BR112018016870B1 - APPARATUS FOR EXTRUSION OF A POLYMER RESIN - Google Patents

Abstract

A piston extrusion apparatus that includes a die with multiple thermal zones, a feed hopper for introducing a granular polymer resin into the die, and a piston for moving the granular polymer resin through the thermal zones of the die and out from one end outlet at a temperature above the crystalline melting temperature of the polymer resin. The feed hopper may be designed to distribute the polymeric resin into a resin inlet of the matrix in a plurality of specifically measured amounts. which may vary over a width of the resin input end of the matrix. The apparatus may further include one or more finishing tables positioned after the exit end of the die to receive and move the extruded resin away from the exit end of the die so that there is no back pressure on the extruded resin and to provide compression force and even cooling for the extruded resin.

Description

RELATED REQUEST

[0001] The present application is a continuation in part of United States Patent Application Serial No. 15/047,935, filed on February 19, 2016, the entire contents of which are incorporated herein by reference.

FIELD OF INVENTION

[0002] The present invention relates, generally, to piston extrusion machinery and, more particularly, to an apparatus capable of rapid and continuous extrusion of thin and wide panels of ultra-high molecular weight polymers.

BASICS OF THE INVENTION

[0003] Large plastic panels can be produced through a number of techniques, including compression molding, piston extrusion and sintering. Piston extrusion of granular polymer resins typically uses equipment comprising a piston and die assembly. The polymeric material to be extruded is introduced into an inlet end of a die and forward strokes of a reciprocating piston compact the material and force it through the heated die in a continuous manner to form an uninterrupted shape of a desired profile.

[0004] Many types of plastic materials, such as polyvinyl chloride plastic and ABS plastic, have been successfully extruded in this way. However, this seemingly simple procedure has proven to be quite difficult in practice when employing ultra-high molecular weight (UHMW) polymer resins. Such resins are sensitive to shear forces, particularly when extrusion pressures are very high (approaching 50,000 psi), which is complicated by the fact that they tend to exert significant frictional forces on a die during the forming process. extrusion. Furthermore, these resins are sensitive to high temperatures, often showing degradation due to oxidation at temperatures above 260 °C, so the residence time within the matrix becomes important. Reduced temperatures that may allow for longer dwell times, however, are not economical and generally do not completely melt the resin.

[0005] Early attempts at extrusion of UHMW polymeric resins often resulted in defects such as undesirable internal voids, cracks or noticeable separations between the various charges propelled by repeated piston strokes. Sometimes they even included regions that still exhibited the original powdery or granular structure of the material, evidently having been insufficiently softened in the matrix.

[0006] Recent advances in piston extrusion processes have allowed the production of larger panels of material, but, in general, these panels are several centimeters thick and limited in width. Unless the heating protocols used to produce these panels are tightly controlled, the extrudate may be deformed or the final dimensions may not be maintained within acceptable tolerances. Furthermore, if air gains access to the compacted resin and/or the temperature increases too much, an oxidation process can begin, which reduces the molecular weight of the polymers and degrades or negatively affects the physical properties of the final product.

[0007] The production of wider and thinner panels was also limited by the piston extrusion apparatus. To produce a large UHMW polymer resin flat panel, a die is employed that has a large top and bottom surface. Such a matrix can experience increasing internal pressures that are difficult to control, especially for panels that have a thinner profile. For example, high pressures can cause the central region of these wider dies to bow, thus producing a panel with a greater thickness in the middle than at the edges. This curvature is more evident for thinner panels. Prior art attempts to solve this problem have used dies that are curved convexly toward the center so that they oppose the large external forces generated during the extrusion process.

[0008] Furthermore, upon leaving the heated die, if the panels are not cooled equally and at a uniform rate, the crystallinity of the extrudate becomes heterogeneous, to the point that the resulting solid panel is not flat, stress-free, or has the homogeneous physical properties necessary for the satisfactory end use of the UHMW polymeric product. That is, the large surface area and high axis ratio of such panels generally cause them to distort when cooled below the crystalline melting temperature outside the matrix. Differences in the rate of cooling and crystallization can cause warping, bowing, thickness and surface irregularities, and so on. Such defects would then require at a minimum scraping the surface and machining to size. However, some defects, for example warping and bowing, may be impossible to remove.

[0009] Consequently, there is a need in the art for improved systems and methods for the extrusion of UHMW polymeric resins and, particularly, for the extrusion of large aspect ratio panels of UHMW polymeric resin.

SUMMARY OF THE INVENTION

[0010] The presently described invention overcomes many of the deficiencies of the prior art by providing systems and methods for the piston extrusion of thin and wide panels of UHMW polymer resin. Systems and methods capable of distributing specifically measured quantities of a granular UHMW polymer resin across a width of a die inlet in a piston extrusion apparatus are described. The measured quantities may be the same or may vary across the width of the die inlet and/or during the extrusion process (i.e., as a function of time). Systems and methods for uniformly compressing and/or cooling UHMW polymer resin panels after exiting a die outlet of a piston extrusion apparatus are further described.

[0011] Thus, according to its main aspects, and briefly, the present invention includes an apparatus for extrusion of a polymeric resin comprising a matrix having an input end, an output end and a plurality of spaced thermal zones. along a width and length of the die, a piston mounted for movement within the inlet end of the die from a retracted position to an extended position, and at least one feed hopper for containing and distributing a granular polymer resin to a resin inlet of the matrix. Further included are a device for independently regulating a temperature of the plurality of thermal zones to temperatures above or below the crystalline melting temperature of the polymeric resin and a device for imparting movement of the piston along a longitudinal axis of the die to move the polymeric resin from the entering resin through the plurality of thermal zones and out the outlet end of the die, the polymeric resin being melted and compressed to form a die extrusion profile during progression through the thermal zones of the die.

[0012] In accordance with certain aspects of the apparatus, the die may comprise an upper portion, a lower portion, and side portions defining the extrusion profile of the die, the extrusion profile having a thickness of no more than 1.0 inch. (2.5 cm) and a width of 40 inches (100 cm) or greater. Furthermore, thermal zones near the inlet end of the die, such as near the resin inlet and piston, may remain unheated or may be cooled to a temperature below the crystalline melting temperature of the polymeric resin. Thermal zones along a remaining portion of the matrix may be heated to a temperature at or above the crystalline melting temperature of the polymer resin. More than one thermal zone may be included so that a temperature gradient or curve can be maintained over a length and/or width of the die profile.

[0013] According to certain aspects of the apparatus, a thermal insulation may be incorporated between the input end of the die and the heated regions of the die or heated thermal zones. That is, a thermal insulation may be incorporated into each of the upper and lower die plates of the die prior to resin input, wherein the thermal insulation defines at least one heated thermal region comprising thermal zones spaced between the thermal insulation and the output end of the die. In general, the polymer resin is extruded from the exit end of the die at a temperature that is at or above the crystalline melting temperature of the polymer resin. In certain cases, the region between the resin inlet or the inlet end of the die and the thermal insulation can be cooled to a temperature below the crystalline melting temperature of the polymeric resin.

[0014] According to certain aspects of the apparatus, the at least one feed hopper of the apparatus may be configured to distribute the polymeric resin in a granular state into the resin inlet of the matrix in a plurality of specifically measured amounts. The specifically measured amounts may be the same or may vary across a width of the resin input end of the matrix. Furthermore, specifically measured quantities may change during the course of an extrusion (i.e., over time). In general, the resin inlet is close to the inlet end of the die and before the retracted position of the piston.

[0015] Various methods and apparatus are provided that achieve the distribution of varying amounts of the polymeric resin across the width of the resin inlet. In certain aspects, the at least one feed hopper may comprise a plurality of feed tubes spaced along the width of the matrix resin inlet, each of the plurality of feed tubes comprising a distal end that is proximal to the matrix resin inlet and a proximal end in hydraulic communication with at least one feed hopper. Each of the plurality of feed tubes may comprise a screw feeder, a vibrating feeder or a rotary feeder which is independently controllable to deliver the plurality of specifically measured amounts of polymeric resin. Alternatively or additionally, each of the plurality of feed tubes may be independently movable in a direction perpendicular (e.g., top to bottom or side to side) to the longitudinal axis of the die and/or parallel to the longitudinal axis of the die to distribute the plurality of specifically measured amounts of polymeric resin.

[0016] According to certain aspects of the apparatus, each of the plurality of supply tubes may comprise a shoe at its distal end configured to uniformly distribute the polymeric resin from each of the plurality of supply tubes to the resin inlet. of the matrix. The plurality of supply tubes may be evenly spaced across the width of the matrix resin inlet to allow for contiguous delivery of the polymeric resin across the width of the matrix resin inlet.

[0017] According to certain aspects of the apparatus, the extruded polymer resin ("extrudate") that exits the exit end of the die at a temperature that is at or above the crystalline melting temperature of the polymer resin can be uniformly cooled and/or or vertically compressed as it exits the exit end of the die. This can help provide a constant and uniform crystallization rate for the polymeric resin, such as a UHMW polymeric resin, so that the structural characteristics of the polymeric resin (e.g., strength) and the panel (e.g., no warping or sagging) , uniform thickness), can be tightly controlled.

