JPH02271372A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain the compact image forming device which has the satisfactory toner transfer rate and cleaning characteristic, and provides a stable picture free from picture quality variation by using spherical toner for development. CONSTITUTION:In the image forming device which performs both development and removal of unnecessary residual toner on the surface of a photosensitive body, and forms a toner image longer than the circumference of the photosensitive body, toner used for development is constituted of spherical toner. In this constitution, since the spherical toner is used, residual toner is also spherical, and it is in point-contact with the smooth surface of the photosensitive body. When discharge ions are supplied, they are almost uniformly adsorbed on the surface of the photosensitive body except the point where toner is in point- contact with the surface, therefore obstacle to uniform electrification, which is caused by residual toner, does not occur. As a result, toner is selected to suppress nonelectrostatic detaining to the photosensitive body, and the transfer rate is improved; additionally, a picture of satisfactory quality can be obtained by reversal development, etc. Since a cleaning blade does not abut on the photosensitive body, the service life of the photosensitive body can be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compact image forming apparatus that forms an image according to an electrostatic latent image, and more particularly to an image forming apparatus that uses spherical toner powder.

[Background of the invention]

Although electrophotographic copying devices are widely used and useful as office automation equipment, their bulk and weight have made them difficult to fit into modern office formats, and furthermore, they have become necessary as end devices to have at least a receiving function. ing.

Although efforts are being made to make copying devices more compact, it appears that the conventional configuration in which one original image is accommodated within the circumference of a photoreceptor has already reached its limit.

In response to this situation, a compact recording apparatus has been proposed that uses a photoreceptor with a small circumference and electrically removes residual toner at a toner development portion of a series of image forming steps. (Unexamined Japanese Patent Publication No. 63-133179, 63-13
No. 3180, No. 63-133181, etc.).

However, problems such as nonuniform charging during the charging process due to residual toner after transfer, light attenuation during the exposure process, and color turbidity when forming ghost images or multicolor images have been observed. An image forming system that does not occur is desired.

On the other hand, if we look at this technical field from the perspective of developing toner, we can see that it has fluidity that improves toner charging properties, regularity of toner consumption that eliminates the distortion in which small particles are gradually consumed from large particles, and high-density images. Issues include cleaning properties to ensure good transfer rates and repeatable copying with good reproducibility.

Toner particles are spheroidized as a means of increasing the fluidity of the toner and achieving frictional efficiency and uniform charging stability.

However, spheroidization is not necessarily advantageous; spheroidization increases the adhesion of toner to the photoreceptor or developing sleeve, resulting in a decrease in transfer rate and poor cleaning. According to the findings of the present inventors, the adhesion increases as the sphericity increases.

The adhesion is due to physical and/or electrical mutual forces,
It also depends on the hardness and flatness of the surface of the photoconductor, sleeve, etc. Regarding the photoconductor, there are some causes of deterioration and softening of the photoconductor surface due to corona discharge, oxidation, etc., and increase in stickiness. In forward development using toner that gives a polar charge, the polarity of the photoconductor charge and the toner band! Coulomb force is added due to the positive and negative ffl properties.

An increase in the adhesion amount and adhesion strength reduces the transfer rate to the transfer material and also causes cleaning failures.

On the other hand, electrostatic methods are not very effective in removing adhesion of spherical toner, in which electrostatic factors are not very involved, and mechanical scraping is effective. However, when downsizing to the extent described above, there are many problems that need to be solved in order to make full use of the small-sized photoreceptor type image forming apparatus, such as the lack of sufficient space to store the parts to be removed. be.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact image forming apparatus that provides stable images with good toner transfer rate and cleaning performance and no variation in image quality.

[Structure of the invention]

An object of the present invention is to provide an image forming apparatus that is equipped with a developing device that performs both development and removal of unnecessary residual toner on the surface of a photoreceptor and that forms a toner image that is longer than the circumference of the photoreceptor, in which the toner used for development is spherical toner. This is achieved by an image forming apparatus having the following characteristics.

In an aspect of the present invention, it is preferable that the binder of the photosensitive layer of the photoconductor contains at least a thermosetting resin, and in addition, it is preferable that the binder of the photosensitive layer of the photoconductor contains at least a thermosetting resin. It is preferable that the development method is based on a magnetic brush development method and that the development is a reversal development method.

[Operations and Effects of the Invention] Conventionally, when forming an electrostatic latent image on the surface of a photoreceptor, the surface of the photoreceptor must be cleaned to a pure state.
The steps of charging, image exposure, development, and transfer were underway.

