Abstract:
A variable cutoff printing press is provided. The variable cutoff printing press includes a first plate cylinder, a second plate cylinder, a continuous belt blanket contacting the first and second plate cylinders and a movable support cylinder supporting the belt blanket. The first and second plate cylinders, the continuous belt blanket and the movable support cylinder form a first print section and the movable support cylinder is movable to change the print length of the first print section. A method of printing images with a printing press is also provided.

Description:
Priority is claimed to U.S. Provisional Application No. 60/937,621, filed Jun. 28, 2007, the entire disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates generally to a printing press and more specifically to a variable cutoff printing press and method. 
     U.S. Pat. No. 6,205,921 discloses a continuous image transfer belt which is useable in a variable image size offset press system and which is adapted to permit the press to print a variety of different sized printed matter is provided. The belt is used in an offset printing system having the capability to print variable-sized images. The system includes a source of ink; at least one plate cylinder and a replaceable sleeve for the plate cylinder, and a printing plate which is adapted to receive ink from the ink source. The system also includes at least one blanket cylinder; the image transfer belt positioned to contact the printing plate in a nip formed between the plate and blanket cylinders; an image transfer belt tensioning system to register the image transfer belt to the blanket cylinder position in the area of desired image transfer; and an image belt cleaning station adapted to remove residual ink from the surface of the belt. 
     U.S. Pat. No. 6,327,975 discloses a method and apparatus for printing elongate images on a web. A first printing unit prints a first image portion on the web at prescribed spacings, by moving the impression cylinder away from the blanket cylinder each time one first image portion is printed. A second printing unit prints a second image portion on the spacings left on the web by the first printing unit, also by moving the impression cylinder away from the blanket cylinder each time one second image portion is printed. A variable velocity motor rotates each blanket cylinder, while each time the associated impression cylinder is held away to create a space on the web for causing printing of the first or the second printing portion at required spacings. 
     U.S. Pat. No. 7,066,088 discloses a variable cut-off offset press system and method of operation which utilizes a continuous image transfer belt. The offset printing system comprises at least two plate cylinders adapted to have thereon respective printing sleeves. Each of the printing sleeves is adapted to receive colored ink from a respective ink source. The system further comprises at least an impression cylinder, wherein the image transfer belt is positioned to contact each of the printing sleeves at respective nips formed between respective ones of the plate cylinders and the at least one impression cylinder. 
     BRIEF SUMMARY OF THE INVENTION 
     A variable cutoff printing press is provided. The variable cutoff printing press includes a first plate cylinder, a second plate cylinder, a continuous belt blanket contacting the first and second plate cylinders and a movable support cylinder supporting the belt blanket. The first and second plate cylinders, the continuous belt blanket and the movable support cylinder form a first print section and the movable support cylinder is movable to change the print length of the first print section. 
     A method of printing images with a printing press is also provided. The method includes transferring a first image from a first plate cylinder to a belt blanket at a first location; transferring a second image from a second plate cylinder to the belt blanket at a second location directly adjacent to the first location; and printing the first and second images from the belt blanket to a web. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described below by reference to the following drawings, in which: 
         FIG. 1  shows an embodiment of a printing unit of the present invention having printing blankets in the form of belts; 
         FIG. 2  shows an enlarged schematic side view of a upper printing section shown in  FIG. 1  printing images on a web; and 
         FIG. 3  shows a schematic side view of an embodiment of upper printing section shown in  FIG. 2  equipped with plate cylinders including relieved portions. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an embodiment of a printing unit  10  of the present invention having printing blankets  24 ,  26  in the form of belts. Printing unit  10  includes an upper printing section  20  and a lower printing section  22 . Upper printing section  20  includes a first upper plate cylinder  12  and a second upper plate cylinder  14  and each plate cylinder  12 ,  14  transfers images to belt blanket  24 . Belt blanket  24  is wrapped around support cylinders  30 ,  32 ,  34 . Belt blanket  24  prints images received from plate cylinders  12 ,  14  on one side of a passing web  36 . On the other side of web  36 , lower printing section  22  includes a first lower plate cylinder  16  and a second lower plate cylinder  18  and each plate cylinder  12 ,  14  transfers images to belt blanket  26 . Belt blanket  26  is wrapped around support cylinders  40 ,  42 ,  44 . Belt blanket  26  prints images received from plate cylinders  16 ,  18  on one side of a passing web  36 . In a preferred embodiment, plate cylinders  12 ,  14 ,  16 ,  18  each include a printing plate. In an alternative embodiment, images may be directly burned onto plate cylinders  12 ,  14 ,  16 ,  18 . 
