DE4001479C1 - Thermoplastic material extruding appts. - has two or more extruders to form melt streams, co-extrusion adaptor, with two or more inlets, side channels, co-extrusion nozzle, etc. - Google Patents

Abstract

An arrangement for producing an extrusion, with at least two layers, of a thermoplastic by coextrusion, includes at least two extruders for forming at least two melt streams, a coextrusion adaptor with at least two inlet openings, a side channel, a coextrusion nozzle and a cooling agent for the extruded material. The arrangement has devices for measuring the thickness of the extruded material over a number of points over its width, and a slider adjusting mechanism. ADVANTAGE - The arrangement is simple and irregularities in the layers can be eliminated during extrusion.

Description

The invention relates to a coextrusion adapter for the Production of coextruded sheets from two or more thermoplastically processable plastics. The Coextrusion adapter has the task of two or more extruders conveyed molding material flows into one common, two or multi-layer strand merge and this into a slot nozzle forward in the desired width stretched and reduced in thickness accordingly becomes. The average thickness of the layers involved increases thereby in the same ratio as the total thickness.

State of the art

DE-A 34 05 257 describes a coextrusion adapter known there as a collector's block and forming unit was designated. In the coextrusion adapter are a thicker main strand and a thinner secondary strand merged. From a subsequent slot nozzle the combined strand into a multilayer plate or Extruded film that a thin top layer from the Contains material of the secondary strand.

Control engineering methods are known for the thickness ratio of the different layers within a given framework hold; see. F. Hensen, "Kunststoffberater" 11/1989, pp. 59-64; W. Green et al. "Kautschuk + Gummi.Kunststoffe" Volume 38, No. 3/1985, Pp. 193-199. Thickness fluctuations in the layers are indeed possible Master in the longitudinal direction, but not in the transverse direction.

As a rule, the top layer is not completely uniform distributed over the width of the extruded web. This can have a number of causes, e.g. B. irregularities in the cross-sectional shape of the main and secondary line, uneven temperatures within the main train or the secondary line, from which different  Melt viscosities and a correspondingly different one Flow behavior follow, or different Flow resistances of the molding compound strands within the Coextrusion adapter or the extrusion nozzle. It is difficult, the causes of the uneven Recognizing thickness distribution, and even more difficult to identify them to exclude.

According to DE 34 05 257 A1, the thickness and This ensures uniformity of the coextruded layer influenced that the thickness profile of the secondary strand in Coextrusion adapters regulated by special actuators. One uses one by adjusting screws adjustable slider, which in the secondary channel in which the secondary line towards the union both strands flow, protrudes more or less deeply. By actuating the set screws on the slide act, the flow resistance in the secondary line and thus also its thickness in relation to the main strand to be influenced.

However, this setting option is not suitable for Non-uniformities in the distribution of the layer thickness equalize across the width of the extruded sheet for example if the top layer is thicker in the middle or thinner than the edges or another has a non-linear profile. In this case, one uses in Coextrusion adapter a slider, the profile of which to the Profile of the top layer is designed opposite; d. H. the slide protrudes the deeper into the Melt flow into it, the thicker the profile of the top layer of the extruded sheet and vice versa. The  Slider profile can only be empirically linked to the Adjusted irregularities of the top layer profile because it’s hardly possible that way certain point of the slide profile a certain Assign the area of the top layer profile. Furthermore is it is unpredictable how strong the slider profile is must be changed to one in the transverse direction Non-uniformity of the top layer profile found selectively balance.

To adjust the slide profile, the extrusion interrupted in each case, the coextrusion adapter cooled and opened, the slide is removed and mechanically reworked, reinstalled and the Extrusion can be started again. It turns out the change made as inadequate, the Repeat the adjustment process until the required uniformity of the top layer profile is reached. Even then an adjustment can be made again become necessary if the Flow conditions in the extrusion system changed and new surface layer irregularities occur.

