Patent Publication Number: US-2005141054-A1

Title: Recording apparatus and recording method

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a recording method and recording apparatus for recording information, such as images and characters, particularly information, such as color images and characters using color tones of K, C, M and Y colors, on a recording medium.  
      2. Description of the Related Art  
      For the recording of images and characters, there is known a recording method in which an image receiving sheet and a transfer sheet are layered one on the other, and in this state, are fixed onto a drum, and those are exposed to laser light. In this case, the image receiving sheet is wound around the drum in a state that its image receiving layer is directed upward. The transfer sheet is wound on the drum in a state that its toner layer is layered on the image receiving layer of the image receiving sheet. A recording head of the laser exposure type is reciprocatively moved in directions parallel to the rotational shaft of the drum. The recording head emits laser light and takes the form of a plurality of spots of light when it lands on the recording medium. The plural spots  1 , as shown in  FIG. 15 , are linearly arrayed in the moving direction of the recording head. In the recording method, the rotational direction of the drum is coincident with a main scan direction, and the moving direction of the recording head is coincident with a sub scan direction. Accordingly, when the rotational motion of the drum and the linear motion of the recording head are combined, the transfer sheet is scanned with the spots to thereby transfer a desired image on the image receiving sheet.  
      In the recording method, optical energy of the laser light is transduced into thermal energy by the optical-to-thermal transducing layer at a recording local area or part irradiated with the laser spots. At this time, the heat generation is instantaneously performed, and water and organic solvent, which are contained in the optical-to-thermal transducing layer and the toner layer, are volatilized, and called gas is generated. Accordingly, in the recording method in which the image receiving sheet and the transfer sheet are layered one on the other, and an acting layer acting in connection with the laser light is sandwiched between those sheets, the gas generated is hard to run out into the air, and stays between the image receiving sheet and the transfer sheet.  
      At both ends of the spot array, the gas is easy to run out in the sub-scan direction (the right side or left side in  FIG. 15 ). At the central part of the spot array, the generated gas is hard to run out in the sub-scan direction, and it stagnates at the central part of the spot array.  
      At the central part of the spot array, the generated gas is put between the toner layer and the image receiving layer, so that the toner layer and the image receiving layer are not in close contact with each other. In this state, the toner layer is not transferred to the image receiving layer even at a part of the recording medium irradiated with the laser light. As a result, no color or thin color is formed on that part in the final image. When this phenomenon is observed macroscopically (by the eye), a stripe (vertical stripe)  3  appears which extends in the drum rotational direction, as shown in  FIG. 15 , and it will be an image defect.  
      For example, when 32 spots are arrayed at an interval of 10 μm (2450 dpi), a distance between the spots located at both ends of the spot array in the sub-scan direction, is 310 μm. In an another example where 256 spots are arrayed at an interval of 10 μm (2450 dpi), a distance between the spots located at both ends of the spot array in the sub-scan direction, is 2550 μm. As the spot-to-spot distance between both ends of the spot array becomes larger, the gas is harder to run out at the central part, and also when it is observed by the eye, it becomes the image unevenness and it is easily recognizable.  
      To be more specific, the gas stagnates at the central part of the spot array, and the toner layer and the image receiving layer are not in close contact with each other. In this state, heat generated in the optical-to-thermal transducing layer of the transfer sheet does not flow to the image receiving layer; in a usual case, it flows to the latter. And heat is accumulated in the transfer sheet. The result is that the optical-to-thermal transducing layer of the transfer sheet and the toner layer are heated and its temperature is higher than that in the normal state. When the temperature rises till the optical-to-thermal transducing layer and the toner layer are decomposed, gas is further generated, and the optical-to-thermal transducing layer and the toner layer are molten and decomposed to thereby lose their normal state. In this state, an optical density at the central part is low, or the optical-to-thermal transducing layer, which should not be transferred, is transferred onto the image receiving layer. More serious image defect occurs.  
     SUMMARY OF THE INVENTION  
      Accordingly, an object of the present invention is to provide a recording method and recording apparatus in which the gas generated at the recording local area does not stagnate in an already recorded area between the toner layer and the image receiving layer, thereby preventing the formation of the image defect resulting from the spot array.  
      To achieve the above object, there is provided an image recording method executed by a recording apparatus having a recording medium fixing member for fixing a recording medium, which is formed by coupling together a toner layer of a transfer film as a heat mode sensitive material and an image receiving layer of a receiver film in a layering manner, and a recording head capable of irradiating the recording medium with a plurality of spots of light, wherein the recording head exposes the recording medium in accordance with image/character data to thereby record a desired image on the recording medium, in a manner that the recording head is moved relative to the recording medium fixed to the recording medium fixing member in a main scan direction in which the recording head is moved relative to the recording medium, and the plurality of spots irradiated and arrayed on the recording medium are moved in a sub-scan direction orthogonal to the main scan direction, the exposure operation being performed by relatively moving the recording head from a position near the original point of the sub-scan to a position near the end of the sub-scan.  
      The image recording method thus constructed is improved in that in a first exposure operation, which is performed by moving the recording head from a position near the original point of the sub-scan to a position near the end of the sub-scan, the recording medium is exposed to the light containing information of image/character data, while forming pixel groups (referred to as island patterns) each consisting of a predetermined number of pixels consecutively arrayed on the recording medium in the main and sub-scan directions, and in a second exposure operation and the subsequent ones, the pixels in an unexposed area other than the island patterns on the recording medium are successively exposed to the light.  
      According to another aspect of the invention, there is provided a recording apparatus having a recording medium fixing member for fixing a recording medium, which is formed by coupling together a toner layer of a transfer film as a heat mode sensitive material and an image receiving layer of a receiver film in a layering manner, and a recording head capable of irradiating the recording medium with a plurality of spots of light, wherein the recording head exposes the recording medium in accordance with image/character data to thereby record a desired image on the recording medium, in a manner that the recording head is moved relative to the recording medium fixed to the recording medium fixing member in a main scan direction in which the recording head is moved relative to the recording medium, and the plurality of spots irradiated and arrayed on the recording medium are moved in a sub-scan direction orthogonal to the main scan direction. The recording apparatus thus constructed is improved by an exposure controller device operating such that in a first exposure operation, which is performed by moving the recording head from a position near the original point of the sub-scan to a position near the end of the sub-scan, the recording medium is exposed to the light containing information of image/character data, while forming pixel groups (referred to as island patterns) each consisting of a predetermined number of pixels consecutively arrayed on the recording medium in the main and sub-scan directions, and in a second exposure operation and the subsequent ones, the pixels in an unexposed area other than the island patterns on the recording medium are successively exposed to the light.  
      In a preferred embodiment of the image recording apparatus, in the first exposure operation, after the recording head reaches a position near the end of the sub-scan and returns to a position near the original point of the sub-scan in the first exposure operation, the pixels in the unexposed area not having been exposed in the preceding exposure operation are exposed R times (R: positive integer).  
      In another preferred embodiment of the image recording apparatus, in the first exposure operation, after the recording head reaches the position near the end of the sub-scan in the first exposure operation, the recording head returns to the position near the original point of the sub-scan while exposing the pixels in the unexposed area not having been exposed in the preceding exposure operation.  
      In yet another preferred embodiment of the image recording apparatus, at the R-th exposure by the recording head, the recording head may expose the pixels as defined by the image/character data in an area on the recording medium other than the area on the recording medium which has been exposed in the first to (R−1) th exposure operations.  
      In still another preferred embodiment of the image recording apparatus, at the first exposure operation, a percentage of the island patterns to the whole image/character data to be exposed is 20% to 80%.  
      In a further preferred embodiment of the image recording apparatus, a percentage of the pixels as defined by the image/character data in an area on the recording medium other than the area on the recording medium which has been exposed in the first to (R−1) th exposure operations, to the whole image/character data to be exposed is 20% or higher.  
      According to yet another aspect of the invention, there is provided an image recording method executed by a recording apparatus having a recording medium fixing member for fixing a recording medium, which is formed by coupling together a toner layer of a transfer film as a heat mode sensitive material and an image receiving layer of a receiver film in a layering manner, and a recording head capable of irradiating the recording medium with a plurality of spots of light, wherein the recording head exposes the recording medium in accordance with image/character data to thereby record a desired image on the recording medium, in a manner that the recording head is moved relative to the recording medium fixed to the recording medium fixing member in a main scan direction in which the recording head is moved relative to the recording medium, and the plurality of spots irradiated and arrayed on the recording medium are moved in a sub-scan direction orthogonal to the main scan direction, the exposure operation being performed by relatively moving the recording head from a position near the original point of the sub-scan to a position near the end of the sub-scan. The image recording method is improved in that where the spots of light are divided into an “n” umber of blocks (n=positive integer of 2 or larger), the recording medium is exposed by using the first block of spots, while forming pixel groups (referred to as island patterns) each consisting of a predetermined number of pixels consecutively arrayed on the recording medium in the main and sub-scan directions, and the pixels in an unexposed area other than the island patterns on the recording medium are gradually exposed by using the 2nd to (n−1)th blocks of spots, and the remaining pixels in the unexposed area are exposed by the n-th block of spots.  
      According to still another aspect of the invention, there is provided a recording apparatus having a recording medium fixing member for fixing a recording medium, which is formed by coupling together a toner layer of a transfer film as a heat mode sensitive material and an image receiving layer of a receiver film in a layering manner, and a recording head capable of irradiating the recording medium with a plurality of spots of light, wherein the recording head exposes the recording medium in accordance with image/character data to thereby record a desired image on the recording medium, in a manner that the recording head is moved relative to the recording medium fixed to the recording medium fixing member in a main scan direction in which the recording head is moved relative to the recording medium, and the plurality of spots irradiated and arrayed on the recording medium are moved in a sub-scan direction orthogonal to the main scan direction, the exposure operation being performed by relatively moving the recording head from a position near the original point of the sub-scan to a position near the end of the sub-scan. The recording apparatus is improved by an exposure controller device operating such that where the spots of light are divided into an “n” umber of blocks (n=positive integer of 2 or larger), the recording medium is exposed by using the first block of spots, while forming pixel groups (referred to as island patterns) each consisting of a predetermined number of pixels consecutively arrayed on the recording medium in the main and sub-scan directions, and the pixels in an unexposed area other than the island patterns on the recording medium are gradually exposed by using the 2nd to (n−1)th blocks of spots, and the remaining pixels in the unexposed area are exposed by the n-th block of spots.  
      In a preferred embodiment of the image recording apparatus as mentioned above, a percentage of an unexposed part at the exposure by the first block of spots to the whole image/character data to be exposed is 20% to 80%.  
      In another preferred embodiment of the image recording apparatus, a percentage of image/character data other than that exposed by the 1st to (n−1)th blocks of spots at the exposure by the n-th block of spots, to the whole image/character data to be exposed is 20% or higher.  
      In yet another preferred embodiment of the image recording apparatus, the island pattern is configured to be flat or outcurved at its downstream side as viewed in the main scan direction.  
      In still another preferred embodiment of the image recording apparatus, the outcurved part of the island pattern consists of at least two pixels consecutively arrayed in the sub-scan direction.  
      In further preferred embodiment of the image recording apparatus, the island pattern is configured to be slanted to the downstream side in the sub-scan direction, and to the upstream side in the main scan direction.  
      In an additional preferred embodiment of the image recording apparatus, an array of the plural island patterns is directed to the downstream side in the sub-scan direction and to the upstream in the main scan direction.  
      As described above, in the recording method in which the image receiving sheet and the transfer sheet are layered one on the other, and an acting layer acting in connection with the laser light is sandwiched between those sheets, the recording medium is exposed to light containing image data in the form of island patterns thereon. Therefore, the following useful effects are produced: 
          a. “Gas stagnation” is removed, and image unevenness is lessened;     b. The exposure method effectively operates for the image part of which the area rate (dot %) is 70% or higher.       

