Polymer co-extrusion head having a dual-channel nozzle

Abstract

To provide a composite spinning nozzle capable of manufacturing a two-component polymer fiber having less risk of separation.SOLUTION: A co-extrusion head for manufacturing a two-component polymer fiber includes a dual channel nozzle 100 that includes a first inlet port that receives a core polymer component, a second inlet port that receives a cladding polymer component, an inside channel 102, and an outside channel 104 that incorporates the inside channel. The inside and outside channels are, respectively, in a fluid connection relation with the first and second inlet ports. The dual channel nozzle further includes a confluent channel 106 that establishes a fluid connection among the inside channel, the outside channel, and a nozzle outlet port 108 of the dual channel nozzle. The confluent channel is configured to cause the core polymer component and the cladding polymer component to contact each other so that a contact layer containing an admixture of the core polymer component and the cladding polymer component is formed between the core polymer component and the cladding polymer component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an extrusion device, and more particularly to a device for co-extruding a two-component polymer fiber from two polymer components. [Background and Related Art]

[0002] Extrusion is a popular method for manufacturing polymer fibers. In the simplest case, a molten fluid polymer is pressed through a small circular opening to form a circular cylinder fiber. However, there are applications where polymer fibers with non-circular cross-sections are preferred. An easy way to change the shape of the extrusion opening is known to work as long as the flow through the extrusion opening is laminar. The shape of the co-extrusion opening is a factor that affects laminarity. In particular, in the case of a shape with a large amount of thickness change, that is, when the transition between the thick region and the thin region is within a short distance, turbulent instability can be formed in the polymer flow, which may result in discontinuities and / or defects in the product.

[0003] Two-component polymer fibers can be formed by the simultaneous extrusion (co-extrusion) of two polymer components. In a joint fiber, the two components are separated by an interface. This surface is prone to wear due to aging and external influences. As a result, the two components can peel off, and thus the two-component fiber can be easily separated. This effect is particularly noticeable when the two components are based on polymers with different polarities, such as polar polyamide and non-polar polyethylene.

[0004] Therefore, it would be desirable to have a co-extrusion device configured to produce two-component polymer fibers with less risk of peeling. Preferably, the co-extrusion device is also configured to produce such two-component fibers with a reduced number of discontinuities.

[0005] German Patent Application DE 10 2013 011 956 A1 discloses a spinneret device for manufacturing a two-component polymer filament, where the core polymer component is conveyed through a central tube and the cladding polymer component is conveyed through a hydrostatic throttle joint. Summary of the Invention

[0006] In the independent claims, the present invention provides a coextrusion head and a system for manufacturing a two-component fiber with a lower risk of delamination. Embodiments are given in the dependent claims.

[0007] In one aspect, the present invention provides a coextrusion head for manufacturing a two-component polymer filament. The coextrusion head includes a first inlet for receiving a core polymer component, a second inlet for receiving a cladding polymer component, and a dual-channel nozzle. The dual-channel nozzle includes an inner channel and an outer channel encompassing the inner channel. The inner channel is in fluid connection with the first inlet, and the outer channel is in fluid connection with the second inlet. The dual-channel nozzle further includes a merging channel that establishes a fluid connection between the inner channel, the outer channel, and the nozzle outlet of the dual-channel nozzle. The merging channel is configured to bring the core polymer component and the cladding polymer component into contact with each other such that a contact layer is formed between the core polymer component and the cladding polymer component in response to simultaneously receiving the core polymer component from the inner channel and the cladding polymer component from the outer channel. The contact layer includes a mixture of the core polymer component and the cladding polymer component.

[0008] The co-extrusion head is configured to manufacture a two-component fiber having a core made of a core polymer component and a cladding made of a cladding polymer component. Both components include the majority of the core polymer or the majority of the cladding polymer, respectively, and they are miscible in a fluid state with each other. The core polymer and the cladding polymer may each be a pure polymer or a mixture of two or more polymers. The core polymer and the cladding polymer are miscible but may differ in terms of polarity. In an example, the core polymer is a polar polyamide and the cladding polymer is a non-polar polyethylene.

[0009] In particular, the core polymer component can be a mixture of at least two polymer phases, and an additional polymer is extruded into the core of the two-component fiber together with the core polymer so that beads, threads, or other filamentous structures can be formed when the fiber is manufactured. More specifically, the additional polymer can be immiscible with the core polymer, and thus, a compatibilizer can be extruded into the core as a third polymer phase to bond the additional polymer and the core polymer. Generally, as disclosed in European Patent Application EP 3116942 A1, the core polymer component can be a polymer mixture, a masterbatch, or a compound batch.

[0010] The core polymer component and / or the cladding polymer component may also include, but are not limited to, additives including at least one of the following, namely, wax, a dulling agent, an ultraviolet stabilizer, a flame retardant, an antioxidant, a fungicide, a pigment, and mixtures thereof.

[0011] The co-extrusion head includes a dual-channel nozzle. Attached to a pilot hole having an extrusion opening, the pilot hole acting as an outer channel for guiding the cladding component towards the extrusion opening, compared to co-extrusion with a single-channel nozzle only for the core component, the described dual-channel nozzle may enable a simplified design of the heating part for the minimum number of channels and may enable downsizing of the co-extrusion head. Further, the dual-channel nozzle can be machined with small tolerances, which can lead to improved reproducibility of product characteristics, such as the contact layer thickness of the two-component fiber produced by different nozzles, and smaller variations.

[0012] The dual-channel nozzle includes a confluence channel configured to form a contact layer between the core and the cladding. Within the scope of the present disclosure, the term "confluence channel" refers to, for example, a channel structure inside the dual-channel nozzle of a co-extrusion head that is fluidly connected to a first inlet via an inner channel, fluidly connected to a second inlet via an outer channel, and fluidly connected to the extrusion opening of the head via the nozzle outlet, and the confluence channel is a channel structure that first physically contacts the molten core polymer component and the molten cladding polymer component with each other during the co-extrusion action of the co-extrusion head. The confluence channel is a structural unit of the channel structure inside the dual-channel nozzle that can be distinguished from other structural channel units by its position connecting the inner channel, the outer channel, and the nozzle outlet. Typically, although not essential, the confluence channel may further include structural characteristics such as a diameter that transitions from the diameter of the outer channel to the diameter of the nozzle outlet.

