Abstract:
The present invention relates to a liquid crystal shutter ( 5 ). The liquid crystal shutter ( 5 ) includes a first and a second transparent substrates ( 50 ), ( 51 ) arranged to face each other; a light shielding film ( 52 ) formed on a surface ( 511 ) of the second transparent substrate ( 51 ), which faces the first transparent substrate ( 50 ), for restricting incidence of light travelling from the first transparent substrate ( 50 ) to the second transparent substrate ( 51 ); and transparent electrodes ( 54   b ) laminated over the light shielding film ( 52 ). The transparent electrodes ( 54   b ) are laminated over the light shielding film ( 52 ) via a single insulating layer ( 53   b ). Each of the transparent electrodes ( 54   b ), the light shielding film ( 52 ) and the insulating layer ( 53   b ) is made of an inorganic substance.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a liquid crystal shutter, and a printhead provided with a liquid crystal shutter. 
   2. Description of the Related Art 
   An electronic image captured by a digital camera, for example, can be printed on an ordinary paper based on the digital data by inkjet or thermal transfer. It is also conceivable to print an image as digital data on a photosensitive film by a photosensitive system. In the photosensitive system, an image is formed on a photosensitive film by exposing the photosensitive film to light followed by developing the film using a photo printhead. A typical photo printhead is provided with a liquid crystal shutter for selectively passing or blocking light travelling from an illuminator, for example (See JP-A-2000-280527, for example). 
     FIGS. 7 and 8  show an example of liquid crystal shutter. The liquid crystal shutter  9  shown in the figures includes a plurality of individual shutter portions  90 R,  90 G,  90 B aligned in the primary scanning direction (the direction indicated by arrows A 1 , A 2  in the figure). The liquid crystal shutter  9  includes a first and a second transparent substrates  91   a  and  91   b  arranged to face each other. Between the first and the second transparent substrate  91   a  and  91   b , a rib spacer  97 A is provided to locate at the periphery of the substrates. The rib spacer  97 A, along with the first and the second transparent substrates  91   a  and  91   b , defines a cell  96  for loading liquid crystal  90 . The rib spacer  97   a  defines the height of the cell  96 , i.e., the cell gap. In addition to the liquid crystal  90 , spherical spacers  97   b  are filled in the cell  96 . The spherical spacers  97   b  serve to stabilize the cell gap defined by the rib spacer  97   a.    
   The first transparent substrate  91   a  has a surface facing the second transparent substrate  91   b  and formed with a first transparent electrode  93   a  via an SiO 2  film  92   a . The SiO 2  film  92   a  serves to enhance the adhesion of the first transparent electrode  93   a  to the first transparent substrate  91   a . The first transparent electrode  93   a  is formed into an intended pattern by forming an ITO film and then etching the ITO film, for example. 
   The second transparent substrate  91   b  has a surface facing the first transparent substrate  91   a  and formed with a metal light-shielding film  94  having an opening  94   a . The metal light-shielding film  94  allows light to pass selectively at the opening  94   a . In the opening  94   a  are arranged color filters  98 R,  98 G and  98 B for selectively passing red light, green light and blue light, respectively. The second transparent substrate  91   b  is further formed with a smoothing film  95  covering the color filters  98 R,  98 G and  98 B, an SiO 2  film  92   b  and a second transparent electrode  93   b.    
   The smoothing film  95  serves to compensate for a step formed by the provision of the color filters  98 R,  98 G,  98 B for providing a smooth surface. The SiO 2  film  92   b  serves to enhance the adhesion of the second transparent electrode  93   b  to the smoothing film  95 . The second transparent electrode  93   b  partially overlaps the first transparent electrode  93   a , and the overlapping portions constitute individual shutter portions  90 R,  90 B and  90 B. Similarly to the first transparent electrode  93   a , the second transparent electrodes  93   b  is formed into an intended pattern by forming an ITO film and then etching the ITO film, for example. 
