MXPA97008229A - Given of extrus - Google Patents

Abstract

An extrusion die is disclosed which includes a first member (14) having a surface that includes a plurality of spiral channel segments (36) formed therein and a second member (16) having a surface that includes a plurality of spiral channel segments (37) formed therein. The surfaces of the first and second members are positioned with respect to each other to form a spill space (24) therebetween, wherein the spiral segments of the first and second members are coupled to form a plurality of spiral channels having lines central that undulate back and forth through the spill space. A spiral channel is formed by a spiral channel segment in the first member aligned with a respective spiral channel segment are substantially at 90 ° C out of phase. The respective spiral channel segments have a plurality of interconnected spiral channel segment portions (44, 45, 46, 47, 48, 49) each of which increases in depth from its surface to a point of maximum depth and therefore decreases in depth back to the surface

Description

GIVEN EXTRUSION BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to extrusion dies used in blown film applications and, more particularly, to extrusion dies that include a unique spiral channel configuration that improves mixing and distribution of the dwell time of the material flowing through of the same.

Description of Related Art Conventional extrusion dies for blown film and other annular extruded applications have generally been of the spiral mandrel type, as described in U.S. Patent 4,201,532 to Cole. As seen herein, a plurality of plastic spiral feed channels are cut into the internal flow surface and the external flow surface remains flat, with an overflow space between the internal and external flow surfaces acting as a passageway. Cancel to the ring extrusion hole. More recently, extrusion dies having a disc or trunco-conical configuration have been used, particularly in stacked arrangements that allow various types of material to be joined together as a multiple layer film. Examples of this type of extrusion die are described in U.S. Patent 5,076,776 to Yamada et al., And U.S. Patent 4,798,526 to Briggs et al. In all these die designs, the use of spiral channels has been well known to promote the uniformity of the different layers of material, as well as a better mixing of materials within each layer. The spiral channels used with the different types of extrusion dies in the prior art have generally been formed on only one of the two flow surfaces adjacent to an overflow space therebetween (see Fig. 7). Furthermore, such spiral channels generally have a depth that decreases uniformly from the beginning to the end (see Fig. 8). This spiral channel configuration promotes flow kinematics in which the material at the top of the spiral channel (adjacent to the die surface) flows into the overflow space much more rapidly than the material flowing through at the bottom of the Chanel. Consequently, the residence time for the material flowing in the lower part of the spiral channel is much longer and leads to the degradation of the material. Furthermore, the flow of spillage into the overflow space is such that it does not involve mixing between the adjacent spiral channels to a very high degree. This lack of mixing can cause one or more diagonal welding lines to be formed through the final film product, which affects its uniformity, structural integrity and appearance. As seen in US Pat. No. 3,809,515, a stacked type extrusion die is described having spiral channels formed by engageable slots provided therein within both flow surfaces. In this design, the upper and lower slots have different radial separation, causing the two halves of the spiral channel to move out of phase one of the other. Therefore, the channel half of a flow surface couples with part of the downstream channel half and part of another upstream channel mass formed on the corresponding flow surface. Although the provision calls for promoting inter-spiral mixing, the spill through the overflow space comes from the middle of the spiral channel. Accordingly, the material moving in the uppermost part of the upper groove and in the lower part of the lower groove continues to move through the spiral channel and does not participate in the flow of spill to the end of the spiral channel. This leads to the same negative consequences related to mixing uniformity and dwell time as in the spiral channel design formed only on a surface described above. In light of the above, it would be desirable for extrusion dies, particularly for those used in blown plastic film applications, to include spiral channels that promote improved mixing of the material between the adjacent spiral channels and the uniformity of the improved residence time of the material flowing through. the spiral channels. Furthermore, it would be desirable for such extrusion ducts to include spiral channels having flow kinematics where the material at the top and bottom of such spiral channels is forced to participate in spill flows within the overflow space due to the geometry of the flow. channel.

