JP2002091163A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent image over a long term by preventing the occurrence of fogging toner on the surface of an image carrier at a developing part at image non-forming time even in the case of forcibly discharging toner in an electrifier at inter-paper time or at pre/post-rotation time. SOLUTION: By providing the time to apply only DC voltage without superimposing alternating voltage on bias applied to a magnetic brush electrifier at the image non-forming time, the toner is completely discharged to the surface of a photoreceptor drum 1 even when the toner intrudes in the magnetic brush electrifier. Then, the peak-to-peak voltage value of AC bias applied to the developing sleeve 41 of a developing device 4 by a power source 51 is controlled by a control means 52, and is made larger at the image non-forming time than at the image forming time so as to make fogging removing voltage higher, whereby the toner discharged to the surface of the drum 1 is excellently recovered by the developing device 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine or a printer in which a developing unit also serves as a cleaning unit.

[0002]

2. Description of the Related Art In recent years, digitalization of copiers and printers has been advanced along with full colorization and systemization.

For example, a laser beam printer scans a uniformly charged surface of a photosensitive drum with a laser beam, forms an electrostatic latent image on the photosensitive drum by turning on and off the laser beam, and records a desired image. Devices are becoming widely known. Typical uses are for characters, figures, etc.
It is a value record. In this respect, recording of characters, figures, and the like does not require a halftone, so that the printer structure can be simplified.

There are printers that can form halftones even with such a binary recording system. As such a printer, a printer employing a dither method, a density pattern method, or the like is well known.

However, as is well known, high resolution cannot be obtained with a printer employing a dither method, a density pattern method, or the like.

Therefore, in recent years, a method of forming a halftone pixel in each pixel without lowering the recording density has been proposed. This means that the laser beam is pulse width modulated (P
WM) to form a halftone. According to this method, a high-resolution and high-gradation image can be formed.

FIG. 2 shows an example of such an image forming apparatus.

When a copy (image forming apparatus) start signal is input, the photosensitive drum 1 rotates in the direction of arrow R1, and is charged by the charger 2 to a predetermined potential. On the other hand, an original irradiating lamp for the original G placed on the original platen 20,
The unit 21 integrally formed with the short focus lens array and the CCD sensor scans the original while irradiating the original, and the reflected light of the irradiation scan light on the original surface is imaged by the short focus lens array to be formed on the CCD sensor. Incident. C
The CD sensor includes a light receiving section, a transfer section, and an output section. The light signal is converted into a charge signal in the light receiving section of the CCD, and is sequentially transferred to the output section in synchronization with the clock pulse in the transfer section, and the charge signal is converted into a voltage signal in the output section.
Amplify, lower impedance and output. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to a printer unit. In the printer unit, the light of the solid-state laser element 73 (see FIG. 5), which is turned on and off in response to the image signal, is scanned by a rotating polygon mirror 75 rotating at a high speed, so that the surface of the photosensitive drum 1 is scanned. An electrostatic latent image corresponding to the image is formed.

FIG. 5 shows a schematic configuration of a laser scanning unit 3 for scanning a laser beam in the above-described apparatus. When the laser beam is scanned by the laser scanning unit 3,
First, the solid-state laser element 73 is caused to blink at a predetermined timing by the light emission signal generator 72 based on the input image signal 71. The laser light emitted from the solid-state laser element 73 is converted into a substantially parallel light beam by a collimator lens system 74, and further scanned in a direction indicated by an arrow Co by a rotating polygon mirror 75 rotating in the direction indicated by an arrow R75. The fθ lens group having 76b and 76c forms a spot-like image on the surface of the photosensitive drum 1 which is the surface to be scanned. An exposure distribution for one image scan is formed on the surface of the photosensitive drum 1 by the scanning of the laser light, and the surface of the photosensitive drum 1 is scrolled by a predetermined amount perpendicular to the scanning direction for each scan. An electrostatic latent image is obtained on the surface of the photosensitive drum 1 as an exposure distribution according to an image signal.

Next, the electrostatic latent image is developed by a developing device 4 containing a so-called two-component developer having toner particles and carrier particles, and a toner image is obtained on the photosensitive drum 1.

Here, the developing step will be described.
In general, the developing method is such that non-magnetic toner is coated on a developing sleeve with a blade or the like, and magnetic toner is coated and conveyed by magnetic force and developed in a non-contact state with the photosensitive drum 1 ( One-component non-contact development), a method of developing the toner coated as described above in contact with the photosensitive drum (one-component contact development), and developing a mixture of toner particles and a magnetic carrier. A two-component developer in which the developer is conveyed by magnetic force using a developer as a developer and is in contact with the photosensitive drum (two-component contact development), and a method in which the two-component developer is developed in a non-contact state (two-component non-contact development) Are roughly divided into four types.
The two-component contact developing method is often used from the viewpoint of improving image quality and stabilizing an image.

FIG. 3 is a schematic view of a developing device 4 for two-component magnetic brush development used in the conventional example. 41 in FIG.
Is a developing sleeve, 42 is a magnet roller fixedly arranged in the developing sleeve 41, 43 and 44 are stirring screws, 45 is a regulating blade for forming a thin layer of developer on the surface of the developing sleeve 41, and 46 is a developing container. . The developing sleeve 41 is arranged so that the closest area to the photosensitive drum 1 is about 400 μm, and as shown in the drawing, the direction of movement of the surface of the photosensitive drum 1 is opposite to the direction of movement (counter direction). It is set so that it can be rotated in the direction, and can be developed in a state where the developer contacts the photosensitive drum 1.
The position of the developing main pole is 0 ° in the rotation direction of the photosensitive drum.
And the true specific gravity of the toner in the developer is 1.1 g / cm
³ , the true specific gravity of the carrier is 3.6 g / cm ³ , the toner particle size is 6 μm, the carrier particle size is 35 μm, the toner concentration (weight ratio of the toner to the total developer weight) is 8%. The peripheral speed ratio with respect to the photosensitive drum 1 is usually set to 1.5 to 2 times.

