Current adult disposable absorbent products, e.g., adult briefs, that exist in the market today utilize what is known as a fiberized bleached wood fluff pulp and a SAP (Super Absorbent Polymer) mixture for the absorbent core. At low ratios of 30% or less SAP to pulp ratio, the core mixture may or may not be wrapped in an absorbent tissue to prevent the SAP from falling apart or out of the core. At higher levels of SAP at 50% or more, the core must be wrapped to prevent the loose SAP from being shaken out. Also a core adhesive may be added to prevent the heavier SAP particles from being separated from the fluff pulp fibers. This is the most advanced technology of today that is employed in infant sized disposable absorbent products. The pulp fiber in these products is required to rapidly manage the body fluid exudates until the SAP can desorb the fluff fibers to prepare the fluff fibers for the next exudates. For an infant, their body can produce up to 150 ml (grams) of urine and deliver it into the absorbent core over about 70 seconds. This delivery rate starts off rapidly and can achieve approximately 10 to 15 ml per second after the first 5 seconds or so and then trail down to zero. For an adult the amount of exudate is much larger and can easily exceed 300 ml or more delivered over a time period of more than 70 seconds at a rate similar or less than what infants void.
A significant problem with the current absorbent products that contain wood fluff pulp or even wrapped with a tissue or airlaid is in all cases their construction results in a core which feels wet against the body after it has received the voided fluid(s). This wetness feeling is akin to the feeling of wearing a cotton T-Shirt, getting it wet and then continuing to wear the wet cotton T-Shirt long after it should have been changed to a drier shirt. To address this wet feel, almost all current absorbent product designs employ a distancing layer of synthetic fibers on top of the “wet core” as an attempt to create a “feel drier” layer. This synthetic distancing layer is often called a “fluid transfer layer”, “fluid acquisition layer”, or “acquisition distribution layer (ADL)” and is typically much smaller than the core that it covers, leaving the edges of the core exposed. Moreover, despite their design goal, such fluid acquisition layers only work to a limited degree. In this regard as the exudate leaves the body at 98 degrees Fahrenheit it quickly drops to about 90 degrees Fahrenheit as it enters the core of the absorbent product. This creates a cooling effect when touched by the skin, which may increase during the time worn. If left on for an extended period of time, the wet product will achieve a thermal equilibrium and equilibrate somewhere between room temperature and about 90 degrees Fahrenheit, depending upon ambient temperature and clothes worn. This difference can be further exacerbated depending upon the thermal conductivity of the materials chosen to absorb the exudate. But in all cases current wood pulp fluff absorbent products will feel wet and/or cold to the skin the longer the product is worn.
The current state of the art product design for the synthetic absorbent cores is based upon a synthetic continuous fiber matrix inter-layered with superabsorbent particles (SAP). For example a polypropylene tow fiber similar to tow used in cigarette filter making was chosen. This material is purchased in a continuous form and is pulled out of the box and proceeds into an air trumpet or similar device or the like, to expand the fiber tow matrix. Then SAP particles are intermixed, adhesive is sprayed into the fiber SAP matrix and the entire matrix is wrapped to result in what is the state of the art of current “Pulpless” core technology. This type of core has the major limitations of a slow absorbency rate. That rate is highly dependent upon the SAP chosen and on the adhesive type and amount required to attach the SAP to the tow fiber matrix. For example, if enough adhesive is provided to ensure that the SAP remains in its desired location within the core, that adhesive may limit the SAP's absorbent swelling due to coating part of the SAP particles. If less adhesive is utilized, while it may permit greater swelling and absorption of the exudate by the SAP, it may allow the SAP particles to fall from their positions in the core to the bottom of the crotch area, rendering it heavier and wetter in the crotch area when voided into and less absorbents at the ends.
Another example of current pulpless core technology is gluing the SAP to the back sheet or inside the top or body facing sheet. This bonding process may limit the SAP from being fully expanded and utilized in absorbing the exudate.
When bonded in such a matter, the SAP may be also be applied in continuous rows to provide space for the fluid to travel unhindered. Or the SAP may be intermixed with ground wood pulp fibers of similar size to enhanced fluid movement in this inefficient design.
Current SAP limitations require having to choose between a higher absorbent capacity, with the disadvantage of having slower speed, or a faster SAP with less absorbing capacity. If the current SAPs are mixed, the fast acting SAP will very rapidly swell and may “gel-block” the slower acting, but higher absorption capacity SAP. If gel-blocking occurs, it will limit, or even prevent, the higher capacity SAP from desorbing the faster but lower capacity SAP.
In the past a cellulose acetate fiber core with a single SAP has been developed and commercially available, as has a non-SAP version. Current polypropylene filament tow technology has also been used for the absorbent cores. In this regard, such polypropylene tow cores used in the market today make use of round or oval homo-polymer polypropylene fibers, which provide minimal resistance to fluid flow through the SAP/tow fiber matrix, thereby only providing minimal dwell time for the fluid to be absorbed by the SAP.
While such prior art absorbable products containing wood fluff pulp are generally suitable for their intended purposes, they still leave much to be desired. In particular, the thickness of today's disposable absorbent products containing wood fluff pulp and the state of the art in pulp fiberizing technology result in an absorbent product that is significantly thicker than current cotton underwear. This results in a thicker product on the body which may not allow normal clothes or their usual size normal clothing to be worn. In addition the increased thickness of such products results in increased storage, transportation and handling costs and increased retail display space.
In our aforementioned patent application there is disclosed and claimed a disposable absorbent garment, which overcomes many of the disadvantages of art absorbable products containing wood fluff pulp. In particular, that patent application discloses an exemplary absorbent assembly comprising a core formed of a synthetic tow or of synthetic nonwoven layers and having first section comprising a slow acting but high absorption capacity SAP and a second section comprising a fast acting but lower absorption capacity SAP, all of which is wrapped in a wrapper to hold the SAP in place. The absorbent assembly may be quilted and corrugated. The undergarment also includes releasably securable fasteners to enable it to be readily removed and a suspension system to ensure that the garment fits properly and doesn't leak even when holding a large amount of exudate. Odor removal/masking and treatment features may be provided. It addition the undergarment may include a wetness indicator.
The subject invention is directed to an absorbent core assembly which constitutes an improvement over the absorbent cores of our aforementioned patent application. Thus the absorbent core assembly of this invention case be used in the absorbent garment of that patent application, or can be used in any other type of absorbent garment or in other absorbent product designed to quickly and efficiently absorb liquids without leakage therefrom.