JP2004134395A - Organic electroluminescence element, exposure device using the same, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescence element with a large emitted light quantity, an exposure device using the same, and an image forming apparatus. <P>SOLUTION: This organic electroluminescence element has an anode which is an electrode to inject holes, a cathode which is an electrode to inject electrons, light emitting layers which are formed between the anode and the cathode respectively and include two or more light emission regions, and a charge generating layer which injects electrons into the light emitting layer on a side close to the anode and injects holes into the light emitting layer on a side close to the cathode, on a substrate. A work function of the charge generating layer is set to be higher than an ionizing potential of the light emitting layer on the side close to the anode. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an organic electroluminescence element used as a light emitting element in various apparatuses, an exposure apparatus using the same, and an image forming apparatus.

Electroluminescent elements are light-emitting devices that utilize the electroluminescence of solid fluorescent substances.Currently, inorganic electroluminescent elements that use inorganic materials as light emitters have been put into practical use, and are used in backlights of liquid crystal displays, flat displays, etc. The application development of is partially planned. However, since the inorganic electroluminescence element requires a voltage as high as 100 V or more to emit light and emits blue light, it is difficult to achieve full color by three primary colors of RGB. In addition, since the inorganic electroluminescent element has a very large refractive index of a material used as a light-emitting body, it is strongly affected by total reflection at an interface or the like, and the light extraction efficiency into the air for actual light emission is 10 to 20%. % And it is difficult to achieve high efficiency.

On the other hand, research on electroluminescent devices using organic materials has been attracting attention for a long time, and various studies have been conducted. However, since the luminous efficiency is very poor, research into practical use has not progressed.

However, in 1987 C.C. W. Tang et al. Have proposed an organic electroluminescent device having a function-separated type laminated structure in which an organic material is divided into two layers, a hole transport layer and a light emitting layer, and 1000 cd / m ² or more despite a low voltage of 10 V or less. It was found that high emission luminance was obtained (see Non-Patent Document 1). Since then, organic electroluminescent devices have suddenly attracted attention, and research on organic electroluminescent devices having a similar function-separation type laminated structure has been actively conducted, especially for practical use of organic electroluminescent devices. Investigations on high efficiency and long life, which are indispensable for such devices, have been sufficiently studied. In recent years, displays and the like using an organic electroluminescence element have been realized.

Here, the configuration of a conventional general organic electroluminescent element will be described with reference to FIG. FIG. 11 is a cross-sectional view showing a main part of a conventional organic electroluminescence element.

As shown in FIG. 11, an organic electroluminescence element has an anode 52 made of a transparent conductive film such as ITO formed on a substrate 51 made of glass or the like by a sputtering method, a resistance heating evaporation method, or the like; N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-diphenyl-4,4′-diamine (hereinafter, also referred to as “resistive heating evaporation method”) on the anode 52. abbreviated as TPD.) and hole transport layer 53 made of such, 8-hydroxyquinoline Aluminum formed by resistance heating deposition method or the like on the hole transport layer 53 (hereinafter, abbreviated as Alq _3.) composed of such as a light emitting A layer 54 and a cathode 55 made of a metal film having a thickness of about 100 nm to 300 nm formed on the light emitting layer 54 by a resistance heating evaporation method or the like.

When a direct current voltage or a direct current is applied with the anode 52 of the organic electroluminescence device having the above configuration as a positive electrode and the cathode 55 as a negative electrode, holes are emitted from the anode 52 to the light emitting layer 54 via the hole transport layer 53. The electrons are injected from the cathode 55 into the light emitting layer 54. In the light-emitting layer 54, recombination of holes and electrons occurs, and a light-emitting phenomenon occurs when the exciton generated thereby shifts from the excited state to the ground state.

In such an organic electroluminescence device, light emitted from the phosphor in the light emitting layer 54 is normally emitted in all directions around the phosphor, and is transmitted to the hole transport layer 53, the anode 52, and the substrate 51. Radiated into the air via Alternatively, the light is once directed in a direction opposite to the light extraction direction (the direction of the substrate 51), is reflected by the cathode 55, and is radiated into the air via the light emitting layer 54, the hole transport layer 53, the anode 52, and the substrate 51. You.

In addition, about the element structure of an organic electroluminescent element, there exist some which are disclosed by (patent document 1), (patent document 2), etc.
CW Tang, SA Vanslyke, "Applied Physics Letter (Appl. Phys. Lett)" (USA), Vol. 51, 1987, p. 913 U.S. Pat. No. 5,917,280 U.S. Pat. No. 5,932,895

Here, an image forming apparatus based on electrophotography is provided with an exposure light for writing an electrostatic latent image on the photosensitive member by irradiating the photosensitive member uniformly charged to a predetermined potential with exposure light corresponding to image data. A device is provided. As a conventional exposure method in an exposure apparatus, a laser beam method and an LED array method are mainly used.

(4) When the exposure method is a laser beam, the space occupied by optical components such as a polygon mirror and a lens is large, and it is difficult to reduce the size of the apparatus. Further, in the case of an LED array, it is difficult to reduce the cost of the device because the substrate is expensive.

These problems can be solved by using the above-mentioned organic electroluminescence element as a light source.

However, since the light emitted from the organic electroluminescent device is diffused light, the conventional device could not obtain the amount of light necessary for forming an image of the diffused light on the photosensitive member.

Accordingly, it is an object of the present invention to provide an organic electroluminescence element having a large amount of emitted light, an exposure apparatus and an image forming apparatus using the same.

In order to solve this problem, the organic electroluminescence device of the present invention is formed with an anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, and between the anode and the cathode, A light-emitting layer having a plurality of light-emitting regions and a charge-generating layer for injecting electrons into the light-emitting layer on the side closer to the anode and injecting holes into the light-emitting layer on the side closer to the cathode; The work function of the layer is set higher than the ionization potential on the side closer to the anode.

Further, in order to solve this problem, the organic electroluminescent element of the present invention is formed between an anode which is an electrode for injecting holes, a cathode which is an electrode for injecting electrons, and an anode and a cathode. A light emitting layer having a plurality of light emitting regions, a charge generating layer for injecting electrons into the light emitting layer near the anode, and injecting holes into the light emitting layer near the cathode, on the substrate, The electron affinity of the generating layer is set lower than the electron affinity of the light emitting layer closer to the anode, and the ionization potential of the charge generating layer is set higher than the ionization potential of the light emitting layer closer to the cathode.

Furthermore, in order to solve this problem, the organic electroluminescence element of the present invention is formed between an anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, and an anode and a cathode. A light emitting layer having a plurality of light emitting regions, a charge generating layer for injecting electrons into the light emitting layer on the side closer to the anode, and injecting holes into the light emitting layer on the side closer to the cathode, The potential difference between the electron affinity of the light emitting layer closer to the cathode and the charge generating layer and the potential difference between the ionization potential of the light emitting layer closer to the cathode and the charge generating layer are set to 0.6 eV or less.

In order to solve this problem, the exposure apparatus of the present invention uses any one of these organic electroluminescence elements as a light source.

In order to solve this problem, an exposure apparatus of the present invention includes an anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, and a plurality of light emitting devices formed between the anode and the cathode. A light emitting layer having a region, a charge generating layer for injecting electrons into the light emitting layer near the anode and injecting holes into the light emitting layer near the cathode, and an organic electroluminescent element having a substrate as a light source. It was used.

In order to solve this problem, an exposure apparatus of the present invention includes a plurality of anodes which are electrodes for injecting holes, a plurality of cathodes which are arranged alternately with the anodes and which are electrodes for injecting electrons, and an anode and a cathode. And an organic electroluminescence element having a plurality of light emitting layers each having a light emitting region formed on a substrate and having a light emitting region on a substrate.

