Multilobal para-aramid fiber

Abstract

The invention pertains to a process for the manufacture of para-aramid filaments having a filament cross section with multiple lobes, comprising: - preparing a spin dope comprising para-aramid polymer and sulfuric acid, - passing the spin dope through a spinneret, - subsequently passing the spin dope through a gap with inert gas and a coagulation bath to form the filaments, wherein said spinneret comprises separate orifice clusters A, where an orifice cluster A comprises at least three separate spinning orifices B, wherein the spin dope is passed through the separate spinning orifices B to form a number of para-aramid filaments corresponding to the number of orifice clusters A. The invention also pertains to para-aramid filament having a filament cross section with multiple lobes, to multifilament yarn and to a textile fabric, paper, linear tension member, hose, composite or a penetration-resistant article comprising them.

Description

[0001] CQN3314

[0002] Multilobal para-aramid fiber

[0003] Description:

[0004] The present invention pertains to a process for the manufacture of para-aramid filaments having a filament cross section with multiple lobes and to para-aramid filaments with a multilobal cross section and multifilament yams comprising them. The invention in particular is directed to textile fabrics, linear tension members, papers, composites and hoses comprising the filaments and / or yarns and more in particular to penetration-resistant articles.

[0005] Para-aramid fibers are well-known and are used in a variety of applications where synthetic fibers with excellent mechanical properties in combination with low weight and a high temperature resistance are desired. For example, para-aramid fibers are used for penetration-resistant materials (e.g. anti-ballistic articles), for paper, for linear tension members and for the reinforcement of e.g. composites, hoses and mechanical rubber goods.

[0006] There is a desire to provide improved para-aramid filaments, in particular paraaramid filaments showing improved performance in a range of application areas, in particular when used in penetration-resistant articles and linear tension members. The performance of para-aramid fibers may be improved in various manners by modifying the para-aramid fibers. It is known to modify the cross section of aramid fibers to improve e.g. the adhesion between fiber and other materials, such as e.g. rubber.JP2018162529A describes a para-aramid fiber with a cross section having 2 to 15 concave portions, preferably 3 to 10. The fibers are produced by passing the spin dope through an accordingly shaped spinneret and through an air gap. The aim of the application is to provide a fiber with improved adhesion to matrix or resin materials, such as rubber. Due to the modified filament cross section, the surface area and the adhesiveness is increased. The fibers are particularly suitable for rubber reinforcement.

[0007] EP3286363A1 discloses cords comprising multifilament para-aramid yam comprising filaments, wherein the filaments have a non-round cross section having a smaller and a larger dimension. The cords have excellent fatigue properties. The spinneret orifices for obtaining this yarn have non-round, e.g. rectangular, openings.

[0008] KR19950014665B1 pertains to a wholly aromatic polyamide fiber having a modified cross section and a skin core structure which is produced by dissolving polyparaphenylene terephthalamide in sulfuric acid and extruding the spinning solution through a Y-shaped or T-shaped spinneret through an air layer into a coagulating solution.

[0009] JP2020059931 relates to aramid fiber bundles including fibers with a cross section having three convex portions and fibers with a cross section having four convex portions. These filaments are mixed in the fiber bundle. The purpose of using such filaments is to obtain a high-density fabric having high heat resistance. To obtain the filaments, spinnerets with Y or cross-shaped holes are used.

[0010] JP2014122448A discloses a wholly aromatic polyamide fiber having a modified cross section. In particular, the fiber has a shape in which at least two circles having the same diameter are overlapping in a straight line or are directly adjacentto each other. The fiber is suitable for use in resin-impregnated tape-like composites. Due to the alignment of the circles in a straight line, the fibers of JP2014122448A have an elongated cross section defined by a length and a width. JP2014122448A is silent on polygonal fiber cross sections.

[0011] KR20220049249A describes an aramid fiber with a peanut cross section. This shape causes excellent gloss when the fibers are used in a fabric and is also attractive for making a paper with a small amount of pores. The cross section of the fiber has two regions arranged along an axis. Hence, also KR20220049249A discloses fibers with an elongated cross section. KR20220049249A is silent on polygonal fiber cross sections.

[0012] There is a need in the art to provide further improved para-aramid filaments, in particular para-aramid filaments that provide articles comprising them with improved properties, in particular providing penetration-resistant article and linear tension members with improved properties such as improved penetration resistance or increased breaking strength at the same weight. In addition, there is a need for a simple process to obtain such filaments, preferably using simple spinning orifice geometries.

[0013] The present invention provides a process for manufacturing such filaments. The invention pertains to a process for the manufacture of para-aramid filaments having a filament cross section with multiple lobes, comprising:

[0014] - preparing a spin dope comprising para-aramid polymer and sulfuric acid,

[0015] - passing the spin dope through a spinneret,

[0016] - subsequently passing the spin dope through a gap with inert gas and a coagulation bath to form the filaments,

[0017] wherein said spinneret comprises separate orifice clusters A, where an orifice cluster A comprises at least three separate spinning orifices B,wherein the spin dope is passed through the separate spinning orifices B to form a number of para-aramid filaments corresponding to the number of orifice clusters A.

[0018] Preferably, the separate spinning orifices B are arranged in the form of a polygon.

[0019] In the context of the invention, filaments are to be understood as relatively flexible units of matter having a high ratio of length to width (where the width is perpendicular to their length and is defined by the cross section).

[0020] The process results in continuous para-aramid filaments, i.e. para-aramid filaments having a length of more than 100 cm. Usually, continuous filaments are of practically unlimited length, as obtained by a continuous spinning process.

[0021] Filaments obtained by such process result in an improved breaking strength and bending behavior of ropes, in an improved breaking strength of textile fabrics and in improved penetration-resistant properties.

[0022] Further advantages of the present invention and specific embodiments thereof will become apparent from the further specification.

[0023] The process employs a spinneret wherein a number of separate spinning orifices B are used to create one filament. The separate spinning orifices B are arranged in separate orifice clusters A in the spinneret and each orifice cluster A results in one filament.

[0024] Preferably, the separate spinning orifices B have a round cross section. More preferably, all separate spinning orifices B within a cluster A have the same, even more preferably round, cross section. Preferably, all separate spinning orifices B within the spinneret (i.e. in all separate orifice clusters A) have the same, preferably round, cross section. Preferably, the cross sections of all separate spinning orifice B within an orifice cluster and / or within a spinneret have the same diameter. Hence, by using a spinneret with (same-sized) round orifices, paraaramid filaments with a non-round filament cross section may be created. It is well-known and easier to produce spinnerets with conventional round orificescompared to producing spinnerets with non-conventional orifice cross sections such as the Y-shaped, cross shaped or T-shaped orifices described in the prior art for producing aramid fibers with modified cross section.

[0025] During the spinning process, which will be further elucidated below, the spin dope exiting the separate spinning orifices B will pass through a gap with inert gas (which may also be referred to as air gap) and the separate spin dope streams originating from one orifice cluster A will be at least partially fused into one filament during passage through the air gap. In the cross section of the para-aramid filaments the origin from separate orifices is still to some extent visible and the filaments obtained from instant process have a multilobal cross section.

[0026] In one embodiment, the number of separate spinning orifices B (within one separate orifice cluster A) is equal to the number of lobes present in the cross section of the resulting filament. For example, using a spinneret comprising separate orifice clusters A comprising 3 separate spinning orifices B will result in a para-aramid filament having a trilobal cross section.

[0027] While it is possible to produce a monofilament with instant method when using a spinneret with a single orifice cluster A, the method is particularly suitable to manufacture bundles of filaments (also referred to as multifilament yam). In the embodiment where a multifilament yarn comprising multiple para-aramid filaments having a cross section with multiple lobes is produced, the number of the separate orifice clusters A (NA) will determine the number of filaments, while the number of separate spinning orifices B (NB) per separate orifice cluster A will determine the number of lobes per filament. NA X NB provides the total number of openings in the spinneret.

[0028] It is noted that during a regular spinning process where one spinning orifice results in one filament, by mistake a fusion of (usually at most two) filaments may also occur. However, in those cases the (partial) fusion may occur in the coagulation bath which will result in a different cross section as can be determined by theskilled person by microscopy. Fig. 1a shows a microscopy image of cross sections of filaments according to the invention with 3 lobes and Fig. 1b shows an example of a non-intentional fusion of a low number of filaments.

[0029] Furthermore, the non-intentional fusion shown in the image of Fig. 1b will at most occur for a few filaments of a bundle of filaments while instant method results in a bundle of filaments where at least 90% of the filaments, preferably at least 95%, even more preferably 100% of the filaments (based on the number of filaments in a bundle) have a cross section with multiple lobes. This percentage may be determined by microscopy of a cross section of the bundle.

[0030] The number of separate spinning orifices B (NB) comprised in a separate orifice cluster A is preferably in the range of 3 to 10, more preferably 3 to 7. NB may for example be 4, 5 or 6. Preferably, the number of separate spinning orifices B is the same in each orifice cluster A of one spinneret, more preferably, all separate spinning orifices B of one spinneret have the same, preferably round, cross section and dimension.

