Patent Application
20160281272
The present disclosure relates to a composite formed with a bimodal binder. In particular, the present disclosure relates to a ballistic resistant composite formed from a plurality of fibers and a bimodal binder and a method of forming the same.
Ballistic resistant articles may contain high-strength fibers which can be formed into various articles, such as vests, helmets, vehicle panels, additional articles of clothing, and additional items for military or police applications which resist penetration of bullets, shrapnel, and shells. Exemplary high-strength fibers are polyethylene fibers, aramid fibers, graphite fibers, nylon fibers, glass fibers, and the like. For many applications, such as ballistic resistant articles of clothing, the fibers may be used in a woven or knitted fabric. For other applications, the fibers may be encapsulated or embedded in a polymeric matrix material to form woven or non-woven composites.
Hard or rigid body armor provides good ballistic resistance but can be bulky and stiff. Therefore, body armor garments, such as ballistic resistant vests, are preferably formed from flexible or soft armor materials. However, while such flexible or soft armor materials have good ballistic resistant qualities, these materials may also exhibit low abrasion resistance, which affects the durability of the armor. Additionally, it is necessary for hard and soft ballistic resistant articles to withstand environmental conditions which may degrade the ballistic resistance of the material. For example, due to the nature of military applications, ballistic resistant articles may be exposed to a variety of environmental conditions which may degrade the material, such as sea water, gasoline, gun lubricant, and petroleum. As such, the ballistic resistant articles are formed to resist such degradation when exposed to environmental conditions or substances.
Referring to
Composite 14 may be comprised of high-performance fibers and a binder. The binder may be at least partially formed of a polymeric material and may be applied to the fibers through conventional coating processes (e.g., casting, dispersions).
As composite 14 enters steel belt press 2, first and second belts 10, 12 are configured to apply a continuous pressure up to approximately 70 bar or 1,000 psi to composite 14 as composite 14 advances through steel belt press 2. Additionally, composite 14 passes through temperature unit 8 which includes a heating portion 8a and a cooling portion 8b. As such, composite 14 receives continuous high pressure from first and second belts 10, 12 while being both heated and cooled, which results in a high degree of compaction and a reduction of air voids in composite 14. It is believed that the compaction from steel belt press 2 removes voids and other interstices within composite 14, thereby providing a smooth surface which is resistant to corrosive and degrading conditions.
One disadvantage of using steel belt press 2 to produce ballistic resistant composite 14 is that the costs associated with producing composite 14 may be high, due to the high expense of steel belt press 2. However, other less expensive processing techniques configured to apply pressure, heat, and cooling to composite 14 may not be configured to apply similar levels of pressure and/or continuous pressure. Additionally, body armor and other ballistic resistant materials produced by these less expensive processing techniques should be configured to withstand environmental conditions (e.g., fuel, salt water, humidity, etc.) thought to degrade the material properties of such composites without compromising the ballistic resistant properties thereof. Therefore, a need exists for a low-cost method of producing soft ballistic resistant articles which can withstand various environmental conditions.
The present disclosure provides a ballistic resistant composite which includes a plurality of fibers and a bimodal binder applied to the plurality of fibers.
In one form thereof, the present disclosure provides a ballistic resistant composite comprising a plurality of fibers and a bimodal binder applied to the plurality of fibers. The binder has a crystalline component with a melting temperature and an amorphous component with a softening temperature. The crystalline component and the amorphous component have at least one of the following properties relative to one another: (1) the melting temperature of the crystalline component is less than the softening temperature of the amorphous component; (2) at a temperature above the melting temperature of the crystalline component, a viscosity of the crystalline component is less than a viscosity of the amorphous component; and (3) at a temperature above the melting temperature of the crystalline component, a surface energy of the crystalline component is less than a surface energy of the amorphous component.
In certain embodiments, the crystalline component is a wax material selected from the group consisting of carnauba wax, stearamide wax, polyethylene wax, paraffin wax, polyolefin wax, and microcrystalline wax, and the amorphous component is a polymeric material selected from the group consisting of acrylic, polyurethane, nitrile rubber, acrylonitrile butadiene copolymer, and fluorocarbon. Additionally, the plurality of fibers may be comprised of polyethylene.
In certain embodiments, the plurality of fibers defines at least a first fiber ply and a second fiber ply oriented 90 degrees from the first fiber ply.
In certain embodiments, the amorphous component comprises 60-95 wt. % of the bimodal binder and the crystalline component comprises 5-40 wt. % of the bimodal binder.
In certain embodiments, the melting temperature of the crystalline component is about 50-140° C.
In another form thereof, the present disclosure provides a method of forming a ballistic resistant composite comprising providing a first plurality of fibers in a unidirectional orientation, providing a second plurality of fibers in a unidirectional orientation, and providing a binder having an amorphous component and a crystalline component. The method further comprises coating the first plurality of fibers with the binder, coating the second plurality of fibers with the binder, positioning the first plurality of fibers at a 90 degree angle to the second plurality of fibers, heating the first and second pluralities of fibers to a temperature within a melting temperature range of the crystalline component, applying a pressure of less than one bar to the first and second pluralities of fibers when at a temperature within the melting point range of the crystalline component, and cooling the first and second pluralities of fibers.
