CA2066772A1 - Ballistic-resistant articles and method of manufacture thereof - Google Patents
Ballistic-resistant articles and method of manufacture thereofInfo
- Publication number
- CA2066772A1 CA2066772A1 CA 2066772 CA2066772A CA2066772A1 CA 2066772 A1 CA2066772 A1 CA 2066772A1 CA 2066772 CA2066772 CA 2066772 CA 2066772 A CA2066772 A CA 2066772A CA 2066772 A1 CA2066772 A1 CA 2066772A1
- Authority
- CA
- Canada
- Prior art keywords
- fiber
- type
- ballistic
- weight
- resistant article
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 9
- 238000000034 method Methods 0.000 title claims description 14
- 239000000835 fiber Substances 0.000 claims abstract description 84
- 229920000098 polyolefin Polymers 0.000 claims abstract description 13
- -1 polyethylene Polymers 0.000 claims abstract description 12
- 239000004698 Polyethylene Substances 0.000 claims abstract description 8
- 229920000573 polyethylene Polymers 0.000 claims abstract description 8
- 239000004743 Polypropylene Substances 0.000 claims abstract description 4
- 229920001155 polypropylene Polymers 0.000 claims abstract description 4
- 230000008569 process Effects 0.000 claims description 7
- 239000002002 slurry Substances 0.000 claims description 6
- 230000035515 penetration Effects 0.000 description 15
- 239000004744 fabric Substances 0.000 description 9
- 239000000203 mixture Substances 0.000 description 9
- 239000004927 clay Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 5
- 229920000271 Kevlar® Polymers 0.000 description 4
- 239000004761 kevlar Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000011120 plywood Substances 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 3
- 239000004615 ingredient Substances 0.000 description 3
- 238000005054 agglomeration Methods 0.000 description 2
- 230000002776 aggregation Effects 0.000 description 2
- 239000004760 aramid Substances 0.000 description 2
- 229920003235 aromatic polyamide Polymers 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 239000012634 fragment Substances 0.000 description 2
- 229920013683 Celanese Polymers 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229920000690 Tyvek Polymers 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004359 castor oil Substances 0.000 description 1
- 235000019438 castor oil Nutrition 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 229920002301 cellulose acetate Polymers 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000000254 damaging effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- ZEMPKEQAKRGZGQ-XOQCFJPHSA-N glycerol triricinoleate Natural products CCCCCC[C@@H](O)CC=CCCCCCCCC(=O)OC[C@@H](COC(=O)CCCCCCCC=CC[C@@H](O)CCCCCC)OC(=O)CCCCCCCC=CC[C@H](O)CCCCCC ZEMPKEQAKRGZGQ-XOQCFJPHSA-N 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229920001903 high density polyethylene Polymers 0.000 description 1
- 239000004700 high-density polyethylene Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000002655 kraft paper Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000000344 soap Substances 0.000 description 1
- 239000011122 softwood Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000004094 surface-active agent Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
- D21H13/10—Organic non-cellulose fibres
- D21H13/12—Organic non-cellulose fibres from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D21H13/14—Polyalkenes, e.g. polystyrene polyethylene
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
- F41H5/00—Armour; Armour plates
- F41H5/02—Plate construction
- F41H5/04—Plate construction composed of more than one layer
- F41H5/0471—Layered armour containing fibre- or fabric-reinforced layers
- F41H5/0485—Layered armour containing fibre- or fabric-reinforced layers all the layers being only fibre- or fabric-reinforced layers
Landscapes
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Nonwoven Fabrics (AREA)
- Paper (AREA)
- Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
Abstract
A ballistic-resistant article of manufacture which comprises an agglomerated web of two types of discrete fibers. The first type is a fiber formed from polyolefin filament having, in the case of polyethylene filament, a weight average molecular weight of at least about 500,000, a tensile modulus of at least about 300 g/denier and a tenacity of at least about 15 g/denier, and in the case of polypropylene filament, a weight average molecular weight of at least 750,000, a tensile modulus of at least about 160 g/denier and a tenacity of at least about 8 g/denier. The second type is a high density polyolefin fiber having an average fiber length substantially shorter than the first type. The article has a sufficient thickness to absorb the energy of a projectile.
Description
WO9~/04X~ 2 0 G ~ CT/US~0/05137 BALLISTIC-RESISTANT ARTICLES
AND
METHOD OF MANUFACUTURE THEREOF
BACKGROUND OF THE INVENTION
The present invention relates to ballistic-resistant articles of manufacture, as well as to a method of manufacture thereof. The ballistic-resistant articles of the present invention comprise high strength polyolefin fibers.
Ballistic-resistant 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 15 Har~ell et al U.S. Patent No. 4,457,985 Harpell et_al U.SO Patent No. 4,501,856 Harpell et al U.S. Patent No. 4,623,574 Hareell et al U.S. Patent No. 4,650,710; and Harpell et âL U.S. Patent No. 4,681,792.
Another Allied Corporation patent directed to high strength polyethylene fiber i9 Kavesh et al, U.S.
Patent No. 4,413,ll0.
