JP2008194897A - Light emitting apparatus and printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting apparatus capable of decreasing an thermal influence generated mutually between respective light emitting elements by increasing the heat capacity of the light emitting element, and stably feeding the amount of light. <P>SOLUTION: The light emitting apparatus equipped with a plurality of light emitting elements 20 arranged in an array shape at specified intervals on a light emitting element substrate 21, is equipped with a rod lens part 2B projecting a light injected from the light emitting elements 20 as an upright equal-fold image. An intermediate liquid fills a closed space 73 being a region between the light emitting element substrate 21 and the rod lens part 2B. The light emitting elements 20 are arranged zigzag in a plurality of lines in relation to a specified direction on the light emitting element substrate 21. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting device and a printing device that use a light emitting element as a light source.

  2. Description of the Related Art Conventionally, light emitting devices that use light emitting elements as light sources are known, and are used, for example, as exposure devices in printing apparatuses. By the way, in a light emitting device using a light emitting element as a light source, an attempt is made to cool the light emitting element. For example, Patent Document 1 discloses a technique for efficiently cooling a light emitting element using a Peltier element.

That is, according to the technique disclosed in Patent Document 1, the heat generated in the light emitting element is directly absorbed by the heat absorption side electrode that is a Peltier element. Further, by bringing the heat generation side electrode in the Peltier element into contact with the substrate, the heat transferred to the heat generation side electrode is smoothly radiated through the substrate.
JP 2006-147826 A

  In a light emitting device applied to a printing apparatus, a plurality of light emitting elements are generally arranged in a line, but there is a tendency that heat radiation becomes difficult as the distance between the plurality of pixels becomes shorter.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light emitting device and a printing device that efficiently cool a light emitting element.

In order to achieve the above object, a light emitting device according to a first aspect of the present invention is a light emitting device having a plurality of light emitting elements that emit light at a predetermined position of a photosensitive drum.
The light emitting elements are arranged in a staggered manner in a plurality of rows in a predetermined direction.

  The light emitting device according to claim 1, wherein the light emitting element disposed on the substrate is sealed by a counter substrate, and a Peltier element may be provided on the counter substrate.

  The light emitting device according to claim 1, further comprising lens means for projecting light emitted from the light emitting element as an erecting equal-magnification image.

  The printing apparatus of the present invention includes the light emitting device according to any one of claims 1 to 3.

  According to the present invention, there is provided a light emitting device capable of increasing the heat capacity of a light emitting element as a light emitter to reduce the mutual thermal effect between the respective light emitting elements and stably supplying a light amount. Can do.

  Hereinafter, a light-emitting device and a printing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of a configuration of a printing apparatus using a light emitting device according to the present embodiment. First, as shown in FIG. 1, a printing apparatus using the light emitting device according to the present embodiment includes a photosensitive drum 1, a light emitting device 2 including a case portion 2A and a rod lens portion 2B, a charging roller 3, and the like. , An eraser light source photoreceptor 4, a cleaning member 5, a developing device 6 including a developing roller 6 a, a transfer roller 8, a fixing roller 9, and a conveyor belt 11. Note that reference numeral 7 denotes printing paper. The rod lens unit 2B is a lens array in which SELFOC (registered trademark) lenses are arranged in one or a plurality of columns, and is a lens unit that forms incident light on the photosensitive drum 1 as an equal-magnification erect image. .

  The photoreceptor drum 1 is a negatively charged OPC (Organic Photo Conductor) photoreceptor (organic photoreceptor). In view of this, the charging roller 3 is a negative charger. The developing device 6 is a developing device for developing with negatively charged toner. The case portion 2A of the light emitting device 2 includes a plurality of organic EL elements (light emitting elements) 20 arranged in an array, as will be described in detail later.

  By the way, in the printing apparatus shown in FIG. 1, printing is roughly performed by the following processes. First, when the charging roller 3 comes into contact with the surface of the rotating photosensitive drum 1, the contacted surface of the photosensitive drum 1 is uniformly charged with a negative potential. Subsequently, light emitted from the light emitting element 20 of the light emitting device 2 is incident on a predetermined position of the photosensitive drum 1 via the rod lens portion 2B, and an electrostatic latent image is formed on the photosensitive drum 1. Is formed. Thereafter, the developer 6 attaches toner to the electrostatic latent image. Then, the toner attached to the electrostatic latent image is transferred to the printing paper 7 by the transfer roller 8. Hereinafter, such a printing process will be described in detail.

