JPH05119541A - Conductive magnetic carrier for developer, developer, and image forming method - Google Patents

Abstract

PURPOSE:To give large conductivity to a carrier, to enable development with an insulating toner by back exposure/simultaneous development method, and to realize plane paper transfer. CONSTITUTION:A conductive magnetic carrier is obtd. by forming a conductive thin film 15 such as ITO, on the surface of a magnetic particle 13 and treating the particles to have conductivity to obtain a conductive magnetic carrier. This carrier is mixed with an insulating toner to obtain a two-component developer. With this developer, a developer reservoir is formed between a developer sleeve and a photosensitive body so that charges are injected to the photosensitive body through a magnetic brush comprising the conductive magnetic carrier to electrify the photosensitive body. A latent image is formed by exposing the back surf ace and a toner image comprising the insulating toner is formed by development, which is then electrostatically transferred to plane paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming method, a developer and a carrier for a developer, which are used in printers, digital copying machines, facsimiles, copying machines and the like.

[0002]

2. Description of the Related Art An electrophotographic method represented by the Carlson method is widely used at present, in which uniform charging of a photosensitive member → formation of a latent image by selective exposure → formation of a toner image by a developer →
The basic process is transfer → fixing.

On the other hand, various reports have recently been made on a non-Carlson image forming method which employs a backside exposure recording method, and it is said that the apparatus can be downsized and the process can be simplified (image electronic). Journal, 16, (5),
306, (1987), JP-A-61-149968, JP-A-63-10071, and JP-A-63-214781.
Publication).

The backside exposure recording system is one in which a developer is supplied to the surface side of a photoconductor to form a developer pool, and cleaning is carried out by the developer pool, uniform charging of the photoconductor-rear image exposure-simultaneous development. Therefore, cleaning, charging, image (signal) exposure and development can be performed simultaneously.

However, in a relatively short developer pool (charging / exposure / development zone), a charge amount necessary for development is injected into the photoreceptor through the developer, and further, a sharp and stable toner image is developed. Since it is necessary to obtain the above-mentioned requirements, there are many demands on each functional material and system, and there are many difficult problems to realize.

Further, since the charge is injected through the developer, the toner is required to be conductive in the one-component developer, and the conductive magnetic toner is required. Therefore, plain paper transfer cannot be performed using an electrostatic transfer method such as a corona transfer method or a bias roller transfer method, and it is necessary to use high-resistance paper.

Japanese Patent Publication No. 60-59592 discloses a method of obtaining a multicolor recorded image on plain paper by rear image exposure. However, a photoconductor in which an insulating layer is laminated on an optical semiconductor layer is used. Therefore, repeated use becomes difficult. As a countermeasure for this, it is said that the charge image is erased by utilizing a transfer electric field, but it is difficult to obtain a stable and good image in many practical problems.

As a method of using an insulating toner, a two-component developer consisting of an iron powder carrier of 10 ⁴ to 10 ⁸ Ω · cm and an insulating magnetic toner is used, and a charging bias electrode and a developing bias electrode are used. It is reported that two counter electrodes of No. 2 are provided and the image is formed by performing rear surface image exposure-simultaneous development (Electrophotographic Society, Vol. 27, No. 27).
3, p442, 1988, JP-A-61-46961).

However, if this system is mounted on an actual machine, it is difficult to control in practice, stable and clear images cannot be obtained, and the structure of the apparatus is complicated. Regarding image formation with a developer using a magnetic resin carrier in which a magnetic material is dispersed in a binder resin, a developer combined with an insulating non-magnetic toner (Japanese Patent Laid-Open No. 53-
No. 33152, No. 55-41450), and a developer combined with an insulating magnetic toner (JP-A-53-33).
No. 152, No. 53-33633, No. 53-3
No. 5546) has been reported. However, in all of these, the carrier has an insulating property, and development is performed by the usual Carlson process. further,
Such a magnetic resin carrier is (1) difficult to obtain a sufficient magnetic force, (2) has weak mechanical strength and is easily broken, and is unstable (3) has an unstable surface shape and has uneven properties. There were drawbacks such as easy to become.

[0010]

SUMMARY OF THE INVENTION The present invention is capable of imparting both high conductivity and large magnetic force, and is a carrier which is stable in terms of strength and characteristics, and a developing agent containing the carrier. To provide the agent.

The present invention provides a new image forming method of the backside exposure system, which can favorably perform charge injection and development with toner and has excellent transfer characteristics.

[0012]

The conductive magnetic carrier for a developer of the present invention is characterized in that the surface of a magnetic material is subjected to a conductive treatment.

The developer of the present invention is characterized in that the carrier is mixed with an insulating toner.

