Exposure head and image forming apparatus

Abstract

To provide an exposure head and image forming apparatus in which a lens array and a retaining member are well bonded.SOLUTION: An exposure head includes a substrate assembly including a first light emitting chip, a second light emitting chip, and a substrate on which the first light emitting chip and the second light emitting chip are mounted so as to partially overlap each other when viewed from a sub-scanning direction, a lens array, a retaining member, and a first adhesion portion. When an area on the substrate where the end portion in a main-scanning direction of the second light emitting chip and the end portion in the main-scanning direction of the first light emitting chip overlap when viewed in the sub-scanning direction is referred to as a first area, and an area of the lens array superposed with the first area when viewed in an optical axis direction of the lens array is referred to as a second area, the first adhesion portion is configured to adhere both end portions of the lens array in the sub-scanning direction to the retaining member in the second area.SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] The present invention relates to an exposure head and an image forming apparatus suitable for use in an electrophotographic image forming apparatus such as a printer, a copying machine, a facsimile machine or a multifunction machine. [Background technology]

[0002] Electrophotographic image forming apparatuses include an exposure device that irradiates the surface of a photosensitive drum with light to form an electrostatic latent image. Known examples of such exposure devices include an LED array exposure head (see Patent Document 1). The LED array exposure head includes an LED chip on which multiple LEDs serving as light-emitting elements are aligned in the main scanning direction, a substrate on which the multiple LED chips are arranged in a staggered pattern in the main scanning direction, a lens array, and a housing that holds the substrate and the lens array. The lens array includes multiple lenses aligned in the main scanning direction, which focus light emitted from the LEDs on the LED chip onto the surface of the photosensitive drum. The multiple lenses each have a light incident surface onto which light emitted from the LEDs is incident and a light exit surface from which the light incident from the light incident surface exits.

[0003] The housing is formed in an elongated shape that is long in the main scanning direction and has a generally U-shaped cross section, and the lens array and substrate are disposed in this housing at upper and lower installation positions in the vertical direction with a gap between them. The lens array is attached to the housing with an adhesive so that the light exit surface of the lens is exposed on the photosensitive drum side, and the substrate is attached to the housing with an adhesive so that it faces the light entrance surface of the lens. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-154632 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is room for improvement in the adhesion between the lens array and the housing.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure head and an image forming apparatus in which a lens array and a holder are bonded well. [Means for solving the problem]

[0007] One aspect of the present invention is a substrate assembly including: a first light-emitting chip having a plurality of light-emitting elements arranged in a main scanning direction; a second light-emitting chip having a plurality of light-emitting elements arranged in the main scanning direction; and a substrate on which the first light-emitting chip and the second light-emitting chip are mounted so as to partially overlap when viewed from a sub-scanning direction; a lens array having a plurality of lenses for condensing light emitted from the light-emitting elements of the first light-emitting chip and the second light-emitting chip; a holder that holds the substrate assembly and the lens array so that the lens array faces the light-emitting elements; and a first adhesive portion, This exposure head is characterized in that, when a first region is defined as a region on the substrate where an end of the second light-emitting chip in the main scanning direction overlaps an end of the second light-emitting chip in the main scanning direction when viewed from the sub-scanning direction, and where an end of the second light-emitting chip in the main scanning direction overlaps an end of the first light-emitting chip in the main scanning direction when viewed from the sub-scanning direction, and a second region is defined as a region of the lens array that overlaps with the first region when viewed from the optical axis direction of the lens array, the first adhesive portion bonds both ends of the lens array in the sub-scanning direction to the holder in the second region. [Effects of the Invention]

[0008] According to the present invention, the lens array and the holder can be adhered well to each other. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an external perspective view showing an image forming apparatus suitable for using the exposure head of the present embodiment. [Figure 2] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [Figure 3] FIG. [Figure 4] (a) A perspective view of the exposure substrate, (b) A view of the exposure substrate from the photosensitive drum side, (c) A view showing the LEDs on the exposure substrate, (d) A view of the lens array from the photosensitive drum side, and (e) A perspective view of the lens array. [Figure 5] FIG. [Figure 6] FIG. 4 is a perspective view showing the rear surface of the exposure head. [Figure 7] FIG. 10 is a diagram showing a physical model for simulating the contribution of the adhesive to the movement and twisting of the exposure substrate relative to the exposure housing. [Figure 8] Graph (a) showing the contribution of movement of the exposed substrate to the exposure housing, and graph (b) showing the contribution of twist of the exposed substrate to the exposure housing. [Figure 9] FIG. 10 is a schematic diagram showing the bonding between the exposure substrate and the exposure housing. [Figure 10] FIG. 10 is a perspective view for explaining bonding of an exposed substrate with a UV adhesive and a thermosetting adhesive. [Figure 11] 1A and 1B are top and bottom views of an exposed substrate for explaining bonding of the exposed substrate with a UV adhesive and a thermosetting adhesive. [Figure 12] FIG. 10 is a perspective view for explaining bonding of an exposed substrate with a sealant. [Figure 13] FIG. 10 is a bottom view for explaining bonding of an exposed substrate with a sealant. [Figure 14] FIG. 10 is a diagram showing a physical model for simulating the contribution of movement and twist of the lens array to the exposure housing due to the adhesive. [Figure 15] 10A is a graph showing the contribution of the movement of the lens array to the exposure housing, and FIG. 10B is a graph showing the contribution of the twist of the lens array to the exposure housing. [Figure 16] FIG. 10 is a schematic diagram showing the adhesion between the lens array and the exposure housing. [Figure 17] FIG. 10 is a perspective view for explaining bonding of a lens array with a UV adhesive and a thermosetting adhesive. [Figure 18] 10A and 10B are a top view and a bottom view of a flat portion of an exposed substrate, respectively, for explaining bonding of a lens array using a UV adhesive and a thermosetting adhesive. [Figure 19] FIG. 10 is a perspective view for explaining adhesion of the lens array with a sealant. [Figure 20] FIG. 10 is a bottom view illustrating the adhesion of the lens array with a sealant. DETAILED DESCRIPTION OF THE INVENTION

[0010] To focus the light emitted from the LEDs using lenses and form an image on the photosensitive drum, the lens array is positioned relative to the housing with its distance from the substrate adjusted. However, the adhesive that attaches the lens array to the housing can expand due to the heat generated by the LEDs. In this case, in conventional cases, the relative position of some of the lens array with the housing can change from its original position, resulting in a difference in the amount of light irradiated onto the photosensitive drum, particularly at points corresponding to the staggered arrangement of LED chips on the substrate, which can degrade the optical performance of the exposure head relative to the photosensitive drum.

[0011] In this embodiment, an exposure head is provided that suppresses degradation of the optical performance of the exposure head caused by the adhesive portion that bonds the lens array having a plurality of lenses to the holder.

[0012] <Image forming device> An image forming apparatus suitable for using the exposure head of this embodiment will be described below with reference to Figures 1 and 2. Figures 1 and 2 show an image forming apparatus 100 of an internal discharge type as an example. The image forming apparatus 100 shown in Figure 1 includes an apparatus main body 100A and an original reading device 900 that reads image information from an original, and an output tray 21 is formed between the apparatus main body 100A and the original reading device 900 to hold recording material P discharged from the apparatus main body 100A. The image forming apparatus 100 forms a toner image on the recording material in accordance with an image signal sent from the original reading device 900 or an external device (not shown) such as a personal computer.

