WO2014204966A1

WO2014204966A1 - Three-dimensional spacer fabrics and articles comprising them

Info

Publication number: WO2014204966A1
Application number: PCT/US2014/042750
Authority: WO
Inventors: Uday Vaidya; Haibin Ning; Vinoy Thomas
Original assignee: The Uab Research Foundation
Priority date: 2013-06-17
Filing date: 2014-06-17
Publication date: 2014-12-24

Abstract

In one embodiment, a three-dimensional spacer fabric includes a first layer of material, a second layer of material, core strands that extend between the two layers of material, and a cured resin coating the two layers and the core strands, the cured resin enabling the fabric to flex to absorb rotational acceleration.

Description

THREE-DIMENSIONAL SPACER FABRICS

AND ARTICLES COMPRISING THEM

Cross-Reference to Related Application(s)

This application claims priority to co-pending U.S. Provisional Application

Serial Number 61/836,078, filed June 17, 2013, which is hereby incorporated by reference herein in its entirety.

Background

Sports concussion and traumatic brain injury have become important issues in both the athletic and medical communities. As an example, in recent years much attention has been focused on the mild traumatic brain injuries (concussions) sustained by professional and amateur football players, as well as the long-term effects of such injuries. It is currently believed that repeated brain injuries such as concussions may lead to diseases later in life, such as depression, chronic traumatic encephalopathy (CTE), and amyotrophic lateral sclerosis (ALS).

Protective headgear, such as helmets, is used in many sports to reduce the likelihood of brain injury. Current helmet certification standards are based on testing parameters that were developed in the 1960s, which focus on the attenuation of linear impact and prevention of skull fracture. An example of a linear impact is a football player taking a direct hit to his helmet from a direction normal to the center of his helmet or head. Although the focus of headgear design has always been on attenuating such linear impact, multiple lines of research in both animal models and biomechanics suggest that both linear impact and rotational acceleration play important roles in the pathophysiology of brain injury. Although nearly every head impact has both a linear component and a rotational component, rotational acceleration is greatest when a tangential blow is sustained. In some cases, the rotational acceleration from such blows can be substantial. For instance, a football player's facemask can act like a lever arm when impacted from the side, and can therefore apply large torsional forces to the head, which can easily result in brain trauma.

Although the conventional wisdom is that the components of modern protective headgear that are designed to attenuate linear impact inherently attenuate rotational acceleration, the reality is that such components are not designed for that purpose and therefore do a relatively poor job of attenuating rotational acceleration. It therefore can be appreciated that it would be desirable to have a way to attenuate not only linear impact to but also rotational acceleration of the head, so as to reduce the likelihood of brain injury.

Brief Description of the Drawings

The present disclosure may be better understood with reference to the following figures. Matching reference numerals designate corresponding parts throughout the figures, which are not necessarily drawn to scale. Fig. 1 is a perspective view of an embodiment of a three-dimensional spacer fabric.

Fig. 2 is a side view of a first embodiment of a composite pad that includes a three-dimensional spacer fabric.

Fig. 3 is a side view of a second embodiment of a composite pad that includes a three-dimensional spacer fabric.

Fig. 4 is a side view of a third embodiment of a composite pad that includes a three-dimensional spacer fabric.

Fig. 5 is a side view of a fourth embodiment of a composite pad that includes a three-dimensional spacer fabric.

Fig. 6 is a side view of a fifth embodiment of a composite pad that includes a three-dimensional spacer fabric.

Fig. 7 is a graph that compares NOCSAE severity index results for helmets comprising various types of pads.

Fig. 8 is a Fourier transform infrared (FTIR) spectrogram for a standard

Schutt™ helmet pad.

Fig. 9 is an FTIR spectrogram for a hard (60 Shore A) three-dimensional spacer fabric.

Fig. 10 is an FTIR spectrogram for a soft (40 Shore A) three-dimensional spacer fabric.

Fig. 1 1 is an FTIR spectrogram that compares the hard spacer fabric (top), soft spacer fabric (middle), and Schutt™ pad (bottom).

