Image forming apparatus

Abstract

The present disclosure provides an image forming apparatus including: an exposure light source having an organic light emitting element; and a photoreceptor that receives light emitted from the organic light emitting element. When L0 is an emission intensity of light emitted from the organic light emitting element at the end of supply of a current to the organic light emitting element, T1 is a period of time from the end of supply of the current to the organic light emitting element to extinction of the organic light emitting element, and T2 is a period of time from the start of supply of the current to the organic light emitting element to the end of supply of the current to the organic light emitting element, T1 is not less than T2.

Description

Technical Field

[0001] This invention relates to an image forming apparatus. Background Technology

[0002] Image forming apparatus using electrophotographic systems is widely and commonly used in copiers, fax machines, and printers. Such image forming apparatus includes an exposure light source with a light-emitting element. Examples of light-emitting elements include those using light-emitting diodes (LEDs) and those using organic light-emitting elements (OLEDs). A photosensitive drum comprising an organic electrophotographic photoreceptor (OPC) (hereinafter sometimes referred to as the "photoreceptor") is exposed to light emitted from these light-emitting elements, and an image corresponding to the latent image formed on the photosensitive drum is printed onto recording paper.

[0003] Patent document 1 describes an image forming apparatus equipped with an exposure light source including an organic light-emitting element (hereinafter sometimes referred to as an "organic electroluminescent element" or "organic EL element").

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-128040 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Organic light-emitting elements (OLEDs) have the characteristic of continuing to emit light even after the supply current has ended, and their luminous intensity decreases over time. Therefore, when OLEDs are used as exposure light sources, it is necessary to consider the light emitted from the OLED after the supply current has ended (hereinafter sometimes referred to as "afterglow").

[0009] However, Patent Document 1 does not disclose the relationship between the exposure time of an organic light-emitting element (hereinafter sometimes referred to as an "organic electroluminescent element" or "organic EL element") relative to a photoreceptor and the time from the end of the current supply to the organic light-emitting element until the organic light-emitting element is turned off, and there is a problem with the durability of the organic light-emitting element.

[0010] The present invention was made in view of the above-mentioned problems, and its object is to provide an image forming apparatus that can achieve excellent component durability.

[0011] Solution for solving the problem

[0012] According to one aspect of the invention, an image forming apparatus includes an exposure light source comprising an organic light-emitting element and a photoreceptor receiving light emitted from the organic light-emitting element, wherein when the luminous intensity from the organic light-emitting element is L0 at the end of current supply to the organic light-emitting element, the time period from the end of current supply to the organic light-emitting element until the organic light-emitting element is denoted as T1, and the time period from the start of current supply to the organic light-emitting element until the end of current supply to the organic light-emitting element is denoted as T2, T1 and T2 satisfy the relationship of equation (a):

[0013] (a) T1≥T2.

[0014] According to another aspect of the invention, an image forming apparatus includes an exposure light source comprising an organic light-emitting element and a photoreceptor for receiving light emitted from the organic light-emitting element, wherein when the luminous intensity from the organic light-emitting element is L0 at the end of current supply to the organic light-emitting element, the time period from the end of current supply to the organic light-emitting element until the organic light-emitting element is extinguished is T1, and the time period from the end of current supply to the organic light-emitting element until the start of current supply to the organic light-emitting element is T3, T1 and T3 satisfy the relationship of equation (c):

[0015] (c)T1≥T3.

[0016] The effects of the invention

[0017] According to the present invention, an image forming apparatus capable of achieving excellent component durability can be provided. Attached Figure Description

[0018] [ Figure 1A [Illustration] is a schematic diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention.

[0019] [ Figure 1B [ ] is a schematic diagram illustrating an example of an exposure light source of an image forming apparatus according to an embodiment of the present invention.

[0020] [ Figure 1C [ ] is a schematic diagram illustrating an example of an exposure light source of an image forming apparatus according to an embodiment of the present invention.

[0021] [ Figure 2 [Illustration] is a schematic diagram illustrating the operation of the image forming apparatus according to this embodiment.

[0022] [ Figure 3 [Illustration] is a schematic diagram showing one form of the light-emitting device according to this embodiment.

[0023] [ Figure 4A [This is a schematic three-dimensional view of the head substrate.]

[0024] [ Figure 4B[ ] is a diagram showing the arrangement of multiple light-emitting elements disposed on the head substrate.

[0025] [ Figure 4C ]yes Figure 4B A magnified view of a portion of it. Detailed Implementation

[0026] In this specification, the luminous intensity from the organic light-emitting element when the current supply to the organic light-emitting element ends is L0, the time period from the end of the current supply to the organic light-emitting element until the organic light-emitting element is turned off is T1, the time period from the start of the current supply to the organic light-emitting element until the end of the current supply to the organic light-emitting element is T2, and the time period from the end of the current supply to the organic light-emitting element until the start of the current supply to the organic light-emitting element is T3.

[0027] The extinction of an organic light-emitting element (OLED) refers to a state where the luminous intensity has decreased to the point where the OLED can no longer form a latent image on the photoreceptor. For example, the extinction of an OLED can occur when the luminous intensity becomes L0 / 2, L0 / e, or L0 / 10. e is Napier's constant.

[0028] In this specification, the host material is the compound that has the largest mass ratio among the compounds constituting the luminescent layer. The guest material is the compound whose mass ratio among the compounds constituting the luminescent layer is smaller than that of the host material, and is responsible for primary luminescence. The auxiliary material is the compound whose mass ratio among the compounds constituting the luminescent layer is smaller than that of the host material, and contributes to the luminescence of the guest material. The auxiliary material is also referred to as the second host. The host material may be referred to as the first compound, and the auxiliary material may be referred to as the second compound.

[0029] <Image forming equipment>

[0030] The image forming apparatus according to this embodiment will be described with reference to the accompanying drawings.

[0031] Figure 1AThis is a schematic diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. The 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 transport roller 33, and a fixing unit 35. The photoreceptor 27 and the exposure light source 28 are configured to face each other, and light 29 is emitted from the exposure light source 28 to form an electrostatic latent image on the surface of the photoreceptor 27. The exposure light source 28 includes one or more organic light-emitting elements. More specifically, the photoreceptor 27 receives light 29 emitted from one or more organic light-emitting elements included in the exposure light source 28, thereby forming an electrostatic latent image on the surface of the photoreceptor 27. The exposure light source 28 may further include a lens array. The exposure light source 28 may include multiple rows of light-emitting elements, or may include a single row of light-emitting elements. The developing unit 31 includes a toner, etc. The charging unit 30 charges the photoreceptor 27. The transfer unit 32 transfers the developed image to a recording medium 34. The transport roller 33 transports the recording medium 34. The recording medium 34 is, for example, paper. The fixing unit 35 fixes the image formed on the recording medium 34.

[0032] Figure 1B and Figure 1C This diagram shows the exposure light source 28 and is a schematic diagram showing the arrangement of multiple light-emitting portions 36 on a strip-shaped substrate. Arrows 37 each indicate a direction parallel to the axis of the photoreceptor and indicate the column direction of the light-emitting portions 36, including organic light-emitting elements. This column direction is the same as the direction of the axis around which the photoreceptor 27 rotates. This direction can also be referred to as the long axis direction of the photoreceptor 27. Figure 1B The light-emitting portion 36 is arranged along the long axis of the photoreceptor 27. Figure 1C It shows the relationship with Figure 1B Different configurations exist, in which the light-emitting portions 36 are alternately arranged in each of the first and second columns in the column direction. The first and second columns are arranged at different positions in the row direction. In the first column, multiple light-emitting portions 36 are arranged at intervals. The second column includes light-emitting portions 36 at positions corresponding to the intervals between the light-emitting portions 36 in the first column. That is, multiple light-emitting portions 36 are also arranged at intervals in the row direction. Figure 1C The configuration can also be described, for example, as a state in which the light-emitting part 36 is configured in a grid pattern, a state in which the light-emitting part 36 is configured in an interlaced pattern, or a state in which the light-emitting part 36 is configured in a checkerboard pattern.

[0033] The image forming apparatus according to this embodiment has the following features (a) or (b).

[0034] (a) Organic light-emitting elements satisfy T1≥T2.

[0035] (b) Organic light-emitting elements satisfy T1≥T3.

[0036] These features will be described below.

[0037] (a) Organic light-emitting elements satisfy T1≥T2.

[0038] The image forming apparatus according to this embodiment has a configuration where T1 is greater than or equal to T2. Utilizing this feature, the image forming apparatus according to this embodiment can achieve high image quality.

[0039] Reference Figure 2 This section provides a detailed description of the image forming apparatus according to this embodiment. Figure 2 In this context, the moment when the luminous intensity of the organic light-emitting element (OLED) becomes L0 / e is the moment when the OLED turns off. Figure 2 In this diagram, t1 and t1' are the moments when current is supplied to the organic light-emitting element (OLED), t2 and t2' are the moments when current supply to the OLED ends, and t3 and t3' are the moments when the OLED turns off. Here, the time interval from t1 to t2 can be called the first emission time interval, the time interval from t1' to t2' can be called the second emission time interval, and subsequent time intervals can be called the third emission time interval, the fourth emission time interval, and so on. T1 is the time interval from t2 to t3 or from t2' to t3', and T2 is the time interval from t1 to t2 or from t1' to t2'. In this specification, T1 can be referred to as the afterglow lifetime.

[0040] exist Figure 2 In the illustrated embodiment, the organic light-emitting element emits light with the same luminous intensity during both the first and second emission periods; however, the organic light-emitting element is not limited to this. The luminous intensity can differ between the first and second emission periods. Specifically, the luminous intensity during the first emission period can be higher than that during the second emission period, or vice versa. Alternatively, the luminous intensity can vary during the first (second) emission period.

