Patent Publication Number: US-6901859-B2

Title: Washing device and its method for impression cylinder jacket in sheet-fed offset two-sided printing press

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to, and claims priority from Japanese Patent application No. 2003-046177 filed in the Japanese Patent Office on Feb. 24, 2003, the contents of which are hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a washing device and its method for an impression cylinder jacket in a sheet-fed offset two-sided (perfecting) printing press. 
   2. Description of the Related Art 
   The sheet-fed offset two-sided printing press with multicolor units is divided into two categories: one being an arrangement where the sheet is reversed during the course of its travel through plural printing units arranged only on one side of the sheet passage (either the top or the bottom) in order to be printed on both sides of the sheet, and the other being an arrangement where both sides of the sheet is alternately printed without reversing it by plural printing units arranged on both sides of the sheet passage. 
   In either case, while the ink on the already printed side of the sheet is not set yet and is still in contact with the impression cylinder, the other side of the sheet is printed as the sheet is pressed between a blanket cylinder and the impression cylinder. As a result, the ink on the already printed side of the sheet is transferred to the impression cylinder. Since the ink transferred to the impression cylinder is transferred back to the sheets to be fed thereafter, it causes staining in the printing process, thus making multicolor printing impossible under such a condition. 
   In order to solve this problem, technologies such as the one disclosed by Unexamined Publication No. JP-A-8-12151 are proposed. The technology disclosed by said publication intends to prevent the ink on paper immediately after printing from being transferred to the jacket installed on the impression cylinder by means of installing a jacket having smooth concave-convex profile with a surface roughness of Rmax of 20-40 μm formed by coating a metallic plate with porous ceramics by means of thermal spray, and then coating on top of it with a low surface energy resin of the silicone group resin, etc. (herein after called “separating compounds”). Thanks to this technology, it has become possible to conduct two-sided printing with multicolor on paper such as art paper or coated paper which does not absorb ink too well. 
   However, even when this jacket is used, it becomes necessary to wash the jacket once every 60,000 sheets of printing when the jacket is new, and every 10,000 sheets as the separating compounds in the convex areas of the ceramics coating layer (hereinafter called “ceramic convexes”) on the jacket surface wears out. 
   If the jacket is to be manually washed, it requires the workers to work with unstable postures in very narrow space, so that there are problems in terms of safety and work efficiency. Consequently, various automatic washing devices for an impression cylinder jacket have been proposed and are used in order to solve the problems related to washing jacket by hand. 
   Let us now describe various types of conventional automatic washing devices for an impression cylinder jacket and their problems. 
   (1) First type of washing device with nonwoven fabric cloth impregnated with a washing liquid directly pressed against the impression cylinder 
     FIG. 1  shows the first type of conventional washing device for an impression cylinder jacket. In the device shown in  FIG. 1 , while the machine is operated with a plate cylinder  121 , a blanket cylinder  122 , and an impression cylinder  123  rotating at a slow speed and all cylinders  121 - 123  are maintaining some distances from each other, nonwoven fabric cloth  131   b  impregnated with a washing liquid is directly pressed against impression cylinder  123 , on which the jacket is mounted. This causes the ink on the jacket to be softened and the softened ink is then wiped out by the nonwoven fabric cloth. Also, blanket cylinder  122  is washed in a similar manner as nonwoven fabric cloth  131   a  is directly pressed against blanket cylinder  122 . This type of washing device is divided into two types, one in which the washing liquid is sprayed from a nozzle on the dry nonwoven fabric cloth and the other in which the nonwoven fabric cloth is impregnated with a washing solvent beforehand. 
   However, the first type of washing device has a problem that not only the separating compounds in the convex ceramic areas but also the separating compounds in the concave areas on the jacket surface get worn out as the coarse nonwoven fabric cloth rubs the surface of the impression cylinder jacket strongly. The separating compounds is the key in preventing the ink from attaching to the jacket mounted on the impression cylinder. Therefore, if the separating compounds disappears as a result of the abrasion, the jacket can become easily stainable, thus causing staining on the printed matters, and causing a need for the jacket&#39;s replacement. In case of washing the jacket by hand to clean it, the life time of the jacket&#39;s replacement is typically required once in every 20 to 30 million printings, while the same cycle time becomes as short as once in 15 million printings, or approximately one half of the cycle time of the manual washing, when the first type of automatic washing device is used where the nonwoven fabric cloth is pressed directly against the impression cylinder. 
   When the impression cylinder rotates with the nonwoven fabric cloth pressed against the impression cylinder, the fibers of the nonwoven fabric cloth get tangled with the ceramic convexes on the surface of the jacket mounted on the impression cylinder and remain fibers on the jacket even after the washing process. These fibers can appear as white dots defects on the printed surface in the next printing job and caused the problem of printing defects. 
   Furthermore, the first type of washing device requires an expensive capital investment for the equipment since a washing device having a complicated mechanism with nonwoven fabric cloth needs to be installed into two very narrow spaces among blanket cylinder  122  and impression cylinder  123 . Moreover, its running cost is quite high as the nonwoven fabric cloth needs to be frequently replaced. 
