US2600487A - Siftproof bag bottom - Google Patents

Description

June 17, 1952 M. E. CRAIG 2,600,487

SIFTPROOF BAG BOTTOM Filed July 6. 1948 2 Sl-lEETS-SHEET 1 INVENTOR. M ERLE E CRAIG ATTOR N E! June 17, 1952 M. E. CRAIG SIFTPROOF BAG BOTTOM 2 SHEETS-SHEET 2 Filed July 6, 1948 INVENTOR. MERLE E CRAIG.

ATTORNEY Patented June 17, 1952 .SIETPROOF BAG BOTTOM Merle Craig, Camas, Wash 'assignor to Crown -Zellerbach Corporation, San Francisco, Calif.,

a'corporation-of Nevada 7 Application July 6, 1948, Serial No. 37,232'

'1 Claim. 1 This invention relatesto-multi-ply paper bags having pasted bottom ends.

'More particularly this invention relates to with a bottom which will remain sift-proof.

From' time to-timevarious improvements have been made in pasted bag bottoms in an endeavor to make them more nearly sift-proof, among which the improvements described'in'U'S. Letters Patent No. 1,960,929, issued May 29, 1934, to

Taggert, are particularly well known. While the adoption of some of these improvements by the trade has resulted in'some reduction in loss in the shipping of carbon black, nevertheless, I have found, in the course of considerable observation and experience in the handling of bags of carbon black,that the percentage ofthese bags which are found to'be ruptured or leaky is still fairly large in spite of such improvements.

In mystudy of this-problem Ihave'found that these bag failures are largely attributable to the following causes:

(1) Failure in a pasted seam of one of the bot tom'flaps;

(2) Tearing'occurring in a ply where an end slit had been made in forming the bag bottom;

(3) Formation of'bag bottom in such'manner that unequal or excessive strain is imposed on one of the plies'alone.

Observance of failures occurring in the pasted seams in the bottoms of carbon black bagsand tests which I'have made in this connection, have shown that such'failures inthe pasted seams are less apt'to'occur if the application of the paste has takenplace'on'both of the opposed surfaces or faces which are pasted one over the other, than when the paste is applied to'only one of the'faces. In other words, when'a flap is folded over and pasted down on the bag bottom, I have found that there is less likelihood-of any failureoccurring along the pasted seamlines-if the paste has been applied not only on the underside of the fiapbut also on the'surface to which such underside of the flap is to be secured. This will be readily understood as'one considers the-speed and the'manner in which paste is applied for the seams in modern bag machines.

One of the objects of the present invention therefore is to provide an improved bag bottom structure'in'which such double application of pastewill' occur along a greater extent of the bottom seam without necessitating any change in the present manner or method of applying paste.

While tearing of the paper at the ends of the slits, which slits are'required' to be made in the plies to form the bottom sections of standard types of bags, may be due to one cause or another, obviously reduction in the number of'slits required will reduce the number of chances for such tears to occur. Furthermore, I have found thatreducing the amount of slitting required in the paper tubing in the formation of the bag makes the bag easier to run on the bag machine. Accordingly another object of the present invention is to provide an improved multi-ply leakproof bag in which less slitting of the plies will be required than heretofore.

In my opinion it is not feasible to manufacture bags of the type used for carbon black without some slitting of the paper tubing for forming the bottom section. In multi-ply bags the slits of the inner plies are of primary importance, and in the bags now commonly used for carbon black I have found that leaks are more likely to start at the ends of the slits of the inner plies. Therefore an additional object of the present invention is to provide a bag bottom construction for a multi-ply bag in which there will not only be fewer such slits but in which the slit portions of the inner ply will ultimately be so positioned as to be subjected to a minimum amount of strain from the pressure set up in the packed bag incidental to its handling. 7

The manner in which these objects and other "advantages are obtained in my improved bag bottom construction, will be pointed out in the course of the following brief description with reference to the accompanying drawings.

In the drawings:

Fig. 1 is a view, in perspective, of the multi-ply paper tubing from which my bag is made, showing the first folding of the tubing to make the bellows-like side portions of the bag, and also showing the slitting of the tubing as required for my improved bag bottom construction;

Fig. 2 illustrates the bottom forming portion of the-multi-ply-paper tubing with the first stage of the bottom folding having taken place and with the paste then having been applied to the bottom;

Fig. 3 is a similar view illustrating the same bottom portion, showing the inner main flap of the bottom folded over onto the bottom in the next stage of the forming of the bag bottom; Fi '4 is -a view of the completed bag '"b-otto'm 3 with the outer main flap of the bottom folded over on the inner main flap, a portion of the outer ply of the paper being shown torn away to show the underlying ply and paste line more clearly;

Fig. 5 is a perspective view, drawn to a smaller scale, of the completed bag showing the bag opened out and ready for filling.

For the sake of simplicity in illustrating my improved bag bottom construction, the drawings show the bag as formed of only two plies, thus an inner ply and an outer ply. Generally for carbon black bags, at least three plies are used, in which case two plies take the place of the single outer ply which I have shown in the drawings. It is to be understood therefore that a double ply or double thickness of the paper would probably be used for the single outer ply shown in the drawings and that two or more thicknesses or plies could be substituted also for the single inner ply as well as for the single outer ply of the drawings.