[0041] The image forming apparatus according to this embodiment forms a latent image by selecting organic light-emitting elements (pixels) to emit light based on image data of the image to be formed and exposing a rotating photoreceptor 27 to light. At this time, when the afterglow lifetime of the afterglow emitted from the organic light-emitting element is greater than or equal to the exposure time, the required luminous intensity for the next luminous period can be suppressed. This will refer to... Figure 2 Detailed description.

[0042] exist Figure 2At t1' which is the second light emission time period, the light emission intensity of afterglow from the organic light-emitting element is A. At this time, at t1', it is necessary to apply a current (voltage) such that the light emission intensity of light emitted from the organic light-emitting element becomes L0, and the value of the current (voltage) only needs to correspond to the light emission intensity L0-A. On the other hand, when the afterglow lifetime is shorter than the exposure time, the light emission intensity of afterglow from the organic light-emitting element is 0 at t1', and therefore, at t1', it is necessary to apply a current (voltage) such that the light emission intensity of light emitted from the organic light-emitting element becomes L0, and the value of the current (voltage) corresponds to the light emission intensity L0. Therefore, the image forming apparatus according to the present embodiment can suppress the current (voltage) applied in the next (second) light emission time period, and thus the element durability of the organic light-emitting element is excellent.

[0043] In the image forming apparatus according to the present embodiment, the value of T2 / T1 is 1.0 or less, preferably 0.90 or less, more preferably 0.80 or less, further preferably 0.70 or less, further preferably 0.60 or less, further preferably 0.50 or less, and particularly preferably 0.40 or less. Specifically, 0<T2 / T1≤1.0 may be satisfied, 0<T2 / T1≤0.7 may be satisfied, 0<T2 / T1≤0.5 may be satisfied, or 0<T2 / T1≤0.4 may be satisfied. T1 may be 10 ns or more, may be 50 ns or more, may be 1 μs or more, may be 2 μs or more, may be 5 μs or more, may be 10 μs or more, may be 15 μs or more, or may be 50 μs or more.

[0044] (b) The organic light-emitting element satisfies T1≥T3.

[0045] The image forming apparatus according to the present embodiment has a configuration in which T1 is greater than or equal to T3. With this feature, the image forming apparatus according to the present embodiment can achieve high image quality.

[0046] referring to Figure 2 , the image forming apparatus according to the present embodiment is specifically described. In Figure 2 , the time point at which the light emission intensity of the organic light-emitting element becomes L0 / e is the time point at which the organic light-emitting element is turned off. In Figure 2In this diagram, t1 and t1' are the moments when current is supplied to the organic light-emitting element (OLED), t2 and t2' are the moments when current supply to the OLED ends, and t3 and t3' are the moments when the OLED turns off. Here, the time interval from t1 to t2 can be called the first emission time interval, the time interval from t1' to t2' can be called the second emission time interval, and subsequent time intervals can be called the third emission time interval, the fourth emission time interval, etc. T1 is the time interval from t2 to t3 or from t2' to t3', and T3 is the time interval from t2 to t1' or from t2' to the start of current supply to the OLED in the third emission time interval. In this specification, T1 can be called the afterglow lifetime, and T3 can be called the emission interval time interval.

[0047] exist Figure 2 In the illustrated embodiment, the organic light-emitting element emits light with the same luminous intensity during both the first and second emission periods; however, the organic light-emitting element is not limited to this. The luminous intensity can differ between the first and second emission periods. Specifically, the luminous intensity during the first emission period can be higher than that during the second emission period, or vice versa. Alternatively, the luminous intensity can vary during the first (second) emission period.

[0048] The image forming apparatus according to this embodiment forms a latent image by selecting organic light-emitting elements (pixels) to emit light based on image data of the image to be formed and exposing a rotating photoreceptor 27 to light. At this time, when the afterglow lifetime of the afterglow emitted from the organic light-emitting element is greater than or equal to the emission interval time period, the required emission intensity for the next emission interval time period can be suppressed. This will refer to... Figure 2 Detailed description.

[0049] exist Figure 2 In the second emission time period (t1'), the luminous intensity of the afterglow from the organic light-emitting element is A. At this time, at t1', a current (voltage) needs to be applied so that the luminous intensity of the light emitted from the organic light-emitting element becomes L0, and the value of the current (voltage) only needs to correspond to the luminous intensity L0-A. On the other hand, when the afterglow lifetime is shorter than the exposure time, the luminous intensity of the afterglow from the organic light-emitting element is 0 at t1'. Therefore, at t1', a current (voltage) needs to be applied so that the luminous intensity of the light emitted from the organic light-emitting element becomes L0, and the value of the current (voltage) corresponds to the luminous intensity L0. Therefore, the image forming apparatus according to this embodiment can suppress the current (voltage) applied in the next (second) emission time period, thus resulting in excellent element durability of the organic light-emitting element.

[0050] In the image forming apparatus according to the present embodiment, the value of T3 / T1 is 1.0 or less, preferably 0.90 or less, more preferably 0.80 or less, further preferably 0.70 or less, further preferably 0.60 or less, and particularly preferably 0.50 or less. Specifically, 0<T3 / T1<1.0 may be satisfied, 0<T3 / T1≤0.80 may be satisfied, 0<T3 / T1≤0.70 may be satisfied, 0<T3 / T1≤0.60 may be satisfied, or 0<T3 / T1≤0.50 may be satisfied. T1 may be 10 ns or more, may be 50 ns or more, may be 1 μs or more, may be 2 μs or more, may be 5 μs or more, may be 10 μs or more, may be 15 μs or more, or may be 50 μs or more.

[0051] An image forming apparatus according to another embodiment may have both features (a) and (b). By using both features (a) and (b), higher image quality can be achieved.

[0052] The image forming apparatus according to the present embodiment may further have the following configurations. The image forming apparatus may have any one of the following configurations (c) to (g), or may have a plurality of configurations among (c) to (g).

[0053] (c) The organic light-emitting element has a top emission configuration.

[0054] (d) The organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits fluorescence.

[0055] (e) The organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits phosphorescence.

[0056] (f) The organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits delayed fluorescence.

[0057] (g) A plurality of pixels of the organic light-emitting element are two-dimensionally arranged at high density.

[0058] These configurations will be described below.

[0059] (c) The organic light-emitting element has a top emission configuration.

[0060] The image forming apparatus according to the present embodiment preferably has a top emission configuration. This is because the top emission configuration is excellent in light extraction efficiency as compared with the bottom emission configuration. The bottom emission configuration is a light emission form in which light is extracted from the side where the pixel circuit described below is provided. The top emission configuration is a light emission form in which light is extracted from the side opposite to the side where the pixel circuit described below is provided.

[0061] In this embodiment, it is further preferred that the organic light-emitting element has 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 sequentially from the substrate side, the organic light-emitting element has a configuration in which the optical distance between the reflective electrode and the light-emitting layer enhances the emission wavelength. In this case, a layer made of an insulating material or a transparent material such as ITO (indium tin oxide) or IZO (indium zinc oxide) can be disposed between the reflective layer and the first electrode. Furthermore, when the organic light-emitting element includes a first electrode, a light-emitting layer, and a second electrode sequentially from the substrate side, it is preferable that the light emitted from the light-emitting layer can be enhanced between the first electrode and the second electrode. In this case, it is preferable that the first electrode can reflect the light emitted from the light-emitting layer.

[0062] (d) An organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits fluorescence.

[0063] Preferably, the image forming apparatus according to this embodiment has an organic light-emitting element comprising a light-emitting layer containing a light-emitting material, and the light-emitting material emitting fluorescence.

[0064] Furthermore, since high luminescence intensity can be emitted in the image forming apparatus according to this embodiment, the luminescent material must be stable during repeated luminescence processes. Therefore, a luminescent material having a fused polycyclic hydrocarbon backbone is preferred as the luminescent material emitting fluorescence. Specifically, the fused polycyclic hydrocarbon backbone preferably comprises a perylene backbone, and more preferably a perylene backbone. Hydrocarbon compounds are more preferably luminescent materials emitting fluorescence. This is because hydrocarbon compounds have high bond stability and can suppress degradation during repeated luminescence. Specific examples of luminescent materials emitting fluorescence include the example compounds RD1 to RD6 described below, but the luminescent material is not limited to these.

[0065] From another perspective, in luminescent materials, freely rotatable single bonds are preferably carbon-carbon bonds, more preferably sp2 carbon-sp2 carbon bonds, and all freely rotatable single bonds are more preferably carbon-carbon bonds, and even more preferably sp2 carbon-sp2 carbon bonds. In this specification, a freely rotatable single bond refers to a bond between unit A and unit B that is not fused when the single bond between unit A and unit B is represented by "AB". Units A and B can be atoms such as carbon and nitrogen atoms, or molecules such as benzene and carbazole. Table 1 presents the bond energies of the corresponding bonds.

[0066] [Table 1]

[0067]

[0068] F1 and F2, each containing a carbon-nitrogen bond, have a bond energy of 3.9 eV. On the other hand, F3, with a freely rotatable carbon-carbon bond, has a bond energy of 4.5 eV, and F4, with a freely rotatable bond between sp2 carbons, has a bond energy of 5.0 eV. Therefore, when the freely rotatable single bond is a carbon-carbon bond, the framework is preferred because the framework is less likely to decompose. Among carbon-carbon bonds, the bond between sp2 carbons has a particularly high bond energy, thus a framework where the freely rotatable single bond is an sp2-sp2 carbon bond is further preferred because the framework is even less likely to decompose.

