Patent Publication Number: US-8117962-B2

Title: Equipment for preparing dampening solutions for offset printing

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an installation for preparing dampening solutions for offset printing with a device for preparing a dampening solution and a device for feeding one or more basic liquid materials for preparing the dampening solution into the device for preparing the dampening solution. 
     In offset printing, it is necessary to wet the surface of the offset printing plate with a dampening solution, which prevents acceptance of printing ink by the non-printing places of the offset printing plate. It is generally customary to cycle the dampening solution between the printing press and a device for preparing dampening solution, in which the dampening solution is formulated from different basic materials. In this way, the dampening solution, consumed in the printing process, can be replaced continuously by fresh dampening solution. 
     Such systems for preparing and supplying dampening solutions are generally known, for example, from the European patent application 02 004 480 of the Applicant. The known equipment comprises cooling devices, which ensure that the prepared dampening solution, supplied to the printing press, has a suitable process temperature, so that the alcohol, contained in the dampening solution, does not evaporate and the flowing and wetting behaviors are optimized. For wet offset printing, a dampening solution temperature ranging from 8° to 12° C. is typical and must be adhered to with a tolerance not exceeding ±1° C. Fluctuations in the temperature of the dampening solution, supplied to the printing rollers, lead to a change in the quality of the printing result. It is therefore appropriate that the cooling system in the dampening solution cycle comprises a control segment, which, on the basis of an actually measured temperature of the dampening solution, controls the temperature of the dampening agent, supplied to the printing rollers, at a nominal value. 
     If new basic materials, the temperature of which differs appreciably from the temperature existing in the cycling dampening solution, are fed into the device for preparing dampening solution for the purpose of preparing fresh dampening solution, it may happen that the device for cooling the dampening solution cannot eliminate this difference because of the reaction time required by the control segment, so that the temperature of the dampening solution is subjected to fluctuations. In such a case, the temperature may leave the specified tolerance range, so that problems arise in the printing process. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to construct an installation of the type described above in such a manner that, independently of the temperature of the basic materials, which are available for feeding the device for preparing dampening solution, cooling of the prepared dampening solution to a specified process temperature is possible. In particular, it is an object to avoid larger fluctuations in the process temperature of the dampening solution prepared, which may have a negative effect on the printing process. 
     In order to accomplish this object, the inventive installation for preparing dampening solution is characterized by the distinguishing features of claim  1 . 
     Pursuant to the invention, the device for feeding basic materials to the device for preparing dampening solution is intended to cool the basic materials, so that the latter reach the device for preparing the dampening solution already in a pre-cooled state. If the basic materials are already cooled down largely to the desired process temperature of the dampening solution, temperature fluctuations in the cycling dampening solution, which arise suddenly, can be avoided. The remaining small temperature differences can be equalized by the already known cooling devices in the cycling dampening solution in the feed line to the printing roller. By the inventive pre-cooling of the basic materials in this way, it is achieved that the process temperature of the dampening solution always remains within the tolerance range, in which the printing result has a constant quality. 
     Preferred embodiments of the invention arise out of the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, preferred examples of the invention are explained in greater detail by means of the drawing, in which 
         FIGS. 1 to 3  show diagrammatic presentations of different embodiments of the inventive installation for preparing dampening solution. 
     
    
    
