JPH01259385A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of transparency of a transparent dust- proof plate, in a multicolor toner image forming device for forming repeatedly each color toner image by setting a distance between the transparent dust-proof plate provided on a latent image forming laser beam use slit and an image forming body to a necessary value. CONSTITUTION:An image forming body 60 is irradiated by a laser beam 52 corresponding to an image passing through a reflecting mirror 54 through a slit 58, and an electrostatic latent image is formed on the forming body 60, converted to a developed image by a color toner and transferred. By such repetition by each color toner, a multicolor toner image is transferred and formed. A distance h3 between the surface of dust-proof glass 55 of a transparent dust-proof plate provided on the opposite side of the forming body 60 of this slit 58 and the body 60 is set in advance to 7-30mm of a value to which scattered toner does not adhere, and the deterioration of transparency of the glass 55 is prevented satisfactorily. As a result, a distinct multicolor image can be formed stably and satisfactorily.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an image forming system in which color toner images are superimposed on an image forming member to form a multicolor toner image, which is then transferred onto a transfer paper. The present invention relates to a forming apparatus, particularly an image forming apparatus that prevents toner scattering during spot exposure of second and subsequent colors.

[Background of the Invention] An image forming apparatus that records an image using a laser beam modulated with an image signal is disclosed in Japanese Patent Application Laid-Open No. 59-193.
415 Publication".

FIG. 4 is a configuration diagram showing an example of the image forming apparatus disclosed in this publication.

In the figure, 1 is an image forming body (photosensitive drum);
Facing the circumferential surface of the image forming body 1 or in the vicinity of L, there are provided a charging device 2, a developing device 3, a paper feed cassette 4, a paper feed roller 5, a registration roller 6, a transfer device 7, and a fixing device 8. , cleaner 9, etc. are all placed.

10a is an optical device 10 that houses one nose beam optical system.
The housing includes a laser oscillator 11, and a polygon mirror 12 that is rotationally driven by a drive motor 13 deflects a laser beam in the main scanning direction.

The deflected laser beam is guided to the surface of the image forming body 1 through the f/theta lens 14, the filter 15, the reflecting mirror 6, and the transparent dustproof plate 17, and image exposure is performed.

Here, the transparent dustproof plate 17 is located at the tip of the opening of the optical device housing 10a as shown in the figure, and is located at the tip of the opening of the optical device housing 10a.
The optical system inside the housing 10a is prevented from being contaminated by toner and other dust.

Incidentally, in recent years, image forming apparatuses have been proposed that scan an image forming body with a laser beam modulated by image information and record a multicolor image using an electrophotographic method. The multicolor image forming apparatus disclosed in Japanese Patent Publication No. 76766 is excellent in that the apparatus is compact, there is no transfer deviation of each color toner image, and high image quality can be obtained.

In the image forming apparatus described in this publication, by repeating uniform charging, spot exposure with a laser beam, and reversal development with a developer containing color toner, multicolor toner is formed on the image forming body. An image is formed and transferred onto transfer paper at once to form a multicolor image.

[Problems to be Solved by the Invention] Incidentally, in an image forming apparatus that performs color recording by multicolor development, as described above, spot exposure with a laser beam and reversal development are repeated to create a multicolor image on the image forming body. Since a color toner image is formed, there is a problem in that the optical device 10 is contaminated by toner scattering.

In particular, the influence of contamination on the transparent dustproof plate 17 is large. The reason for this will be explained below.

That is, in the image forming process of the image forming apparatus as described above, when the toner image formed in the first image forming process is recharged and there is spot exposure near the image, the electric field near the toner image increases. Since the distribution changes rapidly, the toner particles fly off due to the repulsive force between the toner particles and adhere to the area where the Coulomb force acts.

For example, it adheres to the tip of the housing 10a of the optical device 10 facing the image forming body 1, the transparent dustproof plate 17, and the like.

A particular problem with such toner adhesion is the adhesion to the transparent dustproof plate 17. This is because toner adhesion to the transparent dustproof plate 17 causes an insufficient amount of laser beam light to be applied to the image forming body 1, resulting in insufficient exposure. When underexposure occurs,
The effects of toner adhesion are significant as image quality deteriorates.

