WO2009108078A2

WO2009108078A2 - Plastic bag with friction fields for opening, method for producing and device for producing

Info

Publication number: WO2009108078A2
Application number: PCT/RS2009/000006
Authority: WO
Inventors: Novica Paunovic
Original assignee: Novica Paunovic
Priority date: 2008-02-26
Filing date: 2009-02-23
Publication date: 2009-09-03
Also published as: RS20080078A; WO2009108078A3; RS52275B

Abstract

Plastic bag with friction fields for opening, which has friction fields (4) applied, on the outer sides of bag walls (2), close to the bag end which is opened, friction fields having the coefficient of friction with human fingers greater than the coefficient of friction between the bag walls and the fingers. If these two facing friction fields are touched by fingers (e.g. one field by the thumb and the facing one by the index finger) and the fingers perform a sliding movement to open the bag, such construction would render the opening of the bag much easier.

Description

PLASTIC BAG WITH FRICTION FIELDS FOR OPENING, METHOD FOR PRODUCING AND DEVICE FOR

PRODUCING

Technical field

The present invention relates to the field of manufacture of plastic bags used in shops by customers to put in and carry away their purchases.

Technical problem

The invention addresses the problem of frequent difficulties with opening lightweight and thin plastic bags used in shops.

Background Art

In contemporary shops, from the smallest of green-grocer's or grocer's shops to the hugest of commercial hypermarkets, the customers usually carry away their purchases in plastic bags. Bags made of some other materials, paper in particular, are also in use to a considerable extent, however, plastic bags have imposed themselves as an absolute winner for a number of reasons. Plastic is a strong material and bags can be made of very thin sheets allowing for low consumption of plastic and low price of such bags, thus making in possible for vendors to offer such bags for free along with purchased goods. Although plastic bags may be very thin and lightweight, they are quite strong and can carry reliably a load weighing several kilos. Because they are thin, they adapt easily to the shape of purchases. They take up very little space before use, and a large number of such bags may fit into a package thick only several centimetres. They are very convenient for printing different advertising contents, etc.

Such bags are usually stacked at the exit, at the check-out counter, and customers take such bags themselves and place their purchases into them. There are often noticeable problems in opening such bags. This in particular occurs with bags with very thin walls. As the bag walls are very thin and flexible, they adhere to one another quite well, and they are also very smooth, so it often happens that shoppers are unable to open a bag easily or they loose time trying to open it. This may particularly be common with elderly shoppers, whose fingers are less dexterous, or for instance in winter months, when fingers, having been exposed to low temperatures are less nimble and need some time in warm space for their functions to become normalized. This invention solves the observed problem of opening bags.

Disclosure of Invention

As envisaged by this invention, on the outer sides of bag walls, close to the bag end which is opened, a plastic bag has two friction fields, i.e. areas whose coefficient of friction with fingers is greater than the coefficient of friction between the bag walls and the fingers and greater than the coefficient of friction between the bag walls themselves. If these two facing friction fields are touched by fingers (e.g. one field by the thumb and the facing one by the index finger) and the fingers perform a sliding movement to open the bag, such construction largely makes it much easier to open the bag. Brief Description of Drawings

The invention is thoroughly described in the drawing wherein:

Fig. 1 - illustrates a plastic bag with friction fields for opening. Fig. 2 - illustrates a cross section through A-A in Fig 1, enlarged.

Fig. 3 - illustrates a solution according to version I, with friction fields made of materials comprising coarsening particles.

Fig. 4 - illustrates a solution according to version II, with friction fields made by applying coarsening particles to the friction field basis. Fig. 5 - illustrates a solution according to version III, with friction fields achieved by spraying small droplets of coarsening material onto bag walls.

Fig. 6 - illustrates a cross section through B-B in Fig 5, enlarged.

Fig. 7 - illustrates a solution according to version IV, with relief friction fields, with relief in the form of stripes. Fig. 8 - illustrates a cross section through C-C in Fig 7, enlarged.

Fig. 9 - illustrates a solution according to version V, with relief friction fields, with relief in the form of criss-crossed stripes.

Fig. 10 - illustrates a solution according to version VI, with relief friction fields, with relief in the form of stripes grouped in columns. Fig. 11 - illustrates a solution according to version VII, with relief friction fields, with relief in the form of concentric stripes.

Fig. 12 - illustrates a solution according to version VIII, with relief friction fields, with relief in the form of a net.

Fig. 13 - illustrates a solution according to version IX, with relief friction fields, with fragmentised friction field surface.

Fig. 14 - illustrates a solution according to version X, with friction fields comprising a sub-layer for increase of mechanical rigidity.

Fig. 15 - illustrates a cross section through D-D in Fig 14, enlarged. Fig. 16 - illustrates an example of a device for producing of plastic bags 80 with friction fields using the method of spraying through screen. Fig. 17 - illustrates a lateral view of the device in Fig. 16. Fig. 18 - illustrates a device for producing of plastic bags with friction fields using the method of applying coarsening particles.

Fig. 19 - illustrates a cross section through E-E in Fig 18, enlarged. 85 Fig. 20 - illustrates a cross section through E-E in Fig 18, the version showing head with cover, enlarged.

