EP2471986A1

EP2471986A1 - A multiple-use nonwoven fabric structure

Info

Publication number: EP2471986A1
Application number: EP10197394A
Authority: EP
Inventors: Stuart Smith; André Lang; Marc Jolly; Jos Van Hattum
Original assignee: Norafin Industries (Germany) GmbH
Current assignee: Norafin Industries (Germany) GmbH
Priority date: 2010-12-30
Filing date: 2010-12-30
Publication date: 2012-07-04

Abstract

The present invention relates to a method for manufacturing a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace. The method comprises the steps of providing a web of inherently fire-resistant fibers, bonding the fibers of the web by means of needle-punching to form a nonwoven fabric layer, and bonding the nonwoven fabric layer by means of spunlacing to form the non-woven fabric structure.

Description

Field of the Invention

The present invention relates to a method for manufacturing a multiple-use nonwoven fabric structure for arc flash protection, a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace.

Background Art

An electrical arc flash is defined as a condition where electric current passes through ionized gases in the air. It is caused by an electrical fault and results in a dangerous release of intense energy into the space surrounding the electrical equipment.
This energy is released as a combination of:

Extreme heat - temperatures can reach approximately 19,000 degrees Celsius (35,000 degrees Fahrenheit) in less than a second. This thermal release can ignite flammable clothing or textiles and cause 1st, 2nd, or 3rd degree burns to humans.
Intense light can lead to temporary or permanent loss of vision for humans watching the arc flash.
Acoustic and Pressure shock waves can rupture eardrums, collapse lungs, or result in severe impact injuries for humans.
Debris - an arc flash can propel molten metal and debris at high velocities.

Flame retardant clothing is worn as part of the personal protective equipment (PPE) systems used to protect workers who could potentially be exposed to arc flash situations. Many countries have established government standards which specify the level of performance required with respect to the clothing to be worn. In the USA, the guidelines for arc flash safety in the workplace are specified in NFPA 70E - Standard for Electrical Safety in the Workplace. This standard specifies two methods to determine performance arc flash performance; ASTM F1506 - Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, and ASTM F1959 - Standard Test Method for Determining the Arc Rating of Materials for Clothing.
Using ASTM F1959, the arc flash performance of the material is expressed as an Arc Thermal Performance Value (ATPV). Dependent on the ATPV, NFPA 70E defines four different categories of protection, or Hazard Rating Categories (HRC).

ATPV [Cal/cm²] Hazard Rating Category

4 - 8 1

8 - 25 2

25 - 40 3

>40 4
In Europe, one of the primary methods used to determine arc performance is EN 61482-1-2 - Live Working - Protective Clothing Against the Thermal Hazards of an Electric Arc. This method uses two different test currents, 4kA and 7kA, to generate an arc. The current level is chosen according to the class of protection required for the practical usage conditions defined by the customer, tests performed using a 7kA current being more demanding. If the combination of time taken and maximum temperature rise fall below the allowed temperature rise to avoid 2^nd degree burning as defined using STOLL curves, then the material is either rated as Class 1 using a 4kA test current, or Class 2 using a 7kA test current.
For protecting humans against arc flash occurrences, currently available fully durable, re-usable, or multi-launderable PPE apparel are typically made from traditional textiles such as woven and knitted materials. There are many different types of fully durable woven and knitted materials available in the market, however, they fall into two distinct categories.

1. Fabrics manufactured using inherently flame retardant fibers. Within this category, materials are further differentiated by the type of fabric construction, weight, and types of fibers used.
2. Fabrics manufactured using non flame retardant fibers that are chemically treated after formation to provide flame retardancy. Materials within this category are differentiated by the fabric construction, weight, and chemical type(s) used to provide flame retardancy.

The major disadvantage of current woven materials is that the arc flash performance is heavily dependent on the weight of the material. As an example related to the US standards, typically, the most light-weight single layer woven materials available that meet the HRC 2 requirement are approximately 237 g/m², and even at this weight, the ATPV is only between approximately 8.4 and 8.7 Cal/cm² (minimum ATPV for HRC 2 is ≥ 8 Cal/cm²). As an example related to the European standard EN 61482-1-2, current materials which meet the requirement of Class 2 have either a minimum basis weight of approximately 400 g/m², or use multiple layers of lighter weight materials to achieve the level of protection.
To obtain any improvement in ATPV, the weight of the material must be further increased. However, as the weight of the material is increased, other important performance attributes of the material such as its breathability and permeability and comfort are negatively impacted.