[0069] The image forming apparatus according to this embodiment may include a first organic compound, different from the fluorescent material, in the light-emitting layer of the organic light-emitting element. The first organic compound may be a compound having a lower excitation singlet state energy higher than that of the fluorescent material. The first organic compound preferably has a fused polycyclic aromatic hydrocarbon (PAH) skeleton. Specifically, the fused PAH skeleton is a naphthalene skeleton, anthracene skeleton, phenanthrene skeleton, fluorene skeleton, pyrene skeleton, triphenylene skeleton, phenylene skeleton, tetraphenylene skeleton, or perylene skeleton. In the first organic compound, the freely rotatable single bonds are preferably carbon-carbon bonds, more preferably sp2 carbon-sp2 carbon bonds, all freely rotatable single bonds are more preferably carbon-carbon bonds, and all freely rotatable single bonds are more preferably sp2 carbon-sp2 carbon bonds.

[0070] Furthermore, the image forming apparatus according to this embodiment can include a delayed fluorescence material, different from the luminescent material emitting fluorescence, in the luminescent layer of the organic light-emitting element. Specifically, the delayed fluorescence material is a compound whose minimum excitation singlet state energy and minimum excitation triplet state energy differ from the delayed fluorescence material by less than 0.20 eV. The delayed fluorescence material allows excitons to undergo reverse intersystem crossing from the triplet state to the singlet state. The delayed fluorescence material can be a compound having a minimum excitation singlet state energy higher than that of the luminescent material emitting fluorescence. Furthermore, when the luminescent layer contains a delayed fluorescence material, the luminescent layer can further contain the aforementioned first organic compound. This configuration is called a TADF-assisted fluorescence (TAF) configuration and exhibits higher luminous efficiency than conventional fluorescence luminescence.

[0071] In this specification, the luminescent material emitting fluorescence may contain other luminescent components besides fluorescence. For example, in addition to fluorescence, it may contain delayed fluorescence or phosphorescence. However, fluorescence needs to be contained in a larger amount than other luminescent components. This also applies to luminescent materials emitting phosphorescence and luminescent materials emitting delayed fluorescence.

[0072] (e) An organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits phosphorescence.

[0073] Preferably, the image forming apparatus according to this embodiment has an organic light-emitting element comprising a light-emitting layer containing a light-emitting material, and the light-emitting material emitting phosphorescence.

[0074] Typically, it is known that excitons generated by electrical energy are distributed between the triplet and singlet states in a 3:1 ratio. Therefore, emission (phosphorescence) from the triplet state has a higher luminous efficiency than emission (fluorescence) from the singlet state. Thus, the image forming apparatus according to this embodiment is preferred because of its excellent luminous efficiency.

[0075] Phosphorescence is generally known to have a long afterglow lifetime. As mentioned above, a long afterglow lifetime is preferred because it allows for image forming apparatuses with excellent component durability.

[0076] Phosphorescent materials can be compounds containing metal complexes, preferably iridium or platinum complexes. Examples of ligands contained in the metal complexes include substituted or unsubstituted phenyl-isoquinoline ligands, substituted or unsubstituted phenyl-benzoisoquinoline ligands, and substituted or unsubstituted phenyl-naphthoisoquinoline ligands. Specific examples of phosphorescent materials include the example compounds RD9 to RD16 described below, but the luminescent materials are not limited thereto.

[0077] The image forming apparatus according to this embodiment may include a second organic compound, different from the phosphorescent luminescent material, in the luminescent layer of the organic light-emitting element. The second organic compound may be a compound having a lower excitation triplet energy higher than that of the phosphorescent luminescent material. The second organic compound is preferably a compound having a fused polycyclic hydrocarbon skeleton that may have substituents, or a compound having a heterocyclic skeleton that may have substituents. From another perspective, in the second organic compound, the freely rotatable single bonds are preferably carbon-carbon bonds, more preferably sp2 carbon-sp2 carbon bonds, all freely rotatable single bonds are more preferably carbon-carbon bonds, and all freely rotatable single bonds are more preferably sp2 carbon-sp2 carbon bonds.

[0078] The fused polycyclic hydrocarbon skeleton can be a skeleton with 10 to 25 carbon atoms, and specific examples include the naphthalene skeleton, fluorene skeleton, anthracene skeleton, phenanthrene skeleton, pyrene skeleton, β skeleton, triphenylene skeleton, tetraphenylene skeleton, fluoranthene skeleton and perylene skeleton.

[0079] The heterocyclic skeleton can be a skeleton with 3 to 30 carbon atoms or a skeleton with 3 to 18 carbon atoms, and examples include the dibenzofuran skeleton, the dibenzothiophene skeleton, the xanthone skeleton, the thioxanthone skeleton, the carbazole skeleton, the indolocarbazole skeleton, and the triazine skeleton.

[0080] The second organic compound is preferably a compound having a triphenylene skeleton, a xanthonone skeleton, or an indolocarbazole skeleton. These skeletons have high planarity, which further improves charge mobility. Therefore, the organic light-emitting element can be expected to exhibit a lower driving voltage.

[0081] (f) The organic light-emitting element includes a light-emitting layer containing a light-emitting material, and the light-emitting material emits delayed fluorescence.

[0082] Preferably, the image forming apparatus according to this embodiment has an organic light-emitting element comprising a light-emitting layer containing a light-emitting material, and the light-emitting material is configured to emit delayed fluorescence. Here, delayed fluorescence refers to fluorescence emission emitted via reverse intersystem crossing of excitons or fluorescence emission emitted via triplet-triplet fusion (TTF).

[0083] In the image forming apparatus according to this embodiment, the emissive layer comprises a delayed-fluorescence material. The delayed-fluorescence material is a compound whose minimum excited singlet state energy differs from its minimum excited triplet state energy by less than 0.20 eV. The delayed-fluorescence material allows excitons to undergo reverse intersystem crossing from the triplet state to the singlet state. In this case, the emissive layer may further comprise the first organic compound described in (d), and the first organic compound may be a compound having a minimum excited singlet state energy higher than that of the delayed-fluorescence material.

[0084] Typically, excitons generated by electrical energy are known to be distributed between triplet and singlet states in a 3:1 ratio. Since the luminescent layer contains a delayed-fluorescence material, excitons distributed in the triplet state can undergo reverse intersystem crossing to the singlet state, thus the organic light-emitting element exhibits higher luminous efficiency. Therefore, the image forming apparatus according to this embodiment is preferred because of its excellent luminous efficiency.

[0085] Delayed fluorescence is typically known to have a long afterglow lifetime. As mentioned above, a long afterglow lifetime is preferred because it allows for image forming apparatuses with excellent element durability.

[0086] Furthermore, in the image forming apparatus according to this embodiment, the light-emitting layer may have a configuration using TTF. TTF is a configuration in which triplet excitons collide with each other to generate excitons with higher energy, and the excitons are used to emit light from the singlet state. Using TTF is preferred because triplet excitons can be used for fluorescence emission, thus obtaining an organic light-emitting element with excellent luminous efficiency.

[0087] Delayed fluorescence is typically known to have a long afterglow lifetime. As mentioned above, a long afterglow lifetime is preferred because it allows for image forming apparatuses with excellent element durability.

[0088] (g) Multiple pixels of the organic light-emitting element are arranged in a high-density two-dimensional configuration.

[0089] The image forming apparatus according to this embodiment includes a plurality of pixels arranged two-dimensionally along the rotation direction of the photoreceptor and the rotation axis direction of the photoreceptor. Therefore, the organic light-emitting elements are densely packed in two dimensions, and the luminous intensity during exposure is improved. Specifically, the organic light-emitting elements can have a pixel density of 600 dpi or more, a pixel density of 1200 dpi or more, a pixel density of 2400 dpi or more, or a pixel density of 4800 dpi or more.

[0090] When improving luminescence intensity, image forming devices excel in a series of mechanisms that effectively excite the photosensitive layer of the photoreceptor and rapidly transfer charge to the charge transport material, thus suppressing residual charge and preventing degradation of image quality.

[0091] The configuration of the exposure light source 28 included in the image forming apparatus according to this embodiment is described in more detail below.

[0092] (First Implementation Plan)

[0093] Figure 3 This is a schematic diagram illustrating one form of a light-emitting device included in an image forming apparatus according to this embodiment. The light-emitting device according to this embodiment has a rectangular shape, having a long side parallel to a first direction and a short side parallel to a direction intersecting the first direction. For example, the first direction may be a direction along the rotation axis of the photoreceptor of the image forming apparatus.

[0094] The substrate 1701 has a polygonal shape, and an example of a rectangular substrate 1701 will be described herein. In this specification, the direction of the long side of the rectangular substrate 1701 is referred to as the first direction, and the direction of the short side orthogonal to the long side is referred to as the second direction. Furthermore, the polygonal shape in this specification includes shapes with rounded corners. A moisture-resistant ring 1700 for suppressing and preventing moisture from entering the light-emitting device is disposed on the rectangular substrate 1701. The moisture-resistant ring 1700 may be, for example, a protective ring composed of a wiring layer.

[0095] The light-emitting area 1702, contact area 1703, pad 1704, and circuit 1706 are disposed inside the moisture-resistant ring 1700. In this embodiment, the contact area 1703 includes a first contact area 1703_1, a second contact area 1703_2, and a third contact area 1703_3. Furthermore, the pad 1704 includes a first pad 1704_1, a second pad 1704_2, and a third pad 1704_3.

[0096] Circuit 1706 is part of a circuit that drives a light-emitting device. Specific examples include, but are not limited to, input protection circuits, input circuits for inputting data for various driving operations, and logic circuits for processing the data.

