US20200190710A1

US20200190710A1 - Flame retardant fabric composed of thermoplastic core-spun yarns

Info

Publication number: US20200190710A1
Application number: US16/703,050
Authority: US
Inventors: Thomas Edward Schmitt
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-12-12
Filing date: 2019-12-04
Publication date: 2020-06-18

Abstract

A fabric that includes an air jet core-spun yarn including a core composed of continuous filament thermoplastic yarns and a sheath composed of cellulose staple wrapper fibers or cellulose-rich staple fibers, wherein the fabric is treated with a flame retardant compound.

Description

CROSS REFERENCE TO RELATED PATENT APPLICATION

The present non-provisional patent/patent applications claims priority to U.S. Provisional Patent Ser. No. 62/778,470 filed Dec. 12, 2018 and entitled “THERMOPLASTIC CORE-SPUN YARNS FOR FLAME PROTECTIVE CLOTHING,” the contents of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to air jet core-spun yarns used in flame-retardant fabrics wherein the air jet core-spun yarns comprise a core composed of thermoplastic continuous filament yarns and a sheath composed of staple wrapper fibers. The staple wrapper fibers of the sheath may be non-inherently flame-retardant staple fibers, inherently flame-retardant staple fibers, or mixtures of thereof. When non-inherently flame-retardant staple fibers such as cellulose are used, fabrics comprising such air jet core-spun yarns may be rendered flame-retardant by treating with flame-retardant fabric finishes.

BACKGROUND OF THE INVENTION

Flame-retardant (FR) fabrics for protective clothing are crucial in both military and non-military environments. Electricians, petro-chemical workers, firefighters, and combat soldiers all require protection from flames and high energy radiant bursts. In addition, garments must be durable, comfortable, affordable, and easy to maintain.
For an FR garment to offer protection, the fabric used must not sustain a flame, not melt and stick to the wear's skin, have minimal high temperature shrinkage, insulate the user, and resist fabric rupture leading to direct flame impingement upon the user.
There are basically two types of flame-retardant fabrics used in protective clothing: (1) Fabrics made from flame-retardant organic fibers (e.g. aramid, flame-retardant rayon, polybenzimidazole, modacrylic, etc.; and (2) Flame-retardant fabrics made from conventional materials (e.g. cotton or wool) that have been post treated to impart flame retardancy.
Generally, fabrics made with flame resistant organic fibers are uncomfortable and expensive, while FR treated cotton fabrics are less expensive, but heavier and less durable. Therefore, a need exists to develop an FR-treated cotton fabric which is stronger and can be made at a lesser weight and possess greater durability and the necessary flame and thermal resistance. Industry standards promulgated by the National Fire Protection Association (NFPA) govern some single layer thermal protective clothing performance standards. Among these standards are:

NFPA 1975: Standard on Station/Work Uniforms for Fire and Emergency Services (2004)

NFPA 2112: Standard on Flame Resistant Garments for Protection of Industrial Personnel Against Flash Fire (2007).

NFPA 70E: Standards for Electrical Safety in the Workplace (Personal Protective Equipment) (2018)

For the U.S. Military, one current specification is:

GL_PD-07-12: Purchase Description Cloth, Flame Resistance

Typical fabric properties for this fabric are found in Table 6.
To meet industry standards, manufacturers developed numerous ‘engineered blends’ of fiber combinations wherein each fiber contributes particular functions such as preventing flame propagation and penetration, lowering fabric shrinkage at high temperatures, and controlling fabric melting and dripping. Fibers also contribute to functional features such as dyed colors, comfort, durability, and lower cost.
Currently, many fire protective fabrics contain inherently flame-resistant fibers such as para- or meta-aramid, FR rayon, or modacrylic fibers. Unfortunately, garments comprising aramid fibers are often expensive and uncomfortable to wear while fabrics comprising FR rayon or modacrylic are less durable.
Fabrics comprising 50/50 percent nylon and cotton (‘NYCO’) fabrics are used in military and work wear uniforms not requiring flame resistance. These fabrics are durable, comfortable, and easy to maintain. Unfortunately, these fabrics do not possess the necessary flame and thermal resistance for thermal protective garments. Typical fabric properties are listed in Table 7.
One ammoniation finishing method for cellulose fabrics is trade named the Proban® finishing process in which the cellulose fibers are impregnated with an organophosphorus pre-polymer and crosslinked using ammonia gas. Rhodia Group UK is the supplier of the Proban flame retardant. Flame-retardant fabrics using this process are offered by Westex, Inc under the Ultrasoft® or Indura® trade names. Typical fabric properties are found in Table 8.
Examples of ammoniation cured phosphorus-based fabric finishing schemes for cotton-containing fabrics are taught in US patents including:
Cole (U.S. Pat. No. 4,145,463) granted Mar. 20, 1979
Baitinger (U.S. Pat. No. 4,154,878) granted May 15, 1979
Cole (U.S. Pat. No. 4,494,951) granted Jan. 22, 1985
Johnson (U.S. Pat. No. 4,748,705) granted Jun. 7, 1988
Fleming (U.S. Pat. No. 5,468,545) granted Nov. 21, 1995
Cole (U.S. Pat. No. 5,942,006) granted Aug. 24, 1999
Others, (including Li and Mayernik U.S. Pat. No. 9,091,020), have disclosed THP phosphorus-based systems which are thermally crosslinked to avoid the technical and economic difficulties of using ammonia gas in the FR finishing process. The preferred fabrics treated with this system are comprised of intimate blends of cellulose and synthetic staple fibers.
Ultrasoft fabrics are an intimate blend of 88% cotton and 12% thermoplastic high tenacity nylon 6,6 staple fibers and treated using the Proban-type flame retarding finishing process. Ideally, for fabric strength and garment durability the nylon fiber content should be raised above the 12% level. However, when attempted, the fabrics lack adequate commercial flame resistance after laundering and, today, treated fabrics comprising 12% thermoplastic nylon staple and 88% cotton fiber remain the most popular FR finished cotton fabrics.
Fleming (U.S. Pat. No. 5,480,458 Table 4) teaches that abrasion resistance of nylon/cotton fabric can be increased 300% when compared to 100 percent cotton fabrics but fail to have durable flame resistance after laundering.
Fleming (U.S. Pat. No. 5,480,458) and Underwood U.S. Pat. No. 8,528,120), teach more durable fabrics which utilize the ammoniation process, by replacing some of the cotton fiber content with synthetic, thermoplastic or non-thermoplastic, inherently FR fibers such as meta aramid. As in other prior art, the fabrics are not formed from air jet core-spun yarns.
Li and Mayernik (U.S. Pat. Nos. 8,012,890 and 8,012,891) and (U.S. Pat. No. 9,091,020), teach fabrics with up to 50% thermoplastic fibers (nylon, polyester, or polyphenylene sulfide) content with thermally-cured THP chemistry. However, an additional halogenated FR finish might be required. As in other prior art, the fabrics are not formed from air jet core-spun yarns.
By contrast to all of the above teaching wherein fabric comprising staple spun yarns of cotton and/or cotton fibers blended with thermoplastic or non-thermoplastic staple fibers, Li and Mayernik (U.S. Pat. No. 7,713,891) and (U.S. Pat. No. 7,741,233) teach that abrasion resistance may be improved when the thermoplastic fiber is a continuous filament yarn spaced between staple spun yarns comprised of heterogeneous staple fibers.
Despite the work of many inventors, there still exists the need for a more durable, yet economical, cotton-rich fabric which can be FR treated using phosphorus chemistry and provide garments with thermal and flame protection and comfort.
In U.S. Pat. No. 5,468,545 (Col. 2; Lines 35-42 and Col. 2; Lines 60-3/9), Fleming describes a mechanism which limits the amount of non-flame resistant synthetic fibers which can be used in a phosphorus-treated FR cotton fabric. His hypothesis is that non-cotton fibers in an intimate staple yarn blend will receive a surface coating of FR chemistry. However, the cured phosphorus chemistry is only durable to cotton or cellulose fibers. FR chemistry deposited on non-cellulose fibers contributes no FR properties after the FR chemistry is removed during laundering. The goal of the present invention is to partition the cellulosic and non-cellulosic fibers so that the maximum FR chemistry is preferentially applied to cellulose fibers.
This goal is attained by using air jet core-spun yarns and fabrics comprising a primary cellulose staple fiber sheath wrapped around a thermoplastic continuous filament yarn core which when treated with THP chemistry produces a fabric with excellent strength, abrasion resistance, shrinkage control, appearance, and price, all with necessary flame resistance.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a fabric includes an air jet core-spun yarn including a core composed of continuous filament thermoplastic yarns and a sheath composed of cellulose staple wrapper fibers, wherein the fabric is treated with a flame retardant compound.
According to another embodiment of the present invention, a fabric includes an air jet core-spun yarn including a core composed of continuous filament thermoplastic yarns and a sheath composed of cellulose-rich staple wrapper fibers, wherein the fabric is treated with a flame retardant compound.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers denote like method steps and/or system components, respectively, and in which:

FIG. 1 is a picture of a comparative example of woven fabric in comparative example 5 after 1000 cycles of Taber tester abrasion (ASTM D3884);

FIG. 2 is a picture of another comparative example of woven fabric in comparative example 6 after 1000 cycles of Taber tester abrasion (ASTM D3884);

FIG. 3 is a picture of a knit fabric having a composition as described in Example 1 after 1000 cycles of Taber tester abrasion (ASTM D3884);

FIG. 4 is a picture of a knit fabric having a composition as described in Example 2 after 1000 cycles of Taber tester abrasion (ASTM D3884); and

FIG. 5 is a picture of woven fabric having a composition as described in Example 6 after 1000 cycles of Taber tester abrasion (ASTM D3884).