BRIEF DESCRIPTION OF THE INVENTION According to one aspect of the present invention, an extrusion die including a first member having a surface including a plurality of spiral channel segments formed therein and a second member having a surface including a plurality is described. of spiral channel segments formed therein. The surfaces of the first and second members are positioned in relation to each other to form a spill space between them from an inlet end to an outlet end, wherein the spiral channel segments of the first and second members are coupled to form a plurality of spiral channels having center lines that undulate back and forth through the common spill space. The extrusion die may be of the disc type design, wherein the first member is an upper die plate with a lower surface having the plurality of spiral channel segments formed therein and the second member may be a plate lower die with an upper surface having the corresponding plurality of spiral channel segments formed therein. Alternatively, the first member may be a central mandrel with a cylindrical outer surface having the plurality of spiral channel segments formed therein and the second member would be a cylindrical die body surrounding the central mandrel with an internal surface having the corresponding plurality of spiral channel segments formed therein. According to a second aspect of the present invention, each spiral channel is composed of a spiral channel segment formed on a surface of the first member aligned with a spiral channel segment formed on the splice surface of the second member. Each of the spiral segment segments of the first and second members have a plurality of interconnected spiral channel segment portions, which include at least a portion of an input spiral channel segment and an extreme spiral channel segment portion. The interconnected spiral channel segment portions of the spiral channel segments gradually increase in depth from the respective surface to a point of maximum depth and subsequently gradually decrease in depth back to the respective surface. The interconnected spiral channel segment portions also have a substantially arcuate cross section in a plane transverse thereto, with the spiral channels having a substantially cylindrical cross section in a plane transverse to the center line thereof. The maximum depth point of each successive interconnected spiral channel segment portion decreases from the input spiral channel segment portion to the extreme spiral channel segment portion, thereby causing the cross-sectional area of each spiral channel decrease from one input end to one termination end. According to a third aspect of the present invention, a flow channel is formed between the first and second members by means of their splice surfaces. The flow channel is defined by the spill space between the first and second members, as well as a cross section through the spiral channels formed in that way. Although the width of the spill space between the splicing surfaces remains substantially constant, the overall depth of the flow channel decreases from the inlet end of the extrusion die to the outlet end.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a sectional view of an extrusion die according to the present invention having a plurality of disk-shaped modules stacked with spiral channels of a single configuration formed therein; Fig. 2 is a bottom view of an upper die plate for a die module illustrated in fig. 1; Fig. 3 is a top view of a lower die plate for a die module illustrated in Fig. 1; Fig. 4 is a partial, elongated cross-sectional view of a flow channel between the upper and lower die plates of a die module illustrated in FIG. 1; Fig. 5 is a partial, elongated cross-sectional view of a spiral channel formed by the upper and lower die plates of Figs. 2 and 3; Fig. 6 is an enlarged schematic cross-sectional view of a spiral channel illustrating the relative depth thereof in the upper and lower die plates of Figs. 2 and 3; Fig. 7 is a partial, elongated cross-sectional view of the prior art spiral channel; Fig. 8 is a schematic cross-sectional view of a spiral channel of the prior art illustrating the relative depth thereof in the flow surfaces; Fig. 9 is a schematic cross-sectional view of the binary flow separator located in a die body of the extrusion die shown in Fig. 1; and Fig. 10 is a view taken along line 10-10 in Fig. 1, where the spiral channels have been omitted for clarity.

DETAILED DESCRIPTION OF THE INVENTION Referring now in detail to the drawings, in which identical numbers indicate the same elements through the figures, fig. 1 illustrates a radial feed extrusion die 10, otherwise known as an extrusion head, for use in film blowing and other annular extrusion applications. Extrusion die 10 is shown having preferably a plurality of disc-shaped die modules 12 in a stacked arrangement and designated as die modules 12a-g. To provide thermal insulation between each adjacent die module 12, to allow materials of varying temperature characteristics to be used, an air space 13 is provided therebetween. More specifically, it will be seen in Figs. 1-3 that each die module 12 includes an upper die plate 14 and a lower die plate 16, where a lower surface 18 of the upper die plate 14 is positioned adjacent to (or in splice relationship with) a surface upper 20 of the lower die plate 16. The relationship between the upper and lower die plates 14 and 16 is preferably such that a spill space 24 is formed therebetween (see Figs 4 and 5). It will be noted that the extrusion die 10 includes a hollow central mandrel 25 having a lower portion 26 below a lowermost die module 12g and a upper lip portion 28 positioned on a more upper die module 12a. The mandrel 25 forms a common extrusion passage 29 with the internal surfaces of the modules 12 through which the combined polymer layers are moved upward towards an annular extrusion orifice 30. A lower plate member 27 is preferably located below of the base portion of the mandrel 26 to facilitate connection to the air supply (not shown) and a top plate member 31 is located between the lip portion 28 and the die module 12a. It will be understood that the extrusion die 10 can be configured to include any number of die modules 12 to be stacked therein, whereby a corresponding number of layers of thermoplastic material can be used to form the finished film product. A corresponding number of external die feed modules (designated 33a-g) surround the modules 12 to form a general cylindrical die body 34. The annular feed modules 33 include passages by which the melt or polymer is supplied from a extruder towards the die modules 12, as will be described hereinafter.