Best Modes for Carrying Out of the Invention

90

Figures 1 and 2 illustrate the basic solution. Figure 1 illustrates a plastic bag with friction fields for opening (although it is self-evident, the bag is marked with 1). Bag walls 2 are made of plastic sheet and joined together in some of the usual ways, so as to obtain the well-known shape of the bag, which can be 95 opened on one side, i.e. on one end. On the outer sides of walls 2, close to the bag end which can be opened, two friction fields 4 are formed, lying facing each other. Figure 2 illustrates a partial cross section through walls 2 and friction fields 4, made through A-A in Fig. 1, and Figure 2 offers a better presentation of the described construction. Figure 2 furthermore specifies that bag walls 2

100 evidently consist of two walls, 2' and 2", and that friction fields 4 consist of friction fields 4' and 4", placed on the outer sides of the above walls 2' and 2", facing each other. Because friction fields 4' and 4" have the same function and are symmetrically arranged, they shall be referred to hereinafter as friction fields 4 in any and all cases when there is no need to differentiate between friction

105 fields 4' and 4". The same applies analogously to walls 2 i.e. 2' and 2". Different versions of friction fields shall be marked as 4a, 4b, 4c etc, and if necessary, analogous types 4a'/4a", 4b'/4b" etc shall be identified. For reasons of clarity, the cross section in Fig. 2 is partly enlarged, and the thickness of walls 2 and friction fields 4 is not proportionate. Pursuant to the idea of the invention, friction fields 4 have a high coefficient of friction in contact with human fingers, i.e. the coefficient of friction between the surface of friction fields 4 and the fingers is greater than the coefficient of friction between walls 2 and the fingers (and also greater than the coefficient of friction between walls 2' and 2"). If these two facing friction fields 4' and 4" are touched by fingers {e.g. one friction field by the thumb and the facing friction field by the index finger) and the fingers perform the usual sliding movement to open the bag {e.g. in the direction of arrows F in Fig 2), the opening of the bag will be rendered considerably easier.

Friction fields 4 can be formed in different ways. The easiest way is to apply a layer of coat with a high coefficient of friction in the course of bag production, or when they are commercially decorated (printed). This can be achieved by method of screen printing which is commonly used for bag decoration. Other printing methods, such as offset printing or others might also be used. The alternative methods will be discusses further down. A high coefficient of friction of friction fields 4 may be an inherent feature of the material used for their producing, or can be achieved by different methods to increase the coefficient of friction, such as increasing the coarseness. Figure 3 illustrates a solution according to version I, where a high coefficient of friction of friction fields 4a (shown in cross section, similar to Fig 2) is achieved by using, as material for friction fields 4a, the material (such as ink or coat) which is mixed with fine particles 6 whose edges and surfaces increase its coarseness and thus its coefficient of friction. Particles 6 may be obtained from glass, quartz, polymer, plastic, elastomer (rubber, latex...), ceramic, some other appropriate material or a combination of materials. Figure 4 illustrates a solution according to version II where a high coefficient of friction of friction fields 4b is achieved by means of fine particles 6 lying on the surface of friction fields 4b and increasing their coarseness and thus their coefficient of friction with their edges and surfaces. In other words, friction fields 4b comprise basis 5 to whose surface particles 6 are applied. These particles 6 are the same as in version I and can be made from the same materials as mentioned above.

Figure 5 illustrates a solution according to version III where a high coefficient of friction of friction fields 4c exists because friction fields 4c comprise grains 7 stuck to the surface of bag walls 2, whereby coarseness of friction fields 4c is achieved. Figure 6 is an enlarged cross section through B-B in Fig 5, also illustrating the structure of friction fields 4c. For better clarity, the size of grains 7 is not proportionate to the thickness of walls 2 or the size of friction fields 4c. Grains 7 consist of material which may comprise particles 6 (as in previous versions I and II) for additional increase of coarseness, however, this is generally not a requirement.

Figures 7-15 illustrate versions where an additional increase of coefficient of friction of friction fields is achieved by means of a relief surface of friction fields, i.e. the cross section of friction fields is of variable thickness, with areas of greater or smaller thickness, or the friction fields comprise areas alternately covered and not covered with friction fields material. In a preferred solution, the material used to create friction fields has an already increased coefficient of friction by means of adding fine particles as in some of the previous versions (however this is not absolutely necessary, since if thickness of friction fields is great enough, the very relief of friction fields may produce a coefficient of friction great enough for the entire of friction field). There are several versions of this idea which will be presented by way of illustration, however the idea is not essentially limited by the presented examples.

Figure 7 illustrates a solution according to version IV. In this version, friction fields 4d have a relief surface in the shape of stripes i.e. friction fields 4d comprise a series of stripes 8 made of material for creating friction fields 4d, separated by stripes to which a layer of such material has not been applied. Figure 8 is a cross section of friction fields 4d made through C-C in Fig 7, where the profile of this structure is shown with more clarity. For reasons of clarity of presentation in Figure 8, the thickness of friction fields 4d and stripes 8 is vastly

170 disproportionate to the width of stripes 8, as in reality the thickness of friction fields 4d and stripes 8 is much smaller than the width of stripes 8. The relief character of the profile of friction fields 4d results in a significant increase of their coefficient of friction and an easier opening of the bag. It is worth noting that the term stripes should be given a broad meaning, i.e., they need not be

175 linear stripes of constant width, and could also be stripes in the form of waves, stripes of changeable width, stripes in the shape of arches, or some other shape. Furthermore, the stripes need not be equal in width, nor the width of the stripes need to equal the width of the interstices between the stripes.

