Optical print head and image forming device

An optical print head, including: an elongated substrate having a line-shaped region in which light-emitting elements are arranged; an optical member condensing light from the light-emitting elements onto an irradiation target; a holding member holding the optical member; a base member holding the substrate and the holding member; an integrated circuit mounted in a first region in proximity of an end in a longitudinal direction of the substrate on a first surface of the substrate facing the base member, heat being generated in the integrated circuit during optical writing; and a thermally conductive member between the integrated circuit and the base member. In the optical print head, the holding member has a support portion contacting the substrate in a second region at a position differing from the first region in plan view on a second surface of the substrate not facing the base member.

This application claims priority to Japanese Patent Application No. 2017-038184 filed Mar. 1, 2017, the contents of which are hereby incorporated herein by reference in their entirety.

BACKGROUND

Technical Field

The present disclosure relates to optical print heads (also referred to as optical writing devices) and image forming devices, in particular to a technology for helping prevent image quality deterioration caused by heat from a semiconductor component that controls light amount emitted from the optical print head.

Description of the Related Art

Recently, in the technical field of electrophotographic image forming devices, optical print heads using organic light-emitting diodes (OLEDs) for light-emitting elements are developed in order to achieve downsizing and cost reduction.

As illustrated inFIG. 7andFIG. 8, an optical print head700that uses OLEDs forms an electrostatic latent image through condensing light emitted from the OLEDs712onto an outer circumferential surface of a photoreceptor drum750with use of a lens array730.

The lens array730includes many rod lenses731integrated with use of resin732, and is held by a lens holder720. The lens holder720is fixed by a base holder740.

A rotational axis752of the photoreceptor drum750is supported by photoreceptor positioning members751, and the lens holder720contacts the photoreceptor positioning members751. This structure defines a distance from the lens array730to the outer circumferential surface of the photoreceptor drum750.

The OLED panel710includes a glass substrate711and a thin film transistor (TFT) circuit713that includes the OLEDs712and that is disposed on the glass substrate711. A light-emitting region on the glass substrate711is sealed by a sealing material714in order to protect the OLEDs712from external air. Through fixing the sealing material714to the base holder740, the light-emitting region of the OLED panel710is positioned relative to the photoreceptor drum750.

In proximity of one end in a longitudinal direction of the OLED panel710, a driver integrated circuit (IC)800for switching on and off the OLEDs712is disposed outside the region sealed by the sealing material714. That is, the OLED panel710is supported at only one end, and in a region around the driver IC800, the OLED panel710is in contact with neither the lens holder720nor the base holder740.

Temperature increase of the driver IC800occurring in accordance with optical writing operations may cause malfunction or the like. Accordingly, the driver IC800is cooled through heat dissipation. However, thermal expansion of the lens holder720and thermal expansion of the photoreceptor positioning members751caused by heat conducted through the lens holder720may occur in accordance with how heat is dissipated from the driver IC800.

Such thermal expansion causes changes in positions of the components relative to each other and a reduction in condensing ratio of light emitted from the OLEDs712and condensed onto the outer circumferential surface of the photoreceptor drum750, and consequently causes image quality deterioration. Accordingly, it is desirable that heat from the driver IC800be dissipated to the base holder740.

In view of this, for example, conventional technology describes disposing a thermally conductive member903between a high heat generating part901and a display device fixing frame902as illustrated inFIG. 9(see Japanese Patent Application Publication No. 2006-032615). Application of such conventional technology would help heat from the driver IC800to be dissipated to the base holder740through disposing a thermally conductive member between the driver IC800and the base holder740.

However, when a thermally conductive member is disposed between the driver IC800and the base holder740, a load is added around the driver IC800due to a reaction force from the thermally conductive member. When the OLED panel710deforms because of this load, the OLEDs712are displaced relative to the lens array730and the photoreceptor drum740, and consequently condensing ratio of light emitted from the OLEDs712deteriorates.

One possible measure for overcoming this problem is to provide a support portion for supporting the lens holder720at a surface of the glass substrate711behind a surface of the glass substrate711on which the driver IC800is disposed. However, because the lens holder720is in contact with the photoreceptor positioning member751, heat of the driver IC800may be conducted through the support portion to the lens holder720and the photoreceptor positioning member751. Accordingly, it is not desirable to provide, on the glass substrate711, a support portion for supporting the lens holder720.

SUMMARY

The present disclosure has been achieved in view of the above problems, and an aim thereof is to provide an optical print head and an image forming device that help suppress displacement of OLEDs and conduction of heat from a driver IC to a lens holder.

