

inner flaps

23a and 23b. Such an offsetting is considered to be the full equivalent of the illustrated straight line 19b, and where the term hinge line or transverse line is used in this application, it should be understood to include such a partially offset line.

Various features of the invention are set forth in the claims which follow.

What is claimed is:

1. A container made of corrugated fiberboard comprising four interconnected side panels defined by parallel fold lines and arranged to define a tubular enclosure of rectangular cross section and four interconnected closure panels hinged along a line to aligned edges of said side panels, a first pair of said closure panels being hinged to opposed side panels and a second opposed pair of said closure panels being each divided only by a pair of converging diagonal score lines into a trapezoidal flap and a pair of flanking triangular foldback flaps, said first closure panels serving as first closure flaps which are hinged to said fold-back triangular flaps, one of said first closure panels containing a pair of first score lines oriented at an angle between about 82 and 89 to said hinge line, said first score lines defining said first closure flap, and the angle between said first score lines and the adjacent diagonal score line being less than the angle between said diagonal score line and said hinge line, the width of said first pair of closure panels being greater than the width of said sec- 0nd pair of closure panels and said length of said closure panels being such that said first pair of closure flaps overlap each other in closed position, said first closure flaps being folded inward of said trapezoidal flaps and said first closure flap which contains said first score lines being folded inward after said other first closure flap whereby said closure becomes biased into its inward closed position upon folding of said closure flaps.

2. A container in accordance with claim 1 wherein said first score lines are provided in both of said first closure panels.

3. A container in accordance with claim 1 wherein said diagonal score lines are oriented at an angle of between about 46 and about 54 with said hinge line.

4. A container in accordance with claim 1 wherein the longitudinal length of each of said four closure flaps is equal.

5. A container in accordance with claim 1 wherein said length of said closure panels is between about 52 and about 60 percent of the width of one of said second closure panels.

6. A container having four interconnected side panels arranged to define a tubular enclosure of rectangular cross section and four interconnected closure panels hinged along a line to the aligned edges of each of said side panels, a first opposed pair of said closure panels forming first closure flaps and a second opposed pair of said closure panels being each divided by a pair of diagonal score lines into a central flap and two flanking triangular fold-back flaps, glue flap means hingedly connected along a vertical score line to one of said side panels and to one of said first closure panels, means adhering said glue flap with the inner surface thereof in contact with the outer surface of a side panel and of a second closure panel, first slit means in said glue flap aligned with said hinge line between said side panel and said second closure panel, and second slit means in said glue flap generally aligned with the underlying diagonal score line in said second closure panel upon which said glue flap is adhered.

7. A container in accordance with claim 7 wherein said central flaps are trapezoidal and said closure panels are of equal longitudinal length.

8. A container in accordance with claim 7 wherein said diagonal score lines are disposed at an angle between about 46 and 54 degrees to said hinge line and wherein said first pair of closure panels are folded inward of said second pair of closure panels.

9. A container blank of corrugated fiberboard which blank comprises four interconnected side panels defined by parallel longitudinal score lines, first and second pairs of closure panels alternately connected to said side panels along a transverse line as longitudinal extensions of said side panels and being also defined by said parallel score lines, said first closure panels being longer than said second closure panels and having a length between 52 and about percent of the width of one of said second closure panels, a pair of first diagonal score lines in one of said first pair of closure panels defining a first trapezoidal closure flap, and only a pair of second diagonal score lines in each of said second closure panels which define second trapezoidal flaps and triangular fold-back flaps which are hingedly connected to and disposed in flanking relationship with said second trapezoidal flaps, said first and second diagonal lines meeting at an angle less than the angle between the second diagonal line and said transverse line, whereby said blank is adapted for formation into a tubular container having an improved bellows-type closure when said first closure panels are folded interiorly of said second closure panels.

10. A blank in accordance with claim 9 wherein each of said first closure panels has a pair of said first diagonal score lines.

11. A blank in accordance with claim 9 wherein said parallel score lines are disposed in one surface of said blank and said first diagonal score linesare disposed in the surface of said blank opposite from said one surface.

12. A blank in accordance with claim 9 wherein said first diagonal lines are disposed at an angle between about 82 and 89 with said'transverse line.