[0013] The confluence path is designed such that these two miscible polymers mix with each other in a bonding region, herein referred to as the "contact layer", when they move towards contact. The effect of providing a two-component fiber having a contact layer in which the materials of the core and cladding components are mixed is not only a feature of the process, but rather, the core-cladding mixing occurs internally in a manner that is well-controlled to yield the desired result (the contact layer), which is pointed out to be the result of the structural features of the dual-channel nozzle that define the parameter space for the coextrusion process.

[0014] According to multiple embodiments, the dual-channel nozzle is designed to result in the formation of a uniform and small-scale contact layer in which the flows of two adjacent coextrusion components include a mixture of both components at the interface of the two components with respect to at least one set of processing parameter ranges. In particular, the occurrence of controlled small-scale mixing of the two coextrusion components (i.e., the core polymer component and the cladding polymer component) depends on the inner channel, the outer channel, and the spatial arrangement of the nozzle outlets relative to each other according to the respective designed supply rates through the first inlet and the second inlet, the spatial arrangement of the discharge openings of the inner channel and the outer channel towards the confluence path, and the dimensions of the inner channel, the outer channel, and the nozzle outlet, and can be the result of an appropriate selection of the dimensions of the confluence path with respect to one or more adjacent channel structures (outer channel, inner channel, and nozzle outlet) and / or with respect to the respective designed flow rates in each of the inner channel and the outer channel.

[0015] The flow pattern of both coextrusion components through the confluence path is thus defined by the structural features of the dual-channel nozzle, and the confluence path should be selected such that the core and cladding polymer components mix in the interfacial contact layer between the core and the cladding with respect to at least one set of processing parameter ranges without limitation to these structural features explicitly mentioned herein.

[0016] During the production of the two-component polymer fiber, the two components are heated to a liquid state, joined together in a confluence channel, and pressed through the extrusion opening of a co-extrusion head. Thus, when the two-component fiber precursor formed by co-extrusion is cooled, the two polymers solidify, and thus, the contact layer forms a solid connection between both components without any contact surface. The contact layer forms a three-dimensional quasi-monolithic structure that may include a gradual transition of the polymer type. That is, the number density of the molecules of the core polymer component gradually decreases from the core in the outer direction, and similarly, the number density of the molecules of the cladding polymer component decreases from the cladding in the inner direction. In the special case of the same core and cladding polymers, the number density of the polymer molecules remains constant, but only the concentration of the additive that can be shown in only one of the binding components forms the amount of change in the direction of each other component.

[0017] As a result, the confluence channel is configured to connect the core and the cladding by a substance-to-substance joint formed by a polymer mixture that is held together by intermolecular forces that are stronger than mere adhesive forces acting across two different polymers that are close but not mixed. The molecules of the two polymers are joined together by topographic entanglement and intermolecular forces similar to the adhesive intermolecular forces present in single-component fibers. The two-component fiber produced by the co-extrusion head according to an embodiment of the present invention will thus have a higher resistance to shear loads acting in the axial direction of the fiber and thus a lower possibility of core-cladding delamination. Such two-component fibers may thus feature improved wear resistance.

[0018] Using a dual-channel nozzle, the coextrusion head is configured to manufacture cylinder polymer fibers, where the term "cylinder" refers to a general upright cylinder, i.e., one whose main axis is oriented perpendicular to its bottom surface or cross-section. Specifically, each fiber produced can be a non-circular cylinder, i.e., one having a non-circular cross-section. Examples of non-circular cross-sections include elliptical or polygonal. The cross-sections of the core and the cladding can be selected independently of each other, and it is understood that each of the core and the cladding can have a non-circular cross-section. In a non-limiting example, the core has a triangular cross-section, while the cladding has a circular cross-section. In another non-limiting example, an elliptical core is surrounded by a kidney-shaped cladding. In yet another non-limiting example, the fiber has a circular core and a cladding having two protrusions extending from the core by at least the diameter of the core.

[0019] Another advantage can be that no compatibilizer or other bonding material layer is required to bring the core and the cladding into contact. This can result in a simplified design of the coextrusion head and enable the production of a two-component fiber that is simpler and more cost-effective.

[0020] The confluence channel can be designed such that a stable turbulent flow occurs between the core polymer component and the cladding polymer component. The size and mechanics of the turbulent flow can depend on the specific selection of materials and / or the process parameters for the coextrusion process. The said parameters can include the feed rate of one or both components, the difference in feed rates, temperature, pressure, and / or the viscosity of one or both components at a given temperature and / or pressure.

[0021] The structure and dimensions of the confluence path are set to dimensions and shapes that generate stable turbulent flow. The structure and dimensions of the confluence path, the inner channel and the outer channel upstream of the confluence path are selected such that stable turbulent flow is formed between the core polymer component and the cladding polymer component (both referred to herein as "co-extrusion components"). The applicant notes that the dimensions disclosed herein provide the desired thickness to the stable contact region for most polymer types used in the manufacture of artificial turf fibers, such as polyethylene and polyamide. In some cases, the dimensions of the ducts and other elements of the extrusion head may only fit slightly with other types of polymers.

[0022] The creation of the mixture of co-extrusion components that defines the contact layer can also be affected by the length x1 of the confluence path. Starting from the induction position, the turbulent flow can spread over the length of the confluence path rather than being restricted and staying at the above-mentioned induction position. The applicant notes that the co-extrusion process involves the risk that the dimensions of the turbulent flow (e.g., the diameter of the vortex) may vary over the axial length of the confluence path. A confluence path that is too long may lead to instability of the turbulent flow, and thus the thickness of the contact layer may become variable and / or the components may partially separate again. A confluence path that is too short may result in an insufficient mixture of the co-extrusion components. Therefore, the size and shape of the components of the dual-channel nozzle, especially at the confluence path length x1, should be selected as described herein to ensure that the thickness and / or degree of mixing of the contact layer is maintained within the desired range in embodiments of the present invention.

