Patent Application
20090076783
The digitally optimized fastener assembly and method of making the same relate generally to fastener assemblies for disposable absorbent articles, and more particularly to a digitally optimized fastener assembly and method of making the same utilizing finite element analysis (FEA) methods.
Fastener assemblies for disposable absorbent articles or garments such as, for example, disposable diapers, training pants, adult incontinent pads, sanitary napkins, pantiliners, incontinent garments, and the like, which are generally worn in cooperation with garments and disposed against a body surface by infants or adult incontinent individuals. The absorbent article is employed to collect and absorb body fluid discharge, such as, for example, blood, menses, urine, aqueous body fluids, mucus and cellular debris. For example, the absorbent article may be disposed between the legs of an individual adjacent a crotch area, and positioned in engagement with a body surface of the crotch area to collect fluid discharge.
As is known in the art, absorbent articles typically include a fluid permeable cover stock for engaging the body surface, a fluid impermeable backsheet and an absorbent core supported therebetween. The backsheet serves as a moisture barrier to prevent fluid leakage to the garment. The absorbent core usually includes a liquid retention material that faces the body surface. The absorbent core can include, for example, loosely formed cellulosic fibers, such as, for example, wood pulp, fluff pulp, etc., for acquiring and storing body discharge. Elasticized regions can be provided around the edges of the article to secure the article about the waist and legs of a wearer.
Additionally, fastening of the absorbent articles on an individual requires the use of fasteners and/or ear members and closure tabs that extend laterally from the body of the absorbent article. Moreover, the closure tabs can conventionally have mechanical closure material, for example, hook and loop material, adhesive tape, and the like. For example, in typical diaper-type garments, the garment can be affixed to a wearer by attaching one or more closure tabs that extend across the wearer's hips to hold front and rear portions of the garment to one another.
FEA methods are also well known. Generally, FEA uses a complex system of points called nodes which make a grid called a “mesh.” This mesh is programmed to contain the material and structural properties which define how the structure will react to certain loading conditions. Nodes are assigned at a certain density throughout the material depending on the anticipated stress levels of a particular area. Regions which will receive large amounts of stress usually have a higher node density than those which experience little or no stress. Points of interest may consist of: fracture point of previously tested material, fillets, corners, complex detail, and high stress areas. The mesh acts like a spider web in that from each node, there extends a mesh element to each of the adjacent nodes. This web of vectors is what carries the material properties to the object, creating many elements. After the FEA model is prepared, the model is “run” to produce failure characteristics which are analyzed to ascertain whether there are potential defects in the design and/or whether any changes in the design can or should be made to improve the failure characteristics. “Running” the model means initiating the FEA program to evaluate the stresses and strains on the FEA model.
Conventional manners to develop and improve cost-effective materials and designs for fastener assemblies that display superior failure characteristics involve a great deal of time, effort and expense. Much of this time and expense can typically be associated with making and testing multiple prototype fastener assemblies which incorporate various design and material characteristics in order to determine the particular designs and materials, and combinations thereof, which exhibit desired failure characteristics. This process can often be an iterative process in which many different prototypes are made and tested in succession, each incorporating different designs and/or types of materials, in an effort to identify the particular combination which provides the most superior failure characteristics. As can be appreciated, this process can be both expensive and time consuming.
Therefore, it would be desirable to provide a digitally optimized fastener assembly and method of making the same utilizing FEA methods which enable a relatively large number of possible design and/or material combinations of fastener assemblies to be tested and evaluated in a comparatively short period of time. Such method can at the same time eliminate the added time and expense of having to create and test a prototype of each possible design and/or material combination.
A digitally optimized fastener assembly and method of making the same are described hereinafter. A method of making a digitally optimized fastener assembly for a disposable absorbent article can generally comprise (a) creating a first FEA model of a first fastener assembly, the first fastener assembly having first design properties; (b) running the first FEA model to obtain first failure characteristics; (c) evaluating the failure characteristics; and (d) at least one of: (i) making a fastener assembly corresponding to the first fastener assembly; and (ii) repeating the previous steps for at least a second FEA model for a second fastener assembly having second design properties, wherein the first design properties are modified to create the second design properties.
An embodiment of a digitally optimized fastener assembly can generally comprise a fastener assembly made according to one or more of the steps set forth in the method of making a digitally optimized fastener assembly described above.
