Patent Application
20170102306
Mass production of disposable diapers began in the 1960s. The early diaper cores consisted of 100% fluff pulp. The performance of these early cores was not sufficiently efficient, as the liquid absorbed by the fluff pulp was easily expressed from the structure upon application of pressure to a saturated core. The introduction of super absorbent polymers (SAP) in the early 1980s allowed for higher performance diaper cores. The use of SAP allowed for the reduction or complete removal of the bulky fluff pulp from the absorbent core. This allowed the diapers to become thinner while maintaining an improved performance. The reduction in physical s was a desired feature for consumers and also led to savings in handling and transportation of such products.
Absorbent products such as baby diapers, feminine hygiene pads and adult incontinence products are typically constructed of several different types of materials. These products typically include a permeable non-woven top sheet, an impermeable back sheet and an absorbent core sandwiched therebetween. The absorbent core typically consists of either wood fluff or synthetic fiber, e.g a TOW, and a liquid-absorbing polymer, e.g. a SAP.
The super absorbent polymers are typically based on acrylic acid and sodium acrylate, and are able to swell so as to absorb and retain a quantity of liquid several times the weight of the SAP, consequently forming a gel. The gel formation from the absorbed liquid allows the SAP to act as a fluid locking system, even under pressure.
The TOW fibers are a continuous “rope” of fibers consisting of many filaments loosely joined side-to-side. Filament is a continuous strand consisting of anything from 1 filament to many. Synthetic fiber is most often measured in a weight per linear measurement basis, along with cut length. Denier and Dtex are the most common weight to length measures. Cut-length only applies to staple fiber. Those fibers are oriented in machine direction and are capable of spontaneously transporting liquid on their surfaces. Presently available absorbent articles such as diapers, sanitary napkins, incontinence briefs, and the like are generally very good at absorbing aqueous fluids such as urine and blood. Generally with TOW in a diaper or similar article, which starts and stops at the ends of the diaper, or a staple fiber of some specified cut length, the ability to move fluid ceases once the fluid reaches the ends of the fibers unless “sinks” for the fluid are provided.
A weakness of TOW and SAP wrapped with tissue or nonwoven technology is bad SAP stability, which may lead to some areas with no SAP and other areas with high concentrated SAP, both of which may lead to gel blocking and leakage.
According to at least one exemplary embodiment, an absorbent article is disclosed. The absorbent article can include a liquid permeable top sheet, a pulpless absorbent core, the core including synthetic fibers (TOW) and an open formation high loft layer with fibers oriented in Z direction wherein a super absorbent material is disposed therebetween. The absorbent article may further include a liquid impermeable backsheet. The absorbent core may be situated between the top sheet and the backsheet.
Advantages of embodiments of the present invention will be apparent from the following detailed description of the exemplary embodiments. The following detailed description should be considered in conjunction with the accompanying figures in which:
Aspects of the invention are disclosed in the following description and related drawings directed to specific embodiments of the invention. Alternate embodiments may be devised without departing from the spirit or the scope of the invention. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention. Further, to facilitate an understanding of the description discussion of several terms used herein follows.
As used herein, the word “exemplary” means “serving as an example, instance or illustration.” The embodiments described herein are not limiting, but rather are exemplary only. It should be understood that the described embodiments are not necessarily to be construed as preferred or advantageous over other embodiments. Moreover, the terms “embodiments of the invention”, “embodiments” or “invention” do not require that all embodiments of the invention include the discussed feature, advantage or mode of operation.
Embodiments disclosed herein relate to absorbent products, such as disposable diapers, incontinence pads, sanitary napkins, and the like, which have an absorbent core that includes synthetic fibers and super absorbent material, such as super absorbent polymers (SAP), settled in loft layer holes. Such an absorbent material may simultaneously optimize SAP stabilization as well as permeability, thereby providing improved absorption, rewetting and comfort. In an exemplary embodiment, the loft layer may be a high loft layer made of a low density, thick fabric. The high loft layer may have a high ratio of thickness to weight per unit area. In at least some exemplary embodiments, high loft battings may have no more than 10% solids by volume and may be thicker than 3 mm (0.13 inches).
The inclusion of an open formation high carrying loft layer with fibers oriented in a Z direction at the bottom side of the absorbent core may allow the SAP to settle inside the voids and between the fibers oriented in a Z direction of the open formation high loft layer and the TOW fibers. This may improve the SAP fixation and stability to a uniform core. The fibers may be bonded together with spray hot melt adhesive. In such an exemplary embodiment, the SAP may have the advantageous ability to migrate in a Z direction toward the bottom of the diaper.
An exemplary embodiment may lead to better leakage performance and SAP migration thru the core, avoiding SAP blocking. The high loft layer may further provide improved softness or comfort.
According to at least one exemplary embodiment, about 60% to about 100% of the SAP can be attached between the synthetic fibers and the open formation high loll layer with fibers oriented in a Z direction.
According to at least one exemplary embodiment, the absorbent core can be made from about 50% to about 95% of super absorbent polymer SAP settled inside the voids and between the fibers oriented in a Z direction of the open formation high loll layer. The developed SAP material stability can improve the liquid spreading and can prevent excessive rewetting and leakage.
According to at least one exemplary embodiment, an absorbent article can include an absorbent core having a super absorbent polymer SAP settled inside the voids and between the fibers oriented in a Z direction of the open formation high loft layer and the synthetic fiber TOW. The absorbent core may be pulpless. The absorbent article structure can result in a thin product. Such absorbent articles can include disposable diapers, incontinence pads, sanitary napkins, and the like, wherein the absorbent core includes synthetic fibers and super absorbent polymer SAP settled inside the voids and between the fibers oriented in Z direction of the open formation high loft layer. The SAP can be between about 50% to about 95% of the weight of the absorbent core.
