JP2008062411A - Line head, exposure apparatus, and exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a line head which can attain a long service life and a low power consumption, and to provide a driving method for the line head. <P>SOLUTION: This line head H is equipped with a first luminescence section Ha1 for exposure and a second luminescence section Ha2 for exposure. In this case, the first luminescence section Ha1 for exposure has an organic EL element 33 which respectively emits light to each exposure spot which constitutes a beam into a line form. The second luminescence section Ha2 for exposure has an organic EL element 33 which respectively emits light to each exposure spot which constitutes a beam into a line form in the same manner. The value of the work function or the ionization potential of a second electron injection layer material which constitutes the organic EL element 33 of the second luminescence section Ha2 for exposure is set to be larger than the value of the work function or the ionization potential of a first electron injection layer material which constitutes the organic EL element 33 of the first luminescence section Ha1 for exposure for the constitution of the line head. At each exposure spot, the organic EL element 33 of the first luminescence section Ha1 for exposure is made to emit light when the exposure is performed at a low radiance luminescence, and the organic EL element 33 of the second luminescence section Ha2 for exposure is made to emit light when the exposure is performed at a high radiance luminescence. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a line head, an exposure apparatus, and an exposure method.

An image forming apparatus using an electrophotographic system uses a line head (exposure head) as a light emitting device that exposes a photosensitive drum as an image carrier to form a latent image. In general, a laser beam is used as a light source of the line head. Incidentally, in recent years, line heads are required to have low cost, space saving, and low power consumption. In view of this, attention has been focused on the use of an organic electroluminescence element (organic EL element) as a light source of a line head. For example, in Patent Document 1, in order to improve the light extraction efficiency,
There has been proposed a lens for collecting light emitted from the organic EL element, a so-called microlens, provided on the light extraction surface.

JP 2003-291404 A

However, in the above-described line head, although the light extraction efficiency is improved by the microlens, the lifetime of the organic electroluminescence element (organic EL element) as a light source is shorter than that of a conventional laser light source. Are known. Accordingly, the replacement time is shortened, and the load for maintenance becomes a problem.

The present invention has been made to solve the above-described problems, and an object of the present invention is to increase the life of the line head and to reduce the power consumption and to drive the line head. It is to provide a method.

The line head of the present invention is a line head in which a first light emitting unit in which a plurality of first light emitting elements are arranged and a second light emitting unit in which a plurality of second light emitting elements are arranged are provided on a substrate. And
When the first light emitting element and the second light emitting element are driven with the same light emission luminance, the power consumption of the first light emitting element is smaller than the power consumption of the second light emitting element, and the first light emitting element. The light emission luminance attenuation amount with respect to the element driving time is larger than the light emission luminance attenuation amount with respect to the second light emitting element driving time.

According to this line head, when emitting light for exposure by emitting light with low luminance (low light amount), the first light emitting element of the first light emitting unit emits light and emits light with high luminance (high light amount). When the exposure light is emitted, the second light emitting element of the second light emitting unit can emit light. As a result, the load on the light emitting elements of the first and second light emitting units is reduced, and the light emission can be controlled by a driving power source suitable for the first light emitting element and the second light emitting element, thereby reducing power consumption. be able to.

In this line head, the first light emitting element and the second light emitting element may be organic electroluminescent elements including at least one organic layer having a light emitting function.

According to this line head, when the light for exposure is emitted by emitting a high amount of light, the second light emitting element of the second light emitting unit is caused to emit light, and the light for exposure is emitted by emitting a low amount of light. If
The first light emitting element of the first light emitting unit may emit light. As a result, the load on the organic electroluminescence elements of the first and second light emitting units is reduced, and the light emission can be controlled by a driving power source suitable for the first light emitting element and the second light emitting element. Can be reduced.

In this line head, the difference between the work function or ionization potential value of the light emitting material constituting the organic layer having the light emitting function of the first light emitting element and the work function or ionization potential value of the electron injection material is The difference between the work function or ionization potential value of the light emitting material constituting the organic layer having the light emitting function of the two light emitting elements and the work function or ionization potential value of the electron injection material may be different.

According to this line head, for example, the first light emission is performed with the same formation conditions of at least a layer made of the light emitting material of the organic electroluminescent element of the first light emitting unit and the light emitting material of the organic electroluminescent element of the second light emitting unit. When the work function or ionization potential value of the first electron injection material of the organic electroluminescence element of the part is smaller than the work function or ionization potential value of the second electron injection material of the organic electroluminescence element of the second light emitting part, Due to the difference in electron injection property from the layer consisting of at least the electron injecting material to the layer consisting of the light emitting material, the organic electroluminescent element of the second light emitting part has a higher light intensity than the organic electroluminescent element of the first light emitting part. Durable against light emission. In addition, the organic electroluminescence element of the first light emitting unit can reduce the driving current and reduce the power consumption with respect to the light emission with a low light intensity, compared with the organic electroluminescence element of the second light emitting unit.

  In the line head, the light emitting unit may be made of an inorganic LED.

According to this line head, when emitting light for exposure by emitting light with a high amount of light, when emitting light for exposure by emitting light of a second light emitting element of the second light emitting unit and emitting light with a low amount of light Is the first
The first light emitting element of the light emitting unit can emit light. As a result, the load on the light emitting elements of the first and second light emitting units is reduced, and the light emission can be controlled by a driving power source suitable for the first light emitting element and the second light emitting element, thereby reducing power consumption. be able to.

In this line head, each light emitting section may be formed on one flexible substrate.

According to this line head, since it is easy to bend the flexible substrate, it is possible to easily align the light emitting elements corresponding to each light emitting unit to the same point of the emitted object.

In the line head according to the aspect of the invention, the first light emitting unit includes a plurality of first light emitting elements arranged in one direction, and the second light emitting unit includes a plurality of second light emitting elements arranged in one direction. The first light emitting unit and the second light emitting unit are arranged in parallel on the substrate.
Further, the first light emitting unit includes a plurality of first light emitting element rows in which a plurality of first light emitting elements are arranged in one direction and arranged in parallel, and the second light emitting unit includes a plurality of second light emitting elements. A plurality of second light emitting element arrays in which elements are arranged in one direction are arranged in parallel, and the first light emitting part and the second light emitting part are arranged in parallel on the substrate. Features.

