Method for manufacturing a blown film web as well as a blown film line

Abstract

In a method for manufacturing blown film web on a blown film line, film is heated above the takeoff device and then treated mechanically. This allows the film to be brought from initial heat to an easy-to-process temperature level with little energy. A horizontally oriented treatment roll path is provided between the takeoff and a reversing device is arranged above the takeoff. In both aspects, controlling is performed to achieve a uniform film gauge after stretching.

Claims

1. Method for manufacturing a blown film web on a blown film line with the steps: a. Extruding a film tube; b. Inflating the film tube in a tube forming zone and taking off a double-layer film web formed from the film tube with a takeoff roll pair for drawing the film tube longitudinally and transversely; c. Cooling the rising film tube using a means of cooling; d. Laying flat the film tube into the double-layer film web; e. Routing double-layer film web further upwards above takeoff roll pair and through a treatment roll pathwith disposed above the takeoff roll pair, the treatment roll path having a means of heating for heating double-layer film web; f. Treating double-layer film web on treatment roll path; namely stretching double-layer film web in a stretching path of treatment roll path; g. Routing double-layer film web through a reversing unit disposed above the treatment roll path for laying; wherein the additional step of h. Controlling the film gauge of the double-layer film web stretched monoaxially in the machine direction by means of a predetermined target gauge profile, whereby the film gauge profile of the tube film produced on blown film line is controlled in such a manner that the predetermined target gauge profile has variances from a uniform film gauge that are used to compensate for the change in film gauge over the film width resulting from the subsequent monoaxial stretching in the machine direction so that, by means of stretching, a film with a transverse gauge profile having the least possible variances from the mean film gauge over the entire film width is produced; whereby for threading double-layer film web upon startup of blown-film line, a roll of treatment roll path is slid or pivoted from its operating position, and double-layer film web is tensioned after threading.

2. Method according to claim 1, wherein in treatment step f, double-layer film web in addition to being stretched, is embossed, irradiated, and/or subjected to corona treatment.

3. Method according to claim 1, wherein the extruded tube film is controlled to a predetermined target gauge profile via its circumference.

4. Method according to claim 1, wherein the target profile laying resulting from the reversing takeoff is compensated over the film width and continuously adjusted, whereby the assignment of one or several circumferential points and/or sectors of the laid-flat tube film to one or several control zones in the control algorithm is taken into account for controlling the segmented control zone.

5. Method according to claim 1, wherein the predetermined target gauge profile is controlled by means of an algorithm from the readings of a measuring device that measures the film gauge across the entire film width after monoaxial stretching in the machine direction.

6. Method according to claim 1, wherein the control algorithm for controlling the individual segmented control zones includes a superimposition of the base profile from the film gauge profile control of the blown-film line; of the stretching profile from the laying of the tube film by means of the reversing takeoff and impacts from the stretching process; and optionally, of the roll profile from the evaluation of the film roll.

7. Method according to claim 1, wherein the target gauge profile is set manually in the control system.

8. Method according to claim 1, wherein the film is routed to the stretching device in the treatment roll path blocked.

9. Method according to claim 1, wherein the tube film is slit open on one or both side(s), folded open, and routed to the stretching device.

10. Method according to claim 1, wherein for the purpose of controlling, the film gauge is measured above takeoff roll pair according to the routing of the film web proposed here.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the disclosure is explained in greater detail based on six exemplary embodiments with reference to the drawings.

(2) In the drawings:

(3) FIG. 1 shows schematically, as a vertical section perpendicular to a takeoff roll pair, a first variant of a treatment roll path with five rolls and a reversing device arranged above the latter;

(4) FIG. 2 shows, in a view otherwise unchanged from FIG. 1, a second variant of a treatment roll path with five rolls and a reversing device arranged above the former;

(5) FIG. 3 shows, in a view otherwise unchanged from FIG. 1, a third variant of a treatment roll path with five rolls and a reversing device arranged above the former;

(6) FIG. 4 shows, schematically as a vertical section through a takeoff roll pair, a fourth variant of a treatment roll path with five rolls and a reversing device arranged above the former, at a lower built height, in particular, as a configuration for an MDO unit,

(7) FIG. 5 shows, schematically as a vertical section through a takeoff roll pair, a fifth variant of a treatment roll path with four rolls and a reversing device arranged above the former, in particular, as a configuration for a layflat package; and

(8) FIG. 6 shows, highly schematically, a possible sixth variant for a treatment roll path with the least possible built height;

(9) FIG. 7 shows a diagram on the development of longitudinal tensile stress over an elongation c of a plastic film;

(10) FIG. 8 shows, schematically as a vertical section through a takeoff roll pair, a sixth variant of a treatment roll path with five rolls and a reversing device arranged above the former;

(11) FIG. 9 shows, schematically as a vertical section through a takeoff roll pair, a seventh variant of a treatment roll path with six rolls for four treatment stations and with a reversing device arranged above the former;

(12) FIG. 10 shows, highly schematically, a blown film line from prior art, also like FIGS. 11 through 13 from EP 2 277 681 A1, with a downstream stretching device, in which the process located there for controlling the film gauge is applied;

(13) FIG. 11 shows a top view of the blown film line from FIG. 10;

(14) FIG. 12 shows an exemplary actual gauge profile of a film tube with two thin spots; and

(15) FIG. 13 shows an exemplary actual gauge profile of a film tube with one thin spot.