To achieve at least one of the abovementioned objects, an optical print head reflecting at least one aspect of the present disclosure includes: an elongated light source substrate that has a line-shaped region in which a plurality of light-emitting elements are arranged; an optical member that condenses light emitted from the light-emitting elements onto an irradiation target; a holding member that holds the optical member; a base member that holds the light source substrate and the holding member; an integrated circuit that is mounted in a first region on a first surface of the light source substrate, the first surface facing the base member and the first region being in proximity of an end in a longitudinal direction of the light source substrate, heat being generated in the integrated circuit during optical writing; and a thermally conductive member that is disposed between the integrated circuit and the base member, wherein the holding member has a support portion contacting the light source substrate in a second region on a second surface of the light source substrate, the second surface not facing the base member and the second region being at a position differing from the first region in plan view.

DETAILED DESCRIPTION

The following describes an embodiment of an optical print head and an image forming device pertaining to the present disclosure, with reference to the drawings.

[1] Structure of Image Forming Device

The following describes a structure of an image forming device pertaining to the present embodiment.

InFIG. 1, an image forming device1is a so-called tandem-type color printer device, and includes image forming units101Y,101M,101C, and101K forming images of colors yellow (Y), magenta (M), cyan (C), and black (K), respectively. The image forming unit101Y includes an optical print head100Y, a photoreceptor drum110Y, an electricity charging device111Y, a developing device112Y, and a cleaning device114Y. Similarly, the image forming unit101M includes an optical print head100M, a photoreceptor drum110M, an electricity charging device111M, a developing device112M, and a cleaning device114M; the image forming unit101C includes an optical print head100C, a photoreceptor drum110C, an electricity charging device111C, a developing device112C, and a cleaning device114C; and the image forming unit101K includes an optical print head100K, a photoreceptor drum110K, an electricity charging device111K, a developing device112K, and a cleaning device114K.

When forming a color image, the image forming units101Y,101M,101C, and101K respectively cause outer circumferential surfaces of the photoreceptor drums110Y,110M,110C, and110K to be uniformly charged by the electricity charging devices111Y,111M,111C, and111K. Then the image forming units101Y,101M,101C, and101K respectively cause the optical print heads100Y,100M,100C, and100K to each form an electrostatic latent image, and respectively cause the developing devices112Y,112M,112C, and112K to develop the electrostatic latent images.

Primary transfer rollers113Y,113M,113C, and113K electrostatically transfer the toner images of the colors Y, M, C, and K respectively carried on the outer circumferential surfaces of the photoreceptor drums110Y,110M,110C, and110K onto an intermediate transfer belt102in sequence, so that the toner images overlap each other. A color toner image is thus formed. Then, toner remaining on the outer circumferential surfaces of the photoreceptor drums110Y,110M,110C, and110K is removed by the cleaner devices114Y,114M,114C, and114K, respectively.

The intermediate transfer belt102is an endless belt, and rotates in a direction indicated by arrow A in order to convey the color toner image to a second transfer roller pair103. In accordance with this, a recording sheet S contained in a sheet feed tray104is picked up and conveyed to the secondary transfer roller pair103. Then the color toner image on the intermediate transfer belt102is electrostatically transferred onto the recording sheet S. Then the color toner image on the recording sheet S is thermally fixed by a fixing device105, and the recording sheet S is ejected onto a sheet ejection tray106.

Because the following description applies to all of the optical print heads100Y,100M,100C, and100K irrespective of their toner colors, the letters Y, M, C, and K in the reference signs are hereinafter omitted.

[2] Structure of Optical Print Head100

The following describes a structure of the optical print head100.

InFIG. 2andFIG. 3, the optical print head100includes an OLED panel210, a lens holder220, a lens array230, and a base holder240. The OLED panel210is a light emitting substrate elongated in a main scanning direction and has a thin film transistor (TFT) circuit213including a plurality of (for example, 15,000) organic light-emitting elements (OLEDs)212arranged in a line-shaped region on a glass substrate211.

A driver integrated circuit (IC)215is connected to the TFT circuit213, and during optical writing, the driver IC215turns on and off the OLEDs212in accordance with image data. The OLEDs212are arrayed in a line or a plurality of lines in a staggered pattern, and the light-emitting region including the OLEDs212is sealed by a sealing member214in order to protect the OLEDs212from dust.

The sealing member214is in contact with a support portion241of the base holder240. The support portion241may be a semispherical protrusion or hardened adhesive. The sealing member214contacts the support portion241to position the OLED panel210. The base holder240is a member molded out of a sheet metal. The sheet metal material for the base holder240is a steel material such as stainless steel (SUS) having thermal conductivity Kh of approximately 20 W/m·K.

