Image forming apparatus

Abstract

An image forming apparatus includes an exposure light source including an organic light-emitting element, and a photoreceptor configured to receive light emitted from the organic light-emitting element, where an emission intensity of the organic light-emitting element at an end of supply of a current to the organic light-emitting element is defined as L0, a time period from the end of the supply of current to the organic light-emitting element to the end of the organic light-emitting element is defined as T1, a time period from the start of the supply of current to the organic light-emitting element to the end of the supply of current to the organic light-emitting element is defined as T2, and T2 is greater than T1.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus. Background Art

[0002] Image forming devices using an electrophotographic mode are widely and commonly used as copiers, fax machines, and printers. This type of image forming device includes an exposure light source including a light-emitting unit. The light-emitting element used is an LED (Light Emitting Diode) or an organic light-emitting diode (OLED). This light-emitting element emits light that is used to expose a photosensitive drum (hereinafter referred to as a "photosensitive body") using an organic electrophotographic photoconductor (OPC) to print an image corresponding to the latent image formed on the photosensitive drum onto a recording sheet.

[0003] Japanese Patent Laid-Open No. 2007-128040 (PTL 1) describes an image forming apparatus including an exposure light source using an organic light emitting element (hereinafter may be referred to as an "organic electroluminescent element" or "organic EL element").

[0004] Organic light-emitting elements continue to emit light even after the supply current ends, and the light intensity decays over time. Therefore, when using an organic light-emitting element as an exposure light source, it is necessary to consider the light emitted from the organic light-emitting element after the supply current ends (hereinafter referred to as "afterglow").

[0005] However, PTL 1 does not propose the relationship between the exposure time of a photoreceptor using an organic light-emitting element (hereinafter referred to as "organic electroluminescent element" or "organic EL element") and the time from the end of current supply to the organic light-emitting element to quenching, and therefore there are problems with image quality. Summary of the Invention

[0006] The present disclosure provides an image forming apparatus that can provide high image quality.

[0007] An image forming apparatus according to one aspect of the present disclosure includes an exposure light source including an organic light-emitting element and a photoreceptor configured to receive light emitted from the organic light-emitting element, wherein the luminous intensity of the organic light-emitting element at the end of supplying current to the organic light-emitting element is defined as L0, a time period from the end of supplying current to the organic light-emitting element to the quenching of the organic light-emitting element is defined as T1, and a time period from the start of supplying current to the organic light-emitting element to the end of supplying current to the organic light-emitting element is defined as T2, and T1 and T2 satisfy the relationship of formula (a):

[0008] (a)T1 <T2。

[0009] An image forming apparatus according to another aspect of the present disclosure includes an exposure light source including an organic light-emitting element and a photoreceptor configured to receive light emitted from the organic light-emitting element, wherein the luminous intensity of the organic light-emitting element at the end of supplying current to the organic light-emitting element is defined as L0, a time period from the end of supplying current to the organic light-emitting element to the quenching of the organic light-emitting element is defined as T1, and a time period from the end of supplying current to the organic light-emitting element to the start of supplying current to the organic light-emitting element is defined as T3, and T1 and T3 satisfy the relationship of formula (c):

[0010] (c)T1 <T3。

[0011] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1A is a schematic diagram of an example of an image forming apparatus according to an embodiment of the present disclosure.

[0013] Figure 1B is a schematic diagram of an example of an exposure light source in an image forming apparatus according to an embodiment of the present disclosure. Figure 1C is a schematic diagram of an example of an exposure light source in an image forming apparatus according to an embodiment of the present disclosure.

[0014] Figure 2 is a graph showing light emission intensity with respect to time during operation of the image forming apparatus according to the embodiment.

[0015] Figure 3 is a schematic diagram showing the form of a light emitting device according to the embodiment.

[0016] Figure 4A is a schematic perspective view of a head substrate. Figure 4B The diagram shows the arrangement of a plurality of light emitting elements disposed on the head substrate. Figure 4C yes Figure 4B An enlarged view of a portion of . DETAILED DESCRIPTION

[0017] In this specification, the luminous intensity of the organic light-emitting element at the end of current supply to the organic light-emitting element is defined as L0; the time period from the end of current supply to the organic light-emitting element to the quenching of the organic light-emitting element is defined as T1; the time period from the start of current supply to the organic light-emitting element to the end of current supply to the organic light-emitting element is defined as T2; and the time period from the end of current supply to the organic light-emitting element to the start of current supply to the organic light-emitting element is defined as T3.

[0018] Note that "quenching of the organic light-emitting element" refers to a state in which the emission intensity decreases, making it impossible for the organic light-emitting element to form a latent image on the photoreceptor. For example, the organic light-emitting element may be quenched when the emission intensity reaches L0 / 2, L0 / e, or L0 / 10. e is the Napier number.

[0019] In this specification, the host material is the compound with the highest mass ratio among the compounds constituting the light-emitting layer. The guest material is a compound constituting the light-emitting layer that has a lower mass ratio than the host material and primarily contributes to the emission of light. The auxiliary material is a compound constituting the light-emitting layer that has a lower mass ratio than the host material and assists the guest material in emitting light. Note that the auxiliary material is also referred to as a second host. The host material may also be referred to as a first compound. The auxiliary material may also be referred to as a second compound.

[0020] Image forming equipment

[0021] An image forming apparatus according to an embodiment will be described with reference to the drawings.

[0022] Figure 1A is a schematic diagram illustrating an example of an image forming apparatus according to an embodiment of the present disclosure. Image forming apparatus 40 is an electrophotographic image forming apparatus and includes a photoreceptor 27, an exposure light source 28, a charging unit 30, a developing unit 31, a transfer unit 32, a conveying roller 33, and a fixing unit 35. Photoreceptor 27 and exposure light source 28 are arranged facing each other. Exposure light source 28 emits light 29 to form an electrostatic latent image on the surface of photoreceptor 27. Exposure light source 28 includes a single organic light emitting element or a plurality of organic light emitting elements. Specifically, light 29 emitted from the organic light emitting element of exposure light source 28 is received by photoreceptor 27, thereby forming an electrostatic latent image on the surface of photoreceptor 27. Exposure light source 28 may further include a lens array. Exposure light source 28 may include a plurality of light emitting element rows or a single light emitting element row. Developing unit 31 includes toner, etc. Charging unit 30 charges photoreceptor 27. Transfer unit 32 transfers the developed image to recording medium 34. Conveying roller 33 conveys recording medium 34. The recording medium 34 is, for example, paper. The fixing unit 35 fixes the image formed on the recording medium 34.

[0023] Figure 1B and Figure 1C Schematic diagram of exposure light source 28 in which multiple light-emitting units 36 are arranged on a substrate. Arrow 37 indicates a direction parallel to the axis of the photoreceptor and represents the row direction in which light-emitting units 36, including organic light-emitting elements, are arranged. The row direction is the same as the direction of the rotation axis of photoreceptor 27. This direction can also be referred to as the long axis direction of photoreceptor 27. Figure 1B A form is shown in which the light emitting units 36 are arranged in the long-axis direction of the photoconductor 27 . Figure 1C Shown with Figure 1B A different configuration is provided, in which the light-emitting cells 36 in the first and second rows are arranged alternately in the row direction. The first and second rows are arranged at different positions in the column direction. In the first row, the plurality of light-emitting cells 36 are arranged with gaps between them. In the second row, the light-emitting cells 36 are arranged at positions corresponding to the gaps between the light-emitting cells 36 in the first row. In other words, the plurality of light-emitting cells 36 are also arranged with gaps between them in the column direction. Figure 1C The arrangement in may also be referred to as, for example, a lattice pattern, a houndstooth check pattern, or a checkered pattern.

[0024] The image forming apparatus according to the embodiment has the following feature (a) or (b).

[0025] (a) Organic light-emitting element meets T1 <T2

[0026] (b) The organic light-emitting element satisfies T1 <T3

[0027] Hereinafter, these will be described.

[0028] (a) Organic light-emitting element meets T1 <T2

[0029] The image forming apparatus according to the embodiment has a feature in which T2 is longer than T1. Due to this feature, the image forming apparatus according to the embodiment can provide high image quality.

[0030] Reference Figure 2 , the image forming apparatus according to the embodiment will be described in detail. Figure 2 In the , the moment when the luminous intensity of the organic light emitting element reaches L0 / e is defined as the quenching moment of the organic light emitting element. Figure 2 In the figure, t1 and t1' are the moments when current is supplied to the organic light-emitting element, t2 and t2' are the moments when the current supply to the organic light-emitting element ends, and t3 and t3' are the moments when the organic light-emitting element is quenched. The time period from t1 to t2 may also be referred to as the first light-emitting time period; the time period from t1' to t2' may also be referred to as the second light-emitting time period; and the subsequent time periods may be referred to as the third light-emitting time period and the fourth light-emitting time period. T1 is the time period from t2 to t3 or the time period from t2' to t3'. T2 is the time period from t1 to t2 or the time period from t1' to t2'. In this specification, T1 may be referred to as the afterglow lifetime.

[0031] Notice, Figure 2A non-limiting embodiment is shown in which the organic light-emitting element emits light with the same light-emitting intensity in the first light-emitting period and in the second light-emitting period. Alternatively, the light-emitting intensities of the first light-emitting period and the second light-emitting period may be different. Specifically, the light-emitting intensity of the first light-emitting period may be higher than that of the second light-emitting period, or the light-emitting intensity of the first light-emitting period may be lower than that of the second light-emitting period. The light-emitting intensity may vary during the first (second) light-emitting period.

