Patent Application
20160311263
The present invention generally relates to tape elements containing crack guiding ridges and fiber reinforced rubber articles having tape elements containing ripstop ridges.
Reinforced rubber goods are used in a wide variety of consumer and industrial applications. The performance of reinforced molded rubber goods depends on the adhesion of the reinforcement to the rubber. Fabrics made with synthetic yarns tend to be difficult to bond to rubber.
In practice several things are done to improve adhesion, most of them involving coating fibers and/or fabric with an adhesion promoter. For example, as the fibers are drawn a spin finish may be applied which may contain an adhesion activator such as an epoxy resin.
A typical passenger car radial tire has two steel belt packages configured at +/− θ bias (θ can be roughly 21°). The steel belts are unequal in width and the result is a roughly ½″ wide step-change on either ends, as seen from the schematic above. This belt-edge being unconstrained, is the one of the highest strained regions and hence also the region that sees the largest operating temperature. Cap-ply provides restraining force to reduce the belt-edge flexure and this becomes more important at high speeds.
There remains a need for reinforced rubber articles having fibrous layers with enhanced adhesion due to geometry and other physical properties.
A tape element having at least a first layer containing a first thermoplastic polymer, at least one ripstop ridge in a surface of the tape, and at least one reciprocal elongated hill in the opposite surface of the tape, where the ridges and hills in the two surfaces are in registration. The ripstop ridges have an aspect ratio of width to height of between about 1:5 and 10:1, has a height at least 10% of the thickness of the tape in the segments, and extend along at least a portion of the length of the tape. Rubber articles containing the tape element are also disclosed.
This invention includes a highly-drawn, high-tenacity tape element that has surface features that create distinct segments that are partially or wholly separated or are separable from its neighboring segments; the method of manufacturing the same and the die designs that create the desired product. The segments are separated by boundaries that are different in cross-section preferably higher in cross-section compared to its neighbors called ripstop ridges.
The segmented construction of the tape elements with the ripstop ridges in-between segments essentially acts like a two-way hinge and provides the ability to flex in the transverse direction enabling a conforming configuration at the step change in between the steel-belts in a cured tire and other applications requiring conformity along the width of a tape element. The segmented tape construction with ripstop ridges enable good orientation of the polymer in the segments and hence maintains the high-modulus similar to that of the highly drawn monolithic tape geometry. The segmented tape is expected to maintain the good adhesion benefits seen with the tape geometry.
The ripstop ridge and its features reduce the stress concentration when the segmented tape is loaded. The ripstop ridges, hence control the failure (crack) pathways in the full width of the wide tape by acting as a barrier. This overcomes the uncontrolled and unpredicted failure pathways typically seen in monolithic tape constructions at widths greater than 6 mm.
The segmented wide tape has the top and bottom faces of segments parallel to each other—which implies no crimp.
The ripstop ridges maintain the connectivity of the high-modulus segments in a segmented wide-tape and this implies uniform load sharing between the segments when the wide tape is loaded.
Referring now to
A cap ply layer 310 is located between the belt plies 232 and the tread 500. The cap ply layer 310 shown is formed from a cap ply tape 310 wound around the tire circumferentially in a flat helical pattern. Some suitable cap ply fabrics are described in U.S. Pat. Nos. 7,252,129, 7,614,436, and 7,931,062, each of which are incorporated herein by reference in their entirety.
Any fabric extending between the bead and the tread is defined herein as a “sidewall fabric” including chipper, flipper, and chafer fabrics. This includes fabrics that also extend around the bead to the inside of the tire such as a flipper fabric, as long as at least part of the fabric is located between the bead and the tread.
A tire carcass is required to have substantial strength in the radial direction running from bead to bead transverse to the direction rotation during use. To provide this strength, the fabric stabilizing material (also known as tire cord) has typically been a woven fabric with substantially inextensible pre-stressed high tenacity yarns running in the warp direction (also known as the “machine direction”) which are drawn and tensioned during the fabric formation and/or finishing process. This fabric is then cut in the cross-machine direction (i.e. transverse to the warp yarns). Individual pieces of the fabric are then rotated 90 degrees and are assembled to one another for placement in the carcass such that the high strength warp yarns are oriented in the desired radial direction between the beads. Thus, in the final construction, the weft yarns are oriented substantially circumferentially (i.e. in the direction of tire rotation.)
