JPS645293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method in electrophotography or electrostatic recording, particularly a type of developing method in which a latent image is developed using a one-component developer. Specifically, it relates to a method in which the surface of a carrier such as a rotatable conductive elastic roller or belt is coated with a one-component toner, and this roller is transferred to an electrostatic image for development.

Conventionally, in this type of development method, toner comes into contact with the image surface regardless of the presence or absence of an electrostatic image, so toner adhesion occurs even in non-image areas, that is, areas where there is no electrostatic image, which causes fog. It was easy to smudge the image surface. Further, since the conductive roller and the electrostatic image are pressed into contact with each other through an extremely thin layer of toner, and a strong electric field is formed between the two, the electrostatic image may be disturbed due to dielectric breakdown.

The purpose of the present invention is to solve the above-mentioned drawbacks by applying an alternating current or pulsating current bias between the conductive elastic roller and the support electrode of the electrostatic image-holding layer, and to realize a developing method with high gradation. It is about providing.

The present invention will be explained below with reference to the drawings.

Embodiment 1 FIG. 1 is a configuration diagram showing one embodiment of the present invention. An electrostatic image is formed on the electrostatic image holding layer 2 on the supporting electrode 1 by a conventionally known electrostatic image forming device (not shown), and the electrostatic image is transferred to a developing section. The supporting electrode 1 may be an aluminum drum or a metal-deposited film belt, and the electrostatic image holding layer may be an electrostatic recording insulating film or a photoconductive insulating layer such as Se or CdS. Furthermore, a structure in which a light-transmissive insulating film is laminated on a photoconductor layer has good durability and is suitable for the contact development method of the present invention. As the electrostatic image forming device, if a pin electrode or a photoconductor is used, a conventional device such as a corona discharge device or an image exposure device can be used. A conductive rubber roller 3 as a developing roller is provided in pressure contact with such an electrostatic image holding layer 2. The conductive rubber roller 3 has a metal shaft 4 and a surface layer 5.
The surface layer 5 preferably has a rubber hardness of about 25° to 50°. As a structure that satisfies both hardness and surface properties, a porous rubber layer (sponge) may be provided around the shaft 4, and this may be adhesively coated with conductive rubber, such as a conductive silicone tube. This surface layer may be made of rubber or synthetic resin as long as it is a moderately elastic material. Further, this surface layer is selected to have a triboelectrification type so as to impart an electric charge of a polarity opposite to the latent image potential to the one-component insulating toner used by mass charging. A container wall 6 is provided above (or to the side of) the conductive rubber roller 3 to form a hopper Ho that absorbs the insulating toner. A blade 7 for coating the surface of the conductive rubber roller 3 with toner is brought into contact and slid between the hopper and the outlet of the conductive rubber roller 3 in the rotational direction. This blade 7 may be conductive or insulative, such as a metal flake or rubber, and its material and construction are selected to impart a tripo charge to the toner and to obtain the appropriate thickness. The toner in the hopper comes into strong contact with the blade 7 and rubber roller 3 near the exit due to gravity and friction with the roller 3, obtains a frictional charge, and is coated on the developing roller with a limited thickness. . At this time, the toner is restrained on the roller by the physical adhesion force and the reflection force of the charge of the toner onto the surface of the conductive rubber roller. The roller surface approaches the surface of the electrostatic image-retaining layer at approximately the same speed, and is lightly pressed through the toner layer at the contact point, and at this time, an electric field due to a strong electrostatic image is created between the electrostatic image and the conductive roller. occurs, and the toner layer on the roller is strongly attracted to the electrostatic image. When the latent image holding surface that has passed the closest point and the roller surface separate, the toner image is transferred to the electrostatic image area and development is completed.

In the present invention, furthermore, a direct current bias voltage to prevent fogging is simply applied between the supporting electrode 1 of the electrostatic image holder and the conductive developing roller 3, that is, including the closest point P, and between the front and rear regions thereof. Instead, an alternating current or pulsating voltage is applied to form an electric field corresponding to the applied voltage.In this electric field formation, at least in the non-image area (bright area), this electric field strength is applied to the toner surface layer 5 of the roller. The electric field in the direction of transfer from the surface of The electric field in the direction of returning to the surface is set to be larger than the threshold electric field strength for transition in this direction, thereby eliminating fog. Furthermore, in the present invention, such an applied electric field is limited so as not to inhibit the transfer of toner in the image area (dark area). The electric field is greater than the threshold electric field strength required for transfer, and the electric field in the opposite direction is less than the transfer threshold electric field required for the transferred toner to return to the roller. In the illustrated example device, a DC bias source 8 and an AC or pulsating current bias source 9 are connected together. blade 7
When the roller 3 is made of a conductive material, the same voltage is also applied to the blade in order to eliminate the potential difference between the roller 3 and the blade 7.

