MXPA99002957A - Method of throttle-valving control for the co-extrusion of plastic materials as for molding and the like, and apparatus therefor - Google Patents

Abstract

A novel multiple-plastic stream co-extruder and method, as for injection-molding cavities, in which the extruder is internally provided therewithin and therealong with a restrictor or throttle pin, rod or element that forces combined plastic material streams, formed with an interior core stream encased in outer and inner stream layers, into corresponding concentric annular flow stream layers that are ultimately split transversely in opposite directions into a cavity gated to the extruder, and with the core stream at a region of zero gradient in the transverse flow velocity profile within the extruder and cavity.

Description

METHOD OF CONTROL OF THE ADMISSION VALVE FOR THE COEXTRUSION OF PLASTIC MATERIALS AS WELL AS FOR THE MOLDING AND SIMILAR, AND EQUIPMENT PARA1 THIS Field of the Invention The present invention relates to the co-extrusion of two or more streams of plastic material and the like, as well as the introduction into molding apparatus or similar applications; it is more particularly directed to the problems of providing better control of such coextrusion and allowing a more uniform molding of the extruded materials and with greater flexibility of use of a wide range of different proposed materials, extrusion temperatures and other conditions. With specific reference to the injection systems for co-injection of at least two materials, the present invention relates to an improved technique and apparatus for combining the different fluid streams of materials, wherein a velocity profile of the combined stream that is produced in the melt distribution system, it is similar to the velocity profile of the combined stream in the injection molding cavity, to ensure uniformity in the resulting molded article.

BACKGROUND OF THE INVENTION A common problem in the field of coinjection molding resides in the need to maintain the leading edge of the central (inner) layer uniform, with respect to the thickness of the rear portions of the central (inner) layer that enter the molding cavity. A tapered leading edge will produce a molded part that is not uniform in its properties near the furthest penetrating position of the inner layer. Usually, the leading edge of the central layer (inside) tapers as it flows through a cylindrical central channel of prior art co-ejection nozzles, placed downstream of the nozzle combination area and when flowing through the cylindrical gate portion of the cavity of molding. Typically, such nozzles are those described, for example in U.S. Patent Nos. 4,895,504 and 4,892,699. The amount of the taper depends on the velocity profile of the combined flow that produces a velocity gradient between the radially innermost portion and the radially outermost portion of the leading edge. The amount of taper also depends on the total axial distance of the cylindrical flow between the combination area and the end of the cavity of the cylindrical gate.

To minimize tapering of the leading edge, such prior art nozzles have been constructed with a short axial flow distance between the combination area and the end of the cavity of the cylindrical gate. Typically, this axial flow distance is between about 5 mm and 25 mm / and the length of the resultant leading edge taper is greater than about 1.8 mm for the shortest axial flow distance and 9 mm for the axial flow distance longer. Thus, the short axial flow distance requires that the combination means be part of the nozzle. Another problem with the current technique is that the outermost diameter of the coinjection nozzle near the gate is larger than the nozzle diameters used in the injection molding of a single material. This larger size requires a hole with a larger opening in the mold, which makes it difficult to provide adequate cooling of the mold cavity near the gate. Some current art designs use combination means having a conical or frusto-conical portion, to minimize the outermost diameter near the gate; even so, this diameter of the nozzle, near the gate, can be twice the size of a nozzle for a single material.

OBJECTS OF THE INVENTION An object of the present invention is to provide a novel and improved method and a coextrusion apparatus that will not be subject to the above and other disadvantages of the prior art., but, on the contrary, through a radically different conversion of the nozzle to an intake control extruder, provides a significantly improved, more uniform and more flexible operation. Another object is to provide a novel extrusion apparatus, in which a combined flow having a velocity profile is produced within and downstream of the combination area of the extrusion materials, which has a velocity gradient of substantially zero through of the leading edge of the central (inner) layer, such a velocity profile allows the front edge of the central (inner) layer not to tilt, as in the prior art nozzles, as it flows from the combination area towards the end of the mold gate cavity. Yet another object of the invention is to provide a novel apparatus, in which the combination means are far from the area of the nozzle gate, so that the design of the mold and the cooling of the mold are not compromised. A further object that is achieved by such novelty, results from the radical conversion of prior art cylindrical nozzle designs, into an extruder structure containing admission or restriction rods or rods, which force the annular extrusion; and, in the case of the internal core molding, creates concentric external and internal annular extrusion currents, with the annular current forming the encapsulated center within the coextruded, annular outer and inner current layers. A further object is to provide a novel extruder, in which a vestige of the gate is left on the molded part, which is smaller than that which can be obtained by the molding systems of a single material. A further object of the invention is to provide a novel method and coextrusion apparatus, wherein the velocity profile of the combined stream of the plastics materials downstream of the combination area is substantially the same as the velocity profile of the combined current in the cavity, so that improved properties in part and improved cycle times are possible. The others and other objects will be explained hereinafter, and are delineated more particularly in the appended claims.

