Patent Publication Number: US-9427968-B2

Title: Liquid discharge head and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosures herein generally relate to a liquid discharge head and an image forming apparatus. 
     2. Description of the Related Art 
     As an image forming apparatus, an apparatus adopting a liquid discharge recording method, for example, an inkjet recording apparatus, has been known that uses a recording head including, for example, a liquid discharge head (a liquid droplet discharge head) to discharge liquid droplets. 
     As a liquid discharge head, a head has been known that includes a passage plate formed by having multiple plate-shaped members bonded, to form an individual passage communicating with a nozzle to discharge liquid droplets (see Patent Document 1). 
     Also, a head has been known that reduces forced-out excessive adhesive, by narrowing a bonding part when parts constituting the head are bonded by the adhesive (see Patent Document 2). 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     
         
         [Patent Document 1] Japanese Laid-open Patent Publication No. 2014-054816 
         [Patent Document 2] Japanese Laid-open Patent Publication No. 05-330065 
       
    
     Incidentally, for example, if the passage plate is formed with three plate-shaped members stacked and bonded by an adhesive, and the plate-shaped members are bonded to the nozzle plate and a wall surface member by the adhesive, fillets are formed by the forced-out adhesive between the plate-shaped members, and the nozzle plate and the wall surface member. 
     However, virtually no fillets are generated at a bonding part between separation wall parts that form separation walls between individual liquid chambers formed by multiple plate-shaped members constituting the passage plate. 
     Therefore, there is a problem that the bond strength of the separation wall parts is reduced only at a center portion in the stacking direction of the multiple plate-shaped members, and hence, the liquid chamber rigidity is reduced. Also, there is a problem that the multiple plate-shaped members tend to deform, and the plate-shaped members are strongly affected by the deformation at the center portion in the stacking direction. 
     SUMMARY OF THE INVENTION 
     In the view of these problems, it is a general object of at least one embodiment of the present invention to raise the bond strength when forming a passage plate by stacking and bonding multiple plate-shaped members, to raise the liquid chamber rigidity. 
     According to an embodiment of the present invention, a liquid discharge head includes a nozzle plate configured to have a plurality of nozzles arrayed to discharge liquid droplets; a passage plate configured to form individual liquid chambers communicating with the respective nozzles; and a wall surface member configured to form a wall surface of the individual liquid chambers. The passage plate is formed with at least three plate-shaped members stacked and bonded by an adhesive. The nozzle plate and one of the plate-shaped members of the passage plate are bonded by the adhesive, and another of the plate-shaped members of the passage plate, and the wall surface member are bonded by the adhesive. The three plate-shaped members include separation wall parts forming separation walls between the individual liquid chambers. At least one of the three plate-shaped members has a separation wall width as a width in a nozzle arrangement direction of the separation wall part, different from a separation wall width of the other plate-shaped members. Fillets of the adhesive are formed between the wall surface of the separation wall part of the plate-shaped member whose separation wall width is relatively narrow, and a bonded surface of the plate-shaped member whose separation wall width is relatively wide, between the nozzle plate and the wall surface of the separation wall part of the plate-shaped member, and between the wall surface member and the wall surface of the separation wall part of the plate-shaped member, in a direction along the nozzle arrangement direction. 
     According to an embodiment of the present invention, it is possible to raise the bond strength when forming a passage plate by stacking and bonding multiple plate-shaped members, to raise the liquid chamber rigidity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and further features of embodiments will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an external perspective view that illustrates an example of a head unit including a liquid discharge head according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view that illustrates the head unit; 
         FIG. 3  is a cross-sectional view of a liquid discharge head in a direction perpendicular to the nozzle arrangement direction (the longitudinal direction of an individual liquid chamber) according to a first embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a liquid discharge head in the nozzle arrangement direction (the lateral direction of an individual liquid chamber) taken along the line A-A in  FIG. 3 ; 
         FIG. 5  is a plane view taken along the line B-B in  FIG. 3 ; 
         FIG. 6  is a cross-sectional view that illustrates a part corresponding to a passage unit; 
         FIG. 7  is a cross-sectional view that illustrates a part corresponding to a passage unit of a liquid discharge head according to a second embodiment of the present invention; 
         FIG. 8  is a cross-sectional view that illustrates a part corresponding to a passage unit of a liquid discharge head according to a third embodiment of the present invention; 
         FIG. 9  is a side view that illustrates an example of a mechanical part of an image forming apparatus according to an embodiment of the present invention; and 
         FIG. 10  is a plane view that illustrates a core part of the mechanical part. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the present invention will be described with reference to the drawings. A head unit including a liquid discharge head will be described according to an embodiment of the present invention with reference to  FIG. 1  and  FIG. 2 .  FIG. 1  is an external perspective view of the head unit, and  FIG. 2  is a cross-sectional view of the same. 