Fig. 12 is a perspective view of an embodiment of a protective helmet that comprises composite pads that include a three-dimensional spacer fabric. Detailed Description

As described above, current protective headgear is primarily designed to attenuate linear impact. However, it has been determined that both linear impact and rotational acceleration from torsional forces contribute to brain injury, such as concussion. Disclosed herein are three-dimensional spacer fabrics that, when used in protective helmets, attenuate rotational acceleration that results from impacts to the head. The three-dimensional spacer fabrics enable the shell of the helmet to move relative to the wear's head so as to decouple the shell from the head. In some embodiments, this three-dimensional spacer fabric is adapted to yield to tangential forces to enable this decoupling. In such a case, rotational forces applied to the shell from impacts are not directly transmitted to the head. Instead, these forces are dissipated over time to reduce brain shear.

In the following disclosure, various embodiments are described. It is to be understood that those embodiments are example implementations of the disclosed inventions and that alternative embodiments are possible. All such embodiments are intended to fall within the scope of this disclosure.

Described in the following disclosure are three-dimensional spacer fabrics that can be used to reduce rotational acceleration of the brain that results from impact to the head. Although this specific application has been identified, it is noted that the disclosed three-dimensional spacer fabrics can be used in various other applications. For example, the fabrics can be used to create body pads that are intended to protect the wearer against injury from impacts with other objects, including other persons. Accordingly, it will be appreciated that the disclosed three-dimensional spacer fabrics are not limited to use in protective helmets. For example, the fabrics can be used in head bands, chin straps, neck braces, body pads, joint pads, and shoes.

Fig. 1 illustrates an example three-dimensional spacer fabric 10, which results from infusing a base fabric with a curable resin. As shown in this figure, the fabric 10 generally comprises a first or top layer of material 12 that is separated from a generally parallel second or bottom layer of material 14. The two layers 12, 14 can each comprise a fabric that includes a plurality of strands 16. The strands 16 can comprise individual fiber filaments ("fibers") or yarns that are composed of groups of fiber filaments. Irrespective of the particular nature of the strands 16, the strands can be woven together or otherwise associated (knitted, entangled, etc.) with each other to form the layers 12, 14. In some embodiments, each layer is approximately 3 to 25 mm thick and comprises yarns that have approximately 400 to 600 individual filaments that range from approximately 65 to 300 tex. Each filament can be approximately 8 to 15 μιη in diameter. In some embodiments, the layers 12, 14 have approximately 60 to 80 pick ends and approximately 60 to 70 warp ends per square 10 mm.

Extending between the two layers of material 12, 14 are multiple core stands 18 that maintain the separation between the two layers and absorb lateral and rotational shear forces. As shown in Fig. 1 , the core strands 18 can, in some embodiments, be generally perpendicular to the layers of material 12, 14. Of course, other orientations are possible. Like the strands 16 of the layers 12, 14, the core strands can comprise individual fiber filaments ("fibers") or yarns that are composed of multiple fiber filaments. In some embodiments, each strand 18 has similar characteristics to the strands 16 used to form the layers 12, 14. Regardless, the strands 18 are coupled to the layers 12, 14. In some embodiments, the strands 18 are alternately threaded through the top and bottom layers 12, 14 in a continuous fashion so that each strand can have multiple lengths that extend between the two layers. As can be appreciated from Fig. 1 , those lengths can be curved. More particularly, the lengths can form S-shapes and inverted S-shapes that, when viewed together from a side of the fabric 140, form a repeating figure-8 pattern (see, e.g., Fig. 2).

The fibers used to construct the three-dimensional spacer fabric 10 can be made from any material that provides the desired level of lateral and rotational acceleration dissipation. In some embodiments, the fibers are glass fibers. A commercial example of a base fabric that can be used to form the three-dimensional spacer fabric 10 is Parabeam™, which is available from Parabeam b.v. in The Netherlands. In other embodiments, the fibers are aramid fibers, such as meta- aramid or para-aramid fibers (or combinations thereof). Because of their high strength, aramid fibers may be desirable when greater impact resistance is desired. In still other embodiments, the fibers can be carbon fibers. Such fibers may be desirable when lighter weight is desired. Of course, the three-dimensional spacer fabric 10 can be made from any combination of these materials and can further include other materials. By varying the fiber types, the density of the fabric 10 and its compression stiffness can be tailored to suit a particular application.

