Abstract
The invention relates to an apparatus for providing marks on extruded films, in particular on stretched films, which are exiting an extrusion lip of a film extruder and a respective method. The apparatus comprises at least one nozzle means for directing a gas stream, preferably an air stream to a surface of the film exiting the extrusion lip of the film extruder, wherein the nozzle means are configured and arranged in such a manner that the gas stream locally causes a cooling of the extruded film to create a local mark.
Claims
1. A method for providing marks on extruded films, in particular on stretched films, which are exiting an extrusion lip of a film extruder, comprising the step of: directing at least one gas stream to a surface of the film exiting the extrusion lip of the film extruder using at least one nozzle means, in such a manner that the gas stream creates a local mark, and controlling the delivery of gas to the at least one nozzle means by using control means, wherein the gas is continuously provided for a predetermined time to one of the at least one nozzle means to create an array of linear marks.
2. Method according to claim 1, wherein the gas stream locally causes a cooling of the extruded film to create the local mark.
3. Method according to claim 2, wherein the cooling of the extruded film results in a detectable mark in the form of a local change of a characteristic of the film without changing the thickness of the film.
4. Method according to claim 1, wherein the marks of the linear array are placed at predetermined distances from each other.
5. Method according to claim 1, wherein the gas is provided intermittently to one of the at least one nozzle means.
6. Method according to claim 1, comprising the further step of: providing n nozzle means being arranged in a linear array, wherein n is in the range of 2 to 20, more preferably 5 to 10.
7. Method according to claim 6, wherein the n nozzle means are arranged in a 1 to m correspondence with respect to individual adjusting means for adjusting the local width of the film extruder, wherein m is in the range of 1 to 20 and more preferably 1 to 5.
8. Method according to claim 6, wherein the n nozzle means are activated at different time periods.
9. Method according to claim 1, wherein directing at least one gas stream comprises automatically directing a gas stream to the surface of the film exiting the extrusion lip of the film extruder in cycles, wherein the cycles are based on events which are significant in the manufacturing process.
10. Method according to claim 9, wherein the cycles are based on events that are significant on a neck-in effect such as a change of production, a change of the width of the film, a change of the distance between a dye and a chill roll or a change of vacuum box conditions.
Description
BRIEF DESCRIPTION OF FIGURES
[0041] The present invention will now be explained with reference to preferred embodiments and the drawings, in which:
[0042] FIG. 1 shows a schematic perspective view of a system for manufacturing films comprising an apparatus for providing marks on films, according to an embodiment of the present invention.
[0043] FIG. 2 shows a schematic side view of a system as shown in FIG. 1,
[0044] FIG. 3 shows a schematic diagram as a top view on the extruded film in the system of FIG. 1
[0045] FIG. 4 shows a schematic diagram of the measurement result representing the thickness variation resulting from marks created on an extruded film,
[0046] FIG. 5 a) and b) show a schematic perspective view of a system for manufacturing films according to another embodiment of the present invention and
[0047] FIG. 6 shows a schematic diagram as a top view on the extruded film in the system of FIGS. 5a and b.
DETAILED DESCRIPTION OF THE INVENTION
[0048] FIG. 1 shows a schematic view of a system according to an embodiment of the present invention which comprises an apparatus for creating marks according to an embodiment of the present invention. FIG. 1 shows a film extruder 1 comprising an elongated extrusion lip 3 and a plurality of adjusting means 5 being arranged adjacent to each other along the width of the extrusion lip. The adjusting means 5 can comprise respective bolts, and the adjusting means can be used for changing the width of the extrusion lip 3 and more specifically wherein individual adjustments can be made to adjust the thickness individually at specific parts of the extrusion lip. FIG. 1 further schematically shows an extruded film 7 which exits the extrusion lip 3 and which is rolled on a chill roll 9. As further schematically shown in FIG. 1 the extruded film has a wider width at the exit of the film extruder which substantially corresponds to the width of the extrusion lip 3. Due to a thermal contraction the width of the extruded film is smaller when reaching the chill roll 9. More specifically, due to this thermal contraction the extruded film comprises on the left lateral side a neck-in portion 7a and on the right lateral side a neck-in portion 7b.