   (2) Second type of washing device having a brush roller pressed against and rotated with the impression cylinder in which the washing liquid is fed to the roller 
     FIG. 2  shows the second type of conventional washing device for an impression cylinder jacket. In the device shown in  FIG. 2 , while the machine is operated with a plate cylinder  121 , a blanket cylinder  122 , and an impression cylinder  123  rotating at a slow speed and each of cylinders  121 - 123  is maintaining some distances from each other, a brush roller  141   b,  to which a washing liquid is fed, is directly pressed against impression cylinder  123  having the jacket. This makes it possible to wash down the ink on the jacket. Two different kinds of washing liquids can be fed through two nozzles  142   b  and  143   b.  Blanket cylinder  122  can also be washed similarly by having brush roller  141   a,  to which two different kinds of washing liquids are fed through two nozzles  142   a  and  143   a,  directly pressed against blanket cylinder  122 . The used washing liquids can be either recycled or wasted. 
   However, the second type of washing device can not only remove the separating compounds on the ceramic convex areas on the jacket surface but also cause wears of the separating compounds in the concave areas, so that it shortens the life time of the jacket substantially similar to the abovementioned first type, since the brush is directly contacting the jacket surface while it is rotating. 
   Furthermore, similar to the first type of washing device, it requires an expensive capital investment for the equipment since a washing device having a complicated mechanism with a brush roller needs to be installed into two very narrow spaces among blanket cylinder  122  and impression cylinder  123 . Moreover, it requires an expensive investment for the detergent recycling device if it is used, and if the washing liquid is not recycled, it requires a large scale waste liquid process. 
   (3) Third type of washing device having a cleaning unit that can be selectively contacted to the blanket cylinder that is opposing the impression cylinder, in which the blanket cylinder rotates for a definite period of time while it is contacting the impression cylinder with the cleaning unit pressed against the blanket cylinder 
     FIG. 3  shows the third type of conventional washing device for an impression cylinder jacket. This third type of washing device is disclosed in said Unexamined Publication No. JP-A-8-12151, and is a washing device for washing a jacket formed a hybrid coating layer consisting of a thermal sprayed ceramic layer and a separating compounds layer. 
   In the device shown in  FIG. 3 , the machine (each of cylinders  121 - 123 ) is rotated at a slow speed while only plate cylinder  121  is separated from other cylinders with blanket cylinder  122  and impression cylinder  123  are contacted with each other, and nonwoven fabric cloth  131   a  impregnated with a washing liquid is pressed against blanket cylinder  122 . Therefore, the ink on the jacket mounted on impression cylinder  123  softens as a result of a small amount of washing liquid transfered from blanket cylinder  122  while the blanket cylinder  122  and impression cylinder  123  make contact rotations, and the ink is transferred back to the blanket cylinder very easily because the jacket surface is coated with the separating compounds. Thus, the jacket mounted on impression cylinder  123  can be completely washed only by means of the washing mechanism having nonwoven fabric cloth  131   a  mounted on blanket cylinder  122 . 
   Moreover, although blanket cylinder  122  and impression cylinder  123  are pressed to each other with a strong pressure, no abrasion occurs on the separating compounds on the surface of the jacket mounted on the impression cylinder because there is not any slip between the two cylinders at all. Further, needless to say, the nonwoven fabric cloth is not contacting the jacket directly so that there does not happen any problem about residual of the fibers from the nonwoven fabric cloth left on the jacket; it is indeed an excellent washing device. 
   This third type of washing device can be retrofitted on an existing press with a minimum capital investment as it requires almost no modification, requiring simply an addition of an electrical sequence, if blanket cylinder  122  can be stopped at a position when it contacts with impression cylinder  123 , as it uses a method of causing blanket cylinder  122  to contact with impression cylinder  123  first and then contact with plate cylinder  121  as a means of causing plate cylinder  121  to contact with blanket cylinder  122 , and blanket cylinder  122  with impression cylinder  123  (cylinder engagement mechanism system of the printing press). 
   However, the most popular cylinder engagement mechanism system at the moment is the method of causing blanket cylinder  122  to contact with plate cylinder  121  first, and then to contact with impression cylinder  123 . If blanket cylinder  122  is washed while blanket cylinder  122  is in contact with impression cylinder  123  in such a cylinder engagement mechanism system, the jacket mounted on impression cylinder  123  gets washed of course, but the washing liquid transfers to plate cylinder  121  via blanket cylinder  122 . If the washing liquid puts on plate cylinder  121 , a plate installed on plate cylinder  121  can become sensitized, which causes staining, which is considered a defective printing. Therefore, this third type of washing device presents a problem that it cannot be adopted in current mainstream of printing presses. 
   On the other hand, if the third type of washing device is to be applied as is to the current mainstream of printing presses, it is necessary to modify the mechanism to allow blanket cylinder  122  to contact only with impression cylinder  123  in order to prevent the washing liquid from transferring to plate cylinder  121 . This requires a substantial design change in the mechanism and the capital investment for the modification can be quite large. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a washing device and its method for an impression cylinder jacket in a sheet-fed offset two-sided printing press, which are improved for solving the abovementioned problems. 
   A more specific object of the present invention is to provide a washing device and its method for an impression cylinder jacket providing a high washing effect, without causing any abrasion or removal of the separating compounds by washing process, without leaving any fibers from the nonwoven fabric cloth, with an extremely inexpensive initial and running costs, and having a simple mechanism despite the fact that they are based on the cylinder engagement mechanism system. 
