Abstract:
A film for use in absorbent articles is first microscopically textured and then macroscopically apertured while maintaining the microscopic texture. The micro-texturing may be done by a variety of means including vacuum forming, and may include micro-apertures. The macroscopic texture may be done by a variety of means including thermo-mechanical means with a heat shielding means. Where heated pins are used, the heat shielding means protects the micro-texture from the heat so that the heat does not deform the micro-texture.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/435,942, filed Dec. 20, 2002. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to the formation of three-dimensional thermoplastic films, and more particularly those with both micro-texture and macro-apertures.  
         BACKGROUND  
       DESCRIPTION OF RELATED ART  
         [0003]    There has always been a need to create cloth-like textures in poly-olefin films that can in turn become three-dimensionally apertured fluid transporting structures. In the past this texturing was achieved through the creation of a plurality of micro-apertures that stick out from the surface of film. This fragile micro-texture can be created through the use of water forming or vacuum forming as described in the prior art. However, once micro-texturing is completed, it is difficult to create the three-dimensional (“3D”) funnel-shaped aperture that allows the fluid to pass through the film into the absorbent layer underneath without destroying the micro-texture. Water or needle perforation has been attempted, however, the water approach is not at a high enough temperature to create a permanently deformed and stress annealed aperture. Thus, a large 3D aperture formed using water perforation could have the tendency to become flat again if subjected to stress or to pressure at the time the aperture is formed. Use of a hot needle is not effective either, because the heat from the hot needle will melt the surrounding, very delicate micro-texture if the needle is hot enough to impart any permanent deformation into the cone. If the micro-texture is micro-apertures, the heat of the needle causes the edges of the micro-apertures to “crisp” or become very stiff as a result of the exposure to the heat. This sort of stiffening of the edges makes the final product rough to the touch.  
           [0004]    A novel method of using thermo-mechanical perforation with a matching set of needles, grooves and protective surface to create such product is disclosed herein. Further, this invention teaches how, in one pass, a product can have large 3D fluid transport holes imparted into a micro-textured film and how a fluid transport layer may be attached under the fluid transport sheets to direct the fluid away from the 3D funnel of the micro-textured film. The final product produced via such process is primarily intended for use as a body-contacting, textured formed film top sheet in an absorbent hygienic product or wound dressing. Further, this product can be used as a sub-layer in such an absorbent article or as a top layer in a baby diaper.  
         SUMMARY  
         [0005]    A film is first microscopically textured and then macroscopically textured while maintaining the microscopic texture. The micro-texturing may be done by a variety of means including vacuum forming, and may include micro-apertures. The macroscopic texture may be done by a variety of means including thermo-mechanical means with a heat shielding means. Where heated pins are used, the heat shielding means protects the micro-texture from the heat so that the heat does not deform the micro-texture.  
           [0006]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic view of a method of forming a micro-texture in a film.  
         [0008]    [0008]FIG. 2 is a cross sectional view of a film with micro-texture formed by the process shown in FIG. 1.  
         [0009]    [0009]FIG. 3 is a schematic view of a method of forming a macro-texture in a film.  
         [0010]    [0010]FIG. 4 is a cross sectional view of a film with both a micro-texture and a macro-texture as formed by the processes of FIG. 1 and FIG. 3.  
         [0011]    [0011]FIG. 5 is a schematic view of a method of forming a macro-texture in a film while combining a nonwoven layer with the film.  
         [0012]    [0012]FIG. 6 is a cross sectional view of a film adjacent to a nonwoven layer and with both a microtexture and a macro-texture as formed by the processes of FIG. 1 and FIG. 5.  
         [0013]    [0013]FIG. 7 is a schematic view of a method of forming a macro-texture in a film.  
         [0014]    [0014]FIG. 8 is a cross sectional view of a film with both a micro-texture and a macro-texture as formed by the processes of FIG. 1 and FIG. 7.  