   The second transparent substrate  91   b  is made larger in dimension than the first transparent substrate  92   a . The second transparent electrode  93   b  extends over the second transparent substrate  92   b  up to a portion projecting outward relative to the first transparent substrate  92   a . On the second transparent substrate  91   b , a drive IC  99   a  is mounted for electrical connection to the second transparent electrode  92   b . The drive IC  99   a  is connected to a flexible cable  99   b  via a signal electrode  99   c.    
   The liquid crystal shutter  9  has the following disadvantages due to the provision of the smoothing film  95  for covering the color filters  98 R,  98 G,  98 B. 
   The smoothing film  95  is generally made of transparent resin and relatively soft. Therefore, spherical spacers  97   b  dispersed in the liquid crystal  90  may sink into the smoothing film  95  through the second transparent electrode  93   b  and the SiO 2  film  92   b . Such a phenomenon may occur at some locations in the cell  96 , and the cell gap reduces at the locations where the spherical spacers  97   b  have sunk. Therefore, even when the same voltage is applied, the resulting electric field strength varies between a portion where the intended cell gap is maintained and a portion where the cell gap is reduced. As a result, the transmittance varies among the individual shutter portions  90 R,  90 G,  90 B. The spherical spacers  97   b  are not dispersed evenly in the liquid crystal  90 , and such unevenness of dispersion increases the variation of transmittance. 
   To achieve high-speed printing, the cell gap need be made relatively small for the purpose of driving the liquid crystal shutter  9  at high speed. However, when the cell gap is small, the influence of the unevenness of the cell gap due to the sinking of the spherical spacers  97   b  in the smoothing film  95  becomes relatively large. Therefore, in the liquid crystal shutter  9  having a relatively small cell gap, the variation of transmittance is large. In this point, the provision of the smoothing film  95  hinders the achievement of high speed printing. 
   Although the adhesion of the second transparent electrode  93   b  to the smoothing film  95  is enhanced by the SiO 2  film  92   b , the adhesion between the SiO 2  film  92   b  and the smoothing film  95  is insufficient. Therefore, overetching is likely to occur in the etching process for forming the second transparent electrode  93   b , so that the second transparent electrode  93   b  may become smaller than the intended pattern. In this case, the size of the individual shutter portions  90 R,  90 G,  90 B differs between a portion where overetching has occurred and a portion where overetching has not occurred. At the individual shutter portion  90 R,  90 G,  90 B corresponding to the portion where overetching has occurred, the numerical aperture becomes smaller, whereby the transmission efficiency at the shutter portion is reduced. 
   To reliably eliminate the step caused by the color filters  98 R,  98 G,  98 B, the smoothing film  95  needs to have a relatively large thickness. In this case, a large amount of light is absorbed by the smoothing film  95 , which further deteriorates the transmission efficiency. 
   To compensate for the deterioration of the transmission efficiency and to reliably irradiate the photosensitive film with a sufficient amount of light, the amount of light to be emitted from the illuminator need be increased, or the irradiation time for the photosensitive film need be increased. However, such measures are disadvantageous in terms of the running cost, and the increase of the irradiation time leads to the increase of the printing time. 
   Moreover, since the adhesion between the SiO 2  film  92   b  and the smoothing film  95  is insufficient, when a stress is exerted on the interface between these films, the second transparent electrode  93   b  or the signal electrode  99   c  may be removed from the smoothing film  95  together with the SiO 2  film  92   b . Therefore, the mounting reliability of the drive IC  99   a  and the flexible cable  99   b  is deteriorated. In some cases, the mount surface of the second transparent electrode  93   b  or the signal electrode  99   c  may be physically rubbed for cleaning before mounting the drive IC  99   a  or the flexible cable  99   b , or the drive IC  99   a  or the flexible cable  99   b  may be once removed for remounting. At that time, the second transparent electrode  93   b  or the signal electrode  99   c  may be removed, which hinders the mounting of the drive IC  99   a  or the flexible cable  99   b.    