     Support cylinders  30 ,  32 ,  34  rotate clockwise to translate continuous belt  24  in a path that passes between nips  31 ,  33 ,  35 . Nip  31  is formed between support cylinders  30 ,  40 , nip  33  is formed between support cylinder  32  and plate cylinder  12  and nip  35  is formed between support cylinder  32  and plate cylinder  14 . As belt blanket  24  passes through nip  35 , plate cylinder  14  transfers a first inked image to belt blanket  24 . After belt blanket  24  receives the first inked image and transport the first inked image past nip  33 , plate cylinder  12  prints a second inked image directly following the first inked image on belt blanket  24 . 
     Plate cylinders  12 ,  14  each have an outer surface portion that is prepared as a print area, which transfers images to belt blanket  24 , and an outer surface portion that is prepared as a non print area, which does not transfer images to belt blanket  24 . After plate cylinder  12  prints a first image on belt blanket  24 , plate cylinder  14  continues to rotate and non print area of plate cylinder  14  passes by belt blanket  24 , leaving a blank space on belt blanket  24  for plate cylinder  12  to print a second image. Plate cylinder  14  is phased such that after the proper length of blank space is left on blanked belt  24  for plate cylinder  12  to print a second image, print area of plate cylinder  14  contacts belt blanket  24 , and plate cylinder  14  prints another first image on belt blanket  24 . After plate cylinder  12  prints a second image on belt blanket  24 , plate cylinder  12  continues to rotate and non print area of plate cylinder  12  passes by belt blanket  24  as a first image printed by plate cylinder  14  passes by plate cylinder  12 . Plate cylinder  12  is phased such that after a first image printed by plate cylinder  14  passes by plate cylinder  12 , print area of plate cylinder  14  contacts belt blanket  24 , and plate cylinder  12  prints another second image on belt blanket  24  directly following a first image. Plate cylinders  12 ,  14  continuously operate in this manner, printing first and second images on belt blanket  24 , ultimately leaving no blank space on belt blanket  24  between first and second images. 
     First and second images printed on belt blanket  24  are transferred from belt blanket  24  to passing web  36  at nip  31 . Because first and second images on belt blanket  24  do not have intervening spaces, first and second images printed on web  36  do not have intervening spaces. Support cylinder  40  co-acts with support cylinder  30  during printing on web  36  by belt blanket  24 , while belt blanket  26  prints images on the opposite side of web  36 . Belt blanket  26  prints in the same manner as belt blanket  24 , receiving images from plates cylinders  16 ,  18  at nips  37 ,  39 , respectively, and printing the images on web  36  at a nip  31 . In order to align the images printed by plate cylinder  12  with the images printed by plate cylinder  14 , the circumferential phasing between plate cylinder  12  and plate cylinder  14  is a function of a length of blanket belt  24  between nips  33 ,  35 . Similarly, the circumferential phasing between plate cylinder  16  and plate cylinder  18  is a function of a length of blanket belt  26  between nips  37 ,  39 . 
     In a preferred embodiment, axes of cylinders  30 ,  32 ,  40 ,  42  are stationary and axes of cylinders  34 ,  44  are movable. In order to vary cutoff lengths of images printed by printing unit  10  on web  36 , plates on plate cylinders  12 ,  14 ,  16 ,  18  may be exchanged with replacement plates carrying images of different lengths. When replacement plates are introduced, belt blankets  24 ,  26  may be accordingly replaced with replacement belt blankets of different lengths and the positions of support cylinders  34 ,  44 , respectively, may be adjusted to accommodate the replacement belts. When only small changes in belt length are desired, belt blankets  24 ,  26  may be stretched by the adjustment of the positions of support cylinders  34 ,  44 , respectively. 