[0031] However, it is also possible to combine in one spinneret separate orifice clusters A including a different number of separate spinning orifices B to obtain a yam comprising para-aramid filaments with different multilobal cross section, e.g. including filaments with trilobal and quadrilobal cross section. The ratio between the numbers of separate orifice cluster A with different NB may be varied.

[0032] In a preferred embodiment, the para-aramid filament has a trilobal cross section and the spinneret comprises 3 separate spinning orifices B per separate orifice cluster A. More preferably, each separate spinning orifice B of the spinneret has a round cross section of the same dimension in this embodiment.

[0033] The number of separate orifice clusters A (NA) in one spinneret may be in the range of 100 to 5000, preferably 300 to 3000, more preferably 350 to 2000, even more preferably 400 to 1000, resulting in a corresponding filament number.Depending on the number of separate spinning orifices B within one orifice cluster A, the separate spinning orifices B may be arranged differently. Preferably, the separate spinning orifices B are arranged in a regular geometric pattern within one orifice cluster A, i.e. if NB is 3, the separate spinning orifices may be arranged in the form of a triangle, preferably an equilateral triangle within orifice cluster A. If NB is 4, the separate spinning orifices may be arranged in the form of a rectangle, preferably a square form. If NB is 5, the separate spinning orifices may be arranged in the form of a pentagon, preferably an equilateral pentagon. If NB is 6, the separate spinning orifices may be arranged in the form of a hexagon, preferably an equilateral hexagon etc.

[0034] Hence, where NB is at least 3, the separate spinning orifices B will not be arranged in a straight line. Preferably, where NB is at least 3, the separate spinning orifices B of a cluster A will be arranged in the form of a polygon, more preferably a regular (i.e. equilateral and equiangular) convex polygon. However, the separate spinning orifices B may also be arranged in the form of an irregular polygon in one embodiment.

[0035] The separate spinning orifices B form separate openings in the material of the spinneret such that separate streams of spin dope leave the orifices. The separate spinning orifices B do not overlap and are not in contact with each other or adjacent in contact to each other. Preferably, the separate spinning orifices B have a diameter in the range of 30 to 70, preferably 40 to 60 pm and a center-to-center distance between neighboring separate spinning orifices B of an orifice cluster A is in the range of 50 to 500, preferably 100 to 250 pm. The diameter and center-to-center distance refer to the dimensions of the orifices at the exit surface of the spinneret plate. As described in EP2764141, the spinning orifices in a spinneret form a (usually cylindrical) capillary between the entrance and exit surface of the spinneret plate. The capillary may have a wider opening in the entry surface and a smaller opening in the exit surface, e.g., by having a conical entrance. Preferably the capillary at the exit is cylindrical.

[0036] Preferably, the minimum distance between the centers of adjacent orifice clusters A is at least 500 pm, more preferably in the range of 700 to 1200 pm, where thecenter of an orifice cluster A is the point which is equidistant to the center of each separate spinning orifice B within said orifice cluster A.

[0037] Spinnerets for the spinning of para-aramid filaments are known to the person skilled in the art. The spinnerets used for the method of instant invention may be produced in the known way from known materials, provided that the desired number of separate spinning orifices B are arranged in separate orifice clusters A in any of the embodiments described above. Further reference is made to EP0904431 , which describes how orifices may be arranged within a spinneret plate. In the same way, the orifice clusters A may be arranged in fields within a spinneret. EP1470271 also discloses spinnerets, their dimensions and a detailed description of a suitable spinning process. Further reference is made to EP0741805, which discloses gold-platinum alloys which are suitable for making spinnerets suitable for a spin dope comprising para-aramid polymer and sulfuric acid.

[0038] The process of instant invention comprises the preparation of a spin dope.

[0039] For preparation of the spin dope, para-aramid polymer and as solvent sulfuric acid are combined.

[0040] For the purpose of this invention, the term para-aramid refers to a class of wholly aromatic polyamide polymers and copolymers having at least 60%, preferably at least 80% and more preferably at least 90% of para-oriented bonds between the aromatic moieties. In one embodiment, at least 95% or all (i.e. 100%) of the bonds are para-oriented bonds.

[0041] Typical para-aramids are poly(para-phenylene terephthalamide) (PPTA), poly(4,4'-benzanilide terephthalamide), poly(para-phenylene-4,4'-biphenylene dicarboxamide) and poly(para-phenylene-2,6-naphthalene dicarboxamide), 5,4'-diamino-2-phenylbenzimidazole or copolymers thereof. A preferred para-aramid polymer for instant invention is PPTA. Methods to synthesize para-aramid polymerare known to those skilled in the art and typically involve the polycondensation of aromatic diamines with aromatic diacid halides.

[0042] Preferably, the sulfuric acid used as solvent for the para-aramid polymer has a concentration of at least 95%, more preferably at least 98% and even more preferably of at least 99%.

[0043] In one embodiment the sulfuric acid has a concentration of at least 100%, or even at least 102%. Sulfuric acid having a concentration of more than 100% may be obtained by combining sulfuric acid and oleum.

[0044] The sulfuric acid may be in liquid or solid form. Solid sulfuric acid is obtained by freezing sulfuric acid below its solidifying temperature.

[0045] Preferably, the para-aramid polymer and the sulfuric acid are mixed in a mixing device with a continuous flow.

[0046] The mixing device may for example be a kneader or extruder, preferably a single shaft kneader, double shaft kneader, single screw extruder or twin screw extruder. Reference is made to EP1805248, EP0823872 and EP2118176 which describe different suitable embodiments of preparing a spin dope in detail.

[0047] Preferably, the spin dope has a para-aramid concentration of 12-22 wt%, more preferably the spin dope has a para-aramid concentration in the range of 15-21 wt%, even more preferably a para-aramid concentration of 18-20 wt%, even more preferably a para-aramid concentration of 18.5 to 19.8 wt% or 18.7 to 19.3 wt%, based on the weight of the aramid spin dope.

[0048] Subsequently, the para-aramid spin dope is processed into a para-aramid filament by the well-known dry-jet wet spinning process. This process is described in more detail for instance in US3414645 and US4016236. The dry-jet wet spinning process comprises extruding the liquid spin dope through the spinneret into a gap with inert gas, such as air, and immediately afterwards into a coagulation bath. In the air zone (also referred to as air gap) through which the spinning mass passes, the para-aramid is drawn. Preferably, the drawing ratio is in the range of 3 to 12,more preferably in the range of 5 to 10, where the drawing ratio refers to the ratio of [the speed (meters / minute) of winding of the yam onto a bobbin after drying] divided by [the speed (meters / minute) of extrusion at the spinneret].

[0049] Preferably, the spinning speed, i.e. the speed of winding of the filaments onto a bobbin after drying is at least 200 m / min, more preferably at least 250 m / min.

[0050] Preferably, this gap with inert gas has a length in the range of 6 to 25 mm, more preferably 10 to 20 mm, even more preferably 12 to 18 mm. Hence, the air gap length is preferably longer than in a conventional spinning process where no fusion is intended. By adjusting the length of the air gap and by adjusting the distance between separate spinning orifices B within one orifice cluster A the extent of fusion of the spin dope originating from one orifice cluster A may be adjusted.

[0051] Usually, the separate spin mass streams exiting the separate spinning orifices B originating from one orifice cluster A will be at least partially fused during passage through the air gap.

[0052] After the air gap, the spin mass in the form of filaments will be passed through the coagulation bath to coagulate the filaments.

[0053] The composition of the coagulation bath may vary. It may entirely or partly consist of water or other substances, such as bases, acids, salts and organic solvents. The coagulation bath preferably consists of dilute aqueous sulfuric acid having a concentration of 0-40% by weight, preferably 5-20 wt%. According to one embodiment, the coagulation bath may consist of a diluted caustic aqueous solution e.g. an aqueous NaOH solution with a concentration of 0-10% by weight, preferably 0.05 to 5% by weight and in particular 0.1 to 1% by weight. According to another embodiment, the coagulation bath has a pH of between 4 and 11 , preferably between 5 and 10 and in particular between 6 and 8. The coagulation bath may consist of water, in particular softened or demineralized water.The temperature of the coagulation bath may have any value desired. Depending on the other spinning conditions the temperature of the coagulation bath is generally in the range of -10°C to 50°C, and preferably between 0°C and 25°C.

[0054] As small amounts of residual acid may have a detrimental influence on the fiber properties, the sulfuric acid used should preferably be removed from the spun filaments, in particular by washing or neutralization and washing. Hence, after the coagulation the filaments formed are preferably removed from the coagulation bath, washed, dried and taken up on a bobbin. In one embodiment, after a first washing step, the filaments are neutralized and washed again before being dried. The filaments may be subjected to a wet or hot drawing step before or after taking them up on a bobbin.

