Composite melt filament

Abstract

A composite melt filament (10) comprising: a polymer sheath (12) having a longitudinal axis (22) along which a length (16) of the composite melt filament (10) is defined, wherein the polymer sheath (12) consists of a thermoplastic polymer having a melting temperature (T M ) has; one or more mesogenic reinforcement bodies (14) enclosed by the polymer shell (12), wherein the one or more mesogenic reinforcement bodies (14) consist of a thermotropic liquid crystal polymer having organized crystalline fibrils (24) aligned longitudinally along the longitudinal axis (22) of the polymer shell (12), wherein the thermotropic liquid crystal polymer of the one or more mesogenic reinforcement bodies (14) has a clearing temperature (T C ) which is greater than the melting temperature (T M ) of the thermoplastic polymer of the polymer sheath (12); wherein the thermotropic liquid crystal polymer has a crystallinity ranging from 50% to 100%; wherein the crystallinity is a ratio of a volume of the organized crystalline fibrils (24) to a total volume of the thermotropic liquid crystal polymer expressed as a percentage; and wherein the remainder of the total volume of the thermotropic liquid crystal polymer consists of amorphous regions (28) of the thermotropic liquid crystal polymer.

Description

[0001] Manufacturing processes are becoming increasingly sophisticated. For example, the production of multi-component articles may require two workpiece parts—at least one of which may be molded from a composite material—to be secured together. During automobile assembly, prefabricated composite parts can be used at various locations throughout the vehicle to selectively reduce overall vehicle weight without compromising the vehicle's in-service integrity and performance. Several examples of automotive components that can be incorporated into a vehicle as a composite part include hoods, quarter panels, fenders, and truck bodies. The workpiece composite elements used for these and other applications typically consist of a thermoplastic polymer matrix reinforced with embedded fillers such as fibers and / or particles.While the use of composite parts has some advantages over their more conventional metal counterparts, the process of attaching a composite part to another workpiece part (composite or non-composite) is typically more time-consuming and laborious compared to metal joining techniques, as some form of mechanical fastening is required to firmly hold the workpiece parts together. The present specification describes a composite fused filament that can enable the meaningful joining of a composite workpiece. The apparent composite fusion filament may also have other uses. In particular, the composite fused filament may be used for an additive manufacturing process known as fused deposition modeling.

[0002] US Pat. No. 6,254,987 B1 describes a sheath-core monofilament with improved abrasion resistance. The core is a liquid-crystalline polyester, and the sheath is a blend of 1-5 weight percent polycarbonate and a polyester.

[0003] US Pat. No. 5,753,736 A describes dimensionally stable, shrink-resistant polyester fibers, nonwovens, and fabrics containing a nucleating agent incorporated into the fibers. Methods for incorporating the nucleating agent into the polyester are disclosed.

[0004] US 6 207 273 B1 describes a method for producing a filament assembly consisting of a thermotropic liquid crystal polymer, comprising melt-extruding a thermotropic liquid crystal polymer through an orifice die into a high-speed fluid to thereby maintain filaments spun directly below the spinneret at a high temperature so that the filaments are taken up by the frictional force of the high-speed fluid at a high draw ratio.

[0005] US 2014 / 0 291 886 A1 describes three-dimensional printers and reinforced filaments, as well as their methods of use. A void-free reinforced filament is fed into an extrusion die. The reinforced filament comprises a core, which can be continuous or semi-continuous, and a matrix material surrounding the core. The reinforced filament is heated to a temperature above the melting temperature of the matrix material and below the melting temperature of the core before the filament is extruded from the extrusion die.

[0006] A composite melt filament according to the invention comprises a polymer sheath having a longitudinal axis along which a length of the composite melt filament is defined. The polymer sheath consists of a thermoplastic polymer having a melting temperature, T M, has. The composite melt filament further comprises one or more mesogenic reinforcing bodies enclosed by the polymer shell. The one or more mesogenic reinforcing bodies consist of a thermotropic liquid crystal polymer having organized crystalline fibrils aligned longitudinally along the long axis of the polymer shell. The thermotropic liquid crystal polymer of the one or more mesogenic reinforcing bodies has a clearing temperature, T C , which is greater than the melting temperature, T M, of the thermoplastic polymer of the polymer shell. The thermotropic liquid crystal polymer has a crystallinity ranging from 50% to 100%. Crystallinity is a ratio of a volume of organized crystalline fibrils to a total volume of the thermotropic liquid crystal polymer, expressed as a percentage, and the remainder of the total volume of the thermotropic liquid crystal polymer consists of amorphous regions of the thermotropic liquid crystal polymer.

[0007] According to one embodiment, the melting temperature of the thermoplastic polymer is between 160°C and 350°C, and the clearing temperature of the thermotropic liquid crystal polymer is between 250°C and 400°C. As a further embodiment, the melting temperature of the thermoplastic polymer is between 240°C and 280°C, and the clearing temperature of the thermotropic liquid crystal polymer is between 280°C and 310°C. Furthermore, the thermoplastic polymer can be an aliphatic polyamide or polyethylene terephthalate. According to another embodiment, the thermotropic liquid crystal polymer is poly(hydroxybenzoic acid) or poly(1,4-phenylene terephthalate). The thermotropic liquid crystal polymer can also be a copolyester.According to a further embodiment, the thermotropic liquid crystal polymer is poly(4,4'-dihydroxybiphenyl-co-terephthalic acid), poly(4,4'-dihydroxybiphenyl-co-terephthalic acid-co-isophthalic acid), poly(hydroxybenzoic acid-co-2-hydroxy-6-naphthoic acid), poly(ethylene terephthalate-co-hydroxybenzoic acid), or poly(p-acetoxybenzoic acid-co-ethylene terephthalate). According to a further embodiment, the thermotropic liquid crystal polymer is a copolyesteramide. According to a further embodiment, the thermotropic liquid crystal polymer is poly(6-hydroxy-2-naphthoic acid-co-terephthalic acid-co-4-aminophenol).

