JP2009271292A - Image forming apparatus and developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, adopting a non-magnetic single component development system using a hard roller and effectively restraining uneven density of an image due to bending of the roller; and to provide a developing device. <P>SOLUTION: The image forming apparatus includes: a photoreceptor 2; a charging device for charging the surface of the photoreceptor 2; an exposure device for forming a latent image by exposing the charged photoreceptor 2; a developing roller 12 carrying a non-magnetic single component developer and opposite to an image support through a void; and a supply roller 13 pressed to the developing roller 12 in the direction of approaching the photoreceptor 2, wherein the developing roller 12 is a hard roller, the inside of an image area in the axial central portion of the developing roller 12 is roughened, the outside of the image area at both axial end portions is not roughened, and surface roughness is larger at a position rather closer to the end within the image area as compared with that in a position rather closer to the center. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-magnetic one-component developing type developing device and an image forming apparatus using the same. More specifically, the present invention relates to an image forming apparatus and a developing apparatus in which a developing roller is disposed in non-contact with an image carrier and an electric field is formed in a gap therebetween to perform development processing.

  Some non-magnetic one-component developing systems have an image carrier and a developing roller that are not in contact with each other. For example, there are some in which gaps of about several tens to several hundreds of micrometers are provided and these are arranged in parallel to each other. In some developing devices, a supply roller formed of foam or the like is pressed against the developing roller in order to supply the developer to the developing roller. In the case where the supply roller is disposed on the opposite side of the image carrier as viewed from the developing roller, the direction of pressure contact by the supply roller is the direction in which the developing roller is pushed toward the image carrier. When the developing roller is not sufficiently rigid, there is a problem that the central portion of the developing roller bends toward the gap due to the pressure contact force of the supply roller.

  In recent years, there has been an increasing demand for cost reduction and space saving in image forming apparatuses. For this reason, for example, a developing roller of a developing device employs a small-diameter hard roller. This is because a hard roller without an elastic layer can be manufactured at a lower cost than a soft roller in which a core is coated with rubber or the like. However, if the developing roller has a small diameter, the rigidity generally decreases accordingly. Therefore, the developing roller is likely to be bent due to the pressure contact of the supply roller.

  When the developing roller is bent as described above, the gap between the developing roller and the image carrier is narrower at the center of the developing roller than at the end. For this reason, there is a difference in the amount of toner that moves beyond the gap between the central portion and the end portion of the developing roller, which is one cause of development unevenness. Therefore, there is a type in which the central portion of the developing roller is cut to correspond to the bending amount and processed into a so-called inverted crown shape. Thereby, the distance between the developing roller after bending and the surface of the image carrier is made as constant as possible.

Patent Document 1 discloses a two-component developing type image forming apparatus in which the surface roughness of the outer surface of the developing sleeve is gradually roughened from the center to both ends. Thereby, it is said that the amount of pumping at both ends where the magnetic force of the magnet roller becomes weak can be increased.
JP 2007-86092 A

  However, in the countermeasure for making the developing roller in an inverted crown shape, a cutting process is added as compared with the one before the countermeasure, so that the time and cost for manufacturing increase. Also, if the bending amount is large, it is necessary to cut the central part by that much. If the amount to be cut is large, the pressing force to the developing roller by the regulating member, the supply roller, or the like may be uneven. In such a case, there is a problem that image fogging, density unevenness, and the like occur due to non-uniform toner charge amount or non-uniform toner supply amount.

  In addition, since the image forming apparatus described in Patent Document 1 is a two-component developing type image forming apparatus, there is little possibility that toner and carriers are scattered beyond the width of the magnet roller to the longitudinal end of the developing roller. . Therefore, it was sufficient to simply increase the pumping volume at both ends. However, in the non-magnetic one-component developing method, the toner scattering beyond the end of the developing roller in the axial direction is one of the problems that may occur conventionally. Therefore, the method for adjusting the surface roughness described in Patent Document 1 cannot be applied as it is to a non-magnetic one-component developing type developing apparatus.

