JP2020163611A - Optical print head and image formation apparatus having the same - Google Patents

Abstract

To reduce the variations in a light amount in a light-emitting diode element in a light-emitting chip.SOLUTION: In an optical print head, a light-emitting chip comprises: a substrate; a light-emitting diode element group which is formed of a plurality of light-emitting diode elements 32; a plurality of individual electrodes 34 which are connected via an anode electrode 37 through a contact hole 39 provided on an insulation film 38 to the respective light-emitting diode elements 32; a plurality of electrode pads; and a plurality of wires 36 connecting the individual electrodes 34 and the electrode pads. The size of the contact hole 39 is larger toward the one corresponding to the light-emitting diode element 32 located on the end of the light-emitting diode element group from the one corresponding to the light-emitting diode element 32 located on the center of the light-emitting diode element group.SELECTED DRAWING: Figure 4

Description

The present invention relates to an optical print head used as an exposure means in an image forming apparatus such as an electrophotographic printer and an image forming apparatus including the optical print head.

Some image forming devices such as electrophotographic optical printers employ an optical print head in which a plurality of light emitting diode elements are arranged in the main scanning direction as an exposure means.

In an image forming apparatus equipped with an optical print head, a light emitting diode element is selectively emitted based on image data, and the light is irradiated to an electrophotographic photosensitive member through a lens array of the optical print head. The surface of a uniformly charged electrophotographic photosensitive member (hereinafter, also referred to as a photosensitive member) is exposed. An electrostatic latent image is formed on the surface of the exposed photoconductor. The electrostatic latent image formed on the photoconductor is converted into a toner image through a process such as development with toner, and the image is recorded by transferring the toner image to a recording paper and fixing the image.

As such an optical print head, one in which a plurality of light emitting chips each having a plurality of light emitting diode elements are mounted in a row along the main scanning direction has been proposed.

Then, as the speed and image quality of the optical printer are increased, it is required to reduce the light emission variation of the light emitting diode element in the light emitting chip. To this end, it has been proposed to improve the light extraction efficiency of the light emitting diode element and reduce the variation in the amount of light between the elements (see, for example, Patent Documents 1 and 2).
JP-A-2002-314133 Japanese Unexamined Patent Publication No. 2011-161908

However, in the light emitting chip mounted on the circuit board in the optical print head, the light emitting diode elements are arranged in close proximity to each other at high density, whereas the electrode pad that supplies the driving power for causing the elements to emit light is Since the size of the individual electrodes of the elements must be larger and the intervals must be set wider, they are arranged so as to occupy a wider area. Then, the wiring connecting the individual electrodes and the electrode pads is arranged so as to spread from the plurality of light emitting diode elements toward the plurality of electrode pads.

Therefore, the wiring connecting the light emitting diode element located at the end of the row and the electrode pad is longer than the wiring connecting the light emitting diode element located in the center of the row and the electrode pad. The electrical resistance of the wiring increases. Therefore, when the drive power from the constant current power source is applied, the applied voltage increases according to the electric resistance, and the amount of light emitted by the light emitting diode element located at the end is larger than that in the center of the line, and the inside of the light emitting chip. The light intensity unevenness may occur in the image, and the density unevenness may also occur in the image. This problem tends to become more apparent when the amount of light of the light emitting diode element is increased as the speed of the optical printer is increased.

Therefore, in the optical print head, it is required to reduce the variation in the amount of light in the light emitting diode element in the light emitting chip.

The optical print head according to the present invention is an optical print head including a circuit board and a plurality of light emitting chips mounted in a row on the circuit board, and the light emitting chips include a rectangular substrate and a rectangular substrate. A group of light emitting diode elements composed of a plurality of light emitting diode elements arranged in a row along the first edge in the longitudinal direction of the substrate and each of the plurality of light emitting diode elements are passed through a contact hole provided in an insulating film. Corresponds to each of the plurality of individual electrodes connected via the anode electrodes and arranged in a row, and the plurality of individual electrodes arranged in a row along the second longitudinal edge of the substrate. It has a plurality of electrode pads, and a plurality of wirings connecting the corresponding individual electrodes and the electrode pads, and the size of the contact hole is such that the size of the contact hole is located at the center of the light emitting diode element group. The size increases from the one corresponding to the light emitting diode element to the one corresponding to the light emitting diode element located at the end of the light emitting diode element group.

The image forming apparatus according to the present invention includes the above-mentioned optical print head according to the present invention, a constant current power source electrically connected to each of the plurality of electrode pads to drive the plurality of light emitting diode elements, and the light. It comprises an electrophotographic photosensitive member whose charged surface is exposed by a printhead.