[0008] Additionally, the ratio of the cross-sectional area of the polymer sheath to the cross-sectional area of one or more mesogenic reinforcing bodies can range from 0.1 to 20 when the composite fusion filament is cut perpendicular to the length of the thread. In another embodiment, the ratio of the cross-sectional area of the polymer sheath to the cross-sectional area of one or more mesogenic reinforcing bodies can range between 1 and 2, and the thickness of the polymer sheath can range between 1.0 mm and 10.0 mm. And, in one implementation, the polymer sheath has an outer surface that defines an outer diameter of the composite fusion thread.

[0009] The exact shape and construction of the composite melt filament can vary. According to another embodiment, the polymer shell is an annular polymer shell, and the one or more mesogenic reinforcement bodies are a single elongated liquid crystal polymer core circumferentially surrounded by the annular polymer shell and having the same length as the annular polymer shell. According to another embodiment, the polymer shell comprises an annular polymer shell portion, and the one or more mesogenic reinforcement bodies are a series of elongated liquid crystal polymer cores arranged in axial alignment along the longitudinal axis of the polymer shell.According to another embodiment, the polymer shell comprises an annular polymer shell portion, and the one or more mesogenic reinforcement bodies are a plurality of continuous, elongated liquid crystal polymer cores spaced apart within the polymer shell and surrounded by the annular polymer shell portion of the polymer shell. Each of the plurality of continuous, elongated liquid crystal polymer cores has the same length as the polymer shell. According to another embodiment, the polymer shell comprises an annular polymer shell portion, and the one or more mesogenic reinforcement bodies are multiple rows of elongated liquid crystal polymer cores arranged in axial alignment along the longitudinal axis of the polymer shell.

[0010] To understand the features of the claimed composite melt filament, a process is described below that includes steps that include features of the claimed composite melt filament. In one step, a composite melt filament is fed to a melt deposition head containing a liquefier and a nozzle. The composite melt filament consists of a polymer shell and one or more mesogenic reinforcing bodies contained within the polymer shell. The polymer shell consists of a thermoplastic polymer with a melting temperature, and the one or more mesogenic reinforcing bodies consist of a thermotropic liquid crystal polymer with a clearing temperature higher than the melting temperature of the thermoplastic polymer.In a further process step, the composite melt filament is heated in the condenser to a processing temperature that is above the melting temperature of the thermoplastic polymer of the polymer sheath, but below the clearing temperature of the thermotropic liquid crystal polymer of the mesogenic reinforcement body(s). A further step of the process consists in applying the composite melt filament to a substrate comprising a thermoplastic polymer compatible with the thermoplastic polymer of the polymer sheath of the composite melt filament. A further step of the process consists in curing a deposited molten form of the polymer sheath of the composite melt filament and a molten contact portion of the thermoplastic polymer of the substrate to form a polymer bond. Fig.1 is a partial cross-section of a composite melt filament with the thread cut along a length dimension; Fig. Figure 2 is a cross-sectional view of the composite melt filament, with the thread cut along a thickness dimension located at cut lines 2-2 of Fig. 1 was taken; Fig. Figure 3 is a DSC curve for polycaprolactam (PA6), where the y-axis represents heat flow and the x-axis represents temperature in degrees Celsius, and where the upward movement on the y-axis represents an endothermic event and the downward movement on the y-axis represents an exothermic event. Fig. Figure 4 is a DSC curve for polyethylene terephthalate (PET), where the y-axis represents heat flow and the x-axis represents temperature in degrees Celsius, and where the upward movement on the y-axis represents an endothermic event and the downward movement on the y-axis represents an exothermic event; Fig.Figure 5 is a representative DSC curve for a thermotropic liquid crystal polymer, where the y-axis represents heat flow and the x-axis represents temperature, and where upward movement on the y-axis represents an endothermic event and downward movement on the y-axis represents an exothermic event; Fig. 6 is a partial cross-section of a composite melt filament with the thread cut along a length dimension; Fig. 7 is a partial cross-sectional view of a composite melt filament with the thread cut along a length dimension; and Fig. Figure 8 is a cross-sectional view of the composite melt filament according to Fig. 6, wherein the thread is cut along a thickness dimension which is at the cutting lines 8-8 of Fig. 7 was taken; Fig.9 is a partial cross-sectional view of a composite melt filament with the thread cut along a length dimension; and Fig. 10 is an elevated cross-sectional view of a melt deposition apparatus operable to deposit a composite melt filament onto a substrate comprising a compatible thermoplastic polymer.