  First, the photosensitive drum 1 is initialized to a negative potential supplied from a charging power source (not shown) and relatively close to or equal to a developing voltage output from a developing device 6 described later. A charging voltage is applied by the charging roller 3. As a result, the peripheral surface of the photosensitive drum 1 is uniformly negatively charged and is initialized in terms of potential (becomes an initialized charging state).

  Then, the light emitting device 2 performs optical writing (exposure) according to the printing information on the photosensitive drum 1 whose peripheral surface has been initialized. As a result, the initialization charging portion that remains in the initialization charged state because no exposure is performed, and the exposure charging voltage of about −50 (V) that is a negative potential relatively higher than the initialization charging portion by the exposure. Is formed on the peripheral surface of the photosensitive drum 1.

  Here, the toner charged in the developing unit 6 and charged to a weak negative potential is rotated and conveyed by the developing roller 6a to the opposing portion between the developing roller 6a and the photosensitive drum 1. At this time, the developing roller 6a is applied with a developing voltage of about −250 (V), which is lower than the exposure charging unit, from a power source (not shown). Therefore, the exposure charging portion of about −50 (V) of the electrostatic latent image on the photosensitive drum 1 is about 200 (V) higher than the development voltage, and the initialization charging portion is different from the development voltage. Is a voltage whose absolute value is sufficiently smaller than 200 (V).

  Due to the difference in potential difference from the development voltage in these electrostatic latent images, the exposure charging portion in the electrostatic latent image having a positive polarity relative to the developing roller 6a is charged to a negative polarity. On the other hand, the toner image does not adhere to the initialization charging portion because an electric field that attracts the toner electrostatically does not occur in the initialization charging portion.

The toner image is conveyed to a transfer portion where the photosensitive drum 1 and the transfer roller 8 face each other by the rotation of the photosensitive drum 1.

  The toner adhesion amount (developed image density) in the toner image formed as described above is generated according to the exposure amount of the photosensitive drum 1 by the light emitting device 2. It is determined by the amount of potential attenuation on the circumferential surface.

  By the way, as described above, when the toner image is transported to the transfer unit, the printing paper 7 is transported to the transfer unit by the transport belt 11. In the transfer unit, the toner image is transferred onto the printing paper 7 by the transfer roller 8. The printing paper 7 to which the toner image is transferred in this way is further conveyed downstream, and after the toner image is thermally fixed by the fixing roller 9, the printing paper 7 is discharged to the outside of the printing apparatus. The

  In the case portion 2A of the light emitting device 2, the main scanning direction of exposure scanning onto the photosensitive drum 1 shown in FIG. 1 (the width direction of the photosensitive drum 1, that is, the width direction of the printing paper 7). ), An organic EL array comprising a large number of light emitting elements 20 is arranged in a line. If the printing apparatus is a printing apparatus capable of printing at a printing density of 1200 dpi (dots / inch) to the full width using, for example, A4 size printing paper in the vertical direction, this organic EL array is approximately 14,000 pieces. The light emitting element is provided. A signal in accordance with print information output from a host device (not shown) is applied to these individual light emitting elements. That is, the light emission of each light emitting element is selectively controlled.

  Hereinafter, the basic structure of the organic EL element which is a light emitting element will be described with reference to FIG.

  The light emitting element 20 is formed on a light emitting element substrate 21 such as glass as shown in FIG. 2, and is sandwiched between opposing substrates 28 such as glass. The periphery of the light emitting element substrate 21 and the counter substrate 28 is sealed with a sealing material (not shown). Specifically, as the light emitting element 20, on the light emitting element substrate 21, the pixel electrode 23, the hole transport layer (HTL) 24, the light emitting layer 25, the electron transport layer (ETL) 26, and the counter electrode (transparent electrode; ITO) 27) are formed in this order, and are sealed by the counter substrate 28. In the light emitting element 20, it is preferable that the upper surface of the counter electrode is further sealed with a sealing film 34.