     DETAILED DESCRIPTION 
     The installation, shown in  FIG. 1 , comprises a device  10  for preparing a dampening solution for an offset printing press  12 . This device  10  for preparing a dampening solution comprises a dampening solution tank  16 , which, at the same time, is a component of the dampening solution cycle  18 , in which the dampening solution  14  is pumped to the printing press  12  and back again to the dampening solution tank  16 . For this purpose, a pump  22  is disposed in the inlet  20  of the printing press  12 . The dampening solution, returning through the return line  24 , is filtered through a filter  26  before it reaches the dampening solution tank  16  once again. In this way, contamination and foreign material, which accumulate in the dampening solution during the printing process, are filtered out of the dampening solution cycle  18 . 
     In order to achieve an optimum printing result, the dampening solution  14  is cooled to a specified process temperature. For this purpose, a portion of the dampening solution, circulating in the dampening solution cycle  18 , is diverted through a secondary pipeline  28  out of the inlet  20  of the printing press  12  and supplied to a cooling unit  30 . The dampening solution, cooled by the cooling unit  30 , is passed through a return pipeline  32  back into the dampening solution tank. The temperature of the dampening solution  14  in the dampening solution tank  16  can be controlled by the cooling performance of the dampening solution cooling unit  30  and by the proportion of dampening solution, which is diverted through the secondary pipeline  28  from the inlet  20  of the printing press  12 . Typically, this temperature is constant, ranging from about 6° to 12° C. with a tolerance of ±1° C. and preferably of ±0.5° C. Fluctuations of the temperature in the dampening solution cycle  18  can be equalized by a control segment, which is not shown and extends between the cooling unit  30  and the tank  16  of the dampening solution. The output of the cooling unit  30  is increased if the temperature of the dampening solution  14 , which is stored in the dampening solution tank  16 , increases. Alternatively, the proportion of dampening solution, diverted to the cooling unit  30 , can be increased. Furthermore, it is possible to measure the actual temperature of the dampening solution by means of a sensor at a different place in the dampening solution cycle  18 , for example, directly in the region of the printing roller. 
     During the printing process, dampening solution is consumed, so that the amount of dampening solution  14 , kept in the dampening solution tank  16 , gradually becomes less. This loss is compensated for in that the basic liquid materials for producing new dampening solution are supplied to the device for preparing dampening solution through a feeding device, which is generally labeled  40  in  FIG. 1  on the left. The basic liquid materials are, in particular, water, alcohol, as well as additives, such as antimicrobial materials, surfactants or the like. For each of the individual basic materials, it is possible to use a separate feeding device  40  of the type here. Alternatively, a single feeding device  40  can be used for an already existing mixture of basic materials or such a mixture, as explained in even greater detail in the following, may be formed within the feeding device  40  itself. 
     The basic material  42  is passed through a basic material feed line  44  into a prechamber  46 . The basic material feed line  44  comprises a shut-off valve  48 , which permits the material, flowing through the feed line  44 , to be controlled or the latter to be shut off completely. 
     In the example shown here, the prechamber  46  and the dampening solution tank  16  are located in a single container  50  and are separated from one another by a partition  52 . If the prechamber  46  is filled over the basic material feed line  44 , the basic material  42  can flow over an overflow  54  in the upper region of the partition  52  out of the prechamber  46  into the dampening solution tank  16 . If several basic material feed lines  44  for different basic materials, such as water, alcohol and the like, discharge into the prechamber  46 , then a mixture of basic materials, which forms the dampening solution, is already present within the prechamber  46 . In the strict sense of the word, the present invention therefore relates not only to a pre-cooling of individual basic materials, but also to the pre-cooling of a mixture of basic materials, which forms a dampening solution kept within the pre-chamber  46  and is passed into the dampening solution tank  16  in the pre-cooled state and is available there to the above-described dampening solution cycle  18 . 
     In the example shown here, this pre-cooling takes place due to the thermal coupling between the pre-chamber  46  and the dampening solution tank  16 , which are separated from one another only by the partition  52  within the tank  50 . Accordingly, the basic material  42  or the mixture of basic materials within the prechamber  46  is cooled through the partition  52  by the dampening solution  14  in the dampening solution tank  16 , which is cooled constantly to the process temperature by the dampening solution cooling unit  30 . By these means, excessive temperature fluctuations, which cannot be equalized in good time due to the inertia of the control system of the cooling unit  30 , are avoided when the dampening solution tank  16  is filled with basic materials or the dampening solution mixture from the prechamber  46 . The process temperature of the dampening solution can therefore also be kept largely constant also during the refilling process. 
     The prechamber  46  can also be coupled thermally with the dampening solution tank  16  in other ways. For example, the prechamber  46  may be constructed as an independent container, one wall of which is in contact with the outer wall of the dampening solution tank  16 . Furthermore, it is conceivable to construct the prechamber  46  in such a way, that it is surrounded at least partly by the dampening solution tank  16 . 
       FIG. 2  shows a modification of the embodiment of  FIG. 1 , for which the feeding device  60  of the installation for preparing dampening solution comprises a cooling unit  64  for cooling the basic material  42 . This cooling unit is a cooling coil  64 , which extends within the prechamber  46  for cooling the basic material  42  and through which a cooling medium, such as water, flows. In this way, the basic material  42  or a mixture of basic materials within the prechamber  46  is cooled not only through the partition  52  separating the dampening solution tank  16  and, with that, by the dampening solution  14  itself, which is kept in the dampening solution tank  16 , but also through an independent cooling unit. 
     The feeding device  70  of the installation for preparing dampening solution in  FIG. 3  feeds a basic material  42  or mixture of basic materials, already precooled within the basic material feed line  44 , into the dampening solution tank  16 . Interim storage of the basic material  42  within a prechamber is omitted here, since the basic material  42  is already precooled by a cooling unit  73  to such an extent, that its introduction into the dampening solution tank cannot lead to a temperature fluctuation within the dampening solution cycle  16 . In the ideal case, the cooling unit  73  cools the basic material  42  within the basic material feed line  44  already to the process temperature, so that, when the dampening solution  14  lost is compensated for, additional cooling performance by the dampening solution cooling unit  30  is not required. 
     In a further embodiment, not shown in the Figures, the basic material can be passed through a coil around the dampening solution tank, so that it is coupled thermally with the latter. Before the basic material flows out of the end of the coil into the dampening solution tank  16 , it is accordingly cooled through the outer wall of the dampening solution tank  16 . The coil, in much the same way as the prechamber  46 , forms a buffer, in which a flowing volume of basic material, which is coupled thermally with the dampening solution  14  within the dampening solution tank  16 , is pre-cooled by the latter. 
     In all the embodiment shown here, it is possible to integrate the device  10 ,  62 ,  72  for preparing the dampening solution, which is connected by the dampening solution cycle  18  with the printing press  12 , and the feeding device  40 ,  60 ,  70  in a peripheral device, which is to be made available to a printing press, so that a space-saving and compact construction is attained.