Abstract:
Apparatus for applying a liquid medium such as a printing medium to a rotatable cylinder is disclosed including a chambered doctor blade with an elongated frame, a pair of doctor blades in wiping engagement with the surface of the rotatable cylinder, a seal disposed axially with respect to the cylinder including first and second seals, with the elongated frame, the doctor blades, the seal and the surface of the cylinder forming an elongated chamber containing the liquid medium, and at least one drainage channel including an inlet in the space between the two seals for diverting leaking medium from the space. Also disclosed is such apparatus which includes at least one spray nozzle within the elongated chamber for cleaning the chamber, the nozzle being movable between a number of outlet directions. A method for sealing the chambered doctor blade is also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device in a chambered doctor blade for use in a printing unit. The present invention also relates to a method for end sealing a chambered doctor blade. 
       BACKGROUND OF THE INVENTION 
       [0002]    A chambered doctor blade is preferably used as a device for inking a screen roller in a flexoprinting unit. 
         [0003]    A modern chambered doctor blade generally comprises an elongated frame which, along both of its parallel long sides holds a doctor blade parallel to the long side, and at its ends contains an arrangement functioning as an end seal. 
         [0004]    The doctor blades are, as seen in cross section arranged so that their free longitudinal shanks incline inwardly against each other, at a certain distance from each other, so that when the frame of the chamber is arranged parallel to the axis of the screen roller and is moved towards the roller, both of the doctor blades will rest against the envelope surface of the screen roller along its entire length. 
         [0005]    The doctor blades are generally longer than the envelope surface of the screen roller, such that they extend slightly outside of the envelope surface on both sides thereof. 
         [0006]    In this manner, the frame of the chambered doctor blade forms, along with its parallel fixed doctor blades, an elongated chamber against the envelope surface of the screen roller. The chamber is parallel to the axis of the screen roller and is delimited at its ends by an end seal of compressible material, or by a construction which provides a similar function, and which fills and seals the cross section of the elongated chamber at the ends of the chamber. The end seal arrangement consequently seals internally against the frame of the chamber and its doctor blades and against the envelope surface of the screen roller between the doctor blades. An end seal may typically require a length of 10 to 30 mm of the envelope surface. 
         [0007]    When the chambered doctor blade bears upon the surface of the rotating screen roller and is entirely or partially filled with printing ink, the envelope surface of the screen roller is continuously supplied with fresh ink through the opening, which is defined by doctor blades and end seals. 
         [0008]    The doctor blades are constituted by a thin band-shaped resilient material, for example, spring steel or plastic. The doctor blades often have an angle of application against the envelope surface of the screen roller of approximately 35 degrees counting from the outside of the doctor blades against the tangent of the roller at the contact point. 
         [0009]    When the chamber is pressed against the roller the doctor blades will thus be resiliently pressed inwardly against the chamber, whereby the end seals have to be elastically deformable and follow the movements of the doctor blade, in order to not loose its sealing ability. 
         [0010]    End seals are often built up of molded or form died materials, which may be thin, flexible, simple or multiple layered or thicker, or foamed with gas in order to provide resilient properties to the material. Fibrous materials are also used in a portion of the entire end seal, and the material may be impregnated with solvents. 
         [0011]    Most end seals leak. Certain end seals may be completely tight as long as they are new and soaked with solvent and sealing agent, but generally start to leak after a certain period of operation of the printing unit. Many printing offices experience this leakage as disturbing, as it gives rise to loss of ink and unnecessary cleaning of details in the printing unit. 
         [0012]    The leaking flow of ink is often small, but it is hard to deal with, precisely because of the flow being so small. The ink often manages to dry in the collecting device, which may be constituted by an end housing or a groove, before the ink is somehow lead further back to the ink vessel in the printing unit. The ink may also easily be soiled by dust particles in the air on its way to the ink vessel, making it unusable for further use as a printing ink. 
         [0013]    Thin solvent drying inks have, among other things, the characterising property of drying when subjected to blowing air. 
         [0014]    In a printing unit air currents often occur from rotating rollers and running webs. At the ends of the screen roller an air current occurs which is generated by the end cover of the rotating roller, which centrifuges the air closest to this surface. New air is supplied from the roll neck. 
         [0015]    A chambered doctor blade is generally somewhat longer than the screen roller being inked by same. The chambered doctor blade generally has its end seals placed close to the ends of the roller. Therefore, the end seals are subjected to a continuous air current, which entirely or partially dries the leaking ink immediately outside the end seals. 