In another embodiment, the carcass stabilizing fabric is formed is a warp knit, weft inserted fabric having weft insertion yarns formed from the relatively inextensible reinforcing cords. Alternatively, the carcass stabilizing fabric may be a woven fabric having weft yarns formed from relatively inextensible reinforcing cords or a laid scrim. More information about this stabilizing having relatively inextensible reinforcing cords in the weft direction of the textile may be found in U.S. patent application Ser. No. 12/836,256 filed on Jul. 14, 2010, which is incorporated herein by reference in its entirety.
The fibrous layer 100 in the tire of
Referring now for
Some other reinforced rubber products 200 include printer blankets and transmission belts. In offset lithography the usual function of a printing blanket is to transfer printing ink from a printing plate to an article such as paper being printed whereby the printing blanket comes into repeated contact with an associated printing plate and the paper being printed. Printer blankets typically include a fabric embedded into rubber. Transmission belts and other types of belts also contain reinforced rubber with fibers.
Pneumatic springs commonly referred to as air springs, have been used with motor vehicles for a number of years to provide cushioning between movable parts of the vehicle, primarily to absorb shock loads impress on the vehicle axles by the wheels striking an object in the road or falling into a depression. These air springs usually consist of a flexible elastomeric sleeve or bellows containing a supply of compressed air or other fluid and having one or more pistons located within the flexible sleeve to cause compression and expansion as the vehicle experiences the road shocks. The pistons cause compression and expansion within the spring sleeve and since the sleeve is of a flexible material permits the pistons to move axially with respect to each other within the interior of the sleeve. The ends of the sleeve usually are sealingly connected to the pistons or end members and have one or more rolled ends which permit the end members to move axially with respect to each other between a jounce or collapsed position and a rebound or extended position without damaging the flexible sleeve.
It is desirable that a damping mechanism or device be used in combination with such air springs to provide damping for controlling the movement of the air springs. In one embodiment, the rubber reinforced article is used in an air spring. In some embodiment, the rubber reinforced article is used as o a spacer for the piston or bead plate of an air spring assembly.
The fibrous layer 100 is formed from fibers 16, preferably tape elements 16. The fibers 16 may be any suitable fiber for the end use. “Fiber” used herein is defined as an elongated body. The fiber may have any suitable cross-section such as circular, multi-lobal, square or rectangular (tape), and oval. In one embodiment, the fibers are tape elements 16. The tape elements 16 may have a rectangular or square cross-sectional shape. These tape elements may also be sometimes referred to as ribbons, strips, tapes, tape fibers, and the like.
One embodiment of the fiber being a tape element is shown in
In one preferred embodiment, the tape element 16 has a rectangular cross-section. The tape element is considered to have a rectangular or square cross-section even if one or more of the corners of the rectangular/square are slightly rounded or if the opposing sides are not perfectly parallel. Having a rectangular cross-section is preferred for some applications for a variety of reasons. Firstly, the surface available for bonding is greater. Secondly, during a de-bonding event the whole width of the tape is under tension and shear points are significantly reduced or eliminated. In contrast, a multifilament yarn has very little area under tension and there are regions of varying proportions of tension and shear along the circumference of the fiber. In another embodiment, the cross-section of the tape element 16 is a square or approximately square. Having a square cross section could also be preferred in some cases where the width is small and the thickness is high, thereby stacking more tapes in a given width thereby increasing the load carrying capacity of the entire reinforcement element.
In one embodiment, the tape elements 10 have a width of between about 2 and 15 mm, more preferably between about 6 and 15 mm, and more preferably between about 10 and 12.7 mm. In another embodiment, the tape elements have a thickness of between about 0.02 and 1 mm, more preferably between about 0.03 and 0.5 mm, and more preferably between about 0.04 and 0.3 mm. In one embodiment, the tape elements have a width of approximately 13.3 mm and a thickness of approximately 0.2 mm.