   According an aspect of the invention, there is provided a washing device for an impression cylinder jacket in a sheet-fed offset two-sided printing press equipped with an impression cylinder installed with a jacket having a flexible metal plate, a base layer formed to have concave-convex profile on the surface of said metal plate and a low surface energy resin layer formed on said base layer, comprising: a cleaning unit capable of being in contact with or separated from a blanket cylinder that opposes said impression cylinder; a water dampening unit equipped with a water form roller capable of being in contact with or separated from a plate cylinder that opposes said blanket cylinder and supplying water to said plate cylinder; an inking unit equipped with an ink form roller capable of being in contact with or separated from said plate cylinder and supplying ink to said plate cylinder; and a controller that executes a first control of causing said plate cylinder to contact with said blanket cylinder and said blanket cylinder to contact with said impression cylinder, and causes each cylinder to rotate under those contacts for a specified period of time while said cleaning unit is in contact with said blanket cylinder; and a second control of separating said plate cylinder from said blanket cylinder, and causing said water form roller and said ink form roller with said plate cylinder. 
   As abovementioned, the third type of washing device is an excellent washing device for an impression cylinder jacket, but its biggest problem is that it causes sensitization of the surface of the plate cylinder (plate surface) by the washing liquid during the process of washing the blanket cylinder and the impression cylinder on a printing press using a method of causing the blanket cylinder to contact with the plate cylinder first and then with the impression cylinder as the cylinder engagement mechanism system. The present invention provides a solution to such a problem. 
   In the present invention, the plate, blanket and impression cylinders are rotated at a slow speed for a definite period of time with the blanket cylinder being brought into an engagement causing the blanket cylinder to contact to the plate cylinder and the blanket cylinder to contact also to the impression cylinder with rotations, while the cleaning unit is pressed against the blanket cylinder, so that the blanket cylinder and the impression cylinder can be washed simultaneously. Moreover, in the present invention, after washing the blanket cylinder and the impression cylinder and also separating the blanket cylinder from the plate cylinder, an ink form roller is pressed against the plate cylinder while feeding water to the plate cylinder by pressing a water form roller against the plate cylinder. 
   When water is supplied to the plate cylinder after washing the blanket cylinder and the impression cylinder and also separating the blanket cylinder from the plate cylinder, the non-image areas of the plate surface comes to have a strong hydrophilicity so that the residual washing liquid, which has been put on the plate from the cleaning unit via the blanket cylinder, floats on the water membrane and furthermore can be easily adsorbed into the ink form roller by contacting the ink form roller with the plate surface. This effectively prevents the sensitization of the plate surface. Since this prevents the residual washing liquid from reaching the water form roller as the residual washing liquid is moved away by the ink form roller, there will not be caused the bad influence to the downstream printing job. 
   Also, most of the sheet-fed offset two-sided printing presses with multicolor are equipped with a washing mechanism for a blanket as a standard equipment having a cleaning unit capable of arbitrarily contacting with and separating from the blanket cylinder. Therefore, the adoption of the washing method according to the present invention makes it possible to wash the blanket cylinder, the impression cylinder and the plate cylinder all at once by merely adding a small modification to the electrical sequence in the conventional printing press and using only a washing mechanism for the blanket cylinder without requiring a washing mechanism for the impression cylinder. Moreover, the offset printing press is always equipped with a water dampening unit and an inking unit, and they can be used for the abovementioned purpose without causing any need for adding them anew. 
   Thus, it is possible to provide a washing device for an impression cylinder jacket featuring a simple mechanism, a high washing efficiency, and extremely inexpensive initial and running costs, that does not leave any nonwoven fabric fibers and is applicable regardless of the type of cylinder engagement mechanism system. 
   Furthermore, adopting the washing method according to this invention makes it possible to remove paper dust easily in addition to the ink on the jacket mounted on the impression cylinder by means of a blanket washing mechanism equipped with a cleaning unit to which the washing solvent and water are supplied during the washing cycle. The washing liquid normally used in the washing mechanism of the blanket cylinder is a petroleum-based solvent, so that, while it can dissolve the ink on the blanket cylinder and the jacket on the impression cylinder, it is not sufficient for removing paper dust (coating materials such as calcium carbonate, etc., coated on paper) put on the jacket by itself. 
   According another aspect of the invention, there is provided a washing method for an impression cylinder jacket in a sheet-fed offset two-sided printing press equipped with an impression cylinder installed with a jacket having a flexible metal plate, a base layer formed to have concave-convex profile on the surface of said metal plate and a low surface energy resin layer formed on said base layer, comprising the steps of: 1) rotating said impression cylinder, a blanket cylinder opposing said impression cylinder, and a plate cylinder opposing said blanket cylinder; 2) causing a cleaning unit capable of being in contact with or separated from said blanket cylinder to contact with said blanket cylinder; 3) causing said plate cylinder to contact with said blanket cylinder and said blanket cylinder to contact with said impression cylinder while keeping said cleaning unit in contact with said blanket cylinder; 4) separating said plate cylinder from said blanket cylinder after causing each cylinder to rotate in such contacts for a specified period of time; and 5) causing a water form roller capable of being in contact with or separated from said plate cylinder in a water dampening unit capable of supplying water to said plate cylinder, and an ink form roller capable of being in contact with or separated from said plate cylinder in an inking unit to contact with said plate cylinder. 
