Cooling device, use of a cooling device and blown film system

Abstract

Cooling device for a film on a blown film system, comprising a first and a second supply device for cooling fluid to the film and a discharge device for the cooling fluid which exerts a suction force on the cooling fluid, characterized in that the discharge device is a longitudinal distributor for distributing the suction force along the longitudinal extent of the rising film.

Description

[0001] The invention relates to a cooling device for a film in a blown film plant, the use of such a cooling device and a blown film plant.

[0002] Blown film lines are often equipped with cooling rings or double cooling rings to increase throughput. Between the first and second cooling rings, the melt is already drawn out to a certain ratio. This means that the melt can be more easily cooled at the upper cooling ring due to its reduced thickness.

[0003] More than two cooling rings can easily be used.

[0004] DE 32 41 192 C2 describes a blown film system with a first cooling ring, which is arranged downstream directly after a nozzle, a second cooling ring, which is arranged shortly before the calibration and an optional iris diaphragm arranged in between, which is intended to prevent fluttering of the film tube.

[0005] DE 44 05 463 A1 discloses a blown film system in which the film tube is blown with a very dry and very cold cooling air stream. In the blown-in area, the tube is shielded from the ambient air. The cooling air is then extracted from the shielded area, cooled again, and fed back into the cooling ring. With the existing cooling ring and the shielded area, an energy-saving circuit is created, allowing the cooling air to be easily kept below 0°C.

[0006] Another blown film system is known, for example, from DE 34 36 881 A1.

[0007] EP 0 958 910 A1 describes a device for improving process control in blown film production. For this purpose, the film's product parameters are measured and controlled by controlling influencing variables along the film production line depending on the measured values.

[0008] US 2005 0 285 315 A1 discloses a process for producing a thermoplastic blown film. The outer surface of the film tube is treated with a cooling gas to solidify the film tube. This cooling gas is drawn through a suction ring positioned before the film tube is folded into a double-layer web.

[0009] US Pat. No. 3,888,609 A describes a process for producing polymer films. The process involves extruding a polymer film, treating the film's surface with a solution to improve adhesion and surface quality. This solution is applied to the film's surface using a coating mechanism. The resulting product exhibits an optimized surface finish.

[0010] JP S59-7 019 A describes a method for producing composite materials. The process involves layering different materials to create the composite product. The application of an adhesive layer ensures a bond between the individual layers.

[0011] JP S54-29 370 A describes a process for producing thermoplastic molded parts. The process involves shaping thermoplastic materials using a molding process that offers control over the cooling and forming phases. Temperature control is intended to improve the dimensional stability and surface quality of the molded part.

[0012] The object of the invention is to enable improved cooling.

[0013] This object is achieved by a cooling device having the features of the main claim as well as by a use and a blown film system having the features of the independent claims.

[0014] Advantageous optional features can be found in the dependently formulated patent claims.

[0015] The invention is based on the surprising finding that the air flow at the lower cooling ring is limited according to the prior art because a large portion of the air from this cooling ring is also forced through the inlet area of ​​the second, upper cooling ring. This leads to an increase in the radial distance of the melt from the upper, second cooling ring, thus potentially causing bubble instabilities and resulting in only slight increases in throughput compared to a system with a single cooling ring.

[0016] There are, of course, systems in the state of the art that incorporate an extraction system in the form of a circular slot in the upper, second cooling ring. In terms of design, a ring similar to a cooling ring is usually used, except that it is equipped with an extraction system instead of an air supply. However, the extraction capacity of such a ring is very limited, since the suction force not only acts on the cooling fluid, usually air, but also draws in the melt. Furthermore, such an arrangement is associated with high costs, even when two or more cooling rings are already present.

[0017] The present invention takes the suction force acting on the film into account. This cannot be avoided anyway. However, by distributing the suction force over a larger area along the rising melt, with a suitable design, critical radial expansion due to the suction of the film does not occur.