One of ordinary skill in the art will understand that fastener assembly designs can likely be obtained which have failure characteristics that are superior in some respects, yet inferior in other respects, to designs of preceding models. Therefore, it is to be understood that the determination of whether a design has sufficiently desirable failure characteristics such as to be selected as the basis to manufacture an actual fastener assembly according to such design can result from the failure characteristics of such design having superior failure characteristics which are considered superior only in certain respects, and not necessarily superior in all possible respects.
Certain illustrative aspects of the digitally optimized fastener assembly and method of making the same are described herein in connection with the following description and the appended drawings. These aspects may be indicative of but a few of the various ways in which the principles of the digitally optimized fastener assembly and method of making the same may be employed, and which is intended to include all such aspects and any equivalents thereof. Other advantages and features of digitally optimized fastener assembly and method of making the same may become apparent from the following detailed description, when considered in conjunction with the appended drawing figures.
A more complete understanding of the digitally optimized fastener assembly and method of making the same can be obtained by considering the following description in conjunction with the accompanying drawings, in which:
The digitally optimized fastener assembly and method of making the same for disposable absorbent articles are discussed in terms of fluid absorbent articles, and more particularly, in terms of an absorbent article including fasteners that cooperate to improve attachment and fit. As used herein, the term “absorbent article,” “absorbent garment” or “garment” refers to absorbent articles that absorb and contain body liquids, discharge and waste, and more specifically, refers to absorbent articles that are placed against or in proximity to the body of the wearer to absorb and contain the various body liquids, discharge and waste. A non-exhaustive list of examples of absorbent articles includes diapers, diaper covers, disposable diapers, training pants, feminine hygiene products and adult incontinence products. The term absorbent article includes all variations thereof, including disposable absorbent articles that are intended to be discarded or partially discarded after a single use and unitary disposable absorbent articles that have essentially a single structure. As used herein, the term “diaper” refers to an absorbent article generally worn by children and incontinent persons about the lower torso. The claims are intended to cover all of the foregoing classes of absorbent articles, without limitation, whether disposable, unitary or otherwise. The invention will be understood to encompass, without limitation, all classes of absorbent articles, including those described above.
Absorbent articles and diapers may have a number of different constructions. In each of these constructions it is generally the case that an absorbent core is disposed between a liquid pervious, body-facing topsheet and a liquid impervious, exterior facing backsheet. In some cases, one or both of the topsheet and backsheet may be shaped to form a pant-like garment. In other cases, the topsheet, backsheet and absorbent core may be formed as a discrete assembly that is placed on a main chassis layer and the chassis layer is shaped to form a pant-like garment. The garment may be provided to the consumer in the fully assembled pant-like shape or may be partially pant-like and require the consumer to take the final steps necessary to form the final pant-like shape, such as by fastening one or more fasteners or fasteners.
In the case of some diapers and most adult incontinent products, the garment often is provided fully formed with factory-made side seams and the garment is donned by pulling it up the wearer's legs. In the case of most diapers, wherein, for example, a child lies on his or her back, a caregiver usually places the diaper between the child's legs, pulls the front end of the diaper up between the legs and then attaches one or more closure tabs to the front waist region of the diaper, thereby forming a pant-like structure. For clarity, the present invention is described herein only with reference to a diaper-type garment in which the topsheet, backsheet and absorbent core are assembled into a structure that forms a pant-like garment when secured on a wearer using fastening devices, although the invention may be used with any other type of absorbent garment that may benefit from the use or addition of fasteners.
Referring now to the drawing figures wherein like reference numerals are used to refer to like elements throughout, an example of an FEA model 10 which can be utilized according to an embodiment of a method of making a digitally optimized fastener assembly is illustrated in
An overview of the modeling process can generally be: quantifying the geometry for the fasteners; collecting material properties; constructing the geometric model for FEA; applying material properties to the FEA model; and “running” the FEA model. The FEA model 10 can be created using, for example, a known stretch tab configuration, and then existing tab failure data can be used to validate the FEA model 10. Changes to the dimensions and shape of the fastener assembly can then be made, as can changes to the attachment system, and/or changes to the material types. For example, new stretch materials can then be characterized, and the FEA model 10 can be used to substitute in the new materials and predict the behavior of the stretch tab with the new materials in specific tab configurations. Similarly, changes to the dimensions, configuration and/or attachment system can be made and tested to predict the behavior of a fastener assembly incorporating any such changes. In this way, the most cost efficient and/or best performing stretch tab configuration and/or materials can be determined for a specific stretch tab configuration. Moreover, new fastener assembly designs can also be screened for possible defects before actually making the articles. Accordingly, the end result is a fastener attachment assembly design which is digitally optimized in for strength, shape, and overall performance, before manufacture and without having to make and test any prototypes.
