METHOD FOR PRODUCING PLASTIC BAGS AND BAGS MADE USING SUCH A METHOD

Abstract: During a stage in the production cycle of the plastic bags, for example during the stage in which they are customized by means of printing, the top part of the initially visible faces (103, 203) of each bag (3) - which part is designed to engage with the opening and gripping members - is coated externally with thin layers (1, 1') of varnish having a high coefficient of friction in order to ensure that the opposite faces of the bag are gripped correctly by the said gripping members.

Description: TITLE: "Method for producing plastic bags and bags made using such a method" DESCRIPTION The invention relates to devices of the type described in Italian patent application no. 22456 A/89 of 21 November 1989 in the name of the present applicant, which devices are designed to be positioned at the checkouts of supermarkets or other similar sales outlets and comprise a reel consisting of a continuous web of plastic bags connected together one after the other by means of tear lines and including means which unwind the said reel and transfer the continuous web of bags to superjacent means which detach the lead bag from the continuous web, position it vertically, open it and support it while it is filled with the products that have been purchased, which are inserted via a hopper located immediately above the open bag. Discharge means then remove the full bag from the filling station and trigger the positioning of the next bag in the said station. The means which open the bag comprise a pair of opposing gripping members which can move horizontally closer together and then away from each other. Each gripping member is fitted with a jaw carrying rubber pads positioned at regular intervals and in line with the corresponding gaps between the teeth of the opposite jaw which is comb-shaped. The gripping members are open as they are moved closer together and, at the end of the advance stroke, the jaws of these gripping members interlock both horizontally and vertically so that a top portion of the plastic bag is folded zigzag fashion between the gripping members. At the end of the advance stroke, the gripping members close automatically such that they grip the portion of bag placed between them. The external surfaces of the opposite faces of the bag come into contact with the rubber pads on the jaws of the two gripping members, which have a high coefficient of friction relative to the film from which the bag is made, so that when the two gripping members are moved away from each other and held in the closed position, the jaws of one gripping member slip out from the jaws of the other gripping member and each gripping member takes a portion of the opposite face of the bag with it, while the internal surfaces of the two faces of the said bag slide over each other easily as a result of the low coefficient of friction of the film from which the bag is made. In order to facilitate opening of the plastic bags, the prior art envisages the use of powder additives which reduce the coefficient of friction of the superimposed surfaces of the said bag. These additives tend to accumulate on the rubber pads of the gripping members which open the bags so that, and partly also on account of the gradual ageing of the rubber itself, the gripping members tend, over time, to lose the gripping properties needed to entrain and open the opposite faces of the plastic bag, resulting in the obvious consequences. It is the object of the invention to overcome these disadvantages by implementing the following solution. The external surfaces of the opposite faces of each bag, and in particular those portions of the surfaces that are designed to engage with the said opening and gripping members, are coated with a thin layer of a material having a high coefficient of friction, which material can be visible or invisible. This material can advantageously consist of a suitable varnish which is applied to the opposite faces of the bags during the printing stage, in which the said plastic bags are customized and adapted to the various requirements of the supermarkets. More detailed characteristics of the invention, as well as the advantages deriving therefrom, will become more apparent from the following description of a preferred embodiment of the said invention which is illustrated purely by way of non-limiting example in the figures of the attached sheets of drawings, in which: - Fig. 1 illustrates a perspective view of the continuous web wound around a reel from which the plastic bags are torn off, each bag being improved according to the invention; - Fig. 2 illustrates details of an improved plastic bag according to the invention, in cross section on the plane ll-ll in Figure 1 ; - Figs 3 and 4 illustrate a side view, with some parts in section, of the pair of gripping members of the known device for opening a plastic bag, during successive stages of the cycle for opening the said bag; and - Fig. 5 illustrates a perspective view of the top of an improved plastic bag which has been opened by the gripping members shown in Figures 3 and 4. In Figure 1 , the reference 3 denotes the plastic bags in question, positioned one after the other so as to form a continuous web which is unwound from a reel B. The base of each bag is connected to the handles M of the next bag by means of tear lines L. Seen in cross section as in Figure 2, each bag has side gussets S, S'. According to the invention, the opposite faces 103, 203 of the bag - at least on the outside and on the top part designed to engage with the gripping members of the opening device mentioned above - are treated across their entire width or preferably over symmetrically positioned areas 1 , 1 ' of suitable size in any manner such that the coefficient of friction of these areas is greater than that of the material from which the said bag is made. The frictional areas 1 , 1 ' are preferably located on that portion of the faces 103, 203 found between the handles M but not on the handles themselves. The treatment advantageously consists in applying a preferably transparent varnish having a high coefficient of friction to the said areas 1 , 1 ' at any point during the bag production cycle, for example during the stage in which the bag is customized by means of printing. It goes without saying, however, that in place of the abovementioned areas 1 , 1 ' text and/or a decorative and/or advertising image could be applied using a suitable frictional varnish. From Figure 3 it can be seen that when the gripping members P1 and P2 of the device for opening the bag are moved closer together while still open, the smooth comb-shaped jaw 86 of the gripping member P2 slots in between the corresponding jaws 83 and 84 of the gripping member P1 , the jaw 84 also being smooth and comb-shaped while the jaw 83 has rubber pads 87 which align with the gaps between the teeth of the jaw 84. The jaw 85 of the gripping member P2 also has rubber pads 88 which align with the gaps between the teeth of the jaw 86. The bag to be opened 3 is positioned vertically such that the gripping members P1 and P2 act on the top part of the bag, on that part with the said areas 1 , 1 ' having a high coefficient of friction. Once the gripping members have interlocked, they close and the bag is grasped by them, held by three consecutive portions folded into a zigzag. One portion of the bag is held between the rubber pads 87 of the jaw 83 of P1 and the toothed jaw 86 of the gripping member P2, a subsequent portion is held between the toothed jaw 86 of P2 and the toothed jaw 84 of P1 , and a third portion of the bag is held between the said jaw 84 of P1 and the pads 88 of the jaw 85 of P2. According to the invention, the areas 1 , 1 ' having a high coefficient of friction are positioned such that one is held between the jaws of the gripping member P1 and the other between the jaws of the gripping member P2, as illustrated in Figure 3 by the thick dashed line. The result is that, as the gripping members P1 and P2 move away from each other as illustrated in Figure 4, the portion of the bag face 103 bearing the frictional areas 1 remains securely attached to the gripping member P1 , while the portion of the bag face 203 bearing the frictional areas 1 ' remains securely attached to the gripping member P2, while the faces 103 and 203 slide over each other easily as a result of the low coefficient of friction of their internal and initially superimposed surfaces. As soon as the gripping member P1 slips out of engagement with the gripping member P2, the jaws of these gripping members snap shut and trap those portions of the faces 103 and 203 gripped between them and the bag is opened as illustrated in Figure 5.

