JP4552601B2 - Exposure apparatus and image forming apparatus - Google Patents

Description

The present invention includes the exposure light device that put the image forming apparatus, an image forming apparatus including the exposure apparatus.

  A line printer (image forming apparatus) is known as an electrophotographic printer. In this line printer, devices such as a charger, a line-shaped printer head (line head), a developing device, and a transfer device are arranged close to each other on the peripheral surface of a photosensitive drum serving as an exposed portion. That is, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum charged by the charger by selective light emission operation of a light emitting element provided in the printer head, and this latent image is formed. It is developed with toner supplied from a developing device, and the toner image is transferred onto a sheet by a transfer device.

By the way, as the light emitting elements of the printer head as described above, there are used, for example, two rows of inorganic or organic light emitting diodes (LEDs) arranged in a staggered manner. However, this has a problem that it is extremely difficult to arrange thousands of light emitting points with high accuracy. Therefore, in recent years, there has been proposed an image forming apparatus provided with a light-emitting element array having a light-emitting element as an organic electroluminescent element (organic EL element) capable of producing a light-emitting point with high accuracy (for example, Patent Documents). 1).
JP 11-198433 A

However, the organic EL element has a significantly lower light emission luminance than, for example, inorganic LEDs. Therefore, it is difficult to secure a sufficient amount of light (brightness) necessary for exposure with a line head using the organic EL element as a light emitting element. It is. In order to increase the light emission luminance, it is conceivable to increase the current leading to this, but in this case, the lifetime is extremely shortened. This is because, in general, in an organic EL element, when the luminance is doubled, the lifetime is reduced to about ３.
In addition, since the absolute luminance, that is, the amount of light of the organic EL element is much lower than that of, for example, an inorganic LED, in a line head using this organic EL element as a light emitting element, the gradation required for exposure, for example, 32 In order to produce gradation, it is difficult to divide the luminance by gradation.
Furthermore, if there is a luminance variation between pixels made of each organic EL element in the line head, there is a problem that the luminance variation between these pixels becomes uneven printing as it is. For example, if there is only one organic EL element with low luminance among the aligned organic EL elements, the printed matter obtained when exposed and printed using this line head corresponds to the organic EL element with low luminance described above. The gradation level is lower than the surroundings only at the position, and this is visually recognized as a streak, for example.

The present invention has been made in view of the above circumstances, and an object of the present invention is to secure a sufficient amount of light necessary for exposure, to ensure a sufficient level of gradation, and between pixels. in is to provide a can Ru eXPOSURE apparatus to overcome this for problems caused by variations in luminance, an image forming apparatus including the exposure apparatus.

An exposure method of the present invention is an exposure method by an exposure apparatus including a line head in which a plurality of EL elements are arranged and a rotatable photosensitive drum exposed by light from the line head,
As the line head, one having a plurality of EL element arrays formed such that the alignment direction of the EL elements is parallel to the rotation axis of the photosensitive drum,
The same drawing point on the photosensitive drum is exposed using a plurality of EL elements selected from a plurality of EL elements corresponding to the plurality of EL element rows.

According to this exposure method, the same drawing point on the photosensitive drum is exposed from a plurality of EL elements selected from among a plurality of EL elements corresponding between a plurality of EL element arrays. By exposing the same drawing point from multiple EL elements, it is possible to secure the necessary light intensity by exposure from multiple EL elements even if sufficient luminance (light intensity) cannot be obtained with one EL element. become.
Further, there is a variation in luminance between pixels composed of each organic EL element. For example, even if there is an organic EL element having a low luminance due to this variation, in particular, the same drawing point is exposed from a plurality of EL elements. Accordingly, the organic EL element having low luminance does not expose many drawing points alone. Therefore, printing defects such as streaking due to EL elements having different luminances are prevented.

Further, in the exposure method, when the same drawing point on the photosensitive drum is exposed by the EL element, depending on how many EL elements of the plurality of EL elements are selected and exposed, It is preferable to change the gradation as the degree.
In this way, although the absolute luminance (light quantity) of each organic EL element is not sufficient, the total light quantity of all the corresponding organic EL elements becomes the maximum light quantity. By selecting the number of EL elements to be exposed from a plurality of organic EL elements, it is possible to ensure a sufficient degree of gradation.

Moreover, in the said exposure method, it is preferable to perform the gradation used as the said degree of exposure with the pulse width gradation of the drive signal applied to the said EL element.
This makes it possible to control the gradation in combination with the above-described method of changing the gradation as the degree of exposure depending on how many EL elements of the plurality of EL elements are selected and exposed. By doing so, it becomes possible to ensure a sufficient level of gradation more easily.

In the exposure method, it is preferable that the line head is configured so that the EL element is driven in an active matrix.
In this way, the exposure control by the line head can be easily performed, and the drive circuit for driving each EL element can be made relatively compact, whereby the drive circuit is placed in the line head. It becomes possible to form by internal.

The exposure apparatus of the present invention is an exposure apparatus comprising a line head in which a plurality of EL elements are arranged and a rotatable photosensitive drum exposed by light from the line head,
The line head includes a plurality of EL element rows formed such that the alignment direction of the EL elements is parallel to the rotation axis of the photosensitive drum,
A plurality of EL elements selected from among a plurality of corresponding EL elements between the plurality of EL element arrays are configured to be exposed to the same drawing point on the photosensitive drum. .