[0018] Various methods and devices are foreseen that achieve vertical compression and even cooling of the extrudate after leaving the die. Furthermore, such devices can allow movement of the extrudate away from the exit end of the die so that no horizontal compression is exerted on the extrudate. That is, any device for moving the extrudate away from the exit end of the die does not apply a compressive force on the extrudate parallel to a longitudinal axis (i.e., with the direction of flow of the polymer resin through the piston extrusion apparatus). ), but can apply a compressive force on the extrudate perpendicular to the longitudinal axis (i.e., on the top and bottom sides of the extrudate).

[0019] According to certain aspects of the invention, the apparatus may further comprise one or more finishing tables which move the extrudate away from the exit end of the die so that there is no back pressure on the extrudate (i.e., horizontal compression ) and which even promote cooling and intermittent vertical compression of the extrudate. Each one or more finishing tables may comprise top and bottom plates, wherein the top plate is movable in a direction perpendicular to the longitudinal axis of the die through a range of positions which include at least (a) one open position that does not contact the extrudate, (b) a downward position that contacts the extrudate but does not apply a compressive force to the extrudate, and (c) a fixed position that contacts and applies the compressive force to the extrudate.

[0020] The one or more finishing tables may include a device for controlling a temperature of the upper and lower plates below the crystalline melting temperature of the polymer resin. Such devices can, directly or indirectly, control the temperature of the cards, such as through fans. Furthermore, the top and bottom plates of each of the one or more finishing tables may comprise a high relief or low relief pattern. When more than one finishing table is included, the temperature of the top and bottom plates of a second or subsequent finishing table may be lower than the temperature of the top and bottom plates of a first or previous finishing table.

[0021] According to certain aspects of the apparatus, a first finishing table may be positioned after the output end of the die and may be movable in a direction parallel to the longitudinal axis of the die. When included, a second finishing table may be positioned after the first finishing table and may be movable in a direction parallel to the longitudinal axis of the die. The second finishing table may be configured to (A) move away from the first finishing table when the top plate of the second finishing table is in the down or fixed position and the top plate of the first finishing table is in any position and if move toward the first finishing table when the top plate of the second finishing table is not in the fixed position and the top plate of the first finishing table is in the down or fixed position; (B) move in unison with the first finishing table; or (C) remain in a static position in which, when the top plate of the first finishing table is in any position, the top plate of the second finishing table is in the down position to allow uniform temperature dissipation (i.e., cooling ) for the extrudate, but without compression force on the extrudate.

[0022] In accordance with certain aspects of the present invention, the top and bottom plates of each of the one or more finishing tables may comprise a rigid material, such as a material that has a minimum unit bending stiffness of 13,400 inch-pounds2 (942 kg/cm2). In accordance with certain aspects of the present invention, the top plate of the first finishing table may comprise a thin, flexible material, such as a material having a maximum unit bending stiffness of 13,400 inch-pounds. In accordance with certain aspects of the present invention, the upper plates of one or more finishing tables may be operatively connected to one or more drivers through a distal end of a driver piston rod, wherein the drivers effect movement of the plate. top in a direction perpendicular to the longitudinal axis of the matrix. The driver piston rods may include a pressure plate at their distal end.

[0023] The present invention also includes a method for producing polymeric panels using a piston extruder. The method may comprise introducing specifically measured amounts of a granular polymer resin across a width of an inlet end of a piston extruder die, the die having a profile defined by a thickness of less than 1.0 inch (2. 5 cm) and a width of 40 inches (100 cm) or greater; incrementally pushing the granular polymer resin towards an exit end of the die under pressure from a piston; heat the granular polymer resin to a temperature at or above the crystalline melting temperature as the granular polymer resin progresses through the die to the exit end, wherein the granular polymer resin is melted and compressed to conform to the profile of the die ; and extruding the molten polymer resin as an extrudate from the exit end of the die at a temperature above the crystalline melting temperature of the granular polymer resin. According to certain aspects of the method, the input end of the die can be cooled to a temperature below a crystalline melting temperature of the granular polymer resin.

[0024] According to certain aspects of the method, specifically measured amounts of the granular polymer resin may comprise a plurality of specifically measured amounts that may vary across a width of a matrix resin inlet. In general, the resin inlet is close to the inlet end of the die and before the retracted position of the piston. Various methods and apparatus are provided for achieving distribution of varying amounts of polymeric resin across the width of the resin inlet. The granular resin may be supplied from at least one feed hopper having a plurality of feed tubes that are individually controllable and movable in directions substantially perpendicular to and/or substantially parallel to the direction of movement of the piston. For example, more resin may be dispensed from feed tubes near the edges of the die profile than from feed tubes in the middle of the die.

[0025] According to certain aspects of the method, the extrudate may leave the exit end of the die and pass to at least a first finishing table that may move the extrudate away from the exit end of the die so that there is no back pressure on the extrudate. The first finishing table may comprise upper and lower plates that intermittently apply a vertical compressive force to the extrudate and evenly distribute heat from the extrudate.

[0026] According to certain aspects of the method, the extrudate can be pulled or pushed from the first finishing table to a second finishing table comprising upper and lower plates that intermittently apply a compressive force to the extrudate and evenly distribute heat from the extrudate. extruded. In cases where the extrudate is pushed onto a second finishing table, no significant horizontal compression (i.e., back pressure) is exerted on the extrudate. That is, any pushing force would not provide enough backpressure to distort an extrudate shape.

[0027] The present invention also includes UHMW polymer resin panels with a thickness of less than 1.0 inch (2.5 cm), such as less than 0.75 inch (1.9 cm) or even less than 0. 5 inch (1.27 cm) and a width of 40 inches (100 cm) or greater, such as 54 inches (136.16 cm) or even 66 inches (167.64 cm), which are produced using any of apparatus or methods described herein. In particular, the present invention includes UHMW polyethylene or polytetrafluoroethylene panels that have a thickness between 0.50 to 0.55 inch (1.27 cm to 1.40 cm) and a width of 40 inches to 66 inches (100 cm to 166cm).

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Aspects, characteristics, benefits and advantages of the embodiments herein will be evident in relation to the detailed description, attached claims and attached drawings. In the following figures, similar numerals represent similar features in the various views. It should be noted that the features and components in these drawings, which illustrate views of embodiments of the present invention, unless otherwise indicated, are not necessarily drawn to scale.

[0029] Figure 1A illustrates a sectional view along a longitudinal axis of a die comprising a piston in a retracted position in accordance with certain aspects of the present invention;

[0030] Figure 1B illustrates a sectional view of the die shown in Figure 1A, with the piston in an extended position;

[0031] Figure 1C illustrates a sectional view along a longitudinal axis of a die comprising a piston in a retracted position in accordance with certain aspects of the present invention;

[0032] Figure 1D illustrates a sectional view of the die shown in Figure 1C, with the piston in an extended position;

[0033] Figure 2A illustrates a cross-sectional view of a piston extrusion apparatus showing die plates and pressure blocks in accordance with certain aspects of the present invention;

[0034] Figure 2B illustrates a cross-sectional view of a piston extrusion apparatus showing die plates and pressure blocks in accordance with certain aspects of the present invention;

[0035] Figure 3 illustrates a side view of a piston extrusion apparatus showing the relative positions of die plates and pressure blocks and a piston and hydraulic cylinders in accordance with certain aspects of the present invention;

[0036] Figure 4A illustrates a sectional view of the matrix as shown in Figure 1B along line 4A - 4A;

[0037] Figure 4B illustrates a similar sectional view as shown in Figure 4A for a matrix in accordance with certain aspects of the present invention;

[0038] Figure 5 illustrates a transparent view of a matrix showing internal thermal zones in accordance with certain aspects of the present invention;

[0039] Figure 6 illustrates an end view of a feed hopper and die in accordance with certain aspects of the present invention;

[0040] Figure 7 illustrates a transparent view of a piston extrusion apparatus showing the relative positions of a feed hopper, a die and two finishing tables in accordance with certain aspects of the present invention; It is

[0041] Figure 8 illustrates a perspective view of a first finishing table of a piston extrusion apparatus in accordance with certain aspects of the present invention.

DETAILED DESCRIPTION

[0042] In the following description, the present invention is presented in the context of various alternative embodiments and implementations involving systems and methods for producing thin wide panels of ultra-high molecular weight (UHMW) polymers that have a large defined axis ratio by a thickness of equal to or less than 1.0 inch (2.5 cm), such as less than 0.75 inch (1.9 cm) or less than 0.5 inch (1.27 cm), and a width of 40 inches (100 cm) or greater, such as 54 inches (136.16 cm) or up to 66 inches (167.64 cm). Unique piston extrusion apparatus and methods are described that optimize the distribution of a granular polymer resin at an inlet end of a die and provide uniform cooling and compression forces on the extrudate after exiting an outlet end of the die, thereby mode, producing panels that have a consistent thickness and excellent performance characteristics more economically and in greater volume than has previously been possible.

[0043] Various aspects of the piston extrusion apparatus can be illustrated with reference to one or more exemplary implementations. As used herein, the term "exemplary" means "to serve as an example, case or illustration", and should not necessarily be construed as preferred or advantageous over other variations of the apparatus, systems or methods described herein. Furthermore, the word "comprising" as used herein means "including, but not limited to."

