Electrophotographic photoreceptor, and image forming method and apparatus using the photoreceptor

Abstract

An electrophotographic photoreceptor including an electroconductive substrate, a photosensitive layer located overlying the electroconductive substrate, and optionally a protective layer overlying the photosensitive layer, wherein an outermost layer of the photoreceptor includes a filler, a binder resin and an organic compound having an acid value of from 10 to 700 mgKOH / g. The photosensitive layer can be the outermost layer. A coating liquid for an outermost layer of a photoreceptor including a filler, a binder resin, an organic compound having an acid value of from 10 to 700 mgKOH / g and plural organic solvents. A method for preparing a photoreceptor including forming a photosensitive layer, and coating the coating liquid on the photosensitive layer. An image forming method and apparatus and a process cartridge using the photoreceptor are also provided.

Description

[0001] The present invention relates to an electrophotographic photoreceptor. In addition, the present invention relates to an electrophotographic image forming method and apparatus using the photoreceptor. Further, the present invention relates to a process cartridge for electrophotographic image forming apparatus, which includes the photoreceptor.DISCUSSION OF THE BACKGROUND[0002] Recently the growth of information processing system using electrophotography is remarkable. In particular, digital copiers capable of recording digital information using light after converting information to digital signals have been drastically improving in recording qualities and reliability. In addition, the technique has been applied to full color laser printers and copiers by being combined with a high speed recording technique. In the light of this background, a need exists for a photoreceptor which not only produces high quality images but also has high durability.[0003] As the photoreceptor used...

AI Technical Summary

Benefits of technology

[0050] Another object of the present invention is to provide an image forming method by which high quality images can be stably produced at a high speed for a long period of time without frequently changing the photoreceptor.

[0051] A further object of the present invention is to provide a small-size image forming apparatus and a process cartridge by which high quality images can be stably produced at a high speed for a long period of time without frequently changing the photoreceptor.

Problems solved by technology

However, photosensitive layers of organic photoreceptors are easily abraded when the photoreceptors are repeatedly used.

When a photosensitive layer is largely abraded, various image quality problems such that the potential of the charged photoreceptor decreases; the photosensitivity thereof deteriorates; background fouling occurs in the resultant images; and image density decreases tend to occur.

Therefore the abrasion of photoreceptors have been a big problem to be solved.

However, when an electrical insulating filler is included in a protective layer, the resistance of the protective layer increase, resulting in increase of residual potential of the resultant photoreceptor.

However, a problem tends to occur such that the resultant images have unclear outlines, i.e., blurred images are produced.

Therefore, this technique cannot be used for small-size photoreceptors typically provided in current small image forming apparatus.

In addition, when a drum heater is provided, the resultant image forming apparatus becomes large in size.

Further, the image forming apparatus have other drawbacks such that it is needed for the image forming apparatus to continuously work the heater, resulting in increase of power consumption, and it takes a long warm-up time.

When a photoreceptor has a high residual potential due to use of a filler having high insulating property, the potential of a lighted area of the photoreceptor increases, resulting in deterioration of image density and half toner reproducibility of the resultant images.

However, when the dark-area potential is increased, the electric field strength is increased, and therefore not only undesired images such as background fouling are produced, but also the life of the photoreceptor is shortened.

However, imagewise light is absorbed by the protective layer, and therefore the quantity of light which reaches the photosensitive layer decreases, resulting in decrease of the photosensitivity of the photoreceptor.

Therefore, this method is of little effect.

However, its effect of preventing increase of residual potential is not insufficient, and therefore the problem cannot be solved.

This is because the increase of residual potential is caused by charge trapping due to the added filler and uneven dispersion of the filler rather than deterioration of charge generation efficiency.

Therefore, there is a limit to improvement of the increase of residual potential only by increasing the charge mobility.

Accordingly, the demand for a photoreceptor having good durability cannot be satisfied only by this method.

It is considered that these methods are aimed to improve the charge injection at the interface between the protective layer and the charge transport layer, and portions having a low resistance are formed in the protective layer, such that the charge can reach the surface of the protective layer, resulting in decrease of residual potential.

The residual potential increase problem can be improved to some extent by these methods, but the increase of residual potential of a durable photoreceptor having a protective layer including a filler cannot be avoided by these methods because the reason for the residual potential increase problem occurred for such a durable photoreceptor is different from the reason for the residual potential increase problem improved by these methods mentioned above.

