JP2006084524A - Developing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve charging uniformity and toner jumping property and to obtain uniform image quality without filming even in continuous printing. <P>SOLUTION: A developing system of a toner having a positive charging external additive having 0.5 to 5% isolation rate is characterized in that: a supply bias with superposition of an AC component is applied between a developing roller and a supply roller; and the waveform of the supply roller surface voltage is different from that of the developing roller surface voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a development system using a toner having a positively chargeable external additive.

In a toner to which silica (SiO ₂ ) is externally added to impart fluidity and titanium oxide (TiO ₂ ) is externally added as a charge control agent, the liberation rate of Si atoms and Ti atoms is set to 0.5 to 10%. (Patent Document 1), the number release rate of titanium oxide is 1.0 to 50%, and the number release rate of silica is 0.01 to 4% so that the image density is not lowered and good images for a long time. Has been proposed (Patent Document 2).
Japanese Patent Laid-Open No. 11-258847 JP 2002-72544 A

  Even in the conventional techniques that define the free external additives shown in Patent Document 1 and Patent Document 2, the free external additives are particularly prone to agglomerate at specific parts of a developing device such as a developing roller, and electrostatically. Since it easily adheres to the surface of the developing roller and is difficult to reset, there is a problem that charging uniformity is disturbed due to filming of the developing roller and overcharging caused by the aggregate of free external additives.

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, and by using a free positively charged external additive, it is possible to improve charging uniformity and toner flying property, and to develop a uniform image quality without causing filming even in continuous printing. The purpose is to provide a system.
To this end, the present invention applies a supply bias in which an AC component is superimposed between a developing roller and a supply roller in a toner development system having a positively chargeable external additive having a liberation rate of 0.5 to 5%. The surface voltage waveform is different from the developing roller surface voltage waveform.
Further, the present invention is characterized in that the potential of the supply roller surface voltage waveform is higher than the potential of the development roller surface voltage waveform.
Further, the present invention is characterized by having a toner container that has an opening under the developing roller and the supply roller, receives a free external additive that is peeled off between the developing roller and the supply roller and freely falls.
Further, the present invention is characterized in that the free external additive that has fallen freely is circulated in the toner container and reused.
Further, the present invention is characterized in that the free external additive is 100 nm to 200 nm.
Further, the present invention is characterized in that the rotational movement direction of the developing roller and the supply roller peripheral surface in the nip portion is on the free fall side with respect to the opening.

  The present invention uses a toner having a positively chargeable external additive having a liberation rate of 0.5 to 5%, applies a supply bias in which an AC component is superimposed between the developing roller and the supply roller, and also supplies a supply roller surface voltage waveform. And the development roller surface voltage waveform, the microcarrier effect and spacer effect of external additives improve toner chargeability and toner flying performance, prevent filming, and improve image quality even in continuous printing. Can be made uniform.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an image forming apparatus and a developing apparatus using the toner manufactured in the present invention will be described. FIG. 1 is a cross-sectional view showing the overall configuration of an image forming apparatus taking a tandem type as an example. The image forming apparatus 1 includes a housing 3, a paper discharge tray 5 formed on the top of the housing 3, and a door that opens and closes. The housing 7 is provided with an exposure unit 9, an image forming unit 11, a blower fan 13, a transfer belt unit 15, and a paper feed unit 17. A paper transport unit 19 is provided.

  The image forming unit 11 includes four image forming stations 21 in which four developing devices that store different color toners can be set. The four image forming stations 21 are for yellow, magenta, cyan, and black developing devices, and are denoted by reference numerals 21Y, 21M, 21C, and 21K in the drawing. In each of the image forming stations 21Y, 21M, 21C, and 21K, a photosensitive drum 23, a corona charging unit 25 provided around the photosensitive drum 23, and the developing device 100 of the present invention are disposed.