With this configuration. It becomes easy to arrange the rotating shaft of the photosensitive drum, the first light emitting unit, and the second light emitting unit in parallel, and the application to the exposure apparatus becomes easy.

In the line head of the present invention, the first light emitting unit includes a plurality of first light emitting elements arranged in a staggered pattern, and the second light emitting unit includes a plurality of second light emitting elements in a staggered pattern. It is characterized by being arranged. With this configuration, the light amount or luminance of the line head can be improved.

The exposure apparatus of the present invention is an exposure apparatus comprising a line head in which a plurality of light emitting elements are arranged and a rotatable photosensitive drum exposed by light from the line head, wherein the line head As described above, the line head according to any one of claims 1 to 8 is used, and the rotation axis of the photosensitive drum, the first light emitting unit, and the second light emitting unit are arranged in parallel. It is characterized by.

Furthermore, the exposure apparatus of the present invention includes a control circuit, which controls the first gradation data for driving the first light emitting unit based on the exposure data supplied from the outside, and the first Second gradation data for driving the two light emitting units is generated. With this configuration, the first light emitting unit or the second light emitting unit can be selected to emit light.

An exposure method of the present invention includes a line head provided with a first light emitting unit in which a plurality of first light emitting elements are arranged and a second light emitting unit in which a plurality of second light emitting elements are arranged on a substrate, An exposure method using an exposure apparatus including a rotatable photosensitive drum exposed by light emitted from the line head, wherein the first light emitting unit and the second light emitting unit are the first light emitting element. And the second light emitting element are driven with the same light emission luminance, the power consumption of the first light emitting element is smaller than the power consumption of the second light emitting element and the driving time of the first light emitting element The attenuation amount of the emission luminance is formed to be larger than the attenuation amount of the emission luminance with respect to the driving time of the second light emitting element, and when the photosensitive drum is exposed by causing the line head to emit light with low luminance. The first light emitting unit When the photosensitive drum is exposed by selecting and emitting light, and the photosensitive drum is exposed by causing the line head to emit light with high brightness, the photosensitive member is selected by causing the second light emitting unit to emit light. The drum is exposed.

Furthermore, in the exposure method of the present invention, the exposure apparatus has a control circuit to which exposure data supplied from the outside is input, and the exposure data causes the line head to emit light at a low luminance to cause the photosensitive drum to be driven. In the case of exposing, the control circuit generates first gradation data for driving the first light emitting unit, and the first light emitting unit is selected to emit light, thereby exposing the photosensitive drum. When the exposure data causes the line head to emit light with high brightness to expose the photosensitive drum, the control circuit performs a second operation for driving the second light emitting unit.
The photosensitive drum is exposed by generating gradation data and selecting the second light emitting unit to emit light.

According to this line head driving method, for example, when exposure light is emitted with low luminance (low light intensity) emission based on exposure data, the first light emitting element of the first light emitting unit emits light to perform exposure. When the exposure light is emitted with high luminance (high light amount) emission based on the data, the second light emitting element of the second light emitting unit can emit light. This reduces the load on the light emitting elements of the first and second light emitting units. Since light emission can be controlled by a driving power source that matches the light emission luminance of the first light emitting element and the second light emitting element, power consumption can be reduced.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Embodiments of the invention will be described below with reference to the drawings.
(First embodiment)

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS. FIG. 1 is a schematic side sectional view showing an electrophotographic printer as an image forming apparatus.

As shown in FIG. 1, an electrophotographic printer 10 (hereinafter simply referred to as a printer 10) as an image forming apparatus includes a housing 11 formed in a box shape. In the housing 11, a driving roller 12, a driven roller 13 and a tension roller 14 are provided, and the driving roller 1
2. Intermediate transfer belt 1 as a transfer medium with respect to driven roller 13 and tension roller 14
5 is stretched. The intermediate transfer belt 15 is rotated by the rotation of the driving roller 12.
It is provided so that it can be circulated in the direction of the arrow in FIG.

Above the intermediate transfer belt 15, four photosensitive drums 16 as image carriers are provided so as to be rotatable in the extending direction of the intermediate transfer belt 15 (sub-scanning direction Y). A photosensitive layer 16 a (see FIG. 4) having photoconductivity is formed on the outer peripheral surface of each photosensitive drum 16. The photosensitive layer 16a is charged with a positive or negative charge in the dark, and when irradiated with light having at least a predetermined wavelength region, the charge at the irradiated portion is lost. That is, the printer 10 is a tandem type printer constituted by these four photosensitive drums 16.

Around each photosensitive drum 16, a charging roller 19 as a charging means, an organic electroluminescence array exposure apparatus 20 (hereinafter simply referred to as an exposure apparatus 20) as a light emitting device constituting the exposure means, and a developing means. The toner cartridge 21, the primary transfer roller 22 constituting the transfer means, and the cleaning means 23 are disposed.

The charging roller 19 is a semiconductive rubber roller that is in close contact with the photosensitive drum 16. When a DC voltage is applied to the charging roller 19 to rotate the photosensitive drum 16, the photosensitive layer 16a of the photosensitive drum 16 is charged to a predetermined charging potential over the entire circumferential surface.

The exposure device 20 emits light in a predetermined wavelength region to the photosensitive drum 16. When the exposure device 20 emits light based on the print data in the vertical direction Z (see FIG. 1) (emits the photosensitive drum 16 rotating in the rotation direction Ro), the photosensitive layer 16a is exposed to light in a predetermined wavelength region. Is done.
Then, the photosensitive layer 16a loses the electric charge of the exposed part (exposure spot) and forms an electrostatic image (electrostatic latent image) on the outer peripheral surface thereof. Note that the wavelength region of light exposed by the exposure apparatus 20 is a wavelength region that matches the spectral sensitivity of the photosensitive layer 16a. That is, the peak wavelength of the light emission energy of the light exposed by the exposure device 20 is substantially the same as the peak wavelength of the spectral sensitivity of the photosensitive layer 16a.

