METHOD AND DEVICE FOR THE PRODUCTION OF A PLASTIC FOIL

Abstract

A method and device for producing of a plastic foil especially a multi-layer stretch film, at which plastic material is extruded from a flat extrusion die and subsequently guided around a cooling roll following in the conveying direction and cooled. The foil is guided between the flat extrusion die and the cooling roll around a temperature controlling roll along a given angle of contact. The temperature controlling roll has a center region and two edge regions. The foil is kept at least in sections at a distance from the temperature controlling roll in the center region by creating an air cushion in the center region between the surface of the temperature controlling roll and the foil by supplying heated air between the surface of the temperature controlling roll and the foil in the center region. The foil is brought into contact with the temperature controlling roll in the edge regions.

Claims

1. A method for the production of a plastic foil, especially of a multi-layer stretch film, at which plastic material is extruded from a flat extrusion die and is subsequently guided around at least one cooling roll following in the conveying direction and is cooled thereby, wherein the foil is guided between the flat extrusion die and the cooling roll around a temperature controlling roll along a given angle of contact, wherein the temperature controlling roll has a center region and two edge regions adjoining to the same, wherein the foil is kept at least in sections at a distance from the temperature controlling roll in the center region by creating an air cushion in the center region of the temperature controlling roll between the surface of the temperature controlling roll and the foil by supplying heated air between the surface of the temperature controlling roll and the foil in the center region of the temperature controlling roll, wherein the foil is brought into contact with the temperature controlling roll in the edge regions.

2. The method according to claim 1, wherein in a region which extends along the width of the foil and from the side of the foil which is averted from the temperature controlling roll up to the cooling roll a vacuum against the ambient pressure is created, wherein the vacuum is created especially in the region from the lift off of the foil from the temperature controlling roll up to the contact of the foil with the cooling roll along the width of the foil.

3. The method according to claim 1, wherein the temperature of the pressurized air at its supply into the temperature controlling roll is between 60 C. and 350 C., preferably between 100 C. and 250 C.

4. The method according to claim 3, wherein the contact between the foil and the temperature controlling roll is created by electrostatic forces and/or that the contact between the foil and the temperature controlling roll is created by applying of an airstream onto the foil, wherein the contact between the foil and the temperature controlling roll is preferably limited to the edges of the foil.

6. The method according to claim 1, wherein the creation of the air cushion takes place by supplying the heated pressurized air through a porous material of the temperature controlling roll in the center region of the temperature controlling roll between the surface of the temperature controlling roll and the foil.

6. The method according to claim 1, wherein the temperature of the heated air is above of the Vicat softening temperature of the material of the foil, especially of an undercoating of the foil (1).

7. The method according to claim 1, wherein the temperature controlling roll is kept on a higher temperature in the center region than in the edge regions, wherein the temperature in the edge regions is preferably kept between 10 C. and 95 C.

8. The method according to claim 1, wherein the foil is conveyed with speed of at least 400 m/min, preferably of at least 750 m/min and specifically preferred with at least 900 m/min from the cooling roll.

9. The method according to claim 1, wherein the foil is free from further laminated layers and as applied onto the temperature controlling roll is conveyed from the cooling roll.

10. A device for the production of a plastic foil, especially of a multi-layer stretch film, comprising a flat extrusion die by which plastic material can be output and at least one cooling roll following subsequently in the conveying direction for cooling the foil, wherein a temperature controlling roll is arranged between the flat extrusion die and the cooling roll and around which the foil can be guided along a given angle of contact, wherein the temperature controlling roll has a center region and two edge regions adjoining to the same, wherein the regions are formed by separate roll parts which follow in axial direction to another, wherein the temperature controlling roll consists in the center region at least in sections and at least partially from a porous material which is connected with at least one conduit for the supply of air into the porous material to create an air cushion between the foil and the center region and wherein means are arranged in the edge regions for creation of a contact between the foil and the temperature controlling roll.

11. A device according to claim 10, wherein means for creation of a vacuum are provided in a region which extends along the width of the foil and from the side of the foil which is averted from the temperature controlling roll up to the cooling roll.

12. A device according to claim 10, wherein in the edge regions means are arranged for creation of an electrostatic field and/or means for applying of an airstream onto the foil.

13. A device according to claim 10, wherein the temperature controlling roll consists in the center region and also in both edge regions of rotationally symmetric parts which each are connected with an electromotive drive to drive at the one hand the rotationally symmetric part of the center region and at the other hand the rotationally symmetric parts of both edge regions with individual rotational speed.