Brief Description of the Invention In summary, however, from one of its broader aspects, the invention encompasses a method for coextruding multiple plastic materials by injection, through a gate region in a molding cavity to produce a molded product, comprising, combining streams of such fluid plastic materials with at least one internal stream serving as the inner core of a resultant molded plastic product within the internal and external streams of the plastic material, which serve as layers of plastic coating material; restricting the combined streams to flow along concentric annular flow paths, within and along a tubular extruder extending longitudinally towards the region of the cavity gate, with the annular central stream encapsulated by the current layers of plastic material of the outer annular cover; in the region of the gate, divide the concentric annular currents along opposite transverse directions to be injected into the corresponding cross sections of the cavity. The modalities of the best mode and the preferred apparatus designs for practicing the novel method of the invention are described more fully hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in relation to the accompanying drawings, Figure 1 of which, shows a cross section of a complete system that includes the system of the source of materials, distribution and combination of materials and molding cavity; Figure 2 is a cross section of the flow of the area of combination of the material towards the molding cavity, showing that the central (inner) layer flows along the zero gradient of the velocity profile according to the technique and construction of the present invention; Figure 3 illustrates in cross-section the annular flow channel of this construction, which also shows the central (inner) layer along the zero gradient of the velocity profile; Figure 4 is a cross-sectional view of an annular flow channel as in Figure 3, but with poorly distributed internal and external annular flow layers, which cause the central (inner) layer to deviate from the middle part of the layers. annular diameters; Figure 5 presents a cross section of the cylindrical flow of the prior art, showing the central (inner) layer in a high velocity gradient area, which contrasts with the conditions of the invention presented in Figures 3 and 4; Figure 6 is similar to Figure 5, but shows the cylindrical flow of the prior art with poorly distributed outer and inner layers; Figure 7 is a cross-sectional view showing the velocity profiles of the layer (interior) in the area of the annular flow nozzle, area of the annular flow gate and cavity; Figure 8 is similar to Figure 7, which shows, however, the effect of poorly distributed flow of the outer and inner layers on the relative position of the leading edge of the central (inner) layer in the molding cavity; Figures 9 and 10 are views similar to the respective Figures 7 and 8, but showing the cylindrical flow of the prior art in the gate of the nozzle and cavity; Figure 11 is a cross-sectional view of a molded part formed by the structure of the invention, showing the amount of tapering of the leading edge caused by the annular flow length in Figure 8, 75 mm of the combination area at side of the cavity gate, when the internal and external maldistribution is 10%; Figure 12 is a view similar to that of Figure 11, but of a molded part made by the cylindrical nozzle structure of the prior art of Figure 10, showing the amount of tapering of the leading edge caused by poor internal distribution and external 10% cylindrical flow; Figure 13 is a cross section of a modified extruder constructed in accordance with the invention, and in which, the flow of the manifold is through flat disk combination means with fixed intake valve means, through the nozzle of annular flow in the gate towards the cavity; Figure 14 is a cross section of a further modification, in which axial combination means and fixed intake valve means are provided as part of the nozzle itself; Figure 15 is a more complete cross section of the axial combination means with the fixed intake valve means of Figure 14, which is a cross-sectional view of the combination means consisting of three concentric axial cylinders, around central fixed intake valve means, which extend through the combination area, through the separate nozzle and through the gate to the mold; Figure 16 is a view similar to that of Figure 13, but showing movable intake valve means; Figure 17 is an enlarged cross-section of the combination means and the movable intake valve of Figure 16; Figures 18 and 19 are annular of Figure 17, showing the valve in a neutral position, with admission positions for reduced and increased inner layer flow rates, respectively; Figure 20 illustrates, on an amplified scale, the relative locations of the end and gate of the nozzle towards the cavity, wherein the intake valve maintains the desired annular flow towards the cavity; Figure 21 is similar to Figure 20, but provides a conical valve corresponding to a conical gate to produce a reduced gate mark on the molded part; Figure 22 is again similar to Figure 20, but the intake valve is combined before the gate allows molding plastics that require an open gate; Figure 23 is, once again, similar to the Figures and 22, but the intake valve is adjusted to act as a gate valve, shown in the open position; while in Figure 24, it is shown in the closed position; Figure 25 is a cross section of the end of the nozzle of the invention, the gate and a partially filled cavity, showing the outer layers and the central (inner) layer operated at the same temperature; while in Figure 26, the outer layers are injected at a much higher temperature than that of the central (inner) layer; Figures 27 (a) - (d) show the filling sequence for a central (inner) layer, which is uniformly distributed through the molded part; Figures 28 (a) - (d) are similar to Figures 27 (a) - (d), but show a filling sequence for a central (inner) layer, where the maximum amount of core or center is injected into the molded part using a fixed intake valve; Figures 29 (a) - (d) again are similar to Figures 27 and 28, but show the filling sequence for a central (inner) layer, where the maximum amount of core or center is injected into the molded part, using combination means designed to produce an external layer flow at a higher velocity relative to the inner annular layer, to obtain a thicker outer layer on the side of the gate of the molded part; whereas Figure 30 shows the opposite; Figure 31 is a cross section of the gate and cavity area, showing the filling sequence using a movable admission valve, which increases the flow of the inner annular layer relative to the outer annular layer during the flow shown in FIG. Figure 31 (b), thus injecting more material from the central (inner) layer on the side of the gate of the molded part; Figure 32 is a cross section of the gate and cavity area, showing the filling sequence, wherein the intake valve moves to decrease the flow of the inner annular layer relative to the outer annular layer (i.e. , the relative flow opposite to that of Figure 31) during the flow shown in Figure 32 (b), thereby injecting more material from the central (inner) layer towards the side of the molded part opposite the gate; Figure 33 is a graph that graphs the average velocity / velocity and flow fraction in the annular channel and the cavity; and Figure 34 is a graph that graphs the average velocity / velocity and flow fraction in a previous cylindrical channel, by way of comparison with the results of Figure 33.