However, the toner remaining on the surface of the photoreceptor is electrostatically adsorbed to the next newly formed image area, so if the toner is the same, the remaining toner in the area corresponding to the image area will not be absorbed. There is no need to remove it.

Furthermore, if the residual toner does not interfere with the newly performed charging, image exposure, and development, it is sufficient to remove the unnecessary or harmful residual toner left by the previous image during development and transfer the image to the transfer process. .

If spherical toner is used for toner development, the remaining toner will naturally also be spherical toner, and will be in point contact with the smooth photoreceptor surface.

When ions are newly supplied to the photoreceptor surface using a corona discharge such as a suflotron while the spherical toner in point contact is placed on the photoreceptor surface, even though the ion flow is directional and is deposited on the surface, it may interact with air molecules along the way. Due to collision or re-discharge on the toner particles, the remaining spherical toner particles enter the shadow area 1 and are almost uniformly adsorbed onto the surface of the photoreceptor except for the toner contact points.

In addition, the hindrance to uniform charging due to the residual charge of the remaining toner is buried in the rich charge atmosphere of the generated ions and poses almost no problem.

Therefore, at least as long as spherical toner is used, uniform charging will not be hindered by residual toner.

In addition, in image exposure, unless the spherical toner particles are extremely large particles, even in the case of coherent laser light, light may go around the shadow area due to light diffraction at the periphery. It is considered that the exposure effect is sufficiently extended to the surface of the photoreceptor.

Furthermore, residual toner that survives the development process is toner that is located in the newly formed image area and can be used as is, and toner that is located in the non-image area and is unnecessary and that its presence impairs image quality.
It is divided into harmful toner.

The Coulomb force between the unnecessary particles to be removed and the surface of the photoreceptor has already been attenuated, and it is thought that they can be easily removed by gentle rubbing with a developing magnetic brush or the like.

Particularly in the case of reversal development, the charge polarity of the photoreceptor and the charge polarity of the toner are the same, and there is no residual toner in the non-image area where the development bias is strong enough to prevent even newly charged toner from adhering. Adhesion cannot be maintained.

In other words, in a magnetic brush development method with a squeezing effect and a reversal development method, hardly any remains of residual toner can be seen except in the new image area.

From this point of view, - the toner image of the original image is divided several times in the circumference using a photoreceptor with a small circumference shorter than the printing length, and several image divisions of the toner image are performed. This makes it possible to create an image forming apparatus using a "reverse printing" method using a photoreceptor with a small circumference, in which the entire toner image is completed by printing.

In the present invention, a spherical toner having particularly good fluidity, charging uniformity, and regularity of toner consumption is used, and preferably the hardness of the photosensitive layer of the photoreceptor is increased to prevent the spherical toner from being applied to the surface of the photoreceptor in a non-electrostatic manner. Improves transfer rate by suppressing locking properties, and also enables reversal development,
The magnetic brush development method ensures high quality images.

Next, the present invention will be specifically explained in detail.

In the present invention, as a technique for spheronizing spherical toner to improve the fluidity of the toner and increase the charging efficiency, for example, a thermal spheronization treatment method (JP-A-56-52758, JP-A-56-59
-127662, etc.), a method of dispersing resin particles in an air stream and melting the surface to make them spherical (Japanese Patent Application Laid-Open No. 134650/1982, etc.), a method of applying temperature and simultaneously pulverizing them and making them spherical (Japanese Patent Application Laid-open No. 61-1989). A method of forming a spherical toner in a solution such as a granulation type method or the like can be used.

The average particle diameter of the spherical toner is preferably 1 to 7 μm, and 1, u
When the thickness is less than 7 μm, cleaning failure occurs, and when it exceeds 7 μm, there is an adverse effect of blocking exposure.

Examples of the resin used in the spherical toner of the present invention include a copolymer of a styrene monomer such as styrene and an acrylic ester monomer such as butyl acrylate and/or a methacrylic ester monomer such as methyl methacrylate. Examples include styrene-acrylic copolymer resins, polyester resins, polyamide resins, polyurethane resins, and polyurea resins obtained by.

When coloring the toner according to the present invention, taking into consideration the absorption spectrum of the colored toner, it is preferable to expose the colored toner to light of a wavelength that is less absorbed, and can pass through the remaining toner to stably form an electrostatic image.

In this respect, laser light with a wavelength longer than that in the visible light region is generally useful.

In particular, if a long-wavelength laser beam such as a semiconductor laser is used, even if the toner is colored, it can be designed to have high transmittance in the infrared region.

