WO1993000564A1

WO1993000564A1 - p-ARAMID BALLISTIC YARN AND STRUCTURE

Info

Publication number: WO1993000564A1
Application number: PCT/US1992/005018
Authority: WO
Inventors: Minshon J. Chiou; Hung Han Yang
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1991-06-26
Filing date: 1992-06-18
Publication date: 1993-01-07
Also published as: IL102244A0; AU2221892A; CN1072225A; MX9203355A

Abstract

A laminated ballistic structure is disclosed using fabrics made from p-aramid yarn with high tenacity and elongation to break and a consequent improved ballistic performance. The ballistic structure is laminated and comprises a plurality of fabric layers made from said p-aramid yarn exhibiting an elongation to break of greater than 4.0 % a modulus of less than 600 g/d, and a tenacity of greater than 23 g/d.

Description

Title p-Aramid Ballistic Yarn and Structure Background of the Invention Field of the Invention This invention relates to ballistic structures made using fabrics woven from p-aramid yarns having high tenacity and high elongation to break. Description of the Prior Art

United States Patent No. 4,850,050 issued July 25, 1989 on the application of Droste et al., discloses body armor made from p-aramid yarns comprising filaments of low individual linear density. The ballistic performance of body armor made in accordance with that invention was reported to represent a 5% improvement over the comparison fabric of the prior art.

United States Patent No. 4,859,393 issued August 22, 1989 on the application of Yang and Chiou, discloses a process for making p-aramid yarns said to have a high elongation at break. United States Patents No. 3,869,429 and

4,560,743, issued March 4, 1975 and December 24, 1985, respectively, each disclose para-aramid fibers of high quality. There is no disclosure of any specially recognized utility for fabrics from these fibers in ballistic protection.

Summary of the Invention The present invention provides a p-aramid ballistic structure which utilizes yarns having a combination of especially high tenacity and elongation to break. The ballistic structure is laminated and comprises a plurality of fabric layers made from that p-aramid yarn exhibiting an elongation to break of greater than 4.0%, a modulus of less than 600 gpd, and a tenacity of greater than 23 gpd. Detailed Description of the Invention

Protective garments and other ballistic materials have long been made using p-aramid fibers. P- aramid fibers are extremely strong on a weight basis and provide good ballistic protection with a relatively high There has been great effort expended in developing yarns and fabrics with improved ballistic performance because even small improvements save the lives of users of ballistic garments. Each improvement is hard- won and highly significant. The present invention represents an improvement in ballistic performance, measured by V5_0/ of about 5%.

Poly(p-phenylene terephthalamide) fibers made by the usual processes, such as by processes described in United States Patent No. 3,869,429, exhibit yarn tenacities of greater than about 21 grams per denier, moduli of 400 to 700 grams per denier, and elongations to break of about 2.8 to 4.1%.

While strength is important to ballistic performance, strength is not the only factor which need be considered. It has now been found that the ballistic performance of fibers having a tenacity of greater than about 20 grams per denier will not be significantly improved by increase in tenacity, alone. By the same token, modulus is not now seen as an important factor in ballistic performance. Fibers with moduli greater than about 500 grams per denier will not be significantly improved in ballistic performance by increase in modulus.

Of all of the tensile properties usually tested, it has been found that the combination of tenacity and elongation to break is one of the most important parameters for ballistic performance. Yarn toughness, that is, the ability to absorb energy, is significantly affected by the combination of tenacity and elongation to break, of the fiber. While p-aramid fibers exhibit remarkable ballistic performance even at a moderate tenacity of 23 grams per denier and low elongation to break of 3.0%, the ballistic performance is rather dramatically improved with any increase in toughness. Ballistic structures of this invention are made with yarns which are woven into fabrics; and the fabrics are formed into garments or other structures for ballistics protection. The kind of fabric or weave to which the yarn is applied is not important to realize the benefit of the invention. That is, for any fabric or weave pattern, ballistic performance obtained using the yarn of this invention will be improved over that obtained using a similar yarn having a lower toughness due to lower tenacity or lower elongation to break.

Body armor using ballistic fabrics is usually made with several layers of fabric laid or sewn together to yield a laminated structure. The laminated structure can include additional layers of other materials such as decorative or moisture resistant covering fabrics or other shock absorbing materials. The form of the laminated structure and whether or not it includes additional layers of other materials is not important to realization of the improved ballistic performance of this invention. It has been discovered that the effectiveness of any ballistic structure will be improved by utilization of yarn having relatively higher tenacity and/or elongation to break instead of similar yarn having relatively lower tenacity and/or elongation to break. Test Methods

Ballistic Limit

Ballistic tests of the composite samples are conducted in accordance with MIL-STD-662e as follows: A lay-up to be tested is placed in a sample mount to hold the lay-up taut and perpendicular to the path of test projectiles. The projectiles are 17-grain fragment simulating projectiles (MIL-P-46593) , except where indicated otherwise, and are propelled from a test barrel capable of firing the projectiles at different velocities. The first firing for each lay-up is for a projectile velocity estimated to be the likely ballistic limit (V₅₀) •