Figure 9 illustrates a solution according to version V where the relief

180 surface of friction fields has the form of alternate stripes, similar to version IV, however, in this case, stripes 8a' and 8a" in respective friction fields 4e' and 4e" (respectively lying on the outer sides of walls 2' and 2") are criss-crossed, i.e. the axis of stripes 8a' in friction field 4e' forms an angle of 90° with the axis of stripes 8a" in friction field 4e". This slant removes the possibility (extant in

185 version IV) of stripes 8a' in friction field 4e' falling slightly into the interstices between stripes 8a" in friction field 4e" (which would result in a reduced efficiency of the operation), while the bag is being opened and walls 2' and 2" are sliding one over another (and thus friction fields 4e' and 4e" are sliding one above another). Figure 9 illustrates that stripes 8a' and stripes 8a" mutually form

190 an angle of 90°, but this may also be an angle of a different degree, e.g. 120°, or any other appropriate angle. It is worth noting, although the context makes it clear, that friction fields 4e' and 4e" in Fig 9 are shown one above another for reasons of clarity, while in reality they are placed one beneath another, on the outer sides of walls 2' and 2" (and the figure shows what they would look like

195 viewed from the same side of the bag).

Figure 10 illustrates a solution according to version VI, where the relief surface of friction fields 4f and 4f " has the form of alternate stripes 8b' and 8b", grouped in this case in columns 10' and 10" (respectively placed on friction fields 4f and 4f" located on walls T and 2"). Columns 10' in friction field 4f

200 are arranged so as to be positioned above the interstices between columns 10" in friction field 4f". In this way, while the bag is being opened and walls 2' and 2" are sliding one over another and consequently friction fields 4f and 4f" are sliding one above another, this relief character of the surface allows for a high coefficient of friction of friction fields 4f and 4f ' with the fingers, while at the

205 same time, there is no interference between stripes 8b' and 8b".

Figure 11 illustrates a solution according to version VII where the relief surface of friction fields 4g has a form of concentric stripes 8c, which may be closed as in the figure, or may have interruptions. Figure 12 illustrates a solution according to version VIII where the relief surface of friction fields 4h has the

210 appearance of net 12. Figure 13 illustrates a solution according to version IX where the surface of friction fields 4k is fragmentised into a large number of areas 14. These areas 14 may take on any shape and size, for example, they may be in the shape of dots of such dimensions that they are barely visible or invisible to the naked eye. Each of these three versions has its own peculiarities

215 when it comes to its behaviour when the bag is being opened and the friction fields are sliding one above another, resulting in different total coefficient of friction. Naturally, other variations of the form of relief are possible, and only some that are particularly specific or characteristic are provided herein.

The issue of the thickness of friction fields ought to be considered. On one

220 hand, the least possible thickness of friction fields could be the objective, as the consumption of material for their creation in such case is the least, and in the process of production itself (e.g. screen printing) the thinner layers dry more quickly allowing for better productivity. On the other hand, friction fields could be made to have a greater thickness allowing them certain mechanical rigidity

225 (suitable thickness depends on different factors such as material of friction fields, material and thickness of bag walls, shape and size of friction fields, as well as the shape of any relief surface on the friction fields). This may aid the process of opening the bag, as the force whereby the finger affects the friction field may now be distributed more evenly over the entire surface of the friction

230 field.

An alternative solution, shown in Figures 14 and 15 (version X), could be for friction fields 4m to comprise (at least) two layers, sublayer 16 furnishing friction fields 4m with an increased mechanical rigidity, and friction layer 18 providing to friction fields 4m the required high coefficient of friction. Figure 15

235 is a cross section through friction fields 4m made through D-D in Fig 14, and it illustrates more clearly the idea of double-layered friction fields 4m. In Figures 14 and 15, sublayer 16 has the appearance of a continuous surface, while friction layer 18 has the appearance of a relief surface, whereas in reality, any combination of sublayer 16 and friction layer 18 is possible, e.g. : continuous

240 sublayer 16-continuous friction layer 18, continuous sublayer 16-relief friction layer 18, relief sublayer 16-continuous friction layer 18, relief sublayer 16-relief friction layer 18.

It is worth noting that friction fields may be transparent, i.e. made of material which is (to a smaller or greater degree) transparent. If the friction 45 fields are, for example, made of material which cures by exposure to UV radiation (common method in screen printing technique), this radiation does not penetrate so easily through thicker layers, thus transparent material for friction fields has certain advantages. Moreover, the relief structure of friction fields resulting in great friction capacities may have the visual appearance which is 50 inadequate for some reason {e.g. marketing). The invention requires that the customer must know the position of friction fields on the bag, consequently, if transparent materials are used to make friction fields, there must be adequate visual markers indicating their position (e.g. painted line or surface around friction fields, or painted surface beneath them, or even painted areas combined

255 (mixed) with friction areas).