In order to simplify the adjustment of the slide, R. Reitemeyer ("Kunststoffe" Vol. 78, 1988, No. 5, pp. 395-397) proposed to design the coextrusion adapter so that the slider laterally into a cassette Appropriate guidance can be inserted. Thereby will complete disassembly of the adapter  avoided every adjustment step, but not that Interruption of coextrusion. Furthermore, he has proposed to design the slide in several parts, apparently in order to differ in depth in the Sections projecting into the melt stream combine to can.

In an extrusion device according to DE 37 41 793 A1 further developed this configuration so that the in the transverse direction side by side in the side channel protruding sections of the multi-part slide arranged in the direction of displacement against each other and can be adjusted by separate adjusting means. The the respective setting of the sections is indicated by a Measuring device scanned and the measured variable for Influencing the control means used. As such, you can Piezotranslators are used. The recorded values can, based on the special plastic sheet, the is currently being manufactured, fed to a computer and in programming will be included.

This makes it possible to get the extrusion line up quickly and largely automatically on different, before set extrusion conditions. On the other hand does not allow the known device that Extrusion device itself in operation adapt to changing extrusion conditions. Such Changes can occur for a variety of reasons; for example due to temperature fluctuations Air movements in the vicinity of the extrusion system  can result by changing the melt viscosity due to a slightly different nature of the supplied plastic or by changing the Flow resistance of the melt flow due to Wear or corrosion in the flow paths. It can in such cases, the melt flow in the Coextrusion adapter by acting on the actuators adapt to the changed conditions or that Change the setting program accordingly, but one sets such adaptation always deliberate interventions by the Operating personnel advance only with significant Delay can occur.

Task and solution

The invention has for its object a Coextrusion adapter with adjustable slide To be provided without disassembly, if necessary during extrusion operation, according to each occurring irregularities of the extruded Can set top layer profile.

The object is achieved according to the invention generic device for producing a at least two-layer strand of thermoplastic Plastic by coextrusion, full

• a) at least two extruders to form at least two melt streams thermoplastic,  
• b) a coextrusion adapter with at least two Inlets to which the extruders are connected and with a main channel and at least one in the main channel connecting secondary channel, with means to regulate the Auxiliary channel flowing melt stream in the form a multi-part slide from several in Transverse direction side by side in the side channel protruding sections, which in Actuating direction can be shifted against each other arranged and by separate adjusting means are adjustable, as well as with an outlet opening for the at least two-layer strand,
• c) an extrusion nozzle which is connected to the outlet opening of the Coextrusion adapter is connected and in the the two or multi-layer strand on the desired width stretched and as two or multilayered web is extruded,
• d) means for cooling and optionally smoothing the coextruded web,

solved in such a way that the device additionally

• e) means for selective thickness measurement of individual Layers of co-extruded web on several, across the width locations distributed on the railway and
• f) adjusting means for setting the multi-part slide of the Coextrusion adapter depending on the of the extruded sheet includes measured thicknesses.

Mode of operation and advantages of the invention

While the well-known coextrusion adapter by separate Setting the sections of the multi-part slide each on a specific, predetermined Operating point is set, it is with the device according to the invention possible for the first time Coextrusion adapter during operation immediately after the properties of the extruded sheet re-enact as necessary. In particular it is possible to make such an adjustment automatically perform. The finer the slider is divided, the more a narrowly defined area in which a Deviation from the nominal value of the layer thickness occurs, readjust. For this reason, it is advantageous if the multi-part slide from more than three sections exists, especially if none of the sections of the multi-part slide more than half of the Makes up the overall width, but rather the sections are the same width.

Therefore, during the ongoing extrusion According to the invention, either wider or narrower Portions of the slider independently Set separate adjusting means without the extrusion interrupted and the coextrusion adapter should be taken apart.

To adapt the coextrusion adapter to a specific one Extrusion die is the effect of adjusting a  single adjusting agent on the extrudate in the running Operation determined. As a result, each actuator is one certain width range assigned to the extruded web and at the same time the extent of the adjustment with the related layer thickness change related. After that, any measured thickness deviation from the set point an exact manipulated variable for a specific actuator be assigned.

Implementation of the invention

To explain the invention Figs. 1 to 3 are used, which represent in a schematic way, a simple embodiment of the coextrusion.

