Stock material or miscellaneous articles – Structurally defined web or sheet – Including grain – strips – or filamentary elements in...
Reexamination Certificate
1998-12-23
2001-05-29
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including grain, strips, or filamentary elements in...
C428S221000, C428S156000, C428S170000, C428S171000, C428S172000, C428S295100
Reexamination Certificate
active
06238768
ABSTRACT:
The invention relates to an antiballistic shaped part comprising a stack of composite layers which are not linked to one another, each composite layer comprising two or more monolayers of unidirectionally oriented fibres in a matrix, the fibres in each monolayer being at an angle to the fibres in an adjoining monolayer. The invention also relates to a method for fabricating said shaped part and body armour in which the shaped part is used.
Such a shaped part is disclosed by WO 89/01125, which describes composite packets which are largely not linked to one another and contain high-performance polyethylene fibres and at least 10% by weight of polymeric matrix material.
The drawback of the shaped part from the prior art is that the ratio between energy absorption of the shaped part, which is a measure for the ballistic protection level, and the weight of the shaped part is unfavourable. This implies that a relatively heavy shaped part is required to achieve a certain required protection level. If the shaped part, on the other hand, does have a low weight, the shaped part provides a relatively low protection level against ballistic hits. For a large number of applications the lowest possible weight of the shaped part in conjunction with a certain required protection level is of great importance. This is the case, for example, in the field of personal protection, such as, for example, in clothing. Similarly, for applications in, for example, vehicles, the lowest possible weight for a certain required protection level is important.
The object of the invention is to provide an antiballistic shaped part which offers a higher protection level at a certain weight than the known shaped part.
This object is achieved according to the invention by the fibres being aramid fibres or poly(p-phenylenebenzobisoxazole) fibres, the composite layer containing at most 10% by weight of an elastomeric matrix material, each of the composite layers having a total weight of at most 800 g/m
2
, and the fibre content in each monolayer being between 10 and 200 g/m
2
.
A further advantage of the shaped part according to the invention is that, in addition to having a favourable ratio between the protection level and the areal density, the shaped part is flexible, the scope for applications of the shaped part in antiballistic articles being increased as a result. This makes the shaped part particularly suitable for applications where high flexibility is desirable, such as in body armour.
Antiballistic shaped parts are shaped parts which can be used in articles, for example protective clothing and armouring of vehicles, which offer protection against ballistic impacts such as by bullets and shrapnels.
The antiballistic shaped part according to the invention contains a stack of composite layers which are not linked to one another. A stack of composite layers which are not linked to one another cannot, however, be further processed as such, because it lacks any coherence required for further processing. To achieve this coherence the shaped part can, for example, be stitched through. As little of this is done as possible, however, for example only at the corners. Another possibility is to enclose the composite layers in a flexible cover. Thus the composite layers in the shaped part remain able to shift with respect to one another, whereas the shaped part in itself does have coherence.
A composite layer is a layer composed of two or more monolayers, each monolayer being at an angle to the adjoining, underlying monolayer, and the separate monolayers being linked to one another. The angle, which means the smallest angle enclosed by the fibres of the adjoining monolayers, is between 0° and 90°. Preferably, the angle is between 45° and 90°. Most preferably, the angle is between 80° and 90°. Shaped parts in which the fibres in the adjoining monolayers are at such an angle to one another have better antiballistic characteristics. The term monolayer refers to a layer of unidirectionally oriented fibres embedded in a matrix. The term fibre comprises not only a monofilament but, inter alia, also a multifilament yarn or flat tapes. The term unidirectionally oriented fibres refers to fibres which, in one plane, are essentially oriented in parallel.
The term matrix refers to a material which binds the fibres together and encloses the fibres in their entirety or in part. In addition to the elastomeric material the matrix may, if desired, contain the usual fillers for polymers or other substances. The matrix is homogeneously distributed over the entire surface of the monolayer.
It was found, surprisingly, that it is precisely as a result of the combination of aramid fibres or poly(p-phenylenebenzobisoxazole) fibres and a very low content of elastomeric matrix material, that a very high energy absorption in the event of a hit by a projectile, very high flexibility and good coherence of the composite layer in the antiballistic shaped part according to the invention are obtained. With a view to obtaining even higher energy absorption, the content of elastomeric matrix material in the composite layer is chosen to be as low as possible. Preferably, the elastomeric matrix material content of the composite layer in the antiballistic shaped part according to the invention is at most 7% by weight and more preferably at most 5% by weight. A certain minimum content (at least 1-2% by weight) of elastomeric matrix material must, however, be used to ensure that adequate fibre bonding is present in the composite layer, in order to provide the composite layer with adequate coherence.
Preferably, the elastomeric matrix material in the shaped part comprises a thermoplastic elastomer having a modulus in tension (determined in accordance with ASTM D638, at 25° C.) of less than 40 MPa. This makes the matrix material sufficiently elastic for the desired flexibility in the fibre-fibre bond in the monolayers and in the composite layers to be obtained. It was found that very good results are obtained if the elastomeric matrix material in the shaped part is a styrene-isoprene-sytrene block copolymer.
In a special embodiment of the invention, the matrix in the shaped part according to the invention also contains, in addition to the elastomeric matrix material, a filler in an amount of from 5 to 80% by volume, calculated on the basis of the total volume of the elastomeric matrix material and the filler. More preferably, the amount of filler is from 10 to 80% by volume and most preferably from 20 to 80% by volume. It was found that as a result, the flexibility of the shaped part increases without significant adverse effects on the antiballistic characteristics.
The fillers do not contribute to the bonding between the fibres, but serve for volumetric dilution of the matrix between the fibres, as a result of which the shaped part is more flexible and has a higher energy absorption. The filler preferably comprises a finely dispersed substance having a low weight or density. The filler may be a gas, although using a gas as a filler presents practical problems in processing the matrix material. The filler may also, inter alia, comprise the substances customary for preparing dispersions, such as emulsifiers, stabilizers, binders or a finely dispersed powder.
It was found that if the matrix contains an amount of filler below 80% by volume, the amount of elastomeric matrix material is sufficient to achieve adequate bonding between the fibres, with a constant total quantity of matrix material. It was also found that if the matrix contains a quantity of filler greater than 5% by volume, the flexibility of the shaped part increases.
Preferably, a separating layer is disposed on one or on both sides of the composite layer. The separating layer used may, for example, comprise Stamylex®, a linear low-density polyethylene.
This embodiment has the advantage that the flexibility of the shaped part is higher, and is preferable, in particular, if a tacky matrix material is used. A separating layer is a layer of a particular material which is placed between the composite laye
Dixon Merrick
DSM N.V.
Pillsbury Madison & Sutro LLP
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