Abstract:
A plate fixed to a recording drum is irradiated with a laser beam emitted from an objective lens of a recording head, to generate gas. The recording head has a gas diffusion/suction unit forming an air stream in front of the objective lens. Further, a second suction unit elongated along the rotational axis of the recording drum is arranged between a transport unit supplying the plate to the recording drum and the recording head. Thus, it is possible to prevent the gas not only from contaminating the objective lens but also from diffusing in a housing following rotation of the recording drum. Consequently, an image recorder employing a photosensitive material generating gas in reaction to heat resulting from the laser beam emitted from the recording head can minimize contamination of the recording head, the transport unit etc. arranged in the housing of the apparatus with the gas.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image recorder for fixing an image recording material to the outer peripheral surface of a recording drum and rotating the recording drum while moving a recording head in a subscanning direction parallel to the rotational axis of the recording drum and applying a laser beam thereby recording a two-dimensional image on the image recording material. More particularly, the present invention relates to an image recorder recording an image on an image recording material generating gas by thermal reaction. It is assumed that the term “gas” includes not only pure gas constituents such as sublimates generated from the image recording material but also a gas mixture of solid components such as dust and ash. 
   2. Description of the Background Art 
   In an image recorder employing an image recording material generating gas, the gas may adhere to an objective lens of a recording head or the like to tarnish the surface of the objective lens and deteriorate the quality of an image formed on the image recording material. In order to solve this problem, Japanese Patent Application Laying-Open Gazette No. 2000-56400 discloses a technique of diffusing the aforementioned gas by producing an air stream intersecting with a laser beam emitted from a recording head for preventing the gas from adhering to an objective lens of the recording head. 
     FIG. 8  is an explanatory diagram schematically showing a recording drum  101  and a recording head  108  in a conventional image recorder. A plate  100  employed as an image recording material is fixed to the outer peripheral surface of the recording drum  101  with a front clamp  102  and a rear clamp  103 . The recording head  108  applies a laser beam to the plate  100  for recording images. This recording head  108  comprises a gas diffusion/suction unit  180 . The gas diffusion/suction unit  180  injects clean air from an air injection port  182  and sucks the atmosphere from a gas suction port  183  thereby forming an air curtain in front of an objective lens  186  for preventing the gas from adhering to the objective lens  186 . 
   The image recorder shown in  FIG. 8  diffuses gas etc. generated from the plate  100  with the air injected from the air injection port  182  and sucks the atmosphere containing the diffused gas from the gas suction port  183 . Thus, the image recorder can suck most of the gas generated from the plate  100  through the suction port  183 . 
   In recent years, however, a recording material generating a large quantity of gas has been employed due to development of the so-called processless printing plates requiring no development or the like after image recording, and it is apprehended that the image recorder cannot completely suck the entire gas through the aforementioned suction port  183 . 
   In order to improve gas collection efficiency, the area of the gas suction port  183  of the gas diffusion/suction unit  180  may be enlarged. If the gas diffusion/suction unit  180  fixed to the recording head  108  is enlarged in scale, however, the recording head  108  may be hindered from moving in a subscanning direction. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an image recorder applying a laser beam to an image recording material thereby recording a two-dimensional image on this image recording material. 
   According to the present invention, the image recorder comprises a recording drum having an outer peripheral surface to which the image recording material is fixed, a rotation element rotating the recording drum, a recording head having a laser beam source emitting a laser beam and an objective lens applying the laser beam to the image recording material fixed to the outer peripheral surface of the recording drum, a recording head moving element moving the recording head in a subscanning direction parallel to the rotational axis of the recording drum, a gas injection element moving in the subscanning direction along with the recording head for diffusing gas generated from the image recording material irradiated with the laser beam by injecting prescribed gas in the vicinity of the objective lens, a first suction element, moving in the subscanning direction along with the recording head, located downstream beyond the gas injection element in relation to the rotational direction of the recording drum for sucking the gas diffused by the gas injection element and a second suction element located downstream beyond the first suction element in relation to the rotational direction of the recording drum for sucking the gas diffused by the gas injection element over the total width of an image recording area of the image recording material in the subscanning direction. 