[0044] Various aspects of the piston extrusion apparatus can be illustrated by describing components that are coupled, connected and/or joined together. As used herein, the terms "coupled", "attached" and/or "joined" are used interchangeably to indicate a direct connection between two components or, where appropriate, an indirect connection to each other through intermediate or intervening components. In contrast, when a component is said to be "directly coupled", "directly connected" and/or "directly joined" to another component, there are no intervening elements shown in said examples.

[0045] Relative terms such as "lower" or "lower" and "higher" or "higher" may be used here to describe the relationship between one element and another element illustrated in the drawings. It should be understood that relative terms are intended to encompass different orientations of aspects of the piston extrusion apparatus in addition to the orientation depicted in the drawings. By way of example, if the aspects of the piston extrusion apparatus shown in the drawings are turned, the elements described as being on the "lower" side of the other elements would then be oriented to the "higher" side of the other elements, as shown in relevant design. The term "inferior" may therefore encompass both "inferior" and "superior" orientation, depending on the particular orientation of the drawing.

[0046] It should also be noted that, as used herein and in the appended claims, the singular forms "a", "an", "the" and "a" include plural references unless the context clearly dictates the contrary. Thus, for example, reference to "a hopper", "a finishing table" or "a feed tube" is a reference to one or more of each and their equivalents known to those skilled in the art, and so on. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art.

[0047] It is a primary object of the present invention to provide a new method and apparatus for the continuous extrusion of UHMW polymeric resins as panels having a thickness equal to or less than 1.0 inch (2.5 cm) and a width of 40 inches (100 cm) or larger. The length of extruded panels may vary and can be determined as needed, as defined by a specific end product configuration, storage location or shipping method.

[0048] Referring now to the drawings, embodiments of the piston extrusion apparatus of the present invention are shown in Figure 1-8. Figures 1A - 1D illustrate cross-sectional views of a die 10 and a reciprocating piston 18. As shown in Figure 1A, the die 10 comprises an upper plate 72 and a lower plate 74 defining a die opening 15 having an end input end 14 and an output end 16. A reciprocating piston 18 may be positioned near the input end 14 of the die 10, before a resin inlet 32 of a feed hopper 30 which is positioned near the input end 14 of the die 10. The piston 18 may have a rectangular shaped piston head 19, which may produce a back and forth movement along a longitudinal axis 100 coincident with the openings of the die 15. Charges of a granular polymer resin may be distributed from the feed hopper 30 for resin inlet 32 before the retracted piston 18. In accordance with certain aspects of the invention, the feed hopper 30 may also comprise a feed tube 34 or chute to which a lower end of the feed hopper 30 connects. to the resin inlet 32.

[0049] As shown in Figure 1B, the piston 18 may alternate to an extended position within the die opening to compact the charge of granular polymer resin and advance the compacted charge through a series of thermal zones 50 in the die 10, from where it may exit an outlet end 16 of the die 10. The various thermal zones 50 in the die 10 may be cooled or heated. For example, thermal zones 50 to the left of the resin inlet 32 (i.e., toward the inlet end 14 of the die) may be cooled to prevent the granular resin from melting and/or oxidizing prior to compaction and air extraction in excess, while those to the right of the resin inlet 32 (i.e. towards the outlet end 16 of the die) can be heated. Furthermore, thermal zones 50 to the right of the resin inlet 32 may be differentially heated so that a gradient or curve of dissimilar heating is applied to the polymeric resin as it progresses through the die opening to the die outlet 16. The temperature of thermal zones 50 at or near the outlet of die 16 may be at or above the crystalline melting temperature of the polymer resin.

[0050] An alternative configuration of the feed hopper 30 and the resin inlet 32 is shown in Figures 1C and 1D. Figure 1C shows the upper plate 72 and the lower plate 74 that define the opening of the die 15 that has an end of inlet 14 and an outlet end 16, wherein the feed hopper 30 and resin inlet 32 are positioned in close proximity to the inlet end 14 of the die. A reciprocating piston 18 may be positioned before the resin inlet 32. Figure 1D shows the piston 18 and piston head 19 in an extended position that produced a back-and-forth movement along a longitudinal axis 100 coincident with the opening of the die 15 Charges of a granular polymeric resin distributed from the feed hopper 30 to the resin inlet 32 before the retracted piston 18 are now pushed into the die opening and through the die to the outlet end 16 of the die.

[0051] Also shown in Figure 1D is a thermal insulation (80, 82) on each of the upper and lower plates (72, 74) of the matrix. Thermal insulation (80, 82) generally separates the thermal zones 50 of the matrix so that the cooling regions and heating regions remain separate. For example, as shown in Figure 1D, the thermal insulation 80 in the top plate 72 may comprise a portion of the top plate 72 that has been removed so that the region is exposed to ambient air. Likewise, the thermal insulation 82 in the bottom plate 74 may comprise a portion of the bottom plate 74 that has been removed so that the region is exposed to ambient air. Alternatively, the thermal insulation may comprise a portion of the top and/or bottom plates (72, 74) that has been replaced with a different material, such as a non-conductive material or high temperature composite, which can insulate the various thermal regions. Furthermore, the thermal insulation may simply comprise one or more thermal zones (50) that are maintained at a constant neutral temperature such as, for example, ambient temperature.

[0052] As shown in Figure 2A, the die plates (72, 74) of the piston extrusion apparatus can be sandwiched between the upper pressure blocks 102 and lower 104. These pressure blocks (102, 104) can help to maintain the die plates (72, 74) in a constant position independent of the internal pressure exerted on the die opening (i.e., resist external forces that can cause bowing of the plates in the middle, which can produce a panel that is thicker in the middle). For the production of panels that are not very wide, such as less than 24 inches (60.96 cm) wide and/or generally thicker than the present invention, such as about 2 inches (5.08 cm) wide thickness or more, the pressure blocks (102, 104) can provide sufficient strength to oppose the internal pressures that cause the matrix plates (72, 74) to bow. However, as will be discussed below, even very large pressure blocks (102, 104) may not provide sufficient resistance to such internal pressure during the production of the thin and wide sheets of the present invention.

[0053] Also shown in Figure 2A are tension pins 550 that can be used to hold the die plates (72, 74) and pressure blocks (102, 104) in position relative to each other and a support base 120. Although a set of two rows of tension pins 550 are shown on both sides of the die opening, any number of rows of tension pins 550 may be included, such as a single row on each side of the die opening. Furthermore, any number of tension pins 550 may be included in each row such as, for example, 2 to 8 tension pins 550. The position of each row of tension pins may also be varied, so that the space between the rows ( 575) and on the edge of the pressure blocks (585) can be varied. Such variations, that is, the number and positions of tension pins, may depend on the length, width and thickness of the die opening.

[0054] As indicated above with reference to Figures 1A-1D, the die comprises several thermal zones 50 that can be cooled, such as near the inlet end 14 of the die, or heated, such as the region between the resin inlet 32 and the output end 16 of the die. Various means for cooling or heating these various thermal zones 50 are possible. For example, as shown in Figure 2A, grooves 55 can be machined in the upper and lower pressure blocks (102, 104). These slots 55 may be sized to hold cartridge heaters or coolers that may be used to provide heating or cooling to the thermal zones of the die. The cartridge heaters or coolers may contact, or may be partially inserted into, a face of the die plates (72, 74) that is opposite the die opening (15). These slots 55 may be spaced along the width of the die opening 15 and may be filled with cartridge heaters or coolers that may be independently controlled to provide a thermal gradient or curve across the width of the opening or may be wired in groups or all together to provide a constant temperature across all or part of the width of the die.

[0055] As indicated in Figure 1A, thermal zones can also span the length of the die opening (along the longitudinal axis 100, see Figure 1A). As such, the slots 55 may be filled with cartridge heaters or coolers that may span the length of the die opening and may be independently controlled to provide a thermal gradient or curve along the length of the opening or may be wired in groups or all together to provide a constant temperature along all or part of the length of the die. In general, cooling by any means is employed only near the inlet end of the die, such as near the resin inlet 32, and heating by any means is employed throughout the remainder of the die, such as throughout the region after the die. resin inlet and up to and including the outlet end 16 of the die.

[0056] Thus, according to certain aspects of the invention, thermal zones 50 in front of or in proximity to the resin inlet 32, or before a thermal insulation (80, 82 of Figure 1D), can be cooled, such as by water or coolant lines through the top and bottom plates (see 72, 74 of Figure 1D) or by cartridge coolers or water coolers installed in machined grooves 55 in the pressure blocks (see 102, 104 in Figure 2A) or by cartridge coolers or water coolers installed in slots machined in the upper and lower die plates (see 72, 74 in Figure 2B) or any combination thereof. Such cooling is generally done to prevent heating of the die opening and piston so that the polymeric resin is not melted and/or oxidized at the entrance to the die opening and before deaeration and compression of the resin can occur. Thus, cooling is generally at a temperature below the crystalline melting temperature of the polymer resin.

[0057] Thermal zones 50 after resin input 32, or after thermal insulation (80, 82 of Figure 1D), can be heated to temperatures at or above the crystalline melting temperature of the polymer resin. Heating may be through ducts in the top and bottom plates (see 72, 74 of Figure 1D), or by cartridge heaters or similar installed in slots 55 machined in the pressure blocks (see 102, 104 in Figure 2A), or by heaters cartridge or similar installed in slots machined in the upper and lower die plates (see 72, 74 in Figure 2B) or any combination thereof. Such heating may be done in a gradient along the longitudinal axis (100 of Figure 1A) of the die opening, such as in two or more thermal zones, and may vary along the width of the die opening, such as heating near the edges of the die opening which is different from heating in the middle of the die opening. These heated thermal zones are generally used to heat the matrix and melt the polymer resin to transform it into the shape of the matrix. The polymer panel generally exits the die as an extrudate that is at or above the crystalline melting temperature of the polymer resin.