     This head unit  101  integrates a liquid discharge head  102  to discharge liquid droplets, which will be described later in the following embodiments, an electric circuit board  103  having electronic devices mounted that are connected with the liquid discharge head  102 , and a tank  104  to contain liquid to be supplied to the liquid discharge head  102 . 
     Next, a liquid discharge head will be described according to a first embodiment of the present invention with reference to  FIG. 3  to  FIG. 5 .  FIG. 3  is a cross-sectional view of the liquid discharge head in a direction perpendicular to the nozzle arrangement direction (the longitudinal direction of an individual liquid chamber),  FIG. 4  is a cross-sectional view of the liquid discharge head in the nozzle arrangement direction (the lateral direction of an individual liquid chamber) taken along the line A-A in  FIG. 3 , and  FIG. 5  is a plane view taken along the line B-B in  FIG. 3 . 
     This liquid discharge head has a nozzle plate  1 , a passage plate  2 , and a vibration plate member  3  as a wall surface member stacked and bonded. In addition, the liquid discharge head includes a piezoelectric actuator  11  to displace the vibration plate member  3 , and a frame member  17  as a common liquid chamber member. 
     The nozzle plate  1 , the passage plate  2 , and the vibration plate member  3  form individual passages  5  communicating with multiple nozzles  4  to discharge liquid droplets, and a common liquid chamber  18  on the downstream side of a filter  9 . 
     Taking the side on which the nozzles  4  are disposed as the downstream side, an individual passage  5  is configured to have an individual liquid chamber  6  communicating with a nozzle  4  on the downstream side, and a fluid resistant part  7  and a liquid introduction part  8  that form a liquid supply path to supply liquid to the individual liquid chamber  6 . The individual passages  5  are separated from each other by separation walls  50  between the individual liquid chambers  6  in the nozzle arrangement direction. 
     Also, the common liquid chamber  18  on the downstream side of the filter  9  is an opening provided for the multiple individual passages  5  arranged in the nozzle arrangement direction. 
     Liquid flows into the common liquid chamber  18  on the downstream side of the filter  9 , from the common liquid chamber  10  of the frame member  17 , through the filter part  9  that is an inlet part formed on the vibration plate member  3 . The liquid is introduced into the liquid introduction part  8  from the common liquid chamber  18  on the downstream side of the filter  9 , and then, supplied to the individual liquid chamber  6  from the liquid introduction part  8  via the fluid resistant part  7 . 
     Note that the nozzle plate  1  is formed of a metal plate made of nickel (Ni), and is manufactured by an electroforming method. The plate is not limited to be made of nickel, but another metal member, a resin member, or a stacked member of a resin layer and a metal layer can be used for it. The nozzle plate  1  has the nozzles  4  formed that correspond to the individual liquid chambers  6 , and is bonded to the passage plate  2  by an adhesive. Also, this nozzle plate  1  has a liquid repellent layer on the surface from which liquid droplets are discharged (the surface in the discharge direction, or the surface on the reverse side of the individual liquid chambers  6 ). 
     As will be described later in detail, the passage plate  2  has multiple (three in the present embodiment) plate-shaped members  21 ,  22 , and  23  stacked and bonded, to form the individual liquid chambers  6 , the fluid resistant parts  7 , and the liquid introduction parts  8  constituting the individual passages  5 , and through holes to form the common liquid chamber  18  on the downstream side of the filter  9  (a concavity may be formed in some cases). 
     The vibration plate member  3  is a wall surface member to form a wall surface of the individual passages  5  of the passage plate  2 . This vibration plate member  3  has a two-layer structure. The first layer is positioned on the side of the passage plate  2 , and on the first layer, deformable vibration areas  30  are formed at areas corresponding to the individual liquid chambers  6 . 
