Patent Publication Number: US-2019169793-A1

Title: Anti-fray formulation for aramid yarns

Description:
FIELD OF THE INVENTION 
     The invention herein pertains to fabric treatments generally, and particularly pertains to a chemical bath formulation of colloidal silica, polyurethane dispersion, and phosphonate chemicals to imbue a fabric formed from the treated aramid yarns with reduced fraying and unraveling characteristics. 
     DESCRIPTION OF THE PRIOR ART AND OBJECTIVES OF THE INVENTION 
     The use of filament yarns over spun yarns is desirable for a wide range of reasons including yarn strength and durability, but one drawback is that by virtue of the comparatively smooth yarn surfaces, fabrics formed from filament yarns typically experience a higher degree of fraying, unraveling, and slipping at the seams when compared to fabric formed from spun yarn species. This drawback inhibits efficient cutting and sewing of articles. Another reason to choose filament yarns over spun yarns is for appearance, sheen, and smoothness of the finished article. As with all synthetic fibers, filament meta-aramid and para-aramid yarns may be chosen over spun versions to accomplish the end use strength, appearance, and thermal goals.” 
     Thus, in view of the problems and disadvantages associated with prior art devices, the present invention was conceived and one of its objectives is to provide a fabric formed from filament yarns that is resistant to fraying, slipping, and/or unraveling. 
     It is another objective of the present invention to provide a fabric formed from meta-aramid filament yarns that is treated with a formulation to reduce fabric fraying, seam slipping, and unraveling. 
     It is still another objective of the present invention to provide a fabric formed from meta-aramid filament yarns that is treated with a chemical formulation to reduce fabric fraying, seam slipping, and unraveling. 
     It is yet another objective of the present invention to provide a textile finishing formulation including colloidal silica. 
     It is a further objective of the present invention to provide a textile finishing formulation including a polyurethane dispersion. 
     It is still a further objective of the present invention to provide a textile finishing formulation including a flame retardant chemical such as phosphonate. 
     It is yet a further objective of the present invention to provide a liquid textile finishing formulation formed at least from colloidal silica, polyurethane dispersion, and phosphonate, that when applied to a woven fabric reduces fabric fraying, seam slipping, and unraveling while adding 5% or less by weight to the fabric. 
     Various other objectives and advantages of the present invention will become apparent to those skilled in the art as a more detailed description is set forth below. 
     SUMMARY OF THE INVENTION 
     The aforesaid and other objectives are realized by providing a textile formulation for woven fabrics formed primarily of meta-aramid filament yarns that results in a resistance to the unraveling, fraying, and slipping of seams typical of fabrics formed from filament yarns. This anti-fray formulation is comprised of colloidal silica, polyurethane dispersion, and phosphonate combined to form a chemical bath in which the woven fabric may be dipped. This formulation adds 2%-5% or less to the dry weight of the woven fabric, and does not impact the beneficial properties of fabrics formed from filament yarns such as structural stability or flame retardancy as judged by vertical flammability testing, but does create a fabric that is more resistant to the unraveling, fraying, and slipping of seams described above. 
     A method of forming an anti-fray woven fabric formed from woven meta-aramid yarns includes the steps of forming a fabric primarily of meta-aramid yarns, providing colloidal silica, polyurethane dispersion, and phosphonate, combining at least the aforementioned chemicals into a chemical bath, and dipping, submerging, or otherwise engaging the fabric with the bath. Excess volume of the chemical bath is compressed away from the fabric substrate with one or more rollers, and the treated fabric is then dried down a tenter frame and cured in an oven. This process, known as a “pad-dry-cure” process, adds 2% or more but 5% or less by weight to the fabric, and the method overall produces a fabric that is resistant to the unraveling, fraying and slipping of seams common in fabrics formed from aramid yarns without inhibiting the beneficial properties of fabrics formed from such yarns, such as structural stability or flame retardancy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic representation of a textile treated with a finishing formulation that reduces yarn fraying, seam slipping, and unraveling compared to conventional textiles. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND OPERATION OF THE INVENTION 
     For a better understanding of the invention and its operation, turning now to the drawings,  FIG. 1  demonstrates a schematic representation of the treatment of a fabric  10  with a finishing formulation  11  formed at least from colloidal silica, polyurethane dispersion, and phosphonate, that when applied to fabric  10  reduces fabric fraying, seam slipping, and unraveling when compared to conventional fabrics. In the preferred embodiment, fabric  10  is a woven textile created in a manner as known in the art formed with filament yarns. By way of example, weavings patterns may include, but are not limited to, plain, flat, twill, and herringbone woven patterns. In an embodiment, these filament yarns are defined by a synthetic material, preferably in the aramid family of materials, and in the most preferred embodiment, the filament yarns are defined by a meta-aramid material selected for its retardancy to fire. While this resistance characteristic is desirable, it is known that the use of meta-aramid filament yarns in the construction of woven textiles results in a loose weave, due at least in part to the smooth surface of the filament yarn compared to spun yarns. It is this loose weave that is at least partially responsible for fabrics formed from aramid yarns being known to fray, unravel, and slip at the seams. For the purposes of this disclosure “slipping of seams” or “seam slippage” is considered a defect consisting of separated yarns occurring when sewn fabrics pull apart at the seams. Seam slippage is more prone to occur in smooth-yam fabrics produced from manufacturing filament yarns than those fabrics formed from spun yarns. 