[0058] Various means for heating or cooling thermal zones are possible and are within the scope of the present invention. As shown in Figures 1A-1D, 4A, 4B and 5, the thermal zones may be ducts in the die plates (72, 74) that span the width of the die opening. Alternatively, and as shown in Figure 2A, the thermal zones may include slots machined into the upper and lower pressure blocks (102, 104) that contact the upper and lower die plates (72, 74) on a face opposite the die opening. 15. Small openings can also be machined in the upper and lower die plates (72, 74), as shown in Figure 2A, which can receive a small portion of the cartridge heaters or coolers. Alternatively, and as shown in Figures 2B and 3, the thermal zones may include slots or channels machined into the upper and lower die plates (72, 74) on a face opposite the die opening. In any of the described configurations, various means and apparatus such as, for example, cartridge heaters, coolers, fluid lines and combinations thereof that can provide heating and/or cooling to the die plates (72, 74) and/or to the die opening 15 are provided for and are within the scope of the present invention.

[0059] It will be understood that the temperatures of the various thermal zones of the matrix are adjusted to heat the polymeric resin to a temperature at or above the crystalline melting temperature of the polymeric resin or to cool the polymeric resin to a temperature below the crystalline melting temperature of polymer resin. As such, the temperature profile of the die may depend on the specific polymer resin chosen for extrusion. It should also be understood that the temperatures cited above, unless otherwise indicated, are die temperatures as distinguished from material temperatures and that these die temperatures will have a direct relationship with, and depend on, the cross-section of the profile to be extruded.

[0060] For example, a thermal cooled region near the inlet end, or before a thermal insulation, can be any temperature below the crystalline melting temperature of the polymer resin. A heated thermal region after resin input, or after thermal insulation, may include a plurality of thermal zones that heat the die plates to a temperature at or above the crystalline melting temperature such as, for example, about 300°C at about 420°C. Care can be taken to ensure that the temperatures of the various thermal zones do not exceed the degradation point of the polymeric resin which is generally above 500°F (260°C) for most UHMW polymeric resins.

[0061] An exemplary number of thermal zones and temperature ranges in each thermal zone is as follows for a UHMW polyethylene resin (UHMW-PE) that has a crystalline melting temperature between 266°F (130°C) and 277° F (136.11 °C): Various thermal zones along the longitudinal axis of the die opening that include: (a) before thermal insulation, below 260 °F (126.67 °C), generally below 200 °F (93.33 °C) (b) after thermal insulation, 300 °F (148.89 °C) to 320 °F (160 °C) (c) intermediate region, 330 °F (165.56 ° C) at 420°F (215.56°C) (d) outlet region, 300°F (148.89°C) to 350°F (176.67°C). Furthermore, toward the exit region, the temperature near the edges of the die (near the side portions 76, see Figure 5) may be higher than the middle region (i.e., in the center of the die) to prevent the resin from polymer may adhere during an interruption or restart and prevent the extrudate from sticking to the edges of the panel due to frictional forces.

[0062] For example, and with reference to Figures 3 and 5, the thermal zone (a) may comprise water lines 45 and ducts or openings (50A), the thermal zones (b) and (c) may comprise ducts or openings (50B), while the thermal zone (d) may comprise ducts or openings (50C). Since the ducts or openings (50C) run parallel to the longitudinal axis of the die opening (see 100 of Figure 1A), heating can vary across the width of the die opening near the outlet end 16.

[0063] The granular polymer resin employed here may comprise an ultra-high molecular weight (UHMW) polymer resin, such as polyethylene, polytetrafluoroethylene, polyamidoimide, polyamide (nylon, Kevlar), polyacetal (polyoxymethylene), polyethylene terephthalate or polybutylene terephthalate. Preferably, the granular polymer resin may comprise a UHMW polyethylene or polytetrafluoroethylene.

[0064] Furthermore, the UHMW polymeric resin may comprise additional additives such as, for example, dyes and pigments, antioxidants, UV stabilizers, thermal stabilizers, nucleating and clarifying agents, lubricants, electrically conductive materials, filler materials and others. reinforcing materials and combinations thereof. The amounts of such additives are generally small, such as up to 5% by weight or between 0.1% by weight and 3% by weight. Exemplary lubricants include waxes and oils, such as silicone oils. Lubricants can reduce the coefficient of friction and/or add release properties, and can also increase the shine of the final product. For example, 2 wt % polydimethylsiloxane oil added to a UHMW polyethylene resin produced a panel with a gloss between 22 and 30, as measured by a 60° gloss meter.

[0065] Furthermore, in cases where the polymer resin is a non-semicrystalline polymer resin, such as polyester or polycarbonate resins, the heating temperatures may be temperatures above the melting temperature of the resin and the cooling temperatures may be temperatures below the melting temperature of the resin. As such, although certain semicrystalline resins and temperatures have been discussed, a variety of other resins can be formed into panels using the apparatus and methods described herein. These other resins may include at least non-semicrystalline resins, such as polyesters or polycarbonates, or semi-crystalline resins, such as polyolefins, or highly crystalline resins, such as polyketones. In certain cases, resins which can melt and flow in the absence of additives may still find use in the apparatus and methods described herein when they are supplemented with fibers or are highly cross-linked.

[0066] The combination of temperature of the various thermal zones of the matrix and the pressure exerted on the polymeric resin by the action of the piston can combine to soften and melt the polymeric resin so that it can become a homogeneous mass that has characteristics similar to mass, in which a complete bond is created between the successive charges of the polymer particles. This mass of polymeric resin can be compressed within the die opening to conform to the profile of the die opening (i.e., generally rectangular shape).

[0067] As shown in Figure 3, polymer resin enters the die opening through resin inlet 32 and is compressed and pushed along a longitudinal axis (see 100 of Figure 1A) to the outlet end 16 of the die by a piston 18. The piston 18 may be a plate having a rectangular piston head 19 attached to one end which is configured to produce a reciprocating movement between a retracted position and an extended position as described above. The piston 18 can be driven by hydraulic cylinders 118, pneumatic cylinders, jacks or any other means known in the art.

[0068] The piston head 19 may be smaller than the die opening (e.g., thinner and slightly less wide) to prevent friction and binding in the die. A wiper plate may be used to push the piston head 19 against the bottom surface of the die opening to prevent the piston 18 from lifting and forcing expelled air and forming fines into the chamber opening (see resin inlet 32 , feed tube 34 and feed funnel 30 of Figure 1A). The rear section of the piston 18, which is generally exterior to the die opening, may also be cooled with water channels 45 in the die plates (72, 74) to prevent oxidation of the polymer resin at the powder charge interface. and prevent melting before compression.

[0069] Also shown in Figure 3 are several thermal zones that can heat or cool different regions of the die and die opening. As mentioned above, regions of the die before the thermal insulation (80, 82) on the top and bottom plates (72, 74) of the die (i.e., to the right of the thermal insulation in Figure 3) can be cooled. For example, water channels 45 are shown in the lower die plate 74 near the rear section of the piston 18 which may generally be exterior to the die opening and machined channels or openings (50A) are shown near the water inlet. resin 32, but before thermal insulation (80, 82). Additionally, regions of the die after thermal insulation (80, 82) on the top and bottom plates (72, 74) of the die (i.e., to the left of the thermal insulation in Figure 3) may be heated. For example, machined channels or openings are shown that may run perpendicular to the longitudinal axis of the die (50B) and/or may run parallel to the longitudinal axis of the die (50C). The addition of machined channels or openings that run parallel to the longitudinal axis of the die (50C) can provide a variety of heating schemes across the width of the die, specifically at the die exit.

[0070] The piston extrusion apparatus of the present invention may also comprise high-temperature composite layers (310A, 310B) that are sandwiched between the die plates (72, 74) and the pressure blocks (102, 104). These high temperature composite layers can act as a thermal insulation and can help insulate the pressure blocks from the temperatures of the die plates and thus provide protection for the various heating/cooling components. Thermal insulation can also speed up startup times, as thermal zones will reach operating temperatures more quickly and can reduce the cost of maintaining operating temperatures (no energy wasted when heating pressure blocks).

[0071] Also shown in Figure 3 are tension pins 550, ducts or slots that can, for example, pass fluids or hold a cartridge heater/cooler, respectively, and base 120 that can support the piston extrusion apparatus. .

[0072] Shown in Figure 4A is a sectional view of the die opening taken along line 4A-4A of Figure 1B. The upper and lower die plates (72, 74) are shown separated by side portions 76 which together define a die profile having a width 52 and thickness 78. Also shown is a thermal zone 50 which, in this illustration , is represented as a duct. In cases where thermal zones can be displaced, only one duct (thermal zone 50) appears in a cross-sectional view, as shown in Figure 4A.

[0073] Illustrated in Figure 4B is a sectional view of a die opening, also taken along line 4A-4A of Figure 1B. In accordance with certain aspects of the present invention, the upper and lower die plates (72, 74) may have integral side portions that define the profile of the die and which meet to form an enclosed die opening (15).

