JP2008152192A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus having image characteristics hardly affected by environmental changes, and having improved reliability, by reducing a change in the triboelectric charge amount of a developer even when a conductive member is used as a developer regulating member. <P>SOLUTION: In the developing apparatus 14, the developing blade 25 is conductive, and connected to a power source or a ground, wherein a contact angle of the water on the surface of a developing roller 23 is set ≥100°. Consequently, the friction opportunity between the toner moistened under a high temperature and humidity environment and the developing roller 23 is increased, then, the triboelectric charge amount is increased, and the image characteristics hardly affected by the environment and the high reliability are obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus having a function of forming an image on a recording material (recording medium) such as a copying machine, a printer, or a facsimile machine. More specifically, the present invention relates to a developing device and a process cartridge provided in these devices.

  Conventionally, in an image forming apparatus, an electrostatic latent image formed on an electrostatic latent image carrier is visualized as a developer image by a developing device.

  As such a developing device, a dry one-component contact developing device has been proposed and put into practical use. In this case, the electrostatic latent image bearing member and the developer bearing member are rotated and pressed or brought into contact with an appropriate relative peripheral speed to develop the electrostatic latent image. In addition, no magnetic material is required, and the apparatus can be easily simplified and downsized. Moreover, application to a full-color image forming apparatus is possible by using a nonmagnetic developer.

  As the developer carrying member, a developing roller having elasticity and conductivity can be used. In the contact developing device, the developing roller is pressed or brought into contact with the electrostatic latent image carrier. For this reason, when the electrostatic latent image carrier is a rigid body, the electrostatic latent image carrier is damaged. In order to avoid this, the developing roller is made of an elastic body. Further, a conductive layer may be provided on the surface of the developing roller or in the vicinity of the surface, and a developing bias may be applied for use.

  Further, for the purpose of imparting electric charge to the developer and forming a uniform developer layer, it is possible to bring a developing blade into contact with the developer carrying member as a developer regulating member. In this case, the developing blade is made of rubber or a metal thin plate having spring elasticity. Further, when the developing blade has conductivity, the developing blade can be used by being connected to a power source or a ground.

  FIG. 5 is a diagram showing a conventional developing device.

  The developing roller 51, which is a developer carrier, has a silicone rubber as a base layer and a urethane rubber as a surface layer. The developing roller 51 is an elastic roller having conductivity and is driven to rotate in the direction of arrow C. The developing blade 52 is a metal blade having electrical conductivity, and is supported by a blade support sheet metal 53. The developing blade 52 is in contact with the outer peripheral surface of the developing roller 51 in the vicinity of the free end. At this time, the toner layer coated on the surface of the developing roller 51 is frictionally charged by friction with the developing blade 52.

  Further, the elastic roller 54 contacts the developing roller 51 and is driven to rotate in the direction of arrow D. The elastic roller 54 is a sponge roller, which supplies toner to the developing roller 51 and strips off toner remaining on the developing roller without being developed. The elastic roller 54 is disposed upstream of the developing blade 52 in the rotation direction of the developing roller 51. The toner 55 is a nonmagnetic one-component developer. An appropriate amount of hydrophobic silica is externally added for the purpose of improving the chargeability and transferability of the toner.

  In the developing device having the above-described configuration, the developing blade achieves triboelectric charging to the toner and formation of a uniform toner layer, and can be developed satisfactorily.

As a document disclosing related conventional examples, there is Patent Document 1.
JP 2001-83796 A

  However, when the developing blade has conductivity and is connected to a power source or ground, the triboelectric charge applied to the toner layer by friction may be discharged through the developing blade.

  For this reason, there may be a problem that the triboelectric charge applied to the toner layer by friction decreases due to discharge. When the triboelectric charge amount of the toner layer formed on the surface of the developing roller decreases, an image fogging defect may occur. Therefore, it is required to obtain an image having no image fogging defect.