   The objects, features, and characteristics of this invention other than those set forth above will become apparent from the description given herein below with reference to preferred embodiments illustrated in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the first type of conventional washing device for an impression cylinder jacket. 
       FIG. 2  shows the second type of conventional washing device for an impression cylinder jacket. 
       FIG. 3  shows the third type of conventional washing device for an impression cylinder jacket. 
       FIG. 4  shows the system layout of a sheet-fed offset two-sided printing press to which a washing device for an impression cylinder jacket according to an embodiment of the invention is applied. 
       FIG. 5  shows an example system arrangement of a printing unit. 
       FIG. 6  shows an example structure of an impression cylinder. 
       FIG. 7  is a partially enlarged cross-sectional view schematically showing an example structure of a jacket. 
       FIG. 8  is a further enlarged cross-sectional view showing a part of FIG.  7 . 
       FIG. 9  is a flowchart for describing the washing process. 
       FIG. 10  is a time chart for describing the washing process. 
       FIG. 11  is a diagram showing the status of each cylinder, a washing mechanism, a water form roller and ink form rollers during washing process of a blanket cylinder. 
       FIG. 12  is a diagram showing the status of each cylinder, a washing mechanism, a water form roller and ink form rollers during a simultaneous washing process of a blanket cylinder, an impression cylinder and a plate cylinder. 
       FIG. 13  is a diagram showing the status of each cylinder, a washing mechanism, a water form roller and ink form rollers during a removal cycle of residual washing liquid from a plate. 
   

   DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS 
   The embodiments of this invention will be described below with reference to the accompanying drawings. 
     FIG. 4  shows the system layout of a sheet-fed offset two-sided printing press to which a washing device for an impression cylinder jacket according to an embodiment of the invention is applied. 
   The sheet-fed offset two-sided printing press shown in  FIG. 4  has a printing section  10  for making a specified printing on a sheet of paper P (hereinafter simply called “paper”) being transferred, a feeding section  70  for separating stacked paper P one by one and feeding it out to the printing section  10 , and a delivery section  80  for stacking printed paper transferred from printing section  10 . 
   Printing section  10  consists of plural printing units  11  through  18 . Printing units  11  through  14  are arranged on the upper side of the transfer passage for paper P and are suitable for printing the top face of paper P, while printing units  15  through  18  are arranged on the lower side of the transfer passage for paper P and are suitable for printing the bottom face of paper P. Printing units  11  and  15  use black (B) ink, printing units  12  and  16  use cyan (C) ink, printing units  13  and  17  use magenta (M) ink, and printing units  14  and  18  use yellow (Y) ink. As can be seen from the above, the printing press shown in  FIG. 4  describes a system layout of a sheet-fed offset two-sided 4/4 colors printing press on which a method of alternate printing both sides of paper without reversing paper. 
     FIG. 5  shows an example system arrangement of a printing unit  11 . The operation of printing unit  11  will be described below and descriptions for other printing units  12  through  18  are omitted because they are identical with printing unit  11 . 
   As shown in  FIG. 5 , printing unit  11  has a plate cylinder  21  on which a plate (not shown) is attached to, a blanket cylinder  22  for transferring ink of printing image on the plate attached to plate cylinder  21  to the paper, and an impression cylinder  23  that grips the paper with grippers (not shown) and presses the paper against blanket cylinder  22 . A rubber layer is arranged on the surface of blanket cylinder  22  to control a proper printing pressure. As shown in the drawing, blanket cylinder  22  is arranged as opposed to impression cylinder  23 , while plate cylinder  21  is arranged as opposed to blanket cylinder  22 . The paper is transferred one by one from the right hand side in the drawing, gripped by the grippers of impression cylinder  23 , and made to contact with blanket cylinder  22  under a pressure. 
     FIG. 6  shows an example structure of an impression cylinder  23 . As shown in  FIG. 6 , impression cylinder  23  consists of a impression cylinder member  24  and a jacket  25  set around impression cylinder member  24 . 
     FIG. 7  is a partially enlarged cross-sectional view schematically showing an example structure of jacket  25 , and  FIG. 8  is a further enlarged cross-sectional view showing a part of FIG.  7 . As shown in  FIG. 7 , jacket  25  has a flexible metal plate  26 , a base layer  27  having a surface of concave-convex profile formed on metal plate  26 , and a low surface energy resin layer  28  formed on base layer  27 . Base layer  27  consists of a hard metal thermal sprayed layer  27   a  formed by thermally spraying a metal, and a porous ceramic thermal sprayed layer  27   b  formed by thermally spraying a ceramic on metal thermal sprayed layer  27   a.  However, base layer  27  is not limited to said structure, but can be consisted of only metal thermal sprayed layer  27   a.    