[0074] Illustrated in Figure 5 is a transparent view of a die showing an upper die plate 72 that is separated from a lower die plate 74 by a set of spacers 76 that define an internal profile of the die opening. Also shown are thermal insulations (80, 82) on the top and bottom die plates, and a configuration which can be used to obtain thermal zones (see 50 of Figure 1A). As shown, the thermal zones can be ducts through the die plates that are perpendicular to the direction of travel of the polymeric resin (45, 50A, 50B; from inlet 14 to outlet 16) or parallel to the direction of resin travel (50C). . Thermal zones (45, 50A) before thermal insulation can be cooled, while those after thermal insulation can be heated (50B, 50C). Ducts can be used to pass fluids, such as water or refrigerant. Alternatively, the matrix plates (72, 74) may comprise rows of small openings, each opening receiving or contacting a portion of a cartridge heater or cooler. Still, the matrix plates (72, 74) may not comprise any ducts or openings and may be heated or cooled through direct contact with the various heaters or coolers which, in accordance with certain aspects of the invention, may be positioned in the pressure blocks (102, 104).

[0075] As indicated above, and with reference to Figure 1A, the polymeric resin may be distributed to the resin inlet 32 of the matrix in amounts that are constant across the width of the resin inlet or in amounts that vary across the width of the matrix. resin input. Typical piston extrusion uses a "flooded feed hopper", meaning that the entire resin inlet of the die is charged with enough resin to completely fill the die cavity with each piston stroke. As such, there is no means to feed more or less granular polymer resin to a specific area of the die without exerting back pressure on the extrudate. Thus, control of product linearity, voltage and load lines is commonly done using friction brakes after exit from the die. In certain prior art solutions, this backpressure is used to force the polymeric resin to completely conform to the matrix profile. When extruding thin panels with a high axis ratio, braking at the die exit will cause the soft, molten polymer resin to collapse. Furthermore, this method has proven to be of limited use, since the polymer resin exhibits memory, which causes the shape molded during melting to be restored afterwards, i.e., stored in the form of tension in the product.

[0076] Thus, a main object of the present invention is an apparatus and method that allows the distribution of varying amounts of the polymeric resin across the width of the die inlet and during the period of a production operation (i.e., the varying amounts of polymer resin distributed over the width of the die opening can change as a function of time and therefore also over a production period). In accordance with certain aspects of the present invention, varying amounts of the polymeric resin can be distributed across the width of the resin inlet of the die to maintain an adjustable resin distribution that can control powder loading, metering, extrudate straightness, flatness and tension. of the extrudate into the final panel product.

[0077] Various methods and apparatus are foreseen that can achieve this objective. For example, the polymer resin may be distributed from more than one feed hopper 30 through feed tubes 34 with different diameters or through feed tubes 34 that are positioned at a different height relative to the bottom plate 74 of the die. Feed tubes 34 that are wider or positioned further away from the lower die plate 74 can deliver more granulated resin to the resin inlet 32 of the die 10. Alternatively or additionally, the feed tube 34 of each feed hopper 30 can comprise a screw feeder, vibratory feeder or rotary feeder that may be individually controllable, so that varying amounts of the polymeric resin may be distributed from each feed hopper 30 across the width of the resin inlet 32.

[0078] Alternatively, each feed hopper 30 and/or feed tube 34 may comprise a series of baffles, redirectors, controlled sliding openings and/or gravimetric weighing containers, for example, which may provide a plurality of varying amounts of the polymer resin along the width of the die inlet. Thus, in accordance with certain aspects of the present invention, one or more feed hoppers 30 can be used to supply the granular polymer resin.

[0079] Furthermore, and as shown in Figure 6, each feed hopper 30 may have one or more feed tubes 34 (four are shown in Figure 6). The feed tubes 34 may have a proximal end 38 that is connected to the feed funnel 30, such as along a lower portion 40 of the feed funnel, and a distal end 36 which is proximal to the resin inlet 32 of the matrix. (at or proximal to the inlet end 14 of the die opening). The upper pressure block 102 and the upper die plate 72 may be machined to provide an opening (resin inlet 32) for powdered or granular polymer resin to enter the die opening. As a reminder, this opening may be at or near the inlet end 14 of the die opening (as shown in Figure 1C) or positioned partially within the die opening (as shown in Figure 1A).

[0080] Referring further to Figure 6, the feed tubes 34 can be moved individually along an axis 60 which is perpendicular to the longitudinal axis of the die opening (wherein the longitudinal axis is shown as 100 in Figure 1A) , such as telescopically. Furthermore, the feed tubes 34 can be moved individually along an axis that is parallel to the longitudinal axis of the die opening. Although four feed tubes 34 are shown in Figure 6, any number of feed tubes 34 may be connected to any number of feed hoppers 30. For example, three feed hoppers 30 could be employed, each having 1 or 2 tubes. feed hopper 34, or a feed hopper 30 having 3 to 6 feed tubes 34. In this way, for example, different amounts of the granular polymer resin could be distributed in the middle of the die opening (e.g., less) than at the along the edges of the die opening (e.g. plus).

[0081] As shown in Figure 6, each feed tube 34 may also comprise a shoe 80A-80D attached to its end 36. Individual shoes 80A-80D may help provide a uniform distribution of the granular resin across the width of the inlet. of resin and may constitute a means for forming a continuous flow of resin from the plurality of supply tubes (i.e., uninterrupted charging of resin across the width of the resin inlet). Each shoe 80A-80D may be movable along an axis that is perpendicular to the longitudinal axis of the die opening (60°, generally with feed tube movement) or parallel to the longitudinal axis of the die opening (e.g., tilt , wherein tilting away from the resin inlet 32 can provide a larger space into which the granulated resin can fall, thereby supplying more granulated resin to the resin inlet 32 of the matrix 10). Each of the movements of the feed tubes 34 and/or shoes 80A-80D may be individually controllable, so that varying amounts of the polymeric resin may be distributed from one or more feed hoppers 30 across the width of the resin inlet 32. For For example, the feed tubes/shoes on the outer edges (80A, 80D) may supply a different quantity than the feed tubes/shoes in the center (80B, 80C) of the die opening.

[0082] Furthermore, instead of, or in addition to, the various movements of the feed tubes 34 and shoes 80A-80D, each feed tube 34 may comprise a screw feeder, vibratory feeder or rotary feeder that may be individually controllable, so that varying amounts of the polymeric resin can be distributed from one or more supply tubes 34 across the width of the resin inlet 32.

[0083] The amount of granular polymer resin distributed across the width of the resin inlet can be controlled automatically or manually, such as by a machine operator, observing the panels exiting the machine. The quantities of each of the feed hoppers 30 and/or feed tubes 34 may be controlled to correct warpage or surface imperfections as indicated. For example, if the panel is thicker in a certain region, such as toward the center of the panel, less resin may be deposited from the feed hoppers 30 and/or feed tubes 34 near the center of the resin inlet 32 of the die. or more resin may be deposited from the feed hoppers 30 and/or feed tubes 34 near the edges of the resin inlet 32 of the die.

[0084] Such a process can be easily implemented as an automatic process in hardware and/or software, for example, scanning the platform transversely at one or more positions along its length by means of an optical comparator or similar, or sensor gauges, etc., which detect warping, thickness or sagging, and make corrections automatically. It should be noted that due to the nature of the problems associated with high aspect ratio piston extrusion, several factors cause instability, e.g., fluctuations in coolant temperature, batch changes of raw material, etc.

[0085] Also shown in Figure 6 is a high-temperature composite layer 310A that can be positioned between the upper pressure block 102 and the upper die plate 72. Not shown are the lower pressure block 104, the lower die plate 74 and the high temperature composite layer (310B) that can be positioned between them.

[0086] Once the polymeric resin has passed through the various thermal zones and is fully compressed to conform to the profile of the die opening (i.e., generally rectangular shape), it can exit the die outlet 16 as an extrudate. The extrudate may pass from the die outlet 16 to a cooling table, where pressure may be applied along an axis perpendicular to the direction of movement of the extrudate (see arrow 60 of Figure 7, which is perpendicular to the longitudinal axis 100 of the opening of the matrix, represented by arrow 100). As discussed previously, differences in the rate of cooling and crystallization can cause warping, bowing, thickness and surface irregularities, and so on. Thus, one or more finishing tables can be provided that provide cooling and compression of the extrudate.

[0087] The extrudate may exit the exit end 16 of the die at a temperature that is at or above the crystalline melting temperature of the polymer resin. For UHMW polyethylene (UHMW-PE), the crystalline melting temperature is generally considered to be between 266°F (130°C) and 277°F (136.11°C). As the extrudate exits through the exit end of the die, the extrudate travels through a cooling zone, such as one or more finishing tables, where the temperature is gradually reduced to a temperature below the crystalline melting temperature, such as for a temperature between 100 - 130 °F (37.78 °C - 54.44 °C). At this temperature, the finished product can be completely self-supporting.

[0088] As indicated above, the extrudate leaves the exit end 16 of the die at or above the crystalline melting temperature of the polymer resin and retains sufficient heat to remain in an amorphous state for a few minutes after leaving the exit end 16. It is the treatment of the material at this critical stage that is a further object of the present invention. The soft extrudate can deform and collapse as it exits the die unless it is restrained vertically. Additionally, controlling the cooling rate so that the temperature gradient from the middle of the extrudate to the edges is minimized can help reduce stress on the finished product.