Preferred Modes of the Invention Referring to Figure 1, and in the exemplary context of the invention applied to plastics (such as PET, EVOH, polycarbonates and the like), coinjection molding systems adapted to inject at least two materials into one cavity of a mold, the system comprises respective sources Si and S2 of each material, means, such as a manifold D, to distribute each material stream to combination means C upstream of each mold gate, and a novel intake valve which controls the nozzle means of the extruder E to distribute the combined current to the gate, towards the mold M. The sources Si and S2 of each material are shown as oscillating screw injection units; the means for distributing the material streams are a multiple block M with separate flow channels, respectively Ci and C2, for each material arranged so that the flow is balanced and equal for each; the combination means C are placed upstream of the intake nozzle means E with its internal coextensive intake needle T, which distributes the combined current to each region of the gate G of the mold. In the embodiments described here, Figure 2, the currents forming each layer L of the molded product are combined in an annular channel A of the combination means C, so that the leading edge of the central (inner) layer is placed in the zero velocity gradient portion of the combined flow stream, as explained more fully below. The extruder nozzle means extending longitudinally E with the central longitudinal intake or flow restricting needle T, downstream of the combination means C, provide an uninterrupted continuation of the annular flow developed in the combination means. In the three layer combined flow stream mode of Figure 2, two materials L and I are provided, each from its own source; the first material L, which forms the outer or cover layers 0LX and ILi of the molded part, forms the inner and outer layers OL and IL of the combined annular flow stream at A, formed by the presence of central intake T; the second material I, which forms the central (inner) layer Ii of the molded part, forms the middle or inner or inner annular layer IA of the combined annular flow A. The first material L is distributed through its channel flow to the combining means C, where it is divided from a single stream into two streams, one forming the aforementioned internal annular layer IL of the combined annular flow stream, and the other forming the aforementioned outer annular layer * OL . The second material I is distributed through its flow channel to the combination means C, where it is deposited to form the middle or inner annular layer A of the combined concentric annular flow streams, as shown also in the cross section of the annular flow channel of Figure 3. Preferably, as shown, the central intake or restrictor needle is of reduced diameter 1"at the open distal end of the extruder and the injection end of the cavity gate The nozzle means, thus, have an internal orifice, which surrounds the intake valve bolt to form an annular channel to distribute the combined flow stream to the gate while maintaining the profile of speed previously mentioned, placing the material of the central layer (interior) so that it is in the zero gradient of the velocity profile VPa, the leading edge of the central layer (interior) n or tapers, regardless of the distance of the axial flow between the combination means and the gate to the cavity. The axial length of the nozzle, unlike the prior art nozzles, can therefore be made as long as required to provide good mold cooling. The outermost diameter of the nozzle is typically not as large as that required for the molding of a single material, so the design of the mold or the cooling of the mold is compromised. This modality, moreover, also makes it easier to convert a mold designed to mold a single material to be used for coinjection. The region of the gate G adjacent to the proximal distal end of the restrictor or intake needle, rod or element T ', the annular flow streams are divided laterally and the flow is injected in opposite directions transversely to the corresponding open sections of the cavity. molding, as shown by the arrows in Figure 2. In this and in the last described modalities that place the material forming the central layer (interior) of the molded part to be in the middle layer of the combined flow stream , a part can easily be molded with its central (inner) layer at a melting temperature that is less than that of the outer layers of the molded part. In the molding of a single layer, on the other hand, the temperature of the material as it is provided in its source, must be sufficiently high 1) to decrease its viscosity to facilitate the flow between the walls of the injection cavity and 2) to produce a good cosmetic appearance on the external surfaces of the molded part. Because the material of a molded part with a single layer is provided by a source of a single material, the temperature of its inner layer will be the necessary temperature to facilitate the flow of the cavity and surface appearance, and the necessary cooling time to cool the inside of the molded part, depends on the melting temperature provided by the source. Using the present invention, however, the central (inner) layer can be provided at a temperature very different from the material temperature of the outer layer, thereby producing several unexpected improvements compared to the single layer molding. Although some other systems of the prior art can also allow this effect, it is effected in a particularly simple and efficient manner with the technique and construction of the invention. The improvements that can be produced by providing the outer layers at normal or higher than normal temperature and the central (inner) layer at a correspondingly lower temperature, include: 1) the filling pressure of the cavity will be lower because the viscosity of the outer layer will be lower than normal; 2) the surface appearance of the part will improve due to the melting temperature of the hotter outer layer; 3) . the cooling time, and therefore the cycle time, will be reduced if the relative increase in the melting temperature of the outer layer is lower than the decrease in the melting temperature of