Patent Publication Number: US-6213591-B1

Title: Injet recording apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus employing an inkjet recording method, and more particularly to an apparatus that ejects particulate matter such as pigment matter and toner matter by making use of an electric field. 
     2. Description of the Related Art 
     There has recently been a growing interest in non-impact recording methods, because noise while recording is extremely small to such a degree that it can be neglected. Particularly, inkjet recording methods are extremely effective in that they are structurally simple and that they can perform high-speed recording directly onto ordinary medium. One inkjet recording method there is an electrostatic inkjet recording method. 
     The electrostatic inkjet recording apparatus generally has an electrostatic inkjet recording head and a counter electrode which is disposed behind the recording medium to form an electric field between it and the recording head. The electrostatic inkjet recording head has an ink chamber which temporarily stores ink containing toner particles and a plurality of ejection electrodes formed near the end of the ink chamber and directed toward the counter electrode. The ink near the front end of the ejection electrode forms a concave meniscus due to its surface tension, and consequently, the ink is supplied to the front end of the ejection electrode. If positive voltage relative to the counter electrode is supplied to a certain ejection electrode of the head, then the particulate matter in ink will be moved toward the front end of that ejection electrode by the electric field generated between the ejection electrode and the counter electrode. When the coulomb force due to the electric field between the ejection electrode and the counter electrode considerably exceeds the surface tension of the ink liquid, the particulate matter reaching the front end of the ejection electrode is jetted toward the counter electrode as an agglomeration of particulate matter having a small quantity of liquid, and consequently, the jetted agglomeration adheres to the surface of the recording medium. Thus, by applying pulses of positive voltage to a desired ejection electrode, agglomerations of particulate matter are jetted in sequence from the front end of the ejection electrode, and printing is performed. A recording head such as this is disclosed, for example, in Japan Laid-Open Patent Publication No. 60-228162 and PCT International Publication No. WO93/11866. 
     Particularly, in the Publication (60-228162), there is disclosed an electrostatic inkjet printer head where a plurality of ejection electrodes are disposed in an ink nozzle, and the front end of each ejection electrode is formed on the projecting portion of a head base which projects from the ink nozzle. The front end of this projecting portion has a pointed configuration, and the ejection electrode is formed in accordance with the direction of the pointed end. An ink meniscus is formed near the front end of the ejection electrode. 
     However, in the aforementioned conventional electrostatic inkjet recording heads, it is not easy to obtain high resolution, that is, a reduction in the pitch between the ejection electrodes and a fine printing dot. If the pitch between the ejection electrodes is reduced, the ink meniscus will flood the front end of the head base and an undesired ejection of ink will arise from a point differing from the ejection electrode to which a drive pulse signal was applied, and consequently, ejection cannot be performed with high reliability and stability. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide an apparatus which generates an agglomeration of particulate matter suitable for high resolution. 
     Another objective of the present invention is to provide an inkjet apparatus which is capable of stably ejecting ink from a plurality of ejection electrodes. 
     According to the present invention, an inkjet recording apparatus includes an insulating support member having a major surface on which a plurality of ejection electrodes formed with an ejection portion of each of the ejection electrodes protruding from an ejection end of the insulating support member. Each of the ejection electrodes is coated with an insulating material. The inkjet recording apparatus is further provided with a cover member for covering the insulating support member to form a space between them and an opening at an ejection end of the cover member, the ejection portion of each ejection electrode protruding from the ejection end of the cover member through the opening. 
