Abstract:
A method for cleaning a nozzle plate includes applying a first solution to a surface of the nozzle plate, and applying a second solution different from the first solution to the surface of nozzle plate to remove the first solution from the surface of nozzle plate. The first solution wets the nozzle plate and is a solvent to dried ink deposited on the surface of the nozzle plate. The surface of the nozzle plate is non-wetting to the second solution.

Description:
TECHNICAL FIELD 
       [0001]    This description relates to cleaning a nozzle plate having a non-wetting layer. 
       BACKGROUND 
       [0002]    A fluid ejector (e.g., an ink jet printhead) typically has an interior surface, an orifice through which fluid is ejected, and an exterior surface. When fluid is ejected from the orifice, the fluid can accumulate on the exterior surface of the fluid ejector. This fluid can dry, creating debris. When fluid or debris accumulates on the exterior surface adjacent to the orifice, further fluid ejected from the orifice can be diverted from an intended path of travel or blocked entirely by interaction with the accumulated fluid (e.g., due to surface tension). 
         [0003]    Some materials from which fluid ejectors are fabricated (e.g., silicon) are hydrophilic, which typically exacerbates the problem of accumulation when fluids are ejected. A non-wetting coating can coat the exterior surface of the fluid ejector. 
       SUMMARY 
       [0004]    A cleaning fluid can be applied to an exposed face of a fluid ejector to loosen debris, e.g., by rehydrating dried ink. This can be done in conjunction with mechanical wiping in order to remove both the debris and the cleaning fluid. However, one problem is that wiping the nozzle plate can introduce errors into the jetting direction and can damage the non-wetting coating. Without be limited to any particular theory, the cleaning fluid is wetting to the non-wetting coating in order to adhere to the surface and loosen the debris, and the wiping must be sufficiently forceful to remove the cleaning fluid, which can damage to the non-wetting coating. At least some of these problems can be alleviated by applying a high surface energy rinsing fluid that will mix with the cleaning fluid. By making the mixture non-wetting to the non-wetting coating after the debris has been loosened or dissolved, mechanical wiping can be performed at lower force or can be eliminated. 
         [0005]    In one aspect, a method for cleaning a nozzle plate includes applying a first solution to a surface of the nozzle plate, and applying a second solution different from the first solution to the surface of nozzle plate to remove the first solution from the surface of nozzle plate. The first solution wets the nozzle plate and is a solvent to dried ink deposited on the surface of the nozzle plate. The surface of the nozzle plate is non-wetting to the second solution. 
         [0006]    Implementations can include one or more of the following features. The second solution may be applied at an angle ≠0 with respect to a normal of the surface of the nozzle plate. A component of a momentum of the second solution may be in the plane of the surface of the nozzle plate and the first solution may be removed from the surface of the nozzle plate by the momentum imparted by the second solution. The component of the momentum of the second solution may remove debris from the surface of the nozzle plate. The second solution may be miscible with the first solution and may form a mixture solution comprising the first solution, the second solution and the dissolved dried ink. The mixture solution may not wet the surface of the nozzle plate. The surface of the nozzle plate may be contacted with a first surface after the first solution is applied to the surface of the nozzle plate. The second solution the second solution may be more non-wetting than the mixture solution. The second solution may be a high polarity high surface energy fluid. The second solution may be deionized water. The surface of the nozzle plate may be contacted with a first surface while the first solution is applied to the surface of the nozzle plate. The first surface may include an element selected from a group consisting of: a brush, a piece of cloth, a piece of leather, a sharp blade, a sponge and an open cell foam. The first surface may be used to apply a shearing force to debris deposited on the surface of the nozzle plate. A blade of air may be used to remove second solution from the surface of the nozzle plate. Applying a second solution may include contacting the nozzle plate with a jet of the second solution and causing relative motion between the nozzle plate and the jet. The surface of the nozzle may include a coating that is non-wetting to the ink. 
         [0007]    In another aspect, an apparatus may include a printbar having a surface with a plurality nozzles, and a maintenance station. The maintenance station has a washing station include a first plurality of outlets that directs a first solution towards the printbar, and a rinsing station comprising a second plurality of outlets that directs a second solution at an oblique angle to the surface of the printbar. 
