US20080076312A1

US20080076312A1 - High performance fire resistant fabrics and the garments made therewith

Info

Publication number: US20080076312A1
Application number: US11/858,242
Authority: US
Inventors: George GEHRING
Original assignee: Gehring Textiles Inc
Current assignee: Gehring Textiles Inc
Priority date: 2006-09-25
Filing date: 2007-09-20
Publication date: 2008-03-27

Abstract

A fire retardant fabric for safety garments useful for dangerous activities, e.g. firemen, policemen, armed forces, etc., is knit from a first yarn system of fire retardant modacrylic fibers, a second yarn system of flexible fibers and, optionally a third yarn system of aramid fire retardant fibers. One of the yarn systems also includes fibers formed of a conductive material, such as silver.

Description

RELATED APPLICATIONS

This application claims priority to provisional application Ser. No. 60/847,002 filed Sep. 25, 2006 and incorporated herein by reference.
The subject application is also related to the following applications:

Knit Elastic Mesh Loop Pile Fabric for Orthopedic and other Devices

60/847,186 filed Sep. 26, 2006; U.S. patent application Ser. No. ______ filed ______,

Fabric for Protection against Electric Arc Hazards

60/847,305 filed Sep. 26, 2006; U.S. patent application Ser. No. ______ filed ______ and

Under Body Armor Cooling Vest and Fabric Thereof

60/847,307 filed Sep. 26, 2006; U.S. patent application Ser. No. ______ filed ______.

BACKGROUND OF THE INVENTION

a. Field of Invention
This invention pertains to a high performance fire resistant fabric and, more particularly, to a fabric for making fire resistant garments of various weights that includes modacrylic fibers comingled with conductive fabrics, and optionally, aramid fire resistant fibers.
b. Description of the Prior Art
High performance materials are frequently used to make safety clothing articles (such as undergarments) for personnel involved in hazardous industrial and military activities. These materials ideally provide thermal protection at high temperatures, experienced, for example, by exposure to fire from fuel, vapors or gas, as well as explosives or burning materials.
Preferably, high performance materials used for safety clothing should have other characteristics as well. For example, they should be comfortable to wear under various weather conditions, including hot or cold climates and under high humidity conditions.
Other desirable characteristics for such fabrics are related to aesthetic and hygienic factors. Clothing made of high performance fabrics may be worn for long time periods during which other clothing or washing facilities may not be available. Therefore, it is advantageous if they can provide significant reduction in the growth of bacteria, fungi, yeast, mold and other micro-organisms and thereby prevent infection and development of objectionable odors in the clothing.
Yet another desirable characteristic of such fabrics garments is efficient moisture management. That is, a high performance fabric should be able to remove perspiration effectively from the wearer's skin and evaporate it into the ambient air, especially under adverse weather conditions, as discussed above.
The types of fabrics currently used in the manufacture of garments for the military and hazardous services do not meet most of the above described requirements and suffer from a number of other drawbacks as well. This is particularly true of garments having a high polyester content. These fibers are very popular in garment manufacture due to their ready availability in diverse forms, low cost and ease of processing. However, polyester has several undesirable characteristics. One of these characteristics is that it has the propensity of melting and dripping when it is ignited by open flames, thereby potentially causing serious third burns to the wearer and/or others. Also, polyester has very low moisture absorptive and evaporative characteristics. Hence, a polyester garment quickly becomes saturated with perspiration, thereby rendering it uncomfortable to wear, and promoting the growth of mold and bacteria, as well as generating undesirable odors.
The standard warm weather Army issue undershirt (commonly designated as “Under armor” (not related to the ballistic body armor), is currently composed of 95% polyester and 5% Spandex®. The fabric of this undershirt has a moisture vapor transport index (MVT) of 1250 units. While this index value is generally acceptable, novel fabrics, including the fabric described, can achieve much better results.
Polyester fabrics currently used in the manufacture of fire retardant garments suffer from several disadvantages:
1). Polyester fabrics when exposed to high temperatures or fire will ignite and continue to burn while melting and dripping. Molten polyester inflicts severe burns to the skin.
2). Polyester fabrics manage moisture poorly, resulting in perspiration buildup against the wearer's skin, which produces a sensation of clamminess and discomfort.
3). Polyester fabrics designed for hazardous service applications are not sueded or napped, resulting in garments of thin volume and limited thermal insulation value.
4). Polyester fabrics currently used in the manufacture of the above mentioned garments lack the anti-microbial features to stop the development of “Jungle rot” and other micro-organism based infections as well as the development of objectionable odors.
5). Polyester fabrics now in use lack the anti-static fiber components to neutralize the potentially hazardous static electricity charges. Under dry atmospheric conditions, the friction generated by rubbing of the garment parts can create a high enough static voltage to produce a spark discharge with dangerous consequences.
6). Current polyester fabrics exhibit a relatively high shrinkage potential.

