Abstract:
An image recording apparatus includes an ink jet head which ejects ink toward a recording medium to record an image thereon, a paper feed unit which feeds the recording medium, a recording medium conveyance unit which conveys the recording medium, an intake fan provided at the recording medium conveyance unit to adsorb the recording medium by negative pressure, and an exhaust fan to remove dust from between the paper feed unit and the recording medium conveyance unit. The image recording apparatus prevents the ink jet head from not discharging ink drops and discharging ink drops curvedly because of paper dust and dust in the air, and prevents ink drops from failing to land in a proper position because of an airflow to form a new flow path in the apparatus, thereby recording a high-quality image with high reliability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-223762, filed Jul. 30, 2004, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image recording apparatus having a mechanism to remove dust from inside the apparatus. 
     2. Description of the Related Art 
     In an image recording apparatus, generally, a recording medium such as recording paper is brought into contact with a component located on a recording medium conveyance path, such as a paper feed unit for feeding the recording medium and a registration roller for stabilizing the conveyance direction of the recording medium, when the recording medium is conveyed. This contact generates a large amount of paper dust from the recording medium in the apparatus. When the recording medium is placed in the paper feed unit, the paper dust intrudes into the image recording apparatus together with dust in the air. 
     In an image recording apparatus using an ink jet head for a recording element, paper dust or dust is attached to a nozzle of the ink jet head for ejecting ink drops or intruded into the nozzle. If cut paper is used as a recording medium, the amount of paper dust to be generated varies with the quality of cutting of the cut paper. 
     For example, Jpn. Pat. Appln. KOKAI Publication No. 2003-220695 is known as prior art. This Publication discloses an apparatus wherein an airflow is generated from an ink jet head to a paper feed unit in order to prevent paper dust and dust from being attached to the ink jet head. 
     The Publication also discloses that air flows into a conveyance mechanism housing  101  from outside a recording head housing  102  through a wind-direction guide  104  by fans  104   a  and  104   b , as shown in  FIG. 12 . This air is blown toward recording heads  114   a  to  114   d  from outside the recording head housing  102 . 
     In a prior art image recording apparatus, an airflow is formed as illustrated in  FIG. 13 . More specifically, air  114  is generated close to a resist roller  109 , a backup roller  110  and an ink head  100  by an adsorption fan  106  and flows under an ink jet head  100 . Then, the air  114  flows toward a conveyor belt  141  through an adsorption hole  103  formed in a platen  112 . 
     In the above Publication, the wind-direction guide  104  is provided to prevent the blown air from hitting directly on the ink jet head. However, the Publication does not take into consideration any paper dust or dust that intrudes from a flow path of the conveyance mechanism housing  101 , a flow path between the wind-direction guide  104  and a recording medium, and the sides of the apparatus. In other words, the apparatus of the Publication is configured not to remove dust, such as paper dust and dust in the air, by the blown air, but to make it difficult that dust intrudes into the recording head housing  102 . Since the Publication does not take into consideration the flow path of the conveyance mechanism housing  101  or the flow path between the wind-direction guide  104  and a recording medium, there is fear that dust or air will not properly be discharged to the outside of the apparatus but remain in the apparatus. 
     In the prior art image recording apparatus shown in  FIG. 13 , dust  113 , such as paper dust around the ink jet head  100  and dust in the air, flow as shown in  FIG. 14 . In this flow, part of the dust  113  flows under the platen  112  through the adsorption hole  103 , while the other dust flows toward the ink jet head  100 . The dust  113  that flows toward the ink jet head  100  are likely to be attached to a nozzle  140  for ejecting ink drops. If the dust  113  is attached to the nozzle  140 , there is fear that the ink drops will not be ejected or ejected cursedly to cause displacements and blur of an image and thus lower its quality remarkably. In the prior art image recording apparatus, the dust flows into the apparatus and are attached to or intruded into the ink jet head. Thus, the ink drops do not land in a proper position to degrade the quality of a recorded image remarkably. Furthermore, there is fear that dust or air will not properly be discharged to the outside of the apparatus but remain in the apparatus since the wind-direction guide is provided. 