The image forming method of the present invention comprises a photoreceptor having at least a light-transmissive conductive layer and a photo-conductive layer sequentially provided on a light-transmissive support, a carrier in which the surface of a magnetic material is electrically conductive, and an insulating toner. And a developing means which is disposed on the photoconductive layer side of the photoconductor and supplies the developer to the surface of the photoconductor, and a translucent conductive layer of the photoconductor and the developing means. By using a means for applying a voltage between them and an exposing means arranged on the light-transmitting support side of the photoconductor so as to face the developing means, the developer is brought into contact with the surface of the photoconductor, While applying a voltage between the light-transmissive conductive layer and the developing means, the selected light is irradiated from the light-transmissive support side to the photoconductive layer in the vicinity of the portion facing the developing means, and the photosensitive material is exposed. It is characterized in that a toner image corresponding to the light irradiation is formed on the body.

[0015]

EXAMPLE FIG. 1 is a schematic view showing an example of the carrier of the present invention, in which a conductive thin film 15 is formed on the surface of magnetic particles 13 to form a conductive layer, and a surface conductive treatment is applied. The carrier 11 is configured.

The conductive thin film 15 is made of ITO (Indium).
-Tin-Oxide), indium oxide, tin oxide, a thin film of aluminum, nickel, chromium, gold, or the like may be formed by a thin film formation method such as a CVD method, an evaporation method, or a sputtering method.

The magnetic particles 13 are magnetite,
Gamma iron oxides and other spinel ferrites, spinel ferrites containing one or more metals (Mn, Ni, Mg, Cu, etc.) other than iron, magnetoplumbite type ferrites such as barium ferrite, irons with an oxide layer on the surface Or alloy particles can be used. Its shape is
It may be granular, spherical or acicular. Particularly when high magnetization is required, it is preferable to use ferromagnetic fine particles such as iron. On the other hand, in consideration of chemical stability, it is preferable to use ferromagnetic particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. The carrier 11 having a desired magnetization can be obtained by appropriately selecting the type of the ferromagnetic fine particles.

FIG. 2 is a schematic view showing another embodiment of the carrier of the present invention, in which a binder resin layer 17 as a binder is formed on the surface of the magnetic particles 13 and the binder resin layer 17 is electrically conductive. The carrier 11 is formed by fixing the conductive fine particles 19 to form a conductive layer and subjecting the conductive layer to a surface conductivity treatment. In the present invention, the conductive layer does not necessarily have to be a continuous layer that uniformly coats the magnetic particles 13, and at least a conductive portion is formed on the surface of the magnetic particles 13 so that the conductivity required for the carrier is A discontinuous layer may be used as long as it is applied. Therefore, for example, the conductive fine particles 19
Does not need to completely and continuously cover the surface of the magnetic particles 13, and as shown in FIG. 2, some uncoated portions may exist.

Examples of the binder resin used in the binder resin layer 17 include vinyl resins represented by polystyrene resins, polyester resins, nylon resins, polyolefin resins and the like.

As the conductive fine particles 19, carbon black, tin oxide, conductive titanium oxide (titanium oxide coated with a conductive material), silicon carbide, or the like is used, and conductivity is obtained by oxidation by oxygen in the air. Those that do not lose are desirable.

Conductive fine particles 1 on the surface of the magnetic particles 13
For example, the magnetic particles 13 on which the binder resin layer 17 is formed and the conductive fine particles 19 are uniformly mixed, and the conductive fine particles 19 are adhered to the surface of the binder resin layer 17 and then mechanically or thermally fixed. Conductive particles 19
Is fixed in the binder resin layer 17 by driving. As such a surface treatment device, a hybridizer (manufactured by Nara Machinery Co., Ltd.) and the like are commercially available. It is preferable that the conductive fine particles 19 are not completely embedded in the binder resin layer 17, but are fixed so that a part thereof protrudes from the binder resin layer 17. The average particle diameter of the conductive fine particles 19 is 0.5 μ.
m or less, more preferably 0.01 to 0.2 μ
m.

By thus fixing the conductive fine particles 19 on the surface of the carrier 11 to form the conductive layer, it is possible to efficiently impart high conductivity to the carrier 11.

The carrier 11 has a volume resistivity of 10 ⁵ Ω.
· It is suitable that it is not more than cm, preferably 10 ⁴
Ω · cm or less, more preferably 10 ² to 10 ⁴ Ω · cm. If the volume resistivity becomes too large, the characteristics as a conductive carrier are impaired. For example, when used in a backside exposure system, charges are not injected promptly and the photoreceptor becomes insufficiently charged. The conductivity of the carrier 11 is mainly given by the conductive layer.

Regarding the volume resistivity of the carrier 11, 1.5 g of the carrier 11 is put into a Teflon cylinder having an inner diameter of 20 mm and an electrode having an outer diameter of 20 mmφ, and a load of 1 kg is applied from the top. It is the value when it was measured.

