Patent Publication Number: US-11034150-B2

Title: Ink jet head and ink jet printer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-050104, filed on Mar. 18, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an ink jet head and an ink jet printer. 
     BACKGROUND 
     An ink jet head that ejects an ink droplet from a nozzle by pressurizing ink with a piezoelectric member or the like is known. Such an ink jet head may have a structure imparted with ink repellency so the ink will not adhere to a nozzle plate surface or the like. Methods for imparting ink repellency may include forming an ink repellent film containing fluorine-based resin on the nozzle plate surface. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of an ink jet head according to an embodiment. 
         FIG. 2  illustrates an exploded perspective view of an actuator plate, a frame, and a nozzle plate in the ink jet head according to the embodiment. 
         FIG. 3  illustrates a partially cut top view of the ink jet head according to the embodiment. 
         FIG. 4  illustrates a cross-sectional view of a part of the ink jet head illustrated in  FIG. 3  along a plane perpendicular to a Y-axis in  FIG. 3 . 
         FIG. 5  is a graph illustrating an example of an XPS spectrum according to Example 1, Comparative Example 1, and Reference Example 1. 
         FIG. 6  is a schematic diagram illustrating an ink jet printer according to the embodiment. 
         FIG. 7  is a graph illustrating ink repellency according to Example 1, Comparative Example 1, and Reference Example 1. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments provide an ink jet head with preferable liquid repellency and an ink jet printer equipped with such an ink jet head. 
     In general, according to an embodiment, an ink jet head includes a nozzle plate base including a plurality of nozzles and a liquid repellent film on a surface of the nozzle plate base. The liquid repellent film comprises a polymeric compound formed of repeating units with a cyclic structure. A portion of the repeating units with the cyclic structure are ring-opened. 
     According to another embodiment, an ink jet printer is provided. The ink jet printer includes the ink jet head according to an embodiment and a medium conveyer. 
     1. Ink Jet Head 
     1-1. Configuration 
     Hereinafter, example embodiments will be described with reference to the drawings. 
       FIG. 1  illustrates a perspective view of an on-demand type ink jet head  1  that can be mounted on a head carriage of an ink jet printer according to an embodiment. In the following description, an orthogonal coordinate system including an X-axis, a Y-axis, and a Z-axis is used. For the sake of convenience, a direction indicated by an arrow in the figure is a positive direction. The X-axis direction corresponds to a print width direction. The Y-axis direction corresponds to a direction along which a recording medium, such as a sheet of paper, is conveyed. The plus Z-axis direction is a direction orthogonal to a surface of the recording medium. 
     As depicted in  FIG. 1 , the ink jet head  1  includes an ink manifold  10 , an actuator plate  20 , a frame  40 , and a nozzle plate  50 . 
     The actuator plate  20  has a rectangular shape whose longitudinal direction is the X-axis direction. Examples of the material of the actuator plate  20  include alumina (Al 2 O 3 ), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), aluminum nitride (AlN), and lead zirconate titanate (PZT: Pb(Zr,Ti)O 3 ). 
     The actuator plate  20  is overlaid on the ink manifold  10  so as to close an open end of the ink manifold  10 . The ink manifold  10  is connected to an ink cartridge via an ink supply pipe  11  and an ink return pipe  12 . 
     The frame  40  is attached on the actuator plate  20 . The nozzle plate  50  is attached on the frame  40 . A plurality of nozzles N are provided on the nozzle plate  50  at predetermined intervals along the X-axis direction so as to form two rows along the Y-axis. 
       FIG. 2  illustrates an exploded perspective view of the actuator plate  20 , the frame  40 , and the nozzle plate  50  included in the ink jet head according to the embodiment.  FIG. 3  illustrates a partially cut top view of the ink jet head according to the embodiment.  FIG. 4  illustrates a cross-sectional view of a part of the ink jet head illustrated in  FIG. 3  along a plane perpendicular to the Y-axis. 
     This ink jet head  1  is a side-shooter type of a so-called shear mode shared-wall type. 
     As illustrated in  FIGS. 2 and 3 , in the actuator plate  20 , a plurality of ink supply ports  21  are provided at intervals along the X-axis direction so as to form a row at a central portion in the Y-axis direction. In the actuator plate  20 , a plurality of ink discharge ports  22  are provided at intervals along the X-axis direction so as to respectively form rows in the plus Y-axis direction and the minus Y-axis direction with respect to the row of ink supply ports  21 . 