         [0016]    If dried up ink is successively built up outside of the end seals, there is a considerable risk that their function will successively deteriorate, so that the end seals start to release ink over the ends of the screen roller. This then results in this ink being centrifuged/thrown out of the ink unit, with accompanying negative consequences in the form of ink loss and splashing of the printing unit with expensive ink. 
         [0017]    Each time the printing ink in a printing unit is to be changed to a new ink, in order to carry out a new printing task, all of the surfaces inked from the first ink must be cleaned. A change of ink made from a darker to a lighter ink is expressed as a “critical” change of ink. By this it is meant that even a small amount of ink of the first ink easily contaminates the other ink, such that it is no longer possible to print the shade of color which is intended to be printed. In this manner, the quality of the finished print is affected in a negative way or in a totally devastating way. If the ink is too contaminated by the first ink, and this is not established until the new printing task is running, the second ink must generally be changed by a fresh new ink, with accompanying costs in the form of loss of ink and loss of production time in the printing unit. 
         [0018]    In modern printing units, utilizing printing smaller editions with many changes of ink per day, some kind of automatic washing system must be provided in order to simplify and shorten each change of ink. 
         [0019]    A variant is to use spray nozzles. Regarding spray nozzles, there are a great number of arrangements of the like used in chambered doctor blades for automatic cleaning. The spray nozzles are fixedly mounted and immobile and often of the flat jet type. Spray nozzles of the cone type, filled or hollow, also exist. Due to the elongated, narrow space, bound by the frame of the chamber, its doctors and the surface of the screen roller between the doctor blades, which need to be rinsed out/cleaned, a greater amount of spray nozzles need to be mounted. 
         [0020]    Printing ink ending up outside of end seals and doctor blades, or on the outside thereof, is very hard to reach with fully automatic or semiautomatic cleaning systems which operate when the chambered doctor blade is in its operating position against the screen roller in the printing unit. The more ink ending up outside the chambered doctor blade, and the more dried up this ink is, the more extensive the manual cleaning needs to be made in order to facilitate a critical change of ink. Ink ending up on surfaces normally not subjected to printing ink may of course be allowed to remain, if only this ink will not contaminate upcoming inks. Such ink may instead be removed by more extensive cleaning operations. 
         [0021]    One object of the present invention is to minimize manual cleaning of a chambered doctor blade in a flexoprinting unit. 
         [0022]    Another object of the present invention is to substantially eliminate the above mentioned end sealing problems of a chambered doctor blade. 
       SUMMARY OF THE INVENTION 
       [0023]    These and other objects have now been realized by the discovery of apparatus for applying a liquid medium to a rotatable cylinder comprising a chambered doctor blade including an elongated frame disposed parallel to the outer surface of the rotatable cylinder, a pair of doctor blades operatively arranged parallel to the rotatable cylinder and parallel to and separated from each other for wiping engagement with the surface of the rotatable cylinder, sealing means disposed axially with respect to the rotatable cylinder and comprising a first sealing member and a second sealing member spaced apart from the first sealing member to form a space therebetween, the elongated frame, the pair of doctor blades, the sealing means, and the surface of the rotatable cylinder forming an elongated chamber containing the liquid medium for application to the surface of the rotatable cylinder, and at least one drainage channel including an inlet disposed in the space between the first and second sealing members for diverting leaking liquid medium from the space. Preferably, the liquid medium is a liquid such as an ink, such as a printing ink, lacquer, adhesives, or the like. 
         [0024]    In accordance with one embodiment of the apparatus of the present invention, the inlet of the at least one drainage channel is disposed in a lower portion of the elongated frame. 
         [0025]    In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a pump connected to the at least one drainage channel for pumping out the liquid medium. 
         [0026]    In accordance with another embodiment of the apparatus of the present invention, the at least one drainage channel diverts the liquid medium into a tank. 
         [0027]    In accordance with another embodiment of the apparatus of the present invention, the apparatus includes at least one spray nozzle disposed above the inlet of the at least one drainage channel for intermittently supplying solvent thereto for maintaining drainage and preventing drying of the liquid medium. Preferably, the at least one spray nozzle is disposed for cleaning the elongated chamber. In another embodiment, the at least one spray nozzle is movable between a plurality of outlet directions. In yet another embodiment, the at least one spray nozzle is rotatable about its axis. 