Summary of the Invention

An object of the present invention is to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide a method for manufacturing a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace.
Additionally, it is an object of the present invention to provide a multiple-use nonwoven fabric structure, which meets or exceeds all the additional requirements or performance standards for these applications, such as flame retardancy, strength, wash durability, etc.
The above objects, together with numerous other objects, advantages, and features which will become evident from the below description, are accomplished by a solution in accordance with the present invention, by a method for manufacturing a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace, the method comprising the steps of:

providing a web of inherently fire-resistant fibers,
bonding the fibers of the web by means of needle-punching to form a nonwoven fabric layer, and
bonding the nonwoven fabric layer by means of spun-lacing to form the non-woven fabric structure.

Hereby a fast and flexible manufacturing method is obtained, which exceeds the flexibility of the traditional textile processing, the complicated number of steps involved, and extended development time.
The fire-resistant fibres may be thoroughly opened and blended to ensure a uniform distribution and blend of the fire-resistant fibers before they are formated into the web.
The web is formated by preparing a uniform web of fire-resistant fibers, where the fire-resistant fibers within the web are individualised, uniformly blended, and have a uniform weight and density throughout the web. Hereby, the orientation of the fibers within the web significantly influences the strength and durability of the final fabric structure. While the parallel-laid web yields excellent blend uniformity and weight/density distribution, the strength properties of the web are not well suited to e.g. apparel applications - it has significantly higher strengths in its length or machine direction, compared to its width or cross machine direction. In apparel applications, it is desirable to have approximately equal strengths in both machine and cross machine directions, both with regard to subsequent processing and the performance of the finished garment.
In one embodiment, the web may be folded back and forth upon itself to form a web in which the fire-resistant fibers are more equally oriented in both a length direction and a width direction of the web, yielding approximately equal strengths in both directions. In order to achieve the desired attributes of blend uniformity, excellent weight and density distribution, and approximately equal strengths in both machine and cross machine directions, the web is cross-laid. Due to the build-up and folding action of multiple web layers, the cross laying system allows for the manufacture of significantly heavier basis weight materials than would be possible if a parallel-laid web was used. Additionally, the width of the material that can be produced is independent of the width of the web formation system.
Moreover, the web may be drafted, or combed, through a series of toothed rollers consisting of multiple sets of 3 roller trios, running at increasing speeds between each trio. Hereby, fiber uniformity and basis weight distribution are further improved. Additionally, this effect removes any folds or lapping marks for the previous process, i.e. the cross-laying step.
Additionally, the needle-punching may be performed by penetrating the web with an array of barbed needles that carry tufts of the web's own fire-resistant fibres in a vertical direction through the web. As the needles move through the web, their barbs hook the fibres and interlock them with adjoining fibres.
Further, the needle-punching may be performed in two stages, a first pre-needling stage consisting of single-sided needle penetration to initially consolidate the web from web drafting, and subsequently a second needling stage which fully consolidates the web by penetration with needles from both the top and bottom surfaces of the web. The needle penetration and number of needle penetrations play a major role in determining the strength and durability of the final fabric structure.
Also, the first pre-needling stage may have a punch density greater than 150 punches/cm², and the second needling stage may have a punch density greater than 300 punches/cm². By punch density is meant number of needle penetrations per unit area.
Furthermore, the nonwoven fabric layer subsequent to the needle-punching may be wound into rolls of a predetermined length.
The rolled nonwoven fabric layer may be arranged on a tension-controlled unwind station before the spunlacing step.
Moreover, additional bonding to form the nonwoven fabric structure may be achieved by spunlacing.
The nonwoven fabric layer, i.e. after the needle-punching step, is then mechanically bonded together using the spunlacing/hydro-entanglement process. The spunlacing process consists of passing the nonwoven fabric layer beneath a series of high pressure, small diameter water jets. As the water jets impinge on the fibres within the nonwoven fabric layer, the individual fibres are moved and interlocked. Mechanical bonding by hydro-entanglement yields fabric structures which are very clean with an appearance that can be modified to be similar to woven materials. It has a minimal effect on the bonded fabric structure, and the fabric structures are therefore soft, drapable, and more comfortable to wear. Also, hydro-entanglement does not damage the fibres within the nonwoven layer during bonding, allowing improved strength, abrasion, and durability performance to be achieved.
Hydro-entanglement may be performed by means of a pressure in the range of 20 MPa (200 bars) to 150 MPa (1500 bars). Tests have shown that the pressure level is related to the energy intake of the fabric, and furthermore that the strength of the fabric increases with the pressure increase to a certain limit.
In addition, the nonwoven fabric structure, after the hydro-entanglement step, may be placed in a series of vacuum boxes, before being dried in a through-air oven in order to remove excess water and moist from the fabric structure.
The nonwoven fabric structure may be chemically after treated, such as coloured, printed, dyed or applied with performance-enhancing chemicals, or a combination thereof.
The present invention further relates to a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace, said multiple-use nonwoven fabric structure comprising a nonwoven layer which comprises fire-resistant fibers, the fire-resistant fibers first being bonded by needle-punching and subsequently by spunlacing.
In one embodiment, the inherent fibers may be, but are not limited to, FR Viscose, meta-aramid, para-aramid, melamine, Polybenzimidazole (PBI), Silex, Basalt, or a combination thereof.
Also, the fibers may have a linear density between 0.5 and 5 dtex and a staple fiber length between 10 and 100 mm. With fibers in this linear density range, the number of fibers per unit area in the nonwoven part of fabric structure can be optimised to yield a more dense structure contributing to the improved ATPV performance exhibited. Likewise, the appearance and coverage of the nonwoven fabric structure are improved. Fibers with staple lengths between 10 and 100 mm allow optimum bonding to be achieved during mechanical bonding, positively impacting many fabric characteristics such as strength, wash durability, abrasion resistance, etc.
Further, the fabric structure may comprise one or more additional layers, the one or more additional layers being introduced into the fabric structure before the spunlacing bonding.
Moreover, the one or more additional layers may be a dry-laid carded web, a nonwoven layer, a woven layer, a knitted layer, a net/mesh, or a combination thereof.
The fabric structure may be dyed and/or printed.
Additionally, the fabric may have a basis weight of 40 to 1000 g/m².
The present invention also relates to a garment made of a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2.
Moreover, the present invention relates to the use of an arc flash protection, multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace for garments, blankets, flash fire PPE, molten metal splash PPE, fire fighters PPE, apparel, awnings, curtains, floor covers, work wear, and military uses.

