Abstract:
An apparatus and method for lamination are provided, which are advantageously used in intermittent lamination and fixed-gap lamination, the apparatus comprising first and second laminating rollers defining a laminating gap therebetween and at least one gapping block positioned between the first and second rollers such that the gapping block determines and maintains a minimum gap width. The gapping block comprises a rigid gapping block body, which may be adjustable in width, and four or more load wheels rotatably attached to the gapping block body which ride on a portion of the first and second rollers.

Description:
FIELD OF THE INVENTION 
     This invention relates to method of lamination and an apparatus comprising first and second laminating rollers defining a laminating gap therebetween and at least one gapping block positioned between the first and second rollers such that the gapping block determines and maintains a minimum gap width. The gapping block comprises a rigid gapping block body, which may be adjustable in width, and four or more load wheels rotatably attached to the gapping block body which ride on a portion of the first and second rollers. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 6,347,585 discloses a gap adjusting device for a rotary press comprising two rollers separated by an adjustable eccentric member. 
     U.S. Pat. No. 5,456,871 discloses a system for adjusting a calendaring gap which employs load measuring units and active feedback, typically mediated by a microprocessor. 
     U.S. Pat. App. Pub. No. US2002/0014509 A1 discloses a nipping roller gap adjusting device having a minimum gap setting means which includes an opposing pair of stops, one attached to a moving assembly that bears a roller and the other attached to the apparatus frame. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention provides an apparatus comprising first and second rollers defining a gap therebetween and at least one gapping block positioned between the first and second rollers such that the gapping block determines and maintains a minimum gap width. The gapping block comprises a rigid gapping block body and four or more load wheels rotatably attached to the gapping block body and is positioned between the first and second rollers such that at least two load wheels contact each roller. In a further embodiment, the width of the gapping block may be adjustable. 
     In another aspect, the present invention provides a method of laminating two or more sheet materials together by passing the sheets concurrently into a gap between a first roller and a second roller of a laminating apparatus, which apparatus additionally comprises at least one gapping block positioned between the first and second rollers such that the gapping block determines and maintains a minimum gap width. 
     In another aspect, the present invention provides a method of laminating two or more sheet materials together by passing the sheets concurrently into a gap between a first roller and a second roller of a laminating apparatus, which apparatus additionally comprises at least one gapping block positioned between the first and second rollers such that the gapping block determines and maintains a constant gap width which remains constant throughout the lamination. 
     In another aspect, the present invention provides an adjustable gapping block comprising: a first gapping block body element having two or more load wheels rotatably attached; a second gapping block body element having two or more load wheels rotatably attached, where the second gapping block body element is assembled with said first gapping block body element so as to allow linear motion of the two elements relative to each other in the direction of gapping block body width, and where at least one surface of either gapping block body element is canted with respect to a facing surface of the other gapping block body element when so assembled; a wedge disposed between the facing surfaces; and an adjusting screw to determine the position of the wedge between the facing surfaces, thereby determining the gapping block body width. 
     In this application, “to laminate” means to bond together two or more sheet materials. 
     It is an advantage of the present invention to provide a method of lamination which prevents damage to the continuous web during intermittent lamination of non-continuous sheets to a continuous web. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1 and 2 illustrate a gapping block according to the present invention. 
     FIGS. 3 and 4 are cross-sections of the gapping block depicted in FIGS. 1 and 2. 
     FIG. 5 is a cross-section of an apparatus according to the present invention taken through the axes of the two rollers of the apparatus. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-4, a gapping block according to the present invention comprises a gapping block body which comprises a first gapping block body element  10  and a second gapping block body element  20 . Two load wheels  31 ,  32  are rotatably attached to the first gapping block body element  10 . Two load wheels  33 ,  34  are rotatably attached to the second gapping block body element  20 . Additional load wheels may be mounted to either gapping block body element. Alternately, where no adjustment to gapping block body width will be needed, the gapping block body can be a single body element to which four or more load wheels are mounted. Arrow A indicates the dimension which represents body width of the gapping block. In use with a pair of rollers, the gapping block body width is the linear dimension of the gapping block body measured in the direction parallel to the measurement of the gap width between the first and second rollers. In use, motion of the gapping block body elements in a direction perpendicular to the gapping block body width must be prevented. First gapping block body element  10  may comprise arms  15  which prevent motion of second gapping block body element  20  in one or more direction perpendicular to the gapping block body width. In addition, one or more lateral constraints attached to or forming a part of the apparatus frame (shown in FIG. 5, discussed below) may prevent motion of second gapping block body element  20  relative to first gapping block body element  10  in one or more directions perpendicular to the gapping block body width. First and second gapping block body elements  10 ,  20  may be bolted to one or more lateral constraints after adjustment of the gapping block body width through tapped holes  12 ,  22 . 
     First gapping block body element  10  and second gapping block body element  20  comprise facing surfaces  11  and  21 , respectively. One or both of facing surfaces  11  and  21  is canted. By interaction with surfaces  11  and  21 , wedge  40  may be used to adjust gapping block body width. Adjusting screw  41  may be used to alter the position of wedge  40  and thereby the gapping block body width. In one embodiment, adjusting screw  41  has threaded shaft which engages a tapped hole in a lateral constraints attached to or forming a part of the apparatus frame (shown in FIG. 5, discussed below). Typically, first gapping block body element  10  is bolted to one or more lateral constraints through tapped holes  12 , gapping block body width is adjusted by means of adjusting screw  41 , and then second gapping block body element  20  is bolted to one or more lateral constraints through tapped holes  22 . 
