Abstract:
A printing image is provided on a rewritable surface of a printing form within a press. The steps of providing the image, including erasing the surface, generating the image on the surface, fixing the imaged surface, and conditioning the imaged surface, are carried out in a section-by-section manner over the entire surface, and all the steps, or sub-combinations of the steps, may be carried out in parallel. In the apparatus for producing the printing image, the devices for erasing, imaging, fixing, and conditioning may be mounted on a common platform movable along a longitudinal direction of the printing form to allow the steps to be performed in parallel.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a method and apparatus for producing printing forms, in particular to the production of a printing form of the rewritable type.  
       BACKGROUND OF THE INVENTION  
       [0002]     During printing with a printing form, in principle a distinction is drawn between methods which operate on the one hand with a printing form that can be written once or on the other hand with a rewritable printing form. Printing methods which use rewritable printing forms are also brought together under the keyword “computer to press/direct imaging”. The invention present here relates to a method and an apparatus for producing a permanent and erasable image on such a rewritable printing form.  
         [0003]     Under the product description “DICOweb”, the applicant markets digital presses which operate with rewritable and erasable printing forms. During the production of such printing forms, a basic printing form cylinder is preferably subjected to an erasure step and an imaging step. An erasing apparatus which can be used when erasing such a printing form is disclosed, for example, in DE 100 08 214 A1. DE 100 23 319 A1 discloses a device for imaging such printing forms. With regard to further principles of the DICOweb technology, reference can be made to “Handbuch der Printmedien” [Printing Media Manual], Helmut Kipphan, pages 674-680, 2000, Springer-Verlag.  
         [0004]     According to the prior art, the erasure of surface of the printing form over the entire length of the printing form is carried out in one step and in a manner decoupled from the imaging. The result here is, firstly, large overall sizes for an apparatus for producing the printing forms and therefore the press, and secondly that the erasure and subsequent imaging of such a printing form takes a long time.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In view of the foregoing, it is an object of the present invention to prove a novel apparatus and method for producing printing forms, with the goals of reducing the overall size of the apparatus and speeding up the process of providing an image on a printing form.  
         [0006]     This object is achieved by the apparatus and method of the invention for producing printing forms. According to the invention, the erasure of the printing form and the imaging of the form are carried out section by section along the entire printing form or the entire surface of the same. In this case, the erasure and the imaging are preferably carried out in parallel.  
         [0007]     For this purpose, a relative movement path is preferably established between the printing form and the corresponding erasing and imaging devices in the longitudinal direction of the printing form. This makes it possible to reduce the overall size needed for the apparatus and for the implementation of the method. Presses having apparatuses of this type can accordingly be designed to be more compact overall. Moreover, the parallel execution of the erasure and imaging allows the changeover time on a press to be significantly reduced.  
         [0008]     The imaged surface is preferably fixed and, after or before the fixing of the image on the form, conditioning of the imaged surface is carried out section by section on the entire surface of the printing form, just like the erasure, the imaging and the fixing.  
         [0009]     According to a preferred development of the invention, for the purpose of erasing and imaging and, if appropriate, fixing and conditioning, appropriate devices are moved in the longitudinal direction of the stationary printing form, past the entire surface of the same, all the processing steps being carried out section by section on the entire surface and at least some of the processing steps being carried out in parallel.  
         [0010]     The apparatus according to the invention for producing a permanent and erasable image on a surface of a printing form has at least one erasing device for erasing the surface and an imaging device for imaging the erased surface. The erasing device and the imaging device are constructed in such a way that the erasure and the imaging can be carried out section by section and preferably in parallel along the entire printing form or the entire surface of the same.  
         [0011]     Preferred embodiments of the invention will be explained in greater detail below with reference to the drawing, of which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  shows, in a schematic view, an embodiment of an apparatus according to the invention for producing printing forms during the erasure and during the imaging of a surface of a printing form; and  
         [0013]      FIG. 2  shows the apparatus of  FIG. 1  during the conditioning and during the fixing of the imaged surface of the printing form. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     In the following text, with reference to  FIGS. 1 and 2 , the invention will be described by way of example for offset printing by the DICOweb technology, the offset printing variant of the DICOweb technology also being designated “DICOweb litho.” 