  The present invention has been made to solve the problems of the conventional image forming apparatus and developing apparatus described above. That is, the subject is a non-magnetic one-component developing type developing device using a hard roller and an image forming device having the same, and an image forming device and a developing device that can effectively suppress image density unevenness due to roller bending. Is to provide.

  The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, includes an image carrier, a charging device for charging the surface of the image carrier, and exposure for forming a latent image by exposing the charged image carrier. An apparatus, a developer carrier facing the image carrier through a gap while carrying a non-magnetic one-component developer, and a supply roller pressed against the developer carrier in a direction approaching the image carrier In the image forming apparatus, the developer carrying member is a hard roller, the surface of the developer carrying member is roughened in the axial central portion, and the developer carrying member is outside the image region at both axial end portions. Is not roughened, and the surface roughness at the position near the end in the image area is larger than the position near the center.

  According to the image forming apparatus of the present invention, the developing roller is a hard roller, and the end side of the image area in the axial direction is not roughened. In the hard roller having no elastic layer, the developer hardly adheres to the unroughened portion. Therefore, even in the non-magnetic one-component development system, there is no possibility that the developer leaks outside the end in the axial direction. Further, in the image area, the surface is roughened so that the surface roughness is larger at the end in the axial direction than at the center. At locations where the surface roughness of the developing roller is large, the developer transport amount is large. Accordingly, the surface roughness can be adjusted so as to cancel the image density unevenness due to bending.

Furthermore, in the present invention, it is desirable that the surface roughness in the image region is continuously increased from the central portion toward the end portion.
If this is the case, there will be no place where the surface roughness changes abruptly.

Furthermore, in the present invention, it is desirable that the developer carrying member is a hollow pipe made of aluminum and roughened by blasting.
Aluminum hollow pipes are lightweight and suitable for developer carriers. In addition, if the blasting process is used, a roughening process suitable for a non-magnetic one-component developer is possible.

Further, in the present invention, it is desirable that the diameter of the developer carrier does not exceed 1/15 of the axial length of the image forming area.
In such a thin developer carrier, bending is more likely to occur. In the present invention, good results can be obtained even with such a developer carrier.

Furthermore, in the present invention, it is desirable that the size of the gap between the developer carrier and the image carrier does not exceed 200 μm.
Even with such a small gap, good results can be obtained according to the present invention.

  Furthermore, the present invention provides a developer carrying member that supports a non-magnetic one-component developer while facing the image carrying member through a gap, and a supply roller that presses the developer carrying member toward the image carrying member. The developer carrying member is a hard roller, the surface of the developer carrying member in the axial center portion is roughened, and the image regions at both axial end portions are provided. The surface is not subjected to a roughening process, and the position near the end in the image area extends to a developing device having a larger surface roughness than the position near the center.

  According to the image forming apparatus and the developing apparatus of the present invention, even in a non-magnetic one-component developing type developing apparatus using a hard roller and an image forming apparatus having the non-magnetic one-component developing system, image density unevenness due to roller bending is effectively prevented. Can be suppressed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus having a non-magnetic one-component developing device.

  As shown in FIG. 1, the image forming apparatus 100 according to this embodiment includes four color image forming units 20 </ b> Bk, 20 </ b> C, 20 </ b> M, and 20 </ b> Y arranged along the intermediate transfer belt 1. Each of the image forming units 20Bk, 20C, 20M, and 20Y has a photoreceptor 2. Further, a charging device 21, an exposure device 22, a developing device 10, a primary transfer device 24, and a cleaner device 25 are disposed around the photoreceptor 2. Further, the intermediate transfer belt 1 is rotated as indicated by an arrow A in the drawing at the time of image formation. A secondary transfer device 26 is disposed downstream of the image forming units 20Bk, 20C, 20M, and 20Y in the rotational direction of the intermediate transfer belt 1.