[0089] The present inventors have discovered that controlled cooling of the extrudate after leaving the exit end of the die opening leads to improved performance characteristics of the extrudate (no warping, sagging or stress) and reduced production costs. More specifically, the prior art methods involved using an annealing furnace to reheat the extruded panels to reduce stresses caused by uneven cooling of the UHMW polymer resins. The methods and apparatus of the present invention eliminate the need for an extra heating step, such as in the annealing furnace.

[0090] Various methods and apparatus are provided that can achieve cooling and compression forces on the extrudate. For example, and with reference to Figure 7, the piston extrusion apparatus may comprise one or more finishing tables (500, 502) that move the extrudate away from the exit end of the die so that there is no back pressure on the extrudate. Additionally, one or more finishing tables can promote uniform cooling and provide intermittent compression to the extrudate. Each of the one or more finishing tables (500, 502) may comprise upper (504, 512) and lower (506, 510) plates, wherein the upper plate is movable in a direction perpendicular (direction of arrow 60) to the axis longitudinal (direction of arrow 100) of the die through a variety of positions which include at least (a) an open position that does not contact the extrudate, (b) a downward position that contacts the extrudate but does not apply a pulling force. vertical compression on the extrudate and (c) a fixed position that contacts and applies a vertical compression force on the extrudate.

[0091] Furthermore, each of the one or more finishing tables (500, 502) may include a device for controlling a temperature of the upper (504, 512) and lower plates (506, 510) below the crystalline melting temperature of the polymer resin. The top and bottom plates can be cooled or temperature controlled directly, such as through heating or cooling the plates, or indirectly, such as through fans and so on that can be positioned externally and/or are not in contact with the signs.

[0092] When more than one finishing table is included, the temperature of the upper and lower plates (510, 512) of a second (or subsequent) finishing table (502) may, in general, be lower than the temperature of the upper and lower plates (504, 506) of a first (or previous) finishing table (500).

[0093] Furthermore, the upper (504, 512) and lower (506, 510) plates of each of the one or more finishing tables (504, 512) may comprise a high relief or low relief pattern to allow calendering of a non-extruded texture. In general, the first finishing table 500 may have top and bottom plates (504, 506) which may be used to print a pattern (high relief or low relief) on the extruded product, since the material may have a sufficient temperature. to have such a standard. Subsequent finishing tables may have cooled the extrudate or may receive the extrudate cooled to an insufficient degree to print a pattern.

[0094] In accordance with certain aspects of the present invention, a first finishing table 500 may be positioned after the exit end 16 of the die and may be movable in a direction parallel to the longitudinal axis 100 of the die. When included, a second or subsequent finishing table 502 may be positioned after the first or previous finishing table 500 and movable in a direction parallel to the longitudinal axis 100 of the die. The second finishing table 502 may be configured to (A) move away from the first finishing table 500 when the top plate 512 of the second finishing table 502 is in the lowered or fixed position and the top plate 504 of the first finishing table 500 is in the lowered or fixed position. any position and moves toward the first finishing table 500 when the upper plate 512 of the second finishing table 502 is not in the fixed position and the upper plate 504 of the first finishing table 500 is in the lowered or fixed position; (B) move in unison with the first finishing table 500; or (C) remain in a static position wherein, when the top plate 504 of the first finishing table 500 is in any position, the top plate 512 of the second finishing table 502 is in the lowered position to provide uniform cooling to the extrudate, but no compression force on the extrudate.

[0095] More simply described, one or more finishing tables may comprise a stationary lower plate and an upper plate, which produces a reciprocating motion, vertically operatively mounted on a plurality of driving piston rods correspondingly connected to plate drivers such as , for example, pneumatic cylinders (560A, 560B), which can be supported above the finishing table, such as by a support rail (580A, 580B). Other exemplary plate actuators include at least electrical (e.g., screw) actuators and hydraulic actuators.

[0096] The vertical reciprocity of the driving piston rod within the pneumatic cylinder (560A, 560B) can be synchronized with the horizontally reciprocating stroke of the piston so that when the piston makes its inward stroke, (a) the top plate is lifted to the open position is either in a downward position that does not restrict movement of the extrudate or (b) the top plate is fixed and the finishing table moves forward (away from the exit end of the die). As the piston is withdrawn to the retracted position, the top plate may remain open or may move down to the lowered or fixed position, and the finishing table may remain in place.

[0097] In accordance with certain aspects of the present invention, the upper (504, 512) and lower plates (506, 510) of each of the one or more finishing tables (500, 502) may comprise a rigid material, such as a material that has a minimum unit flexural stiffness of 13,400 inch-pounds2 (942 kg/cm2). Exemplary rigid materials include a 1/2-inch (1.27 cm) thick sheet of aluminum, which has a unit bending stiffness of 104,000 inch-pounds2 (7,311 kg/cm2). As such, any compression force provided by the pneumatic cylinders (560A, 560B) when in the fixed position can be evenly distributed to the top plates (504, 512).

[0098] According to certain aspects of the present invention, the upper plate 504 of the first finishing table 500 may comprise a more flexible material. For example, the top plate 504 may be formed from a material that has a maximum unit bending stiffness of 13,400 inch-pounds2 (942 kg/cm2). As used herein, the term "unit bending stiffness" is defined as the product of the modulus of elasticity (E) and the second moment of area (I), and is defined for a 1-inch (2.5 cm) section of width of the plate so that the cross section used to calculate the second moment of area (I) has a base b = 1 inch (2.5 cm) and a height h = plate thickness. Thus, the top plate 504 can have a unitary bending stiffness that allows it to conform to the soft extrudate without requiring so much force as to deform the extrudate or create back pressure on the extrudate at the exit of the die. This may provide a means of reducing the surface roughness of the extrudate (i.e., further smoothing the surface of the extrudate).

[0099] Exemplary materials for a flexible top plate 504 include, for example, a 3/8 inch (0.95 cm) thick sheet of 6061 aluminum (unit bending stiffness = 13000 inch-pounds2 (942 kg/cm2) ), steel plate with a thickness of 0.175 inch (0.45 cm) or less, or a 1/16 inch (0.16 cm) aluminum plate (unit bending stiffness = 0.2 inch-pounds2(0.014 kg /cm2)). Other thermally conductive materials may be used to form the flexible top plate 504 such as, for example, any other metal, modified plastic or composite material that has a maximum unit flexural stiffness of 13,400 inch-pounds2 (942 kg/cm2).

[0100] The flexibility of the top plate 504 can allow additional contact between the extrudate and the top plate 504 during vertical compression and ensure that the top plate 504 conforms to or remains in contact with the entire surface of the extrudate. To achieve vertical reciprocity with respect to the bottom plate and impart compressive forces, the top plate 504 may be operatively mounted on a plurality of actuating piston rods connected to a plurality of plate actuators, such as pneumatic, hydraulic, or electrical actuators ( e.g. air cylinders, springs, hydraulic cylinders or other actuators). These plate drivers can be used across a width and/or length of the top plate 504. Additionally, the plate drivers can act in unison, can act individually, or some combination thereof, and can provide vertical compression to the plate. upper 504 in order to distribute the compression force evenly across the width and/or length of the plate.

[0101] Illustrated in Figure 8 is an exemplary apparatus comprising a first finishing table 500 that includes a thinner and more flexible upper plate 504A and a lower plate 506. A plurality of plate drives, such as pneumatic cylinders (are shown in Figure 8; 610A - 610E), supported above the flexible top plate 504A of the first finishing table 500 by a support rail 680A, may be included to achieve vertical reciprocity of the top plate. Additionally, more than one row of plate drivers may be included, with each row supported on a support rail, to achieve vertical reciprocity of the top plate. For example, Figure 8 shows three rows of plate drivers supported by three support rails (680A, 680B, 680C), where each row includes five plate drivers (610A-610E; 620A-620E; 630A-630E).

[0102] The plate drivers may be controlled individually or in unison, such as unified drive of a row of plate drivers on a support rail or a row of plate drivers parallel to the longitudinal axis of the extrudate or any combination thereof. For example, as shown in Figure 8, the plate actuators (e.g., pneumatic cylinders) supported on the first two support rails (680A, 680B) are actuated individually (only a subset of the manual buttons 615A, 625A; and the control panels pressure reading 616A, 626A are labeled for clarity), while the plate actuator assembly on the third support rail 680C is controlled in unison (hand button 635 and pressure reading panel 636).

[0103] Plate drivers can be controlled automatically or manually, such as by a machine operator, who observes the panels leaving the machine. The amount of pressure exerted by each plate driver, or set of plate drivers, can be controlled to correct warping or surface imperfections as observed by the operator. Such a process can be easily implemented as an automatic process in hardware and/or software, for example, by scanning the platform transversely at one or more positions along its length by means of an optical comparator or similar, or sensitivity meters, switches limiters, temperature gauges, etc., which detect warping, surface characteristics, temperature, thickness, sagging, etc., and make corrections to the pressure exerted automatically by the plate actuators.

