Flame retardant ballistic laminate

A ballistic laminate includes a layer including first fibers of a first material oriented at both a first direction and a second direction and second fibers of a second material oriented at both the first direction and the second direction. The first fibers are flammable, and the second fibers are flame retardant. A periodic distance greater than about 9 mm is between the second fibers of the second material oriented at the first direction. A periodic distance greater than about 9 mm is between the second fibers of the second material oriented at the second direction.

BACKGROUND

The present invention relates to a ballistic laminate. It finds particular application in conjunction with a ballistic laminate that offers both ballistic and flame retardant properties and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.

Ballistic resistant body armor and vehicle armor are made from either woven fabrics or unidirectional fabrics comprising high performance fibers such as ultra-high-molecular-weight-polyethylene (UHMWPE) fibers, aramid fibers, and glass fibers, etc. Unidirectional fiber reinforced composite where fibers are encapsulated in a polymeric matrix materials generally has better ballistic resistance than traditional woven fabrics.

Various unidirectional composite constructions are currently used for formation of soft and hard armors in ballistic protection applications. Some composite constructions use high performance fibers such as UHMWPE fibers in matrix materials. However, some high performance fibers such as UHMWPE fibers are flammable when exposed to fire and heat. There is a growing demand for fire resistance armors.

One conventional composite construction use a layer-by-layer hybrid composite construction (i.e., one or more layers comprising flame resistant fibers and one or more layers comprising flammable fiber to improve the flame resistance of the composite). One multilayer composite design includes one or more first layers of flammable fibers in a matrix and at least one second layer adjacent to the first layer. The second matrix includes a fire retardant material. The second matrix is different than the first matrix.

Another conventional composite construction includes at least one layer of UHMWPE fibers or aramid fibers in a matrix and at least one fire retardant layer. The fire retardant layer includes a fire retardant agent that absorbs heat when exposed to fire and heat in a matrix. The matrix includes one or more relatively high chart yield resins that results in better flame resistant performance.

Another conventional composite construction includes a molded ballistic panel for use in aircraft and land vehicles for structural, ballistic, and fire resistant performance. The molded panel is formed by inserting a honeycomb between panels including non-woven high performance fiber layers and one or more fire resistant fiber layers.

U.S. Pat. No. 7,288,307 to Bhatnagar, et al. discloses hybrid laminated unidirectional fiber sheets produced from continuous roll of unidirectional prepregs, having application for impact absorption, ballistic resistance, and penetration resistance. The laminated unidirectional fiber sheets include two or more types of unidirectional fibers with different composition in a matrix. The two or more types of fibers are arranged in a side by side position. The periodic distance between fibers that have the same composition is not greater than 9 mm. However, neither distinguishes flame resistant fibers compared with flammable fibers nor gives any description on hybrid fiber-by-fiber composite constructions and/or fiber arrangements that improve the flame resistance performance of a composite.

The present invention provides a new and improved apparatus and method which addresses the above-referenced problems.

SUMMARY

In one aspect of the present invention, it is contemplated that a ballistic laminate includes a layer including first fibers of a first material oriented at both a first direction and a second direction and second fibers of a second material oriented at both the first direction and the second direction. The first fibers are flammable, and the second fibers are flame retardant. A periodic distance greater than about 9 mm is between the second fibers of the second material oriented at the first direction. A periodic distance greater than about 9 mm is between the second fibers of the second material oriented at the second direction.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT

With reference toFIG. 1, a top view of a simplified diagram of an exemplary ballistic laminate10is illustrated in accordance with one embodiment of the present invention. The laminate10includes a first layer12. The first layer12includes first fibers14of a first material16oriented at both a first direction D1and a second direction D2. The first layer12also includes second fibers20of a second material22oriented at both the first direction D1and the second direction D2.

As shown inFIG. 1, the first direction D1is contemplated to be defined as 0°. The second direction D2is contemplated to be at as right angle to the first direction D1. Therefore, if the first direction D1is defined, as 0°, the second direction D2is defined as 90°. Although the first and second directions D1, D2are described as 0° and 90°, respectively, it is to be understood that any other orientation system is also contemplated. Also, other embodiments are contemplated in which the first and second directions are not perpendicular to each other.