[0032] The image forming apparatus according to the embodiment selects an organic light-emitting element (pixel) for light emission based on data of an image to be formed and exposes a rotating photoreceptor 27 to form a latent image. At this time, after the supply of current to the organic light-emitting element ends, afterglow may be emitted to the photoreceptor 27, thereby forming an unexpected latent image on the photoreceptor 27. To solve this problem, in the organic light-emitting element of the image forming apparatus according to the embodiment, T1 is made shorter than T2, thereby reducing the occurrence of vertical stripes, ghost images, etc. Due to this feature, the formation of an unexpected latent image on the photoreceptor 27 can be suppressed, and the image forming apparatus according to the embodiment can provide high image quality.

[0033] In the image forming apparatus according to the embodiment, the value of T2 / T1 is greater than 1.0, or 10 or more, or 20 or more, or 100 or more. The value of T2 / T1 may be 1000 or less, may be 500 or less, or may be 100 or less. Specifically, the value of T2 / T1 may be 1.0 < T2 / T1 ≤ 100, may be 1.0 < T2 / T1 ≤ 500, or may be 1.0 < T2 / T1 ≤ 1000. T1 may be 10 μs or less, may be 2 μs or less, may be 1 μs or less, may be less than 1 μs, may be 50 ns or less, or may be 10 ns or less.

[0034] (b) The organic light-emitting element satisfies T1 < T3

[0035] The image forming apparatus according to the embodiment has a feature in which T3 is longer than T1. Due to this feature, the image forming apparatus according to the embodiment can provide high image quality.

[0036] Refer to Figure 2 , the image forming apparatus according to the embodiment will be specifically described. In Figure 2 , the moment when the light-emitting intensity of the organic light-emitting element reaches L0 / e is defined as the quenching moment of the organic light-emitting element. In Figure 2Among them, t1 and t1' are the times when current is supplied to the organic light-emitting element, t2 and t2' are the times when the supply of current to the organic light-emitting element ends, and t3 and t3' are the times when the organic light-emitting element quenches. The time period from t1 to t2 can also be referred to as the first light-emitting time period; the time period from t1' to t2' can also be referred to as the second light-emitting time period; and the subsequent time periods can be referred to as the third light-emitting time period and the fourth light-emitting time period. T1 is the time period from t2 to t3 or from t2' to t3'. T3 is the time period from t2 to t1' or the time period from t2' to the start of current supply to the organic light-emitting element in the third light-emitting time period. In this specification, T1 can be referred to as the afterglow lifetime and T3 can be referred to as the light-emitting interval time period.

[0037] Note that Figure 2 FIG. shows a non-limiting embodiment in which the organic light-emitting element emits light with the same light-emitting intensity in the first light-emitting time period and in the second light-emitting time period. Optionally, the light-emitting intensities of the first light-emitting time period and the second light-emitting time period can be different. Specifically, the light-emitting intensity of the first light-emitting time period can be higher than that of the second light-emitting time period, or the light-emitting intensity of the first light-emitting time period can be lower than that of the second light-emitting time period. The light-emitting intensity can vary during the first (second) light-emitting time period.

[0038] The image forming apparatus according to an embodiment selects the organic light-emitting elements (pixels) for light emission based on the data of the image to be formed and exposes the rotary photoreceptor 27 to form a latent image. At this time, after the supply of current to the organic light-emitting element ends, the afterglow can be emitted to the photoreceptor 27, thereby forming an unintended latent image on the photoreceptor 27. Specifically, the afterglow from the organic light-emitting element to the photoreceptor 27 causes the formation of a latent image, which may cause the occurrence of vertical stripes or ghost images, etc. To solve this problem, in the organic light-emitting element of the image forming apparatus according to the embodiment, T1 is made shorter than T3. Due to this feature, the formation of an unintended latent image on the photoreceptor 27 can be suppressed, so that the image forming apparatus according to the embodiment can provide high image quality.

[0039] In the image forming apparatus according to the embodiment, the value of T3 / T1 is greater than 1.0, or 5.0 or more, or 10 or more, or 15 or more, or 20 or more, or 50 or more. The value of T3 / T1 can be 1.0 < T3 / T1 ≤ 5, can be 1.0 < T3 / T1 ≤ 15, can be 1.0 < T3 / T1 ≤ 20, or can be 1.0 < T3 / T1 ≤ 50. T1 can be 10 μs or less, can be 2 μs or less, can be 1 μs or less, can be less than 1 μs, can be 50 ns or less, or can be 10 ns or less.

[0040] Note that an image forming apparatus according to another embodiment may have both features (a) and (b). An image forming apparatus having both features (a) and (b) can provide higher image quality.

[0041] Note that the image forming apparatus according to the embodiment may further have the following features: When the image forming apparatus has such features, it may have any one of the following (c) to (g), or may have a plurality of features among (c) to (g).

[0042] (c) The organic light-emitting element has a top emission structure

[0043] (d) The organic light-emitting element includes a light-emitting layer containing a light-emitting material and the light-emitting material emits fluorescence

[0044] (e) The organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits phosphorescence

[0045] (f) The organic light-emitting element includes a light-emitting layer containing a light-emitting material and the light-emitting material emits delayed fluorescence

[0046] (g) The organic light-emitting element includes a plurality of pixels arranged two-dimensionally at a high density.

[0047] Hereinafter, these features will be described.

[0048] (c) The organic light-emitting element has a top emission structure

[0049] The image forming apparatus according to the embodiment may have a top emission structure. The top emission structure provides higher light extraction efficiency than the bottom emission structure. The bottom emission structure is a light emission form in which light is extracted from the pixel circuit side described later. The top emission structure is a light emission form in which light is extracted from the side opposite to the pixel circuit side described later.

[0050] In the embodiment, the organic light emitting element may have an interference structure. Specifically, when the organic light emitting element includes a reflective layer, a first electrode, a light emitting layer and a second electrode in sequence from the substrate side, the optical distance between the reflective electrode and the light emitting layer is set so that the emission wavelength is enhanced. In this case, a layer formed of an insulating material or a transparent material such as ITO (indium tin oxide) or IZO (indium zinc oxide) can be configured between the reflective layer and the first electrode. When the organic light emitting element includes a first electrode, a light emitting layer and a second electrode in sequence from the substrate side, the light emitted from the light emitting layer can be enhanced between the first electrode and the second electrode. In this case, the first electrode can reflect the light emitted from the light emitting layer.

[0051] (d) The organic light-emitting element includes a light-emitting layer containing a light-emitting material and the light-emitting material emits fluorescence

[0052] The image forming apparatus according to the embodiment may have a configuration in which the organic light emitting element includes a light emitting layer containing a light emitting material, and the light emitting material emits fluorescent light.

[0053] Generally, it is known that luminescence from a singlet excited state has a very short afterglow lifetime. As described above, a short afterglow lifetime can provide high image quality, and therefore luminescence from a singlet excited state can be used. Specifically, luminescence from a singlet excited state can be fluorescent luminescence.

[0054] The image forming apparatus according to the embodiment can emit light with high luminous intensity, and therefore the luminescent material needs to be stable during repeated luminescence. Therefore, the fluorescent luminescent material can be a luminescent material having a condensed polycyclic hydrocarbon skeleton; specifically, the skeleton can have a perylene skeleton. In particular, the fluorescent luminescent material can be a hydrocarbon compound. This is because hydrocarbon compounds have high bond stability and can suppress degradation during repeated luminescence. Non-limiting specific examples of fluorescent luminescent materials include the exemplary compounds RD1 to RD6 described below.

[0055] From another perspective, for a light-emitting material, a freely rotatable single bond may be a carbon-carbon bond, a freely rotatable single bond may be an sp2 carbon-sp2 carbon bond, all freely rotatable single bonds may be carbon-carbon bonds, and all freely rotatable single bonds may be sp2 carbon-sp2 carbon bonds. In this specification, a freely rotatable single bond refers to a single bond of "AB" in which unit A and unit B are bound via a single bond and unit A and unit B are not fused. Units A and B may be atoms such as carbon atoms or nitrogen atoms, or molecules such as benzene or carbazole. Table 1 describes the bond energies of the bonds.

[0056] Table 1

[0057]

[0058] F1 and F2 having carbon-nitrogen bonds have a bond energy of 3.9 eV. On the other hand, F3 having a freely rotatable carbon-carbon bond has a bond energy of 4.5 eV, and F4 having a freely rotatable bond between sp2 carbon atoms has a bond energy of 5.0 eV.

[0059] Therefore, when the freely rotatable single bond is a carbon-carbon bond, the skeleton is less likely to decompose and can be more useful. Among carbon-carbon bonds, the bond between sp2 carbons has a particularly high bond energy. Therefore, a skeleton in which the freely rotatable single bond is an sp2 carbon-sp2 carbon bond is even less likely to decompose and can therefore be more useful.

[0060] The image forming apparatus according to the embodiment may include a first organic compound different from the light-emitting material emitting fluorescence in the light-emitting layer of the organic light-emitting element. The first organic compound may be a compound having a lower excitation singlet energy than the lower excitation singlet energy of the light-emitting material emitting fluorescence. The first organic compound may have a condensed polycyclic hydrocarbon skeleton, particularly a naphthalene skeleton, an anthracene skeleton, a phenanthrene skeleton, a fluorene skeleton, a pyrene skeleton, a triphenylene skeleton, In the first organic compound, the freely rotatable single bond may be a carbon-carbon bond, the freely rotatable single bond may be an sp2 carbon-sp2 carbon bond, all freely rotatable single bonds may be carbon-carbon bonds, and all freely rotatable single bonds may be sp2 carbon-sp2 carbon bonds.

