US 3545441 A
Description (OCR text may contain errors)
United States Patent  Inventor Gunnar Gravdahl  References Cited Hashim, Norway UNITED STATES PATENTS No 123%?1968 1,974,578 9/1934 Medoff 128/290 2,964,039 12/1960 Johnson, Jr., et a1 128/290 [451 Patented 3 430 629 3/1969 Mu h 128/284 Assignee Saba s 113 y Tonsberg, Norway Primary Examinercharles F. Rosenbaum  Priority Feb. 8, 1967 Attorney-Wenderoth, Lind and Ponack  Norway [31 No. 166,765
ABSTRACT: An absorbent, pillow-shaped core, intended for  Q use in a sanitary napkin, a diaper, compresses or the like, rawmg made of fibrous material, the fibrous material provided with  US. Cl 128/284, gradually varying mass density, such that a greater number of 161/124 fibers per volume is present in the portion of the core having  Int. Cl A6lf 13/16 the greatest need for absorption power, the mass density  Field of Search 128/284, gradually reduced in direction away from said portion, the
287, 290, 296; 16 l/l24 core having substantially the same thickness all over.
PATENTED on: 8 I970 GNNAR GR AVDAHL JNVENTOR.
ABSORBENT CORE This invention relates to fibrous, absorbent, pillow-shaped cores of the kind used in sanitary napkins, diapers, compresses etc.
The invention is particularly useful for disposable sanitary napkins and shall in the following be described and illustrated. The invention can, however, be utilized for a number of various absorbent articles of the kind which are to be used once only, i.e. diapers, compresses, as long as these articles comprise an absorbent pillow-shaped core, which is encompassed by some kind of a wrapper.
A disposable sanitary napkin consists usually of two main parts, namely the absorbent core, which during use shall absorb and confine the moisture, and a wrapper which primarily keeps the core in place and carrying same, and also serves the purpose of preventing that the absorbed liquid leaves the napkin.
A sanitary napkin core is usually about to cm. long and 4 to 8 cm. wide. The secretion of the menstruation liquid takes place, however, in a relatively concentrated manner. The need for absorbing capacity or ability is therefore far the greatest in the centre portion of the napkin, since it is in this area the substantial part of the liquid not only must be absorbed, but also must be confined. In order to reach optimal utilization of the total absorbing capacity of the napkin it is of importance that the napkin is so constructed and shaped that the moisture or liquid is distributed also sideways or laterally, and then preferably in the longitudinal direction of the core.
When hitherto faced with the task to make a core having the greatest absorbing' power or ability in the centre portion of the core, the industry has provided a core, which viewed in side elevation presents a substantially elliptical shape. Such a shape is sometimes advantageous and sometimes disadvantageous. In a sanitary napkin it will be advantageous that the napkin has such a shape during use, since a flattened front portion on the napkin will be less revealing under fight clothes, and a flattened rear portion will be more comfortable when the wearer is sitting. An elliptical shape will, however, involve disadvantages during the production stage and in connection with the further handling in factory, particularly in connection with'mass packing machinery. It is also difficult to make an attractive packed product when same has an uneven thickness, such as the before mentioned elliptically-shaped article, particularly if the wrapping material is soft and flexible, for instance a plastic material.
The object of the invention is to provide a new embodiment for such cores, with improved absorbing characteristics and also possessing a shape which simplifies handling and packing and provides an attractive product.
The invention is based on the concept of making the fibrous pillow-shaped core such that the fibre material is present in the core with gradually varying mass quantity per unit volume in the core such that a greater number of fibres per volume constitutes the portion of the core having the greatest need for absorbent ability, the mass quantity per volume decreasing gradually in all directions away from said portion, the core having substantially the same thickness all over. A core in accordance with the invention will thus possess a systematic or predetermined gradually-varying mass-density distribution.
Within this inventive concept one can make cores having a wide variety of characteristics, making it possible to suit any particular need and having the characteristics and qualities desired.
In connection with a core for a sanitary napkin the concept will involve that the core mass is designed to have the greatest density in the centre portion of the core, the density gradually decreasing to both sides laterally outwardly and in longitudinal direction of the core, simultaneously as the cross-sectional area depth of the core can be made to be substantially constant. Hereby is obtained that the absorbing capacity is concentrated in the area where the need is greatest, i.e. in the centre portion, since this portion will contain most mass per volume. Simultaneously, however, a gradually reduced mass density to both sides in longitudinal direction of the core will result in that the absorbed liquid easily will be distributed from the centre of the core. The resistance against liquid penetration and thus the liquid distribution ability of the core will (always) increase as the mass density decreases. This property is efiectively utilized by the invention such that conventional special distribution layers or the like can be entirely omitted.
