Multi-screw extruder implemented with a vacuum vent hole and screws designed to compact material processed through the extruder or to extract fluid from it, and processes

Abstract

Multi-screw extruder (50) implemented with a vacuum vent hole (62) positioned between spaced material feed locations (70, 72) of an extruder cylinder (52) to facilitate the compaction of material fed into a material feed location (70, 72) downstream of the vacuum vent hole (62), the extraction of unwanted fluid from material fed into the extruder (50), or both, the extruder (50) comprising: a thermally controlled extruder cylinder (52) with several linked cylinder segments (1, 2, 4, 5, 8, 10, 12) defining a longitudinal axis (54) and an interior (56) of the extruder cylinder (52) through which several axially spaced extruder screws (58) extend, wherein the interior (56) of the extruder cylinder (52) has an inner surface (60); a first feed point (70) associated with a first opening formed in a first cylinder segment of the several linked cylinder segments (1, 2, 4, 5, 8, 10, 12), and a second feed point (72) associated with a second opening formed in a second cylinder segment of the several linked cylinder segments (1, 2, 4, 5, 8, 10, 12), the second cylinder segment being positioned downstream of the first cylinder segment; a vacuum vent hole (62) associated with a vent hole opening formed in a third cylinder segment of the multiple linked cylinder segments (1, 2, 4, 5, 8, 10, 12) and positioned between the first and second feed points (70, 72), wherein the vacuum vent hole (62) is configured to apply a vacuum to the vent hole opening in the third cylinder segment for passage through the vacuum vent hole (62) to a free volume (74) between the inner surface (60) of the extruder cylinder (52) and a section (73) of each of the multiple extruder screws (58), wherein the sections (73) of the multiple extruder screws (58) function as a filter zone (76); and wherein each section (73) of the multiple extruder screws (58) of the filter zone (76) has longitudinal mixing elements (78) arranged between the vacuum vent hole (62) and the second opening associated with the second feed point (72), wherein the mixing elements (78) of the filter zone (76) are configured to allow a polymer material introduced at the first feed point (70) to flow as molten polymer material through the filter zone (76) along the longitudinal axis (54) of the extruder barrel (52), and to capture material introduced at the second feed point (72) in order to prevent the vacuum from drawing a significant amount of the material through the vacuum vent hole (62), and the mixing elements (78) of the filter zone (76) are configured to prevent,that the flow of molten polymer material completely fills the free volume (74) between the extruder screws (58) and the inner surface (60) of the extruder barrel (52) in order to avoid forming a dynamic seal, and thereby allow the negative pressure to extract unwanted fluid present in the filter zone (76) through the negative pressure vent hole (62).

Description

Related registration

[0001] This application claims the benefit of U.S. Patent Application No. 62 / 649,845, filed March 29, 2018. Copyright notice

[0002] © 2019 Entek Manufacturing LLC. A portion of the disclosure of this patent document contains material subject to copyright protection. The copyright owner does not object to the facsimile reproduction by anyone of the patent document or patent disclosure as it appears in the patent file or patent records of the Patent and Trademark Office, but otherwise reserves all copyright rights of any kind. 37 CFR § 1.71(d). Technical area

[0003] This disclosure relates to multi-screw extruders, and more particularly to such an extruder to which a negative pressure is applied to compress material fed into the extruder or to extract fluid therefrom, or both. Background information

[0004] Fig. 1A shows a thermally controlled multi-screw extruder 10a conventionally designed with a barrel 12 comprising interlinked barrel segments 1-12. At least one polymer material is introduced into the extruder 10a at barrel segment 1 through a primary feed opening 14. Extruder screws (not shown) rotating within the barrel 12 form molten polymer from the polymer material introduced at barrel segment 1. The extruder 10a is designed with an opening for a back-atmosphere vent 16. The opening for the back-atmosphere vent 16 is located at barrel segment 5.Barrel segment 5 is adjacent to and upstream of barrel segment 6, which has a secondary feed port 18 so that moisture, air, or other gases accompanying a particulate filler material introduced at the secondary feed port 18 can escape through the atmosphere back vent 16 to slightly densify the particulate filler material. Each of the extruder screws has a section located between the back vent port 16 and the secondary feed port 18 that is designed so that the molten polymer and other material moving through the extruder 10a do not completely fill any free volume in the space between the screws and the inner surface of the barrel, so as not to form a dynamic seal.A dynamic seal is a dam or plug of flowing polymer material that is continuously replenished by new material entering and leaving an internal extruder zone.

[0005] In certain conventionally designed extruders, a second atmosphere-forward vent 20 located on the barrel segment 8 downstream of the secondary feed port 18 allows the escape of air accompanying the particulate filler material introduced at the secondary feed port 18. The escape of air through the atmosphere vent 20 results in moderate compaction of the introduced particulate filler material. Extruder screw sections located between the secondary feed ports 18 and the atmosphere-forward vent 20 are designed such that the molten polymer and other material moving through the extruder 10a do not completely fill the free volume between the extruder screws and the inner surface of the barrel, so as not to form a dynamic seal.