According to this exposure apparatus, a plurality of EL elements selected from a plurality of corresponding EL elements between a plurality of EL element arrays are configured to be exposed to the same drawing point on the photosensitive drum. Therefore, by exposing the same drawing point from a plurality of EL elements, even if sufficient luminance (light quantity) cannot be obtained with one EL element, the necessary light quantity is secured by exposure from the plurality of EL elements. It becomes possible to do.
In addition, there is a variation in luminance between pixels composed of each organic EL element, for example, even if there is an organic EL element with low luminance due to this variation, by exposing the same drawing point from a plurality of EL elements in particular, An organic EL element having low luminance does not expose many drawing points alone. Therefore, printing defects such as streaking due to EL elements having different luminances are prevented.

In the exposure apparatus, when the same drawing point on the photosensitive drum is exposed by the EL element, the number of EL elements out of the plurality of EL elements is selected and exposed. It is preferable that the gradation of the degree is changed.
In this way, although the absolute luminance (light quantity) of each organic EL element is not sufficient, the total light quantity of all the corresponding organic EL elements becomes the maximum light quantity. By selecting the number of EL elements to be exposed from a plurality of organic EL elements, it is possible to ensure a sufficient degree of gradation.

Further, in the exposure apparatus, it is preferable that the gradation that is the degree of exposure is a pulse width gradation of a drive signal applied to the EL element.
This makes it possible to control gradation in combination with the above-described configuration in which the gradation that becomes the degree of exposure is changed depending on how many EL elements of the plurality of EL elements are selected and exposed. By doing so, it becomes possible to ensure a sufficient level of gradation more easily.

In the exposure method, it is preferable that the line head is configured so that the EL element is driven in an active matrix.
In this way, the exposure control by the line head can be easily performed, and the drive circuit for driving each EL element can be made relatively compact, whereby the drive circuit is placed in the line head. It becomes possible to form by internal.

The image forming apparatus of the present invention is characterized in that the exposure apparatus is provided as an exposure unit.
According to this image forming apparatus, as described above, it becomes possible to secure a necessary light amount by exposure from a plurality of EL elements, and stripes are visually recognized due to EL elements having different luminances. Such printing defects are prevented.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings referred to below, the dimensions and the like of each component are appropriately changed and described for easy understanding of the drawings.

(Exposure equipment)
First, the exposure apparatus of the present invention will be described.
FIG. 1 is a view showing an embodiment of the exposure apparatus of the present invention, and reference numeral 100 in FIG. 1 denotes an exposure apparatus. The exposure apparatus 100 is used as an exposure unit in an image forming apparatus to be described later. The line head 1, a lens array (optical imaging system) 31 that forms an image of light from the line head 1, and the lens array The photosensitive drum 9 is exposed to light from the line head 1 that has passed through the line head 1.

(Line head module)
The line head 1 and the lens array 31 are integrally held by the head case 52 in an aligned state, thereby forming the line head module 101. FIG. 2 is a perspective sectional view of the line head module 101. As shown in FIG. 2, the line head module 101 couples the light from the line head 1 to the line head 1 in which a plurality of organic EL elements are arranged and arranged. A lens array 31 in which lens elements to be imaged are arranged and arranged, and a head case 52 that holds the outer periphery of the line head 1 and the lens array 31 are provided. Here, in the present embodiment, as the lens array 31, a SELFOC (registered trademark) lens array which is an erecting equal-magnification imaging system (trade name of Nippon Sheet Glass Co., Ltd .; hereinafter, SELFOC (registered trademark) lens is SL, SELFOC (registered trademark) lens array is referred to as SL array). Based on such a configuration, the line head module 101 is configured to image the light emitted and emitted from the line head 1 on the photosensitive drum 9 at an erecting equal magnification.

(Line head)
FIG. 3 is a diagram schematically showing the line head 1. The line head 1 is formed by forming a plurality of light emitting element arrays (EL element arrays) 3 </ b> A formed by arranging a plurality of organic EL elements 3 on a long and thin rectangular element substrate 2. Although not shown in FIG. 3, the line head 1 is formed with a drive element group including drive elements for driving the organic EL elements 3, and driving for controlling the driving of these drive elements. A circuit is integrally formed in the line head 1 by so-called internal attachment.

  Here, as shown in FIG. 1, the line head 1 is arranged such that its light emitting side surface faces the photosensitive drum 9, and at this time, the row of the light emitting element rows 3A is arranged. The direction (alignment direction of the light emitting elements) is arranged in parallel with the rotation axis of the photosensitive drum 9. In addition, as shown in FIG. 3, the light emitting element rows 3A are formed in 10 rows in this embodiment, and the organic EL elements 3 are arranged in a staggered manner especially between the odd rows and the even rows. That is, in the present embodiment, the first column, the second column, the third column, the fourth column,..., The ninth column and the tenth column with the column numbers shown in FIG. Accordingly, in the present embodiment, five sets each including the organic EL elements 3 arranged in a staggered manner are formed. Further, the organic EL elements 3 are arranged in the same row in the odd-numbered columns in each set by being staggered between the odd-numbered columns and the even-numbered columns in this way. Similarly, the organic EL elements 3 arranged in the same row also correspond to each other in the even-numbered columns in each set.

  In each set in which the organic EL elements 3 are arranged in a staggered pattern, the odd-numbered columns and the even-numbered columns are arranged with a half-pitch shift, so that the appearance between the organic EL elements 3 in the longitudinal direction of each set is set. The upper pitch is half of the pitch in odd or even rows. Therefore, the pitch between the organic EL elements 3 is narrowed in each set, so that the resolution of the image forming apparatus described later can be improved.

