JP2004318092A - Image forming apparatus and image forming method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep down leaking of applied potential between a developing roll and a photoreceptor drum when carrying out hybrid developing in an electrophotographic method image forming apparatus. <P>SOLUTION: In the image forming apparatus, a developing roll 2 is an aluminum roll with an aluminum oxidized film which is ≥5μm thick formed on its surface. The distance between the developing roll and a photoreceptor base tube 3 is set to be between 150 to 300μm. When AC is applied to the developing roll to have toner scattered from the developing roll to the photoreceptor, the frequency of AC current in non-image formation is controlled to be greater than in image formation and developing is carried out by having the electrified toner scattered selectively to an electrostatic latent image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method such as a copying machine, a printer, a facsimile, or a multifunction machine using an electrophotographic method, and more particularly, to a method of charging a non-magnetic toner using a magnetic carrier. Using a two-component developer on the surface of a magnetic roller using a two-component developer, transferring only the charged toner in the developer onto the developing roller, and causing the toner to fly to an electrostatic latent image The present invention relates to a non-contact developing type image forming apparatus for developing the latent image and an image forming method using the same.

  Conventionally, using a two-component developer of this type, a developing roller facing an image carrier carrying an electrostatic latent image, and a magnetic roller disposed on the opposite side of the image carrier with respect to the developing roller and spaced apart from the developing roller An image forming apparatus having a so-called hybrid developing device is already known as disclosed in Patent Document 1 or Patent Document 2. In recent years, as a high-speed color image forming method, in particular, a plurality of image forming units including a charger, an exposure optical system, a developing device, and the like corresponding to a plurality of colors are provided on a photoreceptor, and one drum color for sequentially forming a color image is provided. It has also been considered for use in the overlapping system. According to this method, it is possible to form a color image with less color misregistration by accurately overlaying the toner on the photoreceptor, and it is attracting attention as a technique for improving color image quality. In such a color image forming apparatus, the above-described developing method has attracted attention as a developing method that does not disturb a toner image formed by an image forming unit of another color. More recently, the contact speed has been increased in a tandem system in which a plurality of photoconductors corresponding to the toner colors are used to form a color image in synchronization with the transfer of a transfer member and to superimpose colors on the transfer member. As a result, the above-described developing method has been attracting attention as a non-contact developing method that does not give an unnecessary addition to the photosensitive member.

In the case of this developing method, the presence of undeveloped fine powder, external additives, and the like in the developer causes deterioration in developability. Therefore, if the distance between the developing roller and the photosensitive drum is reduced or the AC peak voltage (Vpp) is increased in order to improve the developability, leakage of the applied potential occurs during that time. As a result, the purpose of moving only the sufficiently charged toner to the developing roller without moving the carrier of the two-component developer cannot be sufficiently fulfilled.
JP-A-6-67546 (Claim 1 etc.) JP-A-7-92804 (Claim 1 etc.)

  Therefore, an object of the present invention is to provide an image forming apparatus that forms an image by developing an electrostatic latent image on a photoreceptor with a thin toner layer formed on the surface of a developing roller via a magnetic brush of toner and a carrier of a magnetic roller. SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus effective for suppressing leakage of an applied voltage between a developing roller and a photosensitive drum and an image forming method using the same.

  In order to solve the above-mentioned problems, the present inventors first examined the material constituting the developing roller, selected an aluminum pipe, and used a developing roller having its surface subjected to an aluminum oxide film treatment. As a result, the present inventors have found that it is effective in preventing leakage of an applied voltage between the photosensitive drum and the photosensitive drum. Further, when the relationship between the distance between the developing roller subjected to the aluminum oxide film treatment and the photosensitive drum tube and the applied voltage leak was examined, it was found that setting the distance to 150 to 300 μm was extremely effective. Obtained. When the thickness of the aluminum oxide film at this time is set to 5 μm or more, applied voltage leakage is well prevented.

On the other hand, when developing using the above-described image forming apparatus, when applying an AC voltage to the developing roller in order to cause toner to fly from the developing roller to the photosensitive member, the frequency of the AC current during non-image formation is changed during image formation. It has been found that if the control is made to be larger than the above, there is an effect of suppressing carrier pulling during non-development.
The present invention has been completed by further study based on these findings, and relates to the following image forming apparatus and an image forming method using the same.