As noted above, the three-dimensional spacer fabric 10 is formed by infusing a base fabric with a curable resin. When no resin has been applied to the base fabric, the fabric is very flexible and in a relatively compressed state in which the core strands 18 are not generally perpendicular to the top and bottom layers 12, 14 as shown in Fig. 1 . When the base fabric is infused with a curable resin, however, the fabric can expand and become more rigid. The structural rigidity or integrity and tailored flexibility provided by the cured resin are what enable the three-dimensional spacer fabric 10 to absorb linear impact and shear forces. In some embodiments, the completed three-dimensional spacer fabric 10 has a shear strength of approximately 15 to 25 psi and a shear modulus of approximately 250 to 350 psi. In some embodiments, the three-dimensional spacer fabric 10 has compression and shear characteristics that are approximately equivalent to a 40 to 100 A durometer shore hardness material. Such a fabric possesses substantially instantaneous spring-back characteristics. Accordingly, the fabric can deform to absorb forces but immediately returns to its original orientation once the force is no longer applied.

The resin infused into the base fabric is selected so as to provide the above- mentioned absorption and spring-back functionalities. In some embodiments, these functionalities are obtained when thermoplastic resins are used. Example thermoplastic resins include urethane elastomers, polyurethanes, rubber elastomers, silicones, polyamides, polycarbonates, polypropylenes, thermoplastic polyesters, and the like.

The base fabric can be infused with resin using various methods. In a first method, resin can be applied using vacuum-assisted resin transfer molding (VARTM). In this process, double-sided tape is applied to a clean, flat processing surface, such as a table surface, so as to trace the outline of the base fabric to which the resin is to be infused but with a 2 to 3 inch excess margin. Before removing the release paper from the top surface of the tape, the table surface can be sprayed with a mold-release spray, such as Fekote™ NC700.

A base fabric (which is also referred to as the "preform") of a desired thickness is laid on the table within the boundary defined by the tape. A low-friction fabric, such as polytetrafluoroethylene (PTFE) fabric, can be laid on top of the base fabric and a high-permeability mesh, such as a nylon mesh, can then be laid on top of the surface of the low-friction fabric. During the infusion process, the high- permeability mesh helps to "wet out" the base fabric and the low-friction fabric, which has a relatively low permeability, and slows down the infusion process to a desirable level. Therefore, the low-friction fabric and high-permeability mesh act as a distribution media for the resin. Together, the base fabric, low-friction fabric, and high-permeability fabric are referred to as the "lay-up."

Vacuum and infusion lines are placed on opposite sides of the lay-up with a breather cloth (a thick, permeable fabric) to provide a path for venting air. The lay-up is then covered with a vacuum bagging film, such as a nylon film, and the film is adhered to the table with the tape (after the release paper has been removed). A vacuum is then applied to the lay-up ensuring that no leaks occur. In some embodiments, the vacuum is approximately -12 to -14 psi. The vacuum is applied for an extended period of time, such as 2 or more hours, to perform de-bulking, which removes any entrapped air. It is noted that the core strands of the base fabric fully collapse when the vacuum is applied. While the fabric is in this orientation, the infusion process is similar to impregnating two-dimensional stacks of fiber.

Prior to infusion, the resin is pre-mixed with one or more curing agents for several minutes and the resin is then drawn into the lay-up under vacuum. Resin slowly begins to wet out the base fabric and progresses from one end to the other, i.e. from the infusion end to the vacuum end. The time to complete infusion can vary depending on the size of the base fabric and the viscosity of the resin. By way of example, it can take up to 10 minutes for a 350 centipoise resin to fully wet out a 12" x 12" base fabric. Once the resin has fully wet out, the base fabric and has saturated the fabric for several minutes (e.g., up to 15 minutes), the vacuum bagging film is carefully cut open to enable the wetted fabric to expand. In some embodiments, the fabric will expand to its full, final thickness (height) within a few minutes (e.g., 4-5 minutes). The thickness depends upon the dimensions of the base fabric, which can be selected according to the intended application. In some embodiments, the fabric thickness is approximately 3 to 25 mm. For example, the fabric can be produced in standard thicknesses of 3, 6, 10, 15, 18, 21 , and 25 mm.