         [0015]    [0015]FIG. 9 is a schematic view of a method of forming a macro-texture in a film while combining a nonwoven layer with the film.  
         [0016]    [0016]FIG. 10 is a cross sectional view of a film adjacent to a nonwoven layer and with both a microtexture and a macro-texture as formed by the processes of FIG. 1 and FIG. 9.  
         [0017]    Like reference symbols in the various drawings indicate like elements. 
     
    
     DETAILED DESCRIPTION  
       [0018]    As used herein, “micro” refers to individual features that are not individually discernable when viewed by the human eye from about 18 inches, although a change in texture on a whole may be discernable, while “macro” refers to features that are individually discernable when viewed by the human eye from about 18 inches. For example, micro-apertures with a mesh of between about 30 apertures per linear inch and 100 apertures per linear inch will change the surface texture of a film, but the individual apertures will not be individually discernable by the human eye from a distance of about 18 inches. Likewise, macro-apertures with a spacing of about 5 to about 11 holes per square centimeter will be individually discernable by the human eye from a distance of about 18 inches.  
         [0019]    A film material  10 , which is typically thermoplastic, is extruded onto a forming screen  12 . Forming screen  12  contains a micro-texture. The forming screen  12  may have a variety of micro-texture patterns. The film material  10  is thereby formed into a microscopically three-dimensional film  14 . The film material  10  may be apertured as part of the vacuum forming or may be allowed to stay intact.  
         [0020]    The film material  10  may be a thin film consisting of a 50/50 blend of LDPE and LLDPE extruded from a cast die  16  or a blown die. While the film material  10  is still in a semi-molten, malleable state a pressure is applied by differential pressure means, such as a vacuum, blown air, etc., to the film material  10  to have the film material  10  form to a screen  12 . The pressure may be applied by known vacuum forming techniques as shown in FIG. 1, although other means may be acceptable. The screen  12  imparts a micro-texture  16  to the film material  10 . The resultant micro-textured film  14  will have a micro-texture  16 , which may include micro-apertures, micro-ridges, micro-dots, or other micro-textures known in the art, as it is removed from the screen  12  as shown in FIG. 2. If the micro-texture  16  is micro-apertures, the micro-apertures may have a density of between about 30 holes per linear inch and about 100 holes per linear inch, also known as about 30 mesh to about 100 mesh, and preferably between about 40 mesh and about 60 mesh. Where micro-textures  16  are formed of micro-apertures, they may be three-dimensional micro-funnels to increase their effect on tactile response as well as fluid handling properties. Where micro-textures  16  are formed of micro-apertures they may be round, elongated, octagonal, oval, hexagonal, ellipsoid, rectangular, square, or any other shape or pattern depending on the preferred texture or fluid handling properties.  
         [0021]    The film material  10  may contain surfactants in the resin, or surfactants may be added to the micro-textured film  14 . Surfactants increase the philicity of the normally phobic film material  10  and may affect the performance of the finished product as discussed below. Alternatively, surfactants may not be added, resulting in a phobic film material  10 .  
         [0022]    In a preferred embodiment, the micro-textured film  14  is then thermo-mechanically perforated to produce a macroscopic three-dimensional aperture  18 . The macro-aperture  18  forms a macroscopic texture on the film, and therefore the terms macro-texture and macro-aperture  18  are used throughout. Heat shielding  22  allows the use of heated pins  20  to perforate the micro-textured film  14  without destroying the micro-texture  16 . Without heat shielding  22 , the heated pins  20  may soften the material of film  14  such that micro-texture  16  is destroyed or the heated pins  20  may crisp the edges of the micro-texture  16  as described above. If micro-textured film  14  is sufficiently heated by heated pins  20 , the micro-texture  16  will melt back to a film, thus losing the texture created by screen  12 . The heat shield  22 , shown in FIGS. 3, 5,  7 , and  9 , is a shielding material  26  having a higher melting point than the film, such as a nonwoven polypropylene, which passes through the perforating nip  30  between the micro-textured film  14  and a drum  24  carrying heated perforating pins  22 . Two effective examples of shielding material  26  are nonwovens known in the art as Spun-Meltblown-Spun 19 gsm and Thermo-bonded Carded 24 gsm. The selection of an appropriate nonwoven material to be used as shielding material  26  should be based on finding a nonwoven that has a melting point higher than the film material  10 . Other heat shields would include various other materials, which may be able to run on a continuous loop with a cooling cycle, a cooled drum/heated pin arrangement, and various fluid-cooling means.  
