BACKGROUND OF THE INVENTION

The present invention relates to ballistic and puncture resistant articles of manufacture, as well as to a method of manufacture such articles. The ballistic and puncture resistant articles of the present invention comprise high strength, high melting fibers such as polyaramid fibers.

Ballistic and puncture resistant articles formed from high strength fibers such as polyolefin and nylon (polyamide) fibers are known. For example, such articles formed from high strength polyolefin fibers are known from a series of U.S. Patents assigned of record to Allied Corporation. These are: Harpell et al U.S. Patent No. 4,403,012 Harpell et al U.S. Patent No. 4,457,985 Harpell et al U.S. Patent No. 4,501,856

Harpell et al U.S. Patent No. 4,623,574 Harpell et al U.S. Patent No. 4,650,710; and Harpell et al U.S. Patent No. 4,681,792. Another Allied Corporation patent directed to high strength polyethylene fiber is Kavesh et al _r U.S. Patent No. 4,413,110.

These patents describe ballistic-resistant articles of manufacture comprising a flexible network of polyolefin fibers. The Harpell et al patents

listed above are particularly directed to ballistic- resistant articles formed by winding a continuous filament of the high strength polyethylene around a steel plate to form a network of parallel fibers. Harpell et al reported this construction was found to be superior to KEVLAR (trademark of Dupont for aramid yarn) in arresting projectile penetration.

The use of aramid ibers in the construction of puncture resistant and/or ballistic resistant articles is, of course, well-known. Numerous patents disclose the use of polyaramid fibers, and in particular KEVLAR fibers, in the construction of puncture and ballistic resistent materials. For example, U.S. Patent Nos. 4,864,661; 4,779,290; 4,729,303; 4,608,716; 4,475,248; 4,384,449 and

3,902,196 disclose the use of KEVLAR fibers in the construction of puncture resistant fabrics or materials. U.S. Patent Nos. 4,380,245; 4,678,702; 4,608,717; 4,574,105; 4,522,871; 4,510,200; 4,485,491; 4,475,247; 4,443,506; 4,428,998; 4,404,889; 4,316,404; 4,292,882; 4,200,677; 4,186,648; 4,181,768; 4,090,005; 4,079,464; 4,057,359; and, 3,958,276 disclose the use of KEVLAR fibers in the construction of ballistic resistant materials, and in particular ballistic-resistant clothing.

There remains a need, however, for ballistic and puncture resistant articles capable of arresting projectile penetration more effectively than those discussed above at a given basis weight of ballistic or puncture resistant material, or, correspondingly, that are equally as effective at a lower basis weight. This is particularly true for articles comprised of aramid fibers. There is also a need for a method of making ballistic and puncture resistant materials comprised of polyaramid fibers such as

KEVLAR in a more efficient and cost effective manner.

A major object of the present invention is therefore to provide ballistic resistant articles of manufacture that offer effective penetration resistance and are prepared in a more efficient and cost effective manner.

Another object of the invention is to provide a method for manufacturing such ballistic and puncture resistant articles that is easily adapted to an industrial scale, preferably by modifying conventional processing apparatus.

A further object of the present invention is to provide ballistic and puncture resistant articles that offer penetration resistance at least equal to articles of the prior art, but at significantly lower material basis weight, thereby greatly expanding the useful applications for such articles.

These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.

SUMMARY OF THE INVENTION

In accordance with the foregoing objectives, there is provided a ballistic resistant and/or puncture resistant wet-laid, non-woven structure comprised of high strength, high melting fibers, such as aramid fibers, and a binder which binds the fibers. The degree of binding of the fibers and the basis weight of the wet-laid, non-woven structure are such as to impart penetration resistance to the structure. It is most preferred that the high strength, high melting fibers are KEVLAR aramid fibers, i.e., fibers of poly (p-phenylene terephthala ide) .