Brief Description of the Drawings

The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings which for the purpose of illustration show some non-limiting embodiments and in which

Fig. 1 shows schematically the process steps for manufacturing a nonwoven fabric structure,
Fig. 2 shows a more detailed schematic diagram of the manufacture of a needle-punched nonwoven fabric layer,
Fig. 3 shows a more detailed schematic diagram of the manufacture of a spun-laced nonwoven fabric structure, and
Fig. 4 shows a more detailed schematic diagram of the manufacture of a final material or final garment.

All the figures are highly schematic and not necessarily to scale, and they show only parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.

Detailed description of the invention

In the following, some different possible embodiments of the fabric structure are explained to allow a greater understanding of the invention.
Initially, the types, blends, and dimensions of the fire resistant fibers to be used to construct the nonwoven layer of the fabric structure must be determined, the primary criteria for selection being the method used to impart flame retardancy to the fabric structure, which is a prerequisite for, e.g., an arc flash protective fabric, and the reaction of the fibers to high temperatures - while a fiber may be flame retardant, it may still melt in the presence of heat and cause burns to the wearer of the material.
The nonwoven fabric structure comprises inherently flame retardant fibers which do not need a chemical aftertreatment to impart flame retardancy. Many types are available, including FR Viscose, meta-aramid, para-aramid, melamine, Polybenzimidazole (PBI), Silex, Basalt, or a combination thereof.
Irrespective of the fiber type, the preferred dimensions of the different fiber types are a linear density between 0.5 and 5 dtex and a staple fiber length between 10 and 100 mm.
Fig. 1 shows a schematic diagram of a method for manufacturing a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace comprising three steps 1, 2, 3.
The first step is to provide a web of inherently fire resistant fibers. This is done by a web formation process 1 where a dry, parallel-laid, web formation system is used to prepare a uniform sheet of fibers, or web, where the fibers within the web are individualized, uniformly blended, and have a uniform weight and density throughout the web. The orientation of the fibers within the web may significantly influence the strength and durability properties of the final material. While the parallel-laid web yields excellent blend uniformity and weight/density distribution, the strength properties of the web are not well suited to apparel applications, since they have significantly higher strengths in the length, or machine direction, compared to the width, or cross machine direction. In apparel applications, it is desirable to have approximately equal strengths in both machine and cross machine directions, both for ease of subsequent processing and in the performance of the finished garment. To achieve desired attributes of blend uniformity, excellent weight and density distribution, and approximately equal strengths in both machine and cross machine directions, the carded web may be cross-layed.
The second step is to bond the fibers of the web by a needle-punching process 2 to form a nonwoven fabric layer, which is obtained by needling (needle-punching). The needle-punching process 2 may consist of mechanically binding a web to form a fabric layer by penetrating the web with an array of barbed needles that carry tufts of the web's own fibers in a vertical direction through the web. As the needles move through the web, their barbs can hook the fibers and interlock them with adjoining fibers. There are many variations in needle design, barb placement, barb angle, and barb shape which may be tailored to achieve the intended final fabric performance. The needle-punching process 2 may be performed in two stages; a pre-needling stage consisting of single-sided needle penetration to initially consolidate the web from web drafting, and then a secondary needling stage which fully consolidates the web by penetration with needles from both the top and bottom surfaces. The primary process settings are punch density (number of needle penetrations per unit area) and needle penetration and both settings play a major role in determining the strength and durability characteristics of the final fabric structure. In a needle-punching process 2, the pre-needling punch density may be greater than 150 punches/cm² whereas the main needling punch density may be greater than 300 punches/cm².
The third step is to bond the nonwoven fabric layer by a spunlacing process 3 to form the nonwoven fabric structure. The spunlacing process 3 bonds the fabric layer mechanically together using the spun-lacing process 3. The basic principle of the spun-lacing process 3 consists of passing the fabric layer beneath a series of high pressure, small diameter water jets. As the water jets impinge on the fibers within the fabric layer, the individual fibers are moved and interlocked. The spun-lacing process 3 is again an entangling step which is performed to entangle the fibers further. The spun-lacing process 3 may be performed by using a water pressure in the range of 20 MPa (200 bars) to 150 MPa (1500 bars). The strength of the fabric structure can be increased to a certain limit by increasing the water pressure, since the water pressure level is related to the energy intake of the fabric structure, which again is related to the strength of the fabric structure.
