Abstract:
An extrusion apparatus which simplifies changing the relative order of layers of a coextruded laminate, is provided. Advantageously, the apparatus includes an interchangeably disposed, layer sequence selecting device which can be changed out without disassembly of other extrusion apparatus.

Description:
FIELD OF THE INVENTION 
     This invention relates to changing the layer sequence of a coextrusion extrudate. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 4,839,131 to Cloeren and U.S. Pat. No. 5,102,323 to Blemberg disclose an exchangeable plug for changing the relative order of layers of an extrudate, in which the circumferential plug surface is provided with a plurality of channels. Under certain circumstances, leakage between plug channels can occur because of the mechanical clearance for plug removal. Reduction in the mechanical clearance can result in galling of the plug to the bore. Furthermore, manufacturing a tapered bore and a mating tapered plug with precise registering of channels, is an arduous task not practical in mass production. 
     Other approaches for changing the relative order of layers of an extrudate are illustrated by UK Patent Application No. 2,220,164 published January 1990, and U.S. Pat. Nos. 3,924,990, 4,443,397 and 4,483,669. The UK Application describes use of a set of distribution blocks interchangeably disposed between an entry block (or feed source) and a coextrusion block, and that an individual distribution block may comprise a stack of interchangeable plates. The U.S. Patents similarly describe changing the order of layers by exchanging apparatus disposed between rigidly connected feed pipes and a forming means shaping individual streams into a shape suitable for layering. However, a drawback of these approaches is that loosening or disconnecting feed pipes from the coextrusion apparatus, separation of feed sources from the forming means, and/or separation of the die body from the coextrusion apparatus is typically necessary for the exchange. 
     Accordingly, there is a need for a coextrusion apparatus which simplifies changing the relative order of layers of a coextruded extrudate. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a coextrusion apparatus which includes an interchangeably disposed device for selecting a relative order of layers in a combined stream. In fluid communication therewith, the apparatus further includes a channeled arrangement for suitably directing flow of a plurality of streams. 
     In a preferred embodiment, the interchangeably disposed, layer sequence selecting device is beneficially used in combination with a directing/combining assembly which includes a plurality of feed channels for directing feed streams to the layer sequence selecting device, and a plurality of connecting channels in fluid communication with, and for directing the streams from the layer sequence selecting device to, a downstream combining channel. The layer sequence selecting device includes a plurality of flow sequence selecting channels which register with the respective feed channels and connecting channels. An advantageous feature is that a feed channel exit opening is disposed relative to an entry opening of a respective connecting channel so that flow through the exit opening is in a direction generally opposite to the direction of flow through the entry opening. 
     In a second preferred embodiment, the interchangeably disposed, layer sequence selecting device is advantageously used in combination with a flow directing block and with an assembly for combining a plurality of streams and coextrusion of a multilayer extrudate which includes a combining channel and downstream thereof, an extrusion orifice. The flow directing block includes a plurality of feed channels for directing feed streams to the layer sequence selecting device, and a plurality of connecting channels in fluid communication with, and for directing the streams from the layer sequence selecting device to, the combining/extruding assembly. As before, the layer sequence selecting device includes a plurality of flow sequence selecting channels registering with the respective feed channels and connecting channels, and a feed channel exit opening is beneficially disposed relative to an entry opening of a respective connecting channel so that flow through the exit opening is in a direction generally opposite to the direction of flow through the entry opening. 
     Beneficially, an apparatus in accordance with the invention, provides for changing the relative order of layers of a coextrusion extrudate without disassembly of extrusion apparatus structure other than removal and interchanging of the layer sequence selecting device. In addition, such an apparatus avoids need for mechanical clearance as is necessary between a removable plug and its respective bore. 
     Additional advantages and beneficial features of the present invention are set forth in the drawing and detailed description, and in part will become apparent to those skilled in the art upon examination of the drawing and detailed description or may be learned by practice of the invention. In the drawing and detailed description, there are shown and essentially described only preferred embodiments of this invention, simply by way of illustration of the best mode contemplated of carrying out this invention. As will be realized, this invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawing and the detailed description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Reference is now made to the accompanying drawing, which forms a part of the specification of the present invention, and depicts preferred embodiments of an apparatus in accordance with the present invention. 