DETAILED DESCRIPTION OF THE DRAWINGS

(16) Blown film line 1 (upper area shown only) in FIG. 1 includes an extruder, a die head with an annular slit die, a rising section arranged above the latter for an extruded film tube, a calibrating cage, a layflat frame, and a takeoff roll pair 2 above the layflat frame, whereby a first takeoff roll 3, which is finely adjustable in its position is supported by a first bracket 4, while a second takeoff roll 5 is supported on a sliding bearing mount 7 to be horizontally slideable by means of servo cylinder 6. Servo cylinder 6 can thus move second takeoff roll 5 horizontally towards and away from the first takeoff roll 3.

(17) Above takeoff roll pair 2, a treatment roll path 8 is provided. In the latter, there are a total of five rolls, namely a first roll 9, a second roll 10, a third roll 11, a fourth roll 12, and a fifth roll 13.

(18) The five rolls of treatment roll path 8 are alternately arranged on different sides of a virtual plane 14 that lies in parallel with center shafts 15 (identified as examples) of the two takeoff rolls and runs vertically through the nip between the two takeoff rolls. The virtual plane contains the area which the laid-flat film would move through if the laid-flat film would simply rise vertically upwards coming from the nip of the takeoff rolls. In the vertical sectional view perpendicular to center shafts 15, virtual plane 14 thus shows as a vertically running line, namely following the vertical direction of the film's rising, and starting at the nip of the takeoff roll pair.

(19) First roll 9, third roll 11, and fifth roll 13 lie on a first side 16 of virtual plane 14; second roll 10 and fourth roll 12, however, lie on an opposite second side 17 of virtual plane 14.

(20) At the same time, all five rolls of treatment roll path 8 are set so closely together vertically that, in the case of horizontal projection of the rolls onto virtual plane 14, one overlap each of first roll 9 with second roll 10, second roll 10 with third roll 11, third roll 11 with fourth roll 12 and fourth roll 12 with fifth roll 13 results, and namely each about by a third of the entire diameter size of the five rolls.

(21) The first four rolls 9, 10, 11, 12 of treatment roll path 8 are embodied to be the same size, while the two takeoff rolls 3, 5 of takeoff roll pair 2 and fifth roll 13 are embodied larger.

(22) Clearances 18 (identified as examples) of the five rolls of treatment roll path 8 between each other are at least 50 mm each.

(23) First roll 9 is equipped with a speed control unit so that its surface speed during a rotation can be adjusted quite precisely to a specified amount.

(24) Second roll 10 is equipped with a drive and a speed control unit that can adjust roll 10 to a clearly higher circumferential speed than first roll 9.

(25) Third and fourth rolls 11, 12 can be drivable, then e.g. at a same speed as second roll 10, or preferably more slowly than second roll 10.

(26) Fifth roll 13 can also be drivable, then e.g. at least at essentially the same speed as fourth roll 12, or preferably more slowly than fourth roll 12.

(27) It should be noted here that it can be advantageous to slow down after a stretching process in order to let stresses in the film dissipate.

(28) First roll 9 is also equipped with an active means of heating and a temperature sensor (neither one shown), namely piping for a heating fluid with a heat-conducting connection to the surface of first roll 9, while the temperature sensor can either record the surface temperature of first roll 9, and/or of the running double-layer film web by means of no-contact measuring.

(29) Preferably, the temperature sensor is arranged in a heating fluid return so that, while accepting a certain imprecision, it can be assumed that the film will run somewhat cooler that the return line temperature of the heating fluid is.

(30) Ideally the process temperature of a double-layer film web will assume exactly the temperature of the roll surface. In practice, however, the running film will always be a bit warmer or cooler, depending on whether it was cooled or heated by the roll.

(31) The person skilled in the art can, for implementation in an especially precise embodiment, measure the process temperatures of the individual rolls; e.g., non-contact via infrared sensor, and adjust the roll temperatures according to the actual film temperatures.

(32) Second roll 10, third roll 11, and fourth roll 12 can, independently of each other, each also be equipped with such an active means of heating.

(33) At any rate, one rollhere fifth roll 13is equipped with a temperature measuring device and an active means of cooling.