Fig. 2 shows a more detailed schematic diagram of the manufacture of a needle-punched fabric layer. After selecting the fibers, the fibers are thoroughly opened and blended in a fiber opening/blending process 4 using conventional staple fiber preparation equipment to assure a uniform distribution and blend of the selected fiber types in such a form which is suitable for subsequent feeding to a web formation system 1. Up to four individual fiber types may be intimately blended.
The next step is to provide a web of inherently fire resistant fibers. This is done by a web formation process 1 as described in the description of Fig. 1. Multiple types of web formation systems exist. However, the principle of the different systems is essentially the same - to prepare a uniform sheet of the fibers, or web, where the said fibers within the web are individualized, uniformly blended, and have a uniform weight and density throughout the web.
The main differences between the types of web formation systems are the way in which the individual fibers within the web are oriented. Parallel systems yield web structures where the fibers are essentially running predominantly in the same direction.
The next step is to cross-lay the parallel systems from the preceding step in a cross-laying process 5. Cross-laid systems take a web produced on a parallel system and then fold it back on forth upon itself to form a web in which the fibers are more equally oriented in both the length and width directions. Random web forming systems yield webs that orient the fiber not only in the length and width directions, but also vertically through the web.
The orientation of the fibers within the web significantly influences the strength properties of the final material. Parallel-laid webs have significantly higher strengths in the length, or machine direction, compared to the width, or cross direction. Cross-laid webs, as used in the preferred embodiment, have approximately equal strengths in the machine and cross machine directions. Due to the build-up and folding action of multiple carded web layers, the cross laying system allows for the manufacture of significantly heavier basis weight materials than would be possible if a carded parallel-laid web was used. Additionally, the width of the material that can be produced is independent of the width of the carding system.
For apparel applications, it is desirable to have approximately equal strengths in both machine and cross machine directions, both for ease of subsequent processing and in the performance of the finished garment. Enhanced appearance and coverage provide for instance a more aesthetically pleasing garment.
The next step helps to further improve fiber uniformity and basis weight distribution. To obtain this the cross-laid web is drafted, or combed, by a web drafting process 6 through a series of toothed rollers consisting of multiple sets of three roller trios, running at increasing speeds between each trio. Additionally, this effect removes any folds or lapping marks for the previous process.
When the web has been drafted, the web is further processed by the needle-punching process 2 which is also described in the description of Fig. 1. The needle-punching process 2 may be split into two separate processes; a pre-needling process 21 and a needling process 22. The pre-needling process 21 consists of a single-sided needle penetration to initially consolidate the web from the web drafting process 6, and then a secondary needling process 22 which fully consolidates the web by penetration with needles from both the top and bottom surfaces.
Finally, needle-punched fabric layer is wound in a winding process 7. Dependent on the requirements of the next step of the process, the fabric layer may be wound into rolls of a suitable length, and if necessary, cut or slit to a specific width.
Fig. 3 shows a more detailed schematic diagram of the manufacture of a spun-laced fabric structure. First step is to unwind the needle-punched fabric layer from the needle-punching process 2 by an unwinding process 8. The unwound fabric layer is subsequently spun-laced in a spun-lacing process 3. The spunlacing process 3 may be carried out on unwound needle-punched fabric layer coming from one or more un-winding processes, depending on how many layers are going to be spun-laced in the same spun-lacing process 3. Different layers may come from various un-winding processes 8 of needle-punched fabric layers or un-winding processes 81 of other materials or directly from the fiber blending/opening process 4 and web formation process 1. The different layers may then subsequently be assembled into a multiple layer fabric structure and spun-laced in the spun-lacing process 3.
After the spun-lacing process 3, the excess water may be removed from the material by a drying process 9, e.g. in a through-air oven. The drying process 9 may comprise an additional step of vacuum extraction via a series of vacuum boxes before being dried.
Finally, spun-laced fabric structure is wound in a winding process 7. Dependent on the requirements of the next step of the process, the fabric structure may be wound into rolls of a suitable length, and if necessary, cut or slit to a specific width.