     Since the ejection electrodes coated with the insulating material protrudes from the ejection end of the cover member through the opening, a reduction in the pitch between the ejection electrodes and a fine printing dot can be easily obtained. Further, since the ink containing particulate matter is supplied from the space within the cover member to the opening, the ink is stably supplied to the ejection electrodes, resulting in improved reliability of ink ejection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages will become apparent from the following detailed description when read in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a part-fragmentary perspective view of an electrostatic inkjet recording head according to a first embodiment of the present invention; 
     FIG. 2 is an enlarged part-plan view of the ink nozzle of the first embodiment shown in FIG. 1; 
     FIG. 3 is a sectional view of the ink nozzle in FIG. 2 taken substantially along line A—A of FIG. 2; 
     FIG. 4 is a schematic plan view of TAB (tape automated bonding) tape that is used in the first embodiment; 
     FIG. 5 is an enlarged part-plan view of the ink nozzle of an electrostatic inkjet recording head according to a second embodiment of the present invention; 
     FIG. 6 is a sectional view of the ink nozzle of an electrostatic inkjet recording head according to a third embodiment of the present invention; 
     FIG. 7 is an enlarged part-plan view of the ink nozzle of an electrostatic inkjet recording head according to a fourth embodiment of the present invention; 
     FIG. 8 is a sectional view of the ink nozzle in FIG. 7 taken substantially along line A—A of FIG. 7; 
     FIG. 9 is a sectional view of the ink nozzle in FIG.  7  taken substantially along line B—B of FIG. 7; 
     FIG. 10 is a part-fragmentary perspective view of an electrostatic inkjet recording head according to a fifth embodiment of the present invention; 
     FIG. 11 is an enlarged part-plan view of the ink nozzle of the fifth embodiment shown in FIG. 10; 
     FIG. 12 is a sectional view of the ink nozzle in FIG. 11 taken substantially along line A—A of FIG. 11; 
     FIG. 13 is a schematic plan view of TAB tape that is used in the fifth embodiment; 
     FIG. 14 is a part-fragmentary perspective view of an electrostatic inkjet recording head according to a sixth embodiment of the present invention; 
     FIG. 15 is a part-sectional view showing the structure of the sixth embodiment shown in FIG. 14; 
     FIG. 16 is a part-sectional view showing another structure of the sixth embodiment shown in FIG. 14; 
     FIG. 17 is a part-sectional view showing the structure of an electrostatic inkjet recording head according to a sixth embodiment of the present invention; 
     FIG. 18 is a part-fragmentary perspective view of an electrostatic inkjet recording head according to an eighth embodiment of the present invention; 
     FIG. 19 is an enlarged part-plan view of the ink nozzle of the eighth embodiment shown in FIG. 18; 
     FIG. 20 is a sectional view of the ink nozzle in FIG.  19  taken substantially along line A—A of FIG. 19; 
     FIG. 21 is a front view of the recording head showing a layout example of the ejection electrodes in the eighth embodiment; 
     FIG. 22 is a schematic plan view of TAB tape that is used in the eighth embodiment; 
     FIG. 23 is a timing diagram illustrating an example of a drive method of the ejection electrodes in the eighth embodiment; 
     FIG. 24A is a schematic view showing the offset distance between the ejection electrodes in the eighth embodiment; and 
     FIG. 24B is a schematic view showing an example of the printing performed by the drive method in the eighth embodiment shown in FIG.  23 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIRST EMBODIMENT 
     Referring now in greater detail to the drawings and initially to FIGS. 1 through 3, there is shown an electrostatic inkjet recording head in accordance with a first embodiment of the present invention. A substrate  101  is made of an insulator such as a plastic and has a base film  102  mounted thereon. The base film  102  is made of an insulator such as polyimide and has a thickness of about 50 μm. A plurality of ejection electrodes  103  are formed integrally on the base film  102  in accordance with a predetermined pattern. One end of each ejection electrode  103  protrudes from the substrate  101  and the base film  102  to form part of an ejection portion, while the other end is formed with an electrode pad  104 . The ejection electrodes  103  are formed by plating the base film  102  with conductive material of about 20 to 30 μm thick in the predetermined pattern and are arranged with a pitch of 300 dpi, that is, at intervals of about 85 μm. The respective ejection electrodes  103  of the ejection portion protrude independently from the end face of the base film  102  by about 80 to 500 μm. The surface of the ejection electrode  103  is covered uniformly with an insulating layer  109  of about 10 μm thick, made of parylene resin. 
     A cover  105  made of an insulating material is attached to the substrate  101  having the base film  102  and the ejection electrodes  103  formed thereon. The cover  105  is formed with an ink supply port  106  and an ink discharge port (not shown). The space, defined by the base film  102  and the cover  105 , constitutes an ink chamber  113 . From the ink supply port  106 , ink containing toner particles is filled into the ink chamber  113 . 
     The front end of the cover  105  is cut out to form a slit-shaped ink nozzle  107  between the cover  105  and the base film  102 . The aforementioned ejection portions of the ejection electrodes  103  are disposed in the ink nozzle  107 . As shown in FIGS. 2 and 3, an ink meniscus  110  is formed among the ejection portions of the ejection electrodes  103  in the ink nozzle  107 . 