  Furthermore, the amount of water contained on the toner surface and inside increases in a high temperature and high humidity environment. When the amount of water contained in and on the toner surface increases, the toner adheres to the surface of the developing roller through the water, and the chance of friction between the toner and the developing roller surface decreases. When the chance of friction between the toner and the developing roller surface decreases, the amount of triboelectric charge applied to the toner layer decreases. That is, when the amount of water contained in and on the toner increases, the amount of triboelectric charge imparted to the toner decreases, and image fogging may occur.

  The present invention has been made in view of the above-described circumstances, and even when the developer regulating member is made conductive, the change in the triboelectric charge amount of the developer is reduced, and the image has less influence on environmental changes. An object is to provide an apparatus having excellent characteristics and reliability.

In order to achieve the above object, the present invention provides:
A developer carrier for carrying and conveying the developer;
A developer regulating member that is provided in pressure contact with the developer carrying member and regulates the amount of the developer carried on the developer carrying member;
With
In the developing device in which the developer regulating member has electrical conductivity, and the developer regulating member is electrically conducted to the conducting portion.
The developer carrying member is provided such that a contact angle with respect to water on the surface of the developer carrying member is 100 degrees or more.

  According to the present invention, even when the developer regulating member is made conductive, a change in the triboelectric charge amount of the developer is reduced, and an apparatus having excellent image characteristics and reliability with little influence on environmental changes is provided. It becomes possible.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  In the present invention, when the developer regulating member has electrical conductivity and the developer regulating member is electrically connected (conductive) to the power source or the earth as the conducting portion, for example, the developer carrier surface is in contact with water. A configuration in which the angle is 100 degrees or more is adopted.

That is, since the developer regulating member is conductive, even when the triboelectric charge applied to the developer layer is discharged through the developer regulating member, the triboelectric charge is imparted to the developer layer due to an increase in the friction opportunity. Therefore, no image fogging defect occurs.

  Hereinafter, the application of the triboelectric charge amount to the developer layer due to an increase in the friction opportunity will be described in detail.

  As the environment changes such as temperature and humidity, the amount of water contained on the developer surface and inside changes. When the amount of water contained in and on the developer surface increases, the adhesion between the developer and the surface of the developer carrying member increases. Here, when the contact angle with respect to the water on the surface of the developer carrying member is set to 100 degrees or more, the surface of the developer carrying member has the property of repelling the developer containing moisture on the surface and inside. For this reason, the developer and the surface of the developer carrying member do not adhere via moisture. As a result of preventing adhesion between the developer and the surface of the developer carrier, the chance of friction between the developer and the surface of the developer carrier increases, and the amount of triboelectric charge imparted to the developer increases.

  That is, the triboelectric charge amount of the developer can be increased even when the amount of water contained on the surface and inside of the developer increases with environmental changes such as temperature and humidity.

  As a result, even when the triboelectric charge is discharged through the developer regulating member, the triboelectric charge of the developer layer formed on the surface of the developer carrier increases. As a result, the occurrence of image fogging defects is remarkably reduced, and an apparatus having excellent image characteristics and reliability with little influence on environmental changes can be obtained.

  FIG. 1 is a schematic sectional view of an image forming apparatus 10 to which the present invention is applied, and FIG. 2 is a schematic sectional view of a developing apparatus 14 to which the present invention is applied. First, an image forming operation by the image forming unit will be described.

  In FIG. 1, a photosensitive drum 11 as an electrostatic latent image carrier rotates in the direction of arrow A. First, the photosensitive drum 11 is uniformly charged by the charging device 12. Thereafter, exposure is performed with a laser beam 13 from a laser optical device as an exposure unit, and an electrostatic latent image is formed on the surface thereof. The electrostatic latent image is developed by a developing device 14 disposed so as to press and contact the photosensitive drum 11 with a predetermined amount of penetration, and visualized as a developer image (toner image) (the developing device 14 is visualized as a photosensitive drum). 11 is developed). The visualized toner image on the photosensitive drum 11 is transferred to the recording material 16 by the transfer roller 15.