These patents describe ballistic-resistant articles of manufacture comprising a flexi~le network of polyolefin fibers having, in the case of polyethylene filament, a weight average molecular weight of at least about 500,000, a tensile modulus of at least about 300 g/denier and a tenacity of at leask about 15 g/denier, and in the case of polypropylene filament, a weight average molecular weight of at least WO9l/0485~ ~ O S ~ 7 7 ~' PCT/US90/05137 750,000, a tensile modulus of at least about 160 g/denier and a tenacity of at least about 8 g/denier, said fibers being formed into a network of sufficient thickness to absorb the energy of a projectile.
As will be discussed hereinafter, the filament described in the above patents is a preferred ingredient for use in forming the ballistic-resistant articles according to the present invention.
Accordingly, the disclosure of the above patents is hereby expressly incorporated by reference, to the extent not inconsistent herewith.
Other patents of general interest with respect to ballistic-resistant articles include Zeqlen, U.S.
Patent No. 604,870, and Hawkinson, U.S. Patent No.
15 4,428,998.
The Har~ell et al patents listed above are 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. This construction was found to be superior to KEVLAR (trademark of Dupont for aramid yarn) in arresting projectile penetration.
There remains a need, however, for ballistic resistant articles capable of arresting projectile penetration more effectively than those discussed above at a given basis weight of ballistic-resistant material, or, correspondingly, that are equally as Pffective at a lower basis weight.
SUMMARY OF THE INVENTION
A major object of the present invention i5 to provide ballistic resistant articles of manufacture that offer improved penetration resistance as compared to ballistic-resistant articles of the prior art.
W091/048~ 2 0 6 6 7 7 ~' Pcr/us90/05l37 Another object of tne invention is to provide a method for manufacturing such ballistic-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 resistant articles that offer penetration resistance equal to articles of the prior art, but at significantly lower material basis weight, thereby greatly expanding th~ useful applications for such articles.
These and other objects according to the present invention are accomplished by ballistic resistant articles having as a principal ingredient the high strength polyolefin filament discussed above, but in which that filament has been converted to discrete fibers of a much shorter and definite length, and in which those discrete fibers have been formed into an agglomerated web together with a minor amount of much shorter polyolefin fibers.
The ballistic resistant articles according to the present invention are preferably formed by conventional papermaking techniques~ In this manner, a uniform web of the high strength fibers can be readily generated, and the process can be carried out on an industrial scale without extensive original plant design.
It has been found that an agglomerated web of the high strength Allied fiber alone does not offer significantly improved penetration resistance.
Instead, i is necessary to form the web with a minor amount of a much shorter, high density polyolefin fiber such as that marketed commercially under the trademark PULPEX rademark of ~Prcules Inc., a Delaware Corporatior., for high density polyethylene pulp having WO91~0~85~ 2 ~ ~ ~ 7 7 ~ PCT/US90/05137 an avPrage fiber length of 0.6 - 1.2 mm, made water-dispersible with polyvinyl alcohol treatment).
Accordingly, the present invention relates in one aspect to ballistic resistant articles of manufacture comprising an ag~lomerated web of discrete fibers formed from (1) polyolefin filament having, in the case of polyethylene filament, a weight average molecular weight of at least about 500,000, a tensile modulus of at least about 300 g/denier and a tenacity of at least about 15 g/denier, and in the case of polypropylene filament, a weight average molecular weight of at least 750,000, a tensile modulus of at least about 160 g/denier and a tenacity of at least about 8 g/denier;
and ~2) high density polyolefin fibers having an average fiber length of about 0.5 to about 1.5 mm; said article having a sufficient thickness to absorb the energy of a projectile.
In another aspect, the present invention relates to a process for making such ballistic-resistant articles, in which an aqueous slurry of the two types of fibers is de-watered on a wire screen, to form the agglomerated web according to the invention.
BRIEF DESCRIPTION OF ~HE DRAWING
The Figure of the drawing graphically depicts the experimental results of Table 1.
DETAIIED DESCRIPTION OF T~ PREFERRED EMBODIMENTS
OF THE PRESENT INVENTION
A high strength polyolefin filament such as that described in the aforementioned Allied patents is converted, for use in the present invention, to fibers having a length from about 0.5 to about 1.5 inches, WO9l/04X5~ 2 Q ~ 6 ~ 7 ~ PCT/US90/05137 preferably from about 0.5 to about l inch, and optimally about 0.75 inch (re~erred to hereinafter as "long fiber"). This fiber i5 then formed into an aqueous slurry together with a lesser amount of high density polyethylene fiber having an average fiber length of about 0.5 to about 1.5 mm, preferably about 0.6 to about 1.2 mm (referred to hereinafter as "short fiber"). The slurry is then converted to an agglomerated web, for example by using a Fourdrinier wire and appropriate suction rolls.
Experimentation with the relative amounts of long fiber and short fiber, as will be set forth hereinafter, has revealed the optimum composition to be one containing from about -75 to about 85% long fiber and from about 15 to about 25~ short fiber.
Compositions containing from about 65 to about 95% long fiber and from about 5 to about 35% short fiber, however, are also within the scope of the invention.
Moreover, because various additives may be included in the formulations according to the invention, the optimum ratio of long fiber to short fiber may also be expressed as preferably 65 to 95 parts long fiber to 35 to 5 parts short fiber, more prPferably 75 to 85 parts long fiber to 25 to 15 parts short fiber.
