Abstract:
A method of calculating the humidity dissipation of an absorbent article including the steps of collecting relative humidity data from an absorbent article for a selected period of time, generating a graph plotting relatively humidity versus time for the absorbent article, differentiating the relative humidity versus time graph to obtain a differential graph.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to method for measuring the relative humidity of a disposable absorbent article, and more particularly to a method of measuring the humidity dissipation properties of a disposable absorbent article. 
       BACKGROUND OF THE INVENTION 
       [0002]    Externally worn, sanitary absorbent napkins are one of many kinds of feminine protection devices currently available. Sanitary napkins conventionally have a laminate construction including a body-facing liquid permeable layer, an absorbent core layer or layers, and a liquid impermeable garment facing layer. A problem with conventional napkins, due to the laminate construction thereof, is that such articles are not particularly breathable within the absorbent layers of the article. This lack of “internal breathability” within the article construct can cause comfort problems for the user during use of the article. In particular, the lack of internal breathability in conventional articles may cause the users body temperature to rise in a localized area thereby creating discomfort during use. Further, once the article becomes wet, the lack of internal breathability may prevent the article from drying thereby imparting a wet sensation to the user during use. 
         [0003]    The inventors of the present invention have discovered a method of measuring the humidity dissipation properties of a disposable absorbent article such as a sanitary napkin. The method allows the inventors to evaluate the humidity dissipation performance of a disposable absorbent article and thereby predict the comfort attributes of the article. 
       SUMMARY OF THE INVENTION 
       [0004]    In view of the foregoing, the present invention provides a method of calculating the humidity dissipation of an absorbent article including the steps of collecting relative humidity data from an absorbent article for a selected period of time, generating a graph plotting relatively humidity versus time for the absorbent article, differentiating the relative humidity versus time graph to obtain a differential graph, obtaining a first tangent line from the differential graph, obtaining a second tangent line from the relative humidity versus time graph, transcribing the first and second tangent lines onto the relative humidity versus time graph, and calculating a humidity dissipation A RH  value by determining the area located between the first and second tangent lines and the relative humidity versus time graph. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Examples of embodiments of the present invention will now be described with reference to the drawings, in which: 
           [0006]      FIG. 1  is a schematic view of an apparatus for measuring relative humidity of an absorbent article; 
           [0007]      FIG. 2  is a perspective view of an absorbent article with the temperature and relatively humidity microsensors of the apparatus depicted in  FIG. 1  inserted under the cover layer and into the core layer thereof; 
           [0008]      FIG. 2   a  is a detailed sectional view of the absorbent article shown in  FIG. 2  depicting the insertion of the temperature and relatively humidity microsensors into the core layer of the absorbent article; 
           [0009]      FIG. 3  is a partially exploded view depicting additional features of the apparatus shown in  FIG. 1 ; 
           [0010]      FIG. 4  is a perspective view showing the absorbent article positioned for testing in the apparatus shown in  FIG. 3 ; 
           [0011]      FIG. 5  is a graph plotting relatively humidity versus time for an absorbent article tested according to the test method set forth herein; 
           [0012]      FIG. 6  is a graph depicting the differential plot of the graph shown in  FIG. 5 ; 
           [0013]      FIG. 7  is a graph showing the manner in which X 1  and Y 1  are determined according to the test method set forth herein; 
           [0014]      FIG. 8  is a graph showing how a first tangent line is determined for the graph shown in  FIG. 5  based on X 1  and Y 1 ; 
           [0015]      FIGS. 9 and 10  are graphs depicting the manner in which a second tangent line is determined for the graph shown in  FIG. 5 ; and 
           [0016]      FIG. 11  is graph depicting the manner in which A RH  is calculated based upon the first and second tangent lines. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The method described herewith will be described with reference to a sanitary napkin, however the inventive method may be used to evaluate other disposable absorbent article such as panty liners, incontinence products, and the like. 
         [0018]    Reference is made to  FIG. 1  which schematically depicts an apparatus  10  for measuring the humidity dissipation characteristics of an absorbent article according to the test method set forth in detail below. The apparatus  10  generally includes a relative humidity microsensor  12  for measuring the relative humidity of an absorbent article, a microsensor  14  for measuring the temperature of an absorbent article, a temperature and humidity sensor  16  for measuring the temperature and relative humidity of a laboratory in which the test is being conducted, a signal conditioner  20 , a connector block  22  and a computer  24  for recording the measured data. The apparatus  10  further includes a heating plate  26  as shown in  FIGS. 3 and 4 . 
         [0019]    Two acrylic plates  28  each having dimensions of 5.0 cm (length) by 5.0 cm (width) by 0.2 cm (thick) are used in the test method described below. One of the above described acrylic plates  28  is depicted in  FIG. 3 . A cotton panty  30 , as shown in  FIG. 3 , is also required to perform the test method set forth below. 