Fig. 4 shows a more detailed schematic diagram of the manufacture of a final material or final garment. Again, the fabric structure may initially have to be unwound, if the fabric structure was wound in an antecedent process step, before proceeding with an aftertreatment of the fabric structure. The aftertreatment process 10 may comprise several separate processes depending on the performance requirements of the final application. The fabric structure may be subjected to one or more chemical aftertreatment processes which typically, at least as a minimum for apparel applications, include colouring (either a single uniform colour or a multiple colour pattern design). Two primary methods of coloring are dyeing and printing performed using traditional textile finishing equipment. The material can be colored using dyeing or printing or by using both. The types of dyes used are the same as those used for dyeing traditional textiles, which typically depend on the type or types of fibers used. Pigment colouration typically comprise the use of pad, dip, or spray applications. Furthermore, several other types of performance enhancing chemicals can be applied to the fabric structure using traditional textile finishing technology. The types of fabric structure finishes which may be obtained vary significantly, and the aftertreatment processes are therefore tailored to meet the performance requirements of the application and may include processes to enhance: wash durability, abrasion resistance, repellency (water, oils, alcohols), antistaticness, absorbency, softness, etc.
To further enhance the performance of the final nonwoven fabric structure with regards to attributes such as wash durability and abrasion resistance, the fabric structure may be treated with cross-linking, film forming synthetic binders. The binders may be applied by pad, dip, or spray applications. In one preferred embodiment, an acrylic copolymer binder and melamine formaldehyde resin mixture are padded into the fabric structure.
A potential final aftertreatment step is a combined process to soften the fabric structure, and reduce the shrinkage which can occur due to repeated launderings during the life of the fabric structure. A commonly known, traditional method of achieving a softer and more shrink-resistant fabric structure is via the process of sanforization, whereby, in the presence of water or steam, the fabric structure is stretched, shrunk, and fixed in the length and width directions.
When the fabric structure has been submitted to the relevant aftertreatment processes 10, the fabric structure is wound in a winding process 7 and if necessary cut or slit to a specific width.
Finally, the aftertreated fabric structure can be converted to a garment by a garment converting process 11. The fabric structure is converted into garments using traditional cut and sew methodologies.
The preceding description is relevant to the preparation of a single layer of nonwoven fabric structure. However, different embodiments of the invention are encompassed by being composed of two or more individual layers, said layers being assembled from any combination of dry-laid carded webs, dissimilar nonwoven, knitted, woven, net/mesh, or film materials. All of the different layers that are to be incorporated into the fabric structure must be assembled together prior to forming an intimately bonded fabric structure.
As mentioned above, the performance of the fabric structures were determined using the standards and requirements identified in ASTM F1959 - Standard Test Method for Determining the Arc Rating of Materials for Clothing, ASTM F 1506 - Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, and EN 61482-1-2 - Live Working - Protective Clothing Against the Thermal Hazards of an Electric Arc.
The ATPV performance of the fabric structures as determined by ASTM F1959 - Standard Test Method for Determining the Arc Rating of Materials for Clothing, easily exceeds the performance of currently available woven materials in the market when comparing the materials on a weight for weight basis. The different embodiments of the invention have an ATPV to fabric basis weight ratio of greater than 500 cal/g. Currently available woven materials have an ATPV to fabric basis weight ratio ranging from approximately 270 - 370 cal/g.
To express this performance improvement in terms of just ATPV, and to illustrate the conversion; $ATPV (cal / {cm}^{2}) = \frac{ATPV to Basis Weight Ratio (cal / g) x Fabric Basis Weight (g / m^{2})}{10, 000}$
Therefore, considering an embodiment of the invention having a basis weight of 200 g/m², the ATPV will be at least; $\begin{matrix} ATPV (cal / {cm}^{2}) & = \frac{500 x 200}{10, 000} \\ = 10 cal / {cm}^{2} \end{matrix}$
In addition to ATPV, to be approved for use as an arc flash protective material in the USA, the nonwoven fabric structure must also meet all the requirements of ASTM F 1506 - Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards. When tested in accordance with this standard, the present nonwoven fabric structure meets or exceeds all requirements.
When tested in accordance with EN 61482-1-2 - Live Working - Protective Clothing Against the Thermal Hazards of an Electric Arc, the nonwoven fabric structure can meet a Class 1 performance level at a basis weight less than 200 g/m². A Class 2 performance level can be achieved at a basis weight less than 325 g/m² - currently available woven materials have basis weights of approximately 400 g/m² or higher to achieve this same performance.
While not a defined requirement for the nonwoven fabric structure to be used in arc flash protection, the thermal mannequin performance of the fabric structure provides an additional important indication of how well a material performs in thermal or fire-related end-uses. When tested in accordance with EN469 Protective Clothing for Fire Fighters, using a 4 sec flame time, many nonwoven fabric structures maintain a total burn of less than 60% through at least 25 washing cycles when washed in accordance with AATCC Method 135 (3, IV, A iii).

