WO2008038130A2

WO2008038130A2 - Method of winding rolls for final use of plastic films, preferably extendable plastic films, and winding plant implementing the same

Info

Publication number: WO2008038130A2
Application number: PCT/IB2007/002865
Authority: WO
Inventors: Francesco Lombardini
Original assignee: Colines S.P.A.
Priority date: 2006-09-26
Filing date: 2007-09-21
Publication date: 2008-04-03
Also published as: ITMI20061813A1; WO2008038130A3

Abstract

A method of winding rolls for final use of plastic film comprises the step which consists of feeding a plastic film (11) coming from a plastic film source (20,40) to at least two rewinding machines (31) independent of each other.

Description

METHOD OF WINDING ROLLS FOR FINAL USE OF PLASTIC FILMS, PREFERABLY EXTENDABLE PLASTIC FILMS, AND WINDING PLANT IMPLEMENTING THE SAME

The present invention relates to a method of winding rolls for final use of plastic films, preferably- extendable plastic films, and winding plant implementing the same.

Extendable plastic film, also called stretch film, is a widely used product in the packing field, representing the most widespread packing type in Europe and in the United States.

There are many applications of such film type which cover most products of common use, both industrially and in domestic environments . Plastic films are differentiated by their composition, which permits obtaining films with different characteristics including toughness, stretching, ultimate tensile strength, elastic memory, puncture, and so on. They can be composed of three or more layers constituted, for example, by mixtures of linear low density polyethylene (LLDPE) , low density and ultra low density polyethylene (LDPE, VLDPE, ULDPE) , metallocene on polyethylene base (mLLDPE) , ethylene-vinyl-acetate in different percentages (EVA from 9% to 20%) , polypropylene homopolymer, copolymer or terpolymer (PP homo, PP copo, PP ter) or biodegradable materials (Mater-Bi) .

There are therefore many different formulations achieved by means of production lines having combinations of two or more extruders in order to obtain stratifications which can satisfy the requirements of the applications to which they are intended.

According to the type and thickness of the film, different application fields can be recognised, the most important of which including food manufacturers, pharmaceutical manufacturers, paper factories, tile and ceramic manufacturers, mechanical industry, large distribution, agriculture and domestic use. Such great variety of use implies an equally wide variety of film types, both regard to composition and thickness, generally variable from 12 μm up to over 100 μm, and additionally from the standpoint of the winding, which presents itself under different forms according to how the film must be subsequently used, i.e. according to a subsequent manual use, in automatic, semi-automatic machines and so forth. For example, in the case of stretch film rolls for industrial packing, setting aside the film's own mechanical strength and ultimate elongation characteristics, particular automatic packing machines or "palletisers" are used, on which stretch rolls are positioned of well-defined size and weight. In particular, for this type of application, there are rolls of overall weight of about 12.5 kg which are wound on cardboard cores having inner diameter of about 76 ram and with a strip width equal to about e 500 mm. In the same manner, the rolls for manual use have instead cores of inner diameter equal to 50 mm and overall weight of about 2.5 kg, thus resulting more manageable . One particular need of the sector is therefore the optimisation of the plastic film production line so to obtain the best return of such lines, automating them as much as possible to reduce the error possibility to a minimum, speeding up the production and at the same time preserving the high flexibility characteristics. The flexibility of the lines, in particular, assumes increasing importance if one considers that for reducing to a minimum the enormous logistic expenses for storage, transport and so on, one always tends towards a "just in time" production. One such production strategy is possible only if the plants are capable of offering a flexibility sufficient for producing film rolls which are differentiated by film or winding type, with minimal time loss in particular during the procedures of equipment change, start-up, and unloading of the production lines.

The plastic film production lines comprise extrusion and cooling plants constituted by a variable number of extruders, according to the characteristics which it is desired to give to the product, downstream of which winding plants are positioned which receive the extruded and cooled film and wind it into rolls. The extrusion and cooling part does not present particular difficulties in terms of flexibility, but requires having very high production volumes, considering the high costs involved and the fact that the final products have a very limited added value, such that for reaching sufficient operating margins it is necessary to utilise the effects of a large scale production.

To such end, there is the need to produce plastic films at extremely high actual speeds, close to if not greater than 500 m/min.