(4) Since light is emitted from the plurality of light-emitting layers, the amount of light emitted from the organic electroluminescence element can be increased.

{Circle around (4)} Since the hole injection efficiency and the electron injection efficiency to the light emitting layer are increased, the light emitting amount in the light emitting layer is further increased, and as a result, the light emitting amount of the organic electroluminescence element can be further increased.

According to the present invention, since light is emitted from a plurality of light-emitting layers, an effective effect that the amount of light emitted from the organic electroluminescence element can be increased can be obtained.

The invention according to claim 1 of the present invention has an anode as an electrode for injecting holes, a cathode as an electrode for injecting electrons, and a plurality of light emitting regions formed between the anode and the cathode. A light-emitting layer and a charge-generating layer that injects electrons into the light-emitting layer nearer to the anode and injects holes into the light-emitting layer closer to the cathode on the substrate; This is an organic electroluminescent element that is set higher than the ionization potential on the side closer to, and emits light in a plurality of light-emitting layers, and thus has the effect of increasing the amount of light emitted from the organic electroluminescent element. Also, since the work function of the charge generation layer is set higher than the ionization potential of the light emitting layer near the cathode, the efficiency of hole injection into the light emitting layer near the cathode increases, so that the light emission near the cathode closes. This has the effect that the amount of emitted light in the layer becomes larger, and as a result, the amount of emitted light of the organic electroluminescence element can be further increased.

The invention according to claim 2 of the present invention has an anode which is an electrode for injecting holes, a cathode which is an electrode for injecting electrons, and a plurality of light-emitting regions formed between the anode and the cathode. A light-emitting layer and a charge-generating layer that injects electrons into the light-emitting layer nearer to the anode and injects holes into the light-emitting layer closer to the cathode on the substrate; An organic electroluminescent device in which the electron affinity of the light-emitting layer closer to the cathode is set lower and the ionization potential of the charge generation layer is set higher than the ionization potential of the light-emitting layer closer to the cathode. Is performed, the light emission amount of the organic electroluminescence element can be increased. Also, the electron affinity of the charge generation layer was set lower than the electron affinity of the light emitting layer near the anode, and the ionization potential of the charge generation layer was set higher than the ionization potential of the light emitting layer near the cathode. Since the hole injection efficiency and the electron injection efficiency to the light emitting layer are increased, the amount of light emitted from these light emitting layers is further increased, and as a result, the amount of light emitted from the organic electroluminescence element can be further increased.

The invention according to claim 3 of the present invention has an anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, and a plurality of light emitting regions formed between the anode and the cathode. A light-emitting layer and a charge generation layer that injects electrons into the light-emitting layer on the side closer to the anode and injects holes into the light-emitting layer on the side closer to the cathode, and has a light-emitting layer on the substrate closer to the anode. An organic electroluminescent device characterized in that the potential difference between the electron affinity and the electron affinity of the charge generation layer and the potential difference between the ionization potential of the light emitting layer near the cathode and the ionization potential of the charge generation layer are set to 0.6 eV or less. Since it is a luminescence element, light emission is performed in a plurality of light-emitting layers, and thus has an effect that the amount of light emitted from the organic electroluminescence element can be increased. In addition, by adopting such a configuration, the hole injection efficiency and the electron injection efficiency to each light emitting layer are increased, so that the light emission amount in these light emitting layers is increased, and as a result, the light emission of the organic electroluminescence element is increased. This has the effect that the amount of light can be further increased.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the charge generation layer is a first generation layer located at least on the light emitting layer side closer to the anode. And a second generation layer located on the side of the light-emitting layer closer to the cathode, wherein the first generation layer is set to have a lower electron affinity than the second generation layer, and the second generation layer is set to the first generation layer. This is an organic electroluminescence device that is set to a higher ionization potential than the generation layer.The efficiency of hole injection and electron injection into each light-emitting layer is increased, so that the amount of light emitted from these light-emitting layers is increased, and as a result, organic light is emitted. This has the effect that the amount of light emitted from the electroluminescent element can be further increased.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the generation layer formed first is an organic electroluminescence element formed by resistance heating, and alleviates damage during film formation. It has the effect that it becomes possible.

In the invention according to claim 6 of the present invention, in the invention according to any one of claims 1 to 5, the charge generation layer is made of a dielectric, and the relative permittivity of the charge generation layer is equal to that of the light emitting layer. An organic electroluminescent element having a relative dielectric constant or higher, which has an effect that the amount of light emitted from the organic electroluminescent element can be increased.

The invention according to claim 7 of the present invention is the invention according to any one of claims 1 to 6, wherein the light-emitting layer near the anode and the light-emitting layer near the cathode are formed of the same member. The organic electroluminescent element is configured, and has an effect that the amount of emitted light of the organic electroluminescent element can be increased.

The invention according to claim 8 of the present invention is directed to a buffer formed of a wide gap semiconductor between the anode which is an electrode for injecting holes, the cathode which is an electrode for injecting electrons, and the anode and the cathode. An organic electroluminescence device comprising a plurality of light-emitting layers having a light-emitting region formed through a layer, wherein light is emitted in the plurality of light-emitting layers through a buffer layer. Has an effect that the amount of emitted light can be increased. In addition, since a material can be appropriately selected from many semiconductor materials such as a metal oxide, a metal sulfide, a compound semiconductor, and an organic semiconductor, a high-performance organic electroluminescent element can be easily formed. Has an action.

According to a ninth aspect of the present invention, there is provided the light-emitting layer according to any one of the first to eighth aspects, or a hole-transporting layer formed as necessary in the light-emitting layer, or An organic electroluminescent element characterized in that, of the organic thin film layer composed of an electron transport layer, a layer that is in contact with the charge generation layer on the substrate side is formed of a polymer material, and is said to mitigate damage during film formation. Has an action. Further, in order to alleviate the damage of these organic thin film layers during film formation, an optional process is performed on a layer which is in contact with the charge generation layer on the substrate side, that is, on an organic thin film layer which is a base when forming the charge generation layer. It can be used to form a charge generation layer. Therefore, the selectivity of the process of forming the charge generation layer is increased, and the film can be formed by a simple process. Further, since the limitation of the film forming process of the charge generation layer is removed, the material of the charge generation layer can be appropriately selected from various materials, and the selectivity of the material of the charge generation layer itself is also increased. .

The invention according to claim 10 of the present invention is the invention according to any one of claims 1 to 9, wherein the light-emitting layer, or a hole-transport layer formed as necessary in the light-emitting layer, or An organic electroluminescence device characterized in that all layers of an organic thin film layer composed of an electron transport layer are formed of a polymer material, and have an effect of reducing damage during film formation. Further, since the organic thin film layer is formed of a polymer material, the organic thin film layer is stable against heat of the light emitting layer, and has an effect of realizing an organic electroluminescent element having high stability during driving. Furthermore, since the organic thin film layer is formed of a polymer material, the generation of defects and pinholes at the interface between the layers can be suppressed, so that an organic electroluminescent device having high stability can be formed. .

An invention according to claim 11 of the present invention is the organic electroluminescence device according to any one of claims 1 to 10, wherein the charge generation layer is formed of a polymer organic film, In addition to alleviating damage during film formation, the film can be formed by the same process as that for the light emitting layer, so that the process is simplified.

According to a twelfth aspect of the present invention, in the invention according to any one of the ninth to eleventh aspects, the organic thin film layer and the charge generation layer are formed by a wet film forming method. This is an organic electroluminescence element characterized by the function of reducing material loss during film formation. In addition, by using a wet film forming method, a large-scale vacuum device is not required, so that a film can be formed with inexpensive equipment and an element can be easily enlarged. Further, by using a wet film formation method, the adhesion between the layers is improved, so that a short circuit in the element can be suppressed, and an organic electroluminescence element having high stability can be formed.