The toner cartridge 21 is formed in a box shape and accommodates toner T as colored particles therein. Note that the four toner cartridges 21 in this embodiment contain toner T of corresponding four colors (black, cyan, magenta, and yellow). The toner cartridge 21 is provided with a developing roller 21a and a supply roller 21b in this order from the photosensitive drum 16 side. The supply roller 21b is configured to convey the toner T to the developing roller 21a by rotating. The developing roller 21a includes a supply roller 21
The toner T conveyed by the supply roller 21b is charged by friction with b, etc., and
The charged toner T is uniformly attached to the outer peripheral surface of the developing roller 21a.

In a state where a bias potential substantially equal to the charging potential is applied to the photosensitive drum 16,
The supply roller 21b and the developing roller 21a are rotated. Then, the photosensitive drum 16 applies an electrostatic attraction force relative to the bias potential between the exposure spot and the developing roller 21a (toner T). The toner T that has received the electrostatic attraction force moves from the outer peripheral surface of the developing roller 21c to the exposure spot and is attracted thereto. As a result, each photosensitive drum 16 (each photosensitive layer 1
On the outer peripheral surface of 6a), a single-color visible image (visualized image) corresponding to the electrostatic latent image is formed (see FIG.
Developed).

Primary transfer rollers 22 are provided on the inner surface 15 a of the intermediate transfer belt 15 at positions facing the respective photosensitive drums 16. The primary transfer roller 22 is a conductive roller, and rotates while its outer peripheral surface is in close contact with the inner surface 15 a of the intermediate transfer belt 15.
A DC voltage is applied to the primary transfer roller 22 so that the photosensitive drum 16 and the intermediate transfer belt 15 are applied.
, The toner T adsorbed on the photosensitive layer 16a is sequentially moved and adsorbed to the outer surface 15b of the intermediate transfer belt 15 by the electrostatic adsorption force toward the primary transfer roller 22 side.

That is, the primary transfer roller 22 primarily transfers the visible image formed on the photosensitive drum 16 to the outer surface 15 b of the intermediate transfer belt 15. The outer transfer surface 15b of the intermediate transfer belt 15 is subjected to primary transfer of at least a single color image four times by each photosensitive drum 16 and the primary transfer roller 22, and a full color image is obtained by superimposing these images. (Toner image) is obtained.

The cleaning unit 23 includes a light source such as an LED (not shown) and a rubber blade, and discharges the charged photosensitive layer 16a by irradiating the photosensitive layer 16a after the primary transfer with light. Then, the cleaning unit 23 mechanically removes the toner T remaining on the removed photosensitive layer 16a with a rubber blade.

Below the intermediate transfer belt 15, a recording paper cassette 24 that stores the recording paper P is disposed. Above the recording paper cassette 24, a paper feeding roller 25 for feeding the recording paper P to the intermediate transfer belt 15 side is disposed. A secondary transfer roller 26 that constitutes a transfer unit is disposed above the paper feed roller 25 and at a position facing the drive roller 12. The secondary transfer roller 26 is a conductive roller similar to each of the primary transfer rollers 22, and presses the back surface of the recording paper P so that the surface of the recording paper P contacts the outer surface 15 b of the intermediate transfer belt 15. Yes. Then, a DC voltage is applied to the secondary transfer roller 26 to apply the intermediate transfer belt 1.
5 is rotated, the toner T adsorbed on the outer surface 15b of the intermediate transfer belt 15 is transferred to the recording paper P.
It moves on the surface and adsorbs sequentially. That is, the secondary transfer roller 26 is connected to the intermediate transfer belt 1.
5 is secondarily transferred onto the surface of the recording paper P.

Above the secondary transfer roller 26, a heat roller 27a containing a heat source and a pressure roller 27b for pressing the heat roller 27a are disposed. Then, the recording paper P after the secondary transfer
Is conveyed between the heat roller 27a and the pressure roller 27b, the toner T transferred onto the recording paper P is softened by heating and penetrates into the recording paper P and hardens. As a result, the toner image is fixed on the surface of the recording paper P. The recording paper P on which the toner image is fixed is discharged to the outside of the housing 11 by a paper discharge roller 28.

Therefore, the printer 10 exposes the charged photosensitive layer 16a by the exposure device 20, and forms an electrostatic latent image on the photosensitive layer 16a. Next, the printer 10 develops the electrostatic latent image on the photosensitive layer 16a to form a monochromatic visible image on the photosensitive layer 16a. Subsequently, the printer 10 uses the photosensitive layer 16a.
Are sequentially transferred onto the intermediate transfer belt 15 to form a full-color toner image on the intermediate transfer belt 15. The printer 10 secondarily transfers the toner image on the intermediate transfer belt 15 onto the recording paper P, fixes the toner image by heat and pressure, and ends printing.

Next, the exposure apparatus 20 provided in the printer 10 will be described in detail. FIG. 2 is a schematic front sectional view showing the exposure apparatus 20. FIG. 3 is a front view of the exposure device 20 as viewed from the photosensitive drum 16 side. FIG. 4 is a schematic sectional side view showing the exposure apparatus 20.

As illustrated in FIG. 2, the exposure apparatus 20 includes a light-transmissive flexible substrate 30 in the line head H. In this embodiment, the flexible substrate 30 is formed of a plastic substrate made of acrylic resin. The flexible substrate 30 is formed such that the length in the width direction is slightly longer than the width in the axial direction of the photosensitive drum 16.

In this embodiment, the flexible substrate 30 has an upper surface (photosensitive drum 1
The surface opposite to the sixth side) is a light emitting element forming surface 30a, and the lower surface (the surface on the photosensitive drum 16 side) is a light extraction surface 30b.