[0013] The device main body 100A is provided with an operation unit 46 on the front side, which has a display unit capable of displaying various information and keys for inputting various information in response to user operations. In this specification, the side on which a user stands when operating the operation unit 46 to operate the image forming device 100 is referred to as the "front," and the opposite side is referred to as the "rear." Furthermore, the left side when viewing the image forming device 100 from the front is referred to as the "left," and the right side when viewing the image forming device 100 from the front is referred to as the "right."

[0014] The recording material conveyance process of the image forming apparatus 100 will be described. As shown in FIG. 2, recording materials P are stored in a cassette 12 and are fed one by one to a conveyance path 11 by a supply roller 13 in accordance with the image formation timing. Alternatively, recording materials P stacked on a manual feed tray (not shown) may be fed one by one to the conveyance path 11. The recording material P is conveyed to a registration roller 15 disposed midway along the conveyance path 11, where it is subjected to skew correction and timing correction before being sent to a secondary transfer portion T2. ​​The secondary transfer portion T2 is a transfer nip formed by an opposing inner secondary transfer roller 10 and outer secondary transfer roller 16. At the secondary transfer portion T2, a secondary transfer voltage is applied to the inner secondary transfer roller 10, thereby secondarily transferring the toner image from the intermediate transfer belt 6 to the recording material P.

[0015] The image forming process for an image sent to the secondary transfer unit T2 at the same timing as the process for transporting the recording material P to the secondary transfer unit T2 described above will now be described. First, the image forming units 1Y, 1M, 1C, and 1K will be described. However, the image forming units 1Y to 1K are configured almost identically except that the toner colors used in the developing units 5Y, 5M, 5C, and 5K are different: yellow, magenta, cyan, and black. Therefore, the following description will be given using the yellow image forming unit 1Y as a representative example, and descriptions of the other image forming units 1M, 1C, and 1K will be omitted.

[0016] The image forming unit 1Y includes a photosensitive drum 2Y, a charger 3Y, an exposure head 4Y, and a developing unit 5Y. The surface of the photosensitive drum 2Y as a photosensitive member is uniformly charged in advance by the charger 3Y, and then an electrostatic latent image is formed on the photosensitive drum 2Y by the exposure head 4Y, which is driven based on a signal of image information. The exposure head 4Y is formed in an elongated shape extending in the direction of the rotation axis of the photosensitive drum 2Y (main scanning direction), and exposes the photosensitive drum 2Y using a plurality of light-emitting elements arranged along the main scanning direction. The light-emitting elements are, for example, light-emitting diodes (Light Emitting Diodes) or organic electroluminescence (EL) elements. The exposure head 4Y will be described in detail below.

[0017] The electrostatic latent image formed on the photosensitive drum 2Y is developed with toner by the developer 5Y and made visible. Thereafter, a predetermined pressure and primary transfer voltage are applied by a primary transfer roller 6Y, which is arranged opposite the image forming unit 1Y with the intermediate transfer belt 9 sandwiched therebetween, and the toner image formed on the photosensitive drum 2Y is primarily transferred onto the intermediate transfer belt 9. In other words, the intermediate transfer belt 9 and the primary transfer roller 6Y form a primary transfer unit that primarily transfers the toner image formed on the photosensitive drum 2Y onto the intermediate transfer belt 9. Any small amount of residual toner remaining on the photosensitive drum 2Y after the primary transfer is removed by a photosensitive drum cleaner (not shown) to prepare for the next image creation process.

[0018] The intermediate transfer belt 9 is stretched around an inner secondary transfer roller 10 and multiple tension rollers and driven to move counterclockwise. The image formation process for each color performed by the image forming units 1Y-1K is performed in a timed relationship with the toner image of the color upstream in the movement direction that was primarily transferred onto the intermediate transfer belt 9. As a result, a full-color toner image is ultimately formed on the intermediate transfer belt 9 and transported to the secondary transfer unit T2. The secondary transfer unit T2 is configured by sandwiching the intermediate transfer belt 9 between the inner secondary transfer roller 10 and the outer secondary transfer roller 16. By applying a transfer bias, the full-color toner image on the intermediate transfer belt 9 is transferred to a sheet. The primary transfer unit and the secondary transfer unit T2 form a transfer unit that transfers the toner image formed on the photosensitive drum to a recording material. Residual toner after passing through the secondary transfer unit T2 is removed from the intermediate transfer belt 9 by a secondary transfer cleaner (not shown).

[0019] Through the conveying process and image creation process described above, the timing of the recording material P and the full-color toner image are synchronized at the secondary transfer portion T2, and the toner image is secondarily transferred from the intermediate transfer belt 9 to the recording material P. The recording material P is then conveyed to the fixing device 19, where the toner image is fixed to the recording material P by applying pressure and heat thereto. In the case of single-sided printing, the recording material P with the fixed toner image is discharged to the discharge tray 21 by the forward-rotating discharge rollers 20. On the other hand, in the case of double-sided printing, the recording material P is conveyed by the forward-rotating discharge rollers 20 until the trailing edge of the recording material P passes the switching member 30, and then the discharge rollers 20 are switched to reverse rotation, and the leading and trailing edges are swapped, and the recording material P is conveyed to the double-sided conveying path 31. The recording material P is then sent back to the conveying path 11 by the re-supply rollers 32. The subsequent conveying and the image creation process for the second side are the same as those described above, and therefore will not be described here.

[0020] Toner bottles 22Y-22K, which contain toner to be supplied to the developing devices 5Y-5K, are detachably attached to a toner supply mechanism (not shown) above the intermediate transfer belt 9. The toner supply mechanism supplies the corresponding developing devices 5Y-5K with an appropriate amount of toner at an appropriate time from the toner bottles 22Y-22K.

[0021] <Exposure head> Next, the exposure head 4Y will be described with reference to FIG. 2 and FIGS. 3 to 6(e). As shown in FIG. 3, the exposure head 4Y includes a substrate assembly 500, a lens array 52, an exposure housing 54 serving as a holder for holding the substrate assembly 500 and the lens array 52, and a housing support member 55 for supporting the exposure housing 54. The substrate assembly 500 includes an LED chip 53 having an array of multiple LEDs 51, and an exposure substrate 50 on which the multiple LED chips 53 are mounted. The exposure substrate 50 is an insulating resin substrate, and the LED chips 53 are mounted on one side thereof. In addition, the exposure substrate 50 includes a circuit for controlling the light emission of the LED chips 53, which is formed by a printed wiring pattern formed on the surface of the substrate and circuit elements such as numerous electronic and electrical components (e.g., a driving IC, resistors, capacitors, etc.) mounted on the surface of the substrate.

