Abstract:
An array of dies having a closed configuration is used in a method and apparatus for making a closed composite article that comprises multilayered materials. In the method and apparatus, at least two extruders are used to extrude at least two material streams through the die array to provide an extrudate comprised of alternate layers of material from the at least two material streams. The compositions in the two material streams can be the same or different.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method and apparatus for extruding a multi-layered product. More particularly, the apparatus and product formed have a closed configuration such as an ellipse or circular.  
         BACKGROUND OF THE INVENTION  
         [0002]    Forming articles of multiple layers, whether the layers are of similar or different materials, is known. Layered rubber articles comprised of many alternating layers of different rubbers have been described by Frerking in U.S. Pat. No. 5,178,702, wherein air barrier/low temperature properties are improved in horizontally layered composites. Such composites can be prepared by hand by plying up alternating layers of two or more different rubber compounds.  
           [0003]    Sluijters in U.S. Pat. No. 3,051,453 describes a mixing apparatus designed to mix two streams of liquid by splitting and rejoining the streams in a particular geometric way (a static mixer), which the instant inventors have found can be used with rubber to produce a layered, instead of a mixed product. Reilly et al. in U.S. Pat. No. 5,866,265 have used this concept to split elastomer streams and have caused the streams to flow back together to form a layered material. Said patent is incorporated herein by reference.  
           [0004]    The apparatus and method taught by Reilly et al. comprised a single set of stacked dies and was useful for proving that the concept could be used to produce a layered material for laboratory characterization. No apparatus or method is known in the art for making commercially usable microlayered elastomeric materials.  
           [0005]    All of the known methods and techniques are directly to forming linear, continuous products.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to an apparatus and a method for producing a multi-layered closed article. The layers may be of identical, similar, or different extruded materials. The layers may be arranged concentrically or in vertical type sectors about the closed article. The closed article being defined as an article that has a defined interior and exterior and may be continuous in only one plane.  
           [0007]    In the apparatus disclosed, the apparatus has extruding means for extruding at least two streams of material, at least two die plates attached to the output end of the extruding means and a profile die attached to the last of the at least two die plates wherein the layered streams are merged to form a closed unitary layered article. The die plates receive the extruded material streams and each die plate has an array of flow channels. The array is arranged in a closed rectilinear or curvilinear configuration to produce the desired closed article. Each flow channels has a separation means whereby the material streams being received into each die plate are split into portions by the separation means, and the portions are directed to be stacked to form layered streams.  
           [0008]    In one aspect of the disclosed invention, the die array has at least 6 pairs of die channels. The closed configuration assumed by the die array may be circular, elliptical, square, or rectangular.  
           [0009]    In the disclosed method, the method has the following steps: providing extruding means for simultaneously extruding at least two different material streams, directing a first material stream into a first die channel, directing a second material stream into a second die channel, whereby said first die channel and said second die channel direct said first material streams to be stacked and pressed side by side as it exits the die channels, and providing a plurality of die channels side by side to form a die array to provide an extrudate of a closed configuration comprising at least four layers of the first material and the second material are being stacked alternately side by side vertically or concentrically.  
           [0010]    In one aspect of the disclosed method, the material compositions for the at least two different material streams are different. In another aspect of the method, the two different material streams are two different plastic or thermoplastic materials. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention will be described by way of example and with reference to the accompanying drawings in which:  
         [0012]    [0012]FIG. 1 illustrates two extruders, head to head, for extruding two streams of material through a die to form a multi-layered extrudate;  
         [0013]    [0013]FIG. 2 illustrates a perspective view of the portion of the apparatus where material enters the die;  
         [0014]    [0014]FIG. 3 illustrates one side of the die array of a die plate to producing a closed multi-layered article;  
         [0015]    [0015]FIG. 4 illustrates, in reverse, the die array of a die plate;  
         [0016]    [0016]FIG. 5 illustrates a pair of channels;  
         [0017]    [0017]FIG. 6 illustrates a stack of channel pairs;  
         [0018]    [0018]FIG. 7 illustrates the reverse side of the die plate of FIG. 3;  
         [0019]    [0019]FIG. 8 is a cross-sectional of a product with radial layering; and  
         [0020]    [0020]FIG. 9 is a cross-sectional of a product with sector layering. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    With reference now to FIG. 1, a very simplistic schematic is illustrated for the production of a multi-layered article. Two extruders  12  and  12   a  are illustrated oriented head-to-head whereby the two extruders are used to extrude the same or different rubber or plastic, or mixtures thereof (hereinafter referred to as material), simultaneously through barrels  14  and  14   a . Extruders  12  and  12   a  may be single screw extruders, mixing extruders, such as twin screw extruders, or they may be injection mold extruders. Those skilled in the art will recognize that other orientations of the extruders are possible, e.g., above and below, and side by side.  