  Here, the light emitting element 20 has either a bottom emission structure that emits the light 29 of the light emitting layer 25 from the light emitting element substrate 21 side, or a top emission structure that emits the light 29 of the light emitting layer 25 from the counter substrate 28 side. You can choose.

  The pixel electrode 23 functions as an anode, and in the case of top emission, a reflective metal layer such as an aluminum alloy located on the lower layer side, and tin-doped indium oxide (ITO) or zinc-doped located on the upper layer side. A laminated reflective structure having a transparent conductive metal oxide layer having a transparent electrode material such as indium oxide or a single layer of a reflective metal layer such as an aluminum alloy may be used. In the case of bottom emission, the transparent structure includes the transparent conductive metal oxide layer.

  The counter electrode 27 functions as a cathode, and in the case of top emission, an electron injection layer having a low work function such as barium, magnesium, or lithium located on the lower layer side and a transparent conductive oxidation similar to the above located on the upper layer side. A laminated transparent structure with a metal layer may be used. Further, in the case of bottom emission, a multilayer reflective structure of the low work function electron injection layer on the lower layer side and a high work function metal layer such as light reflective aluminum on the upper layer side may be used. The counter electrode 27 is preferably a single electrode common to the plurality of light emitting elements 20.

  When the pixel electrode 23 is a cathode and the counter electrode 27 is an anode, the carrier transport layer in contact with the pixel electrode 23 is an electron transport layer, and the carrier transport layer in contact with the counter electrode 27 is hole transport. Become a sex layer.

  The light emitting layer 25 includes an organic material that emits light by recombining holes transported from the HTL 24 and electrons transported from the ETL 26. The carrier transport layer of the light-emitting element 20 is not limited to the three-layer structure of the HTL 24, the light-emitting layer 25, and the ETL 26. For example, the carrier transport layer may have a two-layer structure of a hole transport layer and an electron transport light-emitting layer. There may be only a transporting light emitting layer, a hole transporting light emitting layer and an electron transporting layer, and there is no particular limitation such that another carrier transporting layer is interposed therebetween. Carrier transport layers such as the HTL 24, the light emitting layer 25, and the ETL 26 are collectively referred to as an EL layer.

  Then, by applying a predetermined voltage between the pixel electrode 23 and the counter electrode 27, holes are injected from the pixel electrode 23, and electrons are injected from the counter electrode 27 into the light emitting layer 25. In the light emitting layer 25, holes and electrons recombine to emit light. In the case of bottom emission, the light 29 generated by this light emission is transmitted through the pixel electrode 23 and the substrate 21 and completely diffused. In the case of top emission, the light 29 is transmitted through the counter electrode 27 and the counter substrate 28 and completely diffused. To do.

  By the way, when the light emitting element 20 is sandwiched between the transparent substrates (the light emitting element substrate 21 and the counter substrate 28), the light is naturally emitted inside the substrate. Has been devised.

  For example, by providing a fiber function for each of the plurality of light emitting elements formed on the light emitting element substrate 21, a pseudo light emitter is formed on the surface of the light emitting element substrate 21. In order to provide such a fiber function, a known technique called, for example, a photonic crystal fiber is used. Specifically, a photonic crystal fiber in which an air hole corresponding to a clad extends in the thickness direction of the light emitting element substrate 21 is provided in the light emitting element substrate 21 or formed integrally with the light emitting element substrate 21. Has been. Since such a fiber for controlling the directivity of light is provided, the light of the light emitting element 20 can be efficiently emitted from the light emitting element substrate 21.

  By the way, in this embodiment, a light spot having a small diameter is formed on the photosensitive drum 1 at a distance of millimeter order from the light emitting device 2 by the light emitting device 2 having the case portion 2A and the rod lens portion 2B. To create a light beam that resolves each dot. Hereinafter, the light emitting device 2 will be described with reference to FIGS. 3 and 4.

  FIG. 3 is a view showing an appearance of the light emitting device 2. In the case portion 2A, a plurality of light emitting elements 20 (not shown) are arranged in the main scanning direction of exposure scanning on the photosensitive drum 1 (the width direction of the photosensitive drum 1, that is, the width direction of the printing paper 7). Form an organic EL array arranged in a row.