Figures 2a to 2c show examples of the voltage and electric field when a conventional DC bias is applied between the roller 3 and the support electrode 1, and Figure 2a shows the voltage at each part on the vertical axis. , image area potential V _d , non-image area potential V _L , and roller 3 potential _VR during development are shown as relative values. FIG. 2b shows the electric field E _D in the image area of the developing roller 3 and the image holding surface 2, and shows that the electric field becomes stronger as the two come closer together, and becomes weaker as the two move farther apart. FIG. 2c also shows the electric field E _L in the non-image area, which is a reverse electric field that prevents toner transfer.

Figures 3a to 3c are voltage and electric field diagrams in one embodiment of the _bias voltage applied in the present invention. The voltage relationship is shown in .
At this time, in the image area, as shown in FIG. 3b,
The closest point P and the development promoting electric field E _I before and after it are obtained. The maximum value of this promoting electric field E _I is larger than the maximum value of E _D in FIG. 2b. In addition, in the case of the non-image area shown in Figure 3c, the electric field at the nearest point P and before and after it
E _N is shown, and the maximum value of the transition blocking electric field is larger than the maximum value of E _L in FIG. 2c. By making this maximum value larger than the threshold electric field E _T (indicated by the broken line) required for the toner that has once reached the non-image area to return to the roller 3, the closest point P between the roller 3 and the support electrode 1 is set to the image plane. The toner adhesion in the non-image area, that is, the fog, is successfully removed in the area A where the toner passes through and is further away from the roller 3.

Figures 4a to 4c show the case where a pulsating current or AC voltage with a larger amplitude is applied to the roller 3, and Figure 4a
is the voltage relationship at that time, Figure 4b is Figure 3b
Similarly, it shows the electric field in the image area.

As shown in FIG. 4b, the development promoting bias in this case produces not only a stronger promoting electric field E _I1 ' but also a reverse electric field E _I2 ' projecting below the horizontal axis.
This direction becomes a toner peeling electric field that transfers the toner transferred from the roller 3 to the image plane back to the roller. However, this peeling electric field E _{I2 ′} is the peeling threshold electric field.
If it is smaller than ER, no peeling will occur, so substantially only the promoting electric field E _I1 ' can be increased.

FIG. 4c shows the electric field in the non-image area, where the anti-fogging electric field E _N1 ' is even stronger. However, an electric field E _N2 ' in the opposite direction to this, which protrudes above the horizontal axis, is also generated, and this becomes an electric field in the developing direction, which is a direction that promotes fogging. However, even in this case, roller 3
By setting the electric field threshold E _S to be smaller than the electric field threshold E S required for the developer to be transferred from the developer to the image plane, there is virtually no fear that fog will be promoted.

In this way, by applying a periodic displacement voltage such as a pulsating current or an alternating current to the developing roller 3, the development of the developing portion of the image area is promoted without causing the toner adhering to the image area to peel off again. In the non-image area, it is possible to realize a developing method in which an electric field is applied in the fog removal direction without promoting toner fog.

5a to 5c show another embodiment of the applied bias electric field of the present invention, in which a periodic displacement voltage with a larger amplitude than that in FIG. 4 is applied. In the image area, the development promoting electric field E _I1 '' can be made even larger as shown in FIG. 5b.
However, on the other hand, the peeling electric field E _I2 ″ of the developed toner becomes larger than the peeling electric field threshold E _R , and peeling (retransfer to the roller 3) actually occurs.However, in the latter half of the development, the roller 3 and the image surface 2 The electric field weakens as the distance increases, and in region B, the peeling electric field E _I2 '' becomes smaller than the peeling threshold electric field _ER , and only development takes place, so that the peeling becomes substantially harmless.
Also, in the non-image area, as shown in Fig. 5c, the fog promoting electric field E _N2 '' is larger than the fog threshold electric field E _S and fog occurs, but this is also because only fog removal is performed in the area C in the latter half of development. Another effect of this embodiment is that the reciprocating movement of the toner makes the development more precise and improves the reproducibility of the tone.

As described above in detail with the specific embodiments, the present invention can easily remove the fog caused by the toner on the developing roller being pressed against the electrostatic image holding surface, which is an advantage of the developing roller. Since development can be carried out by making full use of the strong electric field produced by the close proximity of the electrostatic image holding surface and the electrostatic image holding surface, it has been possible to put it into practical use at high densities without fogging.

In the present invention, both magnetic toner and non-magnetic toner can be used as the toner. Further, as the roller, a non-magnetic rotating cylinder with an elastic conductive layer and housing a fixed or rotating magnet inside can also be used. Further, a magnetic blade that cooperates with the magnet to form a magnetic curtain to coat the magnetic toner can also be used as the coating blade.

