A FLEXIBLE BALLISTIC RESISTANT ELASTOMER COATED FABRIC AND APPLICATIONS THEREOF

Abstract

A FLEXIBLE BALLISTIC RESISTANT ELASTOMER COATED FABRIC, METHOD OF SYNTHESIS AND APPLICATION THEREOF The present invention relates to flexible ballistic resistant elastomer coated fabric that is lightweight and durable and a method of synthesis thereof. Particularly, the present invention provides a flexible ballistic resistant elastomer coated fabric comprising of a polyurethane elastomer that is coated on a plain-woven fabric. The fabric is applicable in soft armor vests and helmets for bullet proof protection. Moreover, the flexible fabric is used in the manufacture of armor vests for protection against a wide range of ballistic weapons, a low-cost scale manufacturing, easy integration with hard armors, no involvement of any carrier fluids or solvents and no issues related to the chemical bonding of the coating medium.

Specification

Description:A FLEXIBLE BALLISTIC RESISTANT ELASTOMER COATED FABRIC AND APPLICATIONS THEREOF

FIELD OF INVENTION:

[1] The present disclosure is in the field of fabrics. More particularly, the present invention relates to a flexible ballistic resistant elastomer coated fabric and a method of synthesis thereof. The flexible ballistic resistant elastomer coated fabric is applicable in the area of bullet proof vests.

BACKGROUND OF INVENTION:

[2] Since ages, people have been protecting themselves from various injuries with different types of materials and technologies. Earlier, animal skin was used in order to protect body from sharp objects and weaponry. But as weaponry got advanced, many things like wood and metal shields were also implemented for defensive purposes. After continuous research and development, people came up with bullet resistant vests with additional features like waterproofing, durability and wearability.

[3] Bulletproof fabrics are typically made from high-strength fibers like Kevlar, Dyneema or Spectra. These materials are known for their durability and ability to absorb and disperse the energy from bullets. The fabric is usually woven into a tight, dense structure and is layered to increase its protective capabilities. Beyond personal body armor, bulletproof fabrics are often used in a variety of applications including vehicle armor, protective shields and some type of building materials.

[4] However, no fabric can guarantee complete protection against all types of ammunition or projectiles. The effectiveness of bulletproof fabric depends on factors like the type of ammunition and the velocity of the bullet. Conventionally, a significantly large number of (layers of fabric are layered together to make a basic soft armor vest for defence purpose. Although reasonably effective in offering resistance for bullet threats, they are usually found to be less flexible, heavy and bulky. Further, they are mostly suitable only for low range of impact velocities. Although many new ballistic armor materials have evolved, they still cause blunt trauma and other injuries to the users.
[5] Reference is made to US7687412B2, which discloses a flexible ballistic resistant composite material that has improved resistance to pick-up water and other liquids, where the composite material comprises of a plurality of non-woven fibrous layers. The fibrous layers are formed from a network of high tenacity fibers (aramid fibers, extended chain polyethylene fibers and/or rigid rod fibers). However, several layers of unidirectional fabrics stacked at different orientation were used for the construction of the ballistic product. The article only demonstrates improvement in V50 velocity, which means that there is still 50% chance for the bullet to penetrate through the fabrics.

[6] Reference is further made to WO2009048674A2, which discloses a ballistic resistant composite material useful in rigid armor applications. The composite material includes at least one consolidated network of high tenacity fibers in a thermoplastic matrix material in an aqueous medium. The resin is a thermoplastic polyurethane resin that is semi-crystalline at room temperature. Since an aqueous based polyurethane resin was used in this cited prior art, additional heating was used during the manufacturing for the removal of water. Moreover, application of heat and compaction was used for the manufacturing of the ballistic product that ultimately resulted in the ballistic product becoming a stiff composite panel and not a flexible structure.