[0097] In the light-emitting region 1702, light-emitting elements EL are arranged in rows and columns. Each light-emitting element EL includes an organic light-emitting element having the features of this invention. The contact region 1703 is a region where wiring is disposed to be electrically connected to the common electrode of the light-emitting element EL. Pad 104_1 electrically connects the contact region 1703 to external components.

[0098] The outer periphery of the moisture-resistant ring 1700 may include multiple recesses. These portions can serve as contact areas, for example, to which ribs, which are part of the deposition mask in the film formation step, come into contact.

[0099] As described above, each of the plurality of light-emitting elements (ELs) arranged in a matrix in the light-emitting region 1702 includes a light-emitting layer and a first electrode and a second electrode that hold the light-emitting layer. In this embodiment, an example is shown where the first electrode is an independent electrode provided for each light-emitting element (EL), and the second electrode is a common electrode provided for all light-emitting elements (ELs).

[0100] For example, when the light-emitting elements EL are arranged in four rows in the light-emitting area 1702, such as Figure 3 As shown, the initial positions of the light-emitting elements EL in the first row and the second row can be offset from each other along the X-direction by 1 / 4 of the X-direction dimension of the light-emitting element EL. When n is an integer greater than 2 and there are n rows, the initial positions of the light-emitting elements EL in the first row and the second row can be offset from each other along the X-direction by 1 / n of the X-direction dimension of the light-emitting element EL. This configuration is beneficial for improving resolution.

[0101] The contact area 1703 is the area adjacent to the light-emitting area 1702 of the substrate 1701 and is disposed inside the moisture-proof ring 1700. In addition, at least one of the first contact area 1703, the pad 104 and the circuit 1706 can be disposed together with the recess of the moisture-proof ring 1700 between the light-emitting area 102 and one long side end of the substrate 1701, and can be arranged in series relative to the long side direction.

[0102] In this way, by setting the contact area 1703, the pad area 1704, and the circuit 1706 at the same position along the short side, the length of the light-emitting device along the short side can be reduced, and the light-emitting device can be miniaturized.

[0103] The light-emitting device of this embodiment includes multiple contact regions 1703 along the long side of the light-emitting device between the common electrode of the light-emitting element EL and the power supply wiring. When the common electrode is made of, for example, a transparent electrode material with relatively high resistance, the voltage drop may increase along the long axis. Therefore, the voltage applied to each OLED varies depending on the distance from the contact region to which the supplied potential is located. As a result, among OLEDs to which the same voltage is applied to make the OLED emit light at the same brightness (luminous intensity), the actual luminous brightness (luminous intensity) differs, and shading may occur. In this embodiment, the multiple contact regions 1703 are arranged along the long axis, thus suppressing the voltage drop of the common electrode along the long side and suppressing the occurrence of shading.

[0104] (Second Implementation Plan)

[0105] In this implementation plan, reference will be made to Figures 4A to 4C This describes an example of a head substrate 1800 for an exposure head of an image forming apparatus, where a light-emitting device is used.

[0106] Figure 4A This is a schematic perspective view of the head substrate 1800. Figure 4B The arrangement of multiple light-emitting elements EL disposed on the head substrate 1800 is shown, and Figure 4C yes Figure 4B A magnified view of a portion of it.

[0107] LED chip 1803 is mounted on head substrate 1800. As LED chip 1803, for example, the light-emitting device described in the first embodiment can be used.

[0108] like Figure 4A As shown, an LED chip 1803 is disposed on one surface of a head substrate 1800, and a strip-shaped flexible flat cable (FFC) connector 1807 is disposed on another surface. The one surface of the head substrate 1800 mentioned here is the surface on which the LED chip 1803 is disposed (top, front). The other surface of the substrate is the surface opposite to the side on which the LED chip 1803 is disposed (bottom, back).

[0109] The FFC connector 1807 is attached to another surface (bottom or back) of the head substrate 1800, such that the length direction of the FFC connector 1807 is along the length direction of the head substrate 1800. The elongated FFC connector 1807 allows control signals (drive signals) to be input from the control circuitry of the image forming apparatus body and transmitted to each LED chip 1803. The LED chips 1803 are driven by the control signals input to the head substrate 1800 (to perform light-emitting and extinguishing operations).

[0110] The LED chip 1803 mounted on the head substrate 1800 will be described. For example... Figure 4B and Figure 4C As shown, multiple light-emitting elements (ELs) are disposed on one surface of the head substrate 1800. For example, LED chips 1803-1 to 1803-29 (29 LED chips) are disposed thereon. Figure 4B LED chips 1803_1, 1803_13, 1803_14, 1803_15, 1803_16 and 1803_29 are shown. In each of LED chips 1803-1 to 1803-29, a plurality of light-emitting elements EL are arranged along its length, and for example, 516 light-emitting elements EL are arranged.

[0111] Along the length of LED chip 1803, the center-to-center distance k2 between adjacent light-emitting elements EL corresponds to the resolution of the image forming apparatus. For example, when the resolution of the image forming apparatus in this embodiment is 1200 dpi, the light-emitting elements EL are arranged such that the center-to-center distance k2 between adjacent light-emitting elements EL is 21.16 μm along the length of LED chips 1803-1 to 1803-29. Therefore, the exposure range of the exposure head in this embodiment is approximately 314 mm.

[0112] The width of the photosensitive layer of the photosensitive drum is 314 mm or more. Since the length of the long side of A4 size recording paper and the length of the short side of A3 size recording paper are both 297 mm, the exposure head according to this embodiment has an exposure range capable of forming images on both A4 and A3 size recording papers. Although Figures 4A to 4C An example of multiple light-emitting elements EL arranged along the length direction is shown, but in addition to the length direction, the light-emitting elements EL can also be arranged along the short side direction.

[0113] Multiple LED chips 1803-1 to 1803-29 are arranged along the axial direction of the photosensitive drum. Specifically, the LED chips 1803-1 to 1803-29 are arranged alternately in two rows along the axial direction of the photosensitive drum. That is, as shown... Figure 4B As shown, odd-numbered LED chips 1803-1, 1803-3, ... 1803-29, counting from the left, are arranged in a row along the length of the substrate 1800. Conversely, even-numbered LED chips 1803-2, 1803-4, ... 1803-28, counting from the left, are arranged in a row along the length of the substrate 1800. The LED chips 1803 are configured in this manner.

[0114] Using this configuration, such as Figure 4CAs shown, along the length of LED chip 1803, the center-to-center distance k1 between light-emitting elements EL can be equal to the center-to-center distance k2 between light-emitting elements EL. Here, the center-to-center distance k1 between light-emitting elements EL represents the center-to-center distance between light-emitting elements EL disposed at one end of LED chip 1803_13 and light-emitting elements EL disposed at the other end of LED chip 1803_14. The center-to-center distance k2 between light-emitting elements EL represents the center-to-center distance between adjacent light-emitting elements EL in LED chip 1803_14.

[0115] That is, one of the light-emitting elements EL can be disposed at one end of an LED chip 1803, and the other light-emitting element EL can be disposed at the other end of another LED chip 1803. The center-to-center distance k1 between adjacent light-emitting elements EL is equal to the center-to-center distance k2 between adjacent light-emitting elements EL on one LED chip 1803.

[0116] In this embodiment, the light-emitting element EL is an organic light-emitting element and a current-driven light-emitting element. The organic light-emitting element is arranged in lines on a thin-film transistor (TFT) substrate along the main scanning direction (the axial direction of the photosensitive drum 2) and is electrically connected in parallel through power supply lines also arranged along the main scanning direction.

[0117] When the light-emitting device is used in the exposure head, linear exposure is performed. Therefore, compared to when the light-emitting device is used in a display device or the like, the ratio of the length direction (first direction X) to the short side direction (second direction Y) of the shape of the light-emitting region 1702 is larger. In addition, the shape of the LED chip substrate also has a large ratio of the length direction (first direction X) to the short side direction (second direction Y).

[0118] Specifically, for example, the length of the long side of the LED chip (or light-emitting area 1702) is more than 5 times the length of the short side of the LED chip (or light-emitting area 1702), and can be more than 10 times its length. For example, the length of the long side of the LED chip (or light-emitting area 1702) can be more than 20 times the length of the short side of the LED chip (or light-emitting area 1702).

[0119] The length of the long side of the LED chip is determined by the length of the photosensitive drum 2 along the axial direction, the number of LED chips arranged along the axial direction, and the arrangement of the LED chips 1803. In addition, the length of the short side of the LED chip 1803 is determined by whether the light-emitting element EL is arranged in the light-emitting area 1702 along the direction perpendicular to the axis of the photosensitive drum, and by the arrangement of the pads 1704 and the contact area 1703.

[0120] The organic layer 66 may have a composition including a light-emitting layer that emits red light due to the wavelength dependence of the photosensitivity of the photosensitive drum 2.

[0121] LED chip 1803 may include a color filter. Using a color filter, stray light from unexpected directions can be absorbed without reducing the amount of normal light incident on the photosensitive drum, thus improving print quality.

[0122] Organic light-emitting elements

[0123] Organic light-emitting elements will be described in detail below. However, organic light-emitting elements are not limited to those described below.

[0124] The specific component configuration of the organic light-emitting element according to this embodiment includes a multilayer component configuration in which electrode layers and organic compound layers, listed in (A) to (F) below, are sequentially stacked on a substrate. In any component configuration, the organic compound layer must include a light-emitting layer containing a light-emitting material.