1) In an image forming apparatus for forming an image by developing an electrostatic latent image on a photoreceptor with a thin toner layer formed on the surface of a developing roller through a magnetic brush made of a toner and a carrier of a magnetic roller,
The developing roller is made of aluminum, an oxide film of aluminum having a thickness of at least 5 μm is formed on the surface thereof, and the interval between the developing roller and the photosensitive drum tube is set to 150 to 300 μm. Image forming apparatus.

2) The image forming apparatus according to 1) above, wherein the thickness of the aluminum oxide film is 10 to 20 μm, and the distance between the developing roller and the photosensitive drum base is 150 to 280 μm.
3) When forming an image by developing an electrostatic latent image on a photoreceptor with a thin toner layer formed on the surface of a developing roller through a magnetic brush of toner and a carrier of a magnetic roller,
An image forming apparatus, wherein the developing roller is made of aluminum, an oxide film of aluminum having a thickness of at least 5 μm is formed on the surface thereof, and an interval between the developing roller and the photosensitive drum tube is set to 150 to 300 μm. make use of,
A DC voltage on which an AC voltage is superimposed is applied to the developing roller,
Control is performed so that the frequency of the direct current at the time of development of the electrostatic latent image is higher than the frequency of the alternating current at the time of non-development, and the charged toner is developed while selectively flying on the electrostatic latent image. An image forming method.

4) The image forming method according to the above item 3), wherein the frequency during the development is 1 to 4 kHz.
5) The image forming method according to the above item 3), wherein the frequency during the development is 1 to 3 kHz.
6) The image forming method described in 3) above, wherein the frequency at the time of non-development is 4 to 8 kHz.

7) The image forming method as described in 3) above, wherein the frequency at the time of non-development is 5 to 8 kHz.
In the present invention, the aluminum oxide film formed on the surface of the aluminum developing roller has a thickness of 5 μm or more, preferably 10 μm or more, in order to prevent an applied voltage leak. The upper limit of the thickness is not particularly limited, but about 20 μm is sufficient. If the thickness is larger than this, only the cost increases, and there is no difference in effect.

  The frequency at the time of image formation (at the time of development) is generally set to around 1 to 3 kHz since a ghost image becomes worse if the frequency is too high. However, with this frequency setting, so-called carrier pulling occurs in which the carrier moves from the magnetic brush onto the developing roller during non-development, and moves on the photosensitive drum. Therefore, in the image forming method of the present invention, the carrier is prevented from being pulled by setting the frequency during non-development to preferably 4 to 8 kHz using the above image forming apparatus.

According to the present invention, in an image forming apparatus for forming an image by developing an electrostatic latent image on a photoreceptor with a thin toner layer formed on the surface of a developing roller through a magnetic brush of toner and a carrier of a magnetic roller, There is provided a developing means effective for suppressing leakage of an applied voltage between the roller and the photosensitive drum and obtaining an image having good image characteristics.

A system configuration focusing on development in the image forming apparatus of the present invention will be described with reference to FIGS.
In FIG. 1, a photosensitive member 3 and a developing roller 2 are disposed, and a predetermined interval is provided from the developing roller 2 to form a cylindrical member of a non-magnetic metal material. A plurality of fixed magnets are disposed in the cylindrical member. A magnetic roller 1 having a sleeve configured to be rotatable around the fixed magnet is provided.

  10a and 10b are paddle mixers, and developing bias voltages DC7a and AC7b are applied between the photosensitive member 1 and the developing roller 2, and a developing bias voltage DC8 is applied to the magnetic roller 1 (see FIG. 2). Reference numeral 9 denotes a regulating blade for controlling the thickness of the magnetic brush. In the present invention, the gap between the regulating blade 9 and the surface of the magnetic roller 1 is preferably in the range of 0.45 to 0.65 mm.

Next, the operation of the photoconductor 3, the magnetic roller 1 in the developing device, and the developing roller 2 will be described.
As shown in FIG. 2, the magnetic roller 1 generates a magnetic brush 10 by a carrier 4 that charges and holds a toner 5. A thin toner layer 6 is formed on the surface of the developing roller 2 by the toner 5 supplied from the magnetic brush 10. The photoreceptor 3 forms an image by selectively flying the toner of the thin toner layer 6 according to the electrostatic latent image. This image is transferred to a print 14 passing between the primary transfer roller 13. The preferred range of the carrier particle size in the present invention is 35 to 50 μm.