The friction fields shown in figures generally have round shapes, however, they can be of any other shape, e.g. the shape of square, rectangle, triangle, an irregular shape, the shape of a letter, text, sign (e.g. suitable for trademark) or any other shape. Generally, friction fields need not have the same

260 shape on both sides of the bag. The size of friction fields may vary, however it is preferable that it be as small as possible so as to allow for least possible consumption of material for making friction fields, and on the other hand their size should be large enough to allow for sufficient contact surface for contact with fingers. The recommended size corresponds to the size of the thumb ball

265 area, meaning 2-3 cm in diameter or 3-10 cm² surface area, but obviously, this is only a general recommendation.

A description of the invention envisages that the friction fields be located on both outer sides of the bag (giving rise to the plural form in term "friction fields"), in view of the fact that this is the most efficient solution, however it is

270 very much worth noting that a friction field may be located on one side of the bag only. This construction is less efficient and reliable when it comes to bag opening, however, it is easier and cheaper in terms of production, as the friction field is applied only to one side of the bag, making it easier to modify the existing methods for bag producing. On the other hand, the possibility of a

275 larger number of friction fields, whether on both sides or only one side of the bag, may also be envisaged, or in other words, the possibility of friction field being split up into two or several parts. In summary, a plastic bag related to this invention contains at least one friction field.

Even though it is self-evident from the invention, it should be noted

280 explicitly that friction fields 4' and 4" need not have the same shape, nor be made of the same material. They need not have the same relief surface. Optionally, only one friction field may have a relief surface, unlike the other. It is also worth noting that friction fields 4' and 4" may be made by different methods, i.e. 4' by using one method and 4" by using another. Furthermore, they

285 need not even be exactly facing one another, they may be shifted ("off-centred") in relation to each other. The foregoing, obviously, applies to all the versions of friction fields, not only to friction fields 4' and 4" shown in Figure 2.

A plastic bag with friction fields for opening may be produced employing different methods. As already mentioned, the simplest method to make the

290 friction fields is to apply a layer of coat with a high coefficient of friction in the course of bag production, or while they are being commercially decorated (printed). This can be achieved for instance by method of screen printing which is commonly used for bag decoration. Other printing methods, such as offset printing or other might also be used.

295 Another way of producing a plastic bag with friction fields for opening is for example to create friction fields by spraying through screen, as shown in Figures 16 and 17; more precisely, by way of illustrating this method, a device which may be used to apply this method is shown in Figure 16, and Figure 17 is a lateral view of the construction shown in Fig. 16. The material with a high

300 coefficient of friction, used to make friction fields 4p, with the aid of spray 20 is dispersed into fine droplets 22 and sprayed through screen 24 having opening 26 of a desired shape. A jet of droplets 22 falls onto walls 2 of bag 1 forming friction field 4p whose shape is determined by the shape of opening 26. Subsequently, the material of the applied friction field 4p cures, whether by

305 drying, heating, exposure to UV radiation or otherwise, depending on the material used. Naturally, opening 26 may have any shape, for example the shape required to create relief friction fields in Figures 7, 9, 10 etc.

As a rule, it is desirable that the used material should comprise fine particles to increase coarseness (and consequently the coefficient of friction) as 310 already mentioned. The quantity of the material applied in creating friction field 4p may be metered so as to create a compact (continuous) layer, i.e. so that the created friction field should correspond to the structure shown in Figure 3. On the other hand, the quantity of the applied material may be reduced to the extent that after landing on walls 2, there are not enough droplets 22 to merge into a

315 compact (continuous) layer, and instead, what remains on walls 2 are more or less separated droplets which, following the above curing process, form solid grains, corresponding to grains 7 in Figures 5 and 6 in version III, i.e. this would be the process of creating friction field 4c in Figures 5 and 6.

Figure 4 illustrates a solution according to version II where a high

320 coefficient of friction of friction field 4b was achieved by means of fine particles 6 lying on the surface of friction field 4b and increasing its coarseness and thus its coefficient of friction with their edges and surfaces.

Such friction field 4b with coarsening particles on the surface of friction field 4b may be created by first applying to bag walls 2 a layer of material (in

325 liquid or semi-liquid state) forming basis 5 to friction field 4b, and applying to the surface of such basis 5 particles 6 which serve to increase its coarseness. Basis 5 may be applied using screen printing, another printing method, spraying or otherwise. The application of particles 6 can be made by mixing such particles with a stream of carrying gas (e.g. air) and blowing such mixture in a 30 jet onto the surface of basis 5, in the course of which particles 6 stick to basis 5 (due to adhesion) and following the curing of basis 5 (whether by drying, heating, exposure to UV radiation or otherwise), they become firmly attached to it and considerably increase the coefficient of friction of the created friction field 4b with their edges and surfaces. 35 If the material for forming basis 5 of friction field 4b comprises a volatile component (solvent) whose evaporation results in curing of basis 5 and binding particles 6 (as is the case with e.g. screen printing inks which cure by drying), then the above jet of carrying gas may cause partial drying of the surface layer of basis 5 and a reduced efficiency of adhesion of particles 6 to basis 5 surface.

340 It may therefore be beneficial to add to the carrying gas the vapours of the above volatile component (solvent) of basis 5, and it may be even better if the carrying gas is saturated with the vapours of such volatile component. This has the effect of drastically reducing the drying of basis 5 surface during the application of particles 6. Naturally, if basis 5 comprises several volatile components, the

345 carrying gas may also comprise vapours of several components.