[0022] As shown in FIG. 4( a), LED chips 53 serving as light-emitting chips are mounted on one side of the exposure substrate 50, and FFC connectors 57 are mounted on the opposite side of the exposure substrate 50. One end of a flexible flat cable (hereinafter referred to as FFC), not shown, is connected to the FFC connector 57. The other end of the FFC is connected to a control unit (not shown) provided in the apparatus main body 100A of the image forming apparatus 100 via a main body connector. A printed wiring pattern for supplying control signals to each LED chip 53 is provided on the surface of the exposure substrate 50, and the FFC connector 57 is electrically connected to the printed wiring pattern. Therefore, when a control signal is input to the exposure substrate 50 from the control unit of the image forming apparatus 100 via the FFC and FFC connector 57, the LED chips 53 are driven (to emit light or turn off) in accordance with the input control signal.

[0023] <LEDチップ> As shown in FIG. 4(b), a plurality of LED chips 53-1 to 53-17 (17 in this example) are arranged on one surface of the exposure substrate 50. Each of the LED chips 53-1 to 53-17 has a plurality of LEDs 51 arranged along its longitudinal direction (main scanning direction). As shown in FIG. 4(c), the center-to-center distance "k2" between adjacent LEDs 51 in the LED chip 53 corresponds to the recording resolution of the image forming apparatus 100. For example, when the recording resolution of the image forming apparatus 100 is "1200 dpi," the LEDs 51 are arranged so that the center-to-center distance "k2" between adjacent LEDs 51 is "21.16 μm." In this embodiment, the exposure range of the exposure head 4Y is "approximately 314 mm." The length of the photosensitive layer of the photosensitive drum 2 in the direction of the rotation axis is "314 mm" or more. Since the length of the long side of an A4-sized recording material P and the length of the short side of an A3-sized recording material P are 297 mm, the exposure head 4Y of this embodiment has an exposure range capable of forming images on A4-sized recording material P and A3-sized recording material P.

[0024] The LED chips 53-1 to 53-17 are alternately arranged in a staggered pattern in the main scanning direction (longitudinal direction) at different positions in the sub-scanning direction (short direction). As shown in Fig. 4(b) , the odd-numbered LED chips 53-1, 53-3, ... 53-17 counting from the left are a plurality of first light-emitting chips arranged in a line at intervals in the longitudinal direction of the exposure substrate 50 to form a first chip group. The even-numbered LED chips 53-2, 53-4, ... 53-16 counting from the left are a plurality of second light-emitting chips arranged in a line at intervals in the longitudinal direction of the exposure substrate 50 at positions different in the sub-scanning direction from the first light-emitting chips 53-1, 53-3, ... 53-17 to form a second chip group.

[0025] In this embodiment, the LED chips 53-1 to 53-17 are arranged so as to partially overlap when viewed from the sub-scanning direction. For example, as shown in FIG. 4(c), the LED chips are arranged in a staggered pattern in the longitudinal direction such that the right end of the first LED chip 53-1 and the left end of the second LED chip 53-2 overlap in the main scanning direction when viewed from the sub-scanning direction. Although not shown, the right end of the second LED chip 53-2 overlaps with the left end of the third LED chip 53-3, and the right end of the third LED chip 53-3 overlaps with the left end of the fourth LED chip 53-4. The remaining LED chips also overlap in the main scanning direction. In this manner, the first light-emitting chips 53-1, 53-3, . . . 53-17 and the second light-emitting chips 53-2, 53-4, . . . 53-16 are arranged so that the ends of the first light-emitting chips 53-1, 53-3, . . . 53-17 and the second light-emitting chips 53-2, 53-4, . . . 53-16 overlap with each other at their opposite ends in the main scanning direction when viewed from the sub-scanning direction. That is, in the overlapping portion between the first light-emitting chip and the second light-emitting chip, if an end of the first light-emitting chip is defined as one end (second end) in the main scanning direction, this one end of the first light-emitting chip overlaps with the other end (first end) in the main scanning direction of the second light-emitting chip. Note that, hereinafter, the region on the exposure substrate 50 where the end of the first light-emitting chip and the end of the second light-emitting chip overlap as viewed from the sub-scanning direction will be referred to as the overlap region F or the first region. As described above, a plurality of first regions F exist on the exposure substrate 50.

[0026] In the example shown in FIG. 4(c), in the overlap region F where the LED chips 53-1 and 53-2 overlap, three LEDs 51 are positioned at the ends of each of the LED chips 53-1 and 53-2, overlapping as viewed from the sub-scanning direction. Within the overlap region F (the first region), the three LEDs 51 of the LED chip 53-1 and the three LEDs 51 of the LED chip 53-2 are approximately aligned with each other at a center-to-center distance "k2." This allows the LEDs 51 used for exposure to be switched between the LED chips 53-1 and 53-2 without causing a difference in light intensity. Even if there are differences in the longitudinal lengths of the LED chips 53-1 and 53-2 or the positions of the LEDs 51 located at their ends, the LED chips 53-1 and 53-2 are arranged on the exposure substrate 50 so that their respective LEDs 51 are not misaligned relative to each other in the longitudinal direction. The same applies to the other LED chips. This makes it difficult for unevenness in the amount of light to occur in the longitudinal direction when exposing the photosensitive drum 2Y. Note that the number of LEDs 51 that overlap in the overlap region F when viewed from the sub-scanning direction may be at least one.

[0027] <Lens array> The lens array 52 is disposed on one side of the exposure substrate 50 on which a plurality of LED chips 53 are mounted, with a gap between it and the exposure substrate 50 (see FIG. 3). As shown in FIG. 4(d), the lens array 52 is a lens assembly having a plurality of lenses 521 arranged in two rows along the longitudinal direction, and focuses light emitted from the LEDs 51 onto the surface of the photosensitive drum 2Y. As shown in FIG. 4(e), the lenses 521 of the lens array 52 are alternately arranged such that each lens 521 in one row is in contact with both of the lenses 521 adjacent to each other in the arrangement direction of the lenses 521 in the other row. Each lens 521 is, for example, a cylindrical glass rod lens, and has a light incident surface 52b onto which light emitted from the LEDs 51 enters and a light exit surface 52a from which the light incident from the light incident surface 52b exits (see FIG. 3). The material of the lenses 521 is not limited to glass, but may also be plastic. Furthermore, the shape of the lens 521 is not limited to a cylindrical shape, but may be a polygonal prism such as a hexagonal prism.

[0028] The dotted line Z in FIG. 4(e) indicates the optical axis of the lens 521. The exposure head 4Y is mounted on the device main body 100A so as to be movable in a direction generally along the optical axis of the lens 521 indicated by the dotted line Z (hereinafter referred to as the optical axis direction) by a retraction mechanism (not shown). The optical axis of the lens 521 here refers to the line connecting the center of the light exit surface 52a of the lens 521 to the focal point of the lens 521. As described above, since the lens array 52 is a lens assembly having multiple lenses 521, strictly speaking, the "optical axis" refers to the optical axis of any one of the multiple lenses 521. Here, due to tolerances during assembly of the exposure head 4Y, the multiple lenses 521 in the lens array 52 may be slightly tilted relative to each other. However, even in such cases, the optical axes of the multiple lenses 521 can be considered to be in the same direction without considering deviations due to tolerances.

