Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With liberating or forming of particles
Reexamination Certificate
2001-12-14
2003-11-11
Lechert, Jr., Stephen J. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With liberating or forming of particles
C264S121000, C264S122000, C264S126000
Reexamination Certificate
active
06645407
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for making absorbent material useful in personal care absorbent articles, medical absorbent articles and the like, in which a superabsorbent polymer component of the absorbent material is synthesized during manufacture of the absorbent material.
BACKGROUND OF THE INVENTION
Processes for forming absorbent composite materials from cellulose fibers and the like are known. U.S. Pat. No. 5,350,624 to Georger et al.; U.S. Pat. No. 4,902,559 to Eschwey et al.; U.S. Pat. No. 4,818,464 to Lau and U.S. Pat. No. 4,100,324 to Anderson et al. disclose processes for combining absorbent cellulose fibers with thermoplastic fibers to make absorbent composites. At least one meltblown die head, used for making meltblown fibers, is arranged near a chute, or as in the case of Eschwey the continuous fibers are spun into a duct containing fiberized pulp. Cellulose fibers and, possibly, other materials are injected from the chute into the nascent fiber stream while the fibers are forming. Pre-formed particles or fibers of superabsorbent material may also be added through the chute. These processes are generally referred to as “coform” processes.
Various processes for making superabsorbent polymers which are useful in absorbent composite materials are also known. U.S. Pat. No. 5,962,068, issued to Tsuchiya et al., discloses a process for producing a water-absorptive composite. First, an aqueous monomer solution containing a polymerizable monomer capable of producing a water-absorptive polymer is provided. Then, polymerization is initiated using a redox polymerization initiator. The resultant reaction mixture, which is partially polymerized, is applied dropwise onto a fibrous substrate. The polymerization is completed on the substrate.
One feature that the known processes have in common is that they require at least some separate process steps for polymerizing or partially polymerizing the superabsorbent material before it can be added to the forming process for the absorbent composite. In other words, neither process totally integrates the superabsorbent polymer formation with the ultimate process for forming the absorbent composite.
Definitions
The term “cellulose fibers” refers to fibers from natural sources such as woody and non-woody plants, regenerated cellulose, and derivatives from these fibers by means of chemical, mechanical or thermal treatment, or any combination of these. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for instance, cotton, flax, esparto grass, milkweed, straw, jute hemp, and bagasse. Regenerated cellulose fibers include, for instance, viscose and rayon. The cellulose derivatives include, for instance, microcrystalline cellulose, chemically crosslinked fibers, and chemically uncrosslinked, twisted fibers.
The term “average pulp fiber length” refers to a weighted average length of pulp determined using a Kajaani fiber analyzer Model No. FS-100 available from Kajaani Oy Electronics in Kajaani, Finland. Under the test procedure, a fiber sample is treated with a macerating liquid to ensure that no fiber bundles or shives are present. Each fiber sample is dispersed in hot water and diluted to about a 0.001% concentration. Individual test samples are drawn in approximately 50 to 500 ml portions from the dilute solution and tested using the standard Kajaani fiber analysis procedure. The weighted average fiber lengths may be expressed by the following equation:
∑
X
1
>
0
k
(
X
1
*
n
i
)
/
n
where
k=maximum fiber length,
X
i
=individual fiber length,
n
i
=number of fibers having length X
i
and n=total number of fibers measured.
The term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in diameter, and are generally self bonding when deposited onto a collecting surface.
The term “spunbonded fibers” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are quenched and generally not tacky on the surface when they enter the draw unit, or when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and may have average diameters larger than 7 microns, often between about 10 and 30 microns. In both cases above the fibers are attenuated to their final diameter by aerodynamic drawing processes.
The term “staple filaments or fibers” means filaments or fibers which are natural or which are cut from a manufactured filament prior to forming into a web, and which have a length ranging from about 0.1 -15 cm, more commonly about 0.2-7 cm.
The term “microfibers” means small diameter fibers having an average diameter not greater than about 75 microns, for example, having an average diameter of from about 0.05 micron to about 50 microns, or more particularly, having an average diameter of from about 0.1 micron to about 10 microns, or even more typically 0.5 micron to about 5 microns.
The term “substantially continuous filaments or fibers” refers to filaments or fibers prepared by extrusion from a spinnerette, including without limitation spunbonded and meltblown fibers, which are not cut from their original length prior to being formed into a nonwoven web or fabric. Substantially continuous filaments or fibers may have lengths ranging from greater than about 15 cm to more than one meter; and up to the length of the nonwoven web or fabric being formed. The definition of “substantially continuous filaments or fibers” includes those which are not cut prior to being formed into a nonwoven web or fabric, but which are later cut when the nonwoven web or fabric is cut.
The term “nonwoven fabric or web” means a web having a structure of individual fibers or filaments which are interlaid, but not in an identifiable manner as in a knitted fabric. The terms “fiber” and “filament” are used herein interchangeably. Nonwoven fabrics or webs have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, air laying processes, and bonded carded web processes. The term also includes films that have been perforated or otherwise treated to allow air to pass through. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91.)
The term “polymer” generally includes but is not limited to, homopolymers, copolymers, including block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
The term “wettable” and/o
Jackson David Martin
Kellenberger Stanley R.
Ko Young C.
Laumer Jason M.
Ranganathan Sridhar
Kimberly--Clark Worldwide, Inc.
Lechert Jr. Stephen J.
Pauley Petersen & Erickson
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