The magnetic force of the carrier 11 needs to be large to some extent or more, and the maximum magnetization (magnetic flux density) in a magnetic field of 5 KOe (Oersted) is preferably 55 emu.
/ G or more, more preferably 55 to 90 emu / g, and further preferably 60 to 85 emu / g. Also, 1K
The maximum magnetization in a magnetic field of Oe is preferably 40 emu / g or more, preferably 40 to 60 emu / g, and more preferably 45 to 60 emu / g. Carrier 1
When the magnetic force of 1 becomes too small, the developer transportability deteriorates, and the carrier 11 is developed together with the toner, causing so-called carrier pulling.

The average particle size of the carrier 11 is 5 to 100 μm.
m is suitable, preferably 5 to 50 μm, more preferably 10 to 40 μm. If the carrier 11 is too large, it becomes difficult to uniformly charge the photoconductor, and the toner concentration T / C cannot be increased. On the other hand, if it is too small, the transportability of the developer on the developing sleeve deteriorates, and it becomes difficult to apply a constant potential to the photoconductor.

The true density of the carrier 11 is 3.0 to 4.5.
A range of g / cm ³ is preferred. The bulk density is 2.5
g / cm ³ or less well, preferably 2.0 g / cm ³ or less, more preferably 1.5 g / cm ³ or less.

The carrier 11 of the present invention has magnetic properties that substantially reflect the magnetic particles 13, and sufficient magnetic properties can be obtained. Therefore, a stable magnetic brush is formed, uniform charging of the photoconductor and good development characteristics are obtained, and so-called carrier pulling, in which the carrier along with the toner is transferred to the photoconductor, is prevented. Also, unlike a resin carrier, it has high mechanical strength and excellent durability. further,
The surface characteristics are stable, and uniform charging of the photoconductor is easy. In addition, the fluidity of the carrier is good, and the transportability is also excellent.

A developer is prepared by mixing the above carrier and toner. As the toner, a usual insulating toner is used, and the volume resistivity thereof is preferably 10 ¹⁴ Ω · cm or more, preferably 10 ¹⁵ Ω · cm or more. This value is measured as for the carrier.

As the toner, one having the same structure as the conventional one is used, and, for example, a binder resin, a colorant, a charge control agent, an offset preventing agent and the like can be blended.
It is also possible to add a magnetic substance to obtain a magnetic toner,
It is effective in preventing toner from scattering inside the machine. As the binder resin, a vinyl-based resin represented by polystyrene-based resin such as styrene-acrylic copolymer, a polyester-based resin, or the like is used.

Various pigments and dyes such as carbon black are used as colorants; quaternary ammonium compounds, nigrosine, nigrosine bases, crystal violet, triphenylmethane compounds and the like are used as charge control agents; anti-offset agents and fixing improvement. An olefin wax such as low molecular weight polypropylene, low molecular weight polyethylene or a modified product thereof can be used as an auxiliary agent, and magnetite or ferrite can be used as a magnetic material.

In the developer of the present invention, the ratio (carrier) / (toner) of the average particle size of the carrier and the toner is preferably 1 to 5, preferably 1 to 3. If the toner becomes significantly smaller than the carrier, the surface area of the carrier covered by the toner at a constant toner concentration increases, and the toner concentration of the developer cannot be increased. As a result, the toner is applied to the image forming method of the present invention. In that case, the image density may decrease depending on the conditions. The average particle diameter of the toner is generally preferably 20 μm or less, more preferably 15 μm or less.

As in the case of the carrier 11 shown in FIG. 2, the charging characteristics of the toner can be controlled by fixing the chargeable fine particles to the surface of the toner mother particles to form a toner.

The volume resistivity value as a developer is 10 ⁶ Ω
-Cm or less is suitable, preferably 10 ⁵ Ω-cm or less, and more preferably 10 ³ to 10 ⁵ Ω-cm. This value is measured similarly to the carrier. If the resistance becomes too large, the photoreceptor will be insufficiently charged.

The toner concentration of the developer (toner / carrier, that is, T / C) is preferably 10% by weight or more, preferably 20% by weight or more, more preferably 20 to 20% by weight.
It is 50% by weight. If the toner density is too low, a sufficient image density cannot be obtained when applied to the image recording method of the present invention. On the other hand, if the toner concentration is too high, the photoreceptor will be insufficiently charged. In the image forming method of the present invention,
Since almost the same image density can be obtained in a wide range of the toner density T / C, the toner density control can be substantially unnecessary or greatly simplified.