For example, a black toner can be made by blending pigments used in Y, M, Cl-toners, and the like. This black toner is
High transmittance for infrared light.

For this reason, even if toner is attached during exposure, it is unlikely to interfere with the optical attenuation of charges.

In the present invention, it is preferable to use a charge control agent to control the charge amount and charge polarity of the toner.

As the charge control agent, for example, nigrosine dyes, metal complex dyes, ammonium salt compounds, aminotriphenylmethane dyes, etc. can be used.

The charge control agent is contained in an amount of O to 5vt per 100 parts by weight (abbreviated as vt) of the binder resin of the toner.

Further, conventional techniques such as mixing fine silica particles treated with an amine compound and other fluidizing agents (Japanese Patent Application Nos. 62-108213, 1982-119482, etc.) in addition to the charge control agent are used.

Further, polyolefin or the like may be added to improve offset properties.

Further, the toner of the present invention may be mixed with inorganic fine particles such as a fluidity improver. Examples of such inorganic fine powders include silica powder, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, silica sand, clay mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide,
Examples include red iron oxide, antimony dioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, and silicon nitride, and fine silica powder is particularly preferred.

The magnetic material used in the developer carrier or magnetic toner according to the present invention includes metals or alloys exhibiting ferromagnetism such as iron, cobalt, nickel, etc., including ferrite and magnetite, or compounds containing these elements, and others. can be mentioned.

The developer used for reversal development is a two-component developer, which is versatile in the present invention and is convenient for eliminating the problem of toner remaining after transfer. In reversal development, the photoreceptor and toner are charged to the same polarity, so they are less likely to interfere with cleaning.

Furthermore, it is desirable to use a developing bias during this reversal development in which an alternating current component is superimposed on a direct current bias.

This alternating current component forms an alternating electric field in the developing area, and has the effect of returning toner to the developing sleeve when too much toner is attached to the photoreceptor, and when too little toner is attached to the photoreceptor. It has the effect of accelerating development.

For this reason, even if toner has adhered in advance, the influence can be reduced.

In this way, in the present invention, the harm caused by residual toner after transfer can be avoided.

By increasing the transmittance of the toner with respect to the exposure light described above and by superimposing an alternating current component on this developing bias, the adverse effects of the residual toner after transfer can be further avoided.

Next, examples of thermosetting resins used in the binder of the photoreceptor of the present invention include phenol resins, urea resins, epoxy resins, unsaturated polyester resins, melamine resins, silicone resins, polyurethane resins, diallyl phthalate resins, furan resins, etc. be able to. Among these, those with good electrical insulation properties, film-forming properties, other physical properties, chemical resistance, etc. are selected, but in the present invention, phenolic resins having the structural units shown in the following formula are preferred.

- In the formula, R, R, are hydrogen atoms or methyl groups, R2 is hydrogen atoms or epoxy groups, R,, R4 and R6 are halogen atoms, hydrogen atoms, hydroxy groups, nitro groups, cyano groups, ami7 groups, Carboxy group or sulfonic acid group or salt thereof,
Alternatively, it is a saturated or unsaturated chain hydrocarbon group having 1 to 3 carbon atoms which may have a substituent.

The polymerization degree of these resins is 2 to ooo, preferably 2 to 100.

Moreover, the phenolic resin represented by the above-mentioned -formation is melamine,
Those modified with resins such as lignin, chroman, indene, hydrocarbons, polyvinyl alcohol, fatty acid amides, acetates, lactones, acetals, chlorophenols, thiophenes, or styrenated phenols, or their monomers are also effectively used ( Japanese Patent Publication No. 54-1230
No. 35, etc.).

As the photoconductive semiconductor used in the present invention, conventionally known and commonly used photoconductive semiconductors are used.
No. 34189, No. 49-4338, No. 49-1753
No. 5, No. 47-30328, No. 47-30329,
Preferred are phthalocyanine photoconductive pigments described in Japanese Patent No. 50-38543 and Japanese Patent No. 51-23738.

Specifically, it is a phthalocyanine pigment represented by the general formula (C@H4Nz)+Rn, and among these, metal-free phthalocyanine and α-, β-, γ-, χ-, K-, or ε-type copper phthalocyanine are particularly preferred. Particle size is 0.1~0
．． 01 μm is preferable.

The charge-light decay curve of the phthalocyanine is insensitive to low illuminance, with little charge decay in the low exposure range, forming a flat plateau, and steeply cutting off from a certain exposure range. .

