Abstract:
An ink-jet recording head for an ink-jet recording apparatus, includes a plurality of pressure generating chambers, a nozzle plate in which a plurality of nozzle apertures which communicate with the pressure generating chambers are formed, and a protective layer formed in the vicinity of the nozzle apertures, wherein when a cleaning blade for cleaning the nozzle plate of leavings of at least ink, comes in contact with the nozzle apertures when the blade is pressed on the nozzle plate, the blade elastically contacts the protective layer and the nozzle plate without damaging an ink-repellent layer disposed around the nozzle apertures, as the blade is moved in a direction toward an open exhaust port disposed on a side of an end of the nozzle plate, such that the leavings are exhausted through the open exhaust port by movement of the blade.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an ink-jet recording head for jetting ink pressurized in a pressure generating chamber by pressurizing means from a nozzle aperture as an ink droplet, and in more detail, relates to an ink-jet recording head in which a nozzle aperture can be prevented from being clogged by a wiping member. 
     DESCRIPTION OF THE RELATED ART 
     An ink-jet recording head is provided with a nozzle plate wherein nozzle apertures are made at a predetermined pitch in a thin plate, a pressure generating chamber communicating with each nozzle aperture and a reservoir for supplying ink to a pressure generating chamber as is well-known, and is constituted so that an ink droplet is jetted from a nozzle aperture by pressurizing ink in a pressure generating chamber by a piezoelectric vibrator, a heater element and others. 
     As dust on recording paper and the leavings of ink adhere to a nozzle aperture and the vicinity and the nozzle aperture is often clogged because an ink-jet recording head executes printing at an interval to the extent that the ink-jet recording head almost comes in contact with recording paper and ink including a solid component such as dye is used, a nozzle plate is wiped by a blade of a rubber plate every predetermined time to remove dust on recording paper and the leavings of ink. 
     In the meantime, as described above, as an interval between a nozzle plate and recording paper is extremely small, the recording paper comes in contact with a nozzle aperture and an ink-repellent layer provided around the nozzle aperture may be worn. 
     Therefore, as shown in FIG. 21A, a measure to prevent recording paper from coming in contact with a protective layer in the vicinity of each nozzle aperture N by forming the protective layer composed of a metallic layer 1 to 30 μm thick in an area apart by approximately 100 to 150 μm from each nozzle aperture N of a nozzle plate P so that a concave portion C is formed around each nozzle aperture N is taken. 
     As the width of a concave portion C between adjacent nozzle apertures in the same column is extremely small to form an independent concave portion C every nozzle aperture as described above in recent cases, a pitch at which the nozzle apertures are arranged is 180 dpi per column and extremely small to thus enhance printing quality, it is very difficult to form such a concave portion. Therefore, as shown in FIG. 21B, a rectangular common concave portion C′ is formed around nozzle apertures N in one column. 
     A recording head H provided with the nozzle plate P constituted as described above is relatively moved in the direction D or D′ of a blade B (cleaning means) as shown as II and II′ after the blade B is lifted on the side of the recording head H with the recording head located on the upstream side of the blade B arranged on a path of movement as shown in FIG. 22 (I). The blade B is elastically touched to the recording head H as shown as III and III′ and hereby, cleaning is executed. 
     At this time, as the most area of the blade B is dropped in the-concave portion C′, comes in contact with and rubs an ink-repellent layer F with strong pressure, there is a problem that the ink-repellent layer F is worn, scratched leavings K of ink are accumulated particularly along a wall W 2  on the downstream side out of walls W 1  and W 2  partitioning the concave portion C′ as shown in FIGS. 23A and 23B, and the recording paper is dirtied, a direction in which an ink droplet is jetted varies, or the like. 