    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram schematically showing a recording apparatus constructed according to the present invention,  
       FIG. 2  is an enlarged, perspective view showing a recording section of the recording apparatus,  
       FIG. 3  is a cross sectional view showing a structure including an image receiving sheet and a transfer sheet, which is used in the recording method and the recording apparatus of the invention,  
       FIG. 4  is a diagram for conceptually showing a recording process,  
       FIG. 5  is a diagram useful in explaining the main scan direction, sub-scan direction, laser spot numbers, line numbers in the sub-scan direction in the recording apparatus, those items being used for an island pattern exposure of the invention,  
      FIGS.  6 ( a ) and  6 ( b ) are diagrams showing an “island pattern exposure process” which forms a first embodiment of the invention, specifically showing an exposure state on the recording medium after a first exposure operation is performed,  
      FIGS.  7 ( a ) and  7 ( b ) are diagrams showing an “island pattern exposure process” which forms the first embodiment, specifically showing an exposure state on the recording medium after a second exposure operation is performed,  
      FIGS.  8 ( a ),  8 ( b ), and  8 ( c ) are diagrams showing a second instance of the first embodiment of the invention,  
      FIGS.  9 ( a ),  9 ( b ),  9 ( c ), and  9 ( d ) are diagrams for explaining a shape of an island pattern not having gas stagnation, which is a second embodiment of the invention,  
      FIGS.  10 ( a ),  10 ( b ),  10 ( c ), and  10 ( d ) are explanatory diagrams for explaining an island pattern free from the pattern omission, which forms a third embodiment of the invention,  
      FIGS.  11 ( a ),  11 ( b ),  11 ( c ), and  11 ( d ) are explanatory diagrams for explaining an inappropriate island pattern which blocks the flowing of gas generated in the preceding thin-out exposure operation to the outside of the recording medium,  
      FIGS.  12 ( a ),  12 ( b ),  12 ( c ), and ( d ) are diagrams showing a fourth embodiment of the invention, which defines island patterns enabling the flowing of gas generated in the preceding thin-out exposure operation to smoothly flow out of the recording medium,  
       FIG. 13  is a block diagram showing a process in which an image signal coming from a computer is processed and an image signal to be applied to the recording head is generated,  
      FIGS.  14 ( a ),  14 ( b ),  14 ( c ),  14 ( d ), and  14 ( e ) are diagrams showing image data the blocks in  FIG. 13 ,  
       FIG. 15  is a diagram showing an array of spots of laser light irradiated by the conventional recording method,  
      FIGS.  16 ( a ),  16 ( b ), and  16 ( c ) are diagrams showing exposure states on the recording medium at the m-th to (m+2)th rotation of the drum in a first instance of the fifth embodiment according to the invention,  
      FIGS.  17 ( a ),  17 ( b ), and  17 ( c ) are diagrams, subsequent to  FIG. 6 ( c ), showing exposure states on the recording medium at the (m+3)th to (m+5)th rotation of the drum,  
      FIGS.  18 ( a ),  18 ( b ), and  18 ( c ) are diagram showing exposure states on the recording medium at the m-th to (m+2)th rotation of the drum in a second instance of the fifth embodiment according to the invention,  
      FIGS.  19 ( a ),  19 ( b ), and  19 ( c ) are diagrams, subsequent to  FIG. 18 ( c ), showing exposure states on the recording medium at the (m+3)th to (m+5)th rotation of the drum,  
      FIGS.  20 ( a ),  20 ( b ),  20 ( c ),  20 ( d ),  20 ( e ), and  20 ( f ) are diagrams useful in explaining the direction of the “thin-out exposure process” according to the invention,  
      FIGS.  21 ( a ) and  21 ( b ) are tables showing a spot array of laser light in a conventional “sub-scan direction thin-out exposure” type of the interlace recording technique,  
      FIGS.  22 ( a ) and  22 ( b ) are tables showing a spot array of laser light in a conventional “main scan direction thin-out exposure” type of the interlace recording technique,  
      FIGS.  23 ( a ),  23 ( b ), and  23 ( c ) are diagrams showing a first exposure operation in a “thin-out exposure process” according to the sixth embodiment of the invention,  
      FIGS.  24 ( a ),  24 ( b ), and  24 ( c ) are diagrams showing a second exposure operation in the “thin-out exposure process” according to the sixth embodiment of the invention,  
      FIGS.  25 ( a ),  25 ( b ),  25 ( c ),  25 ( d ),  25 ( e ), and  25 ( f ) are diagrams for explaining the thinning-out direction in the second embodiment of the invention,  
       FIG. 26  is a block diagram showing a process in which an image signal coming from a computer is processed and an image signal to be applied to the recording head is generated,  
      FIGS.  27 ( a ),  27 ( b ), and  27 ( c ) are diagrams showing image data of the blocks in  FIG. 26 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The preferred embodiments of a recording method and recording apparatus according to the present invention will be described with reference to the accompanying drawings.  
       FIG. 1  is a diagram schematically showing a recording apparatus constructed according to the present invention;  FIG. 2  is an enlarged, perspective view showing a recording section of the recording apparatus;  FIG. 3  is a cross sectional view showing a structure including an image receiving sheet and a transfer sheet, which is used in the recording method and the recording apparatus of the invention;  FIG. 4  is a diagram for conceptually showing a recording process;  FIG. 5  is a diagram useful in explaining the main scan direction. sub-scan direction, laser spot numbers, line numbers in the sub-scan direction in the recording apparatus, those items being used for an island pattern exposure of the invention; and  
       FIGS. 6 through 11  are explanatory diagrams for explaining an “island pattern exposure process” of the invention, which is carried out by using the laser light spots emitted from a recording head.  
      A recording apparatus  1 , as shown in  FIG. 1 , includes an image receiving sheet supply section  100 , a transfer sheet supply section  200 , a recording section  300  and a discharge section  400 . The recording apparatus  1  is covered with a body cover  510  and is supported by leg parts  520 .  
      In the recording apparatus  1 , the image receiving sheet supply section  100  supplies an image receiving sheet to the recording section  300 . The transfer sheet supply section  200  is capable of supplying plural kinds of transfer sheets and selectively supplies one of those transfer sheets to the recording section  300 . In the recording section  300 , another transfer sheet is wound on the image receiving sheet, which is wound around a drum  310  as a recording medium fixing member. In this state, laser exposure is carried out in accordance with image information of an image to be recorded onto the recording medium formed by superimposing the transfer sheet on the image receiving sheet. An image is formed on the image receiving sheet in a manner that toner on a portion of the transfer sheet which is heated by the laser exposure process, is transferred and attached to the image receiving sheet by its adhesion deterioration, fusion or sublimation. Further, toners of different colors (e.g., black, cyan, magenta and yellow) on the transfer sheets are attach to the same image receiving sheet, to thereby forming a color image on the receiving sheet. As will be described later, this is realized in such a manner that the exposed transfer sheets are successively exchanged with transfer sheets of other colors, and subjected to the laser exposure process.  
      The image receiving sheet on which the image is formed, is discharged through the discharge section  400  and is taken out from the recording apparatus. Subsequently, in an image transfer section which is additionally provided and is not shown, the image receiving sheet is heated and pressed in a state that the image forming surface of the image receiving sheet is placed on a paper sheet to be printed. By so doing, the toner is transferred onto the desired paper sheet (printing sheet), whereby the image is formed.  
      The outline of the recording apparatus  1  is as mentioned above.  
      For the recording material, reference is made to Japanese patent laid-open No. 296594/1992, No. 327982/1992 and No. 327983/1992. For the device using the above recording material, reference is made to Japanese patent laid-open No. 290731/1995. For the citation of the recording apparatus using the embodiment, reference is made to Japanese patent laid-open No. 277831/1999.  
      The image receiving sheet supply section  100 , the transfer sheet supply section  200 , the recording section  300  and the discharge section  400  will be described successively.  
      The image receiving sheet supply section  100  includes an image receiving sheet roll  130 . The image receiving sheet roll  130  is formed by winding the image receiving sheet  140  around the core. The image receiving sheet  140 , as shown in  FIG. 3 , includes a supporting layer  140   a , a cushion layer  140   b  and an image receiving layer  140   c . The cushion layer  140   b  and the cushion layer  140   b  are successively laminated on the supporting layer  140   a . PET (polyethylene) base, TAC (triacetyl-cellulose) base, PEN (polyethylene naphthalate) base or the like may be used for the supporting layer  140   a . The image receiving layer  140   c  receives the toner to be transferred. The cushions layer  140   b  functions to absorb steps formed when a plurality of different toner layers are layered on upon the other. In the image receiving sheet roll  130 , the image receiving layer  140   c  is wound so that the image receiving layer  140   c  is located outside with respect to the supporting layer  140   a  (the image receiving sheet roll thus wound will be referred to as an “outer winding” image receiving sheet roll). The image receiving sheet roll  130  is disposed so that it rotates about the central axis of the core.  
      The image receiving sheet supply section  100  further includes an image receiving sheet transporting part  150 . The image receiving sheet transporting part  150  includes a motor (not shown), a drive force transmitting belt or a chain (not shown), transporting rollers  154  and  155 , a supporting guide  156 , an image receiving sheet cutting part  160  and a detection sensor (not shown) for detecting an end point of the image receiving sheet.  
      Each of transporting rollers  154  and  155  consists of a couple of rollers. With this driving mechanism, the image receiving sheet  140  is transported to the recording section  300 , and is returned from the recording section  300 .  
      To start, in a state that the leading end of the image receiving sheet roll  130  is nipped between the paired transporting rollers  154 , the image receiving sheet  140  is pulled out by the driving mechanism including the motor. With this, the image receiving sheet roll  130  rotates, and the image receiving sheet  140  is successively transported. The image receiving sheet  140  thus transported is further transported, while being nipped between the transporting rollers  155  and guided by the supporting guide  156 .  
      The image receiving sheet  140  thus transported by the image receiving sheet transporting part  150  is cut by the image receiving sheet cutting part  160  to have a predetermined length. The detection sensor is used for measuring the length of the image receiving sheet. The length measurement is conducted in a manner that the leading end of the image receiving sheet  140  is detected by the detection sensor, and the number of revolution of the motor is allowed for. The image receiving sheet  140  is cut to have a predetermined length on the basis of the measuring result, and then the sheet thus cut is supplied to the recording section  300 . The image receiving sheet cutting part  160  includes a cutter, a supporting part and a guide (which are not shown). The image receiving sheet  140  delivered from the image receiving sheet roll  130  by the driving mechanism, is stopped in its transportation on the basis of the result of measuring the image receiving sheet, and is cut by the cutter to have a predetermined length.  
      In this way, the image receiving sheet supply section  100  delivers and cuts a part of the image receiving sheet roll  130 , whereby the image receiving sheet  140  of a predetermined length is supplied to the recording section  300 .  
      The transfer sheet supply section  200  will be described.  
      The transfer sheet supply section  200  includes a rotary rack  210 . The rotary rack  210  is rotated about a rotary shaft  213 , as will be described later. A plurality of transfer sheet rolls  230  (six in the figure) are installed in the rotary rack  210 , and those are radially arranged about the rotary shaft  213 .  
      Each of the transfer sheet rolls  230  includes a core, a transfer sheet  240  wound around the core, and flanges (not shown) inserted into both sides of the core. The transfer sheet roll  230  is rotatably supported about the core. The outside diameter of the flange is larger than that of the transfer sheet wound around the core, so that the rolled transfer sheet will not be deformed.  