[0006] Fig. Figure 1B shows a thermally controlled multi-screw extruder 10b which, except as characterized below, is conventionally constructed in the manner described for the multi-screw extruder 10a of Fig. 1A. Common components and features of extruders 10a and 10b share the same reference numerals. Extruder 10b illustrates the arrangement of atmospheric vent 16 and a downstream vacuum vent 22 to remove moisture from polymers and material introduced through primary feed port 14. Atmospheric vent 16 is located on barrel segment 5, whereby the polymer material flowing through barrel 12 is not fully melted and no dynamic seal exists.The atmosphere vent 16 also allows gases generated by the initial melting of the polymer material introduced at the barrel segment 1 to escape from the extruder 10b, and allows moisture content to escape from the polymer material before it melts to an extent that would result in hydrolysis of the molten polymer as it progresses along the length of the extruder 10b. The vacuum vent 22 is located downstream of the barrel segment 10, and dynamic seals on either side of the vacuum vent 22 promote a strong vacuum for the removal of unwanted fluid.

[0007] There are other extruders designed to compact material being processed by a multi-screw extruder. U.S. Patent No. 8,360,627, owned by Coperion GmbH, describes an extruder that applies a negative pressure to the interior of an extruder barrel or to a fixed feeder through a sintered metal filter disposed on the inner surface of the barrel to compact materials entering the extruder. U.S. Patent Application Publication No. US 2015 / 0001045, owned by The Japan Steel Works, LTD, describes a side-feed vent system in which a negative pressure is applied directly to a feeder attached to an opening on the side of an extruder to compact materials in the side feed.A multi-screw extruder is also known from US 2012 / 0235090 A1, wherein the vent openings of the extruder are dimensioned in such a way that venting takes place to a satisfactory extent and at the same time no material can leave the extruder through the vent opening. Summary of Revelation

[0008] The disclosed multi-screw extruder combines the application of negative pressure to a vacuum vent positioned between material feed locations of the extruder and the use of specially designed extruder screws to extract gases, primarily air, from the extruder to compress the materials fed into them and extract unwanted fluid from material introduced for mixing with molten polymer material flowing through the extruder. The disclosed multi-screw extruder is operationally versatile in that it is capable of performing the material compression and fluid extraction processes either separately or simultaneously.

[0009] In a preferred embodiment, the disclosed multi-screw extruder is implemented with a vacuum vent positioned between spaced-apart material feed locations of an extruder barrel to facilitate the compaction of material introduced into a material feed location downstream of the vacuum vent, the extraction of unwanted fluid from material introduced into the extruder, or both. The extruder includes a thermally controlled extruder barrel comprising a plurality of interlinked barrel segments defining a longitudinal axis and an interior of the extruder barrel through which a plurality of axially spaced extruder screws extend. The interior of the extruder barrel has an interior surface.A first feed location associated with a first opening is formed in a first cylinder segment of the plurality of linked cylinder segments, and a second feed location associated with a second opening is formed in a second cylinder segment of the plurality of linked cylinder segments. The second cylinder segment is positioned downstream of the first cylinder segment.

[0010] A vacuum vent hole associated with a vent hole opening is formed in a third cylinder segment of the plurality of linked cylinder segments and is positioned between the first and second feed locations. The vacuum vent hole is configured to apply a vacuum to the vent hole opening in the third cylinder segment for passage through the vacuum vent hole to a free volume between the inner surface of the extruder barrel and a portion of each of the plurality of extruder screws. The portions of the plurality of extruder screws function as a filter zone, and each portion of the plurality of extruder screws of the filter zone includes longitudinal mixing elements disposed between the vacuum vent hole and the second opening associated with the second feed location.The mixing elements of the filter zone are configured to allow polymer material introduced at the first feed location to flow as molten polymer material through the filter zone along the longitudinal axis of the extruder barrel and to trap material introduced at the second feed location to prevent the negative pressure from drawing a significant amount of the material through the negative pressure vent. The mixing elements of the filter zone are configured to prevent the flow of molten polymer material from completely filling the free volume between the extruder screws and the inner surface of the extruder barrel, so as not to form a dynamic seal and thereby allow the negative pressure to draw unwanted fluid present in the filter zone through the negative pressure vent.

[0011] In one embodiment of the multi-screw extruder, the material introduced at the second feed location comprises a material that acts as a particulate filler for the molten material in the filter zone, and the unwanted fluid present in the filter zone comprises air, and the extraction of air performs a significant densification of the particulate filler.

[0012] In a second embodiment of the multi-screw extruder, the material introduced at the second feed location comprises moisture-containing material, and the unwanted fluid extracted through the vacuum vent hole comprises moisture removed from the moisture-containing material.

[0013] In a third embodiment of the multi-screw extruder, the material introduced at the second feed location comprises liquid supplied to mix with the molten polymer material in the filter zone, and the unwanted fluid extracted through the vacuum vent hole comprises a residual amount of the supplied liquid.

