Blown-Form Identification in a Blown Film System

Abstract

The invention relates to a blown film system for producing a film tube made of plastics material, comprising: an annular nozzle, out of which a plastic melt having a closed cross-section can be brought; a take-up device, by means of which the plastic melt can be drawn up from the direction of the annular nozzle so as to form the film tube; an air-provision device, which is downstream of the annular nozzle when viewed in the transport direction of the film tube and by means of which an amount of air can be provided; and a calibration device, which is downstream of the annular nozzle when viewed in the transport direction of the film tube and surrounds the film tube and by means of which the outer circumference of the film tube can be delimited. At least one detector is contained that has a plurality of detection elements, by means of which electromagnetic radiation emitted or reflected at various points of the film tube can be detected, such that at least one planar region and/or contoured region of the film tube can be detected with regard to characteristic properties, wherein the detector comprises at least 32 detection elements.

Claims

1. Blown film line for the production of a film tube made of plastic with an annular nozzle from which a plastic melt with a closed cross-section can be discharged an extraction device with which the plastic melt can be extracted from the direction of the annular nozzle, forming the film tube an air supply device downstream of the annular nozzle, as seen in the transport direction of the film tube, with which an air quantity can be supplied a calibrating device that, viewed in the transport direction of the film tube, engages around the film tube and by means of which the outer circumference of the film tube can be limited characterized by at least one detector with several detection elements, with which electromagnetic radiation emitted or reflected from different points of the film tube can be detected, so that at least one surface region and/or one contour region of the film tube can be detected with regard to characteristic properties, wherein the detector comprises at least 32 detection elements.

2. Blown film line according to claim 1, characterized in that at least one swivel arrangement is provided, by means of which the detector can be swiveled in the circumferential direction of the film tube.

3. Blown film line according to claim 1, characterized in that at least one second detector is to be provided, which is arranged offset from the first detector in the circumferential direction of the annular nozzle.

4. A method for producing a plastic film tube with a blown film line, wherein a plastic melt with a closed cross-section is discharged with an annular nozzle the plastic melt is drawn off from the direction of the ring die with an extraction device, forming the film tube an air supply device arranged downstream of the annular nozzle, as seen in the transport direction of the film tube, can be used to supply a quantity of air the outer circumference of the film tube is limited by means of a calibration device which is arranged downstream of the annular nozzle, as seen in the transport direction of the film tube, and which engages around the film tube. characterized in that electromagnetic radiation is reflected at different points of the film tube by at least one detector having a plurality of detection elements so that at least a surface region and/or a contour region of the film tube is detected with respect to characteristic properties.

5. Method according to claim 4, characterized in that after leaving the annular nozzle, a point of interference is imprinted on the film tube, the position of which in and/or transversely to the transport direction is detected with the detector at different points in time in order to determine a positional and/or velocity profile of the point of interference.

6. Method according to claim 5, characterized in that the point of interference is a thick or thin spot, a stipple, or a particle inserted into or attached to the film tube.

7. Method according to claim 5, characterized in that the point of interference is impacted during a roller or job change.

Description

[0046] Further advantages, features, and details of the invention will become apparent from the following description, in which various examples of embodiments are explained in detail with reference to the figures. The features mentioned in the claims and in the description may be, each individually or in any combination, essential to the invention. Within the scope of the entire disclosure, features and details described in connection with the process according to the invention apply of course also in connection with the blown film line according to the invention and vice versa, so that reference is or can always be made mutually to the individual aspects of the invention in the disclosure. The individual figures show:

[0047] FIG. 1 Side view of a blown film line according to the invention

[0048] FIG. 2 View II-II from FIG. 1

[0049] FIG. 3A further embodiment of the invention with several detectors

[0050] FIG. 4 An embodiment of the invention with a swiveling device Illustration of a

[0051] FIG. 5 The process according to the invention

[0052] FIG. 1 shows apparatus 1 for the production of a film tube, namely a blown film line 1, which initially comprises at least one extruder 2, with which, for example, plastic present in granular form can be plasticized. The plastic melt thus produced is fed via line 3 to an extrusion tool 4, which can also be referred to as a nozzle head, from which this melt is transferred into a film tube 6, so that this melt stream can be withdrawn from an annular nozzle 5, which is not visible in this figure, in the direction of transport or withdrawal z. A yet unconsolidated film tube 6 var is now in place. This is inflated from the inside by a slight overpressure so that it has a large diameter inside the calibration device 7. For this purpose, an air supply device 13 is provided, which is located inside the annular nozzle 5 and extends partially in the transport direction. This air supply device is supplied with air through the extrusion tool.

[0053] The film tube is solidified by cooling, whereby part of the heat of the film tube is released into the environment, in particular by means of a temperature control device 8, which is often referred to as a cooling ring due to its annular design that encloses the film tube.

[0054] After passing through the calibration device, film tube 6 enters the active area of a flattening device 9, in which the circular film tube is converted into an elliptical cross-section with increasing eccentricity until it forms a double-layered plastic film which is joined together at its sides, under the influence of the extraction device which comprises two extraction rollers 10.