According to the optical print head according to the present invention, in the light emitting chip, individual electrodes are connected to the light emitting diode element via the anode electrode through the contact hole provided in the insulating film, and the size of the contact hole is determined by the light emitting diode element. Since the size increases from the one corresponding to the light emitting diode element located in the center of the group to the one corresponding to the light emitting diode element located at the end of the light emitting diode element group, the light emitting diode element connected through the contact hole The contact resistance between the individual electrodes can be adjusted according to the size of the contact hole. Therefore, the wiring resistance in the plurality of wirings varies depending on the length from the wiring corresponding to the individual electrode located in the center of the light emitting diode element group to the wiring corresponding to the individual electrode located near the end of the light emitting diode element group. While it tends to be high, the unevenness of the wiring resistance of those wirings can be reduced by adjusting the contact resistance. Thereby, the unevenness of the applied voltage of the driving power applied to the light emitting diode element can be reduced. As a result, it is possible to reduce the occurrence of uneven light emission between the light emitting diode elements in the light emitting diode element group.

According to the image forming apparatus according to the present invention, since the optical print head according to the present invention is provided, it is possible to reduce the occurrence of uneven light emission between the light emitting diode elements, so that the main scanning of the image by the image forming apparatus can be reduced. The density unevenness in the direction can be reduced, and a high-quality image can be obtained.

It is a top view which shows the schematic structure of an example of embodiment of the optical print head which concerns on this invention. It is a top view which shows the schematic structure of the light emitting chip in an example of embodiment of the optical print head which concerns on this invention. It is sectional drawing which shows the schematic structure of the light emitting diode element in an example of embodiment of the optical printhead which concerns on this invention. It is a top view of the perspective state which shows the schematic structure of the light emitting diode element in an example of embodiment of the optical print head which concerns on this invention. It is a schematic cross-sectional view which shows the schematic structure of the example of the embodiment of the image forming apparatus which concerns on this invention.

Hereinafter, an optical print head according to the present invention and an image forming apparatus including the optical print head will be described with reference to the accompanying drawings.

FIG. 1 is a plan view showing an example of a circuit board included in the optical print head according to the present invention. A plurality of light emitting chips 3 are mounted in a row on the circuit board 2 of the optical print head 1. The plurality of light emitting chips 3 are arranged in a so-called staggered pattern so that the light emitting diode elements described later are arranged in one row and are alternately opposed to each other in two rows in the main scanning direction. The drive circuit 4 supplies various drive signals for controlling the light emission of the light emitting diode elements in the plurality of light emitting chips 3, and has a function as a constant current power source. Here, the wiring connecting the drive circuit 4 and the light emitting chip 3 is not shown. Further, above the plurality of light emitting chips 3, the lens array 5 shown by the broken line is arranged. In addition to these, the optical print head 1 is configured to appropriately include members such as an exterior and a connection cable with an external control circuit.

Here, the schematic configuration of the light emitting chip in an example of the embodiment of the optical print head according to the present invention is shown in a plan view in FIG. As shown in FIG. 2, the light emitting chip 3 is formed on a substrate 31, a light emitting diode element group 33 composed of a plurality of light emitting diode elements 32, individual electrodes 34 connected to each of the light emitting diode elements 32, and individual electrodes 34. It has a corresponding electrode pad 35, and a wiring 36 that connects the corresponding individual electrode 34 and the electrode pad 35.

The substrate 31 has a rectangular shape and is made of a semiconductor material such as silicon (Si) or gallium arsenide (GaAs) or aluminum gallium arsenide (AlGaAs). Alternatively, a layer made of the above-mentioned semiconductor material may be laminated on the upper surface of an insulating substrate made of an insulating material such as sapphire. The plurality of light emitting diode elements 32 are arranged in a row along the first edge (first long side) in the longitudinal direction of the substrate 31. Usually high density in one row, for example 300 dpi
It is arranged at a density such as (dots / inch) or 600 dpi, but may be arranged at a higher density such as 1200 dpi depending on the required specifications. The arrangement direction of the light emitting diode elements 32 arranged in a row coincides with the main scanning direction in the image forming apparatus. The light emitting diode element group 33 is composed of these plurality of light emitting diode elements 32.

Further, the schematic configuration of the light emitting diode element in an example of the embodiment of the optical print head according to the present invention is shown in a cross-sectional view in FIG. 3 and in a plan view in FIG.