     This vibration plate member  3  is formed of a metal plate made of nickel (Ni), and is manufactured by an electroforming method. The plate is not limited to be made of nickel, but another metal member, a resin member, or a stacked member of a resin layer and a metal layer can be used for it. 
     On the side of this vibration plate member reverse to the side facing the individual liquid chamber  6 , a piezoelectric actuator  11  is placed that includes an elelectromechanical transducer as a drive unit (an actuator unit or a pressure generation unit) to deform the vibration areas  30  of the vibration plate member  3 . 
     This piezoelectric actuator  11  includes multiple laminated piezoelectric members  12  that are bonded by an adhesive on a base member  13 . The piezoelectric members  12  have half-cut dicing applied to have grooves, to form a predetermined number of pectinate, piezoelectric pillars  12 A and  12 B at predetermined intervals for each of the piezoelectric members  12 . 
     Although the piezoelectric pillars  12 A and  12 B of the piezoelectric member  12  are the same, they are distinguished by different codes where a piezoelectric pillar driven by a given drive waveform is referred to as the drive piezoelectric pillar (drive pillar)  12 A, and a piezoelectric pillar not given a drive waveform and simply used as a pillar is referred to as the non-drive piezoelectric pillar (non-drive pillar)  12 B. 
     A drive pillar  12 A is bonded to a convex part  30   a  that is an island-shaped thick part formed on the vibration area  30  of the vibration plate member  3 . Also, a non-drive pillar  12 B is bonded to a convex part  30   b  that is a thick part on the vibration plate member  3 . 
     This piezoelectric member  12  has piezoelectric layers and internal electrodes stacked alternately. The internal electrodes are drawn out on edge surfaces, respectively, to form an external electrode. To send a drive signal to the external electrode of the drive pillar  12 A, a flexible printed circuit board having flexibility, or an FPC  15  (see  FIG. 2 ) is connected. 
     Note that since the piezoelectric actuator  11  is used here, the wall surface member is formed by the vibration plate member  3 . However, if using a thermal actuator, the actuator substrate having electrothermal transducers placed forms the wall surface member. 
     The frame member  17  is made of stainless, and formed by a mechanical process, in which the common liquid chamber  10  is formed and to which liquid is supplied from the tank  104  described above. 
     In the liquid discharge head configured in this way, for example, by lowering the voltage applied to the drive pillars  12 A from a reference potential, the drive pillars  12 A contract, and the vibration areas  30  of the vibration plate member  3  fall to expand the capacity of the individual liquid chambers  6 . This makes liquid flow into the individual liquid chambers  6 . 
     After that, by raising the voltage applied to the drive pillars  12 A to expand the drive pillars  12 A in the stacking direction, the vibration areas  30  of the vibration plate member  3  are deformed in the direction toward the nozzles  4 , and the capacity of the individual liquid chambers  6  is contracted. This applies pressure to the liquid in the individual liquid chambers  6 , to discharge (jet out) liquid droplets from the nozzles  4 . 
     Then, by returning the voltage applied to the drive pillars  12 A to the reference potential, the vibration areas  30  of the vibration plate member  3  resume the initial positions, and the individual liquid chambers  6  expand to generate negative pressure. This makes liquid from the common liquid chamber  10  fill the individual liquid chambers  6 . Then, after having vibration of the meniscus surfaces of the nozzles  4  damped to be stable, the operation is transitioned to discharging liquid droplets for the next time. 
     Note that the drive method of the head is not limited to the above example (discharging by pull-push), but depending on a drive waveform to be given, it is possible to execute discharging by pull, or discharging by push. 
     Next, a part of a passage unit including the passage plate in the present embodiment will be described in detail with reference to  FIG. 6 .  FIG. 6  is a cross-sectional view of a part of the passage unit. 
     As described above, the passage plate  2  is configured to have an odd number of, or three plate-shaped members  21  to  23  stacked and bonded. Note that “configured to have stacked and bonded” is not limited to a configuration obtained by forming an independent passage plate  2 , and then, bonding it to the nozzle plate  1  and the wall surface member. Namely, “configured to have stacked and bonded” means to include stacked, bonded, multiple plate-shaped members obtained as a result of bonding the nozzle plate  1  to a plate-shaped member, bonding the wall surface member to a plate-shaped member, and then, bonding these to an intermediate plate-shaped member on the respective sides. 