[0061] The image forming apparatus according to the embodiment may include a delayed fluorescent material different from a fluorescent emitting material in the light-emitting layer of the organic light-emitting element. Specifically, the delayed fluorescent material is a compound in which the difference between the lowest excited singlet energy and the lowest excited triplet energy is 0.20eV or less. The use of a delayed fluorescent material can provide a reverse intersystem crossing (reverse intersystem crossing) of an exciton from a triplet state to a singlet state. The delayed fluorescent material may be a compound in which the lowest excited singlet energy is higher than the lowest excited singlet energy of the fluorescent emitting material. When the light-emitting layer includes a delayed fluorescent material, it may further include the above-mentioned first organic compound. This composition is called TADF-assisted fluorescence (TAF) composition and exhibits a luminous efficiency higher than that of commonly used fluorescent luminescence.

[0062] Note that in this specification, a fluorescent luminescent material may contain non-fluorescent luminescent components. For example, in addition to fluorescence, it may contain delayed fluorescence or phosphorescence. Note that the content of the fluorescent luminescent component must be higher than the content of other luminescent components. This also applies to luminescent materials that emit phosphorescence and luminescent materials that emit delayed fluorescence.

[0063] (e) The organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits phosphorescence

[0064] The image forming apparatus according to the embodiment may have a configuration in which the organic light emitting element includes a light emitting layer containing a light emitting material, and the light emitting material emits phosphorescence.

[0065] Typically, excitons generated by electrical energy are distributed in triplet and singlet states at a ratio of 3:1, and therefore it is known that light emitted from the triplet state (phosphorescence) has a higher luminous efficiency than light emitted from the singlet state (fluorescence). Therefore, the image forming apparatus according to the embodiment has high luminous efficiency.

[0066] The phosphorescent light-emitting material may be a compound containing a metal complex, and may be an iridium complex or a platinum complex. Examples of the ligand of the metal complex include substituted or unsubstituted phenyl-isoquinoline ligands, substituted or unsubstituted phenyl-quinoline ligands, substituted or unsubstituted phenyl-benzoisoquinoline ligands, and substituted or unsubstituted phenyl-naphthoisoquinoline ligands. Non-limiting specific examples include the exemplary compounds RD9 to RD16 described below.

[0067] The image forming apparatus according to the embodiment may include a second organic compound different from the phosphorescent light-emitting material in the light-emitting layer of the organic light-emitting element. The second organic compound may be a compound having a lowest excited triplet energy higher than the lowest excited triplet energy of the phosphorescent light-emitting material. The second organic compound may be a compound having a condensed polycyclic hydrocarbon skeleton that may have a substituent or a heterocyclic skeleton that may have a substituent. From another point of view, for the second organic compound, the freely rotatable single bond may be a carbon-carbon bond, the freely rotatable single bond may be an sp2 carbon-sp2 carbon bond, all freely rotatable single bonds may be carbon-carbon bonds, and all freely rotatable single bonds may be sp2 carbon-sp2 carbon bonds.

[0068] The condensed polycyclic hydrocarbon skeleton may be a skeleton having a carbon number of 10 or more and 25 or less, and specific examples include a naphthalene skeleton, a fluorene skeleton, an anthracene skeleton, a phenanthrene skeleton, a pyrene skeleton, skeleton, triphenylene skeleton, tetracene skeleton, fluoranthene skeleton and perylene skeleton.

[0069] The heterocyclic skeleton may be a skeleton having 3 to 30 carbon atoms, or may be a skeleton having 3 to 18 carbon atoms; examples include a dibenzofuran skeleton, a dibenzothiophene skeleton, a xanthone skeleton, a thioxanthone skeleton, a carbazole skeleton, an indolocarbazole skeleton, and a triazine skeleton.

[0070] The second organic compound may be a compound having a triphenylene skeleton, a xanthone skeleton, or an indolecarbazole skeleton. These are skeletons with high planarity and thus provide higher charge mobility. Therefore, it is expected that the organic light-emitting element has a lower driving voltage.

[0071] (f) The organic light-emitting element includes a light-emitting layer containing a light-emitting material and the light-emitting material emits delayed fluorescence

[0072] The image forming apparatus according to the embodiment may have a configuration in which the organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits delayed fluorescence. Delayed fluorescence as used herein refers to fluorescence emitted by reverse intersystem crossing of excitons or fluorescence emitted by triplet-triplet fusion (TTF).

[0073] In the image forming apparatus according to the embodiment, the light-emitting layer includes a delayed fluorescent material. The delayed fluorescent material is a compound in which the difference between the lowest excited singlet energy and the lowest excited triplet energy is 0.20 eV or less. The use of the delayed fluorescent material can provide reverse intersystem crossing of excitons from triplet to singlet. In this case, the light-emitting layer may further include the first organic compound described in (d), and the first organic compound may be a compound having a lowest excited singlet energy higher than the lowest excited singlet energy of the delayed fluorescent material.

[0074] It is generally known that excitons generated by electrical energy are distributed in a triplet state and a singlet state in a ratio of 3:1. The inclusion of a delayed fluorescent material can induce reverse intersystem crossing of excitons distributed in the triplet state to the singlet state, resulting in an organic light-emitting element exhibiting higher luminous efficiency. Therefore, the image forming apparatus according to the embodiment has high luminous efficiency.

[0075] The image forming apparatus according to the embodiment may have a configuration in which the light-emitting layer uses TTF. TTF refers to a configuration in which collisions between triplet excitons are induced, thereby generating excitons with higher energy, which are used to emit light from the singlet state. The use of TTF can provide triplet excitons for fluorescent emission, resulting in an organic light-emitting element with high luminescence efficiency.

[0076] (g) The organic light-emitting element includes a plurality of pixels arranged two-dimensionally at a high density.

[0077] An image forming apparatus according to an embodiment includes a plurality of pixels arranged two-dimensionally in the direction of rotation of a photoreceptor and in the direction of the rotation axis of the photoreceptor. As a result, the organic light-emitting elements are two-dimensionally packed at a high density, thereby increasing the luminous intensity during exposure. Specifically, the organic light-emitting elements can be stacked at 600 dpi or more, packaged at 1200 dpi or more, packaged at 2400 dpi or more, or packaged at 4800 dpi or more.

[0078] The increase in luminous intensity contributes considerably to a mechanism including a series of processes in which the photosensitive layer of the photoreceptor is efficiently excited and charges are quickly moved to a charge transporting substance, whereby residual charges can be suppressed and degradation of image quality can be suppressed.

[0079] Hereinafter, the configuration of the exposure light source 28 in the image forming apparatus according to the embodiment will be described in further detail.

[0080] First embodiment

[0081] Figure 3The figure is a schematic diagram illustrating the configuration of a light-emitting device in an image forming apparatus according to this embodiment. The light-emitting device according to this embodiment has a rectangular shape having long sides parallel to a first direction and short sides parallel to a direction intersecting the first direction. For example, the first direction may be a direction extending in the direction of the rotation axis of a photoreceptor in the image forming apparatus.

[0082] Substrate 1701 has a polygonal shape. Hereinafter, an example of a rectangular substrate 1701 will be described. In this specification, the long-side direction of rectangular substrate 1701 is referred to as the first direction, while the short-side direction, orthogonal to the long-side direction, is referred to as the second direction. The term "polygonal" as used herein encompasses shapes that include rounded corners. A moisture-resistant ring 1700 is disposed on rectangular substrate 1701 to inhibit or prevent moisture from entering the light-emitting device. Moisture-resistant ring 1700 may be, for example, a guard ring formed from a wiring layer.

[0083] Within moisture-resistant ring 1700, a light-emitting region 1702, contact regions 1703 (shown as 1703_1 to 1703_5), solder joints 1704 (shown as 1704_1 to 1704_3), and circuitry 1706 (shown as 1706_1 to 1706_2) are arranged. In this embodiment, contact region 1703 includes a first contact region 1703_1, a second contact region 1703_2, and a third contact region 1703_3. Solder joints 1704 include a first solder joint 1704_1, a second solder joint 1704_2, and a third solder joint 1704_3.

[0084] Circuit 1706 is a part of a circuit for driving a light emitting device. Circuit 1706 includes a first circuit 1706_1 and a second circuit 1706_2. Non-limiting specific examples include an input protection circuit, an input circuit for inputting data items for driving, and a logic circuit for processing data.

[0085] Within light-emitting region 1702, light-emitting elements EL are arranged in columns and rows. Light-emitting elements EL include organic light-emitting elements having the features of the embodiments of the present disclosure. Contact region 1703 is a region where wiring electrically connected to the common electrode of light-emitting elements EL is arranged. Solder pads 1704_1 electrically connect contact region 1703 to external elements.

[0086] The moisture-resistant ring 1700 may have an outer peripheral shape including a plurality of recessed portions, which may be used as, for example, abutting regions against ribs that are part of a vapor-deposition mask in a film-forming process.

[0087] Each of the plurality of light-emitting elements EL arranged in the column direction and the row direction in the light-emitting region 1702 includes a light-emitting layer as described above, and a first electrode and a second electrode sandwiching the light-emitting layer therebetween. This embodiment describes an example in which the first electrode is an independent electrode provided individually in the light-emitting element EL and the second electrode is a common electrode provided to be shared by the light-emitting elements EL.

[0088] For example, in the light emitting region 1702, when four rows of light emitting elements EL are arranged, as shown in FIG. Figure 3 In the example shown, the positions of the first light-emitting elements EL in the first row and the first light-emitting elements EL in the second row may be offset in the X direction (row direction) by 1 / 4 of the X-direction size of the light-emitting elements EL. In the case of n rows where n is an integer greater than or equal to 2, the positions of the first light-emitting elements EL in the first row and the first light-emitting elements EL in the second row may be offset in the X direction by 1 / n of the X-direction size of the light-emitting elements EL. This configuration is advantageous in improving resolution.