Further, although the rotation of the roller is caused by sliding with the electrostatic image or driven separately, the relative speed can be approximately the same as that of the electrostatic image surface, or may be slightly slower or faster. Also, as mentioned above, the bias is determined by the relationship between the image area and the non-image area of the electrostatic image, but usually the voltage of the image area is 1000~1000~
300V, and the voltage in the non-image area is 200 to -200V (the polarity can be reversed), so the amplitude peak to peak value is 1600 to 500V DC component | 400 to 0 | V (+ or - depending on the polarity of the latent image) ) to be selected from. Also, instead of superimposing the DC voltage on the AC voltage, the AC voltage may be distorted. The frequency is preferably several cycles within the development process and depends on the development speed.
1000~100Hz is appropriate. However, when this frequency becomes extremely low (for example, below 100Hz),
Frequency-related unevenness tends to occur in developed images. The lower limit of the frequency to avoid such unevenness depends on the development conditions, especially the development speed (or process speed, Vpmm/sec), and as a result of experiments, this lower limit value is min = 0.3 x Vp. be. The waveform can be a sine wave, sawtooth wave, or square wave, but
A sine wave or something close to it is advantageous in terms of cost.

The second and subsequent embodiments will be described below with reference to the drawings. In these embodiments, unless otherwise specified, each element is the same as the first embodiment described above, and also in the drawings, the elements are the same as the first embodiment. Elements common to those in the figures are given the same reference numerals to clarify their correspondence.

Embodiment 2 FIGS. 6a and 6b are schematic sectional views showing a second embodiment of the present invention. For the purposes of the present invention, a hopper Ho is provided above the rubber roller 13, which is a movable member that rotates in the direction of the arrow, to accommodate insulating magnetic toner Do having a specific resistance value of 10 ⁸ Ω·cm or more. When the toner D is supplied onto the rubber roller 13 from the lower opening of the hopper Ho, the toner D adheres to the surface of the rubber roller 13 to form a toner layer. This toner layer is conveyed as the rubber roller 13 rotates, and is delivered to the exit of the hopper Ho.
A blade 17 made of a magnetic material is provided opposite a magnet 16 provided inside the rubber roller. The magnetic field between the magnet 16 and the magnetic blade 17 keeps the toner layer D on the rubber roller thin. Regarding the formation of a thin toner layer by the action of the magnetic blade 17 and magnet 16, see, for example, Japanese Patent Laid-Open No. 54-43037. The toner layer on the rubber roller, homogenized in this way, is brought into contact with an electrostatic image produced by processes described in the well-known literature and made visible. Various rubber rollers can be used as the rubber roller 13, but a specific resistance value of 10 ⁸ Ω·cm or less is preferable, and preferably 10 ⁴ Ω·cm.
Good. Further, in order to improve the adhesion of toner, it is preferable to provide surface roughness to the roller surface. For example, by roughening the surface with sandpaper or by making the surface consist of a conductive region and a non-conductive region, an image with good gradation can be obtained.

In addition, in the relationship between the electrostatic attraction force for the toner of the electrostatic image and the holding force for the toner of the rubber roller 16, the former is larger than the latter.
A countercurrent electric field as described in the first embodiment of the present invention is applied between the two. In this second embodiment, an aluminum cylinder 14 is coated with conductive rubber 15 to which carbon black is added, and the developing roller 13 is coated with a conductive rubber 15 containing carbon black.
And so. The gap between the developing roller surface and the electrostatic image holder 2 in the developing section is maintained at approximately 80μ, the gap between the developing roller and the blade is maintained at approximately 200μ, and the magnetic field generated between the iron blade 7 and the magnet 6 is maintained at approximately 200μ. Therefore, the average magnetic field between the two was 1600 Gausston, and the thickness of the coating layer was approximately 80μ. In the developing section, there is a surface of the developing roller inside the developing roller facing the electrostatic image holder.
An 800 Gauss magnet 10 was provided to form a magnetic brush of toner.

As a toner, the specific resistance value is 10 ¹² to 10 ¹³ Ω・cm
One-component insulating magnetic toner is mixed with 75 parts of polystyrene, 15 parts of magnetite, 3 parts of charge control agent, and 6 parts of carbon, and the average particle size is 7 to 15 μm, which is formed by a well-known method. I had it. Since the electrostatic image has positive polarity, the toner was made to have negative polarity. When an alternating waveform with an amplitude (peak value) of 900 V and a DC voltage of 300 V superimposed on an AC voltage with a frequency of 200 Hz was applied between the electrostatic image holder and the developing roller, a solid black with good gradation and no fog was obtained. An image with sufficient density was obtained.

Embodiment 3 In FIG. 7, reference numeral 1 denotes a photoreceptor on which an electrostatic latent image is formed in the same manner as in the previous embodiment.

The developing device 20 includes a conductive elastic developing roller 21,
It has a container 22 and a coating blade 23.