   The gas generated from the image recording material is diffused by the gas injection element and thereafter sucked by the first suction element, not to contaminate the objective lens of the recording head. Further, the second suction element sucking the gas over the total width of the image recording area can suck the part of the gas not sucked by the first suction element. Thus, the image recorder can be prevented from contamination with the gas. 
   Accordingly, an object of the present invention is to provide an image recorder improved in gas collectability. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side elevational view of an image recorder according to an embodiment of the present invention; 
       FIG. 2  is an exploded perspective view of a recording head employed in the image recorder shown in  FIG. 1 ; 
       FIG. 3  is a top plan view of a recording drum, a recording head and a second suction unit in the image recorder shown in  FIG. 1 ; 
       FIG. 4  is a conceptual diagram illustrating an air stream around the recording head in the image recorder shown in  FIG. 1 ; 
       FIG. 5  is a sectional view of the second suction unit; 
       FIGS. 6A ,  6 B and  6 C are a perspective view, a front elevational view and a longitudinal sectional view of a diffusion/suction unit respectively; 
       FIG. 7  is a timing chart illustrating the relation between operation timings of an air supply pump and first and second exhaust pumps and a timing for applying a laser beam from the recording head; and 
       FIG. 8  is a side elevational view showing a recording drum and a recording head of a conventional image recorder. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a schematic side elevational view of an image recorder according to an embodiment of the present invention. 
   This image recorder comprises a cylindrical recording drum  1 , a recording head  8 , a transport unit  9 , a punch  10 , a base part  11 , an air supply pump  70 , a first exhaust pump  79  and a pair of clamp arms  50  in a housing  15  partially formed with an air inlet  88 . A filter  89  is disengageably engaged in the air inlet  88  of the housing  15 . 
   The recording drum  1  is arranged to be rotatable about a rotational axis  1   a  with respect to a bearing  12  arranged on a base  11  in the housing  15  of the image recorder. A motor (not shown) rotates the recording drum  1  along arrow A. An aluminum plate  100  is mounted on the outer peripheral surface of the recording drum  1  as an image recording material. A plurality of front clamps  2  arranged on the outer peripheral surface of the recording drum  1  and a plurality of rear clamps  3  (not shown in  FIG. 1 ) detachable from the outer peripheral surface of the recording drum  1  fix first and second ends of the plate  100  to the outer peripheral surface of the recording drum  1  respectively. 
   The recording head  8  is arranged on a pair of rails  21  in front of the recording drum  1 . The recording head  8  is fitted with a feed shaft  14  rotated by a motor  13 , to be movable along the direction of the rotational axis  1  a of the recording drum  1 . 
   As shown in  FIG. 1 , the image recorder comprises the pair of clamp arms  50 . A driving bar  7  is mounted between the pair of clamp arms  50 . The pair of clamp arms  50  are rockable in directions for approaching and separating the driving bar  7  to and from the recording drum  1  respectively. The driving bar  7  is provided with a driving pin  51  for fixing and detaching the rear clamps  3  to and from the recording drum  1  and a release pin  52  for releasing the front clamps  2  when mounting the plate  100 . 
   As shown in  FIG. 1 , the transport unit  9  is rockably arranged above the recording drum  1 . The transport unit  9  has first and second transport paths  91  and  92  for introducing and discharging the plate  100  respectively. In order to introduce the plate  100 , the transport unit  9  supplies the plate  100  onto the recording drum  1  through the first transport path  91 . In order to discharge the plate  100 , on the other hand, the transport unit  9  discharges the plate  100  detached from the recording drum  1  through the second transport path  92 . 