  The light emitting element 20 is electrically connected to the host device (not shown) by control cables 31A and 31B as shown in FIG. Here, the connection method between the control cables 31A and 31B and the light emitting element 20 may be any connection method as long as the light emitting element 20 can be driven.

  Hereinafter, the structure of the light-emitting device 2 according to the present embodiment will be described with reference to FIGS. 4 and 5A and 5B.

  FIG. 4 is a side sectional view of the light emitting device 2. FIG. 5A is a diagram showing the light emitting element substrate 21 when viewed from the rod lens portion 2B side. FIG. 5B is a diagram showing the light emitting element substrate 21 when viewed from the counter substrate 28 side. In the present embodiment, the light emitting element 20 is set to a bottom emission structure.

  First, the light emitting element substrate 21 is bonded to the front case 51 with an adhesive resin 52 as shown in FIG. More specifically, as shown in FIG. 5A, the adhesive resin 52 is disposed so as to surround the light emitting elements 20 arranged in an array, and the light emitting element substrate 21 and the front surface are surrounded by the adhesive resin 52. The case 51 is bonded and fixed. Further, a rear case 53 is fitted into the front case 51 as shown in FIG.

  Here, as shown in FIG. 4, the light emitting element substrate 21 has a surface on the opposite side of the surface on which the adhesive resin 52 is provided and the light emitting element 20 is not provided. A driver IC 55 for driving 20 is provided in electrical connection with the pixel electrode 23 and the counter electrode 27. More specifically, as shown in FIG. 5B, a plurality of driver ICs 55 (four in this embodiment) are provided around the counter substrate 28 in the light emitting element 20.

  The driver IC 55 receives a synchronization signal, a clock signal, an image signal, and the like from a head controller (not shown), and the driver IC 55 determines the pixel electrode 23 and the counter electrode 27 based on these signals. Control is in progress.

  In the present embodiment, due to the structure of the printing apparatus, the light emitting device 2 is a single device, and thus there is a possibility that a force is applied to the connection wiring during assembly or replacement. Therefore, regarding the cable of the connection wiring between the light emitting element substrate 21 and the head controller (not shown), the cable outside the case portion 2A has a higher strength as a separate cable inside and outside the case portion 2A. In order to obtain a cable having high workability and excellent workability, a relay connector 59 is provided on the rear case 53 as shown in FIG.

  By the way, the front case 51 is provided with a convex portion 71, an opening is formed in the convex portion 71, and the rod lens portion 2 </ b> B is fitted into the opening so as to face each light emitting element 20. And the rod lens portion 2B are sealed with an adhesive. For this reason, even if the front case 51 is opaque to visible light, the light emitted from the light emitting element 20 is incident on the rod lens portion 2B through the sealed space 73 formed in the convex portion 71. Become. The convex portion 71 is filled with an intermediate liquid 65 having a refractive index higher than that of air.

  The light-emitting element 20 shown in FIG. 4 has a bottom emission structure in which the substrate 21 faces the rod lens portion 2B, but faces the opposing substrate 28 so as to face the rod lens portion 2B. It may be a top emission structure.

  According to the prior art, air (refractive index of about 1.0) is interposed between a light emitting element and a lens such as a rod lens. Since air has a lower refractive index than the light-emitting element (substrate), the total reflection critical angle at which the light emitted from the light-emitting element is reflected at the interface between the light-emitting element (substrate) and air is reduced and is easily reflected. In other words, the degree of refraction of light increases at this interface, and the amount of light that can be captured by the lens is extremely limited.

  By the way, the ratio of the amount of photons actually incident on the rod lens portion 2B to the amount of photons generated inside the light emitting element 20 is referred to as light extraction efficiency. If air is interposed in the light path where the light 29 travels between the light emitting element 20 and the rod lens portion 2B as in the prior art, about 80% of the photons generated in the light emitting element 20 are actually The light is not incident on the rod lens portion 2B, and the light extraction efficiency is considerably low.