As shown in FIG. 7, the developing roller 21 is composed of a conductive rigid core layer 24, an elastic intermediate layer 25 such as a sponge, and a non-stretchable and flexible toner retaining surface layer 26. The toner retaining surface layer 26 is adhered onto the elastic intermediate layer 25, and its surface has a concavo-convex shape with a large number of micro holes. The toner supplied from the toner replenisher on the layer 26 is appropriately aggregated and stuffed into the holes, and frictional charging is performed to apply the toner to the developing roller 21 and give a predetermined charge to the toner on the layer 26. . Thereafter, when the electrostatic image holder 1 and the roller 21 are brought into pressure contact and rolled, the toner is electrostatically attracted and adhered to the image area, and the toner is retained by the toner retaining surface layer 26 in the non-image area. In this way, development on the electrostatic image holder 1 is performed.

The aspects of each part of the developing device 20 will be explained below.
The blade member has an appropriate surface roughness and may be electrically conductive or insulating. Light contact with the toner holding surface layer is sufficient. The member shape may be a rotating body or a blade shape. It may rotate in the same direction as the developing roller or in the opposite direction, or it may be stationary.

Further, the blade is selected so that the toner is charged to a predetermined polarity so that the frictional charging series is distant from the material of the toner. A preferred example is a 60° (hardness) nylon material with a thickness of 3 mm and a width of 30 mm.
(see figure). In addition to the blade-shaped frictional charging member as in this embodiment, corona charging may be used.

The depth of the recesses in the toner-retaining surface layer must be at least 1/4 part or more, preferably 1/3 to 3 times the average particle size of the toner used, to improve halftone reproduction and image quality. Gives good results to concentration.
If it is less than 1/4 to 1/3 times, the toner adhesion force, that is, the toner conveyance force will be weak, and the density will not be sufficient and the image will be pale. If it is 3 times or more, the toner conveyance will be improved and the density will be sufficient, but the image will have a high γ (because the toner that has entered the recesses will be taken out a little during development).
However, in the developing method according to the present invention, since a contact or pressure contact method is used, toner is well coated in the image area and an image with good resolution can be obtained. Regarding the shape and manufacturing method of the toner retaining surface layer, it is possible to cover the elastic intermediate layer with a non-stretchable sheet, and further cover with a screen mesh made of fibers having a circular cross section. (plain weave, twill weave, white weave, etc.)
Alternatively, in an embodiment in which this may be further deformed under pressure, a tube-shaped net (outer diameter 38 mm) made of nylon 200 mesh yarn with a diameter of 40 μm and an opening ratio of 40% was used.

If it is made from a metal plate, the desired uneven surface can be obtained by etching the same pattern on one side or both sides using photoresist. However, in the case of etching, it is necessary to reduce the thickness of the unetched portion at the bottom of the recess to such an extent that the elastic intermediate layer of the developing roller does not reduce the pressure applied to the toner during development. The material of the toner retaining surface layer 26 is such that when the roller in contact with the image surface expands and contracts during contact, the developed image and the roller will be relatively misaligned and the image will be seen. It prevents this from happening, and can be used as a substantially non-stretchable fabric if it is the same as normal cloth.

The toner retaining surface layer can be made not only by etching a metal plate as shown in FIG. 7, but also by making at least one of the bottom of the recess and the bank of the recess in the toner surface layer electrically conductive. Combinations of toner-retaining surface layers are possible depending on the development characteristics of the respective developers used. For example, if the toner holding layer is made conductive, the development density increases.
Applying an AC bias to the conductive portions of the elastic intermediate layer 25 or the toner holding surface layer 26 in this manner has the effect of reducing fog. Furthermore, the density tends to increase, probably because the toner moves actively.

The elastic roller 21 makes uniform contact with the photoreceptor due to its elasticity, and does not damage the photoreceptor. As a specific example, the pressure of the roller to the drum is 0.5 to 3
Kg/30cm. Within this range, there was no significant difference in image quality, and the elastic intermediate layer had the effect of absorbing the pressure between the drum rollers and keeping the pressure applied to the toner constant. A conductive sponge rubber roller with an outer diameter of 40 mm was used as the elastic roller. The hardness was approximately 30° when measured using an Asuka C hardness meter. The conductivity is determined by the amount of carbon black added to commonly used sponge rubber, and is 10 ⁸ Ω・cm.
The following is preferred in this embodiment: 10 ₄ to
10 ⁵ Ω・cm was used. carbon in toner
10 parts polystyrene 90 parts average particle size 7~
A powder with a resistance value of 10 ¹³ Ω·cm at 15μ was used.

There is an amplitude between the electrostatic image holder and the developing roller.
When V _P-9 = 1400 V and a DC voltage of 450 V was applied superimposed on an AC voltage with a frequency of 300 Hz, an image with sufficient developed density, no fog, and good halftone reproducibility was obtained. This is because the elasticity of the outermost layer is suppressed, so there is less disturbance and distortion of the image, and the pressure of the blade when bringing the toner application blade 7 into contact with the developing roller and the contact to hold the electrostatic image during development are reduced. The pressure is received by the toner holding surface layer 26, which not only reduces the pressure applied to the toner, but also has the function of the elastic intermediate layer 25 to keep the pressure applied to the toner constant, so that the aggregation of the toner in the holes on the surface is moderate. This is due to its stability and good development characteristics.

