Ballistic-resistant moulded article and manufacturing method therefore

Abstract: The invention relates to a ballistic-resistant article containing a compressed stack of monolayers, with each monolayer containing unidirectionally oriented reinforcing fibres and a matrix consisting of a polymer, the fibre direction in each monolayer being rotated with respect to the fibre direction in an adjacent monolayer. The moulded article has both a high structural stiffness and dimensional stability and a high protection level and a low trauma effect because the monolayer has a fibre content of between 20 and 145 g/m 2 and a matrix content of at most 25 wt.%, the reinforcing fibres are aramid fibres and the matrix polymer has a modulus of elasticity of more than 200 MPa.

Description: The invention relates to a process for manufacturing a ballistic-resistant moulded article containing a compressed stack of monolayers, with each monolayer containing unidirectionally oriented reinforcing fibres and a matrix consisting of a polymer, the fibre direction in each monolayer being rotated with respect to the fibre direction in an adjacent monolayer, the reinforcing fibres being aramid fibres, and the matrix polymer having a modulus of elasticity of more than 200 MPa. Such a moulded article is called a UD-composite. EP 0 658 589 (which is a basis for the preamble of claim 1) discloses armour panels made by moulding a stack of fibre network layers wherein the fibres are unidirectionally aligned, successive layers of such unidirectionally aligned fibres can be rotated with respect to the previous layers, the fibres may be aramid fibres, the matrix has a modulus of more than 6900 MPa. The examples comprise fibre network layers of high strength polyethylene fibres, with 20 wt.% matrix content. A moulded article of this kind is described in US-A-4,623,574, in which the matrix consists of an elastomer. A disadvantage of this structure is that the structural stiffness and dimensional stability of these moulded articles are unacceptably low for many applications. US-A-4,623,574 also describes moulded articles with a high structural stiffness but these have an unacceptably low protection level and an unacceptably high backface deformation upon the impact of a projectile. On account of the high backface deformation their application for body protection is out of the question because of the risk of injury (trauma effect). The object of the invention is therefore to provide a process for manufacturing a ballistic-resistant moulded article which on the one hand has a high structural stiffness and dimensional stability and on the other hand offers a high protection level and a low trauma effect. This object is achieved according to the invention by manufacturing the monolayer by wetting the aramid fibres in the form of continuous multifilament yarns having a yarn titre of at least 1200 denier, with a solution of the matrix material having a viscosity of lower than 500 mPa.s. and the monolayer having a fibre content of between 20 and 145 g/m 2 , and the matrix content being at most 15 wt.%. A further advantage of the moulded article according to the invention is that the moulded article retains its good ballistic-resistant properties at high temperatures (for example above 90°C) and does not delaminate upon repeated exposure to high temperatures because it is dimensionally stable. Because of these properties the moulded article is very suitable for protecting non-living objects (off-the-body armour), for example as a structural member of military vehicles, helicopters and the like. The fibre content in the ballistic resistant moulded article according to the invention is preferably between 20 and 120 g/m 2 . More preferably, the fibre content in the monolayer is at most 100 g/m 2 and most preferably at most 75 g/m 2 . The advantage of a lower fibre content is that, in combination with the use of the specified matrix material, a lower matrix content may suffice to achieve sufficient fibre bonding as a result of which the advantages of the invention are even more pronounced. A fibre content of less than 20 g/m 2 is unattractive from an economic point of view. In view of obtaining even better anti-ballistic properties the matrix content of the ballistic resistant moulded article is preferably chosen as low as possible. The matrix content of the ballistic resistant moulded article according to the invention is at most 15 wt.% and more preferably at most 10 wt.%. The matrix in the moulded article consists of a polymer with a modulus of elasticity higher than 200 MPa. The modulus of elasticity of the matrix material is determined to ASTM D638. It has been found that very good results are obtained if the matrix polymer in the ballistic resistant moulded article contains a vinyl ester. The monolayer can be manufactured by known methods, for example as described in US-A-4.623.574. Preferably by pulling a number of fibres, preferably in the form of continuous multifilament yarns, from a fibre bobbin frame over a comb, causing them to be parallelly oriented in one plane. Preferably, before or after being parallelly oriented in one plane the fibres are coated with a quantity of a liquid substance which contains the matrix material or a precursor which at a later stage in the manufacture of the moulded article reacts to form the polymeric matrix material with the required modulus of elasticity. Precursor is here understood to be a monomer, an oligomer or a crosslinkable polymer. The liquid substance may be a solution, a dispersion or a melt. The moulded article is manufactured by stacking a number of monolayers crosswise in a known manner, preferably at an angle of about 90°, and forming the stack into a consolidated structure via an increase in temperature and/or pressure. The moulded article is preferably manufactured by compressing monolayers onto each other at a compressive pressure of at least 1 MPa, preferably at least 2.5 and most preferably at least 5 MPa at a temperature of more than 100°C and subsequently cooling without pressure. The great advantage of this method is a much shorter cycle time, leading to a substantial reduction in production costs. In the method for manufacturing a moulded article the monolayer is manufactured by wetting continuous multifilament yarns with a solution of the matrix material. The viscosity of the solution is lower than 500 mPa.s. The advantage of this is that it enables the required low matrix percentage in the moulded article according to the invention to be achieved more easily while a good fibre bond, which is required in view of the objective of the invention, is maintained. By using a solution, good wetting of the filaments in the yarns is achieved on account of the low viscosity, despite the small total amount of matrix material applied. The viscosity of the solution of the matrix material is measured with the aid of a Brookfield viscometer according to ASTM D2393-68. In addition, with a view to achieving the required low matrix percentage the yarn titre is at least 1,200 and most preferably at least 1,500 denier. The ballistic-resistant moulded article according to the invention obtainable according to the method described above preferably has an SEA of at least 25 Jm 2 /kg, more preferably at least 28, even more preferably at least 30 and most preferably at least 32 Jm 2 /kg. Backface deformation is preferably at most 20 mm, more preferably at most 15 mm. SEA and backface deformation are defined in the example. Example: A monolayer was manufactured using the method and apparatus described in WO 95/00318. As reinforcing fibres Twaron 2000® yarns with a titre of 1680 dtex were used. The yarns were parallelly oriented in one plane with a yarn weight of 50.4 g/m 2 . As matrix material a vinyl ester polymer based on Adlac 580/05® mixed with Dispercol KA 8584® in combination with Trigonox C® as curing agent was used. The modulus of elasticity of the matrix material was 3800 MPa. The matrix material was dissolved in styrene. The viscosity of the solution was 200 mPas. The solution was applied by passing the fibres through the solution. The amount of matrix material (after drying) was 9 wt.%. A flat moulded article (30x30 cm.) was made by compressing 160 monolayers of 55.5 g/m 2 at 120°C for 20 minutes at a pressure of 10 bar, after which the moulded article was cooled without pressure. The specific energy absorption (SEA) was determined according to the STANAG 2920 test, in which .22 calibre FSPs (Fragment Simulating Projectile), hereinafter referred to as fragments, with a weight of 1.1 g (to US MIL-P-46593), are fired at the ballistic structure in a defined manner. The energy absorption (EA) is calculated from the kinetic energy of a fragment having the V 50 velocity. The V 50 is the velocity at which the probability of bullets penetrating the ballistic structure is 50%. The specific energy absorption (SEA) is calculated by dividing the energy absorption EA by the areal density AD of the moulded article. The trauma effect is measured by placing the ballistic-resistant moulded article against a clay background and measuring the depth of the backface deformation upon impact. The V 50 was 707 m/s, the SEA was 31 Jm 2 /kg, backface deformation was 15 mm. The stiffness was high, which means that the moulded article proves to be suitable for use in structural mouldings.