     SUMMARY OF THE INVENTION 
     An ink-jet recording head according to the present invention comprises plural pressure generating chambers arranged at a predetermined pitch linearly in one or more columns for pressurizing ink by pressurizing means and a nozzle plate in which plural nozzle apertures each of which communicates with each pressure generating chamber are formed, and a protective layer for regulating so that a part of a blade comes in contact with a nozzle aperture when the blade is pressed on the nozzle plate is formed in the vicinity of the above nozzle aperture in a state in which an open exhaust port is secured on the side of the end of the protective layer in a direction in which the blade for cleaning is moved. 
     Therefore, a first object of the present invention is to provide an ink-jet recording head wherein ink which adheres to the nozzle plate, the leavings of ink and dust on paper can be securely exhausted in an area which has no effect upon jetting an ink droplet without wearing an ink-repellent layer and further, the ink-repellent layer can be prevented from being worn or broken by contact between the ink-repellent layer and recording paper. 
     A second object of the present invention is to provide an ink-jet recording apparatus provided with cleaning means suitable for the above recording head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective drawing showing an embodiment of a recording apparatus using an ink-jet recording head according to the present invention; 
     FIGS. 2A and 2B are a side view and a top view respectively showing the structure in the vicinity of a cleaning device; 
     FIG. 3 is a section view showing an embodiment of the ink-jet recording head a riding to the present invention; 
     FIGS. 4A and 4B show an embodiment of a nozzle plate of the above recording head, FIG. 4A is a front view, FIG. 4B shows the section viewed along a line A—A; 
     FIG. 5 shows a state in which a blade is in contact with the nozzle plate for cleaning; 
     FIG. 6 is a front view showing the structure of a nozzle plate equivalent to another embodiment of the present invention; 
     FIGS. 7A and 7B show the structure of a nozzle plate equivalent to further another embodiment of the present invention, FIG. 7A is a front view and FIG. 7B shows the sectional structure viewed along a line B—B; 
     FIG. 8 is a front view showing the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention; 
     FIGS. 9A and 9B show the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention, FIG. 9A is a front view, FIG. 9B shows the sectional structure viewed along a line C—C; 
     FIG. 10 shows a state in which a blade is in contact with the nozzle plate for cleaning; 
     FIGS. 11A and 11B show the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention, FIG. 11A is a front view and FIG. 11B shows the sectional structure viewed along a line D—D; 
     FIGS. 12A and 12B show the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention, FIG.  12 A is a front view and FIG. 12B shows the sectional structure viewed along a line E—E; 
     FIGS. 13A and 13B are respectively front views showing the structure of nozzle plates equivalent to furthermore another embodiment of present invention; 
     FIGS. 14A and 14B show the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention, FIG. 14A is a front view and FIG. 14B shows the sectional structure viewed along a line F—F. 
     FIGS. 15A and 15B show the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention, FIG. 15A is a front view and FIG. 15B shows the sectional structure viewed along a line G—G; 
     FIGS. 16A and 16B show the structure of a nozzle plate equivalent to the other embodiment of the present invention, FIG. 16A is a front view and FIG. 16B shows the sectional structure viewed along a line H—H; 
     FIGS. 17A,  17 B,  18 A,  18 B,  19 A,  19 B,  20 A, and  20 B respectively show a cleaning state of the nozzle plate shown FIGS. 16; 
     FIGS. 21A and 21B respectively show conventional type examples of nozzle plates of an ink-jet recording head used for a recording apparatus; 
     FIGS. 22 (I) to (III′) are explanatory drawings for explaining wiping operation by blade and further; and 
     FIGS. 23A and 23B are a front view and a sectional view respectively showing a state of cleaning. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments showing the details of the present invention in the drawings will be described below. 