According to a thirteenth aspect of the present invention, in the invention according to any one of the ninth to twelfth aspects, the drying temperature of the organic thin film layer on the side close to the cathode is the same as that of the organic thin film layer on the side close to the anode. An organic electroluminescent device characterized by having a temperature not exceeding the glass transition temperature, wherein a plurality of organic thin-film layers (light-emitting layer or light-emitting layer In forming a hole transport layer or an electron transport layer formed by the above method, the organic thin film layer near the cathode can be formed without damaging the organic thin film layer near the anode. Having.

According to a fourteenth aspect of the present invention, there is provided an exposure apparatus using the organic electroluminescence element according to any one of the first to thirteenth aspects as a light source. Has the effect that it is possible to obtain the amount of light required for exposure without increasing the size of.

The invention according to claim 15 of the present invention has an anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, and a plurality of light-emitting regions formed between the anode and the cathode. Exposure using a light-emitting organic electroluminescent element having a light-emitting layer and a charge generation layer for injecting electrons into the light-emitting layer near the anode and injecting holes into the light-emitting layer near the cathode on a substrate. An organic electroluminescent element that emits light in a plurality of light-emitting layers and emits light in a plurality of light-emitting layers. The organic electroluminescent element has an effect that a light amount necessary for exposure can be obtained without increasing the size of the device.

The invention according to claim 16 of the present invention is the exposure apparatus according to claim 15, wherein the light emitting layer near the anode and the light emitting layer near the cathode are formed of the same member. This has the effect that the amount of light emitted from the organic electroluminescence element can be increased.

The invention according to claim 17 of the present invention is the invention according to claims 14 to 16, wherein the light-emitting layer is located between the electrode formed first and the charge generation layer, The contacting layer is an exposure device made of a polymer, and has an effect that damage during film formation can be reduced.

The invention according to claim 18 of the present invention is characterized in that a plurality of anodes which are electrodes for injecting holes, a plurality of cathodes which are arranged alternately with the anodes and which are electrodes for injecting electrons, and the anode and the cathode. Each is formed, a plurality of light-emitting layers having a light-emitting region, and an exposure apparatus using an organic electroluminescence element having a substrate on the light source, the anode and the cathode, at least one each through the light-emitting layer It is an exposure device that is arranged alternately, and it is possible to obtain the light amount required for exposure without increasing the size of the device by using an organic electroluminescent element that emits light in a plurality of light emitting layers and emits a large amount of light. Has an action.

According to a nineteenth aspect of the present invention, in the invention according to the eighteenth aspect, a layer including a light emitting layer located between an electrode formed first and an electrode formed next is formed of a polymer. This is an apparatus, and has an effect that damage during film formation can be reduced.

According to a twentieth aspect of the present invention, in the invention according to any one of the fourteenth to nineteenth aspects, there is provided an exposure apparatus driven by an alternating current, an alternating voltage or a pulse wave, and a plurality of light emitting layers. The organic electroluminescent element which emits light at a large amount of light has an effect that it is possible to obtain a light amount required for exposure without increasing the size of the apparatus.

The invention according to claim 21 of the present invention is the exposure apparatus according to any one of claims 14 to 20, wherein exposure light is extracted from a side surface of the organic electroluminescent element, and the light emitting layer includes a plurality of light emitting layers. The organic electroluminescent element that emits a large amount of emitted light has an effect that it is possible to obtain an amount of light necessary for exposure without increasing the size of the apparatus.

According to a twenty-second aspect of the present invention, there is provided an image forming apparatus including the exposure apparatus according to any one of the fourteenth to twenty-first aspects, and a photoconductor on which an electrostatic latent image is formed by the exposure apparatus. An exposure apparatus using an organic electroluminescence element having a large amount of emitted light, which emits light in a plurality of light emitting layers, as a light source has an effect that a compact image forming apparatus can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a configuration of a color image forming apparatus according to Embodiment 1 of the present invention, FIG. 2 is an explanatory view showing an exposure unit in the color image forming apparatus of FIG. 1 in detail, and FIG. FIG. 4 is an explanatory view showing a photosensitive section in the apparatus in detail, FIG. 4 is an explanatory view showing a developing section in the color image forming apparatus in FIG. 1 in detail, and FIG. 5 is a main part of an organic electroluminescence element used as a light source of an exposure section in FIG. FIG. 6 is a cross-sectional view showing a main part of an organic electroluminescence element which is a modification used as a light source of the exposure unit in FIG.

Referring to FIG. 1, a color image forming apparatus 1 includes developing units 2, 3, 4, for forming toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. 5 are arranged in order, and are provided with exposure units (exposure devices) 6, 7, 8, 9 and photosensitive units 10, 11, 12, 13 corresponding to these developing units 2 to 5, respectively.

As shown in FIG. 2, the exposure units 6 to 9 are mounted on the head support members 6a, 7a, 8a, 9a and the base members 6b, 7b, 8b, 9b and provided on the head support members 6a to 9a. Organic electroluminescent elements 6d, 7d, 8d, 9d as light sources hermetically sealed with sealing materials 6c, 7c, 8c, 9c, and provided on substrates 6b, 7b, 8b, 9b to correspond to image data The organic EL device includes drivers 6e, 7e, 8e, and 9e that supply the generated voltage to the organic electroluminescent elements 6d to 9d and emit light. Further, on the bases 6b, 7b, 8b, 9b, prisms 6f, 7f, 8f, 9f for refracting irradiation light from the organic electroluminescent elements 6d to 9d, and a fiber array 6g for collecting light from the prisms 6f to 9f. , 7g, 8g, 9g, and cylindrical lenses 6h, 7h, 8h, 9h for narrowing down light from the fiber arrays 6g to 9g in the sub-scanning direction.

As shown in detail in FIG. 3, the photosensitive units 10 to 13 are rotatably provided as photosensitive drums (photosensitive members) 10a, 11a, 12a, and 13a as image carriers, and are pressed against the photosensitive drums 10a to 13a. (Charging means) 10b, 11b, 12b, 13b for charging the surfaces of the photosensitive drums 10a to 13a to a uniform potential, and a cleaner for removing toner remaining on the photosensitive drums 10a to 13a after image transfer. 10c, 11c, 12c, and 13c.

感光 The photosensitive drums 10a to 13a rotating in the circumferential direction are arranged in a line so that their rotation center axes are parallel to each other. The chargers 10b to 13b pressed against the photosensitive drums 10a to 13a rotate with the rotation of the photosensitive drums 10a to 13a.

Further, as shown in detail in FIG. 4, the developing units 2 to 5 adhere toner to the photosensitive drums 10a to 13a on which the electrostatic latent images are formed on the peripheral surfaces by the irradiation light from the exposure units 6 to 9, and statically apply the toner. Developing rollers (developing means) 2a, 3a, 4a, 5a for visualizing the electrostatic latent image as toner images, stirring members 2b, 3b, 4b, 5b for stirring toner 14 in the tank, and toner 14 for stirring. The supply rollers 2c, 3c, 4c, 5c for supplying the toner 14 to the developing rollers 2a to 5a, and the doctor blade for charging the toner 14 by friction while adjusting the toner 14 supplied to the developing rollers 2a to 5a to a predetermined thickness. 2d, 3d, 4d, and 5d.

As shown in FIG. 1, toner images of the respective colors visualized on the photosensitive drums 10 a to 13 a are placed on paper (at positions opposed to the exposure units 6 to 9, the photosensitive units 10 to 13, and the development units 2 to 5). A transfer unit 15 is formed on the recording medium P for transferring the images one over another to form a color toner image.