In certain embodiments, said pressure step includes is conducted with a flat-bed laminator.
In certain embodiments, said applying step includes applying a first pressure of less than 0.5 psi to the composite during said heating step and applying a second pressure of 10 psi-300 psi when the composite is at the temperature within the melting point range of the crystalline component.
In certain embodiments, the composite may be heated and/or cooled for as little as 0.01 seconds, 0.50 seconds, 1.0 seconds, 1.5 seconds, 2.0 seconds, 2.5 seconds, 3.0 seconds, or as much as 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes, or any range delimited by any pair of the foregoing values.
Also provided is a method of forming a ballistic resistant composite comprising:
providing a first fiber ply comprising a plurality of unidirectionally oriented first fibers, wherein said first fibers are coated with a first bimodal binder that comprises an amorphous component and a crystalline component;
providing a second fiber ply comprising a plurality of unidirectionally oriented second fibers, wherein said second fibers are coated with a second bimodal binder that comprises an amorphous component and a crystalline component;
positioning the first fiber ply and second fiber ply in a stacked arrangement, heating the first fiber ply and the second fiber ply to a temperature within a melting temperature range of the crystalline component;
applying a pressure of less than one bar to the first fiber ply and to the second fiber ply when said plies are at a temperature within the melting temperature range of the crystalline component, whereby the first fiber ply and second fiber ply are attached to each other and thereby form a ballistic resistant composite; and cooling the first fiber ply and the second fiber ply.
The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of embodiments taken in conjunction with the accompanying drawings, wherein:
The present disclosure relates to a ballistic resistant composite 20 including a bimodal binder, the composite formable in a manner in which it is exposed to low pressure for a short duration of time and at a controlled temperature. More particularly, the bimodal binder of composite 20 allows the composite to be formed with a flat-bed laminator, for example, which may be less expensive than other processing methods, such as a steel belt press.
Composite 20 includes a plurality of fibers 20a embedded in a bimodal polymeric matrix or binder material 20b (
A. Fiber Material
Ballistic resistant composite 20 includes fiber material 20a which is embedded with bimodal binder material 20b. Fiber material 20a is formed from a plurality of fibers, each of which has an elongate body with a length much greater than the transverse dimensions of width and thickness. The cross-sections of the fibers of fiber material 20a may be circular, flat, or oblong. Accordingly, the term “fiber” includes filaments, ribbons, strips, and the like having regular or irregular cross-sections. Each fiber of fiber material 20a also may be of regular or irregular multi-lobal cross-section projecting from the linear or longitudinal axis of the fiber.
Exemplary fiber material 20a comprises a non-woven, cross-plied, unidirectional fabric. More particularly, fiber material 20a includes a plurality of plies of unidirectional fibers oriented in a cross-ply configuration in which a first ply of fiber material 20a is oriented 90-degrees to an adjacent second ply of fibers. The fibers within each ply are adjacent and parallel to each other and, therefore, are oriented in a unidirectional arrangement. In one embodiment, each fiber may be approximately 0.063 inches or 1.588 mm in diameter.
Fiber material 20a may be comprised of polyethylene fibers, aramid fibers, graphite fibers, nylon fibers, glass fibers, and the like. For example, in one embodiment, fiber material 20a is comprised of ultra-high molecular weight polyethylene, such as Honeywell 1150-denier SPECTRA® Merge 95121 UHMWPE fibers and/or Honeywell 1300-denier SPECTRA® Merge 95159 UHMWPE fibers. Each fiber ply of the fiber material 20a may have a fiber areal density of from about 15 g/m2 to about 250 g/m2, typically from about 20 g/m2 to about 100 g/m2, and often from about 25 g/m2 to about 70 g/m2, and most preferably about 35 g/m2. The fiber areal density refers to the weight of the fibers only (i.e., not including the binder) per unit area. Additional details of fiber material 20a may be disclosed in U.S. Pat. No. 7,994,075, issued on Aug. 9, 2011, and U.S. Pat. No. 8,017,530, issued on Sep. 13, 2011, the complete disclosures of which are expressly incorporated by reference herein.
B. Bimodal Binder Material
Bimodal binder material 20b is applied to fiber material 20a to form ballistic resistant composite 20. Exemplary binder material 20b is a bimodal binder comprised of the amorphous component which has amorphous phases discernible through magnification and the crystalline component which has crystalline phases discernible through magnification, as is known to one of ordinary skill in the art.
1. Amorphous Component
The amorphous component of binder material 20b is characterized as amorphous because it does not have long-range order which is characteristic of a crystalline material. The lack of long-range order allows the amorphous component to be flexible which allows for flexibility in composite 20 and may be necessary when forming soft body armor that is configured to bend and move when being worn. The exemplary amorphous component of binder material 20b defines the majority component of binder material 20b. For example, the amorphous component may comprise at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or within any range delimited by any pair of the foregoing values, of the overall weight of binder material 20b.
