KR890002683B1 - Multi manifold extrusion die and coextrusion process - Google Patents

Abstract

Multimanifold extrusion dies are designated to minimize or eliminate the curtaining effect in coextruded polymer films. the manifold communicates with pressure compensating restriction channels (64,66) of increasing cross-sectional area from mid point to each side so that the melt polymer exits it with equal pressure from side to side. There are expansion chambers (58,60,62) and, before the convergent point, tappered flow restriction channels (64,66,68). The pressure compensating restriction channels (52, 54,56) are formed in part by the head portion of the free floating dividers (26,28) which automatically pivot in response to any difference in the flow rates of the melt streams so that they converge at the same velocities.

Description

Coextrusion method and multimanifold extrusion die

1 is a plan view of a part of a two-layer laminate in which a part of the upper layer which actually shows the retaining effect in each layer is removed.

2 is a view showing the removal and display of an end plate of a three-layer multi-manifold extrusion die according to the present invention.

FIG. 3 is a cross-sectional view at the center of the die of FIG. 2 showing the reduced cross-sectional area of the pressure compensating restricition channel respectively compared to the respective cross-sectional areas as indicated in FIG.

4 is a partially enlarged cross-sectional view taken along the 4-4 line of the pressure compensation restriction passage of the die of FIG. 3, showing the difference in the size of the restriction passage as the intersection or low viscosity thermoplastic material passes through the passage. Illustrated Drawing.

5 and 6 are enlarged cross-sectional views of the tapered flow restriction channel, expansion chamber, and pressure compensation restriction passage of the die of FIG. 3, wherein the tapered flow restriction passage is a maximum or minimum flow restriction. A diagram showing that the input compensation restriction passage has a tapered shape regardless of whether it is in the lower portion.

＊ Explanation of symbols on main parts of drawing

10: die 12, 14, 16: distribution channel

18: confluence point 20: preland channel

26, 28: divider 46, 48, 50: manifold chamber

52, 54, 56: pressure compensation restriction passage 58, 60, 62: expansion chamber

64, 68: flow restriction passage

FIELD OF THE INVENTION The present invention relates to melt laminates of thermoplastics, and in particular, the present invention seeks to reduce the curtaining effect and to eliminate flow instability between melt streams of layers of thermoplastics of different properties.

In the molded extruded layer of thermoplastic material, it is a problem that a long time solution is required for the occurrence of the cooling effect. Figure 1 shows a two-layer laminate of thermoplastics, which shows that the covering effect is in both layers. In multi-layer coextrusion, the flow instability between the melt flows of the layered thermoplastic is also difficult. 18 pp. 620-623 (1978) of Polymer Engineering and Science published by Schlenk and others, and 18 180-186 (1978) of Polymer Engineering and Science published by Han and others. ) Is the most representative research literature describing flow instability.

The present invention is directed to solving these problems in multi-manifold extrusion dies. Many melt chamber extrusion dies are known, as disclosed in U.S. Patent No. 3,877,857 to Melid. The die of this structure has two split dies with a central divider extending therebetween, and each split die has an upstream melt chamber or manifold chamber connected by a transfer passage having a narrow cross-sectional area. The melt flows from the downstream manifold chamber via a second passage having a narrow cross-sectional area and joins with another melt to form a melt laminate.

Also disclosed by U.S. Patent No. 3,694,119 by shibbling is an extruded nozzle having a central tongue separating two flow paths ending in the discharge groove. In a particular embodiment of the extrusion nozzle, the transport passageway of the molten thermoplastic material and / or the longitudinal grooves connected to the passageway are constructed such that the cross section narrows toward the center of the transport passageway or the longitudinal groove, which flows out of the extruder. The pressure distribution is further improved in the resulting material, resulting in a very uniform layer. In one embodiment of the nozzle, the melt flow of the thermoplastic material flows through a pair of distribution passages connected by narrow flow passages.

On the other hand, as disclosed by U.S. Patent No. 4,344,907 to Harrington, coaxial tubular extrusion molding that restricts flow in a flow passage of low viscosity resin to increase the pressure intensification of the resin as the molten resin passes through the die. Co-axial tubular extrusion dies are known. Separating the two flow paths of this die is a divider with walls that form a flow restriction in part. Also illustrated in FIG. 3 of US Pat. Nos. 4,152,387 and 4,197,069 are multi-manifold coextrusion dies having adjustable dividers installed between two flow passages, each flow passage having a back pressure cavity. a back pressure cavity and a flow restriction passage located between the back pressure cavity and the flow passage confluence point. The coextrusion die is provided with a flow restricting passage width adjusting device so that the converging thermoplastic melt flows at a substantially uniform speed, and the thickness of each layer can be varied indefinitely by the operation of an adjustable divider.