Embodiment 4 In FIG. 8, 30 is a conductive elastic developing roller, Ho is a hopper, 7 is a blade-like triboelectric charging member, and 2 is a photoreceptor. The developing roller 30 has a fur brush 32 provided on an elastic rubber roller 31, and developer is supplied from a hopper Ho and is conveyed while rotating in the direction of the arrow while adhering to the surface of the developing roller. Next, a frictional charging member 7 is placed in pressure contact with the developing roller 30.
The toner 5 charged to a predetermined polarity by the toner 5 comes into contact with the electrostatic latent image on the photoreceptor 2 and is developed.

The structure of the developing roller is conductive rubber roller 3.
1 and a fur brush 32 on which nylon bristles are implanted. The former is made of conductive NBR rubber with added carbon black and has a rubber hardness of approximately 30° (as measured by an Asuka hardness meter) and an outer diameter of 40 mm, while the latter is a nylon thread with a conductive part exposed on a part of the surface of the system. The brush is made of this nylon type.

As an example other than this, materials other than nylon are also possible, and the conductive portion does not necessarily need to be partially exposed, but may be covered. As a conductive treatment method, a conductive treatment agent may be spray applied to nylon.

In this embodiment, a 10 ⁴ Ω·cm conductive nylon flocked brush with a length of 3 mm, a thickness of 3 denier, and a density of 60,000 brushes/square inch was used. If this flocking is made conductive, an electrode is present near the toner during development, so whether the sponge roller 31 is conductive or insulating, the flocking can be carried out in a relatively low electric field with a low electrostatic latent image potential. The toner adhering to the image will move onto the photoreceptor. A curve with sufficient solid black density and poor gradation properties can be obtained. On the other hand, if the flocked hair is insulative, there is no electrode close to the toner during development, so when the sponge roller is insulative, an image with almost no density can be obtained. In this case, when the sponge roller is conductive, an image with relatively good gradation can be obtained although the solid black is pale. In any case, if the flocked hair is insulating, the result will be an image with a low density and a tendency to fog.

As a toner, a powder mainly composed of 10 parts of carbon and 90 parts of polystyrene and having an average particle size of 7 to 15 microns was used, and a nylon system and a nylon blade 7 were used as described above so that the toner was triboelectrically charged to a negative polarity.

In this embodiment, the distance between the surface of the electrostatic image holder and the surface of the conductive sponge roller is maintained at 1 to 2 mm so that the toner contacts through the flocking, and this gap is applied with an amplitude of V _pp =800 V and an alternating current of a frequency of 200 Hz. When a DC voltage of 250 V was superimposed on the voltage and applied, an image with good gradation, no fogging, and sufficient solid black density was obtained.

Embodiment 5 In FIG. 9, a ferromagnetic material 36 is divided into minute area units and held inseparably on the surface of a non-magnetic sleeve 35 for forming a conductive elastic roller 33.

The division form of the ferromagnetic material 36 is arbitrary, but
One example is an example in which ferromagnetic bodies 36 with a diameter of 0.1 to 4 mm are densely embedded on the sleeve 35 at intervals of 0.1 to 5 mm, and ferromagnetic bodies 36 of similar size
Example of attaching the ferromagnetic material 36 alternately in a staggered pattern, elongated ferromagnetic material 36 with a width of 0.1 to 4 mm is attached in the generatrix direction of the sleeve.
There are examples where they are embedded at intervals of 0.1 to 5 mm.

In the method of embedding the ferromagnetic material, for example, a mixture of small pieces of magnetic material 36 mixed in silicone resin as a binder is coated on the surface of the aluminum cylinder 34 . Alternatively, a photosensitive resin is coated on the surface of the aluminum cylinder, micropores are created on the coated surface by baking and etching a halftone pattern, and a magnetic material is embedded in the micropores. These micropores can also be easily created by anodizing aluminum.

The magnetic developing sleeve configured as described above is rotated in the direction of the arrow by a rotation drive mechanism (not shown). Therefore, the toner 38 supplied onto the sleeve 33 is applied to a constant thickness by the blade 17. On the other hand, magnetic induction occurs in the ferromagnetic material 36 on the sleeve surface facing the fixed bar magnet, and a concentrated high-density magnetic field appears on the ferromagnetic material surface. That is, each of the ferromagnetic bodies 36 in a minute area unit forms a minute magnet. The magnetic flux density is partially amplified to .S/s, where S is the magnetic flux exerted by the internal permanent magnet on the sleeve surface, the sleeve surface S, and the area covered by the ferromagnetic material 36. The above magnetic field causes the toner on the sleeve 33 facing the permanent magnet to stand up in the direction perpendicular to the sleeve surface to form a magnetic brush 39 due to the influence of the ferromagnetic materials 36 having minute areas adjacent to each other. It acts on in this case,
Compared to the conventional case of simply using a cylindrical sleeve with magnets arranged inside, the length of the magnetic brush is increased, which prevents background fog. In addition, since a high-density magnetic field is generated partially according to the distribution of the ferromagnetic material 36, the ears on the sleeve at the magnetized location become dense.
The panicles in each micro area unit are sparse. Therefore, a good image without narrowing of fine lines can be obtained.

