Patent Publication Number: US-2005121838-A1

Title: Method of microembossing

Description:
RELATED APPLICATION  
      This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/509,470 filed on Oct. 7, 2003. The entire disclosure of this provisional application is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      This invention relates generally, as indicated, to a method of microembossing and, more particularly, to a microembossing method wherein microsized architecture is formed on an article.  
     BACKGROUND OF THE INVENTION  
      Microsized architecture refers to one or more microsized (e.g., having a dimension no greater than 1000 microns) structures arranged in a predetermined pattern on a substrate that can be, for example, a rigid or flexible sheet. Typical microsized architecture includes channels, wells, and/or recesses having depths less than the thickness of the unformed original substrate. Microembossing is commonly used to form microsized architecture and, in many applications, the use of rigid tooling to emboss this architecture has been highly effective. However, when curved articles are required and/or when two-sided embossing is necessary, such rigid tooling does not always yield satisfactory results.  
     SUMMARY OF THE INVENTION  
      The present invention provides a microembossing method that is especially useful when microembossing an article having a curved geometry and/or when microembossing opposite surface regions (e.g., top and bottom) of an article.  
      More particularly, the present invention provides a method of making an article having a desired microembossed architecture. The method comprises the steps of placing a substrate having an exterior surface within a sheet having an interior surface with a microstructure corresponding to the desired microembossed architecture; evacuating the area around the sheet, whereby the microstructure will contact the exterior surface of the substrate; and thermally processing the sheet so that the microstructure embosses at least a region of the exterior surface of the substrate so as to form the desired microembossed architecture. In one embodiment of the invention, a pouch is provided which has an interior surface with a microstructure corresponding to the desired microembossed architecture, the substrate being sealed within the pouch, and the pouch being evacuated, whereby the microstructure will contact the exterior surface of the substrate sealed therein. In another embodiment of the invention, a sleeve is provided which has an interior surface with the microstructure corresponding to the desired microembossed architecture, the substrate being wrapped in the sleeve, the wrapped substrate being sealed within a pouch, and the pouch being evacuated, whereby the microstructure on the sleeve will contact the exterior surface of the substrate wrapped therein.  
      These and other features of the invention are fully described and particularly pointed out in the claims. The following description and drawings set forth in detail certain illustrative embodiments of the invention, which are indicative of but a few of the various ways in which the principles of the invention may be employed. 
    
    
     DRAWINGS  
       FIG. 1  is side view of an article having a desired microembossed architecture on an exterior surface thereof.  
       FIGS. 1A and 1B  are close-up views of microembossed architecture on two regions of the exterior surface of the article.  
       FIG. 1C  is a close-up view of microembossed architecture on the exterior surface of a modified form of the article.  
       FIG. 2  is a schematic view of sheets used to form a pouch according to the microembossing method of the present invention.  
       FIGS. 2A and 2B  are close-up views of the interior surfaces of the sheets, the interior surfaces having a microstructure corresponding to the desired microembossed architecture.  
       FIG. 3  is a top view of the sheets shown in  FIGS. 2A and 2B  after they have been joined along three edges to form a pouch with an access opening.  
       FIG. 4  is a schematic side view of the joined sheets with a substrate inserted through the access opening, the substrate corresponding to the shape of the article, absent the microarchitecture.  
       FIGS. 4A and 4B  are schematic close-up views of the exterior surfaces of the substrate.  
       FIG. 4C  is a schematic close-up view of the exterior surface of a modified form of the substrate.  
       FIG. 5  is a schematic side view of the pouch after the access opening has been sealed, whereby it can be evacuated.  
       FIG. 6  is a schematic view of the pouch after it has been evacuated.  
       FIG. 6A  is a close-up schematic view showing the microstructure on the interior surfaces of the pouch contacting the exterior surfaces of the substrate.  
       FIG. 7  is a schematic side view of the sealed, evacuated pouch being heated.  
       FIG. 8  is a schematic side view of the sealed, evacuated pouch being cooled.  
       FIG. 9  is a schematic side view of the pouch being opened and the microembossed article being removed.  
       FIG. 10  is a schematic side view of a sheet used to form an interior sleeve according to another microembossing method of the present invention.  
       FIG. 10A  is a schematic close-up view of a surface of the sheet, the sheet having a microstructure corresponding to the desired microembossed architecture.  
       FIG. 11  is a schematic side view of a substrate placed on the sheet adjacent to the surface containing the microstructure.  
       FIG. 12  is a schematic side view of the sheet wrapped around the substrate to form a sleeve.  
       FIG. 13  is a schematic side view of the wrapped substrate inside a sealed pouch.  
       FIG. 14  is a schematic side view of the pouch after it has been evacuated.  
       FIGS. 14A and 14B  are close-up schematic views showing the microstructure on the interior surface of the sleeve contacting the exterior surfaces of the substrate.  
       FIG. 15  is a side schematic view similar to  FIG. 13  with a modified form of a pouch.  
       FIG. 16  is a side schematic view similar to  FIG. 13  with a bladder being provided inside the pouch.  
       FIG. 17  is a side schematic view similar to  FIG. 13  with a pressurizing chamber also being provided. 