A core in accordance with the invention is suitably made by having the core material, for instance defibrated cellulosis continuously produced in the shape of a web in per se known machinery having varying or alternating mass density in the longitudinal direction, the cycles or frequency of the alternations corresponding to the desired length of each individual sanitary napkin core. Simultaneously the web is given uniform or substantially uniform thickness and width, i.e. constant cross-sectional area per unit length. The web is thereafter cut transversely through the portions having the least mass density into individual napkin cores.
In the following the invention shall be described in detail with reference to the accompanying drawing, where,
FIG. 1 shows a longitudinal sectional view through a core of conventional type,
FIG. 2 shows a similar longitudinal sectional view through a sanitary napkin core made in accordance with the present invention.
FIG. 3 shows the napkin core shown in FIG. 2, having the shape it will attain when the napkin wrapper is subject to tension and/or sideways compression.
The conventional napkin core 2, shown in FIG. 1, comprises several layers 4, 4, etc. each having decreasing length viewed from the centre portion, such that the core in longitudinal sec tion (and possibly in cross section) is attaining substantially elliptical shape, as indicated with dotted lines 6. One or more liquid distributing layers can bepositioned between the layers. In the FIG. is shown a distributing layer 8 in the centre of the core.
A napkin core 10 in accordance with the invention is shown in longitudinal section in FIG. 2. As it appears, the mass density-which is visualized by the degree of the hatching-is vary- .ing, and it is greatest in the centre. Furthermore, it will be observed that the core, seen in longitudinal section, has a rectangular shape. To what extent the rectangular cross-sectional shape of the core will be retained subsequently (and provided with wrapping) will depend upon several factors, such as the flexibility of the material (i.e. the elasticity of the fibres), the mass density and the specific properties of the material. By treating the core with binding, adhesion or stiffening compositions one can eliminate or reduce the propensity of the materialto return to the original shape and condition subsequent to a compression or squeezing together.
In most cases the core will possess, however, subsequent to its making, some inherent propensity to expand, the magnitude of this expansion force will be somewhat proportional to the mass density, such that the core may, if desired, sub sequent to its making immediately attain a shape which can be compared with the shape of the core shown in FIG. 1, but a core in accordance with the invention will still retain such greater mass density in the centre portion, such as illustrated in FIG. 2.
When making cores for sanitary napkins it has proved advantageous, as mentioned before, to make the core such that the core has a substantially rectangular shape, viewed in longitudinal section, among other reasons because this shape facilitates the handling of the core and the packing of the napkins, and which among other operations involves that the mp respective ends are attached to a belt) particularly the end portions of the napkin core will be subject to compression or sideways squeezing, such as schematically illustrated in FIG.
ing mass density from the centre the squeezing together of the end portions of a core in accordance with the invention will be much larger, and the compression forces K towards the end portions of the core also will result in a force component designated with the capital letter F directed towards the centre and thereby contribute to deliberation of inherent expansion propensity of the fibres and the mass in the centre portion of the core, so that the centre portion in fact may tend to expand. Tests have shown, however, that a napkin core in accordance with the invention still will retain a much larger mass density in the centre portion, so that this portion possesses greater absorbing capacity and maintain ability to distribute moisture and liquid to the surrounding, more porous material.
In that the end portions of .the napkin core are squeezed together-more or less-during use, the napkin will thereby attain the desirous elliptical cross-sectional shape enhancing wearing comfort etc. The napkin core may nevertheless initially have a rectangular cross-sectional shape with the described advantages attained thereto.
By varying the mass density of the core, particularly the mass density variation in longitudinal direction, it has proved to be possible to make napkin cores having just the absorbing and expanding qualities which are desirable for the particular need in question.
1. An absorbent core having substantially the same thickness throughout before being used and not being subjected to external forces of compression, for use in a sanitary napkin, a diaper, compresses and the like comprising a flat unitary, integral body of absorbent fibrous material, said fibrous material in said body having a gradually varying mass density so that a greater number of fibres per volume is present in that portion of said body having the greatest need for absorbing power, said mass density being gradually reduced in a direction away from said portion.
2. An absorbent core in accordance with claim 1 wherein said body when exposed to substantially evenly distributed compressional forces against the side face areas thereof attains a substantially oval shape in a longitudinal cross section 3. An absorbent core in accordance with claim 1 wherein said body is resilient.