The ballistic-resistant articles according to the invention are formed using conventional papermaking techniques, such as passing an aqueous slurry of the admixed long and short fibers onto an endless wire screen, followed by dewatering and drying o~ the thus-formed sheet. The sheet is then heat-treated with or without pressure as is known to those skilled in the paper-maXing art. The heat treatment is generally of sufficient temperature and pressure to melt or sinter the short fiber,-which results in a bonding of the long WO91/0485~ 2 0 ~ ~ 7 7 ~ PCT/US90/0~137 fibers. It will be appreciated that in such 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.
It is also contemplated to form the agglomerated web by a hydroentangling process. 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 damaging 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.
A series of experimental handsheets were prepared, whose formulations were both within and without the scspe of the present invention, and subjected to ballistic testing to determine their penetration resistance. The handsheets were prepared by dewatering an aqueous slurry of the constituent ingredients, to form an agglomerated web, followed by drying on a steam-heated drum and bonding in a 130C
oven for ten minutes. The handsheets thus formed WO91/0485~ ~0~S 6 7 7 rd PCT/US90/05137 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 ~e increased 2, 4 or 8 times by folding one of these sheets once, twice or thxee times, respectively. The specimens tested thus tend to have basis weights increasing by multiples of eight~ because th~ basis weight of a specimen was generally increased by 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 formed 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 clav is the backing used for determining the baLlistic resistance of body armor (U.S. Department of Justice - National Institute of Justice, NI~ Standard 0101.03).
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 "Spectra" is a trademark of Allied Corporation for high strength polyethylene as described in the Harpell et al patents, whereas the term "Pulpex" is a trademark of Hercules Corporation for their short fiber polyethylene synth~tic pulp. The Pulpex was used in its 2 0 ~ ~ 7 7 .~ Pc-r/lJs9l)/osl37 commercially available form, whereas the Spectra filament was modified by chopping it to ~orm fibers haviny an average length of about 0.75 inch. All number entries are p~rcent by weight, except ~or "Basis Weight", which is in units of lb/3000 ft2, and refers to the basis weight of the specimen tested.
Ex. Spectra PulpexOther Basis P~ne-AdditivesWeight tration 1 50 25*25 Albacell 2880 N
2 ~ - ll 2400 N
AND
METHOD OF MANUFACUTURE THEREOF
BACKGROUND OF THE INVENTION
The present invention relates to ballistic-resistant articles of manufacture, as well as to a method of manufacture thereof. The ballistic-resistant articles of the present invention comprise high strength polyolefin fibers.
Ballistic-resistant 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 15 Har~ell et al U.S. Patent No. 4,457,985 Harpell et_al U.SO Patent No. 4,501,856 Harpell et al U.S. Patent No. 4,623,574 Hareell et al U.S. Patent No. 4,650,710; and Harpell et âL U.S. Patent No. 4,681,792.
Another Allied Corporation patent directed to high strength polyethylene fiber i9 Kavesh et al, U.S.
Patent No. 4,413,ll0.
These patents describe ballistic-resistant articles of manufacture comprising a flexi~le network of polyolefin fibers having, in the case of polyethylene filament, a weight average molecular weight of at least about 500,000, a tensile modulus of at least about 300 g/denier and a tenacity of at leask about 15 g/denier, and in the case of polypropylene filament, a weight average molecular weight of at least WO9l/0485~ ~ O S ~ 7 7 ~' PCT/US90/05137 750,000, a tensile modulus of at least about 160 g/denier and a tenacity of at least about 8 g/denier, said fibers being formed into a network of sufficient thickness to absorb the energy of a projectile.
As will be discussed hereinafter, the filament described in the above patents is a preferred ingredient for use in forming the ballistic-resistant articles according to the present invention.
Accordingly, the disclosure of the above patents is hereby expressly incorporated by reference, to the extent not inconsistent herewith.
Other patents of general interest with respect to ballistic-resistant articles include Zeqlen, U.S.
Patent No. 604,870, and Hawkinson, U.S. Patent No.
15 4,428,998.
The Har~ell et al patents listed above are 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. This construction was found to be superior to KEVLAR (trademark of Dupont for aramid yarn) in arresting projectile penetration.
There remains a need, however, for ballistic resistant articles capable of arresting projectile penetration more effectively than those discussed above at a given basis weight of ballistic-resistant material, or, correspondingly, that are equally as Pffective at a lower basis weight.
SUMMARY OF THE INVENTION
A major object of the present invention i5 to provide ballistic resistant articles of manufacture that offer improved penetration resistance as compared to ballistic-resistant articles of the prior art.
W091/048~ 2 0 6 6 7 7 ~' Pcr/us90/05l37 Another object of tne invention is to provide a method for manufacturing such ballistic-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 resistant articles that offer penetration resistance equal to articles of the prior art, but at significantly lower material basis weight, thereby greatly expanding th~ useful applications for such articles.
These and other objects according to the present invention are accomplished by ballistic resistant articles having as a principal ingredient the high strength polyolefin filament discussed above, but in which that filament has been converted to discrete fibers of a much shorter and definite length, and in which those discrete fibers have been formed into an agglomerated web together with a minor amount of much shorter polyolefin fibers.
The ballistic resistant articles according to the present invention are preferably formed by conventional papermaking techniques~ In this manner, a uniform web of the high strength fibers can be readily generated, and the process can be carried out on an industrial scale without extensive original plant design.