The winding plants downstream of the extrusion and cooling plants must therefore have a sufficient winding capacity such to handle the quantity of film produced over time. The winding of the film at high speeds, therefore, leads to the physiological presence of air trapped between the laps, which in fact makes the subsequent use of the film itself difficult, representing in any case a waste of space in transport . In fact, the very reduced added value of such products ensures that the transport cost has a considerable affect on the production costs, thus also for this reason, in addition for the practical film usability reasons given above, "hard" and compact rolls are required, i.e. without air interposed between the laps. In particular, in the case of a stretch film, the very nature of the film, very sticky, moreover renders obligatory the contact winding, i.e. with the "squeezing" of the roll against a motorised cylinder which favours the expulsion of the air inevitably picked up by the film itself in its winding motion around the mandrel.

Moreover, the need to have differentiated productions obliges frequent roll changes, which while occurring quickly, on the order of a few seconds, they have always represented the maximum limit for the production speed of the entire line.

In order to have high line winding capacities, it has therefore been found that the winding of so-called "jumbo" rolls was easier; such rolls have a strip equal to 500 mm but outer diameter up to 500 mm and beyond, which even if wound at a reduced speed which favours the side evacuation of the air otherwise present in the laps, keeps the winding capacity high due to their high diameter dimensions. The production of jumbo rolls however brings with it various drawbacks, including the transport and storage costs of such rolls, as well as the need to arrange rewinding machines which allow, starting from the - S -

"jumbo" rolls above, obtaining small final rolls with longitudinal extensions of a few hundred meters, even only 150 m in the limit cases.

The current rewinding machines have a maximum winding speed up to about 2000 m/min, but they need continuous cycles comprising the starting phases, acceleration, winding at speed, deceleration and stopping, to be carried out in a few seconds, because they execute the unloading and then the substitution of the finished rolls during the stopping phase.

Consequentially the average effective winding speed does not reach 500 ÷ 600 m/min; moreover, thanks to the characteristics of the winding cycle mentioned above, the rolls produced therein have a good surface aspect, relative to the last laps wound at very low speed, but the core of the roll, wound at speeds close to 2000 m/min, is inevitably rich with air trapped between the laps, with the consequences mentioned previously. For the reasons mentioned above, the winding of rolls directly in line for final manual use is not possible today, attributed the extremely reduced substitution times necessary for ensuring productivity, obviously related to the speed of the plant, in line with the market demands . The general object of the present invention is that of resolving the drawbacks mentioned above of the prior art in an extremely simple, economic and particularly functional manner.

Another object is that of devising a method for winding plastic films by which it is possible to make rolls for final use of high quality, ensuring a remarkable production speed.

Not the last object of the present invention is that of ideating a winding system for the implementation of the innovative method. Considering the above mentioned objects, according to the present invention, one has thought to make a winding method of plastic films and an implementing plant for the same, having the characteristics set forth in the attached claims. The structural and functional characteristics of the present invention and its advantages in comparison with prior art will result clearer and more evident by examining the following description, referring to the attached drawing, that show a winding method of plastic films and a winding plant made according to the innovative principles of the same invention. In the drawings : figure 1 illustrates a plan view of a first production line employing the winding method and the winding plant according to the present invention; - figure 2 is a plan view of a second production line employing the winding method and the winding plant according to the present invention; — R —

figure 3 is a plan view of the rewinding line employing the method and the winding plant according to the invention.

With reference to figure 1 and 2, a production line of plastic films that achieves the method of the object is altogether indicated with 10, and in the illustrated examples includes an extrusion and cooling plant 20 and a winding plant 30 according to the invention, arranged downstream of such extrusion and cooling plant 20. The extrusion and cooling plant 20 includes a plurality of extruders 21 connected to a head 22 for forming and joining the film 11 layers and subsequent cooling. The extruders 21 are each fed by a material in granulate form of thermoplastic type, which undergoes thermal treatment and is fed in fluid form to the head 22.

The thermoplastic materials can possibly be of different type according to the particular composition of the plastic film that one wishes to obtain. Downstream from the head 22 there is a drawing device 23 that transports the film 11 thus obtained to the winding plant 30 which includes at least two rewinding machines 31 to carry out the winding, directly in line, of rolls 32 for final use, or rather presenting a band that varies according to the embodiment but which generally does not exceed 500÷550 mm. Such rewinding machines 31 are possibly equipped with cutting units for cutting the film before the introduction of the same in the relative machine 31. Otherwise, the line foresees convenient cutting means arranged upstream of the rewinding machines 31. In particular in figure 1 a first embodiment is shown of the winding plant 30 employing two rewinding machines 31, while in figure 2 a second embodiment is shown of the winding plant 30 employing three rewinding machines 31. The method according to the invention therefore includes the phase that consists in the feeding of a plastic film coming from a source of plastic film to at least two rewinding machines 31 independent of each other. The use of more rewinding machines 31 offers an elevated production flexibility and different advantages including the possibility to simultaneously produce rolls on cores with different diameter and therefore to simultaneously produce rolls 32 for use in automatic machines or for manual use.