The structures are prepared using a wet-laid paper making technique, thereby permitting manufacture in a most effective and cost efficient manner. Most preferably, a foam technique is used in the non-woven.formation. Such use of foam has been found to produce a most consistent structure free of lumps. In a most preferred embodiment, the penetration resistant wet-laid, non-woven structure comprises as the binder a second fiber, e.g., an acrylic fiber,

which is heat bondable to the surface of the high strength, high melting fibers. The final structure is achieved by subjecting the wet-laid, non-woven structure to a heat bonding step. The resulting wet-laid, non-woven structure can be used in the manufacture of a variety of penetration resistant articles, e.g., vests, gloves, jackets, wall coverings and structural panels.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS OF THE PRESENT INVENTION

The penetration resistant structures according to the invention are formed using conventional papermaking techniques, such as passing an aqueous slurry of aramid fibers and binder onto an endless wire screen, followed by dewatering and drying of the thus-formed sheet. One of the advantages of the present invention is that the penetration resistant structure is quite readily manufactured using a most efficient method and conventionally available apparatus.

The penetration resistant structure of the present invention is therefore a wet-laid, non-woven structure comprised of a high strength, high melting fiber and a binder therefor. Aramid fibers are the preferred high strength, high melting fibers for use in the structures of the present invention, with

KEVLAR aramid fibers (KEVLAR being a trademark of E.I. DuPont de Nemours) being most preferred. While aramid fibers such as KEVLAR aramid fibers will be used in describing the preferred embodiments of the present invention, it should be understood that the scope of the present invention is intended to encompass high strength, high melting fibers which in general have a tenacity of at least 15 grams/denier, more preferably at least 20 grams/denier, an energy- to-break of at least 18 Joules/gram and a melting point of at least 200°C. Specific examples of such fibers include not only KEVLAR aramid and aramid copolymer fibers, but also polybenzobisthiazole (PBT) fibers, polybenzoxazole (PBO) fibers, liquid crystalline polyester fibers and extended-chain polyvinyl alcohol fibers e.g., as exemplified in the following Table:

TABLE

polyvinyl alcohol

Two important factors in achieving a structure exhibiting penetration resistance in accordance with the present invention are the basis weight of the structure and the degree of binding which occurs. Both of these factors are affected by the relative amounts of fiber and the particular binder used. Generally, it is preferred that the aramid fibers comprise a major amount of the wet-laid, non-woven structure, and more preferably at least 60% by weight, and most preferably at least 70% by weight. The two foregoing factors are important in achieving penetration resistance as it is believed that the structure of the present invention works because of its unique capability of absorbing energy. With regard to the degree of binding, it is important to realize that the fibers cannot be too strongly bound by the binder, or the fibers are believed to simply break when struck by a bullet. If the fibers are too weakly bound by the binder, the fibers of the structure will simply pull apart when struck. With regard to basis weight, the lower the effective basis weight the more preferable. The effective basis weight of a particular structure, however, will vary greatly depending upon the particular binder used and the degree of binding employed. Structures having a basis weight of less than a thousand lb/3000 ft ² have been found effective, wherein generally, structures

having a basis weight of at least 2000, and 3000 or higher, have been found most effective and still practical. It is the combination of basis weight, degree of binding and particular binder used which must be considered. Thus, achieving a proper balance and combination of the basis weight of the structure and the ratio of particular binder to fiber content, a wet-laid non-woven structure is obtained which exhibits surprisingly good penetration resistance. By penetration resistance for the purposes of the present invention is meant that a sheet of the material of the present invention will stop a Winchester high velocity .22 caliber long rifle bullet fired from 3 feet away. The bullet will not pass through the sheet. While ballistic resistance is a very important aspect and advantage of the structures of the present invention, the structures also exhibit excellent puncture resistance with regard to knifes, ice picks and other sharp objects. The overall advantages of the present invention therefore relates to penetration resistance in general.

