JPH0968839A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good color image even when temp. is changed due to generation of heat in an exposure element by specifying the difference in the coeffts. of linear expansion among a base body of a photosensitive drum, a holding member of an exposure device and a holding member of an exposure element. SOLUTION: The difference of the coeffts. of linear expansion among a transparent base body of a photoreceptor drum 10, the holding member 20 of an exposure device 12 and the holding member 12c of an exposure element is specified to 30×10<-6> deg.C<-1> as the max. Namely, as for the base body of the photoreceptor drum 10, an acryl resin having 60 to 80×10<-6> deg.C<-1> coefft. of linear expansion, preferably a polymer of methylmethacrylate monomers is used. As for the holding member 20 of the exposure device 12, an ABS resin having 70 to 90×10<-6> deg.C<-1> coefft. of linear expansion, heat resistance and strength is used. As for the holding member 12c of the exposure element which fixes the exposure element 12a, the same material as that of the holding member 20 of the exposure device is preferably used. Thereby, even when temp. elevates by 30 deg.C due to heat generation of an LED in the exposure element 12a and as a whole temp. changes by 5 to 60 deg.C, the drum 10 is in the position within the depth of focus of a 'Selfoc<(> R<)> ' lens 12b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, an F
In an image forming apparatus such as AX, a charging unit is provided around the image forming body,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus that arranges an image exposing unit and a developing unit, and particularly relates to an image forming unit in which a plurality of charging units, an image exposing unit and a developing unit are arranged around the image forming body. The present invention relates to an electrophotographic color image forming apparatus that forms a color image by superimposing toner images while rotating.

[0002]

2. Description of the Related Art Conventionally, as one method of forming a multi-color image, a color image is formed by sequentially performing charging, image exposure and development for each color within one rotation of one image forming body. Image forming apparatuses are known.

[0003] However, the above-mentioned color image forming apparatus is capable of forming a high-speed image in a method of forming a multi-color image, but the charging means, image exposing means and developing means within one rotation of the photosensitive member. Need to be installed in multiple sets,
The image exposure means may be contaminated by toner leaking from the adjacent developing means and impair the image quality, and in order to avoid this, it is necessary to increase the distance between the image exposure means and the developing device, so the diameter of the photoconductor is inevitably increased There is a drawback that the apparatus becomes large in size. For the purpose of avoiding this drawback, a photoconductor substrate is formed of a transparent material, a plurality of image exposure means are accommodated therein, and an image is exposed on the photoconductor layer formed on the outer periphery thereof through the substrate. An apparatus has been proposed, for example, in Japanese Patent Application Laid-Open No. 5-307307.

[0004]

In the apparatus according to the above-mentioned proposal, it is necessary that the image exposure means arranged inside the image forming body and the space between the image forming bodies are accurately positioned and maintained. Further, the plurality of image exposure units also need to be aligned and maintained with high accuracy by aligning the resist positions with each other.

However, as shown in FIG. 5, the cylindrical image forming body 310 is formed by the heat generation of the exposure element 312a as a light source of the image exposure light provided in the image exposure means 312, for example, the LED as shown in FIG. The cylindrical transparent substrate used is thermally expanded in the radial direction from the central axis of the image forming body indicated by the solid line arrow, and the diameter of the image forming body 310 is changed to cause image blurring and deteriorate the image quality. Similarly, the holding member 320 holding the image exposing means 312 also thermally expands in the radial direction indicated by the dotted arrow, and the relative difference in thermal expansion between the two causes the focus of the SELFOC lens 312b as an equal-magnification imaging element. If the image is out of depth, image blurring occurs and the image quality deteriorates.