Further, as shown in FIG. 4, the line head 1 is configured such that each organic EL element 3 is driven in an active matrix by using a thin film transistor (hereinafter abbreviated as TFT) as a switching element. Has been. That is, the line head 1 includes a plurality of scanning lines 105, a plurality of signal lines 102 extending in a direction perpendicular to the scanning lines 105, and a plurality of power supply lines extending in parallel to the signal lines 102. 103 are respectively wired, and pixel regions X are provided in the vicinity of the intersections of the scanning lines 105 and the signal lines 102.
The signal line 102 is connected to a data line driving circuit 106 including a shift register, a level shifter, a video line, and an analog switch. Further, a scanning line driving circuit 107 including a shift register and a level shifter is connected to the scanning line 105.

  Further, in each pixel region X, a switching TFT 112 to which a scanning signal is supplied to the gate electrode via the scanning line 105, and a storage capacitor for holding a pixel signal shared from the signal line 102 via the switching TFT 112. 113, a driving TFT 123 to which a pixel signal held by the holding capacitor 113 is supplied to a gate electrode, and a driving current from the power supply line 103 when electrically connected to the power supply line 103 via the driving TFT 123 Are provided, and a functional layer 110 sandwiched between the pixel electrode 23 and the cathode 50 is provided. The pixel electrode 23, the cathode 50, and the functional layer 110 constitute the organic EL element 3. The functional layer 110 is composed of a hole transport layer and a light emitting layer as will be described later.

With this configuration, when the scanning line 105 is driven and the switching TFT 112 is turned on, the line head 1 holds the potential of the signal line 102 at that time in the holding capacitor 113, The on / off state of the driving TFT 123 is determined according to the state. Then, current flows from the power supply line 103 to the pixel electrode 23 through the channel of the driving TFT 123, and further current flows to the cathode 50 through the functional layer 110. The functional layer 110 emits light according to the amount of current flowing through it.
The detailed structures of the organic EL element 3 and the drive element 4 will be described later. Moreover, in this line head 1, although the organic EL element 3 is used as an EL element, it can replace with this and can also use an inorganic EL element.

  In the line head 1, each of the organic EL elements 3 is driven in an active matrix, so that a plurality of organic EL elements 3 corresponding particularly between the plurality of EL element rows 3 </ b> A are arranged on the photosensitive drum 9. The same drawing point can be exposed. That is, the organic EL elements 3 arranged in the same row in each odd column of each set can be exposed to the same drawing point on the photosensitive drum 9, and similarly, The organic EL elements 3 arranged in the same row in each even-numbered column can be exposed to the same drawing point on the photosensitive drum 9.

As shown in FIG. 3, when the alignment direction of the organic EL elements 3 aligned in each column (each group) is the X-axis direction (X coordinate) and the alignment direction of each column is the Y-axis direction (Y coordinate), The organic EL elements 3 arranged in the same row in the even-numbered columns or the odd-numbered columns and corresponding to each other have the same position in the X-axis direction, that is, the X coordinate. Therefore, as will be described later, the photosensitive drum 9 rotates during exposure, and the drawing point on the photosensitive drum 9 relatively moves in the Y-axis direction. The same drawing point can be exposed.
However, in practice, not all of the corresponding organic EL elements 3 are exposed to the same drawing point. As will be described later, one or a plurality of selected ones of the corresponding organic EL elements 3 are selected. The organic EL element 3 is exposed to the same drawing point on the photosensitive drum 9.

  In the line head 1, the luminance of the light emitted from the organic EL element 3 changes according to the pulse width gradation of the drive signal applied to the organic EL element 3. Thus, in each organic EL element 3, the gradation that is the degree of exposure to the photosensitive drum 9 is controlled by the pulse width gradation of the drive signal applied thereto.

(SL array)
FIG. 5 is a perspective view of an SL array as the lens array 31. This lens array (SL array) 31 is configured by arranging (arranging) SL elements 31a in two rows in a staggered manner. The gaps between the SL elements 31a arranged in a staggered manner are filled with a black silicone resin 32, and a frame 34 is arranged around the silicone resin 32.

The SL element 31a has a parabolic refractive index distribution from the center to the periphery. For this reason, the light incident on the SL element 31a travels while meandering in the constant cycle. Therefore, if the length of the SL element 31a is adjusted, an image can be formed upright at an equal magnification. In the SL element 31a that forms an erecting equal-magnification image in this way, images formed by adjacent SL elements 31a can be superimposed, and a wide range of images can be obtained. Therefore, the lens array 31 shown in FIG. 5 can accurately form light from the entire line head 1.

(Head case)
Returning to FIG. 2, details of the line head module 101 will be described. The line head module 101 includes a head case 52 that supports the outer periphery of the line head 1 and the lens array 31. The head case 52 is formed in a slit shape by a rigid material such as Al. The cross section perpendicular to the longitudinal direction of the head case 52 has a shape in which both upper and lower ends are opened, and the upper half side walls 52a and 52a are arranged in parallel to each other, and the lower half side walls 52b and 52b are Each is inclined and arranged toward the center of the lower end. Although not shown, the side walls at both ends in the longitudinal direction of the head case 52 are also arranged in parallel to each other.

The above-described line head 1 is arranged inside the upper half side wall 52a of the head case 52.
FIG. 6 is an enlarged view of a connecting portion (A portion in FIG. 2) of the line head. As shown in FIG. 6, a stepped base 53 is formed on the inner surface of the side wall 52 a of the head case 52 over the entire circumference. The line head 1 is disposed horizontally with the lower surface of the line head 1 abutting on the upper surface of the pedestal 53. Although details will be described later, the line head 1 is a bottom emission type, and is arranged with the element substrate 2 facing downward and the sealing substrate 30 facing upward.

