Ballistic-resistant curved molded article
The present invention provides a process for producing a ballistic-resistant curved molded article said process comprising pressing in a mold a stack comprising a plurality of layers of unidirectionally aligned polyolefin fibers substantially absent a bonding matrix and a plurality of layers of adhesive; characterized in that a means for dispersing pressure is employed against at least one surface of the stack. Also provided are a ballistic-resistant curved molded article and a press-pad having substantially the shape of a curved mold.
1. A process for producing a ballistic-resistant curved molded article, said process comprising the steps of:
(a) providing a mold defining a curved pressing surface;
(b) pressing in the mold a stack comprising:
a plurality of layers of unidirectionally aligned polyolefin fibers substantially absent a bonding matrix; and
a plurality of layers of adhesive disposed between adjacent layers of the unidirectionally aligned fibers, and
(c) positioning a pressure dispersing medium capable of assuming a curved shape corresponding to the curved pressing surface of the mold between the curved pressing surface of the mold and at least one surface of the stack, and
(d) applying pressure to the at least one surface of the stack and, during application of the pressure, employing the pressure dispersing medium positioned between the at least one surface of the stack and the curved pressing surface of the mold to disperse applied pressure against the at least one surface of the stack and thereby form the ballistic-resistant curved molded article.
2. The process according to claim 1 , wherein step (d) comprises employing the pressure dispersing medium to disperse against two surfaces of the stack.
3. The process according to claim 1 , wherein the pressure dispersing medium is a press-pad.
4. The process according to claim 1 , wherein the pressure dispersing medium is a fluid in any one of an autoclave, a hydroclave or a diaphragm molding machine.
5. The process according to claim 1 , wherein the ballistic-resistant curved molded article comprises at least one filler ply.
6. The process according to claim 1 , wherein the ballistic-resistant curved molded article is a helmet shell or a radome.
7. The process according to claim 1 , wherein the adhesive is present in the ballistic-resistant curved molded article in a total amount of less than 15.0 wt. %, based on the total weight of the molded article.
8. The process according to claim 1 , wherein each layer of unidirectionally aligned polyolefin fibers is oriented at an angle of from 45° to 135° with respect to the orientation of an adjacent layer of unidirectionally aligned polyolefin fibers.
9. The process according to claim 1 , wherein each layer of unidirectionally aligned polyolefin fibers is separated from an adjacent layer of unidirectionally aligned polyolefin fibers by a layer of adhesive.
10. A ballistic-resistant curved molded article obtained by the process according to claim 1 .
11. A ballistic-resistant curved molded article which comprises:
a plurality of layers of unidirectionally aligned polyolefin fibers, wherein the layers are substantially absent of a bonding matrix; and
a plurality of layers of adhesive disposed between adjacent layers of the unidirectionally aligned fibers, wherein
the ballistic-resistant curved molded article has an areal density of at most 11 Kgm −2 and meets NIJ level III+performance against 7.62×39 mm MSC (AK47).
12. The ballistic-resistant curved molded article according to claim 11 , which further comprises at least one filler ply.
13. The ballistic-resistant curved molded article according to claim 11 , which is a helmet shell or a radome.
14. The ballistic-resistant curved molded article according to claim 11 , wherein the adhesive is present in the ballistic-resistant curved molded article in a total amount of less than 15.0 wt. %, based on the total weight of the molded article.