The first layer 12 of the tape element 16 comprises a first thermoplastic polymer which may be any suitable orient-able (meaning that the fiber is able to be oriented) thermoplastic. Some suitable thermoplastics for the first layer include polyamides, co-polyamides, polyesters, co-polyesters, polycarbonates, polyimides, and other orient-able thermoplastic polymers. In one embodiment, the first layer contains polyamide, polyester, and/or co-polymers thereof. In one embodiment, the first layer contains a polyamide or polyamide co-polymer. Polyamides are preferred for some applications as it has high strength, high modulus, high temperature retention of properties, and fatigue performance. In another embodiment, the first layer contains a polyester or polyester co-polymer. Polyesters are preferred for some applications as it has high modulus, low shrink and excellent temperature performance.
In one embodiment, the first layer 12 of the tape element 16 is a blend of polyester and nylon 6. The polyester is preferably polyethylene terephthalate. Polyester is employed because of its high modulus and high glass transition temperature which has resulted in the employment of polyester in tire cords and rubber reinforcement cord, primarily due to its flat-spotting resistant nature. Nylon 6 is employed for multiple reasons. It is easier to process than Nylon 6 6. One of the main reasons to incorporate nylon 6 in these embodiments is to function as an adhesion promoter. Nylon 6 has surface groups to which the resorcinol formaldehyde latex can form primary chemical bonds through the resole group. This blend is a physical blend, not a co-polymer and polyester and nylon 6 are immiscible in each other. In one embodiment, powder or pelts of polyester and nylon 6 are simply mixed in the un-melted state to form the blend that will then be feed to an extruder. The extruded tape elements from this physical blend provide good adhesion to rubber and a high modulus.
Preferably, the tape elements 16 are monoaxially oriented meaning that they are oriented in a molten or semi-molten state in primarily one direction. Typically during the monoaxially orienting process, the tape will neck in and lose width.
The tape elements 16 contain at least one ripstop ridge 80 in the upper surface 16a. The ripstop ridge 80 formed is intentional and significantly larger than a small bump in the surface of the tape. The tape elements 16 also contain at least one reciprocal elongated hill 90 in the lower surface 16b of the tape element 16. This reciprocal elongated hill 90 is in registration with the ripstop ridge 80 in the upper surface 16a of the tape element 16. As the ridges and hills 80, 90 are reciprocal, the number of ripstop ridges 80 will always equal the number of reciprocal elongated hills 90.
The ripstop ridges 80 and the reciprocal elongated hills 90 extend along the length of the tape element 16 and could be considered continuous along the length of the tape element 16. Preferably, the ridges 80 and hills 90 are formed as the tape element is being extruded from an extrusion die.
As shown in
Preferably, the height of the ripstop ridges 80 is between about 1 and 100% of the thickness of the tape element 16, more preferably between about 20 and 45%. The areas of the tape element along its width that are outside of the ridges 80 are defined to be segments 70, such as shown in
Preferably, the tape elements 16 comprise between 1 and 10 ripstop ridges 80 (and the same number of reciprocal elongated hills 90), more preferably between 1 and 6, more preferably between 2 and 5. The tape elements 16 will always contain 1 more segment than ridge 80. In one embodiment, the ripstop ridges 80 are evenly spaced along the width of the tape elements 16. In another embodiment, the ripstop ridges 80 are unevenly spaced along the width of the tape elements 16. In one embodiment, the width between the ripstop ridges 80 (the segments 70) are between about 1 and 6 mm, more preferably between about 2 and 3 mm.
A crack front reaching a ridge area in the wide tape is expected to require a larger energy for propagation and hence will be prevented from going across the width of the tape. The ridge essentially acts as a crack propagation barrier.
In one embodiment, the tape element 16 has a crack located where a segment 70 and a ridge 80 meet, forming a crack through the entire thickness of the tape element 16. The crack formed may be small (less than an inch), may be larger (between about an inch and a foot), or may be very large (a foot or longer). In one embodiment, at least one of the segments 70 in a tape element is completely separated from the tape element 16. When the crack is very large, the segments 70 of the tape elements 16 separate and may act as tape elements on their own.