Examples

In the following, two examples of the present multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace will be further described.

Example 1

In example 1, the nonwoven fabric structure consists of a single layer.
The fabric structure is constructed from FR Viscose and p-aramid fibers, the FR Viscose fibers having an average staple length of approximately 51 mm and a linear density of 2.2 dtex, and the p-aramid fibers having an average staple length of approximately 50 mm and a linear density of 1.7 dtex.
The said fibers were thoroughly opened and blended in a ratio of 85% FR Viscose and 15% p-aramid using conventional staple fiber preparation equipment to ensure a uniform distribution and blend of the two fiber types in a form suitable for subsequent feeding to the web formation system. The pre-opened and blended fibers were fed into the web formation system, in this case a parallel-laid system.
In this example, the basis weight of the web formed was approximately 20 g/m².
The formed web was cross-lapped into multiple layers to produce an unconsolidated web weight of approximately 140 g/m².
The cross-lapped web was then drafted and needle-punched to produce a needle-bonded nonwoven fabric layer of approximately 130 g/m² in weight.
The nonwoven fabric layer was wound into rolls and mounted in the unwind station in the spun-laced line.
The nonwoven fabric layer was then spun-laced to achieve maximum strength, integrity, and durability.
The resultant spun-lace nonwoven fabric structure yielded a basis weight of 130 g/m².
The nonwoven fabric structure was tested to all parameters defined in ASTM F 1506 -Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards. Actual results are shown in Table 1 in comparison to the requirements of the standard.
It is important to note that different minimum performance 5 requirements are defined in the standard depending on the type of material. Currently, only minimum performance requirements for woven and knitted fabrics are defined in the standard.
Additionally, dependent upon the weight of the material, the minimum performance requirements defined in ASTM F1506 are different - the values in the table below are those defined for woven fabrics between 102 and 200 g/m2 and knitted fabrics between 102 and 271 g/m².
As can be seen from the results, the fabric according to Example 1, having a basis weight of 130 g/m2, meets or exceeds all criteria of the standard for knitted as well as for woven fabrics in this weight range.