Fig. 1 shows a longitudinal section through the coextrusion adapter in the direction of extrusion;

FIG. 2 shows a cross section along the line AA in FIG. 1.

Fig. 3 shows another arrangement of sections of the slide and adjusting means in longitudinal and cross section.

In Fig. 1, 1 designates the main channel 2 and the sub-channel. The slide 3 is displaceably arranged in a guide 4 so that it can protrude more or less deeply into the secondary channel 2 and change its height depending on the position of the adjusting means 5 . A sealing strip made of a heat-resistant elastomer material is expediently arranged in a groove 6 in the wall of the slide guide 4 . The slider 3 is divided into several sections 3 ', 3'' , etc., which are arranged displaceably in relation to each other and can be adjusted independently of one another by separate adjusting means 5', 5 '' , etc. The individual sections 3 ', 3'' can be sealed under themselves by sealing tapes 6' .

It is expedient that none of the sections of the multi-part slide more than half of the Total width. As a rule, the slide exists from more than three subsections, preferably all are about the same width. To a very fine regulation of the It can make sense to effect the thickness of the secondary strand be the slider in for example 5 to 20 lamellar sections of only a few each To split millimeters in width. The number of A section is only limited if everyone is influenced by their own means of control, because even with a staggered position, these cannot be arbitrary are arranged close to each other and operated. Each denser the independently adjustable actuators are arranged the easier it is possible Thickness fluctuations in narrowly limited areas balance.

However, it is not fundamentally necessary that each section has its own actuating means.  

As shown in Fig. 3, a larger number of lamellar sections 3 ', 3''can be influenced by means of a smaller number of adjusting means 5', 5 '' if the actuating force via a band 7 of suitable elasticity in each case to a group of several Sections acts, which in this respect are only partially adjustable independently of one another by separate adjusting means. In this way, a fairly evenly curved profile of the slide can be set, which is useful, for example, if the thickness distribution is nonuniform from the center to the edge and is to be compensated for over a correspondingly wide range. So that the sections also follow a stroke movement of the adjusting means, their heads 8 should grip around the band 7 and the lower ends of the adjusting means be tensile, z. B. by screws 9 , connected to the band 7 .

The main channel can have a thickness in the coextrusion adapter for example 2 to 20 and a width of 30 to 100 mm to have. The secondary channel or channels are preferred, however not necessarily thinner than the main channel. In the Extrusion nozzle becomes a from the combined strand multilayered web, e.g. B. a plate or film web 0.1 to 12 mm thick and 500 to 3000 mm wide molded from individual layers from 0.01 to 12 mm thick can exist. In a preferred embodiment the extruded web consists of a main or Core layer formed from the main strand and 80 up to 99.9% by weight of the material passing through  contains, and at least one, preferably two adhesive cover layers covering the remaining part of the Materials included and from the side strings or be formed. In the core layer can Longitudinal direction of the extruded web through core pieces that are arranged in the outlet slot of the extrusion die, Cavities are formed, possibly only through narrow webs are separated from each other.

Devices which are also used in known coextrusion adapters for slide adjustment are suitable as adjusting means 5 . Bolts are suitable for longer travel distances. The head protruding from the coextrusion adapter can be turned using an adjusting wheel or an adjusting key. A positioning robot that can be moved from one actuating device to the other or servomotors permanently attached to each actuating device are suitable for technical operation. Hydraulic pistons can also be used as controllable actuators. Electrically heated thermal expansion bolts and piezotranslators are suitable for fine adjustment during automatic control.

Any adjustment device can be adjusted by trial and error Area of effect assigned in the extruded web will. For the selective thickness measurement of individual There are tried and tested layers of a coextruded web spectro-photometric or radiometric methods that on the different absorption behavior of the involved thermoplastics  are based. The actual value determined in this way can be compared with the target Value compared and the difference over a controller in a corresponding manipulated variable for the associated one Actuators are implemented. Common can do this Control technology, such as microprocessors or Calculator can be used.