         [0008]    Implementations can include one or more of the following features. A wiping station may include an element configured to apply a mechanical force to a surface of the printbar. The element may be selected from a group consisting of a brush, a piece of cloth, a piece of leather, a sharp blade, a sponge and an open cell foam. The washing station may include an element integrated with the plurality of outlets to apply a mechanical force to the printbar while the plurality of outlets direct the first solution towards the printbar. The element may be selected from a group consisting of a brush, a piece of cloth, a piece of leather, a sharp blade, an air blade, a sponge and an open cell foam. The maintenance station may be configured to be selectively advanced to a position under the printbar prior to activating the washing station and rinsing station, and the maintenance station may be configured to be selectively retracted from under the printbar upon deactivation of the washing station and rinsing station. The printbar may include a printhead module having a nozzle plate, and a surface of the nozzle plate may include a non-wetting coating. The first solution may be a cleaning solution that dissolves dried ink on the surface of the nozzle plate and the second solution may be a high polarity, high surface energy fluid with respect to the non-wetting coating. The second solution may be deionized water. An element may be configured to remove debris from the surface of the nozzle plate while the first solution is directed to the surface of the nozzle plate. The element may be an irrigated sponge. The element is a brush comprising a plurality of segments of bristles. A device may be configured to hold the printbar with the surface at an oblique angle relative to gravity. 
         [0009]    These and other features and aspects, and combinations of them, can be expressed as systems, components, apparatus, methods, means or steps for performing functions, and in other ways. 
         [0010]    Other features, aspects, implementations, and advantages will be apparent from the description and the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0011]      FIGS. 1A and 1B  are a schematic system side-views of the printing apparatus and the maintenance station. 
           [0012]      FIG. 2A  is a schematic perspective view of a nozzle plate. 
           [0013]      FIGS. 2B and 2C  are schematic side views of a non-wetting liquid and a wetting liquid, respectively, on a nozzle plate. 
           [0014]      FIG. 2D  is a schematic side view of a droplet of liquid on a tilted nozzle plate. 
           [0015]      FIG. 2E  is a schematic perspective view of a nozzle plate having debris. 
           [0016]      FIG. 2F  is a schematic side view of a system in which a rinsing solution is directed at an angle onto a nozzle plate. 
           [0017]      FIGS. 3A-3C  are pictures of a nozzle plate after different cleaning steps. 
           [0018]      FIGS. 4A-4G  are schematic side views of various implementations of a maintenance station. 
           [0019]      FIGS. 5A and 5B  illustrate a shearing force applied by the maintenance station to remove debris from the nozzle plate. 
       
    
    
       [0020]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0021]      FIGS. 1A and 1B  show a printing apparatus  100  and a movable maintenance station  110 . Printing apparatus  100  includes a printbar  120  onto which at least one printhead module  130  is mounted. A protrusion  135  of the printhead module  130  from the printbar  120  is exaggerated and is not drawn to scale. In some figures, only the printbar  120  is illustrated, but it should be understood that the printbar  120  contains printhead modules  130  each having an exposed surface  211  that is mounted parallel to a layer surface  121  of the printbar. Each printhead module can include a nozzle plate  200 . A non-wetting coating  210  can be formed on the nozzle plate  200 . The exposed surface  211  can be the outer surface of the non-wetting coating  210 , or the outer surface of the nozzle plate  200  if the non-wetting coating  210  is absent. The non-wetting layer  210  can be a monolayer formed from a precursor vapor that includes 1H,1H,2H,2H perfluorodecyltrichlorosilane (FDTS). Alternatively the non-wetting layer  210  can be a molecular aggregation formed from a similar precursor vapor, or can be another non-wetting coating, e.g., a fluorocarbon polymer such as Teflon. 
         [0022]    A controller  111  having a drive mechanism  112  moves the movable maintenance station  110  under the printbar  120  when maintenance to be performed on the printing apparatus  100 . The maintenance station  110  includes substations  141  and  142  which contain cleaning solutions and wiping tools. The maintenance station  110  can be used, for example, to remove adhered ink and other debris collected at the exposed face  211  of the printhead module  130 . 
         [0023]    The maintenance station  110  may be deployed by the controller  111  after a set period of time, for example, a set number of hours of run-time of the printing apparatus  100 , or after a set number of sheets have been printed. The maintenance station  110  may also be deployed after an optical detector  113  detects a problem with the jetting process due to the buildup of adhered ink and debris on the nozzle plate caused by the generation of ink mist during the jetting process. When the maintenance station  110  is not being deplored, the drive mechanism  112  retracts the maintenance station to a storage position  114 . Alternatively, the maintenance station can be stationary and the print bar can be moved to the maintenance station after a printing operation is completed. 