   To solve the above problem, the smoothing film  95  should not be provided between the second transparent substrate  91   b  and the SiO 2  film  92   b  at portions where the drive IC  99   a  and the flexible cable  99   b  are to be mounted. For this purpose, however, a patterning process to select the portions to form the smoothing film  95  need be added to the smoothing film formation step, which deteriorates the manufacturing efficiency and is disadvantageous in terms of the manufacturing cost. 
   DISCLOSURE OF THE INVENTION 
   An object of the present invention is to provide a liquid crystal shutter which is used for e.g. a printhead for irradiating a photosensitive recording medium with light and is capable of preventing the amount of light emission from varying among shutter portions and reducing the manufacturing cost and the running cost without hindering the achievement of high speed printing. 
   According to a first aspect of the present invention, there is provided a liquid crystal shutter comprising: a first and a second transparent substrates arranged to face each other; a light shielding film formed on a surface of the second transparent substrate facing the first transparent substrate for restricting incidence of light travelling from the first transparent substrate to the second transparent substrate; and a transparent electrode laminated over the light shielding film via a single insulating layer. 
   According to a second aspect of the present invention, there is provided a liquid crystal shutter comprising: a first and a second transparent substrates arranged to face each other; a light shielding film formed on a surface of the second transparent substrate facing the first transparent substrate for restricting incidence of light travelling from the first transparent substrate to the second transparent substrate; and a transparent electrode laminated over the light shielding film via a single insulating layer. Each of the transparent electrode, the light shielding film and the insulating layer is made of an inorganic substance. 
   The insulating layer may be made of an inorganic oxide, for example. As the inorganic oxide, it is preferable to use SiO 2  or Ta 2 O 5 . 
   The insulating layer may have a thickness of no more than 2000 Å or preferably in the range of 1000 to 2000 Å, for example. 
   The method for forming the insulating layer is not limitative, and any method can be employed as long as it can suppress the thickness of the insulating layer to no more than 2000 Å. However, it is preferable to employ dip coating, bias sputtering or plasma CVD. 
   For instance, the light shielding film is made of a metal. As the metal, use may be made of chromium, molybdenum, tungsten, nickel, germanium, gold or aluminum. Preferably, the obverse surface of the light shielding film is made of a highly light absorbent material such as chromium oxide, for example. 
   The light shielding film may be formed with an opening for selectively allowing incidence of light passing through the first transparent substrate onto the second transparent substrate. Preferably, the opening has a tapered edge. Examples of technique for tapering the edge of the opening include liftoff and taper etching. 
   The light shielding film may have a thickness of no more than 3000 Å or preferably in the range of 2000 to 3000 Å, for example. Since the light shielding film is formed as a thin film having a thickness of no more than 3000 Å, the formation of the opening in the light shielding film does not cause the formation of a large step between the periphery of the opening and the surrounding portion. Moreover, since the edge of the opening is tapered, good step coverage can be obtained by covering the light shielding film by the insulating layer. 
   According to a third aspect of the present invention, there is provided a printhead provided with a liquid crystal shutter. The liquid crystal shutter comprises: a first and a second transparent substrates arranged to face each other; a light shielding film formed on a surface of the second transparent substrate facing the first transparent substrate for restricting incidence of light travelling from the first transparent substrate to the second transparent substrate; and a transparent electrode laminated over the light shielding film via a single insulating layer. 
   According to a fourth aspect of the present invention, there is provided a printhead provided with a liquid crystal shutter. The liquid crystal shutter comprises: a first and a second transparent substrates arranged to face each other; a light shielding film formed on a surface of the second transparent substrate facing the first transparent substrate for restricting incidence of light travelling from the first transparent substrate to the second transparent substrate; and a transparent electrode laminated over the light shielding film via an insulating layer. Each of the transparent electrode, the light shielding film and the insulating layer are made of an inorganic substance. 
   Preferably, the printhead according to the present invention further comprises an illuminator capable of individually emitting red light, green light and blue light. With this structure, a liquid crystal shutter which does not include a color filter can be used. As a result, a smoothing film for reducing the step formed by the provision of a color filter need not be formed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view showing an example of printhead according to the present invention. 
       FIG. 2  is a sectional view of the printhead shown in  FIG. 1 . 