  Untransferred toner remaining on the photosensitive drum 11 without being transferred is scraped off by a cleaning blade 17 as a cleaning member and stored in a waste toner container 18. The cleaned photosensitive drum 11 repeats the above operation to form an image. On the other hand, the recording material 16 to which the toner image has been transferred is permanently fixed by the fixing device 19 and then discharged outside the apparatus.

  The developing device 14 will be further described with reference to FIG.

  In FIG. 2, reference numeral 21 denotes a developing container for storing a negatively chargeable non-magnetic one-component toner 22 (hereinafter sometimes simply referred to as toner) as a developer. The developing device 14 includes a developing roller 23 that is located in an opening extending in the longitudinal direction in the developing container 21 and that is disposed to face the photosensitive drum 11 and carries toner as a developer carrying member. The electrostatic latent image is developed and visualized.

The photosensitive drum 11 is a rigid body in which an aluminum cylinder is used as a base and a photosensitive layer having a predetermined thickness is applied around the aluminum cylinder. At the time of image formation, the photosensitive drum 11 is charged with a charging potential Vd by a charging device.
= -700V is uniformly charged, and the portion exposed by the laser according to the image signal becomes Vl = -150V. A DC voltage = Vdc = −300 V is applied as a developing bias to the core of the developing roller 23 with respect to the Vl portion, and reverse development is performed with negatively charged toner.

  In the opening, the developing roller 23 having elasticity protrudes from the developing container 21 in a substantially right half circumference as shown in the drawing, and is disposed horizontally with a substantially left half circumferential surface exposed from the developing container 21. The surface exposed from the developing container 21 faces the photosensitive drum 11 positioned on the left side of the developing device 14 so as to be pressed and brought into contact with the photosensitive drum 11 by a predetermined amount. In the present embodiment, the developing roller 23 enters 50 μm and comes into contact with the photosensitive drum 11. The developing roller 23 is rotationally driven in the direction of arrow B.

The developing roller 23 in this embodiment has a two-layer structure in which a silicone rubber is used as a base layer and a fluorine rubber is coated on the surface layer, and the surface roughness (arithmetic average roughness (Ra)) is Ra = 0.2 μm. Rz = 0.5 μm and Rmax = 0.7 μm. The developing roller 23 has a resistance of 10 ⁴ to 10 ⁶ Ω. The contact angle of the surface layer of the developing roller 23 with respect to water is 110 degrees. In this embodiment, the surface layer of the developing roller is composed of a fluorine-based rubber having a thickness of 30 μm that has good water repellency with respect to toner containing moisture on the surface and inside.

  As the surface layer of the developing roller 23, in addition to fluorine-based rubber, any material such as nylon-based resin, silicone-based resin, urethane-based resin, or acrylic-based resin can be suitably used as long as the contact angle to water is 100 degrees or more. Can do. Further, not only the surface layer material of the developing roller but also surface modification using coating on the surface layer, electric discharge, etc., any can be used as long as the contact angle is 100 degrees or more. The contact angle was measured using a contact angle meter FACE from Kyowa Interface Science by dropping 1 μL to 2 μL of pure water onto the developing roller and measuring the contact angle.

On one side of the developing roller 23, a developing blade 25 as a developer regulating member having conductivity and elasticity is supported by a support metal plate 26, and the vicinity of the free end is in surface contact with the outer peripheral surface of the developing roller 23. It is provided so as to abut (pressure contact). The developing blade 25 presses the developing roller 23 with a linear pressure of 40 g / cm, and uniformly forms a 0.5 mg / cm ² toner layer on the surface of the developing roller 23.