[0125] (A) Anode / Light-emitting layer / Cathode

[0126] (B) Anode / Hole Transport Layer / Light Emitting Layer / Electron Transport Layer / Cathode

[0127] (C) Anode / Hole Transport Layer / Light Emitting Layer / Electron Transport Layer / Electron Injection Layer / Cathode

[0128] (D) Anode / Hole Injection Layer / Hole Transport Layer / Light Emitting Layer / Electron Transport Layer / Cathode

[0129] (E) Anode / Hole Injection Layer / Hole Transport Layer / Light Emitting Layer / Electron Transport Layer / Electron Injection Layer / Cathode

[0130] (F) Anode / Hole Transport Layer / Electron Blocking Layer / Light Emitting Layer / Hole Blocking Layer / Electron Transport Layer / Cathode

[0131] However, these examples of component configurations are only basic, and organic light-emitting elements are not limited to these. For example, various layer configurations can be used, such as providing an insulating layer, adhesive layer, or interference layer at the interface between the electrode and the organic compound layer, providing an electron transport layer or hole transport layer comprising two layers with different ionization potentials, and providing a light-emitting layer comprising two layers containing different light-emitting materials.

[0132] In the organic light-emitting element according to this embodiment, conventionally known low-molecular-weight and high-molecular-weight hole-injecting or hole-transporting compounds, host compounds, luminescent compounds, and electron-injecting or electron-transporting compounds may be used as needed. Examples of such compounds are listed below.

[0133] Materials with high hole mobility are preferred as hole injection and transport materials to facilitate hole injection from the anode and transport of the injected holes to the light-emitting layer. Furthermore, materials with high glass transition temperatures are preferred to suppress film quality degradation in organic light-emitting elements, such as crystallization. Examples of low-molecular-weight and high-molecular-weight materials with hole injection and transport properties include triarylamine derivatives, arylcarbazole derivatives, phenylenediamine derivatives, violet derivatives, phthalocyanine derivatives, porphyrin derivatives, poly(vinylcarbazole), poly(thiophene), and other conductive polymers. Moreover, the aforementioned hole injection and transport materials are also suitable for electron blocking layers. Specific examples of compounds used as hole injection and transport materials are listed below, but the compounds are not limited thereto.

[0134] [Chemical Formula 1]

[0135]

[0136] Examples of luminescent materials primarily involved in luminescence include fused-ring compounds (e.g., fluorene derivatives, naphthalene derivatives, pyrene derivatives, perylene derivatives, tetraphenylene derivatives, anthracene derivatives, rubrene, etc.); quinacridone derivatives; coumarin derivatives; zirconia derivatives; organoaluminum complexes, such as tris(8-hydroxyquinoline)aluminum; iridium complexes; platinum complexes; rhenium complexes; copper complexes; europium complexes; ruthenium complexes; and polymeric derivatives, such as poly(phenylenevinylene) derivatives, poly(fluorene) derivatives, and poly(phenylene) derivatives. Furthermore, the concentration of the luminescent material is preferably 0.01% by mass or more and 20% by mass or less, and more preferably 0.1% by mass or more and 10% by mass or less, based on the entire luminescent layer. Specific examples of compounds used as luminescent materials are listed below, but the compounds are not limited thereto.

[0137] [Chemical Formula 2]

[0138]

[0139] [Chemical Formula 3]

[0140]

[0141] Specific examples of host or auxiliary materials included in the luminescent layer include, for example, aromatic hydrocarbon compounds or derivatives thereof, carbazole derivatives, azazine derivatives, xanthonesone derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, organoaluminum complexes such as tris(8-hydroxyquinoline)aluminum and organobryllium complexes, but the host or auxiliary materials are not limited to these. Specific examples are listed below.

[0142] [Chemical Formula 4]

[0143]

[0144] Electron transport materials can be freely selected from materials capable of transporting electrons injected from the cathode to the light-emitting layer, and the selection should take into account factors such as the balance with the hole mobility of hole transport materials. Examples of materials with electron transport properties 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, thionyl derivatives, and anthracene derivatives). Furthermore, the aforementioned electron transport materials are also suitable for hole blocking layers. Specific examples of compounds used as electron transport materials are listed below, but of course, the compounds are not limited to these. Specific examples are listed below.

[0145] [Chemical Formula 5]

[0146]

[0147] Electron-injecting materials can be freely selected from materials that allow for easy injection of electrons from the cathode, taking into account factors such as balance with hole injection. Organic compounds also include n-type dopants and reducing dopants. Examples include alkali metal-containing compounds such as lithium fluoride, lithium complexes such as lithium hydroxyquinoline, benzimidazolidene derivatives, imidazolidene derivatives, fulvalene derivatives, and acridine derivatives. Electron-injecting materials can also be used in conjunction with the aforementioned electron transport materials.

[0148] Examples of luminescent materials exhibiting luminescence from a singlet excited state in this invention include compounds represented by BD1 to BD8, BD10, GD1 to GD9, and RD1 to RD8. Of course, luminescent materials are not limited to these compounds.

[0149] Examples of phosphorescent materials exhibiting luminescence from a triplet excited state in this invention include compounds represented by BD9, GD10 to GD18, and RD9 to RD16. Of course, phosphorescent materials are not limited to these compounds.

[0150] Examples of TADF materials in this invention include compounds represented by EM35 to EM38. Of course, TADF materials are not limited to these compounds.

[0151] <More detailed composition of organic light-emitting elements>

[0152] Next, the organic light-emitting element according to this embodiment will be described in more detail. The organic light-emitting element is disposed 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, and a microlens, etc., can be disposed on the second electrode. When a color filter is disposed, a planarization layer can be disposed between the color filter and the protective layer. The planarization layer can be made of an acrylic resin, etc. This also applies when a planarization layer is disposed between the color filter and the microlens.

[0153] [Substrate]

[0154] Examples of substrates include quartz, glass, silicon wafers, resin, and metals. Furthermore, switching elements such as transistors and wiring can be disposed on the substrate, and an insulating layer can be disposed thereon. The material of the insulating layer is not limited, as long as contact holes can be formed, allowing wiring to be formed between the insulating layer and the first electrode, and ensuring insulation from unconnected wiring. For example, resins such as polyimide, silicon oxide, or silicon nitride can be used.

[0155] [electrode]

[0156] As electrodes, a pair of electrodes can be used. This pair of electrodes can be an anode and a cathode. When an electric field is applied along the direction of light emission from the organic light-emitting element, the electrode with the higher potential is the anode, and the other electrode is the cathode. Alternatively, 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.

[0157] Materials with the highest possible work function are preferred for use as anode components. For example, elemental metals such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, and tungsten, mixtures containing these metals, alloys obtained by combining these metals, and metal oxides such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide can also be used. Conductive polymers such as polyaniline, polypyrrole, and polythiophene can also be used.

[0158] These electrode materials can be used alone or in combination of two or more. Additionally, the anode can consist of a single layer or multiple layers.

[0159] When the electrode is used as a reflective electrode, materials such as chromium, aluminum, silver, titanium, tungsten, molybdenum, their alloys, or stacks thereof can be used. These materials can also function as a reflective film that does not act as an electrode. When the electrode is used as a transparent electrode, a transparent conductive oxide layer, such as indium tin oxide (ITO) or indium zinc oxide, can be used, but transparent electrodes are not limited to these. Photolithography can be used to form the electrode.

[0160] On the other hand, materials with a low work function are preferred as constituent materials of the cathode. Examples 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 containing these metals. Alternatively, alloys obtained by combining these elemental metals can also be used. For example, magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper, and zinc-silver alloys can be used. Metal oxides such as indium tin oxide (ITO) can also be used. These electrode materials can be used alone or in combination of two or more. Furthermore, the cathode can have a single-layer or multi-layer structure. Silver is preferred, and silver alloys are more preferred to reduce silver aggregation. The ratio of silver to other metals is not limited as long as silver aggregation is reduced. For example, the ratio of silver to other metals can be 1:1 or 3:1.

[0161] There are no particular limitations on the cathode, and the organic light-emitting element can be a top-emitting element using a conductive oxide layer such as ITO, or a bottom-emitting element using a reflective electrode such as aluminum (Al). There are no particular limitations on the method of forming the cathode. However, methods such as DC sputtering or AC sputtering are preferred because they allow for better film coverage and easier reduction of resistance.

[0162] [Organic compound layer]

[0163] The organic compound layer includes at least a light-emitting layer, and in addition to the light-emitting layer, may further include, as needed, a hole injection layer, a hole transport layer, and an electron blocking layer on the anode side, and a hole blocking layer, an electron transport layer, and an electron injection layer on the cathode side. The organic compound layer is primarily made of organic compounds, but may also contain inorganic atoms or inorganic compounds. For example, the organic compound layer may contain copper, lithium, magnesium, aluminum, iridium, platinum, molybdenum, or zinc.

[0164] The organic compound layer included in the organic light-emitting element according to an embodiment of the present invention can be formed using dry methods such as vacuum deposition, ionization deposition, sputtering, or plasma deposition. Instead of dry methods, wet methods can also be used, which involve dissolving the material in a suitable solvent and forming the layer using known coating methods (e.g., spin coating, dip coating, casting, LB coating, or inkjet coating, etc.).

[0165] Here, when the layer is formed by vacuum deposition or solution coating, crystallization is unlikely to occur, and excellent stability over time is obtained. Furthermore, when the film is formed by coating, it can also be combined with a suitable binder resin.

[0166] Examples of adhesive resins include polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin and urea resin, but adhesive resins are not limited to these.

[0167] These adhesive resins can be used alone as homopolymers or copolymers, or two or more can be mixed and used together. Furthermore, additives such as known plasticizers, antioxidants, and UV absorbers can be used together as needed.