[0029] <Exposure housing> 3, the exposure housing 54 holds the lens array 52 and the exposure substrate 50 at upper and lower installation positions in the vertical direction with a gap between them. The exposure housing 54 is a metal member formed by bending a plate material, for example, a galvanized steel plate or a cold-rolled steel plate. As an example, the exposure housing 54 is formed by pressing a metal plate such as a thin iron plate into a substantially U-shaped cross section.

[0030] As shown in FIG. 3, the exposure housing 54 has a flat portion 54U in which a first opening 54a is formed, through which the lens array 52 is inserted. The flat portion 54U is a portion of the exposure housing 54 that faces the photosensitive drum 2Y in the optical axis direction of the lenses of the lens array 52, and holds the lens array 52. ​​Note that this flat portion 54U is not limited to a flat surface, and may be a slightly curved surface. The exposure housing 54 also has an extension portion 54R on one side of the flat portion 54U in the short-side direction (sub-scanning direction) that extends in a direction away from the photosensitive drum 2Y. The exposure housing 54 also has an extension portion 54L on the other side of the short-side direction of the flat portion 54U that faces the extension portion 54R and extends in a direction away from the photosensitive drum 2Y.

[0031] The exposure housing 54 has a planar portion 54U as a first holding portion and a pair of extension portions 54R and 54L as second holding portions, which are integrally formed to have a generally U-shaped cross section so that the lens array 52 and the substrate assembly 500 can be held at an interval above and below the planar portion 54U. The exposure housing 54 has a generally U-shaped cross section, and the pair of extension portions 54R and 54L form a second opening 54b at their distal ends. The substrate assembly 500 is inserted through the second opening 54b. The substrate assembly 500 inserted through the second opening 54b is positioned by a jig (not shown) to an installation position where the light is focused on the surface of the photosensitive drum 2Y, specifically, where the distance between the exposure substrate 50 (specifically, the LEDs 51) and the lens array 52 (specifically, the light incident surface 52b) is a predetermined value. The substrate assembly 500 inserted through the second opening 54b is adhered to the extension portions 54L, 54R at both ends in the sub-scanning direction of the exposure substrate 50 by adhesive portions 200. As will be described later, an ultraviolet-curing (photo-curing) adhesive, a sealant, or a thermosetting adhesive is used for the adhesive portions 200.

[0032] On the other hand, the lens array 52 is inserted into the first opening 54a of the flat portion 54U so that the light exit surface 52a of the lens is exposed on the side where the photosensitive drum 2Y is arranged. The lens array 52 inserted into the first opening 54a is positioned, while its tilt is adjusted by a jig (not shown), at a position where the distance between the LED chips 53 (specifically, the LEDs 51) mounted on the exposure board 50 and the lens array 52 (specifically, the light entrance surface 52b) is a predetermined value. The lens array 52 inserted into the first opening 54a is adhered to the flat portion 54U at both ends in the sub-scanning direction by adhesive portions 201. As will be described later, an ultraviolet-curing adhesive, a sealant, or a thermosetting adhesive is used for the adhesive portions 201.

[0033] <Housing support member> Furthermore, in the exposure head 4Y, a housing support member 55 formed with a substantially U-shaped cross section is provided on the second opening 54b side of the exposure housing 54. The housing support member 55 is an elongated member extending in the main scanning direction, and is provided integrally with the exposure housing 54 so as to support the exposure housing 54, which holds the substrate assembly 500 and the lens array 52, along the longitudinal direction.

[0034] 5 and 6, the housing support member 55 has a generally U-shaped cross section (see FIG. 3) and includes a left side wall 55L, a right side wall 55R facing the left side wall 55L in the sub-scanning direction (left-right direction), and a bottom surface 55D facing the flat surface 54U of the exposure housing 54 between the left side wall 55L and the right side wall 55R. As shown in FIG. 6, a plurality of openings 55a are formed in the bottom surface 55D of the housing support member 55 in the longitudinal direction. These openings 55a are formed between the left side wall 55L and the right side wall 55R in the sub-scanning direction at positions facing the surface (back surface of the exposure board 50) opposite the mounting surface on which the LEDs 51 of the exposure board 50 are mounted (front surface of the exposure board 50).

[0035] <Adhesion of exposure substrates> As described above, the exposure substrate 50 is adhered to the exposure housing 54 by the adhesive portion 200. When adhering the exposure substrate 50, it is conceivable to adhere the exposure substrate 50 to the exposure housing 54 at multiple locations in the longitudinal direction of the exposure substrate 50 using an ultraviolet-curable resin adhesive (ultraviolet-curable adhesive) that hardens when exposed to ultraviolet light. Furthermore, in order to seal the gap between the exposure substrate 50 adhered with the ultraviolet-curable adhesive (hereinafter referred to as UV adhesive) and the exposure housing 54 (more specifically, the extension portions 54L and 54R), it is conceivable to adhere almost the entire longitudinal area of ​​the exposure substrate 50 using a sealant with a lower viscosity than the UV adhesive. The linear expansion coefficient of the cured UV adhesive is smaller than the linear expansion coefficient of the cured sealant (sealing member), and the Young's modulus of the cured UV adhesive is greater than the Young's modulus of the cured sealant.

[0036] Incidentally, since circuit elements are mounted on the exposure substrate 50, the heat generated by these circuit elements causes the temperature of the exposure housing 54 to rise. When the temperature of the exposure housing 54 rises, the difference in the linear expansion coefficient of the UV adhesive bonding the exposure substrate 50 to the exposure housing 54 and the linear expansion coefficient of the sealant can cause variations in the volumetric change of the adhesive. This can cause the exposure substrate 50 to move horizontally in the sub-scanning direction (left and right direction) relative to the exposure housing 54, or the exposure substrate 50 to twist in the vertical direction so that one end of the sub-scanning direction moves up and down relative to the other end, which has conventionally been the case on the order of several to several tens of μm.

[0037] When the exposure substrate 50 moves in the sub-scanning direction or twists vertically, the distance from the LED chips 53 mounted on the exposure substrate 50 to the incident surface 52b of the lens array 52 changes, and the amount of light incident on the lens array 52 changes. That is, the relative positional relationship between the LED chips 53 and the lens array 52 changes. When the LED chips 53 are arranged in a staggered pattern along the longitudinal direction on the exposure substrate 50 (substrate), for example, the amount of light increases as the odd-numbered LED chips 53 move closer to the lens array 52, and decreases as the even-numbered LED chips 53 move farther away from the lens array 52. ​​In particular, in the overlap region F between the odd-numbered LED chips 53 and the even-numbered LED chips 53 (see FIG. 4(c)), the offset of the LEDs 51 in each chip in the sub-scanning direction increases. This causes a sudden change in the amount of light incident on the lens array 52 in the overlap region F, which may result in image defects such as density unevenness, which causes discontinuities in the toner image formed on the recording material P. That is, the optical performance of the exposure head 4Y may be degraded due to the adhesive.