As shown in FIG. 2, the toner image formed on the photosensitive drum 1 is transferred to a transfer material P such as paper supplied by a paper feed roller 8, a registration roller 9, and the like.
Is electrostatically transferred by the transfer charger 5. Thereafter, the transfer material P is electrostatically separated by the separation charger 6, transported by the transport belt 10 and transported to the fixing device 11,
After the heat fixing, the sheet is discharged onto a sheet discharge tray 13 by a discharge roller 12.

On the other hand, the photosensitive drum 1 after the transfer of the toner image
Adhered contaminants such as toner (transfer residual toner) remaining on the surface are removed by the cleaner 7, the electricity is eliminated by the pre-exposure device 8, and the next image is formed.

The above configuration is an example, and there are various types of charging device 2 such as a charging roller instead of a corona charging device, and a transfer roller 5 also as a transfer roller.
Basically, as described above, charging, exposure, development, transfer,
An image is formed in a fixing and cleaning process.

By the way, in recent years, the miniaturization of such an image forming apparatus has been advanced.
There has been a limit to the miniaturization of each of the development, transfer, fixing and cleaning processes. Further, the transfer residual toner is collected as waste toner by the cleaner 7, but it is preferable that this waste toner does not have environmental protection.

Therefore, the above-mentioned cleaner 7 is removed, the transfer residual toner on the photosensitive drum 1 is once collected by a contact charger, the photosensitive drum 1 is charged to a desired potential, and the collected toner is placed on the photosensitive drum 1. A cleanerless device that discharges and performs simultaneous development and cleaning by the developing device 4 has also appeared. The developing-cleaning here, the toner remaining slightly on the photosensitive drum is discharged and recovered in contact charger at the time of transfer, and recovering by fog removal bias V _back at the time of development.

According to this method, the transfer residual toner is collected and reused at the time of development, so that waste toner can be eliminated. Further, the advantage in terms of space is great, and the size can be significantly reduced.

[0019]

However, in the above-described system for simultaneous cleaning with development, for example, when the image ratio is large, or when the transfer efficiency is significantly reduced due to the environment, paper type of the transfer material, or humidity condition. For example, there is a possibility that a series of processes of collecting the transfer residual toner with the contact charger and discharging the toner onto the photosensitive drum may not be established. That is,
If a state where the amount of collected toner is large and the amount of discharged toner is small (a state in which the discharging process cannot keep up with the collecting process) occurs, the amount of toner in the contact charger increases, and the photosensitive drum charging capability of the contact charger is increased. And the V-Dγ characteristics of the image fluctuate, and the toner accumulated in the contact charger scatters.

Such a problem is caused by the problem that the transfer residual toner accumulated in the contact charger is not formed during non-image formation (between papers or during pre / post rotation (rotation of the photosensitive drum and developing sleeve before and after image formation)). The solution is to set the sequence mode to force ejection.

As the method, for example, the bias voltage applied to the contact charger at the time of non-image formation is changed to only the DC bias, or V _pp (peak-to-peak voltage) of the superposed AC bias is reduced. The charging capability of the photosensitive drum is reduced (the toner is mixed in the charging device, so that the resistance increases and the charging capability is reduced), and the potential difference between the contact charging device and the photosensitive drum causes the potential difference on the photosensitive drum. And a method of forcibly discharging the collected transfer residual toner.

However, when such a method is adopted, the charging ability is reduced, and the difference between the charging potential and the potential of the DC bias applied to the developing sleeve is V.sub.V.
_{The back} becomes small, and the fogging toner adheres to the photosensitive drum in the developing section during non-image formation, which tends to have an adverse effect on the subsequent steps.

The present invention has been made in view of the above-mentioned circumstances, and even when the toner in the contact charger is forcibly discharged at the time of inter-sheet or post-rotation, even when non-image formation,
An object of the present invention is to provide an image forming apparatus in which toner fogging on an image carrier (photosensitive drum) in a developing unit does not occur.

[0024]

According to a first aspect of the present invention, there is provided an image bearing member, a charging means for uniformly charging the surface of the image bearing member, and the image bearing member after charging. In an image forming apparatus comprising: an exposure unit configured to expose a surface of a carrier to form an electrostatic latent image; and a developing unit configured to develop the electrostatic latent image, the image carrier may have a volume resistivity of 10 ⁹ -10
^A charging member having a surface layer of ¹⁴ Ωcm, and a charging member having a contact charging member for contacting the surface layer of the image carrier and injecting charge directly into the surface layer; A two-component developer having a magnetic carrier and a magnetic carrier is transported to a developing position, and a direct current bias on which an alternating voltage is superimposed causes toner to adhere to the electrostatic latent image to develop as a toner image, and also causes the toner to adhere to the surface of the image carrier. The cleaning device also collects the transfer residual toner carried and conveyed, and furthermore, the peak-to-peak voltage value of the alternating voltage applied to the developing device is different between the time of image formation and the time of non-image formation. A control means for controlling is provided.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control means sets the DC bias applied to the contact charging member to V _chg , thereby controlling the surface of the image carrier. when the charge potential was Vd, the difference between them is that ΔV = | V _{ch g} -Vd | controls differently during image formation and non-image formation, and wherein the.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the above image forming apparatus, the control unit controls the peak-to-peak voltage value of the alternating voltage applied to the developing unit to be larger during non-image formation than during image formation.

The present invention according to claim 4 is based on claims 1, 2,
In the image forming apparatus of (3), a potential difference between a potential of a white background portion formed on the image carrier during non-image formation and a potential of a DC bias applied to the developing unit is 100 V or more.
00V or less.

The present invention according to claim 5 is based on claims 1 and 2,
3 or 4, the absolute value of the triboelectric charge amount per unit weight of the toner is 1.0 × 10 ⁻² C /
kg or more and 4.5 × 10 ^-2 C / kg or less.

The present invention according to claim 6 is based on claims 1 and 2,
The image forming apparatus according to any one of 3, 4, or 5, wherein the contact charging member of the charging unit is a magnetic particle.

The present invention according to claim 7 is based on claims 1, 2,
The image forming apparatus according to any one of 3, 4, 5, and 6, wherein the toner in the developer accommodated in the developing unit is a toner generated by a polymerization method.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 shows an example of an image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a laser beam printer.