Optionally, other mechanical actions can be performed prior to full curing of the resin to alter the characteristics of the completed fabric. For example, the wetted fabric can be physically manipulated to alter the core strand orientations or to change the shape of the lay-up. Regardless of whether or not such actions are performed, full curing can be achieved in approximately 5 to 30 minutes after the vacuum has been released. It is noted that this curing can be performed at room temperature or at an elevated temperature depending upon the resin and the speed of curing that is desired.

Another method that can be used is a melt process within a mold. This method may be particularly useful when infusing the base fabric with a high-viscosity resin. In the melt process, a base fabric is placed within an interior cavity of a metal mold, the cavity being approximately 0.5 to 1 inches tall. The lateral dimensions of the cavity depend upon the size of the base fabric but may be up to 24 inches or greater. Films of solid resin are stacked on both sides of the base fabric within the mold to form the lay-up. As an example, approximately 4 to 8 thermoplastic polyurethane (TPU) films of approximately 10 mil thickness are stacked on either side of the base fabric. The temperature is of the mold is raised to the melt temperature of the resin films. In the case of TPU films, this temperature is approximately 400 to 500°F. The mold is held at the elevated temperature to enable the films to melt and the resin to flow through the base material via capillary action. In some embodiments, pressure is applied to the lay-up by the mold to facilitate this flow. For example, the mold can be compressed to raise the pressure within the cavity to approximately 50 to 100 psi. In some embodiments, the compression step is performed for a short period of time (e.g., less than 60 seconds) to enable spring back of the wetted base fabric.

Yet another method that can be used to wet the base fabric with resin is with pressure applied by a squeegee using a hand roller. In such a process, a base fabric can be secured within a frame and resin can be manually forced into the fabric. This method can be particularly useful when using a silicone elastomer resin, such as a two-part silicone elastomer.

Once it has been produced, the three-dimensional spacer fabric can be used by itself as a pad that is provided within a protective helmet or otherwise positioned on the body or another object. In embodiments in which the pad contacts the body, the three-dimensional spacer fabric can be used in conjunction with a polymeric foam pad for comfort. For example, such a pad can used with a three-dimensional spacer fabric in a stacked configuration, such as that shown in Fig. 2. As illustrated in this figure, a composite pad 20 is formed when a foam pad 22 is placed on top of a three-dimensional spacer fabric 24. In some embodiments, the foam pad 22 is made of urethane and is approximately 5 to 12 mm thick. In cases in which the composite pad 20 is used in a helmet, the three-dimensional spacer fabric 24 can be secured to the inner surface of the helmet shell and the foam pad 22 can contact the wearer's head. Such an embodiment is illustrated in Fig. 12 in which multiple composite pads 20 are provided within a helmet shell S.

Fig. 3 illustrates another example of a composite pad 30. As shown in Fig. 3, the pad 30 comprises two foam pads 32 and 34 that are stacked on a three- dimensional spacer fabric 36. In such a case, the foam pads 32, 34 can have different characteristics, such as different densities.

Fig. 4 illustrates another composite pad 40. In this example, the composite pad 40 includes a single foam pad 42 but two stacked three-dimensional spacer fabrics 44 and 46, which can have different characteristics, such as hardnesses.

Fig. 5 illustrates yet another composite pad 50. In this embodiment, the pad

50 includes a single foam pad 52 and a single three-dimensional spacer fabric 54 that are in a stacked arrangement. In addition, the stack is encapsulated by a thin layer 56 of relatively rigid material that provides increased structural integrity to the pad 50 so as to reduce the potential for collapse of the pad. In some embodiments, the relatively rigid material is a self-reinforced polypropylene having a thickness of approximately 0.9 to 1 .2 mm. Such material can be obtained from Propex under the trade name Curv™.

Fig. 6 illustrates another encapsulated composite pad 60. In the embodiment of Fig. 6, however, the pad includes one foam pad 62 and two three-dimensional spacer fabrics 64 and 66 that are encapsulated by an outer layer 68.

While particular embodiments of composite pads have been illustrated in Figs. 2-6, it is noted that many other embodiments are possible. For example, other composite pads can be hybrid versions of a pad that combine features shown in Figs. 2-6. Fig. 7 shows the results of a comparison of conventional helmet pads and pads incorporating a three-dimensional fabric. More particularly, Fig. 7 compares the National Operating Committee on Standards for Athletic Equipment (NOCSAE) severity index for a Schutt™ Vengence™ football helmet fitted with a variety of different padded liners. The various helmets included the following:

Baseline: Helmet fitted with the standard Schutt™ pads.