         [0020]    A suitable commercially available microsensor  12  is the relative humidity microsensor model HIH-400 manufactured by Honeywell International, Inc., Morristown, N.J. 
         [0021]    A suitable commercially available microsensor  14  is temperature microsensor model NTC manufactured by BetaTherm, Inc., Hampton, Va. 
         [0022]    The same commercially available temperature and relative humidity microsensors described above may be used as the sensor  16  to measure the temperature and relative humidity of the laboratory in which the test is being conducted. 
         [0023]    The electronic interface  20  is a conventional signal conditioner circuit. 
         [0024]    A suitable commercially available connector block  22  is connector block model NISCC-68 manufactured by National Instruments Corporation, Austin, Tex. 
         [0025]    The computer  24  is a Microsoft Windows based system equipped with LabView, version 7.1, manufactured by National Instruments Corporation, Austin, Tex. The identified software is used to collect and process the transmitted data. 
         [0026]    A suitable commercially available heating plate  26  is the Multi-Blok Heater, Model 2050, manufactured by Lab-Line Instruments, a subsidiary of Breanstead Thermolyne, Melrose Park, Ill. 
         [0027]    The cotton panty  30  used in the test method may be any conventional commercially available panty having a composition of at least 90% cotton. 
         [0028]    As shown in  FIG. 4 , the apparatus  10  further includes a cylindrical mass  34  having an outer diameter of 3.0 cm, a length of 8.5 cm and a mass of 77.3 g. The cylindrical mass  34  may be constructed as an acrylic tube filled with sand or the like to achieve the required mass and sealed on each end thereof. The cylindrical mass  34  is connected to a rigid swing arm  35 , which is in turn connected any suitable apparatus capable of moving the mass  34  in a repeating up and down vertical motion to thereby apply a repeating force to the acrylic plate  28  as shown in  FIG. 4 . The apparatus to which the mass  34  it attached, by means of the swing arm  35 , should be selected such that the mass  34  applies a force of 12 g once per second to the acrylic plate  28 . A suitable commercially available apparatus capable of moving the swing arm  35  and mass  34  in this manner, and applying the required force, is a thermostatic bath Haake SWB 20 Fisons TYP 000-8582/194015695002 KL DIN 12879 manufactured by Haake Fisons. 
         [0029]    As shown in  FIG. 3 , one of the surfaces of the acrylic plate  28  is covered by a 5 cm (length)×5 (width) cm×0.1 cm (thickness) swatch of nonwoven material  36 . The nonwoven material  36  is attached to the acrylic plate  28  by applying 3.6 gsm (g/m 2 ) adhesive (Pritt non-toxic Stick manufactured by Henkel Capital, S.A., Mexico) over a 25 cm 2  area to the acrylic plate facing surface of the nonwoven material  36 . The nonwoven material  36  has a basis weight of 180 gsm and a composition of 100% wool fibers. A suitable commercially available material of this type is available from Indústria de Feltros Santa Fé Av. Antônio Bardella, 780, Cumbica, Guarulhos-SP Brazil. 
         [0030]    Prior to conducting the test method set forth below the product specimens to be measured are conditioned by leaving them in a room that is 22° C., +/−2° C. and 55%, +/−3.0% relative humidity for a period of twelve (12) hours. In addition, for each product specimen to be tested, two acrylic plates  28 , with the nonwoven swatch of material  36  attached thereto, are conditioned by leaving them in a room that is 22° C., +/−2° C. and 55%, +/−3.0% relative humidity for a period of twelve (12) hours. Three identical product specimens are required for each product to be tested. 
         [0031]    The test method described below should be conducted in a laboratory setting having a temperature of 22° C., +/−2° C., and a relative humidity of 55%, +/−3.0%. 
         [0032]    As shown in  FIGS. 2 and 2   a , the test method is initiated by inserting the microsensor  12  and the microsensor  14  under the cover layer  42  and into the absorbent core layer  44  of the absorbent article  40  at the intersection of the longitudinally extending centerline  50  and transversely extending centerline  52  of the absorbent article  40 . A small hole may be formed in the cover layer  42 , if necessary, to facilitate the insertion of the microsensors  12  and  14 . 
         [0033]    After the microsensors  12  and  14  are inserted under the cover layer  42  and into core layer  44  the absorbent article  40  is attached to the panty  30  by means of positioning adhesive located on the garment facing surface of the barrier layer  60  of the absorbent article  40 . If the article to be tested does not include positioning adhesive the article may be attached to the panty  30  using conventional masking tape or the like. 