As shown in FIG. 3, on the light emitting element forming surface 30a of the flexible substrate 30, a first exposure light emitting part Ha1 and a second exposure light emitting element in which a plurality of light emitting elements are arranged and formed in the width direction (X arrow direction). A light emitting portion Ha2 is provided, and the first exposure light emitting portion Ha1 and the second exposure light emitting portion Ha2 are formed at a predetermined interval.

A plurality of pixel formation regions 31 are formed in the first exposure light emission unit Ha1 and the second exposure light emission unit Ha2. As shown in FIG. 3, each pixel formation region 31 is two-dimensionally arranged in a staggered pattern, and each includes a driving transistor Q1, a switching transistor Q2 (see FIG. 8) made of thin film transistors, and a light emitting element or a first light emitting element. Alternatively, the pixel 3 including at least an organic electroluminescence element (hereinafter referred to as an organic EL element) 33 as the second light emitting element.
4. The drive transistor Q1 is turned on by a data signal generated based on the print data, and the organic EL element 33 emits light based on the on state.

As shown in FIG. 5, the organic EL element 33 is formed on a light-transmitting circuit forming layer S formed on the light emitting element forming surface 30a. In the circuit forming layer S, a driving transistor Q1 and a switching transistor Q2 (not shown in FIG. 5) for driving the organic EL element 33 are formed. Further, the circuit forming layer S includes a first exposure light emitting unit Ha1 and a second exposure light emitting unit Ha1.
Various circuits for selectively driving each organic EL element 33 of the light emitting section Ha2 for exposure (see FIG. 8)
Are formed outside the pixel formation region 31.

Further, as shown in FIG. 5, at a position corresponding to the pixel formation region 31 on the circuit formation layer S, a bank B is formed in which the organic EL elements 33 are two-dimensionally arranged in a staggered pattern. . A light-transmitting anode Pa such as ITO is formed at the bottom of the recess defined by the bank B. The anode Pa is electrically connected to the corresponding driving transistor Q1 through a contact hole (not shown in FIG. 5). The anode Pa and the contact hole are formed before the bank B is formed.

On the anode Pa, an organic electroluminescence layer (hereinafter referred to as an organic EL layer) OEL made of at least a polymer organic material is formed. The organic EL layer OEL is an organic compound layer composed of at least two layers of a hole transport layer OEL1 and a light emitting layer OEL2, and an electron injection layer Ei having a function of supplying electrons to the light emitting layer OEL2 at the upper side thereof. Further, on the upper side, a cathode Pc made of at least a metal film having light reflectivity such as aluminum.
Is formed. The cathode Pc is formed so as to cover substantially the entire surface on the light emitting element formation surface 30a side, and is shared by each pixel 34 of the first exposure light emitting section Ha1 and the second exposure light emitting section Ha2, thereby allowing each organic EL element 33 to be shared. A common potential is supplied. And organic EL
The element 33 includes the anode Pa, the organic EL layer OEL, the electron injection layer Ei, and the cathode Pc.

A support substrate 38 that is bonded to the cathode Pc (flexible substrate 30) by the adhesive layer La is disposed above the cathode Pc. The support substrate 38 is a colorless and transparent plastic flexible substrate formed in the same size as the flexible substrate 30 when viewed in a plan view, and has a sufficient thickness to obtain mechanical strength. .

When a drive current corresponding to the data signal is supplied to the anode Pa, the organic EL layer OEL (
The light emitting layer OEL2) emits light with a luminance corresponding to the driving current. At this time, the organic EL layer OEL
The light emitted from the cathode Pc side (upper side in FIG. 5) is reflected by the cathode Pc. Therefore, most of the light emitted from the organic EL layer OEL is transmitted through the anode Pa, the circuit forming layer S, and the flexible substrate 30, and is on the light extraction surface 30b side (photosensitive drum 1).
6 side).

In the present embodiment, the formation conditions of the organic EL element 33 of the first exposure light-emitting portion Ha1 and the organic EL element 33 of the second exposure light-emitting portion Ha2 are different. More specifically, the work function or ionization potential value of the first electron injection layer material constituting the organic EL element 33 of the first exposure light emitting part Ha1 constitutes the organic EL element 33 of the second exposure light emitting part Ha2. It was made smaller than the work function or ionization potential value of the second electron injection layer material.

As shown in FIG. 6, the larger the work function or ionization potential of the electron injection material,
It is known to have a long life. In the case of emitting light with high luminance, it is known that the rate of change of the lifetime with respect to the work function or ionization potential of the electron injection material is large, and the lifetime is longer as the work function or ionization potential of the electron injection material is larger. In addition, when emitting light with low brightness, the rate of change of the lifetime with respect to the work function or ionization potential of the electron injection material is smaller than that with high brightness, and the lifetime increases as the work function or ionization potential of the electron injection material increases. It has been.

Further, as shown in FIG. 7, the emission luminance with respect to the work function or ionization potential of the electron injection material in a state where a constant voltage is applied to the organic EL element, the smaller the work function or ionization potential of the electron injection material, It is known that the brightness can be increased.

That is, by increasing the work function or ionization potential of the second electron injection layer material constituting the organic EL element 33 of the light emitting portion Ha2 for second exposure, light is emitted with high brightness by increasing the drive voltage compared to the small one. This means that it is durable and can lead to a long life. Further, even if the power supply voltage supplied to the organic EL element 33 of the first exposure light emitting unit Ha1 is smaller than the power supply voltage supplied to the organic EL element 33 of the second exposure light emitting unit Ha2, light is emitted with a desired light emission luminance. Therefore, power consumption can be reduced.

As shown in FIGS. 2 and 4, on the light extraction surface 30 b of the flexible substrate 30, at positions facing the organic EL elements 33 of the first exposure light emitting part Ha <b> 1 and the second exposure light emitting part Ha <b> 2, Microlenses 40 are formed respectively. The microlens 40 is a convex lens having a hemispherical optical surface having a sufficient transmittance with respect to the wavelength of the light emitted from the organic EL layer OEL, and is an organic EL element 33 (organic EL element). The center position of the layer OEL) is formed on the optical axis A.