[0023] According to a plurality of embodiments, the confluence path is restricted by the conical taper of the dual-channel nozzle. The tapered confluence path can stabilize the mass flow laminarity with respect to the cladding component, and thus the turbulent flow in the contact region required to obtain a contact layer containing a mixture of the core polymer and the cladding polymer can be controlled by temperature and / or feed rate without feedback to the mass flow of the cladding polymer.

[0024] According to a plurality of embodiments, the inner channel has a circular cross-section, the confluence channel has an axial length x1 between the nozzle outlet and the inner channel, and the axial length x1 is 3 to 7 times the diameter of the inner channel. According to a plurality of embodiments, the inner channel has a circular cross-section with a diameter between 0.5 and 1.5 mm, preferably 1.25 mm.

[0025] This can enable the dimensions in the confluence channel to be adjusted with specific properties of the polymer components involved, such as viscosity or shear coefficient, and with specific process parameters such as temperature or pressure, providing beneficial rheological properties for establishing a stable bond between the core and cladding of the two-component fiber. If the selected length of the confluence channel is too long, turbulence may be suppressed by the feedback of increased wall-polymer interaction. On the other hand, a confluence channel that is too short may disrupt the stability of the turbulence such that the contact layer becomes variable, for example, in thickness and position. Two-component fibers produced with a joining region that is too short may no longer exhibit the beneficial surface properties that are expected to arise from distinct features between the core and cladding.

[0026] According to a plurality of embodiments, the coextrusion head further has an extrusion opening and a coextrusion path that establishes a fluid connection between the nozzle outlet and the extrusion opening, and the coextrusion path is configured to simultaneously receive a core polymer component, a cladding polymer component, and a contact layer from the nozzle outlet such that the coextruded polymer strand is formed in the coextrusion path, and the coextruded polymer strand includes a core, a cladding that encompasses the core, and a contact layer that binds to the core and the cladding.

[0027] The coextrusion path downstream of the confluence path can beneficially provide a channel that allows the combined polymer strands to return to laminar flow. This can enable the formation of the outer contour of the fiber in a separate process without the turbulent flow required to form the contact layer. Joining the cladding and the core together to form the cladding into its final shape can thus be considered a separate process step, allowing for more precise control of process parameters to produce a two-component polymer fiber with stable and reproducible properties. The laminar flow upstream of the extrusion opening can be desirable as it can result in a smooth and uniform contour along the entire length of the product. This can be particularly beneficial for fibers with thin edges.

[0028] According to multiple embodiments, the extrusion opening has a non-circular cross-section and the coextrusion path has a non-circular cross-section. According to multiple embodiments, the confluence path has a circular cross-section.

[0029] A coextrusion path shaped to have the desired contour of the finished fiber to be produced can enable the coextruded polymer strands emerging from a dual-channel nozzle to be formed into a non-circular shape. In a preferred example, the coextruded polymer strands emerge from a dual-channel nozzle having a circular cross-section and are shaped by the coextrusion path into a non-circular cross-sectional shape. For example, the non-circular cross-section of the coextruded polymer strands can be symmetric, repetitive, or irregular, and can be polygonal, elliptical, lens-shaped, flat, pointed, or elongated. The nozzle exit can be in direct contact with the coextrusion path, thus locally relaxing the pressure holding conditions imposed by the nozzle and allowing the cladding polymer component to diffuse into the non-circular portions of the profile. The non-circular cross-section can thus enable a very wide variety of shapes of two-component polymer fibers with less risk of delamination, which can increase the number of possible applications.

[0030] According to multiple embodiments, the coextrusion path has an axial length x2 between the nozzle exit and the extrusion opening.

[0031] According to multiple embodiments, the axial length x2 is selected such that the cladding satisfies a non-circular cross-section at the extrusion opening. This enables the length of the co-extrusion path to be such that the cladding can completely fill the profile of the extrusion opening, long enough to assume an axially directed flow across the entire cross-section of the opening, but short enough to enable minimizing losses due to friction. This can impart smoothness and stability to the outer cladding surface of the finished polymer fiber exiting the extrusion opening. A co-extrusion path that is too short causes turbulent flow at the extrusion opening such that the profile of the fiber emerging at the extrusion opening returns to a circular cross-section instead of maintaining a non-circular cross-section.

[0032] According to multiple embodiments, the axial length x2 is between 1.5 and 4.0 mm. This range can be a beneficial choice for some polymer materials commonly used to produce artificial polymer fibers such as polyethylene or polyamide. The length of the co-extrusion path can be selected from this range to reflect the viscosity of the co-extruded polymer strands and the process parameters. Polymers with a low viscosity at the design process temperature fill the profile of the extrusion opening more easily than high-viscosity polymers, so the required co-extrusion path can be shorter. In particular, when two components are co-extruded at different feed rates, the length of the co-extrusion path can be configured for the effective viscosity of the co-extruded polymer strands as a whole, rather than the viscosity of the pure cladding polymer component, since the layered core-cladding interaction can affect the space required to fill the profile.

[0033] According to multiple embodiments, the axial length x1 of the confluence channel is between 5 and 50 percent of the axial length x2 of the coextrusion channel. For a given selection of polymer component materials and design process parameters, the independently determined ideal path lengths x1 and x2 can typically have a ratio within this range. Thus, the design of the coextrusion head can be simplified, for example, by selecting an appropriate confluence channel length x1 from the range of x1 described above for the selected polymer component materials and design process parameters, and by deriving an appropriate coextrusion channel length x2 that conforms using an appropriate ratio from the above range. A smaller ratio x1:x2 can be beneficial in situations where it is expected that the layer-core cladding interaction in the coextrusion channel leads to a greater effective viscosity of the coextruded polymer strands compared to the viscosity of the pure cladding polymer component, and vice versa.

[0034] According to multiple embodiments, the coextrusion head has a hierarchical stack of at least two dual-channel nozzles and channel plates, each of the channel plates includes a first channel and a second channel, the first channel establishes a fluid connection between a first inlet and each inner channel of the at least two dual-channel nozzles, the second channel establishes a fluid connection between a second inlet and each outer channel of the at least two dual-channel nozzles, and the number of channels per channel plate is constant or increases in the downstream direction.