[0104] In accordance with certain aspects of the present invention, plate actuators used to achieve vertical reciprocity of the thin, flexible plate 504A may have pressure plates (618A, 628A, 638A) attached to a distal end of a piston rod. driver (617A, 627A, 637A) over the plate driver so that vertical compression force can be applied more evenly across the entire width and/or length of the thin, flexible top plate 504A. Pressure plates (618A, 628A, 638A) may be made of rigid, thermally conductive materials, such as any metal 3/8" thick or thicker, such as 5/8 inch (1.59 cm) thickness or 1/2 inch (1.27 cm) thick. Alternatively, pressure plates can be made from rigid, non-thermally conductive materials such as wood, plastic, or composites.

[0105] Although specific designs for finishing tables have been discussed and/or illustrated in the figures, the general configuration of one or more finishing tables may depend on several factors. That is, the number of in-line piston rods/plate drivers, the number of rows of plate rods/drivers, the longitudinal placement of rows of plate rods/drivers, the dimensions and materials of any pressure plate included in the distal end of each piston rod and the scheme by which the plate actuators are controlled (i.e., individually or in some combination) may depend on any number of factors, including at least: (a) the unit bending stiffness of the plate top of the finishing table, (b) the temperature of the extrudate, (c) the type of granular resin used to form the extrudate, and (d) the size of the extrudate. As an example, a more flexible top plate may require a greater number of piston rods/plate drivers per row and/or a greater number of rows of piston rods/plate drivers to evenly distribute a compressive force over the extrudate compared to to a rigid top plate.

[0106] With specific reference to Figure 7, each finishing table may be mounted on a rail or may include wheels (300, 302) or any other means by which movement may occur that is not restricted by excessive frictional forces. As indicated above, the movement of the finishing table(s) can be coordinated with the movement of the piston. Furthermore, the distance moved by each finishing table can also be coordinated with the piston movements. For example, each finishing table can be configured to oscillate between limit switches positioned approximately 2" apart to match a 2" piston stroke. When the table has extracted 2" of extrudate, for example, it can open the top and bottom plates (open or down position), move back to the front of the stroke, re-clamp the extrudate between the plates, and begin pulling again .

[0107] In general, the finishing table(s) do not restrict the movement of the extrudate away from the die and can assist in the movement of the extrudate away from the die. Additionally, the table(s) plates can be placed in a variety of positions that include at least one downward position that does not restrict movement of the extrudate but does provide cooling to the extrudate.

[0108] Referring further to Figure 7, to prevent the upper and lower plates (504, 506) of the first finishing table 500 from producing a frictional force opposite to the extrusion direction, a second finishing table 502 can be used to apply tension to the extrudate and help overcome the frictional force created by the first finishing table 500. As such, the first finishing table 500 can be held stationary and the second finishing table 502 can oscillate to match the movements of the piston as described above.

[0109] The first and second finishing tables, and any subsequent thereto, may be connected by table drives (503, 505), such as hydraulic, electrical or pneumatic drives (e.g., air cylinders) that provide the tractive force. This can provide a means of connecting and/or synchronizing the movement of the various finishing tables without the need for a direct connection between the plates of the various finishing tables. In this way, heat will not be conducted from the plates (504, 506) of the first finishing table 500 to the plates (510, 512) of the second finishing table 502 or any subsequent thereto. This allows the second finishing table 502 to be cooled, such as with fans, without adversely affecting the first finishing table 500, which may remain hot. Furthermore, the first finishing table 500 may be connected to the end of the die by an air piston (503) that may allow movement along the longitudinal axis.

[0110] Alternatively, or in addition to the table drives (503, 505) which can connect the various finishing tables, each finishing table can include wheels (300, 302) and/or can be mounted on a rail system. which can allow movement of tables towards or away from the matrix. As mentioned above, such movement can be synchronized with the movements of the piston and/or a previous finishing table.

[0111] Various methods and apparatus are provided that achieve cooling and vertical compression forces on the extrudate, but do not exert horizontal counterpressure on the extrudate. In general, the present invention is directed to apparatus and methods that can be used to keep the extrudate warm through compression perpendicular to the direction of flow through the die and apparatus and methods that can cool the extrudate in a controlled manner. Thus, the present invention may include any number of means for moving an extruded panel that has exited the die at a temperature above the melting point, or crystalline melting temperature, by alternating or clamping it consistently between upper and lower controlled surfaces. of temperature, at the same time as the containment apparatus or clamp advances incrementally with the powder charge and the resulting emergence of the extrudate.

[0112] For example, instead of finishing tables, the extrudate may be pulled from the exit end of the die using a tractor or belt, reciprocating puller, Caterpillar puller, or similar. For example, a belt puller may be used that pulls the extrudate away from the exit end of the die between two belts. Directly adjacent to each belt there may be a plate such as, for example, an aluminum sheet, which can be cooled and thus can provide uniform cooling to the extrudate, while at the same time applying a compressive force to the extrudate. More than one belt puller may be used to provide different cooling zones with different temperatures (e.g., gradual temperature reduction) and/or pressures and/or to allow certain belts to have a raised or lowered pattern.

[0113] Although specific devices have been described that drive the movement, such as the hydraulic cylinder 118 that moves the piston, the pneumatic cylinders (560A, 560B) that move the upper plates on the finishing tables and the air cylinders ( 503, 505) that move the various finishing tables, any number and variety of apparatus that can provide movement are possible and are within the scope of the presently described invention. Furthermore, a more sophisticated method for triggering the advancement of one or more finishing tables is possible, including electronic encoder controls and proximity switches programmed to coincide with piston movements and are within the scope of the present invention.

[0114] An electrical panel may also be provided to the piston extrusion apparatus with appropriate switches, thermostats, temperature indicating dials and such related instruments as are necessary to control operating conditions, such as temperature, pressure and so on, and provide a visual indication thereof.

Example A

[0115] A first exemplary piston extrusion apparatus is described here. Although specific temperatures and dimensions are provided, these are provided to describe an exemplary embodiment only and may vary within the limits defined and described above. Reference numbers are provided to aid understanding of this specific embodiment, and may refer to Figures 1-8.

[0116] A die 10 comprising two highly polished steel die plates (72, 74), each three (3) inches (7.62 cm) thick, is sandwiched between two steel blocks (102, 104 ) with 24 (twenty-four) inches thick. The die boards are separated by rigid spacers (76, panel thickness; <^ inches (1.9 cm)) and have a width of 40 to 66 inches (100 cm to 166 cm) (panel width; typically 54 inches (136.16 cm)) and a length of just over 32 inches (81.28 cm) (die opening length, not panel length) to form a rectangular opening.

[0117] The input end of the die has water coolers installed in slots machined in the die plates to prevent the powdered resin from oxidizing before entering the die.

[0118] Die 10 is heated by electric cartridge heaters installed in slots machined in the plates (72, 74). The heaters are organized into twelve (12) individually controlled zones along the length of the array and eight (8) paired zones along the array outlet. Additional heating zones across the die exit face (as at 50C, see Figure 1D, 3 and 5) are provided so that different temperature profiles can be used across the entire width of the die at its exit: the outer edges of the matrix include an additional heat input to prevent the plastic from sticking during an outage or restart and to prevent the load (extrusion) lines from hanging over the edges of the panel.

[0119] An exemplary heating profile for a UHMW polyethylene resin may include three thermal zones along the longitudinal axis of the die opening: after thermal insulation, 300 °F (148.89 °C) to 320 °F (160 °C); mid region, 330°F (165.56°C) to 420°F (215.56°C); exit region, 300°F (148.89°C) to 350°F (176.67°C).

[0120] The inlet end of the upper block and the die plate are machined to provide an opening (resin inlet 32) for powdered UFIMW polymeric resin to be introduced into the die opening of a feed hopper 30 comprising a plurality of tubes (e.g., 4; supply tubes 34) extending to the inlet of the die. Each tube can be raised or lowered to regulate the supply to the area below each tube. Alternatively, each feed tube may comprise a screw feeder, vibrating feeder or rotary feeder. 80 aluminum shoes are attached to the bottom of the tubes to help distribute the resin.

[0121] A steel plate (piston head 19) measuring one-half (0.5) of an inch (1.27 cm) x fifty-four (54) inches (136.16 cm) with a rectangular cross-section is attached to an oriented plate (piston 18) that is driven by hydraulic cylinders (118). The piston is capable of a six (6) inch (15.24 cm) linear stroke that extends two (2) inches to the die inlet. The piston is significantly thinner than the die opening to prevent friction and sticking in the die. A wiper plate is used to push the piston against the bottom surface of the die to prevent the piston from lifting and forcing expelled air and fines into the chamber opening. The rear section of the piston is cooled with water channels to prevent resin oxidation.

[0122] Two finishing tables (500, 502) are provided after the exit end of the die, each finishing table comprising an upper and lower plate. The plates are 3/4 inch (1.9 cm) thick aluminum (good thermal conductivity and sufficient rigidity). Pneumatic cylinders (560A, 560B) are used to apply pressure to the plates so that the plastic is secured and also to ensure surface contact between the plastic and aluminum to promote consistent thermal conductivity.

[0123] The tables are connected only by the two pneumatic cylinders (503, 505) that provide the traction force, so that heat is not conducted from the plates of the first finishing table to the plates of the second finishing table. The second finishing table can swing between limit switches positioned approximately 2" apart. When the table has pulled out 2" of plastic, for example, it will open the aluminum plates, return to the front of travel, re-clamp the panel and will start pulling it again.