The light emitting diode element 32 of the example shown in FIG. 3 is, for example, on a substrate 31 made of an n-type semiconductor material, an n-type clad layer 41 made of a semiconductor layer, a light emitting layer 42, a p-type clad layer 43, and a contact layer 44, respectively. Are stacked in order. Further, the insulating film 38 is formed so as to cover the laminated body composed of the plurality of semiconductor layers, and the contact hole 39 is provided in a part of the insulating film 38 located on the upper surface of the contact layer 44. On the other hand, on the back surface of the substrate 31, the cathode electrode 40 is formed including at least a region corresponding to a region on the upper surface where the light emitting diode element 32 is formed. Then, the anode electrode 37 is arranged from the individual electrode 34 arranged on the insulating film 38 in the vicinity of the laminated body to the upper surface of the laminated body along the insulating film 38, and the anode electrode 27 passes through the contact hole 39. Is connected to the contact layer 44. In this way, the individual electrode 34 is connected to the light emitting diode element 32. A protective film 45 made of silicon oxynitride (SiON) or the like is formed on the light emitting diode element 32 so as to cover the insulating film 38 and the anode electrode 37, and the individual electrodes 34 are exposed from the protective film 45. are doing.

Looking at the light emitting diode element 32 in a plan view, a portion C located at the center of the light emitting diode element group 33 and a portion E located at the end of the light emitting diode element group 33, which are surrounded by dotted lines in FIG. 2, and those. The size of the contact hole 39 is different from that of the portion M located in the middle of the above, as shown by C, M and E in FIG. 4, respectively. That is, as shown in FIG. 4, the size of the contact hole 39 is the portion C located at the center of the light emitting diode element group 33.
It is located at the end of the light emitting diode element group 33 through the one corresponding to the light emitting diode element 32 of the above, the one corresponding to the light emitting diode element 32 of the portion M located between the center and the end of the light emitting diode element group 33. It becomes larger toward the one corresponding to the light emitting diode element 32 of the part E. In FIG. 4, the individual electrodes 34, the anode electrodes 37, the insulating film 38, and the contact holes 39 are shown in a see-through state so that they can be easily understood.

As described above, each of the plurality of light emitting diode elements 32 is connected to the corresponding ones of the plurality of individual electrodes 34 via the anode electrode 37 as described above. Similar to the plurality of light emitting diode elements 32, the plurality of individual electrodes 34 are also arranged in a row so as to be along the first edge in the longitudinal direction of the substrate 31.

Further, a plurality of electrode pads 35 corresponding to each of the plurality of individual electrodes 34 are arranged in a row along the second edge (second long side) in the longitudinal direction of the substrate 31. The second edge of the substrate 31 is usually paired parallel to the first edge, but is not necessarily parallel. Since the plurality of electrode pads 35 are connected to the corresponding wirings on the circuit board 2 by wire bonding, for example, their respective sizes are larger than those of the individual electrodes 34. Therefore, the length of the row of the plurality of electrode pads 35 is longer than the length of the row of the plurality of individual electrodes 34.

The plurality of individual electrodes 34 and the plurality of electrode pads 35 are connected to each other by wiring 36. At this time, since the length of the row of the plurality of electrode pads 35 is longer than the length of the row of the plurality of individual electrodes 34, the length of the wiring 36 is the individual located in the center of the light emitting diode element group 33. The length gradually increases from the one corresponding to the electrode 34 to the one corresponding to the individual electrode 34 located at the end of the light emitting diode element group 33. That is, the length of the wiring 36 corresponding to the individual electrode 34 located at the center of the light emitting diode element group 33 is shorter than the others, and the wiring corresponding to the individual electrode 34 located at the end of the light emitting diode element group 33. The length of 36 is longer than others. In FIG. 2, the electrode pads 35 and the wiring 36 are omitted for the sake of clarity, and only five corresponding to the center and both ends of the light emitting diode element group 33 and the middle thereof are shown. Shown.

Here, when the wiring 36 is routed and arranged as in the example shown in FIG. 2, the widths of the plurality of wiring 36 are usually the same, so that the wiring 36 has a short length. The resistance is low, while the wiring resistance is high when the length of the wiring 36 is long. Therefore, when the light emitting diode element 32 is driven by the drive circuit 4 that functions as a constant current power source to emit light in such a state, the light emitting diode element 32 (located in the center of the light emitting diode element group 33) having a low wiring resistance of the wiring 36. The applied voltage is relatively low, and the light emitting diode element 32 (located at the end of the light emitting diode element group 33), which has a high wiring resistance of the wiring 36, has a relatively high applied voltage. There is a relative difference in the amount of light emitted by the light emitting diode element 32. Therefore, in correspondence with the unevenness of the light amount of the light emitting diode element 32, the density unevenness may also occur in the image produced by the image forming apparatus including the optical print head 1.