When the first firing yields a complete lay-up penetration, the next firing is for a projectile velocity of about 50 feet per second less in order to obtain a partial penetration of the lay-up. On the other hand, when the first firing yields no penetration or partial penetration, the next firing is for a velocity of about 50 feet per second more in order to obtain a complete penetration. After obtaining one partial and one complete projectile penetration, subsequent velocity increases or decreases of about 50 feet per second are used until enough firings are made to determine the ballistic limit (V5₀) for that lay-up. The ballistic limit (V₅₀) is calculated by finding the arithmetic mean of an equal number of five of the highest partial penetration impact velocities and five of the lowest complete penetration impact velocities, provided that there is not more than 125 feet per second between the highest and lowest individual impact velocities. Tensile Properties

Tenacity is reported as breaking stress divided by linear density. Modulus is reported as the slope of the initial stress/strain curve converted to the same units as tenacity. Elongation is the percent increase in length at break. Both tenacity and modulus are first computed in g/denier units which, when multiplied by 0.8826, yield dN/tex units. Each reported measurement is the average of 10 breaks.

Tensile properties for yarns are measured at 24°C and 55% relative humidity after conditioning under the test conditions for a minimum of 14 hours. Before testing, each yarn is twisted to a 1.1 twist multiplier (for example, nominal 1500 denier yarn is twisted about 2.1 turns/inch) . Each twisted specimen has a test length of 25.4 cm and is elongated 50% per minute (based on the original unstretched length) using a typical recording stress/strain device. The twist multiplier (TM) of a yarn is defined as:

(tpi) (Denier)V2 (tpc) (dtex) 2

TM = =

73 30.3 Wherein tpi = turns per inch and tpc = turns per centimeter Tensile properties for yarns are different from and lower than tensile properties for individual filaments and such values for yarns cannot successfully and accurately be estimated from filament values.

Description of the Preferred Embodiments EXAMPLE 1 Poly(p-phenylene terephthalamide) (PPD-T) fibers having high tenacity and high elongation were spun as described in United States Patent No. 4,340,559, using Tray G thereof. The PPD-T had an inherent viscosity of 6.3 dL/g. To make the spinning dope, the PPD-T was dissolved in 100.1% sulfuric acid to a concentration of

19.4 weight percent. The dope was deaerated under vacuum and spun through a spinneret having 672 capillaries of 2.5 mil (0.0635mm) diameter. Spinning was at a dope temperature of about 71°C directly through an air gap.0.64 cm in length and then into a spin tube together with coagulating liquid which was an aqueous solution of 8% by weight sulfuric acid maintained at 20°C. The spin stretch factor was 6.3. The coagulated yarn was forwarded to a water-washing stage, to a neutralization stage, to a drying stage on a pair of internally steam-heated rolls with surface temperature of 150°C, and then to windup on bobbins at a moisture content of about 12 weight percent. Yarn tension during washing/neutralization was 0.2 to 0.4 grams per denier (gpd) and during drying was 0.05 to 0.2 gpd. The resulting yarn was 1000 denier (1111 dtex) and 1.5 denier per filament (dpf) (1.67 dtex per filament). The yarn exhibited an elongation to break of 4.3%, a modulus of 450 gpd, and a tenacity of 24 gpd.

Test fabrics were made using the yarn of this example and control test fabrics were made using commercially-available aramid yarn sold by E. I du Pont de Nemours & Co. under the trademark designation Kevlar® 29. The control yarn exhibited an elongation to break of 3.4%, a modulus of 605 gpd, and a tenacity of 23 gpd. The control yarn was, also, 1000 denier and 1.5 denier per filament. The fabrics were plain weave with a basis weight of about 244 g/m² (7.1 oz/yd²) and a construction of about 29 x 26 (W x F/inch) . Finish was removed from each of the fabrics by washing in water with detergent and rinsing in water. Thirteen layers of each of the fabrics were laid together and tested in accordance with MIL-STD-662e using the 22 caliber, 17-grain fragment simulating projectile specified in MIL-P-46593. The ballistic test result, shown in Table 1, below, was that the V5₀ for the structure of this invention was 6.4% greater than the V₅₀ of the control.

For reasons not fully understood, the benefits of this invention are realized with non-deforming projectiles; but do not appear to extend to deformable lead bullets. Tests performed on fifteen layers of the above-described fabrics using 9 mm, full-metal jacketed lead, 124-grain NATO projectiles, yielded V₅₀ of about 418 m/s with no significant difference between the fabrics. EXAMPLE 2

For this example, PPD-T yarn was spun by the same process as was used in Example 1, above, except that the spinneret had 1000 capillaries of 2.5 mil (0.0635 mm) diameter to produce a yarn of 1500 denier (1667 dtex) and 1.5 dpf. This yarn exhibited an elongation to break of 4.8%, a modulus of 365 gpd, and a tenacity of 23.3 gpd.