the corresponding central (inner) layer, so that the total heat content of the combined melt is less than normal for the molding of a single material; 4) an increase in the melt viscosity of the central (inner) layer will increase the volume of the central (inner) layer in relation to the decrease in the volume of the outer layer, if this is a desirable property of the molded part; and 5) a material of the central (inner) layer having a coefficient of thermal expansion greater than that of the outer layer can be used, without causing undue molding efforts, etc. Other improvements can occur by providing different relative melting temperatures of the materials of the central (inner) and outer layers. One such reason is to control the relative shrinkage between the layers when the central (inner) layer has a coefficient of thermal expansion different from that of the outer layer material. Another reason is to produce parts that have lower molding efforts by using temperature differences to reduce the relative contraction between the central (inner) and outer layers, without affecting the cosmetic appearance of the part's surface. Returning to the flow distribution illustrated in Figures 2 and 3, the structure of the extruder of the present invention can accommodate the poorly distributed or non-symmetrical outer and inner annular flow layers, so, as shown in Figure 4 , can cause the central (inner) annular layer IA to deviate from the middle part of the annular diameters of the internal and external layers IL and OL encapsulants. From the velocity profile VPi 'of Figure 4, it will be observed that the center, although deviated, is no closer to the zero gradient velocity profile, allowing even better results. This contrasts with the cylindrical flows in the prior art nozzles E ', used in Figures 5 and 6, for symmetrical and asymmetric conditions, and where the central layer is subjected to areas of a high velocity gradient in the VPi profiles. '' and VPi '' ', with the concomitant limitations and disadvantages previously described. In the restricted or reduced center coextruder of Figure 7, where the extruder E is shown connected to an annular flow gate G 'and a cavity, the velocity profiles of the annular central layer IA in the area of the annular extruder (VP2) and in the area of the annular flow gate (VP) and in the cavity (VP3), they are all present, demonstrating the conservation of the zero gradient through the flow and the injection process of the cavity of the invention . Substantially, these benefits are also obtained in the case of misalignment or maldistribution of the flow of the external and internal layers, Figure 8, with the illustrated effect of a maldistribution of the flow of the external and internal layers on the relative position? l of the leading edge of the central (inner) layer in the molding cavity. Figures 9 and 10 show cylindrical nozzles of the prior art, corresponding, respectively, to the extruder of the invention shown in Figures 7 and 8, and illustrate undesirable high velocity gradients for the flow of the central (inner) layer in the nozzle E '(VP2') and in the gate (VP3 '), with the gradient of the velocity profile of zero reached only in the cavity (VP4'). Figure 10 shows the taper development of the leading edge of the core caused by the effect of the speed difference through the poorly distributed central leading edge, when it flows through the extruder E '. When the front edge flow line LA '1 flows at a higher speed than IA'3, the tapering occurs at the moment when the core or center enters the cavity through the gate G '. Even if the central layer Ii remains deviated from the central line of the cavity flow, the velocity difference across the tapered leading edge in the cavity is still small, so that the increase in? L in the cavity is small compared to the one developed in the prior art extruder E '. In addition, to contrast the significantly improved molding results and the achievable tolerances with the annular flow construction of the invention with the cylindrical nozzles of the prior art, Figure 11 illustrates the minimum acceptable amount of front edge taper contained in a molded part. for a maldistribution of the internal and external flow of 10% with the annular flow of the structure of the invention (Figure 8) for an annular flow length of 75 mm of the combination area C towards the side of the cavity of the gate G; while Figure 12 shows the much greater taper of the leading edge in the molded part of which the technique had to accept with the previous cylindrical flow nozzles, for the same maldistribution of 10% with a cylindrical flow length of 75 mm. Combination area next to the gate cavity (Figure 10). To achieve a minimum acceptable amount (6 to 6 mm) of tapering of the leading edge as shown in Figure 11 when the prior art is used, the length of the combined flow in the central channel of the combination area to the surface of the part molded, should not exceed approximately 11 mm, if poor distribution of internal and external flow is as shown in Figure 6 and Figure 34. To provide a minimum amount of cooling of the mold near the gate, the short length of the central channel of the prior art requires that the shape of the combination means be conical or frusto-conical. Such a shape will still require that the distal end of the nozzle be twice as close to the outer diameter of a nozzle of a single material, thereby causing part of the cooling near the nozzle to be compromised. Figure 13 illustrates another embodiment of the invention, wherein the three layer combination means consist of four flat discs FD surrounding a central fixed intake valve bolt TT ', which forms the wall of the internal flow channel for the layer internal of the combined flow stream. The flow channels d ', C2', etc., are created between the three flat coupling surfaces of the FD discs uniformly, to place each flow layer to produce a uniform flow of the respective materials flowing from each channel to the combination area C, so that each layer of the combined flow stream is uniformly annularly placed, as it flows from the combination means through the restricted or reduced nozzle means of the extrusion E and the gate G towards The cavity.