  The transfer belt unit 15 is stretched between a driving roller 27 that is rotationally driven by a driving source (not shown), a driven roller 29 provided obliquely above the driving roller 27, a tension roller 31, and each of these rollers. The intermediate transfer belt 33 is circulated and driven in the counterclockwise direction X, and the cleaning means 34 is in contact with the surface of the intermediate transfer belt 33. The driven roller 29, the tension roller 31 and the intermediate transfer belt 33 are arranged side by side so as to be inclined with respect to the drive roller 27. When the intermediate transfer belt 33 is driven by this, the belt conveyance direction X is downward. The belt surface 35 is located on the lower side, and the belt surface 37 with the conveying direction facing upward is located on the upper side.

  The photosensitive drum 23 is pressed against the belt surface 35 along an arched line and is driven to rotate in the direction indicated by the arrow in FIG. By adjusting the position of the tension roller 31, the tension of the intermediate transfer belt 33, the curvature of the arch, and the like can be controlled.

The drive roller 27 also serves as a backup roller for the secondary transfer roller 39.
Further, on the peripheral surface of the drive roller 27, for example, a rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed, and the secondary transfer roller is grounded through a metal shaft. The secondary transfer bias conductive path supplied via the line 39 is configured. Further, the diameter of the drive roller 27 is smaller than the diameters of the driven roller 29 and the tension roller 31, so that the recording paper after the secondary transfer can be easily peeled by the elastic force of the recording paper itself. The driven roller 29 also functions as a backup roller for the cleaning means 34.

  The cleaning unit 34 is provided on the side of the belt surface 35 facing downward in the conveyance direction, and a cleaning blade 41 that removes toner remaining on the surface of the intermediate transfer belt 33 after the secondary transfer, and a toner conveyance path that conveys the collected toner. 42. The cleaning blade 41 is in contact with a portion where the intermediate transfer belt 33 is wound around the driven roller 29. Further, the primary transfer member 43 abuts the back surface of the intermediate transfer belt 33 at a position facing the photosensitive drum 23 of each of the image forming stations 21Y, 21M, 21C, and 21K, and a transfer bias is applied to the primary transfer member 43. It has come to be.

  The exposure unit 9 is provided in a space obliquely below the image forming unit 11, and a blower fan 13 is provided obliquely above the exposure unit 9. A paper feed unit 17 is provided below the exposure unit 9. In the exposure unit 9, a scanner means 49 comprising a polygon mirror motor 45 and a polygon mirror 47 is vertically arranged on the bottom. In addition, a single f-θ lens 51 and a reflection mirror 53 are provided in the optical path B, and a plurality of folds are provided above the reflection mirror 53 so that the scanning light paths of the respective colors fold in parallel with the photosensitive drum 23. A mirror 55 is provided.

  In the exposure unit 9, an image signal corresponding to each color is emitted from the polygon mirror 47 with a laser beam modulated and formed based on a common data clock frequency, and passes through the f-θ lens 51, the reflection mirror 53, and the folding mirror 55. The photosensitive drums 23 of the image forming stations 21Y, 21M, 21C and 21K are irradiated to form latent images. The optical path length from the polygon mirror 47 of the exposure unit 9 to the photosensitive drum 23 with respect to each image forming unit 11 is configured to be substantially the same, so that the scanning width of the light beam scanned in each optical path is also substantially the same. It is the same, and no special configuration is required for forming the image signal. Accordingly, the laser light source can be modulated and formed based on a common data clock frequency in spite of being modulated in accordance with images of different colors by different image signals. Color misregistration caused by a relative difference in the scanning direction can be prevented, and a simple and inexpensive color image forming apparatus can be configured.

The blower fan 13 functions as a cooling unit, guides air in the direction of the arrow, and performs a function of releasing heat from the exposure unit 9 and other heat generating units.
As a result, the temperature rise of the polygon mirror motor 45 can be suppressed, the deterioration of the image quality can be prevented, and the life of the polygon mirror motor 45 can be extended.

  The paper feed unit 17 includes a paper feed cassette 57 in which the recording media P are stacked, and a pickup roller 59 that feeds the recording media P from the paper feed cassette 57 one by one. The paper transport unit 19 includes a gate roller pair 61 that defines the timing of feeding the recording medium P to the secondary transfer unit, a secondary transfer roller 39 that is pressed against the drive roller 27 and the intermediate transfer belt 33, and a fixing unit 63. A pair of paper discharge rollers 65 and a duplex printing conveyance path 67.

