Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
2000-12-29
2003-04-29
Calvert, John J. (Department: 3765)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C156S073100, C156S091000, C156S580000, C604S385010
Reexamination Certificate
active
06555731
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to disposable personal care products, such as diapers, feminine care products and adult incontinence products. More specifically, the invention relates to products having improved absorbent core integrity, and methods for producing such products through ultrasonic compressions.
BACKGROUND OF THE INVENTION
Disposable care products are typically comprised of at least three general layers. These include an absorbent core placed between a liquid permeable inner liner and a liquid impermeable outer cover. The inner liner and outer cover can comprise one or more individual layers of materials, and additional layers can also be interposed between any of the general layers. For example, in the disposable diaper, the inner liner can comprise a surge layer consisting of thermoplastic fibers positioned beneath a thermoplastic mesh. Additionally, a tissue material, or wrap sheet, is often positioned between the outer cover and absorbent core, and between the surge layer and the absorbent core. At the diaper periphery, the material layers extending to the periphery are held together by conventional means, such as adhesives, crimping, fusing, or other methods known in the art.
The absorbent core receives and retains bodily fluids. It consists of a natural fiber batt that has a strong affinity for water and other hydrophilic components of bodily secretions. A dispersion of superabsorbent particles can also be incorporated into the fibrous core.
Maintaining a continuous, intact core, especially when these articles are used, is a recurring issue in the disposable garment industry. Breaks in the continuum of the core create open spaces that prevent the transport of fluid into the core, and the wicking of the fluid in the core. This breakdown of the core structure can cause fluids to leak out of the periphery of the diaper. The core breakdown also results in its sagging, which is visually unappealing to the consumer.
In the disposable diaper, adhesives used to bond various material interfaces within the diaper have not eliminated the breakdown of the absorbent core. The adhesive is conventionally applied in a swirl, spray or bead pattern between the outer cover and the wrap sheet, and/or between the surge layer and the wrap sheet. Moreover, adhesives placed between the wrap sheet and the inner liner reduce the absorbent property of the core by blocking the transport of fluids between these layers. The addition of an adhesive also increases the raw material costs associated with assembling disposable diapers. The standard adhesive loading is 0.31 to 0.33 grams of adhesive per diaper. Core integrity is not maintained at this loading. Additionally, it has been found that increasing the adhesive weight by tenfold, i.e., 3.1 to 3.3 grams per diaper does not appreciably improve core integrity.
Ultrasonically compressing the absorbent core between the inner liner and outer cover can be used in place of an adhesive to maintain the core integrity. Ultrasonic bonding involves high frequency mechanical energy transfers in the form of a reciprocating vertical motion. When ultrasonic energy is applied to several material layers, the vibrations within each material layer generate heat. Ultrasonic vibrations within a thermoplastic material will soften or melt the thermoplastic material if the heat generated increases the temperature of the thermoplastic material above the glass transition temperature or melting temperature, respectively. Thermoplastic materials are thus considered fusible.
The high crystallinity and high melting point of natural fibers makes these fibers infusible at the temperatures needed to soften or melt conventional thermoplastics. Since natural fibers are in general infusible, few attempts have been made to ultrasonically bond or weld a natural fiber core between two fusible materials. To ultrasonically bond a natural fiber core between two fusible materials, enough energy must be applied, and maintained within the layers, to fuse the fusible materials at the surface of the core, or to each other through the interstitial void volume in the core, without sufficiently deforming the fusible layers.
European Patent Application 0 438 113 A1 to S. J. Anapol et al. discloses an absorbent batt structure that has a discrete pattern of hydrogen bonded compressed portions formed on at least one surface of the batt. The batt contains fibers that are formed from a loose assemblage of cellulose, and, if needed, thermoplastic fibers, that has a discrete pattern of bonded compressed portions formed on at least one surface of the batt. These discrete compressions result in a batt structure with discrete density gradients, uniformly placed across the surface of the batt. These density gradients, in turn, result in enhanced fluid transfer between adjacent compressed portions, while substantially maintaining the absorbency of the batt. A water spray is applied to the surface of the batt and then an embossing roll, or ultrasonic energy, is applied to the surface to define a plurality of substantially, uniformly spaced, hydrogen-bonded compressed portions. Here, the core only is compressed and assembled into the final product, and a water spray is required to form the compressions in the core. Thus, a costly intermittent compression step is needed. The water spray may be needed to provide water molecules for hydrogen bond formation.
Other work involving absorbent articles disclose an actual fusion, or mechanical bonding of the material layers, as opposed to a pure compression of the these layers. For example, U.S. Pat. Nos. 4,823,783 and 5,059,277 to W. Willhite et al. disclose a method and apparatus for ultrasonically bonding continuous moving webs to one another using a stationary vibrating horn and a slick, thermally resistant slip layer. The slip layer is placed between the webs and the horns to prevent web damage. In this method, at least one of the webs to be bonded is comprised of a polymeric material which can be locally melted or softened by the input of mechanical energy. The slip layer maximizes heat retention in the web to be bonded, and ensures that neither the relatively delicate polymeric webs or the more resilient highly compressible webs are damaged in the bonding process. Two or more webs can be bonded together, but the protective slip layer is not bonded to the resultant laminate structure. The nature of the bond formed between one or more heat softened polymeric webs and other layers in the structure will vary depending on the chemical makeup of the other layers. If one or more layers does not soften by the input of mechanical energy, but exhibits significant interstitial void volume, the bonding will likely comprise mechanical entanglements of the melted or softened polymeric webs with the infusible web or webs, and/or the fusing of the polymeric webs to one another through the interstitial void volume in the infusible web.
U.S. Pat. Nos. 5,269,860 discloses the fusion of a thermoplastic sheet onto a thermoplastic or a non-thermoplastic fibrous textile. The thermoplastic sheet can be ultrasonically fused to a textile substrate that has an equivalent or higher melting temperature than the thermoplastic sheet. Ultrasonic energy is applied to the thermoplastic sheet, and the sheet melts before the textile surface begins to soften. This results in a fusion between the melted thermoplastic and the textile fibers. The ultrasonic energy can be applied to localized sections of the thermoplastic sheet to form various patterns of the fused thermoplastic sheet and fiber substrate. U.S. Pat. No. 5,609,702 to V. E. Andersen discloses a method for mutually bonding at least two moving continuous webs to form a laminate containing at least one puckered material layer. These webs can be bonded by thermal or ultrasonic techniques. At least one of the webs comprises weldable material; however, the preferred approach is to bond webs, each containing a weldable material.
Other work in the area of articles containing an absorbent core have combined natural
Betrabet Chinmay S.
LaChapell Ruth A.
Calvert John J.
Grayson Angela J.
Kilpatrick & Stockton LLP
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