The amorphous component may be comprised of a liquid or powder resin, such as a polyurethane resin, acrylic resin, nitrile rubber resin, acrylonitrile butadiene copolymer resin, a fluorocarbon resin, polybutadiene resin, polyisoprene resin, ethylene-propylene resin, polysulfide resin, polyacrylate resin, polyester resin, and/or polyether resin. For example, the amorphous component of binder material 20b may be a waterborne dispersion of an acrylonitrile butadiene copolymer, supplied at 40% solids, such as TYLAC® 873 commercially available from Mallard Creek Polymers of Charlotte, NC000000, and/or a waterborne dispersion of a fluorocarbon resin, such as NUVA® 2040 commercially available from Clariant GMBH Corporation of Germany.
The exemplary amorphous component of binder material 20b has a greater viscosity, surface energy, and/or softening temperature than the crystalline component when at a temperature within the melting temperature of the crystalline component. More particularly, in one embodiment, the crystalline and amorphous components are selected such that the melting temperature of the crystalline component is less than the softening temperature of the amorphous component and/or a viscosity of the crystalline component is less than a viscosity of the amorphous component when at a temperature above the melting temperature of the crystalline component. Additionally, the amorphous and crystalline components may be selected so that, at a temperature above the melting temperature of the crystalline component, a surface energy of the crystalline component is less than a surface energy of the amorphous component. For example, in one embodiment, the softening temperature of the amorphous component of binder material 20b is less than a degradation temperature of fiber material 20a but substantially greater than the melting temperature of the crystalline component such that when the crystalline component melts and begins to flow, the amorphous component does not does appreciably melt or undergo a physical change and may even exhibit a resistance to flow. More particularly, amorphous materials may not have a distinct melting point but will start to soften within a softening temperature range and will continue to soften as the temperature increases. Conversely, crystalline materials have a true melting temperature and change drastically from a hard solid to a fluid over a much shorter temperature range. In this way, the amorphous component is incompatible with the crystalline component because the amorphous component is not physically modified or chemically reactive with the crystalline component during a physical transformation of the crystalline component. In one example, Honeywell 1150-denier SPECTRA® Merge 95121 UHMWPE fibers and/or Honeywell 1300-denier SPECTRA® Merge 95159 UHMWPE fibers may have a degradation temperature of about 140° C. and the crystalline component may have melting temperature up to 140° C., as detailed further herein. Therefore, the softening temperature of the amorphous component may be as little as 90° C., 100° C., 110° C., 120° C., 130° C., 140° C., 150° C., 160° C., 170° C., 180° C., 190° C., or as great at 200° C., 210° C., 220° C., 230° C., 240° C., 250° C., 260° C., or more, or may be within any range delimited by any pair of the foregoing values.
Alternatively, in one embodiment, the softening temperature of the amorphous component may be less than the melting temperature of the crystalline component. However, because the viscosity and/or surface energy of the amorphous component is greater than that of the crystalline component when at a temperature within the melting temperature of the crystalline component, the amorphous component will remain solid or highly viscous and, therefore, the crystalline component will flow around the amorphous component such that the amorphous and crystalline components do not mix. Additional details of the amorphous component of binder material 20b may be disclosed in U.S. Pat. No. 7,994,075, issued on Aug. 9, 2011, and U.S. Pat. No. 8,017,530, issued on Sep. 13, 2011, the complete disclosures of which are expressly incorporated by reference herein.
2. Crystalline Component
The crystalline component of binder material 20b is added to, or doped into, the amorphous component. The crystalline component of binder material 20b is characterized as crystalline because it includes a highly ordered molecular structure defined by a crystal lattice. The crystal lattice of the crystalline component may be discernible through magnification, as is known to one of ordinary skill in the art. Unlike the amorphous component, the crystalline component may have less flexibility but is included in binder material 20b because it allows for the compaction and densification of composite 20 at processing conditions with decreased pressure, thereby increasing the ballistic resistant properties of composite 20. Also, as discussed further below, during processing of the present composite, the crystalline material undergoes a phase change, such as melting, which allows the crystalline material to flow relative to the amorphous material, with subsequent re-solidification to provide desirable properties such as smoothness and density enhancement to provide resistance to corrosive environments.
The crystalline component of binder material 20b is the minority component thereof. For example, the crystalline component may comprise 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 1% or may be within any range delimited by any pair of the foregoing values of the overall weight of binder material 20b.
The crystalline component may be comprised of any crystalline polymer which is incompatible with the amorphous component. More particularly, the crystalline component may be incompatible with the amorphous component such that the two components do not mix or act as a single material. For example, the crystalline component of the present disclosure may be a wax material, such as a carnauba wax, a polyethylene wax, polyolefin wax, a paraffin wax, stearamide wax, and/or a microcrystalline wax. Waxes are generally defined as materials that are solids at room temperature but melt or soften without decomposing above about 40° C. Waxes are generally organic and insoluble in water at room temperature but may be water wettable and may form pastes and gels in some solvents, such as non-polar organic solvents. The molecular weight of a wax may range from about 400 to about 25,000 g/mol and may have melting points ranging from about 40° C. to about 150° C. Waxes generally do not form stand-alone films like higher order polymers and generally are aliphatic hydrocarbons that contain more carbon atoms than oils and greases.
