Abstract:
A film transfer device guides a transfer film at least partly around a transfer cylinder having a channel. As a result of entrainment of the transfer film by an edge region of the channel during indexing, considerable impairment to web tension occurs, requiring an indexing speed to be reduced so as not to cause damage to the film. In order to increase an indexing frequency, in one region, i.e. more precisely in an edge region of the channel of the transfer cylinder, a coating is provided having such a nature that it at least reduces an adhesion of a rear side of the transfer film to the edge region of the channel, i.e. to the transfer cylinder in this case. In this way, the film slides better off the edge region of the channel and a higher indexing speed can be achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2010 020 250.9, filed May 11, 2010; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a film transfer device including an applicator for applying an adhesive to at least some regions of a printing material led through the applicator, and a transfer unit disposed downstream of the applicator and having a transfer nip for transferring a transfer layer from a carrier film, which together form a transfer film, to at least some regions of the printing material. The transfer nip is formed by a transfer cylinder and an impression cylinder, the transfer film is led at least partly around the transfer cylinder and the transfer cylinder has a channel. 
         [0003]    Film transfer devices of the generic type are used in finishing printed products, for example in order to produce gloss effects. Such machines can be subdivided into hot film embossing machines and cold film embossing machines. In the latter, the transfer layer is transferred to flat material, i.e. to a printing material such as a sheet, only under pressure but not additionally under the action of heat. As a rule, in the case of cold film transfer devices, i.e. cold film embossing equipment having a printing unit which is disposed upstream of the transfer device, adhesive is printed on, so that a printed image made of adhesive remains on the sheet and, within a film transfer unit, is able to pull a corresponding transfer layer off the transfer film being used, so that the transfer layer adheres to some regions of the sheet. In that case, the transfer layer can be partially transferred in the transfer nip under the action of pressure, substantially to the regions to which adhesive has been applied. 
         [0004]    The problem with that film transfer technology is that the transfer film has to be moved at the same speed as the printing material during the transfer and that, as a rule, only small regions on the printing material are intended to be covered with the transfer layer. In particular, a transfer cylinder involved in the transfer nip frequently has a so-called channel, in which a printing blanket can be fixed. In the region of the channel, no transfer from the transfer layer through the use of pressure can be carried out. Therefore, the intention is always as far as possible to control the situation in such a way that the printing material dips into the transfer nip between the transfer cylinder and an impression cylinder when the channel cannot be in the region of the printing material. Other regions, in which the transfer film is transported unused through the transfer nip, are regions in which no transfer layer is intended to be transferred to the printing material. 
         [0005]    For the purpose of better utilization of the transfer film and to reduce consumable materials, provision is made, for example according to European Patent EP 932 501 B1, corresponding to U.S. Pat. Nos. 6,334,248 and 6,491,780, to move the transfer film over a pair of dancer rolls, which are moved cyclically at the same indexing rate as the channel of the transfer cylinder, so that the transfer film is braked to a speed of zero, for example, in the region of the channel. For that purpose, the two dancer rolls are coupled to each other in such a way that transfer film webs, coming from a supply roll which continues to move, are stored by a first leading dancer and simultaneously released to a take-up roll by a second, trailing dancer. In that way, a certain constancy of the web tension in the region of the supply and take-up roll can be ensured. For that purpose, in order to save transfer film, both dancers are moved in a coupled manner in a braking direction. The film can, in particular, also be pulled back out of the transfer nip. 
         [0006]    In such devices, with dancers running in the same direction, there is a problem when the transfer cylinder is enclosed by the transfer film and has rotated to such an extent that the transfer film is already able to dip into the channel before the transfer nip, while the transfer film after the transfer nip is still set completely against the transfer cylinder and wraps around the latter. A dancer roll which is disposed after the transfer nip sees nothing of the channel already acting on the film, as a result of the transfer cylinder being set against the impression cylinder. However, a dancer roll which is provided before the transfer nip already “notices” the channel that is present. The leading and the trailing dancer roll are substantially decoupled from each other by the transfer nip. While the web tension remains constant in the region of the trailing dancer roll, it is already decreasing on the side of the leading dancer roll. 
         [0007]    Similar effects also occur when the channel is already set with its trailing edge against the impression cylinder. 
         [0008]    Whenever the leading and the trailing dancer roll are decoupled from each other, different web tensions therefore occur on the two sides. In addition, a general dip in the web tension occurs on the two sides when the channel is in the region of the transfer nip. 