  In this embodiment, toner images of respective colors are formed on the photoreceptor 2 by the image forming units 20Bk, 20C, 20M, and 20Y, respectively. Then, the images are sequentially transferred to the intermediate transfer belt 1 and toner images of respective colors are superimposed. The superimposed toner images are transferred onto the recording paper by the secondary transfer device 26.

  As shown in FIG. 2, the developing device 10 of the present embodiment is arranged to face the photosensitive member 2 and supplies developer to the electrostatic latent image on the photosensitive member 2. The developing device 10 includes a housing 11, a developing roller 12, a supply roller 13, a regulating blade 14, a charge removal sheet 15, and an elastic material 16. The developing roller 12, the supply roller 13, the regulating blade 14, and the elastic material 16 are disposed inside the housing 11.

  The developing roller 12 carries an appropriate amount of developer, faces the photoreceptor 2, and supplies the developer to the photoreceptor 2. In this embodiment, a non-magnetic one-component developer that does not use a carrier is used as the developer. The developing roller 12 is arranged in parallel to the photoreceptor 2 with a gap. In this embodiment, the size of the gap between the photosensitive member 2 and the developing roller 12 does not exceed 200 μm. The gap value is a design value defined by a DS roller provided between the roller shaft at the end of the developing roller 12 and the shaft of the photosensitive member 2. At the time of image formation, as indicated by an arrow in FIG.

  The supply roller 13 is for supplying the developer in the housing 11 to the development roller 12. The supply roller 13 is an elastic roller and is pressed against the developing roller in a direction perpendicular to the axis. Further, the supply roller 13 is rotated in the counter direction with respect to the developing roller 12 as shown by an arrow in FIG.

  The regulating blade 14 is for regulating the layer thickness of the developer carried on the developing roller 12 and charging the developer by rubbing. The regulating blade 14 is arranged in contact with the surface of the developing roller 12 on the downstream side with respect to the rotation of the developing roller 12 from the contact portion between the developing roller 12 and the supply roller 13.

  The neutralization sheet 15 is for neutralizing the developer remaining on the development roller 12 even after passing through the development area. The developing area is a range in which the developing roller 12 and the photosensitive member 2 face each other and the developer can be supplied from the developing roller 12 to the electrostatic latent image formed on the photosensitive member 2. For this reason, the static elimination sheet 15 is disposed in contact with the surface of the developing roller 12 on the downstream side of the rotation of the developing roller 12 with respect to the location where the developing roller 12 and the photosensitive member 2 face each other. In this embodiment, the static elimination sheet 15 is pressed against the developing roller 12 by an elastic material 16 fixed to the housing 11.

  In this embodiment, a partially blasted aluminum pipe is used as the developing roller 12. This is lighter than iron pipes and aluminum rods made of muku material, and cheaper than a soft roller with a rubber layer on the surface. When such a hard roller is used as the developing roller 12, it is known that the smaller the surface roughness, the smaller the amount of developer that can be conveyed. That is, the developer hardly adheres to the smooth surface of the aluminum pipe as it is. By increasing the surface roughness, more developer can be adhered to the surface of the developing roller 12.

  The blasting process is a process in which abrasive particles such as glass beads having an average particle diameter of about 60 μm are made to collide with the roller surface by an air flow, thereby finely scratching the surface of the aluminum pipe. It is. The surface roughness of the developing roller 12 can be adjusted by the size of the air flow or the processing time during the blasting process. The developing roller 12 of the present embodiment is such that the surface roughness is large at the axial end portion and the surface roughness is small at the central portion in the image area by adjusting the degree of blasting. Furthermore, the surface roughness is not a step change, but gradually varies in the axial direction.