[0011] A composite melt filament is described that includes a thermoplastic polymer shell and one or more mesogenic reinforcing bodies contained within the thermoplastic polymer shell. Each of the one or more mesogenic reinforcing bodies consists of a thermotropic liquid crystal polymer with organized crystalline fibrils aligned longitudinally along a longitudinal axis (length dimension) of the polymer shell. The one or more mesogenic reinforcing bodies can be in the form of a single continuous elongated liquid crystal polymer core ( Fig. 1-2), a series of elongated liquid crystal polymer cores in axial alignment ( Fig. 6), a plurality of continuous elongated liquid crystal polymer cores ( Fig. 7-8) or several rows of elongated liquid crystal polymer cores in axial alignment ( Fig.9). The composite melt filament can be produced by coextrusion with any of these embodiments of the one or more mesogenic reinforcing bodies, since the heat and shear forces applied to the filament during coextrusion promote the crystallization and orientation of the crystalline fibrils.

[0012] Each of the thermoplastic polymers used in the polymer shell and the thermotropic liquid crystal polymer used in the one or more mesogenic reinforcement bodies can be selected from a variety of suitable candidates, as long as the thermoplastic polymer has a melting temperature lower than a clearing temperature of the thermotropic liquid crystal polymer. This relationship between the melting temperature of the thermoplastic polymer and the clearing temperature of the thermotropic liquid crystal polymer allows the composite melt filament to be heated to a temperature at which the polymer shell melts and undergoes viscous flow, while the thermotropic liquid crystal polymer of each mesogenic reinforcement body maintains an anisotropic liquid crystal state.The ability to melt the polymer sheath of the composite melt filament while leaving the one or more mesogenic reinforcing bodies structurally intact allows the filament to bond via the molten polymer sheath to a compatible thermoplastic polymer of a substrate on which the filament is deposited while maintaining a manipulable fiber shape via the one or more mesogenic reinforcing bodies.

[0013] The composite melt filament can be heated and selectively deposited onto a substrate by any applicable deposition technique to facilitate bonding between them, provided the substrate contains a thermoplastic polymer compatible with the thermoplastic polymer forming the polymer sheath of the melt filament. Thermoplastic polymers are compatible when they have the same polymer composition, such as when the thermoplastic polymers are both polycaprolactam (polyamide 6, PA 6, or nylon 6), because polymers of the same composition can simply blend without changing their chemistry or properties. Thermoplastic polymers are also considered compatible when the polymers have different polymer compositions but are still miscible, because when mixed, the polymers form a single-phase mixture exhibiting a single glass transition temperature.An example of compatible thermoplastic polymers that have different polymer compositions is polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).

[0014] With reference to Fig.1-2, a composite fusion thread 10 according to one embodiment of the present description is shown. The composite melt filament 10 includes a polymer sheath 12 and one or more mesogenic reinforcement bodies 14 contained within the polymer sheath 12. The composite melt filament 10 has a length dimension 101 and a thickness dimension 103. The length dimension 101 is the most extended dimension of the filament 10, along which a length 16 of the filament 10 is measured, and the thickness dimension 103 is the largest dimension of the filament 10 in a section plane oriented perpendicular to the length dimension 101, along which a thickness 18 of the filament 10 is measured. The composite melt filament 10 is, as shown here, preferably circular in cross-section, such that the thickness 18 of the thread 10 is simply an outer diameter 18' of the thread 10.In alternative embodiments, the composite fusion filament 10 can take on other cross-sectional shapes such as square, hexagonal, or octagonal, to name a few. The length 16 of the composite fusion filament 10 may be at least 100 times greater than the thickness 18 of the filament. And while the length 16 of the composite fusion filament 10 can vary greatly, in many cases a longer length is preferred so that the filament 10 can be spooled for easier handling.

[0015] The polymer sheath 12 consists of a thermoplastic polymer, which may optionally contain a reinforcing filler (not shown). The polymer sheath 12 has an outer surface 20 and supports the mesogenic reinforcing body(s) 14 beneath this outer surface 20. In the case of multiple bodies 14, it also fixes the mesogenic reinforcing body(s) 14 in a fixed position relative to one another. The outer surface 20 of the polymer sheath describes the cross-sectional shape of the composite melt filament 10. The cross-sectional profile of the outer surface 20 determines the thickness dimension 103 of the filament 10 and, in turn, defines the thickness 18 of the filament 10. In addition, the polymer sheath 12 has a longitudinal axis 22. The extension of the polymer sheath 12 along the longitudinal axis 22 determines the length dimension 101 of the filament 10 and thus defines the length 16 of the filament 10.The specific size and shape of the polymer sheath 12 may vary depending on a variety of factors, including the intended end use of the composite melt filament 10, the expected processing window of the filament 10, and the desired properties of the filament 10 at room and elevated processing temperatures.

[0016] Each of the one or more mesogenic reinforcing bodies 14 consists of a thermotropic liquid crystal polymer, which may optionally contain a reinforcing filler (not shown). The thermotropic liquid crystal polymer of each body 14 has a plurality of organized crystalline fibrils 24 that form regions of ordered mesogenic units of the polymer molecules. The organized crystalline fibrils 24 are aligned longitudinally along the long axis 22 of the polymer shell 12, i.e., the long axes of the crystalline fibrils 24 have an orientation along the long axis 22 of the polymer shell 12, such that a director 26 (or common axis) of the fibrils 24 runs parallel to the long axis 22. The crystalline fibrils 24 are distributed throughout the liquid crystal polymer.The fibrils 24 may be axially and radially spaced from one another, which, as shown, may result in the fibrils becoming entangled by a portion of the long axis of one or more of the fibrils 24 intersecting with a portion of the long axis of one or more other fibrils 24. The thermotropic liquid crystal polymer has a crystallinity (i.e., the ratio of the volume of the crystalline fibrils to the total volume of the liquid crystal polymer, expressed as a percentage) that can range from 50% to 100%, with the remainder consisting of amorphous regions 28 of the liquid crystal polymer. The multitude of organized crystalline fibrils 24, which can be formed to a certain crystallinity by heat and shear stress, impart anisotropy to each of the mesogenic reinforcement bodies 14.