The manifold combination means may, in addition, be incorporated as part of the extruder mouth structure by themselves as shown, for example, in Figure 14, where the axial combination channels Ci ", C2", etc., are provided in the upper part of the extruder E itself, with a fixed intake valve T extending along and inside the extrusion nozzle. Another embodiment (shown in Figure 15) uses three concentric frames Si ', S2' and S3 'surrounding a central intake bolt T, which forms the wall of the internal flow channel for the internal layer of the combined flow stream. The flow channels created between the frames and between the inner frame and the intake valve bolt, are designed to produce an uniform flow of the respective materials flowing from each channel to the combination area, so that each The combined flow stream layer is uniformly annularly positioned as it flows from the combination means through the nozzle means into the cavity. In this embodiment, the combination means C is a separate sandwich assembly between the manifold manifold D and the die of the extruder E. This allows the extruder nozzles to be identical in design as those used in the molding of a single material. The combination means are coaxial with respect to the extruder nozzle so that the intake bolt T and the cylindrical wall of the extruder nozzles, form a uniform annular channel A. While the admission or restriction valve bolts that extend longitudinally in the center so far described have been shown as fixed, as, for example, in the embodiment of Figure 13, also they can be made moe, by means of an adjusting rod R, Figure 16, for various useful adjustment purposes or valve valving, which provide a greater flexibility not present in the cylindrical nozzles of the prior art. The bolt of the intake valve or mobile restriction T-T 'can vary the percentage of the material of the outer layers in the inner annular flow layer vs. the external annular flow layer of the combined flow stream downstream of the combination area. Changing the relative volumes of the outer layers diverts the position of the central (inner) layer in the molding cavity to produce a part with a thickness of the outer layer controlled on both surfaces of the molded part. If the flow of the outer layer is evenly distributed between the inner annular flow layer and the external annular flow layer, the thickness of the outer layer will be similar on both surfaces of the molded part. If the flow of the outer layer is diverted to any of the inner or outer annular flow layers, the thickness of the outer layer in the molded part will also be deflected over the corresponding surface molded from the diverted annular layer. The material of the inner annular flow layer forms the outer layer of the molded part by the wall of the cavity opposite the gate in the cavity, and the material of the external annular flow layer forms the outer layer of the molded part by the wall of the cavity adjacent to the gate. The use of a mobile intake valve bolt is typically appropriate in cases where it is advantageous to vary, during each injection; the relative percentage of the material of the outer layers in the inner annular flux layer vs. the outer annular flux layer. The mobile intake bolt is not used to start or end the flow of any material from any layer. For cases where the relative thickness of the outer layer on both surfaces of the molded part can remain in fixed proportion to each other, the mode uses a fixed intake valve bolt. In the amplified views of Figures 17, 18 and 19, the intake valve T is shown placed by the rod R in a neutral position with the discoidal channels C'i, C'2, etc., open to balance the flow of the inner layer with respect to the flow of the outer layer , in a lower position to reduce the flow velocity of the inner layer with respect to the flow velocity of the outer layer (Figure 18); and in an elevated position, Figure 19, to increase the flow velocity of the inner layer, with respect to the flow velocity of the outer layer. Moving, now, to the structures of the distal end or of the nozzle gate of the extruder, having adjusted the position of the intake bolt, the position shown in Figure 20 allows the intake valve bolt to maintain the annular flow towards the cavity, as described above. To produce a reduced gate vestige height, the distal end of the intake valve bolt T 'tapers even more in T "when approaching the end of the cavity G, as in Figure 21. The shape of this distal end with respect to the gate length, taper and diameter, is of the same nature as that used to produce a reduced gate vestige height on molded parts of a single material, because the material in the area of the gate at the beginning and end of each cycle, it is only the material of the outer layer, some molding materials, however, such as PET (Polyethylene Terephthalate), require that the flow of the gate be cylindrical instead of In the embodiment of Figure 22, fitted for such materials, the intake valve bolt ends at the end of the nozzle means, so that the cylindrical flow occurs only through the valve. ompuerta G, thereby minimizing the possible harmful effects on the