While my invention requires a minimum .of two plies or two thicknesses of paper, my invention can be carried out with any reasonable number of thicknesses or plies. The plies will constitute two groups in any event, thus an outer ply or group of plies and an inner ply or group of plies, corresponding to the outer and inner plies of the drawings. The different plies or thicknesses of paper are secured together :by spot pasting, and, in order to form the bag tube each ply has a separate longitudinal seam, the longitudinal seams being staggered, all of this being customary and well known in multi-ply bag construction.

Throughout the accompanying drawings the reference character It indicates the outer ply, which may be regarded as representative of the outer group of plies as previously mentioned, and l I similarly indicates the inner ply.

Referring first to Fig. l, the bag tubing [2, composed of two plies Ill and H is given the longitudinal folds l3, M, [5 on each side in the usual manner to form the bellows-like sides for a square-bottom bag. A pair of slits is out in each of the plies, thus the slits I 6, I6 are cut in the outer ply l0 and the corresponding slits l1, I! are cut in the inner ply i I, the slits of each pair being equally spaced from the longitudinal side folds and the slits H, ll on the inner ply H being placed closer together and being shorter than the slits l6, l6 of the outer ply 10. These slits are similar in arrangement to those now common in multi-ply bags except that only one pair of such slits is made in each ply instead of the customary two opposite pairs of slits in each ply.

After the longitudinal side folding and the slitting have taken place, as illustrated in Fig. 1, the end of the tubing from which the bottom part of the bag is to .be made is drawn out, folded and pressed, as shown in Fig. 2, so as to form two similar trapezoidal main bottom sections i8 and i9 in the customary manner. The pair of slits l6 (Fig. l) in the outer ply IE will cause an outer lateral flap 28 (Fig, 2) to extend from one end of the two main bottom sections [8 and I9, the length of the side edges 2| of the flap 20 corresponding to the length of the slits l6. Similarly the pair of slits 1? (Fig. 1) in the inner ply il will result in a smaller inner lateral ilap 22 (Fig. 2) with side edges 23 determined by the length of the shorter slits ll. The inner flap 22 is centrally spaced within the outer flap 20. The formation and arrangement of such lateral flaps is old in the art. However, contrary to the established practice, these outer and inner lateral flaps 20 and 22 are formed at one end only of the main bottom sections [8 and I9 since the outer and inner plies each have only one pair of slits instead of the customary two pairs, as previously mentioned.

When the main bottom sections [8 and 3, with the outer andinner end lateral flaps 20 and 22, have been arranged as shown in Fig. 2, the paste is applied in the usual manner in two broad parallel paste strips 24 and 25 joined by a transverse paste strip 26 at one end over the flaps 26 and 22, and thus having the paste cover the areas indicated by the stippling in Fig. 2. The paste strips 24 and 25 are preferably made as wide as possible while still leaving a slight margin between the inside edges of these paste strips 24 and 25 and theadjacent edges of the paper, and also leaving a slight margin between the outer edges of these paste strips and the outer edges of the outer lateral flap 20. This is necessary so that the paste will not be pressed beyond these edges of the paper in the finished bag.

After the applicagon of the paste along the paste strips 24, 25, 26, the bottom forming portion of the bag is folded over on itself on the crease line 27 and thus the bottom portions will be arranged in the formation shown in Fig. 8, this folded over portion forming the inner main triangular fold 28, which is pressed against the underlying bottom sections. Since the paste strips 24 and 25 extend over both the overlying and underlying faces beneath this main triangular fold 28, there is practically no possibility of any failure in the two paste seams which secure this main fold 28 to the underlying bag bottom sections. Furthermore, since the plies in the main triangular fold 28 have not been slit, if any shifting of the bag contents is to take place past or through this main fold 28, such sifting must occur either at the inner fold corners 29 at the tip of the main fold 28 or between these corners 29 and the adjacent inner edges of the paste strips 24 or 25.

After the inner triangular main fold 28 has been secured in place as illustrated in Fig. 3, the final step in the completion of the bag bottom consists in folding the opposite end of the bottom forming portion of the bag over on the crease line 30 and pressing this second and outer folded-over portion 31 (Figs. 4 and 5) down on the underlying bottom sections and down on top of the inner main triangular fold 28.

In my improved bag bottom the length and spacing of the pair of slits of the inner ply which determine the side edges of the inner and smaller lateralflap 22 are so arranged that when the outer portion 3| is finally. folded over on top of the inner main triangular fold 28, the corners 32 of the flap 22 of the inner ply N (Fig. 4), formed at the inner ends of the slits of the inner ply, will overlie the inner main triangular fold 28 but will be located close to its edges. Lo eating the slit corners 32 at these points has two distinct advantages. The slit corners of the inner ply represent the points at which the tearing of the bag paper is most likely to occur when strain is produced in the packed bag. By having the strong unslitted inner main triangular fold of the bottom extending under these corners and capable of withstanding any reasonable strain occasioned by pressure from the filled bag, these corners 32 are guarded and protected, and the possibility of any tearing of the inner ply of paper occurring at these corners after the bag is completed is reduced to a minimum.