[0038] In view of the above-mentioned problems, the inventors simulated the contribution of the adhesive to the movement of the exposed substrate 50 relative to the exposure housing 54 and the contribution of the twisting of the exposed substrate 50 using a physical model. FIG. 7 shows a physical model for simulating the contribution of the adhesive to the movement of the exposed substrate 50 relative to the exposure housing 54 and the contribution of the twisting of the exposed substrate 50. In FIG. 7, "Lgap" is an index indicating the contribution of the adhesive portion 200 in the gap between the exposure housing 54 and the exposed substrate 50 in the sub-scanning direction, and "Lbb" is an index indicating the contribution of the adhesive portion 200 in the adhesive range of the exposed substrate 50 in the sub-scanning direction. Furthermore, "Linh" is an index indicating the contribution of the adhesive portion 200 in the overlapping portion of the exposure housing 54 and the exposed substrate 50 in the vertical direction, and "Lbh" is an index indicating the contribution of the adhesive portion 200 in the adhesive range of the exposure housing 54 excluding "Linh" in the vertical direction. 8(a) and 8(b), the "linear expansion coefficient" and "Young's modulus (modulus of longitudinal elasticity)" are indices that indicate the characteristics of the adhesive joint 200. The adhesive joint 200 referred to here is made of a hardened adhesive, and the concept of this adhesive also includes the above-mentioned sealant.

[0039] 8(a) is a graph showing the contribution of movement of the exposure-exposed substrate 50, and FIG. 8(b) is a graph showing the contribution of twisting of the exposure-exposed substrate 50. As shown in FIGS. 8(a) and 8(b), the simulation results show that the contribution of the "linear expansion coefficient" of the adhesive part 200 to the movement and twisting of the exposure-exposed substrate 50 is greater than the other indicators. Therefore, by using an adhesive with a linear expansion coefficient smaller than that of the sealant, it is possible to suppress the movement and twisting of the exposure-exposed substrate 50 caused by the volumetric change of the adhesive when the temperature of the exposure housing 54 rises.

[0040] Therefore, in this embodiment, in addition to the UV adhesive and sealant described above, a thermosetting adhesive that hardens when heated is used to bond the exposed substrate 50. In this embodiment, the linear expansion coefficient of the thermosetting adhesive used as the fifth adhesive portion is smaller than the linear expansion coefficient of the sealant used as the fourth adhesive portion, for example, 3.0×10 -5 / K” or more “6.0×10-5 is less than or equal to " / K". In other words, the encapsulant has a larger coefficient of thermal expansion than the thermosetting adhesive.

[0041] Next, the adhesion between the exposure housing 54 and the exposure substrate 50 in the present embodiment will be described with reference to FIGS. 9 to 13. In the present embodiment, as shown in FIG. 9, in order to adhere the exposure substrate 50 to the extended portions 54L and 54R of the exposure housing 54, specifically, although it will be described later in detail, the thermosetting adhesive 77a is used in the overlap region F (see FIG. 4(c)).

[0042] <Adhesion of the exposure substrate with the UV adhesive> The exposure substrate 50 inserted into the exposure housing 54 through the second opening 54b is temporarily fixed to the exposure housing 54 by being adhered to the extended portions 54L and 54R of the exposure housing 54 with a UV adhesive at both ends in the sub-scanning direction (left-right direction). In the present embodiment, an acrylic-based UV adhesive having the property of being curable in a short time even at room temperature by ultraviolet irradiation is used. By using the UV adhesive, the working time required to position and temporarily fix the exposure substrate 50 at a desired installation position with respect to the exposure housing 54 by means of tools or the like can be shortened.

[0043] The exposure substrate 50 temporarily fixed to the exposure housing 54 is fixedly attached to the exposure housing 54 by being adhered to the extended portions 54L and 54R of the exposure housing 54 with a thermosetting adhesive 77a at both ends in the sub-scanning direction. In the present embodiment, an epoxy-based thermosetting adhesive 77a is used. The thermosetting adhesive 77a is cured, for example, by heating in an oven at 100°C for several hours.

[0044] As shown in FIGS. 10 and 11, the UV adhesive 77c and the thermosetting adhesive 77a adhere the exposure substrate 50 at a plurality of locations spaced apart in the main scanning direction (front-rear direction) at both ends in the sub-scanning direction (left-right direction) of the exposure substrate 50. In FIG. 11, for easy understanding of the description, the upper surface and the lower surface of the exposure substrate 50 are shown.

[0045] In this embodiment, the UV adhesive 77c is provided in temporary fixing areas other than the multiple overlapping areas F on the exposure substrate 50, and forms an adhesive portion that bonds the exposure substrate 50 to the exposure housing 54. The UV adhesive 77c is preferably provided in overlapping areas as viewed from the sub-scanning direction, and at approximately equal intervals in the main scanning direction. In order to prevent warping of the exposure substrate 50, the UV adhesive 77c should be provided in at least one, and preferably three or more, of the multiple temporary fixing areas in the main scanning direction.

[0046] 11, UV adhesive 77c is provided at approximately equal intervals at one end of the exposure substrate 50 in the sub-scanning direction in all temporary fixing regions between the overlapping regions F of the LED chips 53-1 to 53-17 in the main scanning direction, in other words, in all (15) regions overlapping the LED chips 53-2 to 53-16 excluding the overlapping region F as viewed from the sub-scanning direction. The UV adhesive 77c is preferably provided based on the center of each temporary fixing region in the main scanning direction. Furthermore, to further suppress warping of the exposure substrate 50, the UV adhesive 77c may also be provided in regions outside the exposure range H on the photosensitive drum at both ends of the exposure substrate 50 in the main scanning direction.

[0047] In this embodiment, the linear expansion coefficient of the UV adhesive 77c is smaller than that of the thermosetting adhesive 77a, for example, 3.0×10 -5 This is because it is necessary to prevent the exposure substrate 50, which is temporarily fixed with the UV adhesive 77c, from moving relative to the exposure housing 54 when the thermosetting adhesive 77a is heated to harden it.

[0048] <Adhesion of exposed substrates using thermosetting adhesives> On the other hand, the thermosetting adhesive 77a is provided in multiple overlapping regions F on the exposure substrate 50 to form adhesive portions that bond the exposure substrate 50 to the exposure housing 54. The thermosetting adhesives 77a are preferably provided in overlapping locations as viewed from the sub-scanning direction and at approximately equal intervals in the main scanning direction. To prevent movement or twisting of the exposure substrate 50, the thermosetting adhesive 77a is provided in at least one, preferably three or more, of the multiple overlapping regions F in the main scanning direction. Furthermore, the thermosetting adhesive 77a is provided in a position that does not come into contact with the circuit elements mounted on the exposure substrate 50, since contact with the circuit elements may damage them. Furthermore, the thermosetting adhesive 77a is provided in the overlapping regions F so as to point-bond the exposure substrate 50 to the exposure housing 54. This is because the thermosetting adhesive 77a is intended to fix the exposure substrate 50 and the exposure housing 54 together, and point bonding can provide sufficient strength to fix the exposure substrate 50 and the exposure housing 54. By using point bonding in this way, the amount of thermosetting adhesive 77a used can be reduced compared to when the thermosetting adhesive 77a is provided uniformly in the overlap region F, thereby reducing costs.

