Patent Abstract:
A composite media comprising a backing sheet, a covering sheet, and a layer disposed between said backing sheet and said covering sheet, said layer having particles of active ingredient, binder particles, and stabilizing particles, wherein the active particles are coalesced by the binder particles, wherein each of the stabilizing particles bonds with both the backing sheet and the covering sheet, and wherein the stabilizing particles are larger than the binder particles.

Full Description:
This application is a continuation-in-part of co-pending U.S. patent application No. 08/903,395, filed Jul. 22, 1997, U.S. Pat. No. 6,077, 588, which is a division of U.S. patent application Ser. No. 08/813,055, filed Mar. 7, 1997 and issued as U.S. Pat. No. 5,792,513. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to activated media. More particularly, the present invention relates to a method of stabilizing activated media and media produced thereby. 
     BACKGROUND OF THE INVENTION 
     It is often desirable to impregnate, cover, or otherwise treat a base material with an active or activated material, such as an absorbent or adsorbent material. One example would be a non-woven medium coated with agents having fluid adsorption and/or odor adsorption characteristics, as found in children&#39;s diapers, adult incontinence products, feminine hygiene products, and other adsorbent articles of clothing. Other examples include coated paper tissues and toweling, as well as surgical bandages and sanitary napkins. Other materials may be used as adsorbent materials, such as cyclodextrins or zeolites for odor control, or other adsorbents such as silicates, aluminas, or activated carbons. 
     The active, i.e., adsorbent, materials used to coat a base material may be fibrous or particulate materials. However, certain materials known in the art (e.g., fluff pulp fibers) have limited adsorption capacity, and hence perform disappointingly during normal wear. In addition, products containing such materials are often heavy and/or bulky. Thus, it is preferable to use at least some portion of particles composed of super adsorbent polymers (SAP). 
     Yet, it is difficult to immobilize powdered or small granular particles of SAP. Historically, microscopic active materials were immobilized on foams or on surfaces coated with a thin layer of pressure-sensitive adhesive. U.S. Pat. No. 5,462,538 to Korpman is an example of a method of immobilizing adsorbent material on a surface coated with a thin layer of pressure-sensitive adhesive. Using this method may produce large gaps between individual microscopic adsorbent elements. Also, the resulting adsorbent core has only a single layer of adsorbent material. PCT Publication No. WO 94/01069 to Palumbo is another example of a method of immobilizing particulate adsorbent material. However, the adsorbent particles are not bonded to the substrates. Moreover, the adsorbent particles are not in significant contact with the binder particles. Thus, neither method effectively restrains powdered or small granular particles of an active ingredient. 
     As a more effective alternative, U.S. Pat. No. 5,792,513, which is fully incorporated herein by reference, discloses a product formed from a composite mixture of adsorbent particles and binder particles fused to a substrate. While this product provides excellent absorption characteristics, the particles swell when exposed to fluid and then separate from the substrate and each other during normal use. This loose material is then free to slump or move. 
     In light of the foregoing, there remains a need for media, and a method of producing such media, in which the particles of an active ingredient are substantially immobilized even after they have become swollen, while maintaining excellent composite integrity. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved composite medium, in which the particles of an active ingredient are substantially immobilized. A further object is to provide absorbent or adsorbent articles having stabilizing particles dispersed throughout a coalesced composite layer of particles of an active ingredient and binder particles. By substantially immobilizing the particles of an active ingredient the present invention effectively prevents migration of the particles of an active ingredient, thereby creating an adsorbent product with enhanced integrity throughout the use cycle of the product. 
     Accordingly, the present invention provides composite media and a method of producing them. The composite media contain a coalesced composite mixture of particles of an active ingredient and binder particles. The binder particles preferably also fuse the composite structure to front and back substrates. The composite media also have stabilizing particles that fuse with both the particles of the active ingredient and the substrates, thereby forming a composite medium according to the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side plan-view of the composite media of the present invention; and 
     FIG. 2 is a schematic diagram illustrating an apparatus for the practice of the method of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings and, in particular, FIG. 1, there is provided a composite medium generally indicated as  1 . Composite medium  1  has a backing substrate  10  and a covering substrate  20 . 