That is, conventionally, as the holding member 320 for holding the image exposure means 312, it is said that a metal member having a small thermal expansion and a small deformation is preferable, and particularly an aluminum material (coefficient of linear expansion 23 × 10 ^-6 ° C ^-1) ) Is used, and an acrylic resin (coefficient of linear expansion of 60 to 80 × 10 ⁻⁶ ° C. ⁻¹ ) is used as a transparent substrate. For example, an acrylic member having a diameter of 180 mm is used as a transparent substrate of an image forming body. And a cylindrical aluminum material having a diameter of 140 mm is used as a holding member of the image exposure unit, the LED is used for room temperature (ambient temperature) 5 ° C to 30 ° C.
The temperature rise due to the heat generation of 30 ℃ is 5 ℃ as a whole
A temperature change of 60 ° C occurs, but at this time the diameter is 500 μm
A difference of (250 μm in the radial direction) occurs, and the maximum depth of focus of a bright SELFOC lens as a unity-magnification imaging element deviates from 200 μm, resulting in image blur.

Further, when assembled at room temperature, during use, the operating temperature of each member becomes 35 ° C. to 60 ° C. due to the temperature rise due to the heat generation of the LED, and the thermal expansion causes the resist between the plurality of image exposure means to go wrong. Problem arises.

The present invention solves this problem and improves the result.
Even if a temperature change occurs due to heat generated from the exposure element used in the image exposure means, the difference in thermal expansion between the substrate of the image forming body, the holding member of the image exposure means, and the exposure element holding member of the image exposure means is reduced. To provide an image forming apparatus in which the image forming apparatus is suppressed, and the image exposing means is attached so that the resist between the plurality of image exposing means is not misaligned due to thermal expansion even during use. It is an object of the present invention to provide a color image forming apparatus that can maintain accuracy and obtain a good color image.

[0009]

The above object is to provide a cylindrical image forming body for forming a latent image, a charging means and a developing means outside the image forming body, and a plurality of image exposing means inside. By disposing the image forming member, the image forming member is charged by the charging unit, image exposed by the image exposing unit, and a toner image is formed on the toner image by developing by the developing unit. In a color image forming apparatus for forming an image by superimposing the toner image on an image forming body, the image exposing means is provided with an exposure element holding member for holding an exposure element, and the base of the image forming body and the image are formed. The difference in the linear expansion coefficient of at least two members of the holding member that holds the exposing device and the exposure element holding member that is provided in the image exposing device is 30 × 10 ^-6 ° C ^-1 or less at maximum. To It is achieved by color image forming apparatus (first invention).

Further, the object is to provide a cylindrical image forming body for forming a latent image, a charging means and a developing means outside the image forming body, and a plurality of image exposing means inside. On the image forming body, the image forming body is charged by the charging unit, image exposed by the image exposing unit, and a toner image is formed on the toner image by the developing unit. In a color image forming apparatus for forming an image by superimposing the toner image on the image forming means, the image exposing means is attached to a holding member at a temperature of 3
The present invention is achieved by a color image forming apparatus characterized by being performed in a member and an environment of 5 ° C to 60 ° C (second invention).

[0011]

EXAMPLES The following examples will be described as examples of the present invention. The image forming process and each mechanism of the color image forming apparatus of this embodiment will be described with reference to FIGS.
1 is a sectional configuration diagram of a color image forming apparatus of this embodiment, FIG. 2 is an enlarged view of a main part of a central portion of FIG. 1, and FIG.
FIG. 4 is a diagram showing details of an image exposure unit.

In the color image forming apparatus of this embodiment, a photosensitive drum having a conductive layer and a photosensitive layer provided on the outer peripheral surface of a transparent substrate is used as an image forming body, and an image is formed inside the photosensitive drum. It has a structure in which an exposure unit is arranged and an image forming process unit such as a charger, a developing unit, a transfer unit, a charge eliminator, and a cleaning device is arranged outside.

The photosensitive drum 10, which is an image forming body, is provided with a cylindrical substrate formed of a transparent member of transparent acrylic resin inside, and a transparent conductive layer, an a-Si layer or an organic photosensitive layer (OPC). ) Is formed on the outer circumference of the substrate, and is rotated clockwise in the state of being grounded as shown by the arrow in FIG.