For example, in a light emitting chip 3 having a light emitting diode element group 33 in which 256 light emitting diode elements 32 are arranged at a density of 1600 dpi (dots / inch), the thickness of the wiring 36 made of gold (Au) is 0.8 μm. Consider the case where the width of the wiring 36 is 5 μm. Wiring 36 at this time
The length of the wiring 36 corresponding to the individual electrode 34 located at the center of the light emitting diode element group 33 is, for example, about 0.9 mm, and the length of the wiring 36 corresponding to the individual electrode 34 located at the end of the light emitting diode element group 33 is, for example. For example, it is about 2.4 mm. When a driving power of 3 mA is applied to each light emitting diode element 32 through the wiring 36, the voltage applied to the light emitting diode element 32 located at the center of the light emitting diode element group 33 becomes about 2.60 V. Therefore, the voltage applied to the light emitting diode element 32 located at the end of the light emitting diode element group 33 is about 2.66 V, which causes a voltage difference of about 2.3%, and the amount of light varies accordingly. ..

On the other hand, according to the optical print head 1 according to the present invention, in the light emitting chip 3, the individual electrodes 34 are connected to the light emitting diode element 32 through the contact hole 39 provided in the insulating film 38 via the anode electrode 37. The size of the contact hole 39 corresponds to the light emitting diode element 32 located in the center of the light emitting diode element group 33 (part C) to the light emitting diode element 32 located at the end of the light emitting diode element group 33. The contact resistance between the light emitting diode element 32 connected through the contact hole 39 and the individual electrode 34 should be adjusted according to the size of the contact hole 39 because it increases toward the object (part E). Can be done. Therefore, the wiring resistance in the plurality of wirings 36 changes from the wiring 36 corresponding to the individual electrode 34 located in the center of the light emitting diode element group 33 to the wiring 36 corresponding to the individual electrode 34 located near the end of the light emitting diode element group 33. On the other hand, the unevenness of the wiring resistance of those wirings 36 can be reduced by adjusting the contact resistance according to the size of the contact hole 39, while the length tends to increase.

Further, as shown in FIG. 4, the shape of the contact hole 39 in this example depends on the shape of the light emitting diode element 32 formed in a rectangular shape so as to secure the required amount of light emission while arranging the contact holes 39 at high density. , It has a rectangular shape, and in order to change its size, it is preferable to make the width of the contact hole 39 the same and change the length. That is, the contact hole 39 is longer from the one corresponding to the light emitting diode element 32 located at the center of the light emitting diode element group 33 to the one corresponding to the light emitting diode element 32 located at the end of the light emitting diode element group 33. It is preferable that the length is long. According to this, the contact resistance is adjusted by adjusting the size of the contact hole 39 without changing the size of the anode electrode 37 arranged in a band shape so as not to block the light emission of the light emitting diode element 32 as much as possible. It is preferable because it can be used.

That is, according to the optical print head 1 according to the present invention, in the light emitting chip 3, the size of the contact hole 39 corresponds to the light emitting diode element 32 located at the center of the light emitting diode element group 33, so that the light emitting diode element Since it increases toward the light emitting diode element 32 located at the end of the group 33, the length of the wiring 36 corresponding to the light emitting diode element 32 located near the end of the light emitting diode element group 33 is Even if it becomes longer, the contact resistance can be lowered by the contact hole 39 against the increase in the wiring resistance in the wiring 36, so that the wiring is compared with the wiring 36 corresponding to the individual electrode 34 located in the center of the light emitting diode element group 33. It is possible to suppress an increase in the combined resistance of the resistance and the contact resistance. Therefore, since the unevenness of the wiring resistance in the plurality of wirings 36 can be reduced, the unevenness of the applied voltage of the driving power applied to the light emitting diode element 32 can be reduced. As a result, it is possible to reduce the occurrence of uneven light emission between the light emitting diode elements 32 in the light emitting diode element group 33. As a result, the density unevenness in the main scanning direction in the image produced by the image forming apparatus can be reduced, and a high-quality image can be obtained.

In the case of the light emitting chip 3 having the light emitting diode element group 33 of 1600 dpi as described above, the thickness of the wiring 36 made of gold (Au) is 0.8 μm and the width is 5 μm, and it is in the center of the light emitting diode element group 33. The length of the wiring 36 corresponding to the located individual electrode 34 is about 0.9 mm, and the length of the wiring 36 corresponding to the individual electrode 34 located at the end of the light emitting diode element group 33 is about 2.4 m.
Consider the case of m. With respect to this wiring 36, the size of the contact hole 39 in the light emitting diode element 32 corresponding to the center of the light emitting diode element group 33 is 2 μm in width × 10 μm in length, and the light emitting diode corresponding to the end of the light emitting diode element group 33. The size of the contact hole 39 in the element 32 is 2 μm in width × 20 μm in length. When a driving power of 3 mA is applied to each light emitting diode element 32 through the wiring 36 and the contact hole 39, the voltage applied to the light emitting diode element 32 located at the center of the light emitting diode element group 33 is about 2.63 V. On the other hand, the voltage applied to the light emitting diode element 32 located at the end of the light emitting diode element group 33 is also about 2.63 V, the voltage difference becomes a substantially negligible level, and the light amount unevenness is also substantially. It becomes a level that can be ignored.

