JP2000039763A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device having such constitution that the suppression of the surface staining of a latent image carrier and a uniform and solid developing characteristic can be established. SOLUTION: This image forming device is constituted so that an image is formed by forming an electrostatic latent image on a latent image carrier which is previously uniformly electrified and whose friction coefficient (μ) of the surface is set to be 0.1<=μ<=0.4 by an optical writing action visualizing the electrostatic latent image by making a developer carrier carrying developer abut on the electrostatic latent image, transferring it on a transfer medium and fixing the transferred image. Then, the friction coefficient (μ') of the developer carrier is set to be larger than that of the latent image carrier and the value (μ') is set to be μ'<0.6.

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, and more particularly, to an image forming apparatus using an electrophotographic process for controlling developer adhesion between a latent image carrier and a developer carrier. Regarding the configuration.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic process such as a printer, a copying machine or a facsimile machine, an electrostatic latent image formed on a latent image carrier such as a photosensitive drum is supplied from a developing device. A visible image is processed by a developer such as toner, and the visible image is electrostatically transferred to a transfer material such as recording paper to obtain a copy.

When the developer from the developing device is supplied to the latent image carrier, a developer layer carried on the surface of developer supplying means such as a developing roller provided in the developing device, The so-called toner layer is in contact with the surface of the latent image carrier, and the toner in the toner layer is electrostatically attracted by the electrostatic force from the electrostatic latent image and adheres to the electrostatic latent image. However, in actuality, the non-electrostatic force generated by the contact state between the toner layer and the latent image carrier causes the toner to be applied to the surface of the latent image carrier, particularly, to the background portion where the electrostatic attraction of the latent image does not act on the toner. In some cases, the latent image carrier may adhere to the ground, and the latent image carrier may be significantly contaminated.

Conventionally, the degree of background contamination is detected by detecting the toner density outside the image area of the latent image carrier, and the amount of the lubricant applied to the surface of the latent image carrier is lubricated according to the degree of the background contamination. A configuration in which the supply effect is controlled by adjusting the contact pressure of the agent application means to improve a cleaning effect performed after image transfer (for example, Japanese Patent Application Laid-Open No. 8-254933), or a toner layer composed of a one-component developer is carried. The relative linear velocity ratio when the developing roller included in the developing material supply means is rotated while being in contact with the photosensitive member as the latent image carrier is set to 1.2 to 3.0 times, particularly 1.5 times. A configuration of up to 2.5 times (for example, JP-A-9-73299) has been proposed.

[0005]

The contact pressure of the lubricant applying means with respect to a latent image carrier such as a photoreceptor and the linear velocity ratio between the latent image carrier and the developing roller of the developer supplying means are changed. In such a case, there were the following problems.

Since the latent image carrier and the developer carrier are in contact with each other via the toner layer, the toner may adhere to the surface of the latent image carrier due to non-electrostatic force as well as electrostatic force. Background stain on the image carrier, so-called background stain, may be worsened. In order to avoid such a situation, when setting the image formation setting process conditions, the contact pressure between the two members or the linear speed ratio of the developer carrier to the latent image carrier is increased. . But,
Increasing the contact pressure increases the load on the driving means for setting the contact pressure, so that an abnormal image due to rotational unevenness called banding is likely to occur, and a line relative to the latent image carrier is generated. When the speed ratio is increased, a state in which the image density is non-uniform, which is referred to as a toner shift, tends to occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having a configuration capable of suppressing the problem of the above-described conventional image forming apparatus, in particular, preventing the latent image carrier from becoming dirty and establishing uniform solid development characteristics. is there.