     At the inner rear end of the cover  105 , an electrophoresis electrode  108  is provided in contact with the ink within the ink chamber  113 . If voltage with the same polarity as toner particles is applied to the electrophoresis electrode  108 , then an electric field will arise in the ink chamber  113  between the electrode  108  and a counter electrode (not shown) and toner particles will be moved toward the front end of the ejection portions of the ejection electrodes  103  due to an electrophoresis phenomenon. 
     The inkjet recording head in this embodiment is connected to an ink tank (not shown) through tubes (not shown), and a negative pressure of about 1 cmH 2 O is applied to forcibly circulate ink through the tubes. The ink is one where an electrification control agent and colored thermoplastic resin corpuscles (i.e., toner particles) are dispersed in a petroleum-base organic solvent such as an isoparaffin solvent. The toner particles are charged with an apparent positive polarity by a zeta (ζ) potential. 
     The base film  102 , as shown in FIG. 3, has a tapered support portion  112  so that part of the bottom portion of each ejection electrode  103  protruding from the base film  102  is reinforced, in order to reinforce the mechanical strength of the ejection electrode  103 . As previously described, ink forms the ink meniscus  110  in the ink nozzle  107  by its surface tension. Since negative pressure is given to the ink within the ink chamber  113  and also the ejection electrodes  103  protrude from the base film  102  and the cover  105 , the ink meniscus  110  has a concave configuration when viewed in a horizontal direction, as shown in FIG.  3 . Also, because the ejection electrodes  103  individually protrude outside the ink nozzle  107 , the ink meniscus  110  has a concave configuration between adjacent electrodes  103  when viewed in a vertical direction, as shown in FIG.  2 . 
     For the above reason, when a high-voltage pulse signal is applied to one of the ejection electrodes  103 , an electric field is concentrated on the protruding front end of the ink meniscus  110  of that ejection electrode  103 . The charged toner particles in the ink are conducted by this electric field, then are pulled out of the protruding front end of the ink meniscus  110 , and become a toner group  111 . The toner group  111  is jetted toward a counter electrode (not shown) arranged in opposition to the recording head, that is, toward the recording medium such as a paper. The toner group, which adhered to the recording medium and formed a recording dot, is heated and fixed by means of a heater. 
     In reference to FIG. 4, a brief description will now be made of a method of fabricating TAB (tape automated bonding) tape  201  which is used in the first embodiment shown in FIGS. 1 through 3. Flash plating is first given to a tape-shaped polyimide base film having sprocket holes  202  at both ends. Then, a dry film is placed on top of the plated base film, and exposure and development are performed to form a predetermined pattern. Next, the base film is plated with copper (Cu) in accordance with the predetermined pattern and is etched to form through-holes  203 . Thereafter, the photoresist film is removed and finish plating is given. Finally, parylene resin is chemically deposited on a required place to form the insulating layer  109 . In this process, when the base film  102  is etched, the exposed inner lead portions  204  constitute the ejection electrodes  103 . In this way, the base film  102  having the ejection electrodes  103  formed thereon is bonded fast to the substrate  101 . 
     SECOND EMBODIMENT 
     FIG. 5 illustrates an electrostatic inkjet recording head constructed according to a second embodiment of the present invention, where elements similar to those previously described with reference to FIGS. 1-3 are denoted by the same reference numerals and the details of these elements are omitted. This embodiment is characterized in that a base film  102  has a flat, tapered support portion  301  for each ejection electrode  103  in order to reinforce the mechanical strength of ejection electrodes  103 . Also, in this embodiment, patterning is performed so that the flat, tapered support portion  301  is formed when the base film  102  is etched to form through-holes as shown in FIG.  4 . The front end of each ejection electrode  103  is disposed so as to protrude from the support portion  301  of the base film  102 . 
