JPS63210877A - Image forming device - Google Patents

Abstract

PURPOSE:To permit sufficient transfer even with a photosensitive body of a relatively small diameter as sufficiently large discharge current flows by using a Scorotron charger having a corona wire which generates electric charge and a grid which controls the quantity of the electric charge to be applied to a material to be transferred for a control means. CONSTITUTION:After an electrostatic latent image is formed on an image carrying body 22, the latent image is developed by a developer to form a developer image. The developer image is carried to a transfer charger 30 where the image is transferred onto the material to be transferred. The charge generated by the corona wire 48 is controlled by the grid 64 in the transfer charger 30, by which the region and voltage of the charge to be applied to the material to be transferred are controlled. The sufficient corona charge in the prescribed region of the material to be transferred is permitted by using the Scorotron charger 45 for said transfer charger 30. Splashing of the developer at the time of the transfer is, therefore, prevented and the sure transfer of the developer image is permitted.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention develops an electrostatic latent image formed on an image carrier and transfers the developer image to a transfer material. The present invention particularly relates to an image forming apparatus that forms an image.

(Prior Art) As this type of image forming apparatus, for example, a laser beam printer 1 as shown in FIG. 10 is known. In the conventional laser beam printer 1, first, the surface of the photoreceptor 2 is charged by a charger 3 placed around the photoreceptor 2. The surface of the charged photoreceptor is irradiated with a laser beam 4 to form an electrostatic latent image. Next, a developer is supplied to the electrostatic latent image by the developing device 5 to form a developer image. Subsequently, the developer image is transported to a transfer position.

At the transfer position, a charge having a polarity opposite to that of the developer is applied by a transfer charger 6 to the back surface of the paper that has been conveyed in synchronization with the rotation of the photosensitive drum. As a result, the paper adheres to the photoreceptor, and the developer image is electrostatically attached and transferred to the paper.

Conventionally, a corotron charger equipped with substantially only a corona wire has been used as a transfer charger, and ions (charge) generated by corona discharge are directly applied to the paper.

Subsequently, the charge applied to the sheet of paper is canceled by the peeling charger 7, and the sheet of paper is peeled off from the photoreceptor.

After the transfer, the paper is conveyed to a fixing device, and the developer transferred to the paper is fixed. On the other hand, the surface of the photoreceptor after the transfer is conveyed to a cleaning device 8, where the remaining developer is removed, and then light is irradiated from the static elimination lamp 8 to make it static! The latent image is removed.

In the conventional laser beam printer 1, the diameter of the photoreceptor 2 is approximately 80II! 1 to ioomm, and the contact area between the paper and the photoreceptor is relatively wide. If the transfer area is relatively wide, even if ions generated by corona discharge are scattered over a wide range, there is no problem because the contact area between the paper and the photoreceptor is relatively large, and sufficient transfer can be achieved.

On the other hand, in recent years, due to market demands, research has been conducted into reducing the size of laser beam printers. In such small printers, it is necessary to downsize the photoconductor drum, but as the diameter of the photoconductor drum becomes smaller (for example, the diameter is about 30+1111), when transferring the developed image to paper, the photoconductor drum becomes smaller. Since the radius of curvature of is small, the contact area between the paper and the photosensitive drum becomes narrow.

(Problems to be Solved by the Invention) In small laser printers, the contact area between the photoreceptor and paper is small and the contact time is short.

Therefore, when a corotron charger is used as a transfer charger, ions (N charges) generated by corona discharge are diffused over a wide range, making it impossible to concentrate the ions only in the contact region m.

Therefore, there is a problem that the developed image cannot be transferred reliably and a clear image cannot be obtained.

In addition, if the rotation speed of the photoreceptor is slow, for example, about 60
1/sec or less, as shown in Figure 9, the amount of charge on the paper between the black solid area and the character area is attenuated, so if the voltage applied to the transfer charger during transfer is constant, the black Although sufficient transfer is achieved at the edge, there is a problem in that the text cannot be transferred reliably.