     BRIEF SUMMARY OF THE INVENTION 
     There is provided an image recording apparatus which prevents an ink jet head from not ejecting ink drops and ejecting ink drops cursedly because of paper dust and dust in the air, and prevents dust from intruding into the apparatus from outside, thereby recording a high-quality image with high reliability. 
     According to an aspect of the present invention, there is provided an image recording apparatus comprising an ink jet head unit which ejects ink toward a recording medium to record an image thereon, a paper feed unit which feeds the recording medium to a platen that is provided opposite to an ejecting outlet of the ink jet head unit from which ink is ejected, a recording medium conveyance unit which conveys the recording medium, which is fed onto the platen, to a discharge outlet, an intake fan provided at the recording medium conveyance unit to adsorb the recording medium by negative pressure while the recording medium is being conveyed, and an exhaust fan to remove dust from between the paper feed unit and the recording medium conveyance unit, wherein the image recording apparatus further comprises a cover member on an outside thereof, and an inner part of the apparatus, which is covered with the cover member, is maintained at positive pressure with air from which dust is removed, in space including the ink jet head unit. 
     Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of the internal structure of an image recording apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the image recording apparatus according to the first embodiment of the present invention; 
         FIG. 3  is a perspective view of the image recording apparatus according to the first embodiment of the present invention; 
         FIG. 4  is a diagram showing an example of a loop formed in the image recording apparatus according to the first embodiment of the present invention; 
         FIG. 5  is a schematic view of the image recording apparatus according to the first embodiment of the present invention, in which paper dust are generated; 
         FIG. 6  is a sectional view taken from a discharge outlet of the image recording apparatus according to the first embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of the image recording apparatus according to the first embodiment of the present invention, in which no recording medium is placed on a conveyor belt; 
         FIG. 8  is a cross-sectional view of the image recording apparatus according to the first embodiment of the present invention, in which a recording medium is placed on the conveyor belt; 
         FIG. 9  is a schematic view of an image recording apparatus according to a second embodiment of the present invention, which has an opening above a head unit; 
         FIG. 10  is a schematic view of an image recording apparatus according to a third embodiment of the present invention, which has a partition plate near a discharge outlet; 
         FIG. 11  is a schematic view of an image recording apparatus according to a fourth embodiment of the present invention, which has a rotating cylindrical platen; 
         FIG. 12  is a schematic view of a prior art image recording apparatus for generating air; 
         FIG. 13  is a schematic view of a prior art image recording apparatus in which air flows; and 
         FIG. 14  is a diagram showing a flow of dust near an ink jet head arranged in the prior art image recording apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     In the following descriptions, the conveyance direction of recording mediums is defined as an X-axis direction or a sub-scanning direction, a direction that is two-dimensionally perpendicular to the conveyance direction is defined as a Y-axis direction or a main scanning direction, and a direction that is three-dimensionally perpendicular to the X- and Y-axis directions is defined as a Z-axis direction or a vertical direction. 
     An image recording apparatus according to a first embodiment of the present invention will be described with reference to  FIGS. 1 ,  2 ,  3  and  6 .  FIG. 1  is a schematic diagram of the internal structure of the image recording apparatus.  FIG. 2  is a cross-sectional view of the image recording apparatus.  FIG. 3  is a perspective view of the image recording apparatus.  FIG. 6  is a sectional view taken from a discharge outlet  23  of the image recording apparatus. 
     The image recording apparatus comprises an ink jet head  1  including a plurality of nozzles capable of ejecting ink of different colors, such as black (K), cyan (C), magenta (M) and yellow (Y) and then recording color images. These nozzles are arranged in the same direction as the conveyance direction and each have an ejecting outlet for ejecting ink in the gravitational direction (vertical direction). 
     In the first embodiment, the ink jet head  1  can be formed as a nozzle array having such a length as to cover the recording (maximum width) of a recording medium, or it can be formed as at least two nozzle arrays arranged in the main scanning direction and each having a plurality of short heads whose length is less than the width of a recording medium. Some of the short heads of the nozzle arrays are arranged in the conveyance direction of the recording mediums. In this case, the nozzle arrays are so fixed that they are arranged at regular pitches in the sub-scanning direction (conveyance direction). Since the nozzle arrays of the ink jet head  1  are arranged in the main scanning direction, their ejecting timings are controlled individually. With this control, the nozzle arrays of the head  1  can be formed as one line in the main scanning direction or in the width direction of each of recording mediums  7  and driven in the same manner as a conventional single line head. 