  As a material of the developing blade 25, in the present embodiment, a conductive stainless steel thin plate having a thickness of 80 μm is used. The surface roughness is Ra = 0.1 μm, Rz = 0.5 μm, Rmax = 0.7 μm. As the abutting direction, the free end side of the abutting portion is a counter direction located upstream in the rotation direction of the developing roller 23. Further, a DC voltage of V = Δ−200 V is applied to the developing blade 25 with respect to the developing bias by a blade bias power source. Here, the blade bias power source constitutes a voltage applying means or a power source.

  An elastic roller 24 is in contact with the other side of the developing roller 23 and is rotatably supported. The elastic roller 24 is preferably a sponge structure or a fur brush structure in which fibers such as rayon and nylon are planted on a core metal from the viewpoint of supplying toner to the developing roller 23 and stripping off undeveloped toner. In this embodiment, it is a urethane sponge roller, and is driven to rotate in the same direction as the developing roller 23.

  In this embodiment, a substantially spherical toner (spherical toner, spheroidized toner) is used for the negatively chargeable nonmagnetic one-component toner 22 as a one-component developer in order to improve transfer efficiency. .

As a toner manufacturing method, for example, a conventional pulverized toner surface can be subjected to plastic spheroidization treatment by thermal and mechanical stress. It is also possible to use a method of directly producing a toner by a turbid polymerization method, or a dispersion polymerization method in which an aqueous organic solvent that is soluble in the monomer and insoluble in the obtained polymer is used to directly produce the toner. is there. It is also possible to use an emulsion polymerization method represented by a soap-free polymerization method in which a toner is produced by direct polymerization in the presence of a water-soluble polar initiator.

  In this example, a turbid polymerization method under normal pressure or under pressure in which a particle size distribution of 4 to 8 μm with a sharp particle size distribution is obtained is used. Then, styrene and n-butyl acrylate as monomers, a salicylic acid metal compound as a charge control agent, a saturated polyester as a polar resin, and a colorant are added to produce the following toner. That is, a negatively chargeable toner having a weight average particle diameter of about 7 μm and toner particles having a weight average particle diameter of 4 μm or less is 25% by number or less is manufactured.

  Thereafter, 1.5 wt% of hydrophobic silica is externally added as a fluidity imparting agent. Of course, the amount of external addition is not limited to this. By coating the toner surface with an external additive, the negative charging performance is improved, and the flowability is improved by providing a minute gap between the toners.

  Using the image forming apparatus 10 and the developing apparatus 14 described above, a printout test was performed by leaving it in a high temperature and high humidity environment (30 ° C., 80% RH) for one day. As a result, it was possible to obtain a high-quality image without causing image fogging failure.

  In the following, this embodiment will be described in detail.

  When a conventional developing apparatus was left in a high temperature and high humidity environment (30 ° C., 80% RH) for 1 day and a printout test was performed, an image fogging defect occurred. On the other hand, the conventional developing device was left in a low temperature and low humidity environment for 1 day to conduct a printout test. However, no image fogging occurred. The experimental results are shown in Tables 1 and 2.

  As a result of examining image fog defects in detail, image fog defects occurred when the developing blade and the developing roller were equipotential, the developing blade was thinned, and the rotation speed of the developing roller was decreased in a high temperature and high humidity environment.

  In other words, the cause of image fogging failure is the surface of the developing roller when the developing blade and developing roller are equipotential, the developing blade is thinned, or the developing roller is slowed down in a high temperature and high humidity environment. This is because the triboelectric charge amount of the formed toner layer is insufficient. In other words, since the developing blade has conductivity and the developing blade is connected to a power source or ground as a conducting portion, the triboelectric charge applied to the toner layer is discharged through the developing blade, so the triboelectric charge amount of the toner layer Was lacking.

  Specifically, the amount of water contained in the toner surface and inside increases in a high temperature and high humidity environment. When the amount of water contained in and on the toner surface increases, the adhesion between the toner and the developing roller surface increases. As the adhesive force increases, the chance of friction between the toner and the developing roller surface decreases, and the triboelectric charge amount of the toner layer decreases. Further, when the developing blade and the developing roller are equipotential, the triboelectric charge applied to the toner layer is discharged through the developing blade, and the triboelectric charge is reduced. Even when the developing blade is thin and the rotation speed of the developing roller is slowed, the chance of friction between the toner and the developing blade surface, the toner and the developing roller surface, and the toner decreases, and the amount of triboelectric charge applied to the toner layer decreases. Was.