(34) Above treatment roll path 8, two non-driven reversing rolls 19 (identified as examples) are arranged on the way to a reversing unit 20 arranged above takeoff roll pair 2 and treatment roll path 8, whereby reversing rolls 19 and reversing unit 20 are known from prior art and shall thus not be further explained here.

(35) Both the two takeoff rolls 3, 5 of takeoff roll pair 2 and the five treatment rolls of treatment roll path 8 and ultimately also reversing rolls 19 are supported at their faces on a machine rack 21.

(36) On the side of machine rack 21, two temperature conditioning devices 22 (identified as examples) are provided. By means of temperature conditioning devices 22, the temperature-conditioned rolls of treatment roll path 8 are connected by means of coolant lines or means of heating agent lines, preferably also by means of temperature sensor data lines (not shown). Contained in temperature conditioning devices 22, or at any rate, having access to the temperature conditioning devices 22, electronic microcontrollers (not shown) are provided, which can control the set temperature of the temperature-controlled rolls, based on the fluid return.

(37) In the operation of blown film line 1, a film tube (not shown) is extruded by the extruder (not shown) through the annular slit die (not shown). The film tube is drawn upwards along blown film line 1, through the calibrating cage (not shown) and the layflat unit (not shown). At the end of the layflat unit, the film tube is mostly flattened and enters takeoff roll pair 2 in this shape. From there on, word shall be of a double-layer film web 23.

(38) Double-layer film web 23 can optionally be routed in a straight upward direction above takeoff roll pair 2, congruent with virtual plane 14, through rolls 9, 10, 11, 12, 13 of treatment roll path 8, and immediately to reversing rolls 19, and from there to reversing unit 20.

(39) In this case blown film system 1 corresponds to a conventional blown film system. The reversing unit rotates during operation of blown film line 1 and thus generates on a roll (not shown) on the floor of the erection area (not shown) a film roll that shall be wound as uniformly as possible.

(40) In an alternativeand here, preferredfilm routing path, however, double-layer film web 23 is routed around each of the five rolls 9, 10, 11, 12, 13 of treatment roll path 8; wherebydue to the rolls' geometry among each otheran arc of contact of more than 180 results, at any rate, on second roll 10, third roll 11, and fourth roll 12. The arc of contact of first roll 9 is governed, in particular, by the positioning height of first roll 9 vis-a-vis takeoff roll pair 2, as well as by the diameters of the three rolls and in addition, by the clearance between first roll 9 and virtual plane 14. In the arrangement selected here, the arc of contact at first roll 9 is about 170.

(41) The same applies to fifth roll 13, whereby here, in particular, the positioning vis-a-vis virtual plane 14, first reversing roll 19, and the diameter between fifth roll 13 and first reversing roll 19 are relevant.

(42) 1] In the configuration described, double-layer film web 23 then runs in the direction of extrusion; i.e., in machine direction, upwards through takeoff roll pair 2, and is then first routed clockwise (all information regarding clockwise/counterclockwise refers to the section views of the Figures) around first roll 9. First roll 9 is used as a holding roll. At the same time, a first of a total of three warming agent or coolant circuits flows through first roll 9 within treatment roll path 8; i.e. a heating circuit.

(43) Given a configuration of the first variant of blown film line 1 in FIG. 1, the double-layer film web 23 can, e.g., come from takeoff roll pair 2 at an incoming film temperature of about 60 C. to about 80 C.

(44) First roll 9 is set in such a manner that its circumferential speed is the same as the one double-layer film web 23 experiences also in takeoff roll pair 2. In the clearance between takeoff roll pair 2 and first roll 9, double-layer film web 23 thus does not experience any mechanical influence.

(45) Due to the large arc of contact of double-layer film web 23 around first roll 9, double-layer film web 23 runs on first roll 9 with adhesive friction; thus exactly at the same speed as the one determined by the roll surface, even if the adhesive friction does not exist across all of the arc of contact.

(46) The first temperature circuit; i.e., the heating circuit that flows through first roll 9 in its function as a holding roll is, e.g., set to a temperature differential generation in the film of between plus 5 K and plus 10 K, relative to the film temperature at the exit from the preceding first takeoff roll 3. Double-layer film web 23 is thus heated by about plus 5 K to plus 10 K when it goes around first roll 9. This minor temperature differential is already sufficient for significantly increasing the processability of double-layer film web 23, for blown film line 1 is (below the areas shown in FIG. 1) set in such a manner that the film does not cool off until it is rising and thus, when passing takeoff rolls 3, 5, still has a temperature that is quite highbetween 60 C. and 80 C. in the tested example.

(47) Thus, with only very little energy, which must be provided by temperature conditioning device 22, the film can be brought to a very well processable temperature level in order to make longitudinal stretching easier.