[0049] FIG. 1 further schematically shows the apparatus 10 for providing marks on the extruded film. The apparatus 10 comprises a plurality of nozzles 11 which are arranged close to the extrusion lip and directed to the top surface of the film. FIG. 1 schematically shows three nozzles 11 on both lateral sides of the extruded film. In this example, each nozzle 11 is connected via a respective line 13 to a manifold 15. The manifold 15 for distributing gas to the several lines 13 is connected at one end via an electro valve 17 to a compressed air supply 19. The compressed air supply 19 can be connected to a compressor (not shown) for supplying the compressed air. The apparatus 10 comprising the nozzle 11 can be supported by a first frame which is arranged above the extrusion lip 3.
[0050] As shown in the side view of FIG. 2 one air regulator 14 can be provided for each line 13 connecting one nozzle 11 with the manifold 15. As schematically shown in FIGS. 1 and 2 the nozzles are arranged along a line parallel to the extrusion lip 3. The tip end of the nozzle 11 is arranged adjacent to a respective adjusting means 5 of the film extruder 1. In the example of FIG. 1 three nozzles 11 are arranged on both lateral sides of the film, i.e. in a border region of the film. More specifically, as schematically shown the outer most nozzle 11 is arranged on the left side at a specific distance from the left end of the extrusion lip, i.e. it is placed close to the fourth adjusting means from the left side of the extrusion lip. The second and third neighbour nozzle is arranged at equal distances such that the second nozzle 11 is arranged adjacent to the sixth adjusting means 5 and the third nozzle 11 is arranged close to the eighth adjusting means 5. The other three nozzles are similarly arranged on the right lateral side of the extrusion lip. Thus, there is a 1 to 2 correspondence between the number of nozzles on both lateral sides and the respective number of adjusting means in these border regions. This is just an example. Any arbitrary combination can be used, for example, a first nozzle is arranged at the second adjusting means, a second nozzle is arranged at the fifth adjusting means, a third nozzle is arranged at the tenth adjusting means and the fourth nozzle is arranged at the twentieth adjusting means. The arrangement on the other lateral side can be mirror-symmetric but also non-symmetric.
[0051] FIG. 3 schematically shows a top view of an extruded film coming out from the extrusion lip 3 wherein between the extrusion line Y and a measurement line X a neck-in portion 7a is formed on the left side and a neck-in portion 7b is formed on the right side of the schematic drawing of FIG. 3. FIG. 3 illustrates that the contraction of the film specifically occurs along the border region of a film on both lateral sides. FIG. 3 further shows schematically a number N of adjusting means 5 designated with numbers 1, 2, 3 to 11 and N−10, N−9 to N. In the middle region between the adjusting means 10 to N−9 substantially no thermal contraction occurs. This is again an example. The numbers depend for example on the width of the neck-in area or production and line conditions like viscosity of the material or mechanical dimensions of the production line. The total number of adjusting means N may be in the range of 30 to 350. Therefore, in FIG. 3 both lateral sides are shown in an enlarged manner. As can be seen the width of the film along the extrusion line is wider than the width along the measurement line. As can be further seen there is a specific relation of the position of the part of the film exiting for example the adjustment means 1, i.e. the position along the axis Y and the respective position of this part of the film along the measurement line which corresponds to a position along the axis X. In other words, there is a specific function y=f(x). Those parts which exit the extrusion lip 3 at a particular individual adjusting means 5 can be marked with the present system by blowing air to the surface of the film. By using an array of air blows located above the adjusting means, i.e. the bolts on both lateral sides of the film extruder local film cooling can be caused. The air flow can be simultaneously or individually be directed to the surface of the film such that the film coming out of the extrusion lip 3 is cooled and as a consequence a mark is created on the film having a specific thickness.
[0052] By using a measurement sensor head 21 along the measurement line X the thickness can be measured and the marks can be detected. This measurement sensor head can move back and forth along the measurement line X to measure the thickness of the film over its whole width. For example, a second frame (not shown) may be arranged above the measurement line X along which the measurement sensor head traverses.
[0053] As schematically shown in FIG. 4 the film thickness profile comprises three peaks on both sides wherein one peak corresponds to a respective mark detected by the measurement sensor head 21. The thickness peaks schematically shown in FIG. 4 correspond to linear marks created on respective parts of the film when exiting the extrusion lip. More specifically these marks correspond to respective adjusting means 5 where a nozzle 11 directs a gas stream on the surface of the extruded film.
[0054] These data can be processed to adjust the function y=f(x) in a way that gives more accuracy in the characterization of the real film contraction. The air blow marking cycle can be initiated manually or automatically. The air blow marking can be used continuously or in the case of events which are significant on the manufacturing of the extruded film in particular significant on the neck-in effect. For example, in case of a change of production, a change of the width of the film, a change of the distance between the dye and the chill roll and a change of vacuum box conditions the air blow marking cycle can be initiated.