It is contemplated that the first fibers14of the first material16are relatively more flammable than the second fibers20of the second material22. In one example, the first fibers14of the first material16may have a Limiting Oxygen Index (LOI) less than or equal to 25, and the second fibers20of the second material22may have an LOI greater than 25. LOI is defined as the minimum amount of oxygen required in the mixture of oxygen and nitrogen, expressed as a percentage, to support combustion of fibers. The higher the LOI, the more flame retardant fibers are. Usually, fibers with an LOI higher than 25 are considered to be flame retardant (e.g., resistant), while fibers with an LOI less than or equal to 25 are considered flammable. Therefore, in this embodiment, the first fibers14of the first material16are flammable, while the second fibers20of the second material22are flame retardant. In one example, the first fibers14of the first material16are UHMWPE in a matrix. However, it is also contemplated that the first fibers14of the first material16may be polypropylene fibers in a matrix, or any other fiber having an LOI less than or equal to 25.

In one example, the second fibers20of the second material22are at least one of aramid fibers and liquid crystal polymer (LCP) fibers. However, it is also contemplated that the second fibers20of the second material22may be at least one of glass fibers, PBO fibers, carbon fibers, ceramic fibers, PTFE fluoropolymer fibers, and steel wires, or any other fiber having an LOI greater than 25.

With reference toFIGS. 1 and 2, the first layer12includes a plurality of plies. In the illustrated embodiment, the first layer12includes two (2) plies, for example a first ply30and a second ply32. The first ply30of the first layer12includes at least a portion of the first fibers14and the second fibers20oriented at the first direction D1. The second ply32of the first layer12includes at least a portion of the first fibers14and the second fibers20oriented at the second direction D2. The first ply30is adjacent to the second ply32to form the first layer12. In one embodiment, it is contemplated that the first ply30is attached to the second ply32to form the first layer12. For example, in the embodiment illustrated inFIG. 2, the first ply30and the second ply32are bonded together in the matrix. Other embodiments, in which the first ply30and the second ply32are secured together in different ways are also contemplated.

With reference toFIG. 3, an enlarged portion of a top view of a portion of the first ply30is illustrated. The first ply30includes at least one (1) first section34of the first fibers14of the first material16and at least one (1) second section36of the second fibers20of the second material22. Each of the first sections34is adjacent to at least one of the second sections36. In the illustrated embodiment, the first ply30includes alternate sections of the first section34and the second section36.

For ease of illustration, first fiber bundles or fiber tapes6411to6441and6412to6442(collectively64) (hereinafter the first fiber bundles) including the first unidirectional fibers14(seeFIGS. 1 and 2) of the first material16(seeFIGS. 1 and 2) are shown as short, vertical lines in the first section34, and second fiber bundles or fiber tapes6611to6631and6612to6632(collectively66) (hereinafter the second fiber bundles) including the second unidirectional fibers20(seeFIGS. 1 and 2) of the second material22(seeFIGS. 1 and 2) are illustrated as short, vertical lines in the second section36. It is to be understood that the first section34includes additional fibers bundles of first fibers14(seeFIGS. 1 and 2) of the first material16(seeFIGS. 1 and 2) beyond those illustrated inFIG. 3. Additionally, it is to be understood that the second section36includes additional fiber bundles of second fibers20(seeFIGS. 1 and 2) of the second material22(seeFIGS. 1 and 2) beyond those illustrated inFIG. 3.

A periodic distance between second fibers20of the second material22is a distance between a last of the second fiber bundles66in one of the second sections36and a first of the second fiber bundles66in a next, adjacent one of the second sections36. For example, the distance between a last of the second fiber bundles6631positioned substantially along a right edge of a first one361of the second sections36and a first of the second fiber bundles6612positioned substantially along a left edge of a second one362of the second sections36is the periodic distance between the second fibers20. For ease of illustration, only four (4) of the first fiber bundles64are illustrated in the first sections34, and only three (3) of the second fiber bundles66are illustrated in the second sections36.