         [0023]    The thermo-mechanical perforating unit shown in FIG. 3 uses heated pins  20  mated into an unheated female roll  28  to form a nip  30 . The micro-textured film  14  and above-mentioned shielding material  26  are fed into the nip  30  such that the heated pins  20  form macroscopic three-dimensional apertures  18  in the micro-textured film  14 . The shape of the apertures is determined by the relationship between pins  20  and roll  28 . The macro-apertures  18  of this preferred embodiment have a density of between about 4 holes per square centimeter and about 15 holes per square centimeter, and preferably between about 5 holes per square centimeter and about 12 holes per square centimeter. The macro-apertures  18  may be formed into a cone that extends from an upper surface of the film  14  to a lower surface spaced apart by a distance greater than the initial thickness of film  14 . The taper of the cone will depend on the shape of female roll  28  and heated pins  20 . Depending on the relative speed at which the film  14 , heated pins  20 , and female roll  28  are moving, the macro-apertures  18  may be round or elongated.  
         [0024]    Female roll  28  may be temperature controlled to maintain a consistency to the macro-apertures  18  formed at the nip  30 . The temperature control may include cooling or heating as needed for the desired results. For example, an operating temperature of 30 degrees Celsius may require cooling in some environments, heating in others.  
         [0025]    The film  32  of the preferred embodiment will have a vacuum formed micro-texture  16  and a thermo-mechanically formed macro-texture  18 , as shown in FIGS. 4 and 8. The micro-textured film  14  of FIG. 2 has a caliper of about 25 microns while the caliper of the film  32  of FIGS. 4 and 6 is about 400 microns to about 1500 microns, preferably between about 800 microns and 1300 microns. The film  32  of this preferred embodiment will have a desirable texture provided by the micro-texture  16  and a resilient structure provided by the macro-texture  18 .  
         [0026]    As shown in FIGS. 5 and 9, a second material  34 , such as a wicking nonwoven, may be fed into the nip  30  of the thermo-mechanical forming means to simultaneously bond the second material  34  to the film layer  14  thus creating a composite material  36 . The second material  34  may be positioned between the film layer  14  and female roll  28  so that the micro-texture  16  is still exposed. Heated pins  20  would puncture second material  34  at macro-apertures  18 . In this manner, a composite material  36  may be formed having the tactile impression and fluid handling abilities of a micro-apertured film backed by a wicking material and the fluid handling abilities of macro-apertures  18  unobstructed by the second material  34  as shown in FIG. 6. The second material  34  is effective in wicking moisture away from the film layer  14 , thus improving the wetback performance.  
         [0027]    As can be seen by comparison of FIGS. 4 and 8 or FIGS. 6 and 10 where the micro-textures  16  are micro-apertures, the micro-apertures may extend in the same direction as the macro-apertures  18 , FIGS. 8 and 10, or in the opposite direction as the macro-apertures  18 , FIGS. 4 and 6.  
         [0028]    Absorbent articles typically have a body facing topsheet, a backsheet opposite the topsheet, and an absorbent core between the topsheet and backsheet. Additionally, modem absorbent articles may contain an intermediate layer between the topsheet and the absorbent core. The film  32  or composite material  36  may be used as a topsheet or an intermediate layer in an absorbent article.  