    
    
     DETAILED DESCRIPTION  
      Referring now to the drawings in detail, and initially to  FIG. 1 , an article  10  made by the microembossing method of the present invention is shown. The article  10  has an exterior surface  12  and, in the illustrated embodiment, the article  10  has a curved (i.e., non-flat) geometry and thus its exterior surface  12  has curved regions, namely a top region  14  and a bottom region  16 . As explained in more detail below, the present invention may be especially useful when microembossing articles having such curved geometries. As is also explained in more detail below, the present invention additionally or alternatively may be especially useful when microembossing opposite surface regions (e.g., top and bottom) of an article.  
      As shown in  FIGS. 1A and 1B , the top surface region  14  and the bottom surface region  16  each have a desired microembossed architecture  18 . The microembossed architecture  18  can include, for example, channels, wells, and/or recesses having depths less than the thickness of the article  10 . Typically, such microsized architecture will have at least one dimension (e.g., length, height, and/or width) of less than 1000 microns.  
      In the embodiment shown in  FIGS. 1, 1A  and  1 B, the article  10  comprises a main body  20  of an embossable material, and the architecture is embossed therein. In a modified form shown in  FIG. 1C , the article  10 ′ comprises a main body  20 ′ of a not necessarily embossable material and a coating  22 ′ of embossable material in which the architecture  18 ′ is embossed.  
      Referring now to  FIGS. 2-9 , the elements and steps of the preferred microembossing method of the present invention are schematically shown. In  FIG. 2 , two sheets  30  are shown which are used to form a pouch (namely pouch  36 , introduced below). The sheets  30  have interior surfaces  32  and, as shown in  FIGS. 2 and 2 B, the interior surfaces  32  include a microstructure  34  corresponding to (e.g., the negative of) the desired microembossed architecture  18 . The microstructure  34  on the respective sheets  30  can be the same or different, depending upon the desired architecture  18  for the respective surface regions  14  and  16  on the article  10 .  
      As explained in more detail below, the sheets  30  must be made of a flexible material to allow contraction during the evacuation steps. The material selection for the sheets  30  will be, to some degree, dictated by thermal processing requirements. Specifically, for example, the sheets  30  should have a glass transition temperature higher than that used during thermal processing steps so that the microstructure  34  maintains its integrity during embossing steps. Possible material candidates for the sheets  30  include, but are not limited to, polyester, such as a nylon film. That being said, any film material, thermoplastic, thermosetting or otherwise, compatible with the manufacturing method, is contemplated by the present invention.  
      The microstructure  34  can be formed on the interior surfaces  32  of the sheets  30  by microreplication such as, for example, stamping by a master tool. The master tool can be made in a conventional manner, such as ruling, diamond turning, photolithography, deep reaction ion etching, plasma etching, reactive ion etching, deep x-ray lithography, electron beam lithography, ion milling, or combinations thereof.  
      In the illustrated embodiment, the sheets  30  are rectangular in shape and, as is shown in  FIG. 3 , they can be joined together along three edges to form a pouch  36  having an access opening  38 . The joining can be accomplished by adhesives, welding, or any other seaming method which results in an air tight seal. It may also be noted that the sheets  30  need not be rectangular, as they can be any other polygonal, non-polygonal, circular, regular or irregular shape.  
      As shown in  FIG. 4 , a substrate  40  is placed inside the pouch  36  (via the access opening  38  in the illustrated embodiment). The substrate  40  has an exterior surface  42  and an overall geometry corresponding to the geometry of the article  10 . Thus, the substrate  40  has a curved (i.e., non-flat) geometry and, thus, its exterior surface  42  has curved regions, namely a top region  44  and a bottom region  46 . As is shown in  FIGS. 4A and 4B , at this stage in the method, the surface regions  44  and  46  have a smooth “non-embossed” profile.  
      To produce the article  10  shown in  FIGS. 1, 1A  and  1 B, the substrate  40  comprises a main body portion  50  formed of an embossable material, as is shown in  FIGS. 4A and 4B . To produce the modified article  10 ′ shown in  FIG. 1C , a modified substrate  40 ′ shown in  FIG. 4C  is used. This substrate  40 ′ comprises a main body  50 ′ of a not necessarily embossable material and a coating  52 ′ of embossable material. In either case, the embossable material can comprise a thermoplastic material, such as polyolefins, both linear and branched, polyamides, polystyrenes, polyurethanes, polysulfones, polyvinyl chloride, polycarbonates, and acrylic polymer and copolymer. In one embodiment, the thermoplastic material includes at least one filler, such as, for example, silicates. In any event, it is important that the embossable material of the substrate  40  have a glass transition temperature lower than the glass transition temperature of the material used to make the pouch  36 .  
      As shown in  FIG. 5 , the pouch  36  is sealed in the illustrated embodiment by joining the fourth edges of the respective sheets  30  previously defining the access opening  38 , as is shown in  FIG. 5 . It may be noted at this point that the steps shown schematically in  FIGS. 2-5  simply illustrate one way of sealing the substrate  40  within the pouch  36  so that the pouch  36  can be evacuated. Other ways and means of accomplishing this result are certainly possible with, and contemplated by, the present invention. For example, the pouch  36  can be formed in one piece and/or formed around the substrate  40 . Also, the evacuation step discussed below can be performed after such sealing step, during such sealing step, and/or prior to such sealing step.  