[0055] The neutralization may be done by subjecting the fiber obtained by coagulation to a treatment at room temperature or at elevated temperature with solutions of alkaline substances, for instance caustic solutions of NaOH, NaHCOs or Na2CO3. In one embodiment, the filaments are treated after coagulation with solutions having a NaOH concentration in the range of 0.1 to 2 wt%, preferably 0.3 to 1 wt%. Preferably, the neutralization solution has a pH of at least 9, more preferably at least 11.

[0056] In one embodiment, the filaments are only treated with water or diluted acid (e.g. demineralized water or softened water) after coagulation, in particular once, twice, three or more than three times (only washing, without neutralization).

[0057] In a preferred embodiment, the filaments are washed, neutralized and again washed.

[0058] After they have been washed, the filaments are dried. This may be done in any convenient way, either on-line or off-line. It is preferred that the drying should be carried out immediately after (neutralization and) washing, e.g. by passing the filaments over heated rollers having a temperature in the range of 50 to 220°C,preferably in the range of 75 to 200°C, more preferably in the range of 100 to 175°C or 125 to 150°C.

[0059] The filaments may be subjected to a (dry) heat treatment, in which the filaments are heated under tension in an inert or non-inert gas. The heat treatment may be carried out after the drying step (online) or otherwise after the winding of the filament (offline).

[0060] The heat treatment may comprise one or multiple steps of heating under tension. In one embodiment, the process according to the invention comprises heating the filament in at least one heating step to a temperature in the range of 180 to 400°C, preferably in the range of 280 to 350°C, preferably in the range of 300 to 320°C.

[0061] The heat treatment of the filament may comprise at least two steps. In one process according to the invention, the filament obtained in the first heating step as described above is heated in a second heating step to a temperature in the range of 190 to 400°C, preferably in the range of 280 to 350°C, preferably in the range of 300 to 320°C.

[0062] In a preferred embodiment, during at least one of the heating steps a tension is applied which results in a drawing ratio in the range of 1.0 to 2.0, preferably 1.001 to 1.050 and during the other heating step no tension (relaxation) is applied or a tension which is sufficient to allow transport of the filament over processing equipment (e.g. guiding rolls). Higher tension may be applied either in the first or the second heating step. Preferably, a higher drawing ratio is applied in the first heating step.

[0063] In another embodiment, during each of the heating steps a tension is applied, which results in a total drawing ratio in the range of 1.0 to 2.0, preferably 1.001 to 1.050.

[0064] At this stage of the process, the drawing ratio may be defined as [length of the filament after heating step] I [length of the filament before heating step]. The drawing ratio refers to one heat treatment step, the total drawing ratio to thedrawing achieved in all applied heat treatment steps (accumulated). For a continuous online process the drawing ratio may also be determined based on the speed of the godets guiding the yarn before and after the heat treatment, thus [speed of godet after at least one heating step] I [speed of godet before at least one heating step].

[0065] Instant invention also pertains to a para-aramid filament obtainable by the embodiments of the process described above.

[0066] Instant invention also pertains to a para-aramid filament having a filament cross section with n lobes, where n is at least 3 and wherein the filament comprises multiple para-aramid subfilaments, where n = 3, 4, 5 or 6, and the lowest secondary minimum M2 of the Distance Distribution Function (DDF) of the filament cross section has a normalized value m2 in the range of 0.2 to 0.8, preferably in the range of 0.3 to 0.7, and more preferably in the range of 0.4 to 0.6, as determined by OpenCV image analysis software version 4.10.0 for Python. The para-aramid subfilaments form the lobes of the cross section and originate from the spin dope passing through separate spinning orifices B.

[0067] The para-aramid subfilaments are at least partially fused. As described above, the (at least partial) fusion may occur when the spin dope passes through the air gap. The para-aramid filaments comprise fused subfilaments, forming the lobes of the filament. In the cross section of every filament the subfilaments may be modelled as overlapping circles. The lobes (or circles) form convex portions of the cross sections. Where the lobes meet at the perimeter of the cross section, the cross section will usually have a groove or incision-shaped concavity or indentation. The grooves may also be visible using microscopy when observing the surface of the filaments along their length direction.

[0068] The subfilaments, lobes and indentations are visible in a microscopy image of a cross section of the para-aramid filaments. In some embodiments, the fusion sites within the filament cross section (and in some embodiments the number thereof) are also visible in the microscopy images. Preferably, the subfilaments formprojections along a circumferential direction of the filament. Preferably, in the filament cross section, the center points of the circular projections are arranged on a (nearly) circular form where the center points are preferentially clustered on one side of this (nearly) circular form.

[0069] This can e.g. be seen in Fig. 1a: the darker sites within the filament cross section are fusion sites. However, visible fusion sites may also be (almost) absent from the cross section. Both cases are different from filaments spun from Y-, cross- or T-shaped spinnerets of the prior art where no fusion occurs but instead the filament is extruded from a spinneret opening with the respective shape.

[0070] In some embodiments, the fusion sites may create defect-like structures extending at least partly in the longitudinal direction within the para-aramid filaments.

[0071] Therefore, in some embodiments longitudinal cross sections of the para-aramid filaments may show localized defects.

[0072] In some embodiments, the fused character of the filaments may be reflected in the behavior of the filaments upon mechanical impact or stress. For example, the filaments may split into the number of subfilaments corresponding to the number of lobes present in the cross section.

[0073] For example, upon mechanical impact which breaks the filament, the filament may split up into the subfilaments, such as shown in Fig. 2.

[0074] Preferably, the para-aramid filaments (including the subfilaments) have a linear density in the range of 0.5 to 25 dtex, preferably 1 to 15 dtex, more preferably 1.5 to 10 dtex.

[0075] Preferably, the para-aramid filaments have a trilobal cross section. Para-aramid filaments having a trilobal cross section may be obtained by spinning from a spinneret where NB is 3.The filaments may comprise more than 3 subfilaments by spinning from a spinneret where NB is larger than 3 and accordingly, the cross section of the paraaramid filaments may comprise more than 3 lobes. For example, the filaments may comprise 4 subfilaments (NB = 4) and the corresponding number of lobes, 5 subfilaments (NB = 5) and the corresponding number of lobes or 6 subfilaments (NB = 6) and the corresponding number of lobes.

[0076] The para-aramid filaments having a cross section with multiple lobes have a distinct cross sectional shape, which is influenced by NB and the geometrical pattern of the separate spinning orifices B within an orifice cluster A. The filament cross section shape may be characterized by different parameters.

[0077] To determine the cross sectional shape, microscopy images of the filament cross sections may be analyzed using the OpenCV image analysis software version 4.10.0 for Python as described herein and in the Methods section below. In particular, the normalized value m2 of the lowest secondary minimum M2 of the Distance Distribution Function (DDF) and the value of the n-circle shape factor Sn may be used to define the shape of the filament cross section with n lobes.

[0078] Usually, the cross section of the multilobal para-aramid filament is characterized by a Distance Distribution Function that preferably has two main peaks, which are the left-most and the right-most peaks of the DDF, and one or more secondary minima, which are located between these two main peaks. The two main peaks (indicated as P1 and P2 in Figures 3a and 4a) may be symmetry-related to good approximation in terms of position, width and height. Fig. 3a shows the DDF of a trilobal filament cross section and Fig. 3b the fit of a 3-circle model to the trilobal cross section. Fig. 4a and 4b show the same for a filament with a 6-lobal cross section. For the multilobal para-aramid filaments of the invention with n lobes, where n = 3, 4, 5, or 6, the lowest secondary minimum M2 of the DDF of the filaments preferably has a normalized value m2 in the range 0.2 to 0.8, more preferably in the range 0.3 to 0.7, and even more preferably in the range 0.4 to 0.6 or of 0.35 to 0.5, as determined by OpenCV image analysis software version 4.10.0 for Python.In one embodiment, the multilobal para-aramid filament with n lobes, where n = 3, 4, 5, or 6, is characterized by an n-circle shape factor Sn in the range 0.85 to 1.0, preferably 0.87 to 0.96, more preferably 0.9 to 0.98, as determined by OpenCV image analysis software version 4.10.0 for Python.

[0079] A detailed description of the method how to determine M2 and Sn is provided below and in the Methods section. The values m2 and Sn are average values based on the determination of at least 10 filament cross sections.