FIG. 3 is an explanatory view showing an embodiment of the image forming method of the present invention. A light-transmitting conductive layer 25 and an amorphous silicon (a-Si) -based photosensitive layer 27 are formed on a light-transmitting hollow-cylindrical light-transmitting support 23 such as glass. 21 is configured. A belt (sheet) is used instead of the drum-shaped photoconductor 21.
A photoreceptor may be used.

As the photosensitive layer 27, in addition to the a-Si layer,
Both the Se alloy layer and the organic photosensitive layer can be adopted,
It is desirable to have high sensitivity and high mobility of charge carriers.
An example of such a photosensitive layer is an a-Si photosensitive layer, and in particular, at least a transparent conductive layer, an a-Si photoconductive layer, and a carrier injection blocking surface layer are sequentially provided on the transparent support 23. Those provided are preferable.

FIG. 4 shows such an a-Si type photosensitive member 2.
1 is an explanatory cross-sectional view showing details of the layer structure of No. 1, in which a carrier-side carrier injection blocking layer 26, an a-Si based photoconductive layer 29, and a carrier injection blocking surface layer 28 are laminated to form a photosensitive layer 27. The layer 27 is formed on the translucent conductive layer 25 to form the photoconductor 21.

The carrier-side carrier injection blocking layer 26 has a surface of the photoreceptor 21 which is a developer 71 to which a developing bias voltage is applied.
By blocking the injection of carriers having a polarity opposite to that of the developing bias from the translucent conductive layer 25 to the a-Si photoconductive layer 29 when contacted with, the image noise is removed and the exposed portion and the non-exposed portion are removed. And improve the image quality by reducing the background fog during development.

The carrier-side carrier injection blocking layer 26 has an electrical characteristic of blocking carrier injection from the transparent conductive layer 25 and does not absorb image exposure light from the transparent support 23 side. Has a high light-transmitting property (a large optical band gap or a high light transmittance), and further has good adhesion to the light-transmitting conductive layer 25 and the a-Si-based photoconductive layer 29.
It is necessary to have a characteristic that the quality of the a-Si-based photoconductive layer 29 does not significantly change even when it is heated.

The carrier-side carrier injection blocking layer 26 is made of amorphous silicon carbide (a-SiC).
x), amorphous silicon oxide (a-SiO)
x), amorphous silicon nitride (a-SiN)
x), a-SiC.O, a-SiC.N, a-SiO.
A, Si-based layers such as N, a-SiC / O / N, polyethylene terephthalate, parylene, polytetrafluoroethylene, polyimide, polyfluoroethylenepropylene, urethane resin, epoxy resin, polyester resin, polycarbonate resin, cellulose acetate It is preferable to use a resin or another organic material layer. In the a-Si system layer, C,
It is also possible to use those in which the contents of N, O, etc. are changed in the layer thickness direction.

As the carrier-side carrier injection blocking layer 26, an a-Si-based p-type or n-type semiconductor layer can be used. In this case, in order to make the optical band gap larger than that of the a-Si-based photoconductive layer 29, or to further improve the adhesiveness, an element such as C, O, or N is contained, and the light-transmitting conductive film is added. An impurity element is contained in order to prevent carrier injection from the layer 25.

That is, in order to prevent the injection of the negative charge carriers, the group IIIa element of the periodic table (hereinafter, the group IIIa element of the periodic table is abbreviated as the group IIIa element) is 1 to 10,
000 ppm, preferably 100 to 5,000 ppm, on the other hand, in order to prevent the injection of positive charge carriers, an element of group Va of the periodic table (hereinafter referred to as group V of the periodic table).
The a-group element is abbreviated as Va-group element) should be contained in an amount of 5,000 ppm or less, preferably 300 to 3,000 ppm. Then, these elements may be provided with a gradient in the layer thickness direction, in which case the average content of the entire layer may be within the above range.

Thus, the carrier injection blocking layer 2 on the support side
When III contains a Group IIIa element, a positive development bias is used, while when it contains a Va group element, a negative development bias is used.

Here, as the IIIa group element and the Va group element, the B element and the P element respectively have excellent covalent bond with Si and can sensitively change the semiconductor characteristics, and in addition, they have an excellent injection blocking ability. It is desirable in that it can be obtained.

The thickness of the carrier-side carrier injection blocking layer 26 is preferably in the range of 0.05 to 5 μm, preferably 0.1 to 3 μm, which makes it easy to secure good injection blocking ability.
Further, unnecessary absorption of light exposure in the support-side carrier injection blocking layer 26 can be suppressed to effectively generate photocarriers in the a-Si based photoconductive layer 29, and further increase in residual potential can be suppressed.