As the photoreceptor 3, a positively charged organic photoreceptor (positive OPC) is stable in electrification with little generation of ozone and the like. Particularly, even when a single-layer positive OPC is used for a long time and the film thickness changes, Since there is little change in the photosensitive characteristics and the image quality is stable, it is optimal for a long-life system. In addition to this, an a-Si photoconductor can also be used.
In the case of a long-life system, it is advantageous to set the thickness of the positive OPC to about 20 to 40 μm. The positive OPC is preferably set to 20 μm or more in order to prevent black spots from being generated due to dielectric breakdown when the film thickness decreases to 10 μm when used for image formation and reaches 10 μm. If it exceeds, the sensitivity is lowered, which tends to cause the image quality to be lowered.

As the exposure apparatus 11, a system using a semiconductor laser or an LED is appropriate. In this case, a wavelength around 770 nm is effective for positive OPC, and a wavelength around 685 nm is effective for a-Si photoreceptor. Hereinafter, a case where the normal OPC is used will be described as an example.
The charging device 12 charges the positive OPC 3 serving as an electrostatic latent image carrier to 400V. Thereafter, when exposure is performed using an LED having a wavelength of 770 nm, the post-exposure potential is set to 70V. The positive OPC 3 is arranged with a space of about 250 μm with respect to the developing roller 2. No wire electrode or the like is used in this space.

  In the present invention, the surface of the developing roller 2 is a rotating body made of conductive aluminum. A thin toner layer is formed on the developing roller 2 by the potential difference between the developing roller 2 and the magnetic roller 1. With respect to the potential difference, when the potential of the developing roller is set to 70 V and the potential of the magnetic roller is set to 400 V, a toner layer of about 1 to 1.5 mg / cm 2 is formed on the developing roller 2. The appropriate charge amount of the toner at this time is approximately 10 to 20 μC / g. When the charge amount does not reach 10 μC / g, toner scattering is conspicuous. It becomes difficult to fly.

  By applying an AC voltage to the developing roller in order to cause the toner to fly from the developing roller 2 to the photoreceptor 3, the developability is improved. As for the voltage, image density, dot reproduction, and fog removal can be balanced at PP = 1.5 KV and f = 3.0 kHz. DUTY ratio (duty ratio of an AC voltage applied to the developing roller, a time for applying a voltage to move the toner to the photoconductor side to the developing roller is a, and the toner is in the opposite direction to the photoconductor (that is, the developing roller direction) The generation time of the developing ghost can be suppressed by setting the duty ratio = a / (a + b) (× 100)%) to 30%, where b is the time for applying a voltage that moves to the developing roller to the developing roller.

When the potential of the developing roller 2 over the toner layer surface is measured, it is about 320 V. It can be said that 320 V-70 V (photoreceptor potential after all exposures) = 250 V is the actual development execution potential.
The gap between the magnetic roller 1 and the developing roller 2 is usually set to 400 μm, and the gap between the regulating blade 9 and the magnetic roller 1 is adjusted according to the carrier particle size. For example, for a carrier having an average particle diameter of 35 μm and a developer containing 10% of toner, the thickness is set to 350 to 500 μm, and the magnetic brush contacts the developing roller 2. If the gap between the developing roller 2 and the magnetic roller 1 is too narrow, the developer cannot pass between the rollers and overflows. If the gap is too wide, the developer cannot contact the developing roller and it becomes difficult to collect toner from the developing roller. When the operation is repeated, the toner gradually adheres to the developing roller 2 and the toner cannot fly on the photoconductor 3.

  In the present invention, the distance between the photosensitive drum tube 3 and the developing roller 2 is set to 150 to 300 μm. More specifically, the adjustment is made while observing the applied potential leak and the developing performance. When this interval is narrower than the above range, the developability is increased and the rise of fine powder in the developing device is suppressed, which is effective from the viewpoint of extending the life. However, if the width is too narrow, there is a problem that a margin for applied potential leak becomes narrow.

  In the present invention, in order to satisfy the relationship between the developability and the prevention of applied potential leak, aluminum is first used as the material of the developing roller, and the surface thereof is coated with an aluminum oxide film having a thickness of 5 μm or more. Making the aluminum oxide film 5 μm or more is effective in preventing applied potential leakage, and more preferably 10 μm or more. The upper limit of the thickness may be 20 μm for the purpose of preventing leakage of the applied potential, and increasing the thickness beyond that is disadvantageous in cost.

  Next, when developing using the image forming apparatus of the present invention, when applying an AC voltage to the developing roller in order to cause the toner to fly from the developing roller to the photosensitive drum, The frequency is controlled so as to be higher than the frequency at the time of developing the electrostatic latent image. Here, the non-development time is the time during which the developing roller is rotating and the photosensitive drum is charged, excluding the time during which the electrostatic latent image is being developed.