[0080] The Distance Distribution Function d(s) is a signature of the filament cross section, where s is the position along the filament cross section perimeter starting at the point on the perimeter which has the shortest distance to the center of gravity of the cross section (at this point of the perimeter s = 0). The coordinates X and Y of the center of gravity (X, Y) are the averages of the coordinates x and y respectively of all pixels of the cross section. The function d(s) gives for each s the distance at position s to the center of gravity of the cross section. Here s ranges from 0 to 1 , since it is normalized with the total length A of the filament cross section perimeter and the distance d(s) is greater than or equal to 1 , since it is normalized by the shortest distance. In general, the peaks of the DDF of any cross section correspond to the lobes of the cross section and the minima of the DDF correspond to the concavities in the cross section. The DDF is a useful tool to characterize the filament cross section shape of the para-aramid filaments according to the invention, since these para-aramid filaments preferably comprise (partially) fused subfilaments, where each subfilament forms a lobe of the filament cross section, with concavities where the lobes meet at the perimeter of the filament cross section. Thus, the DDF of multi-lobal para-aramid filaments according to the invention with NB = 3 shows preferably 3 peaks (see Fig. 3a), with NB = 4 the DDF shows preferably 4 (overlapping) peaks, and so on. Although the number of peaks of the DDF may be different depending on NB, the normalized value m2 of the lowest secondary minimum M2 between the two main peaks P1 and P2 may be similar, see Fig. 3a and 4a. The two main peaks P1 and P2 correspond to the 2 main lobes of the filament cross section of the invention, whichare preferably related by mirror symmetry. The lowest minimum M1 of the DDF is located at s = 0 with DDF value d(0) = 1. This is the primary minimum, which corresponds to the main concavity of the filament’s cross section, see Figures 3a, 3b, 4a and 4b. The secondary minima of which M2 is the lowest, are preferably less deep and correspond to the filament’s minor concavities.

[0081] The fused subfilaments that preferably form the cross section of every n-lobal filament with NB = n according to the invention can be modelled as n overlapping circles. Preferably, para-aramid filaments according to the invention with a trilobal cross section may have a close to triangular-shaped cross section. Interestingly, if the separate spinning orifices B within an orifice cluster A are arranged in a triangular pattern with 3-fold rotational symmetry the filament cross section may not have this 3-fold rotational symmetry, but the cross section may display (approximate) mirror symmetry, i.e. a triangle placed in the cross section (where the corners of the triangle correspond to the center points of the subfilaments) is not an equilateral triangle, but instead the triangle has a base which is larger than its two other sides, i.e. the triangle is an isosceles triangle. When NB is higher than 3 and the separate spinning orifices B within an orifice cluster A are arranged in a regular geometrical pattern (e.g. a square, an equilateral pentagon, an equilateral hexagon, i.e. a polygon), the filament cross section will comprise the respective number of subfilaments, but the subfilaments may be arranged in a different shape compared to the arrangement of the separate spinning orifices B, e.g. in the form of a curved row of subfilaments resulting in a cross section with corresponding lobes, similar to a sickle. Thus, in the cross section the centers of all lobes (or subfilaments) of one filament may not be arranged in a straight line, but as a polygon. The sickle can be modelled, e.g. by an isosceles trapezium for a 4-lobal cross-section, as outlined in the Methods section. Images of cross sections of para-aramid filaments having 4, 5 or 6 subfilaments are shown in the Example section. For n-lobal filaments with n = 4, 5 or 6, the cross section shape may display (approximate) mirror symmetry, the mirror plane being perpendicular to the plane of the cross section. Clearly a cross-section shape that displays(approximate) mirror symmetry will have an (approximately) symmetric DDF, since the DDF is a quantitative description of the shape of the cross-section.

[0082] The cross section of para-aramid filaments with a trilobal cross section according to the invention may be modelled using a 3-circle model, thus modelling the 3 (partially) fused subfilaments. In this model the centers of 3 circles with equal diameters form an isosceles triangle where the center points of the circles are at the corners of the isosceles triangle. Each individual filament cross section in a microcopy image is fitted using the 3-circle model employing image analysis software as described in the Methods section. In a constrained fit the difference between the 3-circle outer perimeter and the filament cross section perimeter is minimized (see Fig. 3b), the fit parameters being the circle radius and the 2 parameters that define the isosceles triangle, i.e. its base length and angle. The 3-circle shape factor S3 is a goodness-of-fit factor that measures how well each filament cross section can be described by the 3-circle model. The shape factor is based on the area common to the cross section area of the trilobal filament and the area bounded by the outer perimeter of the fitted 3 circles. The shape factor is determined automatically by the OpenCV image analysis software version 4.10.0 for Python. The S3 factor quantifies the degree to which the filament shape can be described by 3 equal-diameter fused subfilaments with their center points at the isosceles triangle comers:

[0083] S3 = (common area of A and Asc)21 ( ■ Asc),

[0084] where A is the area of the filament cross section and Asc is the area bounded by the outer perimeter of the fitted 3 circles of the 3-circle model. A perfect filament formed from 3 (partially) fused subfilaments with their center points at isosceles triangle comers has a shape factor S3 of 1 , which is the highest value possible. By analogy, the n-circle shape factor Sn is defined for multilobal filaments produced with NB = n where n = 4, 5, or 6.

[0085] Present invention also pertains to a multifilament yam comprising the para-aramid filament of any of the embodiments described above.Preferably, the multifilament yam comprising the para-aramid filaments comprises at least 90%, more preferably at least 95%, even more preferably 100% of paraaramid filaments having a cross section with multiple lobes.

[0086] The multifilament yam may comprise 100 to 5000, preferably 300 to 3000, more preferably 350 to 2000, even more preferably 400 to 1000 para-aramid filaments having a filament cross section with multiple lobes.

[0087] The multifilament yam may have a linear density of 500 to 2500 dtex, preferably 700 to 2000 dtex.

[0088] Surprisingly, even though the filaments comprise (at least partly) fused subfilaments, the multifilament yam of present invention has good mechanical properties.

[0089] The multifilament yam preferably has a breaking tenacity of at least 1800 mN / tex, more preferably at least 2100 mN / tex, even more preferably at least 2300 mN / tex. The multifilament yam preferably has a modulus of at least 60 GPa, more preferably at least 70 GPa, even more preferably at least 80 GPa.

[0090] The multifilament preferably has an elongation at break in the range of 2 to 5%, preferably 2.5 to 4 %.

[0091] The multifilament yam preferably has a toughness at rupture (ToAR) of at least 30 J / g, preferably at least 35 J / g, more preferably at least 40 J / g. The toughness at rupture is also referred to as toughness, breaking toughness or fracture toughness. Toughness is the ability of the fiber to resist breaking under stress. The toughness is the area under the stress-strain curve.

[0092] The mechanical properties are determined according to ASTM D7269 as described in the method section.

[0093] The multifilament yam comprising para-aramid filaments according to the invention, in particular comprising filaments with a trilobal cross section, may havea close packing fraction higher than the hexagonal close packing fraction of filaments with circular cross section (0.91). If the trilobal filaments are modelled using the 3-circle model as outlined in the Methods section, a close packing fraction of trilobal filaments higher than 0.91 may be obtained, preferably at least 0.93. The close packing fraction is defined as the largest surface fraction that can be obtained by covering a surface with filament cross sections placed side-by-side touching each other. This fraction can be determined using OpenCV image analysis software version 4.10.0 for Python, see Fig. 13, which shows an example that has a close packing fraction of 0.939, where the parameters of the 3-circle model are average parameters (i.e. averaged over 1172 trilobal filaments).

[0094] The filaments and the multifilament yam according to the invention are particularly suitable for use in textile fabrics, papers, linear tension members, rubber reinforcements, such as e.g. in tires and hoses, and composites.

[0095] Hence, instant invention also pertains to a textile fabric, paper, linear tension member, tire, hose or composite comprising the filaments and / or the multifilament yam of any of the embodiments described herein. Surprisingly, even though the mechanical properties of the multifilament yam may be comparable to para-aramid multifilament yam comprising filaments with conventional circular cross section or even lower in some instances, the fabrics, ropes and other article comprising the filaments and multifilament yams according to the invention show improved mechanical properties.

[0096] Papers comprising the para-aramid filaments or multifilament yam may have higher strength, in particular when comprising trilobal para-aramid filaments. The para-aramid filaments or multifilament yam may be used in the form of short-cut or pulp. The papers may comprise or consist of the para-aramid filaments having a filament cross section with multiple lobes.

[0097] Present invention also pertains to pulp comprising the para-aramid filaments having a filament cross section with multiple lobes. Pulp may be obtained byfibrillating multifilament yarn in a watery slurry in a refiner, e.g. as described in EP2013411, EP2992139 and EP2871282.

[0098] The para-aramid filaments and multifilament yams of present invention provide also attractive properties to linear tension members. Linear tension members are defined as elongated objects of which one dimension is much larger than the other two dimensions, which have a linear mass density of at least 10000 dtex, preferably at least 25000 dtex. Non-limiting examples of linear tension members are ropes, lines, tethers, mooring lines, tow lines and cables. The linear tension member of the present invention preferably comprise multiple multifilament yams comprising para-aramid filaments having a filament cross section with multiple lobes, preferably with 3 lobes, being in close contact which each other obtained by twisting, spiralling, braiding, entangling, knitting or any combination of these methods.

[0099] In a linear tension member the filaments or multifilament yams and / or strands formed thereof are generally arranged in lengthwise direction.