From the light emitting diode element 32 located at the center of the light emitting diode element group 33 toward the light emitting diode element 32 located at the end, the change in the lengths of the plurality of wirings 36 becomes large and the increase in the wiring resistance becomes large. In that case, the increase in the wiring resistance can be reduced by the contact resistance due to the size of the contact hole 39, but it may not be possible to adjust the increase. In such a case, the increase in the wiring resistance in the wiring 36 may be reduced by increasing the width of the wiring 36, and may be combined with the reduction in the contact resistance due to the size of the contact hole 39. Specifically, from the wiring 36 connecting the individual electrode 34 located in the center of the light emitting diode element group 33 and the corresponding electrode pad 35, the individual electrode 34 located at the end of the light emitting diode element group 33 and the corresponding electrode pad The width of the wiring 36 may be set to be wider toward the wiring 36 connecting the 35. At this time, it is not always necessary to widen the width of the wiring 36 over the entire wiring 36, and the width may be widened within a predetermined range to adjust the reduction amount of the wiring resistance. ..

The individual electrode 34, the electrode pad 35, the wiring 36, and the anode electrode 37 are made of a conductive material such as aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), silver (Ag), and gold (Au). Consists of. These metals are adhered to a substrate 31 provided with a light emitting diode element group 33 in a film shape by a vapor deposition method or a sputtering method, and patterned by photolithography to form individual electrodes 34 and electrode pads in a desired pattern. 35, wiring 36 and anode electrode 37 are formed.

The size of the individual electrode 34 may be appropriately set according to the size of the corresponding light emitting diode element 32. For example, when the arrangement density of the light emitting diode element 32 is 300 dpi, the size of the individual electrodes 34 may be set to, for example, about 40 μm in width × 40 μm in length. Further, for example, when the arrangement density of the light emitting diode element 32 is 600 dpi, the size of the individual electrodes 34 is
For example, the width may be set to about 20 μm × the length may be set to about 20 μm.

Further, the size of the anode electrode 37 may be appropriately set in consideration of the light emitting area according to the size of the corresponding light emitting diode element 32. For example, when the arrangement density of the light emitting diode element 32 is 300 dpi, the size of the anode electrode 37 may be set to, for example, about 10 μm in width × 40 μm in length. Further, for example, when the arrangement density of the light emitting diode element 32 is 600 dpi, the size of the anode electrode 37 may be set to, for example, about 5 μm in width × 20 μm in length.

Further, the size of the electrode pad 35 is appropriately adjusted to the size of the wire bonding pad required when connecting to the wiring (not shown) on the circuit board 2 for connecting to the drive circuit 4, for example, by wire bonding. You can set it. The size of such an electrode pad 35 may be set to, for example, about 60 μm in width × 100 μm in length. The size of the electrode pads 35 does not need to be changed according to the arrangement density of the light emitting diode elements 32, but when the density increases from 300 dpi to 600 dpi, for example, the number of electrode pads 35 doubles. Therefore, when the electrode pads 35 are arranged in a row along the second edge of the substrate 31, the electrode pads 35 cannot be arranged in a row even if the size is adjusted. In such a case, the electrode pads 35 may be alternately arranged in two rows so as to have a high density corresponding to the arrangement density of the light emitting diode elements 32. Alternatively, the plurality of electrode pads 35 may be arranged in two to four rows in response to a higher density of the light emitting diode elements 32.

When the electrode pads 35 are arranged in two rows, a row near the light emitting diode element group 33 and a row far from the light emitting diode group 33, the row farther than the length of the wiring 36 connected to the electrode pads 35 in the near row (first row) ( Second column)
The length of the wiring 36 connected to the electrode pad 35 of the above will be increased. Therefore, the size of the contact hole 39 in the light emitting diode element 32 connected to the electrode pad 35 in the second row is compared with the size of the contact hole 39 in the light emitting diode element 32 connected to the electrode pad 35 in the first row. The size may be increased to reduce the unevenness of the wiring resistance by adjusting the contact resistance. In this case, when the sizes of the contact holes 39 in the adjacent light emitting diode elements 32 are compared, the contact holes 39 corresponding to the center of the light emitting diode element group 33 to the contact holes 39 corresponding to the ends of the light emitting diode element group 33. The size of the contact hole 39 may become larger or smaller toward the LED. However, in such a case, the size of the contact hole 39 emits light from the light emitting diode element 32 corresponding to the center of the light emitting diode element group 33 when viewed from each of the contact holes 39 corresponding to each row. As a general tendency, the size of the contact hole 39 may increase toward the light emitting diode element 32 corresponding to the end of the diode element group 33.