     With reference to FIG. 5, an apparatus according to the present invention comprises gapping blocks as described above comprising first gapping block body element  10 , second gapping block body element  20 , load wheels  32 ,  34 , wedge  40 , and adjusting screw  41 . Lateral constraints  50  prevent motion of second gapping block body element  20  relative to first gapping block body element  10  in a direction perpendicular to the gapping block body width. Lateral constraints  50  are attached to the apparatus frame by connections not shown. First gapping block body elements  10  may be bolted to lateral constraints  50  by through holes  51  and tapped holes  12 . Adjusting screws  41  have threaded shafts which engages tapped holes  53  in lateral constraints  50 . Gapping block body width is adjusted by means of the action of adjusting screws  41  on wedges  40 . Second gapping block body elements  20  may then be bolted to lateral constraints  50  by through holes  52  and tapped holes  22 . 
     The apparatus additionally comprises a first roller  60  comprising a pressing zone  61  having a radius r p1  and two gapping block zones  62 ,  63  having a radius r g1 . As shown, the first roller additionally comprises axle portions  64 ,  65  which interact with bearing surface mechanisms  72 . Second roller  80  comprising a pressing zone  81  having a radius r p2  and two gapping block zones  82 ,  83  having a radius r g2 . Typically, r p1  equals r p2  and r g1  equals r g2 . As shown, the first roller additionally comprises axle portions  84 ,  85  which interact with bearing surface mechanisms  92 . A narrow laminating gap is formed between first roller  60  and second roller  80 , which are not in contact. The laminating gap of the embodiment shown in FIG. 5 is too narrow to be clearly depicted. Either or both of first roller  60  and second roller  80  may be driven by known means such as motors and the like. Typically both are driven. Typically first roller  60  and second roller  80  are geared together so that they have the same speed at the gap. In one embodiment, first roller  60  and second roller  80  are driven by a belt drive mechanism interacting with pulleys  68  and  88 . 
     Bearings comprise bearing housings  71 ,  91  and bearing surface mechanisms  72 ,  92  which are of known types such as ball bearings, roller bearings, needle bearings, and the like. Bearing housings  71 ,  91  are attached to the apparatus frame  100  such that pressure can be brought or maintained on bearing housings  71 ,  91  which tends to bring together first and second rollers  60 ,  80 . The bearing housings may be fixedly attached to frame  100  or attached by means of pneumatic or hydraulic pistons  101  and cylinders  102 , as shown. Bearing mechanisms may form a part of drive mechanisms for either or both rollers. 
     In the laminating method according to the present invention, two or more sheet materials are pressed together by passing them concurrently into a narrow gap between first roller  60  and second roller  80 . Typically one or both of first roller  60  and second roller  80  are driven; more typically both. Heat, solvents or adhesives may be applied to one or more layers to aid in bonding. First roller  60  and second roller  80  may be heated by any suitable method but are typically internally heated by a method such as electrical heating or circulation of hot air, water or oil. 
     The apparatus and method according to the present invention are used to advantage where intermittent lamination is desired, i.e., where one or more of the layers to be laminated is not continuously present in the laminating gap during lamination. In this case, the product may be a continuous web with non-continuous patches of additional sheet materials laminated thereto. In the case of intermittent lamination, the continuous web could be crushed or damaged if the full laminating pressure were applied when the non-continuous sheet material was not present in the gap. This damage to the continuous web may be prevented by use of the method and apparatus according to the present invention, which maintains a minimum gap width. In addition, if the full laminating pressure were applied when the non-continuous sheet material was not present in the gap, the leading edges of the intermittent laminate may be rounded during the laminating process, which may be avoided by use of the method and apparatus according to the present invention. 
     The apparatus according to the present invention has the additional advantage that bearing clearance in the roller bearings is removed from consideration in determining gap width, and therefore variation in bearing clearance is also removed from consideration. Variation in bearing clearance may be especially problematic where laminating rolls are heated. More accurate and consistent gap width may be set using the apparatus according to the present invention. In addition, the apparatus according to the present invention can be used for fixed-gap lamination, where the gap width is essentially constant throughout lamination. To achieve fixed-gap lamination, sufficient force must be applied to the rollers to overcome any resisting force generated by the materials to be laminated. 
     The apparatus and method according to the present invention are used to advantage in the lamination of catalyst decals to polymer electrolyte membranes, in particular membranes of sulfonated fluoropolymer membranes such as Nafion™ or Flemion™. Catalyst decals typically comprises a thin layer of a catalyst dispersion on a backing layer. After lamination of the catalyst dispersion to the polymer electrolyte membrane, the decal backing layer is removed. The apparatus and method according to the present invention are used to advantage with cast membranes of delicate or thin films, typically 100 micrometers in thickness or less, more typically 50 micrometers in thickness or less, and more typically 30 micrometers in thickness or less. 
     Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and principles of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth hereinabove. All publications and patents are herein incorporated by reference to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.