JPH10161395A - Electrostatic charging member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the contamination of an electrostation charging member and to prevent the generation of white drop-out stripes on an image by the pressure contact of the electrostatic charging member. SOLUTION: The electrostatic charging member having a conductive elastic rubber layer and a surface layer covering its surface and facing the material to be electrostatically charged is so formed that the surface layer contains >=0.1 to <=10% charge control agents. If the polarity of toners for development is +(positive), the positive charge control agent is added to the surface layer. If the polarity of the toners for development is -(negative), the negative charge control agent is added to the surface layer. The negative charge control agent is added to the surface layer in the form of electrostatically charging a non-OPC photoreceptor consisting of amorphous silicon, selenium, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member for charging the surface of a charge carrier, and in particular, though not intended to be limited thereto, in contact with or in close proximity to a photoreceptor for image formation. The present invention relates to a charging member for charging the photosensitive member or a charging member for contacting or in close proximity to a recording paper contacted with the photosensitive member for transfer for transfer. Such charging members are used, for example, in copiers, facsimile machines or laser printers.

[0002]

2. Description of the Related Art Heretofore, in an electrophotographic image forming apparatus, a corona discharger has been widely used as a charging method for uniformly charging the entire surface of a photosensitive member. Although this corona discharger is effective as a means for uniformly charging the photosensitive member to a certain potential, it requires a high-voltage power supply and has a disadvantage that ozone is generated by corona discharge. When a large amount of ozone is generated, the environment is adversely affected, and the charging member, the photoconductor and the like are deteriorated by the ozone.

On the other hand, a contact roller charging system has been developed in which a charging roller (charging member) is brought into contact with a photoreceptor and a voltage is applied to the surface of the photoreceptor while the roller is driven to rotate. The equipment tends to increase mainly in printers. This charging roller system has great advantages such as small size, energy saving and low ozone generation. However, when the charging roller is used for a long time as a charging roller of an image forming apparatus, since the charging roller is in direct contact with the image carrier (photoreceptor), residual toner particles remaining on the photoreceptor and the like are removed. Since the entire surface of the charging roller is in contact with the surface of the charging roller or in the form of stripes, the electrical resistance of the charging roller is increased, the charging potential is reduced, and charging unevenness occurs. That is, a very small amount of toner remaining on the photoreceptor surface, which has passed through the cleaning unit and remained on the photoreceptor even after cleaning of the photoreceptor and has no influence on image quality, remains in the charging area. Since it is in contact with the photoconductor, the residual toner adheres to the charging roller and accumulates for a long period of time. As a result, the surface of the charging roller is stained with toner, the electrical characteristics are changed, and the resistance is increased. When the entire surface is contaminated, the charging potential is lowered, and when the surface is partially contaminated, charging unevenness occurs.

Further, if the charging roller is kept in contact with the photosensitive member when the image forming apparatus is stopped, a charge memory effect occurs on the photosensitive member at a portion which comes into contact with the charging roller, resulting in a streak-like contact. It often produces traces. All of these have a great relation to the physical and chemical properties of the charging roller, especially of the surface layer. Also, both toner smearing and charge memory effects may occur simultaneously.

On the other hand, most image forming apparatuses are provided with a cleaning device for a charging roller, but it is not easy to remove toner attached to a roller mainly composed of rubber.
Only the effect of slightly delaying the progress of dirt is obtained.

There are several possible causes for the charge memory effect of the photoreceptor when left in contact, but a major factor is often the contact charging between the charging roller and the photoreceptor. If the charge is trapped by the contact charge in the polarity where the photoreceptor has no photosensitivity (+ side in the photoreceptor using organic semiconductor (OPC)), the portion is charged by charge in the next normal copy cycle. As a result, the charged potential becomes low, and as a result, an abnormal image in the form of white stripes occurs. Conversely, if the negative charges are trapped, a black streak-like abnormal image is generated.

[0007] These trapped charges cannot be easily removed and may remain during several copy cycles. On the other hand, in an actual image forming apparatus, measures are taken by separating the charging roller from the photoconductor when image formation is not performed. However, a mechanism for that purpose is naturally complicated and the cost is increased.

In addition, studies have been made on countermeasures against toner contamination and the effect of memory on the photosensitive member.
Selecting a coat-like resin material on the roller surface and clearing
This has been dealt with by improving the tanning method. For example, JP-A-3-
Japanese Patent No. 062056 proposes stabilizing the charging performance by mixing one or two kinds of metal particles such as aluminum and titanium and abrasive particles in the surface layer of the charging roller, and further reducing the memory effect on the photoreceptor. doing. In addition, Japanese Unexamined Patent Publication
In Japanese Patent Application Laid-Open No. 119374, the surface of the charging roller is
The charging performance is stabilized by adding a polymer having a quaternary ammonium salt structure. Japanese Patent Application Laid-Open No. Hei 5-341627 discloses that in order to perform uniform charging, epichlorohydrin rubber, which has semiconductivity by itself, is used for an elastic layer and its surface is covered with a non-adhesive surface layer. , Charging roller
La is easy to get dirty and has low durability. In JP-A-7-49602, epichlorohydrin rubber (elastic layer) is coated with a carbon-containing fluororesin-based surface layer. JP 1
No. 205180 discloses that the surface layer is formed of N-alkoxymethylated nylon.

