Abstract:
A fabric having balanced stress-strain characteristics in the warp and weft directions. A method of processing the fabric includes overfeeding a woven fabric web along a first direction at one or more steps of a treatment process to facilitate crimping of the woven fabric web in the first direction. The overfeeding is indicative of a predetermined differential between a feed rate and a process rate at the one or more steps. The differential is adapted to cause the crimping in the first direction to substantially match a the level of crimping in a second direction.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to the field of fabrics. In particular, the invention relates to a coated textile fabric with substantially similar elongation characteristics in the warp and weft directions.  
         [0002]     Fabric for certain applications, such as airbags for vehicle safety restraint systems, may be required to meet certain stringent requirements. This fabric is typically a woven fabric that may be required to have, for example, a certain elasticity. The elasticity of a fabric can be measured as the elongation of the fabric. It is desirable that the crimp of the fabric be controlled during the manufacturing process so that the resulting fabric has substantially balanced elongation in each direction. Conventional fabrics generally exhibit a higher tensile strength (lower elongation) in the warp direction.  
       SUMMARY OF THE INVENTION  
       [0003]     According to an embodiment of the present invention, a method of treating fabric includes overfeeding a woven fabric web along a first direction at one or more steps of a treatment process to facilitate crimping of the woven fabric web in the first direction. The overfeeding is indicative of a predetermined differential between a feed rate and a process rate at the one or more steps. The differential is adapted to cause the crimping in the first direction to substantially match a desired level relative to a level of crimping in a second direction.  
         [0004]     In a preferred embodiment, the desired level equals the level of crimping in the second direction.  
         [0005]     It is to be understood that both the foregoing general description and the following detailed description are exemplary and exemplary only, and are not restrictive of the invention as claimed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
         [0007]      FIG. 1  illustrates the transformation of a fabric from a non-crimped state before treatment to a crimped state after treatment;  
         [0008]      FIG. 2  illustrates a section of a fabric in its relaxed state (solid lines) and stretched states in each direction (dashed lines);  
         [0009]      FIG. 3  illustrates an apparatus for treating a fabric according to an embodiment of the invention;  
         [0010]      FIG. 4  illustrates an apparatus for treating fabric according to another embodiment of the invention; and  
         [0011]      FIG. 5  illustrates an apparatus for treating fabric according to yet another embodiment of the invention.  
         [0012]      FIG. 6  is a graph of stress strain curves for a prior art fabric.  
         [0013]      FIG. 7  is a graph of stress strain curves for a fabric according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]     Referring to  FIG. 1 , a cross-sectional view of a fabric web  100  is illustrated in its pre-treatment state (fabric web  100   a ) and post-treatment, crimped state (fabric web  100   b ). The treatment process, embodiments of which are described below with reference to  FIGS. 3-5 , may involve coating the fabric with silicone, for example. Preferably, the fabric web is shrunk prior to the treatment process. In this regard, the effects of the treatment process, in addition to the silicone coating, are generally limited to the crimping.  
         [0015]     The fabric web  100   a  is a typical woven fabric formed of longitudinal warp threads  110   a  and lateral weft threads  120   a.  The warp threads  110   a  and the weft threads  120   a  are interlaced to form the fabric web. It will be understood by those skilled in the art that the interlacing of weft and warp threads can be achieved in any number of configurations. Accordingly, the present invention is not limited to any specific configuration.  
         [0016]     Prior to the treatment process, the warp threads  110   a  of the fabric web  100   a  in the relaxed state may interlace a certain density of weft threads  120   a  per unit length of the fabric web. For example, one inch of the fabric web  100   a  may include warp threads  110   a  interlacing one hundred weft threads  120   a.  After the treatment process, the density of weft threads  120   b  interlaced with the warp threads  110   b  in an inch of the fabric web is increased, as illustrated in the fabric web  100   b  in the bottom portion of  FIG. 1 .  
         [0017]      FIG. 2  illustrates a segment of a fabric that has been processed according to an embodiment of the invention. The segment  200  is shown at rest in solid lines. At rest, the segment  200  has a length l  210  and width w  220 . The length l is measured in the direction in which the fabric was processed, for example, in an apparatus such as those illustrated in  FIGS. 3-5 . The “machine direction” or warp direction is indicated by the block arrow  230 . Accordingly, the width w is measured in a “cross-machine direction” or weft direction that is perpendicular to the machine direction.  
         [0018]     The crimp of a fabric is the amount the fabric stretches when a load is applied to one end while the other end is secured. Referring again to  FIG. 2 , when a load is applied in the machine direction, the length stretches to l‘ 210 ’. Similarly, when a corresponding load is applied in the cross-machine direction, the width stretches to w‘ 220 ’. The crimp can be expressed as the percentage of increase in the dimension. For example, the crimp in the machine direction can be expressed as:  
         C   M     =         (       l   ′     -   l     )     l     *   100.         
 
 The crimp in the cross-machine direction can be similarly expressed as:  
         C   x     =         (       w   ′     -   w     )     w     *   100.         