   In manufacturing jacket  25 , metal thermal sprayed layer  27   a  is formed by thermally spraying, e.g., Ni—Cr, on the surface of a metal plate  26 , e.g., of stainless steel (SUS) plate, prepared by degreasing and shot-blasting it to produce a coarse surface, and then a ceramic thermal sprayed layer  27   b  is formed on top of it. A ceramic material such as gray alumina (G-Al 2 O 3 ) is normally used for forming ceramic thermal sprayed layer  27   b.  The surface of a ceramic thermal sprayed layer  27   b  thus formed is a coarse surface having a composition of short cyclic concaves and convexes with very sharp protrusions (pitch like concaves and convexes) and longer cyclic concaves and convexes (wavy concaves and convexes) as shown in the drawing, preferably with a surface roughness of approximately Rmax 30-50 μm. Ceramic thermal sprayed layer  27   b  is a porous layer preferably with a porosity of 5-20% having minute pores of diameters ranging from 0.1 μm to several ten μm. A low surface energy resin (separating compounds) of silicone-based resin and the like is coated by impregnation and dried to solidify on top of said ceramic thermal sprayed layer  27   b.  This forms a low surface energy resin layer  28  on the surface and in the pores of ceramic thermal sprayed layer  27   b  as shown in FIG.  7  and FIG.  8 . 
   Although low surface energy resin layer  28  covers essentially the whole surface of ceramic thermal sprayed layer  27   b,  the layer  28  is covered thicker in the wavy concave areas and thinner in the wavy convex areas. Consequently, the surface is smoother than when only ceramic thermal sprayed layer  27   b  is formed. The concave-convex profile formed in ceramic thermal sprayed layer  27   b  does not completely flattened out, rather said wavy concaves and convexes are generally maintained so that a coarse surface with a smooth concave-convex profile will be formed. It is preferably to have a typical final surface roughness of approximately Rmax 20-40 μm. It is preferable that the convex areas (convex parts in said waviness) in the final smooth concave-convex profile are preferable to be scattered evenly to appear once in every 0.2 mm×0.2 mm to 1 mm×1 mm squares. The convex area mentioned here is defined as a convex area having a peak higher than 70% of the highest protrusion measured by scanning two dimensionally a square area of 20 mm×20 mm. 
   When impression cylinder  23  mounted with a jacket  25  manufactured in such a way makes a contact with the paper as an object to be printed, the contact does not occur on the whole surface of jacket  25 ; rather it occurs only on the abovementioned smooth convexes, and there is hardly any transfer of the ink from the paper occurred thanks to the presence of low surface energy resin layer  28  on the surface of the jacket. 
   Washing device for the impression cylinder jacket applied on the printing press shown in  FIG. 4  will be described with reference to the system arrangement drawing of the printing unit shown in FIG.  5 . Washing device for the impression cylinder jacket according to this embodiment has a washing mechanism  30  including nonwoven fabric cloth  31  as a cleaning unit capable of arbitrarily contacting with and separating from blanket cylinder  22 , a water dampening unit  50  capably of supplying water to plate cylinder  21 , and an inking unit  60  capable of supply the ink to plate cylinder  21 . 
   Washing mechanism  30  has a rewinding shaft  32  for rewinding nonwoven fabric cloth  31 . Nonwoven fabric cloth  31  is rewinded by rewinding shaft  32  once in several seconds so that a new surface of the cloth always stands by against blanket cylinder  22 . Used nonwoven fabric cloth  31  will be replaced with a new one. Nonwoven fabric cloth  31  used in this embodiment is nonwoven fabric cloth, which is impregnated with the washing liquid (washing solvent and water) supplied during the washing process. Washing solvent or water is sprayed toward nonwoven fabric cloth  31  alternately from a nozzle mounted in head unit  33 . However, it can be also available nonwoven fabric cloth impregnated with the washing solvent in prior to the washing process. The washing mechanism according to the invention is not limited to the one that uses nonwoven fabric cloth, but rather it can be also available a washing mechanism with a brush to which the washing liquid (washing solvent and water) is supplied at the time of the washing process. 
   Water dampening unit  50  has a water form roller  51  capable of arbitrarily contacting with or separating from plate cylinder  21  and a water pan  52  for keeping the water to be supplied to water form roller  51 . Water dampening unit  50  shown in  FIG. 5  is just an example and the water dampening unit of this invention is not limited to it and various other water dampening system can be used. 
   Inking unit  60  has plural ink form rollers  61  capable of arbitrarily contacting with or separating from plate cylinder  21 . Inking unit  60  shown in  FIG. 5  is another example. 
   These mechanism, washing mechanism unit  30 , water dampening unit  50  and inking unit  60 , as abovementioned, are provided on a typical sheet-fed offset two-sided printing press with multicolor. 
   Washing device for the impression cylinder jacket according to this embodiment has a control unit  90  (see  FIG. 4 ) capable of executing an electrical sequence for causing cylinders  21  through  23  to rotate under contact for a definite period of time while maintaining plate cylinder  21  and blanket cylinder  22  as well as blanket cylinder  22  and impression cylinder  23  in contact with each other, and also nonwoven fabric cloth  31  of washing mechanism  30  and blanket cylinder  22  in contact with each other, and an electrical sequence for pressing a water form roller against the plate cylinder while supplying water to the plate cylinder and pressing ink form rollers against the plate cylinder as well so as to cause them to rotate under contact. 
   Next, the operation of the washing device for the impression cylinder jacket in the embodiment will be described with reference to FIG.  9  through FIG.  13 .  FIG. 9  shows a flowchart for describing the washing process and  FIG. 10  is a time chart for describing the washing process. 
   Washing process for the impression cylinder jacket is executed after the printing job is completed and the printing press is temporally stopped (each of cylinders  21  through  23  is separated from each other). At this point in time, the surfaces of plate cylinder  21  (plate), blanket cylinder  22 , and impression cylinder  23  (jacket  25 ) are covered with the ink related to the image patterns of the previous printing job. 