     FIG. 1 is a perspective view of a preferred coextrusion apparatus in accordance with the present invention; 
     FIG. 2 is a partially exploded perspective view of a portion of the apparatus of FIG. 1; 
     FIG. 3 is like FIG. 2 but from a different perspective; 
     FIGS. 4 and 5 are partially exploded perspective views similar to FIGS. 2 and 3, respectively, of apparatus of FIG. 1 with a different layer sequence selecting device; and 
     FIG. 6 is a partially exploded perspective view similar to FIG. 3, of the layer sequence selecting device of FIGS. 1-3 in combination with a flow directing block. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a coextrusion apparatus in accordance with the present invention, is shown. The apparatus includes an assembly  12  for directing flow of multiple streams and for combining multiple streams into a combined stream, a die body  14 , and a die plate  16  which conveniently connects assembly  12  to die body  14 . In addition, in accordance with the invention, the apparatus beneficially includes an interchangeably disposed, layer sequence selecting device  20 . Feed pipes  30  for feed streams A,B,C,D conveniently connect between extruders (not shown) and assembly  12  via mounting blocks  32 . Typically, the feed streams will differ from one another, and combining of feed streams thus produces a composite stream. 
     Referring also to FIG. 2, a plurality of bolts  21  secure die plate  16  to assembly  12 , and a channel  22  of the die plate connects between an exit channel (not shown) of assembly  12  and an input channel (not shown) of die body  14 . An arrow depicts the direction of flow of the combined stream in the exit channel, channel  22  and the input channel. Within the die body the combined stream, in addition to flow in the main flow direction shown by the arrow, undergoes transverse flow, and thereafter a wider, thinner multilayer extrudate exits from an exit orifice  24 . 
     Beneficially, a flexible lip  26  forms the exit orifice. A plurality of lip adjustment rods  28  spaced apart from one another along the width of the exit orifice, conveniently control the gap of the exit orifice, advantageously through lengthwise expansion and contraction of rods  28  under automated control. 
     With reference also to FIG. 3, directing/combining assembly  12  includes a flow directing block portion  18 , which includes a plurality of feed channels  40   a-d  for receiving feed streams A,B,C,D and appropriately directing the feed streams. Flow from channels  40   a-d  is directed through outlets  42   a-d  disposed in a face  44  of block portion  18 . An arrow which begins at outlet  42   b  denotes the direction of flow from channel  40   b;  and referring also to FIG. 2, this direction of flow is generally opposite to the main direction of flow shown by the arrow depicting the direction of flow from channel  22 . It will be understood that there is a like direction of flow through outlets  42   a,c,d.    
     Face  44  is generally perpendicular to inlet faces  46 , 48 . The feed channels are appropriately configured to provide for this generally perpendicular relationship. To this end, the feed channels include an about 90° turn between the inlet faces and face  44 . 
     Block portion  18  of directing/combining assembly  12  also includes a plurality of connecting channels  50 , 51 , 52 , 53 , 54  (indicated by the channel inlets) in fluid communication with, and for directing multiple feed streams from layer sequence selecting device  20  to, a combining channel (not shown) after shaping of the streams into a shape suitable for layering and converging of the shaped streams. The channel inlets are in face  44  of assembly  12 . The direction of flow into connecting channel  50  is denoted by an arrow entering channel  50 , it being understood that there is a like direction of flow into channels  51 - 54 . 
     Beneficially, as shown in FIG. 3, the flow through outlet  42   b  and the flow through the entry opening of connecting channel  50  are in generally opposite directions. In addition, stream B at inflow to layer sequence selecting device  20  is generally parallel to stream B at outflow from device  20 . Likewise, advantageously, flow through face  44  for the other paired feed and connecting channels, is in generally opposite directions, and a particular stream is generally parallel at inflow to, and outflow from, device  20 . 
     As will be understood by one skilled in the art, combining multiple streams into a composite stream includes shaping the individual streams into a shape suitable for layering, and converging the shaped streams. Thus, assembly  12  includes structure and features necessary to shape streams and converge the shaped streams into a composite stream, details of which may be suitably found in the prior art. The combining channel conveniently leads to the exit channel, through which the combined stream passes from assembly  12 . Shaping and combining occur in combining portion  56  of assembly  12 , and side plates  58  (only one shown) enclose the combining portion including the combining channel. A plurality of fasteners  59  secure the endplates to assembly  12 . 
     As shown in FIG.  6  and described later in further detail, flow directing block portion  18  of assembly  12  could be a separate structure from combining portion  56 . 