 
         [0019]     Referring now to  FIGS. 3-5 , embodiments of treatment processes according to the invention will be described via description of apparatuses adapted to perform the processes.  FIG. 3  illustrates an apparatus for performing a first embodiment of a treatment process according to the present invention. In this embodiment, a machine  300  is adapted to receive a fabric web  320  from, for example, a roll (not shown). The fabric web  320  is delivered into the machine through a feeding device, such as rollers  310 . The rollers  310  control the rate at which the fabric web  320  is delivered into the machine  300 .  
         [0020]     The fabric web  320  is delivered by the rollers  310  onto a conveyor  330  for transporting the web through the various stages of the machine  300 . The rate of transport of the conveyor  330  may be determined according to the requirements of the different stages of the treatment process. Once on the conveyor  330 , the fabric web  330  is transported to a heat-setting stage  340 . In this stage, the fabric web  320  may be exposed to repeated cycles of heating and cooling. Such heat-setting is well known to those skilled in the art.  
         [0021]     Once the fabric web  320  has been heat set, the conveyor  330  transports the fabric web  320  to a coating stage  350 . A silicone coating is applied to at least one surface of the fabric web at the coating stage  350 . The silicone coating is then cured at a curing stage  360  of the machine  300 .  
         [0022]     The crimp level in the machine direction (left-right in  FIG. 3 ) can be controlled by varying the rate at which the fabric web  320  is delivered to the heat-setting stage  340  of the machine  300 . In this regard, the rollers  310  may overfeed the fabric web  320  to the heat-setting stage  340 . In the embodiment illustrated in  FIG. 3 , overfeed may simply be defined as the differential between the rate at which the rollers  310  deliver the web  320  to the heat-setting stage  340  and the rate at which the web  320  is processed by the heat-setting stage  340 . The rate at which the web  320  is processed is associated with the rate of transport of the conveyor  330 .  
         [0023]     Thus, by overfeeding, the rollers  310  cause compression of the fabric web  320  onto the conveyor  330 , as illustrated in  FIG. 3 , by the sinusoidal appearance of the web  320 . The web  320  in a compressed state is processed through the heat-setting stage, which substantially sets the crimp characteristics of the fabric web  320 . Thereafter, the fabric web  320  is transported through the remaining stages of the treatment process in the compressed state, but the crimp characteristics may not be substantially affected.  
         [0024]     The crimp of the fabric web  320  in the cross-machine direction, C X , is unaffected by the differential between the rate of the rollers  310  and the processing rate of the heat-setting stage  340 . Accordingly, differences between the crimp characteristics in the machine direction, C M , and the crimp characteristics in the cross-machine direction, C X , may be reduced by varying the differential to thereby control the crimp characteristics in the machine direction, C M , as described above.  
         [0025]     The above-described embodiment is suitable for use with a wet fabric web (e.g., a fabric web produced on a water jet loom). If the fabric web is already dry (e.g., a fabric web produced on a rapier or air jet loom), there is no need to pre-dry the fabric web. Thus, the heat-setting stage  340  may be eliminated so that the rollers  310  overfeed the fabric web  320  directly to the coating stage  350 . The silicone coating is applied to at least one surface of the fabric web at the coating stage  350  and is cured at the curing stage  360 , which substantially sets the crimp characteristics of the fabric web  320 .  
         [0026]     In a preferred embodiment, the machine-direction crimp is desired to be identical to the cross-machine-direction crimp.  
         [0027]      FIG. 4  illustrates another apparatus for performing an embodiment of a treatment process according to the present invention. In this embodiment, a machine  400  is adapted to receive a fabric web  420  for delivery into the machine  400  through a feeding device, such as rollers  410 , which places the fabric web  420  onto a conveyor  430 . The fabric web  420  is transported on the conveyor  430  through a dryer stage  440  for preparing the fabric web  420  for coating with silicone, which is performed at the coating stage  450 . The fabric web  420  is transported through the dryer stage  440  and the coating stage  450  substantially with no overfeed. It will be understood by those skilled in the art that, under certain circumstances, some overfeed may be required to accommodate any shrinking that may occur during the dryer stage  440  and/or the coating stage  450 .  
         [0028]     The coated fabric web  420  is then delivered by a second set of rollers  470  onto a second conveyor  480  for transporting the web through a curing stage  460  of the machine  400 . An overfeed differential between the second set of rollers  470  and the second conveyor  480  causes compression of the fabric web  420  as it is processed through the curing stage  460 . The compression is illustrated in  FIG. 4  by the sinusoidal appearance of the web  420 .  
         [0029]     In this embodiment, the crimp level in the machine direction can be controlled by varying the differential between the rate at which the second set of rollers  470  deliver the web  420  to the curing stage  460  and the rate at which the web  420  is processed by the curing stage  460 , which is associated with the rate of transport of the second conveyor  480 .  