[7] Reference is further made to R. Mia et al. in Improving ballistic performance of Kevlar fabrics by resin treatment: The Journal of The Textile Institute, 113(8), 1603-1626, which discusses about ways of increasing inter-yarn friction by using polyurethane resin for superior ballistic protection without affecting the weight. Here, 12% polyurethane (PU) as solute in dimethylformamide (DMF) solution was used to make resin to extemporize the inter yarn friction along with improvised ballistic structure in plain Kevlar fabric. The cited art demonstrates improvement in ballistic performance only in the laboratory environment and also shows that the bullets still penetrated through the fabrics.

[8] Reference is also made to X. Wang et al. in Materials and Design 196 (2020) 109015, which introduces polyurethane (PU) into the aramid fabric through impregnation directly or after mixing with shear thickening fluid (STF) and the pertinent performances of the as-prepared composites were carefully investigated. A method of preparation of STF/aramid fabric composite is also discussed. However, when the adhesion was too high (with different mass of polyurethane coating), the fabric broke instantaneously and resulted in lower ballistic performance.

[9] The abovementioned prior arts are related to composite material or fabric having several disadvantages such as low chemical bonding of the coating medium or its adhesiveness, low range of impact velocities, low flexibility, low ballistic performance, several layers of unidirectional fabric, additional heating step, low tensile strength of the fabric, heavy and bulky nature of the armour made out of the aramid fabric. Moreover, there are generally issues related to evaporation and/or leakage of the coating medium in the preparation of said fabric or material.

[10] In view of above, there exists a dire need in the state of art to provide a lightweight and flexible ballistic resistant elastomer coated fabric for soft armor material and bullet protection against a wide range of velocities and weaponry injuries and a method of synthesis for the same. Moreover, no additional pressure or temperature was applied during the manufacturing of the composite fabric, resulting in a highly flexible ballistic resistant coated fabric.

OBJECTS OF THE INVENTION:

[11] The principal object of the present invention is to provide a flexible ballistic resistant elastomer coated fabric that is lightweight and durable.

[12] Another object of the present invention is to provide a method for synthesising a flexible ballistic resistant elastomer coated fabric in a simple, easy and economical manner.

[13] Yet another object of the present invention is to provide a method including a simple coating technique without the requirement of carrier fluids and/or solvents, that is easily scaled up for large-scale manufacturing.

[14] Another object of the present invention is to provide a flexible ballistic resistant elastomer coated fabric by stacking multiple layers of the fabric together without any adhesion, compression and/or bonding of the fabric.
[15] Yet another object of the present invention is to provide a flexible ballistic resistant elastomer coated fabric that shows zero penetration with 0% chance of penetration of bullet against high impact velocity with less layers of fabric.

[16] Yet another object of the present invention is to provide a lightweight and flexible ballistic resistant elastomer coated fabric made of only 50 layers and weighing 2.8 kg with zero penetration of bullets against weapons like 9 mm pistols and MP5 machine guns.

SUMMARY OF THE INVENTION:

[17] In one aspect, the present invention provides a flexible ballistic resistant elastomer coated fabric, comprising: (a) a base material; and (b) a resin; wherein, multiple layers of said coated fabric are stacked together without any adhesion between the layers.

[18] In another aspect, the present invention provides a method for preparing a flexible ballistic resistant elastomer coated fabric as described herein, comprising of the following steps: (i) providing the base material of an appropriate size; (ii) mixing the resin and the hardener followed by degassing the same to obtain a coating mixture; coating the base material of step (i) on one side by the coating mixture of step (ii) by damping surface of the base material with the coating mixture then spreading the coating mixture with paint rollers followed by squeezing out excess resin out of the base material and curing the same; (iii) repeating the coating of the base material on the other side and curing the material to obtain resin coated fabric; and (iv) stacking multiple layers of the resin coated fabric of step (iii) together to form a flexible ballistic resistant elastomer coated material.

[19] Therefore, the present invention provides a flexible ballistic resistant elastomer coated fabric that is lightweight and durable and a method of synthesis for the same. The present invention also provides the flexible ballistic resistant elastomer coated fabric for protection against at least pistol and machine gun with zero penetration of bullets.

DESCRIPTION OF ACCOMPANYING FIGURES:
[20] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention, which are used to describe the principles of the present invention together with the description.