     The plate-shaped member  21  is a plate-shaped member bonded to the nozzle plate  1 , the plate-shaped member  23  is a plate-shaped member bonded to the wall surface member or the vibration plate member  3 , and the plate-shaped member  22  is an intermediate plate-shaped member bonded between the plate-shaped member  21  and the plate-shaped member  23 . 
     The plate-shaped member  21  has through holes  51  formed to form the individual liquid chambers  6 , the plate-shaped member  22  has through holes  52  formed to form the individual liquid chambers  6 , and the plate-shaped member  23  has through holes  53  formed to form the individual liquid chambers  6 . 
     Note that the plate-shaped member  22  also has through holes  54  formed to form the fluid resistant parts  7  communicating with the through holes  52  to form the individual liquid chambers  6 , and has through holes  55  formed to form the liquid introduction parts  8 . By putting the plate-shaped member  22  between the plate-shaped members  21  and  23 , the fluid resistant parts  7  are formed by the through holes  53 . 
     Here, the width wa of the separation wall parts  50   a  and  50   c , which constitute the separation walls  50  of the plate-shaped member  21  and the plate-shaped member  23  between the individual liquid chambers  6 , in the nozzle arrangement direction (referred to as the “separation wall width” below) is formed to be narrower than the separation wall width wb of the separation wall parts  50   b  of the plate-shaped member  22 , which also constitutes the separation walls  50  between the individual liquid chambers  6 . 
     In other words, the width of the through holes  51  and  53  of the plate-shaped member  21  and the plate-shaped member  23  that constitute the individual liquid chambers  6 , are formed to be wider than the width of the through holes  52  of the plate-shaped member  22  that also constitutes the individual liquid chambers  6 . 
     Namely, the passage plate  2  is formed by an odd number of the plate-shaped members  21  to  23 , and the separation wall width wa of the plate-shaped members  21  and  23  that are odd-numbered (first and third) counting from the nozzle plate  1  side, is narrower than the separation wall width wb of the even-numbered (second) plate-shaped member  22 . 
     Configured in this way, steps are formed on the separation walls  50  between the individual liquid chambers  6 , by the wall surfaces of the separation wall parts  50   a  and  50   c  of the plate-shaped members  21  and  23 , the wall surfaces of the separation wall parts  50   b  of the plate-shaped member  22 , and the bonded surfaces the separation wall parts  50   b  of the plate-shaped member  22 . 
     Here, the nozzle plate  1  and the plate-shaped member  21 , the plate-shaped members  21  and  22 , the plate-shaped members  22  and  23 , and the plate-shaped member  23  and the vibration plate member  3  are bonded by the adhesive, respectively. 
     Consequently, the fillets  60   a  are formed by the forced-out adhesive between the nozzle plate  1  and the wall surfaces of the separation walls part  50   a  of the plate-shaped member  21 . Also, the fillets  60   b  are formed by the forced-out adhesive between the wall surfaces of the separation wall parts  50   a  of the plate-shaped member  21 , and the bonded surfaces of the separation wall parts  50   b  of the plate-shaped member  22 . Also, the fillets  60   c  are formed by the forced-out adhesive between the bonded surfaces of the separation wall parts  50   b  of the plate-shaped member  22 , and the wall surfaces of the separation wall parts  50   c  of the plate-shaped member  23 . Also, the fillets  60   d  are formed by the forced-out adhesive between the wall surfaces of the separation walls part  50   c  of the plate-shaped member  23 , and the vibration plate member  3 . 
     In this way, the fillets  60  are formed not only between the passage plate  2 , the nozzle plate  1 , and the vibration plate member  3 , but also between the plate-shaped members  21 ,  22 , and  23 . Therefore, the bond strength is raised by forming the passage plate by having multiple plate-shaped members stacked and bonded, and hence, the liquid chamber rigidity can be raised. 
     In this case, the fillets  60   a  to  60   d  are formed so that their cross-sectional shapes in the nozzle arrangement direction are virtually the same. 
     Next, an assembly process of these members will be described specifically. 
     The nozzle plate  1 , the plate-shaped members  21 ,  22 , and  23 , and the vibration plate member  3  are bonded by the adhesive to form a passage unit. 