         [0024]    The nozzle plate  200  is the outermost component of the printhead module  130  and the nozzle plate  200  has an exposed surface  211  in which one or more rows  221  of nozzle openings  222  are defined (see  FIG. 2A  where two rows are illustrated, but there could be just one row). The nozzle openings  222  define the end of nozzles apertures  223  that extend through the nozzle plate  200 . The non-wetting layer  210  includes apertures aligned with the openings  222  so that the non-wetting layer  210  does not obstruct the nozzle openings  222 . The printhead module  130  includes pumping chambers, piezoelectric elements (not illustrated in  FIGS. 1A and 1B ) that are associated with each of the nozzle openings  222  defined in the nozzle plate  210 . The exposed surface  211  of the nozzle plate  200  faces a medium  223  onto which ink droplets  149  of an ink  150  from the printhead module  130  are jetted (see  FIG. 1B ).  FIG. 2A  shows a bottom-up view of the nozzle plate  200  having the non-wetting layer  210  coating on its exposed surface  211 . 
         [0025]    In general, the non-wetting layer  210  is a surface having a smaller surface energy compared to the surface tension of a liquid (e.g., the ink  150 ) that will be jetted from the printhead module  130 . As a result of the smaller surface energy of the non-wetting layer, a drop of the liquid (e.g., the ink  150 ) forms a static contact angle  250  at a liquid/surface interface  251  that is larger than  90  degrees, as shown in  FIG. 2B . The surface tension of a liquid is determined by the forces of attraction between molecules of that liquid. A wetting surface  253  (shown in  FIG. 2C ) has a large enough surface energy to overcome the surface tension forces that hold the molecules of the liquid together, as a result, the liquid (e.g., the ink  150 ) forms a static contact angle  255  at a liquid/surface interface  252  that is smaller than 90 degrees (i.e., the liquid spreads and wets the wetting surface  253 ). For example, the forces between the hydrocarbon molecules that make up the polymers are weak and consequently polar liquids tend to form droplets on a polymeric surface rather than spread out. 
         [0026]    Dynamic contact angles of liquid can be used to characterize a liquid that moves along a liquid-surface interface.  FIG. 2D  shows a surface  285  on which a liquid-surface interface  284  of a liquid droplet  288  is formed. When the surface  285  makes an angle with respect to a horizontal plane  286 , the angle  292  at which the liquid droplet  288  starts moving is related to the dynamic contact angles which include an advancing angle  290  and a receding angle  291  of the liquid droplet  288 . A liquid droplet  288  that slides easily off the surface  285  has a small value for the angle  292 . Static and dynamic contact angles are not necessarily related. 
         [0027]    In general, the ink  150  can be broadly considered to include a solvent  151  in which a pigment  152  is dissolved or suspended, as depicted in an area  271  shown in  FIG. 2E . Notwithstanding the presence of the non-wetting layer  210 , pigment  152  may adhere to the non-wetting layer  210  (shown in an area  272  of  FIG. 2E ) as dried ink or debris after the solvent  151  in the ink  150  has evaporated, for example, when the printhead  130  is mounted in such a way that the nozzle plate  200  is held horizontally. The adhered dry ink (that is, the pigment  152 ) can be removed by washing the exposed surface  211  of the nozzle plate  200  using a cleaning solution  280  that is a solvent for the pigment  152  (shown in an area  273  of  FIG. 2E ). The cleaning solution should also be miscible with whatever residual solvent  151  there might remain in the adhered dry ink. In addition, the cleaning solution should have a lower surface tension than the surface tension of the non-wetting layer  210 . Thus, the cleaning solution itself, or when mixed with any solvent  151  that remains on the exposed surface  211 , is wetting to the non-wetting layer  210 . The cleaning solution can have a sufficiently low surface tension that the cleaning solution  280  spreads over the surface and wets the non-wetting layer  210 , ensuring more thorough cleansing. 
         [0028]    Any other debris  153  that is not re-solvated by the cleaning solution  280  can be mechanically removed from the nozzle plate  200 , for example, by a brush or by wiping. The cleaning solution  280  can be applied using a fountain  143  in a washing substation  143  on the maintenance station  110  (see  FIG. 1A ). 
         [0029]    The substation  142  in the maintenance station  100  may be a wiping station that is used to simultaneously i) remove the cleaning solution  280  that wets the non-wetting layer  210  from the exposed surface  211  and to ii) mechanically remove any debris  153  that may be present. However, mechanical wiping can result in directionality errors in the printhead module  130  that are dependent on the wiping direction. For example, without being limited to any particular theory, the wiping direction may have an effect on jetting direction of ink droplet from the printhead module  130  due to inadvertent packing of debris  153  into nozzle openings  222 , or residual cleaning solution  280  may still accumulate around the nozzle opening  222  on the nozzle plate  200  and deviate ink droplets  149  jetted from the printhead module  130  from their original trajectories in the absence of the residual cleaning solution  280 . 