Therefore, charge is lost due to light in the low-illuminance area at the edge of the image that occurs due to light diffraction on the image exposure surface, typically in the rising area of the exposure intensity approaching the image in dot exposure, and the tail light in the falling area at the end of the image. Instead, sharp rises and falls of charge occur at the peripheral edge of the image, making it possible to provide a sharp image.

The photoreceptor according to the present invention comprises the photoconductive fine powder and resin, optionally a sensitizing agent such as rose bengal, auramine, bromophenol blue, bromothymol blue, tsuksin, and other sensitizers as described in 2.4. 7-) Dinitro-9-fluorenone, 2.4,5゜7-titranitrofluorenone in an organic solvent such as benzene, toluene, xylene, trichloroethylene, ethyl acetate, acetone, methyl ethyl ketone, etc., for example, for 100 volts of photoconductive powder, Resin 1 = 1000wt.

Infection charge 0.05-1 Ovt, organic solvent 50-5000
A photosensitive layer paint is prepared by mixing and dispersing the photosensitive layer paint in a proportion of wt, and this photosensitive layer paint is coated on a metal plate such as copper, iron, nickel, aluminum or stainless steel, or on a paper or plastic film such as aluminum, gold, silver, etc. A powder of the metal or metal oxide or a powder of carbon black is applied to a support obtained by vapor depositing or laminating a metal such as copper nickel or a metal oxide such as tin oxide, or to paper or a plastic film. Supports obtained by coating a layer dispersed in fat, etc.
The film thickness after drying is 5 to 30 μm on various conductive supports.
It is created by coating and drying to form a photosensitive layer.

Further, an intermediate layer such as an organic polymer compound or a rectifying semiconductor layer can be provided as necessary.

By equipping the photoreceptor prepared as described above, a latent image forming process can be performed in which a good latent image is formed not only by analog image exposure following the charging process but also by dot exposure of pulse width modulated spot light. An image forming process incorporating a reversal development process and an image forming apparatus including the process are configured.

In the present invention, in consideration of the absorption spectrum of the toner, it is preferable to expose the toner with light having a wavelength that is less absorbed by the toner, and in this respect, laser light having a wavelength generally longer than that in the visible light region is preferable.

The laser l= used for exposure is He-Ne, He-Cd
Alternatively, a gas laser such as Ar or a semiconductor laser such as GaAQAs is used, and since the wavelength thereof is generally 700 nm or more, the photoreceptor generally requires spectral sensitization treatment depending on the material mentioned above.

〔Example〕

Hereinafter, the present invention will be explained using the drawings.

FIG. 1 shows an overview of the image forming apparatus of the present invention.

This image forming apparatus uses a semiconductor laser to perform image exposure, and a two-component developer is applied at the same location using a magnetic brush.

This device can also be connected to a phoslo system (not shown), which is an external device such as a computer or a word processor, or an image reading device via a transmission control (not shown) such as an interface circuit.

Upon receiving the print start signal, the photoreceptor 21 rotates and is charged by the charger 22 . Next, the modulated laser beam with a wavelength of 800 nm is sent to the polygon scanner 2.
The charged photoreceptor 21 is
is scanned and exposed to form an electrostatic latent image.

The electrostatic latent image is developed by a developing device 25 to form a toner image. Next, the toner image is transferred onto the transfer material 27 transported from the cassette 26 using the transfer charger 22, and the toner image is fixed onto the transfer member 27 by the fixing device 29.
It is discharged onto the tray 30.

As shown in FIG. 1, the developing device 25 includes a developing roller 25a consisting of a magnet 78 and a developing sleeve 79, and a sliding contact portion between the developing magnetic brush formed on the surface of the developing roller 25a and the photoreceptor 21. It is provided upstream in the rotational direction from the development position, and accommodates a magnetic rod 74 that regulates the thickness of the developer magnetic brush and a developer stirring body 76 housed in a developer storage section 75 . Furthermore, the developing device 25 and the photoreceptor 21 are built in a casing 77.

In the developer storage portion 75, there are toner t of 7 μm and toner t of 80 μm.
A carrier made of resin-coated m ferrite (
Contains a developer consisting of magnetic powder).

The reverse development bias is +500V1 as a DC component.
As an AC component, 3KHz and IKV are superimposed and used).

Further, the developing roller 25a is composed of a magnetic roll 78 and a sleeve 79 that fits into the magnetic roll 78 and rotates freely. Surface potential of photoreceptor 21 and photoreceptor 21
The above toner conditions etc. change sequentially as the process progresses.

