Abstract:
A method for applying fluids to a strand and useable for bonding adhesive coated strands to substrates in the production of bodily fluid absorbing hygienic articles, by drawing the strand along an isolated path, moving a fluid or adhesive fiber back and forth across a path of the strand as the fluid fiber is dispensed toward the strand, and capturing substantially all of the fluid fiber on the isolated strand, and in some applications contacting an adhesive coated strand with the substrate to bond the strand thereto. The adhesive fiber is vacillated back and forth across a path of the strand beyond opposing sides thereof to at least partially coat all sides thereof with adhesive. In bodily fluid absorbing hygienic articles, the methods substantially eliminate fabric stiffening and loss of moisture absorbing capacity thereof, provide substantially uniformly bonding along the axial dimension of the strand to ensure uniform bunching of fabrics, optimum fluid absorption, and comfort.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a division of U.S. application No. 09/451,118, filed on Dec. 7, 1999, and is related to U.S. application No. 08/843,224, filed Apr. 14, 1997, entitled “Improved Meltblowing Method and System”, now U.S. Pat. No. 5,904,298, and to U.S. application No. 08/717,080, filed Oct. 8, 1996, entitled “Meltblowing Method and Apparatus”, now U.S. Pat. No. 5,902,540, all commonly assigned and incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates generally to adhesive dispensing systems, and more particularly to processes for bonding one or more relatively elongated strands to one or more substrates, especially bonding stretched elastic strands to fabrics in the manufacture of bodily fluid absorbing hygienic articles.  
           [0003]    It is often desirable to bond or adhere relatively elongated members, or strands, onto substrates. In the manufacture of a variety of bodily fluid absorbing hygienic articles including diapers, incontinence pads and other undergarments, for example, stretched elastic strands are bonded between fabrics to form waste bands and other stretchable portions thereof. In diapers, the waste bands and particularly the leg bands must provide relatively fluid tight seals between the undergarment and the body.  
           [0004]    In known bodily fluid absorbing hygienic article manufacturing processes, adhesive is sprayed onto stretched elastic strands disposed on or very near an underlying fabric substrate moving relative to one or more adhesive dispensing nozzles. The adhesive is usually a hot melt adhesive dispensed in a swirling spiral pattern by a spiral nozzle, and is applied generously to both the substrate and the elastic strands simultaneously. The stretched elastic strand is usually bonded between overlapping fabric layers. As the stretched elastic strands contracts, the fabric adhered thereto is bunched together forming generally pleated waste bands and other stretchable portions of the undergarment. It is important that the elastic strand be bonded to the fabric substantially continuously along its axial length to ensure uniform pleating, or bunching, of the fabric, which is necessary for optimum comfort and fluid absorption, and to provide an aesthetically pleasing product.  
           [0005]    U.S. Pat. No. 5,507,909, issued Apr. 16, 1996, entitled “Apparatus For The Manufacture Of An Elongated Element Comprising Helically Patterned Adhesive” discloses a process and apparatus for helically wrapping adhesive onto an elastic strand, which is bonded to a substrate in the manufacture of disposable absorbent products without coating adjacent areas of the substrate with large amounts of adhesive. To helically coat the elastic strand with adhesive, the strand is rotated about its axis as it is drawn past an adhesive flow from a dispensing orifice, for example by drawing the elastic strand between a nip roll assembly rotated at an angle relative thereto, or by other disclosed but less certain strand rotating means.  
           [0006]    The known processes, however, generally apply much more adhesive onto the elastic strands and underlying substrate than is required for bonding, resulting in unnecessarily increased costs. The excess adhesive, which is usually hot, also has a tendency to deform the relatively thin, temperature sensitive fabric, thereby providing an undesirable appearance. In extreme cases the hot adhesive may destroy the fabric by burning a hole therethrough.  