[0008]

According to the first aspect of the present invention,
Uniformly charged beforehand, the surface friction coefficient (μ) is 0.1 ≦ μ
An electrostatic latent image is formed by light writing on the latent image carrier set to ≦ 0.4, and the developer carrier carrying the developer is brought into contact with the electrostatic latent image, and In an image forming apparatus for forming an image by processing an electro-latent image into a visible image, transferring the image to a transfer medium and fixing the transferred image, the friction coefficient (μ ′) of the developer carrier is determined by the latent image carrier. It is characterized by being larger than the body and having a value (μ ′) of μ ′ <0.6.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the surface roughness (R
_Z ) is set to satisfy 1 <(R _Z ) <6 (μm).

[0010]

FIG. 1 is a schematic diagram for explaining the relationship between a photosensitive drum 1 corresponding to an image carrier and a developing device 2 corresponding to a developer supply means in an image forming apparatus according to an embodiment of the present invention. In FIG. 1, the photosensitive drum 1 is made of an inorganic or organic photosensitive member having a diameter of 50 mm.
The friction coefficient (μ) of the surface is set to 0.1 ≦ μ ≦ 0.4. This coefficient of friction is based on the experiment shown in FIG. FIG. 2 is a schematic diagram showing an experimental structure for obtaining a friction coefficient by the Euler belt method. In FIG. 2, measurement paper (Ricoh PPC
Paper TYPE6200A4 size T) S is 297x
The sheet S is cut into a size of 30 mm, and the center of the measurement sheet S is wound in a range of 90 degrees (π / 2 rad.) In the circumferential direction of the photosensitive drum 1. On one end of the measurement sheet S in the winding direction,
A weight W having a constant weight (0.98 N (100 g)) is attached, and a digital push-pull gauge DS is attached to the other side. The measuring paper S is pulled at a constant speed while the weight W is not shaken, and the photosensitive drum is driven. The value of the digital push-pull gauge DS is measured at the moment when the measuring paper S starts to move on the surface of No. 1. If the measured value at this time is F (N), the friction coefficient (μ) is μ = In (F / 0.98) / (π / 2)
Is required. Among the friction coefficients obtained from the above experimental structure, when the toner is rubbed against the surface of the photosensitive drum 1 by the pressure from the toner layer, the friction coefficient (μ) that can prevent the toner from adhering due to the frictional force due to the rubbing pressure. The values in the following ranges were obtained as values that can prevent background contamination. The coefficient of friction (μ) in the case where a lubricant or the like is not applied to the surface of the photoconductor drum 1, that is, when it is untreated, is 0.4 to 0.6, but tends to increase with time. On the other hand, the friction coefficient (μ) of the photosensitive drum 1 coated with the lubricant is 0.1 to 0.6.
The result was obtained. From these results, by setting the coefficient of friction (μ) of the photosensitive drum to 0.1 to 0.4, the toner adhesion when the surface of the photosensitive drum 1 is rubbed, particularly the electrostatic latent image It is possible to prevent the toner from adhering to the so-called background portion other than the portion where the is formed.

The friction coefficient of the surface depends on the particle diameter of the toner used for the visible image processing, but when the volume average particle diameter is 4 to 10 μm, the friction coefficient of the photosensitive drum is reduced. This is maintained by applying a so-called lubricant. For this purpose, the lubricant is supplied directly for each predetermined number of image forming operations, i.e., every time a copying operation is performed, or the application means carrying the lubricant is applied to the surface of the photosensitive drum 1 constantly or every predetermined number of copying operations. This is done by contact. The photosensitive drum 1 is charged to a predetermined surface potential in advance by a known charging unit, and an electrostatic latent image corresponding to a document image or written information is formed by a known optical writing unit.

The developing device 2 includes a developing roller 2B facing the photosensitive drum 1 in a developing tank 2A, and a developing roller 2B.
B, a supply roller 2C for supplying a toner composed of a one-component developer, a regulating blade 2D for regulating the layer thickness of the toner carried on the developing roller 2B, and an agitator 2
E.

The toner used in the developing device 2 is obtained by mixing a charge control agent (CCA) and a colorant with a resin such as polyester, polyol or styrene acryl, and externally adding a substance such as silica or titanium oxide to the surroundings. It is configured. The average particle size of the toner is selected from 3 to 12 μm, and in this embodiment, 7.5 μm is used. As for the particle size, it is possible to satisfy the demand for high resolution and to reduce the particle size.

