Patent Publication Number: US-6709727-B1

Title: Bookbinding structure and method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates rally to the field of bookbinding, and more particularly, to a bookbinding structure and method that may be used with a wrap-around book cover. 
     2. Description of Related Art 
     Bookbinding systems utilizing binder strips are well known. Binder strips are used to bind pages together to form a book in which the binder strip forms the spine of the book. Binder strips which use a heat activated adhesives of low and high viscosity are used to bind a stack of sheets using heat and pressure which are applied to the strip and stack using a special purpose binding machine. 
     U.S. Pat. No. 4,496,617, the contents of which are hereby fully incorporated herein by reference, describes such a binding strip. The strips include an elongated paper substrate and an adhesive matrix disposed on the substrate. The matrix includes a central adhesive band which is heat activated and which has a relatively low viscosity when activated and a pair of outer adhesive bands. The outer bands are also heat activated, but are of a relatively high viscosity. The central adhesive band functions to secure the edges of the pages to be bound together and to the substrate and the outer bands function to secure the front and back cover pages to the substrate. 
     Such prior art binder strips are, however, not suitable for some applications due to the appearance of books bound by such strips. The spines of books bound by the conventional binder strips are often devoid of any printed information because the binder strips require specialized equipment for printing on the strip. Moreover, it is sometimes desirable to have a uniform cover having a continuous design from the front cover to the back cover, frequently including the spine. A conventional binder strip cannot provide a bound book having a cover with such a continuous design. 
     One approach to address the shortcomings of the above-described prior art involves the use of a binder strip having a second adhesive layer which permits the cover to be applied after the binding sequence. As will be explained, this approach permits a printed cover to be applied after the binding sequence so that the cover can be preprinted with heat sensitive inks. 
     Referring to the drawings, FIG. 1A shows one embodiment of a prior art binder strip which permits a cover to be added after the binding sequence is completed. FIG. 1A is an exploded perspective view of the various layers of a first embodiment of the prior art bookbinding structure  1 . In the first embodiment, the bookbinding structure  1  includes an elongated substrate  6  having a length which corresponds to the length of the stack of pages (not depicted) to be bound and a width which exceeds the thickness of the stack by at least a minimum amount so that the edges of the substrate  6  will extend around the edge of the stack and slightly over the front and back pages of the stack, as will be described. Substrate  6  is preferably made of a formable material such as heavy weight paper. 
     A layer of pressure activated adhesive  3  is disposed on one surface of the substrate  6 , with a heat activated adhesive matrix  4  being disposed facing the opposite substrate surface. The pressure activated adhesive  3  is typically a permanently binding adhesive which, once activated by applying pressure, produces a relatively permanent bond. One such pressure activated adhesive is sold under the designation HL-2593 by H. B. Fuller Company of St. Paul, Minn. The Fuller HL-2593 pressure activated adhesive can be subjected briefly to high temperatures, up to about 425 degrees F, without decomposing. The ability of the pressure activated adhesive  3  to withstand high temperatures is important because the bookbinding structure  1  is subjected briefly to high temperatures during the binding process, which will be described in more detail below. The pressure activated adhesive is preferably 0.003 to 0.005 inches thick. 
     The pressure activated adhesive  3  is covered with a removable release liner  5 , as shown in FIG. 1A, to act as a barrier between the pressure activated adhesive  3  and the environment. The release liner  5  is preferably a silicon coated paper, such as made by Akrosil, Inc. of Menasha, Wis. under the designation Silox ® SBL60SC F1U/F4B. The surfaces of the coated paper can have varying release levels, with a low or easy release level indicating that the paper can be separated with little force and a high or tight release level indicating the separation requires a relatively large amount of force. The designation F4B indicates that the release level of the liner surface contacting the pressure sensitive adhesive layer  3  has a medium release level, with the opposite surface of the liner having a low or easy release level as indicated by the designation F 1 U. 
     The heat activated adhesive matrix  4  is comprised of a center adhesive  4 A which extends along the longitudinal axis of the substrate  6  and a pair of outer adhesive bands  4 B. The center adhesive band  4 A, which is a heat activated adhesive of relatively low viscosity, is the primary adhesive for binding the pages together. The center adhesive  4 A is typically 0.015 inch thick. An adhesive, sold under the designation Cool Bind 34-1301 by National Starch &amp; Chemical Company of Bridgewater, N.J., has been found to be suitable as the center adhesive band  4 A. The center adhesive band  4 A preferably extends over slightly less than the full length of the bookbinding structure  1  so that there are end gaps without the center adhesive  4 A. In addition, the center adhesive band is at least as wide as the thickness of the stack  13  to be bound so that all of the pages of the stack will be exposed to the low viscosity adhesive. 
     The outer adhesive bands  4 B are comprised of a heat activated adhesive of relatively high viscosity when activated and possesses a high degree of tackiness. The outer adhesive bands  4 B function to attach the substrate  6  to the front and back pages of the stack. The outer adhesive bands  4 B preferably extend along the entire length of substrate  6  and are 0.010 inch thick. An adhesive sold under the designation HB HL-1777 by H. B. Fuller Company of St. Paul, Minn., may be used for the outer adhesive bands  4 B. 