[0089] Contact region 1703 is adjacent to light-emitting region 1702 of substrate 1701 and is disposed within moisture-resistant ring 1700. At least one of first contact region 1703, solder joint 1704, and circuit 1706 is disposed between light-emitting region 1702 and one end of a long side of substrate 1701, along with the recessed portion of moisture-resistant ring 1700, and may be arranged in a row along the long side.

[0090] When the contact region 1703 , the pad region 1704 , and the circuit 1706 are arranged at the same position in the short side direction, the short side length of the light emitting device can be reduced, thereby miniaturizing the light emitting device.

[0091] The light-emitting device of this embodiment includes a plurality of contact areas 1703 for a common electrode and power wiring of the light-emitting element EL along the end portion of the long side of the light-emitting device. When the common electrode is formed of, for example, a transparent electrode material having a relatively high resistance, the amount of voltage drop in the long axis direction may be large. Therefore, the voltage applied to the OLED varies depending on the distance from the contact area to which the potential is supplied. As a result, the OLED to which a voltage is applied in order to make the OLED emit light with the same brightness (luminous intensity) may actually differ in terms of luminous brightness (luminous intensity), which may cause shadows, etc. In this embodiment in which a plurality of contact areas 1703 are arranged in the long axis direction, the voltage drop of the common electrode in the long side direction can be suppressed to suppress the occurrence of shadows, etc.

[0092] Second embodiment

[0093] In this embodiment, referring to FIG. 4 , an example in which the light emitting device is applied to a head substrate 1800 of an exposure head of an image forming apparatus will be described.

[0094] Figure 4A is a schematic perspective view of the head substrate 1800 . Figure 4B The arrangement of the plurality of light emitting elements EL arranged in the head substrate 1800 is shown. Figure 4C yes Figure 4B An enlarged view of a portion of .

[0095] On the head substrate 1800, an LED chip 1803 is mounted. The LED chip 1803 may be, for example, the light emitting device described in the first embodiment.

[0096] like Figure 4A As shown, an LED chip 1803 is disposed on one surface of a head substrate 1800, and a long flexible flat cable (FFC) connector 1807 is disposed on the other surface of the head substrate 1800. One surface of the head substrate 1800 is the surface (upper surface or front surface) on which the LED chip 1803 is disposed. The other surface of the substrate is the surface (lower surface or back surface) opposite to the surface on which the LED chip 1803 is disposed.

[0097] The FFC connector 1807 is attached to the other surface (lower surface or back surface) of the head substrate 1800 so that the length direction of the FFC connector 1807 extends in the length direction of the head substrate 1800. The long strip-shaped FFC connector 1807 is provided to input a control signal (driving signal) from the control circuit unit of the main body of the image forming apparatus. The control signal is transmitted to the LED chip 1803.

[0098] The LED chip 1803 is driven (to emit light or quench light emission) according to a control signal input into the head substrate 1800 .

[0099] The LED chip 1803 mounted on the head substrate 1800 will be described. Figure 4B and Figure 4C As shown, a plurality of light emitting elements EL are arranged on one surface of the head substrate 1800. For example, LED chips 1803_1 to 1803_29 (29 chips) are arranged. Figure 4B LED chips 1803_1, 1803_13, 1803_14, 1803_15, 1803_16, and 1803_29 are shown as examples. For each of the LED chips 1803_1 to 1803_29, a plurality of light-emitting elements EL are arranged in the longitudinal direction of the chip; for example, 516 light-emitting elements EL are arranged.

[0100] The center-to-center distance K2 of adjacent light-emitting elements EL along the length of LED chip 1803 corresponds to the resolution of the image forming apparatus. For example, when the resolution of the image forming apparatus of this embodiment is 1200 dpi, the light-emitting elements EL are arranged along the length of LED chips 1803_1 to 1803_29 so that the center-to-center distance K2 of adjacent light-emitting elements EL is 21.16 μm. Therefore, the exposure range of the exposure head of this embodiment is approximately 314 mm.

[0101] In the photosensitive drum, the photosensitive layer is formed to have a width of 314 mm or more. The long side length of A4-sized recording paper and the short side length of A3-sized recording paper are 297 mm, and the exposure head according to the embodiment has an exposure range that can form an image on A4-sized recording paper and A3-sized recording paper. Note that, Figure 4B and Figure 4C An example is shown in which a plurality of light emitting elements EL are arranged in the length direction; alternatively, the light emitting elements EL may be arranged in the width direction in addition to the length direction.

[0102] The LED chips 1803_1 to 1803_29 are arranged in a plurality of rows in the axial direction of the photosensitive drum. Specifically, the LED chips 1803_1 to 1803_29 are alternately arranged in two rows in the axial direction of the photosensitive drum. Figure 4B As shown, LED chips 1803_1, 1803_3, ..., 1803_29 at odd-numbered positions from the left are mounted in a single row along the length of substrate 1800. Furthermore, LED chips 1803_2, 1803_4, ..., 1803_28 at even-numbered positions from the left are mounted in a single row along the length of substrate 1800. The LED chips 1803 are arranged in this manner.

[0103] Results, such as Figure 4C As shown, along the length direction of LED chip 1803, the center-to-center distance K1 and the center-to-center distance K2 of the light-emitting elements EL can be equal. The center-to-center distance K1 of the light-emitting elements EL refers to the center-to-center distance between the light-emitting elements EL arranged at the end of LED chip 1803_13 and the light-emitting elements EL arranged at the end of LED chip 1803_14. The center-to-center distance K2 of the light-emitting elements EL refers to the center-to-center distance K2 of adjacent light-emitting elements EL in LED chip 1803_14. Figure 4C Components other than EL are omitted.

[0104] In other words, the center-to-center distance K1 between adjacent light-emitting elements EL arranged at the end of an LED chip 1803 and the end of another LED chip 1803 can be made equal to the center-to-center distance K2 between adjacent light-emitting elements EL on a single LED chip 1803 .

[0105] Note that in the embodiment, the light-emitting element EL is an organic light-emitting element and is a current-driven light-emitting element. The organic light-emitting elements are arranged in a row in the main scanning direction (the axial direction of the photosensitive drum 27) on a TFT (thin film transistor) substrate, for example, and are electrically connected in parallel via power supply wiring similarly arranged in the main scanning direction.

[0106] Note that when the light-emitting device is applied to an exposure head in which exposure is performed linearly, the shape of the light-emitting region 1702 has a larger ratio of the length in the longitudinal direction (first direction X) to the length in the width direction (second direction Y) than when the light-emitting device is applied to a display device or the like. The shape of the substrate of the LED chip also has a larger ratio of the length in the longitudinal direction (first direction X) to the length in the width direction (third direction Y).

[0107] Specifically, for example, the length of the long side of the LED chip (or the light-emitting region 1702) may be 5 or more times or 10 times the length of the short side of the LED chip (or the light-emitting region 1702). For example, the length of the long side of the LED chip (or the light-emitting region 1702) may be 20 or more times the length of the short side of the LED chip (or the light-emitting region 1702).

[0108] The length of the long side of the LED chip depends on the axial length of the photosensitive drum 27, the number of LED chips arranged in the axial direction, and the arrangement of the LED chips 1803. The length of the short side of the LED chip 1803 depends on whether the light-emitting elements EL are arranged in the direction perpendicular to the axis of the photosensitive drum in the light-emitting region 1702 or whether the solder joints 1704 or the contact regions 1703 are arranged.

[0109] From the viewpoint of wavelength dependency of the sensitivity of the photosensitive drum 27 , the organic light emitting element may have a configuration including a light emitting layer that emits red light.

[0110] The LED chip 1803 may include a color filter. With this color filter, stray light in an unintended direction can be absorbed without reducing the amount of normal light incident on the photosensitive drum, thereby improving printing quality.

[0111] organic light-emitting diodes

[0112] Hereinafter, the organic light emitting element will be described in detail. However, the present disclosure is not limited to this description.

[0113] Specific examples of the element configuration of the organic light emitting element according to the embodiment include a multilayer type element configuration in which electrode layers and organic compound layers described in the following (A) to (F) are stacked in this order on a substrate.

[0114] Note that in any element configuration, the organic compound layer must include a light-emitting layer containing a light-emitting material.

[0115] (A) Anode / light-emitting layer / cathode

[0116] (B) Anode / Hole Transport Layer / Emitting Layer / Electron Transport Layer / Cathode

[0117] (C) Anode / Hole Transport Layer / Emitting Layer / Electron Transport Layer / Electron Injection Layer / Cathode

[0118] (D) Anode / Hole Injection Layer / Hole Transport Layer / Emitting Layer / Electron Transport Layer / Cathode

[0119] (E) Anode / Hole Injection Layer / Hole Transport Layer / Emitting Layer / Electron Transport Layer / Electron Injection Layer / Cathode

[0120] (F) Anode / Hole Transport Layer / Electron Blocking Layer / Emitting Layer / Hole Blocking Layer / Electron Transport Layer / Cathode

[0121] However, these examples of element configurations are non-limiting examples of basic element configurations. For example, various layer configurations may be employed: an insulating layer, an adhesive layer, or an interference layer may be provided at the interface between the electrode and the organic compound layer; an electron transport layer or a hole transport layer may be composed of two layers having different ionization potentials; or a light-emitting layer may be composed of two layers containing different light-emitting materials.

[0122] For the organic light-emitting element according to the embodiment, known compounds such as low-molecular-weight or high-molecular-weight hole-injecting compounds or hole-transporting compounds, compounds serving as hosts, luminescent compounds, electron-injecting compounds, and electron-transporting compounds can be used as needed. Examples of such compounds will be described below.