Furthermore, if ions are scattered over a wide area from the transfer charger during transfer and adhere to parts of the paper that are not in contact with the photoreceptor, the image transferred to the paper will scatter, making it impossible to obtain a clear image. There is a problem.

To solve this problem, it is possible to make the opening of the case where the ions are emitted smaller to reduce the area where the ions are dispersed, but in this case, it is difficult to obtain sufficient discharge current to discharge into the case. Therefore, there is a problem that the charging required for transfer cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus that can obtain clear images.

[Structure of the Invention] (Means for Solving the Problems) An image forming apparatus according to the present invention includes a latent image forming means for forming an electrostatic latent image on an image bearing member, and an electrostatic latent image formed by the latent image forming means. In an image forming apparatus, the image forming apparatus includes a developing device that electrostatically attaches a developer to an electrostatic latent image to develop the image, and a transfer device that transfers the developed developer image to a transfer material, wherein the transfer device generates an electric charge. The present invention is characterized by comprising a scorotron charger having a corona wire that controls the amount of charge applied to the transfer material, and a grid that controls the amount of charge applied to the transfer material.

(Function) According to the present invention, after an electrostatic latent image is formed on the image carrier, it is developed with a developer to form a developer image. The developer edge is then transported to a transfer charger where it is transferred to a transfer material. In the transfer charger, the charge generated by the corona wire is controlled by a grid to control the area and voltage of the charge applied to the transfer material.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 8 of the accompanying drawings.

As shown in FIG. 2, the laser beam printer 10 according to the embodiment of the present invention is provided with a paper feed cassette 14 in its lower portion for storing paper 12 on which an image is to be formed. Approximately in the center of the printer 10, an image forming unit 16 is provided that forms an image on the paper 12 conveyed from the paper cassette 14, and above the printer 10, the image formed on the paper is transferred to a fixing tray 18. A paper discharge tray 2o is provided to receive the fixed image after fixing. Paper cassette 14
An optical unit 24 is disposed between the image forming unit 16 and the image forming unit 16. The optical unit 24 irradiates light onto a photoreceptor drum 22, which will be described later, in accordance with an image information signal.

As shown in FIG. 1, the image forming unit 16 includes a charger 2 around the photoreceptor drum 22 that charges the surface of the photoreceptor.
5. An exposure device 26 that scans and exposes the charged photoreceptor drum 22 with a laser beam to form an electrostatic latent image, a developer bag @ 28 that supplies developer to the electrostatic latent image and develops it, and a developer image. The transfer charger 30 that transfers the image onto the paper is arranged in this order. A snow removal lamp 32 is arranged between the transfer charge 1730 and the charging device 25 to remove an afterimage after the transfer. In this embodiment, the electrostatic latent image is developed by a reversal development method.

As shown in FIG. 3, the photosensitive drum 22 has an outer diameter of 30 mm.
+nm cut aluminum cylinder (thickness: 0.8n+n) 3
A charge generation layer 34 and a charge transport layer 36 are coated in this order on the outer peripheral surface of No. 3.

The charge generation layer 34 is made by coating τ-type phthalocyanine and butyral resin in a weight ratio of 1:1 to a thickness of 0.1 μm.

The charge transport layer 36 was formed by coating 9-ethylcarbazole-3-carboxyaldehyde-methylhydrazone (ECMP: trade name) and polyarylate (U-100; trade name) at a weight ratio of 0.65 to a thickness of 17 μm. It is something.

This charge transport layer 36 is translucent and is located above the charge generation layer 34, so even if toner particles 40 of 30 μm or less are present on the surface, when the photoreceptor drum 22 is exposed to light, diffracted light 38 and The reflected and scattered light 42 within the charge transport layer 36 hardly casts any shadows on the toner particles. in this case,
The charge transport layer 36 may be made of any material as long as it is permeable to the exposure light source, and its thickness may be at least the average particle diameter of the toner. That is, the thickness of the charge transport 1136 is smaller than the average particle diameter of the toner, that is, when the toner particles 40 are 30
If it is .mu.m or more, white spots will appear on the black solid surface, resulting in image defects.