[0014] The disclosed thermally controlled extruder, which includes a plurality of interlinked barrel segments defining a longitudinal axis and a plurality of rotatable extruder screws configured to mix material introduced into the extruder, can be used to perform a high throughput process for forming a composite comprising polymer material and particulate filler material mixed by operation of the thermally controlled extruder without appreciable vacuum vent removal of the particulate filler material from the extruder.

[0015] The method includes introducing polymer material into a first feed location associated with a first opening formed in a first barrel segment of the extruder. The polymer material is processed by rotation of the plurality of extruder screws to form a flow of molten polymer material. A portion of each of the plurality of extruder screws includes longitudinal mixing elements, and the portions of the plurality of extruder screws function as a filter zone. The method also includes introducing a particulate filler material into a second feed location associated with a second opening formed in a second barrel segment of the extruder. The second barrel segment is positioned downstream of the first barrel segment such that the plurality of extruder screws mix the particulate filler material with the flow of molten polymer material.The method also includes applying a negative pressure to a vacuum vent hole associated with a vent hole opening in a third cylinder segment positioned between the first and second feed locations. The mixing elements, which function as a filter zone, are disposed between the vacuum vent hole and the second opening associated with the second feed location.The mixing elements of the filter zone cooperate to allow the flow of molten polymer material to move along the longitudinal axis of the extruder, to prevent the negative pressure through the negative pressure vent hole from sucking a significant amount of the particulate filler material introduced at the second feed location, and to extract air present in the filter zone, thereby performing significant compaction of the particulate filler as the plurality of extruder screws rotate to form a composite with the compacted particulate filler material mixed with the flow of molten polymer material.

[0016] The disclosed thermally controlled extruder, which includes a plurality of interlinked barrel segments defining a longitudinal axis and a plurality of rotatable extruder screws configured to mix material introduced into the extruder, can be used to perform a method for extracting unwanted fluid present during operation of the thermally controlled extruder forming a composite by mixing polymer material with added material.

[0017] The method includes introducing a first amount of polymer material into a first feed location associated with a first opening formed in a first barrel segment of the extruder. The first amount of polymer material is processed by rotation of the plurality of extruder screws to form a flow of molten polymer material. The method also includes introducing a second amount of polymer material, or a combination of added material and a second amount of polymer material, into a second feed location associated with a second opening formed in a second barrel segment of the extruder.The second barrel segment is positioned downstream of the first barrel segment such that the plurality of extruder screws mix the second amount of polymer material, or the combination of the added material and the second amount of polymer material, with the flow of molten polymer material. The method also includes applying a vacuum to a vacuum vent associated with a vent opening in a third barrel segment positioned between the first and second feed locations.Each of the plurality of extruder screws includes a first polymer flow sealing zone portion located between the first barrel segment and the vent hole opening in the third barrel segment, a filter zone portion located between the vacuum vent hole and the second opening associated with the second feed location, and a second polymer flow sealing zone portion located downstream of the second opening associated with the second feed location. The first polymer flow sealing zone portions, the filter zone portions, and the second polymer flow sealing zone portions of the plurality of extruder screws function as a first polymer flow sealing zone, a filter zone, and a second polymer flow sealing zone, respectively.The filter zone includes longitudinal mixing elements that allow the flow of molten polymer material to move along the longitudinal axis of the extruder, prevent the vacuum through the vacuum vent from drawing in any significant amount of any added material introduced at the second feed location, and allow the vacuum through the vacuum vent to extract unwanted fluid present between the first and second polymer flow sealing zones. The first and second polymer flow sealing zones prevent loss of vacuum resulting from air entering the extruder from locations other than the second feed location.

[0018] Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. Brief description of the drawings Fig. Figure 1A is a simplified diagram of a thermally controlled conventionally designed multi-screw extruder constructed with one atmosphere rear vent and one atmosphere forward vent to allow moisture, air, and other gases accompanying particulate material introduced at a secondary feed to escape from the extruder barrel. Fig. Figure 1B is a simplified diagram of a thermally controlled conventionally designed multi-screw extruder constructed with a vacuum vent and a downstream vacuum vent to remove moisture from polymer and other materials flowing through the extruder barrel. Fig. Figure 2 is a simplified diagram of a preferred embodiment of a thermally controlled multi-screw extruder implementing the disclosed vacuum feed technology to form an extrudate of a densified particulate filler material mixed with a flow of molten polymeric material at a high throughput rate. Fig. Figure 3 is an enlarged cross-sectional view of the axially spaced co-rotating extruder screws located inside the multi-screw extruder of Fig. 2 are included. Fig. Figure 4 is a diagram of the extruder screws spaced apart and outside the barrel of the extruder of Fig. 2 are shown. Fig. Figure 5 is a graph illustrating an increase in the rate of extrudate throughput of polypropylene blended with talc mineral achieved by implementing the disclosed vacuum feed technology compared to that achieved by implementing atmospheric venting in the conventionally designed extruder of Fig. 1 is reached. Fig. Figure 6 is a simplified diagram of a preferred embodiment of a thermally controlled multi-screw extruder implementing the disclosed vacuum feed technology to extract unwanted fluid from material introduced into a feed location and mixed with a flow of molten polymer material. Detailed description of preferred embodiments