   A first transport mechanism  94  has a transport roller driving motor  940 , a plurality of transport rollers  943 ,  944  and  945 , a pulley  941   a  coupled to the transport roller driving motor  940 , pulleys  941   b ,  941   c  and  941   d  coupled to the transport rollers  943 ,  944  and  945  respectively, a belt  942  extended along the pulleys  941   a ,  941   b ,  941   c  and  941   d , a nip roller  963  arranged oppositely to the transport roller  943 , a rock member  962  mounted with the nip roller  963  on its forward end and a nip roller driving motor  960  rocking the rock member  962  for approaching/separating the nip roller  963  to/from the transport roller  943 . 
   A second transport mechanism  95  has a transport roller driving motor  950  and transport rollers  951  and  952  driven by this transport roller driving motor  950 . 
   The transport path switching mechanism  93  is constituted of a transport path switching motor  930 , a gear  931 , a cam gear  932 , a cam follower  933  and a cam follower guide  934 . The transport switching motor  930  is mounted with the gear  931  meshing with the cam gear  932 , to which the cam follower  933  is fixed. The cam follower  933  engages with the cam follower guide  934 . The cam follower guide  934  is fixed to a unit body part  900  of the transport unit  9 , and a prescribed support member supports the unit body part  900  to be rockable about the rear portion with respect to the housing  15 . 
   Upon rotation of the transport path switching motor  930 , the cam gear  932  rotates through the gear  931  for vertically moving the cam follower guide  934  through the cam follower  933  fixed to the cam gear  932 . Thus, the transport unit  9  rocks between positions opposite to the punch  10  and the drum  1  respectively. 
   The punch  10  is arranged in front of the transport unit  9 , in order to form a recording drum index hole and a printer index hole in the plate  100 . The plate  100  is supplied to the punch  10  through the first transport path  91  of the transport unit  9  before the same is supplied onto the recording drum  1 , so that the recording drum index hole and the printer index hole are formed on the forward end thereof. A registration pin  15  provided on the outer peripheral surface of the recording drum  1  engages in the recording drum index hole of the plate  100 . 
   The recording head  8  comprises the laser beam source  30  (not shown in  FIG. 1 ) therein. This laser beam source  30  is controlled on the basis of an image signal for emitting a laser beam toward the plate  100  fixed to the outer peripheral surface of the recording drum  1 . The motor  13  successively moves the recording head  8  in a direction (subscanning direction) parallel to the rotational axis  1   a  of the recording drum  1  in synchronization with the rotation of the recording drum  1 , thereby forming a desired two-dimensional image on the plate  100  fixed to the recording drum  1 . 
   The plate  100  used in this image recorder is a thermal plate changed in thermal mode through irradiation with a high-power laser beam, for example. This plate  100  generates gas due to the laser beam applied thereto. It is undesirable that this gas adheres to the members such as the recording head  8 , the transport unit  9  and the punch  10  arranged in the housing  15 , in view of maintenance/management of the image recorder. 
   In order to prevent the gas from adhering to the aforementioned members, a gas diffusion/suction unit  80  is arranged between the recording head  8  and the recording drum  1  while a long second suction unit  60  extending along the rotational axis  1   a  of the recording drum  1  is arranged between the recording head  8  and the transport unit  9  in this image recorder. The second suction unit  60 , having a suction port substantially along the outer peripheral surface of the recording drum  1 , is fixed to the bearing portion  12  by a pair of support arms  61 . 
   The air supply pump  70  is a member cleaning air outside the housing  15  of the image recorder through a prescribed filter and feeding the same into an air supply pipe  73 . The air supply pipe  73  communicating with the recording head  8  pressurizes the recording head  8  by feeding the air. Thus, the outside air hardly flows into the recording head  8 . The air supply pipe  73  is coupled to a second air supply pipe  76  through a branch pipe  74 . The second air supply pipe  76  is coupled to the gas diffusion/suction unit  80  through an air supply port  84 , for supplying air to the gas diffusion/suction unit  80  through this air supply port  84 . 