   After switching to a washing mode (S 1 ) by means of a switch (not shown), the machine (plate cylinder  21 , blanket cylinder  22 , and impression cylinder  23 ) is rotated at a specified slow speed (S 2 ; {circle around ( 1 )} of FIG.  10 ). Although the rotating speed is set to a definite fixed speed, e.g., 3500 rph, it can be arbitrarily adjusted. 
   Next, washing mechanism  30  is turned on (S 3 ; {circle around ( 2 )} of FIG.  10 ). In other words, nonwoven fabric cloth  31  of washing mechanism  30  is pressed against the surface of blanket cylinder  22  as shown in FIG.  11 . Also, washing solvent and water are supplied alternately to nonwoven fabric cloth  31  to impregnate it with them as shown in FIG.  10 . The switching interval time between the washing solvent (period shown by a solid line) and water (period shown by a dotted line) is, although exaggerated in  FIG. 10  for ease of view, preferably in terms several seconds and is arbitrarily adjustable. At this time, each of cylinders  21  through  23  is separated from each other and the washing is concentrated on only blanket cylinder  22 , which is most heavily attached with the ink related to the image patterns of the previous printing. The washing for blanket cylinder  22  only is executed for 30 seconds, for example, the execution time is arbitrarily adjustable. This process can remove most of the ink left on blanket cylinder  22 . 
   Next, the cylinder engagement is performed (S 4 ; {circle around ( 3 )} of FIG.  10 ). In other words, blanket cylinder  22  is pressed against plate cylinder  21  and impression cylinder  23  while the machine is running at a slow speed rotation as shown in FIG.  12 . At this time, washing mechanism  30  follows the movement of blanket cylinder  22 . Thus, the contact between washing mechanism  30  and blanket cylinder  22  is maintained, washing solvent and water are alternately supplied to nonwoven fabric cloth  31 , and the washing by washing mechanism  30  continues on. 
   A printing pressure applied between blanket cylinder  22  and impression cylinder  23  is indicated by the volume (distance) of relative movement of the two cylinders from the point when a sheet of paper having a certain thickness is placed between the two cylinders and the paper and the two cylinders are just contacting with each other with no pressure between them. The printing pressure is set up for each printing press as a fixed condition (value) and is normally set at 0.15 mm. Therefore, the distance between blanket cylinder  22  and impression cylinder  23  is adjusted depending on the thickness of the paper used to control a printing pressure of 0.15 mm. The thickness of the paper used can be set up as a printing pressure preset value. For example, if the printing pressure preset value is to be set up to be 0.05 mm, the distance between blanket cylinder  22  and impression cylinder  23  is adjusted so that the printing pressure will be 0.05 mm using a sheet of paper with a thickness of 0.05 mm. In this case, blanket cylinder  22  and impression cylinder  23  are moved closer 0.1 mm (=0.15 mm−0.05 mm) relative to each other from the condition that the two cylinders are contacting with zero pressure with having the paper between them. In this embodiment, the pressing condition between blanket cylinder  22  and impression cylinder  23  can be set, for example, arbitrarily between 0.05 and 0.10 mm. 
   This condition is held for a prescribed time (e.g., several minutes, which is adjustable arbitrarily). Consequently, the ink remaining on jacket  25  mounted on impression cylinder  23  will be softened by the washing liquid from blanket cylinder  22  and easily transferred back to blanket cylinder  22  and washed clean thanks to the contact rotation of blanket  22  and impression cylinder  23  leaving jacket clean. What is important here is that, although it takes a lot of time for the ink put on the impression cylinder to be completely transferred to the blanket cylinder in case of the impression cylinder used in the conventional printing press (impression cylinder having smooth roughness prepared by simply chromium plating the steel surface), the staining of the impression cylinder jacket can be easily transferred to the blanket cylinder and be washed clean quickly thanks to the repulsive nature of the low surface energy resin against ink and oil as the impression cylinder jacket coated with the low surface energy resin in case of the present invention. Moreover, since no slip occurs between the blanket cylinder and the impression cylinder, no abrasion occurs in the separating compounds on the surface of the jacket mounted on the impression cylinder. Since the nonwoven fabric cloth does not contact directly with jacket  25 , fibers from the nonwoven fabric cloth would not be left on jacket  25 , so that white dots defects in the next printing can be prevented. Moreover, the blanket cylinder and the impression cylinder can be simultaneously cleaned using only the blanket cylinder washing device by modifying the electrical sequence slightly on the conventional printing press without requiring a separate washing mechanism for the impression cylinder. 
   Furthermore, it is possible to remove paper dust easily as well as the ink on the jacket mounted on the impression cylinder by adopting a blanket washing mechanism equipped with a cleaning unit to which the washing solvent and water are supplied during the washing process. 
   This embodiment is constituted in such a way that all washing jobs for blanket cylinder  22  and impression cylinder  23  be completed simultaneously with the completion of the washing process for nonwoven fabric cloth  31  supplying water. This makes it possible to minimize the washing solvent remaining on the plate surface. 