[0009]

In spite of the fact that the charging roller system has many advantages in terms of miniaturization, energy saving and low ozone generation, it has been proposed to use electrophotographic technology such as copying machines, printers, faxes and the like including high-speed machines. The biggest reason why the used image forming apparatus cannot become mainstream is that reliability is still low in terms of durability. That is, generally, the higher the speed, the higher the quality and the higher the stability (stable for the number of copies is for a long time).
However, the charging roller method still has problems such as deterioration of quality over time due to roller contamination and streak images due to a charge memory effect in contact leaving as described above, and these lower reliability. .

As described above, although the conductive elastic layer is covered with the surface layer and the resin material of the surface layer is selected, although a certain result has been obtained, it cannot be said to be complete.

An object of the present invention is to solve the above-mentioned problems. More specifically, a first object is to provide a charging member that is less likely to be contaminated, a second object is to provide a charging member that facilitates removal (cleaning) of contaminants, and a charge memory is provided for a photoconductor. A third object is to provide a charging member having substantially no effect.

[0012]

According to the present invention, there is provided a charging member having a conductive elastic rubber layer and a surface layer which covers the surface thereof and faces a material to be charged, wherein the surface layer contains a charge control agent. Features.

The charge control agent is added to the toner for developing an electrostatic latent image in an electrophotographic apparatus in order to determine the charging polarity when frictionally charging the toner.
Positive charge controller (Nigrosine dye, triphenylmethane dye, ammonium salt, etc.) and negative charge controller (azo metal complex, metal complex, etc.)
There is. For example, in the case of a charging member used in an electrophotographic apparatus,
In an embodiment in which a negative potential or zero potential portion of an electrostatic latent image is developed with a positively charged toner, the surface of the charging member is frictionally contacted with the photoreceptor by adding a positive charge control agent to a surface layer covering the elastic rubber layer. Since the toner is positively charged by the charging and repulses the toner electrostatically, the toner stain is reduced. In the embodiment in which the positive potential or zero potential portion of the electrostatic latent image is developed with a negatively charged toner, toner stain is reduced by adding a negative charge control agent to the surface layer.
In the case of positive development, when the photosensitive member is easily charged to a positive potential having no photosensitivity due to contact charging of the charging member to the photosensitive member (contact peeling discharge), a negative charge control agent is added to the surface layer. As a result, the polarity of the contact-peeling discharge changes to a negative potential, and discharge occurs by light exposure, so that white spots do not occur.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has developed a surface layer for covering an elastic rubber of a charging roller [a coat having a medium resistance controlled by a carbon or the like usually used for a charging roller]. Resin (nylon, urethane, Teflon-containing resin, etc.)], toner
It has been found that by adding a charge control agent used for controlling the polarity of the toner, toner contamination of the roller can be greatly reduced. This effect was obtained when the amount of the charge control agent was 0.1 Wt% (% by weight) or more, and no effect due to an increase in the amount of the charge control agent was observed even when the amount exceeded 10 Wt%.

(1) First, as shown in FIG.
In a charging roller (charging member) in which an elastic rubber layer was formed on a cored bar and its surface was covered with a surface layer, hydrin rubber was used as the elastic rubber layer, and a nylon layer whose resistance was controlled by carbon was used as the surface layer. When this charging roller is used as a charging device for an organic semiconductor (OPC), as shown in FIG. 2, a non-woven fabric cleaner pad is pressed against the charging roller, but 20 × 1000 sheets or less. After a long period of use of printing 30 x 1000 sheets, the roller surface becomes dirty with toner and the charging performance decreases (lower charging potential and uneven charging)
I've been. This is because the toner remaining on the photoreceptor adheres to the surface of the roller and cannot be removed and is stuck after being used for a long period of time. In this state, replacement or cleaning by a service person is required.

On the other hand, according to the present invention, when the surface layer of the charging roller is added with 2 wt% of a dye nigrosine used as a positive charge controlling agent of the toner (other formulations are the same). In the same test as above, no contamination of the charging roller occurred. Furthermore, the cleaner
When the pad was removed and tested, the charging roller was slightly soiled but did not affect charging performance. This is because the charge control agent is added to the surface layer of the charging roller, so that the charging roller has the same polarity as the toner with the photoreceptor (OPC) frictionally or peelably, and the residual toner or floating toner on the photoreceptor This is considered to be due to electrostatic repulsion, which prevents the toner from adhering to the charging roller.

