JPH0934261A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device employing a latent image carrier having a friction factor as low as possible so as to improve a cleaning effect and capable of preventing the occurrence of an abnormal image likely to occur under this condition. SOLUTION: A magnet P1 is arranged inside a developing sleeve 9 so as to form repulsive magnetic fields by adjacent magnetic poles having the same polarity by setting the surface of a photosensitive drum 1 to a static friction factor of 0.2 to 0.4 for a cotton No.3 indicated by JISL 803 and placing the magnet P1 opposite to the photosensitive drum 1 via a developing nip part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.
The latent image formed on the latent image carrier is adsorbed by adsorbing the developer containing the magnetic powder on the latent image carrier holding the latent image and the non-magnetic developing sleeve containing the magnetic field generating means inside. And a developing device that develops at the developing position with the developer on the developing sleeve.

[0002]

2. Description of the Related Art Conventionally, in the copying process of an image forming apparatus of this type, in order to improve the cleaning performance of the surface of a latent image carrier, in many cases, a solid lubricant (for example, Teflon, polyethylene, polypropylene, stearin) is used. A means for adding or supplying fine powder of a low surface energy substance such as zinc acid) to the surface of the latent image carrier in a developer or via a cleaning brush is used. Such means is employed because when the surface of the latent image bearing member is coated with the solid lubricant, the frictional resistance of the surface decreases, so that the deposits attached to the surface can be easily removed from the surface. This is because it is possible to improve the cleaning performance and prevent scratches on the surface. In addition, when the static friction coefficient with respect to cotton No. 3 shown in JIS L0803 is 0.4 or less, preferably 0.3 or less, there is an effect that good cleaning can be performed.

[0003]

However, in this structure, when the solid lubricant in the form of a fine powder, which is a low surface energy substance, adheres to the surface of the latent image carrier or excessively adheres to it, toner development is performed. At this time, the problem that the toner is prevented from sitting on the latent image of the latent image carrier becomes remarkable. As a result, in particular, when the solid lubricant excessively adheres to the surface of the latent image bearing member, specifically, when the friction coefficient is 0.3 or less, white stripes are disturbed in the black portion of the image. In some cases, the trailing edge of the image may appear white, or fine lines may be cut. Therefore, the present applicant has previously proposed an image forming apparatus in which the application amount of the solid lubricant is finely controlled in accordance with the toner concentration on the latent image carrier in order to prevent the above-mentioned problems. Further, the same applicant has proposed a latent image carrier which can prevent the sliding phenomenon of toner particles by roughening the surface (Japanese Patent Publication No. 1-1586).
No. 4). Furthermore, the same applicant has proposed an image forming apparatus in which a metal roller having a roughened surface is brought into contact with the surface of the latent image carrier to remove the solid lubricant excessively attached to the surface. (Jitsuko Sho 62-3940
No. 6 publication). However, when these devices are applied, there are problems that the manufacturing cost increases and the configuration becomes complicated. Further, as described above, from the viewpoint of improving the cleaning effect on the surface of the latent image bearing member, it is desirable that the friction coefficient of the surface is as low as possible, but from the viewpoint of not generating an abnormal image such as a ears trace. However, it is desirable that the coefficient of friction of the surface is as high as possible, and it is difficult to satisfy such conflicting conditions.

The present invention has been made in view of the above problems, and an object of the present invention is to employ a latent image carrier having a friction coefficient as low as possible in order to improve the cleaning effect. An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of an abnormal image that may occur below.

[0005]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention comprises a latent image carrier that holds a latent image and a non-magnetic developing sleeve that accommodates magnetic field generating means inside. An image forming apparatus including: a developing device that adsorbs a developer containing magnetic powder on the upper surface, and develops the latent image formed on the latent image carrier at a developing position with the developer on the developing sleeve. In JIS, the surface of the latent image carrier is
0803 has a static friction coefficient of 0.
2 to 0.4, and the magnetic field generating means is configured to form a repulsive magnetic field at the developing position by adjacent magnetic poles of the same polarity.