The transfer unit 15 includes transfer rollers 16, 17, 18, and 19 disposed corresponding to the respective photosensitive drums 10a to 13a, and springs 20, 21 for pressing the respective transfer rollers 16 to 19 against the photosensitive drums 10a to 13a. , 22, and 23.

給 紙 On the opposite side of the transfer unit 15, a paper supply unit 24 in which the paper P is stored is provided. Then, the paper P is taken out one by one from the paper feed unit 24 by the paper feed roller 25.

(4) A registration roller 26 that feeds the paper P to the transfer unit 15 at a predetermined timing is provided on a paper transport path from the paper supply unit 24 to the transfer unit 15. Further, a fixing unit 27 is arranged on a paper transport path on which the paper P on which the color toner image is formed in the transfer unit 15 travels. The fixing unit 27 is provided with a heating roller 27a and a pressing roller 27b pressed against the heating roller 27a, and the color image transferred onto the paper P is generated by the pressure and heat caused by the sandwiching rotation of the rollers 27a and 27b. The image is fixed on the sheet P.

In the image forming apparatus having such a configuration, first, a latent image of the yellow component color of the image information is formed on the photosensitive drum 10a. This latent image is visualized as a yellow toner image on the photosensitive drum 10a by a developing roller 2a having yellow toner. Meanwhile, the sheet P taken out of the sheet feeding unit 24 by the sheet feeding roller 25 is sent to the transfer unit 15 at a timing by the registration roller 26. Then, the sheet is nipped and conveyed between the photosensitive drum 10a and the transfer roller 16, and at this time, the above-described yellow toner image is transferred from the photosensitive drum 10a.

(4) While the yellow toner image is being transferred to the paper P, a magenta component color latent image is subsequently formed, and the magenta toner image of magenta toner is visualized by the developing roller 3a. Then, the magenta toner image is transferred onto the sheet P on which the yellow toner image has been transferred, so as to overlap the yellow toner image.

(4) Image formation and transfer are performed in the same manner for the cyan toner image and the black toner image, and the superposition of the four color toner images on the paper P is completed.

Then, the paper P on which the color image is formed is transported to the fixing unit 27. In the fixing unit 27, the transferred toner image is heated and fixed on the sheet P, and a full-color image is formed on the sheet P.

The paper P on which a series of color image formation has been completed in this way is then discharged onto the discharge tray 28.

Here, the organic electroluminescent elements 6d, 7d, 8d, and 9d, which are light sources provided in the exposure units 6 to 9, are formed on the substrate 31 by a sputtering method, a resistance heating evaporation method, or the like, as shown in FIG. An anode 32 is formed of a transparent conductive film and is an electrode for injecting holes, and a cathode 33 is formed by a resistance heating evaporation method or the like and is an electrode for injecting electrons. Between the anode 32 and the cathode 33, a first light emitting layer 34 having a light emitting region and located on the anode 32 side and a second light emitting layer 35 having a light emitting region and located on the cathode 33 side Are respectively formed, a first hole transport layer 36 is provided between the anode 32 and the first light emitting layer 34, and a second hole transport layer 36 is provided between the charge generation layer 38 and the second light emitting layer 35. The hole transport layer 37 is formed. Further, between the first light emitting layer 34 and the second light emitting layer 35, a charge generating layer 38 for injecting electrons into the first light emitting layer 34 and injecting holes into the second light emitting layer 35 is provided. Is formed.

When a DC voltage or a DC current is applied with the anode 32 of the organic electroluminescence device having the above configuration as a positive electrode and the cathode 33 as a negative electrode, the first light-emitting layer 34 is subjected to the first hole transport from the anode 32. Holes are injected through the layer 36 and electrons are injected from the charge generation layer 38, and electrons are injected into the second light emitting layer 35 from the cathode 33 and second holes are injected from the charge generation layer 38. Holes are injected through the transport layer 37. In the first light-emitting layer 34 and the second light-emitting layer 35, the holes and electrons injected as described above are recombined, and the excitons generated thereby move from the excited state to the ground state. At that time, a light emission phenomenon occurs.

{Circle around (2)} Since the light is emitted by the plurality of light emitting layers of the first light emitting layer 34 and the second light emitting layer 35, the amount of light emitted from the organic electroluminescence element can be increased.

In such an organic electroluminescence device, light emitted from the phosphor, which is a light emitting region in the first and second light emitting layers 34 and 35, is emitted in all directions around the phosphor, and the light is emitted from the substrate 31 to the substrate 31. Radiated via Alternatively, the light is once reflected by the cathode 33 in a direction opposite to the light extraction direction (the direction of the substrate 31) and emitted via the substrate 31.

Next, each member constituting the organic electroluminescence element will be described.

As the substrate 31 of the organic electroluminescent element of the present invention, a transparent or translucent substrate that is opaque when not used as a light extraction surface can be used, as long as the substrate has sufficient strength to hold the organic electroluminescent element. . In the present invention, the definition of “transparent” or “translucent” indicates a degree of transparency that does not hinder the visual recognition of light emission by the organic electroluminescence element.

The substrate 31 is made of, for example, inorganic oxide glass, inorganic fluoride such as transparent or translucent soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz glass. Inorganic glass such as glass, or a polymer such as transparent or translucent polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polyether sulfone, polyvinyl fluoride, polypropylene, polyethylene, polyacrylate, amorphous polyolefin, fluorine resin, etc. films, or transparent or translucent _{As 2 S 3, As 40 S} 10, S 40 Ge 10 etc. chalcogenide maytansinoid _{glass, ZnO, Nb 2 O, Ta} 2 O 5, SiO, Si 3 N 4, HfO _2, metal oxides such as TiO ₂ and nitrides Material, or opaque silicon, germanium, silicon carbide, gallium arsenide, gallium nitride, or other semiconductor material, or the above-mentioned transparent substrate material containing a pigment or the like, or a metal material whose surface has been subjected to insulation treatment, etc. And a stacked substrate in which a plurality of substrate materials are stacked can be used.

Also, a circuit composed of a resistor, a capacitor, an inductor, a diode, a transistor, etc. for driving the organic electroluminescence element may be formed on the surface of the substrate or inside the substrate.

Further, depending on the application, a material that transmits only a specific wavelength, a material that converts light into a specific wavelength having a light-to-light conversion function, and the like may be used. Further, the substrate is preferably insulative, but not particularly limited, and may have conductivity depending on the range in which the driving of the organic electroluminescent display element is not hindered or depending on the application.

As the anode 32 of the organic electroluminescence element, ITO (indium tin oxide), ATO (SnO ₂ doped with Sb), AZO (ZnO doped with Al), or the like is used.

Here, in the present embodiment, the organic thin film layers are each configured by a two-layer structure of the hole transport layer 36 (37) and the light emitting layer 34 (35). Any of a single-layer structure of only a layer, a two-layer structure of a light-emitting layer and an electron transport layer, and a three-layer structure of a hole transport layer, a light-emitting layer, and an electron transport layer may be used. Specifically, between the two electrodes of the anode 32 and the cathode 33, the light emitting layers 34, 35 are provided via the charge generation layer 38 without providing the hole transport layers 36, 37, or the positive electrode shown in FIG. A configuration in which only one of the hole transport layers 36 and 37 is provided may be employed. Further, in FIG. 5, without providing the second hole transport layer 37, a second light emitting layer 35 is provided at the position of the second hole transport layer 37, and the second light emitting layer 35 in FIG. A configuration in which an electron transport layer is provided at a position may be employed. In FIG. 5, an electron transport layer may be provided between the second light emitting layer 35 and the cathode 33, and further, an electron transport layer may be provided between the first light emitting layer 34 and the charge generation layer 38. It may be provided. As described above, the first light emitting layer 34 and the second light emitting layer 35 may be formed between the two electrodes of the anode 32 and the cathode 33 with at least the charge generation layer 38 interposed therebetween. At least one of the hole transport layers 36 and 37 may be provided on the anode 32 side of the light emitting layers 34 and 35, and at least one of the electron transport layers may be provided on the cathode 33 side of the light emitting layers 34 and 35 as necessary.

