DE19802646C1 - Multilayer plastic strip manufacture with low thickness variation across width by combining streams for outer layers before they are widened for combining with central layer - Google Patents

Abstract

Melt for a central layer (62) flows initially through a narrow feed channel (13) of a multichannel die (6) and is then spread out in a broad distribution channel (15). At a point beyond this channel in the flow direction further layers (60,61,63) flow onto the upper and lower sides of the middle layer with at least two on one side, both of which were fed together in a narrow channel (9) before reaching a separate distribution channel (11).

Description

The invention relates to a method for producing a multilayer web made of thermoplastic materials, at for which a melt for a middle layer first flows through a narrow inflow channel before it is then in one the inflow channel adjoining distribution channel is distributed over a larger width, and one in the flow direction the melt behind this distribution channel position further layers on the top and bottom of the middle Layer flow in, with at least on one side of the middle layer flow in at least two layers that were previously merged into a narrow channel and only then together in a separate, adjacent channel separate distribution channel have been distributed.

Similar processes are from W. Michaeli, extrusion tools for plastics and rubber, 2nd edition, Carl Hanser Verlag, Munich, Vienna; Page 220, Figure 6.4 and from F. Hensen, W. Knappe, H. Potente, Handbuch der Kunststoff- Extrusion Technology, Volume II Extrusion Systems, Carl Hanser Verlag Munich, Vienna; Page 162, Figure 36, and from DE-OS 16 29 360 and EP 02 99 736 A1 known.

With these known arrangements, the layers located in the interior of the web can be connected to the adapter be fed, do not achieve a particularly good layer thickness consistency across the width of the individual layers, since the layers merged via the adapter on the relatively small width of the inflow channel into the Multi-channel tools are fed in and only in the distribution channel of the multi-channel tool to the final width of the web be distributed. With this distribution, the layer thicknesses of the individual layers usually inevitably change not exactly predictable. For this reason, the geometry required is very narrow Flow channels in the adapter are still primarily determined and optimized empirically. Here is the low ratio between the flow channel width in the adapter and the web width is usually particularly problematic in practice. Based on these technical conditions, the layer thickness tolerances that are not so good can be achieved using the adapter, as if the layer was fed directly into the multi-channel tool and only then distributed individually over the final width, before being combined with further layers to their full readiness.

Now there are many multi-layered webs on the market, in which middle layers consist of expensive raw materials. For example, multi-layer packaging films usually consist of very expensive EVOH Barrier layer and the likewise expensive adhesion-promoting layers as a rule inside the layer structure. For One must therefore strive to increase the economic efficiency, the thickness variations present in these layers to keep it as small as possible. In the state of the art, however, it is precisely these inner layers that are covered by a Multi-channel tool upstream adapter on a relatively small width under unfavorable geometric conditions united and only then distributed together in the multi-channel mold over the full exit width. The invention lies hence the task of designing a method of the generic type in such a way that especially in middle layers a smaller layer thickness variation across the width of the web can be achieved.

This object is achieved in that at least one inner layer, which is additionally below two layers combined via the adapter, directly into the multi-channel tool via the conveyor unit is fed in and then distributed to the exit width in its own distribution channel and only then with it full width flows together with the layers combined via the adapter. This will open up the possibilities of  Reduction of melt flow differences across the web width of critical layers located inside the web are significantly improved, on the one hand, the determination of a uniform local melt flow above the the entire width of the runner geometry required on the full width of the outlet Flow channel can be done more sensitively, and on the other hand no subsequent spreading of the combined Melt strand must be done. With this procedure, significantly more control elements can be used if required Use homogenization of the melt flow across the width, since a larger width is available than in the adapter stands. It is also advantageous that the location at which a change in the flow channel geometry must be made can be easily assigned to the associated location on the web, since no subsequent stretching of the web more done.

If you feed the layer through an upstream adapter, you always have the problem that the Melt flow on a very small flow channel width, as it must be present in the adapter, and that this setting then by the distribution of the combined melt flow in the distribution channel of the Multi-channel tool is still changed. In the case of webs with a very large number of layers, it can also make sense as in claim 2 proposed to connect two adapters to the multi-channel tool, in which the inner layers are combined, with which the outer layers are brought together. It can often be advantageous to have several feed inner layers directly into the multi-channel tool, or according to claim 4 further adapters Upstream multi-channel tool.

One achieves particularly good thickness tolerances of individual layers if, according to claim 5, they are wider than the width Layers of adjusting elements integrated in the tool or in the adapter, with which the flow channel geometry is added can change the current process locally. The adjustment is most effective if, according to claim 6 Flow channel geometry can be freely changed from the outside over its entire width exactly over the confluence area. The Greatest operational safety and also the smallest thickness tolerances are in a method according to claim 7 or 8 achieve, in which the control elements are automatically controlled by a controller and thus the single layer thickness to one constant value.