[21] Figure 1 illustrates an uncoated fabric in part (a); and elastomer coated fabric in part (b), in accordance with an implementation of the present invention.

[22] Figure 2 illustrates a pictorial representation of ballistic impact test set up in part (a); and boundary condition in part (b), in accordance with an implementation of the present invention.

[23] Figure 3 illustrates the status of bullet penetrations in uncoated and elastomer coated fabrics, in accordance with an implementation of the present invention.

DETAILED DESCRIPTION OF THE INVENTION:

[24] While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims.

[25] Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[26] The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[27] In the present invention, Flexon PUR70 polyurethane resin is termed as "resin" and/or "elastomer".

[28] In the present invention, Kevlar fabric is referred to as "Aramid fabric" and vice-versa.

[29] As discussed in the background section of the present invention, the existing methods reported in the literature relate to bulletproof composite or material. The reported prior arts focus on composite materials with significantly large number of layers, which are heavy in weight and thus reduce significant movement of the body while wearing armor made of the same material.

[30] Therefore, to overcome the existing problems in the art, the present invention provides a lightweight, durable and flexible ballistic resistant elastomer coated fabric and a method for synthesizing the same.

[31] Overall, the present invention is different and technically advance over the conventional prior art(s) in view of the following advantages:
a) Commercially available starting materials: The present invention utilizes a commercially available elastomer as a starting material for coating of the plain-woven fabric in a simple and economical manner.
b) Simple method of synthesising flexible ballistic resistant elastomer coated fabric: The present invention provides a method to synthesise a flexible ballistic resistant elastomer coated fabric by simply stacking together multiple layers of elastomer coated fabric without any adhesion between them. The layers were not compressed or bonded and simply formed into a single sample of several layers. This resulted in a flexible ballistic resistant elastomer coated fabric. The prepared fabrics were just stacked together, i.e., they were not compacted or glued together by applying heat and/or pressure. Such compaction would result in making the fabric a hard composite panel. Therefore, by avoiding such compaction, the fabric remained flexible in the present invention.
c) Enhanced ballistic performance of the synthesized fabric: The present invention provides a flexible ballistic resistant elastomer coated fabric that significantly deforms without breaking and thereby increases ballistic energy absorption. When tested at lab scale using a ~9 mm bullet, ballistic resistance was found up to as high as 650 m/s with just 12 layers of fabric. It is to be noted here that the fabrics demonstrate zero penetration with 0% chance of bullet penetration in these experiments, depicting that the fabrics completely stopped the bullets and did not allow the bullet to penetrate through the fabrics.
d) Lightweight and flexible ballistic resistant elastomer coated fabric: The present invention provides a lightweight and flexible ballistic resistant elastomer coated fabric made of only 50 layers and weighing only 2.8 kg with proven capability against weapons like 9 mm pistol and MP5 machine gun.
e) Easy coating technique: The present invention provides a simple coating method without the involvement of any carrier fluid or solvent, leading to no issues related to evaporation and/or leakage of the coating medium.

[32] In an embodiment, the present invention provides a flexible ballistic resistant elastomer coated fabric, comprising: (a) a base material; and (b) a resin; wherein, multiple layers of said coated fabric are stacked together without any adhesion between the layers.

[33] In another embodiment, the present invention provides a fabric as described herein, wherein said multiple layers are in a range of 3 to 50 layers.

[34] In another embodiment, the present invention provides a fabric as described herein, wherein said base material comprises of a plain-woven fabric.

[35] In another embodiment, the present invention provides a fabric as described herein, wherein said plain-woven fabric is an aramid fabric.

[36] In another embodiment, the present invention provides a fabric as described herein, wherein said resin is a flexible polyurethane elastomer, Flexon PUR70 that is coated on said base material.

[37] In another embodiment, the present invention provides a fabric as described herein, wherein said fabric is used in bullet proof vests.