  In addition, sealing materials 54 a and 54 b are disposed on the entire corner of the corner formed by the side wall 52 a of the head case 52 and the line head 1. A sealing material is also disposed in the gap between the inner surface of the side wall 52 a of the head case 52 and the side surface of the line head 1. Thereby, the line head 1 is hermetically bonded to the head case 52. Among them, the sealing material 54b disposed on the upper side of the line head 1 is made of an ultraviolet curable resin such as acrylic. Moreover, the sealing material 54a arrange | positioned under the line head 1 is comprised with thermosetting resins, such as an epoxy.

  Note that a getter agent may be contained in these sealing materials 54a and 54b. A getter agent means a desiccant or an oxygen scavenger and adsorbs moisture and oxygen. According to this configuration, moisture and oxygen can be reliably blocked by the sealing materials 54a and 54b. Therefore, it becomes possible to suppress moisture absorption and oxidation of the organic EL element formed on the line head, and it is possible to prevent the durability of the organic EL element from being lowered and the life from being shortened.

  Returning to FIG. 2, the lens array 31 is disposed in the slit-shaped opening formed in the lower end portion of the head case 52. Sealing materials 55a and 55b are disposed at the corner formed by the side wall 52b of the head case 52 and the lens array 31 over the entire circumference. A sealing material is also disposed in the gap between the inner surface of the side wall 52 a of the head case 52 and the side surface of the line head 1. Thereby, the lens array 31 is hermetically bonded to the head case 52. Among them, the sealing material 55a disposed on the upper side of the lens array 31 is made of a thermosetting resin such as epoxy. Further, the sealing material 55b disposed under the lens array 31 is made of an ultraviolet curable resin such as acrylic. Furthermore, a getter agent may be contained in these sealing materials 55a and 55b.

  A chamber 56 is formed between the line head 1 and the lens array 31 inside the head case 52. As described above, since the line head 1 and the lens array 31 are hermetically joined to the head case 52, the chamber 56 is hermetically sealed. The interior of the chamber 56 is filled with an inert gas such as nitrogen gas or kept in a vacuum.

(Organic EL element and driving element)
Next, a detailed configuration of the organic EL element, the drive element, and the like in the line head will be described with reference to FIG.
In the case of a so-called bottom emission type in which the light emitted from the light emitting layer 60 is emitted from the pixel electrode 23 side, the light emitting light is extracted from the element substrate 2 side. Therefore, the element substrate 2 is transparent or translucent. Things are adopted. For example, glass, quartz, resin (plastic, plastic film) and the like can be mentioned, and a glass substrate is particularly preferably used.

In the case of a so-called top emission type in which the light emitted from the light emitting layer 60 is emitted from the cathode (counter electrode) 50 side, the emitted light is extracted from the sealing substrate side that is the opposite side of the element substrate 2. Therefore, either a transparent substrate or an opaque substrate can be used. Examples of the opaque substrate include a thermosetting resin and a thermoplastic resin in addition to a ceramic sheet such as alumina and a metal sheet such as stainless steel that has been subjected to an insulation treatment such as surface oxidation.
In the present embodiment, a bottom emission type is adopted, and therefore transparent glass is used for the element substrate 2.

  On the element substrate 2, a circuit unit 11 including a driving TFT 123 (driving element 4) connected to the pixel electrode 23 is formed, and an organic EL element 3 is provided thereon. The organic EL element 3 includes a pixel electrode 23 functioning as an anode, a hole transport layer 70 for injecting / transporting holes from the pixel electrode 23, a light emitting layer 60 made of an organic EL material, and a cathode 50 in this order. It is configured by being formed. Based on such a configuration, the organic EL element 3 emits light when the holes injected from the hole transport layer 70 and the electrons from the cathode 50 are combined in the light emitting layer 60. .

In this embodiment, which is a bottom emission type, the pixel electrode 23 that functions as an anode is formed of a transparent conductive material, and specifically, ITO is preferably used.
As a material for forming the hole transport layer 70, in particular, a dispersion of 3,4-polyethylenediosithiophene / polystyrene sulfonic acid (PEDOT / PSS), that is, 3,4-polyethylenedioxy in polystyrene sulfonic acid as a dispersion medium. A dispersion in which thiophene is dispersed and further dispersed in water is preferably used.
In addition, as a forming material of the positive hole transport layer 70, various things can be used, without being limited to the said thing. For example, a material obtained by dispersing polystyrene, polypyrrole, polyaniline, polyacetylene or a derivative thereof in an appropriate dispersion medium such as the aforementioned polystyrene sulfonic acid can be used.

  As a material for forming the light emitting layer 60, a known light emitting material capable of emitting fluorescence or phosphorescence is used. In this embodiment, for example, a light emitting layer whose emission wavelength band corresponds to red is adopted, but of course, a light emission layer whose emission wavelength band corresponds to green or blue may be adopted. In this case, the photoconductor used has sensitivity in the light emitting region.

  Specific examples of the material for forming the light emitting layer 60 include (poly) fluorene derivative (PF), (poly) paraphenylene vinylene derivative (PPV), polyphenylene derivative (PP), polyparaphenylene derivative (PPP), and polyvinylcarbazole (PVK). ), Polythiophene derivatives, and polysilanes such as polymethylphenylsilane (PMPS) are preferably used. In addition, these polymer materials include polymer materials such as perylene dyes, coumarin dyes, rhodamine dyes, rubrene, perylene, 9,10-diphenylanthracene, tetraphenylbutadiene, Nile red, coumarin 6, and quinacridone. It can also be used by doping a low molecular weight material such as.