[0017] The compositions of thermoplastic polymer contained in the polymer shell 12 and the thermotropic liquid crystal polymer contained in the one or more mesogenic reinforcing bodies 14 are selected such that a melting temperature (T M ) of the thermoplastic polymer is lower than a clearing temperature (T C ) of the thermotropic liquid crystal polymer. The melting temperature (T M ) of the thermoplastic polymer is the peak melting temperature or melting point of the thermoplastic polymer and can be determined by Differential Scanning Calorimetry (DSC). For example, Fig. 3 a DSC curve for polycaprolactam (PA6) and Fig.Figure 4 shows a DSC curve for polyethylene terephthalate (PET). The melting endotherm 30 for PA6 and the melting endotherm 32 for PET provide thermal information about the phase transition of their respective polymers into an isotropic liquid in which the polymer molecules are disordered and the polymer can flow viscously. The melting temperature (T M ) for PA6 (indicated by the dashed line with reference number 34) and PET (indicated by the dashed line with reference number 36) is the temperature corresponding to the peak of their respective melting endotherms 30, 32.

[0018] The clarification temperature (T C ) of the thermotropic liquid crystal polymer differs slightly from the melting temperature (T M ) of the thermoplastic polymer. The clearing temperature (T C) is the temperature above which the liquid crystal polymer is an isotropic liquid, free of crystalline regions containing ordered mesogenic units of the polymer molecules. This specific temperature can be determined by DSC. To explain the concept of the clearing temperature, Fig.Figure 5 shows a representative liquid crystal polymer DSC curve. As is common for liquid crystal polymers, the DSC curve shows a step change in the glass transition temperature (indicated by the dashed line with reference number 38), one or more liquid crystal phase change endotherms 40, which represent shifts between liquid crystal phases such as the smectic and nematic phases, and a melting endotherm 42. The melting endotherm 42, as before, provides thermal information about the phase transition from liquid crystalline polymer to an isotropic liquid in which the polymer molecules are disordered and the liquid crystalline polymer can flow viscously. The clearing temperature (T C) of the liquid crystal polymer (indicated by the dashed line with the reference number 44) is the maximum temperature associated with the melting endotherm 42. The liquid crystal polymer is thus in a liquid crystalline state, which can exhibit various liquid crystal phases or mesophases, between the glass transition temperature and the clearing temperature (T C ) before.

[0019] According to various designs of the composite melt filament 10, the melting temperature of the thermoplastic polymer can be between 160°C and 350°C or more narrowly between 240°C and 300°C and the clearing temperature of the thermotropic liquid crystal polymer can be between 250°C and 400°C or more narrowly between 280°C and 330°C.Some specific examples of preferred thermoplastic polymers for the polymer sheath 12 are polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polystyrene, acrylonitrile-styrene polymer, acrylonitrile-butadiene-styrene, polyacrylates, polymethacrylate, polyethylene, polypropylene, aliphatic polyamides (PA46, PA6, PA66, PA11, PA12), fully or partially aromatic polyamides, polyacetals, polybenzimidazole, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyphenyl ethers, polyphenylene oxides, polyphenylene sulfide, polyethersulfones, polyetheretherketones, polyetherketones, polyetherimides, polylactides, polyoxymethylenes, thermoplastic polyurethanes or a combination or heteropolymer of two or more of these resins.

[0020] The thermotropic liquid crystal polymer can be any aromatic polymer capable of transitioning into and through a liquid crystalline state in response to temperature changes. The thermotropic liquid crystal polymer can be a homopolymer or a heteropolymer. As an example of a suitable homopolymer, the liquid crystalline polymer can be a polyester such as poly(hydroxybenzoic acid) and poly(1,4-phenylene terephthalate). And as an example of a suitable heteropolymer, the liquid crystal polymer can be a copolyester such as poly(4,4'-dihydroxybiphenyl-co-terephthalic acid), poly(4,4'-dihydroxybiphenyl-co-terephthalic acid-co-isophthalic acid), poly(hydroxybenzoic acid-co-2-hydroxy-6-naphthoic acid), poly(ethylene terephthalate-co-hydroxybenzoic acid), or poly(p-acetoxybenzoic acid-co-ethylene terephthalate).As another example of a suitable heteropolymer, the liquid crystalline polymer can be a copolyester-amide such as poly(6-hydroxy-2-naphthoic acid-co-terephthalic acid-co-4-aminophenol). The liquid crystalline polymers mentioned here and others are commercially available. Specific commercially available liquid crystalline polymers that can be employed as one or more mesogenic reinforcement bodies 14 include Vectra® and Zenite® from Celanese Corporation (based in Irving, Texas), Vectran® from Kuraray America, Inc. (based in Houston, Texas), and the RTP 3400 series of liquid crystalline polymers from RPT Company (based in Winona, Minnesota).

