Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing multilayer work or article
Reexamination Certificate
2000-11-27
2003-11-25
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing multilayer work or article
C264S517000, C264S112000, C264S113000, C425S081100
Reexamination Certificate
active
06652798
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for the manufacture of absorbent cores or pads for absorbent articles such as disposable diapers, sanitary napkins, incontinence pads and the like. More particularly, the present invention relates to an apparatus for forming multi-layered absorbent cores by the air-laying technique.
Multi-layered absorbent cores in accordance with the present invention comprise at least two layers of air-laid fibrous material webs, one of the layers being superimposed on the other and comprising fibers mixed with discrete particles. The fibers of the respective layers can be the same or different and consist of hydrophilic or hydrophobic fiber material or a mixture of both. Additionally, the fibers can comprise a cellulosic or chemical pulp. The discrete particles are provided to enhance the absorbing property and the ability to retain body fluids and wastes, also under pressure, and generally comprise an absorbent gelling material in the form of hydrogel particles. PreferablY, the absorbent gelling material comprises so-called superabsorbent. However, the type of fiber and discrete particles of absorbent gelling material does not form an essential part of the present invention and any combination thereof suitable for the intended purpose of the absorbent core can be selected.
For the purposes of the present invention, a standard absorbent article has at least a dual-layer or triple-layer absorbent core wherein an outer (first) or both outer (first and third) layers are formed by a shaped core component essentially consisting of an air-laid fibrous material web. An inner or middle core (second) substantially uniform mixture of fibrous material and discreted particles of absorbent material. The outer layer or layers generally define the shape of the absorbent core and follow the shape of the absorbent article in which the core is incorporated. The insert or middle core layer can either have the same shape as the outer layer or layers or it can have a smaller shape and be placed at a location where the body fluid or liquid absorption and retaining properties thereof are most desired and beneficial in the absorbent article incorporating it.
BACKGROUND OF THE INVENTION
An apparatus for the manufacture of multi-layered absorbent pads is known from U.S. Pat. No. 4,598,441. In order to produce a dual-layer absorbent pad, two air-laying apparatus respectively in the form of rotatable drums with perforated forming moulds on their peripheries are provided to form the two fibrous web layers. A first transfer roll is provided between the two air laying drums and picks up a formed first fiber web from the first air-laying apparatus and places this on a second fiber web already formed on the second air-laying drum. This dual-layer absorbent pad is then removed by a further transfer roll from the second air-laying drum and placed on a conveyor for further processing. An optional feature of this known apparatus is the placement of an insert between the two main fiber layers, said insert possibly being a superabsorbent medium. The superabsorbent medium is applied as a discrete layer in powdered or granulated form on the first fiber web while the latter is transferred on the first transfer roll from the first to the second air-laying drum. Suction boxes are provided inside the respective cylinders forming the air-laying drums and the transfer rolls to maintain the fiber layers thereon while they are being transported through the apparatus. However, the air-laying of a fibrous web substantially uniformly mixed with discrete particles of superabsorbent is not disclosed. In any case, this known apparatus is not suitable for producing an absorbent core comprising such a fibrous web uniformly mixed with discrete particles because such particles would fall out along the long path of conveyance through the apparatus. Additionally, the known apparatus is relatively bulky.
Another example of a method and an apparatus for forming-air-laid fibrous absorbent cores is known from FR-A-2 690 843. A first supply of air-entrained fibrous material is deposited on a first movable forming element, and a second supply of air-entrained fibrous material is deposited on a second movable forming element. Subsequently, the first formed component is positioned on an assembly cylinder, and the second formed component is positioned onto the first formed component on the assembly cylinder. In addition, the device comprises a transfer cylinder to transfer the absorbent cores to a conveyor belt. However, the. manner in which superabsorbent material could be included and whether such material was dispersed with the fibrous material or not is not disclosed. Moreover, the apparatus according to FR-A-2 690 843 is relatively bulky as well because of the additional assembly and transfer cylinders.
A method and an apparatus for forming absorbent cores or pads is also known from GB-A-2 124 264. The absorbent core comprises two layers of air-laid fibrous webs which may be of the same or different types. Separate streams of air-entrained fibers are air-laid on an endless perforated belt at locations spaced from each other along the moving belt to form a layered pad. Air from the air-entrained fiber streams is removed via a vacuum chamber disposed beneath the perforated belt.
However, various problems arise in air-laying absorbent cores with a multiplicity of layers including one or more layers containing a mixture of fibers and discrete particles. As the air must be removed from beneath the perforated forming element of the air-laying apparatus, some of the discrete particles mixed with the fibers can be drawn through the perforated forming element so that these particles, which may consist of expensive absorbent gelling materials, are lost. This has the additional disadvantage that the absorbent core is reduced in absorbent capacity. A further problem that can arise is the blocking of air flow through the perforated forming element by larger absorbent particles lodged in the perforations so that the finished absorbent pad does not have the desired structure.
These problems are partially solved by a method and an apparatus disclosed in EP-A-0 292 624 for forming air-laid absorbent cores having a multiplicity of layers. For an absorbent core comprising two main layers, air-entrained fibrous material is split into streams and fed to two separate air-laying apparatus arranged along a conveyor system. In the first drum-type air-laying apparatus for producing the layer comprising a fibrous web mixed with discrete particles of an absorbent gelling material, a so-called dusting layer is first formed by blowing a first air-entrained fiber stream onto the perforated forming element of the air-laying apparatus. A main stream of air-entrained fibrous material mixed with discrete particles is then blown onto the dusting layer to form the main fibrous layer mixed with the discrete particles. The dusting layer acts as a filter screen to prevent passage of small discrete particles through the forming element and prevent large particles from plugging the openings therein.
However, the method and apparatus known from EP-A-0 292 624 have various disadvantages. The final absorbent core is produced from the respective fibrous webs formed in the two air-laying apparatus located at a distance from each other in that the two formed webs are placed on separate endless conveyor belt systems and conveyed from there to a location at which they are only then united to produce the finished absorbent core. Therefore, the speed of the arrangement is limited as too high a speed of the respective conveyers may result in the fibrous webs located thereon being damaged or lifted off the conveyor due to air resistance. Further, the apparatus as a whole takes up a lot of space and requires a complicated and expensive conveying system. A particular disadvantage also lies in that the fibrous web comprising the discrete particles must travel long distances along which particles can fall out of the web so that t
SCA Hygiene Products AB
Theisen Mary Lynn
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