Figures 18 and 19 illustrate a device for producing plastic bags with friction fields for opening employing the above described method. Head 28 is the most important part of the device, positioned so as to cover basis 5 which has previously (using some of the foregoing methods) been applied to walls 2 of

350 bag Ib.

Bag Ib may rest (as is usually the case) on a supporting surface 29 lending it support, and such supporting surface 29 could be, for example, a plate on which bag Ib is resting in the screen-printing device, or conveyor (or immobile) line on which bag Ib travels through the device etc. Such supporting

355 surface 29 need not be flat as shown in Figure 18, it may also be curved in any appropriate way, it may even be in the shape of a roller and bag Ib would slide over such roller.

Figure 19 is a schematic cross section through E-E in Fig. 18, and it shows in more details the most important parts of head 28, as well as its

360 functioning principle. Head 28 comprises semi-chamber 30 which encloses and covers basis 5 previously applied to walls 2 (using any of the above methods). The above particles 6 are blown into semi-chamber 30 with the aid of a current of carrying gas. Rim 30a of semi-chamber 30 stands slightly apart from bag walls 2, so the carrying gas and particles 6 may circulate between rim 30a of

365 semi-chamber 30 and walls 2. Arrows indicate the circulation flow of the carrying gas with particles 6. The carrying gas circulating in semi-chamber 30 carries particles 6 and hits basis 5, thus some of particles 6 attach to basis 5 (due to adhesion). Most of particles 6 leave semi-chamber 30 on the carrying gas through the space between rim 30a of semi-chamber 30 and bag walls 2. In

370 order to prevent the release of particles 6 into atmosphere of the working room and their significant loss, semi-chamber 30 is enclosed within enclosing semi- chamber 32 whose rim 32a is likewise positioned at a small distance from bag walls 2 (this distance is adjusted to minimise the loss of the carrying gas and particles 6 from the suction zone of enclosing semi-chamber 32, however large

375 enough to allow for unobstructed travel of walls 2 and friction field 4b. The air is sucked in from enclosing semi-chamber 32, and Figure 19 shows that most of particles 6 escaping semi-chamber 30 will be caught in the air current being sucked into enclosing semi-chamber 32, which will largely eliminate their loss. In case some particles 6 can escape even enclosing semi-chamber 32, enclosing

380 semi-chamber 32 may be enclosed within second enclosing semi-chamber 34 whose rim 34a also stands slightly apart from bag walls 2 (at a distance sufficient to allow suction of outside air). The air is likewise sucked in from second enclosing semi-chamber 34, and particles 6 which may have managed to escape even the suction zone of enclosing semi-chamber 32 will almost certainly

385 be sucked in with the air which is being sucked in by second enclosing semi- chamber 34 (if necessary, second enclosing semi-chamber 34 may also be enclosed within additional similar semi-chambers from which the air is sucked in). In this way, particles 6 are efficiently applied to basis 5 and friction field 4b is created with minimum waste and loss of particles 6.

390 Preferably, the distance between rim 32a of enclosing semi-chamber 32 and bag walls 2 should be smaller than that between rim 30a of semi-chamber 30 and bag walls 2, and also smaller than the distance between rim 34a of second enclosing semi-chamber 34 and bag walls 2, as shown in Figure 19. This results in easier capture of carrying gas and particles 6 by enclosing semi-

395 chamber 32, minimization of their escape beyond the suction zone of enclosing semi-chamber 32, and enhancement of suction effect of the second enclosing semi-chamber 34.

In Figures 18 and 19, semi-chamber 30, enclosing semi-chamber 32 and second enclosing semi-chamber 34 are shown as cylindrical (i.e. having a

400 circular cross section), however they can obviously take any appropriate shape. Likewise, head 28 may comprise different additional elements. For reasons of simplicity, Figures 18 and 19 show the creation of a friction field on one side of a bag, however, it is quite obvious that friction fields may be created on both sides of the bag, which is the preferred solution.

405 Obviously, the functioning of head 28 requires appropriate accessory devices and systems to ensure the above circulation of the carrying gas and particles 6. Figure 18 illustrates in a schematic form a possible assembly of such accessory devices. Head 28 (more precisely semi-chamber 30, enclosing semi- chamber 32 and second enclosing semi-chamber 34 comprised in it) is

410 connected to repository 38 by means of lines 36. Repository 38 stores a supply of particles 6 applied to basis 5 by head 28 in order to create friction field 4b. With the aid of pumps 40 (or a compressor or another similar equivalent device) the carrying gas is conducted through lines 36 and it carries particles 6 from repository 38 to head 28 (more precisely its semi-chambers) and back to

415 repository 38. The device may also comprise valves 42 regulating the circulation of the carrying gas and/or particles 6. The device may also comprise enricher 44 which enriches the carrying gas with vapours reducing the drying of basis 5 surface due to circulation of carrying gas, which is a possibility that has already been discussed.

420 This is obviously only the basic and general scheme of such accessory devices and numerous variations, modification and supplements are possible. The device does not have to comprise pumps 40 on each of lines 36, i.e. it may have any required number of pumps, for example only one pump which would circulate the carrying gas throughout the system. The device does not have to 425 comprise valves 42 on each of lines 36, i.e. it may have any required number of valves. Lines 36 themselves may be interconnected through any accessory system of lines. Optional enricher 44 is shown in Figure 18 as being attached to one of lines 36, but it may be connected to any appropriate point in the system, e.g. to repository 38. The device may obviously have appropriate control devices

430 to control the system operations.