[0055] Instead of, or optionally in addition, to marking by a gas nozzle as described above it is possible to create a mark using a spray nozzle situated above and/or below the film at the extrusion lip. In this embodiment, a substance preferably a liquid or paste-like material more preferably an ink or a resin is directed to the surface of the film to create a mark which is visible or invisible to the human eye. The mark is positioned in a defined relationship with respect to a specific part of the extrusion lip. In the following, ink is used from the list of substances as to describe the embodiment by example. The ink can be of any material and/or color to create a mark on the extruded film which can be detected by an appropriate sensor, e.g. an optical camera or other non-contact type sensors like beta ray, x-ray, infrared sensors or interference type sensors. Preferably, the ink can be a fluorescent ink that is invisible for the human eye on the extruded film. Fluorescent inks particularly suitable might either be UV curable or thermally dried. This has the advantage that the marked part of the extruded film can stay on the extruded film, i.e. it does not have to be cut away in post-processing. The use of an ink spray nozzle is advantageous as there is no contact between the nozzle and the extruded film. Furthermore, the thickness of the film is not changed apart from the thin layer of ink deposited on the film.
[0056] Next, the marking by an ink spray nozzle will be described referring to FIGS. 5a and b and FIG. 6. The description of features which have been described above already will not be repeated. Rather, full reference is made to the above description and the new features of this specific embodiment will be described in detail. According to FIGS. 5a and b the ink with or without fluorescent characteristics will be put into a pressure vessel connected to an air pressure system with a pressure regulating valve in between. An electric valve in the front of the spray nozzle 6 is provided to control the application of ink to the extruded film. The ink spray nozzle 6 is situated in scanning traversing position on a beam that has a mechanical lay out and assembly compatible with the lay out and the assembly of the machinery (extrusion die plus chill roll) where it is mounted on. The ink spray nozzle 6 is supported by a vertical translation to support the installation in narrow spaces. Furthermore, the ink spray nozzle 6 can have different spray angles and different spray volumes and can mark the film with correspondence to any specific part of the extrusion lip or the respective bolt, preferably one of the bolts at the extrusion lip in the border region. FIG. 6 is an illustration showing the marking of the bolt 3 of the extrusion lip (indicated by the thick black line). As can be seen, the mark on the film follows the specific form of the neck-in portion.
[0057] Even though the above described marking apparatus according to FIGS. 5a and b has been described by employing one spray nozzle, multiple spray nozzles in one array corresponding to the respective bolts can be employed. Furthermore, it is possible to provide one or two opposite transversal scanning spray nozzles, which, depending on the peculiarity of the products may spray a gas that leaves a mark preferably as a change of thickness that is detected by the thickness measurement system, and/or spraying a substance, for example an ink, that leaves a visible or invisible mark detected by an optical system built-in with the sensor heads of the thickness measurement system.
[0058] The detection system according to this embodiment is outlined next. The ink is detected by a sensor, preferably by an optical camera. Preferably, the optical camera is mounted onto the first measurement sensor head 21 as shown in FIG. 3. The optical camera can be used to detect visible ink. In case fluorescent ink is used to mark the extruded film, an additional light source might be used to make the mark, i.e. the fluorescent ink, visible for detection by an optical camera. Preferably, the light source is mounted onto a second measurement sensor head. The second sensor head might be movable back and forth in the same direction as the first sensor head but independently from each other. The source of light can be selected according to the choice of ink used for the specific application and/or the camera system can be selected accordingly. As described above the sensor can be selected to be any suitable sensor to detect the mark on the extruded film and the additional light source is selected according to the sensor used or can be omitted completely.
[0059] Again, the track left by the ink spray nozzle 6 on the film allows determining a univocal correlation between the bolt at the extrusion lip and the correspondent material stripe running below the gauge. Using both the information of the location of the mark and the information from the two edge detectors the functional relationship like the function f(x) can be adjusted in a perfect manner, preferably to respond to changes of surrounding conditions as described above.
[0060] The present invention has now been described with reference to embodiments. The foregoing detailed description and example have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the present invention. In particular, although features and elements of the present invention are described with reference to the aspects in particular combinations, each feature or element can be used alone without the other features and elements of the aspects or in various combinations with or without other features and elements of the invention. Therefore, the scope of the present invention should not be limited to the apparatus, system and methods described herein, but only by the language of the claims and the equivalence of those apparatus, systems and methods.