     A plurality of piezoelectric members  30  are provided between the row of ink supply ports  21  provided at the central portion and one row of ink discharge ports  22 . These piezoelectric members  30  form a row extending in the X-axis direction. The plurality of piezoelectric members  30  are also provided between the row of ink supply ports  21  provided at the central portion and the other row of ink discharge ports  22 . These piezoelectric members  30  also form a row extending in the X-axis direction. 
     As illustrated in  FIG. 4 , each of the rows formed with the plurality of piezoelectric members  30  includes a first piezoelectric body  301  and a second piezoelectric body  302  laminated on the actuator plate  20 . Examples of the material of the first piezoelectric body  301  and the second piezoelectric body  302  include lead zirconate titanate (PZT), lithium niobate (LiNbO 3 ), and lithium tantalate (LiTaO 3 ). The first piezoelectric body  301  and the second piezoelectric body  302  are polarized in opposite directions along the thickness direction. 
     In a laminate composed of the first piezoelectric body  301  and the second piezoelectric body  302 , a plurality of grooves each extending in the Y-axis direction and arranged in the X-axis direction are provided. These grooves are open on the second piezoelectric body  302  side, and have a depth larger than the thickness of the second piezoelectric body  302 . Hereinafter, portions of the laminate that are sandwiched between adjacent grooves are referred to as channel walls. Each of these channel walls extends in the Y-axis direction and is arranged in the X-axis direction. 
     The piezoelectric member  30  forms a pressure chamber  32  at a position communicating with a nozzle N described below and ejects ink in the pressure chamber  32  by changing pressure in the pressure chamber  32 . The pressure chamber  32  through which ink circulates is a space positioned in the groove between two adjacent channel walls. The width of the pressure chamber  32 , here, the dimension along the X-axis direction of the pressure chamber  32  is preferably in the range of 20 μm to 100 μm, and more preferably in the range of 50 μm to 80 μm. 
     An electrode  33  is formed on the side walls and the bottom surrounding the pressure chamber  32 . That is, the electrode  33  is formed on a portion of the piezoelectric member  30  adjacent to the pressure chamber  32 . These electrodes  33  are connected to wiring patterns  31  extending along the Y-axis direction. The electrode  33  applies the drive pulse to the piezoelectric member  30 . 
     An electrode protective film  34  is formed on the surface of the actuator plate  20  including the electrode  33  and a wiring pattern  31  except for a connection portion used to make a connection to a flexible printed board described below. The electrode protective film  34  has an insulating property. The electrode protective film  34  is a film containing a polymeric compound having a polyparaxylylene backbone, for example. 
     The frame  40  has an opening as illustrated in  FIGS. 2 and 3 . The opening is smaller than the actuator plate  20  and larger than a region of the actuator plate  20  where the ink supply port  21 , the piezoelectric member  30 , and the ink discharge port  22  are provided. The frame  40  is made of ceramics, for example. The frame  40  is joined to the actuator plate  20  by an adhesive, for example. 
     The nozzle plate  50  is larger than the opening of the frame  40 . The nozzle plate  50  is joined to the frame  40  by an adhesive, for example. 
     In the nozzle plate  50 , a plurality of nozzles N that eject ink toward the recording medium are provided. These nozzles N form two rows corresponding to the pressure chambers  32 . The nozzle N has a diameter that increases from the recording medium facing surface toward the pressure chamber  32 . The dimension of the nozzle N is set to a predetermined value according to an ink ejection amount. The nozzle N can be formed, for example, by performing laser machining using an excimer laser. 
     The actuator plate  20 , the frame  40 , and the nozzle plate  50  are integrated as illustrated in  FIG. 1 , and form a hollow structure. A region surrounded by the actuator plate  20 , the frame  40 , and the nozzle plate  50  is an ink circulation chamber. Ink is circulated in such a way that ink is supplied from the ink manifold  10  to the ink circulation chamber through the ink supply port  21 , passes through the pressure chamber  32  and excess ink returns from the ink discharge port  22  to the ink manifold  10 . A part of the ink is ejected from the nozzle N while flowing through the pressure chamber  32  and is used for printing. 
     A flexible printed board  60  is connected to the wiring pattern  31  at a position outside the frame  40  on the actuator plate  20 . A drive circuit  61  that drives the piezoelectric member  30  is mounted on the flexible printed board  60 . 