           [0007]    Another adverse effect of applying excessive amounts of adhesive onto fabrics is that the adhesive tends to stiffen the fabric. This stiffening is particularly undesirable in diaper and other undergarment applications where the elastic strand bunches the fabric to form waste bands and other stretchable portions that contact the body intimately. More particularly, the stiffened fabric tends not to bunch as freely and uniformly as it would otherwise, thereby compromising the ability of the fabric to form an effective fluid seal when stretched against the wearer&#39;s body.  
           [0008]    The excess adhesive applied onto the fabric may also reduce the fluid absorbing capacity thereof, resulting possibly in the leakage of bodily fluids and in the accumulation of perspiratory moisture on the wearer&#39;s body, which may be particularly uncomfortable where waste and leg band portions of the garment contact the skin directly. Additionally, the adhesive stiffened fabric may be slightly abrasive against the skin, and in some extreme cases may irritate allergically sensitive skin.  
           [0009]    The process and apparatus disclosed in the prior art U.S. Pat. No. 5,507,909 entitled “Apparatus For The Manufacture Of An Elongated Element Comprising Helically Patterned Adhesive” allegedly reduce the amount of adhesive applied to the substrate and apply more conservative amounts of adhesive onto the elastic strand, but the uniform application of adhesive helically about the strand requires consistently and uniformly controlling the rotation of the strand during the drawing thereof. It is questionable whether the elastic strand may be consistently rotated uniformly as required to uniformly apply adhesive helically thereabout in manufacturing operations. If the adhesive is not applied uniformly along the axial dimension of the strand, the stretched strand will not bond uniformly to the substrate, which adversely affects uniform bunching of the fabric. Non-uniform bunching is undesirable from an aesthetic viewpoint, and more substantively non-uniform bunching of the fabric compromises the ability of the fabric to form an effective fluid seal, and reduces the softness and comfort thereof when stretched against the wearer&#39;s body.  
           [0010]    The present invention is drawn generally toward advancements in the art of applying fluids including adhesives onto strands, and more particularly toward bonding adhesive coated strands to substrates, especially adhesive coated elastic strands to fabrics in the manufacture of bodily fluid absorbing hygienic articles.  
           [0011]    It is an object of the invention to provide novel methods for applying fluids to strands, and for bonding adhesive coated strands to substrates, and combinations thereof, that are economical and overcome problems in the prior art.  
           [0012]    It is another object of the invention to provide novel methods for applying hot melt adhesives to elastic strands, and for bonding adhesive coated elastic strands to fabrics to form waist bands and other stretchable portions in the manufacture of a variety of bodily fluid absorbing hygienic articles and disposable absorbent products using reduced amounts of adhesive.  
           [0013]    It is a further object of the invention to provide novel methods for bonding adhesive coated elastic stands to fabric substrates in the manufacture of a variety of bodily fluid absorbing hygienic articles, wherein the elastic strand is bonded to the fabric substantially uniformly along an axial length thereof to ensure uniform bunching of the fabric, thereby providing optimum comfort and fluid absorption, and an aesthetically pleasing, more marketable product.  
           [0014]    It is yet another object of the invention to provide novel methods for reducing the amount of adhesive applied to elastic strands bonded to underlying fabric substrates in the manufacture of a variety of bodily fluid absorbing hygienic articles to reduce the possibility of melting the fabric with hot melt adhesives, to substantially eliminate fabric stiffening and to eliminate loss of moisture absorbing capacity thereof, and to reduce costs, especially costs associated with excess adhesive usage.  
           [0015]    It is a more particular object of the invention to provide novel methods for applying fluids to a strand, useable for bonding the strand to a substrate in the production of bodily fluid absorbing hygienic articles, by drawing the strand along an isolated path, moving a fluid fiber across a path of the strand as the fluid fiber is dispensed toward the strand so that the fiber contacts the strand, and capturing substantially all of the fiber on the isolated strand. The fiber is preferably vacillated back and forth across a path of the strand, and beyond opposing sides thereof to at least partially coat all sides thereof with fluid.  
