US 3896714 A
A side-gusseted flat bag having side gussets and a simple bottom seam is made first. The side gussets are subsequently spread to transform the bottom portion of the bag into a block bottom in such a manner that the underside of the bag and the lower folded edge are retained in a portion which extends from the bottom seam by a distance equal to the gusset depth. The upper folded edge and/or the upper side of the bag is gripped by movable gripping means, and the gripping means are moved relative to the support so as to form the block bottom. The gripping means which grip the upper folded edge and/or the upper side of the bag are moved tangentially to the support for the bag during the transformation of the bottom portion whereas a lifting component of motion is avoided.
Description (OCR text may contain errors)
United States Patent [191 Bosse [451 July 29,1975
[ PROCESS OF MANUFACTURING BLOCK BOTTOM BAGS  Inventor: Frank Bosse, lbbenburen-Dorenthe,
Germany 22 Filed: Nov. 14,1973
21 Appl. No.: 415,513
 Foreign Application Priority Data Nov. 20, 1972 Germany 2256913  References Cited UNITED STATES PATENTS Richens 93/35 SB Haslacher 93/35 SB 3,606,822 9/1971 Platz et al. 93/35 SB Primary Examiner-Roy Lake Assistant Examiner.lames F. Coan Attorney, Agent, or FirmFleit & Jacobson  ABSTRACT A side-gusseted flat bag having side gussets and a simple bottom seam is made first. The side gussets are subsequently spread to transform the bottom portion of the bag into a block bottom in such a manner that the underside of the bag and the lower folded edge are retained in a portion which extends from the bottom seam by a distance equal to the gusset depth. The upper folded edge and/or the upper side of the bag is gripped by movable gripping means, and the gripping means are moved relative to the support so as to form the block bottom. The gripping means which grip the upper folded edge and/or the upper side of the bag are moved tangentially to the support for the bag during the transformation of the bottom portion whereas a lifting component of motion is avoided.
1 Claim, 5 Drawing Figures PROCESS OF MANUFACTURING BLOCK BOTTOM BAGS This invention relatesto a process of manufacturing a block bottom bag, in which a bag having side gussets and a simple bottom seam (side-gusseted flat bag) is made first, the side gussets are subsequently spread to transform the bottom portion of, the bag intoya block bottom in such amanner that the underside of the bag and the lower folded edge are retained. in a portion which extends from the bottom seam by a distance equal to the gusset depth, the upper foldededge and/or the upper side of the bagis gripped by movable gripping means, and the gripping means are moved relative to the support so as to form the block bottom. 1
Such procedure is known from the US. Patent-Specification No. 634,081, the German Patent Specification No. 830,157, and .the French Patent Specification No. 1,308,838. In the known processes, the movable grippers perform a semi-circular movement so that .those wall portions of the bag which are shaped to form the bottom are stretched tightly adjacent to the bottom. The side gussets are first spread adjacent to the bottom until they stand up atright angles-to the plane of the side-gusseted bag-and the spreadparts are then-backfolded. 1 i
This procedure has the advantage that a block bottom bag can bemade with relatively simple apparatus. The semicircular relative movementhas also the advantage that the bag material is substantially stretched during the formation of the bottom and a wrinkling of the bag material is avoided.so that neat bottom folds are obtained. On the other hand, this. procedure has the disadvantage that the pulling openof. the side-gusseted bag adjacent to the bottom like opening bellows during the formation of the block bottom gives-rise to the formation of a large cavity, which must fill with air. To enter the cavity, this air must flow through the filling opening and throughout the length of the flat sidegusseted bag. Because the side-gusseted bag is flat, it presents a high resistance to the flow of the air. As the cavity opens adjacent to the bottom, its suction increases the flatness and resistance to flow of the bag. The faster the cavity opens, the higher is the resistance to flow. For this reason, only a limited number of bags can be made per unit of time in the process mentioned first hereinbefore of making block bottom bags. This number depends mainly on the stiffness of the bag material, which determines the deviation of the bag from an exactly flat condition. The higher the flexibility of a bag material, the lower is the number of bags which can be made per unit of time. Specifically, only a small number of side-gusseted bags made from plastics material sheeting can be transformed per unit of time into block bottom bags because the sheeting is flexible. On the other hand, plastics material sheeting cannot easily be adhesively joined so that it is particularly desirable with this material first to make a sidegusseted flat bag having a simple bottom seam weld and then to transform this bag into a block bottom bag. Block bottom bags are known to have the convenient property of opening readily into the subsequent parallel-epipedic shape as they are filled manually or by machine.
It is an object of the invention so to modify the process mentioned first hereinbefore of manufacturing block bottoms that a large number of simple sidegusseted flat bags made from flexible material can be transformed per unit of time into block bottom bags.
-2 According to the invention this object is accomplished inthatthe gripping means which grip the upper folded edge and/or the upper side of the bag are moved tangentially to the support for the bag during the transformation of thebottom portion whereas a lifting component of motion is avoided. As a result, the block bottom is formed substantially within the plane, of the bag in that the superimposed wall portions of the bag are peeled from each other and any vacuum formed adja- -cent to the bottom is utilized.