[0019] Fig. Figure 2 is a simplified diagram illustrating, as a preferred embodiment, a co-rotating twin-screw extruder 50 configured with a thermally controlled extruder barrel 52 comprising a plurality of interlinked barrel segments numbered 1-12. The barrel segment numbers in ascending order indicate barrel segments located further downstream along the extruder 50. Barrel segments 1-12 define a longitudinal axis 54 and an interior 56 of the extruder barrel 52. Fig. Figure 3 shows axially spaced rotatable extruder screws 58 extending through the interior 56 of the extruder barrel 52, which has a figure-eight profile and an inner surface 60. Fig. Figure 4 shows the two extruder screws 58 outside the barrel 52. The extruder screws 58 have the same design and mesh with each other to effect unified rotation during extruder operation. The extruder 50 is constructed with a vacuum vent hole 62 and extruder screws 58 designed and arranged according to the disclosed design.

[0020] The thermal control of extruder barrel 52 maintains the individual barrel segments 2-12 at temperature setpoints. Barrel segment 1 is typically not heated, and heating and cooling processes are performed on each of barrel segments 2-12.

[0021] Materials, including polymeric materials, are fed into the co-rotating extruder screws 58 of the extruder 50 through an opening located on the barrel segment 1 for the primary feed 70. Materials are also fed into an opening located on the barrel segment 8 for a secondary feed 72 downstream of the opening for the primary feed 70. The secondary feed 72 is attached to the side surface of the extruder barrel segment 8 with an opening and sealed thereto by a gasket to allow the secondary feed 72 to force the material into the side of the extruder 50. A vacuum is applied to an opening in the extruder 50 for passage through the vacuum vent hole 62. The opening for the vacuum vent hole 62 is located between the opening for the primary feed 70 and the opening for the secondary feed 72.The applied negative pressure increases the density of the material introduced at the secondary feed opening 72. The applied negative pressure also removes so-called volatiles such as air or moisture from materials introduced at the secondary feed location 72.

[0022] A portion 73 of each extruder screw 58, located between the vacuum vent hole 62 and the secondary feed opening 72, is designed such that the polymer materials introduced at the primary feed 70 do not completely fill a free volume 74 in the space between the screws 58 and the inner surface 60 of the barrel 52, so as not to form a dynamic seal. The portion 73 of each extruder screw 58 is also designed such that a vacuum applied through the vacuum vent hole 62 between the primary feed openings 70 and the secondary feed 72 extracts at most a very small percentage of the materials introduced into the extruder 50 through the secondary feed opening 72. The portions 73 of the extruder screws 58 function together as a filter zone 76, which in Fig. 4 is identified by a rectangular box in dashed line around the sections 73. Each section 73 of the filter zone 76 is designed with mixing elements, for example kneading discs 78, which have a forward conveying skew angle.

[0023] The filter zone 76 is an area within the extruder barrel 52 where the molten polymer flows downstream in the path of vacuum and mixing elements 78 to capture and mix with the material fed at the secondary feed port 72. The mixing elements 78 prevent the flow of molten polymer material from filling the free volume 74 to prevent a dynamic seal and allow the extraction of unwanted fluid present in the filter zone 76. The rotation of the mixing elements 78 in the filter zone 76 results in turbulent molten polymer material randomly coming into contact with the inner surface 60 of the extruder barrel 52.The turbulent molten polymer material captures most of the particulate filler material, but leaves sufficient free volume gaps to allow unwanted fluid to pass through the filter zone 76 and exit the vacuum vent hole 62. In this embodiment, the filter zone 76 is positioned between the vacuum vent hole 62 on barrel segment 5 and the secondary feed 72 on barrel segment 8 when the screws 58 are installed in the extruder barrel 52. This configuration of the mixing elements 78 does not form a dynamic seal with the materials introduced at the primary feed 70 and secondary feed 72 locations.

[0024] Fig. Figure 4 shows the exterior of the conveying elements 80 of the filter zone 76, which move the mixed material through the extruder 50, and mixing elements, such as neutral kneading discs 821, which act as a dam and thereby form a dynamic seal outside the filter zone 76. The mixing elements 821 are positioned downstream of the primary feed 70 on barrel segment 1 and upstream of the filter zone 76 to prevent negative pressure from sucking a significant amount of material fed into the extruder 50 at the opening for the primary feed 70 through the vacuum vent hole 62. The mixing elements 821 are preferably arranged on barrel segment 4 when the screws 58 are installed in the extruder barrel 52. Any type of extruder screw element that forms a dynamic seal cannot be used in the filter zone 76 sections of the extruder screws 58.The number of mixing elements and the length of the filter zone 76 can vary based on the bulk density of the material fed into the extruder 50 at the secondary feed port 72 and the properties of the polymer fed into the extruder 50 at the primary feed port 70. If the filter zone 76 of the mixing elements is too short for a given type of material fed at the secondary feed port 72 and the primary feed port 70, the material fed at the secondary feed port 72 would be extracted through the vacuum vent 62 and into the vacuum system (not shown).A densification zone, which includes the filter zone 76 and extends to the secondary feed 72, is the area where air, but not the material fed at the secondary feed port 72, is extracted from the interior 56 of the extruder barrel 52 to densify the mixture of molten polymer and material flowing therethrough.