           [0016]    It is another more particular object of the invention to provide novel methods for bonding strands to substrates in the production of bodily fluid absorbing hygienic articles by drawing the strand along a path separated spatially from the substrate, dispensing an adhesive fiber toward the strand so that at least a portion of the adhesive fiber crosses the path of the strand and contacts the strand, capturing substantially all of the adhesive fiber on the strand when the strand is spatially separated from the substrate to at least partially coat the strand with adhesive, and contacting the adhesive coated strand with the substrate to bond the strand thereto. The fiber is preferably vacillated back and forth across a path of the strand, and beyond opposing sides thereof to at least partially coat all sides thereof with adhesive.  
           [0017]    These and other objects, aspects, features and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced generally by corresponding numerals and indicators. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a partial side [view] elevational view of a system for applying fluids to strands, and for bonding adhesive coated strands to substrates according to an exemplary embodiment of the invention.  
         [0019]    [0019]FIG. 2 a  is a partial sectional view of fluid fibers dispensed toward corresponding strands.  
         [0020]    [0020]FIG. 2 b  is an end view of an exemplary nozzle for dispensing a plurality of fluid fibers toward a corresponding plurality of strands.  
         [0021]    [0021]FIG. 3 is a partial perspective view of a strand at least partially coated with fluid on all sides thereof according to an exemplary embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    [0022]FIG. 1 is a system  10  for practicing methods of applying fluids including adhesives to strands, and in some applications, bonding adhesive coated strands onto substrates according to the present invention. The exemplary system  10  dispenses hot melt adhesive fibers  40  from one or more adhesive dispensing nozzles  20 , which are preferably meltblowing nozzles having one or more adhesive orifices and corresponding first and second air dispensing orifices disposed on opposing sides thereof as shown in FIG. 2 and discussed further below. The present invention is applicable more generally to applying fluids  40  to strands  30 , which capture substantially all of the fluid dispensed from the nozzle  20  to prevent unwanted application of fluid onto an underlying substrate or other areas and to reduce fluid waste.  
         [0023]    An exemplary application is the bonding of adhesive coated stretchable elastic strands  30  onto fabric substrates  50  in the manufacture of a variety of bodily fluid absorbing hygienic articles. The methods of the present invention are particularly useful in applications where it is desirable generally to precisely control the dispensing of relatively viscous fluids, including but not limited to hot melt adhesive fibers, onto a strand, and in some applications thereafter to bond adhesive coated strands onto substrates as discussed further below. Thus the fluid fibers  40  dispensed from the nozzle  20  are not necessarily limited to meltblown fibers, but are more generally any fluid that may be controllably dispensed so that substantially the entire fluid is captured by the strand  30 .  
         [0024]    In FIG. 1, the nozzle  20  dispenses a fluid fiber  40  toward an isolated strand  30  drawn along a path so that at least a portion of the fluid fiber  40  crosses the path of the strand  30  and contacts the strand so that the fluid fiber  40  attaches thereto. The spatially isolated strand  30  captures substantially all of the fiber fluid  40  dispensed from the nozzle  20 , whereby the strand  30  is at least partially coated with fluid. By capturing substantially all of the fluid dispensed from the nozzle  20  onto the spatially isolated strand  30  there is little or no wasted fluid, thereby economizing the application thereof. Capturing all of the fluid fiber  40  onto the strand  30  also reduces the likelihood that fluid will spill-over or be applied inadvertently to unintended areas, for example underlying substrates.  
         [0025]    The fluid fiber  40  is preferably a substantially continuous fiber, although it may be intermittently discontinuous so long as a portion of the fiber crosses the path of the strand and attaches thereto. FIG. 2 a  illustrates the fluid fiber preferably moving back and forth across the path of the strand  30  as the fluid fiber  40  is dispensed toward the strand  30 . The viscosity, mass, and range of movement of the fluid fiber  40  back and forth across the path of the strand  30  are selected or controlled so that the spatially isolated strand  30  captures substantially all of the fluid fiber  40  dispensed from the nozzle  20 . Variations in the dispensing of the fluid fiber  40  from the nozzle  20 , resulting for example from supply pressure changes and residue accumulation in the nozzle orifice and other factors, may result in fluid fiber  40  discontinuities or in fluid dispensing irregularities that occasionally prevent the fibers  40  or portions thereof from being captured entirely by the strand  30 .  