FEA Model Development
The FEA modeling and analysis can be performed by any qualified vendor. The model development described herein can have three basic components: (1) quantify tab geometry; (2) develop material stress-strain properties for the various components; and (3) analyze the tabs under specified loading conditions. The geometry can be acquired by inspection of a physical diaper or through drawings. In either case, both the overall geometric dimensions and a description of the various material components is generated for the particular configuration to be modeled. By way of example only, the particular FEA model 10 described herein was developed using two dimensional membrane elements and solved in NASTRAN. The loading conditions were developed to be consistent with a testing protocol that could be duplicated and used for comparison between the experimental results and the theoretical predictions. Two loading cases were considered: a straight pull (arrow 31), with the load applied perpendicular to the seam between the diaper and the top/bottom nonwoven material; and an angled pull (arrows 34), with the load applied at a 45 degree angle to the first pull. In both loading cases, the “diaper edge” (i.e., the part of the fastener assembly that is attached to the diaper, or base absorbent system 19) was held with a three inch wide grip that prohibits any displacement of material. This is comparable to a fixed grip in a tensile testing frame. Also, in both cases the hook attachment region 28 was considered to be held in a grip and load was applied to this material. To perform the finite element analysis it was necessary to have stress-strain descriptions of the various component materials. This was obtained using actual samples from the provided materials which were subjected to mechanical testing. Most of the material involved is a continuous fabric with two different mechanical properties, so tests were performed on each of the components independently. The stress strain curves for the constituent materials where then developed and applied to the FEA model 10. To validate the FEA model 10, the stretch tabs were tested physically and the results compared with the FEA predictions.
Referring now to
The design properties can generally comprise dimensions, attachment configurations, and material properties of the fastener assembly. The attachment configurations can be, e.g., as in the example case described hereinafter, whether the fastener assembly is a 2-piece or 3-piece assembly. Each of various different design properties can be modified, altered and/or substituted to create different FEA models of fastener assemblies. The failure characteristics exhibited by different FEA models of fastener assemblies can be run and evaluated relative quickly, with the goal being to obtain an overall fastener design which exhibits superior failure characteristics, and without having to make and test a prototype each time any change in structural design or material properties are made. This process can also be used to screen proposed new designs for potential defects before making any actual articles having such proposed new fastener assemblies.
An embodiment of a digitally optimized fastener assembly can generally comprise a fastener assembly made according to the above described method.
One of ordinary skill in the art will understand that fastener assembly designs can likely be obtained which have failure characteristics that are superior in some respects, yet inferior in other respects, to designs of preceding models. Therefore, it is to be understood that the determination of whether a design has sufficiently desirable failure characteristics such as to be selected as the basis to manufacture an actual fastener assembly be based upon failure characteristics which may be considered superior only in certain respects. The failure characteristics thus need not be superior in all possible respects to be considered “desirable.”
Three particular configurations were studied, according to one or more embodiment of the method described above. Two objectives of this particular study, for example, were to determine (1) what type of fastener assembly design would exhibit preferred failure characteristics, and (2) whether different types of materials would exhibit preferred failure characteristics when the fastener assembly design is identical. The three particular configurations studied in this example are as follow:
The results of the study are illustrated in the following table:
As shown in the table, two different load cases were used, one at 5 lb. load and one at 2.5 lb. load, as were two different material types, Type A and Type B. The results of the tests show that the 3-piece model has less stretch and more stress than either of the 2-piece designs. Additionally, the 2-piece reduces the stress at equal stretch, and also that the 2-piece design with the Type B stretches three times more than the Type B material, and with less than one half of the stress of the Type A material. In this particular example, the Type A material can be Tredegar 308™ and the Type B material can be Tredegar Fabriflex 506™.
As a result of these tests, it was possible—without having to create and test a physical prototype- to determine that a 2-piece design had more desirable failure characteristics than the 3-piece design, and also that substituting a different material, in otherwise identical designs, provided improved failure characteristics. Thus, a digitally optimized fastener assembly could be identified for manufacture in a more efficient and less expensive manner than heretofore done according to conventional methods.
Therefore, what has been described above includes exemplary embodiments of a digitally optimized fastener assembly for disposable absorbent articles and method of making the same. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of this description, but one of ordinary skill in the art may recognize that further combinations and permutations are possible in light of the overall teaching of this disclosure. Accordingly, the description provided herein is intended to be illustrative only, and should be considered to embrace any and all alterations, modifications, and/or variations that fall within the spirit and scope of the appended claims.