The developing roller 2B has a surface friction coefficient (μ ′) larger than that of the photosensitive drum 1 (μ ′).
Elastic material such as rubber set to <0.6 is used,
The outer diameter is set to 10 to 30 mm, in this embodiment to 16 mm, and the surface roughness (R _Z ) is set to 1 <(R _Z ) <6 (μm). It rotates with a speed difference in the direction. The relationship between the friction coefficient between the photosensitive drum 1 and the developing roller 2B is set based on the following reason. If the friction coefficient of the developing roller 2B is smaller than that of the photosensitive drum, the scavenging force of the developing roller 2B decreases, and the toner adhered to the background of the photosensitive drum 1 does not return to the developing roller 2B. Background dirt is generated on the body drum 1. When the friction coefficient (μ ′) of the developing roller 2B is 0.6 or more,
Banding when rotation unevenness occurs due to an increase in rotation torque due to the contact between the developing roller 2B and the photosensitive drum 1 is likely to occur, thereby causing an abnormal image. Therefore, the occurrence of the background stain and the occurrence of the abnormal image as described above can be prevented by the friction coefficient of the developing roller 2B.

The rubber material used for the developing roller 2B includes silicone rubber, butadiene rubber, nitrile-butadiene rubber (NBR), hydrin, ethylene-propylene-gen rubber (EPDM) and the like. Further, the surface of the developing roller 2B can be coated with a coating material in order to stabilize the quality over time, and in this case, a silicon-based or Teflon-based material is used. The former material has good chargeability of the toner, and the latter material has excellent releasability. Furthermore, it is also possible to contain a conductive material such as carbon black in order to improve conductivity, and the thickness of the coating layer is set to 5 to 50 μm. Is preferred.

The developing roller 2B is in contact with the photosensitive drum 1 via a toner layer.
Pressing means such as a coil spring or a leaf spring is used. In this embodiment, the hardness (HS) of the developing roller 2B is 30 ° (J).
IS-A), the contact pressure is 3 to 16 g · f / mm
Is set to The greater the number of pressing means for contact, the smaller the contact unevenness between the opposing surfaces of the developing roller 2B and the photosensitive drum 1; It is preferable to secure When the contact pressure is below the lower limit of the appropriate range, the developing ability becomes non-uniform, and a sufficient developing amount cannot be obtained. If the upper limit is exceeded, the scavenging force of the developing roller 2B will increase and the toner layer will be compressed and condensed. The residual image is left on the roller 2B, and an abnormal image such as unevenness of a solid image is easily generated. By setting the contact pressure in the appropriate range as described above, occurrence of an abnormal image can be prevented.

The supply roller 2C of the developing device 2 is made of a flexible material such as polyurethane foam, and has a thickness of 50-500.
The cell has a diameter of μm and has a structure that can easily hold the toner on the surface. Further, the surface hardness is 10 to 30 mm (JIS-
A) is set to be relatively low in hardness, so that it can uniformly contact the developing roller 2B, and the amount of biting into the developing roller 2B is set to 0.5 to 1.5 mm.
The linear velocity ratio between the developing roller 2B and the developing roller 2B is set in the range of 0.5 to 1.5, and in this embodiment, the linear velocity ratio is set to 0.9. (The direction of movement).

In the case of the present embodiment, the effective width of the unit that can be developed by the developing device 2 is 240 mm, which corresponds to the width of the A4 size transfer paper when it is fed in the vertical direction.
1.5 to 2.5, which is the required torque for
kg · fcm is obtained. The biting amount and the above-described linear speed ratio are set to optimal conditions in a wider range because of the dependence on the characteristics of the motor and gear head in the drive system of the developing device 2 and the charging characteristics and supply of the toner. It is also possible.