The a-Si photoconductive layer 29 is formed by, for example, glow discharge decomposition method, sputtering method, ECR method, vapor deposition method, etc., and hydrogen (H) or halogen element for the termination of the dangling bond is used in the formation thereof. -40% by atom. Further, in order to obtain desired characteristics with respect to electrical characteristics such as dark conductivity and photoconductivity of the a-Si photoconductive layer 29 and optical bandgap, a group IIIa element or V
It is preferable to contain an a-group element or an element such as C, N, or O. Above all, when a-SiC is used for the photoconductive layer 29,

[0048]

[Chemical 1] X value of 0 <x ≦ 0.5, preferably 0.05 ≦ x ≦ 0.
It is good to set it in the range of 45, and in this range, a-
It is desirable in that the resistance becomes higher than that of the Si layer and good carrier travel can be ensured. IIIa group elements and V
As the a-group element, the B element and the P element each have excellent covalent bond properties with Si and can sensitively change semiconductor characteristics.
In addition, it is desirable in that excellent photosensitivity characteristics can be obtained.

Further, in the a-Si photoconductive layer 29,
When a photoexcitation layer region having an improved function of generating photocarriers and a carrier transport layer region having a function of carrier transport are laminated, photosensitivity, electrostatic contrast, withstand voltage and the like can be enhanced.

At this time, in the photoexcitation layer region, in order to enhance the generation of photocarriers, under the conditions at the time of film formation, (1) the film formation is performed at a low film formation speed, and (2) the dilution ratio with H ₂ or He is set. It is preferable to increase, (3) contain more doping element than the transport layer region.

Further, the carrier transport layer region mainly serves to increase the withstand voltage of the photoconductor 21 and to allow the carriers injected from the excitation layer region to smoothly travel to the surface of the photoconductor 21. In this layer region, Are also generated by the light transmitted through the photoexcitation layer region, and the photoconductor 21
Contribute to the photosensitivity of.

When the a-Si photoconductive layer 29 is formed by laminating a photoexcitation layer region and a transport layer region, the thickness of the photoexcitation layer region is set to this layer for light of the wavelength of image exposure. It is preferable to set the thickness almost equal to the thickness of the light absorption layer obtained from the absorption coefficient of the region.

The carrier injection blocking surface layer 28 can be formed of either an organic material or an inorganic material.

As the inorganic material used for the carrier injection blocking surface layer 28, for example, a-SiC is suitable, and in addition, a-SiN, a-SiO, a-SiC.O, a-.
There is SiN / O, which is formed by a thin film forming means. When an a-SiC layer is used as the carrier injection blocking surface layer 28,

[0055]

[Chemical 2] X value of 0.3 <x <1.0, preferably 0.5 ≦ x ≦
The range of 0.95, and more preferably 0.6 ≦ x ≦ 0.95 is preferable.

The thickness of the carrier injection blocking surface layer 28 is 0.
The thickness may be set to 05 to 5 μm, preferably 0.1 to 3 μm, and more preferably 0.1 to 2 μm.

If this thickness is less than 0.05 μm,
The surface layer 28 cannot sufficiently improve the image density and the withstand voltage, and when it is repeatedly used, it has a short life due to abrasion. When the thickness exceeds 5 μm, an electric field (electric force line) is generated in the surface layer 28 in forming a fine charge pattern.
Occurs in the direction of the film surface, which lowers the resolving power and does not provide sufficient resolution.Moreover, the amount of charges remaining on the surface increases the residual potential, resulting in lower image density and background fog. Alternatively, problems such as a change in image density and occurrence of an afterimage may occur during repeated use.

The total thickness of the photosensitive layer 27 thus obtained depends on the settings of the above-mentioned layers, but an LED as an exposure light source is used.
When EL or EL is used, it is preferably about 1 to 20 μm, preferably 1 to 15 μm, and more preferably 3 to 1
It is 0 μm. By setting the film thickness within this range, the exposure is sufficiently absorbed to exhibit good photosensitivity, the withstand voltage as the photoconductor can be secured, and a good image can be obtained even with a low bias voltage.

An LED array 41 as an exposing means (image signal exposing device) is arranged inside the translucent support 23, that is, on the back side of the photoconductor 21 so as to face the developing unit 31. Back exposure is performed via the condensing element 43 (selfoc lens). Further, as the exposure means, instead of the LED array, an EL light emitting element array,
It is also possible to use a plasma light emitting element array, a phosphor dot array, a shutter array in which a light source is combined with a liquid crystal or PLZT, an optical fiber array, or the like.

A developing unit 31 is provided around the photoconductor 21.
A transfer unit 51 and a fixing unit 61 are provided. FIG. 5 is a partial view showing the vicinity of the facing portion of the photoconductor 21 and the developing unit 31, and for convenience of illustration, a part thereof is shown in detail with respect to FIG. 3 and a part thereof is simplified.