The cathode 50 is formed so as to cover the light emitting layer 60. For example, Ca is formed to a thickness of about 20 nm, and Al is formed thereon to a thickness of about 200 nm to form an electrode having a laminated structure, and the Al is reflected. It also functions as a layer.
Further, a sealing substrate (not shown) is stuck on the cathode 50 via an adhesive layer.

In addition, the circuit unit 11 is provided below the organic EL element 3 as described above. The circuit unit 11 is formed on the element substrate 2. That is, a base protective layer 281 mainly composed of SiO ₂ is formed on the surface of the element substrate 2 as a base, and a silicon layer 241 is formed thereon. A gate insulating layer 282 mainly composed of SiO ₂ and / or SiN is formed on the surface of the silicon layer 241.

In the silicon layer 241, a region overlapping with the gate electrode 242 with the gate insulating layer 282 interposed therebetween is a channel region 241a. The gate electrode 242 is a part of a scanning line (not shown). On the other hand, a first interlayer insulating layer 283 mainly composed of SiO ₂ is formed on the surface of the gate insulating layer 282 that covers the silicon layer 241 and on which the gate electrode 242 is formed.

  Further, in the silicon layer 241, a low concentration source region 241b and a high concentration source region 241S are provided on the source side of the channel region 241a, while a low concentration drain region 241c and a high concentration drain are provided on the drain side of the channel region 241a. The region 241D is provided to form a so-called LDD (Light Doped Drain) structure. Among these, the high-concentration source region 241S is connected to the source electrode 243 through a contact hole 243a that opens over the gate insulating layer 282 and the first interlayer insulating layer 283. The source electrode 243 is configured as a part of a power supply line (not shown). On the other hand, the high-concentration drain region 241D is connected to the drain electrode 244 made of the same layer as the source electrode 243 through a contact hole 244a that opens through the gate insulating layer 282 and the first interlayer insulating layer 283.

  On the first interlayer insulating layer 283 on which the source electrode 243 and the drain electrode 244 are formed, for example, a planarizing film 284 mainly composed of an acrylic resin component is formed. The planarizing film 284 is formed of a heat-resistant insulating resin such as acrylic or polyimide, and has surface irregularities caused by the driving TFT 123 (driving element 4), the source electrode 243, the drain electrode 244, and the like. It is a well-known thing formed in order to eliminate.

  A pixel electrode 23 made of ITO or the like is formed on the surface of the planarizing film 284 and connected to the drain electrode 244 through a contact hole 23a provided in the planarizing film 284. That is, the pixel electrode 23 is connected to the high concentration drain region 241D of the silicon layer 241 through the drain electrode 244.

On the surface of the planarization film 284 on which the pixel electrode 23 is formed, the pixel electrode 23 and the above-described inorganic partition wall 25 are formed, and on the inorganic partition wall 25, an organic partition wall 221 is formed. On the pixel electrode 23, the hole transport layer 70 and the light emitting layer 60 are formed inside the opening 25 a formed in the inorganic partition wall 25 and the opening 221 a formed in the organic partition wall 221, that is, in the pixel region. Are stacked in this order from the pixel electrode 23 side, thereby forming a functional layer.
In this example, the driving element 4 such as a TFT is formed on the element substrate 2 as an element for driving the EL element. However, the driving element 4 is not formed on the element substrate 2, and the driving element 4 is driven. 4 may be externally attached. Specifically, the driver IC may be COG mounted on the terminal area of the EL element substrate, or a flexible circuit board on which the driver IC is mounted may be mounted on the EL element substrate.

Next, a usage pattern of the exposure apparatus 100 having the above configuration will be described.
As shown in FIG. 1, the line head module 101 configured as described above irradiates the photosensitive drum 9 as an exposed portion with light to form an image and expose it. At this time, since the line head 1 and the lens array 31 are integrally held in the head case 52 in a state of being aligned with each other, the line head module 101 is simply aligned with the photosensitive drum 9 in use. Good.
Therefore, in the exposure apparatus 100 provided with this line head module 101, alignment with respect to the photosensitive drum 9 becomes easier than in the case where the line head 1 and the lens array 31 are prepared separately, resulting from poor alignment. Uneven exposure can be reliably prevented.

Here, in particular, the line head 1 is aligned so that the alignment direction of the organic EL elements 3 is parallel to the rotation axis of the photosensitive drum 9. Further, as described above, the line head 1 and the lens array 31 are integrally held in the head case 52 in a state of being aligned with each other, so that the line head module 101 is simply aligned with the photosensitive drum 9 in use. Just do it.
Therefore, in the line head module 101, the alignment with respect to the photosensitive drum 9 becomes easier than in the case where the line head 1 and the lens array 31 are prepared separately, and uneven exposure due to poor alignment is surely prevented. Will come to be.

Next, an exposure method using such an exposure apparatus 100 will be described.
In this exposure apparatus 100, when the photosensitive drum 9 is exposed by the line head 1 based on the drive signal, each organic EL element 3 is used as a unit pixel, and light is emitted from these unit pixels. The drawing point at is exposed. That is, as shown in FIG. 8, from each of the EL element rows 3A from the first row to the tenth row (indicated by 1 to 10 in FIG. 8) of the line head 1, the selected drawing point on the photosensitive drum 9 is set. On the other hand, exposure is performed. For example, as shown in FIG. 8, a unit pixel (organic EL element 3) in the first EL element row 3A exposes the drawing point P on the photosensitive drum 9, and the second row. The drawing point Q is exposed from a certain unit pixel (organic EL element 3) in the EL element row 3A.