     As illustrated in  FIG. 4 , the nozzle plate  50  includes a nozzle plate base material  501  and a liquid repellent film  502  provided on the recording medium facing surface, also referred to as the ejection surface. The nozzle plate base material  501  is made of a resin film such as a polyimide film, for example. The liquid repellent film  502  may also be provided on the back side surface of the nozzle plate base material  501 . 
     The liquid repellent film  502  comprises a polymeric compound containing a repeating unit with a cyclic moiety. According to an example, the liquid repellent film  502  is primarily comprised of the polymeric compound containing the repeating unit with the cyclic moiety. A portion of the cyclic structures of the cyclic moieties have been ring-opened. In other words, the compound contained in the liquid repellent film  502  contains both (closed) cyclic portions and corresponding ring-opened portions. The closed and ring-opened portions can be are randomly arranged within the polymeric compound, for example. 
     The cyclic moiety preferably includes a fluorine atom thereon or therein. The cyclic structure can be an aliphatic ring, or preferably a fluorinated aliphatic ring. When the aliphatic ring is fluorinated, liquid repellency of the liquid repellent film  502  tends to increase. The cyclic structure is preferably a heterocyclic compound composed of carbon and oxygen, and more preferably, a heterocyclic compound including an ether bond (C—O—C). When the cyclic structure contains an ether bond, the liquid repellency of the liquid repellent film  502  tends to increase. 
     The polymeric compound with a repeating unit that contains the cyclic moiety structure is preferably a fluororesin, more preferably an amorphous fluororesin. When a fluororesin is used, the liquid repellency of the liquid repellent film  502  tends to increase. 
     A repeating unit containing a cyclic moeity is represented by the following chemical formula (1), for example. As one example compound having the following chemical formula (1) as the repeating unit, for example, CYTOP® manufactured by AGC Inc. can be used. The cyclic structure contained in the repeating unit may be a 5-membered ring or a structure other than a 5-membered ring. 
     
       
         
         
             
             
         
       
     
     In the liquid repellent film  502 , a portion of the cyclic structures represented by the chemical formula (1) has been ring-opened. The corresponding ring-opened structure for chemical formula (1) is represented, for example, by the following chemical formula (2). In chemical formula (2), an end (terminal) of the ring-opened chain can be modified to include a substituent R thereon or thereat. R is, for example, a hydroxyl (OH) group. The two substituent Rs illustrated in the chemical formula (2) may be the same or different from each other. The compound in the liquid repellent film  502  may be a co-polymer in which units of chemical formula (1) and units of chemical formula (2) are randomly arranged. 
     
       
         
         
             
             
         
       
     
     Confirmation that the liquid repellent film  502  contains the repeating unit and that the repeating unit contains the cyclic structure can be obtained by, for example, nuclear magnetic resonance (NMR) analysis and mass (MS) analysis. 
     Confirmation that only a portion of the cyclic structures in the liquid repellent film  502  have been ring-opened can be obtained by, for example, X-ray photoelectron spectroscopy (XPS). Specifically, by comparing areas of peaks which characteristically belong to bonds in the cyclic structures in an XPS spectrum of a liquid repellent film in which all of the cyclic structures are unopened to areas of those peaks in an XPS spectrum of a liquid repellent film in which all of the cyclic structures have been ring-opened, then an XPS spectrum of a liquid repellent film in which a only a portion of the cyclic structures have been ring-opened can be observed and the portion estimated. 
     That is, in an XPS spectrum of a liquid repellent film in which a portion of the cyclic structures have been ring-opened, the peak area I 1  corresponding to a bond contained in the cyclic structure is smaller than a peak area  12  of corresponding to the same bond in an XPS spectrum of a liquid repellent film in which none of the cyclic structures have been ring-opened, but will be larger than a peak area I 3  corresponding to the same bond in an XPS spectrum of a liquid repellent film in which all of the cyclic structures have been ring-opened. In other words, when the peak area I 1  is smaller than the peak area I 2  but larger than the peak area I 3 , it can be said that some portion of the cyclic structures in the liquid repellent film  502  have been ring-opened. 
     Here, an example case in which a compound containing the repeating unit represented by the chemical formula (1) is used for a liquid repellent film  502  will be described.  FIG. 5  is a graph illustrating XPS spectra for Example 1, Comparative Example 1, and Reference Example 1.  FIG. 5  is an XPS spectrum relating to C1s. In  FIG. 5 , Example 1 is a liquid repellent film containing a compound in which some of the repeating units represented by the chemical formula (1) have been ring-opened, Reference Example 1 is a liquid repellent film containing a compound in which none of the repeating units represented by the chemical formula (1) have been ring-opened, and Comparative Example 1 is a liquid repellent film containing a compound in which all of the repeating units represented by the chemical formula (1) have been ring-opened. 