  As a result, the purpose of the present development system of moving only the sufficiently charged toner to the developing roller without moving the carrier among the two-component developer can be achieved favorably. The AC voltage (alternating electric field) frequency during the development is preferably 1 to 4 kHz, more preferably 1 to 3 kHz. Further, the frequency of the AC voltage during non-development is preferably 3.5 to 8 kHz, more preferably 3.5 to 7 kHz. More specifically, when the sleeve DC at the time of non-development is used at 100 V or less, the frequency is preferably 4 to 8 kHz or more, and when it is used at 100 to 200 V, the frequency is preferably 5 to 8 kHz or more.

  The formation of an aluminum oxide film on the surface of the aluminum developing roller can be performed by a method known per se. In other words, when an aluminum roller is used as an anode and electrolyzed in a bath of sulfuric acid, oxalic acid, chromic acid, etc., due to oxygen generated at the anode, the aluminum surface is porous but has high electrical insulation and corrosion resistance. And a wear-resistant oxide film can be formed.

Hereinafter, the present invention will be described in more detail by way of examples. However, these are merely examples of the present invention, and the scope of the present invention is not limited to the description.
(Examples 1 to 9 and Comparative Examples 1 to 4)
In the system configuration centering on development shown in FIG. 1, the distance between the photosensitive drum tube 3 and the developing roller 2 was set to 180 μm. The DC voltage applied to the developing roller was set to 100 V, and Vpp (the voltage between the maximum value and the minimum value of the voltage when AC was applied) was set at 1.4 to 1.7 kV. The frequency was controlled to 3 kHz during development and 6 kHz during non-development.

  Table 1 shows the relationship between the thickness of the aluminum oxide film and the number of leak points on the paper surface when 10 white images were continuously passed. Here, the leak point was measured by counting the number of leak points on the paper surface after continuously passing 10 blank paper images. If a leak occurs to the photoconductor, the photosensitive layer is destructed and cannot be charged, so that a black point (leak point) appears. The peripheral speed of the photosensitive drum tube 3 was set to 100 mm / s, the peripheral speed of the developing roller was set to 150 mm / s, and the peripheral speed of the magnetic roller 1 was set to 225 mm / s. The control was performed so that the toner concentration in the developer could be maintained at 10%.

  As a result, it can be understood that the occurrence of the leak is eliminated by forming the aluminum oxide film on the aluminum roller. Here, when the thickness of the oxide film is 5 μm, the leak can be suppressed up to Vpp of 1.5 kV, but when Vpp is increased to 1.6 kV or more, the leak occurs. By setting the oxide film to 10 μm or more, the leakage was successfully suppressed at a practical working voltage of 1.4 kV to 1.7 kV.

  Table 2 shows that the thickness of the oxide film of aluminum was 10 μm, Vpp was 1.7 kV, and the other experimental conditions were the same as those in Table 1, and the gap between the photosensitive drum tube 3 and the developing roller 2 was set. The relationship between (interval) and the occurrence of leak points was shown. Assuming that the gap is 130 μm, 12 leak points are generated even when the thickness of the oxide film is 20 μm and Vpp is 1.4 kV. Therefore, it was found that the interval was required to be 150 μm or more in order to prevent the leak point. . When the interval was set to 320 μm, the image density decreased to 1.24, which was lower than the prescribed 1.30. Therefore, it has been found that the interval needs to be 300 μm or less in order to make the image density equal to or more than the specified value. The image density was measured using a reflection density meter RD-918 manufactured by Macbeth.

* 1: Even when the oxide film is 20 μm and Vpp is 1.4 KV, 10 leak points are generated. * 2: The image density is 1.24 which is equal to or less than the specified value (1.3), and the reproducibility of the line image is poor.

Next, Table 3 shows the relationship between the frequency of the AC applied to the developing roller during development and the image quality. In this case, the thickness of the aluminum oxide film is 20 μm, the distance between the photosensitive drum tube 3 and the developing roller 2 is 180 μm, the AC voltage Vpp is 1.6 kV, and the AC frequency applied to the developing roller during non-development is: It was set to 6 kHz. When the frequency is 0.5 kHz, the image density becomes 1.30 or less of the specified value, and when the frequency is 4.0 kHz, a ghost image starts to be generated. When the frequency is 5 kHz, regardless of the DC voltage applied to the developing roller, Ghost images become noticeable. Therefore, it is understood that the frequency of the AC during development is preferably 1 to 4 kHz, and more preferably 1 to 3 kHz. The evaluation of the ghost image is set so that a halftone image having a longer length in the paper transport direction than the solid black image comes next to the solid black image in the paper transport direction. The interval between the leading ends is set to the circumference of the developing roller 2. When the ghost phenomenon occurs, a black shadow unnecessary image is generated in the halftone image, so that it is possible to determine whether the ghost phenomenon has occurred.