     To combat the perceived deficiencies of utilizing a meta-aramid yarn in the fabric formation process, a fabric finishing formulation  11  has been developed that does not impact the desirable characteristics of meta-aramid yarns such as flame resistance, but that vastly improves the problem of the loose yarn weave described above. The preferred formulation  11  includes an effective amount of silica, polyurethane, and phosphonate, an effective amount defined as the amount by weight of the respective component necessary to bestow a given textile characteristics sufficient to rate greater than 10 Kgf/cm in the edge comb test, as defined by ASTM D6479. Colloidal silicas (SiO 2  in H 2 O) are typically suspensions of fine amorphous, nonporous, and typically spherical silica particles in a liquid phase (also referred to as an aqueous dispersion). Several commercially available colloidal silicas are known in the art, and it is expected that under the described conditions any one of them may serve the disclosed purpose. In the preferred embodiment, the amount of colloidal silica is between 25 and 90 grams by weight, and more preferably between 50 and approximately 70 grams (+/−1 gram) by weight. This measurement and resulting concentration is based on the final weight of the total formulation bath in making 1 liter (1000 grams) of formulation  11 . While the specific amount by weight of colloidal silica may vary, particularly based on the amount of water involved in the formation of formulation  11 , the preferred embodiment of formulation  11  includes colloidal silica relative to the amount of water in formulation  11  of about 3:50, or about 6% by weight of the bath. 
     The preferred formulation  11  further includes an effective amount of urethane or polyurethane, more preferably a polyurethane dispersion. Embodiments of such aqueous and anionic dispersions may be high molecular weight polyether aliphatic polyurethanes. Numerous polyurethane dispersions are known, and it is expected that under the described conditions any one of them may serve the disclosed purpose. In the preferred embodiment of formulation  11 , the amount of polyurethane by weight is between 80 grams and 120 grams by weight, and more preferably between 90 and approximately 110 grams (+/−1 gram) by weight. Similar to the colloidal silica, this measurement and resulting concentration is based on the final weight of the total formulation bath in making 1 liter (1000 grams) of formulation  11 . While the specific amount by weight of polyurethane dispersion may vary, for example based on the amount of water contained within formulation  11 , the preferred formulation  11  includes polyurethane dispersion relative to the amount of water in formulation  11  of about 1:10, or about 10% by weight of the bath. 
     The preferred formulation  11  also includes an effective amount of phosphonate. Although several phosphonate compounds are known, one preferred embodiment is defined as a halogen-free dimethyl hydroxymethylphosphonate. In the preferred embodiment of formulation  11 , the amount of phosphonate by weight is between 30 and 60 grams by weight, and more preferably approximately 50 grams (+/−1 gram) by weight. Like the colloidal silica and polyurethane, this measurement and resulting concentration is based on the final weight of the total formulation bath in making 1 liter (1000 grams) of formulation  11 . While the specific amount by weight of phosphonate may vary, particularly based on the amount of water involved in the formation of formulation  11 , the preferred formulation  11  includes phosphonate relative to the amount of water in formulation  11  of about 1:20, or about 5% by weight of the bath. 
     In addition to the colloidal silica, polyurethane, and phosphonate, embodiments of formulation  11  may include additional additives for additional or differing characteristics. To render the formulation aqueous, formulation  11  may include one or more predetermined volumes of water, totaling at least 700 grams by weight, between 750 and 850 grams by weight, and preferably about 770 grams by weight. Embodiments of formulation  11  may include a wetting agent, and embodiments of formulation  11  may include such a wetting agent with at least 1.0 gram by weight, and preferably between 1.0 and 1.5 grams by weight. Embodiments of formulation  11  may further include a cross-linking compound for improved efficiency, durability, and resistance of polyurethane dispersions, and embodiments of this cross-linker may be included in formulation  11  between 8 and 18 grams by weight, and more preferably about 13 grams (+/−1 gram) by weight. Embodiments of formulation  11  may also include ammonium hydroxide, and a preferred embodiment of formulation  11  includes ammonium hydroxide between 1.0 gram and 5.0 grams by weight, and preferably about 3.5 grams (+/−1 gram) by weight. All the above measurements and resulting concentrations are based on the final weight of the total formulation bath in making 1 liter (1000 grams) of formulation  11 . 
     A method of forming a textile formed primarily from filament yarns such as meta-aramid yarns that is resistant to the fraying, seam slipping, and unraveling conventionally associated with fabrics woven from filament yarns is also provided. The method includes weaving the filament yarns into a textile, although it should be noted that other methods of fabric formulation are considered within the scope of the instant invention. An effective amount of colloidal silica, polyurethane dispersion, water, wetting agent, and cross-linker are combined with an effective amount of ammonium hydroxide, phosphonate and water. The resulting formulation is stirred to form a chemical bath to which the textile is exposed, for example by submerging therein, dipping, spraying, or the like. An example preparation is demonstrated below as Example 1. 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Water 
                 770 
                 grams 
               