         [0030]    In addition, excessive wiping may damage the non-wetting layer  210 . The high forces required to perform both tasks (removing the wetting cleaning solution  280  from the non-wetting layer  210  and removing debris  153 ) simultaneously can cause substantial abrasion to the non-wetting layer  210 . The high forces can also increase the chance that debris  153  may get inadvertently pushed into nozzle openings  222 , rendering that particular nozzle inoperable. Finally, the removal of the cleaning solution  280  from the non-wetting layer  210  may not be complete. For example,  FIG. 3A  shows a drop  379  of the cleaning solution  280  on a glass slide  370  having a non-wetting layer  210  coated thereon.  FIG. 3B  shows small droplets  381  of residual cleaning solution  280  that remain on the glass slide  370  after wiping. A mark  375  is made on the glass slide  370  for identifying the position of the drop  379  of cleaning solution  280 . 
         [0031]    As shown in  FIG. 4A , instead of using a single wiping station  142  that mechanically removes both the debris  153  and the cleaning solution  280 , an additional substation  141  that functions as a rinsing station is included in the maintenance station  110 . The rinsing station applies a flow of high polarity, high surface energy rinsing solution  380  through a fountain  381 . A high polarity fluid typically has a high dielectric constant (e.g., more than 15). A high polarity fluid dissolves other polar substances well. The rinsing solution  380  is non-wetting to the non-wetting layer  210 . The rinsing solution  380  has a low dynamic wetting angle. 
         [0032]    Without being limited to any particular theory, the rinsing solution  380  can mix with the cleaning solution  280 , leaving a mixture that is more non-wetting, and thus easier to remove from the external surface  211 . Since the mixture is easier to remove, wiping forces can be reduced, the danger of damage to the non-wetting coating  120  can be reduced, and the useful lifetime of the device can be increased. 
         [0033]    A glancing flow of the rinsing solution can be applied to the nozzle plate  200 . As shown in  FIGS. 2F and 4D , a glancing flow makes an angle  0  from a normal  201  of the nozzle plate  200 . The use of a glancing flow imparts a component of velocity of the fluid stream, denoted by the arrow  202 , in the plane of the nozzle plate  200 . The glancing flow can result from either directing the rinsing solution  380  at an angle to a horizontally held nozzle plate  200  as shown in  FIG. 2F , or the nozzle plate  200  or the printbar  120  can be misaligned from a horizontal position as shown in  FIG. 4D . Small rotational adjustments can be applied to orient the printbar  120  to the optimal angle for rinsing and removal of the cleaning and rinsing solutions  280  and  380 . 
         [0034]    The use of a glancing flow of fluid also allows the advancing dynamic contact angle to be achieved more easily, easing the flow of the rinsing liquid  380 , which is miscible with the cleaning solution  280 , from the non-wetting layer  210  of the nozzle plate  200 . In this way, minimal mechanical wiping is required to remove the cleaning solution  280  from the nozzle plate  200 .  FIG. 3C  shows the removal of all small droplets  381  of cleaning solution  280  after the rinsing solution  380  is used, a marked improvement from the situation shown in  FIG. 3B . The wiping station  142  can then be dedicated to the removal of debris  153 , using smaller wiping forces than would be required if both debris and the cleaning solution  280  were to be actively removed from the nozzle plate  200 . An example of a suitable high polarity, high surface energy fluid is deionized water (DI). In some cases, the wiping station  142  can be eliminated, as shown in  FIG. 4B , in which the maintenance station  110  includes only a washing station  143  and the rinsing station  141 . 
         [0035]    The separation of the removal of debris  153  from the removal of the cleaning solution  280  permits more methods to be used for wiping or scrubbing debris off the nozzle plate  280 . For example, a brush having either synthetic or natural bristles, cloth strips, or strips of pliable leather, such as Chamoix or synthetic Chamoix, can be used in either a lateral (i.e. linear) scrubbing motion, a rotary scrubbing motion or a combination of lateral and rotary scrubbing motion can be used instead of being restricted to the use of a cloth (the latter is suitable for the removal of cleaning solution  280 ). The brush can include brush segments that work in concert or in sequence with one another. One segment of the brush may have finer bristles than another segment, and the motion of the brushes in different segments may vary in terms of direction, type of motion or the speed of motion relative to the nozzle plate  200 . 