In one embodiment, all of the ripstop ridges 80 are in the upper surface 16a of the tape element 16 and all of the corresponding reciprocal elongated hills 90 in the lower surface 16b of the tape element 16. In another embodiment, the upper and lower surfaces 16a, 16b contain ripstop ridges 80 and corresponding reciprocal elongated hills 90. By distributing the ridges on both the surfaces of the tape element 16, a mid-plane symmetry is created for the tape and this results in the ability to flex both ways in the transverse direction of the tape element enabling a conforming configuration.
In one embodiment, the tape elements preferably have a draw ratio of at least about 5, a modulus of at least about 2 GPa, and a density of at least about 1.2 g/cm3. In another embodiment, the first layer has a draw ratio of at least about 6. In another embodiment, the first layer has a modulus of at least about 3 GPa or at least about 4 GPa. In another embodiment, the first layer has a density of at least about 1.3 g/cm3 and a modulus of about 9 GPa. A first layer having a high modulus is preferred for better performance in applications such as tire cord, cap-ply, overlay or carcass ply for tires. Lower density for these fibers would be preferred so as to yield a lower weight. Voided fibers would generally tend to have lower densities than their un-voided counterparts.
In one embodiment, the tape elements 16 contains a second layer on the upper surface 16a of the tape element 16 and also may contain an additional third layer on the lower surface 16b of the tape element 16.
The optional second layer and third layer may be formed at the same time as the first layer 12 in a process such as co-extrusion or may be applied after the first layer 12 is formed in a process such as coating. The second layer preferably comprises a second thermoplastic polymer and the third layer preferably comprises a third thermoplastic polymer. The second and third layers preferably contain a polymer of the same class as the polymer of the first layer, but may also contain additional polymers. In one embodiment, the second and/or third layers contain a polymer a block isocyanate polymer. The second and third layers may help adhesion of the fiber to the rubber. Preferably, the melting temperature (Tm) of the first layer 12 is greater than the Tm of the second layer and third layer.
In one embodiment, the tape elements contain a plurality of voids. “Void” is used herein to mean devoid of added solid and liquid matter, although it is likely the “voids” contain gas. While it has been generally accepted that voided fibers may not have the physical properties needed for use as reinforcement in rubber articles, it has been shown that the voided fibers have some unique benefits. Firstly, presence of voids in the fiber occurs at the cost of the polymer mass. This means that the density of these fibers would be lower than their non-voided counterparts. The volume fraction of the voids would determine the percentage by which the density of this fiber would be lower than the polymer resin. Secondly, the voids act as bladders for an adhesive promoter to be infused into the voided layer/voided fiber, thus providing an anchoring effect. Thirdly, the shape of these voids may control the crack propagation front in an event such as fatigue. The extra surface available for crack propagation would reduce the stress concentration in a cyclic fatigue event involving tensile and/or compressive loading. For the thermoplastic polymers making up the first layer 12 of the tape element 16, the high shear flows during the over-drawing layers to chain orientation and elongation leading to the presence of polymer depleted regions or voids. The voids may be present in any or all of the layers. In addition, the fibrous layer 100 may contain some fibers having no voids and some fibers having voids.
The voids typically have a needle-like shape meaning that the diameter of the cross-section of the void perpendicular to the fiber length is much smaller than the length of the void due to the monoaxially orientation of the fiber. This shape is due to the monoaxially drawn nature of the tape elements 16.
In one embodiment, the voids are in the fiber in an amount of between about 3 and 20% by volume. In another embodiment, the voids are in the fiber in an amount of between about 3 and 18% vol, about 3 and 15% vol, 5 and 18% vol, or about 5 and 10% vol. The density is inversely proportional to the void volume. For example if the void volume is 10%, then the density is reduced by 10%. Since the increase in the voids is typically observed at higher draw ratios (which results in higher strength), the reduction in density leads to an increase in the specific strength and modulus of the fiber which is desired for several applications such as high performance tire reinforcements.