  Here, in general, the organic EL element 3 has a remarkably lower absolute luminance (light quantity) than, for example, an LED. Therefore, although the absolute luminance (light quantity) of each organic EL element 3 is not sufficient, the corresponding plurality of organic EL elements 3 are exposed to the same drawing point, whereby each organic EL element is exposed. By summing the light quantity of 3, the light quantity for exposure is secured. That is, as shown in FIG. 8, the drawing point P is exposed from the unit pixel in the first EL element column 3A, and the drawing point Q is exposed from the unit pixel in the second EL element column 3A. After exposure, when the photosensitive drum 9 rotates and moves in the Y-axis direction relative to the line head 1, unit pixels in the third EL element row 3 </ b> A with respect to the drawing point P, Overlap exposure is performed in the order of unit pixels in the fifth EL element array 3A,..., Unit pixels in the ninth EL element array 3A. That is, in the present embodiment, a maximum of five times of overexposure can be performed. Similarly, a maximum of five times of overexposure can be performed on the drawing point Q.

  Therefore, in the present embodiment, although the absolute luminance (light quantity) is not sufficient with one organic EL element 3, the exposure is performed by exposing the same drawing point with a maximum of five organic EL elements 3. The necessary amount of light is secured. In this embodiment, ten EL element rows 3A arranged in a staggered pattern are formed so that the same drawing point can be exposed five times at the maximum. However, when a larger amount of light is required. Therefore, the number of EL element rows 3A may be increased so as to correspond to the necessary light quantity.

  However, the line head 1 does not always expose all of the corresponding organic EL elements 3 to the same drawing point, but as described above, the line head 1 is selected from the corresponding organic EL elements 3. With one or a plurality of organic EL elements 3, the same drawing point on the photosensitive drum 9 is exposed. In this way, by selecting the number of organic EL elements 3 that are exposed to the same drawing point, the gradation that is the degree of exposure can be changed.

  That is, as described above, since the absolute luminance (light quantity) of the organic EL element 3 is remarkably lower than that of, for example, an inorganic LED, only the single organic EL element 3 has a gradation level required for exposure, For example, it is difficult to divide the luminance into gradations so as to produce 32 gradations. Therefore, as described above, the maximum exposure can be performed five times at the same drawing point, so that the exposure can be controlled in five gradations from one exposure to five overlap exposures. In the present embodiment, as described above, the luminance (light quantity) of each organic EL element 3 is changed according to the pulse width gradation of the drive signal applied thereto. Therefore, by combining these gradation control methods, it is usually possible to more easily ensure the gradation required in exposure. Specifically, by setting the pulse width gradation to 6 gradations, 30 gradations can be formed by 5 × 6 by multiplying the gradation by the overlap exposure.

  In such an exposure method using the exposure apparatus 100, one or a plurality of organic EL elements 3 selected from among a plurality of corresponding organic EL elements 3 between the plurality of EL element rows 3A are used on the photosensitive drum 9. Since the same drawing point is exposed, particularly by exposing the same drawing point from the plurality of organic EL elements 3, a sufficient amount of light necessary for the exposure can be secured.

  In particular, if a large number of EL element rows 3A (for example, 20 rows, 30 rows, etc.) are formed, and the maximum luminance (light quantity) by the individual organic EL elements 3 is reduced accordingly, each of the organic EL elements 3 The service life can be extended and the line head 1 itself can be extended. As described above, in general, in an organic EL element, when the luminance is doubled, the lifetime is reduced to about 1/3. In other words, halving the luminance improves the lifetime by about three times.

  Further, when a large number of EL element rows 3A are formed in this way, the pixel area (opening area) of each organic EL element 3 constituting the EL element row 3A is reduced, and between the pixels (between the organic EL elements 3). The resolution of exposure can be increased by narrowing the pitch. When the pixel area (opening area) of the organic EL element 3 is reduced, the luminance (light quantity) of each organic EL element 3 is reduced. However, as described above, by forming a large number of EL element rows 3A, multiple exposure is performed. This is because the necessary amount of light can be secured.

  Further, there is a variation in luminance between pixels composed of each organic EL element 3, and even if there is an organic EL element 3 having a low luminance due to this variation, for example, the same drawing point is exposed from a plurality of organic EL elements 3 in particular. By doing so, the organic EL element 3 with low luminance does not expose many drawing points alone. Accordingly, it is possible to prevent a printing defect such as a streak being visually recognized due to the organic EL elements 3 having different luminances.

  In the exposure apparatus 100, since the organic EL elements 3 of the line head 1 are configured to be driven in an active matrix, exposure control by the line head 1 can be easily performed, and each organic A drive circuit for driving the EL element 3 can be made relatively compact, and thus the drive circuit can be formed in the line head 1 internally. Therefore, the line head 1 itself becomes compact, and the exposure apparatus 100 and further the image forming apparatus using the exposure apparatus 100 as an exposure unit can be downsized.

Next, an image forming apparatus provided with the exposure apparatus of the present invention as exposure means will be described.
(Tandem image forming device)
FIG. 9 is a diagram showing a first embodiment of the image forming apparatus of the present invention, and reference numeral 80 in FIG. 9 denotes a tandem image forming apparatus. In this image forming apparatus 80, the organic EL array line heads 101K, 101C, 101M, and 101Y are arranged on four corresponding photosensitive drums 41K, 41C, 41M, and 41Y, respectively, so that an exposure apparatus is provided. Is a tandem system.