     In the embodiment shown in  FIG. 1 , plate cylinders  12 ,  14 ,  16 ,  18  are the same size and plate cylinders  12 ,  14 ,  16 ,  18  are rotated by individual motors  102 ,  104 ,  106 ,  108 , respectively. Support cylinders  30 ,  32 ,  34  are driven by a motor  110  and support cylinders  40 ,  42 ,  44  are driven by a motor  112 . A controller  100  controls motors  102 ,  104 ,  106 ,  108 ,  120 ,  122 . In another embodiment plate cylinders  12 ,  16  may be rotated by a single motor and plate cylinders  14 ,  18  may be rotated by a single motor. In other embodiments support cylinders  30 ,  32 ,  34 ,  40 ,  42 ,  44  may be driven by a single motor or one or more support cylinders  30 ,  32 ,  34 ,  40 ,  42 ,  44  may not be driven. 
     Plate cylinders  12 ,  14 ,  16 ,  18  may be rotated by motors  102 ,  104 ,  106 ,  108  at varying velocities during printing. When one half of the surface of each plate cylinder  12 ,  14 ,  16 ,  18  is prepared as print area, plate cylinders  12 ,  14 ,  16 ,  18  are rotated at a constant velocity during printing. When less than one half or more than one half of the surface of each plate cylinder  12 ,  14 ,  16 ,  18  is prepared as print area, plate cylinders  12 ,  14 ,  16 ,  18  are rotated at a varying velocities during printing operation. 
     Plate cylinders  12 ,  14 ,  16 ,  18  are rotated at varying velocities during each revolution to allow plate cylinders  12 ,  14 ,  16 ,  18  to travel at a velocity equal to respective belt blankets  24 ,  26  while each plate cylinder  12 ,  14 ,  16 ,  18  is printing an image on web  36 , but also to be in a proper rotational position to print a next image on respective belt blanket  24 ,  26 . Web  36  is traveling at a constant velocity and belt blankets  24 ,  26  are traveling at the same constant velocity as web  36 . Thus, while plate cylinders  12 ,  14 ,  16 ,  18  transfer images to respective belt blankets  24 ,  26  plate cylinders  12 ,  14 ,  16 ,  18  must have constant surface velocities equal to those of belt blankets  24 ,  26 . If greater than one half of the surface of a plate cylinder  12 ,  14 ,  16 ,  18  is prepared as the print area, the plate cylinder  12 ,  14 ,  16 ,  18  is decelerated after printing so that the plate cylinder  12 ,  14 ,  16 ,  18  is in proper position to print a next image. If less than one half of the surface of a plate cylinder  12 ,  14 ,  16 ,  18  is prepared as the print area, the plate cylinder  12 ,  14 ,  16 ,  18  is accelerated after printing so that the plate cylinder  12 ,  14 ,  16 ,  18  is in proper position to print a next image. 
       FIG. 2  shows an enlarged schematic side view of upper printing section  20  shown in  FIG. 1  printing images A, B on web  36 . Lower printing section  22  shown in  FIG. 1  has been omitted for illustrative purposes only. Printing section  22  is configured similarly to printing section  20  and prints on the opposite side of web  10  in a manner similar to printing section  20 . Plate cylinders  12 ,  14  include printing plates  52 ,  54 , respectively, which print images A, B, respectively, on belt blanket  24 . In one embodiment image A and image B may form one continuous image having a cutoff length. Plates  52 ,  54  are shown divided into print areas  62 ,  64 , respectively, and non print areas  72 ,  74 , respectively, for illustrative purposes. Print areas  62 ,  64  are longer than non print areas  72 ,  74 . It should be noted that, in another embodiment, plates  52 ,  54  may not occupy the entire outer circumferences of plate cylinders  12 ,  14  and plates  52 ,  54  may not extend beyond print areas  62 ,  64  to non print areas  72 ,  74 , as plates  62 ,  64  may be completely prepared as print areas  62 ,  64 . 
     Outer surfaces of print areas  62 ,  64  are the same length. An outer surface of belt blanket  24  is six times the length of the outer surface of each print area  62 ,  64 , or three times the cutoff length of the continuous image formed by image A and image B. Having a belt blanket  24  with an outer surface that is an integer multiple of the combined length of print areas  62 ,  64  can allow smudge-free printing without the use of belt cleaning devices, as plate cylinders  12 ,  14  print on the same portions of the outer surface of belt blanket  24  with each revolution of belt blanket  24 . Belt blanket  24  is shown schematically divided into six printing spaces  81 ,  82 ,  83 ,  84 ,  85 ,  86 . Plate cylinder  12  prints images A in spaces  81 ,  83 ,  85  and plate cylinder  14  prints images B in spaces  82 ,  84 ,  86 . 