In one embodiment, the size of the voids formed have a diameter in the range of between about 50 and 400 nm, more preferably 100 to 200 nm, and a length of between about 1 and 6 microns, more preferably between about 2 and 3 microns.
The voids in the tape elements may be formed during the monoaxially orientation process with no additional materials, meaning that the voids do not contain any void-initiating particles. The orientation in a fiber bundle is the driving factor for the origin of voids in the fibers. It is believed that slippages between semi-molten materials lead to the formation of voids. The number density of the voids depends on the viscoelasticity of the polymer element. The uniformity of the voids along the transverse width of the oriented fiber depends on whether the complete polymer element has been oriented in the drawing process along the machine direction. It has been observed that in order for the complete polymer element to be oriented in the drawing process, the heat has to be transferred effectively from the heating element (this could be water, air, infra-red, electric and so on) to the polymer fiber. Conventionally, in industrial processes that utilize a hot air convective heating, one feasible way to orient polymer fibers and still maintain industrial speeds is to restrict the polymer fibers in terms of its width and thickness. This means that complete orientation along the machine direction would be achievable more easily when the polymer fibers are extruded from slotted dies or when the polymer is extruded through film dies and then slit into narrow widths before orientation.
In another embodiment, the tape elements contain void-initiating particles. The void-initiating particles may be any suitable particle. The void-initiating particles remain in the finished fiber and the physical properties of the particles are selected in accordance with the desired physical properties of the resultant fiber. When there are void-initiating particles in the first layer 12, the stress to the layer (such as mono-axial orientation) tends to increase or elongate this defect caused by the particle resulting in elongation a void around this defect in the orientation direction. The size of the voids and the ultimate physical properties depend upon the degree and balance of the orientation, temperature and rate of stretching, crystallization kinetics, and the size distribution of the particles. The particles may be inorganic or organic and have any shape such as spherical, platelet, or irregular. In one embodiment, the void-initiating particles are in an amount of between about 2 and 15% wt of the fiber. In another embodiment, the void-initiating particles are in an amount of between about 5 and 10% wt of the fiber. In another embodiment, the void-initiating particles are in an amount of between about 5 and 10% wt of the first layer. In one preferred embodiment, the void-initiating particle is nanoclay.
The fibrous layer 100 containing tape elements 16 may be any suitable fibrous layer such as a knit, woven, non-woven, and unidirectional textile. Preferably, the fibrous layer 100 has an open enough construction to allow subsequent coatings (such as rubber) to pass through the fibrous layer 100 minimizing window pane formation. In another preferred embodiment, the fibrous layer 100 is formed from a single end of tape element 16 continuously wrapped around a rubber article forming a unidirectional fibrous layer. In some embodiments, inducing spacing between the fibers may lead to slight rubber bleeding between the fibers which may be beneficial for adhesion. The fibrous layer 100 of
In another embodiment, the fibrous layer 100 contains fibers and/or yarns that have a different composition, size, and/or shape to the tape elements 16. These additional fibers may include, but are not limited to: polyamide, aramid (including meta and para forms), rayon, PVA (polyvinyl alcohol), polyester, polyolefin, polyvinyl, nylon (including nylon 6, nylon 6,6, and nylon 4,6), polyethylene naphthalate (PEN), cotton, steel, carbon, fiberglass, steel, polyacrylic, polytrimethylene terephthalate (PTT), polycyclohexane dimethylene terephthalate (PCT), polybutylene terephthalate (PBT), PET modified with polyethylene glycol (PEG), polylactic acid (PLA), polytrimethylene terephthalate, nylons (including nylon 6 and nylon 6,6); regenerated cellulosics (such as rayon or Tencel); elastomeric materials such as spandex; high-performance fibers such as the polyaramids, and polyimides natural fibers such as cotton, linen, ramie, and hemp, proteinaceous materials such as silk, wool, and other animal hairs such as angora, alpaca, and vicuna, fiber reinforced polymers, thermosetting polymers, blends thereof, and mixtures thereof. These additional fibers/yarns may be used, for example, in the warp direction of a woven fibrous layer 100, with the fibers 16 being used in the weft direction.