     The FIG. 1A bookbinding structure further includes an undercoat adhesive layer  7  disposed intermediate the adhesive matrix  4  and the substrate  6 . The undercoat adhesive is heat activated and is relatively thin, typically 0.003 inches thick. The undercoat is preferably the same type of adhesive used in the outer adhesive bands  14 B and functions to act as a barrier so as to prevent the low viscosity central adhesive band  4 A from passing through the substrate  6 . In addition, the undercoat adhesive prevents all of the low viscosity adhesive of central band  4 A from being drawn up between the pages of the stack which may leave essentially no adhesive intermediate the edges of the pages and the substrate  6 . 
     The manner in which the FIG. 1A prior art bookbinding structure  1  is applied to the stack  13  and used to bind the stack will be subsequently described. However, once the stack of pages has been bound, the structure  1  and stack  13  appear as shown in FIG.  4 . As can be seen, the structure  1  is positioned on the bound edge of stack  13 . Note that the bound stack  13  does not include a cover at this stage of the sequence, with top of the stack being the first page and the bottom of the stack being the last page. The pressure sensitive adhesive  3  is exposed by manually removing the release liner  5  as shown in the drawing. A cover assembly or book cover  2  is positioned on a flat surface as shown in FIG.  5 . The bound book  13  is then carefully positioned above the cover  2  so that the stack is aligned with the right hand portion of the cover, with the bound edge of the stack being positioned near the center of the cover. 
     After alignment, the stack  13  is lowered on to the book cover  2  so that the bottom portion of the exposed adhesive contacts the cover. The adhesive  3  is very aggressive in order to secure the cover assembly  2  adequately. 
     Unfortunately, if the cover assembly  2  is not properly aligned, it is generally not possible to separate the stack  13  from the cover since the adhesive bond is permanent. Accordingly, it is important that the alignment be correct in the first instance. It has been found that an “L” shaped ruler, referred to as a carpenter&#39;s square, can be placed on the work surface and used to carry out the alignment. An apparatus to assist in aligning the stack  13  and cover assembly  13  together is disclosed in U.S. application Ser. No. 60/204,220 filed on May 15,00 and entitled “Apparatus and Method of Binding Soft Cover Book”, the contents of which are hereby fully incorporated by reference into the present application. 
     As shown in FIG. 6, once the stack  13  has been properly positioned on the cover assembly  2 , the assembly is manually folded around the edge of the bound stack. Pressure is applied to the outer surface of the cover assembly  2  in the spine region to ensure that the cover assembly is secured in all areas where the pressure sensitive adhesive is present. This results in a bound book  14  having a cover assembly  2  forming the front and rear book cover together with the book spine. 
     FIG. 7 is a cross-sectional end view of the bound book using the first embodiment prior art bookbinding structure  1  which is not shown to scale so that all of the various layers can be seen. Preferably, the cover assembly  2  is pre-scored at the two locations so that the cover assembly can easily be folded at the proper locations. The cover assembly  2  can be previously printed using any type of process, including printing processes that utilize heat sensitive inks since the cover assembly is never subjected to elevated temperatures when using the first embodiment bookbinding structure  1 . 
     Note that the cover assembly  2  need only cover that portion of the spine which includes the pressure sensitive adhesive  3 . FIG. 9A shows a cross-section of a bound book where the cover assembly covers that front and rear pages of the book together with the spine, as previously described in connection with FIG.  7 . FIG. 9B shows a bound book where the cover assembly  2  covers only the front page, a very small portion of the back page and the spine. Finally, FIG. 9C shows a bound book where the cover assembly  2  only covers the spine and a small portion of the front and back pages sufficient to cover the pressure sensitive adhesive. 
     The manner in which the first embodiment prior art bookbinding structure  1  is applied to the stack  13  so as to bind the stack will now be described. One significant advantage of the present invention is that an existing, commercially available binding machine can be used to carry out the binding sequence. One such machine is described in U.S. Pat. No. 5,052,873, the contents of which are hereby fully incorporated herein by reference. The binding sequence set forth in U.S. Pat. No. 5,052,873 uses a conventional binder strip of the type disclosed in previously noted U.S. Pat. No. 4,496,617. 
     FIG. 2 depicts a conventional binding machine  8  such as described in U.S. Pat. No. 5,052,873. Machine  8  has a stack  13  to be bound inserted into the machine input. The thickness of the stack is automatically measured and the appropriate width binding structure I is displayed. As is the case with conventional binder strips, the binding structure  1  is preferably available in three widths to accommodate stacks  13  of varying width. Such widths include “Narrow”, “Medium” and “Wide”, with the width of the central adhesive band  4 A being altered for each binder structure  1  width. Machine  8  will specify a structure  1  width having a central adhesive  4 A width that is at least as wide as the measured thickness of the stack  13 . A binding structure  1  of the appropriate width is then manually fed into the strip feed input of the machine  8 . The machine then automatically carries out the binding sequence by appropriately positioning the structure  1  relative to the edge of the stack  13  and applying a combination of heat and pressure as will be described. 