It has been found that an agglomerated web of the high strength Allied fiber alone does not offer significantly improved penetration resistance.
Instead, i is necessary to form the web with a minor amount of a much shorter, high density polyolefin fiber such as that marketed commercially under the trademark PULPEX rademark of ~Prcules Inc., a Delaware Corporatior., for high density polyethylene pulp having WO91~0~85~ 2 ~ ~ ~ 7 7 ~ PCT/US90/05137 an avPrage fiber length of 0.6 - 1.2 mm, made water-dispersible with polyvinyl alcohol treatment).
Accordingly, the present invention relates in one aspect to ballistic resistant articles of manufacture comprising an ag~lomerated web of discrete fibers formed from (1) polyolefin filament having, in the case of polyethylene filament, a weight average molecular weight of at least about 500,000, a tensile modulus of at least about 300 g/denier and a tenacity of at least about 15 g/denier, and in the case of polypropylene filament, a weight average molecular weight of at least 750,000, a tensile modulus of at least about 160 g/denier and a tenacity of at least about 8 g/denier;
and ~2) high density polyolefin fibers having an average fiber length of about 0.5 to about 1.5 mm; said article having a sufficient thickness to absorb the energy of a projectile.
In another aspect, the present invention relates to a process for making such ballistic-resistant articles, in which an aqueous slurry of the two types of fibers is de-watered on a wire screen, to form the agglomerated web according to the invention.
BRIEF DESCRIPTION OF ~HE DRAWING
The Figure of the drawing graphically depicts the experimental results of Table 1.
DETAIIED DESCRIPTION OF T~ PREFERRED EMBODIMENTS
OF THE PRESENT INVENTION
A high strength polyolefin filament such as that described in the aforementioned Allied patents is converted, for use in the present invention, to fibers having a length from about 0.5 to about 1.5 inches, WO9l/04X5~ 2 Q ~ 6 ~ 7 ~ PCT/US90/05137 preferably from about 0.5 to about l inch, and optimally about 0.75 inch (re~erred to hereinafter as "long fiber"). This fiber i5 then formed into an aqueous slurry together with a lesser amount of high density polyethylene fiber having an average fiber length of about 0.5 to about 1.5 mm, preferably about 0.6 to about 1.2 mm (referred to hereinafter as "short fiber"). The slurry is then converted to an agglomerated web, for example by using a Fourdrinier wire and appropriate suction rolls.
Experimentation with the relative amounts of long fiber and short fiber, as will be set forth hereinafter, has revealed the optimum composition to be one containing from about -75 to about 85% long fiber and from about 15 to about 25~ short fiber.
Compositions containing from about 65 to about 95% long fiber and from about 5 to about 35% short fiber, however, are also within the scope of the invention.
Moreover, because various additives may be included in the formulations according to the invention, the optimum ratio of long fiber to short fiber may also be expressed as preferably 65 to 95 parts long fiber to 35 to 5 parts short fiber, more prPferably 75 to 85 parts long fiber to 25 to 15 parts short fiber.
The ballistic-resistant articles according to the invention are formed using conventional papermaking techniques, such as passing an aqueous slurry of the admixed long and short fibers onto an endless wire screen, followed by dewatering and drying o~ the thus-formed sheet. The sheet is then heat-treated with or without pressure as is known to those skilled in the paper-maXing art. The heat treatment is generally of sufficient temperature and pressure to melt or sinter the short fiber,-which results in a bonding of the long WO91/0485~ 2 0 ~ ~ 7 7 ~ PCT/US90/0~137 fibers. It will be appreciated that in such 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.
It is also contemplated to form the agglomerated web by a hydroentangling process. 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 damaging 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.
A series of experimental handsheets were prepared, whose formulations were both within and without the scspe of the present invention, and subjected to ballistic testing to determine their penetration resistance. The handsheets were prepared by dewatering an aqueous slurry of the constituent ingredients, to form an agglomerated web, followed by drying on a steam-heated drum and bonding in a 130C
oven for ten minutes. The handsheets thus formed WO91/0485~ ~0~S 6 7 7 rd PCT/US90/05137 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 ~e increased 2, 4 or 8 times by folding one of these sheets once, twice or thxee times, respectively. The specimens tested thus tend to have basis weights increasing by multiples of eight~ because th~ basis weight of a specimen was generally increased by 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 formed 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 clav is the backing used for determining the baLlistic resistance of body armor (U.S. Department of Justice - National Institute of Justice, NI~ Standard 0101.03).
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 "Spectra" is a trademark of Allied Corporation for high strength polyethylene as described in the Harpell et al patents, whereas the term "Pulpex" is a trademark of Hercules Corporation for their short fiber polyethylene synth~tic pulp. The Pulpex was used in its 2 0 ~ ~ 7 7 .~ Pc-r/lJs9l)/osl37 commercially available form, whereas the Spectra filament was modified by chopping it to ~orm fibers haviny an average length of about 0.75 inch. All number entries are p~rcent by weight, except ~or "Basis Weight", which is in units of lb/3000 ft2, and refers to the basis weight of the specimen tested.