The stacking arrangement of the modules 12 and 33 in the extrusion die 10 is then achieved by holding each external die body feed module 33 to a die module 12 adjacent thereto by means of a fastener 32 (see the die body feed 33g and module 12g in Fig. 1). Each die module 12 preferably includes an annular flange 39 extending therefrom (from the lower die plate 16 in Fig. 1) to facilitate this union. Additionally, a plurality of holes 35 (see left portion of Fig. 1 and Fig. 10) are provided within each die module 12, lower portion 26 of central mandrel 25 and upper plate member 31 to be aligned and a fastening bolt or other fastening arrangement (not shown) can interconnect them. A plurality of holes 37 are also provided in the die modules 12 so that a fastener (not shown) can interconnect each pair of upper and lower die plates 14 and 16 (see the right portion of Fig. 1 and fig. 10). With respect to each die module 12, it is seen in Fig. 2 that the lower surface 18 of the upper die plate 14 includes a plurality of spiral channel segments 36 formed therein. In the same way, fig. 3 illustrates a plurality of spiral channel segments 38 formed in the upper surface 20 of the lower die plate 16. As seen herein, the spiral channel segments 36 and 38 preferably have the same substantially arcuate length and are placed with other spiral channel segments formed in their respective die plate to build a turbulent pattern. Eight separate spiral channel segments 36 and 38 are shown in Figs. 2 and 3 with respect to the upper and lower die plates 14 and 16, the inlets thereof being circumferentially spaced along an outer periphery and leading inward towards their radially internal terminating ends. Depending on the needs and requirements of the extrusion die 10 (e.g., a desired flow rate, any number of spiral channel segments 36 and 38 can be provided respectively.) It will be noted that each spiral channel segment 36 has a plurality of portions. interconnected spiral channel segment segments, including at least a portion of input spiral channel segment 44 and an end spiral channel segment portion 46. Preferably, one or more intermediate spiral channel segment portions 48 are provided therebetween Likewise, each spiral channel segment 38 has a plurality of interconnected spiral channel segment portions that include at least a portion of input spiral channel segment 45 and an extreme spiral channel segment portion 47, as well as one or more intermediate spiral channel segment portions 49 therebetween although the spiral channel segments 36 and 38 are each shown by including three spiral channel segment portions in Figs. 2 and 3, any numbers of interconnected spiral channel segment portions can be used for desired residence times of the material therein and the frequency of the periodic spill by material flow along the channel surface within the flow channel described in detail herein. More importantly, when the upper die plate 14 and the lower die plate 16 are positioned so that the lower surface 18 and the upper surface 20 are adjacent to each other, a plurality of spiral channels 50 are produced in which the center lines thereof ripple up and down the spill space 24 between the upper and lower die plates 14 and 16 (as best seen in Fig. 6), giving the spiral channels 50 a wavy configuration. It will be understood that each spiral channel 50 is defined by a coupled pair of spiral channel segments 36 and 38 in the upper and lower die plates 14 and 16 respectively. The corrugated design of the spiral channels 50 is achieved by the design of the spiral channel segments 36 and 38, as well as by their relationship to each other. As illustrated in Figs. 5 and 6, each interconnected spiral channel segment portion of the spiral channel segments 36 and 38 has a substantially arcuate cross section of variable size in a plane transverse thereto. Accordingly, each interconnected spiral channel segment portion of the spiral channel segments 36 and 38 gradually increases in depth along a first arcuate surface 54 and 56, respectively, to a point of maximum depth 58 and 60. Subsequently, a second arcuate surface 62 and 64 for each spiral channel segment portion that gradually decreases in depth extends from the maximum depth points 58 and 60 to the lower surface 18 and the upper surface 20, respectively. It will be seen in Fig. 6 that there is an included angle α between the first arcuate surface 54 and the second arcuate surface 62 and there is an included angle ß between the first arcuate surface 56 and the second arcuate surface 64. Preferably, the angles a and ß are increased between the successive interconnected spiral channel segment portions of the spiral channel segments 36 and 38 from the input spiral channel segment portions 44 and 45 to the extreme spiral channel segment portions 46 and 47. The maximum depth points 58 and 60 for successive interconnected spiral channel segment portions preferably decrease from the input spiral channel segment portions 44 and 45 to the extreme spiral channel segment portions 46 and 47. Therefore , it will be understood that each spiral channel 50 decreases in cross-sectional area from the input spiral channel segment portions 44 and 45 to the extreme spiral channel segment portions 46 and 48.