Example 2

In example 2, the fabric structure consists of two layers.
The fabric structure is constructed from two needle-punched nonwoven fabric layers. Layer 1 is constructed from FR Viscose and p-aramid fibers, the FR Viscose fibers having an average staple length of approximately 51 mm and a linear density of 2.2 dtex, and the p-aramid fibers having an average staple length of approximately 50 mm and a linear density of 1.7 dtex.
Layer 2 is constructed from FR Viscose fibers, having an average staple length of approximately 51 mm and a linear density of 2.2 dtex.
For both layers: In layer 1 the said fibers were thoroughly opened and blended in a ratio of 85% FR Viscose and 15% p-aramid for using conventional staple fiber preparation equipment to ensure a uniform distribution and blend of the two fiber types in a form suitable for subsequent feeding to the web formation system. The pre-opened and blended fibers were fed into the web formation system, in this case a parallel-laid system. In layer 2, 100% of FR Viscose fibers were opened using the same system as above.
For both layers, the basis weight of the web formed was approximately 20 gsm. For layer 1, the formed web was cross-lapped into multiple layers to produce an unconsolidated web weight of approximately 80 g/m². For layer 2, the formed web was cross-lapped into multiple layers to produce an unconsolidated web weight of approximately 100 g/m².
The cross-lapped web from layer 1 was then drafted and needled to produce a needle-bonded nonwoven fabric layer of approximately 60 g/m² in weight. The cross-lapped web from layer 2 was then drafted and needled to produce a needle-bonded nonwoven fabric layer of approximately 70 g/m² in weight.
Both needle-bonded nonwoven fabric layers were wound into rolls and mounted in the unwind station in the spun-laced line.
Layer 1 and 2 needle-punched nonwoven fabric layers were then unwound on top of each other and spun-laced to achieve maximum strength, integrity, and durability. The resultant spun-lace base material yielded a basis weight of 130 g/m².
The fabric structure was tested to all parameters defined in ASTM F 1506 - Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards. Actual results are shown in the Table 1 in comparison to the requirements of the standard.
It is important to note that different minimum performance 5 requirements are defined in the standard depending on the type of material. Currently, only minimum performance requirements for woven and knitted fabrics are defined in the standard.
Additionally, dependent upon the weight of the material, the minimum performance requirements defined in ASTM F1506 are different - the values in the table below are those defined for woven fabrics between 102 and 200 g/m² and knitted fabrics between 102 and 271 g/m².

As can be seen from the results, the fabric according to Example 2, having a basis weight of 130 g/m², meets or exceeds all criteria of the standard for knitted as well as for woven fabrics in this weight range.

Table 1

Characteristic	Test method	ASTM F1506 Minimum performance requirements		Example 1	Example 2
Basis weight (g/m2)		N/A	N/A	130	130
Tensile at	ASTM	134 min.	N/A	317	228
Break (N)	D5034
Tear	ASTM
	11 min.	N/A	>11	>11
Resistance (N)	D1424
Burst Strength	ASTM	N/A	179	TBD	TBD
(N)	D3786
Seam Slippage	ASTM		6 mm max. at 134 N	N/A	N/A	N/A
	D434		6 mm max. at 134 N

Colourfastness
Laundering	AATCC	Class	3 min.	Class 3 min.	>3	>3
(Class)	61 IIA
Dry Cleaning	AATCC	Class	3 min.	Class 3 min.	>3	>3
(Class)	132

Dimensional Change
Dry Clean	AATCC	3 max.	N/A	<3	<3
Shrinkage (%)	158
Laundry	AATCC	3 max.	N/A	<3	<3
Shrinkage (%)	135

Initial Flammability
Char Length	ASTM	152 max.	152 max.	23	26
(mm)	D6413
Afterflame (s)	ASTM D6413	2 max.	2 max.	0	0
Melting Drip	ASTM	0 max.	0 max.	0	0
(s)	D6413