         [0030]     Thus, the silicone coating is cured with the web  420  in a compressed state, which substantially sets the crimp characteristics of the fabric web  420 . Again, the crimp of the fabric web  420  in the cross-machine direction, C X , is unaffected by the differential between the rate of the second set of rollers  470  and the processing rate of the curing stage  460 . Accordingly, differences between the crimp characteristics in the machine direction, C M , and the crimp characteristics in the cross-machine direction, C X , may be reduced by varying the differential to thereby control the crimp characteristics in the machine direction, C M , as described above.  
         [0031]     The above-described embodiment is suitable for use with a wet fabric web (e.g., a fabric web produced on a water jet loom). If the fabric web is already dry (e.g., a fabric web produced on a rapier or air jet loom), there is no need to pre-dry the fabric web. Thus, the dryer stage  440  may be eliminated so that the first conveyor  430  transports the fabric web  420  directly to the coating stage  450  substantially with no overfeed. The coated fabric web  420  is then delivered by the second set of rollers  470  onto the second conveyor  480  for transporting the web through the curing stage  460  of the machine  400 . The overfeed differential between the second set of rollers  470  and the second conveyor  480  causes compression of the fabric web  420  as it is processed through the curing stage  460 , which substantially sets the crimp characteristics of the fabric web  420 .  
         [0032]     A third apparatus for performing an embodiment of a treatment process according to the present invention is illustrated in  FIG. 5 . In this embodiment, the crimp characteristics are set during an initial drying stage  540  by processing the fabric web  520  in a compressed state through the drying stage  540 . A machine  500  is adapted to receive a fabric web  520  through a feeding device, such as rollers  510 . The rollers  510  control the rate at which the fabric web  520  is delivered into the machine  500 .  
         [0033]     The fabric web  520  is delivered by the rollers  510  onto a conveyor  530  for transporting the web through a drying stage  540  of the machine  500 . An overfeed differential between the rollers  510  and the conveyor  530  causes compression of the fabric web  520  as it is processed through the drying stage  540 . The compression is illustrated in  FIG. 5  by the sinusoidal appearance of the web  520 .  
         [0034]     In this embodiment, the crimp level in the machine direction can be controlled by varying the differential between the rate at which the rollers  510  deliver the web  520  to the drying stage  540  and the rate at which the web  520  is processed by the drying stage  540 , which is associated with the rate of transport of the conveyor  530 .  
         [0035]     The conveyor  530  then transports the fabric web  520  to a coating stage  550 . The silicone coating is then cured through a heat-set process at a heat setting stage  560 .  
         [0036]     As in the previous embodiments, the crimp of the fabric web  520  in the cross-machine direction, C X , is unaffected by the differential between the rate of the rollers  510  and the processing rate of the drying stage  540 . Accordingly, differences between the crimp characteristics in the machine direction, C M , and the crimp characteristics in the cross-machine direction, C X , may be reduced by varying the differential to thereby control the crimp characteristics in the machine direction, C M , as described above.  
         [0037]     The above-described embodiment is suitable for use with a wet fabric web (e.g., a fabric web produced on a water jet loom). If the fabric web is already dry (e.g., a fabric web produced on a rapier or air jet loom), there is no need to pre-dry the fabric web. Thus, the dryer stage  540  may be eliminated so that the rollers  510  overfeed the fabric web  520  directly to the coating stage  550 . The silicone coating is applied to at least one surface of the fabric web at the coating stage  550  and is cured at the heat-setting stage  560 , which substantially sets the crimp characteristics of the fabric web  520 .  
         [0038]     According to an embodiment of the present invention, a fabric is provided wherein the fabric exhibits substantially the same elongation characteristics in both the warp and weft directions. The fabric may be formed through an suitable process such as, for example, the processes described above.  
         [0039]     In a conventional fabric, the tensile strength of the fabric in the warp direction was substantially greater than the tensile strength of the fabric in the weft direction. For example, the tensile strength of the fabric in the warp direction was typically more than 20 percent greater than the tensile strength of the fabric in the weft direction. A stress-strain diagram for a conventional fabric is shown in  FIG. 6 . As shown in  FIG. 6 , the stress-strain curve  700  for the fabric in the warp direction is higher than the stress-strain curve  705  for the fabric in the weft direction. As described above, this difference is indicative of a tensile strength variation of 20 percent or greater between the warp and weft directions of the fabric.  
         [0040]     According to an embodiment of the present invention, the fabric exhibits balanced elongation and stress-strain characteristics in the warp and weft directions. For example, according to an embodiment of the present invention, the tensile strength of the fabric in the warp direction is substantially equal to the tensile strength of the fabric in the weft direction. According to an embodiment of the present invention, the tensile strength of the fabric in the warp direction is only 10 percent or less greater than the tensile strength of the fabric in the weft direction. A stress-strain diagram for an embodiment of the present invention is shown in  FIG. 7 . As shown in  FIG. 7 , the stress-strain curve  800  for the fabric in the warp direction is higher than the stress-strain curve  805  for the fabric in the weft direction. As described above, this difference is indicative of a tensile strength variation of 10 percent or less between the warp and weft directions of the fabric.  
         [0041]     Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.