In the illustrated embodiment, the periodic distance40between second fibers20of the second material22in the first direction D1of the first ply30is greater than a predetermined distance. In one embodiment, the predetermined distance is about 9 mm. Similarly, with reference toFIG. 2, the periodic distance42between second fibers20of the second material22in the second direction D2of the second ply32is greater than the predetermined distance (e.g., greater than about 9 mm).

With reference again toFIG. 3, it is contemplated that the periodic distance40between second fibers20of the second material22may also be determined based on a number of the first fiber bundles64of the first material16between adjacent ones of the second fiber bundles66of the second material22. In one embodiment, as illustrated inFIG. 3, it is contemplated that there are at least one (1) of the first fiber bundles64of the first material16between adjacent ones of the second fiber bundles66of the second material22. Similarly, with reference toFIG. 2, the periodic distance42between second fibers20(seeFIG. 3) of the second material22(seeFIG. 3) in the second direction D2of the second ply32may also be determined based on a number of the first fiber bundles64(seeFIG. 3) (e.g., at least one (1)) of the first material16between adjacent ones of the second fiber bundles66(seeFIG. 3) of the second material22.

FIG. 3illustrates the periodic distance between second fibers20of the second material22in the first direction D1of the first ply30is greater than 9 mm when there are at least a predetermined number of the first fiber bundles6412to6442of the first material16between adjacent ones of the second fiber bundles6631and6612of the second material22. For example, it is contemplated that the predetermined number of the first fiber bundles6412to6442between adjacent ones of the second fiber bundles6631and6612is at least one (1).

AlthoughFIG. 3illustrates alternate sections34,36of the first fibers14(seeFIGS. 1 and 2) of the first material16and the second fibers20(seeFIGS. 1 and 2) of the second material22, other arrangements are also contemplated. For example, it is contemplated that there may be a plurality (e.g., two (2)) of adjacent sections of the first fibers14(seeFIGS. 1 and 2) of the first material16, and then a plurality (e.g., two (2)) of adjacent sections of the second fibers20(seeFIGS. 1 and 2) of the second material22. Such other arrangements are contemplated as long as there are a plurality of at least the predetermined number of first fiber bundles64of the first material16between any two (2) adjacent second fiber bundles66of the second material22and as long as the periodic distance between second fibers20(seeFIGS. 1 and 2) of the second material22in the first and second directions D1, D2is greater than the predetermined distance (e.g., about 9 mm).

With reference toFIG. 4, it is contemplated that the first layer12may also include additional plies. For example, the first layer12may include the first ply30, the second ply32, a third ply34, and a fourth ply36. The third ply34includes at least a portion of the first fibers14of the first material16and at least a portion of the second fibers20of the second material22in the first direction D1. The fourth ply36includes at least a portion of the first fibers14of the first material16and at least a portion of the second fibers20of the second material22in the second direction D2. The first ply30is adjacent to the second ply32; the second ply32is adjacent to the third ply34; and the third ply34is adjacent the fourth ply36.

It is to be understood that additional layers are constructed similar to the first layer12.

The layers include respective first layers12, which have a periodic distance greater than about 9 mm between the second fibers20of the respective second material22oriented at both the first and second directions D1, D2, respectively, have been found to provide good ballistic performance while, at the same time, providing desirable flame resistant properties. Although it would be expected that increasing the amount of second fibers20of the second material22, which are flame retardant, would increase the flame resistant properties of the layers, the opposite has been found to be true. However, when the first fibers of the first material are UHMWPE fibers, increasing the amount of second fibers20of the second material22would decrease ballistic resistance properties of the layers.

Experimentation was conducted on layers including alternate first fibers14of the first material16(i.e., UHMWPE in the experiment) and second fibers20of the second material22(i.e., aramid in the experiment). The alternate first fibers14of the first material16(UHMWPE) and second fibers20the second material22(aramid) did increase the flame resistant properties of the laminate layers, but offered relatively low ballistic performance compared to laminate layers including only first fibers14of the first material16(UHMWPE). The laminate layers described herein provide between about 90% and about 96% of the ballistic performance of the laminate layers including, only first fibers14of the first material16(UHMWPE), while also providing similar or the same level of flame resistant properties of the laminate layers including alternate first fibers14of the first material16(UHMWPE) and second fibers20of the second material22(aramid).