         [0022]    Portion  16  of FIG. 1 is magnified in FIG. 2 to show the detail of the die configuration used with extruders  12  and  12   a . A wedge or V-block  18 , shown as transparent so its relationship to the die stack  21  can be seen, can be used as a directing means to direct material streams  19  and  19   a  in the direction of a stack  21  of die plates  20 . Mixing of the material streams would prevent the stated purpose of the invention, i.e., providing separate, layered materials, and accordingly, the apex  18   a  of the V-block is held tightly against the top die plate  20  in the die plate stack  21 . Other directing means can also be used to direct the flow of separate material streams into channels in a die array without mixing the streams, such as providing a sufficient space between the two materials stream. Wedge  18  has an advantage in that the pressure exerted by each of the extruders is directed against pressure exerted by the other, whereas some other directing means may require special augmentation to handle the pressure from the two extruders. Whatever means is used, in the present invention of forming a closed article, when positioned above the first plate  20  in the stack  21 , the separating means is circular to create two separate concentric streams of material into the first die.  
         [0023]    A top side of an individual die plate  20  is illustrated in FIG. 3. For convenience, this side will be referred to as the horizontal plate side  20   a . The die plate  20  has a circular die array  30  formed by a plurality of rectangular die channels  32 . On the horizontal plate side  20   a , the longer axis of the rectangular channel is oriented along a sector of the circular plate  20 . Were the channels  32  of the array  30  to be arranged linearly, the longer axis would be horizontally oriented, thus this side of the plate  20  is identified as the horizontal plate side. The die channels  32  are stacked in pairs  34 . The channels  32  in each pair  34  are separated by a septum  36 . To compensate for the circular array of rectangular channels, the area between the channels  32  is flared at the radially outer end relative to the center of the die plate  20 . The number of channels  32 , as well as the size of the channels  32 , in the array  30  can vary. Ideally, the array  30  has at least six pairs of channels, thus having at least  12  individual channels.  
         [0024]    The center of the die plate  20  may be solid or removed; the center of the plate  20  of FIG. 3 is removed. If the closed article is to be extruded onto a mandrel, than the center of the die plates  20  are removed to create a central channel  40  for the mandrel. The choice of whether or not to build on a mandrel is based upon the article use, materials, and manufacturing method of the article. Additionally, if the mandrel is solid, than the central channel is left completely open. If the mandrel is a hollow mandrel, the engineer may choose to provide a central plate thereby creating an open ring in the die plate  20  through which the mandrel passes. The successive series of central plates may be secured to one another by securing means passing through all of the central plates and may be sized differently to accommodate different mandrel sizes.  
         [0025]    [0025]FIG. 4 illustrates the reverse side  20   b  of the plate  20 , which will be referred to as the vertical plate side  20   b . The vertical plate side  20   b  has a plurality of radially extending rectangular channels  32  separated by septums  37 . Again, the channels  32  are paired. The first channel  32   c  tapers radially inward and the second channel  32   d  tapers radially outwardly.  
         [0026]    Each channel pair  34  has one radially inner channel  32   a  that tapers clockwise as viewed from the horizontal plate side  20   a , and one radially outer channel  32   b  that tapers counter-clockwise as viewed from the horizontal side  20   a , see FIGS. 3 and 5. FIGS.  5 - 7  illustrates the plates  20  and the die array  30  and channels  32  in reverse; that is, what is drawn are the edges of the open channels to more clearly illustrate the configuration of the channels  32  and the re-orientation of each channel  32 . The array of FIGS. 3 and 5 may be considered to have a clockwise hand configuration, based on the inner ring of channels  32 . In the die plate stack  21 , alternating die plates  20  may have a different hand configuration. For example, if the first die plate  20  in a stack  21  has a clockwise hand configuration, then the subsequent die plate  20  will have a counter-clockwise configuration, based on the inner ring of channels, wherein the inner ring of channels taper counter-clockwise. FIG. 6 illustrates a channel pair  34  with a counter-clockwise hand. The counter-clockwise hand configuration is the mirror image of the clockwise hand configuration. This makes it possible to provide a vertical stack of dies since the first die moves the material streams to clockwise and the adjacent die moves the material stream back counter-clockwise, so that the vertical offset of the produced article does not change. However, since the produced article is a closed array, the stack  21  may be characterized by plates all having a clockwise or counter-clockwise configuration.  