  The present invention has been made in view of such circumstances. In the present embodiment, the sealed space 73 is filled with a liquid (intermediate liquid 65) having a higher refractive index than air instead of air. The refractive index of the space between the light emitting element substrate 21 provided with the light emitting element 20 and the rod lens 2B is approximated to the refractive index of the light emitting element (substrate) or the rod lens, and the total reflection critical angle is increased. Alternatively, the light extraction efficiency is increased by suppressing refraction at the interface.

  Further, since the convex portion 71 secures the optical path length from the light emitting element 20 to the rod lens 2B to a certain length, there is an effect that the distance between the rod lens 2B and the photosensitive drum 1 can be easily set. Since the adhesive resin 52 is provided around the outside of the convex portion 71, the thickness of the adhesive resin 52 is set to the optical path length when filling the intermediate liquid 65 only in the space surrounded by the adhesive resin 52. It doesn't have to be about length.

  By the way, in general, light emission luminance in a light emitting element such as an organic EL element increases in proportion to the magnitude of an interelectrode current across the light emitting layer of the light emitting element. Therefore, when high-speed printing is performed by a printing apparatus including a light-emitting device that uses a light-emitting element as a light source, a considerable amount of energy is required to obtain the amount of light required for the high-speed printing.

  In such a case, Joule heat is generated due to overcurrent. Therefore, as a result, the temperature of the light emitting element rises, and accordingly, the light emission efficiency is lowered and the lifetime is shortened. And it became clear from experiments that the decrease in light emission efficiency and the decrease in lifetime depend on the area of the light emitting surface of the light emitting element.

  That is, even if the light emitting surface of the light emitting element is the same quadrangle, when the light emitting element is driven by supplying the same current per unit area, the heat generation temperature varies depending on the area of the light emitting surface. Here, it has been found from experiments that a light-emitting element having a small area can emit light with higher luminance (large current).

  Incidentally, the element spacing in the main scanning direction of the light emitting elements in the exposure unit of the printing apparatus is determined by the printing resolution. On the other hand, the element spacing in the sub-scanning direction may be synchronized with the printing speed in view of the fact that the sub-scanning direction is the paper feed direction of the printing paper. As a comparative example shown in FIG. It can be said that there is no need to arrange in a row like the arrangement of elements. In the present embodiment, focusing on this point, the light emitting elements 20 are arranged in the light emitting elements.

  Hereinafter, the arrangement of the light emitting elements 20 unique to the present embodiment will be described with reference to FIGS. 6B and 6C while comparing with the arrangement of the light emitting elements shown in FIG. .

  In the present embodiment, the pitch in the main scanning direction between the light emitting elements 20 adjacent to each other (main scanning direction pitch) is maintained at r in the case of the one-row arrangement as shown in FIG. The distance between the light emitting elements 20 adjacent to each other is twice (see FIG. 6 (B)) or more than three times (see FIG. 6 (C)) compared to the conventional arrangement as shown in FIG. 6 (A). To. Here, as shown in FIG. 6A to FIG. 6C, a heat conduction distribution region which is a three-dimensional range in which the individual light emitting elements 20 can affect the regions adjacent to each other. 200 becomes spherical.

  Specifically, in the present embodiment, the light emitting elements 20 are staggered so as to form a plurality of rows in the sub-scanning direction as shown in FIGS. 6B and 6C. FIG. 6B shows an example of staggered arrangement of two rows, and FIG. 6C shows an example of staggered arrangement of three rows. In FIG. 6B, a regular triangle in which the main scanning direction pitch between two adjacent light emitting elements 20 is kept constant at r, and each angle θ1 of the triangle surrounded by the three adjacent light emitting elements 20 is 60 °. Then, the distance between the light emitting elements 20 is 2r. In FIG. 6C, the main scanning direction pitch between two adjacent light emitting elements 20 is kept constant at r, a certain light emitting element 20 (for example, n1) is the apex, and the pitch from the light emitting element 20 to the main scanning direction is the same. The apex angle θ2 surrounded by the light emitting element 20 (for example, n2) separated by r and the light emitting element 20 (for example, n4) separated by 3r in the main scanning direction from the light emitting element 20 has cos θ2 = 1/3. By setting so as to satisfy, the distance between the light emitting elements 20 is 3r. That is, in the k-row staggered arrangement, the main scanning direction pitch between two adjacent light emitting elements 20 is kept constant at r, and a certain light emitting element 20 is set at the apex, and the pitch r from the light emitting element 20 in the main scanning direction is r. The apex angle θx surrounded by the light emitting element 20 that is separated from the light emitting element 20 and the light emitting element 20 that is separated from the light emitting element 20 in the main scanning direction by k × r may be set to satisfy cos θx = 1 / k. . Thus, by arranging the light emitting elements 20 in a staggered arrangement of a plurality of rows, the distance between the light emitting elements 20 in the main scanning direction is increased while keeping the main scanning direction pitch of the light emitting elements 20 constant at r. be able to. The rod lenses of the rod lens portion 2B are also arranged in accordance with the arrangement of the light emitting elements 20.