[0018] Numerous structural designs are possible for the longitudinal distributor: For example, it is conceivable to provide one or more fluid discharge devices in the area between the first and second cooling rings, generally between two supply devices for the cooling fluid, with these devices acting at different points along the longitudinal extent of the rising melt. By distributing the total fluid discharge capacity across several discrete points and / or longer distances, a single discharge device is still preferably provided, in accordance with the wording of the patent claim, but with separate discharge points. A seal may also be provided.

[0019] In a simple embodiment of this idea, hose nozzles can be connected to a pump, in particular a suction pump, and the hose nozzles can be arranged at different points in the longitudinal course of the rising melt between the two or more cooling rings.

[0020] Another idea for the design of a longitudinal distributor is that the area between two supply devices, in particular between two cooling rings, is sealed from the ambient air at least over a certain length, and the fluid is extracted from this seal. By widening the sealed space relative to the actual discharge line, the extraction force acting through one or more suction nozzles is distributed more or less evenly across the sealed area, significantly reducing the local force acting on the melt.

[0021] Ideally, when implementing this design concept, the space between the two cooling rings is completely sealed as airtight as possible. For example, a bellows can be attached.

[0022] It goes without saying that the technically optimal seal does not have to be achieved. For example, a gap remains between the cooling device and the melt on one side and the environment on the other.

[0023] One or more air outlets are connected to one or more fans around the perimeter of the seal.

[0024] Ideally, the air outlets are installed in the lower area of ​​the seal, i.e. closer to the first, upstream cooling ring.

[0025] Preferably, the power of the connected fan is coupled with the fan of the lower, first cooling ring.

Claims

[1] Cooling device for a film on a blown film line, with a first and a second supply device for cooling fluid to the film and with a discharge device for the cooling fluid, which exerts a suction force on the cooling fluid, characterized by that the discharge device is a longitudinal distributor for distributing the suction force along the longitudinal extent of the ascending film. [2] Cooling device according to claim 1, characterized by that the first and / or the second feed device have a cooling ring. [3] Cooling device according to claim 1 or 2, characterized by that a seal is provided in an area between the first and the second feed device. [4] Cooling device according to one of the preceding claims, characterized by that the discharge device is arranged to act essentially on cooling fluid from the first supply device, which is arranged upstream of the second supply device. [5] Cooling device according to one of the preceding claims, characterized by that the first feed device is mounted directly above a nozzle. [6] Cooling device according to one of the preceding claims, characterized by that a distance between the feeding devices can be adjusted. [7] Cooling device according to one of the preceding claims, characterized by that the longitudinal distributor has a fluid outlet at or near the first feed device. [8] Cooling device according to one of the preceding claims, characterized by that the longitudinal distributor has a fluid outlet between the first and the second feed device. [9] Cooling device according to one of the preceding claims, characterized by that the discharge device has a nozzle. [10] Cooling device according to one of the preceding claims, characterized by that the discharge device discharges the cooling fluid rotationally symmetrically. [11] Cooling device according to claim 5, characterized by that a guide device is mounted rotationally symmetrically around the nozzle for the targeted guidance of a fluid flow delivered by the first feed device. [12] Cooling device according to one of the preceding claims, characterized by that a quantity of the cooling fluid supplied via the first supply device and its removal are coupled. [13] Cooling device according to one of the preceding claims, characterized by that more fluid is discharged than is supplied by the first supply device. [14] Cooling device according to one of claims 1 to 12, characterized by that less fluid is discharged than is supplied by the first supply device. [15] Cooling device according to one of the preceding claims, characterized by that a closed circuit is provided for the cooling fluid of the first supply device. [16] Cooling device according to one of the preceding claims, characterized by that the cooling fluid comprises or is air, moist air in the form of an aerosol, nitrogen or another cold gas. [17] Use of a cooling device according to one of claims 1 to 16 in combination with an internal heat sink. [18] Blown film plant with a cooling device according to one of claims 1 to 16. [19] Blown film plant according to claim 18 and with an extruded film, wherein the discharge device has a distance from the film of at least 50 mm, preferably of more than 100 mm, especially of at least 250 mm. [20] Blown film plant according to claim 18 or 19 with an extruded film, wherein the discharge device has a distance from the film of at most 2500 mm, preferably of at most 2000 mm, in particular of at most 1000 mm, especially of at most 500 mm.