[0021] While a variety of combinations are certainly possible, the selection and pairing of the thermoplastic polymer and the thermotropic liquid crystal polymer can be tailored to a specific end application of the composite melt filament 10. In a particular application, the thermoplastic polymer is selected so that its melting temperature is between 240°C and 280°C, and the thermotropic liquid crystal polymer is selected so that its clearing temperature is between 280°C and 310°C, with the melting temperature, of course, being lower than the clearing temperature conditioned above. These temperature ranges provide a convenient processing window for using the composite melt filament 10 as a bonding medium to join two substrates together when one or both substrates are a composite substrate.Some example polymer combinations that meet the above temperature conditions are an aliphatic polyamide, in particular PA6 (polycaprolactam) and PA66 (polyhexamethylene adipamide), or polyethylene terephthalate as the thermoplastic polymer, and a copolyester such as poly(hydroxybenzoic acid-co-2-hydroxy-6-naphthoic acid), poly(ethylene terephthalate-co-hydroxybenzoic acid), poly(p-acetoxybenzoic acid-co-ethylene terephthalate) or poly(6-hydroxy-2-naphthoic acid-co-terephthalic acid-co-4-aminophenol) as the thermotropic liquid crystal polymer.

[0022] As already mentioned, the polymer shell 12 and the mesogenic reinforcement body(s) 14 can each contain a reinforcing filler in addition to the respective thermoplastic and thermotropic liquid crystal polymers. The reinforcing filler can, if desired, help to adjust the mechanical properties of the polymer shell 12 and / or the one or more mesogenic reinforcement bodies 14. The reinforcing filler can contain fibers, particles such as spheres or flakes, or a combination of fibers and particles. Some examples of reinforcing fibers that can be used are carbon fibers, glass fibers (e.g., glass fiber, quartz), basalt fibers, para-aramid fibers (e.g., Kevlar®, polyphenylene benzobisoxazole (PBO)), polyethylene fibers (e.g., high-strength ultra-high molecular weight (UHMW) polyethylene), polypropylene fibers (e.g., high-strength polypropylene), natural fibers (e.g., cotton flax, cellulose, spider silk), and combinations of two or more such fibers.Some examples of reinforcing particles are glass particles and mineral particles including those of talc, wollastonite, calcium carbonate, mica, aluminosilicate clays, halloysite and combinations of two or more such particles.

[0023] The exact structure of the composite melt filament 10 is subject to a certain degree of variability. In the form described here and in Fig.1-2, in which the composite melt filament 10 has a circular cross-section along the thickness dimension 103, the polymer sheath 12 has the shape of an annular thermoplastic polymer sheath 46 that circumscribes the longitudinal axis 22 of the polymer sheath 12. The polymer sheath 46 includes an inner peripheral surface 48 and an outer peripheral surface 50 as the outer surface 20. The inner peripheral surface 48 defines an inner cavity 52, while the outer peripheral surface 50 forms the outside of the polymer sheath 46 and thus defines the outer diameter 18' (and the thickness 18) of the composite melt filament 10. The inner and outer peripheral surfaces 48, 50 additionally define a radial thickness 54 of the polymer shell 46.The outer diameter 18' and the radial thickness 54 of the polymer sheath 46, along with other features of the composite melt filament 10, including the compositions of the thermoplastic polymer and the liquid crystal polymer, can be adjusted as needed to optimize the properties and behavior of the filament 10 for a particular application.

[0024] Furthermore, the mesogenic reinforcement body(s) 14 are in the form of a single elongated liquid crystal polymer core 56 that occupies the inner cavity 52 of the annular thermoplastic polymer shell 46 and coincides in length with the shell 46. The elongated liquid crystal polymer core 56 is elongated along the longitudinal axis 22 of the polymer cladding 12 and has an outer surface 58 that defines a thickness 60 of the core 56 in the thickness dimension 103 of the composite fusion thread 10. The outer surface 58 of the elongated liquid crystal polymer core 56 is circumferentially surrounded by the inner peripheral surface 48 of the polymer shell 46 and can assume any number of shapes and surface contours. Here, as best shown in Fig.2, the elongated liquid crystal polymer core 56 has a circular cross-section when cut along the thickness dimension 103, and thus the outer surface 58 of the core 56 is cylindrical and circular in cross-section with a diameter 60' defining the thickness 60 of the elongated liquid crystal polymer core 56. Other cross-sectional shapes of the elongated liquid crystal polymer core 56 are certainly possible. The single elongated liquid crystal polymer core 56 can be formed within the annular thermoplastic polymer shell 46 by coextrusion, with the heat and shear applied during coextrusion to establish the organized crystalline fibrils 24 with their orientational alignment.

[0025] The outer diameter 18' of the annular polymer shell 46 (and thus of the filament 10) and the diameter 60' of the elongated liquid crystal polymer core 56 can be varied to adjust the thermal properties and behavior of the filament 10. The outer diameter 18' of the shell 46 can, for example, be from 1.0 mm to 10.0 mm, or more narrowly from 1.75 mm to 6.0 mm, 1.75 mm to 4.5 mm, 1.75 mm to 3.0 mm, or 1.75 mm to 2.85 mm, while at the same time the diameter 60' of the elongated liquid crystal polymer core 56 is such that a ratio (R ArS / ArC ) of the cross-sectional area 62 of the annular polymer shell 46 to a cross-sectional area 64 of the elongated liquid crystal polymer core 56 in the thickness dimension 103 of the filament 10 is in the range of 0.1 to 20 or narrower from 0.2 to 10, 0.5 to 3 or 1 to 2. To achieve these surface ratios, a ratio (R DS / DC) of the outer diameter 18' of the polymer shell 46 to the diameter 60' of the elongated liquid crystal polymer core 56 may be in the range of 1.05 to 4.6 or narrower from 1.1 to 3.3, 1.22 to 2, or 1.41 to 1.73, as summarized in Table 1 below for the widest range (i.e., 0.1 to 20) of R ArS / ArC While the area ratio R ArS / ArC As shown here in connection with the diameters 18', 60', the same area ratio ranges also apply to filament constructions in which the polymer sheath 12 and / or the mesogenic reinforcing body(s) 14 have a non-circular cross-section in the thickness dimension 103. Table 1: Summary of shell and core diameters Outer diameter of the shell (mm) R ArS / ArC RDS / DC Diameter of the extended core (mm) 1.0 0.1 - 20 1.05 - 4.6 0.22 - 0.95 1.75 0.1 - 20 1.05 - 4.6 0.38 - 1.67 2.85 0.1 - 20 1.05 - 4.6 0.62 - 2.71 3.0 0.1 - 20 1.05 - 4.6 0.65 - 2.85 4.5 0.1 - 20 1.05 - 4.6 0.98 - 4.26 6.0 0.1 - 20 1.05 - 4.6 1.30 - 5.71 10.0 0.1 - 20 1.05 - 4.6 2.17 - 9.52