leading edge of the central (inner) layer. To produce a vestigial height of the gate from zero, the movable intake valve bolt may have a distal end formed with respect to the gate length, taper and diameter similar to those used to produce a vestigial height of the gate. from zero in a single molding material. The intake valve can be further adjusted to also serve as a gate valve in the gate to the region of the cavity, if desired; shown in the open position in Figure 23, and in the closed position in Figure 24. It has already been mentioned at the outset that the novel structures of the present invention are themselves endowed with greater flexibility in use at similar or different temperatures. In the extrusion in the cavity shown in Figure 25, in a manner similar to that described above in Figure 2, the system is illustrated operated with the horizontally flowing annular IL and IL layers containing the central annular layer encapsulated therein ( interior) IA, at the same melting temperature of, for example, approximately 260 ° C (500 ° F) for ABS-type plastics, during transverse division as opposed to the lateral directions towards the cavity, which produces a filling to the same temperature of the cavity of the outer layers, OLi and ILa, which cover or encapsulate the material of the core or center I '. In Figure 26, on the other hand, the system allows a core material or core I 'more cooled, that is, at 204.44 ° C (400 ° F), for the reasons explained above, extruded and molded with external layers OLa The hottest, of, say, 260 ° C (500 ° F); and so on, for any desired variations depending on the properties of the plastic material and the desired molding effects. Next in order, it is to examine the filling sequence of the annular extruded material within the molding cavity for an inner core layer I (EVOH, for example), as shown in succession in Figures 27 (a), (b), (c) and (d), demonstrating a remarkably uniform distribution achievable with the structures of the invention, when concentric plastic annular streams are divided on opposite sides of the intake or restrictor element T 'and injection towards the opposite sides of the molding cavity, (the relatively thick outer layers are, for example, PET). In Figures 28 (a), (b), (c) and (d), the same filling sequence is shown for the injection of a maximum amount of material from the center I 'into the molded part (polycarbonate, for example) , this is achieved with a fixed intake valve bolt T ', as shown, which produces a flow of the outer layer (recycled polycarbonate plastic, for example), equally distributed between the inner and outer annular layers IL and OL. The flexibility of the fitted intake structure of the invention is best shown in Figures 29 (a) - (d), which again show the filling sequence of the cavity for a maximum amount of internal core material in the molded part, but using an adjustment of the intake valve which produces a flow of the outer layer OL at a speed relatively greater than that of the inner annular layer IL, to obtain a thicker external layer OL on the side of the gate of the molded part (Figure 29 (d)), that the inner layer ILi. The operation in Figures 30 (a) - (d), produces the opposite, with the layer ILi, thicker than the OL layer on the side of the gate, of the molded part (Figure 30 (d)). The position of the mobile intake bolt R shown in Figure 20 will produce the increased OL and OLi of Figure 29. The position of the movable intake bolt shown in Figure 19 will produce an increase in IL and ILi of Figure 30. For embodiments using a fixed intake bolt, for example T of Figure 15, the relative thickness difference of OLi and ILi can be created by the appropriate corresponding design of the channels of the combination means CV and C3 'of the Figure 13 and Ci "of Figures 14 and 15. Figures 31 (a) - (d) and 32 (a) - (d) are similar cross-sectional patterns of the fill sequence of the cavity, using an element of mobile intake valve, respectively, by increasing the flow of the inner annular layer and the flow of the outer annular layer to inject more central (inner) layers I 'next to the gate and the opposite side to the gate, respectively, of the Molded part, adjustment of the v The relative flow rate of OL, IA and IL during each extrusion. The relative volumes and flow velocities of the core layer and the coating layers are controlled by Si and S2, while the relative flow rates between the coating layers are controlled by adjusting the moving admission R of Figure 17, for example. During each extrusion, Si, S2 and R are controlled to produce a central layer I 'having a leading edge LE, which flows along a flow line, which has a V / V that prevents LEi from flowing through of the flow front FF of the coating layers. After the FF has progressed further into the cavity away from the gate G, the flow velocity of the core layer IA is increased relative to the flow of the OL and IL coating layers and the relative flow rates of OL and IL they fit closer to a central position of R, so that a central leading edge LE2 is created along the maximum velocity flow line of the cavity. The LE2 flowing at a speed greater