  The fixing unit 63 includes a rotatable fixing roller pair 69 containing a heating element such as a halogen heater in at least one side, and at least one roller of the fixing roller pair 69 is pressed and biased to the other side to form a secondary sheet. The secondary image transferred to the recording medium is fixed to the recording medium at a predetermined temperature at a nip portion formed by the fixing roller pair 69. Is done.

  The developing device 100 used in the present invention is of a type that circulates and uses toner, and is set in each of the image forming stations 21Y, 21M, 21C, and 21K. The construction of these developing devices is basically the same.

  FIG. 2 is a cross-sectional view of the developing device 100. The developing device 100 includes a housing 103 in which a substantially cylindrical toner accommodating portion 101 is formed. A supply roller 105 and a developing roller 107 are provided to the housing 103. In a state in which the developing device 100 is set in the image forming station (see FIG. 1), the developing roller 107 is adjacent to the photosensitive drum 23 with a slight gap (for example, 100 to 300 μm). It has a function of developing the latent image formed on the photosensitive drum 23 with the toner supplied to the peripheral surface of the developing roller 107 while being rotationally driven in the direction opposite to the rotation direction (see the arrow in the drawing). Such a developing action applies a developing bias in which an AC voltage is superimposed on a DC voltage from a developing bias power source (not shown) to the developing roller 107, thereby causing an oscillating voltage to act between the developing roller and the photosensitive drum, This is performed by supplying toner from the developing roller 107 to the electrostatic latent image portion formed on the photosensitive drum 23. It is also possible to perform development by bringing the developing roller 107 into contact with the peripheral surface of the photosensitive drum 23.

  The supply roller 105 has a surface made of urethane sponge, and rotates and moves in the same direction as the peripheral surface of the developing roller 107 with the peripheral surface of the supply roller 105 in contact with the developing roller 107. A voltage waveform in which an AC voltage is superimposed on a DC voltage synchronized with the developing bias voltage applied to the developing roller 107 is also applied to the supply roller 105. As will be described in detail later, the voltage waveform is applied to the developing roller and the supply roller. Different voltage waveforms.

  A regulating blade 109 is pressed against the developing roller 107 so that it is always uniform over the longitudinal direction of the peripheral surface of the developing roller 107 by the action of the leaf spring member 111 and the elastic member 112 provided below the leaf spring member 111. In addition, an excessive amount of toner adhering to the peripheral surface of the developing roller 107 is scraped off so that a certain amount of toner is carried on the peripheral surface of the developing roller 107. The regulation blade 109 also has a function of appropriately charging the toner 113.

  The toner that has been scraped off naturally falls and is mixed into the toner 113 in the toner storage unit 101. At the same time, the positively charged positive external additive that has been peeled off between the developing roller and the supply roller spontaneously falls and falls. This is reused after being circulated in 101, which will be described in detail later. Further, the other end side of the seal member 115 whose one end is fixed to the housing 103 is in pressure contact with the upper surface of the developing roller 107, thereby preventing the toner 113 in the housing 103 from being scattered outside. Yes.

  An agitator 119 that rotates in the clockwise direction in FIG. 2 around the rotation shaft 117 is provided in the toner storage unit 101. The agitator 119 includes two arm members 121 extending in opposite directions around the rotation shaft 117, and each arm member 121 is set to a dimension slightly shorter than the diameter of a circle in the cross section of the toner containing portion 101. A stirring fin 123 extends from the tip of each arm member 121 in the direction opposite to the rotational direction of the agitator 119. The stirring fin 123 is composed of a flexible sheet member, and the tip side thereof is in pressure contact with the inner peripheral surface of the cylindrical toner accommodating portion 101 by an elastic force resulting from the flexibility. With such a configuration, when the agitator 119 rotates, the toner 113 existing in the region 125 between the inner peripheral surface of the toner containing portion 101 and the stirring fin 123 is scraped up by the stirring fin 123 so as to be described later. It can be conveyed on a member.