     The binding sequence is depicted schematically in FIGS. 3A through 3F. End views are shown of the stack  13  and the binding structure  1 . Referring to FIG. 3A, the stack  13  to be bound, after loading, is gripped between a pair of clamps  10  and  11  and is initially supported on a cool platen  9 . A strip positioning apparatus (not depicted) positions the binding structure  1  previously fed into the machine so that the adhesive matrix  4  is facing the stack  13 . The vertical position of the structure  1  relative to the stack  13  is automatically set in accordance with the thickness of the stack as previously measured. A thin stack  13  will result in the structure  1  being positioned relatively high so that the edges of the structure  1  will extend equally over the front and rear pages of the bound stack. Similarly, a thick stack will result in the structure  1  being positioned somewhat lower. A heated platen having a rotating segment  12 A and a non-rotating segment  12 B is positioned facing the binding structure  1 . The platen segments  12 A and  12 B are at least as long as the length of the stack and the length of the elongated binding structure  1 . 
     As shown in FIG. 3B, the stack  13  is moved laterally away from the cold platen  9  towards the rotating platen segment  12 A. This movement is carried out by way of clamps  10  and  11  which support and move the stack. The lower portion of the stack  13  is forced against the heated rotating platen portion  12 A, with one edge of the binding structure I being disposed between the platen portion  12 A and the stack  13 . Note that the binding machine element which supports the opposite side of stack  13  at this point in the sequence is not depicted in the drawings. The resultant heat and pressure applied to one edge of the bookbinding structure  1  results in activation of one of the outer adhesive bands  14 B (FIG.  1 A). This will cause an adhesive bond or seal to be formed between the structure  1  and the front page of stack  13 . Since the outer adhesive bands  14 B are high tack when activated, the binding structure  1  remains bonded to the front page of the stack  13  when the stack is moved away from the heated rotating platen portion  12 A as shown in FIG.  3 C. 
     As shown in FIG. 3D, the rotating platen segment  12 A is rotated 90 degrees so that both the rotating and fixed platen segments  12 A and  12 B define a flat upper surface. This permits stack  13  to be moved to the right over the platen segments. This causes the bookbinding structure  1  to be folded around the lower edge of the stack  13 . The binding machine  8  pauses briefly in this position so that the central adhesive band  4 A will have time to become molten and to flow upward by way of capillary action between the individual pages of the stack  13  thereby fulling wetting the pages with the adhesive. The rotating platen segment  12 A is then rotated 90 degrees back to the original position as shown in FIG.  3 E. This results in the remaining edge of the bookbinding structure  1  to be folded around the edge of the stack  13 , with the remaining outer adhesive band  4 B being positioned facing the rear page of the stack  13 . The stack  13  is then forced against the rotating platen portion  12 A thereby activating the outer adhesive band  4 B so as to form the final adhesive bond. The bound stack  13  is then removed from the binding machine and permitted to cool for a few minutes so that the adhesives have an opportunity to set. The cover assembly  2  is then secured to the stack as previously described in connection with FIGS. 4,  5  and  6 . 
     Note that the first embodiment bookbinding structure  1  could also be implemented without substrate  6 . In that event, undercoat adhesive layer  7  is disposed directly on the pressure activated adhesive layer  3 . The release liner  5  then provides the additional function of acting as a substrate and supporting the structure  1  during the binding sequence previously described in connection with FIGS. 3A through 3E. 
     A second embodiment of the prior art bookbinding structure is depicted in FIG.  1 B. The second embodiment bookbinding structure  1  includes an adhesive matrix  4  similar to that of the first embodiment structure of FIG. 1A. A substrate  6  is provided having the same shape as that of the first embodiment, with there being an undercoat adhesive layer  7  similar to layer  7  of FIG.  1 A. The second embodiment structure  1  does not include, among other things, the pressure activated adhesive  3  of the first embodiment. 
     A stack  13  is bound using the second embodiment structure  1  in the same manner as that of the first embodiment structure. Once the steps of FIGS. 3A through  3 E are carried out using the conventional binding machine  8 , the bound stack is permitted to cool. The substrate  6  is then manually removed from the stack in much the same manner as the release liner  5  is removed from the stack as depicted in FIG.  4 . Thus, the substrate  6  of the second embodiment also functions as a release liner. 
     Removal of substrate  6  exposes the undercoat adhesive layer  7 . Adhesive layer  7  together with the remaining adhesive of the adhesive matrix  4  is then used to attach a cover assembly  2  to the bound stack  13 . Since the adhesives are heat activated, it is necessary to reheat the adhesives so that they can be used for this purpose. It is possible to again use a conventional binding machine  8  to carry out the sequence for attaching the cover assembly  2  to the bound stack  13 , as will be described. 