The light-emitting layers 34 and 35 of the organic electroluminescence element preferably have a fluorescent or phosphorescent property in the visible region and have a good film-forming property. In addition to Alq ₃ and Be-benzoquinolinol (BeBq ₂ ), 2 , 5-Bis (5,7-di-t-pentyl-2-benzooxazolyl) -1,3,4-thiadiazole, 4,4′-bis (5,7-bentyl-2-benzoxazolyl) ) Stilbene, 4,4′-bis [5,7-di- (2-methyl-2-butyl) -2-benzoxazolyl] stilbene, 2,5-bis (5,7-di-t-bentyl) -2-benzoxazolyl) thiophene, 2,5-bis ([5-α, α-dimethylbenzyl] -2-benzoxazolyl) thiophene, 2,5-bis [5,7-di- (2 -Methyl-2-butyl) -2-benzoxa Lyl] -3,4-diphenylthiophene, 2,5-bis (5-methyl-2-benzoxazolyl) thiophene, 4,4′-bis (2-benzoxazolyl) biphenyl, 5-methyl-2 -[2- [4- (5-methyl-2-benzoxazolyl) phenyl] vinyl] benzoxazolyl, 2- [2- (4-chlorophenyl) vinyl] naphtho [1,2-d] oxazole and the like A benzothiazole such as 2,2 ′-(p-phenylenedivinylene) -bisbenzothiazole, 2- [2- [4- (2-benzimidazolyl) phenyl] vinyl] benzimidazole, 2- [ 2- (4-carboxyphenyl) vinyl] benzimidazole-based fluorescent whitening agents such as benzimidazole, tris (8-quinolinol) aluminum, (8-quinolinol) magnesium, bis (benzo [f] -8-quinolinol) zinc, bis (2-methyl-8-quinolinolate) aluminum oxide, tris (8-quinolinol) indium, tris (5-methyl-8- (Quinolinol) aluminum, 8-quinolinol lithium, tris (5-chloro-8-quinolinol) gallium, bis (5-chloro-8-quinolinol) calcium, poly [zinc-bis (8-hydroxy-5-quinolinonyl) methane] Metal-chelated oxinoid compounds such as 8-hydroxyquinoline-based metal complexes and dilithium epindridione, 1,4-bis (2-methylstyryl) benzene, 1,4- (3-methylstyryl) benzene, , 4-bis (4-methylstyryl) benzene, distyrylbenzene, Styrylbenzene compounds such as 2,4-bis (2-ethylstyryl) benzene, 1,4-bis (3-ethylstyryl) benzene, 1,4-bis (2-methylstyryl) 2-methylbenzene; 5-bis (4-methylstyryl) pyrazine, 2,5-bis (4-ethylstyryl) pyrazine, 2,5-bis [2- (1-naphthyl) vinyl] pyrazine, 2,5-bis (4-methoxy Distilpyrazine derivatives such as styryl) pyrazine, 2,5-bis [2- (4-biphenyl) vinyl] pyrazine, 2,5-bis [2- (1-pyrenyl) vinyl] pyrazine, naphthalimide derivatives, Perylene derivatives, oxadiazole derivatives, aldazine derivatives, cyclopentadiene derivatives, styrylamine derivatives, coumarin derivatives, aromatic dimethylide And the like. Further, anthracene, salicylate, pyrene, coronene and the like are also used. Alternatively, a phosphorescent material such as fac-tris (2-phenylpyridine) iridium or a polymer light emitting material such as PPV (polyparaphenylenevinylene) or polyfluorene may be used. In addition, the first light emitting layer 34 and the second light emitting layer may be formed of the same member or different members.

As the hole transport layers 36 and 37 of the organic electroluminescence element, those having high hole mobility, transparency and good film forming property are preferable, and in addition to TPD, porphine, tetraphenylporphine copper, phthalocyanine, copper phthalocyanine , Porphyrin compounds such as titanium phthalocyanine oxide, 1,1-bis {4- (di-P-tolylamino) phenyl} cyclohexane, 4,4 ′, 4 ″ -trimethyltriphenylamine, N, N, N ′, N'-tetrakis (P-tolyl) -P-phenylenediamine, 1- (N, N-di-P-tolylamino) naphthalene, 4,4'-bis (dimethylamino) -2-2-2'-dimethyltriphenylmethane , N, N, N ', N'-tetraphenyl-4,4'-diaminobiphenyl, N, N'-diphenyl-N, N'-di-m- Aromatic tertiary amines such as lyl-4, 4'-diaminobiphenyl and N-phenylcarbazole, 4-di-P-tolylaminostilbene, 4- (di-P-tolylamino) -4'- [4- (di-P-tolylamino) styryl] stilbene compounds such as stilbene, triazole derivatives, oxazizazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, Annealed amine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styryl anthracene derivatives, fluorenone derivatives, hydrazone derivatives, silazane derivatives, polysilane-based aniline-based copolymers, polymer oligomers, styrylamine compounds, , Aromatic dimethylidin compounds And an organic material such as a polythiophene derivative such as poly-3,4 ethylenedioxythiophene (PEDOT) or poly-3-methylthiophene (PMeT). A polymer-dispersed hole transport layer in which a low molecular weight organic material for a hole transport layer is dispersed in a polymer such as polycarbonate is also used. Further, these hole transport materials can be used as a hole injection material or an electron block material.

Further, as the electron transport layer of the organic electroluminescence element, oxadiazole derivatives such as 1,3-bis (4-tert-butylphenyl-1,3,4-oxadiazolyl) phenylene (OXD-7), anthraquinodi A polymer material composed of a methane derivative, a diphenylquinone derivative, a silole derivative, or the like is used. Further, these electron transport materials can be used as an electron injection material or a hole blocking material.

Further, as the cathode 33 of the organic electroluminescence element, a metal or an alloy having a low work function is used, and a metal such as Al, In, Mg, and Ti, a Mg alloy such as a Mg—Ag alloy and a Mg—In alloy, An Al alloy such as an Al-Li alloy, an Al-Sr alloy, or an Al-Ba alloy is used.

These organic thin-film layers comprising a light-emitting layer, or a hole-transport layer optionally formed in the light-emitting layer, or an electron-transport layer also formed optionally in the light-emitting layer, are formed of a polymer material. When it is made of (polymer material), when another material is laminated on these organic thin film layers, damage at the time of film formation can be reduced. Even if a sputtering method, a resistance heating evaporation method, or the like is used as a film forming method of laminating another material on the organic thin film layer, if the organic thin film layer is formed of a polymer material, it is formed of a low molecular material. The damage received by the film formation is smaller than in the case where the film is formed. Further, even when a plurality of organic thin film layers are laminated, if the organic thin film layers to be laminated are made of a polymer material, a film forming method that causes less damage to the underlying layer can be selected.

Further, a film can be formed with a small amount of material, and a film can be formed with a uniform film thickness even in a large area, so that a large-area organic electroluminescence element can be formed. Further, the stability of the light-emitting layer against heat is increased, and the generation of defects and pinholes at the interface between the layers can be suppressed, so that an organic electroluminescent element with high stability can be formed.

