Layered absorbent structure

#This invention relates to absorbent products and particularly to such products which are to be worn by a user against the body and are designed to absorb body exudates, e.g., diapers, sanitary napkins, catamenial tampons and the like.

#These products generally comprise an absorbent element such as a pad or core of absorbent material, optionally enveloped by a cover which is pervious to body exudate at least on the side in contact with the body. Frequently, as is the case with disposable diapers and some sanitary napkins, the side worn away from the body is provided with a barrier sheet, i.e., a sheet of material impervious to body fluid, to protect the garments of the wearer. This barrier sheet may form a part of the cover enveloping the absorbent material or may underlie such a cover on the side away from the body.

#In the main, such products have performed their primary function, i.e., they have absorbed and retained body fluid. A major drawback associated with such products, however, is that after the user has worn them for a period of time, the products may fail before they become fully saturated by having fluid strike through onto an external surface contacting the user's garment or by having the surface worn against the body become so wet with fluid that the resulting discomfort causes the user to discard the product. Accordingly, there is a need for an absorbent product which makes full use of the absorbent material provided and keeps absorbed fluid away from the external surfaces of the product.

#Referring to the drawings:

#FIG. 1 is a perspective view of a sanitary napkin incorporating therein the absorbent structure of this invention with parts removed therefrom in order to illustrate internal features;

#FIG. 2 is a transverse cross-sectional view of the napkin of FIG. 1, taken through line 2--2;

#Referring to the drawings, FIGS. 1 and 2 illustrate in perspective and transverse cross-sectional views, respectively, a sanitary napkin incorporating as an absorbent element the structure of this invention. The napkin 10 comprises an absorbent element 12 enveloped by a fluid-pervious cover 14 which may be any woven or non-woven material pervious to body fluid striking its surface, such covers being well-known in the art. A fluid-impervious barrier sheet 16 is provided on the side of the napkin to be worn against the garment and away from the body and is sandwiched between the cover 14 and the element 12. The barrier sheet inhibits fluid from passing onto an undergarment and may be constructed of any thin, flexible, relatively body fluid impervious material, for example a polymeric film such as polyethylene, polypropylene, cellophane or a usually fluid-pervious material that has been treated to be impervious such as impregnated fluid-repellant paper. The illustrated napkin is of a kind to be positioned in the undergarment of the user by adhesive means. To that end, the side facing the undergarment is provided with a longitudinally extending element of pressure-sensitive adhesive 18. A protective strip 20 is provided, overlying the adhesive element 18, to protect the adhesive element prior to use.

#In accordance with the teachings of this invention, the absorbent element 12 is made up of a plurality of absorbent layers. A first layer 22 comprises cellulosic fibers and may, for example, comprise loosely associated fibers of wood pulp, regenerated cellulose, cotton fibers, or such chemically or physically modified cellulose fibers as alkyl-carboxylated cellulose, grafted cellulose or the like. Alternatively, the first layer may take the form of a more ordered cellulose fiber configuration such as wadded tissue paper or other bonded structures. Adjacent to this first layer 22, and in face-to-face relationship therewith, is a second layer 24 which is described in my co-pending application, Ser. No. 7280, filed together herewith which was, in turn, a continuation-in-part of my co-pending application Ser. No. 879,832 filed on Feb. 21, 1978. This second layer 24 comprises, in admixture, peat moss and finely ground mechanical wood pulp in a weight ratio of at least about 0.35 grams of said mechanical wood pulp per gram of peat moss. Preferably there is at least 0.4 grams of said finely ground mechanical wood pulp per gram of peat moss. Such finely ground mechanical wood pulp may be selected from such materials as groundwood pulp, refiner wood pulp or, thermomechanical wood pulp. Groundwood pulp is essentially trees and branches which have been debarked, cleaned and then ground into particle matter. Refiner wood pulp differs from groundwood pulp only in that the grinding step utilizes a refiner, i.e., a disk-like device well known in the art and generally having metallic ribs at the peripheral sections thereof which last contact the wood particles and help to separate the wood fibers without excessively damaging them. Thermomechanical wood pulp is similar to refiner pulp with the exception that the wood particles are heated when in the refiner, usually with steam, and this heating further aids in separating the wood fibers. The common characteristic of these mechanical pulps is that no attempt has been made to separate the fibers by chemical means although they may later, after being reduced to fine particulate matter, be subjected to chemical treatment, e.g., bleaching.

#The particle size of the mechanical wood pulp can be characterized by the Canadian Standard Freeness (hereinafter CSF, measured by TAPPI Test Method T-227). Preferably the mechanical wood pulp will have a CSF value of from 30-600, and more preferably from 60-300. The second layer may also comprise longer fibered absorbent materials such as chemical wood pulp and/or rayon. Preferably, the peat moss is bleached to a lightness of at least about 70, as measured on the Hunter Colour Scale System "C".