Fabrics, again, were made using the yarn of this example and control test fabrics were made using commercially-available aramid yarn sold by E. I du Pont de Nemours & Co. under the trademark designation Kevlar® 29. The control yarn exhibited an elongation to break of 3.6%, a modulus of 560 gpd, and a tenacity of 23 gpd. The control yarn was, also, 1500 denier and 1.5 denier per filament. The fabrics were plain weave with a basis weight of about 325 g/m² (9.6oz/yd²) and a construction of about 24 x 24 (W x F/inch) . Finish was removed from each of the fabrics by washing in water with detergent and rinsing in water.

Ten layers of each of the fabrics were laid together and tested in accordance with MIL-STD-662e using the 22 caliber, 17-grain fragments imulating projectile specified in MIL-P-46593. The ballistics test result, shown in Table 2, below, was that the V5₀ for the structure of this invention was 4.1% greater than the V50 of the control.

Tests performed on twelve layers of the above-described fabrics using 9 mm, full-metal jacketed lead, 124-grain NATO projectiles, yielded V50 of 395 m/s with no significant difference between the fabrics. EXAMPLE 3

Poly(p-phenylene terephthalamide) (PPD-T) fibers having high tenacity and high elongation were spun as described in United States Patent Application Serial No. 07/673,552, filed March 8, 1991. The PPD-T had an inherent viscosity of 6.3 dL/g. To make the spinning dope, the PPD-T was dissolved in 100.1% sulfuric acid to a concentration of 19.4 weight percent. The dope was deaerated under vacuum and spun through a multiple-orifice spinneret having capillaries of 2.0 mil (0.051mm) diameter. Spinning was at a dope temperature of about 71°C directly through an air gap 0.64 cm in length and then into a spin tube together with coagulating liquid which was an aqueous solution of 8% by weight sulfuric acid maintained at 2°C. The spin stretch factor was 4.14. The coagulated yarn was forwarded to a water-washing stage, to a neutralization stage, to a drying stage on a pair of internally steam-heated rolls with surface temperature of 125°C, and then to windup on bobbins at a moisture content of about 12 weight percent. Yarn tension during washing/neutraliza ion was 0.2 to 0.3 grams per denier (gpd) and during drying was 0.2 to 0.3 gpd. The resulting yarn was 1500 denier (1667 dtex) and 1.5 denier per filament (dpf) (1.67 dtex per filament). It exhibited an elongation to break of 4.2%, a modulus of 510 gpd, and a tenacity of 26.2 gpd.

Test fabrics were made using the yarn of this example and control test fabrics were made using commercially-available aramid yarn sold by E. I du Pont de Nemours & Co. under the trademark designation Kevlar® 29. The control yarn exhibited an elongation to break of 3.4%, a modulus of 605 gpd, and a tenacity of 23 gpd. The control yarn was, also, 1500 denier and 1.5 denier per filament. Two fabrics were woven: one was a plain weave with a basis weight of about 339 g/m² (10.0 oz/yd²) and a construction of about 24 x 24 (W x F/inch) ; and the other was a 2x2 basket weave with a basis weight of about 474 g/m² (14.0 oz/yd²) and a construction of about 36 x 35.

Finish was removed from each of the fabrics by washing in water with detergent and rinsing in water.

Twelve layers of each of the basket weave and 17 layers of each of the plain weave fabrics were laid together and tested in accordance with MIL-STD-662e using the 22 caliber, 17-grain fragment simulating projectile specified in MIL-P-46593. The ballistic test result, shown in Table 3, below, was that the V5₀ for the structure of this invention was 7.4% greater than the V₅₀ of the control for the basket weave fabric construction and 3.0% greater than the V5₀ of the control for the plain weave fabric construction.

TABLE 3

V₅₀ (m/s) Basket Weave Plain Weave This This Test Control Invention Control Invention

A 532 . 2 558 . 4 559 . 0

B 507.2 555.7 560.5 567.8

C 520.6 562.4 555.0 581.3 Average 520.0 558.7 558.0 574.6

Improvement — +7.4% — +3.0%

In a second experiment, using the same yarn as was previously used in this example, a second test fabric was woven having a 2X2 basket weave with a basis weight of about 494 g/m² (14.6 oz/yd²) and a construction of 35X35. The ballistic test was conducted in the same way and the V5₀ for this test was found to be 539.6 m/s compared with 501.5 m/s for the control fabaric. The ballistic structure of this invention, thus, yielded a V₅₀ which was 7.6% greater than that of the control.

EXAMPLE 4

Using the same yarn as was used in Example

2, a test fabric was woven the same as that used in Example 3. The ballistic test resulted in V5₀, for the test fabric, of 548.2 m/s and V5_0/ for the control fabric, of 520.0 — an improvement of 5.4%.

Claims

1. A laminated ballistic structure comprising a plurality of fabric layers made from p-aramid yarns exhibiting an elongation to break of greater than 4.0%, a modulus of less than 600 gpd, and a tenacity of greater than 23 gpd.

2. The laminated ballistic structure of Claim 1 wherein there are additional layers of other materials included in the structure.

3. The laminated ballistic structure of

Claim 1 wherein the p-aramid is poly(p-phenylene terephthalamide) .