In particular, when these organic thin film layers are composed of a polymer material (polymer material), damage during the film formation of the charge generation layer laminated thereon can be reduced, so that the layer in contact with the charge generation layer on the substrate side, That is, the charge generation layer can be formed on the organic thin film layer serving as a base during the formation of the charge generation layer by using an arbitrary process. Therefore, the selectivity of the process of forming the charge generation layer is increased, and the film can be formed by a simple process. Further, since the limitation of the film forming process of the charge generation layer is eliminated, the material of the charge generation layer can be appropriately selected from various materials, and the selectivity of the material of the charge generation layer itself can be expanded. In order to further alleviate the damage to the underlying organic thin film layer during film formation, if the charge generation layer is made of a polymer material, the damage to the underlying layer is smaller than that of a sputtering method or the like. The membrane method can be selected.

When these organic thin film layers (light-emitting layer, or hole transport layer, electron transport layer formed as necessary) are formed of a polymer material, a spin coating method, a casting method, a dipping method, And a wet film forming method such as a bar code method and a roll coating method. This eliminates the need for a large-scale vacuum device, so that it is possible to form a film with inexpensive equipment, to easily create a large-area organic electroluminescent element, and to make each layer of the organic electroluminescent element easy to use. The short circuit in the device can be suppressed and the organic electroluminescence device with high stability can be formed.

Note that the temperature of the heating and drying when forming the light emitting region should not exceed the glass transition temperature of any high molecular organic substance used for the formed layer, so as not to damage the previously formed layer. Is desirable. In particular, the drying temperature of the light emitting layer closer to the cathode (or the hole transporting layer or the electron transporting layer formed as necessary) is set at the drying temperature of the light emitting layer closer to the anode (or formed as needed). The temperature is preferably not higher than the glass transition temperature of the hole transport layer and the electron transport layer. In this case, the light emitting layer near the cathode is formed without damaging the light emitting layer near the anode. Therefore, an organic electroluminescence device having a multilayer structure can be easily formed.

For the charge generation layer 38 of the organic electroluminescence element, a material that is transparent to light emitted from the light emitting layer and that can efficiently inject a hole-electron pair is used. Metal oxides such as tin oxide) and V ₂ O ₅ (vanadium oxide), or organic substances such as 4F-TCNQ (tetrafluorotetracyanoquinodimethane) may be used. In particular, when the light-emitting layer is formed of a polymer organic film, it is preferable to use a polymer organic material for the charge generation layer. In this case, the light-emitting layer and the charge generation layer are formed in the same process while reducing damage during film formation. Therefore, an organic electroluminescence element in which a plurality of layers are stacked can be formed by a simple process.

他 In addition, for the charge generation layer 38, various members such as a conductor, a semiconductor, a dielectric, and an insulator, or a laminated film in which a plurality of materials are laminated can be used.

In particular, it is preferable to use a material called “wide gap semiconductor”. As the example _{materials, MoO X, SiO X, MgO} X, CaO X, ZnO X, TiO X, VO X, BiO X, FeO X, GaO X, GdO X, TaO X, NbO X, ScO X, WO X , ZrO _x , AlN, CdS, CdSe, CdTe, GaN, GaP, ZnSe. Specifically, it is preferable to use MoO ₃ , SiO, MgO, CaO, ZnO, TiO ₂ , or these widegap semiconductors. May be mixed, for example, a material such as SiO ₂ / MgO, MoO ₃ / Al ₂ O ₃ , or ZnO / SiO ₂ .

By the way, in the present invention, these materials called “wide gap semiconductors” are presumed to have at least a function of generating electric charges, but may be different from those of a so-called conductor. Although the detailed mechanism of the material called “widegap semiconductor” is not clear, in the present invention, especially, a layer formed of the material called “widegap semiconductor” is given a different definition from the charge generation layer. This is called a buffer layer. Therefore, when the charge generation layer 38 described above or below is formed of a material called a “wide gap semiconductor”, it is to be read as a buffer layer.

Here, in the organic electroluminescence device having the above configuration, when the charge generation layer 38 is a conductor, the work function of the charge generation layer 38 is set higher than the ionization potential of the second light emitting layer 35. Alternatively, when the charge generation layer 38 is a semiconductor, a dielectric, or an insulator, the electron affinity of the charge generation layer 38 is set lower than the electron affinity of the first light emitting layer 34, and the ionization potential of the charge generation layer 38 is set to the second. Is desirably set higher than the ionization potential of the light emitting layer 35.

This is because if the electron affinity of the charge generation layer 38 is lower than the electron affinity of the first light-emitting layer 34, the efficiency of electron injection from the charge generation layer 38 to the first light-emitting layer 34 increases, and the charge generation layer 38 If the work function is higher than the ionization potential of the second light emitting layer 35, or if the ionization potential of the charge generation layer 38 is higher than the ionization potential of the second light emission layer 35, the charge generation layer 38 to the second light emission layer Since the efficiency of injecting holes into 35 increases, the amount of light emitted from the first light emitting layer 34 and the second light emitting layer 35 increases, and as a result, the amount of light emitted from the organic electroluminescence element can be further increased.

When the charge generation layer 38 is made of an inorganic material, the ionization potential of the second light emitting layer 35 is generally higher than the ionization potential of the charge generation layer 38. In this case, if the potential difference between the two layers is made as small as possible, for example, the potential difference is made 0.6 eV or less, even if the ionization potential of the charge generation layer is lower than the ionization potential of the second light emitting layer, Thus, the efficiency of hole injection into the second light emitting layer 35 is not reduced, and high efficiency can be obtained.

The ionization potential is the energy required to completely extract one electron from neutral atoms or molecules, and the work function is the energy required to completely extract electrons from the crystal surface of a metal or semiconductor. Energy, the electron affinity is the energy released to add one electron to a neutral atom or molecule, and is generally represented by the difference from the vacuum level. This is synonymous with the magnitude of the absolute value of the energy value, and a high work function indicates that the absolute value of the energy value of the work function is large.

{Circle around (2)} By using such an organic electroluminescence element as a light source of an exposure unit, it is possible to obtain a light amount required for exposure without increasing the size of the apparatus.

Furthermore, by using such an exposure apparatus for an image forming apparatus, a compact image forming apparatus can be obtained.

As shown in FIG. 6, the charge generation layer 38 includes a first generation layer 38a located on the first light emitting layer 34 side and a second generation layer 38b located on the second light emitting layer 35 side. It may have a layered structure or a multilayer structure having more layers.

In this case, it is preferable to set the first generation layer 38a to a lower electron affinity than the second generation layer 38b and set the second generation layer 38b to a higher ionization potential than the first generation layer 38a. .

(4) The first generation layer (the first generation layer 38a or the second generation layer 38b) is preferably formed by resistance heating. This is to prevent the first light emitting layer 38a from being damaged when, for example, forming the first generating layer 38a on the first light emitting layer 34. The generation layer formed thereafter can be formed by sputtering, plasma CVD, ion beam, electron beam, or the like.

Here, when a dielectric material is used for the charge generation layer 38, the relative permittivity of the charge generation layer 38 is set to be equal to or higher than the relative permittivity of the first light emitting layer 34 and the second light emitting layer 35. Is preferably about 8 to 10, and the relative permittivity of the first light emitting layer 34 and the second light emitting layer 35 is preferably about 3.

Further, the light emitting layer and the hole transporting layer (the first light emitting layer 34 when the anode 32 is formed first) are located between the electrode (the anode 32 or the cathode 33) formed first and the charge generating layer 38. When the first hole transport layer 36 and the cathode 34 are formed first, the layer in contact with the charge generation layer 38 in the second light emitting layer 35 and the second hole transport layer 37) Among the layers including the layer, the layer in contact with the charge generation layer 38 is preferably made of a polymer that is not easily damaged when the charge generation layer 38 is formed. In the case of a single-layer structure of only the light-emitting layer, a two-layer structure of the light-emitting layer and the electron transport layer, and a three-layer structure of the hole-transport layer, the light-emitting layer, and the electron transport layer, the charge generation layer 38 includes The contacting layer is composed of a polymer.