Double-deck All Side Retro: Helmet in which all pads were replaced with pads that comprised a layer of hard spacer fabric (60 Shore A), a layer of soft spacer fabric (40 Shore A), and a layer of foam, which were encapsulated by a thermoplastic polyurethane film cover.

Double-deck Jaw Pad: Helmet in which the jaw pads were replaced with pads that comprised a layer of hard spacer fabric (60 Shore A), a layer of soft spacer fabric (40 Shore A), and a layer of foam, which were encapsulated by a thermoplastic polyurethane film cover.

Sides Retro, All Hard, No Curv: Helmet in which the side pads were replaced with pads that comprised a layer of hard spacer fabric (60 Shore A) and a layer of foam, which were encapsulated by a thermoplastic polyurethane film cover.

Sides Retro, All Hard: Helmet in which the side pads were replaced with pads that comprised a layer of hard spacer fabric (60 Shore A), a layer of foam, and a layer of Curv™, which were encapsulated by a thermoplastic polyurethane film cover.

Jaw Pad Single Hard: Helmet in which the jaw pads were replaced with pads that comprised a layer of hard spacer fabric (60 Shore A), a layer of foam, and a layer of Curv , which were encapsulated by a thermoplastic polyurethane film cover.

Sides Retro Single Hard: Helmet in which the side pads were replaced with pads that comprised a layer of hard spacer fabric (60 Shore A), a layer of foam, and a layer of Curv™, which were encapsulated by a thermoplastic polyurethane film cover.

Jaw Pad Soft Single: Helmet in which the jaw pads were replaced with pads that comprised pads that comprised a layer of soft spacer fabric (40 Shore A), a layer of foam, and a layer of Curv™, which were encapsulated by a thermoplastic polyurethane film cover.

As can be appreciated from the results of Fig. 7, three of the helmets that incorporated a three-dimensional spacer fabric equaled or exceeded the performance of the standard helmet, while also providing attenuation of rotational acceleration that the standard helmet does not provide.

The chemistry of the resin can be altered to alter the characteristics of fabrication or the resulting three-dimensional spacer fabric. In one embodiment, a two-part thermoset urethane elastomer can be used that can be infused and cured at room temperature. For example, thermoplastic polyurethane can be mixed with urethane rubber to form the elastomer. When these materials are mixed in different ratios, a three-dimensional spacer fabric can be produced that ranges from soft to hard. The relatively soft fabrics can have durometers of approximately 20 to 50 Shore A and the relatively hard fabrics can have durometers of approximately 50 to 90 Shore A. During experimentation, soft (40 Shore A) and hard (60 Shore A) three- dimensional spacer fabrics made of glass fiber and thermoplastic polyurethane resin were fabricated having thicknesses of 10 mm and 21 mm After fabrication, the fabrics were post-cured at approximately 80 to 150°F. Fourier transform infrared (FTIR) spectroscopy was then performed on the fabrics and a standard blue Schutt™ pad to compare their compositions. The results of this spectroscopy are shown in Figs. 8-1 1 . Fig. 8 shows the results for the standard Schutt™ pad, Fig. 9 shows the results for the hard (60 Shore A) three-dimensional spacer fabric, Fig. 10 shows the results for the soft (40 Shore A) three-dimensional spacer fabric, and Fig. 1 1 compares the results for the hard spacer fabric (top), soft spacer fabric (middle), and Schutt™ pad (bottom).

In other embodiments, TPU additives can be introduced to a urethane elastomer to provide TPU chemistry blended in with urethane elastomer. Such a material is processable like a thermoset polymer but has light cross-linking characteristics like a thermoplastic. For example, low temperature processable TPU or TPU solubilzable in easily-evaporable solvents, such as tetrahydrofuran (THF), can be blended in liquid form during the processing reaction. As the urethane elastomer cures it entangles with already-formed TPU and forms thermoplastic semi- interpenetrating networks (semi-IPN). This imparts hybrid characteristics with a reduction in chemical crosslinking. Depending on the percentage of blending and the nature of the soft and hard segment chemistry, the TPU characteristics can be added and formulated. The hybrid TPU-urethane elastomer can provide the physical crosslinking commonly observed in TPUs via hydrogen bonding interactions via urethane-urethane hydrogen, ether-urethane, or urea-urethane hydrogen bonding. The hydrogen bonding characteristics can break and easily re-form to provide additional fatigue durability to the urethane elastomer.