As a result, these dies create a laminar flow at the confluence and allow for infinite variations in the thickness of each layer in the laminate formed. However, a drawback of such multi-manifold illustrated extrusion dies is that the laminate layer formed thereby exhibits a curtaining effect. In addition, even though the confluence of melt flows occurs at nearly uniform speeds as a result of the tendency to flow instability of the types described in the previously published Schlenk and Han papers, this type of flow instability is defined between layered melt flows. Can be found in Therefore, in addition to retaining the technical advantages provided in the prior art dies of U.S. Patent Nos. 4,152,387 and 4,197,069, there is a need to minimize or even eliminate the totaling effect on multi-manifold extrusion dies. have.

Such an improved die would be very good if it could eliminate its effect on the various viscous resins by simply removing its components and replacing them with exchangeable components precisely designed for specific resin viscosity. have. There is also a need for a multi-manifold extrusion die that reduces or eliminates flow instability between layered melts. Such a die can improve the process for thermoplastic melt laminates. It is therefore an object of the present invention to provide a multi-manifold die device that minimizes or eliminates the curtaining effect and, in addition, forms a flow of laminate at the confluence, and can give an infinite variation in the thickness of each layer in the formed laminate. It also provides a multi-manifold, die structured to overcome the retaining impact on resins of various viscosities by simply removing or replacing interchangeable components precisely designed for specific resin viscosities. There is.

Another object is to provide a die of a structure that reduces or eliminates the flow instability between layered melts, while minimizing or eliminating the curtaining effect, and reduces the flow instability between the layered melts. It is to provide an improved method for melt laminate of thermoplastics to be resolved.

As described above, the present invention minimizes and eliminates the curtaining effect, forms the flow of the laminate at the confluence point, and allows infinitely varying the thickness of each layer in the formed laminate, as previously described. It is to provide a multi-manifold extrusion die.

This extrusion die includes an adjustable divider or metering vane blade disposed between two flow paths and a plurality of flow paths that cross at the die and eventually gather at the confluence points in the die. Each divider has a head and a tip, and the head is equipped with an adjustment device that is used to rotate the head around the axis of the divider to move the tip and control and define the transverse area. . Each of the flow passages includes a manifold chamber located upstream from the divider, and also includes a pressure compensating restriction passage, an expansion chamber, and a tapered flow restricting passage down to the downstream side. The manifold chamber has a sufficient longitudinal size such that the melt flow of molten thermoplastic flowing out of the manifold chamber is subjected to relatively greater pressure at the midpoint of the side and side than at its side.

The pressure compensation restriction passage increases the cross-sectional area from its center to both ends, thereby supplying reverse resistance to the flow of the melt, thereby flowing at a relatively higher pressure at the midpoint than before flowing the pressure compensation restriction passage. It flows out of this passage at almost uniform pressure from to side.

The pressure compensation restriction passage is formed in part by the head of the divider, and the tapered flow restriction passage has a cross-sectional size that is precisely defined by the tip of the divider by manipulating the adjusting device at the head of the divider. . The expansion chamber has a larger cross section than the cross section of the pressure compensation confinement passage, which also has a larger cross section than the tapered flow restriction passage.

The expansion chamber and tapered flow restriction passages each have a longitudinal size that allows the melt flow to be maintained under substantially uniform pressure from side to side. The melt flows from the side to side in a tapered flow restriction passage under substantially the same pressure, and merges in one place with at least one other melt that flows from side to side at about the same pressure and in fact at the same rate Will join. Also provided by the present invention is a method of minimizing or eliminating the curtain effect in the melt laminate of thermoplastics, which method melts a molten thermoplastic material that flows at a relatively higher pressure at the side and side space points than at the side. The flow includes a reverse resistance to the flow, whereby the melt flows at the same pressure from side to side while actually maintaining the same pressure, expanding the thickness of the cross section of the melt, As long as the thickness of the cross section of the expanded melt flow is narrowed down to the size of the cross section of the required, there is at least one other thin melt and thin melt flows that actually maintain the same pressure and flow from side to side under substantially the same pressure. Are joined until the melt laminate is ejected from the extrusion die. Each melt flow of the resulting melt laminate is actually kept at a uniform pressure from side to side.