Heat from the driver IC215is conducted through a thermally conductive silicone member260to the base holder240. The thermally conductive silicone member260may be silicone grease applied to the driver IC215and hardened, or may be a sheet-like silicone member sandwiched between the driver IC215and the base holder240.

A region A from an end in a longitudinal direction of the glass substrate211to the driver IC215has a length Da that is shorter than a length Db of a region B from the sealing member214to the driver IC215. Because the glass substrate211has a constant width in a transverse direction irrespective of positions in the longitudinal direction, the region A has a smaller area than the region B. A glass material for the glass substrate211has thermal conductivity Kp of approximately 1.0 W/m·K.

The lens array230includes a plurality of rod lenses231arranged in two or more rows in the main scanning direction in a staggered pattern and fixed by resin232. The lens array230condenses light P emitted from the OLEDs212onto the outer circumferential surface of the photoreceptor drum110. For example, a SELFOC lens array (SLA; SELFOC is a registered trademark of Nippon Sheet Glass Co. Ltd.) may be used for the lens array230.

The lens holder220includes resin and is fixed to the base holder240with the lens array230held by the lens holder220. The lens holder220has, in proximity of each end in a longitudinal direction of the lens holder220, a protrusion221. Each protrusion221has a semispherical tip that contacts a corresponding one of positioning members250of the photoreceptor drum110. This structure defines positions relative to each other of the outer circumferential surface of the photoreceptor drum110, the rod lenses231, and the OLEDs212. The resin material for the lens holder220has thermal conductivity Ks ranging from 0.4 W/m·K to 0.5 W/m·K.

For the resin material for the lens holder220, for example, orienting resin obtained through adding a reinforcing agent such as glass fiber to a general-purpose engineering plastic can be used. Alternatively, resin that does not include glass fiber may be used. For the general-purpose engineering plastic, liquid crystal polymer resin, polycarbonate, synthetic resin of polycarbonate and acrylonitrile butadiene styrene (ABS) resin, synthetic resin of polycarbonate and polystyrene, or the like may be used.

InFIG. 4, a positioning member250has an end surface251contacting a protrusion221. The photoreceptor drum110includes a flange portion301, a drum portion302, and a rotational axis401. The rotational axis401passes through the positioning member250. Further, the positioning member250is screwed to the housing (not illustrated) of the image forming unit101at a middle portion252between a portion of the positioning member250through which the rotational axis401passes and the end surface251.

The lens holder220has a support portion222. The support portion222contacts a main surface of the glass substrate211facing the lens array230. Further, the support portion222contacts the glass substrate211at a position in a longitudinal direction between the driver IC215and the support portion241of the base holder240.

Note that components such as cables for connecting the optical print head100and other portions of the image forming device1are not illustrated inFIG. 2,FIG. 3, orFIG. 4.

[3] Suppression of Displacement of OLEDs212in Optical Axis Direction

Grease silicone shrinks when hardened. Further, a silicone sheet shrinks in an optical axis direction (direction parallel to optical axes of the rod lenses731) after being fitted to the driver IC215and the base holder240. When the thermally conductive silicone member260shrinks, while the base holder240does not deform due to having high rigidity, the glass substrate211deflects due to having low rigidity. When the glass substrate211deflects, the driver IC215is attracted toward the base holder240.

In cases where the lens holder220does not have the support portion222and the glass substrate211deflects with the support portion241of the base holder240serving as a fulcrum due to a load that corresponds to a reaction force from the thermally conductive silicone member260, a light-emitting region of the glass substrate211where the OLEDs212are mounted deflects toward the base holder240. This causes the OLEDs212to be displaced in the optical axis direction. When the OLEDs212are displaced and a distance from the OLEDs212to the outer circumferential surface of the photoreceptor drum110changes, condensing ratio of light emitted from the OLEDs212becomes lower. This leads to image quality deterioration.

The reaction force causes the glass substrate211between the driver IC215and the light-emitting region of the glass substrate211to deflect toward the lens holder220. In contrast, in the present embodiment, the support portion222of the lens holder220contacts the glass substrate211between the driver IC215and the light-emitting region of the glass substrate211. This structure helps prevent the glass substrate211from deflecting toward the lens holder220. As a result, the light-emitting region of the glass substrate211can be prevented from deflecting toward the base holder240.

[4] Suppression of Conduction of Heat from Driver IC215to Lens Holder220

As described above, the support portion222of the lens holder220contacts the glass substrate211at a position in the longitudinal direction between the driver IC215and the support portion241of the base holder240. Accordingly, in order for heat from the driver IC215to be conducted to the lens holder220, the heat is conducted through the glass substrate211.