         [0009]    In order to take control of the problem of changing web tension, it has been proposed in German Published Patent Application DE 10 2009 020 106 A1, corresponding to U.S. Patent Application Publication No. US 2009/0294038 A1, to decouple the dancer shafts from each other and to move them asynchronously in relation to each other, in order to compensate for the different web tension changes before and after the channel in that way. 
         [0010]    However, it still remains a problem that at least brief changes in the position and in the tension of the film in the channel itself occur. As a result, in particular when the film is intended to be pulled back counter to the feed direction of the sheet during the indexing, the speed with which the film can be transferred to a printed sheet is considerably restricted. That therefore results, amongst other things, in that, in particular as the film is pulled back, the latter is laid at least briefly around the edge region of the channel and can thus be carried along by the channel. Depending on the direction of movement of the film, that occurs on all of the edge regions of the cylinder channel and also on the surfaces of the cylinder channel covering. As a result of that entrainment of the transfer film by the edge region of the channel, considerable impairment of the web tension itself occurs. In order to still ensure proper functioning of the film transfer, the speed of the channel, i.e. the rotational speed of the impression cylinder and of the blanket cylinder, must therefore be reduced in order not to cause any damage to the film. 
       SUMMARY OF THE INVENTION 
       [0011]    It is accordingly an object of the invention to provide a film transfer device, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and with which a higher indexing speed can be achieved. 
         [0012]    With the foregoing and other objects in view there is provided, in accordance with the invention, a film transfer device, comprising an applicator for applying an adhesive to at least some regions of a printing material led through the applicator, and a transfer unit disposed downstream of the applicator. The transfer unit has a transfer cylinder and an impression cylinder. The transfer cylinder has a channel and the transfer cylinder guides a transfer film, having a transfer layer and a carrier film, at least partly around the transfer cylinder. The transfer cylinder and the impression cylinder form a transfer nip for transferring the transfer layer of the transfer film to at least some regions of the printing material. A coating is disposed in the region or vicinity of the channel for at least reducing adhesion of a rear side of the transfer film to the transfer cylinder. 
         [0013]    Therefore, in the film transfer device according to the invention, in one region, i.e. more precisely in an edge region of the channel of the transfer cylinder, a coating is provided which is of such a nature that it at least reduces the adhesion of the rear side of the transfer film to this edge region of the channel, i.e. to the transfer cylinder in this case. In this way, the film slides better off the edge region of the channel and a higher indexing speed can be achieved, since the engagement of the edge region of the channel in the film is reduced. The effects on the tension of the transfer film are reduced to such an extent as a result that, even given relatively high indexing speeds, no damage to the transfer film itself is to be expected. 
         [0014]    In accordance with another feature of the film transfer device of the invention, provision is made for this coating to be provided both on the edges of the channel and also additionally or alternatively on the top side of a channel covering of the channel. In particular, it can always be provided only in the edge regions of the channel covering and of the channel. For this purpose, the coating is provided axially with respect to the axis of the transfer cylinder, particularly preferably over the entire width or at least in the regions in which the transfer film makes contact with the transfer cylinder. 
         [0015]    In accordance with a further feature of the invention, the coating can, in particular, involve a strip which can also subsequently be adhesively bonded to the edge and/or to the channel covering. 
         [0016]    In accordance with an added feature of the invention, possible adhesive strips which are adhesively bonded to the channel covering and/or to the edge of the channel can, in particular, be crêpe paper or a non-stick paper. In addition, a surface of the printing blanket of the transfer cylinder itself can be involved. The transfer cylinder should, in particular, have a substantially smooth surface and only in the regions of the channel have a surface structure differing therefrom, which has an appropriate coating in order to reduce the friction with the transfer film. The materials of the non-stick paper or the surface of the printing blanket can, for example, be silicone or PTFE. 
         [0017]    In accordance with an additional feature of the invention, since, as a result of such coatings of the printing blanket, it is possible for effects on the film transfer itself to occur but which are undesired, since they can be detected in the printed image, provision is particularly advantageously made for the peripheral direction, i.e. the width, of this coating or the strip, which is adhesively bonded to the transfer cylinder or applied in another way, to be restricted substantially to a region of the edge of the channel which cannot come into contact with a region of the printing material that should be coated or printed, is intended to be coated or printed or has been coated or printed. In this way, the effect of this coating or this strip on the printing material cannot be detected in a resulting printed image. 