         [0028]    In accordance with another embodiment of the apparatus of the present invention, the sealing means comprises first sealing means, and the apparatus includes second sealing means including a third sealing member and a fourth sealing member spaced apart from the third sealing member for forming a second space therebetween. 
         [0029]    In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a plurality of the sealing means provided in the axial direction of the rotatable cylinder. 
         [0030]    In accordance with the present invention, these and other objects have also been realized by the discovery of apparatus for supplying a liquid medium to a rotatable cylinder comprising a chambered doctor blade including an elongated frame disposed parallel to the outer surface of the rotatable cylinder, a pair of doctor blades operably arranged parallel to the rotatable cylinder and parallel to and separated from each other for wiping engagement with the rotatable cylinder, sealing means disposed axially with respect to the rotatable cylinder, the elongated frame, the pair of doctor blades, the sealing means, and the surface of the rotatable cylinder defining an elongated chamber containing the liquid medium for application to the surface of the rotatable cylinder, and at least one spray nozzle disposed within the elongated chamber for cleaning the elongated chamber, the at least one spray nozzle being movable between a plurality of outlet directions. Preferably, the at least one spray nozzle is rotatable about its axis. 
         [0031]    In accordance with one embodiment of the apparatus of the present invention, the sealing means comprises a first sealing member and a second sealing member spaced apart from the first sealing member to form a space therebetween. Preferably, the apparatus includes at least one drainage channel including an inlet disposed in the space between the first and second sealing members for diverting leaking liquid medium from the space. In a preferred embodiment, the inlet of the at least one drainage channel is disposed in a lower portion of the elongated frame. In another embodiment, the apparatus includes a pump connected to the at least one drainage channel for pumping out the liquid medium. In the preferred embodiment, the at least one drainage channel diverts the liquid medium into a tank. 
         [0032]    In accordance with another embodiment of the apparatus of the present invention, the at least one spray nozzle is disposed above the inlet of the at least one drainage channel for supplying solvent into the elongated space for maintaining drainage and preventing drying of the liquid medium. 
         [0033]    In accordance with another embodiment of the apparatus of the present invention, the sealing means comprises first sealing means, and including second sealing means including a third sealing member and a fourth sealing member spaced apart from the third sealing member to form a second space therebetween. 
         [0034]    In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a plurality of the sealing means provided in the axial direction of the rotatable cylinder. 
         [0035]    In accordance with the present invention, a method has also been provided for sealing a chambered doctor blade for use in applying a liquid medium to a rotatable cylinder wherein the chambered doctor blade includes an elongated frame disposed parallel to the outer surface of the rotatable cylinder, a pair of doctor blades operatively arranged parallel to the rotatable cylinder and parallel to and separated from each other for wiping engagement with the rotatable cylinder, and wherein the elongated frame, the pair of doctor blades, the sealing means, and the surface of the rotatable cylinder define an elongated chamber containing the liquid medium for application to the rotatable cylinder, the method comprising draining the liquid medium from the elongated chamber through the sealing means. In a preferred embodiment, the method includes intermittently supplying solvent into the elongated chamber for preventing drying of the liquid medium and/or dissolving dried liquid medium. 
         [0036]    In accordance with one embodiment of the method of the present invention, the method includes pumping liquid medium from the elongated chamber. 
         [0037]    In accordance with another embodiment of the method of the present invention, the method includes diverting the liquid medium to a tank. 
         [0038]    These and other objects, apparent from the following description, are achieved by a device in a chambered doctor blade, and a method for sealing a chambered doctor blade. 
         [0039]    The device according to the present invention is characterised by sealing means comprising a first and a second part forming a space therebetween extending in the axial direction of the cylinder in which an inlet of at least one drainage channel is provided for diverting leaking medium from the space, and several inconveniences with prior art are now overcome. The drainage channel results in the ink being diverted through the closed channel such that the risk of ink or the like accumulating outside of the first sealing part is substantially reduced. The double end seal arrangement hereof results in the advantage that the first sealing part and its leaking ink is protected against undesired air currents, such that the risk of the ink drying is reduced. An additional advantage is that it becomes easier to take care of the leaking flow of ink as the ink does not manage to dry, for example, before it manages to leak back to the ink vessel in the printing unit. An additional advantage is that on its way to the ink vessel the ink is not soiled by dust particles in the air which would make it unusable for further use as a printing ink. The drainage channel consequently results in substantially improved sealing and reduces the need for manual cleaning. 