         [0027]    To understand how the how the streams flow through the die array to form a layered article, a pair of stacked die channel pairs  34   u ,  34   l  is shown in FIG. 7. The channels have a counter-clockwise configuration. Assuming that a single stream of a single material enters each top channel  50 ,  51  of the upper channel pair  34   u , the streams entering the top channels  50 ,  51  are compressed through the respective taper of the channels  50 ,  51  and reoriented as the streams exit the channels  50 ,  51 . But as the streams exit the channels  50 ,  51 , they are each split into two streams by the septum  36  of the adjacent channel pair  34   l . Thus, each channel  52 ,  53  of the lower channel pair  34   l , receives one-half of each initial stream. Each half stream received in each lower channel  52 ,  53  are forced to merge by the respective tapers, creating a new layered stream (having 2 distinct layers) that is then divided by the septum of the next channel pair. In the subsequent channel pair (not illustrated), the two layered stream, having been split by the septum of the subsequent channel pair is forced to merge with another two layered stream, forming a four layered stream.  
         [0028]    In this manner, by stacking die plates  20  on top of one another, the material streams are divided, merged, and rerouted as they pass through each subsequent die plate. This occurs until the material streams have a final convergence at the profile die  26 , which consolidates the individual streams into extrudate  28 . In this manner, the original two streams of material are divided and stacked producing a function of 2 n  layers of material in the extrudate  28  that exits the profile die  26 , where n is the number of die arrays  30  in the die plate stack  21 . Since the article being produced is a closed article, the profile die  26  has a closed passageway to form a final closed article. Similar to the die plates  20 , the profile die  26  may have means to allow for passage of a mandrel if required.  
         [0029]    The closed articles produced by the die plates  20  have can two different layering configurations. The first closed article  40  has the two materials in alternating concentric rings, see FIG. 8. The second article  42  has the two materials in alternating sectors along the cross-section of the annular article, see FIG. 9. Both articles are formed using identical die plates  20  of the type described above, the difference being in the stacking manner of the top two die plates  20 .  
         [0030]    When a die plate  20  is oriented such that the flow streams enter the plate  20  from the horizontal side  20   a , the resulting exit streams are vertically arranged, relative to the center of the die. When the series of hand alternating dies  20  are stacked such that the material entrance side is always the horizontal side, than the final product will be defined by the materials in alternating sectors as in FIG. 9.  
         [0031]    To form the alternating concentric rings of FIG. 8, the material entrance side of the first die plate  20  is the horizontal side, but the material entrance side of the second die plate is the vertical side. Thus, as the materials leave the first die plate in a vertical orientation and enter the second die plate, the streams are not instantly reoriented to horizontal. The streams are instead horizontally reoriented as they exit the die plate. Each subsequent die plate is then stacked to have the vertical plate side as the material entrance side so that as the material exits the last die plate and enters the profile die  26 , the layers are horizontally oriented and become concentrically arranged in the formed article due to merging of the streams at the profile die  26 .  
         [0032]    To achieve a concentrically arranged article  40 , the first die plate may also be oriented to have the material entrance side by the vertical side to achieve instantly horizontally oriented streams. However, maintaining separation of the two material streams at the first die plate  20 , while possible, is more complicated. In such a stack  21 , all the dies  20  have the vertical plate side as the material entrance side.  
         [0033]    The die plate  20  and die array  30  can be used to form any type of closed configuration article. The possible array configuration include any closed curvilinear configuration such as circular, elliptical, or obround, or any closed rectilinear configuration such as tetragon, rectangular, square, or trapezoidal. The closed configuration will depend on the finished article and further manufacturing steps. The configuration of the profile die  26  may mimic the array configuration or may vary slightly; the selection is dependent upon the desired product.  
         [0034]    The choice of materials can vary also. The materials  19 ,  19   a  from each extruder may be identical wherein just the act of layering the material in the disclosed manner improve the desired article properties. The materials  19 ,  19   a  may be compounded such that one stream  19  is a non-reactive mix and stream  19   a  contains the cure package such that cure begins along the layer boundaries created by the die plates  20 . The materials  19 ,  19   a  may be two completely different materials. The selection of materials  19 ,  19   a  is endless and limited only by what can be produced and extruded into the die plates.  
         [0035]    The closed article may be a hose. Tubes of different types and sizes can be also be produced. Another application is the formation of tire tread rings. The tread rings can be formed as a continuous tube that is then cut to a length equivalent to the tread width. Such a method of production can also be a first step in,producing rolls of bags of the type used in the produce department of grocery stores or help-yourself sections of food stores. The applications are many.