     The cover assembly  2  of appropriate dimensions is first placed on a flat surface and the bound stack  13  is positioned over the assembly in much the same manner as previously described in connection with the first embodiment. The cover assembly  2  is folded around the stack  13  to the desired final position. Preferably, the assembly is pre-scored to facilitate this step. Since the adhesives are not activated at this point, proper positioning is somewhat easier to accomplish as compared to the first embodiment. The cover assembly/stack combination  2 , 13  is then inserted into the conventional binding machine  8 , taking care to hold the cover assembly  2  in place until the combination is gripped by the machine clamps  10  and  11  (FIG.  3 A). The binding machine  8  must be slightly modified to carry out the cover assembly  2  attachment sequence since the machine normally requires activation when a binder strip is manually fed into the machine as shown in FIG.  2 . Such modification would simply simulate the detection of a binder strip being fed into the machine. Alternatively, it is possible to activate the machine  8  by momentarily inserting a binder strip into the machine so as to initiate the sequence and to then rapidly withdraw the strip from the machine since the strip is not needed and should not be present. 
     FIG. 8A shows a book  14 , which includes the bound stack  13  and the folded cover assembly  2 , installed in the binding machine  8  and resting on the cool platen  9  (not depicted). Book  14  is secured by opposing clamps  10  and  11  (not depicted). This point in the binding machine sequence corresponds to that shown in FIG. 3A where the binding structure  1  is being applied to the stack  13 . Note that FIG. 8A does not include a binding structure as does FIG. 3A since the structure was previously applied. The stack  13  is then forced against heated platen segment  12 A so that one of the outer adhesive bands  4 B is activated and compressed between the cover assembly  2  and the front page of the stack  13  as shown in FIG.  8 B. This corresponds to FIG. 3B of the binding machine  8  sequence. Thus, a first adhesive seal in created between the stack  13  and the cover assembly  2 . 
     The stack  13  with cover  2  is then moved away from the heated platen segments  12 A and  12 B as indicated in FIG.  8 C and the rotating platen segment is rotated  90  degrees as shown in FIG.  8 D. The stack  13  is then positioned over the heated platen sections  12 A and  12 B so that a seal will be formed between the edge of the stack  13  and that part of the cover  2  which forms the spine. FIGS. 8C and 8D correspond generally to FIGS. 3C and 3D, respectively. 
     The rotating platen segment  12 A is then rotated back 90 degrees, with the stack  13  and platen segment  12 A then being forced together as shown in FIG. 8E which corresponds to FIG.  3 E. The resultant application of heat and pressure will cause a further adhesive seal to be formed between the cover  2  and the last page of the stack  13 . This will complete the binding sequence so that the bound book can be removed from the binding machine and permitted to cool. 
     Since the cover assembly  2  is heated when the second embodiment bookbinding structure  1  is used, any printing on the cover assembly should be carried out using inks not sensitive to heat. Further, substrate  6  must be made of a material that will support the various molten adhesives applied to the substrate when the bookbinding structure is fabricated and will provide sufficient support during the binding sequence of FIGS. 3A through 3E so that the structure  1  can be manipulated and heated by the binding machine  8  in order to carry out the sequence. Still further, the substrate  6  must be made of a material that has a sufficiently high release value to permit the substrate to be manually separated from the bound book  13 . It has been found that the substrate material of the second embodiment should not contain free silicon since this material has been found to contaminate the adhesives and destroy the adhesive properties. Thus, the material must be either fully reacted silicon based or be non-silicon based. The substrate could be fabricated from a liner material having a repositionable adhesive such as a product sold under the designation ReMount 6091 by the Industrial Tape and Specialties Division of 3M located in St Paul, Minn. 
     FIG. 1C is an exploded view of a third embodiment prior art bookbinding structure. The third embodiment is similar to the first embodiment (FIG. 1A) except that a solvent activated adhesive  15  is used instead of a pressure activated adhesive  3 . This feature eliminates the requirement for a release liner, such as liner  5  of the first embodiment. The solvent activated adhesive  15  must be able to withstand temperatures up to about 425F which are created during the binding sequence as depicted in FIGS. 3A through 3E. One suitable solvent activated adhesive is an adhesive sold under the designation Weldbond by Frank T. Ross and Sons, Inc. in Spring Grove, Ill. The Weldbond adhesive may be activated by either water or alcohol. 
     The manner in which the stack  13  is bound using the third embodiment bookbinding structure  1  is the same as the first embodiment except that the exposed adhesive  15  must be activated by application of water or alcohol prior to placement of the bound stack  13  on the cover assembly  2 . Since the cover assembly  2  is never subjected to elevated temperatures, it is possible to print the cover assembly  2  using printing techniques that require heat sensitive inks. 