               
                   
                 Ammonium Hydroxide 
                 3.5 
                 grams 
               
               
                   
                 Phosphonate 
                 50 
                 grams 
               
               
                   
                 Wetting agent 
                 1.5 
                 grams 
               
               
                   
                 Polyurethane dispersion 
                 100 
                 grams 
               
               
                   
                 Cross-linking agent 
                 13 
                 grams 
               
               
                   
                 Colloidal silica 
                 60 
                 grams 
               
               
                   
                   
               
            
           
         
       
     
     Example 1 
     The fabric exits the chemical bath and any excess bath volume is compressed away from the fabric substrate with one or more rollers, and the treated fabric is then dried down a tenter frame and cured in an oven in a process known as a “pad-dry-cure” process. Pad roller speed may variable, with pressure between 1.0-3.0 bar, more preferably between 2.0 and 2.5 bar, and the curing may take place within an oven at about 195° C. (+/−5° C.) for 1-2 minutes. The resulting material is resistant to the unraveling, fraying and slipping of seams common in fabrics formed from aramid yarns without inhibiting the beneficial properties of fabrics formed from such yarns, such as structural stability or flame retardancy. Table 1 illustrates that the force necessary to complete the “edge comb” test as mandated by ASTM D6479. This test is performed by a set of pins that penetrate through the fabric, and are pulled toward the edge of the fabric. This is a rake-like action and the amount of force needed to pull away the perpendicular yarns out from the fabric is reported in Kilogram Force/centimeter. 
                                     TABLE 1                       Specimen   Kgf/cm   Average                                                            Untreated   1   2.0   2.2           (Control)   2   1.9               3   2.7           Formulation 11   1   15.2   15.6               2   16.8               3   14.9                        
As clearly illustrated in Table 1, the fabric samples treated with formulation  11  are vastly superior in terms of the force needed to displace the perpendicular yarns relative to the untreated sample.
 
     The illustrations and examples provided herein are for explanatory purposes and are not intended to limit the scope of the appended claims.