JP4867315B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In recent years, there has been a demand for a small and highly reliable image forming apparatus. In particular, there is an increasing demand for an image forming apparatus that is compact and easy to maintain while maintaining high image quality. For this purpose, the toner remaining on the image carrier after transfer is not scraped off, but is left on the image carrier, passed through the charging device and the exposure device, and collected and reused by the developing device. An image forming apparatus has been reported (for example, Patent Document 1).

  However, in the cleanerless image forming apparatus, since charging / exposure is performed in a state where the residual toner is placed on the image carrier, exposure is hindered and exposure occurs. Therefore, an afterimage of the formed image remains as a memory in the electrostatic latent image, and the previous image appears as noise during subsequent image formation.

  Therefore, the toner remaining on the image carrier after the transfer is temporarily taken into a toner holding means such as a rotating brush at the time of image formation, temporarily held, and discharged on the image carrier at times other than the time of image formation. There has been proposed a cleanerless image forming apparatus that collects the toner in a developing device.

  However, in the cleanerless image forming apparatus as described above, it is difficult to efficiently take in the toner remaining on the image carrier after the transfer into the brush, and the toner once held on the brush is temporarily not used during image formation. It was difficult to efficiently eject the toner onto the image carrier.

  If the residual toner was not successfully taken in from the image carrier, toner that passed through the brush without being taken in was remarkably generated. When such a toner is prominently present, image exposure is hindered during the next image formation (exposure button), and image noise due to exposure button is also generated.

  If the toner was not successfully discharged from the brush to the image carrier, the brush was contaminated with toner, and the toner was fixed on the brush and fine fixed matter of the toner spilled due to contact with the image carrier. When this toner spilled on the paper, it appeared as random noise on the image. Further, scraping with the brush becomes difficult due to contamination of the brush, and the toner passing through the brush becomes prominent, so that image noise due to the exposure button is also generated. Further, due to contamination of the brush, it becomes difficult to charge the toner with the brush, and toner that is discharged without being controlled to the intended charge level is remarkably generated. For this reason, the poorly charged toner contaminates the charging device, causing uneven charging on the surface of the image carrier, and the unevenness appears as uneven density on the image. The occurrence of density unevenness was particularly remarkable when a contact-type charging device was used.

As described above, in the cleanerless image forming apparatus in which the residual toner is temporarily taken in and held by the brush and then discharged to the image carrier and collected by the developing device, the taking in and discharging by the brush is unstable, and the long-term In the current situation, high quality images cannot be obtained stably.
JP 2003-167476 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a cleanerless image forming apparatus capable of stably obtaining a high-quality image over a long period of time. Specifically, an object of the present invention is to provide a cleanerless image forming apparatus capable of stably obtaining a high-quality image free from image noise due to exposure cracks or toner spills or density unevenness due to charging device contamination over a long period of time. And

The present invention is formed by at least an image carrier, a charging device that charges the surface of the image carrier, an exposure device that forms an electrostatic latent image on the image carrier charged by the charging device, and the exposure device. A developing device that forms toner images by applying toner to an electrostatic latent image, a transfer device that transfers a toner image formed by the developing device to a transfer target, and remains on the image carrier after transfer by the transfer device An image forming apparatus that includes a brush roller that temporarily captures and holds the residual toner and discharges the residual toner onto the image carrier, and collects the toner discharged from the brush roller onto the image carrier to the developing device,
The present invention relates to an image forming apparatus characterized in that the toner is a toner having an acid value of 5 KOHmg / g or more produced by a wet granulation method.

  In the cleanerless image forming apparatus of the present invention, since the residual toner is taken in and discharged by the brush roller stably and smoothly, a high-quality image free from image noise due to exposure and toner spillage and density unevenness due to charging device contamination is obtained. Can be obtained over a long period of time.

(Image forming device)
The image forming apparatus according to the present invention employs a cleanerless system in which toner remaining on the image carrier after transfer is temporarily taken in and held by a brush roller, and then discharged to the image carrier and collected by the developing device. It is a thing. In the present specification, cleanerless means that a cleaner that requires disposal of toner is not used.

  The image forming apparatus of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus of the present invention.

  As shown in FIG. 1, the image forming apparatus 10 of the present invention includes at least an image carrier 20, a charging device 30 for charging the surface of the image carrier, and an electrostatic latent image on the image carrier charged by the charging device. An exposure device 40 that forms an image, a developing device 50 that forms a toner image by applying toner to the electrostatic latent image formed by the exposure device, and a toner image formed by the developing device is transferred to the transfer target 11 And a brush roller 70 that temporarily takes in and holds the residual toner remaining on the image carrier after transfer by the transfer device, and discharges the toner onto the image carrier. Then, the toner discharged onto the image carrier 20 is collected by the developing device 50.

  The image carrier 20 is capable of forming an electrostatic latent image corresponding to a predetermined image on the surface, and an organic photoreceptor of a type that performs so-called reversal development is used.

  The charging device 30 is not particularly limited as long as the surface of the image carrier can be uniformly charged, and may be of a contact type or a non-contact type with respect to the image carrier. Here, a contact-type charging roller is used as the charging device 30, but the invention is not limited to this, and a non-contact charging device such as a scorotron may be used. In the present invention, it is preferable to use a contact type charging device. This is because the contact-type charging device is likely to be contaminated with toner by the toner, but in the present invention, contamination can be effectively suppressed even when such a charging device is used. The image bearing member usually has the same polarity as the charging polarity of the toner and an absolute value of 300 to 1000 V, particularly 400 to 800 V, and a surface potential (V1) of the image carrier is achieved by the charging device.

  The exposure device 40 is not particularly limited as long as an electrostatic latent image corresponding to a predetermined image can be formed on the surface of the image carrier charged by the charging device, and a conventionally known device can be used. With the exposure device, the image carrier usually achieves a surface potential (V2) of the same polarity as the toner charging polarity and an absolute value of 30 to 250 V, particularly 70 to 150 V in the image area.

  The developing device 50 is not particularly limited as long as a toner image can be formed by applying toner to the electrostatic latent image on the surface of the image carrier formed by the exposure device, and is not limited to a so-called non-magnetic one-component developing method, magnetic one-component developing. Any one of the development method, the non-magnetic two-component development method, and the magnetic two-component development method may be adopted. From the viewpoint of reducing the size of the image forming apparatus, it is preferable to employ a non-magnetic one-component development system. The developing device 50 may be a non-contact type in which a so-called developer carrier provided in the device does not contact the image carrier, or may be a contact type.

  As the toner (not shown) accommodated in the developing device 50, a toner having an acid value of 5 KOHmg / g or more, preferably 5 to 45 KOHmg / g, more preferably 10 to 30 KOHmg / g manufactured by a wet granulation method is used. To do.

In the present invention, by using the toner as described above in the cleanerless system as described above, the residual toner can be taken in and discharged by the brush roller 70 stably and smoothly. Therefore, it is possible to obtain an effect that a high-quality image free from image noise due to exposure and toner spillage and density unevenness due to charging device contamination can be stably obtained over a long period of time. Although the details of the mechanism for obtaining such an effect are not clear, it is considered to be based on the following mechanism. That is, when the toner is produced by a wet granulation method and has the above acid value, acidic groups such as carboxyl groups and sulfone groups appear effectively on the surface of the toner particles, and H ₂ O is adsorbed to the acidic groups appropriately. Therefore, the electric resistance on the toner particle surface can be effectively reduced. Therefore, excessive frictional charging of the toner by the brush is prevented, and the toner adheres to the brush with an appropriate force. Accordingly, it is considered that the toner taken in by the brush roller is stably and smoothly discharged to the image carrier and the contamination of the brush is suppressed, so that toner spillage is suppressed and random image noise can be suppressed. Further, when the contamination of the brush is suppressed, the residual toner is effectively scraped off by the brush, so that the residual toner is stably and smoothly taken into the brush roller. For this reason, it is considered that the toner that passes through the brush without being taken in is effectively reduced, and image noise due to exposure failure can be suppressed. Furthermore, if the contamination of the brush is suppressed and the residual toner is stably and smoothly taken into the brush roller, the toner chargeability is effectively controlled by the voltage applied to the brush. It can be suppressed.

  If the acid value of the toner is too small, the electrical resistance on the surface of the toner particles is increased and excessive frictional charging of the toner by the brush occurs, so that the toner adheres to the brush with a relatively large force. Therefore, the toner taken in by the brush roller cannot be stably and smoothly discharged to the image carrier, resulting in brush contamination. Therefore, toner spills and random image noise occurs. Further, when the brush is contaminated, the residual toner is not effectively scraped off by the brush, so that toner that passes through the brush without being taken in by the brush roller is remarkably generated, and image noise is generated due to exposure. Further, when the brush is contaminated, the toner chargeability is not effectively controlled by the voltage applied to the brush, so that density unevenness occurs due to charging device contamination.

  Further, when the toner is produced by a method other than the wet granulation method, for example, a pulverization method, the effect of the present invention cannot be obtained even if the toner has an acid value within the above range. Even if the toner is manufactured by a pulverization method, acidic groups such as carboxyl groups and sulfone groups do not appear on the toner particle surface effectively, and the electric resistance on the toner particle surface cannot be effectively reduced. Charging occurs. As a result, brush contamination occurs, and it is considered that the effect of the present invention cannot be obtained.