In order that the spiral channels 50 have the desired wavy design, each coupled pair of spiral channel segments 36 and 38 is preferably 90 ° out of phase (at depth). It is seen in Fig. 6 that the points of maximum depth 58 and 60 of the spiral channel segments 36 and 38 are not in alignment, but are placed across a high point of the opposite die plate, known as dots. of spillage 70 and 71, located between adjacent spiral channel segment portions. This is achieved by varying the arcuate lengths of the interconnected spiral channel segment portions for the spiral channel segments 36 and 38. In particular, the arcuate lengths of the interconnected spiral channel segment portions for the spiral channel segments 36 preferably decrease. in the arcuate length from the input spiral channel segment portion 44 to the intermediate spiral channel segment portion 48 and then from the spiral channel segment portion 48 to the extreme spiral channel segment portion 46. With respect to the corresponding interconnected spiral channel segment portions of the spiral channel segments 38, the arcuate length is preferably increased from the input spiral channel segment portion 45 to the intermediate spiral channel segment portion 49 and then from the portion of intermediate spiral channel segment 49 towards the segment portion of c extreme spiral anal 47. It will be understood that this is only a design to achieve the corrugated design of the spiral channels 50 and does not mean that it limits the scope of the invention.

As seen in Fig. 4, a flow channel 72 is formed between the opposite surfaces of the upper and lower die plates 14 and 16 from an outer perimeter 74 towards an internal perimeter 76 of the die module 12. It will be seen that the channel flow 72 is defined by the spill space 24 between the upper and lower die plates 14 and 16, which opens radially inwardly within an annular extrusion passage 29, as well as a cross section through the plurality of spiral channels 50. It is preferred that the width of the spill space 24 between the upper and lower die plates 14 and 16 remain substantially constant, although the overall depth of the flow channel 72 preferably decreases from the outer perimeter 74 towards the perimeter internal 76. Although not shown, it will be understood that spill space 24 may increase in size between internal and external perimeters 76 and 74, with the direction of increase if endo the same as the direction of flow. The cross-section through the spiral channels 50 inherently includes the cross-section of several spiral channel segments 36 and 38 in the upper and lower die plates 14 and 16, which occurs in varying positions in rotated lengths thereof ( and therefore has variable depths). As illustrated in fig. 4, this includes the cross sections through the spiral channel segments in the outer and inner perimeters 74 and 76 (to promote the symmetrical flow of the material in and out of the flow channel 72) and alternating cross sections of channel segments spirals 36 and 38 between them. As previously stated, the spill points 70 and 71 are high points of the spiral channel segments 36 on the lower surface 18 of the upper die plate 14 and the spiral channel segments 38 on the upper surface 20 of the spline plate. lower die 16, respectively, which are located between each adjacent spiral channel segment portion of the spiral channel segments 36 and 38. For example, as seen in FIG. 6, the spill points 70a and 71 a are located between the input spiral channel segment portions 44 and 45 and the intermediate spiral channel segment portions 48 and 49, and the spill points 70b and 71b are located between the extreme spiral channel segment portions 46 and 47 and the intermediate spiral channel segment portions 48 and 49. It is at the spill point 70 that each portion of the material that it flows along the arcuate surfaces 54 and 62 and the spill point 71 that the portion of the material flowing along the arcuate surfaces 54 and 64 is forced to flow into the flow channel 72, which is substantially transverse to the flow direction through the spiral channel 50. The flow kinematics of the material through the spiral channels 50 is produced by the V-shaped configuration of each portion of spiral channel segment, where the material flows from the surface of the die plate to the point of maximum depth and then back to the die plate surface. Therefore, the maximum dwell times for the material within each interconnected spiral channel segment portion is substantially uniform and prevents material degradation that occurs in the previous spiral channel designs. More specifically, it will be understood from the diagrammatic illustration in Fig. 6 that since the material flowing through the spiral channel is a viscous material (e.g., a polymer melt), it has laminar flow characteristics. As seen therein, a portion 73 of the material 75 flowing through the inlet spiral channel segment portions 44 and 45 comes out in the flow channel 72 at the pour point 71a. The material 75 along the arcuate surface 54 of the input spiral channel segment portion 44 to the point of maximum depth 58 and then to the second arcuate surface 62 of the input spiral channel segment portion 44. Subsequently , a portion 79 of the material 75 flows into the intermediate spiral channel segment portion 49 and a portion 81 flows into the flow channel 72 at the spill point 70a. The material 79 is directed towards the second arcuate surface 64 of the intermediate spiral channel segment portion 49 of the spiral channel segment 38, which causes the material 79 to flow towards the upper surface 20 of the lower die plate 16. A portion of the material 83 flows into the flow channel 72 at the spill point 71b and a portion 85 continues toward the second arcuate surface 62 of the intermediate spiral channel segment portion 48 of the spiral channel segment 36. This process continues through of each portion of the spiral channel segment until any material remaining at the termination end 68 of the spiral channel 50 is finally forced into the flow channel 72. Accordingly, the entry of the material into the flow channel 72 occurs throughout the length of the spiral channels 50, with the spill from the material flowing adjacent to the arcuate