Ex. Spectra PulpexOther Basis P~ne-AdditivesWeight tration 1 50 25*25 Albacell 2880 N
2 ~ - ll 2400 N
3 " " " 1920 P
4 " 50 - 1440 P
" " - 1920 P
6 " " - 3360 P
7 ~ _ 3840 P
8 " " - 4800 N
9 " " - 5760 N
ll " " - 1920 P
12 " " - 2~00 P
13 " " - 2880 P
14 " " - 3840 P
" " - 4800 N
16 " 20 20 CA2 1920 N
17 ~ - 14~0 P
19 " " " 1440 N
21 ll ll ll 1440 P
22 70 30 - 1440 P,P,N,N
23 " " (dry) 1680 N
24 ll " (wet) 1680 P
" " dry, heat pressed 1680 N
WO ~1/04~55 2 ~ ~ 'o 7 ~ ~ pcr/us~n/osl37 _9_ 26 " " wet, heat precsed 1680 P
27 ~ add ' 1 20% EL3 1440 P
28 " " " 1920 P
29 " " " 1440 P
530 " " " 1688 P
31 " " " 1920 P
32 70 25* 5 AL 1920 N
33 " " " 1440 P
34 " 25 5 AP4 960 P
1035 " " " 1440 N
36 " " 5 KF5 960 P
37 " " " 1440 N
38 " 10* 20 AL 1920 N
39 " " " 1440 N
1540 " " " 960 P
41 " 20* 10 AL 1920 N
42 " " " 1440 N
43 " 22*3 AL, 5 M6 1440 N
44 " 25 5 CA 1440 N,P
2045 " " 5 M 1440 P,N
46 i' 30 SC7 1920 P
47 " " " 1680 P
48 " " " 1440 P
2550 " " " 960 . N, P, P
51 75 25 - 1440 ~-52 " " - 960 P
53 80 20 - 1440 N,N, P
54 ~ 960 P,P,N
- 56 " " - 960 P, P
" " - 1920 P
6 " " - 3360 P
7 ~ _ 3840 P
8 " " - 4800 N
9 " " - 5760 N
ll " " - 1920 P
12 " " - 2~00 P
13 " " - 2880 P
14 " " - 3840 P
" " - 4800 N
16 " 20 20 CA2 1920 N
17 ~ - 14~0 P
19 " " " 1440 N
21 ll ll ll 1440 P
22 70 30 - 1440 P,P,N,N
23 " " (dry) 1680 N
24 ll " (wet) 1680 P
" " dry, heat pressed 1680 N
WO ~1/04~55 2 ~ ~ 'o 7 ~ ~ pcr/us~n/osl37 _9_ 26 " " wet, heat precsed 1680 P
27 ~ add ' 1 20% EL3 1440 P
28 " " " 1920 P
29 " " " 1440 P
530 " " " 1688 P
31 " " " 1920 P
32 70 25* 5 AL 1920 N
33 " " " 1440 P
34 " 25 5 AP4 960 P
1035 " " " 1440 N
36 " " 5 KF5 960 P
37 " " " 1440 N
38 " 10* 20 AL 1920 N
39 " " " 1440 N
1540 " " " 960 P
41 " 20* 10 AL 1920 N
42 " " " 1440 N
43 " 22*3 AL, 5 M6 1440 N
44 " 25 5 CA 1440 N,P
2045 " " 5 M 1440 P,N
46 i' 30 SC7 1920 P
47 " " " 1680 P
48 " " " 1440 P
2550 " " " 960 . N, P, P
51 75 25 - 1440 ~-52 " " - 960 P
53 80 20 - 1440 N,N, P
54 ~ 960 P,P,N
- 56 " " - 960 P, P
5~ 2 0 ~ ~ 7 7 ~ PC~/US90/05137 57 90 10 - 1440 P,P,N
58 " " - 1920 N
59 ~ - 960 P
" " - 480 P
Notes: * Pulpex grade A321 - "bondable"
pulp, treated to have increased hydrogen bonding;
otherwise, Pulpex grade ED (unmodified) 1. Albacel southern softwood kraft pulp 2. Cellulose acetate fibrit (Celanese Corp'n) 3. Elastoplast resin added as saturant, about 20% pick up 4. Apyeil (Japanese aramid fibrid) 5. Kevlar Fibrid 6. Microfibrillated cellulose from ITT
58 " " - 1920 N
59 ~ - 960 P
" " - 480 P
Notes: * Pulpex grade A321 - "bondable"
pulp, treated to have increased hydrogen bonding;
otherwise, Pulpex grade ED (unmodified) 1. Albacel southern softwood kraft pulp 2. Cellulose acetate fibrit (Celanese Corp'n) 3. Elastoplast resin added as saturant, about 20% pick up 4. Apyeil (Japanese aramid fibrid) 5. Kevlar Fibrid 6. Microfibrillated cellulose from ITT
7. Caschem - a surfactant based on a castor oil soap ~glycerol monoricinolate CAS-1323382), 0.5 g/handsheet added for formation improvement In the above table, "N" indicates that the bullet was stopped by the specimen, whereas "P" 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 "P". The results of these tests are somewhat qualitative, because the clay backing appeared to WO9l/0485~ 2 Q ~ ~ 7 ~ ~ PCT/US90/05137 improve slightly the performance of the specimen.