[0055] The flattening device is positioned so that it can rotate, whereby the axis of rotation is substantially aligned with the tube or symmetry axis 11, which is indicated by a dashed line in FIG. 1. The rotatability of the flattening device is indicated by arrow 12. The rotatability of the flattening device is indicated by arrow 12.

[0056] FIG. 1 further shows a reversing device 15, which fulfills the task of guiding the flattened film tube from the flattening device to the stationary roller 16 without damage occurring.

[0057] The arrow 17 indicates that this film tube, after passing through the reversing device 15, is guided for further processing, which is not specified in more detail here.

[0058] Seen in the transport direction z, between the annular nozzle 5 and the calibration basket 7, at least one detector 20 is placed, with which surface elements of film tube 6 can be detected. The detector is arranged outside film tube 6 but directed towards it. The detector can be attached directly or indirectly to any component of the blown film line 1. However, it is also conceivable to set up the detector independently of the blown film line 1 on its own stand, for example, a tripod, within the production facility.

[0059] FIG. 2 shows section II-II and thus an arrangement with only one detector directed at the film tube. Due to the small spatial extension of the detector in comparison with the film tube, the detector does not have an overview of the entire width of the film tube and therefore, an angular error occurs. The area observed by the detector is characterized by the viewing angle a, which depends on the distance of the detector to the symmetry axis of the film tube, which essentially corresponds to the transport direction of the film tube, and the width of the film tube. From these two sets of information, the detector can now be calibrated and the actual shape of the film tube, in particular, the contour, can be calculated. The illustration refers to the plane that is essentially orthogonal to the transport direction of the film tube. Nevertheless, the same principle is also relevant for a plane spanned by the transport direction and the position of the detector.

[0060] FIG. 3 shows an embodiment example with two cameras 20, and 20′, which are positioned offset by an angle in the circumferential direction of the film tube. Both detectors are preferably located on a common plane that is orthogonal to the transport direction z of the film tube 6. In this way it is possible, for example, to analyze the contour of the film tube from two different perspectives and, in particular, to identify the non-roundness of the film tube. For example, an undesired oval cross-section of film tube 6 can be avoided.

[0061] The design shown in FIG. 4 pursues in particular the same objective as the design example in FIG. 3, namely the detection of out-of-roundness of the film tube. In contrast to FIG. 3, preferably only one detector is present, which, however, is arranged on or at a swivel arrangement. This allows detector 20 to be pivoted in the direction of the double arrow 401 about the symmetry axis of the film tube. In the present example, this swivel arrangement is designed as a rail system 400. On these rails, a sliding sled (not shown) is assembled on which the detector is mounted.

[0062] FIG. 5 illustrates, in figure part 5a, a film tube divided into a right and a left half, separated by the dash-dotted center line. The left half is labeled A and the right half is labeled B. Both halves are of different shapes with the same initial and final diameters. In half A, the film tube is initially extended in the transport direction, and only in the further course is it extended in the transverse direction. In the case of B, the film tube is stretched in the transverse direction immediately after leaving the annular nozzle in the transverse direction, but also in the transport direction.

[0063] These differences can be determined by means of a detector if a point of interference is introduced into the film tube and the position of this point of interference is recorded as a function of time.

[0064] Figure part 5b shows the speed profiles of points of interference in the transport direction of the film tube in the respective half of the film tube shown. The axis h indicates the height, i.e., the position in the transport direction, whereas the axis V indicates the speed. The examples of velocity profiles shown can be determined with the detector in the described manner. Graph A of half A in FIG. 5a initially shows a sharper increase in speed than graph B. Graph A flattens out in the further course of the transport direction. Graph B, for example, has a linear increase in velocity. Generally, similar graphs can also be obtained for the transverse direction of the points of interference.

[0065] Overall, such a measurement method will allow conclusions to be drawn about the orientation of the molecules contained in the film. In the case of an initial stretching in the transport direction (half A), initially, molecules oriented parallel to the transport direction can be obtained. In further progress, there is hardly any orientation in the transport direction, but rather transverse to it. Thus, the molecular orientation can be in the transverse as well as in the longitudinal direction. In the case of B, the molecules are initially oriented in the transverse direction but in further progress increasingly in the longitudinal direction, so that overall, the orientation prevails in the longitudinal direction. The predominant orientation of the molecules will influence the characteristic properties of the film.

TABLE-US-00001 Reference list 1 Apparatus for the production of a film tube 2 Extruder 3 Line 4 Extrusion tool 5 Annular nozzle 6 Film tube 7 Calibration device 8 Temperature device 9 Flattening device 10 Extraction rollers 11 Tube or symmetry axis 12 Rotatability of the flattening device 13 14 15 Reversing device 16 Roller 17 Arrow 18 19 20, 20′ Detector/Camera 400 Rail system 401 Double arrow A Left half B Right half h Height V Velocity z Transport or direction, respectively