(Embodiment 2)
FIG. 7 is a cross-sectional view illustrating a main part of an organic electroluminescence element used as a light source of an exposure unit of a color image forming apparatus according to Embodiment 2 of the present invention. In the present embodiment, the device configuration of the color image forming apparatus is the same as that shown in FIGS. 1 to 4 used in the first embodiment.

The illustrated organic electroluminescent element as an exposure light source includes an anode 32, a first hole transport layer 36, a first light emitting layer 34, a cathode 33, a charge generation layer 38, and a second hole transport layer on a substrate 31. Layer 37, second light emitting layer 35, charge generating layer 38, third hole transport layer 36, third light emitting layer 34, charge generating layer 38, fourth hole transport layer 37, fourth light emitting layer 35 and a cathode 33 are sequentially laminated. In the present embodiment, the structure is such that four light emitting layers are arranged via the charge generation layer 38, and the first and third light emitting layers and the second and fourth light emitting layers are provided. Have the same configuration, but the number and configuration of the light-emitting layers are not limited to this, and can be freely configured by disposing a charge generation layer between light-emitting layers of any configuration. Can be.

When a direct current voltage or a direct current is applied with the anode 32 of the organic electroluminescence element having such a configuration as a positive pole and the cathode 33 as a negative pole, the first light emitting layer 34 is applied with the anode 32 on the substrate 31 side. Holes are injected through the first hole transport layer 36, and electrons are injected from the charge generation layer 38 interposed between the first light emitting layer and the second light emitting layer. Holes are injected from the charge generation layer 38 sandwiched between the first light emitting layer and the second light emitting layer via the second hole transporting layer 37, and the second light emitting layer and the third light emitting layer Electrons are injected from the charge generation layer 38 interposed between the layers, and the third light emitting layer 34 has a third hole transporting from the charge generation layer 38 interposed between the second light emitting layer and the third light emitting layer. Holes are injected through the layer 36 and the third light emitting layer and the fourth light emitting layer Electrons are injected from the interposed charge generation layer 38, and the fourth light emitting layer 37 has a third light emitting layer and a fourth hole transport layer 38 interposed between the charge generating layer 38 interposed between the fourth light emitting layers. And electrons are injected from the cathode 33. In the first, second, third, and fourth light emitting layers 34 (35), the holes and electrons injected in this manner recombine, and the excitons generated thereby are excited. A light emission phenomenon occurs when the state transitions from to the ground state.

Therefore, even with such a configuration, light emission is performed in the plurality of light-emitting layers of the first, second, third, and fourth light-emitting layers 34 (35), so that the amount of light emitted from the organic electroluminescence element is increased. be able to.

In the present embodiment, the organic thin film layers are each constituted by a two-layer structure of the hole transport layer 36 (37) and the light emitting layer 34 (35). In addition to this structure, FIG. As shown in FIG. 9, a single-layer structure of only a light-emitting layer, or a two-layer structure of a light-emitting layer and an electron transport layer, and a three-layer structure of a hole-transport layer, a light-emitting layer, and an electron transport layer as shown in FIG. Either structure may be used. FIGS. 8 and 9 are cross-sectional views showing a main part of another example of the organic electroluminescence element used as the light source of the exposure unit of the color image forming apparatus according to Embodiment 2 of the present invention. In FIG. 9, reference numeral 40 denotes an electron transport layer. Further, in the case of the two-layer structure of the light emitting layer and the electron transport layer, the first to fourth hole transport layers 36 (37) shown in FIG. 9 are not provided.

In the present embodiment, the light emitting layer and the hole transport layer located between the anode and the cathode are preferably made of a polymer that is not easily damaged. In the case of a single-layer structure of only the light-emitting layer, a two-layer structure of the light-emitting layer and the electron transport layer, and a three-layer structure of the hole transport layer, the light-emitting layer, and the electron transport layer, any of these layers is formed of a polymer. Is good. Further, all of the light emitting layer and the hole transport layer may be composed of a polymer. In this case, the charge generation layer may be composed of a polymer organic film. Further, in the case of using a polymer, the light emitting layer or the charge generation layer is preferably formed by a wet film formation method in order to reduce material loss at the time of preparation, and is close to the cathode in the wet film formation method. The drying temperature when drying the organic film on the side is preferably a temperature that does not exceed the glass transition temperature of the organic film on the side closer to the anode.

In the above description, the organic electroluminescent element as the exposure light source is driven by a direct current, but may be driven by an alternating voltage or an alternating current, or a pulse wave.

Further, the exposure light, which is light emitted by the organic electroluminescence element, is extracted from the substrate 31 side, but may be extracted from the side opposite to the substrate 31 (here, the cathode 33) or from the side. .

In the above description, the case where the present invention is applied to a color image forming apparatus has been described. However, the present invention can also be applied to a monochrome image forming apparatus such as black. Further, when applied to a color image forming apparatus, the developed colors are not limited to four colors of yellow, magenta, cyan and black.

(Embodiment 3)
FIG. 10 is a cross-sectional view illustrating a main part of an organic electroluminescence element used as a light source of an exposure unit of a color image forming apparatus according to Embodiment 3 of the present invention. In the present embodiment, the device configuration of the color image forming apparatus is the same as that shown in FIGS. 1 to 4 used in the first embodiment.

The illustrated organic electroluminescent element as an exposure light source includes an anode 32, a first hole transport layer 36, a first light-emitting layer 34, a cathode 33, an insulating layer 39, an anode 32, and a second positive electrode 32 on a substrate 31. It has a structure in which the hole transport layer 37, the second light emitting layer 35, and the cathode 33 are sequentially laminated.
That is, the anode 32 and the cathode 33 have a structure in which they are alternately arranged via the light emitting layer 34 (35) and the hole transport layer 36 (37).

It is not necessary that all anodes and cathodes sandwich the light emitting layer or the like. For example, as shown in the relationship between the anode 32 and the cathode 33 which are the intermediate layers in FIG. Layers may be interposed.

When a DC voltage or a DC current is applied with the two anodes 32 of the organic electroluminescent device having such a configuration as the positive pole and the two cathodes 33 as the negative pole, the first light emitting layer 34 has the substrate 31 side The holes are injected from the anode 32 of the first through the first hole transport layer 36, and the electrons are injected from the cathode 33 on the insulating layer 39 side. Electrons are injected and holes are injected from the anode 32 on the insulating layer 39 side via the second hole transport layer 37. In the first light-emitting layer 34 and the second light-emitting layer 35, the holes and electrons injected as described above are recombined, and the excitons generated thereby move from the excited state to the ground state. At that time, a light emission phenomenon occurs.

Therefore, even with such a configuration, light emission is performed by the plurality of light-emitting layers of the first light-emitting layer 34 and the second light-emitting layer 35, so that the amount of light emitted by the organic electroluminescent element can be increased.

Note that the insulating layer 39 may not be formed. Also, in this embodiment, the organic thin film layers are each constituted by a two-layer structure of the hole transport layer 36 (37) and the light emitting layer 34 (35). , A two-layer structure of a light-emitting layer and an electron transport layer, and a three-layer structure of a hole transport layer, a light-emitting layer, and an electron transport layer.

Further, in the case of the drawing, two layers of the anode 32 and the cathode 33 are alternately formed, but at least one of them may be alternately arranged.