[0049] In the example shown in FIG. 11, at one end of the exposure substrate 50 in the sub-scanning direction, thermosetting adhesives 77a are provided at approximately equal intervals in 16 locations in the overlapping regions F of all of the LED chips 53-1 to 53-17 in the main scanning direction. Here, the thermosetting adhesives 77a are provided between the UV adhesives 77c. The Young's modulus of the thermosetting adhesives 77a is greater than that of the UV adhesives 77c and the sealant, and is, for example, 10,000 MPa or greater. In other words, the rigidity of the thermosetting adhesives 77a after curing is greater than that of the UV adhesives 77c after curing and the sealant. As shown in FIG. 11, the thermosetting adhesives 77a are preferably provided based on the center of the overlapping regions F (indicated by the dotted line J) in the main scanning direction.

[0050] <Adhesion of exposed substrates using sealant> As described above, in the exposure housing 54 and exposure board 50 that are bonded with the UV adhesive 77c and the thermosetting adhesive 77a, a sealant is used to seal the gap between the exposure board 50 and the exposure housing 54 (more specifically, the extensions 54L and 54R) in the sub-scanning direction. As shown in Figures 9, 12, and 13, the sealant 59a is provided over the entire area in the main scanning direction (front-rear direction) so as to cover the UV adhesive 77c and the thermosetting adhesive 77a at both ends in the sub-scanning direction (left-right direction).

[0051] In this embodiment, a silicone-based moisture-curing adhesive, which has a lower viscosity than the acrylic-based UV adhesive 77c or the epoxy-based thermosetting adhesive 77a, is used for the sealant 59a. Because the sealant 59a has a low viscosity, it can penetrate into the gap between the exposure substrate 50 and the exposure housing 54, following the shapes of the cured UV adhesive 77c and thermosetting adhesive 77a, and seal the gap. Furthermore, because the sealant 59a is a moisture-curing adhesive, it can be easily cured in a room temperature and humidity environment without any special work.

[0052] In this way, the gap between the exposure board 50 and the exposure housing 54 is sealed with the sealant 59a, so that the LEDs 51 mounted on the exposure board 50 are less likely to become soiled by toner, dust, etc. Note that the sealant 59a only seals the gap between the exposure board 50 and the exposure housing 54, and most of the exposure board 50, including the FFC connector 57, is exposed.

[0053] As described above, in order to fix the substrate assembly 500 to the exposure housing 54, the exposure substrate 50 of the substrate assembly 500 is adhered to the exposure housing 54 with multiple adhesives. The adhesives used to adhere the exposure substrate 50 include a UV adhesive 77c that temporarily fixes the exposure substrate 50 to the exposure housing 54, a sealant 59a that seals the gap between the exposure substrate 50 and the exposure housing 54, and a thermosetting adhesive 77a that permanently fixes the exposure substrate 50 to the exposure housing 54. The UV adhesive 77c is provided in a temporary fixing region other than the overlap region F where the LED chips arranged in a staggered pattern on the exposure substrate 50 overlap. The sealant 59a is provided over the entire area of ​​the exposure substrate 50 in the main scanning direction, including the overlap region F. The thermosetting adhesive 77a is provided in the overlap region F where the LED chips arranged in a staggered pattern on the exposure substrate 50 overlap. The thermosetting adhesive 77a has a smaller linear expansion coefficient than the sealant 59a, and therefore the thermosetting adhesive 77a undergoes smaller volume changes due to heat than the sealant 59a. In this embodiment, the thermosetting adhesive 77a is provided in the overlap region F, which is particularly affected by movement and twisting of the exposure substrate 50 due to volume changes in the adhesive when the exposure housing 54 is heated, thereby suppressing deterioration in the optical performance of the exposure head caused by the adhesive.

[0054] <About lens array adhesion> Next, the bonding between the exposure housing 54 and the lens array 52 will be described with reference to Fig. 3 and Figs. 14 to 20. As described above, the lens array 52 is bonded to the exposure housing 54 by the adhesive portion 201 (see Fig. 3). The lens array 52 may be bonded to the exposure housing 54 at multiple locations in the longitudinal direction of the lens array 52 using a UV adhesive. In addition, in order to seal the gap between the lens array 52 bonded with the UV adhesive and the exposure housing 54 (more specifically, the first opening 54a of the flat portion 54U), it may be possible to bond almost the entire area in the longitudinal direction of the lens array 52 using a sealant with a lower viscosity than the UV adhesive.

[0055] As described above, the lens array 52 focuses light emitted from the LEDs 51 onto the surface of the photosensitive drum 2Y. To achieve this, as shown in FIG. 3, the lens array 52 is positioned so that the distance between the LED chips 53 (specifically, the LEDs 51) mounted on the exposure board 50 and the lens array 52 (specifically, the light incident surface 52b) is a predetermined value. However, when the exposure housing 54 is heated by heat generated by the circuit elements of the exposure board 50, the difference in the linear expansion coefficient of the UV adhesive bonding the lens array 52 to the exposure housing 54 and the linear expansion coefficient of the sealant can cause variations in the volumetric change of the adhesive. As a result, in the conventional method, the lens array 52 moves in the sub-scanning direction or twists vertically relative to the exposure housing 54, changing the distance between the LED chips 53 on the exposure board 50 and the lens array 52. ​​This can result in image defects such as density unevenness in the toner image formed on the recording material P.

[0056] In view of the above-mentioned problems, the inventors simulated the contribution of the adhesive to the movement of the lens array 52 relative to the exposure housing 54 and the contribution of the twisting of the lens array 52 using a physical model. FIG. 14 shows a physical model for simulating the contribution of the adhesive to the movement of the lens array 52 relative to the exposure housing 54 and the contribution of the twisting of the lens array 52. ​​In FIG. 14, "Lgap" is an index indicating the contribution of the adhesive portion 201 in the gap between the exposure housing 54 (more specifically, the flat portion 54U) and the lens array 52 in the sub-scanning direction, and "Lbw" is an index indicating the contribution of the adhesive portion 201 in the adhesive range of the exposure housing 54 in the sub-scanning direction. Furthermore, "Linh" is an index indicating the contribution of the adhesive portion 201 in the overlapping portion of the exposure housing 54 and the lens array 52 in the vertical direction, and "Lbh" is an index indicating the contribution of the adhesive portion 201 in the adhesive range of the lens array 52 excluding "Linh" in the vertical direction. 15(a) and 15(b), the "linear expansion coefficient" and "Young's modulus (modulus of longitudinal elasticity)" are indices that indicate the characteristics of the adhesive portion 201. The adhesive portion 201 referred to here is made of a hardened adhesive, and the concept of this adhesive also includes the above-mentioned sealant.

[0057] FIG. 15(a) is a graph showing the contribution degree of the movement of the lens array 52, and FIG. 15(b) is a graph showing the contribution degree of the twist of the lens array 52. As shown in FIGS. 15(a) and 15(b), according to the simulation results, it can be understood that the contribution degree of the movement of the lens array 52 and the contribution degree of the twist of the lens array 52 are such that the contribution degree of the "linear expansion coefficient" of the adhesive portion 201 is larger than other indexes. Therefore, if an adhesive having a linear expansion coefficient smaller than that of the sealant is used, it is possible to suppress the movement of the lens array 52 and the twist of the lens array 52 caused by the volume change of the adhesive when the above-described exposure housing 54 is heated.