The invention is based on the following description of individual process arrangements and of the drawings, explained in more detail.

It shows

Fig. 1 A process arrangement according to the invention

Fig. 2 is a sectional view AA of Fig. 1

Fig. 3 is a sectional view BB of FIG. 1

Fig. 4 A process arrangement with two adapters upstream of the multi-channel tool

Fig. 5 shows a process arrangement in which the flow channel geometry can be adjusted either manually or automatically during the process from the outside via single disposed over the width of the respective flow channel Stellelmente.

As can be seen in FIG. 1, in the process for the production of multilayer webs, the melts for the layers 60-63 are conveyed through conveyors 1-4 , such as, for. B. via extruders or gear pumps, fed into the adapter 5 or the multi-channel tool 6 , the adapter 5 being flanged directly to the multi-channel tool 6 . The adapter 5 has two inflow channels 7 and 8 , into which the melts for the layers 60 and 61 , which unite in the region E, are fed and an outflow channel 9 . The melts for the layers 60 and 61 flow together from the adapter 5 into the inflow channel 10 of the multi-channel tool 6 , which generally has the same width as the outflow channel 9 of the adapter 5 . Then the melts for the layers 60 and 61 reach the distribution channel 11 , where they are distributed together over the exit width. The distribution channel 11 is followed by a further flow channel piece 12 , which leads the melts 60 and 61 to the merging area F, where they are used for the layers 62 and 63 , each separately, using the melts fed directly into the multi-channel tool 6 via the extruders 3 and 4 are fed into the multi-channel tool 6 via the inflow channels 13 and 14 and are distributed over the outlet width in the distributor channels 15 and 16 . Then all the melts fed in by the extruders 1-4 for the layers 60-63 flow together out of the multi-channel tool 6 through the outflow channel 17 . The melt web 20 , consisting of the individual melts for the layers 60-63 fed in by the extruders 1-4 , is finally pulled out of the mold, calibrated and cooled via cooled smoothing and take-off rolls 18 and 19 .

From FIGS. 2 and 3, it is clear that the area E in the adapter 5 in which the fed from the extruders 1 and 2 melts are combined for the layers 60 and 61 is significantly narrower than the region F in the multi-channel tool 6 , in which the melts for the layers 62 and 63 from the extruders 3 and 4 flow towards the already co-flowing melts for the layers 60 and 61 from the extruders 1 and 2 . It is therefore understandable that influencing the local mass flow across the width of the flow channel by means of a change in the flow channel geometry before or in area E is much more difficult to achieve than in the much wider channel area 12 or in the union area F. So if you have layers, for which one strives for the smallest possible variation in thickness for technical or economic reasons, it is advisable not to feed these layers into the adapter 5 , but rather directly into the multi-channel tool 6 according to FIG. 1.

Of course, an additional adapter 21 , as shown in FIG. 4, can also feed a further layers 64 into the multi-channel tool. In principle, more than two adapters can also be flanged to the multi-channel tool 6 . Likewise, this method can of course not only be used to produce webs made of thermoplastic plastics, but also webs made of other materials that are flowable under certain conditions.

Since it is still not possible to precisely calculate the flow channel geometries required for a uniform melt flow across the width of all layers, it is advantageous to choose a method according to FIG. 5 in which at least one flow channel geometry is used while the system is running can adjust outside. In Fig. 5 is a process diagram is shown for preparing a 7-layer web by way of example. The individual melts are fed via feed units 22-28 into the multi-channel tool 29 or into the two adapters 30 and 31 . According to the invention, the melts which are in the middle of the finished multilayered web are each fed separately into the multi-channel tool 29 via inflow channels 32-34 . They are then distributed from the small inflow width to the outlet width in separate distributor channels 35-37 before they flow together in the areas H and I over the entire width. In the adapters 30 and 31 , the respective melts for the cover layers from the conveying units 22 and 23 , as well as 27 and 28 flow together directly on the small flow channel width of the adapters 30 and 31 in the areas J and K. They then flow together into the narrow inflow channels 39 and 40 into the multi-channel tool 29 and are distributed there together in the distributor channels 41 and 42 over the exit width before they are placed in the area L on the already combined melts from the extruders 24 , 25 and 26 become. The then seven-layer web is pulled out of the multi-channel tool 29 via calibrated smoothing and take-off rollers 43 and 44 , calibrated and cooled.