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to the following detailed description of the invention taken in connection with the accompanying drawing figures, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention. Any and all patents and other publications identified in this specification are incorporated by reference as though fully set forth herein.
The present invention is directed towards an air jet core-spun yarn, wherein the core is composed of a drawn, textured or non-textured (‘flat’) thermoplastic continuous filament yarn including, but not limited to, thermoplastic polyamides and/or thermoplastic polyesters. The thermoplastic polymer continuous filament yarns may also comprise a flame-retarding polymer monomer or additive. The sheath is composed of staple wrapper fibers. The staple wrapper fibers of the sheath may be non-inherently flame-retardant staple fibers, inherently flame-retardant staple fibers, or mixtures of thereof. When non-inherently flame-retardant staple fibers such as cellulose are used, fabrics comprising such air jet core-spun yarns may be rendered flame-retardant by treating with flame-retardant fabric finishes.
For the thermoplastic core yarns, non-halogen flame retarding additives rich in nitrogen or phosphorous may be added during polymerization or melt spinning. The additives may be selected from the groups consisting of:
A. Condensation products of melamine (including melam, melem, and melon);
B. Reaction products of melamine with phosphoric acid including melamine phosphate, melamine pyrophosphate, and melamine polyphosphate (MPP);
C. Condensation products of melamine with phosphoric acid (including melam polyphosphate, melem polyphosphate, melon polyphosphate), and melamine cyanurate (MC);
D. Phosphorous salt compounds including zinc diethylphosphinate (DEPZn), and aluminum diethylphosphinate (DEPA);
E. Thermoplastic phosphorous-rich compounds can be added during polymerization or melt spinning of polyester or polyamides. These include derivatives of 9,10-Dihydro-9-Oxa-10-Phosphaphenantrene-10-oxide (DOPO), 3-Hydroxyphenylphosphinyl-propanoic acid (CEPPA), and 2-carboxyethyl(methyl)phosphinic acid (CEMPA);
F. Combinations of the above.
Core-Spinning is a process which permits selective placement of fibers in the center of the yarn or in a wrapper sheath. Often a filament yarn is the core and the staple fibers form the wrapping sheath of the core-spun yarn.
At least three spinning processes exists to manufacture core-spun yarns. They include:

- 1. Conventional ring core-spinning which inserts a filament yarn under the last drafting roll in spinning and the drafted staple sliver and filament yarn are twisted together using the conventional ring and traveler process. A common product manufactured using this core-spinning technique is sewing thread. One example is taught by Guevel in U.S. Pat. No. 4,840,021. If the filament yarn is laid in the center of the drafted sliver, the filament yarn will be in the center of the final yarn. Locating the filament yarn more to the left or right of the drafted sliver will result in filament yarn wrapped on the outside of the yarn bundle which must be prevented. A guide device to present dual wrapper rovings and a core roving or continuous filament core yarn is taught by Sawhney and Folk in U.S. Pat. Nos. 4,976,096 and 5,531,063. A conventional ring spinning system is used to insert twist into the yarn. The inventors cite improved cover yarns comprising continuous filament thermoplastic core yarns and cotton staple wrapper fibers but do not teach use in flame-retardant fabrics.
- 2. Friction spinning (often called DREF spinning after the name of the machine) is disclosed in U.S. Pat. Nos. 4,107,909, 4,249,368, and 4,327,545. The machine has capabilities to spin yarns with cores of continuous filament, parallel staple fibers, or both.
- 3. Air jet spinning (e.g. MJS or Vortex air jet spinning using equipment manufactured by Murata Machinery Incorporated). The spinning apparatus is described in U.S. Pat. Nos. 5,540,980; 4,718,225; 4,551,887; and 4,497,167.

Core-spun yarns comprising cores of continuous filament inorganic yarns and staple fiber sheaths are used in flame-retardant fabrics and protective garments.
Examples of friction spun flame-retardant core-spun yarns and processes are disclosed in U.S. Pat. Nos. 4,958,485 and 5,033,262 (Montgomery), U.S. Pat. No. 5,141,542 (Fangeat), and U.S. Pat. No. 5,506,043 (Lilani). Unlike the present invention, each of these patents claim high temperature resistant non-thermoplastic staple fiber or continuous filament yarns as the core component.
Examples of flame-retardant air jet spun yarns are taught in U.S. Pat. No. 4,927,698 (Jaco), U.S. Pat. No. 5,540,980 (Tolbert) which use fire resistant inorganic filament core yarns. In a series of patents (U.S. Pat. Nos. 6,146,759; 6,287,690; 6,410,140; 6,553,749, 6,606,846), Land teaches ‘double core-spun’ yarns formed by spinning an air jet core-spun yarn and then using this yarn as a core yarn for a second air jet spinning step which permits a second sheath fiber to be wrapped on top of the first core-spun air jet yarn.
Unlike the present invention, the final yarn contains in part a high temperature resistant continuous filament core and none of the yarns comprise cotton wrapper fibers with flame-retardant fabric finishes.
In U.S. Pat. No. 5,802,826, Sawhney teaches a combination process in which air jet spun core fibers are wrapped by a friction spinning step to continuously produce a core-spun yarn in a single step.

Flame-Retardant Treated Cellulosic Fabrics:

It is possible to improve the flame resistance of fabrics comprising nylon and 50% or more cotton fibers by applying a flame retarding finish to the formed fabric by a tetra(hydroxymethyl) phosphonium (THP) treating process. These finishes may comprise phosphorus compounds which are char formers and particularly effective on cellulose fibers. Phosphororus compounds' include tetra(hydroxymethyl) phosphonium (THP) salts such as salts of sulfate (THPS ‘Pyroset’) and chloride (THPC ‘Proban’).
In a THP treating process, the fabric is immersed in a phosphonium salt pre-condensate, cured by ammonia gas, oxidized with hydrogen peroxide to a pentavalent state and neutralized by washing steps.
If used at an acceptably low content, thermoplastic fibers may be used in flame-retardant fabrics. One commercial example of flame-retardant cotton/nylon fabrics are Indura and Ultrasoft fabrics available from Westex, a division of Milliken and Company. The woven Indura fabric is comprised of staple spun yarn consisting of a 25/75 weight percent blend of high tenacity nylon 6,6 staple fibers and cotton fibers in the warp direction and a 100 percent cotton staple spun yarn in the weft direction. The final fiber content is approximately 12/88 percent nylon/cotton by weight. To render the fabric flame-retardant, the fabric is immersed in a phosphonium salt pre-condensate, cured by ammonia gas, oxidized with hydrogen peroxide to a pentavalent state and neutralized by washing steps.
In U.S. Pat. No. 5,468,545, Fleming discloses that the abrasion resistance of flame-retardant treated cotton can be increased by over 300 percent when as little as 12 percent nylon staple fibers are included in the fabric. In US 4,920,00, Green discloses a similar effect.
Fleming (U.S. Pat. No. 5,468,545) identifies the problem when treating fabrics rich in non-flame resistant synthetic fiber content. In Column 2/Lines 35-40: “The introduction of thermoplastic fibers into cotton fabrics makes it very difficult to flame-retardant treat the fabrics. In addition to the flammability of the thermoplastic fibers, they are also hydrophobic and can therefore make it difficult for the flame-retardant treatments to penetrate yarn bundles and when penetration does occur, the aqueous flame retardant solutions migrate to the surface of yarn bundles more rapidly than with 100% cotton.”
The flame-retardant reacted on the surface of the thermoplastic fiber is not available to treat the cotton fibers and is not durable to laundering. It is desirable to encapsulate the thermoplastic core yarn with cellulosic fibers which contain fully cured flame-retardant chemistry.
Another limitation with the present ammoniation process, as stated by Fleming, is the poor physical penetration of ammonia gas into the intimately-blended nylon/cotton yarn bundle to react the THP salt pre-condensate. Positioning all of the cellulosic fibers near the yarn surface improves the ammonia gas penetration and the quality of the reaction between the FR chemistry and cellulosic fibers.
Numerous references teach imparting flame retardancy characteristics to synthetic/cellulose materials. Some patents claim systems to treat fabrics comprising up to 50% nylon (or in one case, polyester) fibers. None of the patents describe air jet core-spun yarns as a necessary component for providing durable flame-retardant fabrics.

Test Methods

Some of the tests used to measure and compare the flame and thermal resistance, protection potential, and durability of textile materials for industrial workwear and military combat uniforms include:

- 1. ASTM D6413: Standard Test Method for Flame Resistance of Textiles (Vertical Test).
- 2. ASTM F2703—Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame Resistant Materials for Clothing with Burn Injury Prediction (Thermal Protective Performance Test).
- 3. ASTM F1930: Standard Test Method for Evaluation of Flame Resistant Clothing for Protection Against Flash Fire Simulation Using an Instrumented Manikin.
- 4. ASTM D4966: Standard Test Method for Abrasion Resistance of Textile Fabrics (Martindale Abrasion Tester Method).
- 5. ASTM D3884: Standard Guide for Abrasion Resistance of Textile Fabrics (Rotary Platform, Double-Head Method)
- 6. ASTM D3787: Standard Test Method for Bursting Strength of Textiles Constant-Rate-of-Traverse (CRT) Ball Burst Test