First, the document G is set on the document table 20 with the surface to be copied facing downward. Next, copying (image formation) is started by pressing a copy button. A unit irradiation lamp, a short-focus lens array, and a CCD sensor are integrated to constitute a unit 21. The unit 21 scans while irradiating the original G, and the original surface reflected light of the illumination scanning light becomes An image is formed by the short focus lens array and is incident on the CCD sensor. The CCD sensor includes a light receiving unit, a transfer unit, and an output unit. The light signal is converted into an electric signal in the CCD light receiving section, and is sequentially transferred to the output section in synchronization with the clock pulse in the transfer section. The output section converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the signal. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to a printer unit.

The printer section receives the above image signal and forms an electrostatic latent image as follows. The photosensitive drum 1 as an image carrier is driven to rotate in a direction of an arrow R1 at a predetermined peripheral speed (process speed) about a center support shaft, and in the rotation process, a magnetic brush charger is driven to rotate in a direction of an arrow R2. (Charging means) A uniform charging process of negative polarity is performed by 2A.

Here, as the photosensitive drum 1 used in the present invention, a commonly used organic photosensitive member (OPC photosensitive member) or the like can be used, but preferably, the resistance thereof is 10 ⁹ on the organic photosensitive member. When a material having a surface layer having a material of 10 to 10 ¹⁴ Ω · cm or an amorphous silicon photoreceptor (a-Si photoreceptor) is used, charge injection charging can be realized, ozone generation is prevented, and power consumption is reduced. Is effective. Further, the chargeability can be improved.

Therefore, in the present embodiment, a negatively charged organic photoreceptor, in which five layers of the following first to fifth layers are sequentially provided from the inner side on an aluminum drum substrate having a diameter of 30 mm. A drum was used.

The first layer is a subbing layer, and is a conductive layer having a thickness of 20 μm provided for smoothing defects or the like of an aluminum substrate (hereinafter referred to as “aluminum substrate”).

The second layer is a positive charge injection preventing layer, which serves to prevent positive charges injected from the aluminum substrate from canceling negative charges charged on the surface of the photoreceptor, and comprises an amylan resin and methoxymethylated nylon. 1 × 10 ⁶ Ω
This is a medium-resistance layer having a thickness of 1 μm and a resistance adjusted to about cm.

The third layer is a charge generation layer, and is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin.
Exposure generates positive and negative charge pairs.

The fourth layer is a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, negative charges charged on the surface of the photoreceptor cannot move through this layer, and only positive charges generated in the charge generation layer can be transported to the surface of the photoreceptor.

The fifth layer is a charge injection layer, which is a coating layer of a material in which ultrafine SnO ₂ particles are dispersed in a binder of an insulating resin. Specifically, SnO ₂ particles having a particle diameter of about 0.03 μm, obtained by doping an insulating resin with antimony which is a light-transmitting insulating filler to reduce the resistance (conducting conductivity), are dispersed in the resin by 70% by weight. This is the coating layer of the material.

The coating liquid thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. to form a charge injection layer.

In this embodiment, the magnetic brush charger 2A is used as the charger. The magnetic brush charger 2A used in the present embodiment has a magnetic carrier (magnetic particles) as a contact charging member on a rotatable non-magnetic sleeve having a fixed magnet provided therein and having an outer diameter of 46 mm. The magnetic carrier is transported as the non-magnetic sleeve rotates. The magnetic carrier is brought into contact with the photosensitive drum 1. Further, the non-magnetic sleeve is moved in the counter direction (arrow R) with respect to the photosensitive drum 1.
In this embodiment, the magnetic brush charger 2A rotates at 150 mm / sec with respect to the rotation speed of the photosensitive drum 1 of 100 mm / sec.
By applying a charging voltage to the non-magnetic sleeve, a charge is given from the magnetic carrier onto the photosensitive drum 1, and the surface of the photosensitive drum 1 is charged to a potential corresponding to the charging voltage. As for the rotation speed of the non-magnetic sleeve, the higher the rotation speed, the better the charging uniformity.

A magnetic carrier used as a contact charging member
The average particle diameter is 10 to 100 μm, and the saturation magnetization is
20-250 emu / cm^Three, Resistance is 1 × 10^Two~ 1 ×
10 ^TenΩ · cm is preferable.
Considering the existence of insulation defects such as holes
1 × 10⁶Ω · cm or more is preferred
No. To improve the charging performance,
In this embodiment, it is better to use
Uniform particle size 25 μm, saturation magnetization 200 emu / cm^Three,resistance
Is 5 × 10⁶A magnetic carrier of Ω · cm was used.

Here, the resistance value of the magnetic carrier is determined by adding ² g of the carrier to a metal cell having a bottom area of 228 mm ² ,
The measurement was performed by applying a load of 6.6 kg / cm ² and applying a voltage of 100 V.

As a magnetic carrier, a resin carrier formed by dispersing magnetite as a magnetic material in a resin and dispersing carbon black for conductivity and resistance adjustment, or a single magnetite surface such as ferrite is oxidized and reduced. A material which has been subjected to resistance adjustment by treatment or a material which has been subjected to resistance adjustment by coating with a magnetite simple substance resin such as ferrite may be used.

The nip width formed between the magnetic brush charger 2A and the photosensitive drum 1 is adjusted to be approximately 6 mm.

In this embodiment, the bias applied to the magnetic brush charger 2A is a rectangular alternating voltage of 1000 V with respect to a DC voltage of -600 V during image formation.
By applying a bias in which Hz and 700 V were superimposed, good charging properties could be obtained.

As described above, the light of the solid-state laser element 73 (see FIG. 5), which is turned on and off in response to the image signal, is applied to the uniformly charged surface of the photosensitive drum 1 by the collimator lens system 74. The electrostatic latent images corresponding to the original images are sequentially formed on the surface of the photosensitive drum 1 by being passed through and scanned by the rotating polygon mirror 75 rotating at a high speed.

