Abstract:
An apparatus for a rotary offset printing press includes a print cylinder having a radially inward extending groove and a rubber blanket having a main section coupled to the print cylinder. The rubber blanket includes at least first, second and third layers in the main section. The first layer is a self-adhering layer which faces the print cylinder and is adapted to attach the rubber blanket to the print cylinder. The second and third layers are a support layer and a cover layer, respectively, which both face away from the print cylinder. The rubber blanket has a leading end section, as seen in a production direction of the print cylinder, and a trailing end section, as seen in the production direction of the print cylinder. The end sections directly adjoin the main section and at least the leading end section of the rubber blanket is inserted into the groove of the print cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of the European Patent Application No. 09160532.9, filed on May 18, 2009, the subject matter of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a print cylinder with a rubber blanket for a rotary offset printing press. Rotary offset printing presses use print cylinders embodied as rubber blanket print cylinders which are provided, for example, with a special fabric coated with rubber, the so-called rubber blanket. 
         [0003]    The rubber blanket is an important link in the offset printing operation which functions to transfer the image and text information from the printing plate to the material for printing (paper or foils). The quality of a printing image is influenced, for example, by the composition of the materials used (fabric and type of rubber) and is also influenced decisively by the condition of the rubber blanket surfaces. 
         [0004]    A rough distinction can generally be made between non-compressible rubber blankets and compressible rubber blankets, the so-called air-cushion blankets. 
         [0005]    Conventional, non-compressible rubber blankets are composed of a base fabric layer and one or more additional layers of fabric and intermediate layers (reinforcing layers), as well as the actual rubber layer having a thickness of approximately 0.4 mm to 0.6 mm. The conventionally configured rubber blanket is nearly non-compressible, but can be deformed. Radial stresses consequently lead to a tangential displacement of the rubber material and the therewith associated forming of a bulge. 
         [0006]    Non-conventional, compressible rubber blankets, also called air-cushion blankets, are composed of a base layer of fabric, an intermediate fabric layer with air enclosures, and a rubber cover layer. The air enclosures are embedded in the form of microscopic air bubbles or air channels, thus resulting in a deformability of the rubber blanket as a whole. The bulge forming that occurs with conventional rubber blankets can be avoided in this case owing to the compression of the intermediate fabric layer while, at the same time, the wear and tear on the printing form is also reduced. 
         [0007]    These types of conventional or non-conventional rubber blankets, meaning rubber blankets composed of layers, are normally fitted onto, wrapped around or glued to the print cylinders. The invention described in the following relates to a print cylinder with self-adhering rubber blankets. 
         [0008]    Self-adhering rubber blankets, as disclosed in the art, are glued to the print cylinder and do not require an additional attachment to the print cylinder. The rubber blanket is provided for this with a flat self-adhering layer for gluing it to the print cylinder. The problem, however, is a joining location where the ends of the rubber blanket abut or where the ends of the rubber blanket at least are positioned opposite each other. 
         [0009]    Such joining locations are sealed with various types of sealing agents to prevent cleaning agents and printing ink from entering. The edges of the rubber blanket at the joining locations are damaged by grinding or milling prior to the sealing operation. With sealing operations of this type, there is a need to optimally shorten the hardening period for the sealing agent and thus shorten the waiting period until the next use of the print cylinder provided with the rubber blanket. A further problem is that despite the sealing operation, cleaning agents and/or printing ink can enter between the ends of the glued-on rubber blanket and, in particular, can result in separating the self-adhering layer. 
       SUMMARY 
       [0010]    An object of the present invention is to solve the aforementioned problems with self-adhering blankets at the joining location, such that the self-adhering layer between rubber blanket and print cylinder is reliably protected to prevent solvents or printing ink from entering. In addition, this location should present the smallest possible attack surface for a rubber blanket washing system. The size of the non-printing strip may also be taken into consideration to avoid exceeding a pre-determined joining location width, for example, but not limited to approximately 3 mm. 