The data of Table l, for handsheets containing mixtures of Spectra type fiher and Pulpex fiber, may be represented graphically, as is shown in the accompanying Figure, by plotting increasing long fiber/decreasing short fiber percentage on the abscissa, and ~tal basis weight of specimen on the ordinate. From this Figure, it appears that a composition range of 75-85~ long fiber to 15-25% short fiber is optimum for use in the invention.
A number of interesting observations can be made from the above table. If the tensile strength of varying long fiber/short fiber compositions is calculated, it appears that specimens with a very high tensile strength required a much higher basis weight per specimen to display penetration resistance, as compared to specimens with a much lower tensile strength. This is shown below in Table 2, where there are listed the minimum basis weights at which each of a variety of long fiber/short fiber compositions displayed penetration resistance.
Long Fiber~ 50-50 60-40 70-3080-20 90-10 short fiber 25 Bullet Pene- NO N0 NO NO NO
tration Total basis 4800 4800 1440 960 1440 weight Tensile, lb/in 2800 2850 567 256 144 Basis weight 2400 2880 1008 778 1296 long fiber It is indeed surprising hc poorly the 50-50 composition fared in penetr-ation resistance, as it has WO91/0485~ 2 0 S ~ 7 7 ~ PCT/US90/05137 has the highest tensile strength of the specimens listed. This is entirely contrary to the teaching of the prior art, notabl~ the Harpell et al patents and Kevlar ballistic-resistant articles, where high tensile strength is taught to be directly related to increased penetration resistance.
The explanation for these discrepant results is that the present invention operates on an entirely different principle than the prior art discussed above, owing to its unique structure and attendant properties.
In the HarPell et al patents, and in woven Kevlar fabrics, when a bullet strikes the wound or woven filament, the kinetic eneryy of the bullet causes the filament to rupture. By contrast, in the present invention, the filament is present as relatively short fibers in a ra~domly oriented paper-like agglomeration.
When a bullet strikes this structure, the predominant mechanism is one in which the relatively short fibers are caused not to rupture, but rather to be pulled out from the entangled paper-like structure. It has been found that more kinetic energy is consumed by pulling a fiber out of an entangled structure than by rupturing a fiber.
This can be demonstrated by a kinetic energy calculation comparing a specimen according to the present invention (identical to Example 22 of Table l, but having a slightly higher total basis weight of 1488 lb/300 ft2) with the best performing fabric disclosed in Harpell et al, U.S. Patent No. 4,650,710, as well as a another ballistic article prepared according to the teaching of this same patent. The ~abrics from Har~ell 1710 are those designated Examples F-l and F-5, appearing in Table lB at column 9, lines ~0-30. It should be further noted that the data used for the wet WO9l/04855 2 0 ~ 6 l ~ ~ Pcr/us~o/os137 laid nonwoven structure of the present invention is for no bullet penetration, while the data Of ~3E~ell e~ al is for 50~ bullet penetration.
Calculations 1. Ballistic resistant article according to the present invention:
Specimen basis weight = 1488 lb/ream or 2.427 kg/m2 Long fiber basis weight = 1041 lb/ream or 1.7 1 0 kg/m2 Velocity, no penetration = 1250 ft/s = 381 m/s Bullet = 40 grains = 2.592 g = 0.002593 kg Kinetic energy = 1/2 mv2 - (0.5)(0.002593)(381)2 = 188 kg m /s Kinetic energy/specimen basis weight = 188/2.427 = 78 Joules/(kg/m2) Kinetic energy/long fiber basis weiyht = 188/1.7 = 111 Joules/(kg/m2~
2. Example F-l according to Har~ell '710 (best-performing):
Fabric basis weight = 1079 lb/ream or 1.76 kg/m2 Velocity, 50gO penetration = 1318 ft/s = 402 m/s Bullet = 19 grain fragment = 0.0012312 kg Kinetic energy = 1/2 mv2 = (0.5)(0.0012312)(4022) = 99-4 kg m2/s2 Kinetic energy/fabric basis weight = 99.4/1.76 = 5~ Joules/tkg/m2) 3. Example F-5 according to Har~ell '710:
Fabric basis weight = 3005 lb/ream or 4.95 kg/m2 W~l/04~ CT/US~J0/~5137 Bullet = 19 grain fragment = 0.0012312 kg Kinetic energy = 1/2 mv2 = ~0.5)(0.0012312)(4052) - 101.6 kg m2/s~
Kinetic energy/fabric basis weight = 101.6/4.95 = 21 Joules/(kg/m2) The above comparison shows that a given basis weight of the same type of filament as used in the Har~ell et al patents, when present as relatively short fibers in a paper-like agglomeration according to the present invsntion, absorbs nearly twice the kinetic energy as the most preferred use disclosed by the teaching of the prior art.
While the present invention has been described in connection with various preferred embodiments thereof, it will be appreciated that it should not be construed to be limited thereby. Modifications remain possible, without departing from the scope and spirit of the appended claims.
The data of Table l, for handsheets containing mixtures of Spectra type fiher and Pulpex fiber, may be represented graphically, as is shown in the accompanying Figure, by plotting increasing long fiber/decreasing short fiber percentage on the abscissa, and ~tal basis weight of specimen on the ordinate. From this Figure, it appears that a composition range of 75-85~ long fiber to 15-25% short fiber is optimum for use in the invention.