      Each of the transfer sheet  240 , as shown in  FIG. 3 , includes a supporting layer  240   a , an optical-to-thermal transducing layer  240   b  and a toner layer  240   c . The optical-to-thermal transducing layer  240   b  and the toner layer  240   c  are successively laminated on the supporting layer  240   a . A material of the supporting layer  240   a  may be selected from among general supporting member materials (e.g., the same material as that of the supporting layer  140   a  as mentioned above), if it allows the laser light to transmit therethrough. The optical-to-thermal transducing layer  240   b  functions to transduce laser energy to heat. A material of the optical-to-thermal transducing layer  240   b  may be selected from among general optical-to-thermal transducing materials if those materials are capable of transducing optical energy to thermal energy. Examples of those materials are carbon, black substance, infrared absorption dyestuff and a specific wavelength absorbing material. Toner sheets of black (K), cyan (C), magenta (M) and yellow (Y) are used for the toner layer  240   c.    
      In the transfer sheet roll  230 , the toner layer  240   c  is wound so that the toner layer  240   c  is located outside with respect to the supporting layer  240   a  (the transfer sheet roll thus wound will be referred to as an “outer winding” transfer sheet roll). As will be described later, the toner layer  240   c  containing toner ink is transferred to the image receiving sheet by laser exposure.  
      In  FIG. 1 , there is illustrated a case where the six transfer sheets rolls  230  are installed within the rotary rack  210 . Those six transfer sheets may be six kinds of transfer sheets, for example, transfer sheets of four colors, black, cyan, magenta and yellow, and the transfer sheets of two special colors (e.g., gold and silver).  
      The rotary rack  210  further includes transfer sheet delivering mechanisms  250  corresponding to those transfer sheet rolls  230 . Each of the transfer sheet delivering mechanisms  250  includes a pair of feed rollers  254  and a supporting guide  256 . In the figure, the rotary rack is provided with six transfer sheet delivering mechanisms  250 . The feed rollers  254  includes a roller  254   a  and a roller  254   b . The roller  254   a  is connected to a motor through a gear mechanism and is driven by the motor, as will be described later. The roller  254   a  cooperates with the roller  254   b  to nip the transfer sheet  240  therebetween at a predetermined pressing force. The roller  254   b  rotates in a direction opposite to that of the roller  254   a , and transports the transfer sheet  240 . The transfer sheet  240  is nipped between the rollers  254   a  and  254   b , and is moved forward or backward. As the transfer sheet  240  is transported, the transfer sheet roll  230  rotates.  
      The transfer sheet  240  is supplied to the recording section  300  by the transfer sheet delivering mechanism  250  thus constructed. In a state that the leading end of the transfer sheet  240  is caught between the paired feed rollers  254 , the feed rollers  254  are driven by the driving mechanism such as the motor. By the driving, the transfer sheet  240  is delivered. Further, the transfer sheet  240  is cut to have a predetermined length at a transfer sheet transporting part  270  to be described later, and is supplied to the recording section  300 .  
      As described above, the rotary rack  210  containing a plurality of the transfer sheet rolls  230  is capable of selectively supplying the desired transfer sheet  240  to the transfer sheet transporting part  270 .  
      The transfer sheet supply section  200  further includes the transfer sheet transporting part  270 . The transfer sheet transporting part  270  includes a motor (not shown), a belt or chain (not shown) for transmitting a drive force, transporting rollers  274  and  275 , a guide  276 , a transfer sheet cutting part  280  and a detection sensor (not shown) for detecting an end of the transfer sheet. Each of the transporting rollers  274  and  275  consists of a pair of rollers. The transporting rollers  274  and  275  are connected to the motor by way of the belt or chain for transmitting the drive force, and driven by the motor to thereby transport the transfer sheet  240 .  
      The transfer sheet  240  may be delivered to the recording section  300  or moved backward by the driving mechanism thus constructed. The transfer sheet  240  thus delivered is cut to have a predetermined length by the transfer sheet cutting part  280 . The detection sensor is used for measuring the length of the transfer sheet  240 . The length measurement may be conducted in a manner that the end of the transfer sheet  240  is detected by the detection sensor, and the number of revolution of the motor is allowed for. The transfer sheet  240  is cut to have a predetermined length on the basis of the measuring result, and then the sheet thus cut is supplied to the recording section  300 . The transfer sheet cutting part  280  includes a cutter, a supporting part, a guide and the like (which are not shown).  
      In this way, the transfer sheet supply section  200  delivers and cuts a part of the transfer sheet roll  230 , whereby the transfer sheet  240  of a predetermined length is supplied to the recording section  300 .  
      When the transfer sheet  240  is consumed, it is necessary to detach the used transfer sheet roll  230  from the related part and to replace it with a new transfer sheet  240 .  
      The replacement work of the transfer sheet roll  230  may be carried out in a state that a lid  511  is opened. To carry out the replacement work, the rotary rack  210  is turned, and the transfer sheet roll  230  to be replaced is moved to a predetermined replacement position corresponding to the lid  511 . The replacement work for the image receiving sheet roll  130  is also performed after the lid  511  is opened.  
      The recording section  300  will be described.  
      The recording section  300  includes the drum  310 . The drum  310 , as shown in  FIG. 2 , is hollow and cylindrical in shape, and is rotatably supported by a frame  320 . In the recording apparatus  1 , the rotary direction of the drum  310  is coincident with the main scan direction. The drum  310  is coupled to a rotary shaft of a motor and is driven to rotate by the motor. A plurality of holes are formed in the surface of the drum  310 . The holes are communicatively coupled to a suction device such as a blower or a vacuum pump (not shown).  
      The image receiving sheet  140  and the transfer sheet  240  are put on the drum  310 , and when the suction device is operated, those sheets are attracted and stuck onto the drum  310 .  
      The drum  310  has a plurality of grooves (not shown), and those grooves, and those grooves are arrayed in a straight line and parallel to the rotary shaft of the drum  310 . Above the drum  310 , a plurality of peeling-off pawls (not shown) are arrayed in a straight line and parallel to the rotary shaft of the drum  310 .  
      The recording section  300  includes a recording head  350 . The recording head  350  is capable of emitting a laser light Lb. Toner ink at a position on the transfer sheet  240 , which is irradiated with the laser light Lb, is transferred onto the surface of the image receiving sheet  140 . The recording head  350  is linearly moved by a driving mechanism (not shown) along a guide rail  322  in a direction parallel to the rotary shaft of the drum  310 . In the recording apparatus  1 , the moving direction of the recording head is coincident with the sub-scan direction. When the rotating motion of the drum  310  and the liner movement of the recording head  350  are combined, the recording head is able to irradiate, for exposure, a desired position on the transfer sheet  240  covering the image receiving sheet  140  with laser light emitted therefrom. Accordingly, a desired image may be transferred to the image receiving sheet  140  in a manner that the surface of the transfer sheet  240  is scanned with the image-depicting laser light Lb, and only the positions on the sheet as defined by image information are exposed to the laser light.  
      The laser light Lb emitted from the recording head  350  will be described in detail.  
      The recording head  350  includes a light emitting element (not shown) for emitting the laser light Lb or includes an optical modulating element for modulating the laser light emitted from the light emitting element. Laser light spots may be arrayed as desired in a manner that a plurality of light emitting elements are arrayed at desired positions, and a modulation windows are arrayed at desired positions.  
      In the embodiment, the laser light emitted from the recording head  350  is used for executing an “island pattern exposure process” of the invention ( FIGS. 6 through 11 ). This will be described later in detail after the remaining portions of the recording apparatus of the invention are described.  
      The operation of winding the image receiving sheet  140  and the transfer sheet  240  onto the drum  310  will be described.  
      The two kinds of sheets, the image receiving sheet  140  and the transfer sheet  240 , are wound around the drum  310 . To start, the image receiving sheet  140  supplied from the image receiving sheet supply section  100  is wound on the drum  310 . As described above, a plurality of holes (not shown) are formed in the surface of the drum  310 , and the image receiving sheet  140  is attracted thereto by the suction device (not shown). With this, the image receiving sheet  140  is wound around the drum  310  with the rotation of the drum  310 , while being attracted to the drum  310 .  
      Subsequently, a single transfer sheet  240  supplied from the transfer sheet supply section  200  is wound on the image receiving sheet  140 . The two kinds of sheets, the image receiving sheet  140  and the transfer sheet  240 , are different in size. The transfer sheet  240  is larger than the image receiving sheet  140  in the longitudinal and lateral directions. Therefore, the transfer sheet  240  is attracted to the drum  310  by its portion exceeding the image receiving sheet  140 . With rotation of the drum  310 , the transfer sheet  240  is wound while being attracted to the drum  310 .  
      When the image receiving sheet  140  and the transfer sheet  240  are wound on the drum  310 , the toner layer  240   c  of the transfer sheet  240  is in contact with the image receiving layer  140   c  of the image receiving sheet  140 . Toner ink on the toner layer  240   c  thus positionally related is exposed to the laser light by the recording head  350 , as described above, and is transferred to the image receiving sheet  140 . The transfer sheet  240  having undergone the transferring operation is peeled off from the drum  310 .  
      Next, the peeling-off process will be described.  
      To start, the drum  310  is rotated to a predetermined position at which the transfer sheet is peeled off. The tip of each peeling-off pawl is moved from a standby position at which the pawls are not in contact with the drum  310 , to a position at which the pawls come in contact with the drum  310 . At the time of moving of the pawls, the tip of each peeling-off pawl is kept away from the transfer sheet  240 . With the rotation of the drum  310 , the peeling-off pawls relatively move on the drum  310  and along the surface of the drum  310  in the circumferential direction. The tip of each peeling-off pawl relatively moves along the groove formed therein on the surface of the drum  310 , and advances to under the transfer sheet  240 . At this time, the transfer sheet  240  moves along the upper surface of the peeling-off pawls, and then the transfer sheet  240  is peeled off from the drum  310 .  
      The peeling-off pawls rise in a direction in which the pawls move apart from the drum  310  before those come contact with the image receiving sheet  140 , and move to the standby position. After the leading end of the transfer sheet  240  is peeled off, the transfer sheet  240  is further peeled off from the drum  310  and the image receiving sheet  140 , with the rotation of the drum  310 . At this time, the image receiving sheet  140  remains attracted to the drum  310  by the sucking force of the sucking device, and accordingly, only the transfer sheet  240  may be peeled off.  
      The transfer sheet  240  thus separated, is discharged outside the apparatus by way of the discharge section  400  to be described later.  
      Subsequently, a transfer sheet  240  of another color is wound, by the above procedure, on the image receiving sheet  140  remaining wound on the drum  310 . After the above-mentioned operation is performed, and the toner ink of the transfer sheet  240  is transferred on the image receiving sheet  140  by the laser exposure process, the transfer sheet  240  is peeled off and discharged.  
      A similar same operation is repeated for given plural kinds of transfer sheets  240 . The operation is repeated for four kinds of transfer sheets  240  of, for example, black, cyan, magenta and yellow, so that a color image is transferred on the image receiving sheet  140 .  
      Finally, the image receiving sheet  140  having the plural kinds of toner inks thus transferred thereon is peeled off. The image receiving sheet  140  is peeled off in a similar way to that of peeling off the transfer sheet  240 . At this time, the peeling-off pawls approach plural grooves and separate the image receiving sheet  140  from the drum  310 . The same peeling-off pawls as used when the transfer sheet  240  is peeled off may be used, so that the mechanical structure thereof may be simplified. Accordingly, the apparatus reliability is improved.  
      The image receiving sheet  140  thus separated is discharged to the discharge section  400 .  
      The discharge section  400  will be described.  
      The discharge section  400  includes a sheet common transporting part  410 , a transfer sheet discharge part  440  and an image receiving sheet discharge part  450 .  
      The sheet common transporting part  410  includes a motor (not shown), a belt or chain (not shown) for transmitting drive force, transporting rollers  414 ,  415  and  416 , supporting guides  418  and  419 , and a detection sensor (not shown). The sheet common transporting part  410  further includes a movable guide part made up of a guide plate  438  and a driving mechanism (not shown). The guide plate  438  is movable between two positions to be described later when it is driven by the driving mechanism.  
      The transfer sheet discharge part  440  is used for discharging the processed transfer sheet  240  to a transfer sheet recovering box  540 .  