  Further, in this embodiment, the blasting process is not performed in the area outside the image area at the axial end of the developing roller 12. In other words, it remains the surface of the aluminum pipe of the material. For this reason, the developer is hardly transported in the area where the blasting process is not performed, that is, in the area outside the image area of the developing roller 12. The image area is a length range corresponding to a range in which the electrostatic latent image of the photosensitive member 2 can be formed in the axial length of the developing roller 12. Therefore, the scattering of the developer from the end portion in the axial direction of the developing roller 12 to the outside of the developing device 10 is suppressed.

  Further, since the surface roughness varies depending on the position in the axial direction within the image area, the developer transport amount also varies. In other words, the developer transport amount is small in the central portion where the surface roughness is small in the image area of the developing roller 12 of this embodiment. The conveyance amount is large at the end portion having a large surface roughness. On the other hand, when the amount of developer carried on the developing roller 12 at a time is small, charging by the regulating member is performed more efficiently. For this reason, the charge amount per unit amount of the developer is larger than that in the case where the amount of the developer is large. In other words, the charge amount of the developer is large in the central portion where the surface roughness is small in the image area of the developing roller 12 of this embodiment. The charge amount is small at the end portion having a large surface roughness.

  In this embodiment, as shown in FIG. 2, there is no member in contact with the developing roller 12 on the opposite side of the supply roller 13. Further, since the developing roller 12 is an aluminum pipe, it is not very rigid. For this reason, it is inevitable that the central portion of the developing roller 12 bends to the photosensitive member 2 side by pressing the supply roller 13. That is, with respect to the axial direction of the developing roller 12, the gap with the photoconductor 2 is narrow at the center, and the gap is wide at the end. Of course, this gap difference is not stepwise, but gradually varies in the axial direction.

  In the developing device 10 of this embodiment, the above-described conditions can be adjusted so that image density unevenness does not occur in the axial direction of the developing roller 12. That is, when the both end portions of the image area are used as a reference, the gap with the photosensitive member 2 is narrow at the center portion. This works toward increasing the image density at the center. On the other hand, since the central portion has a small surface roughness, the transport amount of the developer is small. This works toward reducing the image density at the center. In addition, the amount of charge per unit amount of developer is large. This indicates that the amount of developer necessary for canceling the charge amount of the electrostatic latent image on the photosensitive member 2 can be reduced, and this works toward reducing the image density at the center. Therefore, by adjusting the surface roughness of the developing roller 12, the amount of the developer that adheres to the photosensitive member 2 with respect to the electrostatic latent image having the same charge amount is substantially the same at the central portion and the end portion. Can be.

  For example, the number and speed of the particles that collide with the roller differ depending on the pressure of the air flow that causes the abrasive particles to fly during the blasting process, the time for which the blasting process is continued, and the like. As a result, the number of scratches per unit area on the roller surface and the depth of the scratches are different. For example, when the blasting pressure is increased, the number of scratches per unit area increases and the depth of the scratches increases. In the present invention, this state is said to have a large surface roughness. In addition, when the blasting pressure is lowered, the number of scratches per unit area decreases, and the depth of the scratches decreases. In the present invention, this state is said to have a small surface roughness. These differences can also be obtained as the magnitude of the value of the arithmetic average roughness Ra that can be detected by, for example, a surface roughness meter. That is, the value of Ra is large when the surface roughness is large. The value of Ra is small when the surface roughness is small.

  Therefore, in this embodiment, the blast processing conditions may be adjusted so that an appropriate surface roughness can be obtained according to the position in the axial direction of the developing roller 12. For example, an aluminum pipe roller having a length of 220 mm and a diameter of 12 mm can be blasted to be used as the developing roller 12 of this embodiment. In the developing roller 12 having a bending amount of about 90 μm when attached to the image forming apparatus, the arithmetic average roughness Ra may be about 0.7 μm at the center and about 1.1 μm at the end. As a result, the influence on the image density due to bending and the influence on the surface roughness cancel each other, and the occurrence of uneven image density at the center and at the edge can be suppressed.