In other embodiments, modified resin formulations can be used that combine urethane elastomers with organosilane adhesive or ionomers using carboxylic acids such as 2,2- bis (hydroxyl ethyl) propanoic acid (anionomers). The organosilane adhesive can enable enhanced bonding with fibers of the base fabric and a urethane coating can form because of enhanced resin-filler interactions. The acid modification can provide better hydrophilic character to the urethane elastomer. Amine or hydroxyl terminated alkyl phosphonic acids are hydrolytically stable and therefore are good candidates for formulating the urethane resin matrix.

In still another embodiment, a solvent-based TPU coating can be used for infusion. Pure TPU is soluble in solvents such as tetrahydrofuran (THF), dimethyl formamide (DMF), and dimethyl acetamide (DMAc). These elastomers are characterized by multi-block structures comprised of long-soft segments (poly ether, ester or siloxane functional groups) and short-hard segments (aromatic or aliphatic) and provide for micro-phase separation between the segments. The termly- reversible hydrogen bonding interactions or physical cross-links among the hard segments allow the "packing" of the hard segments in an amorphous matrix of soft segments. The ability to dissolve and impregnate the solution provides more freedom for mixing and blending of various TPUs (mixed soft segments and hard segments in varying ratios) so that desired properties such as hardness, hydrolytic durability, and light-stability can be achieved.

Claims

CLAIMS Claimed are:

1 . A three-dimensional spacer fabric, comprising:

a first layer of material;

a second layer of material;

core strands that extend between the two layers of material; and

a cured resin coating the two layers and the core strands, the cured resin enabling the fabric to flex to absorb rotational acceleration.

2. The fabric of claim 1 , wherein the first and second layers of material are woven.

3. The fabric of claim 1 , wherein the first and second layers comprise filament fibers.

4. The fabric of claim 3, wherein the filament fibers include glass, aramid, or carbon fibers.

5. The fabric of claim 1 , wherein the core strands are made of filament fibers.

6. The fabric of claim 5, wherein the filament fibers include glass, aramid or carbon fibers.

7. The fabric of claim 5, wherein each strand comprises multiple filament fibers.

8. The fabric of claim 1 , wherein the resin is a thermoplastic resin.

9. The fabric of claim 1 , wherein the resin is a urethane elastomer, a polyurethane, a rubber elastomer, a silicone, or a combination thereof.

10. The fabric of claim 1 , wherein the fabric has a shear strength of approximately 15 to 25 psi and a shear modulus of approximately 250 to 350 psi.

1 1 . The fabric of claim 1 , wherein the fabric has compression and shear characteristics that are approximately equivalent to a 40 to 100 A durometer shore hardness material.

12. A method for making a three-dimensional fabric, the method comprising:

infusing a base fabric with a resin, the base fabric including a first layer of material, a second layer of material, and core strands that extend between the two layers; and

enabling the resin to cure.

13. The method of claim 12, wherein infusing comprises performing vacuum-assisted resin transfer molding.

14. The method of claim 12, wherein infusing comprises melting a solid resin and pressing it into the base fabric at an elevated pressure.

15. The method of claim 12, wherein infusing comprises manually infusing the resin into the base fabric using a squeegee.

16. A protective pad comprising:

a three-dimensional spacer fabric including a first layer of material, a second layer of material, and core strands that extend between the two layers of material, wherein the two layers and the core strands are coated in a cured resin; and

a foam pad.

17. The protective pad of claim 16, wherein the core strands are made of filament fibers.

18. The protective pad of claim 16, wherein the resin is a thermoplastic resin.

19. The protective pad of claim 16, wherein the foam pad is a polymeric foam pad.

20. The protective pad of claim 16, further comprising a relatively stiff outer layer that encapsulates the foam pad and the three-dimensional spacer fabric.