     With continued reference to FIGS. 2 and 3 in particular, interchangeably disposed, layer sequence selecting device  20  includes a plurality of flow sequence selecting channels  60   a-d.  Arrows within each channel  60  indicate direction of flow. Each flow sequence selecting channel registers with one of the feed channels and at least one connecting channel. Thus, channel  60   a  registers with channels  40   a , 52 , channel  60   b  registers with channels  40   b , 50 , channel  60   c  registers with channels  40   c , 54 , and channel  60   d  registers with channels  40   d , 51 , 53 . In this way, each stream exits the respective feed channel, is positioned in a selected relative order by the respective selecting channel, and enters the respective connecting channel or channels. 
     Again with reference to FIG. 3 in particular, the inflow of flow stream B into the layer sequence selecting device and its outflow from the device are in generally opposite directions. As can be understood, a like opposite direction of flow into and from device  20  exists for streams A,C,D. 
     Layer sequence selecting device  20  beneficially consists of a plurality of plates  62 , 64 , 66  with surface channels and bores as shown, which combine to form channels  6 O a-d.  Accordingly, for instance, channel  60   b  is provided by spaced apart throughbores  67 A (inflow), 68 A (outflow) in plate  62 , spaced apart bore holes  67 B, 68 B in plate  64  which register with throughbores  67 A, 68 A, respectively, and an inverse J-shaped channel  70  in a face  71  of plate  64  which registers with an inverse J-shaped channel  72  in a face  73  of plate  66 , and connects between bore holes  67 B, 68 B. Similarly, channel  60   d  is provided by a bore hole  69  (inflow) and spaced apart bore holes  74  (outflow) in plate  62 , and a surface channel  75  in a face  76  of plate  62  which registers with a like surface channel in a face  77  of plate  64  and connects between bore hole  69  and bore holes  74 . 
     Alignment pins  78  and alignment bores  79  advantageously provide for alignment of plates  62 , 64 , 66  with one another and with face  44  of assembly  12 . After alignment, the plates are advantageously removably attached to face  44  by a plurality of threaded bolts  82  (only several shown), which extend though bores  83  of the plates and into threaded bores  84  of assembly  12 . 
     Beneficially, faces  80 , 76  of plate  62 , and face  73  of plate  66  include undercut surfaces  86 , 87 , 88  disposed interior of edges of the plates. The undercut surfaces reduce the sealing surface area, thereby increasing the seal surface pressure when the plates are fastened together, to ensure a positive seal between contacting plate surfaces. In this way, flow sequence selecting channels  60   a-d  are isolated from one another. For purposes of this description, the term “positive seal” means a seal provided by contacting surfaces. Thus, the mechanical clearance necessary between a prior art plug and its plug bore, prevents a positive seal as herein defined. 
     Conveniently, face  44  to which device  20  is attached, is disposed opposite to a face  90  (see FIG. 2) attached to die body  14  via die plate  16 . Alternatively if desired, device  20  could be attached to face  92  or  94  of assembly  12 ; but in either case, the feed channels and connecting channels would need to be changed so that the feed channel outlets and connecting channel inlets register with channels  60   a-d  of device  20 . Also, block portion  18  could be reconfigured to provide faces  92 , 94  with the feed channel inlets and face  44 ,  46  or  48  with the feed channel outlets and connecting channel inlets. 
     In use, feed streams A,B,C,D enter assembly  12  passing through feed channels  40   a-d.  Thereafter, the streams enter device  20  and pass through flow sequence selecting channels  6 O a-d,  and exit device  20  and re-enter assembly  12  as follows: stream A enters connecting channel  52 , stream B enters connecting channel  50 , stream C enters connecting channel  54 , and stream D enters connecting channels  51 , 53 , giving a relative order of streams of BDADC. Then, the streams in this order are passed via connecting channels  50 - 54  to combining portion  56  of assembly  12 , in which the individual streams are shaped into a shape suitable for layering and thereafter converged. The composite stream passes from assembly  12  through its exit channel, passes through die plate channel  22  to die body  16 , and is extruded from die body  16  with a layer sequence of BDADC. 
     Depending upon the desired multilayer extrudate, the flow directing block portion may include more or less than five connecting channels, more or less than four feed channels, and an appropriate layer sequence selecting device will be selected. Furthermore, the apparatus could include downstream of face  44 , features of the prior art such as a selector plug to change the relative layer sequence received from device  20 , or could split a particular connecting channel into subchannels. 