[0035] The core polymer component and the cladding polymer component are each supplied through their respective inlets (usually one inlet per component) to a coextrusion head and distributed through first and second channels respectively to a dual-channel nozzle. Since the total polymer flux per channel plate is constant, the number of channels increases with each branch from the inlet towards the nozzle, and the specific width or diameter of the channels decreases accordingly with respect to the subsequent hierarchical level. For a given channel plate, the level-specific channel width is thus smaller than the respective specific channel width or diameter of the preceding (upstream) level of channel plate if it exists, and larger than the respective specific channel width or diameter of the subsequent (downstream) level of channel plate if it exists. As an example, the first and second channels in a particular channel plate selected from the center of the coextrusion head may each have half the cross-section of the first and second channels in the channel plate directly preceding the channel plate under consideration, while in the channel plate directly following the channel plate under consideration, they may each have twice the cross-section of the first and second channels.

[0036] The coextrusion head may further have pressure chambers for each component that can provide uniform pressure distribution through downstream channels. The pressure chambers are essentially large cavities that hydraulically interconnect several channels of one channel type. Preferably, the pressure chambers span substantially the entire width of the coextrusion head and thus match at least one parallel arrangement of coextrusion nozzles along that width. Supplying uniformly along the entire length of the pressure chamber may require a parallel arrangement of channels upstream of an appropriate width or hierarchical step. The channels downstream of the pressure chamber may be at the same or the next hierarchical step as the upstream channels feeding the pressure chamber, and thus the hierarchy is not affected by the presence of the pressure chamber. This can result in a more uniform flow of material through the coextrusion head, and thus the pressure variation with respect to both coextrusion components is minimized and a consistent quality is achieved for all two-component fibers coextruded in parallel.

[0037] The channels on each channel plate are typically machined as half-channels on one of the faces of the plate, and it is understood that the mirroring layout of the half-channels of subsequent plates is such that the half-channels on two adjacent faces of a directly subsequent plate result in a complete channel when the plates are joined together.

[0038] According to multiple embodiments, the channel plates are removable from each other and reattachable to each other. This can facilitate the cleaning and / or maintenance of the co-extrusion head.

[0039] According to multiple embodiments, at least two dual-channel nozzles are replaceable components, one of the channel plates at the most downstream position within the hierarchy of the channel plates is an extrusion plate, at least one channel plate preceding the extrusion plate includes through-holes for each of the at least two dual-channel nozzles, the extrusion plate includes heating channels for each of the at least two dual-channel nozzles, the heating channels and the through-holes are configured in their respective plates to be aligned with each other to form cavities, each of the cavities includes one of the at least two dual-channel nozzles, each of the heating channels further includes an extrusion opening, and the extrusion opening is in fluid connection with the nozzle outlet of the dual-channel nozzle and is included in the cavity formed by the heating channel.

[0040] The dual-channel nozzle can be implemented as a replaceable part that can be replaced at the end of its life cycle. This can avoid having to clean the narrow (typically millimeter-scale) channel portions. Also, the replaceable nozzle allows for a faster and more economical recovery from defects or incompatibilities, as only the affected nozzle needs to be replaced instead of replacing the entire extrusion plate. The replaceable dual-channel nozzle is preferably provided in a co-extrusion head by inserting it into each through-hole of the channel plate upstream of the extrusion plate.

[0041] Preferably, the fluid connection between the nozzle outlet and the extrusion opening is constructed by direct contact of the nozzle tip (the wall surrounding the nozzle outlet) with a heating channel (e.g., below the heating channel surrounding the extrusion opening), and thus does not require additional parts to seal the fluid connection. This may require precise machining of the dual-channel nozzle (e.g., related to its axial length), and / or the channel plate (e.g., related to the positioning of the through-holes into which the replaceable nozzle is inserted into the heating channels).

[0042] According to multiple embodiments, the heating channel includes a recess for receiving the dual-channel nozzle. This can improve the accuracy of positioning of the nozzle at the co-extrusion opening or along the co-extrusion path. Additionally, the recess can simplify the assembly or reassembly of the head and increase the strength of the fluid connection between the nozzle and the co-extrusion opening or co-extrusion path.

[0043] According to multiple embodiments, the channel plate is configured such that the thermal decomposition removal of the polymer is at a temperature between 450 and 750 °C. This can have the advantage that mechanical cleaning is omitted or reduced to a minimum, the useful life of the channel plate can be extended, and / or the number of maintenance times of the coextrusion head can be reduced. The compatibility of thermal decomposition can be achieved by manufacturing the channel plate from a suitable material (e.g., stainless steel) and / or by providing a plate having a coating resistant to the desired thermal decomposition temperature.

[0044] According to multiple embodiments, the dual-channel nozzle is configured to operate at a temperature between 180 and 270 °C. This can have the advantage of improving resistance to thermal aging and / or reducing chemical interaction with the coextruded polymer components. Suitable materials can be metals or metal alloys (e.g., stainless steel or aluminum) or ceramic materials. Preferably, the dual-channel nozzle has the same coefficient of thermal expansion as the channel plate so as to make the strength of the fluid connection independent of temperature.

[0045] According to multiple embodiments, the dual-channel nozzle is a replaceable part. This can bring the advantage of separating the manufacture of those parts that serve to form the core-cladding contact layer from the parts of the coextrusion head. For example, the dual-channel nozzle can be manufactured in a process that is not feasible or not compatible with a given coextrusion head or its manufacturing method. In this way, the dependence on the quality of the manufacture or assembly of the coextrusion head (e.g., the accuracy of nozzle positioning within the receiving cavity) can be reduced, so that the quality of the contact layer (e.g., including the degree of mixing of the core polymer mixture with the cladding polymer components inside the contact layer and / or the stability of its thickness) can be improved and the reliability can be increased.

[0046] An interchangeable dual-channel nozzle can also simplify the assembly of a co-extrusion head or its reassembly when, for example, the head is disassembled for maintenance or cleaning. Further, since the dual-channel nozzle, which is one of those parts of the head with the smallest channel diameter, can be replaced instead of being cleaned, the interchangeable nozzle can simplify the cleaning of the disassembled head.