  In this specification, the acid value of the toner refers to the number of mg of potassium hydroxide required to neutralize acidic groups such as carboxyl groups and sulfone groups contained in 1 g of the toner. A sample is dissolved in a benzene-ethanol mixed solvent or the like, and titrated with a potassium hydroxide solution having a known titer, and the neutralized amount is calculated. It should be noted that the “toner 1 g” does not include an external additive as described later that is externally added to the toner particles.

  In this specification, specifically, the acid value of the toner is a value measured by the following method, but neutralizes acidic groups such as carboxyl groups and sulfone groups contained in 1 g of the toner. It may be measured by any method as long as the number of mg of potassium hydroxide required for the measurement can be measured and calculated.

Specifically, the toner acid value was measured by the following method. 5 g (x; g) of toner is dissolved in 50 g of a benzene-ethanol mixed solvent (volume ratio 2: 1) and titrated with a potassium hydroxide solution to measure the neutralization amount (y; g). Thereafter, the toner solution is filtered, the residue is taken out, washed and dried, and the external additive (z; g) contained in the toner is measured. The acid value was obtained by substituting x, y and z into the following equation.
Toner acid value = y / (x−z)

  In the present invention, the toner preferably has a volume median diameter of 3 to 9 [mu] m, particularly 4.5 to 7.5 [mu] m, from the viewpoint of toner production cost and high image definition.

In the present invention, the volume median diameter uses a value measured by Coulter Multisizer III (manufactured by Beckman Coulter).
Specifically, the volume median diameter is measured by the following method.
Measurement of toner volume median diameter (volume D50% diameter) Measurement and calculation are performed using a device in which a computer system for data processing (manufactured by Beckman Coulter) is connected to Coulter Multisizer III (manufactured by Beckman Coulter).
As a measurement procedure, 0.02 g of toner is blended with 20 ml of a surfactant solution (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing the toner). After that, ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion. This toner dispersion is injected into a beaker containing ISOTON II (manufactured by Beckman Coulter) in a sample stand with a pipette until the display density of the measuring instrument becomes 5% to 10%. By setting this concentration range, a reproducible measurement value can be obtained. In the measuring machine, the measurement particle count is set to 25000 and measured. The aperture diameter was 50 μm.

  The transfer device 60 is not particularly limited as long as the toner image on the surface of the image carrier formed by the developing device can be transferred to the transfer target 11, and is made of, for example, a cylindrical body having conductivity, and normally has a toner charging polarity. In contrast, a DC component (voltage) having a reverse polarity and an absolute value of 1000 to 2800 V, particularly 1400 to 2300 V, is applied to promote transfer of the toner image.

  The transfer target 11 may be a recording paper, an OHP sheet, or the like, or an intermediate transfer belt for secondarily transferring the image to a recording paper, an OHP sheet, etc. after temporarily holding the image on itself. The intermediate transfer member may be used. When the image forming apparatus 10 of the present invention is used for forming a full-color image, the transfer target 11 is usually an intermediate transfer member.

  The brush roller 70 has a conductive and flexible linear member planted around a rotation shaft, and is provided so that the longitudinal direction of the brush roller is parallel to the axial direction of the image carrier. The entire image forming width in the axial direction is covered. The brush roller 70 is disposed so as to be rotatable around the rotation axis of the brush roller at a position downstream of the transfer device 60 and upstream of the charging device 30 in the rotation direction of the image carrier, and the leading end of the linear member is the image carrier. Touching the surface. Such a brush roller takes in and holds the residual toner on the image carrier when a predetermined voltage is applied by a power source (not shown), and holds it when another predetermined voltage is applied. The toner is discharged onto the image carrier.

The voltage applied to the brush roller is different at the time of image formation (at the time of capture) and at other times (at the time of discharge).
Hereinafter, the operation principle of taking in and discharging with a brush will be described in detail by taking the case of reversal development using negative polarity toner as an example. Even when the polarity of the toner is positive, the operation principle is the same except that the polarity is reversed.

First, the principle of capturing operation will be described. FIG. 3 is a diagram for explaining a capturing operation in the case of reversal development using negative polarity toner. The toner developed on the image bearing member is usually transferred to the transfer member by applying a charge having a polarity opposite to that of the toner at the time of transfer. For this reason, the charge amount of the transfer residual toner is slightly shifted to the polarity opposite to the original polarity.
At the time of capturing, a voltage in which an AC component and a DC component are superimposed is applied to the brush. By setting the AC component Vpp (V10) to be relatively higher than the discharge operation and setting the DC component applied voltage (V11) to the same polarity as the original toner, the superimposed waveform voltage is on the same polarity side as the toner. The absolute value is large and the absolute value is small on the reverse polarity side. By setting in this way, discharge occurs between the brush and the toner only when a voltage having the same polarity as the original toner polarity is applied (T10), and the toner charge is adjusted to the original polarity. On the other hand, in the time (T11) during which the voltage on the opposite polarity side to the original toner polarity is applied, the potential (V12) on the plus side with respect to the image portion potential (V2) of the image carrier when the voltage having the opposite polarity is applied. By setting the values of the Vpp and DC components of the AC component so as to be applied, a force that electrostatically attracts the toner to the brush side is applied, and the toner is taken into the brush. Furthermore, the toner application efficiency is improved by setting the voltage application time (T11) on the opposite polarity side to the original toner polarity to be longer than the voltage application time (T10) on the same polarity side. That is, in one cycle of the AC component, the toner charge is adjusted to be negative when a high minus voltage is applied for a short time (T10), and is taken into the brush when a low plus voltage is applied for a long time (T11).

Specifically, at the time of loading, the DC component (V11) having the same polarity as the toner charging polarity and an absolute value of 20 to 500 V, the frequency of 500 to 3000 Hz, and the Vpp (amplitude) of 500 to 2500 V are usually included in one cycle. The AC component (V10) in which the voltage application time (T11) on the opposite polarity side of the toner is longer than the voltage application time (T10) on the same polarity side is applied to the brush roller.
That is, when the charging polarity of the toner is negative, the positive voltage application time in one cycle is negative with a DC component of -20 to -500 V, a frequency of 500 to 3000 Hz, and Vpp (amplitude) of 500 to 2500 V. An AC component longer than the voltage application time on the side is applied to the brush roller.
On the other hand, when the charging polarity of the toner is positive, the DC voltage component of 20 to 500 V, the frequency of 500 to 3000 Hz, Vpp (amplitude) of 500 to 2500 V, and the negative voltage application time in one cycle is positive. An AC component longer than the voltage application time is applied to the brush roller.
Preferably, at the time of capturing, a DC component having the same polarity as the charging polarity of the toner and having an absolute value of 100 to 300 V, a frequency of 1 K to 2 KHz, and a Vpp (amplitude) of 800 to 1500 V is opposite to the toner in one cycle. An AC component having a voltage application time longer than the voltage application time on the same polarity side is applied to the brush roller.

  The “voltage application time on the side opposite to the toner” (T11) in one AC component cycle (T10 + T11) is preferably 60% or more and less than 100%, and more preferably 80% or more and 98% or less.

  By such superimposed application of the DC component and the AC component, the residual toner on the image carrier remaining after the transfer is efficiently taken in electrically. In addition, since the charge amount of the taken-in toner can be made uniform with the original toner charging polarity so that the absolute value is not too large by the superimposition application, the toner can be reused for development again after being discharged from the image carrier. The charge amounts of the toner and the toner supplied from the toner hopper can be made substantially the same value, and the developability is stabilized. Hereinafter, an applied voltage composed of a DC component and an AC component under the above conditions is referred to as a “capture voltage”.

  The charge polarity of the toner can be detected by sucking the toner on the developing roller and measuring the charge amount with a suction-type charge amount measuring device (manufactured by Model 210HS Trek Japan).

  The image forming time when the capturing voltage is applied is when the image carrier is rotated for image formation. Normally, when images are continuously formed, the image carrier continues during the continuous image formation. The voltage for capturing is applied. While the capturing voltage is applied, the residual toner on the image carrier is continuously captured by the brush roller and held. In addition, when a large amount of continuous image formation is performed, for example, when an A4 size image is continuously formed, the application of the capturing voltage is interrupted every 50 to 500 sheets, and the discharge voltage described later is used instead. And the toner held on the brush roller may be discharged and collected.