In one embodiment, the fibers are surrounded at least partially by an adhesion promoter such as an RFL. A frequent problem in making a rubber composite is maintaining good adhesion between the rubber and the fibers and fibrous layers. A conventional method in promoting the adhesion between the rubber and the fibers is to pretreat the yarns with an adhesion layer typically formed from a mixture of rubber latex and a phenol-formaldehyde condensation product wherein the phenol is almost always resorcinol. This is the so called “RFL” (resorcinol-formaldehyde-latex) method. The resorcinol-formaldehyde latex can contain vinyl pyridine latexes, styrene butadiene latexes, waxes, fillers and/or other additives. “Adhesion layer” used herein includes RFL chemistries and other non-RFL rubber adhesive chemistries.
In one embodiment, the adhesion chemistries are not RFL chemistries. In one embodiment, the adhesion chemistries do not contain formaldehyde. In one embodiment the adhesion composition comprises a non-crosslinked resorcinol-formaldehyde and/or resorcinol-furfural condensate (or a phenol-formaldehyde condensate that is soluble in water), a rubber latex, and an aldehyde component such as 2-furfuraldehyde. The composition may be applied to textile substrates and used for improving the adhesion between the treated textile substrates and rubber materials. More information about these chemistries may be found in U.S. application Ser. No. 13/029,293 filed on Feb. 17, 2011, which is incorporated herein in its entirety.
The adhesion layer may be applied to the fibers before formation into a fibrous layer or after the fibrous layer is formed by any conventional method. Preferably, the adhesion layer is a resorcinol formaldehyde latex (RFL) layer or rubber adhesive layer. Generally, the adhesion layer is applied by dipping the fibrous layer or fibers in the adhesion layer solution. The fibrous layer or fibers then pass through squeeze rolls and a drier to remove excess liquid. The adhesion layer is typically cured at a temperature in the range of 150° to 200° C. Preferably, at least one of the surfaces 16a, 16b is covered in a coating comprising an RFL. More preferably, all of the surfaces of the tape elements 16 are covered in an RFL. Preferably, there is a second coating comprising solvated rubber (or other rubber cement coating) on top of and covering the RFL coating.
The adhesion promoter may also be incorporated into a skin layer (the second and/or third layer) of the fiber or may be applied to the fiber and/or fibrous layer is a freestanding film. Thermoplastic films in this category consist of various polyamides and co-polymers thereof, polyolefins and co-polyolefins thereof, polyurethanes and methymethacrylic acid. Examples of these films include 3M™ 845 film, 3M™ NPE-IATD 0693, and Nolax™ A21.2242 film.
The tape elements 16 may be formed in any suitable manner or process. There are two preferred methods for forming the reinforced rubber article. The first preferred method starts by slit extruding polymer to form tape elements. The die typically contains between 1 and 20 slits, each one forming a fiber (tape element), more preferably between 2 and 6 slits. In one embodiment, the each slit die has a width of between about 15 mm and 80 mm and a thickness of between about 0.6 and 2.5 mm. The fibers once extruded are typically 2 to 15 mm wide. The fibers may be extruded having one layer or may have a second layer and/or a third layer using co-extrusion.
The extrusion of the tape elements can be carried out by slitting a profiled slit film extrudate at the desired width or by using a slotted die construction. The resulting extrudate is then drawn via multi-stage operation with or without the use of heat. The protrusions from the die gets transferred to the extrudate, these ridges in the extrudate maintain the segment separation proportionate to that in the die through the natural draw process.
In one embodiment a die is used that comprises a die body having a polymer inlet side, a die face, and at least one slot extending through the die body from the inlet side and terminating at the die face at a slot shaped opening. The slot shaped opening has a width and a thickness, wherein the slot comprises an upper surface and a lower surface. The upper surface comprises at least one elongated depression at the die face and extending at least 4 mm into the die body. The elongated depression has a width and a depth and an aspect ratio of width to depth between about 1:4 to 2:1. The depth of the depression is between about 1 and 100% of the thickness of the slot shaped opening preferably between 35 and 50%.