(48) Second roll 10 is embodied as a stretching roll in the exemplary embodiment shown. In the positive tests, it was driven at triple or quadruple the circumferential speed relative to first roll 9. With stretch ratios trending more towards 1:3, a film quality resulted that seemed more suitable for silage prestretch; at higher stretch ratios, however, i.e., trending more towards 1:4 or above, a wider range of processability resulted; in particular with regard to the visual film qualities.

(49) In the positive test, second roll 10, i.e., the stretch roll, was used as the first of a total of three rolls of a second temperature circuit; i.e., an annealing circuit. The annealing circuit flows through second roll 10, third roll 11, and fourth roll 12. The temperature in the annealing circuit return was set at plus 5 K to plus 20 K relative to the return of preceding first roll 9; i.e., the holding roll.

(50) Thus, second roll 10 has two functions: it is both a stretching roll and an annealing station in the shape of a annealing roll.

(51) Third roll 11 and fourth roll 12 are embodied as annealing rolls; i.e., they maintain the rather high temperature level of the stretching roll, at least essentially, and thus result in relaxation of the transversely stretched double-layer film web 23, which helped minimize a memory effect of the reshrinking that would have otherwise occurred.

(52) Fifth roll 13, embodied as a chill roll, is connected to the third of the three temperature circuits; namely a cooling circuit. The temperature level in the cooling circuit return was ideally between minus 10 K and minus 20 K relative to the return of the preceding roll; i.e., the most recent annealing roll.

(53) On all five rolls of treatment roll path 8, double-layer film web 23 runs mostly with adhesive friction. Ideally, the five rolls are thus surface-coated; the idea is, in particular, spiral muting or silicon coating.

(54) It is understood that for each roll, at least one contact roll or pressure roll can be provided. But in the prototype tests, running without contact rolls has proven to be quite sufficient.

(55) Water has proven itself as heating and cooling medium for temperature conditioning devices 22 and the three temperature conditioning circuits.

(56) At its discharge section, blown film line 1 was run with a film speed between 94 m/min and 340 m/min, and with a stretch ratio of 1:2 and 1:3 between first roll 9 and fifth roll 13; whereby again the lower stretch ratio; i.e., trending towards 1:2, seemed suitable more for silage prestretch products.

(57) Implementing the different disclosure aspects, blown film line 1 provides, above takeoff roll pair 2, a treatment roll path 8 with a means of heating for double-layer film web 23; namely with the heated fluid circuit in first roll 9 and additionally with the annealing circuit in second roll 10, in third roll 11, and in fourth roll 12.

(58) Thus, present here, even several active means of heating for double-layer film web 23 are provided; namely in a total of four different rolls.

(59) Providing a means of heating in several rolls, two rolls at least, especially with two different fluid circuits, is also an advantage per se.

(60) Implementing the second aspect of the disclosure, above takeoff roll pair 2, a transversely oriented treatment section is provided each, for from roll to roll within treatment roll path 8, the rolls are oriented at an angle of about 35 to 40 from horizontal; i.e., they are oriented more horizontally than vertically towards each other. This results in the rolls, due to their sufficient lateral offset, being arrangeable in such a low form factor that they, in a projection [onto] virtual plane 14, result in overlaps; so, in total are less high than what the addition of the five rolls' diameters would amount to.

(61) In the second variant of a blown film line 1 in FIG. 2, the line can be embodied identically or similarly up to takeoff roll pair 2.

(62) Above takeoff roll pair 2 and below reversing unit 20, again, five rolls are arranged; namely, a first roll 9, a second roll 10, a third roll 11, a fourth roll 12, and a fifth roll 13, before next, at the top, a reversing roll 19 is provided.

(63) The five rolls perform the same function as described in the first variant from FIG. 1, and the same three temperature conditioning circuits are also present.

(64) However, in the second variant, second roll 10 and fourth roll 12 are arranged on the same side of virtual plane 14 as first roll 9, third roll 11, and fifth roll 13. I.e., all rolls are arranged on the same side of virtual plane 14.

(65) A direct connection between the nip of takeoff roll pair 2 and reversing roll 19 is free so that double-layer film web 23 can either be routed rising directly upwards without going around the rolls in treatment roll path 8.

(66) Preferably, however, this line is also arranged as an MDO line; i.e. for longitudinal stretching of the film beyond the plastic flowing of double-layer film web 23.

(67) The five rolls of treatment roll path 8 have very little clearance from each other; it is below 5 cm, at any rate. Thus, when starting up blown film line 1, it is very difficultin the shown operating position of the rolls in treatment roll path 8to thread the film in between them, even if each of the rolls is driven in the opposite direction from its predecessor.