     THIRD EMBODIMENT 
     FIG. 6 illustrates an electrostatic inkjet recording head constructed according to a third embodiment of the present invention, where elements similar to those previously described with reference to FIGS. 1-3 are denoted by the same reference numerals and the details of these elements are omitted. In the figure, a base film  102  has a tapered support portion  302  so that part of the bottom portion of an ejection electrode  103  protruding from the base film  102  is supported, in order to reinforce the mechanical strength of the ejection electrode  103 . Therefore, ink forms an upper ink meniscus  110  in an ink nozzle  107  between the front end of a cover  105  and the ejection electrode  103  by its surface tension and also forms a lower ink meniscus  1101  between the ejection electrode  103  and the tapered support portion  302 . For this reason, when a high-voltage pulse signal is applied to an arbitrary ejection electrode  103 , an electric field is concentrated on the protruding front end of the lower ink meniscus  110 ′ of the support portion  302 . The charged toner particles in the ink are conducted by this electric field, then are pulled out of the protruding front end of the lower ink meniscus  110 ′, and become a toner group  111 . The toner group  111  is jetted toward a counter electrode (not shown) arranged in opposition to the recording head, that is, toward the recording medium. 
     FOURTH EMBODIMENT 
     FIGS. 7 through 9 illustrate an electrostatic inkjet recording head constructed according to a fourth embodiment of the present invention, where elements similar to those previously described with reference to FIGS. 1-3 are denoted by the same reference numerals and the details of these elements are omitted. In the figures, a cover  105  is attached to a base film  102  at the position where the protruding portions of ejection electrodes  103  are not covered. The cover  105  is made of an insulating material and is previously formed with ink supply and discharge ports (not shown). The space between the base film  102  and the cover  105  constitutes an ink chamber  113 , which is filled with ink supplied from the ink supply port. In this embodiment, the cover  105  is attached closely to the base film  102  without forming an opening therebetween. However, since the pattern for the electrode  103  on a base film  102  has a thickness of about 20 to 30 μm, the space between a portion having no pattern for the electrode  103  and the cover  105  constitutes an ink passage  303 , as shown in FIG.  9 . Each ink passage  303  forms an ink nozzle for the corresponding ejection electrode  103 , and an ink meniscus is formed in the ink nozzle. Thus, in this embodiment the ink nozzle is formed without especially cutting out part of the front end of the cover  105 . 
     According to the first through the fourth embodiments, the following advantages are obtained. A first advantage is that stable ejection from a designated ejection point alone can be performed. The reason for this is that since the front end of each ejection electrode  103  is used as an ejection portion and also the respective ejection electrodes  103  protrude independently from both the substrate  101  and the base film  102 , toner particles flow smoothly between the ejection electrodes  103  and a meniscus is stably formed at all times for each ejection point. 
     A second advantage of the aforementioned embodiments is that the recording head is inexpensive. This is because the ejection electrode  103  of the recording head is formed by coating the inner lead of the tape which is employed in TAB with an insulating material. 
     A third advantage is that an increase in the mechanical strength of the ejection electrode  103  minimizes the bending of the ejection electrode and also makes stable ejection possible. This is because the ejection electrode  103  is supported from the bottom surface by part of the base film or TAB tape. 
     A fourth advantage is that toner particles flow smoothly near the ejection electrodes  103 . The reason for this is that since the front end of the base film  102  projects from the front end of the ejection electrode (see FIG.  6 ), toner particles are not deposited between the base film  102  and the ejection electrode  103 . 
     A fifth advantage is that the meniscus is always stable at the front end of the ejection electrode  103 . The reason for this is that since the meniscus is also supported by the tapered support portion of the base film formed between the ejection electrodes (see FIGS.  5  and  6 ), the meniscus is hardly influenced by disturbance such as pressure fluctuation. 
     FIFTH EMBODIMENT 
     FIGS. 10 through 12 illustrate an electrostatic inkjet recording head constructed according to a fifth embodiment of the present invention. In the figures, a substrate  101  is made of an insulator such as a plastic and has a base film  102  mounted thereon. The base film  102  is made of an insulator such as polyimide and has a thickness of about 50 μm. A plurality of ejection electrodes  103  are formed integrally on the base film  102  in accordance with a predetermined pattern. One end of each ejection electrode  103  protrudes from the substrate  101  and the base film  102  and forms part of an ejection portion, while the other end is formed with an electrode pad  104  to which a drive voltage pulse signal is applied. The ejection electrodes  103  are formed by pattern-plating the base film  102  with conductive material such as copper (Cu) of about 20 to 30 μm thick. The ejection electrodes  103  are arranged, for example, with a pitch of 300 dpi, that is, at intervals of about 85 μm. The respective ejection electrodes  103  of the ejection portion protrude independently from the end face of the substrate  101  and the base film  102  by about 80 to 500 μm. The surface of each ejection electrode  103  is covered uniformly with an insulating layer  109  of about 10 μm thick, made of parylene resin. 