[0026] The composite melt filament can take on other constructions in addition to the construction described above. Fig.For example, Figure 6 shows an alternative embodiment of the composite melt filament, designated by the reference numeral 110. In the following discussion of this particular embodiment, reference numerals corresponding to the reference numerals used in the description of the previous embodiment are used to identify the same or similar elements with the same or similar functionality. For this purpose, the description of aspects of the previously described embodiment in the Fig.1-2 also apply to aspects of the following embodiment, which are identified by corresponding reference numerals unless expressly described otherwise. In this embodiment, the composite melt filament 110 includes, as one or more mesogenic reinforcement bodies 114, a row 166 of elongated liquid crystal polymer cores 156 in axial alignment along the longitudinal axis 122 of the polymer cladding 112, which, as shown, includes an annular polymer sheath portion 146 circumferentially surrounding the row 166 of elongated liquid crystal polymer cores 156.As used herein, the phrase "in axial alignment along the longitudinal axis" means that the elongated liquid crystal polymer cores 156 are coaxially aligned end to end along the longitudinal axis 122 of the polymer cladding 112, or that the cores 156 are aligned end to end and extend along the longitudinal axis 122 without necessarily maintaining a strict coaxial relationship with the polymer cladding 112.

[0027] Each of the elongated liquid crystal polymer cores 156 has the same composition and properties—including the presence of the organized crystalline fibrils 124 and the shape and diameter ranges—as the single elongated liquid crystal polymer core 56 described above. Each of the liquid crystal polymer cores 156 is also elongated along the longitudinal axis 122 of the polymer cladding 112 and has an outer surface 158 that defines a thickness 160 of the core 156 in the thickness dimension 103 of the composite melt filament 110. However, in this embodiment, the elongated liquid crystal polymer cores 156 are axially aligned within the polymer cladding 112 by separating the cores 156 from one another by gaps 168 that are axially spaced along the longitudinal axis 122 of the polymer cladding 112.These gaps 168 are occupied by polymer plugs 170 that are integral with the polymer sheath portion 146 and extend transversely to the longitudinal axis 122 of the polymer sheath 112 so that the ends of adjacent elongated liquid crystal polymer cores 156 are separated from each other. To produce the composite melt filament 110 of this embodiment, a coextrusion process similar to that used to produce the filament 10 of FIG. Fig. 1-2, although here additional dislocations are introduced into the single continuous, elongated liquid crystal core resulting from coextrusion by twisting the filament over a tight bending radius or by periodically squeezing the filament lengthwise to form the series 166 of axially aligned, elongated liquid crystal polymer cores 156.

[0028] Fig.7-8 show another alternative embodiment of the composite melt filament, designated by reference numeral 210. In this embodiment, the one or more mesogenic reinforcement bodies 214 are in the form of a plurality of continuous, elongated liquid crystal polymer cores 256 spaced apart within the polymer cladding 212, which, as shown, may include an annular polymer cladding portion 246 circumferentially surrounding the plurality of continuous, elongated liquid crystal polymer cores 256. Each of the continuously elongated liquid crystal polymer cores 256 is elongated along the longitudinal axis 222 of the polymer cladding 212 and has the same length as the polymer cladding 212.Each of the continuously elongated liquid crystal polymer cores 256 has the same composition and properties—including the presence of the organized crystalline fibrils 224—as the single elongated liquid crystal polymer core 56 described above. Accordingly, the polymer cladding 212 defines a plurality of spaced-apart internal cavities 272 as opposed to a single internal cavity. Each of the internal cavities 272 is preferably circular in cross-section and occupied by an elongated liquid crystal polymer core 256 having an outer surface 258. The outer surfaces 258 of the elongated liquid crystal polymer cores 256 may be cylindrical and circular in cross-section. Regarding the diameter of the plurality of continuous, elongated cores 256, the ratio (R ArS / ArC) of the cross-sectional area 262 of the polymer sheath 212 to the combined cross-sectional area 264 of the cores 256 in the thickness dimension 103 of the thread 210 is still between 0.1 and 20, or narrower from 0.2 to 10, 0.5 to 3 or 1 to 2. The composite melt filament 210 of this embodiment can be formed by a modified coextrusion process so that the desired number of continuous, elongated liquid crystal polymer cores 256 are formed within the polymer sheath 212 and surrounded by the annular sheath part 246.