[0124] The first section of the table is heated on the top and bottom plates, which may have a partially or fully embossed or embossed texture to allow calendering of a texture into the panel. The second table section advances simultaneously with the first and is mechanically connected to the first section, but consists of separate top and bottom plates. This second table is cooled, as with fans, without adversely affecting the first table, which remains hot.

Example B

[0125] A second exemplary piston extrusion apparatus is described herein, in which the die 10, the reciprocating piston 18 and the feed hopper 30 are as described in Example A. Reference numerals are provided to aid an understanding of this embodiment specific and may refer to any of Figures 1-8.

[0126] As described for Example A, two finishing tables (500, 502) are provided after the exit end of the die, wherein each finishing table comprises an upper and lower plate. The top plate (504A of Figure 8) of the first finishing table 500 is aluminum with a thickness of 3/8 inch (0.95 cm), while the top plate 512 of the second finishing table 502 and the bottom plates (506 and 510, respectively) of the first and second finishing tables are 3/4 inch (1.9 cm) thick aluminum. The top plate 504A of the first finishing table is raised or lowered by three rows of plate drivers which are supported on the top plate on support rails (680A, 680B, 680C). Each of the three rows of plate drivers includes nine (9) pneumatic air cylinders (see, e.g., 610, 620, 630 of Figure 8). The first and second rows (the row closest to the output end of the die is the "first row", near the 540 end of the table shown in Figure 8) of the plate drivers are individually controllable, while the third row (farthest row of the end of the die; near the end 542 of the table shown in Figure 8) of plate drivers is controlled in unison. Operatively connected to the end of the piston rod (617A, 627A, 637A) of each plate driver is a pressure plate (618A, 628A, 638A) formed from 3/4 inch (1.9 cm) aluminum. Further details of the piston extrusion apparatus are those described for Example A.

[0127] Although specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and changes and applications can be developed in light of the general teachings of the description. Accordingly, the particular configurations, systems, apparatus and methods described are intended to be illustrative only and not limiting the scope of the invention.

Claims (12)

1. Apparatus for extrusion of a polymeric resin, comprising: a die (10) having an input end (14) and an output end (16); a piston (18) mounted for movement within the inlet end (14) of the die (10), from a retracted position to an extended position; at least one feed hopper (30) for introducing the polymeric resin in a granular state into a resin inlet (32), wherein the resin inlet (32) is close to the inlet end (14) of the die (10) and downstream of the retracted position of the piston (18); a plurality of thermal zones (50, 50A, 50B, 50C) in the matrix (10) spaced along a width and a length of the matrix (10); a device for heating a given plurality of thermal zones (50, 50A, 50B, 50C) including at least thermal zones (50, 50A, 50B, 50C) proximate the outlet end (16) of the die (10), to a temperature above the crystalline melting temperature of the polymer resin; a device for imparting movement to the piston (18) along a longitudinal geometric axis (100) of the die (10) to move the polymeric resin from the resin inlet (32) through the plurality of thermal zones (50, 50A, 50B, 50C), and out the exit end (16) of the die (10) as an extrudate, the polymeric resin being melted and compressed to form an extrusion profile of the die (10) during progression through the plurality of thermal zones. (50, 50A, 50B, 50C) of the die (10), a device for uniformly cooling and compressing the extrudate after exiting the exit end (16) of the die (10), characterized in that the resin is extruded from the end exit end (16) of the die (10) as an extrudate at a temperature at or above the crystalline melting temperature of the polymer resin, wherein the apparatus comprises means for moving the extrudate away from the exit end (16) of the die (10) matrix (10); and wherein the device for moving the extrudate away from the exit end (16) of the die (10) does not apply a compressive force to the extrudate parallel to the longitudinal geometric axis (100), but applies a compressive force to the extrudate perpendicular to the longitudinal geometric axis (100) of the die (10), wherein the device for moving the extrudate away from the exit end (16) of the die (10) comprises one or more finishing tables that move the extrudate away from the exit end (16) of the die (10) exit (16) of the die (10) so that there is no back pressure on the extrudate and that promotes uniform cooling and intermittent vertical compression of the extrudate, wherein the device for moving the extrudate away from the exit end (16) of the die (10) applies a vertical compressive force on the extrudate perpendicular to the longitudinal geometric axis (100) of the die (10), additionally in which the device for moving the extrudate away from the die exit (10) and for cooling and compressing uniformly the extrudate comprises: one or more finishing tables (500) positioned after the exit end (16) of the die (10) and movable in a direction parallel to the longitudinal geometric axis (100) of the die (10), at one or more further finishing tables (500) comprising upper and lower plates (504, 506), wherein the upper plate (504) is movable in a direction perpendicular to the longitudinal axis (100) of the die (10) through a variety of positions , which include at least: (a) an open position that does not contact the extrudate, (b) a down position that contacts the extrudate but does not apply a compressive force to the extrudate, and (c) a fixed position that applies compression force to the extrudate, whereby the one or more finishing tables (500) move the extrudate away from the exit end (16) of the die (10), so that there is no back pressure on the extrudate and promotes uniform cooling of the extrudate between the upper and lower plates (504, 506) when in the down or fixed position. 2. Apparatus according to claim 1, characterized in that it additionally comprises: at least one second finishing table (502) positioned after the first finishing table (500) and movable in the direction parallel to the longitudinal geometric axis (100 ) of the die (10), the second finishing table (502) comprising upper and lower plates (512, 510), wherein the upper plate (512) is movable in the direction perpendicular to the longitudinal geometric axis (100) of the die (10 ) through a variety of positions that include at least: (a) an open position that does not contact the extrudate, (b) a down position that contacts the extrudate but does not apply a compressive force to the extrudate, and (c) a fixed position that applies compressive force to the extrudate, wherein the second finishing table (502) is configured to: (A) move away from the first finishing table (500) when the top plate (512) of the second finishing table (502) is in the down or fixed position and the top plate (504) of the first finishing table (500) is in any position, and move towards the first finishing table (500) when the plate upper plate (512) of the second finishing table (502) is not in the fixed position and the upper plate (504) of the first finishing table (500) is in the down or fixed position; (B) move in unison with the first finishing table (500); or (C) remain in a static position, wherein when the top plate (504) of the first finishing table (500) is in any position, the top plate (512) of the second finishing table (502) is in the position to low to provide uniform cooling of the extruded resin but no compressive force on the extrudate. 3. Apparatus according to claim 2, characterized in that at least one of the first and/or second finishing tables (500, 502) includes a device for controlling the temperature of the upper and lower plates to below the crystalline melting temperature of the polymer resin. 4. Apparatus according to claim 1, characterized in that the matrix (10) comprises an upper matrix plate (72) and a lower matrix plate (74), each comprising a thermal break (80, 82) downstream of the resin inlet (32), wherein the thermal break (80, 82) defines at least one heated thermal region comprising thermal zones (50, 50A, 50B, 50C) spaced between the thermal break (80, 82) and the output end (16) of the die (10). 5. Apparatus according to claim 4, characterized in that the thermal break (80, 82) additionally defines a cooled thermal region comprising thermal zones (50, 50A, 50B, 50C) spaced between the inlet end (14) of the matrix (10) and thermal break (80, 82). 6. Apparatus according to claim 1, characterized in that at least one feed funnel (30) is configured to introduce the polymeric resin into the resin inlet (32) of the matrix (10) in a plurality of specifically measured amounts in a width of the resin input end (14) of the matrix (10). 7. Apparatus according to claim 6, characterized in that the specifically measured amounts of polymeric resin vary over a width of the resin inlet (32) of the matrix (10). 8. Apparatus according to claim 1, characterized in that at least one feed hopper (30) comprises a plurality of feed tubes (34) spaced along the width of the resin inlet (32) of the matrix (10), each of the plurality of feed tubes (34) comprising a distal end (36) that is proximal to the resin inlet (32) of the matrix (10) and a proximal end (38) in fluid communication with the feed funnel ( 30). 9. Apparatus according to claim 8, characterized in that each of the plurality of supply tubes (34) is independently movable in a vertical direction that is perpendicular to the longitudinal geometric axis (100) of the matrix (10) to provide the plurality of specifically measured amounts of the polymeric resin, wherein the plurality of specifically measured amounts of the polymeric resin are the same or vary across a width of the resin inlet end (14) of the matrix (10). 10. Apparatus according to claim 8, characterized in that each of the plurality of feed tubes (34) comprises a screw feeder, a vibrating feeder or a rotary feeder, which is independently controllable to supply the plurality of specifically measured quantities of polymeric resin, wherein the plurality of specifically measured quantities varies over a width of the resin inlet end (14) of the matrix (10). 11. Apparatus according to claim 8, characterized in that each of the plurality of supply tubes comprises a shoe (80A-80D) at the distal end (36) thereof configured to uniformly distribute the polymeric resin from each of the plurality of supply tubes (34) for the resin inlet (32) of the matrix (10). 12. Apparatus according to claim 1, characterized in that the device for transmitting the movement of the upper plate (504) of the first finishing table (500) comprises: at least one support rail (580A, 580B) positioned on a surface top of the top plate (504), and a plurality of plate drivers (610A - 610E) fixed to the at least one support rail (580A, 580B), wherein each of the plurality of plate drivers (610A - 610E) has a driver rod (617A, 627A, 637A) operatively attached to the upper surface of the top plate (504) through a distal end of the driver rod (617A, 627A, 637A).