  The upper surface 114 of the toner 113 accommodated in the toner accommodating portion 101 is set to be lower than the location 127 where the regulating blade 109 is in contact with the peripheral surface of the developing roller 107. This is because if the amount of toner is so large that the regulating blade 109 is buried, the toner scraped off by the regulating blade 109 exists near the regulating blade, so that the circulation path to be returned to the toner storage unit 101 is obstructed. This is because the function of the regulating blade 109 scraping off excess toner from the developing roller 107 and regulating the amount of toner conveyed to the developing area and the function of appropriately charging the toner are hindered.

  In the present embodiment, the position of the upper surface 114 of the toner 113 accommodated in the toner accommodating portion 101 is more specifically lower than the lower end of the regulating blade 109, and the leaf spring member 111, the elastic member 112, and the like. The position of the intersection 128 is set as the upper limit. If the position of the upper surface 114 of the toner 113 in the toner containing portion 101 reaches above the intersection 128, the movement of the leaf spring member 111 may be restrained, which may result in failure to obtain an appropriate regulation pressure. As a result, there is a possibility that the “function of carrying a certain amount of toner on the peripheral surface of the developing roller 107” and the “function of properly charging the toner” may be hindered. However, as described above, by setting the upper limit of the upper surface 114 position of the toner 113 to the position of the intersection point 128, it is possible to eliminate the possibility of the functions being hindered.

  The toner between the portion 127 where the regulating blade 109 is in contact with the peripheral surface of the developing roller 107 and the upper surface 114 of the toner 113 accommodated in the toner accommodating portion 101 is inclined at an angle greater than the repose angle of the toner 113. A toner guide surface 129 that is inclined obliquely toward the upper surface 114 is formed as a part of the housing 103. The toner guide surface 129 has a function of guiding the toner 113 scraped off from the peripheral surface of the developing roller 107 by the regulating blade 109 to the toner containing portion 101 side.

  The toner 113 scraped off from the peripheral surface of the developing roller 107 by the regulating blade 109 does not necessarily have to be guided to the toner storage portion 101 by the toner guide surface 129, and the toner 113 scraped off is directly applied to the toner storage portion 101. It is good also as a structure which falls in the. The toner 113 scraped off from the circumferential surface of the developing roller 107 by the regulating blade 109 is guided to the toner accommodating portion 101 below the portion 127 where the regulating blade 109 is in contact with the circumferential surface of the developing roller 107 as described above. For this purpose, a toner guide space 131 is formed.

  A toner guide member 133 is provided above the toner container 101. The toner guide member 133 is provided at an end portion 134 on the side away from the supply roller 105, and has a scraper 135 formed at an acute angle for scraping off the toner 113 conveyed by the stirring fin 123, and more than the scraper 135. On the supply roller 105 side, the upper surface side is inclined at an angle equal to or greater than the repose angle of the toner 113 and is formed in a plane, and is formed on the downstream side of the flat conveyance portion 137, and the upper surface side forms a concave curved surface. And a contact portion 143 that is in contact with an appropriate linear pressure set on the peripheral surface of the supply roller 105 on the downstream side of the bending portion 141. The surface roughness of the toner guide member 133 including the flat conveying portion 137, the curved portion 141, and the contact portion 143 is formed to be less than the average particle diameter of the toner.

  Further, the presence of the contact portion 143 prevents the toner 113 adhering to the lower surface side of the supply roller 105 from dropping due to gravity, thereby preventing a decrease in image density due to a decrease in the amount of toner that can be supplied to the developing roller. be able to. In addition, a temporary toner storage portion 139 is formed between the curved portion 141 and the peripheral surface of the supply roller 105 so that the cross section narrows in a wedge shape. Here, the wedge-shaped cross section means that the entrance side is relatively large and becomes narrower in the toner traveling direction, and is sufficiently narrow so that the toner does not slip naturally on the front end side of the wedge.

  In the toner guide member 133 having such a shape, after the toner 113 conveyed by the stirring fins 123 is scraped off by the scraper 135, the toner 113 extends along the width direction of the flat conveyance unit 137 and its inclination. Gravity drops at a uniform speed at any point in the direction, and are temporarily stored in the temporary toner storage unit 139. In the temporary toner storage portion 139 that narrows in a wedge shape, as the toner 113 advances to a narrow region, the pressure contact force against the peripheral surface of the supply roller 105 gradually increases. And the toner 113 is easily carried on the peripheral surface. When the toner 113 is pushed out beyond the contact portion 143, the toner 113 falls down the toner guide space 131 and is guided directly or by the toner guide surface 129 and returned to the toner storage portion 101.