The electrostatic latent image is developed by a developing device (developing means) 4 described later to form a toner image on the photosensitive drum 1. The toner image formed on the photosensitive drum 1 is electrostatically transferred onto the transfer material P by the transfer charger 5. Thereafter, the transfer material P is electrostatically separated from the surface of the photosensitive drum 1 by the separation charger 6, and is conveyed to the fixing device 11, where it is thermally fixed by the fixing device 11 to output an image.

Here, the developing step will be elaborated. In general, the developing method is such that a non-magnetic toner is coated on a developing sleeve with a blade or the like, and a magnetic toner is coated by a magnetic force and conveyed.
A method in which the toner coated as described above is developed in contact with the photosensitive drum (one-component contact development); On the other hand, a method in which a mixture of magnetic carriers is used as a developer and conveyed by magnetic force to develop the photosensitive drum in contact with the photosensitive drum (two-component contact development); And two types of development (two-component non-contact development). The two-component contact development method is often used from the viewpoint of high image quality and high stability. The developing method is not limited to any of the above-mentioned methods, but in the present embodiment, the developing method is 2
A component contact development method was used.

This configuration is an example. For example, the magnetic brush charger 2A may be an injection charger using a conductive brush or the like. Although the transfer charger 5 is also a transfer roller, there are various methods, but basically, an image is formed by the steps of charging, exposure, development, transfer, and fixing as described above. The untransferred toner is collected by an injection charger disposed downstream of the photosensitive drum 1 in the rotation direction, discharged again onto the photosensitive drum 1, and then collected by the developing device 4.

The developing device (developing means) 4 of the present embodiment will be described with reference to FIG. The developing device 4 is the same as that of the conventional example, but will be described in more detail.

The developing device 4 has a developer container 46. The inside of the developer container 46 is separated into a developing chamber (first
Chamber T1 and a stirring chamber (second chamber) T2, and a toner storage chamber T3 is formed above the stirring chamber T2 with a partition wall 47 interposed therebetween. (Magnetic toner) 48 is accommodated. In addition, a supply port 50 is provided in the partition wall 47, and a supply toner 48 in an amount corresponding to the consumed toner is dropped and supplied into the stirring chamber T2 via the supply port 50.

On the other hand, a developer 49 is contained in the developing chamber T1 and the stirring chamber T2. The developer 49 is obtained by externally adding 1% by weight of titanium oxide having an average particle diameter of 20 nm to a negatively charged toner having an average particle diameter of 6 μm manufactured by a polymerization method described later, and has a saturation magnetization of 205 emu / cm.
^{3 is} a two-component developer comprising a magnetic carrier (carrier) having an average particle size of 35 μm. The mixing ratio was such that the nonmagnetic toner was 8% by weight.

An opening is provided in a portion of the developer container 46 close to the photosensitive drum 1, and a developing sleeve 41 protrudes outside from the opening. The developing sleeve 41 is rotatably incorporated in the developing device 46. The current sleeve 41 is made of a non-magnetic material, and has a magnet 42 fixed therein as a magnet generating means.

The magnet 42 has a developing magnetic pole N1, a magnetic pole S3 located downstream thereof, and magnetic poles N2, S2 and S1 for transporting the developer 49. The magnet 42
The developing magnetic pole N1 is arranged in the developing sleeve 41 so as to face the photosensitive drum 1. The developing magnetic pole N1 forms a magnetic field near the developing section between the developing sleeve 41 and the photosensitive drum 1, and the magnetic field forms a magnetic brush.
In this position, with the rotation of the developing sleeve 41,
The developer carried in the direction of the arrow contacts the photosensitive drum 1, and the electrostatic latent image on the photosensitive drum 1 is developed. At this time, in the proximity position (developing portion) between the developing sleeve 41 and the photosensitive drum 1, the surface of the developing sleeve 41 and the photosensitive drum 1 are
It moves in the opposite direction to the surface (counter direction).

The power supply 51 supplies the developing sleeve 41 with an AC voltage (alternating voltage) and a DC voltage (DC bias).
Is applied. These AC voltage and DC voltage are controlled by the control means 52. The dark portion potential (non-exposed portion potential) and bright portion potential (exposed portion potential) of the electrostatic latent image are located between the maximum value and the minimum value of the vibration bias potential. As a result, an alternating electric field whose direction changes alternately is formed in the developing section. The toner and the carrier vibrate violently in this alternating electric field, and the toner is removed from the electrostatic restraint by the developing sleeve 41 and the carrier, and the toner amount corresponding to the latent image potential is attached to the photosensitive drum 1. The difference (peak-to-peak voltage) between the maximum value and the minimum value of the oscillation bias voltage is preferably 1 to 5 kV, and the frequency is preferably 1 to 15 kHz. As the waveform of the oscillation bias voltage, a rectangular wave, a sine wave, a triangular wave, or the like can be used. The DC voltage component is between the dark portion potential and the bright portion potential of the electrostatic latent image, and the value of the dark portion potential is closer to the dark portion potential than the minimum bright portion potential in absolute value. It is preferable to prevent the fog toner from adhering to the potential region.

Below the developing sleeve 41, a blade 4
5 is arranged at a predetermined distance from the developing sleeve 41. The interval between the developing sleeve 41 and the plate 45 is 40
0 μm. The blade 45 is fixed to the developer container 46. The blade 45 is made of aluminum, SUS31
6, the thickness of the developer 49 on the developing sleeve 41 is regulated.

A transport screw 43 is accommodated in the developing chamber T1. The transport screw 43 is rotated in the direction of the arrow in the drawing, and the developer 49 in the developing chamber T1 is transported in the longitudinal direction of the developing sleeve 41 by the rotation of the transport screw 43.

A transport screw 44 is accommodated in the stirring chamber T2. The transport screw 44 transports the toner along the longitudinal direction of the developing sleeve 41 by its rotation. This toner has been freely dropped from the supply chamber T3 into the stirring chamber T2 via the toner supply port 50.