     FIG. 1 shows an embodiment of a recording apparatus using an ink-jet recording head according to the present invention, a carriage  1  is connected to a pulse motor  3  via a timing belt  2 , the carriage is constituted so that it is guided by a guide member  4  and reciprocated in the direction of the width of recording paper  5  and ink-jet recording heads  6  and  7  described later are attached to the surface opposite to the recording paper  5 , the lower surface in this embodiment. The ink-jet recording heads  6  and  7  are respectively supplied with ink by ink cartridges  8  and  9  mounted on the carriage  1 , respectively jet an ink droplet on the recording paper  5  as the carriage  1  is moved, respectively form one or plural dots per one pixel and respectively print images and characters on the recording paper  5 . 
     A capping device  10  is provided in a non-printing area, seals nozzle apertures of the recording heads  6  and  7  during rest to prevent the nozzle apertures from being dry and in the meantime, also functions as a receptacle for receiving an ink droplet jetted from the recording heads  6  and  7  by flushing operation executed during printing. 
     A cleaning device  11  is provided in the vicinity of the capping device in the non-printing. area and arranged so that a blade  12  for touching the nozzle plates of the recording heads  6  and  7  as shown in FIGS. 2 has a gradient of an angle θ with a direction perpendicular to a direction in which nozzle apertures are arranged, that is, a direction in which the carriage  1  is moved. 
     FIG. 3 shows an embodiment of the above recording head and pressure generating means, a piezoelectric vibrator  13  in this embodiment and a passage unit  14  to which displacement from the above piezoelectric vibrator is applied are fixed to a holder  15 . 
     The passage unit  14  is constituted by laminating an elastic plate  16  which is in contact with the end of the piezoelectric vibrator  13  and to which elastic deformation is applied, a spacer  20  partitioning a pressure generating chamber  17 , an ink supply port  18  and a reservoir  19 , and a nozzle plate  22  provided with a nozzle aperture  21  communicating with the pressure generating chamber  17 . 
     The nozzle plate  22  is provided with two columns of nozzle apertures  21  each of which is formed at predetermined pitch as shown in FIGS. 4, and long and narrow protective layers  23  extended in parallel with a wiping direction at the same pitch as a pitch between adjacent nozzle apertures  21  so that at least the protective layer opposite to the nozzle aperture  21  is discretely formed at each column of nozzle apertures  21 . The height H of the protective layer  23  is set to approximately 2 to 10 μm and is formed so that the length L is at least larger than the diameter d of the nozzle aperture  21 . 
     These protective layers  23  can be formed by etching a substrate to be the nozzle plate  22 , electroforming metallic material on the nozzle plate  22  in a shape equivalent to the protective layer  23  or sticking a thin piece formed beforehand as another member. 
     In this embodiment, when the end of the blade  12  is touched to the nozzle plate  22  and wiping is executed if an ink droplet is not jetted from the nozzle aperture  21 , the central area between the protective layers  23  elastically comes in contact with the face of the nozzle aperture  21  with weak strength suitable for removing the leavings of ink and dust on the paper because the surface of the blade  12  elastically comes in contact with the protective layer  23  as shown in FIG.  5 . 
     In this state, when the blade  12  is relatively moved in a direction in which the protective layer  23  is extended, the leavings of ink and dust on the paper in the vicinity of the nozzle aperture  21  and further, ink which adheres to the blade  12 , are swept into an area not related to jetting an ink droplet from a clear aperture O open at the other end of the protective layer  23  on the downstream side in a direction in which the blade  12  is moved without rubbing an ink-repellent layer formed around the nozzle aperture  21  with strong strength uselessly. 
     In the above embodiment, the protective layer  23  is formed at the same pitch as a pitch between adjacent nozzle apertures, however, one protective layer  23  per plural nozzle apertures  21  may be also formed as shown in FIG.  6 . 
     FIGS. 7A and 7B respectively show a second embodiment of the present invention and in this embodiment, a band  24  is formed by connecting the side of the admission port of a blade  12  of each protective layer  23  so that the downstream side of each protective layer  23  in a direction in which the blade  12  is moved is open. 