Next, details of the developing system of the present invention will be described. Evaluation items and evaluation methods are as follows.
〔Evaluation methods〕
(1) Release rate of positively chargeable external additive The release rate of the external additive (titanium oxide fine particles) was measured using a PT1000 particle analyzer (manufactured by Yokogawa Electric Corporation). Details of the method for measuring the liberation rate of the external additive are described in a patent document (Japanese Patent Laid-Open No. 2002-202622, etc.), but briefly described, this principle is that toner particles are introduced into plasma. The toner particles are excited and emitted. At this time, since the emission spectrum is different between the base material and the external additive, the liberation rate is determined by measuring the intensity and the emission timing. That is, the isolation rate of TiO ₂ introduces toner particles TiO ₂ was externally added to the plasma, measuring the emission intensity of the TiO ₂ in the toner particles. From the light emission intensity, the particle diameter (equivalent particle diameter) of TiO ₂ is obtained assuming that the toner particles to which TiO ₂ is externally added are true spherical particles. Diameter (equivalent particle diameter) is required). Liberated TiO ₂ also, as in the case of the toner particles, the equivalent diameter of the TiO ₂ is determined from the emission intensity. However, since the emission intensity of liberated TiO ₂ is small, the equivalent particle size is small. Therefore, by comparing the equivalent particle diameters, the external additive added to the toner particles is distinguished from the free external additive. Therefore, when the total number of detected external additives TiO ₂ is determined and an individual having a small equivalent particle diameter is defined as the number of free external additive particles, the following expression 1 is obtained.

Further, TiO ₂ adhering to the toner particles emits light at the same time in synchronism with the toner particles (base material), but TiO ₂ not adhering to the toner particles does not emit light at the same time as the toner particles, and the time is shifted. Emits light (asynchronous). Using this, it is discriminated whether TiO ₂ is attached to the toner particles or free. Based on this measured value, the liberation rate is obtained by the following equation (2).

In this embodiment, the method represented by the formula 1 is adopted.
Here, the relationship between the light emission voltage obtained by the PT1000 particle analyzer and the particle size of the external additive will be described. As an ideal external addition model, the external additive adheres with a certain uniform thickness regardless of the size of the base material. The particle size of the base material at this time is 2R, and the thickness of the external additive is D. Assume that D corresponds to the particle size of the external additive. In the particle analyzer, the cube root voltage Vx of the base material is obtained by the following equation (3).

  Further, the third root voltage Vy of the external additive is obtained by the following equation (4).

  When R is eliminated from Equation 3 and Equation 4, the relationship between the third root voltage Vy of the external additive and D is obtained by the following Equation 5.