[0025] The secondary feed 72, located at the secondary feed port, could be designed to be airtight to optimize the extraction of air from the materials introduced at the secondary feed port 72. A second dynamic seal filling the free volume 74 prevents the loss of negative pressure at the vacuum vent hole 62 and of air entering the extruder 50 from locations other than the secondary feed 72. The second dynamic seal can be implemented as mixing elements 822, for example, of the same type as the mixing elements 821, or as a restriction such as the exit nozzle 84 located at the extrudate outlet end of the barrel segment 12. The exit nozzle 84 restricts the flow of molten composite material, causing it to back up and create a seal.

[0026] The following example describes a preferred length of the filter zone 76 filled with mixing elements 78 (forward helical mixing elements) of the extruder screw 58 for mixing molten polymer and a specified talc mineral. EXAMPLE

[0027] The secondary feed 72 receives the material IMI Fabi Talc HTP1 with a bulk density of 0.26 g / cm 3 , an average particle size diameter D 50 of 1.9 µm and an upper cut D 98of 8.0 µm. Each of the extruder screws 58 has a length l and a diameter d. This particular talc powder material is well filtered (l / d = 48:1) by the mixing elements of the filter zone 76 of the extruder screws 58, each of which has a minimum l / d = 4:1 and a maximum l / d = 8:1 of forward screw mixing elements in the filter zone 76. This range of l / d ratios prevents large quantities of talc mineral powder fed at the secondary feed 72 from being sucked into the vacuum pumping system and achieves a desired densification of the talc mineral powder. The l / d ratio is determined by the powder material particle size and corresponding amounts of entrained air.The l / d range of the filter zone 76 from about 4:1 to about 8:1 varies based on the chemical composition, particle size distribution, and physical properties of the powdered material introduced at the secondary feed 72 and the properties of the polymeric material introduced at the primary feed 70.

[0028] In general, an l / d ratio of the filter zone 76 is within an operating range between about 0.25:1 and about 12:1.

[0029] Fig. Figure 5 is a graph showing, for different extruder screw speeds and two different amounts of talc mineral, an improvement in extrudate throughput achieved by the disclosed vacuum feeding technology implemented as in Fig. 2, Fig. 3 and Fig. 4, compared to the prior art atmospheric venting, which is implemented as in Fig. 1. The Fig. The data shown in Figure 5 were generated by blending polypropylene and IMI Fabi Talc HTP-1. These materials were blended through 2064 mm long, co-rotating, 43 mm diameter twin extruder screws, with a vacuum applied to the vacuum vent hole 62, creating an absolute pressure of approximately 13500 Pa (135 millibars). The applied vacuum compacted the talc powder fed into the extruder. Increasing the bulk density of the talc powder in the molten polymer material resulted in the movement of more material through the extruder in a given unit of time and a consequent reduction in conversion costs. The data demonstrate the production of an extrudate at a rate of up to 1.8 times the rate of extrudate throughput achieved using an extruder conventionally configured to utilize atmospheric venting.

[0030] Acceptable compaction of powder can be achieved by applying a vacuum that produces an absolute pressure of not more than about 67500 Pa (675 millibars).

[0031] It is unusual for a vacuum vent hole and a secondary feed to be provided in the Fig. 2 described combination. It is conventional for a vacuum vent hole to be provided at an extruder barrel opening between the secondary feed opening (e.g., at the location of barrel segment 10 or 11, as shown in Fig. 1B) and the outlet end of the extruder. However, if the vacuum vent hole in the Fig. 2, mixing elements forming a dynamic seal, such as mixing elements 821 or 822, would be intentionally included in portions of the filter zone 76 of the extruder screws located in the barrel segments between the vacuum vent and secondary feed ports. This conventional arrangement would form a dynamic seal to prevent materials from being extracted from the secondary feed port into the vacuum system.

[0032] Those skilled in the art will recognize that the design of the sections of the extruder screws 58 in the filter zone 76 between the vacuum vent opening 62 and the secondary feed opening 72 can be optimized for the extraction of gas that is primarily air. The distance between the vacuum vent opening 62 and the secondary feed opening 72 can also be optimized.

[0033] Fig. 6 is a reproduction of Fig. 2, which is illustrated for use in describing fluid extraction processes in which the extruder 50 is provided with the extruder screws 58 designed and configured as shown in Fig. 3 and Fig. 4 and described with reference thereto, extracts unwanted fluid present during operation of the extruder 50, which forms a composite by mixing a flow of molten polymer material with added material, or with a combination of added material and a second amount of polymer material, introduced at the secondary feed 72. In a fluid extraction process described below, the extruder 50 is used as a drying chamber for polyethylene terephthalate (PET) polymer as it is melted and processed.