Decoration 46 (picture, inscription etc) may be applied to bag Ib, as usual. If friction field 4b is created concurrently with decoration 46, more precisely while the ink used for decoration 46 has not yet dried (cured), the described process/device must be supplemented. Assume that bag Ib in the

435 course of the producing process is travelling in the direction of arrow A in Fig. 18 (e.g. bag Ib being actually part of plastic sheet unrolling from the reel and going through the bag producing device, which is not shown in the Figure). Such movement of bag Ib in the direction of arrow A would cause decoration 46 (with ink layer still wet) to pass underneath head 28, and as consequence

440 particles 6 would also attach and stick to the parts of decoration 46 passing underneath head 28. This would result in an unnecessary consumption of particles 6, alteration of tactile sensation of parts of decoration 46 and possibly even a modification of the visual appearance of parts of decoration 46 which have passed underneath head 28. 45 In such a case, it is necessary to prevent the application of particles 6 to bag Ib while decoration 46 is passing underneath head 28. This can be achieved in a number of ways, some of which will be suggested.

The simplest thing to do this is to automatically, with the aid of valve 42, cut the supply of carrying gas with particles 6, or possibly cut only the supply of 50 particles 6 (leaving the supply of carrying gas) while decoration 46 is passing underneath head 28. Likewise, this could be further elaborated by actually cutting only the supply of carrying gas and/or particles 6 to semi-chamber 30, while suction by enclosing semi-chamber 32 and second enclosing semi- chamber 34 would continue.

455 Another way is to enable head 28 to move in a direction transversal to the direction of movement of bag Ib, i.e. in the direction marked by arrow B in Fig. 18. In this way, after particles 6 have been applied to basis 5 and friction field 4b has been created, head 28 (with the aid of an additional device which has not been shown in the Figure; e.g. with the aid of a lever attached to head 28 and an

460 appropriate actuator) may be moved to an area underneath which decoration 46 does not pass.

The third way .is illustrated in Figure 20. In this example, head 28 comprises cover 48 which may rotate and this open and close enclosing semi- chamber 32 and consequently semi-chamber 30, and thus enable particles 6 to

465 come into contact with basis 5 when head 28 is above basis 5, or disable particles 6 from coming into contact with decoration 46 when head 28 is above, decoration 46. Cover 48 may rotate with the aid of appropriate actuator 50, the term actuator meaning any suitable device whereby necessary mechanical activity may be achieved (e.g. electric motor, electromagnet etc.).

470 A description of the invention provided in the application serves as an illustration of the idea of the invention. Consideration must be given to the fact that different variations can be made, including, but not limited to variations in design, shape, details, dimensions and selection of material for producing, together with use of equivalent

475 elements, parts and constructions, retaining the spirit and intention of the invention, all within the scope of statements contained in patent claims.

Claims

1. Plastic bag with friction fields for opening made of plastic sheet forming bag walls (2), where walls (2) are joined so as to allow the bag to open at one end, characterized in that at the outer side of walls (2) close to the end of the bag which is opened, there is at least one friction field (4) whose coefficient of friction with human fingers is greater than the coefficient of friction between walls (2) and human fingers.

2. Plastic bag with friction fields for opening according to claim 1, characterized in that at the outer sides of both walls (2', 2") forming bag walls (2), there are friction fields (4', 4").

3. Plastic bag with friction fields for opening according to claim 2, characterized in that friction fields (4^", 4") at the outer sides of bag walls (2', 2") are essentially positioned one facing the other.

4. Plastic bag with friction fields for opening according to claim 1, characterized in that friction fields (4a) are made of material comprising fine particles (6) which increase the coefficient of friction of friction fields (4a) with their edges and surfaces.

5. Plastic bag with friction fields for opening according to claim 1, characterized in that friction fields (4b) comprise basis (5) to whose surface fine particles (6) are applied, increasing the coefficient of friction of friction fields (4b) with their edges and surfaces.

6. Plastic bag with friction fields for opening according to claim 1, characterized in that friction fields (4c) comprise a large number of grains (7) stuck to the surface of bag walls (2).

7. Plastic bag with friction fields for opening according to claim 6, characterized in that grains (7) forming friction fields (4c) further comprise fine particles (6) which further increase the coefficient of friction of friction fields (4c) with their edges and surfaces.

8. Plastic bag with friction fields for opening according to any of claims 4, 5 or 7, characterized in that particles (6) are at least partially made from any material selected from the group consisting of glass, quartz, polymers, plastic, elastomers and ceramic.

9. Plastic bag with friction fields for opening according to any of claims 4, 5 or 7, characterized in that particles (6) comprise glass.

10. Plastic bag with friction fields for opening according to any of claims 4, 5 or 7, characterized in that particles (6) comprise quartz.

1 1. Plastic bag with friction fields for opening according to any of claims 4, 5 or 7, characterized in that particles (6) comprise some polymer.

12. Plastic bag with friction fields for opening according to any of claims 4, 5 or 7, characterized in that particles (6) comprise some plastic.