     First, the nozzle plate  1  and the plate-shaped member  21  are bonded to each other by the adhesive  60 . The adhesive  60  is of one component, and is applied to the plate-shaped member  21  by a spray, which is then heated in a pressurized state to be bonded. 
     Note that an application amount of the adhesive  60  is determined by the width of the fillet  60   a  to be obtained after the bonding. Denoting a target value of the fillet width after the bonding by wr, wr=(wa+wb)/2 where wa represents the separation wall width of the separation wall parts  50   a  and  50   c  of the plate-shaped members  21  and  23 , and wb represents the separation wall width of the separation wall parts  50   b  of the plate-shaped member  22 . An application amount that results in the fillet width wr is determined by an experiment. 
     Next, the plate-shaped member  23  and the vibration plate member  3  are bonded to each other by the adhesive  60 . This bonding is also done by applying the adhesive  60  to the plate-shaped member  23  by the spray. The application amount is determined by the same method used for the nozzle plate  1  and the plate-shaped member  21  described above. 
     Next, a combined plate of the nozzle plate and the plate-shaped member  21 , and a combined plate of the plate-shaped member  23  and the vibration plate member  3 , are bonded to respectively surfaces of the plate-shaped member  22 . This bonding is done by applying the adhesive  60  to both surfaces of the plate-shaped member  22 . The application amount is determined by the same method used for the nozzle plate  1  and the plate-shaped member  21 . In this case, however, the condition is extracted for each of the surfaces. 
     Note that the passage unit is bonded to the piezoelectric actuator  11  by the adhesive. 
     The bonding for the above configuration generates the fillets  60   b  of the adhesive  60  because the separation wall width wb of the plate-shaped member  22  is relatively wider than the separation wall width wa of the plate-shaped member  21 . The projection amount of the separation wall part  50   b  on the plate-shaped member  22  toward the individual liquid chamber  6  is set longer that the distance from the separation wall part  50   c  of the plate-shaped member  23  to the vibration area  30  of the vibration plate member  3 . This is because it is necessary to prevent the adhesive  60  from flowing out to reach the vibration area  30  for the bonding between the vibration plate member  3  and the plate-shaped member  23 . 
     Therefore, the fillets  60   b  and  60   c  generated on the separation wall parts  50   b  of the plate-shaped member  22  have the same width in the nozzle arrangement direction as the width of the fillets  60   d  generated between the vibration plate member  3  and the plate-shaped member  23 . Also, the fillets  60   a  generated at the bonding between the nozzle plate  1  and the plate-shaped member  21  have the same width because the plate-shaped member  21  and the plate-shaped member  23  have the same separation wall width. 
     Thus, the uniform fillets  60   a  to  60   d  are formed for all bonding. 
     Configured in this way, differences of the bond strengths are reduced among the stacked plate-shaped members, and a highly reliable head can be obtained. Also, by having the bond strength improved, the crosstalk performance is improved, and a head having less fluctuation of droplet speed can be obtained irrespective of the number of drive channels (the number of simultaneously driven nozzles). 
     Next, a liquid discharge head will be described according to a second embodiment of the present invention with reference to  FIG. 7 .  FIG. 7  is a cross-sectional view that illustrates a part of a passage unit of the liquid discharge head. 
     In the present embodiment, a roughening process (a process to roughen a surface) is applied to surfaces to be bonded of an intermediate plate-shaped member  22  to obtain the rough surfaces  70 . 
     Configured in this way, the rough surfaces  70  have an anchor effect to the adhesive  60 , with which the bond strength can be further raised between the plate-shaped member  22  and the plate-shaped members  21  and  23 . 
     Next, a liquid discharge head will be described according to a third embodiment of the present invention with reference to  FIG. 8 .  FIG. 8  is a cross-sectional view that illustrates a part of a passage unit of the liquid discharge head. 
     In the present embodiment, an odd number of, or five plate-shaped members  21  to  25  are stacked and bonded to form the passage plate  2 . The five plate-shaped members  21  to  25  have through holes formed to form the individual liquid chambers  6 , and the separation wall parts  50   a  to  50   e  to form separation walls  50  between the individual liquid chambers  6 . 