     The image recording apparatus comprises a belt unit that is opposed to the ink jet head  1 . The belt unit includes a conveyor belt  4  that is put on three conveyor belt driving rollers  5  and an intake fan  6  provided close to the driving rollers  5 . The apparatus also comprises a platen  2  that is opposed to the ink jet head  1 . The platen  2  has a number of intake holes  3  for adsorbing the recording mediums  7  by taking air by the intake fan  6 . This air is discharged outside the apparatus by an exhaust fan  29  provided on a rear cover  25 . The conveyor belt  4  has a number of small holes (not shown) for adsorbing and holding the recording mediums  7 . Accordingly, the recording mediums  7  are conveyed in the direction of arrow  11  as the conveyor belt  4  moves while adsorbing the recording mediums  7 . 
     Around the belt unit, there are a feeder  19  for storing the recording mediums  7  to be fed, a paper feed roller  8  for picking up the recording mediums  7  from the feeder  19  one by one and then feeding them, a resist roller  9  for aligning the conveyance direction of the recording mediums  7  fed by the paper feed roller  8 , a backup roller  10  having a function of aligning the recording mediums  7  in the conveyance direction and serving as a driven roller of the conveyor belt, a discharge roller  38  for discharging the recording mediums  7 , and a discharge outlet  23  for discharging the recording mediums. 
     The apparatus comprises partition plates  15   a  and  15   b . The partition plate  15   a  is provided in contact with the backup roller  10  on its downstream side to prevent paper dust, which is generated when the recording mediums  7  contact the paper feed roller  8 , resist roller  9  and backup roller  10 , and dust in the air from being sent to the ink jet head  1 . The partition plate  15   b  is provided in contact with the most upstream one of the conveyor belt driving rollers  5 . The contact pressure of the partition plate  15   a  is set at a very low value, such as 0.1 N or lower, to prevent the conveyability of the backup roller  10  from decreasing. With these partition plates  15   a  and  15   b,  a chamber including the paper feed roller  8 , resist roller  9  and backup roller  10  and a chamber including the ink jet head  1  can completely be separated from each other. The former chamber also includes an exhaust fan  16  in its upper part. The exhaust fan  16  is used to exhaust foul air containing a great amount of paper dust out of the apparatus in the direction indicated by arrows  41 . Clean air that is introduced through a fan unit  21  with a filter and a duct  22  is not blown directly to the ink jet head  1 . In the first embodiment, the clean air flows toward the discharge outlet  23  and exhaust fan  29  through a flow path between the ink jet head  1  and each of a front cover  24  and a read cover  25  as shown in  FIG. 6 . 
       FIG. 3  is a perspective view of the image recording apparatus according to the first embodiment. The entire main body of the apparatus is almost hermetically sealed with covers including a front cover  24 . This sealed apparatus includes a rear cover  25  that is opposed to the front cover  24  and a conveyance path. An ink bottle unit  20  for storing ink is provided on the roof of the chamber including the paper feed roller  8 , resist roller  9  and backup roller  10 . The fan unit  21  with a filter is provided on the roof of the chamber including the ink jet head  1 , with the duct  22  interposed therebetween. The fan unit  21  allows clean air to be introduced into the chamber including the ink jet head  1  through the duct  22 . 
     In image recording, the recording mediums  7  are picked out by the paper feed roller  8  and conveyed to the resist roller  9 . The recording mediums  7  are each placed into contact with the resist roller  9  and then formed like a loop between the resist roller  9  and backup roller  10  to align their conveyance directions. The conveyance speed of the backup roller  10  is set lower than that of the resist roller  9  until the recording mediums  7  are each formed like a given loop. 
     An example of a loop will be described in detail with reference to  FIG. 4 . Referring to  FIG. 4 , a recording medium  7  is formed like a loop between the resist roller  9  and backup roller  10  as indicated by broken line  12 . After the loop is formed, when the conveyance direction of the recording medium  7  is corrected and part of the recording medium  7  is adequately adsorbed by the conveyor belt  4 , a driving gear (not shown) of the resist roller  9  is released and dragged together with the recording medium  7 . At this time, the recording medium  7  is suddenly flattened. In the first embodiment, a loop is formed between the resist roller  9  and backup roller  10 ; however, it can be done between the paper feed roller  8  and resist roller  9 . 