         [0026]    [0026]FIGS. 2 a  and  3  illustrate the fluid fiber  40  moving back and forth across a path of the strand  30 , wherein fluid fiber portions  42  and  44  move beyond corresponding opposing sides  32  and  34  of the strand  30  as the fluid fiber  40  is dispensed toward the strand  30 . Fluid fibers thus dispensed are captured substantially entirely by the strand  30 , whereby all sides of the strand  30  are at least partially coated with fluid. Thus applied, the adhesive fibers  40  coat the strand  30  substantially uniformly along the axial dimension or length thereof, which is desirable in many applications, particularly in the manufacture of bodily fluid absorbing hygienic articles where it is desirable to uniformly bond an adhesive coated elastic strand onto a fabric substrate to uniformly bunch the fabric forming waste bands and other stretchable portions thereof. Substantially uniformly applying the adhesive fibers  40  along the axial dimension of the strand  30  without coating the entire strand also substantially reduces adhesive usage while providing relatively uniform bonding to the substrate.  
         [0027]    [0027]FIG. 3 illustrates, more particularly, the fiber portions  42  and  44  draping downwardly along the corresponding sides  32  and  34  of the strand  30  after other fiber portions  41  contact the strand  30 . The fiber portions  42  and  44  are preferably dispensed by the nozzle  20  to extend sufficiently outwardly beyond the corresponding sides  32  and  34  of the strand  30  so that portions thereof  43  adhere also to an underside  36  of the strand  30 . In some applications, the fiber portions  42  and  44  may even extend and adhere down along one side of the strand, across the underside thereof, and back upwardly along the opposing side of the strand  30 , sometimes wrapping more than once about the strand.  
         [0028]    The portions  42  and  44  of the fiber moving back and forth across the path of the strand  30  drape over the strand  30  under the influence of momentum or gravity or a combination thereof, and ultimately the fiber  40  adheres at least partially to all sides of the strand  30  including a top side  31 , opposing sides  32  and  34 , and the underside  36  thereof. The adhesive fiber  40  is dispensed preferably from the nozzle  20  located above the isolated strand  30 , and adheres initially to the top side  31  of the strand  30 . The fiber  40  then migrates downwardly along the sides of the strand  30  and across the underside thereof to at least partially coat all sides thereof. The adhesive may thus be applied uniformly along the axial dimension of the strand  30 , without coating the entire strand, thereby economizing on the application of adhesive and at the same time applying adequate amounts thereof to the strand to ensure uniform bonding of the strand  30  along the axial dimension thereof to the substrate.  
         [0029]    The fiber portions  42  and  44  preferably are not dispensed to extend so far outwardly beyond the corresponding sides  32  and  34  of the strand  30  that the fluid fiber  40  can not be captured substantially entirely by the strand  30 . The fluid fiber mass flow rate, fluid viscosity, and size and stability of the strand  30  are among the factors that limit the extent to which the fiber  40  may extend beyond the sides of the strand  30  and ultimately be substantially entirely captured thereby.  
         [0030]    Precisely controlling the dispensing of fluid fibers from the nozzle  20  ensures that the strand  30  captures substantially all of the fluid fiber  40 . Precisely controlling the dispensing of the fluid fibers  40  also ensures that fluid is applied at least partially to substantially all sides of the strand  30  and substantially uniformly along the axial dimension thereof. By appropriately controlling the dispensing of the fluid, and generally the rate at which the strand  30  is drawn relative to the nozzle  20 , it is possibly to accurately control the amount or quantity of fluid applied to the strand.  