         [0011]    The above and other objects are accomplished according to one aspect of the invention wherein there is provided an apparatus for a rotary offset printing press which, in one embodiment, includes a print cylinder having a radially inward extending groove; and a rubber blanket having a main section coupled to the print cylinder, the rubber blanket comprising at least first, second and third layers in the main section, the first layer comprising a self-adhering layer which faces the print cylinder and is adapted to attach the rubber blanket to the print cylinder, and the second and third layers comprising a support layer and a cover layer, respectively, which both face away from the print cylinder, wherein the rubber blanket has a leading end section as seen in a production direction of the print cylinder and a trailing end section as seen in the production direction of the print cylinder, wherein the end sections directly adjoin the main section, and 
         [0012]    wherein at least the leading end section of the rubber blanket is inserted into the groove of the print cylinder. 
         [0013]    According to one embodiment, the main section extends over the total effective length of the rubber blanket which corresponds approximately to the circumference of the print cylinder. The main section may be adjoined by a leading end section as well as a trailing end section of the rubber blanket, in production direction of the print cylinder. 
         [0014]    According another embodiment, the print cylinder is provided in at least one location along the circumference, radially on the outside, with a radially inward extending channel into which at least the leading end section of the rubber blanket is inserted. The channel may take the form of an axial groove in the surface area of the print cylinder. This groove may be normally open on the front side; alternatively, closed grooves are also possible. The groove furthermore need not extend in the axial direction, but can also extend at an angle. 
         [0015]    According to a further embodiment, the trailing end section of the rubber blanket may adhere on one side of the joining location to the outer surface of the print cylinder, without being inserted into the channel. During the operation of the rotary offset printing press, the trailing end may be pressed against the print cylinder which acts counter to an undesirable separating. 
         [0016]    According to one embodiment, the leading end section as well as the trailing end section of the rubber blanket may be inserted into the groove. Providing a groove, which is very unusual in itself for generic self-adhering rubber blankets, for inserting at least one end section of the rubber blanket into this radially inward directed groove on the print cylinder may protect the self-adhering layer between the rubber blanket and the print cylinder, thereby avoiding any type of sealing problems along a joining location. The leading end section or both end sections of the rubber blanket may be positioned, radially angled toward the inside, against each other inside the groove, either indirectly or directly parallel to each other. 
         [0017]    According to another embodiment, the self-adhering layer may end at the radially outer edge of this groove, but may also end in the groove itself or may extend over the complete length of the rubber blanket. In either case, the self-adhering layer may be protected in at least one end section by the rubber blanket itself. 
         [0018]    According to a further embodiment, the leading end section and/or the trailing end section may contain a reduced number of layers as compared to the main section. The thinner end sections, as compared to the main section, may thus be inserted easier into the groove. Above all, the reduction in the thickness itself is advantageous for an uncomplicated insertion into a narrow groove. As a result, extremely narrow, non-printing strips of the rubber blanket, respectively the print cylinder can be achieved. 
         [0019]    According to one embodiment, at least one end section of the rubber blanked may contain an insertion aid. This insertion aid may be arranged in the form of a reinforcing layer on one side of the respective end section. The insertion aid may be constructed from metal, plastic or ceramic material. 
         [0020]    In another embodiment, one or both end sections may be inserted into the groove. This can prevent an unintended sliding of the end sections from the groove. 
         [0021]    According to a further embodiment, the insertion aid can be embodied as a reinforcing layer on one side of the rubber blanket. It is conceivable in that case to embody the fabric layer thicker or saturated with a special plastic material to stiffen an end section. However, the end sections or the layers of the end sections can also be composed of metal, plastic or ceramic materials. Corresponding layers can also be applied later on to the end sections to be inserted into the groove. Insertion aids of this type last a particularly long time and are cost effective, depending on the requirements. 
         [0022]    According to one embodiment, the leading and/or the trailing end section is provided with a gliding layer, wherein this gliding layer may be applied permanently to the end section. One example of the gliding layer is a coating of polytetrafluorethylene or another substance having gliding properties. Gliding layers of this type make it easier to insert the respective end section since the friction between the groove wall and the rubber blanket is reduced. Whether a permanently applied gliding layer is selected or a gliding layer that is applied separately for each application, e.g. consisting of fats, alcohol or also a mixture of hydrocarbons (benzene, Vaseline), depends on the type of use of the respective print cylinder. 