In this embodiment, it is sufficient that the photoconductive layer of the photosensitive drum has an exposure light amount capable of imparting an appropriate contrast. Therefore, the light transmittance of the transparent substrate of the photosensitive drum in this embodiment does not need to be 100%, and may have a characteristic that some light is absorbed when the exposure beam is transmitted. As a material of the light-transmitting substrate, an acrylic resin, particularly one obtained by polymerization using a methyl methacrylate monomer is preferably used because it is excellent in transparency, strength, precision, surface properties, etc. Various translucent resins such as acryl, fluorine, polyester, polycarbonate, polyethylene terephthalate and the like can be used. The light-transmitting conductive layer was made of indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, Ni, Al, etc. A metal thin film is used, and as a film forming method, a vacuum vapor deposition method, an active reaction vapor deposition method, various sputtering methods, various CVs.
D method, dip coating method, spray coating method and the like are used.
Further, as the photoconductor layer, amorphous silicon (a
-Si) alloy photosensitive layer, amorphous selenium alloy photosensitive layer, and various organic photosensitive layers (OPC) can be used.

The scorotron charger 11, which is a charging means, is used in the image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K), and the above-mentioned organic photosensitive member of the photosensitive drum 10 is used. The body layer is charged by a control grid held at a predetermined potential and a corona discharge by a discharge wire to give a uniform potential to the photoconductor drum 10.

An exposure device 12 as an image exposure means for each color.
Are FL (phosphor emission), EL (electroluminescence), PL arranged in the axial direction of the photoconductor drum 10.
(Plasma discharge), LED (light emitting diode) and other linear light exposure elements arranged in an array, or LISA
(Photomagnetic effect optical shutter array), PLZT (transmissive piezoelectric element shutter array), LCS (liquid crystal shutter), and the like. An exposure element 12a that emits exposure light such as a linear exposure element in which elements having an optical shutter function are arranged. And a SELFOC lens 12b as an equal-magnification imaging element, an exposure element 12a,
The unit is configured as a unit attached to an exposure element holding member 12c that holds a SELFOC lens 12b as a unity-magnification image forming element, and is attached to a holding member 20 that holds the exposure device provided inside the photosensitive drum 10. The image signals of the respective colors stored in the memory are sequentially read out from the memory and input as electric signals to the exposure device 12 for the respective colors. The emission wavelength of the light emitting device used in this example is in the range of 600 to 900 nm.

The developing device 13, which is a developing means for each color, contains one-component or two-component developers of yellow (Y), magenta (M), cyan (C) and black (K), respectively, and is exposed to light. A developing sleeve 131 is provided which rotates in the same direction with a predetermined gap from the peripheral surface of the body drum 10.

The developing device 13 for each of the colors described above applies the developing bias voltage to the electrostatic latent image formed on the photoconductor drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure device 12. Reverse development is performed in a non-contact state by a non-contact developing method.

As the original image, an image read by an image pickup device of an image reading apparatus separate from this apparatus or an image edited by a computer is temporarily stored as an image signal for each color of Y, M, C and K. Store and store in.

At the start of image recording, a photoconductor drive motor (not shown) is rotated to rotate the photoconductor drum 10 in the clockwise direction in FIG. 1, and at the same time, a Y scorotron charger arranged on the left side of the photoconductor drum 10. The charging action of 11 starts the application of the potential to the photoconductor drum 10.

After the photoconductor drum 10 is applied with a potential, a first color signal, that is, Y
The exposure by the electric signal corresponding to the image signal is started, and the electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface by the rotational scanning of the drum.

The latent image is reversal-developed by the Y developing device 13 with the developer on the developing sleeve in a non-contact state, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.

Next, the photoconductor drum 10 is charged on the yellow (Y) toner image and further by a charging action of a magenta (M) scorotron charger 11 arranged on the left side of the photoconductor drum 10 and above Y. Exposure is performed by the electric signal corresponding to the second color signal of the M exposure device 12, that is, the image signal of M, and the yellow (Y) color is developed by the non-contact reversal development by the developing device 13 of M. A magenta (M) toner image is sequentially superposed on the toner image.

A cyan (C) scorotron charger 1 disposed on the photosensitive drum 10 by the same process.
Further, a cyan (C) toner image corresponding to the third color signal is generated by the exposure devices 12 of C and C and a developing device 13 of C, and a black (K) color image is disposed below C on the right side of the photosensitive drum 10. ), A black (K) toner image corresponding to the fourth color signal is sequentially superposed by the scorotron charger 11, the exposure device 12, and the developing device 13, and the peripheral surface of the photosensitive drum 10 is rotated within one rotation. A color toner image is formed on top.