         [0040]    Preferably, the device of the present invention has the further advantage of the inlet of the drainage channel being arranged at the bottom of the chambered doctor blade so that the medium may flow gravimetrically through the closed channel. 
         [0041]    Preferably, the device of the present invention has the advantage, with a pumping device being connected to the drainage channel for pumping away leaking medium through any of the sealing parts that the medium may then be led to a desired location, independent of its spatial position, such as to the ink vessel in the printing unit or the like. 
         [0042]    Preferably, the device of the present invention has the further advantage, with the at least one drainage channel debouching into a tank for taking care of a diverted medium, that the medium may then be reused such that loss of ink is substantially eliminated. 
         [0043]    Preferably, the device of the present invention has the further advantage, with a spray nozzle for supplying solvent or the like above the inlet of the drainage channel, that it is thus guaranteed that no leaking ink is dried and that the ink is diluted and thereby becomes more thinly liquid and may more easily flow through the drainage channel. An additional advantage is that the spray nozzles may be used for effectively rinsing the space between the first and second seals during cleaning of the chamber in the printing unit. The portion of the screen roller running between the first and second seals is also intended to be rinsed/washed by solvent from these spray nozzles. 
         [0044]    Preferably, the device of the present invention has the advantage, with arranging at least one spray nozzle for cleaning of chamber, that unnecessary cleaning of details in the printing unit is minimized. An additional advantage is that manual cleaning by changing the ink is minimized. 
         [0045]    Preferably, the device of the present invention has the further advantage, with a spray nozzle being movable with varying outlet directions, that such a spray nozzle sprays a much larger area or a much larger section of the chambered doctor blade, whereby a considerably lower number of spray nozzles may be used with the same effect as several immobile spray nozzles. Less spray nozzles means less details to maintain, simpler installation with fewer holes in the frame of the chamber, and less hoses to draw and connect to a second pump supplying these with washing liquid. 
         [0046]    Preferably, the device of the present invention has the further advantage that the roller may be inked with several ink colors at the same time. This is facilitated since the sealing means according to the present invention is completely tight. 
         [0047]    Preferably, the device of the present invention has the further advantage that the roller may be provided with inking of different widths. This is facilitated since the sealing means according to the present invention is completely tight. 
         [0048]    As the device according to the present invention comprises spray nozzles which are movable with varying outlet directions, such a spray nozzle thus sprays a much larger area or a much larger section of the chambered doctor blade, whereby a considerably lower number of spray nozzles may be used with the same effect as several immobile spray nozzles. Less spray nozzles means less details to maintain, simpler installation with fewer holes in the frame of the chamber and less hoses to draw and connect to a second pump supplying them with washing liquid. Consequently the need for manual cleaning is reduced. 
         [0049]    Preferably, the device of the present invention has the further advantage that the first sealing part and its leaking ink are protected against undesired air currents, such that the risk of the ink drying is reduced. 
         [0050]    Preferably, the device of the present invention has the further comprises apparatus such that the drainage channel results in the ink being diverted through the closed channel, such that the risk of ink or the like accumulating outside of the first sealing part is substantially reduced. An additional advantage is that it becomes easier to take care of the leaking flow of ink as the ink does not manage to dry, for example, before it manages to be led back to the ink vessel in the printing unit. An additional advantage is that the ink, on its way to the ink vessel, is not soiled by dust particles in the air, which makes it unusable for further use as a printing ink. The drainage channel consequently results in a substantially improved sealing and reduces the need for manual cleaning. 
         [0051]    Preferably, the device of the present invention has the further advantage that the ink or the like may flow gravimetrically through the closed channel. 
         [0052]    Preferably, the device of the present invention has the further advantage that the ink or the like may be led to a desired location, independent of spatial position, such as to the ink vessel in the printing unit or the like. 
         [0053]    Preferably, the device of the present invention has the further advantage that the ink or the like then may be reused, such that loss of ink is substantially eliminated. 
         [0054]    Preferably, the device of the present invention has the advantage that it is guaranteed that no leaking ink is dried and that the ink is diluted and thereby becomes more thinly liquid and may more easily flow through the drainage channel. An additional advantage is that the spray nozzles may be used to effectively rinse the space between the first and second seals, during cleaning of the chamber in the printing unit. The portion of the screen roller running between the first and second seals is also intended to be rinsed/washed by solvent from these spray nozzles. 