[0100] In one embodiment for at least some of the filaments or multifilament yams the distance of fibers or yams to a central longitudinal axis within the linear tension members varies over the length of the linear tension member. This means that at least some of the fibers or yams are arranged to show a repeating oscillation pattern. Generally, the fiber or yam in such a linear tension member has a helix angle of more than 2°.

[0101] In another embodiment the filaments or multifilament yams of the linear tension member are combined by laying at least two multifilament yams or strands in parallel and surrounding them by a sleeve, wrap or polymeric coating to keep the individual yams or strands tightly together and to protect the linear tension member. Generally, if arranged in parallel, the yams or strands have a helix angle of 2° or less. Such an arrangement results in a unidirectional (UD) linear tension member.Independently of the way of combining the fibers of the linear tension member, a mantle may be used to protect the linear tension member from particle ingress, e.g. from sand particles. The mantle, possibly in form of a sleeve, wrap or coating can cover the whole length of the linear tension member, only parts of it or e.g. only the splice site. At splice sites the ends of two linear tension members are combined to result in one, longer linear tension member.

[0102] Surprisingly, linear tension members comprising the filaments or multifilament yams of the invention show improved fatigue properties, i.e. improved resistance against repeated stresses such as bending and compression (as determined by the Alma Bending Fatigue test and the Goodrich Block Fatigue test), i.e. require more cycles at specific loads to fail. Furthermore, the linear tension members may have an increased breaking strength (15 - 20%) compared to linear tension members comprising filaments with circular cross section of the same linear density. In addition, the linear tension members of the invention preferably have an increased Flory abrasion resistance, as determined in an AYY (yam to yam) dry and wet abrasion test.

[0103] The para-aramid filaments and multifilament yams of instant invention may also be used for the reinforcement of hoses and composites.

[0104] The para-aramid filaments and multifilament yams of instant invention are particularly suitable for use in textile fabrics.

[0105] A textile fabric is a two dimensional (2D) plane-like structure made of textile materials such as e.g. fibers (which may take the form of e.g. filaments, yams or spun yams).

[0106] The textile fabric may be selected from a woven fabric, a knitted fabric, a laminate, a unidirectional layer, multiaxial layer or a biaxial layer.Textile fabrics based on para-aramid filaments may be used for a wide range of application areas, in particular for cut-resistant and penetration-resistant applications.

[0107] For example, textile fabrics may be used to make protective clothing, e.g. cut-resistant clothing, such as protective gloves. These woven and knitted textile fabrics may have improved processability, improved touch hand and feel (i.e. they feel softer) combined with the same cut resistance compared to textile fabrics based on spun yams made from para-aramid fibers with conventional round cross section. They may also show improved wickability. Usually, spun yams based on para-aramid staple fibers are used for making such cut resistant textile fabrics. This process requires the manufacture of staple fibers, crimping them and producing spun yam from them which can subsequently be processed into a textile fabric. For multifilament yam comprising para-aramid filaments having a filament cross section with multiple lobes, in particular comprising 3 lobes, these steps are not necessary, instead the multifilament yam may be directly processed into a (knitted or woven) textile fabric which results in a more efficient and lower-cost process.

[0108] Preferably, the multifilament yam comprising para-aramid filaments having a filament cross section with multiple lobes having a twist in the range of 200 to 400 tpm is used for textile fabrics, in particular for such cut-resistant articles, more preferably in the form of woven or knitted textile fabrics.

[0109] Preferably, the para-aramid filaments or the multifilament yam comprising said filaments is subjected to hot washing (e.g. using a washing liquid having a temperature of 98°C) and / or the fabric is subjected to a dry hot treatment.

[0110] Hence, instant invention also pertains to a cut-resistant article comprising the para-aramid filaments and / or the multifilament yam and / or the textile fabric of the embodiments described herein, preferably an article of clothing.The para-aramid filaments having a filament cross section with multiple lobes and the multifilament yams comprising them are particularly advantageous for use in textile fabrics for penetration-resistant articles and increase the V50 and V05 of such articles at the same areal weight. V50 is the velocity at which 50% of the bullets are stopped and 50% of the bullets give full penetration, V05 is the velocity at which 95% of the bullets are stopped and 5% of the bullets give full penetration. Such textile fabrics offer penetration-resistance, i.e. protection against attacks by projectiles, stabbing, and explosive weapons (which may also be referred to as ballistic resistant). The attack with projectile weapons can occur with bullet-shaped or fragmented ammunition, so that a penetration-resistant textile fabric should preferably provide protection from both bullets and fragments. It is noted that the term “penetration-resistance” includes the situation where the material is partially penetrated and captures the projectile or fragment or stabbing object and hence the attack is stopped by the material.

[0111] In view of the para-aramid filament characteristics, i.e. the fused character of the filament, a person skilled in the art would have to expect that the protection against penetration of a textile fabric which comprises a yarn of this type would be reduced. Therefore, it is indeed surprising for a person skilled in the art when the protection against penetration of a textile fabric which contains a yam of this type is increased. It may be speculated that the fused filament is (at least partly) split into the subfilaments upon impact and that this increases the potential to dissipate the energy of the impact and hence increases the penetration resistance.

[0112] Hence, instant invention also pertains to a penetration-resistant article comprising the para-aramid filaments and / or the multifilament yam and / or the textile fabric of the embodiments described herein, preferably an article of clothing, a panel, a helmet, a (vehicle) armor plate, a fragment protection mat, a bullet-resistant vest, a flak jacket or a stab-resistant vest.

[0113] Preferably, the penetration-resistant article comprises at least one textile fabric in form of a fibrous layer comprising the para-aramid filaments with a filament crosssection having multiple, preferably three, lobes. The fibrous layer may be formed as a nonwoven, knitted or woven fabric, or as a unidirectional, biaxial or multiaxial layer, preferably as a unidirectional layer, i.e. the fibers are unidirectionally aligned so that they are substantially parallel to each other along a common fiber direction. While unidirectional layers are preferred, the textile fabric may also be a woven fabric having a plain, satin and / or twill weave. It may also be possible to combine woven fabrics and unidirectional layers. It may also be possible to make fabrics of the multifilament yam which combine within one fabric regions of different density, e.g. by combining different weaves within one fabric, such as described in EP2293932. Preferably, multiple fibrous layers are stacked to result in a penetration-resistant article. The fibrous layer may comprise the para-aramid filaments or multifilament yams of the invention and a matrix material. The term "matrix material" means a material, which in particular bonds fibers within a single fibrous layer to one another and thereby stabilizes the single fibrous layer. The matrix material may e.g. be a styrene butadiene random copolymer resin, a selfcrosslinking or crosslinkable acrylic resin, a polyvinylbutyral resin as described in EP2753890 or a thermoplastic resin.

[0114] The weight percentage of the matrix material with respect to combined weight of the filaments and the matrix material is in the range of 1 to 30 wt%, preferably 5 to 25 wt%, more preferably 10 to 20 wt%. The use of the para-aramid filaments of instant invention may allow to lower the matrix material content.

[0115] The penetration-resistant article may comprise 2 to 250 fibrous layers, preferably 10 to 100 fibrous layers. Where unidirectional fibrous layers are combined, they may preferably be cross-plied at a cross-plying angle ranging from 0° to 90°, the latter being preferred. Subsequently, the fibrous layers may be adhered to one another e.g. by laminating, pressing or by any other procedure which is capable to generate adhesion between the adjacent fibrous layers. The temperature and pressure conditions are chosen dependent on the matrix material. The textile fabrics according to the invention may also be formed into laminates by stacking them alternatingly with thermoplastic layers, e.g. thermoplastic elastomer layers as described in EP1399703.However, the textile fabrics according to the invention may also be used without matrix, e.g. for soft ballistic applications.

[0116] The textile fabrics according to the invention may also be combined with other materials to form hybrids, e.g. hybrid materials comprising the multilobal filaments of the invention and polyolefin tapes or filaments, e.g. polyethylene tapes or filaments.

[0117] The invention is described in more detail in the following examples, which should not be construed to limit the scope of present invention.

[0118] Methods

[0119] 1. Microscopy & Image analysis

[0120] a. Sample preparation

[0121] Filament cross section slices are prepared by embedding about 3 cm of yam in epoxy resin in a small plastic tube. After hardening of the resin, the sample is removed from the tube and a slice is cut with a thickness of about 2 mm. The slices are either polished on one side producing a sample slice of about 1 mm thickness, or polished on both sides producing a sample slice with a thickness of 10 pm. Subsequently, the resulting slice is brought (polished side up) with a drop of paraffin oil on a microscopy slide with cover glass.

[0122] b. Microscopy

[0123] Filament cross section images are made of the 10 pm sample slices using an Olympus BX61 microscope at 200 times magnification, employing visible light in transmission mode, see e.g. Fig. 9. The image analysis outlined below was carried out on fluorescence microscopy images of the 1 mm sample slices, employing the BX61 microscope at 200 times magnification in reflection mode, using nonpolarized green light (510 nm to 550 nm) for excitation and visualization through a red transmission filter (> 600 nm), see e.g. Fig. 10. The scale bar corresponds to alength of 50 pm in all microscopy images, except for Fig. 2, where the scale bar corresponds to a length of 100 pm.