     The repeating unit represented by the chemical formula (1) contains a CF 2 O bond, a CF 2  bond, and a CF bond in its cyclic structure. As illustrated in  FIG. 5 , in an XPS spectrum, the peak P 1  belonging to the CF 2 O bond appears on the high bond energy side within the range of 1 eV or more and 1.3 eV or less than bond energy of the peak P 2  belonging to the CF 2  bond. The peak P 3  belonging to the CF bond appears on the low bond energy side within the range of 1.7 eV or more and 2 eV or less than the bond energy of the peak P 2  belonging to the CF 2  bond. 
     The peak P 1  belonging to the CF 2 O bond is an indicator that the liquid repellent film has a cyclic structure. Accordingly, when a ratio A 1 /A 2  between an area A 1  of the peak P 1  and an area A 2  of the peak P 2  is greater than 0 but is less than or equal to 0.8, it can be said that some of the cyclic structures in the liquid repellent film have been ring-opened. That is, when the ratio A 1 /A 2  is greater than 0.8, it can be said that none of the cyclic structures of the compounds in the liquid repellent film are ring-opened. When the ratio A 1 /A 2  is 0, it can be said that all of the cyclic structures of the compounds in the liquid repellent film have been ring-opened. Peak areas of the peaks P 1 , P 2 , and P 3  are obtained by performing peak separation on the XPS spectrum relating to C1s. 
     The film thickness of the liquid repellent film  502  is preferably 10 nm to 200 nm. When the film thickness of the liquid repellent film  502  is within this range, good liquid repellency can be maintained over a long period. 
     1-2. Ink Ejection 
     Hereinafter, the operation of the piezoelectric member  30  will be described with reference to  FIGS. 3 and 4 . Here, the operation will be described assuming that the pressure chambers  32  are also formed on both sides of the central pressure chamber  32 . It is assumed that the electrodes  33  corresponding to the three adjacent pressure chambers  32  are electrodes A, B and C, respectively, and the electrode  33  corresponding to the central pressure chamber  32  is the electrode B. 
     In order to eject ink from a nozzle N corresponding to the central pressure chamber  32 , first, for example, a voltage pulse having higher potential than potentials of the adjacent electrodes A and C is applied to the central electrode B to generate an electric field in a direction perpendicular to the channel wall. Thus, the channel walls are driven in the shear mode and a pair of channel walls sandwiching the central pressure chamber  32  is deformed so that the central pressure chamber  32  expands. 
     Next, a voltage pulse having higher potential than the potential of the central electrode B is applied to both adjacent electrodes A and C to generate an electric field in a direction perpendicular to the channel wall. Thus, the channel walls are driven in the shear mode and the pair of channel walls sandwiching the central pressure chamber  32  is deformed so that the central pressure chamber  32  is reduced. By this operation, pressure is applied to ink in the central pressure chamber  32  and the ink is ejected from the nozzle N corresponding to the pressure chamber  32  to land on the recording medium. Thus, in the ink jet head  1 , ink is ejected from the nozzle N using the piezoelectric member  30  as an actuator. 
     In the printing process using the ink jet head  1 , for example, all the nozzles N are divided into three groups and the driving operation described above is performed in a time-sharing manner for three cycles to perform printing on the recording medium. 
     1-3. Manufacturing Method 
     Next, a method for manufacturing the ink jet head  1  illustrated in  FIGS. 1 to 4  will be described. 
     First, as illustrated in  FIGS. 2 and 3 , a structure in which the piezoelectric member  30  is provided on the actuator plate  20  is formed by a method known in the related art. Next, as illustrated in  FIGS. 2 to 4 , the wiring pattern  31  and the electrode  33  are formed on the piezoelectric member  30  and the actuator plate  20  by, for example, plating. Next, as illustrated in  FIG. 4 , the electrode protective film  34  is formed on the electrode  33  and a portion of the second piezoelectric body  302  that is not covered with the electrode  33  by, for example, a chemical vapor deposition (CVD) method. Next, as illustrated in  FIG. 2 , the frame  40  is attached to the upper surface of the actuator plate  20  through an adhesive. 