Flammability After 25 Washes (washed in accordance with AATCC 135)
Char Length	ASTM	152 max.	152 max.	23	26
(mm)	D6413
Afterflame (s)	ASTM D6413	2 max.	2 max.	0	0
Melting Drip	ASTM	0 max.	0 max.	0	0
(s)	D6413

Arc Flash Test
Afterflame	ASTM	5 max.	5 max.	0	0
time (s)	F1959
Arc Rating (cal/cm²)	ASTM F1959	4 - 8 (Hazard Risk Category 1)		>8.5	>8.5
		8 - 25 (Hazard Risk Category 2)
ATPV / Basis weight Ratio	-	25 - 40 (Hazard Risk Category 3)		>650	>650
(cal/g)		40 + (Hazard Risk Category 4)

Table 2

Material	Basis Weight	ATPV	ATPV / Basis Weight
Nomex® Limitedwear	109 g/m²	5.1 cal/cm²	468 cal/g (HRC 1 Only)
Tecasafe™ plus	237 g/m²	8.4 cal/cm²	354 cal/g
Indura® Ultrasoft™	237 g/m²	8.7 cal/cm²	367 cal/g
Example 1	130 g/m²	>8.5 cal/cm²	>650 cal/g
Example 2	130 g/m²	>8.5 cal/cm²	>650 cal/g

From the above Table 2, it is easily deduced that the fabric structure according to Example 1 as well as Example 2 outperform the currently available woven materials in the market in terms of arc flash performance at significantly lower basis weights.
Although the invention above has been described in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.

Claims

A method for manufacturing a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace, the method comprising the steps of:
- providing a web of inherently fire-resistant fibers,

- bonding the fibers of the web by means of needle-punching to form a nonwoven fabric layer, and

- bonding the nonwoven fabric layer by means of spun-lacing to form the non-woven fabric structure.
A method according to claim 1, wherein the web is folded back and forth upon itself to form a web in which the fire-resistant fibers are more equally oriented in both a length direction and a width direction of the web, yielding approximately equal strengths in both directions.
A method according to claim 1 or 2, wherein the needle-punching is performed by penetrating the web with an array of barbed needles that carry tufts of the web's own fire-resistant fibers in a vertical direction through the web.
A method according to any of the preceding claims, wherein the needle-punching is performed in two stages, a first pre-needling stage consisting of single-sided needle penetration to initially consolidate the web from web drafting, and subsequently a second needling stage which fully consolidates the web by penetration with needles from both the top and bottom surfaces of the web.
A method according to claim 4, wherein the first pre-needling stage has a punch density greater than 150 punches/cm², and the second needling stage has a punch density greater than 300 punches/cm².
A method according to any of the preceding claims, wherein additional bonding to form the nonwoven fabric structure is achieved by spunlacing.
A multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace', said multiple-use nonwoven fabric structure comprising a nonwoven layer which comprises fire-resistant fibers, the fire-resistant fibres first being bonded by needle-punching and subsequently by spunlacing.
A multiple-use nonwoven fabric structure according to claim 7, wherein the inherent fibers are, but not limited to, FR Viscose, meta-aramid, para-aramid, melamine, Polybenzimidazole (PBI), Silex, Basalt, or a combination thereof.
A multiple-use nonwoven fabric structure according to claim 7 or 8, wherein the fibers have a linear density between 0.5 and 5 dtex and a staple fiber length between 10 and 100 mm.
A multiple-use nonwoven fabric structure according to any of the claims 7 to 9, wherein the fabric structure comprises one or more additional layers, the one or more additional layers being introduced into the fabric structure before the spunlacing bonding.
A multiple-use nonwoven fabric structure according to claim 10, wherein the one or more additional layers is/are a dry-laid carded web, a nonwoven layer, a woven layer, a knitted layer, a net/mesh, or a combination thereof.
Garment made of a multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace'as claimed in any one of claims 7 to 11.
Use of an arc flash protection, multiple-use nonwoven fabric structure having an Arc Thermal Protection Value (ATPV) to fabric basis weight ratio greater than 500 cal/g and being a Hazard Risk Category 2 in accordance with NFPA 70E Standard for Electrical Safety in the Workplace'as claimed in any one of claims 7- 11 for garments, blankets, flash fire PPE, molten metal splash PPE, fire fighters PPE, apparel, awnings, curtains, floor covers, work wear, military uses.