The evaluation criteria in the above are as follows.
×: Image density is less than 1.30 or a ghost is clearly visible visually Δ: Image density is 1.30 to 1.35 or ghost is slightly visible ○: Good (image density is 1.3 or more and Ghosts cannot be visually identified

Table 4 shows the relationship between the frequency applied to the developing roller during non-development and the carrier pull. Here, the evaluation was performed under the same conditions as in Table 3 except that the frequency of the AC applied to the developing roller during development was set to 3 kHz. The evaluation was performed by forming a toner image having a printing rate of 5% on paper and printing 10,000 sheets. Further, the carrier pull was not transferred and remained on the photoreceptor, and was evaluated by the amount of the carrier contained in the waste toner collected from the photoreceptor drum by the cleaning device.

The evaluation criteria in the above are as follows.
×: Carrier pull of 1.5 g or more after printing 10,000 sheets △: Carrier pull of 0.5 g or more and less than 1.5 g after printing 10,000 sheets ○: Carrier pull of less than 0.5 g after printing 10,000 sheets X2 : Image density decrease (it does not reach the standard value of 1.30 when printing 10,000 sheets)
The amount of the developer was 220 g, and the life of the developing device was set to 200,000.

As a result, when the DC component of the developing bias applied to the developing sleeve at the time of non-development is used at 100 V or less, it is 4.0 kHz or more, and when it is used at 100 to 200 V, carrier pulling is good at 5.0 kHz or more. Was suppressed. If the frequency exceeds 8 kHz, the ability to collect toner from the developing roller 2 at the time of non-development is reduced. Therefore, if continuous printing is performed, fine powder of toner with poor developability increases on the developing roller. It becomes difficult to develop the electrostatic latent image, and the density of the formed image decreases as printing is repeated. For example, in this embodiment, in each case, the image density falls below the standard value of 1.30 by repeating printing of 10,000 sheets.

  INDUSTRIAL APPLICABILITY The present invention is useful as a developing unit in an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine using an electrophotographic method.

1 shows an example of an image forming apparatus of the present invention focusing on a system for a developing process. FIG. 4 is a diagram illustrating the flow of toner during image formation and non-image formation.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Magnetic roller 2 Developing roller 3 Photoreceptor drum 4 Carrier 5 Toner 9 Regulator blade 10a, 10b Mixer 11 Exposure device 12 Charging device 13 Primary transfer roller 14 Printed material 15 Toner container

Claims (7)

In an image forming apparatus for forming an image by developing an electrostatic latent image on a photoreceptor with a thin toner layer formed on the surface of a developing roller through a magnetic brush of toner and a carrier of a magnetic roller,
The developing roller is made of aluminum, an oxide film of aluminum having a thickness of at least 5 μm is formed on the surface thereof, and the interval between the developing roller and the photosensitive drum tube is set to 150 to 300 μm. Image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the thickness of the aluminum oxide film is 10 to 20 μm, and an interval between the developing roller and the photosensitive drum tube is 150 to 280 μm. When forming an image by developing an electrostatic latent image on a photoreceptor with a thin toner layer formed on the surface of a developing roller through a magnetic brush of toner and a carrier of a magnetic roller,
An image forming apparatus, wherein the developing roller is made of aluminum, an oxide film of aluminum having a thickness of at least 5 μm is formed on the surface thereof, and an interval between the developing roller and the photosensitive drum tube is set to 150 to 300 μm. make use of,
A DC voltage on which an AC voltage is superimposed is applied to the developing roller,
The frequency of the AC current at the time of development of the electrostatic latent image is controlled to be higher than the frequency of the AC current at the time of non-development, and the charged toner is developed while selectively flying on the electrostatic latent image. An image forming method.   4. The image forming method according to claim 3, wherein the frequency during the development is 1 to 4 kHz.   4. The image forming method according to claim 3, wherein the frequency during the development is 1 to 3 kHz.   4. The image forming method according to claim 3, wherein the non-developing frequency is 4 to 8 kHz.   4. The image forming method according to claim 3, wherein the non-developing frequency is 5 to 8 kHz.

Images