Next, the discharge operation principle will be described. The discharging operation is performed as necessary to discharge toner from the brush at a time other than during image formation. FIG. 4 is a diagram for explaining the discharging operation in the case of reversal development using negative polarity toner.
A voltage obtained by superimposing an AC component and a DC component is applied to the brush even during discharge. However, when discharging, the AC component Vpp (V20) is set to be relatively smaller than that during the capturing operation, and the DC component applied voltage (V21) is set to the same polarity as the original toner. During normal ejection, the surface potential of the image carrier is almost zero although a slight residual potential remains, so the absolute value as a requirement for causing ejection is not particularly limited. By setting the DC component to the same negative polarity as the original toner polarity, an electrostatic force acts on the toner in the direction of the image carrier on average, so that the toner is discharged to the image carrier.
In addition, if the discharge speed is too high, recovery in the developing device cannot catch up, so it is necessary to optimize the setting conditions such as reducing the discharge speed by reducing the DC component applied voltage and increasing the recovery time. Do. That is, it is important to increase the capture efficiency at the time of capture so as not to leave a residue, but at the time of discharge, the discharge speed is adjusted as necessary.
Depending on the combination of the brush, the toner and the image carrier, the triboelectric charge contributes to the discharge of the image carrier even when the brush is connected to the ground without applying a DC voltage having the same polarity as the toner and set to 0V. Sometimes. In this case, the DC voltage (V21) applied for adjusting the discharge speed may be a voltage having a weak reverse polarity to that of the toner. That is, the main mechanism is to discharge toner to the image carrier by applying a DC component (V21) having the same polarity as the original toner polarity or a DC component (V21) having a reverse polarity and a small absolute value. By superimposing the component (V20), the toner is shaken to help discharge.

Specifically, at the time of discharging, normally, a DC component (V21) having a polarity opposite to the charging polarity of the toner and having an absolute value of 100 V to the same polarity and an absolute value of 300 V, and Vpp (amplitude) of 10 to 10 at a frequency of 50 to 500 Hz. An AC component (V20) of 450 V is applied to the brush roller.
That is, when the toner charging polarity is negative, a DC component in the range of +100 V to −300 V and an AC component of Vpp (amplitude) of 10 to 450 V at a frequency of 50 to 500 Hz are applied to the brush roller.
On the other hand, when the charging polarity of the toner is positive, a DC component in the range of −100 V to +300 V and an AC component of Vpp (amplitude) of 10 to 450 V at a frequency of 50 to 500 Hz are applied to the brush roller.
The brush roller preferably has a DC component having a polarity opposite to the toner charging polarity and an absolute value of 50 V to the same polarity and an absolute value of 150 V, and an AC component of Vpp (amplitude) of 30 to 300 V at a frequency of 100 to 300 Hz. To be applied.

  Due to the superimposed application of the DC component and the AC component, the toner taken into the brush roller is discharged on the image carrier efficiently and efficiently. Therefore, excessive toner does not accumulate on the brush roller, and the system for taking in and discharging toner is stabilized. Further, since the residual toner remaining after the transfer is once taken in by the brush and discharged to the image carrier, the toner discharged on the image carrier is collected by the developing device in a state of being appropriately dispersed. For this reason, it is not necessary to take in toner that exceeds the amount of toner that can be taken in at a specific location of the developer carrying member, and toner that cannot be collected is not generated. Accordingly, the collection and development are stabilized, and the image density, in particular, the halftone density unevenness is eliminated and the image quality is stabilized. Hereinafter, the applied voltage composed of the DC component and the AC component under the above conditions will be referred to as “discharge voltage”.

  The time other than the time of image formation to which the discharge voltage is applied is an arbitrary time when the image forming operation is not performed, and is usually 50 to 500, for example, when an A4 size image is formed. A discharge voltage is applied every time image formation on a sheet is completed, and the toner held on the brush roller is discharged and collected. Once applied, the discharge voltage is applied continuously for 2 to 30 seconds. While the discharge voltage is applied, the toner held on the brush roller is continuously discharged onto the image carrier.

  There is no particular limitation on the waveform of the AC component in any of the voltage for capturing or the voltage for discharging. For example, an arbitrary waveform such as a rectangular wave, a sine wave, or a saw wave can be used. In particular, it is preferable to use a rectangular wave for taking in and discharging.

The electric resistance value of the linear member constituting the brush roller 70 is preferably 10 ⁶ to 10 ⁹ Ω · cm, and particularly preferably 10 ⁷ to 10 ⁸ Ω · cm. If it is less than 10 ⁶ Ω · cm, the charge amount of the toner discharged on the image carrier becomes too large, and the development tends to be unstable. When it is larger than 10 ⁹ Ω · cm, the toner ejection efficiency decreases. As such a linear member, a material obtained by adding a conductive component such as carbon black to a resin component such as a polyester resin, a fluorine resin, a polyamide resin, or an acrylic resin can be used. The resistance value of the linear member can be controlled by changing the type and amount of the conductive component added.

  Specific examples of the polyester resin constituting the linear member of the brush roller include, for example, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polytrimethylene naphthalate, polybutylene naphthalate, and the like. Specific examples of the fluorine resin include, for example, polytetrafluoroethylene, polytrichlorotrifluoroethylene, polyvinylidene fluoride, and the like. Specific examples of the polyamide-based resin include nylon-6, nylon-12, nylon-6, 12 and the like. Specific examples of the acrylic resin include polymethyl methacrylate, polyethyl methacrylate, methyl methacrylate-styrene copolymer, and the like.

  The linearity of the linear member is preferably 0.5 to 6 denier, particularly preferably 1 to 3 denier. If the linearity is less than 0.5 denier, the rubbing force by the brush is insufficient and the efficiency of taking in the transfer residual toner is lowered. When it is larger than 6 denier, scratches are generated on the surface of the image carrier.

  The flocking density of the linear member is preferably 80 kF / square inch to 600 kF / square inch, and particularly preferably 300 to 500 kF / square inch. When the flocking density is less than 80 kF / square inch, the brush becomes too sparse and the toner intake efficiency decreases. If it is larger than 600 kF / in 2, the brush becomes too dense and toner discharge efficiency decreases.

  The bite amount of the linear member is preferably 0.3 mm to 0.8 mm, particularly preferably 0.4 to 0.6 mm. When the biting amount is smaller than 0.3 mm, the contact with the image carrier is insufficient, and the toner capturing efficiency is lowered. If it is larger than 0.8 mm, the wear of the image carrier increases. The amount of biting of the linear member can be calculated by subtracting the distance from the base of the linear member to the surface of the image carrier on the brush roller from the length of the linear member.

  An arbitrary length of the linear member can be used, but if it is too short, the resistance value may be insufficient in a high-temperature and high-humidity environment, so 2 mm or more is preferable.

  Various shapes such as a pile shape other than straight hair can be used at the tip of the linear member.

  The brush roller may be rotated in the same direction as the image carrier or in the opposite direction, but the opposite direction is preferred. If the rotation direction of the brush roller is opposite to that of the image carrier, the relative speed with respect to the image carrier can be secured in a state where the number of rotations of the brush itself is small, and toner-like scattering is unlikely to occur.

  The rotational peripheral speed (mm / sec) of the brush roller is preferably in the range of 0.8 to 2 times, more preferably 1 to 1.5 times the rotational peripheral speed of the image carrier. When the rotation speed of the brush roller is slower than 0.8 times, the toner intake efficiency decreases. When the ratio is larger than twice, the toner is likely to be scattered like a smoke, and the wear of the image carrier increases, so that the life is likely to be shortened.

The operation of the image forming apparatus 10 of the present invention will be described.
The surface of the image carrier 20 is uniformly charged by the charging device 30. Next, an electrostatic latent image based on the image data is formed by the exposure device 40. The formed electrostatic latent image is developed by the developing device 50 to form a toner image. The toner image is conveyed by the rotation of the image carrier and is transferred to the transfer target 11 by the transfer device 60. At this time, the toner remaining on the image carrier 20 without being transferred to the transfer target 11 is residual toner.

  When the image carrier 20 is further rotated, the residual toner adheres to the surface of the image carrier 20, faces the brush roller 70 that rotates in contact with the image carrier 20, and is loosened by the rotation of the brush roller 70. It is leveled. At this time, the take-in voltage is applied to the brush roller 70. For this reason, the residual toner is taken into the brush roller 70 and, at the same time, the charge amount is adjusted. That is, even if the toner taken into the brush roller 70 includes toner having a polarity opposite to the predetermined polarity or toner having an absolute value smaller than the predetermined charge amount, The polarity and charge amount of the toner are corrected.

  At the time of such image formation, since the voltage for capturing is normally applied to the brush roller 70 simultaneously with the start of rotation of the image carrier, transfer of residual toner between the brush roller 70 and the image carrier 20 is performed. Is done smoothly. That is, the residual toner smoothly moves from the image carrier 20 to the brush roller 70 and is only taken into the roller.

  When the discharge voltage is applied to the brush roller, the toner which has been corrected in polarity and charge amount at the time of capture and has been captured by the brush is discharged from the brush roller 70 mainly by electrostatic force and discharged onto the image carrier 20. It is. The discharged toner is recovered by the AC component and DC component bias voltages applied to the developing device 50 (that is, the developer carrying member). Of the recovery bias voltage applied to the developer carrier, the DC component is set to a potential opposite to the original toner charging polarity with respect to the surface potential of the image carrier, and the AC component is developed from the image carrier. The frequency and Vpp are set so as to promote the movement / collection of the toner onto the agent carrier. When the toner is discharged from the brush roller, the surface potential of the image carrier is normally almost zero. Therefore, the DC component is set to an absolute value of 20 to 200 V, for example, opposite to the original toner charging polarity, and the AC component. Is set to Vpp 1000 to 2000 V at a frequency of 1 KHz to 3 KHz, for example. Such a recovery bias voltage is normally applied to the developer carrying member simultaneously with the application of the discharge voltage to the brush.