     With reference to FIGS. 4 and 5, numerals in the 100 series are used for parts of a layer sequence selecting device  120  like device  20 , and its description is correspondingly abbreviated; and easy interchangeability of device  120  for device  20 , and its use with assembly  12 , die plate  16  and die body  14  of apparatus  10 , are indicated. Specifically and referring briefly to FIG. 3, fasteners  82  are removed and device  20  is detached from assembly  12 , and thereafter referring to FIG. 5 in particular, plates  162 , 164 , 166  of device  120  are aligned with one another and with assembly  12  using alignment pins  78  and then fastened to assembly  12  using fasteners  82 . 
     Layer sequence selecting device  120  includes a plurality of flow sequence selecting channels  160   a-d.  Arrows within each channel  160  indicate direction of flow. Each flow sequence selecting channel registers with one of the feed channels and at least one connecting channel. Thus, channel  160   a  registers with channels  40   a , 51 , 53 , channel  160   b  registers with channels  40   b , 54 , channel  160   c  registers with channels  40   c , 50 , and channel  60   d  registers with channels  40   d , 52 . Each stream exits the respective feed channel, passes through the respective flow sequence selecting channel, and enters the respective connecting channel or channels. In use, the result is a relative order of streams of CADAB. 
     With reference to FIG. 5 in particular, the inflow of stream B into the layer sequence selecting device and its outflow from the device are in generally opposite directions. As can be understood, a like opposite direction of flow into and from device  120  exists for streams A,C,D. 
     Layer sequence selecting device  120  beneficially consists of plates  162 , 164 , 166  with surface channels and bores as shown, which combine to form channels  160   a-d.  For instance, channel  160   b  is provided by spaced apart throughbores  167 A (inflow), 168 A (outflow) in plate  162 , spaced apart bore holes  167 B, 168 B in plate  164  which register with throughbores  167 A, 167 B, respectively, and an arc-shaped channel  170  in a face  171  of plate  164  which registers with an arc-shaped channel  172  in a face  173  of plate  166 , and connects between bore holes  167 B, 168 B. Similarly, channel  160   d  is provided by a bore hole  169  (inflow) and a bore hole  174  (outflow) in plate  162 , and a surface channel  175  in a face  176  of plate  162  which registers with a like surface channel in a face  177  of plate  164  and connects between bore hole  169  and bore hole  174 . 
     Beneficially, as with device  20 , faces  180 , 176  of plate  162 , and face  173  of plate  166  include undercut surfaces  186 , 187 , 188 , which reduce the sealing surface area, thereby increasing the seal surface pressure when the plates are fastened together, to ensure a positive seal between contacting plate surfaces. 
     Advantageously, not only can device  120  be exchanged for device  20  without disassembly of other extrusion apparatus structure, but in certain instances, individual plates from different layer sequence selecting devices can be interchanged. Also if desired, the layer sequence provided by device  20  or  120  can be obtained by use of only two plates. A difference between a three plate system and a two plate system, relates to the flow sequence selecting channels. Specifically, in the three plate system shown, channel halves register to form a channel, whereas in a two plate system, each channel would consist of a channel half only. The latter channel type may be suitable for polymers exhibiting a lower propensity for degradation. As can be understood, it would be advantageous to use four or more plates in certain instances. 
     Referring to FIG. 6, layer sequence selecting device  20  is used with a flow directing block  118 , instead of block portion  18  of assembly  12  of FIG.  1 . Otherwise, block  118  is like block portion  18  in its details. Thus, identical numerals, letters and arrows are used in connection with block  118  as are used for block portion  18 , and the description of block  118  is correspondingly abbreviated such that reference should be made to the description of block portion  18  for details of block  118 . 
     As previously indicated, block  118  can be used with a combining block (not shown) like combining portion  56  in function. In such case, the combining block would, as in FIG. 1, be in flow communication with a downstream die body for coextrusion of a multilayer extrudate. 
     Alternatively, block  118  can be used with a multimanifold die body (not shown). In such case, the streams in the relative order selected by the layer sequence selecting device are directed by connecting channels  50 - 54  to the multimanifold die body, and the multimanifold die body carries out the processing steps of shaping individual streams into a shape suitable for layering, converging the shaped streams in a channel (not shown) leading to an extrusion orifice, and coextrusion of a multilayer extrudate. 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. Several variants or modifications have been briefly mentioned for purposes of illustration.