However, the glass substrate211has low thermal conductivity due to including a glass material, which has low thermal conductivity, and due to having small thickness in the optical axis direction. Accordingly, less heat from the driver IC215is conducted to the lens holder220compared to structures in which the heat conduction path from the driver IC215to the lens holder220has a minimum length due to disposition of the support portion241at a position overlapping the driver IC215in plan view from the optical axis direction.

Also, heat from the driver IC215is dissipated through the thermally conductive silicone member260to the base holder240. This further helps reduce heat amount conducted from the driver IC215to the lens holder220.

Thus, the structure pertaining to the present embodiment helps suppress heat amount conducted from the driver IC215to the lens holder220. This helps prevent a decrease in condensing ratio of light emitted from the OLEDs212caused by thermal deformation of the lens holder220and the positioning members250, and consequently helps prevent image quality deterioration.

Structures in which the positioning members250contact the base holder240incur high costs because sheet metal working is used in order to provide the base holder240with protrusions contacting the positioning members250. In contrast, the lens holder220is formed through resin molding with use of a metal mold. That is, the protrusion is formed by simply using a metal mold designed for forming the lens holder220along with the protrusion221. This helps reduce costs because a process of working each instance of the lens holder220is not necessary.

Further, in structures in which the positioning members250contact the base holder240, heat conducted from the driver IC215through the thermally conductive silicone member260to the base holder240may further be conducted to the positioning members250. This may cause image quality deterioration due to thermal deformation of the positioning members250. As described above, the present embodiment helps prevent such image quality deterioration.

[5] Suppression of Conduction of Heat Making Use of Thermal Resistance

As described above, the glass substrate211has a smaller area in the region A than in the region B. Accordingly, the region B has greater thermal resistance, and thus suppresses heat increase to a greater extent than the region A. Accordingly, the structure of the present embodiment in which the support portion222contacts the region B has a greater effect of helping suppression of conduction of heat from the driver IC215to the lens holder220compared to structures in which the support portion222contacts the region A.

[6] Suppression of Bending Moment

The support portion222of the lens holder220contacts the OLED panel210at a position differing in the longitudinal direction from the position of the support portion241of the base holder240. Specifically, in the present embodiment, the support portion222contacts the glass substrate211at a position closer to the driver IC215than the support portion241. Such a structure helps suppress bending moment of the OLED panel210, and consequently helps prevent the OLEDs212from being displaced in the optical axis direction.

[7] Control of Thermal Conductivity Making Use of Differences in Thermal Conductivity between Materials

Typically, a material having low thermal conductivity has great thermal resistance. Accordingly, a glass substrate211including a material having low thermal conductivity helps suppress conduction of heat from the driver IC215, which is disposed on the glass substrate211, through the glass substrate211to other components. This structure helps improve heat dissipation efficiency through helping heat from the driver IC215to be conducted through the thermally conductive silicone member260to the base holder240.

When thermal conductivity Ks of the resin material for the lens holder220is lower than thermal conductivity Kp of the glass material for the glass substrate211and lower than thermal conductivity Kh of the sheet metal material for the base holder240, conduction of heat to the lens holder220and conduction of heat through the lens holder220to the positioning members250can further be suppressed.

Although description of the present invention has been provided with reference to an embodiment of the present invention, the present invention should not be construed as being limited to the above embodiment, and for example the following modifications are possible.

(1) The above embodiment takes a case in which a tip of the support portion222of the lens holder220is flat as an example. However, the present invention of course should not be construed as being limited to this, and may be configured as follows. When the tip of the support portion222is notched, and consequently has a large surface area as inFIG. 5AandFIG. 5B, the support portion222has great heat dissipating property. This consequently helps suppress conduction of heat from the driver IC215through the glass substrate211and the support portion222to a main body of the lens holder220and the positioning members250.

The notches at the tip of the support portion222may be grooves or a plurality of protrusions.

Further, the tip of the support portion222may be rounded as inFIG. 6AandFIG. 6B. In such a structure, contacting area between the glass substrate211and the lens holder220is small, and this helps suppress conduction of heat from the driver IC215to the lens holder220and the positioning members250.

(2) In the above embodiment, description is given taking a case in which the base holder240has the support portion241as an example. However, the present invention of course should not be construed as being limited to this, and may be configured as follows. For example, when a surface of the base holder240facing the OLED panel210is a flat surface that does not have the support portion241and the OLED panel210is fixed to the base holder240with the flat surface in surface contact with the sealing member214, the support portion222of the lens holder220may contact the glass substrate211at a position in the longitudinal direction between the driver IC215and a position at which the sealing member214is fixed to the base holder240.