As the toner particles, those produced by a pulverization method may be used. For example, if a toner produced by a polymerization method is used, it is more preferable in the case of simultaneous development and cleaning as in the present embodiment. is there. Since the polymerized toner has a shape close to a sphere, the external additive is uniformly coated,
This is because the releasability from the photosensitive drum 1 is extremely good, and the transfer residual toner itself is small. For example, when the transfer efficiency (toner amount per unit area transferred on paper / toner amount per unit area on the photosensitive drum 1) of the pulverized toner and the polymerized toner is compared, the pulverized toner is 90%. Thus, when the polymerized toner was used, the efficiency was as high as 97%. When such a polymerized toner is used, the transfer residual toner is extremely small and the releasability is high. Therefore, when simultaneous cleaning with contact charging / development is performed, a decrease in charging ability is reduced. In addition, the process of collecting and discharging the transfer residual toner from the magnetic carrier as the contact charging member is facilitated, the recoverability of the residual toner on the photosensitive drum 1 in the developing unit is improved, and the occurrence of a positive coat or the like is reduced.

Here, a method of measuring the triboelectric charge amount (two-component developer) of the toner will be described with reference to FIG.

FIG. 4 is an explanatory view of an apparatus for measuring the triboelectric charge amount of the toner. First, a two-component developer whose triboelectric charge amount is to be measured is placed in a polyethylene bottle having a capacity of 50 to 100 ml in a metal measuring container 62 having a 635-mesh screen 63, and is manually placed for about 10 to 40 seconds. Shake, add about 0.5 to 1.5 g of the developer, and close the metal lid 64. The weight of the entire measurement container 62 at this time is weighed and set as W1 (g). Next, in the suction device 61 (at least a portion in contact with the measurement container 62 is an insulator), the vacuum gauge 65 is adjusted by adjusting the air volume control valve 66 by suctioning through the suction port 67.
Is 250 mmAq. In this state, suction is sufficiently performed, preferably for 2 minutes, to remove the resin by suction. The potential of the electrometer 69 at this time is set to V (volt). Where 68
Is a capacitor and its capacity is C (F). Further, the entire weight of the measurement container 62 after the suction is weighed and defined as W2 (g). The frictional charge of the toner (the frictional charge of the toner per unit weight) is calculated by the following equation.

Amount of triboelectric charge of resin (C / kg) = (C × V
× 10 ^-3 ) / (W1-W2)

As will be described later, in the present embodiment, a negatively charged toner is used, and the triboelectric charge amount is -1.0 × 10
^-2 to -4.5 × 10 ^-2 C / kg was used.

The toner having a volume average particle diameter of 4 to 15 μm can be suitably used. Here, as the volume average particle diameter of the toner, for example, the one measured by the following measurement method is used.

As a measuring device, a Coulter counter TA is used.
-Type II (manufactured by Coulter), connected to an interface (manufactured by Nikkaki) for outputting the number average distribution and volume average distribution and a CX-i personal computer (manufactured by Canon), and using primary sodium chloride as the electrolyte 1% NaCl
Prepare the aqueous solution.

The measuring method is as follows.
In 150 ml, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and the particle size distribution of 2 to 40 μm particles was measured using the above-mentioned Coulter Counter TA-II using a 100 μm aperture. Is measured to determine the volume distribution. From these determined volume distributions, the volume average particle size of the sample is obtained.

In addition to the toner described above,
By covering the toner surface with an external additive, there are two effects in terms of hardware. One is that the fluidity is improved, and the replenishment toner is easily mixed and stirred with the two-component developer in the developing container. The other is that the external additive is interposed on the toner surface, so that the photosensitive drum is That is, the releasability of the toner developed on the photosensitive drum is improved, and the transfer efficiency is improved.

The external additive used in the present invention preferably has a particle size of 1/10 or less of the weight average particle size of the toner particles from the viewpoint of durability when added to the toner. The particle size of the additive means an average particle size obtained by observing the surface of the toner particles with an electron microscope. As the external additive, for example, the following are used.

Metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, tin oxide, zinc oxide, etc.), nitrides (silicon nitride, etc.), carbides (silicon carbide, etc.)
Metal salts (calcium sulfate, barium sulfate, calcium carbonate, etc.), fatty acid metal salts (zinc stearate, calcium stearate, etc.), carbon black, silica, etc.

The external additive is used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the toner particles.
0.05 to 5 parts by weight are used. These external additives may be used alone or in combination. Respectively,
Those subjected to a hydrophobic treatment are more preferable.

In this embodiment, the average particle diameter is 20 n
m of titanium oxide externally added by 1% by weight.

As the carrier constituting the developer used in the present invention together with the toner described above, conventionally known carriers can be used. For example, magnetite is dispersed as a magnetic material in a resin. To make it conductive,
In addition, a resin carrier formed by dispersing carbon black for resistance adjustment, or a magnetite single surface such as ferrite that has been oxidized and reduced to adjust the resistance, or coated with a magnetite single surface resin such as ferrite The one after the resistance adjustment can be used. The method for producing these magnetic carriers is not particularly limited. In the present embodiment, the weight average diameter is 20
-100 μm, preferably 20-70 μm.

The developing step of the present invention was carried out by the method and apparatus as described above.

On the other hand, the transfer residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image. The transfer residual toner often reverses its charging polarity due to peeling discharge or the like at the time of transfer.
It is difficult to collect in the developing device 4 at the same time as the development.
Then, the transfer residual toner that has reached the charging area with the rotation of the photosensitive drum 1 is taken into the magnetic brush charger 2A, and is rubbed with the magnetic brush charger 2A to be a normally charged toner (in the present embodiment, negatively charged). )I do. At this time,
Applying a DC voltage only to the magnetic brush charger 2A does not sufficiently take in the toner into the charger, but applying an alternating voltage to the magnetic brush charger 2A causes the photosensitive drum 1 to be charged.
-The toner is easily taken into the magnetic brush charger 2A by the vibration effect of the electric field between the magnetic brush chargers 2A.

By doing so, the magnetic brush charger 2
By rubbing with A, it is possible to convert the toner into a normally charged toner and simultaneously recover the developed image in the developing device 4, but on the other hand, applying an alternating voltage to the magnetic brush charger 2A greatly increases the charging ability. Problems arise. The DC component of the bias applied to the magnetic brush charger 2A and V _chg, [Delta] V = a difference between when the surface potential of the charged photosensitive drum 1 surface at this time was set to Vd | V _{ch g} -Vd |, the present When V _{chg is set} to −600 V and an alternating voltage having a frequency of 1000 Hz and V _{pp of} 700 V is applied to the magnetic brush charger as in the embodiment, ΔV = 10 V because Vd becomes −590 V.