      The image receiving sheet discharge part  450  includes an image receiving sheet exit port  451 , rollers  454  and  455 , and a guide  458 . The image receiving sheet  140  having an image transferred thereto is discharged to a tray  550 , through the image receiving sheet discharge part  450 .  
      Each of transporting rollers  414 ,  415 ,  416 ,  454  and  455  consists of a pair of rollers, like as other transporting rollers already stated. The paired rollers nip the image receiving sheet  140  and the transfer sheet  240 , and in this state, transport those sheets.  
      The discharge section  400  having such a mechanism discharges the image receiving sheet  140  and the transfer sheet  240  in the following manners.  
      The discharging of the transfer sheet  240  will first be described.  
      The transfer sheet  240 , which has been laser exposed in the recording section  300  and been out of use, is peeled off from the drum  310  by the above procedures. The transfer sheet  240  separated is transported forward, while being supported by the peeling-off pawls, the supporting guides  418  and  419 , and the guide plate  438 , and being nipped between the transporting roller pairs  414 ,  415  and  416 .  
      Next, the discharging of the image receiving sheet  140  will be described.  
      After the image receiving sheet  140  receives the toner ink and is processed in the recording section  300 , it is peeled off from the drum  310 , as mentioned above. The separated image receiving sheet  140  is transported forward, while being supported by the peeling-off pawls, the supporting guides  418  and  419 , and the guide plate  438 , and being nipped between the transporting roller pairs  414 ,  415  and  416 .  
      The sheet common transporting part  410  is also used for the discharging of the transfer sheet  240 . Therefore, the sheet transport mechanism is simpler than in the case where the transport parts are respectively provided for those sheets. In the sheet common transporting part  410 , the transfer sheet  240  is transported in a state that the toner layer thereof is directed downwards. The image receiving sheet  140  is transported in a state that the image receiving layer thereof is directed upwards. Therefore, when the image receiving sheet  140  and the transfer sheet  240  are successively transported by utilizing the same transporting path, there is no fear that the image formed on the image receiving layer of the image receiving sheet  140  is soiled.  
      The image receiving sheet  140  is transported by the transporting rollers  414 ,  415  and  416 , and is temporarily discharged outside the apparatus. In this case, however, the whole image receiving sheet  140  is discharged outside. To be more specific, in a state that the trailing end of the image receiving sheet  140  is put on the guide plate  438  and is nipped between the transporting roller pair  416 , the driving by the motor is temporarily stopped, and the motor is reversely turned to move the image receiving sheet  140  back to the image receiving sheet exit port  451 . That is, the “switch-back” operation is performed. A timing of stopping the driving by the motor is determined by using a signal derived from the detection sensor. The detection sensor detects that the trailing end of the image receiving sheet  140  passes the position of the detection sensor. Then, the image receiving sheet  140  is transported and reaches a predetermined position, and at this time, the driving by the motor is stopped.  
      Here, the “predetermined position” means a position at which the trailing end of the image receiving sheet  140  is put on the guide plate  438  and is nipped between the transporting roller pair  416 . Whether or not the image receiving sheet  140  is moved a predetermined distance till it reaches this position, is judged from, for example, the number of pulses representative of a rotation of the motor, which is counted from an instant that the detection sensor detects the trailing end of the image receiving sheet.  
      The guide plate  438  of the movable guide part is driven by a driving mechanism (not shown) and is movable between a position indicated by a solid line and another position by a broken line. Thus, the guide plate  438  is moved by the driving mechanism. When the motor being standstill is reversely rotated, the transporting rollers  416 ,  454  and  455  are driven in the reverse direction. By the reverse rotation, the image receiving sheet  140  is moved backward. The image receiving sheet  140  is further transported, by the transporting rollers  454  and  455 , to the tray  550 , while being supported by the guide  458 . The image receiving sheet having been delivered to the tray  550  is taken out from the recording apparatus, as described above, and is additionally processed at an image transfer section, which is separately provided. As a result, the image is printed on a desired printing sheet.  
      The operation described above is controlled by a controller section (not shown).  
      The controller section controls the image receiving sheet supply section  100 , the transfer sheet supply section  200 , the recording section  300 , the discharge section  400  and the like. In the respective sections, the controller section controls the driving part including the motor and the like. Particularly, in the recording section  300 , the controller section further controls the air part, such as the suction device, and an image processing part for processing image data. The driving part of the transfer sheet supply section  200  includes two driving systems, i.e., a rotation driving system for the rotary rack  210  and a sheet-transport driving system for supplying the transfer sheet  240  from the transfer sheet roll  230  to the drum  310 . For the driving of the motor in the sheet-transport driving system drives the motor, the driver for motor driving is used commonly for the plurality of transfer sheet delivering mechanisms, as described above. Accordingly, the drive circuit system is simplified.  
      The recording apparatus as described above is capable of forming a desired color image on the image receiving sheet  140 .  
      Description will be given on operation procedures when a color image is formed by using four colors, black, cyan, magenta and yellow.  
      To start with, as shown in  FIG. 4 , in a step  1 , the image receiving sheet supply section  100  supplies an image receiving sheet  140  to the drum  310 . In this case, the image receiving sheet  140  is supplied in a manner that a part of the outer-winding image receiving sheet roll  130  is delivered and cut, and is wound on the drum  310 .  
      In a step  2 , the transfer sheet supply section  200  supplies a transfer sheet  240  of black (K) to the drum  310 .  
      Specifically, the rotary rack  210  of the transfer sheet supply section  200  rotates to thereby move the transfer sheet roll  230  of black to a position facing the transfer sheet transporting part  270 . The transfer sheet  240  is supplied in a manner that a part of the outer-winding transfer sheet roll  230  is delivered and cut, and is wound on the drum  310 . At this time, the leading end of the transfer sheet  240  being delivered from the transfer sheet roll  230  is at a position near the cutter  280  disposed outside the rotary rack  210 . In this case, following the supply of the transfer sheet  240 , the transfer sheet delivering mechanism  250  reversely turns the feed roller  254  to store the leading end of the transfer sheet roll  230  on the inner side of the outer peripheral of the rotary rack  210 . Also in this case, the feed rollers  254  still nip the leading end of the transfer sheet roll.  
      In a step  3 , the transfer sheet  240  is heated and pressed, and laminated. This laminating process is omitted sometimes.  
      In a step  4 , a latent image is formed on the image receiving sheet  140  in accordance with image data previously applied. The image data is further color separated into image data of respective colors. Laser exposure is performed in accordance with the color separated image data of the respective colors. The recording head  350  irradiates the transfer sheet  240  with image forming laser light spots Lb in accordance with the color image data after color separated. Toner ink of the transfer sheet  240  is transferred onto the image receiving sheet  140 , and an image is formed on the image receiving sheet  140 .  
      In a step  5 , only the transfer sheet  240  of “K” is peeled off from the drum  310 . The transfer sheet  240  having been separated from the drum  310  is discharged through the discharge section  400  to the transfer sheet recovering box  540 .  
      At this time, judgement is made as to whether or not the transfer operation has been performed for the transfer sheets  240  of all colors. If the supply of another kind of transfer sheet  240  is needed, the sequence of operations from the steps  2  to  5  is repeated. In other words, the sequence of operations steps  6  to  17  is repeated for the transfer sheets  240  of other colors, cyan, magenta and yellow. As a result, the toner inks of K, C, M and Y of four-color transfer sheets are transferred to one image receiving sheet  140 , so that a color image is formed on the image receiving sheet  140 .  
      When the process ends, it is judged that the laser exposure of the final transfer sheet  240  is completed.  
      And, the image receiving sheet  140  is peeled off from the drum  310 . The peeled image receiving sheet  140  is discharged through the discharge section  400  to the tray  550 , while undergoing the switch-back operation. In the image transfer part separately provided, the toner ink is further transferred from The image receiving sheet  140  as discharged onto a desired printing sheet. By this, the color printing for color proofing is performed.  
      The “island pattern exposure process” of the invention will be described by taking a called “solid recording” as an example.  FIG. 5  is a diagram for explaining the main scan direction, sub-scan direction, laser spot numbers, line numbers in the sub-scan direction in the recording apparatus, which are used for the island pattern exposure process of the invention.  
      In the figure, the main scan direction of the recording apparatus is coincident with the rotational direction of the drum, and in the figure, the drum rotates in the upward direction as indicated by an arrow. Accordingly, a relative motion of the laser spot takes a downward direction as indicated by an arrow in the figure. The sub-scan direction is coincident with the moving direction of the recording head, and the recording head moves from left to right as indicated by an arrow in the figure. 24 number of laser spots to be formed on the recording medium by a laser beam emitted from the recording head are substantially horizontally arrayed, and those spots are numbered  1  to  24  in the order from the end of the sub-scan. In this instance, the number of laser spots is set at 24. Such number is selectively used for ease of explanation, but actually, 32 to 2000 number of laser spots are used. A distance between the center of one laser spot to the center of another laser spot adjacent to the former may be set within a range from 1 μm to 30 μm. Description will be given using a case where the center-to-center distance is about 10 μm.  
      Numerals “1s” are printed at positions under the line numbers  1  to  24  arranged in the sub-scan direction, respectively. Of those line Nos.  1  to  24 , the line No.  1  does not indicate a start position of the sub-scanning operation, but it indicates a desired sub-scanning position during the course of exposure operation, as a generalization. The lines are numbered  1  to  24 ,  25 ,  26 , . . . from the upstream position as viewed in the sub-scan direction. In the description, the sub-scan line No.  1  is aligned with the spot No. n ( 24 ).  
       FIGS. 6 and 7  show an “island pattern exposure process” according to the first embodiment. A first exposure operation is performed while forming island patterns, by moving the recording head to a position near the end of the sub-scan (FIGS.  6 ( a ) and  6 ( b )). Then, the recording head is returned to a position near the original position of the sub-scan, and an exposure operation is performed again, while forming inverted patterns (FIGS.  7 ( a ) and  7 ( b )).  
      (1)  FIG. 6 ( a ) shows an exposure state on the recorded recording medium fixed to the drum at the m-th rotation of the drum. A letter S indicates an island pattern configured according to the invention. This island pattern S consists of an aggregation of “black squares” indicative of exposed pixels recorded at the m-th rotation of the drum.  
      Other white squares other than the island patterns S are unexposed pixels. Specifically, at the m-th rotation of the drum in the first exposure operation, an area defined by the lines Nos.  1  to  24  arrayed in the sub-scan direction (area A) are exposed by using the spots Nos.  1  to  24 , to thereby form an array of island patterns as of the “black squares” of  FIG. 6 ( a ) in the figure.  
      (2) Then, at the (m+1)th rotation of the drum in the first exposure operation, an area defined by the lines Nos.  25  to  48  (area B) arrayed in the sub-scan direction are exposed by using the spots  1  to  24 , to thereby form an array of island patterns as of the “black squares” of  FIG. 6 ( a ). An array of the island patterns is similar to that of the island patterns of the “black square” of  FIG. 6 ( b ) in the figure.  
      (3) Subsequently, the recording head is successively moved to the line No.  49  and the subsequent ones, while repeating the sequence of exposure operations mentioned above.  
      The recording head is moved to a position near the end position of the sub-san, and the first exposure operation in the sub-scan direction ends.  
      (4) After the first exposure operation (sub-scanning operation of the recording head) ends, the recording head is returned to the original point of the sub-scan, and the recording by the second exposure operation is performed as shown in FIGS.  7 ( a ) and  7 ( b ).  
      In  FIG. 7 ( a ), the unexposed portion, which is thinned out in the first island pattern exposure, in the area defined by the lines Nos.  1  to  24  (area A) arrayed in the sub-scan direction are exposed as indicated by “dot” marks by using the spots Nos.  1  to  24 .  
      (5) At the (m+1)th rotation of the drum in the second exposure operation, as in  FIG. 7 ( b ), an area defined by the lines Nos.  25  to  48  arrayed in the sub-scan direction (area B) are exposed as indicated by “dot” marks by using the spots Nos.  1  to  24 .  