[0123] The hole injection transport material may be a material with a high hole mobility so that holes are injected from the anode and the injected holes are transported to the light-emitting layer. In order to suppress the degradation of film quality such as crystallization in the organic light-emitting element, a material with a high glass transition temperature can be used. Examples of low molecular weight or high molecular weight materials with hole injection transport capabilities include triarylamine derivatives, arylcarbazole derivatives, phenylenediamine derivatives, stilbene derivatives, phthalocyanine derivatives, porphyrin derivatives, poly (vinylcarbazole), poly (thiophene) and other conductive polymers. The hole injection transport material is also suitable for use in an electron blocking layer. The following are non-limiting specific examples of compounds used as hole injection transport materials.

[0124]

[0125] Examples of luminescent materials primarily related to luminescent functions include fused ring compounds (e.g., fluorene derivatives, naphthalene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, anthracene derivatives, and rubrene), quinacridone derivatives, coumarin derivatives, stilbene derivatives, organoaluminum complexes such as tris(8-hydroxyquinolinolato)aluminum, iridium complexes, platinum complexes, rhenium complexes, copper complexes, europium complexes, ruthenium complexes, and polymer derivatives such as poly(phenylenevinylene) derivatives, poly(fluorene) derivatives, and poly(phenylene) derivatives. The concentration of the luminescent material can be 0.01% by mass to 20% by mass, or 0.1% by mass to 10% by mass, relative to the total mass of the luminescent layer.

[0126] The following are non-limiting specific examples of compounds useful as light-emitting materials.

[0127]

[0128]

[0129] Non-limiting specific examples of the host or auxiliary agent contained in the light-emitting layer include aromatic hydrocarbon compounds or derivatives thereof, carbazole derivatives, azine derivatives, xanthone derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, organic aluminum complexes such as tris(8-hydroxyquinoline)aluminum, and organic beryllium complexes.

[0130] The following are specific examples.

[0131]

[0132] The electron transport material can be appropriately selected from materials that can transport electrons injected from the cathode to the light-emitting layer, and is selected in consideration of, for example, a balance with the hole mobility of the hole transport material. Examples of materials having electron transporting ability include oxadiazole derivatives, oxazole derivatives, pyrazine derivatives, triazole derivatives, triazine derivatives, quinoline derivatives, quinoxaline derivatives, phenanthroline derivatives, organoaluminum complexes, and fused ring compounds (e.g., fluorene derivatives, naphthalene derivatives, Derivatives and anthracene derivatives). Electron transporting materials are also suitable for use in the hole blocking layer.

[0133] The following are non-limiting specific examples of compounds useful as electron transporting materials. The following are specific examples.

[0134]

[0135] The electron injection material can be appropriately selected from a material that can easily realize electron injection from the cathode, and is selected in consideration of the balance with the hole injection performance. As an organic compound, n-type dopants and reductive dopants are also included. Examples include alkali metal-containing compounds such as lithium fluoride, lithium complexes such as lithium hydroxyquinoline, benzimidazolidine derivatives, imidazolidine derivatives, fulvalene derivatives and acridine derivatives. The electron injection material can also be used together with the above-mentioned electron transport material.

[0136] Non-limiting examples of the light-emitting material that emits light from a singlet excited state in the present disclosure include compounds represented by BD1 to BD8, BD10, GD1 to GD9, and RD1 to RD8.

[0137] Non-limiting examples of the phosphorescent light-emitting material that emits light from a triplet excited state in the present disclosure include compounds represented by BD9, GD10 to GD18, and RD9 to RD16.

[0138] Non-limiting examples of the TADF material in the present disclosure include compounds represented by EM35 to EM38.

[0139] More detailed structure of organic light-emitting elements

[0140] The organic light-emitting element according to the embodiment will be described in further detail below. The organic light-emitting element is configured by forming an insulating layer, a first electrode, an organic compound layer, and a second electrode on a substrate. A protective layer, a color filter, or a microlens, etc., may be configured on the second electrode. When a color filter is configured, a planarization layer may be configured between the color filter and the protective layer. The planarization layer may be formed from an acrylic resin, etc. The same applies to the case where a planarization layer is configured between the color filter and the microlens.

[0141] substrate

[0142] The substrate may be made of quartz, glass, a silicon wafer, a resin, or a metal. Switching elements such as transistors and wiring are arranged on the substrate, and an insulating layer may be arranged thereon. The insulating layer may be formed of any material as long as a contact hole can be formed to form wiring to the first electrode and insulation from unconnected wiring can be ensured. Examples of the material include resins such as polyimide, silicon oxide, and silicon nitride.

[0143] electrode

[0144] As the electrodes, a pair of electrodes may be used, and the pair of electrodes may be an anode and a cathode.

[0145] When an electric field is applied in the direction in which the organic light-emitting element emits light, the electrode at a higher potential is the anode, and the other electrode is the cathode. In other words, the electrode that supplies holes to the light-emitting layer is the anode, and the electrode that supplies electrons to the light-emitting layer is the cathode.

[0146] The anode can be formed of a material having a work function as high as possible. Examples of such materials include elemental metals such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, and tungsten, mixtures thereof, alloys of the aforementioned combinations, and metal oxides such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide. Other examples include conductive polymers such as polyaniline, polypyrrole, and polythiophene.

[0147] These electrode materials may be used alone or in combination of two or more thereof. The anode may be composed of a single layer or may be composed of multiple layers.

[0148] When such an electrode is used as a reflective electrode, it can be formed of, for example, chromium, aluminum, silver, titanium, tungsten, molybdenum, an alloy thereof, or a multilayer structure thereof. Such a material can be used to provide a reflective film that does not function as an electrode. When such an electrode is used as a transparent electrode, non-limiting examples include transparent conductive oxide layers such as indium tin oxide (ITO) or indium zinc oxide.

[0149] The electrodes can be formed by photolithography.

[0150] On the other hand, the constituent material of the cathode may be a material with a lower work function. Examples of constituent materials include alkali metals such as lithium, alkaline earth metals such as calcium, elemental metals such as aluminum, titanium, manganese, silver, lead and chromium, and mixtures thereof. Alternatively, alloys of combinations of such elemental metals may be used. Examples include magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper and zinc-silver. Metal oxides such as indium tin oxide (ITO) may also be used. Such electrode materials may be used alone or in combination of two or more thereof. The cathode may have a single-layer structure or a multilayer structure. In particular, silver may be used, and in order to reduce the aggregation of silver, a silver alloy may be used. Any alloy ratio may be used as long as the aggregation of silver can be reduced. For example, the ratio of silver to other metals may be 1:1 or 3:1, etc.

[0151] The cathode is not particularly limited: a conductive layer of an oxide such as ITO can be used to provide a top-emitting element, or a reflective electrode such as aluminum (Al) can be used to provide a bottom-emitting element. The cathode formation method is not particularly limited; however, for example, a DC or AC sputtering method can be used, resulting in high film coverage and a tendency to reduce resistance.

[0152] Organic compound layer

[0153] The organic compound layer includes at least a light-emitting layer and, in addition to the light-emitting layer, may include, as needed, a hole injection layer, a hole transport layer, or an electron blocking layer on the anode side and a hole blocking layer, an electron transport layer, or an electron injection layer on the cathode side. The organic compound layer is mainly formed of an organic compound, but may contain inorganic atoms or inorganic compounds. The organic compound layer may contain, for example, copper, lithium, magnesium, aluminum, iridium, platinum, molybdenum, or zinc.

[0154] The organic compound layer constituting the organic light-emitting element according to the embodiment of the present disclosure can be formed by a dry method such as vacuum deposition, ionized deposition, sputtering, or plasma. Alternatively, instead of the dry method, a wet method can be used in which the material is dissolved in an appropriate solvent and a known coating method (such as spin coating, dipping, casting, LB method, or inkjet method) is performed to form a layer.

[0155] In the case where a vacuum deposition method or a solution coating method is performed to form a layer, crystallization is less likely to occur and high temporal stability is provided. When a coating method is performed to form a film, an appropriate binder resin may be additionally used to form the film.

[0156] Non-limiting examples of the binder resin include polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, and urea resin.

[0157] Such a binder resin may be used alone as a homopolymer or a copolymer, or in combination of two or more thereof. In addition, known additives such as a plasticizer, an antioxidant, and an ultraviolet absorber may be additionally used as needed.

[0158] Charge generation layer

[0159] The charge generation layer may be formed using a p-layer and an n-layer to form an n / p junction, or a p-doped layer or an n-doped layer may be used. For example, when the charge generation layer is formed solely of a p / n junction, an electron injection layer may be formed to further inject electrons extracted from the p-layer into the electron transport layer. Alternatively, an n-doped layer and a p-doped layer may be formed. Such combinations in the charge generation layer are not limited in the present disclosure.

[0160] For the p-doped layer, for example, a Lewis acid such as HAT-CN or molybdenum trioxide, which has high electron-attracting properties, and an aromatic amine compound can be mixed. HAT-CN and molybdenum trioxide are n-type materials and can be used as a multilayer structure for extracting electrons. The p-doped layer, or np junction, composed of multiple layers of n-type and p-type materials serves as a p-charge generation layer.

[0161] The n-doped layer can be formed from a material with a low work function and easily electron-doped, such as an alkali metal or alkaline earth metal. In the present disclosure, the n-doped layer serves as an n-charge generating layer. Alternatively, LiF or the like can be combined with a reducing metal film to provide an electron injection layer, and an n-type layer / p-type layer can be formed to generate charge.

[0162] Examples of n-dopants include alkali metals such as Li, Na, K, Rb, and Cs, alkaline earth metals such as Mg, Ca, Sr, and Ba, rare earth metals such as Yb, compounds of the foregoing (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), and rare earth metal compounds (including oxides, halides, and carbonates).