The above tests use small specimens that are representative, to the extent possible, of the material or assembly being evaluated. The rate at which flames travel in various directions along surfaces depends upon the physical and thermal properties of the material, product or assembly under test, the specimen mounting method and orientation, the type and level of fire or heat exposure, the availability of air, and properties of the surrounding enclosure. If different test conditions are substituted or the end-use conditions are changed, it may not always be possible by or from these tests to predict changes in the fire-test-response characteristics measured.
The results from any flame or thermal performance test are valid only for the test exposure conditions described in each test method.
As used in the specification, including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. As used herein, the term “about” means plus or minus 20% of the numerical value of the number with which it is being used. Therefore, about 50% means in the range of 40%-60%. Further, all ranges include not only the beginning and ending numbers of a range, but every number in between, in any combination, as that is the very definition of a range.
The terms “flame-retardant,” “flame-resistant,” “fire-resistant,” or “fire resistance,” as used herein, means that the composition exhibits a limiting oxygen index (LOI) of at least 27. “Flame-retardant,” “flame-resistant,” “fire-resistant,” or “fire resistance,” may also refer to the flame reference standard ASTM D6413 for textile compositions, flame persistent test NF P 92-504, and similar standards for flame-resistant fibers and textiles.
The term ‘self-extinguishing’ used herein means that a fibrous structure comprising the inventive fabric will not continue to burn in its entirety after the flame source is removed during test method ASTM D6413.
A polyamide fiber is defined as: ‘A manufactured fiber in which the fiber forming substance is a long-chain synthetic polyamide in which less than 85% of the amide-linkages are attached directly (—CO—NH—) to two aliphatic groups’.
Thermoplastic polyamide fibers, such as nylon 6 and nylon 6,6 fibers are most useful in the present invention as a thermoplastic continuous filament yarn. The thermoplastic continuous filament yarn may also be composed of other thermoplastic polyamide fibers including, but not limited to, Nylon 6-10, nylon 11, nylon 12, nylon 4-6, nylon 6-12, nylon 6-6T, nylon 6T, nylon 6I-6T, MXD6, or any combinations of these.
A polyester fiber is defined as: ‘A manufactured fiber in which the fiber forming substance is any long-chain synthetic polymer composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephthalic units, p(—R—O—CO—C6H4-CO—O—)_xand para substituted hydroxy-benzoate units, p(—R—O—CO—C6H4-O—)_x’.
Whereas polyethylener terephthalate (PET) is most useful in the present invention, polyester fibers including polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT) may be used.
The thermoplastic polyamide fibers and the thermoplastic polyester fibers used in the present invention may have any thickness or diameter, and the thickness or diameter of the fibers may vary by their intended use. For example, in textiles for apparel, where stiffness may be objectionable, the fiber diameter may be less than 18-19 μm or approximately 3 denier/filament.
A “denier” is a well-known unit of linear density in the textile arts and is defined herein as the weight in grams of 9000 meters of a linear fiber or yarn.
The selection of the total air jet core-spun yarn denier depends upon the desired fabric weight and thread count. A general rule for air jet core-spun yarns is for the sheath fibers to comprise at least 40% sheath of the total air jet core-spun yarn, but this is subject to optimization depending upon the spinning machine, fabric design, and fabric performance requirements.
The air jet core-spun textile yarn as disclosed herein may be used to manufacture flame-retardant treated fabrics. The fabrics are comprised of air jet core-spun textile yarns composed of a thermoplastic continuous filament yarn core and primarily cellulose staple wrapper fibers sheath. The primarily cellulose staple wrapper fibers sheath means that a fraction of cellulose, such as cotton, in the sheath is replaced with an inherently flame resistant non-thermoplastic staple fibers with superior char strength. In a preferred embodiment, the primarily cellulose staple wrapper fiber sheath comprises less than 10% of an inherently flame resistant non-thermoplastic staple wrapper fiber to improve the strength of charred fabric of the present invention. The inherently flame resistant non-thermoplastic staple wrapper fibers include, but are not limited to, meta- and para-aramids, polybenzimidazole, polybenzoxazole, novoloid, oxidized polyacrylonitrile, polyoxadiazole, polyacrylate, polyimide, modacrylic, melamine, or combination thereof.
While the general scope of the present invention is to use a sheath comprising primarily cotton, or other cellulosic fibers such as viscose or lyocell may be used. If viscose or lyocell is used, a fraction of the viscose or lyocell may be replaced with an inherently flame resistant non-thermoplastic stable fibers with superior char strength to form the sheath. The inherently flame resistant non-thermoplastic staple wrapper fibers includes, but is not limited to, meta- and para-aramids, polybenzimidazole, polybenzoxazole, novoloid, oxidized polyacrylonitrile, polyoxadiazole, polyacrylate, polyimide, modacrylic, melamine, or combination thereof.
When of comparable yarn size and fiber composition, thermoplastic continuous filament yarns have increased strength when compared to staple yarns spun on any spinning system. Also, thermoplastic continuous filament yarns have greater abrasion resistance than staple spun yarns. The position of the thermoplastic polyamide fibers or the thermoplastic polyester fiber as the core of the core-spun yarn of the present invention prevents any interference with the absorption of the aqueous FR cotton treatment into the cotton fibers as recognized by Fleming. The thermoplastic continuous filament yarn core is less compress-able than conventional ring spun yarns, so the nip rolls after padding on the finish will remove less of the FR finish liquor. By surrounding the thermoplastic continuous filament yarn core with staple wrapper fibers of the sheath composed of cellulose, such as a primarily cotton staple wrapper fiber, molten polymer will not flow out when the fabric is exposed to a flame.

Example 1

An air jet core-spun yarn comprising a 100 denier/34 filament textured nylon 6 filament core yarn and 100% carded cotton sheath fibers was produced on a Murata MJS air jet spinning machine. The nylon 6 core yarn was produced from recycled post-industrial polymer. The filament core yarn tenacity and breaking elongation were 5.0 grams/denier and 29.9%, respectively. The combined air jet core-spun yarn size is 265 denier or 20/1 Ne cotton count. The nylon 6 core yarn represents approximately 38% by weight of the combined air jet core-spun yarn. The yarn was tested by a Textechno Statimat tensile tester and strength and breaking elongation are found in Table 1.
FIG. 3 shows the knit fabric of Example 1 for Taber Abrasion Comparison (1000 cycles, 500 gram weight, CS-10 abrasion wheel). The fabric is composed of 38%/62% nylon 6 filament core/carded cotton wrapper (6.0 oz/yd²knit fabric; FR treated only). The fabric exhibited a color change (residue from testing printed fabrics), but no thread breaks or pilling.

Example 2

An air jet core-spun yarn comprising a 150 denier/34 filament continuous filament polyester filament core yarn and 100% carded cotton sheath fibers was produced on a Murata MJS air jet spinning machine. The filament core yarn tenacity and breaking elongation were 4.95 g/d and 22.0%, respectively. The combined air jet core-spun yarn size is 265 denier or 20/1 Ne cotton count. The polyester core yarn represents approximately 57% by weight of the combined air jet core-spun yarn. The yarn was tested by a Textechno Statimat tensile tester and strength and breaking elongation are found in Table 1.
FIG. 4 shows the knit fabric of Example 2 for Taber Abrasion Comparison (1000 cycles, 500 gram weight, CS-10 abrasion wheel). The fabric is composed of 57%/43% polyester filament core/carded cotton wrapper (6.0 oz/yd²knit fabric; FR treated only). The fabric exhibited color change (residue from testing printed fabrics), but no thread breaks or pilling.