The toner of the present embodiment is positively charged and positive, and has first titania having a small average particle diameter and second titania having a large average particle diameter as external additives. The reason why the lower limit of the cube root voltage is limited to 3V is that in Equation 5, D is 0.1 μm which is the average particle diameter of the second titania, the cube root voltage Vx of the base material is the maximum value of the horizontal axis range. By substituting 10 which is, the cube root voltage corresponding to an equivalent particle diameter of about 100 nm is determined to be about 3V.
(2) Specific PT1000 Measuring Method Particle Analyzer PT1000 manufactured by Yokogawa Electric Corporation
Number of C (base material) detected in one measurement: 4000 to 6000 Number of scans per sample (number of measurements): 6 Noise cut level: 1.5 V or less Sort time: 30 digits
Gas used: He gas containing 0.1% O ₂ (3) Charge amount and charge uniformity The charge amount of the toner was measured as follows using an E-SPART analyzer manufactured by Hosokawa Micron Corporation. The toner prepared in Examples and Comparative Examples shown below and a carrier were mixed and stirred to charge the toner. Thereafter, the toner and the carrier were separated by blowing nitrogen gas onto the mixture of the toner and the carrier. Next, the charge amount (Q / m) for each toner was measured to determine the distribution of the toner charge amount. The toner charge amount uniformity is determined by measuring the maximum charge amount (Q ₁ / m ₁ ) and the measured total charge amount of toner in the number distribution of the charge amount (Q / m) of _one toner. The smaller the absolute value of (Q ₁ / m ₁ ) − (Q ₂ / m ₂ ), the sharper the distribution of the charge amount (uniform), the difference from the value divided by (number) (Q ₂ / m ₂ ). The larger the absolute value of (Q ₁ / m ₁ ) − (Q ₂ / m ₂ ), the wider the charge amount distribution is determined to be broader (non-uniform). In addition, as a carrier, Hitachi Metals Co., Ltd. KBN100 ferrite carrier was used.
(4) Toner flying property evaluation The toner is put into an LP-9000C machine (printer) manufactured by Seiko Epson Corporation and 3000 sheets are printed with a 5% consumption printing pattern. From the uniformity of the image before and after printing, the toner The flight performance was evaluated.
(5) Filming evaluation The filming evaluation on DR was performed by filming evaluation on DR after printing 3000 sheets in accordance with the toner flying property evaluation of (4) above. When filming occurs on the DR, since a scrutiny is generated in the rotational direction on the DR, it can be confirmed whether filming has occurred.
<Toner preparation method>
(Mother particles)
A monomer mixture comprising 80 parts by mass of styrene monomer, 20 parts by mass of butyl acrylate monomer, and 5 parts by mass of acrylic acid monomer was prepared. This mixture was mixed with 105 parts by weight of water, 1 part by weight of a nonionic emulsifier (New Coal 506: manufactured by Nippon Emulsifier Co., Ltd.), 1.5 parts by weight of an anionic emulsifier (Ribotac TE: manufactured by Lion Corporation), and persulfate. In addition to an aqueous solution consisting of 0.55 parts by mass of potassium, dispersion and emulsification were carried out to carry out emulsion polymerization to obtain a milky white resin emulsion having a particle size of 0.25 μm. 200 parts by weight of the obtained resin emulsion, 20 parts by weight of polyethylene wax emulsion (manufactured by Sanyo Chemical Industries, Ltd.) and 7 parts by weight of phthalocyanine blue, 0.2 parts by weight of sodium dodecylbenzenesulfonate (surfactant) Dispersed in the contained water. Next, after adding diethylamine and adjusting pH to 5.5, 0.3 mass part of aluminum sulfate which is electrolyte was added, stirring. Subsequently, the mixture was stirred at a high speed with a TK homomixer and dispersed. Furthermore, 40 parts by mass of styrene monomer, 10 parts by mass of butyl acrylate, and 5 parts by mass of zinc salicylate were added together with 40 parts by mass of water, and the mixture was heated to 90 ° C. while stirring under a nitrogen stream, and hydrogen peroxide was added. For 5 hours to grow particles. After the polymerization was stopped, the temperature was raised to 95 ° C. and maintained at 95 ° C. for 5 hours while adjusting the pH to 5 or more in order to improve the bond strength of the associated particles. The obtained particles were washed with water and vacuum-dried at 45 ° C. for 10 hours. By this method, toner base particles having a volume average particle diameter of 7.0 μm were prepared. The obtained toner base particles had an average circularity of 0.97.
(External additive)
Table 1 shows external additives that are externally added to the toner base particles in this embodiment.

In Table 1, silica is used for imparting fluidity, the first titanium oxide (B1) having an average particle size of 20 nm in the major axis of the rutile anatase type, the second of the rutile anatase type having an average particle size of 100 to 120 nm. Titanium oxide (B2) is used. Since the second titanium oxide having a large particle size is less likely to adhere to the mother particles than the first titanium oxide and has a higher liberation rate (small synchronization rate) than the first titanium oxide, it is shown in FIG. In a developing machine that circulates toner in a container, it acts as a microcarrier to contribute to the charging of the toner, and acts as a spacer on the developing roller to contribute to an improvement in toner flying performance. is doing.
(External processing)
For the external treatment, an FM20B type Henschel mixer manufactured by Mitsui Mining Co., Ltd. and a Q20L type mixer manufactured by Mitsui Mining Co., Ltd. were used.
A mixing tank is used to mix the toner base particles and the external additive. However, the weight of the external additive particles is a few percent of the weight of the toner base particles, avoiding adhesion in the mixing tank. In order to do this, the external additive particles are introduced after the toner base particles as the order of introduction into the mixing tank.