Deterioration in the transparency of the transparent dustproof plate 17 also accompanies exposure unevenness.

FIG. 5 is a diagram for explaining the cause of such toner scattering.

The vertical axis shown in FIGS. 5A to 5E indicates the negative potential of the surface of the image forming member 1, which is a potential obtained by uniformly charging (negatively charging) the surface with the charger 2.

The horizontal axis indicates the position of the surface of the image forming body 1.

Figure A shows a state in which the surface of the image forming body 1 is uniformly charged to a potential of -E volts (for example, -500V to -700V) by the charger 2.

Figure B shows that the range indicated by La on the surface of the image forming body 1 is exposed, and the potential of that part increases, for example, to about -50V to -100V due to the exposure.

In Figure C, the exposed portion La of the image forming body 1 is the developing device 3.
When passing through the toner, the negatively charged toner from the developing sleeve 3a, which has approximately the same potential as the uniformly charged potential of the image forming member 1, is directed toward the exposed portion L a of the image forming member 1. This shows a state in which the toner flies, adheres to the exposed area La, and is developed.

The surface of the image forming body 1 on which the first color toner image has been formed is uniformly charged again by the charger 2 for the second time while the toner image is still formed on the surface.

The same figure shows the potential during the second uniform charging.

Next, image exposure is performed using an image signal corresponding to the second color.

11E shows a state in which image exposure is performed in the vicinity Lb of the first color toner image, and the potential of that portion Lb is higher than the potential of the initially exposed portion La.

By the way, each toner particle of the first color toner image adheres to the surface of the image forming body 1 mainly due to the action of Coulomb force and van der Waals force.

However, since the toner particles are charged with the same polarity, a repulsive force acts between the toner particles.

On the other hand, since toner particles are negatively charged, if there is a region with a higher potential than the current position, the toner particles will try to move toward the higher potential while following the direction of the electric field formed there. Force acts.

When this force for movement exceeds the adhesion force (=1) on the surface of the image forming body, the toner flies toward the side with a higher potential.

FIG. The figure shows how the amount adheres to the optical device 1o, which has the same high potential.

Therefore, especially when toner adheres to the transparent dust-proof plate 17, the transparency of the transparent dust-proof plate 17 decreases, thereby reducing the amount of laser beam light reaching the surface of the image forming body 1, resulting in insufficient exposure and uneven exposure. occurs.

In this case, the quality of the recorded image deteriorates, and recording of a clear color image is hindered.

Therefore, the present invention proposes an image forming apparatus that solves these conventional problems with a simple structure and prevents toner from adhering to a transparent dustproof plate.

[Means for Solving Problems] In order to solve the above-mentioned problems, in the present invention, a laser beam 11 modulated by an image signal is spot-exposed on an image forming body that is uniformly charged. By repeating the steps of forming an electrostatic latent image and developing the electrostatic latent image to form a color toner image multiple times, a multicolor toner image is formed on the image forming body. In an image forming apparatus that transfers a laser beam onto a transfer paper at once, a slit that forms a path for the laser beam is provided in a portion of the optical device that faces the surface of the image forming body, and a A transparent dustproof plate is provided in the opening on the opposite side, and the gap between the transparent dustproof plate and the image forming body is set to a distance that prevents charged toner from adhering.

[Function] The transparent dustproof plate 55 is attached to the opening side of the slit 58 on the opposite side to the image forming body 60.

The gap between the transparent dustproof plate 55 and the image forming body 60 is set to 7 mm or more and 30 mm or less.

This is because, as shown in FIG. 3, at a distance of 7 mm or less, the Coulomb force is still large, so much toner adheres, and the transparency of the transparent dustproof plate 55 deteriorates significantly.

When the thickness exceeds 7 mm, the Coulomb force decreases significantly, and the amount of toner adhesion decreases accordingly. This greatly improves transparency.

Further, if the transparent dustproof plate 55 is attached at a distance of 30 mm or more, the optical device 10 becomes larger although the transparency is not improved much.