That is, the photoreceptor 21 is charged with, for example, +600V by the charger 22.
is charged with electricity. At this time, the toner L on the photoreceptor 21 that was not completely transferred in the previous copying operation is also charged, and the photoreceptor 21 under the torch t is also charged.

In the apparatus of this embodiment, a scorotron charger is used to equalize the surface potential, so the potential of the part of the photoreceptor 21 under the toner t is slightly lower than that of the part without the toner t. It has been standardized to a level where there is no problem at all.

Further, the surface potential of the photoreceptor 21 is attenuated by receiving a pulse width modulated laser beam scanned by the optical system 24, thereby forming an electrostatic latent image.

Due to the light attenuation property of the phthalocyanine, the periphery of the electrostatic latent image formed here approximates a rectangular shape with sharp charge rises and falls.

This electrostatic latent image is developed by the developing device 25, but at this time, the toner t that is unnecessary for the image and has adhered to the photoreceptor 21 as a transfer residue is simultaneously transferred to the developing device 25.
Cleaned by 5.

Further, the electrostatic latent image on the photoreceptor 21 is supplied with toner (toner) by the developing device 25 to form a toner image, and then transferred onto the transfer material 27 on the belt 28 by the transfer charger 22.

A high voltage having a polarity opposite to that of the positively charged toner T is applied to the transfer charger 22, and a negative corona discharge is performed from the back of the belt 28 to negatively charge the toner L.
It plays the role of attracting the material to the transfer material 27. After the image is transferred in this way, the belt 28 is transferred to the static eliminator 101.
Static electricity is removed by

In addition to the above operations, it is effective to provide a uniform exposure lamp 31 upstream of the charger 22 shown in FIG. . It is desirable that this irradiation light has the same translucency to the toner as the exposure light.

Further, in order to prevent the difficulty of setting conditions for developing and cleaning the toner remaining after transfer in the developing area at the same time, it is effective to provide a leaning blade 32 that can be pressed and released.

This cleaning blade 32 is pressed during image formation, scrapes off and retains the residual toner after transfer, and is then released after image formation is completed. The retained toner can be easily cleaned by a developing device.

Next, the photoreceptor 21 will be described in detail.

The photoreceptor 21 is composed of a double-sided aluminum cylinder (thickness: 0.8+am) with an outer diameter of 301 mm, and a photosensitive layer coated on the surface of this cylinder carrier.

The photosensitive layer contains the phthalocyanine (manufactured by Toyo Ink) and the phenol resin according to the present invention in a weight ratio of 1:2 and a thickness of 2.
It was applied to a thickness of 0 μm. FIG. 2 shows the measurement results of potential characteristics from charging to optical attenuation using an electrometer.

Further, the average particle diameter of the toner particles is preferably 20 μm or less.

Even if toner particles t of 20 μm or less exist on the surface as transfer residual toner, shadows of the toner particles t are caused by diffracted light at the particle edges when the photoreceptor 21 is exposed and reflected and scattered light within the carrier transport layer. The obstacles are almost negligible, or they are so thin that they pose no practical problem.

However, when the diameter of the toner particles t exceeds 20 μm, an image defect occurs as a memory of a white spot on a black pattern.

If the toner particles are transparent to the exposure light source, the memory is reduced. Furthermore, the thickness is preferably 30 μm or less in view of the residual potential characteristics of the toner layer after charging and image exposure.

[Effects of the Invention] As explained above, according to the present invention, since the developer remaining on the photoreceptor is rubbed off by the developing means at the same time as development, there is no need for a collection box as in the past. Since there is no cleaning blade in contact with the photoreceptor, the life of the photoreceptor can be extended, and there is no risk of contamination.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus, and FIG. 2 is a diagram showing potential characteristics of a photoreceptor. 21... Photoreceptor (image carrier) 24... Optical system (image forming means) 25... Developing device (developing means) 27... Transferred material

Claims (3)

[Claims] (1) In an image forming apparatus that is equipped with a developing device that performs both development and removal of unnecessary residual toner on the surface of the photoreceptor and forms a toner image that is longer than the circumference of the photoreceptor, the toner used for development must be spherical toner. An image forming apparatus characterized by: (2) The image forming apparatus according to claim 1, wherein the photosensitive layer binder of the photoreceptor contains at least a thermosetting resin. (3) The image forming apparatus according to claim 1 or 2, wherein the development in the operation of simultaneously performing the development and removing unnecessary residual toner on the surface of the photoreceptor is reversal development using a magnetic brush development method.