[0029] Fig.Figure 9 shows another alternative embodiment of the composite melt filament, designated by reference numeral 310. Here, the one or more mesogenic reinforcing bodies 314 are in the form of multiple rows 366 of elongated liquid crystal polymer cores 356 in axial alignment along the longitudinal axis 322 of the polymer cladding 312, which, as shown, may include an annular polymer cladding portion 346 circumferentially surrounding the multiple rows 366 of axially aligned elongated liquid crystal polymer cores 356. Each series 366 of axially aligned elongated liquid crystal polymer cores 356 corresponds to the configuration described above in connection with Fig.7 described series 166 of elongated cores 156. In this context, the axially aligned liquid crystal polymer cores 356 in each series 366 are separated by gaps 368 occupied by polymer plugs 370 integrated with the annular shell portion 346 of the polymer housing 312. Anywhere from 2 to 20 series 366 of axially aligned, elongated liquid crystal polymer cores 356 can be present within the polymer shell 312. In addition, as before, the ratio (R ArS / ArC ) of the cross-sectional area of the polymer sheath 312 to the combined cross-sectional area of the cores 356 in the thickness dimension 103 of the filament 310 satisfy the same ranges. To produce the composite melt filament 310 of this embodiment, the coextrusion process is similar to that used to produce the filament 210 from Fig.7 is practiced, wherein in addition the plurality of continuous elongated liquid crystal cores formed by coextrusion in the same manner as described above are offset to the multiple rows 366 of axially aligned elongated cores 356.

[0030] The composite melt filaments 110, 210, 310 of the various alternative embodiments may have properties or features that are more suitable for certain applications than the Fig.1-2. For example, the composite melt filaments 110, 310 containing one or more series 166, 366 of axially aligned, elongated liquid crystal polymer cores 156, 356 may have increased flexibility and may therefore be more easily bent and / or compressed due to intermittent fractures between the aligned cores 156, 356.As another example, the composite melt filament 210 containing a plurality of continuous, elongated liquid crystal nuclei 256 may allow certain regions of the filament 210 to have its properties more strongly dominated by the elongated liquid crystal nuclei 256 or the polymer cladding 212 by grouping the elongated liquid crystal nuclei 256 off-center within the polymer cladding 212, arranging the cores 256 at different distances relative to one another, varying the thickness and / or cross-sectional shape across the cores 256 based on their position within the polymer cladding 212, or a combination of the above factors.Of course, those skilled in the art will understand that there may be other differences between the various embodiments of the composite melt filaments described herein that may make each of the filaments 10, 110, 210, 310 more desirable for a particular application.

[0031] The composite melt filament 10, 110, 210, 310 can be used for a variety of purposes, including (1) bonding a pair of workpiece elements together when at least one, and preferably both, of the workpiece elements is a composite workpiece element containing a thermoplastic polymer matrix, and (2) additively manufacturing a three-dimensional article by building up the article layer by layer, such that each deposited layer (except the first layer) is deposited onto a partially formed and growing article containing a solidified thermoplastic polymer. With reference to Fig. 10 now shows the use of the composite melt filament for these and other applications. In Fig.10, the various described versions of the composite melt filament 10, 110, 210, 310 are collectively identified by reference numeral 510, while the various structural components of the thread 510 are also identified by reference numeral 500, which collectively correspond to the same or similar structural components of the various embodiments described above.

[0032] The composite melt filament 510 is applied to a substrate 580 and forms a polymeric bond with the substrate 580. The substrate 580 contains a thermoplastic polymer 582 and can take on a variety of constructions, including a single composite part, a pair of composite parts held together, a growing article produced by melt deposition modeling, or any other thermoplastic polymer-containing object. The thermoplastic polymer 582 of the substrate 580 can be any of the thermoplastic polymers listed above in connection with the polymer cladding 512 of the composite melt filament 510. In addition, in some cases, the substrate 580 can additionally contain a reinforcing phase 584 dispersed in a matrix of the thermoplastic polymer 582. The reinforcing phase 584 can be fibers (as shown) or particles embedded in the matrix 582.The reinforcement phase 584 may contain, for example, carbon and / or glass fibers, among others.

[0033] The composite melt filament 510 can be heated and applied to the substrate 580 using a melt deposition device 586. The melt deposition system 586 includes a deposition head 588 that is computer-controlled and movable relative to the substrate 580. The deposition head 588 includes a wire feeder 590 that, using gear- or roller-based torque, draws the composite melt filament 510 from a spool 592 and forces it through a liquefier 594 and out an orifice 596 of a possibly restricted nozzle 598. The liquefier 594 heats the composite melt filament 510 to a processing temperature and can be configured to supply heat to the filament 510 in a variety of ways, e.g., by a resistive heating coil contained within the liquefier 594. The feed rate of the composite melt filament 510 into the liquefier 594 is typically controlled by a stepper motor.To ensure that a strong and durable polymer bond is formed between the composite melt filament 510 and the substrate 580, the thermoplastic polymer of the polymer sheath 512 of the filament 510 is selected to be compatible with the thermoplastic polymer 582 of the substrate 580. And, as previously mentioned, the different thermoplastic polymers are compatible if they have the same polymer composition or are miscible with each other.