         [0055]    Preferably, the device of the present invention has the further advantage that the roller may be inked with several ink colors at the same time. This is facilitated since the sealing means according to the present invention is completely tight. 
         [0056]    Preferably, the device of the present invention has the further advantage that the roller may be provided with inking of different widths. This is facilitated since the sealing means according to the invention is completely tight. 
         [0057]    By means of the method according to the present invention in which drainage of leaking ink through the first sealing and through a closed drainage channel having its inlet between a second and a first part of a sealing means, the risk of ink or the like accumulating outside of the first sealing part is substantially reduced. An additional advantage is that it becomes easier to take care of the leaking flow of ink as the ink does not manage to dry, for example, before it manages to be led back to the ink vessel in the printing unit. An additional advantage is that the ink, on its way to the ink vessel, is not soiled by dust particles in the air which makes it unusable for further use as a printing ink. The drainage channel consequently results in a substantially improved sealing and reduces the need for manual cleaning. 
         [0058]    Preferably, the device of the present invention has the further advantage that it is guaranteed that no leaking ink is dried and that the ink is diluted and thereby becomes more thinly liquid and may more easily flow through the drainage channel. An additional advantage is that the space between the first and second seals is also cleaned. 
         [0059]    Preferably, the device of the present invention has the further advantage that the ink may be led to a desired location, independent of its spatial position, such as to the ink vessel in the printing unit or the like. 
         [0060]    Preferably, the device of the present invention has the further advantage that the ink or the like then may be reused such that loss of ink is substantially eliminated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]    A better understanding of the present invention will be had with reference to the following detailed description when read in conjunction with the accompanying drawings, wherein like reference characters refer to like parts throughout the several views, and in which: 
           [0062]      FIG. 1   a  is a side, perspective, exploded view of a sealing arrangement according to a preferred embodiment of the present invention; 
           [0063]      FIG. 1   b  is a side, elevational view of the sealing arrangement shown in  FIG. 1   a;    
           [0064]      FIG. 1   c  is a side, perspective view of the sealing arrangement shown in  FIG. 1   a , in an assembled state; 
           [0065]      FIG. 2  is a side, partially schematic view of a chambered doctor blade according to a preferred embodiment of the present invention; 
           [0066]      FIG. 3  is a side, perspective view of the chambered doctor blade shown in  FIG. 2 , viewed from the side of the roller; 
           [0067]      FIG. 4   a  is a top, partial, elevational view of a portion of the chambered doctor blade shown in  FIG. 2 , viewed obliquely from above; 
           [0068]      FIG. 4   b  is a bottom, elevational view of the chambered doctor blade shown in  FIG. 2 , viewed obliquely from below; 
           [0069]      FIG. 5  is a side, partly exploded, perspective view of the chambered doctor blade shown in  FIG. 2 , viewed from the side opposite the roller; 
           [0070]      FIG. 6  is a side, perspective view of the chambered doctor blade shown in  FIG. 2 , viewed from the side opposite the roller; 
           [0071]      FIG. 7   a  is a side, perspective view  6   f  a spray nozzle for supplying of liquid between the sealing parts of the sealing means of the present invention; 
           [0072]      FIG. 7   b  is a side perspective view of the spray nozzle shown in  FIG. 7   a;    
           [0073]      FIG. 8   a  is a front plane view of a rotating spray nozzle for cleaning of chamber of the present invention; 
           [0074]      FIG. 8   b  is a side, elevational, cross-sectional view of the spray nozzle shown in  FIG. 8   a;    
           [0075]      FIG. 8   c  is a side, elevational, cross-sectional exploded view of the spray nozzle shown in  FIG. 8   a;    
           [0076]      FIG. 8   d  is a side, perspective, exploded view of the nozzle shown in  FIG. 8   a ; and 
           [0077]      FIG. 8   e  is a side, perspective view of the spray nozzle shown in  FIG. 8   a.    
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0078]    Referring to the figures,  FIGS. 1   a - 1   c  show sealing arrangement  1  according to a preferred embodiment of the present invention. The sealing arrangement  1  comprises holding means  10  and sealing means  20 , which means comprises a first sealing plate  21  and a second sealing plate  22 . The holding means  10  comprises first and second holding elements,  11  and  12 , and a spreader  13 , which are held together by tightening means,  14   a ,  14   b ,  15   a , and  15   b , which preferably consist of nuts,  14   a  and  14   b , and screws,  15   a  and  15   b . The spreader  13  of the holding means  10  includes third and fourth holding elements,  16  and  17 , which are mutually parallel and connected at a distance from each other in such a way that a space is formed therebetween. 
