Coextrusion apparatus, single-layer extrusion apparatus and retrofit kit as well as a method for measuring a layer thickness, for producing a plastic film, and for retrofitting an extrusion apparatus

Abstract

A coextrusion apparatus, a single-layer extrusion apparatus, a retrofit kit, as well as to a method for measuring a layer thickness, for producing a plastic film, and for retrofitting an extrusion apparatus. From the state of the art, it is known to add a detection agent in the form of a fluorescent granulate into the starting material at the extruder, in order to be able to measure the layer thickness of the layer in the film composite produced from this starting material. However, it is proposed to feed in a detection agent only beyond the extruder. This leads to a clearly shorter running time of the detection agent through the system and thereby to clearly faster measurability of changes in the production parameters.

Claims

1. A method for measuring a layer thickness of a plastic film in an extrusion apparatus having an extruder, comprising: adding a detection agent to extruded starting material on the way from the extruder to an extrusion tool; and measuring the layer thickness in contact-free manner, using the detection agent, beyond the extrusion tool, wherein two separate channels in a feed from the extruder to the extrusion tool are treated differently when the detection agent is added, and wherein the adding the detection agent is varied by turning addition of detection agent on and off or by switching the addition from one to another of the separate channels of the feed of a starting material.

2. The method according to claim 1, wherein the detection agent is supplied to only one of two separate channels of the same starting material.

3. The method according to claim 1, wherein different detection agents are added into feeds from different extruders and/or into separate channels of the same starting material.

4. The method according to claim 1, further comprising: providing measured results to a controller by a detection device, whereupon the controller acts on an electronic or mechanical setting element of a layer thickness influencing unit in order to achieve regulation of a layer thickness, so that the layer thickness is regulated to be thinner if the measured results lie above a predetermined reference value, and regulated to be thicker if the measured results lie below the reference value.

5. A method for producing a plastic film, using the method according to claim 1, wherein regulation of layer thicknesses of the film takes place on the basis of measured results obtained.

6. The method according to claim 5, wherein a plurality of detection agent additional devices and/or a plurality of addition units are connected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

(2) The single FIGURE shows, in a rough schematic, a system, thereby an apparatus, for producing a five-layer plastic film in a symmetrical composite, having a central layer, two inner outside layers, and two outer outside layers, supplied by three extruders.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(3) The system 1 in the FIGURE essentially consists of a first extruder 2, a second extruder 3, and a third extruder 4, each having a filling funnel 5 (indicated as an example), as well as, connected to this, a feed 6 to an extrusion tool (not shown), for example a broad-slit die, in the form of a coextrusion block.

(4) The system 1 produces a plastic film composite 7. The plastic film composite 7 consists of the central layer 8, two inner outside layers 9, 10, as well as two outer outside layers 11, 12.

(5) Precisely one extruder, namely the first extruder 2, supplies plastic melt (not shown) to the central layer 8 through the feed block.

(6) The second extruder 3 and the third extruder 4 each have a division 13 (numbered as an example) in their feed 6, starting from which the melt coming from the respective extruder is passed to the two related layers through two separate channels 14, 15, therefore, in the case of the second extruder 3, to the first inner outside layer 9 and to the second inner outside layer 10.

(7) If the layer thicknesses of the film composite 7 produced is now determined by means of white-light interferometry, then according to the state of the art, which feeds the particles into the funnels 5, only the thickness of the central layer 8 can be reliably determined. The two inner outside layers 9, 10, in contrast, just like the two outer outside layers 11, 12, can only be determined in total. If one of the two actually symmetrical layer halves deviates downward from the reference value, in each instance, but at the same time the other one deviates upward from the reference value, the sum of the measured layer thickness will not necessarily change. Therefore, it is not possible to definitely conclude from the measured values determined that a symmetrical film composite continues to be produced.

(8) According to the invention proposed here, in contrast, particles or another detection agent can be introduced differently into the separate channels 14, 15 of the feed of an extruder, here, in other words, of the second extruder 3, but also or instead, for example, of the third extruder 4, in other words differently in terms of time, differently in terms of amount and/or with a different detection agent. In this way, it becomes possible to individually measure the individual layer 9, 10 or 11, 12 with regard to their layer thicknesses.

(9) Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.

(10) REFERENCE SYMBOL LIST:

(11) 1 system 2 first extruder 3 second extruder 4 third extruder 5 filling funnel 6 feed 7 plastic film composite 8 central layer 9 inner outside layer on the one side 10 inner outside layer on the other side 11 outer outside layer on the one side 12 outer outside layer on the other side 13 division 14 separate channel on the one side 15 separate channel on the other side 16 machine direction and extrusion direction