[0034] The composite melt filament 510 is guided through the liquefier 594 in a feed direction 600 and heated in the liquefier 594 to a processing temperature which is above the melting temperature (T M ) of the thermoplastic polymer containing the polymer coating 512, but below the clearing temperature (T C) of the thermotropic liquid crystal polymer containing one or more mesogenic reinforcement bodies 514. In this way, the liquefier 594 melts the polymer shell 512 of the composite melt filament 510, but not the mesogenic reinforcement body(s) 514, into an isotropic liquid. Instead, the one or more mesogenic reinforcement bodies 514 are maintained in a liquid crystal phase and thus remain structurally intact while the filament 510 is passed through the liquefier 594 and exhibits anisotropy. Thus, when the composite melt filament 510 is passed through the nozzle 598 onto the substrate 580 while at the processing temperature, the polymer shell 512 is in molten or liquefied form. And, although in molten form, the polymer shell 512 still covers the one or more mesogenic reinforcement bodies 514; it is just in a less viscous and more flowable state.

[0035] The composite melt filament 510 is deposited onto the substrate 580 in any desired pattern by relative movement between the movable coating head 588 and the substrate 580. As the composite melt filament 510 contacts the substrate 580 while the filament 510 is at its processing temperature, heat is transferred from the filament 510 to the substrate 580 at the interface between the filament 510 and the substrate 580. More specifically, heat is transferred from a deposited molten form 602 of the polymer cladding 512 of the filament 510 to the substrate 580, including the thermoplastic polymer 582 of the substrate 580. In fact, so much heat is transferred to the substrate 580 that a contact portion 604 of the thermoplastic polymer 582 of the substrate 580 melts to a depth within the substrate 580.The molten contact portion 604 of the thermoplastic polymer 582 mixes with the deposited melt 602 of the polymer cladding 512. Finally, after some time, the contact portion 604 of the thermoplastic polymer 582 and the deposited melt 602 of the polymer cladding cool and harden to form an interconnected polymer bond 606. The polymer bond 606 may be structurally reinforced by one or more mesogenic reinforcing bodies 514, which merge into the polymer bond 606 as the bond 606 hardens.

Claims

[1] A composite melt filament (10) comprising: a polymer sheath (12) having a longitudinal axis (22) along which a length (16) of the composite melt filament (10) is defined, wherein the polymer sheath (12) consists of a thermoplastic polymer having a melting temperature (T M ) has; one or more mesogenic reinforcement bodies (14) enclosed by the polymer shell (12), wherein the one or more mesogenic reinforcement bodies (14) consist of a thermotropic liquid crystal polymer having organized crystalline fibrils (24) aligned longitudinally along the longitudinal axis (22) of the polymer shell (12), wherein the thermotropic liquid crystal polymer of the one or more mesogenic reinforcement bodies (14) has a clearing temperature (T C ) which is greater than the melting temperature (T M ) of the thermoplastic polymer of the polymer sheath (12); wherein the thermotropic liquid crystal polymer has a crystallinity ranging from 50% to 100%; wherein the crystallinity is a ratio of a volume of the organized crystalline fibrils (24) to a total volume of the thermotropic liquid crystal polymer expressed as a percentage; and wherein the remainder of the total volume of the thermotropic liquid crystal polymer consists of amorphous regions (28) of the thermotropic liquid crystal polymer. [2] The composite melt filament (10) according to claim 1, wherein the melting temperature (T M ) of the thermoplastic polymer between 160°C and 350°C and the clearing temperature (T C ) of the thermotropic liquid crystal polymer is between 250°C and 400°C. [3] The composite melt filament (10) of claim 1, wherein the thermotropic liquid crystal polymer is a copolyester. [4] The composite melt filament (10) according to claim 3, wherein the thermotropic liquid crystal polymer is poly(4,4'-dihydroxybiphenyl-co-terephthalic acid), poly(4,4'-dihydroxybiphenyl-co-terephthalic acid-co-isophthalic acid), poly(hydroxybenzoic acid-co-2-hydroxy-6-naphthoic acid), poly(ethylene terephthalate-co-hydroxybenzoic acid) or poly(p-acetoxybenzoic acid-co-ethylene terephthalate). [5] The composite melt filament (10) of claim 1, wherein the thermotropic liquid crystal polymer is a copolyesteramide. [6] The composite melt filament (10) according to claim 5, wherein the thermotropic liquid crystal polymer is poly(6-hydroxy-2-naphthoic acid-co-terephthalic acid-co-4-aminophenol). [7] The composite melt filament (10) of claim 1, wherein the polymer cladding (12) is an annular polymer shell (46) and wherein the one or more mesogenic reinforcing bodies (14) is a single elongated liquid crystal polymer core (56) circumferentially surrounded by the annular polymer shell (46) and having the same length as the annular polymer shell (46). [8] The composite melt filament (110) of claim 1, wherein the polymer sheath (112) comprises an annular polymer sheath portion (146) and the one or more mesogenic reinforcing bodies (14) is an array (166) of elongated liquid crystal polymer cores (156) arranged in axial alignment along the longitudinal axis (122) of the polymer sheath (112). [9] The composite melt filament (210) of claim 1, wherein the polymer sheath (12) includes an annular polymer sheath portion (246) and the one or more mesogenic reinforcing bodies (214) is a plurality of continuous, elongated liquid crystal polymer cores (256) spaced within the polymer sheath (212) and surrounded by the annular polymer sheath portion of the polymer sheath (212), each of the plurality of continuous, elongated liquid crystal polymer cores having the same length (16) as the polymer sheath (212). [10] The composite melt filament (310) of claim 1, wherein the polymer sheath (312) comprises an annular polymer sheath portion and the one or more mesogenic reinforcing bodies (314) is a multiple row (366) of elongated liquid crystal polymer cores (356) that are in axial alignment along the longitudinal axis (322) of the polymer sheath (312).

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