     Next, the nozzle plate  50  including the liquid repellent film  502  is prepared. Specifically, first, the nozzle plate base material  501  is prepared. The nozzle plate base member  501  includes a hole to serve as a nozzle. When the hole to be a nozzle is provided after the liquid repellent film  502  is formed, the nozzle plate base material  501  having no holes may be used. 
     A liquid repellent film material-containing liquid is coated onto one main surface of the nozzle plate base material  501  to form a coating film. As a method for forming the coating film, for example, a spin coating method or an immersion method is used. The coating film may be formed on both surfaces of the nozzle plate  501 . Prior to coating the liquid repellent film material-containing liquid, the surface of the nozzle plate base material  501  may be subjected to pretreatment. Examples of the pretreatment include silane coupling agent coating, plasma treatment, and the like. When such pretreatment is performed, the adhesion between the nozzle plate base material  501  and the liquid repellent film  502  can be enhanced. 
     The liquid repellent film material-containing liquid may contain the compound containing the repeating unit that contains the cyclic structure and a solvent capable of dissolving the compound. The liquid repellent film material-containing liquid contains, for example, a fluorine-based organic material and a fluorine-based organic solvent capable of dissolving the fluorine-based organic material. The compound contained in the fluorine-based organic material may be capable of forming a polymer having a structure, which includes a cyclic structure formed at a specific temperature (so-called cyclic-bond temperature), as a repeating unit. As the fluorine-based organic material, A-type CYTOP® manufactured by AGC Inc. may be used. 
     This coating film is subjected to heating treatment to form the liquid repellent film. In the heating treatment, the heating temperature is set to a cyclic-bond temperature or higher, preferably 100° C. to 200° C., and the heating time is more preferably 30 minutes to 2 hours. In the liquid repellent film immediately after film formation, it is considered that substantially none of the cyclic structures in the compounds have been ring-opened. 
     Next, the nozzle plate base material  501  is attached to the frame  40  through an adhesive so that the main surface has the liquid repellent film faces outward and the nozzle N and the pressure chamber  32  communicate with each other. Next, the attached nozzle plate base material  501  and frame  40  are heated at a temperature of 100° C. to 180° C. for several hours, for example. With this configuration, the nozzle plate base material  51  is bonded to the frame  40 . 
     Through a series of treatments including this heating treatment, all of the cyclic structures contained in the repeating units in the liquid repellent film are ring-opened. The liquid repellent film in which all of the cyclic structures have been ring-opened has significantly lower liquid repellency than that of the liquid repellent film immediately after film formation (that is, before ring-opening of the cyclic structures). 
     Next, reheating treatment is performed on the liquid repellent film. In the reheating treatment, the heating temperature is set to be equal to or higher than the cyclic-bond temperature. The heating temperature is preferably in a range of 120° C. to 210° C. It is preferable that the heating time in this reheating treatment is in a range of 30 minutes to 2 hours. Next, the liquid repellent film after the reheating treatment is cooled until reaching a temperature of 40° C. or lower, for example. By this reheating treatment and cooling treatment, a part of the ring-opened cyclic structures in the liquid repellent film are reverted back to the cyclic structures again. With this configuration, the liquid repellent film  502  containing a compound containing a cyclic structure as a repeating unit, of which a part of these cyclic structures in the repeating units have been ring-opened, is obtained. 
     In the cooling, it is preferable to gradually cool the liquid repellent film at a rate in the range of 0.4° C./min to and 3° C./min until a temperature of, for example, 40° C. or less is reached. By gradually cooling, the liquid repellency of the liquid repellent film  502  can be further enhanced. 
     The ink jet head  1  according to the embodiment can be manufactured by the method as described above. 
     2. Ink Jet Printer 
     2.1 Configuration 
     In  FIG. 6 , a schematic diagram of an ink jet printer  100  is illustrated. 
     The ink jet printer  100  according to the embodiment includes ink jet heads  115 C,  115 M,  115 Y, and  115 Bk, and a medium holding mechanism  110  that holds the recording medium facing the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk. Each of the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk is the ink jet head  1  described with reference to  FIGS. 1 and 2 . 