[0163] protective layer

[0164] On the second electrode, a protective layer can be configured. For example, a glass plate on which a moisture absorbent is configured can be placed and bonded to the second electrode to reduce the entry of water, etc. into the organic compound layer and reduce the occurrence of poor display. Alternatively, in another embodiment, a passivation film formed of silicon nitride, etc. can be configured on the second electrode to reduce the entry of water, etc. into the organic compound layer. For example, the second electrode formed in a vacuum can be transported to another chamber in a vacuum, and a CVD process can be performed to form a silicon nitride film having a thickness of 2 μm and serving as a protective layer. After the CVD process is performed to form the film, an atomic layer deposition process (ALD process) can be performed to form a protective layer. The material used for the film in the ALD process is not limited, and examples include silicon nitride, silicon oxide, and aluminum oxide. On the film formed by the ALD process, silicon nitride can be further formed by the CVD process. The film formed by the ALD process can have a film thickness that is less than the film thickness of the film formed by the CVD process. Specifically, the film formed by the ALD process can have a film thickness that is less than 50% or less than 10% of the film thickness of the film formed by the CVD process.

[0165] Color Filters

[0166] A color filter may be placed on the protective layer. For example, a color filter selected based on the size of the organic light-emitting element may be placed on another substrate and bonded to the substrate on which the organic light-emitting element is placed, or the color filter may be formed by patterning the protective layer using photolithography. The color filter may be formed from a polymer.

[0167] planarization layer

[0168] A planarization layer can be placed between the color filter and the protective layer. This layer reduces the unevenness of the underlying layer. For the purpose of not limiting the layer, the planarization layer may also be referred to as a material resin layer. The planarization layer can be formed from an organic compound; the organic compound can be a low-molecular-weight compound or a high-molecular-weight compound, preferably a high-molecular-weight compound.

[0169] Such a planarization layer can be arranged above and below the color filter and the layer can be formed of the same constituent material or different constituent materials. Specific examples include polyvinyl carbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin and urea resin.

[0170] microlenses

[0171] An organic light emitting element or a light emitting device including an organic light emitting element may include an optical component, such as a microlens, on the emission side. The microlens may be formed of an acrylic resin, an epoxy resin, or the like. The microlens may be configured to increase the amount of light extracted from the organic light emitting element or the light emitting device or to control the direction of the extracted light. The microlens may have a hemispherical shape. When the microlens has a hemispherical shape, among the tangents contacting the hemisphere, there is a tangent parallel to the insulating layer, and the point of intersection between the tangent and the hemisphere is the vertex of the microlens. The vertex of the microlens can be similarly determined in an appropriate cross-sectional view. Specifically, among the tangents of the semicircle contacting the microlens in the cross-sectional view, there is a tangent parallel to the insulating layer, and the point of intersection between the tangent and the semicircle is the vertex of the microlens.

[0172] For a microlens, a midpoint can be defined. In a cross-section of a microlens, an imaginary line segment can be drawn from one end point of an arc to the other end point of the arc, and the midpoint of this line segment can be referred to as the midpoint of the microlens. The cross-section where the vertex and midpoint are determined can be a cross-section perpendicular to the insulating layer.

[0173] Opposite substrate

[0174] A counter substrate may be disposed on the planarization layer. The counter substrate is disposed at a position corresponding to the aforementioned substrate and is therefore referred to as a counter substrate. The counter substrate may be made of the same material as the aforementioned substrate. When the aforementioned substrate is defined as the first substrate, the counter substrate may be the second substrate.

[0175] pixel circuit

[0176] A light-emitting device including an organic light-emitting element may include a pixel circuit connected to the organic light-emitting element. The pixel circuit may be an active matrix type configured to independently control the light emission of each of a plurality of organic light-emitting elements. The active matrix type circuit may be driven by a voltage programming mode or a current programming mode. The driving circuit includes a pixel circuit for each pixel. The pixel circuit may include an organic light-emitting element, a transistor configured to control the light emission brightness (light emission intensity) of the organic light-emitting element, a transistor configured to control the light emission timing, a capacitor configured to maintain the gate voltage of the transistor (which is configured to control the light emission brightness (light emission intensity)), and a transistor not connected to GND via the light-emitting element.

[0177] The light-emitting device includes a display area and a peripheral area arranged around the display area. The display area includes a pixel circuit, and the peripheral area includes a display control circuit. The transistors constituting the pixel circuit may have a lower mobility than the transistors constituting the display control circuit.

[0178] The gradient of the voltage-current characteristic of the transistor constituting the pixel circuit may be smaller than the gradient of the voltage-current characteristic of the transistor constituting the display control circuit. The gradient of the voltage-current characteristic can be measured as the so-called Vg-Ig characteristic. The transistor constituting the pixel circuit is a transistor connected to the organic light-emitting element.

[0179] Pixel

[0180] A light emitting device including an organic light emitting element may include a plurality of pixels.

[0181] In such a pixel, an area called the pixel aperture emits light. This area is the same as the first area. The pixel aperture can have a size of 15 μm or less, or can have a size of 5 μm or more. Specific examples of sizes include 11 μm, 9.5 μm, 7.4 μm, and 6.4 μm.

[0182] In a plan view, the pixels can be arranged in a known arrangement. The arrangement may be, for example, a stripe arrangement, a delta arrangement, a PenTile arrangement, or a Bayer arrangement. Examples of such pixel shapes include quadrilaterals such as rectangles and rhombuses, as well as hexagons. Obviously, shapes that are not exact rectangles but are similar to rectangles are also included in rectangles. Such sub-pixel shapes and such pixel arrangements can be used in combination.

[0183] Hereinafter, the photoconductor 27 in the image forming apparatus according to the embodiment will be described in detail.

[0184] Photosensitive layer

[0185] The photosensitive layer of a photosensitive drum is mainly divided into (1) a multilayer photosensitive layer and (2) a single layer photosensitive layer. (1) A multilayer photosensitive layer is a photosensitive layer comprising a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance. (2) A single layer photosensitive layer is a photosensitive layer containing both a charge generating substance and a charge transporting substance.

[0186] (1) Multi-layer photosensitive layer

[0187] The multi-layer photosensitive layer includes a charge generating layer and a charge transporting layer.

[0188] (1-1) Charge Generation Layer

[0189] The charge generating layer may contain a charge generating substance and a resin.

[0190] Examples of charge generating substances include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among them, azo pigments and phthalocyanine pigments can be used. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments can be used.

[0191] In the charge generating layer, the content of the charge generating substance may be 40% by mass or more and 85% by mass or less, or 60% by mass or more and 80% by mass or less, relative to the total mass of the charge generating layer.

[0192] Examples of the resin include polyester resins, polycarbonate resins, polyvinyl acetal resins, polyvinyl butyral resins, acrylic resins, silicone resins, epoxy resins, melamine resins, polyurethane resins, phenolic resins, polyvinyl alcohol resins, cellulose resins, polystyrene resins, polyvinyl acetate resins, and polyvinyl chloride resins. Among them, polyvinyl butyral resin can be used.

[0193] The charge generation layer may further contain additives such as antioxidants and ultraviolet absorbers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

[0194] The charge generating layer can be formed by preparing a charge generating layer-forming coating liquid containing the above-mentioned materials and a solvent, forming a coating film on the lower layer using the coating liquid, and drying the coating film. Examples of the solvent used in the coating liquid include alcohol solvents, sulfoxide solvents, ketone solvents, ether solvents, ester solvents, and aromatic hydrocarbon solvents.

[0195] The charge generating layer may have a film thickness of 0.1 μm or more and 1 μm or less, or 0.15 μm or more and 0.4 μm or less.

[0196] (1-2) Charge transport layer

[0197] The charge transport layer may contain a charge transport substance and a binder material.

[0198] When a protective layer described later is not provided, the charge transport layer serves as a surface layer of the photosensitive drum.

[0199] Examples of the charge transporting substance include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, triarylamine compounds, and resins having groups derived from such substances. Among them, triarylamine compounds can be used.

[0200] In the charge transport layer, the content of the charge transport substance may be 25% by mass or more and 70% by mass or less, or may be 30% by mass or more and 55% by mass or less, relative to the total mass of the charge transport layer.

[0201] The binder material used is a thermoplastic resin (hereinafter also referred to as "resin").

[0202] Examples of thermoplastic resins include polyester resins, polycarbonate resins, acrylic resins, and polystyrene resins. Among them, polycarbonate resins and polyester resins can be used. The polyester resin can be a polyarylate resin.

[0203] The content ratio (mass ratio) of the charge transporting substance to the resin may be 4:10 to 20:10, or 5:10 to 12:10.

[0204] The charge transport layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, and leveling agents. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, silicone modified resins, silicone oils, polystyrene resin particles, polyethylene resin particles, and boron nitride particles.

[0205] The charge transport layer can be formed by preparing a charge transport layer-forming coating liquid containing the above-mentioned materials and a solvent, forming a coating film on the charge generating layer using the coating liquid, and drying the coating film. Examples of solvents used in the coating liquid include alcohol solvents, ketone solvents, ether solvents, ester solvents, and aromatic hydrocarbon solvents. Among these solvents, ether solvents and aromatic hydrocarbon solvents can be used.

[0206] The charge transport layer may have a film thickness of 5 μm or more and 50 μm or less, or 8 μm or more and 40 μm or less, or 10 μm or more and 30 μm or less.

[0207] (2) Single-layer photosensitive layer

[0208] The single-layer type photosensitive layer can be formed by preparing a photosensitive layer-forming coating liquid containing a charge generating substance, a charge transporting substance, a resin, and a solvent, forming a coating film on the lower layer using the coating liquid, and drying the coating film.

[0209] The charge generating substance, the charge transporting substance and the resin are the same as those exemplified above in "(1) Multilayer type photosensitive layer".