Here, the latent image carrier may be made of a material having a surface friction coefficient of 0.2 to 0.4, or a latent image carrier such as selenium or OPC generally used. The friction coefficient may be adjusted within the above range by applying a desired amount of the above solid lubricant to the surface of the image bearing member.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as copying machine) which is an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of a copying machine according to the present embodiment. The copying machine shown in FIG. 1 includes a charge eliminating lamp 2, a charging charger 3, an optical system 4, a developing device 5, a transfer charger 6, a cleaning brush 7, a cleaning blade 8 and the like around a photosensitive drum 1. In order to obtain a copy by using such a device, first, the surface of the photosensitive drum 1 is charged by the charging charger 3, and the optical system 4 irradiates a light image (image exposure) to form a latent image, and then the developing device 5 is used. Developing with the toner carried on the developing sleeve 9 to form a visible image, then the toner image is transferred onto the transfer paper 10 by the action of the transfer charger 6, and the toner on the transfer paper 10 is further removed. The fixing means (not shown) heat-bonds and pressure-fixes the transfer paper 10. Then, the surface of the photosensitive drum 1 after the toner image is transferred onto the transfer paper 10 is cleaned by the cleaning brush 7 and the cleaning blade 8, further discharged by the discharging lamp 2 and charged by the charging charger 3 again. After that, the same steps are repeated.

FIG. 2 is a schematic configuration diagram of a developing device applied to the copying machine of this embodiment. In FIG. 2, the developing device 5 is a two-component dry developing device that uses a so-called two-component developer (hereinafter, simply referred to as a developer) including toner and carrier, and includes a developing container 11 and a hopper portion 12. It A replenishing roller 13 for replenishing the toner stored in the hopper section 12 to the developing section is provided in an opening of the hopper section 12 that communicates with the developing container 11. Further, inside the hopper section 12, a hopper is provided. An agitator 14 is provided for facilitating the replenishment of toner from the section 12 to the developing container.

Inside the developing container 11, a paddle 15 and a stirring impeller 16 are provided along the bottom of the developing container 11 as a fixing member. Further, in the opening portion of the developing container 11 facing the surface of the photosensitive drum 1, the photosensitive drum 1
By rotating in the direction of arrow b with a predetermined linear velocity ratio,
A developing sleeve 9 that supplies a developer to the photosensitive drum 1 is provided. Inside the developing sleeve 9, a magnet (hereinafter, referred to as a cut magnet) P1 as a magnetic field generating means for forming a repulsive magnetic field proposed in Japanese Patent Laid-Open No. 54-95243 is provided via a developing nip portion to a photosensitive drum. It is arranged at a position facing 1 and, in addition to this, is provided with a plurality of magnets in the circumferential direction of the sleeve. Further, in order to make the height of the spikes of the developer held on the surface of the developing sleeve 9 constant on the downstream side in the rotation direction from the position where the paddle 15 supplies the developer to the surface of the sleeve 9, the surface of the sleeve 9 is developed. The doctor 17 for scraping off the agent is provided in a state where the tip portion thereof has a predetermined gap with the developing sleeve 9. Also,
In the vicinity of the position where the doctor 17 is arranged, the doctor 1
The developer scraped from the surface of the developing sleeve 9 by 7 is agitated in the rotation axis direction of the developing sleeve 9 (hereinafter, referred to as a lateral direction) while the transport screw 18 is rotatably held. A separator 20 having a plurality of guide plates 19 is provided to convey the impeller 16 to the vicinity thereof.

Next, the developing device 5 configured as described above.
The operation will be described with reference to FIG. In the developing device 5 of this embodiment, the toner concentration in the developer is lowered by, for example, reading the density of the toner image formed on the surface of the photosensitive drum 1 under a certain condition with a photosensor (not shown). If so, the clutch (not shown) is turned on.
Then, the rotational driving force is transmitted from the main body of the copying machine to the supply roller 13, and the supply roller 13 starts to rotate. The stirrer 14 also starts rotating when it is determined that the toner concentration in the developer has become low. By the rotation of the replenishing roller 13 and the rotation of the agitator 14, the toner is replenished from the hopper 12 into the developing container 11. The toner replenished in the developing container 11 is carried to a space d surrounded by the side wall of the developing container 11 and each blade 16a of the impeller 16 for stirring, and the developing which has been present in the developing container 11 in advance in the space is carried out. Mix with the agent. Further, since the stirring impeller 16 rotates in the direction of the arrow c, this rotation causes the newly replenished toner and the developer already existing in the developing container 11 to stir in the developing container 11 while being stirred. Bottom wall and each blade 16
It is transported to a space e surrounded by a.