In addition, as the light emitting diode element 32 in the light emitting diode element group 33 becomes denser, the electrode pads 35 may be arranged in three rows or more in order to arrange the electrode pads 35 in a high density. Therefore, the variation in the wiring resistance caused by the variation in the length of the wiring 36 may be reduced by adjusting the size of the contact hole 39.

The size of the contact hole 39 is set so that each of the contact holes 39 gradually increases from the one corresponding to the center of the light emitting diode element group 33 to the one corresponding to the edge. It is not required, and the tendency as a whole should increase from the one corresponding to the center to the one corresponding to the edge. For example, the rate of increase in the size of the contact hole 39 may be changed according to the rate of change in the length of the wiring 36. Further, a group may be appropriately set from the one corresponding to the center to the one corresponding to the edge, and the size of the contact hole may be increased for each group.

Further, when the electrode pads 35 are arranged in a plurality of rows such as 2 to 4 rows, the light emitting diode element group is provided for the contact holes 39 of the light emitting diode elements 32 connected to the plurality of electrode pads 35 in each row. The size of the contact hole 39 may increase from the one corresponding to the center of 33 to the one corresponding to the edge.

The size of the contact hole 39 gradually increases from the one corresponding to the light emitting diode element 32 located in the center of the light emitting diode element group 33 to the one corresponding to the light emitting diode element 32 located at the end of the light emitting diode element group 33. It may be larger. In this case as well, it is not always necessary to make minute settings such that each of the contact holes 39 gradually widens, and the tendency as a whole corresponds from the one corresponding to the center to the edge. It suffices if it grows gradually toward things. For example, when the electrode pads 35 are densely arranged in a plurality of rows of 2 to 4 rows, the length of the wiring 36 connected to the electrode pads 35 of each row and adjacent to each other corresponds to each row. Therefore, there is a difference in length, and the row far from the light emitting diode group 33 is larger than the size of the contact hole 39 in the light emitting diode element 32 connected to the electrode pad 35 in the row closer to the light emitting diode group 33. The size of the contact hole 39 in the light emitting diode element 32 connected to the electrode pad 35 of the above may be set large. In this case, when looking at the light emitting diode elements 32 corresponding to each row of the electrode pads 35, the light emitting diode element group 33 from the one corresponding to the light emitting diode element 32 located in the center of the light emitting diode element group 33, respectively. The size of the contact hole 39 may be gradually increased toward the one corresponding to the light emitting diode element 32 located at the end.

In the example shown in FIG. 2, the plurality of wirings 36 are linearly connected to the central portion of the light emitting diode element group 33 substantially perpendicular to the row of the light emitting diode element 32, and the light emitting diode element group 33. The shape is such that the wires are connected at an angle toward the end and are bent from the middle to be parallel to each other, but the shape of the plurality of wirings 36 is not limited to this. For example, any wiring 36 may be connected to the light emitting diode element group 33 vertically and in parallel with each other, and may have a shape that bends from the middle of the wiring 36 and spreads toward the corresponding electrode pad 35. ..

In the optical print head 1 according to the present invention including the light emitting chips 3 having the above-described configuration, as shown in FIG. 1, a plurality of light emitting chips 3 are arranged in a row in the direction of arrangement of the plurality of light emitting diode elements 32. A plurality of wirings 36 in the adjacent light emitting chips 3 are arranged alternately on both sides of the arrangement of the light emitting chips 3. That is, on the circuit board 2 of the optical print head 1, a plurality of light emitting chips 3 are arranged so as to alternately face two rows in the main scanning direction so that the light emitting diode element groups 33 are arranged in one row, so-called staggered. It is arranged in a shape. Then, each of the light emitting chips 3 and the drive circuit 4 are connected by a circuit wiring (not shown).

The lens array 5 guides the light emitted from the light emitting diode element 32 of the light emitting chip 3 to the surface of the electrophotographic photosensitive member in the image forming apparatus, and faces the light emitting chip 3 via a member (not shown). It is being held. For the lens array 5, for example, a rod lens array having a plurality of rod lenses is used. The rod lens is a rod-shaped lens having a refractive index distribution, and functions as an upright first-magnification optical system that irradiates an irradiated surface such as the surface of an electrophotographic photosensitive member at the same magnification to form an image. Is.

The lens array 5 is arranged in a row in the main scanning direction substantially directly above the light emitting diode element group 33 of the plurality of light emitting chips 3, for example, in a straight line in one row or in a staggered pattern in two rows. They are arranged in a shape.