(68) Consequently, for threading a beginning (not shown) of double-layer film web 23, two rollsnamely second roll 10 and fourth roll 12, can be shifted to the left, i.e., the opposite side of virtual plane 14. Then, double-layer film web 23 can simply be threaded through the five rolls, and then second roll 10 and fourth roll 12 will be moved back to the same side 17 of virtual plane 14, just as the remaining rolls are positioned, and the extrusion process can be run as a steady-state process.

(69) Preferably, second roll 10 can optionally be adjusted up to the imaginary plane made up of the axes of rolls 9, 11, 13, or even beyond this plane, resulting in a variably adjustable stretching section. In preliminary tests, adjustability of the stretching length has proven to be advantageous from a process technology point of view; e.g., because a higher error tolerance for faulty spots resulted if the imaginary plane was passed through.

(70) In the threading position of second roll 10 and fourth roll 12, blown film line 1 can be operated like a conventional blown film line.

(71) In the third variant of blown film line 1 in FIG. 3, essentially the same design was chosen as in the second variant of blown film line 1 in FIG. 2; however, the five rolls of the treatment roll path 8 are all located on the first side 16 of virtual plane 14. As an infeed side to reversing unit 20 is also located on the first side 16 of virtual plane 14, routing is possible directly from fifth roll 13 to reversing unit 20. A reversing roll 19 is not necessary.

(72) In addition, fifth roll 13 has been arranged relative to the four preceding rolls in such a manner that its edge that faces plane 14 protrudes over the four preceding rolls so that double-layer film web 23 can be routed around the four preceding rolls without threading and without passing treatment roll path 8. Despite this, the arc of contact of double-layer film web 23 around the fifth roll 13 is almost 90 even without threading, and in the threaded state, it is even almost 180, so that sufficient guidance is ensured.

(73) In the third variant of blown film line 1 in FIG. 3as in the second variant of blown film line 1 from FIG. 2combing of the second and fourth rolls is provided for so that the beginning of the film can be threaded by simply guiding it straight in when the line is started up.

(74) The fourth embodiment of blown film line 1 in FIG. 4 is embodied identically to the variants described above up to a takeoff roll pair 2.

(75) The first takeoff roll 3 located on the same side 16 as the infeed for reversing unit 20 is, however, embodied to be slideable for threading and for closing takeoff roll pair 2 in the fourth variant of blown film web line 1. However, a second takeoff roll 5 located on an opposite side 17 of virtual plane 14, is embodied to be fixed in principle.

(76) Above takeoff roll pair 2, four rolls of a treatment roll path 8 lie arranged horizontally next to each other, and offset from these to the side and in height, a fifth roll 13.

(77) Thus, with regard to virtual plane 14 above the takeoff roll pair 2, three rolls of treatment roll path 8 are located on the second, here right-hand, side 17 while two rolls of treatment roll path 8 are located on the first, here left-hand, side of virtual plane 14; i.e., on the same side as the infeed for reversing unit 20.

(78) For this purpose, a machine rack 21 for the rolls of treatment roll path 8 has a cantilever 24, which protrudes laterally from a main body of machine rack 21. The cantilever 24 supports first roll 9.

(79) Due to the horizontal arrangement next to each other of several rolls of treatment roll path 8 i.e., here a total of four rolls of treatment roll path 8, blown film line 1 overall has a very low form factor, despite the fact that the reversing unit 20 is arranged above takeoff roll pair 2 and treatment roll path 8.

(80) Two of the rolls within treatment roll path 8, here second roll 10 and fourth roll 12, are again embodied to be combingly slideable, thus making threading into the line easier at start-up. Especially under tight space conditions, however, pivoting can also be provided for; e.g., second roll 10 can also be embodied to be pivotable around first roll 9; at the same time fourth roll 12 e.g. can be embodied to be pivotable around fifth roll 13 or around third roll 11.

(81) Extending straight above takeoff roll pair 2, i.e., in virtual plane 14, a straight path 25 for double-layer film web 23 is left open so that double-layer film web 23 can also be produced without running through MDO treatment roll path 8. Then the film web runs straight up to a straight-line path reversing roll 26, and from there further into infeed 27 of reversing unit 20.

(82) Alternatively, double-layer film web 23 can be routed along an MDO path 28 that pivots directly onto the opposite side 17 of virtual plane 14relative to infeed 27and runs around the outside of first roll 9. Then follows the passage already described above through the additional four rolls, which also have the same functions as already described above.

(83) From fifth roll 13, the double-layer film web 23 finally runs either over another reversing roll 29 or, if the arc of contact of fifth roll 13 is already sufficient, directly to infeed 27 of reversing unit 20.