14. A device according to claim 10, wherein the temperature controlling roll consist of rotationally symmetric parts in both edge regions which each are connected with an electromotive drive, wherein the part of the temperature controlling roll which forms the center region is arranged in a non-rotatable manner.

15. A device according to claim 14, wherein the center region is formed by a non rotationally symmetric part.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0051] In the drawing:

[0052] FIG. 1 shows in the side view a device for the production of a multi-layer plastic foil and

[0053] FIG. 2 shows in the front view a part of the device according to FIG. 1 in which additionally the attaching of the foil which has to be produced at a temperature controlling roll is shown.

DETAILED DESCRIPTION OF THE INVENTION

[0054] In the figures a device is shown by which a multi-layer stretch film 1 can be produced. For doing so plastic melt which is already prepared as a multi-layer laminate is extruded via an outlet of a flat extrusion die 2 so that a foil with a certain width is provided. From the outlet of the flat extrusion die 2 the foil is applied onto a temperature controlling roll 4 which functions as a relaxation device. The foil 1 enlaces thereby the temperature controlling roll 4 around an angle of contact . From the temperature controlling roll 4 the foil 1 reaches a cooling roll 3 from which the cooled foil is taken off by an lifting roll 10 from the cooling roll 3 and is further conveyed (in conveying direction F).

[0055] To make sure that between foil 1 and cooling roll 3 at the explained guidance of the foil no air gets around the cooling roll 3 means 6 are provided for the creation of a vacuum (vacuum box) which apply at the outer surface of the foil 1 in the region of the temperature controlling roll 4 and end at the outer circumference of the cooling roll 3. From this region air is evacuated what is indicated in FIG. 1 by the arrow at the means 6.

[0056] To make sure that the foil 1 at its cooling by means of the cooling roll 3 contacts the same well it is pressed and drawn respectively to the cooling roll in its both edge regions by means 9 for creation of a contact between the foil 1 and the cooling roll 3. This can take by means of an airstream or by means of electrostatic charging.

[0057] Between the discharge of the foil 1 from the flat extrusion die 2 and the means 6 for the creation of a vacuum an infrared heater 11 is arranged to make sure additionally that the foil 1 can be kept at a desired temperature.

[0058] In FIG. 2 details of the embodiment of the temperature controlling roll 4 are depicted whereby the same comprises a center region M as well as two lateral edge regions R. The center region M is formed by a surface made of porous material which is in connection with a conduit 8 for the introduction of air (see arrow in FIG. 2 in the region of the reference numeral 8). However in the two edge regions R of the temperature controlling roll 4 means 7 are provided for the creation of a contact between the foil 1 and the temperature controlling roll 4 which are realized preferably by an airstream or by means for the creation of an electrostatic charging. Accordingly air is supplied via the conduit 8 and discharged via the porous material in the center region M of the temperature controlling roll 4 so that an air cushion 5 is created between the surface of the temperature controlling roll 4 in its center region and the foil 1 which keeps the foil 1 away from the temperature controlling roll 4. This is schematically shown in FIG. 2, wherein this is shown in the figure pivoted from the actual contact plane between foil 1 and temperature controlling roll 4.

[0059] The air which is supplied via the conduit 8 to the temperature controlling roll is thereby heated by suitable means (e. g. by means of an industrial blow dryer) in such a manner that the air cushion 5 has a respective high temperature to maintain the above-mentioned process conditions.

[0060] of the flat extrusion die 2 and is casted with short distance onto the below arranged relaxation device in the form of the temperature controlling roll 4. The foil curtain is fixed in the edge region R on the rotating roll body of the temperature controlling roll 4 by means of edge strip electrodes which are working according to the principle of the electrostatic charging. The center region M of the temperature controlling roll 4 has a micro-porous surface from which air is leaving which is introduced via the conduit 8; thereby the air cushion 5 is formed on which the casted foil 1 can slide without damage. The casted foil 1 enlaces the temperature controlling roll 4 along an angle of contact a which is about 120 in the embodiment and is then with short distance transferred to the below arranged cooling roll 3. The foil 1 is fixed again at the cooling roll 3 with edge fixation means 9 (electrostatic charging electrodes or airstream).

[0061] To prevent an air entry between foil 1 and surface of the cooling roll 3 the exit of the vacuum box 6 is arranged in the gap between the temperature controlling roll 4 and the cooling roll 3 and so a vacuum is created in that region.