[0210] protective layer

[0211] In the present disclosure, a protective layer may be disposed on the photosensitive layer. The protective layer may provide improved durability.

[0212] When the protective layer is provided, the protective layer serves as the surface layer of the photosensitive drum.

[0213] The protective layer can be formed into a cured film by polymerizing the raw materials of the binder material, for example, a composition containing a monomer with a polymerizable functional group. In this case, the example of the reaction includes thermal polymerization, photopolymerization, and radiation polymerization. For monomers with polymerizable functional groups, examples of polymerizable functional groups include isocyanate groups, blocked isocyanate groups, methylol groups, alkyl methylol groups, epoxy groups, metal alkoxy groups, hydroxyl groups, amino groups, carboxyl groups, thiol groups, carboxylic anhydride groups, and groups containing carbon-carbon double bonds. Examples of groups containing carbon-carbon double bonds include acryloyl groups and methacryloyl groups. As monomers with polymerizable functional groups, monomers with charge transporting ability can be used.

[0214] The cured product of the monomer having a polymerizable functional group is the binder material of the protective layer.

[0215] The monomer having a polymerizable functional group may be a hole transporting compound having a chain polymerizable functional group.

[0216] The hole transporting compound having a chain-polymerizable functional group may be a compound represented by the following formula (CT-1) or (CT-2).

[0217]

[0218] In formula (CT-1), Ar 11 to Ar 13 Each independently represents a substituted aryl group or an unsubstituted aryl group. The substituted aryl group may have a substituent that is an alkyl group having 1 to 6 carbon atoms or a monovalent functional group represented by any one of the following formulas (P-1) to (P-3). Note that the compound represented by formula (CT-1) has at least one monovalent functional group represented by any one of the following formulas (P-1) to (P-3).

[0219]

[0220] In formula (CT-2), Ar 21 to Ar 24 Each independently represents a substituted aryl group or an unsubstituted aryl group, and Ar25 represents a substituted arylene group or an unsubstituted arylene group. The substituted aryl group may have a substituent which is an alkyl group having 1 to 6 carbon atoms, or a monovalent functional group represented by the following formulas (P-1) to (P-3). The substituted arylene group may have a substituent which is an alkyl group having 1 to 6 carbon atoms, or a monovalent functional group represented by the following formulas (P-1) to (P-3). Note that the compound represented by formula (CT-2) has at least one monovalent functional group represented by any one of the following formulas (P-1) to (P-3).

[0221]

[0222] In formula (P-1), Z 11 represents a single bond or an alkylene group having 1 to 6 carbon atoms, and X 11 represents a hydrogen atom or a methyl group.

[0223]

[0224] In formula (P-2), Z 21 It represents a single bond or an alkylene group having 1 to 6 carbon atoms.

[0225]

[0226] In formula (P-3), Z 31 It represents a single bond or an alkylene group having 1 to 6 carbon atoms.

[0227] The protective layer may contain fluorine-containing resin particles. When the fluorine-containing resin particles are contained, the protective layer may have improved wear resistance.

[0228] Examples of the resin contained in the fluorine atom-containing resin particles are as follows.

[0229] The resin may be a polytetrafluoroethylene resin, a polychlorotrifluoroethylene resin, a polytetrafluoroethylene propylene resin, a polyvinyl fluoride resin, a polyvinylidene fluoride resin, or a polydichloroethylene fluoride resin. Particles containing a variety of the above resins may be used. Among the above resins, the fluorine-containing resin particles may be formed from a polytetrafluoroethylene (PTFE) resin from the viewpoint of improving dispersibility.

[0230] In cross-sectional observation of the surface layer, for fluorine-containing resin particles, from the viewpoint of improving dispersibility and suppressing potential fluctuations, the arithmetic mean of the major diameter of the primary particles measured from a secondary electron image taken using a scanning electron microscope (average primary particle size) can be 150 nm or more and 300 nm or less. The average primary particle size of the fluorine-containing resin particles can be 180 nm or more and 250 nm or less.

[0231] In the protective layer, the content of the fluorine atom-containing resin particles can be 5% by mass or more and 40% by mass or less, or 25% by mass or more and 35% by mass or less, relative to the total mass of the protective layer.

[0232] The protective layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, and leveling agents. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, silicone modified resins, silicone oils, polystyrene resin particles, polyethylene resin particles, and boron nitride particles.

[0233] The protective layer can be formed by preparing a protective layer-forming coating liquid containing the above-mentioned materials and a solvent, forming a coating film on the photosensitive layer using the coating liquid, and drying and / or curing the coating film. Examples of the solvent used in the coating liquid include alcohol solvents, ketone solvents, ether solvents, sulfoxide solvents, ester solvents, and aromatic hydrocarbon solvents.

[0234] The protective layer may have a film thickness of 0.50 μm or more and 10 μm or less, or 1 μm or more and 7 μm or less.

[0235] Surface processing of photosensitive drums

[0236] In the present disclosure, the photosensitive drum can be subjected to surface processing. Surface processing can further stabilize the behavior of the cleaning unit (cleaning blade) in contact with the photosensitive drum. Examples of surface processing methods include a method of pressing a mold having a convex portion to the surface of the photosensitive drum to transfer the shape, a method of mechanically grinding to impart a concave-convex shape, and a method of causing powder to collide with the surface of the photosensitive drum to roughen the surface. In this way, concave or convex portions are formed in the surface layer of the photosensitive drum, thereby further stabilizing the behavior of the cleaning unit in contact with the photosensitive drum.

[0237] The concave portion or convex portion may be formed on the entire area of ​​the surface of the photosensitive drum, or may be formed in a portion of the surface of the photosensitive drum. When the concave portion or convex portion is formed in a portion of the surface of the photosensitive drum, the concave portion or convex portion may be formed at least on the entire area in contact with the cleaning unit (cleaning blade).

[0238] In the case of forming the recessed portions, a mold having convex portions corresponding to the recessed portions may be pressed against the surface of the photosensitive drum to transfer the shape, thereby forming the recessed portions in the surface of the photosensitive drum.

[0239] Example

[0240] Hereinafter, the present disclosure will be described in further detail with reference to Examples. However, the present disclosure is not limited to the Examples.

[0241] In the embodiment, a top-emission multilayer organic EL element is produced, wherein an anode, a hole injection layer, a hole transport layer, a light-emitting layer, a first electron transport layer, a second electron transport layer, an electron injection layer, a cathode, a first protective layer, a second protective layer, and a third protective layer are sequentially formed on a substrate. The light-emitting layer is formed using a red light-emitting material and a host material.

[0242] A 40nm thick titanium (Ti) film was sputtered onto a silicon substrate with a wiring layer configured thereon as an anode. This film was patterned using photolithography to form a Ti pixel array with square pixel holes and wiring. The pixel holes were formed to have a side of 20μm.

[0243] Subsequently, the silicon substrate and the material that had been subjected to UV / ozone cleaning were attached to a vacuum deposition apparatus and the apparatus was evacuated to a vacuum of 1.0×10 -4 Pa(1×10 -6 Subsequently, a hole injection layer is formed to a thickness that provides an interference structure that enhances the emission wavelength. Subsequently, a light-emitting layer containing a red light-emitting material is formed. Subsequently, a first electron transport layer, a second electron transport layer, and an electron injection layer are sequentially formed to a thickness that provides an interference structure that enhances the emission wavelength. Subsequently, a cathode is formed.

[0244] Furthermore, a first protective layer of a silicon nitride film formed by a CVD process, a second protective layer of an aluminum oxide film formed by an ALD process, and a third protective layer of a silicon nitride film formed by a CVD process were sequentially formed. In this way, an organic light emitting element was produced.

[0245] Afterglow lifetime and exposure time

[0246] In each example, the afterglow lifetime of the organic light emitting element was measured.

[0247] For the afterglow lifetime, excitation is caused using a pulsed laser, and the time that elapses until the luminous intensity decays to 1 / e of the initial value is measured and calculated.

[0248] The exposure time was evaluated at 1 μs and 20 μs.

[0249] Image quality evaluation

[0250] The organic light emitting element (OLED) chips produced on the silicon substrate were cut and 17 chips were attached to the PCB substrate. The PCB substrate on which the OLED chips were mounted was prepared and arranged on a housing equipped with a lens array to produce a print head.

[0251] The print head thus produced was mounted on a remodeled model of a copy machine manufactured by CANON KABUSHIKI KAISHA (trade name: imageRUNNER iR-ADVC5051) and evaluation of image quality was performed.

[0252] Subsequently, the electrophotographic photoreceptor was mounted on the magenta process cartridge station. A test chart with a 5% image ratio was output on 30,000 A4-sized sheets in portrait orientation. Subsequently, a halftone image was output and the image quality (whether vertical streaks or ghosting occurred) was evaluated based on the following scale. The results are shown in Table 2.

[0253] A: Defects such as vertical streaks and ghosting were not observed.

[0254] B: Vertical streaks or ghosting are observed under magnification.

[0255] Table 2

[0256]

[0257] As shown in Table 2, the configurations of Examples 1 to 4 provide high image quality after outputting 30,000 sheets. The configurations of Examples 1 to 4 provide high image quality presumably because the exposure time is longer than the afterglow lifetime and thus the emitted afterglow has less influence on the photoreceptor.

[0258] On the other hand, the configurations of Comparative Examples 1 and 2 provided low image quality after outputting 30,000 sheets. This is presumably because, in the configurations of Comparative Examples 1 and 2 where the afterglow lifetime was longer than the exposure time, afterglow was emitted to the photoreceptor, forming an unintended latent image on the photoreceptor.

[0259] Therefore, the afterglow life of the organic light emitting element is made shorter than the exposure time of the photoreceptor, thereby providing an image forming apparatus that provides high image quality.