     The ink jet printer  100  illustrated in  FIG. 6  includes a casing having a paper discharge tray  118 . In the casing, cassettes  101   a  and  101   b , paper feed rollers  102  and  103 , conveyance roller pairs  104  and  105 , a registration roller pair  106 , a conveyance belt  107 , a fan  119 , a negative pressure chamber  111 , conveyance roller pairs  112 ,  113 , and  114 , ink jet heads  115 C,  115 M,  115 Y, and  115 Bk, ink cartridges  116 C,  116 M,  116 Y, and  116 Bk, and tubes  117 C,  117 M,  117 Y, and  117 Bk are provided. 
     The cassettes  101   a  and  101   b  accommodate recording media P of different sizes. The paper feed roller  102  or  103  picks up the recording medium P corresponding to the size of a selected recording medium from the cassette  101   a  or  101   b  and conveys the recording medium P to the conveyance roller pairs  104  and  105  and the registration roller pair  106 . 
     The conveyance belt  107  is tensioned by a driving roller  108  and two driven rollers  109 . Holes are provided on the surface of the conveyance belt  107  at predetermined intervals. The negative pressure chamber  111  connected to the fan  119  for adsorbing the recording medium P to the conveyance belt  107  is provided inside the conveyance belt  107 . The conveyance roller pairs  112 ,  113 , and  114  are provided downstream of the conveyance belt  107  in the conveyance direction. A heater for heating a print layer formed on the recording medium P can be provided in a conveyance path from the conveyance belt  107  to the paper discharge tray  118 . 
     Above the conveyance belt  107 , four ink jet heads that eject ink onto the recording medium P according to image data are disposed. Specifically, an ink jet head  115 C that ejects cyan (C) ink, an ink jet head  115 M that ejects magenta (M) ink, an ink jet head  115 Y that ejects yellow (Y) ink, and an ink jet head  115 Bk that ejects black (Bk) ink are disposed in this order from the upstream side. 
     Above the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk, a cyan (C) ink cartridge  116 C, a magenta (M) ink cartridge  116 M, a yellow (Y) ink cartridge  116 Y, and a black (Bk) ink cartridge  116 Bk that respectively contain inks corresponding to the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk are provided. These ink cartridges  116 C,  116 M,  116 Y, and  116 Bk are connected to the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk by the tubes  117 C,  117 M,  117 Y, and  117 Bk, respectively. 
     Although not illustrated, the ink jet printer  100  may include a heater for heating the liquid repellent film on the nozzle plates of the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk. When liquid repellency of the liquid repellent film of the ink jet head is lowered, the liquid repellency of the liquid repellent film can be restored by reheating the liquid repellent film. 
     2-2. Image Formation 
     Next, an image forming operation of the ink jet printer  100  will be described. 
     First, an image processing unit starts image processing for recording, generates an image signal corresponding to image data, and generates a control signal for controlling operations of various rollers, the negative pressure chamber  111 , and the like. 
     Under the control of the image processing unit, the paper feed roller  102  or  103  picks up the recording medium P of the selected size one by one from the cassette  101   a  or  101   b  and conveys the recording medium P to the conveyance roller pair  104  or  105  and the registration roller pair  106 . The registration roller pair  106  corrects skew of the recording medium P and conveys the recording medium P at a predetermined timing. 
     The negative pressure chamber  111  sucks air through the holes of the conveyance belt  107 . Accordingly, the recording medium P is sequentially conveyed to positions below the ink jet heads  115 C,  115 M,  115 Y, and  115 Bk as the conveyance belt  107  moves in a state of being attracted to the conveyance belt  107 . 
     The ink jet heads  115 C,  115 M,  115 Y, and  115 Bk eject ink in synchronization with the timing at which the recording medium P is conveyed under the control of the image processing unit. With this configuration, a color image is formed at a desired position on the recording medium P. 
     Thereafter, the conveyance roller pairs  112 ,  113 , and  114  discharge the recording medium P on which the image is formed to the paper discharge tray  118 . When a heater is provided in the conveyance path from the conveyance belt  107  to the paper discharge tray  118 , the print layer formed on the recording medium P may be heated by the heater. When heating with the heater is performed, particularly, when the recording medium P is impermeable, adhesion of the print layer to the recording medium P can be improved. 
     3. Effect 
     The ink jet head  1  described above includes the liquid repellent film  502  containing the compound which contains a repeating unit containing a cyclic structure and some portion of the repeating units have the cyclic structure ring-opened. According to such a configuration, excellent liquid repellency can be achieved. This is considered in this instance to be due to the reason(s) described below. 