       FIG. 3  is an exploded perspective view of an illuminator used in the printhead shown in  FIG. 1 . 
       FIG. 4  is a sectional view of a liquid crystal shutter according to the present invention. 
       FIG. 5  is a partial sectional view for describing the structure of the light shielding film of the liquid crystal shutter. 
       FIG. 6  is a plan view showing a principal portion of the liquid crystal shutter. 
       FIG. 7  is a sectional view showing a prior art liquid crystal shutter. 
       FIG. 8  is a plan view showing a principal portion of the prior art liquid crystal shutter. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A printhead X shown in  FIGS. 1 and 2  includes a frame  1  comprising a first through a fourth holder portions  10 – 13 , and a rod lens array  2 , a prism  3 , an illuminator  4  and a liquid crystal shutter  5  which are held by the frame. 
   The first holder portion  10  of the frame  1  serves to hold the illuminator  4  along with the liquid crystal shutter  5  and has a channel-like mount surface  10   a . The liquid crystal shutter  5  is mounted on the mount surface  10   a  in close contact therewith. 
   The second holder portion  11  of the frame  1  serves to hold a reflector  15  and has an inclined surface  14  inclined relative to the direction indicated by arrows B 1 , B 2  (horizontal direction) by 45 degrees. The inclined surface  14  is elongated in the direction indicated by arrows A 1 , A 2  (primary scanning direction). 
   The reflector  15 , which is in the form of a plate, serves to bend the light emitted from the liquid crystal shutter  5  by 90 degrees toward the direction indicated by the arrow B 1  (secondary scanning direction) in the figure. Preferably, the obverse surface of the reflector  15  is a mirror surface made of e.g. aluminum for regularly reflecting light. 
   The third holder portion  12  of the frame  1  serves to hold the rod lens array  2 . 
   The rod lens array  2  serves to efficiently collect the light reflected at the reflector  15  for emitting the light toward the prism  3 . The rod lens array  2  comprises a holder  22  formed with a plurality of through-holes  21  and rod lenses  23  each held in a respective through-hole  21 . The rod lenses  23  are arranged in a row extending in the primary scanning direction A 1 , A 2 , with the axis of each rod lens  23  extending in the direction indicated by the arrows B 1 , B 2  (secondary scanning direction) in the figure. In this embodiment, the rod lenses  13  form an actual size erect image. 
   The fourth holder portion  13  of the frame  1  serves to hold the prism  3  and is open toward the B 1  direction in the figure. 
   The prism  3  serves to bend the light emitted from the rod lens array  2  by 90 degrees toward the direction indicated by the arrow C 2 , causing the light to be emitted from the printhead X in the C 2  direction. The prism  3  includes a light incident surface  31 , a light reflecting surface  32  and a light emitting surface  33 . Thus, the light from the reflector  15  enters the prism  3  through the light incident surface  31  and is then reflected at the light reflecting surface  32  to change its traveling direction by 90 degrees. Thereafter, the light is emitted through the light emitting surface  33 . The prism  3  is made of a material having a refractive index higher than that of air, such as transparent glass or acrylic resin. 
   The illuminator  4  serves to emit linear light in the direction indicated by the arrow C 1 , C 2  in the figure and is held in close contact with the liquid crystal shutter  5 . As clearly shown in  FIGS. 2 and 3 , the illuminator  4  includes a light guide  42  and a light source device  43  which are arranged in a space defined by a first and a second light shields  40 ,  41 . In the illuminator  4 , the light emitted from the light source device  43  passes through the light guide  42  and is then emitted outside through an opening  401  formed in the first light shield  40 . 
   The light source device  43  includes three point light sources  43 R,  43 G and  43 B which are mounted on an insulating substrate  45  and which can be turned on and off individually. The point light sources  43 R,  43 G and  43 B comprise LED chips. The point light source  43 R emits red light, the point light source  43 G emits green light and the point light source  43 B emits blue light. Each of the point light sources  43 R,  43 G and  43 B has an upper surface and a lower surface respectively formed with electrodes (not shown). The upper electrode is a transparent electrode made of ITO, for example. 