     As previously noted, it can be difficult to reliably position the bound stack  13  on the cover assembly  2  as shown in FIG.  5 . If the alignment is not correct in the first instance, it is not possible to remove the cover assembly  2  without damage to the cover assembly  2 . Although the apparatus noted above and disclosed in U.S. application Ser. No. 60/204,220 is very useful in assisting in such alignment, such apparatus will not always be available to many users, particularly users binding a small number of books. In addition, when a stack  13  is bound as shown in FIG. 7, the spine section of the cover assembly is secured to the end of the stack  13  the full width of the stack. Thus, when the bound book is opened, the spine section of the cover assembly  2  is compressed and deformed. Once the book is opened and closed several times by a reader, the compression and deformation tend to damage any printing on the spine thereby detracting from the appearance of the book. This compression and deformation also tends to prevent the book from lying flat on a surface when the book is opened. 
     The present invention addresses the above-noted shortcomings of the prior art bookbinding structure. A user is able to accurately align the stack and cover assembly in the first instance. This is easily accomplished without the need of any special alignment apparatus. Further, in one embodiment of the present invention, the spine section of the cover can separate from the spine of the bound book so that compression and deformation of the spine section is reduced. This will significantly reduce any damage to the printed matter on the spine. Further, the appearance of the bound book will more accurately simulate that of a book bound using prior art mass production techniques. These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following Detailed Description of the Invention. 
     SUMMARY OF THE INVENTION 
     A bookbinding structure for binding a stack of sheets, with the stack of sheets having a thickness, a width and a length. The structure includes an elongated substrate having a length that corresponds to the length of the substrate and a width somewhat greater than the thickness of the stack. A first adhesive matrix is disposed on what will be the inner surface of the substrate. Typically, the first adhesive matrix is heat activated and operates to bind the individual sheets together and to the substrate. Preferably, this part of the binding sequence is carried out using a conventional desk top binding machine. 
     A second pressure activated adhesive matrix is disposed on what will be the outer surface of the substrate. The second adhesive matrix functions to secure a cover assembly, which includes front and back cover sections and a spine section intermediate the front and back cover sections, to the bound stack. The cover apparatus can be preprinted prior to being applied to the bound stack. Heat sensitive inks can be used for printing since the binding sequence, which uses heat to activate the first adhesive matrix, takes place prior to attaching the cover apparatus to the bound stack. 
     The second pressure activated adhesive matrix includes a first segment that extends substantially along the full length of the substrate and a second segment that extends substantially along the full length of the substrate. First and second separate release liners are disposed over the first and second segments of the pressure activated adhesive matrix, respectively. The liners prevent the underlying pressure activated adhesive from becoming adhered to anything until the cover apparatus is to be attached to the bound stack. The first release liner it typically first manually removed, typically be peeling the liner away from the bound stack, with the second liner remaining in place. The user then positions the bound stack between the front and back cover sections of the cover apparatus, with the bound edge of the stack being positioned adjacent the spine section. The presence of the second release liner allows the user to more easily manipulate stack and cover assembly so that optimum alignment is achieved without the pressure activated adhesive prematurely adhering to the cover apparatus. If this were to occur, it is very difficult to separate the cover apparatus and bound stack apart so that repositioning can be carried out. Once proper alignment has been achieved, the user presses the cover apparatus against the exposed adhesive there by securing the cover apparatus to the stack in one location. The user then removes the second release liner so that the cover apparatus is secured to the cover apparatus at additional locations on the cover apparatus. In one example, the cover apparatus is secured to the stack only at the front and rear cover sections so that the spine section of the cover apparatus is free to move with respect to the edge of stack. Thus, when the bound book is opened, the spine section of the cover assembly is free to move away from the folded spine so that the opened book will tend to lay flat and so the spine section will remain unfolded thereby reducing potential damage to any printed matter on the spine section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reference to the attached figures in which: 
     FIG. 1A is an exploded view of the various layers of a first embodiment of a prior art bookbinding structure. 
     FIG. 1B is an exploded view of a second embodiment of a prior art bookbinding structure. 
     FIG. 1C is an exploded view of a third embodiment of a prior art bookbinding structure. 
     FIG. 2 shows the prior art bookbinding structure of FIGS. 1A,  1 B or  1 C being inserted into a conventional binding machine to bind the pages. 
     FIGS. 3A-3E show the sequence of binding a stack using the prior art bookbinding structures of FIGS. 1A,  1 B or  1 C and the binding machine of FIG.  2 . 
     FIG. 4 shows the release liner being peeled away from the pressure activated adhesive of the FIG. 1A bookbinding structure after the book has been bound. 
     FIG. 5 is a perspective view of the bound book positioned on a wrap-around book cover prior to folding of the cover. 
     FIG. 6 shows the wrap around book cover being folded over the book and adhered to the pressure activated adhesive of the FIG. 1A bookbinding structure. 
     FIG. 7 is an end view of the covered book bound with the FIG. 1A bookbinding structure. 
     FIGS. 8A through 8E show the sequence for attaching the cover to the bound stack using the FIG. 2A bookbinding structure where the FIG. 2 binding machine is used to activate the adhesive used to attach the cover. 
     FIG. 9A is an end view of a bound book having a wrap-around book cover which extends over the front, back and spine of the book. 