         [0018]    In accordance with a concomitant feature of the invention, the strip according to the invention can advantageously be formed as an adhesive strip or other holding possibilities, such as magnetic or electrostatic methods, are also conceivable in this case. 
         [0019]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0020]    Although the invention is illustrated and described herein as embodied in a film transfer device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0021]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0022]      FIG. 1  is a diagrammatic, vertical-sectional view showing a structure of a film transfer unit with indexing; 
           [0023]      FIG. 2  is a reduced, fragmentary, vertical-sectional view of a film transfer device having a corresponding film transfer unit; and 
           [0024]      FIG. 3  is an enlarged, fragmentary, cross-sectional view of an edge region of a transfer cylinder channel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring now in detail to the figures of the drawings, which show an exemplary embodiment of the invention, from which further inventive features can also be gathered but to which the invention is not restricted, and first, particularly, to  FIG. 1  thereof, there is seen a film transfer unit  1  in which a transfer film  2  is led through a transfer nip  3 . 
         [0026]    The transfer nip  3  is formed by a transfer cylinder  5  and an impression cylinder  4 . The transfer film  2  is unwound from a supply roll  7  and pulled in the direction of the transfer nip  3  by a leading feed device  9 . The supply roll  7  is located on a non-illustrated friction shaft and is driven at a speed which is lower than the speed of printing material  21 . A drive for the supply roll  7  is provided through the friction shaft. The transfer film  2  is pulled off the supply roll  7  by the leading feed device  9 , while rollers of the leading feed device  9  are driven at a higher speed than the friction shaft of the supply roll  7 . However, the leading feed device  9  must always be operated at a lower speed than the speed of the printing material  21 . 
         [0027]    The unwound transfer film  2  is led over a leading dancer  13  of an indexing module  11  and over further deflection rollers  6  through the transfer nip  3  in such a way that it enters into a wrap angle α with the transfer cylinder  5 . After the transfer nip  3 , the transfer film  2  is deflected further over deflection rollers  6  and fed to a trailing dancer  12 , which deflects the transfer film  2  and feeds it to a trailing feed device  10 , which is faster than the leading feed device  9 . The film  2  is deflected onto a take-up roll  8  by the trailing feed device  10 . The take-up roll  8  is also mounted on a friction shaft, which is driven more quickly than the trailing feed device. At least the friction shaft is driven in such a way that the peripheral speed of the take-up roll  8  is higher than the speed of the trailing feed device  10 . In this way, there is slippage between the friction shaft and the actual take-up roll  8 . The same is true in the same way of the supply roll  7 . 
         [0028]    The printing material  21  is led over the impression cylinder  4  through the transfer nip  3  together with the transfer film  2 . During the transfer of a non-illustrated transfer layer, the transfer film  2  and the printing material  21  are moving at the same speed. 
         [0029]    The transfer cylinder  5  has a non-illustrated printing blanket which is clamped-in through a channel  20 . The channel  20  is also able to accommodate possible grippers on the side of the impression cylinder  4 . 
         [0030]    When a leading edge  113  of the channel  20  comes into the transfer nip  3 , a web tension between the dancer  13  and the transfer nip  3  collapses. During the transfer of the transfer layer to the printing material  21 , the sum of the speed of the leading feed device  9  and of the leading dancer  13  gives the speed of the printing material  21 . For this purpose, the dancer  13  is moved in an acceleration direction  18  along a path which is identified by a double arrow  16 . As a result of the leading edge  113  of the channel  20  making contact with the impression cylinder  4 , the leading dancer  13  is decoupled from the trailing dancer  12 . In order to now compensate for the diminishing web tension, provision is made for the leading dancer  13  to be driven through a motor  15  in such a way that it is initially accelerated highly in a braking direction  19 . In this way, a constant web tension is achieved in this region. For this purpose, a control apparatus  22  acts in an appropriate way on the motor  15  of the leading dancer  13 . Once the channel  20  is completely in the region of the transfer nip  3 , then the dancer  13  is moved in the braking direction  19  with a lower acceleration, so that the transfer film  2  comes to a standstill and is pulled back. 
         [0031]    If the channel  20  is “seen” for the first time by the dancer  12 , then the trailing dancer  12  is initially accelerated in the braking direction  19  with a lower acceleration in order to compensate for this dip and subsequently accelerated with a higher speed, so that standstill of the transfer film  2  can be achieved. For this purpose, the control apparatus  22  is also connected to a motor  14  of the trailing dancer  12 . 