      As shown in  FIG. 6 , the sealed pouch  36  is then evacuated, whereby its interior surfaces  32  contract inwardly and its microstructure  34  contacts the exterior surface  42  of the substrate  40 . The level of evacuation is sufficient (upon subsequent thermal processing steps) to cause embossing of the surface  42  of the substrate. It may be noted that the contraction of the pouch  36  allows the “mold” to transform shape to accommodate the geometry of the substrate  40 , making the present invention especially useful when microembossing articles having curved geometries. It may also be noted that the encompassing nature of the contracting pouch  36  allows the simultaneous embossing of both the top region  44  and the bottom region  46 , making the present invention especially useful when microembossing opposite surface regions (e.g., top and bottom) of an article.  
      As shown in  FIGS. 7 and 8 , the pouch  36  (with substrate  40  sealed therein) is then thermally processed so that the microstructure  34  embosses the exterior surface  42  of the substrate to form the desired microembossed architecture  18 . The thermal processing step can comprise heating the evacuated pouch  36  by, for example, placing it in a oven, flowing forced air over it, and/or supplying an IR light source ( FIG. 7 ). The temperatures used during such a heating step will depend upon the material make-up of the pouch  36  and/or the substrate  40 . For example, the processing temperature could be designed to be just above the glass transition temperature of the embossable material of the substrate  40  which, as discussed above, would preferably be well below the glass transition temperature of the pouch  36 . The thermal processing step can also comprise a subsequent cooling step ( FIG. 8 ).  
      After completion of the thermal processing steps, the pouch  36  can be opened (e.g., by severing a seam and/or a sheet) and the substrate  40 , now the article  10 , removed. Preferably, the pouch  36  is designed so that one-time uses are economical, whereby the pouch  36  can be discarded.  
      Referring now to  FIGS. 10-14 , the elements and steps of another preferred microembossing method according to the present invention are schematically shown. As shown in  FIG. 10 , a single sheet  60  is used in this method, the sheet  60  having a surface  62  which includes a microstructure  64  ( FIG. 10A ) corresponding to the desired architecture  18 . The material selection and/or microstructuring method can be the same as those used with the sheets  30  discussed above. As shown in  FIGS. 11 and 12 , the sheet  60  is wrapped around the substrate  40 .  
      The wrapped substrate  40  is then sealed inside a pouch  66 , which is then evacuated, whereby the sheet&#39;s interior surface  62  contracts inwardly and its microstructure  64  contacts the exterior surface  42  of the substrate  40 . Again, the contraction of the pouch  66  allows the “mold” to transform its shape to accommodate the geometry of the substrate  40 , making the present invention especially useful when microembossing articles having curved geometries. Also, the encompassing nature of the contracting pouch  66  allows the simultaneous embossing of both the top region  44  and the bottom region  46  of the substrate  40 , making the present invention especially useful when microembossing opposite surface regions (e.g., top and bottom) of an article. After the evacuation step, heating, cooling, and removing steps are performed as discussed above to complete the microembossing process.  
      Referring now to  FIG. 15 , the pouch  66  can be modified to include a shrinking section  70  aligned with the convex region (e.g., the top region  44  in the illustrated embodiment) of the substrate  40 . The section  70  can be made of shrink film or another appropriate material. In any event, the shrinkage of this section  70  during evacuation and/or thermal processing can help to eliminate wrinkles, provide more uniform pressure, and/or create more pressure by tightening up the contacting section of the pouch  66 .  
      Referring now to  FIG. 16 , a bladder  72  (or other suitable component) can be aligned with the concave region (e.g., the lower region  46  in the illustrated embodiment) of the substrate  40 . As the pouch  66  contracts, it will push the bladder  72  into the concave region thereby ensuring tight engagement of the sleeve  60  with the substrate  40 . It may be noted that another bladder (having an appropriate shape) could be aligned with the convex region (e.g., the upper region  44  in the illustrated embodiment) of the substrate  40 . Additionally or alternatively, the bladder  72  could be used in combination with the shrink section  70  discussed above. A further option is to place bladders outside of the pouch  66  which expand upon evacuation to insure tight engagement of the sleeve  60  with the substrate  40 . The bladder can contain a gas or a liquid, and could be a sealed unit or connected to a pumping device which could inflate and deflate the bladder as required.  
      Referring now to  FIG. 17 , the pouch  66  is shown within a pressurizing chamber  74 . With such a chamber  74 , a fluid is used to apply pressure to the contracting pouch  66  as evacuation occurs. The fluid is preferably a liquid, such as water, and applies supplemental external pressure during and after evacuation to enhance the embossing procedure. Such external pressure could be applied instead by, for example, a mechanical press, foam rollers or other suitable pressure-applying components.  
      Although the invention has been shown and described with respect to certain preferred embodiments, it is evident that equivalent and obvious alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such alterations and modifications and is limited only by the scope of the following claims.