  The image forming apparatus shown in FIG. 1 may be used for mono color or may be used for full color.

  A full color image forming apparatus using the image forming apparatus shown in FIG. 1 for full color will be briefly described with reference to FIG. FIG. 2 is a schematic configuration diagram of an embodiment of a full-color image forming apparatus to which the image forming apparatus shown in FIG. 1 is applied.

  The full-color image forming apparatus 100 in FIG. 2 includes image forming units 10Y, 10M, 10C, and 10Bk for each color, and the image forming apparatus 10 in FIG. 1 is applied as these image forming units. The full-color image forming apparatus 100 further includes an intermediate transfer belt 11 (corresponding to the transfer target 11 in FIG. 1), a secondary transfer device 12, and a belt cleaner 13. The image forming units 10Y, 10M, 10C, and 10Bk for the respective colors are arranged along the intermediate transfer belt 11 and form the toner images of the respective colors on the intermediate transfer belt 11. The superimposed toner images are transferred to the recording paper 14 by the secondary transfer device 12. The toner remaining on the intermediate transfer belt 11 is scraped off by the belt cleaner 13. 2, the same members and parts as those in the apparatus of FIG. 1 are denoted by the same reference numerals as those in FIG.

  In FIG. 2, the full-color image forming apparatus is a tandem type full-color image forming apparatus having four image forming units provided with one developing device and one brush roller in parallel for one image carrier. However, the present invention is not limited to this. For example, in a so-called cycle-type full-color image forming apparatus having a cycle-type developing unit having four developing devices and one brush roller for one image carrier. There may be.

(Toner production method)
The toner used in the present invention has a specific acid value produced by wet granulation as described above. The wet granulation method is a method including a step of granulating by dispersing a monomer component or a polymer component in an aqueous medium, for example, a resin particle association method, a suspension polymerization method, an emulsion polymerization method, an emulsion dispersion. Law. Since the toner is produced by such a wet granulation method, acidic groups such as carboxyl groups and sulfone groups appear effectively on the surface of the toner particles, and as a result, the effects of the present invention as described above can be obtained. Among the wet granulation methods, the resin particle association method is preferable from the viewpoint of easy control of the particle size and shape of the toner.

  Hereinafter, various toner manufacturing methods will be described.

-Resin Particle Association Method The resin particle combination method is a method in which resin particles and colorant particles are salted out / fused in an aqueous medium to associate with each other. The method is not particularly limited, and examples thereof include methods disclosed in JP-A-5-265252, JP-A-6-329947, and JP-A-9-15904. That is, a plurality of fine particles composed of resin particles and colorant and other constituent particles or resin and colorant are associated. In particular, after dispersing these in water using an emulsifier, a coagulant with a critical coagulation concentration or higher is added for salting out, and at the same time, the fused polymer is heated and fused at a temperature above the glass transition temperature of the formed polymer itself. Gradually grow the particle size while forming the shape, stop the particle size growth by adding a large amount of water when the target particle size is reached, further smooth the particle surface while heating and stirring, and control the shape, The toner of the present invention can be formed by heating and drying the particles in a fluid state while containing the water. Here, a solvent that is infinitely soluble in water may be added simultaneously with the flocculant.

  The resin particles can be prepared by polymerizing a polymerizable monomer in an aqueous medium by a granulation polymerization method such as an emulsion polymerization method. As the polymerizable monomer used to obtain the resin particles, an acidic group-free radical polymerizable monomer and an acidic group-containing radical polymerizable monomer are used as essential components, and if necessary, A crosslinkable monomer (crosslinking agent) may be used.

  In the resin particle association method, the acid value of the toner is controlled by adjusting the ratio of the acid group-containing radical polymerizable monomer, particularly the carboxyl group-containing radical polymerizable monomer, to the total monomer components constituting the toner. Is possible. Increasing the proportion of the acidic group-containing radical polymerizable monomer increases the acid value of the toner. On the other hand, when the use ratio of the acidic group-containing radical polymerizable monomer is lowered, the acid value of the toner is lowered. In the resin particle association method, the proportion of the acidic group-containing radical polymerizable monomer, particularly the carboxyl group-containing radical polymerizable monomer, is usually 1% by weight or more based on the total monomer components constituting the toner, preferably Is from 2 to 10% by weight, more preferably from 3 to 8% by weight.

(1) Acid group free radical polymerizable monomer:
The acidic group free radical polymerizable monomer is not particularly limited, and a conventionally known radical polymerizable monomer can be used. Moreover, it can be used combining 1 type (s) or 2 or more types so that the required characteristic may be satisfy | filled.
Specifically, aromatic vinyl monomers, (meth) acrylic acid ester monomers, vinyl ester monomers, vinyl ether monomers, monoolefin monomers, diolefin monomers , Halogenated olefin monomers and the like can be used.

  Examples of the aromatic vinyl monomer include styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, p-methoxy styrene, p-phenyl styrene, p-chloro styrene, p-ethyl styrene, p. -N-butyl styrene, p-tert-butyl styrene, pn-hexyl styrene, pn-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene, 2, Examples thereof include styrene monomers such as 4-dimethylstyrene and 3,4-dichlorostyrene and derivatives thereof.

  Examples of (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, and methacrylic acid. Examples include butyl, hexyl methacrylate, 2-ethylhexyl methacrylate, ethyl β-hydroxyacrylate, propyl γ-aminoacrylate, stearyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and the like.

  Examples of vinyl ester monomers include vinyl acetate, vinyl propionate, and vinyl benzoate.

Examples of the vinyl ether monomer include vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, vinyl phenyl ether and the like.
Examples of the monoolefin monomer include ethylene, propylene, isobutylene, 1-butene, 1-pentene, 4-methyl-1-pentene and the like.
Examples of the diolefin monomer include butadiene, isoprene, chloroprene and the like.

(2) Crosslinkable monomer:
As the crosslinkable monomer, a radical polymerizable crosslinking agent may be added in order to improve the properties of the finally obtained toner. Examples of the radical polymerizable crosslinking agent include those having two or more unsaturated bonds such as divinylbenzene, divinylnaphthalene, divinyl ether, diethylene glycol methacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, and diallyl phthalate.

(3) Acid group-containing radical polymerizable monomer:
Examples of the acidic group-containing radical polymerizable monomer include α, β-ethylenically unsaturated compounds having a carboxyl group (—COOH) and α, β-ethylenically unsaturated compounds having a sulfonic acid group (—S ₃ OH). Can be mentioned.

  Examples of the α, β-ethylenically unsaturated compound having a carboxyl group (carboxyl group-containing radical polymerizable monomer) include, for example, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, cinnamic acid, and maleic acid mono Examples thereof include butyl esters, maleic acid monooctyl esters, and metal salts thereof such as sodium (Na) and zinc (Zn).

  Examples of the α, β-ethylenically unsaturated compound having a sulfonic acid group include sulfonated styrene and a sodium salt thereof, allylsulfosuccinic acid, octyl allylsulfosuccinate, and a sodium salt thereof.

A known chain transfer agent can be used for the purpose of adjusting the molecular weight of the resin particles.
The chain transfer agent is not particularly limited, for example, a mercapto compound having a mercapto group such as octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, etc. is used. A mercapto compound having a short molecular chain is preferably used because a toner with a sharpness is obtained and storage stability, fixing strength and offset resistance are excellent.
Specifically, preferable examples of the chain transfer agent include propyl thioglycolate, octyl thioglycolate, mercaptopropionic acid n-octyl ester, and octyl mercaptan.

In the present invention, any radical polymerization initiator may be used as long as it is water-soluble. For example, persulfates (potassium persulfate, ammonium persulfate, etc.), azo compounds (4,4′-azobis-4-cyanovaleric acid and its salts, 2,2′-azobis (2-amidinopropane) salts, etc.), A peroxide compound etc. are mentioned.
Furthermore, the radical polymerization initiator can be combined with a reducing agent as necessary to form a redox initiator. By using a redox initiator, the polymerization activity is increased, so that the polymerization temperature can be lowered and the polymerization time can be further shortened.
The polymerization temperature may be any temperature as long as it is equal to or higher than the lowest radical generation temperature of the polymerization initiator, and for example, a range of 50 ° C to 90 ° C is used. However, in the case of using a polymerization initiator that starts at room temperature, for example, a hydrogen peroxide-reducing agent (ascorbic acid or the like) combination, it is possible to polymerize at room temperature or higher.

  In order to perform polymerization using the above-mentioned radical polymerizable monomer, it is preferable to disperse oil droplets in an aqueous medium using a surfactant. Although it does not specifically limit as surfactant which can be used here, The following ionic surfactant can be mentioned as an example of a suitable thing.

