Thermal bonding of nonwoven textiles containing cellulose acetate fibers

Abstract

Nonwoven fabrics and textiles containing cellulose ester fibers particularly cellulose acetate fibers are thermally bonded. An aqueous plasticizing solution is applied to the surface of a nonwoven web and thereafter the web is thermally bonded to create a thermally bonded nonwoven textile. Alternatively, water can be applied to the dry surface of a nonwoven web containing organic plasticizer treated cellulose ester fibers to create the moistened nonwoven web and thereafter thermally bonding the moistened nonwoven web to make a thermally bonded nonwoven textile. The fabrics exhibit an increase in tensile strength and toughness greater than the individual contributions of water and plasticizer alone and greater than the additive contributions of water and plasticizer alone.

What we claim is: 
     
         1 . A process for making a fabric comprising:
 a. providing a nonwoven web comprising cellulose ester fibers, and   b. thermally bonding said nonwoven web at a thermal bonding temperature to make a fabric,   wherein at least a portion of the cellulose ester fibers have a native Tg that is greater than the thermal bonding temperature, and said process is conducted in the absence of:   (i) adding adhesives or binder onto said nonwoven web; and   (ii) using solvents for the binder fibers.   
     
     
         2 . The process of  claim 1 , comprising a nonwoven web obtained from dry laid or spun bond fibers. 
     
     
         3 . The process of  claim 1 , comprising a nonwoven web comprising base fibers and binder fibers, said binder fibers comprising monocomponent fibers comprising cellulose ester fibers, wherein at least 90 wt. % of the cellulose ester fibers are solvent spun monocomponent fibers, based on the weight of the fibers containing cellulose ester polymer. 
     
     
         4 . The process of  claim 1 , comprising a nonwoven web that does not contain any binder powder, binder particles, or binder films or sheets. 
     
     
         5 . The process of  claim 1 , comprising a nonwoven web comprising cellulose ester fibers that are not coated or otherwise do not contain a dry plasticizer or are coated or otherwise contain a dry plasticizer in an amount of not more than 2 wt. % FOY. 
     
     
         6 . The process of  claim 1 , comprising a nonwoven web comprising binder fibers, said binder fibers comprising CE fibers having one or more of the following features:
 a) a crimp frequency of 7 to 30 CP, or 7 to 25 CPI, or 7 to 23 CPI, or 7 to 20 CPI, or 8 to 30 CPI, or 8 to 27 CPI, or 8 to 25 CPI, or 8 to 23 CPI, or 8 to 20 CPI crimps per inch, or   b) a crimp amplitude of at least 1.0 mm, or   c) an average effective length that is not more than 75% of the actual length, or   d) a retained tenacity of at least 80%, or   e) a CPI:DPF of 5:1 to 14:1, or 7:1 to 12:1, or   f) any combination of two or more of the above.   
     
     
         7 . A process for making a fabric comprising:
 a. providing a nonwoven web comprised of base fibers and binder fibers, and   b. applying either (i) water or (ii) water and a plasticizer to the nonwoven web to produce a wetted plasticized nonwoven web, provided that water and a plasticizer are applied to the nonwoven web if the binder fibers do not contain a plasticizer; and   c. thermally bonding the wetted plasticized nonwoven web to produce said fabric.   
     
     
         8 . The process of  claim 7 , comprising applying water and a plasticizer to the nonwoven web before thermal bonding, optionally as a solution. 
     
     
         9 . The process of  claim 7 , comprising applying water and a plasticizer to the nonwoven web in a spray or by a coating method comprising a squeeze, lick, or kiss roll coating method. 
     
     
         10 . The process of  claim 7 , comprising thermally bonding a water wetted plasticized nonwoven web obtained from a nonwoven web comprising CE fibers coated with or containing a dry plasticizer, wherein water is applied to said web to create a wetted plasticized nonwoven web. 
     
     
         11 . The process of  claim 7 , comprising thermally bonding a water wetted plasticized nonwoven web obtained from a nonwoven web, wherein an aqueous solution of plasticizer is continuously applied before, during, or after hydroentangling the nonwoven web. 
     
     
         12 . The process of  claim 7 , comprising applying water to the nonwoven web before thermal bonding to produce a wetted plasticized nonwoven web having a moisture content, or a moisture content as introduced to an element for thermal bonding, of at least 10 wt. %, based on the weight of the wetted plasticized nonwoven web. 
     
     
         13 . The process of  claim 7 , comprising thermally bonding a wetted plasticized nonwoven web, said nonwoven web not being solvent fused, hydroentangled, or stitched. 
     
     
         14 . The process of  claim 7 , comprising thermally bonding a wetted plasticized nonwoven web, said thermal bonding process comprising point bonding. 
     