   After washing blanket cylinder  22  and impression cylinder  23 , washing mechanism  30  is turned off (S 5 ; {circle around ( 4 )} of FIG.  10 ), and the cylinders are disengaged (S 6 ; {circle around ( 5 )} of FIG.  10 ). Moving blanket cylinder  22  away to separate each of cylinders  21  though  23  from each other is called “cylinder disengagement.” After the cylinder disengagement, the rotational speed of the machine (plate cylinder  21 , blanket cylinder  22 , and impression cylinder  23 ) is increased to a specified speed, e.g., 6500 rph. 
   Next, water form roller  51  is contacted with plate cylinder  21  (S 7 ; {circle around ( 6 )} of FIG.  10 ). In other words, water form roller  51  in water dampening unit  50  is pressed against the surface of plate cylinder  21  and water is supplied to plate cylinder  21  as shown in FIG.  3 . Water form roller  51  of water dampening unit  50  is rotated at a specified speed (water volume). 
   Ink form rollers  61  are contacted with plate cylinder  21  in several seconds after water form roller  51  is contacted with plate cylinder  21  (S 8 ; {circle around ( 7 )} of FIG.  10 ). In other words, ink form rollers  61  of inking unit  60  are pressed against the surface of plate cylinder  21  as shown in FIG.  13 . As a result, the residual washing solvent put on the surface of the plate mounted on the plate cylinder via the blanket cylinder during the washing of the blanket cylinder and the impression cylinder is absorbed by and transferred to the ink form rollers. 
   In the present embodiment, even if the cylinder engagement mechanism system is constituted in such a way that blanket cylinder  22  first contacts with plate cylinder  21  and then with impression cylinder  23 , the washing liquid which is transferred to the plate via the blanket cylinder causes separation of the residual washing solvent put on the plate comes up on the water as the water is supplied to the plate in step S 7  after the simultaneous washing of the blanket cylinder and the impression cylinder, so that the residual washing liquid can be easily absorbed by the ink form rollers by causing the ink form rollers to contact with the plate. Thus, the sensitization of the plate surface can be prevented. Moreover, since this prevents the residual washing liquid from being transferred to water form roller  51  by transferring the residual washing liquid to ink form rollers  61 , there will not be caused the bad influence to the downstream printing job. 
   After achieving the process of removing the washing liquid remaining on the plate by contacting water form roller  51  and ink form rollers  61  with plate cylinder  21  for 30 seconds (arbitrarily adjustable), water form roller  51  and ink form rollers  61  are separated from plate cylinder  21 . In other words, water form roller  51  and ink form rollers  61  are separated from the surface of plate cylinder  21  (S 9 ; {circle around ( 8 )} of FIG.  10 ). 
   When the removal of the residual washing liquid from the plate surface is finished, the machine (each of cylinders  21  through  23 ) is run continuously for, e.g., 30 seconds (arbitrarily adjustable), and then will be stopped (S 10 ; {circle around ( 9 )} of FIG.  10 ). This terminates the washing mode, ending the washing process for the impression cylinder jacket. Rotating each of cylinders  21  through  23  after the cylinder disengagement causes blanket cylinder  22  and impression cylinder  23  to dry up. 
   Next, an example will be described. 
   An impression cylinder jacket with a surface roughness of approximately Rmax 35 μm was prepared by thermally spraying Ni—Cr on a stainless steel (SUS) plate of a thickness of 0.3 mm to a coating thickness of 30 μm, then thermally spraying ceramics (G-Al 2 O 3 ) up to a coating thickness of 40 μm to make the total plate thickness of 0.37 mm, and then finally coating with a silicone-based separating compounds. This impression cylinder jacket was installed on a sheet-fed offset two-sided printing press (40″ format Two-sided 4/4 colors Printing Press Model Lithrone 440SP by Komori Corporation). 
   Two-sided 4 colors (black, cyan, magenta and yellow) printing was conducted on coated paper using this printing press. Although staining of the impression cylinder jacket was not almost appeared in the early stage of the printing, a certain amount of ink transferred from the paper was appeared on the jacket surface after printing approximately 10000 sheets of paper. 
   The prior practice has been to wash the blanket after printing approximately 10000 sheets of paper with washing mechanism for a blanket cylinder (a type of pressing nonwoven fabric cloth impregnated with washing liquid against the blanket cylinder jacket) and to wash the impression cylinder jacket with washing mechanism for an impression cylinder (a type of pressing nonwoven fabric cloth impregnated with washing liquid against the impression cylinder). In this case, the fibers left on the jacket were washed out from the jacket by hand as the finishing process. 
   In an embodiment of the invention, after printing 10000 sheets of paper, the machine (each of cylinders) was rotated at a slow speed (constant 3500 rph) with the washing mechanism turned on to wash only the blanket cylinder to begin with. The nonwoven fabric cloth of the washing mechanism was impregnated with washing solvent and water alternately every two seconds during the washing process. The cylinders were engaged (rotating the blanket cylinder while in contact with the plate cylinder and the impression cylinder) 30 seconds after turning on the washing mechanism. The preset value of the printing pressure between the blanket cylinder and the impression cylinder was 0.05 mm (the condition with both cylinders pushed in 0.1 mm). During the cylinder engagement, the contact between washing mechanism  30  and blanket cylinder  22  was maintained. While the nonwoven fabric cloth is pressed against the blanket cylinder, the plate cylinder, blanket cylinder and the impression cylinder were rotated under contact for 120 seconds to wash the blanket cylinder, the impression cylinder and the plate cylinder together. 