  By disposing the light emitting elements 20 as described above, the heat capacity of each of the light emitting elements 20 can be increased. If the light emitting element 20 is considered to be a point light source, the spherical volume of the heat conduction distribution 200 is approximately proportional to the cube of the distance r.

  For example, when the distance in the main scanning direction between the light emitting elements 20 is doubled, the volume of the heat conduction distribution region 200 of the light emitting elements 20 is a cube of 2, that is, 8 times, and the heat capacity is also about 8 times. Similarly, when the distance between the light emitting elements 20 in the main scanning direction is tripled, the volume of the heat conduction distribution region 200 of the light emitting element 20 is the third power of 3, that is, 27 times, and the heat capacity is also about 27 times. .

  As described above, in this embodiment, the light emitting elements 20 are dispersed over a wide area by arranging the light emitting elements 20 in a plurality of rows in a staggered arrangement, so that the heat conduction of the light emitting elements 20 is achieved. The heat capacity of the distribution region is increased, and the thermal influence between the light emitting elements 20 can be reduced.

  In such a structure, the first row of light emitting elements 20 arranged in the main scanning direction (in FIG. 6B, n1, n3, n5,..., N (2m-1)) emit light in synchronization first. Then, after making it enter a predetermined row position of the photosensitive drum 1, after rotating the photosensitive drum, the second row of light emitting elements 20 (n2, n4,..., N (2m) in FIG. 6B). Are set so that the light from each light emitting element 20 is incident on the predetermined line of the photosensitive drum 1 so that the light is emitted in synchronization with the light and the light is incident on the predetermined line of the photosensitive drum 1.

  Note that the heat generated in the light emitting element 20 needs to be finally radiated to the outside of the light emitting element 20. That is, it is necessary to provide a cooling structure around the light emitting element 20. Here, a cooling structure of the light emitting element 20 in the present embodiment will be described with reference to FIG. The conduction thermal resistance Rcond, which is an index for evaluating the thermal conductivity of the material, is expressed by the following equation.

Rcond = L / λ · A
L: Path length λ: Thermal conductivity A: Heat transfer area Here, in order to conduct heat efficiently, it is necessary to reduce the value of the conduction heat resistance. Therefore, it is necessary to select each of the above parameters efficiently.

  In the present embodiment, as shown in FIG. 7, a high thermal conductivity material is used for the liquid planarization layer 70 (described later in detail) and the sealing film 34, and the counter substrate 28 is thinned to the limit. By doing so, the conduction heat resistance is reduced. Further, a Peltier element 61 is provided so that a Peltier cathode 65 is in contact with a surface of the counter substrate 28 that is not in contact with the liquid planarization layer 70. A heat sink 67 is provided so as to contact the Peltier anode 63 in the Peltier element 61.

  By adopting such a cooling structure, although it is a simple structure, the heat transfer from the heat absorption of the heat generated in the light emitting element 20 to the heat dissipation is smoothly performed, thereby enabling efficient cooling. That is, a sufficient cooling effect of the light emitting element 20 can be obtained.

  Of course, instead of glass as the counter substrate 28, silicon or metal, which is a highly heat conductive material, is used for sealing, so that heat conduction may be further promoted.

  Hereinafter, the liquid planarization layer 70 will be described.