     As described above, in the manufacturing process of the ink jet head  1 , all of the cyclic structures may be ring-opened and become branches of chain-type structures. However, when the cyclic structures are thus all ring-opened, the liquid repellency of the liquid repellent film is significantly reduced. 
     The ink jet head according to the embodiment includes a liquid repellent film in which only a portion of the cyclic structures of the repeating units are ring-opened. That is, only some portion of repeating units are ring-opened and thus the remaining portion retain (or have) the closed (unopened) cyclic structure. Accordingly, the ink jet head according to the embodiment achieves excellent liquid repellency as compared with the ink jet head including the liquid repellent film in which all of the cyclic structures are ring-opened. 
     In the manufacturing method described above, not all of the branches formed by allowing the cyclic structure to be ring-opened will revert back to form the cyclic structure in the reheating treatment and the cooling treatment. 
     Some of the branches that do not form the cyclic structure may react with functional groups on the surface of the nozzle plate base material  501 . With this configuration, adhesion of the nozzle plate base material  501  and the liquid repellent film  502  can be improved. 
     The cyclic structure in the compound contained in the liquid repellent film is considered to be a portion that exhibits good liquid repellency. That is, the liquid repellent film can exhibit better liquid repellency by exposing the cyclic structure portion to the external surface at which ink can come into contact. Other branches that do not form the cyclic structure may prevent the re-formed cyclic structure(s) from rotating around the main chain and help prevent the cyclic structure portion from moving from the external surface to the inside of the liquid repellent film. With this configuration, the ink jet head according to the embodiment can maintain excellent liquid repellency over a long period of time. 
     EXAMPLES 
     Examples will be described below. 
     Reference Example 1 
     First, a fluorine-based resin-containing liquid in which fluorine-based resin was dissolved in a fluorine-based solvent was prepared. As the fluorine-based resin, A-type CYTOP® manufactured by AGC Inc. was used. 
     Next, using a spin coating method, the fluorine-based resin-containing liquid was coated onto the surface of the nozzle plate base material and the coating film was subjected to heating treatment. In the heating treatment, the heating treatment temperature was 180° C. and the heating treatment time was 30 minutes. A polyimide film was used as the nozzle plate base material. 
     In this way, a nozzle plate including a liquid repellent film containing a compound having a cyclic structure was obtained. The film thickness of the liquid repellent film was 200 nm. 
     Example 1 
     The ink jet head  1  was manufactured by the method described above using the nozzle plate obtained by the method of Reference Example 1. In the reheating treatment, the heating temperature was 205° C. and the heating time was 2 hours. The cooling treatment was performed at a rate of 1.5° C./min until reaching 40° C. 
     In this way, an ink jet head including a liquid repellent film containing a compound in which a part of the cyclic structure was ring-opened was obtained. 
     Comparative Example 1 
     An ink jet head was manufactured by the same method as in Example 1 except that the reheating treatment and the cooling treatment were omitted. 
     In this way, an ink jet head including a liquid repellent film containing a compound in which all of the cyclic structures were ring-opened was obtained. 
     XPS Analysis 
     For the liquid repellent film of the ink jet head manufactured in Example 1 and Comparative Example 1 and the liquid repellent film of the nozzle plate obtained in Reference Example 1, the XPS spectrum was measured by the method described above.  FIG. 5  described above illustrates the result. 
     Liquid Repellency Evaluation 
     For the nozzle plate of the ink jet head according to Example 1 and Comparative Example 1 and the nozzle plate according to Reference Example 1, the time required for the nozzle plate to repel ink was measured. 
     First, ink was prepared. A water-based ink was used as the ink. 
     Next, the nozzle plate was held vertical at an upper end portion thereof, and substantially the entire nozzle plate was immersed into the ink. The upper end of the immersed nozzle plate was pulled up from the ink by a length of 60 mm, and the time required for the ink to disappear from the pulled up portion was measured. The result is illustrated in  FIG. 7 . 
       FIG. 7  is a graph illustrating the time for repelling the ink of the nozzle plates according to Example 1, Comparative Example 1, and Reference Example 1. As illustrated in  FIG. 7 , the liquid repellency of the nozzle plate according to Example 1 was higher than the liquid repellency of the nozzle plate according to Comparative Example 1. 
     The ink jet head according to at least one embodiment as described above includes a repellent film containing a compound which contains a repeating unit containing a cyclic structure and in which a part of the cyclic structure is ring-opened. Accordingly, the ink jet head according to the embodiment can achieve excellent liquid repellency. 
     While certain of embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.