The viscosity of waxes may range from low to high, typically depending on the molecular weight of the wax and the crystallinity. The viscosity of waxes above their melting point is typically low. As used herein, a “low viscosity wax” describes a wax having a melt viscosity of less than or equal to about 500 centipoise (cps) at 140° C. Preferably, a low viscosity wax has a viscosity of less than about 250 cps at 140° C., most preferably less than about 1.00 cps at 140° C. However, some linear polyethylene waxes (molecular weight of about 2,000 to about 10,000 g/mol) and polypropylene waxes may have moderate to high viscosity, i.e., as high as 10,000 cps after melting. Viscosity values are measured using techniques that are well known in the art and may be measured, for example, using capillary, rotational or moving body rheometers. A preferred measurement tool is a Brookfield rotational viscometer.
Suitable waxes include both natural and synthetic waxes and non-exclusively include animal waxes, such as beeswax, Chinese wax, shellac wax, spermaceti and wool wax (lanolin); vegetable waxes, such as bayberry wax, candelilla wax, carnauba wax, castor wax, esparto wax, Japan wax, Jojoba oil wax, ouricury wax, rice bran wax and soy wax; mineral waxes, such as ceresin waxes, montan wax, ozocerite wax and peat waxes; petroleum waxes, such as paraffin wax and microcrystalline waxes; and synthetic waxes, including polyolefin waxes, polyethylene, polypropylene waxes, Fischer-Tropsch waxes, stearamide waxes (including ethylene bis-stearamide waxes), polymerized α-olefin waxes, substituted amide waxes (e.g. esterified or saponified substituted amide waxes) and other chemically modified waxes. Also suitable are waxes described in U.S. Pat. No. 4,544,694, the complete disclosure of which is expressly incorporated by reference herein. Of these, the preferred waxes include paraffin waxes, micro-crystalline waxes, Fischer-Tropsch waxes, branched and linear polyethylene waxes, polypropylene waxes, large particle size polyethylene waxes, carnauba waxes, ethylene bis-stearamide (EBS) waxes, and combinations thereof.
For example, exemplary crystalline materials of binder material 20b may be a waterborne dispersion of carnauba wax, supplied at 35% solids, such as HYDROCER™ EC-35 wax commercially available from Shamrock Technologies Inc. of Newark, N.J.; a waterborne dispersion of large particle size polyethylene wax, supplied at 40% solids, such as LL405 commercially available from Michelman, Inc. of Cincinnati, Ohio; a waterborne dispersion of high density polyethylene wax, supplied at 35% solids, such as Michelman, Inc. LL411; a waterborne dispersion of paraffin wax, supplied at 32% solids, such as Michelman, Inc. 454; a waterborne dispersion of microcrystalline wax, supplied at 40% solids, such as Michelman, Inc. HL-480; and/or a waterborne dispersion of Fischer Tropsch polyethylene wax, supplied at 40% solids, such as Michelman, Inc. ME98040.
The exemplary crystalline component of binder material 20b may have a low melt viscosity and a melting temperature of 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., 100° C., 105 ° C., 110° C., 115° C., 120° C., 125 C, 130° C., 135° C., 140° C., or any range delimited by any pair of the foregoing values. More particularly, a carnauba wax may have a melting point of approximately 75-85° C. and a low melt viscosity. Similarly, a micro-crystalline wax may be have a melting temperature of approximately 60-90° C. and a low melt viscosity. Additionally, a Fischer-Tropsch wax may have a melting temperature of 95-100° C. and a low melt viscosity. Also, a paraffin wax may have a melting temperature of 50-70° C. and a low melt viscosity. Additionally, polyethylene waxes may have a melting temperature of 90-140° C. and, depending on the structure of the polyethylene wax, may have low, moderate, or high viscosity. As such, the crystalline component has a sharp melting temperature range that may only span about 5-50° C. which allows the crystalline component to melt and cool rapidly.
As detailed herein, the melting point and melt viscosity of the crystalline component may be different than the softening temperature and viscosity of the amorphous component. In this way, when the crystalline component is exposed to a temperature within its melting point range, the crystalline component melts rapidly and begins to flow around the solid amorphous component which does not appreciably melt at temperatures within the melting point range of the crystalline component. The molten crystalline component is then able to fill any voids within the blended binder material 20b and also within composite 20. Additionally, when the crystalline component is exposed to a temperature that is less than its melting point range, the crystalline component cools rapidly to again form a solid phase. However, because the crystalline component flowed around the solid amorphous component when at its melting temperature, the crystalline component is embedded and mixed with the amorphous component once cooled.
For example, if an amorphous synthetic rubber defines the amorphous component of binder 20b and a crystalline polyurethane resin defines the crystalline component of binder 20b, a cast film of binder material 20b maintains discreet regions of the crystalline polyurethane resin within the larger mass of the amorphous synthetic rubber. Upon applying heat to composite 20, for example in a flat-bed laminator, the amorphous regions of the synthetic rubber remain solid but the discreet crystalline regions of the polyurethane resin melt and flow into voids within fiber material 20a which improves the fluid resistance of composite 20 by reducing capillary forces and reducing the total effective surface area of composite 20. In this way, composite 20 remains flexible due to the amorphous synthetic rubber but has improved ballistic resistance due to the crystalline polyurethane resin.