         [0029]    Performance Measures  
         [0030]    Various materials were tested as topsheets against comparative topsheet materials. One of the comparative materials is a hydro-formed topsheet used in the Procter &amp; Gamble sanitary napkin product “Lines Petalo Blu” and referred to herein as “HFF”. Another of the comparative materials is the nonwoven phobic topsheet used in the SCA sanitary napkin product “Nuvenia Libresse” and referred to herein as “NW”. The materials used for the different examples are as follows:  
         [0031]    Example 1: A micro-texture  16  of 60 mesh micro-apertures in a philic film material  10  and macro-apertures  18  with a spacing of about 5.6 apertures per square centimeter.  
         [0032]    Example 2: Similar to Example 1, but with a micro-texture  16  of 40 mesh micro-apertures.  
         [0033]    Example 3: Similar to Example 1, but with a phobic film material  10 .  
         [0034]    Example 4: Similar to Example 2, but with a phobic film material  10 .  
         [0035]    Example 5: Similar to Example 1, but with a second material  34  of 25 gsm air through bonded nonwoven (ATB 25 RAM).  
         [0036]    Example 6: Similar to Example 2, but with a second material  34  of 25 gsm air through bonded nonwoven (ATB 25 RAM).  
         [0037]    Example 7: Similar to Example 5, but with macro-apertures  18  with a spacing of about 11 apertures per square centimeter.  
         [0038]    Example 8: Similar to Example 6, but with macro-apertures  18  with a spacing of about 11 apertures per square centimeter.  
         [0039]    Strikethrough is a measure of the rate of absorption through a topsheet into an absorbent article and was conducted on finished articles as indicated below. In order to test strikethrough the original topsheet material is removed from the article and replaced with the topsheet material to be tested, except when testing the sample of the original material. The article is then insulted with a 10 ml sample of Menstrual Internal Synthetic Solution (MISS) and the strikethrough time is recorded using a Lister apparatus as described in EDANA Recommended Test Method ERT 150.5-02 Liquid Strike Through Time Test Method. Lower strikethrough numbers reflect a fast absorption and are desired in most absorbent articles.  
         [0040]    Wetback is measured on the same samples used in the strikethrough test described above. After the strikethrough is measured the samples are carefully removed from the test apparatus and positioned on a flat surface. A 4 kg weight with a surface of 10 cm by 10 cm is placed on the insult area of the sample for three minutes. At three minutes the weight is removed and 5 preweighed pick up papers are placed over the insult area and the weight is placed over the pickup paper. At two minutes the weight is removed and the pickup paper is removed and reweighed. The weight gained by the pickup paper is reported as the wetback. This method is based on EDANA Recommended Test Method ERT 151.3-02 Wetback. Lower wetback numbers reflect more complete absorption and less leakage to the insult surface and are desired in most absorbent articles.  
         [0041]    The following data refers to the tests performed on “Lines Petalo Blu” articles tested under the method described above:  
                                                       Topsheet   Strikethrough (seconds)   Rewet (grams)                           HFF   49.0   0.93           Example 1   38.7   0.72           Example 2   13.0   0.36           Example 5   54.8   0.43           Example 6   27.8   0.27           Example 7   47.0   0.42           Example 8   32.0   0.26                      
 
         [0042]    The following data refers to the tests performed on “Nuvenia” articles tested under the method described above:  
                                                                         Topsheet   Strikethrough (seconds)   Rewet (grams)                                        NW   &gt;500   1.3           Example 1   143.6   1.2           Example 2   73.4   1.2           Example 3   325.3   1.1           Example 4   164.0   1.1           Example 7   91.78   0.465           Example 8   61.13   0.570                      
 
         [0043]    As can be seen from the above results, all of the Examples showed improvement over the original topsheet material used in the absorbent article.  
         [0044]    While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. The appended claims are therefore intended to cover all such changes and modifications that are within the scope of this invention.