The developing unit 31 is disposed on the photosensitive layer 27 side of the photoconductor 21 and supplies the developer 71 to the surface of the photoconductor 21. In the conductive sleeve 35 of the developing unit 31,
A developing bias power source 39 that applies a voltage is connected between the transparent conductive layer 25 of the photoconductor 21 and the developing unit 31. The developing unit 31 includes several magnetic poles (N, S
The electroconductive sleeve 35 encloses a mag roller 33 having a pole), and a doctor blade 37 for regulating the layer thickness of the developer 71 is provided. In this embodiment, the photoconductor 2
1 and the sleeve 35 are rotated in the directions of arrows P and S, respectively, to convey and supply the developer 71 to the surface of the photoconductor 21. The mag roller 33 may be fixed or rotated.

As described above, when the developer 71 is rotated in the direction opposite to the photoconductor 21, the developing unit 31 (sleeve 3
5) and the photoconductor 21 at the closest position (portion A in FIG. 5), a developer pool 73 is formed on the downstream side (the side away from the developer 71) in the rotation direction of the photoconductor 21. A portion of the developer 71 that protrudes beyond the original height is the developer pool 73. The conveying speed of the developer 71, the height of the developer 71, the gap between the sleeve 35 and the surface of the photoconductor 21, etc. Two
It is appropriately set according to the rotation speed of 1 and the required size of the developer pool 73.

When the photoconductor 21 and the developer 71 are rotated in the opposite directions, a developer pool 73 is generated on the downstream side of the closest position between the developing unit 31 and the photoconductor 21.
Is rotated in the same direction as the photoconductor 21 and the peripheral speed of the developer 71 is made higher than the peripheral speed of the photoconductor 21. Therefore, in order to obtain the developer reservoir 73 stably and with good reproducibility, it is preferable to rotate the photoconductor 21 and the developer 71 in opposite directions.

The developer 71 is composed of a conductive magnetic carrier and an insulating toner. As the carrier, a carrier having the surface of the magnetic material made conductive as described above is preferable.
The preferable properties of the toner, carrier and developer are as described above.

The conductive and magnetic carrier 11 forms a magnetic brush, on which the toner adheres. When the toner is a magnetic toner, it is attached to the carrier 11 mainly by a magnetic force, and when the toner is a non-magnetic toner, it is attached by a charge.

At the time of image formation, the developing agent 71 is conveyed to the developing agent reservoir 73 by the sleeve 35, and a positive developing bias voltage is applied to the conductive sleeve 35 from the developing bias power source 39. In this embodiment, the toner having a positive charging property is used, but the charging property of the toner and the positive / negative of the bias voltage are determined by the characteristics of the photoconductor. Photosensitive layer 27
From the time when the toner comes into contact with the developer 71, charges are injected into the photoconductor 21 by the developing bias power source 39 via the magnetic brush composed of the carrier 11 of the developer 71, and erase and erasure of the residual charge at the time of the previous image formation. The body is charged. At the same time, the residual toner remaining on the photoreceptor 21 without being transferred by the transfer unit 51 is cleaned by the magnetic brush.

The LED array 4 disposed on the light-transmissive support 23 side of the photoconductor 21 so as to face the developing unit 31.
1 (exposure means), the developing unit 31 and the photoconductor 21.
The image signal is irradiated in the vicinity of the facing portion of the.

When the image signal exposure is selectively performed by the LED array 41, the potential of the photosensitive layer 27 in the exposed portion is rapidly lowered and a potential difference is created. At this time, the toner dissipates the magnetic force or electrostatic force from the magnetic brush due to this potential difference, and adheres onto the photosensitive layer 27. Then, when the photosensitive layer 27 and the developer layer of the developer reservoir 73 are separated from each other, the developed toner remains on the photosensitive layer 27 without being disturbed, and a toner image 75 is formed on the surface of the photoconductor 21. In this developing step as well, since the stable magnetic brush is formed by the magnetic carrier 11 as in the above, the developer pool 7
3 is constant, and a sharp and stable image is obtained.

The position where image exposure is performed by the LED array 41 is not at the closest position A between the surface of the photoconductor 21 and the developing sleeve 35, but at the developer reservoir 73 formed on the downstream side in the rotation direction of the photoconductor 21. The position is preferable, and it is more preferable that the latter half of the downstream side of the developer pool 73, that is, the position B where the developer 71 and the photoconductor 21 separate from each other.

By performing the exposure at the position of the developer pool 73, the application of the developing bias voltage to the photosensitive member 21 is sufficiently stabilized until the exposure and the influence of the history of the photosensitive member 21 is suppressed. In addition to being charged, the residual toner on the surface of the photoconductor 21 and the toner on the image background portion are sufficiently collected. Further, since the application of the developing bias voltage to the photoconductor 21 is sufficiently stabilized and the exposure is performed to generate the photocarriers, a good toner image 75 is formed. Then, after the toner image 75 is formed, the photoconductor 21 is covered with the developer 7
3, the toner image 75 on the surface of the photoconductor 21 is not disturbed by mechanical force such as collision or friction with the developer 71, and the toner image 75 with good resolution is obtained. Be done.