         [0031]    In the exemplary application, the fluid fiber  40  is a substantially continuous hot melt adhesive fiber dispensed from an adhesive orifice G of a meltblowing nozzle  20 . FIG. 2 a  illustrates the adhesive fiber  40  vacillating back and forth across the path of the strand  30  and beyond opposing sides thereof under the influence of first and second air flows dispensed from first and second air orifices A 1  and A 2  disposed on opposing sides of corresponding adhesive orifices G 1  and G 2  of the nozzle  20 . The amplitude and frequency of vacillation of adhesive fibers  40  is controlled by the first and second air flows as disclosed more fully in the referenced copending U.S. Application No. 08/843,224, entitled “Improved Meltblowing Method and System”, and copending U.S. Application No. 08/717,080, entitled “Meltblowing Method and Apparatus”. In an alternative embodiment, hot melt adhesive fibers are dispensed from a spiral nozzle in a swirling pattern to move the adhesive fiber back and forth across the path of the strand as the adhesive fiber is dispensed toward the strand. The meltblowing nozzles of the types disclosed in the referenced copending U.S. Application No. 08/843,224, entitled “Improved Meltblowing Method and System”, and copending U.S. Application No. 08/717,080, entitled “Meltblowing Method and Apparatus”, however, are believed to provide relatively superior control over the adhesive flow in comparison to known spiral nozzles, and are particularly suitable for applying adhesive fibers, which are capturable substantially entirely by corresponding strands according to the present invention.  
         [0032]    In applications where the strand  30  is bonded between substrates and where the strand  30  has a tendency to twist prior to bonding onto a single substrate, it is desirable to at least partially coat all sides of the strand  30  with adhesive, to ensure complete bonding of the strand  30  to the substrate  50 . It is desirable in other applications, for example where an elastic strand  30  forms a waste band or other stretchable portion of a garment, to apply adhesive substantially uniformly along the axial dimension thereof, and preferably at least partially to all sides of the strand, to ensure uniform bonding of the strand  30  along an axial dimension thereof to a fabric substrate, thereby providing substantially uniform bunching of the fabric as the elastic strand contracts. The extent to which the strand  30  is coated with adhesive is controlled generally by the adhesive fiber mass flow rate, fiber vacillation amplitude and frequency, and the strand drawing rate.  
         [0033]    [0033]FIG. 1 illustrates the application of adhesive fibers onto a strand  30  and bonding of the adhesive coated strand  30  to a substrate  50 . Initially, the strand  30  is drawn along a path separated spatially from the substrate  50 . The adhesive fiber  40  is dispensed toward the isolated strand  30  so that at least a portion of the adhesive fiber  40  crosses the path of the strand  30  and attaches thereto, as shown in FIG. 2. As discussed above, the fiber  40  is preferably vacillated back and forth across the path of the strand  30 , beyond opposing sides thereof. The strand  30  captures substantially all of the adhesive fiber  40  when the strand  30  is spatially separated from the substrate  50  to at least partially coat the strand  30  with adhesive. Preferably, the adhesive is applied at least partially to all sides of the strand  30  to ensure uniform bonding of the strand along an axial dimension thereof to the substrate  50 . The adhesive coated strand  30  is then contacted with the substrate  50  to bond the strand  30  thereto before the adhesive sets.  
         [0034]    In the manufacture of bodily fluid absorbing hygienic articles, the subtrate  50  is fabric, and the strand  30  is an elastic strand that is stretched by applying tension thereto before bonding to the substrate  50 . FIG. 1 illustrates the strand  30  and the substrate  50  both drawn by common roller  60 . In this exemplary application, the stretched adhesive coated elastic strand  30  is also bonded to a second fabric substrate  70 , which may also be drawn by the roller  60 , whereby the strand  30  is disposed between and bonded to the substrate  50  and the substrate  70 . The adhesive is applied at least partially to all sides of the strand  30  and preferably substantially uniformly along the axial dimension thereof as discussed above to ensure that the strand  30  bonds uniformly to both fabric substrates  50  and  70 .  