[0034] With reference to Fig. 6, from about 1 wt. % to about 25 wt. % of PET polymer is introduced through the primary feed opening 70, which defines a first feed location. This first amount of PET polymer introduced at barrel segment 1 melts to form a first dynamic seal through the operation of the mixing elements 821 contained within a first polymer flow sealing zone positioned between the primary feed 70 on barrel segment 1 and the vacuum vent opening 62 on barrel segment 5. The moisture content of the first amount of PET polymer is of minimal importance in the PET polymer drying process. The first polymer flow sealing zone prevents the vacuum from sucking the polymer material introduced at the primary feed opening 70 into the vacuum vent 62. The remaining from about 75 wt. % to about 99 wt.-% PET polymer contains some moisture and is introduced through the secondary feed opening 72, which defines a second feed location. The PET polymer may be in powder, flake, or pellet form. In contrast to polymer, added particulate filler material may be introduced at the secondary feed 72. Such a particulate material may be, for example, wood flour, which contains about 8% moisture and from which moisture is drawn into the vacuum vent hole 62, or talc mineral, from which, by comparison, primarily air is drawn into the vacuum vent hole 62.

[0035] The negative pressure applied to the vent hole opening in the extruder 50 for passage through the vacuum vent hole 62 draws the moisture out of, and therefore dries, the PET polymer supplied through the secondary feed 72. The mixing elements of the filter zone 76 capture the material fed at the secondary feed opening 72 and mix it with the material flowing in the extruder barrel 52. The mixing elements of the filter zone 76 do not form a dynamic seal, as described above with reference to Fig.4. A second polymer flow sealing zone formed downstream of the secondary feed 72 on barrel segment 8 prevents the loss of negative pressure occurring at the filter zone 76 and prevents air from entering the extruder 50 from locations other than the opening for the secondary feed 72. The second polymer flow sealing zone may be formed by the operation of the mixing elements 822 positioned between the secondary feed 72 on barrel segment 8 and one of the barrel segments (e.g., barrel segment 10 or 11) located proximal to, but downstream of, the secondary feed 72. The second polymer flow sealing zone may optionally be formed by a restriction of the material flow in the extruder barrel 52, such as the exit nozzle 84 positioned at the extrudate outlet end of the final barrel segment 12.

[0036] The effectiveness of the extruder 50 in performing the compaction of material and the extraction of unwanted fluid introduced at the secondary feed 72 is achieved in part by the use of the first polymer flow seal zone formed between the primary feed 70 and the vacuum vent 62 and the second polymer flow seal zone formed at a location downstream of the secondary feed 72. The first and second polymer flow seal zones prevent loss of vacuum pressure resulting from air entering the extruder 50 from locations other than the second feed location.

[0037] Those skilled in the art will recognize that the polymer material introduced through the primary feed port 70 need not comprise the same polymer as that contained in the polymer material introduced through the secondary feed port 72. The amount of polymer material introduced through the primary feed port 70 need not be a sacrificial, i.e., small, amount of polymer, as long as it does not exhibit an appreciable moisture content that would result in the hydrolysis of the flow of polymer material through the extruder 50.

[0038] It will be apparent to those skilled in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the disclosed extruder and method for extracting volatiles. For example, although intended for plastics extrusion, extruder 50 could be applied to food and other extrusion processes utilizing co-rotating twin-screw extruders. The disclosed design of extruder 50 could be used for all sizes of co-rotating twin-screw extruders. The scope of the present invention should therefore be determined only by the following claims.