A conductive rubber with a hardness of 75% is coated on this aluminum cylinder, and the surface of the non-magnetic sleeve 34 is coated with a hardness of 0.1 to 4.
Alternating strips of ferromagnetic material 35 mm in size from 0.1 to
A magnetic developing sleeve was used which was constructed by inserting a roll magnet with N and S magnetic poles magnetized in the circumferential direction in place of the magnet in the sleeve 34, which was embedded densely at intervals of 5 mm. When a fixed magnet 39 magnetized to about 800 Gauss was placed inside the sleeve, the average magnetic flux density near the ferromagnetic material on the sleeve passing in front of the fixed magnet reached about 1500 Gauss or more.

The gap between the image forming body 2 and the developing roll 33 is
300μ, and when a blade 17 made of a magnetic material is provided facing the magnet provided inside the sleeve and the gap between the magnetic developing sleeve and the blade 17 is 200μ, the developing roll 33 rotating in the direction of the arrow. On top, a monocomponent magnetic toner D supplied from a hopper Ho is applied to a layer thickness of 70 μm. The applied toner stands in spikes at a position facing the image forming body 2 under the action of the magnetic field of the roll magnet 39 within the sleeve 34. The spikes of magnetic toner form a magnetic brush.

As in the previous embodiments, an appropriate development bias is applied to the sleeve 6. For example, when using a magnetic toner that forms a charge latent image of positive polarity on the image forming body and is charged to negative polarity, the image forming body 2
is grounded, and the peak voltage across the sleeve 34 is V _pp =
When applying an AC voltage of 1600V (+peak value 1150V and -peak value 450V) distorted to the positive side of a frequency of 600Hz, there is no ground fog, good reproduction of thin midtones, and solid black density. A high quality image was obtained.

Embodiment 6 This will be explained with reference to FIG.

2. Description of the Related Art Conventionally, a developing device is known that applies an electric charge to, for example, a one-component high-resistance magnetic toner on a non-magnetic cylinder (sleeve), and conveys this toner to a developing section to perform a developing process. In this developing device, a blade-shaped or roller-shaped triboelectric charging member is brought into direct contact with the sleeve surface as a means for applying an electric charge to the toner.
There are known devices that charge toner by frictional charging. Alternatively, corona discharge is known as a method for applying an electric charge to the toner without contacting the sleeve surface.

In addition to applying the bias described above, the developing device shown in this embodiment is a path of a belt-shaped conveying body that supplies and conveys one-component toner to the electrostatic latent image surface, and a corona discharger that has grit and grit bias control means. Therefore, this developing device converges and charges the toner to a specific polarity and allows the toner to reach the latent image surface while the charged charges remain to perform development.

The advantage of applying a charge to the toner by corona discharge is that there is no fluctuation in the amount of charge on the toner due to wear of the rubber blade, and uniform charging is possible even in a high-speed copier.

Furthermore, if grit bias control is performed on the charger, the toner can be charged to the opposite polarity by switching the polarity of the bias voltage applied to the grit.
No special changeover switch is required and safety is high.

Furthermore, when using alternating current as a high-voltage power source and controlling the toner charge with bias-applied grit, a capacitor is connected in series between the high-voltage power source and the corona discharge electrode, and the discharge becomes unstable due to environmental changes. Since the DC component of the current is blocked by the capacitor, the toner can be converged to a value approximately equal to the grit potential.

Further, providing a charging device to a normal developing device leads to an increase in the size of the developing device, making the mechanical structure complicated and large, which is not preferable. Therefore, in this embodiment, the toner conveyance path is made into a belt shape, and toner supply and application and charge imparting are performed at a location away from the developing section, thereby reducing the space occupied by the developing device located near the electrostatic image holder. It is something.

FIG. 10 is a sectional view of the developing device. As the sleeve 40 rotates in the direction of the arrow in the figure,
The magnetic toner D supplied from the hopper Ho is coated onto a conductive rubber belt 43 that is movable as a sleeve having a magnet 42 fixed therein rotates, and is applied by a doctor blade 44 provided at the hopper outlet. A toner layer 45 having a constant thickness is formed. In the figure, a magnet 42 is sequentially and alternately magnetized with S and N poles, and a doctor blade 44 made of a magnetic material is provided at a position facing one magnetic pole S of the magnet. The toner layer 45 held on the belt 43 is given a certain amount of charge with a predetermined polarity by a corona discharger 46 . The charged toner is conveyed by the belt, and is caused to stand up on the belt 43 by a magnetic pole 49 provided at a position facing the photoreceptor 2, thereby performing development. At this time, the same periodic displacement developing bias as previously described in Embodiment 1 is applied. In other words, _Vpp = 1200V (+
AC voltage with a frequency of 400 Hz was applied.