         [0079]    The sealing arrangement  1  is intended for sealing printing units with a chambered doctor blade device  30 , which is shown in  FIGS. 2-6 . As can be seen in  FIGS. 4   a  and  4   b  the sealing arrangement  1  is placed at the end of an elongated chambered doctor blade  30 , which is arranged in a printing unit including rotatable roller  31  such that its longitudinal axis is parallel to the longitudinal axis of the roller. The chambered doctor blade  20  includes an elongated frame  32 , having a substantially U-shaped cross section, with outwardly projecting flanges,  33  and  34 , at which two elongated doctor blades,  35  and  36 , are mounted by means of holding means,  37  and  38 . The frame  32  and the doctor blades,  35  and  36 , define a chamber  40  having a primarily trapezoidal cross section, and having a primarily trapezoidal opening at each end. The sealing arrangement  1  is intended to be mounted on the chambered doctor blade  30  at the respective opening in order to sealingly close same. The chamber  40 , which may contain liquid, such as ink, lack or glue, further has a substantially rectangular opening, which is partly delimited by the doctor blades,  35  and  36 . In either its operating or active position the chambered doctor blade  30  is fixed to the roller  31 , the elongated substantially rectangular opening facing the envelope surface of the roller for applying, for example, ink on the envelope surface. 
         [0080]    The holding elements,  11 ,  12 ,  16 , and  17 , are substantially trapezoidal. Between the third and fourth holding elements,  16  and  17 , of the respective spreader  13  fasteners,  18  and  19 , are arranged in the end, connecting the holding elements,  16  and  17 , which fastener is intended to be fastened to the chambered doctor blade  30  substantially opposite the rectangular opening of the chamber  30 . The fastener preferably consists of a screw and a nut. 
         [0081]    As can be seen in  FIGS. 1   b  and  1   c  the sealing plates,  21  and  22 , outside of the holding means  10 , have extending portions,  21 ′ and  22 ′, intended to be sealingly fixed against the inner side of the surrounding frame  32  chambered doctor blade  30 , the doctor blade holders,  37  and  38 , the doctor blades,  35  and  36 , and the envelope surface of the roller between the doctor blades. 
         [0082]    The sealing plates,  21  and  22 , are preferably formed in a foamed polymer material, such as polyethylene, and are each preferably approximately 5-10 mm thick. 
         [0083]    Further, the sealing plates,  21  and  22 , in the disclosed method are substantially trapezoidal, having two opposite long sides or bases and two opposite oblique, none parallel sides, and having a circumferential edge divided into six edge portions,  23 ,  24 ,  25 ,  26 ,  27 , and  28 , which is apparent from  FIG. 1   b . The first edge portion  23  is U-shaped and includes the shorter base or long side of the trapezoid, both of its non-parallel sides, and is arranged to seal against the inside of the frame  32  of the chambered doctor blade  30 . The sealing plates,  21  and  22 , have an second opposite curve-shaped edge  24 , which, in the operating position of the chambered doctor blade, is arranged to bear against the roller  31 . Further, the third and fourth edge portions,  25  and  26 , of the sealing plates,  21  and  22 , corresponding to the chamfered corners of the plates, arranged to seal against each of the doctor blades  35  and  36 , farthest away from the roller lying portion thereof. The fifth and sixth edge portions,  27  and  28 , of the sealing plates,  21  and  22 , are intended to seal against the second portion of the part of each holding means,  37  and  38 , bearing against the inside of the chambered doctor blade  30  and outwardly projecting flange,  33  and  34 , respectively. The respective sealing plates,  21  and  22 , are provided with two holes for the screws. 
         [0084]    As can be seen from  FIGS. 2-6 , through the first sealing plate  21 , leaking ink is arranged to be led away through a hose connected channel  50 , the inlet  51  located at the bottom of the chambered doctor blade  30 , between the first and second sealing plates,  21  and  22 , at the respective ends of the chambered doctor blade  30 . The ink or the like may, depending on its viscosity, either flow gravimetrically through the hose or be pumped away with a small pump placed, for example, in connection with the end/ends of the chambered doctor blade  30 . 