[38] In another embodiment, the present invention provides a fabric as described herein, wherein said fabric withstands impact velocity in a range of 55 to 180 m/s with 3 layers of fabric and 350 to 650 m/s with 12 layers of fabric without any penetration of bullet. Moreover, the fabric exhibits zero penetration with 0% chance of bullet penetration through the fabrics.

[39] In another embodiment, the present invention provides a fabric as described herein, wherein said fabric is made of only 50 layers of fabrics while weighing 2.8 kg with zero penetration of bullets against 9 mm pistol and MP5 machine gun.

[40] In another embodiment, the present invention provides a method for preparing a flexible ballistic resistant elastomer coated fabric as described herein, comprising: (i) providing the base material of an appropriate size; (ii) mixing the resin and the hardener followed by degassing the same to obtain a coating mixture; coating the base material of step (i) on one side by the coating mixture of step (ii) by damping surface of the base material with the coating mixture then spreading the coating mixture with paint rollers followed by squeezing out excess resin out of the base material and curing the same; (iii) repeating the coating of the base material on the other side and curing the material to obtain resin coated fabric; and (iv) stacking multiple layers of the resin coated fabric of step (iii) together to form a flexible ballistic resistant elastomer coated material.

[41] In another embodiment, the present invention provides a method as described herein, wherein said coating in step (iii) is performed manually by hand.

[42] In another embodiment, the present invention provides a method as described herein, wherein said coating is carried out using multiple automated fiber and/or resin dispensers together with compaction rollers for large-scale manufacturing.

[43] In another embodiment, the present invention provides a method as described herein, wherein said coating is carried out using a customized 3D printing machine for large-scale manufacturing.

[44] In another embodiment, the present invention provides a method as described herein, wherein said curing in step (iii) is carried out for a time period in a range of 4-8 hours at room temperature.
[45] In another embodiment, the present invention provides a method as described herein, wherein said method does not involve any carrier fluids or solvents.

[46] In another embodiment, the present invention provides a method as described herein, wherein said fabric is prepared without any compression and/or bonding between multiple layers of the same and formed into a single sample of multiple layers.

[47] The present invention is illustrated hereunder in greater detail in relation to non-limiting exemplary embodiments as per the following examples:

EXAMPLES

[48] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and the description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all and only experiments performed. The methodology of preparing few of the preferred embodiments shall become clearer with working examples provided below.

CHEMICALS AND INSTRUMENTS USED:

[49] Aramid fabrics (commercially called as Kevlar fabrics) were used as the base fabric (bare uncoated fabric). The areal weight of the bare fabric was 230 GSM with ~17 yarns/inch. Commercially available Flexon PUR70 polyurethane elastomer was used as the coating material. This particular grade of elastomer is highly flexible with elongation (tensile strain) as high as ~300%. Flexon PUR70 polyurethane resin (i.e., Part A of Flexon PUR70) and hardener (i.e., Part B of Flexon PUR70) obtained from Chemzest, Chennai were used for the coating.

Example 1: Method of synthesis of a flexible ballistic resistant elastomer coated fabric

[50] The aramid fabric is coated with a commercially available flexible elastomer by a simple method, used to significantly improve the bullet impact resistance of aramid fabrics. The commercially available flexible polyurethane elastomer used was Flexon PUR70 for the coating of the aramid fabrics. A simple method of coating the elastomer by hand was used here.