In addition, when an organic acid is included in a protective layer in combination with a filler, the dispersion of the filler in the protective layer tends to deteriorate and therefore the resultant images are blurred.

Thus, these methods produce adverse effects.

In addition, as can be understood from the below-mentioned description, a satisfactory effect cannot be exerted by this method against a photoreceptor including a filler in the outermost layer to improve its durability.

On the other hand, blurred images are also produced due to ozone and NOx.

In particular, when a filler is included in an outermost layer, residual potential seriously increases, resulting in deterioration of initial image qualities.

Therefore this technique cannot be used for a photoreceptor having a protective layer including a filler because residual potential thereof seriously increases and high quality images cannot be produced.

However, a technique by which serious increase of residual potential due to addition of a filler in a protective layer can be improved has not been discovered.

Therefore a toner image formed of scattered toner particles is formed, resulting in deterioration of resolution of the toner image.

In addition, when imagewise light irradiates such a protective layer including an agglomerated filler, the light is scattered by the filler, resulting in deterioration of light-transmittance, and thereby resolution of the resultant image deteriorates.

When a filler seriously agglomerates (i.e., a filler is poorly dispersed), not only the abrasion resistance of the resultant photoreceptor deteriorates but also uneven abrasion tendsto occur.

Therefore a desired durability cannot be imparted to the resultant photoreceptor.

However, a solution by which these problems are solved at the same time has not been discovered.

Namely, when a filler is included in an outermost layer of a photoreceptor to improve its durability, blurred images tend to be produced and residual potential tends to increase, and therefore a problem in that high quality images cannot be produced still remains.

However, a drum heater cannot be provided in a small-sized photoreceptor, which is especially desired to have good durability.

Therefore, there is no small-size photoreceptor having good durability and capable of producing high quality images.

To install a drum heater is an obstruction to a small-size image forming apparatus and having low electric power consumption.

However, the method has drawbacks such that residual potential increases, and image qualities deteriorate, e.g., blurred images are produced.

In addition, blurred images are formed and resolution is decreased and therefore image qualities deteriorate.

Therefore, it is difficult to provide a photoreceptor having good durability and capable of producing high quality images.

When fillers having a low resistance or acidic fillers are used, a chance that blurred images are produced increases but residual potential of the photoreceptor hardly increases.

Namely, conventional photoreceptors have a drawback such that blurred images tend to be produced.

When a hydrophilic inorganic filler, which typically has a poor affinity to organic solvents and binder resins, the filler tends to agglomerate in the coating liquid and the resultant layer.

To the contrary, when the filler in the outermost layer is agglomerated, straight movement of the charges injected to the layer is obstructed by the agglomerated filler, resulting in deterioration of resolution of the resultant images.

When an electroconductive filler is included in the outermost layer of a photoreceptor, the resistance of the outermost layer decreases and charges formed on the outermost layer tend to move in the horizontal direction, resulting in occurrence of the blurred image problem.

When a large amount of an acid remains in the filler used, the blurred image problem tends to occur, and in addition dispersion of the filler in the resultant layer deteriorates.

To the contrary, as the zeta potential approaches zero, the particles tend to agglomerate, and thereby the particles become unstable.

As mentioned above, when the dispersion of the filler used deteriorates, various problems occurs such that the transparency of the resultant layer decreases, coating defects are produced, the abrasion resistance of the layer deteriorates and uneven abrasion of the resultant layer occurs.

Therefore, a photoreceptor having good durability and capable of producing high quality images cannot be prepared.

When a filler treated with a silane coupling agent is used, the blurred image problem tends to occur.

However, by treating a filler with a combination of one or more of the above-mentioned treating agents with a silane coupling agent, there is a possibility that the blurred image problem is not caused.

When the amount of the treating agent is too small, dispersibility of the filler cannot be improved.

To the contrary, when the amount of the treating agent is too large, residual potential of the resultant photoreceptor tends to increase.

When the average primary particle diameter is too small, the filler tends to agglomerate and therefore abrasion resistance deteriorates.

To the contrary, when the average primary particle diameter is too large, various problems occurs such that the filler tends to precipitate in the coating liquid, image qualities deteriorate and undesired images are produced.

When the content is too low, the abrasion resistance is hardly improved.