Then, the developer frictionally charged by the stirring impeller 16 is conveyed to the paddle 15. Here, although the developer conveyed to the paddle 15 is charged, it is not sufficiently stirred and the toner distribution is uneven.
By rotating the paddle 15 at a high speed of, for example, 100 rpm or more, the developer is agitated by the centrifugal force due to the rotation, and the developer is agitated to make the toner distribution uniform.

The developer, which is splashed and agitated by the paddle 15, adheres to the surface of the developing sleeve 9 by the action of the cut mag P1 contained in the developing sleeve 9 and rotates together with the rotation of the developing sleeve 9. , And is conveyed to a space g formed by the developing sleeve 9 and the separator 20. The developer is subjected to pressure by passing through the space g where the gap is gradually narrowed in the rotation direction of the developing sleeve 9, and is again triboelectrified.

The developer having passed through the space g is further conveyed along with the rotation of the developing sleeve 9 to be conveyed in the direction of the nip portion N between the developing sleeve 9 and the photosensitive drum 1, and the doctor 17 Part of it is scraped off to form ears with a certain height. The developer spikes having the constant height are conveyed to the nip portion N and develop the latent image formed on the surface of the photoconductor drum 1 to form a toner image.

On the other hand, the excess developer scraped off by the doctor 17 slides down on the upper surface of the separator 20 while being regulated by the guide plate 19 disposed on the upper surface of the separator 20. The guide plate 19 is provided obliquely from the back side to the front side, and the developer is fed from the back side to the front side and is laterally stirred. Further, a hole is provided in a part of the front side of the upper surface of the separator 20, and a part of the excess developer reaches the vicinity of the conveying screw 18 through the hole, and the developer is conveyed by the conveying screw 18 to the front side. Is transported to the back side. By the conveyance from the back side to the front side by the guide plate 19 and the conveyance from the front side to the back side by the conveyance screw 18, the developer is uniformly stirred in the lateral direction. And
The developer uniformly stirred in the lateral direction slides down the separator 20 and is conveyed to the space d surrounded by the side wall of the developing container 11 and each blade 16a, and thereafter, the above-described operation is repeated.

Here, the friction coefficient (μ) on the surface of the photosensitive drum 1 decreases as the amount of the solid lubricant 21 shown in FIG. 1 attached to the surface of the photosensitive drum 1 increases. Then, when the friction coefficient decreases, an abnormal image due to the above-mentioned ear mark is generated due to this. The photosensitive drum 1 when the lubricant 21 is not attached
The friction coefficient (μ) of the surface is about 0.4 to 0.5 for a commonly used selenium type photoreceptor or OPC type photoreceptor.

Therefore, the inventors of the present invention have made earnest studies on the relationship between the friction coefficient (μ) on the surface of the photosensitive drum 1 and the above-mentioned problems, and the results shown in FIG. 3 have been obtained.
FIG. 3 shows the photoconductor drum for a case in which a normal magnet having one peak is used at a position facing the photoconductor drum 1 through the developing nip portion and the case where a cut magnet P1 having two peaks is used. Friction coefficient of 1 (μ)
The degree of spikes (a phenomenon in which vertical white stripes appear in the black portion of the image, the trailing edge of the image is white, or fine lines are cut) when the image is changed, and the degree of background stain on the photosensitive drum 1 are shown. It is a graph. The linear velocity vr of the developing sleeve 9
Linear velocity ratio (vr / v) between the linear velocity vp of the photosensitive drum 1 and
p) is 2.0 and the rotation speed vp of the photosensitive drum 1 is 430
mm / sec. The vertical axis of FIG. 3 indicates the degree of the traces of the ears by the developer magnetic brush and the degree of the background stain of the photosensitive drum 1, and the smaller the value is, the stronger the degree is. That is, a good level with no noise is rank 5, a level with which noise is not noticeable is rank 4, a degree with noise is within a practical range to a rank 3, and a level with which noise hinders practical use. Is ranked as Rank 2, and the degree to which noise is severely unusable at all is ranked as Rank 1. The horizontal axis represents the friction coefficient (μ) of the photosensitive drum 1. In addition, the characteristic lines of the ear trace and the background stain when a magnet having one peak is used are indicated by a and b, respectively, and the characteristic lines of the ear trace and the background stain when using the cut mag P1 are indicated by a ′ and b ′. Shows.