In the present embodiment, the light emitting layer and the hole transport layer located between the first electrode and the second electrode are preferably made of a polymer which is not easily damaged. In the case of a single-layer structure of only the light-emitting layer, a two-layer structure of the light-emitting layer and the electron transport layer, and a three-layer structure of the hole transport layer, the light-emitting layer, and the electron transport layer, any of these layers is formed of a polymer. Is good.

In the above description, the organic electroluminescent element as the exposure light source is driven by a direct current, but may be driven by an alternating voltage or an alternating current, or a pulse wave.

Further, the exposure light, which is light emitted by the organic electroluminescence element, is extracted from the substrate 31 side, but may be extracted from the side opposite to the substrate 31 (here, the cathode 33) or from the side. .

In the above description, the case where the present invention is applied to a color image forming apparatus has been described. However, the present invention can also be applied to a monochrome image forming apparatus such as black. Further, when applied to a color image forming apparatus, the developed colors are not limited to the four colors of yellow, magenta, cyan and black.

The organic electroluminescence element of the present invention, the exposure apparatus and the image forming apparatus using the same, the organic electroluminescence element used as a light emitting element in various devices that need to increase the light emission amount of the organic electroluminescence element, and the same The present invention can also be applied to the use of an exposure apparatus and an image forming apparatus using the same.

1 is a schematic diagram illustrating a configuration of a color image forming apparatus according to Embodiment 1 of the present invention. Explanatory diagram showing an exposure unit in the color image forming apparatus of FIG. 1 in detail. FIG. 2 is an explanatory diagram showing a photosensitive unit in the color image forming apparatus of FIG. 1 in detail. Explanatory diagram showing a developing unit in the color image forming apparatus of FIG. 1 in detail. FIG. 2 is a cross-sectional view showing a main part of an organic electroluminescence element used as a light source of the exposure unit in FIG. Sectional drawing which shows the principal part of the organic electroluminescent element which is a modification used as the light source of the exposure part of FIG. Sectional view showing a main part of an organic electroluminescence element used as a light source of an exposure unit of a color image forming apparatus according to Embodiment 2 of the present invention. Sectional drawing which shows the principal part of the organic electroluminescent element of another example used as the light source of the exposure part of the color image forming apparatus in Embodiment 2 of this invention. Sectional drawing which shows the principal part of the organic electroluminescent element of another example used as the light source of the exposure part of the color image forming apparatus in Embodiment 2 of this invention. Sectional view showing a main part of an organic electroluminescence element used as a light source of an exposure unit of a color image forming apparatus according to Embodiment 3 of the present invention. Sectional view showing main parts of a conventional organic electroluminescence element

Explanation of reference numerals

6,7,8,9 Exposure unit (exposure device)
6d, 7d, 8d, 9d Organic electroluminescence element 31 Substrate 32 Anode 33 Cathode 34 First light emitting layer 35 Second light emitting layer 36 First hole transport layer 37 Second hole transport layer 38 Charge generation layer 38a First generation layer 38b Second generation layer 39 Insulation layer 40 Electron transport layer

Claims (22)

An anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, a light emitting layer formed between the anode and the cathode, and having a plurality of light emitting regions, A charge generation layer that injects electrons into the light emitting layer and injects holes into the light emitting layer on the side closer to the cathode; and a light emitting layer on the side closer to the anode that has a work function of the charge generating layer closer to the anode. An organic electroluminescent device, wherein the organic electroluminescent device is set to have a higher ionization potential. An anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, a light emitting layer formed between the anode and the cathode, and having a plurality of light emitting regions, A charge-generating layer that injects electrons into the light-emitting layer and injects holes into the light-emitting layer on the side near the cathode; and a light-emitting layer on the side near the anode that has an electron affinity of the charge-generating layer. Wherein the charge generation layer is set to have a lower ion affinity than that of the light-emitting layer closer to the cathode. An anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, a light emitting layer formed between the anode and the cathode, and having a plurality of light emitting regions, A charge generation layer that injects electrons into the light emitting layer and injects holes into the light emitting layer on the side near the cathode, on the substrate, the electron affinity of the light emitting layer near the anode and the electron on the charge generating layer. An organic electroluminescent device, wherein a potential difference with an affinity and a potential difference between an ionization potential of a light emitting layer near a cathode and an ionization potential of a charge generation layer are set to 0.6 eV or less. The charge generation layer has at least a first generation layer located on the light-emitting layer side closer to the anode and a second generation layer located on the light-emitting layer side closer to the cathode.
The first generation layer is set to a lower electron affinity than the second generation layer, and the second generation layer is set to a higher ionization potential than the first generation layer. The organic electroluminescence device according to any one of claims 1 to 3. The organic electroluminescent device according to claim 4, wherein the generating layer formed first is formed by resistance heating. The organic electroluminescence according to any one of claims 1 to 5, wherein the charge generation layer is made of a dielectric, and a relative permittivity of the charge generation layer is equal to or higher than a relative permittivity of the light emitting layer. element. The organic electroluminescent device according to any one of claims 1 to 6, wherein the light emitting layer near the anode and the light emitting layer near the cathode are formed of the same member. . An anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, and a light-emitting region formed between the anode and the cathode with a buffer layer made of a wide gap semiconductor interposed therebetween. An organic electroluminescent device comprising a plurality of light emitting layers. Of the light emitting layer, or a hole transporting layer formed on the light emitting layer as needed, or an organic thin film layer composed of an electron transporting layer, a layer which is in contact with the charge generation layer on the substrate side is high. The organic electroluminescent device according to any one of claims 1 to 8, wherein the organic electroluminescent device is formed of a molecular material. The light-emitting layer, or a hole transport layer formed as needed in the light-emitting layer, or all layers of an organic thin film layer formed of an electron transport layer are formed of a polymer material. The organic electroluminescence device according to claim 1. The organic electroluminescence device according to any one of claims 1 to 10, wherein the charge generation layer comprises a polymer organic film. The organic electroluminescence device according to any one of claims 9 to 11, wherein the organic thin film layer and the charge generation layer are formed by a wet film forming method. The drying temperature of the organic thin film layer on the side near the cathode is a temperature not exceeding the glass transition temperature of the organic thin film layer on the side near the anode. 3. The organic electroluminescent device according to 1.). An exposure apparatus using the organic electroluminescence element according to claim 1 as a light source. An anode that is an electrode for injecting holes, a cathode that is an electrode for injecting electrons, a light emitting layer formed between the anode and the cathode, and having a plurality of light emitting regions, An exposure apparatus, wherein an organic electroluminescence element having a charge generation layer for injecting electrons into the light emitting layer and injecting holes into the light emitting layer nearer to the cathode on a substrate is used as a light source. The exposure apparatus according to claim 15, wherein the light emitting layer near the anode and the light emitting layer near the cathode are formed of the same member. 17. The layer containing the light emitting layer located between the electrode and the charge generation layer formed first, wherein the layer in contact with the charge generation layer is made of a polymer. The exposure apparatus according to claim 1. A plurality of anodes, which are electrodes for injecting holes, and a plurality of cathodes, which are arranged alternately with the anodes and are electrodes for injecting electrons, are formed between the anode and the cathode, respectively, and have a light emitting region. An exposure apparatus, wherein an organic electroluminescence element having a plurality of light-emitting layers on a substrate is used as a light source. 19. The exposure apparatus according to claim 18, wherein the layer including the light emitting layer located between the first electrode formed and the second electrode formed is made of a polymer. The exposure apparatus according to any one of claims 14 to 19, wherein the organic electroluminescence element is driven by an AC current, an AC voltage, or a pulse wave. The exposure apparatus according to any one of claims 14 to 20, wherein exposure light is extracted from a side surface of the organic electroluminescence element. An exposure apparatus according to any one of claims 14 to 21,
A photosensitive member on which an electrostatic latent image is formed by the exposure device.

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