   The insulating substrate  45  is formed with individual wirings  44 R,  44 G and  44 B, and a common wiring  44 C. The lower electrodes of the point light sources  43 R,  43 G and  43 B are electrically connected to the individual wirings  44 R,  44 G and  44 B. The upper electrodes of the point light sources  43 R,  43 G and  43 B are connected to the common wiring  44 C via conductor wires, for example. With such a circuit structure, the point light sources  43 R,  43 G and  43 B can be driven individually. 
   The light guide  42  serves to cause the light emitted from the light source device  43  and entered the light guide through an end surface thereof to be emitted as linear light corresponding to the configuration of the opening  401  formed in the first light shield  40 . 
   As clearly shown in  FIG. 4 , the liquid crystal shutter  5 , which serves to select the passing or blocking of the light emitted from the illuminator  4 , includes a first and a second transparent substrates  50  and  51  arranged to face each other. 
   The first transparent substrate  50  has a facing surface  501  which faces the second transparent substrate  51  and which is formed with an insulating layer  53   a . The insulating layer  53   a  is light permeable and may be made of SiO 2  or Ta 2 O 5  by dip coating, bias sputtering or plasma CVD, for example. The facing surface  501  of the first transparent substrate  50  is further formed with a common electrode  54   a . The common electrode  54   a  is formed as a transparent electrode in the form of a strip extending in the direction indicated by the arrows A 1 , A 2 . The common electrode  54   a  may be made by subjecting an ITO film to etching. 
   The second transparent substrate  51  is larger in dimension than the first transparent substrate and includes an extension  510  extending outward relative to the first transparent substrate  50  in the direction indicated by the arrow B 1 . The second transparent substrate  51  has a region  511  oriented toward the first transparent substrate  50  and formed with a light shielding film  52 . 
   The light shielding film  52  is a thin film having a thickness of no more than 3000 Å or preferably in the range of 2000 to 3000 Å, for example. As shown in  FIGS. 4 through 6 , the light shielding film  52  is formed with an opening  524  extending in the direction indicated by the arrows A 1 , A 2 . The opening  524  is formed at a location corresponding to the opening  401  of the first light shield  40  of the illuminator  4 . The opening  524  of the light shielding film  52  has tapered edges  525 . The edges  525  may be formed by techniques such as liftoff or taper etching, for example. The light shielding film  52  has a three-layer structure consisting of a chromium oxide layer  521 , a chromium layer  522 , and a chromium oxide layer  523  stacked in the mentioned order on the region  511  of the second transparent substrate  51 , for example. Each of the layers  521 ,  522  and  523  may be formed by techniques such as vapor deposition or sputtering, for example. 
   The light shielding film  52  may be made of a metal other than chromium and chromium oxide. Examples of usable metal include molybdenum, tungsten, nickel, germanium, gold and aluminum. Instead of the above metal, the light shielding film  52  may be made of an inorganic substance having a light shielding property. 
   On the light shielding film  52  is formed an insulating layer  53   b . The insulating layer  53   b  is a light permeable thin film made of an inorganic oxide such as SiO 2  or Ta 2 O 5  and having a thickness of no more than 2000 Å or preferably in the range of 1000 to 2000 Å, for example. The light shielding film  52  may be made by dip coating, bias sputtering or plasma CVD, for example. 
   As noted above, the light shielding film  52  is a thin film having a thickness of no more than 3000 Å, and the edges  525  of the opening  524  are tapered. Therefore, although the opening  524  is provided in the light shielding film  52 , a large step is not formed between the opening  524  and the peripheral portion even when the thickness of the insulating layer  53   b  is small. Therefore, good step coverage by the insulating layer  53   b  relative to the light shielding film  52  can be obtained even when the film thickness of the insulating layer  53   b  is set to the above-described range. 