[0168] [charge generation layer]

[0169] The charge generation layer is formed from an n / p junction with p and n layers, or by using a p-doped layer and an n-doped layer. For example, when the charge generation layer is formed only from a P / N junction, it is preferable to provide an electron injection layer to further inject electrons extracted from the P layer into the electron transport layer. Alternatively, an n-doped layer / p-doped layer can be used. This invention is not limited to the combination of charge generation layers used.

[0170] For p-doped layers, for example, highly electron-withdrawing HAT-CN or Lewis acids such as molybdenum trioxide can be mixed with aromatic amine compounds. HAT-CN and molybdenum trioxide are n-type materials, which means that electrons can be extracted and can be constructed using stacks. The np junction, composed of p-doped layers or stacks of n-type and p-type materials, is treated as a p-charge generating layer.

[0171] For n-doped layers, materials with low work functions that readily donate electrons, such as alkali metals or alkaline earth metals, are preferred. In this invention, the n-doped layer is treated as an n-charge generating layer. Optionally, LiF, etc., can be combined with reducing metal thin films to form an electron injection layer, and an n-type / p-type layer can be formed to generate charge.

[0172] As n-dopers, 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; and their compounds can be used. Examples of compounds include alkali metal compounds (including oxides, 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).

[0173] [Protective Layer]

[0174] A protective layer can be formed on the second electrode. For example, glass with a desiccant can be bonded to the second electrode. This reduces the ingress of water and the like into the organic compound layer and reduces the occurrence of display defects. In another embodiment, a passivation film, such as silicon nitride, can be formed on the second electrode to reduce the ingress of water and the like into the organic compound layer. For example, after forming the second electrode, the resulting structure can be transferred to another chamber without breaking the vacuum, and a silicon nitride film with a thickness of 2 μm can be formed by CVD to form a silicon nitride film as a protective layer. After forming the film by CVD, a protective layer formed using atomic layer deposition (ALD) can be formed. The material of the film formed by ALD is not limited, but can be silicon nitride, silicon oxide, or aluminum oxide, etc. Silicon nitride can be further formed on the film formed by ALD by CVD. The film formed by ALD can have a smaller thickness than the film formed by CVD. Specifically, the thickness can be less than 50%, or even less than 10%.

[0175] [Color Filter]

[0176] Color filters can be disposed on the protective layer. For example, a color filter designed to accommodate the size of the organic light-emitting element can be disposed on another substrate, which can be bonded to the substrate on which the organic light-emitting element is disposed. Optionally, the color filter can be patterned on the aforementioned protective layer using photolithography. The color filter can be made of a polymer.

[0177] [Planning Layer]

[0178] A planarization layer can be placed between the color filter and the protective layer. The purpose of the planarization layer is to reduce the unevenness of the underlying layer. However, it is not limited to this purpose; the planarization layer can also be called a material resin layer. The planarization layer can be made of organic compounds and can be a low-molecular-weight or high-molecular-weight material, but a high-molecular-weight material is preferred.

[0179] The planarization layer can be disposed on each of the upper and lower sides of the color filter, and the constituent materials of the planarization layers can be the same or different from each other. Specific examples of constituent materials include polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, and urea resin.

[0180] [Microlens]

[0181] Organic light-emitting elements (OLEDs) or light-emitting devices including OLEDs may include optical components, such as microlenses on their light-emitting side. Microlenses may be made of acrylic resins or epoxy resins, etc. Microlenses may be designed to increase the amount of light extracted from the OLED or light-emitting device, or to control the direction of the extracted light. Microlenses may have a hemispherical shape. When a microlens has a hemispherical shape, there exists a tangent parallel to the insulating layer in the tangent line contacting the hemisphere, and the point of tangency between the tangent line and the hemisphere is the vertex of the microlens. The vertex of the microlens can be similarly determined in any cross-sectional view. That is, in the cross-sectional view, there exists a tangent parallel to the insulating layer in the tangent line contacting the semicircle of the microlens, and the point of tangency between the tangent line and the semicircle is the vertex of the microlens.

[0182] Alternatively, the midpoint of the microlens can be defined. In the cross-section of the microlens, an imaginary line segment can be drawn from one end of one arc to the other, and the midpoint of this line segment can be called the midpoint of the microlens. The cross-section used to determine the vertex and midpoint can be a cross-section perpendicular to the insulating layer.

[0183] [Opposing substrate]

[0184] The opposing substrate can be disposed on the planarization layer. The opposing substrate is called an opposing substrate because it is disposed at a position corresponding to the aforementioned substrate. The material of the opposing substrate can be the same as the material of the aforementioned substrate. When the aforementioned substrate is defined as the first substrate, the opposing substrate can be a second substrate.

[0185] [Pixel Circuit]

[0186] A light-emitting device including an organic light-emitting element (OLED) may include pixel circuitry connected to the OLED. The pixel circuitry may be an active matrix type that independently controls the light emission of each of a plurality of OLEDs. Active matrix type circuitry can be voltage-programmed or current-programmed. Driving circuitry includes pixel circuitry for each pixel. The pixel circuitry may include an OLED, a transistor controlling the luminance (luminous intensity) of the OLED, a transistor controlling the timing of light emission, a capacitor maintaining the gate voltage of the transistor controlling the luminance (luminous intensity), and a transistor connected to GND without passing through the OLED.

[0187] The light-emitting device includes a display area and a peripheral area disposed around the display area. The display area includes pixel circuitry, and the peripheral area includes display control circuitry. The mobility of the transistors constituting the pixel circuitry may be less than the mobility of the transistors constituting the display control circuitry. The slope of the current-voltage characteristic of the transistors constituting the pixel circuitry may be less than the slope of the current-voltage characteristic of the transistors constituting the display control circuitry. The slope of the current-voltage characteristic can be measured using the so-called Vg-Ig characteristic. The transistors constituting the pixel circuitry are transistors connected to the organic light-emitting element.

[0188] [pixel]

[0189] A light-emitting device that includes an organic light-emitting element may include multiple pixels.

[0190] Within a pixel, an area also known as the pixel aperture emits light. This area is the same as the first area. The pixel aperture can be less than 15 μm or greater than 5 μm. More specifically, the pixel aperture can be 11 μm, 9.5 μm, 7.4 μm, or 6.4 μm, etc.

[0191] In a planar drawing, pixels can take on known configurations. For example, pixels can be in stripe, delta, PenTile, or Bayer configurations. Examples of shapes include quadrilaterals such as rectangles and rhombuses, as well as hexagons. Of course, shapes that are not exact figures are also included in rectangles, as long as the shape approximates a rectangle. Subpixel shapes and pixel configurations can be combined.

[0192] The photoreceptor 27 included in the image forming apparatus according to this embodiment is described in detail below.

[0193] [Photosensitive layer]

[0194] The photosensitive layer of a photosensitive drum is mainly divided into (1) multilayer photosensitive layer and (2) single-layer photosensitive layer. (1) Multilayer photosensitive layer is a photosensitive layer that includes a charge-generating layer containing charge-generating material and a charge-transporting layer containing charge-transporting material. (2) Single-layer photosensitive layer is a photosensitive layer that includes both charge-generating material and charge-transporting material.

[0195] (1) Multilayer photosensitive layer

[0196] A multilayer photosensitive layer includes a charge generation layer and a charge transport layer.

[0197] (1-1) Charge generation layer

[0198] The charge-generating layer preferably comprises a charge-generating substance and a resin.

[0199] Examples of charge-generating substances include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Of the phthalocyanine pigments, titanium dioxide phthalocyanine pigments, gallium chloride phthalocyanine pigments, and hydroxy gallium phthalocyanine pigments are preferred.

[0200] The content of charge-generating material in the charge-generating layer is preferably 40% by mass or more and 85% by mass or less based on the total mass of the charge-generating layer, and more preferably 60% by mass or more and 80% by mass or less.

[0201] Examples of resins 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 these, polyvinyl butyral resin is more preferred.

[0202] Furthermore, the charge-generating layer may further contain additives, such as antioxidants and ultraviolet absorbers. Specific examples include hindered phenolic compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

[0203] The charge-generating layer can be formed by preparing a coating solution for the charge-generating layer, the coating solution containing the above-mentioned materials and solvents, forming a coating film of the coating solution on a base layer, and drying the coating film. Examples of solvents used for the coating solution include alcohol solvents, sulfoxide solvents, ketone solvents, ether solvents, ester solvents, and aromatic hydrocarbon solvents.

[0204] The thickness of the charge generation layer is preferably 0.1 μm or more and 1 μm or less, more preferably 0.15 μm or more and 0.4 μm or less.

[0205] (1-2) Charge transport layer

[0206] The charge transport layer preferably comprises a charge transport substance and a binder material.

[0207] When the following protective layer is not provided, the charge transport layer is used as the surface layer of the photosensitive drum.

[0208] Examples of charge-transporting substances include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, triarylamine compounds, and resins having groups derived from these substances. Among these, triarylamine compounds are preferred.

[0209] The content of charge transport material in the charge transport layer is preferably 25% by mass or more and 70% by mass or less based on the total mass of the charge transport layer, and more preferably 30% by mass or more and 55% by mass or less.

[0210] Thermoplastic resin (hereinafter also referred to as "resin") is used as a binder material.

[0211] Examples of thermoplastic resins include polyester resins, polycarbonate resins, acrylic resins, and polystyrene resins. Among these, polycarbonate resins and polyester resins are preferred. As a polyester resin, polyarylate resins are particularly preferred.

[0212] The ratio (mass ratio) of charge transport material to resin is preferably 4:10 to 20:10, more preferably 5:10 to 12:10.