  In such a high temperature and high humidity environment, when the developing blade and developing roller are equipotential, the developing blade is thinned, and the rotation speed of the developing roller is slow, the triboelectric charge amount is insufficient and poor image fogging has occurred. It was.

  Therefore, the present inventors have aimed to increase the frictional charge amount of the toner layer, and specifically, to increase the chance of friction between the toner and the developing roller surface in a high temperature and high humidity environment. . That is, the present invention aims to increase the chance of friction between the toner and the developing roller surface even when the amount of water contained in the toner surface and inside increases in a high temperature and high humidity environment. As a result, attention was paid to the contact angle of the developing roller surface with water.

Table 3 below shows the contact angle between the surface layer material of the developing roller and water, and the results of poor image fogging. Further, the configuration other than the developing roller is left as it is in the conventional developing device, and a high temperature and high humidity environment (30 ° C., 8 ° C.).
FIG. 3 shows the result of a printout test using a developing device left at 0% RH for 1 day.

  As is apparent from FIG. 3, there was a correlation between the contact angle of the developing roller surface with water and poor image fogging. That is, by changing the surface layer material of the developing roller and setting the contact angle of the developing roller surface with water to 100 degrees or more, it was possible to suppress the occurrence of image fogging failure.

  This is because, by setting the contact angle of the surface of the developing roller to water to 100 degrees or more, the surface of the developing roller has a property of repelling toner containing moisture on the surface and inside in a high temperature and high humidity environment. For this reason, the adhesion force between the toner and the developing roller surface does not increase. As a result of preventing an increase in the adhesion between the toner and the surface of the developing roller, it is considered that the chance of friction between the toner and the surface of the developing roller increases, and the amount of triboelectric charge imparted to the toner layer increases. At this time, the amount of triboelectric charge imparted to the toner layer is considered to depend only on the contact angle with respect to water, regardless of the charging series of the surface layer material of the developing roller. That is, in the developing roller surface layer material, silicone and Teflon (registered trademark) should show the opposite tendency in the charging series, but both materials have a high contact angle and tend to increase the triboelectric charge amount. It was. For this reason, it is considered that the triboelectric charge applied to the toner layer depends only on the contact angle with water.

  As described above, even when the charge applied to the toner is discharged through the developing blade, the amount of frictional charge applied to the toner due to the increase in the frictional opportunity is sufficient, and therefore the frictional charge amount of the toner layer does not decrease.

  As a result, even when the developing blade has conductivity and the developing blade is connected to a power source or ground, the triboelectric charge amount of the toner layer increases without being affected by environmental fluctuations, and the occurrence of image fogging defects can be suppressed.

  Further, by setting the arithmetic average roughness (Ra) of the surface roughness of the developing roller 23 to 0.3 μm or less, the chance of friction between the toner and the developing roller surface can be increased, and the frictional charge amount of the toner layer can be increased. It is possible to increase the number of image fogging defects.

  Further, by applying a DC bias voltage to the developing blade 25 and providing a potential difference with the developing roller 23, it is possible to inject charges into the toner layer by the DC bias voltage and increase the triboelectric charge amount of the toner layer. The occurrence of image fogging defects can be reduced.

  Further, since the toner is a non-magnetic one-component developer, a carrier is not required as compared with the two-component developer, so that it is not necessary to pay special consideration to carrier deterioration during development.

  Further, by making the toner substantially spherical, the chance of friction between the developing blade 25 and the toner, the chance of friction between the developing roller 23 and the toner, and the chance of friction between the toners can be increased, and the amount of frictional charge of the toner layer is increased. And occurrence of image fogging defects can be reduced.