Note that the thickness of the charge transport layer 36 is preferably 30 μm or less from the viewpoint of residual potential characteristics. In this example, the thickness of the charge transport layer 36 has a sensitivity of half-attenuation light amount of 6.2 erg/m, and the exposure light amount is 20 to 30 era/d.

The transfer charger 30 and the charger 25 each use a scorotron charger 45 and have the same configuration, so the transfer charger 30 will be described in detail and the charger 25 will be described in detail.
The explanation of is omitted. Figure 4 shows Scorotron charger 4.
5 is shown in an exploded perspective view. The casing 46 with the opening groove 44 formed on the back side has a diameter of about Q. It is formed from a stainless steel material with a thickness of 3 mm into a substantially square prism shape. A corona wire 48 is stretched in the center of the casing 46 .

The surface of the corona wire 48 is coated with gold to prevent uneven generation of negative corona. One end of the corona wire 48 is fixed to a metal fitting 52 via a tension spring 50. A power supply bottle 54 is screwed to the metal fitting 52, and the metal fitting 52 and the power supply bottle 54
is fixed within the power supply terminal 56. The other end of the corona wire 4B is fixed to the terminal 60 with a plastic hook 58. Each terminal 56, 60 is covered with a respective terminal cover 62, 64 to prevent exposed portions to which high pressure is applied.

The casing 46 is a 650cm Zener diode 66.
and its cathode is connected to the charger guide 67. On the other hand, charger guide 6
7 is connected to a ground terminal.

In the casing 46, a mesh-shaped grid 68 is provided on the side facing the opening groove 44. This grid 68 is formed integrally with the casing 46 and maintains flatness. The sides 70, 72 of the casing 46 adjacent to the grid 68 are configured to have the same bias voltage when a corona discharge occurs within the casing, in which case the corona current flowing through the casing 46 is also reduced. Improves current efficiency.

Furthermore, since the opening groove 44 is formed on the back surface of the casing 46, the air inside the casing 46 can flow well and no ozone or the like is trapped, so the photoreceptor 22 is not damaged and the photoreceptor 22 is not damaged. It is possible to extend the life of the image and prevent image blurring.

Approximately -5K is applied to the power supply bin 54 from a voltage transformer (not shown).
When V (kilovolts) is applied, a corona discharge occurs within the casing 46. In this case, current flows through the casing 46, but due to the rectifying characteristics of the Zener diode 66, the potential within the casing rises to -650V and remains constant. Therefore, the grid 68 naturally becomes -650V, so the photosensitive drum 2 located 211 m away from the grid 68
The surface potential of 2 is slightly lower than the potential of grid 68;
It is kept constant at about 600■. In the figure, 73 is the charger, and 74 and 76 are the springs.

Also, charged I! As shown in FIG. 1, the scorotron charger 45 used in
are arranged sideways or upwards with respect to the photoreceptor 22. In this case, if the carrier mixed in the developer is attached to the photoreceptor 22, it is conceivable that this carrier will enter the casing 46, but if the carrier enters the casing in this way, the casing 46 The corona wire 48 will be short-circuited. Furthermore, it is conceivable that the carriers may clog the grid 68 and cause a discharge failure, resulting in a defective image.