         [0035]    In applications where the substrate  50  is adjacent the strand  30  and opposite the adhesive dispensing nozzle  20 , it is necessary to spatially separate the substrate  50  from the strand  30  by a distance “d” greater than a droop distance of the adhesive fiber  40  below the strand  30  opposite the adhesive nozzle  20  to prevent adhesive from inadvertently adhering to the substrate  50 . In other applications, the adhesive  40  may be applied to the strand  30  away from the substrate  50 , to ensure that no adhesive  40  is inadvertently applied thereto, wherein the substrate  50  may be supplied for example from below roller  80  along the path  52  away from fluid fibers  40  dispensed from the nozzle  20 .  
         [0036]    [0036]FIG. 2 a  illustrates the nozzle  20  dispensing a plurality of at least two fluid or adhesive fibers  40  from a corresponding plurality of adhesive orifices G 1  and G 2  toward corresponding isolated strands  30 , wherein each of the plurality of adhesive fibers  40  is vacillated back and forth across the path of the corresponding strand  30  with a plurality of corresponding first and second air flows dispensed from first and second air orifices A 1  and A 2  disposed on opposing sides of the corresponding adhesive orifices G 1  and G 2 , according to the modes of operation discussed above, and particularly those disclosed more fully in the referenced copending U.S. application No. 08/843,224, entitled “Improved Meltblowing Method and System”, and copending U.S. application No. 08/717,080, entitled “Meltblowing Method and Apparatus”.  
         [0037]    Each strand  30  captures substantially all of the adhesive fiber  40  dispensed from the corresponding adhesive orifice G 1  and G 2  when the strand  30  is spatially separated from the substrate to at least partially coat the strand  30  with adhesive. The adhesive fibers are preferably vacillated back and forth across the path of the corresponding strand beyond opposing sides thereof to at least partially coat all sides of each strand with adhesive, preferably substantially uniformly along the axial dimension thereof. In some applications, the plurality of adhesive coated strands are subsequently contacted with one or more substrates to bond the plurality of strands thereto as discussed above.  
         [0038]    [0038]FIG. 2 a  illustrates the plurality of adhesive orifices G 1  and G 2  and corresponding air orifices of the nozzle  20  arranged generally in a series. In one embodiment illustrated in FIG. 2 b,  adjacent adhesive fibers are dispensed from adhesive orifices G 1  and G 2  with corresponding air orifices A 1  and A 2  disposed, or offset, relative to each other in different planes of the nozzle  20 . For example, all odd numbered adhesive orifices G 1  and G 3  and the corresponding air orifices are disposed serially in a first plane, and all even numbered adhesive orifices G 2  and G 4  and the corresponding air orifices are disposed serially in a second plane different from the first plane, whereby adjacent adhesive flows are offset axially along the strand  30 , as illustrated by adhesive flows  40  and  49  in FIG. 1. Alternatively, all of the adhesive dispensing orifices may be disposed in series in a single common plane. These various aspects of the adhesive dispensing nozzles are disclosed more fully in the referenced copending U.S. application No. 08/843,224, entitled “Improved Meltblowing Method and System”, and copending U.S. application No. 08/717,080, entitled “Meltblowing Method and Apparatus”.  
         [0039]    [0039]FIG. 2 a  illustrates the amplitude of vacillation of adjacent fibers  40  apparently overlapping without interference therebetween. More particularly, when the adhesive dispensing orifices G 1  ad G 2  are adjacent to each other in a common plane, the vacillating fibers  40  dispensed therefrom have a tendency to synchronize or to deflect from the common plane one way or the other along an axial direction of the corresponding strand  30  to avoid interference with each other. This phenomenon permits dispensing fluid or adhesive fibers  40  from relatively closely space adhesive dispensing orifices toward relatively closely spaced corresponding strands  30 , wherein the adhesive fibers  40  vacillate apparently overlappingly but without interference therebetween. The vacillating fibers  40  are thus captured substantially entirely by the corresponding strands  30 , as discussed above, without interference from adjacent fibers  40  and without spillage or overspray of adhesive resulting from interference between or entanglement of the adjacent fibers.  
         [0040]    While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will appreciate and acknowledge the existence of variations, combinations, and equivalents of the specific exemplary embodiments herein. The invention is therefore to be limited not by the exemplary embodiments, but by all embodiments within the scope and spirit of the appended claims.