      Thus, when the exposed part by the first exposure operation and the exposed part by the second exposure operation are combined, a solid recording is formed. Further, the laser energy is not concentrated to the sub-scan lines No.  1  to  24  at a dash, unlike in the conventional technique, but the same lines arrayed in the sub-scan direction are exposed by plural exposure operations (two exposure operations in this instance). Accordingly, the load by the heat of the recording medium is small, and an amount of gas generated through one main scan is small.  
      In the first instance of the first embodiment, after the first exposure operation ends, the recording head is returned to a position near the original point in the sub-scan direction. In alternative, the recording head peforms the second exposure operation, while the recording head returns from the end point of the sub-scan direction to near the original point. The alternative gains the time taken till it returns to the original point to thereby lead to improvement of the productivity.  
      In the description thus far made, the “island pattern exposure process” is executed by two exposure operations, viz., the “island pattern exposure process” is executed by repeating the exposure operation two times, or the exposure operation for the “island pattern exposure process” is divided into two operations. However, it will readily be understood that the number of divisions of the exposure operation for the “island pattern exposure process” is not limited to 2, but may be 3 or R, larger 3. As the number R of divisions is increased, the productivity becomes low, but the resultant image recorded is clear with lessened image defects.  
      In this case, at the first exposure, a percentage of the island patterns of the whole image/character data to be exposed is preferably 20% to 80%.  
      At the R-th exposure, a percentage of the image/character data other than those exposed in the first to (R−1)th exposure operations to the whole image character data to be exposed is preferably 20% or higher.  
      FIGS.  8 ( a ),  8 ( b ), and  8 ( c ) are diagrams showing a second instance of the first embodiment in which the “island pattern exposure process” is executed by only one exposure operation. In the second instance, all the spots Nos.  1  to  24  by the recording head shown in  FIG. 5  are divided into two blocks, a first block consisting of the spots Nos.  1  to  12 , and a second block of the spots Nos.  13  to  24 . The recording head is moved from the original point of the sub-scan to a position of the end thereof, while executing the “island pattern exposure process” by using the first block of spots, and executing the inversion exposure of the unexposed pixels other than the island patterns by using the second block of spots. In this case, it is preferable that the spots are equally divided into two blocks.  
      (1) In  FIG. 8 ( a ) showing an exposure state on the recorded recording medium at the m-th rotation of the drum, an area defined by the lines Nos.  1  to  12  (area A) arranged in the sub-scan direction is subjected to the “island pattern exposure process” which is carried out by using the first block (consisting of the spots Nos.  1  to  24  in  FIG. 5 ) to thereby record a pattern of “black squares” in the figure on the recording medium.  
      (2) Subsequently, at the (M+1)th rotation of the drum, the recording medium is exposed to have a pattern of black parts in  FIG. 8 ( b ). Specifically, an area defined by the lines Nos.  13  to  24  on the recording medium (area B) are subjected to the “island pattern exposure process” which is carried out by using the first block (spots Nos.  1  to  12 ). The remaining portion (unexposed area) of the area defined by the lines Nos.  1  to  12  on the recording medium is subjected to the inversion exposure which is carried out by using the second block (spots Nos.  13  to  24 ).  
      Accordingly, as the result of the exposure operations at the m-th rotation and the (M+1)th rotation of the drum, a solid recording of the area defined by the lines Nos.  1  to  12  on the recording medium as indicated in  FIG. 8 ( c ), is completed.  
      Thus, the recording medium is exposed two times; a first exposure operation is executed for the area containing the island patterns on the recording medium and the other exposure operation is for the remaining area. Further, the laser energy is not concentrated, at a dash, to the sub-scan lines No.  1  to  24  arrayed in the sub-scan direction. Accordingly, the load by the heat of the recording medium is small, and an amount of gas generated through one main scanning operation is small.  
      In the description thus far made, the spots of the recording head is divided into two groups of spots; however, those may be divided into “n” (n=3 or larger) number of groups of spots. As the number “n” of divisions is increased, the productivity becomes low, but the resultant image recording is clear with lessened image defects.  
      In this case, a percentage of the island patterns, which are formed by the exposure using the first block, to the whole image character data to be exposed is preferably 20% to 80%.  
      At the exposure by the n-th block, a percentage of the image character data other than those exposed in the first to (n−1)th exposure operations to the whole image character data to be exposed is preferably 20% or higher.  
      FIGS.  9 ( a ),  9 ( b ),  9 ( c ), and  9 ( d ) are diagrams for explaining a shape of an island pattern not having gas stagnation, which is a second embodiment of the invention.  
      At a recording local area of the recording medium, which is irradiated with the laser spots, optical energy of the laser light is instantaneously converted into thermal energy by the optical-to-thermal transducing layer. And water and organic solvent, which are contained in the optical-to-thermal transducing layer and the toner layer, are volatilized, and called gas is generated. Therefore, in the recording method in which the image receiving sheet and the transfer sheet are placed one on the other, and an acting layer acting in connection with the laser light is placed between those sheets, the gas generated is hard to run out into the air, and stays between the image receiving sheet and the transfer sheet. The island pattern of the second embodiment is configured so as not to have gas stagnation.  
      An island pattern shown in FIGS.  9 ( a ), ( 9 ( b ),  9 ( c ), and  9 ( d ) has an inappropriate shape in which gas is easy to stagnate. An island pattern contains a recessed part T which is not exposed in the preceding exposure operation by the first block, on its downstream side as viewed in the main scan direction. This part is a part at which gas will possibly stagnate. This will be described with reference to FIGS.  9 ( a ),  9 ( b ),  9 ( c ), and  9 ( d ). All the spots of the recording head are divided into two blocks of spots. The “island pattern exposure process” is executed by using the first block of spots. The unexposed pixels other than the island patterns are subjected to the inversion exposure which is carried out by using the second block of spots.  FIG. 9 ( a ) shows an exposure state on the recording medium when an “island pattern exposure process” of an area defined by the lines Nos.  1  to  12  arrayed in the sub-scan direction, which is carried out by using the first block (spots Nos.  13  to  24 ) at the m-th rotation of the drum, is completed. It is assumed that gas is generated at an areal part including the lines Nos.  4  and  5 , and the ninth row.  
       FIG. 9 ( b ) shows an exposure state on the recording medium that the exposure of the sub-scan direction proceeds to a point near the ninth row at the (m+1) rotation of the drum. In the figure, the lines Nos.  13  to  24  arrayed in the sub-scan direction are thinned out by the exposure operation using the first block (spots Nos.  13  to  24 ) thereby form an island pattern. When the unexposed part defined by the lines Nos.  1  to  12  arrayed in the sub-scan direction are progressively exposed, gas G appears in a part near the ninth row. In the exposed part, the image receiving sheet and the transfer sheet are in close contact with each other. Therefore, it is impossible for gas G to stagnate at the exposed part. As the exposed part moves in the main scan direction, the gas G is driven to move to the upstream side in the main scan direction. Accordingly, the gas G is driven to move in the direction of an arrow. If the recessed part T, which is not exposed by the preceding exposure operation by the first block of spots, is present in the arrow direction, the gas G will enter into the recessed part.  
       FIG. 9 ( c ) shows a state on the recording medium when the gas G has been driven to flow into the unexposed recessed part T of the island pattern.  
      In turn, the gas having been put in the unexposed, recessed part T of the island pattern cannot further move forward since an upstream part in the main scan direction is not exposed. Accordingly, the gas stagnates at this recessed part.  
       FIG. 9 ( d ) shows an exposure state on the recording medium after the island pattern containing the stagnant gas G therein has been exposed in the main scan direction. The gas trapped in the recessed part T of the island pattern hinders the close contact between the image receiving sheet and the transfer sheet, possibly causing white voids.  
      As seen from foregoing description, such a problem arises from the fact that the island pattern shown in FIGS.  6 ( a ) and  6 ( b ) includes the unexposed, recessed part on its downstream side as viewed in the main scan direction. In other words, the solution to the problem is to eliminate that recessed part. To solve the problem, what a designer has to do is to configure the island pattern so as to be flat or outcurved at its downstream side as viewed in the main scan direction.  
      FIGS.  10 ( a ),  10 ( b ),  10 ( c ), and  10 ( d ) are explanatory diagrams for explaining an island pattern free from the pattern omission, which forms a third embodiment of the invention.  
      FIGS.  10 ( a ) and  10 ( b ) show an inappropriate island pattern in which the omission of pattern is easy to occur.  FIG. 10 ( a ) shows its island pattern, and  FIG. 10 ( b ) shows the same in an enlarged fashion.  FIG. 10 ( c ) and  10 ( d ) show an example of the island pattern free from the pattern omission phenomenon, which forms a third embodiment of the invention.  FIG. 10 ( c ) shows its island pattern, and  FIG. 10 ( d ) shows the same in an enlarged fashion.  
      In  FIG. 10 ( a ), as shown in the enlarged view of  FIG. 10 ( b ), each island pattern includes a 1 dot protruded part (X part), which is protruded from each of the four sides of the island pattern by a distance of one dot. It was found that the protruded part causes the pattern omission. The reason for this follows. The area around the three sides of the top, bottom, right and left sides of the one-dot protruded part is the unexposed part and cold. Accordingly, if one dot protruded part is exposed, the resultant heat dissipates in three directions. As a result, the pattern omission phenomenon occurs.  
      Island patterns shown in  FIG. 10 ( c ), as shown in  FIG. 10 ( d ) of the same figure in an enlarged manner, each island pattern includes two-dot protruded parts (marked with circles) each protruded from its four sides by a distance of two or more dots, not the one-dot protruded parts. With provision of the two-dot protruded parts, there is eliminated the pattern omission. The reason for this is reverse to the reason for the pattern omission previously stated. In this island pattern, the cold area is the area adjacent to only two sides of the top, bottom, right and left sides of each two-dot protruded part. Accordingly, the recording local area can be heated to a temperature necessary for image transferring.  
      As seen from the description of the third embodiment, it is preferable to configure the island pattern such that at least two sides of the island pattern have recording dots.  
       FIGS. 11 and 12  show diagrams useful in explaining a fourth embodiment of the invention. FIGS.  11 ( a ),  11 ( b ),  11 ( c ), and  11 ( d ) are explanatory diagrams for explaining an inappropriate island pattern which blocks the flowing of gas generated in the preceding thin-out exposure operation to the outside of the recording medium. FIGS.  12 ( a ),  12 ( b ),  12 ( c ), and  12 ( d ) are diagrams showing a fourth embodiment of the invention, which defines island patterns enabling the flowing of gas generated in the preceding thin-out exposure operation to smoothly flow out of the recording medium.  
       FIG. 11 ( a ) shows an exposure state of the recording medium when the (M+1)th rotation of the drum ends, and a solid recording in an area defined by the lines Nos.  1  to  12  arrayed in the sub-scan direction, which is performed by using the second block (spots Nos.  13  to  24 ), is completed, and an “island pattern exposure process” of an area defined by the lines Nos.  13  to  24  arrayed in the sub-scan direction, which is performed using the first block (spots Nos.  1  to  12 ), is completed. It is assumed that at this time, gas indicated by G is generated at a part including the lines Nos.  16  to  17 , and the rows Nos.  12  to  14 .  
       FIG. 11 ( b ) shows an exposure state on the recording medium that the solid recording (dotted area) has reached a position near the 11th line in the main scan direction at the (M+2)th rotation of the drum. In the figure, an area defined by lines Nos.  13  to  24  arrayed in the sub-scan direction is inversion exposed by using the second block (spots Nos.  13  to  24 ), whereby the solid recording is executed. The recording process under progression encounters the gas G. In the exposed part, the image recording sheet and the transfer sheet are in close contact with each other. Accordingly, the gas G cannot stagnate in the exposed part, and this part functions to drive the gas G to move in the main scan direction. The island pattern is configured such that as the recording head moves in the main scan direction, the gas G is driven to move upstream in the sub-scan direction (=an arrow direction). Accordingly, the gas G flows to the already exposed area located upstream in the sub-scan direction, as shown in  FIG. 11 ( c ). And the gas G is trapped at a recorded part where the exposure is completed as indicated in  FIG. 11 ( d ), possibly forming a void.  