In some exemplary embodiments, the SAP 112, the top loft layer, synthetic fiber matrix 110 and the bottom loft layer can be contained within a wrap 114. Wrap 114 can be made of a material that can impede the passage of SAP 112 therethrough. Such materials can chide tissue, for example a single-ply white tissue having a high wet strength, and synthetic non-woven materials, for example polyolefin fibers such as polyethylene or polypropylene fibers.
Top sheet 106 may be any permeable polymeric non-woven sheet known in the art. A suitable top sheet 106 may be made from, for example, perforated plastic films, polyolefin fibers (e.g., polyethylene or polypropylene fibers), or combinations thereof.
Back sheet 108 may be any impermeable polymeric plastic and/or non-woven sheet known in the state of the art. For example, a suitable back sheet may be made from films of polyethylene, polypropylene, polyester, nylon, polyvinyl chloride or blends of these materials.
Absorbent core 102 may include SAP 112 in addition o a synthetic fiber matrix 110. The synthetic material used for matrix 110 can be, for example, polyolefins (e.g., polypropylene and polyethylene), rayon, polycarbonates, bicomponent fibers, cellulose acetate, and so forth. Such fibrous material is known in the art as TOW, and may be a crimped TOW. TOW is a continuous band composed of several thousand filaments, which can be held loosely together by a crimp, i.e, a wave configuration set into the band during its manufacture. The TOW band may be formed by combining the filaments from several spinnerets. The combined bundle of filaments can then be crimped to facilitate TOW band cohesion as well as suitable bulk and firmness when processed. Prior to making an absorbent composite that includes a TOW fiber, the TOW fiber can typically be unwound, opened, and then cut at various lengths and may be oriented in machine direction, so as to provide a fibrous mass of material. TOW having crimped filaments may be easier to open.
The TOW fiber can be any continuous or discontinuous thermoplastic filament TOW fiber that is capable of being opened and used in combination with SAP 112 in an absorbent core 102. The denier per fiber (dpf) of the TOW fiber can be in the range of about 1 dpf to about 9 dpf, for example about 5 dpf to about 8 dpf. For products having the same weight, filaments of lower dpf may provide increased surface area and increased moisture absorption. Total denier may vary within the range of about 26,000 denier to about 40,000 denier, depending upon the process used.
The SAP 112 may be polymers that can absorb and retain large amounts of a liquid relative to their own mass. A suitable SAP may be, for example, a sodium-neutralized cross-linked polyacrylate. Such a SAP may be formed by polymerization of a large quantity of units of acrylic acid blended with sodium hydroxide in the presence of an initiator. The acrylic acid and sodium hydroxide may be mixed together in the presence of water, an initiator, and a cross-linker. The resulting solution may undergo a polymerization process to form a three-dimensional polymer chain network, which may take the form of an aqueous gel. Subsequently, the aqueous gel may be chopped, crushed and dried to form SAP granules. The SAP granules may then be ground and sieved to obtain a desired particle size. At this point, the SAP granules may be further cross-linked so as to obtain desired absorbance under pressure characteristics.
The open formation bottom high loft layer may be made of air-through bonded fibers PET or PP or bi-component fibers PET/PE or PET/PP, with a basis weight varying between 40 gsm and 80 gsm and a width varying between 90 mm and 130 mm and a thickness varying between 1.5 mm and 4 mm.
In yet other exemplary embodiments, the SAP 112 may be attached to the synthetic fiber matrix 110, the wrap 114, or the back sheet 108 and may be stabilized by the open formation bottom loft layer with fibers oriented in a Z direction. This can facilitate increasing the performance of the absorbent garment 100. Various chemical, mechanical, thermal or electrical means of attaching the SAP 112 to the synthetic matrix 110 may be employed. Any attachment capabilities may be suitable as long as it does not interfere with the ability of the SAP 112 to absorb liquid. Such capabilities include adhesives, heat sonication, embossing or sonic bonding patterns. It should also be understood that a combination of treatments may be used.
The zoning testing 700 can include a digital scale with a precision of 0.01 g, container with hanging clips, stop wash timer, stapler and centrifuge apparatus with inner basket diameter of 28 cm, RPM 1400, scissors and zoning mask.
The test procedure may be as follows: In step 702, the cuffs and elastics may be cut off to make the diaper flat. In step 704, the zoning mask may be set on the backside of the diaper even with the pad front side. Next, in step 706, the zones may be marked with a pen. In an exemplary embodiment, there may be 7 zones. Zone 1 may be at the backside (tape level) and zone 7 may be at the front side (frontal tape level). In step 708, the zones may be cut using scissors. In step 710, each zone may be wrapped with non-woven. In an exemplary embodiment, the wrap may be secured with staples. Next, step 712, each wrapped zone may be weighed individually and the wrapped zone weight may be recorded. In step 714, the zones may be soaked in liquid saline solution for approximately 5 minutes. In step 716, the zones may be put into a centrifuge apparatus for approximately 1 minute. in step 718, the zones may be re weighed individually and their weight may he recorded as the “Wet Weight”. For the final step 720, the retention per zone may be calculated using the following formula:
Detention per zone=Wet Weight−Wrapped weight
The aqueous NaCl solution may be prepared as follows: approximately 9 g of sodium chloride crystals may be weighed and added along with approximately 1000 mL of de-ionized water to a clean dry flask, such as a 1000 mL flask. The concentration of the saline solution may be measured with a salt-meter to insure approximately 0.9% concentration.
The foregoing description and accompanying figures illustrate the principles, preferred embodiments and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art.
Therefore, the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims.