At the position of the developer reservoir 73, the position A where the surface of the photosensitive member 21 and the developing sleeve 35 are closest to each other
The distance between the surface of the photoconductor 21 and the mag roller 33 becomes larger than that. Therefore, the magnetic force for attracting the developer 71 to the mag roller 33 side becomes weak, and a part of the toner image 75 formed on the surface of the photoconductor 21 is magnetically attracted to the developing unit 3.
It is possible to prevent the image density from being reduced by being collected on the side of No. 1 and the resolution from being deteriorated by being disturbed by the magnetic force.

The developing bias voltage in this charging and simultaneous exposure development is preferably a low bias of 250 V or less, more preferably 10 to 200 V, further preferably 30 to 150 V. If the bias voltage is too low, charging and development will not be performed sufficiently. on the other hand,
When the bias voltage is too high, even the carrier 11 is developed, and this is remarkable when the particle size of the carrier 11 is small. The a-Si type photoreceptor as described above is suitable for such low bias development.

The dynamic resistance of the developer 71 can be measured by measuring the current flowing into the surface of the photoconductor 21 with the developer reservoir 73. In the present invention, the dynamic resistance is preferably 10 ⁷ Ω or less, more preferably 10 ⁶ Ω or less, further preferably 1 Ω or less.
It is 0 ⁴ to 10 ⁶ Ω.

The toner image 75 on the photoconductor 21 is transferred to the paper 81 (transfer target member) by the transfer roller 51 to which a negative bias voltage is applied by the transfer bias power source 55 in the transfer unit 51. In the present invention, since the toner is insulative, stable transfer can be performed with high transfer efficiency even when plain paper is used. Next, the transfer toner is transferred to the paper 81 by the fixing roller 63 (heating roller) in the fixing unit 61.
Is fixed in. Reference numeral 65 indicates a pressure roller. The residual toner on the photoconductor 21 after the transfer is transferred to the carrier 1 when the photoconductor 21 comes into contact with the developer 71 at a position facing the developing unit 31.
It is removed by the magnetic brush No. 1 and there is no need to provide a separate cleaning member. Of course, a cleaning unit may be separately provided before the developing unit 31.

Further, the transfer unit 53 and the developing unit 3
It is also possible to provide a charge eliminating means (for example, a charge eliminating light source) in order to eliminate the electric charge remaining in the photosensitive layer 27 during the period 1.
FIG. 6 is a partial explanatory view corresponding to FIG. 5, showing another embodiment of the image forming method of the present invention. This embodiment is the same as the embodiment shown in FIGS. 3 to 5 except that the developing unit 31 is provided with the control electrode 32 and members associated therewith.

The control electrode 32, which can control the voltage separately from the developing bias power source 39, includes the photoconductor 21 and the developing unit 31.
Is provided in the vicinity of the facing portion of the photoconductor 21, but as shown in the figure, it is preferably provided upstream of the exposure position of the LED light in the photoconductor 21, and in FIG.
It is provided at the closest point A to. The control electrode 32 is insulated from the sleeve 35 by an insulator 34, and a voltage is applied independently of the developing bias power source 39 by a control electrode power source 36 (voltage applying means). The control electrode 32 and the insulator 34 are not attached to the sleeve 35 but are fixed, and the sleeve 35 and the photoconductor 21 are fixed.
Is always located at the closest position A regardless of the rotation. Further, the control electrode 32 has a strip shape along the length direction (axial direction) of the sleeve 35 so that a uniform electric field can be applied to the photoconductor 21 and the developer 71.

The potential of the control electrode 32 is controlled by the control electrode power source 3
6, the potential is adjusted to a predetermined potential independently of the potential of the sleeve 35. For example, the control electrode 32 is grounded to have a common potential with the translucent conductive layer 25. Alternatively, the potential of the sleeve 35 is set low or high.

As described above, by providing the control electrode 32 capable of applying a potential independently of the sleeve 35, the potential on the surface can be made uniform and the influence of the history of the photoconductor 21 due to the previous image forming process can be canceled. As a result, when repeatedly used, for example, when the photoconductor 21 is rotated several times to obtain one image, a stable development state and a recorded image can be obtained.

Here, if the potential of the control electrode 32 is adjusted,
Optimal image forming conditions for image density, background fog, etc. can be adjusted. In addition, although the mechanism is not clear at present, in the image evaluation experiment of the present inventors, by increasing the potential of the control electrode 32 and decreasing the potential of the sleeve 35, the toner adheres to the non-exposed portion. However, so-called reversal development, in which toner does not adhere to the exposed portion, is also possible.