Alternatively, in one embodiment, the softening temperature of the amorphous component may be less than the melting temperature of the crystalline component. However, because the viscosity and/or surface energy of the amorphous component is greater than that of the crystalline component when at a temperature greater than the melting temperature of the crystalline component, the amorphous component will remain solid or highly viscous and, therefore, the crystalline component will flow around the amorphous component and the amorphous and crystalline components do not mix. More particularly, in one embodiment, the crystalline and amorphous components are selected such that the melting temperature of the crystalline component is less than the softening temperature of the amorphous component and/or the viscosity of the crystalline component is less than the viscosity of the amorphous component when at a temperature above the melting temperature of the crystalline component. Additionally, the amorphous and crystalline components may be selected so that, at a temperature above the melting temperature of the crystalline component, the surface energy of the crystalline component is less than the surface energy of the amorphous component. Additional details of the crystalline component of binder material 20b may be disclosed in U.S. Pat. No. 7,994,075, issued on Aug. 9, 2011, and U.S. Pat. No. 8,017,530, issued on Sep. 13, 2011, the complete disclosures of which are expressly incorporated by reference herein.
C. Ballistic Resistant Composite
To form bimodal binder material 20b, the crystalline and amorphous components are mixed together through various processes.
1. Preparing the Bimodal Binder
In one embodiment, the crystalline and amorphous components may be mixed by forming wet blend emulsions and/or wet blend solutions. More particularly, the wet blend emulsion and/or wet blend solution includes a solvent in which both the amorphous component and the crystalline component are soluble. This wet blend solution and/or wet blend emulsion then may be cast into a dry film in which the crystalline component and the amorphous component are maintained in discreet regions in this dry film.
Binder material 20b may also be mixed by coarsely dispersing a solid form of the crystalline component into either a waterborne emulsion of the amorphous component or into a solvent-based solution of the amorphous component (
2. Applying the Bimodal Binder to the Fibers
Once mixed, binder material 20b is applied to fiber material 20a to form composite 20. Binder material 20b is applied to fiber material 20a through various processes, such as with a spray gun, fiber pultrusion, fiber impregnation, hot melt extrusion, gravure coating, and/or other roll coating methods. For example, a fiber impregnation method may be used to apply binder material 20b to fiber material 20a. Using the fiber impregnation method, an excess of a waterborne emulsion or dispersion of binder material 20b is applied to fiber material 20a. Then a series of stationary bars and pressure rollers squeeze out the excess binder material 20b to form composite 20. Composite 20 may then be temporarily cast onto and transported by a silicone-coated release paper and, when the water is dried, composite 20 is wound onto a roll for further processing.
Additionally, a combination of the aforementioned methods may be used to apply binder material 20b to fiber material 20a. For example, a single waterborne emulsion of the amorphous component may be applied to fiber material 20a through the fiber impregnation method. Next, the crystalline component may be applied in a dry form to the surface of composite 20 by way of an electrostatic sprayer. The dry form of the crystalline component can be applied to fiber material 20a either before or after the water from the waterborne emulsion of the amorphous component has dried.
Additionally, in one embodiment, the amorphous component may be applied to fiber material 20b as a solvent-cast film using the aforementioned fiber impregnation method. The crystalline component is then applied in a dry form to the surface of the solvent-cast film of the amorphous component.
Regardless of the method selected to apply binder material 20b to fiber material 20a, fiber material 20a may be scoured with de-ionized water and dried before binder material 20b is applied thereto. Fiber material 20a then may be plasma treated at an energy flux of 50-80 watts/ft2/min, preferably 67 watts/ft2/min Binder material 20b is subsequently applied to fiber material 20a through one or more of the aforementioned processes for adhering the individual fibers of fiber material 20a together and for adhering the various plies of fiber material 20a to each other. More particularly, fiber material 20a is coated with binder material 20b at a resin content of 5-30%, and preferably at a resin content of 17%. Once binder material 20b is applied to fiber material 20a, fiber material 20a may be rolled onto spools and stored as rolls until further processing occurs.
3. Flat-Bed Laminator
Referring to
Composite 20 then may be formed with a flat-bed laminator 30 which includes a first or upper belt 32 rotatable about a plurality of rollers 33 and a second or lower belt 34 rotatable about a plurality of rollers 35. First and second belts 32, 34 may be coated with a non-stick coating, for example a fluoropolymer-based material such as TEFLON®, commercially available from E. I. Du Pont De Nemours and Company of Wilmington, Del. First and second belts 32, 34 are spaced apart from each other by a passageway 36 for composite 20 to pass through. As shown in
Flat-bed laminator 30 of
As composite 20 leaves heating portion 38, pressure is applied to composite 20 through pressure rollers 42 while the crystalline component is melted. Pressure rollers may be comprised of various materials, such as metals (e.g., steel), polymers (e.g., elastic rubber), and/or ceramics. Additionally, one of pressure rollers 42 may have a fixed position and the other of pressure rollers 42 may be movable when a force is applied thereto, such that when a force is applied to one of pressure rollers 42, a force also is applied to composite 20. More particularly, pressure rollers 42 may apply a pressure of less than one bar to composite 20. For example, pressure rollers 42 may apply a nip pressure to composite 20 of 10 psi, 30 psi, 50 psi, 70 psi, 90 psi, 110 psi, 130 psi, 150 psi, 170 psi, 190 psi, 210 psi, 230 psi, 250 psi, 270 psi, 290 psi, 310 psi, or within any range delimited by any pair of the foregoing values. In one embodiment, pressure rollers may apply a pressure of 14 psi to composite 20. The greatest pressure applied to composite 20 occurs at a tangent 50 of pressure rollers 42 which is parallel to first and second belts 32, 34. However, due to the circular cross-section of pressure rollers 42, smaller amounts of pressure are applied to composite 20 as the surfaces of pressure rollers 42 adjacent tangent 50 are in contact with composite 20. For example, as a portion of composite 20 moves through flat-bed laminator 30, an increasing amount of pressure is gradiently applied to composite 20 as composite 20 is initially positioned between pressure rollers 42. As composite 20 moves toward tangent 50 of pressure rollers 42, greater pressure is applied to composite 20, with the greatest pressure applied to composite 20 when directly between tangents 50 of pressure rollers 42. Additionally, as composite 20 moves past tangent 50, a decreasing amount of pressure is gradiently applied to composite 20 until composite 20 is no longer positioned between pressure rollers 42.