     Backing substrate  10  and covering substrate  20  may be formed of various materials depending upon the application. By way of example, substrates  10 ,  20  may be a permeable material, such as a non-woven fibrous material, e.g., spun-bonded polyester or polyolefin. Woven substrates may also be used. Furthermore, substrates  10 ,  20  may optionally be formed using cellulosic materials, such as paper, or a combination of cellulosic and thermoplastic fibers. Either substrate  10  or  20  may also be an impermeable material, such as a plastic film (e.g., Mylar®), a permeable backsheet or membrane or another suitable material. 
     The particular material selected for substrates  10 ,  20  can also effect the kinetics of adsorption of composite medium  1 . For example, substrates  10 ,  20  can modify the mean pore size and the overall porosity, provide supplemental adsorption, improve tensile strength, flexibility, and pleatability, and effect wicking and fluid distribution. 
     Between substrates  10 ,  20 , there is a layer, generally indicated as  2 . Layer  2  has particles of an active ingredient  30 , binder particles  40 , and stabilizing particles  50 . Particles of an active ingredient  30  are coalesced or fused together by binder particles  40 . An amount of binder particles  40  may also be fused to points on either substrates  10  or  20 , thereby also binding particles  30  to substrates  10  and  20 . However, binding particles  40  will only be fused with one of substrates  10  and  20 , rather than both. Stabilizing particles  50  may also be bonded to particles of an active ingredient  30  and, in contrast to binding particles  40 , are fused to both backing substrate  10  and covering substrate  20 , thereby forming a stabilizing bond or quilting effect. 
     In other words, as shown in FIG. 1, because of their smaller size, each binding particle  40  may bind to either substrate  10  or substrate  20 , but not both, or to neither of substrates  10  and  20 . 
     The thickness of layer  2  will vary depending on a variety of factors, including the size of the particles  30 ,  40 , and  50 , the quantity of particles  30 ,  40 , and  50 , the degree of coalescence between particles  30 ,  40 , and  50 , and whether other particles or fibers, such as fluff pulp, are used in layer  2 . Preferably, the thickness of layer  2  is about 0.2 mm to about 5 mm. 
     Particles of an active ingredient  30  can potentially be formed of any material. For example, particles of an active ingredient  30  may absorb or adsorb fluids or gases. Furthermore, particles of an active ingredient  30  may be used to release fluids or gases held therein, for example, to deliver fluids, such as medicaments. Materials such as iodinated resin, activated carbon, activated alumina, aluminum powders, nickel powders, alumina-silicates, ferromagnetic materials, ion-exchange resins, manganese or iron oxides, zeolites, glass beads, ceramics, diatomaceous earth, and cellulosic materials can also be used as particles of an active ingredient  30 . In addition, particles of an active ingredient  30  may also be polymeric materials, such as SAP. The cross sectional size of particles of an active ingredient  30  is preferably within a range of about 5 microns to about 5000 microns. 
     Materials forming binder particles  40  may potentially include any material known in the art. In particular, thermoplastic and thermoset materials are useful for the practice of the present invention. For example, binder particles  40  may be polyethers, polyolefins, polyvinyls, polyvinyl esters, polyvinyl ethers, ethylene-vinyl acetate copolymers, or a mixture thereof. Also, suitable binder particles may be produced from particulate thermoset resins known in the art, such as phenol-formaldehyde or melamine resins, with or without additional crosslinking agents. Preferably, binder particles  40  are present in such an amount and at such a size that they do not substantively interfere with the functioning of particles  30 . Binder particles  40  are preferably about 5 microns to about 50 microns in size. 