[0213] In addition, the charge transport layer may contain additives such as antioxidants, UV absorbers, plasticizers, and leveling agents. Specific examples include hindered phenolic compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, polystyrene resin particles, polyethylene resin particles, and boron nitride particles.

[0214] The charge transport layer can be formed by preparing a coating solution for the charge transport layer, the coating solution containing the aforementioned materials and solvent, forming a coating film of the coating solution on the charge generation layer, and drying the coating film. Examples of solvents used for the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents or aromatic hydrocarbon-based solvents are preferred.

[0215] The thickness of the charge transport layer is preferably 5 μm or more and 50 μm or less, more preferably 8 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

[0216] (2) Single-layer photosensitive layer

[0217] A single-layer photosensitive layer can be formed by preparing a coating liquid for the photosensitive layer, the coating liquid containing a charge-generating substance, a charge-transporting substance, a resin, and a solvent, forming a coating film of the coating liquid on a base layer, and drying the coating film. Examples of charge-generating substances, charge-transporting substances, and resins are the same as those of the materials in "(1) Multilayer Photosensitive Layers" above.

[0218] [Protective Layer]

[0219] In this disclosure, a protective layer can be provided on the photosensitive layer. Providing a protective layer can improve durability.

[0220] When a protective layer is applied, it serves as the surface layer of the photosensitive drum.

[0221] The protective layer can be formed into a cured film by polymerizing, for example, a composition containing monomers with polymerizable functional groups, which serve as raw materials for adhesive materials. Examples of reactions in this case include thermal polymerization, photopolymerization, and radiation polymerization. Examples of polymerizable functional groups in monomers include isocyanate groups, terminal isocyanate groups, hydroxymethyl groups, alkyl hydroxymethyl 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. Monomers with charge-transporting capabilities can be used as monomers with polymerizable functional groups.

[0222] Here, the cured monomer with polymerizable functional groups is the adhesive material of the protective layer.

[0223] Hole-transporting compounds with chain-polymerizable functional groups are preferred as monomers with polymerizable functional groups.

[0224] Hole-transporting compounds having chain-polymerizable functional groups are more preferably compounds represented by the following formula (CT-1) or (CT-2).

[0225] [Chemical Formula 6]

[0226]

[0227] In formula (CT-1), Ar11 to Ar13 each independently represent a substituted aryl group or an unsubstituted aryl group. The substituted aryl group may have substituents that are alkyl groups having 1 or more but less than 6 carbon atoms, or monovalent functional groups represented by any of the following formulas (P-1) to (P-3). However, the compound represented by formula (CT-1) has at least one monovalent functional group represented by any of the following formulas (P-1) to (P-3).

[0228] [Chemical Formula 7]

[0229]

[0230] In formula (CT-2), Ar21 to Ar24 each independently represent 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 substituents that are alkyl groups having 1 or more but less than 6 carbon atoms, or monovalent functional groups represented by any of the following formulas (P-1) to (P-3). The substituted arylene group may have substituents that are alkyl groups having 1 or more but less than 6 carbon atoms, or monovalent functional groups represented by any of the following formulas (P-1) to (P-3). However, the compound represented by formula (CT-2) has at least one monovalent functional group represented by any of the following formulas (P-1) to (P-3).

[0231] [Chemical Formula 8]

[0232]

[0233] In formula (P-1), Z11 represents a single bond or an alkylene group having 1 or more but less than 6 carbon atoms, and X11 represents a hydrogen atom or a methyl group.

[0234] [Chemical Formula 9]

[0235]

[0236] In formula (P-2), Z21 represents a single bond or an alkylene group having 1 or more carbon atoms but less than 6 carbon atoms.

[0237] [Chemical Formula 10]

[0238]

[0239] In formula (P-3), Z31 represents a single bond or an alkylene group having 1 or more carbon atoms but less than 6 carbon atoms.

[0240] The protective layer may contain resin particles containing fluorine atoms. Incorporating resin particles containing fluorine atoms can improve the wear resistance of the protective layer.

[0241] Examples of resins included in fluorine-containing resin particles include: polytetrafluoroethylene resin, polychlorotrifluoroethylene resin, polytetrafluoroethylene propylene resin, polyvinylidene fluoride resin, polyvinylidene fluoride resin, and polydichlorodifluoroethylene resin. It is also preferable to use particles containing multiple types of the above-mentioned resins. Of the above, from the viewpoint of improving dispersibility, fluorine-containing resin particles are more preferably made of polytetrafluoroethylene (PTFE) resin.

[0242] In cross-sectional observation of the surface layer, from the viewpoint of improving dispersibility and suppressing potential changes, the fluorine-containing resin particles preferably have an arithmetic mean (average primary particle size) of the major diameter of the primary particles measured from secondary electron images taken using a scanning electron microscope, which is 150 nm or more and 300 nm or less. Furthermore, the fluorine-containing resin particles are more preferably having an average primary particle size of 180 nm or more and 250 nm or less.

[0243] The content of fluorine-containing resin particles in the protective layer is preferably 5% by mass or more and 40% by mass or less based on the total mass of the protective layer, more preferably 25% by mass or more and 35% by mass or less.

[0244] In addition, the protective layer may contain additives such as antioxidants, UV absorbers, plasticizers, and leveling agents. Specific examples include hindered phenolic compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, polystyrene resin particles, polyethylene resin particles, and boron nitride particles.

[0245] The protective layer can be formed by preparing a coating solution containing the aforementioned materials and solvent, forming a coating film of the coating solution on a photosensitive layer, and drying and / or curing the coating film. Examples of solvents used for the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0246] The thickness of the protective layer is preferably 0.50 μm or more and 10 μm or less, more preferably 1 μm or more and 7 μm or less.

[0247] [Surface treatment of the photosensitive drum]

[0248] In this disclosure, the photosensitive drum can undergo surface treatment. Surface treatment can further stabilize the behavior of the cleaning unit (cleaning blade) in contact with the photosensitive drum. Examples of surface treatment methods include pressing a mold with protrusions against the surface of the photosensitive drum to transfer a shape, mechanically grinding to impart an uneven shape, and roughening the surface by colliding powder with the surface of the photosensitive drum. In this way, recesses or protrusions are provided in the surface layer of the photosensitive drum, so that the behavior of the cleaning unit in contact with the photosensitive drum can be further stabilized.

[0249] The recess or protrusion may be formed on the entire surface of the photosensitive drum, or on a portion of the surface of the photosensitive drum. When the recess or protrusion is formed on a portion of the surface of the photosensitive drum, it is preferable that the recess or protrusion is formed at least over the entire contact area with the cleaning unit (cleaning blade).

[0250] When forming a recess, the recess can be formed on the surface of the photosensitive drum by pressing a mold with a protrusion corresponding to the recess against the surface of the photosensitive drum to transfer the shape.

[0251] Example

[0252] The invention will be described in further detail below using examples. However, the invention is not limited thereto.

[0253] In this embodiment, a top-emitting stacked organic EL device is produced, in which 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-emitting material and a host material.

[0254] A 40 nm thick titanium (Ti) film is sputtered onto a silicon substrate with a wiring layer to serve as the anode. The film is then patterned using photolithography to form a Ti pixel array and wiring with square pixel openings. The pixel openings are formed with edges of 20 μm.

[0255] Subsequently, the UV / ozone-cleaned silicon substrate and materials were attached to the vacuum deposition equipment, and the equipment was evacuated to 1.0 × 10⁻⁶. -4 Pa(1×10 -6(The process involves several steps.) Next, a hole injection layer and a hole injection layer are formed to achieve a film thickness that provides an interference structure to enhance the emission wavelength. Then, an emission layer containing a red-emitting material is formed. Next, a first electron transport layer, a second electron transport layer, and an electron injection layer are sequentially formed to achieve a film thickness that provides an interference structure to enhance the emission wavelength. Then, a cathode is formed. Furthermore, a silicon nitride film is formed as a first protective layer using CVD, an aluminum oxide film is formed as a second protective layer using ALD, and a silicon nitride film is formed as a third protective layer using CVD, thereby producing an organic light-emitting element.

[0256] [Afterglow lifespan and exposure time]

[0257] The afterglow lifetime of the organic light-emitting elements in each embodiment was measured.

[0258] For the afterglow lifetime, pulsed lasers are used for excitation, and the time elapsed until the luminescence intensity decays to 1 / e of the initial value is measured and calculated.

[0259] Evaluation was conducted using exposure time modes of 1 μs, 10 μs, and 20 μs.

[0260] [Image Quality Evaluation]

[0261] Organic light-emitting element (OLED) chips, fabricated on a silicon substrate, are diced, and 17 chips are mounted on a PCB substrate. The PCB substrate with the OLED chips mounted on it is then fabricated and housed in a housing equipped with a lens array, thereby producing the printhead.

[0262] The produced printhead was installed on a modified copier manufactured by Canon Corporation (product name: imageRUNNER iR-ADV C5051), and the image quality was evaluated.

[0263] Next, the electrophotographic sensor was mounted on the station of the magenta processing box. Test images with an image ratio of 5% were output on 30,000 sheets of A4 portrait paper. Subsequently, halftone images were output, and image quality was evaluated as follows (presence of vertical stripes or ghosting). The results are listed in Table 2.

[0264] A: No abnormalities were observed.

[0265] B: An anomaly was observed.

[0266] [Table 2]

[0267]

[0268] As listed in Table 2, the configurations described in Examples 1 to 4 provide high image quality after 30,000 images have been output. Since the configurations described in Examples 1 to 4 have a longer afterglow lifetime than exposure time, element degradation of the organic light-emitting element can be reduced. As a result, normal light emission is obtained from the organic light-emitting element even after 30,000 images have been output. This is considered to result in high image quality.