The relative amounts of fiber and binder used in preparing a structure of the present invention will vary based upon the particular binder used and the ultimate desired basis weight of the structure. The binder can be any component, fibrous or non-fibrous,

which can bind the fibers. Generally, the binding is achieved through a bonding of the binder with the fibers, however, the binding can also be purely physical or mechanical. A fibrous binder is preferably a fiber which can be heat bonded to the surface of the matrix fiber, e.g., aramid fiber. Any suitable fiber, preferably synthetic, can be used as the binder fiber, especially if it is heat-bondable. Preferred examples include acrylic, polypropylene and polyester fibers, with acrylic fibers being most preferred. In a preferred embodiment, the wet-laid, non-woven penetration resistant structure comprises from about 70-80 wt % aramid fiber and from about 20-30 wt % acrylic fiber.

When using a heat bondable fiber, the last step in preparing the penetration resistant material of the present invention is to heat bond the non-woven material. This heat bonding step can be achieved by any conventional technique, e.g., heating in an oven. The temperature necessary to achieve heat bonding, of course, will vary depending on the second fiber employed.

Examples of preferred non-fibrous binders include, for example, polyvinyl alcohol. The polyvinyl alcohol can be added as a powder to the furnish in preparing the wet-laid, non-woven

structure. Other powder or particulate binders can also be used.

The length of the aramid fiber used can vary, with about 3/4 inch being the most preferred length due to its availability and success achieved using such fiber. In general, as the length of the fiber increases, it is preferred that the relative denier of the fiber increases. Since longer fibers have more contact points, less binder may also be required to achieve optimum performance.

Refinement of the binder fiber may also warrant some consideration, as it goes to the bonding ability of the binder fiber with the aramid fibers. For example, 120 CSF (Canadian Standard Freeness, TAPPI T 227 om-85) acrylic fiber is preferred in general to 376 CSF acrylic fiber.

Conventional additives, such as surfactants, can also be employed in the furnish.

In the preparation of the wet-laid, non-woven structures of the present invention, it will be appreciated that in employing a conventional paper- making type process, what might otherwise be a conventional technique interacts with the materials employed to form a resultant product having properties of penetration resistance that could not have been predicted from the starting materials and technique alone. The structures prepared can be used

in the manufacture of many different penetration resistant articles of manufacture. Such articles generally incorporate the structure of the present invention as one of many layers. For example, the structure can be combined or covered with layers of fabric, paint, wallpaper or other synthetic polymers in the manufacture of vests, gloves, jackets and structural panels.

In a most preferred embodiment, the method for manufacturing the non-woven structures of the present invention invokes the use of a foam furnish. For it has been found that an excellent product is achieved when employing a foam furnish as the foam is believed to prevent entanglement of the fibers, which can cause lumps in the final material. The use of a foam furnish in preparing a non-woven fibrous web is well- known to the art, and any of the conventional techniques can be employed, for example, as described in U.S. Patent Nos. 3,716,449 and 3,871,952 issued to Wiggins Teape Research and Development Limited.

It is also contemplated to use a hydroentangling process in preparing the wet-laid, non-woven web of the present invention. The hydroentangling technique is generally employed prior to any activation of the binder, e.g., whether drying or heat-bonding.

Hydroentangling is a process for producing nonwoven fabrics by impinging a plurality of fine columnar

streams of a fluid, such as water or air, onto a fibrous web carried by an apertured or patterned conveying means. There is thus produced a felt-like material in which even relatively short fibers can be mechanically intertwined without the dεunaging effects of needling. One example of a patent describing hydroentangling is U.S. Patent No. 3,485,706, the disclosure of which is hereby expressly incorporated by reference, to the extent not inconsistent herewith. In this patent, an apertured hydroentangled fabric is produced wherein the apertures in the fabric correspond to knuckles in the wire screen used to support and convey the fibrous web. Patterned supporting means are disclosed for imparting to the resulting hydroentangled fabric a desired ornamental appearance.

The invention will be illustrated in greater detail by the following specific examples. It is understood that these examples are given by way of illustration and are not meant to limit the disclosure or the claims to follow. All percentages in the examples, and elsewhere in the specification, are by weight unless otherwise specified.