   The first exhaust pump  79  exhausts the gas diffusion/suction unit  80  through a gas recovery port  85  for cleaning gas through a prescribed filter and discharging the same from the housing  15 . 
     FIG. 2  is a perspective view for illustrating the recording head  8  in detail. The recording head  8  has a case  20 , the laser beam source  30  arranged in the case  20  and the gas diffusion/suction unit  80  mounted on the front surface of the case  20 . 
   The case  20  is a closed container consisting of a lower case  20   a  and an upper case  20   b . The lower and upper cases  20   a  and  20   b  are so combined with each other as to cut off the laser beam source  30  from the atmosphere in the housing  15  of the image recorder. A laser beam emission hole  87  (see  FIG. 4 ) is formed on a surface of the lower case  20   a  opposite to the recording drum  1 . 
   The laser beam source  30  is arranged on the bottom surface of the lower case  20   a . This laser beam source  30  has two laser units  31  and  32 , a synthesizer  33  synthesizing two laser beams emitted from the laser units  31  and  32  respectively, a modulator  34  selectively reflecting the synthesized laser beam in response to the image signal and an imaging optical system  35  focusing the laser beam reflected by the modulator  34  on the plate  100  through the laser beam emission hole  87  and an objective lens  86 . 
   The air supply pipe  73  supplies air to the recording head  8 . This air supply pipe  73  is coupled to the recording head  8  on the rear surface thereof. The air supply pipe  73  is further coupled to the second air supply pipe  76  by the branch pipe  74  on an intermediate position. The second air supply pipe  76  supplies air to the gas diffusion/suction unit  80  arranged in front of the recording head  8 . A regulating valve  75  regulates the quantity of air supplied to the gas diffusion/suction unit  80 . 
   The second suction unit  60  is now described.  FIG. 3  is a top plan view showing the recording drum  1 , the second suction unit  60 , the recording head  8  and the like.  FIG. 4  is a side elevational view of a portion around the recording head  8  including a section of the second suction unit  60  taken along the line A—A in  FIG. 3 .  FIG. 5  is a sectional view, taken along the line B—B in  FIG. 2 , showing the second suction unit  60  as viewed from the recording head  8 . 
   As shown in  FIGS. 3 to 5 , the second suction unit  60  has a long second suction unit body  62  extending along the rotational axis la of the recording drum  1  and having a partially cylindrical form, a pair of side plates  63  blocking the side surfaces of the second suction unit body  62 , an opening  64 , elongated along the rotational axis  1   a  of the recording drum  1 , formed on the upper surface of the second suction unit body  62  and a reducing part  65  coupled to the opening  64 . 
   As shown in  FIG. 3 , the length of the second suction unit  60  along the rotational axis  1   a  of the recording drum  1  is larger than the length of the recording drum  1  in the same direction. Therefore, this length is larger than the width of the plate  100  mounted on the recording drum  1 , as a matter of course. Further, the length of the second suction unit  60  is larger than the movable range of the recording head  8 . Therefore, the second suction unit  60  can be located on a position opposite to the gas generated from the plate  100  irradiated with the laser beam emitted from the recording head  8  regardless of the location of the recording head  8  in the subscanning direction. The second suction unit  60 , having the length larger than that of the recording drum  1  along the rotational axis  1   a  thereof in this embodiment, may have a length at least larger than the movable range of the recording head  8 , i.e., an image recording area of the recording head  8 . 
   As shown in  FIG. 4 , the second suction unit body  62  is in the partially cylindrical form having two bowed portions  62   a  and  62   b . The lower bowed portion  62   b  (closer to the recording head  8 ), having an end extending only toward a position separating from the outer peripheral surface of the recording drum  1  to some extent as compared with the upper bowed portion  62   a , can readily suck the gas generated from the plate  100  irradiated with the laser beam emitted from the recording head  8  into the second suction unit body  62 . The upper bowed portion  62   a  has a lower end approaching the outer peripheral surface of the recording drum  1  to approximate the upper surface of the front clamps  2  or the rear clamps  3 . Therefore, no gas generated from the plate  100  to penetrate the second suction unit body  62  through the lower bowed portion  62   b  leaks from the second suction unit body  62  along the rotational direction of the recording drum  1 . 