According to FIG. 3, the characteristic lines a and a'are both
It can be understood that the smaller the friction coefficient (μ) is, the lower the ear spike rank is, but the use of the cut mug P1 is less likely to lower the ear spike rank. However, the cut mug P
When the friction coefficient (μ) is 0.4 or more, the characteristic line b ′ when the cut mag P1 is used is more soiled than the characteristic line b when the normal magnet is used. The rank of will decrease.

Also, in the case of a normal magnet, the chain of developer ears at the developing nip portion is strong, but due to the frictional force with the photoconductor drum 1, the chain is broken or the carrier rotates, and the phenomenon of ears traces is noticeable. Although it does not affect the image quality because it disappears, when the friction coefficient (μ) decreases, the chain does not break and the rotation of the carrier also decreases, so the phenomenon of spikes is conspicuous and the image quality deteriorates. On the other hand, in the cut mag P1, the chain is weakly connected, and a gap is easily formed in the developing nip portion, and the movement of the developer is relatively free, so that the developing ability is enhanced and the reproducibility of the line is particularly improved. The present inventors have found that the effect of improving the sprouting rank is better when the cut magnet P1 is used than when the normal magnet is used, particularly in the region (0.
3 or less). In particular, when the cut mug P1 is used, when the friction coefficient (μ) is high, the background stain tends to appear as shown in the figure. Therefore, by lowering the friction coefficient, the margin for the background stain is increased. be able to.

FIG. 4 shows the magnetic flux density distribution on the developing sleeve 9. In the figure, the solid line shows the characteristics when the cut mag P1 is used, and the broken line shows the characteristics when the usual magnet having one peak is used. In addition,
The numerical value shown in the parentheses in the figure is the peak value of the magnetic flux density of the cut mag P1. Here, in the developing nip portion, in addition to the cut magnet P1 as shown in FIG. 4, block magnets of the same polarity are arranged side by side, or a magnetic material of the same polarity is magnetized close to a cylindrical magnetic body. Although a cut magnet can be used, the cut magnet is more advantageous than other magnets in terms of downsizing, maintaining the accuracy of the magnetic flux density, and so on. A cut mug as shown in 2 is used.

From the above, by setting the friction coefficient of the surface of the photosensitive drum 1 to 0.2 to 0.4, the cleaning performance of the surface of the photosensitive drum 1 can be improved.
In addition, by setting the friction coefficient to 0.2 or more, a remarkable effect can be obtained in the point of preventing the ears by using the cut mag that forms the repulsive magnetic field at the position P1, and the formed image can be obtained. White stripes, white spots on the rear edge of the image,
It is possible to prevent the occurrence of an abnormal image such as a thin horizontal line. Further, by setting the coefficient of friction to 0.4 or less, it is possible to suppress toner adhesion to the background portion which is likely to occur when using the cut mag. Therefore, a good image can be obtained. Further, when the surface of the photoconductor drum 1 after the visualized toner image is transferred to the transfer paper 10 is cleaned by the cleaning brush 7 or the cleaning blade 8, the frictional force with the photoconductor drum 1 is reduced. It is possible to prevent the cleaning member and the surface of the photosensitive drum 1 from being deteriorated due to wear over time, and it is possible to extend the life of each of them. Further, in the present embodiment, since the solid lubricant is used to reduce the friction coefficient, it is possible to easily remove the blurred material remaining on the photosensitive drum and prevent the occurrence of a blurred image. it can.