Therefore, in this embodiment, as shown in FIG. 5, a magnet 78 is attached to the outside of the upper side portion 70 of the casing 46. Before the carrier attached to the photosensitive drum 22 reaches the charger 25, it is previously attracted to the magnet 78 and removed. The tip 80 of the magnet 70 protrudes from the upper side 78 of the casing 46 toward the photosensitive pair, and when Y is the distance between the photoconductor 22 and the tip of the magnet 78, the distance Y is approximately 0.5111.
1 to about 21111 is preferred. If it is further away than this (the value becomes large), the attraction force of the carrier is weak, and if it is too close to this (the value becomes small), the carrier gradually accumulates on the tip of the magnet, and eventually comes into contact with the photoreceptor and damages it. Otherwise, carrier spikes may form and stick to the grid or penetrate into the casing 46. According to this configuration, good images can be obtained even when 100,000 sheets of A4 paper are printed.

As shown in FIG. 2, the optical unit 24 includes a polygon scanner 88 that includes a polygon mirror 84 having a pentagonal cross section and a motor 86 that drives the polygon mirror 84 in a housing 82, as shown in FIG. The laser beam from the polygon scanner 88 passes through an FE lens 90, reflective mirrors 92 and 94, and a correction lens 96 of the exposure device 26.
The photoreceptor drum 22 is guided through the photoreceptor drum 22. These mirrors, lenses, etc. are integrally fixed within the casing 82. Therefore, differences in beam diameter and scanning speed on the photoconductor due to laser path length errors can be kept to a minimum, and the laser Adjustment becomes easy.
゛The exposure device 26 has a housing 99 as shown in FIG.
A protective transparent glass 100 is adhered to the slit 98 to prevent foreign matter from entering through the slit 98 formed here. On the protective glass 100, there is a toner adhesion prevention film 101.
The toner adhesion prevention film 101 is made of a polyester film 102 as a transparent member and ITO (indium oxide) [111] as a transparent conductive film.
04 are stacked in this order. This I
TOI1104 has a bias voltage of the same polarity as the toner,
Here, since the toner has negative polarity, a negative voltage is applied to prevent the scattered toner from adhering to the protective glass 100 by electrically repelling it.

Note that the applied voltage is approximately -400V, and any transparent conductive film may be used as long as it transmits exposure light. Further, a magnet 106 is provided on the toner adhesion prevention film 101 except for the optical path portion through which the laser passes, that is, the area corresponding to the slit 98 . The magnet 106 attracts carriers that have fallen or scattered from the photoreceptor, and prevents the carriers from adhering to the toner adhesion prevention film 101 on the optical path.

Furthermore, the magnet 106 is grounded or
It is connected to a power source 108 that applies a voltage of opposite polarity to that of the toner. This prevents toner from falling here, similar to the ITO film 104. In this case, magnet 1
A voltage of +300V is applied to 06. Incidentally, interposed between the toner adhesion prevention [1101] and the magnet 106 is an insulator 1!1110 formed from a Mylar sheet of about 75 mm. Further, the magnet 106, the insulating film 110, and the toner adhesion prevention film 104 are removably attached so that they can be periodically inspected, cleaned, and replaced. Further, as shown in FIG. 1, this exposure device 26 is integrated with a developing device 28, and can be removed and replaced at the same time.

Therefore, the exposure device 26 can prevent carriers or particles from accumulating on the transparent glass and blocking the laser beam. Image defects such as spots or streaks that conventionally occur due to the volume of carriers can be prevented.

The developing device 28 includes a casing 11 as shown in FIG.
1 includes a developing roller 112, a doctor blade 114 for regulating the thickness of the developer magnetic brush, and a developer stirring member 11.
6 and 117, and a toner hopper 118 are provided. A so-called two-component developer containing toner and carrier is stored as the developer. Developing roller 112
is a magnetic roll 120 and a sleeve 1 rotating outside the magnetic roll 120.
22. The magnetic roll 120 has two S-pole magnetic pole parts 124 and 126 and an N-pole magnetic pole part 12B,
! The angle A between the N-pole magnetic pole part 128 and the S-pole magnetic pole part 124 with respect to the rotation center of the 1fflO-ru 120 is 150°,
The angle B between the N-pole magnetic pole portion 128 and the S-pole magnetic pole portion 126 is set to 120°.