[51] Firstly, bare aramid fabrics were cut to the required sizes of 150 mm x 150 mm. The areal weight of the uncoated fabric was 230 GSM (grams per sq. meter). The fabrics were coated on one side and the resin was allowed to cure for 6 hours at room temperature. The resin and hardener were mixed in the ratio of 120:100, degassed and then coated with hand. Resin is Part A of Flexon PUR70 and Hardener is Part B of Flexon PUR70 (both are liquid polyurethane elastomers). Resin is called Flexon PUR70 Part A and hardener is called Flexon PUR70 Part B. Resin and hardeners were supplied by the supplier in separate containers, but they were added and mixed together in a single container. While coating, just around 25 grams of resin (plus hardener mixture) was chosen to damp the entire surface of the fabric. The resin (plus hardener mixture) was spread over the surface using paint rollers and the excess resin (plus hardener mixture) was squeezed out of the fabric. Only one layer of coating was carried out to damp the fabrics. Then, the fabrics were turned upside down and coated with the elastomer by hand. The above-mentioned coating process was repeated. Again, the fabrics were allowed to cure for 6 hours at room temperature. After curing, the weight of the coated fabrics was measured. It was found to be consistent between fabric to fabric and it was measured as 530 GSM (grams per sq. meter). Thus, the weight of the resin (plus hardener mixture) was found to be as ~ 300 GSM (grams per sq. meter). Then, multiple layers of resin coated fabrics were stacked together and tested further for protection against bullet impacts. Here, the fabrics were simply stacked together without any adhesion between them. They were not compressed or bonded but formed into a single sample of several layers.

Example 2: Ballistic performance

[52] The properties of Flexon PUR70 polyurethane elastomer are as shown in Table 1.

Table 1: Properties of Flexon PUR70 polyurethane elastomer
Property Value
Tensile strength ~1.8 MPa
Tensile strain ~300%
Modulus at 100% elongation ~0.90 MPa
Modulus at 150% elongation ~1.5 MPa
Ultimate strength at 300% break elongation ~ 1.8 MPa
Resin: Hardener ratio 120:100
Viscosity 1500-2000 cps
Working time 15-20 min
Cure time 6 hrs

[53] The elastomer coated fabric is made from commercially available Kevlar/Aramid fabric and flexible polyurethane (Flexon PUR70 elastomer). However, due to the said combination of aramid fabric and flexible polyurethane, i.e., Flexon PUR70 elastomer, significantly improved ballistic performance is observed and a lightweight, flexible elastomer coated aramid fabric armour material with high-performance is manufactured. Moreover, the very low modulus (high flexibility) of the PUR70 synergistically combined with the high energy absorption capacity of aramid fabric to result in the development of soft armour material with significantly high efficacy. The improved results are attributed to the very low modulus (highly flexible) of Flexon PUR70 elastomer. The modulus is very low, i.e., 0.9 MPa at 100% elongation.

[54] For the preparation of armour, a material that would further enhance the flexibility of the Kevlar fabric so as to absorb more impact energy (at the same time without compromising the strength of the Kevlar) was required. The objective was to create a strong and flexible armour material that would absorb more impact energy. First, a low modulus (flexible) thermoplastic Nylon film was used along with Kevlar fabric. At the same time, Flexon PUR70 was found to have an unusually low modulus (high flexibility). Hence, Flexon PUR70 was used along with Kevlar fabric to realize the synergistic effect of low modulus (high flexibility of PUR70) and high strength (of Kevlar fabric).

[55] The selection of material and product configuration was done by performing systematic laboratory experiments. First, the experiments were conducted on a single layer of fabrics coated with a commercial thermoplastic nylon film (that is normally used for vacuum bagging) and then with Flexon PUR70 elastomer. The boundary condition during the testing was such that the fabric was firmly fixed on all four sides of the fabric. Compared to the bare fabric (without any coating) as well as nylon coated fabric, the Flexon PUR70 coated fabric was found to have significantly high ballistic energy absorption. The test details and test results are as shown in Table 2.

Table 2: Summary of results with single layer of fabric



[56] The areal weight of the fabric before the coating was 230 GSM and after coating, the areal weight of the elastomer coated fabric was found to be 530 GSM. Although the fabrics remained highly flexible even after the coating, the areal weight of the fabrics increased by ~130% after the coating. However, this increment in the areal weight was found to be insignificant considering the tremendous improvement in the bullet impact resistance of the coated fabrics. Figure 1 shows the pictorial representation of uncoated (bare) fabric in part (a) and elastomer coated fabrics in part (b). Multiple layers of elastomer coated fabric were stacked together and tested for protection against bullet impacts. The fabrics here were just stacked together without any adhesion between them. They were not compressed or bonded but simply formed into a single sample of several layers.