     
         15 . The process of  claim 7 , comprising thermally bonding, at a line speed and nip force, a wetted plasticized nonwoven web obtained from a nonwoven web, said thermal bonding process comprising one or more calendar rolls, and the upper temperature limit of at least one calendar roll, or on all calendar rolls, is below the native melting point temperature of CE fibers in the nonwoven web, or in the wetted plasticized nonwoven web at the line speed and nip forces applied. 
     
     
         16 . The process of  claim 7 , comprising thermally bonding a wetted plasticized nonwoven web obtained from a nonwoven web comprising CE fibers, said thermal bonding process comprising one or more calendar rolls, and the temperature of at least one calendar roll, or the first calendar roll effective to thermally bond the wetted plasticized nonwoven web, or on the majority of calendar rolls, or on all calendar rolls, (i) is below the temperature at which the CE fibers in the nonwoven web, or alternatively in the wetted plasticized nonwoven web, would reach their native Tg at the line speed and nip forces applied, or (ii) are below the native Tg of the CE fibers in the nonwoven web, or alternatively in the wetted plasticized nonwoven web, by at least 5° C., or at least 8° C., or at least 10° C., or at least 12° C., or at least 15° C., or at least 18° C., or at least 20° C., or at least 22° C., or at least 24° C., or at least 26° C., or at least 28° C., or at least 30° C., and in each case, the calendar roll at said temperature also exceeds the Tg of the CE fibers in their plasticized state. 
     
     
         17 . A fabric comprising cellulose ester fibers, said fabric having a basis weight of not more than 35 gsm and destructive thermally fused bonds, wherein the fabric is obtained by thermally bonding a nonwoven web in the absence of adhesives, hydroentaglement, solvents for fusion, or thermoplastic binder powders. 
     
     
         18 . The fabric of  claim 17 , comprising thermally bonding a wetted plasticized nonwoven web obtained from a nonwoven web, said thermal bonding process comprising point bonding to produce a fabric having at least 10 points per square inch. 
     
     
         19 . The fabric of  claim 17 , wherein at least 80% of the bonds are destructive bonds, and said wetted plasticized nonwoven web is not hydroentangled and does not contain binder powders, and the fabric does not contain adhesives and is not laminated with a thermoplastic film. 
     
     
         20 . The fabric of  claim 17 , wherein the ratio of the cumulative surface area of unbonded portions to the cumulative surface area of bonded portions is at least 2:1, and the thickness of unbonded portions are greater than the thickness of the bonded portions. 
     
     
         21 . The fabric of  claim 17 , wherein said fabric is ultrasonic welded. 
     
     
         22 . The fabric of  claim 17 , wherein said fabric comprises wipes, filters, non-medical garments such as shirts or pants or jackets or socks or undergarments, geotextiles, roofing felts, insoles, paper maker felts, fiberfill webs, needle felt including floor coverings, furniture fill and fabric, sanitary products, medical products such as wound dressings or bandages or sterilization wraps or medical bedding, medical garments such as surgical caps and hoods or face masks or drapes or surgical gowns or caps, automobile interior fabric and cushion fill, bedding (comforters, mattresses), protective clothes, moisture permeable heat retention films and sheets for agriculture/crop protection, carpet backing webs, packing material, wall paper fabrics, art paper-fabric, clothing including interlinings, construction insulation webs, coverstock, upholstery, food coverings, tea bags, personal care products such as diapers or adult incontinence products or feminine hygiene products or training pants, protective covers for vehicles or outdoor equipment, outdoor table covers, or other outdoor fabric covers such as tarpaulins or canopies or tents or agricultural fabrics. 
     
     
         23 . The fabric of  claim 17 , said fabric having:
 a. a break force tensile strength greater than the combined increase in tensile strength obtainable by the individual use of water and plasticizer, as measured by NWSP 110.4.R0 (15) using 25+/−1 mm tensile strip, constant-rate-of-extension (CRE) tensile testing instrument, extension rate of 300 mm/min, and gage length set to 75 mm, or   b. a toughness greater than the combined increase in toughness obtainable by the individual use of water and plasticizer, calculated from break force and elongation measurements taken under NWSP 110.4.R0 (15) using 25+/−1 mm tensile strip, constant-rate-of-extension (CRE) tensile testing instrument, extension rate of 300 mm/min, and gage length set to 75 mm.   
     
     
         24 . The fabric of  claim 17 , said fabric having:
 a. a ratio of machine direction tensile break force in grams to basis weight of the fabric or nonwoven web used to make the fabric in gsm, of at least 40 g/gsm, or   b. a ratio of toughness to basis weight of the fabric or nonwoven web used to make the fabric in gsm, of at least 100 g/gsm, or at least 175 g/gsm.