The exposure of the organic photosensitive layer of the photoconductor drum 10 by these Y, M, C and K exposure devices 12 is performed from the inside of the drum through the transparent substrate. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and the same exposure as the image corresponding to the first color signal is performed. It is possible to form an electrostatic latent image.

Developers for replenishment of each color are replenished from the replenishing tank 81 to the developing device 13 of the corresponding color, and the developing sleeve 131.
Is supplied to. The developing device 13 has a predetermined value, for example, 100 μm to 1 with respect to the photosensitive drum 10 by an abutting roller (not shown).
The developing sleeve 13 is maintained in a non-contact state with a gap of 000 μm, and the developing sleeve 13 is used for the developing action of the developing device 13 for each color.
A developing bias in which a direct current or an alternating current is applied to 1 is applied, jumping development is performed by a one-component or two-component developer accommodated in the developing device, and the transparent conductive layer is grounded to the photosensitive drum 10. Non-contact reversal development is performed in which a DC bias having the same polarity as that of the toner is applied to attach the toner to the exposed portion.

A transfer sheet P, which is a transfer material, is sent out from a paper feed cassette 15 which is a transfer material storage means, and is conveyed to a timing roller 16. The color toner image formed on the peripheral surface of the photoconductor drum 10 is transferred to the photoconductor drum 10 by driving the timing roller 16 in the transfer device 14a.
It is transferred onto a transfer paper P which is a transfer material that is fed in synchronization with the above toner image.

The transfer paper P on which the toner image has been transferred is removed from the charge by the static eliminator 14b and separated from the peripheral surface of the drum, and is then transferred to the fixing device 17 by the transfer belt 14e which is a transfer unit. Heating in the fixing device 17
After the pressure-bonded toner is fused and fixed on the transfer paper P, it is ejected from the fixing device 17 and is conveyed by the paper ejection conveyance roller pair 18 a to pass through the paper ejection rollers 18 and the toner image surface on the tray on the upper side of the apparatus is the lower surface. And then discharged.

On the other hand, the photosensitive drum 10 from which the transfer paper is separated
In the cleaning device 19, the surface of the photoconductor drum 10 is rubbed by the cleaning blade 19a in the cleaning device 19 to remove the residual toner, and the toner image of the original image is continuously cleaned or temporarily stopped, or the toner image of the new original image is temporarily stopped. Take formation. The waste toner scraped off by the cleaning blade 19a and the cleaning roller 19b is discharged to the waste toner container 82 through the toner transport screw 19c and the toner transport pipe 19d. After the cleaning is completed, the cleaning blade 19a and the cleaning roller 19b are kept apart from the photoconductor drum 10 in order to prevent damage to the photoconductor drum 10.

An acrylic resin having a linear expansion coefficient of 60 to 80 × 10 ^-6 ° C. ^-1 , preferably a methacrylic acid methyl ester monomer polymer is used as the transparent substrate of the photosensitive drum 10 shown in FIG. Holding member 20 for holding
As an ABS resin having heat resistance and strength, and having a linear expansion coefficient difference of 30 × 10 ⁻⁶ ° C. ⁻¹ or less as compared with an acrylic resin, for example, an ABS resin having a linear expansion coefficient of 70 to 90 × 10 ⁻⁶ ° C. ⁻¹ , Polycarbonate resin having a linear expansion coefficient of 60 to 80 × 10 ⁻⁶ ° C. ⁻¹ is used.