Claims: Process for manufacturing a ballistic-resistant moulded article containing a compressed stack of monolayers, with each monolayer containing unidirectionally oriented reinforcing fibres and a matrix consisting of a polymer, the fibre direction in each monolayer being rotated with respect to the fibre direction in an adjacent monolayer, the reinforcing fibres being aramid fibres, the matrix polymer having a modulus of elasticity of more than 200 MPa, characterised in that the monolayer has been manufactured by wetting the aramid fibres in the form of continuous multifilament yarns having a yarn titre of at least 1200 denier, with a solution of the matrix material having a viscosity of lower than 500 mPa.s, and that the monolayer has a fibre content of between 20 and 145 g/m 2 , and that the matrix content is at most 15 wt.%. Process according to claim 1, characterised in that the moulded article is manufactured by compressing monolayers onto each other at a compressive pressure of at least 1 MPa at a temperature higher than 100°C and subsequently cooling without pressure. Process according to claim 1 or 2, characterised in that the fibre content in the monolayer is between 20 and 120 g/m 2 ; Process according to any one of the claims 1 - 3, characterised in that the matrix content is at most 10 wt.%. Process according to any one of the claims 1 -4, characterised in that the matrix material contains a vinyl ester polymer.

Inventors: VAN DE GOOT ERNST LORENZO, VAN DE GOOT, ERNST LORENZO
Applicants: DSM NV, DSM N.V.
Application year: 1996
Main classification: F41H5
IPC codes: F41H5