SUMMARY OF THE INVENTION

A fire resistant fabric for garments constructed in accordance with this invention includes a first system of yarns made of fire resistant fabric made of modacrylics or similar materials and a second system of yarns made of flexible fibers which render the fabric more supple and stretchable. Preferably the first set of yarns is mixed with some electrically-conductive yarns that discharge and dissipate any static electricity generated in the fabric and provide other advantageous characteristics. For example, electrically conductive yarns are typically also good at conducting heat, thereby equalizing the temperature across or through a garment. In one embodiment of the invention, the conductive fibers include fibers coated with silver.
For heavier garments suitable for cold weather, the fabric further includes a third yarn system formed of fire resistant fibers such as an aramid fiber. This type of fiber is important because it is an excellent fire retardant material. Preferably, the subject fabric is made by knitting the two or three sets of fibers together. Preferably, the resultant fabric does not have homogeneous structure, but rather, it has more of the aramid fibers located closer to its front face disposed at the outer surface of the garment and more of the modacrylic fibers located closer toward the backface. These characteristics insure that the aramid fibers protect the other components of the fabric. The modacrylic fibers not only provide fire protection, but also provide moisture management.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fireman wearing a garment constructed in accordance with this invention; and

FIG. 2 shows a fabric used for the garment.

DETAILED DESCRIPTION OF THE INVENTION

A high performance composite fabric having excellent fire resistant characteristics and constructed in accordance with the present invention includes, in one embodiment, a combination of at least two types of fire retardant spun fibers. To make the fabric more flexible and supple, a third set of yarns is provided which is made of flexible fibers. One of the fire retardant fibers is an aramid (short for aromatic polyamide) fiber. Aramid fibers are available from different manufacturers under different trade names, such as Nomex® and Kevlar® by DuPont, PBI by Celanese and FR rayon. The other fire retardant fiber is preferably a modacrylic yarn available from various companies under different trade names such as Kanecaron® by Kaneka Corporation, Creslan® by the American Cyanamid Corporation, Verel® by Kodak, Orion® by DuPont, Acrilan® by Monsanto, just to name of few.
Preferably, the modacrylic fibers are blended with electrically conductive fibers. One such fiber is known as X-Static (fiber produced by Noble Fiber Technologies, Inc. Such fibers are available from Bekaert. This fiber is a coated with a layer of silver preferably less than a micron in thickness. The fiber is advantageous because the layer of silver provides anti-static, germicidal and other beneficial properties, discussed in more detail below. The germicidal properties prevent the development of objectionable odors as well as the so-called “Jungle rot,” a sort of a fungus infection afflicting soldiers in humid environments, and also kill spores, molds, etc. The silver ions of the fiber's coating kill the microbes by binding sites on their surface. Other anti-static fibers of this kind are available under various trade names from other sources, such as Negastat® from DuPont, Resistat® from Shakespeare Conductive Fibers, LLC. Fine stainless steel or copper wires having a diameter of about 0.035 mm may also be used.
Moreover, a conductive fabric in accordance with the invention prevents the build up of static electricity, thereby preventing sparks that may ignite gasoline, or cause explosions, in an environment with gas or fuel vapors or which might possibly set off explosives in military environment.
Preferably the subject fabric further includes a flexible yarn that is inserted in order to impart the fabric with a four-way stretch, which enhances the wearing comfort, freedom of movement and shape retention of the garment. The flexible yarn may be Spandex® or other natural or synthetic elastic fiber.
The flexible component is placed well inside the fabric structure to protect it from the hazard of melting and dripping on exposure to high temperature or fire.
The fabric according to the present invention is knit using a circular weft knitting machine. However, it may also be made on warp knit or weaving equipment adapted for this purpose.
Thus, in one embodiment, the present fabric is knitted from three fibers or yarns: an aramid fiber, a modacrylic fiber and a flexible fiber. One of these fibers, preferably the modacrylic fiber, is blended with a small amount of conductive fibers. Other high performance, flame resistant yarns may also be used.
The yarns are furnished to the feeds of the circular knitting machine in a plaited relationship arranged so that the modacrylic component is placed on the technical back of the fabric (against the wearer's skin) and the aramid fiber is placed on the face of the fabric for optimum high temperature or fire protection.
The choice of aramid and modacrylic fibers in this application is based on their excellent fire retardant performance combined with non-melt, non-drip and self extinguishing properties. Garments made with fabrics featuring this fiber system are self extinguishing, a very important consideration in hazardous environments. If sufficiently high temperatures are reached on exposure to fire, the garment will just carbonize by forming a charred barrier. This prevents the spread of flames and protects the wearer from severe burn injuries.
Modacrylic fibers have a high LOI value compared with other fibers. (LOI represents the minimum oxygen concentration of an O₂/N₂mixture required to sustain combustion of a material). The LOI is determined by the standard test ASTM D 2863-77. A standard polyester fiber has an LOI value of 20-22, while a modacrylic fiber has an LOI value of about 33.