[0124] c. Image analysis

[0125] Quantitative cross section analysis is carried out with the OpenCV image analysis software version 4.10.0 for Python. A Gaussian filter with a kernel size of 15x15 pixels and kernel standard deviation of 2.6 is applied to the cross section images to reduce background noise. This size is relatively small compared to the image resolution of 3088 x 2076. Subsequently, the images are binary segmented using Otsu’s automatic threshold. In a first image-processing step of a microscopy cross section image an isolated filament is hand-picked to act as reference area. With this reference area, all areas which are over 20% bigger than it are removed, e.g. closely packed filaments. Similarly, all areas which are less than 80% of the reference are removed. Subsequently, the software carries out the shape parameter evaluation for each filament cross section that remains in the image. This shape evaluation consists of determining the distance distribution function d(s) with m2 parameter and 3-circle model fitting for the determination of the shape factor S3. The 3-circle model fitting is carried out such that the centers of 3 circles with equal radii form an isosceles triangle where the center points of the circles are at the comers of the isosceles triangle. The fitting procedure employs constrained fitting, the constraints are as follows: (i) the centers of the two circles corresponding to the two main lobes should always be within the smallest-area bounding box of the filament. The third circle may be outside of this bounding box, (ii) the radius of the circles can at maximum be 40% of the minimum Feret diameter, (iii) all 3 circles should overlap each other or at least have touching boundaries. The Feret diameter is a measure of an object's size along a specified direction, as measured between two parallel tangential lines, it is also referred to as a caliper diameter. By analogy, the n-circle shape factor Sn is determined for multilobal filaments where n = 4, 5, or 6. For n = 4 the centers of the 4 circles are at the comers of an isosceles trapezium, for the n = 5 fit 3 isosceles triangles are employed, for n = 6 an isoscles trapezium together with 2 isosceles triangles are employed. For n = 5 and 6 the outer 2 isosceles triangles are identical. In all casesthe diameters of the circles in the fit are identical. As an illustration, Figures 3b and 4b show a 3-circle fit and 6-circle fit respectively.

[0126] The normalized value m2 of the lowest secondary minimum M2 of the distance distribution function d(s) of a filament cross section is determined as follows: m2 = d(M2) I dmax,

[0127] where dmax is the maximum value of the distance distribution function of that filament cross section. In Figures 3a and 4a the lowest secondary minimum is indicated by M2.

[0128] The constrained fitting procedure and parameter determination are implemented using Python scripts, which enable automatic image processing. Each value provided is an average value over multiple filament cross sections. For a single yam at least 10 filament cross sections are evaluated automatically by the software from each cross section image.

[0129] 2. Mechanical properties

[0130] The breaking tenacity (BT), modulus (CMA), elongation at break (EAB) and the toughness at rupture (ToAR) are determined according to ASTM D7269 after conditioning at 20°C and 65% relative humidity for 14 hours in accordance with ASTM D1776.

[0131] 3. V50 & V05

[0132] The V50 (m / s) value and V05 (m / s) value is determined against .44 magnum ammunition with 15 shots per pack. The V50 and V05 is calculated based on 60 shots (4 packs) per configuration with the values calculated according to Ballistic Resistance of Body Armor NIJ Standard-0101.06.

[0133] 4. Twist efficiency

[0134] The twist efficiency is determined based on the breaking tenacities (BT) of the untwisted yam from which the twisted yam is made:Twist efficiency (%, tenacity based) = (BT of twisted yarn - BT of untwisted yarn) / BT of untwisted yarn x 100%.

[0135] The twist efficiency indicates how much yarn tenacity is added due to twisting. The breaking tenacity of the untwisted and twisted yam (twisted at 110 tpm) is determined as described above on 15 samples and the mean twist efficiency is calculated.

[0136] 5. Loop breaking tenacity

[0137] To determine the effect of extreme transverse compression on the yam, the loop breaking tenacity may be determined.

[0138] The loop breaking tenacity was measured by applying the method described in ASTM D3217, modified for aramid yam. In this test, two interlocked loops of aramid yam are pulled in opposite directions until breakage. The standard test method for breaking tenacity of manufactured textile fibers in loop or knot configurations was applied using the following procedure which has been modified for aramid yams. The aramid yam was twisted prior to measuring (twist of 110 tpm).

[0139] The twisted yam was pre-dried on the twisting bobbin for 3 hours in a ventilated oven at 45±5°C and subsequently conditioned for at least 16 hours in a standard test atmosphere (temperature 20±2°C; relative humidity 65±2%). The loop breaking test was performed under the same conditions.

[0140] The number of determinations per sample was n=15 (clamp breaks not included) from which a mean loop breaking tenacity and a standard deviation is calculated. The loop breaking tenacity is given in mN / tex.

[0141] The gauge length in the tensile testing machine measured between the two effective clamping points is 500±1 mm. Rate of extension of the tensile testing machine is 250±10 mm / min (the usual rate is 50% of gauge length per minute). The measuring range for the force is set to obtain a maximum force exerted during the test which is between 10 and 90% of that range. Air pressure for pneumatic clamps is set so that no slippage or specimen break occurs in the clamp. Approx.50 m of yarn from the outside layer of the bobbin are removed and discarded before test samples are taken.

[0142] Test samples are taken from material of a twisting bobbin. Bobbin with material is placed in a holder so that the material can be drawn off tangentially. Each sample consists of two pieces of yam taken from one twisted bobbin. Both ends of one piece are mounted in the jaws of the upper clamp, the length of the loop being approximately equal to half the gauge length, and the clamp is closed. In mounting the loops in the clamps any change in twist of the pieces of yam is avoided.

[0143] 6. Pin loop breaking tenacity

[0144] In the pin loop breaking tenacity test, transverse compression is generated by bending fibers over approximately 180° around cylindrically shaped pins. The free ends are clamped together in a single clamp of the tensile tester. By connecting the pin to the other clamp and activating the tensile tester, the fiber is put under stress. The fiber conveys a net force to the pin which is neutralized by a local transverse pressure from the pin onto the fiber. Ignoring friction effects, the transverse pressure was considered uniform over the contact area between fiber and pin surface. The pin loop breaking tenacity test is designed to investigate the reduction in axial yam strength caused by this transverse pressure. The dimensions of the pin, to be more precise pin diameter and pin width (the width of the groove the fiber is guided over), determine the level of transverse pressure. Stress and strain in the fiber are built up in the usual way as for axial tensile testing according to ASTM D7269 until fiber failure (the fiber most likely to fail at the pin surface). The axial stress in the fiber at failure is called the pin loop strength, which is recorded for two pins (with different pin dimensions). From the pin loop strength determined for different transverse stress, a pin loop breaking tenacity at arbitrary transverse stress is found by linear regression. The pin loop breaking tenacity is reduced with respect to the standard breaking tenacity of a fiber being purely axially loaded (without pin), which is attributed to transverse compression of the fiber.The aramid yarn (having a nominal linear density of 840 dtex) was twisted prior to measuring (twist of 110 tpm).

[0145] The twisted yam was pre-dried on the twisting bobbin for 3 hours in a ventilated oven at 45±5°C and subsequently conditioned for at least 16 hours in a standard test atmosphere (temperature 20±2°C; relative humidity 65±2%). The number of determinations per sample and per pin was n=15 (clamp breaks not included) from which a mean pin loop breaking tenacity was calculated.

[0146] Two different pins were used, where the yarn was guided over a defined pin width and pin diameter with the following dimensions:

[0147] Pin 1 : radius of 1.505 mm, width of 0.409 mm, resulting in a ratio of transverse / axial stress of 0.098941

[0148] Pin 2: radius of 0.486 mm, width of 0.439 mm, resulting in a ratio of transverse / axial stress of 0.285454

[0149] The ratio of transverse / axial stress is calculated according to the following formula

[0150]

[0151] where w is the pin width, R is the pin radius, p is the material density of the yarn (1.44 g / cm3), pi_o is the linear density of the yam (dtex), ot is the transverse stress, oais the axial stress and ap is constant for each pin.

[0152]

[0153] 19.5 wt% PPTA (poly(p-phenylene terephthalamide), having a relative viscosity Qrei of 5.0 were dosed into a 20 mm Theysohn twin screw extruder and 80.5 wt% sulfuric acid were injected into the extruder. The sulfuric acid had a purity of 99.8%. The speed of the screws was about 300 rpm. Vacuum for degassing was set to 10 mbar (absolute pressure). The output pressure of the extruder was 15 bar. The temperature of the dissolving process was 85°C.The liquid spin dope that was formed, was transported through a filter. After filtration, the liquid spin dope was, by use of a spin pump, extruded with an extrusion speed of 40.42 m / min, through a spinneret containing 63 circular orifices (B) of 45 pm diameter into a 12 mm air gap where it was drawn, and immediately afterwards into a coagulation bath of water at 5°C. The orifices were arranged in 21 clusters A, in each cluster arranged in an equilateral triangle. After their coagulation the formed filaments were removed from the coagulation bath, washed, neutralized, washed again, dried and taken up on a bobbin at 280 m / min. The yam was spun with a linear density of ca. 51 dtex, corresponding to a filament linear density of 2.4 dtex.