Claims: CLAIMS 1 ) Method for producing plastic bags which are particularly suited to being handled by the devices for automatically feeding and opening bags, characterized in that the bag production cycle includes a stage in which the said bags undergo a localized treatment so that the top part of the opposite and initially visible faces (103, 203) of each bag (3) has, externally and on those portions designed to engage with the gripping members (P1 , P2) of the said handling devices, a coefficient of friction greater than that of the film from which the said bags are made, so that these areas of the bags engage with the said gripping members with a high coefficient of friction and consistently, which ensures that these areas are gripped securely and reliably by the said gripping members. 2) Method according to Claim 1 , in which the localized treatment aimed at increasing the coefficient of friction consists in applying a thin layer of varnish having a high coefficient of friction to the external surface of the initially visible faces of the bags. 3) Method according to Claim 2), in which the said stage is carried out during the stage in which the bags are printed in order to customize them, including for advertising purposes. 4) Method according to Claim 2), in which the varnish having a high coefficient of friction is transparent and is applied to the top part of the visible faces of each bag, solely in symmetrically positioned areas (1 , 1 '). 5) Method according to Claim 2), in which the varnish having a high coefficient of friction is coloured and such as also to produce decorative and/or advertising areas on the bags. 6) Plastic bag particularly suited to being handled by the devices for automatically feeding and opening bags, characterized in that the top external part of its initially visible and superimposed faces (103, 203) has areas (1 , 1 ') having a high coefficient of friction. 7) Plastic bag according to Claim 6), in which there are at least two of the said areas having a high coefficient of friction (1 , 1 ') on each face of the bag and these areas are symmetrically positioned. 8) Plastic bag according to Claim 7), in which the areas having a high coefficient of friction (1 , 1 ') are produced using a transparent varnish. 9) Plastic bag of the type with gussets and in which the initially visible faces (103, 203) carry the handles (M), in which the said areas (1 , 1 ') coated with the varnish having a high coefficient of friction are located at the ends of that portion found between the two handles but preferably not on the handles themselves.

Inventors: CAPPI ANGELO, RIMONDI RENATO, CAPPI, ANGELO, RIMONDI, RENATO
Applicants: AWAX PROGETTAZIONE, CAPPI ANGELO, RIMONDI RENATO, A.W.A.X. PROGETTAZIONE E RICERCA S.R.L., CAPPI, ANGELO, RIMONDI, RENATO
Application year: 2000
Main classification: B65D33
IPC codes: B31B1, B65D33