The ABS resin, the polycarbonate resin, etc. used as the holding member 20 have a difference in linear expansion coefficient of 30 × 10 ^{−6 as} compared with the acrylic resin used for the photosensitive drum 10.
A hexagonal columnar ABS resin having a temperature of ^-1 or less, for example, an acrylic resin member having a diameter of 180 mm as the transparent substrate of the photosensitive drum 10, and a side having a passing diameter D of 140 mm serving as the holding member 20 of the exposure device 12. In the case of using, the exposure element 1 is used at room temperature (ambient temperature) of 5 ° C. to 30 ° C.
Even if the temperature rise due to the heat generation of the LED as 2a is 30 ° C. and the temperature change of 5 ° C. to 60 ° C. occurs as a whole, the photosensitive drum 10 thermally expands in the radial direction from the central axis of the photosensitive drum indicated by the solid arrow. The difference in expansion and contraction due to thermal expansion between the cylindrical transparent base of acrylic resin and the holding member 20 of ABS resin that thermally expands in the radial direction shown by the dotted arrow is suppressed to 200 μm or less in the radial direction, and the SELFOC lens 12
A good image can be obtained without deviating from the depth of focus of b.

Further, as shown in FIG. 3, the SELFOC lens 12b is fixed to the exposure element holding member 12c by an adhesive indicated by a black circle and the exposure element 12a is indicated by an oblique line. The exposure element holding member 12c is fixed to the holding member 20 with an adhesive or screws. The member used for the exposure element holding member 12c is preferably the same member as the member used for the holding member 20 that holds the exposure device 12, for example, AB having a linear expansion coefficient of 70 to 90 × 10 ⁻⁶ ° C. ⁻¹ .
S resin or polycarbonate resin having a linear expansion coefficient of 60 to 80 × 10 ⁻⁶ ° C. ⁻¹ is used. Therefore, the photosensitive drum 10
The difference in the coefficient of linear expansion is 30 × 10 ⁻⁶ ° C. ⁻¹ or less, and the difference in expansion and contraction due to thermal expansion from the transparent acrylic resin substrate used for the photosensitive drum 10 is the SELFOC lens 12b. A good image can be obtained without deviating from the focal depth of. A holding member 2 that holds the substrate of the photoconductor drum 10 and the exposure device 12 by combining the above members.
0 and the exposure element holding member 1 provided on the exposure element 12a
The difference in the maximum linear expansion coefficient of the three parties of 2c is also 30 × 10 ^-6 ℃ ^-1
It is preferable to be suppressed below.

A holding member 2 for holding the exposure device 12
0 and the exposure element holding member 12c of the exposure device 12 are the same member, the holding member and the exposure element holding member in the axial direction of the photoconductor drum 10 shown by the arrow in FIG. There is no difference in expansion and contraction, and the exposure elements 12a arranged in the axial direction of the photoconductor drum 10 are not deformed.
A length of at least 250 mm to 300 mm is required, and a difference in expansion and contraction due to thermal expansion is likely to occur, so that there is no difference in expansion and contraction in the axial direction of the photoconductor drum 10 and the exposure element is not deformed.

FIG. 4 shows how to attach the exposure device as the image exposure means to the holding member.

The exposure device 12 added to the gripping portion H of the fine movement stage S as a mounting jig is shown in FIG. 4B with respect to the holding member 20 mounted on a fixing member (not shown). , Z-axis movement, and y, z-axis rotation directions are adjustable by fine movement stage S. In this state, the exposure device 12 is fixed to the holding member 20 with an adhesive shown by diagonal lines in FIG.

On the other hand, the exposure apparatus 12 has a room temperature (ambient temperature) of 5
C. to 30.degree. C., the temperature rise due to heat generation of the LED as the exposure element 12a is 30.degree. C., which is used in the temperature range of 5.degree. C. to 60.degree. C. as a whole. The temperature (operating temperature) is 35 ° C-6
It becomes 0 ° C.

Therefore, the holding member 2 of the exposure apparatus 12 described above.
When assembling to 0, for example, a heater 21 is incorporated in the holding member 20 to detect the temperature of a thermistor 22 attached to the holding member 20 so that the power is supplied to the power source (not shown) so that the temperature is 35 ° C. to 60 ° C. This is performed by controlling the connected heater 21. 35 ° C to 6 by thermistor 22
The temperature is controlled to a set temperature T1 within the range of 0 ° C. Furthermore,
By driving the LED as the exposure element 12a of the exposure device 12 fixed to the holding member 20 with an adhesive and detecting the temperature of the thermistor 23 attached to the exposure device 12, the LED connected to the power supply and the control unit (not shown) is detected. Take control. Also in this case, the temperature is controlled by the thermistor 23 to the set temperature T2 within the range of 35 ° C to 60 ° C.