Further, as an elastic rubber layer, carbon-containing E
PDM (ethylene-propylene-dieneterpolymer rubbe
r) When the surface layer uses a fluorine-containing urethane resin charging roller, the charging roller is
The part that is in contact with is white in the form of a streak. This is because when the OPC is stopped, the charging roller and the OPC come into close contact with each other and peel off when the OPC rotates next time. The reverse charge is trapped in that portion of the OPC, and the potential of this portion during charging is lower than the normal charging potential. It occurs to become. Of course, this depends on the combination of materials of the photoconductor and the surface layer of the charging roller. However, in a charging roller having a surface layer of a fluorine layer to which toner does not easily adhere, OPC is easily charged to + (positive) by peeling charging.
This is OPC by charging roller (application of charging voltage to)
Of the (negative) charged potential (absolute value) of +
(Positive) The adhesion amount of the toner at the potential is small, and the above-mentioned white spots are easily generated.

On the other hand, according to the present invention, when the surface layer of the charging roller is formed by adding the above-mentioned nigrosine, which is a positive charge control agent for toner, to 5 wt%, the occurrence of white spots can be hardly confirmed. Improved. This is because by adding a charge control agent to the surface layer, the polarity of the contact peeling discharge to the OPC changes, and the OPC has photosensitivity.
This is due to the (negative) charge side.

As described above, according to the present invention, the charge control agent of the toner is charged on the surface layer of the charging roller (the positive charge control agent / the negative charge of the toner in the mode of positively charging the toner for development). By adding a negative charge control agent), it becomes possible to prevent toner contamination of the charging roller and to suppress streak-like white spots due to the charge memory effect of the photoconductor.

(2) However, in the case of a printer performing reversal development (a mode in which toner is negatively charged for development), the positive charge control described in the above (1) is performed even with the same OPC. In a charging roller having a surface layer to which an agent is added, there is no effect in preventing contamination of the toner, and 2 wt% of zinc salicylate, a negative charge control agent used in the toner for reversal development, is added to the surface layer. By doing so, the effect of preventing toner contamination was obtained.

However, also in this case, the effect of the memory effect due to the contact charging occurs, resulting in streak-like contamination. However, in this case, as in the case of the normal development, both the prevention of toner contamination and the prevention of streak-like white spots due to the memory effect cannot be achieved at the same time.
It is necessary to use different negative charge control agents.

(3) Of course, the photoconductor is not OPC,
In the case of amorphous silicon, selenium, etc., the photoreceptor is positively charged by a charging roller. The relationship is determined.

(4) Further, the charge control agents for toners described above are only examples, and any charge control agent which is generally known naturally has the same effect. On the other hand, it is necessary to add a charge control agent having the same (or the same polarity) as that of the toner used in the development to the surface layer. To suppress the charge memory effect of the photoreceptor, a charge control agent added to prevent toner contamination in positive development (positive-positive development) has an effect, but in reverse development (negative-positive development), toner contamination prevention is effective. Therefore, the polarity of the charge control agent to be added is opposite to the polarity of the charge control agent to be added for suppressing the charge memory effect. It is necessary to select according to the size. In the case of a printer for binary recording (recording of characters, lines, etc.), since a digital signal is used and the effect of the memory effect of the photoreceptor is inconspicuous on an image, a charge control agent effective for preventing toner contamination is added to the surface layer. Is preferred.

Representative charge control agents for toner are as follows: Positive charge control agent: Nigrosine dye, triphenylmethane dye, ammonium salt, etc. Negative charge control agent: Azo-based metal-containing complex, metal Complexes, etc.

[0025]

As described above, in an application for charging a charge carrier (photoreceptor) of an electrophotographic apparatus, a surface layer covering an elastic rubber layer of a charging member contains toner contained in toner for development. By adding a charge control agent that determines toner polarity,
Streak-like white spots due to toner contamination of the charging member and the charge memory effect of the photoconductor can be prevented. When the toner polarity for development is + (positive), by adding a positive charge control agent to the surface layer, the toner member is prevented from being soiled and the charge memory effect of the photoconductor is reduced. Both effects of preventing streak-like white spots can be obtained at the same time. When the toner polarity for development is-(negative), by adding a negative charge control agent to the surface layer, there is an effect of preventing toner contamination of the charging member. Further, in a mode in which a non-OPC photoconductor such as amorphous silicon or selenium is charged, the surface layer is added with a negative charge control agent to prevent streak-like white spots due to the charge memory effect of the photoconductor. The effect is obtained. The effect described above can be obtained by adding 0.1% by weight or more of the charge control agent. When the amount exceeds 10% by weight, the effect is not improved even if the amount of the charge control agent is increased. The content is preferably from 1 wt% to 10%.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional charging roller.

FIG. 2 shows a conventional charging roller, a photosensitive member, and a cleaner.
It is a cross-sectional view showing a positional relationship with a pad.

Claims (4)

[Claims] 1. A charging member having a conductive elastic rubber layer and a surface layer covering the surface thereof and facing a material to be charged, wherein the surface layer contains a charge control agent. 2. The charging member according to claim 1, wherein the charge control agent is a positive charge control agent. 3. The charging member according to claim 1, wherein the charge control agent is a negative charge control agent. 4. The addition amount of the charge control agent in the surface layer is 0.1
4. The charging member according to claim 1, wherein the charging member is not less than Wt% and not more than 10%. 5.