[0021]

[Example] As a result of a copy test conducted under the following conditions, a good image was obtained. Linear velocity of photosensitive drum 1 vp: 430 mm / sec Toner density: 1.5 to 2.5% / w Toner charge amount: 20 to 30 μc / g Carrier average particle diameter: 70 μm Toner average particle diameter: 9 μm Type and photoconductor diameter: OPC, 100mm Development sleeve diameter: 25mm

FIG. 5 shows the relationship between the linear velocity ratio (vr / vp) between the developing sleeve and the photoconductor drum 1 and the ears traces and the background stain for the friction coefficients (μ) of 0.2 and 0.45. It is the graph shown. Here, the characteristic lines of the ear trace and the background stain when the friction coefficient is 0.45 are shown by c and d, respectively, and the characteristic lines of the ear trace and the background stain when the friction coefficient is 0.2 are c ′, respectively. It is indicated by d '. According to this figure, assuming that the standard of the rank of the ear trace and the background stain is 3.5 or more, for the photoconductor drum 1 having a friction coefficient (μ) of 0.45,
When the linear velocity ratio (vr / vp) is in the range of 1.5 to 2.5, it becomes good, and the characteristic lines c and d have the same rank of 2.0.
Near is preferred. Further, when the friction coefficient (μ) is about 0.2, it becomes good in the range of 1.2 to 2.0, and it is preferable that the vicinity of 1.5 where the ranks of the characteristic lines c ′ and d ′ are the same.

[0023]

According to the image forming apparatus of the first aspect of the present invention, the coefficient of friction of the surface of the latent image carrier is set to 0.2 to 0.4 to improve the cleaning performance of the surface of the latent image carrier. In addition, it is possible to suppress the abrasion caused by the cleaning means and the surface of the latent image carrier rubbing against each other, and it is possible to prolong the life of each. Also,
By setting the friction coefficient to 0.2 or more, by using a magnet that forms a repulsive magnetic field at the developing position as the magnet located at the developing main pole, a remarkable effect can be obtained from the standpoint of preventing ears. It is possible to prevent abnormalities such as white streaks, white spots at the rear end of the image, and thinning of horizontal lines from occurring in the formed image. Further, by setting the friction coefficient to 0.4 or less, it is possible to suppress toner adhesion to the background portion that is likely to occur when using a magnet that forms a repulsive magnetic field at the developing position. From the above, there is an excellent effect that a good image can be obtained.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of an electrophotographic copying machine according to an embodiment.

FIG. 2 is a front view showing a schematic configuration of a developing device applied to the copying machine of FIG.

FIG. 3 is an explanatory diagram showing a relationship between a friction coefficient of a photosensitive drum and a degree of background dirt and ear marks.

FIG. 4 is an explanatory diagram showing a magnetic flux density distribution of a cut mag housed inside a developing sleeve.

FIG. 5 is a linear velocity ratio (vr) between the developing sleeve and the photosensitive drum.
/ Vp), and an explanatory view showing a relationship between the background stain and the degree of the ear mark.

[Explanation of symbols]

 1 Photoreceptor Drum 2 Charge Eliminating Lamp 3 Charging Charger 4 Optical System 5 Developing Device 6 Transfer Charger 7 Cleaning Brush 8 Cleaning Blade 9 Developing Sleeve 10 Transfer Paper 11 Developing Container 12 Hopper 13 Replenishing Roller 14 Stirrer 15 Paddle 16 Stirring Impeller 16a Blade 17 Doctor 18 Transfer Screw 19 Guide Plate 20 Separator 21 Solid Lubricant P1 Cut Mug

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chiemi Kenko 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (1)

[Claims] 1. A latent image bearing member for holding a latent image and a non-magnetic developing sleeve containing a magnetic field generating means therein, and a developer containing magnetic powder is adsorbed on the latent image bearing member. And a developing device for developing the formed latent image at a developing position with a developer on the developing sleeve, wherein the surface of the latent image carrier is subjected to static friction against cotton No. 3 as specified in JIS L0803. An image forming apparatus, wherein the coefficient is set to 0.2 to 0.4, and the magnetic field generating means is configured to form a repulsive magnetic field at the developing position by adjacent magnetic poles of the same polarity.