FIG. 5 is a schematic cross-sectional view showing a schematic configuration of an example of an embodiment of the image forming apparatus according to the present invention. The image forming apparatus 100 of this example adopts the Carlson method of electrophotographic method as an image forming method, and as shown in FIG. 5, as an electrophotographic photosensitive member (photoreceptor) 10, a charger 11, and an exposure device. It is equipped with an optical print head 1, a developer 13, a transfer device 14, a fuser 15, a cleaner 16, and a static eliminator 17.

The charger 11 plays a role of charging the surface of the photoconductor 10 positively or negatively. If it is negatively charged, the charging voltage is set to, for example, -1000V or more and -200V or less. For the charger 11 in this example, for example, a contact type charger formed by coating a core metal with conductive rubber and polyvinylidene fluoride is adopted, but instead of this, a non-contact type chargeer including a discharge wire is adopted. A device (for example, a corona charger) may be adopted.

The optical print head 1 plays a role of exposing a charged surface to form an electrostatic latent image on the photoconductor 10. Specifically, the optical print head 1 has a wavelength λ that is sufficiently absorbed by the photosensitive layer of the photoconductor 10 in response to an image signal (for example, if the photosensitive layer is made of an amorphous silicon material). By irradiating the surface of the uniformly charged photoconductor 10 with an exposure of (650 nm, etc.), the potential of the exposed portion of the charged photoconductor 10 is attenuated to form an electrostatic latent image. The wavelength λ of this exposure depends on the light sensitivity of the photoconductor 10, but is preferably 400 to 680 nm, for example.

Further, the optical print head 1 is electrically connected to each of the plurality of electrode pads 35 via the drive circuit 4, and is a constant current that supplies drive power for driving the plurality of light emitting diode elements 32 to emit light. A power supply (not shown) is connected. Further, in the optical print head 1, a control circuit for supplying a drive signal (control signal) for driving a plurality of light emitting diode elements 32 according to a pattern of an image to be formed is electrically connected to the drive circuit 4. ing.

The developer 13 plays a role of developing an electrostatic latent image of the photoconductor 10 to form a toner image. The developer 13 in this example is a dry developing system and includes a magnetic roller 13A that magnetically holds the developer (toner) T.

The developer T constitutes a toner image formed on the surface of the photoconductor 10, and is triboelectrically charged in the developer 13. Examples of the developer T include a two-component developer containing a magnetic carrier and an insulating toner, and a one-component developer containing a magnetic toner.

The magnetic roller 13A plays a role of transporting the developer to the surface (developing region) of the photoconductor 10. The magnetic roller 13A conveys the triboelectric developer T in the developing device 13 in the form of a magnetic brush adjusted to a constant spike length. The conveyed developer T adheres to the surface of the photoconductor 10 by the electrostatic attraction of the electrostatic latent image in the developing region of the photoconductor 10 to form a toner image, and visualizes the electrostatic latent image. The charge polarity of the toner image is opposite to the charge polarity of the surface of the photoconductor 10 when the image is formed by normal development, and the charge polarity of the surface of the photoconductor 10 when the image is formed by reverse development. Is the same polarity as.

Further, a liquid developing type developer may be used as the developing device 13. A liquid developing type developer is provided outside with a liquid developing agent tank for storing a liquid developing agent containing toner. The liquid developer is composed of toner particles and a carrier liquid which is an insulating liquid. The carrier liquid is a non-polar, that is, electrically neutral solvent such as silicone oil, and is adjusted so that toner particles are dispersed in the solvent at a high concentration. The toner particles are composed of a binder resin such as epoxy, a charge control agent that gives a predetermined charge to the toner, a coloring pigment, and the like.

Inside the liquid developing type developer, there is a mechanism for supplying the liquid developer to the developing roller, and the developing roller supplied with the liquid developing agent comes into contact with the surface of the photoconductor 10 and the photoconductor 10 A liquid developer is supplied to the surface of the. Then, the toner image can be formed on the photoconductor 10 by supplying the liquid developer from the developing roller as the developer carrier to the photoconductor 10 on which the electrostatic latent image is formed.

The transfer device 14 plays a role of transferring the toner image of the photoconductor 10 to a recording medium P such as paper supplied to the transfer region between the photoconductor 10 and the transfer device 14. The transfer device 14 in this example includes a transfer discharger 14A and a separation discharger 14B. In the transfer device 14, the back surface (non-recording surface) of the recording medium P is charged by the transfer discharger 14A in the opposite polarity to the toner image, and the toner is placed on the recording medium P by the electrostatic attraction of the charged charge and the toner image. The image is transferred. Further, in the transfer device 14, at the same time as the transfer of the toner image, the back surface of the recording medium P is erased by the AC discharge in the separation discharger 14B, and the recording medium P is quickly separated from the surface of the photoconductor 10. ..