According to the research and experiments of the present applicant, this Δ
Unless V exceeds 50 V, it has been found that the transfer residual toner taken in the magnetic brush charger 2A is not easily discharged onto the photosensitive drum 1. For this purpose, the magnetic brush charger 2
The contamination of A gradually occurs, and depending on the toner resistance value and the like, if a predetermined amount or more of toner is mixed into the magnetic brush charger 2A, the charging ability will be reduced even when the alternating voltage is superimposed. In addition, if the taken-in toner is excessively accumulated in the magnetic brush charger 2A, the toner accumulated in the space inside the magnetic brush charger 2A may be scattered (such toner has no charge). ). Such a decrease in charging ability caused by mixing toner having a higher resistance than the magnetic carrier, which is a constituent member, into the bleeding brush charger 2A prevents the magnetic brush charger 2A from uniformly contacting the surface of the photosensitive drum 1. Therefore, the uniformity of the charge generated is reduced. Such a phenomenon similarly occurs when only a DC voltage having a low chargeability is applied.

Conversely, when the transfer residual toner amount is large, that is, when an image with a high image ratio is continuously taken, or when the transfer efficiency is deteriorated due to the paper type of the transfer material P or the humidity control state, The charging ability decreases, and during image formation,
In the developing section, the difference between the charging potential and the potential of the DC bias applied on the developing sleeve 41 (fogging voltage V _back ) becomes small, and fogging occurs.

Therefore, in the present embodiment, during the non-image formation, the alternating voltage is not superimposed on the bias applied to the magnetic brush charger 2A, and the time for applying only the DC voltage is provided. As described above, the uniformity of charging is poor when only a DC voltage is applied, but there is no particular problem during non-image formation. In this way, when only a DC voltage is applied,
Surface potential Vd approximately -545V next to the photosensitive drum 1 surface, ΔV = | V _chg -Vd | since the approximately 55V discharged is able to perform sufficiently.

Further, for example, by providing an application time of only a DC voltage before image formation, the magnetic brush charger 2A
The toner on the surface of the photosensitive drum 1 is uniformly discharged onto the surface of the photosensitive drum 1 by uniformly discharging the toner on the surface of the photosensitive drum 1 and collecting the toner in an amount that can be collected by the developing device 4. After the toner on the surface is positively collected by the developing device 4, the image is formed while applying the alternating voltage, so that the image is always formed without the contamination of the charger and a good image is maintained. It becomes possible.

With this configuration, even if toner is mixed in the magnetic brush charger 2A, the toner can be sufficiently discharged, so that contamination of the magnetic brush charger 2A can be prevented. Even when a voltage is superimposed, it is possible to solve the problem that the charging ability is not sufficiently obtained and an image defect occurs.

In this embodiment, the toner on the magnetic brush charger 2A is uniformly discharged to the surface of the photosensitive drum 1 by providing the application time of only the DC voltage during non-image formation, but the alternating voltage is completely reduced. Even without the pause, for example, even when the amplitude of the alternating voltage is reduced to approximately 200 V or less, the charging ability is reduced, and it can be confirmed that the toner discharging effect can be obtained.

Further, in the present embodiment, the timing of applying only the DC voltage is simply defined as the time of non-image formation, but may be any time during non-image formation, for example, during pre-rotation,
Alternatively, it may be performed at the time of post-rotation, and may be performed at every image formation or at regular intervals.

As described above, by providing the forced discharge mode, the charged potential at the time of image formation was guaranteed, and a high-quality image could be formed. However, when the number of formed images is increased and the toner gradually accumulates in the magnetic brush charger 2A, or when image formation is continued with a large amount of transfer residual toner, that is, when an image having a high image ratio is continuously obtained. When the image formation is continued while the transfer efficiency is deteriorated due to the paper type of the transfer material P or the humidity control state, the charging ability at the time of non-image formation decreases, and the charging potential of the photosensitive drum 1 and the developing sleeve 41 are reduced. The fog toner adhered to the surface of the photosensitive drum 1 in the developing unit during non-image formation. As a result, the toner adhering to the surface of the photosensitive drum 1 is removed by the magnetic brush charger 2.
A, the charging potential is further reduced, and if that area is an image forming area in the next step, fogging occurs,
D.gamma. Characteristics may change or fog toner may adhere to the surface of the photosensitive drum 1 in a non-image forming area in the next process. Further, in a configuration using a transfer drum or a transfer belt, which is not taken in the configuration of the present embodiment, there is also a problem that each of them is stained by the fog toner on the surface of the photosensitive drum 1.

As a result of some investigations, when the above-described configuration is adopted, the developing bias V _pp (peak) during image formation is prevented in order to prevent fogging toner from adhering to the surface of the photosensitive drum 1 during non-image formation. It has been found that it is more effective to increase V _pp during non-image formation than to increase the voltage (inter-voltage).
In general, when fogging (here, ground fogging, which indicates a situation in which normally charged toner (corresponding to negatively charged toner in the embodiment) adheres) is likely to occur, when V _back is small, the toner charge amount Is when is large. That is,
The background fogging occurs when the adhesion to the surface of the photosensitive drum 1 due to the reflection force is large and there is no electrostatic force enough to peel the fogging toner off the surface of the photosensitive drum 1. Therefore, in order to suppress fogging, it is necessary to increase V _back and reduce the toner charge amount. On the other hand, if V _back is 100 V or more, the V bias of the developing bias is reduced.
_{Increasing pp} is also a measure. V _back is 10
With a limitation of 0 V or more, if V _pp is increased, the toner adhered to the surface of the photosensitive drum 1 is easily peeled off the surface of the photosensitive drum 1, and the peeled toner moves toward the developing sleeve 41 due to V _back ( V _back is 100
On the other hand, if the value of V _pp is larger than V, fogging becomes easier. ). With such a configuration, in the case where the configuration of simultaneous cleaning of development according to the present embodiment is employed, the recoverability of the toner discharged from the magnetic brush charger 2A in the developing unit is also improved.