[Embodiment] Next, an example of an image forming apparatus according to the present invention will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 1 is a sectional view showing an example of a color image forming apparatus to which the present invention can be applied, and FIG. 2 is a sectional view of a main part of a laser beam optical device 1o incorporated in this image forming apparatus.

In FIG. 1, A is a reading unit, B is an old unit, C is an image forming section, and D is an abrasive supply section.

The reading unit I-A is a unit for optically reading image information of a document.

21 is the platen glass, and the original 22 is the platen glass 2.
placed on top of 1.

The document 22 is illuminated by fluorescent lamps 25 and 26 provided on a carriage 24 that moves on a slide rail 23.

The movable mirror unit 28 includes a second mirror 29a and a third mirror 29a.
A mirror 29b is provided and moves on the slide rail 23, and in combination with the first mirror 27 provided on the carriage 24, image information (light image) of the original 22 is guided to the lens reading unit 38.

The carriage 24 and the movable mirror unit 28 are moved by pulleys 31, 32, 33, and 34, which are driven by a stepping motor 30 via a wire 35, respectively.
are driven in the same direction at a speed of V.

Standard white plates 36 are installed on the back side of both ends of the platen glass 21.
．． 37, and is configured so that a standard white signal can be obtained before the start of document reading scanning and after the end of scanning.

The lens reading unit 38 includes a lens 39 and a prism 4.
2. The first installation is on the board 40. A CCD 41 for red light, a second mounting board 42, and a CCD 43 for cyan light.

First mirror 27, second mirror 29a1, third mirror 29b
The original optical image transmitted with the optical path deflected by the lens 3
8, and is separated into a red light image and a cyan light image by a prism 44, which in this example includes a gicchroic mirror.

(7) The red color-separated image is focused on the light-receiving surface of the CCD 41 for red light and photoelectrically converted.Similarly, the cyan color-separated image is focused on the light-receiving surface of the CCD 43 for cyan light. A photoelectrically converted image signal is obtained from this image.

Fluorescent lamps 25 and 26 are commercially available warm white fluorescent lamps to prevent emphasis or attenuation of specific wavelengths based on the light source when reading color documents, and to prevent flickering, 4.
It can be lit and controlled with a high frequency power source of about 0kHz. At the same time, in order to maintain a constant temperature of the tube wall or promote warm-up,
It is kept warm by a POSISTOR heater.

Although not shown, the image signals output from the CCDs 41 and 43 are processed by the image processing section, and in this example, red, blue, and black color signals are output, and these are input to the writing unit.

Semiconductor laser emission 11N provided in writing unit B
A laser beam 52 generated by rA (not shown) is deflected by a polygon mirror 51 rotated by a drive motor 50.

The laser beam 52 deflected by the polygon mirror 51 is
After passing through the f-O lens 53a and the tilt angle correction lens 53b, the optical path is bent by the reflecting mirror 54 and reaches the surface of the image forming body 60. The laser beam 52 is a polygon mirror 51
Therefore, the laser beam 52 scans the image forming body 60 and writing is completed.

The reflecting mirror 54 is completely housed within the optical device 56.

When scanning is completed, the laser beam 52 is detected by an index sensor (not shown), and modulation of the beam by the first color signal is started in synchronization with the output of the index sensor.

The modulated laser beam 52 scans over the image forming body 60 which has been charged in advance to -500 to -700V by the charger 61. A latent image corresponding to the first color is formed on the drum surface by the main scanning by the laser beam 52 and the sub-scanning by the rotation of the image forming body 60.

This latent image is developed by a developing device 63 filled with red toner, for example, to form a toner image on the drum surface.

The toner image attached to the drum surface passes under a cleaning device 66 that is controlled to be separated from the image forming drum surface while being held on the drum surface, and enters the next copy cycle. The image forming body drum 60 is charged again by the charger 61.

Next, the second color signal output from the image processing section is input to the writing unit B, and is written on the drum surface in the same manner as the first color signal to form an electrostatic latent image. be done.

The electrostatic latent image is developed by a developer 64 loaded with toner of a second color, for example blue. This blue toner image is formed over the already formed red toner image.