Although the magnet 42 is of the 8-pole magnetized type in the figure, it is not limited to this type, for example, 3-pole, 4-pole magnets, etc.
It can be extreme. In addition, although the magnet is fixed and the sleeve rotates, the sleeve may be fixed and the magnet rotates. In this case, it is preferable to rotate the magnet in the opposite direction to the sleeve and use a non-magnetic material for the doctor blade toner leveling member. . Other developing machine configurations are not limited to those shown in the drawings.

In the figure, 46 is a corona discharger for toner charging, and as an example, the width l ₁ = 35 mm, the depth l ₂ = 28 mm, the gap between the grit and the belt d ₁ = 1.5 mm, and the width between the grits.
It consists of a dimension of d ₂ =2 mm. The corona discharge polarity consists of a gold-plated tungsten wire with a diameter of 60μ. Twelve grids 48 made of gold-plated wires with a diameter of 100 μm are stretched along the magnetic toner 45 on the sleeve surface at equal intervals of 2 mm in an arc shape with a gap of 1.5 mm. 49 is AC corona discharge power supply, 50
51 is a grit bias power supply, and 51 is a toner charging polarity switching switch for switching the grit bias power supply between positive and negative.

As a magnetic toner, the composition is 70% polystyrene,
A toner layer with an average particle size of 10μ consisting of 20% magnetite, 8% carbon, and 2% other materials is formed into a toner layer of about 50μ, and the dark area latent image potential is increased by a well-known method.
500V, when the bright and dark latent image potential is set to -100V,
AC corona discharge voltage 8KV (effective value), total discharge current
When the magnetic toner layer was charged under the conditions of 950 .mu.A and grit bias DC-100 V, the amount of charge per toner was approximately 5.times.10.sup. ^-16 coulombs, and a good image was obtained.

In addition, when the charged polarity of the toner was set to be positive, a positive charge could be given to the toner by operating the grit bias changeover switch shown in the figure, and a good negative image was obtained with respect to the above-mentioned latent image potential. In addition, when considering the durability of grit wire,
Although 100μ is better, experiments have confirmed that 60μ provides almost the same charging effect.

In this embodiment, a conductive rubber belt is used as the toner holding and conveying member, but a magnet may be provided on the back surface of the belt (on the side opposite to the toner holding surface) in order to further ensure that the toner is held and conveyed.

In each of the above embodiments and other embodiments of the present invention, other examples of coating methods for forming a uniform layer of a one-component insulating toner on the surface of a conductive and elastic carrier are briefly described below. Let me explain. Of course, it is not limited to these.

In addition to the above-mentioned blade, various types of toner coating means can be considered, such as a magnetic brush contact type, a rotating roller type, and a local vibration coating type, two examples of which are shown in FIGS. 11 and 1.
It is shown in Figure 2.

Referring to FIG. 11, this example separates toner coating and development, and is suitable for a developing device that can provide sufficient image density.

A toner replenishment hopper Ho is provided above the conveyance roller 51 having the toner holding layer 52, and as the conveyance roller 51 rolls, the conveyance roller 5
One-component toner D is supplied to the toner holding layer 52 on top of the toner holding layer 52 . A frictional charging member 55 is provided between the toner replenisher Ho and the development position to apply a predetermined charge to the toner.

Next, the developing roller 3 is provided in contact with or close to the conveying roller 51 (see FIG. 1).
The toner layer formed by the toner retaining layer of the conveying roller is transferred, and the latent image on the photoreceptor 2 is developed in the developing section.

FIG. 12 shows an example in which toner is applied to the developing roller by vibration, and the same elements as those shown in FIG. 1 are given the same reference numerals and explanations will be omitted.

The one-component non-magnetic toner D is stored in the hopper Ho, and is supplied in small amounts to the coating chamber 56 at the bottom of the hopper. The upper wall of this coating chamber 56 is formed in a semicircular shape so as to cover the upper half of the conductive carrier 3 provided in this coating chamber, and the toner layer Da is disturbed between it and the carrier 3. A gap 57 is formed so that there is no gap. The vibrating member 58 consists of a reciprocating rod 58a that penetrates the wall of the coating chamber 56 and a plate 58b attached to the tip of the retracting rod 58a facing the carrier 3, and vibrates only the toner in the portion that is scooped up by the carrier 3. give.

In the case of insulating toner, the carrier 3 of the vibrating member 58
It is extremely effective to selectively configure the plate surface facing the surface of the toner and facing the direction of vibration with a charging material that triboelectrically charges the toner to a predetermined polarity in order to promote triboelectrification of the toner. . 59 is a vibration generating means that vibrates the vibrating member;
AC voltage is applied to the coil 59b of the electromagnet 59a, and the vibrating member 58 is vibrated via the permanent magnet 58c attached to the end thereof. Reference numeral 58d denotes a shock absorbing elastic member, such as a leaf spring, provided between the chamber wall and the permanent magnet 58c.