   The second suction unit body  62  has a bowed inner surface provided with neither flexed portion nor projection, so that gas readily flows along this inner surface without retention. In other words, the second suction unit  62  has no element inhibiting a gas stream. Therefore, only a small quantity of gas adheres to the inner surface of the second suction unit body  62 . 
   The inner surface of the second suction unit body  62  is covered with a film  62   c  detachable from this inner surface. 
   The upper surface of the second suction unit  62  is supported by the pair of support arms  61  and fixed to the bearing portion  12 . 
   The opening  64  elongated along the rotational axis  1   a  of the recording drum  1  is formed on the upper surface of the second suction unit body  62 , as shown in  FIG. 5 . 
   The gas generated from the plate  100  may include that solidified in a jellied (greasy) or powdered state. Therefore, a jellied or powdered substance may adhere to portions exposed to the gas. The area of the opening  64  for exhausting air containing the gas from the second suction unit body  62  is so sufficiently increased that no deposit blocks the opening  64 . 
   The second suction unit  60  further has the reducing part  65 . As described later, the reducing part  65  serves as a decompression chamber reducing the speed of the gas accelerated by the rotation of the recording drum  1  to penetrate the second suction unit body  62  at a high speed. Thus, the second suction unit body  62  is prevented from simultaneous penetration of a large quantity of gas and from a state incapable of collecting the gas. 
   An exhaust pipe  78  is coupled to the top portion of the reducing part  65 . The inner diameter of the reducing part  65  is gradually narrowed from the portion coupled to the opening  64  toward the exhaust pipe  78 , as shown in  FIGS. 4 and 5 . Therefore, the gas hardly adheres to the inner surface of the reducing part  65 . Further, the portion coupling the reducing part  65  and the exhaust pipe  78  with each other has a smoothly bowed shape provided with neither flexed portion nor projection, not to inhibit an air stream. Therefore, the gas also hardly adheres to the inner surface of the portion coupling the reducing part  65  and the exhaust pipe  78  with each other. 
   The exhaust pipe  78  is coupled to a second exhaust pump  81  arranged outside the housing  15  of the image recorder. The second exhaust pump  81 , having a larger output than the aforementioned first exhaust pump  79 , sucks gas containing the gas generated from the plate  100  through the second suction unit  60 , filtrates the same through a filter  90  and thereafter discharges the same to the atmosphere. The filter  90  is detachably mounted on an exhaust port (not shown) of the second exhaust pump  81 . 
   The gas diffusion/suction unit  80  is now described.  FIGS. 6A ,  6 B and  6 C are a perspective view, a front elevational view and a longitudinal sectional view showing the gas diffusion/suction unit  80  of the recording head  8  respectively. 
   Referring to  FIGS. 6A to 6C , the gas diffusion/suction unit  80  is constituted of an upper block  80   a  and a lower block  80   b . A circular lens hole  80   c  is provided on a portion coupling the upper and lower blocks  80   a  and  80   b  with each other. The objective lens  86  is mounted on this lens hole  80   c . The lens hole  80   c  is coaxial with the laser beam emission hole  87  formed in the case  20  of the recording head  8 . 
   The upper and lower blocks  80   a  and  80   b  are readily separable from each other. Therefore, the objective lens  86  can be simply adjusted/cleaned/exchanged. 
   A plurality of air injection ports  82  are provided on the front surface of the lower block  80   b . The air injection ports  82  communicate with the air supply port  84  provided on a side surface of the lower block  80   b . These air injection ports  82  are arranged upstream the rotational direction (along arrow A) of the recording drum  1  beyond the objective lens  86 . These air injection ports  82  are substantially directed toward the position on the recording drum  1  to which the laser beam is applied through the objective lens  86 . Thus, the gas diffusion/suction unit  80  diffuses the gas resulting from application of the laser beam with air and forms a substantially semicircular air curtain on the recording drum  1  which is upstream of the laser applied position in relation to the rotational direction of the recording drum  1 , not to diffuse the gas generated from the plate  100  upstream the rotational direction of the recording drum  1 . 