The development station H 28 has a so-called cleaning and simultaneous development process that develops the electrostatic latent image and removes toner that has adhered to the photoreceptor as a residue from previous transfer. Normally, it is known that when the development potential is higher than 300V, memory occurs due to poor cleaning, but this is because the image density does not increase even if the development potential exceeds 300V, but the actual amount of toner adhesion increases. This is considered to be because the amount of toner remaining after transfer is also increasing at the same time.

It is preferable to apply a cleaning potential of about 500V to reduce such memory.

In this case, the cleaning potential is the difference between the developing bias potential and the charged potential on the surface of the photoreceptor. It is desirable to be charged to Q. FIG. 7 shows the cleaning efficiency in terms of the amount of charge of the toner particles, with the vertical axis representing the cleaning efficiency % and the horizontal axis representing the band 1ii1 of the toner particles. As described above, the toner remaining on the photoreceptor 22 as a transfer residue is
It is cleaned by the developing device 28.

The transfer charger 30 has the same structure as the charging machine 25 shown in FIG. 4, as described above. A high voltage having a polarity opposite to that of the toner, that is, +5.0 cm, is applied to the corona wire 46. Then, the back side of the paper is charged with electricity, attracting negative toner to the paper. A Zener diode is installed in the grid 68 in a direction opposite to the charging direction so that the voltage is +1200. The width W of the opening of the transfer scorotron in the paper feeding direction (see Fig. 1) is
It is set to less than half the diameter of 2. When a scorotron charger is used as a transfer charger, the capacitance between the transfer paper and the photoreceptor drum is small, so the specified voltage is easily reached, and a sufficiently large discharge current flows, so even a relatively small diameter photoreceptor drum can be transferred. can be made sufficient.

In addition, since the potential applied to the paper can be kept constant, even if there is a large amount of toner between the transfer paper and the photoreceptor drum, and the transfer paper is partially separated from the photoreceptor,
Even when the toner adhesion area is narrow, such as a character image, a good transferred image can be obtained.

FIG. 8 shows the relationship between transfer efficiency and applied voltage when the scorotron charger 45 is used as the transfer charger 30. In FIG. 8, the vertical axis shows the transfer efficiency %, the horizontal axis shows the applied voltage KV (kilovolts), and the relationship between each applied voltage and the transfer efficiency in the character area and the black edge is plotted. As is clear from FIG. 8, when the applied voltage is about 4 volts or more, an excellent transfer efficiency of 90% can be obtained in both solid black areas and character areas.

Note that good images were obtained even at a comparatively slow speed ratio of a grid voltage of 800 to 2000 V1 and a drum circumferential speed of 35 m1 of the photoreceptor. In this case, if the grid voltage is less than 800V, there will be insufficient transfer, and if it is more than 2000V, there will be excessive charge, resulting in poor transfer.

Furthermore, since the potential of the transfer paper does not rise more than necessary when the paper is peeled off from the photosensitive drum after transfer, a solid image due to peel discharge does not occur even if the charge is not removed by a peel charger. Moreover, even when an image is formed on OHP paper (plastic transparent sheet), image avatars due to peeling discharge hardly occur.

Since the transfer charger 30 has the grid 68 facing down and facing the photoreceptor, paper scraps, toner, carriers, etc. do not fall onto the grid 68 and adhere to it, so the grid is not clogged. It can be used stably for a long period of time.

As shown in FIG. 1, a pre-transfer static eliminator 134 is provided between the developing device 28 and the transfer charger 30 to neutralize the electrostatic latent image of the toner image developed with the toner.

The pre-transfer static eliminator 134 has a guide path 136 that guides the light of the static eliminator 132 to the photoreceptor 22 along the transport path 130 through which the static eliminator 132 and the paper are transported to the transfer charger 30 . A Mylar sheet 138 with a transparent conductive film ITO is attached to the tip of the guide path 136 (the side facing the photoreceptor 22).