     An upper cover  401  and a lower cover  402  consisting of an insulating material are attached to the top surface and the bottom surface of the substrate  101  having both the base film  102  and the ejection electrodes  103  formed thereon. The front ends of the upper and lower covers  401  and  402  are formed with slit-shaped gaps, which constitute an ink nozzle  403 . The front ends of the upper cover  401  and the lower cover  402 , as shown in FIG. 12, are disposed at a position where the ejection electrodes  103  protruding from the substrate  101  and the base film  102  are interposed between the upper and lower covers and where the front end of each ejection electrode  103  is not covered with the upper and lower covers. In other words, the front ends of a plurality of ejection electrodes  103 , arranged in a row, protrude from the substrate  101  and the base film  102  and further protrude outside the recording head through the slit-shaped ink nozzle  403  formed between the front ends of the upper and lower covers  401  and  402 . 
     The upper cover  401  is formed with an ink supply port  404 , while the lower cover  402  is formed with an ink discharge port (not shown). The space, defined by the base film  102  and the upper cover  401 , constitutes an upper ink chamber  113 . The upper ink chamber  113  is filled with ink containing toner particles supplied from the ink supply port  406 . The space, defined by the base film  102  and the lower cover  402 , constitutes a lower ink chamber  114 . The ink, filled in the upper ink chamber  113 , passes between the ejection electrodes  103  arranged in the form of a grid in the vicinity of the ink nozzle  403 , then flows into the lower ink chamber  114 , and finally is discharged from the ink discharge port (not shown). 
     The inkjet recording head according to the fifth embodiment as shown in FIGS. 10 through 12 is connected to an ink tank (not shown) through tubes (not shown), and a negative pressure of 1 cmH 2 O is applied to forcibly circulate ink through the tubes. The ink is one where an electrification control agent and colored thermoplastic resin corpuscles (i.e., toner particles) are dispersed in a petroleum-base organic solvent such as an isoparaffin solvent. The toner particles are charged with an apparent positive polarity by a zeta (ζ) potential. 
     The ink within the ink chambers  113  and  114  forms an ink meniscus  110  in the ink nozzle  403  by its surface tension. Since negative pressure is given to the ink within the ink chambers and also the ejection electrodes  103  protrude from the substrate  101 , the base film  102 , the upper cover  401  and the lower cover  402 , the ink meniscus  110  on the side of the upper cover  401  has a concave configuration when viewed in a horizontal direction, as shown in FIG.  12 . Likewise, the ink meniscus  110  on the side of the lower cover  402  also has a concave configuration. These concave configurations are substantially symmetrical with respect to the ejection electrode  103 . Furthermore, because the ejection electrodes  103  individually protrude outside the ink nozzle  107 , the ink meniscus  110  has a concave configuration between adjacent electrodes  103  when viewed in a vertical direction, as shown in FIG.  11 . For this reason, when a high-voltage pulse signal is applied to any one of the ejection electrodes  103 , an electric field is concentrated on the protruding front end of the ink meniscus  110  of that ejection electrode  103 . The charged toner particles in the ink are conducted by this electric field, then are pulled out of the protruding front end of the ink meniscus  110 , and become a toner group  111 . The toner group  111  is jetted toward a counter electrode (not shown) arranged in opposition to the recording head, that is, toward the recording medium. The toner group, which adhered to the recording medium and formed a recording dot, is heated and fixed by means of a heater. 
     In reference to FIG. 13, a brief description will be made of a method of fabricating TAB tape  201  which is used in the fifth embodiment shown in FIGS. 10 through 12. Flash plating is first given to a tape-shaped polyimide base film having sprocket holes  202  at both ends. Then, a dry film is placed on top of the plated base film, and exposure and development are performed to form a predetermined pattern. Next, the base film is plated with copper (Cu) in accordance with the predetermined pattern and is etched to form through holes  203 . Thereafter, the photoresist film is removed and finish plating is given. Finally, parylene resin is chemically deposited on a required place to form the insulating layer  109 . In this process, when the base film  102  is etched, the exposed inner lead portions  204  form the ejection electrodes  103 . 