As described above, the present invention relates to an improved method of melt laminates of thermoplastics with an improved multi-manifold extrusion die, and in particular, the present invention minimizes or eliminates the effect of the known defects in laminate layers of thermoplastics. Can be. That is, the present invention aims to minimize or eliminate the curtaining effect, to generate a flow of the laminate at the confluence point of the melt flows of the molten thermoplastic materials joining at the same time, and to change the thickness of each laminated layer infinitely.

Moreover, the present invention aims to reduce and eliminate flow instability in such structures as described in the Schlenk and Han technique described above. Moreover, the present invention is useful for forming laminates from thermoplastics having the same or different flow properties. Thermoplastics, on the other hand, are not limited to low and high density polyethylene, polypropylene, polycarbonate esters, polyamides, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, polyacrylonitrile and copolymers thereof. )to be.

Hereinafter will be described in detail with reference to the accompanying drawings.

2 and 3 show a multi-manifold extrusion die 10 according to the present invention. The die 10 is provided with flow paths 12, 14 and 16 for three thermoplastic resin passages, and the joining of these resins at the confluence point 18 to form a three-layer melt laminate. Is done.

It will be appreciated that the die of the present invention may be used, for example, to form two, five or seven layers, or may be used to form laminates having a greater number of layers. The molten laminate passes through an outlet passage consisting of a free tapered passage 20, conveniently tapered, and a land passage 22, typically shown in cross section, which typically forms a parallel wall, and then at the opening 24. It is discharged to the outside.

An adjustable divider or flow control vane blade 26 is located between the flow paths 12 and 14, the divider 28 is located between the flow paths 14 and 16, and the divider 26 and Reference numeral 28 has heads 30 and 32 and leading ends 34 and 36 as shown in the figure.

Each of the heads 30 and 32 is provided with adjusting devices 38 and 40, and the adjusting devices 38 and 40 are easily operated from the outside of the die 10. That is, it is possible to rotate in any direction of the arrows 42 and 44.

By manipulating the adjusters 38 and 40, each of the heads 30 and 32 has its periphery around its axis to define and adjust the lateral zone by actuation of the tips 34 and 36. I can turn it.

Each of the flow passages 12, 14, and 16 includes manifold chambers 46, 48, 50, and pressure compensation restriction passages 52, 54, 56, and expansion chambers. (58), (60), (62), and flow restriction passages (64), (66), and (68). In order to simplify the description, the following description relates to one type of these distribution channels, but it will be appreciated that the description also applies to the other two distribution channels of the die 10.

The manifold chamber 46 is located upstream of the divider 26, and the manifold chamber 46 is in the shape of a hanger. That is, the manifold 46 has a narrow cross-sectional area from its center toward its respective ends, and this manifold chamber 46 is characterized in that it represents the end 70 of the manifold chamber 46. It is shown by comparing with the cross section of the manifold chamber 46 of 2 degree | times. The manifold may be, for example, a constant cross section or a cross section which is variable depending on the needs of each thermoplastic.

Manifold chambers that have a constant cross section from end to end are known as keyhole manifolds, and the residence time of thermoplastics in these keyhole manifold chambers is longer than in hanger shaped manifolds. Therefore, the latter is preferred where it is advantageous, for example, to have a short stay time because of the thermal sensitivity. In addition, a hanger-shaped manifold chamber is preferable to a keyhole manifold because new thermoplastics flow more quickly when used thermoplastics are removed. In the manifold, transverse flow of the molten resin occurs as a result of the molten resin being distributed longitudinally over the entire length of the manifold. In the multi-manifold die 10, the longitudinal size of the manifold chamber is considerable.

That is, the melt flow out of the manifold chamber, approximately 10-60 inches or more, results in relatively greater pressure at the side and center points of the manifold chamber than at the side of the manifold chamber. The size of the manifold chamber for the cross section is determined by the required throughput of the thermoplastic. As shown in FIG. 3, the amount of material to be processed through the manifold chamber 48 in the die 10 is needed, so that the manifold chamber 46 has fewer cross sections than the manifold chamber 48. You can see what you have.