  Examples of ionic surfactants include sulfonates (sodium dodecylbenzenesulfonate, sodium arylalkylpolyethersulfonate, 3,3-disulfonediphenylurea-4,4-diazo-bis-amino-8-naphthol-6 Sodium sulfonate, ortho-carboxybenzene-azo-dimethylaniline, 2,2,5,5-tetramethyl-triphenylmethane-4,4-diazo-bis-β-naphthol-6-sodium sulfonate, etc.), sulfuric acid Ester salts (sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, etc.), fatty acid salts (sodium oleate, sodium laurate, sodium caprate, sodium caprylate, sodium caproate, potassium stearate) Beam, calcium oleate and the like).

  Nonionic surfactants can also be used. Specifically, polyethylene oxide, polypropylene oxide, combination of polypropylene oxide and polyethylene oxide, ester of polyethylene glycol and higher fatty acid, alkylphenol polyethylene oxide, ester of higher fatty acid and polyethylene glycol, ester of higher fatty acid and polypropylene oxide, sorbitan ester Etc.

  The toner of the present invention contains resin particles (hereinafter referred to as “release agent”) containing a crystalline substance having a release property which is a fixing property improving agent (hereinafter also simply referred to as “release agent”) as necessary. Also referred to as “resin particles containing an agent”).

  The release agent is not particularly limited, and polyolefin waxes such as low molecular weight polypropylene and low molecular weight polyethylene, paraffin wax, Fischer-Trosch wax, ester wax and the like can be used.

  As the colorant, for example, magnetic powders such as magnetite and ferrite, inorganic pigments, organic pigments, dyes and the like can be used, and conventionally known inorganic pigments, organic pigments and dyes can be used.

Examples of the black inorganic pigment include carbon black such as furnace black, channel black, acetylene black, thermal black, and lamp black.
These inorganic pigments can be used alone or in combination of two or more as required.

  Examples of organic pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of organic pigments for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 180, C.I. I. Pigment yellow 185, C.I. I. Pigment yellow 155, C.I. I. And CI Pigment Yellow 156.

  Examples of organic pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  Examples of the dye include C.I. I. Solvent Red 1, 49, 52, 58, 63, 111, 122, C.I. I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, C.I. I. Solvent Blue 25, 36, 60, 70, 93, 95, etc. can be used, and mixtures thereof can also be used.

  These organic pigments and dyes can be used alone or in combination of two or more as required.

  A colorant whose surface is modified can also be used. As the surface modifier, conventionally known ones can be used, and specifically, silane coupling agents, titanium coupling agents, aluminum coupling agents and the like can be preferably used.

As an example of a method for producing the toner of the present invention by the resin particle association method,
(1) a dissolution step of dissolving a release agent in a polymerizable monomer to prepare a monomer solution;
(2) A dispersion step of dispersing the obtained monomer solution in an aqueous medium,
(3) a polymerization step of preparing a dispersion (latex) of resin particles containing a release agent by polymerizing an aqueous dispersion of the resulting monomer solution;
(4) a salting-out / fusing step in which toner particles are obtained by salting out / fusing the obtained resin particles and the colorant particles in an aqueous medium;
(5) A filtration / washing step of filtering out the obtained toner particles from an aqueous medium and washing away the surfactant from the toner particles.
(6) Consists of a drying process of the washed toner particles,
(7) An external additive adding step of adding an external additive to the dried toner particles may be included.

  In such a toner production method, the volume median diameter of the obtained toner is controlled by adjusting the “time from the addition of the aggregating agent until the growth of the associated particles stops” in the salting-out / fusion process. Is possible.

  For example, if the time from when the flocculant is added to when the growth of the associated particles is stopped is set longer, the particle size of the toner becomes larger. On the other hand, if the time is set shorter, the particle size of the toner becomes smaller.

(1) dissolution step;
The method for dissolving the release agent in the polymerizable monomer is not particularly limited.
An oil-soluble polymerization initiator and other oil-soluble components can also be added to the monomer solution.

(2) dispersion step;
The method of dispersing the monomer solution in the aqueous medium is not particularly limited, but a method of dispersing by mechanical energy is preferable, and in particular, a surfactant having a concentration equal to or lower than the critical micelle concentration is dissolved. In the aqueous medium, it is preferable to disperse the monomer solution in oil droplets using mechanical energy, which is an essential aspect in the mini-emulsion method. The disperser for dispersing oil droplets by mechanical energy is not particularly limited, and examples thereof include “CLEARMIX”, ultrasonic disperser, mechanical homogenizer, Manton Gorin and pressure homogenizer. Can do. The dispersed particle diameter is 10 to 1000 nm, preferably 30 to 300 nm.

(3) polymerization step;
In the polymerization step, a granulation polymerization method such as an emulsion polymerization method, a suspension polymerization method, or a seed polymerization method can be basically employed. As an example of a preferable polymerization method, a mini-emulsion method can be mentioned. Moreover, in the polymerization step, to obtain composite resin particles formed by a resin having different molecular weight distribution by performing the polymerization reaction in multiple stages, a molecular weight gradient is formed toward the surface layer of the particles, It is preferable to use a so-called multistage polymerization method.

Here, the “composite resin particle” means one or two or more coating layers made of a resin having a different molecular weight and / or composition from the resin forming the core particle so as to cover the surface of the core particle made of the resin. It refers to resin particles having a multilayer structure formed.
“Multi-stage polymerization method” means that a monomer (n + 1) is polymerized (n + 1 stage) in the presence of resin particles (n) obtained by polymerizing monomer (n) (n stage). And a coating layer (n + 1) comprising a polymer of the monomer (n + 1) (a resin having a different dispersion and / or composition from the constituent resin of the resin particle (n)) on the surface of the resin particle (n). For example, when the resin particle (n) is a core particle (n = 1), the “two-stage polymerization method” is used, and when the resin particle (n) is a composite resin particle (n ≧ 2) is a multi-stage polymerization method of three or more stages.

  As a preferred embodiment of the multistage polymerization method, a central part (core) formed from a high molecular weight resin, an intermediate layer formed from an intermediate molecular weight resin containing a release agent, and an outer layer (shell) formed from a low molecular weight resin And so-called three-stage polymerization method.

  When adopting the multistage polymerization method, the proportion of acidic group-containing radically polymerizable monomer in the outermost layer, particularly the carboxyl group-containing radically polymerizable monomer, is based on the total monomer components constituting the outermost layer. The use ratio of the acidic group-containing radical polymerizable monomer in the resin particle association method may be within the same range. When the acid group-containing radical polymerizable monomer, especially the carboxyl group-containing radical polymerizable monomer, is distributed more as a monomer component constituting the outermost layer, the acid value of the toner can be increased more effectively. Can do.

(4) Salting out / fusion process;
In the salting-out / fusion step, a dispersion of colorant particles is added to the dispersion of resin particles obtained by the polymerization step, and the resin particles and the colorant particles are salted out in an aqueous medium. Fuse. In the salting-out / fusion step, internal additive particles such as charge control agents (fine particles having a mass average primary particle diameter of about 10 to 1000 nm) and the like can be fused together with the resin particles and the colorant particles.

  Here, “salting out / fusion” means that salting out (aggregation of particles) and fusing (disappearance of the interface between particles) occur simultaneously, or act of causing salting out and fusing at the same time. Say. In order to perform salting-out and fusion at the same time, it is necessary to agglomerate particles (resin particles, colorant particles) under a temperature condition equal to or higher than the glass transition temperature (Tg) of the resin constituting the resin particles.

  In the present specification, the “aqueous medium” refers to a material whose main component (50% by mass or more) is water. Examples of components other than water include organic solvents that dissolve in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran. Among these, alcohol-based organic solvents such as methanol, ethanol, isopropanol, and butanol, which are organic solvents that do not dissolve the resin, are particularly preferable.

  The dispersion of resin particles used in the salting-out / fusion process has a CV value (standard deviation in terms of average particle diameter) indicating that the dispersion of the mass average primary particle diameter, which is the particle diameter of the resin particles, indicates the spread of the particle size distribution. The coefficient of variation) is preferably 20% or less. In order to obtain such dispersibility, for example, a mechanical disperser “CLEAMIX” (manufactured by M Technique Co., Ltd.), an ultrasonic disperser, a mechanical homogenizer, a manton gorin, a pressure homogenizer, or the like is used. It is possible to use a technique in which energy is made uniform by mechanical dispersion by a machine and repeatedly dispersed. In addition, the mass average primary particle diameter concerning a resin particle is a particle diameter of the resin particle measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.).

  A dispersion of colorant particles used in the salting out / fusion process can be prepared by dispersing the colorant in an aqueous medium. The dispersion treatment of the colorant is performed in a state where the surfactant concentration is set to a critical micelle concentration (CMC) or more in water. The disperser used for the dispersion treatment of the colorant is not particularly limited, but preferably a shearing force is generated by a screen that forms the stirring chamber and a rotor that rotates at high speed in the stirring chamber, and the action of the shearing force (further, , Collision force, pressure fluctuations, cavitation, potential core action) to obtain fine particles by finely dispersing the colorant in an aqueous medium containing a surfactant. Specifically, the mechanical disperser “CLEAMIX (M Technique Co., Ltd.), ultrasonic dispersers, mechanical homogenizers, pressure dispersers such as Manton Gorin and pressure homogenizers, sand grinders, medium type dispersers such as Getzmann mills and diamond fine mills. . Moreover, as a surfactant used, the same thing as the above-mentioned surfactant can be mentioned.