     According to this embodiment, as recording paper can be lifted up to the height of the protective layer  23  owing to the band  24  even if the end of the recording paper is in contact with the nozzle plates  10  of the recording heads  6  and  7  due to a jam of recording paper and others, an accident that strong strength is uselessly applied to the protective layer  23  by the end of the recording paper and the protective layer is lost can be prevented beforehand. 
     In the above embodiment, a direction perpendicular to a direction in which nozzle apertures  21  are arranged is a horizontal direction. However, as shown in FIG. 8, if the protective layer  23  is tilted by the approximately similar angle θ′ in case the blade  12  is tilted by an angle θ with a direction in which the nozzle apertures are arranged, the leavings of ink, dust on paper and ink can be efficiently exhausted into an area not related to jetting an ink droplet without reducing the rejection ratio. 
     FIGS. 9 show the structure of a nozzle plate equivalent to further another embodiment of the present invention, a protective layer  30  is formed between nozzle apertures  21  formed at predetermined pitch in a nozzle plate  22 . 
     The protective layer  30  comprises the body  30   a  parallel to a direction in which recording heads  6  and  7  are moved and a wider branch  30   b  than the width of the body which is perpendicular to the direction in which the recording heads  6  and  7  are moved and in the center of which the end of the body  30   a  is located. 
     The height H of the protective layer  30  is set to approximately 2 to 10 μm, and the body  30   a  and the branch  30   b  are formed so that each length La and Lb is at least larger than the diameter of the nozzle aperture  21 . 
     These protective layers  30  are arranged at a predetermined pitch, at the same pitch as the nozzle aperture  21  in this embodiment so that an interval Lc is made between the end of the body  30   a  and the branch  30   b  of adjacent protective layers  30  to open at least a direction in which a blade  12  is moved. 
     These protective layers  30  can be readily formed by etching a substrate to be the nozzle plate  22  in a desired shape, forming them on the nozzle plate  22  by electroforming metallic material such as nickel in a shape equivalent to the protective layer  30  or forming a thin piece in a shape equivalent to the protective layer as another member and bonding the thin piece to the nozzle plate  22  as in the case of the above protective layer  23 . 
     A reference number  31  denotes an ink-repellent layer and the ink-repellent layer is formed by coating or electrolytic plating ink-repellent material a few hundred nm to a few pm thick formed around the nozzle aperture  21  such as fluoropolymers. 
     In this embodiment, when the end of the wiper blade  12  is touched to the nozzle plate  22  and wiping is executed, the end of the blade  12  elastically comes in contact with a part between the bodies  30   a  of the protective layers  30  as shown in FIG. 10 when the blade passes the nozzle aperture  21 . When the wiper blade  12  is relatively moved in the axial direction of the body  30   a  in this state, the leavings of ink and dust on the paper in the vicinity of the nozzle aperture  21  are removed, preventing the ink-repellent layer  31  from being worn or deteriorated because the ink-repellent layer  31  formed around the nozzle aperture  21  is never rubbed with strong contact force. 
     Ink and dust on the paper at the nozzle aperture  21  and in the vicinity which are wiped by the wiper blade  12  as described above, are swept in an area not related to jetting an ink droplet from an exhaust port located on the downstream side of the adjacent protective layers  30  and never remain around the nozzle aperture  21 . 
     Further, as the blade  12  comes in contact with the branch  30   b  of the protective layer  30  formed in the following vicinity when the recording heads  6  and  7  and the blade  12  are relatively moved and reach the vicinity of the next column of nozzle apertures, ink and dust on the paper which respectively adhere immediately before are rubbed by the branch  30   b  formed in an area not related to jetting an ink droplet and the blade  12  is refreshed. 
     Therefore, even if plural columns of nozzle apertures are continuously wiped by the blade  12 , ink, the leavings of ink and dust on the paper at the nozzle aperture  21  immediately before, can be possibly prevented from adhering to the nozzle aperture  21  in the next column and the vicinity. 