A heater (not shown) may be provided in the exposure device 12 instead of lighting the exposure element 12a. A heater (not shown) for setting the environmental temperature may be separately provided.

The set temperatures T1 and T2 are experimentally determined by the structure, dimensions, materials, etc. of the holding member 20, the exposure device 12, the photosensitive drum 10, and the like. Therefore, T1 and T
2 may be equal. Further, the heater may be provided on at least one of the holding member 20 and the exposure device 12. Further, the base member of the photosensitive drum, the holding member for holding the exposure device, and the exposure element holding member provided in the exposure device are made of the same resin member as described in FIGS. The difference in expansion and contraction due to expansion can be further reduced.

Since the exposure apparatus as the image exposure means is attached and assembled to the holding member at the operating temperature of the exposure apparatus, the registration between the plurality of exposure apparatuses during the image formation of the color image forming apparatus is guaranteed. A good image can be obtained.

[0041]

According to the present invention, the holding member for holding the transparent substrate used for the photosensitive drum or the image exposing means or the exposing element holding member provided for the image exposing means by the heat generation of the exposing element. The difference in expansion and contraction due to thermal expansion in the radial direction of the central axis of the photoconductor drum is suppressed within the depth of focus of the SELFOC lens, which is an equal-magnification imaging element, and good images can be obtained without image blurring. can get.

According to the fourth or fifth aspect of the invention, since the image exposing means is attached to the holding member in the vicinity of the operating temperature of the image exposing means, a plurality of image exposing means are being formed during image formation in the color image forming apparatus. The resist is guaranteed and a good color image can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus of this embodiment.

FIG. 2 is an enlarged view of a main part of a central portion of FIG.

FIG. 3 is a diagram showing details of an image exposure unit.

FIG. 4 is a diagram showing how to attach an exposure device as an image exposure means to a holding member.

FIG. 5 is a diagram showing a conventional problem.

[Explanation of symbols]

 10 Photoreceptor Drum 12 Exposure Device 12a Exposure Element 12b SELFOC Lens 12c Exposure Element Holding Member 20 Holding Member 21 Heater 22,23 Thermistor S Fine Movement Stage

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor ▲ Hama ▼ Shuta Ta, 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock company (72) Inventor Toshihide Miura 5-14-14 Midori-cho, Koganei-shi, Tokyo

Claims (5)

[Claims] 1. A cylindrical image forming body for forming a latent image, a charging means and a developing means outside the image forming body, and a plurality of image exposing means inside the image forming body. Are sequentially charged by the charging means, image-exposed by the image exposing means, and formed with a toner image by the developing means to develop the toner image on the image forming body. In a color image forming apparatus for forming an image by superimposing the two, the image exposure unit is provided with an exposure element holding member for holding an exposure element, and a base member of the image forming body and a holding member for holding the image exposure unit. A color image forming apparatus, wherein a difference in linear expansion coefficient of at least two members from the exposure element holding member provided in the image exposure unit is 30 × 10 ⁻⁶ ° C. ⁻¹ or less at maximum. 2. An acrylic resin as a base of the image forming body, and an AB as the holding member and the exposure element holding member.
The color image forming apparatus according to claim 1, wherein an S resin or a polycarbonate resin is used. 3. The color image forming apparatus according to claim 1, wherein the image exposure unit is provided with the linear exposure elements arranged in the axial direction of the image forming body. 4. A cylindrical image forming body for forming a latent image, a charging means and a developing means outside the image forming body, and a plurality of image exposing means inside the image forming body. Are sequentially charged by the charging means, image-exposed by the image exposing means, and formed with a toner image by the developing means to develop the toner image on the image forming body. In a color image forming apparatus for forming an image by superposing the above, the color image forming apparatus is characterized in that the image exposing means is attached to a holding member in a member having a temperature of 35 ° C. to 60 ° C. and in an environment. 5. The color image forming apparatus according to claim 4, wherein a heater is provided on at least one of the image exposure unit and the holding member.