[0269] In contrast, the configurations described in Comparative Examples 1 and 2 provide low image quality after 30,000 images are output. This is believed to be because the configurations described in Comparative Examples 1 and 2 have an exposure time longer than the afterglow lifetime, thus reducing the durability of the organic light-emitting element and making it impossible to obtain normal light emission from the organic light-emitting element.

[0270] As described above, when the afterglow lifetime of the organic light-emitting element is shorter than the exposure time of the photoreceptor, an image forming apparatus exhibiting high image quality can be obtained.

[0271] As described above, the configuration in this invention, where the exposure time is shorter than the afterglow lifetime, enables the provision of an image forming apparatus with excellent element durability for the organic light-emitting element. It also provides an image forming apparatus with excellent image quality. The configuration where the emission interval time is shorter than the afterglow lifetime further enables the provision of an image forming apparatus with excellent element durability for the organic light-emitting element. It also provides an image forming apparatus with excellent image quality.

[0272] The present invention may also have the following configuration.

[0273] (Component 1)

[0274] An image forming apparatus comprising:

[0275] An exposure light source, comprising an organic light-emitting element; and a photoreceptor that receives light emitted from the organic light-emitting element.

[0276] Wherein, when the luminous intensity from the organic light-emitting element is L0 at the end of the current supply to the organic light-emitting element, the time period from the end of the current supply to the organic light-emitting element until the organic light-emitting element is turned off is T1, and the time period from the start of the current supply to the organic light-emitting element until the end of the current supply to the organic light-emitting element is T2,

[0277] T1 and T2 satisfy the relationship of equation (a):

[0278] (a) T1≥T2.

[0279] (Component 2)

[0280] According to the image forming apparatus described in configuration 1, T1 and T2 satisfy the relationship of equation (b):

[0281] (b)T2 / T1≤1.0.

[0282] (Component 3)

[0283] According to the image forming apparatus described in configuration 1 or 2, when 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 T3...

[0284] T1 and T3 satisfy the relationship of equation (c):

[0285] (c)T1≥T3.

[0286] (Component 4)

[0287] An image forming apparatus comprising:

[0288] An exposure light source, comprising an organic light-emitting element; and a photoreceptor that receives light emitted from the organic light-emitting element.

[0289] Specifically, when the luminous intensity from the organic light-emitting element is L0 at the end of the current supply to the organic light-emitting element, the time period from the end of the current supply to the organic light-emitting element until the organic light-emitting element is turned off is T1, and the time period from the end of the current supply to the organic light-emitting element until the start of the current supply to the organic light-emitting element is T3,

[0290] T1 and T3 satisfy the relationship of equation (c):

[0291] (c)T1≥T3.

[0292] (Component 5)

[0293] The image forming apparatus according to any one of 1 to 4, wherein the organic light-emitting element has a top-emitting configuration.

[0294] (Composition 6)

[0295] According to any one of the image forming apparatuses comprising 1 to 5, the organic light-emitting element includes a light-emitting layer comprising a light-emitting material, and the light-emitting material emits fluorescence.

[0296] (Component 7)

[0297] According to any one of the image forming apparatuses comprising 1 to 5, the organic light-emitting element includes a light-emitting layer comprising a light-emitting material, and the light-emitting material emits phosphorescence.

[0298] (Composition 8)

[0299] According to the image forming apparatus of configuration 6, the luminescent material has a fused polycyclic hydrocarbon backbone.

[0300] (Composition 9)

[0301] According to the image forming apparatus described in configuration 8, the luminescent material is a hydrocarbon compound.

[0302] (Composition 10)

[0303] According to any one of the following image forming apparatuses comprising 6 to 9, the light-emitting layer comprises a compound different from the light-emitting material, and the compound has a fused polycyclic hydrocarbon backbone.

[0304] (Composition 11)

[0305] According to the image forming apparatus of configuration 10, the fused polycyclic hydrocarbon skeleton is a naphthalene skeleton, anthracene skeleton, phenanthrene skeleton, fluorene skeleton, pyrene skeleton, triphenylene skeleton, β skeleton, tetraphenylene skeleton or perylene skeleton.

[0306] (Composition 12)

[0307] According to the image forming apparatus described in configuration 7, the light-emitting material is a metal complex.

[0308] (Composition 13)

[0309] According to the image forming apparatus of configuration 12, the light-emitting material is an iridium complex or a platinum complex.

[0310] (Composition 14)

[0311] According to the image forming apparatus described in configuration 6, the fluorescence is delayed fluorescence.

[0312] (Composition 15)

[0313] According to the image forming apparatus of configuration 6, 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 light-emitting material.

[0314] (Composition 16)

[0315] According to the image forming apparatus of configuration 15, the light-emitting layer further comprises an organic compound different from the delayed fluorescence material, and the lowest excitation singlet energy of the organic compound is higher than that of the light-emitting material.

[0316] (Composition 17)

[0317] According to any one of the image forming apparatuses comprising 1 to 16, wherein T1 is 1 μs or more.

[0318] (Composition 18)

[0319] The image forming apparatus according to any one of 1 to 17, wherein the organic light-emitting element has an interference structure.

[0320] (Composition 19)

[0321] According to the image forming apparatus of configuration 18, the organic light-emitting element includes a reflective layer, a first electrode, a light-emitting layer, and a second electrode, and

[0322] The reflective layer and the luminescent layer are configured to enhance the light emitted from the luminescent layer between the reflective layer and the luminescent layer.

[0323] (Composition 20)

[0324] According to the image forming apparatus of configuration 18, the organic light-emitting element includes a first electrode, a light-emitting layer, and a second electrode, and

[0325] The first electrode and the second electrode are configured to enhance the light emitted from the light-emitting layer between the first electrode and the second electrode.

[0326] This invention is not limited to the embodiments described above, and various changes and modifications can be made within the spirit and scope of this invention. Therefore, the claims are appended to inform the public of the scope of this invention.

[0327] This application claims the benefit of Japanese Patent Application No. 2024-047055, filed on March 22, 2024, the entire contents of which are incorporated herein by reference.

[0328] Explanation of reference numerals in the attached figures

[0329] 27 Photoreceptors

[0330] 28 Exposure Light Source

Claims

1. An image forming apparatus, comprising: Exposure light source, which includes organic light-emitting elements; and a photoreceptor that receives light emitted from the organic light-emitting element, Specifically, when the luminous intensity from the organic light-emitting element is L0 at the end of the current supply to the organic light-emitting element, the time period from the end of the current supply to the organic light-emitting element until the organic light-emitting element is turned off is T1, and the time period from the start of the current supply to the organic light-emitting element until the end of the current supply to the organic light-emitting element is T2, T1 and T2 satisfy the relationship of equation (a): (a) T1≥T2.

2. The image forming apparatus according to claim 1, wherein T1 and T2 satisfy the relationship of equation (b): (b)T2 / T1≤1.

0.

3. The image forming apparatus according to claim 1 or 2, wherein, When 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 T3. T1 and T3 satisfy the relationship of equation (c): (c)T1≥T3.

4. An image forming apparatus, comprising: Exposure light source, which includes organic light-emitting elements; and a photoreceptor that receives light emitted from the organic light-emitting element, Specifically, when the luminous intensity from the organic light-emitting element is L0 at the end of the current supply to the organic light-emitting element, the time period from the end of the current supply to the organic light-emitting element until the organic light-emitting element is turned off is T1, and the time period from the end of the current supply to the organic light-emitting element until the start of the current supply to the organic light-emitting element is T3, T1 and T3 satisfy the relationship of equation (c): (c)T1≥T3.

5. The image forming apparatus according to claim 1 or 4, wherein the organic light-emitting element has a top-emitting configuration.

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

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

8. The image forming apparatus of claim 6, wherein the luminescent material has a fused polycyclic hydrocarbon backbone.

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 or 7, wherein the light-emitting layer comprises a compound different from the light-emitting material, and the compound has a fused polycyclic hydrocarbon backbone.

11. The image forming apparatus according to claim 10, wherein the fused polycyclic hydrocarbon skeleton is a naphthalene skeleton, anthracene skeleton, phenanthrene skeleton, fluorene skeleton, pyrene skeleton, triphenylene skeleton, β-skeleton skeleton, tetraphenylene skeleton, or perylene skeleton.

12. The image forming apparatus according to claim 7, wherein the light-emitting material is a metal complex.

13. The image forming apparatus according to claim 12, wherein the light-emitting material is an iridium complex or a platinum complex.

14. The image forming apparatus of claim 6, wherein the fluorescence is delayed fluorescence.

15. The image forming apparatus of 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 light-emitting material.

16. The image forming apparatus of claim 15, wherein the light-emitting layer further comprises an organic compound different from the delayed fluorescence material, and the lowest excitation singlet energy of the organic compound is higher than that of the light-emitting material.

17. The image forming apparatus according to claim 1 or 4, wherein T1 is 1 μs or more.

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

19. The image forming apparatus of claim 18, wherein the organic light-emitting element comprises a reflective layer, a first electrode, a light-emitting layer, and a second electrode, and The reflective layer and the light-emitting layer are configured to enhance the light emitted from the light-emitting layer between the reflective layer and the light-emitting layer.

20. The image forming apparatus of claim 18, wherein the organic light-emitting element comprises a first electrode, a light-emitting layer, and a second electrode, and The first electrode and the second electrode are configured to enhance the light emitted from the light-emitting layer between the first electrode and the second electrode.

Images