  As described above, even when the developing blade 25 has conductivity and the developing blade 25 is connected to a power source or the ground, the contact angle of the developing roller 23 with respect to water is set to 100 degrees or more, so that the surface of the developing roller The triboelectric charge amount of the toner layer formed on the toner can be increased.

  That is, even when the amount of moisture contained in the toner surface and inside increases with environmental changes such as temperature and humidity, the toner and the developing roller surface do not adhere via moisture. As a result of preventing adhesion between the toner and the surface of the developing roller, the chance of friction between the toner and the surface of the developing roller increases, and the amount of frictional charge applied to the toner increases.

  As a result, even when the developing blade 25 has electrical conductivity, the amount of toner triboelectric charge can be increased, and the occurrence of image fogging defects can be reduced.

  As described above, according to this embodiment, the variation in the triboelectric charge amount of the toner layer formed on the developing roller 23 can be reduced, and the substantially uniform image characteristics and high reliability with little influence on the environmental change. It becomes possible to obtain sex.

  FIG. 4 is a schematic sectional view showing an example of the process cartridge 40 to which the present invention is applied.

  The process cartridge 40 includes a developing device 44, a photosensitive drum 45, a charging unit 46, and a cleaning unit 47, and is integrally formed into a cartridge by plastic developing frame members 48 and 49. Here, the developing device 44 includes a developing roller 41 as a developer carrying member, a developer regulating member 42 provided so as to come into surface contact with the outer peripheral surface of the developing roller 41, an elastic roller 43, and the like. Is done.

  That is, the process cartridge 40 of the present embodiment is a unit in which the developing device 14 described in the first embodiment and the process components that act on the photosensitive drum 45 are integrated. Accordingly, all the developing device components described above are similarly applied to the process cartridge 40. The process cartridge 40 is detachably attached to the image forming apparatus. Also in this embodiment, the same effect as that of Embodiment 1 can be obtained.

1 is a schematic cross-sectional view illustrating an example of an image forming apparatus to which the present invention is applied. It is a schematic sectional drawing which shows an example of the image development apparatus to which this invention is applied. 6 is a graph showing a relationship between a contact angle of water on the developing roller surface with respect to water and an image fogging defect. It is a schematic sectional drawing which shows an example of the process cartridge to which this invention is applied. It is a schematic sectional drawing of the conventional image development apparatus.

Explanation of symbols

14 Developing device 22 Non-magnetic one-component toner 23 Developing roller 25 Developing blade

Claims (8)

A developer carrier for carrying and conveying the developer;
A developer regulating member that is provided in pressure contact with the developer carrying member and regulates the amount of the developer carried on the developer carrying member;
With
In the developing device in which the developer regulating member has electrical conductivity, and the developer regulating member is electrically conducted to the conducting portion.
The developing device, wherein the developer carrying member is provided so that a contact angle with respect to water of the surface of the developer carrying member is 100 degrees or more.   The developing device according to claim 1, wherein the surface roughness of the developer carrying member is 0.3 μm or less in terms of arithmetic average roughness (Ra). Voltage application means for applying a DC bias voltage to the developer regulating member;
By applying a DC bias voltage to the developer regulating member by the voltage applying means and providing a potential difference between the developer carrying member and the developer carrying member, a charge is imparted to the developer carried on the developer carrying member. The developing device according to claim 1, wherein the triboelectric charge amount of the developer is increased.   The developing device according to claim 1, wherein the developer is a non-magnetic one-component developer.   The developing device according to claim 1, wherein the developer is provided in a spherical shape.   6. A process cartridge comprising the developing device according to claim 1, wherein the process cartridge is detachably attached to the image forming apparatus.   The process cartridge according to claim 6, further comprising an electrostatic latent image carrier that is developed by the developing device. An electrostatic latent image carrier;
The developing device according to any one of claims 1 to 5, wherein a developing action is performed on the electrostatic latent image carrier.
An image forming apparatus comprising:

Images