     FIG. 9B is an end view of a bound book having a wrap-around book cover which extends over the spine, the front and a small portion of the rear of the book. 
     FIG. 9C is an end view of a bound book having a cover which extends over the spine and a small portion of the front and rear of the book. 
     FIG. 10 is an end view of a first embodiment of a bookbinding structure in accordance with the present invention. 
     FIG. 11 is a bottom view of the first embodiment bookbinding structure showing the removable release liners. 
     FIG. 12 is a plan view of a cover assembly suitable for use with the FIG. 10 bookbinding structure. 
     FIG. 13 is an elevational sectional view of the FIG. 10 bookbinding structure with one of the two release liners removed and showing the cover assembly being applied to one side of the bound book. 
     FIG. 14 is an elevational sectional view of the FIG. 10 bookbinding structure with the second one of the release liners removed and showing the cover assembly being applied to the other side of the bound book. 
     FIG. 15 is an elevational sectional view of the FIG. 10 bookbinding structure showing the bound book after both sides of the book having been secured to the cover assembly. 
     FIGS. 16A-16F further illustrate the manner in which the cover assembly is secured to a book bound with the FIG. 10 bookbinding structure. 
     FIG. 17 is an elevational sectional view of a bound book using the FIG. 10 embodiment book binding structure illustrating the lay flat feature of that embodiment. 
     FIG. 18 is a plan view of a cover assembly for use with a second embodiment book binding structure. 
     FIG. 19 is a bottom view of the second embodiment book binding structure showing the two release liners of the structure. 
     FIG. 20 is an end elevational view of the second embodiment bookbinding structure. 
     FIG. 21 is a elevational sectional view of the FIG. 20 bookbinding structure with one of the release liners removed and with the cover assembly being folded around the bound book. 
     FIG. 22 is an elevational sectional view of the FIG. 20 bookbinding structure after the cover assembly has been folded around the book with one of the release liners removed and with the second release liner in place. 
     FIG. 23 is an elevational sectional view of the FIG. 20 bookbinding structure after the cover assembly has been manually forced against one side of the bound book so as to secure the assembly at that location and with the second release liner removed so that the remainder of the assembly can be folded back around the bound book so as to secure the remainder to the cover assembly to the book. 
     FIG. 24 is an elevational sectional view of the FIG. 20 bookbinding structure showing the bound book after both sides of the book having been secured to the cover assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring again to the drawings, FIGS. 10 and 11 are end and bottom views, respectively, of a bookbinding structure  16  in accordance with a first embodiment of the present invention. The bookbinding structure  16  includes an elongated substrate  18  similar to substrate  6  of the FIG. 1A prior art structure and which is somewhat wider than the thickness of stack of sheets to be bound and is the same length as that of the stacks. A central heat activated band  20 A of adhesive is provided on what will be the inner surface of substrate  16  which is similar in composition, dimensions and function to the central band  4 A of the FIG. 1A structure. Similarly, a pair of outer heat activated bands  20 B of adhesive are disposed on the inner surface of substrate  16  which are similar in composition, dimensions and function to the outer bands  4 B of the FIG. 1A structure. Although not shown in FIG. 10, a thin layer of undercoat adhesive can be used similar to undercoat adhesive  7  of the FIG. 1A structure. 
     The bookbinding structure  16  further includes a pair of outer adhesive bands  22 A and  22 B disposed on what will be the outer surface of substrate  18  and, which preferably extend the full length of the substrate along the outer edges of the substrate. Bands  22 A and  22 B are comprised of a pressure activated adhesive similar in composition to the pressure activated adhesive used in adhesive layer  3  of the prior art FIG. 1A structure. Adhesive band  22 A is covered by an elongated release liner  24 A which completely covers band  22 A, as can be seen in FIG.  11 . Similarly, adhesive layer  22 B is covered a second release liner  24 B similar in shape to liner  24 A. Release liners  24 A and  24 B are preferably made of a silicon coated paper as previously described in connection with the release liner  5  of the FIG. 1A structure. As will be described in greater detail, adhesive bands  22 A and  22 B operate to secure a cover assembly to a stack of sheets bound by the binding structure  16 . 
     Typically, the bookbinding structures  16  are made in three widths, as in the case of the FIG. 1A structure, to accommodate stacks of varying thickness. However, in order to reduce the amount of binding products that needs to be maintained in stock, it would be possible to use a single relatively wide bookbinding structure  16  for a majority of stack thicknesses. In that case, it may be desirable to modify the binding machine, such as machine  8  shown FIG. 2, which is used to bind the stack, as will be described. A stack of sheets to be formed into a book are bound together in the same manner as previously described in connection with the prior art FIG. 1A embodiment and as illustrated in FIGS.  2  and  3 A- 3 E. FIG. 12 shows one cover assembly  26 , somewhat similar to cover assembly  2  previously described in connection with the FIG. 1A structure, that can be applied to the bound stack. 