[0047] An interchangeable dual-channel nozzle can also make it possible to maintain one or more sets of spare nozzles. This can make it possible to reuse the nozzles instead of disposing of them. In an example, while the head is disassembled for cleaning, a used first set of dual-channel nozzles is removed from the head and replaced with a clean second set of nozzles. In this way, the operation of the co-extrusion head can continue while the first set is being cleaned externally for future reuse.

[0048] Once more attention is paid to the influence of the dimensions and structure of the confluence channels on the formation of a stable, continuous, and well-defined contact layer, further advantages of the interchangeable dual-channel nozzle become clear, namely, the interchangeable dual-channel nozzle can make it possible to maintain while preparing different sets of dual-channel nozzles, each set including nozzles specifically structured for a particular combination of co-extrusion components. Like the confluence channels, the structure and dimensions of the inner and outer channels of the dual-channel nozzle can also be specifically developed for each particular combination of co-extrusion components. For example, a larger cross-sectional area can be selected for channels designated to carry co-extrusion components with a higher viscosity, and vice versa.

[0049] According to multiple embodiments, the inner channel and the outer channel have a circular cross-section, the inner channel includes a terminal section of a constant diameter that opens into the confluence channel, and the outer channel concentrically surrounds the terminal section of the inner channel with a constant diameter. According to multiple embodiments, the terminal section of the inner channel has an axial length that is at least 10 times the diameter of the terminal section of the inner channel. According to multiple embodiments, the confluence channel (106) has an axial length x1 between the nozzle outlet (108) and the inner channel (102), and the terminal section of the inner channel has an axial length between 2 times and 15 times the axial length x1 of the confluence channel (106).

[0050] These embodiments may have the advantage of ensuring that the co-extruded components are introduced into the confluence channel in laminar flow in response to the confluence channel simultaneously receiving the core polymer component from the inner channel and the cladding polymer component from the outer channel. In this way, controlled initial conditions can be formed, and then a higher amount of control can be provided over the physical conditions that govern the turbulent flow that forms the contact layer.

[0051] In another aspect, the present invention provides a co-extrusion system including a co-extrusion head according to an embodiment of the present invention, a first supply device for supplying a core polymer through a first inlet, and a second supply device for supplying a core polymer through a second inlet.

[0052] The above supply speed range includes supplying the core polymer component at a supply speed greater than the cladding polymer component. This can have the advantageous effect that the flow in the confluence channel is maintained as a stable small-scale turbulent flow. This can support the formation of a thin contact layer of a certain thickness between the core and the cladding where the core polymer and the cladding polymer are mixed. As a result, the configuration can provide a two-component polymer fiber with increased shear stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In the following, embodiments of the present invention will be described in more detail, by way of example only, with reference to the drawings.

Figure 1

Figure 2

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Figure 3

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DETAILED DESCRIPTION OF THE INVENTION

[0057] Conventional two-component polymer fibers consist of two polymer components formed into monofilaments, and the two components are adhesively connected to each other. Such fibers can be produced by the simultaneous extrusion (co-extrusion) of the two polymer components. Since wear and aging can lead to deterioration or loss (peeling) of the adhesive connection, it would be desirable to have a co-extrusion device that enables the production of two-component polymer fibers with a stronger connection between the two polymer components.

[0058] A preferred design of the dual-channel nozzle 100 attached to the cavity of the co-extrusion head is shown in FIG. 1. When the co-extrusion head is implemented as a stack of channel plates, each cavity of the co-extrusion head can be formed by a heating channel in the extrusion plate and a through-hole upstream by at least one plate from the extrusion plate, and the through-hole is aligned with the heating channel. The dual-channel nozzle 100 of FIG. 1 is inserted into the heating channel 112 of the extrusion plate 110 through the aligned through-holes of the channel plates attached to the upper part of the extrusion plate 110. The heating channel 112 is further configured to include heating means (not shown) for maintaining the nozzle 100 and thus the two polymer components at a predefined temperature. The heating of the nozzle 100 can advantageously avoid the blockage of the narrow capillary channels 102, 104 inside the nozzle due to the adhesion of the polymer components to the channel walls.

[0059] The nozzle 100 includes an inner channel 102 for receiving the molten core polymer component and an outer channel 104 for receiving the molten cladding polymer component. The core polymer component can be supplied to the inner channel 102 through the central transport channel of the co-extrusion head, while the cladding polymer component can be supplied to the outer channel 104 through a ring channel (as shown in FIG. 1) or a side channel of the co-extrusion head.

[0060] The merging channel 106 disposed at the end segment of the dual-channel nozzle 100 is in fluid connection with the inner channel 102 and the outer channel 104. The end segment also includes a tapered shape in which the outer channel 104 is guided towards the center. The fluid core polymer component can be supplied to the merging channel 106 through the inner channel, where contact with the fluid cladding polymer component can be brought about by simultaneous supply.

[0061] The flow rate characteristics of the core polymer component and the cladding polymer component in the confluence channel 106 are visualized in FIG. 2. Process parameters, mainly temperature and feed rate, are selected such that a balance between the laminar flows 202, 204 and the turbulent flow 206 is achieved in the confluence channel 106. Since the molecules from both components do not mix significantly, mere laminar flows 202, 204 would result in a similarly weak adhesive bond between the core and the cladding. On the other hand, significant turbulent flow 206 would introduce an instability that would at least locally disrupt the core-cladding structure.

[0062] Therefore, the process parameters are preferably balanced such that small-scale turbulence is formed in which the molecules of the core and the cladding mix within a thin contact region of approximately constant width around the core. The contact region constitutes a transition region in which the molecular densities of the core polymer and the cladding polymer mix without forming an adhesive interface. In this manner, a joint strength between the core and the cladding can be obtained that exceeds the bonding strength achievable by adhesive bonding.

[0063] The confluence channel 106 is structured in a manner that prioritizes inducing the turbulent velocity field 206 into the streaming pattern 204 of the core polymer component. Accordingly, a velocity field is formed by small-scale and prominent directional changes, which can be changed into a stable turbulent velocity field 206 by continuous mass transport.

