Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-08-31
2002-10-01
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S916000
Reexamination Certificate
active
06458877
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a composition comprising a thermoplastic component and at least one superabsorbent polymer, methods of use for such composition, and articles comprising such composition. The composition may be formed into a film layer or applied to an article with various hot melt adhesive application techniques. The composition is useful for a variety of end-uses, particularly for use in disposable absorbent articles such as disposable diapers, feminine napkins and medical dressings.
BACKGROUND OF THE INVENTION
Water-insoluble, water swellable hydrogel-forming absorbent polymers, also referred to as superabsorbent polymers (SAP), are capable of absorbing large quantities of liquids such as water, body fluids (e.g., urine, blood), industrial fluids, household fluids and are further capable of retaining such absorbed liquids under moderate pressures.
For example, SAP is employed in various cable applications to shield the penetration of moisture. When the outer sheath of the cable is damaged allowing penetration of fluids, the SAP absorbs the incoming liquid and swells, forming a physical barrier to the entry of any further fluid. Particulate SAP is typically held in place by means of a hydrosoluble binder. For example, U.S. Pat. No. 4,837,077 issued to Anton et al., Jun. 6, 1989, relates to a hydroexpansible composite material including a solid flat support having on at least one of its faces a coating with a high proportion of a hydroexpansible polymer powder fixed to the support by means of a hydrosoluble binder, the coating being essentially formed of 95% to 55% by weight of a hydroexpansible polymer powder, 5% to 23% by weight of a hydrosoluble binder, and surfactant in a positive amount of up to 22% by weight. The ingredients are homogenized by means of a liquid. This reference expressly teaches that thermoplastic substances cause an unfavorable effect, the blockage of a part of the hydroexpansible polymer powder, thus limiting its ability to swell in the presence of water.
The absorption characteristics of SAP materials make them especially useful for incorporation into absorbent articles such as disposable diapers, adult incontinent pads and briefs, and catamenial products such as sanitary napkins and the like. A desired characteristic of such disposable absorbent articles is thinness. Thinner disposable articles are less bulky to wear, better fitting under clothing and are less noticeable. Further, thin disposable absorbent articles are more compact, making the product easier for the consumer to carry and store. Compactness in packaging also results in reduced distribution costs for the manufacturer and the distributor, including less shelf space. The ability to provide thinner absorbent articles such as a diaper has been contingent on the ability to develop relatively thin absorbent cores or structures that can acquire and store large quantities of fluid, particularly urine. Therefore, there is a trend towards employing higher concentrations of SAP polymers to achieve this purpose.
SAP is typically available in a particulate or powder form that is sprinkled or sifted into the absorbent core portion, which is sandwiched between a fluid pervious topsheet and a fluid impervious backsheet. The incorporation of particulate SAP into an article tends to generate dust from the SAP fines. Further, conventional absorbent articles have the limitation that the absorbent gelling particles are not immobilized and are free to migrate and shift during the manufacturing process and/or use. Movement of the SAP particles during manufacture can lead to absorbent material handling losses during manufacturing operations as well as improper distribution of the particles.
Other problems occur when these absorbent gelling particles migrate during and after swelling. The inability to fix the particles at optimum locations leads to insufficient fluid storage in one area and over-capacity in other areas due to the movement of the SAP particles to locations other than where originally positioned. Another important factor that has to be considered is the liquid permeability of the SAP. It has been discovered that the fluid transport properties of the gel layer formed as a result of the swelling SAP particles in the presence of fluids is extremely important. Although the formation of a SAP gel layer fluid barrier, known as “gel blocking” is desirable for some applications, such as for use in cables, the formation of gel layers in disposable absorbent products is undesirable since it greatly reduces the efficiency of the SAP. Thus, the advantages of being able to fixate SAP in place are apparent and several ways of accomplishing such have been suggested.
For example, U.S. Pat. No. 4,392,908 issued to Dehnel Jul. 12, 1983, concerns a process for manufacturing a water-absorbent article in which particles of a water swellable polymer are fixed to a water-absorbent substrate. The process includes the steps of forming on the surface of water-swellable particles a coating of a thermoplastic adhesive resin; locating the coated particles in their unswollen state and dry state on or within the water-absorbent substrate also in the dry state; and applying heat to soften the thermoplastic coating of the particles and pressing the particles and substrate to cause the particles to be bound to the substrate. The particles of absorbent material can be coated by mixing the absorbent particle with an aqueous latex of the resin and then drying the mixture, spraying a resin solution or latex onto the particles, adding the resin to the particles when the particles are in a slurry, or incorporating the thermoplastic as a solution or latex during the manufacture of the absorbent material.
Further, SAP particles may be combined with certain thermoplastic compositions.
U.S. Pat. No. 4,977,211 issued to Doi, Dec. 11, 1990, teaches a moldable water-absorptive resin composition which comprises (A) 5% to 95% by weight of a water-absorptive resin and 95% to 5% by weight of (B) a polyolefin resin and (C) an ethylene/alpha-olefin copolymer rubber based on the total content of said components (A), (B) and (C), wherein the contents of (C) amounts to 20% to 80% by weight based on the total contents of said component (B) and (C). An ethylene/vinyl acetate copolymer is exemplified having a vinyl acetate content of 33% by weight and a melt index of 30 g/10 min. Subsequently, the water-absorptive resin composition of the present invention can be molded into a form suitable for its final use. The molded products may be subjected to a secondary molding treatment such as foaming or orientation. The compositions can be molded alone into a film, a sheet, fibers or other products.
Japanese Patent Application 9-176618 published Jul. 8, 1997 relates to a water-swelling hot melt presealant for lap joint construction external wall material. The composition includes 20 wt-% to 50 wt-% thermoplastic elastomer, 5 wt-% to 40 wt-% tackifier, 10 wt-% to 50 wt-% plasticizer and 5 wt-% to 35 wt-% water swellable resin. The plasticizer is described as paraffin type oil, naphthene type oil, aromatic type oil, polybutene liquid rubber, polyisobutylene liquid rubber, polyisoprene liquid rubber and its hydrogenated product.
Japanese Patent Application 60-195299, published Oct. 3, 1985 pertains to a method for preventing water leaks with good operability, especially in engineering work and construction employing a water-swellable composition styrene elastomers, highly water absorbing materials and tackifiers. The proportions of the ingredients are usually 5-100 parts of the highly water-absorbing resin and 100 to 200 parts of tackifier based on 100 parts of the styrene elastomer.
More recently, WO 98/27559A1, published Jun. 25, 1998 concerns a water swellable thermoplastic compound for gluing and coating made from a water insoluble component, a water soluble or water dispersible component, and a water-swellable component. Examples of suitable water-soluble or water dispersible oligomers, homopolymer or copolymers includ
Ahmed Sharf U.
Clapp Leslie J.
Emiru Andualem W.
Kroll Mark S.
Cain Edward J.
Lee Katarzyna W.
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