[0154] The breaking tenacity (BT), modulus (CMA) and elongation at break (EAB) were determined as described above and the results are shown in table 1.

[0155] Table 1

[0156]

[0157] A cross section microscopy image of sample 1-1 is shown in Fig. 5a. Fig. 5b shows the cross section of regular Twaron® para-aramid filaments with circular cross section.

[0158] Example 2

[0159] A spin dope was prepared and filtered in the same way as for example 1. After filtration, the liquid spin dope was, by use of a spin pump, extruded with different extrusion speeds, between 25 and 38 m / min, through the same spinneret as in example 1 into an air gap of different lengths, (6, 9, 12, 15 and 18 mm), where it was drawn, and immediately afterwards passed into a coagulation bath of water at 5°C. After their coagulation the formed filaments were removed from the coagulation bath, washed, neutralized, washed again, dried and taken up on a bobbin at different spinning speeds (200, 250 or 300) m / min. The yarn was spunwith a linear density of ca. 45 dtex. Table 2 below indicates the spinning speed (Vspin), the linear density (dtex, per multifilament yam) and the mechanical properties.

[0160] Table 2

[0161]

[0162] Fig. 6a shows the cross section of samples 2-3, 2-8 and 2-13 (12 mm airgap, from left to right) and Fig. 6b shows the cross section of samples 2-4, 2-9 and 2-14 (15 mm airgap, from left to right).Example 3

[0163] PPTA, having a relative viscosity Qrei of 5.0 was used for the preparation of a spin dope having an aramid concentration of ca. 19.8 wt% by mixing with 99.8% solid sulfuric acid. Mixing was performed in a Nauta mixer (Hosokawa, 1000 L volume) for 8 hours. Mixing started at 8°C and during mixing the temperature increased to a final temperature of 20°C.

[0164] From the solid spin dope a multifilament aramid yam was spun using a dry-jet wet spinning process. This was done by dosing the solid spin dope into a kneader (DTB-60) where it was heated to 85°C to obtain a liquid spin dope. Vacuum for degassing was set to 50 mbar (absolute pressure). In the kneader, the dope is transported to the outlet where it is fed to a series of pumps.

[0165] After filtration, the liquid spin dope was extruded with an extrusion speed of 35.93 m / min, through a spinneret containing 1260 circular orifices (B) of 45 pm diameter into a 15 mm air gap where it was drawn, and immediately afterwards into a coagulation bath of water at 13°C. The orifices were arranged in 420 clusters A, in each cluster arranged in equilateral triangles. After their coagulation the formed filaments were removed from the coagulation bath, washed, neutralized, washed again, dried and taken up on a bobbin at 300 m / min. The yam was spun with a linear density of ca. 865 dtex.

[0166] The mechanical properties were determined, and the results are shown in table 3. Table 3

[0167]

[0168] Fig. 7 shows a cross section image of sample 3-1.Example 4

[0169] A spin dope was prepared in the same way as in example 3. In the kneader, an extra amount of liquid sulfuric acid was injected to reduce the polymer concentration from 19.8% to 18.6%. This spin dope was processed in the same way as in example 3.

[0170] The yam was spun with a linear density of ca. 883 dtex.

[0171] The mechanical properties were determined and the results are shown in table 4. Table 4

[0172]

[0173] Fig. 8 shows a cross section image of sample 4-1.

[0174] Example 5

[0175] Example 4 was repeated with the only difference that the spinning speed was set at 350 m / min. The yam was spun with a linear density of ca. 866 dtex (filament linear density of 2 dtex).

[0176] The mechanical properties were determined and the results are shown in table 5. Table 5

[0177]

[0178] Fig. 9 shows a cross section image of sample 5-1.A braided rope was prepared from 12 strands of each 64 yams of sample 5-1 , resulting in a rope with a linear density of 645120 dtex and having a diameter of 10 mm. In parallel a braided rope was prepared from 12 strands each comprising 16 yams of Twaron 2300 (yam linear density of 3360 dtex, 2000 filaments) resulting in a rope with a linear density of 645120 dtex and having a diameter of 10 mm. The breaking force of the rope based on sample 5-1 was determined to be 90.7 kN, whereas the comparative rope only had a breaking force of 77.2 kN, meaning an increase of the breaking force of more than 17%.

[0179] Example 6

[0180] 19.7 wt% PPTA, having a relative viscosity Qrei of 5.0 was dosed into the double shaft kneader and 80.3 wt% liquid sulfuric acid was injected into the double shaft kneader. The sulfuric acid had a purity of 99.8%. The speed of the kneaders was about 43 and 34.4 rpm. Vacuum for degassing was set to 40 mbar (absolute pressure). The output pressure of the extruder was 4 bar. The dissolving capacity was 40 kg / h. The temperature of the dissolving process was 85°C.

[0181] The liquid spin dope that was formed, was transported through a filter. After filtration, the liquid spin dope was, by use of a spin pump, extruded with an extrusion speed of 36.53 m / min (6-1) or 38.32 m / min (6-2), through a spinneret containing 1260 orifices B having a diameter of 45 pm into a 15 mm air gap where it was drawn, and immediately afterwards into a coagulation bath of water, with 5% sulfuric acid, at 5°C. The orifices were arranged in 420 clusters A, in each cluster arranged in an equilateral triangles. After their coagulation the formed filaments were removed from the coagulation bath, washed, neutralized, washed again, dried and taken up on a bobbin at 300 m / min. The yams were spun with a linear density of ca. 883 dtex.

[0182] The mechanical properties of sample 6-1 were determined and the results are shown in table 6.Table 6

[0183]

[0184] Fig. 10 shows a cross section image of sample 6-1.

[0185] The DDF was determined as described above. Sample 6-1 has an m2 value of 0.43 and Sn (=S3) of 0.96.

[0186] Example 7

[0187] 18.6 wt% PPTA, having Qrei 5.0 were dosed into the double shaft kneader and 81.4 wt% liquid sulfuric acid were injected into the double shaft kneader. The sulfuric acid had a purity of 99.8%. The speed of the kneaders was about 43 and 34.4 rpm. Vacuum for degassing was set to 40 mbar (absolute pressure). The output pressure of the extruder was 4 bar. The temperature of the dissolving process was 85°C.

[0188] The liquid spin dope that was formed, was transported through a filter. After filtration, the liquid spin dope was, by use of a spin pump, extruded with an extrusion speed of 38.32 m / min, through a spinneret containing 1260 holes of 45 pm into a 15 mm air gap where it was drawn, and immediately afterwards into a coagulation bath of water, with 5% sulfuric acid, at 5°C. The 45 pm holes were arranged in equilateral triangles. After their coagulation the formed filaments were removed from the coagulation bath, washed, neutralized, washed again, dried and take up on a bobbin at 300 m / min. The yam was spun with a linear density of ca.

[0189] 883 dtex.

[0190] The breaking tenacity, modulus and elongation at break were determined and the results are shown in table 7.Table 7

[0191]

[0192] Fig. 11 shows a cross section image of sample 7-1.

[0193] The DDF was determined as described above. Sample 7-1 has an m2 value of 0.42 and Sn (=S3) of 0.95.

[0194] Example 8

[0195] A spin dope with a PPTA concentration of 18.6 wt% was prepared in the same way as for example 1.

[0196] The liquid spin dope that was formed, was transported through a filter. After filtration, the liquid spin dope was, by use of a spin pump, extruded with a extrusion speed of 62 m / min, through a spinneret containing 36 orifices (B) having a diameter of 45 pm into an air gap of 18 mm, where it was drawn, and immediately afterwards into a coagulation bath of water at 5°C. The orifices B are arranged in 8 clusters A (4x2 clusters A), each cluster comprising 3, 4, 5 or 6 orifices B, the orifices B within a cluster A being arranged equilaterally, i.e. as equilateral triangle, square etc. The clusters A are arranged in a circle in the spinneret. After their coagulation the formed filaments were removed from the coagulation bath, washed, neutralized, washed again, dried and taken up on a bobbin at 200 m / min. The yam was spun with a linear density of ca. 40 dtex.

[0197] Fig. 12 shows an image of the cross sections obtained for sample 8-1.

[0198]

[0199] A multifilament yarn with a trilobal cross section was prepared as in example 5. Sample 9-1 was used for the construction of a unidirectional fabric (UD) where the UD is made of four layers of fibers arranged in such a way that inside each layer the fibers are arranged parallel to each other, while each subsequent layer is rotated 90 degrees relative to the previous layer, creating a 00 / 90° / 0° / 900configuration. These layers are connected with each other with thermoplastic resin (total resin content about 17 wt% with respect to the combined weight of fibers and resin). This configuration is referred to as one layer of ballistic UD material.