[0260] As described above, using a configuration in which the afterglow lifetime is shorter than the exposure time, an image forming apparatus according to the present disclosure can be provided in which afterglow can be suppressed and image quality is high. Furthermore, using a configuration in which the afterglow lifetime is shorter than the lighting interval time period can be provided in which afterglow can be suppressed and image quality is high.

[0261] The present disclosure may also have the following embodiments.

[0262] Implementation Plan 1

[0263] An image forming apparatus comprising: an exposure light source including an organic light emitting element; and a photoreceptor configured to receive light emitted from the organic light emitting element,

[0264] The luminous intensity of the organic light emitting element at the end of supplying current to the organic light emitting element is defined as L0, the time period from the end of supplying current to the organic light emitting element to the quenching of the organic light emitting element is defined as T1, and the time period from the start of supplying current to the organic light emitting element to the end of supplying current to the organic light emitting element is defined as T2, and

[0265] T1 and T2 satisfy the relationship of formula (a):

[0266] (a)T1 <T2。

[0267] Implementation Plan 2

[0268] The image forming apparatus according to embodiment 1, wherein T1 and T2 satisfy the relationship of formula (b):

[0269] (b)T2 / T1>1.0.

[0270] Implementation Plan 3

[0271] The image forming apparatus according to embodiment 1 or 2, wherein a period from when the supply of current to the organic light emitting element ends to when the supply of current to the organic light emitting element starts is defined as T3, and

[0272] T1 and T3 satisfy the relationship of formula (c):

[0273] (c)T1 <T3。

[0274] Implementation Plan 4

[0275] An image forming apparatus comprising: an exposure light source including an organic light emitting element; and a photoreceptor configured to receive light emitted from the organic light emitting element,

[0276] The luminous intensity of the organic light emitting element when the current is supplied to the organic light emitting element is defined as L0, the time period from the end of the current supply to the organic light emitting element to the quenching of the organic light emitting element is defined as T1, and the time period from the end of the current supply to the organic light emitting element to the start of the current supply to the organic light emitting element is defined as T3, and

[0277] T1 and T3 satisfy the relationship of formula (c):

[0278] (c)T1 <T3。

[0279] Implementation Plan 5

[0280] The image forming apparatus according to any one of Embodiments 1 to 4, wherein the organic light emitting element has a top emission structure.

[0281] Implementation Plan 6

[0282] The image forming apparatus according to any one of Embodiments 1 to 5, wherein the organic light-emitting element includes a light-emitting layer including a light-emitting material, and the light-emitting material emits fluorescent light.

[0283] Implementation Plan 7

[0284] The image forming apparatus according to any one of Embodiments 1 to 5, wherein the organic light-emitting element includes a light-emitting layer including a light-emitting material, and the light-emitting material emits phosphorescence.

[0285] Implementation Plan 8

[0286] The image forming apparatus according to Embodiment 6, wherein the light-emitting material has a condensed polycyclic hydrocarbon skeleton.

[0287] Implementation Plan 9

[0288] The image forming apparatus according to Embodiment 8, wherein the light emitting material is a hydrocarbon compound.

[0289] Implementation Plan 10

[0290] The image forming apparatus according to any one of Embodiments 6 to 9, wherein the light-emitting layer contains a compound different from the light-emitting material, and the compound has a condensed polycyclic hydrocarbon skeleton.

[0291] Implementation Plan 11

[0292] The image forming apparatus according to embodiment 10, wherein the condensed polycyclic hydrocarbon skeleton is a naphthalene skeleton, an anthracene skeleton, a phenanthrene skeleton, a fluorene skeleton, a pyrene skeleton, a triphenylene skeleton, skeleton, tetracene skeleton or perylene skeleton.

[0293] Implementation Plan 12

[0294] The image forming apparatus according to Embodiment 7, wherein the light emitting material is a metal complex.

[0295] Implementation Plan 13

[0296] The image forming apparatus according to Embodiment 12, wherein the light-emitting material is an iridium complex or a platinum complex.

[0297] Implementation Plan 14

[0298] The image forming apparatus according to Embodiment 6, wherein the fluorescence is delayed fluorescence.

[0299] Implementation Plan 15

[0300] The image forming apparatus according to Embodiment 6, wherein the light-emitting layer further contains a delayed fluorescent material, and the lowest excitation singlet energy of the delayed fluorescent material is higher than the lowest excitation singlet energy of the light-emitting material.

[0301] Implementation Plan 16

[0302] The image forming apparatus according to embodiment 15, wherein the light-emitting layer further contains an organic compound different from the delayed fluorescent material, and the lowest excitation singlet energy of the organic compound is higher than the lowest excitation singlet energy of the light-emitting material.

[0303] Implementation Plan 17

[0304] The image forming apparatus according to any one of Embodiments 1 to 16, wherein T1 is less than 1 μs.

[0305] Implementation Plan 18

[0306] The image forming apparatus according to any one of Embodiments 1 to 17, wherein the organic light emitting element has an interference structure.

[0307] Implementation Plan 19

[0308] The image forming apparatus according to embodiment 18, wherein the organic light emitting element includes a reflective layer, a first electrode, a light emitting layer, and a second electrode, and

[0309] Light emitted from the light emitting layer is enhanced between the reflective layer and the light emitting layer.

[0310] Implementation Plan 20

[0311] The image forming apparatus according to embodiment 18, wherein the organic light emitting element includes a first electrode, a light emitting layer, and a second electrode, and

[0312] Light emitted from the light emitting layer is enhanced between the first electrode and the second electrode.

[0313] The present disclosure can provide an image forming apparatus capable of high image quality.

[0314] While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the present disclosure is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus comprising: an exposure light source comprising an organic light emitting element; and a photoreceptor configured to receive light emitted from the organic light emitting element, The luminous intensity of the organic light emitting element when the current is supplied to the organic light emitting element is defined as L0, The time period from the end of supplying current to the organic light emitting element to the quenching of the organic light emitting element is defined as T1, and the time period from the start of supplying current to the organic light emitting element to the end of supplying current to the organic light emitting element is defined as T2, and T1 and T2 satisfy the relationship of formula (a): (a)T1 <T2。 2. The image forming apparatus according to claim 1 , wherein T1 and T2 satisfy the relationship of formula (b): (b)T2 / T1>1.

0.

3. The image forming apparatus according to claim 1 , wherein a period from when current supply to the organic light emitting element ends to when current supply to the organic light emitting element starts is defined as T3, and T1 and T3 satisfy the relationship of formula (c): (c)T1 <T3。 4. An image forming apparatus comprising: an exposure light source comprising an organic light emitting element; and a photoreceptor configured to receive light emitted from the organic light emitting element, The luminous intensity of the organic light emitting element when the current is supplied to the organic light emitting element is defined as L0, The time period from the end of supplying current to the organic light emitting element to the quenching of the organic light emitting element is defined as T1, and the time period from the end of supplying current to the organic light emitting element to the start of supplying current to the organic light emitting element is defined as T3, and T1 and T3 satisfy the relationship of formula (c): (c)T1 <T3。 5 . The image forming apparatus according to claim 1 , wherein the organic light emitting element has a top emission structure.

6. The image forming apparatus according to claim 1 or 4, wherein the organic light emitting element includes a light emitting layer containing a light emitting material, and The luminescent material emits fluorescent light.

7. The image forming apparatus according to claim 1 or 4, wherein the organic light emitting element includes a light emitting layer containing a light emitting material, and The luminescent material emits phosphorescence.

8. The image forming apparatus according to claim 6, wherein the light emitting material has a condensed polycyclic hydrocarbon skeleton.

9. The image forming apparatus according to claim 8, wherein the light emitting material is a hydrocarbon compound.

10. The image forming apparatus according to claim 6, wherein the light emitting layer contains a compound different from the light emitting material, and The compound has a condensed polycyclic hydrocarbon skeleton.

11. The image forming apparatus according to claim 7, wherein the light emitting layer contains a compound different from the light emitting material, and The compound has a condensed polycyclic hydrocarbon skeleton.

12. The image forming apparatus according to claim 10 or 11, wherein the condensed polycyclic hydrocarbon skeleton is a naphthalene skeleton, an anthracene skeleton, a phenanthrene skeleton, a fluorene skeleton, a pyrene skeleton, a triphenylene skeleton, skeleton, tetracene skeleton or perylene skeleton.

13. The image forming apparatus according to claim 7, wherein the light emitting material is a metal complex. 14 . The image forming apparatus according to claim 13 , wherein the light emitting material is an iridium complex or a platinum complex.

15. The image forming apparatus according to claim 6, wherein the fluorescence is delayed fluorescence.

16. The image forming apparatus according to claim 6, wherein the light emitting layer further comprises a delayed fluorescent material, and The lowest excitation singlet energy of the delayed fluorescent material is higher than the lowest excitation singlet energy of the luminescent material.

17. The image forming apparatus according to claim 16, wherein the light emitting layer further comprises an organic compound different from the delayed fluorescent material, and The lowest excited singlet energy of the organic compound is higher than the lowest excited singlet energy of the light-emitting material.

18. The image forming apparatus according to claim 1 or 4, wherein T1 is less than 1 μs.

19. The image forming apparatus according to claim 1 or 4, wherein the organic light emitting element has an interference structure.

20. The image forming apparatus according to claim 19, wherein the organic light emitting element comprises a reflective layer, a first electrode, a light emitting layer, and a second electrode, and Light emitted from the light emitting layer is enhanced between the reflective layer and the light emitting layer.

21. The image forming apparatus according to claim 19, wherein the organic light emitting element comprises a first electrode, a light emitting layer, and a second electrode, and Light emitted from the light emitting layer is enhanced between the first electrode and the second electrode.

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