         [0023]    According to one embodiment, at least one of the rubber blanket layers may be removed in at least one end section. In this embodiment, the rubber blankets can be produced continuously and so that the end sections can be reworked during the finishing work. As a result of the layered configuration, for example, it offers itself to remove one or a plurality of outer layers by making a cut, so that the layer sections to be removed can be pulled off from the cutting location toward the end. 
         [0024]    According to another embodiment, the at least one removed layer includes the self-adhering layer or a plurality of layers on the side facing the print cylinder. 
         [0025]    According to a further embodiment, when cutting the blanket cylinder on the side facing the print cylinder or otherwise removing rubber blanket layers on the side facing the print cylinder, the remaining cover layer of the rubber blanket may extend into the groove. This surface consequently is not damaged at any location and continues to remain robust. 
         [0026]    According to one embodiment, the at least one removed layer may comprise one or a plurality of the rubber blanket layers on the side facing away from the print cylinder. 
         [0027]    According to a further embodiment, the removal of radially outer layers of the rubber blanket can be an advantage, depending on the thickness and rigidity of the cover layer. For example, if the cover layer is especially thick or rigid, then the non-printing strip can be embodied particularly narrow if the cover layer is removed in the end sections. 
         [0028]    According to one embodiment, the at least one end section may be secured inside the groove, such that it can be detached. For example, the end section of the rubber blanket may be secured with the aid of elastic deformation, wherein the groove is embodied with slightly smaller dimensions as compared to the end section to be inserted. An uncomplicated fastening of one or both ends sections inside the groove is thus possible and, in many cases, meets the requirements for a secure operation of the rotary offset printing press. A rubber blanket secured in this way can furthermore be easily detached for a replacement, simply by pulling off the rubber blanket in radial direction toward the outside. 
         [0029]    According to another embodiment, a strip may be arranged adjacent to one of the end sections or, alternatively, between the end sections of the rubber blanket. Alternatively, the strip may be fixedly connected to the rubber blanket as insertion aid and can thus be inserted together with the end section of the rubber blanket into the groove, where the strip can furthermore be embodied separate from the rubber blanket. 
         [0030]    According to one embodiment, after both end sections of the rubber blanket have been inserted into the groove, for example, the strip can be pushed from the outside between the two end sections, so that the print cylinder is securely sealed toward the outside and solvents or printing ink cannot penetrate. Strips of this type can also be provided between the groove wall and the inserted end section, resulting in an elastic deformation of the end section of the rubber blanket which securely seals the print cylinder toward the outside and ensures that the end sections are fixated securely inside the groove. 
         [0031]    According to a further embodiment, at least one spring element may be arranged inside the groove, adjacent to the at least one of the end sections of the rubber blanket. As an alternative, one wall of the groove can also be embodied to be resilient. The goal for this embodiment is again to achieve an elastic deformation of the at least one end section, where spring elements represent a particularly cost-effective solution to this problem. 
         [0032]    According to an additional embodiment, the groove may be arranged parallel to the print cylinder axis in radial inward direction. Its center plane consequently may also extend radially toward the inside. However, it is not necessary for the center plane to extend precisely in radial direction. According to one advantageous embodiment, the center plane may be positioned at an angle, relative to the radial plane, which intersects the circumference of the print cylinder jointly with the center plane of the groove. For example, the leading end section can be inserted at an acute angle while the trailing end section is subsequently inserted at an obtuse angle. 