[57] Then, further tests with multiple layer fabrics and a different boundary condition (fixed only at the four corners) were conducted only on the Flexon PUR70 coated fabrics. However, an uncommon boundary condition, i.e., fixing the fabric only at four corners, was used so as to simulate a test environment close to that of real field environment (where no boundary conditions are used when testing a fabric material). In real field testing, fabrics are just strapped onto the target without any rigid boundary conditions). Bullet or ballistic impact tests were conducted using the set-up as shown in part (a) of Figure 2. Bare and elastomer coated aramid fabrics of size 150 mm x 150 mm were used for testing. The boundary condition was such that the fabrics were fixed only in the corners as shown in part (b) of Figure 2. A steel projectile with spherical nose, diameter of 9 mm and mass ~ 11 grams was used for testing. A high-speed camera was used to record the impact phenomenon and record the impact velocities. Three (3) layers of bare aramid fabrics were stacked together and then clamped as per the boundary condition. Then, the impact tests were carried out at different velocities starting from ~50 m/s. Complete penetration of bullet occurred at ~55 m/s in all the bare fabrics (3 layers of bare fabrics stacked together). Similarly, three (3) layers of elastomer coated aramid fabrics were stacked together and then clamped as per the boundary condition. Then, the impact tests were carried out at different velocities starting from ~50 m/s. On the other hand, no penetration occurred until ~180 m/s in the elastomer coated fabrics (3 layers of elastomer coated fabrics stacked together). The penetration eventually occurred at ~190 m/s in the elastomer coated fabrics. This showed significant improvement in the ballistic energy absorption of elastomer coated aramid fabrics. Table 3 shows the summary of tests conducted with three number of layers and Figure 3 shows the status of penetration of bullet under different tests.

[58] As shown in Figure 3, the laboratory experiments showed that the elastomer coated fabrics underwent significant backside deformation and absorbed significant amount of bullet impact energy by kinetic deformation of the fabrics. The coating allowed the fabrics to undergo significant backside deformation without breaking and thereby resulting in increased ballistic energy absorption. Further experiments at high impact velocities and real field environment were carried out to evaluate the armour fabrics. The real field testing using the real weapons demonstrated the excellent capability of the products.

Table 3: Summary of test results with three number of layers
Sample # of layers Impact velocity (m/s) Result
Uncoated 3 ~55 Complete penetration
Elastomer coated 3 ~55 No penetration
Elastomer coated 3 ~75 No penetration
Elastomer coated 3 ~100 No penetration
Elastomer coated 3 ~125 No penetration
Elastomer coated 3 ~150 No penetration
Elastomer coated 3 ~180 No penetration
Elastomer coated 3 ~195 Complete penetration

[59] The elastomer coated fabrics underwent significant backside deformation until impact velocity of ~180 m/s and absorbed significant amount of impact energy by kinetic deformation of the fabrics. This backside deformation of the fabrics was possible only due to the coating of highly flexible Flexon PUR70 elastomer on the fabrics. Thus, the flexible elastomer coated fabrics were able to withstand higher impact velocity until ~180 m/s. However, at ~195 m/s, the bullet had gained enough impact energy to pierce through the 3 layers of coated fabrics and thus the penetration occurred. Performing ballistic tests with more layers stacked together yielded still better results.