A black toner image is then formed by developing the electrostatic latent image formed by writing the third color signal from the image processing section. 65 indicates a developing device containing this black toner.

The black toner image is formed to overlap the above-mentioned red toner image and blue toner image.

Note that the developing devices 63 to 65 constitute an image forming section C. 6
3a, 64a, and 65a indicate developing rollers (developing sleeves) of each developing device.

62 is a bias power supply, which connects the developing rollers 63a and 6.
A predetermined AC bias and DC bias are applied to 4a and 65a. By applying this bias, the toner in the developing device can be caused to fly toward the image forming body 60.
Electrostatic images can be developed in a non-contact manner and in a reversal manner.

The AC bias for non-contact development of toner is 1~
A voltage of about 5 KV (peak-to-peak value) is used, and a frequency of about 100 Hz to 20 KHz is used.

Further, the DC bias for reversal development has the same polarity as the electrostatic image and is set to a voltage close to this polarity.

The thus developed red toner image based on the first color signal, blue toner image based on the second color signal, and black toner image based on the third color signal are superimposed on the image forming body [30]. A multicolor toner image is formed.

On the other hand, recording paper P is fed from a cassette 80 in the paper feeding section with the timing adjusted by the paper feeding device 81 . A multicolor toner image is transferred onto the fed recording paper P by the transfer device 70.
After being electrostatically transferred using a separator 71 and separated by a separator 71, it is heated and fixed by a heat roll fixing device 72, and then the paper is discharged.

The image forming body 60 after the transfer is cleaned by a blade 67 of a cleaning device 66 and is prepared for the next image formation.

The auxiliary roller 69 is used to remove residual toner left behind on the surface of the image forming body 60 when the blade 67 is released from pressure contact with the image forming body 60. The collection roller 68 is a metal roller for collecting the toner scraped off by the blade 67, and is normally applied with a voltage of opposite polarity to that of the toner, so that it attracts and collects the toner.

Next, an example of a laser beam optical device 56 for writing the modulated laser beam 52 onto the image forming body 60 will be described with reference to FIG.

In the figure, the optical device 56 is attached to the lower casing 57.
a, and a rectangular parallelepiped case 57 including an upper casing 57b.
is configured.

A lens 53b for correcting an inclination angle and a reflecting mirror 54 are housed and fixed at predetermined positions in the case 57, respectively.

A slit 58 as shown in the figure is formed in the lower casing 57a through which the laser beam whose optical path is deflected by the reflection mirror 54 is transmitted. A slit plate 57e as shown in the figure is provided on the lower surface of the lower casing 57a including the slit 58.
can be installed.

A transparent dustproof plate as shown in the figure, that is, dustproof glass 55 is attached to the upper open end side of the slit 58 formed in the lower casing 57a so as to cover it.

As shown in the figure, the dustproof glass 55 is held at a slight inclination (for example, 1 to 2':') with respect to the lower casing 57a.

This is because a part of the laser beam 52 that is completely irradiated onto the image forming body 60 through the dust-proof glass 55 is reflected on the surface of the dust-proof glass 55, causing mutual interference between the irradiated light and the reflected light, and the interference light is This is to prevent interference fringes from being formed by irradiating the image forming body 60 again.

If the dustproof glass 55 is arranged at an angle, the dustproof glass 55
The reflected light from the surface can be diverted out of the optical path of the irradiated light,
No interference fringes occur.

Note that the lower casing 57a may be a plate for integrally supporting the laser beam optical system including the polygon mirror 51 and the like. This plate can be a metal plate or a plastic plate.

The slit plate 57c is a plate for forming, together with the lower casing 57a, a slit 58 through which the laser beam 52 passes. A plastic plate or a metal plate can also be used for this.

59 is an opening of the slit plate 57C facing the image forming body 60.

As described above, in an image forming apparatus that forms a multicolor toner image on the image forming member 60 by a reversal development method, an image forming apparatus that carries a toner image obtained by first developing is used. When the object 60 is exposed to the laser beam 52 after recharging, the image forming object 60 is deposited due to the sudden change in the potential distribution as explained in FIG.・The transparent dust-proof plate becomes dirty due to the spraying of the powder, which causes insufficient light intensity.
Uneven exposure is occurring.