than the LEi will penetrate less deeply, the same or deeper into the cavity LEi, depending on the time of the adjustment of Si, S2 and R during the extrusion. The mobile intake bolt allows the creation of LEi before the creation of LE2, thus a greater volume of central layer can be injected into the cavity than in the prior art, which can create only one central leading edge in each cycle of extrusion. A comparison of the graphs of the flow fraction and the velocity profile of Figures 33 and 34, for the reduced annular channel flow of the invention and the cylindrical channel of the prior art, respectively, graphically demonstrates the significantly improved characteristics achieved by the invention. Figure 33 is the velocity profile Vp = V / V and the volume fraction of the annular flow between the channel formed by the intake valve bolt and the cylindrical wall of the extruder body, represented by -50% and + 50% , respectively, on the horizontal axis of the graph. The average flow diameter is represented as * 0"on the horizontal axis, the velocity profile and the flow fraction were based on the Lw Power model for non-Newtonian fluids (Ref. JS Brydson, Flow Properties of Polymer Melts, second edition, George Godwin Limited in association with the Plástic and Rubber Institute.) If the design and construction of the channels d ', C2', etc., as shown in Figure 13, etc., in the means of combination produces a perfectly annular flow of the inner and outer annular layers, the flow line of the leading edge of the core will be centered over the average diameter of the flow, and thus has a velocity Vm equal to 1.44 x the average velocity V of the flow combined annular In the construction and operation of real equipment, the annular distribution of the inner and outer annular layers is not perfect, and it is not unexpected a maldistribution of 10% within the normal manufacturing tolerances of the channel, distribution of the processing temperature and variations inherent to the melting of the plastic. The effect of such maldistribution is shown in Figure 4, where the central annular layer IA is deviated from the average diameter of the annular channel. The three flow lines IA1, IA2, IA3, in Figure 33, correspond to the three points of the central annular layers shown in Figure 4 as IAl, IA2, IA3. The maximum speed difference between the points on the central leading edge is between the flow lines IA1 and IA2. It can be shown that the taper of the leading edge is calculated by the following equation: ? l =? V x L where? l = taper of the leading edge? V = difference in the speed / V L = total length of the combined flow For the aforementioned maldistribution, ? V - V "-V? = 1.44 V - 1.36 V = 0.08 V L = 75 mm for the example shown in Figure 11 Therefore,? L = 6 mm, as shown in Figure 11. Since the perfect annular flow is not really possible as discussed, the effect of a poor distribution of 10% as shown in Figure 6, where the middle layer deviates from the average flow diameter, will result in a flow with a high and low velocity of the central leading edge corresponding to LA '1 and IA' 3 of Figure 6 and Figure 34. Using the above calculations, the difference of 0.53 V between the high and low speeds of the leading edge will produce a taper of 39.8 mm in the cavity, as shown in Figure 12, if the length of the channel Cylindrical is 75 mm between the combination area and the cavity gate area. This magnitude is almost a factor of 10 larger than the minimum acceptable taper in most applications. Obviously, the prior art required that the cooling of the molding cavity be compromised to shorten the combined flow length. To achieve the same 6mm taper as shown in Figure 11, the length of the prior art should be approximately 11mm for a 10% misalignment. This length is approximate to that used in existing molding systems. A front edge taper of 6 mm is approximately the maximum acceptable taper for a core layer used as a gas barrier layer in preforms of PET containers. In this way, an annular flow combined downstream of the combination means allows a length of up to 75 mm between the combination area and the gate towards the cavity. This allows a normal amount of mold cooling to be created around the area of the mold gate. Figure 34 is the velocity profile and the volumetric fraction for the circular flow channels that are used in the prior art between the combination area and the gate to the cavity. The wall of the flow channel is represented by -100% and + 100% on the horizontal axis. The average flow diameter, ie 50% of the flow volume flowing within this diameter and 50% flowing between this diameter and the channel wall, is shown as IA 'in Figure 5 and Figure 34 For flows, where the central layer IA 'flows between and the inner cylindrical layer IL' having the same volumetric flow rate as the outer annular layer OL 'of Figure 5, the leading edge of the central layer will flow at along a flow line over the mean flow diameter. If the flow created by the combination means is perfectly annular, there will be no tapering of the central leading edge when the leading edge leaves the gate towards the cavity.