         [0015]     In the method according to the invention for producing a printing form having a permanent and erasable image on a surface of a rewritable printing form, the procedure is such that a printing form  10  having a rewritable surface  11  is provided. The rewritable printing form  10  preferably has a cylindrical surface  11 , a central longitudinal axis of the printing form  10  being numbered with the reference number  12  in  FIG. 1 . The erasure of the surface  11 , imaging of the erased surface  11  and fixing and, if appropriate, conditioning of the imaged surface, are carried out in order to provide the permanent and erasable image on the surface of the printing form. As used herein, the term “permanent an erasable image” means the image is long-lasting and does not disintegrate easily by itself, yet can be removed from the surface of the printing form using a proper erasing method.  
         [0016]     In accordance with a feature of the invention, at least the erasure and the imaging of the entire printing form  10  or the entire surface  11  of the printing form  10  are carried out in a section-by-section manner. Particularly preferably, all the method steps for producing the printing form, which include the erasure, the imaging, the fixing and the conditioning, are carried out section by section along the entire surface  11  of the printing form  10 . For this purpose, a relative movement is established between appropriate devices for erasing, imaging, fixing and conditioning the printing form  10  in the direction of the central longitudinal axis  12  and therefore over the entire longitudinal direction of the same, with the erasure, the imaging, the fixing and the conditioning being carried out on the respective sections of the entire surface  11  of the printing form  10  which currently lie in the area of influence of the respective devices as the corresponding devices move past the surface.  
         [0017]     In one embodiment illustrated in  FIG. 1 , an apparatus for implementing the method comprises an erasing device  13  for erasing the surface  111  of the printing form  10 , an imaging device  14  for imaging the erased surface, a fixing device  15  for fixing the imaged surface and a conditioning device  16  for conditioning the imaged surface. The imaging device  14  comprises a thermal transfer ribbon  17  and a laser source  18 . In the exemplary embodiment of  FIGS. 1 and 2 , all the devices  13 ,  14 ,  15  and  16  are fixed on a common platform  19 , such that it is possible for the platform  19  together with all the devices  13 ,  14 ,  15  and  16  to be moved in the longitudinal direction along the entire printing form  10 , relative to the latter, along a crossmember  20  extending parallel to the central longitudinal axis  12  of the printing form  10 .  
         [0018]     In a particularly preferred embodiment of the invention, the erasure and the imaging of the surface  11  of the printing form  10  are carried out in parallel, to be specific during the relative movement (depicted by the arrow  21  in  FIG. 1 ) between the corresponding devices and the printing form  10 . During the relative movement depicted by the arrow  21 , the printing form is stationary in its longitudinal direction but rotating about its axis, and the devices  13  to  16  positioned on the platform  19  are moved across the rotating surface of the printing form  10  from a first end  22  to a second end  23  of the printing form  10 . The relative movement in the sense of the arrow  21  accordingly extends over the entire length of the printing form  10 .  
         [0019]     The fixing and conditioning of the imaged surface  11  of the printing form  10  is carried out during the relative movement, depicted by the arrow  24  in  FIG. 2 , between the printing form  10 , which is stationary in the longitudinal direction but rotating, and the moved platform  19 . As can be gathered from  FIG. 2 , the second relative movement according to arrow  24  runs in the opposite direction to the first relative movement according to arrow  21 , between the second end  23  and the first end  22  of the printing form  10  and therefore over the entire length of the same.  
         [0020]     At this point, it should be pointed out that a “stationary” printing form in this context is understood to mean a printing form  10  of which the axial position in the direction of the central longitudinal axis  12  is unchanging, at least during the conversion of the same. A printing form  10  that is stationary in this way can nevertheless rotate about its central longitudinal axis  12  and therefore execute a rotational movement about the central longitudinal axis  12  during the erasure, imaging, conditioning and fixing of the surface  11  of the printing form  10 .  
         [0021]     In accordance with the present invention, all the sub-processes or steps of the method according to the invention, such as the erasure, imaging, conditioning and fixing, are carried out section by section on the entire surface of the printing form during a relative movement in the longitudinal direction of the printing form. In the case of producing an offset printing form, the erasure, imaging, fixing and conditioning are all carried out section by section or in a traversing manner over the entire length of the printing form  10 .  
         [0022]     In the preferred exemplary embodiment according to  FIGS. 1 and 2 , firstly the erasure and imaging and secondly the fixing and conditioning are carried out in parallel in one pass or in one relative movement in each case. It should be pointed out at this point that it is also possible to carry out four part steps during one relative movement in one pass.  