         [0033]    In general, the above-described print cylinders are suitable for use with rotary offset printing presses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The present invention will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which: 
           [0035]      FIG. 1  is a detail of a radial section through a print cylinder, with a strip inserted into the groove between the end sections of the rubber blanket, according to an embodiment of the invention; 
           [0036]      FIG. 2  is a representation according to  FIG. 1 , wherein only one end section of the rubber blanket is embodied and inserted into the groove; 
           [0037]      FIG. 3  is a detail from a radial section through a print cylinder with a strip arranged between the groove and one end section, according to an embodiment of the invention; 
           [0038]      FIG. 4  is a detail from a radial section through a print cylinder that is comparable to the print cylinder shown in  FIG. 3 , wherein the groove is provided with a spring element; 
           [0039]      FIG. 5  is a detail from a radial section through a print cylinder for which the end sections are inserted into the groove, wherein radially outer layers of the rubber blanket are removed in one case and radially inner layers are removed in the other case, according to an embodiment of the invention; 
           [0040]      FIG. 6  is a representation according to  FIG. 5 , but with the radially outer layer of the rubber blanket removed from both end sections inserted into the groove; 
           [0041]      FIG. 7  is detail from a radial section through a print cylinder with a groove extending radially inward at an angle, according to an embodiment of the invention; and 
           [0042]      FIG. 8  is a complete radial section through a print cylinder, provided with a groove that corresponds to the grooves shown in  FIGS. 1 to 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0043]      FIG. 8  shows a view of a complete radial section through a print cylinder  30 ,  30 ′,  30 ″, provided with a rubber blanket  1 ,  1 ′,  1 ″ and used with a rotary offset printing press. An axis A extends through the center of the print cylinder  30 ,  30 ′,  30 ″. An inward directed groove  34 ,  34 ′,  34 ″ that extends parallel to the axis A is provided on the circumference of the print cylinder  30 ,  30 ′,  30 ″. Inserted into the groove  34 ,  34 ′,  34 ″ are two end sections  10 ,  20 ,  20 ′,  20 ″ of the rubber blanket  1 ,  1 ′,  1 ″ which is attached over the complete circumference of the print cylinder  30 ,  30 ′,  30 ″, wherein the first end section  10  is a leading end section as seen in production direction P of the print cylinder  30 ,  30 ′,  30 ″ and the second end section  20 ,  20 ′,  20 ″ is embodied as a trailing end section. A main section  5  of the rubber blanket  1 ,  1 ′,  1 ″ extends over nearly the total circumference of the print cylinder  30 ,  30 ′,  30 ″ between the end sections  10 ,  20 ,  20 ′ and  20 ″ and is joined by the end sections  10 ,  20 ,  20 ′,  20 ″. 
         [0044]    A first embodiment is shown in  FIG. 1 , which is also part of the total view according to  FIG. 8 . A detail from the radial section through the print cylinder  30  shows an enlarged view of the region surrounding the groove  34 . 
         [0045]    The groove  34  has a groove depth  36  and a groove width  38 . These dimensions define a groove in the outer surface of the print cylinder  30  which holds the end sections  10 , of the rubber blanket  1 . 
         [0046]    The rubber blanket  1  comprises a plurality of layers, meaning it is configured with a plurality of layers  2 ,  3 ,  4  as seen in radial direction, wherein each of the layers has a special function. Not shown are further layers which may exist and are disclosed in the art. In a radial inward direction a self-adhering layer  4  of the rubber blanket  1  is glued to the print cylinder  30 , on the side facing the print cylinder  30 . A support layer  3  which generally consists of a fabric follows in a radial outward direction. The rubber blanket  1  is provided radially on the outside with a cover layer  2  that faces away from the print cylinder  30 . The cover layer  2  meets the respective surface criteria for generating a clean print image on the printing material, which is not shown herein. 
         [0047]    The same layer configuration exists over nearly the complete circumference of the rubber blanket  1 , meaning in the main section  5 . The self-adhering layer  4  and the support layer  3  have been removed from the end sections  10 ,  20 , starting from the outside edges  11 ,  21  of the groove  34  in the radial direction toward the inside. As a result, the end sections  10 ,  20  of first embodiment of the rubber blanket  1  are inserted only with a reduced thickness, namely the thickness of the cover layer  2 , into the groove  34 . 