During slit film extrusion or slotted die extrusion, chips can form at or on the lip of the die. These chips interrupt the flow of the molten polymer coming out from the die face and can create markings on the extrudate surface. Such markings mostly appear only on one surface of the extrudate and are not reproducible in nature and are often discontinuous and random in positioning with the same die arrangement. By creating elongated depressions that extent into the die, the flow of the polymer melt is guided and the die protrusion shape influences the surface of the polymer melt resulting in ridges in the extrudate in a repeatable way. The modification to the flow of the polymer melt due the elongated protrusions also result in a perfectly registered reciprocal elongated hill that is not as sharply pronounced as the die introduced channel.
In one embodiment, the die comprises at least one elongated depression. In another embodiment, the die comprises at least 2 elongated depressions, more preferably at least 3, more preferably at least 4. In one embodiment, the elongated depressions are evenly spaced across the die and in another embodiment, the elongated depressions are unevenly spaced across the width of the die. The die can be any type of die including slit, circular, or the link.
Next, the fibers are monoaxially drawn. In one embodiment, the fibers are drawn to a ratio of preferably about 3 or greater (more preferably at least about 4, more preferably at least about 5) resulting in a fiber having a modulus of at least about 2 GPa and a density of at least about 0.85 g/cm3.
Once the fibers are formed, a second and/or third layer may be applied to the fibers in any suitable manner, including but not limited to, lamination, coating, printing, and extrusion coating. This may be done before or after the monoaxial orientation step.
In one embodiment, the drawing of the fibers causes voiding to occur in the fiber. In one embodiment, the voids formed are in an amount of between about 3 and 18% vol. In another embodiment, the extrudant contains polymer and void-initiating particles causing voiding in the fiber and/or crevices on the surface of the fiber to form.
The fibers are formed into a fibrous layer which includes wovens, non-wovens, unidirectionals, and knits. The fibers are then optionally coated with an adhesion promoter such as an RFL coating and at least partially embedded (preferably fully embedded) into rubber. In the embodiments where the fibers contain crevices, it is preferred the adhesion coating at least partially fills the crevices.
In the second method, a polymer is extruded into a film. The film may be extruded having one layer or may have a second layer and/or a third layer using co-extrusion. The die to create a film would have the same properties as the tape element extruder with the elongated depressions, except that the die would be significantly width and would most likely contain additional elongated depressions along the width of the die.
Next, the film is slit into a plurality of fibers. In one embodiment, the fibers are tape elements having square or rectangular cross-sectional shapes. These fibers are then monoaxially drawn. In one embodiment, the fibers are drawn to a ratio of preferably about 5 or greater resulting in a fiber having a modulus of at least about 2 GPa and a density of at least about 0.85 g/cm3.
Once the fibers are formed, if a second and/or third layer are desired they may be applied to the fibers in any suitable manner, including but not limited to, lamination, coating, printing, and extrusion coating. This may be done before or after the monoaxial orientation step.
In one embodiment, the drawing of the fibers causes voiding to occur in the fiber. In one embodiment, the voids formed are in an amount of between about 3 and 18% vol. In another embodiment, the extrudant contains polymer and void-initiating particles. When monoaxially oriented, this causes voiding in the fiber and/or crevices on the surface of the fiber to form.
The fibers are formed into a fibrous layer which includes wovens, non-wovens, unidirectionals, and knits. The fibers are then optionally coated with an adhesion promoter such as an RFL coating and at least partially embedded into rubber. In the embodiments where the fibers contain crevices, it is preferred the adhesion coating at least partially fills the crevices.
In another embodiment, the fibers are heat treated before they are formed into the fibrous layer. Heat treatment of fibers offers several advantages such as higher modulus, higher strength, lower elongation and especially lower shrinkage. Methods to heat treat the fibers include hot air convective heat treatment, steam heating, infra-red heating or conductive heating such as stretching over hot plates—all under tension.
The invention will now be described with reference to the following non-limiting examples, in which all parts and percentages are by weight unless otherwise indicated.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
This application claims priority to provisional U.S. patent application 62/151,101 filed on Apr. 22, 2015 which is herein incorporated in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62151101 | Apr 2015 | US |