[0200] As reference material a UD material was made of Twaron® 2200 (2200 dtex f2000) with regular circular cross section in the same way (UD42) and a reference UD material was made of Twaron® 1100 dtex f1000 yam with regular circular cross section. The resin and the construction of the reference samples is the same as the construction of the UD material of sample 9-1.

[0201] Soft ballistic packs were made of 24 plies of ballistic UD material, having a square size of 500 mm x 500 mm where all plies are stitched together in the comers in order to keep each individual ply in position. Four ballistic packs made of reference material (Twaron® 2200, Twaron® 1100) and four ballistic packs made of sample 9-1 were tested. The areal weight of each consecutive pack was:

[0202] for Twaron® 2200 (Comparative 1 ): 5.936 g / m215.904 g / m215.924 g / m215.920 g / m2;

[0203] for Twaron® 1100 (Comparative 2): 5.804 g / m215.836 g / m215.800 g / m215.810 g / m2

[0204] for sample 9-1 : 5.816 g / m2 / 5.872 g / m2 / 5.864 g / m2 / 5.844 g / m2

[0205] All panels were tested as described above.

[0206] Table 8 shows the results of the ballistic testing.Table 8

[0207]

[0208] Sample 9-1 showed a 31 m / s higher performance in V50 (504 m / s vs 473 m / s) and 23 m / s higher performance in V05 (486 m / s vs 463 m / s).

[0209] Hence, the trilobal yam according to the invention results at the same areal weight construction in an improvement of the ballistic properties.

[0210] Example 10

[0211] A multifilament yam with a trilobal cross section was prepared according to the invention using a polymer concentration of 19.0 wt% (sample 10-1) and as described in example 4 with a coagulation bath of water at 13°C, containing 10% sulfuric acid, or using a polymer concentration of 19.7 wt% (sample 10-2) and as described in example 3 with a coagulation bath of water at 5°C, containing 5% sulfuric acid.

[0212] As comparative examples, multifilament yams with a trilobal cross section were prepared from a spinneret with a continuous trilobal opening, similar to a Y-shaped opening such as described in JP2018162529A and KR19950014665B1 also using a polymer concentration of 19.0 wt% (comparative sample 10-1) or 19.7 wt% (comparative sample 10-2). The cross section of the spinneret opening of the comparative examples is shown in Fig. 14 and a microscopy image of the corresponding filament cross section of comparative 10-2 is shown in Fig. 15. The total area of the opening of the Y-shaped spinneret hole of the comparative samples was designed to be equal to the total area of the 3 separate spinneret orifices B of the samples according to the invention.Samples 10-1 and 10-2 were spun using an air gap of 15 mm, comparative 10-1 and 10-2 were spun using an air gap of 6 mm. Table 8 shows the mechanical properties of the yarns.

[0213] Table 8

[0214]

[0215] As can be seen, sample 10-1 according to the invention has a much higher toughness at rupture than the comparative example 10-1 which was spun from y-shaped spinneret openings.

[0216] The cross sectional shapes of the samples were analyzed. In particular, the Distance Distribution Function (DDF) and the m2 value of the filament cross section and the 3-circle shape factor S3 were determined by OpenCV image analysis software version 4.10.0 for Python as described above and are shown in Table 9.

[0217] Table 9

[0218]

[0219] The microscopy images and the image analysis show that the filament cross sections of the samples according to the invention show mirror symmetry as highest symmetry, i.e. 2-fold symmetry. The filament cross sections of the comparative samples show 3-fold rotational symmetry as highest symmetry (in addition to mirror symmetry). Surprisingly, the samples according the invention have a lower symmetry than the 3-fold rotational symmetry of the spinneret, whereas the comparative samples have a symmetry that is the same as that of the spinneret. The analysis also shows that the filament cross sections of comparative samples made from Y-shaped spinneret openings have a less good fit with the 3-circle model. This less good fit indicates that a Y-shaped cross section cannot be described very well with a model based on 3 (partially) fused subfilaments.

[0220] These results show that the yarns of the invention when compared to the yarns of the prior art (which are spun from e.g. Y-shaped spinneret openings) have a distinct cross sectional shape. This distinct cross sectional shape may also result in improved properties, in particular an improved toughness at rupture. Usually, yams with an improved toughness at rupture also show improved antiballistic properties.

[0221] Example 11

[0222] To assess the functional properties of samples according to the invention and comparative samples spun from Y-shaped spinneret openings, the twist efficiency, the loop breaking tenacity and the pin loop breaking tenacity of further samples according to the invention and comparative samples were determined. The yams were prepared in the same way as for example 10 from a spin dope with a polymer concentration of 19.7 wt% and spun with an air gap having a length of 15 mm for sample 11-1 and of 8 mm for comparative 11-1, as described in example 3. The properties of the yams are shown in Table 10.Table 10

[0223]

[0224] Tables 11, 12 and 13 show the mean twist efficiency, the loop breaking tenacity and the pin loop breaking tenacity of these two samples.

[0225] Table 11

[0226]

[0227] Table 12

[0228]

[0229] Table 13

[0230]

[0231] The results confirm the improved properties of the sample according to the invention. The twist efficiency, the loop breaking tenacity and the pin loop breaking tenacity of the sample according to the invention are higher than those of the sample according to the prior art. This suggests that the yam according to the invention shows improved properties when exposed to twisting and to different levels of transverse compression. Transverse compression occurs e.g. if fibers arranged in a UD or woven fabric of a penetration-resistant article are transversely loaded by a projectile during ballistic impact.

Claims

1. Multilobal para-aramid fiberClaims:

1. A process for the manufacture of para-aramid filaments having a filament cross section with multiple lobes, comprising:- preparing a spin dope comprising para-aramid polymer and sulfuric acid,- passing the spin dope through a spinneret,- subsequently passing the spin dope through a gap with inert gas and a coagulation bath to form the filaments,wherein said spinneret comprises separate orifice clusters A, where an orifice cluster A comprises at least three separate spinning orifices B,wherein the spin dope is passed through the separate spinning orifices B to form a number of para-aramid filaments corresponding to the number of orifice clusters A.

2. The process according to claim 1, wherein the number of separate spinning orifices B is equal to the number of lobes present in the cross section of a filament.

3. The process according to claim 1 or 2, wherein the number of separate spinning orifices B comprised in separate orifice cluster A is in the range of 3 to 10, preferably 3 to 7.

4. The process according to any of the preceding claims, wherein the filament has a trilobal cross section and wherein the spinneret comprises 3 separate spinning orifices B per separate orifice cluster A.

5. The process according to any of the preceding claims, wherein the gap with inert gas has a length in the range of 6 to 25 mm, preferably 10 to 20 mm, more preferably 12 to 18 mm.

6. A para-aramid filament obtainable by the process of any of claims 1 to 5.

7. A para-aramid filament having a filament cross section with n lobes, where n is at least 3 and wherein the filament comprises multiple para-aramid subfilaments, where n = 3, 4, 5 or 6, and the lowest secondary minimum M2 of the Distance Distribution Function (DDF) of the filament cross section has a normalized value m2 in the range of 0.2 to 0.8, preferably in the range of 0.3 to 0.7, and more preferably in the range of 0.4 to 0.6, as determined by OpenCV image analysis software version 4.10.0 for Python.

8. The para-aramid filament of claim 6 or 7, wherein the para-aramid subfilaments are at least partially fused.

9. The para-aramid filament of any of claims 6 to 8 having a trilobal cross section.

10. The para-aramid filament of any of claims 6 to 9 having a linear density in the range of 0.5 to 25 dtex, preferably 1 to 15 dtex, more preferably 1.5 to 10 dtex.

11. The para-aramid filament of any of claims 6 to 10 having n lobes, where n = 3, 4, 5, or 6, and the n-circle shape factor Sn is in the range 0.85 to 1.0, preferably 0.87 to 0.96, more preferably 0.9 to 0.98, as determined by OpenCV image analysis software version 4.10.0 for Python.

12. A multifilament yam comprising the para-aramid filament of any of claims 6 to13. The multifilament yarn of claim 12 having a close packing fraction of higher than 0.91 , preferably of at least 0.93.

14. A textile fabric, paper, linear tension member, tire, hose or composite comprising the filaments of any of claims 6 to 11 and / or the multifilament yam of claim 12 or 13.

15. The textile fabric of claim 14 selected from a woven fabric, a knitted fabric, a laminate, a unidirectional layer, a multiaxial layer or a biaxial layer.

16. A penetration-resistant or cut-resistant article comprising the filaments of any of claims 6 to 11 and / or the multifilament yarn of claim 12 or 13 and / or the textile fabric of claim 14 or 15, preferably an article of clothing.

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