Bag-producing apparatus and method of producing foil bags

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Reexamination Certificate

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C493S037000, C493S189000, C493S200000, C493S374000

Reexamination Certificate

active

06267714

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS.
This application claims priority from German Patent Application No. 198 24 797.4, filed Jun. 3, 1998.
FIELD OF INVENTION
The present invention relates to a method of producing foil bags, wherein at least two foils, which serve as side foils of the foil bags, are placed one upon the other and are connected to each other and cut into individual foils bags, and to a bag-producing apparatus for performing the method.
BACKGROUND OF THE INVENTION
In a foil-bag producing process, at least two foils are supplied that serve as side foils of the foil bag. The foils are normally supplied by corresponding supply rolls. The individual foils are placed one upon the other and are sealed or bonded to each other at least at the place where the side edges of the foil bags are positioned. The interconnected foil webs are then cut along the connections to form individual foil bags. A bottom foil which in the area of the future bottom of the foil bag is sealed or bonded between the side foils and provides space for the filling material when being folded apart can be placed between the side foils. Moreover, such a bottom foil functions as a standing base. Subsequently, the foil bags which are produced in this way and are closed at three side edges can e.g. be supplied to a filling station in which the filling material is filled in through the fourth edge that has not been closed yet, and this fourth edge of the two side foils is then sealed or bonded.
As a rule, the foil webs which are supplied to the sealing means are already provided with corresponding imprints which furnish information about the product to be contained in the foil bag. For instance, it is exactly determined for each individual foil web already before it is supplied to the sealing or bonding means how much foil material is respectively provided for a foil bag. However, there might be slight variations in the amount of foil material intended for a foil bag. Such variations may e.g. be caused by an unprecise printing machine for forming the imprint. Moreover, the unwinding operation which is carried out on the supply roll might lead to different extensions of the foil material, depending on whether a great or small amount of foil material has been wound onto the supply roll. In view of the large outputs which are nowadays standard in automated production systems, such variations, even though they are small as such, accumulate in an additive manner, possibly resulting in an undesired displacement of the printed pattern relative to the side edges of the future foil bag. Such a problem will be all the more serious if, in addition to the imprint, there are other features provided for, e.g. an insertion hole for a straw in a foil bag for beverages where the straw is displaced with respect to its correct position.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to provide a method and an apparatus in which variations in the amount of the foil material intended for the individual sides of the foil bag are avoided.
In the method according to the invention, at least two foil webs are first of all supplied for forming the side foils of the foil bags. The foils are placed one upon the other and connected to each other at the future side edges of the foil bags. Possibly existing differences in the amounts of foil materials as are provided by the at least two foils in the feed direction for a respective foil bag are eliminated by stretching the foil that provides the smaller amount of foil material for a foil bag.
As a consequence, a step is taken in the method prior to the bonding or sealing process for compensating for possibly differing amounts of foil materials. It is thereby ensured that the individual foil webs come to rest one upon the other in the correct position before they are connected to each other. A displacement, even a slight one, can thereby be prevented, so that the accumulation of incorrect positions is avoided. Since the foil which in actual fact provides the smaller amount of foil for a foil bag in the feed direction is the only one that is subjected to a stretching operation, the method will react to every change in condition.
The stretching operation can easily be carried out when the foil supply of the foil to be stretched is interrupted or slowed down for a short period of time while the discharge operation following the connecting process is continued. As a result, the foil supply is controlled in response to the necessary stretching operation. The foil supply can e.g. be interrupted by clip means which act upon the supplied foil whenever said foil is to be stretched.
In another development of the method the stretching operation is performed by holding the foil to be stretched at two spaced-apart places and by simultaneously increasing the foil tension between the holding points. This method permits a very precise stretching of the foil. In this development the foil may be firmly clamped at the holding points, so that the stretching operation is carried out in the foil section between the holding points.
The foil tension can easily be increased with the help of a stretching body which deflects the foil to be stretched laterally from the unaffected transportation path over the entire width between the two holding points. As a result of the lateral deflection, the foil web is stretched.
The question which one of the stretching means is presently the active one on the at least two supplied foils depends on the question which one of the foil webs is to be stretched. This operation may be carried out automatically or, however, in a manually controlled manner. Whenever the amounts of foil materials provided by the at least two foils in the feed direction for a respective foil bag are approximately identical for the two foils, it may be of advantage when one of the foils is permanently prestretched, for instance, by being supplied at a lower speed. The other foil is then stretched in a corresponding manner according to the method of the invention.
There are various possibilities of detecting the amount of foil material provided for a foil bag in the feed direction. In a particularly advantageous development of the method, the supplied foil has provided thereon respective marks which are applied to the foil material at distances corresponding to the amount of foil material respectively provided for a foil bag. It can easily be determined by measuring the distance of said marks how much foil material is provided in the respective foil for a foil bag. Whenever the distance between the individual marks is smaller than the extension a future foil bag should have in the feed direction, said foil material will be stretched accordingly until the respective marks have the desired distance.
The marks may be formed by notches, holes or structural features. However, a mark which can be sensed optically represents a simple configuration. Such a mark can easily be printed in advance onto the foil material to be supplied, e.g. in the process in which the inscription on the future foil is applied to the foil. An additional process step is not needed for this purpose. In addition, optical marks can very easily be detected and evaluated.
Such marks can be applied in an area of the supplied foil material which is cut off prior to the final formation of the foil bag. A particularly economic variant will however be achieved when the mark is provided in an area which will later form the side foil of a respective foil bag. In such a case foil material need not be wasted for removing the mark. A mark which can be read out optically may thus be very small and can consequently be formed in an unobtrusive manner. Moreover, the optical mark can be integrated into the imprint of the foil that exists at any rate, or part of the existing imprint itself can be used as the optical mark.
The method can be performed on foil webs having a width in a direction perpendicular to the feed direction, the width exactly corresponding to one foil bag. The method, however, can be used in a particular

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