[0064] In addition, FIG. 2 shows the interaction between the mechanical constraints and the length scale related to the formation and maintenance of the stable turbulent flow. First, it is noted that the outlet of the inner channel 102 and the nozzle outlet 108 have equal dimensions. This is in contrast to the mass flow, where the core polymer component forms alone at the outlet of the inner channel 102. However, at the nozzle outlet 108, it exits as a merged polymer strand that includes the core polymer mixture, the cladding polymer component, and the contact layer that binds the two coextruded components. This is mainly manifested by the turbulent flow arrows 206 around the confluence channel 106, and in the turbulent region 206 where the flows of the core polymer component and the cladding polymer component, which are directed in opposite directions to each other, come into contact, causing a mechanical load on the core polymer component.

[0065] The walls defining the outlet of the inner channel 102, the outlet of the outer channel 104, and the nozzle outlet 108 impose mechanical constraints on the merging mass flow so as to fit within a close mutual distance that defines the typical dimensions of the turbulent region 206, that is, within the typical length scale of the space applicable for the formation of the turbulence 208. Thus, a stable turbulent mass flow 206 is induced that cannot become larger than the mentioned typical length scale (due to the mechanical constraints provided by the structure), and cannot become substantially smaller than the typical length scale for the turbulence due to the lack of mechanical constraints at this scale.

[0066] Preferably, the confluence channel 106 is structured and dimensioned in a manner that enables the formation of a stable turbulent flow 206 that is large enough to connect the two coextruded components, but also small enough so that there is sufficient material remaining unmixed with respect to both the core and the cladding for them to perform their respective functions properly. For this purpose, it is necessary to select the structure and dimensions of the confluence channel 106 so as to define the length scale related to the turbulence 206 within the desired range relevant to these considerations. In an example, the structure and dimensions of the confluence channel are selected such that the thickness of the resulting contact layer is between 5 and 25 percent of the minimum diameter of the coextruded monofilament (the diameter measured across the line passing through the center of the core).

[0067] The strands of the merged components exit the merge path 106 and are pressed through the nozzle outlet 108 into a co-extrusion path 114 that ends at an extrusion opening 116. The contour of the opening corresponds to the outer perimeter of the resulting two-component polymer fiber. In the example, the extrusion opening 116 includes two circular or elliptical sections that are arranged on two opposite sides from the extending central axis of the nozzle 100 and are connected to each other via two long and narrow protruding gaps arranged on two further opposite sides from the central axis. The circular or elliptical sections of the opening 116 have a radius larger than the radius of the core strand leaving the nozzle 100. As a result, the center of the merged strands pressed through the opening 116 may include a core strand surrounded by the circular or elliptical section of the cladding. The protruding gaps are filled only by the cladding polymer component.

[0068] In addition to the flow characteristics in the merge path 106, turbulence also has to be controlled in the co-extrusion path 114. The co-extrusion path 114 extends from the rim of the nozzle 100 down to the extrusion opening 116 where the merged strands leave the co-extrusion head as a two-component fiber. Turbulence is allowed here because it can cause the cladding to uniformly and completely fill the protruding gaps up to their outer corners, which is not possible with mere laminar flow. However, too strong turbulence is undesirable because it may break the contact layer just formed in the merge path 106.

[0069] The flow characteristics in the merge path 106 and the co-extrusion path 114 are also affected by the design parameters of the co-extrusion head. For example, the length x1 of the merge path 106 can be selected according to the specific combination of polymer materials to be processed by the co-extrusion device. A parameter that similarly depends on the specific combination of polymers and that can make it possible to control the flow characteristics in the co-extrusion path 114 independently of the merge path 106 is the length x2 of the co-extrusion path 114.

[0070] The co-extrusion head can be implemented in a design that supports the dual-channel design of the nozzle 100. Preferably, the co-extrusion head is a heated-plate co-extrusion head or a spinneret plate through which each of the two components is distributed through a hierarchical channel facing a series of extrusion openings 116 through which a plurality of two-component fibers can be produced in parallel.

[0071] Figures 3 through 5 show exemplary designs of a co-extrusion head assembly including a stack of channel plates 300. Figure 3 shows an exploded view of a set of channel plates 300 that distribute two polymer components to 20 co-extrusion nozzles. Each channel plate 300 includes channels of a defined width or diameter that connect a first inlet (not shown) to the inner channel 102 of each dual-channel nozzle 100 or, alternatively, a second inlet (not shown) to the outer channel 104 of each dual-channel nozzle 100. The two channel types serve to distribute each of the two flow streams from a large-diameter inlet to the small extrusion openings 116, where the large diameter corresponds to the system parameters of the single-component extrusion unit mentioned upstream of the co-extrusion head, and the dimensions of the extrusion openings correspond to the radial dimensions of the two-component polymer fibers being produced, typically in the range of micrometers to millimeters.

[0072] To distribute the two flow streams to the extrusion openings 116 with uniform pressure dispersion, the plates 300 are stacked on top of each other in a manner that allows for the subsequent flow of the components that have passed through all of the channel plates 300, such that a hierarchical sequence is established where the first channel plate 300a includes the largest-diameter channels, followed by the second plate 300b having a smaller diameter than the first but larger than the third, and so on. The last channel plate 300 includes channels for both components that are close in dimension to the dimensions of the inner channels 102, 104 of the dual-channel nozzles 100 attached to the extrusion plate 110 downstream of the last channel plate 300, and the channels end at the center, ring, and / or side transport channels mentioned above.

[0073] The pressure of each polymer component can be made even more uniform between the coextrusion nozzles 100 by providing pressure chambers 312, 322 in at least one of the channel plates 300. On the other hand, each component is envisioned to be dispersed from a large diameter to a small diameter in order to obtain a two-component polymer fiber having a desired dimension. This can lead to an increase in interaction as the surface-to-mass ratio increases for each hierarchical step. On the other hand, the coextrusion nozzle 100 extends over at least one width of the coextrusion head, i.e., the nozzle 100 extends into a cross-sectional area larger than the inlet diameter. The surface effects mentioned can thus lead to a lower pressure in the outer channels of the head. Further, it is desirable to spread the mass flow into as many parallel channels as possible between subsequent plates 300 in order to simplify and miniaturize the design of the coextrusion head. This can enhance the surface forces between subsequent plates 300 and prevent a uniform pressure distribution.