     The critical feature of this invention resides in stabilizing particles  50  that are used to form through-web stabilizing bonds within layer  2 . First, stabilizing particles  50  perform a similar function as binder particles  40 , specifically coalescing or fusing together particles of an active ingredient  30 . However, they are extremely limited in their capacity to stabilize the active ingredient particles because they are large and provide limited surface area to interface with the active ingredient and they are generally present in small amounts, again limiting their ability to stabilize other particles. Stabilizing particles  50  are also adhered or fused to both substrates  10 ,  20  because they are selected to have a particle size roughly equal to or greater than the thickness of layer  2 . Materials forming stabilizing particles  50  are potentially any suitable material, such as the materials listed in reference to binding particles  40 , e.g., a thermoplastic or a thermoset material. Stabilizing particles  50  are preferably present in such an amount and at such a size that they do not substantively interfere with the functioning of particles of an active ingredient  30  and binder particles  40 . It is preferred that stabilizing particles  50  be both larger in size and fewer in number compared to binder particles  40 . Preferably, stabilizing particles  50  are equal to or larger than the thickness of layer  2 , so as to allow stabilizing particles  50  to span the entire thickness of layer  2  and directly adhere to substrates  10 ,  20 . However, stabilizing particles may be smaller than the thickness of layer  2 , for instance, if a ribbed effect for composite medium  1  is desired. In addition, stabilizing particles may be intimately grouped together, thereby binding to both substrates  10 ,  20  in the aggregate. 
     FIG. 2 illustrates an exemplary apparatus for the practice of this invention. A supply roll  100  provides a substrate  120  to be treated, such as a nonwoven tissue or toweling paper. Downstream from supply roll  100  is a knurled roller  130  positioned to receive a mixture of particles of an active ingredient  30 , binder particles  40 , and stabilizing particles  50 , the mixture generally being indicated as  140  and dispensed from a hopper  160 . Mixture  140  is applied to the upper surface of substrate  120  as a continuous coating or, alternatively, as a coating of a specific design such as, for example, stripes. A brush  180  may be employed to aid in removing mixture  140  from knurled roller  130 . Thereafter, substrate  120  is passed through a nip  200  between a heated idler roller  220  and a drive roller  240 . Alternatively, before being passed through nip  200 , substrate  120  may also be preheated, for example, by a convection or infrared oven. A pneumatic cylinder is connected via a rod  280  to the axle of idler roller  220  to maintain a desired pressure on substrate  120  within nip  200 . In passing over the surface of heated roller  220 , mixture  140  is heated to a temperature equal to or greater than the softening temperature of binder particles  40  and stabilizing particles  50 , but lower than the softening temperature of particles of an active ingredient  30 . Within nip  200 , binder particles  40  and stabilizing particles  50  fuse under pressure with particles of an active ingredient  30 , while stabilizing particles  50  also fuse with substrate  120 . An amount of binder particles  40  may fuse with substrate  120 . Furthermore, in a preferred alternative to the above described apparatus, a second supply roll  300  of a substrate  320 , which may be of the same or a different material from that of substrate  120 , is also passed between nip  200  on the top of mixture  140 . Stabilizing particles  50  fuse with substrate  320  and an amount of binder particles  40  may also fuse with substrate  320 . However, while stabilizing particles  50  fuse with both substrate  120  and  320 , binder particles  40  will only fuse with either substrate  120  or  320 . Upon leaving the nip  200 , binder particles  40  and stabilizing particles  50  cool and harden. The composite medium  240  passes onto a takeup roll  360 . 
     Coalescing particles of an active ingredient  30  with interposed binder particles  40  and stabilizing particles  50  results in more complete coverage of the backing substrate  10  and places particles of an active ingredient  30  in closer proximity to each other. In addition, it is possible to vary the depth and porosity of layer  2  and to have multiple layers of active ingredient fully stabilized by binder particles  40 . When composite layer  1  contains SAP and is wetted, the SAP particles swell and generally break their bonds with binder particles  40  and any bonds that might exist with stabilizing particles  50 . However, the bonds between substrates  10  and  20  and stabilizing particles  50  are retained and prevent the wholesale disassembly of composite layer  1 . These stable bonds do not prevent local swelling of the composite layer  1 , but do provide localized stabilization of composite layer  1  at each point where stabilizing particle  50  spans composite layer  1 . These bonds provide a random quilting effect that prevents the movement of the swollen SAP mass. 
     Although composite medium  1 , and the method of producing such a medium, has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present invention may be employed without departing from the spirit and scope of the present invention. 
     Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.

Technology Classification (CPC): 3