In this way one eliminates the dead times in the production line necessary for the substitution of the equipment, generally not inferior to the duration of about two hours, to produce alternatively, rolls for automatic machines or for manual use.

Moreover, it is possible to simultaneously produce rolls 32 of bands having different widths among them, as well as rolls 32 with different external diameters or rather formed by film 11 of different lengths . The particular inventive solution additionally offers the advantage of a reduction of overall bulk not having to produce jumbo rolls and, due to the particular winding system, a reduction in the electric power applied.

In fact, in aforesaid rewinding machines, for the attainment of maximum speeds on the order of 2000 m/min with short acceleration ramps it is naturally necessary to use motors with extremely high torques, and hence power, used for short, continuous transitions. The present invention, on the contrary, allows using decidedly lower power because such quick accelerations are not required and also the maximum speed is, as said, it is inferior. Being a continuous process, the initial operating conditions are in fact engaged only at the start of the line. The winding plant 30 according to the invention is free of the aforesaid drawbacks because it offers a plurality of rolls 32 for final use as end product of sizes and weights all the more manageable with respect to the jumbo rolls. The use of a plurality of rewinding machines 31 downstream of an extrusion and traditional cooling plant 20 ensures a winding capacity similar to that offered by jumbo winding plants of prior art. -li¬

lt is then possible to carry out the winding of rolls 32 for final use directly in line at relatively reduced maximum speeds, but with average effective speed entirely similar to that of the rewinding machines, which ensure a high quality of the resulting rolls .

Moreover, thanks to the winding plant 30 according to the invention, the production of the rolls 32 for final use does not require the rewinding phases . One therefore obtains a further savings in personnel, time and production costs.

Analogously, as shown in figure 3, it is possible to employ the winding plant according to the invention, and therefore the inventive method, even in rewinding phase. In such a case the plastic film 11 is supplied by a source roll 40, for example a jumbo roll.

Due to the inventive method the rewinding step of the source roll 40 requires lesser times because the capacity of the overall winding is increased. This allows, moreover, to drive the single rewinding machines 31 at reduced speeds and to thus obtain better quality products .

Not least, the single rewinding machines 31 can be outfitted with different equipment, so to be able to simultaneously produce rolls for manual use as well as rolls for use in automatic or semiautomatic machines.

From that described above with reference to the figures, it appears evident how a method of winding rolls for final use of plastic films according to the invention as well as the winding plant implementing such method are particularly useful and advantageous. The object mentioned in the description introduction is thus attained.

Naturally, the winding method according to the invention can be achieved with a different number of rewinding machines 31 with respect to what has been mentioned as merely exemplifying in the attached drawings. Moreover, the rewinding machine may be of any type.

Finally, with the method of rewinding according to the invention, rolls of size and weight otherwise not feasible for production by traditional winding plants can be obtained, and in which the single rewinding machines can produce rolls of different format (band, internal diameter and external diameter) at the same time, starting from the same fed film or from an extrusion plant or a mother roll. The protective scope of the invention is therefore delimited by the attached claims.

Claims

1) Method of winding rolls for final use of plastic film comprising the step which consists of feeding a plastic film (11) coming from a plastic film source (20,40) to at least two rewinding machines (31) independent from each other.

2) Method of winding rolls for final use of plastic film according to claim 1 wherein said plastic film source is an extrusion and cooling plant (20) . 3) Method of winding rolls for final use of plastic film according to claim 1 wherein said plastic film source is a source roll (40) .

4) Method of winding rolls for final use of plastic film according to claim 3 wherein said source roll (40) is a jumbo roll.

5) Winding plant implementing the method of winding rolls for final use of plastic film according to any one of the preceding claims constituted by at least two rewinding machines (31) . 6) Winding plant according to claim 5 wherein said at least two rewinding machines (31) comprise a cutting unit .

7) Winding plant according to claim 5 or 6 characterised in that said at least two rewinding machines (31) comprise equipment pieces for winding rolls which are differentiated from each other, said equipment pieces winding rolls of different format.