[0074] The pressure chambers 312, 322 can effectively compensate for the surface-selective pressure losses described by providing additional space in the flow direction to the liquid polymer and achieving a vertical homogenization of the local pressure in the outlet channels of the pressure chambers. The outlet channels can be the same or can be hierarchical steps where the next is smaller, i.e., returning to a larger channel dimension would be an inefficient design as it would oppose the action of the hierarchical channel structure.

[0075] The coextrusion head illustrated in FIGS. 3 to 5 distributes two polymer components to 40 dual-channel nozzles 100 using five channel plates 300a to 300e shown in FIG. 3. The mass flow is directed from the first plate 300a at the top of FIG. 3 to the fifth plate 300e at the bottom. The first plate 300a receives the core polymer component in the upper straight left channel and the cladding polymer component at the tip of the upper visible "V"-shaped right channel.

[0076] The linear channel is the first channel 310 and continues as a vertical feed to the first 1:20 distribution chamber 400, seen in a hanger shape structure in FIG. 4. From the first to the fourth plates 300d, the first channel 310 remains in the center of the plate 300, that is, the center line of the 20 channels of the second plate 300b is the first channel 310, and it connects to the central pressure chamber 312 on the third plate 300c, which is discharged by 20 further first channels 310 in the third plate 300c. Below the third plate 300c, each of the 20 first pressure chamber discharge channels branches into two small channels that connect to circular feed holes on the fifth plate 300e with respect to the inner channel 102 of the dual channel nozzle 100.

[0077] The "V" shaped channel on the first plate 300a is the second channel 320 and continues as two vertical feeds to the second 1:20 distribution chamber 500, respectively, in front of and behind the first plate 300a. Another cross-sectional view of the CAD model is shown in FIG. 5 to visualize the layout of the second channel 320 in the back system. The 20 second channels 320 of the second plate 300b connect to the upper pressure chamber 322 on the third plate 300c, which is discharged by 20 further second channels 320 in the third plate 300c. However, the cladding polymer must be distributed to the outer channel 104 of the dual channel nozzle 100. As can be seen in FIG. 1, each outer channel 104 surrounds the inner channel 102 of its respective nozzle 100, and it is desirable to maintain a uniform pressure of the mass flow along the entire outer periphery of the outer channel 104. Therefore, the upper pressure chamber 322 connects to the lower pressure chamber 322 on the fourth plate 300d, which is discharged by 40 second channels 320, and each two of them are respectively connected to one of the ring channels that supply the outer channel 104 of one dual channel nozzle 100, and the cladding polymer component is supplied to one of the flat feed channels on the fifth plate 300e.

[0078] Another beneficial effect of the channel plate design can be a simplified cleaning procedure where the plates 300 are disengaged from each other and cleaned in a pyrolysis furnace, for example, at 750 °C. The hierarchical channels can be manufactured with dimensional tolerances that allow for proper realignment of the plates 300 when placed together, for example, after maintenance or cleaning. The dual-channel nozzle 100 can further support this adaptability when implemented as an interchangeable part that can be a through-hole pushed in the last channel plate 300 for insertion into the heating channel 112 of the extrusion plate 110 downstream of the last channel plate 300 during (re)assembly of the coextrusion head.