Claims (29)

1. CHAPTER CLAIMANT Having described the invention, it is considered as a novelty and, therefore, the content is claimed in the following CLAIMS: 1. A method for coextruding multiple plastic materials for injection through a gate region in a molding cavity to produce a molded product, characterized in that it comprises combining streams of such fluid plastic materials with at least one internal stream serving as a core inside a molded plastic product, inside the internal and external currents of the plastic material used to cover the layers of plastic material; restricting the combined streams to flow along annular, concentric flow paths, within and along a tubular extruder extending longitudinally to the region of the cavity gate, with the annular central stream encapsulated by current layers of plastic material on the external and internal annular covering; in the region of the gate, divide the concentric annular currents along the opposite transverse directions to inject them into the corresponding opposite cross sections of the cavity. The method according to claim 1, characterized in that the restriction is effected by inserting an admission bolt extending longitudinally in the center in and along the extruder towards an open distal end in the region of the gate. 3. The method according to claim 1, characterized in that the intake bolt is in a fixed position. 4. The method of compliance with the claim 1, characterized in that the intake bolt is longitudinally movably adjusted to vary the positions of the distal end of the bolt and the opening of the region of the extruder gate. 5. The method of compliance with the claim 2, characterized in that the flow is adjusted so that the annular inner central layer flows along a path with a substantially zero gradient of the flow rate profile transversely to the extruder. The method according to claim 5, characterized in that the flow through the region of the gate and into the cavity is adjusted to maintain the path of the inner core layer in a substantially zero gradient of the velocity profile of transverse flow in it. The method according to claim 1, characterized in that the temperatures of the central, internal and other flowing currents are adjusted substantially to the same value within the cavity. 8. The method of compliance with the claim 1, characterized in that the temperatures of the flowing central and external and internal currents are adjusted to different values within the cavity. The method according to claim 8, characterized in that the temperature of the central plastic stream is adjusted to a value lower than the temperatures of the external and internal plastic currents. 10. The method of compliance with the claim 2, characterized in that the combination of the currents is effected by the flow along successive passages between parallel planes. The method according to claim 4, characterized in that the intake bolt is tapered at its distal end. 12. The method according to claim 1, characterized in that the flow is adjusted to provide more or less flow to the internal current in relation to the external current. 13. The method according to claim 2, characterized in that the annular flows are confined along the extruder between the concentric cylindrical frames. 14. An apparatus for coextruding multiple plastic materials for injection through a gate region in a molding cavity to produce a molded product, which has, in combination, stream sources of the flow of plastic material; means for combining the currents of such fluid plastic materials with at least one internal stream serving as the inner core of a molded plastic product resulting within the internal and external streams of the plastic material which serves to coat the layers of plastic material; a longitudinally extending hollow extruder connected to the combination means for receiving the external and internal currents; flow restricting means positioned within and along the extruder to force the combined streams to flow along annular, concentric flow paths, within and along a tubular extruder extending longitudinally to the region of the extruder. gate of the cavity, with the annular central stream encapsulated by the current layers of the plastic material of the outer annular coating; means positioned in the region of the gate to divide the concentric annular currents along the opposite transverse directions to inject them into the corresponding opposite cross-sections of the cavity. 15. The apparatus in accordance with the claim 14, ccterized in that the flow restrictor comprises an intake bolt extending longitudinally in the center in and along the extruder towards an open distal end in the region of the gate. 16. The apparatus according to claim 14, ccterized in that the intake bolt is in a fixed position. The apparatus according to claim 1, ccterized in that the intake bolt is longitudinally movably adjusted to vary the positions of the distal end of the bolt and the opening of the region of the extruder gate. The apparatus according to claim 15, ccterized in that means are provided for adjusting the flow, so that the annular inner central layer flows along a path of a substantially zero gradient of the flow velocity profile transversely to the extruder The apparatus according to claim 18, ccterized in that the flow through the region of the gate and into the cavity is adjusted to maintain the path of the inner core layer to a substantially zero gradient of the velocity profile of transverse flow in it. 20. The apparatus according to claim 14, ccterized in that means are provided for adjusting the temperatures of the central plastic streams, and other fluid internal currents adjusted substantially to the same value within the cavity. 21. The apparatus according to claim 14, ccterized in that the temperatures of the central plastic currents, external and internal flowing, are adjusted to different values within the cavity. 22. The apparatus according to claim 21, ccterized in that the temperature of the central plastic stream is adjusted to a value lower than the temperatures of the external and internal plastic currents. 23. The apparatus according to claim 17, ccterized in that the combination of the currents is effected by the flow along successive passages between parallel planes. 24. The apparatus according to claim 14, ccterized in that the intake bolt is tapered at its distal end. 25. The apparatus according to claim 1, ccterized in that the flow is adjusted to provide more or less flow to the internal current in relation to the external current. 26. The apparatus according to claim 15, ccterized in that the annular flows are confined along the extruder between the concentric cylindrical frames therein. 27. The apparatus according to claim 18, ccterized in that the central layer does not flow in the zero gradient path just upstream and through the region of the gate. 28. The apparatus according to claim 18, ccterized in that the intake bolt ends just upstream of the cavity side of the region of the gate. 29. The apparatus according to claim 18, ccterized in that means are provided for adjusting the flow to provide a leading edge of the central layer flowing along the zero gradient before or after another leading edge of the layer. flow out of the gradient path of zero.