  The mass average particle diameter (dispersed particle diameter) of the colorant particles is not particularly limited, and is usually 30 to 500 nm, preferably 50 to 300 nm. The mass average particle diameter of the colorant fine particles is measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.).

  In the salting-out / fusion method, a salting-out agent composed of a metal salt or the like is added as an aggregating agent having a critical aggregation concentration or more to an aqueous medium in which resin particles and colorant particles are present, and then the resin particles This is a step of performing fusion at the same time as salting-out proceeds by heating above the glass transition point. In this step, an organic solvent that is infinitely soluble in water may be added.

Examples of the aggregating agent include metal salts composed of alkali metals (monovalent metals) such as sodium, potassium and lithium, alkaline earths such as calcium and magnesium, metal salts composed of divalent metals such as manganese and copper, and iron. And metal salts made of trivalent metals such as aluminum, etc. Compared with metal salts made of monovalent metals, metal salts made of divalent and trivalent metals have a critical coagulation concentration (coagulation value or Since the coagulation point is small, it is preferable to use a metal salt made of a divalent or trivalent metal.
These metal salts can be used alone or in combination of two or more.

  Specific examples of the flocculant include sodium chloride, potassium chloride, lithium chloride, calcium chloride, zinc chloride, copper sulfate, magnesium sulfate, manganese sulfate, aluminum chloride, and iron chloride.

  The addition amount of the flocculant may be not less than the critical aggregation concentration, but is preferably 1.2 times or more, more preferably 1.5 times or more the critical aggregation concentration.

  Here, the “critical flocculation concentration” is an index relating to the stability of the aqueous dispersion, and indicates a concentration at which flocculation occurs when a flocculant is added. This critical aggregation concentration varies greatly depending on the emulsified components and the dispersant itself. For example, a detailed critical aggregation concentration can be obtained by the method described in Seizo Okamura et al., “Polymer Chemistry 17,601 (1960) edited by Japan Society of Polymer Science”. As another method, a desired salt is added to the target particle dispersion at a different concentration, the ξ (zeta) potential of the dispersion is measured, and the salt concentration at which this value changes is defined as the critical aggregation concentration. You can ask for it.

  Furthermore, examples of the organic solvent that is infinitely soluble in water include methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, glycerin, acetone and the like, but methanol, ethanol, 1-propanol having 3 or less carbon atoms. 2-propanol is preferable, and 2-propanol is particularly preferable.

In the salting-out / fusion process, a suitable temperature range for salting-out / fusion is (Tg + 10 ° C.) to (Tg + 50 ° C.), where Tg is the glass transition temperature of the resin constituting the resin particles, and particularly preferably. (Tg + 15 ° C.) to (Tg + 40 ° C.). Note that the fusion can be effectively performed by adding an organic solvent that is infinitely soluble in water to the salting out / fusion process system.
In the present invention, the separation of the toner particles obtained by salting out / fusing the resin particles and the colorant particles in the aqueous medium from the aqueous medium is performed by the surfactant present in the aqueous medium. It is preferably performed at a temperature equal to or higher than the craft point, and more preferably performed in a temperature range from the craft point to (craft point + 20 ° C). “Craft point” is a temperature at which an aqueous solution containing a surfactant starts to become cloudy, and is an aqueous medium or surfactant used in a salting out, agglomerating and fusing step (salting out / fusing step in the present invention). Measured by preparing a solution with the actual amount of flocculant added to the solution, storing the resulting solution at 1 ° C. for 5 days, and then gradually heating the solution until it becomes clear while stirring. Is done.

  In the salting-out / fusion step, after the dispersion of the resin particles and the colorant particles reaches a temperature equal to or higher than the glass transition temperature, the temperature of the dispersion is maintained for a certain period of time. It is important to continue wearing. As a result, toner particle growth (aggregation of resin particles and colorant particles) and fusion (disappearance of the interface between the particles) can be effectively advanced, and the durability of the finally obtained toner can be improved. Can be improved.

  Furthermore, after the growth of the associated particles is stopped, the aging treatment is preferably performed by continuing the fusion by heating. In this aging treatment, the temperature of the system in which the growth of the associated particles is stopped is maintained at a temperature 10 to 40 ° C. higher than the glass transition temperature of the resin constituting the outermost layer of the associated particles, and the stirring is continued at a constant strength. This aging treatment can enhance the adhesion of the resin particles between the toners.

(5) Filtration and washing process;
In this filtration / washing step, a filtration treatment for filtering the toner particles from the dispersion of toner particles obtained in the above step, and a surfactant or salt from the filtered toner particles (cake-like aggregate). A cleaning process for removing deposits such as a depositing agent is performed.
Examples of the filtration method include a centrifugal separation method, a vacuum filtration method using Nutsche and the like, and a filtration method using a filter press and the like, and are not particularly limited.

(6) drying step;
This step is a step of drying the washed toner particles.
Examples of dryers used in this process include spray dryers, vacuum freeze dryers, vacuum dryers, etc., stationary shelf dryers, mobile shelf dryers, fluidized bed dryers, rotary dryers It is preferable to use a stirring dryer or the like.
The water content of the dried toner particles is preferably 5% by mass or less, and more preferably 2% by mass or less.

  In addition, when the toner particles that have been dried are aggregated due to weak interparticle attraction, the aggregate may be crushed. Here, as the crushing treatment apparatus, a mechanical crushing apparatus such as a jet mill, a Henschel mixer, a coffee mill, or a food processor can be used.

(7) External additive addition step;
This step is a step of adding an external additive to the dried toner particles. Examples of the apparatus used for adding the external additive include various known mixing apparatuses such as a Turbuler mixer, a Henschel mixer, a Nauter mixer, and a V-type mixer.

The toner of the present invention may be a toner added with materials capable of imparting various functions as a toner material in addition to the colorant and the release agent. Specific examples include charge control agents. These components can be added at the same time as the resin particles and the colorant particles in the above-mentioned fusing step, and can be added by various methods such as a method of inclusion in the toner and a method of adding to the resin particles themselves.
Similarly, various known charge control agents and those that can be dispersed in water can be used. Specific examples include nigrosine dyes, naphthenic acid or higher fatty acid metal salts, alkoxylated amines, quaternary ammonium salt compounds, azo metal complexes, salicylic acid metal salts or metal complexes thereof.

・ Emulsion polymerization method The emulsion polymerization method is a water-soluble radical polymerization of a polymerization composition containing an acidic group-free radical polymerizable monomer, an acidic group-containing radical polymerizable monomer, and, if necessary, a crosslinkable monomer. This is a method of dispersing in an aqueous medium containing an initiator to obtain droplet particles having the same size as a predetermined toner particle diameter and polymerizing them to obtain a toner. The polymerization composition usually contains a colorant, and may further contain a release agent and a charge control agent as necessary. In the emulsion polymerization method, radical polymerizable monomer, acidic group-containing radical polymerizable monomer, crosslinkable monomer, water-soluble radical polymerization initiator, aqueous medium, colorant, charge control agent, etc. The same as in can be used.

  In the emulsion polymerization method, the acid value of the toner is the same as in the resin particle association method. The acid group-containing radical polymerizable monomer, particularly the carboxyl group-containing radical polymerizable monomer, with respect to all monomer components constituting the toner. It is controllable by adjusting the ratio. In the emulsion polymerization method, the ratio of the acidic group-containing radical polymerizable monomer, particularly the carboxyl group-containing radical polymerizable monomer, is usually 1% by weight or more, preferably 1% by weight or more based on the total monomer components constituting the toner. It is 2 to 10% by weight, more preferably 3 to 8% by weight.

Suspension polymerization The suspension polymerization method includes an acid group-free radical polymerizable monomer, an acid group-containing radical polymerizable monomer, an oil-soluble radical polymerization initiator, and a crosslinkable monomer as required. This is a method in which a polymer composition is dispersed in an aqueous medium to obtain droplet particles having the same size as a predetermined toner particle diameter, and this is polymerized to obtain a toner. The polymerization composition usually contains a colorant, and may further contain a release agent and a charge control agent as necessary. In the suspension polymerization method, the radical polymerizable monomer, the acidic group-containing radical polymerizable monomer, the crosslinkable monomer, the aqueous medium, the colorant, the charge control agent, and the like are the same as those in the resin particle association method. It can be used. Examples of the oil-soluble radical polymerization initiator include benzoyl peroxide, lauroyl peroxide, azobisisobutyronitrile, azobisvaleroylnitrile, and the like. Examples of water-soluble radical polymerization initiators include persulfates (potassium persulfate, ammonium persulfate, etc.), azo compounds (4,4′-azobis-4-cyanovaleric acid and its salts, 2,2′-azobis ( 2-amidinopropane) dihydrochloride and the like), peroxide compounds and the like can be used.