A series of experimental handsheets were prepared, whose formulations were both within and without the scope of the present invention, and subjected to ballistic testing to determine their

penetration resistance. Handsheets were prepared by the procedure defined in TAPPI T 205 om-88 with the following modifications. The sheet machine was of the Noble Wood (eight inch by eight inch) design. Approximately 4.03 grams of the fiber and binder were added to the British disintegrator to form a 60 pound per 3000 square foot basis weight handsheet. The sheet was formed on a wire mesh which had been placed on top of the fixed wire mesh in the handsheet machine. The wet sheet and wire was transferred to a Noble Wood wet press. The sheet and wire was pressed in between wet felts as a press pressure of 50 pounds per inch width. The dewatered sheet was then removed from the forming wire and dried on a steam heated drum. This was followed by heat bonding where noted at a suitable temperature.

The handsheets thus formed measured 8 inches by 8 inches square, and were formed so as to have a basis weight of 60 pounds per 3000 square feet. The basis weight of a specimen to be subjected to ballistic testing could easily be increased 2, 4 or 8 times by folding one of these sheets once, twice or three times, respectively. The specimens tested thus tend to have basis weights increasing by multiples of eight, because the basis weight of a specimen was generally increased y adding an additional 8 inch by 8 inch sheet that had been folded three times.

The specimens tested were backed either by plywood or by clay. The first tests were run with plywood as the backing. When plywood backing was used, the plywood had a hole where the bullet was expected to pass (or not pass, depending on whether the specimen stopped the bullet) . Clay backing was also used, primarily since modeling clay is the backing used for determining the ballistic resistance of body armor (U.S. Department of Justice - National Institute of Justice, NIJ Standard 010.03).

The firing was done with a .22 caliber rifle using Winchester high velocity .22 caliber long rifle bullets. According to literature published by Winchester, the muzzle velocity of these bullets is about 1440 feet per second. The target was located about three feet from the muzzle of the rifle.

The results of these experiments are listed in Table 1 below. In Table 1, the term "Pulpex" is a trademark of Hercules Corporation for their short fiber polyethylene synthetic pulp. The Pulpex was used in its commercially available form.

"KEVLAR" is a trademark of E.I. DuPont de Nemours Co. for their aramid fiber. In the Table, the cut length of the aramid fiber used was 3/4 inch.

"Melty" is a 4 denier x 5 mm co-polyester binder fiber available from Unitika of Japan.

"87PW061" refers to a polyacrylamide aqueous emulsion available from Nalco, and is a water thickening agent and dispersing agent.

"AT-2" is a polyurethane resin available from Rhom & Haas and is used as a water thickener and dispersing agent.

"AOK" is an alpha-olefin sulfonate surfactant, available in flake from Arco.

"CasChem 318" refers to a nonionic surfactant wetting/dispersing agent available from Cas Chem.

"L62" refers to Plurionic L62, which is a polyoxypropylene/polyoxyethylene block copolymer useful as a wetting/dispersing agent, marketed by BASF.

"NBF" is a binder fiber supplied by Chori Company, Ltd. of Chuo-Ku, Osaka, Japan. It is a 3 denier by 5 mm long bi-component fiber. "Spetra" is a high molecular weight polyethylene fiber supplied by Allied Fiber of Allied Signal Corporation.

"Marathon Softwood" is a Northern Softwood kraft pulp manufactured by James River Corporation. "Basis Weight" is in units of lb/3000 ft ² , and refers to the basis weight of the specimen tested.

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Xn the above table, ⁿ N ^N indicates that the bullet was stopped by the specimen, whereas "P ^M indicates that the bullet passed through the specimen. Where more than one designation appears, it indicates that the testing was performed a plurality of times. When a clay backing was used, the bullet would sometimes penetrate fairly deeply into the clay backing, yet fail completely to rupture the paper-like structure of the specimen. Nevertheless, if the bullet penetrated more than 0.75 inch into the clay backing, the result was judged ^M P ^H . The results of these tests are somewhat qualitative, because the clay backing appeared to improve slightly the performance of the specimen. While the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and the scope of the claims appended hereto.