With such an arrangement, a thickness control is the extruded web or individual coextruded layers possible. For this purpose the layer thickness to be controlled at several locations across the width of the web measured and automatically the corresponding one Section of the slide usually by means of a electrically controllable adjusting means adjusted. For the Thickness measurement can be several fixed sensors or one that can be moved automatically across the web width Sensor can be used. By the invention it is possible extruded webs with very tight tolerances Generate single layer thicknesses.

It is understood that coextruded in the sense of the invention Lanes from any number of layers with freely selectable, adjustable thicknesses can be. For this purpose, coextrusion adapters used in which several secondary strands in a row be placed on the main strand, each Secondary line regulated by itself in the sense of the invention can be. Likewise, on both sides of the Main strand one or more secondary strands placed will. The main strand itself can  regulated in the same way if necessary will.

The technique of coextrusion is known per se. It bets ahead that the thermoplastic molding compositions of the main and secondary strand undecomposed at the same temperatures are processable and not harmful to each other act.

Are the molding compounds in the main components the same and only by the presence or absence of dyes or distinguished from other additives, so arises in the Usually a co-extruded sheet in which the layers are fixed stick together. The same applies if the strands are off different, but well-tolerated molding compounds. In the case of low tolerance, it can happen that the layers adhere to each other only weakly and the If necessary, the top layer is subtracted from the core layer can be. You can then do a temporary job Take over protective layer.

Claims (10)

1. Device for producing an at least two-layer strand of thermoplastic material by coextrusion, comprising

• a) at least two extruders to form at least two melt streams made of thermoplastic material
• b) a coextrusion adapter with at least two inlet openings, to which the extruders are connected and which are connected to a main channel and at least one secondary channel opening into the main channel, with means for regulating the melt flow flowing through the secondary channel in the form of a multi-part slide consisting of several in Cross sections juxtaposed in the secondary channel projecting sections, which are arranged in the adjusting direction against each other and adjustable by separate adjusting means, and with an outlet opening for the at least two-layer strand,
• c) an extrusion die which is connected to the outlet opening of the coextrusion adapter and in which the two-layer or multi-layer strand is stretched to the desired width and is extruded as a two-layer or multi-layer web through an outlet slot,
• d) means for cooling and smoothing the coextruded web,

characterized,

• e) means for selective thickness measurement of individual Layers of the coextruded web on several, locations distributed across the width of the web,
• f) adjusting means ( 5 ) for setting the multi-part slide ( 3 ) of the coextrusion adapter as a function of the thicknesses measured on the extruded web.

2. Coextrusion adapter according to claim 1, characterized in that none of the sections ( 3 ', 3'' ) of the multi-part slide ( 3 ) makes up more than half of the total width. 3. Coextrusion adapter according to claim 1, characterized in that the multi-part slide ( 3 ) consists of more than three sections ( 3 ', 3'' , etc.). 4. Coextrusion adapter according to claim 1, characterized in that the partial sections ( 3 ', 3'' ) are approximately the same width. 5. Coextrusion adapter according to claim 1, characterized characterized in that as a means of thickness measurement several sensors distributed across the web width are arranged.   6. Coextrusion adapter according to claim 1, characterized characterized in that as a means for measuring thickness Sensor slidably arranged across the web width is. 7. Coextrusion adapter according to claim 1, characterized characterized in that core pieces for Formation of voids in the longitudinal direction of the extruded web are arranged.   8. Process for extruding a multilayered web made of thermoplastic plastic Melt the plastics in at least two Extruding, introducing the melted Plastic strands in a coextrusion adapter Formation of a main strand and at least one Minor strands, union of strands into one multilayer strand, with at least one Secondary strand in the coextrusion adapter by one protruding multi-part slide is regulated, by at least a part of the sections of the multi-part slide during extrusion Actuating direction independent of each other by separate Adjusting means is set, initiating the multilayer strand in an extrusion die, in which it is stretched to the desired width and as multilayer web is extruded, cooling and optionally smoothing the web, thereby characterized in that the thickness of individual layers of extruded multilayer web at several, over  selectively spread the width of the web measured and the subsections of the multi-part Slide depending on the measured thickness be adjusted. 9. The method according to claim 8, characterized in that the sections by means of regulated Actuators can be adjusted.