Comparative Example 1

A 100% cotton yarn of approximately 265 denier or 20/1 Ne cotton count was produced on a Schlafhorst Open End spinning machine. The yarn was tested by a Textechno Statimat tensile tester and results are found in Table 1.

Comparative Example 2

A ring spun staple warp yarn comprising 75% cotton and 25% high tenacity T420 nylon 6,6 (available from INVISTA S.a.r.l.) from greige Ultrasoft fabric was tested for yarn strength and results listed on Table 1.

Comparative Example 3

A ring spun ‘NYCO’ staple yarn comprising 50% combed cotton and 50% high tenacity T420 nylon 6,6 (available from INVISTA S.a.r.l.) was also tested for tensile strength and breaking elongation and results are found in the Table 1. This yarn is used in the fabric of the US Army combat uniform (‘ACU’ Military specification 404436).
FIG. 1 shows the woven fabric of Comparative Example 3 for Taber Abrasion Comparison (1000 cycles, 500 gram weight, CS-10 abrasion wheel). The fabric is 50/50 nylon/cotton (‘NYCO’ Military Combat Uniform Fabric printed. As shown, there is color change but no thread breaks.

Comparative Example 4

A ring-spun staple yarn comprising 65% FR rayon (available from Lenzing Group)/25% para-aramid/10% high tenacity nylon was tested for tensile strength and breaking elongation and results are included in Table 1. This yarn is used in the current US Military flame-retardant army combat uniform (FR ACU′ Purchase Specification GL-P1-07-12).
FIG. 2 shows the woven fabric of Comparative Example 4 for Taber Abrasion Comparison (1000 cycles, 500 gram weight, CS-10 abrasion wheel). As shown, the fabric exhibited abrasion and thread breaks.

TABLE 1

Yarn Tenacities and Elongations

	Tenacity,	Breaking	Tensile
	Grams/	Elongation,	Factor,
Yarn Description	denier	%	T*E^0.5

Example 1: 265 denier air jet core-spun	2.00	24.2	9.8
yarn 38%/62% nylon 6 filament
core/carded cotton wrapper
Example 2: 265 denier air jet core-spun	2.67	22.0	12.5
yarn 57%/43% polyester filament
core/carded cotton wrapper
Comparative Example 1: 265 denier	1.29	7.2	3.5
Open End spun
100% Carded Cotton
Comparative Example 2: 320 denier	1.78	8.3	5.1
ring-spun staple yarn (25%/75% HT
nylon 6,6 staple/Carded Cotton fibers)
Comparative Example 3: (‘NYCO’)	2.11	13.4	7.7
265 denier ring-spun staple yarn
(50%/50% HT nylon 6,6 staple/Combed
Cotton fibers)
Comparative Example 4 (‘FR ACU’)	2.24	7.7	6.2
265 denier ring-spun staple yarn
(65/25/10 FR rayon/para-aramid/nylon
6,6 staple fibers)

For each of the yarns in Table 1, the ‘Tensile Factor’ which is the yarn tenacity in grams/denier multiplied by the square root of the elongation is calculated. The Tensile Factor is an approximation of the area under the stress-strain curve from a yarn tensile tenacity vs. elongation diagram. The Tensile Factor is one measure of the ‘work-to-break’ of the yarn and correlates to fabric properties such as abrasion resistance and durability.
As a measure of core/sheath integrity, tubular knit fabrics of Example 1 and Comparative Example 1 weighing approximately 175 grams/square meter (5.2 oz/yd²) were prepared and subjected to abrasion test ASTM D4966—Standard Test Method for Abrasion Resistance of Textile Fabrics (Martindale Abrasion Tester Method). Following 15,000 cycles, Example 1 reveal no pilling while Comparative Example 1 showed severe pilling as predicted by the ‘Tensile Factors’ of the yarns.
Next, the tubular fabrics of Examples 1 and 2 and Comparative Example 1 were tested for burst strength using ASTM D3787 Standard Test Method for Bursting Strength of Textiles—Constant-Rate-of-Traverse (CRT) Ball Burst Test). Results are found in the following Table 2:

TABLE 2

Comparison of Knit Fabric Burst Strengths

		Burst Strength, lbs.

	Example 1: 265 denier air jet core-spun	135.0
	yarn 38%/62% nylon 6 filament core/carded
	cotton wrapper
	Example 2: 265 denier air jet core-spun yarn	164.0
	57%/43% polyester filament core/carded
	cotton wrapper
	Comparative Example 1: 265 denier Open	81.8
	End spun 100% Carded Cotton

Next, each tubular knit fabric was treated with an ammonia gas-cured tetrakis (hydroxyorgano) phosphonium (THP) finish, oxidized, neutralized, and washed.
Example knit fabrics 1 and 2 were compared to current US military ACU (NYCO) and FR ACU fabrics for abrasion resistance using ASTM D3884. After 1000 cycles of Taber tester abrasion, the fabrics were visually compared. Based upon photographic comparisons, the core-spun fabrics exhibited fewer broken yarns and less abrasion than the FR ACU fabric and equivalent to the ACU fabrics.
After flame-retardant treating under identical conditions, the fabrics were boiled for 24 hours (to simulate 100 industrial laundry cycles) and the phosphorus content of the core-spun fabrics compared to the 100% cotton fabric.
The fabrics were then tested for Vertical Flammability (ASTM D6413) in the machine directions and found to self-extinguish.