  Figure 3 shows an example of a Henschel mixer. The mixing treatment tank 200 has a cylindrical shape, and has a stirring blade that rotates at a high speed at the bottom of the mixing tank, and the object to be processed is moved to the tank wall by the centrifugal force generated by the lower blade 201 that rotates at the bottom of the tank at a high speed. In this case, the vertical tank wall of the cylinder is raised, and the object to be processed slides down the inclined surface formed by the deposition of the object itself due to gravity when the influence of the ascending force due to the centrifugal force is reduced. Mixing is promoted by repeating the up-and-down motion in which the centrifugal force is applied by the blades rotating at high speed and the ascending motion is repeated. In addition, the blades have a two-stage structure, and the upper blades 202 are rotated in the middle of sliding down the inclined surface due to the deposition of the workpieces themselves to promote dispersion.

  An example of a Q-type mixer is shown in FIG. The processing tank 210 has a spherical shape having a relatively large horizontal disk-shaped tank bottom 21 and includes a flange 218 at the center so that the processing tank 210 can be divided into two vertically. In addition, the entire spherical portion is provided with a jacket 219 and has a double structure. By flowing a heat medium therethrough, the object to be processed can be heated or cooled. An input port 216 for supplying an object to be processed is provided in the upper part of the processing tank 210, and an exhaust port 217 for discharging a product is provided in the lower part. A drive shaft 215 passes through the center of the disk-shaped tank bottom 211 and can be rotated by external power. A relatively large conical boss 212 having a rounded tip is attached to the drive shaft 215, and a stirring blade 213 is provided on the outer periphery of the lower end of the boss 212. The stirring blade 213 has a slope opposite to the slope of the outer periphery of the boss 212, and the lower edge thereof is an arc along the spherical inner wall of the processing tank 210. An auxiliary blade 214 having a diameter slightly smaller than that of the stirring blade 213 is provided above the boss 212. In this spherical processing tank, the object to be processed rises smoothly along the spherical tank wall by the stirring blades and reaches the vicinity of the top, and the object to be processed dropped from the top of the tank along the surface of the boss. It falls and reaches the stirring blade on the outer periphery of the lower end of the boss, and smoothly flows along the surface of the boss. And the to-be-processed object which fell along the surface of the boss | hub, and reached | attained the stirring blade is discharged | emitted by the rotational force of a stirring blade, raises along a tank wall, and circulates in the inside of a processing tank.

  Table 2 shows the mixing conditions.

  Specific addition amounts of external additives and processing conditions are shown in Table 3.

  In this embodiment, the second titania having a large particle size is added after the addition of the first titania having a small particle size. Mixing condition A uses a Q-shaped mixer, the peripheral speed of the stirring blade is 60 m / sec, the stirring time is 3 minutes, and the mixing condition A uses a Henschel mixer, the peripheral speed of the stirring blade is 30 m / sec. The time is 5 minutes.

The first titania is less likely to be released due to the effect of the order of addition. First, the first titania is added to strongly strengthen the titania, and then the second titania is added. By adopting this method, the liberation rate of the second titania can be set within a desired range.
(Adjustment of SR / DR surface waveform)
For example, when two power supplies are used, the SR / DR bias surface waveform can be adjusted by changing the setting value of the power supply for supplying bias to SR and DR. In the case of a single power supply, this can be achieved by installing a resistor before supply to SR and DR. In this embodiment, a case where a resistance is applied to the supply bias as shown in FIG. 5 will be described.
(Development bias condition)
A developing machine having the configuration shown in FIG. 2 in which toner and external additives are recycled is used.
Resistance applied to DR: 200 kΩ
AC bias: 1500V
AC frequency: 3 kHz
ACduty: 40% development side from DR to OPC, 60% withdrawal side from OPC to DR
DC bias: -200V
A bias waveform as shown in FIG. 6 was obtained by sandwiching a 200 kΩ resistor against the supply bias from the AC power source to the DR side.
(Examples 1-5 and Comparative Examples 1-3)
The toner was obtained by adding the external additive shown in Table 1 in a predetermined amount shown in Table 3 by a processing method to 100 parts by mass of toner base particles having a styrene-acrylic resin as a binder resin. is there.