The microlens 40 is a light beam emitted from the organic EL element 33 along the optical axis A with the distance between the apex of the lower curved surface (exit surface 40a) and the photosensitive layer 16a as the image side focal length. The intersection (image side focal point F) with the optical axis A is positioned on the photosensitive layer 16a. Thus, the light emitted from the microlens 40 can form an exposure spot having a desired size on the photosensitive layer 16a.

The line head H (flexible substrate 30) is curvedly formed on the arcuate photosensitive drum 16 side. Then, in the first exposure light emitting unit Ha1, by controlling the light emission of the organic EL elements 33 in the first row and the organic EL elements 33 in the second row that are two-dimensionally arranged in a staggered pattern, Further, it is possible to form continuous exposure spots on the same line in the X direction with respect to the surface of the photosensitive drum 16. That is, each organic EL element 33 in the first row and each organic EL element 3 in the second row.
The light emitted from 3 is the axial direction of the photosensitive drum 16 (direction orthogonal to the paper surface in FIG. 1).
An exposure spot (light in an exposure line shape) arranged in the same line in the main scanning direction X) is exposed on the photosensitive layer 16a.

Similarly, in the second exposure light emitting portion Ha2, the light emitted from each organic EL element 33 in the first row and each organic EL element 33 in the second row is in the axial direction of the photosensitive drum 16 (in FIG. 1). Exposure spots aligned in the same line in the direction orthogonal to the paper surface: main scanning direction X) are exposed to the photosensitive layer 16a.

In addition, by forming the curve, the exposure spot by the organic EL element 33 in each part that forms the line-shaped light emitted and formed by the first exposure light emitting part Ha1, and the second exposure light emitting part Ha.
The exposure spots formed by the organic EL elements 33 in the respective portions that form the line-shaped light emitted and formed by 2 overlap each other. That is, the corresponding organic EL elements 33 of the first exposure light-emitting portion Ha1 and the second exposure light-emitting portion Ha2 are respectively in contact with the photosensitive layer 1 of the photosensitive drum 16.
The same point of 6a is exposed.

Next, the electrical configuration of the exposure apparatus 20 configured as described above will be described with reference to FIG.
In FIG. 8, the line head H includes a first exposure light emission unit Ha <b> 1 and a second exposure light emission unit Ha <b> 2.
, A first data line driving circuit 51, a second data line driving circuit 52, a selection signal generating circuit 53, and a control circuit 54 are provided.

The first exposure light emission part Ha1 and the second exposure light emission part Ha2 have a pixel circuit 56 for each of the pixel regions 31 arranged two-dimensionally in a staggered pattern.

Each pixel circuit 56 of the first exposure light emitting unit Ha1 has M data lines Xa1 to Xam, respectively.
(M is an integer) and the selection signal line Y1. In addition, the second exposure light emitting portion Ha
Each of the two pixel circuits 56 is connected between M data lines Xb1 to Xbm (m is an integer) and the selection signal line Y1.

Each pixel circuit 56 of the first exposure light emitting unit Ha1 includes a driving transistor Q1, a switching transistor Q2, and a holding capacitor C1. The driving transistor Q1 and the switching transistor Q2 are N-channel thin film transistors (TFTs).
It is composed of. The drive transistor Q1 has a drain connected to the anode of the organic EL element 33 and a source connected to the corresponding power supply line L. A holding capacitor C1 is connected to the gate of the driving transistor Q1. The other end of the holding capacitor C1 is connected to the power supply line L.

The switching transistor Q2 has a gate connected to the selection signal line Y1. The switching transistor Q2 has a drain connected to the corresponding data line Xa1 to Xam, and a source connected to the gate of the driving transistor Q1 and one end of the holding capacitor C1.

Incidentally, in each pixel circuit 56 of the second exposure light emitting unit Ha2, the source of the drive transistor Q1 is connected to the power supply line L, and the drain of the switching transistor Q2 is connected to the corresponding data lines Xb1 to Xbm.

When the selection signal S1 is output to the selection signal line Y1 for a predetermined period, the switching transistor Q2 of each pixel circuit 56 is turned on for a predetermined period and the data lines Xa1 to Xam, Xb1 to Xb.
Data signals Da1 to Dam and Db1 to Dbm are supplied via m. Then
Data signals Da1 to Dam and Db1 to Dbm are supplied to the holding capacitor C1 through the switching transistor Q2, respectively. The holding capacitor C1 of each pixel circuit 56 accumulates and holds a charge amount corresponding to the data signals Da1 to Dam and Db1 to Dbm. Further, the potential of the gate terminal of the driving transistor Q1 of each pixel circuit 56 is the data signal Da1 to Dam, Db.
1 to Dbm, the data signal D is applied to the drain / source of the driving transistor Q1.
Drive currents corresponding to a1 to Dam and Db1 to Dbm are supplied to the organic EL element 33, respectively. This drive current is generated by the data signals Da1 to Dam and Db1 stored in the holding capacitor C1.
It is a value relative to the amount of charge according to ~ Dbm.

That is, the drive transistor Q1 of each pixel circuit 56 has corresponding data signals Da1 to Da.
m, Db1 to Dbm are turned on in response to each of them, and the conduction state is maintained and a driving current is supplied to each organic EL element 33. Then, at this timing, the organic EL element 33 of each pixel circuit 56 emits light with luminance relative to the data signals Da1 to Dam and Db1 to Dbm.

The first data line driving circuit 51 uses the data signals Da1 to Dam of the pixel circuits 56 based on the first gradation data from the control circuit 54 to the pixel circuits 56 of the first exposure light emitting unit Ha1.
Is generated. Then, the first data line driving circuit 51 transmits the data signals Da1 to Dam generated based on the synchronization signal from the control circuit 54 to the corresponding pixel circuits 56, respectively.
1 to Xam.

The second data line driving circuit 52 generates data signals Db1 to Dbm of the pixel circuits 56 based on the second gradation data from the control circuit 54 to the pixel circuits 56 of the second exposure light emitting unit Ha2.
Is generated. Then, the second data line driving circuit 52 supplies the data signals Db1 to Dbm generated based on the synchronization signal from the control circuit 54 to the corresponding pixel circuits 56 via the data lines Xb1 to Xbm.