According to the structure of the present invention, even if fogging is likely to occur due to a decrease in V _back (V _back is 100 V or more), the fogging is likely to occur on the surface of the photosensitive drum 1 by increasing V _pp . The configuration is such that the toner is easily peeled off.

When the toner of the magnetic brush charger 2A is forcibly discharged during non-image formation, and the amount of reduction in the charging potential during image formation is at a level that does not affect the image, the non-image formation is performed. The fogging on the surface of the photosensitive drum 1 in the developing unit can be suppressed if all of the following conditions are satisfied at least. That is, (1) the absolute value of the triboelectric charge amount of the toner in the developer: 4.5
× 10 ^-2 C / kg or less (however, 1.0 × 10 ^-2 C / k
If it is less than g, the toner may be scattered, so that it is preferably 1.0 × 10 ⁻² C / kg or more. (2) V _back : 100 V or more (However, if it is larger than 400 V, there is a possibility of carrier adhesion, so 400 V
The following is preferred. ) (3) V _pp of the developing bias: l of V _pp at the time of image formation. 2
5 times or more.

Example 1 Fogging on the photosensitive drum during non-image formation was evaluated under the following conditions with the above-described configuration.

The evaluation is based on an all-black solid image per A4 sheet, and an image having an image ratio (30% duty image, in which 30% of the consumed amount is consumed by one A4 sheet). This is performed after outputting 30,000 sheets of paper.

<Conditions] The distance (SD _gap ) between the developing sleeve and the photosensitive drum was set to 400 μm, and the following conditions were satisfied.・ DC bias voltage value V _chg applied to the magnetic brush charger during image formation
= −600 V V _{pp of} the AC bias applied to the magnetic brush charger = 70
0 V photosensitive drum charging potential Vd = −590 V | V _chg −Vd | = 10 V DC bias voltage Vdc = −400 V of developing bias V _pp = 1.7 kV of developing bias AC bias V _back = 190 V Toner unit weight Triboelectric charge per unit = 2.0 × 10 ^-2 C
/ Kg ・ Non-image formation DC bias voltage value V _chg applied to magnetic brush charger
= −600 V V _pp = 40 of the AC bias applied to the magnetic brush charger
0V photosensitive drum charge potential _{Vd = -530V | V chg -Vd |} = 70V developing bias DC bias voltage Vdc = -400 V developing bias AC bias of V _pp = 2.2kV fog-removing bias value V _back = 130V (non V _pp of the developing bias at the time of image formation) / (V _pp of the developing bias at the time of image formation) = 1.29 It should be noted that head, the fog toner on the photosensitive drum surface during non-image formation was sampled from a transparent PET tape Then, the reflection densities of the one affixed to white paper (α) and the one affixed with the same PET tape to white paper (β) are determined, and the fogging density (%) = (reflection density of α) − (β Reflection density). Here, TOKYO D is used to measure the reflection density.
ENSHOKU CO. LTD's DENSITMETE
R TC-DS was used.

The evaluation criteria for fog density are shown in Table 1 below.

(Table 1) One evaluation criterion-fog density <0.5: virtually no fog A 0.5 ≤ fog density <1: almost no fog B 1 ≤ fog density <2: slightly fog C 2 ≤ fog Density <3: fogging D 3 ≦ fogging density: fairly fogging E The evaluation result B or higher is a level that does not cause any problem during the operation of the configuration of this embodiment.

When the image was formed under the above conditions, no fogging was observed, that is, the level was A according to the evaluation criteria in Table 1, and the charging ability of the magnetic brush charger was not reduced at all. An image was obtained.

Example 2 In Example 2, an image was formed using the image forming apparatus of the embodiment shown in FIG. 1 under the following conditions, and the fog on the photosensitive drum surface during non-image formation was evaluated. .

The evaluation was performed by comparing the 50% duty image with 30,000
The test was performed after outputting an equivalent number of sheets.

<Conditions] The distance (SD _gap ) between the developing sleeve and the photosensitive drum was set to 500 μm, and the following conditions were satisfied.・ DC bias voltage value V _chg applied to the magnetic brush charger during image formation
= −600 V V _{pp of} the AC bias applied to the magnetic brush charger = 70
0 V photosensitive drum charging potential Vd = -570 V | V _chg -Vd | = 30 V DC bias voltage value of developing bias Vdc = -400 V AC bias of developing bias V _pp = 2.0 kV Fogging bias value V _back = 170 V Toner unit Amount of triboelectric charge per weight = 1.5 × 10 ^-2 C
/ Kg ・ Non-image formation DC bias voltage value V _chg applied to magnetic brush charger
= −600 V V _pp = 0 V of AC bias applied to the magnetic brush charger Photosensitive drum charging potential Vd = −510 V | V _chg −Vd | = 90 V DC bias voltage value of developing bias Vdc = −400 V AC bias of developing bias V _pp = 2.5 kV Fogging bias value V _back = 110 V (developing bias V _pp during non-image formation) / (developing bias V _pp during image formation) = 1.25 Image formation under the above conditions As a result, no fogging was observed, that is, the charging ability of the magnetic brush charger was not reduced at all at level B according to the evaluation criteria in Table 1, and a very good image was obtained.

Example 3 In Example 3, an image was formed using the image forming apparatus of the embodiment shown in FIG. 1 under the following conditions, and the fog on the photosensitive drum surface during non-image formation was evaluated. .

Evaluation was made at 23 ° C. Using a paper (transfer material) left for a long time in a 5% environment, a 10% duty image
The test was performed after outputting 00 sheets.