  This embodiment is particularly effective for the thin developing roller 12 whose roller diameter does not exceed 1/15 of the length of the image forming area. For example, in the A4 printer, the width of the image area is 220 mm, which corresponds to the axial length of the developing roller 12. According to this embodiment, it is possible to obtain the developing roller 12 that does not cause image density unevenness even when a hard roller having a diameter of 14 mm or less is used. In the A3 printer, the width of the image area is 320 mm. According to this embodiment, it is possible to obtain the developing roller 12 that does not cause uneven image density even with a hard roller having a diameter of 20 mm or less.

  This embodiment is particularly effective for the developing device 10 in which the size of the gap between the photosensitive member 2 and the developing roller 12 is 200 μm or less. As described above, in the developing device 10 having a small gap, in general, even slight bending tends to cause development unevenness. By using the developing roller 12 of this embodiment, even such a developing device 10 can effectively suppress image density unevenness.

  Next, examples verified by the inventors through experiments will be described. In this embodiment, three aluminum pipe rollers having a diameter of 12 mm and a wall thickness of 1.5 mm were prepared as the developing roller 12, and three types of developing rollers were prepared as follows. The length of each developing roller was 240 mm. In this experiment, glass beads having an average particle diameter of 60 μm were used, 10 mm at each end was masked, and the remaining 220 mm was blasted. The distance between the nozzle and the roller of the blast processing apparatus was maintained at 130 mm, and the nozzle was moved at a moving speed of 400 mm / min in the roller axis direction.

  In the example, the blast processing pressure (jet air pressure) at the start position was set to 200 kPa, and the processing pressure was gradually decreased from there toward the center. The pressure at the center was 50 kPa, and the processing pressure was gradually increased from there toward the other end. The blasting pressure was again adjusted to 200 kPa at the other end. In Comparative Example 1, the blasting pressure was 200 kPa from the start position to the other end. In Comparative Example 2, the blasting pressure was 50 kPa from the start position to the other end.

  The surface roughness of each roller of Example, Comparative Example 1, and Comparative Example 2 prepared by this process was measured. The result is shown in FIG. Here, measurement was made at five locations, both ends, the center, and an intermediate portion between both ends and the center. In the example, Ra at the center was about 0.7 μm, both ends were about 1.1 μm, and the middle was about 0.9 μm therebetween. On the other hand, Comparative Example 1 was about 1.1 μm throughout. Comparative Example 2 was about 0.6 μm throughout. In the figure, the results of the examples are indicated by squares and solid lines. The results of Comparative Example 1 are indicated by circles and broken lines, and the results of Comparative Example 2 are indicated by triangles and dashed lines. This also applies to FIGS. 4 to 6.

  Next, using a Konica Minolta Magiccolor 2430 model as a testing machine, the development roller was modified to replace the above three types. This image forming apparatus is of a type using a non-magnetic one-component developer. With respect to these three types of image forming apparatuses, the developer transport amount, developer charge amount, and solid image density were measured. The bending amount when an aluminum pipe roller having a diameter of 12 mm was mounted on this image forming apparatus was about 90 μm.

FIG. 4 shows the result of measuring the developer transport amount, FIG. 5 shows the result of measuring the charge amount of the developer, and FIG. 6 shows the result of measuring the image density of the solid image. As shown in each figure, according to the present embodiment, the developer transport amount was about 6 g / m ² at both ends and about 4 g / m ² at the center, which was a valley-like tendency as a whole. . Further, the charge amount of the developer was about 17 μC / g at both ends and about 25 μC / g at the center, and the whole was in a mountain-shaped tendency. The image density (TD) of the solid image was around 1, and there was no significant unevenness.

On the other hand, in Comparative Example 1, the developer transport amount was about 6 g / m ² , and the developer charge amount was about 17 μC / g. The image density of the solid image was about 1 at both end portions and about 1.4 at the center portion, and the whole image had a mountain-shaped tendency. In Comparative Example 2, the developer transport amount was about 4 g / m ² , and the developer charge amount was about 27 μC / g. None of the differences were significant across the entire roller. The image density of the solid image was about 0.7 at both ends and about 1 at the center, and the whole image had a mountain-shaped tendency.