     SIXTH EMBODIMENT 
     FIGS. 14 and 15 illustrate an electrostatic inkjet recording head constructed according to a sixth embodiment of the present invention, where elements similar to those previously described with reference to FIGS. 10-12 are denoted by the same reference numerals and the details of these elements are omitted. In this embodiment, in addition to the fifth embodiment, an electrophoresis electrode  405  is provided in contact with ink on the inner rear end of an upper cover  401 . The electrophoresis electrode  405  is given voltage with the same polarity as the potential of the toner particles and moves the toner particles in the ink, supplied from an ink supply port  404 , to the vicinity of an ejection electrode  103  along the electric field generated in the upper ink chamber  113  between the electrophoresis electrode  405  and a counter electrode (not shown) by an electrophoresis phenomenon. For this reason, in addition to the supply of the toner particles to the vicinity of the ink nozzle  403  through the compulsory ink circulation performed by a pump, because of the movement of the toner particles caused by the electrophoresis phenomenon, the concentration of the toner particles becomes relatively higher in the vicinity of the ink nozzle  403  than in the upstream side of the ink chamber. Therefore, when a high-voltage pulse signal is applied to any one of the ejection electrodes  103 , the charged toner particles in the ink are conducted by the electric field generated in this ejection electrode  103  and become a sufficient quantity of toner group  111 . The toner group  111  is jetted toward a counter electrode (not shown) arranged in opposition to the recording head, that is, toward the recording medium. At this time, the ink passes through the gaps between the ejection electrodes  103  and is discharged forcibly to the ink discharge port (not shown) along with an excess of toner particles. 
     FIG. 16 illustrates another structure of the sixth embodiment. In addition to the structure of the fifth embodiment, an upper electrophoresis electrode  405  and a lower electrophoresis electrode  406  are provided in contact with ink on the inner rear ends of upper and lower covers  401  and  402 , respectively. The upper and lower electrophoresis electrodes  405  and  406  are electrically connected with each other. The electrophoresis electrodes  405  and  406  are given voltage having the same polarity as the potential of the toner particles and move the toner particles in the ink, supplied from an ink supply port  404 , to the vicinity of an electrode  103  along the electric field generated between the electrophoresis electrode  405  (and  406 ) and a counter electrode (not shown) by an electrophoresis phenomenon. For this reason, in addition to the supply of the toner particles to the vicinity of the ink nozzle  403  through the compulsory ink circulation performed with a pump, because of the movement of the toner particles caused by the electrophoresis phenomenon, the concentration of the toner particles becomes relatively higher in the vicinity of the ink nozzle  403  than in the upstream side of the ink chamber. In addition, toner particles move in an opposite direction to the movement of counter ion toner particles having an opposite polarity to the electric charge of toner particles which is generated when the toner particles are moved by the electrophoresis phenomenon. The counter ion toner particles adhere to the electrophoresis electrodes  405  and  406 . Therefore, when a high-voltage pulse signal is applied to any one of the ejection electrodes  103 , the charged toner particles in the ink are conducted by the electric field generated in this ejection electrode  103  and become a sufficient quantity of toner group  111 . The toner group  111  is jetted toward a counter electrode (not shown) arranged in opposition to the recording head, that is, toward the recording medium. At this time, an excess of toner particles not jetted and the counter ions pass through the gaps between the electrodes  103  and are discharged forcibly to the ink discharge port (not shown). 
     SEVENTH EMBODIMENT 
     FIG. 17 illustrates an electrostatic inkjet recording head constructed according to a seventh embodiment of the present invention, where elements similar to those previously described with reference to FIGS. 14-16 are denoted by the same reference numerals and the details of these elements are omitted. This embodiment is constructed so that the front ends of an upper cover  401  and a lower cover  402  are attached closely to an array of the ejection electrodes  103 . Since the pattern for the ejection electrodes  103  on a base film  102  has a thickness of about 20 to 30 μm, the space between a portion having no pattern for the ejection electrode  103  and the upper cover  401  constitutes an upper ink passage. Similarly, a lower ink passage is formed on the side of the lower cover  402 . The upper ink passage constitutes an ink nozzle  403 , and an ink meniscus  110  is formed in the ink nozzle  403 . Thus, the ink passages and the ink nozzle are formed without especially processing the front ends of the upper and lower covers  401  and  402 . 