         [0034]    After the napkin  40  is attached to the panty  30 , the panty  30  is arranged on the heating plate  26 , as shown in  FIGS. 3 and 4 , such that the panty  30  is adjacent the top surface of the heating plate  26  and the napkin  40  faces away from the top surface of the heating plate  26 . Thereafter one of the conditioned acrylic plates  28  is arranged on top of the napkin  40  such that the center of the plate  28  is arranged over the intersection of the longitudinally extending centerline  50  and transversely extending centerline  52  of the napkin  40 . The plate  28  is arranged such that the nonwoven swatch of material  36  is placed in abutting face to face relationship with the top surface of the cover layer  42 . The cylindrical mass  34  is then positioned such that the central axis thereof is aligned with the longitudinally extending centerline  50  of the napkin  40 . 
         [0035]    After the apparatus  10  is configured as described above, the movement of the cylindrical mass  34  is initiated and the relative humidity and temperature of the napkin  40  is monitored via the readout provided by the computer  24 . The objective of this first step of the method is to obtain an equilibrium temperature and relative humidity within the napkin  40 . Specifically, the objective is to obtain conditions within the napkin  40  such that the temperature of the napkin is between 36° and 38° C. and the relative humidity of the napkin is between 25% to 30%. Equilibrium is established when the napkin  40  has a temperature between 36° and 38° C. and a relative humidity between 25% to 30% for a period of one minute. The temperature of the napkin  40  may be increased, if necessary, to reach the required equilibrium temperature by means of the heating plate  26 . 
         [0036]    Once the equilibrium temperature and equilibrium relative humidity has been established in the napkin  40  as described above, the computer  24  and the LabView 7.1 software are used to begin collecting relative humidity data from the napkin  40 . Data is collected for a fifteen minute period. After the initial fifteen minute period, the first plate  28  is removed and replaced with a new second plate  28 , having the swatch of nonwoven material  36  attached thereto, that has been previously conditioned by leaving the plate  28  and material  36  in a room that is 22° C., +/−2° C. and 55%, +/−3.0% relative humidity for a period of twelve (12) hours. Prior to applying the second plate  28  to the napkin  40 , 0.5 mL of water is applied to nonwoven material  36  using any conventional syringe. After the second plate  28  is applied relative humidity data for the napkin  40  is collected for an additional fifteen minute period. Thereafter, the second plate  28  is removed and relative humidity data for the napkin  40  is collected for an additional 10 minute period. Thus, relative humidity data is collected from the napkin  40  for a total of forty-five minutes. The relative humidity data collected from the napkin  40  is then used to generate a relative humidity (%) versus time (s) graph of the type shown in  FIG. 5 . The graph is generated using the data analysis and graphing software Origin 6.0 commercially available from OriginLab Corporation, Northampton, Mass. 
         [0037]    As will be described in greater detail below the graph of relative humidity shown in  FIG. 5  is used to calculate the humidity dissipation value A RH  of the napkin. 
         [0038]    The A RH  calculation is performed as described below. First the differential of the graph shown in  FIG. 5  is plotted to obtain a graph of the type shown in  FIG. 6 . Thereafter, as shown in  FIG. 7 , the maximum relative humidity %/second value, Y 1 , is determined from the maximum value on the differential graph. Once the maximum value relative humidity %/second value, Y 1  is determined, the time at which this value occurs X 1  can be determined. Using the point defined by X 1  and Y 1 , and the slope of the differential graph at this point, a first tangent line T 1  is obtained in time X 1  can be defined as shown in  FIG. 8 . The first tangent line T 1  is then transcribed on the graph shown in  FIG. 5  as shown in  FIG. 8 . The tangent line T 1  is generated using the Origin 6.0 software. 
         [0039]    A second tangent line T 2  is determined by determining the maximum relative humidity % value, Y 2 , on the graph shown in  FIG. 5  between 900 s and 1800 s, as shown in  FIG. 9 . Using this maximum relative humidity % value, Y 2 , and a slope of zero, a second tangent line T 2  can be defined. The second tangent line T 2  is transcribed on the graph shown in  FIG. 5  as shown in  FIG. 10 . The tangent line T 2  is generated using the Origin 6.0 software. 
         [0040]    Once the first tangent line T 1  and second tangent line T 2  are transcribed on the graph shown in  FIG. 5 , as shown in  FIG. 11 , the area A RH  located between the graph line and first and second tangent lines is calculated using the Origin 6.0 software. The calculated area A RH  is inversely proportional to the relative humidity retention of the napkin  40 . Stated another way the higher the A RH  the greater the humidity dissipation of the napkin  40 . Thus, the higher the A RH  value the lower the relative humidity retention of the product and the cooler and more comfortable the product will feel during use. 
         [0041]    The above described calculation is repeated for three identical product samples and an average A RH  is calculated. 
         [0042]    The above described test method allows the evaluation of the humidity dissipation properties of an absorbent article and thereby allows one to predict the comfort attributes of the absorbent article.