surfaces 54, 56, 62 and 64 that occurs periodically in the p It should also be noted that the material flowing into the flow channel 72 is mixed with another material flowing through adjacent spiral channels located radially inward of the spiral channel 50. This mixing between adjacent spiral channels promotes the diffusion of welding lines, which can be completely avoided if sufficient mixing takes place. Returning now to FIG. 1, it will be recalled that the extrusion die 10 includes the central mandrel 25 which extends through the die modules 12a-g and the die body 34 so that an annular extrusion passage 29 is produced between the central mandrel and internal perimeter 76 of the die modules 12a-g towards the annular extrusion orifice 30. A plurality of openings 82 are provided in an outer circumferential portion of the upper and lower die plates 14 and 16 for each module of die 12 (see Fig. 10), wherein the material is urged to flow through the upper and lower die plates 14 and 16 into an annular extrusion passage 29. The feed openings 82 of the die modules 12 they are in fluid communication with a feed nozzle 84 within the die body 34 as described below. To promote equal distribution of material path length through the die modules 12, and thereby promote a uniform thickness of the material in the layers of the finished film product, a network 86 of passages is provided for feeding material towards the die module apertures 82. As best seen in Figs. 9 and 10, the network 86 includes a single input 88 connected to the feed nozzle 84 and a plurality of radial output passages in which each is in fluid communication with one of the die module openings 82. The The configuration of the network 86 is such that the distance between the network input 88 and each die entry opening 82 is substantially equal. More specifically, it will be understood that the passage network 86 includes a first arcuate passage 92 in fluid communication with the entrance of the network 88 where the first arcuate passage 92 extends approximately a quarter of the circumference of the die block module 12 from entry 88 in each direction. A first connector passage 94 and a second connector passage 96 are in fluid communication with the ends of the first arcuate passage 92, with the first and second connector passages 94 and 96 being oriented substantially perpendicular to the first arcuate passage 92 and placed in directly opposite relation. each other through the die module 12 (see Fig. 10). It will be noted that the transition between the first arcuate passage 92 and the first and second connector passages 94 and 96, as the transition between all the passages in the network 86, is radiated to promote adequate flow between them. A second arcuate passage 98 is provided in fluid communication with the first connector passage 94, wherein the second arcuate passage 98 extends approximately one eighth of the circumference of the die module 121 from the first connector passage 94 in each direction. Similarly, a third arcuate passage 100 is in flow communication with the second connector passage 96, with the third arcuate passage 100 extending approximately one eighth of the circumference of the die module 12 from the second connector passage 96 in each direction . A third connector passage 102 and a fourth connector passage 104 is in fluid communication with the ends of the second arcuate passage 98, with third and fourth connector passages 102 and 104 being oriented substantially perpendicular to the second arcuate passage 98. U n fifth connector passage 106 and a sixth connector passage 108 are in flow communication with the ends of the third arcuate passage 100, with the fifth and sixth connector passages 106 and 108 being oriented substantially perpendicular to the third arcuate passage 100. It will also be seen in FIG. 10 that the fourth and fourth intact connective passages 104 and 106 and the third and sixth connecting passages 102 and 108 respectively, are placed in directly opposite relation to each other through the die module 12. A fourth arcuate passage 1 10 is in communication of flow with the third connector passage 102, wherein the fourth arcuate passage 1 10 extends approximately one sixteenth of the circumference of the die module 12 from the third connector passage 102 in each direction. A pair of outlet passages 1 12 and 1 14 extend radially inward from the fourth arcuate passage 1 10 to be in flow communication with two feed openings 82 in die module 12. Similarly, a fifth is provided. arched passage 1 16, a sixth arched passage 1 18 and a seventh arched passage 120 which are in flow communication with the fourth connector passage 104, the fifth connector passage 106 and the sixth connector passage 108, respectively, wherein each passage arc extends approximately one sixteenth of the circumference of die module 12 from its respective connector passage in each direction. A pair of exit passages (not identified) extend radially inward from the ends of the fifth arched passageway 1 16, the sixth arcuate passage 1 18, and the seventh arcuate passage 120 and are in flow communication with other feed openings 82 in the die module 12 as those outlet passages 1 12 and 1 14 for the fourth arched passageway 1 10. It will be understood that more or fewer arched passages and connectors may be required depending on the number of feed heights 82 in the die module 12. Therefore, such a number will also affect the circumferential length for the arched passage as will be understood by the expert in the art. technique. While the extrusion die described herein involves a plurality of attachable disk-shaped die plates, a central mandrel and the surrounding die body with a spill space therebetween can employ the unique spiral channel design described in FIG. the present. In such a case, the outer surface of the central mandrel and the internal surface of the die body will have the plurality of spiral channel segments formed therein which together comprise the spiral channels having central lines that undulate back and forth through of the spill space. In addition, the material flowing through the extrusion die (as shown and described herein) may be fed laterally or centrally within the spiral channels depending on the die design.