  The image forming apparatus 80 includes a driving roller 91, a driven roller 92, and a tension roller 93, and an intermediate transfer belt 90 is stretched around each of the rollers so as to be circulated and driven in the arrow direction (counterclockwise direction) in FIG. Is. Photosensitive drums 41K, 41C, 41M, and 41Y are arranged at predetermined intervals with respect to the intermediate transfer belt 90. These photosensitive drums 41K, 41C, 41M, and 41Y have a photosensitive layer as an image carrier on the outer peripheral surface thereof.

  Here, K, C, M, and Y in the symbols mean black, cyan, magenta, and yellow, respectively, and indicate that the photoconductors are for black, cyan, magenta, and yellow, respectively. The meanings of these symbols (K, C, M, Y) are the same for the other members. The photosensitive drums 41K, 41C, 41M, and 41Y are driven to rotate in the arrow direction (clockwise) in FIG. 9 in synchronization with the driving of the intermediate transfer belt 90.

Around each photosensitive drum 41 (K, C, M, Y), charging means (corona charger) 42 for uniformly charging the outer peripheral surface of the photosensitive drum 41 (K, C, M, Y), respectively. (K, C, M, Y) and rotation of the photosensitive drum 41 (K, C, M, Y) on the outer peripheral surface uniformly charged by the charging means 42 (K, C, M, Y) And an organic EL array line head 101 (K, C, M, Y) that sequentially performs line scanning.
Here, as described above, the organic EL array line head 101 (K, C, M, Y) is integrally held together with the SL array (not shown) by the head case in a state of being aligned with each other. It is used as.

  Further, a toner as a developer is applied to the electrostatic latent image formed by the organic EL array line head 101 (K, C, M, Y) (line head module) to form a visible image (toner image). As a transfer means for sequentially transferring the developing device 44 (K, C, M, Y) and the toner image developed by the developing device 44 (K, C, M, Y) to the intermediate transfer belt 90 that is a primary transfer target. Primary transfer roller 45 (K, C, M, Y) and a cleaning device as a cleaning means for removing toner remaining on the surface of the photosensitive drum 41 (K, C, M, Y) after being transferred 46 (K, C, M, Y).

  Here, each organic EL array line head 101 (K, C, M, Y) is installed such that each array direction is along the bus line of the photosensitive drum 41 (K, C, M, Y). Then, the emission energy peak wavelength of each organic EL array line head 101 (K, C, M, Y) and the sensitivity peak wavelength of the photosensitive drum 41 (K, C, M, Y) are set to substantially coincide with each other. Has been.

  The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer. The one-component developer is conveyed to the developing roller by a supply roller, for example, and adheres to the surface of the developing roller. The film thickness of the developed developer is regulated by a regulating blade, and the developing roller is brought into contact with or pressed against the photosensitive drum 41 (K, C, M, Y), whereby the photosensitive drum 41 (K, C, M, A developer is attached in accordance with the potential level of Y) and developed as a toner image.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). Primary transfer is sequentially performed on the transfer belt 90. The toner images, which are sequentially superimposed on the intermediate transfer belt 90 and become full color, are secondarily transferred to a recording medium P such as paper by the secondary transfer roller 66 and further pass through a fixing roller pair 61 that is a fixing unit. Then, the toner image is fixed on the recording medium P and then discharged onto a paper discharge tray 68 formed on the upper part of the apparatus by a pair of paper discharge rollers 62.

  In FIG. 9, reference numeral 63 denotes a paper feed cassette in which a large number of recording media P are stacked and held, 64 denotes a pickup roller for feeding the recording media P from the paper feed cassette 63 one by one, and 65 denotes secondary transfer. A pair of gate rollers for defining the supply timing of the recording medium P to the secondary transfer portion of the roller 66; a secondary transfer roller 66 as a secondary transfer means for forming a secondary transfer portion with the intermediate transfer belt 90; A cleaning blade 67 serves as a cleaning unit that removes toner remaining on the surface of the intermediate transfer belt 90 after the secondary transfer.

(4-cycle image forming apparatus)
Next, a second embodiment of the image forming apparatus according to the present invention will be described. FIG. 10 is a vertical side view of a four-cycle image forming apparatus. In FIG. 10, an image forming apparatus 160 includes, as main components, a developing device 161 having a rotary configuration, a photosensitive drum 165 that functions as an image carrier, an image writing unit 167 including the line head module, an intermediate transfer belt 169, A paper conveyance path 174, a fixing roller heating roller 172, and a paper feed tray 178 are provided.

  The developing device 161 is configured such that the developing rotary 161a rotates in the direction of arrow A about the shaft 161b. The inside of the development rotary 161a is divided into four, and image forming units for four colors of yellow (Y), cyan (C), magenta (M), and black (K) are provided. Reference numerals 162a to 162d are arranged in the image forming units for the four colors. The developing rollers rotate in the arrow B direction, and the toner supply rollers 163a to 163d rotate in the arrow C direction. Reference numerals 164a to 164d are regulating blades that regulate the toner to a predetermined thickness.

In FIG. 10, reference numeral 165 denotes a photosensitive drum that functions as an image carrier as described above, 166 is a primary transfer member, 168 is a charger, and 167 is an image writing means, which comprises the above-described line head module. is there. The photosensitive drum 165 and the image writing means (line head module) 167 constitute the exposure apparatus of the present invention.
The photosensitive drum 165 is rotationally driven in the direction of arrow D, which is the direction opposite to the developing roller 162a, by a drive motor (not shown), for example, a step motor. The line head module constituting the image writing unit 167 is arranged in a state where alignment (optical axis alignment) is performed between the line head module and the photosensitive drum 165.

  The intermediate transfer belt 169 is stretched between the driving roller 170a and the driven roller 170b. The driving roller 170 a is connected to the driving motor of the photosensitive drum 165 and transmits power to the intermediate transfer belt 169. That is, the drive roller 170a of the intermediate transfer belt 169 is rotated in the direction of arrow E which is the opposite direction to the photosensitive drum 165 by the drive motor.