<Conditions] The distance (SD _gap ) between the developing sleeve and the photosensitive drum 1 was set to 1000 μm, and the following conditions were satisfied.・ DC bias voltage value V _chg applied to the magnetic brush charger during image formation
= −600 V V _{pp of} the AC bias applied to the magnetic brush charger = 70
0V photosensitive drum charge potential _{Vd = -580V | V chg -Vd |} = 20V developing bias DC bias voltage Vdc = -350V V _pp = 2.0kV fog-removing bias value V _back = 230V toner unit of an AC bias of the developing bias Amount of triboelectric charge per weight = 3.0 × 10 ⁻² C
/ Kg ・ Non-image formation DC bias voltage value V _chg applied to magnetic brush charger
= −600 V V _pp = 40 of the AC bias applied to the magnetic brush charger
0V photosensitive drum charge potential _{Vd = -530V | V chg -Vd |} = 70V developing bias DC bias voltage Vdc = -350 V developing bias AC bias of V _pp = 3.0 kV fog-removing bias value V _back = 180V (non was subjected to image formation in V _pp) / (V _pp of the developing bias at the time of image formation) = 1.5 or more such conditions of the developing bias at the time of image formation, no head, i.e., evaluation criteria in Table 1 At level B, the charging ability of the magnetic brush charger did not decrease at all, and a very good image was obtained.

Comparative Example 1 In Comparative Example 1, an image was formed under the following conditions using the image forming apparatus of the embodiment shown in FIG. 1, and the fog of the photosensitive drum surface during non-image formation was evaluated. .

The evaluation was carried out on a 50% duty image at 15,000.
The test was performed after outputting an equivalent number of sheets.

<Conditions] The distance (SD _gap ) between the developing sleeve and the photosensitive drum was set to 500 μm, and the following conditions were satisfied.・ DC bias voltage value V _chg applied to the magnetic brush charger during image formation
= −600 V V _{pp of} the AC bias applied to the magnetic brush charger = 70
0V photosensitive drum charge potential _{Vd = -560V | V chg -Vd |} = 40V developing bias DC bias voltage Vdc = -400V V _pp = 2.0kV fog-removing bias value V _back = 160 V toner units AC bias of the developing bias Amount of triboelectric charge per weight = 1.5 × 10 ^-2 C
/ Kg ・ Non-image formation DC bias voltage value V _chg applied to magnetic brush charger
= −600 V V _pp = 0 V of AC bias applied to the magnetic brush charger Photosensitive drum charging potential Vd = −490 V | V _chg −Vd | = 110 V DC bias voltage value of development bias Vdc = −400 V AC bias of development bias V _pp = 2.0 kV Fogging bias value V _back = 110 V (developing bias V _pp during non-image formation) / (developing bias V _pp during image formation) = 1.0 Image formation under the above conditions Was performed, there was no fogging, that is, the charging ability of the magnetic brush charger was reduced at level D based on the evaluation criteria in Table 1, and the V-D
The γ characteristics were also starting to fluctuate.

[0106]

As described above, according to the present invention,
Even in the case where the toner in the charger is forcibly discharged at the time of inter-sheet or front / reverse rotation, no fogging toner is generated on the surface of the image carrier in the developing unit during non-image formation.
Good images can be formed over a long period of time.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a longitudinal sectional view showing the configuration of a conventional image forming apparatus.

FIG. 3 is a longitudinal sectional view showing a schematic configuration of a two-component developing device.

FIG. 4 is a perspective view showing a schematic configuration of an apparatus for measuring a triboelectric charge amount of a two-component developer.

FIG. 5 is a schematic diagram illustrating a schematic configuration of a laser scanning unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2A Charging means (magnetic brush charger) 3 Laser scanning part 4 Developing means (developing device) 5 Transfer charger 6 Separation charger 11 Fixing device 41 Developing sleeve 42 Fixed magnet 51 Power supply 52 Control means P transfer material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/00 303 G03G 15/02 102 2H073 15/02 101 15/06 101 2H077 102 21/00 15/06 101 15/08 507B 21/00 9/08 384 21/14 21/00 372 (72) Inventor Masanori Shida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Ichiro Ozawa Tokyo 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term (reference) in Canon Inc. BA13 BA23 CA03 2H077 AA11 AA37 AB02 AB14 AB18 AC02 AC16 AD06 AD13 AD31 AD36 AE01 EA03 GA04

Claims (7)

[Claims] An image carrier; a charging unit configured to uniformly charge the surface of the image carrier; an exposing unit configured to expose the charged surface of the image carrier to form an electrostatic latent image; A developing means for developing a latent image, wherein the image carrier has a volume resistivity of 10 ⁹ to 10 ¹⁴ Ω · cm.
The charging unit has a contact charging member that contacts the surface layer of the image carrier and directly injects charge into the surface layer. The developing unit includes a toner, a magnetic carrier, Is transported to the developing position, and the toner is adhered to the electrostatic latent image to be developed as a toner image by a DC bias on which an alternating voltage is superimposed, and is transported while being carried on the surface of the image carrier. A control unit that also serves as a cleaning unit that collects the remaining transfer residual toner, and further controls the peak-to-peak voltage value of the alternating voltage applied to the developing unit to be different between image formation and non-image formation. An image forming apparatus, comprising: 2. The control means according to claim 1, wherein said DC bias applied to said contact charging member is V _chg , and a charging potential on said image carrier surface is Vd, and a difference between them is ΔV = 2. The image forming apparatus according to claim 1, wherein | V _chg −Vd | is controlled to be different between image formation and non-image formation. 3. The control device according to claim 1, wherein the peak-to-peak voltage of the alternating voltage applied to the developing device is controlled to be larger during non-image formation than during image formation. Or the image forming apparatus according to 2. 4. A potential difference between a potential of a white background portion formed on the image carrier during non-image formation and a potential of a DC bias applied to the developing means is 100 V or more and 400 V or less. Item 4. The image forming apparatus according to item 1, 2, or 3. 5. The absolute value of the triboelectric charge per unit weight of the toner is at least 1.0 × 10 ⁻² C / kg and 4.5 × 1.
The image forming apparatus according to claim 1, wherein the image forming apparatus is set to 0 ⁻² C / kg or less. 6. The image forming apparatus according to claim 1, wherein the contact charging member of the charging unit is a magnetic particle. 7. The toner according to claim 1, wherein the toner contained in the developer contained in the developing unit is a toner generated by a polymerization method. Image forming apparatus.