Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-01-09
2001-07-10
Copenheaver, Blaine (Department: 1771)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S290000, C156S296000, C156S308200
Reexamination Certificate
active
06258196
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sintered porous composite sheet having a multilayered structure, and more particularly relates to a sintered porous composite sheet which is air-permeable or moisture permeable and is useful as a top sheet or back sheet for a sanitary article or medical applications.
BACKGROUND OF THE INVENTION
Generally, sheet articles having a porous structure may be classified into the following five groups according to pore size:
Pore Size (&mgr;m)
Materials
Uses
0.01-0.1
Gas-Barrier Film
Gas Permeability
0.1-1.0
Film Filter
Water-Vapor Permeability
1.0-10.0
Meltblown, Flash-
Biobarrier
spinning Web
10.0-100
Conventional Nonwoven
Porous Articles
Fabric
100-1000
Perforated Nonwoven
Perforated Articles
Fabric
Among these porous sheets, those having a pore size of about 10 &mgr;m or less are generally referred to as “microporous materials.” Such sheets are produced according to special techniques for forming films, such as an extracting method, a phase separation method or a method which comprises adding an inorganic powder in a high concentration and stretching the film in a biaxial direction. Microporous sheets are widely applied to special filters, air permeable water-proof sports wear and the like. Microporous sheets are also used in composites in conjunction with nonwoven fabric and/or woven fabric.
For example, Japanese Patent KOKAI (Laid-Open) No. 14023/89 discloses a method of producing a porous sheet. There, a film of a crystalline polyolefine resin, a rubber-like polymer and an inorganic filler are first drawn and then hot-crimped to orient the film into a mesh-like sheet. The mesh-like sheet is then fixed and thermally contracted. The lack of uniformity of the mesh-like sheet causes deficient performance.
Further, porous sheets manufactured according to the conventional methods are generally hard and fragile. Consequently, porous sheets are not usually satisfactory as a high performance material for application in sanitary articles, medical articles, etc.
These and other drawbacks of the prior art are sought to be overcome by the porous composite sheet of the preferred embodiments.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high-performance porous sheet in which the foregoing defects are eliminated, and which is readily applicable to sanitary articles, medical articles, etc.
It is another object of the present invention to provide a method of producing such a porous sheet.
According to the preferred embodiments of the present invention, a sintered porous composite sheet preferably has A/B component layers in which the A-component layer is easily fusible and the B-component layer is more thermally stable than the A-component layer. The layers are preferably sintered together. When the A-component layer and the B-component layer are sintered together to produce the A/B component layers, the easily fusible properties of the A-component layer and the relatively high thermal stability of the B-component layer are realized.
Furthermore, according to the preferred embodiments of the present invention, there is disclosed a method of producing a sintered porous composite sheet, characterized in that a first porous layer and a second porous layer are superposed, wherein the first layer is easily fusible and the second layer has a relatively higher thermal stability as compared with the first layer. The first and second porous layers preferably are thermal treated under pressure and under such temperature conditions that the A-component layer is molten, while the B-component layer is stable. The melted A-component layer is applied to the B-component layer, and then allowed to cool and solidify. A three layer composite is obtained: an A-component layer which is molten and resolidified, an A/B component layer, and a B-component layer having low thermal deformation.
Moreover, according to the preferred embodiments of the present invention, there is disclosed a water-permeable composite sheet comprising a hydrophilic first layer and a second layer which is positioned so as to be adjacent to said first layer;
said first layer and said second layer contain a common component comprising an easily fusible material; and
said first layer and said second layer are bonded to each other at sintered sites which are formed by mutually sintering said common component which is contained in both layers,
whereby said composite sheet is water-permeable at said sintered sites.
The sintered sites may be formed substantially entirely over the surface of the composite sheet, or may be formed in any pattern over a portion of the surface. The common material which is contained in the first and second layers is preferably an easily fusible fiber. Alternatively, bicomponent fibers having an easily fusible sheath and a higher thermally stable core can be advantageously used as the common material. Furthermore, according to the preferred embodiments of the present invention, there is disclosed an absorbent product comprising a liquid-impermeable outer-sheet, a water-permeable composite inner sheet, and an absorbent core positioned between the outer sheet and the inner sheet.
The inventions of the preferred embodiments are in part founded on the unexpected discovery that a preformed porous layer may be hot-pressed to form a porous sheet having properties entirely different from those disclosed in Japanese Patent KOKAI (Laid-Open) No. 14023/89. Namely, according to the preferred embodiments of the present invention, two porous layers having different fusible properties are combined so that at least part of a fusible layer, i.e., a porous layer which has easily fusible properties, infiltrates voids of a porous layer which has a higher thermal stability. The layers are subsequently press bonded to each other and cooled. Accordingly, a sintered composite sheet which is porous in an extremely large range and has a variety of advantageous properties is obtained by selecting preferred materials and the conditions of the sintering. Table 1 enumerates some of the possibilities:
TABLE 1
Materials Constituting
Materials Constituting
Functional Material
Porous First Layer
Porous Second Layer
Obtained by Sintering
Up to 0.01 d PP/PE
Hydrophobic,
Waterproof Material
Microfibrils
Water-repellent
having Air-permeabil-
ity and Moisture-
permeability
Up to 0.1 d PP/PE Extra
Cotton-Spunlace
Surgical gown having
Fine Fibers
Nonwoven Fabric
Biobarrier properties
Up to 1 d PP Spunbond
PVA Sponge
Dustproof Controlling
Nonwoven Fabric
Material
PE/PET - Bicomponent-
Thermally bonded
Surface Material
Spunbond Nonwoven
Nonwoven Fabric
Fabric
containing Hydrophil-
icated PE/PET-
Bicomponent Fibers
At its basic level, the present invention comprises two bonded porous layers. The first layer is a microporous structure. The A-component layer infiltrates the voids of the second layer to form sintered portions of both the A-component and the B-component. In order to maintain dimensional stability without losing the porous structure of the B-component and without causing thermal contraction, etc., when the A-component is heated to a sintering state, the difference between the melting point of the A-component and the B-component is desirably 30° C. or more, and more desirably 50° C. or more. Preferably, the A-component comprises easily fusible materials, for example, polymeric materials such as PE, PP, PET and derivatives thereof, SEBS, SIS, and SEPS, and the combinations thereof. Suitable, slightly or nonfusible materials can be selected from the group consisting of cellulose, polyurethane, polyvinyl alcohol, polyphenol, polyacrylonitrile, polymeric polyester and nylon materials and derivatives thereof, which have a relatively higher melting point than the A-component. Any combination of these materials having a generally higher melting temperature than the A-component can be used in the practice of this invention.
In the present specification, the term “porous material” means a material having a specific gravity of about 0.2 g/cm
3
or
Fukui Hiroaki
Suzuki Migaku
Copenheaver Blaine
Hunton & Williams
Paragon Trade Brands, Inc.
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