      Turning to FIGS.  12 ( a ),  12 ( b ),  12 ( c ), and  12 ( d ), there is shown an island pattern which allows the gas to move outside the recording medium.  FIG. 12 ( a ) shows an exposure state on the recording medium that the rotation of the (m+1)th rotation of the drum ends, and the solid recording on an area defined by the lines Nos.  1  to  12  arrayed in the sub-scan is completed by using the second block (spots Nos.  13  to  24 ), and an “island pattern exposure process” of an area defined by the lines Nos.  13  to  24  arrayed in the sub-scan direction, which the process is carried out using the first block (spots Nos.  1  to  12 ), is completed. It is assumed that at this time, gas is generated at an areal part including the lines Nos.  16  to  17 , and the 12th to 14th rows.  
       FIG. 12 ( b ) shows an exposure state on the recording medium that the solid recording proceeds to a point near the 11th row as viewed in the sub-scan direction at the (m+2) rotation of the drum. In the figure, an area defined by lines Nos.  13  to  24  arrayed in the sub-scan direction is inversion exposed by using the second block (spots Nos.  13  to  24 ), whereby the solid recording is executed. The recording process under progression encounters the gas G. In the exposed part, the image recording sheet and the transfer sheet are in close contact with each other. Accordingly, the gas G cannot stagnate in the exposed part, and this part function to drive the gas G to move upstream as viewed in the main scan direction. The island pattern is configured such that as the recording head moves in the main scan direction, the gas G is driven to move downstream in the sub-scan direction. Accordingly, the gas G moves to the unexposed part located downstream in the sub-scan direction indicated by an arrow. Accordingly, the gas G moves as shown in  FIG. 12 ( c ), and further moves to the unexposed part located upstream in the main stream and downstream in the sub-scan direction, and finally it is discharged from the end of the recording medium to exterior, as shown in  FIG. 12 ( d ).  
      As described above, it is seen from the third embodiment of the invention that a preferable island pattern is configured to be slanted to the downstream side in the sub-scan direction, and to the upstream side in the main scan direction.  
      It is also seen that for the same reason, an array of plural island patterns is preferably directed to the downstream side in the sub-scan direction and to the upstream in the main scan direction.  
      When the island pattern is so configured and the island patterns are arrayed as mentioned above, there is no chance that the gas stagnates between the toner layer  240   c  ( FIG. 3 ) and the image receiving layer  140   c  in the recorded area, the close contact between the toner layer  240   c  and the image receiving layer  140   c  is maintained, and the image defect arising from the spot array is prevented.  
      The exposure method effectively operates when the dot area rate is 70% or higher, particularly for the solid part (where the dot area rate is 100%).  
       FIG. 13  is a block diagram showing a process in which an image signal coming from a computer is processed and an image signal to be applied to the recording head is generated.  
      1) An image signal coming from a computer is input to an image signal input section in the controller section. An image signal from the computer takes a form as shown in  FIG. 14 ( a ).  
      2) The image signal input section takes out an image signal of the m-th rotation of the drum from the image signal coming from the computer, and sends it to a pattern signal processor section.  
      3) The pattern signal processor section computes the image signals of the first to n-th blocks of the m-th rotation of the drum, and sends it to an image signal output section.  
      4) The image signal output section drives the recording head for exposure in accordance with the incoming image signals.  
       FIG. 14 ( b ),  14 ( c ),  14 ( d ), and  14 ( e ) are diagrams showing a process in which the image signal as shown in  FIG. 14 ( a ) is exposed in a thin-out manner and recorded according to the invention.  FIG. 14 ( b ) shows image data of the first block oft the m-th rotation of the drum. As seen, the recording medium is exposed in thin-out patterns, which are slanted to the downstream side in the sub-scan direction and to the upstream side in the main scan direction.  
       FIG. 14 ( c ) shows image data of the first block of the (m+1)th rotation of the drum.  
       FIG. 14 ( d ) shows image data of the second block produced of the (m+1)th rotation of the drum.  
      As seen, those patterns are slanted to the downstream side in the sub-scan direction and to the upstream side in the main scan direction, and are used for exposing the unexposed area which is thinned out in  FIG. 14 ( b ).  
       FIG. 14 ( e ) show an exposed area defined by the lines Nos.  1  to  12  arrayed in the sub-scan direction, which has undergone the exposure operations of FIGS.  14 ( b ),  14 ( c ) and  14 ( d ). As seen, the image signal coming from the computer is clearly recorded without any gas stagnation, in the form of the same image as of the area defined by the lines Nos.  1  to  12  in  FIG. 14 ( a ).  
      In the embodiments mentioned above, the recording medium fixing member of the outer drum type is presented by way of example. It may be of the inner drum type in which the recording medium is fixed to the incurved surface or the inner peripheral surface of a cylinder, and a laser beam is emitted, for recording, from the center of incurved surface or the cylinder. A recording device of the type in which a laser beam is moved in the main scan direction, and the recording medium is transported in the sub-scan direction by means of a transporting mechanism, may also be used instead of the drum. The recording medium fixing member may be of the flat table type in which it is movable in the main scan direction. While the laser light spots one dimensionally arrayed are used in the embodiments, the laser beam spots two dimensionally arrayed may also be used instead.  
      As seen from the foregoing description, in the recording method and recording apparatus of the invention, in the first exposure operation in which the recording head is moved from the original point in the sub-scan direction to a position near the end point of the same, the image/character data is exposed by the “island pattern exposure process”. In the first exposure operation and the subsequent ones, the pixels in the unexposed area other than the area island pattern exposure processed are successively exposed. Accordingly, the thermal energy is dispersed, and the load by the heat of the recording medium is small.  
      Gas generated at a local area of the recording medium is successively moved to the downstream part in the sub-scan direction and the upstream part in the main scan direction, and moved to the non-recorded area, and finally discharged outside the recording medium. As a result, the invention prevents the gas from stagnating between the toner layer and the image receiving layer, and succeeds in eliminating the cause of the image defect.  
      FIGS.  16 ( a ),  16 ( b ),  16 ( c ),  17 ( a ),  17 ( b ), and  17 ( c ) are diagrams showing a first instance of the fifth embodiment in which the exposure process is executed by only one exposure operation. In the first instance, all the spots Nos.  1  to  24  by the recording head shown in  FIG. 5  are divided into two blocks, a first block consisting of the spots Nos.  1  to  12 , and a second block of the spots Nos.  13  to  24 . The recording head is moved from the original point of the sub-scan to a position of the end point thereof, while executing the “thin-out exposure process” by using the first block of spots, and executing the inversion exposure of the pixels remaining unexposed after the execution of the “thin-out exposure process”, by using the second block of spots. In this case, it is preferable that the spots are equally divided into two blocks.  
      (1)  FIG. 16 ( a ) showing an exposure state on the recorded recording medium at the m-th rotation of the drum, an area defined by the lines Nos.  1  to  12  arranged in the sub-scan direction is subjected to the “thin-out exposure process” using the first block (consisting of the spots Nos.  13  to  24 ) to thereby record patterns of “ 1 ” on the recording medium as shown.  
      (2) Subsequently, at the (M+1)th rotation of the drum, the recording medium is exposed to have patterns of “ 2 ” in  FIG. 16 ( b ). Specifically, an area defined by the lines Nos.  13  to  24  on the recording medium are subjected to the “thin-out exposure process” using the first block (spots Nos.  1  to  12 ). The remaining part (unexposed area) of the area defined by the lines Nos.  1  to  12  on the recording medium is subjected to the inversion exposure using the second block (spots Nos.  13  to  24 ), and a solid recording of this area is completed.  
      (3) At the (M+2)-th rotation of the drum, the recording medium is exposed to have patterns of “ 3 ” in  FIG. 16 ( c ). Specifically, an area defined by the lines Nos.  25  to  36 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the “thin-out exposure process” using the first block (spots Nos.  1  to  12 ). An unexposed area of the area defined by the lines Nos.  13  to  24 , which are arrayed in the sub-scan direction; on the recording medium is exposed to have patterns of “ 3 ”, by the second block (spots Nos.  13  to  24 ).  
      (4) At the (M+3)-th rotation of the drum, the recording medium is exposed to have patterns of “ 4 ” in  FIG. 17 ( a ). Specifically, an area defined by the lines Nos.  37  to  48 , which are in the sub-scan direction, on the recording medium are subjected to the “thin-out exposure process” using the first block (spots Nos.  1  to  12 ). An unexposed area of the area defined by the lines Nos.  25  to  36 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the inversion exposure to have patterns of “ 4 ” using the second block (spots Nos.  13  to  24 ), and a solid recording of this area is completed.  
      (5) At the (M+4)-th rotation of the drum, the recording medium is exposed to have patterns of “ 5 ” in  FIG. 17 ( b ). Specifically, an area defined by the lines Nos.  49  to  60 , which are arrayed in the sub-scan direction, on the recording medium are subjected to the “thin-out exposure process” using the first block (spots Nos.  1  to  12 ). An unexposed area of the area defined by the lines Nos.  37  to  48 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the inversion exposure to have patterns of “ 5 ” using the second block (spots Nos.  13  to  24 ), and a solid recording of this area is completed.  
      (6) At the (M+5)-th rotation of the drum, the recording medium is exposed to have patterns of “ 6 ” in  FIG. 7 ( c ). Specifically, an area defined by the lines Nos.  61  to  72 , which are arrayed in the sub-scan direction, on the recording medium are subjected to the “thin-out exposure process” using the first block (spots. Nos.  1  to  12 ). An unexposed area of the area defined by the lines Nos.  49  to  60 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the inversion exposure to have patterns of “ 6 ”, the exposure being carried out using the second block (spots Nos.  13  to  24 ), and a solid recording of this area is completed.  
      Thus, an array of pixels to be thinned out is directed to the downstream side in the sub-scan direction and to the upstream in the main scan direction. Therefore, the laser energy is not concentrated to the sub-scan lines No.  1  to  24  at a dash, but the same lines arrayed in the sub-scan direction are exposed by plural exposure operations. Accordingly, the load by the heat of the recording medium is small.  
      Gas that is generated in the exposure operation by the first block (spots Nos.  1  to  12 ) stagnates in spaces of the thinned-out part of the recording medium. The gas that is generated in the exposure operation by the second block (spots Nos.  13  to  24 ) and gas having been stagnated are both driven to move upstream in the main scan direction and downstream in the sub-scan direction with the progress of the exposure operation. Finally, those gases are discharged from the ends of the recording medium to exterior. As a result, there is no chance that the gas stagnates between the toner layer  240   c  and the image receiving layer  140   c  in the already recorded area, the close contact between the toner layer  240   c  and the image receiving layer  140   c  is maintained, and formation of the image defect based on the spot array is prevented. This will be described later in detail with reference to FIGS.  20 ( a ),  20 ( b ),  20 ( c ),  20 ( d ),  20 ( e ), and  20 ( f ).  
      FIGS.  18 ( a ),  18 ( b ), and  18 ( c ) are diagrams showing a second instance of the fifth embodiment in which the exposure process is executed by only one exposure operation in a manner that all the spots by the recording head are divided into “n” blocks. Specifically, all the spots by the recording head are divided into “n” blocks (preferably, those spots are equally divided). The “thin-out exposure” is carried out by using the fist block of spots. The unexposed area (not the whole) on the recording medium is gradually exposed by using the second to (n−1)-th blocks of spots. Finally, the remaining unexposed area on the recording medium is exposed by using the n-th block of spots.  