     Ink and dust on the paper which are rubbed by the branch  30   b  of the protective layer  30  and adhere to another branch  30   b  are flushed when the recording heads  6  and  7  are sealed by a capping device  10  and ink is forcedly exhausted from the recording heads  6  and  7  by a suction pump. 
     According to this embodiment, as the body  30   a  and the branch  30   b  approximately surround the nozzle aperture  21 , recording paper can be securely prevented from coming in contact with the ink-repellent layer  31  in the vicinity of the nozzle aperture  21  due to a paper jam, or the like. 
     FIGS. 11 show furthermore another embodiment of the present invention and in this embodiment, the branch  30   b ′ of a protective layer  30  is extended so that it is twice or more as long as a pitch between adjacent nozzle apertures  21  and the bodies  30   a  are arranged at an interval twice or more as long as a pitch between adjacent nozzle apertures  21 . 
     According to this embodiment, the refresh rate of the wiper blade  12  is enhanced by a quantity in which the length of the branch  30   b  is longer than that in the above embodiment shown in FIGS.  9 . 
     FIGS. 12 show furthermore another embodiment of the present invention, a protective layer  30  is constituted so that branches  30   b  longer than pitch between adjacent nozzle apertures  21  are formed at both ends of the body  30   a  with the body located in the center of the protective layer  30  and the protective layers are arranged at a pitch twice as long as the pitch between adjacent nozzle apertures  21  in each column so that they are zigzag. 
     In the above embodiment, the body and the branch are arranged so that they are in the shape of a letter H, however, the similar action is produced even if as shown in FIG. 13A, the body  30   a  is arranged so that it is located between nozzle apertures and branches  30   b  are arranged on the same side, on the upper side in FIG. 13A in this embodiment so that an interval can be formed between the bodies  30   a  of adjacent protective layers  30  and as shown in FIG. 13B, the branches  30   b  are formed in reverse directions in the shape of a key. 
     FIGS. 14 show furthermore another embodiment of the present invention and a protective layer  35  is formed approximately in the shape of a triangle symmetrical in a direction in which a linear part  35   a  which is approximately perpendicular to a path on which the blade is moved on the side opposite to a direction in which the blade  12  is moved and which is longer than pitch between adjacent nozzle apertures  21  and a curved part  35   b  forming a vertex  35   c  tapered from the linear part to the side of the nozzle aperture on the side opposite to the nozzle aperture  21  are perpendicular to a direction in which nozzle apertures are arranged. 
     The pitch between the adjacent protective layers  35  is equal to the pitch between the adjacent nozzle apertures  21  and the protective layers are arranged with them alternately inverted so that the side of the vertex is located on the side of the nozzle aperture. 
     FIGS. 15 show furthermore another embodiment of the present invention and a protective layer  36  is formed so that a linear part  36   a  which is approximately perpendicular to a path on which a blade is moved on the side opposite to a direction in which the blade  12  is moved and which is longer than a pitch between adjacent nozzle apertures  21  and a curved part  36   b  the center of which is the narrowest part are both symmetrical in a direction in which the nozzle apertures are arranged and a direction perpendicular to the direction. 
     These protective layers  36  are arranged at a pitch twice as long as a pitch between adjacent nozzle apertures  21  so that the narrowest part is opposite to the nozzle aperture. 
     In this embodiment, as the blade is also elastically touched to the nozzle aperture with elastic pressure regulated by an interval in a concave portion after the blade is cleaned and refreshed by the linear part, so that ink, the leavings of ink, dust on paper and others in the vicinity of the nozzle aperture can be removed, preventing an ink-repellent layer from being possibly worn. 
     FIGS. 16 show the structure of a nozzle plate equivalent to furthermore another embodiment of the present invention and rectangular concave portions  40  and  40 ′ respectively surrounding nozzle apertures  21  and nozzle apertures  21 ′ in the respective columns and provided with open parts  40   a  and  40   a ′ at the end of a nozzle plate  22  (the lower end in FIG. 16A) are formed. These concave portions  40  and  40 ′ are connected by a concave portion  41  formed in a boundary between them. 