Claims

[1] A multi-screw extruder (50) implemented with a vacuum vent hole (62) positioned between spaced material feed locations (70, 72) of an extruder barrel (52) to facilitate compaction of material introduced into a material feed location (70, 72) located downstream of the vacuum vent hole (62), extraction of unwanted fluid from material introduced into the extruder (50), or both, the extruder (50) comprising: a thermally controlled extruder barrel (52) having a plurality of interlinked barrel segments (1, 2, 4, 5, 8, 10, 12) defining a longitudinal axis (54) and an interior (56) of the extruder barrel (52) through which a plurality of axially spaced extruder screws (58) extend, the interior (56) of the extruder barrel (52) having an inner surface (60); a first feed location (70) associated with a first opening formed in a first cylinder segment of the plurality of linked cylinder segments (1, 2, 4, 5, 8, 10, 12), and a second feed location (72) associated with a second opening formed in a second cylinder segment of the plurality of linked cylinder segments (1, 2, 4, 5, 8, 10, 12), the second cylinder segment being positioned downstream of the first cylinder segment; a vacuum vent hole (62) associated with a vent hole opening formed in a third cylinder segment of the plurality of linked cylinder segments (1, 2, 4, 5, 8, 10, 12) and positioned between the first and second feed locations (70, 72), and wherein the vacuum vent hole (62) is configured to apply a vacuum to the vent hole opening in the third cylinder segment for passage through the vacuum vent hole (62) to a free volume (74) between the inner surface (60) of the extruder barrel (52) and a portion (73) of each of the plurality of extruder screws (58), the portions (73) of the plurality of extruder screws (58) functioning as a filter zone (76); and wherein each section (73) of the plurality of extruder screws (58) of the filter zone (76) has longitudinal mixing elements (78) arranged between the vacuum vent hole (62) and the second opening associated with the second feed location (72), wherein the mixing elements (78) of the filter zone (76) are configured to allow a polymer material introduced at the first feed location (70) to flow as molten polymer material through the filter zone (76) along the longitudinal axis (54) of the extruder barrel (52) and to trap material introduced at the second feed location (72) to prevent the vacuum from sucking a significant amount of the material through the vacuum vent hole (62), and the mixing elements (78) of the filter zone (76) are configured to preventthat the flow of molten polymer material completely fills the free volume (74) between the extruder screws (58) and the inner surface (60) of the extruder barrel (52) so as not to form a dynamic seal, and thereby allow the negative pressure to extract unwanted fluid present in the filter zone (76) through the negative pressure vent hole (62). [2] The multi-screw extruder (50) of claim 1, wherein the material introduced at the second feed location (72) comprises a material that acts as a particulate filler for the molten polymer material in the filter zone (76), the unwanted fluid present in the filter zone (76) comprises air, and the extraction of air performs significant densification of the particulate filler. [3] The multi-screw extruder (50) of claim 1, wherein the mixing elements (78) of the filter zone (76) comprise mixing elements (78) configured in a forward helical extension. [4] The multi-screw extruder (50) of claim 1, wherein the portion (73) of each of the plurality of axially spaced extruder screws (58) has a diameter d and a length l, and wherein an l / d ratio of the portion (73) is within a range between about 0.25:1 and about 12:

1. [5] The multi-screw extruder (50) of claim 1, wherein the negative pressure applied to the vent hole opening produces an absolute pressure of no more than about 67500 Pa (675 millibars). [6] The multi-screw extruder (50) of claim 1, wherein the plurality of axially spaced extruder screws (58) comprise co-rotating twin screws. [7] The multi-screw extruder (50) of claim 1, wherein the material introduced at the second feed location (72) comprises powder material that acts as a particulate filler for the molten polymer material. [8] Multi-screw extruder (50) according to claim 7, wherein the powder material comprises talc mineral. [9] The multi-screw extruder (50) of claim 1, wherein the material introduced at the second feed location (72) comprises moisture-containing material, and wherein the unwanted fluid extracted through the vacuum vent hole (62) comprises moisture removed from the moisture-containing material. [10] The multi-screw extruder (50) of claim 1, wherein the material introduced at the second feed location (72) comprises liquid supplied to mix with the molten polymer material in the filter zone (76), and wherein the unwanted fluid extracted through the vacuum vent hole (62) comprises a residual amount of the supplied liquid. [11] A method for forming a composite comprising polymer material and particulate filler material at a high throughput rate, which are mixed by the operation of a thermally controlled extruder (50) without appreciable vacuum vent hole removal of the particulate filler material from the extruder (50), the extruder (50) comprising a plurality of interlinked cylinder segments (1, 2, 4, 5, 8, 10, 12) defining a longitudinal axis (54) and a plurality of rotatable extruder screws (58) adapted to mix the material introduced into the extruder (50), which comprises: Introducing polymer material into a first feed location (70) associated with a first opening formed in a first barrel segment of the extruder (50), wherein the polymer material is processed by rotation of the plurality of extruder screws (58) to form a flow of molten polymer material, wherein a portion (73) of each of the plurality of extruder screws (58) includes longitudinal mixing elements (78), and the portions (73) of the plurality of extruder screws (58) function as a filter zone (76); Introducing particulate filler material into a second feed location (72) associated with a second opening formed in a second barrel segment of the extruder (50), the second barrel segment being positioned downstream of the first barrel segment such that the plurality of extruder screws (58) mix the particulate filler material with the flow of molten polymer material; and Applying a negative pressure to a vacuum vent hole (62) associated with a vent hole opening in a third cylinder segment positioned between the first and second feed locations (70, 72), wherein the mixing elements (78) function as a filter zone (76) disposed between the vacuum vent hole (62) and the second opening associated with the second feed location (72), and the mixing elements (78) of the filter zone (76) cooperate to allow the flow of molten polymer material to move along the longitudinal axis (54) of the extruder (50) and to prevent the negative pressure through the vacuum vent hole (62) from sucking a significant amount of the particulate filler material introduced at the second feed location (72) and to extract air present in the filter zone (76) to thereby achieve significant densification of the particulate filler,when the plurality of extruder screws (58) rotate to form a composite with the compacted particulate filler material mixed with the flow of molten polymer material., [12] The method of claim 11, wherein the mixing elements (78) of the filter zone (76) comprise mixing elements (78) configured in a forward helical extension. [13] The method of claim 11, wherein the section (73) of each of the plurality of extruder screws (58) has a diameter d and a length l, and wherein an l / d ratio of the section (73) is within a range between about 0.25:1 and about 12:

1. [14] The method of claim 11, wherein the plurality of extruder screws (58) comprise co-rotating twin screws. [15] The method of claim 11, wherein the particulate filler comprises powder material. [16] The method of claim 15, wherein the powder material comprises talc mineral. [17] A method for extracting unwanted fluid present during operation of a thermally controlled extruder (50) which forms a composite by mixing polymer material with added material, the extruder (50) comprising a plurality of interlinked cylinder segments (1, 2, 4, 5, 8, 10, 12) defining a longitudinal axis (54) and a plurality of rotatable extruder screws (58) adapted to mix material introduced into the extruder (50), comprising: Introducing a first quantity of polymer material into a first feed location (70) associated with a first opening formed in a first barrel segment of the extruder (50), wherein the first quantity of polymer material is processed by rotation of the plurality of extruder screws (58) to form a flow of molten polymer material; Introducing a second amount of polymer material or a combination of added material and a second amount of polymer material into a second feed location (72) associated with a second opening formed in a second barrel segment of the extruder (50), the second barrel segment being positioned downstream of the first barrel segment such that the plurality of extruder screws (58) mix the second amount of polymer material or the combination of the added material and the second amount of polymer material with the flow of molten polymer material; and Applying a negative pressure to a negative pressure vent hole (62) associated with a vent hole opening in a third cylinder segment positioned between the first and second feed locations (70, 72), wherein each of the plurality of extruder screws (58) has a first polymer flow seal zone portion disposed between the first cylinder segment and the vent hole opening in the third cylinder segment, a filter zone portion disposed between the negative pressure vent hole (62) and the second opening associated with the second feed location (72), and a second polymer flow seal zone portion disposed downstream of the second opening associated with the second feed location (72), wherein the first polymer flow seal zone portions,the filter zone sections and the second polymer flow sealing zone sections of the plurality of extruder screws (58) function as a first polymer flow sealing zone, a filter zone (76), and a second polymer flow sealing zone, respectively, wherein the filter zone (76) includes longitudinal mixing elements (78) that allow the flow of molten polymer material to move along the longitudinal axis (54) of the extruder (50), prevent the vacuum from sucking a significant amount of any added material introduced at the second feed location (72) through the vacuum vent hole (62), and allow the vacuum to extract unwanted fluid present between the first and second polymer flow sealing zones through the vacuum vent hole (62), and the first and second polymer flow sealing zones prevent the loss of vacuum resulting from air,which enters the extruder (50) from locations other than the second feed location (72). [18] The method of claim 17, wherein the mixing elements (78) in the filter zone (76) comprise mixing elements (78) configured in a forward helical extension. [19] The method of claim 17, wherein the filter zone portion of each of the plurality of extruder screws (58) has a diameter d and a length l, and wherein an l / d ratio of the filter zone (76) is within a range between about 0.25:1 and about 12:

1. [20] The method of claim 17, wherein the first polymer flow sealing zone comprises mixing elements (78) comprising neutral kneading discs (821). [21] The method of claim 20, wherein the first polymer flow sealing zone further comprises mixing elements (78) comprising reverse helical extended conveying elements (80). [22] The method of claim 17, wherein the first polymer flow sealing zone comprises mixing elements (78) comprising reverse helical extended conveying elements (80). [23] The method of claim 17, wherein an exit nozzle (84) is positioned on a final barrel segment (12) of the extruder (50), and wherein the exit nozzle (84) is included in the second polymer flow sealing zone that prevents loss of negative pressure. [24] The method of claim 17, wherein the second polymer flow sealing zone comprises mixing elements (78) comprising neutral kneading discs (821). [25] The method of claim 24, wherein the second polymer flow sealing zone further comprises mixing elements (78) comprising reverse helical extended conveying elements (80). [26] The method of claim 17, wherein the second polymer flow sealing zone comprises mixing elements (78) comprising reverse helical extended conveying elements (80). [27] The method of claim 17, wherein the second polymer flow sealing zone comprises a flow restriction preventing loss of negative pressure. [28] The method of claim 17, wherein the first and second amounts of polymeric material comprise different polymers. [29] The method of claim 17, wherein the first and second amounts of polymer material comprise the same polymer. [30] The method of claim 29, wherein the polymer is polyethylene terephthalate (PET). [31] The method of claim 30, wherein the first amount of polymeric material is about 1 wt% to about 25 wt% PET and the second amount of polymeric material is about 75 wt% to about 99 wt% PET. [32] The method of claim 17, wherein the added material introduced at the second feed location (72) comprises moisture-containing material, and wherein the unwanted fluid extracted through the vacuum vent hole (62) comprises moisture removed from the moisture-containing material. [33] The method of claim 17, wherein the added material introduced at the second feed location (72) comprises liquid supplied to mix with the molten polymer material in the filter zone (76), and wherein the unwanted fluid extracted through the vacuum vent hole (62) comprises a residual amount of the supplied liquid.

Images