         [0036]    The cleaning solution  280  can be applied through or within a brush  410 , as shown in  FIG. 4E  by combining these two functions into a single station  144  (see  FIGS. 4C and 4E ). In this way, the contact time between the nozzle plate  200  and the cleaning solution  280  can be substantially longer because the brush keeps the cleaning solution in contact with the nozzle plate longer than a fountain alone does, increasing the efficacy of re-dissolving the dried ink pigments  151  that adheres to the non-wetting layer  210 . Alternatively, a shorter amount of time is required to re-dissolve a fixed amount of dried ink pigments  151 . 
         [0037]    Besides using a brush, an irrigated sponge  420  can also be used. A soft, open-cell-structured foam or sponge material  421  through which the cleaning solution  280  is pumped can be placed in contact with the nozzle plate  200 . Open-cell-structured foams contain pores that are connected to one another and form an interconnected network that is relatively soft. Open-cell foams fill easily with materials they are surrounded with (e.g., the cleaning solution  280 ). Foam rubber is a type of open-cell foam. The irrigated sponge can be driven in a linear or rotary fashion about the nozzle plate  280 . A stiff sponge  423  can be driven with enough force to create enough friction forces between the sponge and the nozzle plate for the sponge to be pinned to the nozzle plate. A shearing force  425  (shown in  FIG. 5B ) can then be applied to the adhered dried ink pigments  151  effectively without generating undue relative motion between the irrigated sponge and the non-wetting layer  210  to cause the delamination of the layer  210 . 
         [0038]      FIG. 5A  shows an example of how shearing forces help to remove adhered dried ink pigments  151  or debris  153  without increasing the chance of a delamination of the non-wetting layer  210 . An irrigated sponge scrubber  420  is held stationary while the printbar  120  is driven in the direction indicated by an arrow  430 . A bottom surface  421  of the irrigated sponge scrubber is held stationary, and the shearing force generated by the stiff sponge  423  causes the top surface to move with the advancing printbar  120 , deforming the sponge  423 . Due to the closer proximity of the adhered dried ink pigments  151  and the debris  153  to the sponge  423 , a larger force is applied to the adhered dried ink  151  and the debris  153 , enabling them to be dislodged from the non-wetting layer  210 . The non-wetting layer  210  does not delaminate from the nozzle plate  200  because a smaller force is applied by the shearing force from the sponge  423  on it than on the dried ink pigments  151  and the debris  153 . The printbar  120  can also be driven to oscillate linearly in the direction as indicated by a double head arrow  431  while the irrigated sponge scrubber  420  is kept stationary. 
         [0039]    Alternatively, the printbar  120  can be held stationary while the irrigated sponge scrubber  420  is oscillated back and forth. In this case, is the top surface  422  would be held stationary while the sponge is being deformed and the bottom surface  421  would shear. 
         [0040]    The use of irrigated sponge  420  may also help to keep the cleaning solution  280  on the exposed surface  211  of the nozzle plate  200  for a longer period of time than if the fountain  144  were used alone. Chances of scratching the non-wetting layer  210  is reduced when the layer  210  is exposed to a sufficient amount of cleaning solution  280  while mechanical motion by way of either the brush  410  or the sponge  420  is applied to the non-wetting layer  210 . In this way, mechanical forces can be applied to the non-wetting layer  210  without damaging the surface. 
         [0041]      FIG. 4G  shows a shaped, flexible blade  470  oriented at a small angle  471  with respect to the nozzle plate  200  in the printbar  120 —can also be used in place of the brush  410  or sponge  420 . The cleaning solution  280  can be used to re-dissolved dried ink pigments  151  and the flexible blade  470  can then be used to sever or push re-dissolved adhered ink pigments  151  from the nozzle plate  280 . The rinsing solution  380  can be subsequently used to clean the nozzle plate  280 . 
         [0042]    Although the implementations above describe inks with solvents, the ink need not include a solvent, but can still be soluble to another type of liquid. For example, some UV inks do not have solvents in them, but are soluble. In addition, if the rinsing fluid has sufficiently high energy, it may be possible to have a nozzle plate surface that is not non-wetting to the ink, e.g., a surface without a non-wetting coating. For example, with a silicon nozzle plate, the silicon will grow a native oxide layer that is neither wetting nor non-wetting but instead influenced by what it has touched recently. By using a high energy rinsing fluid, ink can still be removed from a surface that is not non-wetting to the ink, e.g., from a native oxide surface of a silicon body. 
         [0043]    Other implementations are also within the following claims.