   A gas suction port  83  is provided on the front surface of the upper block  80   a . This gas suction port  83  is arranged downstream the rotational direction (along A) of the recording drum  1  beyond the objective lens  86  substantially toward the position on the recording drum  1  to which the laser beam is applied through the objective lens  86 . The gas suction port  83  communicates with the gas recovery port  85  provided on the upper surface of the upper block  80   a . Thus, the gas diffusion/suction unit  80  sucks the gas resulting from application of the laser beam along with air. 
   Generation of the gas from the plate  100  and a state of recovering the same in image recording are now described with reference to  FIG. 4 . 
   The laser beam emitted from the recording head  8  is applied toward the plate  100  and images on an irradiation point P. The recording drum  1  mounted with the plate  100  rotates along arrow A at a high speed, whereby the gas generated from the plate  100  mainly flows downstream in relation to the rotational direction of the recording drum  1  and hardly spreads upstream. Further, the air injection ports  82  inject air toward the irradiation point P along arrow B, thereby forming the substantially semicircular air curtain about the irradiation point P upstream the rotational direction of the recording drum  1  of the irradiation point P. Thus, the gas further hardly spreads upstream the rotational direction of the recording drum  1  beyond the irradiation point P. 
   Most part of the gas is recovered through the gas suction port  83 . If the plate  100  generates a large quantity of gas, however, the gas may not be completely recoverable through the gas suction port  83 . The second suction unit  60  sucks the remaining gas for complementation of the suction through the gas suction port  83 . Around the recording drum  1 , the front clamps  2  form air streams C 1 , C 2  and C 3 , for example, following the rotation of the recording drum  1 . The second suction unit body  62 , provided with the lower bowed portion  62   b  having the end separating from the outer peripheral surface of the recording drum  1  to some extent as described above, can efficiently recover the gas also when the air streams C 1 , C 2  and C 3  containing the gas widely spread. 
   When the front clamps  2  approach the second suction unit  60  due to the rotation of the recording drum  1 , the second suction unit  60  must suck a large quantity of gas. In this stage, therefore, the quantity of suction of the second exhaust pump  81  is desirably increased. The second suction unit  60 , having the reducing part  65  communicating with the exhaust pipe  78  with the gradually narrowed inner diameter, can smoothly guide the gas penetrating the second suction unit body  62  to the exhaust pipe  78 . 
   After the front clamps  2  pass through the second suction unit  60 , the quantity of suction of the second exhaust pump  81  is desirably reduced, so that the plate  100  is not floated up from the outer peripheral surface of the recording drum  1  due to adsorption by the second suction unit  60 . When the plate  100  entirely passes through the second suction unit  60 , the quantity of suction of the second exhaust pump  81  may be increased. 
   As hereinabove described, the end of the upper bowed portion  62   a  of the second suction unit body  62  is opposite to the outer peripheral surface of the recording drum  1  at a space allowing passage of the front and rear clamps  2  and  3  fixing the plate  100 . The quantity of the gas flowing out from the second suction unit body  62  is reduced as this space is narrowed, preferably for gas recovery. If the space is too narrow, however, the plate  100  may be floated up as described above. Therefore, the position of the end of the bowed portion  62   a  is decided in consideration of the above. 
   The film  62   c  is detachably mounted on the inner surface of the second suction unit body  62 , as hereinabove described. This film  62   c  is preferably made of a felt substance, so that the gas adhering thereto does not separate to secondarily contaminate the recording head  8  etc. 