  In Table 3, the external additive processing methods for the toners a, c, and d are based on the conditions in Table 2 for both the first stage in which the first titania B1 is added and the second stage in which the second titania B2 is added. In the toner b, the first stage of adding the first titania B1 and the second stage of adding the second titania B2 are in accordance with the conditions A in Table 2. The toner e is an external addition method in which B1 and B2 are added in one process, and the toner f is a case in which the first titania B1 is added in the first stage and titania is added in the second stage.

  Evaluation was performed using toners prepared by the methods shown in Tables 1 to 3. The results are shown in Table 4.

In Examples 1 to 5 in which the liberation rate of the second titania is within 0.5 to 5%, a bias surface waveform difference is formed in SR / DR, and a circulation type developing machine is used, (Q ₁ / m ₁ )-(Q ₂ / m ₂ ) is smaller than Comparative Examples 1 to 3, the charge amount distribution is sharp (uniform), and the image quality uniformity is maintained when printing 3000 sheets. No filming was observed. In Comparative Example 1 and Comparative Example 2 where the liberation rate of the second titania was outside the range of 0.5 to 5%, a bias surface waveform difference was formed in SR / DR, and a circulation type developing machine was used. Although there was no ming, end thinness at the end of durability occurred. In addition, the liberation rate of the second titania is in the range of 0.5 to 5%. However, when the developing device is not of the recycle type, there is no filming but a thin end of the rear end. did.

  In addition, although the said Example demonstrated the example which uses the 1st titanium oxide whose average particle diameter is 20 nm and the 2nd titanium oxide whose average particle diameter is 100-120 nm, as an average particle diameter of 1st titanium oxide, It has been confirmed that uniformity in image quality can be achieved if the average particle size of the second titanium oxide is 10 to 50 nm and the average particle size of the second titanium oxide is 100 to 200 nm.

  According to the present invention, the charging uniformity and toner flying property are improved, and even in continuous printing, filming does not occur, and the image quality can be made uniform. Therefore, the industrial utility value is great.

1 is a cross-sectional view illustrating an overall configuration of a tandem type image forming apparatus. It is sectional drawing of a developing device. It is a figure explaining the example of a Henschel mixer. It is a figure explaining the example of Q type mixer. It is a figure explaining the bias supply method to a supply roller and a developing roller. It is a supply voltage waveform to a supply roller and a developing roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 23 ... Photosensitive drum, 100 ... Developing apparatus, 101 ... Toner accommodating part, 103 ... Housing, 105 ... Supply roller, 107 ... Developing roller, 109 ... Restricting blade, 111 ... Plate spring member, 112 ... Elastic member, 113 ... Toner, DESCRIPTION OF SYMBOLS 200 ... Mixing processing tank, 201 ... Lower blade, 202 ... Upper blade, 210 ... Processing tank, 212 ... Boss, 213 ... Stirring blade, 214 ... Auxiliary blade, 215 ... Drive shaft, 216 ... Input port, 217 ... Discharge port.

Claims (6)

In a toner development system having a positively chargeable external additive having a liberation ratio of 0.5 to 5%, a supply bias in which an AC component is superimposed is applied between the development roller and the supply roller, and the supply roller surface voltage waveform and the development roller A developing system characterized by differentiating the surface voltage waveform. 2. The developing system according to claim 1, wherein the potential of the supply roller surface voltage waveform is higher than the potential of the developing roller surface voltage waveform. A developing system comprising: a toner container having an opening at a lower portion of a developing roller and a supply roller, and receiving a free external additive that is separated between the developing roller and the supply roller and freely falls. 4. The developing system according to claim 3, wherein the free external additive that has fallen freely is circulated in the toner container and reused. 2. The developing system according to claim 1, wherein the free external additive is 100 nm to 200 nm. A developing system characterized in that the rotational movement direction of the developing roller and the supply roller peripheral surface in the nip portion is on the free fall side with respect to the opening.

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