         [0048]    Following the insertion of the end sections  10 ,  20 , an insertion aid  7  that is embodied as strip  9  is inserted in radial direction into the groove  34 , between the end sections  10 ,  20  of the rubber blanket  1 . In the circumferential direction, the end sections  10 ,  20  are clamped into the groove  34  as a result of the strip  9  being thicker as compared to the groove width  38 . The end sections  10 ,  20  in this case are elastically deformed. The insertion aid  7  can alternatively also be embodied as reinforcing layer on one side of the respective end section  10 ,  20 , wherein this layer can consist of metal, plastic or ceramic material. 
         [0049]    The arrangement according to the first embodiment successfully results in a complete sealing of the self-adhering layer  4  toward the outside. The end sections  10 , of the rubber blanket  1 , which are inserted into the groove  34 , are inserted into, pushed into, or fitted into the groove  34  around the radially outer edges  11 ,  21  and are additionally fixated by the strip  9  inside the groove  34 . The dimensions of the groove  34  are smaller, relative to the inserted end sections  10 ,  20  and the strip  9 , so that the end sections  10 ,  20  are clamped into the groove  34  without requiring additional devices, thereby resulting in creating a secure seal toward the outside. 
         [0050]    For the second example shown in  FIG. 2 , the rubber blanket  1  is embodied with only one end section, the leading end section  10 , which inserted into the groove  34 . As a result, it is possible to realize a narrower groove  34  and thus also a narrower non-printing strip of the rubber blanket and/or the print cylinder  30 . In addition, the rubber blanket  1  can be finished easier in this way, meaning the rubber blanket  1  only needs to be cut to the desired length. 
         [0051]      FIG. 3  contains a third embodiment which again shows a detail of a radial section through the print cylinder  30 ′ with glued-on rubber blanket  1 ′, comparable to the representation in  FIG. 1 . The print cylinder  30 ′ is also provided with a groove  34 ′ that is comparable to the groove according to  FIG. 1 , having a groove thickness  38 ′ and a groove depth  36 ′. 
         [0052]    In the same way as for the representation in  FIG. 1 , a cut is made to the rubber blanket  1 ′ on the side facing the print cylinder  30 ′ at the level of the radially outer edges  11 ,  21  of the groove  34 ′. The self-adhering layer  4  and the support layer  3  for the second embodiment are again pulled off for the respective end sections  10 ,  20 ′ of the rubber blanket  1 ′. The rubber blanket  1 ′ is thus also inserted with thinner end sections  10 ,  20 ′ into the groove  34 ′ as compared to the main section  5 . 
         [0053]    An insertion aid  7  that is also embodied as a strip  14  is arranged in the groove  34 ′, between the trailing end section  20 ′ of the rubber blanket  1 ′ and a wall  22  of the groove  34 ′. According to one embodiment, the strip  14  is attached to the trailing end section  20 ′ and is inserted together with the end section into the groove  34 ′. This arrangement is particularly easy to assemble because the leading end section  10  can initially be inserted without problems into the groove  34 ′. To obtain a secure seal for the self-adhering layer  4  against solvents and printing ink, the trailing end section  20 ′ must be pushed into the groove  34 ′, thereby causing the end sections  10 ,  20 ′ to be elastically deformed. For this, the groove  34 ′ is embodied with smaller dimensions as compared to the thickness of the end sections  10 ,  20 ′ and the strip  14 . 
         [0054]    To facilitate the insertion of the trailing end section  20 ′ into the groove  34 ′, the wall  22  of the groove  34 ′ or the strip  14  on the side facing the wall  22  can be provided with a gliding layer  6 . This gliding layer  6  can be applied to the respective surfaces during a replacement of the rubber blanket  1 ′. The strip  14  or the wall  22  can alternatively or additionally also be provided with permanent gliding layers  6 . These types of gliding layers are composed, for example, of polytetrafluorethylene or another substance having gliding properties. The end sections  10 ,  20 ′ of the rubber blanket  1 ′ may consist at least in part of a metal, plastic or ceramic material, wherein these materials can also have gliding properties. 
         [0055]      FIG. 4  shows a fourth embodiment with an enlarged detail of a radial section through a print cylinder  30 ″, comparable to the print cylinder  30 ′ shown in  FIG. 3 . 