     These concave portions  40  and  40 ′ and the concave portion  41  are constituted by providing a protective layer  43  made of metal and others with the thickness of approximately 5 to 30 μm by sputtering, electroless plating, electrolytic plating and others and an ink-repellent layer  44  is formed by material provided with ink repellency inside at least the concave portions  40  and  40 ′. 
     Walls  40   b  and  40   b ′ on the respective sides (on the sides of the upper end in FIG. 16) on which the concave portions  40  and  40 ′ are closed, a wall  41   a  regulating the concave portion  41  and a wall  40   c ′ on the downstream side are formed as a slanted face on the downstream side in a direction in which a blade  12  is moved which is disconnected. 
     In this embodiment, as recording paper is supported by the surface of the protective layer  43  in case the recording paper comes in contact with the surface of the nozzle plate  22  in printing, the recording paper crosses the concave portions  40  and  40 ′, does not come in contact with the ink-repellent layer  44  which has a great effect upon ink jetting performance in the concave portions  40  and  40 ′ and therefore, does not peel the ink-repellent layer. 
     As the blade  12  has an angle θ with a direction in which nozzle apertures  21  are arranged when the blade  12  is elastically touched to the nozzle plates  22  of recording heads  6  and  7  and the blade  12  or the recording head  6  is relatively moved in a direction shown by an arrow D in FIG. 17A, if cleaning is required because of long-time printing, the most of the blade  12  is supported by the surface of the protective layer  43 , only a part enters the concave portions  40  and  40 ′ and is elastically touched to the ink-repellent layer  44  with light force as shown in FIG.  17 B. 
     When the recording head  6  is further relatively moved to the blade  12 , the leavings K of ink are gathered on a wall on the downstream side of the concave portion  40  and as the blade  12  is moved, the leavings of ink are moved in a direction shown by an arrow E in FIG. 18A, that is, on the side of the open port  40   a  as shown in FIG.  18 A. 
     The leavings of ink are exhausted out of the nozzle plate  22  via the open port  40   a . In the other concave portion  40 ′, the leavings K of ink are also gathered on a wall on the downstream side, are moved to the open port  40   a ′ of the concave portion  40 ′ as described above as shown in FIG. 19, are guided to outside along the slope of the wall  40   c ′ regulating the end of the concave portion  40 ′ and are exhausted as shown in FIG.  20 . 
     If the blade  12  is formed so that at least the open ports  40   a  and  40   a ′ in an area in which the blade and the nozzle plate  22  are in contact are located outside the end of the nozzle apertures  21  (on the side of the lower end in FIG.  20 ), the leavings K′ of ink can be guided in an area not related to jetting an ink droplet, further, if the blade is extended up to the end of the nozzle plate  22 , the leavings of ink can be exhausted in an area with which the blade  12  is not in contact and the leavings of ink can be prevented from adhering to the blade  12  again in cleaning. 
     In the above embodiments, the ink-jet recording head of a type that a pressure generating chamber is pressurized by a piezoelectric vibrator is described as an example, however, it is clear that the similar action can be produced even if the present invention is applied to a nozzle plate of a bubble-jet recording head wherein a heater element is sealed in a pressure generating chamber and ink is jetted by thermal energy. 
     As described above, according to the present invention, if recording paper comes in contact with the nozzle plate, it can be prevented from coming in contact with the ink-repellent layer in an area in the vicinity of a nozzle aperture owing to the protective layer. In cleaning, the ink-repellent layer is prevented from being worn by regulating an area with which the blade comes in contact by the protective layer and elastically touching the blade with a light force enough to clean the face of an nozzle aperture. Further, ink, the leavings of ink and dust on paper respectively gathered by the blade can be exhausted in an area not related to jetting an ink droplet via the open port.