Claims (17)

1 . A die module for feeding a thermoplastic material through an extrusion die into an extrusion passage, the die module comprising: (a) a die plate having an upper surface and a lower surface, the lower surface including a plurality of spiral channel segments formed therein; Y (b) a lower die plate having an upper surface and a lower surface, the upper surface including a corresponding plurality of spiral channel segments formed therein; wherein the lower surface of the upper die plate and the upper surface of the lower die plate are positioned with respect to each other to form a spill space from an inlet end of the die plates towards the extrusion passage The annular and spiral channel segments of the upper and lower die plates are coupled in coupled pairs of the channel segments to form a plurality of spiral channels, each channel having a central line undulating up and down the space of spill, each of the spiral channels that have an entrance to receive the thermoplastic material.

2. The die module of claim 1, wherein each of the spiral channel segments of the upper and lower die plates gradually increases in depth from the spill space respectively, to a point of maximum depth and subsequently gradually decreases in depth with respect to the spill space.

3. The die module of claim 1, wherein each of the spiral channel segments of the upper and lower die plates has a substantially arcuate cross section in a plane transverse to the spiral channel segment.

4. The die module of claim 1, each of the spiral channel segments further comprising a plurality of interconnected spiral channel segment portions, wherein each of the channel segment pairs includes a channel segment portion. input spiral located adjacent the inlet end and a portion of end spiral channel segment located adjacent to the annular extrusion passage.

5. The die module of claim 4, each of the interconnected spiral channel segment portions having a first depth surface of gradual increase from the spill space, respectively, up to one point of maximum depth and a second surface of depth of gradual decrease from the point of maximum depth to the spill space.