(84) Fifth roll 13, which serves as a chill roll, and/or an additional reversing roll 29 provided, such as additional cooling units, can be adjustable together or towards each other, and namely individually or together, so that the cooling path is easily adjustable. E.g., fifth roll 13 and the additional reversing roll 29 can be supported together on the machine rack, which rotates about an axis that lies in parallel with the shown rolls; or, e.g., the additional reversing roll 29 can be movable vertically downward or pivotable so that, by means of quite simple movements, the arc of contact of double-layer film web 23 on the MDO path 28 around fifth roll 13 can be set and practically variably dosed. Even with a predetermined cooling temperature it is then possible to set the cooling effect before the double-layer film web 23 enters reversing unit 20.

(85) A similar idea can, e.g., be performed with first roll 9, which ideally serves as a holding roll and simultaneously, as a heating roll. This roll can also be adjusted, e.g., in height or laterally so that the changed geometry of the MDO path of the double-layer film web 23 results in a changed arc of contact around first roll 9, and in a change in stretch length.

(86) A like effect can also be achieved with another contact roll that is provided there.

(87) In the fifth variant of blown film line 1 a layflat path 30 is again located above takeoff roll pair 2, and above, a reversing unit 20 with an infeed 27.

(88) Within layflat path 30, a first roll 31, a second roll 31, a third roll 33, and a fourth roll 34 are provided. From there, a designated film path via a number of passive reversing rolls 35 (the first one shown as an example) to infeed 27 into reversing unit 20 is provided.

(89) The four rolls of layflat path 30 are again provided with lateral clearance from virtual plane 14, resulting in a straight path 25 for the double-layer film web 23 from takeoff roll pair 2 directly to the first passive reversing roll 35, and from there further to reversing unit 20 if the double-layer film web 23 is not supposed to run through the layflat system.

(90) As an alternative, the double-layer film web 23 can be routedhere, e.g., around a first reversing unit 36to first roll 31, from there around roll 32, from there around third roll 33, and finally around fourth roll 34, until double-layer film web 23 rejoins straight path 25 on this layflat path 37.

(91) Two each of the total of four rolls of layflat path 30 are essentially at the same height; they each form a pair with a low form factor. When projected to virtual plane 14, an overlap area results between first roll 31 and second roll 32, and even congruence between third roll 33 and fourth roll 34.

(92) But a small amount of overlap is already sufficient for achieving a lower form factor as compared to the design shown in FIGS. 2 and 3.

(93) All four rolls of layflat path 30 ideally have a contact roll 38 (shown as an example) that will be jointedly pressed into the respective roll by means of a contact arm 39 (shown as an example).

(94) In the present exemplary embodiment, only two of the rolls have been provided with contact rolls, namely first roll 31, which serves as holding roll and heating roll, and second roll 32, which serves as transversely stretching roll and annealing roll.

(95) This results in a transversely stretching section 40 between first roll 31 and second roll 32, and high tangential forces will result on the circumferences of first roll 31 and second roll 32.

(96) Third roll 33 and fourth roll 34, instead, are designed to be chill rolls, [with] the surface speeds set in coordination with the surface speed of second roll 32 in such a manner that no more transverse stretching occurs there, or even slower, so that relaxation can occur.

(97) The described embodiment is envisioned as a layflat unit; i.e., usually with a max. stretch of 1:1.05. The stretching length is quite long compared to the MDO variants.

(98) The longer dwell time in the stretching section resulting from this is advantageous for a wide process window.

(99) As only small little stretching is performed, small drive outputs are sufficient. Individual drives are unnecessary as the film works minimally. It is thus completely sufficient if the holding roll and second roll 32 each are driven, and their speed is adjustable.

(100) As only a low temperature, and thus energy, level must be reached, according to the inventors' prototype tests, a water heating system is completely sufficient.

(101) In the implementation of the layflat unit, the second roll preferably has the same temperature as the first roll. The first roll is used as a heating and holding roll. The second roll is used as a stretching and annealing roll. The section between the second and the subsequent third roll is then an annealing section.

(102) In an MDO embodiment, however, stretching of 1:10 or even more is possible without problems.

(103) The transverse stretching length should be as short as possible in order to reduce transverse contraction, the so-called neck-in.

(104) Process management is clearly more critical because the dwell time in the very short stretch gap is very short.

(105) As more rolls must be temperature-conditioned, there is higher energy expense, and an overall rather long temperature-conditioning path is necessary.

(106) The drives must be quite strong in order to overcome the plastic's yield point and to slightly exceed the flow range.

(107) Individual drives are suggested in order to allow individualized process management.

(108) For simple layflat improvement, an MDO design is actually too big and thus normally, uneconomical.

(109) As MDO requires high temperatures, it is normally proposed that oil heating be used.

(110) In the fifth embodiment variant in FIG. 6, there is also a processing section provided for that lies transversely above the takeoff roll pair; actually a horizontally lying one for four rolls, with a chill roll being arranged further up, and that would allow, above the takeoff roll pair, straight pass-through of the double-layer film web.