The control circuit 54 sequentially inputs exposure data for one line created based on the print data supplied from the external control device. The control circuit 54 supplies the first gradation data supplied to the first data line driving circuit 51 and the second data supplied to the second data line driving circuit 52 based on the exposure data.
Tone data is generated.

The exposure data for one line is provided corresponding to each exposure spot when exposing each exposure spot (light in an exposure line shape) aligned in the axial direction of the photosensitive drum 16 and on the same line. This is gradation data when the organic EL element 33 is caused to emit light. In the present embodiment, the organic EL element 33 can control light emission in 256 steps (256 gradations). For convenience of explanation, light emission luminance of 127 gradations or less is called low luminance light emission, and light emission luminance of 128 gradations or more is called high luminance.

The control circuit 54 drives the organic EL element 33 of the first exposure light emitting unit Ha1 in the case of low luminance light emission, and drives the organic EL element 33 of the second exposure light emission unit Ha2 in the case of high luminance light emission. First gradation data and second gradation data are generated.

For example, the gradation data of the pixel circuit 56 of the first exposure spot is “100” gradation (low luminance emission), and the gradation data of the pixel circuit 56 of the second exposure spot is “200” gradation (high luminance). Light emission) The gradation data of the pixel circuit 56 of the third exposure spot is “220” gradation (high luminance light emission), and the gradation data of the pixel circuit 56 of the fourth exposure spot is “90” gradation (low). Brightness emission).

The control circuit 54 supplies the first gradation data for the first exposure light emitting unit Ha1 to the gradation data of “100” gradation for the pixel circuits 56 of the first and fourth exposure spots, respectively. When"
The gradation data of “0” gradation is created for the pixel circuit 56 of the second and third exposure spots as gradation data of 90 ”gradation. That is, the second and third of the first exposure light emitting portion Ha1.
First gradation data that does not cause the pixel circuit 56 (organic EL element 33) of the first exposure spot to emit light is created.

On the other hand, the control circuit 54 supplies the second gradation data for the second exposure light emitting portion Ha2 to the pixel circuit 56 of the second and third exposure spots, respectively, with a gradation of “200” gradation. The tone data and the tone data of “220” tone are converted into pixel circuits 56 for the first and fourth exposure spots.
In contrast, gradation data of “0” gradation is created. That is, the second gradation data that does not cause the pixel circuit 56 (organic EL element 33) of the first and fourth exposure spots of the second exposure light emitting portion Ha2 to emit light is created.

More specifically, the first and fourth exposure spots are exposed with light from the pixel circuit 56 (organic EL element 33) of the first exposure light emitting portion Ha1, and the second and third exposure spots are Then, the light is exposed to the light of the pixel circuit 56 (organic EL element 33) of the second exposure light emitting portion Ha2.

That is, in the case of low-luminance light emission, the organic EL element 33 of the first exposure light-emitting portion Ha1 is driven, and in the case of high-luminance light emission, the organic EL element 33 of the second exposure light-emitting portion Ha2 is driven. The roles of the organic EL element 33 of the first exposure light emitting unit Ha1 and the organic EL element 33 of the second exposure light emitting unit Ha2 are shared.

Moreover, in the present embodiment, the organic EL element 33 of the second exposure light-emitting portion Ha2 has an organic EL element whose work function or ionization potential value of the second electron injection layer material is provided in the first exposure light-emitting portion Ha1. Since it is configured to be larger than the work function or ionization potential value of the first electron injection layer material constituting the element 33, even if the driving voltage is increased to emit light with high brightness, the lifetime is sufficiently endured. In other words, the organic EL element 33 provided in the first exposure light emitting portion Ha1 does not emit high-luminance light, which leads to a long life.

Accordingly, the control circuit 54 determines whether the light emission luminance at each exposure spot is high luminance light emission or low luminance light emission based on the exposure data for one line, and distributes the gradation data for each exposure spot to perform the first. First gradation data for the pixel circuit 56 of the light emitting unit Ha1 for exposure and second gradation data for the pixel circuit 56 of the light emitting unit Ha2 for second exposure are generated. Then, the control circuit 54
When the first gradation data and the second gradation data are created, they are supplied to the first data line driving circuit 51 and the second data line driving circuit 52, respectively.

The first data line driving circuit 51 generates data signals Da1 to Dam based on the first gradation data from the control circuit 54. The second data line driving circuit 52 generates data signals Db1 to Dbm based on the second gradation data from the control circuit 54. The first data line driving circuit 51 and the second data line driving circuit 52 send the data signals Da1 to Dam and Db1 to Dbm to the corresponding pixel circuits 56 in response to the synchronization signal from the control circuit 54.
m and Xb1 to Xbm, respectively.

In addition, the control circuit 54 outputs a synchronization signal to the selection signal generation circuit 53. The selection signal generation circuit 53 generates a selection signal S1 based on the synchronization signal. Then, the selection signal generation circuit 53
The first data line driving circuit 51 and the second data line driving circuit 52 receive the data signals Da1 to Da1.
At the timing of supplying Dam, Db1 to Dbm, the selection signal S1 is output to the selection signal line Y1 for a predetermined time.

  Next, the operation of the exposure apparatus 20 configured as described above will be described.

When the exposure data for one line is input, the control circuit 54 determines whether the light emission luminance at each exposure spot is high luminance light emission or low luminance light emission, and if the exposure data at the exposure spot is low luminance light emission for each exposure spot. For example, the high-luminance light emission is assigned to the first gradation data of the first exposure light emitting unit Ha1, and the second gradation light emission unit Ha2 is assigned to the second gradation data. At this time, the first
“0” gradation data is assigned to the pixel circuit 56 in which the exposure data at the exposure spot is not distributed in the pixel circuit 56 of the light emitting unit Ha1 for exposure and the light emitting unit Ha2 for second exposure.