  In the suspension polymerization method, the acid value of the toner is the same as in the resin particle association method. The acid group-containing radical polymerizable monomer, particularly the carboxyl group-containing radical polymerizable monomer, with respect to all monomer components constituting the toner. It can be controlled by adjusting the proportion of the body. In the suspension polymerization method, the proportion of the acidic group-containing radical polymerizable monomer, particularly the carboxyl group-containing radical polymerizable monomer, is usually 1% by weight or more, preferably 1% by weight or more based on the total monomer components constituting the toner. Is from 2 to 10% by weight, more preferably from 3 to 8% by weight.

・ Emulsion dispersion method In the emulsion dispersion method, a resin solution in which a toner binder resin is dissolved in a water-insoluble organic solvent is dispersed in an aqueous medium to obtain droplet particles having the same size as a predetermined toner particle diameter. In this method, the toner is obtained by heating this to remove the water-insoluble organic solvent. The resin solution usually contains a colorant, and may further contain a release agent and a charge control agent as necessary. In the emulsion dispersion method, the same aqueous medium, colorant, charge control agent, and the like as in the resin particle association method can be used.

  As the binder resin, known resins that are conventionally used as binder resins for toners can be used, and are not particularly limited as long as they are soluble in a water-insoluble organic solvent. For example, polyester resins, Examples include polyacrylic resins. The polyester resin is not particularly limited, but among them, those containing etherified diphenols as an alcohol component and aromatic dicarboxylic acids as an acid component are preferable. Examples of the polyester resin include urethane-modified polyester resins obtained by reacting a polyester resin with isocyanate, and acrylic-modified polyester resins.

  The water-insoluble organic solvent is not particularly limited as long as it is a solvent that can dissolve or disperse the toner material, and can be appropriately selected according to the purpose. For example, the boiling point is less than 150 ° C. in terms of ease of removal. Volatile ones are preferred, for example, toluene, xylene, benzene, carbon tetrachloride, methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene, chloroform, monochlorobenzene, dichloroethylidene, methyl acetate, acetic acid Examples include ethyl, methyl ethyl ketone, and methyl isobutyl ketone. Among these, toluene, xylene, benzene, methylene chloride, 1,2-dichloroethane, chloroform, carbon tetrachloride and the like are preferable, and ethyl acetate is particularly preferable. These may be used individually by 1 type and may use 2 or more types together. If it can melt | dissolve binder resin, it will not restrict | limit, Preferably a thing with a comparatively low boiling point which is easy to be removed at a subsequent heating process is used.

  In the emulsion dispersion method, the acid value of the toner can be controlled by adjusting the acid value of the binder resin. Increasing the acid value of the binder resin increases the acid value of the toner. On the other hand, when the acid value of the binder resin is lowered, the acid value of the toner is lowered. In the emulsification dispersion method, a binder resin having an acid value within the same range as the desired toner acid value is usually used. As the binder resin, two or more kinds of resins having different acid values may be used. In this case, the sum of the acid values according to the use ratio thereof may be in the same range as the toner acid value. For example, when a binder resin xg having an acid value of a (KOH mg / g) and a binder resin yg having an acid value of b (KOH mg / g) are used in combination, “a × x / (x + y) + b × y / (x + y)” Is within the same range as the toner acid value.

  To the toner of the present invention that can be produced by various methods as described above, so-called external additives can be added and used for the purpose of improving fluidity, chargeability and cleaning property. These external additives are not particularly limited, and various inorganic fine particles, organic fine particles, and lubricants can be used, but external additives composed of inorganic fine particles having an average primary particle diameter of 30 to 500 nm are used. preferable.

[Preparation Example 1 of Resin Particles]
(1) Formation of core particles (first stage polymerization):
In a 5000 ml separable flask equipped with a stirrer, temperature sensor, condenser, and nitrogen inlet, the following formula:
C ₁₀ H ₂₁ (OCH ₂ CH ₂ ) ₂ OSO ₃ Na
A surfactant solution (aqueous medium) in which 7.08 g of an anionic surfactant represented by the following formula (hereinafter also referred to as “anionic surfactant (1)”) is dissolved in 3010 g of ion-exchanged water is charged, and nitrogen is added. The internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under an air stream.
To this surfactant solution, an initiator solution prepared by dissolving 9.2 g of a polymerization initiator (potassium persulfate: KPS) in 200 g of ion-exchanged water was added, the temperature was adjusted to 75 ° C., and then 70.1 g of styrene, n -A monomer mixture composed of 19.9 g of butyl acrylate and 10.9 g of methacrylic acid was added dropwise over 1 hour, and this system was heated and stirred at 75 ° C for 2 hours, thereby allowing a polymerization reaction (first-stage polymerization). Reaction), a dispersion of resin particles made of a polymer resin (hereinafter also referred to as “latex (1H)”) was prepared.

で表される化合物（以下、「例示化合物（Ｗ）」という。）９８．０ｇを、スチレン１０５．６ｇ、ｎ−ブチルアクリレート３０．０ｇ、メタクリル酸６．２ｇおよびｎ−オクチル−３−メルカプトプロピオン酸エステル５．６ｇからなる単量体混合液に添加し、９０℃に加温し溶解させて単量体溶液を調製した。
一方、撹拌装置を取り付けたフラスコに、アニオン系界面活性剤（１）１．６ｇをイオン交換水２７００ｍｌに溶解させた界面活性剤溶液（水系媒体）を仕込み、内温を９８℃に昇温させ、第１段重合によって得られたラテックス（１Ｈ）を、固形分換算で２８ｇ添加した。 (2) Formation of intermediate layer (second stage polymerization):
In a flask equipped with a stirrer, the following formula:

98.0 g of a compound represented by the formula (hereinafter referred to as “Exemplary Compound (W)”), 105.6 g of styrene, 30.0 g of n-butyl acrylate, 6.2 g of methacrylic acid, and n-octyl-3-mercaptopropion. It added to the monomer liquid mixture which consists of 5.6 g of acid ester, heated at 90 degreeC, and it was made to melt | dissolve, and the monomer solution was prepared.
On the other hand, a surfactant solution (aqueous medium) in which 1.6 g of anionic surfactant (1) was dissolved in 2700 ml of ion-exchanged water was charged into a flask equipped with a stirrer, and the internal temperature was raised to 98 ° C. The latex (1H) obtained by the first stage polymerization was added in an amount of 28 g in terms of solid content.

Next, the monomer solution was added to the surfactant solution containing the latex (1H) by a mechanical disperser “CLEARMIX” (manufactured by M Technique Co., Ltd.) having a circulation path. An emulsified liquid in which emulsified particles (oil droplets) having a uniform dispersed particle size were dispersed was prepared by mixing and dispersing over time.
Next, an initiator solution prepared by dissolving 5.1 g of a polymerization initiator (KPS) in 240 ml of ion exchange water and 750 ml of ion exchange water are added to this dispersion (emulsion). A structure in which the surface of resin particles made of a high molecular weight resin is coated with an intermediate molecular weight resin containing the exemplary compound (W) by performing a polymerization reaction (reaction related to the second stage polymerization) by heating and stirring for 12 hours A dispersion of composite resin particles (hereinafter also referred to as “latex (1HM)”) was prepared.
In addition, when the obtained latex (1HM) was dried and the particles constituting the latex (1HM) were observed with a scanning electron microscope, particles containing the exemplary compound (W) as a main component in addition to the composite resin particles (Particle diameter 400-1000 nm) was confirmed.

(3) Formation of outer layer (third stage polymerization):
An initiator solution in which 7.4 g of a polymerization initiator (KPS) was dissolved in 200 ml of ion-exchanged water was added to a flask equipped with a stirrer charged with the total amount of latex (1HM) obtained, and the temperature was set to 80 ° C. In the state kept in the above, a monomer mixed solution composed of 300 g of styrene, 95 g of n-butyl acrylate, 15.3 g of methacrylic acid and 10.4 g of n-octyl-3-mercaptopropionic acid ester was dropped over 1 hour. The system is heated and stirred at 80 ° C. for 2 hours to conduct a polymerization reaction (reaction according to the third stage polymerization), and then the system is cooled to 28 ° C. Is coated with an intermediate molecular weight resin, and the surface of the intermediate layer made of the intermediate molecular weight resin is coated with a low molecular weight resin. Dispersion latex of the resin particles (hereinafter, also referred to as "Latex (1HML)".) Was prepared.
The composite resin particles constituting the obtained latex (1HML) have a weight average particle diameter of 122 nm, and the resins constituting the composite resin particles are 138,000, 80,000 and 13,000. It was confirmed to have three peak molecular weights.

[Preparation Example 1 of Colorant Dispersion]
Anionic surfactant (1) 59.0 g was stirred and dissolved in 1600 ml of ion-exchanged water. While stirring this solution, 420.0 g of carbon black “Regal 330R” (manufactured by Cabot) was gradually added as a colorant, and then a mechanical disperser “Claremix” (manufactured by M Technique Co., Ltd.) was added. A dispersion liquid of colorant particles (hereinafter referred to as “colorant dispersion liquid (1)”) was prepared by using the dispersion treatment.
When the particle diameter of the colorant particles in the obtained colorant dispersion (1) was measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.), the weight average particle diameter was 89 nm. there were.