     A nozzle plate  1  is bonded to the plate-shaped member  21 , and a wall surface member or a vibration plate member  3  is bonded to the plate-shaped member  25 . 
     In addition, the separation wall width wa of the plate-shaped members  21 ,  23 , and  25  that are odd-numbered (first, third, and fifth) counting from the nozzle plate  1  side, is configured to be narrower than the separation wall width wb of the even-numbered (second and fourth) plate-shaped members  22  and  24 . 
     Configured in this way, even though the heights of the individual liquid chambers  6  are higher due to this multi-layer structure, the bond strength can be secured. 
     Next, an example of an image forming apparatus will be described that includes a liquid discharge head according to the embodiments of the present invention with reference to  FIG. 9  and  FIG. 10 .  FIG. 9  is a side view that illustrates a mechanical part of the image forming apparatus, and  FIG. 10  is a plane view that illustrates a core part of the mechanical part. 
     The image forming apparatus is a serial-type image forming apparatus, and holds a carriage  233  by main and sub guide rods  231  and  232  that are guide members to make the carriage  233  slidable in a main scanning direction, and are also lateral bridging parts between left and right side plates  221 A and  221 B. Also, a main scanning motor (not illustrated) is provided to move the carriage  233  for scanning via a timing belt in a direction designated by an arrow (main scanning direction of the carriage). 
     The carriage  233  has two recording heads  234   a  and  234   b  (referred to as the “recording head(s)  234 ” if distinction is not needed below, and the same for the other members) mounted that include liquid discharge heads to discharge ink droplets of several colors. The recording head  234  has an array of multiple nozzles arranged in a sub-scanning direction, which is perpendicular to the main scanning direction, and has its surface for discharging ink droplets directed downward. 
     Here, each of the recording heads  234  includes the liquid discharge head having two lines of nozzles. One recording head  234   a  has a line of nozzles discharging black (K) droplets, and the other line of nozzles discharging cyan (C) droplets. The other recording head  234   b  has a line of nozzles discharging magenta (M) droplets, and the other of nozzles discharging yellow (Y) droplets. Note that although the configuration here has two heads for discharging liquid droplets of four colors, liquid discharge heads may be provided for the colors, respectively. 
     The carriage  233  also has sub tanks  235  attached to supply ink of corresponding colors to the lines of nozzles of the recording head  234 . Ink of the corresponding colors is supplied to the sub tanks  29  from ink cartridges  210  of the corresponding colors by the supply units  224  via supply tubes  236  of the corresponding colors. 
     On the other hand, as a sheet feeding part to feed sheets  242  loaded on a sheet loading part (pressure plate)  241  of a sheet feeding tray  202 , the mechanical part includes a semicircular roller (a sheet feeding roller)  243  to separate and feed the sheets  242  from the sheet loading section  241  one by one, and a separation pad  244  facing the sheet feeding roller  243 . 
     Then, to convey the sheet  242  fed by the sheet feeding part, below the recording head  234 , the mechanical part includes a guide  245  to guide the sheet  242 , a counter roller  246 , a conveyance guide member  247 , and a pressing member  248  having a tip-pressing roller  249 . Further, the mechanical part includes a conveyance belt  251  that is a conveyance unit to attract the conveyed sheet  242  electrostatically, and to convey it to a position facing the recording head  234 . 
     This conveyance belt  251  is an endless belt, and configured to be wrapped around and stretched between a conveying roller  252  and a tension roller  253 , to rotate in a belt conveyance direction (the sub-scanning direction). Also, the mechanical part includes a charging roller  256  as a charging unit to charge the surface of this conveyance belt  251 . This charging roller  256  is disposed to contact the surface layer of the conveyance belt  251 , and to rotate depending on rotary movement of the conveyance belt  251 . This conveyance belt  251  moves rotationally in the belt conveying direction when the conveying roller  252  is driven to rotate by a sub-scanning motor (not illustrated) via a timing belt. 
     Further, as a sheet ejecting part to eject the sheet  242  having recorded by the recording head  234 , the mechanical part includes a separation claw  261  to separate the sheet  242  from the conveyance belt  251 , a sheet ejection roller  262  and a sheet ejection roller  263 , and a sheet ejection tray  203  under the sheet ejection roller  262 . 