[60] Ballistic tests with a greater number of layers were also carried out. This time, an even better bullet with improved geometry for penetration was used for testing. A steel projectile with conical nose, diameter 9 mm and mass ~ 11 grams was used for testing. The range of velocities was chosen in the laboratory tests corresponding to the velocities under which pistols operate. To test at high velocities (corresponding to machine guns (~700 m/s) and rifles (~1000 m/s), real filed tests at National Security Guard (NSG) campus were carried out. No high-speed camera was available during the testing and hence the impact phenomena were not captured. Twelve (12) layers of bare aramid fabrics were stacked together and then clamped as per the boundary condition in Figure 2. Then, the impact tests were carried out at different velocities starting from velocity ~350 m/s. It was observed that the complete penetration of bullet occurred at this velocity in all the bare fabrics (12 layers of bare fabrics stacked together). Similarly, twelve (12) layers of elastomer coated aramid fabrics were stacked together and then clamped as per the boundary condition shown in Figure 2. Then, the impact tests were carried out at different velocities starting from ~350 m/s. No penetration occurred until ~650 m/s in the elastomer coated fabrics, i.e., 12 layers of elastomer coated fabrics stacked together. This showed significant improvement in the ballistic energy absorption of elastomer coated aramid fabrics. Table 4 shows the summary of tests conducted with twelve number of layers. No high-speed camera was available during the testing and hence the backside deformation of the fabrics was not captured. However, as observed in the previous tests with 3 number of layers (as shown in Table 3), the improvement in the performance of elastomer coated fabrics was attributed to the impact energy absorption by kinetic deformation of the fabrics. This backside deformation of the fabrics was possible only due to the coating of highly flexible Flexon PUR70 elastomer on the fabrics. Thus, the elastomer coated fabrics were able to withstand higher impact velocity and offered superior bullet impact resistance. The results showed promising ways to develop light-weight and low-cost armor vests with superior bullet impact resistance.

Table 4: Summary of test results with twelve number of layers
Sample # of layers Impact velocity (m/s) Result
Uncoated 12 ~350 Complete penetration
Elastomer coated 12 ~380 No penetration
Elastomer coated 12 ~565 No penetration
Elastomer coated 12 ~575 No penetration
Elastomer coated 12 ~650 No penetration

[61] Real field testing of the ballistic product was performed in the National Security Guard (NSG) facility in Chennai. Only 50 layers of coated fabric (of size 300 mm x 300 mm) were used to test against ballistic resistance. The weight of the ballistic product was 2.8 kg. The details of the tests are mentioned in the Table 5 below.

Table 5: Summary of real field test results
Type of weapon Number of shots and Firing range Result
9 mm pistol 3 shots and 10 meters All the bullets ricocheted back (bounced back) and they could not penetrate inside the ballistic product.
MP5 machine gun 5 shots and 15 meters All the bullets could not completely penetrate the product. All the bullets penetrated only to few layers - only 25-30 layers of fabric only got damaged. All the bullets were stuck inside the fabric layers and all the bullets were deformed and damaged under the impact.
INSAS 5.56 mm Rifle One shot and 50 meters The bullet completely penetrated 50 layers of fabric.

[62] The ballistic product performed excellently well against pistol and MP5 machine gun type of ballistic threats. It failed against one of the highest kinds of threat - INSAS 5.56 Rifle. However, only 50 layers of coated fabric with a weight of only ~2.8 kg was used in the field testing from a close firing range of 50 meters.

[63] Therefore, using a greater number of layers as it is (exact number of layers must be arrived at after the real field testing) or together with a lightweight hard armor (metal or ceramic plate) provides ballistic resistance against a Rifle threat. The achieved results were significant reduction of the current body armor weight in the market.

[64] The present invention directly measured the performance of the ballistic fabric directly in the real field environment (which is relatively more reliable).
 
ADVANTAGES OF PRESENT INVENTION:

[65] The present invention provides a flexible ballistic resistant elastomer coated fabric and a method of synthesis thereof.