   On the insulating layer  53   b , a plurality of segment electrodes  54   b  as transparent electrodes are formed. The segment electrodes  54   b  are spaced in the direction indicated by the arrows A 1 , A 2 . The segment electrodes  54   b  may be formed by subjecting an ITO film to etching, for example. As shown in  FIG. 6 , each of the segment electrodes  54   b  has a portion which overlaps the common electrode  54   a . The portions where the common electrode  54   a  and the segment electrode  54   b  overlap each other constitute individual shutter portions  55 . The individual shutter portions  55  are located directly below the opening  401  of the first light shield  40  and arranged in a row extending in the direction indicated by the arrows A 1 , A 2 . 
   In the liquid crystal shutter  5 , good step coverage can be achieved, with the thickness of the insulating layer  53   b  set to no more than 2000 Å. Therefore, in the liquid crystal shutter  5 , the absorption of light by the insulating layer  53   b  can be suppressed, whereby the deterioration of light transmittance can be prevented. 
   Further, since the segment electrodes  54   b , the insulating layer  53   b  and the light shielding film  52  are made of an inorganic substance, a higher adhesion is provided between the segment electrodes  54   b  and the light shielding film  52  than when a smoothing film made of a resin is used as is in the prior art liquid crystal shutter (See  FIGS. 7 and 8 ). Therefore, the segment electrodes  54   b  are unlikely to be removed from the light shielding film  52 , whereby overetching in the etching process for forming the segment electrodes  54   b  can be prevented. Therefore, the shutter portions  55  can be made generally equal in size, so that variation of light transmittance and the decrease of the numerical aperture due to variation of the size of the individual shutter portions  55  can be prevented. As a result, it is possible to suppress the deterioration of transmission efficiency at each shutter portion  55  and the variation of transmittance among the shutter portions  55 . 
   Moreover, unlike the prior art liquid crystal shutter (See  FIGS. 7 and 8 ), the liquid crystal shutter  5  does not include a smoothing film, so that the absorption of light by a smoothing film does not occur. This also contributes to the enhancement of transmission efficiency in the liquid crystal shutter  5 , and hence to the reduction of power consumption of the liquid crystal shutter  5  (printhead X). As a result, in the liquid crystal shutter  5  (printhead X), the running cost can be decreased, or the irradiation time by the illuminator  4  can be shortened, which enables the achievement of high speed printing. 
   Between the first and the second transparent substrates  50  and  51 , a rib spacer  56 A is provided to locate at the periphery of the substrates. The rib spacer  56 A, along with the first and the second transparent substrates  50 ,  51 , defines a cell  57 . Specifically, the rib spacer  56 A defines the height of the cell (cell gap). Liquid crystal  58  and spherical spacers  56 B are filled in the cell  57 . As the liquid crystal  58 , use may be made of ferroelectric liquid crystal, antiferroelectric liquid crystal or nematic crystal. When nematic crystal is used as the liquid crystal, an alignment layer is provided to cover the common electrode  54   a  and the segment electrodes  43   b.    
   As shown in  FIG. 2 , the first transparent substrate  50  and the second transparent substrates  51  have respective non-facing surfaces  502  and  512  provided with polarizers  503  and  513 . The polarizers  503  and  513  are so arranged that respective polarization axes extend perpendicularly to each other. For example, therefore, the light passing through the polarizer  503  and through the liquid crystal  58  changes its polarization direction by 90 degrees at a shutter portion  55  to which a voltage no less than a threshold is applied, so that the light can pass through the polarizer  513 . On the other hand, the polarization direction of the light does not change at a shutter portion  55  to which small (or no) voltage is applied, so that the light cannot pass through the polarizer  513 . Thus, the selection of light passing or light blocking can be performed with respect to each of the individual shutter portions  55  by controlling the voltage application to the individual shutter portions  55 . 
   As shown in  FIG. 4 , a drive IC  59  is mounted on the extension  510  of the second transparent substrate  51 . The drive IC  59  is electrically connected to the segment electrodes  54   b . The drive IC  59  is also connected to a flexible cable  591  formed with a signal electrode  592 . Thus, power supply or transmission of various signals to the drive IC  59  is performed through the flexible cable  591  (signal electrode  592 ), and the state of voltage application can be selected with respect to each of the individual shutter portions  55 . 