  In the present embodiment, the liquid planarization layer 70 is provided in contact with the light emitting element 20 through a sealing film 34 that hermetically seals the light emitting element 20. Here, the liquid planarization layer 70 is a liquid medium filled in a gap between the surface side of the light emitting element substrate 21 where the light emitting element 20 is provided and the counter substrate 28.

  By the way, the thermal energy generated in the light emitting element 20 is roughly classified and transmitted in the following two directions. First, one is a downward direction shown in FIG. 7, that is, a direction toward the light emitting element substrate 21, and the other is an upward direction shown in FIG. 7, that is, a direction toward the counter substrate. The heat transmitted in the direction toward the counter substrate 28 is first transmitted to the liquid planarization layer 70 existing between the light emitting element 20 and the counter substrate 28.

  Here, the thermal energy generated in the light emitting element 20 naturally increases the temperature of the peripheral member of the light emitting element 20, and the rate of change in the temperature depends on the size of the heat capacity of the peripheral member. To do. That is, the peripheral member having a larger heat capacity has a lower temperature rise value.

  Therefore, in the present embodiment, the liquid flattening layer 70 is made of a liquid medium having a large heat capacity, so that the temperature rise is further suppressed. Examples of the liquid medium include fluorinated inert liquid Fluorinert (registered trademark) having a heat capacity of 1.92 J / K and silicone oil having a heat capacity of 1.62 J / K.

  More specifically, examples of the fluorinate include FC-3283 manufactured by 3M, and examples of the silicone oil include KF-96L-1cs manufactured by Shin-Etsu Silicone.

  The silicone oil is a chemically stable substance. Therefore, the silicone oil has an advantage that there is not much deterioration or deterioration with time due to irradiation with light generated in the organic EL light emitting layer 20.

  Of course, the heat capacity can be further increased by increasing the volume of the liquid planarization layer 70.

  Hereinafter, as an example of active matrix driving, an example of a configuration of a pixel circuit unit for performing light emission control of the light emitting element 20 by signal voltage gradation control in which two transistors are provided in each pixel is illustrated in FIG. A description will be given with reference to (B). Since this pixel circuit portion is not a feature of the present invention, it will be briefly described.

  First, as illustrated in FIG. 8A, the pixel circuit unit 40 includes a source electrode 41, a drain electrode 42, a gate electrode 43, a semiconductor 44, a gate insulating layer 45, and an insulating layer 46.

  That is, a signal is transmitted by turning on / off a TFT transistor including the source electrode 41, the drain electrode 42, and the gate electrode 43, thereby causing the light emitting element 20 to emit light. That is, light emission control of the light emitting element 20 is performed by switching of the TFT transistor. Here, for example, the counter electrode 27 is fixed to a ground potential, and the pixel electrode 23 is electrically connected to the TFT transistor.

  As shown in FIG. 8B, the counter electrode 27 is a single common electrode common to the plurality of light emitting elements 20. A pixel circuit unit 40 electrically connected to the pixel electrode 23 is provided on the light emitting element substrate 21 along the organic EL array. The pixel circuit 40 includes a selection transistor 101, a drive transistor 103, and a capacitor 105. Both the selection transistor 101 and the drive transistor 103 are, for example, n-channel amorphous silicon TFTs. The drain of the selection transistor 101 is connected to the signal line 107, and the gate of the selection transistor 101 is connected to the scanning line 109. The drain of the driving transistor 103 is connected to the power supply line 111, and the source of the selection transistor 101 and the gate of the driving transistor 103 are connected via a contact hole 110. The counter electrode 27 is fixed at, for example, 0 (V), and the pixel electrode 23 is electrically connected to the source electrode of the driving transistor 103. The capacitor 105 is provided between the gate electrode and the source electrode of the driving transistor 103. The signal line 107, the scanning line 109, and the power supply line 111 are routed to the control cables 31A and 31B and connected to external circuits, respectively.

  By the way, since a light emitting element generally requires a large current for driving, a current supply line 111 for supplying a large current to the current drive TFT 103 is required in addition to the data line 107 and the scanning line 109 for selecting a light emitting pixel. .

  With such a structure, the light emitting element 20 which is a thin film layer in a region sandwiched between the counter electrode 27 and the pixel electrode 23 is subjected to voltage application (current supply). Flashes.