     Also, on a back part of the main body of the apparatus, a duplex unit  271  is provided that can be easily attached or detached. This duplex unit  271  takes in the sheet  242  that has returned by reverse directional rotation of the conveyance belt  251 , flips of the sheet  242 , and feeds the sheet  242  again into a nip between the counter roller  246  and the conveyance belt  251 . Also, a manual feed tray  272  is set on the top surface of the duplex unit  271 . 
     Further, in a non-printing area at one end in the main scanning direction of the carriage  233 , a maintenance and recovery mechanism  281  is provided to maintain and recover a state of the nozzles of the recording head  234 . 
     The maintenance and recovery mechanism  281  includes cap members (referred to as “caps” below)  282   a  and  282   b  (referred to as the “cap(s)”  282  if distinction is not required) for capping the nozzle surfaces of the recording head  234 . The maintenance and recovery mechanism  281  also includes a wiper blade  283 , which is a blade member to wipe the nozzle surfaces. The maintenance and recovery mechanism  281  also includes a blank discharge receiver  284  to receive liquid droplets when blank discharging is executed to discharge liquid droplets, not for contributing to the recording, but for discarding recording liquid having increased viscosity. 
     Also, in a non-printing area at the other end in the main scanning direction of the carriage  233 , a blank discharge receiver  288  is disposed to receive liquid droplets when blank discharging is executed to discharge liquid droplets, not for contributing to the recording, but for discarding recording liquid having increased viscosity during the recording or the like. This blank discharge receiver  288  includes an opening  289  along the lines of nozzles of the recording head  234 . 
     In this image forming apparatus configured in this way, the sheets  242  are separated and fed from the sheet feed tray  202  one by one. The sheet  242  fed and turned in a virtually vertical up direction is guided through the guide  245 , and is conveyed through a nip between the conveyance belt  251  and the counter roller  246 . Further, the sheet  242  has its tip guided by a conveyance guide (not illustrated), to be pressed on the conveyance belt  251  by the tip-pressing roller  249 , and the conveyance direction is turned by about 90°. 
     Then, when the sheet  242  is conveyed on the charged conveyance belt  251 , the sheet  242  is attracted by the conveyance belt  251 , and conveyed in the sub-scanning direction by rotational movement of the conveyance belt  251 . 
     While having the carriage  233  move, the image forming apparatus drives the recording head  24  in response to image signals, to discharges ink droplets onto the suspended sheet  242  to record a line of image data, then conveys the sheet  242  by a predetermined length, and executes recording the next line. When receiving a signal indicating the end of recording, or a signal indicating that the rear end of the sheet  242  has reached the recording area, the image forming apparatus ends the recording operation, and ejects the sheet  242  to the sheet ejection tray  203 . 
     Thus, this image forming apparatus includes a liquid discharge head according to one of the embodiments of the present invention as the recording head, and hence, can stably form images having high picture quality. 
     Note that in the present invention, a medium to be recorded on, a recording medium, recording paper, and a recording sheet are treated as synonyms. Also, image forming, recording, character printing, photo printing, and printing are treated as synonyms. 
     Also, an “image forming apparatus” means an apparatus to form an image by discharging liquid onto media such as paper, strings, fiber, cloth, leather, metals, plastic, glass, wood, ceramics and the like. Also, “image forming” means not only to form images having meanings such as characters, figures and the like onto a medium, but to form images without patterns or meanings onto a medium, such as just discharging droplets onto a medium. 
     Also, if not especially specified, “ink” is not limited to so-called ink, but the term “ink” is used as a generic term to mean any kind of liquid which can be used for image forming such as recording liquid, fixing liquid, liquid and the like. “Ink” may include, for example, DNA samples, photoresist, patterning material, resin and the like. 
     Also, an “image” is not limited to a planar image, but includes an image formed on a three dimensional object, and a solid body formed three dimensionally. 
     Also, if not especially specified, an image forming apparatus may be either of a serial-type image forming apparatus or a line-type image forming apparatus. 
     Also, the pressure generation unit is not limited to a piezoelectric actuator, but may be a thermal actuator that uses an electrothermal transducer such as a thermal resistance element, or an electrostatic actuator including a vibration plate and facing electrodes. 
     Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on and claims the benefit of priority of Japanese Priority Application No. 2014-189543 filed on Sep. 18, 2014, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.