     Cover assembly  26  includes a cover section  28 A, a back section  28 B and a spine section  28 C. Preferably, four creases or scores W, X, Y and Z are formed in the cover assembly  26 C as can be seen in FIG.  12 . Creases X and Y are spaced apart a distance equal to the thickness of the stack to be bound, with W and X being spaced near that location of the cover assembly  26  where the assembly is secured by adhesive bands  22 A and  22 B, as will become more apparent. The apparatus and method described in previously noted U.S. application Ser. No. 60/204,220 can be used in accurately scoring the cover assembly in order to form the creases W, X, Y and Z, but this apparatus is not required. Typically, the cover assembly  26  is printed prior to the binding sequence. Since heat is not used to secure the cover assembly  26  to the stack, it is possible to use heat sensitive inks. In many cases, the cover assembly is slightly larger than required and is trimmed after the binding sequence is completed. 
     Once the stack has been bound using the bookbinding structure of FIG. 10, the cover assembly  26  is secured to the stack. As shown in the FIGS. 16A-16F, the final sequence of securing the cover assembly  26  to the stack  30  is performed manually. First, a user manually folds the pre-scored cover assembly along the score lines or creases X and Y as shown in FIG. 16A illustration. Next, the user manually removes (peels away) the release liner  24 A from the binding structure  16  as shown in FIG.  16 B. The user then positions the bound stack  30  inside the folded cover assembly  26 . At this point, adhesive strip  22 A is exposed, with strip  22 B still being covered by release liner  24 B. The user is able to easily position the bound stack  30  accurately between the front and rear cover sections  28 A and  28 B, that is, between the fold lines at scores X and Y as shown in FIG.  16 C and in FIG.  13 . Exposed adhesive band  22 A will not adhere until the user actually presses the front cover section  28 A against the band. Accordingly, the user is free to reposition the stack  30  and cover assembly  26  as may be required. 
     Once the user presses the cover section  28 A against band  22 A, as illustrated in FIG. 16D the cover assembly is securely attached to the bound book  30 . Next, the user turns the entire assembly over and opens rear cover section  28 B so as to expose the second release liner  24 B. The second liner  24 B is then removed as shown in FIG. 16E so as to expose pressure activated adhesive band  22 B. The user then carefully wraps the cover assembly  26  around the spine of the stack  30  as shown in FIG.  14  and then presses the rear cover section  28 B against the exposed adhesive band  22 B as shown in FIG.  16 F. This completes the bookbinding sequence, with score or crease line Z being located near the point at which the front cover section  28 A is secured by adhesive  22 A, intermediate that point and score or crease Y as shown in FIG.  15 . Score or crease line W is located near the point at which the rear cover section  28 B is secured by adhesive  28 B intermediate that point and score or crease line X. Note that the illustrations of FIGS. 13,  14  and  15  are schematic in nature, with the dimensions being distorted in some cases to more clearly illustrate the invention. 
     It can be seen that the first embodiment binding structure  16 , having separately removable release liners  24 A and  24 B permits a bound stack  30  to be easily aligned and secured to the cover assembly  26 . In addition, the first embodiment permits the bound book to be opened as shown in FIG. 17 so that the spine section  28 C of the cover assembly is free to move away from the bound book. This is possible since the cover assembly is attached to the cover assembly at two spaced-apart locations along and adjacent to score lines W and Z. Thus, when the book is opened, the substrate  18  of the binding structure will remain secured to the edge of the stack and will fold when the stack is folded. The unattached spine section  28 C will move away from substrate  18  as shown in FIG. 17, with this movement being facilitated by the presence of creases or score lines W, X, Y and Z. The spine section  28 C will not be distorted when the book is opened so that any printing on the spine section will remain undisturbed. Further, the movement of the spine section prevents the spine section from resisting opening of the bound book, thereby allowing the bound book to lay open. This is sometimes referred to as a lay flat feature. In addition, this feature makes the book more closely simulate the appearance of conventional high-end paperback books bound using conventional mass production techniques thereby enhancing the appearance of the book. The width of the region on the outer surface of substrate  16  not covered by pressure activated adhesive should be somewhat wider than the thickness of the stack  30  to be bound, that is, slightly wider than the spacing between score lines X and Y. Since the actual width of the stack is not always know prior to the manufacture of the bookbinding structure, at least one half of the center width of outer surface of the substrate  18  is free of the pressure activated adhesive. 
     As previously noted, in some cases it would be desirable to minimize the number of bookbinding structures needed to bind stacks of varying thickness. Machine  2  of FIG. 2 is implemented to position a conventional binder strip so that the strip is centered on the spine of the stack. However, since the bookbinding structure  18  is largely not visible, it possible to fix the location that the adhesive strip  22 A is positioned relative to the spine of the stack  30  and to permit the position of the remaining strip  22 B to vary depending upon the actual thickness of the stack  30 . Since the location of strip  22 A will be fixed, the approximate location in which the first page of the stack  30  is secured to the front cover will be at a fixed, optimum location. This optimum, and therefore attractive, location is something that a reader of the bound book will most likely notice when the book is opened during use. The fact that the location at which the last page of the stack is secured to the rear cover section  22 B may move, depending upon the thickness of the stack  30 , is less critical since this location is less noticeable during normal use of the book. Machine  8  (FIG. 2) can be readily modified by way of software changes so that location that the structure (see relative position of strip  1  and stack  13  of FIG. 3C) is first applied to the bound stack will be fixed and will not be changed, as is the normal case, depending upon the thickness of the stack. 