A number of interesting observations can be made from the above table. If the tensile strength of varying long fiber/short fiber compositions is calculated, it appears that specimens with a very high tensile strength required a much higher basis weight per specimen to display penetration resistance, as compared to specimens with a much lower tensile strength. This is shown below in Table 2, where there are listed the minimum basis weights at which each of a variety of long fiber/short fiber compositions displayed penetration resistance.
Long Fiber~ 50-50 60-40 70-3080-20 90-10 short fiber 25 Bullet Pene- NO N0 NO NO NO
tration Total basis 4800 4800 1440 960 1440 weight Tensile, lb/in 2800 2850 567 256 144 Basis weight 2400 2880 1008 778 1296 long fiber It is indeed surprising hc poorly the 50-50 composition fared in penetr-ation resistance, as it has WO91/0485~ 2 0 S ~ 7 7 ~ PCT/US90/05137 has the highest tensile strength of the specimens listed. This is entirely contrary to the teaching of the prior art, notabl~ the Harpell et al patents and Kevlar ballistic-resistant articles, where high tensile strength is taught to be directly related to increased penetration resistance.
The explanation for these discrepant results is that the present invention operates on an entirely different principle than the prior art discussed above, owing to its unique structure and attendant properties.
In the HarPell et al patents, and in woven Kevlar fabrics, when a bullet strikes the wound or woven filament, the kinetic eneryy of the bullet causes the filament to rupture. By contrast, in the present invention, the filament is present as relatively short fibers in a ra~domly oriented paper-like agglomeration.
When a bullet strikes this structure, the predominant mechanism is one in which the relatively short fibers are caused not to rupture, but rather to be pulled out from the entangled paper-like structure. It has been found that more kinetic energy is consumed by pulling a fiber out of an entangled structure than by rupturing a fiber.
This can be demonstrated by a kinetic energy calculation comparing a specimen according to the present invention (identical to Example 22 of Table l, but having a slightly higher total basis weight of 1488 lb/300 ft2) with the best performing fabric disclosed in Harpell et al, U.S. Patent No. 4,650,710, as well as a another ballistic article prepared according to the teaching of this same patent. The ~abrics from Har~ell 1710 are those designated Examples F-l and F-5, appearing in Table lB at column 9, lines ~0-30. It should be further noted that the data used for the wet WO9l/04855 2 0 ~ 6 l ~ ~ Pcr/us~o/os137 laid nonwoven structure of the present invention is for no bullet penetration, while the data Of ~3E~ell e~ al is for 50~ bullet penetration.
Calculations 1. Ballistic resistant article according to the present invention:
Specimen basis weight = 1488 lb/ream or 2.427 kg/m2 Long fiber basis weight = 1041 lb/ream or 1.7 1 0 kg/m2 Velocity, no penetration = 1250 ft/s = 381 m/s Bullet = 40 grains = 2.592 g = 0.002593 kg Kinetic energy = 1/2 mv2 - (0.5)(0.002593)(381)2 = 188 kg m /s Kinetic energy/specimen basis weight = 188/2.427 = 78 Joules/(kg/m2) Kinetic energy/long fiber basis weiyht = 188/1.7 = 111 Joules/(kg/m2~
2. Example F-l according to Har~ell '710 (best-performing):
Fabric basis weight = 1079 lb/ream or 1.76 kg/m2 Velocity, 50gO penetration = 1318 ft/s = 402 m/s Bullet = 19 grain fragment = 0.0012312 kg Kinetic energy = 1/2 mv2 = (0.5)(0.0012312)(4022) = 99-4 kg m2/s2 Kinetic energy/fabric basis weight = 99.4/1.76 = 5~ Joules/tkg/m2) 3. Example F-5 according to Har~ell '710:
Fabric basis weight = 3005 lb/ream or 4.95 kg/m2 W~l/04~ CT/US~J0/~5137 Bullet = 19 grain fragment = 0.0012312 kg Kinetic energy = 1/2 mv2 = ~0.5)(0.0012312)(4052) - 101.6 kg m2/s~
Kinetic energy/fabric basis weight = 101.6/4.95 = 21 Joules/(kg/m2) The above comparison shows that a given basis weight of the same type of filament as used in the Har~ell et al patents, when present as relatively short fibers in a paper-like agglomeration according to the present invsntion, absorbs nearly twice the kinetic energy as the most preferred use disclosed by the teaching of the prior art.
While the present invention has been described in connection with various preferred embodiments thereof, it will be appreciated that it should not be construed to be limited thereby. Modifications remain possible, without departing from the scope and spirit of the appended claims.
Claims (12)
1. A ballistic-resistant article of manufacture, comprising an agglomerated web of discrete fibers including (1) a first type of fiber formed from polyolefin filament having, in the case of polyethylene filament, a weight average molecular weight of at least about 500,000, a tensile modulus of at least about 300 g/denier and a tenacity of at least about 15 g/denier, and in the case of polypropylene filament, a weight average molecular weight of at least 750,000, a tensile modulus of at least about 160 g/denier and a tenacity of at least about 8 g/denier;
and (2) a second type of fiber, comprising high density polyolefin fibers having an average fiber length substantially shorter than said first type; said article having a sufficient thickness to absorb the energy of a projectile.
and (2) a second type of fiber, comprising high density polyolefin fibers having an average fiber length substantially shorter than said first type; said article having a sufficient thickness to absorb the energy of a projectile.