Then, the first data line driving circuit 51 generates data signals Da1 to Dam for the respective pixel circuits 56 of the first exposure light emitting unit Ha1 based on the first gradation data, and supplies the data lines to the corresponding pixel circuits 56, respectively. Supply via Xa1-Xam. At the same time, the second data line driving circuit 52 generates the data signals Db1 to Dbm for the pixel circuits 56 of the second exposure light emitting unit Ha2 based on the second gradation data, and supplies the data lines to the corresponding pixel circuits 56, respectively. Xb1-X
supplied via bm.

Then, each exposure spot constituting light in an exposure line shape emitted to the photosensitive drum 16 is light of the organic EL element 33 of the first exposure light emitting unit Ha1 in the case of low illuminance (low luminance light emission). In the case of high illuminance (high luminance light emission), exposure is performed with light from the organic EL element 33 of the second exposure light emitting portion Ha2.

  Next, effects of the present embodiment configured as described above will be described below.

(1) According to this embodiment, the line head H includes the organic EL elements 33 that emit light to each exposure spot that constitutes light in the form of an exposure line that is emitted to the photosensitive drum 16. A light emitting portion Ha1 for exposure was provided. Further, the photosensitive drum 1 is also connected to the line head H.
6 is provided with a second exposure light-emitting portion Ha2 having an organic EL element 33 that emits light to each exposure spot that constitutes the light in the shape of an exposure line emitted to 6. Then, the corresponding organic EL elements 33 of the first exposure light-emitting portion Ha1 and the second exposure light-emitting portion Ha2 are exposed to the same exposure spot on the photosensitive layer 16a of the photosensitive drum 16, respectively.

And in each exposure spot, when exposing by low-intensity light emission, the 1st exposure light emission part H
In the case where the organic EL element 33 of a1 is caused to emit light and is exposed with high-luminance light emission, a second exposure light-emitting portion H
The organic EL element 33 of a2 was made to emit light.

Therefore, since the organic EL element 33 of the first exposure light-emitting portion Ha1 and the organic EL element 33 of the second exposure light-emitting portion Ha2 are selectively used according to the luminance to be exposed, the first exposure light-emitting portion Ha.
The load on the organic EL element 33 of the first and second exposure light emitting portions Ha2 is reduced. As a result, the replacement time of the line head H, which is a consumable item, can be lengthened, and the load for maintenance in the printer 10 can be reduced.

(2) In addition, according to the present embodiment, the work function or the ionization potential value of the second electron injection layer material constituting the organic EL element 33 of the second exposure light emitting portion Ha2 is set as the first exposure light emitting portion Ha1. The work function or ionization potential of the first electron injection layer material constituting the organic EL element 33 was set to be larger. That is, the work function or ionization potential value of the second electron injection layer material of the organic EL element 33 of the second exposure light emitting portion Ha2 that emits light with high luminance at a high drive voltage is provided in the first exposure light emitting portion Ha1. The EL element 33 is configured to be larger than the work function or ionization potential value of the first electron injection layer material.

Accordingly, the organic EL element 33 of the second exposure light emitting portion Ha2 can extend the life even when the drive voltage is increased to emit light with high brightness, and the replacement time of the line head H, which is a consumable item, can be further extended. Can do.

(3) According to the present embodiment, the organic EL element 33 of the first exposure light emitting portion Ha1 emits light with low luminance, and the work function or ionization potential of the first electron injection layer material is small. Since the driving voltage with respect to the light emission luminance applied to each organic EL element 33 of the light-emitting portion Ha1 for one exposure can be reduced, the power consumption can be reduced.

(4) According to this embodiment, the line head H is formed of the flexible substrate 30 made of an acrylic resin that can be curved. Therefore, it becomes easy to align the corresponding organic EL elements 33 of the first exposure light emitting portion Ha1 and the second exposure light emitting portion Ha2 to expose the same point of the photosensitive layer 16a of the photosensitive drum 16 with each other. .

  In addition, you may change the said embodiment as follows.

In the embodiment described above, the first exposure light-emitting portion Ha1 and the second exposure light-emitting portion Ha2 are formed in two dimensions in a staggered pattern, that is, by arranging the organic EL elements 33 in two rows. Row or 3
The organic EL elements 33 composed of at least rows are arranged to arrange the first exposure light emitting portions Ha1 and the second.
The light emitting portion Ha2 for exposure may be formed and implemented.

In the above embodiment, the line head H is configured by two light emitting units, the first exposure light emitting unit Ha1 and the second exposure light emitting unit Ha2, but may be implemented by configuring three or more light emitting units. Good. In this case, the light emission luminance is divided according to the number of light emitting portions, and light emitting elements (organic EL elements) of the respective light emitting portions are selected and light emission is controlled based on the exposure data.

In the above embodiment, the printer 10 is embodied as a tandem color printer.
The present invention may be applied to a monochrome printer having at least one exposure device 20.

In the above embodiment, the light emitting element is embodied by the organic EL element 33, but an inorganic EL element or L
You may actualize with other light emitting elements, such as ED.

In the above embodiment, the flexible substrate 30 is made of at least an acrylic resin. However, the present invention is not limited to this, and what is essential is that the substrate only needs to be able to be curved, and may be a plastic substrate such as polyimide.

In the above embodiment, the pixel circuit 56 that controls the light emission of the organic EL element 33 is configured to include two transistors (the drive transistor Q1 and the switching transistor Q2). However, the configuration is not limited thereto, and a configuration in which three or more transistors for controlling the light emission of the organic EL element 33 may be provided, or a configuration in which the flexible substrate 30 is not provided may be provided.

In the above embodiment, the flexible substrate 30 includes the first exposure light emitting unit Ha1, the second exposure light emitting unit Ha2, the first data line driving circuit 51, the second data line driving circuit 52, the selection signal generating circuit 53, and the control. Although the circuit 54 is provided, another circuit or a part other than the first exposure light emitting portion Ha1 and the second exposure light emitting portion Ha2 may be formed on a substrate other than the flexible substrate 30. Good.