[0079] List of reference signs 100 Dual-channel nozzle 102 Inner channel 104 Outer channel 106 Confluence channel 108 Nozzle outlet 110 Extrusion plate 112 Heating channel 114 Coextrusion channel 116 Extrusion opening 202 Flow direction of the cladding polymer component 204 Flow direction of the core polymer component 206 Turbulent flow 300 Channel plate 310 First channel 312 First pressure chamber 320 Second channel 322 Second pressure chamber 400 First distribution chamber 500 Second distribution chamber (Item 1) A coextrusion head for manufacturing a two-component polymer fiber, the coextrusion head comprising a first inlet for receiving a core polymer component, a second inlet for receiving a cladding polymer component, and a dual-channel nozzle (100), the dual-channel nozzle (100) comprising an inner channel (102) and an outer channel (104) encompassing the inner channel (102), the inner channel (102) being in fluid connection with the first inlet, the outer channel (104) being in fluid connection with the second inlet, the dual-channel nozzle (100) further comprising a merging channel (106), the merging channel (106) establishing a fluid connection between the inner channel (102), the outer channel (104), and a nozzle outlet (108) of the dual-channel nozzle (100), the merging channel (106) being configured to bring the core polymer component and the cladding polymer component into contact with each other such that a contact layer is formed between the core polymer component and the cladding polymer component in response to simultaneously receiving the core polymer component from the inner channel (102) and the cladding polymer component from the outer channel (104), the contact layer comprising a mixture of the core polymer component and the cladding polymer component, coextrusion head. (Item 2) The inner channel (102) has a circular cross-section, the merging channel (106) has an axial length x1 between the nozzle outlet (108) and the inner channel (102), and the axial length x1 is 3 to 7 times the diameter of the inner channel (102), the coextrusion head according to item 1. (Item 3) The inner channel (102) has a circular cross-section with a diameter between 0.5 and 1.5 mm, preferably 1.25 mm, the coextrusion head according to item 1 or 2. (Item 4) The merging channel (106) is limited by a conical taper of the dual-channel nozzle (100), the coextrusion head according to any preceding item. (Item 5) The merging channel has a circular cross-section, the coextrusion head according to any preceding item. (Item 6) Further includes an extrusion opening (116) and a co-extrusion path (114), the co-extrusion path (114) establishes a fluid connection between the nozzle outlet (108) and the extrusion opening (116), and the co-extrusion path (114) is configured to simultaneously receive the core polymer component, the cladding polymer component, and the contact layer from the nozzle outlet (108) such that the co-extruded polymer strand is formed in the co-extrusion path (114). The co-extruded polymer strand includes a core, a cladding that includes the core, and a contact layer that interfaces with the core and the cladding, the co-extrusion head according to any previous item. (Item 7) The extrusion opening (116) has a non-circular cross-section, and the co-extrusion path (114) has a non-circular cross-section, the co-extrusion head according to item 6. (Item 8) The co-extrusion path (114) has an axial length x2 between the nozzle outlet (108) and the extrusion opening (116), the co-extrusion head according to item 6 or 7. (Item 9) The axial length x2 is selected such that the co-extruded polymer strand fills the non-circular cross-section at the extrusion opening (116), the co-extrusion head according to item 8. (Item 10) The axial length x2 is between 1.5 and 4.0 mm, the co-extrusion head according to item 8 or 9. (Item 11) The axial length x2 of the co-extrusion path (114) is between 5 and 50 percent of the axial length x1 of the confluence path (106), the co-extrusion head according to item 8, 9 or 10. (Item 12) Comprising a hierarchical stack of at least two of said dual-channel nozzles (100) and channel plates (300), each of said channel plates (300) comprising a first channel (310) and a second channel (320), said first channel (310) establishing said fluid connection between said first inlet and each inner channel (102) of at least two of said dual-channel nozzles (100), said second channel (320) establishing a fluid connection between said second inlet and each outer channel (104) of at least two of said dual-channel nozzles (100), the number of said channels (310, 320) per channel plate (300) being constant or increasing in the downstream direction, the co-extrusion head according to any of the preceding items. (Item 13) The co-extrusion head according to item 12, wherein said channel plates (300) are removable from each other and reattachable to each other. (Item 14) At least two of said dual-channel nozzles (100) are replaceable parts, one of the channel plates (300) at the most downstream position within the hierarchy of said channel plates being an extrusion plate (110), at least one of said channel plates (300) preceding said extrusion plate (110) comprising through-holes for each of at least two of said dual-channel nozzles (100), said extrusion plate comprising heating channels (112) for each of at least two of said dual-channel nozzles (100), said heating channels (112) and said through-holes being configured in their respective plates to be aligned with each other so as to form cavities, each of said cavities comprising one of at least two of said dual-channel nozzles (100), each of said heating channels (112) further comprising an extrusion opening (116), said extrusion opening (116) being in fluid connection with said nozzle outlet (108) of said dual-channel nozzle (100) and being enclosed within the cavity formed by said heating channel, the co-extrusion head according to any of items 12 - 13. (Item 15) The co-extrusion head according to item 14, wherein the heating channel includes a recess for receiving the dual-channel nozzle. (Item 16) The co-extrusion head according to any one of items 11-15, wherein the channel plate (300) is configured such that thermal decomposition of the polymer occurs at a temperature between 450 and 750 °C. (Item 17) The co-extrusion head according to any preceding item, wherein the dual-channel nozzle is configured to operate at a temperature between 180 and 270 °C. (Item 18) The co-extrusion head according to any preceding item, wherein the dual-channel nozzle (100) is a replaceable part. (Item 19) The co-extrusion head according to any preceding item, wherein the merging channel (106) is dimensioned and shaped to form the contact layer by means of a stable turbulent flow between the core polymer component and the cladding polymer component in response to simultaneously receiving the core polymer component from the inner channel (102) and the cladding polymer component from the outer channel (104). (Item 20) The co-extrusion head according to any preceding item, wherein the inner channel (102) and the outer channel (104) have a circular cross-section, the inner channel (102) includes a terminal section of a constant diameter that opens into the merging channel, and the outer channel (104) concentrically surrounds the terminal section of the inner channel (102) with a constant diameter. (Item 21) The co-extrusion head according to item 20, wherein the terminal section of the inner channel (102) has an axial length that is at least 10 times the diameter of the terminal section of the inner channel (102). (Item 22) The above-mentioned confluence path (106) has an axial length x1 between the above-mentioned nozzle outlet (108) and the above-mentioned inner channel (102), and the terminal section of the above-mentioned inner channel (102) has an axial length between 2 times and 15 times the above-mentioned axial length x1 of the above-mentioned confluence path (106). The co-extrusion head according to item 20 or 21. (Item 23) A co-extrusion system including a co-extrusion head according to any previous item, a first supply device for supplying the core polymer component through the first inlet, and a second supply device for supplying the cladding polymer component through the second inlet.

Claims

1. A coextrusion head for manufacturing a two-component polymer fiber, the coextrusion head including a first inlet for receiving a core polymer component, a second inlet for receiving a cladding polymer component, and a dual-channel nozzle, the dual-channel nozzle including an inner channel and an outer channel encompassing the inner channel, the inner channel being in fluid connection with the first inlet, the outer channel being in fluid connection with the second inlet, the dual-channel nozzle further including a confluence channel establishing a fluid connection between the inner channel, the outer channel, and a nozzle outlet of the dual-channel nozzle, an outlet of the inner channel and the nozzle outlet being of equal dimensions, the confluence channel being configured to simultaneously receive the core polymer component from the inner channel and the cladding polymer component from the outer channel flowing radially inwardly into the confluence channel with respect to the flow of the core polymer component and bring the core polymer component and the cladding polymer component into contact with each other.

2. Further including an extrusion opening through which the coextruded polymer strand is extruded and a coextrusion path establishing a fluid connection between the nozzle outlet and the extrusion opening and configured to simultaneously receive the core polymer component and the cladding polymer component from the nozzle outlet such that the coextruded polymer strand is formed. The co-extrusion path has an axial length x between the nozzle outlet and the extrusion opening ２ and the axial length x ２ is between 5 and 50 percent of the axial length x between the nozzle outlet and the inner channel of the confluence path １ ​ The coextrusion head according to claim 1.

3. The inner channel and the outer channel have a circular cross-section, the inner channel including a terminal section of a constant diameter opening into the confluence channel, the outer channel concentrically and with a constant diameter surrounding the terminal section of the inner channel. The terminal section of the inner channel has an axial length at least 10 times the diameter of the terminal section of the inner channel. The confluence path has an axial length x between the nozzle outlet and the inner channel. １ The terminal section of the inner channel has an axial length between 2 times and 15 times the axial length x of the confluence path. The co-extrusion head according to claim 1 or 2. １ ​

4. The coextrusion head according to any one of claims 1 to 3, wherein the dual-channel nozzle includes a tapered shape guiding the outer channel towards a center where the confluence channel is disposed.

5. The confluence path has an axial length x between the nozzle outlet and the inner channel １ and the axial length x １ is 3 to 7 times the diameter of the inner channel. The coextrusion head according to any one of claims 1 to 4

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