The pressure compensation restriction passage 52 is located downstream from the manifold chamber 46, which is a vertical wall 72 of the head 30 of the divider 26 and an inner wall of the die 10. And the passage 52 has an end portion 78 as shown in FIG. 2, and has a cross-sectional area whose area increases from its central portion 76 to the end of each flow path. It is characterized by having. This feature of the passage is also shown in FIG. 4 in the case of the pressure compensation confinement passage 54, and the arrows used in this figure indicate the width at the center of the passage 54. As shown in FIG.

In addition, the size of the pressure-limiting passage is varied depending on whether a relatively high viscosity resin passes through the passage or a relatively low viscosity resin passes through the passage (represented in FIG. 4 for the dashed resin). .

The variable cross section of the pressure compensation restriction passage 52 is countercurrent to flow in the melt flow of thermoplastic material exiting the manifold chamber 46 under relatively high pressure at the midpoint of the side and side rather than at the side of the passage. To supply. The exact size of the cross section used in the pressure-limiting passage 52 is selected according to the viscosity of the particular resin passing through the passage 52 and from the passage 52 under substantially uniform pressure from side to side. Allow the melt to flow out.

Thus, this passage is subjected to reverse resistance to flow in the melt such that the melt flows at a substantially uniform pressure from side to side. Applicants are convinced that this is necessary to reduce or eliminate the curtaining effect in the die.

Referring to FIG. 5 and FIG. 6, the pressure compensating passage 52 shown in the cross section is located at the downstream flow restriction passage 64 at the minimum flow restriction position (figure 6) or at the maximum flow restriction position (figure 5). Taper in the direction of flow, regardless of whether or not the flow restrictor path 64 is in the maximum flow limit position, giving a relatively greater flow limit. Conversely, the pressure limiting passage 52 may be parallel when the flow restricting passage 64 is in the minimum flow restricting position, as indicated by the cross section. From the point of view of the longitudinal and cross-sectional views, the shape required for the pressure compensation restriction passage 52 is usually achieved by the vertical wall 72 of the divider 26 machined to form the vertical wall.

The pressure compensating restriction passage 52 actually supplies resins of molten thermoplastic material flowing under uniform pressure from side to side to the expansion chamber 58, and the expansion chamber 58 of the pressure compensation restriction passage 52 It has a larger cross section than the cross section. In fact, the expansion chamber 58, which consists of a substantially uniform cross section from end to end, is significantly larger in cross section than the pressure-limiting passage 52, as shown in FIGS. 2 and 3. Therefore, an important function provided by the expansion chamber 58 is to expand the thickness of the flow melt, for example, and to allow the melt flow to be regulated by the flow restriction passage 64 to the required cross-sectional thickness. The expansion chamber 58 is formed by the vertical wall 72 of the central portion 76 of the divider 26 and the inner wall 72 of the die 10.

An important feature of the expansion chamber 58 is that it has a longitudinal dimension which keeps the melt flow at a substantially uniform pressure from side to side. Thus, expansion chamber 58 is characterized as having the same longitudinal dimension as manifold chamber 46. However, if the uniform flow pressure achieved by the pressure compensation restriction passage 52 is not reversed as the molten resin flows through the expansion chamber 58, there may be a small deviation in the longitudinal size.

As can be seen from the foregoing description of the expansion chamber 58, the expansion chamber 58 has a function of expanding the thickness of the flowing resin, while maintaining the molten resin at a substantially uniform flow pressure. . Moreover, the upper part of the expansion chamber 58 is configured to prepare for the expansion of the resin flow thickness, while the lower part of the expansion chamber 58 has a passage for allowing the installed melt resin to flow to the confluence point 18 as shown in the cross section. It can be seen from FIG. 2 and FIG. 3 that the taper in the direction of the flow restriction passage 64 is provided.

As indicated by the cross section, the flow restriction passage 64 is tapered in the direction of the confluence point 18. This flow restricting passage 64 is made up of fewer cross sections than the expansion chamber 58, and makes the thickness of the cross section of the expanded melt resin stream thinner. The size of the cross section of the flow restricting passage 64, which is advantageously composed of a substantially constant cross section from end to end, is remotely controlled by precisely rotating the head 30 of the divider 26 about an axis. In particular, the width of the flow restricting passage 64 is precisely set by rotating the head 30 of the divider 26 through the operation of the adjusting device 38 provided outside the die 10. An important feature of the flow restriction passage 64 is that it also has a longitudinal size that allows the molten resin to be maintained at a substantially uniform flow pressure. Therefore, this flow restriction passage 64 normally has the same longitudinal size as the manifold chamber 46.