Different designs of flat-bed laminator 30 may apply different pressures to composite 20. For example, if pressure rollers 42 have outer surfaces comprised of steel, the contact footprint of pressure rollers 42 on composite 20 is relatively small and the average point pressure applied to composite 20 is large. However, if pressure rollers 42 have outer surfaces comprised of elastic rubber, the contact footprint of pressure rollers 32 on composite 20 is relatively large and the average point pressure applied to composite 20 is small.
Pressure from pressure rollers 42 is applied to composite 20 for about 0.02 seconds to about 5 seconds. More particularly, pressure may be applied to composite 20 for a duration of time of as little as about 0.01 seconds, 0.50 seconds, 1.0 seconds, 1.5 seconds, 2.0 seconds, 2.5 seconds, or as great as 3.0 second, 3.5 seconds, 4.0 seconds, 4.5 seconds, 5.0 seconds, or within any range delimited by any pair of the foregoing values. In one embodiment, pressure may be applied to composite 20 for a time duration of 0.01-0.05 seconds. Additionally, because pressure rollers 42 have circular cross-sections, the aforementioned times signify the total time duration that composite 20 experiences pressure. For example, using an order of magnitude calculation, if the length of the footprint between pressure rollers 42 is one cm and the line speed of flat-bed laminator 30 is 5 meters/minute, then the residence time that composite 20 experiences pressure applied by pressure rollers 42 is 0.12 seconds. However, because 0.12 seconds represents the total amount of time that composite 20 experiences pressure from pressure rollers 42, there is a gradient of rising pressure for the first 0.06 seconds and a gradient of decreasing pressure for the last 0.06 seconds. As such, in the embodiment of
After pressure is applied to composite 20 with rollers 42, composite 20 moves through cooling portion 40 and then exits flat-bed laminator 30. In one embodiment, cooling portion 40 is configured for temperatures less than the melting temperature of the crystalline component of binder material 20b. For example, cooling portion 40 may be configured for operation at temperatures of 0° C., 5° C., 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 60° C., 70° C., 80° C., 90° C. or within any range delimited by any pair of the foregoing values, depending on the particular crystalline component included within binder material 20b. Because the length of cooling portion 40 is approximately the same as the length of heating portion 38, composite 20 may be cooled for approximately the same amount of time it is heated. More particularly, composite 20 may be cooled for as little as 0.01 seconds, 0.50 seconds, 1.0 seconds, 1.5 seconds, 2.0 seconds, 2.5 seconds, 3.0 seconds, or as much as 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes, or any range delimited by any pair of the foregoing values. As composite 20 passes through cooling portion 40, it is necessary that composite 20 remain flat and is not bent so as to minimize stresses applied to composite 20 during cooling. Alternatively, because heat transfer occurs rapidly in the crystalline component, cooling portion 40 may be eliminated from flat-bed laminator 30 if it is possible for composite 20 to radiate sufficient heat to its surroundings to decrease its temperature below the melting temperature of the crystalline component to allow the crystalline component to solidify.
Additionally, as detailed herein, it may be desirable to minimize or eliminate stresses to composite 20 when cooling below the melting temperature of the crystalline component of binder material 20b. Because pressure is not applied to composite 20 when cooling, stresses are not introduced into the crystal structure of the crystalline component. Also, because heat transfer occurs rapidly within the crystalline component, the discreet portions of the crystalline component which flowed around the amorphous component and into any voids within fiber material 20a when the crystalline component melted are maintained without chemically or physically mixing with the amorphous component. As such, the amorphous and crystalline components remain discreet within binder material 20b and are incompatible with each other.