6. The die module of claim 5, wherein an included angle is formed between the first and second surfaces of each of the interconnected spiral channel segment portions, the included angle of each segment of spiral channel segment interconnected in the segment of spiral channel increasing from the input spiral channel segment portion to the extreme spiral channel segment portion.

7. The die module of claim 5, wherein the maximum depth point of the spiral channel segment portion interconnected in the input spiral channel segment decreases from the input spiral channel segment portion to the segment portion of extreme spiral channel.

8. The die module of claim 2, wherein the spiral channel segments in the lower die plate are aligned substantially 90 ° out of phase to depth to form the plurality of spiral channels.

9. The die module of claim 1, wherein the width of the spill space between the upper and lower die plates remains substantially constant.

10. The die module of claim 1, wherein a flow channel is formed between the upper and lower die plate from an outer perimeter to an internal perimeter, the flow channel comprising the spill space between the upper die plates and lower and a cross section through the spiral channels.

The die module of claim 5, wherein a spill point is defined between each interconnected spiral channel segment portion of the spiral channel segment for the upper die plate and each adjacent interconnected spiral channel segment portion. of the spiral channel segment for the lower die plate, wherein the flow of the thermoplastic material along the first and second surfaces flows into the spill space.

12. The die module of claim 1, wherein the spill points for the interconnected spiral channel segment portions of the upper die plate in each of the channel segment pairs are aligned with the points of maximum depth of the interconnected spinal channel segment portions of the lower die plate and the spill points for the interconnected spiral channel segment portions of the lower die plate are aligned with the maximum depth points of the channel segment portions interconnected spiral of the corresponding upper die plate.

13. An extrusion die for feeding a polymer material to an extrusion orifice in annular extrusion applications, the extrusion die comprising. (a) a plurality of die modules assembled in a stack having first and second ends to form a die body of the extrusion die, each of the modules further comprising: (1) a top die plate having a top surface, a bottom surface including a plurality of spiral channel segments formed therein, a peripheral edge defining an outer perimeter of the top die plate extending between upper and lower surfaces, and a central hole through the upper die plate that defines an internal perimeter that provides open communication between the upper and lower surfaces; (2) a lower die plate having an upper surface including a corresponding plurality of spiral channel segments formed therein, a lower surface, a peripheral edge defining an outer perimeter of the lower die plate extending between the upper and lower surfaces and, a central hole through the lower die plate defining an internal perimeter that provides open communication between the upper and lower surfaces; wherein the lower surface of the upper die plate and the upper surface of the lower die plate are positioned with respect to each other to form a spill space between them from the outer perimeters towards the internal perimeters thereof and the spiral channel segments of the upper and lower die plates from a plurality of pairs of spiral channels coupled each having central lines undulating above and below the spill space; (b) means for retaining the die modules in position; (c) a central mandrel extending through the central holes of the die modules, wherein an internal annular extrusion passage is produced between the central mandrel and the internal perimeters of the die modules; Y (d) a plurality of openings located in a circumferential portion of each die module, wherein the die material is urged to flow through each die module toward the internal annular passage.

14. The extrusion die of claim 13, further comprising a network of passages adjacent the external perimeter of the die modules for feeding the material to the die module openings, the network having an individual input and a plurality of passages of output, one of the output passages of the network that is in fluid communication with one of the die module openings, wherein the distance between the network input and each of the die module openings is substantially equal .

15. The extrusion die of claim 13, wherein each spiral channel is formed by a spiral channel segment in the upper die plate and a spiral channel segment in the lower die plate.

16. An extrusion die for feeding a viscous material therethrough to an extrusion passage, comprising: (a) a first member having a surface that includes a plurality of spiral channel segments formed therein; Y (b) a second member having a surface that includes a corresponding plurality of spiral channel segments formed therein, the surfaces of the first and second members being positioned with respect to each other to form a spill space therebetween end of entry to the extrusion passage; wherein the channel segments of the first and second members are coupled in opposite pairs to form a plurality of spiral channels, the segments varying in depth from the spill space to form the channels having center lines that undulate back and forth through the spill space.

17. The extrusion die of claim 16, wherein the first member is an upper die plate with a lower surface having the plurality of spiral channel segments formed therein and the second member is a lower die plate with a surface which has the plurality of spiral channel segments formed therein.