And as the molten resin passes through the flow restriction passage 64, there may be some variation in the longitudinal size if the substantially uniform flow pressure of the molten resin is not obstructed in the reverse direction.

From the technical configuration of the flow restriction passage 64 as described above, it can be seen that the molten resin flows out of the passage under a substantially uniform flow pressure from side to side. Moreover, the flow restriction passage 64 functions to thin the expanded molten resin stream into the desired cross section, so that the molten resin stream is actually maintained at a uniform flow pressure.

As a result of the flow restriction passage 64 being located downstream of the expansion chamber 58, another function performed by the expansion chamber 58 is the function of the back pressure cabaty. Similarly, the position of the pressure compensation restriction passage 52 also causes the manifold chamber 46 to function as a rear pressure cavity. As expected, the difficulty in inventing the multi-manifold extrusion die of the present invention is to eliminate or minimize the curtaining effect and at the same time to the multi-manifold die of FIG. 3 of US Patent Nos. 4,152,387 and 4,197,069. To keep all the benefits.

Conveniently, the present invention makes the speed of the molten resins joined at the confluence point 18 almost uniform, and by simply manipulating the adjustable divider 26, the thickness of each layer can be infinitely varied, thereby allowing laminar flow at the confluence point. It forms a laminar flow and can infinitely change the thickness of each layer in the formed laminate.

In addition, the present invention minimizes or eliminates the curtaining effect. Although the molten resin exerts a uniform pressure along the length of the extended flow restriction passage of the adapters of US Pat. Nos. 4,152,387 and 4,197,069, the layer of laminate formed by using the adapter exhibits a curtaining effect. Moreover, the present invention can eliminate or reduce the instability of the flow between the layered melt streams.

인치 정도로 가능한 한 출구 통로를 짧게하여 달성된다. 그렇지 않으면, 출구통로는 예를들어 약 4-6인치일 수 있다.This advantage places the confluence point 18 as close as possible to the opening 24, ie for example

This is accomplished by making the outlet passage as short as possible in inches. Otherwise, the exit passage can be, for example, about 4-6 inches.

Another advantage of the present die 10 is to provide a pressure compensation limit passage 52, 54, 56 that is adapted so that the viscosity of the molten resin passes through the passage through the die 10. For this purpose, each divider 26 and 28 can be removed and replaced with a replaceable divider.

This eliminates the need to use a completely different die differently with the required type of pressure compensation path. This benefit saves time and money. In operation, resins of the molten thermoplastic material enter the passage 12 and pass through the manifold chamber 46, where resins of the molten thermoplastic material spread longitudinally therein, from side to side rather than from side to side. Flows under relatively high pressure at the midpoint of. The molten resin flows through the pressure compensating restriction passage 52 which provides reverse resistance to the flow of the resin, and as a result, the molten resin flows under a relatively uniform pressure from side to side, thereby limiting the pressure compensation. It exits the passage 52 and then passes through the expansion chamber 58, in which the cross-sectional thickness of the melt flow is expanded while in fact a uniform flow pressure is maintained.

The expanded molten resin stream is actually passed through the flow restriction passage 64, in which the thickness of the cross section becomes thin to the required cross-sectional size. The thinned melt resin then joins at confluence point 18 along with two other melt resins that flow under a substantially uniform pressure from side to side, respectively. At the confluence point 18 the melt flow is actually at a constant speed, and the resulting molten laminate passes through the freeland passage 20 and then through the land passage 22 to the last opening 24. From the die 10. In the method of removing or minimizing the curtaining effect in the melt laminate of the resin, an important step is as follows.

Molten thermoplastics flowing at relatively high pressure at the midpoint of the side and side rather than at the side are subjected to reverse resistance to the flow, whereby the melt flow is actually flowed under a uniform pressure from side to side. In this way, the thickness of the resins expands while maintaining a substantially uniform flow pressure. As this flow pressure is continuously maintained, the thickness of the cross section of the expanded resin is thinned to the required cross-sectional size.

The thinned molten resin is joined with at least one other thin molten resin flowing at a substantially uniform pressure from side to side to form the molten laminate. The actual uniform pressure of each melt flow in the melt laminate is maintained until the melt laminate stops flowing.