Further, as the transfer device 14, it is also possible to use a transfer roller that is driven by the rotation of the photoconductor 10 and is arranged with the photoconductor 10 via a minute gap (usually 0.5 mm or less). The transfer roller is configured to apply a transfer voltage that attracts the toner image on the photoconductor 10 onto the recording medium P, for example, by using a DC power supply. When a transfer roller is used, a transfer separation device such as the separation discharger 14B can be omitted.

The fuser 15 plays a role of fixing the toner image transferred to the recording medium P to the recording medium P, and includes a pair of fixing rollers 15A and 15B. As the fixing rollers 15A and 15B, for example, a metal roller whose surface is coated with polytetrafluoroethylene or the like is used. In the fixing device 15, the toner image can be fixed on the recording medium P by applying heat, pressure, or the like to the recording medium P passing between the pair of fixing rollers 15A and 15B.

The cleaner 16 plays a role of removing the toner remaining on the surface of the photoconductor 10 after transfer. The cleaner 16 of this example includes a cleaning blade 16A. The cleaning blade 16A plays a role of scraping residual toner from the surface of the photoconductor 10. The cleaning blade 16A is made of, for example, a rubber material containing polyurethane resin as a main component.

The static eliminator 17 plays a role of removing the surface charge of the photoconductor 10 remaining as an electrostatic latent image. The static eliminator 17 of this example removes static electricity by exposing the photoconductor 10 to light, and is capable of emitting light having a specific wavelength (for example, 780 nm or more). The static eliminator 17 is configured to remove the surface charge (residual electrostatic latent image) of the photoconductor 10 by irradiating the entire surface of the photoconductor 10 with light in the axial direction using a light source such as a light emitting diode. Has been done.

According to the image forming apparatus 100 according to the present invention, since the optical print head 1 according to the present invention is provided, it is possible to reduce the variation in the emission intensity in the light emitting diode element group 33 of the light emitting chip 3, and thus the main scanning direction. The uneven image density can be reduced, and a high-quality image can be obtained.

The present invention is not limited to the above-described embodiment, and various modifications, improvements, and the like can be made without departing from the gist of the present invention. For example, when adjusting the size of the contact hole 39 by changing the length, each contact hole 39 does not have to have the same width as a whole, and the contact hole does not have to have the same width as a whole, depending on the purpose of adjusting the contact resistance. The width of the desired portion of 39 may be adjusted, or the width may be changed between the contact holes 39.

1 ... Optical printed circuit board 2 ... Circuit board 3 ... Light emitting chip
10 ... Electrophotographic photosensitive member (photoreceptor)
31… Board
32 ... Light emitting diode element
33 ... Light emitting diode element group
34… Individual electrodes
35 ... Electrode pad
36 ... Wiring
37… Anode electrode
38… Insulation film
39… Contact hole
100 ... Image forming device

Claims (4)

An optical printed head including a circuit board and a plurality of light emitting chips mounted in a row on the circuit board.
The light emitting chip has a rectangular substrate and
A group of light emitting diode elements composed of a plurality of light emitting diode elements arranged in a row along the first edge in the longitudinal direction of the substrate, and
A plurality of individual electrodes arranged in a row connected to each of the plurality of light emitting diode elements via a contact hole provided in the insulating film via an anode electrode.
A plurality of electrode pads corresponding to each of the plurality of individual electrodes arranged in a row along a second edge in the longitudinal direction of the substrate.
It has a plurality of wirings connecting the corresponding individual electrodes and the electrode pads.
The size of the contact hole increases from the one corresponding to the light emitting diode element located in the center of the light emitting diode element group to the one corresponding to the light emitting diode element located at the end of the light emitting diode element group. ing,
Optical print head. The contact hole becomes longer in length from the one corresponding to the light emitting diode element located in the center of the light emitting diode element group to the one corresponding to the light emitting diode element located at the end of the light emitting diode element group. ing,
The optical print head according to claim 1. The plurality of light emitting chips are arranged in a row in the direction of the arrangement of the plurality of light emitting diode elements, and the plurality of wirings in the adjacent light emitting chips are alternately arranged on both sides of the arrangement of the light emitting chips. Yes,
The optical print head according to claim 1. The optical print head according to any one of claims 1 to 3.
A constant current power source that is electrically connected to each of the plurality of electrode pads to drive the plurality of light emitting diode elements.
An image forming apparatus including an electrophotographic photosensitive member whose charged surface is exposed by the optical print head.

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