     Support cylinders  30 ,  32 ,  34  rotate belt blanket  24  such that a surface velocity of belt blanket  24  matches a velocity of web  36 . Plate cylinder  12  is being rotated so that a surface velocity of plate  52  is equal to the surface velocity of belt blanket  24  as plate cylinder  12  prints image A in space  81  on belt blanket  24 . After plate cylinder  12  completes printing image A, plate cylinder  12  is accelerated, causing plate cylinder  12  to travel at a surface velocity that varies from a velocity of web  36  as non print area  72  passes by belt blanket  24 . Before print area  62  comes back into contact with belt blanket  24  to print image A in space  83 , plate cylinder  12  is decelerated so that the outer surface of plate cylinder  12  is traveling at velocity equal to the outer surface velocity of belt blanket  24 . 
     Plate cylinder  14  is being rotated so that when print area  64  contacts belt blanket  24 , print area  64  is aligned to print image B in space  82  and plate cylinder  14  has a surface velocity that equals the surface velocity of belt blanket  24 . Plate cylinder  14  may be in the process of being decelerated, and thus is traveling at a velocity that varies from the velocity of web  36 , because plate cylinder  14  was accelerated after printing image B in space  86  on belt blanket  24 . 
     The rotation of plate cylinders  14 ,  17  at surface velocities that vary from the velocity of belt blanket  24  may be achieved via relief as shown in  FIG. 2 . Also, for example, surfaces of plate cylinders  14 ,  17  may possibly slip in relation to blanket belt  24  via a special non stick coating on the non print areas  72 ,  74  of plate cylinders  12 ,  14  that does not affect the travel of belt blanket  24 . In one embodiment, such a non stick coating may be used only on plate cylinder  14  if the coating does not prevent smearing by plate cylinder  12  of images B printed by plate cylinder  14  on belt blanket  24 . In another embodiment, to prevent smearing by plate cylinder  12  of images B printed by plate cylinder  14 , a heat setter my dry web  36  as web  36  passes between plate cylinders  12 ,  14 . During slipping, axes of cylinders  12 ,  14  may remain stationary. 
     Belt blanket  24  is printing image B that was printed in space  84  by plate cylinder  14  in a space  93  on web  36 . Belt blanket  24  previously printed image A in a space  92  on web  36 , following printing image B in a space  91  on web  36 . 
       FIG. 3  shows a schematic side view of an embodiment of upper printing section  20  shown in  FIG. 2  equipped with plate cylinders  112 ,  114  including relieved portions  60 ,  70 , respectively. Relieved portions  60 ,  70  do not contact belt blanket  24  during rotation of plate cylinders  112 ,  114  and allow plate cylinders  112 ,  114  to be accelerated and decelerated about center axes  96 ,  98 , respectively, when cylinders  112 ,  114  are not printing images on belt blanket  24 . Plate cylinder  112  prints images in spaces  181 ,  183 ,  185  on belt blanket  24  by contacting belt blanket  24  with a plate  152  that occupies the portion of the surface of plate cylinder  112  that is not relieved. Plate cylinder  114  prints images in spaces  182 ,  184 ,  186  on belt blanket  24  by contacting belt blanket  24  with a plate  154  that occupies the portion of the surface of plate cylinder  114  that is not relieved. Belt blanket  24  prints images printed in spaces  181 ,  182 ,  183 ,  184 ,  185 ,  186  by plate cylinders  112 ,  114  on web  36 . The entire outer surfaces of plates  152 ,  154  are prepared as print areas  162 ,  164 , respectively. 
     A cutoff length of images printed by printing section  20  may be changed, for example, by replacing plates  152 ,  154  with replacement plates equal in length to plates  152 ,  154 , but that include a shorter print area. Plates  152 ,  154  may also be replaced by replacement plates having outer surfaces prepared entirely as print areas, but that are shorter than plates  152 ,  154 . Belt blanket  24  may be removed from support cylinders  30 ,  32 ,  34  and replaced with a belt blanket of a shorter length, which is an integer multiple of the combined length of the new print areas, to accommodate images having shorter cutoffs. A position of support cylinder  34  may be adjusted to fit the replacement belt blanket. 
     In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.