Absorbent members for body fluids using hydrogel-forming...

Details Absorbent members for body fluids using hydrogel-forming... Absorbent members for body fluids using hydrogel-forming...

2000-03-13

2002-08-27

Weiss, John G. (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S366000, C604S372000, C604S375000, C604S378000

Reexamination Certificate

active

06441266

ABSTRACT:

BACKGROUND OF THE INVENTION
The development of highly absorbent members for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins, is the subject of substantial commercial interest. A highly desired characteristic for such products is thinness. Thinner products are less bulky to wear, fit better under clothing, and are less noticeable. They are also more compact in the package, making the products easier for the consumer to carry and store. Smaller products allow reduced distribution costs for the manufacturer and distributor, require less shelf space required in the store per diaper unit, and require less packaging material.
The ability to provide thinner absorbent articles such as diapers is contingent on the ability to develop relatively thin absorbent cores or structures that can acquire and store large quantities of discharged body fluids such as urine or menses. In this regard, the use of certain absorbent polymers often referred to as “hydrogels,” “superabsorbents” or “hydrocolloid” material has been particularly important. See, for example, U.S. Pat. No. 3,699,103 (Harper et al.), issued Jun. 13, 1972, and U.S. Pat. No. 3,770,731 (Harmon), issued Jun. 20, 1972, that disclose the use of such absorbent polymers (hereafter “hydrogel-forming absorbent polymers”, or HFAPs) in absorbent articles. Indeed, the development of thinner products has been the direct consequence of thinner absorbent cores that take advantage of the ability of these hydrogel-forming absorbent polymers to absorb large quantities of discharged body fluids, typically when used in combination with a fibrous matrix as compared with a fibrous matrix alone. See, for example, U.S. Pat. No. 4,673,402 (Weisman et al.), issued Jun. 16, 1987 and U.S. Pat. No. 4,935,022 (Lash et al.), issued Jun. 19, 1990, that disclose dual-layer core structures comprising a fibrous matrix and hydrogel-forming absorbent polymers useful in fashioning thin, compact, products.
Significant prior art describes absorbent structures having relatively low amounts (e.g., less than about 50% by weight) of these hydrogel-forming absorbent polymers. See, for example, U.S. Pat. No. 4,834,735 (Alemany et al.), issued May 30, 1989 (preferably from about 9 to about 50% hydrogel-forming absorbent polymer in the fibrous matrix). There are several reasons for this. The hydrogel-forming absorbent polymers employed in prior absorbent structures have generally not had an absorption rate that would allow them to quickly absorb body fluids, especially in “gush” situations. This has necessitated the inclusion of fibers, typically wood pulp fibers, to serve as temporary reservoirs to hold the discharged fluids until absorbed by the hydrogel-forming absorbent polymer. This fluid is not tightly held in storage cores and can be expressed by pressure or capillary contact back onto the skin of the wearer, resulting in undesirable skin wetness. In order to maintain skin dryness, such fluid must be gelled quickly and completely. Also, cores made with relatively low concentrations of HFAP are inherently relatively thick and bulky.
HFAPs are often made by polymerizing unsaturated carboxylic acids or derivatives thereof, such as acrylic acid or its salt with low levels of crosslinking monomers, typically di- or poly-functional monomer materials such as N, N′-methylenebisacrylamide, trimethylol propane triacrylate, or triallyl amine. The presence of crosslinking monomers renders these polymers water-insoluble, yet water-swellable. Higher levels of cross-linking increase gel strength while reducing gel volumes. Gel strength relates to the tendency of the hydrogel formed from these polymers to deform or “flow” under an applied stress. Gel strength needs to be such that the hydrogel formed does not deform and fill to an unacceptable degree the capillary void spaces in the absorbent structure or article, a phenomenon called “gel blocking”. This would otherwise reduce the rate of absorption and the fluid distribution throughout the structure/article. Various designs have been advocated for reducing or preventing gel blocking, some of which require use of added fibrous material which tends to increase the thickness of the product undesirably. See, for example, U.S. Pat. No. 4,654,039 (Brandt et al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988 as U.S. Reissue Pat. No. 32,649), U.S. Pat. No. 4,834,735 (Alemany et al.), issued May 30, 1989. U.S. Pat. No. 5,652,646 (Goldman et al.), issued Oct. 8, 1996, describes use of HFAPs which have both high porosity and high strength in high concentration cores. This patent therefore addresses the problem of gel blocking in high concentration HFAP regions by using HFAPs that retain porosity such that additional fibers are not necessary.
The effective rate at which these hydrogel-forming polymers will gel in the presence of body fluids (e.g., urine) is also important. A typical current hydrogel-forming polymer will gel completely when exposed to excess aqueous fluids such as urine over a period of about 5-20 minutes.
The rate of gellation of HFAPs in aqueous fluids has been measured by several techniques. The vortex method described in U.S. Pat. No. 5,601,542 involves addition of HFAP to a stirring aqueous solution and measuring the time required for the solution to seize and stop stirring. This patent describes absorbent cores having concentrations of HFAP of 30-100% which also have a Pressure Absorbency Index (PAI) (a value said to relate to insensitivity to pressure, infra) of at least 120 and extractables levels of less than about 13 wt. percent. Claim
29
of this patent describes similar high concentration cores made with HFAPS having a PAI of at least 120 and a vortex time of less than about 45 seconds.
The Free Swell Rate (FSR) method described in U.S. Pat. No. 5,149,335 (Kellenberger et al.) issued Sep. 22, 1992 involves determination of the time required for 1.0 g of HFAP to imbibe 20 mL of test fluid.
Yet another method involves microscopic examination of the HFAP in the gelling solution and measuring the dimensions at specific time intervals (Tanaka, T.; Fillmore, D. J.
J. Chem. Phys
., 1979, 70, 1214).
Still another method involves spectrophotometric monitoring of a dye which is excluded from the gel in excess aqueous solution which becomes concentrated as the gel expands, as described in a Diploma Thesis by Herbert Heitmann, Universitat Dortmund Lehrstuhl fur Thermische Verfahrenstechnik, August 1989.
Each of these methods suffers from certain deficiencies. The vortex method has a subjective end point. This end point may also be unduly influenced by the presence of high molecular weight extractable components which can prematurely thicken the solution. The FSR method and the vortex method do not distinguish between fluid which is actually gelled and fluid which is loosely held interstitially, and thus can be easily expressed by pressure or capillary contact back onto the skin of the wearer. It is believed that a substantial fraction of the fluid (e.g., on the order of about 50% or more) at the FSR endpoint is held interstitially. It is further believed that the fraction of fluid held interstitially at the FSR endpoint will vary depending on particle morphology. Also, the FSR method is not usable for HFAPs which absorb the fluid very quickly as the apparent fluid uptake is achieved before all of the HFAP used in the test is wetted. The FSR method, like the vortex method, has an imprecise endpoint, which is particularly critical for very fast HFAPs. The spectrophotometric method, as described above, is not quickly responsive to changes in gel volume. Such a quick response requires minimal lag time between sampling and the reading of optical absorbency. This obviously becomes important for very fast HFAPs. Also, this method does not filter out floating pieces of small material generated during stirring which tend to interfere with the light path.
Applicants have modified the spectrophotometric method to provide data on the actual rate of gellation critical to

Affiliated with

Also associated with

Rating

Absorbent members for body fluids using hydrogel-forming... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Absorbent members for body fluids using hydrogel-forming..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Absorbent members for body fluids using hydrogel-forming... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2911864