[Production Example of Toner Particles K1]
In a reaction vessel (four-necked flask) equipped with a temperature sensor, a cooling pipe, a nitrogen introducing device, and a stirring device, 420.7 g of latex (1HML) (solid content conversion), 900 g of ion-exchanged water, and a colorant dispersion ( 1) After charging 166 g and adjusting the internal temperature to 30 ° C., 5N aqueous sodium hydroxide solution was added to the dispersion liquid mixture to adjust the pH to 10.0. Next, an aqueous solution in which 12.1 g of magnesium chloride hexahydrate was dissolved in 1000 ml of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, the temperature was started to rise, and the temperature of this association system was raised to 90 ° C. over 10 minutes.

In this state, the particle size of the associated particles was measured with “Coulter Counter TA-II”, and when the volume median diameter reached 6.0 μm, an aqueous solution in which 80.4 g of sodium chloride was dissolved in 1000 ml of ion-exchanged water was added. Then, the particle growth is stopped, and further, the mixture is heated and stirred at a liquid temperature of 95 ° C. for 10 hours to continue the fusing process, and then the system is cooled to 30 ° C. Was added to adjust the pH to 2.0, and stirring was stopped.
The produced particles were filtered, washed repeatedly with ion exchange water at 45 ° C., and then dried with hot air at 40 ° C. to obtain toner particles (hereinafter also referred to as “toner particles (K1)”).

[Production Examples of Toner Particles K2 to K6]
Latex was obtained by the same method as the above latex (1HML) except that the amount of monomer used during outer layer formation was changed as shown in Table 1. Next, toner particles (hereinafter also referred to as “toner particles (K2) to (K6)”) were obtained by the same method as that for the toner particles (K1) except that the obtained latex was used.

[Toner Particle Production Example K7]
Polyester resin (UXK-120P; manufactured by Kao, acid value 32 KOH mg / g) 45 parts by weight Polyester resin (Byron 200; manufactured by Toyobo, acid value <2 KOH mg / g) 55 parts by weight Carbon black 6 parts by weight (Raven 1255: PH 3.5, (Columbian Carbon)
Oxidized low molecular weight polypropylene (Viscol TS-200: manufactured by Sanyo Kasei Co., Ltd.) 3 parts by weight The above materials were sufficiently mixed with a Henschel mixer, then kneaded using a biaxial extrusion kneader, the kneaded product was allowed to cool, and then feathered Coarse pulverization was performed using a mill, and further pulverization was performed using a jet mill. Thereafter, the mixture was dispersed by wind to obtain toner particles K7 having an acid value of 24.3 and a volume median diameter of 8.0 μm.

[Example of toner production]
In each of 100 parts by mass of toner particles (K1) to (K7), 1.0 part by mass of hydrophobic silica (number average primary particle diameter: 12 nm) and hydrophobic titanium oxide (number average primary particle diameter: 25 nm) 2 parts by mass were added and mixed using a Henschel mixer to obtain toners (K1) to (K7).
The shape and particle size of the toner particles constituting these toners did not change depending on the addition of an external additive. All the toners had negative polarity in charge polarity.

  The volume median diameter and acid value of the toner were measured by the methods described above.

<Example / comparative example>
The developing device of the printer (Magicor 5430DL; manufactured by Konica Minolta) was modified to the configuration shown in FIG. The configuration not specified is the same as that of the printer before remodeling. The toner was filled only in the image forming unit 10Bk. The toner and the brush roller, and the voltage applied to the brush roller in the printer used were set as shown in Table 2 or Table 3. The following conditions are common.
Electrostatic latent image formed on the image carrier; background portion potential (V1) -650V, image portion potential (V2) -100V
Rotational peripheral speed (Rv1) of image carrier: 140 mm / sec
(Primary) DC voltage applied to the transfer device 60; 1000V
DC voltage applied to secondary transfer device 12; 1800) V
Capture voltage timing;
Charging, development, and transfer processes are performed sequentially during printing. When the transfer power supply is turned on, the application of the capture voltage starts, and when the print ends and the rotation of the image carrier stops, the capture voltage Application was stopped.
Waveform: Square wave AC component and DC component are superimposed and applied. The negative application time of the AC component is 5% of the AC1 period, and the plus application time is 9 of the AC period.
The asymmetric waveform was 5%.
Timing of discharge voltage;
10 seconds of discharge was performed after every 300 prints.
Waveform: Applied by superimposing AC and DC components of a rectangular wave Both negative application time and positive application time of AC component are symmetrical waveforms of 50% of AC cycle.

Recovery bias voltage for developer carrier: DC component 100 V, AC component (frequency: 1500 Hz, Vpp 1500 V, waveform: rectangular wave AC component and DC component are superimposed and applied, both negative application time and positive application time of AC component Is a symmetrical waveform of 50% of the AC cycle. Timing of recovery bias voltage: Same as discharge voltage Surface potential of image carrier when discharging toner; -20V

(Brush roller manufacturing method)
The brush roller used in each Example / Comparative Example was manufactured by implanting a linear member formed by dispersing carbon black in the resin described in Table 2 or Table 3 around the rotation shaft. Various conditions of the brush roller are as shown in Table 2 or Table 3.

-Image noise due to toner spills 60,000 image charts with an image area ratio of 5% are printed, and black images appearing randomly at the initial stage (at the time of printing 5 sheets) and at the end of life (at the time of printing 60,000 sheets). evaluated. Black spots that appear at random are black spots that do not appear at the same positions as the images formed before and after that, and have no periodicity. Although the brush roller and the image carrier were used without replacing 60,000 sheets, the developing unit including the toner and the developing roller continued printing while being replaced every 6000 sheets.
○: There were no randomly appearing black spots;
Δ: Although there are a few black spots appearing randomly, it was within a practically acceptable range;
X: There were many black spots that appeared at random, and there was a problem in practical use.

-Density unevenness due to contamination of the charging device 60,000 image charts with an image area ratio of 5% are printed, and the images at the initial stage (at the time of printing 5 sheets) and at the end of life (at the time of printing 60,000 sheets) are visually observed. evaluated.
○: There was no density unevenness;
Δ: Although there was a slight density unevenness, it was within a practically acceptable range;
X: Many density unevennesses existed and there was a problem in practical use.

・ Image noise caused by exposure button Print 60,000 image charts with an image area ratio of 5%, visually observe the images at the initial stage (at the time of printing five sheets) and the endurance (at the time of printing 60,000 sheets), and cycle the image carrier The afterimage noise appearing in Fig. 1 was evaluated.
○: There was no afterimage noise;
Δ: Although there was a little afterimage noise, it was within a range where there was no practical problem;
X: Many afterimage noises existed and there was a problem in practical use.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus of the present invention. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus of the present invention. It is a figure explaining the operation | movement at the time of taking-in of this invention. It is a figure explaining the operation | movement at the time of discharge of this invention.

Explanation of symbols

10: 100: Image forming apparatus, 10Y, 10M, 10C, 10Bk: Image forming unit, 11: Transfer target (intermediate transfer belt), 12: Secondary transfer apparatus, 13: Belt cleaner, 14: Recording paper, 20: Image carrier, 30: charging device, 40: exposure device, 50: developing device, 60: transfer device, 70: brush roller.

Claims (2)

At least an image carrier, a charging device that charges the surface of the image carrier, an exposure device that forms an electrostatic latent image on the image carrier charged by the charging device, and an electrostatic latent image formed by the exposure device A developing device for applying toner to the toner to form a toner image, a transfer device for transferring the toner image formed by the developing device to a transfer target, and residual toner remaining on the image carrier after transfer by the transfer device. An image forming apparatus that includes a brush roller that temporarily captures and holds and discharges the toner onto the image carrier, and collects toner discharged from the brush roller onto the image carrier to a developing device,
Toner Ri acid value 5 KOH mg / g or more toner der manufactured by wet granulation,
The brush roller is formed by planting a linear member having a linearity of 0.5 to 6 denier and an electric resistance value of 10 ⁶ to 10 ⁹ Ω · cm around the rotation shaft, and the amount of biting of the linear member is 0.3 mm to 0.8 mm, and the rotational peripheral speed (mm / sec) of the brush roller is 0.8 to 2 times the rotational peripheral speed of the image carrier,
When the image is formed on the brush roller, the same polarity as the charging polarity of the toner, the DC component having an absolute value of 20 to 500 V, the frequency of 500 to 3000 Hz, and the Vpp (amplitude) of 500 to 2500 V is opposite to the toner in one cycle. An AC component having a voltage application time on the polarity side longer than the voltage application time on the same polarity side is applied, and in a range from the absolute value of 100 V to the polarity opposite to the charging polarity of the toner, except for the time of image formation, to an absolute value of 300 V with the same polarity. A DC component and an AC component of Vpp (amplitude) of 10 to 450 V at a frequency of 50 to 500 Hz are applied,
The image forming apparatus in which the image bearing member absolute value a the same polarity as the charging polarity of the toner by the charging device is characterized Rukoto is charged to a surface potential of 300～1000V. The image forming apparatus according to claim 1, wherein the toner has an acid value of 5 to 45 KOH mg / g.

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