     In the fifth through the seventh embodiments, reliable toner ejection is obtainable regardless of printing conditions. The reason for this is that since ink is passed through the gaps between ejection electrodes so that an excess of toner particles and counter ions is forcibly discharged from the vicinity of the ejection electrodes, stable toner particles are always supplied to the vicinity of the ejection electrodes. 
     EIGHTH EMBODIMENT 
     FIGS. 18 through 21 illustrate an electrostatic inkjet recording head constructed according to an eighth embodiment of the present invention. In the figures, a substrate  101  is made of an insulator such as a plastic and has a base film  102  mounted thereon. The base film  102  is made of an insulator such as polyimide and has a thickness of about 50 μm. A plurality of ejection electrodes  103  are formed integrally on the surface of the base film  102 . The front end portion of the base film  102  is divided into a plurality of groups so that a predetermined number of ejection points are determined for each group. As described later, slits are formed on the ejection side of the base film  102 , and according to the shape of the teeth of a saw of the substrate  101 , the front end portion of the base film  102  is divided into a plurality of groups. 
     The ejection electrodes  103  are formed by pattern-plating the base film  102  with conductive material such as copper (Cu) of about 20 to 30 μm thick. The ejection electrodes  103  are arranged, for example, with a pitch of 300 dpi, that is, at intervals of about 85 μm. Also, the respective ejection electrodes  103  protrude independently from the front end faces of the substrate  101  and the base film  102 , and the quantity of protrusion is about 80 to 500 μm. The surface of the front end portion of the ejection electrode  103  is covered uniformly with an insulating layer  109  having a thickness of 10 μm or less. 
     The recording head in this embodiment employs a tape-shaped head where the ejection electrodes  103  are formed integrally on the base film  102 . Specifically, TAB (tape automated bonding) tape that is employed in TAB is used, and the insulating layer  109  is formed by chemical deposition of parylene resin. An upper cover  401  and a lower cover  402  are attached to both surfaces of the base film  102  so that the ejection electrodes  103  protruding from the substrate  101  and the base film  102  are interposed therebetween, at a position where the protruding portions of the ejection electrodes  103  are not covered. The upper and lower covers  401  and  402  are made of an insulating material. The upper cover  401  is formed with an ink supply port  404 , and the space between the base film  102  and the upper cover  401  constitutes an upper ink chamber  113  which is filled with ink supplied from the ink supply port  404 . Between the front end of the upper cover  403  and the base film  102 , there is formed a slit-shaped ink nozzle  403 . On the other hand, the lower cover  402  is formed with an ink discharge port (not shown), and the space between the base film  102  and the lower cover  401  likewise constitutes a lower ink chamber  114 . 
     The ink, supplied to the upper ink chamber  113  on the side of the upper cover  401 , passes through the gaps between a plurality of ejection electrodes  103  from the upper ink chamber  113  and flows from the vicinity of the ink nozzle  403  to the lower ink chamber  114 . Then, the ink is discharged forcibly from the ink discharge port along with an excess of toner particles. The inkjet recording head in this embodiment is connected to an ink tank (not shown) through tubes (not shown), and a negative pressure of 1 cmH 2 O is applied to forcibly circulate ink through the tubes. The ink is one where an electrification control agent and colored thermoplastic resin corpuscles (i.e., toner particles) are dispersed in a petroleum-base organic solvent such as an isoparaffin solvent. The toner particles are charged with an apparent positive polarity by a zeta (ζ) potential. 
     At the inner rear end of the upper cover  401 , an electrophoresis electrode  405  is provided in contact with the ink within the upper ink chamber  113 . The electrophoresis electrode  405  is given voltage having the same polarity as the potential of the toner particles and moves the toner particles in the ink, supplied from an ink supply port  404 , to the vicinity of an electrode  103  along the electric field generated between the electrophoresis electrode  405  and a counter electrode (not shown) by an electrophoresis phenomenon. As a consequence, in addition to the supply of the toner particles to the vicinity of the ink nozzle  403  through the compulsory ink circulation performed with a pump, because of the movement of the toner particles caused by the electrophoresis phenomenon, the concentration of the toner particles becomes relatively higher in the vicinity of the ink nozzle  403  than in the upper ink chamber  113 . 