The toner carried or present on the surface of the supply roller 2C is induced by frictional charging when it is sandwiched between the two members while receiving forces in opposite directions at the point of contact with the developing roller 2B. The toner is held on the surface of the developing roller 2B by the negative charge and by the transport effect due to the surface roughness of the developing roller 2B. Supply roller 2C
The toner layer at the time when the toner layer is transferred to the developing roller 2B is not of a uniform thickness, but is in an excessively attached state (1 to 3 mg / cm
₂ ) The thickness is made uniform by the regulating blade 2D described later. The supply roller 2C can be rotated in a direction opposite to that of the developing roller 2B (a direction in which the facing surface moves in the same direction).

The regulating blade 2D has a distal end extending from a base end supported by the developing tank 2A and a developing roller 2D.
In a state of being directed downstream with respect to the rotation direction of B, the base end is brought into contact with the peripheral surface of the developing roller 2B closer to the base end than the front end, and the plate thickness is 0.1 to 0.15 (mm). ) Set with a metal blade such as SUS304. Note that the regulating blade 2D is
It is also possible to make the contact state with B reverse to the above. Instead of the above materials, a rubber material such as polyurethane rubber having a thickness of about 1 to 2 mm, a silicone resin, or a fluorine-based material having a reverse charging characteristic (for example, ETFE, P
A resin material having relatively high hardness such as TFE, PVdF) resin can be used. Since resistance can be reduced by mixing carbon black or the like other than metal, it is also possible to connect a bias power supply to form an electric field with the developing roller 2B.

The free end length from the base end to the front end is 10 to 15
mm, and the contact pressure with the developing roller 2B is 5 to 250 mm.
(G · f / cm). If the free end length exceeds the upper limit of the above range, the size of the developing device 2 becomes large, so that the developing device 2 cannot be housed compactly. Conversely, if the free end length falls below the lower limit, the developing device 2 vibrates when it comes into contact with the surface of the developing roller 2B. Is likely to occur, and an abnormal image such as horizontal unevenness is likely to be generated on the visible image. When the contact pressure exceeds the upper limit, the toner adhesion amount on the developing roller 2B decreases, and the toner charge amount increases too much. Therefore, the image density decreases due to the decrease in the development amount due to insufficient transfer of the toner. . Conversely, if it falls below the lower limit,
In some cases, the toner thin layer is not formed uniformly, and the toner mass may pass through the regulating blade 2D, so that the image quality is significantly reduced. In this embodiment, the developing roller 2B has a hardness of 30 mm (JIS-A) and a thickness of 0.1 mm.
Is used, and the contact pressure is set to 60 (g · f / cm), so that the amount of toner adhering on the developing roller 2B can be set to a target value. The regulating blade 2D is
10 to the tangential direction at the position facing the developing roller 2B
Developing roller 2B with the tip abutting at an inclination of ~ 45 °
Are arranged toward the downstream side in the rotation direction of the. As a result, the excess toner carried on the developing roller 2B by the regulating blade 2D is scraped off, and the target toner adhesion amount on the developing roller 2B, which is 0.4
A thin layer having a uniform thickness of about 0.8 mg / cm ₂ is formed, and the charge amount of the toner is set to -5 to -30 μC / g and supplied to the electrostatic latent image on the photosensitive drum 1.

Since the present embodiment has the above configuration,
An electrostatic latent image formed by light writing on the photosensitive drum 1 is subjected to visible image processing by toner supply from the developing device 2. In the developing device 2, the toner agitated by the agitator 2E is conveyed toward the supply roller 2C and is carried by the supply roller 2C. The toner carried on the supply roller 2C is carried on the surface of the developing roller 2B by the electrostatic force induced by frictional charging when the supply roller 2C rotates while abutting on the developing roller 2B and the surface roughness of the developing roller 2B. As a result, a toner layer is formed. The toner layer is formed into a thin layer having a uniform thickness of about 0.4 to 0.8 mg / cm ₂ per unit area by regulating the layer thickness by the regulating blade 2D, and the toner charge amount is also -5.
-30 μC / g is supplied to the electrostatic latent image on the photosensitive drum 1.