1 is a schematic side sectional view showing an image forming apparatus according to a first embodiment. Similarly, a schematic front sectional view showing an exposure apparatus. Similarly, the figure which looked at the exposure apparatus from the photosensitive drum side. Similarly, an explanatory view showing a relationship between a line head and a photosensitive drum. Similarly, the expanded sectional view for demonstrating an organic EL element. Similarly, the figure which shows the relationship between the lifetime with respect to the value of the work function or ionization potential of the electron injection material of the organic EL element in high-intensity light emission and low-intensity light emission. Similarly, the figure which shows the relationship of the brightness | luminance in a fixed voltage with respect to the value of the work function or ionization potential of the electron injection material of an organic EL element. Similarly, the electric circuit diagram for demonstrating the electrical structure of exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electrophotographic printer as image forming apparatus, 15 ... Intermediate transfer belt as transfer medium, 16 ... Photosensitive drum as image carrier, 19 ... Charging roller as charging means, 2
DESCRIPTION OF SYMBOLS 0 ... Organic electroluminescence array exposure apparatus as a light-emitting device, 21 ... Toner cartridge as a developing means, 22 ... Primary transfer roller, 26 ... Secondary transfer roller, 30 ... Flexible substrate, 30a ... Light emitting element formation surface, 30b ... Light extraction surface 33... Light emitting element or organic electroluminescence element as first light emitting element or second light emitting element 40... Microlens 51. First data line driving circuit 52 52 Second data line driving circuit 53. Selection signal generation circuit, 54 ... control circuit, OEL ... organic electroluminescence layer, OEL1 ... hole transport layer, OEL2 ... light emitting layer, Ei ... electron injection layer, Pc ... cathode, Pa ... anode, H ... line head, Ha1 ... light emitting part or first light emitting part as first light emitting part, Ha2 ... second exposure as light emitting part or second light emitting part Light unit.

Claims (12)

A line head provided with a first light emitting unit in which a plurality of first light emitting elements are arranged and a second light emitting unit in which a plurality of second light emitting elements are arranged on a substrate,
When the first light emitting element and the second light emitting element are driven with the same light emission luminance, the power consumption of the first light emitting element is smaller than the power consumption of the second light emitting element, and the first light emitting element. A line head characterized in that an emission luminance attenuation amount with respect to an element driving time is larger than an emission luminance attenuation amount with respect to a driving time of the second light emitting element. 2. The line head according to claim 1, wherein the first light emitting element and the second light emitting element are organic electroluminescent elements including an organic layer having at least one light emitting function. The difference between the work function or ionization potential value of the light emitting material constituting the organic layer having the light emitting function of the first light emitting element and the work function or ionization potential value of the electron injection material is the light emission of the second light emitting element. 3. The line head according to claim 2, wherein a difference between a work function or ionization potential value of the light emitting material constituting the organic layer having a function and a work function or ionization potential value of the electron injection material is different. . 2. The line head according to claim 1, wherein the first light emitting element and the second light emitting element are made of at least an inorganic LED. 5. The line head according to claim 1, wherein the first light emitting unit and the second light emitting unit are formed on the same flexible substrate. The first light emitting unit is formed by arranging a plurality of first light emitting elements in one direction,
The second light emitting unit includes a plurality of second light emitting elements arranged in one direction.
The line head according to claim 1, wherein the first light emitting unit and the second light emitting unit are arranged in parallel on the substrate. The first light emitting unit includes a plurality of first light emitting element rows in which a plurality of first light emitting elements are arranged in one direction and arranged in parallel.
The second light emitting unit includes a plurality of second light emitting element rows in which a plurality of second light emitting elements are arranged in one direction and arranged in parallel.
The line head according to claim 1, wherein the first light emitting unit and the second light emitting unit are arranged in parallel on the substrate. The first light emitting unit includes a plurality of first light emitting elements arranged in a staggered pattern,
The line head according to claim 7, wherein the second light emitting unit includes a plurality of second light emitting elements arranged in a staggered pattern. An exposure apparatus comprising a line head in which a plurality of light emitting elements are arranged and a rotatable photosensitive drum exposed by light from the line head,
As the line head, using the line head according to any one of claims 1 to 8,
An exposure apparatus, wherein a rotating shaft of the photosensitive drum, the first light emitting unit, and the second light emitting unit are arranged in parallel. The exposure apparatus includes a control circuit,
The control circuit outputs first gradation data for driving the first light emitting unit and second gradation data for driving the second light emitting unit based on exposure data supplied from the outside. The exposure apparatus according to claim 9, wherein the exposure apparatus generates the exposure apparatus. A line head provided with a first light emitting part in which a plurality of first light emitting elements are arranged and a second light emitting part in which a plurality of second light emitting elements are arranged on a substrate, and light emitted from the line head An exposure method using an exposure apparatus comprising a rotatable photosensitive drum exposed by
When the first light emitting unit and the second light emitting unit drive the first light emitting element and the second light emitting element with the same light emission luminance, the power consumption of the first light emitting element is the second light emitting unit. It is smaller than the power consumption of the element, and the attenuation amount of the light emission luminance with respect to the driving time of the first light emitting element is larger than the attenuation amount of the light emission luminance with respect to the driving time of the second light emitting element. ,
In the case where the photosensitive drum is exposed by causing the line head to emit light with low luminance, the first
The photoconductive drum is exposed by selecting a light emitting portion to emit light,
When the photosensitive drum is exposed by causing the line head to emit light with high brightness, the second
An exposure method comprising exposing the photosensitive drum by selecting a light emitting portion to emit light. The exposure apparatus has a control circuit to which exposure data supplied from the outside is input,
When the exposure data causes the line head to emit light with low brightness to expose the photosensitive drum, the control circuit generates first gradation data for driving the first light emitting unit, The photosensitive drum is exposed by selecting the first light emitting unit to emit light,
When the exposure data causes the line head to emit light with high brightness to expose the photosensitive drum, the control circuit generates second gradation data for driving the second light emitting unit, The exposure method according to claim 11, wherein the photosensitive drum is exposed by selecting the second light emitting unit to emit light.

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