  That is, in both Comparative Example 1 and Comparative Example 2, the developer transport amount and the charge amount are substantially uniform over the entire axial direction, but the density of the formed image is dark at the center and at both ends. It was thin. This is because the gap at the center is reduced by roller bending. On the other hand, in the example, it was confirmed that by adjusting the developer transport amount and the charge amount so as to be different between the central portion and the end portion, no large unevenness occurs in the density of the formed image. . Even after endurance use, the surface roughness of this roller hardly changed. The arithmetic average roughness Ra was a decrease of 0.1 μm or less overall.

  As described above in detail, according to the developing device of this embodiment, the aluminum roller hard roller is subjected to the blasting process, and the developing roller 12 whose surface roughness is different between the central portion and the end portion is used. Yes. Accordingly, the transport amount and the charge amount of the developer can be adjusted to be different between the central portion and the end portion. Therefore, by adjusting these so that the unevenness in image density due to bending is canceled, the unevenness in image density can be suppressed. This makes it possible to effectively suppress uneven development due to bending or the like in a non-magnetic one-component developing type developing device using a hard roller.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the method for adjusting the surface roughness is not limited to blasting. The degree of surface roughness adjustment should be changed according to the relationship between the length and diameter of the roller, the material of the roller, and the like. What is necessary is just to adjust to such an extent that the unevenness of image density is finally suppressed.

1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment. It is a schematic block diagram which shows the developing device which concerns on this form. It is a graph which shows the measurement result of the surface roughness of three types of rollers. It is a graph which shows the measurement result of the conveyance amount of a developer when three types of rollers are used as a developing roller. It is a graph which shows the measurement result of the charge amount of a developer when three types of rollers are used as developing rollers. It is a graph which shows the measurement result of the image density of a solid image when three types of rollers are used as developing rollers.

Explanation of symbols

2 Photosensitive member 10 Developing device 12 Developing roller 13 Supply roller 21 Charging device 22 Exposure device 100 Image forming device

Claims (6)

An image carrier, a charging device that charges the surface of the image carrier, an exposure device that exposes the charged image carrier to form a latent image, and the image while carrying a non-magnetic one-component developer. In an image forming apparatus, comprising: a developer carrier opposite to the carrier through a gap; and a supply roller that presses the developer carrier in a direction approaching the image carrier.
The developer carrier is a hard roller;
A roughening process is performed in the image area at the axially central part of the developer carrier, and a roughening process is not performed outside the image area at both axial end parts.
The image forming apparatus according to claim 1, wherein a surface roughness is larger at a position near the end in the image area than at a position near the center. The image forming apparatus according to claim 1,
2. An image forming apparatus according to claim 1, wherein the surface roughness in the image area increases continuously from the center to the end. The image forming apparatus according to claim 1, wherein:
The developer carrier is
A hollow pipe made of aluminum,
An image forming apparatus characterized by being roughened by blasting. In the image forming apparatus according to any one of claims 1 to 3,
2. An image forming apparatus according to claim 1, wherein the diameter of the developer carrying member does not exceed 1/15 of the axial length of the image forming area. The image forming apparatus according to any one of claims 1 to 4, wherein:
An image forming apparatus, wherein a size of a gap between the developer carrier and the image carrier does not exceed 200 μm. A developing device having a developer carrying member facing the image carrying member through a gap while carrying a non-magnetic one-component developer, and a supply roller that presses the developer carrying member toward the image carrying member In
The developer carrier is a hard roller;
A roughening process is performed in the image area at the axially central part of the developer carrier, and a roughening process is not performed outside the image area at both axial end parts.
The developing device according to claim 1, wherein a surface roughness is larger at a position near the end in the image area than at a position near the center.

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