Method for adjusting the profile of a film in blown extrusion lines, adjusted film and reel

Abstract

A method for the active adjustment of the profile of a film produced with blown extrusion technology, a film obtained with such method and a reel resulting from the winding of the film.

Claims

1. A method for active adjustment of a monolayer or multilayer film profile, in an extrusion line with blown technology, said method comprising: a step of actively adjusting the film profile, wherein said film profile is generated with a sinusoidal wave, transversely movable, with an amplitude substantially equal to a profile tolerance reached with a basic adjustment of the film profile and having a variable sliding frequency, wherein the step of actively adjusting the film profile is performed with a disk with “n” segments, physically divided from each other, which regulate quantity, temperature, or both the quantity and the temperature of a flow of cooling air, wherein the sinusoidal wave has the amplitude and a frequency proportional to an extent of a defect not corrected by a basic adjustment system of the film profile, wherein the amplitude of the sinusoidal wave is defined in an initial development step of film production, and wherein a thickness is detected, and consequently profile defects, in each point of a film produced with the basic adjustment.

2. The method according to claim 1, wherein the sinusoidal wave is defined by a control algorithm.

3. The method according to claim 1, wherein the frequency of the sinusoidal wave is defined in a first production session of the film with application of the sinusoidal wave having a defined amplitude.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an example of a film profile, with FIG. 1A illustrating a film profile produced with a blown extrusion line, without an active adjustment step of the film profile; FIG. 1B illustrating a film profile produced with a blown extrusion line, with an active adjustment step of the film profile; FIG. 1C illustrating a reel profile obtained from the film of FIG. 1A; and FIG. 1D illustrating a reel profile obtained from the film of FIG. 1B.

(2) FIG. 2 illustrates an extrusion line according to the invention.

(3) FIG. 3 illustrates an extrusion line according the invention, which includes an oscillating drive and a system for reading film thickness.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(4) In the attached FIG. 1, an example of a film profile is shown, produced

(5) a) with a blown extrusion line, without the active adjustment step of the film profile according to the method of the present invention and provided with the basic adjustment step of the film profile (FIG. 1A);

(6) b) with a blown extrusion line, provided with both the basic adjustment step of the film profile and the active adjustment step of the film profile according to the method of the present invention (FIG. 1B);

(7) and an example of a reel profile obtained starting from said film a) (FIG. 1C) and from said film b) (FIG. 1D).

(8) From FIG. 1 as a whole, it is clear that not only does the active film system/adjustment method allow the profile of a single film or a single local part of film to be improved, but it also allows a “high-quality” reel to be obtained, i.e. a reel with an improvement in the maximum thickness tolerance of over 30%, an extremely important result.

(9) The regularization of the film profile, in fact, also entails a clear improvement in the reel profile, with an improved result compared to what can be obtained with the rotating drive, which does not physically modify the profile of the film, but simply “spreads” the errors in such a way that they are self-compensated.

(10) An example of an extrusion line which allows the method according to the present invention to be implemented, is schematically represented in FIG. 2, which shows:

(11) at least one extruder 10 (the extruders can be of an absolutely variable number depending on the final product desired);

(12) an extrusion die 11, or “head” (the extrusion die can be of any shape or size, both in terms of outlet diameter and number of layers of the film);

(13) an external cooling ring 12, indifferently using ambient or thermoregulated air;

(14) a segmented disk 13 for the basic adjustment of the profile and for the active adjustment of the profile through the introduction of the “voluntary” defect (as described in detail above, various solutions are possible, by adjusting the air flow or its local temperature, or by the combination of said two parameters, or by any other methods that determine a variation in the local thickness of the film); said segmented disk can exploit the same air used for the cooling ring 12, use an independent air source, or use an air source in common with other uses, whether it is taken directly from the environment or thermoregulated;

(15) a calibrator basket 14;

(16) a series of rollers 15 for flattening the tube;

(17) a drive 16 typically but not exclusively composed of a pair of motorized rollers in contact with each other;

(18) a supporting structure 17, which supports the elements previously described;

(19) a cutting system 18 of the tube, which separates the two final films;

(20) two bridge-type thickness reading systems 19, one for each film produced; the reading system can be of the “portal” type, which, as indicated, is more precise, or also of the “capacitive” type;

(21) a pair of winders 20, for forming the reels.

(22) Obviously, the final configuration of an extrusion line can differ in many details from what is schematically represented in FIG. 2, above, without prejudice to the adjustment concept of the profile so far expressed.

(23) As shown in FIG. 3, for example, with a view to seeking maximum flexibility in the use of the extrusion line, it would also be possible to provide on the line, the presence of an oscillating drive 21 and a system for reading the thickness 22 of the capacitive type, useful if a single reel is to be produced, or without the tubular cutting step. For this type of production, typically not particularly “high-quality” and therefore with less need for having a perfect profile, the traditional solution of the oscillation of the drive together with the only basic adjustment of the thickness of the film through the segmented disc is considered absolutely adequate, whereas the solution proposed herein does not in any case allow an accurate adjustment of the profile, due to the impossibility of determining to which of the two sides forming the tube, the possible profile defect read by the single bridge-measurement system used for the reading, can be ascribed. In the blown extrusion line shown in FIG. 3, therefore, depending on the characteristics of the final film, the method according to the state of the art or the method according to the present invention can be applied.