This last step in the multi-manifold die according to the present invention can be achieved by having each layer of the melt laminate have a longitudinal size that actually maintains a uniform flow pressure. Typically, the outlet passages have the same longitudinal dimensions as the manifold chambers, which will all characteristically have the same longitudinal dimensions.

As previously described, the outlet passage consists of a freeland passage and a land passage, which is tapered as indicated by the cross section, which is necessary to minimize the instability of the flow between the layered melt streams. will be.

As described above, the present invention is not limited to the above description, but may be modified or modified as much as possible within the concept area of the present invention.

Claims (13)

In the die 10, the first and second flow paths 12 and 14, which cross the die and join at the confluence point 18, have the head 30 and the tip 34, and the tip 34 is provided. Between the first and second flow paths 12, 14 having a control device 38 used to rotate the head 30 about its axis to regulate and define the cross-section moving therein. In the multi-manifold extrusion die consisting of an adjustable divider 26 installed in the die, the aforementioned flow passages 12 and 14 are manifold chambers 46 and 48, a portion of which is downstream to the confluence point 18. Pressure compensating restriction passages 52 and 54 formed in the head of the divider 26, expansion chambers 58 and 60, and taper-shaped flow restriction passages 64 and 66, respectively. (58) (60) has a cross sectional area larger than the cross sectional area of each of the pressure compensation restriction passages (52) and (54), and larger than the cross sectional area of each of the tapered flow restricting passages (64) (66), respectively. every The fold chambers 46 and 48 have a longitudinal dimension of sufficient size such that the thermoplastic melt flow discharged therefrom is relatively greater in pressure at the midpoint between the sides than at its sides, with each pressure Compensation restriction passages 52 and 54 have a relatively higher pressure from the side to side of the thermoplastic melt which is relatively higher in pressure at the sides and at the midpoints of the sides before passing through the pressure compensation passages 52 and 54. The cross sectional area is increased from the center of the pressure compensating limit passage to both ends so as to discharge at a uniform pressure, and each of the expansion chambers 58 and 60 and the tapered flow restricting passages 64 and 66 have a respective melt flow. Maintains a substantially uniform pressure from side to side and discharges from each tapered flow restricting passage 64, 66 to define a longitudinal dimension defining the passage for each melt flow joining at confluence 18. Multi-manifold extrusion die which comprises. The multi-manifold extrusion die according to claim 1, wherein each of the flow passages comprises a hanger-shaped manifold. 2. The die manifold of claim 1 wherein each expansion chamber has approximately the same longitudinal dimension as each of the manifold chambers. The multi-manifold extrusion die according to claim 1, wherein the dividers (26) described above are removed and exchanged. 3. The third flow path (16) according to claim 1, wherein the third flow path (16) joins at the confluence point (18) together with the first flow path (12) and the second flow path (14) posted across the die (10). Multi-manifold extrusion die. The thermoplastic melt flow, which is relatively more pressure at the midpoint between the sides than at the sides, is passed through the pressure compensation passage of the multi-manifold die with increasing cross-sectional area from the center to both ends, thereby allowing the melt flow to flow. Subjecting it to reverse resistance so that it flows from side to side with a substantially uniform pressure; expanding the cross-sectional thickness of the melt while maintaining the above substantially uniform pressure; Reducing the cross sectional thickness of the expanded melt while maintaining it, joining the reduced thickness of the melt flowing from side to side with a substantially uniform pressure and at least one other reduced thickness of the melt; To each melt flow of the melt laminate until the joined melt laminate is discharged from the aforementioned multi-manifold die. Method due to the substantially uniform fluid pressure characterized in that it is composed of a step of maintaining the thermoplastic material co-extruded. 7. The method of co-extrusion of thermoplastics according to claim 6, wherein three melt streams are joined to form three layers of melt laminates. The method of co-extrusion of thermoplastics according to claim 6, wherein two or five melt streams are joined to form two or five layer melt laminates. 7. The method of co-extrusion of thermoplastics according to claim 6, wherein the thermoplastics described above comprise low density or high density polyethylene. 8. The method of co-extrusion of thermoplastics according to claim 7, wherein the thermoplastics described above comprise polypropylene. 8. A method as claimed in claim 7, wherein the thermoplastic material described above comprises polyamide. 8. The method of co-extrusion of thermoplastics according to claim 7, wherein the thermoplastics described above comprise polystyrene. 8. The method of co-extrusion of thermoplastics according to claim 7, wherein the thermoplastics described above comprise polyvinylidene chloride.

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