      Description will be given about a case where the spots are divided into three blocks of spots.  
      In  FIG. 5, 24  number of laser spots are substantially horizontally arrayed, and a distance between the center of one laser spot to the center of another laser spot adjacent to the former is about 10 μm. Of those spots, the spots Nos.  1  to  8  form a third block, the spots Nos.  9  to  16  form a second block, and the spots Nos.  17  to  24  form a first block, and the exposure process is executed by one exposure operation.  
      (1)  FIG. 18 ( a ) showing an exposure state on the recorded recording medium at the m-th rotation of the drum, an area defined by the lines Nos.  1  to  8  arranged in the sub-scan direction is subjected to the “thin-out exposure process” using the first block (consisting of the spots Nos.  17  to  24 ) to thereby record patters of “ 1 ” on the recording medium, as shown.  
      (2) Subsequently, at the (M+1)-th rotation of the drum, the recording medium is exposed to have patterns of “ 2 ” in  FIG. 18 ( b ). Specifically, an area defined by the lines Nos.  9  to  16  arrayed in the sub-scan direction on the recording medium is subjected to the “thin-out exposure process” using the second block (spots Nos.  9  to  16 ). A half of the remaining part (unexposed area) of the area defined by the lines Nos.  1  to  12  on the recording medium is subjected to the “thin-out exposure process” using the first block (spots Nos.  17  to  24 ).  
      (3) At the (M+2)-th rotation of the drum, the recording medium is exposed to have patterns of “ 3 ” in  FIG. 8 ( c ). Specifically, an area defined by the lines Nos.  17  to  24  arrayed in the sub-scan direction on the recording medium are subjected to the “thin-out exposure process” using the third block (spots Nos.  1  to  8 ). A half of the remaining part (unexposed area) of the area defined by the lines Nos.  9  to  16 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the “thin-out exposure process” using the second block (spots Nos.  9  to  16 ). The remaining part (unexposed area) of the area defined by the lines Nos.  1  to  12  on the recording medium is subjected to the inversion exposure using the first block (spots Nos.  17  to  24 ), and a solid recording of this area is completed.  
      By so doing, gas that is generated in the area defined by the lines Nos.  1  to  8  arrayed in the sub-scan direction during the exposure operation, flows to the area defined by the lines Nos.  9  to  16  arrayed in the sub-scan direction. As a result, there is no chance that the gas stagnates in the area defined by the lines Nos.  1  to  8  arrayed in the sub-scan direction.  
      (4) At the (M+3)-th rotation of the drum, the recording medium is exposed to have patterns of “ 1 ” in  FIG. 19 ( a ). Specifically, an area defined by the lines Nos.  25  to  32 , which are arrayed in the sub-scan direction, on the recording medium are subjected to the “thin-out exposure process” using the third block (spots Nos.  1  to  8 ). A half of the remaining part (unexposed area) of the area defined by the lines Nos.  17  to  24 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the “thin-out exposure process” using the second block (spots Nos.  9  to  16 ). The remaining part (unexposed area) of the area defined by the lines Nos.  9  to  16  on the recording medium is subjected to the inversion exposure using the first block (spots Nos.  17  to  24 ), and a solid recording of this area is completed.  
      By so doing, gas that is generated in the area defined by the lines Nos.  9  to  16 , which are arrayed in the sub-scan direction, during the exposure operation, flows to the area defined by the lines Nos.  17  to  24  in the sub-scan direction. Accordingly, there is no chance that the gas stagnates in the area defined by the lines Nos.  9  to  16  in the sub-scan direction.  
      (5) At the (M+4)-th rotation of the drum, the recording medium is exposed to have patterns of “ 2 ” in  FIG. 19 ( b ). Specifically, an area defined by the lines Nos.  33  to  40 , which are arrayed in the sub-scan direction, on the recording medium are subjected to the “thin-out exposure process” using the third block (spots Nos.  1  to  8 ). A half of the remaining part (unexposed area) of the area defined by the lines Nos.  25  to  32 , which are arrayed in the sub-scan direction, on the recording medium is subjected to the “thin-out exposure process” using the second block (spots Nos.  9  to  16 ). The remaining part (unexposed area) of the area defined by the lines Nos.  17  to  24  on the recording medium is subjected to the inversion exposure using the first block (spots Nos.  17  to  24 ), and a solid recording of this area is completed.  
      By so doing, gas that is generated in the area defined by the lines Nos.  17  to  24 , which are arrayed in the sub-scan direction, during the exposure operation, flows to the area defined by the lines Nos.  25  to  32  in the sub-scan direction. Accordingly, there is no chance that the gas stagnates in the area defined by the lines Nos.  17  to  24  in the sub-scan direction.  
      (6) At the (M+5)-th rotation of the drum, the recording medium is exposed to have patterns of “ 3 ” in  FIG. 19 ©. Specifically, an area defined by the lines Nos.  41  to  48  arrayed in the sub-scan direction on the recording medium is subjected to the “thin-out exposure process” using the third block (spots Nos.  1  to  8 ). A half of the remaining part (unexposed area) of the area defined by the lines Nos.  33  to  40  arrayed in the sub-scan direction on the recording medium is subjected to the “thin-out exposure process” using the second block (spots Nos.  9  to  16 ). The remaining part (unexposed area) of the area defined by the lines Nos.  25  to  32  on the recording medium is subjected to the inversion exposure using the first block (spots Nos.  17  to  24 ), and a solid recording of this area is completed.  
      By so doing, gas that is generated in the area defined by the lines Nos.  25  to  32  in the sub-scan direction during the exposure operation, flows to the area defined by the lines Nos.  33  to  40  in the sub-scan direction. Accordingly, there is no chance for the gas to stagnate in the area defined by the lines Nos.  25  to  32  in the sub-scan direction.  
      FIGS.  20 ( a ),  20 ( b ),  20 ( c ),  20 ( d ),  20 ( e ), and  20 ( f ) are diagrams useful in explaining the direction of the “thin-out exposure process” of the first embodiment, and exemplarily showing a case where the exposure patterns are obliquely recorded. As executed in the first embodiment, a pattern to be recorded is slanted to the downstream side in the sub-scan direction and to the upstream side in the main scan direction. Where the so recorded pattern is employed, the exposure operation is performed while driving the gas generated in the exposure operation to move downstream in the sub-scan direction. Consequently, the recording operation is performed with no gas stagnation and no density lowered part.  
      FIGS.  20 ( a ),  20 ( b ),  20 ( c ),  20 ( d ),  20 ( e ), and  20 ( f ) exemplarily show a case where gas is generated in the two-divided exposure as described referring to FIGS.  16 ( a ),  16 ( b ), and  16 ( c ).  
      (1)  FIG. 20 ( a ) shows an exposure state on the recording medium when the exposure operation at the m-th rotation of the drum is completed and an exposure operation at the (m+1)-th rotation of the drum, is ready to start. An area defined by the lines Nos.  1  to  12  arrayed in the sub-scan direction is subjected to the “thin-out exposure process” using the first block (spots Nos.  13  to  24 ) to thereby record patterns of “ 1 ” on the recording medium, as shown. It is assumed that gas (each denoted as circle) is generated in the recording operation m-th rotation of the drum, and the gas stagnates at three positions in the unexposed part on the recording medium.  
      (2)  FIG. 20 ( b ) shows an exposure state on the recording medium that the recording has reached a position of the 2nd line in the main scan direction at the (M+1)-th rotation of the drum. Of those gases stagnating at the three positions, the gas located most downstream in the main scan direction is driven to move in an arrow direction as the result of the patterns of “ 2 ” arrayed in the sub-scan direction, viz., it is moved to an unexposed part located downstream in the sub-scan direction and upstream in the main scan direction. The reason for this is that the gas cannot flow into the exposed pixel spaces. Of those gases at the three positions, the two gases positioned upstream in the main scan direction are not subjected to the exposure operation in the sub-scan direction, and therefore those two gases still stagnate at the same positions.  
      Also in the second exposure operation, gas is generated sometimes. The gas generated is also driven to move to the unexposed part of the recording medium, although it is not illustrated.  
      (3)  FIG. 20 ( c ) shows an exposure state on the recording medium that the recording has reached a position of the 6th row in the main scan direction at the (M+1)-th rotation of the drum. With the progress of the exposure operation for the patterns of “ 2 ”, the two gases located downstream in the sub-scan direction on the recording medium are driven to move to an unexposed part thereof located downstream in the sub-scan direction and upstream in the main scan direction, and those gases are combined to form a large mass of gas.  
      (4)  FIG. 20 ( d ) shows an exposure state on the recording medium that the recording has reached a position of the 10th row in the main scan direction at the (M+1)-th rotation of the drum. By the exposure operation recording a pattern of “ 2 ”, the mass of gas has driven to move outside an area (defined by the lines Nos.  1  to  12  arrayed in the sub-scan direction) to be exposed at the m-th rotation of the drum.  
      (5)  FIG. 20 ( e ) shows an exposure state on the recording medium that the recording has reached a position of the 14th row in the main scan direction at the (M+1)th rotation of the drum. The mass of gas remains stagnating at the unexposed part of the recording medium. By the exposure operation of recording patterns of “ 2 ” in the sub-scan direction, of the already existing three gases, the gas located most upstream in the main scan direction is driven to move to an unexposed part located downstream in the sub-scan direction and upstream in the main scan direction.  
      (6)  FIG. 20 ( f ) shows an exposure state on the recording medium that the recording has reached a position of the 17th row in the main scan direction at the (M+2)-th rotation of the drum. By the exposure operation of recording patterns of “ 3 ” arrayed in the sub-scan direction, the mass of gas having stagnated in  FIG. 20 ( e ) is driven to move to an unexposed part located downstream in the sub-scan direction and upstream in the main scan direction. In this way, the gases generated in the exposure operation at the m-th rotation of the drum, are driven to move to the ends of the recording medium, and discharged outside from the ends of the recording medium.  
      When the exposure pattern is so configured and the exposure patterns are arrayed as mentioned above, as shown in  FIG. 20 ( f ), there is no chance that the gas stagnates between the toner layer  240   c  and the image receiving layer  140   c  in the recorded area, the close contact between the toner layer  240   c  and the image receiving layer  140   c  is maintained, and formation of the image defect based on the spot array is prevented.  
      The exposure method effectively operates when the dot area rate is 70% or higher, particularly for the solid part (where the dot area rate is 100%).  
      As described above, one of the features of the invention is that an array of unexposed pixels to be thinned out on the recording medium are directed to the downstream side as viewed in the sub-scan direction and the upstream side in the main scan direction. Where those pixels are arrayed in a direction opposite to that of the above-mentioned one, it is impossible to produce such useful effects produced.  
      Next, the “thin-out exposure process” of the invention will be described by taking a called “solid recording” as an example.  
      FIGS.  23 ( a ),  23 ( b ),  23 ( c ),  24 ( a ),  24 ( b ), and  24 ( c ) show a “thin-out exposure process” according to the sixth embodiment of this invention. A first exposure operation is performed in a thin-out manner, by moving the recording head to a position near the end of the sub-scan (FIGS.  23 ( a ),  23 ( b ), and  23 ( c )). Then, the recording head is returned to a position near the original position of the sub-scan, and an exposure operation is performed again, while forming inverted patterns (FIGS.  24 ( a ),  24 ( b ), and  24 ( c )).  
      (1)  FIG. 23 ( a ) shows an exposure state on the recorded recording medium fixed to the drum at the m-th rotation of the drum. In the figure, patterns of “ 1 ”s are exposed pixels recorded at the m-th rotation of the drum, and other white squares are unexposed pixels. Specifically, at the m-th rotation of the drum in the first exposure operation, an area defined by the lines Nos.  1  to  24  arrayed in the sub-scan direction are exposed in a thin-out manner by using the spots Nos.  1  to  24 , to have patterns of “ 1 ” of  FIG. 23 ( a ).  