13. Plastic bag with friction fields for opening according to any of claims

4, 5 or 7, characterized in that particles (6) comprise some elastomer.

14. Plastic bag with friction fields for opening according to any of claims 4, 5 or 7, characterized in that particles (6) comprise some ceramic material.

15. Plastic bag with friction fields for opening according to claims 1 or 2, characterized in that friction fields have relief surface, i.e. cross section of friction fields is of variable thickness.

16. Plastic bag .with friction fields for opening according to claim 15, characterized in that friction fields consist of the areas covered with material used to create friction fields and the areas which are not covered with such material.

17. Plastic bag with friction fields for opening according to claim 15, characterized in that friction fields (4d) have relief surface in the form of stripes (8).

18. Plastic bag with friction fields for opening according to claim 17, characterized in that direction of stripes (8a') in friction field (4e') lying on one of bag walls (2'), forms an angle with the direction of stripes (8a") in friction field (4e") lying on the_.other wall (2") of the bag.

19. Plastic bag with friction fields for opening according to claim 18, characterized in that the above mentioned angle between stripes (8a', 8a") is about 90°.

20. Plastic bag with friction fields for opening according to claim 18, characterized in that the above mentioned angle between stripes (8a', 8a") is about 120°.

21. Plastic bag with friction fields for opening according to claim 17, characterized in that stripes (8b', 8b") in friction fields (4f , 4f ') are grouped in columns (10', 10"), so that columns (10') in friction field (4f ) lying on one of bag walls (2') are positioned above the interstices between columns (10") in friction field (4f ') lying on the other wall (2") of the bag.

22. Plastic bag with friction fields for opening according to claim 15, characterized in that relief surface of friction fields (4g) has the shape of concentric stripes (8c).

23. Plastic bag with friction fields for opening according to claim 15, characterized in that relief surface of friction fields (4h) has the shape of a net (12).

24. Plastic bag with friction fields for opening according to claim 15, characterized in that relief surface of friction fields (4k) is fragmentised into a large number of areas (14).

25. Plastic bag with friction fields for opening according to claims 1 or 2, characterized in that friction fields (4m) comprise at least two layers, sublayer (16) furnishing friction fields (4m) with a mechanical rigidity, and friction layer

(18) providing to friction fields (4m) a high coefficient of friction.

26. Method for producing plastic bags with friction fields for opening, characterized in that the method comprises a phase wherein on the outer side of

85 bag walls (2), close to the end of the bag which is opened, friction fields (4) are created as areas whose coefficient of friction with human fingers is greater than the coefficient of friction between walls (2) and human fingers.

27. Method for producing plastic bags with friction fields for opening according to claim 26, characterized in that the method comprises a phase

90 wherein a layer of coat forming basis (5) of friction fields (4b) is applied to bag walls (2), and a phase wherein particles (6) are applied to the surface of the above basis (5), increasing the coarseness and coefficient of friction of the created friction fields (4b) with their edges and surfaces.

28. Method for producing plastic bags with friction fields for opening 95 according to claim 27, characterized in that at some point following the application of particles (6) to the surface of the coat forming basis (5) of friction fields (4b), the said coat is cured, whereby particles (6) become firmly attached to basis (5).

29. Method for producing plastic bags with friction fields for opening 100 according to claim 28, characterized in that the said curing of the coat forming basis (5) is achieved by drying.

30. Method for producing plastic bags with friction fields for opening according to claim 28, characterized in that the said curing of the coat forming basis (5) is achieved by heating.

105 31. Method for producing plastic bags with friction fields for opening according to claim 28, characterized in that the said curing of the coat forming basis (5) is achieved by exposure to ultraviolet radiation

32. Method for producing plastic bags with friction fields for opening according to claim 27, characterized in that particles (6) are applied to basis (5)

110 by mixing particles (6) with appropriate carrying gas and directing the current of such mixture of carrying gas and particles (6) toward basis (5), whereby particles (6) adhere to basis (5).

33. Method for producing plastic bags with friction fields for opening according to claim 32, characterized in that the said carrying gas is air. 115

34. Method for producing plastic bags with friction fields for opening according to claim 32, characterized in that the said carrying gas is enriched with gaseous components reducing the drying of the surface of basis (5) to which the current of carrying gas is directed.

35. Method for producing plastic bags with friction fields for opening 120 according to claim 34, characterized in that the said gaseous components added with the aim of reducing the drying of the surface of basis (5) are actually some of the solvents contained in the coat from which basis (5) is made.

36. Method for producing plastic bags with friction fields for opening according to claim 26, characterized in that the said friction fields (4, 4a, 4c .)

125 are created by applying to bag walls (2) a layer of friction material whose coefficient of friction- with human fingers is greater than the coefficient of friction between walls (2) and human fingers.

37. Method for producing plastic bags with friction fields for opening according to claim 36, characterized in that the said layer of friction material is

130 applied by spraying such material in the form of droplets (22) onto the surface of bag walls (2).

38. Method for producing plastic bags with friction fields for opening according to claim 37, characterized in that the said friction material is sprayed in the form of droplets (22) through screen (24) having opening (26) of a desired

135 shape.