When the content is too high, problems occur such that residual potential increases, the blurred image problem occurs, and resolution of the resultant images deteriorates.

In addition, since the interaction between filler particles increases, dispersion of the filler deteriorates, and thereby the filler tends to be released from the layer, resulting in deterioration of the abrasion resistance.

However, when these compounds are used, there is occasionally a case that dispersion of the filler becomes unstable, and the resultant images is slightly blurred.

When such a wetting dispersant as mentioned above is added thereto, the hydrophilic group (such as a carboxyl group) of the wetting dispersant tends to be adsorbed on the polar groups of the filler, resulting in decrease of the residual potential.

When one of the wetting ability and dispersing ability is lacked, problems occur such that dispersion is not satisfactory, dispersion efficiency is not satisfactory and / or dispersion stability is not satisfactory.

In general, since a filler has a poor affinity to a binder resin, i.e., the adhesion of the filler to the binder resin is poor, the filler tends to be easily released from the binder resin.

When the molecular weight is too low, desired steric hindrance cannot be produced when the dispersant is adsorbed on a filler, resulting in increase of interaction between filler particles, and thereby the dispersion and dispersion stability of the filler are deteriorated.

To the contrary, when the molecular weight is too high, wettability and an ability to be adsorbed on a filler deteriorate.

In addition, plural filler particles are adsorbed on a wetting dispersant polymer, resulting in agglomeration of the filler particles.

When the acid value is too high, the resistance of the filler tends to be excessively decreased, resulting in occurrence of the blurred image problem.

To the contrary, when the acid value is too low, the addition quantity has to be increased, and in addition increase of residual potential cannot be fully prevented.

When the content is too high, problems tend to occur such that dispersion of the filler used deteriorates and the blurred image problem occurs.

When the content is too low, dispersion of the filler used and decrease of residual potential cannot be sufficiently improved.

When the thickness is too thin, satisfactory durability cannot be necessarily obtained.

When the thickness is too thick, there is a case in which the residual potential increases and / or the resolution of the produced images deteriorates.

When a filler is included in an outermost layer of a photoreceptor, active gasses such as ozone and NOx gases tend to be adsorbed on the filler and therefore the blurred image problem occurs more frequently than in the case of a photoreceptor having an outermost layer including no filler.

To the contrary, when the content is too high, problems such that abrasion resistance deteriorates and residual potential increases tend to occur.

When zirconia is used as a dispersing element, zirconia is abraded during the dispersion process, resulting in contamination of zirconia in the coating liquid, and thereby residual potential of the resultant photoreceptor tends to increase and the filler tends to easily precipitate in the resultant coating liquid.

A binder resin, a CTM and an antioxidant may be added in the mixture of the filler, organic compound and solvent before the dispersion process, however dispersion of the filler often deteriorates slightly.

However, when a charging roller is repeatedly used while contacting a photoreceptor, the charging roller tends to be contaminated, and thereby the photoreceptor is also contaminated, resulting in production of undesired images and deterioration of abrasion resistance of the photoreceptor.

However, when this proximity charging roller is used, there is a case in which charging becomes uneven and therefore the photoreceptor is unevenly charged.

Among the pollutants adhered on the surface of the photoreceptor, pollutants such as materials generated by charging and external additives included in the toner used cause undesired images particularly under high humidity conditions.

In addition, paper dust is also a pollutant, and not only causes undesired images but deteriorates abrasion resistance and unevenly abrades the photoreceptor.

However, this method needs four scanning processes to form a full color image, and therefore a trouble which occurs is that conventional photoreceptors have too low durability to be used for the method.

In the discharging process, irradiating the photoreceptor with light tends to fatigue the photoreceptor, resulting in deterioration of charging properties and increase of residual potential of the photoreceptor.

When the cleaning process is performed, the surface of the photoreceptor tends to be acceleratedly abraded or hurt, resulting in production of undesired images.

In addition, when the surface of the photoreceptor is contaminated due to insufficient cleaning, not only undesired images are produced but the life of the photoreceptor is seriously shortened.

Therefore, a filming problem in which a toner film is formed on the surface of the photoreceptor occurs and production of undesired images is accelerated.

However, the method has a drawback in that the friction coefficient increases after long repeated use.

In addition, the abrasions of the four photoreceptors tend to be different when the consumption of the color toners is different, resulting in occurrence of problems such that color reproducibility deteriorates and undesired images are produced.

Images