Patent Publication Number: US-6210799-B1

Title: Industrial yarn PA 6.6 with little cotton waste

Description:
The present invention relates to a PA 6,6 industrial yarn consisting of filaments having a total linear density of 900 to 2100 dtex and produced by melt-spinning and drawing of polyamide-6,6 having a pellet viscosity RV &gt;75 at a winding speed v sp  which has to meet the following conditions: 
     
       
           v   sp =( Ft   o   /Ft   x ) 3 *v spo , where Ft=tenacity, Ft o =84  cN/tex , Ft x =eff Ft in cN/tex and v spo =2750 m/min  (1)  
       
     
     in the presence of water, and also to a process for producing a low-defect industrial yarn. 
     As well as its serimetry, its level of defects is a significant quality factor of an industrial yarn. At winding speeds of more than 2750 m/min, polyamide industrial yarns generally have an excessively high defect level of the order of more than 1.5 defects per km. To reduce defects, it was hitherto necessary to reduce the spinning speed, which entails reduced productivity. It has now been found that the defect level depends not only on the spinning and winding speed but also, strongly, on the moisture content of the polyamide polymer fed into the extruder. 
     It is known to moisten PA 66 polymer ahead of the extruder or in the melt. In each case the purpose is to ensure consistent melt quality. The moisture is added in controlled fashion via moist N 2  or as direct metered addition of water, for which the melt pressure ahead of the spinning pump can be utilized as control variable. 
     EP-B-0 092 898 discloses controlling physical properties of meltable polyamides by depolymerization by means of moisture. In said reference, water is added to keep the viscosity constant. The object is considered to be to produce a polymer melt having constant physical properties. 
     The present invention has as its object to provide a PA 66 industrial yarns having a tenacity of at least 84 cN/tex, very rapid processing and a minimum of defects. 
     This object is achieved according to the invention when the PA 6,6 filament combines a tenacity of &gt;84 cN/tex and with less than 1.5 defects/km. 
     In a variant featuring a pellet viscosity RV &gt;90, a moisture content &gt;0.06% and a tenacity Ft x &gt;90 cN/tex, it is possible to obtain at a spinning speed v spo  greater than the spinning speed calculated by the formula (1) an industrial yarn having a high linear density and a surprisingly low number of defects conforming to the following formula: 
     
       
         defects  F 1&lt;( Ft   x   /Ft   o ) 3 * v spx   /v   spo   *Tt   x   /Tt   o , where  (2)  
       
     
     Tt o  is a linear density of 940 [lacuna] and Tt x  is the linear density at the winding speed v spx . 
     The advantage is a low defect level which, if dry PA 66 polymer pellets are used, can otherwise only be achieved at low spinning-drawing speeds. 
     It is particularly advantageous for the water content of the polymer pellets ahead of the extruder to be in the range of 0.04-0.14% by weight, especially 0.06-0.12% by weight. 
    
    
     The invention will now be more particularly described with reference to an example. 
     A polyamide-6,6 polymer post-condensed to a relative viscosity (RV) of about 93 was admixed ahead of the extruder with varying quantities of water so that the resulting total moisture content of the polymer varies between 0.16 and 0.02%. The winding speed was 2750 m/min in all runs. The throughput was a constant 46 kg/h. The tenacity Ft was likewise constant at 85 cN/tex. 
     The relative pellet viscosity was measured in 90% strength formic acid using ASTM method D 789-81. 
     Defects were measured using a Warpstop 450 from Protechna, FRG. Each test was carried out with 24 packages. 
     The results are depicted in FIG.  1 . FIG. 1 shows the plot of the number of defects against the water content of the PA 6,6 polymer pellets ahead of melting. Curve 1 demonstrates the dependence for a linear density of 940 dtex with a pellet RV of 93 and a throughput of 46 kg/h; curve 2 demonstrates the defect trajectory under otherwise identical conditions for a linear density of 1400 dtex, whose curve trajectory is broadly similar. 
     As is further evident from FIG. 1, the defect level initially decreases dramatically with increasing water content in the feed polymer. At a water content of 0.02%, the moisture content ex dryer, a winding speed of 2750 m/min produces defect numbers of around 5 defects per kilometer. At a water content of about 0.09%, surprisingly, minimum values are achieved in relation to defects. As the water content continues to increase, defects increase again sharply. 
     Further examples are recited in the following Table I. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                   
                 Linear 
                 Winding 
                   
                   
                   
               
               
                   
                 density 
                 speed Vsp 
                 Tenacity Ft 
                 Number of 
                 H 2 O 
               
               
                 No. 
                 [dtex] 
                 [m/min] 
                 [cN/tex] 
                 defects/km 
                 [%] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 1880 
                 2260 
                 92.6 
                 1.7 
                 0.08 
               
               
                 2 
                 1400 
                 2040 
                 94.2 
                 1.6 
                 0.08 
               
               
                 3 
                 2100 
                 2050 
                 92.7 
                 2.0 
                 0.08 
               
               
                 4 
                 1400 
                 2750 
                 84 
                  3.5* 
                 0.02 
               
               
                 5 
                 1400 
                 2750 
                 84 
                 0.7 
                 0.07 
               
               
                   
               
               
                 *without addition of water  
               
            
           
         
       
     
     The yarns recited in Examples 1-3 are known as super high tenacity (SHT) yarns, whereas the yarns recited in Examples 4 and 5 are known as HT yarns. In each case, a polymer having a relative pellet viscosity RV 93 was spun. 
     It is evident that less than 1.5 defects per km are achieved at a water content of 0.04 to 0.14 and less than 1 defect per km is achieved at a water content of 0.08 to 0.11. The polyamide yarn of the invention has half the defect level of the prior art. The yarn is preferably suitable for producing cord fabrics for use in rubber, for example for transport belts, drive belts and automobile tyres.