   After the washing of the blanket cylinder and the impression cylinder, the washing mechanism was turned off, disengaged the cylinders and raised the speed of the machine to a constant speed of 6500 rph. 
   Next, the water form roller was contacted with the plate cylinder, followed by the contact of the ink form rollers with the plate cylinder three seconds later, to cause the residual washing liquid on the plate surface to transfer to the ink form rollers. The removal of the residual washing liquid on the plate surface was done for 30 seconds after contacting the water form roller with the plate cylinder. 
   When the water form roller and the ink form rollers were then separated from the plate cylinder, which is followed by an additional 30 seconds of rotating the machine (each of cylinders), and stopping of the machine, an inspection of the plate cylinder, the blanket cylinder and the impression cylinder was conducted, which revealed that the surfaces of not only the blanket cylinder but also the jacket on the impression cylinder were completely removed of the ink. Moreover, no fibers were found on the jacket which are inevitable when it is washed with the nonwoven fabric cloth directly pressed against it, and furthermore paper dust was cleaned as well as a result of water supplied to the jacket because paper dust easily dissolves to water, thus proving that washing device for the impression cylinder jacket of the present invention provides an excellent effect. After washing the blanket cylinder and the impression cylinder and separating the blanket cylinder from the plated cylinder and the impression cylinder, the water form roller and the ink form rollers were rotated while being pressed against the plate cylinder, so that the residual washing liquid on the plate surface as a consequence of washing for the blanket cylinder was absorbed and removed, thus eliminating the possibility of sensitization of the plate surface by the washing liquid from the blanket cylinder and allowing the machine to continue printing jobs without interruption. 
   The washing device for the impression cylinder jacket based on the contact rotation of the blanket cylinder and the impression cylinder using only washing mechanism for the blanket cylinder is a technology disclosed by said Unexamined Publication No. JP-A-8-12151, also a proven technology by many actual usage examples, and it is know to extend the impression cylinder jackets&#39; life time approximately two fold compared to a case of manual washing. On the other hand, when the washing device for the impression cylinder jacket of a type wherein either nonwoven fabric cloth or a brush roll is pressed directly against the impression cylinder jacket is used, the impression cylinder jacket&#39;s life time is reported to be shortened to approximately one half of that of manual washing. As can be seen from the above, the washing device for the impression cylinder jacket disclosed by said publication is an excellent device, it has a limitation that it can be applied only to those sheet-fed offset two-sided printing presses with a cylinder engagement mechanism system wherein the blanket cylinder makes a contact with the impression cylinder first, and then with a plate cylinder. 
   In other words, as already described, the washing device for the impression cylinder jacket disclosed by said publication cannot be used on a printing press with a cylinder engagement mechanism system in which the blanket cylinder inevitably comes to contact with both the plate cylinder and the impression cylinder simultaneously when the blanket cylinder is brought to contact with the impression cylinder for the purpose of washing, because trying to wash using only the washing mechanism that has the cleaning unit for the blanket cylinder while the blanket cylinder is in contact with the impression cylinder, the washing liquid moves from the blanket cylinder to the plate cylinder and causes sensitization of the plate surface. The invention solved said problem that the plate cylinder essentially needs to be separated from the blanker cylinder after the washing in order to avoid its contact with the washing liquid, by first washing the blanket cylinder and the impression cylinder together with the blanket cylinder contacting the plate cylinder and then adding a new process of separating the blanket cylinder from the plate cylinder after the simultaneous washing of the blanket cylinder and the impression cylinder and pressing the water form roller against the plate cylinder to supply water to the plate cylinder while also pressing the ink form rollers against the plate cylinder. This made it possible to prevent the sensitization of the plate surface by allowing the ink form rollers to adsorb the washing liquid put on the plate surface via the blanket cylinder during the washing of the blanket cylinder and the impression cylinder. Consequently, an effect identical to the effect of the abovementioned washing device for the impression cylinder jacket disclosed by said publication can be extended to almost all sheet-fed offset two-sided printing presses and the effect of the invention is quite substantial. 
   It is obvious that this invention is not limited to the particular embodiments shown and described above but may be variously changed and modified without departing from the technical concept of this invention. 
   For example, although the abovementioned embodiment is described assuming a case where the washing device for the impression cylinder jacket of the invention is applied to a sheet-fed offset two-sided printing press designed for printing both sides of paper without reversing paper, it goes without saying that the invention can be applied to a press where the paper is reversed in the middle of the process. 
   Also, it is possible to use nonwoven fabric cloth impregnated with the washing liquid (washing solvent) prior to the washing process in the washing mechanism. In such a case, it is preferable to exchange the order of the executions of step S 7  and step S 8  in the flowchart of FIG.  9 . In other words, since a relatively large amount of washing solvent is remaining on the plate surface at the time when the cylinder disengagement process of step S 6  is done, the ink form rollers is contacted with the plate cylinder first to cause the ink form rollers to adsorb some of the washing solvent and then, after a specified period of time (e.g., 5 seconds), the water form roller is connected with the plate cylinder. By taking such a procedure, it is possible to prevent the washing solvent supplied during the washing for the blanket cylinder from reaching the water form roller. 
   This application is based on Japanese Patent Application No. 2003-46177 filed on Feb. 24, 2003, the contents of which are hereby incorporated by reference.