In the method according to FIG. 5, particularly narrow thickness tolerances can now be achieved if the flow channel geometry of individual layers in the multi-channel tool 29 or in one of the adapters 30 or 31 is designed to be changeable in some areas. This can be achieved by e.g. B. welded flexibly deformable spring steel sheets 45-47 into the flow channels or incorporates other deformable elements which can be adjusted from outside via adjusting elements 48-50 , such as adjusting screws, in order to locally change the melt flow across the width. These adjustment areas can be arranged in front of the confluence areas H and I as in the case of the spring steel sheet 46 or even more advantageously directly in the confluence areas H and I as in the case of the spring steel sheets 38 and 47 . The latter has the advantage that the melt flow can be influenced exactly on the line at which the melts flow together. You can then z. B. in the confluence area H also the width with which the melt fed by the extruder 25 is placed on the melt fed by the extruder 24 , change from the outside when the flow channel in the area H is completely closed in its two peripheral areas with the help of the adjusting elements 50 . This is particularly necessary if the melts fed in by the extruders 24 and 25 have different viscosities.

Of course, it can also be advantageous, as shown in FIG. 5, to make the flow channel adjustable in the areas J and K in the adapters 30 and 31 from the outside in the same way. However, this setting cannot be as sensitive, because the adapters 30 and 31 have the problem already described that the flow channels 56 and 57 are very narrow, and therefore the influence cannot be as sensitive as in the multi-channel tool 29 , in which the full exit width is available for adjustment.

The optimum in layer thickness constancy and in operational reliability can, however, be achieved if, according to the invention, the thickness of at least one of the individual layers fed in with the extruders 22-28 is regulated. For this, z. B. the thickness of the melt fed with the conveyor unit 22 or 24 , measured with a thickness measuring system 51 , which is mounted, for example, on a cross member 52 and traversing the thickness values, selectively across the width of the webs and feeding them to a controller 53 . The controller then makes a target / actual value comparison and calculates correction values for the local flow channel geometry below the adjusting screws 48 and 49 in the area of the spring steel sheets 45 and 46 , which it passes on to actuatable actuators 54 and 55 , which then corrects the local flow channel geometry in areas M and J. Suitable actuators are, for example, geared motors, thermal expansion bolts, piezotranslators or similar systems. Of course, other layers in this form can also be regulated in their mass flow distribution over the width of the respective flow channel.

With the described methods according to the invention, compared to the prior art during production multilayered webs significantly reduced layer thickness tolerances can be achieved. In practice, this leads to a lower material consumption and therefore more economical production of multilayered webs.

Claims (8)

1. A method for producing a multilayered web of thermoplastic material in which a melt for a middle layer first flows through a narrow inflow channel before it then joins the inflow channel Subsequent distribution channel is distributed over a larger width, and one in the direction of flow of the melt behind this distribution channel position further layers on the top and bottom of the middle layer flow in, with at least one side of the middle layer flowing in at least two layers that were previously in merged into a narrow channel and only then together in their own, separate distribution channel have been distributed. 2. A method for producing a multilayered web according to claim 1, characterized in that on both At least two layers flow to the sides of the middle layer, previously in separate narrow channels have been brought together, and only afterwards together in separate distribution channels that are separate connect these narrow channels, have been distributed over a larger width. 3. The method according to claim 1 or 2, characterized in that the flowed together before the distribution channel Layers, after having been distributed together over a larger width in a distribution channel, with at least two other layers flow together, each individually distributed over a larger width in a distribution channel have been. 4. A method for producing a multilayered web according to claims 1-3, characterized in that more than two multi-layer flows, which were previously brought together in their own narrow channels, and first then together in separate, separate distribution channels that join these narrow channels a larger width have been distributed, are placed on the middle layer. 5. A method for producing a multilayered web according to claims 1-4, characterized in that the Flow channel geometry of at least one middle layer over individual control elements, which over the entire width the flow channel are arranged, is freely adjustable while the system is running. 6. A method for producing a multilayered web according to claims 1-5, characterized in that the Flow channel geometry of a layer is exactly free in the confluence area over its entire width from the outside is adjustable. 7. A method for producing a multilayered web according to claims 1-6, characterized in that after exiting the multilayered web from the tool has the thickness of at least one inner one not on the surface located layer is measured selectively, and that the thickness measurement via a controller in the adapter or in Multi-channel tools integrated automatically controllable distributed over the entire exit width of the web Control elements is connected, and that the control elements via a controller corresponding to that in the thickness measurement determined actual value deviation can be adjusted automatically. 8. The method according to claim 7, characterized in that several layers are measured in their thickness, and that the respective layer thickness of these layers using a controller in the adapter or in the multi-channel tool integrated, automatic control elements distributed over the flow channel width.