      As seen from figure, in the operation of exposing and recording the fist line at the m-th rotation of the drum ( FIG. 23 ( a )) in the first exposure operation, the spots Nos.  1  to  24  ( FIG. 5 ), the spots Nos.  24 ,  23 ,  22 ,  18 ,  17 ,  16 ,  12 ,  11 ,  10 ,  6 ,  5 ,  4  are driven to expose the pixels of the lines Nos.  1 ,  2 ,  3 ,  7 ,  8 ,  9 ,  13 ,  14 ,  15 ,  19 ,  20 ,  21  arrayed in the sub-scan direction.  
      In the exposure operation in which at the m-th rotation of the drum, the drum slightly rotates and the 2nd line is positioned under the spots Nos.  1  to  24 , the spots Nos.  23 ,  22 ,  21 ,  17 ,  16 ,  15 ,  11 ,  10 ,  9 ,  5 ,  4 ,  3  of those spots Nos.  1  to  24  are driven to expose the pixels of the lines Nos.  2 ,  3 ,  4 ,  8 ,  9 ,  10 ,  14 ,  15 ,  16 ,  20 ,  21 ,  22  arrayed in the sub-scan direction.  
      Further, in the exposure operation in which at the m-th rotation of the drum, the drum slightly rotates and the 3rd line is positioned under the spots Nos.  1  to  24 , the spots Nos.  22 ,  21 ,  20 ,  16 ,  15 ,  14 ,  10 ,  9 ,  8 ,  4 ,  3 ,  2  of those spots Nos.  1  to  24  are driven to expose the pixels of the lines Nos.  3 ,  4 ,  5 ,  9 ,  10 ,  11 ,  15 ,  16 ,  17 ,  21 ,  22 ,  23  arrayed in the sub-scan direction.  
      Subsequently, as the line number of the lines to be exposed at the same number of rotations of the drum increases, the spots to be driven are successively shifted in the sub-scan direction. With this, an array of pixels to be thinned out is directed to the downstream side in the sub-scan direction and to the upstream side in the main scan direction.  
      In the above description, for ease of explanation, the recording head is not moved in the sub-scan direction during one rotation of the drum. Actually, however, the recording head is also moved in the sub-scan direction during one rotation of the drum. A relationship between the spots Nos.  1  to  24  and the line numbers of the lines arrayed in the sub-scan direction is shifted by an amount of the head movement to the sub-scan direction.  
      (2) Subsequently, at the (m+1)-th rotation of the drum in the first exposure operation, an area defined by the lines Nos.  25  to  48  arrayed in the sub-scan direction is exposed in a thin-out manner by using the spots Nos.  1  to  24 , to have patterns of “ 2 ” of  FIG. 23 ( b ). The thinning-out manner is the same as of “ 1 ” of  FIG. 23 ( a ).  
      (3) Then, at the (m+2)-th rotation of the drum in the first exposure operation, an area defined by the lines Nos.  49  to  72  arrayed in the sub-scan direction are exposed in a thin-out manner by using the spots Nos.  1  to  24 , to have patterns of “ 3 ” of  FIG. 23 ( c ). The thinning-out manner is the same as of “ 1 ” of  FIG. 23 ( a ). Subsequently, the recording head is moved to a position near the end position of the sub-san, while repeating the sequence of exposure operations mentioned above, and the first exposure operation ends.  
      (4) After the first exposure operation (sub-scanning operation by the recording head) ends, the recording head is returned to the original position of the sub-scan, and the recording by the second exposure operation is performed as shown in FIGS.  24 ( a ),  24 ( b ), and  24 ( c ).  
      In ( FIG. 24 ( a ), in the exposure of the 1st line at the m-th rotation of the drum, the spots Nos.  21 ,  20 ,  19 ,  15 ,  14 ,  13 ,  9 ,  8 ,  7 ,  3 ,  2 ,  1  of the spots Nos.  1  to  24  are driven to expose the pixels of the lines Nos.  4 ,  5 ,  6 ,  10 ,  11 ,  12 ,  16 ,  17 ,  18 ,  22 ,  23 ,  24  arrayed in the sub-scan direction, and the remaining part, which was thinned out in the first exposure operation, is exposed to have patterns of “ 6 ” in the figure.  
      (5) At the (m+1)-th rotation of the drum in the second exposure operation, as shown ( FIG. 24 ( b )), an area defined by the lines Nos.  25  to  48  arrayed in the sub-scan direction, i.e., the remaining parts thinned out in the fist exposure operation, are exposed by using the spots Nos.  1  to  24 , to have patterns of “ 7 ” in the figure.  
      (6) At the (m+2)-th rotation of the drum in the second exposure operation ( FIG. 24 ( c )), an area defined by the lines Nos.  49  to  72  arrayed in the sub-scan direction, i.e., the remaining parts thinned out in the fist exposure operation, are exposed by using the spots Nos.  1  to  24 , to have patterns of “ 8 ” in  
      Thus, the laser energy is not concentrated to the sub-scan lines No.  1  to  24  at a dash, but the same lines arrayed in the sub-scan direction are exposed by plural exposure operations. Accordingly, the load by the heat of the recording medium is small.  
      Gas that is generated in the first exposure operation stagnates in the spaces of the thinned-out part of the recording medium. The gas that is generated in the second exposure operation and gas having been stagnated are both driven to move upstream in the main scan direction and downstream in the sub-scan direction with the progress of the exposure operation. Finally, those gases are discharged from the ends of the recording medium to exterior. As a result, there is no chance that the gas stagnates between the toner layer  240   c  and the image receiving layer  140   c  in the already recorded area, the close contact between the toner layer  240   c  and the image receiving layer  140   c  is maintained, and formation of the image defect resulting from the spot array is prevented. This will be described in detail in the description of the second embodiment of the invention.  
      In the first instance of the first embodiment, the description has made about a case where the “thin-out exposure process” is executed by two exposure operations, viz., the “thin-out exposure process” is executed by repeating the exposure operation two times, or the exposure operation for the “thin-out exposure process” is divided into two operations. However, it will readily be understood that the number of divisions of the exposure operation for the “thin-out exposure process” is not limited to 2, but may be 3 or larger.  
      Further, in the description, after the first exposure operation ends, the recording head is returned to a position near the original position in the sub-scan direction. In alternative, the recording head may perform the second exposure operation, while the recording head returns from the end position of the sub-scan direction to near the original position.  
      FIGS.  25 ( a ),  25 ( b ),  25 ( c ),  25 ( d ),  25 ( e ) and  25 ( f ) are diagrams useful in explaining the thinning-out direction in the “thin-out exposure process” of the second embodiment of the invention.  
      In the second embodiment of the invention, the recording apparatus  1  is characterized by that the exposure patterns are obliquely arranged.  
      As executed in the first embodiment, a pattern to record is slanted to the downstream side in the sub-scan direction and to the upstream side in the main scan direction.  
      By so slanting the patterns, the exposure operation is performed while driving the gas generated in the exposure operation to move downstream in the sub-scan direction.  
      Accordingly, the recording operation is performed with no gas stagnation and no density lowered part.  
      This specific example will be described with reference to FIGS.  25 ( a ),  25 ( b ),  25 ( c ),  25 ( d ),  25 ( e ) and  25 ( f ) showing a process in which after the first exposure operation (the sub-scanning operation by the recording head) ends, the recording head returns to a position near the original point of the sub-scan, and the recording by a second exposure operation is performed as shown in  FIG. 24 ( a ).  
       FIG. 25 ( a ) shows a state on the recording medium before the second exposure operation starts. In the figure, gas (each denoted as a circle) that is generated in the recording of patterns of “ 1 ” in first exposure operation, stagnates in the unexposed part on the recording medium.  
      In  FIG. 25 ( b ), the 1st line in the unexposed part is exposed for recording by the second exposure operation. At this time, since the already existing gas (denoted as a circle) cannot flow into the exposed pixel spaces, it is moved in a direction of an arrow, i.e., to an unexposed part. Further, in  FIG. 25 ( c ), a position of the 2nd line in the main scan direction of the unexposed part is exposed by the second exposure operation. At this time, the already existing gas and gas generated in the second exposure operation are also moved to the unexposed part of the recording medium.  
      As the operation of exposing the lines in the unexposed part progresses, as shown in  FIG. 25 ( d ), the already existing gas and gas generated in the second exposure operation are likewise moved to the unexposed part located downstream in the sub-scan direction and upstream in the main scan direction.  
      And, in  FIG. 25 ( e ), the gas having been driven to move to the ends of the recording medium is discharged outside from the ends of the recording medium.  
      When the exposure pattern is so configured and the exposure patterns are arrayed as mentioned above, as shown in  FIG. 25 ( f ), there is no chance that the gas stagnates between the toner layer  240   c  and the image receiving layer  140   c  in the recorded area, the close contact between the toner layer  240   c  and the image receiving layer  140   c  is maintained, and formation of the image defect resulting from the spot array is prevented.  
      The exposure method effectively operates when the dot area rate is 70% or higher, particularly for the solid part (where the dot area rate is 100%).  
       FIG. 26  is a block diagram showing a process in which an image signal coming from a computer is processed and an image signal to be applied to the recording head is generated.  
      1) An image signal coming from a computer is input to an image signal input section in the controller section. An image signal from the computer takes a form as shown in  FIG. 27 ( a ).  
      2) The image signal input section takes out an image signal of the m-th rotation of the drum from the image signal coming from the computer, and sends it to a pattern signal processor part.  
      3) The pattern signal processor part computes the image signals of the m-th rotation of the drum, and sends it to an image signal output section.  
      4) The image signal output section drives the recording head for exposure in accordance with the incoming image signals.  
      FIGS.  27 ( b ) and  27 ( c ) are diagrams showing a process in which the image signal as shown in  FIG. 27 ( a ) is exposed in a thin-out manner and recorded according to the invention.  FIG. 27 ( b ) shows positions (in the area defined by lines Nos.  1  to  24  in the sub-scan direction) on the recording medium to be recorded by the first exposure operation. As seen, the recording medium is exposed in thin-out patterns, which are slanted to the downstream side in the sub-scan direction and to the upstream side in the main scan direction.  
       FIG. 27 ( c ) shows positions (in the area defined by lines Nos.  1  to  24  in the sub-scan direction) on the recording medium to be recorded by the second exposure operation. This is for exposing the thinned-out, unexposed part thinned in  FIG. 27 ( b ), and is a pattern slanted to the downstream side in the sub-scan direction and to the upstream side in the main scan direction.  
      As the result of performing the first and second exposure operations, the energy is dispersed, and the gas is driven to move outside the recording medium, so that the solid recording is performed while being free from the image defect.  
      In the embodiments mentioned above, the recording medium fixing member of the outer drum type is presented by way of example. It may be of the inner drum type in which the recording medium is fixed to the incurved surface or the inner peripheral surface of a cylinder, and a laser beam is emitted, for recording, from the center of incurved surface or the cylinder. A recording device of the type in which a laser beam is moved in the main scan direction, and the recording medium is transported in the sub-scan direction by means of a transporting mechanism, may also be used instead of the drum. The recording medium fixing member may be of the flat table type in which it is movable in the main scan direction. While the laser light spots one dimensionally arrayed are used in the embodiments, the laser beam spots two dimensionally arrayed may also be used instead.  
      As seen from the foregoing description, in an image recording method and apparatus of the invention, in a first exposure operation in which the recording head is moved from the position near the original point of the sub-scan to the position near the end point of the sub-scan, image/character data is exposed in a thin-out manner, and in a second exposure operation and the subsequent ones, the pixels in the thinned-out, unexposed part are successively exposed. Therefore, gas generated at a local part or area of the recording medium is moved to the downstream in the sub-scan direction and the upstream side in the main scan direction, with movement of the recording head. The gas is forced to flow to the unexposed part or area, and finally discharged outside the recording medium. As a result, the gas stagnation between the toner layer and the image receiving layer at the already recorded area or part is prevented.