Flame resistance of a hard panel comprising multiple laminate layers was determined in accordance with FAR 25.853, Appendix F, Part I, 60 second vertical burn test standard. In the test, a testing specimen of 3″×12″ is vertically mounted on a sample holder. A flame is then applied to the edge of bottom of the tested specimen for 60 seconds and then removed. The flammability requirements are as follows. Average burn length should be less than 6 inches; average flame time after removal of a flame should be less than 15 seconds; drippings may not continue to burn more than 3 seconds. In order to compare flammability of the tested hard panels made with laminate layers of different materials, the comparison should be conducted at the same thickness of the test specimen. As showed in Table 1 and Table 2, one of the hard panel made with laminate layers including only first fibers14of the first material16(UHMWPE), which is relatively more flammable, burned the entire length of a specimen of 3″×12″ when exposed to a flame. The UHMWPE/aramid hybrid hard panel at the thickness of 0.10 inches made with laminate layers including alternate first fibers14of the first material16(UHMWPE) and second fibers20of the second material22(aramid) only burned about 2.5″ of the 12″ length when exposed to a flame. The hard panel at thickness of 0.10 inches made with laminate layers including only second fibers20of the second material22(aramid), which is relatively more flame resistant, burned about 1.5″ to 2.0″ of the 12″ length of the panel when exposed to a flame. The UHMWPE/aramid hybrid hard panels at thickness of 0.10 inches made with laminate layers described above burned about 2.6″ of the 12″ length when exposed to a flame, which did burn more than the panels made with the laminate layers including only second fibers20of the second material22(aramid) and burnt the almost same length with the panels made with the laminate layers including alternate first fibers14of the first material16(UHMWPE) and second fibers20of the second material22(aramid).

The hard UHMWPE/aramid hybrid panels made with laminate layers at the thickness of 0.05″ described above burned 3.0″ of the 12″ length when exposed to the flame, which burned less than both the panels made with the laminate layers including only second fibers20of the second material22(aramid) and the UHMWPE/aramid hybrid panels made with the laminate layers including alternate first fibers14of the first material16(UHMWPE) and second fibers20of the second material22(aramid). Compared to UHMWPE/aramid hybrid panels as described above, the UHMWPE/LCP hybrid panels made with the laminate layers that have a periodic distance greater than about 9 mm between the LCP (flame retardant) fibers showed the better flammability and ballistic performance. The additional ballistic performance offered by the laminate layers described above is desirable. Any material that burns less than about 6″ of the 12″ length when exposed to a flame is acceptable for its flame resistant properties per the FAR 25.853 60 seconds vertical burn test standard.

With reference toFIG. 5, the first layer12, a second layer50and, optionally, additional layers52are stacked and then pressed at pressure (14 to 10,000 psi, preferred range of pressure 1,000 to 3,000 psi) and heat (e.g., if the UHMWPE fiber is used as first material, temperature ranges from 210 to 285° F., preferred temperature ranges from 250-270° F.) to form a hard panel54. It is contemplated that the hard panel54may be used in body armor, vehicle armor, and aircraft armor to provide ballistic protection in, for example, military and civilian applications. Although only a hard panel is described above, it is to be understood that soft panels may also be used in soft body armor, soft spall liner, and ballistic blanket applications.

With reference toFIGS. 1-4, the first layer12is formed by arranging the first fibers14of the first material16and the second fibers20of the second material22in the first direction D1in a first ply30so that at least one (1) of the first fiber bundles64of the first material16are between two (2) adjacent fibers20of the second material22. The first fibers14of the first material16and the second fibers20of the second material22are also arranged in the second direction D2in a second ply32so that at least one (1) of the first fiber bundles64of the first material16are between two (2) adjacent fibers20of the second material22. Optionally, additional plies are formed.

As discussed above, the periodic distance between the second fibers20of the second material22oriented at the first and second directions D1, D2, respectively, are greater than about 9 mm.

The first and second plies30,32are positioned adjacent to one another, as discussed above, to form the first layer12. Additional plies are optionally positioned adjacent each other to increase a thickness of the first layer12.