If any sifting is to occur from the folded-over portion 3| of the bag bottom this would be most likely to take place at the slit corners 32. Material sifting from these corners 32 would be obliged to pass through the pasted seams in some direction in order to escape from the bag bottom. The most likely avenue of escape would be along an outer edge 33 of the inner main triangular fold 28, thus, for example, in the direction indicated by the arrow as in Fig. 4. The reason for this, as apparent, is that when the outer flap 20 is pasted down over this portion of the bottom, the difference in level of the two underlying surfaces along the ridge or fold line 33 increases the difiiculty of producing a perfect seal along such line, this difference in level of the two underlying surfaces along such fold line amounting to at least four thicknesses of paper. The side portions of the flap 20 which constitute the sealing strips over this part of the bottom area, whether constituting one or two thicknesses of paper, will always be at least three thicknesses of paper less than the thickness of the triangular fold section 28, and the reduced thickness of these sealing strips increases the possibility of better sealing. Furthermore, since the paste has been applied both to the underside of the flap 20 and also to the underlying paper surface, which double application of paste extends up to the ridge or fold 33, and since the side portions of the flap 20 extend for a substantial distance beyond the corners 32 and the oblique distance through the paste seam in the direction of the arrow :c is even greater, I have found that when my bag bottom is made exactly as shown in Fig. 4, the likelihood of any material sifting out along the folded outer edges of the portions 28 or 3! of the bag bottom is almost negligible. This fact is another noticeable distinguishing feature between; my improved bag bottom and the bottoms of bags now commonly being used for carbon black and the like.

Previously when considering the possibility of leakage occurring from the inner main fold 28, I have explained that such leakage would have to start at or near the inner corners '29. From such points the only likely avenues of escape of the material would also be along the same ridge or fold lines 33. Assuming that the material might sift part of this distance along such an avenue, it would still have to travel a path such as indicated by the arrow 3: in Fig. 4. The avenue of escape along this path, as already explained, has been most effectively sealed as the result of the improvements in my bag bottom.

Thus I provide my bag bottom with an inner triangular unslitted main fold 29, extending a substantial distance over the bag bottom, and a corresponding outer folded-over portion 3|, overlapping the inner main fold 28. The two plies, or groups of plies, from which the bag tube is formed, are slitted in the outer folded-over por-- tion 3| so as to form two lateral flaps constituting the outer flap 29 and the inner flap 22, the inner flap being located entirely within the outer flap. The two pairs of slits which form the two lateral flaps 20 and 22 are so arranged and proportioned that the inner ends of the slits forming the inner flap will be positioned on the inner main fold 28 near the borders of the same when the inner flap is finally secured in place on the bag bottom, and the side edges 2| of the outer flap 20 will extend to and over the borders of the inner main fold 23 at points a substantial distance out from the side edges of the inner flap 22. Consequently the outer flap 20 not only provides a protective outer sealing layer extending over and beyond the side edges of the inner flap 22, but the side portions of the outer flap also enable two supplemental triangularly-shaped sealed areas to be provided beyond the borders of the inner main fold 28 and the outer foldedover portion 3|, effectively blocking the most likely channels through which sifting of the ba contents from the bag bottom could otherwise possibly occur. In these added sealed areas, as well as along the paste seams sealing the inner and outer folds 28 and 3| to the body of the bag, double application of paste, thus application of paste to both opposed faces of the paper which are sealed to each other, has been provided and in this manner any possible failures in the paste seams are practically eliminated.

Finally my improved bag bottom, whether the bag tubing is formed with two plies or with more than two plies, is so made as to withstand heavy strains; the amount of slitting of the plies in the forming of the bag bottom has been reduced by one-half, making the bag easier to run on the bag machine; and possibility of any tearing occurring at the slits of the inner ply has been considerably lessened.

I claim:

A sift-proof bag bottom of the character described formed on the bottom end of a multiply bag tube, said bag tube initially having a pair of longitudinal slits centrally spaced in the bottom end of one side wall of the outer ply and a pair of centrally spaced longitudinal slits in the bottom end of the same side wall of the inner ply, said slits in said inner ply being considerably shorter and considerably nearer together than the slits in said outer ply, said bottom end of said tube pressed into two identical main portions together comprising a substantially diamond-shaped bottom section having one end substantially triangularly-shaped, said pairs of slits forming tabs on said outer and said inner plies extending from the other end of said bot tom section, said triangularly-shaped end folded over and secured to the bag bottom and extending more than half way across the bag bottom, said other end folded over on said triangularlyshaped end and secured thereto and to said bag bottom, the tab of said inner ply being entirely superimposed on said triangularly-shaped end, and the tab of said outer ply extending considerable distance beyond the edges of said triangularly-shaped end where said ends are overlapped.

MERLE E. CRAIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number

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