2. The ballistic-resistant article of Claim 1, wherein said first type of fiber has an average length of about 0.5 to about 1.5 inches (about 12.7 mm to about 38.8 mm).
3. The ballistic-resistant article of Claim 2, wherein said first type of fiber has an average length of about 0.5 to about 1 inch (about 12.7 mm to about 25.4 mm).
4. The ballistic-resistant article of Claim 3, wherein said first type of fiber has an average length of about 0.75 inch (19.05 mm).
5. The ballistic-resistant article of Claim 1, wherein said second type of fiber has an average length of about 0.5 to about 1.5 millimeters.
6. The ballistic-resistant article of Claim 5, wherein said second type of fiber has an average length of about 0.6 to about 1.2 millimeters.
7. The ballistic-resistant article of Claim 1, comprising about 65 to about 95 % by weight of said first type of fiber, and about 5 to about 35 % by weight of said second type of fiber.
8. The ballistic-resistant article of Claim 7, comprising about 75 to about 85 % by weight of said first type of fiber, and about 15 to about 25 % by weight of said second type of fiber.
9. The ballistic-resistant article of Claim 2, comprising about 65 to about 95 parts by weight of said first type of fiber, and about 5 to about 35 parts by weight of said second type of fiber.
10. The ballistic-resistant article of Claim 9, comprising about 75 to about 85 parts by weight of said first type of fiber, and about 15 to about 25 parts by weight of said second type of fiber.
11. A process for making the ballistic-resistant article of Claim 1, comprising de-watering an aqueous slurry of said first and second types of fibers on a wire screen, thereby to form the said agglomerated web.
12. The process of claim 11, wherein the agglomerated web is heat-treated to sinter or melt the second type of fiber to thereby result in a bonding of the first type of fiber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41374389A | 1989-09-28 | 1989-09-28 | |
| US413,743 | 1989-09-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2066772A1 true CA2066772A1 (en) | 1991-03-29 |
Family
ID=23638434
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2066772 Abandoned CA2066772A1 (en) | 1989-09-28 | 1990-09-14 | Ballistic-resistant articles and method of manufacture thereof |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0494269A4 (en) |
| JP (1) | JPH05507547A (en) |
| AU (1) | AU6899191A (en) |
| BR (1) | BR9007695A (en) |
| CA (1) | CA2066772A1 (en) |
| WO (1) | WO1991004855A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL9200625A (en) * | 1992-04-03 | 1993-11-01 | Dsm Nv | NON-WOVEN POLYOLEFINE FIBER LAYER FOR USE IN A LAYERED ANTIBALLISTIC STRUCTURE. |
| WO1994009336A1 (en) * | 1992-10-13 | 1994-04-28 | Allied-Signal Inc. | Entangled high strength yarn |
| IL107195A (en) * | 1992-10-13 | 1997-07-13 | Allied Signal Inc | Fabric having reduced air permeability comprising multifilament yarn |
| US5567498A (en) * | 1993-09-24 | 1996-10-22 | Alliedsignal Inc. | Textured ballistic article |
| EP0910689B1 (en) * | 1996-07-11 | 2000-12-27 | Dsm N.V. | Method for producing a felt, a felt obtainable in accordance with the said method, and antiballistic-shaped parts fabricated from the said felt |
| NL1003565C2 (en) * | 1996-07-11 | 1998-01-15 | Dsm Nv | Production of a felt suitable for conversion into antiballistic items |
| EP1495859B1 (en) * | 2003-07-08 | 2008-09-03 | Airbus Deutschland GmbH | Lightweight material structure |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4457985A (en) * | 1982-03-19 | 1984-07-03 | Allied Corporation | Ballistic-resistant article |
| US4403012A (en) * | 1982-03-19 | 1983-09-06 | Allied Corporation | Ballistic-resistant article |
| US4501856A (en) * | 1982-03-19 | 1985-02-26 | Allied Corporation | Composite containing polyolefin fiber and polyolefin polymer matrix |
| US4681792A (en) * | 1985-12-09 | 1987-07-21 | Allied Corporation | Multi-layered flexible fiber-containing articles |
| US4820568A (en) * | 1987-08-03 | 1989-04-11 | Allied-Signal Inc. | Composite and article using short length fibers |
| US4808467A (en) * | 1987-09-15 | 1989-02-28 | James River Corporation Of Virginia | High strength hydroentangled nonwoven fabric |
-
1990
- 1990-09-14 CA CA 2066772 patent/CA2066772A1/en not_active Abandoned
- 1990-09-14 JP JP91501026A patent/JPH05507547A/en active Pending
- 1990-09-14 EP EP19910900520 patent/EP0494269A4/en not_active Withdrawn
- 1990-09-14 WO PCT/US1990/005137 patent/WO1991004855A1/en not_active Application Discontinuation
- 1990-09-14 BR BR909007695A patent/BR9007695A/en not_active Application Discontinuation
- 1990-09-14 AU AU68991/91A patent/AU6899191A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JPH05507547A (en) | 1993-10-28 |
| EP0494269A1 (en) | 1992-07-15 |
| WO1991004855A1 (en) | 1991-04-18 |
| EP0494269A4 (en) | 1993-03-17 |
| AU6899191A (en) | 1991-04-28 |
| BR9007695A (en) | 1992-07-21 |
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