         [0056]    In contrast to the representation shown in  FIG. 3 , a spring element  8  is provided inside a groove  34 ″ between the strip  14  and the wall  22 . The spring element  8  can itself be deformed and causes an elastic deformation of the end sections  10 ,  20 ′ of the rubber blanket  1 ′ which are inserted into the groove  34 ″. In addition to the embodiment of a curved sheet metal piece, shown in  FIG. 4 , one skilled in the art is also familiar with spring elements  8  of this type which have a different shape. For example, it is conceivable to have spiral spring elements which are distributed over the length of the groove  34 ″ and can also lead to an elastic deformation of the end sections  10 ,  20 ′ of the rubber blanket  1 ′. 
         [0057]      FIG. 5  shows a detail of a radial section for a fifth embodiment. In the same way as for the previous embodiments, the print cylinder  30 ′ shown herein is also provided on the outer surface with a groove  34 ′ having a groove width  38 ′ and a groove depth  36 ′. 
         [0058]    Analog to the preceding embodiments, a rubber blanket  1 ′ with self-adhering layer  4  is attached to the print cylinder  30 ′. The main section  5  of the rubber blanket  1 ″ again contains the standard layer-type composition, meaning a support layer  3  and a cover layer  2  are embodied in addition to the self-adhering layer  4 . In contrast to the preceding embodiments, however, the cover layer  2  is removed from the trailing end section  20 ″. Otherwise, a strip  14  that facilitates the insertion of the trailing end section  20 ″ is also provided for this embodiment between the wall  22  of the groove  34 ′ and the trailing end section  20 ″ of the rubber blanket  1 ′. 
         [0059]    A different embodiment according to  FIG. 6  shows the removal of the cover layer  2  from the leading end section as well as the trailing end section  10 ,  20 ″ of the rubber blanket  1 ″, wherein this represents an alternative solution that can be used depending on the configuration of the rotary offset printing press. 
         [0060]      FIG. 7  shows yet another example of a print cylinder  30 ′″ having a different design as compared to the overall view shown in  FIG. 8 . The difference to the previously described embodiments is that the groove  34 ′″ extends radially at an angle toward the inside of the print cylinder  30 ′″. 
         [0061]    A further difference can be found in the removal of layers from the end sections  10 ′,  20 ′″ which are inserted into the angled groove  34 ′″. 
         [0062]    For this embodiment, the end section  10 ′ that leads in production direction P of the print cylinder  30 ′″ is inserted at an acute angle α into the groove  34 ′″. To facilitate the insertion of the leading end section  10 ′ into the angled groove  34 ′″, the cover layer  2  of the rubber blanket  1 ′″ is removed past the end section  10 ′ for the embodiment shown herein, meaning only the support layer and, if applicable, the self-adhering layer  4  are inserted into the groove  34 ′″. 
         [0063]    In general, however, the self-adhering layer  4  always ends at the radial outer edge  11 ,  21  of the groove  34 ,  34 ′,  34 ″,  34 ′″, such that the insertion and removal of the respective end section  10 ,  10 ′,  20 ,  20 ′,  20 ″,  20 ′″ of the rubber blanket  1 ,  1 ′,  1 ″,  1 ′″ is not made difficult. 
         [0064]    If the rubber blanket  1 ′″ for the embodiment shown in  FIG. 7  is fitted around the print cylinder  30 ″″ and is glued to the cylinder, then the trailing end section  20 ′″ is inserted at an obtuse angle of 90°+α into the groove  34 ′″. 
         [0065]    The trailing end section  20 ′″ is provided with a strip  14 ′, facing the wall  22  of the groove  34 ′″ and facing away from the leading end section  10 ′ of the rubber blanket  1 ′″, wherein this strip facilitates the insertion of the trailing end section  20 ′″. 
         [0066]    A center plane M of the groove  34 ′″ extends parallel to the inserted end sections  10 ′,  20 ′″ and occupies an angle α to a radial plane R of the print cylinder  30 ′″ and intersects with its circumference together with the center plane M of the groove  34 ′″. 
         [0067]    It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and that the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.