[0058] Therefore, in the present embodiment, in addition to the above-described UV adhesive and sealant, a thermosetting adhesive that is cured by heat is used to adhere the lens array 52. In the present embodiment, the linear expansion coefficient of the thermosetting adhesive is smaller than the linear expansion coefficient of the sealant, for example, "3.0×10 -5 / K" or more and "6.0×10 -5 / K" or less. In other words, the sealant has a larger thermal expansion coefficient than the thermosetting adhesive.

[0059] In the present embodiment, as shown in FIG. 16, in order to adhere the lens array 52 to the flat portion 54U of the exposure housing 54, although details will be described later, a thermosetting adhesive 77b is used in a predetermined region of the lens array 52. The predetermined region of the lens array 52 referred to here is a plurality of main fixing regions (second regions) that overlap with a plurality of overlap regions F (see FIG. 4(c)) of the exposure substrate 50 in the lens array 52 when viewed from the optical axis direction of the lens array 52.

[0060] <Regarding the adhesion of the lens array by the UV adhesive> The lens array 52 inserted into the first opening 54a of the exposure housing 54 is temporarily fixed to the exposure housing 54 by being adhered at both ends in the sub-scanning direction (left-right direction) to the flat surface 54U of the exposure housing 54 with UV adhesive. In this embodiment, an acrylic UV adhesive is used, which has the property of being hardened in a short time even at room temperature when irradiated with ultraviolet light. Using the UV adhesive can reduce the work time required to position the lens array 52 at the desired installation position in the exposure housing 54 and temporarily fix it thereto using a tool or the like.

[0061] The lens array 52 temporarily fixed to the exposure housing 54 is finally fixed to the exposure housing 54 by being adhered at both ends in the sub-scanning direction to the flat surface portion 54U of the exposure housing 54 with a thermosetting adhesive 77b. In this embodiment, an epoxy-based thermosetting adhesive 77b is used. The thermosetting adhesive 77b hardens by heating it in an oven at 100°C for several hours, for example.

[0062] 17 and 18, the UV adhesive 77d and the thermosetting adhesive 77b bond the lens array 52 at multiple locations spaced apart in the main scanning direction (front-rear direction) at both ends in the sub-scanning direction (left-right direction) of the exposure substrate 50. For ease of understanding, Fig. 18 shows the top surface of the exposure substrate 50 and the back surface of the flat portion 54U.

[0063] In this embodiment, the UV adhesive 77d constituting the third adhesive portion is provided in an area other than the permanent fixing area (other than the second area) that overlaps with the overlap area F, i.e., in a temporary fixing area (third area) that does not overlap with the overlap area F of the exposure substrate 50 when viewed from the optical axis direction, to adhere the lens array 52 to the exposure housing 54. The UV adhesive 77d is preferably provided in overlapping areas when viewed from the sub-scanning direction and at approximately equal intervals in the main scanning direction. To suppress warping of the lens array 52, the UV adhesive 77d should be provided in at least one location in the main scanning direction, and preferably three or more locations.

[0064] 18, UV adhesive 77d is provided at approximately equal intervals at one end of the lens array 52 in the sub-scanning direction in all temporary fixing regions that overlap the regions between the overlapping regions F of the LED chips 53-1 to 53-17 as viewed from the optical axis direction, in other words, in all (15) temporary fixing regions that overlap the LED chips 53-2 to 53-16 excluding the overlapping regions F. The UV adhesive 77d is preferably provided based on the center of the temporary fixing region in the main scanning direction. Furthermore, the UV adhesive 77d may also be provided at both ends of the lens array 52 in the main scanning direction to further suppress warping of the lens array 52.

[0065] The linear expansion coefficient of the UV adhesive 77d is smaller than that of the thermosetting adhesive 77b, for example, smaller than "3.0×10-5 / K." This is because it is necessary to prevent the lens array 52 temporarily fixed with the UV adhesive 77d from moving relative to the exposure housing 54 when the thermosetting adhesive 77b is heated to harden.

[0066] <Adhesion of lens arrays using thermosetting adhesive> On the other hand, the thermosetting adhesive 77b constituting the first adhesive portion is provided in the main fixing region of the lens array 52 and adheres the lens array 52 to the exposure housing 54. The thermosetting adhesive 77b is preferably provided in overlapping positions as viewed from the sub-scanning direction and at approximately equal intervals in the main scanning direction. In order to prevent movement or twisting of the lens array 52, the thermosetting adhesive 77b should be provided in at least one or more, preferably three or more, of the multiple main fixing regions in the main scanning direction.

[0067] In the example shown in FIG. 18, thermosetting adhesives 77b are provided at approximately equal intervals at 16 locations in a final fixing region that overlaps all of the overlap regions F of the LED chips 53-1 to 53-17 at one end of the lens array 52 in the sub-scanning direction when viewed from the optical axis direction. Here, the thermosetting adhesives 77b are provided between the UV adhesives 77d. The Young's modulus of the thermosetting adhesives 77b is greater than that of the UV adhesives 77d and the sealant, and is, for example, 10,000 MPa or greater. In other words, the rigidity of the thermosetting adhesives 77b after hardening is greater than that of the UV adhesives 77d and the sealant. As shown in FIG. 18, the thermosetting adhesives 77b are preferably provided based on the center (indicated by the dotted line K) of the final fixing region that overlaps the overlap regions F in the main scanning direction.

[0068] The thermosetting adhesive 77b is provided so as to point-bond the lens array 52 to the exposure housing 54 in the main fixing region that overlaps the overlap region F. This is because the thermosetting adhesive 77b is intended to fix the lens array 52 to the exposure housing 54, and point bonding can fix the lens array 52 to the exposure housing 54 with sufficient strength. By using point bonding in this way, the amount of thermosetting adhesive 77b used can be reduced compared to when the thermosetting adhesive 77b is provided uniformly in the main fixing region, thereby reducing costs.

[0069] <Adhesion of lens arrays using sealant> As described above, in the exposure housing 54 and the lens array 52 that are bonded with the UV adhesive 77d and the thermosetting adhesive 77b, a sealant is used to seal the gap between the lens array 52 and the exposure housing 54 (more specifically, the first opening 54a of the flat portion 54U) in the sub-scanning direction. As shown in Figures 16, 19, and 20, the sealant 59b is preferably provided over the entire area in the main scanning direction (front-rear direction) so as to cover the UV adhesive 77d and the thermosetting adhesive 77b at both ends in the sub-scanning direction (left-right direction).

[0070] In this embodiment, the sealant 59b constituting the second adhesive portion is a silicone-based moisture-curing adhesive, which has a lower viscosity than the acrylic-based UV adhesive 77d or the epoxy-based thermosetting adhesive 77b. Because the sealant 59b has a low viscosity, it can penetrate into the gap between the lens array 52 and the exposure housing 54 (the first opening 54a of the flat portion 54U) along the shapes of the cured UV adhesive 77d and thermosetting adhesive 77b, thereby sealing the gap. Furthermore, because the sealant 59b is a moisture-curing adhesive, it can easily harden in a room-temperature, normal-humidity environment without any special work. Since the sealant 59b seals the gap between the lens array 52 and the exposure housing 54, the lenses 521 of the lens array 52 are less likely to become soiled by toner, dust, or the like.

