Dimensionally stable polyester yarn for high tenacity treated cords

Abstract

Polyethylene terephthalate yarn is prepared by spinning under high stress conditions in the transition region between oriented-amorphous and oriented-crystalline undrawn yarns by selection of process parameters to form an undrawn yarn that is a crystalline, partially oriented yarn with a crystallinity of 3 to 15 percent and a melting point elevation of 2 to 10° C. The spun yarn is then hot drawn to a total draw ratio between 1.5/1 and 2.5/1 with the resulting properties: (A) a terminal modulus of at least 20 g/d, (B) a dimensional stability defined by E 4.5 +FS<13.5 percent, (C) a tenacity of at least 7 grams per denier, (D) a melting point elevation of 9 to 14° C., and (E) an amorphous orientation function of less than 0.75. The resulting treated tire cord provides high tenacity in combination with improved dimensional stability.

What is claimed is:  
     
         1 . A process for production of a drawn polyethylene terephthalate yarn which translates to a high tenacity dimensionally stable tire cord, comprising: 
 (A) extruding a molten melt-spinnable polyethylene terephthalate having an intrinsic viscosity of 0.8 of greater through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn,    (B) solidifying the spun yarn gradually by passing the yarn through a solidification zone which comprises (a) a retarded cooling zone and (b) a cooling zone adjacent said retarded cooling zone wherein said yarn is rapidly cooled and solidified in a blown air atmosphere,    (C) withdrawing the solidified yarn at sufficient speed to form a crystalline, partially oriented yarn with a crystallinity of 3 to 15% and a melting point elevation of 2 to 10° C., and    (D) hot drawing the yarn to a total draw ratio between 1.5/1 and 2.5/1.    
     
     
         2 . The process of  claim 1  wherein the melting point elevation is 2 to 5° C.  
     
     
         3 . The process of  claim 1  wherein φ½ is at least 26°.  
     
     
         4 . The process of  claim 1  wherein the steps A, B, C, and D are performed in a continuous integrated spin-draw process.  
     
     
         5 . The process of  claim 4  wherein the melting point elevation is 2 to 5° C.  
     
     
         6 . The process of  claim 4  wherein φ½ is at least 26°.  
     
     
         7 . A drawn polyethylene terephthalate multifilament yarn having the following combination of properties: 
 (A) a terminal modulus of at least 20 g/d,    (B) a dimensional stability defined by E 4.5 +FS<13.5%,    (C) a tenacity of at least 7 grams/denier,    (D) a melting point elevation of 9 to 14° C., and    (E) an amorphous orientation function of less than 0.75.    
     
     
         8 . The drawn yarn of  claim 7  wherein the melting point elevation is 9-11° C.  
     
     
         9 . The drawn yarn of  claim 7  which has the melting point characteristic defined by Z* greater than or equal to 1.3.  
     
     
         10 . Dimensionally stable yarns of  claim 7  which have the melting characteristic defined by Z greater than or equal to 1.7.  
     
     
         11 . The drawn yarn of  claim 7  which has an effective crosslink density (N) between 10×10 21  and 20×10 21  crosslinks per cubic centimeter.  
     
     
         12 . A high tenacity, dimensionally stable treated tire cord prepared from the yarn of  claim 7 .  
     
     
         13 . A rubber article incorporating as reinforcing material the high tenacity, dimensionally stable cord of  claim 12 .  
     
     
         14 . A composite incorporating as reinforcing material the drawn yarn of  claim 7 .  
     
     
         15 . A drawn polyethylene terephthalate yarn which, when twisted into an 8×8 twists per inch 1000 denier 3-end greige cord and tensilized by the sequence of dipping into a first blocked diisocyanate dipping solution, stretching at 440° F. (227° C.) for 40 seconds, dipping into a second resourcinol-formaldehyde-latex dipping solution, and relaxing at 440° F. (227° C.) for 60 seconds, provides the following treated cord property combinations: 
 (a) a dimensional stability defined by LASE-5 of at least 2.3 grams per denier at 4 percent free shrinkage, and  
 (b) a tenacity of at least 7.0 grams per denier at 4 percent free shrinkage, said dimensional stability and said tenacity being determined by interpolation of LASE-5 versus free shrinkage data to 4 percent free shrinkage.  
 
     
     
         16 . The yarn of  claim 15  which provides a treated cord tenacity of at least 7.4 grams per denier.  
     
     
         17 . A process for the production of a drawn polyethylene terephthalate yarn which translates to a high tenacity dimensionally stable tire cord comprising: 
 (a) extruding a molten melt-spinnable polyethylene terephthalate having an intrinsic viscosity of at least about 0.8 through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn;    (b) solidifying gradually said molten spun yarn by passing said molten spun yarn through a solidification zone which comprises (i) a retarded cooling zone and (ii) a cooling zone adjacent said retarded cooling zone where in said cooling zone, said yarn is rapidly cooled and solidified in a gaseous atmosphere;    (c) withdrawing at sufficient speed said solidified yarn from said solidification zone to form a crystalline partially oriented yarn; and    (d) hot drawing said crystalline partially oriented yarn at a total draw ratio between about 1.5/1 and about 2.5/1 to produce a drawn yarn having an effective crosslink density (N) between about 10×10 21  and about 20×10 21  crosslinks per cubic centimeter.    
     
     
         18 . The process of  claim 17  wherein in said step (d), a draw point localizing jet is used.  
     
     
         19 . The process of  claim 17  wherein in said step (b), said retarded cooling zone comprises a gaseous atmosphere heated at a temperature of 150° C. to 450° C.  
     
     
         20 . The process of  claim 1   7  wherein in said step (b), said retarded cooling zone comprises a heated sleeve.  
     
     
         21 . The process of claim  20  wherein said heated sleeve is at a temperature of 220° C. to 300° C.