In this invention, in order to solve such problems,
A slit 58 is provided, and a transparent dustproof plate, that is, a dustproof glass 55 is provided at the opening end of the slit 58 on the reflection mirror 54 side so as to cover this opening end.

According to repeated experiments conducted by the inventors, the gap h3 between the dustproof glass 55 and the image forming body 60 is 7 mm or more and 30 mm.
The distance is set as follows.

The reason for this is explained below.

FIG. 3 is a graph showing changes in the transparency of the dustproof glass 55 when an image is formed using the multicolor image forming apparatus of FIG. 1 in which the optical device 56 of FIG. 2 is incorporated.

In the figure, the horizontal axis is the distance h between the dustproof glass 55 and the image forming body 60.
3 (ROM), and the vertical axis represents the transparency percentage when the dustproof glass 55 is not contaminated with toner as 100.

In the figure, the transparency was measured when the distance h3 was changed to 3.5.7, 10.20, and 30 mm, and image formation was performed 100 times each time.

As is clear from the figure, when the facing distance h3 is less than 7 mm, the transparency decreases rapidly and practicality is lost. When the thickness exceeds 7 mm, toner adhesion rapidly decreases and transparency increases, reaching a level of transparency that does not pose any practical problem.

The reason for this is not necessarily clear, but it can be inferred that it is because the Coulomb force acting between the image forming body 60 and the dustproof glass 55 decreases rapidly when the facing distance h3 becomes 7 mm or more.

Further, even if the facing distance m h 3 exceeds 30 mm, the transparency hardly changes. However, if such a facing distance is used, the optical device 56 will become unnecessarily large due to its design, thus requiring a compact design of the device.

Roughly speaking, if the facing distance 11111h3 is selected to be 30 mm or more, the distance h4 between the reflection mirror 54 and the image forming body 60 becomes larger, and the bus of the laser beam 52 from the reflection mirror 54 to the image forming body 60 becomes larger. growing.

For this reason, the blurring of the focal point of the beam due to the vibration of the reflection mirror 54 accompanying the mechanical vibration of the image forming apparatus becomes large, and image blurring is likely to occur, resulting in a decrease in resolution when a multicolor image is formed. It ends up.

For this reason as well, it is preferable that the facing distance h3 is 30 mm or less.

Therefore, in this invention, a reasonable facing distance T'S that can be adopted is
h3 is selected to be 7 to 30 mm as described above.

The transparency of the dustproof glass 55 is considered to be influenced by the following technical matters in addition to the facing distance m h s to the dustproof glass 55 described above.

That is, first, the distance 1tz between the opening 59 of the slit 58 and the image forming body 60, the height h2 of the slit 58, the slit diameter φ, etc. are also considered to be related to the contamination of the dustproof glass 55. Therefore, the selection will be made as follows.

The distance h1 is selected to be 3 to 10 mm. Among them, 5 to 10
It is preferable to fall within the range of mm.

With this selection, contamination due to toner scattering within the slit 58 and around the slit opening 59 of the optical device 56 could be suppressed to a level that does not pose a practical problem.

This is because when there is a gap of 5 mm or more, the Coulomb force acting from the image forming body 60 to the slit opening 59 becomes weaker.
As a result, the toner of the previous toner image on the image forming body 60 is
This reduces the amount of toner scattering to the spot exposure area (on the contrary, if the slit opening 59 is too close to the surface of the image forming body 60, the amount of toner scattering to the spot exposure area increases due to a synergistic effect), and It is presumed that this is because the adhesion force of the scattered particles to the slit opening 59 becomes weaker.

Next, the height h2 of the slit 58 is S~18 mm. The slit diameter φ is 3 to 10 mm.

When the height and slit diameter of the slit 58 are selected within the above-mentioned ranges, there is an effect of suppressing toner flying into the slit opening 59 from reaching the dustproof glass 55.
In general, it has the effect of suppressing unnecessary reflected light from the surface of the image forming body from returning to the optical system and forming interference fringes and the like.