The effects of the present invention can be achieved in structures in which the support portion222contacts the glass substrate211of the OLED panel215at a position in the longitudinal direction between the driver IC215and the position of the base holder240at which the base holder240contacts the OLED panel210, irrespective of how the OLED panel210is fixed to the base holder240.

(3) In the above embodiment, description is given while illustrating a state in which the support portion222of the lens holder220contacts the glass substrate211of the OLED panel210. However, the support portion222may be provided in different manners as long as the tip of the support portion222is at a position at which deflection of the glass substrate211caused by the thermally conductive silicone member260can be suppressed. Accordingly, the support portion222may not necessarily be in contact with the glass substrate211when deflection of the glass substrate211is small and does not affect image quality.

(4) In the above embodiment, description is given taking a case in which the image forming device1is a tandem-type color printer as an example. However, the present invention of course should not be construed as being limited to this, and the image forming device1may be a color printer device of a type other than a tandem type or may be a monochrome printer. Further, the present invention achieves similar effects when applied to single-function peripherals such as copiers including a scanner device, facsimile devices having a facsimile communication function, and multi-function peripherals (MFPs) including all such functions.

The above embodiments and modifications represent at least one aspect of the present invention, and are summarized as follows.

That is, an optical print head reflecting at least one aspect of the present disclosure includes: an elongated light source substrate that has a line-shaped region in which a plurality of light-emitting elements are arranged; an optical member that condenses light emitted from the light-emitting elements onto an irradiation target; a holding member that holds the optical member; a base member that holds the light source substrate and the holding member; an integrated circuit that is mounted in a first region on a first surface of the light source substrate, the first surface facing the base member and the first region being in proximity of an end in a longitudinal direction of the light source substrate, heat being generated in the integrated circuit during optical writing; and a thermally conductive member that is disposed between the integrated circuit and the base member, wherein the holding member has a support portion contacting the light source substrate in a second region on a second surface of the light source substrate, the second surface not facing the base member and the second region being at a position differing from the first region in plan view.

In this structure, the support portion of the holding member contacts the light source substrate in a second region on the second surface of the light source substrate at a position differing from the first region in plan view, where the second surface does not face the base member and the first region is a region in which the integrated circuit is mounted on the first surface of the light source substrate. This helps suppress deformation of the light source substrate because of a load in a vertical direction added due to a reaction force from the thermally conductive member. This further helps suppress conduction of heat from the integrated circuit to the holding member.

Further, in the optical print head, the holding member may be in contact with a positioning member defining a distance from the optical member to the irradiation target.

Further, in the optical print head, the support portion may contact the light source substrate at a position that is offset from a straight line extending from the position at which the positioning member contacts the holding member to the integrated circuit in plan view.

Further, in the optical print head, the support portion may contact the light source substrate at a position in the longitudinal direction of the light source substrate between the integrated circuit and the light-emitting elements.

Further, in the optical print head, the support portion may contact the light source substrate at a position in the longitudinal direction of the light source substrate between the integrated circuit and a position at which the base member contacts the light source substrate.

Further, in the optical print head, the light source substrate may include a substrate on which the plurality of light-emitting elements are mounted, a material for the base member may have greater thermal conductivity than a material for the substrate, and the material for the substrate may have greater thermal conductivity than a material for the holding member.

Further, in the optical print head, the support portion may protrude from a main body of the holding member toward the light source substrate, and a tip of the support portion contacting the light source substrate may be notched.

Further, in the optical print head, the support portion may protrude from a main body of the holding member toward the light source substrate, and a tip of the support portion contacting the light source substrate may be rounded toward the light source substrate.

Further, in the optical print head, the light-emitting elements may be organic light-emitting diodes.

An image forming device reflecting at least one aspect of the present disclosure includes an optical print head, including: an elongated light source substrate that has a line-shaped region in which a plurality of light-emitting elements are arranged; an optical member that condenses light emitted from the light-emitting elements onto an irradiation target; a holding member that holds the optical member; a base member that holds the light source substrate and the holding member; an integrated circuit that is mounted in a first region on a first surface of the light source substrate, the first surface facing the base member and the first region being in proximity of an end in a longitudinal direction of the light source substrate, heat being generated in the integrated circuit during optical writing; and a thermally conductive member that is disposed between the integrated circuit and the base member, wherein the holding member has a support portion contacting the light source substrate in a second region on a second surface of the light source substrate, the second surface not facing the base member and the second region being at a position differing from the first region in plan view.

Although one or more embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for the purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by the terms of the appended claims.