TABLE 3

Vertical Flammability Results

		%
		Phosphorus
		Initial/
	Finished	After	After	Char
	Weight,	24-hour	Flame,	Length,
Fabric	osy	boil	sec.	in.

Example 1: 265 denier air jet	6.6	2.8/2.8	0	7.0
core-spun yarn 38%/62%
nylon 6 filament core/carded
cotton wrapper
Example 2: 265 denier air jet	6.8	3.2/2.7	0	6.0
core-spun yarn 57%/43%
polyester filament core/carded
cotton wrapper
Comparative Example 1: 265	7.8	2.6/2.6	0	4.0
denier Open End spun 100%
Carded Cotton

Despite having about 40 to about 60 percent synthetic fiber, the core-spun fabrics retained as much phosphorous as the 100% cotton fabric.
For core-spun fabrics which self-extinguish, the char length can be reduced by incorporating a minor amount of high char strength staple fibers into the sheath. Examples of such fibers include poly-para-phenylene terephthalamide (Kevlar® or Twaron® ‘para-aramid’), polybenzimidazole (‘PBI’), poly-phenylenebenzobisoxazole (‘PBO’), and polyimide (‘P-84’).

Example 3, 4, and 5 (Improved Fabrics)

Air jet core-spun yarns of 20/1 Ne (265 denier) were produced from 100 denier recycled nylon 6 filament core yarn and cotton or cotton/para-aramid sheath. The air jet core-spun yarn was knit into socks and the socks were treated using a THP FR cotton chemistry. The socks weighed approximately 6 ounces per square yard.
Table 4 compares the vertical flammability char lengths of current commercial fabrics (Comparative Examples 5, 6, 7, and 8) to core yarn fabrics of the present examples. By comparing Fabrics 3, 4, and 5 it is shown that three percent para-aramid fiber can reduce the fabric char length below four inches and not reduce the important yarn breaking elongation and yarn tensile factor which influence fabric toughness and durability.

TABLE 4

Yarn Tensile and Fabric Flammability Table

			%
		Yarn	Yarn	Tensile	After	Char
	Yarn	Tenacity,	Elon-	Factor	flame,	Length,
	Blend	g/d	gation	(TE^0.5)	sec	in

Com-
parative
Examples
of
Current
Fabrics
Comp. 5	50/50	2.11	13.4	7.7	>30	Entire
	NY₆₆/CT					Length
	(Staple)
	‘BDU’
Comp. 6	Defender	2.24	7.7	6.2	0	2.75
	M
	(Staple)
	‘ACU’
Comp. 7	88/12	1.79	8.3	5.1	0	3.50
	FRCT
	(Staple)
Comp. 8	100%	1.29	7.2	3.5	0	3.5
	cotton
Examples
of
Improved
Fabrics
3	38/62 FR	2.00	24.2	9.8	0*	7.0*
	NY₆/CT
	(NY₆
	Filament)
4	38/56/6	1.33	12.8	4.8	0*	3.0*
	FR
	NY₆/CT/
	Kevlar ®
	(NY₆
	Filament)
5	38/59/3	1.93	25.5	9.7	0*	3.5*
	FR
	NY₆/CT/
	Kevlar ®
	(NY₆
	Filament)

*After boiling for 24 hours which simulates 100 industrial launderings. Nominal fabric weight 6 osy. The yarn in Example 5 was selected for woven fabric evaluation in Example 6.

Example 6

The 20/1 Ne (265 denier) yarn of Example 5, above, was woven into a rip-stop fabric. After weaving and flame retardant finishing, the fabric was tested and the following properties measured:

TABLE 5

Test	Test Method	Result

Weight, ounces/yd²(grams/m²)	ASTM D3776	5.6 (190)
Thickness, in.	ASTM D1777	0.026
Thread count per inch (Warp × Filling)	ASTM D3775	86 × 56
Grab Tensile Strength, lbs. (W × F)	ASTM D5034	161 × 108
Grab Tensile Breaking Elongation,		49 × 42
% (W × F)
Elmendorf Tear Strength, lbs (W × F)	ASTM D1922	9.5 × 7.4
% Laundry Shrinkage (5 cycles @ 140° F.),	AATCC #124	2.7 × 1.9
% (W × F)
Air Permeability, Cubic feet per minute/ft²	ASTM D737	21.6
Vertical flammability, Warp	ASTM D6413
After Flame, sec		0
Char Length, in.		3.7

FIG. 5 shows the fabric of Example 6 for Taber Abrasion Comparison (1000 cycles, 500 gram weight, CS-10 abrasion wheel). The fabric is composed of 38/59/3 Nylon 6 filament core/carded cotton/para-aramid (5.6 oz/yd²rip-stop woven fabric; FR treated only). The fabric exhibited a color change (residue from testing printed fabrics), but no thread breaks or pilling.
Fabric properties demonstrated herein compare favorably in cost and durability to commercial flame resistant fabrics such as Defender Mused in the Army's Advanced Combat Uniform (ACU) and FR-treated cotton fabrics used in civilian thermal protective workwear.
Tables 6, 7, and 8 display data for comparative woven fabrics:

TABLE 6

Flame-Retardant Combat Uniform Fabric (‘FR ACU’)
(65/25/10 Flame-Retardant rayon/p-aramid/nylon 6,6)
GL_PD-07-12: Purchase Description Cloth, Flame Resistance

Property	Requirement

Weight, oz/yd²(ASTM D3776)
Maximum	5.5
Minimum	8.5
Yarns per linear inch (minimum)
(ASTM D3775)
Warp	70
Filling	60
Breaking Strength, pounds (minimum)
(ASTM D5034-Grab)
Warp	100
Filling	80
Tearing Strength, pounds (minimum)
(ASTM D1922-Elmendorf)
Warp	4.0
Filling	4.0
Air Permeability, cfm/ft²(minimum)	10.0
Flame Resistance, Warp and Filling
(ASTM 6413-Vertical) Initial
After Flame, sec. (maximum)	2.0
After Glow, sec (maximum)	25.0
Char Length, sec. (maximum)	4.5
After Laundering
After Flame, sec. (maximum)	2.0
After Glow, sec (maximum)	25.0
Char Length, sec. (maximum)	4.5

TABLE 7

Military Combat Uniform Fabric (‘NYCO ACU’)
(50/50 High Tenacity Staple Nylon 6,6/combed cotton)

	Property	Requirement

	Weight, oz. yd²(ASTM D3776)
	Maximum	6.0
	Minimum	7.0
	Yarns per inch (minimum) (ASTM D3775)
	Warp	104
	Filling	52
	Breaking Strength, pounds (minimum)
	(ASTM D5034-Grab)
	Warp	200
	Filling	90
	Tearing Strength, pounds (minimum)
	(ASTM D1922-Elmendorf)
	Warp	7.0
	Filling	5.0
	Air Permeability, cfm/ft²(minimum)	15.0
	(ASTM D737)

TABLE 8

Flame Resistant Cotton Fabric Properties
(7.5 oz/yd²88/12 cotton/nylon 6,6)

	Property	Result

	Weight, (oz/yd²)	7.6
	Yarns per inch (Warp × Filling)	92 × 48
	Breaking Strength, pounds (ASTM D5034-Grab)
	Warp	117
	Filling	70
	Tearing Strength, pounds (ASTM-Elmendorf)
	Warp	8.2
	Filling	6.6
	Flame Resistance, Warp and Filling
	(ASTM 6413-Vertical)
	After Flame, sec.	0.5
	Char Length, inches	3.7

Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are intended to be covered by the following claims.

Claims

What is claimed:

1. A fabric, comprising an air jet core-spun yarn comprising a core composed of continuous filament thermoplastic yarns and a sheath composed of cellulose staple wrapper fibers, wherein the fabric is treated with a flame-retardant compound.

2. The fabric according to claim 1, wherein the continuous filament thermoplastic core yarn comprises a flame-retardant monomer or flame-retardant additive.

3. The fabric according to claim 1, wherein a portion of the cellulose staple wrapper fibers of the sheath are replaced by synthetic non-thermoplastic, flame resistant staple fibers.

4. The fabric according to claim 3, wherein the synthetic non-thermoplastic, flame-retardant staple fibers may be selected from the group comprising meta- and para-aramids, polybenzimidazole, polybenzoxazole, novoloid, oxidized polyacrylonitrile, polyoxadiazole, polyacrylate, modacrylic, melamine, polyimide, or combination thereof.

5. The fabric according to claim 3, wherein the cellulose staple wrapper fibers comprise less than 10% of an inherently flame resistant non-thermoplastic staple fiber

6. The fabric according to claim 1, wherein the flame retardant compound is a phosphorous-based flame-retardant compound.

7. The fabric according to claim 1, wherein the flame-retardant compound is a pentavalent tetrakis hydroxymethyl phosphonium (THP) salt compound.

8. The fabric according to claim 1, wherein the fabric self-extinguishes when tested using test method ASTM D6413: Standard Test Method for Flame Resistance of Textiles (Vertical Test).

9. A fabric, comprising an air jet core-spun yarn comprising a core composed of continuous filament thermoplastic yarns and a sheath composed of cellulose-rich staple wrapper fibers, wherein the fabric is treated with a flame-retardant compound.

10. The fabric according to claim 9, wherein the continuous filament thermoplastic core yarn comprises a flame-retardant monomer or flame-retardant additive.

11. The fabric according to claim 9, wherein the cellulose-rich staple wrapper fibers are composed of cellulose and synthetic non-thermoplastic, flame resistant staple fibers.

12. The fabric according to claim 11, wherein the synthetic non-thermoplastic, flame-retardant staple fibers may be selected from the group comprising meta- and para-aramids, polybenzimidazole, polybenzoxazole, novoloid, oxidized polyacrylonitrile, polyoxadiazole, polyacrylate, modacrylic, melamine, polyimide, or combination thereof.

13. The fabric according to claim 11, wherein the cellulose-rich staple wrapper fibers comprise less than 10% of an inherently flame resistant non-thermoplastic staple fiber.

14. The fabric according to claim 9, wherein the flame-retardant compound is a phosphorous-based flame-retardant compound.

15. The fabric according to claim 9, wherein the flame-retardant compound is a pentavalent tetrakis hydroxymethyl phosphonium (THP) salt compound.

16. The fabric according to claim 9, wherein the fabric self-extinguishes when tested using test method ASTM D6413: Standard Test Method for Flame Resistance of Textiles (Vertical Test).