As described above, the developing roller 2B for supplying toner to the photosensitive drum 1 has a friction coefficient (μ ′) on its surface larger than that of the photosensitive drum 1,
(Μ ′) <0.6, so that toner is reliably returned to the developing roller 2B side to eliminate background contamination of the photosensitive drum 1, and that occurrence of banding is suppressed to suppress an abnormal image. Can be prevented from occurring.

Since the coefficient of friction between the photosensitive drum 1 and the developing roller 2B changes depending on the surface roughness of the developing roller 2B, the following relation is maintained in the present invention in order to maintain the above-mentioned coefficient of friction. Is set. In the present embodiment, the range of the surface roughness (R _Z ) of the developing roller 2B is set to 1 <R _Z <6 (μ
m). When the surface roughness (R _Z ) is 1 μm or less, the friction coefficient of the surface may be reduced to become less than the friction coefficient of the photosensitive drum 1, and the above-mentioned background stain becomes remarkable. Further, when the surface roughness (R _Z ) is very small, the toner conveying force is reduced, and it becomes impossible to secure a target toner adhesion amount. On the other hand, the surface roughness (R _Z ) is 6μ.
If it is more than m, the toner will be buried in the surface of the developing roller 2B, and a uniform thin toner layer will not be formed, which may cause an abnormal image. Further, the friction coefficient is increased, and banding is remarkably generated, and an abnormal image is easily generated. Therefore, generation of an abnormal image can be prevented by keeping the surface roughness within the appropriate range.

[0025]

According to the first aspect of the present invention, the surface friction coefficient of the developer carrier is larger than that of the latent image carrier,
Further, by setting the friction coefficient (μ ′) to μ ′ <0.6, the developer transferred to the background portion of the latent image carrier is recovered by effectively using the scavenging force of the developer carrier. Therefore, it is possible to effectively prevent background contamination of the latent image carrier. Moreover, by setting the range of the above-mentioned friction coefficient, it is possible to suppress an increase in the rotational torque generated at the time of contact between the latent image carrier and the developer carrier due to an increase in the friction coefficient, thereby preventing occurrence of an abnormal image due to banding due to uneven rotation. It is also possible to do.

According to the second aspect of the present invention, the developer transferred to the background of the latent image carrier is recovered by setting the surface roughness (R _Z ) of the developer carrier to 1 <R _Z <6. Surface contamination of the latent image carrier can be satisfactorily prevented without lowering the image quality, and banding can be prevented from occurring when the friction coefficient increases, thereby preventing abnormal images from occurring. Become.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a relationship between a latent image carrier and a developer supply unit, which are main components of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining an experimental structure for obtaining a friction coefficient of a latent image carrier used in the image forming apparatus shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum as latent image carrier 2 developing device as developer supply means 2B developing roller as developer carrier

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Hojima 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H027 EA04 2H035 CB01 CD13 2H068 FA11 FC08 2H077 AC04 AD02 AD06 AD13 AD17 BA03 EA14 EA15 FA01 FA12 FA22 FA25 FA26

Claims (2)

[Claims] 1. Uniform charging in advance, friction coefficient (μ) of surface
Develops an electrostatic latent image by light writing on a latent image carrier set to 0.1 ≦ μ ≦ 0.4, and carries a developer on the electrostatic latent image. In an image forming apparatus that forms an image by performing a visible image process on the electrostatic latent image and transferring the image to a transfer medium and fixing the transferred image, wherein the friction coefficient (μ ′ ) Is larger than the latent image carrier, and the value (μ ′) is μ ′ <0.
6. An image forming apparatus, comprising: 2. The image forming apparatus according to claim 1, wherein the surface roughness (R _Z ) of the developer carrier is 1 <(R _Z ) <
An image forming apparatus characterized by being set to 6 (μm).