The process according .to the invention'will'be described more fully hereinafter with reference to the drawing, which shows by way of example several phases of a sequence of operations used in the manufacture of bags. Each of FIGS. 1 to 5 shows the left-hand half of the bottom portion of the bag made by the process according to the invention.
It is shownin FIG. 1. that in the manufacture of bags in accordance with the invention, individual tube sections lare initially provided, which have side gussets 2 having adepth T. These tube sections are severed by cuts along the edge 3 from a virtually endless flat tubing of plastics material'in which the side gussets have been formed in known manner. The tube section is formed at the bottom cut edge with a transverse seam weld 4, as shown in FIG. .2, to form a normal side-gusseted flat bag. Toprepare the formation of a block bottom, transverse sco're lines '5 and 6 are formed throughout the width of the bag before, during or after the welding. These score lines are spaced from that edge of the seam weld 4 which faces the interior of the bag by distances T'and 2T, which are equal to the side gusset depth T and twice the side gusset depth T, respectively. These score lines facilitate the formation of a block bottom with uniform precision in all bags which are made and also serve to preserve the resulting bottom during the storage and shipment of the finished flat bags until they are used. Also to enable or facilitate the formation of the bottom as taught by the invention, tools must engage the bag adjacent to its bottom. The bag is first engaged on both sides by respective holding-down members 7, which are as flat as possible and engage the bag in such a manner that that edge of the holding-down member which faces the bottom end of the bag is approximately flush with the inner score line 6. In addition to these holding-down members, other tools, which are of no interest here, are provided to ensure that all portions of the bag are retained on its support 6 in exact alignment. The side gusset must be opened to form a small gap adjacent to the lower score line 5 so that holding-down members 8 can be laterally introduced between respective side gussets of the bag. The side gussets may be opened by a row of suckers 11, which are indicated by the suction points 9 and the arrows 10 and act on the top face of the bag inside the lower score line 5 between the latter and the seam weld 4, or by individual suckers, which are effective only adjacent to the side gussets. Another row of suckers may act on the underside of the bag shortly behind the score line 5. When the side gusset has been slightly spread, the holding-down member 8 may be introduced. The holding-down member 8 is as flat as possible and is bevelled at an angle of 45 at its forward edge facing the bottom seam weld 4. The holding-down member is introduced in such a manner that its bevelled forward edge crosses the side edge of the bag at the score line 5 so that the holding-down member engages the bag behind the score line 5. As has been mentioned, the underside may also be retained on the support by a row of suckers, which is aligned with the holding-down members 8.
When the bag has thus been fixed adjacent to its bottom and has been engaged by the tools, the sidegusseted flat bag shown in FIG. 3 may be transformed into a block bottom bag. For this purpose, it is sufficient to move the row of suckers 11 tangentially toward the open end relative to the holding-down members 7 and 8 by a distance which equals the side gusset depth T. This movement is indicated by the arrows 12. During this tangential movement a lifting at right angles to the plane of the bag is avoided. This movement results in the transformation of the side-gusseted flat bag into a block bottom bag in that the wall portions slip relative to each other although their movement is not exactly regular at the beginning of the transformation. Creaseresisting plastics material sheeting will readily follow this initial creasing movement without being damaged and without presenting a resistance. Only toward the end of the transforming movement, when the contours of the block bottom become increasingly apparent, does the movement become more regular; neat fold lines which are the same in 'all bags are then formed in the bottom portion as well as a distinctly contoured rectangular bottom 13. This action is assisted by the previously formed score lines 5. FIG. 4 illustrates the beginning of the transformation. FIG. shows a portion of the bag as the transforming movement is being completed and the bag toward the end of the transforming movement so that the block bottom bag has virtually been completed. The vacuum which forms in the interior of the bottom portion of the bag as its wall portions are peeled off is utilized to change the initially irregular transforming movement of the wall portions into an in- 4 creasingly regular movement/Toward the end of the movement, the wall portions are stretched to their desired position by the tools engaging the bottom portion of the bag so that an exact shaping of the bottom is ensured.
What is claimed is: 1. A process of forming block bottom bags from thermoplastic material including the steps of:
forming a simple bottom seamed, side-gusseted, open mouthed flat bag; forming a pair of transverse score lines on said bag extending across the width thereof spaced apart and from the bottom of said bag; supporting said bag on'aflat surface to define top and bottom faces of said bag; holding the bag against the flat surface by engaging said top face at positions adjacent said side gussets and along the score line remote from the bottom seam; opening said side gussets while the portions of the top and bottom faces extending between said opened side gussets remain in engagement with each other; holding the bottom part of each said side gusset adjacent said score line nearer said bottom seam; moving the top face of said bag while in engagement with the bottom face of the bag tangentially with respect to said bottom face in a direction toward the open end of said bag, and in substantially the same plane as said bottom face to effect a peeling of said top face from said bottom face and causing said faces to slip relative to each other; stopping the tangential movement of said top face when said wall portions are moved into a predetermined position by said tangential movement whereby the flat bottom of said bag is formed.