   Operation timings of the first and second exhaust pumps  79  and  81  and a timing for applying the laser beam from the recording head  8  are now described.  FIG. 7  is a timing chart illustrating the relation between the operation timings of the air supply pump  70  and the first and second exhaust pumps  79  and  81  and the timing for applying the laser beam from the recording head  8 . 
   It is assumed that the recording head  8  performs first exposure and second exposure in intervals between times t 1  and t 2  and between times t 3  and t 4  in  FIG. 7  respectively. The recording head  8  performs no exposure in idle periods between times t 2  and t 3  and subsequent to a time t 4 . 
   The air supply pump  70  and the first exhaust pump  79  operate substantially in synchronization with the exposure timing of the aforementioned recording head  8 . In other words, the air supply pump  70  and the first exhaust pump  79  start to operate from a time t 11  slightly ahead (by about 1 minute, for example) of the time t 1  for starting the first exposure and a time t 13  slightly ahead (by about 1 minute, for example) of the time t 3  for starting the second exposure respectively. The air supply pump  70  and the first exhaust pump  79  continue the operations up to a time t 12  slightly subsequent (by about 1 minute, for example) to the time t 2  for ending the first exposure and a time t 14  slightly subsequent (by about 1 minute, for example) to the time t 4  for ending the second exposure respectively. 
   On the other hand, the second exhaust pump  81  is so controlled as to terminate its operation not every time the recording head  8  terminates each exposure but only when the recording head  8  continuously dwells for a relatively long period (about 10 minutes). If the idle period for the exposure is relatively short (in the idle period between the times t 2  and t 3  between the first exposure and the second exposure, for example), therefore, the second exhaust pump  81  continuously operates, in order to entirely collect the gas generated from the plate  100  and conceivably remaining in the atmosphere of the housing  15  in an unrecovered state for a while after the exposure. 
   An exhaust pipe  77  of the gas diffusion/suction unit  80  communicates with the first exhaust pump  79 . A filter (not shown) is interposed in the exhaust pipe  77 . The gas recovered by the gas diffusion/suction unit  80  conceivably has relatively large specific gravity and contains dust or the like, and hence the filter interposed in the exhaust pipe  77  desirably has a coarse mesh. On the other hand, the gas recovered by the second suction unit  60  conceivably has relatively small specific gravity and hardly contains dust or the like, and hence the filter  90  mounted on the second exhaust pump  81  desirably has a fine mesh. The filter and the filter  90  are desirably exchangeable. 
   In the aforementioned embodiment, the second exhaust pump  81  discharges the gas from the housing  15  mainly through the second suction unit  60  and the exhaust pipe  78 . The housing  15  is airtightly constituted for introducing outside air only through the air inlet  88 . The air inlet  88  must have a sufficiently large size so that the internal pressure of the housing  15  is not remarkably reduced beyond the atmospheric pressure upon operation of the second exhaust pump  81 . If the internal pressure of the housing  15  is remarkably reduced beyond the atmospheric pressure, the outside air containing foreign matter not removed through the filter  89  may penetrate the housing  15 . 
   Thus, the image recorder according to this embodiment introduces the outside air into the housing  15  only through the air inlet  88  engaged with the filter  89  and discharges the air from the housing  15  from the second exhaust pump  81  through the filter  90 . Therefore, the image recorder can keep the housing  15  clean and minimize influence on the working environment by not discharging the gas generated from the plate  100  in an untreated state. 
   As hereinabove described, the second suction unit body  62  is fixed to the bearing portion  12  through the pair of support arms  61  (see  FIG. 3 ). The portions connecting the bearing portion  12  and the support arms  61  with each other are desirably separable. In this case, the second suction unit body  62  can be readily exchanged. 
   This is because the ability required to the second suction unit body  62  may conceivably vary with the environmental quality standard of a country or an area in which the image recorder is set or the type of the plate  100  mainly employed by the user of this image recorder. 
   The second suction unit body  62  is rendered so readily exchangeable that the same is readily replaced with another second suction unit body  62  upon variation of the ability required thereto. 
   While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.