As the above-mentioned vibration generating means, a method using a mechanical cam, ultrasonic vibration, etc. can be used.

Further, by appropriately selecting the frequency and amplitude of the vibration generated by the vibration generating means 59, and the relationship between the toner and the sleeve surface shape, a desired application amount can be set.

The above explanation has mainly been given using an example in which the surface potential of the image area is + potential, but it is obvious that the present invention is also applicable to cases where the surface potential of the image area is 1 potential.

In either case, a conductive developer carrier is coated with a uniform layer of insulating toner so that this toner layer contacts the latent image surface at the development position, and A periodic displacement voltage is applied to the development gap between the image plane and the image plane to produce an electric field having the following properties. That is, at least in the latter half of the development process, the electric field in the direction of peeling off the toner once attached to the image area in the image area of the latent image surface is smaller than the specific electric field threshold for actually peeling off the toner from the image area. (Therefore, the adhering toner does not actually peel off), and in the non-image area, the electric field in the direction of adhering the toner to the non-image area is equal to the electric field threshold (fogging electric field threshold) for actually adhering the toner to the non-image area. ) (therefore, actual fog does not occur).

During the first half of the development process, and during most of the development process, the development process is carried out by the applied periodic displacement bias voltage, as described in FIGS. The agent works as follows. That is, in the image area, a development accelerating electric field that acts on the development gap (of course, this gap changes as the development process progresses) causes the toner to separate from the carrier and direct the toner toward the image area on the latent image surface. The applied electric field is greater than the electric field threshold actually required for developer transfer. At this time, an electric field may be applied in a direction that causes the toner once attached to the image area to return to the carrier (see FIG. 5b). In addition, in the non-image area, the electric field that directs the toner from the non-image area toward the toner carrier (anti-fogging electric field) is set to a threshold value ( E _T ) should be larger. In this case, since the toner transfer to the image area is enhanced, an electric field may be applied to the non-image area so as to cause slight fogging (see FIG. 5c). This is because even if fog occurs, it will be removed in the latter half of the subsequent developing process.

The present invention is not limited to the above embodiments and examples, but includes all aspects included within the spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically explaining the principle of the present invention and the configuration of a first embodiment for carrying out the principle, and FIG. 3 is an explanatory diagram of potential at each part, b is an explanatory diagram of the electric field in the image area, c is an explanatory diagram of the electric field in the non-image area, and FIG. 3 is an example of the developing bias based on the present invention. Diagram explaining the potential of each part at the time,
b is an explanatory diagram of the electric field in the image area, c is an explanatory diagram of the electric field in the non-image area, and FIG. 4 a, b, and c are other embodiments of the developing bias of the present invention different from those in FIG. FIGS. 5a, b, and c are potential and electric field explanatory diagrams of yet another embodiment based on the present invention, and FIG. 6a is a sectional view of another embodiment of the present invention. ,
FIG. 6b is a partially enlarged view thereof, FIGS. 7 to 10 are sectional views showing still other embodiments of the present invention, and FIG.
1 to 12 are cross-sectional views showing several other examples of toner coating means applicable to the present invention. 5, 15, 25, 32, 35...developer carrier, 2...latent image carrier, 9...periodic displacement electric field generating means.

Claims (1)

[Scope of Claims] 1. A developing method comprising the following steps of developing a latent image with developer particles. (a) coating an electrically conductive carrier with an insulating monocomponent toner; (b) bringing the carrier bearing the toner layer to a position such that the toner layer contacts a latent image bearing surface; (c) ) Applying a periodic displacement voltage that generates the following periodic displacement electric field between the conductive carrier and the support electrode of the latent image holding surface, and this periodic displacement electric field is applied during the development process. , has the following properties. In the image areas, the development promoting electric field is greater than the electric field threshold required to remove the toner from the carrier, and in the non-image areas, the defogging electric field is greater than the electric field threshold required to remove the toner from the non-image areas. Must be greater than the electric field threshold. 2. The developing method according to claim 1, wherein the insulating toner is charged by friction. 3. The developing method according to claim 1, wherein the insulating toner is charged by corona discharge. 4. The developing method according to claim 1, wherein the toner coating on the carrier is performed by a blade-shaped coating member. 5. The developing method according to claim 1, wherein the carrier is a non-magnetic material containing a magnet, and the insulating toner is a magnetic toner. . 6. The developing method according to claim 1, wherein the carrier has an elastic body on its surface. 7. The developing method according to claim 1, wherein the carrier is coated with toner by a conductive member, and the same voltage as that of the toner carrier is applied to the conductive member. A developing method characterized by: 8. The developing method according to claim 1, wherein the surface of the carrier is a rough surface. 9. The developing method according to claim 1, wherein the carrier is a rubber roller having a resistance of 10 ⁸ Ω·cm or less. 10. The developing method according to claim 1, wherein the surface of the carrier comprises a conductive region and a non-conductive region.