Porous, absorbent, polymeric macrostructures and methods of making the same

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FIELD OF THE INVENTION

The present invention relates to absorbent polymeric compositions which, upon contacting liquids such as water or body exudates, swell and imbibe such liquids. More specifically, the present invention relates to polymeric compositions that are macrostructures such as a sheet, film, or strip. Such absorbent polymeric macrostructures are porous so as to be liquid permeable. These porous, absorbent, polymeric macrostructures are useful by themselves or in absorbent articles such as diapers, adult incontinence pads, sanitary napkins, and the like. The present invention also relates to methods of producing such porous, absorbent, polymeric macrostructures.

BACKGROUND OF THE INVENTION

Particulate, absorbent, polymeric compositions are capable of absorbing large quantities of liquids such as water and body exudates and which are further capable of retaining such absorbed liquids under moderate pressures. These absorption characteristics of such polymeric compositions make them especially useful for incorporation into absorbent articles such as diapers. For example, U.S. Pat. No. 3,699,103 issued to Harper et al. on June 13, 1972 and U.S. Pat. 3,670,731 issued to Harmon on June 20, 1972, both disclose the use of particulate, absorbent, polymeric compositions (also referred to as hydrogels, superabsorbent, or hydrocolloid materials) in absorbent articles.

Conventional particulate, absorbent, polymeric compositions, however, have the limitation that the particles are not immobilized and are free to migrate during processing and/or use. Migration of the particles during processing can lead to material handling losses during manufacturing operations as well as nonhomogeneous incorporation of the particles into structures in which the particles are being used. A more significant problem, though, occurs when these particulate materials migrate during or after swelling. Such mobility leads to high resistance to liquid flow through the material due to the lack of stable interparticle capillary or liquid transport channels. This phenomenon is one form of what is commonly referred to as "gel blocking".

One attempt to overcome the performance limitations associated with particle mobility in the context of their use in absorbent articles has been the incorporation of the particulate, absorbent, polymeric compositions into tissue laminates (layered absorbent members). By encapsulating the particles between tissue layers, the overall particle mobility within an absorbent member is diminished. However, upon liquid contact, the particles within the laminate are often free to move relative to each other resulting in the breakdown of any preexistent interparticle capillary channels.

Another attempted solution has been to immobilize the particulate, absorbent, polymeric compositions by the addition of large quantities of liquid polyhydroxy compounds that act as an adhesive to hold the particles together or to a substrate. An example of this technology is disclosed in U.S. Pat. No. 4,410,571 issued to Korpman on Oct. 18, 1983. While this approach does limit migration before and, to some extent, during swelling, the particles eventually become detached from each other upon presentation of excess liquid to such polymeric compositions, resulting again in the breakdown of any preexisting capillary channels between the particles.

A further attempt to overcome the problem has been to produce a superabsorbent film via extrusion of a solution of a linear polymer and subsequent crosslinking of the polymer. An example of this technology is disclosed in U.S. Pat. No. 4,861,539 issued to Allen et al. on Aug. 29, 1989. While these superabsorbent films may absorb significant quantities of liquids, they have limited liquid transport properties and are prone to gel blocking due to their lack of internal capillary channels.

Therefore, the present invention seeks to resolve the above problems by providing a porous, absorbent, polymeric macrostructure.

Thus, it is an object of the present invention to provide absorbent polymeric macrostructures that are porous.

It is a further object of the present invention to provide absorbent polymeric macrostructures that remain intact and transport liquid even upon saturation with excess liquid.

It is a still further object of the present invention to provide absorbent polymeric macrostructures wherein the component precursor particles and pores retain their relative geometry and spatial relationships even upon saturation with excess liquid.

It is an even further object of the present invention to provide absorbent polymeric macrostructures that increase in liquid permeability upon swelling.

It is another object of the present invention to provide a method for producing such absorbent polymeric macrostructures.

It a further object of the present invention to provide improved absorbent products, absorbent members, and absorbent articles (such as diapers or sanitary napkins) incorporating the absorbent polymeric macrostructures of the present invention.

SUMMARY OF THE INVENTION

The present invention provides an absorbent polymeric macrostructure that is porous. The porous, absorbent, polymeric macrostructure comprises an interparticle crosslinked aggregate having a circumscribed dry volume greater than about 10.0 mm.sup.3. The interparticle crosslinked aggregate comprises a multiplicity of precursor particles of substantially water-insoluble, absorbent, hydrogel-forming, polymer material; and an interparticle crosslinking agent reacted with the polymer material of the precursor particles to form crosslink bonds between different precursor particles. Because of the particulate nature of the precursor particles, the macrostructure has pores between adjacent precursor particles. The pores are interconnected by intercommunicating channels such that the macrostructure is liquid permeable (i.e., has capillary transport channels).

Due to the interparticle crosslink bonds formed between the precursor particles forming the interparticle crosslinked aggregate, the resultant macrostructure has improved structural integrity, increased liquid acquisition and distribution rates, and minimal gel blocking characteristics. It has been found that when the macrostructure is contacted with liquids, the macrostructure swells generally isotropically even under moderate confining pressures, imbibes such liquids into the precursor particles, and absorbs such liquids into the pores. The isotropic swelling of the macrostructure allows the precursor particles and the pores to maintain their relative geometry and spatial relationships even when swollen. Thus, the macrostructures are relatively "fluid stable" in that the precursor particles do not dissociate from each other, thereby minimizing the incidence of gel blocking and allowing the capillary channels to be maintained and enlarged when swollen so that the macrostructure may acquire and transport subseque