Mylar sheet 138 is applied with substantially the same potential as the charged potential of photoreceptor 22, ie, a bias voltage of about -600 V, to prevent colored powder from adhering to it. The bias for preventing this adhesion is the same as the charging of the photoreceptor 22, and is effective if it is higher than the developing bias, but if it exceeds 1000V, discharge with other parts is likely to occur, so it is preferable to set the bias to be higher than the developing bias and lower than 1000V. . In addition, here, the pre-transfer static elimination lamp 132
is transmitted to the developing roller 1 through the light guide path 136.
A transparent acrylic plate 138 is filled in the light guide path 136 to guide the light to the photoreceptor 22 at a distance from the photoreceptor 12 . Note that the static elimination cover 139 is an insulating member to prevent transfer defects due to charge leakage from the guide of the transfer member. Further, the static elimination cover 139 may be made of metal or the like, and an insulating member may be provided on the surface.

In this way, the transfer efficiency can be increased by static elimination before transfer, and the residual toner after transfer can be reduced.

That is, pre-transfer static elimination improves transfer efficiency even in a humid environment.

This invention is not limited to the one embodiment described above, and can be modified in various ways without departing from the gist of the invention.

For example, the same effect can be obtained even if the transfer charger is arranged so as to face down with respect to the photoreceptor, instead of being arranged so that the grid side faces down and facing the photoreceptor.

Further, the paper onto which the toner image has been transferred by the transfer charger is peeled off from the photoreceptor due to the elastic force of the paper, so-called strain, but this is not the only option. good.

[Effects of the Invention] According to the present invention, in the image forming apparatus, a scorotron charger is used as a transfer charger for transferring a developed image to a transfer material, so that the predetermined f! It is possible to sufficiently charge the corona in four regions. Therefore,
Since scattering of the developer can be prevented during transfer and the developer image can be transferred reliably, a clear image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an image forming unit according to the present invention, FIG. 2 is a schematic diagram of a laser beam printer in which the image forming unit shown in FIG. FIG. 4 is an exploded perspective view of the Scorotron charger, FIG. 5 is a sectional view of the charging machine, and FIG.
The figure is a cross-sectional view of an exposure device, Figure 7 is a graph showing the relationship between toner charge and cleaning efficiency, and Figure 8 is a graph showing the relationship between transfer efficiency and applied voltage of a transfer charger according to an embodiment of the present invention. A graph diagram, Figure 9 is a graph diagram showing the relationship between applied voltage and transfer efficiency of a conventional transfer charger.
FIG. 0 is a schematic configuration diagram of a conventional laser beam printer. 22... Photosensitive pair drum, 25... Charging machine, 26...
- Exposure device, 28 developing device, 30... transfer charger, 45... scorotron charger. Applicant's agent Patent attorney Shikihiko Suzushi

Claims (6)

[Claims] (1) a latent image forming means for forming an electrostatic latent image on an image carrier;
An image forming apparatus comprising: a developing device that electrostatically attaches a developer to an electrostatic latent image formed by a latent image forming device to develop the image; and a transfer device that transfers the developed developer image to a transfer material. An image forming apparatus characterized in that the transfer means includes a scorotron charger having a corona wire that generates charge and a grid that controls the amount of charge applied to the transfer material. (2) The image forming apparatus according to claim 1, wherein the image carrier has a drum-shaped photoreceptor, and the diameter thereof is 60 mm or less. (3) The image forming apparatus according to claim 1, wherein the scorotron charger is arranged so that its grid faces downward and faces the image carrier. (4) The image forming apparatus according to claim 2, wherein the peripheral speed of the photoreceptor is 60 mm/sec or less. (5) The image forming apparatus according to item 1, wherein the voltage applied to the grid of the scorotron charger is 800 to 2000 volts. (6) The image forming apparatus according to item 2 or 4, wherein the width of the grid of the scorotron charger in the feeding direction of the transfer material is less than half the diameter of the drum.