         [0085]    In order to guarantee drainage of the leaking ink, the chamber  30  is, as also may be seen in  FIGS. 2-6 , also provided at the respective ends with connecting means  53  for supplying liquid to a spray nozzle  54  which is placed above the inlet  51  of the channel  50  for drainage of the ink or the like. It is intended to intermittently spray solvent through the spray nozzle into the space, between the first and second sealing plates,  21  and  22 , in order to guarantee that no leaking ink or the like dries and the ink is diluted and thereby becomes more thinly liquid and may more easily flow through the drainage channel  50 . 
         [0086]    The first sealing plate  21  is arranged, when mounted to the opening of the chambered doctor blade  30 , to face inwardly towards the chamber  40  containing, for example, ink. Normally the second sealing plate  22  is arranged to when mounted at the opening of the chamber to be placed right at the end of the screen roller  31 . The sealing means  20  according to the present invention, due to bringing about a completely tight sealing of the chamber  40 , in an alternative embodiment results in respective sealing means  20  being placed at an arbitrary distance into the trapezoidal opening of the chambered doctor blade  30 . Further, printing with multiple ink colors abreast in one and the same printing unit is facilitated. This is arranged in such a way that each desired position of the sealing means in the chamber  30  has its own set of threaded holes for drainage, spray nozzle  54  and fixation. These holes are then intended to be plugged with threaded plugs when not in use. The plugs are then intended to be placed in inactive positions. 
         [0087]    Drainage channels and spray nozzles are intended to be unscrewed and moved to the active positions, such that a minimum of channels and spray nozzles are required in order to be able to use the chamber with a maximum number of ink colors abreast. 
         [0088]    The sealing means  20  according to the present invention, together with drainage and spray nozzles, consequently results in completely tight bulkheads between the different ink colors. Possible leaking ink from the first part  21  of the sealing means  20  is arranged to be brought back to the corresponding ink vessel according to above, with minimal loss. 
         [0089]    The only limitation of the arrangement would be how much two adjacent sealing means build in the longitudinal axis of the chamber. 
         [0090]    The spray nozzles  54  are also intended to effectively rinse the space between the first and second sealing plates,  21  and  22 . The portion of the screen roller  31  running between first and second sealing plates,  21  and  22 , are also intended to be rinsed/washed by solvent from these spray nozzles  54 . 
         [0091]    During changing of ink the chambered doctor blade  30  remains in contact with the screen roller  31 , is drained on printing ink, and is rinsed out internally with suitable detergent/rinsing agent by means of special spray nozzles,  54  and  60 . The entire rinsing procedure is handled by a sequence control equipment (PLC). 
         [0092]    By more extensive cleaning and maintenance of the chamber  30 , this is removed from the printing unit. 
         [0093]      FIGS. 8   a - 8   e  show a spray nozzle  60  according to the present invention comprising a substantially tubular portion  61  comprising a supply channel  62  for liquid, which at its outlet end comprises openings  63  and at that end rotatable housing  64  having several openings  65  arranged for discharging liquid. At least some of the openings  65  in the housing run non-radially in order, by means of ejector action, to rotate the housing  64  about its own axis  66 . The spray nozzles  60  are intended to clean the chamber  40  and are preferably arranged in the frame  32  of the chambered doctor blade  30  opposite the roller  31 . Connecting means  67  for supplying liquid by means of a hose to the spray nozzles  60  are connected to the nozzles  60 . 
         [0094]    By using such a spray nozzle  60 , rotating about its own axis  66 , and thereby spraying a much larger area or section of the chambered doctor blade  30 , a significantly smaller amount of spray nozzles  60  may be used with the same effect as several immobile spray nozzles. Using fewer spray nozzles means less details to maintain, simpler installation with less holes in the frame of the chamber and less hoses to draw and connect to a second pump supplying these with washing liquid. The rotating spray nozzles  60  are arranged to spray in all directions, including backwardly against the wall to which they are mounted. One single spray nozzle may cover up to half a meter of a chambered doctor blade, in contrast to a conventional spray nozzle, normally covering one to two decimeters of a chambered doctor blade. 
         [0095]    Embodiments of spray nozzles may nevertheless be conceived of having varying outlet directions, but which are fixed, i.e. non-rotatable. 
         [0096]    Throughout this application it is intended that a spray nozzle, is a kind of nozzle to which a hose or the like is intended to be connected and through which a liquid such as detergent or rinsing agent, is intended to be sprayed. 
         [0097]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.