     A second embodiment  40  of the subject bookbinding structure is shown in FIG.  20 . Embodiment  40  allows the cover assembly to be easily secured to a bound stack  30 . However, this embodiment does not provide the so-called lay flat feature of the first embodiment structure  16 . The second embodiment structure includes a substrate  18  and heat activated adhesive bands  20 A and  20 B disposed on what will be the inner surface of the substrate. Bands  20 A and  20 B are similar in construction, composition and function to the bands  20 A and  20 B of the first embodiment structure. A narrow pressure activated adhesive band  38 A is disposed along one edge of the substrate  18  along what will be the outer surface of the substrate, with substantially all of the remaining outer surface of the substrate  18  being covered by a separate layer or band of pressure activated adhesive  38 B. As can also be seen in FIG. 19, all of adhesive band  38 A is covered by a release liner  36 A and all of adhesive band  38 B is covered by a second release liner  36 B. As long a separate release liners  36 A and  36 B are used, it would be possible to replace adhesive layers  38 A and  38 B with a single continuous layer. However, the use of separate adhesive layers facilitates separate removal of release liners  36 A and  36 B. Also, although not shown in FIG. 20, in order to ensure that none of the pressure sensitive adhesive  38 A/ 38 B is exposed during binding, it is preferred that there be a slight overlap of liners  36 A and  36 B. 
     The second embodiment bookbinding structure  40  is used to bind a stack  30  in the same manner as the first embodiment  16 . Once the stack  30  has been bound, the narrow release liner  36 A is removed, thereby exposing the underlying pressure activated band  28 A. A preprinted cover assembly  32  is then pre-scored along score or crease lines A, B and C as shown in FIG.  18 . The spacing between score lines A and B is selected to match the thickness of the stack  30 . Score line C is located on the front cover section  34 A of the cover assembly and is present so as to facilitate opening of the front cover and to enhance the appearance of the book. 
     The steps from securing the bound stack  30  to the cover assembly are substantially the same as carried out in connection with the first embodiment as illustrated in FIGS. 16A-16F. First, the user folds the cover assembly along the pre-scored lines A, B and C (FIG.  16 A). Next, the user manually removes release liner  36 A (FIG.  16 B), as noted above. The stack  30  is then positioned between the front and rear cover sections  34 A and  34 B (FIG.  16 C), as shown in FIG.  21 . Again, since only narrow adhesive band  38 A is exposed and layer  38 B is covered, there will be no tendency for the cover assembly to adhere to the stack until the user applies pressure to the front cover section  34 A in the region near band  38 A. Thus, the user is free the reposition the stack  30  with respect to the cover assembly to achieve the desired orientation. 
     Once the user achieves the desired position, pressure is applied to the front cover assembly  34 A thereby securing the cover assembly to the stack  30  (FIG.  16 D). The next step is to remove the second release liner  36 B so as to expose pressure activated layer  38 B ( 16 E). One way to carry out this step is to reposition the stack  30  and cover assembly  32  as shown in FIG. 22 with the attached cover section  34 A on the bottom (Note that FIG. 22 does not show adhesive band  38 A contacting the cover section  34 A to simplify illustrating the structure, although the band is contacting the cover section at this point.) The user then folds back the back cover section  34 B and the spine cover section  34 C to expose as most of the second release liner  36 B. The user then manually removes the release liner in much the same way liner  5  is removed as shown in FIG.  4 . The user then folds the rear cover section  34 B and spine section  34 C back over the exposed adhesive layer  38 B. Pressure is then applied to full length of the spine section  34 C and to the rear cover section  34 B in the region of the pressure activated layer  38 B, thereby completing the binding sequence (FIG.  16 F). The final bound book is shown in FIG. 24. A reader can then open the book, with the front cover section  34 A folding along score C, with score C being located so that it is approximately aligned with the edge of substrate  18 . 
     Thus, a novel bookbinding structure has been disclosed which permits a stack of pages to be easily bound which provides a mass produced appearance but using only desk top equipment. Although two embodiments of the structure have been described in some detail, it is to be understood that certain changes can be made by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims. By way of example, release liners  36 A and  36 B can be part of a common release liner, separated by perforations or the like so that the liners can be removed or peeled away separately by the user. In that case, the liners are considered to be separate liners in the present application. Further, it is preferred that the portion of the outer surface of the substrate  18  which will eventually be disposed between lines X and Y in the first embodiment or between lines A and B in the second embodiment either be free of pressure activated adhesive of be covered by a release liner prior to the application of the cover assembly to the bound stack in order to facilitate attaching the cover assembly to the stack.