(111) Within the horizontally lying roll section, again, two rolls are movable; namely, a second roll pivotable about the first roll, and a fourth roll arranged slideably or pivotably on the other side of virtual plane 14.

(112) Besides, the fifth variant in FIG. 6 can be used just like the variants described above in a blown film line.

(113) The diagram in FIG. 7 has a basic graphical description of the behavior of the films to be processed here.

(114) There, on an X-axis 41, the longitudinal stretching c of the film is entered, while on the Y-axis 42, the longitudinal tension within the film is shown; i.e., a parameter that is proportionate to the longitudinal tensile force within the film. Longitudinal tension is named .

(115) Starting from Zero 43, the film usually behaves in a linear tension increase field 44 as longitudinal stretching c increases. From a certain longitudinal stretching * or the concomitant tension *, the film leaves the range of linear tension increase, and the tension curve becomes flatter; i.e., it has s smaller increase compared to X-axis 41.

(116) Starting from longitudinal stretching *, longitudinal stretching applied is irreversible.

(117) Tension then assumes a first maximum 45. At this point, so-called plastic flow of the film starts. The corresponding longitudinal stretching .sup.Streck is called yield limit. A flow range 46 extends from first maximum 45 of longitudinal tension , called .sub.Streck, up to the area the branch 47 that rises again, where longitudinal tension again reaches tension .sub.Streck.

(118) From there, longitudinal tension steadily increases with increasing longitudinal stretching until there is a sudden failure in the shape of film rupture 48.

(119) From the regaining of tension .sub.Streck to the film rupture extends an MDO working range 49.

(120) In contrast, a layflat unit working range lies in the area beyond the linear tension increase field 44, but below yield limit .sup.Streck. Within the linear tension increase field 44, i.e., up to longitudinal extension in machine direction *, the film's behavior is elastic.

(121) Simply put, the extension in machine direction of a layflat package thus takes place between * and the local maximum. In contrast, the strong stretching in machine direction of an MDO takes place from regaining of .sup.Streck.

(122) In terms of its construction with five rolls, treatment roll path 50 in FIG. 8 corresponds in principle to the second variant from FIG. 2 and the third variant from FIG. 3; has, however, with its first roll 51, its third roll 52, and its fifth roll 53 three combing rolls, while its second roll 54 and its fourth roll 55 are designed to be stationarily rotating.

(123) For threading the double-layer film web at the start of the blowing process, the three combing rolls; i.e., first roll 52, third roll 52 and fifth roll 53, are moved out of their combed-in position; i.e., in FIG. 8 to the left of virtual plane 14, so that double-layer film web can simply be guided from nip 56 of takeoff roll pair 57 vertically upwards to reversing roll 58. Reversing roll 58 is the first roll that lies beyond treatment roll path 50. From reversing roll 58, the double-layer film web is routed transversely to infeed 59 into a reversing unit 60.

(124) During combing-in, first roll 51 cannot only be moved into the plane of the stationary rolls; i.e., second roll 54 and fourth roll 55 (shown in FIG. 8 by means of a first contour 61 of combed-in first roll 51); instead, first roll 51 can even be moved through this plane while combing through, so that the center axis of first roll 51 moves beyond the plane formed by the center axes of second roll 54 and fourth roll 55. Thus, first roll 51 can assume a combed-through position for blowing operation (shown in FIG. 8 by means of a second contour 62 of first roll 51).

(125) Prototype tests have shown that a preferably variable adjustability of the combing-in depth; i.e., in particular with a comb-through depth through the plane of the stationary rolls, can be advantageous for process reliability and the resulting film quality.

(126) Treatment roll path 63 according to the seventh variant in FIG. 9 shows a somewhat different construction:

(127) Above nip roll pairs 64 there is treatment roll path 63 in vertical orientation.

(128) A first roll 65 is designed as a heating roll and simultaneously, as a holding roll. It is movable combingly through virtual plane 14. Combing has already been described above several times. Its advantages and also the option of combing through the plane of stationary rolls shall be assumed to be known now.

(129) A second roll 66 has been provided with a clearly smaller diameter than first roll 65.

(130) Third roll 67 has also been provided with a clearly smaller diameter than first roll 65, preferably as designed here with the same diameter as second roll 66.

(131) Second roll 66 and third roll 67 form a stretching station in which third roll 67 is embodied as combing. Due to the variable adjustability of at least one of the two rolls 66, 67 of the stretching station, the stretching length can be variably adjusted, which has been shown in prototype tests to be very advantageous.

(132) Second roll 66, which constitutes simultaneously a first roll of the stretching station, will preferably be driven at the same circumferential speed as first roll 65; i.e., the big holding roll. With regard to the function of the holding station, second roll 66 would be considered part of the holding station rather than of the stretching station; and namely together with first roll 65. Only with regard to its diameter is it also possible to consider second roll 66 together with third roll 67 as part of the stretching station.