Additionally, first and second belts 32, 34 may apply a low pressure to composite 20 which is less than the pressure applied by rollers 42. Because the pressure applied by first and second belts 32, 34 is low, additional stresses are not introduced into composite 20 when passing through cooling portion 40. Alternatively, belts 32, 34 may not apply any pressure to composite 20 when passing through cooling portion 40. In one example, first and second belts 32, 34 may apply a pressure to composite 20 of as little as 0.01 psi, 0.05 psi, 0.10 psi, 0.15 psi, 0.20 psi, or 0.25 psi, or as great as 1.0 psi, 2.0 psi, 3.0 psi, 4.0 psi, 5.0 psi, 6.0 psi, 7.0 psi, 8.0 psi, 9.0, psi or 10.0 psi, or within any range delimited by any pair of the foregoing values, as composite 20 passes through heating portion 38 and cooling portion 40. In one embodiment, the pressure applied by first and second belts 32, 34 is less than 0.5 psi. More particularly, the pressure applied by first and second belts 32, 34 is applied for a time duration which is inversely proportional to the belt speed of flat-bed laminator 30. In one embodiment, the residence time that pressure is applied to composite 20 by first and second belts 32, 34 ranges from as little as 1 second, 3 seconds, 5 seconds, 7 seconds, 9 seconds, or 11 seconds, or as much as 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes, or any range delimited by any pair of the foregoing values. As such, composite 20 may experience two distinct pressures—a first low pressure applied by first and second belts 32, 34 when passing through heating and/or cooling portions 38, 40, and a second higher pressure applied by pressure rollers 42.
Referring to
Referring still to
Flat-bed laminator 30′ of
As shown in
As composite 20 enters heating portion 38, the crystalline component of binder material 20b melts and flows into fiber material 20a to integrate with fiber material 20a. Pressure is applied to composite 20 by pressure rollers 42. More particularly, and as detailed herein with respect to flat-bed laminator 30, pressure rollers 42 may apply a pressure for a duration of time of as little as about 0.01 seconds, 0.50 seconds, 1.0 seconds, 1.5 seconds, 2.0 seconds, 2.5 seconds, or as great as 3.0 second, 3.5 seconds, 4.0 seconds, 4.5 seconds, 5.0 seconds, or within any range delimited by any pair of the foregoing values. After pressure is applied to composite 20 with rollers 42, composite 20 moves through cooling portion 40 and exits flat-bed laminator 30′. As such, the pressure applied by pressure rollers 42 to composite 20 is not continuous because pressure is not applied to composite 20 as composite 20 passes through heating portion 38 and cooling portion 40.
Because the crystalline component of binder material 20b has a lower melt viscosity and lower surface energy, and may have a lower melting temperature, than the amorphous component, there may be greater wetting, greater displacement of air, and greater compaction in the crystalline component when pressure rollers 42 apply pressure to composite 20. As such, the presence of voids, air pockets, interstices, or other internal openings within the amorphous component is decreased during formation of composite 20 in flat-bed laminator 30, 30′. In this way, composite 20 includes a smooth surface generally free of voids which reduces capillary forces and the total effective surface area of composite 20, thereby increasing the ballistic resistance of composite 20 because environmental conditions, such as sea water, gasoline, petroleum, solvents, and lubricants do not penetrate composite 20. Furthermore, besides decreasing voids at the surface of composite 20, internal voids, pockets, and channels within composite 20 are removed or displaced through the compaction of composite 20, thereby reducing the tendency for wicking of fluids or other infiltration. Composite 20 formed according to the aforementioned disclosure may be used for ballistic resistant articles and is resistant to environmental conditions which may degrade composite 20.
Various samples of composites were formed with varying levels of a crystalline component within a binder material. These samples of the composites were then exposed to salt water for an extended period of time to determine if the presence of the crystalline component affected the corrosive resistance of the composites.
To form these samples, various concentrations of a binder material were formed according to Table 1 to define a Comparative Example 1, an Example 1 of composite 20, and an Example 2 of composite 20.
The binder material was applied to fiber material comprised of Honeywell 1150-denier SPECTRA® Merge 95121 UHMWPE fiber. More particularly, using a fiber impregnation coater, the binder material was applied to a first unidirectional fiber web and the coated fiber web was dried. The dried fiber web was wound onto a roll. A second roll of a second unidirectional fiber web also was coated with the fiber impregnation coater, dried, and wound onto a roll. The first coated fiber web on the first roll was cut into squares. The second roll of wound fiber was installed at or near the entrance of flat-bed laminator 30, 30′ and the second fiber web was unrolled and fed through flat-bed laminator 30, 30′. The temperature of heating portion 38 of flat-bed laminator 30, 30′ was set to a temperature below the melting temperature of the crystalline component. As the second coated fiber web began to travel into flat-bed laminator 30, 30′, the squares of the first coated fiber web were placed on top of the second coated fiber web prior to the second fiber web entering flat-bed laminator 30, 30′. The fiber direction of each square of the first fiber web was positioned in a 90-degree orientation to the fiber direction of the second fiber web. Additionally, each square of the first fiber web was positioned to rearwardly abut the previous, adjacent square on the second fiber web to define a continuous, coated, two-ply fiber material. This continuous, two-ply fiber material entered flat-bed laminator 30, 30′ and the pressure applied by rollers 42 adhered the squares of the first fiber web to the second fiber web. However, the pressure from rollers 42 and the heat of heating portion 38 did not melt the crystalline component of the binder material, if any crystalline component was present in the binder material. The two-ply fiber web formed of the cut squares of the first fiber web and the continuous roll of the second fiber web was then wound onto a roll after passing through flat-bed laminator 30, 30′ and adhered together. The temperature of heating portion 38 of flat-bed laminator 30, 30′ was then increased to a temperature within the melting point range of the crystalline component within the binder material, if any crystalline component was present. The roll of the two-ply fiber material was then unrolled and the two-ply fiber material passed through flat-bed laminator 30, 30′. Because the temperature of heating portion 38 was within the melting point range of the crystalline component with the binder material, compaction or densification was imparted to the two-ply fiber material when passing through rollers 42. After passing through flat-bed laminator 30, 30′, the two-ply fiber material was cut into squares and ballistic samples were produced by stacking 52 layers of the two-ply fiber material. The total areal density of each sample, or the total weight per area of multiple layers of the fabric, was 0.89 pounds/ft2.