In the above description, the carrier and the developer of the present invention are mainly used for the backside exposure recording system, but the carrier of the present invention is not limited to this, and the developer has a high conductivity. It can also be used in other image forming methods that require properties and magnetism. Further, the developer of the present invention can also be used for other image forming methods.

[0081]

According to the present invention, the carrier can be provided with high conductivity and strong magnetism. By combining this carrier and an insulating toner, it is possible to form an electrically conductive toner image as a developer and also an insulating toner image. This toner image can be easily transferred to an ordinary paper by an electrostatic transfer method. Is possible.

Further, according to the image forming method of the present invention, it is possible to carry out uniform charging and stable development by using a carrier composed of magnetic particles whose surface is made conductive and an insulative toner. An image can be stably formed with a high image density.

[0083] After the particles having an average 30μm in Experimental Example _{1 CuO · ZnO · Fe 2 O} 3 based spray drying method to ferrite and baking, to obtain a ferrite having an average particle size of 25μm sieved. This resistance was 10 ¹⁰ Ω · cm. Then ITO on this surface
A layer was formed and subjected to a conductivity treatment.

The properties of this conductive magnetic carrier were as follows. Volume resistivity: 10 ² Ω · cm Maximum magnetization (5 KOe): 65 emu / g

70 parts by weight of the carrier and 30 parts by weight of a positively chargeable insulating magnetic toner (average particle size 7 μm) toner were uniformly mixed to prepare a developer. The volume resistivity of this developer was 5 × 10 ⁴ Ω · cm.

An image was formed using the apparatus shown in FIGS. Here, as the photosensitive member, an a-Si photosensitive member having a photoconductive layer having a thickness of 6 μm, in which an ITO transparent conductive layer and an a-Si photosensitive layer were formed on a cylindrical glass substrate having an outer diameter of 30 mm, was used. .

The voltage of the developing bias power source 39 was set to + 50V, and a transfer bias voltage of -200V was applied to the transfer roller for transfer. When a commercially available plain paper was used as the transfer paper for image formation, a good image was stably obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a carrier of the present invention.

FIG. 2 is a schematic view showing another embodiment of the carrier of the present invention.

FIG. 3 is an explanatory diagram showing an embodiment of the image forming method of the present invention.

FIG. 4 is an explanatory diagram showing an example of a photoconductor used in the present invention.

FIG. 5 is a partial explanatory view showing a facing portion of a photoconductor and a developing unit in an embodiment of the image forming method of the present invention.

FIG. 6 is a partial explanatory view showing a facing portion of a photoconductor and a developing means in another embodiment of the image forming method of the present invention.

[Explanation of symbols]

 11 Carrier 13 Magnetic Particles 15 Conductive Thin Film 17 Binder Resin Layer 19 Conductive Fine Particles 21 Photoconductor 23 Translucent Support 25 Translucent Conductive Layer 26 Carrier-side Carrier Injection Blocking Layer 27 Photosensitive Layer 28 Carrier Injection Blocking Surface Layer 29 a-Si photoconductive layer 31 developing unit 32 control electrode 33 mag roller 34 insulator 35 sleeve 36 power source for control electrode 37 doctor blade 39 developing bias power source 41 LED array 43 condensing element 51 transfer unit 53 transfer roller 55 transfer bias power supply 61 Fixing unit 63 Fixing roller 65 Pressure roller 71 Developer 73 Developer pool 75 Toner image 81 Paper A The closest position between the photoconductor 21 and the sleeve 35 B The position where the developer 71 and the photoconductor 21 are separated from each other

Claims (3)

[Claims] 1. A conductive magnetic carrier for a developer, characterized in that the surface of a magnetic material is made conductive. 2. A developer comprising a carrier in which the surface of a magnetic material is made conductive and an insulating toner are mixed. 3. A photosensitive member comprising a transparent support, on which at least a transparent conductive layer and a photoconductive layer are sequentially provided, a conductive magnetic carrier having a surface of a magnetic material subjected to a conductive treatment, and an insulating toner. A voltage is applied between a developer, a developing unit disposed on the photoconductive layer side of the photoconductor and supplying the developer to the photoconductor surface, and a translucent conductive layer of the photoconductor and the developing unit. Applying means and exposing means arranged on the light-transmissive support side of the photoconductor so as to face the developing means, the developer is brought into contact with the surface of the photoconductor, While applying a voltage between the layer and the developing means, the selected light is irradiated from the transparent support side to the photoconductive layer in the vicinity of a portion facing the developing means, and on the photoreceptor, An image forming method comprising forming a toner image corresponding to the light irradiation.