     A situation in which paper dust are generated from the image recording apparatus will be described in detail with reference to  FIG. 5 . For the sake of brevity, the partition plate  15   a , partition plate  15   b,  exhaust fan  16 , ink bottle unit  20 , fan unit  21  and duct  22  shown in  FIG. 1  are omitted from  FIG. 5 . 
     Paper dust  13  are generated most when a recording medium  7  is placed into contact with the paper feed roller  8 , when a recording medium is flattened after it is shaped like a loop between the paper feed roller  8  and resist roller  9 , and when a recording medium is suddenly changed in position from its loop to flatness. The paper dust  13  are also generated from the resist roller  9  and backup roller  10  to keep a difference in speed between each of the rollers  9  and  10  and each of the recording mediums  7 . In the first embodiment, the image recording apparatus adopts a conveyor belt and thus requires the intake fan  6 . Air flow is therefore caused in the image recording apparatus. 
     A flow of air in the image recording apparatus will be described in detail with reference to  FIGS. 1 ,  6 ,  7  and  8 . 
     First, a flow of air to discharge dust from the apparatus when a recording medium  7  is conveyed into the main body of the apparatus, will be described with reference to  FIG. 1 . When the recording medium  7  is formed like a loop, a large number of paper dust  13  are generated in the chamber including the paper feed roller  8 , resist roller  9  and backup roller  10 . Dust in the air is also conveyed from outside the apparatus while being attached to the recording medium  7 . The chamber is thus filled with foul air containing dust. The foul air is exhausted out of the apparatus through the exhaust fan  16  in the direction indicated by arrows  41 . Since the backup roller  10  contacts the recording medium  7 , the paper dust  13  do not flow toward the ink jet head  1  through the contact portion with less frequently. 
     Most of the paper dust  13  attached to the surface of the recording medium  7  and most of the dust attached to the recording medium  7  when it is left in the feeder  19  are detached therefrom when it is suddenly changed from its loop to flatness and when it is placed into contact with the paper conveyance path. These paper dust  13  and dust are floated and discharged from the main body of the apparatus through the exhaust fan  16 . Even though paper dust  13  and dust are attached to the surface of the recording medium  7 , they are compressed by the backup roller  10  and fixed to the recording medium  7  or fixed to the backup roller  10 . Thus, the paper dust  13  float and flow toward the ink jet head  1  with less frequency. 
     In the configuration of the apparatus, the partition plate  15   a  is provided on the downstream side of the backup roller  10  where the recording medium  7  that generates paper dust  13  is formed like a loop and then flattened suddenly when it comes closest to the ink jet head  1 , and the partition plate  15   b  is provided on the upstream side one of the conveyor belt driving rollers  5 . 
     As described above, the partition plates  15   a  and  15   b  are provided close to the backup roller  10  and the conveyor belt driving roller  5 , and the backup roller  10  serves as one for dividing an airflow. The space for the paper feed unit and the space for the ink jet head  1  can thus be separated easily without decreasing paper conveyability. Accordingly, it is possible to reduce paper dust  13  that flow from the paper feed unit to the ink jet head  1 . 
     Clean air  31  that flows from the fan unit  21  through the duct  22  will be described in detail with reference to  FIGS. 1 and 6 . 
     The chamber including the ink jet head  1  ranges from the partition plates  15   a  and  15   b  to the discharge outlet  23 . The clean air  31  introduced through the fan unit  21  flows toward the conveyor belt through a gap formed under a guide plate  26  along two flow paths formed between the front cover  24  and the guide plate  26  and between the rear cover  25  and the guide plate  26 . Most of the clean air  31  does not flow under the conveyor belt  4  but toward the discharge outlet  23  since a guide plate  30  is provided. Part of the clean air that flows under the conveyor belt  4  is exhausted from the apparatus through the exhaust fan  29  provided under the guide plate  30  that is close to the rear panel  25 . The ink jet head  1  is interposed between two guide plates  26  and its top is not open. No flow paths are therefore formed, or no clean air  31  flows into the ink jet head  1  directly. 