[0062] To utilize the cooling length of the cooling roll 3 as far as possible the cooling roll 3 is enlaced by the foil as far as possible, namely in the embodiment till the lifting roll 10 which is arranged immediately adjacent to the mentioned vacuum box 5.

[0063] The air which leaves the porous ceramic of the center region M of the temperature controlling roll 4 forms, as explained, the air cushion 5 on which the foil 1 can slide. Thereby the air which is introduced for the creation of the air cushion 5 is heated, namely up to the above mentioned values. Thereby the temperature of the air which is introduced via the conduit 8 for creating the air cushion 5 can also be selected higher than the melt temperature of the adjacent polymer. Due to the so increased temperature of the air which forms the air cushion 5 the foil 1 over the air cushion 5 is cooled only very slowly or not cooled at all.

[0064] As the case may be, the average foil temperature can thereby be kept above the Vicat temperature so that it does not completely solidify but allows a continued relaxation of the foil structure with high relaxation speed.

[0065] Without the proposed measures the danger would be given that the foil 1 sticks together with the surface of the temperature controlling roll 4 in its center region M. This is prevented by the air which is introduced via the conduit 8 and thus by the so created air cushion 5. The air cushion 5 prevents as well that the porous surface of the center region M of the temperature controlling roll 4 is polluted.

[0066] The edge regions R of the temperature controlling roll 4 correspond with their diameter to the curvature of the center region M which is enlaced by the foil. The edge regions R can also be tempered, wherein here a temperature range between 10 C. and 95 C. is provided. The temperature is here chosen in such a manner that the foil 1 cools down so far that stable foil strips are created in the region of the foil edges between which the center region of the foil 1 which hovers on the air cushion 5 is quasi clamped and is so drawn forward by the edges. The edge regions of the foil which are insofar stabilized thus stable the transport of the center region of the foil 1.

[0067] The temperature controlling roll 4 is driven by an electric motor. The circumferential speed of the temperature controlling roll is thereby preferably 0.5 to 1.0 times of the circumferential speed of the cooling roll 3. The speed is thereby adjusted in just a manner that at the one hand the neck-in of the foil 1 is reduced and but at the other hand the section which hovers over the air cushion 5 does not advance or stays back.

[0068] For the discharge of the hot air from the center region of the temperature controlling roll an air shield can be provided.

[0069] The selection of the temperature of the air cushion depends on the present layers of the foil. If for example PET is present as layer in the foil the melting point of this layer is significantly higher. In this case the air temperature can even be increased above the melting temperature of the cling material of the foil. Despite of this no danger is given that the foil ruptures.

[0070] A high temperature in the center region of the temperature controlling roll is very beneficial with respect to the relaxation and also with regard to the surface quality of the foil when the same contacts the cooling roll.

[0071] Due to the three-part design of the temperature controlling roll (three parts which follow in axial direction subsequently) it becomes possible in a simple manner to carry out a fixation of the edge strip and so to prevent the neck-in of the foil. Apart from this it is reached by the created air cushion that the foil in the center region of the temperature controlling roll slides and hovers respectively on the surface of the roll.

[0072] It can be provided by the proposed method that sufficient time as well as an optimal temperature is given for the relaxation, wherein it is also taken care that an optimized guidance of the foil is given and the same is also guided in a stable manner at high production speeds.

[0073] In this connection it is beneficial if at the one hand the edge regions of the temperature controlling roll and at the other hand the center region of the same are driven independently from another, i. e. with the possibility of different rotational speeds. With the separate drive the possibility is given to rotate the center region faster than the edge parts of the roll and so to create a drag effect.

[0074] By the heated air for creating the air cushion which compensates the cooling of the foil the beneficial possibility is given to keep the relaxation way large by choosing the diameter of the temperature controlling roll correspondingly. However always a stable foil guidance is given.

[0075] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCES

[0076] 1 Plastic foil (multi-layer stretch film) [0077] 2 Flat extrusion die with nozzle outlet [0078] 3 Cooling roll [0079] 4 Temperature controlling roll (relaxation device) [0080] 5 Air cushion [0081] 6 Means for creation of a vacuum (vacuum box) [0082] 7 Means for creation of a contact between the foil and the temperature controlling roll [0083] 8 Conduit for the supply of air [0084] 9 Means for creation of a contact between the foil and the cooling roll [0085] 10 Lifting roll [0086] 11 Infrared heater [0087] M Center region of the temperature controlling roll (made of porous material) [0088] R Edge region of the temperature controlling roll (driven rotating roll body) [0089] F Conveying direction [0090] Angle of contact