A very important aspect of the fire retardant fabric is its superior “moisture management’ factor. The fabric moves the perspiration away from the skin and makes it evaporate into the atmosphere so as to enhance the wearing comfort. While the aramid and modacrylic fibers are essentially hydrophobic, the capillary action of the fibrous mass of the fabric itself wicks the perspiration away from the wearer's skin and moves it to the outer face of the garment where it is free to evaporate. Preferably, the fabric is knitted to form a structure that is inherently highly porous, thereby inhancing the process of moisture evaporation.
The modacrylic fibers of the inside face of the fabric (against the skin) are preferably raised into a short pile either by sueding (e.g., by passing the fabric over an emery covered cylinder) or napping (e.g., by passing the fabric over wire covered rolls) or some other mechanism for raising a pile surface. Such a pile further enhances the moisture management performance of the fabric and contributes to the wearing comfort of the garment.
The fabric disclosed herein can be made in different weights depending on the intended use of the fabric or the resulting garment. For example, if the fabric is used for warm, tropical weather service, it is made with a weight of approximately 4.1 oz/sq. yd. For moderate temperature weather service, the fabric may be made to weigh approximately 6.7 oz/sq.yd. The heavier fabric is preferably bulked by napping it into a thicker pile to provide increased heat insulation, thereby protecting the wearer from hypothermia. The process of napping increases the volume of the fabric and facilitates a more rapid movement of the moisture through it.
In summary, the composite fabric disclosed herein has several advantageous characteristics:
1). The novel fabric has superior high temperature and fire resistance, while eliminating the danger of flammability, or melting and dripping of the fiber mass that can lead to serious burns.
2). The novel fabric has a very effective moisture management system, which significantly improves the wearing comfort. In fact, the novel fabric made for warm weather service as described above has an MVT index of 1780 vs. 1250 for currently used polyester content fabric.
3). The new fabric has a built in 4-way stretch and recovery performance to enhance the freedom of movement.
4). The novel fabric contains an anti-microbial component designed to prevent development of the “Jungle rot” and other infections as well as to suppress objectionable odors.
5). The novel fabric contains a conductive anti-static fiber designed to dissipate static electricity charges. This removes the hazard of sparking in an environment with gas, fuel fumes, or explosives.
6). The silver coated fibers in the garment produce a heat transfer effect equalizing the temperature throughout the garment and thus eliminating hot or cold spots. The garment also feels cooler in warm weather and warmer in cooler weather.
7). The silver coated fibers have a therapeutic effect with respect to skin injuries involving damage to the surface nerves that conduct body electrical charges. The silver coated fibers act as conductors for those charges and speed up the process of healing.
As discussed above, the resulting fabric is ideal for garments used by professionals involved in activities that take place in actual or potential high temperature environments, such as firemen, policemen, armed forces, etc. For example, FIG. 1 shows a garment 10 worn by a fireman from a fabric constructed in accordance with this invention.
The knitting technology involved in producing the novel fabrics is based on plaiting the yarns in a way as to position one yarn component on top of the other component. This results in one component being placed on one side of the fabric and the second component on the other side. FIG. 2 shows schematically a typical fabric that may be used to practice the present invention. Obviously many other fabrics may be used as well. In the drawing, only the modacrylic and the aramid yarns are shown for the sake of clarity since the spandex component is effectively inside the fabric structure and is essentially invisible.
Although the yarn systems described herein are very closely interconnected by the knitting process, the knitting process is selected so that the majority of the yarns in the top component are the yarns (e.g. the component on the outside of the garment) are made of the aramid fibers and the large majority of the yarns of the bottom component (on the inside of the garment, adjacent the skin) are the modacrylic yarns. As discussed above, the second component also includes the flexible and the conductive fibers as well.
In order to achieve the plaiting effect, the machine must be equipped with three yarn carriers, which have their feeding holes to accommodate each yarn separately. These carriers are positioned higher than they would be for conventional knitting, as is well known in the art.
Also, the flexible yarn is fed to the knitting point with the aid of a special feeding device to ensure a consistently perfect plaiting effect. In order to knit the fabric, the machine is fitted with plaiting needles having modified hooks designed to accommodate both yarns in their correct relative positions. These types of needle are available from Groz-Beckert, Mitchel-Gieve, Samsung and other well-known sources.
As mentioned before, the fabric can be constructed so that it has different weights for different climates.
In one aspect of the invention, a fabric is constructed having only two yarn systems: a set of modacrylic yarns blended with conductive yarns and a set of flexible yarns. For example, the lighter weight (4.1 pz/sq. yd.) fiber is constructed as follows:


Yarn system 30/1's c.c. modacrylic/X-static blend	95%
40 denier spandex ®	5%
Machine cut	36 needles/inch. Half
	gaited
Machine diameter	30 inch
Stitch	Jersey

In another aspect of the invention, a heavier fabric (e.g. 6.7 oz/sq.yd.) can be constructed as follows:


Yarn system	30/1's c.c. modacrylic/X-static blend	47%
	40/1's solution dyed arimid (Nomex)	45%
	70 denier spandex	8%

Machine cut	28 needles/inch
Machine diameter	26 inch

Stitch One feed—knit on two needles, welt on one needle

- Second feed—welt on 2 needles, knit on one needle

The above stitch produces horizontal floats on the face of the fabric. These are floats engaged by napper wires in the fabric finishing stage and can be raised into a pile effect.
The fabrics thus generated are dyed and finished using standard processes.
Obviously numerous modifications may be made to this invention without departing from its scope as defined in the appended claims.

Claims

1. A high performance fabric comprising:

a first yarn system consisting of a plurality of fire resistant modacrylic fibers blended with a plurality of conductive fibers; and

a second yarn system including a plurality of flexible fibers;

wherein said yarn systems are knit together to form said high performance fabric.

2. The fabric of claim 1 wherein said yarn system is selected and knit to yield a fabric having a weight in the range of 4-6 oz/sq. yd.

3. The fabric of claim 1 wherein said conductive fibers consist of an elongated filament with a metal coating.

4. The fabric of claim 3 wherein said metal coating is a silver or silver ion.

5. The fabric of claim 1 further comprising a third yarn system including aramid fibers.

6. The fabric of claim 1 wherein said flexible fibers are Spandex fibers.

7. The fabric of claim 1 wherein said first yarn system forms about 85-97% of said fabric.

8. The fabric of claim 1 wherein said second yarn system forms about 3-15% of said fabric.

9. A fire resistant fabric for a garment comprising:

a fabric knit from:

a first yarn system including a plurality of aramid fibers;

a second yarn system including a plurality of modacrylic fibers; and

a plurality of flexible fibers.

10. The fabric of claim 9 wherein said flexible fibers consist essentially of Spandex fibers.

11. The fabric of claim 9 wherein said flexible fibers are included in said second yarn system.

12. The fabric of claim 9 wherein said fabric is knit having an inside surface disposed adjacent to the skin of the wearer in the garment and an outside surface, and wherein a majority of said inside surface is formed of modacrylic fibers and a majority of said outside surface is formed of said aramid fibers.

13. The fabric of claim 9 further comprising conductive fibers.

14. The fabric of claim 13 wherein said conductive fibers are coated with a metallic material.

15. The fabric of claim 14 wherein said conductive fibers are coated with silver or a silver compound.

16. The fabric of claim 15 wherein said conductive fibers are included in said second yarn system.

17. A method of making a fire retardant fabric comprising:

providing a first yarn system made of fire retardant modacrylic fibers;

providing a second yarn system made of flexible, stretchable fibers;

wherein the fibers of at least one of said first and second yarn systems are blended with electrically conductive fibers; and

knitting said fabric from said first and second yarn systems.

18. The method of claim 17 further comprising providing a third yarn system formed of fire retardant aramid fibers, said fabric being knit from said first, second and third yarn systems.

19. The method of claim 18 wherein said fabric is knit with a face and a technical back, wherein said face has a large number of fibers of said third system and said technical back has a large number of fibers from said first system.

20. The method of claim 18 wherein said electrically conductive fibers include nylon fibers coated with one of a metal and a metallic compound.