Comparative Example 1, Example 1, and Example 2 were each soaked in salt water at a concentration of 3.5% sea salt in tap water for 24 hours. Comparative Example 1, Example 1 and Example 2 were hung to drip dry for 15 minutes. Next, Comparative Example 1, Example 1 and Example 2 were each placed onto a clay block or platform, as disclosed further in NIJ STD 0101.06 Level III, and 357 Magnum SJHP Remington shots were fired at Comparative Example 1, Example 1 and Example 2 at a velocity of 1430+/−30 ft/sec.
Each of the two samples of Comparative Example 1, Example 1 and Example 2 were each shot three times with 357 Magnum SJHP Remington bullets to determine the depth each bullet penetrated into each sample. As shown in Table 2, Shots 2 and 3 on each sample of Comparative Example 1 fully penetrated the composite, as indicated by “Complete” in Table 2. However, none of the samples of Example 1 or Example 2 were fully penetrated. More particularly, the bullets penetrated the least into the samples of Example 1, which contained a fluorocarbon amorphous component and carnauba wax crystalline component.
Various samples of composites were formed with varying levels of a crystalline component within a binder material. These samples of the composites were then shot with 9 mm bullets to determine if the presence of the crystalline component affected the ballistic resistance of the composites.
To form these samples, various concentrations of a binder material were formed according to Table 3 to define a Comparative Example 1, an Example 1 of composite 20, an Example 2 of composite 20, and an Example 3 of composite 20. The coating and composite processing conditions for forming these samples are identical to those of Example 1 above.
Testing of the Composites
The samples of Comparative Example 1 and Examples 1-3 were each placed onto a clay block or platform, as disclosed further in NU STD 0101.06 Level III, and 9 mm shots were fired at each sample of Comparative Example 1 and Examples 1-3 at varying velocities shown in Table 4. More particularly, Table 4 provides a theoretical velocity, V50, at which 50% of the bullets stopped within Comparative Example 1 and Examples 1-3 and 50% of the bullets completely penetrated Comparative Example 1 and Examples 1-3. For example, to determine the V50 velocity, a plurality of shots were fired at each sample of Comparative Example 1 and Examples 1-3 at varying velocities to determine the velocity range at which a bullet completely penetrated the sample and a velocity range at which a bullet partially penetrated a sample. These shot groupings on each sample underwent statistical analysis to determine the V50 velocity for each sample of Comparative Example 1 and Examples 1-3 tested.
As shown in Table 4, Comparative Example 1, which was not a bimodal binder, had the lowest V50 velocity compared to Examples 1, 2, and 3. As such, the samples of Examples 1-3 were able to withstand bullets shot at higher velocities without the bullet fully penetrating the sample. Additionally, Example 1, which contained 15% of the crystalline component, and Example 3, which contained 40% of the crystalline component, each had similar V50 velocities.
Various samples of composites were formed with varying levels of a crystalline component within a binder material. These samples of the composites were then shot with 9 mm bullets to determine if the presence of the crystalline component affected the ballistic resistance of the composites.
To form these samples, various concentrations of a binder material were formed according to Table 3 to define a Comparative Example 1, an Example 1 of composite 20, an Example 2 of composite 20, an Example 3 of composite 20, an Example 4 of composite 20, an Example 5 of composite 20, and an Example 6 of composite 20. The coating and composite processing conditions for forming these samples are identical to those of Example 1 above.
Each sample of Comparative Example 1 and Examples 1-6 were each placed onto a clay block or platform, as disclosed further in NU STD 0101.06 Level III, and 9 mm shots were fired at each sample of Comparative Example 1 and Examples 1-6 at varying velocities shown in Table 6. More particularly, Table 6 provides a theoretical velocity, V50, at which 50% of the bullets stopped within Comparative Example 1 and Examples 1-6 and 50% of the bullets completely penetrated Comparative Example 1 and Examples 1-6. For example, to determine the V50 velocity, a plurality of shots were fired at each sample of Comparative Example 1 and Examples 1-6 at varying velocities to determine the velocity range at which a bullet completely penetrated the sample and a velocity range at which a bullet partially penetrated a sample. These shot groupings on each sample underwent statistical analysis to determine the V50 velocity for each sample of Comparative Example 1 and Examples 1-6 tested.
As shown in Table 5, Comparative Example 1, which was not a bimodal binder, had the lowest V50 velocity compared to Examples 1-6. As such, the samples of Examples 1-6 were able to withstand bullets shot at higher velocities without the bullet fully penetrating the sample. Additionally, Example 3, which contained microcrystalline wax, had the greatest V50.
While the present disclosure has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto.
This application claims the benefit of co-pending U.S. Provisional Application Ser. No. 62/138,548, filed on Mar. 26, 2015, the disclosure of which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62138548 | Mar 2015 | US |