[0071] As described above, the lens array 52 is adhered to the exposure housing 54 by an adhesive portion composed of multiple types of adhesives. The adhesives used to adhere the lens array 52 include a UV adhesive 77d that temporarily fixes the lens array 52 to the exposure housing 54, a sealant 59b that seals the gap between the lens array 52 and the exposure housing 54, and a thermosetting adhesive 77b that permanently fixes the lens array 52 to the exposure housing 54. The UV adhesive 77d is provided in a temporary fixing region of the lens array 52 that does not overlap the overlap region F of the exposure substrate 50 as viewed in the optical axis direction. The sealant 59a is provided over the entire area of ​​the lens array 52 in the main scanning direction. The thermosetting adhesive 77b is provided in a permanent fixing region that overlaps the overlap region F of the exposure substrate 50 as viewed in the optical axis direction. Because the linear expansion coefficient of the thermosetting adhesive 77b is smaller than that of the sealant 59b, the thermosetting adhesive 77b experiences less volume change due to heat than the sealant 59b. In this embodiment, in the lens array 52, a thermosetting adhesive 77b is provided in the main fixing area that overlaps the overlap area F, which is particularly affected by the movement and twisting of the exposure substrate 50 due to volume changes in the adhesive when the exposure housing 54 heats up.This makes it possible to suppress the deterioration of the optical performance of the exposure head 4Y due to the adhesive.

[0072] <Other embodiments> In the above-described embodiment, the exposure heads 4Y to 4K are disposed below the photosensitive drums 2Y to 2K, and the "bottom exposure method" is adopted to expose the photosensitive drums 2Y to 2K from below (see FIG. 2), but the exposure method is not limited to this. The exposure method may also be an "top exposure method" in which the exposure heads 4Y to 4K are disposed above the photosensitive drums 2Y to 2K, and the photosensitive drums 2Y to 2K are exposed from above.

[0073] In the above-described embodiment, the image forming apparatus 100 is described as an intermediate transfer type in which the toner image of each color is primarily transferred from the photosensitive drums 2Y to 2K of each color to the intermediate transfer belt 6, and then the toner image of each color is secondarily transferred to the recording material P. However, the present invention is not limited to this. For example, the image forming apparatus may be a direct transfer type in which the toner image on the photosensitive drum is directly transferred to the recording material P by applying a voltage to a transfer roller disposed opposite the photosensitive drum and the conveying belt, with the conveying belt forming a nip portion between the photosensitive drum and the recording material P. [Explanation of symbols]

[0074] 4Y (4M, 4C, 4K)... exposure head, 50... substrate (exposure substrate), 51... light emitting element (LED), 52... lens array, 53... light emitting chip (LED chip), 54... holder (exposure housing), 77b... first adhesive portion (thermosetting adhesive), 500... substrate assembly, 521... lens

Claims

1. a substrate assembly including: a first light-emitting chip having a plurality of light-emitting elements arranged in a main scanning direction; a second light-emitting chip having a plurality of light-emitting elements arranged in the main scanning direction; and a substrate on which the first light-emitting chip and the second light-emitting chip are mounted so as to partially overlap each other when viewed from the sub-scanning direction; a lens array having a plurality of lenses for condensing light emitted from the light emitting elements of the first light emitting chip and the second light emitting chip; a holder that holds the substrate assembly and the lens array so that the lens array faces the light-emitting element; a first adhesive portion; an end portion of the first light-emitting chip in the main scanning direction and an end portion of the second light-emitting chip in the main scanning direction overlap each other when viewed from the sub-scanning direction; When a region on the substrate where an end of the second light-emitting chip in the main scanning direction and an end of the first light-emitting chip in the main scanning direction overlap as viewed from the sub-scanning direction is defined as a first region, and a region of the lens array that overlaps with the first region as viewed from the optical axis direction of the lens array is defined as a second region, the first adhesive portion bonds both ends of the lens array in the sub-scanning direction to the holder in the second region. An exposure head characterized by:

2. a second adhesive portion that adheres both end portions of the lens array in the sub-scanning direction to the holder; the second adhesive portion has a larger linear expansion coefficient than the first adhesive portion; 2. The exposure head according to claim 1.

3. a light-emitting element located in the first region among the plurality of light-emitting elements of the first light-emitting chip and a light-emitting element located in the first region among the plurality of light-emitting elements of the second light-emitting chip overlap each other when viewed from the sub-scanning direction; 2. The exposure head according to claim 1.

4. The first adhesive portion is formed by hardening a thermosetting adhesive that hardens when heated.

2. The exposure head according to claim 1.

5. the second adhesive portion is a sealing member for sealing a gap between the lens array and the holder, and is provided over the entire area of ​​the lens array in the main scanning direction at both end portions of the lens array in the sub scanning direction.

3. The exposure head according to claim 2.

6. the sealing member is provided on top of the first adhesive portion so as to cover the first adhesive portion; 6. The exposure head according to claim 5.

7. a third adhesive portion that adheres both end portions of the lens array in the sub-scanning direction to the holder at positions different from the first adhesive portion; the third adhesive portion has a linear expansion coefficient and a Young's modulus smaller than those of the first adhesive portion; 3. The exposure head according to claim 2.

8. The third adhesive portion is formed by hardening a photo-curable adhesive that is hardened by light.

8. The exposure head according to claim 7.

9. fourth adhesive portions that bond both end portions of the substrate assembly in the sub-scanning direction to the holder; a fifth adhesive portion that bonds both end portions of the substrate assembly in the sub-scanning direction to the holder and has a linear expansion coefficient smaller than that of the fourth adhesive portion; The fifth adhesive portion is provided in the first region.

2. The exposure head according to claim 1.

10. the holder includes a first holder that holds the lens array, and a second holder that holds the substrate assembly so as to leave a gap between the substrate assembly and the lens array in the optical axis direction of the lens array.

2. The exposure head according to claim 1.

11. the first light-emitting chip is one of a plurality of first light-emitting chips that constitute a first chip group and are arranged at intervals in the main scanning direction, the second light-emitting chip is one of a plurality of second light-emitting chips that constitute a second chip group and are arranged at intervals in the main scanning direction, the substrate assembly includes a plurality of first regions in which ends of the second light-emitting chips in the main scanning direction and ends of the first light-emitting chips in the main scanning direction overlap each other when viewed from the sub-scanning direction; The lens array includes a plurality of second regions overlapping the plurality of first regions when viewed from the optical axis direction of the lens array, a plurality of first adhesive portions that bond the lens array and the holder together are provided in all of the second regions, and the first adhesive portion is one of the plurality of first adhesive portions; 2. The exposure head according to claim 1.

12. A photoreceptor; an exposure head according to claim 1, wherein the surface of the photosensitive member is exposed to light to form an electrostatic latent image; a developing device that develops the electrostatic latent image formed on the surface of the photosensitive member with toner; a transfer unit that transfers the toner image formed on the surface of the photoreceptor onto a recording material, An image forming apparatus characterized by:

Images