         [0032]      FIG. 2  shows a portion of a film transfer device  100 . Such a film transfer device  100  can be constructed within a printing press. A sheet  21  is transported through a press nip  109  by an applicator  101 , which is a conventional printing unit of a printing press. In this press nip  109 , the printing material  21  has adhesive applied partially to it. The sheet  21  is then transported further through the film transfer unit  1 . As described, the sheet  21  is led through the transfer nip  3 , in which it picks up the transfer layer of the transfer film  2  from the transfer film  2  in the regions in which it itself has had adhesive applied. 
         [0033]    The sheet  2 , which is treated in this way, can then be transported further through the printing press, i.e. through the film transfer device, so that it is moved to a further, following printing unit  103 , which once more has a press nip  109  that is formed by a blanket cylinder  110  and an impression cylinder  111 . The printing unit  103  additionally has an inking unit  112 . In the printing unit  103 , the sheet  21  to which a transfer layer has been applied can then be overprinted conventionally. 
         [0034]      FIG. 3  shows a portion of a transfer cylinder  5 . This portion shows a trailing edge  114  of the channel  20  of the transfer cylinder  5 . The transfer cylinder  5  shown herein further has a channel covering  200 . This channel covering is conventionally provided in transfer cylinders  5  and also in conventional blanket cylinders  110  in printing units  103  or applicators  101 . In this way, the area of intervention for operators is reduced, so that in this case it is possible for less injury to people to occur and, moreover, the fluctuations of the transfer film  2  are also already reduced by this channel covering  200 . 
         [0035]    The transfer cylinder  5  in this case has a covering, lining or clothing with a printing blanket, i.e. a rubber blanket  201 . In this case, this is, in particular, an especially smooth rubber blanket, for example a so-called Irioblanket™. This printing blanket  201  is held in the channel  20  both in the region of the leading edge  113  and also the trailing edge  114 , by respective clamping devices  202 . 
         [0036]    During indexing of the transfer film  2 , the latter dips at least into a sub-region  203  of the channel  20  and can then be laid around the trailing edge  114  in this case, in particular as the transfer film  2  is pulled back. If the transfer film  2  is moved in a feed direction in the direction of an arrow  204  relative to the transfer cylinder, counter to the reverse pull, then it is possible for the transfer film  2  to be laid around an edge  205  of the channel covering  200  in a corresponding way. The leading region of the channel  20  in the region of the leading edge  113  is constructed symmetrically in relation to the trailing region illustrated herein and thus, as the transfer film  2  is fed in the direction of the arrow  204 , wrapping around the leading edge  113  of the channel  20  occurs in a corresponding way in this case. 
         [0037]    As is illustrated herein, both the channel covering  200  and the trailing edge  114  and, likewise, the leading edge  113  not shown herein, have a strip  206  applied symmetrically thereto. The channel covering  200  is covered completely by the strip  206 , while the trailing edge  114  and, symmetrically thereto, the leading edge  113  have the strip  206  applied to them in such a way that the printing blanket  201  is covered by the strip  206  only in a sub-region  207 . In this case, the strip  206  should end shortly after the respective trailing edge  114  and leading edge  113 , so that in this case a strip  206  is no longer provided in the region of a print start  208 . In this case, print start  208  means the region of the transfer cylinder  5  in which a transfer layer can be transferred from the transfer film  2  to the sheet  21 . 
         [0038]    In the example presented herein, the strip  206  is crêpe tape, which has such a surface nature that it reduces the friction between the trailing side of the transfer film  2  and the printing blanket  201  and, respectively, the channel covering  200 , so that it is not possible for adhesion of the transfer film  2  to the trailing edge  114  of the channel  20 , to the leading edge  113  of the channel  20  or in a region or edge  205  of the channel covering, to occur. Such adhesion limits the indexing speed of the film transfer device and the film transfer unit  1 . The strip  206  can, in particular, also be incorporated into the printing blanket  201  but can preferably be adhesively bonded on because of the ability to be retrofitted. As an alternative to crêpe tape, it is also possible to use a strip which is adapted from PTFE, silicone or a non-stick paper, as is usual, for example, in the cooking oven field. Therefore, the strip  206  can be referred to as a coating or coating element disposed in vicinity of the channel  20 , that is at the edges  113 ,  114 ,  205 . 
         [0039]    Through the use of this coating element that can be applied simply, even subsequently, i.e. through the use of the strip  206 , it is possible to achieve a considerable increase in the indexing speed of the film transfer unit  1 .