13. A blank in accordance with claim 13 wherein said second diagonal lines'are disposed at an angle between about 46 and about 54 with said transverse line.

14. A blank in accordance with claim 9 wherein a glue flap is hingedly connected to one of said side panels and to one of said first closure panels along a line parallel to said parallel score lines and wherein first slit means is provided in said glue flap in alignment with said transverse line and second slit means is provided at an angle to said transverse line generally the same as that at which said second diagonal lines are disposed.

15. A blank in accordance with claim 9 wherein the flutes of said corrugated fiberboard run longitudinally thereof and wherein the longitudinal length of each of.

said closure panels is equal.

15mm STATES PATENT armor QERTEMCATE @F CRECTEON Patent No. 790 932 Dated August l9 7 Inventoz-(s) Donald En It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shovm below:

Column 1, line 20, "tones" should be -tons-.

Column 3, line 4, "tapped" should be taped.

Column 5, line 53, "weighjt" should Toe weight-.

Column 7, lines 33 and 36, claim reference numeral "7", each occurrence, should read 6-.

Column 8, line 30, the claim referenoe numeral "13" should read -l2-.

Signed and sealed this 20th day of November- 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JRa RENE A D. IEGTI IEYER I Attesting Officer Acting Commissioner of Patents 'ORM PO-l 050 (10-69) US COMM'DC 60376-5 69 A QWERNMEYT PRINTING OFFICE: IBID 0-368-334,

Claims

1. A container made of corrugated fiberboard comprising four interconnected side panels defined by parallel fold lines and arranged to define a tubular enclosure of rectangular cross section and four interconnected closure panels hinged along a line to aligned edges of said side panels, a first pair of said closure panels being hinged to opposed side panels and a second opposed pair of said closure panels being each divided only by a pair of converging diagonal score lines into a trapezoidal flap and a pair of flanking triangular fold-back flaps, said first closure panels serving as first closure flaps which are hinged to said fold-back triangular flaps, one of said first closure panels containing a pair of first score lines oriented at an angle between about 82* and 89* to said hinge line, said first score lines defining said first closure flap, and the angle between said first score lines and the adjacent diagonal score line being less than the angle between said diagonal score line and said hinge line, the width of said first pair of closure panels being greater than the width of said second pair of closure panels and said length of said closure panels being such that said first pair of closure flaps overlap each other in closed position, said first closure flaps being folded inward of said trapezoidal flaps and said first closure flap which contains said first score lines being folded inward after said other first closure flap whereby said closure becomes biased into its inward closed position upon folding of said closure flaps.

3. A container in accordance with claim 1 wherein said diagonal score lines are oriented at an angle of between about 46* and about 54* with said hinge line.

9. A container blank of corrugated fiberboard which blank comprises four interconnected side panels defined by parallel longitudinal score lines, first and second pairs of closure panels alternately connected to said side panels along a transverse line as longitudinal extensions of said side panels and being also defined by said parallel score lines, said first closure panels being longer than said second closure panels and having a length between 52 and about 60 percent of the width of one of said second closure panels, a pair of first diagonal score lines in one of said first pair of closure panels defining a first trapezoidal closure flap, and only a pair of second diagonal score lines in each of said second closure panels which define second trapezoidal flaps and triangular fold-back flaps which are hingedly connected to and disposed in flanking relationship with said second trapezoidal flaps, said first and second diagonal lines meeting at an angle less than the angle between the second diagonal line and said transverse line, whereby said blank is adapted for formation into a tubular container having an improved bellows-type closure when said first closure panels are folded interiorly of said second closure panels.

11. A blank in accordance with claim 9 wherein said parallel score lines are disposed in one surface of said blank and said first diagonal score lines are disposed in the surface of said blank opposite from said one surface.

12. A blank in accordance with claim 9 wherein said first diagonal lines are disposed at an angle between about 82* and 89* with said transverse line.

13. A blank in accordance with claim 13 wherein said second diagonal lines are disposed at an angle between about 46* and about 54* with said transverse line.

15. A blank in accordance with claim 9 wherein the flutes of said corrugated fiberboard run longitudinally thereof and wherein the longitudinal length of each of said closure panels is equal.