(133) The two small rolls, i.e., second roll 66 and third roll 67, are not heated, but they are driven. This allows designing second roll 66 and third roll 67 to have very small diameters.

(134) However, third roll 67 is driven at a higher circumferential speed than second roll 66. Thus, a stretching section for the double-layer film web forms between second roll 66 and third roll 67.

(135) If it is assumed that at the existing geometric ratios, adhesive friction exists for about 70 of the circumference of the faster-driven third roll 67, the stretching length of the stretching section for large roll diameters is between about 250 mm and 290 mm, and for small roll diameters between about 100 mm and 140 mm; about 15 cm to 19 cm, actually in a prototype test about 17 cm.

(136) The faster-driven third roll 67 is followed in treatment roll path 63 by a first annealing roll 68 and a second annealing roll 69, whereby the latter can also be combingly brought into its operating position.

(137) The two annealing rolls 68, 69 are followed by a chill roll 70whose diameter was slightly increased in the present example. Chill roll 70 has a contact roll 71.

(138) Chill roll 70 together with its contact roll 71 forms the last station of treatment roll path 63. From there, the double-layer film web is routed to the infeed for the reversing unit.

(139) The rolls of treatment roll path 63 are arranged quite tightly together, with a clearance in vertical arrangement of only about 10 mm to 30 mm in order to achieve the lowest possible form factor.

(140) Preferably, several or even all roll surfaces of treatment roll path 63 have a rough, grippy surface, ideally with embedded silicone.

(141) DE 10 2009 033 171 A1 describes the control process as follows, whereby the statements below are to be an integral part of the total disclosure content of the present patent application.

(142) FIG. 10 shows a blown film line 72 with a downstream stretching unit 73 and winder 74. Via a dosing device, the plastic granules to be processed are fed to an extruder 75, in which they are melted, homogenized and fed to die head 76. If multi-layer films are produced, several extruders will be used according to the number of layers. Die head 76 has an annular nozzle from which the extruded plastic mass exits. Cooling air is routed through die head 76 for inflating tube film 77. Once the plastic is frozen, tube film 77 will be laid flat in layflat unit 79 and continuously taken off and laid down with reversing takeoff 80. Then the blocked film is monoaxially stretch in the machine direction in stretching system 73. The film is routed to winder 74 and wound on film rolls.

(143) Controlling the film gauge profile requires detecting the actual film profile, preferably in two locations. The actual gauge profile at the circumference of tube films 77 is detected at measuring device 81 between segmented control unit 78 and reversing takeoff 80, and the actual gauge profile of the stretched film over its width is detected at measuring device 82 between stretching system 73 and winder 74. Measuring device 81 for measuring the actual gauge profile of tube film 77 is preferably arranged at a constant height above die head 76, rotating around the tube film.

(144) The entire film blowing process is controlled by line controller 83, in particular the drives, cooling air, segmented control zone 78, which is located in the cooling ring, in die head 76, or downstream, as well as the takeoff speed of the tube film.

(145) The actual film profiles measured by measuring devices 81 and 82 are routed to line controller 83 and forwarded to segmented control zone 78 by means of target/actuals comparison signals.

(146) In FIG. 11, the line is shown in a top view. It is clearly shown that reversing takeoff 80 performs a reversing movement between 0 and 180 in all directions (see double arrow) and that thus, tube film 77 is not always laid together at the same edges. If the controller did not take this offset into account, the thin spots that have been imprinted into the gauge profile of tube film 77 during the blowing process, would run back and forth across one area of the width of the laid-flat film and would not represent the film edges.

(147) FIG. 12 shows the actual gauge profile of a film tube with two thin spots 85. Such a gauge profile is, e.g., detected by film gauge measuring device 81 between segmented control zone 78 and layflat device 79 in a balanced control state. The two dashed lines 86 indicate the folding edges formed by the two lateral edges of the laid-flat film. The two thin spots 85 form the two marginal areas when the film is routed to stretching device 73 as a blocked tube.

(148) In another implementation case of this disclosure that has already been described, the blown and laid-flat film tube is slit open at these two positions 86, and then the two flat film webs are each fed to a separate stretching device 73. Here too, the two thinner spots; i.e., one half each of the thin spots 85 shown in FIG. 12, form the marginal areas of the film routed to stretching device 73.

(149) FIG. 13 shows the actual gauge profile of the film tube with only one thin spot 85, as it is used in a third implementation of the disclosure. The film tube is only slit open in one location 86 in the area of thin spot 85. The slit tube is then folded open as a flat web and routed to stretching device 73. Here too, half each of the thin spot 85 can be found again as the marginal area of the film routed to the stretching device.