Method and system for improving creep performance in elastic applications

Abstract

A method and system of using a polyolefin-based, hot melt adhesive improves creep performance of elastic strands adhered to another substrate. Some deflection, greater than 1°, of the exit angle formed by a line normal to the axis of a neutrally-positioned applicator and the elastic strand extending from the applicator is introduced. Preferably, deflection of the entrance angle is also introduced and a head tilt angle is also provided. The use of deflection improves creep performance or allows for a reduced amount of adhesive to be used to achieve the same or similar creep performance. The elastic strands may be used to form a leg cuff in personal care products, such as diapers, and the substrate to which they are applied could be a polyethylene film or non-woven materials.

What is claimed: 
     
         1 . A method of using a polyolefin-based, hot melt adhesive comprising the steps of:
 applying the adhesive in a molten state with an applicator to a primary substrate comprising an elastic strand, wherein an exit angle defined by a line normal to the axis of a neutrally-positioned applicator and the elastic strand extending from the applicator in the downstream direction of travel is at least 1°; and   bonding a secondary substrate to the first substrate by contacting the secondary substrate with the adhesive.   
     
     
         2 . The method of  claim 1 , wherein the exit angle is between 1° and 20°. 
     
     
         3 . The method of  claim 2 , wherein the exit angle is between 2° and 10°. 
     
     
         4 . The method of  claim 3 , wherein the exit angle is between 2.5° and 7.5°. 
     
     
         5 . The method of  claim 1 , wherein, during the applying step, an entrance angle defined by a line normal to the axis of a neutrally-positioned applicator and the elastic strand extending from the applicator in the upstream direction of travel is at least 1°. 
     
     
         6 . The method of  claim 5 , wherein the entrance angle is between 1° and 20°. 
     
     
         7 . The method of  claim 6 , wherein the entrance angle is between 2° and 10°. 
     
     
         8 . The method of  claim 7 , wherein the entrance angle is between 2.5° and 7.5°. 
     
     
         9 . The method of  claim 1 , wherein, during the applying step, a head tilt angle defined by a line tangent to the point of contact of the strand and the applicator tip and an axial line extending along the direction of travel of the adhesive as it exits the applicator is between 1° and 30° or is between 91° and 120°. 
     
     
         10 . The method of  claim 9 , wherein the head tilt angle is between 70° and 88° . 
     
     
         11 . The method of  claim 10 , wherein the head tilt angle is between 80° and 88° . 
     
     
         12 . The method of  claim 1 , wherein the adhesive comprises a polymer component, a plasticizer, a tackifying resin and an antioxidant package, and the polymer component comprises a polyolefin. 
     
     
         13 . The method of  claim 12 , wherein the polymer component comprises at least 50% by weight of said polyolefin. 
     
     
         14 . The method of  claim 1 , wherein the adhesive comprises a polymer component, a plasticizer, a tackifying resin and an antioxidant package, and the polymer component consists essentially of a polyolefin or a blend of polyolefins. 
     
     
         15 . A system for applying a polyolefin-based, hot melt adhesive to a primary substrate comprising an elastic strand comprising:
 an applicator having an applicator tip adapted to contact a linearly moving primary substrate comprising an elastic strand and adapted to apply the adhesive to the primary substrate; and   an outlet roller or idler disposed above the vertical position of the applicator tip to provide an exit angle defined by a line normal to the axis of a neutrally-positioned applicator and the elastic strand extending from the applicator in the downstream direction of travel of at least 1°.   
     
     
         16 . The system of  claim 15 , wherein the exit angle is between 2° and 10°. 
     
     
         17 . The system of  claim 15  further comprising an inlet roller or idler configured above the vertical position of the applicator tip to provide an entrance angle defined by a line normal to the axis of a neutrally-positioned applicator and the elastic strand extending from the applicator in the upstream direction travel of at least 1°. 
     
     
         18 . The system of  claim 17 , wherein the entrance angle is between 2° and 10°. 
     
     
         19 . The system of  claim 15 , wherein the applicator is configured to provide a head tilt angle defined by a line tangent to the point of contact of the strand and the applicator tip and an axial line extending along the direction of travel of the adhesive as it exits the applicator of between 60° and 89° or between 91° and 120°. 
     
     
         20 . The system of  claim 19 , wherein applicator is configured to provide a head tilt angle of between 70° and 88°.