  As described above, according to the present embodiment, while maintaining high definition without changing the pitch between the light emitting elements, the thermal influence between the light emitting elements is reduced, and the light emitting element is made efficient. A light-emitting device that can be cooled well can be provided.

  Specifically, according to the light emitting device according to the present embodiment, the heat capacity of the individual light emitting elements can be increased, and the thermal influence between the individual light emitting elements can be reduced. In addition, since the light-emitting elements, that is, the organic EL light-emitting layers are dispersed over a wide area, the total heat capacity can be increased. Therefore, for example, when the light emitting device according to the present embodiment is applied to an exposure unit in a printing apparatus, it is possible to stably supply a light amount, thereby reducing a print density difference.

  As mentioned above, although this invention was demonstrated based on one Embodiment, this invention is not limited to embodiment mentioned above, Of course, a various deformation | transformation and application are possible within the range of the summary of this invention. is there.

  Further, the above-described embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the column of the effect of the invention Can be extracted as an invention.

1 is a diagram illustrating a configuration example of a printing apparatus using a light emitting device according to an embodiment of the present invention. The figure explaining the basic structure of an organic electroluminescent light emitting element. The figure which shows the external appearance of the light-emitting device which concerns on one Embodiment of this invention. 1 is a side sectional view of an exposure unit of a light emitting device according to an embodiment of the present invention. (A) is a figure which shows the light emitting element substrate at the time of seeing from the rod lens part side. FIG. 5B is a diagram illustrating a light-emitting element substrate when viewed from the counter substrate side. 6A is a diagram showing an arrangement of light emitting elements as a comparative example, and FIG. 6B shows an example of an arrangement of organic EL light emitting layers in a light emitting device according to an embodiment of the present invention. FIG. 6C is a diagram showing an example of the arrangement of the organic EL light emitting layers in the light emitting device according to the embodiment of the present invention. The figure which shows the cooling structure of the organic electroluminescent light emitting layer in the light-emitting device which concerns on one Embodiment of this invention. (A), (B) is a figure which shows an example of a structure of the pixel circuit part in the case of carrying out light emission control of the organic electroluminescent light emitting layer by the 2 transistor system which is a typical circuit of active matrix drive.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 3 ... Charge roller, 4 ... Eraser light source photoconductor, 5 ... Cleaning member, 6 ... Developing device, 6a ... Developing roller, 7 ... Printing paper, 8 ... Transfer roller, 9 ... Fixing roller, 11 ... Conveying belt, 20 ... Light emitting element, 21 ... Light emitting element substrate, 22 ... Reflecting layer, 23 ... Pixel electrode, 24 ... Hole transport layer, 25 ... Light emitting layer, 26 ... Electron transport layer, 27 ... Counter electrode, 28 ... Opposite Substrate, 31A, 31B ... control cable, 34 ... sealing film, 40 ... pixel circuit part, 41 ... source electrode, 42 ... drain electrode, 43 ... gate electrode, 44 ... semiconductor, 45 ... gate insulating layer, 51 ... front case 52 ... Adhesive resin, 53 ... Back case, 55 ... Driver IC, 59 ... Relay connector, 61 ... Peltier element, 63 ... Peltier anode, 65 ... Peltier Cathode, 67 ... Heat sink, 70 ... Liquid flattening layer, 71 ... Projection, 73 ... Sealed space, 101 ... Selection transistor, 103 ... Drive transistor, 105 ... Capacitor, 107 ... Signal line, 109 ... Scanning line, 111 ... Power supply line.

Claims (4)

In a light emitting device having a plurality of light emitting elements that emit light at a predetermined position of a photosensitive drum,
The EL light emitting unit, wherein the light emitting elements are arranged in a staggered manner in a plurality of rows in a predetermined direction.   The light emitting device according to claim 1, wherein the light emitting element disposed on the substrate is sealed by a counter substrate, and a Peltier element is provided on the counter substrate.   2. The light emitting device according to claim 1, further comprising lens means for projecting light emitted from the light emitting element as an erecting equal-magnification image.   A printing apparatus comprising the light-emitting device according to claim 1.

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