39. Method for producing plastic bags with friction fields for opening according to claim 37, characterized in that the said spraying of the friction material in the form of droplets (22) to the surface of bag walls (2) is done in quantities insufficient for droplets (22) to merge into a continuous layer on 140 landing on the surface of walls (2), and instead droplets (22) remain more or less separated from one another and when they have cured, they form grains (7) stuck to the surface of bag walls (2).

40. Method for producing plastic bags with friction fields for opening according to claim 37, characterized in that the friction material from which the

145 said droplets (22) are composed, also comprises particles (6) which further increase the coarseness and coefficient of friction of the created friction fields (4c).

41. Method for producing plastic bags with friction fields for opening according to claim 36, characterized in that the said layer of friction material is

150 applied using the method of screen printing.

42. Method for producing plastic bags with friction fields for opening according to claim 36, characterized in that the said layer of friction material is applied using the method of offset printing.

43. Device for producing of plastic bags with friction fields for opening, 155 characterized in that the devices comprises head (28) comprising semi-chamber

(30) into which carrying gas with particles (6) can be blown, particles (6) serving for coarsening and increasing the coefficient of friction of basis (5) previously applied to walls (2) of bag (Ib), wherein head (28) may be positioned over walls (2) of bag (Ib) so that semi-chamber (30) covers basis (5). 160 44. Device for producing of plastic bags with friction fields for opening according to claim 43, characterized in that semi-chamber (30) is enclosed within enclosing semi-chamber (32) from which carrying gas can be sucked in.

45. Device for producing of plastic bags with friction fields for opening according to claim 44, characterized in that enclosing semi-chamber (32) is

165 enclosed within second enclosing semi-chamber (34) from which carrying gas can be sucked in.

46. Device for producing of plastic bags with friction fields for opening according to any of claims 43, 44 or 45, characterized in that the device further comprises repository (38) storing a supply of particles (6) applied by head (28) 170 to basis (5), lines (36) which connect repository (38) and head (28), and at least one pump/compressor (40) whereby the carrying gas together with particles (6) can be conducted by means of lines (36) between repository (38) and head (28).

47. Device for producing of plastic bags with friction fields for opening according to claim 46, characterized in that with the aid of pump/compressor

175 (40), carrying gas with particles (6) can be conducted via lines (36) from repository (38) towards semi-chamber (30) and blown into semi-chamber (30) covering basis (5).

48. Device for producing of plastic bags with friction fields for opening according to claim 46, characterized in that with the aid of pump/compressor

180 (40), carrying gas can be sucked in from enclosing semi-chamber (32) and conducted towards repository (38) via lines (36).

49. Device for producing of plastic bags with friction fields for opening according to claim 46, characterized in that with the aid of pump/compressor (40), carrying gas can be sucked in from second enclosing semi-chamber (34)

185 and conducted towards repository (38) via lines (36).

50. Device for producing of plastic bags with friction fields for opening according to claim 46, characterized in that the device comprises valves (42) whereby the flow of carrying gas can be regulated as necessary.

51. Device for producing of plastic bags with friction fields for opening 190 according to claim 46, characterized in that the device comprises valves (42) whereby the flow of particles (6) in the carrying gas can be regulated as necessary.

52. Device for producing of plastic bags with friction fields for opening according to claim 46, characterized in that the device comprises enricher (44)

195 allowing the carrying gas to be enriched with gaseous components reducing the drying of basis (5) surface due to circulation of carrying gas over it.

53. Device for producing of plastic bags with friction fields for opening according to claim 44, characterized in that the distance of rim (32a) of enclosing semi-chamber (32) from walls (2) of bag (Ib) is smaller than the

200 distance of rim (30a) of semi-chamber (30) from walls (2) of bag (Ib).

54. Device for producing of plastic bags with friction fields for opening according to claim 45, characterized in that the distance of rim (32a) of enclosing semi-chamber (32) from walls (2) of bag (Ib) is smaller than the distance of rim (34a) of second enclosing semi-chamber (34) from walls (2) of

205 bag (Ib).

55. Device for producing of plastic bags with friction fields for opening according to claim 50, characterized in that if there is, on bag (Ib), some decoration (46) which has not dried i.e. which has not cured, which at certain points, due to the movement of bag (Ib) may pass underneath head (28), the

210 device may with the aid of valves (42) cut the supply of carrying gas to semi- chamber (30) during relevant intervals when decoration (46) is passing underneath head (28).

56. Device for producing of plastic bags with friction fields for opening according to claim 51, characterized in that if there is, on bag (Ib) some.

215 decoration (46) which has not dried i.e. which has not cured, which at certain points, due to the movement of bag (Ib) may pass underneath head (28), the device may with the aid of valves (42) cut the supply of particles (6) to semi- chamber (30) during relevant intervals when decoration (46) is passing underneath head (28).

220 57. Device for producing of plastic bags with friction fields for opening according to claim 43, characterized in that if there is, on bag (Ib) some decoration (46) which has not dried i.e. which has not cured, which at certain points, due to the movement of bag (Ib) may pass underneath head (28), the head (28) may move along the surface of walls (2) of bag (Ib) and be moved to

225 an area underneath which decoration (46) does not travel.

58. Device for producing of plastic bags with friction fields for opening according to claim 44, characterized in that head (28) comprises a cover (48) which may rotate with the aid of appropriate actuator (50) and thus open/close enclosing semi-chamber (32) as appropriate.