     Referring to  FIG. 6 , a gap  42  in the Y-axis direction between the guide plate  26  and the conveyor belt  4  is considerably larger than a gap  43  in the Z-axis direction between the ink jet  1  and the conveyor belt  4 . In the first embodiment, the gap  42  is set at 10 mm and the gap  43  is set at about 2 mm. It is favorable that (the area of) the gap  42  be, for example, five or more times as large as (the area of) the gap  43 . 
       FIG. 7  is a cross-sectional view of the main body of the image recording apparatus. In  FIG. 7 , no recording mediums  7  are adsorbed or conveyed onto the conveyor belt  4 . The ink jet head  1  is not shown in  FIG. 7 . 
     The apparatus is divided into two chambers by the partition plates  15   a  and  15   b : one chamber is a paper feed unit including the paper feed roller  8 , resist roller  9  and backup roller  10 ; and the other chamber is an image recording unit including the ink jet head  1 , conveyor belt  4  and discharge outlet  23 . In the paper feed unit, a paper guide (not shown) and a recording medium  7  is placed into contact with each other to cause dust such as a large number of paper dust  13  and dust in the air. In order to prevent the dust from intruding into the image recording unit, the dust is adsorbed and discharged from between the resist roller  9  and backup roller  10  through the exhaust fan  16 . 
     The clean air  31  that is introduced from the fan unit  21 , which is provided on the top of the apparatus as shown in  FIG. 1 , through the duct  22 , flows into space  33  between the front cover  24  and guide plate  26  and space  34  between the rear cover  25  and guide plate  26 . The space  33  is maintained at positive pressure against outside air, as is the space  34 . As shown in  FIG. 6 , the clean air  31  that flows into the space  33  and space  34  is introduced toward the conveyor belt  4  through the gap  42  between the guide plate  26  and conveyor belt  4  in the Y-axis direction. When no recording medium  7  is conveyed by the conveyor belt  4 , the clean air  31  is introduced toward the conveyor belt  4  from the space  33  and space  34  by the intake fan  6  and exhausted out of the main body of the image recording apparatus by the exhaust fan  29  through the intake holes  3  of the platen  2 . The apparatus is maintained at positive pressure and has a function of preventing dust intruding into the apparatus from the air through the front cover  24  and rear cover  25 . 
       FIG. 8  is another cross-sectional view of the main body of the image recording apparatus in which a recording medium  7  is being conveyed on the conveyor belt  4 . The small holes of the conveyor belt  4  and the intake holes  3  of the platen are almost blocked with the recording medium  7 . The amount of clean air  31  taken from the fan unit  21  by the intake fan  6  is reduced. In order to maintain the positive pressure of the chamber including the ink jet head  1 , the amount of clean air  31  that flows toward the ink jet head  1  from the space  33  and space  34  is reduced. Thus, the amount of displacement in ink drops ejected from the ink nozzle, which is caused by an airflow, is decreased, as is the amount of displacement in color when an image is recorded. Most of the clean air  31  passes through space surrounded by the guide plates  26  and the conveyor belt  4  and then flows in the direction of the discharge outlet  23 . 
     As described above, when no recording medium  7  is conveyed onto the conveyor belt  4 , the clean air  31  flows toward the conveyor belt  4  by the intake fan  6  thereof. No dust is attached to the ink jet head  1 . When a recording medium  7  is conveyed, the intake holes  3  of the platen  2  and conveyor belt  4  are blocked with the recording medium  7  and thus the amount of air flowing toward the conveyor belt  4  is reduced. Consequently, the amount of displacement in ink drops due to the flow of air is small, and a high-quality image can be formed. 
     The chamber including the ink jet head  1  is maintained at the positive pressure in the inner part of the apparatus that is covered with the front cover  24  and rear cover  25 . It is thus possible to prevent dust from intruding into the apparatus from the air and prevent dust from being attached to the nozzle of the ink jet head  1 . Since air flows toward the discharge outlet  23  that is the only large opening, the dust that intrudes into the apparatus can be minimized. 
     An image recording apparatus according to a second embodiment of the present invention will be described with reference to  FIG. 9 . 
     The same constituting elements as those of the first embodiment are indicated by the same reference numerals and their detailed descriptions are omitted. In the second embodiment, an opening  36  is formed in the top of an ink jet head  1  that is interposed between two guide plates  26 , as shown in  FIG. 9 . 