  The paper transport path 174 is provided with a plurality of transport rollers, a pair of paper discharge rollers 176, and the like, so that the paper is transported. An image (toner image) on one side carried on the intermediate transfer belt 169 is transferred to one side of the paper at the position of the secondary transfer roller 171. The secondary transfer roller 171 is brought into contact with and separated from the intermediate transfer belt 169 by a clutch. When the clutch is turned on, the secondary transfer roller 171 is brought into contact with the intermediate transfer belt 169 so that an image is transferred onto a sheet.

  The sheet on which the image has been transferred as described above is then subjected to a fixing process by a fixing device having a fixing heater H. The fixing device is provided with a heating roller 172 and a pressure roller 173. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the direction of arrow F. When the paper discharge roller pair 176 rotates in the reverse direction from this state, the paper reverses its direction and advances in the double-sided printing conveyance path 175 in the direction of arrow G. 177 is an electrical component box, 178 is a paper feed tray for storing paper, and 179 is a pickup roller provided at the outlet of the paper feed tray 178.

  For example, a low-speed brushless motor is used as a drive motor for driving the transport roller in the paper transport path. For the intermediate transfer belt 169, a step motor is used because color misregistration correction is required. Each of these motors is controlled by a signal from a control means (not shown).

  In the state shown in FIG. 10, a yellow (Y) electrostatic latent image is formed on the photosensitive drum 165, and a high voltage is applied to the developing roller 162a, whereby a yellow image is formed on the photosensitive drum 165. Is done. When all of the yellow back side and front side images are carried on the intermediate transfer belt 169, the development rotary 161a rotates 90 degrees in the direction of arrow A.

  The intermediate transfer belt 169 rotates once and returns to the position of the photosensitive drum 165. Next, two images of cyan (C) are formed on the photosensitive drum 165, and this image is carried on the yellow image carried on the intermediate transfer belt 169. Thereafter, the 90-degree rotation of the development rotary 161 and the one-rotation process after the image is carried on the intermediate transfer belt 169 are repeated in the same manner.

  For carrying four color images, the intermediate transfer belt 169 rotates four times, and then the rotation position is further controlled to transfer the image onto the sheet at the position of the secondary transfer roller 171. The paper fed from the paper feed tray 178 is transported by the transport path 174, and the color image is transferred to one side of the paper at the position of the secondary transfer roller 171. The sheet on which the image is transferred on one side is reversed by the discharge roller pair 176 as described above, and stands by on the conveyance path. Thereafter, the sheet is conveyed to the position of the secondary transfer roller 171 at an appropriate timing, and the color image is transferred to the other side. The housing 180 is provided with an exhaust fan 181.

In the image forming apparatuses 80 and 160 shown in FIGS. 9 and 10, the exposure apparatus of the present invention as shown in FIG. 1 is provided as an exposure unit.
Therefore, in these image forming apparatuses 80 and 160, as described above, a necessary amount of light can be secured by exposure from a plurality of organic EL elements, and due to organic EL elements having different luminances, It is possible to prevent a printing defect such as a streak being visually recognized.
The image forming apparatus provided with the exposure apparatus of the present invention is not limited to the above embodiment, and various modifications can be made.

It is a schematic diagram which shows schematic structure of one Embodiment of the exposure apparatus of this invention. It is a perspective sectional view of a line head module concerning an embodiment. It is the figure which showed typically the surface by the side of the light emission of a line head. It is a schematic diagram which shows the wiring structure of a line head. It is a perspective view of SL array. It is an enlarged view in the joint part of a line head. It is principal part side sectional drawing of a line head. It is a schematic diagram for demonstrating the exposure method by exposure apparatus. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus of the present invention. It is a schematic block diagram which shows 2nd Embodiment of the image forming apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Line head, 2 ... Element substrate, 3 ... Organic EL element (EL element),
3A ... EL element array, 9 ... photosensitive drum, 31 ... lens array, 52 ... head case,
60 ... light emitting layer, 70 ... hole transport layer, 80, 160 ... image forming apparatus,
DESCRIPTION OF SYMBOLS 100 ... Exposure apparatus, 101 ... Line head module

Claims (6)

An exposure apparatus comprising a line head in which a plurality of EL elements are arranged and a rotatable photosensitive drum exposed by light from the line head,
The line head includes a plurality of EL element rows formed such that the alignment direction of the EL elements is parallel to the rotation axis of the photosensitive drum,
A plurality of EL elements selected from among a plurality of EL elements corresponding between the plurality of EL element rows are configured to be exposed to the same drawing point on the photosensitive drum ,
An exposure apparatus , wherein the line head and a lens array that forms an image of light from the line head are integrally held in a head case while being aligned with each other to form a line head module . The exposure apparatus according to claim 1, wherein the line head and the lens array are integrally held in a head case by a sealant containing a getter agent. When the same drawing point on the photosensitive drum is exposed by the EL element, the gradation as the degree of exposure varies depending on how many EL elements of the plurality of EL elements are selected and exposed. The exposure apparatus according to claim 1, wherein the exposure apparatus is configured as described above. The exposure apparatus according to any one of claims 1 to 3 , wherein the gradation that is the degree of exposure is a pulse width gradation of a drive signal applied to the EL element. The line head exposure apparatus according to claim 1, wherein the EL element is configured to active matrix driving. As an exposure unit, an image forming apparatus comprising the exposure apparatus according to any one of claims 1 to 5.

Images