Note that, as shown in FIG. 2, the optical device 56 is connected to the image forming body 6.
It is better to set it not directly above 0 but slightly offset.

That is, the laser beam 52 irradiated onto the image forming body 60
Let P be the intersection point with the surface of the image forming body 60, and the image forming body 60
When the rotation center (axis center) of the laser beam 52 is O, the laser beam 52
For example, the intersection angle O between the traveling direction and the line connecting O and P is 1 to 3.
They are placed slightly offset so that

This arrangement is because a part of the laser beam 52 irradiated onto the image forming body 60 is reflected on the surface of the image forming body 60, but this reflected light overlaps the optical path of the irradiated laser beam. This is to prevent the formation of interference fringes.

Next, the present invention will be specifically explained with reference to Examples. However, the embodiments of the invention are not limited thereby.

Based on the above-mentioned image forming apparatus, image forming method, and image forming conditions shown in Table 1, and by changing the slit conditions of the optical device 56 as shown in Table 2, three colors of red, helmet, and black are produced. Six types of tests were conducted using the manuscript.

In each test, the copy test was performed 1000 times in succession and image evaluation was performed.

As a result, as shown in Table 1, in the case of the configuration according to the present invention, clear multicolor images with high resolution were obtained in all cases.

On the other hand, in a device with a similar configuration to the conventional one (comparison device), the light transmittance of the dustproof glass was halved, resulting in insufficient light, resulting in a loss of image contrast and only an extremely unclear multicolor image being obtained. Ta.

Also, as a slit condition, the facing distance M h 3 is 32 mm.
It has been found that if the optical device 56 is used, the device becomes larger and the cost increases. Zarani again,
Under this slit condition, image blurring occurs due to mechanical vibration, and the resolution of the obtained image is as follows. According to the method, even when multicolor images are formed many times, there is no toner contamination of the laser optical device facing the image forming body surface, and in particular, contamination of the transparent dustproof plate can be completely improved. Ta.

Therefore, effects such as insufficient light quantity and uneven exposure did not occur, and a clear multicolor image with high resolution and high contrast could be formed.

Therefore, the image forming device 11 according to the present invention is extremely suitable for application to the above-mentioned multicolor development and single fixing type multicolor image forming Pt system.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an outline of the image forming apparatus of the present invention;
FIG. 2 is a configuration diagram of the main parts of a Lede beam optical device suitable for application to the image forming apparatus of FIG. 1, and FIG. 3 is a characteristic showing the relationship between the facing distance between the image forming body and the dust-proof glass and the transparency. 4 is a block diagram of a conventional image forming apparatus, and FIG. 5 is a diagram illustrating toner scattering (1) and development (2). 25.26...Fluorescent lamps 27.29a, 29b, 54...Reflection mirror 41.43...CCD image sensor 51...Polygon mirror 52...Laser beam 55...Transparent dustproof plate (dustproof Glass) 56...Optical device 57a...Lower casing 57b...Upper casing 57c...Slit plate 58...Slit 59...Slit opening 60...Image forming body 61...) Charging Device 63.64.65...Developer 66...Cleaning device 70...Transfer device? 2...Fixing device 81...Paper feeding device A...Reading unit B...Writing unit C...Image forming section D...Paper feeding unit Patent applicant Koni-Riki Co., Ltd. Flash cutting 4t and μl ゛ Tez Otsu Q me ≠ 4 left ゛:) 13fm next) Fig. 3 Fig. 4

Claims (1)

[Claims] (1) Spot-expose a uniformly charged image forming body with a laser beam modulated by an image signal to form an electrostatic latent image, and develop the electrostatic latent image to form a color toner image. In an image forming apparatus that forms a multicolor toner image on the image forming body by repeating the forming process multiple times, and transfers the multicolor toner image onto a transfer paper at once, the image of the optical device A slit that forms a path for the laser beam is provided in a portion facing the surface of the image forming body, and a transparent dustproof plate is provided at the opening on the opposite side of the slit to the image forming body, and this transparent dustproof plate and the above-mentioned An image forming apparatus characterized in that a gap between the image forming body and the image forming body is set to a distance that prevents charged toner from adhering to the image forming body.