[66] The advantages of the method of the present invention are:
1. The present invention provides an economically friendly flexible ballistic resistant elastomer coated fabric utilizing a polyurethane elastomer (Flexon PUR70) with very high elongation (~300%) for coating.
2. The present invention provides a flexible ballistic resistant elastomer coated fabric that utilizes Flexon PUR70, a polyurethane elastomer. When the fabric is tested for bullet proof applications, the fabric was able to withstand impact velocity until ~180 m/s for 3 layers and ~~650 m/s for 12 layers. The improvement in the performance of elastomer coated fabrics was attributed to the impact energy absorption by kinetic deformation of the fabrics, which was possible only due to the coating of highly flexible Flexon PUR70 elastomer on the fabric.
3. The present invention provides a flexible ballistic resistant elastomer coated fabric that utilizes a plain-woven fabric as a base material. Compared to non-woven fabric, plain-woven fabric has the advantage of high stability in its architecture. It also has the advantage of high inter-yarn friction because of more yarn-yarn interlacements. These advantages provide the fabric better ballistic resistance compared to that of non-woven (unidirectional) fabric.
4. The present invention provides significant improvement in ballistic performance by the synthesized flexible ballistic resistant elastomer coated fabric. When tested at lab scale using ~9 mm bullet, ballistic resistant up to as high as 650 m/s with just 12 layers of fabric. In these experiments, the fabrics demonstrated zero penetration of the bullets, that is the bullets had 0% chance of penetration through the fabrics. With additional number of layers, the elastomer coated fabric has a potential to protect against further higher range of velocities.
5. The present invention provides a lightweight and flexible ballistic resistant product made of only 50 layers and weight 2.8 kg with zero penetration of bullets fired from real weapons like 9 mm pistol and MP5 machine gun.
6. The present invention provides a simple coating technique for the synthesis of flexible ballistic resistant elastomer coated fabric that is capable of easily being scaled up for large-scale manufacturing. The large-scale synthesis is automated without involvement of manual hand. For instance, multiple number of automated fiber and resin (plus hardener) dispensers together with compaction rollers are used for large-scale manufacturing. Alternatively, a customised 3D printing machine is used for the deposition and coating of elastomers on the fabric.
7. The present invention provides a flexible ballistic resistant elastomer coated fabric that is applicable in bullet proof vests and flexible armor material. , Claims:We claim:
1. A flexible ballistic resistant elastomer coated fabric, comprising:
a) a base material; and
b) a resin;
wherein,
multiple layers of said coated fabric are stacked together without any adhesion between the layers.

2. The fabric as claimed in claim 1, wherein said multiple layers are in a range of 3 to 50 layers.

3. The fabric as claimed in claim 1, wherein said base material comprises of plain-woven fabric.

4. The fabric as claimed in claims 1 and 3, wherein said plain-woven fabric is an aramid fabric.

5. The fabric as claimed in claim 1, wherein said resin is a flexible polyurethane elastomer, Flexon PUR70 that is coated on said base material.

6. The fabric as claimed in claim 1, as and when used in bullet proof vests.

7. The fabric as claimed in claim 1, wherein said fabric withstands impact velocity in a range of 55 to 180 m/s with 3 layers and 360 to 650 m/s with 12 layers of fabric with zero penetration.

8. The fabric as claimed in claim 1, wherein said fabric is made with 50 layers of fabric while weighing 2.8 kg with zero penetration of bullets against 9 mm pistol and MP5 machine gun.

9. A method for preparing a flexible ballistic resistant elastomer coated fabric as claimed in claim 1, comprising:
i) providing the base material of an appropriate size;
iii) mixing the resin and the hardener followed by degassing the same to obtain a coating mixture; coating the base material of step (i) on one side by the coating mixture of step (ii) by damping surface of the base material with the coating mixture then spreading the coating mixture with paint rollers followed by squeezing out excess resin out of the base material and curing the same;
iv) repeating the coating of the base material on the other side and curing the material to obtain resin coated fabric; and
v) stacking multiple layers of the resin coated fabric of step (iii) together to form a flexible ballistic resistant elastomer coated material.

10. The method as claimed in claim 9, wherein said coating in step (iii) is performed manually by hand.

11. The method as claimed in claim 9, wherein said coating is carried out using multiple automated fiber and/or resin dispensers together with compaction rollers for large-scale manufacturing.

12. The method as claimed in claim 9, wherein said coating is carried out using a customized 3D printing machine for large-scale manufacturing.

13. The method as claimed in claim 9, wherein said curing in step (iii) is carried out for a time period in a range of 4-8 hours at room temperature.

14. The method as claimed in claim 9, wherein said method does not involve any carrier fluids or solvents.

15. The method as claimed in claim 9, wherein said fabric is prepared without any compression and/or bonding between multiple layers of the same and formed into a single sample of multiple layers.

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