     The apparatus of the second embodiment has a function of preventing dust from intruding into the ink jet head  1  by clean air  31  that is blown from a fan unit  21  with a filter through a duct  22 . The apparatus also has a function of cooling heat generated from a head driving substrate  37 , which is arranged between the opening  36  and the ink jet head  1 , by blowing clean air  31  directly into the substrate  37 . The clean air  31  that has cooled the head driving substrate  37  flows toward a conveyor belt  4 . The substrate  37  can thus be cooled without using any dedicated cooling fan. 
     A slight amount of air that flows toward the conveyor belt  4  from a gap between the ink jet head  1  and a head supporting member (not shown) is part of clean air  31  including no dust. Thus, there is no danger that dust will be attached to the ink jet head  1 . 
     An image recording apparatus according to a third embodiment of the present invention will be described with reference to  FIG. 10 . 
     The same constituting elements as those of the first embodiment are indicated by the same reference numerals and their detailed descriptions are omitted. 
       FIG. 10  shows an enlarged view of a discharge outlet  23  and its periphery. An ink jet head  1 , a conveyor belt  4 , a conveyor belt driving roller  5 , a recording medium  7 , a discharge roller  38  and a partition plate  39  with a slit are arranged close to the discharge outlet  23 . They are included in the image recording apparatus as shown in  FIG. 1 . 
     In the first embodiment, the clean air  31  flows toward the discharge outlet  23  through the space  33  between the front cover  24  and guide plate  26  and the space  34  between the rear cover  25  and guide plate  26 . A large amount of clean air  31  flows toward the end portions of the front and rear covers  24  and  25 , whereas a small amount of clean air  31  flows to the central part near the discharge outlet  23 . When air flows to the surrounding of the apparatus, a backflow of air may occur through the discharge outlet. In the third embodiment, therefore, the partition plate  39  with a slit is provided between the ink jet head  1  and the discharge roller  38  in the longitudinal direction of the discharge outlet  23 . 
     Consequently, in the third embodiment, dust can be prevented from intruding into the apparatus from the air through the discharge outlet  23 . The smaller the width of the slit of the partition plate  39 , the more the air can be prevented from intruding. In the third embodiment, the width of the slit is set at 3 mm in order to secure the conveyability of recording mediums. This conveyability is improved by inclining the partition plate  39  toward the paper feed side with reference to the slit. 
     As described above, the partition plate is provided close to the discharge outlet to minimize dust that intrude into the apparatus from the air and prevent the dust from being attached to the ink jet head. 
     In the third embodiment, the ink jet head  1  is a fixed head capable of covering the maximum width of each of the recording mediums  7 . The ink jet head  1  can be moved in the main scanning direction that is the width direction of the recording mediums  7 . 
     An image recording apparatus according to a fourth embodiment of the present invention will be described with reference to  FIG. 11 . 
     The same constituting elements as those of the first embodiment are indicated by the same reference numerals and their detailed descriptions are omitted. 
       FIG. 11  shows a configuration of an image recording apparatus using a cylindrical platen  44  that rotates. Like a belt platen, the cylindrical platen  44  allows recording mediums  7  to be conveyed horizontally. The cylindrical platen  44  has a recording medium adsorbing function not shown and the mechanism has a hole for adsorbing the recording mediums. 
     The recording mediums  7  are fed from a feeder  19  by a paper feed roller  8  and then conveyed to the cylindrical platen  44  through a resist roller  9  and a backup roller  10 . The recording mediums  7  are adsorbed by the cylindrical platen  44  and discharged from a discharge outlet  23  through a gap between the ink jet head  1  and the platen  44  by a discharge roller  38 . 
     In the fourth embodiment, a paper feed unit can be separated from space around the ink jet head  1  by partition plates  15   a  and  15   b , and dust that intrudes into the apparatus by clean air from a fan unit  21  with a filter can be minimized. 
     According to the present invention, there can be provided an image recording apparatus which prevents an ink jet head from not discharging ink drops and discharging ink drops cursedly because of paper dust and dust in the air, and prevents dust from intruding into the apparatus from outside, thereby forming a high-quality image with high reliability. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.