   As noted above, in the liquid crystal shutter  5 , a smoothing film made of a resin is not interposed between the light shielding film  52  and the insulating layer  53   b , and the light shielding film  52 , the insulating layer  53   b  and the segment electrodes  54   b  are made of an inorganic substance. Therefore, a high adhesion can be provided between the light shielding film  52  and the segment electrodes  54   b  or the signal electrode  592 . As a result, the drive IC  59  and the flexible cable  591  can be reliably mounted on the second transparent substrate  51 . The mount surface of the segment electrode  54   b  or the signal electrode  592  may be physically rubbed for cleaning before mounting the drive IC  59  or the flexible cable  591 , or the drive IC  59  or the flexible cable  591  may be once removed for remounting. Even in such cases, the segment electrode  54   b  and the signal electrode  592  can be prevented from being removed. Therefore, the drive IC  59  and the flexible cable  591  are not wasted, which enhances the yield. 
   Since the liquid crystal shutter  5  does not include a smoothing film, the process for forming a smoothing film is not necessary in manufacturing the liquid crystal shutter. Specifically, the process for selectively forming a smoothing film at intended portions, which is conventionally necessary for reliable mounting of the drive IC  59  and the flexible cable  591 , is not necessary. Therefore, the liquid crystal shutter  5  having improved mounting reliability can be made with high production efficiency. 
   The above-described printhead X may be used for exposing a photosensitive film to form an image on the photosensitive film. In such a case, the point light emitted from the light source device  43  of the illuminator  4  is converted into linear light at the light guide  42  and then travels through the opening  401  of the first light shield  40  before entering the liquid crystal shutter  5 . In the liquid crystal shutter  5 , under the control by the drive IC  59 , light transmitting or light blocking at each of the individual shutter portions  55  (See  FIG. 6 ) is selected based on the image data. The light passing through the individual shutter portion  55  is regularly reflected by the reflector  15 , thereby changing its traveling direction by 90 degrees before entering the rod lens array  2 . The light entering the rod lens array  21  pass through each rod lens  23  and then enters the prism  3  through the light incident surface  31 . The light entering the prism  3  changes its traveling direction by 90 degrees at the light reflecting surface  32  and travels downward in the prism  3  before exiting through the light emitting surface  33 . The light is converged onto e.g. a photosensitive film to irradiate the photosensitive film along a line. 
   As noted above, the printhead X is provided with the illuminator  4  capable of individually emitting red light, green light and blue light. Therefore, the liquid crystal shutter  5  does not require a conventionally used color filter. Accordingly, a smoothing film for reducing the step caused by the provision of a color filter need not be positively formed, and the elimination of a smoothing film causes no problems. The elimination of a smoothing film makes it possible to avoid such a problem that the spherical spacers  56 B sink into the smoothing film at some locations in the cell  57 . As a result, variation of the cell gap among locations in the cell  57  can be prevented. Since such variation of the cell gap is prevented, variation of the electric field strength among individual shutter portions  55  can be prevented when the same voltage is applied to each of the shutter portions  55 . As a result, variation of the light transmittance among the shutter portions  55  can be prevented. Moreover, since variation of the cell gap is prevented, variation of the light transmittance can be prevented even when the cell gap is made small for the purpose of driving the liquid crystal shutter  5  at high speed. Therefore, high-speed printing capable of obtaining a high-quality image can be realized. 
   In the present invention, the insulating layer  53   b  may be made of an inorganic oxide to have a relatively high rigidity. In such a case, the spherical spacers  56 B can be prevented from sinking into the insulating layer  53   b  at some locations in the cell  57 . This also prevents variation of the cell gap and hence the variation of the light transmittance, thereby enabling high-speed printing. 
   The printhead X can be used for black-and-white printing by changing the structure of the light source device  43 . 
   The present invention is not limited to the foregoing embodiment, and the liquid crystal shutter  5  can be used for purposes other than a printhead.