     In FIGS. 19 and 20, ink forms an ink meniscus  110  in the ink nozzle  403  by its surface tension. Since negative pressure is given to the ink within the ink chambers and also the ejection electrodes  103  protrude from the substrate  101 , the base film  102 , the upper cover  401  and the lower cover  402 , the ink meniscus  110  on the side of the upper cover  401  has a concave configuration when viewed in a horizontal direction, as shown in FIG.  20 . Likewise, the ink meniscus  110  on the side of the lower cover  402  has a concave configuration. These concave configurations are substantially symmetrical with respect to the ejection electrode  103 . Furthermore, because the ejection electrodes  103  individually protrude outside the ink nozzle  403 , the ink meniscus  110  has a concave configuration between adjacent electrodes  103  when viewed in a vertical direction, as shown in FIG.  19 . 
     Therefore, when a high-voltage pulse signal is applied to any one of the ejection electrodes  103 , an electric field is concentrated on the protruding front end of the ink meniscus  110  of that ejection electrode  103 . Then, the charged toner particles in the ink are conducted by the electric field that is generated between a counter electrode (not shown) and the ejection electrode  103 . Next, the charged toner particles are pulled out of the protruding front end of the ink meniscus  110  and become a toner group  111 . Consequently, the toner group  111  is jetted toward the counter electrode (not shown) arranged in opposition to the ejection electrode  103 , that is, toward the recording medium. The toner group, which adhered to the recording paper and formed a recording dot, is heated and fixed by means of a heater. 
     As shown in FIG. 21, the ejection electrodes  103 , formed on the base film  102 , are divided into a plurality of groups at the front end portion by slits formed in the base film  102 . Also, the base-film mounting portions of the substrate  101  are inclined at a certain angle so that each ejection electrode  103  is offset (inclined) for each group when viewed from the front side. Furthermore, between the individual groups, the ejection electrodes  103  which are arranged at the same position in correspondence with the inclination are concurrently driven in the form of a matrix. 
     In reference to FIG. 22, a brief description will be made of a method of fabricating TAB tape  201  which is used in the eighth embodiment shown in FIGS. 18 through 21. Flash plating is first given to a tape-shaped polyimide base film having sprocket holes  202  at both ends. Then, a dry film is placed on top of the plated base film, and exposure and development are performed to form a predetermined pattern. Next, the base film is plated with copper (Cu) in accordance with the predetermined pattern and is etched to form through-holes  203 . Thereafter, the photoresist film is removed and finish plating is given. Finally, parylene resin is chemically deposited on a required place to form the insulating layer  109 . The TAB tape  201 , fabricated in this way, is employed as a recording head. In this process, when the base film  102  is etched, the exposed inner lead portions  204  form the ejection electrodes  103 . The slits on the side of the inner lead portion  204  are formed by etching or cutting. 
     In FIGS. 23,  24 A, and  24 B, the corresponding ejection electrodes  103  of each group, connected electrically in the form of a matrix, are driven with a certain offset time T for each group. Consequently, if the ejection electrodes  103  are constructed physically on the same line, an offset error with offset distance L would occur in recorded dots for each group connected in the form of a matrix, as shown in FIG.  24 A. 
     On the other hand, in the present invention, the ejection electrodes  103  have previously been offset so that the offset distance L is compensated. Consequently, as shown in FIG. 24B, position offset due to each offset time T does not occur in recorded dots, and high-quality printing is obtainable. 
     Also, in the recording head of the present invention, while a plurality of ejection electrodes need to be constructed with high density and accuracy, stable ejection electrode spacing and electrode protrusion quantity can be ensured by the aforementioned embodiments. In addition, the head is in the form of tape, so reductions in the thickness and size of the head become possible. Furthermore, since an excess of toner particles and an excess of counter ions are discharged forcibly from the vicinity of the ejection electrodes by constructing the head so that ink is passed through the gaps between the ejection electrodes, toner particle are stably supplied near the ejection electrodes at all times and reliable toner supply is obtained regardless of printing conditions. Moreover, the ejection electrodes, formed on base films, are offset for each base film by the offset time of a matrix drive method, so position offset due to the offset time does not occur and high-quality printing is obtained. 
     While the invention has been described with reference to specific embodiments thereof, it will be appreciated by those skilled in the art that numerous variations, modifications, and embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the scope of the invention.