         [0023]     Furthermore, it is possible to adapt the combination and, if appropriate, the order of the part steps to be carried out in parallel. For example, it is possible to carry out the erasure and imaging and/or the imaging and conditioning and/or the imaging and fixing and/or the conditioning and fixing in the longitudinal direction of the printing form in parallel on the entire surface of the printing form.  
         [0024]     At this point, it should be pointed out that the erasing device  13  can, for example, comprise a narrow cleaning cloth  25 , which is moved past the printing form  10  in the longitudinal direction of the same, with cleaning agents being supplied to the cleaning cloth  25  or to the surface  11  of the printing form  10  to be cleaned. The cleaning agent can, for example, be formed as an alkaline, water-based cleaning liquid and erase an old image from the entire surface  11  of the printing form. The image erased with the aid of the cleaning agent is picked up by the cleaning cloth. When cleaning cloth becomes soiled, it is wound up onto a dirty roll and, for the ongoing cleaning of the printing form  10 , fresh cleaning cloth is unwound from a fresh cloth roll.  
         [0025]     Instead of cleaning liquids, powdery or granular cleaning agents, cleaning gases or cleaning vapours and cleaning plasmas can also be moved in the direction of the cleaning cloth or the surface  11  of the printing form  10  from which an image is to be removed. Instead of the cleaning cloth, a brush or grinding disc can also be moved past the printing form  10 .  
         [0026]     The imaging of the erased or de-imaged surface  11  of the printing form  10  is preferably carried out by using the thermal transfer ribbon  17  shown in  FIGS. 1 and 2 . To that end, the thermal transfer ribbon  17  is brought into contact with the surface  11  of the printing form  10  and, by using a laser beam modulated in accordance with an image, the transfer material in the contact zone between the thermal transfer ribbon  17  and the surface  11  of the printing form  10  is applied to the printing form  10 .  
         [0027]     The fixing of the imaged surface  11  of the printing form  10  is preferably carried out thermally. In this case, for the purpose of the thermal fixing, it is possible to heat the surface  11  of the printing form  10  during the already described relative movement in the longitudinal direction of the printing form  10 , for example inductively, by means of thermal radiation, by means of forced convection, or by means of laser radiation.  
         [0028]     The conditioning of the imaged surface is carried out either after the fixing or before the fixing of the imaged surface. This includes applying a conditioning medium in the region of the imaged surface  11  of the printing form  10  for the purpose of conditioning. The conditioning medium can be supplied and caught by using the cleaning cloth  25  already mentioned. Spraying or applying the conditioning medium via a roller or brush is also possible. The choice of a suitable conditioning medium is left to those skilled in the art addressed here.  
         [0029]     Finally, it should be pointed out once more that, according to a first partial aspect of the present invention, all the part steps for producing a permanent and erasable image on a rewritable surface of a printing form are carried out section by section along the entire surface. This is carried out by establishing a relative translational movement between the devices required for this purpose and the entire surface  11  of the printing form  10 . More particularly, the devices  13  to  16  for erasing, imaging, fixing and conditioning preferably are moved translationally past the entire surface  11  of the printing form  10 . In the process, the printing form  10  then executes a rotational movement about its central longitudinal axis  12 . According to a second aspect of the present invention, at least some of the part steps are carried out in parallel. If the two part aspects are combined with each other, then the result is, firstly, a reduced overall size for the apparatus according to the invention and, secondly, the method according to the invention can be carried out within a short time span.  
         [0030]     Although, with reference to  FIGS. 1 and 2 , the invention has been described by using the example of the production of an offset printing form, the method according to the invention can also be carried out during the production of a gravure printing form. The gravure printing alternative of the DICOweb technology is also designated “DICOweb gravure.” 
         [0031]     In this embodiment of the method according to the invention, following the erasure and before the imaging of the surface of the gravure printing form, bowl-like depressions on the surface of the printing form are filled, preferably with the aid of a squeegee. In this embodiment of the method according to the invention, the erasure, filling and imaging of the printing form are again carried out section by section over the entire surface, a relative movement in the longitudinal direction of the printing form between the printing form and the corresponding devices for carrying out the erasure, filling and imaging again being established for this purpose. It is also possible again to carry out at least some of these part steps in parallel.  
         [0032]     An apparatus according to the invention having the devices  13  to  20  is preferably integrated into every printing unit of a press, in the region of every rewritable printing form. Accordingly, the method is preferably carried out within the press.